Hydrostatic transmission

Claim 2

A hydraulic transmission comprising a reversible hydraulic pump and a hydraulic motor connected inlet to outlet by a pair of fluid lines to form a closed loop for hydraulic fluid flow, each of said pair of fluid lines being alternatively a high-pressure line or a low-pressure line depending upon the direction of fluid flow in said lines, a replenishment fluid network connected to said loop, said network comprising a hydraulic fluid reservoir and a booster pump for supplying hydraulic fluid from said reservoir to said loop, and a combination relief and shuttle valve connected between said pair of fluid lines, said valve being operative to open and limit the maximum pressure in either one of said pair of fluid lines when that line is the high-pressure line and to connect either one of said pair of fluid lines to said replenishment fluid network when that one of said pair of fluid lines is the low-pressure line.

Claim 3

The hydraulic transmission of claim 1 wherein said replenishment fluid network and valve are operable to direct all of the hydraulic fluid pumped through said booster pump into the low-pressure line of said loop and to bleed off to said reservoir from said low-pressure line of said loop at least a portion of the exhaust fluid from the motor.

Claim 4

The hydraulic transmission of claim 1 wherein said replenishment fluid network and valve are operable to direct a portion of the hydraulic fluid pumped through said booster pump to said loop and to direct all excess booster pump fluid not required for makeup of hydraulic fluid leakage in said pump and motor to the interior of a case surrounding at least one of said pump or motor to cool said motor or pump.

Claim 5

The hydraulic transmission of claim 3 wherein only makeup hydraulic fluid is supplied to said loop through said combination relief and shuttle valve, said transmission including a third fluid line connecting said booster pump to a case surrounding said reversible pump, said third fluid line having a check valve therein, said check valve being operable to pass all of the excess hydraulic fluid from said booster pump to said case of said reversible pump to cool said pump.

Claim 6

The hydraulic transmission of claim 1 which includes a third fluid line connected between said combination relief and shuttle valve and said reservoir for returning excess fluid to said reservoir, said third fluid line including a low-pressure relief valve operable to maintain a minimum booster pump pressure in said low-pressure line of said closed loop.

Claim 7

The hydraulic transmission of claim 1 wherein said combination relief and shuttle valve has three ports, two of said ports being connected to said pair of fluid lines and a third port being connected to a line which connects said valve to said reservoir.

Claim 8

The hydraulIc transmission of claim 6 which further includes means to direct all of said booster pump fluid to the low-pressure line of said loop and means to direct the excess hydraulic fluid from said loop to said reservoir through a case surrounding one of said pump or motor.

Claim 9

The hydraulic transmission of claim 1 wherein said combination relief and shuttle valve has at least three ports, the first and second of said ports being adapted to be connected to said pair of fluid lines, a movable pressure relief valve element cooperable with a valve seat in said valve to control the flow of fluid between said first and second ports, means forming a control pressure chamber, the pressure in said chamber acting to urge said pressure relief valve element in a first direction, a movable differential pressure-operated piston having opposite surfaces disposed to be acted upon respectively by the fluid pressures at said first and second ports, first valve means operated by said movable piston for connecting said control chamber with whichever of said first and second ports contains the higher pressure while isolating said control chamber from that one of said first and second ports which contains the lower pressure, and second valve means operated by said piston for connecting whichever of said ports contains the lower pressure to said third outlet port.

Claim 10

The hydraulic transmission of claim 1 wherein said combination relief and shuttle valve has at least three ports, the first and second of said ports being adapted to be connected to said pair of fluid lines, a movable pressure relief valve element cooperable with a valve seat in said valve to control the flow of fluid between said first and second ports, means forming a control pressure chamber, the pressure in said chamber acting to urge said pressure relief valve element in a first direction, means presenting a surface subjected to fluid pressure at said first port for urging said movable valve element in an opposite direction, orifice means through which fluid must flow to enter said control chamber, pilot valve means for controlling the maximum pressure in said control chamber, a movable differential pressure-operated piston having opposite surfaces disposed to be acted upon respectively by the fluid pressures at said first and second ports and arranged to cooperate with said surface-presenting means for urging said movable valve element in said opposite direction when the pressure at said second port is greater than the pressure at said first port, first valve means operated by said movable piston for connecting said orifice means with whichever of said first and second ports contains the higher pressure while isolating said orifice means from that one of said first and second ports which contains the lower pressure, and second valve means operated by said piston for connecting whichever of said ports contains the lower pressure to said third outlet port.

