Research On Tri-motor Control Method For Steering-by-wire Automobile

Wire-control technology mainly includes: steer-by-wire technology, brake-by-wire technology and throttle-by-wire technology. It canceled part of mechanical connection, collects vehicle state information based on electric-control technology, sensor detection technology and CAN technology etc., and then transforms the information into electrical signal and analyzes it. Meanwhile, the road information is fed back to driver, which optimizes driving performance and enhances the security. Steer-by-wire vehicle can optimize the ideal transmission ratio of steering system. The vehicle has high electronic integration. It would be applied widely in EV, FCV, HEV and LEV in the future.This paper includes the following content in the research of tri-motor steer-by-wire system.(1)Choose the steering gear and gear reducer of the tri-motor steer-by-wire system, choose parameters and types of the steering executive motor, power-assist motor and force-sense motor based on the basic function demand of steering system.(2)In the tri-motor steer-by-wire system, the entire vehicle model in Carsim is applied. And a tri-motor steering-by-wire system model is set up based on Simulink/Car Sim program. The system model includes the tyre model, steering wheel model, force-sense motor model, double-motor model of the power-assist motor and executive motor, torque sensor model, rack and pinion steering gear model.Simulate on the tri-motor steer-by-wire system and validate this model in condition of angel-step input and angel-sine input steering test. Validate the tracking ability and continuous tracking capability in center area of steering system. Discuss the compatibility security and reasonability of the steer-by-wire system.(3)This paper put forward the algorithm of force-motor current. The force-sense motor current and output torque are acquired after the executive motor current is dealt with by controller. The force sense is fed back to driver through steering wheel. A smoothing method is adopted to reduce shock coming from rough road to driver.(4)In this paper, the control strategy of the tri-motor steering-by-wire system consists of steering torque control strategy, force-sense control strategy, and parking directional strategy. The steering torque control strategy mainly applies a control method of linear power-assist characteristic, which is similar to the EPS system. Force-sense control strategy mainly lies in the simulation of real road power move. The output force depends on armature current of power-assist motor, which is controlled by the output signal of current sense of the steering executive motor. That provides the driver appropriate handle in the steering operation. Parking directional strategy mainly applies analysis and control of signal by the steer-by-wire system controller. That means judging the vehicle condition through speed value and engine flames first. Then the steering wheels return to their straight-ahead position automatically through steering by-wire after the vehicle stops.Finally, this paper summarizes and discusses the model and algorithm adopted. It also analyzes development of steer-by-wire system and prospect of tri-motor steer-by-wire system in the future vehicle industry.