Information
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Patent Grant
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6682315
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Patent Number
6,682,315
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Date Filed
Wednesday, November 28, 200122 years ago
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Date Issued
Tuesday, January 27, 200420 years ago
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Inventors
-
Original Assignees
-
Examiners
- Yu; Justin R.
- Gray; Michael K.
Agents
-
CPC
-
US Classifications
Field of Search
US
- 417 269
- 417 454
- 417 453
- 092 71
- 091 503
- 029 88806
- 029 888
- 029 888061
- 029 88802
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International Classifications
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Abstract
In an axial piston pump, a plurality of reciprocating pistons are at least partially positioned within a barrel. The barrel includes a ring shaped high pressure collection cavity that is positioned between the piston chambers and the outlet of the pump. In order to minimize potential loses due to leakage from the ring shaped collection cavity, the barrel is made from a casting that utilizes a ring shaped core supported in a mold. This facilitates the formation of the ring shaped cavity while insuring location and dimensional tolerances, and assisting in the latter machining of the casting to its final form.
Description
TECHNICAL FIELD
The present invention relates generally to axial piston pumps, and more particularly to a barrel casting for an axial piston pump having a ring shaped high pressure collection cavity.
BACKGROUND
Co-owned U.S. Pat. No. 6,035,828 to Anderson et al. describes a hydraulically actuated system having a variable delivery fixed displacement axial piston pump. This pump is referred to as a fixed displacement because the swash or drive plate has a fixed angle such that each piston reciprocates a fixed distance and displaces a fixed amount of fluid with each rotation of the drive plate. The pump achieves a variable delivery by utilizing sleeves that surround each piston and cover a spill port for at least a portion of each reciprocation of the individual piston. For instance, if the sleeves are positioned at one location, the spill ports in the pistons remain uncovered throughout each reciprocation such that the pump merely circulates fluid between low pressure areas and no high pressure output is produced. When the sleeves are in another position, the spill ports are closed over the entire reciprocation distance of the piston such that the maximum high pressure output of the pump is achieved. The sleeves can be positioned anywhere between these two extremes via an electro-hydraulic control unit so that the effective high pressure delivery of the pump can be varied and controlled at will.
While this pump has shown considerable promise, there remains room for improvement. For instance, each of the pistons has one end received in a piston bore of a barrel component. A high pressure collection cavity is located between the barrel and the outlet of the pump. In addition, at least one check valve separates the individual piston chambers from the high pressure collection cavity. In the Anderson et al. pump, these various features are located in body components that are different from the barrel. As such, the effectiveness of the pump has the potential for compromise due to leakage between these components. In addition, insuring the proper location and orientation of these body components relative to one another can add substantial machining costs and assembly complications.
The present invention is directed to one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In one aspect, a barrel assembly for an axial piston pump includes a casting that defines a ring shaped collection cavity that is fluidly isolated from a central bore.
In another aspect, a pump includes a barrel assembly mounted in a housing. The barrel assembly includes a casting that defines a ring shaped cavity fluidly isolated from a central bore, and a plurality of parallel piston bores that are open to the ring shaped cavity. A piston is slidably received in each of the piston bores. A drive plate have a slanted drive surface is rotatably mounted in the housing and operably coupled to each of the pistons.
In still another aspect, a method of making a barrel assembly for a pump includes a step of casting metal around a ring shaped core. The ring shaped core is then removed from the casting.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a partially sectioned isometric view of a pump according to a preferred embodiment of the present invention.;
FIG. 2
is a sectioned side diagrammatic view of a barrel assembly according to the present invention;
FIG. 3
is an isometric view of a ring shaped core according to one aspect of the present invention;
FIG. 4
is an isometric view of a base core according to another aspect of the present invention;
FIG. 5
is a sectioned side view of a casting mold according to another aspect of the present invention;
FIG. 6
is a top view of a casting blank according to one aspect of the present invention; and
FIG. 7
is a sectioned side view of the casting blank of
FIG. 5
as viewed along sectioned line
6
—
6
.
