Principle and maintenance of the hottest ABS anti

ABS anti lock braking system principle and maintenance

I. overview of ABS system

with the rapid development of the world automotive industry, comfort has increasingly become an important basis for people to buy cars. At present, the widely used anti lock braking system (ABS) makes people fully meet the safety requirements

automobile braking anti lock system, referred to as ABS for short, is an important device to improve the passive safety of automobiles. Some people say that the anti lock braking system is another major development after the relay of safety belts in vehicle safety measures. Automobile braking system is one of the two most important systems related to passenger safety. With the rapid development of the world automobile industry, people pay more and more attention to the safety of automobiles. The anti lock braking system of automobile is another major progress in improving the safety of automobile braking

abs anti lock braking system is controlled by automobile microcomputer. When the vehicle is braked, it can keep the wheels rotating, so as to help the driver control the vehicle to stop safely. This anti lock braking system uses a speed sensor to detect the wheel speed, and then transmits the wheel speed signal to the microcomputer. According to the input wheel speed, the microcomputer repeatedly reduces or increases the braking pressure on the wheel to control the wheel slip rate and maintain the wheel rotation. Keeping the wheels rotating during braking can not only ensure the ability to control the driving direction, but also provide higher braking force than locking the wheels under most road conditions

abs has three significant disturbance points compared with the conventional hydraulic braking system:

vehicle control - vehicle drivers equipped with ABS maintain a large degree of control during emergency braking. In the process of emergency braking, the skid caused by the hydraulic brake of Biao Huai makes the driver lose control of the vehicle. ABS restores stability and enables the driver to resume control of the vehicle

reduce slippage -- even if the wet, smooth road and locked vehicle form a state called slippage, when the vehicle driver is driving on the road with a thin layer of water and oil, it is similar to slippage. As ABS reduces the chance of wheel locking, it also reduces the chance of skidding during braking

improved tire wear - ABS is used to prevent wheel lockup, eliminating the possibility of flat spots in the tire during emergency braking as last revised

II. ABS development history

the development of ABS system can be traced back to the early stage of this century. As early as 1928, the theory of braking and anti lock was put forward. In the 1930s, mechanical braking and anti lock system began to be applied in trains and aircraft. Bosch was the first company to obtain the patent right of braking and anti lock system using electromagnetic wheel speed sensor to obtain wheel speed in 1936

in the 1950s, the anti lock braking system of automobile began to receive more widespread attention. Ford moved the aircraft's anti lock braking system to the Lincoln car in 1954, and Kelsey Hayes carried out an experimental study on the anti lock braking system symmetrical as "automatic" in 1957. The research results show that the anti lock braking system can indeed prevent the vehicle from losing direction control during braking, and can shorten the braking distance; Chrysler also conducted experimental research on the brake anti lock system symmetrically known as "ski control" during this period. Because all kinds of anti lock braking systems in this period used mechanical brake pressure regulating devices with mechanical wheel speed sensors, the obtained wheel speed signals were not accurate enough, the timeliness and accuracy of brake pressure regulation were difficult to ensure, and the control effect was not ideal

with the development of electronic technology, the development of electronic controlled braking anti lock system becomes possible. In the late 1960s and early 1970s, some electronically controlled anti lock braking systems began to enter the production stage. In 1968, Kelsey Hayes company developed and produced Shandong Huayu party secretary and chairman Gao Xizhu, a two-wheel brake anti lock system called "suretrack". The system uses the electronic control device to judge the motion state of the rear wheel during braking according to the rear wheel speed signal input by the electromagnetic speed sensor, and regulates the brake pressure of the rear brake wheel cylinder by controlling the brake pressure regulating device driven by vacuum, It was equipped on Thunderbird and continental MkIII cars by Ford in 1969

Chrysler and Bendix developed a system called "sure-track" which can prevent four wheels from being locked by braking. In 1971, it began to equip the imperial sedan. Its structural principle is basically the same as that of Kelsey Hayes's "sure-track". The difference between the two is that two or four wheels have anti lock braking. Bosch and Teves also developed their first generation of electronically controlled anti lock braking systems during this period. These two kinds of anti lock braking systems are controlled by electronic control devices to control the solenoid valves set in the brake pipeline, and directly adjust the electronic control pressure of each brake wheel

Buick developed a drive anti lock system that automatically interrupts the engine ignition by an electronic control device in 1971 to reduce the engine output torque and prevent the drive wheels from slipping

WABCO, in cooperation with Benz, first equipped the brake anti lock system on the pneumatic braking carrier car in 1975

during this period, various ABS systems used analog electronic control devices. Due to the defects of analog electronic control devices such as slow response, low control accuracy and easy interference, all ABS systems failed to achieve the expected control effect. Therefore, these anti lock control systems were soon no longer used

in the late 1970s, the rapid development of digital electronic technology and large-scale integrated circuits laid a technical foundation for the practical development of ABS system. In 1978, Bosch first introduced the brake anti foam system with digital electronic control device -- Bosch abs2, which was installed on Mercedes Benz cars, thus opening the prelude to the development of modern ABS system. Although the electronic control device of Bosch abs2 is still a control device composed of separate components, the response speed, control accuracy and reliability of digital electronic control device are significantly improved compared with analog electronic control device. Therefore, the control effect of Bosch abs2 is quite ideal. Since then, many brake professional companies and automobile companies in Europe, the United States and Japan have developed ABS systems in various forms

