The traction and speed properties of the car significantly depend on the design factors. The type of engine, transmission efficiency, transmission ratios, vehicle weight and streamlining have the greatest influence on traction and speed properties.
Engine's type. A gasoline engine provides better traction and speed properties of a car than a diesel engine under similar conditions and driving modes. This is due to the shape of the external speed characteristics of these engines.
On fig. 5.1 shows a graph of the power balance of the same car with different engines: with gasoline (curve N" t) and diesel (curve N" T). Maximum power values N max and speed v N at maximum power for both engines are the same.
From fig. 5.1 it can be seen that a gasoline engine has a more convex external speed characteristic than a diesel engine. This gives him more power. (N" h > N" h ) at the same speed, e.g. v 1 . Therefore, a gasoline-powered vehicle can accelerate faster, climb steeper grades, and tow trailers that are heavier than diesel-powered vehicles.
transmission efficiency. This coefficient allows you to estimate the power loss in the transmission due to friction. The decrease in efficiency caused by the increase in power losses due to friction due to the deterioration of the technical condition of the transmission mechanisms during operation leads to a decrease in the traction force on the driving wheels of the vehicle. As a result, the maximum speed of the vehicle and the road resistance overcome by the vehicle are reduced.
Rice. 5.1. Graph of the power balance of a car with different engines:
N" t - gasoline engine; N" T - diesel; N" h, N" h – corresponding power reserve values at vehicle speed v 1 .
Gear ratios of the transmission. The maximum speed of the car significantly depends on the gear ratio of the main gear. The optimal gear ratio is considered to be the main gear ratio at which the car develops maximum speed, and the engine - maximum power. Increasing or decreasing the gear ratio of the final drive compared to the optimal one leads to a decrease in the maximum speed of the vehicle.
The gear ratio of the I gear of the gearbox affects the maximum road resistance the car can overcome with uniform movement, as well as the gear ratios of the intermediate gears of the gearbox.
An increase in the number of gears in the gearbox leads to a more complete use of engine power, an increase in the average speed of the vehicle and an increase in its traction and speed properties.
Additional gearboxes. Improving the traction and speed properties of the car can also be achieved by using additional gearboxes together with the main gearbox: a divider (multiplier), a demultiplier and a transfer case. Typically, additional gearboxes are two-stage and allow you to double the number of gears. In this case, the divider only expands the range of gear ratios, and the demultiplier and transfer case increase their values. However, with an excessively large number of gears, the weight and complexity of the gearbox design increase, and driving is also difficult.
Hydraulic transmission. This transmission provides ease of control, smooth acceleration and high cross-country ability of the car. However, it worsens the traction and speed properties of the car, since its efficiency is lower than that of a mechanical speed gearbox.
Vehicle weight. An increase in the mass of the car leads to an increase in the forces of rolling resistance, lifting and acceleration. As a result, the traction and speed properties of the car deteriorate.
Car streamlining. Streamlining has a significant impact on the traction and speed properties of the car. When it deteriorates, the reserve of tractive force decreases, which can be used to accelerate the car, overcome climbs and tow trailers, increase power losses due to air resistance and reduce the maximum speed of the car. So, for example, at a speed of 50 km / h, the power loss of a passenger car associated with overcoming air resistance is almost equal to the power loss due to the rolling resistance of a car when it is moving on a paved road.
Good streamlining of passenger cars is achieved by slightly tilting the body roof back, using body sidewalls without sharp transitions and a smooth bottom, installing a windshield and radiator grille with an inclination and placing protruding parts in such a way that they do not go beyond the external dimensions of the body.
All this makes it possible to reduce aerodynamic losses, especially when driving at high speeds, as well as to improve the traction and speed properties of passenger cars.
In trucks, air resistance is reduced by using special fairings and covering the body with a tarpaulin.
BRAKING PROPERTIES.
Definitions.
Braking - creation of artificial resistance in order to reduce speed or hold it in a stationary state.
Braking properties - determine the maximum deceleration of the car and the limit values of the external forces that hold the car in place.
Brake mode - mode in which braking torques are applied to the wheels.
Braking distances - the path traveled by the vehicle from the driver's detection of the obstacle to the complete stop of the vehicle.
Braking properties - the most important determinants of traffic safety.
Modern braking properties are standardized by regulation No. 13 of the Inland Transport Committee of the United Nations Economic Commission for Europe (UNECE).
The national standards of all UN member countries are compiled on the basis of these Rules.
The car must have several brake systems that perform various functions: service, parking, auxiliary and spare.
Working The brake system is the main brake system that provides the braking process under normal vehicle operation conditions. The braking mechanisms of the service brake system are wheel brakes. These mechanisms are controlled by a pedal.
Parking lot The braking system is designed to keep the vehicle stationary. The brake mechanisms of this system are located either on one of the transmission shafts or in the wheels. In the latter case, the brake mechanisms of the working brake system are used, but with an additional control drive for the parking brake system. Management of the parking brake system is manual. The parking brake actuator must be only mechanical.
Spare the brake system is used when the service brake system fails. For some vehicles, the parking brake system or an additional circuit of the working system performs the function of a spare.
There are the following types of braking : emergency (emergency), service, braking on slopes.
emergency braking is carried out by means of a service brake system with the maximum intensity for these conditions. The number of emergency braking is 5…10% of the total number of braking.
