Piston with central directional oil flow and wrist pin lubrication feature and method of construction thereof

A piston has a piston body extending along a central axis. The piston body has an upper crown portion and a lower crown portion. The upper crown portion has an upper combustion wall and an at least one annular upper rib depending from the upper combustion wall to a free end. The lower crown portion has at least one annular lower rib extending to a free end that is fixed to the at least one upper rib and an inner gallery floor extending radially inwardly relative to the at least one lower rib. The upper crown portion has an upper post depending from the upper combustion wall along the central axis to a free end. The lower crown portion has a lower post extending upwardly from the inner gallery floor along the central axis to a free end. Together, the upper post and the lower post form a labyrinth passage.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to pistons for internal combustion engines, and more particularly to pistons having wrist pin lubrication features.

2. Related Art

Piston constructions having one or two (dual gallery) generally closed oil cooling galleries are known. Dual gallery pistons have an annular, radially outer gallery and a central gallery formed between upper and lower crown portions, wherein the central gallery is typically formed as an open gallery beneath the combustion bowl wall. 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 through an opening in a lower inner gallery floor between laterally spaced pin bosses. The outer gallery is particularly effective in cooling an outer ring belt region of the piston, while the central gallery is particularly effective in cooling a central crown region, formed in part by an upper combustion wall, which is directly exposed to hot combustion gases. Although these gallery constructions are generally effective in cooling the piston, the oil flow dynamics through the galleries can be improved, with particular regard to the central gallery, thereby enhancing the ability to cool pistons in use.

SUMMARY OF THE INVENTION

A piston has a piston body with a central axis along which the piston body reciprocates within a cylinder bore. The piston body has an upper crown portion with an upper combustion wall against which combustion threes directly act in the cylinder bore and an at least one annular upper rib depending from the upper combustion wall to a free end. The piston body further includes a lower crown portion having at least one annular lower rib extending to a free end that is fixed to the at least one upper rib. The lower crown portion further includes an inner gallery floor extending radially inwardly relative to the at least one lower rib and a pair of pin bosses depending generally from the inner gallery floor with a space provided between the pin bosses for receipt of a small end of a connecting rod. The upper crown portion has an upper post depending from the upper combustion wall along the central axis to a free end. The lower crown portion has a lower post extending upwardly from the inner gallery floor along the central axis to a free end. The free end of the upper post and the free end of the lower post form a labyrinth passage.

In accordance with another aspect of the invention, the upper and lower post extend axially beyond one another and maintain entire clearance with one another.

In accordance with another aspect of the invention, the lower crown post has an oil flow passage extending along the central axis.

In accordance with another aspect of the invention, the lower crown post has an oil flow passage extending substantially transversely to the central axis.

In accordance with another aspect of the invention, a method of constructing a piston is provided. The method includes providing an upper crown portion having an upper combustion wall against which combustion forces directly act in the cylinder bore and at least one annular upper rib depending from the upper combustion wall to a free end with an upper post depending from the upper combustion wall along the central axis to a free end. Further, providing a lower crown portion having at least one annular lower rib extending to a free end and an inner gallery floor extending radially inwardly relative to the at least one lower rib with a pair of pin bosses spaced for receipt of a small end of a connecting rod and having a lower post extending upwardly from the inner gallery floor along the central axis to a free end. Then, fixing the at least one upper rib of the upper crown portion to the at least one lower rib of the lower crown portion and forming a labyrinth passage between the free end of the upper post and the free end of the lower post.

In accordance with another aspect of the invention, the method includes extending the free end of the upper post and the free end of the lower post axially beyond one another.

