JP5492244B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug used for an internal combustion engine or the like.

  The spark plug is attached to, for example, an internal combustion engine (engine) and used for igniting an air-fuel mixture in the combustion chamber. In general, a spark plug is provided at a cylindrical insulator extending in the axial direction, a central electrode inserted into the insulator, a metal shell provided on the outer periphery of the insulator, and a tip of the metal shell, And a ground electrode that forms a spark discharge gap with the center electrode. In addition, the insulator includes, on the outer periphery thereof, a tapered portion that increases in diameter toward the distal end side, and a step portion that decreases in diameter toward the distal end side at the distal end side with respect to the tapered portion. The insulator is locked to the metal shell directly or indirectly at the stepped portion.

  In addition, a talc is provided between the metal shell and the insulator in order to improve the airtightness between the metal shell and the insulator. The talc is in contact with the tapered portion of the insulator on the rear end side of the metal shell (see, for example, Patent Document 1). In general, the talc is arranged between the metal shell and the insulator and then pressed with a predetermined pressing jig to increase the packing density in order to improve the airtightness more surely.

JP 2006-92955 A

  By the way, when filling (pressing) the talc, a force is applied to the tapered portion or the step portion of the insulator. For this reason, the tapered portion or the stepped portion may move along the radial direction, and the axis of the insulator may be displaced or inclined with respect to the central axis of the metal shell. If an axial deviation or inclination occurs, there is a risk that abnormal spark discharge such as a horizontal spark is likely to occur between the center electrode and the metal shell. In particular, in order to meet the demand for a smaller diameter, spark plugs in which the distance along the radial direction between the tip of the insulator and the inner periphery of the metal shell is set to be relatively small have little shaft misalignment or inclination. Even if it is a thing, generation | occurrence | production of abnormal spark discharge is a concern.

  In recent years, the distance between the tapered portion and the step portion along the axis can be increased in order to increase the length of the spark plug. However, in such a spark plug, the moving amount of the taper portion and the step portion is very small. Even if it is a thing, axis deviation and inclination will become a big thing. That is, in a spark plug in which the distance along the radial direction between the tip of the insulator and the inner periphery of the tip of the metal shell is relatively small, and the distance between the taper and step along the axis is relatively large. However, it is necessary to keep the axis misalignment and inclination very small to suppress abnormal discharge, and high axis alignment accuracy is required. .

  The present invention has been made in view of the above circumstances, and its purpose is that the distance along the radial direction between the distal end portion of the insulator and the inner periphery of the distal end of the metal shell is relatively small, and the axis is In the spark plug having a relatively large distance between the taper portion and the step portion along the axis, it is to dramatically improve the alignment accuracy between the axis of the insulator and the central axis of the metal shell.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The spark plug of this configuration includes an insulator having an axial hole extending in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A cylindrical metal shell disposed on the outer periphery of the insulator;
Comprising a talc filled between the insulator and the metal shell,
The insulator is
A taper portion that expands toward the tip end in the axial direction and contacts the talc,
A step portion that is positioned closer to the distal end side in the axial direction than the tapered portion, has a diameter reduced toward the distal end side in the axial direction, and the metallic shell is directly or indirectly locked; and orthogonal to the axial line The distance between the inner periphery of the front end of the metal shell and the insulator along the direction to be 1.5 mm or less,
A spark plug whose distance from the tip of the tapered portion to the rear end of the step portion along the axis is 22.5 mm or more,
In a cross section including the axis,
The acute angle among the angles formed between the outline of the tapered portion and the straight line orthogonal to the axis is α, and the acute angle of the angles formed between the external line of the stepped portion and the straight line orthogonal to the axis is β In this case, 63 ° ≦ α ≦ 73 °, 23 ° ≦ β ≦ 45 °, and 93 ° ≦ α + β ≦ 115 ° are satisfied.

