Information
-
Patent Grant
-
6491013
-
Patent Number
6,491,013
-
Date Filed
Wednesday, September 19, 200123 years ago
-
Date Issued
Tuesday, December 10, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Reising, Ethington, Barnes, Kisselle, Learman & McCulloch PC
-
CPC
-
US Classifications
Field of Search
US
- 123 1936
- 123 4135
- 092 186
-
International Classifications
-
Abstract
A closed gallery piston includes a piston body having a closed gallery for cooling oil defined in part by a bottom wall and outer wall of the piston body. At least one oil hole is formed in the bottom wall to accommodate a flow of cooling oil within the gallery. The bottom wall is locally thickened in the area bordering the oil hole with an oil hole boss to reinforce the bottom wall in the vicinity of the oil hole. The oil hole boss preferably joins with the outer wall to provide added structural integrity to the piston body at the juncture between the outer wall and bottom wall near the oil hole.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to pistons for diesel engine applications, and more particularly to those having a closed oil gallery.
2. Related Art
It is known in diesel engine applications to provide a piston whose piston body is formed with a closed gallery for cooling oil. The oil circulates through the gallery and cools parts of the piston which are susceptible to damage from the heat of combustion. Such cooling galleries are generally annular or ring-shaped and are provided just inside of the ring belt adjacent the top wall of the piston body. The gallery is bounded by an inner wall and closed at the bottom by a bottom wall. A plurality of access openings are typically provided in the bottom wall for allowing the oil to flow into and out of the gallery. Such oil holes are typically bored in the bottom wall. While such holes are necessary in order to provide for the inflow and outflow of oil to the gallery, such holes present an abrupt discontinuity in the bottom structure of the gallery. Because of the closed gallery structure, the forces exerted by the cylinder pressure on the top wall of the piston are transmitted through not only the inner wall to the pin bosses of the piston, but as well through the outer ring belt and bottom wall to the pin bosses. The presence of the oil holes in the bottom wall, which is structural and load-bearing, sets up a stress concentration point as the loads are transmitted through the outer ring belt and bottom wall regions of the piston. Presently, it is necessary to provide sufficient thickness to the bottom wall and ring belt portions of the piston crown to accommodate stresses that might otherwise lead to failure. Such material, while necessary, adds cost and weight to the piston.
It is an object of the present invention to overcome or greatly minimize the shortcomings of the prior pistons described above.
SUMMARY OF THE INVENTION AND ADVANTAGES
A closed gallery piston for diesel engines constructed according to the invention comprises a piston body having a top wall, an outer wall formed with ring grooves, an inner wall spaced radially inwardly from the outer wall, and a bottom wall interconnecting the outer wall and inner wall, with the walls providing an enclosed annular gallery for cooling oil. A pair of pin boss portions are provided having aligned pin bores. At least one oil access hole is formed in the bottom wall. An oil hole boss defined by a locally thickened portion of the bottom wall boarders the oil hole.
The invention has the advantage of providing a reinforced oil hole structure to a closed gallery piston which provides structural integrity in the region of the oil hole to counteract localized stress concentration which is present due to the hole in the bottom wall.
The invention has a further advantage of forming the reinforcing oil hole boss by way of a locally thickened region of the bottom wall of the gallery, which has the advantage of enabling the remainder of the bottom wall to be decreased in thickness as it is no longer needed to make up for the localized stress induced by the presence of the oil hole. By having only a locally thickened portion bordering the oil hole, a corresponding decrease in the thickness of the remainder of the bottom wall decreases the total material and thus weight and cost of the piston.
The invention has the further advantage of enabling the manufacturer of pistons to engineer the size and shape of the oil hole boss to provide the necessary structural support to counteract the stress concentration effects of the hole while minimizing the overall thickness of the bottom wall and surrounding structure adjacent the hole.
THE DRAWINGS
These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:
FIG. 1
is an elevational view of a piston constructed according to a presently preferred embodiment of the invention;
FIG. 2
is a cross-sectional plan view taken along lines
2
—
2
of
FIG. 1
;
FIG. 3
is a partially sectioned plan view taken generally along lines
3
—
3
of
FIG. 2
, but of the entire piston assembly;
FIG. 4
is a cross-sectional elevation view taken generally along lines
4
—
4
of
FIG. 2
, but of the entire piston assembly;
FIG. 5
is a fragmentary bottom perspective view of the piston of
FIG. 1
;
FIG. 6
is a fragmentary top perspective view, with a top portion of the piston removed, as in
FIG. 2
; and
FIG. 7
is a fragmentary cross-sectional view taken generally along lines
7
—
7
of FIG.
