JPH0152876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a ceramic heater rod suitable for use in a glow plug for preheating the inside of a diesel engine cylinder.

In general, diesel engines have poor startability at low temperatures, so a method is used to increase the temperature inside the cylinder by installing a glow plug inside the cylinder and heating it by passing an electric current through it, thereby improving the startability of the engine. It is being

Conventional glow plugs of this type
The system uses a so-called sheathed heater, which consists of a heat-resistant metal sheath filled with heat-resistant insulating powder and a coiled heating wire buried inside, and because this is indirect heating, it takes too long to raise the temperature inside the cylinder. There was a problem. In other words, the heat generated by passing a current through the heating wire and heating it is transferred to the sheath side through the heat-resistant insulating powder, and the heat is radiated from the sheath into the cylinder, which poses a problem in terms of heat conduction efficiency. be. For example, set the temperature inside the cylinder to 1100
It takes several tens of seconds to bring the temperature down to ℃. If the applied current is increased in order to shorten such a long heating time, the heating wire is likely to melt or the sheath is damaged due to high heat. Furthermore, in the above-mentioned structure, it is desirable to prevent short circuits between the heating wire and the sheath when burying it, and for this purpose, the heating wire is covered with an insulating material in advance, or an insulating layer is placed on the inner wall of the sheath. There is also the problem that it is necessary to take other means to form the structure, and that the manufacturing process is troublesome.

Furthermore, Japanese Patent Application Laid-Open No. 54-109536 discloses a ceramic heater for glow plugs that applies multilayer substrate technology to improve the heat conduction efficiency described above, but this is a ceramic heater for glow plugs that uses a circular resistor printed on it. It is made by laminating a large number of thin ceramic green sheets on a board and integrating them into a rod shape, which is difficult to manufacture and requires extremely complicated work. In particular, a large number of resistors are required on the narrow green sheet surface, and in order to connect the resistors on each sheet, both ends of the resistor exposed on the outer periphery of the sheet must be connected in series or in parallel. Naturally, the work for this is complicated, and it is difficult to imagine that it is possible to easily obtain the desired connection state.

In particular, when forming the above-mentioned glow plug for diesel engines, the problem is to appropriately control the heat generation characteristics of the heat generating part of the heater, to achieve rapid red-hot heating at the tip of the heater, and to Taking these points into account, we have created a system that has excellent rapid heating properties, has a simple structure, and is easy to manufacture, by preventing the effects of heat from reaching the heater part and other parts. Furthermore, it is desired to develop a glow plug for diesel engines that has excellent durability in each part.

The present invention has been made in view of the above circumstances, and a ceramic heater rod is made of a pair of ceramic powder compacts formed into a rod-shaped body having a substantially semi-elliptical cross section made of a silicon-based non-oxide. A simple method is to prepare a resistor and a resistor to be interposed between the flat surfaces facing each other, and to integrally form a pair of ceramic compacts with the resistor by compression firing. By using this method, it is possible to easily manufacture ceramic heater rods that have a direct heat transfer structure that becomes red hot in a short time when heated, improving temperature rise characteristics and exhibiting performance as a fast heating type. The present invention provides a method for manufacturing a ceramic heater rod which is excellent in terms of strength and reliability at each part of the heater rod, is inexpensive, and is suitable for use in glow plugs for diesel engines and the like.

Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

FIGS. 1 and 3 show an embodiment of a glow plug for a diesel engine that employs a ceramic heater rod produced by the manufacturing method according to the present invention. Resistor 1 made of conductive material on the joint surface of
A ceramic heater rod 14 is formed of a pair of ceramic compacts 12 and 13 made of a silicon-based ceramic material which is pressure-fired with the heater rod 1 interposed therein, and this heater rod 14 is held at the tip. An external connection terminal 17 is fitted into the rear end of the holder 15 via an insulating bushing 16 made of synthetic resin or the like, and this external connection terminal 17 is connected to the heater rod 1.
4 through a conducting wire 18 having the required flexibility.

The heater rod 14 has a substantially circular cross section, with a flat surface where one side of the rectangle in cross section is a straight line, and an arcuate surface where the other side opposite to this is an outwardly convex arc. A pair of ceramic compacts 12 and 13 thus formed are joined together and fired under pressure. In this case, heater rod 1
The reason why the cross-sectional shape of 4 is approximately elliptical is to improve the density of the ceramic material compared to a circular shape, and to make its heat resistance strength, insulation properties, and thermal conductivity more effective. The material of the pair of ceramic compacts 12 and 13 mentioned above is a silicon-based non-oxide material, which is a silicon-based ceramic material known as fine ceramics, which has excellent insulation properties and thermal shock resistance. For example, silicon-based nitride is preferable.

