Definitions and indicators for assessing the traction and speed properties of the vehicle. Traction-speed properties of the car Speed \u200b\u200bmode is determined by traction forces
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 cf, 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 of its modes, each of which is characterized by the corresponding indicators of the traction and speed properties of the vehicle.
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)
Specifications Hundai Solaris, Lada Granta, KIA Rio, KamAZ 65117.
OPERATIONAL PROPERTIES OF THE CAR
The operational properties of a car are a group of properties that determine the possibility of its effective use, as well as the degree of its adaptability to operation as a vehicle.
They include the following group properties that provide movement:
- informativeness
- traction-high-speed
- brake
- fuel efficiency
- passability
- maneuverability
- sustainability
- reliability and safety
These properties are laid down and formed during the design and manufacture of the car. Based on these properties, the driver can choose the car that best meets his needs and requirements.
INFORMATIVITY
Informativeness of the car - this is its property to provide the driver and other road users with the necessary information. In all conditions, the volume and quality of the perceived information is critical for the safe driving of vehicles. Information about the features of the vehicle, the nature of the behavior and the intentions of its driver largely predetermines the safety in the actions of other road users and confidence in the implementation of their intentions. In conditions of poor 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 information content ... It depends on the design and arrangement of the driver's cab. The most important for internal information content are visibility, dashboard, internal sound alarm system, handles and car control buttons.
Visibility should allow the driver to take in virtually all the necessary information about any changes in the traffic 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; design of washers, ventilation and heating systems; 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 minimum time to observe them and perceive their readings, without being distracted from observing the road. The location and design of handles, buttons and control keys should make them easy to find, especially at night, and provide the driver through tactile and kinetostatic sensations with the feedback needed to control the accuracy of control actions. 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 cab 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 cab 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.
Inconvenient posture of the driver and the location of the 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 efficiency, the accuracy of perception and control actions.
External information content - a property that affects the ability of other road users to receive information from the car, which is necessary for correct interaction with it at any time. It is determined by the size, shape and color of the body, the characteristics and location of the reflectors, the external light signaling system, and the sound signal.
The information content of vehicles with small dimensions depends on their contrast relative to the road surface. Cars painted in black, gray, green, blue are 2 times more likely to get into accidents than cars 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.
TRACTION-SPEED PROPERTIES OF THE CAR
Traction and speed properties of the car - these properties determine the dynamics of the car's acceleration, the ability to develop its maximum speed, and are characterized by the time (in seconds) required to accelerate the car to a speed of 100 km / h, engine power and maximum speed that the car can develop.
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Introduction
1. Technical characteristics of the car
2. Calculation of the external speed characteristic of the engine
3. Calculation of the car's traction diagram
4. Calculation of the dynamic characteristics of the car
5. Calculation of vehicle acceleration in gears
6. Calculation of the time and way of acceleration of the car in gears
7. Calculation of the stopping distance of the car in gears
8. Calculation of the road fuel consumption of a car
Conclusion
Bibliography
Introduction
It is difficult to imagine the life of a modern person without a car. The car is used in production, and in everyday life, and in sports.
The efficiency of using motor vehicles in various operating conditions is determined by the complex of their potential operational properties - traction and speed, braking, cross-country ability, fuel efficiency, stability and controllability, ride comfort. These performance properties are influenced by the basic parameters of the vehicle and its components, primarily the engine, transmission and wheels, as well as the characteristics of the road and driving conditions.
Increasing the performance of the car and reducing the cost of transportation is impossible without studying the operational properties of the car, since to solve these problems, it is necessary to increase its average speed and reduce fuel consumption, while maintaining traffic safety and ensuring maximum comfort for the driver and passengers.
Performance indicators can be determined experimentally or by calculation. To obtain experimental data, the car is tested on special stands, or directly on the road under conditions close to operational. Testing is associated with the expense of significant funds and labor of a large number of qualified workers. Moreover, it is very difficult to reproduce all operating conditions. Therefore, vehicle testing is combined with a theoretical analysis of operational properties and the calculation of their performance.
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.
