JPH0518313A - Exhaust ion gap - Google Patents

Abstract

PURPOSE:To improve the sensitivity in ion detection by putting the area of the exposed section at the top, which is not covered with an insulator, of the center electrode, which is held by the insulator fixed to the metal fitting having a mounting screw part at the periphery, in 20mm<2> or more. CONSTITUTION:The area of the exposed section, which detects the ions contained in the flames in combustion gas, at the top 6, which is not covered with an insulator 3, of the center electrode 2, which is held by the insulator 3 fixed to a mounting metal fitting 4, is put in 20mm<2> or more. Hereby, even if the number of ions in the flame, which is contained in the combustion gas occurring by the combustion of the mixed air where the air-fuel ratio is made high for lean combustion, decreased, the sure detection of an ion current by the center electrode 2 become possible. Even if the temperature of the combustion gas rises by the lean combustion of the mixed air, it turns out that this can cope enough with the oxidation by the combustion gas at high temperature, by covering the top 6 of the center conductor 2 with one or more cover consisting of noble metal solid material, noble metal, or noble metal alloy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an exhaust ion gap attached to an exhaust system for the purpose of detecting misfire and ignition in an internal combustion engine.

[0002]

2. Description of the Related Art The need for lean combustion of an air-fuel mixture has increased with the recent trend toward fuel saving in internal combustion engines. Therefore, it is necessary to control the combustion state of the air-fuel mixture such as misfire and ignition in the combustion chamber. , Detecting the ions contained in the flame in the combustion gas generated during the combustion of the air-fuel mixture, resulting in misfire in the combustion chamber,
An ion gap for investigating the ignition state is attached to the exhaust system, and the ignition state and other parameters are controlled according to misfire and ignition in the combustion chamber by the ion state detected by the ion gap.

[0003]

However, in the above conventional device, the detection of the ion current by the exhaust ion gap attached to the exhaust system is performed by the flame of the combustion gas exhausted from the combustion chamber of the internal combustion engine. Therefore, in the case of lean combustion, which has been applied to internal combustion engines in recent years, that is, in the case of a high air-fuel ratio air-fuel mixture, the combustion flame of the air-fuel mixture produced by ignition of the spark plug in the combustion chamber disappears before the exhaust valve is opened. Therefore, there is a drawback that the number of ions contained in the flame in the exhaust gas decreases, and detection becomes difficult due to the center electrode forming the exhaust ion gap.

Therefore, the present invention solves the drawbacks of the above-mentioned conventional ones, and by using a mixture having a high air-fuel ratio, the number of ions in the flame in the exhaust gas accompanying the combustion of this mixture is reduced. Nevertheless, it is intended to improve the accuracy of the exhaust ion gap.

[0005]

To this end, in a center electrode held by an insulator fixed to a fitting having a mounting screw portion on the outer periphery, an exposed area of the tip of the center electrode which is not covered by the insulator. Is 20 mm 2 or more.

Further, the tip portion of the center electrode, which is not covered with the insulator fixed by the outer electrode, is covered with one or more coating layers made of solid precious metal or precious metal or precious metal alloy.

[0007]

With the above structure, the exposed area of the tip of the center electrode not covered by the insulator fixed to the mounting member is set to 20 mm 2 or more to obtain a high air-fuel ratio mixture. Even if the number of ions in the flame contained in the combustion gas generated by the combustion of the air-fuel mixture having the high air-fuel ratio decreases, the ion current can be detected by the center electrode.

Further, even if the temperature of the combustion gas rises due to the lean combustion of the air-fuel mixture in the combustion chamber, the tip of the central electrode for detecting the ions contained in the flame in the combustion gas is made of a solid precious metal or a precious metal. Alternatively, by coating with one or more coating layers made of a noble metal alloy, it becomes possible to cope with the oxidizing property at high temperature, and it is possible to reliably detect the ion current.