  In addition, in the cross section including the axis, when the outline of the tapered portion is a curved line or formed by a plurality of line segments extending in different directions (that is, not linear), the angle α is Means an acute angle among angles formed by a straight line connecting the rear end and the front end of the tapered portion and a straight line orthogonal to the axis. Also, in the cross section including the axis, when the outline of the step portion is not linear, the angle β is the angle between the straight line connecting the rear end and tip of the step portion and the straight line orthogonal to the axis. An acute angle.

  According to the said structure 1, it is comprised so that the angle (alpha) of the taper part which a talc contacts may satisfy | fill 63 degrees <= (alpha). Therefore, when filling the talc, in addition to the upper side of the talc (the rear end side in the axial direction), the lower side of the talc (the front end side in the axial direction) will also collapse sufficiently, and the particle size of the talc will be small overall. be able to. Thereby, the packing density of the talc can be made uniform, and the pressing force at the time of filling can be more reliably prevented from being diffused or absorbed by the talc. As a result, the pressing force at the time of filling can be more reliably transmitted to the tapered portion or the stepped portion.

  Then, the pressing force applied to the tapered portion as the talc is filled is decomposed into a force along the tapered portion and a force orthogonal to the tapered portion and pressing the tapered portion toward the axis (see FIG. 9). According to the configuration 1, since the angle α of the tapered portion is configured to satisfy α ≦ 73 °, the force for pressing the tapered portion toward the axis can be made larger. As a result, as described above, in combination with the fact that 63 ° ≦ α is satisfied and the pressing force is more reliably transmitted to the tapered portion, the movement along the radial direction in the tapered portion is extremely effectively suppressed. Can do.

  Further, the pressing force applied to the step portion with the filling of the talc is decomposed into a force orthogonal to the step portion and a force pressing the step portion toward the axis along the step portion (see FIG. 10). According to the configuration 1, since it is configured to satisfy 23 ° ≦ β ≦ 45 °, the force for pressing the step portion toward the axis can be increased. As a result, coupled with the fact that the pressing force is more reliably transmitted to the step portion, it is possible to extremely effectively suppress the movement along the radial direction in the step portion.

  In addition, the configuration 1 is configured to satisfy 93 ° ≦ α + β ≦ 115 °. Therefore, both the force that presses the taper portion toward the axis side and the force that presses the step portion toward the axis line side can be increased more reliably. Therefore, the movement along the radial direction can be more reliably suppressed in both the tapered portion and the stepped portion.

  As described above, according to Configuration 1, the accuracy of alignment between the axis of the insulator and the central axis of the metal shell can be drastically improved due to the synergistic action of the above-described effects.

Configuration 2. The spark plug of this configuration includes an annular front end side packing that contacts the tapered portion and the talc between the insulator and the metal shell in the configuration 1,
The length of the tapered portion along the axis is L2 (mm), and the distance along the axis from the rear end of the tip-side packing that contacts the tapered portion to the tip of the tapered portion is L3. (Mm), L3 ≦ 0.8 × L2 is satisfied.

  According to the said structure 2, since it is comprised so that L3 <= 0.8 * L2 may be met, a talc can be made to contact with the wider range of a taper part. Therefore, the force that presses the tapered portion toward the axial line can be further increased, and the movement of the tapered portion along the radial direction can be more effectively suppressed. As a result, it is possible to further improve the alignment accuracy.

Configuration 3. The spark plug of the present configuration includes an annular rear end side packing disposed between the insulator and the metal shell, with the talc sandwiched between the front end side packing and the insulator in the configuration 2.
In the cross section including the axis, the front end side packing and the rear end side packing are circular in cross section, and the diameter of the front end side packing is smaller than the diameter of the rear end side packing.

  When the packing is deformed due to talc filling, the “packing diameter” refers to the diameter of a circle having the same area as the cross-sectional area of the packing.

  According to the configuration 3, since the diameter of the tip side packing is relatively small, the talc can be brought into contact with a wider range of the tapered portion. Therefore, the movement along the radial direction in the tapered portion can be further suppressed, and the alignment accuracy can be further improved.