DETAILED DESCRIPTION
Referring to
FIG. 1
, there is shown an axial piston pump
10
according to the present invention. Pump
10
includes a housing
11
that includes a front flange
12
and an end cap
13
. Housing
11
includes an inlet
14
and an outlet
15
. When pump
10
is installed as part of a hydraulic system, such as a hydraulically actuated fuel injection system, inlet
14
is connected to a source of low pressure fluid, such as engine lubricating oil. Outlet
15
would be fluidly connected to a high pressure reservoir, such as a high pressure common rail that supplies working fluid to hydraulic actuators, such as those associated with hydraulically actuated fuel injectors and/or hydraulically actuated gas exchange valves, and the like. Pump
10
includes a drive shaft
16
having an external end that is coupled to an appropriate rotational power source, such as the crank shaft of an internal combustion engine. Drive shaft
16
preferably has a keyed connection to rotate a drive plate
17
, which preferably has a fixed slant angle.
A plurality of pistons
20
are distributed around a centerline of the pump and oriented parallel to one another and to drive shaft
16
. In the illustrated embodiment, there are preferably seven pistons; however, those skilled in the art will appreciate that a pump having any number of pistons could be suitable for use in relation to the present invention. Each individual piston
20
defines a hollow interior
21
, and is attached via a ball joint to a shoe
29
that is maintained in contact with drive plate
17
via the continuous urging of a return spring
25
. Rotation of drive plate
17
causes the plurality of pistons to serially reciprocate between up and down positions, displacing fluid in a conventional manner. Each of the pistons
20
also includes a hollow interior
21
, which can be thought of as a portion of that pistons pumping chamber, and at least one spill port
26
distributed around the periphery of the piston and opening into hollow interior
21
. One end of each of the pistons is slidably received in a plunger bore
64
defined by a barrel assembly
18
. Together, plunger bore
64
and hollow interior
21
define the pumping chamber for the individual piston. This pumping chamber is separated from a ring shaped high pressure collection cavity
19
in barrel assembly
18
by a check valve
23
. In other words, the plunger bore
64
for each piston is separated from ring shaped collection cavity
19
by a separate check valve
23
. Ring shaped collection cavity
19
is fluidly connected to outlet
15
via a passage that is not shown, but fluidly isolated from a central bore
67
.
The output of pump
10
is controlled by an electro-hydraulic control unit
27
that is operable to move a control piece
30
up and down along a line that is parallel to that of the pistons. In particular, electro hydraulic control unit
27
moves a control piece
30
, which is operably coupled to a plurality of sleeves
24
via a connector
22
. An individual sleeve
24
is positioned around each individual piston
20
. The location of sleeves
24
relative to spill ports
26
determines how much of the fluid displaced by piston
21
is pushed into high pressure collection cavity
19
or merely recirculated into low pressure interior
28
of the pump housing
11
. In other words, if sleeve
24
maintains spill port
26
covered during the entire reciprocation distance of a piston
20
, virtually all of the fluid displaced is pushed past check valve
23
into high pressure ring shaped cavity
19
. On the other hand, if sleeves
24
are positioned such that spill ports
26
remain open as piston
20
is moved for its pumping stroke, the fluid displaced by piston
20
merely spills back into low pressure area
28
via spill ports
26
for recirculation.
When pistons
20
are undergoing their retracting stroke, low pressure fluid is drawn into hollow interior
21
from low pressure pump interior
28
via a center filled inlet
36
in drive plate
17
and an internal fill passage and slot (not shown) that communicates with an opening
31
in shoes
29
at an appropriate rotational position that is out of plane in the sectioned view of FIG.
1
. In addition to defining the fill passageway, drive plate
17
also defines a plurality of bearing supply passages
37
that communicate fluid from hollow interior
21
to the thrust pads
33
adjacent the underside of drive plate
17
to provide a hydrostatic thrust bearing
34
. A portion of this fluid migrates up the outer radial wall of drive plate
17
to provide a hydrodynamic journal bearing
35
. It should be noted that bearing supply passages
37
are positioned such that they only communicate with openings
31
when the individual piston
20
is undergoing its pumping stroke. When the pistons are undergoing their retracting stroke, they align with a fill slot (not shown) that is fluid communication with center fill inlet
36
.
