Note: Descriptions are shown in the official language in which they were submitted.
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PUMP
BACKGROUND
The present invention relates to a pump such as a hydraulic pump, and
particularly to a pump that maintains balanced axial forces on the pumping
mechanism, even in the event of high inlet and outlet pump pressures.
The hydraulic system disclosed in Tieben U.S. Patent No. 5,916,139
includes a pump, an actuator and a reservoir. In one mode of operation, the
pump inlet is connected to the reservoir and the pump outlet is connected to
the actuator. In another mode of operation, the pump inlet is connected to the
actuator and the pump outlet is connected to the reservoir. This system
encounters relatively high fluid pressures at both the pump inlet and the pump
outlet. As explained in the Tieben patent, such pressures can result in
undesired axial loads on the pumping mechanism, due to the high internal
pressure of the pump. The pump disclosed in the Tieben patent overcomes
this potential problem by providing high-pressure seals at both ends of the
driven shaft of the pump. In this way, hydraulic axial forces on the driven
shaft are balanced, and friction and associated wear are reduced.
One potential drawback of the pump illustrated in the Tieben patent is
that two high-pressure shaft seals are required. Furthermore, under some
conditions cup seals of the type illustrated in the Tieben patent can cause
wear on the sealed shaft and associated leaks.
The present invention is directed to an improved pump that is well-
suited for use in applications having high internal pump pressures and that
overcomes the potential disadvantages described above.
SUMMARY
By way of introduction, the preferred embodiment described below
includes a pump mechanism having a driven shaft. The driven shaft is
connected to an input shaft of the pump via a flexible coupling such as a
splined coupling. A housing is disposed around the driven shaft, and this
housing supports both the driven shaft and the input shaft for rotation.. A
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high-pressure seal such as a mechanical seal is disposed between the housing
and
the input shaft, and a thrust bearing is disposed between the housing and the
input
shaft. The flexible coupling transmits fluid pressure within the housing to
the outer
end of the driven shaft. In this way, fluid pressure on the outer end of the
driven
shaft tends to balance fluid pressure on the inner end of the driven shaft,
thereby
reducing or eliminating asymmetrical axial loads.
In another embodiment, the present invention provides a pump comprising:
a gear pump set comprising a driven gear mounted on a driven gear shaft and a
follower gear mounted on a follower gear shaft, said driven gear shaft
comprising
1o an inner end and a splined outer end, said follower gear shaft comprising
an inner
end and an outer end; an input shaft comprising a splined inner end engaged
with
the splined outer end of the driven gear shaft; a housing comprising a first
portion
that supports the gear shafts for rotation and a second portion that supports
the
input shaft for rotation; a high pressure seal disposed between the housing
and the
input shaft; a thrust bearing disposed between the housing and the input
shaft; the
first and second ends of the driven gear shaft and the first and second ends
of the
follower gear shaft all disposed within the housing and all subjected to
internal
hydraulic pressure of the pump contained by the housing.
Yet another embodiment of the invention provides a pump comprising:
2 o a pump mechanism comprising a driven shaft comprising an inner end and an
outer
end; an input shaft comprising an inner end and an outer end; a coupling
coupled
between the inner end of the input shaft and the outer end of the driven
shaft; a
housing disposed around the coupling, the outer end of the drive shaft, and
the
inner end of the input shaft; said coupling transmitting fluid pressure
generated by
the pump mechanism to the outer end of the driven shaft, whereby fluid
pressure
on the outer end of the driven shaft and fluid pressure on the inner end of
the
driven shaft create respective axial hydraulic forces on the input shaft,
thereby
reducing asymmetrical axial loads on the driven shaft.
The foregoing paragraphs have been provided by way of introduction, and
3 o are not intended to limit the scope of this invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional view of a pump that incorporates a preferred
embodiment of this invention.
Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1.
