Expansible chamber devices – Piston – With separable means for pivotally mounting connecting rod...
Reexamination Certificate
1999-04-19
2001-01-30
Ryznic, John E. (Department: 3745)
Expansible chamber devices
Piston
With separable means for pivotally mounting connecting rod...
Reexamination Certificate
active
06178873
ABSTRACT:
The present invention refers to a particular kind of coupling used to link a connecting rod with the associated piston.
To the purpose of more effectively exemplifying the present invention, said connecting rod is assumed to operate in close association with the compression piston of a refrigeration compressor, in particular a compressor for household-type refrigerators, without this of course limiting the scope of the same invention to just such a kind of coupling.
The practice is known from 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-driven compressor and the respective connecting rod by means of a gudgeon pin that is adapted to engage, during the compression phase, the piston walls owing 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 pin, so that it undergoes a particularly severe, rapid 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.
From GB 2 235 961 a piston assembly for use with a hydraulic cylinder is known; such a piston assembly is including a piston member defining a recess in an end face and an annular insert located in the recess for receiving an end of a piston rod, the insert including first retention means for retaining the piston rod therein, and second retention means which co-operates with a surface of the piston member to inhibit withdrawal of the insert from the recess.
However such form of realization requires complicated processing due to the fact that the metallic piston has to be worked internally undercut.
Furthermore the use of resilient moulded plastic means
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has to be avoided inside an hermetic compressor for refrigerators, as the combined effects of freon corrosion, lubricant oil corrosion and high temperature would rapidly destroy such a plastic material.
From U.S. Pat. No. 4,930,405 a compressor is shown having a connecting rod comprising a first and second eye, the first being connected by means of a wrist pin to the reciprocating piston, and the second eye being connected to a crank pin which is on one end of a crankshaft. This crankshaft is orthogonal to the piston stroke and supportes at its other end the rotor of an electric motor. The motor stator is supported on a crankcase that includes a crankshaft bearing portion, a cylinder, a suction and a discharge muffler. This crankcase is mounted within a housing by means of coil springs and this housing is closed with the top portion forming a hermetically sealed unit.
The solution shown by said US patent comprises a two-piece connecting rod, and more specifically a new arrangement comprising a two-part rod that permit easy mounting of the piston, the connecting rod and the crank pin assembly without requiring the provision of additional connecting parts; however such a solution does maintain a traditional mounting technique between the connectin rod and the piston as the well known wrist pin
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is used for connecting the two parts, and therefore no improvement in the connection between the connecting rod and the piston can be found, and the relevant mass is unchanged.
The patent DE 3030319 shows a solution where the wrist pin is lodged in an hollow element connected with the internal surface of the piston head, instead of in proper holes on the cylindrical surface of said piston.
Such a form of realization does show some advantage from the assembly operation, but it implies a supplementary burdensome working to place and fix such hollow element inside the piston.
It therefore would be desirable, and it actually is a main purpose of the present invention, to provide 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 in the part count.
According to the present invention, such an aim is furthermore capable of being reached through the use of techniques and materials that are simple. cost-effective and readily available on the market, without by any means impairing the performance capabilities and the reliability of the respective compressor.
REFERENCES:
patent: 76448 (1868-04-01), Hinds et al.
patent: 3903752 (1975-09-01), Riffe
patent: 5671655 (1997-09-01), Vollrath
patent: 5701802 (1997-12-01), Junge
patent: 366656 (1923-01-01), None
patent: 1780571 A3 (1992-12-01), None
Pierobon Emilio
Santamato Arcangelo
Pearne & Gordon LLP
Ryznic John E.
Zanussi Elettromeccanica S.p.A.
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