Tomorrow of automobile transportation

1. quality utilization coefficient = cargo volume mass (t/m3)x trunk volume (m3)/ rated loading mass (t)

2. Goods: refers to all goods or materials from the carrier's acceptance to delivery to the consignee. The consignments of goods above 3t are all vehicle cargoes, and the consignments of goods below 3t are all LTL cargoes.

3. Transportation distance: it is the transportation distance (km) of the goods from the loading point to the unloading point.

4. Loading quality utilization coefficient = cargo volume quality (t/m3)x trunk volume (m3)/ rated loading quality (t).

5. Power factor: d =(ft-fw)/g(ft- driving force on the driving wheel; Fw-air resistance; G- vehicle weight).

6. Automobile fuel economy: refers to the ability of an automobile to complete the unit transportation workload with the least fuel consumption.

7. Traction coefficient: = static reaction force of driving wheel/vehicle gravity

8. Active safety: the performance of the car itself to prevent or reduce road traffic accidents.

9. attach rate: = f/FZ(f- wheel tangential force; FZ- normal reaction force of wheels).

10. Vehicle maneuverability: refers to the driver's ability to keep the car on a given route with the minimum correction and turn the steering wheel to change the driving direction according to the driver's wishes.

1 1. Vehicle passability: refers to the ability of a vehicle to overcome various obstacles by passing through various bad roads and roadless areas at a high enough average speed under certain loading quality conditions.

12. Automobile technical condition: the sum of quantitative measurement values representing automobile appearance and performance at a certain moment.

13. Economic service life of automobile: from the brand-new state when the automobile is put into production to the service life with the lowest annual average total cost.

14. compactness: it is an index to evaluate the rational utilization of automobile external dimensions.

15. Attachment conditions of driving: the driving force can only be equal to or less than the adhesion.

16. Economy of automobile use: refers to a performance that the automobile can complete the unit transportation volume with the least cost.

17. passive safety: after an accident, the car itself can reduce personal injury and cargo damage.

18. Deceleration rate: Z=- /g The ratio of the reciprocal of the acceleration rate to the gravitational acceleration during braking.

19. Vehicle handling stability: refers to the ability of the vehicle resistance chart to change the external influence of its position or driving direction.

20. Vehicle ride comfort: refers to the performance of ensuring that passengers will not feel uncomfortable and tired due to the vibration of the car body and keep the transported goods intact when the car is driving within the general driving speed range.

2 1. Automobile working ability: refers to the ability of the automobile to implement the regulations according to the performance indicators specified in the technical documents.

22. Technical service life of automobile: refers to the time when the original automobile loses its use value due to the appearance of new technology after the automobile is put into production from a brand-new state.

23. Vehicle mobility: the ability of a vehicle to turn and turn in the smallest area.

24. Specific loading mass = vehicle loading mass (t)/ trunk volume (m3).

25. Transportation conditions: It is determined by the characteristics and requirements of the transportation object, and refers to various factors that affect the use of vehicles.

26. Road cycle test: a road test method in which vehicles are completely in accordance with the specified speed and time specifications.

27. Steady-state steering angular velocity gain: a/ value when driving in a uniform circle.

28. Understeering: The steering radius of the car is larger than when the rigid wheel is installed.

29. Clearance failure: When the car is driving off-road, due to insufficient clearance with irregular ground, the car may be towed and unable to pass.

30. Comfort reduction limit: within this limit, the human body feels good about the exposed vibration environment and can complete reading, writing and other actions.

3 1. Physical life of an automobile: also known as natural life, refers to the time from the time when the automobile is put into production in a brand-new state to the time when it cannot be used technically according to its original purpose.

32. Vehicle service conditions: refers to various external conditions that affect the completion of vehicle transportation.

33. Dynamic characteristic diagram: refers to the relationship curve between power factor and vehicle speed.

34. Load rate: refers to the ratio of the power generated when the throttle valve is partially opened to the power generated when the throttle valve is fully opened, usually expressed as a percentage.

35. Deviation angle: the included angle between the displacement direction of the tire grounding center and the forward direction of the wheel.

36. Oversteering: The steering radius of the car is smaller than when it is equipped with rigid wheels.

37. Minimum ground clearance: the distance between the lowest point of the car and the road surface except the wheels.

38. Fatigue working efficiency reduction limit: When the driver suffers vibration within this limit, he can still keep driving normally.

