Traction and speed properties are important when operating a car, since their average speed and performance largely depend on them. With favorable traction and speed properties, the average speed increases, the time spent on transporting goods and passengers decreases, and the performance of the vehicle also increases.

3.1. Indicators of traction and speed properties

The main indicators that allow assessing the traction and speed properties of a vehicle are:

Maximum speed, km / h;

Minimum steady speed (in top gear)
, km / h;

Acceleration time (from standstill) to maximum speed t p, s;

Acceleration path (from standstill) to maximum speed S p, m;

Maximum and average acceleration during acceleration (in each gear) j max and j av, m / s 2;

The maximum overcome rise in the lowest gear and at a constant speed i m ax,%;

Length of dynamically overcome rise (with acceleration) S j, m;

Maximum pulling force on the hook (in low gear) R from , N.

IN
as a generalized estimated indicator of the traction-speed properties of a car, you can use the average speed of continuous movement wed , km / h. It depends on the driving conditions and is determined taking into account all its modes, each of which is characterized by the corresponding indicators of the traction and speed properties of the car.

3.2. The forces acting on the car when driving

When driving, a number of forces act on the car, which are called external. These include (Figure 3.1) gravity G, forces of interaction between the wheels of the car and the road (road reactions) R X1 , R x2 , R z 1 , R z 2 and the force of interaction of the car with air (reaction of the air environment) P c.

Figure: 3.1. Forces acting on a car with a trailer when driving:a - on a horizontal road;b - on the rise;in - on the descent

Some of these forces act in the direction of movement and are driving, others are against movement and refer to the forces of resistance to movement. So strength R X2 in traction mode, when power and torque are supplied to the drive wheels, it is directed in the direction of travel, and the forces R X1 and P in - against the movement. The force P p - a component of the force of gravity - can be directed both in the direction of movement and against, depending on the conditions of movement of the car - on the rise or on the descent (downhill).

The main driving force of the car is the tangential reaction of the road. R X2 on the driving wheels. It results from the supply of power and torque from the engine through the transmission to the drive wheels.

3.3. Power and moment supplied to the driving wheels of the vehicle

Under operating conditions, the car can move in different modes. These modes include steady motion (uniform), acceleration (accelerated), deceleration (decelerated)

and
roll forward (by inertia). At the same time, in urban conditions, the duration of the movement is approximately 20% for the steady state, 40% for acceleration and 40% for braking and coasting.

In all driving modes, except for coasting and braking with the engine disconnected, power and torque are supplied to the drive wheels. To determine these values, consider the circuit,

Figure: 3.2. Scheme for determining powertorque and torque, basefrom the engine to the leadingscaffolding car:

D - engine; M - flywheel; T - transmission; K - driving wheels

shown in Fig. 3.2. Here N e - effective engine power; N tr - power supplied to the transmission; N count - power supplied to the driving wheels; J m is the moment of inertia of the flywheel (this value is conventionally understood as the moment of inertia of all rotating parts of the engine and transmission: flywheel, clutch parts, gearbox, cardan gear, main gear, etc.).

When the car accelerates, a certain proportion of the power transmitted from the engine to the transmission is spent on unwinding the rotating parts of the engine and transmission. These power costs

(3.1)

where A -kinetic energy of rotating parts.

Let us take into account that the expression for the kinetic energy has the form

Then the power consumption

(3.2)

Based on equations (3.1) and (3.2), the power supplied to the transmission can be represented in the form

Some of this power is wasted to overcome various resistances (friction) in the transmission. The indicated power losses are estimated by the transmission efficiency tr.

Taking into account the power losses in the transmission, the power supplied to the drive wheels

(3.4)

Engine crankshaft angular speed

(3.5)

where ω to is the angular speed of the driving wheels; u t - transmission ratio

Gear ratio of transmission

Where u k - gear ratio of the gearbox; u d - the gear ratio of the additional gearbox (transfer case, divider, range multiplier); and D - gear ratio of the main transfer.

As a result of the substitution e from relation (3.5) to formula (3.4), the power supplied to the driving wheels:

(3.6)

At constant angular velocity of the crankshaft, the second term on the right-hand side of expression (3.6) is equal to zero. In this case, the power supplied to the driving wheels is called traction.Its value

(3.7)

Taking into account relation (3.7), formula (3.6) is transformed to the form

(3.8)

To determine the torque M to , supplied from the engine to the driving wheels, we represent the power N count and N T, in expression (3.8) in the form of products of the corresponding moments and angular velocities. As a result of this transformation, we obtain

(3.9)

Substitute into formula (3.9) expression (3.5) for the angular velocity of the crankshaft and, dividing both sides of the equality by to get

(3.10)

With a steady motion of the car, the second term on the right side of formula (3.10) is equal to zero. The moment supplied to the driving wheels is in this case called traction.Its magnitude

(3.11)

Taking into account relation (3.11), the moment supplied to the driving wheels:

(3.12)

MINISTRY OF AGRICULTURE AND

FOOD OF THE REPUBLIC OF BELARUS

INSTITUTION OF EDUCATION

"BELARUSIAN STATE

AGRICULTURAL UNIVERSITY

FACULTY OF RURAL MECHANIZATION

FARMS

Department of Tractors and Cars

COURSE PROJECT

By discipline: Fundamentals of the theory of calculating a tractor and a car.

