Regenerative brake system and hydraulic pump/motor for use therein

Abstract

A regenerative brake system and a variable displacement pump/motor for use therein. Each cylinder of the pump/motor having a main piston and a second piston between which is defined a space for hydraulic fluid, and a resilient element acting on the second piston to bias it toward the main piston. Variable displacement is achieved by controlling a volume of pressurized fluid that is injected and exhausted between the main and second pistons. Brake, drive and neutral modes of operation of the pump/motor are achieved by controlling the timing (relative to a drive shaft phase) of the injection and exhaust of the fluid. Regeneration is achieved by storing pressurized fluid generated by the pump/motor in an accumulator in brake mode and using the stored pressurized fluid to power the pump/motor in drive mode.

The invention claimed is: 
     
       1. 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.   
     
     
       2. The regenerative brake system of  claim 1 , the pump/motor comprising:
 a drive shaft operably connected to the axle; and   one or more cylinder units each having:
 a cylinder bore; 
 a main piston for reciprocation in the cylinder bore; 
 a connecting rod for connecting the main piston to the drive shaft; 
 a second piston for reciprocation in the cylinder bore; 
 a resilient element for biasing the second piston toward the main piston and 
 a port in the cylinder bore arranged to provide for the injection and exhaust of fluid into and out of a volume defined between the main piston and the second piston in the cylinder bore. 
   
     
     
       3. The regenerative brake system of  claim 2 , where in the resilient element can be connected to a resilience control unit for varying the resistance of the resilient element responsive to a control signal from the control unit. 
     
     
       4. The regenerative brake system of  claim 2 , the connecting rod and the main piston further comprising a connection mechanism providing for the transfer of power between the connecting rod and the main piston, and for the decoupling of the connecting rod from the main piston responsive to the control unit signaling each of the first control valve and the second control valve to remain closed starting when the main piston is proximate a top dead centre (TDC) position in the cylinder bore. 
     
     
       5. The regenerative brake system of  claim 1 , the control unit further providing for receiving an intervention signal from one of a traction control system (TCS) controller and a vehicle stability control system (VSC) controller, and responsive to the intervention signal varying the power applied in one of the drive mode and the brake mode by varying the duration of the opening and closing of the first control valve and the opening of the second control valve. 
     
     
       6. The regenerative brake system of  claim 1 , the control unit further receiving an intervention signal from a vehicle stability control system (VSC) controller, and responsive to the intervention signal reducing the power applied in the brake mode by one of opening the second control valve and varying the duration of the opening and closing of the first control valve. 
     
     
       7. The regenerative brake system of  claim 1 , the control unit further providing for receiving an intervention signal from an antilock brake system (ABS) controller, and responsive to the intervention signal reducing the power applied in the brake mode by one of opening the second control valve, and varying the duration of the opening and closing of the first control valve. 
     
     
       8. The regenerative brake system of  claim 1 , further comprising:
 a secondary accumulator for storing and supplying pressurized fluid;   a pressure sequence valve for directing pressurized fluid generated in the pump/motor, and having flowed through the proportioning valve, to the secondary accumulator until a pre-determined pressure is reached in the secondary accumulator and then directing the pressurized fluid to the accumulator; and   a solenoid operated valve that responsive to a control signal from the control unit blocks a flow of pressurized fluid from the secondary accumulator to the pump/motor and in the absence of a control signal from the control unit allows a flow pressurized fluid from the secondary accumulator to the pump/motor;   wherein an emergency brake mode is provided by the secondary accumulator and the solenoid operated valve when the control unit fails to provide a control signal to the solenoid operated valve.   
     
     
       9. A piston unit comprising: a cylinder unit having: a cylinder bore; a main piston for reciprocation in the cylinder bore; a bearing mechanism positioned on an underside of the main piston for connecting a connecting rod to the main piston; a second piston for reciprocation in the cylinder bore in conjunction with the main piston, such that the second piston and the main piston are arranged to define a volume between them within the cylinder bore, the volume between a top surface of the main piston opposite the underside and a bottom surface of the second piston; a resilient element for biasing the second piston toward the main piston, the resilient element being a closed container for containing a compressible medium; and a port in the cylinder bore arranged to provide for injection and exhaust of hydraulic fluid into and out of the volume; wherein the injection of the hydraulic fluid into the volume causes compression of the resilient element when both of the pistons move in the cylinder bore toward the resilient element. 
     
     
       10. The piston unit of claim 9, wherein the resilient element is connected to a resilience control unit for varying a resistance of the resilient element. 
     
     
       11. The piston unit of claim 9, wherein the second piston and the cylinder bore define the resilient element between a top surface of the second piston and the cylinder bore. 
     
     
       12. The piston unit of claim 9, wherein movement of the main piston during said reciprocation is relative to the movement of a driveshaft coupled to the connecting rod. 
     
     
       13. The piston unit of claim 9, wherein the resilient element contains a compressible medium selected from the group consisting of air and nitrogen. 
     
     
       14. The piston unit of claim 9, wherein the bearing mechanism provides for decoupling of the main piston from the connecting rod. 
     
     
       15. An apparatus comprising a piston unit having a cylinder unit including: a cylinder defining a bore; first and second pistons for reciprocating in conjunction with one another in said cylinder bore; a port in said cylinder bore, said port being arranged to provide for injection and exhaust of hydraulic fluid into and out of a first volume, said first volume being bounded at least in part by a surface of said first piston; and a resilient element contained in a second volume, said second volume being bounded at least in part by a surface of said second piston, the resilient element being a closed container for containing a compressible medium; wherein the injection of the hydraulic fluid into the first volume causes a reduction in the second volume when both of the pistons move in the cylinder bore toward the resilient element resulting in its compression. 
     
     
       16. The apparatus of claim 15, wherein the first piston has a surface configured to engage a connecting rod. 
     
     
       17. The apparatus of claim 16, wherein the first surface is configured for engaging a corresponding spherical surface of the connecting rod. 
     
     
       18. The apparatus of claim 15, wherein said first volume is further bounded by an additional surface of said second piston. 
     
     
       19. The apparatus of claim 15, further comprising a travel limit member for limiting travel of said first piston within said bore. 
     
     
       20. The apparatus of claim 15, wherein the compressible medium is selected from the group consisting of air and nitrogen. 
     
     
       21. The apparatus of claim 15, further comprising a resistance control element for adjusting an extent of resiliency of the resilient element. 
     
     
       22. The apparatus of claim 15, wherein the resilient element, when compressed, exerts a force urging said first piston to move in a direction that decreases said first volume. 
     
     
       23. An apparatus comprising a piston unit having a cylinder including: a cylinder defining a bore; first and second pistons for reciprocating in conjunction with one another in said cylinder bore; a port in said cylinder bore, said port being arranged to provide for injection and exhaust of hydraulic fluid into and out of a first volume, said first volume being bounded at least in part by a surface of said first piston; and a resilient element contained in a second volume, said second volume being bounded at least in part by a surface of said second piston, the resilient element being a closed container for containing a compressible medium; wherein the injection of the hydraulic fluid into the first volume causes a reduction in the second volume when both of the pistons move in the same direction in the cylinder bore resulting in the compression of the resilient element. 
     
     
       24. The apparatus of claim 23, wherein the compressible medium is selected from the group consisting of air and nitrogen.