JP6442932B2 - Spark plug for internal combustion engine - Google Patents

Description

  The present invention relates to a spark plug for an internal combustion engine having an annular ground electrode arranged so as to face the outer peripheral surface of a center electrode.

  As a spark plug used in an internal combustion engine such as an automobile or a cogeneration system, a spark plug having an annular ground electrode arranged to face the outer peripheral surface of a center electrode is disclosed (Patent Document 1). In the spark plug disclosed in Patent Document 1, the ground electrode is fixed to the housing by being caulked from the outer periphery by a caulking portion at the front end portion of the housing. A spark discharge gap is formed between the outer peripheral surface of the center electrode and the inner peripheral surface of the annular ground electrode.

Japanese Patent No. 5075127

  However, the spark plug disclosed in Patent Document 1 has a structure in which the ground electrode is caulked inside the housing, and the ground electrode is in contact with the housing on the outer periphery thereof. Therefore, the heat dissipation path from the inner peripheral surface of the ground electrode facing the spark discharge gap to the housing tends to be long, and the temperature of the ground electrode is likely to rise. When the temperature of the ground electrode rises, the amount of consumption of the electrode material in the spark discharge gap increases, and the expansion of the spark discharge gap accelerates. Therefore, the time to reach the spark discharge gap distance that determines the life of the plug is shortened, and it is difficult to obtain a long-life spark plug.

  Further, the ground electrode is disposed on the inner side of the housing, and the spark discharge gap is also disposed on the proximal end side with respect to the distal end of the housing. Therefore, there is a problem that the flame due to the discharge generated in the spark discharge gap is difficult to grow, that is, a problem that the cooling loss tends to be large, and it can be said that it is disadvantageous from the viewpoint of ignitability.

  Furthermore, the spark plug disclosed in Patent Document 1 has a structure in which the ground electrode is caulked inside the housing, and it is difficult to adjust the position of the ground electrode and it is difficult to adjust the spark discharge gap. is there. That is, in order to accurately form the spark discharge gap between the outer peripheral surface of the center electrode and the inner peripheral surface of the ground electrode, accuracy of the relative position of the ground electrode with respect to the center electrode is required. However, if there are dimensional variations or assembly variations of components such as the housing, a desired spark discharge gap cannot be formed simply by accurately arranging the ground electrode at a predetermined position with respect to the housing. Therefore, it is necessary to adjust the position of the ground electrode with respect to the center electrode. However, in the structure in which the ground electrode is inserted in the radial direction inside the caulking portion of the housing as described above, the dimensional variation and assembly variation of each component are large. In some cases, movement of the ground electrode in the plug radial direction is restricted, and accurate gap adjustment is difficult.

  The present invention has been made in view of such a background, and is intended to provide a spark plug for an internal combustion engine that has a long life, easily improves ignitability, and easily adjusts a spark discharge gap. is there.

One embodiment of the present invention includes a cylindrical housing;
A cylindrical insulator held inside the housing;
A center electrode that is held inside the insulator and protrudes toward the tip side of the insulator;
An annular ground electrode fixed to the front end side of the housing,
The housing has a reduced-diameter portion whose inner diameter is smaller than that of the other part at the front end of the housing,
The ground electrode is disposed so as to protrude on the tip surface of the reduced diameter portion, and is disposed so that an inner peripheral surface of the ground electrode faces an outer peripheral surface of the center electrode,
The outer diameter of the ground electrode is smaller than the outer diameter of the distal end surface of the reduced diameter portion,
The insulator has a locked stepped portion that is locked in the plug axial direction with respect to a locking stepped portion provided on the inner peripheral side of the housing, and goes from the locked stepped portion to the distal end side. It has an outer diameter reduction part that the outer diameter becomes smaller,
Inner surface of the housing, possess from the engaging step portion to the reduced diameter portion, the inner diameter reduced portion of the inner diameter toward the distal end side becomes small,
The inner diameter reduced portion is in the spark plug for an internal combustion engine, it characterized that you have been formed to the front end side than the tip of the insulator.

