Foreword
Car steering performance is one of the main performances of the car. The performance of the steering system directly affects the handling stability of the car. It is essential to ensure the safe driving of the vehicle, reduce traffic accidents, protect the driver's personal safety, and improve the driver's working conditions. Plays an important role. How to design the steering system reasonably so that the car has good handling performance is always an important research topic for designers. In today's high-speed vehicles, non-professional drivers, and intensive traffic flow, for more different levels of driving people, the design of the car's easy maneuverability is particularly important. The development of Steering – By-Wire System (SBW) is precisely to meet this objective demand. It is a new-generation steering system developed after EPS, which has the characteristics of better steering stability than EPS, and it no longer uses a mechanical connection between the steering wheel and the steering wheel, completely getting rid of the inherent limitations of the traditional steering system. While bringing convenience to the driver, it also improves the safety of the car.
1. Overview of the development of wire-controlled steering systems
In 1990, the German Mercedes-Benz Company began research on front-wheel steer-by-wire and applied the steer-by-wire system developed by it to the concept car F400Carving. Koyo of Japan has also developed a wire-controlled steering system, but in order to ensure the safety of the system, the mechanical part between the steering wheel and the steering wheel is still retained, that is, connected through the clutch, and when the wire-controlled steering fails, it returns to mechanical steering through the clutch combination. The BMWZ22 concept car of the BMW Motors Corporation, which uses SteerByWire technology, reduces the turning range of the steering wheel to 160 °, which greatly reduces the driver's busyness during emergency steering. The concept car "FILO" designed and developed by Bertone in Italy, the "C-Crosser" Citroen off-road vehicle, and the "R129" Daimlerchrysler concept car all use a steering by wire system. In 2003, Honda Japan launched the LexusHPX concept car at the New York International Auto Show. The car also uses a steering by wire system and integrates various control functions on the dashboard to achieve automatic control of the vehicle. It is estimated that in a few years, the mechanical system will be replaced by cables and electronic signals.
Second, the structure and working principle of the steering by wire system
(1) Structure of the steering by wire system
The car steering system by wire is mainly composed of a steering wheel module, a front wheel steering module, a main controller (ECU) and an automatic fail-safe system. Its structure is shown in Figure 1.
1. Steering wheel module
The steering wheel module includes a steering wheel assembly, a steering wheel angle sensor, a torque sensor, and a steering wheel return torque motor. Its main function 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, the main controller sends a control signal to the steering wheel positive torque motor to generate the steering wheel positive torque, In order to provide the driver with corresponding road sense information.
2. Front wheel steering module
The front wheel steering module includes a front wheel angle sensor, a steering execution motor, a motor controller, and front wheel steering components. Its function is to feed back the measured front wheel angle signal to the main controller, and accept the command of the main controller, control the steering wheel to complete the required front wheel angle, and realize the driver's steering intention.
3. The main controller
The main controller analyzes and processes the collected signals, discriminates the movement status of the car, sends commands to the steering wheel return torque motor and the steering motor, and controls the two motors to work in coordination. The main controller can also recognize the driver's operation instructions and determine whether the driver's steering operation is reasonable in the current state. When the car is in an unstable state or the driver issues a wrong command, the front-wheel steering system will automatically perform stability control or shield the driver ’s wrong steering operation, and drive the vehicle automatically in a reasonable way to restore the car to a stable state as soon as possible .
4. Automatic fail-safe system
The automatic fault prevention system is an important module of the wire-controlled steering system. It includes a series of monitoring and implementation algorithms to make corresponding treatments for different fault forms and fault levels in order to maintain the normal driving of the car to the maximum extent. Wire-controlled steering technology uses rigorous fault detection and processing logic to maximize vehicle safety performance.
(2) The working principle of the wire steering system
Its working process: After the information from the steering wheel sensor and the current state of various vehicles is sent to the electronic control subsystem, the computer is used to control the information, and then send commands to the vehicle steering subsystem to turn the vehicle. At the same time, the information given by the steering resistance sensor in the wheel steering subsystem is also transmitted to the components that simulate the road feel in the steering plate system via the electronic control subsystem. The principle is shown in Figure 2.
Because there is no mechanical connection between the steering wheel and the steering wheel in the steering system by wire, it is disconnected, and the necessary information is transmitted through the bus, so this system is also called a flexible steering system.
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