In accordance with another aspect of the invention, the method includes maintaining the upper post and the lower post in spaced relation from one another.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

Referring in more detail to the drawings,FIG. 1illustrates a piston10constructed in accordance with one presently preferred aspect of the invention. The piston10has a piston body12, such as can be constructed of steel, for example, extending along a central axis14along which the piston body12reciprocates within a cylinder bore (not shown). The piston body12includes an upper crown portion16having an upper combustion wall18, represented here, by way of example and without limitation, as providing a recessed combustion bowl20, against which combustion forces directly act in the cylinder bore. The upper crown portion16has at least one, and shown here as a pair of annular upper ribs, referred to hereafter as an upper inner rib22and upper outer rib24, depending generally from the upper combustion wall18to respective free ends26,28. The piston body12further includes a lower crown portion30having at least one, and shown here as a pair of annular lower ribs, referred to hereafter as a lower inner rib32and lower outer rib34, extending to respective free ends36,38arranged in circumferential alignment and in fixed engagement with the upper free ends26,28. The lower crown portion30further includes an inner gallery floor40extending radially inwardly relative to the lower inner rib32and a pair of pin bosses42,44depending generally from the inner gallery floor40. The pin bosses42,44have respective pin bores43,45aligned along a central horizontal pin axis47with a space46provided between the pin bosses42,44for receipt of a small end of a connecting rod (not shown). The upper and lower crown portions16,30interact to provide a central directional oil flow control member extending coaxially along the central axis14, referred to hereafter as oil flow control member48, having a central wrist pin lubrication feature, referred to hereafter as lubrication feature50. The flow control member48extends through an inner gallery, also referred to as central gallery52of the piston10, thereby providing the central gallery52having a toroid configuration. As such, the oil received in the central gallery52is caused to flow along a predetermined dynamic flow path indicated generally by the arrows53. Accordingly, the oil is directed to flow along a generally continuous, uniform path throughout the central gallery52, thereby facilitating uniform, efficient cooling of the upper combustion wall18. In addition, the lubrication feature50provides a regulated or metered flow of the oil from within the central gallery52to the space46, thereby avoiding overheating (“cooking”) the oil within the central gallery52and promoting continuous lubrication of the wrist pin joint at the small end of the connecting rod.

The upper crown portion16is formed having an annular outer oil gallery pocket58extending from the inner and outer upper rib free ends26,28upwardly into an upper ring belt region60adjacent the upper combustion wall18. The upper crown portion16is also formed having an annular inner oil gallery pocket62extending from the upper inner rib free end26upwardly and immediately beneath the combustion bowl20. In addition, the upper crown portion16has an upper post64depending coaxially along the central axis14from the upper combustion wall18. The upper post64forms a portion of the flow control member48and is formed having a predetermined length extending to a free end65and a predetermined outer surface configuration.

The lower crown portion30is constructed having an annular outer oil gallery pocket66extending from the inner and outer lower rib free ends36,38downwardly into a lower ring belt region68, which, in combination with the upper outer oil gallery pocket58forms an outer gallery56. The lower crown portion30also has an annular inner oil gallery pocket70extending from the inner lower rib free end36downwardly, which, in combination with the upper inner oil gallery pocket62forms the central gallery52. An oil flow passage72is formed extending from one of the pin bores43upwardly into the bottom most region of the outer oil gallery pocket66. As such, oil is pumped from the pin bore43upwardly into the outer gallery56. Further, lower crown portion30is represented here as having a pair of oil flow passages54extending through the lower inner rib32. The oil flow passages54are formed, by way of example and without limitation, descending generally from a lowermost region of the central gallery52radially outwardly to a lower most region of the outer gallery56. In addition, the lower crown portion30has a lower post74that forms a portion of the flow control member48. The lower post74extends upwardly from the inner gallery floor40coaxially along the central axis14in coaxial alignment with the upper post64. The lower post74is formed having a predetermined length and outer surface configuration extending to a free end75. The length and outer surface configuration are such that upon fixing the upper crown portion16to the lower crown portion30, such as via friction welding, for example, the free end65of the upper post64do not interfere with one another. In the embodiment illustrated, by way of example and without limitation, a counter bore76is formed in one of the posts64,74, and shown here, by way of example and without limitation, as being formed in the lower post74, to receive the free end65of the upper post64in a clearance fit therein. The counterbore76has a diameter larger than the outer diameter of the upper post64and a depth great enough to provide a clearance between the upper post64and the lower post74. As such, upon fixing the upper crown portion16to the lower crown portion30, a labyrinth seal77having a serpentine flow path is established between the upper post64and the lower post74. Accordingly, the upper post64and lower post74remain detached and spaced radially and entirely from one another, though the upper post free end65and the lower post free end75extend axially beyond one another. As such, the upper and lower posts64,74do not having any effect on the ability to fix the upper crown portion16to the lower crown portion30.