Referring now to
FIG. 2
, the barrel assembly
18
is shown in greater detail. Barrel assembly
18
includes a machined casting
38
and a plurality of attached check valves
23
. Unlike some alternative designed axial piston pumps, barrel assembly
18
of pump
10
remains stationary when the pump is in operation. Those skilled in the art will appreciate that in other axial piston pumps the barrel is rotated by the drive shaft and the drive plate remains stationary. The present invention is compatible with both types of axial piston pumps. As identified earlier, barrel casting
38
includes a ring shaped high pressure collection cavity
19
that is separated from piston bores
64
by a relatively short passage that includes a conical valve seat
65
. Each of the check valves
23
includes external threads that mate to internal threads
69
that are machined in access openings
66
in barrel casting
38
. Thus, check valves
23
are threaded into a position in contact with conical seat
65
. Each check valve
23
includes a check valve member
70
that is biased into a position in contact with a seat
72
via a biasing spring
71
. When in this biased position, a passage
73
is closed to piston bore
64
. When fluid pressure pushing on check valve
70
exceeds the pre-load of biasing spring
71
, check valve member
70
lifts to fluidly connect ring shaped collection cavity
19
to piston bore
64
via passage
73
. Barrel casting
38
also includes a shaft support opening or central bore
67
that extends between first end
63
and second end
68
. Central bore
67
is fluidly isolated from ring shaped cavity
19
.
Referring now to
FIGS. 3
,
4
, and
5
, the various core pieces and mold assembly are illustrated to show how the barrel is casted to include its ring shaped collection cavity
19
(FIGS.
1
and
2
). The barrel is preferably cast in a sand mold using discardable core pieces that are preferably premanufactured using a sand epoxy mixture in a conventional manner. In particular, ring shaped core
40
includes a ring shaped portion
41
and a plurality of pillars
42
that correspond to the number of pistons in the pump. A base core
45
is likewise preferably manufactured from a suitable sand and epoxy mixture to include a central bore core
46
centrally located atop a base portion
48
that defines a plurality of pillar holes
47
. An additional central bore core
49
(
FIG. 5
) can also be used in molding the barrel casting. When placed in mold
50
, the pillars
42
of ring shaped core
40
are received in respective pillar bores
47
in base core
45
. This arrangement insures that ring portion
41
will remain at its desired location when the molten metal is poured into mold
50
. In other words, this mating arrangement between ring shaped core
40
and base core
45
insures that the pillars
48
are properly located in the cast component and that ring portion
41
is precisely located within mold
50
, and remains at that location throughout the molding process.
Referring now in addition to
FIGS. 6 and 7
, a casting blank
60
is illustrated as would be produced using the mold
50
as illustrated in FIG.
5
. Casting blank
60
includes a central bore
61
, a plurality of pillar openings
62
and ring shaped high pressure collection cavity
19
. This casting blank is then machined using conventional techniques to arrive at the barrel casting
38
shown in FIG.
2
. During the machining process, the individual pillar openings
62
are enlarged to produce access openings
66
, internal threads
69
and conical seats
65
.
Industrial Applicability
The present invention finds potential application in any case where there is a desirability to cast a cavity into a casting, especially when it is important to maintain a certain geometry for the cavity and precisely locate the same with regard to the other surface features of the component. In the present case, the casting technique of the present invention allows for the formation of a high pressure ring shaped cavity that is virtually free of potential leakage concerns that could become associated with pumps that utilize one or more joined components to form their high pressure cavity(s). The present invention also exploits that fact that the core for the ring shaped cavity can be located and supported using other attached core components that are located at or near where openings are intended to be located in the finished component. This allows the casting technique to exploit the anticipated location of access openings
66
(
FIG. 2
) in order to help facilitate the formation of internal ring shaped cavity
19
. Furthermore, by combining this technique with the particular structure and attachment strategy of check valves
23
allows the individual check valves to provide the check valve functionality while sealing ring shaped collection cavity
19
from any leakage to the outside in a cost effective and efficient manner.