39. Intangible loss refers to the continuous emergence of more perfect and efficient vehicles under the influence of scientific and technological progress, and the original value of vehicles in use is reduced, or the value of such vehicles is reduced.

40. Physical wear and tear: The automobile breaks down or reduces its technical performance after a period of use.

4 1. Slip rate: the difference between the angular velocities of two wheels divided by the larger one.

42. Neutral steering: The steering radius of a car is equal to the steering angular velocity and rigid wheels.

43. Exposure limit: When the vibration intensity borne by the human body is within this limit, it will remain healthy or safe.

44. Wheel ground specific pressure: refers to the unit pressure of the wheel on the ground.

Step 2 analyze the problem

1. The weight of a car 12KN, the wheelbase is 3m, and the center of gravity is 1.3m from the front axle. There are two kinds of tires to choose from: radial tires, and the cornering stiffness of each tire is 46KN/ radian; Inclined cord tires, the lateral stiffness of each tire is 33KN/ radian. If only the same type of tires can be installed on the same axle, under what circumstances will the car have too many steering characteristics?

Solution: The wheelbase is 3m, and the center of gravity is 1.3m away from the front axle. It is known that the center of gravity is away from the rear axle 1.7m, that is, L 1 = 1.3m, L2 =1.7m. If it has too many steering characteristics, it is K 1L 1 >: K2l2, that is, K. L2/L1=1.7/1.3 =1.31.Therefore, the front axle should be equipped with radial tires, and the rear axle should be equipped with inclined cord tires.

2. When the center of mass moves backward, what will happen to the steering characteristics of the car and why?

A: The backward movement of the center of mass means that the distance from the center of mass to the rear axle decreases, while the distance to the front axle increases, which leads to the increase of k 1l 1 and the decrease of k2l2, which reduces the quality of understeer and even leads to excessive steering characteristics.

3. A car shows neutral steering characteristics when using bias tires with lateral stiffness of 33KN/ radian. If the front axle is fitted with radial tires with lateral stiffness of 46KN/ radian, what kind of smooth steering characteristics will the car have and why? And the handling stability of the car is analyzed.

Answer: Because the tires with diagonal cords have neutral steering characteristics, then k 1l 1=k2l2, that is, l 1=l2, the front axle is replaced by radial tires, and k 1 is increased, and other things remain unchanged, then k1l/kloc-0. K2l2 is characterized by oversteer, because =/[l-ma2 (k1l1-k2l2)/lk1k2], and for oversteer vehicles, k1l1-k2l2 >. At this time, as long as the extremely small forward deflection angle will also lead to a large yaw rate, the car will lose stability.

4. Analyze why the vehicle with excessive steering characteristics has poor handling stability.

Answer: Because =/[L-Ma 2 (k1L1-K2L2)/Lk1K2], for vehicles with excessive steering characteristics, k1L1-K2L2 > 0, so the speed increases rapidly and reaches infinity at a certain speed. At this time, as long as the extremely small forward deflection angle will also lead to a large yaw rate, the car will lose stability.

5. Analyze why the vehicle with moderate understeer characteristics has better handling stability.

Answer: Because =/[L-MA2 (k 1l 1-k2 L2)/lk1K2], for vehicles with insufficient steering characteristics, k1l1-K2L2.

6. Why is it difficult for the front wheel to lock before the rear wheel brakes? The rear wheel brakes earlier than the front wheel, which is easy to cause tail flick?

Answer: When the front wheel is still rolling under the braking force and the rear wheel is locked, if there is still lateral interference force on the basis of braking inertia force, the resultant force will form a certain angle with the longitudinal axis of the vehicle. The lateral interference force must be balanced by the equivalent lateral force acting on the wheel on the ground. Because the rear wheel has slipped, the lateral force can only act on the front wheel. The moment formed by the lateral interference force and the lateral ground will increase the angle formed by the resultant force and the longitudinal axis of the vehicle, and the turning trend of the vehicle will increase. If the front wheel dies first and the rear wheel continues to roll, the corresponding torque will make the included angle smaller, the vehicle will be in a stable state, and the vehicle will continue to move in the original direction, that is, it will not produce side slip.

