Research on the development trend of ABS Technolog

Research on the development trend of automobile ABS technology

introduction

before the emergence of anti lock braking system, 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 the braking force, and the size and type of the brake. Because there is no feedback signal of the wheel motion state, the speed and locking condition of the wheel in the braking process cannot be measured, so it is impossible for the car to adjust the brake pressure of the wheel cylinder or air chamber accordingly. Therefore, in case of emergency braking, the phenomenon of wheel locking and dragging on the ground is inevitable. When the wheels are locked, the lateral adhesion performance of the ground is very poor, and the lateral adhesion provided is very small. Under the action of any small external force, the vehicle will have the problem of directional instability, which is very prone to traffic accidents. When braking on wet roads or ice and snow roads, this kind of directional instability will be more serious. The emergence of anti lock braking system (ABS) fundamentally solves the problem of wheel locking in the braking process. Its basic function is to sense each instantaneous motion state of the wheel through the sensor, and adjust the brake torque accordingly according to its motion state to avoid the locking phenomenon of the wheel, so it is a closed-loop braking system

it is one of the most successful applications of electronic control technology in cars. The anti lock braking system can maintain directional stability and shorten the braking distance when the car is braking, effectively improving the safety of driving

first, the working principle of ABS

when braking, there is a difference between the wheel speed and the vehicle speed, which will lead to slippage between the wheel and the road. When the wheel contacts the road in a pure rolling way, its slippage rate is zero; When the wheel is locked, the slip rate is 100%. When the slip ratio is between 8% and 35%, the maximum braking force can be transmitted. The basic principle of anti lock braking is to control and adjust the braking force according to the above research results, so that the wheel slip rate can be controlled within an appropriate range in the braking process, so as to achieve the best braking effect. The hardware composition 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 with slip rate as the target. The sensor measures the wheel speed and transmits this data to the electronic control device. The control device is a microprocessor, which calculates the vehicle speed according to the wheel speed sensor signal. In the braking process, the wheel speed can be compared with the characteristic curve of the ideal deceleration prepared in advance in the control device. If the control device judges that the wheel deceleration is too fast and the wheel is about to lock up, it will send a signal to the hydraulic regulator, which can control the oil pressure of the caliper or wheel pump of the brake (action, hold, release, reuse) according to the signal from the control device. This action can occur more than 10 times per second

the hole diameter of the oil return valve is much larger than that of the oil delivery valve.

Second, the development and application status of ABS technology.

the braking system based on the braking and anti lock theory is first applied to trains and aircraft. In 1936, Bosch applied for a patent for an electro-hydraulic ABS device, which promoted the application of ABS Technology in automobiles. The use of ABS in cars began in the mid-1950s with Ford Motor Company. In 1954, Ford Motor Company installed the Air France ABS device on Lincoln. The control part of this ABS device is mechanical, with complex structure and relatively single function. Antilock is effective only in specific vehicles and working conditions, so the braking effect is not ideal. The complex mechanical structure makes the ABS device have poor reliability, low control accuracy and high price. The promotion and application of ABS Technology in automobiles is difficult. Until the late 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. Its reaction speed, control accuracy and reliability are significantly improved, and the braking effect is also significantly improved. At the same time, its volume is gradually reduced, its mass is gradually reduced, the control and diagnosis functions are continuously enhanced, and the price is gradually reduced. During this period, many companies have successively developed various forms of 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 developed countries have widely adopted ABS technology, and ABS devices have become necessary equipment for automobiles. The equipment rate of ABS for passenger cars and light trucks in North America and Western Europe has reached more than 90%, the equipment rate of ABS for cars is about 60%, and the equipment rate of ABS for trucks transporting dangerous goods is 100%. ABS device manufacturers mainly include: Bosch Company of Germany (Bosch), which is most used by European, American, Japanese and Korean vehicles; Delco of the United States, general motors of the United States and Daewoo motors of South Korea; Bendix of the United States, adopted by Chrysler of the United States; There are also Teves of Germany, WABCO of Germany, kelseyhayes of the United States, etc. the ABS products of these companies are widely used, and are still developing, updating and upgrading

