JPH044585A - Spark plug with pressure sensor - Google Patents

Abstract

PURPOSE:To enhance the durability against smoke contamination as well as heat resistance at the tip of a central electrode by installing a pressure sensor of piezo type between a body drum and a small dia. leg provided at the foremost of the body drum and having a screw for securing to the engine, and forming the part situated at the leg of insulation from sintering of nitride series ceramics. CONSTITUTION:Insulation 2 provided with a shaft hole 21 is fitted to a cylindrical metal piece 1 as main body and secured, and a central electrode 3 is inserted into this shaft hole 21 and fixed. This metal piece 1 is fitted with a pressure sensor 4. The insulation 2 comprises a long leg 22 at the foremost and a corrugation 23 at the tail, and the whole structure is formed from a ceramic sintering consisting of aluminum nitride. The leg 22 has a tapered base bottom 24, which is in contact with packing. Thereby heat relief is improved to permit prolongation of the leg part insulation, and durability against smoke contamination will accordingly be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spark plug with a pressure sensor used for engine compatibility testing and knocking monitoring.

[Prior Art] A spark plug with a pressure sensor is known, which consists of a center electrode, an insulator surrounding the center electrode, and a mounting bracket that holds the insulator in its inner cavity and has a pressure sensor disposed in its body. (Utility Model Application Publication No. 171989/1989).

[Problems to be Solved by the Invention] However, the conventional spark plug with a pressure sensor has the disadvantage that when used in a rich air-fuel mixture at a low temperature, a misfire occurs due to smoke contamination.

Furthermore, if the length of the long leg portion of the insulator is increased in order to avoid smoldering and contamination, heat conduction becomes poor and heat resistance deteriorates.

An object of the present invention is to provide a spark plug with a pressure sensor that is excellent in explosion resistance and heat resistance.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a method of fixing an insulator with a shaft hole by fitting it into a cylindrical main metal fitting, and inserting and fixing a center electrode into the shaft hole. , a pressure sensor in which a piezoelectric pressure sensor is disposed between a slightly larger diameter body provided in the middle of the metal shell and a smaller diameter leg provided on the tip side thereof and having an engine mounting screw. In the sensor-equipped spark plug, at least a portion of the insulator located at the leg portion is formed of a nitride-based ceramic sintered body.

[Function and Effects of the Invention] (Function) A spark plug with a pressure sensor in which a pressure sensor is disposed between the body and the leg of the metal shell reduces the heat of the insulator compared to a normal spark plug. Heat resistance tends to deteriorate because the pull is deteriorated (due to the long body, volume of liquid in the body, etc.).

However, by adopting the configuration of the present invention, the heat generated at the tip of the center electrode due to spark discharge can be quickly released to the metal shell through the nitride ceramic sintered body with excellent thermal conductivity. This prevents the tip of the center electrode from becoming abnormally heated.

(Effect) Since the heat dissipation is improved, the length of the long leg insulator can be increased, and the explosion and stain resistance is improved by the length.

If you compare the long leg insulators with the same length, they have better heat resistance.

[Example] Next, an example of the spark plug with a pressure sensor of the present invention will be described based on FIGS. 1 and 2.

A spark plug A with a pressure sensor is fixed by fitting an insulator 2 with a shaft hole 21 into a cylindrical main metal fitting 1, and fixing the insulator 2 with a shaft hole 21.
The center electrode 3 is inserted into the hole 1 and fixed. Further, a pressure sensor 4 is disposed on the metal shell 1.

The metal shell 1 is made of low carbon steel, and has a reach portion 11 at the tip.
(small diameter), a hexagonal part 12 at the rear end, and a body part 13 (slightly large diameter) in the center.

The reach part 11 has screws 1 for engine mounting except for the tip.
4 is formed on the outer periphery. An outer electrode 5 (high chromium-nickel alloy) in which 100% iridium 51 is disposed on the firing part side is welded to the tip surface of the reach part 11.

Further, a tapered packing contact surface is formed on the inner wall of the reach portion 11, and a packing is provided around the contact surface.

The hexagonal part 12 has an outer periphery (diameter smaller than the body part 13), and a talcum ring and wire packing are inserted inside.

