WO2005079302A2

WO2005079302A2 - Low cost gear fuel pump

Info

Publication number: WO2005079302A2
Application number: PCT/US2005/004412
Authority: WO
Inventors: Hing L. Chiu
Original assignee: Argo-Tech Corporation
Priority date: 2004-02-13
Filing date: 2005-02-14
Publication date: 2005-09-01
Also published as: US20080240968A1; EP1718865A4; WO2005079302A3; JP2007522384A; EP1718865A2

Abstract

The present invention is directed to a gear pump having a housing (10’) with an interior pumping chamber (200) and an inlet (40’) to and outlet (42’) from the chamber, the outlet being spaced from the inlet. A pair of rotating gears (330,332) is located in the chamber, the gears including teeth which mesh during gear rotation. The gears are preferably powder metal construction and fixedly secured on a shaft (230,232) having an axis of rotation. A pair of one-piece bearings (210,212) is located in the chamber and journal one of first and second end portions of each shaft (320). The one-piece bearings provide precise alignment of the first and second end portions of the shafts and maintain the shafts in parallel relation.

Description

LOWCOST GEAR FUEL PUMP

Cross Reference to Related Applications

[0001] This application claims priority from U.S. Provisional Patent Application Serial

No. 60/544,582 filed February 13, 2004 and is incorporated herein by reference.

Background of the Invention

[0002] This present invention relates generally to gear pumps. More particularly, it relates to an improved bearing and gear assembly construction, particularly one used as a fuel pump, and methods of making the same.

[0003] A typical gear fuel pump is a fixed displacement pumping device. It receives fuel from the fuel tank, pressurizes the fuel, and delivers the fuel at a higher pressure to the fuel nozzle via a fuel control for engine combustion. The gear pump generally includes a housing, such as an aluminum housing, having an interior pump chamber defined by parallel, intersecting, cylindrical bores. First and second gears, usually of similar configuration, are disposed in respective bores and the gears mesh with each other in the area of intersection of the bores inside the housing. A first or drive gear has a splined drive shaft and as it rotates, the first gear drives a second gear, commonly called the driven gear. As the gears rotate-within the housing, fluid is transferred from an inlet to an outlet of the pump. The gears are highly stressed at high pressures and high loads. Gears of either spur or helical configuration can be used; although spur gears are most common. The gears are driven to unmesh adjacent the inlet and convey the fluid around the periphery of the bores to the region where the gears mesh. The meshing of the gears forces the fluid out of the pump chamber where it exits the pump housing through the outlet.

[0004] Since the pressure of the fluid being pumped is greater at the outlet than at the inlet during pump operation, the pressure differential can cause leakage flow from the outlet to the inlet across the interfaces of the various components. This leakage flow lowers the efficiency of the pump. In some instances, there can be substantial variations in the leakage flow from one identically made pump to another. Since the volume pumped is a direct function of the volume displaced by the meshing gears, variation in depth of mesh gears will also greatly affect capacity. Thus, it is important to provide precise alignment an meshing of the gears in order to improve pump efficiency. [0005] Typically, four separate bearings are disposed in the bores and journal or support portions of the gear shafts. The bearings usually have a generally cylindrical exterior configuration with facing and engaging flats along one portion of the periphery that align with region in which the gears mesh. The bearings are sized to fit the pump chamber. In the usual case, the bearings are manufactured paying close heed to the design dimension between the center of the flat and the diametrically opposite side of the otherwise cylindrical bearing. In order to rninimize leakage paths, such bearings are made to form a tight fit within respective bores in the pump and not infrequently, due to tolerance variations, good fitting cannot always be attained. Thus, it has been customary to, during the assembly process, shave material off of the flats of one or more of the bearings in the hope that a precise fit can be achieved. Indeed, the bearings are designed to be shaved so as to accommodate tolerance variation while attempting to maintain a tight fit.

