Patent Publication Number: US-2005129530-A1

Title: Pump compensator

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a pump. In particular, the present invention relates to a pressure compensated variable displacement pump which can operate at high pressures.  
      Positive displacement pumps capture fluid in a chamber and reduce the volume in the chamber to force the fluid from the pump. Fluid pumps create flow while operating on a displacement principle wherein fluid enters an input and displaces to an output via the pump. Fixed displacement pumps discharge fluid in a continuous flow while variable volume pumps discharge fluid in a non-continuous flow, i.e. periods with no discharge.  
      Positive-displacement pumps deliver a definite volume of fluid for each pump cycle operation, regardless of resistance, so long as the pump capacity is not exceeded. If an outlet is closed or exceeds the output pressure, the pump drive will stall or the pump will experience breakdown. Accordingly, positive-displacement pumps require a pressure regulator or pressure relief valve.  
      Pumps are rated according to the volumetric output which is the amount of liquid that a pump can deliver to the outlet per unit of time at a given drive speed. The volumetric output is usually expressed in gallons per minute. Since the pump drive affects volumetric output, pumps are also rated by displacement.  
      Displacement is the amount of fluid transferred from a pump&#39;s inlet to the pump&#39;s outlet in one cycle wherein displacement is either fixed or variable. In fixed displacement, the output can be changed only by varying the drive speed. In variable displacement, the output can be changed by regulating the pressure control and/or changing the drive speed.  
      A typical positive variable displacement pump is a vane pump. Vane pumps use a slotted rotor which rotates within a housing driven by a drive shaft. Vanes slide within the rotor in an expanding configuration from the rotor to push the fluid from the inlet to the outlet. Typically, the vanes are positioned within the slots of the rotor. As the rotor turns, the vanes are thrown outward by a combination of hydraulic pressure and centrifugal force which holds the vanes in contact with a pressure ring which surrounds the rotor/vanes. The ring is offset by the pressure of the pressure regulator used to control maximum system pressure.  
      Vane pumps are typically compact in design and provide excellent horsepower to weight ratios while offering high volumetric efficiencies, good suction characteristics and low noise generation. Accordingly, vane pumps are used in a variety of industries such as machine tools, production and material handling equipment and construction equipment.  
      Typically, since vane pumps are a form of variable displacement pumps, the vane pumps use a compensator as a pressure regulator. A compensator changes the displacement of the pump to match the flow system requirement by controlling the pressure. In other words, variable flow is achieved at a constant pressure setting. The compensator senses downstream pressure and adjusts the displacement to meet the desired flow of the system.  
      Current vane pumps use two traditional compensators: a spring loaded compensator and a hydraulic compensator. In a spring loaded compensator, a spring assembly connects the pressure ring which surrounds the rotor and vanes and applies a force to the pressure ring. Thus, the spring assembly biases between the pump housing and the pressure ring to create a variable pressure around the rotor and vanes. Based on the spring assembly characteristics such as the spring constant, the number of coils and material composition of the coils, the spring compensator varies the pump output displacement. Typically, the spring constant determines the pressure of the pump. Thus, to create variable flow while maintaining constant pressure, the spring compensator is designed with specific criteria for the desired output.  
      A problem with spring compensators, however, is the existence of a pressure limit. Coil spring compensators do not perform at high pressures, such as pressures exceeding 2,000 pounds per square inch (psi). To withstand high pressures, a coil spring compensator would require a burdensome number of coils. The required coils for pressures exceeding 2,000 psi would require a spring housing extending off the pump body at a distance exceeding twelve inches. This extended housing prohibits the vane pump from being used in typical applications because of space constraints of a typical vane pump installation. The spring compensator also applies concentrated loading which leads to increased wear of the springs and ring. Furthermore, the extended spring housing is unwieldy, leading to increased labor installation. Additionally, the extended spring housing results in increased manufacturing costs. As such, the spring compensator is not economically viable for high pump pressures such as pressures exceeding 2,000 psi.  
      In a hydraulic compensator, a valve system uses a piston assembly to sense the system pressure. To vary the flow and to compensate the pressure against the housing, the valve system opens and closes to move the piston assembly against the housing. A problem with hydraulic compensators, however, is contamination. Since the hydraulic compensator requires numerous components comprising the valve and piston assembly, those components are susceptible to failure and fluid leakage. Additionally, the hydraulic compensator requires constant maintenance to check on the valve system, leading to increased maintenance costs.  
      Efficient and economic pump systems are crucial for fluid systems. As such, fluid systems require pumps which can withstand high pressures while providing efficient output. Additionally, fluid systems require minimal pump noise due to government regulations to limit noise on assembly/factory floors. Accordingly, a need exists for a pressure compensated variable pump that can deliver high fluid pressures. A need also exists for a pressure compensated variable pump that is compact in design. The solution, however, must be a vane type pump having low noise output. A need also exists for a pressured compensated variable pump that is easy to install. The solution, however, must minimize contamination and maintenance procedures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  illustrates in an isometric view an embodiment of the fluid pump device.  
