Small end con rod guidance piston

A connecting rod for a piston assembly includes first and second guidance members for guiding a piston assembly within a cylinder during piston stroke along a first axis. The guidance members are supported by first and second support ribs extending from a shaft of the connecting rod and include first and second sliding surfaces for contacting side walls of the cylinder. The connecting rod includes an attachment boss disposed at a first end of the shaft and defines a second axis perpendicular to the first axis. The first and second support ribs extend radially outwardly from the attachment boss and are spaced radially about the second axis by approximately 180 degrees.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention relates generally to a piston assembly and a connecting rod for a piston assembly.

2. Description of the Prior Art

Known piston assemblies include a piston head for reciprocation within a cylinder along a piston stroke. A pair of pin bosses depend downwardly from the piston head, with pin bores defined therein. A connecting rod is pivotably attached via a pin to the pin bores, allowing the connecting rod to oscillate as it translates along the piston stroke. As the piston head translates along the piston stroke, and as the connecting rod oscillates, side loads are induced within the assembly. To take these side loads, piston skirts are provided to slide along the side wall of the cylinder. Known piston skirts depend downwardly from the piston head, or extend outwardly from the pin bosses.

SUMMARY OF THE INVENTION AND ADVANTAGES

A connecting rod for a piston assembly is provided. The connecting rod includes a shaft extending between a first end and a second end and an attachment boss disposed at the first end of the shaft. An attachment bore is defined within the attachment boss for receiving a piston pin. At least one guidance member extends from the shaft and has a sliding surface for engaging a side wall of a cylinder.

A piston assembly is also provided. The piston assembly includes a piston head for translation within a cylinder along a first axis. A pair of pin bosses depends downwardly from the piston head in the direction of the first axis. Pin bores are defined therein and are aligned axially with each other defining a second axis. A connecting rod includes a shaft and an attachment boss disposed at a first end of the shaft. An attachment bore is defined within the attachment boss for axial alignment with the pin bores to pivotably connect the connecting rod to the piston head about the second axis. The connecting rod includes at least one guidance member disposed on the shaft for guiding the piston head during translation within the cylinder.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, an engine is generally indicated at20. Referring toFIG. 1, the engine20includes an engine block22with a bore formed within the engine block22defining a cylinder24extending along a first axis A. A piston assembly is generally shown at26, and is disposed within the cylinder24. The piston assembly26includes a piston head28having a top that extends circumferentially about the first axis A. A combustion bowl30is disposed on an upper surface of the top of the piston head28. A ring belt32depends downwardly from the top in the direction of the first axis A. The ring belt32is cylindrical, depending downwardly from the periphery of the top of the piston head28and includes a plurality of ring grooves34extending circumferentially thereon for supporting a plurality of piston rings74. Although a cylindrical ring belt32is shown, it will be understood that other geometries can be used, such as an oval shape, depending on the type of engine20and the shape of the cylinder24used. As can be seen more clearly inFIG. 2, a piston gallery35is defined in the piston head28, radially inward of the ring belt32and axially beneath the combustion bowl30. The piston gallery35receives oil for cooling the piston during operation of the engine20, and can be closed by a coverplate (not shown).

Referring again toFIG. 1, a connecting rod36is pivotably connected about a second axis B to the piston head28and includes a shaft38and an attachment boss40disposed at a first end of the shaft38, sometimes referred to as the small end. At a second end of the shaft38is a crankshaft boss42defining a crankshaft bore44. The crankshaft boss42is pivotably connected to a crank46, which is in turn connected to a crankshaft48. The piston head28is translatable along the first axis A within the cylinder24, reciprocating between end points, referred to as piston stroke. As the piston assembly26translates along the piston stroke, the shaft38of the connecting rod36oscillates about the second axis B, turning the crank46. This converts the reciprocating motion of the piston head28into rotational motion of the crankshaft48, which can be used to rotate a set of vehicle wheels (not shown).

Referring toFIGS. 1-3, the piston head28includes a pair of pin bosses50depending downwardly from the top, and disposed radially inward from the ring belt32. A set of supports52secure the pin bosses50to the piston head28. A pair of pin bores54are defined within the pin bosses50and are aligned axially with each other along the second axis B. The pin bores54are sized to receive a piston pin56. The attachment boss40of the connecting rod36defines an attachment bore58, and is aligned axially with the pin bores54along the second axis B. The attachment boss40is disposed between the pin bosses50. The piston pin56extends along the second axis B and is inserted through the pin bores54and the attachment bore58of the attachment boss40, to pivotably connect the connecting rod36to the piston head28about the second axis B.