[0006] However, in the shaving process, parallelism of the face of the flat to the axial center line of the bearing may be lost, creating a leakage path. Alternatively, the flatness of the face can be lost during the shaving process, again creating a leakage path across the flats. The shaving process may also result in a loss of squareness or perpendicularity of the face of the flat to the end of the bearing which in turn may not seal properly against the housing end wall, which may prevent the bearing from moving properly in response to shaft deflection during operation, or may misalign the shafts. Shaving may also result in a changed depth of mesh of the gears joumalled by the bearings, thus altering the pump's capacity.

[0007] Another substantial factor resulting in the differing capacities in otherwise identical pumps is the fact that conventionally, each splined drive shaft and corresponding gear are manufactured one-piece bar stock driven gears where the bar portion (i.e. drive shaft) and gear are formed as a single, one-piece unit. As such, opposing end portions of the drive shaft are separately manufactured and may result in differing diameters of the opposing end portions which impacts mating with the bearings.

[0008] Commonly assigned U.S. Patent No.6,042,352 is directed to a gear pump of the type for which the improved gear fuel pump was developed. Other existing gear pump designs are known in the art, including the following: U.S. Pat. Nos. 4,682,938; 4,193,745; 4,097,206; 3,003,426; 2,981 ,200; and 2,774,309. [0009] In light of the foregoing, it is evident that there is a need for an improved gear pump that provides a solution to one or more of the deficiencies in the art. It is still more clear that an improved gear pump, such as a fuel pump, providing a solution to each of the needs inadequately addressed by the prior art while providing a number of heretofore unrealized advantages thereover would represent a marked advance in the art.

Brief Description of the Invention

[0010] A new and improved gear fuel pump assembly is provided. [0011] More particularly, and according to one embodiment of the present invention, the gear pump comprises a housing including an interior pumping chamber and an inlet and outlet in spaced relation that each communicate with the chamber. A pair of rotating gears is located in the chamber, each gear being fixedly secured on a respective shaft having an axis of rotation. The gear teeth mesh to pressurize fluid pumped through the housing. A pair of one-piece bearings is located in the chamber on opposite ends of the gears and journal one of first and second end portions of each shaft. The one-piece bearings provide precise alignment of the first and second the shafts and maintain the shafts in parallel relation.

[0012] Preferably, the gears are formed from powder metal and secured on constant diameter shafts. Each gear is keyed to one of the shafts so as to rotate therewith, and the dimensional tolerance between the shaft and gear provides for proper meshing of the gears if there is any slight misalignment.

[0013] According to another embodiment of the present invention, a method of assembling a gear pump is provided. The method comprises the steps of providing first and second shafts having substantially constant diameters along their lengths. A gear is advanced over each shaft and secured to each shaft. A one-piece bearing is then mounted on the shafts. The bearing and shafts with, gears mounted thereon are installed into a housing of a gear pump.

[0014] According to one aspect of the present invention, the one piece bearings and the gears are made from powder metal. By using powder metal technology, the one- piece bearings and gears can be formed without the requirement of extensive additional machining. [0015] A primary benefit of the present invention resides in the ability to provide homogenous one-piece bearings which have a higher accuracy in alignment compared to conventional bearings.

[0016] Another benefit of the present invention resides in the ability to provide powder metal components for a gear pump which last as long or longer than components formed from conventional materials.

[0017] Still another benefit resides in the precise alignment associated with the use of one-piece bearings.

[0018] A further benefit resides in the substantial savings associated with powder metal components by reducing the extensive additional manufacturing steps associated with conventional bearings, gears and shafts.

[0019] Still other benefits and aspects of the invention will become apparent from a reading and understanding of the detailed description of the preferred embodiments hereinbelow.

Brief Description of the Drawings

[0020] The present invention may take physical form in certain parts and arrangements of parts, preferred embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part of the invention.

[0021] FIGURE 1 is an exploded perspective view of a conventional gear pump assembly.

[0022] FIGURE 2 is a top plan view, partially broken away, of a cover plate and housing of the conventional gear pump assembly of FIGURE 1.

[0023] FIGURE 3 is a.sectional view taken approximately along line 3-3 in FIGURE

2.

