Date of Award

12-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Law, Harry

Committee Member

Ziegert , John C

Abstract

This work deals with the question of relating open-loop handling metrics to driver-in-the-loop performance (closed-loop). The goal is to allow manufacturers to reduce cost and time associated with vehicle handling development. A vehicle model was built in the CarSim environment using kinematics and compliance, geometrical, and flat track tire data. This model was then compared and validated to testing done at Michelin's Laurens Proving Grounds using open-loop handling metrics. The open-loop tests conducted for model validation were an understeer test and swept sine or random steer test. Four commonly used handling metrics (steady state yaw rate gain, yaw rate damping ratio, yaw rate bandwidth, and lateral acceleration phase lag at 1 Hz) were extracted from the frequency response functions of the swept sine test. These are the open-loop handling parameters used to draw relationships to closed-loop performance.
Next, a driver model was coupled to the vehicle model in order to simulate a closed-loop maneuver. Quadratic cost functions are then introduced as a means to measure performance through the closed-loop ISO Double Lane Change maneuver. These quadratic metrics measure path-following ability, and the mental and physical workload of the driver. Driver model parameters were determined by weighting the quadratic cost functions to select the optimum driver with the lowest total cost. In this work, highest priority was given to path-following ability in order to successfully complete the lane change without violating course boundaries. Mental workload and physical workload were given lower priority because of the short length of the maneuver.
As a means to change the vehicle model, three hypothetical tires are introduced. To have an even greater number of configurations, the vehicle model's static weight distribution was altered. This yielded twelve different realistic vehicle configurations from which to draw conclusions. With the twelve different vehicle models considered, qualitative relationships were found between open-loop handling measures and driver-in-the-loop quadratic performance metrics. Two relationships were found to exist--when steady state yaw rate gain and yaw rate bandwidth are increased, path-following ability is enhanced. When yaw rate bandwidth is increased and lateral acceleration phase lag at 1 Hz is decreased, mental and physical workload are reduced on the driver.

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