Before the appearance of anti-lock braking system, all cars used open-loop braking system. Its characteristic is that the braking torque of the brake is only related to the driver's control force, the distribution and adjustment of braking force and the size and type of the brake. Because there is no feedback signal of the wheel motion state, it is impossible to measure the wheel speed and lock-up during braking, and the automobile cannot adjust the braking pressure of the wheel cylinder or air chamber accordingly. Therefore, in the case of emergency braking, it is inevitable that the wheels will lock and mop the floor. When the wheel is locked, the lateral adhesion of the ground is very poor, which provides little lateral adhesion. Under the action of any small external force, cars will have the problem of unstable direction, which is prone to traffic accidents. The instability in this direction will be more serious when braking on wet or snowy roads. The appearance of anti-lock braking system (ABS) fundamentally solves the problem of locking in the process of automobile braking. Its basic function is to sense the instantaneous motion state of the wheel through the sensor, and adjust the braking torque of the brake according to its motion state to avoid the wheel locking phenomenon, so it is a closed-loop braking system.

It is one of the most successful applications of electronic control technology in automobiles. Anti-lock braking system can maintain directional stability during braking, shorten braking distance and effectively improve driving safety.

First, the working principle of ABS

There is a difference between the wheel speed and the vehicle speed when braking, which will lead to the wheel slipping with the road surface. When the wheel contacts the road in a pure rolling way, the slip rate is zero. When the wheel is locked, its slip rate is 100%. When the slip rate is between 8% and 35%, the maximum braking force can be transmitted. The basic principle of anti-lock braking is to control the wheel slip rate in a suitable range by controlling and adjusting the braking force according to the above research results, so as to obtain the best braking effect. The hardware of ABS system is mainly composed of sensors (including wheel speed sensor, deceleration sensor and vehicle speed sensor), electronic control device and brake pressure regulator, forming an automatic control system aiming at slip rate. The sensor measures the wheel speed and transmits the data to the electronic control device. The control device is a microprocessor, which calculates the vehicle speed according to the signal of the wheel speed sensor. During braking, the wheel speed can be compared with the characteristic curve of ideal deceleration preprogrammed in the control device. If the control device judges that the wheel is decelerating too fast and the wheel is about to lock up, it sends a signal to the hydraulic regulator, and the hydraulic regulator controls (acts, maintains, releases and re-acts) the oil pressure of the caliper or wheel pump of the brake according to the signal of the control device. This operation can occur more than 10 times per second.

Second, the development and application status of ABS technology

The braking system based on anti-lock braking theory is first applied to trains and airplanes. 1936, Bosch applied for the patent of electro-hydraulic control ABS device, which promoted the application of ABS technology in automobiles. The use of ABS in automobiles began in Ford Motor Company in the mid-1950s and Lincoln in 1954. Ford Motor Company installed the ABS device of Air France. The control part of this ABS device is mechanical, with complex structure and relatively single function. Anti-lock braking is only effective in specific vehicles and working conditions, so the braking effect is not ideal. The complicated mechanical structure makes the ABS device have poor reliability, low control accuracy and high price. It is difficult to popularize and apply ABS technology in automobiles. Until the end of 1970s, the rapid development of electronic technology provided reliable technical support for the application of ABS technology in automobiles. The ABS control part adopts electronic control, and its response speed, control accuracy and reliability are obviously improved, and the braking effect is also obviously improved. At the same time, its volume is gradually reduced, its weight is gradually reduced, its control and diagnosis functions are continuously enhanced, and its price is gradually reduced. During this period, many companies have successively developed various ABS devices.

After entering the 1990s, ABS technology has been continuously developed and matured, and the control accuracy and control function have been continuously improved. Now ABS technology has been widely used in developed countries, and ABS devices have become necessary equipment for automobiles. In North America and Western Europe, the equipped rate of ABS for passenger cars and light trucks is over 90%, the equipped rate of ABS for cars is about 60%, and the equipped rate of ABS for trucks transporting dangerous goods is 100%. ABS device manufacturers mainly include: Bosch (Germany), mostly used in Europe, America, Japan and South Korea; DELCO (USA), adopted by GM and daewoo motor; BENDIX)； adopted by Chrysler in the United States; And TEVES, WABCO, KELSEYHAYES, etc. ABS products of these companies are widely used and are constantly developing and upgrading.

In recent years, ABS technology has been widely used in China. In the national mandatory standard GB 12676- 1999, the installation of ABS has been regarded as a mandatory regulation. Since then, FAW-Volkswagen, Erqi Fukang, Shanghai Volkswagen, Chongqing Chang 'an and Shanghai GM have all adopted ABS technology, but these ABS devices have no independent intellectual property rights in China.

Domestic research on ABS mainly includes Dongfeng Motor Corporation, Chongqing Highway Research Institute of Ministry of Communications, Jinan Jeter Automotive Electronics Research Institute, Tsinghua University, Xi Jiaotong University, Jilin University, South China University of Technology, Hefei University of Technology and other units. Although it started late, it has also achieved some results. In terms of pneumatic ABS, domestic enterprises include Dongfeng Electronic Technology Co., Ltd., Chongqing Juneng and Guangdong Komi. Have formed a certain production scale. Due to technical difficulties and tight foreign technology blockade, domestic enterprises can't independently produce hydraulic ABS for the time being, but in order to break through the technical barriers of foreign multinational companies, they are also doing independent research and development, and have made some new progress and breakthroughs. For example, Tsinghua University and Zhejiang Asia-Pacific undertook the "Ninth Five-Year Plan" national key scientific and technological project of automobile hydraulic anti-lock braking system, and made great achievements in ABS control theory and method, electronic control unit, hydraulic control unit, development device, matching method and other key technologies. The theory of dissipative power adopted avoids the limitations of the traditional research method of logic gate limit, and makes a theoretical breakthrough, and successfully develops ABS and enters the stage of industrialization and mass production. The matching application of this sample on Nanjing Iveco light bus fully meets the requirements of national standard GB 12676- 1999 and European regulation EECR 13. This is of epoch-making significance to the revitalization of China's automobile industry and auto parts industry, and marks a solid step in the localization of China's automobile hydraulic ABS. At the same time, Hefei University of Technology has also developed an electronic anti-lock braking system with independent intellectual property rights in China, which has been successfully applied to HF6700 light vehicle. Although there is a certain gap between domestic and foreign hydraulic ABS technology, with the strong support of the government and abundant domestic human resources, I believe that China can catch up with the international level in some areas of ABS technology in a relatively short time.