JP6379748B2 - Spark plug for internal combustion engine - Google Patents

Description

  The present invention relates to a spark plug for an internal combustion engine in which a spark discharge gap is formed between a center electrode and a ground electrode.

  In an internal combustion engine such as an engine, a spark plug for discharging a spark voltage generated by an ignition coil and igniting an air-fuel mixture is often used. The spark plug is formed by inserting a cylindrical insulator on the inner peripheral side of a cylindrical housing and inserting a center electrode on the inner peripheral side of the insulator. The spark plug is configured to generate a spark due to discharge in a spark discharge gap formed between a ground electrode and a center electrode provided at a front end portion of the housing.

  For example, Patent Document 1 discloses a spark plug including a center electrode, an insulator holding the center electrode, a metal shell holding the insulator, and an annular packing interposed between the insulator and the metal shell. Yes. The packing is disposed between the insulator leading end surface of the insulator and the metal rear end facing surface of the metal shell. Then, it is disclosed that the positional relationship between the reduced-diameter portion of the metal shell and the packing is defined and the antifouling property of the spark plug is improved by utilizing the cleaning effect by corona discharge.

JP 2009-176525 A

In recent years, the engine has aimed to reduce fuel consumption and efficiency, and is in an environment where the air-fuel mixture in the engine is difficult to burn, and the combustion temperature in the engine is also decreasing. When the combustion temperature is lowered, carbon is likely to be generated particularly at the time of combustion such as at low temperature start, and this carbon is likely to adhere to the insulator. In the spark plug of Patent Document 1, only the positional relationship between the reduced diameter portion of the metal shell and the packing is defined, and the structure of the metal shell is not devised. Moreover, in patent document 1, it aims at obtaining the carbon cleaning effect by suppressing generation | occurrence | production of the leakage (leak) electric current when an insulator is soiled by adhesion of carbon, and generating corona discharge.
However, the magnitude of the corona current that flows during corona discharge is smaller than the magnitude of the leakage current. Therefore, in the spark plug of Patent Document 1, it is not possible to obtain a sufficient effect of burning off carbon adhering to the insulator.

  The present invention has been made in view of such a background, and generates leakage current between the housing shelf and the outer peripheral surface of the insulator, thereby effectively burning out carbon adhering to the outer peripheral surface of the insulator. It was obtained in an attempt to provide a spark plug that can be made to operate.

One embodiment of the present invention includes a cylindrical housing provided with a ground electrode, a cylindrical insulator inserted into the inner peripheral side of the housing, and a center electrode inserted into the inner peripheral side of the insulator In a spark plug in which a spark discharge gap is formed at a tip side position where the tip of the center electrode and the tip of the ground electrode face each other,
The housing has a shelf formed by reducing the diameter of a part of the inner peripheral surface in the central axis direction,
The insulator is formed at a distal end side insulator portion formed at a position close to the distal end side position and at a rear end side of the distal end side insulator portion and having a diameter larger than that of the distal end side insulator portion. A rear end side insulator portion, and a step surface formed between the rear end side insulator portion and the front end side insulator portion,
An annular packing is sandwiched between the rear end side end surface of the shelf and the step surface,
In the spark plug for an internal combustion engine, the inner circumferential surface of the shelf portion is repeatedly formed with irregularities that change the gap with the outer circumferential surface of the tip side insulator portion at a plurality of locations in the circumferential direction. is there.

In the spark plug, irregularities are repeatedly formed at a plurality of locations in the circumferential direction on the inner peripheral surface of the housing shelf. And by forming this unevenness, a leakage current is intentionally generated to burn out carbon adhering to the insulator.
Since the unevenness is formed on the shelf portion of the housing, the gap between the inner peripheral surface of the shelf portion and the outer peripheral surface of the distal end side insulator portion of the insulator is repeatedly changed at a plurality of locations in the circumferential direction. When combustion of the internal combustion engine is performed, carbon adheres to the outer peripheral surface of the tip side insulator portion. At this time, if the gap between the convex portion in the concavo-convex portion and the carbon adhering to the outer peripheral surface of the tip side insulator portion is equal to or less than a predetermined gap, dielectric breakdown occurs due to electric field concentration in the convex portion, and a leakage current flows in this gap. This leakage current is several tens to several hundreds times as large as the corona current.