On the topic: Traction-speed properties and fuel efficiency

car.

5th year student group 45

A.A. Snopkova

Head of KP

Minsk2002.
Introduction.

1. Traction and speed properties of the car.

Traction-speed properties of a car are a set of properties that determine the possible characteristics of the engine or the adhesion of the driving wheels to the road, the ranges of speed variation and the limiting intensities of acceleration and braking of the car when it is operating in traction mode in various road conditions.

Indicators of the trajectory-speed properties of the vehicle (maximum speed, acceleration during acceleration or deceleration during braking, traction force on the hook, effective engine power, lift 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 driving conditions for each type of vehicle.

Traction-speed properties and indicators are determined during the traction calculation of the vehicle. The calculation object is a light-duty truck.

1.1. Determination of vehicle engine power.

The calculation is based on the rated carrying capacity of the vehicle /\u003e in kg (the mass of the installed payload + the mass of the driver and passengers in the cab) or the road train /\u003e, it is equal from the task - 1000 kg.

The engine power /\u003e required to move a fully loaded vehicle at a speed /\u003e given road conditions, characterizing the reduced road resistance /\u003e, is determined from the dependence:

/\u003e unladen weight of the vehicle, 1000 kg;

/\u003e air resistance (in N) - 1163.7 when moving with the maximum speed /\u003e \u003d 25 m / s;

/\u003e - transmission efficiency \u003d 0.93. Rated lifting capacity /\u003e specified in the assignment;

/\u003e \u003d 0.04, taking into account the work of the car in agriculture (coefficient of road resistance).

/\u003e (0.04 * (1000 * 1352) * 9.8 + 1163.7) * 25/1000 * 0.93 \u003d 56.29 kW.

The unladen weight of the vehicle is related to its nominal carrying capacity by the dependence: /\u003e

/\u003e 1000 / 0.74 \u003d 1352 kg.

where: /\u003e - vehicle load-carrying capacity - 0.74.

A car with a particularly low carrying capacity \u003d 0.7 ... 0.75.

The vehicle's load-carrying capacity significantly affects the dynamic and economic performance of the vehicle: the larger it is, the better these performance.

Air resistance depends on the air density, the streamlining coefficient of the sides and bottom (windage coefficient), the frontal surface area F (in /\u003e) of the car and the high-speed mode of movement. Determined by dependency: /\u003e,

/\u003e0.45*1.293*3.2*625\u003d 1163.7 N.

where: /\u003e \u003d 1.293 kg //\u003e - air density at a temperature of 15 ... 25 C.

The streamlining coefficient of the car is /\u003e \u003d 0.45 ... 0.60. I accept \u003d 0.45.

The forehead area can be calculated using the formula:

F \u003d 1.6 * 2 \u003d 3.2 /\u003e

Where: B is the track of the rear wheels, I take it \u003d 1.6m, the value H \u003d 2m. The B and H values \u200b\u200bare specified in subsequent calculations when determining the platform dimensions.

/\u003e \u003d maximum speed of movement on the road with improved surface with full fuel supply, by assignment it is 25 m / s.

Since the car develops, as a rule, in direct transmission, then

where: /\u003e 0.95 ... 0.97 - 0.95 Efficiency of the engine at idle; /\u003e \u003d 0.97 ... 0.98 - 0.975.

Efficiency of the main gear.

/>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 /\u003e and the mass transmitted to the wheel axle) are determined based on the carrying capacity of the vehicle.

With a fully loaded vehicle, 65 ... 75% of the total weight of the vehicle falls on the rear axle and 25 ... 35% - on the front. Therefore, the load factor of the front and rear driving wheels is 0.25… 0.35 and –0.65… 0.75, respectively.

/\u003e /\u003e; /\u003e 0.65 * 1000 * (1 + 1 / 0.45) \u003d 1528.7kg.

to the front: /\u003e. /\u003e 0.35 * 1000 * (1 + 1 / 0.45) \u003d 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 front axle wheel - 411.5 kg.

Based on the load /\u003e and the pressure in the tires, in Table 2, the tire sizes are selected, in m (the width of the tire profile /\u003e and the diameter of the landing rim /\u003e). Then the estimated radius of the driving wheels (in m);

Estimated data: tire name -; its size is 215-380 (8.40-15); calculated radius.

