Closed gallery piston having reinforced oil hole

Information

  • Patent Grant
  • 6491013
  • Patent Number
    6,491,013
  • Date Filed
    Wednesday, September 19, 2001
    23 years ago
  • Date Issued
    Tuesday, December 10, 2002
    22 years ago
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.
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