Abstract: The development and research progress of vehicle brake science and technology are discussed. Vehicle braking is one of the main performances of vehicles. The development of science and technology is directly related to the safe driving of vehicles. In the 21st century, energy and environmental protection technologies, new materials technologies, advanced manufacturing technologies, and information and control technologies have become important areas for the development of science and technology. The advancement of science and technology in these fields will play an important role in promoting the development of vehicle braking science and technology.
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Keywords: vehicle brake science and technology development research progress
1 Overview
From the time the car was born, the vehicle brake system played a vital role in the safety of the vehicle. Increasing the speed of the vehicle is one of the main technical measures to increase the traffic flow. However, when the vehicle is driving at a high speed, it must be based on the premise of ensuring driving safety. In the case of a small road traffic, the vehicle can travel at a high speed, and when it is about to turn, or the road conditions are poor, or the traffic is relatively large, especially when encountering obstacles or there is a danger of a car accident, it is necessary to Reduce the speed to a very low distance and even stop at the shortest possible distance. If the vehicle does not have this performance, it is impractical to obtain the highest speed. When the vehicle is under the long slope, under the action of gravity along the slope component, there is a tendency to continuously accelerate to the dangerous vehicle speed. At this time, the vehicle speed should be maintained at a certain safety. Under the value, and remain stable; in addition, vehicles that have stopped (especially on the ramp) should be reliably parked in place. The above causes the running vehicle to decelerate and stop, so that the downhill vehicle speed is stabilized, and the parking is kept motionless. These actions are collectively referred to as braking.
Vehicle braking is one of the main features of the vehicle, which is directly related to traffic safety. Major traffic accidents are often related to braking, so vehicle braking is an important guarantee for safe driving. Vehicle braking performance is mainly evaluated from three aspects [1]: 1 braking performance, that is, vehicle braking distance and braking deceleration; 2 braking performance stability, that is, resistance to thermal attenuation; The directional stability of the vehicle, that is, the performance of the deviation, side slip and loss of steering ability during braking.
In recent years, with the advancement of vehicle technology and the continuous improvement of vehicle speed, people's safety awareness is getting higher and higher, and new requirements for braking technology are put forward. Numerous automotive engineers have devoted a great deal of effort to the study of improving vehicle braking performance. At present, research on vehicle braking mainly focuses on safety, energy saving and environmental protection.
2. Development of vehicle brake science and technology [2][3][4]
Vehicle braking science and technology is directly related to driving safety. With the development of modern vehicle design, manufacturing technology and the increasing demand for use, vehicle brake science and technology are constantly developing and innovating.
2.1 Development of vehicle braking form
The brake system is an important part of the car. Direct use of pneumatic brakes is one of the earliest forms of vehicle braking. It uses the power of the engine to drive the air compressor as the sole source of energy for the brakes. The driver's physical strength is only used as the control energy. This brake system is called pneumatic brake. system.
The pneumatic brake form quickly evolved into a hydraulic brake. Hydraulic brakes have many advantages over pneumatic brakes: first, it can increase the brake pressure and reduce the volume of the brake structure; secondly, it can eliminate the bulky air cylinder, and more importantly it is electro-hydraulic anti-skid control. The application of the dynamic system provides feasibility. However, the hydraulic brake system also has its shortcomings: heavy weight, easy fire, slow response, and the like.
In order to solve the shortage of hydraulic braking, with the development of electronic technology, electric braking has occurred. The electric brake system and the hydraulic brake system are identical in terms of the braking principle, and the main parts of the wheel and the brake device are the same. The difference is that in the electric brake system, the power source replaces the hydraulic source, and the electromechanical actuator replaces the hydraulic actuator (cylinder seat piston assembly). Compared to hydraulic brake systems, electric brake systems have significant advantages. The electric brake is used in the electric brake system, and there is no oil flow, so the response speed to the brake command is much faster than the hydraulic brake system. The response frequency of the electric actuator is 2 to 3 times the response frequency of the hydraulic device. For the same reason, the response frequency is faster, which helps to improve the anti-slip performance. The elimination of hydraulic accessories reduces the risk of failure, increases safety and reduces weight. In addition, the vehicle's electric brake system also improves the system's fault diagnosis capabilities, reducing maintenance and reducing maintenance requirements. It is worth noting that there is no hydraulic oil and there is no common hydraulic system contamination problem.
