Abstract:
An improved high pressure intermeshing gear pump that achieves high efficiency and a low cost by forming the pumping cavity such that no fillets exist at the corners permitting closed fits without utilizing bearing end plates. In addition an improved coupling between the gears and their supporting shafts is disclosed as is a simplified machining method that eliminates burrs that may be formed during the drilling operations.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to an improved gear pump and method of making such a pump.  
           [0002]    As is well known, gear pumps are widely used for a great variety of purposes. This is due to their ability to generate high pressures. Also these pumps generally have a compact size and shape.  
           [0003]    In one commonly utilized type of gear pump there are a pair of intermeshing gears that are supported for rotation about parallel axes. These gears are positioned within a pumping cavity formed by a pump housing. The pump housing cavity has a generally figure 8 shape and is closed by end walls that are in confronting relationship to the flat end faces of the gears. Passages permit the flow of the pumped fluid to and from the space between the gears. Because of machining problems with the prior art type of pumps and their manufacturing methods it has been the practice to interpose bearing end plates between the gear end faces and the pump housing.  
           [0004]    For example, published Japanese Patent Application Hei 08-93653 shows a typical prior art pump of this type. The pump main housing member is formed with the pumping chamber by a machining operation through one end face thereof. At the bottom of this cavity, a fillet will be formed of machining necessity. Thus the peripheral edge of the gears must be spaced from this projecting area of the pump housing to avoid interference. This spacing can and is accomplished in part by chamfering the edges of the gear teeth. This however leaves a void area where leakage of the pumped fluid will occur and thus the efficiency of the pump is decreased.  
           [0005]    The amount of chamfering required can be reduced by utilizing bearing end plates that engage the flat ends of the gears as shown in FIG. 3 of the noted published Japanese Patent Application. However that adds to the size and cost of the pump. In addition the end plates themselves introduce clearances and areas where leakage can and does occur.  
           [0006]    It is, therefore, a principle object of this invention to provide an improved, simplified pump construction and pump manufacturing methodology.  
           [0007]    It is a further object of this invention to provide an improved, pump construction and pump manufacturing methodology that offers higher efficiencies and more compact construction than heretofore possible.  
           [0008]    In the pumps of this type the gears are supported by gear shafts and at least one of these shafts is driven by some form of prime mover. The gears are expensive to manufacture and are formed from special materials. If they are made integrally with their shafts, as is common practice, the cost increases and the manufacturing can become more difficult. However if the shafts are made separate from the gears, a driving connection must be made to at least the driven gear. This normally is done by a key or pin connection. Those commonly used are costly and troublesome.  
           [0009]    It is therefore a further object of this invention to provide a simplified and low cost way of coupling a pump gear and its shaft.  
         SUMMARY OF INVENTION  
         [0010]    A first feature of the invention is adapted to be embodied in an intermeshing gear pump. The pump is comprised of an outer housing defining a pumping cavity in which a pair of intermeshing gears are journalled for pumping a fluid from a fluid inlet to the pumping cavity to a pumping outlet from the pumping cavity. The intermeshing gears have end faces at opposite sides of the gears extending perpendicularly to the rotational axes of the gears. The outer housing is comprised of a main body part and a pair of separate end plates affixed thereto. The main body part has an opening extending axially therethrough that defines a portion of the pumping cavity that faces the circumferential peripheral surfaces of the gears. The end plates each closing a respective side of the main body part opening and are in confronting relation to respective of the gear end faces for closing the pumping chamber. A fastener arrangement affixes the end plates and the main body part together.  
           [0011]    A further feature of the invention is also adapted to be embodied in an intermeshing gear pump. In accordance with this feature, the pump is comprised of an outer housing defining a pumping cavity in which a pair of intermeshing gears are journalled for pumping a fluid from a fluid inlet to the pumping cavity to a pumping outlet from the pumping cavity. The intermeshing gears have end faces extending perpendicularly to the rotational axes of the gears at at least one side of the gears. The outer housing is comprised of a main body part defining at least in part the pumping cavity and an end plate affixed thereto and closing the pumping cavity. At least one of the gears forms a bore extending therethrough to receive a shaft. The end face of this one gear forms a slot extending perpendicularly to the bore of the gear. A coupling pin extends through the shaft and has at least one end portion received in the slot for non-rotatably coupling the shaft and the one gear.  
