"Department" Automotive transport "N.A. Kuzmin, G.V. Borisov LECTURE SUMMARY FOR THE COURSE "Fundamentals of the performance of technical systems"" NIZHNY NOVGOROD 2015 Lecture topics INTRODUCTION .. 1. ... "

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MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

FEDERAL STATE BUDGET

EDUCATIONAL INSTITUTION

HIGHER PROFESSIONAL EDUCATION

"NIZHNY NOVGOROD STATE TECHNICAL

UNIVERSITY them. R.E. ALEKSEEV

Department of "Motor transport"

N.A. Kuzmin, G.V. Borisov

LECTURE SUMMARY FOR THE COURSE

"Fundamentals of the performance of technical systems"

NIZHNY NOVGOROD

2015

Lecture topics INTRODUCTION …………………………………………………………………...

1. BASIC CONCEPTS, TERMS AND DEFINITIONS IN THE FIELD

………………………………………...

MOTOR VEHICLES

2. PERFORMANCE AND QUALITY OF VEHICLES ......

2.1. Operational properties of cars.………………………

2.2. Implemented indicator of the quality of cars..………………...

3. PROCESSES OF CHANGING THE TECHNICAL CONDITION OF VEHICLES IN OPERATION ………………………………………………….

Wear of surfaces of parts..……………………………… 3.1.

Plastic deformations and strength failures of parts 3.2.

Fatigue failure of materials …………………………………… 3.3.

Corrosion of metals………………………………………………….

Physical-mechanical or temperature changes in materials (aging)……………………………………………………..

4. OPERATING CONDITIONS OF VEHICLES …………………………..

4.1. Road conditions …………………………………………………..

4.2. Transport conditions ……………………………………………...

4.3. Natural and climatic conditions ……………………………………

5. OPERATING MODES OF AUTOMOBILE

UNITS………………………………………………………………..

5.1. Non-stationary modes of operation of automotive units ... ..

5.2. High-speed and load modes of operation of automobile engines ……………………………………………………………..

5.3. Thermal modes of operation of vehicle units ……………….

5.4. Running-in of car units ……………………………………

6. CHANGING THE TECHNICAL CONDITION OF CAR TIRES

………………………………………………………..

IN OPERATION

6.1. Classification and marking of tires ………………………………

6.2. Investigation of factors affecting tire life……

REFERENCES

REFERENCES

1. Regulations on the maintenance and repair of rolling stock of road transport / Minavtotrans RSFSR. - M.: Transport, 1988 -78s.

2. Akhmetzyanov, M.Kh. Resistance of materials / M.Kh. Akhmetzyanov, P.V.

Gres, I.B. Lazarev. - M .: Higher school, 2007. - 334 p.

3. Bush, N.A. Friction, wear and fatigue in machines (Transport engineering): a textbook for universities. - M.: Transport, 1987. - 223 p.

4. Gurvich, I.B. Operational reliability of automobile engines / I.B. Gurvich, P.E. Syrkin, V.I. Chumak. - 2nd ed., add. - M.: Transport, 1994. - 144 p.

5. Denisov, V.Ya. Organic chemistry /V.Ya. Denisov, D.L. Muryshkin, T.V. Chuikova. - M .: Higher School, 2009. - 544 p.

6. Izvekov, B.S. Modern car. Automotive terms / B.S. Izvekov, N.A. Kuzmin. - N.Novgorod: RIG ATIS LLC, 2001. - 320p.

7. Itinskaya N.I. Fuels, oils and technical fluids: a handbook, 2nd ed., Revised. and additional / N.I. Itinskaya, N.A. Kuznetsov. - M.: Agropromizdat, 1989. - 304 p.

8. Karpman, M.G. Material science and technology of metals / M.G. Karpman, V.M. Matyunin, G.P. Fetisov. - 5th ed. – M.: Higher school. – 2008.

9. Kislitsin N.M. The durability of car tires in various driving modes. - Nizhny Novgorod: Volga-Vyatka Prince. publishing house, 1992. - 232p.

10. Korovin, N.V. General chemistry: a textbook for technical areas and special universities / N.V. Korovin. - 12th ed. - M .: Higher School, 2010. - 557p.

11. Kravets, V.N. Testing of automobile tires / V.N. Kravets, N.M. Kislitsin, V.I. Denisov; Nizhny Novgorod. state tech. un-t im. R.E. Alekseev - N. Novgorod: NGTU, 1976. - 56p.

12. Kuzmin, N.A. Automobile reference book-encyclopedia / N.A.

Kuzmin, V.I. Peskov. - M.: FORUM, 2011. - 288s.

13. Kuzmin, N.A. Scientific bases of the processes of changing the technical condition of cars: monograph / N.A. Kuzmin, G.V. Borisov; Nizhny Novgorod. state tech. un-t im. R.E. Alekseeva - N.Novgorod, 2012. -2 p.

14. Kuzmin, N.A. Processes and causes of changes in the performance of cars: textbook / N.A. Kuzmin; Nizhny Novgorod. state tech.

un-t im. R.E. Alekseeva - N.Novgorod, 2005. - 160 p.

15. Kuzmin, N.A. Technical operation of cars: regularities of changes in working capacity: study guide / N.A. Kuzmin.

- M.: FORUM, 2014. - 208s.

16. Kuzmin, N.A. Theoretical foundations for ensuring the performance of cars: a study guide / N.A. Kuzmin. – M.: FORUM, 2014. – 272 p.

17. Neverov, A.S. Corrosion and protection of materials / A.S. Neverov, D.A.

Rodchenko, M.I. Tsyrlin. - Mn .: The highest school, 2007. - 222 p.

18. Peskov, V.I. Car theory: textbook / V.I. Peskov; Nizhny Novgorod. state tech. un-t. - Nizhny Novgorod, 2006. - 176 p.

19. Tarnovsky, V.N. etc. Automobile tires: Device, work, operation, repair. - M.: Transport, 1990. - 272 p.

INTRODUCTION

The level of organization and operation of road transport (AT) largely determines the pace of development of the Russian economy, and indeed of all countries of the world, which is associated with the mobility and flexibility of the delivery of goods and passengers. These properties of AT are largely determined by the level of performance of cars and car parks in general. The high level of AT rolling stock performance, in turn, depends on the reliability of vehicle structures and their structural components, the timeliness and quality of their maintenance (repair), which is the field of technical operation of vehicles (TEA). At the same time, if the reliability of the design is laid down at the stages of designing and manufacturing cars, then the most complete use of their potential is ensured by the stage of actual operation of motor vehicles (ATS) and only under the condition of an effective and professional organization of the TEA.

Intensification of production, increase in labor productivity, saving of all types of resources are the tasks that are directly related to the AT-TEA subsystem, which ensures the operability of the rolling stock. Its development and improvement are dictated by the intensity of the development of the AT itself and its role in the country's transport complex, the need to save labor, material, fuel and energy and other resources during transportation, maintenance (TO), repairs and storage of vehicles, the need to ensure the transport process with a reliable working mobile composition, protection of the public, personnel and the environment.

The purpose of the field of science of TEA is to study the regularities of technical operation from the simplest ones, which describe the change in operational properties and the levels of performance of vehicles and their structural elements (CE), which include units, systems, mechanisms, components and parts, to more complex ones, which explain the formation of operational properties and performance during the operation of a group (park) of vehicles.

The efficiency of TEA in a motor transport enterprise (ATP) is ensured by the engineering and technical service (ITS), which implements the goals and solves the tasks of TEA. Part of the ITS, which is engaged in direct production activities, is called the production and technical service (PTS) of the ATP. Production facilities with equipment, instrumentation - this is the production and technical base (PTB) of ATP.

Thus, TEA is one of the AT subsystems, which in turn also includes the subsystem of the commercial operation of the ATS (transportation service).

The purpose of this training manual does not provide for technical issues of organizing and implementing maintenance (TO) and car repairs, optimization of these processes. The presented materials are intended for the study and development of engineering solutions to reduce the intensity of the processes of changing the technical condition of vehicles, their units and components under operating conditions.

The publication summarizes the research experience of the scientific schools of the State Institute of Pioneer-NSTU of professors I.B. Gurvich and N.A. Kuzmin in the field of the thermal state and reliability of vehicles and their engines in the context of analyzing the processes of changing their technical state in operation. The results of studies on the assessment and improvement of reliability indicators and other technical and operational properties of vehicles and their engines at the design and testing stage are also presented, mainly on the example of vehicles of OJSC Gorky Automobile Plant and engines of OJSC Zavolzhsky Motor Plant.

The materials presented in the training manual are the theoretical part of the discipline "Fundamentals of the performance of technical systems" of the profiles "Automobiles and the automotive industry" and "Automobile service" of the direction of training of the current state educational standard (GOS III) 190600 "Operation of transport and technological machines and complexes". The materials of the manual are also recommended as initial theoretical prerequisites for scientific research of undergraduates of the indicated direction of training in the professional educational program "Technical operation of vehicles" and for mastering the discipline "Modern problems and directions of development of structures and technical operation of transport and transport-technological machines and equipment". The publication is also intended for students, undergraduates and graduate students of other automotive areas, training profiles and specialties of universities, as well as for specialists involved in the operation and production of automotive equipment.

1. BASIC CONCEPTS, TERMS AND DEFINITIONS

IN THE FIELD OF MOTOR VEHICLES

BASIC TERMS OF TECHNICAL CONDITION

CARS

A car and any motor vehicle (ATS) in its life cycle cannot fulfill its purpose without maintenance and repairs that form the basis of TEA. The main standard in this case is the "Regulations on the maintenance and repair of the rolling stock of road transport" (hereinafter the Regulations).

For each special question on the operation of vehicles, there are also corresponding GOSTs, OSTs, etc. The basic concepts, terms and definitions in the field of TEA are:

An object is an object with a specific purpose. Objects in cars can be: a unit, a system, a mechanism, a unit and a part, which are commonly called structural elements (CE) of a car. The object is the car itself.

There are five types of technical condition of the car:

Serviceable condition (serviceability) - the state of the car, in which it meets all the requirements of regulatory and technical and (or) design (project) documentation (NTKD).

Faulty state (malfunction) - the state of the car, in which it does not meet at least one of the requirements of the NTCD.

It should be noted that in fact there are no serviceable cars, since each car has at least one deviation from the STCD requirements. This may be a visible malfunction (for example, a scratch on the body, a violation of the uniformity of the paintwork of parts, etc.), and also when some parts do not comply with the STCD, the deviation in size, roughness, surface hardness, etc.

Working condition (working capacity) - the state of the car, in which the values ​​of all parameters characterizing the ability to perform the specified functions comply with the requirements of the STCD.

Inoperable state (inoperability) - the state of the car, in which the value of at least one parameter characterizing the ability to perform the specified functions does not meet the requirements of the NTCD. An inoperable car is always out of order, and an efficient one can be out of order (with a scratch on the body, a burned-out cab lighting bulb, the car is out of order, but quite operational).

Limit state - the state of the vehicle or CE, in which its further operation is inefficient or unsafe. This situation occurs when the permissible values ​​of the operational parameters of the vehicle CE are exceeded. When the limit state is reached, repair of the CE or the vehicle as a whole is required. For example, the inefficiency of the operation of automobile engines that have reached the limit state is due to increased consumption of motor oils and fuels, a decrease in the operating speeds of vehicles due to a drop in engine power. The unsafe operation of such engines is caused by a significant increase in exhaust gas toxicity, noise, vibration, a high probability of a sudden engine failure when driving in a stream of vehicles, which can create an emergency.

Events of change of technical states of automatic telephone exchange: damages, failures, defects.

Damage is an event consisting in the violation of the serviceable state (loss of serviceability) of the vehicle CE while maintaining its operable state.

Failure is an event consisting in a violation of the operable state (loss of operability) of the vehicle CE.

A defect is a generalized event that includes both damage and failure.

