U.S. patent application number 09/734326 was filed with the patent office on 2001-09-27 for adjustable-displacement gear pump.
Invention is credited to Winmill, Len F..
Application Number | 20010024618 09/734326 |
Document ID | / |
Family ID | 26864048 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024618 |
Kind Code |
A1 |
Winmill, Len F. |
September 27, 2001 |
Adjustable-displacement gear pump
Abstract
A positive displacement fluid pump capable of an output flow
rate can be varied from a maximum to zero at a given pump rotation
speed. The pump is a variable-fluid-displacement-volume, gear pump
having complement elements associated with pumping gears to provide
end seals for a variable-length pumping chamber. A timing
arrangement maintains both pumping gears always in synchronization,
whether engaged or fully disengaged (zero pump output). And a
follower provides effective sealing with a movable face of an
axially-translating pumping gear.
Inventors: |
Winmill, Len F.; (Orem,
UT) |
Correspondence
Address: |
PATE PIERCE & BAIRD
BANK ONE TOWER, SUITE 900
50 WEST BROADWAY
SALT LAKE CITY
UT
84101
US
|
Family ID: |
26864048 |
Appl. No.: |
09/734326 |
Filed: |
December 1, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60168362 |
Dec 1, 1999 |
|
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Current U.S.
Class: |
418/1 ;
418/21 |
Current CPC
Class: |
F04C 14/185
20130101 |
Class at
Publication: |
418/1 ;
418/21 |
International
Class: |
F04C 002/18; F04C
015/04 |
Claims
What is claimed and desired to be secured by United States Letters
Patent is:
1. A pump having a positive displacement per cycle that is
continuously variable between a maximum flow rate and a zero flow
rate comprising: a housing; a first driven gear rotatably movable
with respect to the housing; a second gear rotatably movable with
respect to the housing and meshing with the first gear, wherein the
first and second gears are axially movable relative to each other;
a first complement, secured to rotate with and slide axially along
the first gear; a second complement, secured to rotate with and
slide axially along the second gear; a movable follower sealably
engaged to the first complement and second gear, and slidably
engaged with the first gear, wherein the first complement and
second gear are configured to move continuously between a first
position corresponding to the maximum flow rate and a second
position corresponding to the zero flow rate; a fixed follower
sealably engaged with the second complement and slidably engaged
with the second gear; and a timing gear configured to rotate in
correspondence with said first driven gear.
2. The pump of claim 1, further comprising: a drive shaft carrying
said first driven gear in driving relation.
3. The pump of claim 2, further comprising: an idler axle carrying
said second gear.
4. The pump of claim 3, wherein the timing gear is spaced axially
from the first driven gear by the stationary follower.
5. The pump of claim 4, wherein the stationary follower further
comprises: a sleeve center positioned to cooperate with the second
complement.
6. The pump of claim 5, wherein the sleeve center has an axial
length at least equal to a thickness of the second complement.
7. The pump of claim 6, wherein the movable follower further
comprises: a sleeve positioned to slide axially over said sleeve
center in a sealed relation, further adapted to travel with the
movable follower.
8. The pump of claim 7, further comprising a pump chamber having a
continuously variable length defined by a distance between the
first and second complements.
9. The pump of claim 8, wherein said pump chamber length varies
continuously between a maximum length corresponding to the length
of said first driven gear less the length of the first compliment
and a minimum length, including zero, corresponding with said zero
flow rate.
10. The pump of claim 9, further comprising: an adjuster configured
to continuously vary the length of said pump chamber between said
maximum length and said minimum length.
11. The pump of claim 10, wherein said adjuster comprises: a
mechanical linkage configured to displace the movable follower.
12. The pump of claim 10, wherein said adjuster comprises: a fluid
applied to exert a differential pressure between a proximal piston
face and a distal piston face, wherein the proximal piston face
comprises a proximal end of the follower and a proximal end of the
first complement, and wherein the distal piston face comprises a
distal end of said first driving gear and a distal end of said
sleeve.
13. The pump of claim 10, further comprising a metering valve found
between the movable follower and an output port, wherein said
metering valve operates at reduced chamber length.
14. The pump of claim 11, wherein the timing gear is configured to
reduce energy applied to fluid within the housing.
15. An improved pump, having axially translatable gears, to reduce
energy applied to a working fluid during conditions of reduced pump
output and full drive shaft speed, the improvement comprising: a
pump chamber comprising a sleeve and having a variable length to
proportionally control pump output, the length variable between a
maximum length and a minimum length, the minimum length
corresponding to an effectively zero pump output; the sleeve
forming a pumping seal with a gear when the pump is configured to
produce an output flow; a timing arrangement adapted to keep a
plurality of gears in constant synchronization, whether the gears
are engaged or fully disengaged; and an adjuster to vary the
chamber length between the maximum and the minimum.
