JPH0810750Y2 - Ceramic glow plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention relates to a ceramic glow plug mainly mounted on a diesel engine.

(Prior Art) As shown in FIG. 2, a ceramic glow plug includes a ceramic heater 101, a metal outer tube 103 that covers and supports the periphery of the ceramic heater 101 except the tip side, and a metal outer tube 103 that covers and supports the periphery. It is mainly composed of a mounting tool 105 on the engine side. The ceramic heater 101 and the metal outer tube 103 are joined by brazing, but this joining is more difficult than brazing between metals, and for this reason, JP-A-59-59
In Japanese Patent No. 138812, the borosilicate glass 107 is coated on the peripheral surface of the ceramic heater 101 to facilitate brazing and joining.

(Problems to be Solved by the Invention) In such a conventional ceramic glow plug, the borosilicate glass 107 around the ceramic heater 101 is used.
From the concept of simply coating the joint portion with the metal outer cylinder 103, the portion 109 protruding from the metal outer cylinder 103 is
There is a possibility that it will be even coated. In such a case, when an external force such as a shock wave generated in the engine combustion chamber is applied to the ceramic glow plug, the bending moment is maximized at the end portion 1 of the metal outer cylinder 103.
In the vicinity of 03a, there is a problem that the borosilicate glass having a lower strength than that of the ceramic is damaged, which causes stress concentration on the ceramic heater 101, and the ceramic heater 101 is also damaged.

FIG. 3 compares the bending strength of the ceramic heater 101 when the ceramic heater 101 is glass-coated (solid line) and when it is not (broken line). FIG. 4 is a schematic view of the experimental apparatus, in which the ceramic heater 101 is supported by fulcrums A and B spaced at a distance of 20 mm, and stress is applied from above the substantially central portion (arrow direction). According to this, it can be seen that the bending strength is weaker when the glass coating is applied under the temperature condition below 800 ° C. This is because the glass coating layer has low toughness on the low temperature side, and therefore is more likely to be damaged than a glassless product, and this damage causes the ceramic heater 101
This causes stress concentration on the.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a ceramic glow plug in which the strength of a glass-coated ceramic heater is improved.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention is directed to surrounding the ceramic heater, which faces the metal outer cylinder except the vicinity of the end portion on the tip side of the metal outer cylinder, A glass layer for joining the metal outer cylinder and the ceramic heater to each other by brazing is formed.

(Function) Since the glass layer is not formed around the ceramic heater near the end of the metal outer tube, even if an external force is applied to the ceramic heater, the end of the metal outer tube causes stress on the glass layer. Therefore, the glass layer is prevented from being damaged and the ceramic heater is prevented from being damaged.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a ceramic glow plug used in a diesel engine. The ceramic heater 1 is supported by the metal outer cylinder 3 in a state of protruding from the tip end 3a of the metal outer cylinder 3, and the metal outer cylinder 3 is It is supported by a fixture 5 that covers approximately half of the base side. A screw portion 5a to be fastened and mounted on the engine side is formed at substantially the center of the fixture 5. The joining of the ceramic heater 1 and the metal outer cylinder 3 and the joining of the metal outer cylinder 3 and the fixture 5 are both brazing with silver brazing. Reference numeral 6 is a center shaft having a mounting bracket 5 and a screw portion that is insulated and sealed, and is connected to a power supply device (not shown).

The borosilicate glass 7 is coated on the peripheral surface of the ceramic heater 1 facing the metal outer cylinder 3 except for the vicinity of the end 3a on the tip side of the metal outer cylinder 3 in order to facilitate brazing and joining with the metal outer cylinder 3. is there.

In a ceramic glow plug with such a structure,
When the ceramic glow plug tip facing the engine combustion chamber receives an external force such as a shock wave generated in the combustion chamber,
Since the borosilicate glass 7 is not coated on the tip side from the vicinity of the tip side end portion 3a of the metal outer tube 3 on which the largest bending moment acts, the tip side end portion 3a of the metal outer tube 3 is not coated.
Stress on the borosilicate glass 7 due to the vicinity is avoided.
Thereby, the coating layer of the borosilicate glass 7 is prevented from being damaged, and the ceramic heater 1 is also prevented from being damaged accordingly, so that the durability of the ceramic glow plug is improved.

[Advantage of the Invention] As described above, according to the present invention, the glass layer around the ceramic heater formed at the joint portion with the metal outer cylinder is applied to the metal outer cylinder to which the largest bending moment is applied when an external force is applied. Since it is provided in the part facing the metal outer cylinder except near the tip end, the tip end of the metal outer cylinder does not apply stress to the glass layer when external force is applied, thus preventing damage to the glass layer. Therefore, the durability of the ceramic glow plug is improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a ceramic glow plug according to an embodiment of the present invention, FIG. 2 is a sectional view of a conventional ceramic glow plug, and FIG. 3 is a sectional view of a ceramic heater with and without glass coating. FIG. 4 is an explanatory view showing the bending strength, and FIG. 4 is a schematic view showing an experimental apparatus for measuring the bending strength of FIG. 1 ... Ceramic heater, 3 ... Metal outer cylinder 3a ... Tip end, 7 ... Borosilicate glass

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Ito 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Nihon Special Ceramics Co., Ltd. (56) Reference JP-A-60-216125 (JP, A)

Claims (2)

[Scope of utility model registration request] 1. A ceramic glow plug in which a ceramic heater projects from a tip of a metal outer tube and is supported by the metal outer tube. A ceramic glow plug, wherein a glass layer is formed for joining the cylinder and the ceramic heater to each other by brazing. 2. The ceramic glow plug according to claim 1, wherein the glass layer is borosilicate glass and the brazing is silver brazing.