Information
-
Patent Grant
-
6568916
-
Patent Number
6,568,916
-
Date Filed
Thursday, June 7, 200122 years ago
-
Date Issued
Tuesday, May 27, 200320 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Freay; Charles G.
- Liu; Han L.
Agents
-
CPC
-
US Classifications
Field of Search
US
- 417 269
- 417 270
- 417 283
- 417 284
- 417 289
- 417 490
- 417 494
- 417 495
- 417 63
- 123 446
- 123 447
- 123 506
- 123 299
- 123 300
- 091 499
- 092 122
-
International Classifications
-
Abstract
A variable delivery fixed displacement pump is provided which has a rotating drive plate with a fixed angle. The drive plate has a fill passage extending between its radial outer surface and its drive surface, which allows fluid to be supplied to a fluid journal bearing. The drive plate also has a series of bearing supply passages which fluidly connect the drive surface of the drive plate with a base surface, allowing fluid to be supplied to a fluid thrust bearing. A method of pumping fluid is also provided which is comprised of the steps of reciprocating a plurality of pistons at least in part by rotating the drive plate, and by fluidly connecting a pumping chamber of the pistons to an annular groove that is part of the drive plate fill passage.
Description
TECHNICAL FIELD
The present invention relates generally to axial piston pumps, and more particularly to a variable delivery axial piston pump with outer diameter inlet filling via a fixed angle drive plate.
BACKGROUND
The invention described in U.S. Pat. No. 6,035,828 to Anderson et al. shows a variable delivery fixed displacement pump. Anderson also discloses a fixed angle drive plate and an electronic control unit which can alter the effective fluid displacement achieved by each pumping stroke. This design has met with tremendous success and represents a substantial improvement over earlier systems, however, there remains room for improvement.
For instance, the drive plate in Anderson is mounted on frustoconical roller bearings to ensure smooth rotation. While this design achieves its intended purpose, a significant amount of engine torque is wasted in overcoming the roller bearings' friction. In addition, frustoconical bearings are relatively expensive and subject to failure like any other moveable metallic component. It would thus be desirable to reduce the cost and the friction between the drive plate and the pump housing. In addition, refilling of the hollow piston interiors takes place by drawing fluid from the pump's low pressure interior via an opening in the outer radius of the drive plate. Consequently, engine power used to supply the pump with hydraulic fluid is less than fully exploited, resulting in a reduction in efficiency. It would thus be desirable to employ a design which takes advantage of the hydraulic fluid inlet pressure.
The present invention is directed to overcoming one or more of the problems or disadvantages set forth above.
SUMMARY OF THE INVENTION
In one aspect, a drive plate for an axial piston pump is provided which comprises a metallic component having a centerline and a drive surface oriented at a drive angle that is different from 90 degrees relative to the centerline. The metallic component further includes a radial outer surface surrounding the centerline, and defines a fill passage that extends between the radial outer surface and the drive surface. The fill passage includes an annular groove that is defined by the radial outer surface.
In another aspect, a pump is provided which comprises a housing defining an inlet. A plurality of pistons are provided, each defining a hollow interior, and are arranged around a centerline. A rotatable drive plate is also provided and defines a fill passage extending between a radial outer surface and a drive surface. The hollow interiors of the plurality of pistons are in fluid communication with the inlet via an annular groove defined by at least one of the housing and the drive plate.
In still another aspect, a method of pumping fluid is provided which comprises the step of reciprocating a plurality of pistons at least in part by rotating a drive plate. The method also includes the step of fluidly connecting a pumping chamber of a portion of the pistons to an inlet via an annular groove that is a portion of a fill passage extending between a radial outer surface and a drive surface of the drive plate. The method also includes the step of fluidly connecting a pumping chamber of a different portion of the pistons to an outlet.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a partial sectioned diagrammatic isometric view of a pump according to the present invention;
FIG. 2
is a top view of the drive plate included in the present invention;
FIG. 3
is a sectioned side view of the drive plate as viewed along section line
3
—
3
of
FIG. 2
;
FIG. 4
is a sectioned bottom view of the drive plate as viewed along section line
4
—
4
of FIG.
3
.
DETAILED DESCRIPTION
Referring to
FIG. 1
, there is shown an axial piston pump
1
according to the present invention. Pump
1
includes a housing
3
and an electro-hydraulic control unit
32
. A front flange
5
and an end cap
7
are provided, and are attached to housing
3
at opposite ends. An inlet
8
which is defined by housing
3
allows hydraulic fluid to be supplied to pump
1
from an exterior source (not shown). A barrel assembly
18
is provided which includes a barrel
19
positioned at least partially within housing
3
that is preferably adjacent one end of a plurality of pistons
20
. A drive plate
12
, which is preferably metallic, is positioned adjacent the opposite end. A rotatable drive shaft
9
is attached to drive plate
12
, and is supported by a bearing collar
10
. Drive shaft
9
is preferably coupled directly to the output of an engine (not shown), such that the rotation rate of shaft
9
and drive plate
12
is directly proportional to the rotation rate of the engine drive shaft.
