JP2002083661A - Attachment structure of spark plug, and spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an attachment structure of a spark plug and the spark plug, which is easy to be attached to a plug hole being formed into a cylinder head, property withdraws heat, and has good heat-resistance. SOLUTION: A tip section 12 of a main body metal fitting of the spark plug has almost a cylindrical form in its perimeter face, without having a male screw for attaching the plug, to insert by screwing to the cylinder head SH. Furthermore, it has a tip-corresponding section 36, which corresponds to the tip section 12 of the main body metal fitting in a plug hole P formed in the cylinder head SH. And when an external diameter of the tip section 12 of the main body metal fitting 1 is set to ϕd (units: mm), and an external diameter of the tip corresponding section 36 of the plug hole P is set to ϕD (units: mm), a clearance amount (ϕD-ϕd) satisfies the relation (ϕD-ϕd)<=0.15, in the attachment structure of the spark plug and the cylinder head SH (plug hole P).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug which does not need to be screwed into a plug hole when assembling the spark plug into a plug hole formed in a cylinder head, and a mounting structure thereof.

[0002]

2. Description of the Related Art A spark plug 10 used as an ignition source for an air-fuel mixture in an internal combustion engine includes, for example, a shaft-shaped center electrode 3, an insulator 2 surrounding the center electrode, and a And a metal shell 1 for holding the insulator 2. The metal shell 1 has a flange portion 11 in which a plug seating surface 13 is formed on the front end side (the side where the spark discharge gap g is formed), and a front end portion 12 extending from the plug seating surface 13 to the front end in the direction of the axis O. . A ground electrode 4 forming a spark discharge gap g corresponding to the center electrode 3 is coupled to the distal end surface of the distal end portion 12, and a coupling portion (ground electrode coupling portion) is formed.
17 are formed. Further, a male screw 12a is formed on the outer periphery of the distal end portion 12. Flange 1
A crimping portion 16, a hexagonal portion 15, and a crimping groove portion 14 are formed on the rear end side of the front end portion 1.
2a is formed.

[0003] Looking at the insulator 2 in detail, a head 2b having a corrugation 2c formed thereon, a diamond portion 2e having the largest diameter, and a middle trunk portion 2g having a diameter smaller than the diamond portion 2e.
And the leg length portion 2i located at the most distal end. In general, the locking surface 2h, which is a connecting portion between the leg long portion 2i and the middle trunk portion 2g, is provided with a metal fitting side engaging portion 18 (specifically, an insulating material) that protrudes inward from the inner peripheral surface of the metal shell 1. (The surface to be stopped) via a packing 51. The locking surface 2h of the insulator 2 is connected to the fitting side engaging portion 18 and the packing 5
1 to keep the airtightness between the insulator 2 and the metal shell 1, as well as the center electrode 3 and the leg 2 i of the insulator 2.
Through the insulator 2, the packing 51, the metal fitting side engaging portion 18, and the distal end portion 12 (male screw 12a), and becomes a part of a main path to be dissipated to the cylinder head described below.

Then, such a spark plug 10
Are mounted on a cylinder head of an internal combustion engine and used. When attaching the spark plug 10 to the cylinder head, insert the spark plug 10 into a plug hole formed in the cylinder head, apply a plug wrench to the hexagonal portion 15 of the metal shell 1 and form the plug hole with a predetermined torque. The male screw 12a formed on the distal end portion 12 of the metal shell 1 is screwed into the female screw thus set, thereby performing attachment.

[0005]

Here, when the spark plug 10 is accurately rotated around the central axis of the plug hole in which the female screw is formed, the two are fastened without any problem. . However, when the spark plug 10 is tilted from the center axis of the plug hole, the spark plug 10
Is rotated, the male screw 12a and the female screw do not mesh properly, so that a so-called galling state occurs. As a result, the male screw 12a or the female screw is damaged, and in extreme cases, the combustion gas blows out from the combustion chamber, and the temperature of the distal end portion 12 and the center electrode 3 of the metal shell 1 becomes high, resulting in a preignition (overheating). (Premature ignition) or melting of the electrodes.

Therefore, the spark plug 10 (tip portion 12) is loosely fitted in the plug hole without forming the male screw 12a in the tip portion 12 of the metal shell 1 and without forming the female screw in the plug hole. It is conceivable that the spark plug 10 can be inserted into the cylinder head and the spark plug 10 is separately fixed to the cylinder head by a plug fixing tool or the like. However, conventionally, the heat flowing into the metal shell 1 from the insulator 2, the center electrode 3, and the ground electrode 4 can be dissipated to the cylinder head from the male screw 12a at the tip 12 thereof through the female screw. However, the tip 1
2 does not have the male screw 12a, a gap (clearance) is generated between the distal end portion 12 and the inner wall surface of the plug hole, which tends to make it difficult to transfer heat. For this reason, the temperature of the center electrode 3 is likely to rise, which may cause pre-ignition or cause melting of the electrode.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and is a spark plug which can be easily attached to a plug hole formed in a cylinder head, has good heat drawing, and has good heat resistance. It is an object of the present invention to provide a mounting structure for connecting a plug hole to a plug hole.

[0008]

Means for Solving the Problems and Effects of the Invention A spark plug mounting structure according to the present invention for solving the above-mentioned problems has a center electrode extending in the axial direction and a center electrode disposed on a tip end of the center electrode. An insulator surrounding the radial periphery, the insulator surrounding the radial periphery of the insulator and holding the insulator, and a flange portion having a plug seat surface at the distal end and an axial distal end from the plug seat surface of the flange portion. An attachment structure for a spark plug including a metal shell having an extending tip and a plug hole formed in a cylinder head, wherein the tip of the metal shell has an outer peripheral surface substantially without a male screw for plug attachment. On the other hand, while being formed in a cylindrical shape, the plug hole has a flange corresponding portion and a front end corresponding portion corresponding to the flange portion and the front end portion of the metal shell, respectively. The outer diameter of the tip portion .phi.d (Unit: m
m), the diameter of the hole corresponding to the tip of the plug hole is φD (unit:
mm), a relationship of φD−φd ≦ 0.15 is satisfied.

