Estimation and Decomposition of Rack Force for Driving on Uneven Roads

TL;DR

This paper develops and compares three vehicle and tire model-based estimators for rack force during driving on uneven roads, demonstrating improved accuracy with non-linear tire models especially under aggressive maneuvers.

Contribution

It introduces three real-time rack force estimators using sensed steering and road profile data, highlighting the effectiveness of a semi-empirical Rigid Ring tire model for high-frequency road variations.

Findings

Non-linear tire models improve estimation accuracy during aggressive maneuvers.

The Rigid Ring tire model captures high-frequency road profile effects.

Simulation validates component-wise rack force estimates.

Abstract

The force transmitted from the front tires to the steering rack of a vehicle, called the rack force, plays an important role in the function of electric power steering (EPS) systems. Estimates of rack force can be used by EPS to attenuate road feedback and reduce driver effort. Further, estimates of the components of rack force (arising, for example, due to steering angle and road profile) can be used to separately compensate for each component and thereby enhance steering feel. In this paper, we present three vehicle and tire model-based rack force estimators that utilize sensed steering angle and road profile to estimate total rack force and individual components of rack force. We test and compare the real-time performance of the estimators by performing driving experiments with non-aggressive and aggressive steering maneuvers on roads with low and high frequency profile variations. The results indicate that for aggressive maneuvers the estimators using non-linear tire models produce more accurate rack force estimates. Moreover, only the estimator that incorporates a semi-empirical Rigid Ring tire model is able to capture rack force variation for driving on a road with high frequency profile variation. Finally, we present results from a simulation study to validate the component-wise estimates of rack force.