In this course project, you should perform the necessary calculations based on specific technical data, build graphs and use them to analyze the traction-speed and fuel-economic properties of the VAZ-21099 car. Based on the results of the calculations, it is required to construct the external speed, traction and dynamic characteristics, determine the acceleration of the car in gears, study the dependence of the car speed on the path and the car speed on the time during acceleration, calculate the stopping distance of the car, and study the dependence of fuel consumption on speed. As a result, we can conclude about the traction, speed and fuel and economic properties of the VAZ-21099 car.
1 TECHNICAL CHARACTERISTIC OF THE VEHICLE
1 Make and type of car: VAZ-21099
The car brand is composed of letters and a digital index. The letters represent the abbreviated name of the manufacturer, and the numbers: the first is the class of the car in terms of the engine displacement, the second is the type designation, the third and fourth are the serial number of the model in the class, the fifth is the modification number. Thus, the VAZ-21099 is a small-class passenger car produced by the Volga Automobile Plant, 9 models, 9 modifications.
2 Wheel configuration: 42.
Cars designed for use on improved roads usually have two drive and two non-drive wheels, while cars designed mainly for use in difficult road conditions have all drive wheels. These differences are reflected in the vehicle's wheel formula, which includes the total number of wheels and the number of driven wheels.
3 Number of seats: 5 seats.
For cars and buses, the total number of seats is indicated, including the driver's seat. A passenger car is considered a passenger car with no more than nine seats, including the driver's seat. A passenger car is a car that, by its design and equipment, is designed to carry passengers and baggage with the necessary comfort and safety.
4 Unladen weight of the vehicle: 915 kg (including 555 and 360 kg on the front and rear axles, respectively).
Unladen weight of the vehicle is the vehicle's curb weight without load. Consists of the dry mass of the car (not filled and not equipped), the mass of fuel, coolant, spare wheel (s), tools, accessories and mandatory equipment.
5 Gross vehicle weight: 1340 kg (including front and rear axles, 675 and 665 kg, respectively).
Gross weight - the sum of the vehicle's own weight and the weight of the cargo or passengers transported by the vehicle.
6 Overall dimensions (length, width, height): 400615501402 mm.
7 The maximum vehicle speed is 156 km / h.
8 Reference fuel consumption: 5.9 l / 100 km at a speed of 90 km / h.
9 Engine type: VAZ-21083, carburetor, 4-stroke, 4-cylinder.
10 Displacement of cylinders: 1.5 l.
11 Maximum engine power: 51.5 kW.
12 Shaft speed corresponding to maximum power: 5600 rpm.
13 Maximum engine torque: 106.4 Nm.
14 Shaft speed corresponding to maximum torque: 3400 rpm.
15 Transmission type: 5-speed, with synchronizers in all forward gears, gear ratios - 3.636; 1.96; 1.357; 0.941; 0.784; Z.Kh. - 3.53.
16 Transfer Case (if equipped) - no.
17 Type of main gear: cylindrical, helical, gear ratio - 3.94.
18 Tires and markings: radial low profile, size 175 / 70R13.
2. CALCULATION OF THE EXTERNAL SPEED CHARACTERISTICS OF THE ENGINE
The circumferential force on the drive wheels that propels the vehicle occurs as a result of the engine torque being supplied to the drive wheels through the transmission.
The influence of the engine on the traction-speed properties of the car is determined by its speed characteristic, which is the dependence of the power and torque on the engine shaft on its speed. If this characteristic is taken at maximum fuel supply to the cylinder, then it is called external, if at incomplete supply - partial.
To calculate the external speed characteristic of the engine, it is necessary to take the technical characteristics of the values \u200b\u200bof key points.
1 Maximum engine power:, kW.
Shaft rotation frequency corresponding to maximum power:, rpm.
2 Maximum engine torque:, kNm.
Shaft rotation frequency corresponding to the maximum torque:, rpm.
Intermediate values \u200b\u200bare determined from the polynomial equation:
where is the current value of the engine power, kW;
Maximum engine power, kW;
Current value of the crankshaft rotation speed, rad / s;
The crankshaft speed in the design mode, corresponding to the maximum power value, rad / s;
Polynomial coefficients.