The concept of failure is one of the most important in TEA. The following types of failures should be distinguished:

Structural, production (technological) and operational failures - failures that occur due to an imperfection or violation of: established rules and (or) norms for designing or constructing a car; an established process for the manufacture or repair of a vehicle; established rules and (or) conditions for the operation of vehicles, respectively.

Dependent and independent failures - failures caused or independent, respectively, from failures of other CEs of the vehicle (for example, when the oil pan is broken, engine oil flows out - scuffing occurs on the rubbing surfaces of engine parts, parts jamming - dependent failure; tire puncture - independent failure) .

Sudden and gradual failures are failures characterized by a sharp change in the values ​​of one or more vehicle parameters (for example, a broken piston rod); or resulting from a gradual change in the values ​​of one or more vehicle parameters (for example, generator failure due to rotor wear), respectively.

Malfunction - a self-recovering failure or a single failure that is eliminated without special technical action (for example, water ingress on the brake pads - braking efficiency is violated before the water dries naturally).

An intermittent failure is a repeatedly occurring self-correcting failure of the same nature (for example, the loss of the contact of a lamp of a light device).

Explicit and hidden failures - failures detected visually or by standard methods and means of monitoring and diagnosing; not detected visually or by standard methods and means of monitoring and diagnosing, but detected during maintenance or by special diagnostic methods, respectively.

Degradation (resource) failure is a failure caused by the natural processes of aging, wear, corrosion and fatigue in compliance with all established rules and (or) standards for design, manufacture and operation, as a result of which the vehicle or its CE reaches the limit state.

Basic concepts for maintenance and repair of cars:

Maintenance is a directed system of technical influences on the CE of a vehicle in order to ensure its operability.

Technical diagnostics is a science that develops methods for studying the technical condition of vehicles and its CE, as well as the principles for constructing and organizing the use of diagnostic systems.

Technical diagnostics is the process of determining the technical condition of a vehicle's CE with a certain accuracy.

Restoration and repair - the process of transferring a car or its CE from a faulty state to a serviceable one or from an inoperable state to a working one, respectively.

Serviced (non-maintained) object - an object for which maintenance is provided (not provided) by the NTCD.

Restorable (non-restorable) object - an object for which, in the situation under consideration, restoration is provided for by the NTCD (not provided for by the NTCD); for example, in the industrial enterprises of the regional center, grinding of the crankshaft journals of the engine is easily performed, and in rural areas this is impossible due to the lack of equipment.

A repairable (non-repairable) object is an object whose repair is possible and provided for by the NTCD (it is impossible or not provided for by the NTCD (for example, non-repairable objects in a car are: an alternator belt, a thermostat, incandescent lamps of lighting devices, etc.).

BASIC TERMS OF VEHICLE SPECIFICATIONS

The terms (and their interpretation) used in the field of ATS operation - in the TEA and the organization of road transport are discussed below. Most of them are given in the data sheets of technical characteristics of automatic telephone exchanges.

The curb weight of a car, trailer, semi-trailer is defined as the weight of a fully filled (fuel, oil, coolant, etc.) and equipped (spare wheel, tool, etc.) vehicle, but without cargo or passengers, driver, other attendants ( conductor, freight forwarder, etc.) and their baggage.

The total weight of the vehicle or vehicle consists of the curb weight, the weight of the cargo (in terms of carrying capacity) or passengers, the driver and other attendants. In this case, the total mass of buses (urban and suburban) should be determined for the nominal and maximum capacities. Gross mass of road trains: for a trailer train, this is the sum of the gross masses of the tractor and trailer; for a semi-trailer vehicle - the sum of the curb weight of the tractor, the weight of the personnel in the cab and the total weight of the semi-trailer.

Permissible (structural) total mass is the sum of the axial masses allowed by the design of the vehicle.

Estimated weights (per person) of passengers, attendants and luggage: for cars - 80 kg (person's weight 70 kg + 10 kg of luggage); for buses: urban - 68 kg; suburban - 71 kg (68 + 3); rural (local) - 81 kg (68 + 13); intercity - 91 kg (68 + 23). The attendants of buses (driver, conductor, etc.), as well as the driver and passengers in the cabin of a freight vehicle, are taken in calculations of 75 kg. The weight of the luggage carrier with cargo installed on the roof of a passenger car is included in the total weight with a corresponding reduction in the number of passengers.

The load capacity is defined as the mass of the transported cargo without the mass of the driver and passengers in the cabin.

Passenger capacity (number of seats). In buses, the number of seats for seated passengers does not include seats for service personnel - driver, guide, etc. The capacity of buses is calculated as the sum of the number of seats for seated passengers and the number of seats for standing passengers at the rate of 0.2 m2 of free floor area per one standing passenger ( 5 people per 1 m2) at nominal capacity or 0.125 m2 (8 people per 1 m2) at maximum capacity. The nominal capacity of buses is typical for operating conditions during off-peak times.

Maximum capacity - the capacity of buses during peak hours.

The coordinates of the center of gravity of the vehicle are given for the equipped state. The center of gravity is indicated in the figures by a special icon:

Ground clearances, approach and exit angles are given for vehicles with full weight. The lowest points under the front and rear axles of the PBX are indicated in the figures with a special icon:

Control fuel consumption - this parameter is used to check the technical condition of the vehicle and is not a fuel consumption rate.

The control fuel consumption is determined for the vehicle of the total mass on a horizontal section of the road with a hard surface in steady motion at a specified speed. The "urban cycle" mode (simulation of urban traffic) is carried out according to a special methodology, in accordance with the relevant standard (GOST 20306-90).

Maximum speed, acceleration time, gradeability, coastdown distance and braking distance - these parameters are given for a gross vehicle weight, and for truck tractors - when they operate as part of a gross vehicle combination. The exception is the maximum speed and acceleration time of passenger cars, for which these parameters are given for a car with a driver and one passenger.

The overall and loading height, the height of the fifth wheel coupling, the floor level, the height of the steps of the buses are given for equipped vehicles.

The size from the seat cushion to the inner upholstery of the ceiling of cars is measured with the cushion bent under the action of the mass of a three-dimensional dummy (76.6 kg) using a retractable dummy probe, according to GOST 20304-85.

The run-out of the car is the distance that a car of full weight, accelerated to the specified speed, will travel until it stops on a dry, asphalt, level road with the gear in neutral.

Stopping distance - the path of the car from the beginning of braking to a complete stop, usually given for tests of type "0"; check is made at cold brakes at full weight of the car.

The sizes of brake chambers, cylinders and energy accumulators are indicated by the numbers 9, 12, 16, 20, 24, 30, 36, which corresponds to the working area of ​​the diaphragm or piston in square inches. The standard sizes of chambers (cylinders) and energy accumulators combined with them are indicated by a fractional number (for example, 16/24, 24/24).

Vehicle base - for two-axle vehicles and trailers, this is the distance between the centers of the front and rear axles, for multi-axle vehicles, this is the distance (mm) between all axles through the plus sign, starting from the first axle. For single-axle semi-trailers - the distance from the center of the fifth wheel to the center of the axle. For multi-axle semi-trailers, the base of the bogie (bogies) is additionally indicated through the plus sign.

The turning radius is determined by the track axis of the outer (relative to the turning center) front wheel.

The free steering angle (play) is given when the wheels are in a straight line position. For power steering, readings should be taken with the engine running and at the recommended minimum engine speed (RMS) idle.

Air pressure in tires - for cars, light trucks and buses made on the basis of cars, and their trailers, a deviation from the values ​​\u200b\u200bspecified in the operating instructions by 0.1 kgf / cm2 (0.01 MPa) is allowed, for trucks, buses and trailers to them - by 0.2 kgf / cm2 (0.02 MPa).

wheel formula. The designation of the main wheel formula consists of two digits separated by a multiplication sign. For rear-wheel drive vehicles, the first digit indicates the total number of wheels, and the second - the number of drive wheels to which torque is transmitted from the engine (in this case, dual-wheel wheels are considered as one wheel), for example, for rear-wheel drive two-axle vehicles, 4x2 formulas are used (GAZ-31105, VAZ -2107, GAZ-3307, PAZ-3205, LiAZ-5256, etc.). The wheel formula of front-wheel drive vehicles is the opposite: the first digit means the number of driving wheels, the second - their total number (2x4 formula, for example, VAZ-2108 - VAZ-2118). For all-wheel drive vehicles, the numbers in the formula are the same (for example, the VAZ-21213, UAZ-3162 Patriot, GAZ-3308 Sadko, etc. have a 4x4 wheel arrangement).

For trucks and buses, the wheel formula designation contains the third digit 2 or 1, separated from the second digit by a dot. The number 2 indicates that the driven rear axle has dual tires, and the number 1 indicates that all wheels are single. Thus, for two-axle trucks and buses with dual-wheel drive wheels, the formula has the form 4x2.2 (for example, GAZ-33021 car, LiAZ-5256, PAZ-3205 buses, etc.), and for cases where single wheels are used - 4x2 .1 (GAZ-31105, GAZ-2217 "Barguzin"); the last wheel arrangement is usually also for off-road vehicles (UAZ-2206, UAZ-3162, GAZ-3308, etc.).

For three-axle vehicles, wheel formulas 6x2, 6x4, 6x6 are used, and in a more complete form: 6x2.2 (tractor "MB-2235"), 6x4.2 (MAZx6.1 (KamAZ-43101), 6x6.2 (timber carrier KrAZ- 643701) For four-axle vehicles respectively 8x4.1, 8x4.2 and 8x8.1 or 8x4.2.

For articulated buses, the fourth digit 1 or 2 is entered in the wheel formula, separated from the third digit by a dot. The number 1 indicates that the axle of the trailer part of the bus has a single tire, and the number 2 has a double tire. For example, for the Ikarus-280.64 articulated bus, the wheel formula is 6x2.2.1, and for the Ikarus-283.00 bus, it is 6x2.2.2.

ENGINE SPECIFICATIONS

Well-known information on the technical characteristics of internal combustion engines is presented here solely for reasons of the need to understand the subsequent information on the markings and classifications of vehicles. In addition, most of these terms are given in the data sheets of the technical characteristics of the exchange.

The working volume of cylinders (engine displacement) Vl is the sum of the working volumes of all cylinders, i.e. is the product of the working volume of one cylinder Vh by the number of cylinders i:

–  –  –

The volume of the combustion chamber Vc is the volume of the residual space above the piston at its position at TDC (Fig. 1.1).

The total cylinder volume Va is the volume of space above the piston when it is at BDC. Obviously, the total volume of the cylinder Va is equal to the sum of the working volume of the cylinder Vh and the volume of its combustion chamber Vc:

Va = Vh + Vc. (1.3) The compression ratio is the ratio of the total volume of the cylinder Va to the volume of the combustion chamber Vc, i.e.

Va / Vc = (Vh + Vc) / Vc = 1 + Vh / Vc. (1.4) The compression ratio shows how many times the volume of the engine cylinder decreases when the piston moves from BDC to TDC. The compression ratio is a dimensionless quantity. In gasoline engines = 6.5 ... 11, in diesel engines - = 14 ... 25.

The piston stroke and cylinder diameter (S and D) determine the dimensions of the engine. If the S/D ratio is less than or equal to one, then the engine is called short-stroke, otherwise it is called long-stroke. Most modern car engines are short-stroke.

Rice. 1.1. Geometric characteristics of the crank mechanism of the internal combustion engine The indicator power of the engine Pi is the power developed by the gases in the cylinders. The indicated power is greater than the effective power of the engine by the amount of mechanical, thermal and pumping losses.

The effective engine power Pe is the power developed on the crankshaft. It is measured in horsepower (hp) or kilowatts (kW). Conversion factor: 1 HP = 0.736 kW, 1 kW = 1.36 hp

The effective power of the engine is calculated by the formulas:

–  –  –

– engine torque, Nm (kgf.m); - rotational speed where of the crankshaft (CVKV), min-1 (rpm).

nom Nominal effective motor power Pe is the effective power guaranteed by the manufacturer at a slightly reduced PMCR. It is less than the maximum effective power of the engine, which is done by artificially limiting the PVKV for reasons of ensuring a given engine resource.