Official braking is used to smoothly reduce the speed of the car or stop at a predetermined month
Estimated indicators.
The existing standards GOST 22895-77, GOST 25478-91 provide for the following indicators of braking properties car:
j set - Steady deceleration at a constant effort on the pedal;
S t - the path traveled from the moment the pedal is pressed to the stop (stopping path);
t cf - response time - from pressing the pedal to reaching j set. ;
Σ P torus. is the total braking force.
– specific braking force;
– coefficient of non-uniformity of braking forces;
Steady downhill speed V t. mouth when braking with a brake - retarder;
The maximum slope h t max, on which the car is held by the parking brake;
The deceleration provided by the spare brake system.
The standards for indicators of the braking properties of the vehicle, prescribed by the standard, are given in the table. Designations of categories of automatic telephone exchange:
M - passenger: M 1 - cars and buses with no more than 8 seats, M 2 - buses with more than 8 seats and a total weight of up to 5 tons, M 3 - buses with a gross weight of more than 5 tons;
N - trucks and road trains: N 1 - with a gross weight of up to 3.5 tons, N 2 - over 3.5 tons, N 3 - over 12 tons;
O - trailers and semi-trailers: O 1 - with a gross weight of up to 0.75 tons, O 2 - with a gross weight of up to 3.5 tons, O 3 - with a gross weight of up to 10 tons, O 4 - with a gross weight of over 10 tons.
Normative (quantitative) values of estimated indicators for new (developed) cars are assigned in accordance with the categories.
MINISTRY OF AGRICULTURE AND
FOOD FOOD OF THE REPUBLIC OF BELARUS
EDUCATIONAL INSTITUTION
"BELARUSIAN STATE
AGRICULTURAL TECHNICAL UNIVERSITY
FACULTY OF RURAL MECHANIZATION
FARMS
Department "Tractors and cars"
COURSE PROJECT
By discipline: Fundamentals of the theory and calculation of the tractor and car.
On the topic: Traction and speed properties and fuel efficiency
car.
5th year student 45 groups
Snopkova A.A.
Head of CP
Minsk 2002.
Introduction.
1. Traction and speed properties of the car.
The traction and speed properties of a car are a set of properties that determine the possible ranges of speed changes and the maximum intensity of acceleration and deceleration of the car during its operation in traction mode in various road conditions.
Indicators of the tagging and speed properties of the car (maximum speed, acceleration during acceleration or deceleration during braking, traction force on the hook, effective engine power, climb overcome in various road conditions, dynamic factor, speed characteristic) are determined by design traction calculation. It involves the determination of design parameters that can provide optimal driving conditions, as well as the establishment of limiting road traffic conditions for each type of vehicle.
Traction and speed properties and indicators are determined during the traction calculation of the car. The object of calculation is a light truck.
1.1. Determining the power of a car engine.
The calculation is based on the nominal load capacity of the vehicle
in kg (the mass of the installed payload + the mass of the driver and passengers in the cabin) or road train, it is equal to from the task - 1000 kg.Engine power
, necessary for the movement of a fully loaded car at a speed in given road conditions, characterizing the reduced road resistance , is determined from the dependence: , where the dead weight of the car, 1000 kg; air resistance (in N) - 1163.7 when moving at a maximum speed = 25 m / s; -- Transmission efficiency = 0.93. Rated load capacity is specified in the task; = 0.04 taking into account the operation of the vehicle in agriculture (road resistance coefficient). (0.04*(1000*1352)*9.8+1163.7)*25/1000*0.93=56.29 kW.The dead weight of the vehicle is related to its rated load capacity by the dependence:
1000/0.74=1352 kg. -- coefficient of carrying capacity of the car - 0.74.For an especially light vehicle = 0.7 ... 0.75.
The load-carrying capacity coefficient of a car significantly affects the dynamic and economic performance of the car: the larger it is, the better these indicators.
Air resistance depends on air density, coefficient
streamlining of contours and bottom (sail ratio), frontal surface area F (in) of the car and speed mode. It is determined by the dependence: , 0.45 * 1.293 * 3.2 * 625 \u003d 1163.7 N. \u003d 1.293 kg / - air density at a temperature of 15 ... 25 C.Car streamlining coefficient
=0.45…0.60. I accept = 0.45.The frontal surface area can be calculated using the formula:
Where: B is the track of the rear wheels, I accept it = 1.6m, the value of H = 2m. The values of B and H are specified in subsequent calculations when determining the dimensions of the platform.
= maximum speed on the road with improved surface at full fuel supply, according to the task it is equal to 25 m/s. the car develops, as a rule, in direct gear, then, 0.95 ... 0.97 - 0.95 engine efficiency at idle; \u003d 0.97 ... 0.98 - 0.975.main gear efficiency.
0,95*0,975=0,93.1.2. The choice of the wheel formula of the car and the geometric parameters of the wheels.
Number and dimensions of wheels (wheel diameter
and the mass transmitted to the wheel axle) are determined based on the carrying capacity of the vehicle.With a fully loaded car, 65 ... 75% of the total mass of the car falls on the rear axle and 25 ... 35% on the front. Consequently, the load factor of the front and rear drive wheels is 0.25…0.35 and –0.65…0.75, respectively.
