Load limiting system

Claim 2

In a hydraulic control system including a source of fluid supply; a fluid motor; a control valve connected to said motor; said control valve having an inlet port and a movable valving member which communicates pressure flow to said motor; a fluid responsive valve means connected to said source of fluid supply and said inlet port; a control circuit connected to said control valve and said fluid responsive valve means; said fluid responsive valve means being responsive to said control circuit to control the fluid supplied to said control valve; limit valve means connected to said motor and said control circuit; said limit valve means being responsive to predetermined pressure conditions at said motor to reduce the pressure in said control circuit to thereby reduce the fluid supply and prevent further actuation of said motor.

Claim 3

A control system as claimed in claim 1 wherein said limit valve has at least one fluid responsive area connected to said motor to move said valve to reduce the pressure in said control circuit and a spring resisting such movement.

Claim 4

A control system as claimed in claim 2 wherein said limit valve has an inactive position and a limit position to which it is moved by pressure acting on said fluid responsive area, and said limit valve in said limit position providing a connection between said control circuit and said return conduit.

Claim 5

In a hydraulic system including a source of fluid supply comprising a pump, a fluid motor; a control valve connected to said source and said motor and having an inlet port, first and second motor ports, first and second control ports, and a movable valving member to direct pressure flow to said motor, to receive flow back from said motor; and to connect one of said control ports to one of said motor ports when said one motor port is connected to said inlet port; conduit means connecting said pump to said inlet port, and said motor ports to said motor; a fluid responsive means connected to said conduit means interconnecting said source of fluid supply and said inlet port and responsive to a control signal pressure to control the fluid supplied to said control valve; shuttle valve means connected to said first and said second control ports; a control conduit connecting said shuttle valve and said fluid responsive means; said shuttle valve means being effective to allow fluid from the control port that is connected to the motor port by said movable valving member to flow to said fluid responsive means for use as said control signal pressure; limit valve means connected to said control conduit and said fluid motor; said limit valve means being responsive to predetermined fluid pressure conditions at said motor to reduce the signal pressure in said control conduit and prevent further actuation of said motor; said limit valve means has a fluid responsive area connected to said fluid motor; said limit valve means having an inactive position and a limit position to which it is moved by pressure acting on said fluid responsive area; and said limit valve means in said limit position providing a connection between said control circuit and said return conduit.

Claim 6

In a hydraulic system including a source of fluid supply comprising a pump, a fluid motor; a control valve connected to said source and said motor and having an inlet port, first and second motor ports, first and second control ports, and a movable valving member to direct pressure flow to said motor, to receive flow back from said motor; and to connect one of said control ports to one of said motor ports when said one motor port is connected to said inlet port; conduit means connecting said pump to said inlet port, and said motor ports to said motor; a fluid responsive means connected to said conduit means interconnecting said source of fluid supply and said inlet port and responsive to a control signal pressure to control the fluid supplied to said control valve; shuttle valve means connected to said first and said second control ports; a control conduit connecting said shuttle valve and said fluid responsive means; said shuttle valve means being effective to allow fluid from the control port that is connected to the motor port by said movable valving member to flow to said fluid responsive means for use as said control signal pressure; limit valve means connected to said control conduit and said fluid motor; said limit valve means being responsive to predetermined fluid pressure conditions at said motor to reduce the signal pressure in said control conduit and prevent further actuation of said motor; said limit valve means has a fluid responsive area connected to said fluid motor; said limit valve means having an inactive position and a limit position to which it is moved by pressure acting on said fluid responsive area; and said limit valve means in said limit position providing a connection between said control circuit and said return conduit.

Claim 7

A control system as claimed in claim 4 wherein said fluid motor has two chambers and said limit valve has a fluid responsive area connected to each of said chambers to move said valve to reduce the pressure in said control circuit and a spring resisting such movement.