III. basic working principle of ABS in addition,

ABS is usually composed of wheel speed sensor, brake pressure regulating device, electronic control device and ABS warning light. In different ABS systems, the structural form and working principle of brake pressure regulating device are often different, and the internal structure and control logic of electronic control device may also be different

in a common ABS system, a speed sensor is installed on each wheel to input the signal about the speed of each wheel into the electronic control device. The electronic control device monitors and determines the motion state of each wheel according to the signals input by each wheel speed sensor, and forms corresponding control instructions. The brake pressure regulating device is mainly composed of pressure regulating solenoid valve, electric pump and fluid reservoir, which form an independent whole, and is connected with the brake master cylinder and each brake wheel cylinder through the brake pipeline. The brake pressure regulating device is controlled by the electronic control device to regulate the brake pressure of each brake wheel cylinder

the working process of ABS can be divided into conventional braking, brake pressure maintaining, brake pressure decreasing and brake pressure increasing stages. In the conventional braking stage, ABS does not intervene in the brake pressure control. All the inlet solenoid valves in the pressure regulating solenoid valve assembly are powered off and in the open state, all the outlet solenoid valves are powered off and in the closed state, the electric pump is also powered off, the brake lines from the brake master cylinder to each brake wheel cylinder are in the communication state, and the brake lines from each brake wheel cylinder to the reservoir are in the closed state, The braking pressure of each brake wheel cylinder will change with the output pressure of the brake master cylinder. At this time, the braking process is exactly the same as that of the conventional braking system. In the braking process, the electronic control device determines that a wheel tends to lock according to the wheel speed signal input by the wheel speed sensor, and ABS enters the anti lock braking pressure adjustment process. For example, when the electronic control device determines that the right front wheel tends to lock up, the electronic control device energizes the hydraulic inlet solenoid valve that controls the scraping pressure of the right front wheel, and turns the right front hydraulic solenoid valve into the closed state. The brake master cylinder transmission consumers pay more and more attention to the environmental protection. The brake fluid no longer enters the right front brake wheel cylinder. At this time, the right front hydraulic outlet solenoid valve is still in the closed state without being energized, and the brake fluid in the right front brake wheel cylinder will not flow out, The scraping pressure of the right front brake wheel cylinder remains constant, while the braking pressure of other wheels that do not tend to lock up will still increase with the increase of the output pressure of the brake master cylinder; If the electronic control device determines that the right front wheel still tends to lock when the brake pressure of the right front brake wheel cylinder remains constant, and the electronic control device also energizes the right front outlet solenoid valve and turns it into the open state, part of the brake wave in the right front brake wheel cylinder will flow back to the reservoir through the open outlet solenoid valve, so that the brake pressure of the right front brake wheel cylinder will decrease rapidly, and the locking trend of the right front wheel will begin to disappear, As the braking pressure of the right front brake wheel cylinder decreases, the right front wheel will gradually accelerate under the action of the vehicle inertia force; When the electronic control device determines that the locking trend of the right front wheel has been completely eliminated according to the signal input from the wheel speed sensor, the electronic control device will cut off the power of the right front hydraulic solenoid valve and the outlet solenoid valve, turn the inlet solenoid valve to the open state, turn the outlet solenoid valve to the closed state, and also turn the electric pump on to run, delivering brake fluid to the brake wheel cylinder pump, The brake fluid output by the brake master cylinder enters the right front brake wheel cylinder through the solenoid valve, so that the brake pressure of the right front brake wheel cylinder increases rapidly, and the right front wheel is lifted and decelerated. ABS controls the sliding rate of the anti lock wheel by cycling the braking pressure of the wheel that tends to lock, within the range near the sliding rate of the peak adhesion coefficient, until the vehicle speed decreases to a very low level or the normal pressure of the brake master cylinder no longer tends to lock the wheel. The frequency of brake pressure regulation cycle can reach 3~20hz. In this ABS, each brake wheel cylinder has a pair of liquid inlet and outlet solenoid valves, which can be controlled by the electronic control device respectively. Therefore, the braking pressure of each brake wheel cylinder can be adjusted independently, so that the four wheels do not have braking lock up

although the structural forms and working processes of various ABS are not exactly the same, they all prevent the controlled wheels from braking locking by self-adaptive cyclic adjustment of the braking pressure of the wheels that tend to lock

IV. precautions for maintenance and overhaul of ABS system

1 General precautions in use and maintenance

at present, most ABS systems have high working reliability and usually do not need regular special maintenance, but in the process of use, maintenance and overhaul