Further, the spark plug of the present invention has a center electrode extending in the axial direction, an insulator surrounding the radial periphery by disposing the center electrode on the front end side of the spark plug, surrounding the radial periphery of the insulator, A spark plug attached to a plug hole formed in a cylinder head, comprising: a metal shell having a flange portion having a plug seat surface on the tip side and a tip portion extending from the plug seat surface of the flange portion to the tip end in the axial direction. The distal end of the metal shell is formed in a substantially cylindrical outer peripheral surface without having a male screw for plug attachment, while the plug hole has a flange corresponding to the flange portion and the distal end of the metal shell. Part and a tip corresponding part, and the outer diameter of the tip part of the metal shell is φ
d (unit: mm), when the hole diameter of the corresponding portion of the front end of the plug hole is φD (unit: mm), φD−φd ≦ 0.1
5 is satisfied.

According to the structure of the present invention, the distal end portion of the metal shell constituting the spark plug is formed in a substantially cylindrical shape without having a male screw for plug attachment on the outer periphery.
The plug hole has a flange corresponding portion and a distal end corresponding portion having shapes corresponding to the outer peripheral shapes of the flange portion and the distal end portion of the metal shell, respectively. Thus, when mounting the spark plug, it is only necessary to loosely insert the spark plug into the plug hole, and screwing work using a plug wrench or the like becomes unnecessary. In particular, a recent DOHC engine or the like often has a large-sized intake / exhaust valve, and a plug hole is often designed deeply. In such a plug hole of the engine, however, a spark plug is inserted only loosely. Can be mounted. Therefore, the mounting of the spark plug itself is facilitated, and there is no fear of damage to the screw portion caused by the rotation, although the male screw of the metal shell does not mesh with the female screw of the plug hole.

By the way, since the distal end of the metal shell is formed in a substantially cylindrical outer peripheral surface, the heat which could be released from the male screw formed at the distal end to the cylinder head (the inner wall surface of the plug hole) in the related art is dissipated. It is hard to be done. That is, when the outer diameter of the tip of the metal shell is φd (unit: mm) and the hole diameter of the corresponding portion of the plug hole at the tip is φD (unit: mm), the clearance amount (φD−φd) is extremely small. Although the heat flowing into the metal shell can be dissipated to the inner wall surface of the plug hole, the heat dissipation path becomes insufficient when the clearance (φD−φd) is relatively large. .

That is, depending on the magnitude of the clearance amount (φD−φd), a relatively large air layer (by air) is formed in the gap between the distal end of the metal shell and the inner wall surface of the plug hole (corresponding to the distal end of the plug hole). Formed layer) is interposed. This air layer functions as a heat insulating layer when exposed to a high temperature due to combustion gas or the like, thereby preventing heat flowing into the distal end portion or the like of the metal shell from being dissipated to the plug hole inner wall surface. It is. Therefore, the temperature of the insulator, the center electrode, and the ground electrode tends to be high, and preignition and erosion of the electrode are likely to occur.

On the other hand, in the spark plug of the present invention, the clearance amount (φD−φd) is
It should be noted that the setting is made so as to satisfy the relationship of ≦ 0.15 mm. This clearance amount (φD−φ
When d) is a mounting structure that satisfies the above range, the heat flowing into the metal shell from the insulator, the center electrode, and the ground electrode can be quickly dissipated to the cylinder head through the tip of the metal shell. Become like As a result, the temperatures of the center electrode, insulator, and ground electrode are kept low, and the same or higher heat resistance as that obtained by forming a male screw at the tip is obtained, and pre-ignition and electrode erosion are prevented. A spark plug and a mounting structure for the spark plug can be provided. The clearance amount (φD−φ
The range of d) is 0.05 mm ≦ φD−φd ≦ in consideration of the ease of insertion of the spark plug into the cylinder head.
0.15 mm is preferable, and in consideration of the point of obtaining the above-described ease of insertion and good heat resistance, 0.05 mm ≦ φD−φd ≦
More preferably, the relationship of 0.10 mm is satisfied.

When the clearance amount (φD−φd) is 0.
When the spark plug is 15 mm or less, the reason why the heat resistance of the spark plug is favorably obtained is that the intervening amount of the air layer itself is extremely small, and the influence of the heat insulating effect of the air layer is small, and the influence of the air layer is small. Heat from the tip can be effectively dissipated to the inner wall surface of the plug hole. Another reason is that since the metallic shell is made of a metal material, the clearance amount (φD−φd) is set to 0.1 mm.
If it is 15 mm or less, it is presumed that the metal shell (tip) is exposed to high temperature by combustion gas or the like and the tip undergoes thermal expansion, so that the tip effectively contacts the inner wall surface of the plug hole. You. As a result, it is considered that a heat dissipation path from the tip of the metal shell to the inner wall surface of the plug hole is effectively secured.

By the way, the heat flowing into the center electrode and the insulator is dissipated as a metal passage-side engaging portion (inwardly protruding from the inner peripheral surface of the metal shell to lock the insulator. In detail, it passes through the surface of the fitting side engaging portion that locks the insulator. This heat is dissipated from the engagement portion on the metal fitting side to the cylinder head (the inner surface of the plug hole) through the tip portion, and is dissipated to the cylinder head (the inner wall surface of the plug hole) through the plug seat surface of the flange portion. You. Therefore, as a path for dissipating the heat flowing into the center electrode and the insulator, the plug seat surface is also a main path in addition to the tip of the metallic shell.

Therefore, in the above spark plug,
Distance L (unit: mm) measured from the front end side surface of the plug seat surface to the base end side edge of the metal fitting side engaging portion toward the front end in the axial direction.
Satisfies the relationship of −6 ≦ L ≦ 6.