16. The pump of claim 15, wherein the chamber length is a distance
between a proximal seal and a distal seal.
17. The pump of claim 16, wherein: the distal seal comprises a
stationary follower to form an effective axial seal with an axially
fixed gear; and the proximal seal comprises a movable follower to
form an effective axial seal with an axially translating gear.
18. The pump of claim 17, wherein the stationary follower comprises
a portion of a gear complement, a sleeve center, and a housing
bridge element.
19. The pump of claim 15, wherein the sleeve is cantilevered from a
movable follower and journaled in a housing for axial
translation.
20. The pump of claim 19, wherein a sleeve center, coaxial with the
sleeve, axially spaces a timing gear from another gear.
21. The pump of claim 15, wherein the adjuster comprises a
mechanical linkage structured to translate a movable follower.
22. The pump of claim 15, further comprising a metering valve
between a movable follower and an output port, the metering valve
operable during conditions of reduced chamber length.
23. The pump of claim 15, the timing arrangement comprising: a
timing gear maintained in meshing agreement with a first gear, and
axially spaced apart from the first gear.
24. The pump of claim 15, wherein the adjuster comprises: a working
fluid applied to exert a differential pressure between a proximal
piston face and a distal piston face; the proximal piston face
comprising a proximal end of a follower and a proximal end of a
complement; and the distal piston face comprising a distal end of a
gear and a distal end of the sleeve.
25. The pump of claim 24, wherein the working fluid is pressurized
by a secondary pump between a gear and a timing gear.
26. A method to vary a fluid output rate, between a maximum rate
and essentially zero, during a constant operational speed for a
positive displacement pump, the method comprising: providing a pump
comprising: gears, including first and second pump gears, and a
timing gear to maintain synchronization between the pump gears;
with the first pump gear in pump sealing relation to a sleeve
cantilevered from a movable follower; the pump gears arranged for
meshing engagement and mounted for relative axial translation
between a position of maximum length engagement to complete
disengagement; and axially translating the second pump gear
relative to the first pump gear such that the engagement length
therebetween correspondingly changes between a maximum length and
zero.
27. The method of claim 26, wherein the axial translation is
effected by a mechanical linkage element arranged to translate the
movable follower.
Description
RELATED APPLICATIONS
[0001] This application claims priority to application Ser. No.
60/168,362, filed Dec. 1, 1999, and directed to an
ADJUSTABLE-DISPLACEMENT GEAR PUMP.
BACKGROUND
[0002] 1. The Field of the Invention
[0003] This invention relates to hydraulic and other fluid pumps
capable of a variable fluid throughput rate with respect to a given
input rotational velocity. More particularly, the invention relates
to novel systems and methods for controlling the volumetric
displacement of gear pumps.
[0004] 2. The Background Art
[0005] Hydraulic pumps have been a key component of all hydraulic
actuation systems for many years. Often, a hydraulic pump may be
matched with one or more hydraulic motors. The hydraulic pump
transfers energy to a working fluid. The hydraulic motor removes
energy from the working fluid.
[0006] Currently, diaphragm, as well as vane, pumps are known in
the art. Solid impeller pumps are used in circumstances that may
not require positive displacement. For positive displacement, three
common types of hydraulic pumps are used.
[0007] Vane pumps sweep fluid ahead of a vane mounted on a hub
eccentrically positioned within a chamber. Vanes are urged toward
an outer surface. Meanwhile, the vanes against the outer surface,
are continually closing and opening chambers cyclically. The vane's
extension toward the outer surface changes with the eccentricity of
the hub with respect to the outer chamber, sweeping fluid in and
out of ports positioned in the outer surface, or otherwise
accessing the space between the hub and the outer surface.
[0008] Diaphragm pumps and piston pumps operate with one moving
wall to draw a selected volume into a chamber. Then, using valves
to control input and output ports, the moving wall (piston or
diaphragm) of such pumps drives the working fluid into an output
line. New developments in piston hydraulic pumps have made piston
pumps extremely popular, as evident by the quantity in operation.
In one piston pump type, a crank shaft is replaced by a driven
shaft and a crank plate or "swash plate" that drives substantially
orthogonally extending connecting rods for each piston. Such an
apparatus has conventionally been associated with the manufacturer
Sundstrand.
[0009] Finally, gear pumps are known in the art. Typically, spur
gears sweep the space between teeth thereon through a cavity
containing each gear. The cavity typically provides an axially
oriented seal at the perimeter of the gear teeth. With the two
gears mated together at a central contact position, hydraulic fluid
may be sealed against completing a full circle with either
gear.
[0010] For example, an input side of gears may move past an input
port having access to the gears separating from contact with one
another. At the input port location, the gear teeth are moving out
of engagement and into their respective, circular, surrounding
cavities. Oil (a typical working fluid) is swept with each tooth,
filling the space between that tooth and its predecessor tooth
moving along a rotary path.