           [0012]    Yet another feature of the invention is adapted to be embodied in a method of forming an intermeshing gear pump. The pump is comprised of an outer housing defining a pumping cavity in which a pair of intermeshing gears are journalled on respective shafts for pumping a fluid from a fluid inlet to the pumping cavity to a pumping outlet from the pumping cavity. The intermeshing gears having end faces extending perpendicularly to the rotational axes of the gears at opposite sides of the gears. The outer housing comprises a main body part and at least one separate end plate affixed thereto. The main body part has an opening extending axially therein that defines a portion of the pumping cavity facing the circumferential peripheral surfaces of the gears. The end plate closes a respective side of the main body part opening. A fastener arrangement affixes the end plate and the main body part together. The method comprising the steps of placing a pair of plates in abutting relationship. The abutting plates are held against transverse movement relative to each other. A pair of holes are drilled through the plates from one side of one of the plates and ending through the oppositely facing side of the other of the plates so that any burrs formed by the drilling operation will be formed on the oppositely facing side of the other of the plates. Then a cavity is machined in at least the oppositely facing side of the other of the plates of sufficient size to form the pumping cavity and in an area encompassing that of the previously drilled holes to remove any burrs formed by the drilling operation and form the main body part. Then the one plate is placed and affixed against the main body part in closing relation to the pumping cavity formed therein to form the end plate therefor. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a side elevational view of a marine propulsion unit having a tilt and trim unit powered by a fluid pump embodying the invention and manufactured in accordance with the invention which propulsion unit is shown attached to the transom of a watercraft hull, shown partially and in section.  
         [0014]    [0014]FIG. 2 is an enlarged elevational view of the tilt and trim unit broken away to show the pump.  
         [0015]    [0015]FIG. 3 is a cross sectional view of the pump taken through the gear axes.  
         [0016]    [0016]FIG. 4 is a top plan view of the pump with a portion of the top cover broken away to more clearly show the construction.  
         [0017]    [0017]FIG. 5 is an enlarged view looking in the same direction as FIG. 4 but showing only the connection between one of the pump gears and its shaft.  
         [0018]    [0018]FIG. 6 is a cross sectional view taken along the same plane as FIG. 3, but showing a phase of the manufacturing process. 
     
    
     DETAILED DESCRIPTION  
       [0019]    Referring now in detail to the drawings, FIGS. 1 and 2 show a marine propulsion system, indicated generally by the reference numeral  11 , as this is a typical, but not the only, use of the invention. In the illustrated embodiment, the propulsion system  11  is comprised of an outboard motor  12  and a hydraulically operated tilt and trim unit  13 , that is shown in most detail in FIG. 2.  
         [0020]    Referring now to FIG. 1, the outboard motor  12  is comprised of a power head  14  that contains a powering internal combustion engine that is not shown because of its containment in a surrounding protective cowling. The engine drives a drive shaft (not shown) that is journalled in a drive shaft housing  15  and into a lower unit  16  where it drives a propulsion device such as a propeller  17 .  
         [0021]    The drive shaft housing  15  is connected to a steering shaft (not shown) that is journalled for steering movement about a generally vertically extending axis in a swivel bracket  18  in a manner well known in the art. The swivel bracket  18  is pivotally connected to a clamping bracket  19  by a pivot pin  21 , in a manner that is also well known in the art. The clamping bracket  19  is suitably connected to the transom of a watercraft hull  22 , operating in a body of water  23 .  
         [0022]    Except for its powering pump, to be described shortly, the function and operation of the tilt and trim unit  13  is as well known in the art to trim or tilt the outboard motor  12  up in the direction of the arrow U or down in the direction of the arrow D. In addition the tilt and trim unit  13  may function as a shock absorber to permit the outboard motor  12  to “pop up” when an underwater obstacle is met and to return to the trim adjusted position when it is cleared.  
         [0023]    Referring now primarily to FIG. 2, the tilt and trim unit  13  is comprised of a hydraulic cylinder housing, indicated generally at  23 , having one end pivotally connected to the clamping bracket  19  on the hull  22  by a pivot shaft  24 . The cylinder housing  23  forms a cylinder bore  25  that is divided by a piston  26  into first and second pressure oil chambers  27  and  28 . A piston rod  29  is fixed to the piston  26  and extends through the chamber  28  and out of the cylinder housing  23  where it is connected by a pivot shaft  31  to the swivel bracket  18 . By pressurizing the chamber  27  and exhausting the chamber  28  the outboard motor  12  will move for upward tilting action U. Conversely pressurizing the second pressure oil chamber  28  and exhausting the chamber  27  will effect the outboard motor  12  to move downward for returning action D. The construction and operation of the unit  13  is well known in the art and thus further description except for its pump, next to be described, is not believed necessary. This is particularly true since the use of the pump is not so limited.  
