JP3498252B2 - Spark plug for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug structure for an internal combustion engine, particularly a gas engine using a gaseous fuel such as natural gas, city gas or LPG gas as fuel. About. 2. Description of the Related Art Conventionally, in an internal combustion engine, in particular, a gas engine using a gaseous fuel such as natural gas, city gas or LPG gas as a fuel, continuous operation for a long time due to its use mode. Therefore, it is necessary to increase the interval between maintenance and inspection of the gas engine in order to cope with the use mode that enables continuous operation for a long time. The spark plug used has been required to have sufficient durability. Therefore, in order to ensure sufficient durability and extend the life of the spark plug, a high compression ratio is used due to its properties, and a gaseous fuel such as natural gas, city gas or LPG gas is used as the fuel. Because of this, the discharge voltage as a spark plug is high, so the tip surface of the center electrode is severely consumed due to the high temperature state generated by the combustion in the combustion chamber. Generally, a noble metal tip is used on the tip end surface of the electrode. [0003] However, in the case of the above-mentioned conventional internal combustion engine, particularly in the case of a spark plug of a gas engine using a gaseous fuel such as natural gas, city gas or LPG gas as fuel, the durability is poor. In order to ensure a sufficient discharge voltage and reduce the discharge voltage when performing spark discharge, the distance between the front end surface of the center electrode and the discharge surface of the ground electrode disposed at a position facing the front end surface of the center electrode If the spark gap to be formed is set smaller than that of a gasoline engine, it is possible to certainly reduce the discharge voltage by reducing the spark gap, but the tip surface of the center electrode and the tip surface of this center electrode The spark gap formed between the ground electrode and the discharge surface of the ground electrode disposed at a position facing the Since it is affected by the quenching effect, there is a disadvantage that the ignitability of natural gas, city gas, LPG gas or other gas fuel used as fuel for the gas engine is reduced. [0004] Therefore, fuel generated by setting a small spark gap between the front end surface of the center electrode and the discharge surface of the ground electrode disposed at a position facing the front end surface of the center electrode is set small. The noble metal on the tip surface of the center electrode used to prevent the consumption of the center electrode in order to eliminate the drawback of lowering the ignitability to gaseous fuels such as natural gas, city gas or LPG gas used as fuel It is conceivable to reduce the diameter of the tip to reduce the effect of the quenching action of the electrode and to concentrate spark energy to improve the ignitability of the gaseous fuel used as fuel. By reducing the diameter of the noble metal tip on the tip end surface, the temperature of the noble metal tip becomes extremely high due to spark energy, so it is used to prevent wear of the center electrode. The one which rather promote the consumption of the noble metal tip to be. Further, in the noble metal tip on the tip surface of the center electrode and on the discharge surface of the ground electrode, oxidation of noble metal atoms in the sputtered atoms once diffused in the diffusion of sputtered atoms generated by the spark discharge. Because of the small amount, most of it adheres again to the tip surface of the center electrode and the discharge surface of the ground electrode, and the repetition of this causes the sweating phenomenon that forms sweat particles, particularly the tip surface of the center electrode that becomes negative. It is easy to be generated at the outer peripheral edge of the tip of the platinum-based noble metal tip provided in the above, and by the sweat particles formed by this sweating phenomenon growing, the tip surface of the center electrode performing spark discharge and the center electrode A bridge is formed in the spark gap formed between the tip surface and the discharge surface of the ground electrode located opposite In the event that a bridge is finally formed between the spark gaps, direct electrical conduction between the center electrode and the ground electrode occurs through the bridge, and the leading end surface of the center electrode Spark discharge between the ground electrode and the discharge surface of the ground electrode is no longer performed, which causes a misfire to a gaseous fuel such as natural gas, city gas or LPG gas used as a fuel in a gas engine. is there. SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned drawbacks and the like of the prior art, and is directed to a spark plug of an internal combustion engine, particularly a gas engine using a gas fuel such as natural gas, city gas or LPG gas as fuel. In order to improve the durability, it is intended to prevent a problem such as a misfire of gaseous fuel caused by a sweat phenomenon caused by spark discharge. [0007] For this purpose, a spark gap is provided between a front end surface of a center electrode fixed to an insulator and a ground electrode disposed at a position facing the front end surface of the center electrode. on the formation of, a noble metal tip containing Pt component so as to face each other on the discharge surface of the ground electrode disposed at a position facing the distal end surface of the front end surface and the center electrode of the center electrode forming the spark gap The spar
And a curvature (R) or a width (C) of 0.05 to 0.2 mm on the outer peripheral edge of the noble metal tip of the center electrode. Internal combustion used in gas engines with chamfers