[0011] As the gears each make a full rotation, the gears once again
mesh, forcing oil out from between the teeth. Meanwhile, each
contact line between the teeth forms a seal prohibiting, or greatly
restricting, passage of working fluid back through from the outlet
side to the inlet side of the contact region of the gears.
[0012] In the process of operation, a gear pump of a conventional
design does not permit any variation in the pump displacement for
each revolution of a pump. In more recent times, offsetting pump
gears from one another in an axial direction has been postulated as
a method of varying pump displacement and throughput. However,
sealing the pumping region remains a continuing problem.
[0013] For example, conventional gear pumps maintain sealing
between an end of a gear and a wall of a containment chamber.
Clearances are typically very close, sufficient to maintain a
virtually complete liquid seal. Upon relative axial movement of
gears, the mating gears each may have an open cavity at one end
thereof. This cavity must be filled or the pump has communication
from a high pressure side to a low pressure side of each gear.
[0014] What is needed is a gear pump providing axial displacement
of pump gears with respect to one another, with a close follower
maintaining an end seal for each gear. A close follower may be a
fixed wall for a gear that does not move axially. However, in the
case of the gear that moves axially, the follower must follow
closely enough to an end face of a moving gear to provide a liquid
seal.
[0015] Meanwhile, each gear needs a complement to provide an end
seal for a pump cavity having a variable length. That is, to the
extent that a region of pump gear engagement is reduced, a liquid
seal needs to be provided in the axial direction of each gear to
close off the engaged (fluid driving) portion of the gears from the
non-engaged portion of the gears.
[0016] A complement is needed to fill in the space between teeth in
the disengaged regions of the gears. A variable displacement gear
pump having close followers that always remain positioned sealingly
proximate the end of a moving gear face, and having a complement on
each gear to fill in the voids between teeth in order to present
pseudo-walls defining a length of the active cavity (engaged or
pumping region of a gear) is needed. Such a configuration has not
been found in the prior art. A great advance in the art would
provide an ability to vary displacement of a gear pump through a
full range from zero (idling, no pumping occurring) at operational
rotational speeds, to 100 percent of a maximum capacity when the
gears are engaged to their maximum extent.
[0017] In the art, Applicant has not found any operable design for
a gear pump capable of variable displacement, varying between no
output flow and a full output flow, at a given pump rotational
rate. Moreover, such a performance characteristic has not been
found for any control mechanism for a gear pump.
[0018] An additional desired characteristic in a variable
displacement pump would provide for a reduced amount of energy
being applied to the working fluid during conditions when the pump
is configured for reduced output. Producing a reduced overall pump
output by redirecting pump output, such as in a load bypass or
recirculating circuit, still undesirably applies energy from the
pump to the working fluid. The working fluid is continually
undergoing work in such a recycling pump arrangement, and thereby
suffers from premature wear. This work creates unnecessary heat and
draws unnecessary energy from the source of the rotational power.
It would be an advance in the art to provide a pump capable of: (1)
a variable output; (2) a reduced stress on the working fluid; and
(3) more energy efficient during pump operation under low flow, or
no flow, conditions.
[0019] Moreover, it would be an advance in the art to provide such
a functionality in a gear pump by providing a timing gear that
maintains synchronization between the two pumping gears, even when
the pumping gears are not engaged. Thus, it would be an advance in
the art to provide a variable displacement gear pump having
complements associated with gears to provide end seals, a timing
arrangement for maintaining both gears always in synchronization,
whether engaged or fully disengaged (zero pump output), and a
follower that remains close enough to a movable face of an
axially-translating gear of a gear pump to provide effective
sealing of the working fluid from passing therebetween.
BRIEF SUMMARY OF THE INVENTION
[0020] In accordance with the invention as embodied and broadly
described herein, an apparatus and method are disclosed in suitable
detail to enable one of ordinary skill in the art to make and use
the invention. In certain embodiments, an apparatus and method in
accordance with the present invention may include a case or pump
housing, a pair of mated, rotating, mutually engaging gears. Both
gears having a complement that substantially seals a variable
length end portion of the gear from an engaged portion of the
gear.
[0021] The gear pump may have followers, including solid members
through which supporting axles of each respective gear may pass, as
appropriate. A follower typically maintains a substantially
complete, operational, fluid seal between a portion of itself and
an end face of a pump gear. A follower that always maintains an
effective seal between a portion of itself and a corresponding gear
end face may be characterized as a close follower.
[0022] The apparatus may include a timing gear located remotely
from an axially fixed gear. The timing gear maintains
synchronization between the axially translating gear and the
axially fixed gear. Such synchronization allows the axially
translating gear to engage selectively with the axially fixed
gear.
