WO2008087303A1

WO2008087303A1 - Spark plug for a thermal engine

Info

Publication number: WO2008087303A1
Application number: PCT/FR2007/002077
Authority: WO
Inventors: Thierry Favier
Original assignee: R Et B Products
Priority date: 2006-12-15
Filing date: 2007-12-14
Publication date: 2008-07-24
Also published as: FR2910114A1; TW200900638A

Abstract

The spark plug of the invention includes a main body (1) having a through-bore (1a, 1b) formed therethrough for receiving a central body (3) and an incandescence filament (2) welded at one end of the central body (3). Sealing and electric-isolation closing means are provided between the main body (1) and the central body (3), in the form of a spark-plug intermediate body (6) having a generally tubular shape and made of a deformable material. An outer wall (6a) of the intermediate body (6) comprises a relief for depositing a sealing fluid means in contact with the inner wall of the bore (1a) of the main body and for enhancing the deformation of the intermediate body (6). The main body (3) is inserted into the intermediate body (6) and generates a slight radial deformation thereof (6) towards the outside. The spark plug can be used in a micro-engine for motor-vehicle models.

Description

Spark plug for heat engine

The present invention relates to a spark plug for a heat engine, in particular for a motor-vehicle miniature model micromotor, a candle which is of the incandescent filament type.

Figure 1 of the accompanying drawing shows such a spark plug known, for example, from United States patents US 6,342,690 and US 6,346,688.

According to these documents, the candle comprises a candle main body 1 in which is made a through bore with a first portion 1a of generally cylindrical large diameter intended to house a candle central body 3, and with a second portion 1b also of generally cylindrical shape but of diameter substantially smaller than said large diameter and intended to house an incandescent filament 2 welded to one end of the central body 3.

To start the motor, the filament 2 is preheated by means of a low voltage electric accumulator. The motor is moved by an external driving force which causes the aspiration of the combustion gases. Once the engine is moving, the electronic accumulator is disconnected from the spark plug and the filament 2 is kept incandescent by the successive explosions of the engine.

In the present candles as described by the aforementioned documents, two insulating washers 4a and 4b, cut from mica sheets 0.3 mm thick, are interposed between the main body 1 and the central candle body 3 and ensure an electrical insulation at each end of the central body 3. The insulating washers 4a and 4b are very fragile and delicate to handle, it is difficult to automate assembly operations and adjustment of these washers 4a, 4b between the central body 3 and the main body of candle 1, without damaging them. In addition, the filament 2 is made of platinum, a very expensive material that should be consumed in minimum quantity. However, the central body of candle 3 isolated by the two washers of mica 4a, 4b poorly dissipates heat which reduces the reliability and the life of the filament 2: it is therefore generally expected a filament 2 of significant length to compensate for this wear and guarantee the thermal index of the candle. The spark plug having to withstand the pressure stresses of the combustion chamber of the engine, its sealing is ensured by means of insulating washers 4a and 4b and a closure washer 5 made of steel, brass or stainless steel at one end. the main body 1 opposite said second bore portion 1b and also by crimping the upper part of the candle main body 1. Some manufacturers even carry out several crimping operations.

Another spark plug for model of a motor vehicle is known from patent US 6696670. In the embodiment according to this document, the sealing device consists of two low-profile annular parts, which remain comparable to the washers of the previously discussed. In addition, as before, the upper part of the candle is closed by crimping. The assembly of the components of this candle, in particular the tightening of the lower annular part (washer), is carried out by many intermediaries: upper part of the main body, upper washer, flange and conical wall of the central body, from which a complex and unreliable process. Thus, the candle of US Patent 6696670 remains very comparable to that of the previous documents, and thus retains the same kind of disadvantages. Given the large number of components and the need for precision in their assembly, the cost of such candles is quite high and it is not uncommon for these candles to leak, due to insufficient sealing.

The present invention aims to avoid these drawbacks by proposing a spark plug having a reduced number of components, without component "at risk" of the kind washer mica sheet, whose assembly is simple and can be automated, and offering a better life of the filament filament, the length of the filament being minimized and the heat exchange of the central body with the other components of the candle, improved. For this purpose, the invention essentially consists of a spark plug for a heat engine, of the type presented above, and in which said means for sealing and electrical insulation have the shape of an intermediate shape candle body. general tubular material made of a deformable material and housed in said first bore portion of the main body, and wherein an outer wall of said intermediate body, intended to come into contact with an inner wall of said first portion boring the main body, has a corrugated relief for depositing a fluid sealing means between said walls and to promote the deformation of said intermediate body, said central body coming into said intermediate body causing a slight deformation radial of said intermediate body outwardly, so as to entrench in the main body ..

Thus, the candle has no insulating washers or lock washer but a single insulating intermediate body of generally tubular shape easier to produce, to produce and to assemble.

By deforming in the main body (in the direction of a radial expansion) during the fitting of the central body, the intermediate body seals the candle and allows it to close. The assembly of the candle does not require any particular tool because it is achieved by a simple fitting, which directly causes the expansion of the intermediate body of tubular conformation. The intermediate body of tubular general shape is made for example of aluminum with a surface treatment by anodizing to make it insulating.

According to an advantageous embodiment, the candle central body has a shape of revolution with a median region of reduced diameter delimiting, with an inner wall of the intermediate body, an annular recess between two contact zones of the central body with said wall internal of the intermediate body provided to promote a dissipation of heat. The annular recess makes it possible to adjust the dissipation of the heat provided via the contact zones between the central body and the intermediate body.

The invention will be better understood on reading the following detailed description given by way of illustration with reference to the appended drawing in which;

Figure 1 (already commented) represents a spark plug according to the prior art.