This is an engine spark plug . [0010] The present invention is provided with the above-described structure, and in implementing the present invention, the tip of the center electrode forming the spark gap and the ground electrode disposed at a position facing the tip of the center electrode. After arranging the noble metal tips so as to face each other on the discharge surface, by forming a chamfered portion on at least one of the outer circumferential edges of the noble metal tip of the center electrode, the outer circumferential edge of the noble metal tip of the center electrode is formed. By preventing the concentration of spark discharge energy, and further preventing the concentration of spark discharge, the local temperature rise of the noble metal tip of the center electrode is suppressed, and in particular, the sweating phenomenon at the outer peripheral edge of the noble metal tip is suppressed. Gas, such as natural gas, city gas or LPG gas, in the combustion chamber. Against preventing misfire can also improve durability. In addition, a chamfered portion is formed on the outer peripheral edge of the tip of the noble metal tip provided on the discharge surface at the tip of the center electrode, and a spark gap between the noble metal tip of the ground electrode and the spark gap is 0.3 to 0.1 mm. Even if it is set as small as 5 mm, intensive spark discharge at the tip outer peripheral edge of the noble metal tip is formed by the chamfer formed on the tip outer peripheral edge of the noble metal tip provided on the tip surface of the center electrode and the discharge surface of the ground electrode. Is prevented, and the formation of the bridge between the spark gaps caused by the spark discharge is prevented by preventing the concentration of the spark discharge.Therefore, the setting of the spark gap is reduced, and a low discharge voltage is set. In addition, the spark discharge between the spark gaps becomes possible, and the durability of the spark plug itself can be improved. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; (1) is a spark plug for an internal combustion engine according to an embodiment of the present invention, particularly a gas engine using a gaseous fuel such as natural gas, city gas or LPG gas. An insulator (2) holding a composite center electrode (3) having a copper core covered with a heat-resistant nickel alloy at the tip, and holding the insulator (2),
A ground electrode (5) made of a nickel alloy at a position facing the tip of the center electrode (3) held in the insulator (2)
And a metal shell (4) provided with. In the spark plug (1) for an internal combustion engine, a tip surface (6) of a center electrode (3) fixed to an insulator (2) constituting the spark plug (1) for an internal combustion engine; Since a spark gap (8) is formed between the center electrode (3) and the discharge surface (7) of the ground electrode (5) disposed at a position facing the tip surface (6) of the center electrode (3), Tip surface (6) and ground electrode (5)
For example, platinum (Pt) or platinum (Pt) -iridium (Ir) so as to be opposed to the discharge surface (7).
Noble metal chips (9) and (10), such as alloys and platinum (Pt) -nickel (Ni) alloys, are arranged to form a spark gap (8) and a noble metal tip (9) for the center electrode (3). Curvature (R) at the outer peripheral edge (11) of the tip
Or a chamfered part (12) with a width (C) of 0.05 to 0.2 mm
Is formed. In this embodiment, if the chamfered portion (12) is applied to the noble metal tip (9) on the side of the center electrode (3) where the spark is greatly consumed due to the application of the negative polarity, the sweating phenomenon can be suppressed. Since the spark plug (1) for an internal combustion engine such as a gas engine according to the embodiment of the present invention has the above-described configuration, the tip of the center electrode (3) forming the spark gap (8) is provided. A ground electrode (5) arranged at a position facing the surface (6) and the tip surface (6) of the center electrode (3).
The noble metal tips (9) and (10) are disposed so as to face each other on the discharge surface (7) of the center electrode. ) To form the center electrode (3)
And a noble metal tip (10) of a discharge surface (7) of a ground electrode (5) arranged at a position facing the tip surface (6) of the center electrode (3). ), It is possible to prevent the energy of the spark discharge from being concentrated at the outer peripheral edge (11) at the front end on the side of the center electrode (3), and further to prevent the concentration of the spark discharge. By doing so, the temperature rise due to local concentration of spark discharge can be suppressed, so that the noble metal tip (9) on the tip surface (6) of the center electrode (3) for performing spark discharge
The sweating phenomenon at the outer peripheral edge (11) of the tip can be suppressed, and the sweating phenomenon caused by the spark discharge on the side of the center electrode (3), that is, when the atom is scattered due to the diffusion of the sputtering atom in the spark consumption, the oxidation A small amount of noble metal atoms are re-attached to the surface of the center electrode (3), and are generated between the spark gaps (8) due to the sweat particles formed by the phenomenon of melting and sticking to sweat particles by the heat of the next discharge. Bridge formation is hindered, and it is possible to prevent a misfire of natural gas, city gas or LPG gas or the like in a combustion chamber of a gas engine, and to improve durability of the spark plug (1). it can. As shown in FIG. 3, the outer circumference of the tip (11) of the noble metal tip (9) provided on the tip face (6) of the center electrode (3) fixed to the insulator (2). By forming a chamfer (12) of 2 mm or less,
The chamfered portion (12) of the outer peripheral edge (11) of the noble metal tip (9) suppresses an increase in the discharge voltage and generates a spark discharge that is likely to be generated intensively at the outer peripheral edge (11) of the noble metal tip (9). In addition to preventing the formation of a bridge caused by the sweating phenomenon, it is possible to prevent the sweating phenomenon by suppressing the local temperature rise in the noble metal tip (9) of the center electrode (3). it can.
