Interpreting the Development Status and Trends of Brake Systems
Since the birth of automobiles, vehicle braking systems have played a crucial role in the safety of vehicles. In recent years, with the advancement of vehicle technology and the improvement of vehicle driving speed, this importance has become increasingly apparent. There are many types and forms of automotive braking systems. The traditional structural types of braking systems mainly include mechanical, pneumatic, hydraulic, and pneumatic hydraulic hybrid. Their working principles are basically the same, using braking devices to gradually consume the kinetic energy of the vehicle using the frictional heat generated during operation, in order to achieve the goal of braking and deceleration or stopping the vehicle. With the research and development of energy-saving and clean energy vehicles, the automotive power system has undergone significant changes, with many new structural and functional forms emerging. The emergence of new power systems also requires corresponding changes in the structural and functional forms of braking systems. For example, electric vehicles do not have an internal combustion engine and cannot provide a vacuum source for vacuum boosters. One solution is to use an electric vacuum pump to provide vacuum for the vacuum booster.
The development of automotive braking systems is closely related to the improvement of automotive performance and changes in automotive structural types, and each component of the braking system has undergone significant changes.
1. Composition of Automobile Braking System
The braking system mainly consists of the following four parts:
(1) Energy supply device: that is, braking energy, including the energy required for supplying and regulating braking, as well as various components. The part that generates braking energy is called braking energy;
(2) Control device: including components that generate braking action and control braking effect;
(3) Transmission device: including various components that transmit braking energy to the brake;
(4) Brake: A component that generates forces that hinder the movement or trend of a vehicle, including components in an auxiliary braking system. Modern braking systems also include auxiliary devices such as brake force adjustment devices, alarm devices, and pressure protection devices.
1.1 Development of Energy Supply Devices
The energy supply device mainly refers to braking energy, which includes manual braking, servo braking, power braking, or a combination of the above two.
Human braking is the braking energy source at the beginning of the braking system, which has two forms: mechanical braking and hydraulic braking.
Mechanical braking is mainly used in the parking brake system, which requires the use of mechanical locking methods to ensure that the car stops in place and does not slide under any circumstances.
Hydraulic braking is achieved by pushing the brake master cylinder through the brake pedal, which in turn puts the brake into a working state.
Servo braking uses both manpower and engine as braking energy. Under normal circumstances, braking energy is supplied by the power servo system. When the power servo system fails, braking energy can be supplied by manpower. At this time, servo braking becomes manual braking. Servo braking can use air pressure energy, vacuum energy (negative air pressure energy), and hydraulic energy as servo energy to form various forms of boosters.
The braking energy of the power braking system is the oil pump or air pump driven by the engine, and manpower is only used as the control source, which can be divided into pneumatic braking, pneumatic hydraulic braking, and hydraulic braking. Among them, pneumatic braking is the earliest developed power braking system. It uses an air compressor to provide air pressure, and pneumatic hydraulic braking uses air pressure to push hydraulic action, producing a braking effect.
Hydraulic braking is a widely used braking system with mature technology. The current development of electro-hydraulic composite braking and electronic braking uses electric motors as the braking energy source, and manual stepping on the brake pedal as the control source.
1.2 Development of Control Devices
The earliest manual braking was achieved through mechanical connections to generate braking action. Developed to manual control of braking, the brake pedal is pressed to initiate braking, and then the power transmission device transmits the brake pedal force to the vacuum booster. After the vacuum booster's assistance is expanded, it is transmitted to the brake master cylinder to generate hydraulic pressure, and then the hydraulic pressure is transmitted to each wheel cylinder through the oil circuit to start braking. With the research and application of clean energy vehicles and electric vehicles, as well as the widespread application of electronic technology in automobiles, the control devices of braking systems have also shown an electronic trend. Electric braking completely changes the control and management of the braking system, which will revolutionize the braking system of automobiles. It adopts electronic control, which can achieve braking more accurately and efficiently.
1.3 Development of transmission devices
In the era of manual braking, mechanical transmission devices were used, and pneumatic (hydraulic) pressure was used to transmit braking force to the brake through pneumatic (hydraulic) pressure and connecting pipelines. Electronic braking uses the braking motor to generate braking force and directly apply it to the brake. Its control signal comes from the control unit (ECU), and the braking signal and braking force information are transmitted through signal lines.
1.4 Development of brakes
Brakes are the main component of braking. Currently, automotive brakes are mostly friction brakes, which are divided into two categories based on the different rotating components in the friction pair: drum and disc brakes.
Drum brakes also have structural types such as leading and trailing shoe type, double leading shoe type, bidirectional double leading shoe type, double following shoe type, unidirectional self increasing force type, bidirectional self increasing force type brakes, etc. The disc brake has fixed caliper and floating caliper. The floating caliper includes sliding caliper and swinging caliper. Sliding caliper is a widely used disc brake. Because the disc brake has better thermal and water stability, anti attenuation performance, reliability and safety than the drum brake, it is widely used. However, the disk brake has low efficiency and cannot completely prevent dust and rust. When it is used as a parking brake, it needs a more complex hand drive mechanism, so its application on the rear wheels is limited. Many vehicles use the brake system composed of front disc and rear drum. Electric motors with regenerative braking capabilities in electric and hybrid vehicles play a braking role in recovering braking energy, introducing new types of brakes. As a new type of brake, it is bound to cause a change in the brake type. The electric braking system brake is based on traditional brakes, which are also divided into disc electric brakes and drum electric brakes. Due to the disadvantages of large braking heat attenuation, drum electric brakes will be mainly used in cars in the future.
