Abstract:
A pump assembly comprises a base, a cam, a cylinder, a piston, and a shim clip. The cam rotates about a rotational axis with respect to the base. The cylinder attaches to the base, and has an inlet port and an outlet for fluid. The piston is reciprocally driven by rotation of the cam to draw fluid into the cylinder through the inlet port during a fill stroke, and to close the inlet port and pump fluid in the cylinder toward the offset during a pump stroke. The shim clip is removably insertable between the cylinder and the base to increase the distance between the inlet port and the rotational axis.

Description:
BACKGROUND 
     The present invention relates generally to piston pumps, and more particularly to piston pumps driven by a rotating cam. 
     Piston pumps are commonly used to move fluids such as oil or grease in a wide range of industrial and automotive applications. Piston pumps driven by a rotating cam pump an approximately constant amount of fluid with each rotation of the cam. 
     Piston pumps driven by rotating cams comprise three parts: a cam, a piston coupled to the cam, and a cylinder containing the piston. Cams can be circular, elliptical, or irregularly shaped disks, but in all cases exert a force on the piston as the cam rotates. The piston of a piston pump is typically constrained to move along a straight path inside the cylinder, and is retained against an outer circumferential surface of the cam. The cylinder of a piston pump constrains the piston, and provides a pumping chamber into which fluid is drawn, and from which fluid is pumped by movement of the piston. Many pistons are substantially cylindrical shafts, and most cylinders are substantially cylindrical tubes. Piston cylinders include inlet ports which allow fluid to enter the pumping chamber. These ports are typically holes in the sides of the cylinder. 
     As the cam of a piston pump rotates, the piston is pushed back and forth inside the cylinder with the assistance of a spring, towards and away from the cam. The cam pushes the piston into the cylinder, and the spring returns the piston when the cam retreats. This reciprocating motion of the piston opens and closes at least one port in the piston cylinder by unblocking and blocking the port. While the piston withdraws, fluid flows through the open port into the pumping chamber of the cylinder. When the piston extends, it blocks the port and forces fluid trapped in the pumping chamber out through a pump outlet. 
     Cam-driven piston pumps provide constant displacement with each rotation of the cam. Some piston assemblies allow the displacement of a piston pump to be configured by swapping a cartridge containing a piston and a cylinder of one size for an alternative cartridge with a smaller or larger pump chamber, usually from a smaller or larger piston radius. Such systems enable one pump assembly to be used for a variety of desired displacement amounts, but only by manually removing one cartridge and replacing it with an alternative-displacement equivalent. 
     SUMMARY 
     The present invention is directed toward a pump assembly with a base, a cam, a cylinder, a piston, and a shim clip. The cam rotates about a rotational axis with respect to the base. The cylinder attaches to the base, and has an inlet port and an outlet for fluid. The piston is reciprocally driven by rotation of the cam to draw fluid into the cylinder through the inlet port during a fill stroke, and to close the inlet port and pump fluid in the cylinder toward the offset during a pump stroke. The shim clip is removably insertable between the cylinder and the base to increase the distance between the inlet port and the rotational axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a pump assembly of the present invention, including a cam, a piston in contact with the cam, and a cylinder in which the piston rides. 
         FIG. 2  is a cross-sectional view of the pump assembly of  FIG. 1 . 
