In the course of driving, the car will inevitably encounter various driving conditions. For example, when driving on urban roads, it will often encounter intersections. At this time, the driver must take the brake or even follow the instructions of the traffic lights. Stopping, and also in the case of sudden deceleration of the car in front or a car entering the front line, etc., you need to apply the brakes. Of course, when driving on a high-speed section, when you encounter a steep downhill, you must also take appropriate braking operations. Therefore, it is very necessary for the car to have a safe, stable and maneuverable braking system.
The brake system of a car is also called a brake system, and its working condition will directly affect the driving safety of the car. A large number of rear-end car accidents and car collisions are often related to the decline of the braking system's efficiency. Even serious accidents such as the rollover of some cars are caused by the poor stability of the braking system.
In order to improve the stability of the car during braking, the anti-lock brake system slowly entered the car. This system improves the percentage of the car sliding and rolling by controlling the longitudinal sliding state of the wheel during braking. The stability during braking has been widely used in various vehicles.
With the rapid development of the automobile industry and the increase of highways each year, the driving safety of automobiles has received increasing attention. In order to make the car more and more stable during braking, the braking force distribution is becoming more and more reasonable. The anti-lock braking system has been used more and more on various vehicles. Become more and more mature. The anti-lock brake system belongs to the active safety equipment of the car. When the car is in normal driving and encounters emergency braking during an emergency, this system intervenes in the braking process and changes the braking force according to the change of wheel speed. Intervene in the braking state to improve braking stability and prevent traffic accidents.
I. Research Status of Automobile Brake Anti-lock Braking System
The automobile anti-lock brake system is abbreviated as ABS (Sntilock Braking System). Foreign automobile anti-lock brake systems developed earlier. In 1936, the German company Bosch successfully developed an ABS with an electromagnetic induction wheel speed sensor. 20 After the 1960s, the development of electronic technology made ABS technology gradually mature, and mass production and loading. In 1978, Bosch successfully developed the digital electronic control ABS system, which greatly improved the stability of the car during braking. After entering the 90's, the development of ABS has become increasingly mature, the control functions have been continuously improved, and the control accuracy has been greatly improved. At present, developed countries have widely adopted ABS technology, and ABS devices have become one of the necessary equipment for automobiles. The ABS equipment rate of various types of automobiles in many European and American countries is as high as 90% or more.
The domestic ABS system research started late, but has made great progress so far. Especially in the area of air pressure ABS, domestic enterprises already have a certain production scale. This is of epoch-making significance for the revitalization of China's automobile industry, marking that China's ABS system research level has taken a solid step. However, in the research of hydraulic ABS system, many technical problems were encountered, and it was difficult to solve the problem. Therefore, it has not been able to produce independently, but it also has a certain ability of independent research and development. It is expected to achieve a breakthrough as soon as possible and form mass production.
Second, the structure and function of anti-lock brake system
As the vehicle's active safety component, its braking system has attracted much attention for its safety performance. If the car is not equipped with the ABS system, when it encounters various conditions and takes brakes during driving, the wheel may lock up, that is, the contact point between the wheel and the ground does not change, it does not roll at all, and it is in a constant state. This is a very dangerous state of sliding. Not only will the wheel wear be aggravated, but it will also cause a traffic accident in severe cases. And due to the change of braking efficiency, the following various problems will be encountered: first, the front wheels are locked, and the rear wheels are rolled, which will cause the car to lose steering ability; second, the rear wheels are locked, and the front wheels are rolled, which will cause the car The third is that the wheels on one side are locked, and the other side rolls, causing a slight side slip, which may cause a rollover in severe cases.
The anti-lock braking system of the automobile prevents the wheels from being locked by the brake during the braking process, improves the braking deceleration, effectively improves the directional stability and steering maneuverability of the car, and guarantees the driving safety of the car. Its impact on the performance of the car is mainly reflected in reducing the braking distance, maintaining steering ability during braking, improving driving direction stability, and reducing tire wear.
The automobile anti-lock braking system is mainly composed of three parts: wheel speed sensor, brake pressure regulator and electronic control unit (ECU). The wheel speed sensor is mainly used to continuously monitor the rotation speed of the wheel during the braking process of the car. The electronic control unit is mainly used to receive signals and give instructions. The brake pressure regulator is mainly used to adjust the brake pressure on the current wheel. Each wheel of the car has an independent wheel speed sensor, which monitors the current wheel speed during the braking process of the car and continuously transmits it to the electronic control unit. When one of the wheels has a large braking force, the wheel deceleration increases rapidly, and the wheel speed drops sharply, which is about to exceed the set value, which means that when there is a possibility of locking, the electronic control unit will issue a command to the brake pressure. Regulator, let the solenoid valve on the regulator stop or reduce the brake pressure of the wheel, so that the wheel starts to spin, that is, while rolling, it will prevent the wheel from locking. At the same time, in order to prevent insufficient wheel braking force, the braking pressure must be increased again. During the entire braking control process, it is necessary to continuously measure whether the wheel movement is stable. By adjusting the brake pressure, according to the current speed and the possibility of the wheel locking, the braking force is continuously pressurized, decompressed and maintained. To keep the wheels at the maximum braking force while not being locked. The specific control process is as follows:
Holding pressure process: During the braking process, if it is detected that a certain wheel tends to lock up, the ECU in ABS issues a command to control the brake pressure to keep it from increasing, while the other wheels do not tend to lock up. Motivation continues to increase.
Decompression process: When the brake pressure of the wheel remains constant, the ECU determines that the wheel is still tending to lock up, and the ECU in ABS issues a command to control the braking force to decrease rapidly.
Pressure process: As the brake pressure of the wheel decreases, the wheel will gradually accelerate and completely eliminate the tendency to lock, the ECU in ABS sends a command to control the braking force to increase rapidly, and the wheel starts to decelerate.
III. Development Trend of Automobile Brake Anti-lock Braking System
In recent years, the intelligent development of automobiles has made remarkable progress. As part of the electronic control system on the car, the development of ABS is also obvious to all.
1. Multi-channel development: From the original single-channel and two-channel ABS systems, it has now developed to three-channel and four-channel ABS systems. The number of channels directly determines the effect of independent brake pressure adjustment. Taking the four-channel ABS system as an example, this arrangement can independently control the slip state of the four wheels in the optimal range, make full use of the adhesion of each wheel, and obtain higher braking efficiency. Regardless of whether the adhesion conditions of the roads on which the left and right wheels are similar, or the deviation of the adhesion conditions are large, the independent control of each channel can make the four wheels completely independent brake pressure adjustment during braking, driving stability Huge improvements.
2. Integrated development: With the advancement of the electrification of automobiles, various electronic control systems are slowly emerging, and ASR systems related to ABS are one of them. The ASR system, also known as the drive anti-slip system. ABS is to prevent the wheel from being locked, while ASR is to prevent the wheel from excessively slipping, that is, ABS is to relieve the brake, and ASR is to apply the brake. .
3. Integrated development: The role of ABS is to prevent the wheels from locking when the car is braked. Today, the electronic braking force distribution system (EBD) is integrated into the ABS system to form the ABS + EBD system, and braking starts in ABS. Before the pressure adjustment, calculate the adhesion between the four wheels of the car and the road, and then adjust the distribution of the wheels and adhesion, which can better improve the directional stability during braking and shorten the braking distance.