Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates to rotary pump, and more specifically to high speed piston pumps having variable displacement, such as for use in aircraft fuel and hydraulic systems for pumping, metering and control for aircraft systems including engines.  
         [0005]     2. Description of the Related Art  
         [0006]     Fixed displacement pumps are conventionally employed as fuel pumps for aircraft turbine engines. Such pumps must be capable of providing sufficient fuel pressure and flow to the engine over a wide range of operating speeds from starting to full throttle operation. Therefore, a common practice is for the pump to produce a relatively high output flow rate at all times. The fuel system meters the pump output flow to supply fuel at a rate that is actually required by the engine. The excess flow from the pump bypasses the engine and is recycled to the pump inlet.  
         [0007]     However, circulation in the bypass circuit heats the fuel, which may become excessively hot, especially when a relatively low flow fuel flow rate is demanded by the engine. As a result, a heat exchanger typically is provided in the bypass circuit to cool the fuel before returning it to the pump inlet. This adds complexity, weight and expense to the fuel system.  
         [0008]     Size and weight are also important characteristics of components used in aircraft. Thus it is desirable to refine existing piston pump technology to reduce the size, reduce the weight, and increase the operating limits for speed, while providing a high degree of pump reliability.  
       SUMMARY OF THE INVENTION  
       [0009]     A radial piston pump has a housing with a cavity into which a fluid inlet passage and a fluid outlet passage open. A cylinder ring is located within the cavity and has an aperture within which a cam surface is formed. In a preferred embodiment, the cylinder ring is pivotally supported within the cavity and has a circular aperture with a bearing ring therein that forms an interior cylindrical cam surface, for example.  
         [0010]     A cylinder block is mounted for rotation within the aperture of the cylinder ring and has a plurality of radially extending cylinders. Each radially extending cylinder has a port, which selectively communicates with the fluid inlet passage and a fluid outlet passage as the cylinder block rotates. A plurality of cylinders pistons, which are free to slide, are received within the plurality of cylinders and engage the cam surface of the cylinder ring. An actuator is operably coupled to produce movement of the cylinder ring, which alters the spatial relationship between the cylinder ring and the cylinder block to vary the distance that the pistons move within the cylinders.  
         [0011]     The magnitude of fluid flow produced by the pump is directly related to the stroke of the pistons, (amount of movement) within the cylinders as the cylinder block rotates. Therefore, varying the position of the cylinder ring in relation to the cylinder block controls the magnitude of fluid flow. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is an axial cross section through a radial piston pump according to the present invention; and  
         [0013]      FIG. 2  is a cross section along line  2 - 2  in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     The present invention is being described in the context of a fuel pump for a gas turbine engine for an aircraft, however it should be appreciated that the novel concepts of this invention have application to a wide variety of pumps for other fluids and equipment.  
         [0015]     With reference initially to  FIG. 1 , a pump  10  has a housing  12  formed by first and second segments  11  and  13  that are secured together by bolts or other suitable fasteners with a seal there between. An internal cavity  18  is formed between the two housing segments. A drive shaft  25  projects into the housing  12  through an aperture on one side and engages a pump shaft  26  that extends across the internal cavity  18  and is rotatably mounted in the housing by bearings or bushings  27 . The drive shaft  25  conveys power from the engine gearbox to the pump shaft  26  which is mounted between first and second pump sections  28  and  29  within the housing. Note that the walls of the internal cavity  18  project closer together in a central region adjacent the pump shaft  26  than in an annular outer region farther away from that shaft and those walls abut the first and second pump sections  28  and  29  in that central cavity region.  
         [0016]     An inlet port  14  in the housing  12  is connected by an inlet passage  15  with two branches that lead through the second housing segment  13  to two inlet passage openings  20  and  21  into the internal cavity  18 . A secondary inlet passage  19  in the first housing segment  11  extends from the outer region of the internal cavity  18  to another inlet passage opening  22  in the central region of the cavity. When the pump  10  is operating, a portion of the fluid introduced into the inlet port  14  flows from opening  20  through the outer region of the internal cavity  18  into the secondary inlet passage  19  and continues to flow to the inlet passage opening  22 . An outlet passage  17  extends through the housing  12  from separate openings  23  and  24  in each housing segment  11  and  13 , respectively, to an outlet port  16 . Note that a portion of the outlet passage  17  extends through the housing  12  behind the internal cavity  18  and is not visible in the cross sectional view of  FIG. 1 . The inlet and outlet passage openings  21 - 24  open through the walls in that central region of the internal cavity  18  in relatively close proximity to the axis of shafts  25  and  26  to lower the inlet pressure requirements which improves cylinder block filling and reduces potential cavitation damage. Inlet passage opening  20  is in the outer cavity region.  