; 0.65*1000*(1+1/0.45)=1528.7 kg.to the front:
. 0.35*1000*(1+1/0.45)=823.0 kg.I accept the following values: on the rear axle -1528.7 kg, on one wheel of the rear axle - 764.2 kg; on the front axle - 823.0 kg, on the wheel of the front axle - 411.5 kg.
Based on load
and tire pressure, according to table 2, tire sizes are selected, in m (width of the tire profile and diameter of the landing rim). Then the calculated radius of the driving wheels (in m); .Estimated data: tire name - ; its dimensions are 215-380 (8.40-15); calculated radius.
MINISTRY OF AGRICULTURE AND
FOOD FOOD OF THE REPUBLIC OF BELARUS
EDUCATIONAL INSTITUTION
"BELARUSIAN STATE
AGRICULTURAL UNIVERSITY
FACULTY OF RURAL MECHANIZATION
FARMS
Department "Tractors and cars"
COURSE PROJECT
By discipline: Fundamentals of the theory and calculation of a tractor and a car.
On the topic: Traction and speed properties and fuel efficiency
car.
5th year student 45 groups
Snopkova A.A.
Head of CP
Minsk 2002.
Introduction.
1. Traction and speed properties of the car.
The traction and speed properties of a car are a set of properties that determine the possible ranges of speed changes and the maximum intensity of acceleration and deceleration of the car during its operation in traction mode in various road conditions.
Indicators of the traction and speed properties of the car (maximum speed, acceleration during acceleration or deceleration during braking, traction force on the hook, effective engine power, climb overcome in various road conditions, dynamic factor, speed characteristic) are determined by the design traction calculation. It involves the determination of design parameters that can provide optimal driving conditions, as well as the establishment of limiting road traffic conditions for each type of vehicle.
Traction and speed properties and indicators are determined during the traction calculation of the car. The object of calculation is a light truck.
1.1. Determining the power of a car engine.
The calculation is based on the nominal load capacity of the vehicle /> in kg (the mass of the installed payload + the mass of the driver and passengers in the cab) or the road train />, it is equal to -1000 kg from the task.
Engine power />, necessary for the movement of a fully loaded vehicle at a speed /> in given road conditions, characterizing the reduced road resistance />, is determined from the dependence:
/>vehicle weight, 1000 kg;
/>air resistance (in N) - 1163.7 when driving at maximum speed />= 25 m/s;
/> - transmission efficiency = 0.93. Rated load capacity /> specified in the task;
/>= 0.04 taking into account the work of the car in agriculture (road resistance coefficient).
/>(0.04*(1000*1352)*9.8+1163.7)*25/1000*0.93=56.29kW.
The dead weight of the car is related in its rated load capacity by the dependence: />
/>1000/0.74=1352 kg.
where: /> - coefficient of carrying capacity of the car - 0.74.
For an extra light vehicle = 0.7 ... 0.75.
The load-carrying capacity coefficient of the car significantly affects the dynamic and economic indicators of the car: the larger it is, the better these indicators.
Air resistance depends on the air density, the coefficient /> streamlining of the contours and the bottom (sail coefficient), the frontal surface area F (in />) of the car and the speed mode. Defined by dependency: />,
/>0.45*1.293*3.2*625= 1163.7 N.
where: /> \u003d 1.293 kg //> - air density at a temperature of 15 ... 25 C.
The streamlining coefficient of the car /> \u003d 0.45 ... 0.60. I accept \u003d 0.45.
The area of the frontal surface can be calculated by the formula:
F=1.6*2=3.2 />
Where: B is the track of the rear wheels, I accept it = 1.6m, the value of H = 2m. The values of B and H are specified in subsequent calculations when determining the dimensions of the platform.
/>= the maximum speed of movement on the road with improved coverage at full fuel supply, according to the task it is equal to 25 m/s.
Since /> the car develops, as a rule, in direct gear, then
where: /> 0.95 ... 0.97 - 0.95 efficiency of the engine at idle; />=0.97…0.98–0.975.
main gear efficiency.
/>0,95*0,975=0,93.
1.2. The choice of the wheel formula of the car and the geometric parameters of the wheels.
The number and dimensions of wheels (wheel diameter /> and the mass transferred to the wheel axle) are determined based on the vehicle's carrying capacity.
With a fully loaded car, 65 ... 75% of the total mass of the car falls on the rear axle and 25 ... 35% - on the front. Consequently, the load factor of the front and rear drive wheels is 0.25…0.35 and –0.65…0.75, respectively.
/>/>; />0.65*1000*(1+1/0.45)=1528.7kg.
to the front: />. />0.35*1000*(1+1/0.45)=823.0kg.
I accept the following values: on the rear axle - 1528.7 kg, on one wheel of the rear axle - 764.2 kg; front axle - 823.0 kg, front axle wheel - 411.5 kg.
Based on the load /> and pressure in the tires, table 2 selects the tire sizes, in m (the width of the tire section /> and the diameter of the landing rim />). Then the calculated radius of the driving wheels (in m);
Estimated data: bus name - ; its dimensions are 215-380 (8.40-15); calculated radius.
/>(0.5*0.380)+0.85*0.215=0.37m.
1.3. Determination of the capacity and geometric parameters of the platform.
According to the carrying capacity /> (in t), the capacity of the platform /> in cubic meters is selected. m., conditions:
/> />0,8*1=0,8 />/>
For an onboard car, /> = 0.7 ... 0.8 m., I choose 0.8 m.
