Model Based Control to Decouple Electric Steering Feel and Loop Gain

Paper #:
  • 2017-01-1571

Published:
  • 2017-03-28
Abstract:
An approach to electric steering control is provided that uses vehicle dynamics and quantitative steering objectives to tune the steering system. The steering objective chosen is a torque vs. lateral acceleration target for the driver. The commanded torque vs. lateral acceleration gain is termed the “steering gain”. The steering gain is achieved independently of the ability of the controller to reject unwanted effects such as friction. Two parameters are computed using vehicle dynamics that substantially determine driver feel: the vehicle’s “manual gain” (total steering torque divided by lateral acceleration) and the vehicle’s lateral acceleration gain (lateral acceleration divided by steering angle). Lateral acceleration gain is a well known quantity in the literature but the concept of manual gain is new for steering control. It is shown that, for a typical torque input electric steering topology, loop gain is uniquely related to the vehicle’s manual gain and the commanded steering gain. Loop gain is the total gain inside the controller. The practical impact of this result is obvious to anyone who has ever tuned electric steering in the field evidenced by the constant trades between steering response and friction rejection required to create world class feel. The mathematical proof provided merely supports the reality of the tuning trade experience yet also shows how to minimize the trade space. A topology that fully decouples the loop gain from the steering gain is proposed and implemented. Test results are provided that fully validate the theoretical results.
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