In the preferred embodiment, the plurality of pistons
20
are arranged in a parallel orientation around centerline
11
. Bach individual piston
20
defines e hollow interior
21
, and is attached via a ball joint
36
to a shoe
34
that is positioned in contact with drive plate
12
. Hollow interior
21
is a portion of the pumping chamber for the piston. Return springs
25
continuously urge each piston
20
toward drive plate
12
in a conventional manner such that the piston shoes
34
remain in continuous contact with drive plate
12
. Drive plate
12
has a fixed angle, β (see FIG.
3
), and its rotation causes the plurality of pistons
20
to serially reciprocate between an up and a down position, displacing fluid in a conventional manner. Because each piston shoe
34
is maintained in contact with the drive plate, the pistons' hollow interiors
21
can allow fluid supplied via drive plate
12
(described below) to flow from an opening
37
in each shoe
34
to the opposite end of the piston
20
. From this point, the fluid can be forced past a check valve
26
into a collector ring
28
, and from there to an outlet via an outlet passage
29
.
A sleeve
24
is movably mounted around each of the plurality of pistons
20
. The sleeves'
24
position determines the proportion of displaced fluid flowing to collector ring
28
, and the proportion which flows to the low pressure interior
52
of pump
1
. Each sleeve
24
is attached to a connector
22
which surrounds drive shaft
9
. Connector
22
is movable between an up and a down position by electro-hydraulic control unit
32
in a conventional manner, allowing simultaneous movement of all the sleeves
24
. When the sleeves
24
are in their down position, a plurality of spill ports
30
can fluidly connect the hollow piston interiors
21
to low pressure interior
52
when the pistons
20
travel upward during a pumping stroke. In their up position, sleeves
24
cover the spill ports
30
and allow pressure to build in the piston interiors
21
, resulting in a relatively greater proportion of fluid being forced past check valve
26
and into collector ring
28
by the pistons'
20
pumping action. Because electro-hydraulic control unit
32
can be used to control the vertical position of each sleeve
24
on its respective piston
20
, the relative discharge of pump
1
can be controlled by selectively allowing sleeves
24
to cover or uncover the spill ports
30
during different portions of a piston pumping stroke. Electro-hydraulic control unit
32
defaults when un-energized via spring
69
to bias the piston sleeves
24
in their down position, at which the pump produces no high pressure output.
Referring in addition to
FIGS. 2-4
, there is shown the metallic drive plate
12
of the present invention. Drive plate
12
has a centerline
11
, and a radial inner surface
61
and a radial outer surface
62
which surround the centerline
11
. A drive surface
63
extends between outer surface
62
and inner surface
61
, and is oriented at a drive angle β which should be different from 90 degrees relative to the centerline
11
. Drive plate
12
defines a fill passage
60
which extends between radial outer surface
62
and drive surface
63
. Fill passage
60
includes an annular groove
71
which is preferably machined around radial outer surface
62
, and a fill slot
65
which opens to drive surface
63
. It should be appreciated that the present invention might be designed such that groove
71
was at least partially defined by housing
3
rather than drive plate
12
itself. The cross-sectional area of groove
71
should have sufficient flow area to accommodate the fluid pumping and bearing demands of the pump. The portion of fill passage
60
which connects groove
71
and fill slot
65
can be designed in any suitable manner, so long as adequate flow area is provided. The present description shows, for instance, a plurality of spoke-like bores. However, it should be appreciated that some other design might be employed such as a continuous slot through radial outer surface
62
. In the preferred embodiment, till slot
65
is arcuate shaped, and follows a path that has a substantially constant radius, circle
66
, relative to centerline
11
, preferably sweeping out an angle δ which is less than 180 degrees. As drive plate
12
rotates, the hollow interior
21
of at least one of the plurality of pistons
20
is in fluid communication with inlet
8
via fill passage
60
and annular groove
71
.
