JPH044586A - Spark plug with pressure sensor - Google Patents

Abstract

PURPOSE:To prevent a central electrode from easily oxidizing or corroding by fitting an insulation provided with a shaft hole to a cylindrical metal piece as main body, fixing them, inserting the central electrode in the shaft hole, securing them, and forming the part located at the firing part from a noble metal or thermet. 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. This central electrode 3 is obtained by joining a firing electrode (Pt-20% Ir alloy, or 10% Ir) 32 with the electrode body 31, with no gap formed to the shaft hole 21. Thereby the dia. of the firing part insulation can be shrunk, and the thermal capacity of insulation is lessened, and the attached carbon can be burnt off easily, so that self-cleaning property is enhanced, and there is no fear of exhaustion of the electrode.

Description

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

[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, when conventional spark plugs with pressure sensors are used continuously under high loads, the electrode gap widens due to electrode wear, and the discharge voltage exceeds the maximum voltage of the power supply voltage. case,
There is a drawback that sparks do not fly.

An object of the present invention is to provide a spark plug with a pressure sensor that has excellent resistance to electrode wear.

[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 body portion with a slightly large diameter provided in the middle of the metal shell and a leg portion with a small diameter provided on the tip side thereof and having an engine mounting screw; In this spark plug, the center electrode is made of noble metal or cermet at least in the portion located in the ignition part, and the central electrode is integrally fired at the same time as the insulator is fired.

[Operations and Effects of the Invention (Operations) The portion of the center electrode located at the firing part is made of noble metal or cermet. For this reason, the center electrode does not easily oxidize or corrode even if it is exposed to a high temperature environment or spark energy for a long time due to continuous operation under high load (the center electrode can be made thinner).

Since the center electrode and the insulator are fired simultaneously, there is no gap between the shaft hole and the center electrode.

(Effects) Excellent resistance to electrode wear and can maintain stable spark discharge for a long period of time.

By having a thin center electrode and having no clearance between the center electrode and the insulator, it is possible to reduce the diameter of the insulator in the firing part. Therefore, the heat capacity of the insulator is reduced, and the attached carbon can be easily burned off, thereby improving self-cleaning performance.

[Example] Next, a first example of a spark plug with a pressure sensor according to 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 as a hexagonal opposite side (diameter smaller than the body part 13), and a talc 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 alumina. Further, the base 24 of the long leg portion 22 has a tapered shape and is in contact with the packing.

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 is connected to a pressure detection device (not shown) through the guide hole 10.

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 center electrode 3 and the insulator 2 are simultaneously fired together in a heating furnace while pressing an unfired electrode body made of glass powder with conductive metal powder added thereto using a center axis (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 stepped portion 18 of the body portion 13.

(4) Seam weld 16 the holding fitting 15 to the small diameter portion of the metal shell 1 while pressing the pressure sensor 4 against the stepped portion 18 with the holding fitting 15.

(5) Attach the gasket 17 and complete.

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

(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. Therefore, a stable compatibility test can be performed for a long period of time.

(a) The firing part 132 is made thinner (the diameter of the small diameter part is
1 mm), since there is no gap between the center electrode 3 and the shaft hole 21, the diameter of the insulator 2 of the firing part can be reduced. Therefore, the heat capacity of the insulator 2 becomes small, and even if carbon contamination occurs during a compliance test, the attached carbon can be easily burned off. Therefore, it has excellent self-cleaning properties.

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

(1) A regular plug wrench can be used when installing it in the engine.

FIG. 3 shows the second spark plug with pressure sensor of the present invention.
This is an example.

In the spark plug B with pressure sensor, the insulator 2 located in the long leg portion 22 is made of aluminum nitride, which has excellent thermal conductivity.
The insulator 2 of the corrugation portion 23 is made of a ceramic sintered body of alumina6, and the ignition electrode 32 is made of a cermet-based conductive sintered body mainly composed of molybdenum disilicide.

In addition to the effects shown in the first embodiment, the pressure sensor equipped spark plug B also has the following effects.

Heat from the ignition electrode 32 quickly escapes to the metal shell 1 through aluminum nitride, which has excellent thermal conductivity. For this reason,
The ignition electrode 32 does not undergo an abnormal temperature rise, and has superior heat resistance compared to one having the same size leg portions 22.

When aluminum nitride is used for the leg portions 22, it is necessary to lengthen the insulation path with the center electrode 3 in order to ensure insulation at high temperatures, which increases the diameter of the leg portions 22 and the metal shell 1. This causes trouble in the arrangement of the pressure sensor 4. However, due to the configuration in which the thin firing portion 4fI32 is simultaneously fired, an insulation path can be ensured, and the arrangement of the pressure sensor 4 is not hindered.

[Brief explanation of the drawing]

1 and 2 show a first 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. FIG. 3 shows a second embodiment of the present invention, and is a partial sectional view of a spark plug with a pressure sensor.

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 In a spark plug with a pressure sensor, a piezoelectric pressure sensor is disposed between a large body and a small diameter leg provided on the tip side thereof and has an engine mounting screw. A spark plug with a pressure sensor, characterized in that the part located at the bottom is made of precious metal or cermet, and is fired simultaneously with the firing of the insulator.