With this configuration, heat from the insulator and the center electrode flowing into the fitting side engaging portion (specifically, the surface of the fitting side engaging portion that locks the insulator) flows into the tip end portion. At the same time, the heat easily flows into the plug seat surface, and the heat flowing into the insulator and the center electrode can be efficiently dissipated from the plug seat surface and the tip to the cylinder head (plug hole inner wall surface). As a result, the temperature of the center electrode and the insulator is kept lower, and a spark plug having more excellent heat resistance and a mounting structure thereof can be provided. Note that the range of the distance L is −3 ≦ L ≦ 3
It is preferable to satisfy the relationship in order to further improve the heat resistance.

Here, the base end side edge of the metal fitting side engaging portion serving as a reference for measuring the distance L is a surface of the metal fitting side engaging portion where the surface for locking the insulator is inclined with respect to the axis, that is, In the case of a tapered surface, it indicates the most proximal edge of the tapered surface. On the other hand, in the case where the surface of the metal fitting side that locks the insulator is a surface perpendicular to the axis, that is, a flat surface, the axial position of the proximal end edge locks the insulator. Coincides with the axial position of the surface to be moved. Similarly, when the plug seating surface is a surface inclined with respect to the axis, that is, a tapered surface, the front end side edge of the plug seating surface indicates the most front end edge thereof. On the other hand, when the plug seating surface is a surface perpendicular to the axis, that is, a flat surface, the axial position of the front end side edge thereof is:
It matches the axial position of the plug seat surface.

Further, in the spark plug of the present invention, one or more ends are connected to the metal shell to form a ground electrode connecting portion, and the other end is disposed so as to face the center electrode with a spark discharge gap therebetween. When the spark plug is rotated around the axial direction while inserting the spark plug into the plug hole, at least one of the main body and the tip of the metal shell has a main body corresponding portion and At least one of the distal end corresponding portions has a fitting position limiting shape that fits at one or a plurality of locations, while one or more ground electrode coupling portions have a fitting position limiting shape. It is preferable that the relationship between at least one of the main body and the tip is substantially the same when the spark plugs of the same product number are viewed.

According to this configuration, at least one of the flange portion and the distal end portion of the metal shell has a fitting position limiting shape with respect to the plug hole (at least one of the flange corresponding portion and the distal end corresponding portion of the plug hole), Further, it should be noted that the relationship between the formation position of one or a plurality of ground electrode coupling portions and the flange portion or the tip portion having the fitting position limiting shape is substantially the same. In such a configuration, the position of the ground electrode coupling portion is limited to a specific position in the circumferential direction around the axis of the plug hole itself by inserting the spark plug into the plug hole while loosely inserting and fitting the spark plug. Will be done. That is, only by inserting the spark plug into the plug hole, the ground electrode of the spark plug can be easily and reliably set at a specific position in the combustion chamber.

Usually, it is known that the swirl flow direction and the formation position of the ground electrode coupling portion have an optimal positional relationship so that the swirl flow generated during the compression stroke in the combustion chamber is not obstructed by the ground electrode. ing. Therefore, in consideration of the positional relationship between the swirl flow direction and the ground electrode coupling portion in advance, the relationship between the formation position of the ground electrode coupling portion and the flange portion or the tip portion having the fitting position limiting shape is limited. Thus, the relationship between the flow direction of the swirl and the formation position of the ground electrode coupling portion can always be restricted to be constant for each cylinder and each internal combustion engine. As a result, the ignitability does not vary for each cylinder or internal combustion engine, and good ignitability is obtained, and the internal combustion engine can be driven at a uniform air-fuel ratio (A / F), and furthermore, driven at a lean air-fuel ratio. can do.

Here, the fitting position limiting shape is such that when the flange portion or the front end portion of the metal shell is arranged corresponding to the flange corresponding portion or the front end corresponding portion of the plug hole,
When the spark plug is rotated around the axial direction while being inserted into the plug hole, it may have any shape as long as it fits at one or more locations. More specifically, a key hole extending in the axial direction is formed in the plug hole, and a key projection (which may be a strip or a projection) that fits into the key groove is provided at the tip or the like. Key protrusions, key grooves on the metal shell side, chamfered flanges, etc. of the metal shells, with plug holes shaped to fit this chamfer, and flanges of the main body and plug holes May have an oval, fallen circle, polygonal shape, or the like.

[0023]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 and FIG. 2 are a partially broken sectional view and a sectional view showing an internal structure of a spark plug 100 according to the present embodiment. This spark plug 100
Is a so-called one-pole type in which only one ground electrode 4 is formed, and is a flat sheet which is sealed by a plug seating surface 13 which is a plane provided between a flange portion 11 and a tip portion 12 of the metal shell 1. Type. In addition,
An annular gasket G is mounted on the plug seat surface 13.

The spark plug 100 has a center electrode 3 extending in the direction of the axis O and an insulator 2 surrounding the center electrode 3.
And a metal shell 1 for holding the insulator 2. The metal shell 1 is made of carbon steel and has a plug seat surface 13.
Has a flange portion 11 formed on the distal end side, and a distal end portion 12 extending from the plug seating surface 13 toward the axial line O distal end side. Unlike the conventional spark plug (see FIG. 10), the distal end portion 12 does not have a male screw for plug attachment on the outer periphery and has a cylindrical shape. This tip 1
One end of the ground electrode 4 is connected to the front end surface of the second electrode 2 to form a ground electrode connecting portion 17. And this ground electrode 4
Is extended toward the front end surface of the center electrode 3 and faces the center electrode 3 with a spark discharge gap g interposed therebetween. Further, on the rear end side (base end side) of the flange portion 11, a crimping groove portion 14, a hexagonal portion 15, and a crimping portion 16 are formed in order from the flange portion 11 toward the rear end side. In the present specification, the side where the spark discharge gap g is formed in the direction of the axis O will be described as the front side (front end side), and the opposite side will be described as the rear side (base end side).