The polynomial coefficients are calculated using the following formulas:
where is the coefficient of moment adaptability;
Speed \u200b\u200badaptability coefficient.
Adaptability coefficients
where is the moment corresponding to the maximum power;
Converting the frequency of rpm to rad / s
To check the correctness of the coefficients of the polynomial, the equality must be fulfilled:.
Torque value
The calculated power values \u200b\u200bdiffer from the actual ones transmitted to the transmission due to the engine power loss to the accessory drive. Therefore, the actual values \u200b\u200bof power and torque are determined by the formulas:
where is the coefficient taking into account the power loss for the drive of auxiliary equipment; for cars
0.95 ... 0.98. Accept \u003d 0.98
Calculation of the external speed characteristic of the engine of a VAZ-21099 car.
We take the values \u200b\u200bat key points from the brief technical characteristics:
1 Maximum engine power \u003d 51.5 kW.
Shaft speed corresponding to maximum power \u003d 5600 rpm.
2 Maximum engine torque \u003d 106.4 Nm.
Shaft speed corresponding to maximum torque \u003d 3400 rpm.
Let's convert the frequencies to rad / s:
Then the torque at maximum power
Let us determine the coefficients of adaptability in terms of torque and frequency of rotation:
Here is the calculation of the coefficients of the polynomial:
Check: 0.710 + 1.644 - 1.354 \u003d 1
Therefore, the calculation of the coefficients is correct.
Let's make calculations of power and torque for idle. The minimum speed at which the engine runs stably at full load is for a carburetor engine \u003d 60 rad / s:
We enter further calculations in table 2.1, according to which we build graphs of changes in the external speed characteristic:
Table 2.1 - Calculation of the values \u200b\u200bof the external speed characteristic
|
Parameter |
||||||||
Conclusion: as a result of the calculations, the external speed characteristic of the VAZ-21099 car was determined, its graphs were built, the correctness of which satisfies the following conditions:
1) the power curve passes through a point with coordinates (51.5; 586.13);
2) the curve of the change in the engine torque passes through the point with coordinates (0.1064; 355.87);
3) the extremum of the moment function is at the point with coordinates (0.1064; 355.87).
The graphs of changes in the external speed characteristic are given in Appendix A.
3. CALCULATION OF THE TRACTION CHART OF THE VEHICLE
The traction diagram is the dependence of the peripheral force on the driving wheels on the vehicle speed.
The main driving force of a car is the circumferential force applied to its drive wheels. This force arises from the operation of the engine and is caused by the interaction of the drive wheels and the road.
Each crankshaft speed corresponds to a strictly defined torque value (according to the external speed characteristic). According to the found values \u200b\u200bof the moment, it is determined, and according to the corresponding shaft rotation frequency -.
For steady-state conditions, the circumferential force on the driving wheels
where is the actual value of the moment, kNm;
Transmission gear ratio;
Wheel rolling radius, m;
Efficiency of transmission, the value is defined in the task.
Steady-state is a mode in which there will be no power losses due to a deterioration in filling the cylinder with a fresh charge and thermal inertia of the engine.
The transmission ratio and circumferential force are calculated for each gear:
where is the gear ratio of the gearbox;
Transfer case transfer ratio;
Final drive gear ratio.
Wheel rolling radius
where is the maximum vehicle speed from the technical characteristics, m / s;
UТ - fifth gear ratio;
wp - shaft rotation frequency corresponding to maximum power, rad / s;
Vehicle speed
where is the vehicle speed, m / s;
w - crankshaft rotation frequency, rad / s.
The value of the value limiting the circumferential force on the driving wheels under the conditions of wheel-to-road adhesion is determined by the formula
where is the coefficient of adhesion of the wheel to the road;
Vertical component under the driving wheels, kN;
Vehicle weight per driving wheels, kN;
Vehicle weight per driving wheels, t;
Free fall acceleration, m / s.
Let's calculate the parameters of the traction diagram of the VAZ-21099 car. Transmission ratio when engaging the first gear
Wheel rolling radius
Then the value of the circumferential force
Vehicle speed
m / s \u003d 3.438 km / h
All subsequent calculations should be summarized in Table 3.1.
