JP2002206740A - Glow plug - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a glow plug having high durability against impact during abnormal combustion. The glow plug includes a ceramic heater and an outer cylinder through which the ceramic heater is inserted.
In the above, the glow plug 1 is obtained in which the outer diameter Dc of the ceramic heater 13 is 0.8 or less with respect to the outer diameter Ds of the outer cylinder, and further the Dc / Ds is 0.5 or more. The glow plug 1 has a breaking load D when a load is applied at a constant speed perpendicular to the length direction at a position 2 mm from the tip of the ceramic heater 13 protruding from the outer cylinder 12.
It is at least 1 times that of the ceramic heater having c / Ds of 0.8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a glow plug. More specifically, the present invention relates to a glow plug having a structure with a low probability of breaking even during abnormal combustion. The glow plug of the present invention can be suitably used for a glow plug of a diesel engine.

[0002]

2. Description of the Related Art As a glow plug of a diesel engine, a ceramic body in which a heating resistor containing tungsten carbide or the like and a lead wire is provided is embedded in a base made of an insulating ceramic such as a nitrided sintered body. A heater having a structure in which a heater is further inserted through a metal outer cylinder is known.

[0003]

However, it has not been possible to sufficiently prevent the ceramic heater from being broken during abnormal combustion, and the correlation between the outer diameter of the ceramic heater and the outer diameter such as the outside has not been considered. Has not been considered. on the other hand,
Usually, it is said that pressure is evenly applied in the space surrounded by the cylinder and piston of the engine. However, it is considered that the breakage of the ceramic heater caused during abnormal combustion suggests that an extremely large impact force is applied from a specific direction during abnormal combustion.
On the other hand, it has been extremely difficult to experimentally reproduce this breakage, which is rarely caused by overlapping special conditions. An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a glow plug that can effectively suppress breakage of a ceramic heater that occurs during abnormal combustion.

[0004]

As a result of various studies on the conditions under which the abnormal combustion occurs, the inventors have been able to reproduce the conditions experimentally. The cause of breakage during abnormal combustion was determined by obtaining a correlation between the magnitude of the shock leading to breakage and the structure of the glow plug by an impact test that applies an impact (load is applied in a short time) to the tip of the base of the ceramic heater. Was. However, it was difficult to find a relationship that could be determined to have a correlation from this impact test. On the other hand, we tried to obtain the correlation by the pressure test in which the load was applied for a longer time than the impact test. As a result, when one end is connected to the heating resistor and a lead wire is formed on the connected surface to form a fitting portion having a reaction layer formed thereon, the outer diameter of the outer cylinder and The inventors have found that a correlation can be obtained with the ratio to the outer diameter, thereby completing the present invention.

A glow plug according to the present invention comprises an insulator and a conductor embedded in the insulator. The conductor is embedded with a heating resistor so that one end of the glow plug is electrically connected to the heating resistor. A ceramic heater having a pair of lead wires, the other end of which is exposed from the insulator, and a reaction layer formed at an interface between the heating resistor and the lead wire; In a glow plug including an outer cylinder to be fitted and a metal shell into which the outer cylinder is fitted, when the outer diameter of the ceramic heater is Dc and the outer diameter of the outer cylinder is Ds, Dc / Ds is 0.8 or less.

The above "ceramic heater" is composed of an insulator and a conductor. The “insulator” is a sintered body composed mainly of an insulating component. On the other hand, the "conductor" includes a heating resistor which is a sintered body mainly composed of a conductive component and an insulating component, and a pair of lead wires. The insulating component constituting the insulator and the heating resistor is silicon nitride or the like. On the other hand, the conductive components constituting the heating resistor include W, Ta, Nb, Ti, Mo, Zr, Hf,
V, and a silicide of at least one element selected from Cr and the like,
It is at least one kind of a carbide or a nitride.

It is preferable that the conductive component has a coefficient of thermal expansion that does not greatly differ from the insulating component forming the heating resistor or the insulating component forming the insulator in which the heating resistor is embedded. If the coefficient of thermal expansion is small, the occurrence of cracks in the insulator and the heating resistor when the heater is used can be suppressed. Such conductive components include WC, MoS
i ₂ , TiN or WSi ₂ . Further, it is preferable that the conductive component has a melting point exceeding the operating temperature of the ceramic heater and has high heat resistance. The higher the melting point of the conductive component, the higher the heat resistance of the heater in the operating temperature range.