Liter engine power Pl - the ratio of effective power to displacement. It characterizes the efficiency of using the working volume of the engine and has the dimension of kW/l or hp/l.

The weight power of the engine Pw is the ratio of the effective power of the engine to its weight; characterizes the efficiency of using the mass of the engine and has the dimension of kW / kg (hp / kg).

Net power is the maximum effective power developed by an engine with a complete standard configuration.

Gross power is the maximum effective power for an engine configuration without some serial attachments (without an air cleaner, silencer, cooling system fan, etc.) Specific effective fuel consumption ge is the ratio of hourly fuel consumption Gt, expressed in grams, to effective power Pe engine; has units of [g/kWh] and [g/hp.h].

Since the hourly fuel consumption is usually measured in kg / h, the formula for determining this indicator is:

. (1.7) The external speed characteristic of the engine is the dependence of the engine output indicators on the PVKV at full (maximum) fuel supply (Fig. 1.2) .

–  –  –

UAZ-450, UAZ-4 ZIL-130, ZIL-157 ZAZ-968, RAF-977 KAZ-600, KAZ-608 GAZ-14, GAZ-21, GAZ-24, GAZ-53

–  –  –

In accordance with the new digital classification system in force in the country since 1966, each model of the PBX is assigned an index consisting of at least four digits. Modifications of models correspond to the fifth digit indicating the serial number of the modification. The export version of domestic car models has the sixth digit. The numerical index is preceded by an alphabetic abbreviation indicating the manufacturer. The letters and numbers included in the full model designation give a detailed idea of ​​the car, as they indicate its manufacturer, class, type, model number, its modification, and if there is a sixth digit, the export version.

The most important information is given by the first two digits in the brand of cars. Their semantic meaning is presented in Table. 1.2.

Thus, each number and dash in the designation of a car model carries its own information. For example, the difference in the spelling of GAZ and GAZ-2410 is very significant: if the first model is a modification of the GAZ-24 car, the designation of which is based on the previously operating system, then the latest car model does not exist at all, since according to the modern digital designation

–  –  –

INTERNATIONAL CLASSIFICATION OF ROAD VEHICLES

FUNDS

The rules of the Economic Commission for Europe (ECE) of the United Nations adopted the international classification of vehicles, which in Russia is standardized by GOST 51709-2001 “Vehicles. Safety requirements for the technical condition and methods of verification "

(Table 1.4).

ATS of categories M2, M3 are further subdivided into: class I (city buses) - equipped with seats and places for transporting passengers standing outside the aisles; class II (intercity buses) - equipped with seats, and it is also allowed to carry passengers standing in the aisles; class III (tourist buses) - designed to carry only seated passengers.

Vehicles of categories O2, O3, O4 are further subdivided into: semi-trailers - towed vehicles, the axles of which are located behind the center of mass of a fully loaded vehicle, equipped with a fifth wheel coupling that transmits horizontal and vertical loads to the tractor; trailers - towed vehicles equipped with at least two axles and a towing device that can move vertically in relation to the trailer and controls the direction of the front axles, but transfers a slight static load to the tractor.

Table 1.4 International Classification of Vehicles Cat.

Maximum Class and operational Type and general purpose of the vehicle weight (1), t

–  –  –

2. PERFORMANCE PROPERTIES

AND QUALITY OF CARS

2.1. PERFORMANCE PROPERTIES OF VEHICLES

The effective use of vehicles predetermines their main operational properties - traction and speed, braking, fuel and economic, cross-country ability, ride, handling, stability, maneuverability, load capacity (passenger capacity), environmental friendliness, safety and others.

Traction and speed properties determine the dynamism of the vehicle (necessary and possible accelerations during movement and starting), the maximum speed, the maximum amount of climbs to be overcome, etc. These characteristics provide the basic properties of the vehicle - the power and torque of the engine, gear ratios in the transmission, the mass of the vehicle, its streamlining indicators, etc.

It is possible to determine the traction and speed performance of the vehicle (traction characteristic, maximum speed, acceleration, acceleration time and path) both on the road and in laboratory conditions. Traction characteristic - the dependence of the traction force on the drive wheels Pk on the speed of the vehicle V. It is obtained either in all or in one gear. The simplified traction characteristic represents the dependence of the free traction force Rd on the ATS hook on the speed of its movement.

Free traction force is measured directly with a dynamometer 2 (Fig. 2.1.) in laboratory conditions by testing on a bench.

The rear (driving) wheels of the car rest on a tape thrown over two drums. To reduce friction between the tape and its supporting surface, an air cushion is created. Drum 1 is connected to an electric brake, with which you can smoothly change the load on the driving wheels of the car.

Under road conditions, the traction-speed characteristic of the vehicle can most easily be obtained using a dyno trailer, which is towed by the vehicle under test. At the same time, measuring the traction force on the hook, as well as the speed of the vehicle, using a dynamograph, it is possible to plot the dependence curves of Pk on V. In this case, the total traction force is calculated by the formula Pk \u003d P "d + Pf + Pw. (2.1) where: P "d - traction force on the hook; Pf and Pw are the forces of resistance, respectively, to rolling and air flow.

The traction characteristic completely determines the dynamic properties of the car, however, its obtaining is associated with a large amount of testing. In most cases, when conducting long-term control tests, the following dynamic properties of the car are determined - the minimum stable and maximum speed; time and path of acceleration; the maximum incline that a car can overcome in uniform motion.

Road tests are carried out with equal vehicle loads and no load on a horizontal straight section of the road with a hard and even surface (asphalt or concrete). At the NAMI test site, a dynamometer road is designed for this. All measurements are made when the car drives in two mutually opposite directions in dry calm weather (wind speed up to 3 m/s).

The minimum steady speed of the vehicle is determined in direct gear. Measurements are made on two consecutive sections of the track 100 m long each with a distance between them equal to 200-300 m. The maximum speed is determined in the highest gear when the vehicle passes a measuring section 1 km long. The time of passage of the measured section is fixed with a stopwatch or a photographic gate.

–  –  –

Rice. 2.1. Stand for determining the traction characteristics of the car The braking properties of cars are characterized by the values ​​of maximum deceleration and braking distance. These properties depend on the design features of the brake systems of cars, their technical condition, type and wear of tire treads.

Braking is the process of creating and changing artificial resistance to the movement of a car in order to reduce its speed or keep it stationary relative to the road surface. The course of this process depends on the braking properties of the car, which are determined by the main indicators:

maximum deceleration of the car when braking on roads with various types of coatings and on dirt roads;

the limiting value of external forces, under the action of which the braked car is securely held in place;

the ability to ensure the minimum steady speed of the car downhill.

Braking properties are among the most important operational properties, primarily determining the so-called active safety of the car (see below). To ensure these properties, modern cars, in accordance with UNECE Regulation No. 13, are equipped with at least three brake systems - working, spare and parking. For vehicles of categories M3 and N3 (see Table 1.1), it is also mandatory to equip them with an auxiliary brake system, and vehicles of categories M2 and M3 intended for operation in mountainous conditions must also have an emergency brake.

Evaluation indicators of the effectiveness of the working and spare brake systems are the maximum steady-state deceleration

–  –  –

The effectiveness of these braking systems of the vehicle is determined during road tests. Before they are carried out, the vehicle must be run-in in accordance with the manufacturer's instructions. In addition, the weight load and its distribution over the bridges must comply with the specifications. Transmission and chassis units must be preheated. In this case, the entire braking system must be protected from heating. The wear of the tire tread pattern must be uniform and not exceed 50% of the nominal value. The section of the road where the tests of the main and spare brake systems are carried out, and the weather conditions must meet the same requirements that are imposed on them when assessing the speed properties of the vehicle.

Since the efficiency of brake mechanisms largely depends on the temperature of the rubbing pairs, these tests are carried out under various thermal conditions of the brake mechanisms. According to the standards currently adopted in the country and the world, tests to determine the effectiveness of the service brake system are divided into three types: tests "zero"; tests I;

tests II.

Zero tests are designed to evaluate the effectiveness of the service brake system with cold brakes. During tests I, the effectiveness of the working brake system is determined when the brake mechanisms are heated by preliminary braking; in tests II - with mechanisms heated by braking on a long descent. In the above GOSTs for testing brake systems of automatic telephone exchanges with hydraulic and pneumatic drives, the initial speeds from which braking should be performed, steady-state decelerations and braking distances, depending on the type of vehicles, are determined.

The efforts on the brake pedals are also regulated: the pedal of passenger cars must be pressed with a force of 500 N, trucks - 700 N. The steady-state deceleration during tests of type I and II should be at least 75% and 67%, respectively, of the decelerations during tests of type "zero" . The minimum steady-state decelerations of vehicles in operation are usually allowed to be somewhat smaller (by 10-12%) than for new vehicles.

As an estimated indicator of the parking brake system, the value of the maximum slope on which it ensures the retention of the car of the full mass is usually used. The normative values ​​of these slopes for new cars are as follows: for all categories M - at least 25%; for all categories N - at least 20%.

The auxiliary braking system of new vehicles must, without the use of other braking devices, ensure movement at a speed of 30 2 km / h on a road with a slope of 7%, having a length of at least 6 km.

Fuel economy is measured by fuel consumption in liters per 100 kilometers. During the actual operation of vehicles, for accounting and control, fuel consumption is normalized by allowances (reductions) to the basic (linear) norms, depending on specific operating conditions. Rationing is made taking into account the specific transport work.

One of the main generalizing indicators of fuel efficiency in the Russian Federation and in most other countries is the fuel consumption of a vehicle in liters per 100 km of the distance traveled - this is the so-called travel fuel consumption Qs, l / 100 km. It is convenient to use the travel expense to assess the fuel efficiency of vehicles that are similar in their transportation characteristics. To assess the efficiency of fuel use in the performance of transport work by vehicles of various carrying capacity (passenger capacity), a specific indicator is often used, which is called fuel consumption per unit of transport work Qw, l / t.km. This indicator is measured by the ratio of the actual fuel consumption to the transport work performed (W) for the transportation of goods. If the transport work involves the transport of passengers, the consumption Qw is measured in liters per passenger-kilometer (l/pass km). Thus, the following relations exist between Qs and Qw:

Qw = Qs / 100 P, Qw = Qs / 100 mg and (2.2) where mg is the mass of the transported cargo, t (for a truck);

P - the number of passengers carried, pass. (for the bus).

Fuel efficiency is largely determined by the corresponding performance of the engine. First of all, this is the hourly fuel consumption Gt kg / h - the mass of fuel in kilograms consumed by the engine in one hour of continuous operation, and the specific fuel consumption ge, g / kWh - the mass of fuel in grams consumed by the engine in one hour of work to obtain one kilowatt of power (formula 1.7) There are other estimates of the fuel efficiency of cars. For example, the control fuel consumption is used to indirectly assess the technical condition of the vehicle. It is determined at given values ​​of constant speed (different for different categories of vehicles) when driving on a straight horizontal road in top gear in accordance with GOST 20306-90.

Comprehensive fuel economy ratings for special driving cycles are increasingly being used.

For example, the measurement of fuel consumption in the main driving cycle is carried out for all categories of vehicles (except for city buses) by mileage along the measuring section in compliance with the driving modes specified by the special cycle scheme adopted by international regulatory documents. Similarly, measurements of fuel consumption in the urban driving cycle are made, the results of which allow a more accurate assessment of the fuel efficiency of various vehicles in urban operating conditions.

Cross-country ability - the ability of a car to work in difficult road conditions without slipping of the drive wheels and touching the lowest points on the bumps in the road. Cross-country ability is the property of a car to carry out a transport process in degraded road conditions, as well as off-road and with overcoming various obstacles.

Degraded road conditions include: wet and muddy roads; snow-covered and icy roads; sodden and broken roads that impede the movement and maneuvering of wheeled vehicles, significantly affecting their average speeds and fuel consumption.

