PISTON WITH CENTRAL COOLING GALLERY COOLING FEATURE

Abstract

A piston includes an upper crown portion and a lower crown portion with a pair of pin bosses spaced for receipt of a connecting rod. The pin bosses have pin bores aligned with one another along a pin bore axis. The upper crown portion and the lower crown portion form an outer oil gallery and a central oil gallery. The central oil gallery is formed in part by a floor extending radially inwardly from the outer oil gallery to a plateau. To facilitate cooling the central gallery, the plateau has a through opening and the floor has at least one trough depending axially therein. At least one oil flow passage extends in fluid communication between the outer oil gallery and the central oil gallery, wherein at least one oil flow passage is axially aligned with the at least one trough to provide a direct flow of oil to the trough.

Description

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to pistons for internal combustion engines, and more particularly to pistons having a central oil cooling gallery.

2. Related Art

Piston constructions having a central oil cooling gallery or two substantially closed oil cooling galleries (dual galleries) are known. The dual gallery pistons have an annular, radially outer gallery and an open central gallery formed between upper and lower crown portions. The outer and central galleries can be isolated from one another or in fluid communication with one another via oil passages. In addition, it is known to provide pin lubrication passages extending from one or both of the galleries to a wrist pin. The lubrication passages can extend into a wrist pin bore of a pin boss and/or between laterally spaced pin bosses. The outer gallery is particularly suited for cooling a ring belt region of the piston, while the central gallery is particularly suited for cooling a central crown region formed in part by a combustion bowl wall, which is exposed to hot combustion gasses.

The combustion bowl and central crown region is exposed to extreme heat in use. As such, the aforementioned central gallery needs to receive ample oil flow in order to provide adequately cooling to the central gallery region. Although central galleries, both closed and open, are known, issues remain in providing adequate cooling in the central crown region. In particular, continual efforts remain to both provide sufficient oil flow through the central crown region while at the same time avoiding “cooking” and deteriorating the oil. If the oil directed to the central gallery region is allowed to remain in the region for too long without being recirculated, the oil “cooks”, thereby diminishing both the cooling and lubrication capacity of the oil. On the other hand, if the oil is allowed to flow outwardly from the central gallery too quickly, the cooling function of the oil is diminished, thereby potentially reducing the useful life of the piston.

SUMMARY OF THE INVENTION

A piston includes a piston body having an upper crown portion with an upper combustion wall against which combustion forces act and a lower crown portion with a pair of pin bosses spaced for receipt of a small end of a connecting rod in a pin bore region therebetween. The pin bosses have pin bores aligned with one another along a pin bore axis that extends transversely to a longitudinal central axis along which the piston translates. The upper crown portion and the lower crown portion form an outer oil gallery and a central oil gallery. The central oil gallery is formed in part by a floor extending radially inwardly from the outer oil gallery to a plateau. To further facilitate cooling the central gallery, the plateau has a through opening and the floor has at least one trough depending axially therein. At least one oil flow passage extends in fluid communication between the outer oil gallery and the central oil gallery, wherein at least one oil flow passage is axially aligned with the at least one trough.

In accordance with another aspect of the invention, the piston has a pair of troughs diametrically opposite one another.

In accordance with yet another aspect of the invention, the troughs are diametrically aligned along the pin bore axis.

In accordance with yet another aspect of the invention, each trough extends between about 45 to 90 degrees about the central gallery.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of the invention will become more readily appreciated when considered in connection with the following detailed description of presently preferred embodiments and best mode, appended claims and accompanying drawings, in which:

FIG. 1 is a cross-sectional view taken generally along a pin bore axis of a piston constructed in accordance with one presently preferred aspect of the invention;

FIG. 2 is a cross-sectional view of the piston of FIG. 1 taken generally along an axis extending transversely to the pin bore axis;

FIG. 3 is a broken-away perspective view of the piston of FIG. 1;

FIG. 4 is a plan view of a lower crown of the piston of FIG. 1 looking generally along the line 4-4 of FIG. 1;

FIG. 5 is a plan view looking down on the lower crown of the piston of FIG. 1; and