Having determined the volume, I select the internal dimensions of the car platform in m: width, height and length.
I accept the width of the platform for trucks (1.15 ... 1.39) from the track of the car, that is, = 1.68 m.
I determine the height of the body by the size of a similar car - UAZ. It is equal to - 0.5 m.
I accept the length of the platform - 2.6 m.
According to the internal length /> I determine the base L of the car (the distance between the axles of the front and rear wheels):
I accept the base of the car = 2540 m.
1.4. Braking properties of the car.
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.
1.4.1. Steady-state deceleration while driving.
Slow down />=/>,
Where g is the free fall acceleration = 9.8 m/s; />--coefficient of adhesion of wheels to the road, the values of which for various road surfaces are taken from table 3; /> --coefficient of accounting for rotating masses. Its values for the designed car are 1.05 ... 1.25, I accept = 1.12.
The better the road, the greater the deceleration of the car when braking can be. On hard roads, deceleration can reach 7 m / s. Bad road conditions drastically reduce the intensity of braking.
1.4.2. Minimum stopping distance.
The length of the minimum braking distance />/> can be determined from the condition that the work done by the machine during the braking time must be equal to the kinetic energy lost by it during that time. The braking distance will be minimal with the most intensive braking, that is, when it has a maximum value. If braking is carried out on a horizontal road with constant deceleration, then the path to a stop is equal to:
I determine the stopping distance for various values of />, three different speeds of 14.22 and 25 m/s, and put them in the table:
Table number 1.
Base surface.
Slowdown on the road. Brake power. Minimum stopping distance. Movement speed. 14 m/s 22 m/s
1. Asphalt 0.65 5.69 14978 17.2 42.5 54.9 2. Gravel road. 0.6 5.25 13826 18.7 46.1 59.5 3. Cobblestone. 0.45 3.94 10369 24.9 61.4 79.3 4. Dry primer. 0.62 5.43 14287 18.1 44.6 57.6 5. Primer after rain. 0.42 3.68 9678 26.7 65.8 85.0 6. Sand 0.7 6.13 16130 16.0 39.5 51.0 7. Snow road. 0.18 1.58 4148 62.2 153.6 198.3 8. Road icing. 0.14 1.23 3226 80.0 197.5 255.0
1.5. Dynamic properties of the car.
The dynamic properties of the car are largely determined by the correct choice of the number of gears and the speed mode in each of the selected gears.
The number of transfers from the task is 5. I choose direct gear -4, the fifth one is economical.
Thus, one of the most important tasks in the course work on cars is the correct choice of the number of gears.
1.5.1. Choice of vehicle gears.
Gear ratio />=/>,
Where: /> - gear ratio of the gearbox; /> - gear ratio of the main gear.
The gear ratio of the main gear is found according to the equation:
where: /> -- estimated radius of the driving wheels, m; taken from previous calculations; /> -- engine speed at rated speed.
Transmission ratio in first gear:
where /> is the maximum dynamic factor permissible under the conditions of adhesion of the driving wheels of the car. Its value is in the range - 0.36 ... 0.65, it should not exceed the value:
/>=0.7*0.7=0.49
where: /> - the coefficient of adhesion of the driving wheels to the road, depending on the road conditions = 0.5 ... 0.75; /> -- load factor of the driving wheels of the vehicle; recommended values = 0.65…0.8; the maximum torque of the engine, in N * m, is taken from the speed characteristic for carburetor engines; G is the total weight of the car, N; - The efficiency of the vehicle transmission in first gear is calculated by the formula:
0.96 - Engine efficiency at idle crankshaft cranking; />=0.98 - efficiency of a cylindrical pair of gears; />=0.975 – efficiency of a bevel gear pair; - respectively, the number of cylindrical and conical pairs involved in engagement in first gear. Their number is selected based on the transmission schemes.
In the first approximation, in preliminary calculations, the gear ratios of trucks are selected according to the principle of geometric progression, forming a series, where q is the denominator of the progression; it is calculated according to the formula:
where: z is the number of gears indicated in the task.
The gear ratio of the permanently switched on main gear of the car is taken, in accordance with the ones taken from the prototype = .
According to the gear ratios of the transmission, the maximum vehicle speeds in different gears are calculated. The data obtained are summarized in a table.
Table number 1.
Transfer Gear ratio Speed, m/s. 1 30 6.1 2 19 9.5 3 10.5 17.1 4 7.2 25 5 5.8 31
1.5.2. Construction of a theoretical (external) speed characteristic of a carburetor engine.
The theoretical speed external characteristic /> = f (n) is built on a sheet of graph paper. The calculation and construction of the external characteristic is carried out in the following sequence. On the abscissa axis, we plot the value of the crankshaft speed in the accepted scale: nominal, maximum idle, at maximum torque, minimum, corresponding to engine operation.
The rated speed is set in the job, frequency />,
Frequency />. The maximum rotational speed is taken based on the reference data of the prototype engine -4800 rpm.
Intermediate points of the power values of the carburetor engine are found from the expression, given by the values \u003d /\u003e (at least 6 points).
Torque values /> are calculated according to:
The current values /> and /> are taken from the chart />. The specific effective fuel consumption of a carburetor engine is calculated according to the dependence:
/>, g/(kW, h),
where: /> specific effective fuel consumption at rated power, specified in the task = 320 g/kW*h.