  Configuration 4. The spark plug of this configuration is characterized in that, in any one of the above configurations 1 to 3, at least a surface of the insulator where the talc is located on the outer periphery is covered with a glaze layer.

  According to the said structure 4, the surface of the site | part in which an talc is located in an outer periphery among the insulators is covered with the glaze layer. Therefore, when filling the talc, the frictional force generated between the insulator and the talc can be reduced, and the talc can be more easily flowed to the lower side (the front end side in the axial direction). Thereby, the packing density of the talc can be made more uniform, and the pressing force at the time of filling can be transmitted to the taper part and the step part more reliably. As a result, it is possible to further improve the alignment accuracy.

It is a partially broken front view which shows the structure of a spark plug. (A) is a partial expanded sectional view which shows the structure of a taper part, etc., (b) is a partial enlarged sectional view which shows the structure of a step part, etc. (A), (b) is a partial expanded sectional view which shows another example of a taper part. (A), (b) is the elements on larger scale which show another example of a step part. It is a partial expanded sectional view which shows length L2, distance L3, etc. FIG. It is a partially broken front view which shows one process of a talc filling process. It is a partially broken front view which shows one process of a talc filling process. It is a bottom face schematic diagram of a spark plug tip part for explaining deviation X. It is a cross-sectional schematic diagram for demonstrating the force added to a taper part. It is a cross-sectional schematic diagram for demonstrating the force added to a step part. It is a graph which shows the result of the centering precision evaluation test in the case of changing L3 / L2 variously. It is a graph which shows the result of the centering precision evaluation test in the case of changing the presence or absence of the glaze layer.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the direction of the axis CL <b> 1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

  The spark plug 1 includes an insulator 2 as a cylindrical insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, from the rear end side body portion 10 formed on the rear end side and from the front end of the rear end side body portion 10. A tapered portion 11 extending toward the distal end side and expanding toward the distal end side in the axis CL1 direction, a large diameter portion 12 projecting radially outward on the distal end side relative to the tapered portion 11, and the large diameter portion The middle barrel portion 13 formed with a smaller diameter on the tip side than 12, and a step portion 14 extending from the tip of the middle barrel portion 13 toward the tip side and reducing in diameter toward the tip side in the axis CL1 direction. And a leg length portion 15 formed on the tip side of the step portion 14. In addition, of the insulator 2, the tapered portion 11, the large diameter portion 12, the middle trunk portion 13, the step portion 14, and most of the leg length portions 15 are accommodated inside the metal shell 3. Further, the insulator 2 is locked to the metal shell 3 at the stepped portion 14.

  Further, a shaft hole 4 extending in the direction of the axis CL <b> 1 is formed through the insulator 2, and a center electrode 5 is inserted and fixed to the tip side of the shaft hole 4. The center electrode 5 includes an inner layer 5A made of a metal having excellent thermal conductivity (for example, copper, copper alloy, pure nickel (Ni), etc.) and an outer layer 5B made of an alloy containing Ni as a main component. The center electrode 5 has a rod shape (cylindrical shape) as a whole, and a tip portion of the center electrode 5 projects from the tip of the insulator 2.

  In addition, a terminal electrode 6 is inserted and fixed on the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2.

  Further, a cylindrical resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seal layers 8 and 9, respectively.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw for attaching the spark plug 1 to a combustion device such as an internal combustion engine or a fuel cell reformer on the outer peripheral surface thereof. A portion (male screw portion) 16 is formed. Further, a seat portion 17 is formed to bulge toward the outer peripheral side at the rear end side of the screw portion 16, and a ring-shaped gasket 19 is fitted into a screw neck 18 at the rear end of the screw portion 16. Further, a tool engaging portion 20 having a hexagonal cross section is provided on the rear end side of the metal shell 3 for engaging a tool such as a wrench when the spark plug 1 is attached to the combustion device. A caulking portion 21 that bends inward in the radial direction is provided at the rear end portion of the metal shell 3.

