Research On Yaw Rate Control Methold For In-wheel-motor-driven Electric Vehicles

In recent years, the research on electric vehicles(EVs) becomes more andmore popular in the domestic and foreign automobiles field, especially thoseactive safety technology on electric vehicles which is directly related to people’slives and property has become a top priority. As a vehicle active safety device,the Electronic Stability Control System(ESC) in electric vehicles has a coreproblem which is vehicle yaw stability control. Therefore, focusing on the yawstability control problem of in-wheel-motor-driven electric vehicles, this paperwill mainly research on the yaw rate control methods.Firstly, this article simply analyzes electric vehicle nonlinear dynamiccharacteristics, which includes vehicle dynamics and wheel dynamics and tirenonlinear model. Then these models are simplified appropriately under certainassumptions. At the same time the Ackermann-Jeantand model is used to analyzefront wheel slip ratio constraints determined by front left and right wheel speeddifference. Lastly a yaw rate control model with wheel slip ratio constraints forfront wheel hub-motor-driven electric vehicles is established.Secondly, this paper analyzes and discusses the calculation of desired yawrate on basis of Two Degrees of Freedom(2-DoF) linear vehicle model and thecauses of vehicle steering instability. Then the slip ratio equality constraint isapproximately converted into slip ratio expected value programming. Forrealizing vehicle yaw rate tracking control, the sliding mode controllers whichadjust the motor drive torque at each front wheel based on vehicle states aredesigned based on the depicted control problem. Meanwhile, this paper improvesthe sliding mode controller for eliminating sliding mode chattering as well ashandling with the special situation that the denominator of controller outputvariable is approximately equal to zero.Finally, An existing veDYNA simulation model which is analyzed andappropriately modified in this essay meets the simulation requirements ofin-wheel-motor-driven electric vehicles, which is verified by the drive torqueinput open-loop control simulation analysis. Then the improved veDYNA modelis used to conduct a Lane Change Test for some closed-loop control simulation analyses. Last, veDYNA simulation results have indicated the proposed controlmethod in this paper can achieve satisfactory performance for vehicle yaw ratetracking its desired value and meanwhile improve vehicle handling stability foractive safety.