Modeling, simulation and testing of automobile power steering systems for the evaluation of on-center handling

This dissertation provides a fresh look into the operation of hydraulic power steering systems of passenger vehicles by carefully considering elements that shape the vehicle response and steering feel in on-center driving. New techniques are developed to study important traits of steering gear assemblies for both rack-and-pinion and recirculating ball power steering systems. Special attention was paid to nonlinearities such as friction in power steering systems since they can be an important contributor to steering feel in on-center driving. Based on information obtained from the study, a numerical model of a generic steering system is created and used to predict vehicle response. In addition, specific laboratory techniques are provided to characterize all parameters in the total system model, both for the power steering system as well the simplified vehicle model used in the study.; Using swept sine test steering inputs and on-center weave test steering inputs, the on-center behavior of both a rack-and-pinion type test vehicle and a recirculating ball type test vehicle was determined. Response measurements include yaw rate, lateral acceleration, steering wheel torque and front road wheel angles. These measurements were used to construct typical measures of on-center behavior for the two test vehicles both in the frequency and time domain. The combined vehicle/steering system numerical model was then used to simulate the on-center and swept sine tests for the vehicles considered in the study. Simulation results are used to construct the same standard measures of on-center performance and then compared to the test results. The study shows that very good agreement is obtained between model predicted response and measured vehicle response for the two vehicles considered in the study.