Table 3.1 - Calculation of the parameters of the traction diagram
Based on the obtained values, the dependence of the circumferential force on the driving wheels (FK) on the vehicle speed FK \u003d f (va) (traction diagram) is plotted, on which a limiting line is drawn according to the conditions of wheel adhesion to the road. The number of traction curves is equal to the number of gears in its box.
Let us determine the value of the quantity limiting the circumferential force on the driving wheels by the condition of adhesion of the wheel to the road, according to the formula
Conclusion: the line of limiting the circumferential force according to the adhesion conditions intersects one of the dependencies (for the 1st gear), therefore, the maximum value of the circumferential force will be limited by the adhesion conditions by the value of kN.
The traction diagram of the VAZ-21099 car is given in Appendix B.
4. CALCULATION OF THE DYNAMIC CHARACTERISTICS OF THE VEHICLE
The dynamic characteristic of a car is the dependence of the dynamic factor on the speed. The dynamic factor is the ratio of the free force aimed at overcoming the road resistance forces to the vehicle weight:
where is the circumferential force on the driving wheels of the vehicle, kN;
Air resistance force, kN;
Vehicle weight, kN.
When calculating the air resistance force, the frontal and additional air resistance are taken into account.
Air resistance force
where is the total coefficient taking into account the frontal
resistance, and the coefficient of additional resistance,
which for cars is taken in the range \u003d 0.15 ... 0.3 Ns / m;
Vehicle speed;
Drag area (projection of the vehicle onto a plane,
perpendicular to the direction of movement).
Drag area
where is the area filling factor (for cars it is 0.89-0.9);
Overall vehicle height, m;
Overall width of the vehicle, m
Limitation of the dynamic factor based on the conditions of wheel adhesion
where is the limiting circumferential force, kN.
Since the limitation is observed when the car starts moving, i.e. at low speeds, the value of air resistance can be neglected.
Based on the results of the calculations, a graph of the dynamic characteristics for all gears is built and a line for limiting the dynamic factor is plotted, as well as a line of total road resistance.
On the dynamic characteristic, key points are marked by which vehicles of different masses are compared.
Calculation of the dynamic characteristics of the car VAZ-21099.
Determine the area of \u200b\u200bdrag
Substitute the numeric values \u200b\u200bfor the first point:
All subsequent calculations are summarized in Table 5.1.
Let us calculate the limitation of the dynamic factor according to the conditions of wheel adhesion to the road surface:
Conclusion: from the plotted graph (Appendix B) it can be seen that the line of limitation of the dynamic factor intersects the dependence of the dynamic characteristic in the first gear, which means that the adhesion conditions affect the dynamic characteristics of the VAZ-21099 car and under the given conditions the car will not be able to develop the maximum value of the dynamic factor ... On the dynamic characteristic, key points are marked, by which the comparison of cars of different masses takes place:
1) the maximum value of the dynamic factor in the highest gear Dv (max) and the corresponding speed vк - critical speed: (0.081; 12.223);
2) the value of the dynamic factor at the maximum vehicle speed (0.021; 39.100);
3) the maximum value of the dynamic factor in the first gear and the corresponding speed: (0.423; 3.000)
The maximum speed of movement is determined by the resistance of the road and in these road conditions the car cannot reach the maximum value of the speed according to the technical characteristics.
5. CALCULATION OF VEHICLE ACCELERATIONS IN GEARS
Accelerating the car in gears
vehicle traction acceleration transmission
where is the acceleration of gravity, m / s;
Coefficient taking into account the acceleration of rotating masses;
Dynamic factor;
Rolling resistance coefficient;
The slope of the road.
Coefficient taking into account the acceleration of rotating masses
where are the empirical coefficients, taken within
0,03…0,05; =0,04…0,06;
Gear ratio of the gearbox.
For calculations, we take \u003d 0.04, \u003d 0.05, then
For first gear;
For second gear;
For third gear;
For fourth gear;
For fifth gear.
Find the acceleration for the first gear:
The results of the remaining calculations are summarized in Table 5.1.
Based on the data obtained, a graph of acceleration of the VAZ-21099 car in gears is plotted (Appendix D).