When driving off-road, the wheels interact with various supporting surfaces that have not been prepared for the transport process. This causes a significant reduction in vehicle speeds (by 3-5 or more times) and a corresponding increase in fuel consumption. At the same time, the appearance and condition of these surfaces is of great importance, the entire range of which is usually reduced to four categories:

cohesive soils (clays and loams); non-cohesive (sandy) soils; swampy soils; snow virgin. The obstacles that the ATS has to overcome include: slopes (longitudinal and transverse); artificial barrier obstacles (ditches, ditches, embankments, curbs); single natural obstacles (hummocks, boulders, etc.).

Cars are divided into three categories according to the level of patency:

1. Off-road vehicles - designed for year-round operation on paved roads, as well as on dirt roads (cohesive soils) in the dry season. These cars have a 4x2, 6x2 or 6x4 wheel arrangement, i.e. are non-driven. They are equipped with tires with a road or universal tread pattern, have simple differentials in the transmission.

2. Off-road vehicles - designed to carry out the transport process in degraded road conditions and on certain types of off-road. Their main distinguishing feature is all-wheel drive (4x4 and 6x6 wheel formulas are used), the tires have developed lugs. The dynamic factor of these cars is 1.5-1.8 times greater than that of road cars. Structurally, they are often equipped with lockable differentials, have automatic tire pressure control systems. Vehicles of this category are capable of fording water obstacles up to 0.7-1.0 m deep, and for insurance they are equipped with self-pulling devices (winches).

3. Wheeled cross-country vehicles - designed to work in complete off-road conditions, to overcome natural and artificial obstacles and water barriers. They have a special layout scheme, an all-wheel drive formula (most often 6x6, 8x8 or 10x10) and other structural devices for increasing patency (slip differentials, tire pressure control systems, winches, etc.), a floating hull and propulsion on the water, etc. d.

Ride is the ability of a car to move in a given speed range on roads with uneven surfaces without significant vibration and shock effects on the driver, passengers or cargo.

It is customary to understand the smoothness of the vehicle as a set of its properties that ensure, within the limits specified by regulatory documents, the limitation of shock and vibration effects on the driver, passengers and transported goods from road roughness and other sources of vibration. The smoothness of the ride depends on the disturbing action of the sources of oscillations and vibrations, on the layout characteristics of the vehicle and on the design features of its systems and devices.

Smooth running, along with ventilation and heating, comfortable seats, protection from climatic influences, etc. determines the comfort of the car. Vibration loading is created by disturbing forces, mainly when the wheels interact with the road. Irregularities with a wavelength of more than 100 m are called the macro-profile of the road (it practically does not cause vibrations of the car), with a wavelength of 100 m to 10 cm - a micro-profile (the main source of oscillations), with a wavelength of less than 10 cm - roughness (it can cause high-frequency oscillations) . The main devices that limit the vibration load are the suspension and tires, and for passengers and the driver there are also elastic seats.

Fluctuations increase with an increase in the speed of movement, an increase in engine power, and the quality of the roads has a significant impact on the fluctuations. Body vibrations directly determine the smoothness of the ride. The main sources of fluctuations and vibrations during the movement of the vehicle are: road roughness; uneven operation of the engine and the imbalance of its rotating parts; imbalance and a tendency to excite oscillations in cardan shafts, wheels, etc.

The main systems and devices that protect the vehicle, the driver, passengers and transported goods from the effects of fluctuations and vibrations are: suspension of the vehicle; pneumatic tires; engine mount; seats (for driver and passengers); cab suspension (on modern trucks). To accelerate the damping of arising vibrations, damping devices are used, of which hydraulic shock absorbers are most widely used.

Manageability and stability. These properties of ATS are closely related, and therefore they should be considered together. They depend on the same parameters of the mechanisms - steering, suspension, tires, mass distribution between axles, etc. The difference lies in the methods for assessing the critical parameters of the movement of the vehicle. The parameters characterizing the properties of stability are determined without taking into account control actions, and the parameters characterizing the properties of controllability are determined taking them into account.

Controllability is the property of a vehicle controlled by the driver in certain road and climatic conditions to ensure the direction of movement in strict accordance with the influence of the driver on the steering wheel. Stability is the property of the vehicle to maintain the direction of movement specified by the driver under the influence of external forces that seek to deviate it from this direction.

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The main processes that cause a decrease in the efficiency of machines are considered: friction, wear, plastic deformation, fatigue and corrosion failure of machine parts. The main directions and methods of ensuring the operability of machines are given. Methods for assessing the performance of elements and technical systems as a whole are described. For university students. It can be useful for specialists in the service and technical operation of cars, tractors, construction, road and municipal vehicles.

Technical progress and reliability of machines.
With the development of scientific and technological progress, more and more complex problems arise, the solution of which requires the development of new theories and research methods. In particular, in mechanical engineering, due to the complexity of the design of machines, their technical operation, as well as technological processes, generalization and a more qualified, rigorous engineering approach are required to solve the problems of ensuring the durability of equipment.

Technological progress is associated with the creation of complex modern machines, instruments and working equipment, with a constant increase in quality requirements, as well as with a tightening of operating modes (increase in speeds, operating temperatures, loads). All this was the basis for the development of such scientific disciplines as reliability theory, tribotechnics, technical diagnostics.

CONTENT
Foreword
Chapter 1. The problem of ensuring the operability of technical systems
1.1. Technological progress and machine reliability
1.2. The history of the formation and development of tribotechnics
1.3. The role of tribotechnics in the system of ensuring the operability of machines
1.4. Triboanalysis of technical systems
1.5. Reasons for the decline in the performance of machines in operation
Chapter 2. Properties of working surfaces of machine parts
2.1. Detail profile parameters
2.2. Probabilistic characteristics of profile parameters
2.3. Contact of working surfaces of mating parts
2.4. Structure and physical and mechanical properties of the material of the surface layer of the part
Chapter 3
3.1. Concepts and definitions
3.2. Interaction of working surfaces of parts
3.3. Thermal processes accompanying friction
3.4. The influence of the lubricant on the friction process
3.5. Factors that determine the nature of friction
Chapter 4
4.1. General wear pattern
4.2. Types of wear
4.3. abrasive wear
4.4. fatigue wear
4.5. Seizure wear
4.6. Corrosion-mechanical wear
4.7. Factors affecting the nature and intensity of wear of machine elements
Chapter 5
5.1. Purpose and classification of lubricants
5.2. Lubrication types
5.3. The mechanism of the lubricating action of oils
5.4. Properties of liquid and grease lubricants
5.5. Additives
5.6. Requirements for oils and greases
5.7. Changing the properties of liquid and grease lubricants during operation
5.8. Formation of a complex criterion for assessing the state of machine elements
5.9. Restoring the performance properties of oils
5.10. Restoring the performance of machines with oils
Chapter 6
6.1. Conditions for the development of fatigue processes
6.2. Mechanism of material fatigue failure
6.3. Mathematical description of the process of fatigue failure of a material
6.4. Calculation of fatigue parameters
6.5. Evaluation of fatigue parameters of the material of a part by accelerated testing methods
Chapter 7
7.1. Classification of corrosion processes
7.2. Mechanism of corrosion destruction of materials
7.3. Influence of the corrosive environment on the nature of the destruction of parts
7.4. Conditions for the occurrence of corrosion processes
7.5. Types of corrosion damage of parts
7.6. Factors affecting the development of corrosion processes
7.7. Methods for protecting machine elements from corrosion
Chapter 8
8.1. General concepts of machine performance
8.2. Machine Reliability Planning
8.3. Machine Reliability Program
8.4. Life cycle of machines
Chapter 9
9.1. Presentation of the results of triboanalysis of machine elements
9.2. Determination of performance indicators of machine elements
9.3. Machine Life Optimization Models
Chapter 10
10.1. The performance of the power plant
10.2. The performance of transmission elements
10.3. The performance of the undercarriage elements
10.4. Operability of electrical equipment of machines
10.5. Methodology for determining the optimal durability of machines
Conclusion
Bibliography.

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• Course of materials science in questions and answers, Bogodukhov S.I., Grebenyuk V.F., Sinyukhin A.V., 2005
• Reliability and diagnostics of automatic control systems, Beloglazov I.N., Krivtsov A.N., Kutsenko B.N., Suslova O.V., Shirgladze A.G., 2008

transcript

1 Federal Agency for Education Syktyvkar Forest Institute Branch of the State Educational Institution of Higher Professional Education "St. Petersburg State Forest Engineering Academy named after S. M. Kirov" DEPARTMENT OF AUTOMOBILE AND AUTOMOBILE SECTORITY BASICS OF TECHNICAL SYSTEMS PERFORMANCE Technical operation of automobiles”, “Fundamentals of the theory of reliability and diagnostics” for students of the specialties “Service of transport and technological machines and equipment”, 9060 “Automobiles and automotive economy” of all forms of education Second edition, revised Syktyvkar 007

2 UDC 69.3 O-75 Considered and recommended for publication by the Council of the Forest Transport Department of the Syktyvkar Forest Institute on May 7, 007 Compiled by: art. teacher R. V. Abaimov, Art. Lecturer P. A. Malashchuk Reviewers: V. A. Likhanov, Doctor of Technical Sciences, Professor, Academician of the Russian Academy of Transport (Vyatka State Agricultural Academy); AF Kulminsky, Candidate of Technical Sciences, Associate Professor (Syktyvkar Forestry Institute) FUNDAMENTALS OF TECHNICAL SYSTEMS PERFORMANCE: O-75 method. manual on the disciplines "Fundamentals of the performance of technical systems", "Technical operation of vehicles", "Fundamentals of the theory of reliability and diagnostics" for stud. special "Service of transport and technological machines and equipment", 9060 "Automobiles and automotive economy" of all forms of education / comp. R. V. Abaimov, P. A. Malashchuk; Sykt. forestry in-t. Ed. second, revised Syktyvkar: SLI, p. The methodical manual is intended for conducting practical classes in the disciplines "Fundamentals of the performance of technical systems", "Technical operation of vehicles", "Fundamentals of the theory of reliability and diagnostics" and for performing tests by students of correspondence courses. The manual contains the basic concepts of the theory of reliability, the basic laws of the distribution of random variables in relation to road transport, the collection and processing of materials on reliability, general instructions for choosing job options. The problems reflect the issues of constructing block diagrams, planning tests and take into account the basic laws of the distribution of random variables. A list of recommended literature is provided. The first edition was published in 004. UDC 69.3 R. V. Abaimov, P. A. Malashchuk, compilation, 004, 007 SLI, 004, 007

3 INTRODUCTION During the operation of complex technical systems, one of the main tasks is to determine their performance, i.e., the ability to perform the functions assigned to them. This ability to a large extent depends on the reliability of products, laid down during the design period, implemented during manufacture and maintained during operation. Systems reliability engineering covers various aspects of engineering. Thanks to engineering calculations of the reliability of technical systems, uninterrupted power supply, safe traffic, etc. are guaranteed. For a correct understanding of the problems of ensuring the reliability of systems, it is necessary to know the basics of classical reliability theory. The methodological manual gives the basic concepts and definitions of the theory of reliability. The main quality indicators of reliability are considered, such as the probability of failure-free operation, frequency, failure rate, mean time to failure, failure rate parameter. Due to the fact that in the practice of operating complex technical systems in most cases one has to deal with probabilistic processes, the most commonly used distribution laws of random variables that determine reliability indicators are considered separately. Reliability indicators of the majority of technical systems and their elements can be determined only by test results. In the manual, a separate part is devoted to the methodology for collecting, processing and analyzing statistical data on the reliability of technical systems and their elements. To consolidate the material, it is planned to perform a test, consisting of answers to questions on the theory of reliability and solving a number of problems. 3

4 . RELIABILITY OF CARS.. TERMINOLOGY FOR RELIABILITY Reliability is the property of machines to perform specified functions, keeping their performance within specified limits during the required operating time. Reliability theory is a science that studies the patterns of failures, as well as ways to prevent and eliminate them in order to obtain the maximum efficiency of technical systems. The reliability of the machine is determined by the reliability, maintainability, durability and storability. Cars, like other repetitive machines, are characterized by a discrete process of operation. During operation, failures occur. Finding and eliminating them takes time during which the machine is idle, after which operation is resumed. Operability is the state of the product, in which it is able to perform the specified functions with the parameters, the values ​​of which are set by the technical documentation. In the event that the product, although it can perform its main functions, does not meet all the requirements of the technical documentation (for example, the fender of a car is dented), the product is operational, but defective. Reliability is the property of a machine to remain operational for some operating time without forced interruptions. Depending on the type and purpose of the machine, the time to failure is measured in hours, kilometers, cycles, etc. Failure is such a malfunction, without which the machine cannot perform the specified functions with the parameters established by the requirements of technical documentation. However, not every malfunction can be a failure. There are such failures that can be eliminated during the next maintenance or repair. For example, during the operation of machines, weakening of the normal tightening of fasteners, violation of the correct adjustment of units, assemblies, control drives, protective coatings, etc. are inevitable.