         [0017]     The two pump sections  28  and  29  are identical, but are shown rotated 180 degrees about the pump shaft with respect to each other. Other angles may be selected depending on application requirements. As a consequence, the openings  21  and  23  of the inlet and outlet passages  15  and  17  for the first pump section  28  are oriented 180 degrees around the pump shaft axis with respect to the openings  22  and  24  of the inlet and outlet passages  19  and  17  for the second pump section  29 . That is in the orientation of  FIG. 1  the inlet opening  21  for the first pump section  28  is below the pump shaft  26  whereas the inlet opening  22  for the pump section  29  is above the pump shaft. The respective outlet openings  23  and  24  are likewise on opposite sides of the pump shaft  26 . Inlet and outlet passage openings  21 - 24  abut the hub of a cylinder block  44 .  
         [0018]     The first pump section  28  is shown in detail in  FIG. 2  and comprises a cylinder ring  30 , which is mounted within the housing  12  on a pivot pin  31  that passes through an aperture in one corner of the cylinder ring. Other means of locating the pivot pin  31  may also be used dependent on package space available. A spring  32  the engages housing  12  and pivotally biases the cylinder ring  30  into one extreme rotational position within the cavity  18  that is illustrated in the drawings. As will be described, the first pump section produces a maximum fluid flow in this extreme rotational position. An actuation piston  33  is located within a control bore  34  in the housing  12  and engages a corner of the cylinder ring  30  that is opposite to the engagement point of the spring  32 . Introduction of pressurized fluid into the bore  34  via a control port  35  pushes the actuation piston  33  outward thereby that exerting a force, which rotates the cylinder ring  30  clockwise about the pivot pin  31 , against the force of the spring  32 . Other locations of the actuation piston  33  and spring  32  may also be used dependent on the application requirements.  
         [0019]     The cylinder ring  30  has a circular aperture  36  through which the drive and pump shafts  25  and  26  extend. An annular bushing  38  is located within the circular aperture  36  and a bearing ring  40  is slideably received within the annular bushing. The inner circumferential surface of the bearing ring  40  has an annular groove that forms a cam surface  42  against which a first plurality of valve pistons  48  travel, as will be described. Although the preferred embodiment of the cylinder ring  30  has a circular aperture  36 , that aperture and thus the inner circumferential surface of the bearing ring  40  may have other geometric shapes. It should also be noted that bearing shoes might be placed between the bearing ring  40  and the piston  48 .  
         [0020]     The first pump section  28  is formed by a portion of the cylinder block  44  and fastened to the pump shaft  26  so as to rotate therewith. The cylinder block  44  has a first set of eight cylinders  46  arranged equal distantly around and extending radially outward from the axis of the pump shaft  26 . The interior end of each cylinder has a kidney shaped cylinder port  45  in the cylinder block  44 . In different rotational positions of each cylinder  46 , its port  45  communicates with the opening  21  of the inlet passage  15  or the opening  23  of the outlet passage  17  shown in  FIG. 1 . A separate piston  48  is slideably received within each cylinder  46 . Each piston  48  has an open end facing the center of the cylinder block  44  and a closed end with a curved outer surface that fits within the groove of the cam surface  42  on the bearing ring  40 . As the cylinder block  44  rotates upon being driven by the drive and pump shafts  25  and  26 , the pistons  48  are driven outward into engagement against the bearing ring  40  by centrifugal forces. Drag forces produced by the engagement of the pistons  48  may cause the bearing ring  40  to rotate within the central opening of the cylinder ring  30 .  
         [0021]     In the maximum flow configuration of the pump, the spring  32  pivots the cylinder ring  30  into the extreme counter-clockwise position as illustrated in  FIG. 2 . It should be noted that the pump shaft  26  and the cylinder block  44  remain in a fixed orientation with respect to the pump housing  12  as the cylinder ring  30  pivots. Therefore in the maximum flow configuration, the aperture  36  of the cylinder block  44  is non-coaxially oriented (i.e. eccentrically) within the cam surface  42  of the bearing ring  40 . This results in a larger gap existing between the cylinder block  44  and the bearing ring  40  at a bottom dead center point  50  than at a diametrically opposite top dead center point  52 . As a consequence, the pistons  48  are forced farther out of the cylinders  46  adjacent the bottom dead center point  50  than near the top dead center point  52 . The inlet passage opening  21  for the first pump section  28  is a curved opening that is centered between the bottom dead center point  50  and the top dead center point  52  in the housing wall on one side of the pump shaft  26 . Similarly the outlet passage opening  23  for the first pump section  28  is a curved opening that is centered between the bottom and top dead center points  50  and  52  on the other side of the pump shaft  26 .  