/\u003e (0.5 * 0.380) + 0.85 * 0.215 \u003d 0.37m.

1.3. Determination of the capacity and geometric parameters of the platform.

According to the lifting capacity /\u003e (in t), the platform capacity /\u003e in cubic meters is selected. m., from the conditions:

/> />0,8*1=0,8 />/>

For an onboard car, /\u003e is taken \u003d 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 take the width of the platform for trucks (1.15 ... 1.39) from the vehicle track, that is, \u003d 1.68 m.

The height of the body is determined by the size of a similar car - UAZ. It is equal to - 0.5 m.

I take the length of the platform - 2.6 m.

By the inner length /\u003e 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 \u003d 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 motionless relative to the road.

1.4.1. Steady-state deceleration during vehicle movement.

Slowdown /\u003e \u003d /\u003e,

Where g is the free fall acceleration \u003d 9.8 m / s; /\u003e - coefficient of adhesion of wheels to the road, the values \u200b\u200bof which for various road surfaces are taken from Table 3; /\u003e is the coefficient of accounting for rotating masses. Its values \u200b\u200bfor the designed car are equal to 1.05 ... 1.25, I accept \u003d 1.12.
The better the road, the more the car can decelerate when braking. On hard roads, the deceleration can be as high as 7 m / s. Poor road conditions drastically reduce braking intensity.

1.4.2. Minimum braking distance.

The length of the minimum braking distance /\u003e /\u003e can be determined from the condition that the work performed 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 intense braking, that is, when it has the maximum value. If braking is carried out on a horizontal road with constant deceleration, then the distance to a stop is:

I determine the braking path for various values \u200b\u200bof /\u003e, three different speeds of 14.22 and 25 m / s, and I will enter them into the table:

Table number 1.

Support surface.

Slowing down on the road. Braking force. Minimum braking distance. Travel speed. 14 m / s 22 m / s

1. Asphalt 0.65 5.69 14978 17.2 42.5 54.9 2. Gravel. 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 16 130 16.0 39.5 51.0 7. Snowy road. 0.18 1.58 4148 62.2 153.6 198.3 8. Icing of the road. 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 high-speed mode of movement in each of the selected gears.

The number of transmissions from the task is 5. Direct transmission I choose -4, the fifth - economical.

Thus, one of the most important tasks when performing coursework on cars is the correct selection of the number of gears.

1.5.1.Selection of gears of the car.

Gear ratio /\u003e \u003d /\u003e,

Where: /\u003e - gearbox ratio; /\u003e - final gear ratio.

The gear ratio of the main gear is found by the equation:

where: /\u003e - the estimated radius of the driving wheels, m; taken from previous calculations; /\u003e - engine speed at rated speed.

Gear ratio in first gear:

where /\u003e is the maximum dynamic factor, admissible 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: /\u003e - coefficient of adhesion of the driving wheels to the road, depending on road conditions \u003d 0.5 ... 0.75; /\u003e - load factor of the driving wheels of the car; recommended values \u200b\u200b\u003d 0.65… 0.8; maximum engine torque, in N * m, is taken from the speed characteristic for carburetor engines; G is the total weight of the vehicle, N; - The efficiency of the transmission of the vehicle in the first gear is calculated by the formula:

0.96 - Efficiency of the engine at idle cranking of the crankshaft; /\u003e\u003d0.98 - efficiency of a cylindrical pair of gears; /\u003e\u003d0.975 –KPD of a bevel gear pair; - respectively, the number of cylindrical and conical pairs involved in engagement in the 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 a geometric progression, forming a series, where q is the denominator of the progression; it is calculated by the formula:

where: z is the number of transmissions indicated in the task.

The gear ratio of the permanently engaged main gear of the car is taken, according to the adopted from the prototype \u003d.

According to the gear ratios of the transmission, the maximum speed of the car is calculated in different gears. The data obtained is summarized in a table.

Table No. 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 theoretical (external) speed characteristics of the carburetor engine.

The theoretical speed external characteristic f\u003e \u003d f (n) is built on a sheet of graph paper. Calculation and construction of external characteristics is carried out in the following sequence. On the abscissa axis, we postpone in the accepted scale the value of the crankshaft rotation speeds: nominal, maximum idle, at maximum torque, minimum, corresponding to engine operation.

The nominal frequency of rotation is set in the reference, frequency /\u003e,

Frequency /\u003e. The maximum rotational speed is taken on the basis of the reference data of the prototype engine –4800 rpm.

Intermediate points of the power values \u200b\u200bof the carburetor engine are found from the expression, given by the values \u200b\u200b/\u003e (at least 6 points).

The values \u200b\u200bof the torque /\u003e are calculated depending on:

The current values \u200b\u200bof /\u003e and /\u003e are taken from the graph /\u003e. The specific effective fuel consumption of the carburetor engine is calculated according to the dependence:

/\u003e, g / (kW, h),

where: /\u003e specific effective fuel consumption at rated power, specified in the task \u003d 320 g / kW * h.