[0023] An exemplary adjustable displacement gear pump is capable of
a variable fluid output between a maximum flow rate and zero flow
at a constant drive shaft speed. One embodiment provides complement
elements associated with a pair of pumping gears, the complement
elements being portions of end seals for a pumping chamber having a
variable length between a maximum length and zero length. The
chamber length may be characterized as a distance between a
proximal pumping chamber end seal and a distal pumping chamber end
seal.
[0024] Also present is a timing arrangement for maintaining both
pumping gears always in synchronization, whether the pumping gears
are engaged or fully disengaged. A stationary close follower
provides effective sealing with a fixed face of an axially fixed
gear. A movable close follower provides effective sealing with a
movable face of an axially translating pumping gear. A means to
vary the pumping chamber length from a maximum length to a zero
length provides a way to control pump output.
[0025] A pump may further include a metering valve arrangement
between structure of a follower and structure associated with fluid
input and output ports. The metering valve would operate to further
control pump output during conditions of reduced pump chamber
length.
[0026] One presently preferred timing arrangement uses a timing
gear having a similar cross-section to a first of the pumping
gears. The timing gear may typically be oriented in axial
alignment, maintained in meshing agreement with, and spaced apart
axially from the first pumping gear. The meshing agreement allows a
second of the pumping gears, while meshed with the first pump gear,
to be axially translated to mesh with the timing gear. Whenever the
second gear is axially translated out of mesh with the first gear,
the timing gear maintains synchronization of the gears such that
the second gear may be axially translated back into mesh with the
first gear. A timing arrangement may even be located exterior to a
pump housing. Any convenient way to maintain synchronization
between pumping gears may be adequate for the practice of certain
embodiments of this invention.
[0027] The first chamber end seal typically includes a distal end
of a first complement and structure associated with a movable close
follower. The movable, close follower substantially seals with a
proximal end of a first pumping gear. The first complement is
typically carried by structure associated with the movable close
follower for axial translation in substantially sealed sliding
engagement with an exterior surface of a second pumping gear.
[0028] The second chamber end seal includes a stationary close
follower. A close follower may be one of various structures, such
as a proximal end of a sleeve center, a portion of a proximal end
of a housing bridge structure, and a portion of a proximal end of a
second complement. The second complement is typically fixed in
place axially in rotatable engagement with structure of a pump
housing and in slidable concentric engagement with the first gear.
The second complement functions to allow axial translation of the
first gear while substantially maintaining a fluid seal
therebetween.
[0029] One embodiment of a pump, according to the present
invention, may typically include means to vary the pump chamber
length from a maximum length to zero length. One way to accomplish
changes in chamber length may include applying differential
hydraulic pressure between proximal and distal ends of a piston
structure to control axial displacement of the first pumping gear.
Suitable piston structures may generally include a follower
assembly carrying the first gear.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The foregoing and other features of the present invention
will become more fully apparent from the following description and
appended claims, taken in conjunction with the accompanying
drawings. Understanding that these drawings depict only a typical
embodiment of the invention and are, therefore, not to be
considered limiting of its scope, the invention will be described
with additional specificity and detail through use of the
accompanying drawings in which:
[0031] FIG. 1 is a perspective view in elevation, partially in
section, of an apparatus in accordance with the invention;
[0032] FIG. 2 is an exploded, perspective assembly view of the
internal operating elements of the apparatus of FIG. 1;
[0033] FIG. 3 is a side, elevation, cross-sectional view taken
through a midplane of the apparatus of FIG. 1;
[0034] FIG. 4 is a front, cross-sectional, elevation view taken
through the plane 4-4 indicated in FIG. 3 and looking in the
direction of the arrows;
[0035] FIG. 5 is a front, cross-sectional, elevation view taken
through the plane 5-5 indicated in FIG. 3 and looking in the
direction of the arrows;
[0036] FIG. 6 is a front, cross-sectional, elevation view taken
through the plane 6-6 indicated in FIG. 3 and looking in the
direction of the arrows;
[0037] FIG. 7 is side, elevation, cross-sectional view of the
internal operating elements of the apparatus of FIG. 3, where the
operating elements are arranged in an approximately full flow
configuration;
[0038] FIG. 8 is side, elevation, cross-sectional view of the
internal operating elements of the apparatus of FIG. 3, where the
operating elements are arranged in an approximately half-capacity
flow configuration;
[0039] FIG. 9 is side, elevation, cross-sectional view of the
internal operating elements of the apparatus of FIG. 3, where the
operating elements are arranged in a greatly reduced flow
configuration;
[0040] FIG. 10 is side, elevation, cross-sectional view of the
internal operating elements of the apparatus of FIG. 3, where the
operating elements are arranged in a zero flow configuration.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0041] It will be readily understood that the components of the
present invention, as generally described and illustrated in the
Figures herein, could be arranged and designed in a wide variety of
different configurations. Thus, the following more detailed
description of embodiments of the system and method of the present
invention, as represented in FIGS. 1 through 10, is not intended to
limit the scope of the invention. The scope of the invention is as
broad as claimed herein. The illustrations are merely
representative of certain presently preferred embodiments of the
invention. The invention will be best understood by reference to
the drawings, wherein like parts are designated by like numerals
throughout.
