Oscillation in Electric Power Steering Test Torque Due to Universal Joint Angle and Control Strategy

Abstract

To perform torque load test on an active EPS (electric power steering) system, the EPS column is required to make a userdefined angular displacement under a userdefined test load applied at the end of the pinion shaft. As universal joints are used in the EPS system for spatial arrangement, the angular velocity and torque on the driven shaft vary twice from those on the driving shaft in one rotation circle. This introduces a fluctuation in the velocity and torque on the driven shaft at a frequency twice that of the shaft rotation. The angular acceleration of the pinion shaft exerts on the coupling an inertia load which prevents the required load from precise transmission. To eliminate the oscillatory deviation in the test load applied at a target position in a multibody rotation system while not changing the shafts axes angle arrangement, a control strategy based on a proportional integral derivative controller (PID) with compensation using rotary acceleration feedback, newly developed for torque control, is discussed in this paper. The load control at a target point is achieved by modifying the torque input with a compensation signal to cancel out the oscillatory deviation in the test load.