JP2001176647A - Ceramic heating element and blow plug for diesel engine equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug which is superior in the heat resistance and startability wherein the plug is a ceramic heating element used at the severe environment improving its heat resistance and thereby preventing the failure of the ceramic heating element as far as possible. SOLUTION: In the ceramic heating element 1 that is composed of a ceramic heating member 10 embedded in a ceramic substrate 13 consisting of a ceramic sintered body, an outer diameter size D of circular arcuate end face f of the ceramic substrate 13 and a wall thickness size L between the tip of the ceramic substrate 13 and the tip of exothermic member 10 is made as follows. 0.11<=L/D<=0.35 Bt this way, the ceramic heating element 1 that has a superior heat resistance and less failure of the heating member 10 due to the oxidation can be obtained. This ceramic heating element 1 becomes most suitable for a glow plug for diesel engine, and in this case, not only the failure of the ceramic heating element 1 become less, but also the startability becomes better.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heating element in which a heating member is embedded in a ceramic substrate made of a ceramic sintered body, and is particularly suitably used for a glow plug of a diesel engine.

[0002]

2. Description of the Related Art Various ceramic heating elements constructed by embedding a heating member in a ceramic base have been proposed. This ceramic heating element is suitably used as a heat source for a glow plug of a diesel engine.

[0003]

SUMMARY OF THE INVENTION In a ceramic heating element used for a glow plug of a diesel engine,
The tip of the heating element is strongly affected by high-temperature and high-pressure gas during combustion and exhaust, and is rapidly cooled during intake. Exposed. And due to such a constant thermal shock, the ceramic base at the tip of the heating element is liable to deteriorate, and when this deterioration reaches the heating member,
Oxidation of the heat-generating member progresses rapidly, resulting in fatal damage, resulting in a failure to start the engine or a failure to start the engine due to poor ignition.

The present invention relates to a ceramic heating element used in a harsh environment as described above, which improves the heat resistance of the ceramic heating element, thereby preventing the ceramic heating element from being damaged as much as possible. And a glow plug for a diesel engine having excellent startability.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a ceramic heating element in which a heating member is embedded in a ceramic substrate made of a ceramic sintered body. And a thickness dimension L from the tip of the heating member to the tip of the heating member is in a relationship of 0.11 ≦ L / D ≦ 0.35.

In such a configuration, when the heat resistance of the heating element is taken into consideration, if the thickness L between the tip of the ceramic base and the tip of the heating member at the tip of the heating element is large, the peripheral edge of the tip of the ceramic base will be considered. Even if the ceramic base at the end of the heating element deteriorates due to the thermal shock received from the heating element, the deterioration hardly reaches the heating member, and oxidation of the heating member is prevented as much as possible. For this reason, the heat resistance increases as the thickness L increases. However, on the other hand, when it is used for a glow plug for a diesel engine, the smaller the thickness L is, the better the engine startability is. This is because if the distance between the heating element and the surface of the heater that actually generates heat is reduced, the quick heating property of the heater is increased.

The outer diameter D of the arc-shaped tip surface of the heating element
Is larger, the heat capacity is larger, and therefore, when this is used for a glow plug for a diesel engine, the startability is improved. As described above, the thickness dimension L and the outer diameter dimension D have conflicting effects on reliability against deterioration and engine startability.

[0008] By changing the relationship between the thickness L and the outer diameter D, the reliability of deterioration was examined.
Within the above range, it was found that the heat resistance was good, and the damage of the heat generating member due to oxidation was suppressed as much as possible. In addition, it has been found that when used in a glow plug for a diesel engine, the characteristics can be balanced without impairing the startability.

A ceramic heating element satisfying the relationship between the thickness L and the outer diameter D has excellent heat resistance and is less likely to be damaged. And is optimal for the glow plug.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment in which a ceramic heating element 1 of the present invention is used as a heat source of a glow plug 20 is shown in FIG.
It will be described based on. The glow plug 20 includes a ceramic heating element 1 provided at one end thereof, a metal outer cylinder 3 covering an outer peripheral surface of the ceramic heating element 1 such that a tip 2 of the ceramic heating element 1 protrudes, and further includes the outer cylinder 3. The ceramic heating element 1 includes a cylindrical metal housing 4 or the like that covers from the outside.
And the outer cylinder 3 and between the outer cylinder 3 and the metal housing 4 are respectively joined by brazing.

A rear end of the ceramic heating element 1 has one end of a coupling member 5 formed into a coil spring shape by a metal wire fitted from the outside, and the other end inserted into the metal housing 4. The metal shaft 6 is fitted to the corresponding end. The other end of the metal shaft 6 extends outside the metal housing 4, and a nut 7 is screwed into a screw portion 6 a formed on the outer peripheral surface of the metal shaft 6. 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. A screw portion 5 a for fixing the glow plug 20 to an engine block (not shown) is formed on the outer peripheral surface of the metal housing 4.

