U.S. patent application number 10/589361 was filed with the patent office on 2008-10-02 for low cost gear fuel pump.
Invention is credited to Hing L. Chiu.
Application Number | 20080240968 10/589361 |
Document ID | / |
Family ID | 34886051 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080240968 |
Kind Code |
A1 |
Chiu; Hing L. |
October 2, 2008 |
Low Cost Gear Fuel Pump
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.
Inventors: |
Chiu; Hing L.; (Solon,
OH) |
Correspondence
Address: |
FAY SHARPE LLP
1100 SUPERIOR AVENUE, SEVENTH FLOOR
CLEVELAND
OH
44114
US
|
Family ID: |
34886051 |
Appl. No.: |
10/589361 |
Filed: |
February 14, 2005 |
PCT Filed: |
February 14, 2005 |
PCT NO: |
PCT/US05/04412 |
371 Date: |
October 22, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60544582 |
Feb 13, 2004 |
|
|
|
Current U.S.
Class: |
418/206.7 |
Current CPC
Class: |
F04C 2/18 20130101; F04C
15/0073 20130101; F04C 2240/52 20130101; F04C 2230/22 20130101;
F04C 2/086 20130101 |
Class at
Publication: |
418/206.7 |
International
Class: |
F04C 2/08 20060101
F04C002/08 |
Claims
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 journaling
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; wherein the one-piece bearings are manufactured from
powdered metal whereby each bearing is homogenous and has a
substantially uniform composition throughout.
2. (canceled)
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; forming a bearing from powder metal
whereby the bearing is homogenous; advancing a gear over each
shaft; securing the gear to each shaft; mounting the 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
journaling 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. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Application Ser. No. 60/544,582 filed Feb. 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 and 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 minimize 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 journalled 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. Pat. 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] FIG. 1 is an exploded perspective view of a conventional
gear pump assembly.
[0022] FIG. 2 is a top plan view, partially broken away, of a cover
plate and housing of the conventional gear pump assembly of FIG.
1.
[0023] FIG. 3 is a sectional view taken approximately along line
3-3 in FIG. 2.
[0024] FIG. 4 is an exploded perspective view of a gear pump
assembly according to the present invention.
[0025] FIG. 5 is a top plan view, partially broken away, of a cover
plate and housing of the gear pump assembly of FIG. 4.
[0026] FIG. 6 is a sectional view taken approximately along line
6-6 in FIG. 5.
[0027] FIG. 7 is a bottom plan view of a one-piece first bearing of
the gear pump assembly of FIG. 4.
[0028] FIG. 8 is a sectional view taken approximately along line
7-7 in FIG. 7 showing the first bearing.
[0029] FIG. 9 is a top plan view of the first bearing of the gear
pump assembly of FIG. 4.
[0030] FIG. 10 is a sectional view taken approximately along line
10-10 in FIG. 9.
[0031] FIG. 11 is a top plan view of a one-piece second bearing of
the gear pump assembly of FIG. 4.
[0032] FIG. 12 is a sectional view taken approximately along line
12-12 in FIG. 11 showing the second bearing.
[0033] FIG. 13 is a bottom plan view of the second bearing of the
gear pump assembly of FIG. 4.
[0034] FIG. 14 is a sectional view taken approximately along line
14-14 in FIG. 13.
[0035] FIG. 15 is a plan view of a first shaft of the gear pump
assembly of FIG. 4.
[0036] FIG. 16 is a sectional view taken approximately along line
16-16 in FIG. 15.
[0037] FIG. 17 is a plan view of a second shaft of the gear pump
assembly of FIG. 4.
[0038] FIG. 18 is a side elevational view of the second shaft of
FIG. 17.
[0039] FIG. 19 is a sectional view taken approximately along line
19-19 in FIG. 18.
[0040] FIG. 20 is a top plan view of a gear of the gear pump
assembly of FIG. 4.
[0041] FIG. 21 is a sectional view taken approximately along line
21-21 in FIG. 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 FIG. 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 FIGS. 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 FIG. 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
FIG. 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
FIG. 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 journalled 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, and 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 FIGS. 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, or the 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 FIG. 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 (') refer to 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 FIGS. 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 FIGS. 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 FIG. 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 FIG. 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 FIGS. 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 FIG. 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 (FIG. 4). With
reference to FIGS. 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
(FIG. 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 FIG.
16, shaft 232 also has a constant inner diameter. As shown in FIGS.
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 (FIGS. 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:
TABLE-US-00001 Conventional Design Low Cost Powder Metal Feature
Approach (P/M) Design Approach Gear Gear and journal one piece Gear
blank and journal fabrication formed separately Gear Rough machined
individually Precision Carbide Tooling Teeth and final ground. Part
fabricated once, net shape inspection required. High formed,
millions can be Cost (about $800-$2500 per pressed without changing
set). the tooling. Random sampling is required. High initial
tooling cost but very low formed piece part cost (approximately
$25-$30 each). Gear Cut from a circular bar Separated center-less
Journal stock together with the ground. One journal, no gear. Both
sides of matching problem. Key way journal size to be is needed to
drive the gear matched precisely. blank. Retaining rings to
Integrated with gear, one position the gear blank piece
construction. (approximately $25-$30 each). Gear Matching to about
.0002 Dozen can be ground to the Width inch, large pool of same
height at once, no Matching inventory is required for matching is
required. Two matching. Parallel to sides will be automatically
within about .0002 inch. parallel. Thrust Special super finishing
Not required, as ground. Face operation. Finish De- Required, time
consuming. Tumble finish, a very burring simple operation. Drive
Splined shaft, costly. Hex Drive, low cost. Total Very high
approximately 20% of Cost conventional cost Pres- Two separated
parts One piece construction surized Bearing Drive Fabricated
individually. Designed for Powdered Bearing Final lapping at pump
Metal application. One assembly. single piece. Net shape High
precision machining bronze powdered metal. required. Minimum
machining Driven Fabricated individually, required. One time
initial Bearing different from drive tooling cost, very low per
bearing. Final lapping piece formed part cost at pump assembly.
(approximately $3.00-$5.00 Relatively high cost. each). Loading
Generally 12 for pressurized One Spring bearings Fixed Two fixed
and two One piece construction Bearing pressurized Drive Fabricated
individually. One single piece. Net shape Final lapping at pump
bronze powdered metal. assembly 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 High approximately 25% of Cost conventional
design. Drive Input and Output splines Hex shaft cut from standard
Shaft stock Total High approximately 10% of Cost conventional
design. Total Very High approximately 30%-40% of Gear the
conventional design Pump Ass'y 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.
* * * * *