Further, the resistor 11 in the heater rod 14 is formed of, for example, a high melting point metal material, and the one ceramic compact 1 is connected to the ceramic powder body 1 in the state shown in FIG.
It is formed on the joint surface 12a of No. 2. That is, the resistor 11 includes a heater section 11a provided on the tip end side of the ceramic compact 12, and a heater section 11a that extends from one end of the heater section 11a to the rear of the ceramic compact 12 and extends from the rear end to the outside of the rod. The first thing to be exposed
a lead portion 11b, and a second lead portion 11 extending rearward from the other end of the heater portion 11a and exposed outside the rod body from the side of the central portion of the ceramic powder compact 12.
c, which are formed in series on the joint surface 12a. In this case, it should be noted that the width of the heater portion 11a of the resistor 11 is formed sufficiently narrow so that the resistance is large, while the width of each lead portion 11b and 11c is formed so that the resistance of the heater portion 11a is small. It is to be formed with a wider width than the Moreover, the heater part 11a and each lead part 11b, 11c are made of ceramic compact 1.
When the ceramic compacts 12 and 13 are joined together, the lead parts 11b and 11c are completely buried inside the heater rod 14, and only the ends of the lead parts 11b and 11c are exposed to the outside from the joined part of the ceramic compacts 12 and 13.

Note that the resistor 11 is a ceramic powder compact 12.
It can be easily obtained by printing wiring as a thin conductive film on the bonding surface 12a, pasting a wire or plate of high melting point metal, baking, vapor deposition, etc., and the material is tungsten etc. Metal materials are considered. This is because the firing temperature of ceramics is high, and therefore the resistor 11 needs to be made of a heat-resistant material. Then, such a resistor 11 is connected to the pair of ceramic compacts 12,
These are heated to approximately 1,700 to 200 degrees Celsius while being interposed between 13
The ceramic heater rod 14 described above is obtained by compression firing from the upper and lower directions, that is, from the outside of each arcuate surface, at a high pressure of about 200 to 500 kg/cm ² in a high-temperature atmosphere.

Further, as is clear from FIGS. 1 and 3, metal coating layers 19 and 20 are formed on the outer periphery of the center portion, the outer periphery of the rear end portion, and the end surfaces of the heater rod 14 formed as described above. is formed. These metal coating layers 19,
20 is a resistor 1 embedded in the heater rod 14
1, that is, the ends of each lead part 11b and 11c, are used to electrically connect the ends of each lead part 11b and 11c to the outside. It is formed. This is because metal members cannot be directly welded or brazed to the heater rod 14 made of ceramic material.

A reinforcing metal pipe 21 is fitted into the central portion of the heater rod 14, and a terminal cap 22 for connecting the conductive wire 18 is capped at the rear end of the heater rod 14, respectively.
It is fixed to 4 by silver brazing or the like. That is, the heater rod 14 is assembled while being held at the tip of the holder 15, but in this case, since its cross-sectional shape is approximately elliptical, in order to securely fix it, the tip of the holder 15 must be fixed. It is necessary to form the opening to match the heater rod 14. but,
Molding the tip of the elliptical opening holder 15 as described above is troublesome and undesirable in terms of cost. For this purpose, a metal pipe 21 having a substantially elliptical through hole 21a formed to match the shape of the heater rod 14 is prepared separately from the holder 15, and after fixing this pipe 21 to the heater rod 14, By fitting and fixing the heater rod 14 to the tip of the holder 15, each part can be easily molded and the cost can be reduced.Moreover, the heater rod 14 can be easily and securely attached to the holder 15, and its strength is sufficient. guaranteed. In particular, glow plugs of the species 10
The diesel engine to which the heater rod 14 is attached generates considerable vibration during operation, and the state in which the heater rod 14 is held in the holder 15 becomes a problem.

Note that the elliptical through hole 21a of the metal pipe 21
It is possible to form it with high precision by simple drawing process. Further, one end of the resistor 11 in the heater rod 14, that is, the end of the second lead portion 11c is coated with a metal coating layer 19 and a metal pipe 2.
It is electrically connected to the holder 15 via 1.