[0024] FIGURE 4 is an exploded perspective view of a gear pump assembly according to the present invention.

[0025] FIGURE 5 is a top plan view, partially broken away, of a cover plate and housing of the gear pump assembly of FIGURE 4.

[0026] FIGURE 6 is a sectional view taken approximately along line 6-6 in FIGURE

5.

[0027] FIGURE 7 is a bottom plan view of a one-piece first bearing of the gear pump assembly of FIGURE 4. [0028] FIGURE 8 is a sectional view taken approximately along line 7-7 in FIGURE

7 showing the first bearing.

[0029] FIGURE 9 is a top plan view of the first bearing of the gear pump assembly of

FIGURE 4.

[0030] FIGURE 10 is a sectional view taken approximately along line 10-10 in

FIGURE 9.

[0031] FIGURE 11 is a top plan view of a one-piece second bearing of the gear pump assembly of FIGURE 4.

[0032] FIGURE 12 is a sectional view taken approximately along line 12-12 in

FIGURE 11 showing the second bearing.

[0033] FIGURE 13 is a bottom plan view of the second bearing of the gear pump assembly of FIGURE 4.

[0034] FIGURE 14 is a sectional view taken approximately along line 14-14 in

FIGURE 13.

[0035] FIGURE 15 is a plan view of a first shaft of the gear pump assembly of

FIGURE 4.

[0036] FIGURE 16 is a sectional view taken approximately along line 16-16 in

FIGURE 15.

[0037] FIGURE 17 is a plan view of a second shaft of the gear pump assembly of

FIGURE 4.

[0038] FIGURE 18 is a side elevational view of the second shaft of FIGURE 17.

[0039] FIGURE 19 is a sectional view taken approximately along line 19-19 in

FIGURE 18.

[0040] FIGURE 20 is a top plan view of a gear of the gear pump assembly of

FIGURE 4.

[0041] FIGURE 21 is a sectional view taken approximately along line 21-21 in

FIGURE 20.

Detailed Description of the Invention

[0042] It should, of course, be understood that the description and drawings herein are merely illustrative and that various modifications and changes can be made in the structures disclosed without departing from the spirit of the invention. Like numerals refer to like parts throughout the several views. [0043] With reference to FIGURE 1 , a conventional gear pump assembly GP typically includes a housing 10, generally made from aluminum, having end flanges 12 and 14 and an end plate or lid 16 for sealing the housing. End flange 12 includes a plurality of apertures 18 and the lid includes corresponding apertures 20 dimensioned to receive conventional fasteners F which secure the lid to the housing. As shown in FIGURES 1 and 2, the end flange 12 and the lid 16 are generally polygonal in cross- section, although, it should be appreciated by one skilled in the art that the end flange and lid can have other configurations depending on the use of the gear pump and/or the environment in which the pump is used. The housing further includes a recess 22 which receives a seal 24. End flange 14 also includes a plurality of mounting apertures 26 for mounting the gear pump GP to any source of rotational energy (not shown). [0044] With reference to FIGURE 2, the housing 10 includes a chamber 30, defined by two parallel, intersecting, cylindrical bores 32 and 34. The housing 10 has an inlet 40 and an outlet 42. As shown in FIGURE 1 , the gear pump GP further includes first and second gears 50, 52 disposed within the bores 32 and 34, respectively, so as to be meshed generally in the region of a dotted line designated 54 in FIGURE 3. The gear 50 is integrally formed with a hollow drive shaft or journal 60 while the gear 52 is integrally formed with a hollow driven shaft or journal 62. Typically, the shaft and gear are formed from stock material and machined to the desired diameter of the shaft and the gear detail. As will be appreciated, a substantial amount of stock material is removed in this conventional manufacturing operation. Moreover, as noted in the Background, there are problems associated with that conventional arrangement. [0045] The driven shaft 62 includes a splined internal surface (not shown) which is engaged by a splined end portion of a rotational shaft S which is connected to the source of rotational energy. The rotational shaft S extends through an opening (not shown) in the housing. An o-.ring 68 and a shaft seal 70 are provided about the opening to prevent gear pump external leakage. A seal 72 is normally coupled to the drive shaft. [0046] Within the housing 10, both of the shafts 60, 62 have end portions 76 which are supported or joumalled in respective first and second bearings 80, 82. The bearings 80, 82 are separately formed and generally cylindrical about the rotational axis of the shafts defined by cylindrical openings 84, 86. Each of the bearings is also provided with respective flats 88, 90 on a portion of the circumference immediately adjacent the point 54 where the gears 50, 52 mesh. Each flat 88 on adjacent bearings 80 includes a hole or recess 92. The flats 88 face each other and engaged one another by a pin 94 received in the holes. Similarly, each flat 90 on adjacent bearings 82 include a hole or recess 96 that receive a pin 98. The flats 88 and 90 are intended to be defined by planes parallel to the center line of the openings 84, 86. [0047] Generally, the bearings are longitudinally fixed in the cylindrical bores 32 and 34 of the housing 10. However, a bottom surface 100 of each bearing 82 includes a flange 102 having a plurality of openings (not shown) for receiving individual springs 104. As such, the pressurized bearings are urged or biased in a longitudinal direction along the end portions 76 of the shafts 60, 62 in the cylindrical bores. [0048] The fuel is pumped from the low pressure inlet side of the bearings 82 to the high pressure discharge side of the bearings. The gears 50, 52, which are longitudinally received between the bearings 80, 82, rotate about respective, parallel axes, arid mesh together. Fluid is thus moved from the inlet around the outside of the gears 50, 52 to the outlet in a manner well known in the art.