Table 5.1 - Calculation of the values \u200b\u200bof the dynamic factor and accelerations
Conclusion: at this point, the acceleration of the VAZ-21099 car in gears was calculated. It can be seen from the calculations that the acceleration of a car depends on the dynamic factor, rolling resistance, acceleration of rotating masses, slope of the terrain, etc., which significantly affects its value. The car reaches its maximum acceleration value in first gear m / s at a speed of \u003d 4.316 m / s.
6. CALCULATION OF THE TIME AND DISTANCE OF ACCELERATION OF THE VEHICLE IN GEARS
Acceleration is considered to begin at the minimum steady speed, limited by the minimum steady crankshaft speed. It is also considered that acceleration is carried out with full fuel supply, i.e. the engine runs on an external characteristic.
To plot the time and distance of the vehicle acceleration in gears, the following calculations must be performed.
For the first gear, the acceleration curve is divided into speed intervals:
The average acceleration value is determined for each interval
Acceleration time for each interval
Total acceleration time in a given gear
The path is determined by the formula
Overall acceleration path in gear
In the event that the characteristics of accelerations in adjacent gears intersect, then the moment of switching from gear to gear is carried out at the point of intersection of the characteristics.
If the characteristics do not overlap, switching is carried out at the maximum final speed for the current gear.
The vehicle is coasting during power interruptions. Shift times are dependent on the skill of the driver, the gearbox design and the engine type.
The time of movement of the car with a neutral position in the gearbox for cars with a carburetor engine is within 0.5-1.5 s, and with a diesel engine 0.8-2.5 s.
During gear shifting, the vehicle speed decreases. The decrease in the speed of movement, m / s, when changing gears can be calculated using the formula derived from the traction balance,
where is the acceleration of gravity;
Coefficient taking into account the acceleration of rotating masses (taken \u003d 1.05);
The total coefficient of resistance to translational motion
Gear shift time; \u003d 0.5 s.
The distance traveled during the gear change
where is the maximum (final) speed in the switchable gear, m / s;
Decrease in travel speed when changing gears, m / s;
Gear shift time, s;
The vehicle is accelerated up to speed. The equilibrium maximum speed of movement in the highest gear is found from the graph of changes in the dynamic factor, on which the line of the total coefficient of resistance to translational movement is marked on a scale. The perpendicular, lowered from the point of intersection of this line with the line of the dynamic factor on the abscissa axis, indicates the equilibrium maximum speed.
Calculation example for the first section of the first gear. The first speed interval is
The average acceleration is
The acceleration time for the first interval is
The average speed of passage of the first section is
The path is
The path is determined in the same way at each transmission section. The total distance covered in first gear is
The reduction in travel speed when changing gears can be calculated using the formula:
The distance covered during the gear change is
The vehicle is accelerated to a speed of m / s \u003d 112.608 km / h. All subsequent calculations of the time and distance of vehicle acceleration in gears are summarized in Table 6.1.
Table 6.1 - Calculation of the time and way of acceleration of the VAZ-21099 car in gears
Based on the calculated data, graphs of the dependence of the vehicle speed on the path and on the time during acceleration are plotted (Appendices E, E).
Conclusion: when carrying out the calculations, the total acceleration time of the VAZ-21099 car was determined, which is equal to \u003d 29.860 s30 s, as well as the distance traveled by it during this time 614.909 m 615 m.
7. CALCULATION OF THE STOPPING DISTANCE OF THE VEHICLE IN GEARS
Stopping distance is the distance traveled by the car from the moment it detects an obstacle to a complete stop.
The calculation of the stopping distance of the car is determined by the formula:
where is the full stopping distance, m;
Initial braking speed, m / s;
Driver reaction time, 0.5 ... 1.5 s;
Delay time of the brake drive; for the hydraulic system 0.05 ... 0.1 s;
Deceleration rise time; 0.4 s;
Brake efficiency ratio; at for cars \u003d 1.2; at \u003d 1.
Stopping distance calculations are performed for different coefficients of wheel-road adhesion:; ; - accepted on assignment, \u003d 0.84.
