JPS61225517A - Ceramic glow plug - Google Patents

Abstract

PURPOSE:To improve the breaking strength and operation starting performance by a method wherein a relatively big straight part is formed in the vicinity of the end surface of a fitting or a metal outer cylinder, and the top end of the above big straight part is formed in a tapering shape. CONSTITUTION:A rod-shaped ceramic heater 2 is formed by imbeding and sintering a metal heating wire having high fusing point in a ceramic powder body. A ceramic glow plug is formed by direct joining to the inner bore of a fitting 4 after exposing the top end part of above heater 2, or formed by joining via a metal outer cylinder 1. On above plug, the exposed part of the ceramic heater 2 exposed from the end surface of the fitment or the metal outer cylinder is structured as a straight part 2a at the base part in the vicinity of the end surface, the top end is formed in tapered shape as a taper part 2b. Thus, the ceramic heater is provided with a straight part of which outer diameter is 3.5-4.0mmphi, length is 0.5-3.0mm, top end outer diameter is 2.5-3.0mmphi and exposed part length is 6-15mm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ceramic glow plug that is mainly installed in a diesel engine for starting, and particularly to a ceramic heater that serves as a heating element for the glow plug.

(Prior art) Diesel engines generally have poor starting performance at low temperatures, so a glow plug is attached to the auxiliary combustion chamber provided in the engine head, and when the plug is energized, it becomes red hot and the fuel is injected into the room. A method is used to increase the temperature by combusting a portion of the engine and improve the startability of the engine. In recent years, there has been a trend to use fuel as an afterglow for combustion stabilization not only during startup but also after startup for a long period of time, so it is increasingly necessary to improve its durability.

To achieve this purpose, a ceramic glow plug is used as a rapid heating type glow plug in which a heating wire of a high-melting point metal, such as a tungsten wire, is embedded as a coil in ceramic powder and sintered. As shown in FIG. 2, an example of a ceramic glow plug has a heater rod 2 held in the inner cavity of a metal outer cylinder 1, which has a circular cross-section, and its tip has a diameter around the outer diameter of the heater rod 2. It is rounded with a radius R that is -! It is shaped like a hemisphere. Note that 3 is a heating wire coil, 4 is a mounting bracket, and 5 is a center shaft.

Those with such ceramic heater rods have no directionality with respect to external forces, have stable bending strength, and have a uniform temperature distribution during heat generation, so there is no delay in temperature rise even during rapid temperature rise. However, for example, in self-regulating ceramic glow plugs, a diameter of 3.5mm is used to improve starting performance through simultaneous cranking. An OHφ ceramic heater was used.

(Problems to be Solved by the Invention) However, the ceramic heater with a diameter of 3.0 mmφ is considered to have somewhat insufficient bending ability, and the ceramic heater with a diameter of 5.5 mmφ~4.
, OMφ is desired.

However, if the diameter is set to 3.5 to 4.0 fl.phi., the increased capacity of a portion of the heater will lead to deterioration of the temperature rising characteristics.

Currently the diameter is 2.5~4. The following table shows the results of making an OHφ ceramic heater and examining its strength, temperature rise characteristics, and thermal shock resistance.

Note *1: Breakage occurs at 0, 25a+φ, o, sawsφ, and from the thermal shock QK data of 0.35M, it is clear that the strength is required to be 9 to 60.

Note that it is desirable that the temperature increase characteristic that allows simultaneous cranking be 900° C. and reach within 5 seconds, but this cannot be achieved if the temperature is 3.5 Hφ or more. Note that the breakage of the upper two mixer heaters occurred at the end face of the outer cylinder.

(Means for Solving the Problems) The present invention has been made to solve the above problems.
Ceramic powder white paper using high melting point metal heating wires; A rod-shaped ceramic heater made by embedding and sintering the heating wire with its tip end at 1
! In a ceramic glow plug which is connected to the inner cavity of a mounting bracket directly or via a metal outer cylinder, the structure of the exposed external portion of the ceramic heater from the end face of the mounting bracket or metal outer cylinder is This is a glow plug in which the base near the end face is a straight part and the tip thereof is formed into a tapered part.

(Function) The ceramic heater is started by forming a relatively thick straight part near the end face of the mounting bracket or metal outer cylinder, which is prone to breakage, to increase breakage resistance, and forming a tapered part in a part unrelated to breakage. It is intended to improve sexual performance.

(Example) In one rod, 2a is a straight part and 2b is a tapered part. The preferred dimensions are as follows.

Outer diameter of straight part 3.5~4. OMφ length
0.5-3. OWl Exposed part length 6-15f1 Next, the temperature rise characteristics of the ceramic heater combs shown in Fig. 3 (present invention, referred to as shape A) and Fig. 4 (comparative example, referred to as shape B) were tested to compare. The results are as shown in Figure 5.
It is.

According to this, shape A was heated to 900° C. in 4.5 seconds, while shape B was heated to 900° C. in 5.5 seconds.

Shape A, which has a tapered shape, has a diameter of 5.5 mm because the tapered shape tends to cause heat concentration to occur at the tip. It has the same temperature rise characteristics as a Qwxφ straight-shaped product, but its strength is the same as a straight-shaped product with a diameter of 3.5ffφ, and the breakage resistance is high. (Effects of the Invention) It can be understood from the above examples. According to the present invention, the shape of the ceramic glow plug is such that the base close to the end face of the mounting bracket or metal outer cylinder is straight, giving the required outer diameter and increasing the breakage strength, while tapering the tip side from the straight part. By setting the temperature rise characteristic to 900℃, 5
We were able to achieve an excellent result in that it took less than a second.

It goes without saying that the ceramic glow plug of the present invention can be applied not only to a grounded type of mounting bracket, but also to a two-leg type (two-wire type) and a self-control type.

[Brief explanation of the drawing]

Fig. 4 shows a front view of a prototype of a comparative example with larger dimensions, and Fig. 5 shows the results of a comparative test of the temperature rise characteristics of the prototypes of Figs. 3 and 4. It is a graph. 1... Metal outer cylinder 2... Ceramic heater rod 2a
...Straight part 2b...Tapered part 3.
・・Heating wire 4・Mounting bracket 5・Center shaft agent
Patent Attorney Mamoru Takeuchi 2nd WI Figure 3 Figure 4 Figure 511

Claims (2)

[Claims] (1) A rod-shaped ceramic heater made by embedding and sintering a heating wire of a high-melting point metal in ceramic powder is joined to the inner cavity of a mounting bracket directly or via a metal outer cylinder with its tip exposed. The ceramic glow plug is characterized in that the exposed portion of the ceramic heater from the end surface of the mounting bracket or the metal outer cylinder has a straight portion at the base of the end surface and a tapered portion at the tip thereof. glow plug (2) The outer diameter of the straight part of the ceramic heater is 3.
5~4.0mmφ, the length is 0.5~3.0mm,
The outer diameter of the tip is 2.5 to 3.0 mmφ, and the length of the exposed part is 6
The ceramic glow plug according to claim 1, which has a diameter of 15 mm.