2. Automobile design process: 1. New product development process of automobile II. Conceptual design 3. Target cost 4. Trial production design. Trial production and test of prototype car. Production preparation stage 7. Sales.
3. The classification of cars can be classified according to the engine displacement, the number of passengers, the total mass of cars, the total length of cars and the characteristics of the car body or cab. In China, cars are divided into passenger cars and commercial vehicles.
Different types of cars are mainly reflected in the differences in the number of axles, driving forms and arrangement forms.
4.( 1) Passenger car layout mainly includes engine front wheel drive (FF).
Advantages: the axle load of the front axle is large, and the steering performance is obviously insufficient; The front wheel is the driving wheel, which has strong obstacle-crossing ability; The power assembly is compact in structure; There is no need for a transmission shaft between the transmission and the main reducer, which reduces the height of the convex hull of the floor in the car and is conducive to improving the ride comfort; When the engine is arranged outside the wheelbase, it is beneficial to improve the maneuverability of the car; Good heat dissipation conditions; There is enough trunk space at the rear of the car; The heating mechanism is simple, the heating efficiency is high, and the operating mechanism is simple; The curb weight is very light. When the engine is placed horizontally, the bevel gear of the original main reducer can be replaced by cylindrical gear, which reduces the manufacturing difficulty and does not need to adjust the gear during assembly and use. At this time, the transmission and the final drive can use the same lubricating oil.
Disadvantages: the structure and manufacturing process are complicated, the load of the front axle is heavier than that of the rear axle, and the front wheel is also the steering wheel. The front wheel is in bad working condition, the tire life is short and the climbing ability is reduced. Especially when climbing muddy slopes, the driving wheels are easy to slip, which makes the car lose its handling stability. Because the rear axle load is small, the axle load moves when braking, and the rear wheel is easy to lock, which leads to the side slip of the car. When the engine is placed horizontally, it is difficult to make overall arrangement and the accessibility is poor.
(2) Engine Front Wheel Drive (FR)
Advantages: reasonable distribution of axle load is beneficial to prolonging the service life of tires, without using constant velocity universal joints, reducing the manufacturing cost, simple operating mechanism, simple heating mechanism, high heating efficiency, good engine cooling condition, strong climbing ability, easy to be converted into passenger and cargo vehicles or ambulances, sufficient trunk space, good engine accessibility, separation of main reducer from transmission, and easy disassembly and maintenance.
Disadvantages: There are protruding passages on the floor, which affect the ride comfort. When a car collides with other objects, it is easy to cause the engine to enter the passenger compartment, causing serious damage to the front passengers. The overall wheelbase of the vehicle is long, which increases the kerb quality of the vehicle and affects the fuel economy and power performance of the vehicle.
(3) There are three types of engine rear wheel drive (RR).
Advantages: the rear position of the engine improves the driver's vision, because the transmission shaft is omitted, which improves the conditions for passengers in and out of the middle seat in the back row. The curb weight of the whole vehicle is small, the passenger seats can be arranged in the comfort zone, and the climbing ability is high. When the engine is arranged outside the wheelbase, the wheelbase is short and the vehicle maneuverability is good.
Disadvantages: the heavy load on the rear axle makes the steering tendency of the car too large, the handling becomes worse, the adhesion of the front wheel is small, and the stability is affected. The trunk is not big enough and the control mechanism is complicated. The driver is not as easy to find engine faults as the front engine, which is not conducive to engine cooling and front windshield defrosting. The working noise of the engine is easily transmitted to passengers. Once the car rear-ends, it will cause danger to the rear passengers, and it is difficult to convert it into a van or ambulance.
5. Layout of trucks: According to the relative position between the cab and the engine, trucks can be divided into flat head type, short head type, long head type and offset type.
(1) flat head type
Advantages: good maneuverability, low vehicle curb weight, good driver's vision, improved access to the engine and its accessories by using the inclined cab, and high area utilization.
Disadvantages: the passability of the car is poor, and the cab has a turnover mechanism and a locking mechanism, which is complicated. Getting in and out of the cab is not as convenient as the long-headed car, and the control mechanism is complicated. The working noise, smell, heat and vibration of the engine have great influence on the driver. When a car collides with other objects, it is easy to cause serious injuries to the driver and front passengers, which is not as good as long-headed and short-headed trucks.
