WO2005061962A1

WO2005061962A1 - Glow plug for ceramic heater

Info

Publication number: WO2005061962A1
Application number: PCT/JP2004/018217
Authority: WO
Inventors: Arihito Tanaka; Jian Zhao
Original assignee: Bosch Corporation
Priority date: 2003-12-22
Filing date: 2004-12-07
Publication date: 2005-07-07
Also published as: JP2005180855A

Abstract

The head (4a) side of a ceramic heater (4) has a tapered shape with a small diameter, and the inner diameter of that portion of a metallic outer tube (2) into which the ceramic heater (4) is pressed is made to be uniform. Further, the head (4a) of the ceramic heater (4) has a smaller diameter than the inner diameter of the metallic outer tube (2), and the rear end (4b) of the ceramic heater has a larger diameter than the inner diameter of the metallic outer tube (2). When the ceramic heater (4) is pressed into the metallic outer tube (2), deformation of the metallic outer tube (2) and breakage of the ceramic heater (4) are prevented, and coming off of the ceramic heater (4) in use can be prevented.

Description

Specification

Ceramic heater type plug

Technical field

The present invention relates to a glow plug used for assisting starting of a diesel engine, and more particularly, to a ceramic heater type glow plug using a ceramic heater as a heating element.

Background art

[0002] In general, a ceramic heater type glow plug used for assisting a start of a diesel engine has a ceramic heater held in a metal outer cylinder with a tip end exposed to the outside. The rear side is inserted and fixed in the front end of a cylindrical housing that is a mounting bracket for the cylinder head of the engine, and one electrode of a heating member such as a heating coil embedded in the ceramic heater is made of the metal. While being electrically connected to the outer cylinder, the other electrode is taken out to the outside via an electrode take-out fitting, and is electrically connected to an external connection terminal fixed to the other end of the cylindrical housing via an insulator. It has a configuration.

[0003] In the glow plug for a diesel engine, brazing or press fitting is generally used as a method of fixing a ceramic heater to a metal outer cylinder. When a ceramic heater is fixed in a metal outer cylinder by press-fitting, in the conventional structure, the inside diameter of the portion where the ceramic heater of the metal outer cylinder is press-fitted is made uniform, and the entire length of the metal outer cylinder is fixed in this metal outer cylinder. A ceramic heater having the same outer diameter is press-fitted over the entire area (for example, see Patent Document 1).

Patent Document 1: JP 2001-324141 A

Disclosure of the invention

Problems to be solved by the invention

[0004] A case in which a ceramic heater having the same outer diameter over the entire length is fixed by press-fitting into a metal outer cylinder having the same inner diameter over the entire portion into which the ceramic heater is press-fitted as in the conventional configuration described above. The press-fit length increases, so the press-fit load increases The metal outer cylinder may be buckled or damaged the ceramic heater. In addition, there is a problem that if the dimension control becomes loose, variations in the press-fit load and the like occur.

[0005] As described above, if the load at the time of press-fitting becomes excessive, the ceramic heater may be damaged. Therefore, in the conventional configuration, the press-fit allowance cannot be increased, and the press-fit allowance must be reduced. Helped. When the press-fitting margin is reduced in this way, when the metal outer cylinder is actually attached to the cylinder head of the engine and is used, heat is applied to the metal outer cylinder to thermally expand, and the space between the metal outer cylinder and the ceramic heater is increased. There was a risk that the ceramic heater would relax, slip out of the metal outer cylinder, fall into the combustion chamber of the cylinder, and damage the interior of the engine.

[0006] The present invention has been made to solve the above problems, and when a ceramic heater is pressed into a metal outer cylinder, the metal outer cylinder may be deformed or the ceramic heater may be damaged. It is an object of the present invention to provide a ceramic heater type glow plug which can prevent a ceramic heater from falling off due to a difference in thermal expansion between a metal outer cylinder and a ceramic heater when used in an engine. It is assumed that.

Means for solving the problem

[0007] The invention described in claim 1 has a ceramic heater including a ceramic heater having a distal end exposed to the outside and held in a metal outer cylinder, and a cylindrical housing to which the metal outer cylinder is fixed. In the Lamix heater type glow plug, the ceramic heater has a tapered shape having a small diameter at a tip end side.

[0008] The invention described in claim 2 is characterized in that the ceramic heater is press-fitted into a metal outer cylinder having an inner diameter smaller than an outer diameter of a rear end portion.

[0009] The invention described in claim 3 is characterized in that a portion of the metal outer cylinder holding the ceramic heater has the same inner diameter over the entire length.

[0010] Further, the invention described in claim 4 is characterized in that the metal outer cylinder and the ceramic heater are brazed.