Figure 3 is an enlarged view of portions of the input shaft, the mechanical
seal, and the thrust bearings of Figure 1.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED
EMBODIMENTS
Turning now to the drawings, Figures 1 and 2 show respective cross-
sectional views of a pump 10 that includes a pump mechanism 12. In this
embodiment, the pump mechanism 12 includes a gear set comprising a driven gear
14 mounted on a driven gear shaft 16 having an inner end 18 and an outer end
20.
The driven gear 14 is in meshing engagement with a follower gear 22 that is
mounted on a follower gear shaft 24 having an inner end 26 and an outer end
28.
As best shown in Figure 2, the pump 10 includes a housing 30 having a first
portion 32 that defines an inlet passage 34 and an outlet passage 36 in fluid
communication with a gear chamber 38. The gears 14, 22 are mounted for
rotation
2 o in the gear chamber 38 by means of bushings 40 that receive and position
the
shafts 16, 24 (Figure 1 ). The bushings 40 are held in place by wear plates 42
positioned adjacent to inner retainer plates 44. Also provided is an insert 46
that
is held in place by an outer retainer plate 48.
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The inner retainer plates 44 and the wear plates 42 are conventionally
used in gear pumps, and are well known to those skilled in the art. The wear
plates 42 may for example be formed of brass, and the inner retainer
plates 44 may be formed of steel.
As shown in Figure 1, the pump 10 also includes an input shaft 50
having an inner end 52 and an outer end 54. The inner end 52 forms a
hub 56, and the hub 56 supports a radially extending flange 58.
In this embodiment, the outer end 20 of the driven gear shaft 16
defines a first splined surface, and the hub 56 defines a second splined
surface shaped to receive and mesh with the first splined surface. The
splined surfaces of the driven gear shaft 16 and the input shaft 50 form a
flexible coupling between the two shafts. Though not required, in this
embodiment the driven gear shaft 16 forms a shoulder 60 between the driven
gear 14 and the outer end 20.
The housing 30 also includes a second portion 64 that supports the
input shaft 50 for rotation. Radial bearings 70 are mounted between the input
shaft 50 and the second portion 64 of the housing 30. A thrust bearing 72 is
mounted between the flange 58 and the second portion 64 of the housing 30.
Also, a high pressure seal such as a mechanical seal 74 is mounted between
the input shaft 50 and the second portion 64 of the housing 30.
Figure 3 provides an enlarged view of the mechanical seal 74 of
Figure 1. The seal 74 includes a retainer 92 sealed to the second portion 64
of the housing 30 (not shown in Figure 3), and the retainer 92 holds a first
annular sealing element 96 that extends around the input shaft 50. The seal
74 also includes a second retainer 94 sealed to the input shaft 50, and the
second retainer 94 holds a second annular sealing element 98 in sliding,
sealing contact with the first sealing element 96 by means of springs 100.
Mechanical seals such as the seal 74 are well known to those skilled in the
art. A suitable seal can be obtained from John Crane Co. (Kansas City,
Missouri).
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A li,p seal 78 is mounted between the input shaft 50 and the second
portion 64 of the housing 30, and a weep hole 76 is formed in the second
portion 64 between the mechanical seal 74 and the lip seal 78 (Figure 1 ).
The specific embodiment shown in the drawings also includes a
direction control valve 80 that performs the function of the valve 16 of the
above-identified Tieben patent, and a bypass valve 82 that performs the
function of the valve 24 of the above-identified Tieben patent. Though useful
in some applications, the direction control valve 80 and the bypass valve 82
are not essential aspects of this invention.
The housing 30 defines a chamber 90 in which the hub 56 rotates.
Fluid pressure in the chamber 90 is substantially equal to fluid pressure in
other portions of the pump, as for example adjacent the inner ends 18, 26 of
the shafts 16, 24. The flexible coupling comprising the splined surfaces of
the
driven gear shaft 16 and the input shaft 50 forms a relatively loose
connection
that ensures that the hydraulic pressure in the chamber 90 is transmitted to
the extreme end surface of the driven gear shaft 16.