7. The braking stability of the car with the rear wheel locked and towed when the front wheel is rolling is analyzed.

Answer: If there is a lateral interference force on the basis of the braking inertia force, then the resultant force will form an angle with the longitudinal axis of the vehicle, and the lateral interference force must be balanced by the equivalent lateral force on the wheel. Because the rear wheel has slipped, the lateral force can only act on the front wheel, and the corresponding torque makes the wheel rotate around the vertical axis, which increases the angle, and the turning trend of the vehicle increases, which is in an unstable state.

8. When braking, the ratio of braking force of front and rear axle is greater than the ratio of vertical load of front and rear axle, and its braking stability is analyzed.

A: Because b1/b2 > Fz 1/ Fz2, and =B/Fz, that is to say, when the car brakes, the front wheel locks first and the rear wheel continues to roll. If there is a lateral interference force on the basis of braking inertia force, this resultant force will form a certain angle with the longitudinal axis of the car, and this lateral interference force must be balanced by the equivalent lateral force acting on the wheels on the ground. Because the front wheel is locked, the lateral force can only act on the rear wheel.

9. When braking, the ratio of braking force of front and rear axle is less than the ratio of vertical load of front and rear axle, and its braking stability is analyzed.

A: Because B 1/B2.

10. When the all-wheel drive vehicle starts, the wheels reach the peak attach rate at the same time, and the acceleration of the vehicle at this time is analyzed.

Answer: All wheels have reached the adhesion limit, which means it can be written as follows: because Gz=G*Z, ignoring the lift, Fz 1+Fz2=G, thus Z=Zgrenz=, and Z=- /g, so =-GZ =-G.

1 1. When an all-wheel drive car starts, the wheels slip on the ground, and the acceleration of the car at this time is analyzed.

Answer: At this time, it can be written as Gz=G*Z, ignoring the lift, Fz 1+Fz2=G, so Z =

12. When a car with a gross weight of g brakes suddenly, the wheels lock and are towed at the same time. If the slip coefficient is 0, analyze the deceleration rate that the car can achieve at this time.

Answer: All the wheels are locked and the vehicle slides in a straight line. At this time, it can be written as follows: because Gz=G*Z, ignoring the lift, Fz 1+Fz2=G, so Z =

13. The wheel distance is 1.8m, and the height of the center of gravity is 1.3m during normal loading. If the car is driving on a curve with a turning radius of 50m, how fast is the speed likely to cause rollover?

Solution: the maximum allowable speed without rollover is vamsx = = = 66.3 m/s.

14. When a car is loaded normally, the horizontal distance A and wheelbase L from the center of gravity to the front axle are a=3m and L=4m respectively. If the maximum climbing degree I of the car is 30%, what is the height of the center of gravity H, and is it possible to roll over?

Solution: because GH sini=G(L-a)cosi, h = (l-a)/Tani =1.732m.

15. The braking force of the front and rear axles of the automobile is distributed according to a constant ratio, and the constant ratio coefficient is k. If the front and rear axles of the automobile are locked and towed on the road with adhesion coefficient at the same time, try to analyze how the braking performance will change when the automobile is fully loaded.

Answer: Compared with no load, the center of mass moves backward when fully loaded, so the axle load of the rear axle increases, the axle load of the front axle decreases and the adhesion of the rear axle increases. However, because the braking force of the front and rear axles is distributed according to a fixed proportion, that is, the adhesion of the front and rear axles is also distributed according to a fixed proportion, when the vehicle is fully loaded, the front wheels are locked first, and the rear wheels are locked later, so that the vehicle is in a stable state and it is not easy to flick the tail.

16. The braking force of the front and rear axles of the automobile is distributed according to a constant ratio, and the constant ratio coefficient is k. If the front and rear axles of the automobile are locked and towed on the road with adhesion coefficient at the same time, try to analyze how the braking performance will change when the automobile is empty.

Answer: Compared with full load, the center of mass moves forward, so the axle load of the front axle increases, the axle load of the rear axle decreases, the adhesion of the front axle increases and the adhesion of the rear axle decreases. However, because the braking force of the front and rear axles is distributed according to a fixed proportion, that is, the adhesion of the front and rear axles is also distributed according to a fixed proportion, when the vehicle is braked at no load, the rear wheels are locked first, and the front wheels are locked later, so the vehicle is in an unstable state and prone to tail flick.

