GB2118682A

GB2118682A - Connecting rod structure

Info

Publication number: GB2118682A
Application number: GB08310595A
Authority: GB
Inventors: Mario Palazzetti; Pierangelo Campagna
Original assignee: Fiat Auto SpA
Current assignee: Fiat Auto SpA
Priority date: 1982-04-19
Filing date: 1983-04-19
Publication date: 1983-11-02
Also published as: ES281062Y; ES281062U; FR2525299A1; IT8267510A0; DE3313365A1; GB8310595D0; IT1155160B

Abstract

Connecting rod (1) includes a shank (2) showing at its opposed ends a first bearing seat (9) which can be engaged by an element in rotary movement and a second bearing seat (12) fit for being engaged by an element moving in an alternate straight direction. The connecting rod (1) includes further a belt (3) assembled outside the shank (2) so that said shank (2), when in operation, is always under compression and belt (3) is always under tension. <IMAGE>

Description

SPECIFICATION Light improved connecting rod The present invention concerns a light improved connecting rod.

As known, the connecting rod is an element for connection between a rotary component and a component with alternate straight line movement.

The connecting rod comprises essentially three main portions viz. the big end, the small end and the body or shank. The big end is the portion which evidences a rotary movement and can be therefore open or closed. The open big end has a removable portion, called cap, which is connected to the remaining portion through two or four screws which are gauged and well fixed. In view of the fact that such screws are impact stressed in operation, they must be very carefully manufactured; it is furthermore necessary to arranged a framing containing such screws, which also warrants the indeformability of the cap. The big ends of the rod, when closed, are only used when it appears possible to insert the big end itself directly into the rotary component; it is obvious that in such a case both screws and framing are no longer necessary.The small end of the connecting rod is atthe opposed end of the big end and performs, as already said, an alternate straight line movement, having different structures, e.g. eye shaped ones, fork shaped ones etc. The body or shank is the intermediate portion between the big and the small end; its section can be circular, elliptical, double T shaped and is generally stressed by tensile and compression stress, having a sinusoid progression. This type of stress implies a fatigue shaping of this portion of the connecting rod and, in consequence of this, the cross section of the shank of the traditional connecting rods is quite notable with a considerable use of material.

The material for the manufacture of the connecting rods is generally high quality homogenous steel, which is hammered or peened or stamped: occasionally one uses also steel castings and light alloys. Due to the rather high weight of the connecting rod, it is necessary to have on the rotary component (generally the crankshaft) some counterweights, which also have a decently high weight.

There are also on the market some kinds of rods known as light connecting rods, which are obtained from peculiar materials, although according to the classical line described above.

Scope of the present invention is that of building a light connecting rod, which under equal stresses is evidencing a notably better performance in operation, whilst having a limited weight as against the kinds of connecting rods already known.

The above aim is reached through the present invention, which concerns a connecting rod characterized by the fact of including: - a support having on its opposing ends a first seat which can be engaged by a rotary element and a secont seat which can be engaged by an element moving itself in a straight line; and - involving means assembled outside said support which cause an exchange of mutual pressures so that said support is stressed in operation only by the compression of said moving elements whilst the said involving means are under tensile stress only.

To better understand the present invention, we are now going to describe a preferential embodiment, purely as non limitative example, and with reference to the enclosed drawings on which: Fig. 1 is an elevation of a connecting rod manufactured according to the guiding lines of the present invention; Fig. 2 is a cross section following line 11-Il of the figure 1; and Fig. 3 is a perspective view of a detail of the connecting rod appearing on figures 1 and 2.

Referring us in particular to figure 1, N01 shows on the whole a connecting rod according to the guiding lines of the present invention and including essentially a support 2, a belt 3, with right angle cross section, longitudinally involving support 2, and a belt stretching frame 4 fixed to support 2 and entrusted with the transmission of a preloading to the belt 3. More particularly the support 2 evidences a cut big end 6 formed by a fixed portion 7 and a removabie cap 8 defining as a whole a circular seat 9 fit for engagement in operation into an element (not appearing on the drawing) having a rotary movement.The support 2 has further a small end 11 at the opposed end of the big end 6 and defining a circular seat 12 fit for engaging in operation a non illustrated element with alternate straight line movement.The big end 6 and the small end 11 are connected by a shank or body 1 3 having a double T shaped cross section and evidencing near the fixed portion 7 of the big end 6, two opposed fins 14, 1 5 in transversal extension and building up anchorage means of the belt stretcher's frame 4. As can be observed on the figure 2, in part of the outer surface of the big end 6 a groove is dug (N01 6) with cross section performed at right angle, which is engaged by belt 3.

Referring us now in particular to figure 3, the belt stretching frame 4 is formed by two couples of walls 19, 20 and 21, 22 which are facing each other; the walls 19 and 20 are parallel, having the shape of an isosceles trapezium with skew curved sides and show, on the level of their largest base, rectangular fins 24, 25, each of which is folded in operation on the relevant fin 14, 1 5 in extension from shank or body 13. The walls 21 and 22 of the frame 4 are welded along the skew rims of the walls 19, 20, so as to have a concavity looking outside.