Hourly fuel consumption is determined by the formula:
The values /> and /> are taken from the plotted graphs, and a table is compiled based on the results of calculating the theoretical external characteristic.
Data for constructing a characteristic. Table number 2.
№1 800 13,78 164,5 4,55 330,24 2 1150 20,57 170,86 6,44 313,16 3 1500 27,49 175,5 8,25 300 4 1850 34,30 177,06 9,97 290,76 5 2200 40,75 176,91 11,63 285,44 6 2650 48,15 173,52 13,69 284,36 7 3100 54,06 166,54 15,66 289,76 8 3550 57,98 155,97 17,49 301,64 9 4000 59,40 141,81 19,01 320 10 4266 58,85 131,75 19,65 333,90 11 4532 57,16 120,44 20,01 350,06 12 4800 54,17 107,78 19,97 368,64 /> /> /> /> /> /> /> /> /> />
1.5.4. Universal dynamic characteristic of the car.
The dynamic characteristic of the car illustrates its traction and speed properties with uniform movement at different speeds in different gears and in different road conditions.
From the equation of the traction balance of a car when driving without a trailer on a horizontal support surface, it follows that the difference in forces /> (tangential traction force and air resistance when the car is moving) in this equation is the traction force expended to overcome all external resistance to the movement of the car, with the exception of air resistance. Therefore, the ratio /> characterizes the stock of traction force per unit weight of the car. This measure of the dynamic, in particular, traction and speed, properties of the car is called the dynamic factor D of the car.
Thus, the dynamic factor of the car.
The dynamic factor of the car is determined in each gear during the operation of the engine at full load with full fuel supply.
Between the dynamic factor and the parameters characterizing the resistance of the road (coefficient />) and the inertial loads of the car, there are the following dependencies:
/>/>--with unsteady motion;
/>with steady motion.
The dynamic factor depends on the speed of the car - the engine speed (its torque) and the gear engaged (transmission ratio). The graphic image is called the dynamic characteristic. Its value also depends on the weight of the car. Therefore, the characteristic is built first for an empty car without cargo in the body, and then, by additional constructions, it is converted into a universal one, which allows finding the dynamic factor for any car weight.
Additional constructions for obtaining a universal dynamic characteristic.
We apply the second abscissa axis on the constructed characteristic from above, on the coefficient of the second I put off the values of the vehicle load factor.
On the leftmost point of the upper abscissa axis, the coefficient Г=1, which corresponds to an empty car; at the extreme point on the right, we postpone the maximum value specified in the task, the value of which depends on the maximum weight of the loaded car. Then we put on the upper abscissa a number of intermediate values of the load factor and draw from them down the vertical until they intersect with the lower abscissa.
The vertical passing through the point Г=2 is taken as the second y-axis of the characteristics. passing through the point Г=1. I connect single-valued divisions on both ordinates with inclined lines. The points of intersection of these lines with the rest of the verticals form on each vertical a scale bar for the corresponding value of the vehicle load factor.
The results of calculation of indicators are entered in the table.
Table number 3.
Transmission V, m/s.
Torque, Nm.
D Г=1 Г=2.5 1 1.22 800 164.50 12125 2.07 0.858 0.394 2.29 1500 175.05 12903 7.29 0.912 0.420 3.35 2200 176.91 13040 15.69 0, 921 0.424 4.72 3100 166.54 12275 31.15 0.866 0.398 6.10 4000 141.81 10453 51.86 0.736 0.338 6.91 4532 120.44 8877 66.27 0.623 0.286 7.3 4800 107.78 7944 66.03 0.557 0.255 2 1.90 800 164.50 7766 5.06 0.549 0.291 3.57 1500 175.05 8264 17.78 0.583 0.309 5.23 2200 176.91 8352 38.24 0.588 0.312 7.3 8 3100 166.54 7862 75.93 0.551 0.292 9.52 4000 141.81 6695 126.41 0.464 0.246 10.78 4532 120.44 5686 162.27 0.390 0.207 11.45 4800 107.78 5088 182 .03 0.346 0.184 3 3.44 800 164.50 4292 16.56 0.302 0.160 6.46 1500 175.05 4567 58.26 0.317 0.168 9.47 2200 176.91 4615 125.21 0.319 0.169 13.35 3100 166.54 4345 248.61 0.289 0.154 17.22 4000 141, 81 3700 413.92 0.231 0.123 19.51 4532 120.44 3142 531.34 0.183 0.098 20.64 4800 107.78 2812 596.04 0.155 0.083
5,02 800 164,50 2943 35,21 0,206 0,094 9,42 1500 175,05 3131 123,79 0,212 0,096 13,81 2200 176,91 3165 266,29 0,204 0,090 19,46 3100 166,54 2979 528,73 0,172 0,071 25,11 4000 141,81 2537 880,30 0,144 0,04 28,45 4532 120,44 2154 1130,03 0,069 0,015 30,12 4800 107,78 1928 1267,63 0,043 0,001 5 6,23 800 164,50 2370 54,26 0,164 0,087 11,69 1500 175,05 2522 190,77 0,164 0,088 17,15 2200 176,91 2549 410,36 0,150 0,080 24,16 3100 166,54 2400 814,78 0,110 0,060 31,17 4000 141,81 2043 1356,56 0,044 0,026 35,32 4532 120,44 1735 1741,40 0,001 37,42 4800 107,78 1553 1953,53 /> /> /> /> /> /> /> /> /> />
1.5.5. Brief analysis of the obtained data.
1. Determine in which gears the car will operate under given road conditions, characterized by the reduced coefficient /> road resistance (at least 2 ... 3 values) and what maximum speeds it can develop with uniform movement with different values \u200b\u200b(at least 2) of the load factor G vehicle, without fail including G max.
