Decoupling mechanism for hydraulic pump/motor assembly

Abstract

A positive displacement hydraulic pump/motor assembly ( 1 ) includes a rotary cylinder block ( 3 ) having a central axis ( 5 ) and a generally circular array of cylinders ( 6 ) disposed around the axis. A corresponding plurality of pistons ( 10 ) is reciprocably disposed within the respective cylinders. A drive shaft ( 12 ) extends through a bore ( 13 ) formed in the cylinder block to effect rotation of the cylinder block about the central axis. A drive plate ( 15 ) is disposed at one end of the cylinder block to effect sequentially staggered reciprocation of the pistons in response to rotation of the cylinder block. A stationary valve plate ( 20 ) is disposed at an opposite end of the cylinder block, the valve plate having a valve face ( 21 ) adapted for sliding rotational engagement with a complementary mating face ( 22 ) formed on the cylinder block. The valve plate further includes at least one inlet port ( 24 ) for fluid communication with a source of hydraulic fluid and at least one outlet port ( 26 ) for fluid communication with an hydraulic load. The ports are disposed such that in use, hydraulic fluid is progressively drawn into the cylinders in sequence as the respective pistons are displaced away from the valve plate and subsequently expelled from the cylinders as the pistons are progressively displaced toward the valve plate. The pump/motor assembly further includes a selectively releasable decoupling mechanism ( 14 ) adapted in an engaged mode to connect the drive shaft to the cylinder block and in a disengaged mode to allow the drive shaft to rotate substantially independently of the cylinder block.

What is claimed:  
     
         1 . A positive displacement hydraulic pump/motor assembly including:—
 a rotary cylinder block having a central axis and incorporating a generally circular array of cylinders disposed around the axis;  
 a corresponding plurality of pistons reciprocably disposed within the respective cylinders;  
 drive means including a drive shaft extending through a bore formed in the cylinder block to effect rotation of the cylinder block about the central axis;  
 a drive plate disposed at one end of the cylinder block to effect sequentially staggered reciprocation of the pistons in response to rotation of the cylinder block;  
 a stationary valve plate disposed at an opposite end of the cylinder block, the valve plate having a valve face adapted for sliding rotational engagement with a complementary mating face formed on the cylinder block;  
 the valve plate further including at least one inlet port for fluid communication with a source of hydraulic fluid and at least one outlet port for fluid communication with an hydraulic load;  
 the ports being disposed such that in use, hydraulic fluid is progressively drawn into the cylinders in sequence as the respective pistons are displaced away from the valve plate and subsequently expelled from the cylinders as the pistons are progressively displaced toward the valve plate;  
 the pump/motor assembly further including a selectively releasable decoupling mechanism adapted in an engaged mode to connect the drive shaft to the cylinder block and in a disengaged mode to allow the drive shaft to rotate substantially independently of the cylinder block.  
 
     
     
         2 . A pump/motor assembly according to  claim 1 , wherein the cylinders are disposed in generally parallel relationship with respect to the central axis.  
     
     
         3 . A pump/motor assembly according to  claim 1 , wherein the drive plate takes the form of a stationary swash plate, which is inclined with respect to the central axis of the cylinder block.  
     
     
         4 . A pump/motor assembly according to  claim 3 , wherein floating ends of the pistons remote from the valve plate include followers adapted to traverse the swash plate as the cylinder block rotates.  
     
     
         5 . A pump/motor assembly according to  claim 4 , further including a hold-down plate disposed to capture the floating ends of the pistons and retain the followers in sliding contact with the swash plate.  
     
     
         6 . A pump/motor assembly according to  claim 3 , wherein the angle of inclination of the swash plate is selectively adjustable, to provide variable flow rate characteristics.  
     
     
         7 . A pump/motor assembly according to  claim 6 , wherein the swash plate is able to be selectively inclined in a positive or a negative sense, thereby enabling the assembly alternately to operate as a motor or a pump.  
     
     
         8 . A pump/motor assembly according to  claim 6 , wherein the variable swash plate can be oriented in an intermediate or neutral position, effectively normal to the central axis, such that rotation of the cylinder block causes no movement of the pistons, and hence induces no substantial load.  
     
     
         9 . A pump/motor assembly according to  claim 1 , further including bias means disposed to apply a bias force urging the respective mating faces on the cylinder block and the valve plate into sealing engagement.  
     
     
         10 . A pump/motor assembly according to  claim 9 , wherein the bias force applied by the bias means is selectively variable.  
     
     
         11 . A pump/motor assembly according to  claim 1 , wherein the decoupling means include a clutch mechanism interposed effectively between the drive shaft and the cylinder block, so as selectively to transmit rotary drive therebetween.  
     
     
         12 . A pump/motor assembly according to  claim 11 , wherein the clutch mechanism includes a multi-plate clutch disposed coaxially around the drive shaft.  
     
     
         13 . A pump/motor assembly according to  claim 12 , wherein the clutch mechanism includes a stack of inter-leaved inner and outer clutch plates, configured for splined engagement with the drive shaft and cylinder block respectively.  
     