Returning to
FIGS. 1 and 2
, when in operation, pump
10
can preferably produce between zero and its maximum output depending upon the positioning of electro hydraulic control unit
27
and hence sleeves
24
. As drive shaft
16
rotates, drive plate
17
rotates to cause each of the pistons
20
to reciprocate. Those undergoing their retracting stroke drawl fresh low pressure fluid from low pressure interior
28
through central fill inlet
36
and on to opening
31
via a passage in drive plate
17
not visible in FIG.
1
. The pistons undergoing their pumping stroke push fluid out of piston bore
64
and hollow interior
21
past check valve
23
into high pressure collection cavity
19
for whatever portion of the piston stroke that sleeve
24
covers spill ports
26
. For that portion of the pumping stroke in which spill ports
26
are open, the fluid is merely displaced back into low pressure interior
28
. However, when spill ports
26
are closed, a portion of the fluid displaced by piston
20
is pushed down through bearing supply passages
37
to produce the hydrostatic fluid bearing that separates drive plate
17
from thrust bearing pads
34
.
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 casting technique of the present invention could permit for the formation of more than one ring shaped cavity and possibly permit the usage of a single check valve as opposed to an individual check valve for each of the reciprocating pistons. Thus, those skilled in the art will appreciate the 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. An axial piston pump barrel comprising:a ring shaped collection cavity disposed in said barrel between first and second ends thereof, and a central bore disposed in said barrel and being fluidly isolated from, but encircled by, said ring shaped collection cavity, and said barrel including a casting of metallic material; and a number of piston bores with openings and a number of separate access openings for accommodating a valve, said piston bores and said separate access openings being disposed in said barrel, said piston bores and said separate access openings being equal in number and each opening at a respective end thereof into said ring shaped cavity.
- 2. The barrel of claim 1 wherein said casting defines a plurality of piston bores that open on one end to said ring shaped collection cavity.
- 3. The barrel of claim 2 including a check valve attached to said casting to fluidly separate each of said plurality of piston bores from said ring shaped collection cavity.
- 4. An axial piston pump comprising:a ring shaped collection cavity disposed in said barrel, and a central bore disposed in said barrel and being fluidly isolated from, but encircled by, said ring shaped collection cavity, and said barrel including a casting of metallic material; said casting defines a plurality of piston bores that open at one end to said ring shaped collection cavity; a plurality of check valves attached to said casting, each respective check valve of said plurality of check valves accommodating a respective piston bore of said plurality of piston bores to fluidly separate each of said piston bores from said ring shaped collection cavity; and each said check valve is threadably attached to said casting.
- 5. An axial piston pump barrel comprising:a ring shaped collection cavity disposed in said barrel, and a central bore disposed in said barrel and being fluidly isolated from, but encircled by, said ring shaped collection cavity, and said barrel including a casting of a metallic material; said casting defines a plurality of piston bores that open on one end to said ring shaped collection cavity; and said casting includes a conical valve seat positioned between each of said plurality of piston bores and said ring shaped cavity.
- 6. The barrel of claim 5 including a plurality of check valves that are each attached to said casting in contact with one of said conical valve seats.
- 7. A pump comprising:a housing; a barrel mounted in said housing, and including a casting that defines a ring shaped collection cavity fluidly isolated from a central bore and located between first and second ends of said casting; a plurality of piston bores with openings and a plurality of separate access openings for accommodating a valve, said piston bores and said separate access openings being disposed in said barrel, said piston bores and said separate access openings being egual in number and each opening at a respective end thereof into said ring shaped cavity; a piston slidably received in each of the piston bores; and a drive plate having a slanted drive surface rotatably mounted in said housing and being operably coupled to each said piston.
- 8. The pump of claim 7 wherein said barrel assembly includes a check valve attached to said casting between each of said plurality of parallel piston bores and said ring shaped collection cavity.
- 9. The pump of claim 8 wherein each said check valve is threadably attached to said casting.
- 10. The pump of claim 7 wherein said casting includes a conical valve seat positioned between each of said plurality of piston bores and said ring shaped collection cavity.
- 11. The pump of claim 10 including a plurality of check valves that are each attached to said casting in contact with one of said conical valve seats.
US Referenced Citations (11)
Foreign Referenced Citations (1)
Number |
Date |
Country |
1 193 394 |
Apr 2002 |
EP |