The speed is taken on assignment from the minimum to the maximum equilibrium value.
An example of determining the stopping distance of a VAZ-21099 car.
Stopping distance at and speed \u003d 4.429 m / s is
All subsequent calculations are summarized in Table 7.1.
Table 7.1 - Calculation of stopping distance
Based on the calculated data, graphs of the stopping distance versus movement speed for various conditions of wheel adhesion to the road were built (Appendix G)
Conclusion: based on the graphs obtained, we can conclude that with an increase in the vehicle speed and a decrease in the coefficient of adhesion to the road, the stopping distance of the vehicle increases.
8. CALCULATION OF TRAVEL FUEL CONSUMPTION BY VEHICLE
Fuel efficiency of a car is a set of properties that determine fuel consumption when a car performs transport work under various operating conditions.
Fuel efficiency mainly depends on vehicle design and operating conditions. It is determined by the degree of perfection of the working process in the engine, the efficiency and gear ratio of the transmission, the ratio between the curb and gross vehicle weight, the intensity of its movement, as well as the resistance offered to the movement of the vehicle by the environment.
When calculating fuel efficiency, the initial data are the load characteristics of the engine, which are used to calculate the track fuel consumption:
where is the specific fuel consumption at the nominal mode, g / kWh;
Engine power utilization factor (I);
The utilization factor of the engine speed (E);
Power supplied to the transmission, kW;
Fuel density, kg / m;
Vehicle speed, km / h.
Specific fuel consumption at the nominal mode for carburetor engines is \u003d 260..300 g / kWh. In work, we take \u003d 270 g / kWh.
The values \u200b\u200band for carburetor engines are determined by empirical formulas:
where I and E are the degree of use of power and engine speed;
where is the power supplied to the transmission, kW;
Engine power by external speed characteristic, kW;
Current engine crankshaft speed, rad / s;
Engine crankshaft rotation frequency at nominal mode, rad / s;
where is the engine power spent to overcome the road resistance forces, kW;
Engine power spent to overcome the air resistance force, kW;
Power losses in transmission and to drive auxiliary equipment of the vehicle, kW;
The density of gasoline according to the reference data is taken as 760 kg / m, the value of the coefficient of the total resistance of the road was calculated earlier and is equal to \u003d 0.021,
An example of calculating the road fuel consumption for the first gear. The engine power spent to overcome the road resistance forces is
The engine power spent to overcome the air resistance force is
The power losses in the transmission and to drive the auxiliary equipment of the car is
The power supplied to the transmission is
Travel fuel consumption is
All subsequent calculations are summarized in Table 8.1.
Table 8.1 - Calculation of travel fuel consumption
Based on the calculated data, a graph of fuel consumption versus gear speed is plotted (Appendix I).
Conclusion: the analysis of the graph showed that when the car is moving at the same speed in different gears, the track fuel consumption will decrease from the first gear to the fifth.
CONCLUSION
As a result of the course project to assess the traction-speed and fuel-economic properties of the VAZ-21099 car, the following characteristics were calculated and built:
· External speed characteristic, which meets the following requirements: the power curve passes through the point with coordinates (51.5; 586.13); the curve of the change in the engine torque passes through the point with coordinates (0.1064; 355.87); the extremum of the moment function is at the point with coordinates (0.1064; 355.87);
· Traction diagram of a car, on the basis of which it can be said that the conditions of adhesion of the wheels to the road surface affect the traction characteristic of a given car;
The dynamic characteristic of the car, from which the maximum value of the dynamic factor in the first gear was determined \u003d 0.423 (\u003d 0.423, which shows that the adhesion conditions affect the dynamic response), as well as the maximum value of the speed in the fifth gear \u003d 39.1 m / s;
· Vehicle acceleration in gears. It was determined that the vehicle reaches its maximum acceleration value in first gear, with J \u003d 2.643 m / s at a speed of 3.28 m / s;
· Time and way of vehicle acceleration in gears. The total acceleration time of the car was about 30 s, and the distance covered by the car during this time was 615 m;
· Stopping distance of the car, which depends on the speed and coefficient of adhesion of the wheel to the road. With an increase in speed and a decrease in the coefficient of adhesion, the stopping distance of the car increases. At a speed of \u003d 39.1 m / s and \u003d 0.84, the maximum stopping distance was \u003d 160.836 m;
· Road fuel consumption of a car, which showed that fuel consumption decreases at the same speed of different gears.
