1 Basic principles of ABS/ASR
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1.1 The basic principle of ABS
The ABS (Anti-lock Braking System) is an electronic control system that controls and monitors the speed of a car during braking. In the process of car braking, it acts through the conventional braking system, can automatically control the slip of the wheel in the direction of rotation, and control the corresponding slip rate within the optimal range, which can improve the active safety of the car. Sex.
In the braking process of a car, the external force that causes the car to brake and decelerate is the ground braking force that the road surface acts on the tire tread. However, the ground braking force depends on the friction of the two friction pairs: one is the friction of the brake device on the wheel, that is, the brake force; the other is the friction between the tire and the road surface, that is, the ground adhesion. Only when the car has sufficient brake braking force and ground adhesion, can it obtain sufficient ground braking force.
During the braking process of the car, there is a speed difference between the speed of the vehicle and the rotational speed of the wheel (wheel speed), that is, the slippage between the wheel and the ground. Generally, the slip ratio S is used to indicate the degree of slip.
In the formula: u - vehicle speed; w - wheel speed.
Experimental and theoretical analysis shows that during braking, the slip ratio S is a controllable amount that is closely related to the distance of the brake, the controllability of the direction during braking, and the smoothness of the brake. The reason is that the relationship between the slip ratio and the longitudinal adhesion coefficient μB and the lateral adhesion coefficient μS between the vehicle and the ground has a certain non-linear curve relationship, as shown in the brake control zone of FIG. When the slip ratio S=0, the vehicle is in the non-braking state, the longitudinal adhesion coefficient μB=0, and the lateral adhesion coefficient μS is at the maximum value; when the vehicle is in the braking state, μB increases with the increase of the slip ratio S. , μS decreases with the increase of the slip ratio S. When the slip ratio S reaches a certain value, μB reaches the maximum, and the slip ratio at this time is called the optimal slip ratio (indicated by SK); As the slip ratio increases, μB and μS decrease continuously. When the slip ratio S=100%, the wheel is completely locked, μB drops to a value, μS≈0 has little longitudinal adhesion, and the lateral adhesion ability is almost Loss, the brake stability, directional stability and steering ability of the car will be completely lost.
The slip ratio S is in the range of 0 to Sk, which can ensure stable braking, which is called stable zone; in the range of Sk to 100%, it is unstable zone. When the slip ratio S exceeds Sk, the wheel will soon enter the locked state. . When the slip ratio S is between 10% and 30%, the longitudinal adhesion coefficient μB is in the peak range, and the lateral adhesion coefficient μS is also relatively large, and large longitudinal and lateral adhesion can be obtained at the same time, which is safely braked. Ideal working area.
The basic principle of ABS is to control the braking force of the wheel brake by adjusting the pressure of the brake pipe, so that the wheel speed is maintained within an appropriate range during emergency braking, and the wheel slip rate is controlled at 10% to 30%. On the stable braking section, the wheels are not locked, which can maintain the maximum braking force and fully utilize the wheel adhesion, which greatly improves the braking efficiency.
1.2 Basic Principles of ASR
ASR (Anti-Slip Regulation) is also called Traction Control System (TCS). It is a system developed on the basis of ABS to control the sliding drive wheels together with ABS.
The driving of the car is limited by the traction and adhesion of the driving, that is, to satisfy
Where: ∑Ff——car driving resistance; F1——car traction; Fφ——car adhesion.
If the adhesion coefficient of the road surface is small, it is easy for the traction force of the vehicle to exceed the adhesion limit between the tire and the road surface (ie, Ft>Fφ), resulting in excessive slip of the drive wheel, and the rear-wheel drive car may have a tail-end, front-wheel drive car. The easy direction is out of control, causing the car to shift to one side. The basic principle of driving anti-skid is similar to the brake anti-skid. According to the relationship between the ground adhesion coefficient and the wheel slip ratio (see Figure 1 drive control zone), the wheel slip rate is controlled within a certain range to improve the utilization of ground adhesion. Improve drive performance.
