GB2180321A

GB2180321A - Reciprocating piston assembly

Info

Publication number: GB2180321A
Application number: GB08522300A
Authority: GB
Inventors: Derek Frost
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1985-09-09
Filing date: 1985-09-09
Publication date: 1987-03-25
Also published as: GB8522300D0

Abstract

The invention proposes forming the small end of the connecting rod 50 with a bearing surface 52 which makes direct contact with a matching surface 26 the underside of the piston crown, force being transmitted through this surface instead of through a gudgeon pin. This construction has the advantage of reducing weight and lower the overall engine height. <IMAGE>

Description

SPECIFICATION Reciprocating piston assembly The present invention relates to a reciprocating piston assembly and is particularly applicable to an assembly of a piston and a connection rod for use in an internal combustion engine.

In a conventional piston, a bore is provided in the side of the piston for receiving a gudgeon pin. The forces acting between the piston and the connecting rod are transmitted entirely through the gudgeon pin.

In such a construction, the gudgeon pin and the bore in the piston in which it is received must be of sufficient strength to withstand these forces, which adds considerably to the weight of the piston and connection rod.

The present invention seeks to provide a connection between a piston and a connecting rod of a reciprocating piston machine which enables the inertia of the moving parts to be reduced.

According to the present invention, there is provided a piston and connecting rod assembly for a reciprocating piston machine wherein the end surface of the connecting rod is contoured and and bears directly upon the underside of the piston crown.

Because the connecting rod bears directly on the piston, the forces transmitted through the connection pin are minimal and therefore the latter acts primarily as a fulcrum for the connecting rod. In an internal combustion engine, the only part of the cycle during which a force is transmitted through the connecting pin is during a part of the induction stroke and these loads are relatively small.

It is preferred to connect the piston to the connecting rod by means of two tapered plungers journalled in the piston and resiliently urged in the direction of correspondingly tapered conical or part-conical surfaces in the connecting rod, the latter surfaces being concentric with the contoured end surface of the connecting rod.

The two plungers may conveniently be jour nalled in two lugs projecting from the underside of the piston crown.

The plungers need not be received in continuous tapered bores in the connecting rod and instead the connecting rod may be formed with part-conical cutouts for receiving the plungers.

The plungers may be retained by a spring encircling them or by means of two separate springs inserted into the space between the piston skirt and the lugs.

An advantage of the construction proposed in the invention is that the height of the cylinder may be reduced for any given displacement. Furthermore the wear on the sides of the cylinder may be reduced both because of the improved geometry and because of the reduced inertia of the moving parts.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section through a piston and connection rod assembly of the invention, and Figure 2 is a second section through a piston and connecting rod assembly taken on the line Il-Il in Fig. 1.

In the drawings, there is shown a piston and connecting rod assembly comprising a piston 10 and a connecting rod 50. The piston 10 has a crown 12 and a skirt 14. In the usual manner, grooves 16 are formed in the side of the piston for receiving piston rings (not shown).

Holes 20 are formed in the piston skirt 14 below the piston ring grooves 16 these being coaxial with bores 22 formed in lugs 24 projecting from the underside of the piston crown. The underside of the piston crown has a rounded surface 26 which is also concentric with the axis of the bores 22.

The connecting rod 50 has at its upper end as viewed, normally termed the small end, a rounded bearing surface 52 which bears against the rounded surface 26 on the underside of the piston crown to transmit forces between the piston and the connecting rod.

To retain the connecting rod in contact with the piston, two tapered plungers 54 are located in the bores 22 in the lugs 24. The tapered ends of the plungers 54 are urged by springs 56 against part conical surfaces 58 formed as cutouts in lateral extensions 60 of the connecting rod 50. The cutouts 58 and the lateral extensions are best seen in the section of Fig. 2.

In place of the two springs 56 which are inserted through the holes 20 in the piston skirt, it is alternatively possible to employ a single spring encircling the two plungers 54.

In operation, the connecting rod 50 will bear directly on the underside of the piston crown during all phases of the four strike cycle when a force is being applied to the piston crown, and will pivot about the plungers 54.

On the first half of the induction stroke the piston 10 will be pulled down the cylinder bore via the tapered plungers 54 located in the lugs 24. These plungers 54 should have a small angle of taper in order not to require too great a spring force to retain the plungers in position during this part of the cycle. The angle of taper should also be chosen not to introduce too high a contact force between the plungers 54 and the conical tapers in the connecting rod 50. This means a balance between the forces resulting from the piston inertia and the forces exerted by the retaining springs acting through the tapered surfaces.

The radius on the connecting rod small end is struck from the centre of the two conical plungers 54. These conical ends of the plungers 54 need only be introduced for about 200 over the top of the small end to perform their function. This is sufficient to prevent the separation of the connecting rod from the piston. The radius on surface 52 at end of the connecting rod 50 need only extend over an arc of around 100" which will permit a connecting rod angle that will embrace the throw of the crank and retain good bearing area with the piston 10.

The centreline of the plunger bores 22 in the two lugs 24 must be positioned on the centreline of the minimal radius in the underside of the piston crown or be less than this.

This will avoid a gap between the connecting rod end and permit a bedding in when plungers are not in full 200 contact with the connecting rod tapered cutouts.

It will be appreciated that the diameters of the conical plungers may smaller than the conventionally used gudgeon pin and the plungers may be made hollow for lightness.

The bearing surface between the connecting rod and the piston may be splash lubricated by the oil in the sump. Heat transmission through the piston crown may be high and for this reason it may be advantageous to incorporate a ceramic liner on the underside of the piston crown both to act as a bearing surface and to reduce heat transmission to the connecting rod 50.

By virtue of the proposed construction, the weight of the piston and connecting rod assembly can be reduced and this can reduce the shaking of the engine when it is running.

Furthermore, the height of the engine can be reduced as there is no space between the top of the connecting rod and the underside of the piston crown.

Claims

1. A piston and connecting rod assembly for a reciprocating piston machine wherein the end surface of the connecting rod is contoured and and bears directly upon the underside of the piston crown.

2. An assembly as claimed in claim 1, wherein the piston is connected to the connecting rod by means of two tapered plungers journalled in the piston and resiliently urged in the direction of correspondingly tapered conical or part-conical surfaces in the connecting rod, the latter surfaces being concentric with the contoured end surface of the connecting rod.

3. An assembly as claimed in claim 2, wherein the two plungers are journalled in two lugs projecting from the underside of the piston crown.

4. An assembly as claimed in claim 3, wherein the plungers are retained in position by means of a spring encircling the two plungers.

5. An assembly as claimed in claim 3, wherein the plungers are retained in position by means of two separate springs inserted into the space between the piston skirt and the lugs.

6. An assembly as claimed in any preceding claim, wherein a ceramic liner is arranged on the underside of the piston crown.

7. A piston and connecting rod assembly substantially as herein described with reference to and as illustrated in the accompanying drawings.