  In the spark plug, the outer diameter of the ground electrode is smaller than the outer diameter of the distal end surface of the reduced diameter portion of the housing, and the ground electrode is joined to the distal end surface of the reduced diameter portion of the housing. Means in contact with each other in the plug axial direction. As a result, a large contact area between the ground electrode and the housing can be secured, and a heat radiation path from the inner peripheral surface of the ground electrode facing the spark discharge gap to the housing can be shortened. Therefore, it is possible to efficiently dissipate heat from the ground electrode exposed to combustion and heated to the housing attached to the engine head or the like, and the temperature rise of the ground electrode can be suppressed. Therefore, by suppressing the temperature rise of the ground electrode, it is possible to suppress the electrode consumption on the inner peripheral surface of the ground electrode and to delay the expansion of the spark discharge gap. That is, the life of the spark plug can be extended.

Further, the inner side surface of the housing has an inner diameter reduced portion that decreases in diameter toward the distal end side from the locking step portion to the reduced diameter portion. Thereby, the cross-sectional area of the housing by the plane orthogonal to the plug axis direction can be increased as it approaches the tip side. Moreover, the closer to the tip side, the more solid the housing exists at a position closer to the center electrode, that is, a position closer to the inner peripheral surface (opposing portion) of the ground electrode. Thereby, the heat of the ground electrode can be efficiently radiated through the housing.
As a result, the temperature rise of the ground electrode can be suppressed, the wear resistance of the ground electrode can be improved, and the life of the spark plug can be effectively extended. Further, by suppressing the temperature rise of the ground electrode, it is possible to reduce thermal stress at the joint between the ground electrode and the housing.

  Further, since the ground electrode protrudes from the front end surface of the housing, the spark discharge gap is also arranged on the front end side with respect to the front end of the housing. Therefore, when the flame generated by the discharge in the spark discharge gap grows, it is possible to prevent the flame from being deprived of heat and coming into contact with the housing and preventing the flame from growing. That is, by suppressing the cooling loss, the flame growth is promoted without being hindered, and the ignitability can be improved.

  In the spark plug, an annular ground electrode facing the outer peripheral surface of the center electrode is joined to the distal end surface of the reduced diameter portion of the housing. Therefore, it is easy to adjust the positional relationship with the center electrode when the ground electrode is joined to the housing. That is, when the ground electrode is joined to the housing, the relative position with respect to the center electrode is adjusted while moving the ground electrode along the distal end surface of the reduced diameter portion even when the dimensional variation and assembly variation of each component are large. be able to. As a result, the spark discharge gap between the center electrode and the ground electrode can be easily adjusted.

  As described above, according to the present invention, it is possible to provide a spark plug for an internal combustion engine that has a long life, easily improves ignitability, and easily adjusts the spark discharge gap.

FIG. 2 is a cross-sectional perspective view of the vicinity of the tip of the spark plug in the first embodiment. Sectional drawing by the cross section which passes through the plug center of a spark plug in Example 1. FIG. FIG. 3 is a plan view of the spark plug as viewed from the front end side in the first embodiment. FIG. 3 is a cross-sectional view of the vicinity of the tip of the spark plug in the first embodiment. (A) The top view of a ground electrode in Example 1, (B) The Vb-Vb arrow directional cross-sectional view of (A). FIG. 3 is a cross-sectional view of the vicinity of the tip of the spark plug before the ground electrode is joined in Example 1. FIG. 6 is a cross-sectional perspective view of the vicinity of a tip end portion of a spark plug in Embodiment 2. The top view which looked at the spark plug before joining the ground electrode in Example 2 from the front end side.

The spark plug can be used as an ignition means in an internal combustion engine such as an automobile or a cogeneration.
In the above-described spark plug for an internal combustion engine, the side inserted into the combustion chamber is the front end side, and the opposite side is the base end side.
In this specification, the plug axial direction means the axial direction of the spark plug, the plug radial direction means the radial direction of the spark plug, and the plug circumferential direction means the circumferential direction of the spark plug. To do.

Example 1
Examples of the spark plug for the internal combustion engine and the manufacturing method thereof will be described with reference to FIGS.
As shown in FIGS. 1 to 4, the spark plug 1 of the present example is held inside a cylindrical housing 2, a cylindrical insulator 3 held inside the housing 2, and inside the insulator 3. And a center electrode 4 projecting toward the distal end side of the insulator 3 and an annular ground electrode 5 fixed to the distal end side of the housing 2.
The housing 2 has a reduced diameter portion 21 having an inner diameter D4 smaller than that of other portions at the distal end portion of the housing 2.