At present, ASR commonly used control methods are: First, the engine control to adjust the torque of the engine on the drive wheel. Gasoline engines often reduce their output torque by controlling fuel injection, ignition time, and throttle opening; diesel engines often reduce their output torque by controlling the amount of fuel injected. The second is the brake control that directly applies the brake to the driving wheel that slips. If the driving wheel is on the road surface with different adhesion coefficients, the braking force is reduced by the braking of the sliding driving wheel, and the driving force is improved. For the road surface with the same adhesion coefficient, the anti-drive wheel slip can be realized by engine control, and the two drive wheels of the slip can be braked; to prevent the brake shoe from overheating, when the vehicle speed is higher than a certain value, the brake control will not be It depends on the engine control.
ASR has a very close relationship with ABS and is a natural extension of ABS. The two are relatively close in technology, and some software and hardware can be shared. The sensors and pressure regulators used in ABS can be used by ASR. The electronic control device of ABS only needs to be expanded in function to be used in ASR devices. On the basis of ABS, it is only necessary to add an ASR solenoid valve to brake the excessively slippery wheels. For an electronically controlled engine, the output torque of the engine can be controlled via the bus. For non-electrically controlled engines, the output torque of the engine can be controlled by simply adding some sensors and actuators. Based on this, the two are usually organically combined to form an automotive ABS/ASR anti-skid control system.
2 ABS/ASR development status at home and abroad
2.1 Foreign development status
As early as 1928, the theory of anti-lock braking was proposed. BOSCH first obtained the patent for the anti-lock brake system in 1936. In 1954, FORD installed ABS on a Lincoln sedan. The wheel speed sensors and brake pressure regulators of various ABSs during this period were all mechanical. Therefore, the acquired wheel speed signal was not accurate enough, and the timing and accuracy of brake pressure adjustment were difficult to guarantee.
With the development of electronic technology, ABS entered the era of electronic control. From the late 1960s to the early 1970s, ABS, two-wheel brakes developed by Kelsey Hayes, ABS, BOSCH and TEVES developed by Chrysler and BENDIX The ABS equipped with the BENZ company and developed by the BENZ company in the pneumatic brake truck is controlled by the analog electronic control device for the solenoid valve installed in the brake pipe, directly to each brake wheel. Adjusted by electronically controlled pressure. Due to the slow response speed, low control precision and vulnerability of the analog electronic control unit, various ABSs have not achieved the desired control effect.
In the late 1970s, ABS adopted digital electronic technology, and the response speed, control accuracy and reliability were significantly improved, and ABS entered the practical stage. In 1978, BOSCH first introduced the ABS, the BOSCH ABS2, which uses a digital electronic control unit. Since then, many companies in Europe, the United States, and Japan have developed a variety of ABS. Since 1985, BOSCH, TEVES, BENDIX, WABCO and other companies have begun to invest heavily in the production of ABS to meet the increased demand for ABS.
At present, ABS has become more and more widely used in automobiles in the world, and has become the standard equipment of most automobiles. All kinds of passenger cars and light trucks in North America and Western Europe, the ABS equipment rate has reached more than 90%, the car ABS The equipment rate is about 60%, and the equipment rate of ABS for transporting dangerous goods is 100%.
In 1971, BUICK developed the anti-lock braking system that automatically interrupts engine ignition by electronic control devices to reduce engine output torque and prevent the wheels from slipping. In 1985, Volvo developed the electronic traction control system ETC (Electronic Traction Control) to adjust the engine output torque by adjusting the fuel supply to control the driving wheel slip rate to produce the best driving force. In 1986, BOSCH introduced the company's first traction control system, TCS.
Relying solely on adjusting the engine output torque does not solve the problem that the car starts to accelerate well on the off-road. In order to solve this problem, it is necessary to apply partial braking to the side drive wheel that is not attached well to fully exert the ground driving force on the side with better adhesion conditions. With the continuous development and maturity of ABS technology, this can be achieved by using the ABS pressure regulation system. ASR systems using brake intervention control are usually integrated with ABS to form an ABS/ASR system. In December 1986, BOSCH first combined ABS with ASR to launch the ABS/ASR 2U device with anti-lock brake and anti-skid function. In the same period, BENZ and WABCO jointly developed the ABS/ASR system for use on trucks.