The hourly fuel consumption is determined by the formula:

The values \u200b\u200b/\u003e and /\u003e are taken from the plotted graphs, a table is compiled based on the results of calculating the theoretical external characteristic.

Data for building characteristics. 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 performance of the vehicle.

The dynamic characteristic of the car illustrates its traction and speed properties of 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 represents the traction force consumed to overcome all external resistances to the movement of the car, with the exception of air resistance. Therefore, the ratio /\u003e characterizes the power reserve per unit weight of the vehicle. This meter of dynamic, in particular, traction-speed, properties of a car is called the dynamic factor D of the car.

Thus, the dynamic factor of the car.

The vehicle dynamic factor is determined in each gear when the engine is running at full load with full fuel supply.

There are the following dependencies between the dynamic factor and the parameters characterizing the road resistance (coefficient /\u003e) and the inertial loads of the car:

/\u003e /\u003e - in case of unsteady motion;

/\u003e with steady motion.

The dynamic factor depends on the speed of the car - the engine speed (its torque) and the engaged gear (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 a load in the body, and then, by means of additional constructions, it is converted into a universal one, which makes it possible to find the dynamic factor for any weight of the car.

Additional constructions for obtaining universal dynamic characteristics.

We apply the second abscissa axis on the top of the built characteristic, and put off the values \u200b\u200bof the vehicle load factor on the second one.

On the extreme sling of the upper abscissa, the coefficient Г \u003d 1, which corresponds to an empty car; at the extreme point to 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 \u200b\u200bof the load factor and draw down verticals from them to the intersection with the lower abscissa.

The vertical passing through the point Г \u003d 2 is taken as the second y-axis of the characteristic. Since the dynamic factor at Г \u003d 2 is half that of an empty car, the scale of the dynamic factor on the second y-axis should be twice as large as on the first axis, passing through the point Г \u003d 1. I connect unambiguous divisions on both ordinates with oblique lines. The intersection points of these straight lines with steel verticals form a scale on each vertical for the corresponding value of the vehicle load factor.

The calculation results of the indicators are entered in the table.

Table # 3.

Transfer V, m / s.

Torque, Nm.

D D \u003d 1 D \u003d 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 7.38 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 data obtained.

1. Determine which gears the car will operate in given road conditions, characterized by the reduced coefficient /\u003e 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 Г the 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 the coefficient \u003d 1, the car can move at /\u003e \u003d 0.04 at a speed of 31.17 m / s in 5th gear; /\u003e \u003d 0.07 - 28 m / s, 5th gear; /\u003e \u003d 0.1 - 24 m / s, 5th gear. With a coefficient of \u003d 2.5 (maximum load), the car can move at /\u003e \u003d 0.04 - speed 25 m / s, 4th gear; /\u003e \u003d 0.07 - speed 19 m / s, 4th gear; /\u003e \u003d 0.1 - speed 17 m / s, 3rd gear.

2. Determine by the dynamic characteristic the greatest road resistance that the car can overcome, moving in each gear with a uniform speed (at the inflection points of the dynamic factor curves).

Check the obtained data from the point of view of the possibility of their implementation in terms of adhesion to the road surface. For a car with rear wheel drive:

where: /\u003e - load factor of the driving wheels.

Table 4.

Gear no. Road resistance to be overcome Adhesion to the road surface (asphalt). G \u003d 1 G \u003d 2.5 G \u003d 1 G \u003d 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 4th gear 0.204 0.09 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 snow road; on the 3rd icy road; on the 4th dry dirt road; on the 5th asphalt

3. Determine the ascent angles that the car is able to overcome in different road conditions (at least 2 ... 3 values) in different gears, and the speed that it will develop at the same time.

Table # 5.

Road resistance. No. of gear Lift angle Speed \u200b\u200bD \u003d 1 D \u003d 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 5 gear 11 4 17, 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 5 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. Define:

The maximum steady-state speed in the most typical road conditions for this type of vehicle (asphalt surface). In this case, f values \u200b\u200bfor different 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 transmission at the most common speed for a given type of car (usually a speed equal to half the maximum speed is taken) - 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 maximum value of the dynamic factor in intermediate gears; 2nd gear - 0.588; 3rd gear - 0.317; 5th gear - 0.150;

5. to compare the obtained data with the reference data for the car, which has basic indicators close to the prototype. The data obtained in the calculation is practically similar to the data of the UAZ vehicle.

2. Fuel efficiency of the vehicle.

One of the main fuel efficiency as an operational property is considered to be the amount of fuel consumed per 100 km of track with uniform movement of a certain speed under given road conditions. A number of curves are plotted on the characteristic, each of which corresponds to certain road conditions; When performing work, three road resistance coefficients are considered: 0.04, 0.07, 010.