Over the years, improvements and innovations in modern vehicle braking technology have never stopped, driven by increased braking efficiency and the need for safety, reliability and maintainability. The research and application of rheological brakes is a major technological achievement in the late 20th century, opening up a new world for vehicle braking technology. Rheology braking is still a new braking concept in the theoretical research stage. It enables new star materials such as magnetorheological variants and current variants to rapidly change the viscosity and even change from liquid to liquid when adjusting the applied electric or magnetic field. Solid state. A shear force is created between the dynamic and dynamic disks of the system, thereby creating an obstructive braking torque. The electric field dominated by the electric field is called the electric current variant (ERF), which is called the magnetorheological fluid (MRF). The phenomenon of the material is called the Winslow effect. The brake disc and the static disc are filled with a rheological body, and in the absence of braking, the rheological body does not function, and the movable disc can rotate freely. When the electric field (or magnetic field) is applied during braking, the viscosity of the rheological body changes rapidly, so that a shear force is formed between the dynamic and static disks, thus generating a braking torque that hinders the rotation of the moving plate. The significant advantage of the rheological body brake over the mechanical friction type brake is that the brake is smooth and the efficiency is high, and it has been tried for the braking of the vehicle. The disadvantage is that the structure is complex and can be applied in the car, depending on the progress of the research.
The car braking process is a process of dissipating huge kinetic energy into heat energy. From the motor braking method, the electromagnetic field principle can be applied to the car brake, called electromagnetic field braking. During driving, the wheel is stored as a generator to generate electricity. During the braking process, the wheel acts as a motor. When braking, the motor reverses the voltage to the motor, causing the wheel to generate an electromagnetic torque opposite to the direction of rotation, thereby achieving the purpose of deceleration and stopping. The mechanical energy converted into electrical energy during the braking process can be fed back to the power supply. This assumption is in line with the principle of conservation of energy and should theoretically be feasible. It is in the state of experimental research, which will be a revolutionary innovation in automotive brake technology, because it no longer uses friction braking, but uses electromagnetic field braking and effectively utilizes the energy recovered during driving.
2.2 Development of vehicle brake control system
At present, research on vehicle braking has invested heavily in control, including the theory and methods of brake control, and the adoption of new technologies. The traditional brake control system only does one thing, that is, evenly distributes the oil pressure. When the brake pedal is working, the master cylinder sends an equal amount of oil to each brake to balance the front and rear. However, to achieve a true "balance", the control system must be used.
The most primitive control system relies on the driver manipulating a simple set of mechanical devices to control the force applied to the brakes, which can be met when the vehicle mass is relatively light, the speed is low, and the traffic is small. With the increase of vehicle weight and the continuous improvement of vehicle speed and the development of the automobile industry, especially the development of military vehicles and military technology, the vehicle brake control technology has made a new breakthrough. The machine-liquid control system is followed by the mechanical control system. Another major innovation. In the late 1980s, with the development of electronic technology, the biggest and most remarkable achievement in the world of automotive technology was the use and promotion of the anti-lock braking system (ABS: Antilock Brake System). ABS is a high-tech product integrating electromechanical technology, precision machining technology and hydraulic control technology. Its installation greatly enhances the car's active safety and maneuverability. ABS is based on wheel acceleration and deceleration thresholds and reference slip ratio methods. Different vehicles require different matching techniques. The development of ABS control technology has become the key. Now, a variety of control technologies are applied in the control logic of ABS, such as traditional logic threshold control, PID control, variable structure control, fuzzy control, state-based empty gate and linear feedback theory control, fuzzy Neural network control, intelligent control, etc.
With the wide application of mechatronics in the automotive industry, a monitoring and control integrated brake control system has emerged. The integrated control and control brake control system is a creative electronically controlled brake system that transforms the traditional hydraulic brake system into a more powerful mechatronic system. Its microprocessor is integrated into the vehicle's data and can process information from different electronic controls. In this way, electronic pulses and sensor signals can be quickly converted into brake signals, giving the driver a sense of security and comfort. This control system will be a new milestone in improving the safety of driving.
2.3 Regenerative braking technology
The vehicle braking process is to consume the kinetic energy of the vehicle in the form of heat energy by friction. Therefore, a large amount of energy is consumed during the braking process of the vehicle. If these energy are recovered and stored in other forms for the vehicle to be reused, it will help to improve energy efficiency, reduce fuel consumption, reduce brake heat load, and reduce wear. Improve vehicle driving safety and economical use. Regenerative braking technology has been created.
