Application and development trend of wire control

Application and development trend of automotive wire control technology

with the gradual maturity of automotive electronic technology and automatic control technology and the wide application of automotive network communication technology, automotive wire control technology has gradually been favored and deeply studied. It, together with 42V voltage system and network technology, affects the future development trend of automotive

automotive wire control technology is a system that converts the driver's control action into an electrical signal through the sensor and directly transmits it to the actuator through the cable. At present, the technology of control by wire includes shift by wire system, brake by wire system, suspension by wire system, boost by wire system, throttle by wire system and steering by wire system. Among them, steering by wire system is widely used in luxury cars, sports cars and concept cars, which provides a good platform for automatic driving; Brake by wire system is widely used in industrial vehicles. In the future, with the maturity of control by wire technology, the reduction of cost and the pursuit of automatic driving, control by wire technology will be more and more used in ordinary vehicles. This paper mainly introduces the automobile brake by wire system and steering by wire system

1 wire controlled braking system

wire controlled braking system (bbw, brake 2 by 2 wire) is currently divided into two types, one is electro-hydraulic braking system (EHB), the other is electro-mechanical braking system (EMB). EHB is a multi-purpose and multi form braking system formed by the combination of electronic and hydraulic systems. It is flexibly controlled by electronic systems and powered by hydraulic systems; EMB will completely replace the hydraulic oil or air and other force transmission media in the traditional braking system with electric braking, which is the development direction of the braking control system in the future

1.1 electro hydraulic braking system

in the traditional braking system of small and medium-sized vehicles, the driver establishes the braking pressure in the wheel cylinder through the brake master cylinder, while EHB provides the braking pressure through the accumulator. The accumulator pressure is generated by the plunger pump, which can provide multiple times of continuous braking pressure. EHB is composed of sensor, ECU and actuator (hydraulic control unit), and its structure is shown in Figure 1

there is no direct power transmission between the brake pedal and the brake. When braking, the braking force is controlled by ECU and actuator, and the pedal travel sensor transmits the signal to ECU. ECU collects various signals such as wheel speed sensor and steering sensor, calculates the maximum braking force of each wheel according to the vehicle driving state, and sends instructions to the accumulator of the actuator to implement the braking of each wheel. The high-pressure accumulator can quickly and accurately provide the braking pressure required by the wheel cylinder. At the same time, the control system can also accept the sensor signals of other electronic auxiliary systems (such as ABS, BAS, EBD, esp, etc.), so as to ensure the best deceleration and driving stability

compared with EMB, EHB has the following advantages: (1) it does not need additional space near the wheel brake, nor will it add additional weight. (2) In order to reduce energy consumption, the well-designed 14V power supply can fully meet the requirements. (3) In an emergency, the pressure of the brake master cylinder can also be directly applied to the two front wheels, so there is no need for a backup system. Therefore, at present, EHB is the first step to realize BBW. For heavy vehicles or industrial vehicles, only the hydraulic system can produce large braking torque to meet the braking requirements of large tonnage vehicles. (4) It can improve the performance of the system and the comfort of operators. The brake valve can be installed far away from the cab and closer to the brake to reduce pipeline consumption. The remote operation is easier without using more hydraulic valves and pipelines

1.2 electromechanical braking system

emb is mainly used in small vehicles, mainly including electric brake, ECU, wheel speed sensor, power supply, etc. The biggest difference between it and EHB is the torque provided by the braking force for the motor, rather than the high-pressure oil generated by the plunger pump, and there is an independent power supply to supply power. The functions of each part are shown in Table 1

compared with other traditional brake control systems, EMB has the following advantages: (1) the system structure is simple, eliminating a large number of pipeline systems and components; (2) The braking response time is short, which improves the braking performance; (3) The manufacturing, assembly and testing of the system are simple and fast, with modular structure and simple maintenance; (4) With wire connection, the system has good durability; (5) It is easy to improve and add various electric control functions with slight changes. However, compared with EHB, it still has the following problems to be solved: (1) drive power supply. At present, the 12V power supply system of the vehicle cannot provide such a large amount of energy, and high-quality 42V power supply is required. (2) Control system failure. Since there is no independent active backup braking system, a backup system is needed to ensure safety, which also increases the cost. (3) Anti interference problem. There will be various interference signals in the process of vehicle operation. How to eliminate the impact caused by these interference signals is an urgent problem to be solved

