JPH09184622A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug wherein durability of a ceramic heater is excellent. SOLUTION: This glow plug uses as a heating device a ceramic heater including a ceramic substrate, and a ceramic heater 10 formed into a U shape and buried in the ceramic substrate for producing heat through its resistance by being supplied with electric power through an electrode part connected across its opposite ends. The U shaped ceramic heater 10 includes a curved part 10a forming a U shaped bottom, and two straight line parts 10b extending in the same direction from each end of the curved part 10a, the curved part 10a having a larger cross section than that of each straight line part 10b. A transition point QO from the straight part to the curved part is set to be located on the side of a U shaped opening of the ceramic heater 10 from a transition point Q1 to an outside external configuration line 21 likewise shaped into a U shape.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a glow plug using a ceramic heater.

[0002]

2. Description of the Related Art Heretofore, as a glow plug used for accelerating the starting of a diesel engine, for example, as shown in FIG. 8, a glow plug in which a ceramic heater 102 is held at the tip of a cylindrical metal holder 101 is known. There is. The ceramic heater 102 is, for example, a rod-shaped insulating ceramic substrate 1
A U-shaped ceramic heating element 104 made of conductive ceramics is embedded in the tip of 03, and is energized through electrode portions 105 connected to both ends of the heating element 104 to generate resistance heat. .

[0003]

In the ceramic heater 102 used in the glow plug 100 as described above, between the conductive ceramics forming the ceramic heating element 104 and the insulating ceramics forming the ceramic base 103. Since the linear expansion coefficient is different, when the heat generation / cooling cycle is repeated, as shown in FIG. 9, stress concentration due to the difference in the linear expansion coefficient is caused especially near the tip of the U-shaped curved portion 104a of the ceramic heating element 104. Tends to occur. Therefore, for example, the bending portion 10
4a, a problem may occur in the durability of the ceramic heating element 104.

An object of the present invention is to provide a glow plug having excellent durability of a ceramic heating element.

[0005]

The glow plug of the present invention is formed into a ceramic base and a U-shape embedded in the ceramic base, and is energized via electrode parts connected to both ends thereof. In order to solve the above problems, a ceramic heater provided with a ceramic heating element that generates heat by resistance is used as a heating element, and has the following features. That is, the U-shaped ceramic heating element includes a curved portion that forms a U-shaped bottom portion and two straight portions that extend in the same direction from each end portion of the curved portion, and each curved portion has a different cross section. It is formed larger than the cross section of the straight line portion. The transition point from the straight line portion to the curved portion with respect to the U-shaped outer contour line is located closer to the U-shaped opening of the ceramic heating element than the transition point with respect to the U-shaped outer contour line. Is set as follows.

With this structure, since the strength of the curved portion of the U-shaped ceramic heating element or the transition portion from the straight portion to the curved portion is increased, the durability of the heating element is improved and, by extension, the glow plug The life can be extended.

More specifically, the inner and outer contour lines of the curved portion can be formed so as to form concentric arcs with each other. In this case, the width of the curved portion in the radial direction of the concentric arc passes through the center of the concentric arc,
The width can be set to be larger than the width of the straight line portion in the direction orthogonal to the axis of the straight line portion. With this configuration, the above-mentioned effects can be further enhanced.

[0008]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows a glow plug according to the present invention together with its internal structure. That is, the glow plug 50 has a ceramic heater 1 provided at one end thereof, a metal sleeve 3 that covers the outer peripheral surface of the ceramic heater 1 so that the tip 2 of the ceramic heater 1 projects, and further covers the metal sleeve 3 from the outside. A cylindrical metal housing 4 and the like are provided, and the ceramic heater 1 and the metal sleeve 3 and the metal sleeve 3 and the metal housing 4 are joined by brazing. Further, one end of a coupling member 5 whose both ends are formed of metal wires in the shape of a spiral spring is fitted to the rear end portion of the ceramic heater 1 from the outside, and the other end side is inserted into the metal housing 4. It is fitted to the corresponding end of the metal shaft 6. The other end portion side of the metal shaft 6 extends to the outside of the metal housing 4, and a nut 7 is screwed into a screw portion 6a formed on the outer peripheral surface of the metal shaft 4, and the nut 7 is tightened toward the metal housing 4. The shaft 6 is fixed to the metal housing 4. An insulating bush 8 is fitted between the nut 7 and the metal housing 4. On the outer peripheral surface of the metal housing 4, a screw portion 5a for fixing the glow plug 50 to an engine block (not shown) is formed.