In this example, the center electrode 4 has a substantially columnar shape, and is arranged coaxially with a substantially cylindrical housing 2, a substantially cylindrical insulator 3, and a substantially cylindrical ground electrode 5.
Here, the distal end surface 211 of the reduced diameter portion 21 of the housing 2 indicates a surface of the housing 2 that is located on the most distal end side in the plug axis direction.
As shown in FIG. 1, the front end surface 211 of the housing 2 is a flat surface orthogonal to the plug axis direction. Further, the proximal end surface 52 and the distal end surface 53 of the ground electrode 5 are also flat surfaces. The ground electrode 5 is joined to the housing 2 in a state where the proximal end surface 52 of the ground electrode 5 and the distal end surface 211 of the reduced diameter portion 21 of the housing 2 are in surface contact.

The ground electrode 5 is disposed so as to protrude on the distal end surface 211 of the reduced diameter portion 21 of the housing 2, and the inner peripheral surface 51 of the ground electrode 5 is disposed so as to face the outer peripheral surface 41 of the center electrode 4. The
As shown in FIG. 4, the outer diameter D <b> 1 of the ground electrode 5 is smaller than the outer diameter D <b> 0 of the distal end surface 211 of the reduced diameter portion 21 of the housing 2. The outer diameter D1 is 5 mm to 10 mm, and the outer diameter D0 is 12 mm to 22 mm. More preferably, the outer diameter D1 is 5 mm to 7 mm, and the outer diameter D0 is 14 mm to 22 mm.

  Thus, since the ground electrode 4 having the outer diameter D1 smaller than the outer diameter D0 is joined to the distal end surface 211 of the reduced diameter portion 21 of the housing 2, the ground electrode 4 and the housing 2 are connected in the plug axial direction. Will be opposed to each other. Thereby, it becomes easy to shorten the heat dissipation path from the inner peripheral surface 51 of the ground electrode 5 facing the spark discharge gap to the housing 2, and the temperature rise of the ground electrode 5 can be suppressed.

As shown in FIGS. 1 and 4, the insulator 3 has a locked step portion 31 that is locked in the plug shaft direction with respect to a locking step portion 23 provided on the inner peripheral side of the housing 2, An outer diameter reduction portion 32 having an outer diameter that decreases from the locked step portion 31 toward the distal end side is provided.
The inner surface of the housing 2 has an inner diameter reducing portion 24 that decreases from the locking step portion 23 to the reduced diameter portion 21 toward the distal end side.

  In this example, the outer diameter reduction part 32 and the inner diameter reduction part 24 each have a tapered shape. The taper angle of the outer diameter reduction part 32 is, for example, 5 to 25 °, and the taper angle of the inner diameter reduction part 24 is, for example, 5 to 25 °. Here, the taper angle refers to an angle formed with respect to the plug axis direction in a cross-sectional shape (FIG. 4) by a plane including the plug center axis. Furthermore, the shortest distance between the outer diameter reduced portion 32 of the insulator 3 and the inner diameter reduced portion 24 of the housing 2 has a gap larger than the gap at the time of electrode life of the spark plug. The shortest distance is, for example, 0.7 mm. By securing the shortest distance that is equal to or greater than the gap at the time of electrode life, it is possible to reliably discharge in the spark discharge gap even when the spark discharge gap is widened by using the spark plug.

Further, the outer diameter D1 of the ground electrode 5 is larger than the diameter D2 of the tip portion of the inner diameter reduction portion 24. The outer peripheral edge of the ground electrode 5 is disposed outside the upper end of the inner diameter reduction portion 24 over the entire circumference.
The difference between the outer diameter D1 and the diameter D2 is 7 mm or less.

  The ground electrode 5 is disposed so as to protrude on the distal end surface 211 of the reduced diameter portion 21 of the housing 2, and the inner peripheral surface 51 is disposed so as to face the outer peripheral surface 41 of the center electrode 4. Therefore, since the housing 2 is not positioned in the growth direction of the flame generated by the discharge in the spark discharge gap, it is possible to suppress the growth of the flame from being hindered by the housing 2. That is, it is possible to suppress the cold loss in which the flame is brought into contact with the housing 2 and the heat is taken away, and the ignitability can be improved.