Claim 11

The hydraulic transmission of claim 9 in which said movable differential pressure-operated piston is engageable with said surface-presenting means when the pressure at said second port is greater than the pressure at said first port, and in which said orifice means extends through said surface-presenting means.

Claim 12

The hydraulic transmission of claim 1 wherein said combination relief and shuttle valve includes a valve body having at least three ports therein, the first and second of said ports being adapted to be connected to said pair of fluid lines, an axially movable valve element located within said body and axially movable to control the flow of fluid between said first and second ports, means forming a pressure control chamber, the pressure in which acts to urge said movable element in one axial direction, said movable element having a surface adapted to be subjected to fluid pressure at said first port for urging said movable element in the opposite axial direction, oriFice means extending axially through said movable element through which fluid must flow to enter said control pressure chamber, pilot valve means for controlling the maximum pressure in said control chamber, a movable differential pressure-operated piston, said piston means being movable axially with respect to said movable element and having opposite surfaces disposed to be acted upon respectively by the fluid pressures at said first and second ports, one of said opposite surfaces of said piston means being arranged to cooperate with said surface of said movable element for urging said movable valve element in said opposite direction in response to pressure at said second port when the pressure at said second port is greater than the pressure at said first port, valve means operated by said movable piston means for connecting said orifice means with whichever of said ports contains the higher pressure while isolating said orifice means from that port which contains the lower pressure, and second valve means operated by said piston for connecting whichever of said ports contains the lower pressure to said third outlet port.

Claim 13

The hydraulic transmission of claim 11 wherein the first valve means operated by said movable piston means includes a fluid-flow-restricting passageway between the end surfaces of said piston means, and resilient sealing means mounted in the opposite end of said piston means and surrounding said passageway.

Claim 14

The hydraulic transmission of claim 11 in which said second valve means operated by said piston means comprises at least one land in the peripheral surface of said piston means and a cooperating land in the body of said valve, said cooperating land being connected to said third port of said body.

Claim 15

The hydraulic transmission of claim 2 wherein said combination dual relief and shuttle valve has at least three ports, the first and second of said ports being adapted to be connected to said pair of fluid lines, a movable pressure relief valve element cooperable with a valve seat in said valve to control the flow of fluid between said first and second ports, means forming a control pressure chamber, the pressure in said chamber acting to urge said pressure relief valve element in a first direction, a movable differential pressure-operated piston having opposite surfaces disposed to be acted upon respectively by the fluid pressures at said first and second ports, first valve means operated by said movable piston for connecting said control chamber with whichever of said first and second ports contains the higher pressure while isolating said control chamber from that one of said first and second ports which contains the lower pressure, and second valve means operated by said piston for connecting whichever of said ports contains the lower pressure to said third outlet port, said third outlet port being connected to said reservoir.

Claim 16

The hydraulic transmission of claim 2 wherein said combination relief and shuttle valve has at least three ports, the first and second of said ports being adapted to be connected to said pair of fluid lines, a movable pressure relief valve element cooperable with a valve seat in said valve to control the flow of fluid between said first and second ports, means forming a control pressure chamber, the pressure in said chamber acting to urge said pressure relief valve element in a first direction, means presenting a surface subjected to fluid pressure at said first port for urging said movable valve element in an opposite direction, orifice means through which fluid must flow to enter said control chamber, pilot valve means for controlling the maximum pressure in said control chamber, a movable differential pressure-operated piston having opposite surfaces disposed to be acted upon respectively by the fluid pressures at said first and second ports and arranged to cooperate with said surface-presenting means for urging said movabLe valve element in said opposite direction when the pressure at said second port is greater than the pressure at said first port, first valve means operated by said movable piston for connecting said orifice means with whichever of said first and second ports contains the higher pressure while isolating said orifice means from that one of said first and second ports which contains the lower pressure, and second valve means operated by said piston for connecting whichever of said ports contains the lower pressure to said third outlet port, said third outlet port being connected to said reservoir.

Claim 17

The hydraulic transmission of claim 15 in which said movable differential-pressure-operated piston is engageable with said surface-presenting means when the pressure at said second port is greater than the pressure at said first port, and in which said orifice means extends through said surface-presenting means.

