Expansible chamber devices – Piston – With separable means for pivotally mounting connecting rod...
Reexamination Certificate
1999-12-09
2001-08-21
Lopez, F. Daniel (Department: 3745)
Expansible chamber devices
Piston
With separable means for pivotally mounting connecting rod...
C092S216000
Reexamination Certificate
active
06276260
ABSTRACT:
The present invention relates to a connecting-rod/piston unit for small reciprocating machines, particularly motor-driven compressors for refrigerators and the like,
Units of this type are known from the documents FR-A-2 330 923 and EP-A-0 608 506.
According to the document FR-A-2 330 923, the piston has a pair of diametrally-opposed internal projections which in turn have respective recesses aligned with one another and constituting a bearing seat for the gudgeon pin.
In one embodiment, the sides of the recesses have cold-formed local deformations which hold the gudgeon pin permanently in its bearing seat; in another embodiment, the sides of the recesses and the gudgeon pin are interconnected permanently by electric spot welds called “wart-shaped projections”.
The methods of fixing the gudgeon pin to the piston according to the document FR-A-2 330 932 require either a suitable press for performing the local deformations, or a suitable electric welding station for executing the spot welds.
These methods are not suitable for the assembly of motor-driven compressors or small reciprocating machines of other types on a continuous line because, in order to fix the gudgeon pin to the piston, they require a press or a welding machine separate from the line.
This problem was at least partly solved by the teachings of the document EP-A-0 608 506.
According to this document, the piston of a motor-driven compressor unit again has a pair of diametrally-opposed internal projections which in turn have respective recesses aligned with one another and constituting a bearing seat for the gudgeon pin.
The retaining means i n this case consist of a spring ring surrounding the shank of the connecting rod and having anchoring tabs projecting from its periphery.
In the assembled condition, the retaining ring reacts against the gudgeon pin and keeps it engaged in its seat by virtue of the fact that the tabs of the ring bite into the internal surface of the skirt of the piston, thus achieving a firm anchorage between the ring and the piston by interference.
This arrangement known from the document EP-A-0 608 506 permits a simplified, relatively low-cost assembling operation.
A person responsible for quality control downstream of the assembly station may notice that some part (for example, the connecting rod) is faulty. In this case, the sub-assembly can easily be dismantled by pulling the piston away from the connecting rod and its retaining ring in order to recover the piston and the gudgeon pin.
However, this operation may irreparably damage the piston since, when the spring ring is removed, its tabs which bite into the surface of the skirt may scratch the latter, which is detrimental to the possibility of re-using the piston.
The solution of the document EP-A-0 608 506 also has the disadvantage of requiring the use of pistons which have quite thick skirts and are therefore undesirably heavy; in fact, it has been found that the tabs of the retaining ring deform a fairly thin skirt, causing it to lose its cylindrical shape. For example, in the case of a retaining ring with four tabs, the skirt adopts a four-leafed shape.
The object of the invention is to provide a connecting-rod/piston unit which can be assembled in the manner permitted by the solution of the document EP-A-0 608 506 but which is not liable to deform a thin skirt and which allows a faulty connecting-rod/piston unit to be dismantled easily, for example, in order to recover the piston and the gudgeon pin therefrom without damaging the skirt.
According to the invention, this object is achieved by means of a connecting-rod/piston unit having the characteristics claimed.
The invention is based on the observation that, in a small reciprocating machine such as a motor-driven compressor for refrigerators, the forces acting between the piston and the connecting rod during intake strokes are so weak as to require neither permanent fixing of the gudgeon pin to the piston as in the document FR-A-2 330 923, nor an anchorage which is releasable but may damage the piston, as in the document EP-A 0 608 506.
As will be understood further from the description relating to the drawings, the snap-coupling of the pincer element according to the invention with the gudgeon pin is all that is required to withstand the relatively weak forces which arise during intake strokes but enables the gudgeon pin to be removed from the piston easily as a result of a simple resilient opening-out of the jaws of the pincer element which grasp the gudgeon pin.
The invention also relates to a motor-driven compressor or a similar reciprocating machine comprising a connecting-rod/piston unit as claimed.
REFERENCES:
patent: 5072654 (1991-12-01), MacGregor
patent: 5092290 (1992-03-01), Bartkowicz
patent: 0-608-506 (1994-08-01), None
patent: 2-330-923 (1977-06-01), None
Embraco Europe S.r.l.
Lazo Thomas E.
Lopez F. Daniel
Sughrue Mion Zinn Macpeak & Seas, PLLC
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