  As shown in FIG. 4, the ground electrode 5 is preferably arranged such that the distal end surface 53 is closer to the distal end side than the distal end surface 43 of the center electrode 4. In particular, the positional relationship is such that the distal end surface 53 of the ground electrode 5 is disposed 0.1 mm to 0.3 mm distal to the distal end surface 43 of the center electrode 4, and is 0 from the distal end surface 211 of the reduced diameter portion 21. It is preferable to be disposed on the tip side of 8 mm to 3 mm. Therefore, the difference h in the plug axis direction between the tip surface 43 of the center electrode 4 and the tip surface 53 of the ground electrode 5 in FIG. 4 is in the range of 0.1 mm to 0.3 mm. The height H in the direction is preferably in the range of 0.8 mm to 3 mm.

  Thereby, the electric field strength in the vicinity of the outer peripheral surface 41 of the center electrode 4 can be effectively increased. That is, when a voltage is applied between the ground electrode 5 and the center electrode 4, an electric field is formed in the spark discharge gap between the ground electrode 5 and the center electrode 4. By projecting toward the distal end side, the electric field tends to concentrate on the outer peripheral surface 41 of the center electrode 4. Thereby, electrons are easily emitted from the center electrode 4, and the required voltage required for discharge can be reduced.

  By setting the height H of the ground electrode 5 to 0.8 mm or more, the electric field concentration effect on the outer peripheral surface 41 of the center electrode 4 can be enhanced. Further, the wear resistance of the inner peripheral surface 51 of the ground electrode 5 can be ensured, and the life of the spark plug 1 can be extended. On the other hand, by setting the height H to 3 mm or less, even when a spark discharge is generated in the vicinity of the base end portion of the spark discharge gap, it is possible to suppress misfire due to cooling loss and to ensure ignitability. . Gas enters and exits the internal space 13 of the housing 2 through the spark discharge gap. If the height H is 3 mm or less, the gas smoothly enters and exits the internal space 13 of the housing 2. Can be secured. As a result, the gas is sufficiently introduced into the spark discharge gap, and the ignitability can be ensured.

  The inner diameter D3 of the ground electrode 5 is smaller than the inner diameter D4 of the reduced diameter portion 21 of the housing 2. In this example, the inner diameter D3 is 2.8 mm to 3.4 mm, and the inner diameter D4 is 3.6 mm to 4.0 mm. . Thereby, the spark discharge gap can be easily adjusted while moving the ground electrode 5 in the plug radial direction. In particular, even when there is a dimensional variation or assembly variation of each part in the relationship between the inner peripheral surface 51 of the ground electrode 5 and the inner peripheral edge 212 of the reduced diameter portion 21, the inner peripheral edge of the reduced diameter portion 21 is generated. It is possible to prevent 212 from being positioned radially inward from the inner peripheral surface 51 of the ground electrode 5. Then, the inner peripheral surface 51 of the ground electrode 5 protrudes inward from the inner peripheral end edge 212 of the reduced diameter portion 21 of the housing 2 over the entire periphery, so that a uniform spark discharge gap can be formed. That is, as shown in FIGS. 1 and 4, when the spark plug 1 is viewed in the cross section including the plug center axis, the inner peripheral surface 51 of the ground electrode 5 is disposed in parallel to the outer peripheral surface 41 of the center electrode 4. As shown in FIG. 3, a spark discharge gap is formed across the entire circumference in the plug circumferential direction, and a stable spark discharge can be realized.

  As shown in FIGS. 4 and 5, the ground electrode 5 includes an annular electrode base material 54 and a noble metal layer 55 provided on the inner peripheral surface of the electrode base material 54. For example, the electrode base material 54 is made of a nickel (Ni) based alloy, and the noble metal layer 55 is made of a simple substance such as platinum (Pt) or iridium (Ir), or an alloy thereof. The noble metal layer 55 is diffusion bonded to the electrode base material 54. Further, the thickness of the noble metal layer 55 can be set to about 0.1 mm to 0.5 mm, for example. Since the ground electrode 5 includes the electrode base material 54 and the noble metal layer 55, it is possible to improve the wear resistance of the ground electrode 5 and to effectively extend the life of the spark plug 1. Further, the noble metal layer 55 is joined to the electrode base material 54 by welding, diffusion joining, or the like, but is preferably diffusion joined, and the adhesion strength of the noble metal layer 55 to the electrode base material 54 can be improved. The heat dissipation from the noble metal layer 55 to the electrode base material 54 can be improved. As a result, the life of the spark plug 1 can be further extended.