A base surface
64
is located opposite drive surface
63
and separates radial inner surface
61
from radial outer surface
62
. Base surface
64
preferably lies in a plane that is substantially perpendicular to centerline
11
, and is separated from housing
3
by a fluid thrust bearing
43
. A thrust bearing plate
40
which provides a plurality of thrust pads
42
is positioned beneath fluid thrust bearing
43
(
FIG. 1
) and drive plate
12
. Drive plate
12
defines a plurality of bearing supply passages
67
which extend from base surface
64
through drive surface
63
, and provide the fluid for thrust bearing
43
. The bearing supply passages
67
are preferably distributed on a circle
66
that is centered on centerline
11
and includes the arc swept out by fill slot
65
. In the preferred embodiment, a majority of the radial outer surface
62
is a portion of a regular cylinder and is separated from housing
3
by a fluid journal bearing
44
. Hydraulic fluid is pushed into the area between radial outer surface
62
and housing
3
to provide the journal bearing
44
. Although preferred, it is not necessary that the present invention include both fluid thrust and fluid journal bearings. A conventional roller bearing might be substituted for either of the fluid bearings provided by the present invention.
INDUSTRIAL APPLICABILITY
Returning now to
FIG. 1
, the rotation of drive plate
12
causes pistons
20
to reciprocate up and down by elevating and de-elevating the shoes
34
of each piston
20
as the plate passes underneath. The axial lodes produced by piston reciprocation can be balanced by the plurality of thrust pads
42
. As drive plate
12
passes underneath one of the pistons
20
, drive surface
63
can act on the piston shoe
34
to drive the piston
20
up for a pumping stroke. Each shoe
34
is connected to its respective piston
20
by a ball joint
36
which allows the shoe
34
to remain in continuous contact with drive surface
63
. The amount of fluid displaced by the piston
20
into high pressure collector ring
28
depends on the position of its respective sleeve
24
. When relatively greater fluid displacement is desired, electro-hydraulic control unit
32
can be used to move sleeves
24
up. The sleeves
24
then cover spill ports
30
and a maximum amount of fluid can be displaced by each piston's
20
pumping stroke to flow past check valve
26
into collector ring
28
. By varying the time that the sleeves
24
are held in their up position, a broad spectrum of fluid displacement quantities can thus be obtained.
When drive plate
12
has moved piston
20
its maximum displacement, it begins to move down, its shoe
34
remaining in continuous contact with drive surface
63
. Shortly after the piston
20
begins to retract, the rotation of drive plate
12
brings fill slot
65
under the opening
37
in piston shoe
34
. Because fluid is continuously supplied via inlet
8
to fill passage
60
, the retracting movement of piston
20
acts to draw fluid from fill slot
65
into its hollow interior
21
. Because fill passage
60
is supplied with hydraulic fluid directly from inlet
8
rather than the pump's
1
low pressure interior
52
, fluid is drawn into the pistons' hollow interior
21
more readily than in prior art pumps. Low pressure interior
52
is preferably fluidly connected to inlet
8
via a pressure balancing passage which is not shown. Shortly before the piston
20
reaches its fully retracted position, the rotation of drive plate
12
moves fill slot
65
out of fluid communication with the opening
38
in piston shoe
34
.
As drive plate
12
rotates, fluid which is supplied via inlet
8
is pushed into the area between drive plate
12
's radial outer surface
62
and housing
3
, resulting in a relatively low friction fluid journal bearing
44
. The bearing supply passages
67
which fluidly connect drive surface
63
with base surface
64
allow a continuous supply of fluid to be provided to the area between drive plate
12
and thrust bearing plate
40
, constituting the invention's fluid thrust bearing
43
. In other words, a portion of the fluid pumped by pistons
20
is pushed through bearing supply passages
67
to produce a fluid thrust bearing
43
that separates drive plate
12
from contact with thrust pads
42
. The substitution of conventional roller bearings for the fluid journal
44
and thrust bearings
43
allows the present invention to be manufactured for lower cost and to operate under a significantly decreased frictional load. The present invention represents a further improvement over earlier designs by taking advantage of the fluid supply pressure at the inlet
8
to assist in replenishing the hydraulic fluid in the pistons
20
rather than relying only upon the reciprocating action of the pistons
20
to draw fluid back into their interiors
21
.
The above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. For example, the fluid bearing design utilized in the present invention might be modified to use a combination of fluid and roller bearings. Additionally, the drive plate-fill passage design might be employed as a means of reducing plumbing in a pump with space constraints.
Thus, those skilled in the art will appreciate that other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.
Claims
- 1. A drive plate for an axial piston pump comprising:a metallic component having a centerline and a drive surface oriented at a drive angle that is different from 90° relative to said centerline, and having a radial outer surface surrounding said centerline; and a fill passage disposed in said metallic component and extending between said radial outer surface and said drive surface, said fill passage including an annular groove disposed in said metallic component and opening at said radial outer surface, and said fill passage opening through said drive surface offset from said centerline.