         [0024]    The pump, indicated generally by the reference numeral  32 , comprises an intermeshing gear pump supported by threaded fasteners  33  on the cylinder  23 , a reversible electric motor  34  for driving the gear pump  32 , and, indicated generally at  35  for introducing oil which is a pressurized fluid delivered from the gear pump  32  driven by the electric motor  34  into the cylinder  23 .  
         [0025]    The gear pump  32  is supported by the threaded fasteners  33  on the cylinder  23  and comprises a housing assembly  30 , made of an iron-based sintered metal, constituting the outer shell of the gear pump and defining a pumping cavity, indicated generally by the reference numeral  36 , see now additionally FIGS.  3 - 5 . A pair of spur gears  37 ,  38  are contained in the pumping cavity  36  with their axial centers  39 ,  41  disposed parallel, and meshing with each other. Shaft receiving holes  42 ,  43  are formed in the housing assembly  30  and the gears  37 ,  38  on the axial centers  39 ,  41 . Supporting shafts  44 ,  45  are inserted in these shaft holes  42 ,  43  and journalled at both ends on the housing assembly  30  for supporting these gears  37 ,  38  for rotation about the axial centers  39 ,  41 . At least either one of these supporting shafts  44 ,  45  is driveably connected to the reversible electric motor  34 . The gears  37 ,  38  are of the same shape and the same size and their flat end faces are flush with each other.  
         [0026]    The internal surface of the pumping cavity  36  is formed by a pair of inside cylindrical surfaces  46 ,  47  that extend parallel to the axial centers  39 ,  41  and directly face the two gears  37 ,  38  in close proximity to the outside surfaces thereof. This forms a generally figure 8 shaped recess facing directly the outside circumferential surfaces of the two gears  37 ,  38  in close proximity thereto.  
         [0027]    The housing assembly  30  is made up of first, second and third pieces  48 ,  49 ,  51 , each of a flat plate-like shape. These pieces  48 ,  49  and  51  are stacked together in this order in direct contact with the piece  49  forming the main pump body and the pieces  48  and  49  forming upper and lower end closures therefore. Threaded fasteners  52  detachably fix these first, second and third pieces  48 ,  49 ,  51  together. However locating pins  53  position the first, second and third pieces  48 ,  49 ,  51  to each other prior to the fixing by the threaded fasteners  52 . In addition the threaded fasteners  33  fix the first, second and third pieces  48 ,  49 ,  51  together when the gear pump  32  is supported on the cylinder  23 , and thus have the same function as the threaded fasteners  52 .  
         [0028]    The threaded fasteners  33  pass through holes  54  provided through the housing assembly  30  parallel to the axial centers  39 ,  41  and are screwed into taped openings formed in the cylinder  23 . In a similar manner the threaded fasteners  52  pass through holes  55  provided through the first and second pieces  48 ,  49  parallel to the axial centers  39 ,  41 , and are received in tapped openings  56  formed in the third piece.  
         [0029]    The locating pins  53  are positioned in aligning holes  57  provided in the first, second and third pieces  48 ,  49 ,  51  be parallel to the axial centers  39 ,  41 . As already noted and insertion of the locating pins  53  into the aligning holes  57  allows the first, second and third pieces  48 ,  49 ,  51  to be positioned accurately to each other.  
         [0030]    A coupling device, indicated generally at  58 , is provided for coupling the gears  37 ,  38  and the respective support shafts  44 ,  45  so that the gears  37 ,  38  rotate with the support shafts  44 ,  45 , respectively. The coupling means  58  is shown best in FIG. 5 and comprises coupling grooves  59  formed on one flat face of the gears  37 ,  38  adjacent the housing piece  48 . Theses grooves  59  receive the ends of coupling pins  61  that penetrating radially through suitable openings formed in the support shafts  44 ,  45 . The pins  61  are inserted in the coupling grooves  59  with a small play in a clearance-fit relation.  
         [0031]    As shown in FIG. 3, the lower ends of the shafts  44  and  45  and the upper ends of the shaft holes  42  and  43  are chamfered significantly to facilitate assembly.  
         [0032]    Referring now primarily to FIG. 3 and also FIG. 4, the oil introducing device and reservoir  35  comprises a pair of oil passages  62  and  63  are formed in lower end plate  51  of the housing assembly  30 . The oil passage  62  allows the area of one of two portions of the pumping cavity  36  formed on both sides of the mutual meshing portion of the gears  37 ,  38  to communicate with the outside of the housing assembly  30 . The other oil passage  63  allows the other of two portions of the pumping cavity  36  to communicate with the outside of the housing assembly  30 . The passages  62  and  62  communicate with these portions of the pumping cavity  36  through recesses  64  and  65 , respectively, formed in the lower face of the main housing portion  49 .  
