To the purpose of more effectively exemplifying the present invention, said connecting rod is assumed to operate ln close association with the compression piston of a refrigeration compressor, m particular a compressor for household--type refrigerators, without this of course limiting the scope of the same invention to ]ust such a lcnd of coupling.

The practice is linown fi-om the patent EP 0 608 506 to WHIRLPOOL EUROPE B.V. of bringing about such a coupling between a piston of a hermetically sealed motor-dnven compressor and the respective connecting rod by means of a gudgeon pin that is adapted to engage, during the compression phase, the piston walls owmg-to mere pressure exerted against appropriate recesses provided in the same walls, whereas the suction phase, which notoriously requires just a very small or even no coupling force at all between connecting rod and gudgeon pin (in fact, the pressure itself of the suction gas is such as to ensure the coupling, again by pressure, between said elements), is carried out with the connecting rod that keeps engaging the piston through an elastic element, which has a substantially plane annular shape and is arranged between said two elements.

Such a solution however, although representing a sure improvement with respect to prior-art solutions from a general manufacturing point of view, still has some drawbacks in that - the need still arises for two distinct component parts, ie. connecting rod and gudgeon pin, to be manufactured separately, whereas said connecting rod must anyway be provided with the ring required to accomodate the gudgeon pin; - there still occurs a wear-down effect between said component parts, so that there still is a need for a particular lubrication to be provided therebetween; - the elastic element works by sliding, ie. rubbing against the gudgeon pm, so that it undergoes a palllcularly severe, rapld wear-down effect; - furthermore, the shape itself of the elastic element, due to its working by bending under mere shear stress. does not ensure any absolutely firm coupling between piston and gudgeon pin and this makes it possible for undesired noise to be generated.

It therefore would be desirable. and it actually is a main purpose of the present invention. to provlde a technical solution that, when applied to the piston of a refrigeration compressor eliminates the above mentioned drawbacks and, in particular, simplifies both construction and assembly. especially through a reduction m the part count.

According to the present invention, such an aim is furthermore capable of being reached through the use of techniques and matenals that are slmple, cost-effective and readily available on the market, without by any means impairing the performance capabilities and the reliability of the respective compressor.

These aims are reached in a type of coupling between connecting rod and piston as described below by way of mere non-limiting example with reference to the accompanying drawlngs, in whlch:

- Figures la, lb and lc are three perspective, partially cut-away views of a piston, a respective connecting rod and a respective retaining element, respectively, according to the present invention; - Figure 2 is a perspective, partially cut-away view of the three component parts shown in the three above cited Figures, after the assembly thereof.

With reference to the above listed Figures, it should first of all be noticed how the gudgeon pin, intended as a distinct mechanical element having the function of linking the connecting rod with the piston, is practically eliminated, while its function is carried out as follows: - the piston 1 is deprived of the holes m which the gudgeon pin is usually inserted, since, as pomted out above, said gudgeon pin is suppressed; on the contrary, the same piston i is provided, in its inner surface 2 opposing the working surface on which the pressure is exerted, with a recess 3 having the shape of a portion of a cylinder sectioned by a plane that is parallel to the axis a - a thereof. In other words, said inner surface practically presents a dome in the shape of a portion of a cylindel The connecting rod 4 presents in turn, in correspondence of its end portion facmg the piston. a terrmnal portion 5 shaped as a portion of a cylinder being so slzed as to be able to couple, even only partially, with said recess 3 provided m the inner surface 2 of the piston.

It is anyway clear that, apart from the mutual compatibility of the relative dimenslons, the mimmum coupling ability reguirement calls for the radius of said two portions of cylinder 3 and 5 as descnbed above to be substantially slmilar so as to enable the connecting rod to rotate through a limited arc with its terminal portion 5 within the recess 3, owing to the fact that the cylindrical surfaces facing each other at any moment are always substantially m contact with each other.

Such a solution enables a twofold advantage to be obtained in terms of a greater common working surface between connecting rod and piston, with a corresponding reduction in the pressures involved and, therefore, also in the corresponding wear-down effect, and an enhanced lubrication effect brought about by a substantially perfect coupling of the two common surfaces when working.

Furthermore, such a solution clearly makes it possible for even very high stresses between connecting rod and piston to be transmitted during the compression phase, since these elements are m this phase undergoing pressure stresses that force them against each other, so that the proposed solution of common working surfaces gives full assurance of an effective force transmlsslon and, as a result, an effective, problem-free compression of the gas, with a low wear-down and an enhanced lubrication effect.

During the suction phase there is no particular stress or force that must be transmltted from the connecting rod to the piston, owmg to the low inertia of the latter and owmg also to the fact that, in the first part of the suction stroke. the residual gas available in the cylinder usually keeps up a slight counter-pressure actmg on the piston, so that the pulling force on the piston. already very low, is further reduced by said counter-pressure.

It is however necessary for the piston to remain linked with the connecting rod also during the suction phase and, considering the low forces required, t has been found that such a function can be carried out m a fully satisfactory manner by such an elastic element 6 as best illustrated in Figure lc which shows means m the shape of a closed loop, and having approximately the form of a saddle. in which two opposite "upper" portions 7 and 8 can be distingulshed., alone with two similarly opposite "lower" portions 9 and 10, said upper and said lower elements being arranged alternately.

Said upper portions 7 and 8 are adapted to engage, by slmple contact and pressure. against respective reliefs 11 and 12 provided, as this is best shown m

Figure lb, on the lower side of the terminal portion 5 of said connecting rod, said reliefs being clearly not comprised in and preferably opposite to the cylindrical surface in which the connecting rod terminates.

The "lower" portions 9 and 10 of said elastic element 6 are in turn adapted to engage respective recesses 13, 14 which, preferably in the form of horizontally oriented notches, are provided in appropriate positions inside the inner cylindrical surface 15 of the piston, so as this is best illustrated in Figure 2.

In this manner, after completion of the assembly of the three elements described above, which can be carried out in different manners, and in particular by taking advantage of the elasticity of the element 6, a connecting rod-piston assembly is obtained which is surely effective for use in the mtended application, without any problem whatsoever arising in the compression phase thanks to the afore desciibed reasons, as well as without any problem occurring in the suction phase smce the saddle-like configuration, or 'arch"-like shape, of the elastic element 6. along with the manner it engages the piston. makes it surely possible for the connecting rod to be also able to dnve the piston without any undesired lag or even the slightest delay, exactly for the reason that the arch-shaped structure of the elastic element 6. by working in a compresslve manner during the suction phase, maintains its original shape almost integrally.

In an advantageous manner, furthermore, the afore cited reliefs 11 and 12 can have thelr surfaces contacting the upper portions 7 and 8 of the elastic element 6 reduced to mere segments, this being obtained by sharpemng the lower extreme edges of said reliefs and giving said corresponding portions 7 and 8 the shape of a plane surface.

Furthermore, said Sharp edges so formed by the lower borders of said reliefs 11 and 12 must be arranged along the rotation axis b - b of the terminal portion 5 of said connecting rod with respect to the recess 3. Such a geometric arrangement, In fact, enables fiction between said connecting rod and the elastic element 6 to

be minimized, since these elements only engage each other by pressure when working.

This solution enables the durability of the respective pressure contacts to be increased and, as a result, ebables the related lubncation requirements to be simplified.

It will be appreciated that the above description and illustrations have been given, with reference to the accompanying drawings, to the mere purpose of exemplifying the present invention, and that a number of variants can be implemented and modifications can be made thereto without departing from the scope of the present invention.