6
.
DETAILED DESCRIPTION
A closed gallery piston assembly constructed according to a presently preferred embodiment of the invention is indicated generally at
10
in FIG.
1
and comprises a piston body
12
having an annular top wall
14
with an upper surface
16
. A combustion crater or bowl
18
extends into the top wall
14
from the upper surface
16
. The top wall
14
has a lower or underside surface
22
opposite the upper surface
16
.
The piston body
12
has an outer wall or ring belt
24
that is annular and extends downwardly from the top wall
14
. The outer wall
24
has an outer annular peripheral surface
26
formed with a plurality of ring grooves
28
. The outer wall
24
includes an inner annular surface
30
spaced radially inwardly from the outer surface
26
.
The piston body
12
includes an inner wall
32
projecting downwardly from the combustion bowl
18
and having a radially outwardly facing surface
34
spaced radially inwardly from the inner surface
30
of the outer wall
24
.
The piston body
12
has an annular bottom wall
36
which is spaced from the top wall
14
and extends between and interconnects the outer wall
24
and inner wall
32
adjacent their lower ends. The bottom wall
36
has an upper floor surface
38
and lower surface
40
.
Collectively, the walls
14
,
24
,
32
and
36
define an interior, annular, ring-like cavity or gallery
42
within the piston body
12
that is closed by the walls. As illustrated in
FIGS. 2-4
, the gallery
42
extends completely around the piston body
12
and is bounded at the top by the top wall
14
, at the bottom by the bottom
36
, at the outer periphery by the outer wall
24
, and at the inner periphery by the inner wall
32
. By “closed” it is meant that the gallery
42
is closed at the bottom by a structural component of the piston body
12
, namely the bottom wall
36
, which not only extends between but joins the lower ends of the outer wall
24
and inner wall
32
. As will be explained further below, various openings and passages are provided to allow cooling oil to circulate into and out of the gallery
42
, and thus the term “closed” contemplates the provision of such openings and passages to accommodate the flow of cooling oil through the gallery
42
. It will also be appreciated by those skilled in the art that the terms “top”, “bottom”, “inner” and “outer” in describing the walls are intended and should be construed to represent portions of the surrounding wall structure which enclose the gallery
42
and should not be strictly construed based on the illustrated embodiment shown in the drawings since the particular shape and size of the gallery
42
will likely change from piston to piston depending on the particular cooling requirements necessary for a particular application.
The piston body
12
is further formed with a pair of pin boss portions
44
that are formed and preferably investment cast as one piece with the inner wall
32
and bottom wall
36
from steel. The pin bosses
44
have outer faces
46
that face away from one another and inner faces
48
that face toward one another. The inner faces
48
are each generally planar and preferably divergent toward the bottom of the pin bosses
44
, and define a space
50
between the inner faces
48
for accommodating a connecting rod
52
(FIG.
4
). A dome or cavity
54
may extend above the space
50
, as shown, for cooling the combustion bowl
18
. The surfaces which form the cavity
54
extend from, but out of the plane of, the inner faces
48
of the pin bosses
44
and, in the illustrated embodiment, are provided in part by inner surfaces
56
of the inner wall
32
. The pin bosses
44
are formed with axially aligned pin bores
58
having pin bore surfaces
60
which are substantially cylindrical and aligned about a pin bore axis A (FIG.
3
). The outer and inner faces
46
,
48
surround the pin bores
58
. The pin bores
58
receive a wrist pin (not shown) which serves to interconnect the piston body
12
with the connection rod
52
. The pin bore surfaces
60
provide support to the wrist pin, preferably without the assistance of any bushings, such that the pin bores
58
are preferably bushingless. Each of the pin bores
58
includes an annular snap ring groove
62
for receiving a snap ring to secure the wrist pin (not shown) within the pin bores
58
in usual manner.
The piston body
12
also includes a piston skirt
64
. The piston skirt
64
is preferably cast as a single piece with the pin bosses
44
, thus providing a monobloc piston structure rather than an articulated skirt. The skirt could, however, be formed as a separate structural component from the piston body
12
and joined through the wrist pin (not shown) in articulated manner to the pin bosses
44
, while retaining the closed gallery structure of the piston body
12
, but the monobloc structure is preferred. The piston skirt
64
has an outer surface
66
extending between the pin bosses
44
that is substantially in line and forms a extension of the outer surface
26
of the outer wall
24
. The outer surface
66
is interrupted across the pin bores
58
to provide recessed side faces
68
where the skirt
64
joins the pin bosses
44
. An inner surface
70
of the piston skirt
64
defines a space
72
adjacent the pin bores
58
that is walled off by the skirt
64
.
