JP3508155B2 - Glow plug - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug and is used for a diesel engine using a ceramic heater for a heat generating portion.

[0002]

2. Description of the Related Art Conventionally, for example, in the structure of a ceramic glow plug, a ceramic heater in which a high melting point metal is embedded in a ceramic as a heating element or a ceramic heater in which a conductive ceramic is embedded in an insulating ceramic is used as a heating element. And is held in a cylindrical housing.

First, as a method for holding the ceramic heater inside the housing, generally, a metal pipe is attached to the outer periphery of the ceramic heater by brazing, and then this metal pipe is brazed to one end of the cylindrical housing. The jointed ones are widely adopted, and the ease of manufacturing,
Has a proven track record of reliability. On the other hand, as a method of holding the center shaft inside the housing, it is necessary to firmly fix the center shaft to the housing while maintaining the insulating property. Therefore, JP-A-6
As described in JP-A-3-311022, both ends of the center rod are exposed, and a holding member with an insulating material is provided in a metal pipe at a central portion, and the holding member is inserted into a housing hole. A method has been proposed in which the outer periphery is caulked inwardly and fixed.

[0004]

However, in the above-mentioned conventional method, not only the powder insulation must be filled between the center rod and the metal pipe, but also the metal pipe is used to improve the filling density. The holding member for the center shaft must be formed by performing drawing from the radial direction and holding it. Therefore, it is very difficult to form the holding member for the center shaft.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a glow plug capable of easily holding the center shaft inside the housing.

[0006]

SUMMARY OF THE INVENTION Therefore, according to the present invention, a hollow housing, a heater having one end fitted and protruding from the other end, and electrically connected to one end of the heater are provided by the housing. In addition, the glow plug is characterized by comprising a center shaft inserted into the housing, and a fastening portion formed by tightly winding a thread on an outer peripheral surface of the center shaft and fixing the center shaft inside the housing. Is adopted.

[0007]

With the above structure, as a fastening member for holding the center shaft inside the housing, there is a fastening portion formed by tightly winding the thread around the center of the center shaft. The fastening portion can be formed by simply winding the thread around the center shaft. Therefore, it is very easy to form the fastening portion.

Therefore, the glow plug has a very easy structure for holding the center shaft inside the housing.

[0009]

As described above, the present invention has an excellent effect of providing a glow plug capable of easily holding the center shaft inside the housing.

[0010]

The present invention will be described below based on the embodiments shown in the drawings. In this embodiment, a case where the present invention is applied to the ceramic glow plug 1 will be described. FIG. 1 is a sectional view of a ceramic glow plug 1 showing an example of the structure of the glow plug of the present invention.

In FIG. 1, reference numeral 2 is a ceramic heater, which is made of an insulating ceramic in which a tungsten wire (not shown) such as a refractory metal or a heating wire made of a conductive ceramic is buried. One end of the heating wire (not shown) is led out to the end 2a of the ceramic heater 2 and is electrically connected to the coil-shaped lead wire 5 fitted to the end 2a of the ceramic heater 2. The other end of the heating wire (not shown) is led to the side surface 2b of the ceramic heater 2, and the side surface 2b of the ceramic heater 2 is nickel-plated. Further, the metal pipe 3 for holding the ceramic heater 2 is
It is brazed and fixed so as to include the ceramic heater 2. Then, the outer periphery of the metal pipe 3 is fixed by brazing to one end of a cylindrical metal housing 4 having a mounting screw 4a for an engine head (not shown). With such a configuration, the coil-shaped lead wire 5 fitted to the end portion 2a of the ceramic heater 2 and the metal pipe 3 brazed and fixed to the side surface 2b of the ceramic heater 2 are electrically connected to each other. . The lead wire 5 is electrically connected to a power source (not shown) through a center rod 6 made of carbon steel, and the metal pipe 3 is electrically grounded to a block of an internal combustion engine (not shown) through a metal housing 4. Has been done.

Here, since the center shaft 6 needs to be held inside the metal housing 4 while maintaining insulation, as shown in FIG. 1, the yarns are tightly wound so that no gap is formed between the yarns. A tightly wound portion 7 of the wound yarn is formed in the center portion, leaving both ends of the center shaft 6 bare. Then, the center shaft 6 is fixed by caulking inward from the body outer circumference 4b of the metal housing 4 through the tightly wound portion 7 of the thread.

That is, only by tightly winding the thread around the center shaft 6, the thread tightly wound portion 7 for insulatingly fixing the center shaft 6 inside the metal housing 4 can be formed. Therefore, it is very easy to manufacture. Also, the tightly wound portion 7 of the thread
Since the threads are tightly wound, a frictional force between the threads and a frictional force between the thread and the metal are generated, so that the threads are strong against the twisting force to the center shaft and the pulling force of the center shaft. It is composed.

Next, the yarn wound around the center shaft 6 will be described.
As the threads, natural fibers such as hemp and cotton, synthetic fibers such as nylon and vinylon, and inorganic fibers such as glass fibers and alumina fibers were used, and their fixing strength durability was compared. As conditions, the ceramic glow plug shown in FIG. 1 was prepared, and the test of 1000 cycles was repeated with 5 minutes at room temperature and then 5 minutes at 200 ° C. which is the maximum operating temperature in the actual engine as one cycle. . The results are shown in Table 1. In the table, those marked with ○ indicate a slight deterioration in fixing strength, those marked with △ show deterioration in fixing strength, but those with no practical problems, and those marked with × indicate deterioration in fixing strength. Indicates that it is not applicable to ceramic glow plugs.

[0015]

[Table 1]

In Table 1, it is shown that all the natural fibers and the inorganic fibers have no problem and have good durability.
However, it has been shown that synthetic fibers having low heat resistance are not suitable for practical use. Therefore, as the material of the thread, natural fiber, inorganic fiber, or heat-resistant synthetic fiber may be used. If the thread tightly wound portion 7 is formed of the thread made of these materials and the metal housing 4 is used for caulking, A ceramic glow plug with excellent durability can be obtained.

Next, as another embodiment, the basic construction is shown in FIG.
However, the densely wound portion 7 of the thread of the center shaft 6 is impregnated with a curable heat-resistant resin, for example, an epoxy resin. That is, the tightly wound portion 7 of the yarn is impregnated with the heat-resistant resin, so that the fixing strength is secured by both the yarn and the resin. Therefore, since the tightly wound portion of the curable yarn is formed, compared to the fixing strength of the center shaft of the first embodiment, the twisting force to the center shaft and the pulling force of the center shaft are
A more robust structure can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a ceramic glow plug showing an embodiment of the present invention.

[Explanation of symbols]

2 Ceramic heater 4 metal housing 6 center axis 7 Thread tightly wound part

Claims (2)

(57) [Claims] 1. A hollow housing, a heater having one end fitted and inserted in the other end by the housing, and a heater electrically connected to one end of the heater and inserted into the housing. A glow plug comprising: a center shaft; and a fastening portion that is formed by tightly winding a thread on an outer peripheral surface of the center shaft and that secures the center shaft inside the housing. 2. The glow plug according to claim 1, wherein the fastening portion is impregnated with a curable heat-resistant resin.