Four-wheel steering system structure and working principle

2.1.4 WS system composition

With the technological breakthroughs in information technology, integrated circuits, and microelectronics since the end of the 20th century, automotive electronic control technologies based on these technologies have gradually matured. The development and maturity of the 4WS system is also based on the progress of automotive electronic control technology. The 4WS system uses electronic control technology and motor assist technology for the control of the vehicle's four wheels and the steering distribution of the front and rear wheels. Since the steering methods of the front and rear wheels of the vehicle are different at different speeds during the vehicle's four-wheel steering process, the 4WS structure is relatively independent in the four-wheel steering control, and there is no mechanical connection between the front and rear wheel steering systems of the vehicle, so it can ensure that the steering performance can maintain a high level when the system is operating normally.

The vehicle steering mechanism, ECU, reducer, motor, sensor and other parts together constitute the 4WS system and realize the effective control of the vehicle's four-wheel steering. The electronic control technology is deeply involved in the process of the vehicle's rear wheels participating in the steering, helping the vehicle's rear wheels to perform the correct steering work, meet the normal driving of the vehicle and improve the vehicle's steering performance.

2.2 Working principle of electronically controlled 4WS system

ECU is an electronic control unit, often figuratively referred to as a "driving computer". ECU is a unit in the vehicle's electronic control system that performs analysis and calculations and outputs control signals to corresponding components. In the 4WS system, ECU also undertakes the analysis and calculation of the UI vehicle's motion signal. When the vehicle performs four-wheel steering, the sensor located at the front wheel of the vehicle transmits the steering signal of the front wheel of the vehicle and the vehicle's motion state to the ECU. After the ECU processes, analyzes, and calculates the model, it generates a drive signal to the stepper motor. The stepper motor performs corresponding actions according to the drive signal to act on the vehicle's rear wheel steering mechanism, and controls the steering of the rear wheel through this way. In this process, ECU still monitors the vehicle's motion state throughout the entire process and in real time, calculates the difference between the vehicle's rear wheel steering angle and the target steering angle, and adjusts the rear wheel's steering angle in real time according to the calculation results. Such real-time adjustment is consistent with the vehicle's actual motion state, realizing the four-wheel steering of the vehicle.

The electronically controlled 4WS system is set with two steering modes for the driver to choose from. The driver can choose the traditional 2WS mode through the steering mode switch or continue driving in the 4WS state. Setting these two steering modes not only provides the driver with more choices according to the actual road conditions, but also allows the driver to retain the traditional front-wheel steering setting when the 4WS system fails and cannot perform four-wheel steering normally, ensuring the safety of vehicle operation and the personal safety of drivers and passengers. When the 4WS system fails, the 4WS fault indicator light appears on the dashboard of the cab, reminding the driver that the 4WS system has failed and the vehicle's four-wheel steering system cannot operate normally. The ECU that detects the vehicle's operating status records the fault information in real time, which is convenient for technicians to check the code during fault detection and maintenance.

The above-mentioned 4WS system that can realize the same-phase and opposite-phase steering of the front and rear wheels of the vehicle belongs to an electronic electric four-wheel steering system. The rear-wheel steering device of this system is controlled by the vehicle speed, that is, the deflection angle and direction of the rear wheels of the vehicle are changed according to the size of the vehicle speed, and the change of the rear wheel deflection angle and direction is also a response to the change of the front wheel steering angle and yaw rate. The four-wheel steering control strategy of the vehicle at different speeds is set in the ECU, and the steering of the front and rear wheels is controlled according to the program when the vehicle is at high speed or low speed. When the ECU receives the signal of the high-speed driving state of the vehicle sent by the sensor or the signal of the small angle rotation of the steering wheel, the ECU controls the front and rear wheels of the vehicle to steer in the same phase according to the control strategy program, reduces the yaw rate of the vehicle, reduces the dynamic side deviation of the vehicle body, and helps the vehicle maintain the stability of handling when driving at high speed. When the ECU receives a low-speed driving state or a large-angle steering wheel rotation signal from the sensor, the ECU adopts the control strategy for low-speed operation, and the program controls the front and rear wheels to achieve counter-phase steering. The vehicle's front wheel turning angle increases while the rear wheel deflection angle increases, helping the vehicle driver to easily control the low-speed vehicle to turn, and reducing the vehicle's turning radius at low speed, thereby improving the vehicle's flexibility.