PISTON AND CONNECTING ROD COMBINATION

Abstract: A piston (1) and connecting rod (2) are connected together so that compression forces are transmitted from one to the other by mechanical contact between an end (3) of the connecting rod and a projection (4) on the crown of the piston. The piston and connecting rod are secured together by means, such as a pin (5) which allows relative rotation of the piston and connecting rod and which is required to transmit only relatively small tensile forces.

Description: Title: Piston and Connecting Rod Combination This invention concerns the joining of a piston to a connecting rod. In a reciprocating piston -and cylinder machine such as an internal combustion engine, each piston is conventionally joined to its respective connecting rod by means of a gudgeon pin, which acts as a pivot for rotation of the connecting rod relative to the piston while transmitting axial thrust between piston and connecting rod. The greatest thrust transmitted in an internal combustion engine occurs during the power stroke and applies a compression force to the connecting rod. This is a major criterion in design of the gudgeon pin. Tensile forces applied to the connecting rod, which occur during the induction stroke, are comparatively small. The gudgeon pin is normally of steel, and therefore has significant weight. It also requires lubrication, and is subject to wear. Currently, design effort, particularly in the field of internal combustion engines, is aimed at reducing the reciprocating mass, and fibre reinforced plastics materials have come in for particular interest. This is not least because of their low weight and corrosion resistance. It is generally appreciated also that any reduction in the reciprocating mass within an internal combustion engine can have far-reaching advantageous consequences in improving overall performance. Inertia forces and hence bearing areas can be substantially reduced, lubrication simplified and vibrations reduced, resulting in a lighter, quieter and smoother engine. The present invention provides an alternative to the conventional gudgeon pin, and lends itself particularly to the incorporation of fibre reinforced plastics materials. According to the present invention a combination of a piston and a connecting rod is characterised in having a mechanical contact between the piston and connecting rod through which substantially all compression forces but no tensile forces are transferred, and means securing the piston to the connecting rod which allow the connecting rod to rotate relative to the piston and through which all tensile forces but substantially no compression forces are transferred. Z The means securing the piston to the connecting rod can comprise a pin similar to but, in view of the comparatively small forces which it is required to transmit, much smaller and lighter than a gudgeon pin. Alternatively the means can be a resilient hinge fixed both to the piston and to the connecting rod. Resilient hinges for joining a piston to a connecting rod have been suggested in, for example GB Patents 1,330902, 1,128,622 and 317,000 and European Patent Application EP 0018475A1. The hinges in these prior art publications are required to transmit all forces between the piston and the connecting rod whilst the hinges in the present invention are required to transmit only the comparatively small tensile forces. In one convenient form of the invention, the resilient hinge is then in the form of an elongated strip disposed in the form of a zig-zag having two or more limbs. The zig-zag can be disposed to extend transversely of the piston axis in the plane of rotation of the connecting rod, so that rotation of the connecting rod is accommodated primarily by bending of the strip. Alternatively the zig-zag can be disposed to extend transversely of the piston axis in the plane normal to the plane of rotation of the connecting rod, so that rotation of the connecting rod is accommodated primarily by twisting of the strip. As a third alternative, the resilient hinge may comprise two or more zig-zag strips extending parallel to the piston axis, one on either side thereof. In this case, the zig-zags may be positioned in the plane of connecting rod rotation, so that rotation of the connecting rod is accommodated primarily by compression and extension of the zig-zags. Preferably the resilient hinge includes fibre reinforced elastomer, although other materials such as metals may be suitable in some cases. Preferably the connecting rod includes a relatively stiff fibre reinforced polymeric plastics material. The reinforcing fibres are preferably arranged to extend continuously from the hinge into both the piston and the connecting rod. Preferably the elastomer of the flexible hinge and the polymeric material of the connecting rod sure co-polymerised within a transition region linking these components. This provides a chemical bond between the two materials, and a graded transition from one material to the other. The bond can thus be extremely strong, and the absence of an abrupt transition leads to efficient load transfer and more even stress distribution in the transition regions. Crack formation and propagation is thus inhibited, and fracture toughness is increased. Any combination of elastomeric material and polymeric material can be used, depending upon environment and loading, provided that they are mutually compatible, and