Automotive Electronics Knowledge: Electronic Composition and Function of Automotive Chassis

The function of the chassis is to accept the power of the engine, turn the wheels, and ensure that the car runs normally according to the driver's control. The chassis includes the transmission system, the driving system, the steering system and the braking system. Generally, these four systems are also referred to as the powertrain, the driving system, the steering system and the braking system.

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Drive Train:

We should not be unfamiliar with the drive train. Everyone knows the clutches and transmissions. They are important parts in the powertrain. The driver and their dealings are quite a lot (after the steering wheel). When a car runs down, who can remember to step on it? How many shifts and how many shifts have been changed? From the perspective of power transmission, the drive train is the link between the engine and the wheels, including the clutch, transmission, drive shaft, drive axle, and so on. According to the structure and transmission medium, the automobile transmission system can be divided into four types: mechanical type, hydraulic mechanical type, hydrostatic type and electric type. For most cars, the most common purpose is mechanical and hydraulic mechanical type. These two.

There are many ways to arrange the drive train. The car is usually used in FF mode (ie engine front and front wheel drive); FR mode (ie engine front and rear wheel drive) is commonly used in trucks, most passenger cars and a small number of luxury cars; Passenger cars generally adopt RR mode (ie, rear machine and rear wheel drive); off-road vehicles use nWD (usually all-wheel drive, n indicates the number of wheels); and the car is generally MR-based (ie, the engine is centered, Rear wheel drive). In addition, whether the engine is placed horizontally or vertically will also affect the layout of the drive train. The primary task of the drive train is to work in coordination with the engine to ensure that the car can travel normally regardless of the conditions of use. And has good power and fuel economy. At this point, no matter what type of drive train, at least four basic functions should be available:

1. Deceleration and shifting

We know that the car can start and run normally only when the traction on the drive wheels is sufficient to overcome the resistance of the outside world to the car.

For example, we can take the ordinary Santana sedan as an example. The Santana sedan has a weight of 1070kg, an engine displacement of 1.8 liters, a maximum torque of 150N·m/3100 rpm, a maximum power of 72kw/5200rpm, and a wheel size of 195/60R14. Assume that it runs at a constant speed of 90km/h on a horizontally dry cement road. At this time, the resistance it receives can be calculated by a simplified formula: F=mgf ten CdAua2/21.15 (m is the weight of the car, we said earlier It is 1070kg; g is the acceleration of gravity, which is 9.8m/s2; f is the rolling resistance coefficient of the tire. For cement pavement, f=0.014x (1 ua2/19440); Cd is the air resistance coefficient, about 0.32; A is the windward area of ​​the car, Santana is 1.89m2; ua is the speed, we have set it to 90km/h), and the calculated result is 440N.

Next, let's calculate its driving force. The driving force is calculated as Ft=Ttqigi0nT/r (Ttq is the engine torque, the maximum torque in this example is 150N·m/3100rpm; ig and i0 are the transmission ratio and the main respectively. Reducer transmission ratio; nT is the mechanical efficiency of the drive train; r is the tire radius, r = 14x0.0251 ten 0.195x60% = 0.47m), if the torque of the engine is directly applied to the drive wheel (that is, the power of the engine is not Directly acting on the wheel through the drive train, at this time, both ig and i are 1, and nT is 1). Then the maximum traction that the drive wheel can get is about 319N. Obviously, the traction has not yet had a large driving resistance. In this case, the car cannot start or continue to drive, and it will gradually slow down until it stops.

At the same time, we can also look at if the engine is directly connected to the tire, when the engine is running at 5000 rpm, according to ua = 0.377 r · n / igi. (Parameters are the same as above, n is the engine speed), the speed will reach a staggering 886km / h, such speed is neither practical nor impossible to achieve (because the resistance is very large at this time, the traction is small, the car simply can not advance ). In order to solve the above contradictions, we require that the drive train must have the function of deceleration and twisting (referred to as deceleration), and the final drive plays such a role.

Also, the conditions of use of the car (such as actual loading quality, road grade, road surface condition, and the width and curvature of the road, the speed allowed by traffic conditions, etc.) are constantly changing due to many factors, which requires the traction of the car. And speed must have a considerable range of changes.

On the other hand, since the torque of the engine does not change much over the entire speed range, the power and fuel consumption curves change considerably, which makes the engine maintain a high power and low fuel consumption range (we can call it a favorable speed range). Narrow, in order to keep the engine operating in a favorable speed range, the transmission ratio of the drive train needs to be varied within a certain range. Therefore, from this perspective, the drive train must also have a speed effect, and the transmission will come into being.

2. Realize the car to drive backwards

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 is impossible to reverse the car on those narrow roads. Maybe you will say that the engine is going to turn around, not to mention that there is no such engine at present, that is, for a long time in the future. It is impossible for us to see such an engine. Therefore, the drive train can reverse the vehicle while maintaining the direction of rotation of the engine. This function is realized by the example of the transmission.