FIG. 6 is a perspective view of the lower crown of the piston of FIG. 1.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

Referring in more detail to the drawings, FIGS. 1-3 illustrate a piston 10 constructed in accordance with one presently preferred aspect of the invention. The piston 10 has a piston body 12 extending along a longitudinal central axis 14 along which the piston body 12 reciprocates within a cylinder bore (not shown). The piston body 12 includes an upper crown portion 16 having an upper combustion wall 18, represented here, by way of example and without limitation, as providing a recessed combustion bowl 20, against which combustion forces directly act in the cylinder bore, thereby providing a location where extreme heat is generated. As referenced in FIG. 1, for sake of simplicity, the upper crown portion 16 has at least one, and shown here as a pair of annular upper ribs, referred to hereafter as an upper inner rib 22 and upper outer rib 24, depending from the upper combustion wall 18 to respective free ends 26, 28. The piston body 12 further includes a lower crown portion 30 having at least one, and shown here as a pair of annular lower ribs, referred to hereafter as a lower inner rib 32 and lower outer rib 34, extending to respective free ends 36, 38 configured for abutment with the free ends 26, 28 of the upper ribs to provide, at least in part, an inner or central oil gallery 37 and an annular outer oil gallery 39 extending about the central oil gallery 37. The lower crown portion 30 further includes an inner gallery lower wall, also referred to as floor 40, extending radially inwardly in ascending relation from the lower inner rib 32 to a generally planar, raised plateau 41 to partially enclose the central oil gallery 37. A pair of pin bosses 42, 44 depend generally from the floor 40 to provide a pair of wrist pin bores 43, 45 aligned along a pin bore axis 47 for receipt of a wrist pin (not shown) with a space 46 provided between the pin bosses 42, 44 for receipt of a small end of a connecting rod (not shown). The floor 40 provides a central gallery cooling feature to facilitate cooling the upper combustion wall 18, including at least one trough, and shown here as a pair of troughs 48 depending axially therein in axial alignment with the pin bore axis 47, such that the configuration of the floor 40 is circumferentially non-uniform. The troughs 48 each extend between about 45 to 90 degrees about the central gallery. Further, the plateau 41 has a through opening 50 extending therethrough generally coaxial with the axis 14 to bring the central oil gallery 37 into direct fluid communication with the space 46 in the pin bore region. As such, the configuration of the floor 40, particularly including the troughs 48 and the through opening 50, plays an instrumental role in regulating the flow of oil within and out of the central oil gallery 37 to provide an optimal oil flow such that optimal cooling results without “cooking” the oil. Further, the lower crown portion 30 has a pair of skirt portions 49 spaced diametrically opposite one another on opposite sides of the pin bore axis 47.

The upper crown portion 16 is formed having an annular outer oil gallery pocket 51 extending from the inner and outer rib free ends 26, 28 upwardly into an upper ring belt region 52 and an annular inner oil gallery pocket 54 extending from the inner free end 26 and upwardly beneath the combustion bowl 20. The lower crown portion 30 is formed, such as in a casting or forging process from steel or other metal, having an annular outer oil gallery pocket 56 extending from the inner and outer rib free ends 36, 38 downwardly into a lower ring belt region 58 and an annular inner oil gallery pocket 60 extending from the inner free end 36 downwardly to the valley or trough 48 of the floor 40. Upon attaching the upper crown portion 16 to the lower crown portion 30, the annular outer oil gallery 39, represented here as being substantially closed, and the inner or central oil gallery 37 is formed. The outer oil gallery 39 is bounded by the outer ribs 24, 34 and inner ribs 22, 32, while the central oil gallery 37 is bounded by the inner ribs 22, 32, the upper combustion wall 18 and the floor 40.