[0049] As shown in FIGURES 1 and 2, the bearing arrangement and the cylindrical bores 32 and 34 of the housing 10 have a figure eight configuration. In the manufacture of the prior art bearings 80 and 82, the.controlled tolerance is the distance from the flat 88 and 90 to a diametrically opposite point on the periphery of the bearing. As described above, the flats 88 and 90 are typically shaved so as to allow the bearings 80 and 82 to be fitted to in the gear pump housing 10. As such, the controlled tolerance is lost to some degree during the shaving process. Because the flats on bearings utilized in prior art gear pumps require shaving during assembly, the loss of parallelism of the flat to the center line of the bearing, the loss of flatness, orthe loss of squareness of the flats 88.90 relative to respective top surfaces 110, 112 and bottom surfaces 114, 100 of the bearings 80, 82 occurs. As a result, the gear pump GP may experience leakage or be less efficient than desired.

[0050] As briefly stated above, the gears 50, 52 are integrally formed with the respective shafts 60, 62. Each shaft and corresponding gear are manufactured from a one-piece bar stock where the opposing end portions 76 of the shaft and the gear are formed as a single unit. As such, the opposing end portions of the shaft are separately formed which may result in differing diameters of the opposing end portions. To correct this dimensional difference, the diameter of the larger opposing end portion is typically ground down to match the diameter of the other end portion. However, this grinding process may also result in a loss of squareness or perpendicularity of the shafts 60 and 62 to the integral gears 50 and 52. This can effect the meshing of the gears, and since the volume pumped is a direct function of the volume displaced by the meshing gears, can affect the capacity of the gear pump.

[0051] With reference now to FIGURE 4, a gear pump according to the present invention is shown. Since much of the structure and function is substantially identical, reference numerals with a single primed suffix (') referto like components (e.g., housing 10 is referred to by reference numeral 10"), and new numerals identify new components. Likewise, description of components that remain unchanged is not necessary.

[0052] The gear pump assembly GP^* shown in FIGURES 4-6 includes the housing 10' having a chamber 200, defining a single cylindrical bore 202. The housing 10' receives a pair of bearings 204, 206, each bearing being a one-piece bearing formed from powder metal. That is, the bearings are substantially homogenous components that do not have joint lines, i.e., they are continuous, when compared to the two-piece bearing assemblies of the prior art. Each bearing preferably has a generally oblong cross-section. It will be appreciated that the periphery of each bearing mates with the similarly dimensioned bore 204 of the housing 10'. However, it should be appreciated by one skilled in the art that the bearings and corresponding bore can have other contours which would allow each bearing to be closely received within the chamber 200 of housing 10'.