Claim 18

The hydraulic transmission of claim 2 wherein said combination relief and shuttle valve includes a valve body having at least three ports therein, the first and second of said ports being adapted to be connected to said pair of fluid lines, an axially movable valve element located within said body and axially movable to control the flow of fluid between said first and second ports, means forming a pressure control chamber, the pressure in which acts to urge said movable element in one axial direction, said movable element having a surface adapted to be subjected to fluid pressure at said first port for urging said movable element in the opposite axial direction, orifice means extending axially through said movable element through which fluid must flow to enter said control pressure chamber, pilot valve means for controlling the maximum pressure in said control chamber, a movable differential pressure-operated piston, said piston means being movable axially with respect to said movable element and having opposite surfaces disposed to be acted upon respectively by the fluid pressures at said first and second ports, one of said opposite surfaces of said piston means being arranged to cooperate with said surface of said movable element for urging said movable valve element in said opposite direction in response to pressure at said second port when the pressure at said second port is greater than the pressure at said first port, valve means operated by said movable piston means for connecting said orifice means with whichever of said ports contains the higher pressure while isolating said orifice means from that port which contains the lower pressure, and second valve means operated by said piston for connecting whichever of said ports contains the lower pressure to said third outlet port, said third outlet port being connected to said reservoir.

Claim 19

The hydraulic transmission of claim 17 wherein the first valve means operated by said movable piston means includes a fluid-flow-restricting passageway between the end surfaces of said piston means, and resilient sealing means mounted in the opposite end of said piston means and surrounding said passageway.

Claim 20

The hydraulic transmission of claim 17 in which said second valve means operated by said piston means comprises at least one land in the peripheral surface of said piston means and a cooperating land in the body of said valve, said cooperating land being connected to said third port of said body.

Claim 21

The hydraulic transmission of claim 3 wherein said combination relief and shuttle valve has at least three ports, the first and second of said ports being adapted to be connected to said pair of fluid lines, a movable pressure relief valve element cooperable with a valve seat in said valve to control the flow of fluid between said first and second ports, means forming a control pressure chamber, the pressure in said chamber acting to urge said pressure relief valve element in a first direction, a movable differential pressure-opErated piston having opposite surfaces disposed to be acted upon respectively by the fluid pressures at said first and second ports, first valve means operated by said movable piston for connecting said control chamber with whichever of said first and second ports contains the higher pressure while isolating said control chamber from that one of said first and second ports which contains the lower pressure, and second valve means operated by said piston for connecting whichever of said ports contains the lower pressure to said third outlet port, said third outlet port being connected to a supply line from said booster pump.

Claim 22

The hydraulic transmission of claim 3 wherein said combination relief and shuttle valve has at least three ports, the first and second of said ports being adapted to be connected to said pair of fluid lines, a movable pressure relief valve element cooperable with a valve seat in said valve to control the flow of fluid between said first and second ports, means forming a control pressure chamber, the pressure in said chamber acting to urge said pressure relief valve element in a first direction, means presenting a surface subjected to fluid pressure at said first port for urging said movable valve element in an opposite direction, orifice means through which fluid must flow to enter said control chamber, pilot valve means for controlling the maximum pressure in said control chamber, a movable differential pressure-operated piston having opposite surfaces disposed to be acted upon respectively by the fluid pressures at said first and second ports and arranged to cooperate with said surface presenting means for urging said movable valve element in said opposite direction when the pressure at said second port is greater than the pressure at said first port, first valve means operated by said movable piston for connecting said orifice means with whichever of said first and second ports contains the higher pressure while isolating said orifice means from that one of said first and second ports which contains the lower pressure, and second valve means operated by said piston for connecting whichever of said ports contains the lower pressure to said third outlet port, said third outlet port being connected to a supply line from said booster pump.

Claim 23

The hydraulic transmission of claim 21 in which said movable differential pressure-operated piston is engageable with said surface-presenting means when the pressure at said second port is greater than the pressure at said first port, and in which said orifice means extends through said surface-presenting means. 23 The hydraulic transmission of claim 3 wherein said combination relief and shuttle valve includes a valve body having at least three ports therein, the first and second of said ports being adapted to be connected to said pair of fluid lines, an axially movable valve element located within said body and axially movable to control the flow of fluid between said first and second ports, means forming a pressure control chamber, the pressure in which acts to urge said movable element in one axial direction, said movable element having a surface adapted to be subjected to fluid pressure at said first port for urging said movable element in the opposite axial direction, orifice means extending axially through said movable element through which fluid must flow to enter said control pressure chamber, pilot valve means for controlling the maximum pressure in said control chamber, a movable differential pressure-operated piston, said piston means being movable axially with respect to said movable element and having opposite surfaces disposed to be acted upon respectively by the fluid pressures at said first and second ports, one of said opposite surfaces of said piston means being arranged to cooperate with said surface of said movable element for urging said movable valve element in said opposite direction in response to prEssure at said second port when the pressure at said second port is greater than the pressure at said first port, valve means operated by said movable piston means for connecting said orifice means with whichever of said ports contains the higher pressure while isolating said orifice means from that port which contains the lower pressure, and second valve means operated by said piston for connecting whichever of said ports contains the lower pressure to said third outlet port, said third outlet port being connected to a supply line from said booster pump.