[0042] Those of ordinary skill in the art will, of course,
appreciate that various modifications to the details of the Figures
may easily be made without departing from the essential
characteristics of the invention. Thus, the following description
of the Figures is intended only by way of example, and simply
illustrates certain presently preferred embodiments consistent with
the invention as claimed.
[0043] Referring to FIG. 1, a pump assembly, generally indicated at
10, is illustrated. The pump 10 typically includes a drive shaft
12, which may be rotated in either direction, as indicated by
circumferential double-headed arrow 14. In the pump 10, reversing
the direction of rotation of the drive shaft 12 merely reverses the
direction of fluid flow through the pump 10. That is, intake and
output ports (not shown) of the pump 10 are determined by the
direction of rotation of the drive shaft 12.
[0044] As illustrated in FIG. 1, the drive shaft 12 carries a pump
gear 16 in driving relation at an axially fixed position along the
drive shaft 12. A complement 17 fits the toothed surface of gear 16
in a substantially sealed, slidable, relation. Taken together, the
complement 17 and gear 16 form a substantially solid circular
cross-section. Spaced apart axially from the gear 16, and also
carried in driving relation by the drive shaft 12, is a timing gear
18. Gears 16 and 18 may have identical cross-sections and are
mounted in meshing alignment on the drive shaft 12.
[0045] A sleeve center 20 receives the drive shaft 12 in a sealed
and load-bearing relationship, and also serves as a spacer between
the gears 16 and 18. The sleeve center 20 has a maximum radial
dimension in agreement with a maximum radial dimension of the gears
16 and 18. Alternatively, the sleeve center may be a solid
extension of a receiver housing 36. A sleeve 22 is constructed to
circumscribe and slide over the sleeve center 20. The inside bore
surface of the sleeve 22 provides a wiping, sealing surface for
teeth carried by the gear 16. A follower 24 and the sleeve 22
together form a follower assembly 25.
[0046] The follower 24 provides a structural base from which to
cantilever an idler axle 26. The axle 26 is typically fixed in
position within the follower 24 by a press-fit, although other
mounting methods are also conceivable. An idler gear 28 is carried
in a rotatable bearing relationship by the axle 26. A portion of
the distal face of the follower 24 forms a seal with the proximal
end of the idler gear 28. Therefore, the follower 24 is a close
follower to the idler gear 28.
[0047] Gears 16 and 28 have meshing tooth profiles, and may
typically be identical in cross-section. Gears 16 and 28 need not
be identical, although such a configuration simplifies
manufacturing by reducing the pump parts count, and reducing
costs.
[0048] A gear complement 30 receives the idler gear 28 in an
axially sliding relation, and provides a substantial seal on the
idler gear 28 surface against fluid flow in an axial direction. A
slot 31 (FIG. 3) may be provided on the distal end of axle 26. The
slot 31 functions to hold a split ring (not shown), and maintain
the gear 28 in position on the axle 26. Other retaining structure,
such as keys, sleeves, pins, splines, and so forth, may also be
conceivable.
[0049] Continuing to refer to FIG. 1, a sender housing 32 may be
essentially a solid block having an internal sender cavity 34. In
the illustrated embodiment, the cavity 34 extends completely
through the housing 32. It may be formed by two parallel,
intersecting bores. The resulting cavity 34 has a cross-section
that approximates a numeral 8, or is peanut shaped. The follower
assembly 25 is received in the cavity 34 in an axially sliding,
substantially sealed relationship.
[0050] The receiver housing 36 is similar to the sender housing 32
in that it also may be formed by two intersecting bores to form a
receiver cavity 38. However, additional dividing structures
including the sleeve center 20 and others not shown in FIG. 1 are
also present in the receiver cavity 38. The receiver cavity 38
receives the sleeve 22 in an axially sliding, substantially sealed
relationship. As the follower assembly 25 is moved, from the
illustrated position toward the receiver housing 36, the gear 28
correspondingly moves into the receiver cavity 38. The receiver
cavity 38 may be constructed to provide a portion designed to
receive the gear 28 in an axially slidable, bearing relation.
[0051] For convenience, the pump 10 and its elements will be
described with reference to orientations defined by a proximal end
48 and a distal end 50 of the pump 10. The sender housing 32 is
axially sealed on the proximal end 48 of the pump 10 by a cap plate
40. The distal end of the sender housing 32 seals against a
proximal end of the receiver housing 36. The distal end of the
receiver housing 36 is axially sealed by a cap plate 42.
