Research On EPS Control Strategy Considering Road Adhesion Coefficient

With the development of science and technology, the traditional mechanical steering system and hydraulic steering system have been replaced by electric power steering system. Since EPS has good steering performance and return positive performance, more and more vehicles fitted EPS, EPS performance gradually improved. The traditional EPS control strategy can basically meet the requirements of the vehicle in the conventional road, but it is difficult to meet the requirements of the low road adhesion coefficient on the road. This paper presents a control strategy considering the road adhesion coefficient based on the estimation of road surface adhesion coefficient based on the steering wheel torque signal,, and the hardware in the loop test is verified.First of all, the combined simulation model based on Simulink and CarSim is built in this paper. The EPS system is divided into torsion bar spring module, power assisted curve module and power assisted motor module for system modeling to analysis of steering of the vehicle motion state. Where the Simulink module is used to establish the EPS model, the steering system in CarSim is set a purely mechanical steering system, and use Simulink model to replace it.Secondly, this paper use the torque sensor on the EPS to estimate the total align torque of the left and right steering wheel, and verify the model based on the combined simulation model. This paper analyze the state about align torque of the steering wheel from pneumatic drag based on co-simulation model, and the composition and the generation of the align torque of the tire are described in detail. This paper use characteristic of steering wheel torque is in the linear region in the vehicle steering to estimate align torque of the steering wheel from pneumatic drag based on total align torque estimation of the left and right steering wheel.Again, this paper use iterative method and the derivative method to estimate the road friction coefficient based on align torque of the steering wheel from pneumatic drag estimation of the left and right steering wheel. The traditional EPS control strategy is introduced in detail in this chapter, and the shortcomings of the traditional EPS control strategy on the road with low adhesion coefficient are analyzed. On the basis of the accurate estimation of the road adhesion coefficient, the EPS control strategy considering the road adhesion coefficient is proposed.Finally, this paper use CarSim with 27 degrees of freedom vehicle model, Lab VIEW with sending and collecting the signal, servo motor system with simulating steering resistance moment to establish EPS hardware in the loop test bench. And the EPS control strategy based on the estimation of the road adhesion coefficient is carried out on the test bench.