The lower post74further includes the lubrication feature50, shown here, by way of example and without limitation, as being generally T-shaped, as viewed in axial cross-section, having a vertically extending first oil flow passage, also referred to as a central oil flow passage78, extending coaxially along the central axis14. The oil flow passage78is intersected by a horizontally extending second oil flow passage, also referred to as cross opening80, below the counterbore76, with the cross opening80extending generally transversely to the central axis14through the lower post50to diametrically opposite sides of the annular central gallery52. The height of the cross opening80can be varied in manufacture as desired to provide the desired regulation of oil flow through the oil flow passage78, and to facilitate establishing a predetermined depth or pool of oil in the lower portion of the central gallery52. The oil within the central gallery52flows through the oil flow passage78to facilitate lubricating the wrist pin joint formed at the small end of the connecting rod (not shown).

In accordance with a method of construction of the piston10, as eluded to above, the method includes forming the respective upper and lower crown portions16,30and fixing them to one another, such as via forming respective friction weld joints82,84between the inner rib free ends26,36and the outer rib free ends28,38, for example. While forming the friction weld joints82,84, the upper post64and the lower post74remain entirely spaced from one another, though the respective free ends65,75are caused to extend axially beyond one another, thereby forming the labyrinth seal passage77extending between the upper and lower posts64,74. Accordingly, with the upper post64and lower post74being entirely spaced from one another, they have no affect on the friction welding process.

InFIG. 2, a portion of a piston110is shown constructed in accordance with another aspect of the invention, wherein the same reference numerals as used above, offset by a factor of 100, are used to identify like features. The piston110has an upper crown portion116fixed to a lower crown portion130, such as via a friction welding process, as described above. The notable difference with the piston110is in the configuration of an upper post164and a lower post174. The upper post164depends coaxially along a central axis114over a predetermined length from an upper combustion wall118to a free end165and has recessed pocket90extending upwardly into the free end165along the central axis114therein. The pocket90is constructed having a predetermined depth to a blind bottom surface, shown here, by way of example and with limitation, as extending to, or substantially to the upper combustion wall118. Further, the pocket90has a predetermined diameter to receive the lower post174in clearance fit therein. Accordingly, a labyrinth seal passage177is established between the upper and lower posts164,174.

The lower post174extends coaxially upwardly along the central axis114a predetermined distance from an inner gallery floor140of the lower crown portion130to a free end175. The lower post has an oil flow passage178formed as a central through passage extending coaxially along the central axis114through the free end175. The lower post174is constructed having a predetermined length to remain axially spaced from the blind bottom surface of the pocket90and outer surface configuration or diameter to maintain a clearance fit within the pocket90of the upper post164, while the free end165of the upper post164remains axially spaced from the inner gallery floor140, thereby forming the serpentine labyrinth seal passage177. The height of the lower post174can be varied in manufacture as desired to provide the desired clearance relative to the blind bottom surface of the pocket90, thereby allowing the rate of oil flow through the oil flow passage178to be regulated, and further allowing a predetermined depth or pool of oil to be substantially maintained in a lower portion of a central gallery152. Further, the diameter and radial width of the oil flow passage178can be sized to provide the desired flow rate of oil therethrough, thereby regulating the degree of oil heating within the central gallery152, and thus, controlling the cooling of the piston110. As with the previous embodiment, the upper post164and lower post174have no effect on the friction welding process.