[0008] The amount ratio between the insulating component and the conductive component contained in the heating resistor is not particularly limited.
In the case of volume%, the conductive component can be 15 to 40 volume%, particularly 20 to 30 volume%. When the insulator is made of a silicon nitride sintered body, the sintered body may contain a small amount of aluminum nitride, alumina or the like. Further, it may be a sialon. In addition, a small amount of a conductive component can be contained in order to reduce the difference in thermal expansion coefficient from the conductive component.

The above-mentioned "heating resistor" can generate heat by applying a voltage from a lead wire, and its shape is not particularly limited, but it can be, for example, substantially U-shaped. The above-mentioned “lead wire” is for applying a voltage to the heating resistor, and usually two wires are fitted to the end of the heating resistor, one by one. The components constituting the lead wire are not particularly limited, but it is preferable that at least one of the elements selected from W, Re, Ta, Mo, and Nb is a main component.
Above all, it is more preferable that W is a main component (preferably 90% by mass or more, more preferably 95% by mass or more). The wire diameter of this lead wire is 0.3 mm.
05 to 0.9 mm (more preferably 0.1 to 0.7 m
m, more preferably 0.2 to 0.5 mm). If the linearity of the lead wire is less than 0.05 mm, it is difficult to stably fit the heating resistor during manufacturing. On the other hand, if the wire diameter exceeds 0.9 mm, the mechanical strength of the ceramic heater tends to decrease.

The above-mentioned "reaction layer" is formed when a component constituting a lead wire and a component constituting an unsintered heating resistor serving as a heating resistor react during firing when a ceramic heater is manufactured, and the lead wire and the heating resistor are reacted. It is an extremely thin layer containing both components of the heating resistor and the lead wire formed at the interface with the lead wire. However, this reaction layer is not always formed at the time of manufacturing the ceramic heater, and may or may not be formed due to various factors such as components in the unfired heating resistor to be the heating resistor and firing conditions. .

The "outer cylinder" is inserted into the ceramic heater by a method such as brazing, and one end of the outer cylinder is inserted into and fixed to one end of the metal shell, thereby connecting the ceramic heater to the metal shell. A metal tube to hold. The outer cylinder has a function of protecting the ceramic heater from impact and the like and a function of promoting heat removal of the ceramic heater, in addition to the purpose of fixing the ceramic heater to the metal shell. The constituent material of the outer cylinder is not particularly limited, but it is preferable to use a nickel alloy, stainless steel, or the like. These metals are preferable because they can perform good heat drawing and have high heat resistance.

The above “Dc / Ds” may be 0.8 or less, preferably 0.75 or less, and 0.72 or less.
It is more preferred that: When Dc / Ds exceeds 0.8, that is, when the thickness of the outer cylinder is reduced, breakage due to the impact at the time of abnormal combustion tends to occur, and the brazing material between the ceramic heater and the outer cylinder is reduced. It may elute during use, which is not preferable.

In the glow plug of the present invention, Dc / D
s is preferably 0.5 or more. When Dc / Ds is less than 0.5, that is, when the thickness of the outer cylinder increases,
When the ceramic heater is fixed in the outer cylinder by brazing (by silver brazing or the like), the ceramic heater may be cracked. Therefore, Dc / Ds is further increased to 0.
It is preferably from 5 to 0.8, more preferably from 0.5 to 0.75, even more preferably from 0.6 to 0.72.

Further, in the glow plug of the present invention, the glow plug is fixed, and a load is applied at a constant speed perpendicular to the longitudinal direction at a position 2 mm from the tip of the protruding portion of the ceramic heater protruding from the outer cylinder. The breakage load when added while increasing is preferably at least 1 times the breakage load of the glow plug having Dc / Ds of 0.8.