5 eliminated, it will lead to machine failures and time-consuming repairs. Failures are classified: according to the impact on the performance of the product: causing a malfunction (low tire pressure); causing failure (breakage of the generator drive belt); by source of occurrence: constructive (due to design errors); production (due to violation of the technological process of manufacture or repair); operational (use of substandard operational materials); due to failures of other elements: dependent, due to failure or malfunction of other elements (scuffing of the cylinder mirror due to breakage of the piston pin); independent, not caused by failure of other elements (tire puncture); by the nature (regularity) of occurrence and the possibility of forecasting: gradual, resulting from the accumulation of wear and fatigue damage in machine parts; sudden, occurring unexpectedly and associated mainly with breakdowns due to overloads, manufacturing defects, material. The moment of failure is random, independent of the duration of operation (fuses blown, parts of the undercarriage break when hitting an obstacle); according to the impact on the loss of working time: eliminated without loss of working time, i.e. during maintenance or during non-working hours (between shifts); eliminated with loss of working time. Signs of failures of objects are called direct or indirect effects on the senses of the observer of phenomena characteristic of the inoperable state of the object (oil pressure drop, the appearance of knocks, changes in temperature, etc.). 5

6 The nature of the failure (damage) is specific changes in the object associated with the occurrence of failure (wire break, part deformation, etc.). The consequences of a failure include phenomena, processes and events that occurred after the failure and in direct causal connection with it (engine stop, forced downtime for technical reasons). In addition to the general classification of failures, which is the same for all technical systems, for individual groups of machines, depending on their purpose and nature of work, an additional classification of failures is applied according to the complexity of their elimination. All failures are combined into three groups according to the complexity of elimination, taking into account such factors as the method of elimination, the need for disassembly and the complexity of eliminating failures. Durability is the property of a machine to maintain a working state to the limit with the necessary breaks for maintenance and repairs. Longevity is quantified as the total life of the machine from start-up to retirement. New machines should be designed in such a way that the service life due to physical wear and tear does not exceed obsolescence. The durability of machines is laid during their design and construction, is ensured in the production process and is maintained during operation. Thus, durability is influenced by structural, technological and operational factors, which, according to the degree of their impact, allow us to classify durability into three types: required, achieved and actual. The required durability is set by the design specifications and is determined by the level of technology development achieved in the industry. The achieved durability is determined by the perfection of design calculations and manufacturing processes. Actual durability characterizes the actual use of the machine by the consumer. In most cases, the required durability is greater than the achieved one, and the latter is greater than the actual one. At the same time not rare

7 cases where the actual durability of machines exceeds the achieved. For example, with a mileage before overhaul (KR) equal to 0 thousand km, some drivers, with skillful operation of the car, have reached a mileage without overhaul of 400 thousand km or more. Actual durability is divided into physical, moral and technical and economic. Physical durability is determined by the physical wear of a part, assembly, machine to their limiting state. For units, the determining factor is the physical wear of the basic parts (for the engine, the cylinder block, for the gearbox, the crankcase, etc.). Moral durability characterizes the service life beyond which the use of this machine becomes economically inexpedient due to the emergence of more productive new machines. Technical and economic durability determines the service life, beyond which repairs of this machine become economically unfeasible. The main indicators of the durability of machines are the technical resource and service life. The technical resource is the operating time of the object before the start of operation or its renewal after medium or major repairs until the limit state occurs. The service life is the calendar duration of the operation of an object from its beginning or renewal after an average or major overhaul to the onset of a limiting state. Maintainability is a property of a machine, which consists in its adaptability to the prevention, detection, and elimination of failures and malfunctions by carrying out maintenance and repairs. The main task of ensuring the maintainability of machines is to achieve optimal costs for their maintenance (TO) and repair with the highest efficiency of use. The continuity of technological processes of maintenance and repair characterizes the possibility of using standard technological processes of maintenance and repair of both the machine as a whole and its components. Ergonomic characteristics serve to assess the convenience of performing all maintenance and repair operations and should exclude op-7

8 radios that require the performer to be in an uncomfortable position for a long time. The safety of maintenance and repair is ensured with technically sound equipment, compliance with safety standards and regulations by the performers. The properties listed above together determine the level of maintainability of the object and have a significant impact on the duration of repairs and maintenance. The suitability of the machine for maintenance and repair depends on: the number of parts and assemblies that require systematic maintenance; frequency of service; availability of service points and ease of operation; ways of connecting parts, the possibility of independent removal, the availability of places for gripping, ease of disassembly and assembly; from the unification of parts and operating materials both within the same car model and between different car models, etc. Factors affecting maintainability can be combined into two main groups: design and operational. Calculation and design factors include design complexity, interchangeability, ease of access to units and parts without the need to remove nearby units and parts, ease of replacement of parts, and reliability of the design. Operational factors are related to the capabilities of the human operator operating the machines and the environmental conditions in which these machines operate. These factors include experience, skill, qualifications of maintenance personnel, as well as technology and methods of organizing production during maintenance and repair. Preservability is the property of a machine to withstand the negative impact of storage and transportation conditions on its reliability and durability. Since work is the basic state of an object, the influence of storage and transportation on the subsequent behavior of the object in operating mode is of particular importance. 8

9 Distinguish between the persistence of the object before commissioning and during operation (during breaks in work). In the latter case, the shelf life is included in the lifetime of the object. To assess the shelf life, gamma-percentage and average shelf life are used. Gamma percent shelf life is the shelf life that an object will achieve with a given probability of gamma percent. The average shelf life is the mathematical expectation of the shelf life... QUANTITATIVE INDICATORS OF MACHINE RELIABILITY When solving practical problems related to the reliability of machines, a qualitative assessment is not enough. In order to quantify and compare the reliability of different machines, it is necessary to introduce appropriate criteria. Such applied criteria include: the probability of failure and the probability of failure-free operation during a given operating time (mileage); failure rate (failure density) for non-repairable products; failure rate for non-repairable products; failure streams; mean time (mileage) between failures; resource, gamma-percentage resource, etc. Characteristics of random variables uptime, number of failures at some point in time, etc.). 9

10 Due to the fact that the value of a random variable is not known in advance, it is estimated using probability (the probability that a random variable will be in the interval of its possible values) or frequency (the relative number of occurrences of a random variable in a specified interval). A random variable can be described in terms of the arithmetic mean, mathematical expectation, mode, median, range of the random variable, variance, standard deviation, and coefficient of variation. The arithmetic mean is the quotient of dividing the sum of the values ​​of the random variable obtained from the experiments by the number of terms in this sum, i.e., by the number of experiments N N N N, () where is the arithmetic mean of the random variable; N number of experiments; x, x, x N individual values ​​of a random variable. The mathematical expectation is the sum of the products of all possible values ​​of a random variable and the probabilities of these values ​​(P): X N P. () Between the arithmetic mean and the mathematical expectation of a random variable, there is the following relationship with a large number of observations, the arithmetic mean of a random variable approaches its mathematical expectation. The mode of a random variable is its most probable value, that is, the value that corresponds to the highest frequency. Graphically, fashion corresponds to the largest ordinate. The median of a random variable is the value for which it is equally likely that the random variable will be greater than or less than the median. Geometrically, the median determines the abscissa of the point, the ordinate of which divides the area bounded by the distribution curve.

11 divisions in half. For symmetric modal distributions, the arithmetic mean, mode, and median are the same. The dispersion range of a random variable is the difference between its maximum and minimum values ​​obtained as a result of tests: R ma mn. (3) Dispersion is one of the main characteristics of the dispersion of a random variable around its arithmetic mean. Its value is determined by the formula: D N N (). (4) The variance has the dimension of the square of a random variable, so it is not always convenient to use it. The standard deviation is also a measure of dispersion and is equal to the square root of the dispersion. σ N N (). (5) Since the standard deviation has the dimension of a random variable, it is more convenient to use it than the variance. The standard deviation is also called the standard, basic error, or basic deviation. The standard deviation, expressed in fractions of the arithmetic mean, is called the coefficient of variation. σ σ ν or ν 00%. (6) The introduction of the coefficient of variation is necessary to compare the dispersion of quantities with different dimensions. For this purpose, the standard deviation is unsuitable, since it has the dimension of a random variable.

12 ... Probability of failure-free operation of a machine It is considered that machines operate without failure if, under certain operating conditions, they remain operable for a given operating time. Sometimes this indicator is called the reliability coefficient, which evaluates the probability of failure-free operation for the period of operation or in a given interval of operating time of the machine in given operating conditions. If the probability of failure-free operation of a car during a run of l km is P () 0.95, then out of a large number of cars of this brand, on average, about 5% lose their performance earlier than after a km of run. When observing the N-th number of cars per run (thousand km) in the operating conditions, we can approximately determine the probability of failure-free operation P() as the ratio of the number of properly working machines to the total number of machines under observation during the operating time, i.e. P () N n () N N n / N ; (7) where N is the total number of cars; N() is the number of properly working machines to run time; n number of failed machines; the value of the operating interval under consideration. To determine the true value of P(), you need to go to the limit P () n / () N n lm at 0, N 0. N The probability P(), calculated by formula (7), is called a statistical estimate of the probability of failure-free operation. Failures and failure-free operation are opposite and incompatible events, since they cannot appear simultaneously in a given machine. Hence, the sum of the probability of failure-free operation P() and the probability of failure F() is equal to one, i.e.