[0011] The invention described in claim 5 is a center provided with a ceramic heater having a distal end exposed to the outside and held in a metal outer cylinder, and a cylindrical housing to which the metal outer cylinder is fixed. Each of the Lamix heater type glow plugs includes a ceramic heater having a tapered shape with a small diameter at the distal end, and a cylindrical member for holding the ceramic heater. A first fixing means for fixing the ceramic heater to the cylindrical member; and a second fixing means for fixing the ceramic heater fixed by the first fixing means in the metal outer cylinder. It is characterized by the following.

[0012] The invention described in claim 6 is characterized in that the first fixing means is press-fitting or brazing.

[0013] The invention described in claim 7 is characterized in that the second fixing means is press-fitting or brazing.

The invention's effect

In the ceramic heater type glow plug according to the first aspect of the present invention, the portion of the ceramic heater that is press-fitted into the metal outer cylinder is short, so that the press-fit load does not become excessive. Since the variation in load can be reduced, there is no possibility that the metal outer cylinder will be deformed or the ceramic heater will be damaged during press fitting. In addition, since the press-fit length is reduced, the variation in the press-fit load is reduced, and the tightening amount can be increased.

[0015] In the invention described in claim 2, the outer diameter of the rear end portion of the ceramic heater is larger than the inner diameter of the metal outer cylinder. Even if the ceramic heater is relaxed due to a difference in thermal expansion with the heater, it is possible to prevent the ceramic heater from dropping from the metal outer cylinder to the front side, that is, the inside of the engine.

Brief Description of Drawings

FIG. 1 is a longitudinal sectional view showing a main part of a ceramic heater type glow plug according to one embodiment of the present invention, showing a state in which a ceramic heater and a metal outer cylinder are being assembled. (Example 1)

FIG. 2 is a longitudinal sectional view showing a state at the time of completion of the assembly in FIG. 1.

FIG. 3 is a longitudinal sectional view showing a main part of a ceramic heater type glow plug according to a second embodiment. (Example 2)

FIG. 4 is a longitudinal sectional view showing a main part of a ceramic heater type glow plug according to a third embodiment. (Example 3)

FIG. 5 is a longitudinal sectional view showing the overall configuration of a ceramic heater type glow plug according to a fourth embodiment. (Example 4) Explanation of reference numerals

[0017] 2 Metal outer cylinder

4 Ceramic heater

4a Tip of ceramic heater

4b Rear end of ceramic heater

BEST MODE FOR CARRYING OUT THE INVENTION

Although not shown, the ceramic heater, which is the heating element of the ceramic heater type glow plug, has a heating member such as a heating coil embedded inside a ceramic insulator constituting its main body. A negative lead wire is connected to one end of the coil, and a positive lead wire is connected to the other end. The lead wire on the negative electrode side is taken out from the outer peripheral surface of the ceramic insulator and is electrically connected to the inner surface of the metal outer cylinder, while the lead wire on the positive electrode side is the position where the heating coil is embedded (metal It extends to the end opposite to the end (exposed to the outside of the outer cylinder), and is electrically connected to the end of the electrode extraction bracket by brazing at this end. Furthermore, the rear end force of the metal fitting is connected to the front end of the external connection terminal.

[0019] The ceramic heater is fixed by being press-fitted into a metal outer cylinder, and is fixed to a cylindrical housing, which is a fitting to a cylinder head, via the metal outer cylinder.

[0020] In the ceramic heater type glow plug having the above-described configuration, the front end portion of the ceramic heater is tapered to have a small diameter, and the inside of the metal outer cylinder having an inner diameter smaller than the outer diameter of the rear end portion of the ceramic heater. With the simple structure of press-fitting, when used with the cylinder head of the engine used, the press-fitted part between the ceramic heater and the metal outer cylinder is loosened due to the difference in the coefficient of thermal expansion when heated. In this case, it is possible to prevent the ceramic heater from falling off the metal outer cylinder, and to prevent the ceramic heater from being damaged during press-fitting and the metal outer cylinder from being deformed.

Example 1

Hereinafter, the present invention will be described with reference to examples shown in the drawings. FIGS. 1 and 2 show the essential parts of a ceramic heater type glow plug according to an embodiment of the present invention (a metal outer cylinder 2 and a metal outer cylinder 2). FIG. 4 is a vertical cross-sectional view showing a ceramic heater 4) that is press-fitted into a cylinder 2 and shows a step of press-fitting and fixing the ceramic heater 4 into a metal outer cylinder 2.

In this embodiment, the metal outer cylinder 2 has a cylindrical shape having a large-diameter portion 2a and a small-diameter portion 2b, and the ceramic heater 4 is press-fitted and fixed in the small-diameter portion 2b. The small diameter portion 2b into which the ceramic heater 4 is press-fitted has a uniform inner diameter over the entire length.