Thereby, the tip of the convex portion becomes a starting point of discharge, and a leakage current selectively flows in any convex portion in the circumferential direction of the housing. And the carbon in the outer peripheral surface of an insulator facing a convex part can be effectively burned down by a leakage current.
Therefore, according to the spark plug, it is possible to generate a leakage current between the housing shelf and the outer peripheral surface of the insulator, and to effectively burn off carbon adhering to the outer peripheral surface of the insulator. .

Sectional drawing which shows the front end side part of the spark plug concerning an Example. It is a figure which shows the spark plug of the state concerning the Example seen from the center axis line direction, and is the II sectional view taken on the line of FIG. Sectional drawing which expands and shows the periphery of the shelf part of a housing concerning an Example. Sectional drawing which expands and shows the periphery of the shelf part of the housing of the state concerning the Example seen from the center axis direction. Sectional drawing which expands and shows the periphery of the shelf part of the other housing concerning an Example. Sectional drawing which expands and shows the periphery of the shelf part of the other housing concerning an Example. Sectional drawing which expands and shows the periphery of the shelf part of the other housing of the state concerning the Example seen from the center axis line direction. Sectional drawing which expands and shows the periphery of the shelf part of the other housing of the state concerning the Example seen from the center axis line direction. Sectional drawing which expands and shows the periphery of the shelf part of the other housing of the state concerning the Example seen from the center axis line direction. The graph which shows the relationship between the angular interval of the circumferential direction between adjacent convex parts concerning an Example, and the cycle number when an insulation resistance value becomes less than 10 Mohm. The graph which shows the relationship between the angular interval of the circumferential direction between adjacent convex parts concerning an Example, and electric field strength. The graph which shows the relationship between the clearance gap between the front-end | tip of the convex part in the unevenness | corrugation of a shelf part, and the outer peripheral surface of the front end side insulator part of an insulator, and the cycle number when an insulation resistance value becomes less than 10 Mohm concerning an Example. The graph which shows the relationship between the curvature radius of the corner | angular part of the inner peripheral side tip of the convex part in the unevenness | corrugation of a shelf part, and the cycle number when an insulation resistance value becomes less than 10 MΩ concerning an Example.

Embodiments of a spark plug for an internal combustion engine will be described below with reference to the drawings.
(Example)
As shown in FIGS. 1 and 2, the spark plug 1 of this example includes a cylindrical housing 2 provided with a ground electrode 21, a cylindrical insulator 3 inserted on the inner peripheral side of the housing 2, and And a center electrode 4 inserted on the inner peripheral side of the insulator 3. Further, a spark discharge gap S is formed at the tip side position where the tip of the center electrode 4 and the tip of the ground electrode 21 face each other.

  As shown in FIG. 3, the housing 2 has a shelf portion 22 formed by reducing the diameter of a part of the inner peripheral surface 201 in the central axis direction O. The insulator 3 is formed adjacent to the front end side insulator part 31 formed at a position close to the front end side position and the rear end side of the front end side insulator part 31 and having a diameter larger than that of the front end side insulator part 31. It has a rear end side insulator portion 32 and a step surface 33 formed between the rear end side insulator portion 32 and the front end side insulator portion 31. An annular packing 5 is sandwiched between the rear end side end surface 221 of the shelf 22 and the step surface 33. As shown in FIG. 4, irregularities 23 in which the gap U with the outer peripheral surface 301 of the insulator 3 changes are repeatedly formed at a plurality of locations in the circumferential direction C on the inner peripheral surface 201 of the shelf portion 22.

Hereinafter, the spark plug 1 of this example will be described in detail with reference to FIGS.
As shown in FIG. 1, the spark plug 1 is used in an engine as an internal combustion engine by being connected to an ignition coil that generates a high voltage for spark. The rear end of the center electrode 4 of the spark plug 1 is connected to the high voltage terminal of the ignition coil, and the housing 2 of the spark plug 1 is connected to the cylinder head of the engine.
On the outer periphery of the front end side portion of the housing 2, a male screw portion 24 that is screwed into a screw hole provided at an end portion of the plug hole of the cylinder head is formed. The ground electrode 21 is formed so as to protrude from the front end portion of the housing 2 and bend so as to face the front end of the center electrode 4 from the front end side.

