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

The capability of a road vehicle equipped with an Anti-Lock Braking System (ABS) to come to a safe stop depends on factors such as dynamic force between tire and road, surface adhesion coefficient, and the vertical profile of the road. When in panic, a driver's reaction is to step hard on the brakes to make the vehicle stop as soon as possible. Although the use of modern technologies such as ABS and Electronic Stability Control (ESC) have reduced the number of accidents significantly, any further improvement in stopping distance would only complement these technologies.
Michelin has undertaken the development of a non-pneumatic tire (called the TWEELTM) which can decouple the ride comfort and handling capability of road vehicles. Studies in the ride comfort area have shown reductions in the tire-to-road dynamic force using the TWEELTM. This might lead to shorter stopping distances while braking. The primary focus area of this thesis is to evaluate the straight line braking performance of a 2007 BMW Mini Cooper with TWEELsTM on randomly irregular roads. Different vertical road profiles were utilized to evaluate their effect on braking. A comparison of results is made between the original equipment (OE) tires and the TWEELTM. Additionally, the effect on vehicle braking of tuning the shock absorbers was also studied.
A eight degree-of-freedom model that focuses on vertical and longitudinal dynamics was developed in Simulink. A rather simple brake system with an ideal antilock system (ABS) was used to avoid wheel lock-up in hard braking scenarios. A Pacejka tire model was employed as well. The nonlinear tire stiffness and the nonlinear shock absorber curves were incorporated in the model using look-up tables. The model was validated in the time domain using the results from a vehicle model in CarSim for similar tests.
For simulation on a road profile similar to weathered asphalt at Michelin's Laurens Proving Grounds (WA-LPG), the selection between TWEELTM and OE tire does not affect braking performance. Also, the frequency content of the 'smooth' road profile had minimal effect on stopping distance. However, as RMS roughness of road profiles increased, the stopping distance increased for both the TWEELTM and the OE tire and the 'softer' TWEELTM yielded a shorter stopping distance than the OE tire. When shock damping was altered, no change in stopping distance was found on 'smooth' roads and 'firmer' shocks performed better on 'rough' road profiles.

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