(2) short head type
Advantages and disadvantages: Compared with the long-headed truck, this truck has shorter overall length and wheelbase, smaller minimum turning radius and better maneuverability than the long-headed truck, but it is not as good as the flat-headed truck, and the driver's vision is not as good as that of the flat-headed truck, but it is improved. The control mechanism of powertrain is simple, and the influence of engine noise, smell, heat and vibration on drivers is greatly improved compared with that of flat-headed trucks, but it is not as good as that of long-headed trucks, and the cab space is crowded.
(3) Long head type
Advantages: the engine and its accessories are close to each other, and the maintenance is convenient. When driving on bad roads, the vehicle has strong passing capacity, low floor, convenient driver getting on and off, simple control mechanism and easy arrangement. The working noise, smell, heat and vibration of the engine have little influence on the driver. When the vehicle collides with other objects, the driver and front passengers are much better injured than flat-headed trucks.
Disadvantages: poor handling, high servicing quality, not as good as short-headed trucks, not as good as flat-headed trucks, and low area utilization rate.
(4) Offset: It has some advantages of flat-headed trucks, short wheelbase and good vision. In addition, the cab has good ventilation conditions and is convenient for engine maintenance.
6. The main parameters of automobile include: size parameters, quality parameters and automobile performance parameters.
6. Main dimension parameters of automobile
(1) overall dimensions
Smaller vehicle length can not only reduce the road length occupied during driving, but also increase the traffic density. When parking, the occupied parking area is also small, and the vehicle kerb quality is correspondingly reduced, which is conducive to improving specific power, specific torque and fuel economy.
(2) wheelbase
The wheelbase has an influence on the vehicle mass, the total length of the vehicle, the minimum turning diameter of the vehicle, the length of the transmission shaft and the longitudinal passing radius. It also affects the distribution of shaft load and the included angle of transmission shaft.
(3) Front and rear wheel tracks
Changing the wheel track will affect the width of the car or cab, and the total width, total mass, roll stiffness and minimum turning diameter of the car will change.
(4) Front suspension and rear suspension
The size of the front suspension has an impact on the vehicle's passability, collision safety, the driver's vision, the length of the front leaf spring, the convenience of getting on and off, and the vehicle shape.
The size of the rear suspension has an influence on the passability of the car, the safety of the car when it is rear-ended, the length of the container or trunk, and the shape of the car. , and depends on the axle load distribution and wheelbase requirements.
(5) Head length
(6) Truck size
7. Vehicle kerb quality: refers to the vehicle quality of all equipment (including vehicle tools, spare tires, etc.). ) and filled with fuel and water, but not loaded and manned.
8. Quality coefficient refers to the ratio of vehicle loading quality to vehicle kerb quality.
9. Vehicle performance parameters: (1) Power parameters (including maximum speed, acceleration time t, uphill capacity, specific power and specific torque) (2) Fuel economy parameters (3) Minimum turning diameter of the vehicle (4) Passing geometric parameters (minimum ground clearance, approach angle, departure angle, longitudinal passing radius) (5) Handling stability parameters (5).
10. What requirements should city buses meet when designing dynamic parameters?
Answer: When city buses are designed for different purposes, the standards of dynamic parameters are different. Short-distance buses used to run between bus stops in the city have a top speed of about 40km/h, so the acceleration performance is good, and the acceleration time is short because of frequent stops. When used for intercity passenger transport, the maximum design speed is about 80km/h, and the acceleration performance is better than that of long-distance buses and lower than that of short-distance buses. Long-distance bus, the maximum design speed can reach more than 80km/h, and the acceleration performance is average; In addition, for city buses, the climbing ability varies according to the road environment used, and the climbing ability of mountain buses is better; In addition, due to the large passenger capacity, the specific power and torque of city buses are larger to meet sufficient power.