As shown in FIG. 2, the ceramic heater 1 includes a ceramic heating element 10 formed in a U shape,
Linear or rod-shaped electrode portions 11 and 12 are provided at both ends thereof.
The tip of the is embedded and the ceramic heating element 10
The entire electrode parts 11 and 12 are embedded in a ceramic base 13 having a substantially circular cross section. The ceramic heating element 10 is arranged such that the curved portion 10a forming the U-shaped bottom portion is located near one end of the ceramic base 13. In addition, each of the electrode portions 11 and 12 extends in the ceramic base body 13 in a direction away from the ceramic heating element 10, and one of them (12).
In the metal sleeve 3, the other one (11) is exposed in the vicinity of the other end of the ceramic base 13 and its rear end is exposed on the surface of the ceramic base 13 to form exposed portions 12a and 11a. .

The ceramic heating element is composed of conductive ceramics such as tungsten carbide (WC), molybdenum silicate (Mo ₂ Si ₃ ), a composite of tungsten carbide and silicon nitride (Si ₃ N ₄ ). However, semiconductor ceramics such as silicon carbide (SiC) can also be used. The electrode portions 11 and 12 are made of a refractory metal material such as tungsten (W) or a tungsten-rhenium (Re) alloy. On the other hand, the ceramic base 13 is mainly made of insulating ceramics, for example, alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (Zr
O ₂ ), titania (TiO ₂ ), magnesia (MgO),
Mullite (3Al ₂ O ₃ .2SiO ₂ ), zircon (Zr
O ₂ · SiO ₂ ), cordierite (2MgO · 2Al ₂₎
O ₃ .5SiO ₂ ), silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN) and the like.

In FIG. 2, a thin metal layer (not shown) of nickel or the like is formed on the surface of the ceramic substrate 13 in a region including the exposed portion 12a of the electrode portion 12 by a predetermined method (for example, plating or vapor deposition). The ceramic base 13 and the metal sleeve 3 are joined by brazing through the thin metal layer, and the electrode portion 12 is electrically connected to the metal sleeve 3 through these joined portions. . Similarly, a thin metal layer is formed in a region including the exposed portion 11a of the electrode portion 11, and the joining member 5 is brazed to the thin metal layer. With this configuration, the ceramic heating element 10 is energized from the power source (not shown) via the metal shaft 6 (FIG. 1), the coupling member 5, and the electrode portion 11, and further the electrode portion 12, the metal sleeve 3, It is grounded through the metal housing 4 (FIG. 1) and an engine block (not shown).

As shown in FIG. 3, the ceramic heating element 10 is used.
Is a curved portion 10a forming a U-shaped bottom portion and the curved portion 1
0a and two straight line portions 10b extending in the same direction from the respective end portions of 0a, and the cross section of the curved portion 10a is formed larger than the cross section of each straight line portion 10b. More specifically, the inner outline 20a and the outer outline 21a of the curved portion 10a are formed so as to form concentric arcs with each other, and the width l1 of the curved portion 10a in the radial direction of the concentric arc is the center of the concentric arc. It is set to be larger than the width l0 of the straight line portion 10b in the direction orthogonal to the axis of the straight line portion 10b. Further, the transition point Q0 from the straight portion 10b to the curved portion 10a with respect to the U-shaped outer contour line 20 of the ceramic heating element 10 is smaller than the transition point Q1 with respect to the U-shaped outer contour line 21 of the ceramic heating element. It is set so as to be located on the U-shaped opening side of 10. That is, the transition point Q0
The distance P0 from the bending point 10a to the tip B of the bending portion 10a is set to be larger than the distance P1 from the transition point Q1 to B. Here, it is desirable to set the width l1 of the curved portion 10a as small as possible within a range in which the current-carrying durability characteristic of the ceramic heating element 10 is not insufficient from the viewpoint of increasing the heat generation efficiency in the curved portion 10a.

The ceramic heater 1 can be manufactured by the following method, for example. First, FIG.
As shown in FIG. 3, the electrode material 30 is attached to the metal mold 31 having the U-shaped cavity 32 corresponding to the ceramic heating element 10.
Are arranged so that the ends thereof enter into the cavity 32. Then, in this state, a compound 33 containing a conductive ceramic powder and a binder is injected, so that the electrode material 30 and the U-shaped conductive ceramic powder molding portion 34 are formed as shown in FIG. An integrated injection-molded body 35 in which are integrated is created. The dimensions of each portion of the U-shaped integral injection-molded body 35 are adjusted so that the dimensional relationship between the curved portion 10a and the straight portion 10b of the ceramic heating element 10 after firing is as shown in FIG.