A through hole 6 is formed in the insulator 2 in the direction of the axis O. The terminal electrode 5 is inserted and fixed behind the through hole 6 of the insulator 2, and the center electrode 3 is inserted and fixed forward of the through hole 6 of the insulator 2. Further, between the terminal electrode 5 and the center electrode 3 in the through hole 6,
Ceramic resistor 7 (resistor composition obtained by sintering a mixture of glass powder and conductive material powder by hot pressing or the like)
Is arranged. Both ends of the ceramic resistor 7 are electrically connected to the terminal electrode 5 and the center electrode 3 via conductive glass seal layers 8 and 9, respectively. In addition,
The ceramic resistor 7 may be omitted, and the center electrode 3 and the terminal electrode 5 may be directly joined by one conductive glass seal layer.

As shown in detail in FIG. 2, the insulator 2 has a diamond portion 2e projecting outward in the circumferential direction at a substantially intermediate portion in the direction of the axis O. The insulator 2 has a head portion 2b formed on the rear side of the diamond portion 2e with a smaller diameter. On the other hand, on the front side of the diamond portion 2e, a middle trunk portion 2g smaller in diameter than this and a leg length portion 2i smaller in diameter than the middle trunk portion 2g are formed adjacent to each other. A glaze layer 2d is formed on the outer surface of the head 2b,
A corrugation 2c is formed on the outer periphery on the rear side of the head 2b. In addition, the outer surface of the leg portion 2i, which is located on the foremost side in the direction of the axis O of the insulator 2, has a substantially conical shape whose diameter decreases toward the tip.

Next, the through hole 6 of the insulator 2 has a substantially cylindrical first portion 6a and a substantially cylindrical second portion 6b formed on the rear side of the first portion 6a and having a larger diameter than the first portion 6a. Have. The terminal electrode 5 and the ceramic resistor 7 are accommodated in the second portion 6b, and the center electrode 3 is
Is inserted through. At the base end of the center electrode 3, a convex portion 3a is formed which protrudes outward from the outer peripheral surface. The first portion 6a and the second portion 6b of the through hole 6 are connected to each other in the middle body 2g, and the connection position is provided with a convex portion receiving surface for receiving the convex portion 3a of the center electrode 3. 6c is formed in a tapered surface or an R-shaped surface.

The connecting portion between the middle trunk portion 2g and the leg long portion 2i is stepped to form a locking surface 2h.
An annular plate packing is provided on a metal fitting side engaging portion 18 (more specifically, a surface of the metal fitting side engaging portion which locks an insulator) which protrudes inward from an inner peripheral surface of the metal shell 1. By engaging through the insulator 51, the insulator 2 is prevented from being pulled out toward the front end side in the direction of the axis O. On the other hand, between the inner peripheral surface rear side of the metal shell 1 and the outer peripheral surface of the insulator 2, an annular wire packing 22, a talc 23, and the like that engage with the diamond portion 2e are arranged. Then, the insulator 2 is pushed forward toward the metal shell 1, and in this state, the base edge of the metal shell 1 is crimped inward toward the outer surface of the insulator 2 using a caulking mold. The caulking portion 16 is formed, and the insulator 2 is held by the metal shell 1.

Here, the metal fitting side engaging portion 18 transfers the heat flowing into the center electrode 3 and the insulator 2 (leg long portion 2i) through the packing 51 and the insulator locking surface 2h to the leading end of the metal shell 1. 12 and a part of a main path of heat dissipation to be dissipated to the cylinder seat SH, which will be described later. By the way, as shown in the blowout diagram of FIG. 2, a distance L (unit: measured in the axial direction O) from the front end side edge of the plug seat surface 13 to the base end side edge of the metal fitting side engaging portion 18.
mm) is related to the degree of dissipation of heat flowing into the center electrode 3 and the insulator 2 (note that the gasket G is omitted in the blowout diagram of FIG. 2). On the other hand, in the present embodiment, the distance L is set so as to satisfy the relationship of −6 ≦ L ≦ 6 (for example, L = 0.5 mm). In addition, the measurement result about the change of the heat resistance of a spark plug by changing the said distance L is mentioned later.

Further, a key projection 19 is formed so as to protrude from one of the outer peripheral surfaces of the distal end portion 12 of the metal shell 1. The key projection 19 of the tip 12
As described later, a front end corresponding portion 36 provided with a concave key groove 39 at one place in the plug hole P formed in the cylinder head SH and adapted to the key protrusion 19,
They are designed to fit together.

Next, the cylinder head SH according to the present embodiment will be described with reference to FIG. The head body 31 of the cylinder head SH has a plug hole P penetrating between the head upper surface 32 and the combustion chamber surface 33,
Further, screw holes 32a to 32d for screwing a plug fixing tool 41 described later are formed in the surrounding head upper surface 32. The plug hole P has a depth at which the spark plug 100 is completely inserted, and is formed of three stages of round holes whose diameter decreases in order from the head upper surface 32.

Of these, the insertion portion 34 on the head upper surface 32 side
Is a round hole extending from the head upper surface 32 to the vicinity of the combustion chamber surface 33.
Since the diameter of the flange portion 11 is larger than that of the flange portion 11 having the largest diameter, the spark plug 100 can be loosely inserted. When the spark plug 100 is inserted, the tip corresponding portion 36 on the combustion chamber surface 33 side
The distal end portion 12 of the metallic shell 1 is a portion into which the distal end portion 12 is loosely inserted. Further, a flange corresponding portion 35 is located between the insertion portion 34 and the distal end corresponding portion 36, and the spark plug 100
Is inserted, the flange portion 11 of the main tool 1 is inserted.
Constitute a portion to be inserted in a loose fit. In addition, the sealing surface 37 corresponding to the boundary between the flange corresponding portion 35 and the front end corresponding portion 36 is a surface on which the gasket G mounted on the spark plug 100 abuts to perform sealing. 3A, a key groove 39 having a width and a depth suitable for the key projection 19 of the spark plug 100 is formed in the distal end side corresponding portion 36. The cylinder head SH has a flow hole 38 for flowing cooling water.
Are formed.

