The quality of on-center handling is a growing concern for most modern power steering systems. These steering systems must minimize the effort applied by the driver at low-speed or parking conditions, while maintaining the feedback and 'feel' that the driver demands at highway speeds (on-center handling). The work presented in this thesis is an investigation into the quality of on-center handling of mid-size sport utility vehicles (SUVs). The analysis was completed in two stages including actual testing of two mid-size SUVs and the simulation of the same vehicles.; Through objective testing the on-center 'feel' was examined for different vehicle configurations with high and low levels of vibration due to tire non-uniformities. These configurations include steering rack replacements, rear shock changes, A-arm changes, and a structural brace removal. Several constant-speed maneuvers were used including sinusoidal steer inputs of various amplitudes and frequencies, a sine-sweep (a constant amplitude with a continuously variable frequency), and a hands-free vibration test. The driver of a vehicle uses several perceptions including, sight and steering wheel 'feel' as characterized by the steering hand wheel torque. Therefore the experimental analysis concentrated on the measured steering torque, but included vehicle response as characterized by yaw rate and lateral acceleration.; A vehicle and power steering model were utilized to determine the effects of steering system friction and the effects of rear shocks of a vehicle with and without vibration due to tire non-uniformities. The objective testing of the two vehicles was used to compare and cooraborate simulation results.
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