The thesis investigated regenerative braking for heavy vehicles undertaking delivery manoeuvres in urban environments. The work was partially sponsored by the New Zealand Foundation for Research, Science and Technology (now the Ministry of Science and Innovation).
Regenerative braking has been shown to reduce the fuel consumption for vehicles by recovering energy during braking, and using this stored energy to accelerate the vehicle. In this dissertation, data are compiled on different energy storage methods—batteries, flywheels, hydraulic accumulators and compressed air—and methods for utilising this stored energy. These technologies are then ‘power-matched’ and compared, and hydraulic energy storage/actuation is found to be 16% lighter and 33% smaller than the nearest competing technologies.
The thesis then introduces a computer model of the vehicle constructed in MATLAB/Simulink. This model includes experimentally derived maps for the engine and pump/motor efficiency, and is used to specify a hydraulic regenerative braking system for an HGV tri-axle trailer. The specified system shows a reduction in fuel usage of 5-11% on legislative drive cycles and 5% on realistic hilly cycles.
Different control methods are then discussed, including both ‘greedy’ and ‘heuristic’ algorithms. The greedy algorithm is found to be the only algorithm capable of real-time operation. Model predictive control is implemented, but is seen as too unwieldy for this regenerative braking system, and a global optimisation technique—pattern search—is used to place a lower bound on the vehicle’s fuel usage.
A design of such a regenerative braking system is then suggested and the final design shown.