In the present embodiment, the key groove 39 of the plug hole P and the key projection 19 of the metal shell 1 constituting the spark plug 100 are respectively formed in consideration of the position where the ground electrode coupling portion 17 is formed. It is formed with a specific positional relationship. By the way, it is known that the easiness of ignition of the air-fuel mixture is different depending on the relationship between the flow direction of the swirl generated in the compression stroke in the combustion chamber and the arrangement position of the ground electrode 4 in the combustion chamber. That is, when the ground electrode 4 blocks the swirl from flowing into the spark discharge gap g, the swirl is less likely to flow into the spark discharge gap g, so that there is a tendency for ignition to occur only with a relatively rich mixture.

On the other hand, in the present embodiment, when the spark plug 100 is attached to the plug hole P, the swirl flow direction and the arrangement position of the ground electrode 4 in the combustion chamber satisfy the optimum positional relationship. Electrode coupling part 17
Is formed so that the key projection 19 and the key projection 19 of the distal end portion 12 have a specific positional relationship between the key projection 19 and the key groove 39 of the distal end corresponding portion 36. Have been. The optimum positional relationship between the swirl flow direction and the position of the ground electrode 4 in the combustion chamber is defined as a one-pole type spark plug 1.
At 00, the ground electrode 4 is not disposed on the upstream side or the downstream side in the swirl flow direction, and as shown in FIG. Streamline Lm of swirl M passing
Of the ground electrode coupling part 17 with respect to the upstream intersection S among the intersections of the ground electrode coupling part 17 with the outer peripheral surface of the tip end part 12,
= 90 °.

Next, the plug fixture 41 according to the present embodiment will be described with reference to FIG. The plug fixing tool 41 is made of metal (aluminum or the like) and includes a projecting portion 42 for fixing itself to the cylinder head SH, and a substantially cylindrical tubular portion 43. Although not shown, a plurality of mounting holes are formed in the protruding portion 42 at positions corresponding to the screw holes 32a to 32d of the cylinder head SH, respectively. The outer peripheral surface of the cylindrical portion 43 has a cylinder head SH.
The diameter of the spark plug 10 is slightly smaller than that of the insertion portion 34, and the distal end surface 43a of the distal end thereof has a spark plug 10 as described later.
In order to be able to press the base end face of the flange portion 11 of the metal shell 1 constituting the metal shell 0, the inner peripheral surface thereof is larger in diameter than the hexagonal portion 15.

Then, as shown in FIG.
3, a connection terminal for supplying the coil core 44, the primary winding L <b> 1 and the secondary winding L <b> 2, and the high voltage for discharge generated in the secondary winding L <b> 2 to the terminal electrode 5 of the spark plug 100. 45 is accommodated. The secondary winding L2 is provided around the coil core 44.
Is wound, and a primary bobbin around which a primary winding L1 is wound is arranged around the secondary bobbin. The head 2 of the insulator 2 made of heat-resistant rubber and constituting the spark plug 100 is provided inside the cylindrical portion 43.
An insulating holding member 46 that comes into contact with b is provided so as to cover the periphery of the connection terminal. Further, the secondary winding L2
Connection terminal 45 electrically connected to one end of
Are electrically connected to the terminal electrode 5 by contact with the terminal electrode 5 in a compressed form in the direction of the axis O (see FIG. 4). At this time, the insulating holding member 4
Reference numeral 7 contacts the head 2b of the insulator 2 and performs a function of ensuring insulation between the ignition coil unit 50 and the spark plug 100.

As described above, the plug fixing device 4 of the present embodiment
1 has a built-in ignition coil unit 50, and the spark plug 100 is fixed to the plug hole P by a plug fixing tool 41 as described later, and the ignition coil unit 50
Can also be arranged in the plug hole P, and the connection between the spark plug 100 and the ignition coil unit 50 can be completed. Further, when such a plug fixing tool 41 is used, the spark plug 100 and the ignition coil section 50 are directly connected, so that a high tension cable or the like for connecting both is unnecessary, and noise is reduced. Can be reduced. In addition, since the plug fixture 41 has the ignition coil unit 50 therein, a connector unit 47 for connecting to an external device such as a power supply device or an ECU, and an ignition unit 48 are provided. The ignition unit 48 includes a switching element (not shown) for energizing / cutting a current (primary current) supplied from the power supply device to the primary winding L1 based on an ignition command signal output from the ECU. Built-in. The ignition unit 48 is electrically connected to the connector 47 and is also electrically connected to the ignition coil 50.

Next, the spark plug 100 and the plug fixture 41 are attached to the cylinder head SH. First, as shown in FIG. 4, the spark plug 100 is loosely inserted into the plug hole P of the cylinder head SH. At this time, when the spark plug 100 is inserted while being rotated about the axis O direction, the tip 12
Is fitted in the key groove 39 formed in the front end corresponding portion 36 of the plug hole P, and the spark plug 100 is mounted in the plug hole P. That is, the distal end portion 12 of the metal shell 1 and the distal end corresponding portion 36 of the plug hole P are fitted to each other by the key projection 19 and the key groove 39. As a result, the gasket G comes into contact with the sealing surface 37.

Further, the spark plug 100 is fixed to the cylinder head SH using the plug fixing tool 41 described above. First, as shown in FIG. 4, the cylindrical portion 43 of the plug fixing tool 41 is inserted into the plug hole P. The outer peripheral surface of the cylindrical portion 43 is slightly smaller in diameter than the insertion portion 34, so that it can be inserted in a loose fitting manner, and the distal end surface 43a of the cylindrical portion 43 has a flange portion of the metal shell 1 of the spark plug 100. 11
Abuts on the rear end face located on the side opposite to the plug seating face 13 of the helical member. At this time, the connection terminal 45 is formed inside the cylindrical portion 43.
Contacts the terminal electrode 5 of the spark plug 100 in a pressure contact state.