- 2. The drive plate of claim 1 wherein a portion of said fill passage is a fill slot through said drive surface; andsaid fill slot following an arc having a substantially constant radius relative to said centerline.
- 3. The drive plate of claim 2 wherein said arc sweeps out an angle less than 180° about said centerline.
- 4. The drive plate of claim 2 wherein said metallic component includes a base surface located opposite said drive surface; andsaid metallic component defining a plurality of bearing supply passages extending from said base surface through said drive surface, and said bearing supply passages being distributed on a circle that includes said arc.
- 5. The drive plate of claim 1 wherein a majority of said radial outer surface is a portion of a regular cylinder.
- 6. The drive plate of claim 1 wherein said metallic component includes a base surface separating a radial inner surface from a radial outer surface; andsaid base surface lies in a plane substantially perpendicular to said centerline.
- 7. The drive plate of claim 1 wherein said metallic component includes a base surface separating a radial inner surface from a radial outer surface;said fill passage including an arcuate shaped fill slot disposed in said metallic component and opening at said drive surface, said fill slot being contained within an angle of less than 180° about said centerline; and said metallic component defining a plurality of bearing supply passages extending from base surface through said drive surface.
- 8. The drive plate of claim 7 wherein said bearing supply passages and said fill slot are distributed on a circle centered on said centerline;said base surface lies in a plane substantially perpendicular to said centerline; and a majority of said radial outer surface being a portion of a regular cylinder.
- 9. A pump comprising:a housing having an inlet; a plurality of pistons arranged around a centerline, and each of said pistons having a hollow interior; a rotatable drive plate having a fill passage disposed therein and extending between a radial outer surface and a drive surface, and said fill passage including an annular groove disposed in one of said housing and said drive plate; said hollow interior of an at least one of said plurality of pistons being in fluid communication with said inlet via said fill passage.
- 10. The pump of claim 9 including a barrel at least partially positioned in said housing adjacent one end of said plurality of pistons;said plurality of pistons being oriented parallel to said centerline; said drive plate having a drive surface positioned adjacent an opposite end of each of said plurality of pistons.
- 11. The pump of claim 9 wherein said drive plate has a base surface separated from said housing by a fluid thrust bearing; andsaid drive plate has a radial outer surface separated from said housing by a fluid journal bearing.
- 12. The pump of claim 9 wherein said drive plate defines a plurality of bearing supply passages extending between said base surface through said drive surface.
- 13. The pump of claim 9 wherein a majority of said radial outer surface is a portion of a regular cylinder.
- 14. The pump of claim 13 wherein a portion of said fill passage is a fill slot through said drive surface; andsaid fill slot following an arc having a substantially constant radius relative to said centerline.
- 15. The pump of claim 14 wherein said annular groove is defined by said drive plate.
- 16. The pump of claim 9 wherein said drive plate includes a base surface separating a radial inner surface from said radial outer surface;said fill passage including an arcuate shaped fill slot through said drive surface, and said fill slot being contained within an angle of less than 180° about said centerline; and said drive plate defining a plurality of bearing supply passages extending from said base surface through said drive surface.
- 17. The pump of claim 16 wherein said bearing supply passages and said fill slot are distributed on a circle centered on said centerline;said base surface lies in a plane substantially perpendicular to said centerline; and a majority of said radial outer surface being a portion of a regular cylinder.
- 18. A method of pumping fluid comprising the steps of:reciprocating a plurality of pistons at least in part by rotating a drive plate; fluidly connecting a pumping chamber of a portion of said pistons to an inlet via an annular groove that is a portion of a fill passage extending between a radial outer surface and a drive surface of said drive plate; and fluidly connecting a pumping chamber of a different portion of said pistons to an outlet.
- 19. The method of claim 18 including a step of adjusting an effective pumping stroke of said pistons at least in part by repositioning a plurality of sleeves surrounding different ones of said pistons.
- 20. The method of claim 19 including a step of positioning thrust bearing fluid between a base surface of said drive plate and a pump housing; andpositioning journal bearing fluid between a radial outer surface of said drive plate and said pump housing.
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Date |
Kind |
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Pruvot |
Aug 1974 |
A |
3890883 |
Rometsch et al. |
Jun 1975 |
A |
4579043 |
Nikolaus et al. |
Apr 1986 |
A |
5205124 |
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Apr 1993 |
A |
5603609 |
Kadlicko |
Feb 1997 |
A |
6035828 |
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Mar 2000 |
A |
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Number |
Date |
Country |
10266947 |
Oct 1998 |
JP |