Demand compensated hydraulic system with flow sensitive device

Abstract

A demand compensated hydraulic system includes a pump responsive to pressurized fluid in a demand feedback pilot line. The pilot line is connected to sense fluid demand between a hydraulic motor and its associated control valve which is closed by servo feedback from the motor. A flow sensitive device is interposed in an output line connecting the pump and the control valve to sense when the flow decreases until it is insufficient to operate the function. At a predetermined decreased flow rate, the flow sensitive device operates to momentarily connect the demand feedback pilot line to a reservoir to cause the pump to go into a stand-by condition.

I claim: 
     
       1. An improved hydraulic system of the type having a variable displacement pump with output control means biased to increase pump output fluid flow and responsive to an input of pressurized fluid to decrease pump output fluid flow, a fluid motor, an output line connected between the pump and the motor, a motor control valve interposed in the output line and having servo feedback from the motor for selectively opening and closing the output line, a control line connected between the pump and the output control means, demand valve means interposed in the control line for selectively opening and closing the control line to allow and block the input of pressurized fluid to the output control means in response to pressurized fluid in a pilot line connected to the demand valve means, said pilot line .[.further connected to the output line between.]. .Iadd.operatively associated with .Iaddend.the motor control valve and .Iadd.pressurized by the pressurized fluid to .Iaddend.the motor .Iadd.when the motor control valve is moved from a neutral position, .Iaddend.wherein the improvement comprises: means operatively associated with the output line, the pilot line, and a fluid reservoir responsive to .[.descreasing.]. .Iadd.decreasing .Iaddend.flow through the output line to connect the pilot line to the reservoir and responsive to increasing fluid flow in the output line to block the pilot line from the reservoir. 
     
     
       2. An improved hydraulic system of the type having a variable displacement pump with output control means biased to increase pump output fluid flow and responsive to an input of pressurized fluid to decrease pump output fluid flow, a fluid motor, an output line connected between the pump and the motor, a motor control valve interposed in the output line and having servo feedback from the motor for selectively opening and closing the output control means, a control line connected between the pump and the output control means, demand valve means interposed in the control line for selectively opening and closing the control line to allow and block the input of pressurized fluid to the output control means in response to pressurized fluid in a pilot line connected to the demand valve means, said pilot line .[.further connected to the output line between.]. .Iadd.operatively associated with .Iaddend.the motor control valve and .Iadd.pressurized by the pressurized fluid to .Iaddend.the motor .Iadd.when the motor control valve is moved from a neutral position, .Iaddend.and a restricted reservoir .Iadd.line.Iaddend., wherein the improvement comprises: an additional reservoir line connecting the pilot line to the reservoir; and flow sensitive means interposed in the additional reservoir line and operatively associated with the output line responsive to fluid flow in the output line to block the flow of fluid from the pilot line through the additional reservoir line and to a decrease in the fluid flow to momentarily allow the flow of fluid from the pilot line through the additional reservoir line whereby the pressurized fluid in the pilot line is momentarily disturbed. 
     
     
       3. An improved hydraulic system of the type having a variable displacement pump with output control means biased to increase pump output fluid flow and responsive to an input of pressurized fluid to decrease pump output fluid flow, a fluid motor, an output line connected between the pump and the motor, a motor control valve interposed in the output line and having servo feedback from the motor for selectively opening and closing the output line, a control line connected between the pump and the output control means, demand valve means interposed in the control line for selectively opening and closing the control line to allow and block the input of pressurized fluid to the output control means in response to pressurized fluid in a pilot line connected to the demand valve means, said pilot line .[.further connected to the output line between.]. .Iadd.operatively associated with .Iaddend.the motor control valve and .Iadd.pressurized by the pressurized fluid to .Iaddend.the motor .Iadd.when the motor control valve is moved from a neutral position, .Iaddend.and a restricted reservoir line connecting the pilot line to a fluid reservoir, wherein the improvement comprises: flow sensitive means interposed in the output line between the pump and the motor control valve and connected by a first portion of an additional reservoir line to the pilot line and by a second portion of the additional reservoir line to the reservoir; said flow sensitive means including piston means having fluid passage means and ring means therein; said piston means responsive to increasing pump output fluid flow to successively block the fluid passage means from the first and second portions and to decreasing pump output fluid flow to successively connect the fluid passage means to the second and first portions; and said ring means responsive to piston means response to increasing pump output fluid flow to successively block and not block the fluid passage means from the first portion and to piston means response to decreasing pump output fluid flow to successively connect and block the fluid passage means from the first portion whereby the first and second portions are connected to the fluid passage means only with decreasing pump output fluid flow. 
     
     
       4. An improved hydraulic system of the type having a variable displacement pump with output control means biased to increase pump output fluid flow and responsive to an input of pressurized fluid to decrease pump output fluid flow, a fluid motor, an output line connected between the pump and the motor, a motor control valve interposed in the output line and having servo feedback from the motor for selectively opening and closing the output line, a control line connected between the pump and the output control means, demand valve means interposed in the control line for selectively opening and closing the control line to allow and block the input of pressurized fluid to the output control means in response to pressurized fluid in a pilot line connected to the demand valve means, said pilot line further connected to the output line between the motor control valve and the motor, and a restricted reservoir line connecting the pilot line to a fluid reservoir, wherein the improvement comprises: flow sensitive means interposed in the output line between the pump and the motor control valve, said flow sensitive means having a chamber provided therein; said chamber connected at one end to the pump connected portion of the output line and at the other end to the valve connected portion of the output line; a first fluid line connected at one end to the pilot line proximate the restricted reservoir line and at the other end to the chamber between the ends of the chamber; a second fluid line connected at one end to the reservoir and at the other end to the chamber between the connection of the first line and the one end of the chamber; piston means slidably positioned in the chamber and having an axial hole provided therein, said piston means having an annular groove therein, said piston means slidable toward the other end of the chamber in response to increasing pump output fluid flow to successively block the annular groove from the first and second lines; means biasing the piston means toward the one end of the chamber to successively connect the annular groove to the second and first lines; and ring means positioned in the annular groove and slidable in the chamber by the piston means sliding toward the other end of the chamber to successively block and not block the annular groove from the first line and by the piston means sliding toward the one end of the chamber to successively connect and block the annular groove from the first line whereby the first and second lines are connected to the annular groove only with decreasing fluid flow. 
     
     
       5. The hydraulic system as claimed in claim 4 further including restrictor means disposed in the second line. 
     
     
       6. The hydraulic system as claimed in claim 4 wherein the piston means includes means for minimizing resistance of the flow sensitive means to pump output fluid flow.