Next, as shown in FIGS. 4 and 5, the projections 42 of the plug fixing tool 41 are oriented so that the plurality of mounting holes are adapted to the screw holes 32a to 32d, and the bolts 49a to 49d are removed. Then, the plug fixing tool 41 is screwed to the head upper surface 32 of the cylinder head SH. As a result, an urging force is generated in the cylindrical portion 43 in contact with the rear end surface of the flange portion 11 of the metal shell 1 toward the front end in the direction of the axis O, and the plug seat surface 13 of the flange portion 11 is brought into contact with the cylinder head SH. The plug seat surface 1
The sealing between the sealing surface 3 and the sealing surface 37 can be performed via the gasket G. Then, by fixing the plug fixing tool 41 to the cylinder head SH, the spark plug 100 composed of the metal shell 1 on which the male screw for plug attachment is not formed is fixed to the cylinder head SH. Note that the length (height) of the tubular portion 43 may be appropriately adjusted in consideration of the dimensions of the spark plug 100 and the plug hole P so that the tube can be pressed with an appropriate pressure.

In this way, the spark plug 100
Although it is attached to the cylinder head SH (plug hole P), in this embodiment, in the attachment structure, as shown in FIG.
(Unit: mm), assuming that the hole diameter of the tip corresponding portion 36 of the plug hole P is φD (unit: mm), the clearance amount (φD−φd) satisfies the relationship of φD−φd ≦ 0.15. Have been. The corresponding part 36 at the tip of the plug hole P
There are various sizes of the hole diameter φD for each cylinder head SH design, and the outer diameter φd of the distal end portion 12 is determined so as to satisfy the above range (relationship) for any plug hole P. . In the present embodiment, for example, φD = 13.70 mm, φd = 13.60 m
m, and φD−φd = 0.10 mm.

As described above, the clearance amount (φD−φ
By setting d) to 0.15 mm or less, heat flowing from the insulator 2, the center electrode 3, and the ground electrode 4 to the distal end portion 12 of the metal shell 1 can be quickly dissipated to the cylinder head SH. become. As a result, the temperatures of the center electrode 3, the insulator 2, and the ground electrode 4 are kept low, and the same or higher heat resistance as that obtained by forming a male screw on the tip 12 can be obtained. Has no risk of preignition or electrode erosion.
In addition, the measurement result about the change of the heat resistance of a spark plug by changing the said clearance amount ((phi) D- (phi) d) is mentioned later.

Further, the relationship between the flow direction of the swirl and the ground electrode 4 when the spark plug 100 is attached to the cylinder head SH as described above will be examined. Here, in the present embodiment, the spark plug 1
00 is attached to the cylinder head SH, as described above, in order to satisfy the optimal positional relationship between the flow direction of the swirl and the ground electrode coupling part 17, the formation position of the ground electrode coupling part 17, the key projection 19 and the key groove. Each of the 39 forming positions has a predetermined positional relationship. Therefore, the spark plug 100 is connected to the cylinder head SH.
, The position of the ground electrode coupling portion 17 is always restricted to a specific position. Therefore, the arrangement position of the ground electrode 4 in the combustion chamber is set at a position that does not hinder the flow of the swirl, so that the mixture is reliably ignited by the spark discharge generated in the spark discharge gap g. Can be. Furthermore, the internal combustion engine can always be driven at a lean air-fuel ratio by an arbitrary combination of a spark plug and a cylinder head of the same product number,
It is also possible to improve fuel efficiency.

Although the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment.
It goes without saying that the present invention can be appropriately modified and applied without departing from the scope of the invention. For example, in the above-described embodiment, a single-pole type in which only one ground electrode 4 is coupled to the metal shell is used as the spark plug 100, but a multi-pole type in which the ground electrode 4 is coupled to a plurality of metal shells 1 is used. There may be. Although carbon steel is used as a material for forming the metal shell 1, a copper alloy having better heat conductivity than carbon steel is used in order to enhance the heat dissipation from the insulator 2, the center electrode 3, and the ground electrode 4. The metal shell 1 may be formed of aluminum or an aluminum alloy.

Further, in the above embodiment, as shown in FIG. 6 (a), a convex key projection 19 is formed on the distal end portion 12 of the metal shell 1 constituting the spark plug 100, so as to correspond to the distal end of the plug hole P. Although a concave key groove 39 is formed in the portion 36 and both are fitted at only one place, such a fitting position restriction shape may be another shape. For example, in FIG. 6 (b), a concave key groove 19a is provided in the distal end portion 12 of the metal shell 1, and a convex key projection is provided in the distal end corresponding portion 36 of the plug hole P, contrary to FIG. 39a is provided, and both are fitted.

FIG. 7 (a) shows a flat surface 19b formed by chamfering a part of the outer peripheral side surface of the flange portion 11 of the metal shell 1, and the flat portion 19b of the flange hole 11 of the plug hole P is also provided. Flat surface 3 corresponding to the shape of surface 19a
9b is provided, and both are fitted together. FIG. 7 (b) shows the flange 11
Is not a circle, but a larger diameter portion 19 which bulges out from a circle shown by a broken line.
c has a substantially oval cross section, and the flange corresponding portion 35 of the plug hole P is also provided with an enlarged diameter portion 39c corresponding thereto.
Both are fitted together.

In any of these shapes, the tip 12 of the metal shell 1 and the corresponding portion 36 of the plug hole P, or the flange 11 of the metal shell 1 and the flange corresponding portion 35 of the plug hole P, The mating position is
Limited to one location. Therefore, these fitting position limiting shapes and the ground electrode connecting portion 17 in the spark plug 100 are not limited.
Is limited in consideration of the swirl flow direction, the spark plug 100 is loosely inserted into the plug hole P and fitted into the plug hole P, thereby disposing the ground electrode 4 in the combustion chamber. Can always be specific.

In the above embodiment, as shown in FIG. 4, the front end face 43a of the cylindrical portion 43 of the plug fixing tool 41 is brought into contact with the rear end face of the flange portion 11 of the metal shell 1, and On the other hand, the urging force generated by the fixing of the plug fixing tool 41 is applied to urge the plug seating surface 13 against the cylinder head SH. However, as shown in FIG. 43c is the metal shell 1
The spark plug 100 may be fixed to the cylinder head SH using the plug fixing tool 41 while having a shape capable of contacting the caulking portion 16. Also in this structure, the tip 43c of the cylindrical portion 43 of the plug fixing tool 41 is brought into contact with the caulking portion 16 of the metal shell 1, and the direction of the axis O generated by fixing the plug fixing tool 41 to the cylinder head SH. Apply the urging force toward the tip to the metal shell 1
The plug seat surface 13 is urged toward the cylinder head SH.