     
         14 . A pump/motor assembly according to  claim 13 , wherein the clutch plates are disposed such that compression of the clutch stack upon engagement of the clutch promotes frictional engagement between the inner and outer clutch plates, thereby to transmit torque between the shaft and cylinder block.  
     
     
         15 . A pump/motor assembly according to  claim 14 , wherein the clutch mechanism includes a piston assembly configured selectively to compress the plates in the clutch stack in order to engage the clutch.  
     
     
         16 . A pump/motor assembly according to  claim 15 , wherein the piston assembly is non-rotating.  
     
     
         17 . A pump/motor assembly according to  claim 15 , wherein the piston assembly is configured such that activation and reaction forces are transferred to the drive shaft, thereby substantially isolating clutch-induced compressive loads from shaft end bearings.  
     
     
         18 . A pump/motor assembly according to  claim 11 , wherein the clutch mechanism is selectively capable of substantially complete disengagement, so as to provide for substantially independent rotation of the shaft and the cylinder block.  
     
     
         19 . A pump/motor assembly according to  claim 11 , wherein the clutch mechanism is capable of partial disengagement, so as to transmit a proportion of torque between the shaft and cylinder block.  
     
     
         20 . A pump/motor assembly according to  claim 11 , wherein the clutch mechanism is progressively and controllably actuable between the engaged and disengaged modes of operation, to provide for controlled slippage.  
     
     
         21 . A pump/motor assembly according to  claim 11 , wherein the clutch mechanism is positively engaged and positively disengaged by hydraulic pressure.  
     
     
         22 . A pump/motor assembly according to  claim 21 , wherein the hydraulic pressure for engagement and disengagement of the clutch is provided by the pump/motor assembly.  
     
     
         23 . A pump/motor assembly according to  claim 11 , wherein the clutch mechanism is a wet type design, with the clutch plates submerged at least partially in an oil bath.  
     
     
         24 . An energy management system operable in a driving mode, a braking mode and a neutral mode, the energy management system including:—
 energy accumulation means operable selectively to store and release energy through controlled receipt and release of hydraulic fluid;  
 a positive displacement hydraulic pump/motor assembly as defined in  claim 1 , in fluid communication with the energy accumulation means;  
 a low pressure hydraulic reservoir in fluid communication with the pump/motor assembly; and  
 connection means for connecting the pump/motor assembly to a drive line;  
 the system being arranged such that in the braking mode the pump/motor assembly retards the drive line by pumping hydraulic fluid into the accumulation means, in the driving mode the pump/motor assembly supplies supplementary power to the drive line using pressurised hydraulic fluid from the accumulation means, and in the neutral mode the pump/motor assembly is effectively inoperative and exerts no substantial driving or retarding influence on the drive line.  
 
     
     
         25 . An energy management system according to  claim 24 , wherein the reservoir includes a low-pressure accumulator or constant pressure chamber adapted to supply a positive pressure to a suction port of the pump/motor unit.  
     
     
         26 . An energy management system according to  claim 24 , wherein the drive line forms part of a drive train of a vehicle.  
     
     
         27 . An energy management system according to  claim 26 , wherein the drive shaft of the pump/motor assembly is effectively integral with the drive line of the vehicle.  
     
     
         28 . An energy management system according to  claim 27 , wherein the connection means include a pair of universal joints allowing one sub-section of the drive line to be constituted by the drive shaft of the pump/motor unit, such that the decoupling mechanism provides a releasable connection between the vehicle drive line and the cylinder block.  
     
     
         29 . An energy management system according to  claim 24 , wherein the connection means include an intermediate transmission mechanism disposed to transmit rotary drive between the vehicle drive train and the drive shaft of the pump/motor assembly.  
     
     
         30 . An energy management system according to  claim 24 , wherein the pump/motor assembly includes at least three external ports to permit ingress and egress of hydraulic fluid, with a first port communicating with an inlet of the hydraulic reservoir, a second port communicating with an outlet of the hydraulic reservoir, and a third port communicating with the accumulation means.  
     
     
         31 . An energy management system according to  claim 30 , further including a heat exchanger disposed between the first port and the hydraulic fluid reservoir.  
     
     
         32 . An energy management system according to  claim 24 , wherein a plurality of of said pump/motor assemblies is arranged axially along a common drive shaft.  
     
     
         33 . An energy management system according to  claim 24 , further including a flow control circuit through which hydraulic fluid can be selectively directed, the control circuit providing a controllable resistance enabling the pump/motor assembly selectively to exert a retarding force on the drive shaft when the accumulation means are fully charged.  
     
     
         34 . An energy management system according to according to  claim 24 , wherein the accumulation means include a gas/liquid accumulator comprising a double-ended cylinder and a piston adapted to float sealingly within the cylinder, and wherein side of the cylinder contains a compressible inert gas and the other side of the cylinder is connected hydraulically to the pump/motor assembly.  
     
     
         35 . An energy management system according to  claim 34 , wherein the accumulator is adapted to store energy by pumping hydraulic fluid into one side of the cylinder so as to compress the gas on the other side by displacement of the floating piston, and subsequently to release that energy by expulsion of hydraulic fluid as the compressed gas expands.  
     
     
         36 . An energy management system according to  claim 35 , including a plurality of said accumulators, connected in series or parallel.