GB2171489A

GB2171489A - Fibre reinforced plastics connecting rod

Info

Publication number: GB2171489A
Application number: GB08503536A
Authority: GB
Inventors: Joseph David Aled Hughes; Alan James Wootton
Original assignee: UK Secretary of State for Trade and Industry
Current assignee: UK Secretary of State for Trade and Industry
Priority date: 1985-02-12
Filing date: 1985-02-12
Publication date: 1986-08-28
Also published as: GB8503536D0

Abstract

A connecting rod has a rod member 10, 30 having at one end a U-member 14 which includes a semi- circular portion 15 which defines one half of a big end of the connecting rod. The other half of the big end is defined by a face 20 of a cap member 19. The cap member 19 is positioned between legs 16 of the rod member 10, 30 and is forced towards the rod member 10, 30 by tightening of wedges 26, 65. A bolt 25 passes through the legs 16 and wedges 26 such that when a nut 28 is tightened thereon the wedges 26 are tightened. <IMAGE>

Description

SPECIFICATION Fibre reinforced plastic connecting rods The present invention relates to connecting rods for machines in which reciprocating motion is converted into rotary motion or vice versa.

Machines in which reciprocating motion is converted into rotary motion or vice versa are well-known, two of the best known such machines being internal combustion engines and compressors. Conventionally these machines have been made almost entirely from various metals. A necessary component in the machine is the connecting rod which connects a reciprocating member such as a piston to a rotating member such as a crank shaft. A significant proportion of the energy lost in this type of machine is lost as a result of the need to overcome inertia forces due to the weight of connecting rods used in the machine. There is therefore a continuing need to reduce the weight of these components, this need crashing with the necessity to maintain the structural strength required for the components to withstand the considerable mechanical forces which they are required to transmit.

In recent years the continuing development of Fibre Reinforced Plastics (FRP) materials has led to a state where these materials have sufficient inherent strength and stiffness to be used for the construction of connecting rods.

FRP materials include, for example, glass, carbon, and boron fibres enclosed in a cured resin matrix. They are inherently lighter than metals used for connecting rods, and therefore are potentially useful as a means of reducing connecting rod weights. There are, however, various difficulties which must be overcome before FRP connecting rods can replace conventional metal ones. Metal connecting rods have been in use for many decades, and there is in consequence a great deal of technical knowledge available for their production. This knowledge is not yet available for FRP replacements. For example one of the problems with FRP arises in the area where a con rod is split to allow it to be assembled around a crankshaft.In this region, commonly known as the big end, a metal connecting rod is split along a diameter which lies transverse of a centre line of the rod, and the parts are held together by stud or bolt and nut arrangements. The unavoidable local weakening of the structure due to the consequent bores is difficult to cater for with FRP components. It is frequently impossible to overcome the problem merely by adding more material due to dimensional limitations in engines to which the connecting rods are meant to be fitted.

According to the present invention a connecting rod has a fibre reinforced plastic rod portion and cap portion, the rod portion having a first end and a second end, the first end including means whereby the connecting rod can be connected to a piston and the second end terminating in a semi-circular face and a pair of arms, the semi-circular face having a diameter transverse to a centre line of the rod portion and the arms extending outwardly in the plane of the rod portion and normal to the diameter and each having at its extremity a hole, the holes lying on a common axis, the cap portion having a semi-circular face and a straight face, the straight face being parallel to diameter of the semi-circular face, the diameters of the semi-circular faces of the rod and cap portions being substantially identical, the rod portion and the cap portion being forced together by a bolt passing through the holes in the legs and through wedge means which bear against the straight face of the cap such that tightening of a nut on the bolt forces the rod and cap portions together with their semi-circular faces defining a circle.

The cap portion can be made of metal or can also be of fibre reinforced plastics. In one form of the invention the straight face has therein a groove defined by a surface of revolution, the ends of the groove being part frusto-conical, and the wedge means include frusto-conical bushes on the bolt inward of the arms. Another embodiment of the invention has wedge means in the form of a pair of rectangular cross section wedges having holes therethrough through which the bolt passes.

With this embodiment the wedge bearing against the straight surface of the cap portion is preferably positively located by, for example, a key sliding in a key way in the straight surface.

FRP materials suitable for use with the invention are well-known in the art and will not be described in detail in the present specification.

Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which: Figure 1 is an elevation, partly in section, of a first embodiment of the invention, Figure 2 is a plan view in section along line ll-ll of Fig. 1 of the embodiment of Fig. 1, Figure 3 is a detail in part section along the centre line of the embodiment of Fig. 1, Figure 4 is an elevation of a second embodiment of the invention, Figure 5 is a plan view in section along line IV-IV of Fig. 4 of the embodiment shown in Fig. 4, Figure 6 is an elevation of another construction of the embodiment of Fig. 4, Figure 7 is a plan view, along line VI-VI of the embodiment of Fig. 6, and Fig. 8 is a detail of the embodiment of Fig. 6.