[0053] With reference to FIGURES 8 through 10, the unitary bearing 204, which is generally longitudinally fixed in the housing, includes a first or top surface 220, a second or bottom surface 222, and a pair of openings 224, 226 having center axes coincident with axes of rotation of shafts or journals 230, 232. The bearing further includes first and second elongated sides 236, 238. The first elongated side is generally parallel to the second elongated side, and in the preferred arrangement the elongated sides are generally planar. Opposing ends 240, 242 have an arcuate contour, although as stated above, the ends can have other configurations without departing from the scope and intent of the present invention.

[0054] With continued reference to FIGURE 7, the bottom surface 222 of the bearing 210 includes a dam 250, an inlet face relief 252, and a discharge face relief 254. Thus, the bearing dam 250 is located between the inlet face relief and the discharge face relief. The bearing dam wall forms a sealed dam area between an inlet side 256 and an outlet side 258, thus resulting in a low-pressure area on the inlet side 40' and high- pressure area on the outlet side 42" of the gear pump GP". The bearing further includes a bleed hole 260 for bearing lubrication drain. As shown in FIGURE 10, the bleed hole has a substantially constant diameter along its length and intersects the dam area 250 in a perpendicular fashion.

[0055] With reference to FIGURES 11-14, the unitary bearing 212 includes a first or top surface 270, a second or bottom surface 272, and a pair of openings 274, 276 having center axes coincident with the center axes of the openings 224, 226 of the bearing 210 and the axes of rotation of the shafts 230, 232. Similar to the bearing 210, the bearing 212 further includes generally parallel first and second elongated sides 280, 282 and a pair of arcuate ends 240 and 242.

[0056] Similar to the features of the bottom surface 222 of the bearing 210, the top surface 270 of the bearing 212 includes a dam 290, an inlet face relief 292, and a discharge face relief 294, the bearing dam wall forming a sealed dam area between an inlet side 296 and an outlet side 298, thus also resulting in a low-pressure area on the inlet side 40' and high-pressure area on the outlet side 42" of the gear pump GP'. The bearing further includes a blind hole 300 for the retention of an energized spring 302. [0057] As seen in FIGURE 14, the bottom surface 272 of the bearing 212 includes a flange 310. A seal 312 can be provided about the flange.

[0058] A pair of gears 330, 332 are longitudinally received on the shafts 230, 232 between the bearings 210, 212 (FIGURE 4). With reference to FIGURES 15 through 19, each shaft 230, 232 includes an axial recess 340 and first and second spaced, - circumferential grooves 342, 344 extending radially inward from the outer periphery 346 of each shaft for receiving retaining rings or snap rings 350 (FIGURE 4). The snap rings fixedly secure the gears 330, 332 on the shafts 230, 232 and preclude longitudinal movement of.the gears relative to the respective shaft.