On the other hand, separately from this, by pre-pressing the ceramic powder forming the ceramic base 13 into a die, preforms 36 and 37 formed separately as shown in FIG. 5A. Be prepared. These preforms 36 and 37 are formed in a shape corresponding to each divided part, assuming that the ceramic base 13 is divided into two parts by a cross section substantially parallel to the axis of the preforms 36 and 37. The integral injection-molded body 3 is provided at the corresponding portion.
A recess 38 having a shape corresponding to No. 5 is formed. Then, the integral injection molded body 35 is housed in the recess 38, the upper and lower preformed bodies 36 and 37 are matched with each other, and in this state, the preformed bodies 36 and 37 and the integral injection molded body 35 are further molded. By using and pressing and integrating, a composite molded body 39 as shown in FIG. 5B is created.

The composite molded body 39 thus obtained is first calcined to remove the binder component added to the raw material powder for molding, and then, as shown in FIG. By performing hot press firing at a predetermined temperature while pressurizing between the molding dies 40 configured by, for example, a firing body 41 as shown in FIG. At this time, the conductive ceramic powder molding portion 34 shown in FIG.
Will form the ceramic heating element 10, the preforms 36 and 37 will form the ceramic base 13, and the electrode material 30 will form the electrode portions 11 and 12. Thereafter, the outer surface of the fired body 41 is subjected to processing such as polishing, if necessary, to obtain the ceramic heater 1 as shown in FIG.

[0016]

EXAMPLE As the ceramic heater 1 shown in FIG.
For the dimensions of each part of the ceramic heating element 10 shown in,
Various values of −10 and P0−P1 (unit: mm) were prepared, and the glow plug 50 having the structure shown in FIG. I checked. Specifically, the ceramic heater 1 is energized for 5 minutes so that the maximum temperature reaches 1400 ° C., then the energization is stopped and the operation is cooled at room temperature for 3 minutes, which is repeated as one cycle. The durability characteristics of energization for 10,000 cycles were evaluated. FIG. 7 shows the result. It can be seen that the glow plugs (No. 1 to No. 6) using the ceramic heating element satisfying the dimensional conditions of the present invention show good current-carrying durability characteristics.

[Brief description of the drawings]

FIG. 1 is a front partial sectional view showing an example of a glow plug of the present invention.

FIG. 2 is a front sectional view of the ceramic heater.

FIG. 3 is an enlarged view showing a main part of a ceramic heating element used in a ceramic heater.

FIG. 4 is an explanatory view of the manufacturing process of the ceramic heater.

FIG. 5 is a process explanatory view following FIG. 4;

FIG. 6 is a process explanatory view following FIG. 5;

FIG. 7 is an explanatory diagram showing the relationship between the dimensions of the ceramic heating element and the current-carrying durability characteristics of the glow plug in the example.

FIG. 8 is a schematic diagram showing a structure of a conventional glow plug ceramic heater.

FIG. 9 is an enlarged view of the tip of the same.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heater 10 Ceramic heating element 10a Curved portion 10b Straight portion 20 Inner outer shape line 21 Outer outer shape line Q0, Q1 Transition point 11, 12 Electrode portion 13 Ceramic substrate 50 Glow plug

Claims (2)

[Claims] 1. A ceramic heater comprising a ceramic base and a ceramic heating element which is embedded in the ceramic base and is U-shaped and which generates resistance heat by being energized through electrode parts connected to both ends thereof. In the glow plug having the heating element as a heating element, the ceramic heating element includes a curved portion that forms a U-shaped bottom portion, and two linear portions that extend in the same direction from each end of the curved portion. The cross section of the portion is formed to be larger than the cross section of each of the straight portions, and the transition point from the straight portion to the curved portion with respect to the U-shaped inner contour line is also with respect to the U-shaped outer contour line. A glow plug that is set so as to be located closer to the U-shaped opening side of the ceramic heating element than the transition point. 2. The inside outline and the outside outline of the curved portion are formed so as to form concentric arcs with each other, and the width of the curved portion in the radial direction of the concentric arc passes through the center of the concentric arc. The width is set larger than the width of the straight line portion in a direction orthogonal to the axis of the straight line portion.
Glow plug as described.