Variable pressure hydraulic system

Claim 2

A variable pressure hydraulic system comprising: a variable displacement pump having output control means including a pressure chamber operative to reduce pump output as pressure in the chamber increases; the pump having an outlet; a hydraulic motor connected to the pump outlet; a pump control valve having a movable valve member responsive to pump outlet pressure to move in a direction to operatively interconnect the pump outlet and the pressure chamber; yieldable force-applying means biasing the valve member in an opposite direction to establish a minimum pump output pressure; means responsive to fluid pressure at the hydraulic motor to increase the pressure level at the pump outlet necessary to move the valve member to operatively interconnect the pump outlet and the pressure chamber; means movable by the hydraulic motor; and normally open valve means responsive to the movable means reaching a predetermined position to move to a closed position in which it blocks fluid pressure from the fluid pressure responsive means.

Claim 3

A variable pressure hydraulic system as set forth in claim 1 wherein the valve means connects the fluid pressure responsive means to a fluid reservoir when in the closed position.

Claim 4

A variable pressure hydraulic system as set forth in claim 2 wherein the yieldable force-applying means is a control spring urging the movable valve member in a direction to increase the pressure level at the pump outlet necessary to move the valve member to operatively interconnect the pump outlet and the pressure chamber, and the fluid pressure responsive means includes a piston slidably mounted in a piston bore and acting on the spring to increase the spring force on the valve member.

Claim 5

A variable pressure hydraulic system as set forth in claim 1 wherein the valve means includes a valve element movable between open and closed positions, spring means normally biasing the valve element to the open position; the means movable by the hydraulic motor includes a rockshaft; and an arm on the rockshaft engages the valve element to move the same against the bias of the spring means to a closed position rockshaft the rocQshaft has been rotated to a predetermined position.

Claim 6

A variable pressure hydraulic system comprising: a variable displacement pump having output control means including a pressure chamber operative to vary pump output according to changes in pressure in the chamber; the pump having an outlet; a hydraulic motor; fluid line means connecting the hydraulic motor to the pump outlet; a pump control valve having a movable valve member; means operable by pump outlet pressure to move the valve member in a direction to operatively interconnect the pump outlet and the pressure chamber; first means operable to bias the valve member in the opposite direction to establish a minimum pump outlet pressure; a pilot line connected to the fluid line means to be pressurized in accordance with the pressure at the hydraulic motor; second means responsive to fluid pressure in the pilot line operable to apply a biasing force on the valve member to increase the pressure level at said pump outlet necessary to move the valve member to operatively interconnect the pump outlet and the pressure chamber; means movable by the hydraulic motor; and a normally open valve means interposed in the pilot line and responsive to a predetermined movement of the movable means to close and block fluid communication between the second means and the fluid line means.

Claim 7

A variable pressure hydraulic system comprising: a variable displacement pump having output control means including a pressure chamber operative to vary pump output according to changes in pressure in the chamber; the pump having an outlet; a hydraulic motor; fluid line means connecting the hydraulic motor to the pump outlet; a pump control valve having a movable valve member; means operable by pump outlet pressure to move the valve member in a direction to operatively interconnect the pump outlet and the pressure chamber; first means operable to bias the valve member in the opposite direction to establish a minimum pump outlet pressure; a pilot line connected to the fluid line means to be pressurized in accordance with the pressure at the hydraulic motor; second means responsive to fluid pressure in the pilot line operable to apply a biasing force on the valve member to increase the pressure level at said pump outlet necessary to move the valve member to operatively interconnect the pump outlet and the pressure chamber; means movable by the hydraulic motor; and a normally open valve means interposed in the pilot line and responsive to a predetermined movement of the movable means to close and block fluid communication between the second means and the fluid line means.

Claim 8

A hydraulic system as set forth in claim 5 wherein the first means includes a control spring applying a force on the valve member, and the second means includes a slidable piston acting on the control spring and responsive to fluid pressure in the pilot line to increase the spring force applied to the valve member.

Claim 9

A hydraulic system as set forth in claim 5 wherein the valve means interposed in the pilot line connects the second means to a fluid reservoir when in the closed position.

Claim 10

A hydraulic system comprising: a variable displacement pump having output control means including a pressure chamber operative to vary pump output according to changes in pressure in the chamber; a fluid pressure motor; a high pressure line connected between the pump and motor; a motor control valve interposed in the high pressure line for selectively opening and closing said high pressure line to the motor; fluid passage means between the high pressure line upstream of the motor control valve and the pressure chamber; a spring-loaded normally closed valve in the fluid passage means normally blocking communication between the high pressure line and pressure chamber and responsive to a predetermined pressure in the high pressure line to open and establish communication between the high pressure line and the pressure chamber; a pilot line connected between the high pressure line downstream of the control valve and the spring-loaded valve to apply the pressure in the high pressure line downstream of the control valve to the spring-loaded valve to increase the closing force on the spring-loaded valve; means movable by the fluid pressure motor; and normally open valve means in the pilot line responsive to a predetermined movement of the movable means to close and block communication between the high pressure line downstream of the control valve and the spring-loaded valve.