Claim 24

The hydraulic transmission of claim 23 wherein the first valve means operated by said movable piston means includes a fluid-flow-restricting passageway between the end surfaces of said piston means, and resilient sealing means mounted in the opposite end of said piston means and surrounding said passageway.

Claim 25

The hydraulic transmission of claim 23 in which said second valve means operated by said piston means comprises at least one land in the peripheral surface of said piston means and a cooperating land in the body of said valve, said cooperating land being connected to said third port of said body.

Claim 26

A hydraulic transmission comprising a reversible hydraulic pump and a hydraulic motor connected inlet to outlet by a pair of fluid lines to form a closed loop for hydraulic fluid flow, each of said pair of fluid lines being alternatively a high-pressure line or a low-pressure line depending upon the direction of fluid flow in said lines, a hydraulic fluid reservoir, a booster pump for supplying makeup hydraulic fluid from said reservoir to said loop to compensate for hydraulic fluid leakage in said pump and motor, and a combination relief and shuttle valve connected between said pair of fluid lines, said valve being operative to limit the maximum pressure in either one of said pair of fluid lines and to direct hydraulic fluid supplied to said loop by said booster pump to that one of said pair of fluid lines which is the low-pressure line.

Claim 27

A hydraulic transmission comprising a reversible hydraulic pump and a hydraulic motor connected inlet to outlet by a pair of fluid lines to form a closed loop for hydraulic fluid flow, each of said pair of fluid lines being alternatively a high-pressure line or a low-pressure line depending upon the direction of fluid flow in said lines, a hydraulic fluid reservoir, a booster pump for supplying makeup hydraulic fluid from said reservoir to said loop to compensate for hydraulic fluid leakage in said pump and motor, and a combination relief and shuttle valve connected between said pair of fluid lines, said valve being operative to limit the maximum pressure in either one of said pair of fluid lines and to direct hydraulic fluid supplied to said loop by said booster pump to that one of said pair of fluid lines which is the low-pressure line.

Claim 28

The hydraulic transmission of claim 26 which further includes flow control means operable to direct all of the hydraulic fluid pumped through said booster pump to said loop and to bleed off from said loop all excess booster pump fluid not required for makeup of hydraulic fluid leakage in said pump and motor to said reservoir.

Claim 29

The hydraulic transmission of claim 26 which further includes flow control means operable to direct a portion of the hydraulic fluid pumped through said booster pump to said loop and to direct all excess booster pump fluid not required for makeup of hydraulic fluid leakage in said pump and motor to the interior of a case surrounding at least one of said pump or motor to cool said motor or pump.

Claim 30

The hydraulic transmission of claim 28 wherein only makeup hydraulic fluid is supplied to said loop through said combination relief and shuttle valve, said transmission including a third fluid line connecting said booster pump to a case surrounding said reversible pump, said third fluid line having a check valve therein, said check valve being operable to pass all of the excess hydraulic fluid from said booster pump to said case of said reversible pump to cool said pump.

Claim 31

The hydraulic transmission of claim 26 which includes a third fluid line connected between said combination relief and shuttle valve and said reservoir for returning excess fluid to said reservoir, said third fluid line including a low-pressure relief valve operable to maintain a minimum booster pump pressure in said low-pressure line of said closed loop.

Claim 32

The hydraulic transmission of claim 26 wherein said combination relief and shuttle valve has three ports, two of said ports being connected to said pair of fluid lines and a third port being connected to a line which connects said valve to said reservoir.

Claim 33

The hydraulic transmission of claim 31 which further includes means to direct all of said booster pump fluId to the low-pressure line of said loop and means to direct the excess hydraulic fluid from said loop to said reservoir through a case surrounding one of said pump or motor.