Patent Publication Number: US-2004057836-A1

Title: Hydraulic pump circuit

Description:
TECHNICAL FIELD  
       [0001] The present disclosure is directed to a circuit for a hydraulic pump and, more particularly, to a circuit for bleeding air from the inlet to a hydraulic pump.  
       BACKGROUND  
       [0002] Hydraulic pumps are commonly used for many purposes in many different applications. Vehicles, such as, for example, highway trucks and off-highway work machines, commonly include hydraulic pumps that are driven by an engine in the vehicle to generate a flow of pressurized fluid. The pressurized fluid may be used for any of a number of purposes during the operation of the vehicle. A highway truck, for example, uses pressurized fluid to operate a fuel injection system or a braking system. A work machine, for example, uses pressurized fluid to propel the machine around a work site or to move a work implement.  
       [0003] A hydraulic pump typically draws operating fluid, such as, for example, oil, from a reservoir and applies work to the fluid to increase the pressure of the fluid. The hydraulic pump directs the pressurized fluid into a fluid rail or another similar supply system for use during the operation of the vehicle. The hydraulic pump may be configured to vary the rate at which the pressurized fluid is directed into the fluid rail. This may be accomplished with a variable displacement pump or with a fixed displacement pump that has a variable flow.  
       [0004] A hydraulic pump usually includes a pumping element that applies the work to the fluid to increase the pressure of the fluid. The pumping element includes a sliding, rotating, or spinning part, such as, for example, a gear, gearotor, piston, vane, or swash plate. These moving parts are typically lubricated to prevent excessive wear due to friction.  
       [0005] The engine lubrication system in the vehicle may provide the operating fluid that is pressurized by the hydraulic pump and the lubricating fluid that is used to lubricate the moving parts of the hydraulic pump. The supply of fluid may, however, also include air that is drawn into the system. This is particularly a problem when the engine is starting after having been idle for a period of time. When the engine is not operating, the oil in the lubrication system may drain from the system and return to the reservoir. The draining oil is replaced by air pockets, which are purged from the lubrication system when the engine is started.  
       [0006] The inclusion of air in the flow of pressurized fluid generated by the hydraulic pump may impair or delay the operation of the system that uses the pressurized fluid. As shown in U.S. Pat. No. 5,454,359 to Howell, an air bleed valve may be disposed in the outlet path of the pump. This type of valve can remove any air that is included in the flow of pressurized fluid. However, the hydraulic pump must pressurize both the fluid and the air before the air is purged from the system through the air bleed valve. The additional work that is required to pressurized the air, which is subsequently released from the system, decreases the efficiency of the hydraulic pump.  
       [0007] The hydraulic pump circuit of the present disclosure solves one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0008] According to one aspect, the present disclosure is directed to a circuit for a hydraulic pump. 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.  
       [0009] In another aspect, the present disclosure is directed to a method of removing air from a hydraulic pump. A flow of an operating fluid is supplied to an inlet passageway of the hydraulic pump. A pumping element is operated to increase the pressure of the flow of fluid supplied to the pump and to generate a flow of pressurized fluid. A valve is moved from a first position to a second position to allow 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. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010]FIG. 1 is a schematic and diagrammatic representation of a hydraulic circuit for a hydraulic pump in accordance with an exemplary embodiment of the present invention; and  
     [0011]FIG. 2 is a cross-sectional view of an exemplary embodiment of a valve for a hydraulic circuit in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0012] As shown in FIG. 1, hydraulic circuit  10  includes a tank  12  that contains a supply of fluid. Tank  12  may be part of a lubrication system for the vehicle, such as an oil sump . The fluid within tank  12  may be a hydraulic fluid, such as, for example, a lubricating oil, although tank  12  may store other types of fluids.  
     [0013] As also shown, hydraulic circuit  10  may include a supply pump  14 . Supply pump  14  may be a relatively low pressure pump, such as, for example, a sump pump that may be commonly included in a lubrication system to distribute oil to various systems in an engine. Supply pump  14  may increase the pressure of the fluid to a relatively low pressure, such as about  70  Kpa. This relatively low pressurized fluid may then be directed into an inlet line  16 .  
     [0014] Hydraulic circuit  10  may also include a high pressure pump, such as hydraulic pump  20 , to further increase the pressure of the operating fluid. A high pressure fluid may be required to operate certain systems. For example, in a vehicle, the high pressure fluid may be used to operate a fuel injection system and/or a braking system. One skilled in the art will recognize that the high pressure fluid may be used to operate other types of systems as well.  
