|Title of Invention||
CERAMIC GLOW PLUG
|Abstract||The invention proposes a ceramic glow plug in which a metallic, tubular holder, at its combustion-chamber side end, holds a ceramic u-shaped heating device in a cantilevered manner and, on the side remote from the combustion chamber, has a terminal stud for applying a voltage to the ceramic heating device. At its end which is surrounded by the holder, the ceramic heating device has a section of maximum diameter and is covered with an insulting layer which has for [sic] cutouts for making electrical contact. One cutout is provided on that end side of the ceramic heating device which is remote from the combustion chamber and a second cutout is provided on the outer wall of the ceramic heating device. For [sic] an electrically conductive sealing compound is arranged between the outer wall of the ceramic heating device and the inner wall of the holder.|
The invention starts from a ceramic glow plug for diesel engines of the' generic type of the main claim DE-A 3 837 128 has already disclosed a glow plug of this type in which a ceramic heating device is held by the tip of a cylindrical holder. Here, the ceramic heating device is electrically insulated from the holder. On the side of the cylindrical holder opposite the ceramic heating device, there is a connection device which makes contact with the supply voltage- The ceramic heating device comprises a U-shaped heating portion, the two ends of the U-shaped heating section in each case being brought into contact with the connection device. During a glow operation, a voltage is applied to the ceramic heating device, in such a manner that a current flows from one end of the U-shaped heating portion, via the tip of the heating portion, the said tip being situated on the combustion-chamber side to the other end of the U-shaped heating portion* Owing to the resistance of the ceramic, the current heats the heating portion, with the result that the latter glows and the fuel/air mixture is heated for ignition.
Advantages of the invention
The ceramic - glow plug according to the invention with the features of the main claim has the advantage that very simple contacting of the ceramic heating element without additional sintered-in connection contacts is possible. Furthermore, the fact that contact is made with the ceramic heating device, which is in the form of a glow pin, without a material-to-material bond, by the simple formation of contact
surfaces in the insulation, has the advantage that it is possible to dispense with a sintered-in metallic supply conductor. This ensures that the there is no weakening of the ceramic by sintered-in foreign bodies or damage to the ceramic or the contact during assembly. Ultimately, manufacturing becomes easier and therefore less expensive. At the same time, the introduction of a sealing packing between the housing inner wall and the outer wall of the ceramic heating device provides ' a very good seal with respect to the combustion chamber while, at the same time, improving electrical contact.
Advantageous developments and improvements of the
ceramic glow plug specified in the main claim are
possible by means of the measures presented in the
It is particularly advantageous if the glow pin, in the region remote from the combustion chamber, has a section of larger diameter, since the shoulder formed in this way between the section of smaller diameter and the section of larger diameter, when the glow pin is inserted into the housing, compresses the sealing material and thus ensures very good compression- As a result, the sealing of the components of the glow plug which are remote from the combustion chamber with respect to the combustion chamber is significantly improved. Ultimately, the surface pressures required to achieve reliable earth contacting and engine space sealing are minima zed with the result that, in turn, the tangential tensile stresses in the ceramic glow pin are reduced. The use of a contact spring for attaching that end side of one end of the u-shaped heating device which is opposite the combustion chamber for the purpose of making contact with the supply voltage moreover makes it possible to compensate for different layer thick nesses between the insulating layer and the
cutouts in this insulating layer. As a result, reliable contact-making is ensured once again. Since the compressive forces required for reliable contact in the glow pin according to the invention are low, no additional tensile stresses are - produced in the ceramic glow pin. The use of a powder seal as sealing compound between housing and glow pin ensures that no particular demands are placed on the surface quality for sealing. Consequently, it is impossible for any voltage rises to occur as a result of surface roughness.
Exemplary embodiments of the invention are illustrated in the drawing and explained in greater detail in the description which follows. Figure 1 shows the glow plug according to the invention and Figure 2 shows the ceramic glow pin.