         FIG. 3  is a perspective view of a shim clip of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of pump assembly  10 , comprising cam  12 , driveshaft  14 , piston  16  (with straight shaft  18  and cam follower  20 ), cylinder  22 , port  24 , base  26 , piston spring  28 , piston spring platform  30 , outlet  32 , reservoir attachment ring  36 , and shim clips  38 . Cam  12  is a disc with an outer circumferential wall and an eccentric axis of rotation, such as a circular disk with an axis of rotation offset from the geometric center of the circle. Driveshaft  14  is a rotatable shaft anchored to cam  12  through axis of rotation RA. Piston  16  is a rigid piston which rides cam  12 . Piston  16  comprises straight shaft  18  and cam follower  20 , which is slightly rounded. Cylinder  22  is a substantially cylindrical tube retaining piston  16  such that straight shaft  18  forms a seal with the interior of cylinder  22 . Cylinder  22  features at least one port  24 . As shown, port  24  is a hole through both sides of cylinder  22 . Base  26  is a rigid body which anchors both driveshaft  14  and cylinder  22 . In the depicted embodiment, base  26  is an injection molded plastic piece, but base  26  may generally be any structure which anchors cylinder  22  relative to driveshaft  14 . Cylinder  22  is threaded into base  26 . In other embodiments, cylinder  22  may be removably attached to base  26  by other means. Piston spring  28  extends between cylinder  22  and piston spring platform  30 , which is a disc mounted on piston  16 , near cam follower  20 . Cylinder  22  includes outlet  32 , an exit point for fluid such as fuel, oil, or grease. Outlet  32  has a threaded interior surface for attaching a hose or tube to carry fluid. In alternative embodiments, hoses or tubes may be attached to outlet  32  by other means. A fluid reservoir (not shown) is anchored atop pump assembly  10  at reservoir attachment ring  36 . Together with base  26 , this reservoir forms a space which can be filled with fluid. 
     Driveshaft  14  rotates under power to turn cam  12 . For example, driveshaft  14  may rotate under power from an air motor or an electric motor. As cam  12  turns about eccentric axis of rotation RA, piston spring  28  retains cam follower  20  of piston  16  against the outer circumferential wall of cam  12  via spring force. As cam  12  rotates, it exerts a force on piston  16 , compressing piston spring  28 . As cam  12  continues to rotate, piston spring  28  keeps cam follower  20  in contact with cam  12  while the outer circumferential wall of cam  12  recedes. Straight shaft  18  of piston  16  travels back and forth along piston axis PA (see  FIG. 2 ), through cylinder  22 , driven by cam  12 . 
     Fluid from the reservoir anchored at reservoir attachment ring  36  fills the region surrounding cam  12 , piston  16 , and cylinder  22 . As cam  12  turns, piston  16  translates along a path defined by cylinder  22 . Motion of piston  16  to the left creates a vacuum void within cylinder  22  while port  24  is closed (see  FIG. 2 ). When port  24  opens, this vacuum draws fluid into cylinder  22  through port  24 . Motion of piston  16  to the right drives fluid out of cylinder  22  via outlet  32 , thereby pumping fluid out of the reservoir. 
     Shim clips  38  are clips of a predetermined width, and may, for instance, be formed of stamped metal. Shim clips  38  can be inserted between cylinder  22  and base  26 , as shown, to adjust the position of port  24  relative to cam  12 . Inserting or removing shim clips  38  alters the displacement of pump assembly  10 , as described below with respect to  FIG. 2 . Pump assembly  10  can be used in any suitable system, such as in commercial and industrial lube systems. 
       FIG. 2  is a cross-sectional view of pump assembly  10  through section line  2 - 2  of  FIG. 1 .  FIG. 2  depicts cam  12 , driveshaft  14 , piston  16  (with straight shaft  18 , cam follower  20 , and piston face  21 ), cylinder  22 , port  24 , valve  25 , base  26 , piston spring  28 , piston spring platform  30 , outlet  32 , shim clips  38 , plug  42 , valve spring  44 , and valve spring platform  46 . As described with respect to  FIG. 1 , driveshaft  14  rotates cam  12 , and is anchored to base  26 . Piston  16  slides within cylinder  22  and is retained against cam  12  by spring  28 , reciprocating along piston axis PA. Cylinder  22  has port  24  through which fluid enters cylinder  22 , and outlet  32  through which fluid exits cylinder  22 . In addition, valve  25  forms a seal within cylinder  22 . Valve  25  is a poppet valve comprising plug  42 , plug spring  44 , and plug spring platform  46 . Plug  42  is a plug shaped and sized to seal cylinder  22  against fluid passage when retained in place (as shown) by valve spring  44 . Valve spring  44  is a low strength spring which extends from plug  42  to plug spring platform  46 , and restores plug  42  to a sealing position in the absence of other forces. Plug spring platform  46  includes holes or fluid passages (not shown) to allow fluid to flow through spring platform  46  toward outlet  32 . In one embodiment, plug spring platform  46  is threaded to fit into threads in outlet  32 . The threaded interior of cylinder  22  also allows threaded tubes and hoses to be attached at outlet  32 . 