As shown in FIGS. 1 and 2, the housing 2 has a mounting screw portion 22 for mounting the spark plug 1 to the internal combustion engine, and is made of, for example, an Fe-based alloy.
In addition, the insulator 3 is configured such that the locked step portion 31 provided on the outer peripheral side is locked in the plug shaft direction with the locking step portion 23 provided on the inner peripheral surface of the housing 2. 2 is held. An annular packing 11 is interposed between the locked step portion 31 of the insulator 3 and the locking step portion 23 of the housing 2.

Next, the manufacturing method of the spark plug 1 of this example is demonstrated. This manufacturing method has the following assembly | attachment processes and a joining process.
As shown in FIG. 6, the assembling step is a step of assembling the assembly of the insulator 3 and the center electrode 4 inside the housing 2 so that the center electrode 4 passes through the inside of the reduced diameter portion 21.
The joining step is a step of joining the ground electrode 5 to the reduced diameter portion 21 of the housing 2 as shown in FIG. 4 after the assembly step.
In the joining step, the spark discharge gap between the ground electrode 5 and the center electrode 4 is adjusted.

  In the joining step, the annular ground electrode 5 shown in FIG. 5 is placed on the distal end surface 211 of the reduced diameter portion 21 of the housing 2 in a state where the center electrode 4 is disposed on the inner peripheral side thereof. To do. Then, the ground electrode 5 is positioned on the front end surface 211 of the housing 2 while sliding in the plug radial direction and adjusting the relative position with the center electrode 4. That is, the spark discharge gap between the outer peripheral surface 41 of the center electrode 4 and the inner peripheral surface 51 of the ground electrode 5 is adjusted so as to have a desired size. In other words, the ground electrode 5 is positioned while moving so that the spark discharge gap is uniform over the entire circumference of the plug. Here, if the front end surface 211 of the housing 2 is a flat surface orthogonal to the plug axis direction, the ground electrode 5 can be accurately positioned. In this manner, the ground electrode 5 is welded to the housing 2 in a state where the position of the ground electrode 5 is adjusted to an accurate position. In welding, for example, resistance welding or laser welding can be used. Further, welding can be performed over the entire circumference in the plug circumferential direction between the outer peripheral edge of the base end surface 52 of the ground electrode 5 and the distal end surface 211 of the housing 2.

  Thus, the spark plug 1 as shown in FIGS. 1 to 4 can be obtained in a state where the spark discharge gap is accurately formed between the outer peripheral surface 41 of the center electrode 4 and the inner peripheral surface 51 of the ground electrode 5. it can.

  Further, when the spark plug 1 is manufactured, the spark discharge gap between the ground electrode 5 and the center electrode 4 is adjusted in the joining step. Therefore, when the ground electrode 5 is joined to the reduced diameter portion 21 of the housing 2, the adjustment of the spark discharge gap between the ground electrode 5 and the center electrode 4 can be completed. Thereby, the spark discharge gap can be adjusted easily and accurately.

  As described above, in the spark plug 1 of this example, the inner surface of the housing 2 has the inner diameter reduced portion 24, so that the heat of the ground electrode 5 can be efficiently radiated through the housing 2. Particularly in this example, since the inner diameter reduced portion 24 has a tapered shape, the heat dissipation efficiency of the ground electrode 5 can be further improved, and the life extension of the spark plug 1 can be effectively improved.

  The technical significance of the outer diameter reducing portion 32 of the insulator 3 and the inner diameter reducing portion 24 of the housing 2 will be further described. As described above, the locked step portion 31 of the insulator 3 and the locking step portion 31 of the housing 2 are in contact via the packing 11. When a high voltage is applied to the center electrode 4, a large potential difference is formed between the housing 2 and the center electrode 4, so that the insulator 3 is connected to the center electrode 4 and the housing 2 in order to insulate between the two. It is arranged between. Therefore, the insulator 3 needs to have a sufficient thickness in the plug radial direction so as not to cause dielectric breakdown. And especially in the to-be-latched part 31 of the insulator 3 which contacts the latching step part 23 of the housing 2, it is necessary to provide sufficient thickness. On the other hand, since the insulator 3 and the housing 2 are not in contact with each other on the tip side of the locked step portion 31, the insulating function of the insulator 3 can be secured even if the insulator 3 is relatively thin. . From this point of view, the insulator 3 is provided with an outer diameter reduced-diameter portion 32 whose outer diameter becomes smaller toward the distal end side than the locked step portion 31.