[0052] A set of alignment holes 44, passing completely through both
cap plates 40 and 42 and housings 32 and 36, in the illustrated
embodiment, are provided to assist in assembly of the pump 10.
Another set of holes 46, also passing completely through both cap
plates 40 and 42 and housings 32 and 36, receive tension bolts (not
shown). The tension bolts carry the axial load required to maintain
a fluid seal between all of the pump housings (32 & 36) and cap
plates (40 & 42).
[0053] Referring to FIG. 2, additional details of construction of
the pump 10 are illustrated. The follower 24 has a hole 54 in which
is received the axle 26. A bore 56 in the follower 24 receives the
complement 17 in a substantially sealed, rotating relationship. The
complement 17 is restrained from axial displacement from the bore
56 by a suitable retainer, such as a snap ring (not shown) located
in a groove 57. The rotatable seal prevents significant fluid
escape from the sender cavity 34 (FIG. 1) between the bore 56 and
the complement 17.
[0054] The inner surface of the complement 17 fits in sealing
relation to the toothed surface of the gear 16. The complement 17
is sized to have a thickness to fit between the snap ring and the
distal face of the follower 24. Such a thickness provides a sealing
surface on its distal face being oriented in a plane at the distal
face of the follower 24.
[0055] As illustrated, a portion of the proximal end of the sleeve
22 maintains the complement 17 in registration between the
retaining snap ring at the groove 57 and the distal face of the
follower 24. The follower 24, in combination with the complement 17
and a cross-section through the gear 16, essentially forms a
sliding and sealing plug in the sender cavity 34. The proximal end
of a pumping chamber (FIG. 7, denoted by area 104) is defined by
the alignment and seal provided by the distal ends of the follower
24 and the complement 17.
[0056] Continuing to refer to FIG. 2, the interface between the
gear 16 and the sleeve 22 may be readily visualized. A bore 58 is
sized to fit the perimeter of the gear 16. The bore 58 receives
teeth of the gear 16 in a sliding, wiping, sealed relation. The
sleeve center 20 also is sized to slidingly seal against the bore
58 of the sleeve 22.
[0057] One way to attach the sleeve 22 and the follower 24 is
illustrated as a set of pins 60. In the illustrated apparatus, the
pins 60 may be press-fit or otherwise secured to a depth of about
half their length into a set of receiving holes 62 in the sleeve
22. The remaining portions of the pins 60 are received in a
suitable supporting relation (e.g. a press fit) into corresponding
receiving holes (not shown) in the follower 24. Alternate methods
for forming the resulting structure may be used, including welding
the components together, or machining the follower assembly 25
(FIG. 1) from solid stock.
[0058] Referring now to FIG. 3, additional structural details of
the construction of the pump 10 will be described. FIG. 3 is a side
elevation view of a cross-section taken approximately through a
midplane of the pump 10. The drive shaft 12 drives the gear 16,
which in turn drives the idler gear 28. A single gear tooth face 74
located at the top of the gear 16 is visible in the Figure. A
corresponding gear tooth face 76 is illustrated at the top of the
timing gear 18. FIG. 3 illustrates how the gears 16 and 18 are
oriented in meshing alignment, with gear teeth of both gears being
located at identical azimuths relative to the drive shaft 12. In
the configuration depicted in the illustration, a second gear tooth
76 is also visible at the bottom of the gear 18. A tooth of the
gear 28 (shown in cross-section) obscures most of the tooth located
at the bottom of gear 16.
[0059] Still referring to FIG. 3, the receiver housing 36 is shown
to have a bridge element 78 that serves to form a sealing and
supporting structure. To facilitate manufacturing, a bridge element
78 may be formed as an insert, press-fit or otherwise fastened to
the receiver housing 36. A portion of a proximal end of the bridge
78 receives the complement 30 in rotating and sealing relation.
[0060] The complement 30 is seen, in the illustration, to be
prevented from axial motion by a shoulder 79 in the proximal end of
the housing 36 (including the bridge element 78) in combination
with the distal end of the sender housing 32. The shoulder 79
prevents motion of the complement 30 toward the distal end of the
pump 10 and is spaced from the proximal end of the receiver housing
36 by the thickness of the complement 30.
[0061] The gear 28 may slide axially through the complement 30
while substantially maintaining a fluid seal therebetween. It may
now be realized that the bridge element 78 may have a length,
extending from the proximal end of the receiver housing 36, that is
shorter than illustrated. A minimum length for the bridge element
78 may be selected to be sufficient to provide a portion of the
rotatable seal between the receiver housing 36 and the complement
30 at the proximal end of the receiver housing 36. However, the
bridge element 78 may reasonably have a minimum length equal to the
axial thickness of the complement 30. The complement 30 may be
sufficiently retained axially by the shoulder 79 in the receiver
housing 36 separate from any supporting contribution from the
bridge element 78.