The body portion 13 consists of a large-diameter portion and a small-diameter portion, and a holding fitting 15 having an angular cross-section is seam-welded 16 to the small-diameter portion. A gasket 17 is provided around the holding fitting 15 on the engine side.

The insulator 2 consists of a long leg portion 22 at the tip and a corrugation portion 23 at the rear end, and is entirely formed of a ceramic sintered body made of aluminum nitride (thermal conductivity: 150 W/m-k). The long leg portion 22 has a length of 20 mm, and a tapered base 24 is in contact with the gasket.

The center electrode 3 has a firing electrode (platinum-20%
It is made by joining an iridium alloy (or 100% iridium) 32, and there is no gap between it and the shaft hole 21.

As shown in FIG. 2, the pressure sensor 4 includes an annular packing 41 arranged on the inner bottom of a hollow ring-shaped metal case 40, the upper inner wall of which is electrically insulated with insulating substrates 42, 43, and an annular electrode 44. It is sandwiched between an annular insulating plate 45 and an annular piezoelectric element 46, and an output cable 47 is electrically connected to the electrode 44. Note that the output cable 47 passes through the guide hole 10 and is connected to a pressure detection device (not shown).

A method for manufacturing the main parts of the spark plug A with a pressure sensor will be described.

(1) Fitting the ignition electrode 32 into the shaft hole of the unfired insulator,
The unfired electrode body, which is made by adding conductive metal powder to glass powder, is fired in a heating furnace while being pressed with a center shaft (not shown).

(2) Assemble the spark plug body except the holding fitting 15 and gasket 17.

(3) Pass the output cable 47 downward through the guide hole 10,
The pressure sensor 4 is fitted into the reach portion 11 from below in the figure and brought into contact with the step 18 of the body portion 13.

(4) While pressing the pressure sensor 4 against the step 18 with the holding fitting 15, the holding fitting 15 is seam welded to the small diameter portion of the metal shell 1.
6.

(5) Attach the gasket 17 and complete.

Next, the effects of the spark plug A with a pressure sensor will be described.

(a) Since a ceramic sintered body of aluminum nitride with good thermal conductivity is used for the insulator 2, the temperature of the ignition electrode 32 does not rise abnormally, and there is a margin in the ignition advance angle at which ignition occurs.

In addition, the insulator uses alumina (the leg length is 14 m).
A comparison test with spark plug A was found to be superior in heat resistance despite the fact that spark plug A has a longer leg portion by 6 mm. In this case, the length of the leg portion is 6 mm longer, which is advantageous in terms of smoke stain resistance.

(a) Ignition electrode 3 made of platinum-20% iridium alloy
2, and the outer electrode 5 in which 100% iridium 51 is disposed on the ignition part side, the wear of the electrode due to sparks is extremely small and the durability is excellent.

(1) The firing electrode 32 is made thinner (the diameter of the small diameter part is 1
mm>, so the insulation path of the firing part can be long.

This overcomes the disadvantages of using aluminum nitride insulators (poor insulation properties at high temperatures).

(1) In this embodiment, aluminum nitride is used as the nitride-based ceramic sintered body. This is to obtain good heat conduction at low cost.

(E) The pressure sensor 4 can be easily disposed on the body 13 of the metal shell 1.

(Power) A normal plug wrench can be used when installing to the engine.

[Brief explanation of the drawing]

1 and 2 show one embodiment of the invention. FIG. 1 is a partial sectional view of a spark plug with a pressure sensor, and FIG. 2 is a sectional view of a main part thereof.

Claims (1)

[Scope of Claims] 1) An insulator with a shaft hole is fitted and fixed into a cylindrical metal shell, a center electrode is inserted and fixed into the shaft hole, and a slightly diameter insulator provided in the middle of the metal shell A spark plug with a pressure sensor in which a piezoelectric pressure sensor is disposed between a large body part and a small diameter leg part provided on the tip side thereof and having an engine mounting screw, of the insulator, A spark plug with a pressure sensor, characterized in that at least a portion located in the leg portion is formed of a nitride-based ceramic sintered body.