GB2131518A

GB2131518A - Piston pin of internal combustion engine

Info

Publication number: GB2131518A
Application number: GB08328761A
Authority: GB
Inventors: James William Brogdon
Original assignee: Teledyne Industries Inc
Current assignee: TDY Industries LLC
Priority date: 1982-12-09
Filing date: 1983-10-27
Publication date: 1984-06-20
Also published as: IT1209995B; FR2537686B1; FR2537686A1; IT8368267A0; BR8306868A; DE3338847A1; GB8328761D0; GB2131518B

Abstract

An improved pin (34) is disclosed for connecting a piston (14) to a connecting rod (22) in an internal combustion engine. The pin (34) comprises an elongated tubular body having an inner periphery and an outer periphery. The body is dimensioned so that the wall thickness of the body, i.e., the distance between the inner and the outer peripheries, varies along the longitudinal length of the body in an amount to yield an ovalization stiffness proportional to the magnitude of the transverse force imposed upon the pin, thereby to provide constant deformation of the pin along its length during operation of the engine. <IMAGE>

Description

SPECIFICATION Piston pin of internal combustion engine Field of Invention The present invention relates to an improved piston pin for pivotally connecting a piston to a connecting rod in an internal combustion engine.

Description of the Prior Art In reciprocating piston internal combustion engines, a piston is reciprocally slidably mounted within a cylinder in the engine housing. A connecting rod is pivotally secured to the piston at one end and, at its other end, rotatably secured to a land of a crankshaft so that reciprocation of the piston within its cylinder rotatably drives the crankshaft.

In the previously known internal combustion engines, a throughbore is formed through one end of the connecting rod which registers with bores formed in a boss in the piston. A piston pin is then inserted through the registering bores in the piston and connecting rod to pivotally secure the piston and connecting rod together. These previously known connecting pins are typically tubular and cylindrical in shape and have constant diameter inner and outer peripheries.

The longitudinal axis of the piston pin extends perpendicularly with respect to the axis of reciprocation of the piston. Consequently, during operation of the internal combustion engine, a transverse force is imposed upon the piston pin.

The magnitude of the transverse force, however, varies along the longitudinal length of the piston pin. Typically, the transverse force is greatest at the junction between the connecting rod and the piston and diminishes gradually towards each end of the piston pin.

During operation of the engine, the transverse force imposed upon the piston pin causes the pin to deform slightly from its normal cylindrical shape and to an oval shape. The amount of deformation of the connecting pin, however, must be limited in order to limit the amount of stress imposed by the pin deformation on the piston boss as well as connecting rod.

Since the deformation of the piston pin is maximum at or near the junction of the connecting rod and piston, it has been the previous practice to dimension the wall thickness of the piston pin for the maximum expected transverse force imposed upon the piston pin during operation of the engine.

While this previously known practice is effective in preventing damage caused by deformation of the piston pin to the piston boss and connecting rod, the wall thickness of the piston pin is greater than necessary along portions of the piston pin, for example, adjacent its ends, where the transverse force imposed upon the piston pin is less than the maximum expected amount. This in turn results in increased weight for the piston pin which degrades the performance of the engine. Such degradation of the engine performance is particularly critical in aircraft and high speed engines.

Summary of the Invention The present invention provides an engine having an improved piston pin which overcomes or reduces the above-mentioned disadvantages of previously known piston pins.

Unlike previously known piston pins, the wall thickness of the body, i.e., the distance between the inner and outer peripheries, varies along the longitudinal length of the body so that the ovalization stiffness of the body is proportional to the magnitude of the transverse force imposed upon the body during operation of the engine. In the preferred form of the invention, the inner periphery of the body tapers outwardly from a midpoint and toward each end of the body. The tapered inner periphery of the body not only reduces the weight of the piston pin as contrasted with the previously known piston pins, but also provides for constant ovalation or deformation of the piston pin along its length during operation of the engine.

A better understanding of the present invention will be gained by reference to the following detailed description when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views. In the drawings: Figure 1 is a fragmentary cross-sectional view illustrating a preferred embodiment of the present invention; Figure 2 is a longitudinal sectional view of the preferred embodiment of the invention and diagrammatically illustrating the force distribution imposed upon the piston pin during operation of the engine; and Figure 3 is an end view taken substantially along line 3-3 in Figure 2.

Detailed Description of the Drawings With reference first to Figure 1, a portion of an internal combustion engine 10 is shown having a cylinder 12 in which a piston 14 is slidably reciprocally mounted. Two spaced apart piston bosses 1 6 are formed on the inner end 18 of the piston 1 4. In addition, the bosses 1 6 each include a registering transverse bore 20 so that the axes of the bores 20 are perpendicular to the axis of reciprocation of the piston 1 4.