Three. Summarize the problem

1. How is the righting torque of elastic tire generated? What is the trend of its size change?

A: After the elastic tire turns under the lateral force, the unit lateral reaction force on the footprint where the wheel touches the ground is triangular, so the action point of the resultant force Y is located behind the midpoint of the footprint, the offset is E, and Y*e is the righting moment. With the increase of lateral force, the righting torque increases. However, after the lateral reaction force of the unit at the back of the imprint reaches the attachment limit, the lateral force distribution of the unit on the imprint is trapezoidal, and E decreases. The lateral force continues to increase, the slip zone continues to increase, the distribution tends to be rectangular from trapezoid, and E tends to zero. It can be seen that restoring moment starts to decrease after reaching the maximum.

2. How is the brand of engine lubricating oil divided and selected?

Answer: Engine lubricating oil is classified according to the quality grade and viscosity grade of lubricating oil. The general principle of selecting engine lubricating oil is to select the quality grade of lubricating oil according to the working conditions of the engine.

3. Under what circumstances is high-speed driving more fuel-efficient than low-speed driving? Why?

A: When the main reduction ratio is fixed, it is more fuel-efficient to drive in high gear under certain road conditions. This is because under the same road and speed conditions, although the output power of the engine is not much different, the higher the gear, the smaller the reserve power, the higher the engine load rate and the smaller the effective fuel consumption rate of the engine. Therefore, it is generally possible to drive in a high gear to save fuel.

4. Why is it difficult to start an automobile engine at low temperature?

Answer: The low-temperature startability of the engine is mainly affected by the viscosity of the engine lubricating oil, the evaporation of gasoline or diesel, the low-temperature fluidity of diesel and the working capacity of the battery. With the decrease of temperature, the internal friction of engine oil increases, the engine resistance distance increases, and the power required for engine start-up increases. With the decrease of temperature, the viscosity and relative density of gasoline increase, the fluidity of gasoline in carburetor oil circuit becomes worse, and the atomization in throat becomes worse because of the increase of its surface tension. At low temperature, the heat absorption of engine parts affects the mixture temperature, which is not conducive to fuel vaporization. Most of the fuel enters the cylinder in liquid state, and the mixture is too thin, which makes it difficult to start. At low temperature, it is difficult to start the engine because of the low terminal voltage of the battery and the small flashover energy of the spark plug.

5. What will happen if the automobile engine is overheated at high temperature? Why?

Answer: (1) The higher the temperature, the smaller the air density, which leads to the decrease of the engine inflation capacity; (2) When the ambient temperature is high, the temperature of the mixture entering the cylinder is also high, and the temperature of the whole working cycle of the engine rises, which is more likely to cause deflagration under deflagration sensitive working conditions; (3) In hot and dry areas, there is much dust in the air; In hot and humid areas, the concentration of water vapor in the air is high, and dust and water vapor enter the engine from the air intake system or crankcase vent to pollute the engine oil, resulting in deterioration of the engine oil; (4) High oil temperature, low viscosity and poor oiliness aggravate the wear of parts; (5) After the oil supply system is heated, some gasoline evaporates, resulting in gas resistance of the oil supply system.

6. Explain the determination method of transmission speed ratio.

Answer: Determine the highest speed ratio of the transmission according to the predetermined maximum speed, and determine the lowest speed ratio according to the required maximum traction and minimum traction; Accord to that stable and economical operation of the engine; The transmission ratio of each gear is distributed according to equal ratio series or progressive speed ratio.

7. What are the main pollutants emitted by gasoline engines? What are the main reasons and influencing factors?

A: The main pollutants are carbon monoxide, hydrocarbons and nitrogen dioxide. CO is an intermediate product in the combustion process of hydrocarbon fuel, and the main influencing factor is the concentration of mixed gas; HC has unburned fuel, products of incomplete combustion and products of partial decomposition. The main influencing factors are all the conditions that hinder fuel combustion, such as too rich and too thin mixture, poor fuel atomization or too much mixed exhaust gas. NO2 is produced by the reaction of oxygen and nitrogen in the air at high temperature and high pressure. The main influencing factors are combustion gas temperature, oxygen concentration and high temperature residence time.