2. Development Trends of Brake Systems
The hydraulic braking system, which has been widely used, is now a very mature technology. With the improvement of people's requirements for braking performance, functions such as anti lock braking system, drive anti slip control system, electronic stability control program, and active collision avoidance technology are gradually integrated into the braking system. Many additional devices need to be added to the braking system to achieve these functions, which makes the structure of the braking system complex, The possibility of hydraulic circuit leakage and the difficulty of assembly and maintenance have been increased. The brake system requires a simpler structure, more comprehensive and reliable functions, and the management of the brake system has become a necessary issue to face. The application of electronic technology is the trend.
From the development process of the four components of the braking system, namely the energy supply device, control device, transmission device, and brake, it can be seen that they have all achieved electronicity to varying degrees. As a control energy source, humans activate the braking system and initiate braking attempts; The braking energy comes from storage batteries or other energy supply devices; Adopting a brand new electronic brake and a centralized electronic control unit (ECU) for overall control of the braking system, each brake has its own control unit. The mechanical connection gradually decreases, and the power transmission between the brake pedal and the brake is separated. Instead, it is connected by wires, which transmit energy and data cables transmit signals. Therefore, this type of braking is also called wire controlled braking. This is another leap in the development of braking systems since ABS has been widely used in automobiles.
The electro-hydraulic composite braking system is an effective transition plan from traditional braking to electronic braking, using two types of braking systems: hydraulic braking and electric braking. This braking system not only applies traditional hydraulic braking systems to ensure sufficient braking efficiency and safety, but also utilizes regenerative braking motors to recover braking energy and provide braking torque, improving the fuel economy of the vehicle, while reducing emissions and pollution. However, due to the simultaneous existence of two brake systems, the structure is complex and the cost is relatively high. The complexity of the structure also increases the likelihood of system failure and failure, making maintenance and upkeep more difficult.
Advantages, disadvantages, and existing problems of electric braking
Electronic braking was first applied to aircraft and is currently in the research and improvement stage of being applied to the automotive field. With technological progress, various problems will gradually be solved, and the electric braking system will eventually replace the traditional hydraulic braking control system and the electro-hydraulic composite braking system. Electric braking or brake by wire (BBW) is the direction of future brake system development. The electric brake and electric brake control unit, as well as the braking force simulator, are important components of it, and the feedback braking force generates a braking sensation for the brake pedal. A possible structural form of electric braking. Structurally, electric braking has advantages that cannot be compared to other traditional braking methods:
1) The structure is simple, and the system mass is much lower than that of traditional braking systems, thereby reducing the overall vehicle mass;
2) Short braking response time, improving braking performance and shortening braking distance;
3) There is no brake fluid in the system, which is easy and simple to maintain. It is connected by wires and has good durability performance;
4) The manufacturing, assembly, debugging, and calibration of the system assembly are faster and easier to adopt modular structures;
5) We have developed network communication protocols with fault-tolerant capabilities suitable for automobiles, such as TTP/C, Flex Ray, etc., which can be applied to electric braking systems.
6) Easy to improve and add functionality, it can be integrated into the automotive CAN communication network for centralized management and information sharing.
For most people, the electric braking system is a brand new braking system that provides conditions for future intelligent vehicles. Based on current technical conditions, there are still many issues to be faced in order to fully apply electric braking:
1) The problem of driving energy is that electronic braking requires more electric energy. A disk brake peak requires 1kW of driving energy. At present, the 12V vehicle power system cannot provide such a large amount of energy. In the future, the vehicle power system needs to use high-voltage power to increase energy supply to meet the energy demand of each system, and solve the safety problem of high-voltage power;
2) When not considering the braking system, it is necessary to consider the issue of braking system failure. Electric braking does not have an active backup braking system, whether it is ECU, sensor, brake itself, or wiring harness failure, which can ensure the basic performance of the braking system. In addition to ECU being able to adopt redundant design, a key technology to achieve electric braking is the research and application of information exchange protocols such as TTP/C when the same failure occurs;
3) The integration with other control systems of the automotive chassis still needs to be studied;
4) After using electric braking, the overall mass of the vehicle may decrease, but the unsprung mass may increase, which should be noted;
5) Brakes generate high temperatures during continuous or high-intensity braking, which places high demands on the performance and heat dissipation of motors and transmission devices.
6) The cost is higher than the original hydraulic braking system, and improving the cost-effectiveness of the electric braking system is a problem that needs to be solved.
With the advancement of technology, the various problems mentioned above will gradually be solved.
Driven by the trend of modularization, integration, electronics, and high voltage of vehicle energy supply, vehicle braking systems are also developing in the direction of electronics. Many automobile and component manufacturers have conducted research and promotion of electric braking systems, which will inevitably replace traditional braking systems. The further integration and integration of automobile chassis will lead to a qualitative leap in braking system performance.