JPS6066018A - Ceramic glow plug - Google Patents

Abstract

PURPOSE:To prevent the obstruction of the formation of vortex flow in a combustion chamber approximately, and to increase mechanical strength against vibration, impact, etc. by thinning the outer diameter of a ceramic heater and disposing a heating wire coil within predetermined projecting size by dividing the voltage of a heating wire. CONSTITUTION:A ceramic heater 10 is formed so that the outer diameter D (a long diameter on a heating wire coil, a section thereof does not take a true circle but takes an oval) of the heating wire coil 12 buried in a heater section 10' projecting from the nose surface of a metallic outer cylinder 11 extends over 4.0mm. or less and the projecting size (l) of the heater section 10' projecting from the nose surface of the metallic outer cylinder 11 3D or less. The metallic outer cylinder 11 is braed to a fitting 13 to constitute a negative side electrode. On the other hand, the other end 12b of the heating wire coil 12 is connected to a metallic cap 14 inserted and fixed to the rear end section of the ceramic heater 10, and connected to a resistor 16 through a lead wire 15, and the other end of the resistor 16 is connected to an intermediate shaft 17, thus constituting a positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic glow plug that is mainly installed in a diesel engine for starting, and particularly to a ceramic heater that serves as a heating element for the glow plug.

Generally, in order to improve startability of a diesel engine, a plug is installed in the auxiliary combustion chamber, etc., and when the plug is energized, it becomes red-hot and a part of the fuel injected into the interior is combusted to preheat it. In addition, it is required to have rapid temperature rise characteristics at the time of startup, and since it tends to be used as a 77 targlow for a long time to stabilize combustion even after startup, it is necessary to improve its durability. It is becoming increasingly needed.

As a rapid heating type glow plug suitable for this purpose, a ceramic glow plug using a ceramic heater made by embedding a high melting point metal tungsten (W) heating wire in ceramic powder and sintering it has been known. As shown in FIG. 1, the heating element has a structure in which a ceramic heater 1 protrudes from the tip of a metal outer cylinder 3 which is brazed to the inner cavity of a mounting bracket 2.

By the way, although this heel glow plug is extremely effective for engine starting, etc., since the heater part 1' protrudes into the combustion chamber such as the vortex chamber, it is used as an afterglow to stabilize combustion after starting. In the hourly operation range, this protrusion becomes an obstacle and obstructs the formation of vortices, affecting combustibility, and adversely affecting engine performance such as a reduction in engine output, deterioration of fuel efficiency, and an increase in harmful exhaust gas. Therefore, the heater portion 1' protruding from the metal outer cylinder 3 should be formed so that its protruding dimension l is as short as possible and its outer diameter p is as thin as possible. This is preferable.

However, reducing the outer diameter of the heater part 1' is not easy to damage under conditions such as harsh indoor heating and cooling thermal cycles, vibrations and shocks during operation, and there are restrictions from the mechanical strength perspective. be done. In order to increase this mechanical strength, the second
As shown in the figure, there is an example in which the metal outer cylinder 3' is lengthened to cover and reinforce so that the protruding dimension 11 of the heater part 1' is shortened, but the length of the heating wire coil 4 buried inside is l!
Since the part corresponding to 2 is covered by the metal outer cylinder 3', the heat generation efficiency is not allowed to be inhibited, but the temperature of the heating wire coil in this part increases excessively, and the temperature at the joint with the metal outer cylinder 3' increases. There is a problem with melting the brazing filler metal, and
Simply shortening the protruding dimension of a part of the heater while keeping the material and wire diameter of the heating wire the same as before will reduce the resistance value because the length of the heating wire coil buried inside will become shorter. There was a problem in that the required amount of heat generation could not be obtained.

The present invention has been made in view of the above-mentioned circumstances, and is intended to solve the above-mentioned problems. As a result, the heating wire coil is arranged within a predetermined protrusion dimension, and its feature is that it can be made of pure tungsten (W) or the pure tungsten (W) wire material conventionally used in heating wire coils of ceramic heaters. A part of the heater is made smaller by using a W alloy having a composition described later which has a large specific resistance, and the ceramic heater has a temperature-resistance coefficient (resistance value at room temperature) that is larger than the wire used in the heating wire coil. By connecting in series a combination of resistors using wires with a resistance value that is in proportion to the resistance value at a high temperature of 1000°C, current flow is controlled when the temperature suddenly rises, and overheating of a part of the heater is prevented. The present invention aims to provide a ceramic heater that has a good structure, excellent starting characteristics, and improved durability.