Referring toFIG. 4, the connecting rod36is shown in isolation and includes a first guidance member60disposed on the shaft38to guide the piston head28during the piston stroke. The first guidance member60includes a first sliding surface62that engages a side wall of the cylinder24. A second guidance member64is disposed on the shaft38and includes a second sliding surface66. The first and second sliding surfaces62,66each have an arcuate shape. As viewed from a perspective outside of the piston assembly26, the first and second sliding surfaces62,66form a convex arc. Extending downwardly between the top of the sliding surfaces62,66and an intermediate point between the top and bottom, the first and second sliding surfaces62,66curve away from the first axis A. Extending downwardly between the intermediate point and the bottom, the first and second sliding surfaces62,66curve toward the first axis A.

A first support rib68extends from the shaft38perpendicularly to the second axis B to connect the shaft38to the first guidance member60. A second support rib70extends from the shaft38perpendicularly to the first axis A to connect the shaft38to the second guidance member64. The first and second sliding surfaces62,66are supported by the first and second support ribs68,70and spaced perpendicularly from the first axis A, and from a centerline of the shaft38, to contact the side walls of the cylinder24during the piston stroke.

According to the exemplary embodiment, the first and second support ribs68,70extend radially outwardly from the attachment boss40, and the second guidance member64is spaced radially about the second axis B by approximately 180 degrees from the first guidance member60. The intermediate point defining the outermost point of the convex arc on the sliding surfaces62,66is aligned with the intersection between the first and second axes A, B, as well as the intersection between the centerline of the shaft38and the center of the attachment bore58, such that the distances between the sliding surfaces62,66is the greatest at the center of the attachment bore58.

Referring toFIGS. 1 and 4, the convex outer surface of the sliding surfaces62,66contacts the side wall of the cylinder24at a point of contact, and the oscillating motion of the connecting rod36moves the point of contact to various different points along the first and second sliding surfaces62,66. Maintaining a point of contact prevents excess contact between the sliding surfaces62,66and the side wall of the cylinder24from locking, or jamming, the piston assembly26within the cylinder24.

The first and second guidance members60,64slide along the side walls of the engine20cylinders24, just as a piston skirt (not shown) would. However, the piston assembly26in the exemplary embodiment lacks a piston skirt. Therefore, the first and second support ribs68,70are designed to receive the side loads that are incurred during piston stroke and would normally be absorbed by a skirt. To achieve this, the first and second sliding surfaces62,66are disposed substantially beneath the outer profile of the ring belt32. Referring toFIG. 2, a guidance member radius R1is defined as the distance between the first axis A and the outermost point of one of the sliding surfaces62,66in a direction perpendicular to the first axis A. A piston head radius R2is defined as the distance between the first axis A and the outermost point of the ring belt32in a direction perpendicular to the first axis A. The guidance member radius R1is substantially the same as the piston head radius R2. According to the exemplary embodiment, the guidance member radius R1is within approximately ±5% of the piston head radius R2, so, for example, if the piston head radius R2is 500 millimeters, then the guidance member radius R1would be between approximately 475 millimeters and 525 millimeters.

In order to accommodate the loading imposed on the first and second guidance members60,64, the first and second sliding surfaces62,66could be accommodated with a friction reducing coating, or with a bearing surface, such as a rolling or sliding bearing. Additionally, just as the shape of the ring belt32could differ, the geometry of the first and second sliding surfaces62,66would need to accommodate the specific shape of the cylinder24, depending on the type of engine20used.

In addition, the piston head28is constructed without a skirt, and the size of the ring belt32depending from the periphery of the piston head28needs only to be necessary to support the desired number of piston rings74. Referring toFIGS. 2 and 3, the ring belt32includes a lower distal edge72disposed, in the direction of the first axis A, below the lower-most piston ring74. The lower distal edge72does not need to extend, in the direction of the first axis A, beyond the center of the pin bores54. According to the exemplary embodiment, the lower distal edge72extends, in the direction of the first axis A, no further than the top of the pin bores54. Alternatively, the lower distal edge72can extend to some point intermediate the top of the pin bores54and the center of the pin bores54.

Alternatively, as shown inFIGS. 5-6, the connecting rod36could include a ring74surrounding the first and second guidance members60,64. A coating surface can be provided on said first and second guidance members60,64radially inward of said ring74allowing the connecting rod36to slide relative to the ring as it oscillates during the piston stroke. In this alternative embodiment, the first and second sliding surfaces62,66are disposed on the outer surface of the ring74to engage the cylinder24along the piston stroke. The ring74could optionally include a split78for manufacturing and installation purposes.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the appended claims. These antecedent recitations should be interpreted to cover any combination in which the inventive novelty exercises its utility.