Claim 11

A hydraulic system comprising: a variable displacement pump having output control means including a pressure chamber operative to vary pump output according to changes in pressure in the chamber; a fluid pressure motor; a high pressure line connected between the pump and motor; a motor control valve interposed in the high pressure line for selectively opening and closing said high pressure line to the motor; fluid passage means between the high pressure line upstream of the motor control valve and the pressure chamber; a spring-loaded normally closed valve in the fluid passage means normally blocking communication between the high pressure line and pressure chamber and responsive to a predetermined pressure in the high pressure line to open and establish communication between the high pressure line and the pressure chamber; a pilot line connected between the high pressure line downstream of the control valve and the spring-loaded valve to apply the pressure in the high pressure line downstream of the control valve to the spring-loaded valve to increase the closing force on the spring-loaded valve; means movable by the fluid pressure motor; and normally open valve means in the pilot line responsive to a predetermined movement of the movable means to close and block communication between the high pressure line downstream of the control valve and the spring-loaded valve.

Claim 12

A variable pressure hydraulic system comprising: a variable displacement pump having stroke control means including a pressure chamber operative to decrease the pump stroke as the pressure in the chamber increases; the pump having an outlet; a hydraulic motor; fluid line means interconnecting the pump outlet and the motor; a flow control valve interposed in the fluid line means for selectively opening and closing the fluid line means to the motor; a pump control valve having a movable valve member responsive to pressure at the pump outlet to move in a direction to operatively interconnect the pump outlet and the pressure chamber; yieldable force-applying means biasing the valve member in an opposite direction to establish a minimum pump outlet pressure; fluid pressure responsive means acting on the pump control valve to increase the pressure level at the pump outlet necessary to move the valve member to operatively interconnect the pump outlet with the pressure chamber; pilot line means interconnecting the pressure responsive means with the fluid line means between the hydraulic motor and the flow control valve; normally open valve means interposed in the pilot line means and movable to a closed position in which it blocks fluid pressure from the pressure responsive means; and means movable by the hydraulic motor operatively associated with the valve means to close the valve means upon movement to a predetermined position.

Claim 13

A variable pressure hydraulic system comprising: a variable displacement pump having stroke control means including a pressure chamber operative to decrease the pump stroke as the pressure in the chamber increases; the pump having an outlet; a hydraulic motor; fluid line means interconnecting the pump outlet and the motor; a flow control valve interposed in the fluid line means for selectively opening and closing the fluid line means to the motor; a pump control valve having a movable valve member responsive to pressure at the pump outlet to move in a direction to operatively interconnect the pump outlet and the pressure chamber; yieldable force-applying means biasing the valve member in an opposite direction to establish a minimum pump outlet pressure; fluid pressure responsive means acting on the pump control valve to increase the pressure level at the pump outlet necessary to move the valve member to operatively interconnect the pump outlet with the pressure chamber; pilot line means interconnecting the pressure responsive means with the fluid line means between the hydraulic motor and the flow control valve; normally open valve means interposed in the pilot line means and movable to a closed position in which it blocks fluid pressure from the pressure responsive means; and means movable by the hydraulic motor operatively associated with the valve means to close the valve means upon movement to a predetermined position.

Claim 14

A variable pressure hydraulic system as set forth in claim 9 wherein a restricted reservoir line connects the pressure chamber with a fluid reservoir.

Claim 15

A variable pressure hydraulic system as set forth in claim 10 wherein the valve means interposed in the fluid line means connects the pressure responsive means with the fluid reservoir when in the closed position.

Claim 16

A variable pressure hydRaulic system as set forth in claim 11 wherein the means movable by the hydraulic motor is a rockshaft, and an arm on the rockshaft engages the valve means to close the valve means after the rockshaft has been rotated to a predetermined position.

Claim 17

A variable pressure hydraulic system as set forth in claim 12 wherein the flow control valve is a servo valve operatively associated with and responsive to the position of the rockshaft to close the fluid line means to the hydraulic motor when the rockshaft reaches the predetermined position.

Claim 18

A variable pressure hydraulic system as set forth in claim 11 wherein a check valve is interposed in the fluid line means to prevent reverse flow through the fluid line means.