Description of the exemplary embodiments
Figure 1 shows a longitudinal section through a ceramic glow plug according to the invention. The glow plug in this case comprises a cylindrical tubular metal housing, which represents the plug housing 10. At its
combustion-chamber side end 11, the plug housing 10
comprises a ceramic heating device 12. This ceramic heating device 12 is a glow pin which is embodied as a layered ceramic composite comprising an insulating composite ceramic layer 13, which lies between two electrically conductive composite ceramic layers 14. The electrically conductive composite ceramic layers are arranged substantially in a u shape. At the tip of the ceramic heating device, the two electrically conductive composite ceramic layers 14 are connected by a thin web of electrically conductive composite ceramic- The insulation and electrical contacting of the glow pin is to be explained in more detail below
remote from the combustion chamber, specifically in such a manner tjhat the terminal stud makes contact with one limb of the u-shaped electrically conductive ceramic. The second electrical contact is made on the lateral outer wall of the second limb of the u-shaped, . electrically conductive ceramic. The contact between this second cutout 22 and the plug housing is made via the sealing compound 17, as can be seen from * Figure 1. In Figure 2, the cutouts 21 and 22 are in each case shown as dark areas, Consequently, it can be clearly seen from Figure 2 that the contact areas are selected in such a way that, when a voltage is applied, the glow current flows from one end of the u-shaped heating device, via the combustion-chamber side tip, to the other end of the u-shaped heating device. To provide good electrical contact, the cutouts 21 and 22 may in each case by provided with a metal coating of, for example, nickel.
1, Ceramic glow plug with a tubular metal housing which, at its combustion-chamber side end, holds a ceramic, u-shaped. heating device in the form of a glow pin in a cantilevered manner, with a terminal stud, which is arranged on the side remote from the combustion chamber and makes electrical contact with the ceramic heating device, characterized in' that the ceramic heating device, at least in the region in which it is surrounded by the metal housing, is covered by an insulating layer, and cutouts are provided in this insulating layer, a first cutout being arranged on that end side of one end of the u-shaped ceramic heating device which is remote from the combustion chamber and a second cutout being arranged laterally on the outer wall of the other end of the u-shaped ceramic heating device, and an electrically conductive sealing compound being arranged in the region of the second cutout between the outer wall of the ceramic heating device and the inner wall of the metal housing.
2. Ceramic glow plug according to ■ Claim 1, characterized in that the ceramic heating -device, in the section surrounded by the metal housing in a partial region remote from the combustion chamber has a larger diameter, this larger diameter being selected in such a way that the ceramic heating device, during assembly, can be pushed into the metal housing from the end remote from the combustion chamber.
3 • Ceramic glow plug according to Claim 1 and/or 2, characterized in that the insulating layer is applied by means of glazing.
Ceramic glow plug according to one of Claims 1 to
3, characterized in that the cutouts in the
insulating layer are moralized.
Ceramic glow plug according to one of the preceding claims, characterized in that the electrically conductive sealing compound is an electrically conductive powder.
Ceramic glow plug according to Claim 5, characterized in that the electrically conductive powder is graphite, a metal powder or a powder mixture of ceramic with conductive particles.
Ceramic glow plug according to one of Claims 1 to
4, characterized in that the electrically
conductive sealing compound is a hollow cylinder
wound out of a graphite sheet.
A ceramic glow plug, substantially as herein described with reference to tlie accompanying drawings.
|Indian Patent Application Number||IN/PCT/2001/553/CHE|
|PG Journal Number||50/2007|
|Date of Filing||19-Apr-2001|
|Name of Patentee||M/S. ROBERT BOSCH GMBH|
|Applicant Address||Postfach 30 02 20, D-70442 Stuttgart,|
|PCT International Classification Number||F23Q 7/00|
|PCT International Application Number||PCT/DE1999/03098|
|PCT International Filing date||1999-09-25|