On the other hand, the resistor 1 exposed at the end of the heater rod 14
1, that is, the end of the first lead portion 11b, is connected to an external connection terminal 17 attached to the rear end of the holder 15 via an insulating bushing 16. In this case, this external connection terminal 17 is Heater rod 1
When attached directly to the rear end of 4, the external connection terminal 17
There is a problem that the heater rod 14 may come off due to mechanical external forces such as vibrations or tightening torque applied to the heater rod 14, or damage may occur to the heater rod 14, so it is necessary to connect these elements elastically. In order to ensure strength against the influence of such external force, in this embodiment, the heater rod 14 is
and the external connection terminal 17 are connected by a highly flexible conducting wire 18 such as a flexible lead wire.

In addition, in order to securely fix the conducting wire 18 to the rear end of the heater rod 14, the terminal cap 2 is attached to the terminal cap 2.
2 is used. This terminal cap 2
2, as is clear from FIGS. 1 and 3,
It has a cap-like shape that is capped on the rear end of the heater rod 14, and a mounting piece 22a for fixing the conducting wire 18 is raised from the bottom of the cap. One end of the conducting wire 18 is fixed to this mounting piece 22a by spot welding or the like. Of course, the other end of the conducting wire 18 is also fixed to the tip of the external connection terminal 17 by spot welding or the like.

Note that instead of the above-mentioned highly flexible conductor 18, an electric conductor having a certain degree of flexibility may be used, and this may be connected by holding the mounting piece 22a of the terminal cap 22, or an elastic conductor may be attached to the external connection terminal 17 side. It is also possible to connect at least one end of the metal wire with a curve and utilize its elasticity for connection.

In addition, when connecting using the above-mentioned conducting wire 18, etc., in the space of the holder 15 where this is inscribed,
It may also be filled with heat-resistant insulating powder, for example ceramic powder such as magnesium oxide. In this way, the effect can be exhibited as a measure against vibration of the conducting wire 18 and the like.

The glow plug 10 configured as described above can be easily assembled as follows. First, a pair of ceramic compacts 12 are stacked on top of each other with a resistor 11 interposed between their opposing joint surfaces.
A heater rod 14 with excellent heat generation properties is prepared by joining the rods 13 and compressing and firing them. Then, after fitting the pipe 21 and the terminal cap 22 to the center and rear ends of the heater rod 14 and fixing them by silver brazing or the like, one end of the conducting wire 18 is attached to the mounting piece 22a of the terminal cap 22.
Further, the other end is fixed by spot welding to the tip of the external connection terminal 17 into which the insulating bush 16 is fitted. Furthermore, each of these members is inserted from the rear end of the holder 15, and the pipe 21 holding the heater rod 14 is fixed at the tip of the holder 15 by silver brazing, while the pipe 21 that is fitted into the rear end of the holder 15 is The insulating bush 16 on the outer periphery of the external connection terminal 17 is assembled and fixed by caulking the rear end of the holder 15. This assembled state is shown in FIGS. 3A and 3B.

The glow plug 10 assembled in this manner is screwed into a screw hole formed in the cylinder head of a diesel engine, and is attached with the heater rod 14 at its tip protruding into the cylinder chamber. Then, the external connection terminal 17 and the holder 1
When a voltage is applied between 5 and 5 and a current flows through the resistor 11 in the heater rod 14, the heater portion 11a is heated and the generated heat is transferred to the outer skin made of ceramic material, thereby causing heat to be generated inside the cylinder. The radiation increases the internal temperature of the engine, resulting in better starting performance of the engine.

What should be noted here is that the heater rod 14 in which the resistor 11 is embedded is made of a ceramic material such as silicon-based non-oxide, and this ceramic material not only has good insulation properties but also has excellent thermal shock resistance. It can be used in the heater part of this type of diesel engine glow plug to exhibit its performance. Furthermore, in the heater rod 14 made of such a ceramic material, the resistor 11 serving as the heating element is directly buried inside the heater rod 14, and the heating element is buried in the heat-resistant insulating powder filled in the sheath as in the conventional case. Its thermal conductivity can also be significantly improved compared to that of conventional materials. Therefore, such a heater rod 14 becomes red hot in a short period of time when heated, has improved temperature rise characteristics, and can fully exhibit its performance as a fast heating property. For example, it has been confirmed through experiments that the glow plug according to the present invention can raise the temperature to 1100° C. within 2 seconds. This is a great advantage compared to the conventional method, which can only increase the temperature by about 300° C. in 2 seconds. moreover,
The heater rod 14 described above has the heater portion 1 of the resistor 11 only at the tip, which has the greatest effect on engine startability.
1a, which allows it to fully fulfill its role as a heater rod and significantly improve the startability of the engine. In addition, the heater rod 14
In manufacturing, a pair of ceramic compacts 1
A resistor 11 is formed on one joint surface 12a of the ceramic powder bodies 12, 13.
It is clear that this can be easily done by joining 3 and compressing and firing.