capable of co-polymerisation. By co-polymerisation is meant that by an appropriate curing process the two materials form a chemically cross-linked structure in the transition region, within which molecules of the elastomeric material combine chemically with molecules of the polymeric material of the connecting rod. Suitable elastomeric materials include polyurethanes, silicone elastomers, natural rubber, polyisoprene, styrene butadiene, butadiene, Polyacrylics, isobutene isoprene (butyl rubber), chloroprene (neoprene), nitrile butadiene, chlorosulϋhonated polythylene, chlorinated polyethylene, ethylene proplene, fluorocarbons, epichlorohydrin, fl 'rosilicones, co-poiyesters, styrene co-polymers and olefins. Suitable polymeric materials for the connecting rod are stiffer than the elastomeric material, and include epoxy resins, polyester resins, phenolic resins, vinyl esters, polyamides, and polyimides. One combination which has been found particularly effective is a polyurethane as the elastomeric material (for low temperature applications) or flourocarbon or silicon (for high temperature applications) together with an epoxy resin material for the connecting rod. Suitable fibres for reinforcement of the elastomer and/or the polymeric material of the connecting rod are those which are compatible with the respective matrix in which they are incorporated, and include fibres of carbon, boron, glass, nylon, polyester, polyimides, aromatic polyamides (eg Kevlar - Trade Mark), metals and mixtures of fibres of these materials. Further aspects of co-polymerised materials are described in my co-pending International Patent Application No PCT/GB 84/00214. The invention will now be further described by way of example only with reference to the accompanying drawings, of which Figures 1 to 5 each illustrate a different embodiment of piston and connecting rod combination in accordance with the invention. In Figure 1 is shown a connecting rod 1 having a hemi-spherical small end 3 arranged to bear against a hemi spherical projection 4 on the under-surface of a crown of a piston 2. The piston 2 is secured to the connecting rod 1 by means of a pin 5 secured to a skirt of the piston and passing through a bore 6 (dotted lines) along an axis of rotation (of the connecting rod 1 relative to the piston 2) of the hemi-spherical end 3. A big end 7 of the connecting rod 1 can be connected to a crank-shaft 8 of a conventional internal combustion engine or compressor by means well known in the art. When a connecting rod 1 and piston 2 assembly is in use in, for example, an internal combustion engine compression forces are ■transmitted between the connecting rod and piston almost entirely through contact between the hemi-spherical small end 3 and the hemi- spherical projection 4. Due to the shape of these items and to the positioning of the pin 5 there is only slight relative sliding or rubbing movement. The pin 5 serves to locate the connecting rod 1 and piston 2 and to serve as a fulcrum for relative rotation thereof, and is required only to transmit the relatively small tensile forces. In Figure 2 there is shown a combined connecting rod 1 and piston 2 joined together by a resilient hinge 13. The connecting rod 1 is formed in two halves 14, 15, each of which is made from carbon fibre reinforced epoxy resin material. The two halves are fixed together by means of transverse bolts 16, 17, and conventional bearing shells 10 are provided at the big end for mounting on the crankshaft of an internal combustion engine (not shown). The crown of the piston 2 is formed of, for example, sintered aluminium or ceramic material. The resilient hinge 13 is formed of carbon fibre reinforced high temperature elastomer eg f]uβrocarbon or silicon elastomer. The right-hand part 14 of the connecting rod 1 is formed integrally with the resilient hinge 13, and to increase the integrity of the bond between these components the carbon fibre reinforcement is carried continuously from the hinge into the part 14 of the connecting rod. The elastomer of the hing 13 and the polymer of the connecting rod part 14 are cured simultaneously after assembly, so that within a transition region 18 the two materials are co-polymerised so as to provide chemical cross-linking and a graded transition from one material to the other. The hinge 13 is fixed to the crown of the piston 2 at 19 by use of an adhesive. Alternatively, the fixing could be achieved by moulding-in, or by carrying reinforcing fibres continuously from the hinge 13 into the crown of the piston 2. The resilient hinge 13 is essentially in the form of a pair of elongate strips, each disposed in the form of a zig-zag having two limbs 21, 22 joined by a reflex portion 23. In this region the reinforcing fibres are mainly aligned in the longitudinal direction of the strip as indicated. The resilient hinge 13 is integrally formed with a piston skirt 24 i and a central projection 25 which makes a mechanical rubbing connection with a central projecting portion 26 of the piston 2. The zig-zag resilient hinges 13 are disposed in the plane of rotation of the connecting rod 1, and thus rotation of the connecting rod is accommodated primarily by bending of the limbs 21, 22 and of the reflex portion 23. The resilient hinges 13 are however incapable of transmitting any substantial load between the piston 2 and connecting rod 1. This function is therefore performed by the mechanically