  On the other hand, the heat dissipation of the ground electrode 5 can be improved as the thickness of the solid portion of the housing 2 increases. That is, by increasing the thickness of the housing 2, it is possible to ensure a large heat dissipation path for radiating heat from the ground electrode 5 to the engine head of the internal combustion engine through the housing 2. However, the thickness of the solid portion of the housing 2 is limited by the relationship between the outer diameter of the spark plug 1 (the diameter of the mounting screw portion) and the insulator 3 disposed inside.

  However, as described above, in the portion of the insulator 3 that faces the outer diameter reducing portion 32, the inner surface of the housing 2 is formed on the inner side as much as possible, so that the inside of the housing 2 can be prevented without interfering with the insulator 3. The actual part can be made thicker. Therefore, in the spark plug 1, the heat radiation path of the ground electrode 5 is made as large as possible by providing the inner diameter reduced portion 24 on the inner surface of the housing 2. In addition, it is possible to increase the thickness of the tip side near the ground electrode 5 and to bring the solid portion closer to the spark discharge gap, so that the heat dissipation of the ground electrode 5 can be improved efficiently. .

  As shown in FIG. 4, the outer diameter D <b> 1 of the ground electrode 5 is larger than the diameter D <b> 2 of the distal end portion of the inner diameter reduction portion 24. As a result, the outer peripheral edge of the ground electrode 5 can be disposed outside the upper end of the inner diameter reduction portion 24 over the entire circumference. As a result, a large contact area between the housing 2 and the ground electrode 5 can be ensured, and the heat dissipation of the ground electrode 5 can be improved. Further, the ground electrode 5 can be arranged so as to be suspended from the proximal end side of the small inner diameter distal end portion 21 of the housing 2 to a portion supported by the solid portion of the housing 2. Thereby, when joining the ground electrode 5 to the housing 2, it can prevent that the small inner diameter front-end | tip part 21 deform | transforms so that it may fall down to a base end side.

  Moreover, the heat dissipation of the ground electrode 5 can be improved as the outer diameter D1 is increased with respect to the diameter D2, but when the difference between the outer diameter D1 and the diameter D2 exceeds 7 mm, the increase in D1−D2 is accompanied. The effect of improving heat dissipation is reduced. Further, since there is a limit to the reduction in the diameter D2, an increase in D1-D2 means an increase in D1, leading to an increase in material cost of the ground electrode 5 and an increase in manufacturing cost accompanying an increase in welded parts. Therefore, the difference between the outer diameter D1 and the diameter D2 is 7 mm or less.

  As described above, according to this example, it is possible to provide a spark plug for an internal combustion engine that has a long life, easily improves ignitability, and easily adjusts the spark discharge gap.

(Example 2)
In this example, as shown in FIGS. 7 and 8, a ventilation path 12 is formed between the reduced diameter portion 21 and the ground electrode 5 so as to connect the inner peripheral end and the outer peripheral end of the joint surface of both. It is an example of the spark plug 1 being made.

  The ventilation path 12 is formed as follows. A vent groove 213 extending from the inner peripheral end to the outer side of the outer periphery of the ground electrode 5 is formed on the distal end surface 211 of the reduced diameter portion 21. By arranging the ground electrode 5 so as to cover a part of the ventilation groove 213 from the tip side, the ventilation path 12 is formed between the reduced diameter portion 21 and the ground electrode 5.

A plurality of ventilation paths 12 are formed radially on the distal end surface 211 of the reduced diameter portion 21 in the plug radial direction. In this example, four ventilation paths 12 are provided at equal intervals in the plug circumferential direction.
Others are the same as in the first embodiment. Of the reference numerals used in this example or the drawings relating to this example, the same reference numerals as those used in the first embodiment denote the same components as in the first embodiment unless otherwise specified.