Figure 2 is a schematic sectional view of a spark plug according to the present invention.

Figures 3 to 8 illustrate different successive operations of assembly of the candle of Figure 2; Figure 9 is a schematic sectional view of a variant of the spark plug according to the invention. The candle illustrated in FIG. 2 comprises a main body of candle 1 made of a metallic material and in which a through bore is made, a first cylindrical portion 1a of large diameter of which houses a central candle body 3. The central candle body 3 is a piece of revolution made of a metallic material and has a median region 3a of reduced diameter which facilitates the gripping of the central body 3 during assembly operations of the candle.

A second portion 1b, also cylindrical, of the through bore has a substantially smaller diameter and houses an incandescent filament 2 welded to one end of the central body 3.

Platinum-based, the filament 2 is also welded at one end to the main body 1.

An intermediate candle body 6 of generally tubular shape is housed in the first bore portion 1a of the main body and designed to receive the central body 3.

The intermediate body 6 is made of a deformable metal material, here aluminum, with a surface deposit produced by hard anodizing or decoration to make it insulating. The insulating properties of the intermediate body 6 depend on the thickness of the surface deposit which is an easily adjustable parameter.

An outer wall 6a of this intermediate body 6, intended to come into contact with an inner wall of the first bore portion 1a of the main body 1, has a corrugated relief forming annular "waves" radially projecting so as to allow the deposit of a liquid sealant, said "anaerobic", between these two walls and to facilitate the deformation of the intermediate body 6.

The assembly of this candle, illustrated in Figures 3 to 8, is performed on a laying device 7 in which is installed the main body of candle 1 (see Figure 3).

Anaerobic product is sprayed by means of a nozzle 8 (see FIG. 4) on the inner wall of the first bore portion 1a of the main body 1, then the intermediate body 6 is mounted in this first bore portion 1a (FIG. see Figure 5). Anaerobic product is then sprayed on the inner wall of the intermediate body 6 (see Figure 6) by means of the nozzle 8 and the body central 3 is fitted into the intermediate body 6 (see Figure 7) and causes, by its shapes and dimensions, a slight radial expansion of the intermediate body 6 outwardly, so as to entrench in the main body 1 and to close the end of the main body 1 opposite the second bore portion 1b. Thus, the role of the intermediate body 6 candle is double, namely to isolate the central body 3 of the main body 1, and lock these two elements together.

The assembly of components 1, 6 and 3 of the candle is completed after this fitting operation (see Figure 8). Thus, the assembly, whether done manually or automatically, is achieved by simple vertical fitting, so easy, simple and fast and it finally allows a candle of better quality.

The median region 3a of the central body 3 and the inner wall of the intermediate body 6 delimit an annular recess between two high and low zones (in the drawing) of contact of the central body 3 with the inner wall of the intermediate body 6. This recess annular, which remains filled with air after assembly, allows to adjust the heat dissipation of the central body 3 through its points of contact with the inner wall of the intermediate body 6.

This arrangement ensures a longer life of the filament 2 and allows, for equivalent thermal index, to reduce the length of the filament 2 by about 20% compared to candles of traditional design. Figure 9, in which the elements correspond to those described above are designated by the same reference numerals, represents a variant of the spark plug object of the invention. At the top of this candle, the main body 1 is folded over the intermediate body 6 and the central body 3, to secure the assembly, that is to say to prevent the accidental exit of the internal elements of the candle , in case of manufacturing anomaly. Other means of securing can also be envisaged. The basic assembly remains here by fitting the central body 3 into the intermediate body 6, causing the radial deformation of this intermediate body 6.

Although the invention has been described above in the context of particular embodiments, it is obvious that it is in no way limited to these examples and that it includes all the technical equivalents of described means and combinations thereof if they fall within the scope of the appended claims. Changes in the detail of the shapes of the various components of the candle are, of course, also within the scope of the present invention. Finally, although it is essentially a candle for thermal micromotor model of vehicle, the invention is not limited to this application and can also find applications outside the field of modeling, for all candles. ignition of the incandescent filament type.

Claims

1.- Spark plug for a heat engine, in particular for a motor-vehicle miniature model micromotor, of the type comprising a candle main body (1) in which a through bore is made with a first portion (1a) of cylindrical general shape of large diameter designed to house a candle central body (3), and with a second portion (1b) also of generally cylindrical shape but of diameter substantially smaller than said large diameter and intended to house an incandescent filament (2) welded to one end of the central body (3), electrical insulation means being provided for interposing between the main body (1) and the central body (3), and sealing means being provided for the crimping of the spark plug at one end of the main body opposite said second bore portion (1b), characterized in that said sealing and electrical isolation means have the tubular general body of an intermediate candle body (6) made of a deformable material and adapted to be housed in said first bore portion of the main body (1a), and in that an outer wall (6a) of this intermediate body, (6) intended to come into contact with an inner wall of said first bore portion (1a) of the main body, has a corrugated relief so as to allow the deposition of a fluid sealing means between said walls and to promote the deformation of said intermediate body (6), said central body (3) coming into said intermediate body (6) causing a slight radial deformation of said intermediate body (6) to the outside.

2. Spark plug according to claim 1, characterized in that the intermediate body (6) is made of aluminum with anodizing surface treatment to make it insulating.

3. Spark plug according to claim 1 or 2, characterized in that the candle central body (3) has a shape of revolution with a median region (3a) of reduced diameter defining, with an inner wall of the intermediate body (6), an annular recess between two contact areas of the central body (3) with said inner wall of the intermediate body (6) provided to promote dissipation of heat through the contact areas between the body central (3) and the intermediate body (6).