Abstract:
A method of assembling a tandem pump comprising first and second pumps connected in tandem by an interface. Each pump has a housing and an end cap containing hydraulic porting. The interface connects the end cap of one pump to the housing of the other pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 10/279,329, filed Oct. 24, 2002, now U.S. Pat. No. 6,682,312, which is a continuation of U.S. application Ser. No. 09/702,167 filed Oct. 30, 2000, now U.S. Pat. No. 6,494,686. Both previous applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to hydraulic pumps, although other uses will be apparent from the teachings disclosed herein. In particular, the present invention relates to tandem pumps and Bantam-Duty Pumps (BDPs). 
     Generally BDP units provide an infinitely variable flow rate between zero and maximum in both forward and reverse modes of operation. Pumps discussed herein are of the axial piston design which utilize spherical-nosed pistons, although variations within the spirit of this invention will be apparent to those with skill in the art and the invention should not be read as being limited to such pumps. One such prior art pump is shown in FIG.  1 . The pump is a variable displacement pump  10  designed for vehicle applications. A compression spring  12  located inside each piston  14  holds the nose  16  of the piston  14  against a thrust-bearing  18 . A plurality of such pistons positioned about the center of the cylinder block  20  forms a cylinder block kit  22 . The variable displacement pump  10  features a cradle mounted swashplate  24  with direct-proportional displacement control. Tilt of swashplate  24  causes oil to flow from pump  10 ; reversing the direction of tilt of the swashplate  24  reverses the flow of oil from the pump  10 . The pump is fluidly connected with a motor to form a pump-motor circuit having a high-pressure side and a low-pressure side through which the oil flows. Controlling the oil flow direction, i.e. changing the high- and low-pressure sides, controls the motor output rotation. Tilt of the swashplate  24  is controlled through operation of a trunnion arm  26 . The trunnion arm is connected to a slide, which is connected with the swashplate  24 . Generally, movement of the trunnion arm  26  produces a proportional swashplate  24  movement and change in pump flow and/or direction. This direct-proportional displacement control (DPC) provides a simple method of control. For example, when the operator operates a control shaft, e.g., a foot pedal, that control shaft is mechanically linked to the swashplate  24  resulting in direct control. This direct control is to be contrasted with powered control discussed later. 
     A fixed displacement gerotor charge pump  28  is generally provided in BDP units. Oil from an external reservoir and filter is pumped into the low-pressure side by the charge pump  28 . Fluid not required to replenish the closed loop flows either into the pump housing  30  through a cooling orifice or back to the charge pump  28  inlet through a charge pressure relief valve. Charge check valves  32  are included in the pump  10  and end cap  34  (cap  34 ) to control the makeup of oil flow of the system. A screw type bypass valve  36  is utilized in the pump  10  to permit movement of the machine (tractor, vehicle, etc.) and allow the machine to be pushed or towed. Opening a passage way between fluid ports with the bypass valve  36  allows oil to flow, thereby opening the pump-motor circuit, which allows the motor to turn with little resistance because the vehicle wheels will not back drive the pump  10 . 
     FIG. 2 shows an exploded isometric view of a symmetric hydraulic pump  40  (also more generally referred to as pump  40 ) is connected to a motor in a vehicle via hoses. Typically the hoses are high-pressure hoses. Each symmetric pump  40  includes a symmetric housing  42  and a symmetric end cap  44 . The housing  42  is rotated relative to the end cap  44  to position a control arm as desired. The term “symmetric” does not imply identical structural symmetry, but rather implies functional or application symmetry. The end cap  44  should be sufficiently functionally symmetric to connect to the housing  42  in one of at least two positions, wherein the other position is rotated relative to the first position. For many applications, the housing  42  and the end cap  44  are rotated  180  degrees relative to one another about a predetermined axis, such as the axis of a pump shaft. In a like manner, a symmetric housing  42  is sufficiently symmetric to achieve an objective whether fitting with an end cap, a vehicle, or the like. 
     A bypass valve  46 , also referred to as a bypass spool, is positioned generally opposite one of the system ports to provide easier access to the bypass valve  46  and a cleaner, more direct, closed loop connection. 
     The symmetric housing  42  rotatably supports a pump shaft  48 . The symmetric end cap  44  includes a porting system discussed more fully, along with pumps generally, in U.S. Pat. No. 6,332,393 (commonly assigned herewith) and incorporated herein by reference. In a symmetric end cap  44  the porting system is preferably bi-laterally symmetric, with regards to the system ports. The porting system includes a pair  51  of system ports ( 52  and  54 ) opening external to the end cap  44 . The porting system preferably includes a pair of check orifice assemblies that open external to the end cap  44  and connect with the system ports  51 . 
     The porting system generally includes at least one case drain orifice  56  (and may include a pair of orifices) opening external to the end cap  44 . The case drain  56  is a drain or connection that diverts excessive fluid (e.g. leakage fluid from the pistons) to a reservoir, thereby reducing pressure in the pump housing  42 . 