According to different energy storage mechanisms, regenerative braking technology can be divided into: flywheel energy storage type, high-speed rotating flywheel to store and release energy, ie flywheel battery; hydraulic energy storage type, first kinetic energy of the car during braking or deceleration Converted into the form of hydraulic energy, and the hydraulic energy is stored in the hydraulic accumulator. When the car is restarted or accelerated, the energy storage system reacts the hydraulic energy in the accumulator to the car in the form of mechanical energy to increase the car. The kinetic energy of the vehicle; the electrochemical energy storage type firstly converts the kinetic energy of the car during braking or deceleration into electric energy through the generator and stores it in the accumulator in the form of chemical energy. When the car needs to be started or accelerated, Then the chemical energy in the accumulator is converted into the kinetic energy of the vehicle through the electric motor; the composite energy storage type combines the chemical battery and the super capacitor to combine the electric energy storage element with the power electronic power conversion circuit to perform fast high power. The savings of energy, the regenerative energy released by the buffer is stored in the form of chemical energy.
In addition, the regenerative braking energy recovery technology can greatly reduce the braking noise while performing energy recovery.
2.4 Brake Noise Control Technology
The screaming noise and vibrating sounds that occur in car braking can distract people's attention, causing people to feel nervous, uncomfortable, affecting the environment and harming people's health. With the increase of people's awareness of environmental protection, the problem of car brake noise has been paid more and more attention. Especially in the densely populated area, the brake squeak pollutes people's hearing, and more seriously shows the car braking efficiency. It has fallen, which will bring security risks. Therefore, reducing vehicle braking noise is an important task to improve car comfort and urban environment.
In order to solve the problem of noise pollution, it is first necessary to study the mechanism of brake noise generation and to clarify the relationship between them and the structural design of the friction plates and brake components. Then, under the guidance of the theory, through the development of new brake materials, take the necessary technology (such as damping noise reduction, active control noise suppression technology), or structural optimization design. It is reported that the Automotive Engineering College of Wuhan University of Technology and a Wuhan enterprise jointly developed a pneumatic disc brake, which has been successfully applied to urban bus passengers, which can effectively solve the brake noise problem that has long plagued China's urban public transport. Different degrees of vibration and noise reduction effects, adapt to environmental requirements.
3. Research progress in vehicle brake science and technology
Reviewing the history of vehicle brake science and technology, it is clear that vehicle braking performance is one of the main performances of automobiles, and its scientific and technological development directly affects the driving safety of automobiles. The improvement of human security awareness puts new demands on vehicle braking performance. In the 21st century, energy and environmental protection technologies, new materials technologies, advanced manufacturing technologies, and information and control technologies have become important areas for the development of science and technology. The advancement of science and technology in these fields will play an important role in promoting the development of vehicle braking science and technology.
Research progress in modern vehicle brake science and technology:
(1) Energy saving and environmental protection of vehicle braking systems. Energy conservation and environmental protection are prerequisites for the development of automotive technology. The energy saving and environmental protection of the vehicle brake system includes the energy saving and environmental protection of the brake system itself, as well as the energy saving and environmental protection of the entire vehicle. Developed regenerative braking technology, fully utilizes recycled energy, saves energy; avoids dust pollution caused by brake friction, effectively suppresses brake noise pollution, and protects our living environment.
(2) The application of new materials in the brake system. Materials science and technology are the key areas of science and technology developed in the 21st century. The application of various new star materials in vehicle braking systems has been promoted, and will continue to promote the development of vehicle braking technology and performance. Gradient materials, polymer materials, nano materials, composite materials, etc., due to their own performance characteristics, will have a huge impact on the performance of the brake system. It can effectively extend the life of the brake system, improve braking performance (such as heat decay resistance), and eliminate noise pollution.
(3) Informatization and intelligence of vehicle braking. The intelligent and integrated vehicle braking is a combination of information technology, electronic integration technology and control technology and braking technology. Its characteristic is that according to the braking requirements and the working characteristics of the brake system, real-time control of the braking force is realized through computer intelligent control, which effectively improves the braking performance, safety, reliability and maintainability of the vehicle.
(4) High performance, low cost, small size and light weight of the vehicle brake device. Superior performance, precision, low noise, long life, light weight, small size and low cost have always been the development direction of braking technology. To achieve the above requirements, it is necessary to conduct research on the structural innovation of the brake system, explore new types of brake systems, conduct braking dynamics and vibration research to improve characteristics and reduce noise, and adopt advanced manufacturing techniques to improve the system. Dynamic performance and cost reduction; research on the materials and mechanisms of braking to improve life and reduce quality.
The development of vehicle brake science and technology has gone through a long period of time and has reached a high level in the century. Compared with foreign countries, our gap is relatively large. We need to track and digest foreign advanced technologies, grasp the new trends of development, increase basic investment, integrate resources, conduct in-depth research, strengthen application development, and strive to develop independent intellectual property rights.
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