As shown in FIGS. 1 and 3, the shelf 22 of the housing 2 is formed so as to protrude from the inner peripheral surface 201 of the housing 2 so as to receive the stepped surface 33 of the insulator 3 from below. The shelf 22 is formed on the entire circumference of the inner circumferential surface 201 of the housing 2, and the step surface 33 is formed on the entire circumference of the outer circumferential surface 301 of the insulator 3. The rear end side end surface 221 of the shelf 22 and the step surface 33 of the insulator 3 are formed as inclined surfaces that increase in diameter toward the rear end side.
The outer peripheral surface 301 of the front end side insulator portion 31 of the insulator 3 is formed in a tapered shape whose diameter decreases toward the front end side. The inner peripheral surface 201 of the front end side portion of the housing 2 is formed in parallel to the central axis direction O. The gap between the inner peripheral surface 201 of the front end side portion of the housing 2 and the outer peripheral surface 301 of the front end side insulator portion 31 of the insulator 3 changes so as to become narrower toward the rear end side. The tip portion 41 of the center electrode 4 protrudes from the tip of the tip side insulator portion 31 of the insulator 3.

As shown in FIG. 3, the unevenness 23 in the shelf 22 of the housing 2 is provided over the entire length of the shelf 22 along the central axis direction O of the shelf 22. The depth in the radial direction of the unevenness 23 in this example is constant over the entire length in the central axis direction O of the shelf 22.
In addition, the unevenness | corrugation 23 in the shelf part 22 may be provided from the edge part of the shelf part 22 to the intermediate position along the center axis direction O of the shelf part 22, as shown in FIG. In this case, the unevenness 23 can be formed by a groove provided on the inner peripheral surface 201 of the shelf 22. As shown in FIG. 6, the depth in the radial direction of the unevenness 23 (recessed portion 232) in the shelf portion 22 may change in an inclined manner with respect to the central axis direction O of the shelf portion 22.

  As shown in FIG. 4, the convex part 231 in the unevenness 23 of the shelf part 22 has a triangular shape when viewed from the central axis direction O. And a pair of side surface 234 which forms triangular shape in the convex part 231 is formed in linear form. Moreover, as shown in FIG. 7, the pair of side surfaces 234 in the convex portion 231 may be formed in a curved shape. In these cases, the gap U between the convex portion 231 of the concave and convex portion 23 of the shelf portion 22 and the outer peripheral surface 301 of the tip side insulator portion 31 of the insulator 3 is most at the inner peripheral apex of the triangular convex portion 231. Get smaller.

  Moreover, as shown in FIG. 8, the convex part 231 in the unevenness | corrugation 23 of the shelf part 22 may have a quadrilateral shape when viewed from the central axis direction O. In this case, the pair of side surfaces 235 forming the quadrangular shape in the convex portion 231 may be formed in a straight line shape or a curved shape. In this case, the gap U between the convex portion 231 of the concave and convex portion 23 of the shelf portion 22 and the outer peripheral surface 301 of the distal end side insulator portion 31 of the insulator 3 is an angle on both sides in the circumferential direction C of the quadrangular convex portion 231. It becomes the smallest at the part 233 or the inner peripheral side surface 236.

As shown in FIG. 4, the convex portions 231 in the unevenness 23 of the shelf portion 22 are repeatedly formed at an equal interval in the circumferential direction C at an angular interval θ of 5 to 30 °. This angular interval θ is determined by the number of projections 231 formed in the circumferential direction C of the shelf 22. The triangular convex portion 231 can be formed in an obtuse or acute angle shape according to the protruding height of the convex portion 231 (depth of the concave portion 232) and the number of convex portions 231 formed.
Further, as shown in FIG. 4, the unevenness 23 in the shelf portion 22 can be formed in a shape in which the convex portion 231 and the concave portion 232 are continuously adjacent to each other in the circumferential direction C. As shown in FIG. 231 may be formed in a shape partially protruding from the circumferential inner peripheral surface 201.

As shown in FIGS. 3 and 4, the gap U between the tip of the convex portion 231 and the outer peripheral surface 301 of the tip side insulator portion 31 of the insulator 3 in the unevenness 23 of the shelf portion 22 is 0.05 to 0.4 mm. Is in range. Moreover, the corner | angular part 233 of the inner peripheral side tip of the convex part 231 in the unevenness | corrugation 23 of the shelf part 22 is formed in the curved-surface shape whose curvature radius R is 0.3 mm or less. In addition, this corner | angular part 233 may be formed in the chamfering shape whose chamfering width is 0.3 mm or less.
The annular packing 5 is made of a metal material and is formed by punching from a steel plate. The packing 5 can be made of various materials that serve as a buffer member between the housing 2 and the insulator 3.