In measuring the breaking load, the direction in which the glow plug is fixed is not limited, and the load may be applied perpendicular to the length direction. The load may be applied at a constant speed, but is preferably applied at a rate of 0.5 mm / sec. The “broken load” is the magnitude of the load applied when the ceramic heater is broken. The breaking load of the glow plug of the present invention is preferably at least 1 times (usually 2 times or less) the breaking load of the glow plug having Dc / Ds of 0.8, and more preferably at least 1.05 times. More preferably, it is particularly preferably at least 1.1 times. If this load is less than 0.75 times, the probability of breakage during abnormal combustion in a diesel engine tends to increase. Hereinafter, this test is referred to as a “pressure resistance test”.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the glow plug of the present invention will be described in more detail with reference to embodiments. In the following, one end of the ceramic heater and the glow plug arranged on the combustion chamber side of the engine will be referred to as a front end, and the other end will be referred to as a rear end. [1] Manufacture of glow plug (1) Manufacture of ceramic heater To 86 mass% of silicon nitride raw material powder, 1
0 mass% of Er ₂ O ₃ powder and 4 mass% of SiO ₂ powder were blended to obtain a raw material for an insulating component. This insulating material 4
0% by mass and 60% by mass of WC powder as a conductive component raw material were wet-mixed for 72 hours, and then dried to obtain a mixed powder. Thereafter, the mixed powder and the binder were put into a kneader and kneaded for 4 hours. Next, the obtained kneaded material was cut into pellets, which were then put into an injection molding machine to obtain a U-shaped heat generating resistor having tungsten lead wires embedded at both ends.

On the other hand, 84% by mass of silicon nitride raw material powder is
As a sintering aid, 10% by mass of Er ₂ O ₃ powder, 4% by mass of SiO ₂ powder and 2% by mass of MoSi ₂ powder are blended.
The mixture obtained by wet mixing for 0 hour was granulated by a spray drier method, and two half molds were prepared by pressing the granulated material to form an insulator. Then, the molded body to be the heating resistor is
After being placed at a predetermined position between the half molds and press-molding and embedding, these were integrally pressed at a pressure of 70 atm to obtain an unfired ceramic heater molded body. Next, the ceramic heater molded body was calcined at 600 ° C. to remove the binder, and a calcined body was obtained. The calcined body was set on a graphite pressing die, and heated at 1800 ° C. in a nitrogen atmosphere at 1800 ° C. Hot press firing for .5 hours. Next, the outer shape of the fired body was subjected to centerless polishing, so that the lead wires were exposed from the insulator to produce the ceramic heater 13.

(2) Assembly of glow plug Glass was baked on the portion of the ceramic heater 13 obtained in (1) where the outer cylinder 12 is to be located. Next, the outer cylinder 12 is arranged at a predetermined position from the front end side of the ceramic heater 13 using a jig (parts of the front end side and the rear end side of the ceramic heater are exposed outside the outer cylinder). Thereafter, a winding silver braze whose inner diameter is slightly larger than the outer diameter of the ceramic heater and whose outer diameter is larger than the inner diameter of the outer cylinder 12 is inserted through the ceramic heater from the rear end side to form an outer cylinder. Arranged above. Then, in this state, about 1000 ° C
(This causes the brazing material to flow between the ceramic heater and the outer cylinder, and then is held at room temperature to shrink-fit due to the difference in the coefficient of thermal expansion between the outer cylinder and the ceramic heater.) Is maintained in the state of

Next, the lead coil 14 was soldered to the rear end side of the ceramic heater into which the outer cylinder was inserted, and the lead wire 133 was electrically connected to the outer cylinder. Next, the lead coil 14 'welded to one end of the assembly 15 was fitted from the rear end of the ceramic heater and brazed to electrically connect the lead wire 133' to the center shaft 15. Further, the outer cylinder 12 to which the ceramic heater or the like obtained above was brazed was silver-brazed to one end of the metal shell 11. Thereafter, the assembly 15 is temporarily fixed using a jig to prevent eccentricity in the metal shell 11, and a glass pipe is inserted into and fixed to the assembly 15 from the rear end of the metal shell 11, and then melted. The metal fitting 11 and the assembly 15 were fixed with glass 16.

Thereafter, the insulator 1 is inserted from the rear end of the metal shell 11.
7, the nut 18 and the nut 18 were inserted and then swaged and fixed (the nut 18 and the assembly 15 were insulated from the metal shell 11 by the insulator 17) to obtain the glow plug 1. FIG. 1 is a schematic sectional view of an example of the glow plug 1 of the present invention obtained as described above.

[2] Evaluation (1) Evaluation of breakage in shrink-fitting process A ceramic heater having a diameter of 3.5 mm was shrink-fitted to seven types of outer cylinders by the same method as (2) in [1], and Dc / D
s is 0.9, 0.8, 0.7, 0.6, 0.5, 0.4
And 0.3 glow plugs each of 1000 types.
I got one. The outer cylinder was removed from the obtained assembly of the ceramic heater and the outer cylinder, and the ceramic heater was visually checked for breakage. From this result, the probability of occurrence of breakage was determined and is shown in Table 1.