Since then, major auto companies have begun to apply the ABS / ASR system, making it the standard configuration of the top luxury car. As major companies continue to develop ABS/ASR systems with more compact structure, lower cost, higher reliability and more comprehensive functions, ABS/ASR systems are gradually being applied to medium and low-end cars. By 1997, nearly 50 models of 23 automakers had used the ABS/ASR system.
2.2 Overview of domestic development
Domestic research and development ABS started late, beginning in the mid-1980s. However, China attaches great importance to the system development of ABS and formulates corresponding regulations to promote the development of ABS. GB 13594-92 "Performance Requirements and Test Methods for Automobile Anti-lock Braking System", which was implemented on April 1, 1993, provides test methods and basis for ABS to become standard equipment. GB 12676-1999 "Structure, Performance and Test Methods for Automotive Brake Systems", which was implemented on October 1, 1999, stipulates that after October 1, 2003, large passenger cars and large trucks must be installed in accordance with the provisions of GB 13594. A class of ABS.
At present, the domestic research ABS representative department. The research institutes have the following: National Key Laboratory of Automotive Dynamic Simulation of Jilin University, National Specialized Laboratory of Automotive Power and Emission Testing of Beijing Institute of Technology, Automotive Safety and Festival of Tsinghua University, State Key Laboratory of Energy, Department of Automotive Engineering, South China Institute of Technology and Transportation Jinan Chengjun Electronic Technology Co., Ltd., etc. These units have achieved a lot of results in the research of ABS simulation, control quantity, wheel speed signal anti-interference processing, wheel speed signal rejection, anti-lock solenoid valve action response. At the same time, the calculation of the slip ratio during anti-lock braking, the relationship between slip ratio and adhesion coefficient and the control algorithm of ABS are also deeply studied.
There are many companies that produce ABS in China, but most of them are cooperating with famous ABS companies abroad. Representative domestic companies that fully produce and develop ABS are: Guangzhou Kemi Automobile Brake Technology Development Co., Ltd., Chongqing Jueneng Automotive Technology Co., Ltd., Dongfeng Technology Automotive Brake System Co., Ltd., Xi'an Bohua Electromechanical Co., Ltd. Wait. The products that have been developed and produced include single-channel, three-channel, four-channel, six-channel air pressure and hydraulic type. They are suitable for motorcycles, cars, large and medium-sized passenger cars, heavy-duty trucks, ABS for trailers and related components. The braking performance indicators of these ABS have reached the level of similar foreign products. Some test data are superior to similar products of foreign companies and occupy a certain market in China.
It is estimated that in 2005, China's newly produced medium and heavy-duty trucks, the loading rate of large and medium-sized passenger cars ABS is 100%, while the loading rate of small and mini-bus ABS is 20%, and the ABS loading rate of cars is 50%.
Domestic research on ASR began around the 1990s. Some research institutes such as Tsinghua University, Jilin University of Technology, Beijing Institute of Technology, Tongji University, Shanghai Jiaotong University, Jinan Heavy Duty Truck Technology Center have tracked and studied the development of ASR technology, and have made progress in stages. At present, Chinese researchers mainly study the key aspects of ASR control system control strategy, control algorithm and logic. Due to the limitation of the electronically controlled engine, China's current control theory of the ASR system mostly focuses on the control method based on brake control and engine control. In general, there is still a certain gap from productization research. Therefore, there is no independent research and development of ABS/ASR anti-skid control system products integrating ABS and ASR.
3 Trends in ABS/ASR
3.1 Improvement of ABS/ASR control technology
At present, although ABS/ASR has been widely used, the control method is mainly based on logic threshold control. Although the control method is relatively simple, the logic is complicated, and all the thresholds require a large number of experiments to determine, and it is difficult to debug. Moreover, the ABS/ASR system with logic threshold control is relatively versatile and needs to be redeveloped for different models. With the continuous development and improvement of various modern control theories, servo control and high-precision control can be realized by using the optimal control theory. Applying intelligent control technologies such as fuzzy control and neural network control technology to the ABS/ASR system can improve the adaptability and reliability of the system. Compared with the current slip rate-based control algorithm, the control algorithm based on the road surface adhesion coefficient is easy to achieve continuous control, can adapt to various road surface changes, and control the slip rate near the optimal slip rate, so that the control effect of ABS/ASR Improved.