  In this example, in the smoldering fouling test of JIS D1606, the insulation resistance value between the housing 2 and the insulator 3 is measured at the end of each cycle according to the test conditions, and the number of cycles when the insulation resistance value is less than 10 MΩ. N was measured. Specifically, the measurement was performed on the housing 2 in which the uneven portion 23 of the shelf portion 22 was formed by the triangular convex portion 231 using a 4-cylinder 1.8 L engine. Further, the number N of cycles was measured by changing the dimensions of the convex portion 231 of the concave and convex portion 23 of the shelf portion 22 such as the angular interval θ, the gap U, and the curvature radius R. 10 to 13 show the results of measurement.

In FIG. 10, the horizontal axis indicates the angular interval θ in the circumferential direction C between adjacent convex portions 231 and the vertical axis indicates the number of cycles N when the insulation resistance value is less than 10 MΩ, Show the relationship. As shown in the figure, it was found that when the angular interval θ exceeds 30 °, the cycle number N decreases to 10 times, and when it is 30 ° or less, the cycle number N is large. It was also found that the cycle number N was increased when the angular interval θ was 22.5 ° or less. If the angle interval θ is too small, as shown in FIG. 11, electric field interference occurs between adjacent convex portions 231 and the electric field strength decreases.
From the above results, it is preferable that the convex portions 231 in the concave and convex portions 23 of the shelf portion 22 are repeatedly formed at equal intervals in the circumferential direction C at an angular interval θ of 5 to 30 °, and an angular interval of 5 to 22.5 ° It has been found that it is more preferable to repeat the formation with θ.

In FIG. 12, the horizontal axis indicates the gap U between the tip of the convex portion 231 and the outer peripheral surface 301 of the tip side insulator portion 31 of the insulator 3 on the unevenness 23 of the shelf 22, and the vertical axis indicates an insulation resistance value of 10 MΩ. The relationship between the two is shown by taking the number of cycles N when the number is less than 1. As shown in the figure, when the gap U exceeds 0.4 mm, the cycle number N decreases to 10 times, and when the gap U is 0.4 mm or less, the cycle number N is large. Further, it was found that when the gap U was 0.3 mm or less, the cycle number N was increased. Further, the smaller the gap U is, the larger the electric field strength is, but it is preferable that the gap U is 0.05 mm or more in order to avoid interference between the tip of the convex portion 231 and the outer peripheral surface 301 of the tip side insulator portion 31. .
From the above results, the gap U between the tip of the convex part 231 and the outer peripheral surface 301 of the tip side insulator part 31 in the unevenness 23 of the shelf part 22 is preferably 0.05 to 0.4 mm, 0.05 to It turned out that it is more preferable to set it as 0.3 mm.

In FIG. 13, the horizontal axis represents the curvature radius R of the corner 233 at the inner peripheral side tip of the convex portion 231 in the unevenness 23 of the shelf portion 22, and the vertical axis represents the number of cycles when the insulation resistance value is less than 10 MΩ. N is taken to indicate the relationship between the two. As shown in the figure, when the radius of curvature R exceeds 0.3 mm, the cycle number N decreases to 10 times, and when the radius of curvature is 0.3 mm or less, the cycle number N is large. Moreover, it turned out that the cycle number N increases when the curvature radius R becomes 0.2 mm or less. The smaller the radius of curvature R is, the smaller the electric field strength is. However, it is considered difficult to make it less than 0.05 mm for manufacturing reasons.
From the above results, it is preferable that the curvature radius R of the corner portion 233 at the tip on the inner peripheral side of the convex portion 231 is 0.05 to 0.3 mm, and more preferably 0.05 to 0.2 mm. I understood.

Next, the effect of the spark plug 1 of this example is demonstrated.
In the spark plug 1 of this example, the unevenness 23 is repeatedly formed at a plurality of locations in the circumferential direction C on the inner peripheral surface 201 of the shelf portion 22 of the housing 2. And by forming this unevenness | corrugation 23, the leakage current is intentionally generated and the carbon X adhering to the insulator 3 is burned out.
Since the unevenness 23 is formed on the shelf 22 of the housing 2, the gap U between the inner peripheral surface 201 of the shelf 22 and the outer peripheral surface 301 of the distal end side insulator 31 of the insulator 3 is plural in the circumferential direction C. It has changed repeatedly in places. When the internal combustion engine is combusted, the carbon X adheres to the outer peripheral surface 301 of the tip side insulator portion 31 (see FIGS. 2 and 3). At this time, if the gap between the tip of the convex portion 231 in the concave and convex portion 23 and the carbon X attached to the outer peripheral surface 301 of the tip side insulator portion 31 is equal to or less than a predetermined gap, dielectric breakdown occurs due to electric field concentration in the convex portion 231. Leakage current flows in this gap. This leakage current is several tens to several hundreds times as large as the corona current.