         [0022]     As the cylinder block  44  rotates so that a given cylinder  46  is approaching the bottom dead center point  50 , the piston  48  within that cylinder is moving outward thereby expanding the volume of the cylinder chamber. The direction of rotation is such that as the cylinder chamber is expanding, the port  45  for the given cylinder communicates with the inlet passage opening  21  so that fluid is drawn into the cylinder chamber. At the bottom dead center point  50 , the cylinder port  45  is adjacent solid wall of the housing and no longer communicates with the inlet passage opening  21 . As the cylinder block  44  rotates away from the bottom dead center point  50 , the port  45  of the given cylinder  46  is exposed to the outlet passage opening  23 . Continued rotation of the cylinder block  44  moves the piston  48  into a region where the gap between the cylinder block  44  and the bearing ring  40  decreases thereby pushing the piston into the given cylinder. This action forces the fluid from the cylinder into the outlet passage  17 , pressure resulting from restriction to the fluid flow.  
         [0023]     As the given cylinder  48  passes the top dead center point  52 , its port  45  is closed off from both the inlet and outlet passage openings  21  and  23 . Further rotation of the cylinder block  44  thereafter causes the piston  48  to move out of the given cylinder  46 , which expands the cylinder chamber, while the cylinder port  45  communicates with the inlet passage opening  21  thereby repeating the pumping cycle.  
         [0024]     By applying different levels of pressure into the control bore  34 ; the pump actuation piston  33  is operated to pivot the cylinder ring  30  into different positions within the cavity  18 . The pivoting of the cylinder ring  30  changes the spatial relationship of the bearing ring  40  to the cylinder block  44 , thereby changing the annular gap between those components. Specifically, pivoting the cylinder ring  30  changes the distance of the gap at the bottom dead center point  50  and the top dead center point  52 . This varies the amount of piston travel within each cylinder as the pistons revolve around the axis of the pump shaft  26  and thus alters the amount of fluid delivered by the pistons.  
         [0025]     As noted previously,  FIG. 2  illustrates the cylinder ring  30  in the maximum flow configuration in which the largest gap exists between the cylinder block  44  and the bearing ring  40  at the bottom dead center point  50  and the smallest gap exists at the top dead center point  52 . As pressure in the control bore  34  increases the actuation piston  33  moves farther outward thereby exerting force on the cylinder ring  30 , which rotates clockwise, toward a position in which the bearing ring  40  is coaxial (e.g. concentric) to with the cylinder block  44 . This motion of the cylinder ring  30  decreases the gap between the bearing ring  40  and the cylinder block  44  at the bottom dead center point  50  and increases the gap at the top dead center point  52 . As the difference between the size of the gaps at the bottom and top dead center points  50  and  52  diminishes so too does the flow delivered by the pump. In the opposite extreme pivotal position to that illustrated in  FIG. 2 , the gaps between the cylinder block  44  and the bearing ring  40  at the bottom and top dead center points  50  and  52  are substantially equal thereby producing minimum flow from the pump  10 . The design may also be configured to reverse the inlet and discharge ports to reverse the direction of flow delivery. Therefore, varying the pressure of the fluid applied to the control bore  34 , controls the flow of fluid delivered by the pump.  
         [0026]     The cylinder block  44  has a second set of eight cylinders  60  arranged parallel to the first set of cylinders  46 , which form the second pump section  29  which are visible in  FIG. 1 . A second plurality of valve pistons  62  are slideably located within the second set of cylinders  60  with those pistons traveling against a cam surface of a second cylinder ring  64  that is pivotally attached to the housing  12  by a pivot pin  66 . The second cylinder ring  64  is oriented 180° with respect to the first cylinder ring  30 . As a consequence, the bottom and top dead center points of the second cylinder ring  64  are rotated 180° with respect to the corresponding points on the first cylinder ring  30 . This balances the forces that the flow of fluid and operation of the pistons exert on the cylinder block  44  and shafts  25  and  26 . The components of the second pump section  29  function in the same manner as just described for the first pump section  28 . However the ports of the second set of cylinders  60  communicating with the inlet and outlet passage openings  22  and  24  in the first housing segment  11  are 180 degrees apart with respect to each other from those in the first segment. Application of pressure to the control port  35  moves both cylinder rings  30  and  64  in unison. This is accomplished by the location of a contact arm on both of the cylinder blocks, which cause the cylinder rings to move with respect to each other (feature not shown).  
         [0027]     The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.

Technology Category: f