In the example of Figure 1, the reference symbol A~ is used for the
area of the inner end 18 of the driven gear shaft 16. The area A~ is also
equal
to the area of the inner end 26 and to the area of the outer end 28 of the
follower gear shaft 24. The reference symbol A2 is used for the area of the
shoulder 60, and the symbol A3 is used for the area of the outer end 20 of the
driven gear shaft 16. In all cases, area is measured in a plane transverse to
the longitudinal axis of the respective shafts.
It should be understood that the area A~ is equal to the sum of the area
A2 and the area A3. Since all of the areas, A~, A2, A3, are subjected to
substantially the same hydraulic pressure within the pump 10, axial hydraulic
forces on the driven shaft 16 are substantially balanced and axial faces on
the
follower shaft 24 are substantially balanced. Axial hydraulic forces on the
input shaft 50 are carried by the thrust bearing 72 in a manner that
substantially reduces wear and friction. Because the splined connection
between the driven shaft 16 and the input shaft 50 allows axial as well as
limited radial movement therebetween, the driven gear shaft 16 and the driven
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gear 14 are free to float in the housing 30 in a way that minimizes wear and
friction. Since both of the ends of the driven gear shaft 16 and both of the
ends of the follower gear shaft 24 are situated within the housing and
subjected to the internal hydraulic pressure of the pump, axial forces on
these
shafts are balanced and wear and friction are minimized.
One significant advantage of the pump 10 is that it operates efficiently
and reliably even when subjected to a high pressure at the inlet passage 34.
For example, the pump 10 can be used in the hydraulic system described in
Tieben U.S. Patent 5,916,139. In this system, pressure in the reservoir is
selectively applied to the pump inlet to substantially reduce the power needed
to drive the pump. In conventional pumps, high inlet pressure can result in
undesired axial loads on the pumping mechanism, due to the high internal
pressure of the pump. The pump 10 overcomes this problem by balancing
axial forces on the gear shafts as described above. The pump 10 is well-
suited for use in a wide variety of applications, and it is not limited to the
specific applications described above.
Of course, it should be understood that many changes and
modifications can be made to the preferred embodiment described above.
This invention is not limited to use with gear pumps, but can be applied to
other types of pumps, including pumps using vane-type or piston-type
pumping mechanisms.
The splined connection between the input shaft 50 and the driven
shaft 16 is only one example of a flexible coupling. Other flexible couplings
can be used, including for example chain couplers and flexible couplings
known under the trade names Browning, Para-flex and Lovejoy.
The thrust bearing 72 shown in the drawings is only one example of a
thrust bearing, and other thrust bearings can be substituted. For example,
roller bearings can be used instead of ball bearings, or bushing-type thrust
bearings can be used. Also, the thrust bearing can be formed as part of a
radial bearing. The thrust bearing can be positioned at other places along the
input shaft than the position shown in the drawings. For example, the thrust
bearing can be combined with a radial bearing and positioned at any desired
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point along the input shaft. Similarly, ball bearings, bushing-type radial
bearings or other types of roller bearings may be substituted for the
illustrated
radial bearings.
The mechanical seal 74 may be replaced with other types of high
pressure seals, including cup seals, for example. As used herein, the use of
the term "high pressure seal" is intended to refer to a seal capable of
sealing
hydraulic fluid pressurized to a pressure of at least 500 psi.
The housing 30 is shown in the preferred embodiment as including two
separate portions held together by threaded fasteners. Of course, it should
be recognized that the first and second portions of the housing can be defined
by a single integrated structure rather than the separable structure shown.
When separable elements are used, the junction between the first and second
portions of the housing can be placed at any desired point to facilitate
fabrication and assembly.
The foregoing detailed description has described only a few of the
many forms that this invention can take. For this reason, this detailed
description is intended by way of illustration and not by way of limitation.
It is
only the following claims, including all equivalents, that are intended to
define
the scope of this invention.
