Hydrostatic Circuit Flushing Flow Cancellation

Abstract

Flushing circuits for closed loop hydrostatic circuits enable overriding of the normal function of the flushing circuit during certain machine operational events where flushing can cause undesirable performance issues. The disclosed flushing circuits may prevent flow from leaving the flush valve, may prevent flow from leaving the flushing circuit, may prevent flow from entering the flushing circuit, may prevent the flush valve from shifting from a normally closed position to an open position or may replace the hydro-mechanical control of the flush valve with an electronic control. Cancellation of the flushing function may be commanded by a controller based on fluid temperatures, pressures, turning commands, engine speed, etc.

1 . A hydrostatic circuit comprising:
 a hydrostatic pump connected to first and second input/output lines;   the first and second input/output lines connected to a hydrostatic motor to form a loop;   a flush valve, a control valve and a flush outlet;   the first and second input/output lines also connected to one of the flush valve or the control valve, the flush valve and control valve configured to perform three functions including providing communication between the first input/output line and the flush outlet, providing communication between the second input/output line and the flush outlet and isolating the first and second input/output lines from the flush outlet;   a controller in communication with the control valve for opening the control valve and providing communication between the flush valve and the flush outlet, for closing the control valve and isolating the flush valve from the flush outlet and for reestablishing communication between one of the flush valve and the flush outlet.   
     
     
         2 . The hydrostatic circuit of  claim 1  wherein the control valve is a normally open proportional solenoid control valve. 
     
     
         3 . The hydrostatic circuit of  claim 1  further including a flush flow regulator valve disposed downstream of the flush valve. 
     
     
         4 . The hydrostatic circuit of  claim 1  further including a flush flow regulator valve disposed downstream of the control valve. 
     
     
         5 . The hydrostatic circuit of  claim 2  wherein the normally open proportional solenoid control valve is in communication with the controller and is disposed between the flush valve and the flush outlet, the normally open proportional solenoid control valve being adjustable between a fully open position providing full flow between the flush valve and the flush outlet and a fully closed position stopping flow between the flush valve and the flush outlet. 
     
     
         6 . The hydrostatic circuit of  claim 5  further including a flush flow regulator valve disposed downstream of the normally open proportional solenoid control valve. 
     
     
         7 . The hydrostatic circuit of  claim 6  wherein the flush flow regulator valve is pilot operated. 
     
     
         8 . The hydrostatic circuit of  claim 1  further comprising a temperature sensor linked to the controller for communicating a temperature of fluid in the hydrostatic circuit to the controller, and
 if the temperature of the fluid is below the predetermined temperature, the controller closes the control valve, and 
 if the temperature of the fluid is above the predetermined temperature, the controller opens the control valve. 
 
     
     
         9 . The hydrostatic circuit of  claim 1  further including a first pressure sensor in the first input/output line and a second pressure sensor in the second input/output line, the first and second pressure sensors being linked to the controller, and
 if a first pressure in the first input/output line and a second pressure in the second input/output line are both below a predetermined pressure, the controller closes the control valve. 
 
     
     
         10 . The hydrostatic circuit of  claim 1  further including a first pressure sensor in the first input/output line and a second pressure sensor in the second input/output line, the first and second pressure sensors being linked to the controller, the controller having a memory programmed to calculate differences between pressures sensed by the first and second pressure sensors and if said difference is less than about 20 bar, the controller closes the control valve. 
     
     
         11 . The hydrostatic circuit of  claim 1  wherein the controller is linked to a steering mechanism, the steering mechanism for communicating an operator command for machine steering to the controller, wherein, upon receiving an operator command for machine steering from the steering mechanism, the controller closes the control valve. 
     
     
         12 . The hydrostatic circuit of  claim 11  wherein if the steering command exceeds a predetermined time period, the controller opens the control valve. 
     
     
         13 . The hydrostatic circuit of  claim 11  wherein if the controller receives a straight command from the steering mechanism after receiving an operator command for machine steering from the steering mechanism, the controller opens the control valve. 
     
