Patent Publication Number: US-8974203-B2

Title: Hydraulic pump end cover

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/921,566, filed Apr. 3, 2007, the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to axial piston pumps, and more particularly to an end cover for an axial piston pump having an orifice between the system ports and the charge pump pressure cavity. 
     BACKGROUND 
     Axial piston pumps include an enclosure having an end cover and a housing portion that connects to the end cover. The end cover seals an internal sump of the pump and includes porting for the pump and includes a charge pump running surface. The porting commonly includes (i) an inlet port for providing a fluid inlet to the charge pump; (ii) internal porting from the charge pump to the enclosed axial piston pump; (iii) system ports (commonly referred to as A and B ports) for connection to a hydraulic motor; (iv) valving ports for receiving valves (such as check valve, pressure relief valve, or a combination valve) for preventing pressure spikes and for charging the hydrostatic circuit; (v) optionally a bypass valve port is provided for receiving a bypass valve that may be opened for enabling free flow between the system ports by bypassing the axial piston pump; (vi) optionally a case drain for connection to the internal sump of the hydraulic pump may be formed in the end cover. An end cover having such porting is shown and described in U.S. Pat. No. 6,332,393, hereby incorporated by reference. 
     The valving for the hydraulic pump may include an orifice. The orifice commonly is located in the valve seat of the check, pressure relief, or combination valve or in the end of the bypass valve. U.S. Pat. No. 6,332,393 at FIG. 15 discloses the orifice in the bypass valve. 
     Fluid flows through the orifice so as to soften a transition of the vehicle from a stationary position to a forward or reverse motion. When a swash plate of the pump is angled slightly relative to a neutral or zero position, flow generated by the pump passes through the orifice from a high pressure port to a lower pressure cavity (such as the low pressure port). As a result, a vehicle operated by pumps with such orifices is not set into motion as a result of the slight angle of the swash plate. 
     Problems with the orifices in the valves include the fact that the valves may be accidentally replaced by valves without orifices and that the special orifice valves are expensive. 
     SUMMARY 
     At least one embodiment of the invention provides a hydraulic apparatus comprising: a housing body, an end cover attachable to the housing, the end cover comprising: an end cover body comprising a first system port and a second system port; a charge pump pressure cavity formed in the end cover body between the first system port and the second system port; and a passageway formed through a portion of the housing body connecting at least one of the first and second system ports to the charge pump pressure cavity, the passageway including an orifice. 
     At least one embodiment of the invention provides an end cover for a hydraulic apparatus, the end cover comprising: an end cover body comprising a first system port and a second system port; a first valve port and a second valve port formed coaxially in the end cover body and perpendicular to the system ports; a passageway formed through a portion of the end cover body through a wall of each of the first and second system ports, fluidly connecting the first and second system ports, the passageway including at least one orifice. 
     At least one embodiment of the invention provides a method for producing an end cover for a hydraulic pump, comprising the steps of: forming a first system port, a second system port, and a charge pump pressure cavity in a first side of an end cover; forming a first valve cavity on a second side of the end cover; forming a second valve cavity on a third side of the end cover; forming a first passageway fluidly connecting the first system port to the charge pump pressure cavity, the first passageway including a first orifice; forming a second passageway fluidly connecting the second system port to the charge pump pressure cavity, the second passageway including a second orifice. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of this invention will now be described in further detail with reference to the accompanying drawing, in which: 
         FIG. 1  is a perspective view an embodiment of a hydraulic pump assembly in accordance with an embodiment of the present invention shown including an end cover; 
         FIG. 2  is plan view of a first side of the end cover shown in  FIG. 1 ; 
         FIG. 3  is plan view of a second side of the end cover shown in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view of the end cover taken through a plane parallel to the surfaces of the first and second sides of the end cover at a equal distance from the first and second sides; and 
         FIG. 5  is a detail sectional view of an orifice as shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a hydraulic pump, such as an axial piston pump  110 , having an end cover  10 , in accordance with an embodiment of the present invention. The end cover  10 , as shown in  FIGS. 2-4  has a generally rectangular cross-sectional shape defined by four outer surfaces,  12 ,  14 ,  16 , and  18  (identified in  FIG. 4 ). The end cover also has a first side surface  22 , and a second side surface  23 , shown in  FIGS. 2 and 3 , respectively.  FIG. 4  is a cross-section taken between the first and second side surfaces. 
     Referring now to  FIG. 2 , the first side surface  22  includes the running surface for the charge pump, a port  24  connecting to a charge pump outlet, a port  26  connecting to the charge pump inlet port, a charge pump relief port  28 , and a recirculation port  30 . The second side surface  23 , shown in  FIG. 3 , includes two kidney shaped ports  40  and  42  for the axial piston pump. Port  40  connects to a first system port (shown at  46  in  FIG. 4 ) of the end cover  10  and, port  42  connects to a second system port (shown at  48  in  FIG. 4 ) of the end cover  10 . 
     As shown in  FIG. 4 , the first and second system ports  46  and  48  extend into the end cover  10  from outer surface  16 . The system ports  46  and  48  are connected to a hydraulic motor by fluid conduits for providing fluid to and receiving fluid from the hydraulic motor. Depending upon a desired rotation of the hydraulic motor, fluid may flow out of either system port  46  or  48  and return via the other system port  48  or  46 . 
