The role of the chassis is to receive the power of the engine, make the wheels turn, and ensure the normal driving of the car according to the driver's control. Chassis includes four parts: transmission system, driving system, steering system and braking system. Usually, these four systems are also referred to as transmission system, driving system, steering system and braking system.
We should not be unfamiliar with the transmission system. Everyone knows clutch and transmission, they are the important parts in the transmission system, the driver and they have a lot of communication (next only to the steering wheel). When a train runs down, who can remember how many times he stepped on clutch and changed gears? From the transmission process of power, the transmission system is Connections between engine and wheel, including clutch, transmission, transmission shaft, drive axle, etc. According to the structure and transmission medium, automobile transmission system can be divided into four types: mechanical, hydraulic, hydrostatic and electric. For most automobiles, the most common purpose is mechanical and hydraulic mechanical. There are many ways to arrange the transmission system. FF mode is commonly used in cars (i.e. engine front-wheel drive and front-wheel drive); FR mode is commonly used in trucks, most buses and a few luxury cars (i.e. engine front-wheel drive and rear-wheel drive); RR mode is commonly used in luxury buses (i.e., engine rear-wheel drive and rear-wheel drive); nWD mode is commonly used in off-road vehicles (i.e. full-wheel drive). For exhortation, n means the number of wheels; for racing cars, MR is generally used (i.e., engine mid-position and rear-wheel drive). In addition, whether the engine is horizontally or vertically positioned will also affect the layout of the transmission system.
The primary task of the transmission system is to coordinate with the engine in order to ensure that the vehicle can run normally under the condition of no question. It also has good power and fuel economy. Therefore, no matter what type of transmission system, it should have at least four basic functions of divination:
1. deceleration and speed change
We know that only when the traction used on the driving wheels is enough to overcome the external resistance to the car, the car can start and drive normally. We may take the ordinary Santana car as an example. The Santana car has a self-weight of 1070 kg, engine displacement of 1.8 liters, maximum torque of 150 Nm/3100 rpm, maximum power of 72 kw/5200 rpm and wheel specifications of 195/60R14. Assuming that it travels at a uniform speed of 90 km/h on a horizontally dry cement road, the resistance it suffers can be calculated by simplified formulas: F = m g f 10 CdAua2/21.15 (m is the weight of the car, as we said earlier, 1070kg; G is gravitational acceleration, that is, 9.8m/s2; f is the rolling resistance coefficient of the tire, For cement pavement, f = 0.014x (10ua2/19440); Cd is the air resistance coefficient, about 0.32; A is the windward area of the car, 1.89m2 of Santana; UA is the speed of the car, which we have set at 90km/h, and the calculated result is 440N. Next, we calculate its driving force. The formula of driving force is Ft=Ttqigi0nT/r (Ttq is engine torque, the maximum torque in this case is 150Nm/3100rpm; Ig and I0 are transmission ratio of transmission and transmission ratio of main reducer; nT is mechanical efficiency of transmission system; R is tire radius, r=14x0.025110.195x60%=0.47m). If the engine's torque is directly applied to the driving wheel (that is, the engine's power is directly applied to the wheel without passing through the transmission system), then Ig and I. Both are 1, nT is 1. The maximum traction force of the driving wheel is about 319N. Obviously, the traction force is not strong enough. In this case, the car can not start or continue to drive. It will slow down gradually until it stops. At the same time, we can also see that if the engine is directly connected to the tire, when the engine runs at a speed of 5000rpm, according to UA = 0.377rn/igi. (The same parameter, n is the engine speed), the speed will reach an astonishing 886 km/h, which is neither practical nor achievable (because at this time the resistance is very large, the traction force is small, the car can not go forward at all). In order to solve the above contradiction, we need the transmission system to have deceleration and increase.
The role of torsion (referred to as deceleration), and the main reducer is playing such a role.
Moreover, the use conditions of automobiles (such as actual loading quality, road gradient, road condition, width and curvature of roads, allowable speed of traffic conditions, etc.) are constantly changing due to many factors, which requires that the traction and speed of automobiles have a considerable range of changes. On the other hand, because the torque of the engine varies little in the whole speed range and the power and fuel consumption curve varies considerably, this makes the speed range of the engine maintaining high power and low fuel consumption (which we can call the advantageous speed range) very narrow, in order to keep the engine working in the advantageous speed range. The transmission ratio of the transmission system needs to be changed within a certain range. Therefore, from this point of view, the transmission system must also be subject to speed, so the transmission came into being.
2. Car reversal
If the car doesn't even have this function, it's hard to imagine how people can get in and out of the parking lot, garage, etc. Of course, it's impossible to reverse on those narrow roads. Maybe you'll say to turn the engine upside down, not to mention that there is no such engine at present, it will be in the future for quite a long time. It's impossible for us to see such an engine, so the transmission system can reverse the car while keeping the engine's rotation direction unchanged. This function is achieved through the example gear of the transmission.