BIBLIOGRAPHY
1. Lapsky SL Assessment of traction-speed and fuel-economic properties of a car: a guide for the implementation of course work on the discipline "Vehicles and their performance" // BelGUT. - Gomel, 2007
2. Requirements for the registration of reporting documents for independent work of students: study method. Boykachev MA. other. - Ministry of Education Republic of Belarus, Gomel, BelSUT, 2009 .-- 62 p.
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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-high-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 maximum intensities of acceleration and braking of the car when it is operating in traction mode in various road conditions.
Indicators of the traction and 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 assignment - 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 (road resistance coefficient).
/\u003e (0.04 * (1000 * 1352) * 9.8 + 1163.7) * 25/1000 * 0.93 \u003d 56.29kW.
The unladen weight of the vehicle is related to its rated carrying capacity by the dependence: /\u003e
/\u003e 1000 / 0.74 \u003d 1352 kg.
where: /\u003e - vehicle load-carrying capacity - 0.74.
For 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 density of the air, the coefficient of streamlining of the sides and bottom (windage coefficient), the area of \u200b\u200bthe frontal surface 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 values \u200b\u200bof B and H are specified in subsequent calculations when determining the dimensions of the platform.
/\u003e \u003d maximum speed of movement on the road with improved surface with full fuel supply, by assignment it is equal to 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 - 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 intensive 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 in the table:
Table no. 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 - 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; the 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 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 speeds of the vehicle are calculated in different gears. The obtained data are 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 plotted 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 frequency: 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.
The 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 a 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, and 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 thrust and air resistance when the car is moving) in this equation represents the traction force consumed to overcome all external resistances to the car's movement, 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.
The following dependencies exist 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 vehicle - 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 allows finding 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.
On the extreme sling of the upper abscissa, the coefficient Г \u003d 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 \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, I take as the second axis of ordinates 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 axis of ordinates 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 under 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 coefficient Г the vehicle, necessarily 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 points of inflection 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. In this case, the only variable is 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 of movement 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 surface, 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.
Traction and speed properties of a car significantly depend on design factors. The type of engine, transmission efficiency, transmission gear ratios, weight and streamlining of the vehicle have the greatest influence on the 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 driving conditions and modes. This is due to the shape of the external speed characteristic of these engines.
In fig. 5.1 presents 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 Nat maximum power for both engines are the same.
Fig. 5.1 it can be seen that the gasoline engine has a more convex external speed characteristic than the diesel. This provides him with more power reserve. (N " h\u003e N " s ) at the same speed, for example at speed v 1 . Consequently, a gasoline-powered vehicle can accelerate faster, climb steeper grades, and tow heavier trailers than a diesel vehicle.
Transmission efficiency.This factor allows you to estimate the power loss in the transmission due to friction. A decrease in efficiency caused by an increase in friction power losses due to a deterioration in the technical condition of transmission mechanisms during operation leads to a decrease in tractive force on the driving wheels of the vehicle. As a result, the maximum vehicle speed and road resistance overcome by the vehicle are reduced.
Figure: 5.1. Power balance graph of a car with different engines:
N " t - gasoline engine; N " t - diesel; N " h, N " s – corresponding power reserve values \u200b\u200bat vehicle speed v 1 .
Transmission gear ratios.The maximum speed of the vehicle significantly depends on the final drive ratio. The best final drive ratio is considered to be such that the car develops maximum speed and the engine reaches maximum power. An increase or decrease in the final drive ratio in comparison with the optimal one leads to a decrease in the maximum vehicle speed.
The gear ratio I of the gearbox affects the maximum resistance of the road that the vehicle 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 a 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.An improvement in the traction and speed properties of a car can also be achieved by using, together with the main gearbox, additional gearboxes: a divider (multiplier), a demultiplier and a transfer case. Usually, additional gearboxes are two-stage and double the number of gears. In this case, the divider only expands the range of gear ratios, and the demultiplier and the transfer case increase their values. However, too many gears increase the weight and complexity of the gearbox and make it difficult to drive.