Details C2 will be explained below with reference to the drawings.

FIG. 3 is a longitudinal sectional view of an embodiment of the ceramic globe 2g of the present invention, in which the ceramic heater 10 is suitable for the heating wire coil 12 embedded in the heater part 10' protruding from the tip end surface of the metal outer cylinder 11. For W, rhenium (Re), Tric A
('l'h), zirconia A (Zr).

Cobalt (Co), molybdenum (MO), and a wire rod with a positive temperature coefficient of resistance that is 4 times or less. The metal outer cylinder 11 has a diameter (longer axis if the cross section is not a perfect circle but an ellipsoid) of 4.00 or less.
The heater portion 10' is formed so that the protrusion dimension l thereof is 3D or less.

The outer diameter (D) of the ceramic heater is 4.0M or less,
The reason for setting the protrusion dimension l to 3 times or less of the outer diameter (D) is as follows.
Ceramic heater C2 using a W alloy wire with Re added to the entire heating wire.The following describes an example of a ceramic glow plug of the present invention in which a resistor coil using a Ni wire is connected in series. This is based on the results of a rapid current heating test and a drop impact test.

That is, FIG. 4 is a graph showing the results of the rapid energization heating test, and is a graph showing the results of a ceramic heater having the above-mentioned glow plug (four types of outer diameter CD: 2, 2,0ffff, 3.0mm, and 4.011111.4jiW). 900 per sample using
This is a graph showing the relationship between the heating conditions (time) for each sample up to 900°C and the temperature at which ceramic cracking occurs when each sample is rapidly heated with electricity up to a maximum of 1300°C by changing the heating conditions up to 900°C. , the hatched part on the left side of each curve indicates the zone where ceramic cracking occurs, for example, the outer diameter of the heater (D)
== 4. When looking at the On curve, it is approximately 1300℃
If the heating time to reach 900℃ is within 1.4 seconds, ceramic cracking will occur; at approximately 1125℃, ceramic cracking will occur within 1.3 seconds, and at approximately 1025℃, within 1.2 seconds. As shown in the graph, the smaller the outer diameter (D), the shorter the heating time to 900℃, and the thicker the diameter, the more difficult it is for the ceramic to respond to the temperature rise of the heating wire. This shows that it is difficult to shorten the time taken to raise the temperature to 900°C because the follow-up is delayed and ceramic cracks are more likely to occur due to thermal distortion.

Therefore, in order to satisfy the condition that the heating time to 900°C be within 1.5 seconds, which is required to obtain good startability and combustion stability, the outer diameter of the heater (ρ) must be 4.0M or less. It turns out that it is good.

In addition, Fig. 5 shows that the outer diameter (D) of the ceramic heater is 2.0.
1u, protrusion dimension E is 5.0 silk and 8.0 silk, outer diameter (D) is 3. OWN and protrusion dimension (1) is 5. QMII,
9.0 mtpr and 12.0111 ff, and the outer diameter (D) is 4.0 decoy and the protrusion dimension C1) is 10.
This is a graph showing the results of a drop impact test conducted on eight types of ceramic glow plug samples: OffM, 12.0rltl, and i4.0.

6J shows the relationship between the drop height and heater protrusion dimension <1> when a part of the heater is damaged when a sample is held horizontally and dropped onto a concrete floor.

From a practical standpoint, in order to withstand a drop height of at least 1.5 m, the protruding dimension (J) of the heater must be
It turns out that it is necessary to make it 3D or less.

The ceramic heater 10 configured as described above is bonded to a metal outer cylinder 11 and connected to one end 12a of a heating wire coil 12 buried inside, and the metal outer cylinder 11 is further connected to a mounting bracket 13 by soldering. are in contact with each other to form the θ side electrode.

On the other hand, the other end 12b of the heating wire coil 12 is connected to a metal cap 14 that is inserted and fixed to the rear end of the upper two-layer heater 10, and is connected to a resistor 16 via a lead wire 15 welded to the cap 14. , the other end of the resistor 16 is the center shaft 1T
A metal wire 1 such as tungsten (W), which has a positive temperature coefficient of resistance such that the temperature-resistance coefficient is 5 times or more, is attached to the wire of the resistor. Molybdenum (Mo), Nickel (N), Iron (
Fθ] etc.

Note that the resistance values of the heating wire coil 12 and the resistor 16 are set according to required heating conditions.

