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 normally responsive to fluid pressure delivered to the hydraulic motor to increase the pressure level necessary to move the valve member to operatively interconnect the pump outlet and the pressure chamber; normally open valve means movable to a closed position in which it blocks fluid pressure from the fluid pressure responsive means; and pressure responsive valve control means operatively connected to and for moving the normally open valve means responsive to pressure at the hydraulic motor to move the valve means to the closed position when the fluid pressure at the hydraulic motor reaches a predetermined value to thereby limit the maximum pump output pressure.

Claim 3

A variable pressure hydraulic system as set forth in claim 1 wherein the valve control means includes a solenoid operatively associated with the valve means, an electrical circuit for the solenoid, and a pressure sensitive switch in the electrical circuit.

Claim 4

A variable pressure hydraulic system as set forth in claim 2 wherein the solenoid moves the valve means to the closed position when activated, the pressure sensitive switch is normally biased to the open position and closes to complete the electrical circuit when the fluid pressure at the hydraulic motor reaches the predetermined value.

Claim 5

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; a normally open valve means interposed in the pilot line movable to a closed position in which it blocks fluid communication between the second means and the fluid line means; and control means operatively associated with the valve means responsive to a predetermined fluid pressure at the hydraulic motor to move the valve means to the closed 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; a normally open valve means interposed in the pilot line movable to a closed position in which it blocks fluid communication between the second means and the fluid line means; and control means operatively associated with the valve means responsive to a predetermined fluid pressure at the hydraulic motor to move the valve means to the closed position.

Claim 7

A variable pressure hydraulic system as set forth in claim 4 wherein the control means includes a solenoid connected to and for controlling the movement of the valve means, an electrical circuit for the solenoid, and a pressure sensitive switch in the electrical circuit.

Claim 8

A variable pressure hydraulic system as set forth in claim 5 wherein the pressure sensitive switch includes a movable piston carrying a switch contact and having one end in fluid communication with the hydraulic motor, and spring means acting against the opposite end of the piston to normally move the pistOn in a direction to open the switch.

Claim 9

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 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; normally open valve means in the pilot line movable to a closed position in which it blocks communication between the high pressure line downstream of the control valve and the spring-loaded valve, and pressure sensitive valve control means operatively connected to and for moving the valve means responsive to pressure at the fluid motor to move the valve means to the closed position when the fluid pressure at the fluid motor reaches a predetermined value.

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 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; normally open valve means in the pilot line movable to a closed position in which it blocks communication between the high pressure line downstream of the control valve and the spring-loaded valve, and pressure sensitive valve control means operatively connected to and for moving the valve means responsive to pressure at the fluid motor to move the valve means to the closed position when the fluid pressure at the fluid motor reaches a predetermined value.

Claim 11

A hydraulic system as set forth in claim 7 wherein the valve control means includes a solenoid operatively associated with the valve means, an electrical circuit for the solenoid, and a pressure sensitive switch in the electrical circuit.

Claim 12

A hydraulic system as set forth in claim 8 wherein a check valve is interposed in the high pressure line between the fluid motor and motor control valve, an exhaust line interconnects the fluid motor and motor control valve, the pilot line is connected to the high pressure line between the check valve and motor control valve, and means are provided to afford a controlled bleed of fluid from the pilot line.

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 solenoidcontrolled 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 upon actuation of the solenoid; and normally open pressure responsive switch means responsive to a predetermined fluid pressure level at the hydraulic motor to close and complete an electrical circuit for the solenoid to activate the solenoid.

Claim 14

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 solenoidcontrolled 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 upon actuation of the solenoid; and normally open pressure responsive switch means responsive to a predetermined fluid pressure level at the hydraulic motor to close and complete an electrical circuit for the solenoid to activate the solenoid.

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. 12. A hydraulic system as set forth in claim 11 wherein a check valve is interposed in the high pressure line between the fluid motor and motor control valve, an exhaust line interconnects the fluid motor and motor control valve, the pilot line is connected to the high pressure line between the check valve and motor control valve, and means are provided to afford a controlled bleed of fluid from the pilot line.