1 1. Comparison of advantages and disadvantages between gasoline engine and diesel engine
The pollutants emitted by gasoline engines are mainly carbon monoxide, hydrocarbons and nitrogen oxides. Diesel engines emit lower pollutants and higher nitrogen oxides than gasoline engines. In the exhaust gas of diesel engine, PM is much higher than that of gasoline engine. The overall evaluation is that the emission index of gasoline engine is not as good as that of diesel engine. Due to the high combustion pressure and rising power of diesel engine, the noise of diesel engine is much greater than that of gasoline engine, the vibration of gasoline engine is smaller, the working vibration of diesel engine is greater, and the mass power of diesel engine is greater than that of gasoline engine. Under the same conditions, diesel engines are usually larger than gasoline engines; The reliability of diesel engine is better than that of gasoline engine. In general, the durability of diesel engines is better than that of gasoline engines; Generally speaking, the fuel consumption rate of diesel engine is lower than that of gasoline engine; Large-bore gasoline engine is easy to deflagrate, but it has the advantage of good cold start.
12. Why are gasoline engines used for minivans, passenger cars and diesel engines used for buses and trucks?
Answer: Because of the high combustion pressure and power of diesel engine, the noise of diesel engine is much louder than that of gasoline engine. In addition, the reciprocating motion of crank-connecting rod mechanism, the imbalance of rotating parts and the impact of combustion pressure in cylinder cause engine vibration, which affects the comfort of passengers. Generally speaking, the vibration of gasoline engine is small, and the working vibration of diesel engine is large because of its high combustion pressure and power. Generally speaking, diesel engines are smaller in size than gasoline engines. Considering the demand of minivan and passenger car for passenger comfort, convenient vehicle modeling, improving driver's vision and reducing wind resistance, gasoline engine is needed. Large passenger cars and trucks require high dynamic performance, and the engines often work in a heavy load state. Because the durability and reliability of diesel engine are better than that of gasoline engine, diesel engine is adopted.
13. How to determine the engine power?
Answer: 1 Estimate the maximum power of the engine according to the maximum speed that the designed car should reach. Referring to the statistical value of specific power of the same class car, and then multiplying the specific power value of the newly designed car by the total mass of the car, the required maximum power value can also be calculated.
14. How to choose an engine?
Answer: The selection of the engine is based on the following two main performance indicators, namely 1 the maximum power Pemax of the engine and the corresponding speed np. The corresponding speed of maximum power is as follows: the np of gasoline engine is 3000-7000 r/min, the np of passenger car is above 4000 r/min, and the np of freight car with small total mass is between 4000-5000 r/min, and the total mass is in the middle. The np value of diesel engine is between 1800-4000 r/min. The np value of high-speed diesel engines of passenger cars and trucks with small total mass is often between 3,200 and 4,000 r/min, while that of trucks with large total mass is between1800 and 2,600 r/min. However, although the use of high-speed engine can improve the power, there are also some defects, such as increasing the average speed of piston movement, increasing the thermal load and inertia force of crank-connecting rod mechanism, resulting in increased wear, reduced life, and increased vibration and noise.
15. With the increase of tire pressure, its bearing capacity is stronger, but the adhesion of tire decreases, the vibration frequency increases, and the ride comfort and safety become worse, which also has adverse effects on road surface and automobile.
16. Tire load coefficient: the ratio of the maximum static load borne by an automobile tire to the rated load of the tire. (0.85- 1.00) Overloading will not only reduce tire life, but also reduce handling stability and driving safety. Generally, the load factor of the front wheel is lower than that of the rear wheel.
17.5 baseline
(1) Plane line on the frame: the projection line of the plane of the long wing surface on a side (front) view of the upper edge surface of the middle floor or side beam of the longitudinal beam or the load-bearing car body.
(2) Front wheel centerline: the projected line on the plane side view and top view that passes through the center of the left and right front wheels and is perpendicular to the plane line of the frame.
(3) Automobile centerline: the projection line of the vertical symmetry plane of the automobile on the top view and the front view.
(4) Ground wire: the projection line of the ground plane on the side view and the front view.
(5) Front wheel vertical line: the projection line of the plane passing through the center of the left and right front wheels and perpendicular to the ground on the top view and side view.