I set the following road resistance values: 0.04, 0.07, 0.1 (asphalt, dirt road, primer after rain). With a coefficient = 1, the car can move at /> = 0.04 at a speed of 31.17 m / s in 5th gear; />=0.07 – 28 m/s, 5th gear; />= 0.1 - 24 m/s, 5th gear. With a coefficient = 2.5 (maximum load), the car can move at />= 0.04 - speed 25 m / s, 4th gear; />= 0.07 – speed 19 m/s, 4th gear; />= 0.1 – speed 17 m/s, 3rd gear.
2. Based on the dynamic characteristic, determine the greatest road resistance that the car can overcome, moving in each gear at a uniform speed (at the inflection points of the dynamic factor curves).
The obtained data should be checked from the point of view of the possibility of their implementation under the conditions of adhesion to the road surface. For a vehicle with rear wheel drive:
where: /> - load factor of the driving wheels.
Table number 4.
Gear No. Road resistance to overcome Grip force with the road surface (asphalt). Г=1 Г=2.5 Г=1 Г=2.5 1st gear 0.921 0.424 0.52 0.52 2nd gear 0.588 0.312 0.51 0.515 3rd gear 0.319 0.169 0.51 0.51 0.5 0.505 5th gear 0.150 0.08 0.49 0.5
According to the tabular data, it can be seen that in 1st gear the car can overcome sand; on the 2nd snowy road; on the 3rd icy road; on the 4th dry dirt road; on the 5th asphalt
3. Determine the climb angles that the car is able to overcome in various road conditions (at least 2 ... 3 values) in various gears, and what speeds it will develop in this case.
Table number 5.
Road resistance. No. of gear Climbing angle Speed Г=1 Г=2.5 0.04 1st gear 47 38 3.35 2nd gear 47 27 5.23 3rd gear 27 12 9.47 4th gear 16 5 13.8 15 0.07 1st gear 45 35 3.35 2nd gear 45 24 5.23 3rd gear 24 9 9.47 4th gear 13 2 13.8 5th gear 8 17.15 0.1 1st gear 42 32 3.35 2nd gear 42 21 5.23 3rd gear 22 7 9.47 4th gear 10 13.8 5th gear 5 17.15
4. Determine:
The maximum speed in steady motion in the most typical road conditions for this type of vehicle (asphalted surface). The values of f for various road conditions are taken from the ratio:
Under given road conditions, i.e. on an asphalt highway, the resistance takes on a value of 0.026 and the speed is 26.09 m/s;
The dynamic factor in direct gear at the most common speed for this type of car (usually a speed equal to half the maximum is taken) is 12 m / s;
n the maximum value of the dynamic factor in direct transmission and the value of the speed - 0.204 and 11.96 m/s;
n the maximum value of the dynamic factor in the lowest gear - 0.921;
n is the maximum value of the dynamic factor in intermediate gears; 2nd gear - 0.588; 3rd gear - 0.317; 5th gear - 0.150;
5. compare the obtained data with reference data for a car that has key indicators close to the prototype. The data obtained during the calculation are almost similar to the data of the UAZ car.
2. Fuel efficiency of the car.
One of the main fuel economy as an operational property is considered to be the amount of fuel consumed per 100 km of track with uniform movement at a certain speed in given road conditions. A number of curves are applied to the characteristic, each of which corresponds to certain road conditions; when performing work, three coefficients of road resistance are considered: 0.04, 0.07, 010.
Fuel consumption, l / 100 km:
where: /> - instantaneous fuel consumption of the car engine, l;
where /> - travel time of 100 km, =/>.
From here, taking into account the engine power spent to overcome the resistance of the road and air, we get:
For a visual representation of the economy, a characteristic is built. Fuel consumption is plotted on the ordinate axis, and the speed of movement is plotted on the abscissa axis.
The order of construction is as follows. For various high-speed modes of movement of the car from the dependence
determine the value of the frequency of rotation of the crankshaft of the engine.
Knowing the engine speed from the corresponding speed characteristics determine the values of g.
According to formula 17, the engine power is determined (expression in square brackets) required for the car to move at different speeds on one of the given roads, characterized by the corresponding resistance value: 0.04, 0.07, 0.10.
Calculations are carried out up to the speed at which the engine is loaded to maximum power. The variable in this case is only the speed of movement and air resistance, all other indicators are taken from previous calculations.
Substituting those found for different speeds, the desired values of fuel consumption are calculated.
Table number 6.