2 steering by wire system

steering by wire system (SBW, steering2by2w IRE) removes the mechanical connection between the steering wheel and the steering wheel, reduces the weight of about 5kg, eliminates the impact of the road, and has the advantages of reducing noise and vibration isolation. At present, famous foreign automobile companies and auto parts manufacturers are competing to study the new generation of intelligent steering system, such as Delphi company, TRW company, Nikki Mitsubishi company, Koyo company, Bosch Company, ZF company, BMW company, etc. in the United States are successively developing their own SBW system, and China has also begun to get involved in this related research field

sbw system is composed of steering wheel module, steering execution module and ecu3 main parts, as well as automatic fault prevention system, power supply and other auxiliary modules. Its structure is shown in Figure 2

steering wheel module includes steering wheel, steering wheel angle, torque sensor, steering wheel return torque motor. The main function of the steering wheel module is to convert the driver's steering intention (by measuring the steering wheel angle) into digital signals and transmit them to the main controller; At the same time, it receives the torque signal sent by ECU and generates the steering wheel return torque to provide the driver with the corresponding road feeling signal. The steering execution module includes front wheel angle sensor, steering execution motor, steering motor controller and front wheel steering components. The function of the steering execution module is to receive the command of ECU, control the steering motor to achieve the required front wheel angle and complete the driver's steering intention. ECU analyzes and processes the collected signals, judges the motion state of the vehicle, sends commands to the steering wheel positive force motor and steering motor, and controls the work of the two motors. The automatic fault prevention system is an important module of the steering by wire system. It includes a series of monitoring and implementation algorithms, which deal with different fault forms and levels in order to maintain the normal driving of the car to the greatest extent. Automobile safety is the first factor that must be considered and the basis of all research. Therefore, automatic fault detection and automatic processing is one of the most important components of steering by wire system

sbw's working principle is that when the steering wheel rotates, the steering sensor and steering angle sensor convert the measured driver torque and steering wheel angle into electrical signals and input them to EC2. The filled in experimental parameter u, ECU controls the rotation direction of the torque feedback motor according to the signals of the vehicle speed sensor and the displacement sensor installed on the steering transmission mechanism, and generates feedback torque according to the steering force simulation, Control the rotation direction, torque and rotation angle of the steering motor, and control the steering position of the steering wheel through the mechanical steering device, so that the vehicle can calculate the fracture toughness K1C along the maximum load that can generally fracture instead of the load at the cracking point, and drive along the track expected by the driver

3 key technology of control by wire system

because the control by wire system cancels the traditional pneumatic, hydraulic and mechanical connections and replaces the sensors, ECUs and electromagnetic actuators, the accuracy of sensors, the reliability and anti-interference of ECU Hardware, the reliability and fault tolerance of control algorithm, the rapidity and reliability of actuators and the real-time communication between ECUs of different systems, The fault tolerance, arbitration ability and power supply of bus restrict the wide application of wire control technology. The key technologies that restrict the wire control technology include the following aspects

(1) sensor technology. Sensors are the basic and important units of the control by wire system. Whether EHB, EMB, or SBW, they are composed of many sensors. For example, SBW system is composed of angular displacement sensor, torque sensor, vehicle speed sensor, lateral acceleration sensor, yaw rate sensor, etc., which constitute the main part of SBW. However, the control effect of the automotive electronic control system is closely dependent on the information collection and feedback accuracy of the sensor, so the scientific and technological content of the sensor directly affects the performance of the entire automotive electronic control system. How to manufacture sensors with small volume, low cost, high reliability and high measurement accuracy has become one of the key technologies of the wire control system

(2) bus technology. How the ECU of each automotive electronic system communicates information and how each system integrates depends largely on the bus technology. At present, there are many automobile bus standards, and some bus standards and protocols with high-speed real-time transmission characteristics will be used in the future. This kind of bus standards mainly include time triggered protocol (TTP), byteflight and FlexRay. TTP is a complete communication protocol applied to distributed real-time control system, which can support a variety of fault-tolerant strategies and has the functions of node recovery and re integration; Byteflight of BMW company can be used for the network communication of automotive wire control system. Its characteristics are that it can not only meet the requirements that some high priority messages need time trigger to ensure the determination of delay, but also meet the requirements that some messages need event trigger and interrupt processing; FlexRay is a network communication system especially suitable for the next generation of automotive applications. It has fault-tolerant function and determined message transmission time, and can meet the high-speed communication requirements of automotive control systems

(3) power supply technology. In EHB system, because the braking torque is provided by hydraulic pressure, the well-designed 14V voltage can meet the requirements; In the EMB system, because the braking torque is directly provided by the motor, the required power supply power increases, and increasing the voltage is a good way to increase the power, so the traditional 14V system can no longer meet the requirements; In the SBW system, ECU, two redundant torque feedback motors and two redundant steering motors have a total power of about 550 ~ 880W, and the required power energy is quite large. How to provide enough power to ensure the stable operation of the system has become the key to solve the problem. The research of 42V voltage system and the in-depth research of electric vehicles provide a platform for the solution of this technology, and lay a foundation for the wide application of wire control technology

(4) fault tolerant control technology. In order to meet the requirements of vehicle reliability and safety, fault-tolerant control technology must be adopted in the control by wire system. There are two fault-tolerant control design methods: hardware redundancy method and analytical redundancy method. Hardware redundancy method is mainly to provide backup for important components and fault prone components to improve the fault-tolerant performance of the system; The analytical redundancy method is mainly to improve the redundancy of the whole system by designing the software with stable requirements for lithium cathode materials such as high nickel in the controller, so as to improve the fault-tolerant performance of the system. In SBW system, compared with ECU, sensors and actuators are more prone to failure, and there are some problems between some sensors and actuators