     Advantages of the above prior art were not heretofore available because neither a direct displacement tandem pump nor a bantam-duty tandem pump existed heretofore. Tandem pumps are typically of the, relatively, heavy-duty variety and specifically designed to interface with one another. All prior art tandem pumps include an indirect proportional powered control such as a hydraulic and electromechanical devices (and combinations thereof) to provide powered control to move the swashplate. So, heretofore, a direct displacement tandem pump did not exist. A particular embodiment of the present invention combines the advantages of a direct displacement bantam-duty pump and a tandem pump; other advantages will be apparent to those with skill in the art from the teachings herein. 
     SUMMARY OF THE INVENTION 
     The present invention improves on the prior art by providing a tandem pump comprising pumps connected by an interface, rather than pumps specifically designed for a tandem connection. In a particular embodiment the tandem pump comprises a first pump having a shaft end, a cap end and an oil port; and a second pump axially aligned with the first pump and having a shaft end, a cap end, and an oil port. An interface plate connects the shaft end of the second pump to the cap end of the first pump. A conduit connects the oil port of the second pump with the oil port of the first port. 
     One embodiment is directed toward a tandem pump comprising direct displacement bantam-duty pumps connected by an interface. Those of skill in the art will understand that the present invention more generally provides a means for creating a tandem pump from pumps not specifically designed for such application. 
     One embodiment of the invention is directed toward a pump interface for connecting an end cap of a first pump to a housing of a second pump. The interface comprises a first side adapted to mate with the end cap of the first pump; and a second side adapted to mate with the housing of the second pump. A pump lumen (i.e., a passage through the pump), preferably through the center of the interface, allows a pump shaft positioned in the first pump to be coupled to a pump shaft positioned in the second pump. 
     The present invention may be used to allow standard off-the-shelf pumps, not tandem designed, be placed in tandem. Accordingly, one embodiment of the invention is directed toward an interface kit for connecting two pumps in axial alignment to form a tandem pump. 
     An object of the invention is to provide two pumps with a single input, i.e., a tandem pump, using non-design specific pumps. 
     Another advantage is to compensate for tandem pump loads and allow use of lightweight pumps, where tandem pump loads are heavier at the second pump than at a single pump. 
     Another object is to reduce input connectivity for a tandem pump. A specific object is directed toward eliminating the need for a T-box connection to the individual, linked, pumps. A further specific object is to eliminate the need for a complex belt-pulley input system, e.g., a double pulley system or an elongated belt following a cross-vehicle path may be eliminated while obtaining the advantages of a tandem pump. 
     Another advantage is that the present invention fits in a smaller space due to simpler pump connectivity. A further object is to provide customized tandem pump orientations with ease. 
     Other objects and advantages of the present invention will be apparent from the following detailed discussion of exemplary embodiments with reference to the attached drawings and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an exploded isometric view of a prior art pump having a preferred alignment. 
     FIG. 2 shows an exploded isometric view of a pump having a symmetric housing and symmetric end plate. 
     FIG. 3 is a partially exploded isometric view of a tandem pump according to an embodiment of the present invention including an interface for connecting the two pumps. 
     FIG. 4 shows an exploded view including the first pump shown in FIG.  3 . 
     FIG. 5 shows the first side of the interface, wherein the first side is adapted to mate with an end cap. 
     FIG. 6 shows the second side of the interface, wherein the second side is adapted to mate with a pump housing. 
     FIG. 7 shows a section view through a tandem pump according to an embodiment of the invention. 
     FIG. 8 shows a perspective view sketch of a tandem pump where the trunnion arms and end caps are arranged to place the tandem pump in a first orientation. 
     FIG. 9 is a table showing the arrangements of pump components to form different tandem pump orientations. 
     FIG. 10 (FIGS. 10 a - 10   p ) depict end-view sketches of a tandem pump in orientations corresponding to those tabulated in FIG.  9 . 
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present invention is discussed in relation to a hydraulic pump, and in particular, a bantam-duty variable-displacement pump; other uses will be apparent from the teachings disclosed herein. The present invention will be best understood from the following detailed description of exemplary embodiments with reference to the attached drawings, wherein like reference numerals and characters refer to like parts, and by reference to the following claims. 
     FIG. 3 is a partially exploded isometric view of a tandem pump  60  according to an embodiment of the present invention. The tandem pump of FIG. 3 comprises a first pump  62  and a second pump  64 . FIG. 4 shows an exploded view including the first pump  62  shown in FIG.  3 . The first pump  62  has a shaft end  66 , a cap end  68  and an oil port  70 . Likewise, the second pump  64 , which is axially aligned with the first pump  62 , has a shaft end  72 , a cap end  74  and an oil port  76 . Typically, each pump ( 62  and  64 ) has a pump shaft ( 78  and  80 ) or input shaft and a gerotor  28  (See FIG. 7) on the second pump  64 . The shaft end  72  of the second pump  64  is connected to the cap end  68  of the first pump  62  with an interface, preferably a plate,  82 . 
     The oil ports  70  and  76  of the first and second  62  and  64  pumps are connected with a conduit  84 , preferably a hydraulic hose of suitable material. The suitable material is preferably metal connections with rubber there between. The rubber allows for greater tolerance errors and a reduced length conduit. Again, the size of the pump is thereby reduced compared to prior art connectivity means. Finally, the pump shafts  78  and  80  are connected to each other with a coupling  86 . 