13 P() + F() ; P(0) ; P()0; F(0)0; F()...3. Failure rate (density of failures) The failure rate is the ratio of the number of failed products per unit of time to the initial number under supervision, provided that the failed products are not restored and not replaced with new ones, i.e. f () () n, (8) N where n() is the number of failures in the operating time interval under consideration; N is the total number of products under supervision; the value of the operating interval under consideration. In this case, n() can be expressed as: n() N() N(+) , (9) where N() is the number of properly working products for the running time; N(+) is the number of properly working products for operating time +. Since the probability of failure-free operation of products to the moments and + is expressed: N () () P ; P() N (+) N + ; N N () NP() ; N() NP(+) +, then n() N (0) 3

14 Substituting the value n(t) from (0) into (8), we get: f () (+) P() P. Passing to the limit, we get: f () Since P() F(), then (+ ) P() dp() P lm at 0. d [ F() ] df() ; () d f () d d () df f. () d Therefore, the failure rate is sometimes called the differential law of the distribution of the time of failure of products. Integrating the expression (), we obtain that the probability of failure is equal to: F () f () d 0 By the value of f(), one can judge the number of products that can fail at any operating time. The probability of failure (Fig.) in the operating time interval will be: F () F() f () d f () d f () d. 0 0 Since the probability of failure F() at is equal to one, then: 0 (). f d. 4

15 f() Fig. Probability of failure in a given operating time interval..4. Failure rate Under the failure rate understand the ratio of the number of failed products per unit of time to the average number of working without fail for a given period of time, provided that the failed products are not restored and not replaced by new ones. From the test data, the failure rate can be calculated by the formula: λ () n N cf () (), () where n() is the number of failed products for the time from to + ; considered operating interval (km, h, etc.); N cp () average number of fail-safe items. The average number of fail-safe products: () + N(+) N Nav (), (3) where N() is the number of fail-safe products at the beginning of the considered operating time interval; N(+) is the number of fail-safe products at the end of the operating time interval. 5

16 The number of failures in the considered operating time interval is expressed as: n () N() N(+) [ N(+) N() ] [ N(+) P() ]. (4) Substituting the values ​​N cf () and n() from (3) and (4) into (), we get: λ () N N [ P(+) P() ] [ P(+) + P() ] [ P(+) P() ] [ P(+) + P() ]. Passing to the limit at 0, we get Since f(), then: () λ () [ P() ]. (5) P () () f λ. P () After integrating formula (5) from 0 to we get: P () e () λ d. 0 With λ() const, the probability of failure-free operation of products is equal to: P λ () e...5. Failure flow parameter At the time of operation, the failure flow parameter can be determined by the formula: 6 () dmav ω (). d

17 The operating time interval d is small, and therefore, with an ordinary flow of failures in each machine, no more than one failure can occur during this interval. Therefore, the increment in the average number of failures can be defined as the ratio of the number of machines dm that failed over a period d to the total number N of machines under supervision: dm dm N () dq cf, where dq is the probability of failure over a period d. From here we get: dm dq ω (), Nd d i.e. the failure rate parameter is equal to the probability of failure per unit of operating time at the moment. If we take a finite time interval instead of d and denote by m() the total number of failures in machines during this time interval, then we obtain a statistical estimate of the failure rate parameter: () m ω (), N where m() is determined by the formula: N where m (+) N (+); m () m n N () m (+) m () The change in the failure rate parameter over time for most of the repaired products proceeds as shown in Fig. In the area, there is a rapid increase in the failure rate (the curve goes up), which is associated with the exit from building parts and 7 total failures at time total failures at time.,

18 units with manufacturing and assembly defects. Over time, the parts run in, and sudden failures disappear (the curve goes down). Therefore, this area is called the run-in area. On the site, the failure flows can be considered constant. This is the normal operating area of ​​the machine. Here, mainly sudden failures occur, and wear parts are changed during maintenance and preventive maintenance. In section 3, ω() increases sharply due to the wear of most components and parts, as well as the basic parts of the machine. During this period, the machine usually goes into overhaul. The longest and most significant section of the machine is. Here, the failure rate parameter remains almost at the same level under constant operating conditions of the machine. For a car, this means driving in relatively constant road conditions. ω() 3 Fig. Change in the flow of failures from running time If the parameter of the flow of failures in the section, which is the average number of failures per unit of operating time, is constant (ω() const), then the average number of failures for any period of operation of the machine in this section τ will be : m cf (τ) ω()τ or ω() m cf (τ). τ8

19 Time between failures for any period τ on the -th work area is equal to: τ const. m τ ω(τ) sr Therefore, the time between failures and the failure rate parameter, provided that it is constant, are reciprocals. The flow of failures of a machine can be considered as the sum of the flows of failures of its individual components and parts. If the machine contains k failing elements and for a sufficiently long period of work, the time between failures of each element is, 3, k, then the average number of failures of each element for this operating time will be: m cf (), m (), ..., m () sr srk. Obviously, the average number of machine failures for this operating time will be equal to the sum of the average numbers of failures of its elements: m () m () + m () + ... m (). + avg avg avg k Differentiating this expression by operating time, we get: dmav() dmav () dmav() dmav k () d d d d or the failure flow of the machine is equal to the sum of the parameters of the failure flow of its constituent elements. If the failure flow parameter is constant, then such a flow is called stationary. This property is possessed by the second section of the curve of change in the flow of failures. Knowing the reliability indicators of machines allows you to make various calculations, including calculations of the need for spare parts. The number of spare parts n SP for running time will be: 9 k

20 n sf ω() N. Taking into account that ω() is a function, for a sufficiently large operating time within the range from t to t we get: n sf N ω(y) dy. On fig. Figure 3 shows the dependence of the change in the parameters of the flow of failures of the KamAZ-740 engine under operating conditions in the conditions of Moscow, in relation to vehicles, the operating time of which is expressed in a kilometer of run. ω(t) L (mileage), thousand km 3. Change in the flow of engine failures in operating conditions 0

21 . LAWS OF DISTRIBUTION OF RANDOM VALUES DETERMINING THE RELIABILITY INDICATORS OF MACHINES AND THEIR PARTS Based on the methods of probability theory, it is possible to establish patterns in case of machine failures. In this case, experimental data obtained from the results of tests or observations of the operation of machines are used. In solving most practical problems of operating technical systems, probabilistic mathematical models (i.e., models that are a mathematical description of the results of a probabilistic experiment) are presented in an integral-differential form and are also called the theoretical distribution laws of a random variable. For a mathematical description of the results of the experiment, one of the theoretical laws of distribution is not enough to take into account only the similarity of the experimental and theoretical graphs and the numerical characteristics of the experiment (coefficient of variation v). It is necessary to have an understanding of the basic principles and physical laws of the formation of probabilistic mathematical models. On this basis, it is necessary to conduct a logical analysis of causal relationships between the main factors that affect the course of the process under study and its indicators. A probabilistic mathematical model (distribution law) of a random variable is a correspondence between possible values ​​and their probabilities P(), according to which each possible value of a random variable is assigned a certain value of its probability P(). During the operation of machines, the following distribution laws are most characteristic: normal; log-normal; Weibull distribution law; exponential (exponential), Poisson distribution law.

22 .. EXPONENTIAL DISTRIBUTION LAW The course of many road transport processes and, consequently, the formation of their indicators as random variables, is influenced by a relatively large number of independent (or weakly dependent) elementary factors (terms), each of which individually has only an insignificant effect compared to with the combined effect of all the others. The normal distribution is very convenient for the mathematical description of the sum of random variables. For example, the operating time (mileage) before maintenance is made up of several (ten or more) shift runs that differ from one another. However, they are comparable, i.e., the effect of one shift run on the total operating time is insignificant. The complexity (duration) of performing maintenance operations (control, fastening, lubricating, etc.) is the sum of the labor costs of several (8 0 or more) mutually independent transition elements, and each of the terms is quite small in relation to the sum. The normal law also agrees well with the results of an experiment to evaluate the parameters characterizing the technical condition of a part, assembly, unit and vehicle as a whole, as well as their resources and operating time (mileage) before the first failure. These parameters include: intensity (wear rate of parts); average wear of parts; change of many diagnostic parameters; the content of mechanical impurities in oils, etc. For the normal distribution law in practical problems of the technical operation of vehicles, the coefficient of variation is v 0.4. The mathematical model in differential form (ie differential distribution function) is: f σ () e () σ π, (6) in integral form () σ F() e d. (7) σ π

23 The law is two-parameter. The parameter mathematical expectation characterizes the position of the scattering center relative to the origin, and the parameter σ characterizes the extension of the distribution along the abscissa. Typical graphs f() and F() are shown in fig. 4. f() F(),0 0.5-3σ -σ -σ +σ +σ +3σ 0 a) b) Fig. 4. Graphs of theoretical curves of the differential (a) and integral (b) distribution functions of the normal law From fig. 4 it can be seen that the f() graph is relatively symmetrical and has a bell-shaped form. The entire area bounded by the graph and the abscissa axis, to the right and left of is divided by segments equal to σ, σ, 3 σ into three parts and is: 34, 4 and%. Only 0.7% of all values ​​of a random variable go beyond three sigma. Therefore, the normal law is often referred to as the "three sigma" law. It is convenient to calculate the values ​​of f() and F() if expressions (6), (7) are converted to a simpler form. This is done in such a way that the origin of coordinates is moved to the axis of symmetry, i.e., to a point, the value is presented in relative units, namely in parts proportional to the standard deviation. To do this, it is necessary to replace the variable with another, normalized, i.e., expressed in units of the standard deviation 3

24 z σ, (8) and set the value of the standard deviation equal to, i.e., σ. Then, in new coordinates, we obtain the so-called centered and normalized function, the distribution density of which is determined by: z ϕ (z) e. (9) π The values ​​of this function are given in Appendix. The integral normalized function will take the form: (dz. (0) π z z z F0 z) ϕ(z) dz e . The values ​​of the function F 0 (z), given in the appendix, are given at z 0. If the value of z turns out to be negative, then the formula F 0 (0 z) must be used. For the function ϕ (z), the relation z) F () is true. () ϕ (z) ϕ(z). () The reverse transition from the centered and normalized functions to the original one is done according to the formulas: f ϕ(z) σ (), (3) F) F (z). (4) (0 4

25 In addition, using the normalized Laplace function (app. 3) z z Ф (z) e dz, (5) π 0 the integral function can be written in the form () Ф. F + (6) σ Theoretical probability P() of hitting a random variable , normally distributed, into the interval [ a< < b ] с помощью нормированной (табличной) функции Лапласа Ф(z) определяется по формуле b Φ a P(a < < b) Φ, (7) σ σ где a, b соответственно нижняя и верхняя граница интервала. В расчетах наименьшее значение z полагают равным, а наибольшее +. Это означает, что при расчете Р() за начало первого интервала, принимают, а за конец последнего +. Значение Ф(). Теоретические значения интегральной функции распределения можно рассчитывать как сумму накопленных теоретических вероятностей P) каждом интервале k. В первом интервале F () P(), (во втором F () P() + P() и т. д., т. е. k) P(F(). (8) Теоретические значения дифференциальной функции распределения f () можно также рассчитать приближенным методом 5

26 P() f(). (9) The failure rate for the normal distribution law is determined by: () () f λ (x). (30) P PROBLEM. Let the breakdown of the springs of a GAZ-30 car obey the normal law with parameters 70 thousand km and σ 0 thousand km. It is required to determine the characteristics of the reliability of the springs for the run x 50 thousand km. Solution. The probability of failure of the springs is determined through the normalized normal distribution function, for which we first determine the normalized deviation: z. σ Taking into account the fact that F 0 (z) F0 (z) F0 () 0.84 0.6, the probability of failure is F () F0 (z) 0.6, or 6%. Probability of failure-free operation: Failure rate: P () F () 0.6 0.84, or 84%. ϕ(z) f () ϕ ϕ ; σ σ σ 0 0 taking into account the fact that ϕ(z) ϕ(z) ϕ() 0.40, the frequency of spring failures f () 0.0. f () 0.0 Failure rate: λ() 0.044. P() 0.84 6

27 When solving practical reliability problems, it often becomes necessary to determine the operating time of a machine for given values ​​of the probability of failure or no-failure operation. Such tasks are easier to solve using the so-called quantile table. Quantiles are the value of the function argument corresponding to the given value of the probability function; Let us denote the failure probability function under the normal law p F0 P; σ p arg F 0 (P) u p. σ + σ. (3) p u p Expression (3) determines the operating time p of the machine for a given value of the probability of failure P. The operating time corresponding to the given value of the probability of failure-free operation is expressed: x x σ u p p. The table of quantiles of the normal law (Appendix 4) gives the values ​​of the quantiles u p for probabilities p > 0.5. For probabilities p< 0,5 их можно определить из выражения: u u. p p ЗАДАЧА. Определить пробег рессоры автомобиля, при котором поломки составляют не более 0 %, если известно, что х 70 тыс. км и σ 0 тыс. км. Решение. Для Р 0,: u p 0, u p 0, u p 0,84. Для Р 0,8: u p 0,8 0,84. Для Р 0, берем квантиль u p 0,8 co знаком «минус». Таким образом, ресурс рессоры для вероятности отказа Р 0, определится из выражения: σ u ,84 53,6 тыс. км. p 0, p 0,8 7

28 .. LOG-NORMAL DISTRIBUTION A log-normal distribution is formed if the course of the process under study and its result are influenced by a relatively large number of random and mutually independent factors, the intensity of which depends on the state reached by the random variable. This so-called proportional effect model considers some random variable having an initial state of 0 and a final limit state of n. The random variable changes in such a way that (), (3) ± ε h where ε is the intensity of the random variable change; h() is a reaction function that shows the nature of the change in a random variable. h we have: For () n (± ε) (± ε) (± ε)... (± ε) Π (± ε), 0 0 (33) where П is the sign of the product of random variables. Thus, the limit state: n n Π (± ε). (34) 0 From this it follows that it is convenient to use the logarithmically normal law for the mathematical description of the distribution of random variables, which are the product of the initial data. It follows from expression (34) that n ln ln + ln(± ε). (35) n 0 Therefore, under the logarithmically normal law, the normal distribution is not the random variable itself, but its logarithm, as the sum of random equal and equally independent variables.

