US3449638A

US3449638A - Ignition device

Info

Publication number: US3449638A
Application number: US709479A
Authority: US
Inventors: Otto Beesch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1967-04-27
Filing date: 1968-02-29
Publication date: 1969-06-10
Anticipated expiration: 1986-06-10
Also published as: DE1974605U; FR1558776A

Description

June 10, 1969 o. BEESCH 3,

IGNITION DEVICE Filed Feb. 29, 1968 FIG] FIG.2

18 I u f :I 16 v i a r32 INVENTOR Otto BEESCH y u/ldzwmm his ATTORNEY United States Patent US. Cl. 317--82 5 Claims ABSTRACT OF THE DISCLOSURE A glow plug comprises a first electrode and a second electrode surrounding the first electrode with clearance. An insulating member surrounds the first electrode in the clearance and has an outer circumferential face spaced from the second electrode. A helically convoluted resistance wire overlies the outer circumferential face spaced from the second electrode and is fixed with one end to the second electrode and with the other end to a terminal which is electrically insulated from both electrodes. Intermediate its ends two convolutions of the resistance wire are in part received in two annular grooves provided in the outer circumferential face of the insulating member.

Background of the invention The present invention relates to ignition devices in general, and more particularly to devices for igniting fuel-air mixtures. Still more specifically, the present invention relates to a glow plug for preheating and igniting fuel-air mixtures.

Such glow plugs are already known and find use in various applications for instance in heating devices. Their purpose is to preheat the fuel-air mixture to a. desired temperature, and subsequently to produce a spark which will ignite the thus preheated mixture. Glow plugs of this type thus perform a dual function, namely preheating and subsequently ignition of the fuel-air mixture.

It is known to construct such plugs but providing a center electrode which is surrounded with spacing by a sleeve-like outer or mass electrode. In the spacing between the two electrodes an insulating member surrounds the center electrode except for a portion which defines with the mass electrode a spark gap. There is, however, still a clearance between the outer circumferential face of the insulating member and the inner surface of the sleeveshaped outer electrode. Arranged in this space, overlying the outer circumferential face of the insulating member is a helically convoluted resistance wire one end of which is conductively connected with the outer electrode whereas its other end is conductively connected with a terminal carried by the plug but electrically insulated from both the inner and outer electrodes. This terminal serves to connect the resistance wire with a source of electrical energy.

In glow plugs of this type, the opposite ends of the resistance wire are fixed. However, the wire comprises a plurality of convolutions which are free to move with reference to one another. As a result, it frequently occurs that two or more adjacent convolutions of the wire move into contact with one another. This causes shorting of the convolutions and results in damage to the resistance wire.

It is the object of the present invention to overcome this disadvantage.

More particularly, it is an object of the present invention to provide a glow plug wherein contacting of two or more adjacent convolutions of the resistance wire is prevented.

3,449,638 Patented June 10, 1969 It is a further object of the invention to effect this preventive measure in a simple and inexpensive manner so as to avoid any significant increase in the cost of manufacturing and selling the glow plug.

A further object of the invention is to provide the desired advantages in such a manner that they may be produced by resorting to conventional tools and production techniques.

Summary of the invention In accordance with one feature of my invention I provide a glow plug which comprises an elongated inner electrode and an elongated sleeve-shaped outer electrode. The outer electrode surrounds the inner electrode with clearance and defines with one end of the inner electrode a spark gap. An elongated insulating member surrounds the inner electrode in this clearance and comprises a portion which is provided with an outer circumferential face spaced from the outer electrode. Terminal means is fixedly carried by the plug and is electrically insulated from the inner and outer electrodes and this terminal means is adapted to be connected to a source of electrical energy. A helically convoluted resistance wire overlies the outer circumferential of the insulating member and is spaced from the outer electrode. This resistance wire has a first end fixed to and conductively connected with the outer electrode and a second end fixed to and conductively connected with the terminal means. Finally, I provide spacing means which is provided on the insulating member and which is adapted to maintain adjacent convolutions of the resistance wire out of engagement with one another so as to prevent shorting of such adjacent convolutions.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as toits construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

Brief description of the drawing FIG. 1 is a longitudinal section through a glow plug embodying my invention; and

FIG. 2 is a fragmentary detail view, partly in longitudinal section, of the embodiment illustrated in FIG. 1.

Description of the preferred embodiments Discussing now the drawing in detail, it will be seen that the glow plug therein illustrated comprises a housing 'which is generally identified with reference numeral 10. Fixed in this housing is an insulator 11 usually consisting of ceramic material, and within this insulator 11 surrounded by the same is fixed a center electrode 16. A metal ring or sleeve 12 surrounds a portion of the outer circumferential surface of the insulator 11 Within the housing 10.

FIG. 1 shows that the housing 10 is provided with an external screw thread 14 and with a hex nut 13 which is adapted to be gripped with a wrench or similar tool so that the glow plug may be threaded into a mating screw thread provided on a heating or similar user device which is not illustrated. A sealing ring or gasket 15, which is illustrated as consisting of synthetic plastic material serves to seal the glow plug to the housing of the user device once the plug is threaded thereinto.