contacting portions " 25, 26, which have to tolerate only a small degree of relative sliding or rubbing movement. The embodiment shown in Figure 3 is in most respects similar to that shown in Figure 2, and like reference numerals are used to denote like parts, although as a detail difference the piston crown extends to include a full skirt portion 27, and the bond region 19 extends over its full length. However, in this case the zig-zag resilient hinges 13 are disposed in the plane perpendicular to the plane of rotation of the connecting rod 1. Thus rotation of the connecting rod is accommodated primarily by twisting of the limbs 21, 22 and of the reflex portions 23. In Figure 4 there is shown a further embodiment of the invention comprising a connecting rod 31 of carbon fibre-reinforced epoxide joined to an aluminium piston crown 32 by means of a resilient hinge 33 of carbon fibre-reinforced high temperature elastomer, such as fluαrocarbon. The connecting rod 31 is split longitudinally along the line 34 which extends from its extreme lower «nd almost to its upper end. At the lower end the two halves of the connecting rod are secured together by means of a machine screw 35 which is screwed into a threaded insert 36 moulded into the connecting rod. The two halves of the connecting rod 31 can thus, on removal of the screw 35, be sprung apart so as to enable assembly and replacement of the flanged big end bearing 37. Within the connecting rod 31, the bulk of the fibres are aligned longitudinally, -some fibres being carried continuously around the upper end as indicated at 38 to increase the strength of the joint between the two halves in this region. The piston crown 32 is provided with a carbon fibre-reinforced epoxide skirt 39. Beneath the centre of the.crown 32, theςe is provided a divergent projection 40, and a screw threaded bore 41 which receives a machine screw 42. The resilient hinge 33 comprises two zig-zag strips 43 extending parallel to the piston axis, one on each side of the axis and in the plane of the connecting rod 31. The strips 43 are joined together at their upper ends by a bridge piece 44 which is moulded around the divergent portion 40 so as to be secured to the piston crown 32. The strength of the fixing is increased by the screw 42 which passes through the bridge piece 44. The reinforcing fibres within the hinge 33 are mainly aligned longitudinally along the length of the strip, although a proportion of angled fibres is also desirable. The strips 43 are also joined at their lower ends by a further bridge piece 45 having a central aperture 46 through which the upper end of the connecting rod 31 passes, and is secured therein by adhesive. Alternatively, the connecting rod may be insert moulded and/or co-polymerised with the resilient hinge, in the region of the aperture 46, in the manner already described, and the reinforcing fibres are preferably carried continuously from the connecting rod into the hinge in this region. The head of the screw 42 bears upon the upper end of the connecting rod, and this provides a mechanical contact through which a major proportion of the load is transferred between the piston and the connecting rod. In this embodiment, rotation of the connecting rod relative to the piston is accommodated primarily by compression and extension of the zig-zag strips 43. In Figure 5 there is shown another embodiment similar in many respects to that of Figures2 and 3 , and like reference numerals are used for like parts. However, in this embodiment there is provided a resilient hinge of a design which is substantially different from the hinge 3 of Figs 2 or 3. In this example the hinge is formed mainly of carbon fibre reinforced epoxide material, and comprises a piston skirt portion 51 adhesively bonded at 19 to the crown of the piston 2. Insert moulding would provide an alternative fixing method. From the lower edge of the skirt there extends horizontally inwards a limb 52 of rectangular or other form, which then extends upwards at 53 and invards at 54 to join the upper portion of the half connecting rod 14, with which it is* integrally formed. The carbon fibre reinforcement is aligned longitudinally with respect to the line described, and is continued into the half 14 of the connecting rod. Within the upwardly extending portion, there is included a rectangular limb portion 55 of polyurethene elastomer (for room temperature applications). This is co-polymerised at 56 and 57 with the adjacent expoxide material in the manner already described, and the reinforcing carbon fibres are continued through the two materials. In this embodiment, relative rotation between the connecting rod and the piston are thus accommodated primarily by flexure of the annular portion 55. It will be realised that there are many alternative embodiments within the scope of the present invention. For example in the embodiment as described above with reference to Figure 1 the connecting rod 1, other than in respect of its attachment to the piston 2, is of the conventional construction well known in the art of metal connecting rods. Clearly, fibre reinforced plastic connecting rods similar to those as described with reference to Figures 2 to 5 can be adopted for attachment to the piston 2 in the manner described with, reference to Figure 1. Other appropriate constructions utilising fibre reinforced plastics material will be apparent to those skilled in the art.