[0062] The proximal face of the complement 30, a cross-section
through the gear 28, and the proximal face of the receiver housing
36 cooperatively form a substantially planar sealed surface. The
plane containing the proximal faces of the complement 30, bridge
element 78, and sleeve center 20, defines a sealed region with the
distal end of the gear 16. This collection of elements may
therefore be regarded as a close follower to the gear 16. In this
case the close follower is axially stationary.
[0063] Further in reference to FIG. 3, a bushing 80 ray provide a
sealed bearing support to the shaft 12 passing through the cap
plate 40. A similar bushing 82 may be provided in the cap plate 42.
On the subject of sealing, note that the illustrated embodiment is
simplified to present certain inventive concepts. It is recognized
that additional sealing elements may prove useful. For example,
various surfaces, such as the parting line between housings 32 and
36, may be effectively sealed with o-rings or gaskets, including
adhesives, silicones, shellacs, and the like, which are not shown.
Various wiping seals may also be employed throughout, as on gear
teeth, or shafts and rotating surfaces. Such details are generally
known, obvious variations of the illustrated embodiments need not
be catalogued herein.
[0064] Continuing to refer to FIG. 3, note that no structure is
illustrated with which to move the follower 24 and associated
structure such as the gear 28. Methods and mechanisms for moving
such structure back and forth are generally known. Appropriate
methods to move the pump structures back and forth include applying
differential hydraulic pressure between proximal end of the cavity
34 and the distal end of the cavity 38. A metering valve may be
installed in-line with the pump output stream, or in association
with an independent high pressure source, to direct fluid to the
desired cavity as required. Internal pump structure may then act as
a variable position piston in such case. Mechanical linkages
including elements such as push rods and jack screws being operated
by various mechanical, manual, and electrical actuators may also be
employed. Various combinations of mechanical and hydraulic elements
may also be employed to advantage.
[0065] Reference will now be made to FIG. 4, a cross-section
through section 4-4 in FIG. 3. The follower 24 fits in sealing
relation along the profile of the cavity 34 (see also FIGS. 1 and
3). The follower 24, a cross-section through the shaft 26, the
complement 17, and a cross-section through the gear 16 and drive
shaft 12, effectively act in concert as a slidable stopper in the
sender cavity 34. A keyway 84 is shown as one way to transfer power
from the shaft 12 to the gear 16 without allowing the gear 16 to
slip relative the drive shaft 12. Recall that the gear 16 is
axially fixed in place, and that the complement 17 may slide in
sealed relation along the gear 16. It can now be visualized that
this "stopper" assembly functions as a moving wall, and defines one
movable wall of the pump chamber (FIG. 7, denoted by area 104).
[0066] FIG. 5 is a cross-sectional view in elevation through
section 5-5 in FIG. 3. FIG. 5 shows additional details of the pump
chamber. For convenience, directions of rotation of the gears 16
and 28 are assigned, and are indicated by arrows 86 and 88. Teeth
of the gears 16 and 28 are seen to be in wiping sealed relation
with respect to the sleeve 22 and the sender cavity 34. Under the
illustrated conditions, a low pressure zone 90 is created where
teeth of the gears 16 and 28 rotate out of mesh. The low pressure
area 90 is accessed for fluid supply by an input port 92. A high
pressure zone 94 is created where the gear teeth come into mesh.
The high pressure zone 94 is in open fluid communication with an
exhaust port 96.
[0067] Referring to FIG. 6, a cross-sectional view in elevation
through the section 6-6 in FIG. 3 illustrates a fixed wall of the
pump chamber. The receiver cavity 38 is sealed by structure
including the sleeve 22, the sleeve center 20, the drive shaft 12,
the bridge element 78 of the receiver housing 36, the complement
30, the gear 28, and the axle 26. The sleeve 22 and gear 28 move
axially in sealed relation with the remaining structure. This
arrangement provides a fixed wall forming a sealing plane defining
the distal end of the pump chamber.
[0068] Referring now to FIGS. 7-10, the change in length of the
pump chamber 104 is illustrated. FIGS. 7-10 illustrate
cross-sectional side views in elevation of selected internal
operating elements of the pump 10 according to the present
invention. Notably, the cap plates 40 and 42 and the sender housing
32 are not illustrated in these Figures. In FIG. 7, the elements
are arranged in a position to define the maximum pump chamber
length 104. Note that the complement 17 is located at the proximal
end of the gear 16. FIG. 8 illustrates an arrangement to provide
approximately a one-half the maximum flow rate per revolution. Note
that the follower 24 has been displaced toward a distal end 106 of
the receiver housing 36, and the complement 17 is approximately at
mid-span of the gear 16.