       FIG. 2  illustrates in a cross sectional view an embodiment of the fluid pump device.  
       FIGS. 3   a  and  3   b  illustrate, in a top and side view, pressure elements of the device.  
       FIG. 4  illustrates in a cut away view of an embodiment of the fluid pump device.  
       FIG. 5  illustrates in a side view of the pressure elements of the fluid pump device.  
       FIG. 6  illustrates a cross sectional view of an embodiment of the fluid pump device with the pressure ring in a first position.  
       FIG. 7  illustrates a cross sectional view of an embodiment of the fluid pump device of  FIG. 6 , showing the pressure ring in a second position. 
    
    
     SUMMARY OF THE INVENTION  
      The present disclosure relates to a fluid pump. In particular, the present invention relates to a pressure compensated variable displacement pump which can operate at high fluid pressures. In an embodiment, the disclosure comprises a pump vane assembly positioned within a housing and a pressure ring positioned around the vane assembly and floating within the housing. Additionally, the embodiment comprises a compensator comprising a guide, a first end, a second end and a plurality of individual adjusting elements. The first end of the compensator adjustably bears against the housing. The second end of the compensator is in contact with the pressure ring, wherein each of the plurality of adjusting elements is positioned adjacent to one another, in series and in contact with the pressure ring via guide shoe to vary the pressure created by the vane assembly against the pressure ring.  
      The present disclosure also includes a method of varying pressure comprising rotating a vane assembly within a housing and applying high pressure from the vane assembly against a pressure ring. Next, the method comprises varying the pressure by biasing a plurality of adjusting elements to reciprocate a guide against the pressure ring.  
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT  
      As stated, the present disclosure relates to a pump. In particular, the present invention relates to a pressure compensated variable displacement pump that can operate at high pressures.  FIG. 1  illustrates in an isometric view an exemplary embodiment of the present invention generally shown as  10 . The present invention  10  comprises a pump  12  having a housing  14 , an inlet  16 , an outlet  18  and a compensator  20 . The compensator  20  is positioned on the top of the pump  12  but may be positioned on other sides of the pump  12 . As shown, the pump  12  and compensator  20  are configured together in a compact design to minimize required installation space.  
      Turning to  FIG. 2 , the pump  12  is shown in a cross sectional view, wherein the pump  12  comprises a vane type pump. Accordingly, the pump  12  includes a shaft  22  and vane assembly  23  positioned within the housing  14  wherein the vane assembly  23  includes a plurality of vanes  24  which reciprocate within slots  26  of the shaft  22 . Depending on the cycle portion, the vanes  24  extend out beyond the circumference of the shaft  22  varying amounts, as shown in the art.  
      A pressure ring  28 , positioned within the body  14 , has an internal shaft that surrounds the shaft  22  and vanes  24  wherein the pressure ring  28  floats within the body  14 . To maintain the pressure ring  24  within the body  14 , the pump  12  includes a thrust screw assembly  30  which limits the movement of the pressure ring  28 . The thrust assembly  30  includes a thrust screw  32 , a lock nut  34  and a thrust bearing  36 . The thrust screw  32  extends and retracts within lock nut  34  to position the thrust bearing  36  within the body  14  to contact the pressure ring  28 . Thus, the amount of float of the pressure ring  28  within the body  14  is controlled by the stop assembly  30 . A fixed stop  37  also assists in controlling the position of the pressure ring  28 . The pump  12  further includes a second fixed stop  38  which primarily positions the ring  28  during assembly.  
      As shown in  FIG. 2 , the compensator  20  is positioned on and extends through the body  14 . The compensator  20  includes a compensator body  39 , a compensator adjuster  40 , a plurality of adjusting elements  42 , a pivot plate  44 , a bearing plate  46 , a guide  48  and a guide shoe  50 . The guide  48  has a first end  52  positioned near the compensator adjuster  40  and a second end  54  positioned near the guide shoe  50 , wherein the guide  48  is hollow between the first end  52  and the second end  54 . The plurality of adjusting elements  42  are positioned around the guide  48  between the first end  52  and the second end  54 . Additionally, the pivot plate  44  is positioned between the first end  52  and the plurality of adjusting elements  42  while the bearing plate  46  is positioned between the second end  54  and the plurality of adjusting elements  42 . Further, the guide shoe  50  is attached to the second end  54  while contacting the bearing plate  46 . The guide shoe  50  is sized and shaped to match an outer circumference portion  56  of the pressure ring  28 , as will be discussed.  