     Port  76  is normally a diagnostic port for charge pressure and is accordingly generally capped for most non-tandem applications. Likewise for port  70 . In a tandem application, port  76  feeds charge fluid to port  70 . This charge fluid feed is desirable because a gerotor may be placed only on the second pump  64 . Other designs use internal gerotors with internal fluid passages. This internal fluid passage design generally requires that the pumps be in a fixed orientation, relative to each other. The present invention allows the pumps to be rotated, e.g., around the pump shaft, with relative to each other. This ease of rotation helps provide functional symmetry to obtain a plurality of operable orientations. Still other prior art charge designs use pump designs using a common housing to provide charge pressure to the first pump  62 , if needed. 
     The pump interface  82  preferably comprises a first side  88  adapted to mate with the end cap  69  of the first pump  62  and a second side  90  adapted to mate with the housing  73  of the second pump  64 . A pump lumen  92  allows a pump shaft  78  positioned in the first pump  62  to be coupled to a pump shaft  80  positioned in the second pump  64 . To facilitate assembly, the interface  82  may be provided with alignment holes (not shown) for receiving alignment pins, or it may be provided with integrated pins. To further facilitate assembly, the interface  82  is provided with a drain orifice  94  and a redundant drain orifice  96 . Thus, the interface  82  is adapted to connect to the end cap  69  in one of two positions, wherein the second position is rotated 180°, relative to the first position, about an axis through the lumen  92 . Therefore, one of the two drain orifices ( 94  and  96 ) is in fluid communication with a drain orifice  98  of the first pump  62 , while the other is not. Thus, oil drains from second pump  64  through one of the two drain offices ( 94  or  96 ) to the first pump  62 , and out of the case drain  98  when the cap is removed. The redundant drain orifice is useful because an assembler need not inspect the interface  82  to determine the proper alignment, thus eliminating a major source of error in assembly. 
     This ease of assembly and symmetry feature is further aided by connecting the pumps  62  and  64  with the conduit  84  and locating the conduit  84  external to the housings  63  and  73  of the pumps  62  and  64 . Such external location of the conduit  84  also eliminates the need for a sump housing large enough to contain the two pumps. A gerotor positioned behind charge pump cover  77  is connected to the cap end  74  of the second pump  64  while charge oil is fed to the first pump  62  through the conduit  84 . 
     To facilitate comparison with FIG. 2 of the prior art, in FIG. 3, the system ports of the first pump  62  are designated  51   a  and the system ports of the second pump  64  are designated  51   b.  Similarly, in FIG. 7, the trunnion arms are designated  26   a  and  26   b  and the swashplates are designated  24   a  and  24   b . FIG. 7 is a section view through a tandem pump  60 . 
     In a preferred embodiment, the first pump  62  and the second pump  64  are substantially similar and are symmetric bantam-duty pumps. The second pump  64  may be rotated relative to the first pump  62  about an axis through the pump shafts  78  and  80 . Accordingly, each pump  62  and  64  may comprise a symmetric pump housing ( 63  and  73 ) and a symmetric end cap ( 69  and  75 ) connected to the respective housing. The second pump housing  73  may be rotationally aligned with the first pump housing  63  while the second pump end cap  75  is rotated relative to the end cap  69  of the first pump  62 . Accordingly, the interface  82  is, for some applications, preferably symmetric. 
     FIG. 8 is a sketch perspective view of a tandem pump shown in a first orientation. Referring to the description of the prior art pump of FIG. 2, the trunnion arms  26  are typically rotatable about the pump shaft  48  in at least two positions, 180° apart. Likewise, for system ports  51  positioned in an end cap  44  connected to a pump housing  42 . (See FIG.  2 ). FIG. 8, which roughly corresponds to FIG. 7, shows the arm  26   a  of the first pump  62  in a first position; the system ports  51   a  of the first pump in a first position; the trunnion arm  26   b  of the second pump  64  in a first position; and the system ports  51   b  of the second pump  64  in a first position. FIG. 9 is a table wherein the positions of the trunnion arms  26   a  and  26   b  along with the positions of the system ports  51  and  51   b  are tabulated with the corresponding tandem pump orientation. FIG. 10 (FIGS. 10 a - 10   p ) show end-view sketches corresponding to the orientations tabulated in FIG.  9 . 
     Manufacturing costs are further reduced because the pumps need not be specially designed for tandem configurations. Off-the-shelf bantam-duty pumps may be connected with an interface kit adapted to connect the pumps in axial alignment to form a tandem pump. An interface kit may, for example, comprise an interface  82  having a first side  88  adapted to mate to a pump housing, a second side  90  adapted to mate to an end cap, and a lumen  92  to allow coupling between pump shafts respectively positioned in the separate pump housings or use of a single pump shaft. The kit may also include a pump shaft coupler  86  adapted to couple two pump shafts in axial alignment. Alternatively, or in addition to the coupler  86 , the kit may include an external oil conduit  84  adapted to mate with oil ports in the two pumps. 
     Thus, although there have been described particular embodiments of the present invention of a new and useful pump, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.