[0059] Each shaft 230, 232 is generally hollow and has a substantially constant diameter along its lengths. As shown in FIGURE 16, shaft 232 also has a constant inner diameter. As shown in FIGURES 18 and 19, a portion 352 of an inner surface 350 of the drive shaft 230 is splined. The splined portion is engaged by a splined portion of a rotational shaft S' which is connected to a source of rotational energy. The rotational shaft S' extends through an opening (not shown) in the housing. [0060] The shafts 230 and 232 are formed by conventional metal manufacturing. Each gear 330 and 332 (FIGURES 20-21) on the other hand is manufactured from powdered metal and includes an opening 360 adapted for receipt over one of the shafts 230, 232. The dimensional tolerance between the outer diameter of the shaft and the diameter of opening 360 of the gear provides some self alignment of the teeth 362 of the gears as the gears mesh if the gears/shafts are not precisely aligned. Each gear is secured generally perpendicular on the respective shaft. Each gear further includes an axial groove 364. The axial recess 340 of the shafts and the axial groove 364 of the gear are dimensioned to receive a pin 370 that fixes or keys the gear to the shaft. [0061] Generally, to assemble the gear pump GP", a first snap ring 350 is secured in one of the first and second grooves 342, 344 of the shafts 230, 232. The snap ring prevents axial movement of the gears on the shafts. The pin 370 is placed in the axial recess 340. The gears 330, 332 are then advanced over each shaft in such a manner that the axial groove is aligned with the pin and the axial recess. Thus, the axial recess and groove together form a housing for the pin, the pin preventing rotation of the gears on the respective shafts. A second snap ring 350 is secured in the other groove thereby longitudinally or axially securing the gear to each shaft. The one-piece continuous bearing 212 is then installed in the chamber 202 of the housing 10'. The assembled shafts (i.e. shafts with gears mounted thereon) are mounted on the bearing, shaft portions 320 being journalled in the openings 274, 276 of the bearing. The one- piece bearing 210 is then mounted on the assembled shafts, shaft portions 320 being journalled in the openings 224, 226 of the bearing. Thus, the one-piece bearings provide precise alignment of the shafts and maintain the shafts in parallel relation in the housing. The lid 16' is then secured to the housing via the conventional fasteners F'. [0062] Accordingly, the present invention provides a gear pump having powder metal components with distinct advantages over the conventional components. In addition to the uniqueness of using powdered metal technology to make the bearings 210 and 212, the continuous configuration of the bearing provides a higher accuracy in alignment by avoidance of the connecting separate bearing 80, 82 of the prior art. Thus, it is possible to precisely align the center axes of the openings for the bearings. [0063] Moreover, the one-piece bearings 210, 212 in the preferred embodiment are a straight line design, i.e., across the top and bottom surfaces of the bearing, whereas, the conventional bearing 80, 82, when connected, have a figure eight design. By incorporating the straight line design, a more precise and easier alignment of the bearings 210, 212 into the chamber 200 of the housing 10' can be achieved compared to the conventional figure eight design.

[0064] The one-piece bearing 210, 212 also allows for greater control of the openings in centerline-to-centerline positioning where the control may be as much as plus or minus one hundredth millimeter. However, the two-piece figure of eight design generally needs to be machine leveled to obtain that exactness, which is very time consuming. Further, since the separate bearings 80, 82 are connected, it is possible that separation of the two piece bearing may occur thereby not allowing functional operation. On the other hand, because the bearings 210, 212 have a unitary design, they cannot separate during operation of the gear pump GP'. [0065] Cost benefits over the above described prior art design approach as compared to the low cost powdered metal design approach of the present application are set forth, in one example, in the following Table:

Feature Conventional Design Low Cost Powder Metal Approach (P/M) Design Approach Gear Gear and journal one piece Gear blank and journal fabrication formed separately Gear Teeth Rough machined individually Precision Carbide Tooling and final ground. Part fabricated once, net shape inspection required. High formed, millions can be Cost (about $800-$2500 per pressed without changing the set). tooling. Random sampling is required. High initial tooling cost but very low formed piece part cost (approximately $25-$30 each). Gear Journal Cut from a circular bar stock Separated center-less together with the gear. Both ground. One journal, no sides of journal size to be matching problem. Key way matched precisely. is needed to drive the gear Integrated with gear, one blank. Retaining rings to piece construction. position the gear blank (approximately $25-$30 each). Gear Width Matching to about .0002 Dozen can be ground to the Matching inch, large pool of inventory same height at once, no is required for matching. matching is required. Two Parallel to within about .0002 sides will be automatically inch. parallel. Thrust Face Special super finishing Not required, as ground. Finish operation. Deburring Required, time consuming. Tumble finish, a very simple Feature Conventional Design Low Cost Powder Metal Approach (P/M) Design Approach operation. Drive Splined shaft, costly. Hex Drive, low cost. Total Cost Very high approximately 20% of conventional cost Pressurized Two separated parts One piece construction Bearing Drive Bearing Fabricated individually. Final Designed for Powdered lapping at pump assembly. Metal application. One High precision machining single piece. Net shape required. bronze powdered metal. Minimum machining

Driven Bearing Fabricated individually, required. One time initial different from drive bearing. tooling cost, very low per Final lapping at pump piece formed part cost assembly. Relatively high (approximately $3.00-$5.00 cost. each).

