Braking- 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.
Braking properties- a set of properties that determine the maximum deceleration of a car when it moves on various roads in braking mode, the limiting values of external forces under the action of which a braked car is reliably held in place or has the required minimum steady speeds when moving downhill.
Braking mode- a mode in which braking torques are applied to all or several wheels.
Braking properties are among the most important operational properties that determine the active safety of a vehicle, which is understood as a set of special design measures that reduce the likelihood of an accident.
Due to the great importance of the properties that determine the safety of a car, their regulation is the subject of a number of international documents.
The effectiveness of the action is checked by measuring the braking forces developed on the wheels (the value of the total specific braking force of the working and parking brake systems; the coefficient of unevenness of the braking forces of the axle wheels; the force applied to the brake pedal), as well as by inspecting and testing individual components of the systems.
Meaning coefficient of axial unevenness of braking forces Kn determined separately for each vehicle axle using the formula:
where are the maximum forces developed by the brakes on the right and left wheels of each vehicle axle, respectively. Kn values for passenger cars should be no more than 0.09.
The value of the total braking force γт is determined by the formula:
γт = ΣРт/М
where – ΣРт is the sum of the maximum braking forces on the wheels of the vehicle kg.
M – total mass of the vehicle, kg.
The magnitude of the braking forces is adjusted taking into account the cost of turning the wheels, i.e. data obtained before checking the braking forces.
Brake response time is defined as the time interval from the start of braking to the moment at which the deceleration becomes constant, that is, the braking force reaches its maximum value and then remains constant.
Force on the control (brake pedal): for single vehicles of categories M1 – 490 N, M2, M3, N1, N2, N3 – 686 N; road trains M1 – 490N, M2, M3, N1, N2, N3 – 686N.
The total specific braking force of single vehicles is not less than M1 – 0.64; M2, M3 – 0.55; N1, N2, N3 – 0.46; M1 road trains – 0.47; M2 –0.42; M3 – 0.51; N1 – 0.38; N2, N3 – 0.46.
The braking system response time is no more than s M1 – 0.5; M2,M3 – 0.8; N1 – 0.7; N2, N3 – 0.8; road trains from M1 – 0.5; M2 – 0.8; M3 – 0.9; N1 – 0.9; N2 – 0.7; N3 – 0.9.
The coefficient of unevenness of the braking forces of the axle wheels is not more than M1; M2 – 0.09; M3,N1, N2, N3 – 0.11; road trains – from M1, M2 – 0.09; M3 – 1st axis – 0.09, subsequent axes 0.13; N1 – 0.11; N2, N3 – 1st axis – 0.09, subsequent axes 0.13.
The value of the total specific braking force must be at least 16% relative to the permissible maximum weight of a single vehicle and not less than 12% relative to the maximum permissible weight of a combined vehicle.
During operation, it is possible to evaluate braking performance based on the braking distance and deceleration of the vehicle.
Braking distances- this is the distance that the car travels from the start of braking to a complete stop and is determined by the formula:
S=kv2/ 254φ
Where:
k – braking efficiency coefficient. It takes into account the disproportion of the braking forces on the wheels to the loads placed on them, as well as wear, adjustment and contamination of the brakes. This coefficient shows how many times the actual deceleration of the rolling stock is less than the theoretical maximum possible on a given road. Value k for trucks and buses 1.4…1.6, for cars 1.2
v – speed in km/h
φ – coefficient of wheel adhesion to the road.
Deceleration is the amount by which the vehicle's speed decreases per unit time.