The ceramic heater 4 press-fitted into the metal outer cylinder 2 having the above-described configuration is fixed to the metal outer cylinder 2 and is exposed from the distal end 2 c of the metal outer cylinder 2 to the outside. A heating member such as a coil-shaped resistance heating wire is embedded inside 4a (see FIG. 2) (not shown). The negative lead wire connected to one end of the heating coil is taken out at a position where it comes into contact with the inner surface of the metal outer cylinder 2 with the ceramic heater 4 fixed to the metal outer cylinder 2. It is electrically connected to tube 2. The positive lead wire connected to the other end of the heating coil extends to the rear end 4b (the upper part in FIGS. 1 and 2) of the ceramic heater 4 and is formed at the rear end 4b. In the mounting hole 4c, it is connected to the distal end portion 6a of the electrode take-out fitting 6 by, for example, bonding.

[0024] The rear end of the electrode take-out fitting 6 in which the tip 6a is connected to the lead wire on the positive electrode side of the ceramic heater 4 extends from the large-diameter portion 2a of the metal outer cylinder 2 to the outside. The cylinder 2 is connected to an external connection terminal (not shown) fixed via an insulator to a cylindrical housing (not shown) to which the cylinder 2 is fixed.

[0025] The ceramic heater 4 has a tapered shape with a small diameter at the front end 4a and a large diameter at the rear end 4b. The outer diameter of the rear end portion 4b, which is smaller than the inner diameter of the small diameter portion 2b of the metal outer cylinder 2, is smaller than the inner diameter of the small diameter portion 2b. It is getting bigger.

A process of press-fitting the ceramic heater 4 having the above configuration into the metal outer cylinder 2 and fixing the same will be described. As described above, the ceramic heater 4 has the electrode extraction fitting 6 connected to the rear end 4b in advance. The ceramic heater 4 is inserted into the large-diameter portion 2a of the metal outer cylinder 2 from the small-diameter tip portion 4a side. The distal end 4a side of the ceramic heater 4 is smaller in diameter than the inner diameter of the small diameter portion 2b of the metal outer cylinder 4, so that it is inserted halfway without resistance (the state shown in FIG. 1). Outer diameter force of the ceramic heater 4 After the position corresponding to the inner diameter of the metal outer cylinder 2, the rear end 4 b side of the ceramic heater 4 is pressurized and pressed into the small diameter section 2 b of the metal outer cylinder 2. (Refer to symbol P in Figs. 1 and 2). The press-fitting process is completed by protruding the tip 4a side of the ceramic heater 4 by a predetermined length to the outside of the metal outer cylinder 2 (see FIG. 2).

In the configuration of this embodiment, the length of the portion where the outer diameter of the ceramic heater 4 is larger than the inner diameter of the metal outer cylinder 2, that is, the length of the portion having the press-fitting allowance is shorter than the conventional configuration. The possibility that the metal outer cylinder 2 is deformed or the ceramic heater 4 is damaged at the time of press-fitting without the risk of excessively large incoming load is reduced. The pressing force can be easily controlled, and a sufficient amount of tightening can be secured. Also, since the rear end 4b of the ceramic heater 4 located inside the metal outer cylinder 2 has a larger diameter, the ceramic heater 4 and the metal outer cylinder 3 need not be connected when used in an engine. Even when the thermal expansion difference causes relaxation, the ceramic heater 4 does not escape from the front end 2c side of the metal outer cylinder 2 and falls into the combustion chamber of the engine to damage the inside.

Example 2

FIG. 3 is a longitudinal sectional view showing a main part of a ceramic heater type glow plug according to a second embodiment, that is, a ceramic heater 4 press-fitted into a metal outer cylinder 2 similarly to the first embodiment. It is a figure. In this embodiment, a heating member such as a heating coil buried in the ceramic heater 4 is connected to the tip 106a of a lead wire 106 for taking out an electrode in one electrode force mounting hole 4c. A coil portion 106b is provided at the rear end of the electrode lead-out lead wire 106, and a rigid rod-shaped metal fitting (not shown) is inserted into the coil portion 106a to be electrically connected. Also in this embodiment, the outer diameter of the ceramic heater 4 and the inner diameter of the metal outer cylinder 2 are the same as in the first embodiment, and the same effects can be obtained. In any case, the ceramic heater 4 has a tapered tip end, and the metal outer cylinder 2 has a uniform diameter smaller than the rear end 4b of the ceramic heater 4 and larger than the tip 4a. Any other structure may be used as long as it has an appropriate inner diameter.

When the ceramic heater 4 is fixed by press-fitting into the metal outer cylinder 2 as in each of the above-described embodiments, the ceramic heater 4 and the ceramic heater 4 may be further joined by brazing. By performing such brazing, the reliability of the bonding strength between the two can be further increased. It is possible.