         [0033]    In addition to the oil passages  62  and  63 , the oil introducing device  35  comprises still another two oil passages  66  and  67  for providing communication of the recesses  64  with a reservoir  68  of the device  35 . Ball type check valves  69  in enlargements of the lower end plate passages  66  and  67  permit the drawing of make up fluid from the reservoir  68 .  
         [0034]    The passage  62  communicates with the chamber  27  of the cylinder  23  through a conduit  71  which is external of the pump housing  50 . In a like manner the passage  63  communicates externally with the cylinder chamber  28  through a conduit  72 . As is well known in the art, shuttle valves  73  are provided in the passages  71  and  72  to permit reverse flow. Pressure relief valves  74  and  75  are provided in the conduits  71  and  72  respectively for limiting the maximum pressure exerted in the cylinder chambers  27  and  28 , respectively. There are also provided a pair of pressure relief valves  76  between the shuttle valves  73  and the reservoir  68  for a similar purpose.  
         [0035]    As seen in FIGS. 3 and 4, when the electric motor  34  is operated in the trim up direction to rotate the gears  37 ,  38  in the trim up directions U, respectively, remembering that the gears  37 ,  38  are rotated the opposite directions due to their intermeshing relationship, pressure oil is delivered from the gear pump  32  passages  64  and  62 . This pressurized oil is supplied to the first pressure oil chamber  27  of the cylinder  23  through the oil introducing device  35 , as shown in these figures by the solid lines, so that the cylinder  23  extends to move the outboard motor  12  for upward tilting action U. Since the external circuitry is well known in the art it is not believed necessary to describe its operation any further. It should also be remembered that this environment is only one of many possible uses for the pump  32 .  
         [0036]    On the other hand, when the electric motor  34  is operated in the reverse direction to rotate the gears  37 ,  38  in the reverse directions D, respectively (gears  37 ,  38  are rotated reversely in the directions opposite to those of the previous case), pressure oil delivered from the gear pump  32  is supplied to the second pressure oil chamber  28  of the cylinder  23  through the oil introducing device  35 , as shown in FIGS. 1 and 4 by single dot and dash lines, so that the cylinder contracts to move the outboard motor  12  for downward returning action D. Again, since the external circuitry is well known in the art it is not believed necessary to describe its operation any further.  
         [0037]    Next, by principal reference to FIG. 6, which should also be compared to FIG. 3, a method of forming the gear pump  32  will be described, as this constitutes an important feature of the invention. In FIG. 6, work pieces that will eventually become the main body housing  49 , and the upper and lower end closures  48  and  51 . These work pieces before machining are indicated in FIG. 6 by the reference numerals  81 ,  82  and  83 , respectively. That is the work piece  81  will become after machining the main body housing  49  and the work pieces  82  and  83  will become the upper and lower end closures, respectively.  
         [0038]    First, second and third work pieces  81 ,  82 ,  83  are formed each having the same thickness and size as the respective final housing pieces  48 ,  49 ,  51 . However, for reasons that will shortly become apparent, the work pieces are initially stacked and retained in an order different from their final assembled positions. They are stacked together in the order of the second, the first and the third work pieces  82 ,  81 ,  83  in direct contact and fixed together by a suitable mechanism.  
         [0039]    Then, the shaft holes  42 ,  43  are machined with a tool such as a pair of drills  84  from the lower side of the third work piece  83  through the first work piece  81  toward the upper side of the second work piece  82 . In this case, when the shaft holes  42 ,  43  are drilled in the second work piece  82 , burrs indicated at  85  are normally produced at the edges of the holes on the ending side of the drilling operation. However, the shaft holes  42 ,  43  are not necessarily machined through the upper side of the second work piece  82  to practice the invention.  
         [0040]    Then, in the second work piece  82  is machined, with another cutting tool to form thepumping cavity  36  having a constant cross-sectional shape in the direction of depth, through the entire thickness of the second work piece  82 . This machining is preferably continued into the first work piece  81  on the side adjacent the second work piece  82  to form a recess  86  of the same cross-section in shape and size as the pumping cavity  36  but preferably of lesser axial length. In this case, the burrs  85  are automatically eliminated in association with the formation of the pumping cavity  36 .  
         [0041]    The bolt through holes  54  andlocating pin holes  57  are formed in the first, second and third work pieces  81 ,  82 ,  83  to form the first, second and third pieces  48 ,  49 ,  51 . These pieces are then separated to perform the threading operation in the piece  83  and the oil passage drilling operation and such other machining in the main body work piece  82  and lower end closure work piece  83  as required.  