Here, the above-mentioned ceramic compacts 12, 13
Regarding the characteristics of ^the heater ^rod 14 according ^to
(At 1100℃; conventionally 5Kg/mm ² )
This results in a significant improvement in performance. Moreover, such a heater rod 14
According to , a pair of ceramic powder compacts 1 are placed in a state in which the flat surfaces with resistors 11 interposed thereon are overlapped.
2 and 13 are compressed from the outside of their respective arcuate surfaces, the longer side of the elliptical cross-sectional shape (in the direction of the joint surface of the ceramic compacts 12 and 13) than the axial center part
Increasing the ceramic density on both side edges of
It has a structure that improves strength and can withstand rapid heating. In this method, the ceramic compacts 12 and 13 having a substantially semi-elliptical cross section are connected to the resistor 11.
When compressed with a constant stroke from the outside of each arcuate surface using a mold with a cross-sectional shape that is approximately equal to the arcuate surface, the long side of the elliptical cross-sectional shape has a shape on both sides of the central portion of the long side of the elliptical cross-sectional shape. This can be easily understood from the fact that the distance between the molds becomes narrower in that region, and the compression rate increases. Furthermore, during compression firing in such a mold, the both side edge portions of the ceramic compacts 12 and 13 tend to shrink toward the center in the direction of the joint surface.
Extrusion force is applied to both side walls of the mold by applying pressure from the arc surface side, and the width dimension at both side edge portions can be defined to a predetermined value.

In the above-mentioned embodiment, the cross-sectional shape of the heater rod 14 made of a pair of ceramic compacts 12 and 13 is approximately elliptical, and the metal pipe 21 and terminal cap 22 are formed accordingly.
15 using external connection terminal 1.
7 has been described, the present invention is not limited to this. For example, the heater rod may be held directly at the tip of the holder, or the conductor may be directly soldered without using a terminal cap. It may also be made to be firmly fixed.

Further, the resistor formation pattern within the heater rod is not limited to the above-mentioned embodiment, and can be changed as appropriate to vary the resistance value.
The tip of the heater rod, which affects the startability of the engine, may be configured to become red-hot particularly quickly.

As explained above, according to the present invention, a resistor is interposed between a pair of ceramic green compacts each formed into a rod-like body having a substantially semi-elliptical cross section and the flat surfaces of the compacts which are combined to face each other. By preparing a pair of ceramic compacts with a resistor interposed therein and then compressing and firing them, a ceramic heater rod was formed in one piece.Although it is a simple method, it has excellent heat generation characteristics. It is possible to easily and appropriately manufacture and provide a ceramic heater rod, which has an excellent direct heat transfer structure that becomes red hot in a short time during heating, improves temperature rise characteristics, and exhibits fast heating performance. Furthermore, this heater rod has various excellent effects such as being superior in terms of strength and reliability at each part and being inexpensive in terms of cost.

[Brief explanation of drawings]

The figures show an embodiment of a glow plug for a diesel engine using a ceramic heater rod produced by the manufacturing method according to the present invention. FIG. 3A is a vertical sectional view showing the assembled state of FIG. 1, and FIG. 3B is a side view similarly seen from the tip side. 10...Glow plug, 11...Resistor, 11
a...Heater part, 11b, 11c...Lead part,
12, 13... A pair of ceramic compacts, 14...
...Ceramic heater rod, 15...Holder, 16...
...Insulation bushing, 17...External connection terminal, 18...
...Conducting wire, 19,20...Metal coating layer, 2
1...Metal pipe, 22...Terminal cap.

Claims (1)

[Scope of Claims] 1. A pair of ceramic pressure plates formed with a flat surface in which one side of a rectangle in cross section is a straight line and an arcuate surface in which the other side opposite to this is an outwardly convex arc. Prepare powder and a resistor having a curved part and a straight part to be interposed between the flat surfaces of these ceramic green compacts that are combined facing each other, and insert this resistor between the flat surfaces. By compressing and firing the pair of ceramic compacts from the outside of their respective arcuate surfaces while interposed and stacked on top of each other,
A method for manufacturing a ceramic heater rod, characterized by forming these in one piece. 2. The method for manufacturing a ceramic heater rod according to claim 1, characterized in that the ceramic green compact is formed from a silicon-based non-oxide. 3 The resistor interposed between the ceramic compacts,
2. A method of manufacturing a ceramic heater rod according to claim 1, wherein the ceramic heater rod is made of a high melting point metal material.