JPH0311576Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Industrial Application Field) The present invention relates to a ceramic glow plug that is mainly attached to a diesel engine for starting. (Prior art) Generally, in order to improve startability of a diesel engine, a glow plug is installed in the auxiliary combustion chamber, etc., and a glow plug is energized to make it red-hot and a part of the fuel injected into the interior is combusted to preheat the engine. In addition to being required to have rapid temperature rise characteristics during startup, it is also used for a long time as an afterglow to stabilize combustion after startup, so there is an increasing demand for improved durability. ing. As a rapid heating type glow plug for this purpose, the heating element is a ceramic heater made by embedding a heating wire of a high melting point metal in ceramic powder and sintering it, and the heating wire is melted or thermally shocked due to overheating when electricity is applied. In order to prevent cracking of the ceramic due to heat generation, a resistor made of a wire having a positive temperature coefficient of resistance larger than that of the wire used for the heating wire is connected in series within the bore of the mounting bracket. 2. Description of the Related Art A self-control glow plug is known in which the heating current of a heating wire is controlled by increasing the resistance as the temperature of the resistor increases, thereby suppressing the temperature of the heating element. As a conventional example of this type of glow plug, there is a prior art (Japanese Patent Application No. 1982-209992) by the present applicant, which has a structure as shown in FIG. In this prior art self-control glow plug, one end of the resistor coil 2 is connected to the tip 4a of the center shaft 4 which protrudes from the rear end of the mounting bracket 3 and serves as a side electrode terminal, and the other end is connected to the ceramic heater 5. The lead electrode shaft 6 is connected to the heating wire 1 of the resistor coil 2.
The connection components, including a part of the center shaft 4 and lead electrode shaft 6, are covered with a metal tube 7, and the inner cavity thereof is filled with a heat-resistant insulating material 8, such as magnesia powder.
The metal tube 7 is formed as an integrated assembly 9 embedded in the interior of the mounting bracket 3, and is caulked with the body 3a of the mounting bracket that faces the part of the assembly 9 where the resistor coil is buried. It has a fixed structure. Note that 12 in the figure is an insulating plate that insulates the center shaft 4 and the mounting bracket 3, and 11 is a terminal plate that is screwed onto the center shaft 4. (Problems to be Solved by the Invention) In the conventional self-regulating glow plug having the above-mentioned structure, a resistor coil connected in series to a heating wire is placed inside a metal tube filled with a heat-resistant insulating material, and the center shaft and The sheathed resistor structure is formed as an integrated assembly including the connection part between the heating wire and the lead electrode shaft, which makes it extremely strong, and features easy assembly and excellent mass production. However, an unexpected case occurred in which the resistor coil broke when energized.
Therefore, as a result of investigating and investigating the cause of this disconnection, we found that conventionally, as shown in FIG. It was found that due to the caulking, the resistor coil was partially deformed and became thinner, and that part was locally overheated when energized, leading to fusing. (Means for Solving the Problems) The present invention was made to solve the above problems, and the metal tube 7 of the assembly 9 is buried in the center shaft 4 away from the part where the resistor coil 2 is buried. It has a structure in which the body of the mounting bracket 3 on the outer periphery of the part is caulked and fixed to the mounting bracket. (Function) With the above structure, the caulking portion of the mounting bracket avoids the buried portion of the resistor coil, so that the resistor coil is no longer affected mechanically by caulking. Furthermore, since a strong central shaft is embedded in the inner cavity of the metal tube of the caulking portion, the metal tube and the central shaft are further strengthened. FIG. 1 is a longitudinal sectional view of an embodiment of the self-regulating ceramic glow plug of the present invention, in which the same parts as in FIG. 2 are designated by the same reference numerals. As shown in the figure, in the self-regulating ceramic glow plug according to the present invention, one end of the resistor coil 2 is connected to the tip 4a of the central shaft 4, similar to the conventional example according to the prior art.
The other end is connected to a lead electrode shaft 6 connected to a ceramic heater 5, and these connection components and the tip of the center shaft 4 are covered with a metal tube 7 fitted on the outside thereof. The metal tube 7 of the assembly 9 is formed as an integrated assembly 9 embedded in the heat-resistant insulating material 8 filled in the inner cavity, and the metal tube 7 of the assembly 9 is located at the buried part of the center shaft 4 which is separated from the buried part of the resistor coil 2. It has a structure in which a portion 3b of the outer periphery is caulked by the body of the mounting bracket 3. The metal tube 7 was caulked using the mounting fitting 3 using a die having a square to octagonal cross section, and a strong holding force was obtained for the caulked product. The other structure of the self-regulating ceramic glow plug of this embodiment is completely the same as that of the conventional example shown in FIG. 2, so a description thereof will be omitted. (Effects of the invention) By comparing the glow plug according to the present invention and the conventional glow plug according to the prior art, a comparative evaluation test was conducted on the durability of the resistor coil depending on the caulking position of the mounting bracket. In the test, the number of samples was 5 each, and an overvoltage of 14 V DC was applied to each sample, and the current was repeatedly turned ON and OFF for 1 minute each to check for melting of the resistor coil. The results were as shown in the table below.

[Table] As seen in the above table, it is clear that the self-regulating ceramic glow plug according to the present invention has much superior durability compared to the conventional example.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the self-regulating ceramic glow plug of the present invention, and FIG. 2 is a longitudinal sectional view of a conventional self-regulating ceramic glow plug according to the prior art. 1: Heat generating wire, 2: Resistor coil, 3: Mounting bracket, 3a, 3b: Part of outer periphery, 4: Center shaft, 5: Ceramic heater, 6: Lead electrode shaft, 7: Metal tube, 8: Heat-resistant insulator , 9: Assembly.

Claims (1)

[Scope of utility model registration request] A ceramic heater is used in which a heating wire made of a high-melting point metal is embedded in a ceramic sintered body as a heating element provided at the tip of the mounting bracket, and a resistor is connected in series to the heating wire within the inner cavity of the mounting bracket. , the resistor coil is placed in a separate metal tube with both ends open, and within the tube, one end of the resistor coil is placed at the tip of the center shaft that protrudes from the rear end of the mounting bracket, and the other end is placed at the tip of the center shaft that protrudes from the rear end of the mounting bracket. The tube is connected to the lead electrode shaft connected to the heating element, and the resistor coil and the connecting portion are embedded in a heat-resistant insulating material filled in the inner cavity of the tube, and are formed as an integrated assembly. A self-controlling ceramic glow plug has a structure in which a metal tube of the assembly is caulked from the outer periphery with a part of the body of the mounting bracket and fixed to the inner cavity of the mounting bracket, and the metal tube is attached to the buried part of the resistor coil. A self-controlling ceramic glow plug characterized by being fixed by caulking with a part of a mounting bracket from the outer periphery of an upper center shaft buried part that is separated from the center shaft.