As shown in FIG. 2, the ceramic heating element 1 includes a direction changing portion 10a extending from one base end and changing its direction at the front end to reach the other base end.
a, a heating member 10 made of a substantially U-shaped ceramic resistance material having two linear portions 10b extending in the same direction from the base ends of the heating members 10. Leading ends of the lead wires 11 and 12 are provided at both ends thereof. The heat generating member 10 and the entire lead wires 11 and 12 are embedded in a rod-shaped ceramic base 13 having a circular cross section. The heat generating member 10 is arranged such that the direction changing part 10 a is located on the terminal side of the ceramic base 13. The heating member 10 is formed into the above-described shape by injection molding.

The ceramic substrate 13 is made of, for example, Si₃ N
₄ Y to powder₂ O₃ , Er₂ O ₃ , Yb₂ O
₃ Rare earth oxides or alkalis such as CaO, MgO, etc.
3 to 15% by weight of a sintering aid powder composed of an earth metal oxide
%, Added, mixed and sintered.

The ceramic resistance material forming the heating member 10 is W, Ta, Nb, Ni, Mo, Zr, H
a mixture of at least one selected from f, V, and Cr as a conductive material and silicon nitride as an insulating material; for example, WC powder as conductive ceramic powder; It consists of a mixed powder with Si ₃ N ₄ powder, and further contains the same sintering aid component as that used for the ceramic substrate 13 in the range of 0.8 to 1
It is added, mixed and sintered in the range of 0.5% by weight. The structure of the sintered body is such that WC-based particles (conductive ceramic particles) are contained in a Si ₃ N ₄ -based substrate (matrix ceramic phase).
Are dispersed. On the other hand, the lead wires 11 and 12 are made of metal wires such as W, W-Re, Mo, Pt, niobium, nichrome, and tantalum.

In FIG. 2, the ceramic base 13 and the outer cylinder 3 are joined by brazing, and
2 is electrically connected to the outer cylinder 3 via these joints. The joining member 5 is also brazed to a region including the exposed portion 11a of the lead wire 11. With this configuration, power is supplied from a power supply (not shown) to the heating member 10 via the metal shaft 6 (see FIG. 1), the coupling member 5 and the lead wire 11, and furthermore, the lead wire 12, the outer cylinder 3, It is grounded via the metal housing 4 and an engine block (not shown).

The glow plug 20 having such a structure is screwed to the engine block by screwing the screw portion 5a, and the tip of the ceramic heat generating member 1 is inserted into a pre-combustion chamber or a combustion chamber (not shown) of the diesel engine. Mounted exposed.

Next, an example of a method for manufacturing the ceramic heating element 1 according to the main part of the present invention will be described. The method of manufacturing the ceramic heating element 1 is performed by the following first to seventh steps.

First step: refractory metals such as tungsten and molybdenum or alloys mainly composed of these metals, or carbides of these metals (in this embodiment, a predetermined amount of conductive material made of tungsten carbide (tungsten carbide)) and A ceramic resistor material obtained by mixing silicon nitride Si ₃ N ₄ and a sintering aid is injection-molded into a U-shape, and lead wires 11 and 12 are joined thereto to obtain a conductive material molded body. The heating member 10 is used.

Second step: After a sintering aid is mixed with silicon nitride Si ₃ N ₄ at a predetermined ratio, alcohol wet mixing is performed in a ball mill for 20 hours, followed by drying with a spray dryer and granulation. Thus, a ceramic mixed powder used for the ceramic substrate is obtained.

Third step: The heating member 10 manufactured in the first step is embedded in the above-mentioned ceramic mixed powder and pressed integrally.

Fourth step: The press body in which the heat-generating member 10 is embedded is calcined to remove the binder, and then hot-pressed in a nitrogen atmosphere. The firing conditions were as follows: firing temperature: 1700 ° C., holding time: 90 minutes, pressure: 300 kg
/ Cm ² . As a result, the ceramic mixed powder is fired, and the ceramic heating element 1 including the heating member 10 and the ceramic base 13 is formed.

Fifth step: Next, the outer diameter D (see FIG. 3) of the front end face f of the ceramic base 13 and the ceramic base 13
Grinding was performed so that the thickness L (see FIG. 3) from the tip of the heating member 10 to the tip of the heat generating member 10 became a predetermined size.

Sixth step: The ceramic heating element 1 is
The glow plug 20 was assembled to the metal housing 2 as shown in FIG.