[0069] FIG. 9 illustrates an arrangement that provides a
substantially reduced flow rate compared to the maximum flow rate.
In this circumstance, the follower 24 is displaced an additional
amount toward the distal end 106, compared to the position
illustrated in Figure 8. Note also that distal end of the gear 28
has come into engagement with the timing gear 18. Of note also, the
distal end of the follower 24 is approaching the distal end of the
sender housing 32 (not shown in FIGS. 7-10, see FIG. 1 or 3). The
distal end of the follower 24 may obscure the opening of either or
both of the ports 92 and 96 (see FIGS. 3 and 5). In this
circumstance, the follower 24 may interact with a particularly
formed and cooperative structure of the ports 92 and or 96 to also
form a metering valve or orifice. Such a metering valve may come
into actuation at the lower flow configurations of pump structure.
Such an arrangement may also enable controlled relief of pressure
in closed regions between teeth as closed in by other intermeshing
teeth.
[0070] FIG. 10 illustrates a zero flow arrangement of pump
elements. In this circumstance, the pump "chamber length" 104 is
effectively zero. The distal end of the complement 17 is
illustrated in contact with the sleeve center 20, and no free
volume in which to transfer fluid exists in the pump chamber. The
gear 28 may be completely disengaged, moving in an axial direction
away from the gear 16. The full length of the timing gear 18 is now
engaged by the gear 28, and maintains orientation of the gear 28
relative to the gear 16.
[0071] The illustrated example of the pump 10 has the drive shaft
12 axially fixed relative to the housing elements 32 and 36, and
the movable idler axle 26 carried by the follower assembly 25 (FIG.
1). It is within contemplation to provide an idler axle, axially
fixed in position, and a movable drive shaft. By way of example,
the axle 26 may be lengthened to protrude from one or both cap
plates 40 and 42. In such a configuration, pump flow rate may be
controlled either by displacing the entire pump housing relative to
the drive source, or by fixing the pump in place and moving the
driving source (typically a motor) relative to the pump
housing.
[0072] Certain other modifications to the illustrated apparatus 10
are also within contemplation, including without limitation,
forming a secondary pump within the receiver cavity 38. This
secondary pump may easily be formed by engagement of the timing
gear 18 and the gear 28. With reference to FIG. 3, the timing gear
18 may be moved from its illustrated position to place its proximal
end in sealing relation with the distal end of the complement 30.
The gear 28 may be lengthened to always engage the gear 18.
[0073] A third complement, similar to the complement 30, may form a
distal seal to the newly created secondary pump chamber. The sleeve
center 20 may then be formed as two sleeve centers disposed on
opposite sides of the gear 18. The sleeve 22 and the receiver
cavity 38 may be appropriately lengthened to accommodate the
increase in length of gear 28 and to allow full range in length of
the main pump chamber. The secondary pump output may be used as a
pressurized fluid source to control the length of the main pump
chamber.
[0074] Pump elements may be formed from any appropriate materials,
including, without limitation, ferrous and nonferrous metals, and
engineered plastics or polymers. Depending upon output pressure
requirements, working fluids, and desired pump life, pump gears may
advantageously be formed from stainless steels, cast iron, or
engineered plastics and the like. Seals may be formed throughout
the pump structure by closely fitting the illustrated components,
or by way of strategically added sealing elements. Housings may
alternatively be formed with integral caps and assembled like
opposed cups. A housing may also alternatively be structured as one
deep vessel having a single lid on a single open end. Such
construction details may be driven by manufacturing concerns.
[0075] In summary, it will be appreciated that the present
invention provides a positive displacement pump having a variable
output flow. The instant pump is a gear pump capable of varying its
displacement, and therefore its output at a given rotation rate.
The instant gear pump provides axial displacement of pump gears
with respect to one another, and includes a close follower to
maintain an end seal for each gear. A complement is included to
provide an end seal for a pump cavity having a variable length. To
the extent that an engagement region of the pump gear is reduced, a
liquid seal against leakage in the axial direction past each gear
closes off the engaged (fluid driving) portion of the respective
gears.
[0076] The instant pump provides an ability to vary displacement of
a gear pump through a full range from zero (idling, no pumping
occurring) at operational rotational speeds, to 100 percent of a
maximum capacity when the pumping gears are fully engaged to their
maximum extent. Furthermore, the instant gear pump provides a
timing gear to maintain synchronization between the two pumping
gears, even when the pumping gears are not engaged.
[0077] The present invention may be embodied in other specific
forms without departing from its structures, methods, or other
essential characteristics as broadly described herein and claimed
hereinafter. The described embodiments are to be considered in all
respects only as illustrative, and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims,
rather than by the foregoing description. All changes within the
meaning and range of equivalency of the claims are to be embraced
within their scope.
* * * * *