     Rotation of cam  12  drives piston  16  back and forth along piston axis PA, as described previously. Straight shaft  18  sometimes blocks port  24 , closing port  24  and preventing fluid from exiting cylinder  22  save by outlet  32 . While piston  16  moves to the left from its rightmost extension within cylinder  22 , valve  25  seals cylinder  22 , preventing fluid from exiting seal  22  via outlet  32 . The movement of piston  16  creates a partial vacuum between piston face  21  and plug  42  of valve  25 . Valve  25  is retained in a seal by seal spring  44 , and by vacuum. Movement to the left by piston  16  withdraws straight shaft  18  away from port  24 , unblocking and opening port  24  so that fluid can enter cylinder  22 . Once port  24  is open, the vacuum is exposed to fluid, which is drawn into cylinder  22  via suction until piston  16  reaches its leftmost position. Piston  16  then travels rightward, expelling fluid through port  24  until port  24  is blocked by straight shaft  18  of piston  16 . Continued rightward motion exerts pressure on fluid trapped between piston face  21  and plug  42  of valve  25 , opening valve  25 . Rightward motion of piston  16  from port  24  to the rightmost extension of piston  16  thus pumps fluid out of cylinder  22  via outlet  32 . The total volume of fluid displaced by each cycle of cam  12  and piston  16  is determined by the distance between port  24  and the rightmost extension of straight shaft  18  of piston  16 . 
     Shim clips  38  are inserted between cylinder  22  and base  26 , adjusting the position of cylinder  22 —and therefore of port  24 —relative to cam  12 , and the rightmost extension of straight shaft  18 . Cylinder  22  is screwed tight, holding shim clips  38  in place. One or more regularly sized shim clips  38  may be inserted to displace cylinder  22  from a default position, flush with base  26 . Alternatively, shim clips may  38  may be provided in a variety of thicknesses to adjust the position of cylinder  22  by predetermined amounts. The number and width of shim clips  38  inserted between cylinder  22  and base  26  determines the position of port  24  relative to cam  12 . Accordingly, the displacement of pump assembly  10  can be increased or decreased by a known, predetermined amount by removing or adding, respectively, shim clips  38 . Shim clips  38  can be added or removed by loosening cylinder  22  without fully withdrawing cylinder  22  from base  26 . An O-ring between cylinder  22  and base  26  retains a seal while cylinder  22  is loosened. This allows shim clips  38  to be added or removed while pump assembly  10  contains fluid, without any resulting leakage. 
       FIG. 3  is a perspective view of shim clip  38 , including fingers  42 , tab  44  and slot  46 . Shim clip  38  is a simple piece of rigid material, and may for instance be a piece stamped from sheet metal. Shim clip  38  is shaped to conform to the profile of the exterior of cylinder  22 , and includes fingers  42  which enable it to snap onto cylinder  22 , so that shim clip  38  will not detach from cylinder  22  before cylinder  22  can be tightened into base  26 , thereby securing shims  38  more completely. Fingers  42  hold shim clip in place on cylinder  22  with spring force. Shim clip  38  may include tab  44  for easy insertion or removal, and slot  46  for attaching a lanyard or clamp so that shim clips  38  are not lost while not in use. Slot  46  is also designed to allow insertion of a flat-head screwdriver to remove shim clip  38 . 
     By allowing the position of cylinder  22  to be adjusted relative to cam  12 , the present invention enables the displacement of pump assembly  10  to be adjusted without the need for expensive replacement parts, such as replacement cylinders or pistons. The position of cylinder  22  is adjusted by inserting or removing shim clips  38 . Shim clips  38  are quickly and easily inserted or removed, and are simple and inexpensive to produce. Additionally, shim clips  38  can be inserted or removed without fully withdrawing cylinder  22 , allowing the displacement of pump assembly  10  to be adjusted without leakage, even while fluid is present in pump assembly  10 . 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.