  Further, a protrusion 22 for locking the insulator 2 is formed on the inner peripheral surface of the metal shell 3 so as to protrude radially inward. The insulator 2 is inserted from the rear end side to the front end side with respect to the metal shell 3, and the rear end side of the metal shell 3 with the stepped portion 14 locked to the protrusion 22. Are fixed to the metal shell 3 by caulking the opening portion inward in the radial direction, that is, by forming the caulking portion 21. An annular plate packing 23 is interposed between the stepped portion 14 and the protrusion 22. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas entering the gap between the leg long portion 15 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, each is made annular with a predetermined metal (for example, iron or the like). The formed front end side packing 24 and rear end side packing 25 are provided, and between the packings 24 and 25, powder of talc 26 is filled.

  The front end packing 24 is in contact with the tapered portion 11 and has a circular cross section in a cross section including the axis CL1. Further, the rear end side packing 25 is in contact with the inner peripheral surface of the crimping portion 21 of the metal shell 3 and the rear end side body portion 10 of the insulator 2 on the rear end side with respect to the front end side packing 24. The cross section including the axis CL1 has a circular cross section. In addition, the talc 26 is disposed between the packings 24 and 25 and then pressed and filled by a cylindrical talc press jig 46, which will be described later, toward the tip side in the direction of the axis CL1. Yes.

  Further, a substantially intermediate portion is bent back at the distal end portion of the metal shell 3, and a ground electrode 27 whose distal side surface faces the distal end portion of the center electrode 5 is joined. A spark discharge gap 28 is formed between the tip of the center electrode 5 and the tip of the ground electrode 27, and spark discharge is performed in the spark discharge gap 28 in a direction substantially along the axis CL1. It has come to be.

  In the present embodiment, the metal shell 3 is reduced in diameter in order to reduce the diameter of the spark plug 1. Therefore, the screw diameter of the screw portion 16 is a relatively small diameter (for example, M12 or less). As a result, the direction perpendicular to the axis CL1 between the inner periphery of the tip of the metal shell 3 and the tip of the insulator 2 is obtained. The distance K along the line is 1.5 mm or less. That is, when the axis CL1 of the insulator 2 is tilted or deviated from the central axis of the metal shell 3, the shortest distance between the inner periphery of the tip of the metal shell 3 and the insulator 2 is very large. Thus, an abnormal discharge (so-called side fire) is likely to occur between the center electrode 5 over the surface of the insulator 2 and the tip of the metal shell 3.

  In addition, the spark plug 1 in the present embodiment has a relatively long length along the axis CL1, and the distance L from the tip of the tapered portion 11 to the rear end of the step portion 14 along the axis CL1. Is 22.5 mm or more. That is, even if the movement amount of the taper part 11 and the step part 14 at the time of filling the talc 26 is very small, the axial deviation and the inclination are relatively large.

  As described above, the spark plug 1 according to the present embodiment needs to keep the axis deviation and inclination very small in order to suppress abnormal discharge even though the axis deviation and inclination are likely to be large at the time of manufacture. And high alignment accuracy is required.

  In view of this point, in the present embodiment, the insulator 2, the packings 24, 25, and the like are configured as follows in order to more reliably prevent the axial displacement of the insulator 2 with respect to the metal shell 3.

  That is, as shown in FIGS. 2A and 2B (in FIG. 2 to FIG. 4, the hatching of the insulator 2 is omitted for the sake of illustration), the taper portion in the cross section including the axis line CL <b> 1. 11 is an acute angle among the angles formed by the external line OL1 and the straight line SL1 orthogonal to the axis CL1, and the acute angle is an angle formed between the external line OL2 of the step 14 and the straight line SL2 orthogonal to the axis CL1. Where β is 63 ° ≦ α ≦ 73 °, 23 ° ≦ β ≦ 45 °, and 93 ° ≦ α + β ≦ 115 °.