3. Interrupt the drive if necessary

Anyone who has experience in driving knows. The engine must be started after the clutch is depressed (the clutch is pressed so that the engine does not bear the resistance of the ground, that is, the engine is unloaded, which is not the same as the empty load of the car), and the engine must be kept at a minimum after starting. Above the stable speed, it can guarantee that it will not be extinguished. In addition to the start of the car, it is also common to interrupt the engine's power output to the drive wheels, such as shifting, deceleration, red light, etc., all of which require the drive train to cut off the power output when necessary. The neutral of the clutch and transmission takes on this task.

4. Differential action

Car turning is the most common thing, but have you noticed how the wheels move when the car turns? Maybe you have never noticed the little things about these sesame seeds, then you can look for a corner in the street. At first glance, it will be found that when turning, the left and right wheels of the car rotate at different speeds, and the wheels on the inside of the bend turn slower than the wheels on the outside.

This phenomenon is not difficult to understand because the distances that the left and right wheels pass when turning are different. Please don't underestimate such a simple phenomenon. For non-drive wheels, this is not a problem at all. It can be different for the drive wheels. If the left and right drive wheels rotate at the same speed, the wheels will be opposite. The phenomenon of sliding on the ground not only causes steering difficulties, but also increases the power consumption of the car and accelerates the wear of the tires and the drive train components. To avoid these problems, we use the differential.

Driving system:

The function of the driving system is to accept the torque transmitted by the engine through the transmission system, and to generate the road and the traction force of the vehicle through the adhesion of the driving wheel and the road surface, so as to ensure the normal running of the vehicle; and transmit and bear the various effects of the road surface on the wheel. The reaction force and the torque it forms; in addition, it should mitigate the impact and vibration of the uneven road surface on the vehicle body as much as possible, ensure the smooth running of the car, and work well with the steering system of the car to achieve the direction of the car. Control to ensure the stability of the car's handling. The driving system includes a frame, an axle, a wheel, a suspension, etc., and some vehicles also include a axle housing (such as a truck, a passenger car, an off-road vehicle, etc.). The frame can be said to be the skeleton of the car. Its function is to support and connect the various assemblies and components of the car, and to withstand various loads from inside and outside the car.

The axle is also called the axle. It is connected to the frame (or the body) through the suspension. The wheels are installed at both ends. Its function is to transmit the force in all directions between the frame (or the body) and the wheel, and to withstand the frame and The weight of the body. The axle housing and the axle can withstand the weight of the frame and the body, and withstand the reaction and torque of the road from the wheel. It also protects 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 whole vehicle; easing the rushing force transmitted from the road surface; generating the driving force and braking force through the adhesion between the tire and the road surface, etc. . Suspension is a general term for the force transmission connection between the frame (or body) and the axle (or the umbrella). Its function is to support the traction, traction, braking and lateral forces on the wheel. The torque caused by these forces is transmitted to the frame (or the body) to ensure the normal running of the car.

Steering system:

The steering wheel should be the most familiar part of every driver (the word "close" is used to describe the driver's relationship with the steering wheel), and it is part of the steering system we will mention below. When the car is driving, it is necessary to change the direction of travel (ie, steering) frequently. In addition, when the car is traveling straight, the wheel will be deviated from the direction of travel because the wheel is subjected to lateral jamming force. In this way, we need to constantly correct the direction of the deviation through the steering wheel to maintain the correct direction of travel. Therefore, the role of the steering system is to ensure that the car can travel in the direction chosen by the driver.

According to different steering energy sources, the steering system can be divided into two categories: mechanical steering system and power steering system. The mechanical steering uses the driver's physical strength as the steering energy. All the force transmission components are mechanical. The mechanical steering system consists of three parts: the steering mechanism (steering wheel), the steering gear and the steering gear. Because it is entirely based on human physical strength as a turning energy source, it is easy for the driver to feel tired.

In order to solve this problem, the power steering system has emerged, which uses 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 the car is provided by the driver, while the human part is provided by the engine through the steering assist device, but when the steering assist device fails, it must also be guaranteed by the driver himself. Complete the task of car steering. Therefore, the power steering system adds a set of steering assist devices to the mechanical steering system. In order to fully reduce the burden on the driver, modern cars generally have a power steering system.

Improving the speed of the car as much as possible is one of the main technical measures to improve the transportation productivity, but it must be based on the premise of ensuring the safety of the car. Therefore, in the case of wide flat, small traffic and low traffic, cars can travel at high speeds, and more often, such as turning, uneven roads, two car intersections, obstacles, etc., we all need Reduce the speed and even stop. If the performance of the brake is not available, the car cannot be decelerated or stopped at the driver's intention, and the car is safer to drive. Having said that, the brake system is not difficult to understand. Its function is to slow down or stop the car, and to ensure that the car can reliably stop after the driver leaves.

The brake system of each car should have at least two systems, namely the service brake system and the parking brake system. The function of the service brake system (which can be understood as the foot brake we usually call) is to reduce the speed and stop during the running of the steam. The parking brake system (which can be understood as the hand brake we usually call) is Keep the parked car parked in place. In addition to these two basic braking systems, many countries have stipulated that the car must have a second brake system, which is to ensure normal deceleration and parking after the service brake system fails.

The brake system consists of four parts: the energy supply device, the control device, the transmission device and the brake.