To facilitate cooling the piston 10, one or more oil flow passages are provided in the lower rib 32. For example, as shown in FIG. 1, a pair of oil flow passages 62 extend diametrically opposite one another through the lower inner rib 32 generally along and axially aligned with the pin bore axis 47, and as shown in FIG. 2, another pair of diametrically opposite oil flow passages 64, which are spaced radially from the oil flow passages 62, extend through the lower inner rib 32, shown as extending generally transversely to the pin bore axis 47 to bring the outer oil gallery 39 into fluid communication with the inner or central oil gallery 37. It should be recognized that the oil flow passages 64 can be formed in any radial/angular configuration to channel oil from the outer oil gallery 39 to the central oil gallery 37, and that they need not extend transversely to the oil passages 62. The oil flow passages 62 ascend from a lower most portion of the outer oil gallery 39 to a location spaced axially above the troughs 48 of the floor 40 to channel oil efficiently and directly into the troughs 38, and the oil flow passages 64 ascend from a lower most portion of the outer oil gallery 39 to a lowermost portion of the floor 40. Accordingly, the troughs 48, being fed directly with oil from the oil passages 62, provide a temporary pooling area for the oil so that it can be maintained for a limited period of time within the central oil gallery 37 to maximized its cooling capacity prior to being channeled outwardly from the central oil gallery 37 via the through opening 50.

Further, as shown in FIGS. 4 and 5, a pair of respective inlet and outlet oil flow openings 66, 68 extend through the lower most floor of the outer oil gallery pocket 56 in diametrically opposed relation to one another generally 45 degrees from the axis 47. As such, oil from the crankcase is able to flow upwardly into the outer oil gallery 39 through the inlet opening 66, whereupon the oil is circulated about the outer oil gallery 39 and channeled inwardly through the oil flow passages 62, 64 into the substantially closed central oil gallery 37. Further, oil can flow downwardly out of the outer oil gallery 39 through the outlet opening 68.

Upon the oil being channeled into the central oil gallery 37, a predetermined quantity of the oil is maintained within the central oil gallery 37 and shaken in “cocktail” shaker type fashion before it is channeled outwardly from the central oil gallery 37 via the through passage 50. To facilitate channeling the oil within the central oil gallery 37, a quantity of the oil flows within the closed bottom troughs 48, and thus, this oil is maintained within the central oil gallery 37 and kept from exiting the central oil gallery 37 prior to its expending its full useful cooling capacity. Of course, the oil is continuously flowing within the central oil gallery 37, and so, the oil flowing through the troughs 48 is continuously recycled. Upon expending its full useful cooling capacity, the oil is channeled outwardly from the central oil gallery 37 via the through opening 50.

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 any ultimately allowed claims stemming herefrom, the invention may be practiced otherwise than as specifically described.

Claims

1. A piston, comprising: a piston body extending along a central axis along which the piston reciprocates and having an upper crown portion with an upper combustion wall against which combustion forces act and a lower crown portion with a pair of pin bosses spaced for receipt of a small end of a connecting rod therebetween, said pin bosses having pin bores aligned with one another along a pin bore axis, said upper crown portion and said lower crown portion forming an outer oil gallery and a central oil gallery;said central oil gallery being formed in part by a floor extending radially inwardly from said outer oil gallery to a plateau, said plateau having a through opening and said floor having at least one trough depending axially therein;at least one oil flow passage extending in fluid communication between said outer oil gallery and said central oil gallery; andwherein at least one of said at least one oil flow passage is axially aligned with said at least one trough.

2. The piston of claim 1 wherein said at least one trough includes a pair of diametrically opposite troughs.

3. The piston of claim 2 wherein each one of said pair of troughs has a separate one of said at least one oil flow passage axially aligned therewith.

4. The piston of claim 3 wherein said pair of troughs are axially aligned with said pin bore axis.

5. The piston of claim 1 wherein said at least one of said at least one oil flow passage is axially spaced from said at least one trough.

6. The piston of claim 1 wherein said at least one oil flow passage includes at least one oil flow passage spaced radially from said at least one trough.

7. The piston of claim 1 wherein said at least one trough is axially aligned with said pin bore axis.

8. The piston of claim 7 wherein said at least one of said at least one oil flow passage is axially aligned with said pin bore axis.

9. The piston of claim 1 wherein said at least one trough extends between about 45 to 90 degrees about the central gallery.