A regenerative brake system for use in a vehicle having at least one axle comprising:
- a variable displacement hydraulic pump/motor, connected for energy transfer to and from the axle;
- a hydraulic pressure accumulator for storing and supplying pressurized fluid;
- a proportioning valve for allowing pressurized fluid, above a release pressure threshold, generated in the pump/motor to enter the pressure accumulator;
- a fluid reservoir for receiving, storing and supplying pressure relieved fluid;
- an injection transformer for receiving a first volume of pressurized fluid at a first pressure from the pressure accumulator and supplying a second volume of pressurized fluid at a second pressure to the pump/motor, wherein the injection transformer can draw fluid from the fluid reservoir, the second volume is greater than the first volume and the second pressure is lower than the first pressure;
- a priming pump for drawing fluid from the fluid reservoir and supplying pressurized fluid to the pump/motor;
- a first control valve for controlling the injection of pressurized fluid from any of the pressure accumulator, the injection transformer and the priming pump into the pump/motor, wherein the displacement of the pump/motor is responsive to the volume of pressurized fluid injected;
- a second control valve for controlling the exhaust of pressurized fluid from the pump/motor to the reservoir;
- a first pressure relief valve connected to the pressure accumulator for supplying pressurized fluid at a reduced pressure;
- a second pressure relief valve connected to the pressure accumulator for relieving excess pressurized fluid in the pressure accumulator to the reservoir;
- a third control valve for controlling the flow of pressurized fluid from the accumulator, via the first pressure relief valve, to the injection transformer;
- a fourth control valve for controlling the flow of pressurized fluid from the accumulator to the pump/motor via the first pressure relief valve and the first control valve;
- and
- a control unit for controlling the operation of the regenerative brake system by controlling the release pressure threshold of the proportioning valve, and the timing and duration of the opening and closing of the first control valve, the second control valve, third control valve and the fourth control valve to achieve operation in each of a brake mode in which kinetic energy of the axle is converted to pressurized fluid exhausted by the pump/motor, a drive mode in which potential energy in pressurized fluid injected into the pump/motor is converted to kinetic energy in the axle, and a neutral mode in which substantially no net energy is transferred between the pump/motor and the axle.