     [0015] In the illustrated exemplary embodiment, hydraulic pump  20  is depicted as a fixed displacement variable flow pump. It is contemplated, however, that hydraulic pump  20  may another type of pump. For example, hydraulic pump  20  may be a constant displacement constant flow pump or a variable displacement pump.  
     [0016] Hydraulic pump  20  includes a housing  21  and an inlet  22 . Inlet  22  may be connected to inlet line  16  to receive fluid from supply pump  14 . Inlet  22  directs the low pressure operating fluid to a pumping element  26 .  
     [0017] Pumping element  26  is operable to increase the pressure of the operating fluid provided through inlet  22 . In the illustrated embodiment, pumping element  26  includes a series of pistons  32  that are driven by a swashplate  28 . It should be understood that another type of pumping element  26  may also be used. For example, pumping element  26  may include a gear, gearotor, or vane pump.  
     [0018] As schematically illustrated in FIG. 1, an input shaft  52  is provided to drive pumping element  26 . Input shaft  52  is mounted for rotating movement on a bearing  50 . Input shaft  52  may be driven, for example, by an engine on the vehicle. Input shaft  52  may include a spline or keyed end that may be operatively engaged with the crankshaft or gear train of the engine. Input shaft  52  may be connected to the engine in any manner readily apparent to one skilled in the art.  
     [0019] As schematically illustrated, swashplate  28  has an angled driving surface that is engaged with pistons  32 . The angle surface of swashplate  28  causes each piston  32  to reciprocate within a bore as swashplate  28  rotates. The reciprocating movement of each piston  32  pressurizes fluid contained within the bore and supplied through inlet  22 . It should be noted that the angle of swashplate  28  may be varied to vary the displacement of each piston  32  within hydraulic pump  20 .  
     [0020] A pivoting shoe  30  may be disposed between each piston  32  and the angled surface of swashplate  28 . Each shoe  30  rides along the surface of swashplate  28  as swashplate  28  rotates. Each shoe  30  provides a pivoting motion to accommodate for the angled surface of swashplate  28 .  
     [0021] As further illustrated in FIG. 1, a check valve  36  may be disposed at the outlet of each bore. Each check valve  36  may be configured to open when the fluid within the bore reaches a predetermined level. When pumping element pressurizes the operating fluid to the predetermined pressure, check valve  36  will open to allow the pressurized fluid to flow from the bore.  
     [0022] Hydraulic pump  20  may include a collector  38 . Pressurized fluid released from each bore may be directed to collector  38 . Collector  38  stores a supply of pressurized fluid that is released by pistons  32 .  
     [0023] Pump collector  38  is connected to an outlet  24 , which may be further connected to an outlet line  18 . Outlet line  18  may be connected to a fluid rail  19 . Fluid rail  19  may be configured to distribute pressurized fluid to a system, such as, for example, a fuel injection system associated with the vehicle and/or engine.  
     [0024] As also schematically shown in FIG. 1, hydraulic pump  20  may include a control device  44  that is connected to outlet  24  through a control line  40 . In the illustrated exemplary embodiment, control device  44  governs the flow rate of pressurized fluid produced by hydraulic pump  20  by controlling the position of a metering device  34 . One skilled in the art may recognize, however that control device  44  may perform any controlling function that is common in a hydraulic pump, such as, for example, displacement control, flow rate control, output pressure control, torque or horsepower control, or load control.  
     [0025] The position of metering device  34  may control the flow rate of pressurized fluid produced by each piston  32 . Metering device  34  may be, for example, a metering sleeve that is moveable between a first position and a second position. Movement of metering device  34  from the first position to the second position may act to decrease the flow rate of pressurized fluid generated by each piston  32 .  
     [0026] As also schematically illustrated in FIG. 1, a drain passageway  46  may be connected to inlet  22 . Drain passageway  46  may lead to bearing  50  of input shaft  52 . It should be noted, however, that drain passageway  46  may lead to another bearing within hydraulic pump  20 , another surface within hydraulic pump  20  that requires lubrication, directly to tank  12 , or to some other desired location.  
     [0027] A valve  48  may be disposed in drain passageway  46 . Valve  48  has a first, or closed, position, where valve  48  prevents fluid from flowing through drain passageway  46 . Valve  48  also has a second, or open, position, where valve  48  allows fluid to flow through drain passageway  46 . By controlling the position of valve  48 , a fluid flow through drain passageway  46  may be selectively controlled. Valve  48  may be, for example, a check valve, a spool, valve, or any other type of valve operable to selectively allow a flow of fluid through a fluid passageway.  
