Analysis and Application of Automotive Wire Control Technology
With the gradual maturity of automotive electronic technology, automatic control technology and the extensive application of automotive network communication technology, automotive wire control technology has gradually been favored and in-depth research, it and the 42V voltage system and network technology will influence the future development trend of the car.
The car line control technology is a system that converts the driver's manipulation motion into an electrical signal through a sensor and directly transmits it to the actuator through a cable. Current wire control technologies include wire-controlled shifting systems, line control systems, line-controlled suspension systems, line-controlled boost systems, line-controlled throttle systems, and line-controlled steering systems. Among them, the steer-by-wire system has a wide range of applications in high-class cars, sports cars and concept cars. It provides a good platform for autonomous driving. The line-controlled system is widely used in industrial vehicles. In the future, with the maturity of wire-controlled technology. With the reduction of costs and the pursuit of the impact of autonomous driving, wire-controlled technology will be increasingly used in ordinary vehicles. This article mainly introduces the car line control system and the wire-controlled steering system.
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1-wire control system
Line control system (BBW, Brake 2 By 2 Wire), currently divided into two categories, one is electro-hydraulic brake system (EHB, Electro2Hy2draulic Brake), and the other is electro-mechanical brake system (EMB, Electro2Mechanical Brake ). EHB is a multi-purpose, multi-form brake system that combines electronic and hydraulic systems. It is flexibly controlled by an electronic system that provides power. The EMB transmits hydraulic oil or air from a conventional brake system. The force medium is completely replaced by electric brakes, which is the development direction of the future brake control system.
1.1 Electro-hydraulic brake system
In the traditional braking system of small and medium-sized vehicles, the driver establishes the brake pressure in the wheel cylinder through the brake master cylinder, while the EHB provides the brake pressure through the accumulator. The accumulator pressure is generated by a plunger pump that provides multiple consecutive brake pressures. The EHB is composed of a sensor, an ECU, an actuator (hydraulic control unit), and the like, and its structure is as shown in FIG.
There is no direct power transfer between the brake pedal and the brake. When braking, the braking force is controlled by the ECU and the actuator, and the pedal stroke sensor transmits a signal to the ECU. The ECU collects various signals such as the wheel speed sensor and the steering sensor, and calculates the maximum braking force of each wheel according to the running state of the vehicle, and An accumulator is issued to the actuator to perform braking of each wheel. The high pressure accumulator provides the brake pressure required for the wheel cylinders quickly and accurately. At the same time, the control system can also accept sensor signals from other electronic auxiliary systems (such as ABS, BAS, EBD, ESP, etc.) to ensure optimal deceleration and driving stability.
Compared with EMB, EHB has the following advantages: (1) no additional space near the wheel brake is required, and no additional weight is added. (2) In order to reduce energy consumption, a 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, thus eliminating the need for a backup system. Therefore, for the time being, EHB is the first step to realize BBW. For heavy vehicles or industrial vehicles, only the hydraulic system can generate a 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 the operator. The brake valve can be mounted closer to the brakes away from the cab to reduce pipe consumption. Remote operation is easier without the need for more hydraulic valves and piping.
1.2 Electromechanical brake system
EMB is mainly used in small vehicles, mainly including electric brakes, ECUs, wheel speed sensors, power supplies, etc. The biggest difference between it and EHB is that the braking force is the torque provided by the motor, not the high-pressure oil generated by the plunger pump, and there is a separate power source to supply the 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 piping systems and components; (2) Short braking response time and improved braking performance; (3) System It is simple and quick to manufacture, assemble and test. It adopts modular structure and is easy to maintain. (4) It adopts wire connection, and the system has good durability; (5) It is easy to improve, and various electrical control functions can be added with slight changes. However, compared with EHB, it still has the following problems to be solved: (1) drive power problem. At present, the vehicle's 12V power system cannot provide such a large amount of energy, and a high-quality 42V power supply is required. (2) Control system failure. Since there is no independent active backup braking system, in order to ensure safety, a backup system is required, which also increases the cost. (3) Anti-interference problem. There are various interference signals during the operation of the vehicle. How to eliminate the impact caused by these interference signals is an urgent problem to be solved.