A connecting rod according to the invention (Fig. 1) has a box section FRP compression member 10 formed (2) from two channel sections 10a, 10b welded or bonded together. A rectangular open sided box member 30 encloses the box member 10 and has a first end 11 against which rests a tubular insert 12 by means of which, in use, the connecting rod can be connected to a piston (not shown) and a second end 13 bearing against a U member 14. The U member 14 has a semi-circular portion 15 resting against the second end 13 of the member 30 and a pair of legs 16 extending parallel to a centre line 17 of the member 10. A FRP member 18 encloses the U member 14, box members 30, 10, and tubular insert 12. Holes 27 which have a common axis are formed in the legs 16 and the member 18 where it overlies the legs 16.

A cap portion 19 has a first face 20 of semi-circular section, the diameter being substantially equal to the diameter of the inner face of the semi-circular portion 15 of the U member 14, and a second face 21 which is substantially straight. A channel 22 (see particularly Fig. 3) whose section is a segment of a circle is formed in the straight face 21 and has at its ends frusto-conical sections 23. A bolt 25 on which are mounted two frustoconical bushes 26 passes through the holes 27 and has thereon a nut 28. As the nut 28 is tightened on the bolt 25 the frusto-conical bushes 26 bear against the frusto-conical portions 23 of the channel 22 and the cap portion 19 is forced towards the semi-circular portion 15 of the U member 14 such that the first face 20 of the cap 19 and the inner surface of the U member 14 define a circle within which is mounted a metal bearing shell 29.

In another embodiment of the invention (Figs. 4 and 5) a box section 50 a first end 51 bearing against a tubular insert 52 by means of which, in use, the connecting rod can be secured to a piston (not shown) and a second end 72 which bears against a semicircular portion 53 of a continuous FRP member shown generally at 54. The member 54, in which the fibres extend unidirectionally along the member, extends away from the semi-circular portion 53 to form leg portions 55 and is then folded back on itself to enclose the FRP box section 50 and the tubular insert 52. Holes 56 are formed in the legs 55.

A cap portion 60 has a first face 61 of semi-circular section and a second face 62 of straight section. A key-way shown by the dotted line 63 in Fig. 4 is formed in the face 62. A bolt 64 passes through the holes 56 and has mounted thereon a pair of coacting wedges 65, one of which bears against the straight face 62 and carries a key which mates with the key-way 63. As a nut 66 is tightened on the bolt 64 the nut 66 and bolt 64 act on bushes 71 to force the wedges coact to force the cap portion 60 towards the semi-circular portion 53 such that the first face 61 of the cap 60 and the first face of the semi-circular portion 53 define a circle within which is enclosed a metallic bearing shell 70.

An alternative form of the embodiment described above with reference to Figs. 4 & 5 is illustrated in Figs. 6 to 8. This embodiment has a FRP I-member 100 bearing against a tubular insert 101 and U member 102 similar to those in the embodiment described above with reference to Figs 1 to 3. A FRP member 103, in which the fibres run unidirectionally along the length of the member, surrounds the members 100, 101 and 102, and holes 104 in arms 105 allow a bolt 106 on which are mounted wedge pieces 107 to be passed.

When a nut 108 is tightened on the bolt 106 the wedges 107 coact to force a cap portion 109 towards the semi-circular portion 102 to define a circle within which is clamped a bearing member 110.

It will be realised that many alternative forms of the invention are possible. For example there are many alternative constructions for a rod portion of the connecting rods.

Also the rectangular wedges 65 of Figs. 4 & BR< 5 and 107 of Figs. 6 and 8 have been illustrated and described as having plane holes therein through which bolts 25, 106 pass.

The wedges are in these embodiments forced together by the bushes 71. As one alternative to this arrangement one or other of the wedges can have an internally threaded hole coacting with a threaded section of the bolt, the nuts 28, 108 then being used merely for locking purposes. Many other embodiments will be readily apparent to those skilled in the art.

Claims

1. A connecting rod having a fibre reinforced plastic rod portion and a cap portion, the rod portion having a first end and a second end, the first end including means whereby the connecting rod can be connected to a piston and the second end terminating in a semi-circular face and a pair of arms, the semi-circular face having a diameter transverse to a centre line of the rod portion and the arms extending outwardly in the plane of the rod portion and normal to the diameter and each having at its extremity a hole, the holes lying on a common axis, the cap portion having a semi-circular face and a straight face, the straight face being parallel to diameter of the semi-circular face, the diameters of the semi-circular faces of the rod and cap portions being substantially identical, the rod portion and the cap portion being forced together by a bolt passing through the holes in the legs and through wedge means which bear against the straight face of the cap such that tightening of a nut on the bolt forces the rod and cap portions together with their semi-circular faces defining a circle.