         [0042]    Then the resulting pump pieces are rearranged in their final order. After that, the gears  37 ,  38 , support shafts  44 ,  45 , coupling means  58  and knock pins  56  are incorporated in these pieces and then the first, second and third pieces  48 ,  49 ,  51  are put together directly in this order and fixed with the threaded fasteners  52 . The formation of the gear pump  32  is thereby completed.  
         [0043]    Because of this arrangement, the inside surfaces  46 ,  47  of the pumping cavity  36  face directly the outside surfaces of the gears  37 ,  38 . As previously noted, in the prior art, sliding plates are provided between the end faces of the gears  37 ,  38  and the inside surfaces  46 ,  47  of the pumping cavity  36 . That is not necessary here since no fillet results at the bottom of the pumping cavity  36 . Therefore in this invention, the size of the housing assembly  30  can be decreased, that is, the size of the gear pump  32  can be decreased.  
         [0044]    Therefore, in forming the housing assembly  30 , a hole having the same cross-section in shape and size as the pumping cavity  36  when viewed in the direction of the axial centers  39 ,  41  is first machined through a flat plate member of the same thickness as the second piece  49  to form the second piece  49 . Then the first, second and third pieces  48 ,  49 ,  51  are put together in this order, so that the inside surfaces  46 ,  47  of the pumping cavity  36  are defined by the first and third pieces  48 ,  51 , and the inside circumferential surface  38  of the pumping cavity  36  by the second piece  49 , that is, the piece  30  containing the pumping cavity  36  is formed.  
         [0045]    In this case, it can be ensured more reliably in association with the formation of the pumping cavity  36  that corners of the opening ends of the pumping cavity  36  open to the outsides from the second piece  49  are shaped to be right angular. Therefore, the corners of the pumping cavity  36  defined by the inner surfaces  46 ,  47  and the inside circumferential surface  38  can be each formed into a right angular shape more reliably. Thus, if the peripheral corners of the gears  37 ,  38  are shaped to be right angular and the inside corners and the peripheral corners are fitted together, clearances between the peripheral corners and the inside corners can be significantly decreased compared with when they are shaped in arcs and fitted together.  
         [0046]    Therefore, partial return of pressure oil from the delivery side to the suction side through the foregoing clearances in the prior art constructions is prevented. Thus during operation of the gear pump  32  the pressure of the pressure oil delivered from the gear pump  32  can be increased to a sufficiently high value. Also, because the mating surfaces of the first, second and third housing pieces  48 ,  49 ,  51  are flat these outside surfaces can be easily formed with high accuracy, which allows easy formation of the gear pump  32 .  
         [0047]    Also as described above, the gears  37 ,  38  are formed with shaft holes  42 ,  51  on the axial centers  39 ,  41 , and the support shafts  44 ,  45  are inserted in the shaft holes  42 ,  43 . Therefore, since it is ensured that corners defined by the outside surfaces of the gears  37 ,  38  and the outside circumferential surfaces of the support shafts  44 ,  45  can be shaped to be right angular. Thus the corners of the opening ends of openings of the shaft holes  42 ,  43  into to the pumping cavity  36  are shaped to be right angular and the corners of the gears and those of the opening ends of openings of the shaft holes are fitted together, clearances between these corners can be significantly decreased compared with when they are formed into arcs and fitted together.  
         [0048]    Therefore, partial return of pressure oil from the delivery side to the suction side through the foregoing clearances is prevented more reliably during operation of the gear pump  32 , so that the pressure of the pressure oil delivered from the gear pump  32  can be increased to a sufficiently high value.  
         [0049]    Also as described above, gears  37 ,  38  and support shafts  44 ,  45  are rotatable relative to their axial centers  39 ,  41 , and coupling means  58  is provided for coupling the gears  37 ,  38  and the support shafts  44 ,  45  without fixing to each other such that said gears  37 ,  38  rotate with said support shafts  44 ,  45 . Therefore little play is produced between the gears  37 ,  38  and the support shafts  44 ,  45 , even if a forming error is produced in the degree of right angularity between the inside surfaces  46 ,  47  of the pumping cavity  36  and the axial centers  39 ,  41  of the support shafts  44 ,  45 , this error is absorbed by the foregoing play, and the inside surfaces  46 ,  47  of the pumping cavity  36  can be brought close to the gears  37 ,  38  throughout their outside surfaces in close contact, so that clearances between the inside surfaces  46 ,  47  of the pumping cavity  36  and the outside surfaces of the gears  37 ,  38  can be significantly decreased.  
         [0050]    Thus it should be readily apparent that a pump configured and manufactured as described provides a high output and compact configuration. Those skilled in the art will readily understand that the foregoing description is of preferred embodiments of the invention and that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.