Claim 8

In a hydraulic control system including a source of fluid supply; a first fluid motor having a piston connected to a load for moving the load through one path of movement; a second fluid motor connected to the load to move same through a different path of movement; the first motor having a pair of fluid chambers; the load acting to create a pressure in one of said chambers which will vary directly with the load; a control valve connected to each of said motors and each having an inlet port and a movable valving member adapted to direct pressure flow to the motors to actuate same; a fluid responsive valve connected to said source of fluid supply and said inlet ports; a control circuit connected to said control valves and said fluid responsive valve; said fluid responsive valve being responsive to said control circuit to control the fluid supplied to said control valves; a first limit valve associated with said first motor and connected to said one chamber and said control circuit; a second limit valve associated with said second fluid motor and connected to said one chamber and said control circuit; each of said limit valves being responsive to a predetermined pressure in said one chamber to reduce the pressure in said control circuit to thereby reduce the fluid supply and prevent further actuation of its respective motor.

Claim 9

In a hydraulic control system including a source of fluid supply; a first fluid motor having a piston connected to a load for moving the load through one path of movement; a second fluid motor connected to the load to move same through a different path of movement; the first motor having a pair of fluid chambers; the load acting to create a pressure in one of said chambers which will vary directly with the load; a control valve connected to each of said motors and each having an inlet port and a movable valving member adapted to direct pressure flow to the motors to actuate same; a fluid responsive valve connected to said source of fluid supply and said inlet ports; a control circuit connected to said control valves and said fluid responsive valve; said fluid responsive valve being responsive to said control circuit to control the fluid supplied to said control valves; a first limit valve associated with said first motor and connected to said one chamber and said control circuit; a second limit valve associated with said second fluid motor and connected to said one chamber and said control circuit; each of said limit valves being responsive to a predetermined pressure in said one chamber to reduce the pressure in said control circuit to thereby reduce the fluid supply and prevent further actuation of its respective motor.

Claim 10

A control system as claimed in claim 6 wherein each of said limit valves has a fluid responsive area to move said limit valves to reduce the pressure in said control circuit and biasing means imposing a force on said valve resisting such movement.

Claim 11

A control system as claimed in claim 7 wherein said biasing means imposes a different force on one of said limit valves as compared to the other whereby one of said limit valves will reduce the pressure in said control circuit at a different pressure in said one chamber as compared to the pressure at which said other limit valve will interrupt said control circuit.

Claim 12

A control system as claimed in claim 6 wherein an over-ride valve means is connected between said control circuit and one of said limit valves, cam means connected to said load and movable therewith during lifting and lowering movement of said load, whereby at predetermined heights of said load said over-ride valve will be actuated by said cam means to prevent said limit valve means from interrupting said control circuit.

Claim 13

In a hydraulic control system including a source of fluid supply; a fluid motor having a piston connected to a load; the motor having a pair of fluid chambers; the load acting to create a pressure in one of said chambers which will vary directly with the load; a control valve connected to said fluid motor having an inlet port and a movable valving member to direct pressure flow to said motor; a fluid responsive means connected to said source of fluid supply and said inlet port; a control circuit connected to said control valve and said fluid responsive means; said fluid responsive means being responsive to said control circuit to control the fluid supplied to said control valve; limit valve means connected to said chambers and said control circuit; said limit valve means being responsive to the pressure differential of said chambers to reduce the pressure in said control circuit to thereby reduce the fluid supply and prevent further actuation of said motor.

Claim 14

In a hydraulic control system including a source of fluid supply; a fluid motor having a piston connected to a load; the motor having a pair of fluid chambers; the load acting to create a pressure in one of said chambers which will vary directly with the load; a control valve connected to said fluid motor having an inlet port and a movable valving member to direct pressure flow to said motor; a fluid responsive means connected to said source of fluid supply and said inlet port; a control circuit connected to said control valve and said fluid responsive means; said fluid responsive means being responsive to said control circuit to control the fluid supplied to said control valve; limit valve means connected to said chambers and said control circuit; said limit valve means being responsive to the pressure differential of said chambers to reduce the pressure in said control circuit to thereby reduce the fluid supply and prevent further actuation of said motor.