Figure 6 shows the time when the ceramic globe 2g according to the embodiment of the present invention having the above-mentioned structure with heater outer diameter D = 5ttyt and protrusion size l-5 is energized and rapidly heated, and the heating wire coil. This is a graph showing the result of actually measuring the relationship between the temperature of a part of the heater embedded in the heater and the temperature of the resistor.As is clear from the figure, a W alloy wire rod with a small number of heaters (4 times or less) is used.

This is combined with a resistor using a metal wire with a large temperature-resistance coefficient (more than 5 times) and connected in series, so the resistance value of the resistor is faster than that of the heating wire coil when the temperature rises rapidly due to energization. This shows that the heating current can be reduced by self-control and overheating of one heating wire coil, that is, a part of the heater can be extremely effectively suppressed. In addition, the heating wire coil is not limited to the above embodiment, but may be a conventional W coil.
The object of the present invention can be achieved by using MO wire rods in combination with Ni and Fθ wire rods having particularly large resistance temperature coefficients for the other resistor.

As can be understood from the above explanation, the ceramic glow plug of the present invention can be produced by dividing the pressure of the heating wire of a ceramic heater or by applying pure W, which is conventionally used for the heating wire, to
W alloy wire I with a specific composition that has a higher resistivity than the wire
By using a heating wire coil, the heating wire coil becomes smaller, and the exposed length of a part of the heater becomes shorter, so the mechanical strength of the vortex shape inside the combustion chamber is improved.
In the inner cavity of the mounting bracket, a resistor made of metal wire having a temperature-resistance coefficient larger than that of the heating wire embedded in a part of the heater of the upper two heaters is combined and connected in series with the ceramic heater. Therefore, when the temperature rises rapidly, the resistance value of the resistor increases rapidly as the heating wire coil moves, and by reducing the heating current, overheating of a part of the heater is suppressed, preventing ceramic cracking due to thermal shock and heating wire. It has many features such as being able to prevent coil breakage, solving the conventional problems and improving engine starting characteristics.

It can be provided as a ceramic glove 2 with improved durability.

[Brief explanation of drawings]

Fig. 1 is a front view showing the main parts of the ceramic heater of a conventional ceramic globe jig, Fig. 2 is a longitudinal sectional view of the main parts of another conventional example in which the ceramic heater is reinforced with a metal outer cylinder, and Fig. 3 The figure is a longitudinal cross-sectional view of an embodiment of the ceramic glow plug of the present invention, Figure 4 is a graph showing the relationship between the heating conditions for the outer diameter of the heater and the temperature at which ceramic cracking occurs in a rapid current heating test, and Figure 5 is a drop impact test. FIG. 6 is a graph showing the relationship between the heater protrusion dimension and the fall height at which damage occurs, and FIG.
It is a graph showing the relationship with the temperature of a resistor. Single layer 10: Ceramic heater, i', io': Part of heater, 2.13: Mounting bracket, 3.3', 11: Metal outer cylinder, 4.12: Heating wire coil, 16: Resistor, 17 : Center shaft, L: Projection dimension, D: Outer diameter Attorney Morime Takeuchi, 1 Figure 4 Figure 4 fi'75 Figure 6

Claims (1)

[Scope of Claims] (1) A ceramic heater made by embedding and sintering a heating wire of a high melting point metal in ceramic powder protrudes from the front end surface of a metal outer cylinder and is soldered to the inner cavity thereof. In the ceramic globe 2 in which the metal outer cylinder is joined to the inner cavity of the distal end of the mounting bracket, the outer diameter (q) of the ceramic heater is 4.0 mw or less, and the protrusion dimension (I) from the distal end surface of the metal outer cylinder is 5D or less, a heating wire fill is embedded within the protruding dimension, and a resistor is connected in series to the ceramic heater within the inner cavity of the mounting bracket. (2) A ceramic glow plug according to claim 1, wherein the heat generating wire is made of tungsten (W) or molybdenum (M) wire, and the resistor is made of nickel (N) or iron (F). Ceramic glow plug. (5) The temperature-resistance coefficient (room temperature - 100
Rhenium (R, Thorium (Th), Zirconium (Zr), Cobalt (Co), Mori 7'7") with a positive temperature coefficient of resistance that is 4 times or less (0°C):
/(MO) and the remainder tungsten (W)
Using a W alloy wire consisting of
The ceramic glow plug according to claim 1, which uses a metal wire having a resistance coefficient of 5 times or more.