The ABS/ASR function can be further improved by advanced testing methods. For example, when ABS controls the wheel brake anti-skid, the vehicle speed is not directly measured, but the reference vehicle speed is estimated as the vehicle speed by the fluctuation of the wheel speed, and then the slip ratio is calculated for control. Therefore, the slip ratio of the ABS control cannot be guaranteed. Its accuracy. With the development of sensor manufacturing and integration technology, the addition of body speed sensors to measure body speed can improve the control effect of ABS/ASR.
The line brake system BBW (Brake-by-Wire) is one of the development directions of the brake control system. BBW replaces the force medium such as hydraulic oil or air in the traditional brake system with electric brakes, and electric energy as a source of energy. The brake caliper is driven by the electric motor during braking. There is no liquid or air pressure pipeline in the whole system, and many pipes and sensors can be omitted, so the structure is simple. The BBW transfers energy from the wires, the data lines transmit signals, and the braking reaction time is shortened, which greatly improves the braking safety of the car and provides conditions for future smart car control. In addition, the corresponding program is designed in the electronic control system, and the electronic control unit is operated to control the braking force and the braking force distribution of each axis, and the functions such as ABS and ASR can be fully realized. BBW is a new concept of braking, but there are still some problems to be solved: the current 12 V/24 V power system of the vehicle cannot provide such a large amount of energy, and a high-quality 42 V power supply is required; because there is no independent initiative. The backup brake system requires a backup system to ensure the safety of the brakes; there are various interference signals during the operation of the vehicle. How to eliminate the influence of these interference signals is an urgent problem to be solved.
The Electronic Braking System EBS (Electronically Controlled Braking System) is a comprehensive electronic control system developed on the basis of ABS/ASR to meet the requirements for the gradual improvement of the stability of the brake system of automobiles and trailers. In addition to the basic functions of ABS/ASR, it also has the following features: 1EBS optimizes the braking force distribution between the wheels, the main car and the trailer or semi-trailer. In general, for conventional braking systems, the brake coordination between the tractor and the trailer cannot always be in an ideal match, especially if the trailer with the tractor is frequently replaced. EBS will monitor the incompatibility between the main vehicle and the trailer in any state, automatically adjust the braking force distribution between the main vehicle and the trailer, meet the requirements of the coordination between the main vehicle and the trailer, and improve the safety of the vehicle. The front and rear axle linings are worn and coordinated, the total wear amount is minimized, and all lining replacement intervals are consistent, which shortens maintenance time and reduces operating costs. At the same time, the coordination of the braking force can also increase the braking comfort. 2EBS manages the auxiliary brake and the service brake through the brake management system. It ensures wear-free braking at every braking (relay, engine braking takes up most of the braking work, so the brake brake temperature can be kept to a minimum level, brake lining wear reduce). 3 Improved the function of ABS/ASR, improved braking response time and vehicle braking response, shortened braking distance and improved braking stability. The comfortable brake induction almost reaches the brake feel of the car. 4EBS has comprehensive diagnostic and self-testing capabilities that provide instant information about the brake system, any faults that can be monitored by the system and accurately displayed to alert for repairs. Maintenance specialists troubleshoot accordingly.
At present, EBS is used in trucks and buses, and is a substitute for ABS/ASR in the field of commercial vehicles. The ABS/ASR market will gradually decrease as EBS will be considered for light vehicles.
3.2 Reduce volume and quality, simplify structure
Adding some safety devices to the car, the quality will increase, which is not good for fuel economy. Therefore, under the premise of ensuring safety, minimize the quality. In addition, the installation space is very compact whether it is a large car or a small car, so the volume of the ABS/ASR device is required to be as small as possible. The main way to reduce the volume of ABS/ASR is to optimize the structural design (such as reducing the size of the pressure regulator) and increase the integration. At present, the optimized ABS has integrated the brake master cylinder, pressure regulator and electronic control unit into one, which greatly reduces the size and cost.