18. Percentile of human body: arrange the measured size values from small to large on the number axis, then divide this size segment into 100, and take the value of the nth point as the percentile.
H point: the reference point for accurately determining the position of the driver or passenger on the seat is the "hip point" connecting the rotation points of the trunk and thighs, and the position of the "hip point" measured by the real vehicle is called H point.
R point: according to the general layout requirements, determine the "hip point" when the seat is adjusted to the last lowest position.
19. The suspension is composed of elastic elements, guiding devices, shock absorbers, buffer blocks, lateral stabilizers, etc.
20. Non-independent suspension: Definition: the left and right wheels are connected by an integral axle, and then connected to the frame (or body) through suspension.
Advantages: simple structure, easy manufacture, convenient maintenance and reliable work.
Disadvantages: poor ride comfort and heavy unsprung weight. When driving on uneven roads, the left and right wheels interact with each other, so that the axle and the car body are inclined; The front wheel is prone to shimmy; When the front wheel jumps, the suspension is easy to interfere with the steering transmission mechanism; When the car runs in a straight line on uneven road, not only the camber angle of the wheels changes, but also the adverse axle steering characteristics will appear because the left and right wheels jump in the opposite direction or only one wheel jumps. When the car turns, centrifugal force will also produce unfavorable axle steering characteristics.
Independent suspension: definition: the left and right wheels are connected to the frame (or body) through their respective suspensions.
Advantages: the unsprung weight is small, the suspension occupies small space, the vehicle ride comfort is good, the vehicle running stability is good, the independent movement of the left and right wheels does not affect each other, the inclination and vibration of the vehicle body can be reduced, and at the same time, good ground adhesion ability can be obtained on the undulating road surface.
Disadvantages: complex structure, high cost and difficult maintenance.
2 1. Four parameters used in the evaluation
(1) Height of roll center (2) Change of wheel alignment parameters (3) Stiffness of suspension roll angle (4) Lateral stiffness.
22. See Figure 6-3 for yourself (1page 78)
23. Static deflection of suspension: the ratio of the load on the suspension to the stiffness of the suspension at this time when the car is fully loaded and static.
24. Dynamic deflection of suspension: when the suspension is compressed to the maximum deformation allowed by the structure in the fully loaded static equilibrium position, the vertical displacement of the wheel center relative to the frame or body.
25. 182 Two methods for measuring the deflection of suspension at point 4
26. The roll stiffness of the suspension refers to the elastic restoring moment of the suspension to the car body when the sprung mass produces unit roll (the roll stiffness of the front suspension is slightly greater than that of the rear suspension).
27. The energy storage per unit mass of torsion bar spring is much larger than that of leaf spring, so the mass of torsion bar spring suspension is small, and torsion bar spring has the advantages of reliable work and easy maintenance.
28. The air suspension is composed of compressor, oil-water separator, pressure regulating valve, air storage tank, height control valve, control connecting rod, air spring, air storage tank, air filter, pipeline, guide dowel bar, shock absorber and lateral stabilizer.
The air spring type is to fill air into the rubber airbag of the ply structure, and realize the elastic effect with air as the medium by using the compressible characteristics of air.
29. The working principle of air suspension
When the number of cars increases, the distance between the frame and the axle (axle) shortens. Then, under the action of the linkage mechanism, the inflation valve opens, and compressed air flows into the air spring to increase its pressure. At the same time, raise the frame (body) until the inflation valve is closed. At this point, the frame (body) returns to the height before and after the increase. When the car is empty, the distance between the frame and the axle (shaft) increases. At this time, by controlling the connecting rod to open the air valve, the gas in the airbag is discharged into the atmosphere, and the pressure is reduced until the height of the frame (car body) is restored to the position before unloading.
30. Figure 6-27, Characteristics of Air Spring (page 194)
3 1. Steering system: the mechanism used to keep or change the direction of the car, and ensure the coordination of the angle relationship between the steering wheels when the car turns.
32. Rack and pinion steering gear
Advantages: simple and compact structure, light weight of the steering gear, high transmission efficiency of 90%, automatic elimination of backlash between teeth, improvement of the rigidity of the steering system, prevention of impact and noise generated during work, small occupation volume, increase of steering wheel angle and low manufacturing cost.
