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PhD approved..

last modified Nov 21, 2010 03:58 PM
Jonathan Miller's PhD dissertation 'Advanced Braking Systems for Heavy Vehicles’ has been approved by the university
Summary of the thesis..

This dissertation describes research into the use of advanced emergency braking hardware and wheel slip control algorithms on pneumatically braked heavy goods vehicles.

Anti-lock braking systems (ABS) on commercial heavy vehicles use inefficient control approaches that work on cycles of exceeding the limits of tyre-road adhesion. Long pipe lengths and slow pneumatic brake valves create time delays that limit the speed of response. The result is poor emergency stopping performance. An alternative approach to conventional ABS is wheel slip control, which optimises slip during braking.

Mathematical models were made of the pneumatics and dynamics of a heavy vehicle brake that featured a high-speed actuator placed directly on the brake chamber. The results were used to inform the specifications for a second generation, made-for-purpose actuator. Designing the second generation actuator involved balancing the conflicting requirements for the magnetic circuit subsystem and the mechanical performance. The resulting prototype actuator produced pneumatic response times an order of magnitude smaller than conventional ABS hardware.

A wheel slip control algorithm was derived for pneumatically-braked heavy vehicles. The algorithm was based on sliding mode theory, and was robust to sensor noise and road conditions. A braking force observer based on sliding mode theory, a nonlinear least squares surface identification algorithm, and a recursive least squares brake gain estimator were formulated to support the sliding mode controller. The state and parameter estimation algorithms were evaluated in vehicle simulations and with full-scale test data.

The sliding mode controller was combined with the second generation actuator in vehicle simulations to compare its performance to an alternative actuator with piloted piston valves proposed for a separate project, and to conventional ABS hardware and control algorithms. The second generation actuator produced 8.2% shorter stops and used 70% less compressed air than the alternative actuator. The second generation actuator also produced up to 25% shorter stops and used up to 70% less air relative to conventional ABS.

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