PhD approved..

Jonathan Miller's PhD dissertation 'Advanced Braking Systems for Heavy Vehicles’ has been approved by the university

Summary of the thesis..

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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.

Further Information

• Research theme - Investigation of ABS strategies for heavy vehicles
• Previous PhD dissertations by members of the TRG