Hydraulic pump circuit

Abstract

A circuit for a hydraulic pump is provided. The circuit includes a supply of fluid. A pumping element is operable to increase the pressure of fluid received from the supply of fluid and to generate a flow of pressurized fluid. An inlet passageway connects the pumping element with the supply of fluid. A drain passageway is connected to the inlet passageway. A valve is disposed in the drain passageway. The valve is moveable between a first position where the valve prevents a flow of fluid relative to the drain passageway and a second position where the valve allows a flow of fluid relative to the drain passageway.

What is claimed is:  
     
         1 . A circuit for a hydraulic pump, comprising: 
 a supply of fluid;    a pumping element operable to increase the pressure of fluid received from the supply of fluid and to generate a flow of pressurized fluid;    an inlet passageway connecting the pumping element with the supply of fluid;    a drain passageway connected to the inlet passageway; and    a valve disposed in the drain passageway, the valve moveable between a first position where the valve prevents a flow of fluid relative to the drain passageway and a second position where the valve allows a flow of fluid relative to the drain passageway.    
     
     
         2 . The circuit of  claim 1 , further including a supply pump disposed in the inlet passageway and adapted to increase the pressure of the fluid supplied to the pumping element to a predetermined pressure.  
     
     
         3 . The circuit of  claim 2 , wherein the valve is a check valve configured to move to the second position when exposed to fluid having the predetermined pressure.  
     
     
         4 . The circuit of  claim 3 , wherein the predetermined pressure is approximately 70 Kpa.  
     
     
         5 . The circuit of  claim 1 , further including an input shaft supported by a bearing and wherein the drain passageway directs the flow of fluid from the inlet passageway to the bearing.  
     
     
         6 . The circuit of  claim 1 , further including a fluid rail and wherein the flow of pressurized fluid is directed into the fluid rail.  
     
     
         7 . The circuit of  claim 1 , wherein the pumping element includes a piston slidably disposed in a bore.  
     
     
         8 . The circuit of  claim 7 , wherein the piston is driven by a swashplate.  
     
     
         9 . The circuit of  claim 1 , wherein the fluid is a lubricating oil and the valve allows a mixture of air and lubricating oil to flow through the drain passageway.  
     
     
         10 . A method of removing air from a hydraulic pump, comprising: 
 supplying a flow of an operating fluid to an inlet passageway of the hydraulic pump;    operating a pumping element to increase the pressure of the flow of fluid supplied to the hydraulic pump and to generate a flow of pressurized fluid; and    moving a valve from a first position to a second position to allow a fluid to flow from the inlet passageway to a drain passageway when the pressure of the fluid in inlet passageway is above a predetermined limit.    
     
     
         11 . The method of  claim 10 , further including lubricating a bearing in the hydraulic pump with at least a portion of the fluid flowing through the drain passageway.  
     
     
         12 . The method of  claim 10 , further including moving the valve to the first position when the pressure of the fluid in the inlet passageway is below the predetermined limit.  
     
     
         13 . The method of  claim 10 , wherein the predetermined limit is about 70 Kpa.  
     
     
         14 . A hydraulic pump, comprising: 
 a housing having a fluid inlet and a fluid outlet;    a pumping element operable to increase the pressure of fluid received through the fluid inlet and to generate a flow of pressurized fluid through the fluid outlet;    an inlet passageway connecting the fluid inlet with the pumping element;    a drain passageway connected with the inlet passageway; and    a valve disposed in the drain passageway, the valve moveable between a first position where the valve prevents a flow of fluid relative to the drain passageway and a second position where the valve allows a flow of fluid relative to the drain passageway.    
     
     
         15 . The hydraulic pump of  claim 14 , wherein the valve is a check valve configured to move to the second position when exposed to fluid having a predetermined pressure.  
     
     
         16 . The hydraulic pump of  claim 15 , wherein the predetermined pressure is approximately 70 Kpa.  
     
     
         17 . The hydraulic pump of  claim 14 , further including an input shaft supported by a bearing and wherein the drain passageway directs the flow of fluid from the inlet passageway to the bearing.  
     
     
         18 . The hydraulic pump of  claim 17 , wherein the pumping element includes a piston slidably disposed in a bore.  
     
     
         19 . The hydraulic pump of  claim 18 , wherein the piston is driven by a swashplate supported by the bearing.  
     
     
         20 . The hydraulic pump of  claim 14 , wherein the fluid is a lubricating oil and the valve allows a mixture of air and lubricating oil to flow from the inlet passageway to the drain passageway.