Fuel consumption, l / 100 km:

where: /\u003e - instantaneous fuel consumption by the car engine, l;

where /\u003e is the travel time of 100 km of the path, \u003d /\u003e.

From here, taking into account the engine power spent on overcoming air resistance, we get:

For a visual representation of the economy, a characteristic is built. The ordinate shows the fuel consumption, and the abscissa shows the speed.

The build order is as follows. For various speed modes of car movement depending on

determine the value of the engine crankshaft speed.

Knowing the engine speed, the g values \u200b\u200bare determined from the corresponding speed characteristics.

According to the formula 17, the engine power (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, is determined.

The calculations are carried out up to the speed at which the engine is loaded at maximum power. The variable quantity in this case is only the speed of movement and air resistance, all other indicators are taken from previous calculations.

Substituting the values \u200b\u200bfound for different speeds, the desired fuel consumption values \u200b\u200bare calculated.

Table 6.

/\u003e 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 value of the full use of the installed engine power and the curve c-the most economical speeds.

2.1. Analysis of the economic characteristics.

1. Determine the most economical travel speeds on each road surface (soil background). Indicate their values \u200b\u200band fuel consumption values. Most economical speed, as would be expected on hard surfaces, at half the maximum fuel consumption is 14.5 L / 100 km.

2. Explain the nature of the change in efficiency when deviating from the economic speed to the right and to the left. With a deviation to the right, the specific fuel consumption per kW increases, with a deviation to the left, the air resistance increases very sharply.

3. Determine the control fuel consumption. 14.5 l / 100 km.

4. Compare the obtained reference fuel consumption with that of the prototype vehicle. In the prototype, the control flow is equal to the received one.

5. Based on the vehicle's running reserve (daily), traveled on the road with an improved surface, determine the approximate capacity /\u003e of the fuel tank (in liters) according to the dependence:

The prototype capacity of tanks is 80 liters, I accept such a capacity (it is convenient to refuel it from a canister).

After completing the calculations, the results are summarized in a table.

Table 7.

Indicators 1. Type. Small truck. 2. vehicle load factor (on assignment). 2,5 3. Loading capacity, kg. 1000 4. Maximum speed of movement, m / s. 25 5. The mass of the equipped car, kg. 1360 6. Number of wheels. 4

7. Distribution of the equipped weight along the vehicle axles, kg

Through the rear axle;

Through the front axle.

8. Gross weight of the loaded vehicle, kg. 2350

9. Distribution of the total mass along the axles of the vehicle, kg,

Through the rear axle;

Through the front axle.

10. Wheel dimensions, mm.

Diameter (radius),

Tire profile width;

Internal air pressure in tires, MPa.

11. Dimensions of the cargo platform:

Capacity, m / cube;

Length, mm;

Width, mm;

Height, mm.

12. Car base, mm. 2540 13. Steady-state deceleration during braking, m / s. 5.69

14. Braking distance, m when braking at a speed:

Maximum speed.

15. Maximum values \u200b\u200bof the dynamic factor for gears:

16. The smallest value of fuel consumption on soil backgrounds, l / 100 km:

17. The most economical travel speeds (m / s) on soil backgrounds:

18. Fuel tank capacity, l. 80 19. Vehicle power reserve, km. 550 20. Control fuel consumption, l / 100 km (approximate). 14.5 Engine: Carbureted 21. Maximum power, kW. 59.40 22. 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 the maximum torque, rpm. 2200

Bibliography.

1. Skotnikov V.A., Maschensky A.A., Solonsky A.S. Basics of theory and calculation of a tractor and a car. M .: Agropromizdat, 1986. - 383p.

2. Methodological manuals for the implementation of course work, old and new edition.

According to the theory of a car, traction calculations are carried out to assess its traction and speed properties.

Traction calculations establish the relationship between the parameters of the vehicle and its units on the one hand (vehicle weight - G , transmission ratios - i, wheel rolling radius - r to etc.) and speed and traction properties of the machine: speed – V i , traction forces - R etc. with another.

Depending on what is specified in the traction calculation and what is determined, there can be two types traction calculations:

1. If the parameters of the machine are set and its speed and traction properties are determined, then the calculation will be verification officer.

2. If the speed and traction properties of the machine are set, and its parameters are determined, then the calculation will be design.

Checking thrust calculation

Any task associated with determining the traction and speed properties of a serial machine is the task of a verification traction calculation, even if this task concerns the determination of any private vehicle properties such as maximum speed on a given road, pulling force on a hook, etc.

As a result of the verification thrust calculation, it is possible to obtain general traction and speed properties (characteristics) car. In this case, a full verification thrust calculation is performed.