  As shown in FIGS. 3A and 3B, in the cross section including the axis line CL1, the outline of the taper portion 31 is a curved line, or the outline of the taper portion 32 extends in different directions. The angle α is perpendicular to the axis CL1 and the straight line VL1 (VL2) connecting the rear end and the front end of the tapered portion 31 (32). An acute angle among the angles formed with the straight line SL1.

  Further, as shown in FIGS. 4A and 4B, in the cross section including the axis line CL1, the contour line of the step portion 33 is a curved line, or the contour line of the step portion 34 extends in different directions. The angle β is perpendicular to the axis CL1 and the straight line VL3 (VL4) connecting the rear end and the front end of the step portion 33 (34). An acute angle among the angles formed with the straight line SL2 to be performed.

  In addition, in this embodiment, as shown in FIG. 5, the length of the tapered portion 11 along the axis CL <b> 1 is L <b> 2 (mm), and from the rear end of the portion that contacts the tapered portion 11 in the distal end side packing 24. When the distance along the axis CL1 to the tip of the tapered portion 11 is L3 (mm), L3 ≦ 0.8 × L2 is satisfied. That is, the length L4 along the axis CL1 of the portion where the talc 26 contacts in the tapered portion 11 is configured to be sufficiently larger than the length L2.

  Furthermore, in the cross section including the axis line CL <b> 1, the diameter D <b> 1 of the front end side packing 24 is smaller than the diameter D <b> 2 of the rear end side packing 25. When the front end side packing 24 and the rear end side packing 25 are deformed due to the filling of the talc 26, the “packing diameter” is a circle having the same area as the cross sectional area of the packing. The diameter of

  Moreover, in this embodiment, the whole surface of the said rear end side trunk | drum 10 is covered with the glaze layer. In addition, it is good also as covering only the surface of the site | part in which the talc 26 is located in the outer periphery among the insulators 2 with a glaze layer.

  Next, the manufacturing method of the spark plug 1 comprised as mentioned above is demonstrated.

  First, the metal shell 3 is processed in advance. That is, a rough shape is formed on a cylindrical metal material (for example, an iron-based material or a stainless steel material) by cold forging or the like, and a through hole is formed. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, a straight bar-shaped ground electrode 27 made of an Ni alloy is resistance-welded to the front end surface of the metal shell intermediate. During the welding, so-called “sag” is generated, and after the “sag” is removed, the threaded portion 16 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 3 to which the ground electrode 27 is welded is obtained. In addition, the rear-end part of the obtained metal shell 3 is cylindrical (that is, the caulking part 21 is not formed).

  Next, the metal shell 3 to which the ground electrode 27 is welded is subjected to zinc plating or nickel plating. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

  On the other hand, the insulator 2 is formed separately from the metal shell 3. For example, by using a raw material powder mainly composed of alumina and containing a binder or the like, a green compact for molding is prepared, and a rubber-molded product is used to form a cylindrical molded body. Is obtained. The obtained molded body is ground and shaped, and the shaped product is fired in a firing furnace, whereby the insulator 2 is obtained.

  Separately from the metal shell 3 and the insulator 2, the center electrode 5 is manufactured. That is, the center electrode 5 is produced by forging a Ni alloy in which a copper alloy or the like for improving heat dissipation is arranged at the center.

  Next, the insulator 2 and the center electrode 5, the resistor 7, and the terminal electrode 6 obtained as described above are sealed and fixed by the glass seal layers 8 and 9. The glass seal layers 8 and 9 are generally prepared by mixing borosilicate glass and metal powder and injected into the shaft hole 4 of the insulator 2 with the resistor 7 interposed therebetween, and then from the rear. While being pressed by the terminal electrode 6, it is fired by being heated in a firing furnace. At this time, the glaze layer is simultaneously fired on the surface of the rear end side body portion 10 of the insulator 2. A glaze layer may be formed in advance on the surface of the rear end side body portion 10.

  Thereafter, the insulator 2 and the metal shell 3 respectively manufactured as described above are fixed through a talc pressing process.