Example 3

In each of the above embodiments, the tapered ceramic heater 4 is directly pressed into the metal outer cylinder 2 and fixed, but is not necessarily limited to the one directly fixed to the metal outer cylinder 2. is not. For example, as in the third embodiment shown in FIG. 4, the rear side of the tapered ceramic heater 4 is fixed in a cylindrical member 20 such as a metal pipe by press-fitting or brazing. The ceramic heater section 22 composed of the member 20 may be integrally fixed in the metal outer cylinder 2 by press fitting or brazing. Also in the case of this configuration, the same retaining effect and other effects as in the above embodiments can be obtained.

Example 4

FIG. 5 is a longitudinal sectional view of a ceramic heater type glow plug according to a fourth embodiment. Also in this embodiment, the ceramic heater 104 has a tapered shape in which the tip 104a side has a small diameter. On the other hand, the metal outer cylinder 102 has the same inner diameter over its entire length, and the inner diameter of the metal outer cylinder 102 is larger than that of the tip 104a of the ceramic heater 104, and It is smaller than the end 104b side.

The ceramic heater 104 having the above-described shape is inserted into the metal outer cylinder 102 from the front end 104a side, and the rear end 104b side is pressed into the inner peripheral surface of the metal outer cylinder 102. Similarly to the first embodiment, the distal end portion 104a in which the heat generating member such as the heat generating coil is embedded is fixed in such a manner that the distal end portion 102c of the metal outer cylinder 102 projects outward.

[0034] The metal outer cylinder 102 to which the ceramic heater 104 is fixed by press fitting is inserted into the distal end 108a of the cylindrical nosing 108 and fixed by brazing or press fitting. The cylindrical housing 108 is a fitting for mounting on the wall surface of the cylinder head of the engine, and has a mounting screw 108b formed on the outer peripheral surface, and a hexagonal portion 108c for screw operation is provided at the rear end. .

In this glow plug configuration, one electrode of the ceramic heater 104 is taken out on its outer peripheral surface and electrically connected to the metal outer cylinder 102, and the other electrode is connected to the rear end of the ceramic heater 104. Conductive material (Graphite pill) on the 104b side via a cylindrical body 112 that also becomes insulating material 110 is inserted, and the conductive material 110 is constantly pressed by a rod-shaped electrode extraction metal fitting 116 fixed to the rear end of the housing 108 via an insulator 114 so that electrical connection is made. I have.

If the outer diameter of the ceramic heater and the inner diameter of the metal outer cylinder are uniform over the entire press-fitted portion, as in the conventional configuration, when they are attached to the engine and used, they will relax due to the difference in thermal expansion. However, the ceramic heater may move to the distal end side of the metal outer cylinder, and the electric connection may not be maintained. In this embodiment, the ceramic heater 104 is constantly pressed. Also, since there is no possibility of moving to the tip 102a side of the metal outer cylinder 102, electrical connection can be reliably performed. In the case of this structure, it is also possible to arrange a pressure sensor or the like between the conductive material 110 and the rear end surface of the ceramic heater 104 to measure the pressure in the combustion chamber and the like.

Claims

The scope of the claims

[1] In a ceramic heater type glove plug comprising a ceramic heater having a distal end exposed to the outside and held in a metal outer cylinder, and a cylindrical housing to which the metal outer cylinder is fixed,

A ceramic heater type glow plug, wherein the ceramic heater has a tapered shape with a small diameter at a tip end side.

2. The ceramic heater type glow plug according to claim 1, wherein the ceramic heater is press-fitted into a metal outer cylinder having an inner diameter smaller than an outer diameter of a rear end portion.

3. The ceramic heater type glow plug according to claim 2, wherein a portion of the metal outer cylinder holding the ceramic heater has the same inner diameter over the entire length.

4. The ceramic heater type glow plug according to claim 1, wherein the metal outer cylinder and the ceramic heater are brazed.

[5] In a ceramic heater type glove plug including a ceramic heater having a distal end exposed to the outside and held in a metal outer cylinder, and a cylindrical housing to which the metal outer cylinder is fixed,

A ceramic heater having a tapered distal end portion having a small diameter; a cylindrical member for holding the ceramic heater; first fixing means for fixing the ceramic heater to the cylindrical member; and the first fixing means. A ceramic heater type glow plug, comprising: a second fixing means for fixing the fixed ceramic heater portion in the metal outer cylinder.

6. The ceramic heater type glow plug according to claim 5, wherein the first fixing means is press-fitting or brazing.

7. The ceramic heater type glow plug according to claim 5, wherein the second fixing means is press-fitting or brazing.