3.3 Extension and integration of control functions
Integrating various electronic control systems with different functions, under the premise of realizing their basic functions, it is an inevitable trend of automotive electronic control to form a new integrated electronic control system with more powerful functions. Extending other control systems into an integrated vehicle control system is the development direction of the ABS/ASR system. At present, ABS/ASR is developing in the following directions.
a. Integration with Electronic Brake Force Distribution (EBD) to form an ABS/ASR/EBD system can significantly improve and improve the efficacy of ABS. The function of EBD is to calculate the friction value of four tires due to different adhesion at the moment of car braking, and then adjust the braking device to adjust it at high speed during the movement according to the set procedure to achieve the braking force. Match with friction (traction) to ensure the stability and safety of the vehicle. When the emergency brake wheel is locked, the EBD balances the effective ground adhesion of each tire before the ABS action, preventing the tail and side shift and shortening the braking distance of the car.
b. Integration with the electronic stability program ESP (Electronic Stability Program) system to form an ABS/ASR/ ESP integrated control system that relieves the driver's high requirements for braking, starting and steering. ESP is also known as Vehicle Dynamics Control (VDC). In 1995, BOSCH launched the electronic stability program ESP based on the ABS/ASR system. Based on the advantages of ABS/ASR, ESP adds sensors such as steering sensor, side-slip sensor, lateral acceleration sensor and yaw rate sensor. It has the function of starting to correct and compensate the braking force and the direction of travel of the car. The ESP analyzes the vehicle driving status information transmitted by each sensor, so that the ABS/ASR automatically applies braking force to one or more wheels to keep the vehicle in the lane selected by the driver to help the vehicle maintain dynamic balance. . Therefore, the vehicle can be maintained in an optimum stability under various conditions, and the effect is more pronounced in the case of oversteer or understeer.
c. Integration with the ACC (Adaptive Cruise Control) system to form an ABS/ASR/ACC integrated control system that relieves the driver's high requirements for braking, starting, and maintaining a safe distance. The ACC device is an automotive active safety technology developed in recent years. Equipped with ACC device, it can automatically determine the ideal safety distance of the main vehicle according to the relative distance between the main target vehicle and the main vehicle, the relative speed and the road condition parameters, and automatically adjust the main vehicle speed in real time so that the actual distance is not less than ideal safety. The distance, therefore, can avoid collision accidents to a large extent and has a good safe driving effect. Since ABS/ASR and ACC use the same wheel speed acquisition system, braking force adjustment device and engine adjustment device, add a distance sensor and corresponding solenoid valve based on the hardware of the ABS/ASR integrated device. Implement ACC functionality. Therefore, the integration of ABS/ASR and ACC can not only reduce the cost, but also improve the overall safe driving performance of the car.
3.4 Information exchange and sharing with other control systems to improve overall control performance
As the degree of electronic electronics continues to increase, the number of ECUs on automobiles is increasing. In order to improve the utilization of signals, a large amount of data information is required to be shared among different ECUs, and a large number of control signals in the integrated control system of the vehicle also need to be exchanged in real time. Most of the traditional electrical systems use a single point-to-point communication method, which is far from meeting this demand. To this end, bus technology has been introduced into automotive electronic control systems. In the future, the development of the ABS/ASR control system will be based on bus technology to achieve information sharing with other control systems. For example, with the CAN bus and SAE J1939, data transmission between the mechanical automatic transmission AMT (Automatic Mechanical Transmission) and ABS/ASR can be easily realized, and resource sharing can be realized. The vehicle wheel speed signal collected by ABS can be used to change the output shaft speed of the transmission to AMT, which can reduce the sensor and reduce the cost of the control system. At the same time, the connectors are reduced, which improves the reliability and real-time performance of the AMT and ABS/ASR systems. When ABS works, it can send control information to AMT, request AMT to hang up the file, improve the working performance of ABS, and make the vehicle brake more stable and more effective. When ASR is working, AMT can be required to shift upwards to reduce the torque, so that the control effect of ASR is better. ASR allows AMT to avoid repeated shifts when starting and accelerating on low-attach roads. Therefore, information exchange and sharing can make the functions of the two control systems richer and more efficient than the functions they control individually, making each controller more complete, facilitating more complex control and laying the foundation for vehicle control.
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