Initial data of the verification thrust calculation.The following basic values \u200b\u200bmust be specified as the initial data for the verification calculation:

l. Vehicle weight (mass): curb weight or full weight (G).

2. The total weight (mass) of the trailer (s) - G ".

3. Wheel formula, wheel radii ( r o- free radius, r to - rolling radius).

4. Characteristics of the motor taking into account losses in the motor installation.

For a car with a hydromechanical transmission - the operating characteristic of the engine - hydrodynamic transformer units.

5. Gear ratios at all gear stages and overall gear ratios (i ki, i o).

6. Coefficients of rotating masses (δ).

7. Parameters of aerodynamic characteristics.

8. Road conditions for which the traction calculation is made.

Tasks of verification calculation... As a result of the verification thrust calculation, the following values \u200b\u200b(parameters) should be found:

1. Travel speeds in the given road conditions.

2. The maximum resistance that the machine can overcome.

3. Free traction vultures.

4. Injectivity parameters.

5. Braking parameters.

Calculation graphs... The results of the verification calculation can be expressed by the following graphical characteristics:

1. Traction characteristic (for vehicles with hydromechanical transmission - traction and economic characteristics).

2. Dynamic characteristic.

3. Schedule of the use of engine power.

4. Acceleration schedule.

These characteristics can also be obtained empirically.

Thus, the traction-speed properties of a car should be understood as a set of properties that determine the ranges of speed variation possible by the characteristics of the engine or the adhesion of the driving wheels to the road and the maximum acceleration rates of the vehicle when it is operating in traction mode in various road conditions.

Traction and speed properties of military vehicles (BAT) depend on its design and operational parameters, as well as road conditions and environment. Thus, with a rigorous scientific approach to assessing the traction-speed properties of BAT, a systematic research method is required with the definition, analysis and assessment of traction-speed properties in the driver-vehicle-road-environment system. System analysis is the most modern method of research, forecasting and substantiation, which is currently used to improve the existing and create new military automotive equipment (components - verification and design thrust calculation). The emergence of systems analysis is explained by the further complication of the tasks of improving the existing and creating new technology, when solving which there was an objective need to establish, study, explain, manage and solve complex problems of interaction between a person, technology, road and environment.

However, the systematic approach to solving complex problems of science and technology cannot be considered absolutely new, since this method was used by Gallileo to explain the construction of the Universe; it was the systems approach that allowed Newton to discover his famous laws; Darwin to develop a system of nature; Mendeleev to create the famous periodic table of elements, and Einstein - the theory of relativity.

An example of a modern systematic approach to solving complex problems of science and technology is the development and creation of manned spacecraft, the design of which takes into account the complex connections between man, ship and space.

Thus, at present we are not talking about the creation of this method, but about its further development and application for solving fundamental and applied problems.

An example of a systematic approach to solving problems of the theory and practice of military automotive technology is the development by Professor A.S. Antonov. the theory of power flow, which allows analyzing and synthesizing complex mechanical, hydromechanical and electromechanical systems on a single methodological basis.

However, individual elements of this complex system are probabilistic in nature and can be described mathematically with great difficulty. So, for example, despite the use of modern methods of formalizing systems, the use of modern computer technology and the availability of sufficient experimental material, it has not yet been possible to create a model of a car driver. In this regard, three-element (car - road - environment) or two-element (car - road) subsystems are distinguished from the general system and problems are solved within their framework. This approach to solving scientific and applied problems is quite legitimate.

When completing diploma, term papers, as well as in practical classes, students will solve applied problems in a two-element system - a car - a road, each element of which has its own characteristics and its own factors that have a significant impact on the traction and speed properties of the BAT and which, of course, should be considered.

So, these main design factors include:

Vehicle weight;

Number of driving axles;

Alignment of axles in the vehicle base;

Control scheme;

Type of wheel propeller drive (differential, locked, mixed) or type of transmission;

Engine type and power;

Frontal resistance area;

Gear ratios of gearbox, transfer case and main gear.

Main operational factorsinfluencing the traction and speed properties of BAT are;

Road type and characteristics;

Road surface condition;

Technical condition of the car;

Driver qualifications.

To assess the traction and speed properties of military vehicles, generalized and single indicators .

As generalized indicators for assessing the traction and speed properties of BAT, they usually use average speed and dynamic factor ... Both of these indicators take into account both design and operational factors.

The most common and sufficient for a comparative assessment are also the following unit indicators of traction and speed properties:

1. Maximum speed.

2. Conditional maximum speed.

3. Acceleration time on the way 400 and 1000 m.

4. Acceleration time to the set speed.

5. Speed \u200b\u200bcharacteristic acceleration-run down.

6. Speed \u200b\u200bcharacteristic of acceleration in the highest gear.

7. Speed \u200b\u200bcharacteristic on a road with a variable longitudinal profile.

8. Minimum steady speed.

9. The maximum overcome rise.

10. Steady-State speed on long climbs.

11. Acceleration during acceleration.

12. Pulling force on the hook. ...

13. Length of dynamically overcome ascent. Generalized indicators are determined both by calculation and experimentally.

Individual indicators, as a rule, are determined empirically. However, some of the single indicators can be determined by calculation, in particular, when using a dynamic characteristic for this.