Projecting rearwardly from the housing 10, that is outwardly from. the user device when the glow plug is secured thereto is a bolt or pin 20 Whose screw threaded free end portion 19 serves for connection to an ignition cable. There is further provided a bus bar 21 which, as FIG. 1 shows, is conductively connected with the sleeve or ring 12. A second bus bar 22 is carried by the housing 10, for instance by being welded thereto and is adapted to be connected to a (nonillustrated) source of electrical energy.

The forward end of the housing is provided with a projection 24 on which there is secured a sleeve-shaped electrically conductive member 25 which surrounds the insulating member 11 with clearance and which constitutes the outer or ground electrode. The free end portion of the center electrode .16 defines with the outer electrode 25 a spark gap a and the fuel-air mixture which is to be ignited has access to the clearance, and therefore to the spark gap, from the open front end of the outer electrode 25 as well as via a plurality of apertures 30 which are provided in the outer electrode 25 inwardly of the open front end thereof.

A helically convoluted resistance wire 23 is located in the clearance between the outer circumferential face of the insulating member 11 and the inner surface of the outer electrode 25. FIG. 1 shows that this resistance wire 23 overlies a substantially cylindrical portion of the outer circumferential face of the insulating member 11 and that one end 28 of the wire 23 is conductively and fixedly connected with the outer electrode 25 in the illustrated embodiment by extending into an aperture 29 in the outer electrode 25 and by being suitably secured therein for instance by welding. The other end 26 of the resistance wire 23 is fixedly secured, also by welding or by any other suitable means, to a lug 27 of the sleeve or ring 12, and thereby is in conductive connection with the bus bar 21.

FIG. 2 shows most clearly that the outer circumferential face of the insulating member 11 is provided in the region of the cylindrical portion thereof, with two annular

circumferential grooves

31 and 32 which are so positioned as to be located substantially midway intermediate the

ends

26 and 28 of the wire 23. The

grooves

31 and 32 are located in two parallel planes extending transversely of the elongation of the member 11 or slight spacing with one another in longitudinal direction of the member 11. In accordance with the invention this spacing is such that each of the

grooves

31, 32 can accommodate a portion of a convolution of the wire 23. More specifically, these portions are accommodated in the

respective grooves

31, 32 at

points

33 and 34 which are located substantially diametrally opposite one another and which are longitudinally spaced from one another by a distance corresponding to the spacing of the

grooves

31, 32. Thus, the wire 23 is supported against movement not only at its

opposite ends

26, 28 but also intermediate these ends making it impossible for adjacent convolutions to move into contact with one another and to effect shorting.

It is clear that the present invention is not only highly advantageous but also is very simple and inexpensive. The

grooves

31, 32 can be provided in the member 11 in any suitable form, for instance by material removing tubes, or even simpler, by molding if the member 11 is produced by a molding process. It requires no separate materials or means which could increase the expense of the plug, and yet effects reliable securing of the convolutions of the wire 23 against the aforementioned undesired movement.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions, differing from the types described above.

While the invention has been illustrated and described as embodied in a glow plug, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

\Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

1. A glow plug comprising, in combination, an elongated inner electrode and an elongated sleeve-shaped outer electrode surrounding said inner electrode with clearance and defining with one end of said inner electrode a spark plug; an elongated insulating member surrounding said inner electrode in said clearance and comprising a portion provided with an outer circumferential face spaced from said outer electrode; terminal means fixedly carried by said plug and electrically insulated from said inner and outer electrodes; a helically convoluted resistance wire overlying said outer circumferential face spaced from said outer electrode and having a first end fixed to and conductively connected with the same, and a second end fixed to and conductively connected with said terminal means; and spacing means provided on said insulating member and adapted to maintain adjacent convolutions of said resistance wire out of engagement with one another whereby to prevent shorting of such adjacent convolutions.

2. A glow plug as defined in claim 1, wherein said spacing comprises at least two circular circumferential grooves provided in said face spaced from one another in longitudinal direction of said insulating member, each of said grooves accommodating a portion of one of said convolutions of said resistance wire.

3. A glow plug as defined in claim 1, wherein said spacing means comprises at least two circular circumferential grooves provided in said face spaced from one another in longitudinal direction of said insulating memher and located in parallel transverse planes, each of said grooves accommodating a portion of one of said convolutions of said resistance wire.

4. A glow plug as defined in claim 3, wherein said grooves are located substantially midway inter-mediate said ends of said resistance wire.

5. A glow plug as defined in claim 3, wherein said portions of said convolutions which are accommodated in said grooves are located diametrally opposite one another and are spaced from each other in longitudinal direction by a distance corresponding to the spacing of said grooves.

References Cited UNITED STATES PATENTS 1,427,057 8/1922 Bridgford et al. 317-82 X 1,679,900 8/1928 Higgins et al 317 s2 X 2,492,755 12/1949 McCollum 317-98 2,526,169 10/1950 Steeg 3l796 3,087,980 4/1963 Monnig 123-1465 VOLODYMYR Y. MAYEWSKY, Primary Examiner.

US. Cl. X.R.