2 remote steering system
The steer-by-wire system (SBW, Steering2By2W ire) removes the mechanical connection between the steering wheel and the steering wheel, reducing the weight of approximately 5kg, eliminating the impact of the road surface, and reducing noise and vibration isolation. At present, famous foreign automobile companies and auto parts manufacturers are competing to research intelligent new-generation steering systems, such as Delphi, TRW, Rimu Mitsubishi, Koyo, Bosch, ZF, and BMW. The development of their respective SBW systems has also begun to get involved in this related research field.
The SBW system consists of three main parts: the steering wheel module, the steering execution module and the ECU, as well as auxiliary modules such as fail-safe systems and power supplies.
The steering wheel module includes a steering wheel, a steering wheel angle, a torque sensor, and a steering wheel returning positive 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 a digital signal and transmit it to the main controller. At the same time, it receives the torque signal from the ECU and generates the steering wheel return torque to provide the driver with the corresponding Road signal. The steering execution module includes a front wheel angle sensor, a steering execution motor, a steering motor controller, and a front wheel steering assembly. The function of the steering execution module is to accept the command of the ECU, control the steering motor to achieve the required front wheel angle, and complete the driver's steering intention. The ECU analyzes and processes the collected signals to determine the motion state of the vehicle, and sends commands to the steering wheel to return to the positive force motor and the steering motor to control the operation of the two motors. The fail-safe system is an important module of the line-controlled steering system. It includes a series of monitoring and implementation algorithms to deal with different fault forms and levels to maximize the normal driving of the car. The safety of the car is the first factor to be considered, and it is the basis of all research. Therefore, the automatic detection and automatic processing of the fault is one of the most important components of the wire-steering steering system.
The working principle of the SBW is that when the steering wheel rotates, the steering sensor and the steering angle sensor convert the measured driver torque and the steering wheel angle into electric signals input to the ECU, and the ECU is based on the vehicle speed sensor and the steering gear. The signal of the displacement sensor controls the rotation direction of the torque feedback motor, and generates a feedback torque according to the steering force simulation, controls the rotation direction, the torque magnitude and the rotation angle of the steering motor, and controls the steering position of the steering wheel through the mechanical steering device. The car is driven along the trajectory desired by the driver.
3 key technologies of the line control system
Since the line control system eliminates the traditional pneumatic, hydraulic and mechanical connections, it is replaced by sensors, ECUs, and electromagnetic actuators. The accuracy of the sensor, the reliability of the ECU hardware, the anti-interference, the reliability of the control algorithm, and the fault tolerance. The rapidity and reliability of the actuator and the real-time communication between different system ECUs, the fault tolerance and arbitration capability of the bus and the power supply all restrict the wide application of the line control technology. The key technologies that restrict wire control technology include the following aspects.
(1) Sensor technology. The sensor is a basic and important unit that constitutes the line control system. EHB, EMB, or SBW are composed of many sensors. For example, the SBW system consists of an angular displacement sensor, a torque sensor, a vehicle speed sensor, a lateral acceleration sensor, and a yaw. They are composed of angular velocity sensors and they form the main part of the SBW. The control effect of the automotive electronic control system is closely dependent on the information acquisition and feedback accuracy of the sensor, so the technological content of the sensor directly affects the performance of the entire automotive electronic control system. How to make a sensor with small size, 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 ECUs of the various electronic systems of the car conduct information communication and how the systems are integrated depends largely on the bus technology. There are a variety of automotive bus standards currently in place, and some bus standards and protocols with high-speed real-time transmission characteristics will be used in the future. This type of bus standard mainly includes Time Trigger Protocol (TTP), Byteflight and FlexRay. TTP is a complete communication protocol for distributed real-time control systems. It can support multiple fault-tolerant strategies with node recovery and re-integration functions. BMW's Byteflight can be used for network communication of automotive line control systems. Meeting certain high-priority messages requires time triggering to ensure that latency requirements are met, and that certain messages require event triggering and interrupt processing requirements; FlexRay is a network communication system that is particularly suitable for next-generation automotive applications. Fault-tolerant functions and deterministic message transmission times meet the high-rate communication requirements of automotive control systems.