  More specifically, in the talc pressing process, as shown in FIG. 6, after the insulator 2 is inserted into the metal shell 3, the axis CL1 is aligned along the vertical direction by a metal-made cradle 41. The metal shell 3 is supported so as to extend. At this time, the metal shell 3 is arranged such that its central axis coincides with the central axis of the cradle 41.

  Further, a cylindrical metal guide 42 and an insulator guide 43 are attached to the lower side of the inner periphery of the cradle 41, respectively.

  The metal fitting guide 42 is formed of a predetermined metal material and is urged upward by a first elastic member 44 that can be expanded and contracted along a vertical direction provided below the metal guide 42. Further, at least the inner peripheral side of the upper surface 42A of the metal fitting guide 42 has a tapered shape that gradually decreases toward the outer peripheral side, and when the metal shell 3 is supported by the cradle 41, the upper surface 42A The inner periphery of the tip of the metallic shell 3 contacts the tapered portion. The distal end portion of the metal shell 3 comes into contact with the upper surface 42A (tapered portion) of the metal metal guide 42 biased upward, so that the distal end portion of the metal shell 3 relative to the cradle 41 along the radial direction. Movement is restricted. The upper surface 42A of the metal guide 42 is provided with a recess (not shown) that can accommodate the ground electrode 27. When the metal shell 3 is supported by the metal guide 42, the ground electrode 27 is placed in the recess. Is housed.

  The insulator guide 43 is inserted through the metal guide 42 in a state where the center axis of the insulator guide 43 coincides with the center axis of the metal guide 42, and is formed of a predetermined resin material. Further, a second elastic member 45 that can be expanded and contracted along the vertical direction is provided below the insulator guide 43, and the insulator guide 43 is urged upward by the second elastic member 45. It is in the state. Furthermore, the upper surface 43A of the insulator guide 43 has a tapered shape that gradually increases toward the outer peripheral side. When the metal shell 3 is supported by the cradle 41, the insulator 2 with respect to the upper surface 43A. The outer periphery of the tip of the contact. The distal end portion of the insulator 2 comes into contact with the upper surface 43A of the insulator guide 43 biased upward, so that the relative movement along the radial direction of the distal end portion of the insulator 2 with respect to the cradle 41 is restricted. The A projecting portion 43 </ b> B that protrudes outward in the radial direction and has a larger outer diameter than the inner diameter of the metal fitting guide 42 is provided on the lower side of the insulator guide 43 and exposed from the metal fitting guide 42. . The upper limit position of the insulator guide 43 with respect to the metal fitting guide 42 is set by the protrusion 43B. On the other hand, since the lower limit position of the insulator guide 43 with respect to the metal fitting guide 42 can be adjusted to some extent, even when the spark plug 1 is manufactured with a different amount of protrusion of the insulator 2 relative to the tip of the metal shell 3, The metal fitting guide 42 and the insulator guide 43 can be used in common. In addition, the outer peripheral surface of the metal fitting guide 42 is in contact with the cradle 41 with almost no gap, and the metal fitting guide 42 and the insulator guide 43 cannot move relative to the cradle 41 along their own radial direction. It has become.

  Returning to the description of the manufacturing method, after the metal shell 3 is supported by the cradle 41, an annular space formed between the insulator 2 (the rear end body portion 10 and the taper portion 11) and the metal shell 3. 51, the front end side packing 24 and the talc 26 are arranged in this order.

  Next, as shown in FIG. 7, the cylindrical talc press jig 46 that can move along the direction of the axis CL <b> 1 (vertical) is moved downward, and the talc 26 is pressed by the tip of the talc press jig 46. . The rear end side packing 25 may be arranged on the talc 26 in advance, and the talc 26 may be pressed through the rear end side packing 25.

