A compromise solution for energy recovery in vehicle braking

A combined regenerative-dissipative brake system for a city bus is considered. The regenerative component consists of a fixed displacement hydraulic pump/motor discharging into or receiving high pressure fluid from a hydropneumatic accumulator. The braking force provided by the pump is determined by the pressure in the accumulator. It is brought into action only when a greater total braking force is required, in which case the conventional dissipative brake provides the difference. From a preliminary analysis using probability data for acceleration, an estimated 45% of the total kinetic energy absorbed in braking could be channeled through the hydropneumatic component. The system was conceived as a practical alternative to a more costly fully regenerative system employing a variable displacement pump.