Demand compensated hydraulic system with pressure amplifier

Abstract

A hydraulic system having fluid flow feedback from a fluid motor to a demand control valve which operates to change pump output to compensate for motor demand includes a pressure amplifier between the feedback system and the valve. The pressure amplifier includes a chamber with a piston therein which is slidable to connect or block pump output fluid flow to the valve in response to feedback pressure variations from the motor.

I claim: 
     
       1. An improved hydraulic system of the type having a variable displacement pump with an output control means biased to increase pump output and responsive to an input of pressurized fluid to decrease pump output, a fluid motor, a pressurized output line connected between the pump and the motor, a motor control valve interposed in the output line 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 mens 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 the .Iaddend.motor .Iadd.when the motor control valve is moved from a neutral position.Iaddend., wherein the improvement comprises: pressure amplifier means connected to the output line and interposed between the pilot line and the demand valve means and responsive to pressurized fluid in the pilot line to connect the output line to the demand valve means. 
     
     
       2. An improved hydraulic system of the type having a variable displacement pump with an output control mechanism biased to increase pump output and responsive to an input of pressurized fluid to decrease pump output a fluid motor, a pressurized output line connected between the pump and the motor, a motor control valve interposed in the output line for selectively opening and closing the output line, a control line connected between the pump and the output control mechanism, 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 mechanism 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 the .Iaddend.motor .Iadd.when the motor control valve is moved from a neutral position.Iaddend., a restricted reservoir line leading from the pilot line to a reservoir, wherein the improvement comprises: pressure amplifier means connected to the output line and interposed between the pilot line and the demand valve means and responsive to pressurized fluid in the pilot line to connect the output line to the demand valve means, said pressure amplifier means including restricted passage means for connecting the pilot line to the reservoir. 
     
     
       3. An improved hydraulic system of the type having a variable displacement pump with an output control mechanism biased to increase pump output and responsive to an input of pressurized fluid to decrease pump output, a fluid motor, a pressurized output line connected between the pump and motor, a motor control valve interposed in the output line for selectively opening and closing the output line, the control line connected between the pump and output control mechanism, demand valve means interposed in the control line for selectively opening and closing the control line to allow and block input of pressurized fluid to the output control mechanism 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 the motor when the motor control valve is moved from a neutral position.Iaddend., wherein the improvement comprises: pressure amplifier means having a port therein connected to the output line and a chamber provided therein; piston means slidably received in and dividing the chamber into a pilot side chamber connected to the pilot line and a demand side chamber connected to the demand valve means, said piston means having port means therein connected to the demand side chamber and operatively associated with the port, and said piston means slidable to connect the port means to the port in response to pressurized fluid in the pilot side chamber; and biasing means urging the piston means to a position to block the port means from the port. 
     
     
       4. An improved hydraulic system of the type having a variable displacement pump with an output control mechanism biased to increase pump output and responsive to an input of pressurized fluid to decrease pump output, a fluid motor, a pressurized output line connected between the pump and motor, a motor control valve interposed in the output line for selectively opening and closing the output line, a control line connected between the pump and output control mechanism, 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 mechanism 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 motor, a restricted reservoir line leading from the pilot line to a reservoir, wherein the improvement comprises: pressure amplifier means interposed between the pilot line and the demand valve means having a port connected to the output line, said pressure amplifier means having a chamber provided therein in fluid communication with the port; piston means slidably received in and dividing the chamber into a pilot side chamber connected to the pilot line and the demand side chamber connected to the demand valve means, said piston means having port means therein, said piston means having fluid passage means therein connecting the port means to the demand side chamber and having restricted passage means provided therein connecting the port means to the pilot side chamber, said piston means operatively associated with the port and slidable to connect the port means to the port in response to pressurized fluid in the pilot side chamber; and biasing means urging the piston means to block the port means from the port.