Loading Spring Generally 12 for pressurized One bearings Fixed Bearing Two fixed and two One piece construction pressurized Drive Fabricated individually. Final One single piece. Net shape lapping at pump assembly bronze powdered metal. Minimum machining is Driven Fabricated individually, required. No matching is different from drive bearing. needed. One time initial Matching in height is tooling cost, very low per required. Final lapping at piece formed part cost. . pump assembly. Relatively (approximately $2.00-$4.00 high cost. each). Total Cost High approximately 25% of conventional design. Drive Shaft Input and Output splines Hex shaft cut from standard stock r Total Cost High approximately 10% of conventional design. Total Gear Very High approximately 30%-40% of Pump Ass'y the conventional design Cost [0066] It is to be understood the above percentages and dollar figures are simply estimates and the values may, depending on the implementation, be different from those cited.

[0067] Accordingly, using powder metal to manufacture components for the gear pump GP' result in a much-improved manufacturing cost structure for gear pump fabrication and assembly. This is true since the gears, bearings and shafts constitute the majority of the fuel pump components.

[0068] The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

What is claimed is:

1. A gear pump comprising: a housing including an interior pumping chamber; an inlet to the chamber; an outlet from the chamber and spaced from the inlet; a pair of rotating gears in the chamber, the gears including teeth which mesh during gear rotation, each gear being fixedly secured on a shaft having an axis of rotation; and a pair of one-piece bearings located in the chamber and journalling one of first and second end portions of each shaft, the one-piece bearings providing precise alignment of the first and second end portions of the shafts and maintaining the shafts in parallel relation.

2. The gear pump of claim 1 wherein the one-piece bearings are manufactured from powdered metal.

3. The gear pump of claim 1 wherein each one-piece bearing has a generally oblong cross-section.

4. The gear pump of claim 1 wherein each one-piece bearing includes: a top surface, a bottom surface, a pair of openings having center axes coincident with the axes of rotation of the shafts, and first and second elongated sides, opposing ends of the first side being joined to corresponding opposing ends of the second side by a pair of arcuate ends.

5. The gear pump of claim 4 wherein the first elongated side is parallel to the second elongated side.

6. The gear pump of claim 4 wherein the first and second elongated sides are generally planar.

7. The gear pump of claim 1 wherein each gear is manufactured from powdered metal.

8. The gear pump of claim 7 wherein each gear includes an opening adapted to receive the shaft thereby allowing for self alignment of the teeth of the gears as the gears mesh.

9. The gear pump of claim 1 wherein each shaft includes an axial recess and each gear includes an axial groove dimensioned to receive a pin for preventing rotation of the gears on the respective shafts.

10. The gear pump of claim 1 wherein each shaft includes first and second grooves extending radially about the periphery of each shaft for receiving associated snap rings.

11. The gear pump of claim 1 wherein each gear is secured perpendicularly on each shaft.

12. A method of assembling a gear pump comprising the steps of: providing first and second shafts having substantially constant diameter along their lengths; advancing a gear over each shaft; securing the gear to each shaft; mounting a bearing on the shafts; installing the bearing and shafts with gears mounted thereon into a housing of a gear.pump.

13. The method of claim 12 comprising the further steps of preventing rotation of the gear relative to each shaft.

14. The method of claim 12 comprising the further steps of providing one- piece continuous bearings on each end of the shafts.

15. The method of claim 14 comprising the further steps of joumalling each shaft in the one-piece bearings, the one-piece bearings providing precise alignment of the shafts.

16. The method of claim 12 comprising the further steps of forming each gear from powder metal whereby each gear has a substantially uniform composition throughout.

17. The method of claim 12 comprising the further steps of forming the bearing from powder metal whereby the at least one bearing is homogenous.