Further, the spark plug 1 of the above embodiment
As shown in FIG. 12, in addition to the structure of FIG. 12, a bottomed concave portion (not shown) is provided on the outer peripheral side surface of the flange portion 11 of the metal shell 1 in the circumferential direction, and the concave portion can be elastically deformed. It may be configured by fitting a simple annular elastic material 61 (rubber or the like). In such a spark plug 100,
After being attached to the cylinder head SH, the flange portion 11 and the inner wall of the plug hole P (flange corresponding portion 35)
Is securely sealed by the elastic material 61,
The airtightness between the spark plug 100 and the cylinder head SH is further improved.

(Example 1) In order to confirm the effect of the present invention, the tip 12 of the metal shell 1 shown in FIG. 1 (or FIG. 4) was used.
And the hole diameter φD of the front end corresponding portion 36 of the plug hole P is made constant (13.7 mm).
The heat resistance of the spark plug 100 was evaluated by changing the value of the clearance amount (φD−φd). In addition,
In the spark plug 100, the length T1 of the tip 12 in the axis O direction is 15.0 mm, and the inner diameter φd1 of the tip 12 is
8.4 mm, minimum inner diameter φd2 of metal fitting engaging portion 18 = 7.5
The dimensions were set to mm, and the evaluation was performed (see FIG. 1). The distance L (see FIG. 2) measured from the distal end side edge of the plug seat surface 13 to the base end side edge of the fitting side engaging portion 18 toward the distal end in the axis O direction was set to 0 mm.
Further, in this evaluation, the axis O of the leg 2i of the insulator 2 was used.
The distance T2 in the direction is T2 = 14 mm (outer diameter φd3 of the leg long part 2i = 5.1 mm) and T2 = 17 mm
(External diameter φd3 of tip end portion 2i = 5.1 mm) was performed for each of them (see FIG. 1).

The heat resistance of the spark plug 100 was evaluated by the following method. As shown in FIG.
The spark plug 100 was fixed to the cylinder head SH by a plug fixing tool 41 from which the center of the ignition coil part 50 and the protruding part 42 was removed. This plug fixing tool 41 is formed by forming a through hole 43 b continuous with the inner peripheral surface of a cylindrical portion 43 in a protruding portion 42, fixes the spark plug 100, and has an insulation terminal having a connection terminal 45 connected to a cable 51 inside. The retaining member 46 is inserted through the through hole 43b, and the connection terminal 45 and the terminal electrode 5 of the spark plug 100 are brought into contact with each other in a press-contact state. This cable 51
Are connected to an ignition circuit (not shown) via a diode 52 having a high withstand voltage, and are connected to a preignition tester (not shown) via a diode 53 having a high withstand voltage.

The preignition tester measures a so-called ion current. That is, when preignition occurs, if the spark discharge gap g is wrapped in a flame, ions in the flame bring the spark discharge gap into conduction. Therefore, if a voltage of several hundred volts is applied in advance between the spark discharge gaps, an ion current flows when preignition occurs. Therefore, if the ion current is detected before discharging in the ignition circuit, it can be determined that preignition has occurred.

Then, as described above, the spark plug 10
After fixing 0 to the cylinder head SH, the internal combustion engine is driven (1600 cc, in-line 4-cylinder, throttle fully open state), the over-advancing angle is changed in order of 1 degree from the regular ignition timing, and held for 2 minutes. It was measured whether or not preignition occurred during that time, and the over-advance angle at which preignition occurred for the first time was measured. Each clearance amount (φD-
The relationship between φd) and the over-advance angle is shown in the graph of FIG.

In this evaluation, a conventional spark plug (see FIG. 11) in which a male screw (M14S) was formed at the tip of the metal shell also had a leg length distance T2 = 14.
mm and 17 mm were similarly evaluated (the distance L measured from the tip side surface of the plug seat surface to the base end side edge of the metal fitting side engaging portion was 0 mm). . In the conventional spark plug, when the leg length is T2 = 14 mm, the over-advance angle at which preignition occurs is 20 degrees, and when the leg length is T2 = 17 mm, the over-advance angle is 15 degrees. .

On the other hand, in the spark plug 100 of the present embodiment, as shown in the graph of FIG. 9, when the clearance amount (φD−φd) = 0.15 mm, the leg length 2
It has been found that the two types, i.e., the distance T2 = 14 mm and 17 mm, can be driven without preignition up to an over-advancing angle equivalent to that of the conventional example. In addition, the clearance amount (φD−φd) = 0.02 mm, 0.05 mm, 0.1
At 0 mm, the distance T2 of the leg length 2i = 14 mm, 17 m
It has been found that both types of m can be driven without pre-ignition up to an over-advance angle greater than the above-mentioned conventional example, and the heat resistance is improved. On the other hand, the clearance amount (φD−φd) =
For those exceeding 0.15 mm, the distance T2 of the leg length 2i
= 14 mm and 17 mm were both inferior in heat resistance to the above conventional example.

(Example 2) In the spark plug 100 of the present embodiment used in Example 1, the distance T of the leg portion 2i
2 = 17 mm, clearance amount (φD−φd) = 0.
The distance L measured from the distal end side edge of the plug seat surface 13 to the base end side edge of the metal fitting side engaging portion 18 toward the distal end in the direction of the axis O is -6.5 mm, -3.0 mm. , ± 0
mm (corresponding to that of Example 1), 3.0 mm, 6.0 m
m were prepared by changing five types, and the heat resistance of the spark plug 100 was evaluated in the same manner as in Example 1.