8. What are the characteristics of the running-in period and what technical measures should be taken?

A: The friction is fierce and the wear speed is accelerated. If the car is running at full load, the unit pressure on the friction surface of the parts is very large, which leads to the destruction of the lubricating oil film, the increase of local temperature and the rapid wear and tear of the parts, leading to many driving failures;

Technical measures: (1) Choose a better road during the running-in period and drive at a reduced load and speed limit; (2) During the running-in period, the driver must strictly implement the driving operation rules, maintain the normal working temperature and oil pressure of the engine, and carefully dismantle the engine speed limit device. (3) Do a good job in the daily maintenance of the vehicle, regularly check and tighten the exposed bolts and nuts in various parts, pay attention to the sound and temperature changes of each assembly during operation, and try to make adjustments by the machine. (4) After the running-in period expires, a running-in maintenance should be carried out, and the car should be comprehensively inspected, fastened, adjusted and lubricated in combination with the first-level maintenance, and the speed limiter should be removed; (5) Imported cars shall be carried out according to the running-in regulations of the manufacturer.

9. Explain the causes of pressure resistance.

A: Piezoresistance is the resultant force of normal forces acting on the whole vehicle surface. When the vehicle is driving forward, due to the limitation of its main shape, the phenomenon of vortex separation on the surface is inevitable, and the air separated by the vehicle can not be closed smoothly at the tail and restored to its original state, thus forming a vortex zone at the tail of the vehicle, generating negative pressure, resulting in pressure resistance in the driving direction.

10. Explain the main reasons for the decline in power performance and fuel economy when cars are used in high altitude areas.

A: Influence on dynamic performance: With the elevation, the air pressure gradually decreases and the vacuum degree of intake pipe decreases. Under the original idle throttle opening, the air intake is insufficient, which reduces the engine speed. When the air density decreases, the mixture becomes thicker, and in severe cases, it will be unstable or knock because of too much mixture. Influence on fuel economy: With the increase of altitude, the air-fuel ratio becomes smaller, the mixture becomes richer and the engine fuel consumption increases. Due to the decrease of atmospheric pressure and the increase of fuel evaporation, it is easy to cause problems such as air resistance and air leakage, which leads to the increase of fuel consumption.

How to choose automobile gear oil?

Answer: (1) Selection of quality grade: ordinary vehicle gear oil for medium-speed and heavy-load gears or spiral gears; GL-4 class is selected for gears with low speed, high speed and low torque and hypoid gears with less harsh service conditions. GL-5 is suitable for gears working under high-speed impact load, high-speed low-torque and low-speed high-torque, and hyperbolic gears with mild or harsh service conditions. (2) Brand selection: The viscosity of gear oil should be selected according to the external temperature. When the viscosity reaches 150000MPas, the highest temperature of the selected gear oil should not be higher than the ambient temperature. Hyperbolic gear oil must be selected for the drive axle of hyperbola gear.

12. Analysis on the function of overdrive in automobile transmission system.

A: The advantages of high-speed design and low-speed design can be used at the same time. When the vehicle is running at the maximum speed, the engine speed is low, and at the same time, due to the high engine load rate, the fuel consumption is reduced, and the reserve power is large.

13. Briefly describe the influence of engine speed on the concentration of pollutants emitted by the engine.

Answer: With the increase of engine speed, the contents of HC and CO in the exhaust gas decrease because the turbulence of the mixed gas in the combustion chamber is strengthened and the mixing and combustion are improved. As for the amount of nitrogen oxides produced, it increases when richer mixed gas is used, but decreases when thinner mixed gas is used.

14. What problems will happen when the car is used at low temperature?

A: The engine is difficult to start and the assembly is badly worn. In addition, there are some problems such as damage and corrosion of components, poor thermal state of the assembly, and increased consumption of fuel and lubricating oil.

15. Briefly describe the influence of engine load on the concentration of pollutants emitted by the engine.

A: The air-fuel mixture ratio required by different engine loads is different. An analysis of the influence of load on harmful gases in exhaust gas is actually the influence of air-fuel ratio. When the gasoline engine is fully loaded, the combustion is incomplete and the amount of carbon monoxide produced increases. At medium load, the mixture is slightly lean and the combustion efficiency is the highest. Carbon monoxide and hydrocarbons decrease, but nitrogen oxides increase. At idle speed and light load, NOX emission decreases, while CO and HC increase significantly. When the diesel engine works at full load, the emissions of CO and HC do not increase much, but the NOX produced increases obviously, and a lot of black smoke is produced.