in recent years, ABS technology is also being popularized and applied in China. In the national compulsory standard GB "structure, performance and test methods of automobile braking system" formulated in 1999, the installation of ABS has been regarded as a compulsory regulation. Since then, FAW Volkswagen, FAW Fukang, Shanghai Volkswagen, Chongqing Chang'an, Shanghai General Motors, etc. have begun to adopt 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 the Ministry of communications, Jinan Jiete Automotive Electronics Research Institute, Tsinghua University, Xi'an Jiaotong University, Jilin University, South China University of technology, Hefei University of technology and other units. Although they started late, they have also made some achievements. In terms of pneumatic ABS, domestic enterprises including Dongfeng Electronic Technology Co., Ltd., Chongqing Juneng and Guangdong Kemi have formed a certain production scale. Due to the great technical difficulty and tight technical blockade abroad, domestic enterprises cannot produce hydraulic ABS independently for the time being, but they are also doing independent research and development in hydraulic ABS, trying to break through the technical barriers of foreign multinational companies, and have made some new progress and breakthroughs. For example, Tsinghua University and Zhejiang Asia Pacific have undertaken the "Ninth Five Year Plan" national scientific and technological research project of automotive hydraulic anti lock braking system (ABS), and have made significant achievements in key technologies such as ABS control theory and method, electronic control unit, hydraulic control unit, development device and matching method. The dissipative power theory adopted has avoided the limitations of the traditional logical threshold research method, made a theoretical breakthrough, successfully developed ABS and entered the industrialization and mass production stage. The sample has been matched and used on Nanjing Iveco light bus, which fully meets the requirements of national standard GB and European regulation eecr13. This is of epoch-making significance to the revitalization of China's automotive industry and auto parts industry, marking a solid step in the localization of China's automotive hydraulic ABS. At the same time, Hefei University of technology has also developed a hydraulic braking electronic anti lock system with independent intellectual property rights in China, which takes the lead in matching the application on hf6700 light vehicles to check whether the lifting ring is successfully hung on the key blade. Although there is a certain gap between domestic and foreign hydraulic ABS technology, with the strong support of the government and the cooperation of domestic abundant human resources, it is believed that China can catch up with and surpass the international level in some fields of ABS Technology in a relatively short time

III. ABS control strategy

a core problem of ABS technology is the research of control algorithm. Because ABS system is a nonlinear system, exploring an effective control method is the key to the development of ABS system. In recent years, scholars at home and abroad have done a lot of theoretical research on the control algorithm of ABS, mainly including the following control methods

(I) logic threshold control

the characteristic of this control method is that it does not need to establish the mathematical model of the specific system, and it is very effective for the nonlinear control of the system, which is more suitable for the control of ABS. When it is used for ABS control, a threshold value of angular deceleration can be preselected. When the measured value reaches this threshold value, the controller sends a command to reduce the braking force and increase the wheel speed. A threshold value of angular acceleration is preselected. When the measured value reaches this threshold value, the controller sends a command to increase the braking force and reduce the wheel speed. Taking the wheel angular velocity as a single signal input, as described above, and setting a reasonable threshold value of angular acceleration and angular deceleration in the controller, the anti lock braking cycle can be realized. Therefore, the whole control process is relatively simple, and the structure principle is relatively easy to realize. At the same time, if the control parameters are selected reasonably, the ideal control effect can be achieved and the requirements of various vehicles can be met. However, the logic threshold control itself has some shortcomings. For example, its control logic is complex and fluctuates greatly, and many parameters in the control system are empirical data obtained through repeated experiments, lacking rigorous theoretical basis, and unable to evaluate the stability quality of the system

(II) sliding mode variable structure control

according to the basic principle of anti lock braking, the essential problem of its braking process is to control the slip rate of the wheel at the peak point sk of the adhesion coefficient, then the sliding mode variable structure switches the size and symbol of the control quantity in the way of ideal switch in different control areas according to the current state, deviation and derivative value of the system, so as to ensure that the system is within a small range of the sliding area, The state track s slides to the control target (SK, 0) along the sliding knot changing curve

generally, the braking torque is taken as the control variable U, and the switching condition is

(III) optimal control

the optimal control method is a modern control theory method based on the state space method

according to the mathematical model of vehicle ground system, it can use the concept of state space to study the vehicle anti lock braking system in the time domain. The optimal control method is different from the threshold control method. It is a control method based on model analysis

the idea is to obtain the optimal control target of the anti lock braking system according to the control requirements of the anti lock braking system and the optimization principle. The advantage of this control method is that the process of state change in the control process is considered to make the control process stable; The disadvantage is that the quality of the control effect mainly depends on the mathematical model of the system, and the control quality is difficult to accurately grasp

(IV) PID control

the greatest advantage of PID control method is that it does not need to understand the mathematical model of the controlled object, but only needs to adjust the regulator parameters according to experience. This feature just meets the difficult modeling of ABS control system. Obviously, for the road surface with a single road surface (the expected slip rate is fixed), the characteristics of PID control determine its strong practicability, but it is difficult for us to determine an accurate tire model to determine the expected slip rate under different braking conditions in real time, so it is not applicable in actual products. At present, many researchers focus on the method of establishing accurate tire model or identifying road conditions through other ways, combining expectation with PID control method