(3) Power supply technology. In the EHB system, since the braking torque is supplied by hydraulic pressure, a well-designed 14V voltage can meet the requirements; in the EMB system, since the braking torque is directly supplied by the motor, the required power supply is increased, and the voltage is increased. A good way to increase power, so the traditional 14V system can no longer meet the requirements well; in the SBW system, the ECU, two redundant torque feedback motors and two redundant steering motors have a total power of about 550. ~880W, the required power energy is quite large. How to provide enough power to ensure the stable operation of the system becomes the key to solve the problem. The research of 42V voltage system and the in-depth study of electric vehicle provide a platform for the solution of this technology, which lays 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, the line control system must adopt fault-tolerant control technology. The fault-tolerant control design method includes hardware redundancy method and analytical redundancy method. The hardware redundancy method mainly improves the fault tolerance performance of the system by providing backup for important components and faulty components. The method of analyzing redundancy is mainly to improve the redundancy of the whole system by designing the software of the controller, thereby improving the system. Fault tolerance performance. In the SBW system, sensors and actuators are more prone to failure than ECUs. There are redundancy between some sensors and actuators. Redundancy is the basis for fault-tolerant control. Once a component fails, redundant relationships are available. Other components replace the faulty components to eliminate malfunctions. The reliability of the ECU is relatively high for the relative sensors and actuators, but once the ECU fails, the consequences are more serious and the system cannot perform any operations. Based on the fault-tolerant control technology of the SBW system, the fault-tolerant control technology improves the reliability of the steering system and ensures the normal driving and safety of the vehicle without affecting the system control function. Reliability and security are one of the main bottlenecks restricting the application of SBW systems. When the reliability and safety of the SBW system can reach the level of the ordinary power steering system, its industrialization is just around the corner.
4 Development of line control technology
On wheeled industrial vehicles, line control systems, especially EHB, are widely used. The use of the line control system on industrial vehicles solves the shortcomings of the brake or liquefaction system of the pneumatic or gas-liquid brake system, the need to additionally add a pneumatic system, large volume, large weight and large structure, and easy to cause exhaust pollution. Ensure the safety of the vehicle. And the system can provide flexible control, forming a variety of forms of multi-purpose braking systems such as remote line control, anti-lock braking and traction control, etc. These systems that can improve industrial vehicle control are widely used.
The hybrid line control system is a new type of brake system introduced by Delphi, which is mainly used in passenger cars, SUVs and light vehicles. This system will become an important basis for the electronically controlled electric brake wire control technology, which replaces the traditional rear wheel hydraulic brake caliper with the rear wheel electric brake caliper and integrates with the electric parking brake, while the traditional hydraulic The brake caliper/vacuum booster is still applied to the front wheel brake, and its structure is shown in Figure 3.
This hybrid brake system enables the on-board anti-lock braking system, traction control system, and vehicle stability control system to function better, providing better brake handling and better response. Moreover, the system will provide new functions such as electric parking brakes, uphill anti-skid, vehicle start-up assistance, and vehicle downhill driving. This new technology will simplify the component composition of the vehicle and provide greater freedom in the layout of the interior space. The rear-wheel electric brake caliper of the system is integrated with a DC motor and a mechanical shifting transmission, and its outer shape is only slightly larger than that of a conventional hydraulic brake caliper. The "smart" rear-wheel electric brake caliper is controlled by an embedded microprocessor to provide fast and smooth operation and "fault-tolerant control" performance for rear-wheel brakes.
5 Conclusion
Due to the reliability of the line control system, fault tolerance technology, production cost, sensor accuracy, battery voltage and power, the line control system can only be applied in a small range. However, with the reduction of the cost of electronic products, the gradual improvement of chassis control technology, the increasingly strong requirements for energy conservation, environmental protection and safety of automobile development, and the extensive and in-depth study of new types of vehicles such as hybrid electric vehicles, fuel cell electric vehicles and pure electric vehicles. The application of wire control technology in ordinary vehicles will become a reality.
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