Still referring to Figure 1, an elongated connecting rod 22 is rotatably secured to a land 26 of a crankshaft 28. The other end 30 of the connecting rod 22 is positioned in between the piston bosses 1 6 and includes a throughbore 32 which registers with the piston bores 20. A piston pin 34, which will be subsequently described in greater detail, is inserted through the registering bores 20 and 32 and pivotally secures the piston 14 to the connecting rod 22. Thus, upon reciprocation of the piston 1 4 within its cylinder 12, the piston 14 rotatably drives the crankshaft 28 in the well-known fashion.

With reference now particularly to Figures 2 and 3, the piston pin 34 is shown in greater detail and comprises an elongated tubular body 36 having an outer periphery 38 and an inner periphery 40. The outer periphery 38 of the body 36 is substantially cylindrical in shape and is substantially the same diameter as the piston bores 20 and connecting rod bore 32.

With reference now particularly to Figure 2, during operation of the internal combustion engine, transverse forces are applied to the piston pin 34. These transverse forces are illustrated diagrammatically by the arrows 42 wherein the length of each arrow 42 is representative of the magnitude of the force. These forces are designated Fp to denote the force applied to the pin 34 by the piston. The forces FR are the reaction forces imposed on the pin 34 by the rod 22. As can be seen from Figure 2, the magnitude of the transverse force 42 applied to the piston pin 34 is greatest at its centre and diminishes from a midpoint 37 of the piston pin 34 and outwardly towards the ends of the piston pin 34.

With reference now particularly to Figure 3, the transverse force applied to the piston pin 34 during operation of the engine causes the piston pin body 36 to deform slightly from a cylinder of diameter d, so that its dimension 44 aligned with the direction of the transverse force is somewhat less (d - S) than its dimension 46 (d + N), which is perpendicular to the transverse force.

Consequently, the transverse force causes the piston pin body 36 to become somewhat oval in shape, and this ovalation is greatly exaggerated in Figure 3 of the drawing.

With reference again to Figures 2 and 3, the inner periphery 40 of the pin body 36 is substantially circular in cross-sectional shape but tapers outwardly with an increasing diameter from the midpoint 37 of the pin body 36 and towards the ends of the body 36. Furthermore, the thickness of the body 36 i.e., the distance between the inner periphery 40 and the outer periphery 38 of the body 36, is proportional to the transverse force imposed on the pin body during operation of the engine. Dimensioning the wall thickness of the body 36 in this fashion not only reduces the overall weight of the piston pin 34, but also ensures that the ovalation of the pin body 36 during operation of the engine 1 remains substantially constant along the entire length of the piston pin 34.

It can, therefore, be seen that the piston pin construction of the preferred embodiment provides a low-weight construction which is nevertheless highly effective in operation. The low weight of the piston pin is particularly advantageous for aircraft and/or high-speed engines.

It will be understood, of course, that the distribution of the transverse force applied to the piston pin 34 during operation of the engine and illustrated in the drawing is by way of example only. Furthermore, the distribution of the transverse force along the length of the piston pin may vary for a different piston 14 and connecting rod 22 constructions. In this event, the wall thickness of the piston pin will vary along its length to give an ovalization stiffness proportional to the magnitude of the transverse force distribution in order to achieve a substantially constant deformation of the piston body along its entire length during operation of the engine.

Claims

1. In a reciprocating internal combustion engine of the type having a piston and connecting rod, said piston and said connecting rod having bores adapted to register with each, a pin for pivotally connecting said piston and said connecting rod together comprising: an elongated tubular body having an inner periphery and an outer periphery; said body insertable into said registering bores whereupon said body pivotally connects said piston and said connecting rod together and wherein a transverse force is imposed on said body during operation of the engine which varies in magnitude along the longitudinal length of said body; and wherein said body is dimensioned so that the distance between the inner and outer periphery of the body along length of said body is varied to yield ovalization stiffness proportional to the magnitude of the transverse force imposed on said body during operation of said engine.

2. An engine according to claim 1, wherein the outer periphery of said body is substantially cylindrical.

3. An engine according to claim 2, wherein the inner periphery of said body tapers outwardly from a midpoint and toward each end of said body.

4. An engine according to claim 3, wherein the cross-sectional shape of the inner periphery of said body is circular.

5. An engine according to claim 4, wherein the diameter of the inner periphery of said body increases from a midpoint and toward each end of said body.