The closed gallery structure of the piston body
12
is preferably achieved by forming the piston body
12
from at least two separate parts which are subsequently joined across a joint or joints
74
to effectively yield a united, one piece body structure once joined. While there are a number of ways to join such separate components, all of which are contemplated by the invention, the preferred approach is to join the separately formed components across a friction weld joint
74
, as illustrated in
FIGS. 3 and 4
. In such case, a top part
76
above the joint
74
is separately formed from a bottom part
78
on the opposite side of the joint
74
, and the separately formed parts
76
,
78
are then friction welded together across the joint
74
to yield the united structure as shown in the drawings. Some examples of other joining techniques that are contemplated include other means of welding, bonding, brazing, screw thread joint, and other mechanical and metallurgical means of uniting the separate components together to yield the closed gallery structure of the piston body
12
.
According to a further preferred aspect of the invention, at least the bottom part
78
is investment cast from steel, and the top part
76
may likewise be investment cast from steel or formed by other techniques such as forging or other casting techniques.
Referring now particularly to FIGS.
2
and
5
-
7
, the bottom wall
36
of the piston body
12
is formed with at least one and preferably two oil access holes
80
which extend from the lower surface
40
of the bottom wall
36
within the space
72
into the oil gallery
42
. The oil holes
80
preferably are entry ports for introducing cooling oil into the gallery
42
. When the piston
10
is installed in a diesel engine, the oil holes
80
communicate with associated oil injection nozzles (not shown) which direct a stream of cooling oil from below up into the space
72
and into the gallery
42
through the holes
80
. Once in the gallery
42
, the cooling oil serves to cool the upper part of the piston body
12
, extracting heat from the walls as the oil is moved about in the gallery
42
with a “cocktail shaker” action during reciprocation of the piston
10
.
Because of the closed gallery structure of the piston body
12
, the combustion forces exerted on the top wall
14
which drive the piston
10
downwardly in the cylinder are transferred to the pin bosses
44
not only through the inner wall
32
, but also through the outer wall
24
and interconnecting bottom wall
36
. As such, the outer wall
24
and bottom wall
36
serve as structural load-bearing portions of the piston which must withstand the forces of combustion and transfer such loads to the pin bosses
44
without failure. The oil holes
80
and the bottom wall
36
represent an abrupt discontinuity in the bottom wall structure, and thus a potential site for stress concentration and potential failure. The present invention address this problem by reinforcing the piston body structure in the vicinity of the oil holes
80
to counteract the stress concentration effects caused by the introduction of the oil holes
80
in the bottom wall
36
. According to the invention, the piston body
12
is formed with oil hole bosses
82
bordering the oil holes
80
, which are best shown in
FIGS. 2
,
6
and
7
. The oil hole bosses
82
are defined by localized thickened portions of the bottom wall
36
which immediately border the oil holes
80
in order to give added structural integrity to the bottom wall
36
in the area surrounding the oil holes
80
. As illustrated most clearly in
FIGS. 6 and 7
, the oil hole bosses
82
extend above the upper floor surface
38
, such that the thickness of the bottom wall
36
immediately adjacent the oil hole bosses
82
is thinner than that of the portion of the bottom wall
36
making up the oil hole bosses
82
. The oil hole bosses
82
preferably extend into and are formed as one piece with the outer wall
24
, providing added structural integrity to the transition region between the outer wall
24
and bottom wall
36
in the vicinity of the oil holes
80
. It is preferred that all corners of the oil hole bosses
82
are rounded, as illustrated in
FIGS. 6 and 7
to reduce stress concentration.
As shown best in
FIGS. 2 and 6
, the oil hole bosses, when viewed from above in plan, have a non-circular shape and preferably include generally triangular regions or portions
84
where the oil hole bosses
82
join the outer wall
24
. It will be appreciated that the particular size and shape of the oil hole bosses
82
will be governed in large part by the structure needed to counteract the stress concentration imparted by the presence of the oil holes
80
. One advantage of investment casting the bottom part
78
is that the oil hole bosses
82
can be precisely formed to the net or near net shape needed to provide the desired counteracting structure against stress concentration of the holes
80
.