So, for example, the average speed of movement (generalized parameter) can be determined by the following formula

where S d - the distance traveled by the car during non-stop movement, km;

t d - travel time, h

When solving tactical and technical problems in exercises, the average speed of movement can be calculated using the formula

, (62)

where K v 1 and K v 2 - coefficients obtained empirically. They characterize the driving conditions of the machine.

For all-wheel drive wheeled vehicles moving on unpaved roads, K v 1 \u003d 1.8-2 and K v 2 \u003d 0.4-0.45, when driving on the highway K v 2 \u003d 0.58 .

From the above formula (62) it follows that the higher the specific power (the ratio of the maximum engine power to the total mass of the car or train), the better the traction-speed properties of the car, the higher the average speed.

At present, the power density of all-wheel drive vehicles is within the range: 10-13 hp / t for heavy-duty vehicles and 45-50 hp / t for command and light-duty vehicles. It is planned to increase the power density of all-wheel drive vehicles supplied to the RF Armed Forces to 11 - 18hp / t. The specific power of military tracked vehicles is currently 12-24 hp / t, it is envisaged to increase it to 25 hp / t.

It should be borne in mind that the traction and speed properties of the machine can be improved not only by increasing the engine power, but also by improving the gearbox, transfer case, transmission in general, as well as the suspension system. This must be taken into account when developing proposals for improving the design of vehicles.

So, for example, a significant increase in the average speed of the machine can be obtained through the use of continuous-step transmissions, including those with automatic gear shifting in an additional gearbox; through the use of control systems with several front, with several front and rear steered axles for multi-axle vehicles; regulators of brake sip and anti-lock braking systems; due to kinematic (stepless) regulation of the turning radius of military tracked vehicles, etc. The most significant increase in average travel speeds, cross-country ability, handling, stability, maneuverability, fuel efficiency, taking into account environmental requirements, can be obtained through the use of continuously variable transmissions.

At the same time, the practice of operating military vehicles shows that in most cases, the speed of movement of military wheeled and tracked vehicles operating in difficult conditions is limited not only by traction and speed capabilities, but also by the maximum permissible overloads in terms of smoothness. Oscillations of the hull and wheels have a significant impact on the main tactical and technical characteristics and operational properties of the vehicle: safety, serviceability and operability of the weapons and military equipment installed on the vehicle, reliability, working conditions of personnel, efficiency, speed, etc.

When operating a car on roads with large irregularities and, especially, off-road, the average speed is reduced by 50-60% compared to the corresponding indicators when working on good roads. In addition, it should also be borne in mind that significant machine vibrations hinder the work of the crew, cause fatigue of the transported personnel and ultimately lead to a decrease in their performance.

MINISTRY OF AGRICULTURE AND

FOOD OF THE REPUBLIC OF BELARUS

INSTITUTION OF EDUCATION

"BELARUSIAN STATE

AGRARIAN TECHNICAL UNIVERSITY

FACULTY OF RURAL MECHANIZATION

FARMS

Department of Tractors and Cars

COURSE PROJECT

By discipline: Fundamentals of theory and calculation of a tractor and a car.

On the topic: Traction-speed properties and fuel efficiency

car.

5th year student group 45

A.A. Snopkova

Head of KP

Minsk 2002.
Introduction.

1. Traction and speed properties of the car.

Traction-speed properties of a car is a set of properties that determine the possible ranges of changes in speeds of movement and the maximum intensities of acceleration and deceleration of a car when it is operating in a traction mode of operation in various road conditions.

Indicators of the tag-speed properties of the car (maximum speed, acceleration during acceleration or deceleration during braking, traction force on the hook, effective engine power, lift 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-speed properties and indicators are determined during the traction calculation of the vehicle. The object of the calculation is a light-duty truck.

1.1. Determination of vehicle engine power.

The calculation is based on the rated carrying capacity of the vehicle

in kg (the mass of the installed payload + the mass of the driver and passengers in the cab) or road train, it is equal from the task - 1000 kg.

Engine power

, necessary for the movement of a fully loaded vehicle at a speed in given road conditions, characterizing the reduced resistance of the road, is determined from the dependence: where is the own weight of the vehicle, 1000 kg; air resistance (in N) - 1163.7 when moving at maximum speed \u003d 25 m / s; - transmission efficiency \u003d 0.93. Rated lifting capacity is indicated in the assignment; \u003d 0.04, taking into account the operation of the car in agriculture (road resistance coefficient). (0.04 * (1000 * 1352) * 9.8 + 1163.7) * 25/1000 * 0.93 \u003d 56.29 kW.