      Turning to  FIGS. 3   a  and  3   b , one of the adjusting elements  42  of the illustrated embodiment is shown, wherein each adjusting element  42  has a center  58  and an edge  60 . The center  58  is positioned within an aperture  62  while the edge  60  is positioned at an angle from the center  58 . Accordingly, the adjusting element  42  has a convex side  64  and a concave side  66 . In an embodiment, the adjusting element  42  may comprise a washer such as a Belleville washer. The adjusting elements  42  are sized and shaped to distribute pressure from the center  58  to the edge  60  in a continuous arc pattern.  
      Turning to  FIG. 4 , the adjusting elements  42  are positioned in series. The series comprises a plurality of stacked sets of adjusting elements  42 , each set containing one adjustment element  42  having its side  66  ( FIG. 3   b ) facing pivot plate  44  and the second adjusting element  42  having side  66  ( FIG. 3   b ) face the bearing plate  46 , thus forming a multiple cup-like stack having an inherent resilience. As shown in  FIG. 4 , the adjusting elements  42  are individual elements aligned with each other around the guide  48  between the first end  52  and the second end  54  ( FIG. 2 ). The pivot plate  44  is also shaped similar to the adjusting elements  42  such that the first or top most adjusting element  42  is positioned near the pivot plate  44 . The bearing plate  46 , however, is sized and shaped in a flat configuration.  
      Turning to  FIG. 5 , the adjusting elements  42  are shown aligned in a series described above around the guide  48 . In this alignment, the convex sides  64  of adjacent adjusting elements  42  are in contact with each other. Accordingly, the concave sides  66  of adjacent adjusting elements  42  are oppositely positioned with each other. As such, the concave side  66  of the first adjusting element is positioned opposite both the pivot plate  44  and the bearing plate  46 .  
      During use, the compensator  20  maintains a constant pressure pump while matching flow displacement demands of the pump  12 . Hydraulic forces cause the ring  28  to move against the guide shoe  50  wherein this movement is restricted by the adjusting elements  42 . Turning to  FIGS. 6 and 7 , the plurality of adjusting elements  42  bias the guide shoe  50  downward to reciprocate between a first position ( FIG. 6 ) and a second position ( FIG. 7 ) in tandem with the pressure ring  28 .  
      Since the pressure ring  28  floats within the body  14  and the shaft  22  rotates in a fixed position within the housing  14  and the fluid between vanes  24  applies a pressure to the internal surface  29  of pressure ring  28 , the pressure ring  28  may move in an axial direction and becomes more or less separated from portions of shaft  22  during a portion of the pump cycle. As the shaft  22  rotates, the vanes  24  extend out of the slots  26  to pick up fluid from the inlet  16  (shown in  FIG. 1 ). The vanes  24  then displace the fluid toward the outlet  18  (shown in  FIG. 1 ) creating a high pressure fluid area  68  between the shaft  22  and the pressure ring  28 .  
      To adjust for the high pressure generated in the pump and to maintain a constant fluid flow output, the adjusting elements  42  bias the guide shoe  50  against the pressure ring  28  as shown in  FIGS. 6 and 7 . Accordingly, the guide shoe  50  moves from the first position in  FIG. 6  to the second position of  FIG. 7 . Thus, the high pressure developed in area  68  is distributed from the center  58  to the edge  60  of the adjusting elements  42  ( FIG. 3   a ). The adjusting elements  42 , in turn, are sized, shaped and combined in a stack to compensate for pressures exceeding 500 psi, which biases the guide shoe  50  in tandem against the pressure ring  28 . In an embodiment, the adjusting elements  42  are sized, shaped and configured to compensate for pressures exceeding 2,000 psi. In an embodiment, the adjusting elements  42  are sized, shaped and configured to compensate pressures up to and including 3,200 psi.  
      In comparing  FIGS. 6 and 7  during a cycle, the plurality of adjusting elements  42  bias the guide shoe  50  against the outer circumference pressure ring  28  to compensate for the high pressure created by the vane assembly  23 . In this series configuration of elements  42 , the convex sides  64  of adjacent adjusting elements  42  are in contact with each other and the concave sides  66  of adjacent adjusting elements  42  are oppositely spaced apart and facing each other (see  FIG. 5 ), the plurality of adjusting elements  42  maintain the bias force necessary to compensate for high pressures in a stack of relatively short axial dimension. The plurality of adjusting elements  42  are sized and shaped to maintain a bias force up to and including 3,200 psi. Additionally, since the individual adjusting elements  42  are aligned in series around the guide  48 , the compensator  20  maintains a minimal extension beyond the body  14 . As such, the compensator  20  and the adjusting elements  42  provide a compact vane pump which can withstand high pressures.  
      While the concepts of the present disclosure have been illustrated and described in detail in the drawings and foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only the illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected by the following claims.