29 ch. Graphically, this condition is expressed in the elongation of the right side of the curve of the differential function f () along the abscissa, i.e., the graph of the curve f () is asymmetric. In solving practical problems of the technical operation of vehicles, this law (at v 0.3 ... 0. 7) is used to describe the processes of fatigue failure, corrosion, operating time until loosening of fasteners, and changes in clearance gaps. And also in those cases where the technical change occurs mainly due to wear of friction pairs or individual parts: brake linings and drums, clutch discs and friction linings, etc. The mathematical model of a logarithmically normal distribution has the following form: in differential form: in integral form: F f (ln) (ln) (ln a) σln e, (36) σ π ln (ln a) ln σln e d(ln), (37) σ π ln where is a random variable whose logarithm is normally distributed; a is the mathematical expectation of the logarithm of the random variable; σ ln is the standard deviation of the logarithm of the random variable. The most characteristic curves of the differential function f(ln) are shown in Figs. 5. From fig. 5 it can be seen that the graphs of the functions are asymmetric, elongated along the abscissa axis, which is characterized by the parameters of the distribution shape σ. ln 9

30 F() Fig. 5. Characteristic graphs of the differential function of the log-normal distribution For the log-normal law, the change of variables is as follows: z ln a. (38) σ ln z F 0 z are determined by the same formulas and tables as for the normal law. To calculate the parameters, the values ​​of natural logarithms ln are calculated for the middle of the intervals, the statistical mathematical expectation a: The values ​​of the functions ϕ (), () a k () ln (39) m and the standard deviation of the logarithm of the considered random variable σ N k (ln a) ln n. (40) According to the tables of probability densities of the normalized distribution, ϕ (z) is determined and the theoretical values ​​of the differential distribution function are calculated using the formula: f () 30 ϕ (z). (4) σln

31 Calculate the theoretical probabilities P () of hitting a random variable in the interval k: P () f (). (4) The theoretical values ​​of the cumulative distribution function F () are calculated as the sum of P () in each interval. The log-normal distribution is asymmetric with respect to the mean value of experimental data - M for data. Therefore, the value of the estimate of the mathematical expectation () of this distribution does not coincide with the estimate calculated by the formulas for the normal distribution. In this regard, estimates of the mathematical expectation M () and standard deviation σ are recommended to be determined by the formulas: () σln a + M e, (43) σ (σ) M () (e) ln M. (44) Thus, when generalization and dissemination of the results of the experiment, not the entire population using the mathematical model of the logarithmically normal distribution, it is necessary to apply estimates of the parameters M () and M (σ). The logarithmically normal law obeys the failures of the following parts of the car: driven clutch discs; front wheel bearings; the frequency of loosening threaded connections in 0 nodes; fatigue failure of parts during bench tests. 3

32 CHALLENGE. During bench tests of the car, it was found that the number of cycles before destruction obeys a logarithmically normal law. Determine the resource of parts from the condition of absence 5 of destruction Р () 0.999, if: a Σ 0 cycles, N k σln (ln a) n, σ Σ(ln ln) 0.38. N N Solution. According to the table (Appendix 4) we find for P () 0.999 Ur 3.090. Substituting the values ​​of u p, and σ into the formula, we obtain: 5 0 ep 3.09 0, () cycles. If the system consists of groups of independent elements, the failure of each of which leads to the failure of the entire system, then in such a model the distribution of the time (or run) for reaching the limit state of the system is considered as the distribution of the corresponding minimum values ​​of individual elements: c mn(; ;...; n). An example of the use of the Weibull law is the distribution of a resource or the intensity of a change in the parameter of the technical condition of products, mechanisms, parts that consist of several elements that make up the chain. For example, the life of a rolling bearing is limited by one of the elements: a ball or a roller, more specifically, a cage section, etc., and is described by the specified distribution. According to a similar scheme, the limiting state of the thermal clearances of the valve mechanism occurs. Many products (aggregates, units, vehicle systems) in the analysis of the failure model can be considered as consisting of several elements (sections). These are gaskets, seals, hoses, pipelines, drive belts, etc. The destruction of these products occurs in different places and with different operating hours (mileage), however, the life of the product as a whole is determined by its weakest section. 3

33 The Weibull distribution law is very flexible for evaluating car reliability indicators. With its help, you can simulate the processes of sudden failures (when the distribution form parameter b is close to unity, i.e. b) and failures due to wear (b,5), and also when the causes that cause both of these failures are combined . For example, a fatigue-related failure can be caused by the combined action of both factors. The presence of hardening cracks or notches on the surface of the part, which are manufacturing defects, usually causes fatigue failure. If the initial crack or notch is large enough, it can itself cause failure of the part if a significant load is suddenly applied. This is a case of a typical sudden failure. The Weibull distribution also describes well the gradual failures of car parts and assemblies caused by the aging of the material as a whole. For example, the failure of the car body due to corrosion. For the Weibull distribution in solving the problems of technical operation of vehicles, the value of the coefficient of variation is within v 0.35 0.8. The mathematical model of the Weibull distribution is given by two parameters, which leads to a wide range of its application in practice. The differential function has the form: integral function: f () F b a () a 33 b e b a b a, (45) e, (46) where b is the shape parameter, affects the shape of the distribution curves: at b< график функции f() обращен выпуклостью вниз, при b >bulge up; and the scale parameter characterizes the stretching of the distribution curves along the x-axis.

34 The most characteristic curves of the differential function are shown in fig. 6. F() b b.5 b b 0.5 Fig. 6. Characteristic curves of the Weibull differential distribution function At b, the Weibull distribution is transformed into an exponential (exponential) distribution, at b into the Rayleigh distribution, at b.5 3.5 the Weibull distribution is close to normal. This circumstance explains the flexibility of this law and its wide application. The calculation of the parameters of the mathematical model is carried out in the following sequence. Calculate the values ​​of natural logarithms ln for each value of the sample and determine the auxiliary values ​​for estimating the Weibull distribution parameters a and b: y N N ln (). (47) y N N (ln) y. (48) Estimates of parameters a and b are determined: b π σ y 6, (49) 34

35 γ y b a e, (50) where π 6.855; γ 0.5776 Euler constant. The estimate of the parameter b thus obtained for small values ​​of N (N< 0) значительно смещена. Для определения несмещенной оценки b) параметра b необходимо провести поправку) b M (N) b, (5) где M(N) поправочный коэффициент, значения которого приведены в табл.. Таблица. Коэффициенты несмещаемости M(N) параметра b распределения Вейбулла N M(N) 0,738 0,863 0,906 0,98 0,950 0,96 0,969 N M(N) 0,9 0,978 0,980 0,98 0,983 0,984 0,986 Во всех дальнейших расчетах необходимо использовать значение несмещенной оценки b). Вычисление теоретических вероятностей P () попадания в интервалы может производиться двумя способами:) по точной формуле: P b b βh βb β, (5) (< < β) H где β H и β соответственно, нижний и верхний пределы -го интервала по приближенной формуле (4). Распределение Вейбулла также B является асимметричным. Поэтому оценку математического ожидания M() для генеральной совокупности необходимо определять по формуле: B e M () a +. (53) b e 35

36 . 4. EXPONENTIAL LAW OF DISTRIBUTION The model of formation of this law does not take into account the gradual change of factors influencing the course of the process under study. For example, a gradual change in the parameters of the technical condition of the car and its units, components, parts as a result of wear, aging, etc., but considers the so-called ageless elements and their failures. This law is most often used when describing sudden failures, operating time (mileage) between failures, labor intensity of current repairs, etc. Sudden failures are characterized by an abrupt change in the technical condition indicator. An example of a sudden failure is damage or destruction when the load momentarily exceeds the strength of the object. In this case, such an amount of energy is reported that its transformation into another form is accompanied by a sharp change in the physicochemical properties of the object (part, assembly), causing a sharp drop in the strength of the object and failure. An example of an unfavorable combination of conditions, causing, for example, a breakage of a shaft, can be the action of the maximum peak load at the position of the most weakened longitudinal fibers of the shaft in the load plane. With the aging of the car, the proportion of sudden failures increases. The conditions for the formation of the exponential law correspond to the distribution of the mileage of units and assemblies between subsequent failures (except for the mileage from the start of commissioning and until the moment of the first failure for this unit or unit). The physical features of the formation of this model are that during repairs, in the general case, it is impossible to achieve the full initial strength (reliability) of the unit or assembly. The incomplete restoration of the technical condition after repair is explained by: only partial replacement of failed (faulty) parts with a significant decrease in the reliability of the remaining (not failed) parts as a result of their wear, fatigue, misalignment, tightness, etc.; the use of lower quality spare parts in repairs than in the manufacture of cars; a lower level of production during repairs compared to their manufacture, caused by small-scale repairs (the impossibility of a comprehensive 36

37 mechanization, the use of specialized equipment, etc.). Therefore, the first failures characterize mainly the structural reliability, as well as the quality of manufacture and assembly of vehicles and their components, and the subsequent ones characterize the operational reliability, taking into account the existing level of organization and production of maintenance and repair and the supply of spare parts. In this regard, it can be concluded that starting from the moment the unit or unit is run after its repair (usually associated with disassembly and replacement of individual parts), failures appear like sudden ones and their distribution in most cases obeys an exponential law, although their physical nature is mainly by the joint manifestation of wear and fatigue components. For the exponential law in solving practical problems of the technical operation of vehicles, v > 0.8. The differential function has the form: f λ () λ e, (54) integral function: F (λ) e. (55) The graph of the differential function is shown in fig. 7. f() 7. Characteristic curve of the differential function of the exponential distribution 37

38 The distribution has one parameter λ, which is related to the average value of the random variable by the relation: λ. (56) The unbiased estimate is determined by the normal distribution formulas. Theoretical probabilities P () are determined in an approximate way according to formula (9), in an exact way according to the formula: P B λ λβh λβb (β< < β) e d e e. (57) H B β β H Одной из особенностей показательного закона является то, что значению случайной величины, равному математическому ожиданию, функция распределения (вероятность отказа) составляет F() 0,63, в то время как для нормального закона функция распределения равна F() 0,5. ЗАДАЧА. Пусть интенсивность отказов подшипников ОТКАЗ скольжения λ 0,005 const (табл.). Определить вероятность безотказной работы подшипника за пробег 0 тыс. км, если из- 000км вестно, что отказы подчиняются экспоненциальному закону. Решение. P λ 0,0050 () e e 0, 95. т. е. за 0 тыс. км можно ожидать, что откажут около 5 подшипников из 00. Надежность для любых других 0 тыс. км будет та же самая. Какова надежность подшипника за пробег 50 тыс. км? P λ 0,00550 () e e 0,

39 CHALLENGE. Using the condition of the above problem, determine the probability of failure-free operation for 0 thousand km between runs of 50 and 60 thousand km and the time between failures. Solution. λ 0.005 () P() e e 0.95. The time between failures is equal to: 00 thousand. km. λ 0.005 PROBLEM 3. At what mileage will 0 gearbox gears out of 00 fail, i.e. P() 0.9? Solution. 00 0.9e; ln 0.9; 00ln 0.9 thousand km. 00 Table. Failure rate, λ 0 6, /h, of various mechanical elements Element name Gear reducer Rolling bearings: ball roller Plain bearings Seals of elements: rotating translationally moving Shaft axles 39 Failure rate, λ 0 6 Change limits 0, 0.36 0.0, 0 0.0, 0.005 0.4 0.5, 0, 0.9 0.5 0.6 Average value 0.5 0.49, 0.45 0.435 0.405 0.35 The exponential law quite well describes the failure of the following parameters: operating time to failure of many non-recoverable elements of radio-electronic equipment; operating time between adjacent failures with the simplest failure flow (after the end of the running-in period); recovery time after failures, etc.