/>l/100 km
5,01 800 940,54 46,73 5,36 330,24 5,5 13,1 9,39 1500 940,54 164,2 11,26 300 3,0 13,31 11,59 1850 940,54 250,11 14,97 290,76 2,4 13,91 13,78 2200 940,54 253,39 19,33 285,44 2,0 14,84 19,41 3100 940,54 701,68 34,58 289,76 1,4 19,12 22,23 3550 940,54 920,11 44,86 301,64 1,2 22,55 25 4000 940,54 1168 59,35 320,00 1,0 28,08
dry soil
5,01 800 1654,8 46,73 9,20 330,24 5,5 22,46 7,20 1150 1654,8 96,55 13,61 313,16 3,9 21,92 9,39 1500 1654,8 164,28 18,44 300 3,0 21,82 11,59 1850 1654,8 249,90 23,83 290,76 2,4 22,15 13,78 2200 1654,8 353,39 29,88 285,44 2,0 22,93 16,59 2650 1654,8 512,75 38,84 284,36 1,7 24,66 19,41 3100 1654,8 701,68 49,43 289,76 1,4 27,33 0,1 5,01 800 2351,4 46,73 13,03 330,24 5,5 31,81 7,20 1150 2351,4 96,55 19,12 313,16 3,9 30,79 9,39 1500 2351,4 164,28 25,62 300 3,0 30,32 11,59 1850 2351,4 249,90 32,70 290,76 2,4 30,39 13,78 2200 2351,4 353,39 40,43 285,44 2,0 31,02 4000 4532 4800 /> /> /> /> /> /> /> /> /> /> /> /> /> /> />
To analyze the economic characteristics, two summarizing curves are drawn on it: the envelope curve a-a of the maximum speeds on different roads, the amount of full use of the installed engine power, and the curve c-s of the most economical speeds.
2.1. Analysis of economic characteristics.
1. Determine on each road surface (soil background) the most economical speeds. Indicate their values and fuel consumption values. The most economical speed, as you would expect on pavement, at half the maximum speed, fuel consumption is 14.5 l/100 km.
2. Explain the nature of the change in economy when deviating from the economic speed to the right and to the left. When deviating to the right, the specific fuel consumption per kW increases, when deviating to the left, the air resistance increases very sharply.
3. Determine the control fuel consumption. 14.5 l / 100 km.
4. Compare the obtained control fuel consumption with that of the prototype car. In the prototype, the control flow is equal to the received one.
5. Based on the stock of the car (daily) traveled on the road with improved coverage, determine the approximate capacity /> fuel tank (in l) according to the dependence:
For the prototype capacity of tanks - 80 liters, I accept such a capacity (it is convenient to fill it from canisters).
After the calculations are completed, the results are summarized in a table.
Table number 7.
Indicators 1.Type. Small truck. 2. load factor of the car (by task). 2.5 3. Load capacity, kg. 1000 4. Maximum speed, m/s. 25 5. Weight of equipped car, kg. 1360 6. Number of wheels. 4
7. Distribution of curb weight along the vehicle axles, kg
Through the rear axle;
across the front axle.
8. Gross weight of the loaded vehicle, kg. 2350
9. Distribution of the total mass along the axes of the vehicle, kg,
Through the rear axle;
across the front axle.
10. Dimensions of wheels, mm.
Diameter (radius),
Tire profile width;
Internal air pressure in tires, MPa.
11. Load platform dimensions:
Capacity, m/cube;
Length, mm;
Width, mm;
Height, mm.
12. Vehicle base, mm. 2540 13. Steady deceleration during braking, m/s. 5.69
14. Braking distance, m when braking at a speed:
Maximum speed.
15. Maximum values of the dynamic factor for gears:
16. The lowest value of fuel consumption on soil backgrounds, l / 100 km:
17. The most economical movement speeds (m/s) on soil backgrounds:
18. Fuel tank capacity, l. 80 19. Vehicle driving range, km. 550 20. Control fuel consumption, l/100 km (approximate). 14.5 Engine: Carburetor 21. Maximum power, kW. 59.40 22. The frequency of rotation of the crankshaft at maximum power, rpm. 4800 23. Maximum torque, Nm. 176.91 24. The frequency of rotation of the crankshaft at maximum torque, rpm. 2200
Bibliography.
1. Skotnikov V.A., Mashchensky A.A., Solonsky A.S. Fundamentals of the theory and calculation of the tractor and the car. Moscow: Agropromizdat, 1986. - 383s.
2. Methodological aids for the implementation of course work, old and new editions.
INTRODUCTION
The guidelines provide a method for calculating and analyzing the traction-speed properties and fuel efficiency of carburetor vehicles with a manual transmission. The paper contains the parameters and technical characteristics of domestic cars that are necessary to perform calculations of dynamism and fuel efficiency, indicates the procedure for calculating, constructing and analyzing the main characteristics of these operational properties, gives recommendations on choosing a number of technical parameters that reflect the design features of various cars, modes and conditions their movements.
The use of these guidelines makes it possible to determine the values of the main indicators of dynamism and fuel efficiency and to identify their dependence on the main factors of the vehicle design, its loading, road conditions and engine operation, i.e. solve the problems that are put before the student in the course work.
MAIN OBJECTIVES OF CALCULATION
When analyzing traction and high-speed properties of the car, the following characteristics of the car are calculated and constructed:
1) traction;
2) dynamic;
3) accelerations;
4) acceleration with gear shifting;
5) rolling.
On their basis, the determination and evaluation of the main indicators of the traction and speed properties of the car is carried out.
When analyzing fuel economy of the car, a number of indicators and characteristics are calculated and built, including:
1) characteristics of fuel consumption during acceleration;
2) fuel-speed characteristics of acceleration;
3) fuel characteristics of steady motion;
4) indicators of the fuel balance of the car;
5) indicators of operational fuel consumption.