Table Efficiency standards for braking performance and deceleration (SDA)
|
Name of vehicles |
Braking distance (m, no more) |
Slowdown (m/s 2, no more) |
|
Passenger cars and their modifications for transporting goods |
12,2 (14,6) |
6,8 (6,1) |
|
up to 5 t inclusive over 5 t |
13,6 (18,7) 16,8 (19,9) |
5,7 (5,0) 5,7 (5,0) |
|
up to 3.5 t inclusive from 3.5 to 12 t inclusive over 12 t |
15,1 (19,0) 17,3 (18,4) 16,0 (17,7) |
5,7 (5,4) 5,7 (5,7) 6,2 (6,1) |
|
Two-wheeled motorcycles and mopeds |
7,5 (7,5) |
5,5 (5,5) |
|
Motorcycles with trailer |
8,2 (8,2) |
5,0 (5,0) |
|
Road trains, the tractors of which are passenger cars and their modifications for the transportation of goods |
13,6 (14,5) |
5,9 (6,1) |
|
Buses with maximum weight: up to 5 t inclusive over 5 t |
15,2 (18,7) 18,4 (19,9( |
5,7 (5,5) 5,5 (5,0) |
|
Trucks with maximum weight: up to 3.5 t inclusive from 3.5 t to 12 t inclusive over 12 t |
17,7 (22,7) 18,8 (22,1) 18,4 (21,9) |
4,6 (4,7) 5,5 (4,9) 5,5 (5,0) |
- The braking distance and steady-state deceleration values given in brackets apply to vehicles whose production began before January 1, 1981.
- Tests are carried out on a horizontal section of road with a flat, dry, clean cement or asphalt concrete surface at an initial braking speed of 40 km/h for cars, buses and road trains and 30 km/h for motorcycles and mopeds. Vehicles are tested in loaded condition with the driver by applying a single impact to the control of the service brake system.
- The effectiveness of the service braking system of vehicles can be assessed by other indicators in accordance with GOST 25478-91.
The parking brake system does not provide a stationary position:
- vehicles with full load - on a slope of up to 16% inclusive
- passenger cars and buses in running order - on a slope of up to 23% inclusive
- trucks and road trains in running order - on a slope of up to 31% inclusive
The parking brake system control lever (handle) is not held by the locking device.
An indicator of the effectiveness of the parking brake system is the value of the specific braking force. When testing a vehicle with a permissible maximum mass, the specific braking force must be at least 0.16. for vehicles in running order, the parking brake system must provide a design specific braking force equal to 0.6 of the ratio of the curb weight on the axles affected by the parking brake system in the curb weight.
Test Methods
Checks on benches and in road conditions must be carried out with the engine running and disconnected from the transmission, as well as the drives of additional drive axles and unlocked transmission differentials. The total weight of diagnostic equipment placed on the vehicle should not exceed 25 kg.
Tests must be carried out under safe conditions.
The measurement error must be within the following limits for:
· braking distance - ±5%;
· initial braking speed - ±1 km/h;
steady deceleration - ±4
· longitudinal slope of the braking area - ±1%;
· braking force - ±3%;
· efforts on the control - ±7%;
· braking system response time - ±0.03 s;
· brake system delay time - ±0.03 s;
· deceleration rise time - ±0.03 s;
· air pressure in the pneumatic or pneumohydraulic brake drive - ±5%.
Checking the service brake system when road tests
must be carried out in accordance with the following requirements:
Initial speed – 40 km/h;
Correction of the vehicle's trajectory is not allowed (the steering is in an intact state);
Emergency, single, full braking.
When testing the stability of a vehicle, three stripes must be applied to the site, indicating the axis of movement, the right and left boundaries of the corridor. The car must move straight at the set speed along the corridor axis. The position of the vehicle after braking is completed is determined visually by its projection onto the supporting surface. In the event of the formation of two or more points of intersection of the resulting projection of the car and the boundaries of the corridor, the value of the stability parameter cannot be considered satisfactory.
Road tests can be carried out using universal means of measuring linear-angular quantities and a decelerometer - a mechanical device for measuring steady-state deceleration. In addition, there are now specialized electronic devices. These may include the “Effect” device. This device can comprehensively determine a number of parameters (Table 3.4).
Bench tests
brake systems on roller stands are carried out when there is a driver and passenger in the front seat of cars of categories M1 and N1. During testing, the condition of the stand rollers is important. They are not allowed to wear until the corrugated surface is completely worn out or the abrasive coating is destroyed. Bench tests are carried out using brake testers of various models. The range of these devices is quite diverse. Therefore, when choosing a brake tester, you must be guided by the technical characteristics of the vehicle being tested.
The STS-2 model brake tester is designed to monitor the effectiveness of braking systems and braking stability of passenger cars, small buses, mini-trucks with an axle load not exceeding 19600 N, with a track width of 1200...1820 mm. Its technical data is given in table. 3.5.
