Annexed to the INDUSTRIAL INVENTION Patent Application entitled: EXTENSION FOR AN IGNITION COIL FOR AN ENGINE In the name of: ELDOR CORPORATION S.p.A., domiciled in ORSENIGO 5 (Como), in Via Plinio n. 18.

Designated Inventors: Pasquale Forte, Amedeo Colombotto Representative: Attorney Raffaello Nemni (Bar of Milan), professionally domiciled in Milan, Via San Marco, 23. Filed on No.

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OBJECT OF THE INVENTION

The present invention relates to an extension for an ignition coil for an internal combustion engine of a motor vehicle, suitable for resisting high thermal and electrical stresses to which said type of extension is subjected.

15 STATE OF THE ART

It is well-known that the purpose of the extension of a coil for internal combustion engines for motor vehicles is to conduct the high voltage generated by the electromagnetic circuit to the sparkplug fitted in the engine well.

20 The known extensions are made of rigid plastic or silicone rubber. The known extensions have the disadvantage of not sufficiently resisting the combination of high thermal and electrical stresses to which said extensions are subjected. In particular, extensions in silicone rubber do not have sufficient

25 mechanical rigidity to make them suitable to resist the above-mentioned stresses, and because of their flexibility they do not guarantee a stable contact, while those in plastic are too rigid from a mechanical point of view and have poor resistance to the corona effect and the discharges due to high voltage. DISCLOSURE OF THE INVENTION

The present invention advantageously resolves the drawbacks of the known extensions with an extension, preferably of substantially cylindrical shape, externally in silicone rubber and internally in rigid plastic. Said combination advantageously combines the characteristics of the silicone material for resisting the corona effect and the discharges due to high voltage, and the mechanical characteristics of the plastic which allow a mechanical rigidity which ensures dimensional stability and electrical contact. Said combination also has the advantage of allowing the portions of the coil designated head rubber and sparkplug rubber to be moulded with the silicone part of the extension which is the subject of the present invention. A further advantage of the present invention is the possibility of incorporating circuit elements into the plastic, such as the diode and/or the resistor, in order to be positioned on the inner surface of the extension by virtue of the rigidity of the plastic of which the inner part of said extension is made.

The processes of construction of the geometry of the parts which make up the extension and the circuit elements which are the subject of the present invention can be various, but the process of co-moulding is preferable, it having been possible to observe experimentally that with this process it is possible to obtain an optimal coupling between the silicone and the plastic which make up the extension which is the subject of the present invention. Said process of co-moulding with plastic has also shown itself to be advantageous for the circuit elements coupled together and/or to the hollow element of said extension.

DESCRIPTION OF THE DRAWINGS

Figure i shows a perspective view of the extension (l) which is the subject of the present invention of a substantially cylindrical shape.

Figure 2 shows a perspective view of the extension (l) which is the subject of the present invention, with a hollow element (2) in plastic and a cladding (3) in silicone of said hollow element (2). Said figure also shows a portion (a) suitable for performing the function of coupling element between the coil and the head of an internal combustion engine of motor vehicles (so-called head rubber) and a portion (b) suitable for performing the function of coupling element with the sparkplug of an internal combustion engine of motor vehicles (so-called sparkplug rubber).

The hollow element (2) and the cladding (3) in silicone are preferably coupled together by co-moulding. Figure 3 shows a perspective view of the extension (1) which is the subject of the present invention, with a diode (4) and a resistor (5) incorporated in plastic and located inside said extension (1), mainly inside said hollow element (2). Said incorporation of the diode (4) and/or the resistor (5) in plastic together and/or with the hollow element (2) is preferably performed by co-moulding. The embodiment of the above illustrated drawings is a non limitative example. The various parts which make up the extension which is the subject of the present invention can all be co-moulded together, but also only two components of said extension - hollow element (2) in plastic, cladding (3) in silicone, diode (4), resistor (5) - can be co-moulded together. MODE FOR CARRYING OUT THE PRESENT INVENTION The extension which is the subject of the present invention can be used for ignition coils on any internal combustion engine of any motor vehicle.