40. 5. POISSON DISTRIBUTION LAW The Poisson distribution law is widely used to quantify a number of phenomena in the queuing system: the flow of cars arriving at the service station, the flow of passengers arriving at public transport stops, the flow of buyers, the flow of subscribers picking up at automatic telephone exchanges, etc. This law expresses the probability distribution of a random variable of the number of occurrence of some event for a given period of time, which can only take integer values, i.e. m 0, 3, 4, etc. The probability of occurrence of the number of events m 0, 3, ... for a given period of time in Poisson's law is determined by the formula: P (m a) m (λ t) t m, a α λ e e ​​m! m!, (58) where P(m,a) the probability of occurrence for the considered time interval t of some event is equal to m; m is a random variable representing the number of occurrence of an event for the considered period of time; t is the length of time during which some event is being investigated; λ intensity or density of an event per unit of time; α λt is the mathematical expectation of the number of events for the considered period of time..5.. Calculation of the numerical characteristics of Poisson's law The sum of the probabilities of all events in any phenomenon is, m a α ie e. m 0 m! The mathematical expectation of the number of events is: X a m m α α α (m) m e a e e a m 0!. 40

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Topics of abstracts on the discipline "Fundamentals of the performance of technical systems":

Failures of machines and their elements. Reliability indicators Technological progress and machine reliability. History of the formation and development of tribotechnics. The role of tribology in the system of ensuring the durability of machines. Triboanalysis of mechanical systems Causes of changes in the technical condition of machines in operation Interaction of working surfaces of parts. Thermal processes accompanying friction. Influence of a lubricant on the friction process Factors that determine the nature of friction. Friction of elastomeric materials The general pattern of wear. Types of wear Abrasive wear Fatigue wear Seizure wear. Corrosion-mechanical wear. Selective transfer. Hydrogen wear Factors affecting the nature and intensity of wear of machine elements. The distribution of wear on the working surface of the part. Patterns of wear of machine elements. Forecasting wear of interfaces Purpose, classification and types of lubricants The mechanism of the lubricating action of oils Requirements for oils and plastic lubricants Changes in the properties of lubricants during operation Fatigue of materials of machine elements (development conditions, mechanism, assessment of fatigue parameters by accelerated test methods) Corrosion destruction of parts machines (classification, mechanism, types, methods of protection of parts) Restoration of the performance of parts with lubricants and working fluids Restoration of parts with polymeric materials Design, technological and operational measures to improve reliability. Comparative characteristics and assessment of the degree of influence on the resource of parts.

Requirements:

For decoration. The volume of at least 10 sheets of printed text (table of contents, introduction, conclusion, list of references is not required). Font 14 Times New Roman, justified alignment, line spacing 1.5, indents 2 cm everywhere.

To content. The work must be written by a student with obligatory references to sources. Copying without links is prohibited. The topic of the abstract should be disclosed. If there are examples, then they should be reflected in the work (for example, the topic "abrasive wear" should be supported by an example - the crankshaft journal - main bearings or others, within the framework of this topic, at the discretion of the student). If there are formulas in the sources, then only the main ones should be reflected in the work.

For protection. The work must be read by the student repeatedly. Protection time is no more than 5 minutes + answers to questions. The topic should be presented concisely, highlighting key points with examples, if any.

Main literature:

1. Zorin performance of technical systems: A textbook for students. higher textbook establishments. UMO. – M.: Ed. Center "Academy", 2009. -208 p.

2. Shishmarev automatic control: a textbook for universities. – M.: Academy, 2008. – 352 p.

Additional literature:

1. Technical operation of cars: Textbook for universities. Ed. . - M: Nauka, 2001.

2. Russian motor transport encyclopedia: Technical operation, maintenance and repair of vehicles. T. 3 - M .: ROOIG1 - "For social protection and fair taxation", 2000.

3. Kuznetsov technical systems. Tutorial. - M.: Ed. MADI, 1999, 2000.

4. Crown of operations. Tasks principles methodology. - M.: Nauka, 1988.

5. Kuznetsov and trends in technical operation and service in Russia: Automobile transport. Series: "Technical operation and repair of cars". - M.: Informavtotrans, 2000.

6. Transport and communications in Russia. Analytical collection. - M: Goskomstat of Russia. 2001.

7.3. Databases, information and reference and search systems:

This course work consists of two chapters. The first chapter is devoted to the practical use of engineering reliability theory. In accordance with the assignment for the course work, the following indicators are calculated: the probability of failure-free operation of the unit; the probability of failure of the unit; failure probability density (law of distribution of a random variable); coefficient of completeness of resource recovery; recovery function (leading function of the failure stream); failure rate. Based on the calculations, graphic images of a random variable, a differential distribution function, a change in the intensity of gradual and sudden failures, a scheme for the formation of the recovery process and the formation of a leading recovery function are built.
The second chapter of the course work is devoted to the study of the theoretical foundations of technical diagnostics and the assimilation of practical diagnostic methods. This section describes the purpose of diagnostics in transport, develops a structural-investigative model of steering, considers all possible methods and means of diagnosing steering, analyzes from the point of view of the completeness of fault detection, labor intensity, cost, etc.

LIST OF ABBREVIATIONS AND SYMBOLS 6
INTRODUCTION 6
MAIN PART 8
Chapter 1. Fundamentals of the practical use of the theory of reliability 8
Chapter 2. Methods and means of diagnosing technical systems 18
REFERENCES 21

The work contains 1 file

FEDERAL AGENCY FOR EDUCATION

State Educational Institution of Higher Professional Education

"Tyumen State Oil and Gas University"

Branch Muravlenko

Department of EOM

COURSE WORK

by discipline:

"Fundamentals of the performance of technical systems"

Completed:

Student of the STEz-06 group D.V. Shilov

Checked by: D.S. Bykov

Muravlenko 2008

annotation

This course work consists of two chapters. The first chapter is devoted to the practical use of engineering reliability theory. In accordance with the assignment for the course work, the following indicators are calculated: the probability of failure-free operation of the unit; the probability of failure of the unit; failure probability density (law of distribution of a random variable); coefficient of completeness of resource recovery; recovery function (leading function of the failure stream); failure rate. Based on the calculations, graphic images of a random variable, a differential distribution function, a change in the intensity of gradual and sudden failures, a scheme for the formation of the recovery process and the formation of a leading recovery function are built.

The second chapter of the course work is devoted to the study of the theoretical foundations of technical diagnostics and the assimilation of practical diagnostic methods. This section describes the purpose of diagnostics in transport, develops a structural-investigative model of steering, considers all possible methods and means of diagnosing steering, analyzes from the point of view of the completeness of fault detection, labor intensity, cost, etc.

Assignment for term paper

22 option. Main bridge.
160	160,5	172,2	191	161,7		100	102,3	115,3	122,7	150
175,5	169,5	176,5	192,1	162,2		126,5	103,6	117,4	130	147,7
166,9	164,7	179,5	193,9	169,6		101,7	104,8	113,7	130,4	143,4
189,6	179	181,1	194	198,9		134,9	105,3	124,8	135	139,9
176,2	193	181,9	195,3	199,9		130,5	109,6	122,2	136,4	142,7
162,3	163,6	183,2	196,3	200		133,8	107,4	114,3	132,4	146,4
188,9	193,5	185,1	195,9	193,6		122,5	108,6	125,6	138,8	144,8
158	191,1	187,4	196,6	195,7		105,4	113,6	126,7	140	138,3
190,7	168,8	188,8	197,7	193,5		133	111,9	127,9	145,8	144,6
180,4	163,1	189,6	197,9	195,8		122,4	113,6	128,4	143,7	139,3

List of abbreviations and symbols

ATP - motor transport company

SW - random variables

TO - maintenance

UTT - technological transport management

Introduction

Road transport is developing qualitatively and quantitatively at a rapid pace. Currently, the annual growth of the world car fleet is 10-12 million units, and its number is more than 100 million units.

In the machine-building complex of Russia, a significant number of industries of production and processing of products are combined. The future of motor transport facilities, organizations of the oil and gas complex and utilities in the Yamalo-Nenets region is inextricably linked with their equipment with high-performance equipment. The performance and serviceability of machines can be achieved by timely and high-quality performance of work on their diagnosis, maintenance and repair.

At present, the automotive industry is faced with the following tasks: to reduce the specific metal consumption by 15-20%, increase the service life and reduce the labor intensity of maintenance and repair of vehicles.

The efficient use of machinery is carried out on the basis of a scientifically substantiated preventive maintenance and repair system, which makes it possible to ensure the efficient and serviceable condition of the machines. This system makes it possible to increase labor productivity on the basis of ensuring the technical readiness of machines at minimal cost for these purposes, improve the organization and improve the quality of work on the maintenance and repair of machines, ensure their safety and extend their service life, optimize the structure and composition of the repair and maintenance base and regularity. its development, accelerate scientific and technological progress in the use, maintenance and repair of machines.

Manufacturers, receiving the right to independently trade in their products, must simultaneously be responsible for their performance, provision of spare parts and organization of technical services throughout the entire service life of the machines.

The most important form of participation of manufacturers in the technical service of machines is the development of proprietary repairs of the most complex assembly units (engines, hydraulic transmissions, fuel and hydraulic equipment, etc.) and the restoration of worn parts.

This process can go along the path of creating our own production facilities, as well as with the joint participation of existing repair plants and repair and mechanical workshops.

The development of evidence-based technical service, the creation of a service market and competition impose strict requirements on technical service performers.

With the existing growth in the pace of road transport at enterprises, an increase in the quantitative composition of the automobile fleet of enterprises, it becomes necessary to organize new structural divisions of the ATP, whose task is to carry out maintenance and repair of road transport.

An important element of the optimal organization of repairs is the creation of the necessary technical base, which predetermines the introduction of progressive forms of labor organization, an increase in the level of mechanization of work, equipment productivity, and a reduction in labor costs and funds.

Main part

Chapter 1. Fundamentals of the practical use of the theory of reliability.

The initial data for calculating the first part of the course work are the time to failure for fifty similar units:

Time to first failure (thousand km)

160	160,5	172,2	191	161,7
175,5	169,5	176,5	192,1	162,2
166,9	164,7	179,5	193,9	169,6
189,6	179	181,1	194	198,9
176,2	193	181,9	195,3	199,9
162,3	163,6	183,2	196,3	200
188,9	193,5	185,1	195,9	193,6
158	191,1	187,4	196,6	195,7
190,7	168,8	188,8	197,7	193,5
180,4	163,1	189,6	197,9	195,8

Time to second failure (thousand km) 304,1

331,7 342,6 296,1 271 297,5 328,7 346,4 311,4 302,1 310,7 334,7 338,4 263,4 304,7 314,1 336,6 334 323,7 280,7 316,7 343,5 338,1 302,8 276,7 318 341,6 335,1

Random variables- MTBF (from 1 to 50) arranged in ascending order of their absolute values:

L 1 = L min ; L 2 ; L 3 ;…;L i ;…L n-1 ; L n = L max , (1.1)

Where L 1 ... L n – implementation of a random variable L;

n- number of implementations.

L min \u003d 158; L max =200;