The unladen weight of the vehicle is related to its nominal carrying capacity by the dependence:

1000 / 0.74 \u003d 1352 kg. - coefficient of carrying capacity of the vehicle - 0.74.

For a car with an especially low payload \u003d 0.7 ... 0.75.

The vehicle's load-carrying capacity significantly affects the dynamic and economic performance of the vehicle: the larger it is, the better these indicators.

Air resistance depends on air density, the coefficient

streamlining of the contours and bottom (windage coefficient), frontal surface area F (in) of the car and speed mode. 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

\u003d 0.45 ... 0.60. Accept \u003d 0.45.

The frontal area can be calculated using the formula:

Where: B is the track of the rear wheels, I take it \u003d 1.6m, the value H \u003d 2m. The B and H values \u200b\u200bare specified in subsequent calculations when determining the platform dimensions.

\u003d the maximum speed of movement on the road with improved surface with full fuel supply, according to the assignment it is equal to 25 m / s. the car develops, as a rule, in direct transmission, then, 0.95 ... 0.97 - 0.95 engine efficiency at idle; \u003d 0.97 ... 0.98 - 0.975.

Efficiency of the main gear.

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 vehicle, 65 ... 75% of the total weight of the vehicle falls on the rear axle and 25 ... 35% - on the front. Consequently, the load factor of the front and rear driving wheels is 0.25… 0.35 and –0.65… 0.75, respectively.

; 0.65 * 1000 * (1 + 1 / 0.45) \u003d 1528.7 kg.

on the front:

... 0.35 * 1000 * (1 + 1 / 0.45) \u003d 823.0 kg.

I take 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 front axle wheel - 411.5 kg.

Based on the load

and tire pressure, according to table 2, tire sizes are selected, in m (tire profile width and rim diameter). Then the estimated radius of the driving wheels (in m); ...

Estimated data: tire name -; its size is 215-380 (8.40-15); calculated radius.

INTRODUCTION

The methodological guidelines provide a methodology for calculating and analyzing the traction-speed properties and fuel efficiency of carburetor vehicles with a stepped mechanical transmission. The paper contains the parameters and technical characteristics of domestic cars, which are necessary to perform calculations of dynamism and fuel efficiency, indicates the procedure for calculating, constructing and analyzing the main characteristics of these performance properties, gives recommendations on the selection of a number of technical parameters reflecting the design features of various cars, mode and conditions their movements.

The use of these guidelines makes it possible to determine the values \u200b\u200bof the main indicators of dynamism and fuel efficiency and to reveal their dependence on the main factors of the vehicle design, its load, road conditions and engine operating mode, i.e. solve the problems that are posed to the student in the course work.

MAIN CALCULATION TASKS

When analyzing traction-high-speed properties of the car, the calculation and construction of the following characteristics of the car:

1) traction;

2) dynamic;

3) accelerations;

4) acceleration with gear shifting;

5) roll forward.

On their basis, the determination and assessment of the main indicators of the traction and speed properties of the vehicle is made.

When analyzing fuel efficiency 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. TRACTION-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 sum of all the forces acting on the car expresses the power balance equations:

P i \u003d P q + P o + P tr + P + P w + P j, (1.1)

where P i - indicator traction force, H;

R d, P 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:

P i \u003d P q + P e, (1.2)

where P e is the effective traction force, H.

The P e value is calculated by the formula:

where M e - effective engine torque, Nm;

r - wheel radius, m

i - transmission ratio.

To determine the values \u200b\u200bof the effective torque of a carburetor engine with a given fuel supply, its speed characteristics are used, i.e. the dependence of the effective torque on the crankshaft speed at different positions of the throttle valve. In its absence, the so-called single relative speed characteristic of carburetor engines can be used (Figure 1.1).

Figure 1.1. A single relative partial speed characteristic of carburetor auto engines

The specified characteristic makes it possible to determine the approximate value of the effective engine torque at different values \u200b\u200bof the crankshaft speed and throttle valve positions. To do this, it is enough to know the values \u200b\u200bof the effective engine torque (M N) and rotational speed of its shaft at maximum effective power (n N).

Torque value corresponding to maximum power (M N), can be calculated using the formula:

, (1.4)

where N e max is the maximum effective engine power, kW.

Taking a number of values \u200b\u200bof the crankshaft rotation frequency (Table 1.1), calculate the corresponding series of relative frequencies (n e / n N). Using the latter, according to Fig. 1.1 determine the corresponding series of values \u200b\u200bof the relative values \u200b\u200bof the torque (θ \u003d M e / M N), after which the desired values \u200b\u200bare calculated by the formula: M e \u003d M N θ. The M e values \u200b\u200bare summarized in table. 1.1.