According to another aspect of the invention, at least one and preferably a pair of passages
86
extend from the gallery
42
directly to the inner faces
48
of the pin bosses
44
, so as to provide direct lubrication to the inner faces
48
between the pin bosses
44
and the connection rod
52
. The passages
86
are best shown in
FIGS. 4 and 5
. In the illustrated embodiment, there are thus four such passages
86
, two servicing each inner face
48
of the pin bosses
44
on opposite side of the pin bore axis A. The passages
86
are spaced from the walls which form the dome
54
and open directly to the inner faces
48
to provide direct lubrication in the gap between the pin bosses
44
and the connecting rod
52
.
According to still a further aspect of the invention and as shown best in
FIGS. 1 and 3
, the pin bores
58
are formed with an axial recess or pocket
88
which extends axially in the direction of the axis A of the pin bores
58
and presents a discontinuity in the cylindrical pin bore surfaces
60
. The recesses
88
are preferably concave and are located at least partly above the center line axis A of the pin bores. The recesses
88
extend axially across the full width of the pin bores
58
and thus are co-extensive with the width of the pin bore surfaces
60
between the outer
46
and inner
48
faces of the pin bosses
44
. The recesses
88
are aligned axially with one another and are interrupted by the space
50
between the inner faces
48
of the pin bosses
44
, as are the pin bore surfaces
60
. The recesses
88
are dome-shaped or concave in cross-section when viewed in the direction of the pin bore axis A. Oil passages
90
extend from the gallery
42
and open directly into each of the recesses
88
so as to feed oil to the recesses
88
during operation of the piston
10
across the full width of the pin bores
58
. The oil passages
90
preferably originate from the lowest part of the gallery
42
so as to provide a constant supply of oil to the pin bores
58
during the full cycle of movement of the piston. The entry of each oil passage
90
into its associated recess
88
is preferably about midway between the outer and inner faces
46
,
48
of the pin bosses
44
to promote uniform distribution of oil. The recesses
88
serve as reservoirs or holding pockets for oil and continue to feed oil to the pin bore surfaces
60
during the full stroke of the piston
10
to provide full time uniform lubrication.
Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. The invention is defined by the claims.
Claims
- 1. A closed gallery piston for diesel engines, comprising:a piston body having a top wall, an outer wall formed with ring grooves, an inner wall spaced radially inwardly from said outer wall, and a bottom wall interconnecting said outer wall and said inner wall, said walls providing an enclosed annular gallery within said piston body for cooling oil; pin boss portions having aligned pin bores; at least one oil hole in said bottom wall; and an oil hole boss defined by a locally thickened portion of said bottom wall bordering said at least one oil hole.
- 2. The closed gallery piston of claim 1 wherein said oil hole boss extends above an upper floor surface of said bottom wall adjacent said oil hole boss.
- 3. The closed gallery piston of claim 2 wherein said oil hole boss extends into said outer wall.
- 4. The closed gallery piston of claim 3 wherein said oil hole boss is non-circular in plan view.
- 5. The closed gallery piston of claim 3 wherein said oil hole boss includes generally triangular lobe portions connected to said outer wall.
- 6. The closed gallery piston of claim 1 including a piston skirt formed as one piece with said pin bosses.
- 7. The closed gallery piston of claim 1 wherein said piston body is formed of at least two pieces joined across at least one joint.
- 8. The closed gallery piston of claim 7 wherein said joint comprises a friction weld joint.
- 9. The closed gallery piston of claim 7 wherein at least one of said parts is investment cast.
- 10. A closed gallery piston for diesel engines, comprising:a piston body having an annular closed gallery for cooling oil with an outer wall, an inner wall, and a bottom wall extending between and interconnecting said outer wall and said inner wall; pin boss portions having aligned pin bores; at least one oil hole in said bottom wall; and an oil hole boss defined by a locally thickened portion of said bottom wall bordering said at least one oil hole and joined to said outer wall.
- 11. A method of making a closed gallery piston for diesel engines, comprising:fabricating a piston body having an enclosed gallery for cooling oil defined in part by an outer wall formed with ring grooves, an inner wall spaced radially inwardly from the outer wall and interconnecting the outer and inner walls, and including pin bosses with aligned pin bores; forming at least one oil hole in the bottom wall; and forming at least one locally thickened portion of the bottom wall to provide at least one associate oil hole boss which borders the at least one oil hole.
- 12. The method of claim 11 including extending the at least one oil hole boss to join with the outer wall in the vicinity of the at least one oil hole.
- 13. The method of claim 11 including forming the bottom wall and the at least one oil hole boss by investment casting.
US Referenced Citations (23)