[0022]

[Table 1]

(2) Evaluation by pressure resistance test Ten pieces of each glow plug having different Dc / Ds obtained in (1) were randomly taken out, and the length direction of the glow plug was horizontal as shown in FIG. And fixed to an iron glow plug fixed mold 2 such that Next, a load was applied at a position of 2 mm from the tip of the ceramic heater using a carbide pin at a crosshead speed of 0.5 mm / min to cause breakage, and the breakage load was measured. Then, the average value of the breakage load for each of the ten glow plugs was calculated and is shown in Table 1. When the presence or absence of a reaction layer at the interface between the heating resistor and the lead wire was confirmed, a reaction layer was observed in all glow plugs.

(3) Evaluation by abnormal combustion test on actual machine Four tubes were taken out at random from each glow plug having a different Dc / Ds obtained in (1). I attached it. After that, the glow plug is de-energized and the engine speed 3
Abnormal combustion was caused by injecting a small amount of engine oil from the intake manifold while operating under a no-load condition of 000 rpm. After the test, the glow plug was removed from the engine, disassembled and the ceramic heater was removed, and the breakage of the ceramic heater was visually checked. The results are shown in Table 1. When the presence or absence of a reaction layer at the interface between the heating resistor and the lead wire was confirmed, a reaction layer was observed in all glow plugs.

(4) Evaluation by Cooling / Heat Cycle Endurance Test Ten pieces of each glow plug having different Dc / Ds obtained in (1) were randomly taken out, and the temperature was set at 1400 ° C. so that the temperature at the tip of the ceramic heater was 1400 ° C. Energized for minutes,
Thereafter, a cycle of turning off the electricity for 1 minute was repeated 5000 times. As a result, the presence or absence of elution of the brazing material joining the ceramic heater and the outer cylinder was confirmed, and the number of cycles when elution was confirmed is also shown in Table 1. Glow plugs in which elution was not observed even after 5000 cycles were described as "no elution".

From the results shown in Table 1, it can be seen that when Dc / Ds is 0.5 or more, breakage of the ceramic heater during shrink fitting can be completely prevented. Further, Dc / D
If s is 0.8 or less, the breaking load by the pressure test is 40.
It can be seen that the pressure can be set to 0N or more and breakage at the time of abnormal combustion can be prevented. And when Dc / Ds is 0.
The breaking load in the pressure test of the glow plug, which is 8, is 1
When Dc / Ds is 0.7 to 0.3, 1.25 or more can be obtained. Further, Dc / Ds
Is 0.8 or less, it can be seen that no elution of silver wax is observed even in the thermal cycle test. Therefore, Dc /
It can be seen that the glow plug having Ds of 0.5 to 0.8 is excellent in each characteristic.

[0027]

According to the present invention, it is possible to obtain a glow plug in which the ceramic heater is unlikely to break during abnormal combustion.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram schematically illustrating a pressure resistance test in an example.

[Explanation of symbols]

1; glow plug, 11; metal shell, 12; outer cylinder, 1
3; ceramic heater, 131; insulator, 132; heating resistor, 133, 133 '; lead wire, 14, 14';
Lead coil, 15; assembly, 16; glass seal, 1
7; insulator, 18; nut, 2; glow plug fixed type.

Claims (3)

[Claims] An insulator and a conductor embedded in the insulator, wherein the conductor is embedded with a heating resistor, one end of which is electrically connected to the heating resistor, and the other end of which is embedded. A ceramic heater including a pair of lead wires exposed from the insulator, and a reaction layer formed at an interface between the heating resistor and the lead wire; and an outer cylinder into which the ceramic heater is inserted, A metal fitting to which the outer cylinder is fitted, wherein Dc / Ds is 0.8 or less, where Dc is the outer diameter of the ceramic heater and Ds is the outer diameter of the outer cylinder. A glow plug characterized by the following. 2. The glow plug according to claim 1, wherein Dc / Ds is 0.5 or more. 3. The fixing device according to claim 1, wherein the glow plug is fixed, and the ceramic heater projects from the tip of the ceramic heater.
The breaking load when a load is applied at a constant speed at a position perpendicular to the length direction at a position of mm while the load is increased at a constant speed is at least 1 times the breaking load of a glow plug having a Dc / Ds of 0.8. The glow plug according to claim 1.