Next, as shown in FIG. 3, the outer diameter D of the arc-shaped tip face f of the ceramic base 13 and the thickness L between the tip of the ceramic base 13 and the tip of the heat generating member 10 are different. The ceramic heating element 1 manufactured by the above-described manufacturing method and having various values of the outer diameter dimension D and the wall thickness dimension L is referred to as samples 1 to 28 shown in Table 1, and as a starting test,
Each was mounted on a diesel engine, and the startability was evaluated at -20 degrees.

On the other hand, a sample of D = 3.5 mm and L = 1.0 mm was used as a sample, and this ceramic heating element 1 was alternately exposed to a high-temperature atmosphere and a low-temperature atmosphere, and the consumption of the ceramic substrate was examined. Here, high temperature conditions; O. T 4000rpm × 12
0 seconds low temperature condition; engine off × 120 seconds, the high temperature condition and the low temperature condition
This operation was performed alternately in a state where power was not supplied to 0, and this was made one cycle, and this was repeated for 7,200 cycles.

As a result of applying a temperature shock by this method, it was confirmed that the ceramic substrate 6 was consumed by a maximum of 0.3 mm.
From this, it was found that L indicating the thickness of the tip must be 0.4 mm or more. If the lid is 0.3mm,
By the above-described temperature cycle, the heating member 10 is exposed,
This is because it is rapidly oxidized.

Table 1 shows the above-described engine startability and reliability against deterioration. Here, in terms of engine startability, the double circle could be started quickly, the single circle could be started relatively quickly, the triangle could not be started smoothly, and the cross could not be started easily. Case.
Further, as described above, the reliability against deterioration is L = 0.4 mm so as to withstand a maximum wear of 0.3 mm.
These are the above.

[0028]

【table 1】

In this table, those having excellent or good engine startability and heat resistance (reliability against deterioration) are regarded as improved products (the scope of the present invention). As a result, those having an L / D of 0.11 to 0.35 were found to have well-balanced and good characteristics.

Therefore, 0.11 ≦ L / D ≦ 0.35 can be set as the range of the present invention.

Although the above has described the ceramic heating element 1 used in the glow plug 20 of the diesel engine, the present invention can be applied to a ceramic heating element used in other places that receive thermal shock. Also,
The heat generating member may be a metal resistance wire in which a refractory metal such as tungsten is formed in a predetermined shape such as a coil shape.

[0032]

According to the ceramic heating element of the present invention, the outer diameter D of the arc-shaped tip surface of the ceramic substrate and the thickness L between the tip of the ceramic substrate and the tip of the heating member are 0.11 ≦ L. /D≦0.35 is satisfied, and the relationship between the thickness L and the outer diameter D improves the heat resistance, so that damage due to oxidation of the heat generating member can be suppressed as much as possible. For this reason, there is an excellent effect that is optimal for a ceramic heating element used in a place that receives an extreme thermal shock.

Further, the glow plug of a diesel engine provided with such a ceramic heating element has excellent startability, and has heat resistance even when subjected to an extreme thermal shock during operation, so that the glow plug is oxidized by the heating member. Damage is less likely to occur, which improves durability and reliability, and contributes to safe driving.

[Brief description of the drawings]

FIG. 1 is a side view of a cross section of a left half of a glow plug 20 according to the present invention.

FIG. 2 is a longitudinal sectional view of the ceramic heating element 1 according to the present invention.

FIG. 3 is an enlarged vertical cross-sectional view showing a front end portion of the ceramic heating element 1 according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heating element 4 Metal housing 10 Heat generating member 13 Ceramic base 20 Glow plug

Claims (5)

[Claims] 1. A ceramic heating element having a heating member embedded in a ceramic substrate made of a ceramic sintered body,
The outer diameter D of the arc-shaped front end surface of the ceramic base and the thickness L between the front end of the ceramic base and the front end of the heat generating member have a relationship of 0.11 ≦ L / D ≦ 0.35. And a ceramic heating element. 2. The ceramic heating element according to claim 1, wherein the heating member is made of a ceramic resistance material formed into a predetermined shape by injection molding. 3. The ceramic resistance material is W, Ta, Nb,
It is characterized by comprising a mixture of at least one kind selected from Ni, Mo, Zr, Hf, V and Cr as a conductive material and silicon nitride as an insulating material. The ceramic heating element according to claim 2. 4. The ceramic heating element according to claim 1, wherein the heating member is formed of a metal resistance wire formed in a predetermined shape such as a coil shape. 5. The ceramic heating element according to claim 1, 2, 3 or 4, wherein the ceramic heating element is fitted in a cylindrical metal housing, and the tip of the ceramic heating element is projected. A glow plug for a diesel engine equipped with a characteristic ceramic heating element.