Claims: Claims What is claimed is: 1. A combination of a piston and a connecting rod characterised in having a mechanical contact between the piston and connecting rod through which substantially all compression forces but no tensile forces are transferred, and means securing the piston to the connecting rod which allow the connecting rod to rotate relative to the piston and through which all tensile forces but substantially no compression forces are transferred. 2. A combination as claimed in Claim 1 characterised in that the piston is secured to the connecting rod by means of a pin. 3. A combination as claimed in Claim 2 characterised in that the mechanical contact occurs between a hemi-spherical small end of the connecting rod and a hemi-spherical projection from a crown of the piston. 4. A combination as claimed in Claim 3 charaδterised in that the pin passes through a bore along the axis of the hemi-spherical small end of the connecting rod. 5. A combination as claimed in Claim 1 characterised in that the piston is secured to the connecting rod by means of a resilient hinge. 6. A combination according to Claim 5 characterised in that the resilient hinge is in the form of an elongate strip disposed in the form of a zig-zag having two or more links. 7. A combination according to Claim 6 characterised in that the zig-zag is disposed to extend transversely of the piston axis in the plane of rotation of the connecting rod, so that rotation of the connecting rod is accommodated primarily by bending of the strip. 8. A combination according to Claim 6 characterised in that the zig-zag is disposed to extend transversely of the piston axis in the plane normal to the plane of rotation of the connecting rod, so that rotation of the connecting rod is accommodated primarily by twisting of the strip. 9. A combination according to Claim 6 characterised in that the resilient hinge comprises two or more zig-zag strips extending parallel to the piston axis, one on either side thereof. 10. A combination according to Claim 9 characterised in that zig¬ zags are positioned in the plane of connecting rod rotation, so that rotation of the connecting rod is accommodated primarily by compression and extension of the zig-zags. 11. A combination according to any one of Claims 5 to 10 characterised in that the resilient hinge includes fibre reinforced elastomer. 12. A combination according to any one preceding Claim characterised in that the connecting rod includes a relatively stiff fibre reinforced polymeric plastics material. 13. A combination according to Claim 11 or Claim 12 as dependent on any one of Claims 5 to 9 characterised in that reinforcing fibres are arranged to extend continuously from the hinge into both the piston and the connecting rod. 14. A combination according to any one of Claims 5 to 10 characterised in that the flexible hinge comprises elastomer and the connecting rod comprises polymeric material, and the elastomer of the flexible hinge and the polymeric material of the connecting rod are co-polymerised within a transition region linking these components, so as ' to provide a chemical bond between the two materials, and a graded transition from one material to the other. 15. A combination according to Claim 14 characterised in that the elastomer of the flexible hinge is selected from the group comprising polyurethanes, silicone elastomers, natural rubber, polyisoprene, styrene butadiene, butadiene, polyacrylics, isobutene isoprene (butyl rubber), chloroprene (neoprene), nitrile butadiene, chlorosulphonated polyethylene, chlorinated polyethylene, ethylene propylene, fluαrocarbons, epichlorohydrin, fluorosilicones, co-polyesters, styrene co-polymers and olefins. 16. A combination according to Claim 14 or 15 characterised in that the polymeric material of the connecting rod is selected from the group comprising epoxy resins, polyester resins, phenolic resins, vinyl esters, polyamides, and polyimides. 17. A combination according to any one of Claims 14 to 16 characterised in that the reinforcing fibres are selected from the group comprising fibres of carbon, boron, glass, nylon, polyester, polyimides, aromatic polyamides, metals and mixtures of fibres of these materials.

Inventors: CHANDLER ERIC FREDERIC, HUGHES JOSEPH DAVID ALED, SCOWEN GEOFFREY DAVID, CHANDLER, ERIC, FREDERIC, HUGHES, JOSEPH, DAVID, ALED, SCOWEN, GEOFFREY, DAVID
Applicants: SECRETARY TRADE IND BRIT, THE SECRETARY OF STATE FOR TRADE AND INDUSTRY IN H
Application year: 1986
Main classification: F16J1
IPC codes: F02F7, F16J1