Pump system having open-loop torque control

Abstract

A pump system is disclosed. The pump system may have a pump with a displacement that is variable, and an actuator movable to adjust the displacement of the pump. The pump system may also have an electro-hydraulic valve fluidly connected to the actuator and configured to control movement of the actuator, and a variable resistor mechanically connected to at least one of the actuator and the pump. The variable resistor may be adjustable by movement of the at least one of the actuator and the pump to vary a current passing through the electro-hydraulic valve.

1 . A pump system, comprising:
 a pump having a displacement that is variable;   an actuator movable to adjust the displacement of the pump;   an electro-hydraulic valve fluidly connected to the actuator and configured to control movement of the actuator; and   a variable resistor mechanically connected to at least one of the actuator and the pump, and being adjustable by movement of the at least one of the actuator and the pump to vary a current passing through the electro-hydraulic valve.   
     
     
         2 . The pump system of  claim 1 , wherein the actuator is fluidly connected at a first end to an output of the pump and at an opposing second end to the electro-hydraulic valve. 
     
     
         3 . The pump system of  claim 2 , wherein the electro-hydraulic valve includes:
 a pilot-operated valve element movable from a first position at which the second end of the actuator is fluidly connected to the output of the pump, and a second position at which the second end of the actuator is fluidly connected to a low-pressure tank; and   a solenoid-operated valve element operable to control movement of the pilot-operated valve element between the first and second positions.   
     
     
         4 . The pump system of  claim 3 , further including:
 at least one working actuator;   an outlet passage extending from the pump to the at least one working actuator;   a control valve disposed within the outlet passage and configured to regulate operation of the at least one working actuator;   a first pilot passage extending from the outlet passage, at a first location upstream of the control valve, to a first end of the pilot-operated valve element;   a second pilot passage extending from the outlet passage, at a second location upstream of the control valve and downstream of the first location, to a second end of the pilot-operated valve element; and   a restricted orifice disposed within the second pilot passage.   
     
     
         5 . The pump system of  claim 4 , wherein the solenoid-operated valve element is configured to selectively relieve pressure in the second pilot passage by an amount corresponding to current passing through the electro-hydraulic valve. 
     
     
         6 . The pump system of  claim 5 , wherein the pilot-operated valve element is spring-biased toward the second position. 
     
     
         7 . The pump system of  claim 6 , further including at least one of pressure relief or pressure limiting device fluidly connected to the second end of the pilot-operated valve element. 
     
     
         8 . The pump system of  claim 1 , further including a signal conditioning device located between the variable resistor and the electro-hydraulic valve. 
     
     
         9 . The pump system of  claim 1 , further including a controller in communication with the electro-hydraulic valve and configured to issue an open-loop torque command to the electro-hydraulic valve. 
     
     
         10 . The pump of  claim 3 , further including:
 at least one working actuator;   an outlet passage extending from the pump to the at least one working actuator;   a control valve disposed within the outlet passage and configured to regulate operation of the at least one working actuator;   a first pilot passage extending from the outlet passage, at a first location upstream of the control valve, to a first end of the pilot-operated valve element;   a second pilot passage extending from the outlet passage, at a second location between the control valve and the at least one working actuator, to a second end of the pilot-operated valve element; and   a restricted orifice disposed within the second pilot passage.   
     
     
         11 . A pump system comprising:
 a pump having a displacement that is variable;   at least one working actuator configured to receive pressurized fluid from the pump;   an outlet passage extending from the pump to the at least one working actuator;   a control valve disposed within the outlet passage and configured to regulate operation of the at least one working actuator;   a pump actuator movable to adjust the displacement of the pump, and being fluidly connected at a first end to the outlet passage;   a pilot-operated valve element movable from a first position at which a second end of the pump actuator is fluidly connected to the outlet passage, and a second position at which the second end of the pump actuator is fluidly connected to a low-pressure tank;   a first pilot passage extending from the outlet passage, at a first location upstream of the control valve, to a first end of the pilot-operated valve element;   a second pilot passage extending from the outlet passage, at a second location upstream of the control valve and downstream of the first location, to a second end of the pilot-operated valve element;   a spring configured to bias the pilot-operated valve element toward the second position;   a restricted orifice disposed within the second pilot passage;   a solenoid-operated valve element operable to control movement of the pilot-operated valve element between the first and second positions;   a variable resistor mechanically connected to at least one of the actuator and the pump and being adjustable by movement of the at least one of the actuator and the pump to vary a current passing through the solenoid-operated valve element; and   a controller in communication with the solenoid-operated valve element and configured to issue an open-loop torque command to the solenoid-operated valve element.   
     
     
         12 . A method of controlling a pump, comprising:
 operating the pump to pressurize a fluid;   generating an electronic signal indicative to adjust a displacement of the pump; and   hydro-mechanically adjusting the displacement of the pump based on the signal,   wherein hydro-mechanically adjusting the displacement the pump also simultaneously modifies a resistance of the electronic signal.   
     
     
         13 . The method of  claim 12 , wherein hydro-mechanically adjusting the displacement of the pump includes continuously connecting a pump outlet pressure with a first end of a pump actuator, and selectively connecting a second end of the pump actuator to the pump outlet pressure or a low-pressure tank. 
     
     
         14 . The method of  claim 13 , wherein selectively connecting a second end of the pump actuator to the pump outlet pressure or a low-pressure tank includes directing the electronic signal to move a first valve element that hydraulically biases a second valve element between a first position and a second position. 
     
     
         15 . The method of  claim 14 , further including:
 directing pressurized fluid from the pump through a control valve to a working actuator;   directing first and second flows of pressurized pilot fluid from upstream of the control valve to first and second ends of the second valve element, respectively; and   restricting the second flow of pressurized pilot fluid,   wherein movement of the first valve element results in a least a portion of the second flow of pressurized pilot fluid being directed to the low-pressure tank to reduce a pressure of the second flow of pressurized pilot fluid.   
     
     
         16 . The method of  claim 15 , wherein an amount of the second flow of pressurized pilot fluid directed to the low-pressure tank corresponds with an amount of current in the electronic signal passing to the first valve element. 
     
     
         17 . The method of  claim 16 , further including mechanically biasing the second valve element toward the second position. 
     
     
         18 . The method of  claim 17 , further including relieving a pressure of the second flow of pressurized pilot fluid when a pressure of the second flow of pressurized pilot fluid exceeds a threshold pressure. 
     
     
         19 . The method of  claim 14 , further including:
 directing pressurized fluid from the pump through a control valve to a working actuator;   directing a first flow of pressurized pilot fluid from upstream of the control valve to a first and end of the second valve element;   directing a second flow of pressurized pilot fluid from downstream of the control valve and upstream of the working actuator to a second end of the second valve element; and   restricting the second flow of pressurized pilot fluid,   wherein movement of the first valve element results in a least a portion of the second flow of pressurized pilot fluid being directed to the low-pressure tank to reduce a pressure of the second flow of pressurized pilot fluid.   
     
     
         20 . The method of  claim 12 , wherein generating an electronic signal includes generating an open-loop torque command.