JPS6365234A - Ceramic glow plug - Google Patents

Abstract

PURPOSE:To prevent the ceramic heater part from being demaged so as to lengthen the service life of a glow plug by integrally forming the large diameter part and the small diameter part toward the plug end with a stepped part inbetween of a ceramic heater with a ceramic material of non-oxide group, and brazing the large diameter part to a cavity in the body hardware. CONSTITUTION:A small diameter ceramic heater 2 contains a heat generating element and is made of Si3N4, SiC, etc., and the large diameter part is connected thereto by brazing 12 a ceramic outer tube 5 made of the same material or ceramic of similar non-oxide group and is placed in a cavity in the main body hardware 1 to allow the electrical connection of the ceramic heater 2. A metallic tube 6 connected to the ceramic heater 2 and the ceramic outer tube 5 are mutually connected by brazing 14 at their ends, and both the outer tubes are connected by brazing to the cavity in the main body hardware 1. In this way, even if the large diameter part 2b or ceramic outer tube 5 is exposed to an engine in which a high combustion temperature exists, they will not by damaged, and the strength of the ceramic heater part 2 is adequately reinforced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a ceramic glow plug used primarily as a starting aid for diesel engines.

Conventional Technology 2 Ceramic heaters with a built-in resistor as a heat generating element have excellent heat resistance, but have the disadvantage of being brittle, and as shown in FIG. First, the metal outer cylinder 3 is brazed and joined to the metal outer cylinder 3, and the metal outer cylinder 3 is further brazed and joined to the inner cavity of the metal shell 1, so that the metal outer cylinder is integrated with the metal outer cylinder in a state that it protrudes from the end surface of the metal shell. It forms a glow plug, and has a structure in which it is screwed onto the cylinder head using the threaded portion 4 of the metal shell 1.

Problem 2 to be Solved by the Invention As mentioned above, the ceramic heater 2 has a weak point of brittleness, so it is reinforced with a metal outer cylinder 3, but the metal outer cylinder 3 has lower heat resistance than a ceramic material. When the combustion temperature of the engine is high (over 950'C), the tip of the metal outer cylinder 3 will be severely oxidized and worn out, or metal will melt and lose its ability to reinforce the strength of the ceramic heater. This has the drawback of shortening the lifespan of the glow plug, leading to damage.

Second Means for Solving the Problems The present invention does not employ a configuration in which the metal shell of the ceramic heater is joined to the metal shell via the metal outer cylinder as in the conventional examples and embodiments described above, but instead uses a ceramic heater of 313N4.

Made of non-oxide ceramic material such as SiC, the large-diameter part and the small-diameter part on the tip side are integrally connected via a stepped part, and the large-diameter part is brazed to the inner cavity of the metal shell. As a result, the large-diameter portion protrudes between the combustion chambers from the end surface of the metal shell. FIG. 1 is a sectional view of the embodiment, in which 2a indicates a small diameter portion of the ceramic heater 2, and 2b indicates a large diameter portion. FIG. 2 is a longitudinal cross-sectional view of another embodiment, in which a large-diameter part is a small-diameter ceramic heater 2 with a built-in heating element, and a non-oxide ceramic outer cylinder 5 made of the same material or the same type is joined by soldering 12. The ceramic outer cylinder 5 and the metal outer cylinder 6, which is built into the inner cavity of the metal shell 1 and joined to the ceramic heater 2 in order to provide electrical continuity to the ceramic heater 2, are brazed 14 at their end faces. Both outer cylinders are joined to the inner cavity of the metal shell 1 by brazing. Note that 7 is a resistor, 8 is a sealing material, 9 is an insulator, 1
0 indicates the terminal nut, and 11 indicates the center shaft.

Effects and effects: With the configuration of the present invention, even if the large-diameter portion or the ceramic outer cylinder portion is placed in a state of protruding into the combustion chamber in an engine with a high combustion temperature, the large-diameter portion or the ceramic outer cylinder portion will not be burned out. The strength of a portion of the ceramic heater can be sufficiently reinforced without this. The ceramic heater of the present invention can also be applied to the grounded type ceramic glow plug shown in FIG. 2, in which the resistor portion 7 is removed.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of the ceramic glow plug of the present invention.
FIG. 2 is a vertical cross-sectional view of another embodiment, and FIG. 3 is a vertical cross-sectional view of a conventional ceramic glow plug. 1... Metal shell 2... Ceramic heater-2a.
...Small diameter part 2b...Large diameter part 5...Ceramic outer tube 6...Built-in metal outer tube

Claims (2)

[Claims] (1) A non-oxide ceramic heater consisting of a small-diameter part on the tip side and a large-diameter part connected via a stepped part is installed in the inner cavity of the metal shell so that the large-diameter part projects directly into the engine combustion chamber. Bonded ceramic glow plug. (2) The ceramic glow plug according to claim 1, wherein the large diameter portion is formed by joining a separate non-oxide ceramic cylinder to the small diameter portion.