Thereby, the corner portion 233 of the convex portion 231 becomes a starting point of discharge, and a leakage current selectively flows in any convex portion 231 in the circumferential direction C of the housing 2. And the carbon X in the outer peripheral surface 301 of the insulator 3 which opposes the convex part 231 can be burned off effectively by a leakage current.
As shown in FIG. 4, when the convex portion 231 in the concave and convex portion 23 of the shelf portion 22 has a triangular shape, a leakage current is generated at the inner peripheral side vertex of the convex portion 231, and the convex portion 231 The carbon X can be burned off starting from the portion facing the inner peripheral apex.
In addition, as shown in FIG. 8, when the convex portion 231 in the concave and convex portion 23 of the shelf portion 22 has a quadrangular shape, leakage current is generated in the corner portions 233 on both sides in the circumferential direction C of the convex portion 231. The carbon X can be burned off starting from the portions facing the corners 233 on both sides of the convex portion 231 in the circumferential direction C.

  Therefore, according to the spark plug 1 of this example, the carbon adhering to the outer peripheral surface 301 of the insulator 3 by generating a leakage current between the shelf 22 of the housing 2 and the outer peripheral surface 301 of the insulator 3. X can be burned off effectively.

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Housing 201 Inner peripheral surface 21 Ground electrode 22 Shelf part 221 Rear end side end surface 23 Concavity and convexity 3 Insulator 301 Outer peripheral surface 31 Front end side insulator part 32 Rear end side insulator part 33 Step surface 4 Center electrode 5 Packing

Claims (6)

A cylindrical housing (2) provided with a ground electrode (21), a cylindrical insulator (3) inserted through the inner periphery of the housing (2), and an inner periphery of the insulator (3) A spark having a spark discharge gap (S) formed at a tip side position where the tip of the center electrode (4) and the tip of the ground electrode (21) face each other. In plug (1)
The housing (2) has a shelf (22) formed by reducing the diameter of a portion of the inner peripheral surface (201) in the central axis direction (O).
The insulator (3) is positioned on the distal end side of the distal end side insulator portion (31) formed at a position close to the distal end side position, and on the rear end side of the distal end side insulator portion (31). (31) a rear end side insulator part (32) formed with a larger diameter, and a stepped surface formed between the rear end side insulator part (32) and the front end side insulator part (31) ( 33)
An annular packing (5) is sandwiched between the rear end side surface (221) of the shelf (22) and the step surface (33),
On the inner peripheral surface (201) of the shelf (22), there are uneven portions (23) in which the gap with the outer peripheral surface (301) of the distal end side lever portion (31) changes in a plurality of locations in the circumferential direction (C). A spark plug (1) for an internal combustion engine, wherein the spark plug (1) is formed repeatedly. The unevenness (23) extends along the central axis direction (O) of the shelf (22), over the entire length of the shelf (22), or at the end of the shelf (22) on the tip side. The spark plug (1) for an internal combustion engine according to claim 1, wherein the spark plug (1) is provided from an intermediate position to an intermediate position.   The internal combustion engine according to claim 1 or 2, wherein the convex portion (231) in the concave and convex portion (23) has a triangular shape or a quadrangular shape as viewed from the central axis direction (O). Spark plug for engine (1).   The convex portions (231) in the concave and convex portions (23) are repeatedly formed at equal intervals in the circumferential direction (C) at an angular interval (θ) of 5 to 30 °. The spark plug (1) for internal combustion engines as described in any one of these.   The gap (U) between the tip of the convex portion (231) and the outer peripheral surface (301) of the insulator (3) in the unevenness (23) is in the range of 0.05 to 0.4 mm. A spark plug (1) for an internal combustion engine according to any one of claims 1 to 4.   The corner (233) at the tip on the inner peripheral side of the convex portion (231) in the concave and convex portion (23) is formed in a curved surface shape or a chamfered shape with a radius of curvature (R) or a chamfer width of 0.3 mm or less. 6. A spark plug (1) for an internal combustion engine according to any one of the preceding claims.

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