In operation belt 3 is assembled on the support 2 and preloaded under tensile stress through the belt stretching frame 4, inserting the latter from the side of the small end 11 and folding subsequently the fins 24 and 25 on the relevant fins 14, 1 5, in extension from the shank body 13.

In particular the tensile stress preloading the belt 3 is such that is prevents support 2 from being unloaded on the top dead centre; consequently the belt 3 is never to remain unloaded under the maximum effect of the compression strength acting upon support 2. Due to the belt 3, the big end 6 and the small end 11 of the support 2 are only stressed by a radial compression load evenly distributed along the entire circumference, while shank 13 is only compression stressed in longitudinal direction. In consequence of this the possibility of selecting materials for building the support 2 increases notably, because same can be sized having only in mind the yield point under compression and no longer the fatigue stress.In this context the materials which can be selected for building the support 2 are, besides steel, titanium, magnesium, aluminium and their alloys and also glass and/or ceramic material. As far as belt 3 is concerned it could be conveniently built by using composite material with a metallic or plastic matrix (thermo-hardening under high temperatures) with stiffening formed by glass fibers, aramide, metal etc.

In use the rod experiences varying compressive and tensile loads. The tensile load is maximum at the "top-dead-centre" position when the piston is at its highest point. The belt is tensioned to keep the support 2 always under compression, even at this top-dead-centre position, and the belt is always under tension even when the compression on the support is maximum. This permits use of materials of low tensile strength for the support.

After a survey of the main features of the connecting rod 1, made according to the guiding principles of the present invention, it is obvious that it makes possible the achieving of the aims mentioned hereinbefore.

In fact, thanks to the stronger stresses undergone by support 2, it is possible to lighten the weight of the shank 13, and also that of the big end due to the even distribution of compression strains acting in radial direction on the latter. It is further unnecessary to use tightening boits, with all the drawbacks they entail. Finally, it is possible to lighten or remove in part tile small end 11, because stress or strain can now be transferred directly by the belt 3 to the element which is connected with small end 11 while in operation. Considering that the connecting rod has been made lighter as a whole, the counterweights on the crankshaft can be also reduced.

In consequence of the above, the use of this connecting rod implies some advantages i.e. a better weight-power ratio and/or a better performance due to the possibility of diminishing the organic losses; the reduction of vibrations caused by the external parts; the possibility of using for support materials which are no longer the traditional ones, including e.g. the materials shown a high compression strength and low tensile strength, for instance, as already said, glass and ceramic materials. The use of the latter materials allows further to obtain endless advantages both of economic kind and of functional kind, due to the better performance under load which can be available.

It is also obvious that the connecting rod's shape described under N01 can be modified and varied without leaving the scope of this invention.

For instance the belt-supporting coupling system as well as the type of belt stretcher can be widely modified without leaving the field of this invention, which includes essentially a connecting rod formed by a support working under compression and by a belt which involves the support and works under tensile strength.

Furthermore belt 3 instead of being a closed ring could be conveniently manufactured as an open ring, in which case the opposed edges would be kept in connection by appropriate fixing means.

The particular connecting rod described herein may be used within a cylinder in an internal combustion engine to connect a reciprocating piston to a crank pin on a rotating crank shaft.

Claims

1. A connecting rod comprising a shank and having at its respective opposed ends a first seat which can be engaged by a rotary element and a second seat which can be engaged by a reciprocatory element and compressive means which compress said shank to such an extent that said shank when in operation, is always under compression said compressive means being always under tension.

2. A connecting rod according to claim 1 that said compressive means include a belt wound lengthways around said shank.

3. A connecting rod according to claim 2 wherein a portion of said belt is located within a peripheral groove formed in an end of said shank.

4. A connecting rod according to claim 2 or claim 3 comprising a belt stretching means for adjusting the tension of said belt.

5. A connecting rod according to claim 4 wherein said belt stretching means include a frame anchored to said shank, to grip said belt and hold opposed portions of the belt closer to the shank than in predetermined idle position.

6. A connecting rod according to claim 5 or claim 6 wherein said frame comprises two pairs of facing walls and is anchored to fins extending transversely from said shank.

7. A connecting rod according to claim 5 or claim 6 wherein said frame is configured to be located over an end of the connecting rod and moved lenghwise relative to the shank whilst gripping the exterior of said belt so as to pull opposed portions of said belt inwardly towards the shank.

8. A connecting rod according to any of claims 2-7 wherein said belt forms a closed ring.

9. A connecting rod according to any of claims 2-7 wherein said belt is wound lengthways around said shank and is an open ring, there being fixing means for holding the opposed ends of said belt and maintaining the tension of the belt.

10 A connecting rod according to any preceding claim wherein said shank is made of materials selected from steel, titanium, magnesium, aluminium and their alloys, glass and ceramics.

11. A connecting rod according to any preceding claim wherein said compressive means is made of a composite material with a metallic or plastic matrix (thermohardening at high temperatures) with stiffenings made preferably of materials selected among glass fibres, carbon, aramide, metal.

12. A connecting rod substantially as described herein with reference to the accompanying drawings.

13. A connecting rod having a shank, means at one end of the shank for connecting the rod to a reciprocating member and means at the other end of the shank for connecting the rod to a rotating member, wherein the rod is provided with compression means so that, in use, the shank is always under compression.