The STS-10 brake tester is designed for diagnosing the brake systems of trucks, buses, trolleybuses, trailers as part of road trains with a track width of 1500...2160 mm, a vehicle wheel diameter of 968...1300 mm. Its technical data is given in table. 3.6.
Development of a technological process diagram for repairing EO-4123
This diagram (Figure 4) is a graphical representation of the process route. We construct the scheme on the basis of the route map (Table 1) and the table for the formation of posts (Table 2). Individual posts are shown in the form of blocks, linked by the technological sequence of movement of the product, elements...
Dismantling and assembling the cylinder head
Disassembly. If only one part needs to be replaced, you do not have to completely disassemble the cylinder head and remove only what is necessary for replacement. Place the cylinder head on the stand, remove the carburetor throttle valve drive rod, unscrew the nuts and remove the carburetor with the gasket, and...
Calculation and selection of handling equipment
Disassembly, assembly and repair work require the removal, installation and transportation of bulky elements, components and parts. These works are carried out using lifting and transport equipment, which significantly increases labor productivity and improves the working conditions of repairmen. Lifting and transport equipment...
In table Table 3 shows the limiting values of the coefficient of unevenness of braking forces for wheels of one axle of cars and trailers K N. The total specific braking force developed by the parking brake system must be at least 0.16, or ensure a stationary state of the vehicle with a total weight on a road with a slope of at least 16 %, and for vehicles in running order, on a road with a slope - no less than 23% for passenger cars (category M) and no less than 31% for trucks (category N).
During such a check, the force applied to the parking brake control should be no more than 40 kgf for cars and no more than 60 kgf for other cars. For freight road trains, the value of the compatibility coefficient of road train links K c for a two-link trailed road train is also determined, which is determined by the formula
where is the total specific braking force of the trailer link and the tractor, respectively (numerical values are given in Table 4).
The value of the compatibility coefficient of road train links K c for a three-link trailed road train, which is determined separately for each pair of interconnected links according to the formulas
K c1 = , K c2 = ,
where К с1, К с2 are compatibility coefficients of road train links, characterizing the ratio of the total specific braking force between the tractor and the first trailer.
The value of the compatibility coefficient of road train links, according to GOST requirements, should not be lower than 0.9. In addition, for trucks and buses with pneumatically driven brakes, the tightness of the system is checked, which, when the engine is not running, should not allow a pressure drop of more than 0.5 kgf/cm 3 of the lower control limit within 15 minutes when the service brake system is fully activated or in for 30 minutes – with the brake system free. The asynchronous actuation of brakes along the axles of road trains should not exceed 0.3 s. The values of the braking distance S t, which set the deceleration j set, the response time of the braking system t cf and the initial braking speed V 0 are given in table. 3, 4. These standards are used to assess the effectiveness of the braking system of vehicles when they are tested not on roller stands, but on horizontal, flat, dry platforms.
Bench tests have a number of advantages compared to road tests: thanks to the use of stationary measuring instruments, the accuracy of test results increases; Separate testing of each brake mechanism is possible; Standard test conditions ensure repeatability of results and comparability of data obtained at different times.
The values of braking forces on the wheels of trucks and buses are given in RD-200RSFSR15-0150-81 “Guide to diagnosing the technical condition of rolling stock of road transport”, and on the wheels of passenger cars - in RD-37.009.010-85.” Guidelines for organizing diagnostics of passenger cars at service stations of the “Auto Maintenance” system.
Bench tests are carried out using brake stands of various models, the range of which is quite diverse (for example, the STS-2 model stand for monitoring the brake systems of passenger cars, small buses, mini-trucks with an axle load of no more than 19600 N; the STS-10 stand is intended for tests of brake systems of trucks, trolleybuses and buses; stands model SD-2M, SD-3K, SD-4, produced by the Chelyabinsk ARZ, KI-8901, produced by the Beregovsky SEZ, etc.).
Indicators of the braking efficiency of the service brake system during road tests of cars are the braking distance and the force on the control. During testing, braking by the service brake system is carried out in emergency, full braking mode with a single impact on the control (adjustment of the vehicle's trajectory is not allowed). The initial braking speed is 40 km/h, the time to activate the brake system control is no more than 0.2 s.