Disadvantages: Due to the high reversing efficiency, the car will recoil when driving on uneven roads. The recoil phenomenon will make the driver nervous and it is difficult to accurately control the driving direction of the car. The sudden turning of the steering wheel will cause mobs and hurt the driver.
Layout: the steering gear is located behind the front axle, and the rear trapezoid; The steering gear is located behind the front axle and in the front trapezoid; The steering gear is located in front of the front axle and is in the shape of a rear trapezoid; The steering gear is located in front of the front axle with a front trapezoid.
33. Circulating ball steering gear
Advantages: the sliding friction is changed into rolling friction, and the transmission efficiency can reach 75%-85%; After taking measures in structure and technology, it has enough hardness and wear resistance to ensure sufficient service life; The transmission ratio of the steering gear can be changed; The working seat is stable and reliable; The gap adjustment between the rack and the sector teeth is easy; It is suitable to be used as an integral power steering gear.
Disadvantages: high inverse efficiency, complex structure, difficult manufacturing and high manufacturing accuracy.
34. What are the types of injury prevention institutions?
Answer: 1 The steering shaft is equipped with a universal joint 2, which adopts a two-stage steering shaft 3, a coupling sleeve mechanism for absorbing impact energy 4, an elastic coupling anti-injury mechanism 5, and an energy-absorbing steering main pipe.
35. Positive efficiency: The efficiency that power is input from the steering shaft and output through the steering rocker shaft is called positive efficiency. On the contrary, it is called inverse efficiency. Positive efficiency indicates how easy it is for the driver to turn the steering wheel. Inverse efficiency represents: the ability of steering wheel and steering wheel to automatically return to a straight line after steering.
36. The working principle of variable transmission ratio (page 230)
Answer: Take the rack-and-pinion steering gear as an example: the pitch of base circle of intermeshing gears must be equal to Pb1= π m1cos α1= Pb2 = π m2 cos α 2, that is, the pitch of gear base circle is equal to the pitch of rack base circle. When a gear with standard modulus m 1 and standard pressure angle α 1 and a gear with variable modulus keep π m1cos α1= π m2cos α 2 all the time, they can mesh and run. If the pressure angle of the teeth in the middle of the rack (equivalent to the straight driving position of the car) is the largest, it will gradually decrease to both ends (the modulus will also decrease), so that the meshing radius of the driving wheel will also decrease, so that the rack stroke will also decrease every time the steering wheel rotates for a certain angle. Therefore, the transmission ratio of the steering gear changes.
37. Evaluation criteria of power steering gear: (1) Working efficiency of power steering gear (2) Road feel of hydraulic power steering gear (3) Steering sensitivity (4) Static characteristics of power steering gear.
38. The main characteristics of electric power steering
(1) steering portability and road feel: road feel is enhanced, while steering portability is deteriorated. (2) Linear main force characteristics: divided into three sections: no-assist section, variable-assist section and constant-assist section. (3) Speed-sensitive main force characteristic: When the speed is 0, the position of the assist characteristic curve is above other curves, and the assist intensity reaches the maximum. With the continuous improvement of vehicle speed, the position of the power-assisted characteristic curve gradually decreases until the vehicle reaches the highest speed, at which time the power-assisted intensity is the minimum and the road feel intensity is the maximum.
39. Braking system: it can make the car slow down at an appropriate deceleration until it stops; When driving downhill, keep the car at an appropriate and stable speed; A mechanism that enables a car to park reliably in place or on a ramp.
40. Drum brakes are divided into: lead slave type, single and double lead slave type, two-way double lead slave type, double slave type, one-way booster type and two-way booster type.
Disc type: clamping disc type, full disc type.
4 1. Compared with the drum brake, the disc brake has the following advantages: (1) good thermal stability, (2) good water stability, (3) the braking torque has nothing to do with the moving direction of the car, (4) it is easy to form a double-loop braking system, which makes the system more reliable and safe, (5) it is small in size, light in weight and good in heat dissipation. (9) It is easy to realize the automatic adjustment of the gap.