[0009]

The present invention will be further described with reference to the embodiments shown in the drawings. (1) is an exhaust ion gap that is an embodiment of the present invention, and this exhaust ion gap (1) is a central electrode (for detecting ions contained in a flame generated with combustion of an air-fuel mixture at the tip ( Insulator (3) holding 2) with heat-resistant cement, glass, etc. and insulator (3) holding this center electrode (2) are fixed and held by caulking etc. via packing (9). However, it is composed of a mounting metal fitting (4) having a threaded portion (5) required for mounting on an internal combustion engine on the outer periphery thereof.

Then, in the center electrode (2) held by the insulator (3) fixed to the fitting (4) having the screw portion (5) on the outer periphery, the center electrode not covered by the insulator (3). The exposed area of the tip portion (6) of (2) is set to 20 mm 2 or more.

The reason why the exposed area (S) of the tip portion (6) of the center electrode (2) is set to 20 square millimeters or more is as shown in FIG.
As is clear from the relationship between the exposed area (S) and the ionic current value for A / F 14.0 and A / F 12.0 in m), the larger the S, the better the sensitivity of the ionic current value, This is because at F12.0, if S is not more than 20 square millimeters, the ion current will be small and it will be difficult to determine misfire.

Since the present invention has the above-mentioned structure, it is fixed to the mounting bracket (4) for detecting the ions contained in the flame in the combustion gas generated by the combustion of the air-fuel mixture in the combustion chamber of the internal combustion engine. In the combustion gas of the tip portion (6) of the center electrode (2) which is not covered by the insulator (3) holding the center electrode (2) in the center electrode (2) held by the insulator (3) The number of ions in the flame contained in the combustion gas generated by the combustion of the air-fuel mixture with a high air-fuel ratio due to lean combustion by setting the exposed area for detecting ions contained in Even if the number decreases, the ion current can be reliably detected by the center electrode (2).

Further, as the exposed area of the tip of the center electrode for detecting the ions contained in the flame in the combustion gas increases, the sensitivity of detecting the ions increases. Therefore, as shown in FIG. The top of the tip (6) of (2) may be formed into a disk shape (7) to expand the area where the central electrode (2) for detecting ions can detect ions.

Further, even if the temperature of the combustion gas rises due to the lean combustion of the air-fuel mixture in the combustion chamber of the internal combustion engine, the tip portion (6) of the center electrode (2) for detecting the ions contained in the flame in the combustion gas (6) ) To Ag, Au-Pd, Pd-C
Solid precious metal such as r, or Ag, Pd, Pt, Au-
By coating with one or more coating layers (7) made of a noble metal or a noble metal alloy such as Pd, Pd-Cr, Pt-Ni, etc., it becomes possible to sufficiently cope with oxidation by combustion gas under high temperature. Ions contained in the flame in the combustion gas can be reliably detected at the tip portion (6) of the electrode (2) (FIG. 3).

[0015]

As described above, in the combustion chamber of the internal combustion engine, by expanding the ion detectable area of the center electrode for detecting the ions contained in the flame in the combustion gas generated by the combustion of the air-fuel mixture, The ion detection sensitivity can be improved, and by coating the tip of the center electrode that detects this ion with one or more coating layers made of pure precious metal or precious metal or precious metal alloy, the center at high temperature can be improved. It has an excellent effect that the oxidation resistance of the tip portion of the electrode can be improved to surely detect ions in ignition, misfire, and the like.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an exhaust ion gap that is an embodiment of the present invention.

FIG. 2 is an enlarged perspective view of a main part of the second embodiment.

FIG. 3 is an enlarged cross-sectional view of a main part of a tip end portion of a center electrode in a third embodiment.

FIG. 4 is a graph showing a relationship between an exposed area of a center electrode and an ion current value.

[Explanation of symbols]

1 Exhaust ion gap 2 Center electrode 3 insulator 4 Mounting bracket 5 screw part 6 Tip 7 coating layer 8 top 9 packing

Claims (2)

[Claims] 1. In a center electrode held by an insulator fixed to a fitting having a mounting screw portion on the outer periphery, the exposed area of the tip of the center electrode not covered by the insulator is 20 mm 2 or more. Exhaust ion gap. 2. The exhaust ion gap according to claim 1, wherein the tip of the center electrode which is not covered with an insulator is covered with one or more coating layers made of a solid precious metal or a precious metal or a precious metal alloy.