3. Interrupt transmission if necessary
Anyone with driving experience knows that. The engine must be started after stepping on the clutch (stepping on the clutch will not make the engine withstand the resistance of the ground, that is to say, no-load engine, which is two different things from no-load car), after starting the engine must also be kept above the minimum stable speed to ensure that it does not stall. In addition to starting the car, interruption of the engine power output to the driving wheel is also common, such as shifting, decelerating parking, encountering red lights and so on, all of which require that the transmission system can cut off the power output when necessary, while the clutch and transmission.
The vacancy undertakes this task.
4. Differential effect
Car turning is the most common thing, but have you noticed how the wheels move when the car turns? Maybe you have never noticed these trivial things, then you go to the street and take a look at the corner carefully, you will find that: when turning, the wheels of the car have different rotational speeds on the left and right sides, but on the inside of the corner. The wheels rotate slower than those on the outside. This phenomenon is not difficult to understand, because the distance between the left and right wheels when turning is different. Please do not underestimate such a simple phenomenon. For non-driving wheels, this is not a problem at all, but for driving wheels, it is different. If the left and right driving wheels rotate at the same speed when steering, it will inevitably cause the wheel to slide relative to the ground, which will not only cause steering difficulties, but also increase the car. Power consumption accelerates wear and tear of tyres and transmission parts. To avoid these problems, we use differential.
The function of the driving system is to accept the torque transmitted by the engine through the transmission system, and produce traction force on the road to the vehicle through the adhesion between the driving wheel and the road surface, so as to ensure the normal driving of the vehicle; to transmit and bear the reaction force and the moment formed by the road surface acting on the wheel; moreover, it should be as slow as possible. The impact and vibration of vehicle body caused by uneven road surface ensures smooth driving, and works well with vehicle steering system to realize the control of vehicle driving direction, so as to ensure vehicle handling and stability.
The driving system includes frame, axle, wheel, suspension, etc. Some vehicles also include axle housing (such as trucks, buses, off-road vehicles, etc.). The frame can be said to be the skeleton of a car. Its function is to support and connect the various assemblies and components of the car, and bear various loads from inside and outside the car. The axle, also known as axle, is connected with the frame (or body) by suspension. Wheels are installed at both ends. Its function is to transfer the force in all directions between the frame (or body) and the wheel, and bear the weight of the frame and body. The axle housing and the axle - like can bear the weight of the frame and the body, and the road reaction force and moment transmitted by the wheels, except that. It can also protect the main reducer, differential, drive shaft and other components. Wheels and tires are important components in the driving system, they have many functions: supporting the weight of the vehicle; alleviating the impulse from the road; generating driving force and braking force through the adhesion between tires and the road, etc. Suspension is the general name of the force transfer connecting device between the frame (or body) and the axle (or umbrella wheel). Its function is to transfer the supporting force, traction force, braking force and lateral force of the road surface acting on the wheel and the moment caused by these forces to the frame (or body) to ensure the normal running of the vehicle.
The steering wheel should be the most familiar part of every driver (it's no exaggeration to use the word "close" to describe the relationship between the driver and the steering wheel), and it's part of the steering system that we're going to talk about next.
Vehicles need to change their driving direction (i.e. steering) frequently in the course of driving. In addition, wheels will deviate from the driving direction when they are running in a straight line because of the lateral interference of the road surface. In this way, we need to constantly correct the direction of deviation through the steering wheel to maintain the correct direction of driving. Therefore, the role of steering system is to ensure that the car can drive in the direction chosen by the driver.
According to the difference of steering energy, steering system can be divided into mechanical steering system and power steering system. The mechanical steering system uses the driver's physical strength as the steering energy, and all the force transmission components are mechanical. The mechanical steering system consists of steering control mechanism (steering wheel), steering gear and steering transmission mechanism. Because it uses human's physical strength as the turning energy, it makes the driver feel tired easily. In order to solve this problem, power steering system emerged, which takes the driver's physical strength and engine power as the steering energy. Under normal circumstances, only a small part of the energy required for steering is provided by the driver, while the human part is provided by the engine through the steering booster. But when the steering booster fails, the driver must also ensure that the task of steering can be completed independently by himself. Therefore, the power steering system is based on the mechanical steering system with a set of steering booster. In order to alleviate the driver's burden, modern cars generally have power steering system.
It is one of the main technical measures to improve transportation productivity to increase vehicle speed as much as possible, but this must be based on the premise of ensuring vehicle driving safety. Therefore, in the case of wide and flat, traffic flow is small, the car can be driven at high speed, and in more cases, such as about to turn, through rough roads, two-car rendezvous, encounter obstacles and so on, we need to reduce the speed, or even parking. If it does not have braking performance, the car can not decelerate or stop at the driver's intention, let alone drive safely. At this point, the brake system is not difficult to understand. Its function is to slow down or stop the car and ensure that the car can stop reliably after the driver leaves.
The brake system of each vehicle should have at least two sets of systems, namely, the driving brake system and the parking brake system. The function of the parking brake system (which can be understood as the foot brake) is to reduce the speed and stop the car while it is running. The function of the parking brake system (which can be understood as the hand brake) is to keep the parked car in place. In addition to these two basic braking systems, many countries also stipulate that automobiles must have a second braking system. Its function is to ensure normal deceleration and parking after the braking system fails.
Brake system consists of four parts: energy supply device, control device, transmission device and brake.