Further, when the durability of the spark plug (1) provided with the chamfered portion (12) was confirmed, as shown in FIG. 4, a bridge was formed when the size of the chamfered portion (12) was in the range of 0.05 to 0.2 mm. Therefore, sufficient durability can be obtained. And when it is larger than 0.2 mm, the discharge voltage becomes higher, and also in the durability performance, the electrode consumption is large,
This increases the spark gap and easily causes a misfire. Therefore, in a spark plug (1) for an internal combustion engine used in a gas engine according to an embodiment of the present invention, a noble metal tip (9) is made of a platinum-20% iridium alloy having a diameter of 1.0 mm, The relationship between the value of the chamfer dimension (C) and the discharge voltage under the conditions of a spark gap of 0.3 mm and a pressure of 8 kg / cm · cm (see FIG. 3), 1000 rpm × 100% load, methane gas as fuel, spark gap Under the condition of 0.3 mm, noble metal tip (9) has a diameter of 1.0 mm platinum-20%
When the relationship between the chamfer dimension (C) and the operation time until the occurrence of a defect (see FIG. 4) was used in an iridium alloy and mounted on an actual machine and tested, the effect was sufficiently confirmed. As described above, the chamfered portion having a curvature (R) or a width (C) of 0.05 to 0.2 mm is formed on the outer peripheral edge of the noble metal tip provided on the discharge surface at the distal end surface of the center electrode. By preventing the concentration of spark discharges on the center electrode side by suppressing the formation of a bridge, it is possible to prevent the formation of bridges between the spark gaps causing a misfire, Since the wear of the noble metal tip due to a rise in temperature can be suppressed, the spark plug is set to a value smaller than a general value, that is, 0.3 to 0.5 mm, thereby significantly improving the durability including the wear resistance of the spark plug. It has an excellent effect that enables the following.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional view of a spark plug for an internal combustion engine according to an embodiment of the present invention. FIG. 2 is an enlarged sectional view of a main part of a spark plug for an internal combustion engine according to an embodiment of the present invention. FIG. 3 is a diagram showing a change in a discharge voltage with respect to a chamfer dimension of a chamfered portion at an outer peripheral edge of a noble metal tip. FIG. 4 is a diagram showing a relationship between a chamfered dimension of a chamfered portion at a tip outer peripheral edge of a noble metal tip and an operation time until occurrence of a defect. DESCRIPTION OF SYMBOLS 1 Spark plug for internal combustion engine 2 Insulator 3 Center electrode 4 Metal shell 5 Ground electrode 6 Tip surface (of ground electrode) 7 Discharge surface 8 (of ground electrode) 8 Spark gap 9 Precious metal tip 10 of center electrode 10 Ground Noble metal tip 11 of electrode Electrode 12

Claims (1)

(57) [Claim 1] A spark gap is formed between a tip surface of a center electrode fixed to an insulator and a ground electrode disposed at a position facing the tip surface of the center electrode. After being formed, platinum (Pt) is formed so as to face the discharge surface of the ground electrode disposed at a position facing the front surface of the center electrode and the front surface of the center electrode forming the spark gap.
Or a platinum (Pt) -iridium (Ir) alloy,
The spark gap is 0.3 to 0.5 with a noble metal tip made of any one of a titanium (Pt) -nickel (Ni) alloy.
as well as arranged to mm formed on the tip outer peripheral edge of the noble metal tip of the center electrode, the curvature (R) or the width (C) is obtained by forming a chamfered portion is 0.05~0.2mm moth
Spark plug for internal combustion engine used for spark engine .