     [0028] As illustrated in FIG. 2, valve  48  may be a check valve. In this exemplary embodiment, valve  48  includes a body  60 . Body  60  defines a valve inlet  62  and a valve outlet  64 . A poppet  66  is slidably disposed within body  60 . Poppet  66  is configured to engage a seat  70  that surrounds inlet  62 . A spring  68  may be disposed in housing  60  to bias poppet  66  into engagement with seat  70 . The engagement of poppet  66  with seat  70  prevents fluid from flowing from valve inlet  62  to valve outlet  64 .  
     [0029] Valve  48  may be disposed in drain passageway  46  so that valve inlet  62  is exposed to fluid from inlet  22 . Valve inlet  62  directs this fluid against poppet  66 . When the force exerted by the fluid on poppet  66  exceeds the countering force exerted by spring  68 , poppet  66  will disengage from seat  70  and allow fluid to flow from valve inlet  62  through valve outlet  64 .  
     [0030] Spring  68  may be selected to allow poppet  66  to disengage seat  70  when poppet  66  is subject to a fluid having a predetermined pressure. For example, spring  68  may be configured to allow poppet  66  to disengage seat  70  when the fluid has a pressure of about 70 Kpa. One skilled in the art will recognize that valve  68  may be configured to open at other pressures.  
     [0031] Industrial Applicability  
     [0032] The operation of an exemplary embodiment of the described hydraulic circuit will now be described with reference to the figures. The described hydraulic circuit  10  may be included as part of a vehicle to provide pressurized fluid to a system in the vehicle. The vehicle may be, for example, a highway truck or an off-highway work machine.  
     [0033] When the vehicle, or engine, that includes hydraulic circuit  10  is not in operation, both supply pump  14  and hydraulic pump  20  will be idle. Accordingly, the oil in inlet line  16  and inlet  22  will be at a low pressure, so that valve  48  remains closed. In the closed position, valve  48  prevents oil from draining from inlet line  16  and inlet  22  through drain passageway  46 . Valve  48  will thereby preventing the formation of air pockets in hydraulic circuit  10 .  
     [0034] When the engine of the vehicle is started, both supply pump  14  and hydraulic pump  20  will also start operating. Supply pump  14  will provide a supply of relatively low pressure oil through inlet line  16  and inlet  22 . Pumping element  26  of hydraulic pump  20  further increases the pressure of the oil. The high pressure oil is directed through outlet  24  to fluid rail  19  for use by another system in the vehicle.  
     [0035] Valve  48  may be configured to open when exposed to fluid having a pressure slightly lower than the standard output pressure of supply pump  14 .  
     [0036] Valve  48  will, therefore, open when supply pump  14  is operating normally and providing a stream of fluid at a typical output pressure. The opening of valve  48  will allow oil to flow from inlet  22  through drain passageway  46 .  
     [0037] Drain passageway  46  may be connected with inlet  22  at the highest elevation in inlet  22 . With this placement, the force of gravity will act on the oil to cause the oil to continue to flow through inlet  22  and to pumping element  26 . Any air that is mixed with the oil supplied to hydraulic pump  20  will tend to collect adjacent to or in drain passageway  46 . When valve  48  opens in response to an increase in the pressure of the supply oil, the collected air, along with some of the oil will flow through drain passageway  46 .  
     [0038] Drain passageway  46  may lead to bearing  50  that supports input shaft  52 . The oil flowing through drain passageway  46  will lubricate bearing  50 . The lubrication will prevent excessive wear on input shaft  52 . Thus, the amount of maintenance necessary to keep hydraulic pump  20  operational may be reduced.  
     [0039] As will be apparent, the foregoing disclosure provides a hydraulic circuit  10  for a hydraulic pump  20  that allows for the removal of air at the inlet to the hydraulic pump  20  and may be used to lubricate the moving parts of the hydraulic pump  20 . By removing the air before the air is pressurized by the pumping element  26 , the efficiency of the hydraulic pump  20  may be increased. In addition, the described hydraulic circuit  10  may prevent the formation of air pockets in the flow of pressurized fluid that is used to operate an auxiliary system on the vehicle, such as, for example, a fuel injection system.  
     [0040] It will be apparent to those skilled in the art that various modifications and variations can be made in the described hydraulic circuit without departing from the scope of the invention. Other embodiments may be apparent to those skilled in the art from consideration of the specification and practice of the hydraulic circuit disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the present disclosure being indicated by the following claims and their equivalents.