Research On Vehicle Steer-by-Wire System With Bilateral Control Method

The vehicle steering system is used to realize the driver manipulating intention andmake the road information feedback simultaneously, the performance of it plays animportant role in the whole vehicle’s handling stability and driving safety. The steer-by-wire(SBW) system takes the electronic means instead of the traditional mechanism to transmitcontrol signals. As the mechanical linkages between the steering wheel and the front wheelare removed in the SBW system, both of the angle transmission ratio and force transmissionratio can be designed freely, we can acquire much better steering performance throughmatching them reasonably. All the existing control methods of the SBW system control thefront wheel angle through the steering wheel, and the force feedback to the driver is achievedthrough estimating the tire’s reacting torque or by the vehicle’s status and the steering wheelangle, these control algorithms are complicated, when the tire suffers road impacts they willcause harms to the driver.This paper is based on the projects named Research on the joystick and the bilateralcontrol method for for X-By-Wire Vehicle (No.51105165)and Research on Controlmethods and Key Technology for X-By-Wire Vehicle (No.50775096) by National NaturalScience Foundation of China. The bilateral control method can resolve the problems existingin the current researches of SBW system effectively. This method is first applied in the robottele-manipulating field, as in some operating environment it’s difficult or dangerous forhuman to get close, human can manipulate the robot to accomplish these risky and complexoperations through the master control mechanism. Therefore, the robot acting as the slavecontrol mechanism can feed the environment information it has sensed back to the human,and human will have a real telepresence, that is helpful to improve the accuracy of themanipulations. Bringing the bilateral control mind into SBW system, we can take thesteering wheel module as the master control mechanism and regard the front wheel moduleas the slave control mechanism, thus the driver can feel the road conditions through the forceand position feedback between the two modules, and at the same time the front wheel willfinish the steering actions according to the driver’s commands.In this paper, a new bilateral control structure is proposed for the SBW system, torquedrive-angle feedback bilateral control structure with position gain and force gain, in whichthe driver’s input torque is used to drive the front wheel to rotate directly and the roadcondition is fed by the steering wheel following the steering gear pinion’s movement. In this method, the rotational resistance between the front wheel and the road is not needed toestimate or measure. It’s a new breakthrough for SBW system.As SBW system uses motors to achieve steering purpose and simulation of the roadcondition, the control strategies of the motors are needed to established. According to theproposed control structure, this paper uses the angle-speed-current three closed loop methodto control the steering wheel motor’s position, and uses the current closed loop to control thefront wheel motor’s torque.The characteristics of the force transmission ratio decides the vehicle’s force feedbackperformance, so how to design the force transmission ratio to be more suitable for the driveris an important mission for paper’s research. This paper adopts the curved line style todesign the force transmission ratio, combined with the model simulation debugging, thispaper proceeds with the design of force transmission ratio, to make the vehicle meet thedesired goals.The inertia, damp and friction characters of the two motors used in SBW system make agreat impact on the system’s return-to-center performance. In this situation, the steeringwheel will have residual angles at low speeds and the steering wheel will overshot at highspeeds. The strategies to make up the disadvantages are needed, this paper uses the pinion’sangle following its zero position to make the steering wheel to return to center.To validate the feasibility of above control strategies, this paper sets up the dynamicalmodels of SBW system and the whole vehicle with MATLAB/Simulink software to providethe simulation platform. To further verify the effects of the strategies used in the practicalapplication, this paper carries out real road tests under some related test conditions with xPCTarget technology. Step input of steering wheel angle condition, high speed and low speedreturn-to-center conditions, continuous sinusoidal input of steering wheel angle condition arecarried out in this paper to illustrate the proposed strategies.