Claim 15

In a hydraulic control system including a source of fluid supply; a first fluid motor having a piston connected to a load and adapted to move the load through one path of movement; a second fluid motor connected to the load adapted to move same through a different path of movement; the first motor having a pair of fluid chambers; the load acting to create a pressure in one of said chambers which will vary directly with the load; a control valve connected to each of said motors and each having an inlet port and a movable valving member to direct pressure flow to the motors to actuate same; a fluid responsive valve connected to said source of fluid supply and said inlet ports; a control circuit connected to said control valves and said fluid responsive valve; said fluid responsive valve being responsive to said control circuit to control the fluid supplied to said control valves; a first limit valve associated with said first motor and connected to said chambers and said control circuit; a second limit valve associated with said second fluid motor and connected to said chambers and said control circuit; each of said limit valves being responsive to a predetermined pressure differential between said chambers to interrupt said control circuit to thereby reduce the fluid supply and prevent further actuation of its respective motor.

Claim 16

In a hydraulic control system including a source of fluid supply; a first fluid motor having a piston connected to a load and adapted to move the load through one path of movement; a second fluid motor connected to the load adapted to move same through a different path of movement; the first motor having a pair of fluid chambers; the load acting to create a pressure in one of said chambers which will vary directly with the load; a control valve connected to each of said motors and each having an inlet port and a movable valving member to direct pressure flow to the motors to actuate same; a fluid responsive valve connected to said source of fluid supply and said inlet ports; a control circuit connected to said control valves and said fluid responsive valve; said fluid responsive valve being responsive to said control circuit to control the fluid supplied to said control valves; a first limit valve associated with said first motor and connected to said chambers and said control circuit; a second limit valve associated with said second fluid motor and connected to said chambers and said control circuit; each of said limit valves being responsive to a predetermined pressure differential between said chambers to interrupt said control circuit to thereby reduce the fluid supply and prevent further actuation of its respective motor.

Claim 17

In a hydraulic control system adapted for use with a load-lifting vehicle having at least one hydraulic tilt cylinder for tilting a load; a source of fluid supply; a return conduit to return fluid to said source; said tilt cylinder having a piston connected to a load; the tilt cylinder having a first hydraulic chamber for forward tilting and a second hydraulic chamber for rearward tilting; the load acting to create a pressure in said second chamber which will vary directly with the size of the load; a control valve connected to said cylinder having an inlet port and a movable valving member to direct pressure flow to said motor; a fluid responsive means connected to said source of fluid supply and said inlet port; a control circuit connected to said control valve and said fluid responsive means; said fluid responsive means being responsive to said control circuit to control the fluid supplied to said control valve; limit valve means connected to said first and second hydraulic chambers and said control circuit; said limit valve means being responsive to a predetermined pressure differential between said first and second chambers to reduce the pressure in said control circuit to thereby reduce the fluid supply and prevent further actuation of said motor.

Claim 18

In a hydraulic control system adapted for use with a load-lifting vehicle having at least one hydraulic tilt cylinder for tilting a load; a source of fluid supply; a return conduit to return fluid to said source; said tilt cylinder having a piston connected to a load; the tilt cylinder having a first hydraulic chamber for forward tilting and a second hydraulic chamber for rearward tilting; the load acting to create a pressure in said second chamber which will vary directly with the size of the load; a control valve connected to said cylinder having an inlet port and a movable valving member to direct pressure flow to said motor; a fluid responsive means connected to said source of fluid supply and said inlet port; a control circuit connected to said control valve and said fluid responsive means; said fluid responsive means being responsive to said control circuit to control the fluid supplied to said control valve; limit valve means connected to said first and second hydraulic chambers and said control circuit; said limit valve means being responsive to a predetermined pressure differential between said first and second chambers to reduce the pressure in said control circuit to thereby reduce the fluid supply and prevent further actuation of said motor.

Claim 19

A hydraulic control system as claimed in claim 12 including a hydraulic lift cylinder adapted to move said load to selective heights; said lift cylinder having a pressure chamber and a piston connected to said load; a second limit valve means connected to said first and second hydraulic chambers and said control circuit; said second limit valve means being responsive to a predetermined pressure differential between said first and second hydraulic chambers to interrupt said control circuit to thereby reduce the fluid supply and prevent further lifting of said load by said second hydraulic cylinder.