In the case of this example, it is possible to effectively prevent the gas from remaining in the internal space 13 at the distal end portion of the housing 2. That is, gas enters and leaves the internal space 13 between the inner diameter reduced portion 24 of the housing 2 and the outer diameter reduced portion 32 of the insulator 3 through the gap between the center electrode 4 and the ground electrode 5, that is, the spark discharge gap. However, since the spark discharge gap is narrow, if the spark discharge gap is long in the plug axis direction, there is a possibility that gas does not easily enter and exit the internal space 13. Therefore, by providing the ventilation path 12 between the ground electrode 5 and the reduced diameter portion 21, gas can enter and exit the internal space 13 also from the ventilation path 12, and gas can be replaced efficiently. Can do. As a result, the gas flow in the spark discharge gap can be efficiently formed, and the ignitability can be improved.
In addition, the same effects as those of the first embodiment are obtained.

  In the second embodiment, an example in which the ventilation path 12 is formed by providing the ventilation groove 213 in the distal end surface 211 of the reduced diameter portion 21 is shown. However, the proximal end surface 52 of the ground electrode 5 is formed in the plug radial direction. The ventilation path may be formed by forming an extending groove.

  Further, the inner diameter reduced portion of the housing may have a shape other than the tapered shape as long as the inner diameter decreases toward the distal end side. For example, the inner diameter may be gradually reduced toward the tip side, or the cross-sectional shape including the plug center axis may be a curved shape. The same applies to the shape of the outer diameter reduced portion of the insulator.

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Housing 21 Reduced-diameter part 211 (the diameter-reduced part) front end surface 23 Engagement step part 24 Inner diameter reduction part 3 Insulator 31 Engagement step part 32 Outer diameter reduction part 4 Center electrode 41 Outer circumference (of center electrode) Surface 5 Ground electrode 51 Inner peripheral surface (of ground electrode)

Claims (6)

A tubular housing (2);
A cylindrical insulator (3) held inside the housing (2);
A central electrode (4) that is held inside the insulator (3) and protrudes toward the tip of the insulator (3);
An annular ground electrode (5) fixed to the front end side of the housing (2),
The housing (2) has a reduced diameter portion (21) having an inner diameter (D4) smaller than that of the other portion at the tip of the housing (2),
The ground electrode (5) is disposed so as to protrude on the distal end surface (211) of the reduced diameter portion (21), and the inner peripheral surface (51) of the ground electrode (5) is disposed on the center electrode ( 4) arranged to face the outer peripheral surface (41),
The outer diameter (D1) of the ground electrode (5) is smaller than the outer diameter (D0) of the distal end surface (211) of the reduced diameter portion (21),
The insulator (3) has a locked step (31) locked in the plug axial direction with respect to a locking step (23) provided on the inner peripheral side of the housing (2). And an outer diameter reduced portion (32) whose outer diameter decreases from the locked step portion (31) toward the distal end side,
The inner surface of the housing (2), said engaging step portion from (23) to said reduced diameter portion (21), possess an inner diameter reduced portion of an inner diameter toward the distal end side is smaller (24),
The spark plug (1) for an internal combustion engine, wherein the inner diameter reduced portion (24) is formed to the tip side of the insulator (3 ).   2. The internal combustion engine for an internal combustion engine according to claim 1, wherein the outer diameter reduced portion (32) of the insulator (3) and the inner diameter reduced portion (24) of the housing (2) each have a tapered shape. Spark plug (1).   The spark plug (1) for an internal combustion engine according to claim 2, wherein an outer diameter D1 of the ground electrode (5) is larger than a diameter D2 of a distal end portion of the inner diameter reduction portion (24).   The spark plug (1) for an internal combustion engine according to claim 3, wherein the difference between the outer diameter D1 and the diameter D2 is 7 mm or less.   Between the reduced diameter portion (21) and the ground electrode (5), a ventilation path (12) formed so as to connect the inner peripheral end and the outer peripheral end of the joint surface of both is formed. A spark plug (1) for an internal combustion engine according to any one of claims 1-4.   A vent groove (213) extending from the inner peripheral end to the outer side of the outer periphery of the ground electrode (5) is formed on the distal end surface (211) of the reduced diameter portion (21). The vent groove (213) The ground electrode (5) is disposed so as to cover a part of the ground from the tip side, whereby the ventilation path (12) is formed between the reduced diameter portion (21) and the ground electrode (5). A spark plug (1) for an internal combustion engine according to claim 5, characterized in that it is provided.

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