The over-advance angle at which pre-ignition occurs in the spark plug in which the distance L is changed to five types is 16 degrees when the distance L is -6.5 mm, and-
20 degree for 3.0 mm, 21 for ± 0 mm
The degree was 20 degrees in the case of 3.0 mm and 18 degrees in the case of 6.0 mm. From these results, the distance L is-
For four types of spark plugs satisfying the relationship of 6 mm ≦ L ≦ 6 mm, L = −6.5 where the distance L is less than −6 mm.
It was found that an effect of improving heat resistance, which was superior to that of mm, was obtained.

[Brief description of the drawings]

FIG. 1 is a partially broken cross-sectional view showing an overall shape of a spark plug according to an embodiment.

FIG. 2 is an axial sectional view showing an internal structure of the spark plug according to the embodiment.

3A and 3B are a plan view and an axial cross-sectional view illustrating a shape near a plug hole of the cylinder head according to the embodiment.

FIG. 4 is a perspective view of the spark plug shown in FIG. 1 (FIG. 2);
FIG. 3 is an explanatory view (partially cutaway sectional view) showing a mounting structure of a spark plug in a state where the spark plug is inserted into and fitted into a plug hole of a cylinder head shown in FIG.

FIG. 5 is a perspective view of the spark plug shown in FIG. 1 (FIG. 2);
FIG. 4 is a plan view showing a state where the plug is inserted into the plug hole of the cylinder head shown in FIG.

FIG. 6 is an explanatory diagram showing an example of a fitting position restriction shape in which a distal end portion of a metal shell and a distal end corresponding portion of a plug hole are fitted to each other.

FIG. 7 is an explanatory view showing an example of a fitting position restriction shape in which a flange portion of a metal shell and a flange corresponding portion of a plug hole fit together.

FIG. 8 is an explanatory diagram showing a preignition test of a spark plug (spark plug mounting structure) according to the embodiment.

FIG. 9 shows the preignition test shown in FIG.
6 is a graph showing a result obtained by changing a clearance amount (φD−φd) in the spark plug mounting structure shown in FIG.

FIG. 10 is a partially cutaway sectional view showing the entire shape of a conventional spark plug.

FIG. 11 is an explanatory diagram for explaining a relationship between an arrangement position of a ground electrode of a spark plug and a flow direction of a swirl.

FIG. 12 is an explanatory view showing a mounting structure of another embodiment different from the mounting structure of the spark plug shown in FIG. 4;

[Explanation of symbols]

REFERENCE SIGNS LIST 100 spark plug, 1 metal shell, 11 flange portion, 12 tip portion, 17 ground electrode coupling portion, 18 metal fitting side engaging portion, 19 key projection, 2 insulator, 2i leg length portion, 3 ... Center electrode, 4 ... Ground electrode, 5 ... Terminal electrode, 32
... head upper surface, 33 ... combustion chamber surface, 34 ... insertion part, 35 ...
Flange corresponding part, 36 ... Tip corresponding part, 39 ... Keyway, 4
DESCRIPTION OF SYMBOLS 1 ... Plug fixing tool, 42 ... Projection part, 43 ... Tube part, 44
... Coil core, 45 ... Connection terminal, 50 ... Ignition coil part,
SH: cylinder head, P: plug hole, L1: primary coil, L2: secondary coil, g: spark discharge gap

Claims (5)

[Claims] 1. A center electrode extending in an axial direction, an insulator surrounding the radial periphery by disposing the center electrode on a tip side of the center electrode, and holding the insulator surrounding the radial periphery of the insulator. A spark plug comprising: a metal shell having a flange portion having a plug seating surface on the front end side and a front end portion extending from the plug seating surface of the flange portion to the axially front end side; and a plug hole formed in the cylinder head. The distal end of the metal shell is formed in a substantially cylindrical outer peripheral surface without having a male screw for plug attachment, while the plug hole is formed by a flange portion and a distal end of the metal shell. The outer diameter of the tip of the metal shell is φd (unit: mm), and the diameter of the tip corresponding portion of the plug hole is φd (unit: mm). Is φD (unit: m
m), wherein a relationship of φD−φd ≦ 0.15 is satisfied. 2. A metal fitting side engaging portion for locking the insulator is formed on an inner peripheral surface of the metal shell so as to protrude inward. The distance L (unit: mm) measured toward the distal end in the axial direction up to the base end side edge of the metal fitting side engaging portion satisfies the relationship of −6 ≦ L ≦ 6. Spark plug mounting structure. 3. A central electrode extending in the axial direction, an insulator surrounding the radial periphery by disposing the central electrode on its own tip side, and surrounding the radial periphery of the insulator,
A spark plug attached to a plug hole formed in a cylinder head, comprising: a metal shell having a flange portion having a plug seat surface on the tip side and a tip portion extending from the plug seat surface of the flange portion to the tip end in the axial direction. The distal end of the metal shell is formed in a substantially cylindrical outer peripheral surface without having a male screw for plug attachment, while the plug holes correspond to the flange portion and the distal end of the metal shell, respectively. It has a flange corresponding part and a tip corresponding part. The outer diameter of the tip part of the metal shell is φd (unit: mm), and the hole diameter of the tip corresponding part of the plug hole is φD (unit: m).
m), a spark plug characterized by satisfying a relationship of φD−φd ≦ 0.15. 4. A metal fitting side engaging portion for locking the insulator is formed on an inner peripheral surface of the metal shell so as to protrude inward, and is formed from a tip side edge of the plug seat surface. The distance L (unit: mm) measured toward the distal end in the axial direction up to the base end side edge of the metal fitting side engaging portion satisfies the relationship of −6 ≦ L ≦ 6. Spark plug. 5. The spark plug according to claim 3, wherein one end is coupled to the metal shell to form a ground electrode coupling portion, and the other end is opposed to the center electrode via a spark discharge gap. At least one of the main body and the tip of the metal shell rotates the spark plug around the axial direction while inserting the spark plug into the plug hole. And at least one of the main body corresponding portion and the front end corresponding portion of the plug hole has a fitting position-restricted shape that is fitted to one or more places. When the relationship between the formation position of the coupling portion and at least one of the main body portion and the distal end portion of the metal shell having the fitting position restriction shape is the same as that of the spark plug, Wherein the spark plug is substantially the same.