Road tests are carried out on a straight, horizontal, level and dry road with a cement or asphalt concrete surface.
Bench and road tests must be carried out under safe conditions.
The measurement error must be within:
braking distance – 5%;
initial braking speed – 1 km/h;
steady deceleration – 4%;
maximum slope of the braking area – 1%;
braking force – 3%;
effort on the control – 7%;
braking system response time – 0.03 s;
brake system delay time – 0.03 s;
deceleration rise time – 0.03s;
air pressure in the pneumatic or pneumohydraulic brake drive is 5%.
The vehicle's brake system is considered to have passed the test if the diagnostic parameters comply with the standards. In order for the vehicle's brake systems to successfully pass the test, it is necessary to carry out qualified maintenance or repair of the main components.
Replacement of brake linings, disc pads and drums must be carried out on both wheels of the axle. After replacing these parts, you need to let them run in for a run of 300-400 km.
When checking cars in wet weather or after washing, it is advisable to dry the brakes, especially drum brakes, by braking several times or driving briefly with the car braked. It is also not recommended to test the brakes of a car with studded tires on roller area stands, because the coefficient of adhesion of a steel spike to the steel surface of a drum or platform can be significantly lower.
3.11.2.2. Steering control and testing
The technical condition of the car's steering directly affects traffic safety. Therefore, increased requirements are imposed on its condition, which are contained in GOST R 51709-2001 and in the governing documents RD200 RSFSR 15-0150-81, RD 37.009.010-85 and RD200 RSFSR 0086-79. Requirements for steering control are also contained in the technological documentation for car repair and maintenance and in the operating instructions for specific car models. As a result of prolonged use without the necessary adjustments, the steering wheel play increases.
The GOST numerical indicator that normalizes the operation of the steering mechanism elements is the total play of the steering wheel, which during testing should not exceed the following permissible values:
for passenger cars and trucks and buses created on the basis of their units…………….….10 o;
buses…………………………..20 o;
trucks …………… 25 o.
The total steering play of vehicles can be measured by several instruments. The most common are the electronic play meter model K-526, the mechanical play meter model K-524, the device model K-402, etc.
Tests on vehicles equipped with power steering are carried out with the engine running. The range of relevant test equipment is varied. One of them is the K-465M installation.
The vehicle is considered to have passed the test if the obtained total play values do not exceed the permissible values.
When preparing the vehicle for the inspection stage, it is necessary to carry out regular maintenance of the components and parts of the steering mechanism, check the level of the working fluid and the tension of the pump drive belt in the power steering system, check the tightening and fixation of the threaded connections of the parts and components, the condition of the boots and protective covers.
Standards for braking efficiency of service and emergency brake systems, corresponding to STB 1641-2006, are given in the table:
|
Table. Standards for the braking efficiency of vehicles with working and emergency braking systems during testing on stands
* Not equipped with ABS or received type approval before 01.10.1991. ** Type approved after 1988. Note. The values in parentheses are for vehicles with a manually controlled emergency braking system. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||
The specific braking force Yt is calculated based on the results of checking the braking forces Pt on the wheels of a vehicle separately for a car, a tractor (truck tractor) and a trailer (semi-trailer) according to the formula:
where EРт is the sum of the braking forces Рт on the wheels of the vehicle, N; M is the mass of the vehicle, kg; g - free fall acceleration, m/s2.
When checking the braking efficiency of the service and emergency brake systems on stands, the relative difference F of the braking forces of the axle wheels (as a percentage of the highest value) is allowed to be no more than 30%. In this case, the relative difference is calculated based on the results of checking the braking forces Рт on the wheels of the vehicle using the formula:
where Rt.pr, Rt.left are the maximum braking forces, respectively, on the right and left wheels of the vehicle axle being tested, N; Ртмах - the greatest of the indicated braking forces, N.
The parking brake system for vehicles with a technically permissible maximum weight must provide a specific braking force Yt of at least 0.16, for combined vehicles - at least 0.12. In this case, the force applied to the parking brake system control to activate it must be no more than 500 N for vehicles of category M1 and 700 N for other categories. For vehicles with a manually controlled parking brake system, the specified values should be no more than 400 and 600 N, respectively.