     Outer surface  16  of the end cover  10  also includes an opening for a construction port. The construction port extends into the end cap  10  to provide a charge pump pressure cavity  50  for connecting the charge pump to the system ports  46  and  48 . 
     Outer surface  12  of the end cover  10  is located opposite of the outer surface  16 . An opening to an inlet port  54  is located on outer surface  12 . The inlet port  54  connects the charge pump to a system reservoir (not shown) associated with the hydraulic circuit. 
     Outer surface  14  is located perpendicular to outer surfaces  12  and  16  and includes an opening for a cavity  56  to receive a valve. The opening  56  may or may not include an external boss, but is shown in that manner for illustrative purposes. The cavity  56  extends from the opening on outer surface  14  to a centerline CL of the end cover  10 . Outer surface  18  is located opposite outer surface  14  and perpendicular to outer surfaces  12  and  16 . Outer surface  18  includes an opening for a cavity  58  to receive a valve. The opening  56  may or may not include an external boss, but is shown in that manner for illustrative purposes. The cavity  58  extends from the opening on outer surface  18  to a centerline CL of the end cover  10  and is axially aligned with and connects to cavity  56  at the centerline CL. 
     As shown in  FIG. 4 , each of the system ports  46  and  48  intersect a respective cavity  56  and  58 . The charge pump pressure cavity  50  is located between the system ports  46  and  48  and intersects the valve cavities  56  and  58  along the centerline CL. Although not shown, valves housed in cavities  56  and  58  generally prevent the flow of fluid directly between the system ports  46  and  48 , as well as between system ports  46  and  48  and the charge pressure cavity  50  (unless the valve is actuated). As discussed with respect to the prior art, if the swashplate of the pump is slightly off its neutral position, the pump will cause the vehicle to move as the hydraulic fluid flows through the pump. In the present invention, the above condition is remedied by allowing a small flow of fluid to pass directly from at least one of the system ports to the charge pressure cavity or from one system port to the other system port. 
     The end cover  10  includes at least one orifice passage  60  or  62  extending between a system port  46  or  48  and the charge pump pressure cavity  50 .  FIG. 4  illustrates two orifice passages  60  and  62 . The first orifice passage  60  extends between system port  46  and the charge pump pressure cavity  50  and, the second orifice passage  62  extends between system port  48  and the charge pump pressure cavity  50 . The orifice passages  60  and  62  illustrated in  FIG. 4  are oriented oblique (non perpendicular nor axial with) relative to both the centerline CL and a valve cavity centerline VL. As shown, the openings of the orifice passages  60  and  62  at the intersection with the charge pump pressure cavity  50  are located closer to outer surface  16  than the openings of the orifice passage in the respective system ports  46  and  48 . The orifice passages  60  and  62  illustrated in  FIG. 4  are drilled into the end cover  10  by inserting a drill through the opening of the respective valve cavity  56  and  58  and drilling at an angle toward the charge pump pressure cavity  50 . In one embodiment, after drilling the orifice passages  60  and  62 , the orifice passages  60  and  62  are tapped to create threads on the surfaces defining the orifice passages. Alternatively, the orifice passages  60  and  62  may be cast into the end cover. 
     In one embodiment of the invention, the end cover  10  also includes at least one orifice plug configured capable of receiving an associated orifice passage.  FIG. 4  illustrates a first orifice plug  66  in orifice passage  60  and a second orifice plug in orifice passage  62 . Alternatively, if two orifice passages are formed in the end cap, such as orifice passages  60  and  62  of  FIG. 4 , one of the orifice passages may be plugged with a plug not having an orifice, if so desired. If it is desired to have an orifice connecting both system ports  46  and  48  with the charge pump pressure cavity  50 , then two orifice plugs, such as  66  and  68  of  FIG. 4  may be used. 
       FIG. 5  is an enlarged view of orifice passage  60  and illustrates orifice plug  66  within the orifice passage. Orifice plug  66  includes a threaded outer surface for enabling the orifice plug to be threadedly received in the orifice passage  60 . An orifice  70  extends through the orifice plug  66  to enable fluid flow through the orifice plug between the system port  46  and the charge pump pressure cavity  50 . In one embodiment, the orifice plug  66  is a setscrew type plug formed from metal. Other forms of the orifice plug  66  are also contemplated by this invention. For example, the orifice plug  66  may be formed from plastic or may be metal injection molded. Also, expansion type orifice plugs may be used or orifice plugs may be press fit into the associated orifice passage. 
     The orifice  70  may be of various diameters so as to enable various amounts of flow through between the system port and the charge pump pressure cavity. Also, the present design enables replacement of an orifice plug with either an orifice plug having a different orifice size or no orifice. 
     Although the principles, embodiments and operation of the present invention have been described in detail herein, this is not to be construed as being limited to the particular illustrative forms disclosed. They will thus become apparent to those skilled in the art that various modifications of the embodiments herein can be made without departing from the spirit or scope of the invention. Accordingly, the scope and content of the present invention are to be defined only by the terms of the appended claims.