Hydraulic transmission.This transmission provides ease of control, smooth acceleration and high cross-country ability of the vehicle. However, it worsens the traction and speed properties of the car, since its efficiency is lower than that of a manual step transmission.
Vehicle weight.An increase in vehicle mass leads to an increase in rolling resistance forces, lifting and acceleration. As a result, the traction and speed properties of the vehicle deteriorate.
Car streamlining... Streamlining has a significant impact on the traction and speed properties of the vehicle. With its deterioration, the reserve of tractive force decreases, which can be used to accelerate the car, overcome hills and tow trailers, increase the power loss for air resistance and reduce the maximum speed of the car. For example, at a speed of 50 km / h, the power loss in a passenger car associated with overcoming air resistance is almost equal to the power loss due to the rolling resistance of the car when driving on a paved road.
Good streamlining of passenger cars is achieved by slightly tilting the roof of the body backward, using body sidewalls without abrupt transitions and a smooth bottom, installing a windshield and a radiator lining with a slope and such an arrangement of protruding parts in which they do not go beyond the outer 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 tarpaulins.
BRAKE PROPERTIES.
Definitions.
Braking -the creation of artificial resistance in order to reduce speed or keeping it stationary.
Braking properties -determine the maximum deceleration of the vehicle and the limits of external forces that hold the vehicle in place.
Braking mode -a mode in which braking torques are applied to the wheels.
Braking distances -the distance traveled by the car from the detection of the interference by the driver to the complete stop of the car.
Braking properties -the most important determinants of traffic safety.
Modern braking properties are standardized by Rule No. 13 of the Inland Transport Committee of the United Nations Economic Commission for Europe (UNECE).
The national standards of all UN member states are drawn up on the basis of these Rules.
The car must have several braking systems that perform different functions: working, parking, auxiliary and spare.
Working The braking system is the main braking system that provides the braking process under normal vehicle operating conditions. The braking mechanisms of the service brake system are wheel brakes. These mechanisms are controlled by a pedal.
Parkingthe braking system is designed to keep the vehicle stationary. The brakes of this system are located either on one of the transmission shafts or in the wheels. In the latter case, the brakes of the working brake system are used, but with an additional control drive for the parking brake system. The parking brake system is operated manually. The parking brake actuator must be only mechanical.
Sparethe braking system is used when the service braking system fails. In some cars, the parking brake system or an additional circuit of the working system performs the spare function.
There are the following types of braking : emergency (emergency), service, braking on slopes.
Emergencybraking is carried out by means of the service brake system with the maximum intensity for the given conditions. The number of emergency braking is 5 ... 10% of the total number of brakes.
Servicebraking is used to smoothly reduce the speed of the car or stop in a predetermined month
Estimated indicators.
The existing standards GOST 22895-77, GOST 25478-91 provide for the following braking performance indicators car:
j set - steady deceleration with constant pedal effort;
S t - the path traveled from the moment the pedal is pressed to the stop (stopping distance);
t cf - response time - from pressing the pedal to reaching j set. ;
Σ Р tor. - total braking force.
- specific braking force;
- coefficient of unevenness of braking forces;
Sustained downhill speed V tast. when braking with a retarder;
Maximum slope h t max, at which the car is held by the parking brake;
Deceleration provided by a spare brake system.
The standards for the braking properties of vehicles prescribed by the standard are shown in the table. ATC category designations:
M - passenger: M 1 - cars and buses with no more than 8 seats, M 2 - buses with more than 8 seats and a gross weight of up to 5 tons, M 3 - buses with a total weight of more than 5 tons;
N - trucks and road trains: N 1 - with a total mass 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 total mass of up to 0.75 t, O 2 - with a total mass of up to 3.5 t, O 3 - with a total mass of up to 10 t, O 4 - with a total mass of over 10 t.
The normative (quantitative) values \u200b\u200bof the estimated indicators for new (developed) vehicles are assigned in accordance with the categories.