For the parking brake system, the relative difference F of the braking forces of the axle wheels is allowed to be no more than 50%.
Determining the compliance of the brake systems of vehicles with wet tires on stands is permitted only by the indicators of wheel locking on the stand; in this case, the tires located on both sides of the vehicle must be evenly wet over the entire surface. The stand must be blocked when the difference between the linear speeds of the running surfaces of the tire and the stand rollers at the point of their direct contact reaches at least 10%. When the wheels of an axle are blocked on the stand, the maximum braking forces are taken to be their values reached at the moment of blocking.
B t of the train is determined by the sum of the forces generated by all the brake pads of the rolling stock according to the formulaWhere Κ o is the actual pressing force of the brake pads on the wheelset (on the axle), kN;
n o is the number of brake axles on the train;
φ k - pads. If we take the average value of the friction coefficient for all pads to be the same, then formula (1) will take the expression
, N. (2)
Specific braking force of a passenger train
, N/kN. (3)
For freight train
, N/kN. (4)
The ratio of the sum of the forces applied by the brake pads to the weight of the train is called actual braking coefficient
, kN/kN (5)
then equation (3) takes the form, N/kN:
, N/kN. (6)
In the case when the train has cars with different pressure of the brake pads on the wheel, brake calculations using formula (6) become cumbersome, since the quantities φ to and K must be determined for each pad separately. In these cases, a simpler method is usually used - casting method. It is based on replacing the actual friction coefficient of the pads on the wheels, which depends on the pressing force TO, another meaning - calculated friction coefficient φ kr, independent of force TO.
Actual friction coefficient φ k for standard cast iron pads is determined by the empirical formula
, (7)
a is determined by the empirical formula
, (8)
Actual friction coefficient φ k for composite pads is determined by the formula
, (9)
For determining φ kr are accepted conditional average forces pressing pads on the wheelset: cast iron - K h= 26.5 kN (2.7 tf), composite - K k= 15.7 kN (1.6 tf). Substituting the values K h And K k into formulas (7), (8) and (9), we get:
for cast iron pads
; (10)
for cast iron pads with high phosphorus content
; (11)
for composite pads
. (12)
The values of the calculated friction coefficients of the pads on the wheels, calculated using formulas 10, 11 and 12, are given in Table 1.
In order to maintain the same braking force when braking, it is necessary valid replace the pressing force of the pads on the wheel pair calculated pressing force. The calculated pressing force is determined from the condition of equality of braking forces:
, (13)
where 
, kN. (14)
After substituting values φ to and φ kr into equation (14), the following expressions are obtained: for standard cast iron blocks
, kN; (15)
for cast iron pads with high phosphorus content
, kN; (16)
Calculated friction coefficient value φ brake pads
Table 1
| Speed v, km/h | Cast iron standard | Cast iron with phosphorus | Compositional |
| 0,270 0,198 0,162 0,140 0,126 0,116 0,108 0,102 0,097 0,093 | 0,3 0,218 0,178 0,154 0,138 0,127 0,119 0,112 0,107 0,102 | 0,360 0,339 0,332 0,309 0,297 0,288 0,280 0,273 0,267 0,262 |
for composite pads
, kN. (17)
The calculated forces of pressing the pads on the wheels are calculated for each type of rolling stock and are given in the form of standards established in the operating instructions for auto brakes, tables 2 and 3.
Calculated pressing forces on one cast iron brake pad of locomotives
table 2
Estimated pressing forces on one brake pad of freight and passenger cars
Table 3
| Car type | Brake pads | Pressure force on the block, kN | |||
| Material | Number | Laden | Average | Empty | |
| Freight Four-axle gondola cars Four-axle platforms, covered cars, tanks Six-axle gondola cars Eight-axle gondola cars Eight-axle tank cars Refrigerated Passenger All-metal weight, kN 530-620 480-520 With disc brake With speed regulator | Cast Iron Composite Cast Iron Composite Cast Iron Composite Cast Iron Composite Cast Iron Composite Cast Iron Composite Cast Iron Composite Cast Iron Composite Overlays Cast Iron | 38,2 11,6 23,5 10,3 18,5 8,8 7,5 52,0 | 14,8 23,4 15,4 21,8 13,5 7,4 - - - - - - | 12,6 8,2 12,8 8,5 12,4 7,5 8,6 7,5 4,3 - - - - - - |
If there are cars with cast iron and composite pads on the same train, then the pressing force of the pads on the axle is recalculated for one type of pad (usually cast iron), taking into account the equal efficiency of the brakes, Table 4.