CHAPTER 1. DRIVING AND SPEED PROPERTIES OF THE VEHICLE
1.1. Calculation of traction forces and resistance to movement
The movement of a vehicle is determined by the action of traction forces and resistance to movement. The totality of all forces acting on the car expresses the force balance equations:
Р i = Р d + Р о + P tr + Р + P w + P j , (1.1)
where P i - indicator traction force, H;
R d, R o, P tr, P , P w , P j - respectively, the resistance forces of the engine, auxiliary equipment, transmission, road, air and inertia, H.
The value of the indicator thrust force can be represented as the sum of two forces:
Р i = Р d + Р e, (1.2)
where P e is the effective thrust force, H.
The value of P e is calculated by the formula:
where M e is the effective torque of the engine, Nm;
r - wheel radius, m
i - transmission ratio.
To determine the values of the effective torque of a carburetor engine for a particular fuel supply, its speed characteristics are used, i.e. dependence of the effective torque on the crankshaft speed at various throttle positions. In its absence, the so-called unified relative speed characteristic of carburetor engines can be used (Fig. 1.1).
Fig.1.1. Unified relative partial speed characteristic of carburetor motors
This characteristic makes it possible to determine the approximate values of the effective torque of the engine at various values of the crankshaft speed and throttle positions. To do this, it is enough to know the values of the effective torque of the engine (MN) and the frequency of rotation of its shaft at maximum effective power (nN).
Torque value corresponding to maximum power (M N), can be calculated using the formula:
, (1.4)
Where N e max - maximum effective engine power, kW.
Taking a number of values of the frequency of rotation of the crankshaft (Table 1.1), calculate the corresponding number of relative frequencies (n e /n N). Using the latter, according to Fig. 1.1 determine the corresponding series of values of the relative values of the torque (θ = M e / M N), after which the desired values are calculated by the formula: M e = M N θ. The values of M e are summarized in Table. 1.1.
Specifications of Hyundai Solaris, Lada Granta, KIA Rio, KAMAZ 65117.
OPERATING PROPERTIES OF THE VEHICLE
The operational properties of a car is a group of properties that determine the possibility of its effective use, as well as the degree of its suitability for operation as a vehicle.
They include the following group properties that provide movement:
- informative
- traction and speed
- brake
- fuel economy
- patency
- maneuverability
- stability
- reliability and safety
These properties are laid down and formed at the stage of designing and manufacturing a car. The driver can, based on these properties, choose the car that best suits his needs and needs.
INFORMATION
Informativeness of the car - this is its property to provide the necessary information to the driver and other road users. In all conditions, the volume and quality of perceived information is crucial for the safe driving of vehicles. Information about the features of the vehicle, the nature of the behavior and intentions of its driver largely determines the safety in the actions of other road users and confidence in the implementation of their intentions. In conditions of insufficient visibility, especially at night, information content in comparison with other operational properties of the car has a major impact on traffic safety.
Distinguish internal, external and additional information content car.
The properties of the car that provide the driver with the ability to perceive the information necessary to drive the car at any time are called internal informativeness . It depends on the design and arrangement of the driver's cab. The most important for internal information content are visibility, instrument panel, internal sound alarm system, handles and vehicle control buttons.
Visibility should allow the driver to perceive virtually all the necessary information about any changes in the road situation in a timely manner and without interference. It depends primarily on the size of the windows and wipers; width and location of cab pillars; designs of washers, systems of blowing and heating of glasses; location, size and design of rear-view mirrors. Visibility also depends on the comfort of the seat.
The instrument panel should be located in the cab in such a way that the driver spends minimal time to observe them and perceive their readings, without being distracted from observing the road. The location and design of the handles, buttons and control keys should make it easy to find them, especially at night, and provide the driver with the feedback necessary to control the accuracy of control actions through tactile and kinetostatic sensations. The most accurate feedback signals are required from the steering wheel, brake and gas pedals, and the gear lever.
The design and arrangement of the cabin must meet the requirements of not only internal information content, but also the ergonomics of the driver's workplace - a property that characterizes the adaptability of the cabin to the psychophysiological and anthropological characteristics of a person. The ergonomics of the workplace depends, first of all, on the comfort of the seat, the location and design of the controls, as well as on the individual physical and chemical parameters of the environment in the cabin.
Uncomfortable posture of the driver and the location of controls, as well as excessive noise, shaking and vibration, excessively high or low temperatures, poor air ventilation worsen the conditions for the driver, reduce his performance, the accuracy of perception and control actions.
External informativeness - a property that determines the ability of other road users to receive information from the car, necessary for proper interaction with it at any time. It is determined by the size, shape and color of the body, the characteristics and location of the retroreflectors, the external light signaling system, as well as the sound signal.
The information content of vehicles with small dimensions depends on their contrast with the road surface. Cars painted in black, grey, green, blue colors are 2 times more likely to get into an accident than those painted in light and bright colors, due to the difficulty of distinguishing them. Such cars become the most dangerous in conditions of insufficient visibility and at night.
DRIVING AND SPEED PROPERTIES OF THE VEHICLE
Traction and speed properties of the car - these properties determine the dynamics of the car's acceleration, the ability to reach its maximum speed, and are characterized by the time (in seconds) required to accelerate the car to a speed of 100 km/h, the engine power and the maximum speed that the car can develop.