     
         14 . The hydrostatic circuit of  claim 1  wherein the flush outlet is connected to a fluid tank, the fluid tank including a temperature sensor that is linked to the controller, wherein if the temperature in the tank is below a predetermined temperature, the controller closes the control valve and if the temperature in the tank is above the predetermined temperature, the controller opens the control valve. 
     
     
         15 . A hydrostatic circuit comprising:
 a hydrostatic pump connected to first and second input/output lines;   the first and second input/output lines connected to a hydrostatic motor to form a loop;   the first and second input/output lines also connected to a flush valve, the flush valve including a spool that is moveable between a first position providing communication between the first input/output line and a flush outlet line, a second position providing communication between the second input/output line and the flush outlet line and a third position wherein the flush valve isolates the first and second input/output lines from the flush outlet line;   the flush outlet line terminating at a flush outlet;   a controller linked to at least one flush valve override component selected from the group consisting of
 a normally open solenoid control valve disposed downstream of the flush valve and upstream of the flush outlet and in communication with the controller and being moveable to a closed position for stopping flow from the flush valve to the flush outlet, 
 a normally open solenoid control valve disposed upstream of the flush valve and in communication with the controller and being moveable to a closed position for stopping flow from the first and second input/output lines to the flush valve, 
 a normally open solenoid control valve disposed upstream of the flush valve and in communication with the controller and being moveable to a closed position for preventing communication between the first and second input/output lines and the flush valve, and 
 a pair of solenoids disposed at opposing ends of the flush valve and in communication with the controller for maintaining the flush valve in its normally closed position; and 
   at least one temperature sensor linked to the controller for communicating a temperature of fluid in the hydrostatic circuit to the controller, and   a plurality of pressure sensors linked to the controller for communicating pressures in the first and second input/output lines to the controller.   
     
     
         16 . The hydrostatic circuit of  claim 15  wherein the normally open solenoid control valve disposed downstream of the flush valve and upstream of the flush outlet is a normally open proportional solenoid control valve that is adjustable between a fully open position providing full flow between the flush valve and the flush outlet and a fully closed position stopping flow between the flush valve and the flush outlet. 
     
     
         17 . The hydrostatic circuit of  claim 15  further including a flush flow regulator valve disposed downstream of the flush valve. 
     
     
         18 . The hydrostatic circuit of  claim 17  wherein the override component is disposed downstream of the flush flow regulator valve. 
     
     
         19 . A method for overriding a flushing function of a flush valve of a closed loop hydrostatic circuit, the method comprising:
 overriding the flushing function in response to at least one operating condition selected from the group consisting of:
 a) measuring a temperature of a fluid in the circuit, 
 if the temperature of the fluid is below a predetermined minimum temperature, sending a signal to stop any flushing flow from the circuit to a flush outlet, 
 b) measuring a loop pressure of the fluid in the circuit, 
 if the loop pressure is below a predetermined minimum loop pressure, sending a signal to stop any flushing flow from the circuit to the flush outlet, 
 c) measuring pressures in first and second input/output lines of the circuit, 
 calculating a difference (ΔP) between the pressures in the first and second input/output lines, 
 if the ΔP is below a predetermined minimum ΔP, sending a signal to stop any flushing flow from the circuit to the flush outlet, 
 d) receiving a turning command, 
 sending a signal to stop any flushing flow from the circuit to the flush outlet, 
 e) receiving a turning command, 
 sending a signal to stop any flushing flow from the circuit to the flush outlet, 
 timing a duration of the turning command, 
 if the duration of the turning command exceeds a predetermined maximum turning time period, sending a signal to initiate flushing flow from the circuit to the flush outlet, 
 receiving a straight steering command, 
 sending a signal to initiate flushing flow from the circuit to the flush outlet. 
   
     
     
         20 . The method of  claim 19  wherein the receiving and sending is performed by a controller.