Calculated pressing forces of car brake pads in terms of cast iron ones
Table 4
| Car type | Calculated brake pad pressure TO p, kN/axis |
| All-metal passenger cars with tare weight: q = 520 kN (53 tf) q = 470 kN (48 tf), but? 520 kN q = 412 kN (42 tf), but? 470 kN All-metal passenger cars VL-RIC with KE brake and cast iron brake pads: in passenger mode in high-speed mode All-metal passenger cars of RIC size on TVZ-TsNII “M” bogies with KE brake and composite brake pads (in terms of cast iron pads): in passenger mode in high-speed mode Passenger cars with a length of 20.2 m or less The rest of the passenger fleet Freight cars equipped with cast iron blocks in the mode: loaded medium empty Freight cars equipped with composite blocks (in terms of cast iron blocks) in the mode: loaded medium empty Four-axle isothermal and all-metal luggage cars with one-way braking Refrigerated rolling stock cars with cast iron brake pads in the mode: loaded medium empty Refrigerated rolling stock cars with composite brake pads (in terms of cast iron pads) in the mode: medium empty |
The total calculated pressure of the brake pads is calculated by the number of cars of each type ( n 4 ,n 6 ,n 8), included in the train, the number of locomotive axles of a given series ( n l) and the calculated pressure on one brake axle for each type of carriage and locomotive
If not all axles are brake axes, then this should be taken into account when calculating the total pressure of the brake pads. For this purpose, the total brake pressure for the train (4 n 4 TOр4 + 6 n 6 TOр6 + 8 n 8 TO p8) is multiplied by a coefficient equal to the share of brake axles in the composition. If the proportion of brake axles is specified for each type of car, then the corresponding coefficients are multiplied by each of the terms in expression (18).
After calculating the total calculated pressure of the train brake pads, the value is determined calculated braking coefficient
. (19)
The calculated braking coefficient characterizes the degree to which the train is provided with braking means. The more ϑ p, the greater the braking effect the braking forces create, the faster the train will stop and at a shorter distance. In order to ensure the safety of trains of JSC Russian Railways, the minimum values of the calculated braking coefficients have been established:
for freight trains at speeds up to 90 km/h - 0.33;
for refrigerated and diesel trains at speeds up to 120 km/h - 0.6;
for passenger trains:
at speeds up to 120 km/h - 0.6;
at speeds up to 140 km/h - 0.78;
at speeds up to 160 km/h - 0.8.
The full value of the calculated braking coefficient and the corresponding specific braking force are realized only during emergency braking.
In braking calculations for stopping at stations and separate points provided for by the train schedule, as well as in the case of a decrease in speed in front of a previously known place, service braking is used with the calculated braking coefficient:
for freight trains - 0.5 J R,
for passenger, electric and diesel trains - 0.6 J R,
in case of applying full service braking, take 0.8 J R.
When using braking calculations to determine the minimum distance between standing floor signals, the value of the calculated braking coefficient is taken to be 0.8 J R.
The rules of traction calculations recommend not taking into account the pneumatic brakes of the locomotive and its weight when determining the braking force. cargo trains moving on sections with slopes down to -20 ‰. That is, in formula (5.19) we can exclude P, and in formula (18) exclude the term n l TO rl.
Example. Determine the total and specific braking force of a freight train weighing 40,000 kN, formed from 60 four-axle gondola cars equipped with composite blocks. The speed of the train at the beginning of braking is 60 km/h, the number of brake axles is 80%.
1. Estimated force of pressing on one brake axle of four-axle gondola cars when loaded (see Table 3)
Where n k - number of brake pads per axle.
2. Number of brake axles in the train
Where a T- number of brake axles in the train, a T = 80% = 0,8.
3. The total pressing force of the brake pads on the axle of the train
4. Friction coefficient of composite pads
5. Total braking force of the train (according to formula 5.2)
6. Specific braking force b t, N/kN, with train weight P + Q
N/kN.