  After the talc pressing step, the rear end side packing 25 is arranged on the talc 26 after the portion located on the rear end side in the axis CL1 direction of the talc 26 is cut. Next, the insulator 2 and the metal shell 3 are fixed. More specifically, a load directed toward the front end side in the axis line CL1 direction is applied to the opening on the rear end side of the metal shell 3, and the opening is caulked inward in the radial direction, that is, the caulking portion 21 is formed. By doing so, the insulator 2 and the metal shell 3 are fixed.

  Finally, the spark plug 1 is obtained by bending the ground electrode 27 toward the center electrode 5 and adjusting the size of the spark discharge gap 28 formed between the center electrode 5 and the ground electrode 27. .

  As described above in detail, according to the present embodiment, the angle α of the tapered portion 11 with which the talc 26 contacts is configured to satisfy 63 ° ≦ α. Therefore, when filling the talc 26, in addition to the upper side of the talc 26 (the rear end side in the direction of the axis CL1), the lower side of the talc 26 (the front end side in the direction of the axis CL1) is also sufficiently collapsed. Can be small. Thereby, the filling density of the talc 26 can be made uniform, and the pressing force at the time of filling can be more reliably prevented from being diffused or absorbed by the talc 26. As a result, the pressing force at the time of filling can be transmitted to the taper part 11 and the step part 14 more reliably.

  In the present embodiment, since the angle α of the tapered portion 11 is configured to satisfy α ≦ 73 °, the force for pressing the tapered portion 11 toward the axis CL1 can be made larger. . As a result, coupled with the fact that 63 ° ≦ α is satisfied and the pressing force is more reliably transmitted to the tapered portion 11, the movement along the radial direction in the tapered portion 11 can be extremely effectively suppressed. .

  Furthermore, according to the present embodiment, since it is configured to satisfy 23 ° ≦ β ≦ 45 °, the force for pressing the stepped portion 14 toward the axis CL1 can be made larger. As a result, coupled with the more reliable transmission of the pressing force to the step portion 14, the movement along the radial direction in the step portion 14 can be extremely effectively suppressed.

  In addition, the present embodiment is configured to satisfy 93 ° ≦ α + β ≦ 115 °. Therefore, both the force that presses the taper portion 11 toward the axis CL1 and the force that presses the step portion 14 toward the axis CL1 can be increased more reliably. Therefore, the movement along the radial direction in both the tapered portion 11 and the stepped portion 14 can be further reliably suppressed.

  As described above, according to the present embodiment, the above-described operational effects act synergistically, thereby dramatically improving the alignment accuracy between the axis CL1 of the insulator 2 and the central axis of the metal shell 3. Can do.

  Moreover, since it is comprised so that L3 <= 0.8 * L2 may be met, the talc 26 can be made to contact with the wider area of the taper part 11. FIG. Therefore, the force which presses the taper part 11 to the axis line CL1 side can be made still larger, and the movement along the radial direction in the taper part 11 can be suppressed more effectively. As a result, it is possible to further improve the alignment accuracy.

  In addition, in the cross section including the axis line CL1, the front end side packing 24 and the rear end side packing 25 have a circular cross section, and the diameter D1 of the front end side packing 24 is smaller than the diameter D2 of the rear end side packing 25. . For this reason, the talc 26 can be brought into contact with a wider range of the tapered portion 11. Therefore, the movement along the radial direction in the tapered portion 11 can be further suppressed, and the alignment accuracy can be further improved.

  In addition, since the surface of the rear end side body portion 10 is covered with the glaze layer, when the talc 26 is filled, the frictional force generated between the insulator 2 and the talc 26 can be reduced. It can be made easier to flow to the side (tip side in the direction of the axis CL1). Thereby, the filling density of the talc 26 can be made more uniform, and the pressing force at the time of filling can be transmitted to the taper part 11 and the step part 14 more reliably. As a result, it is possible to further improve the alignment accuracy.

  Moreover, in this embodiment, the relative movement along the radial direction of the front-end | tip part of the insulator 2 with respect to the receiving base 41 is controlled by the insulator guide 43 in the talc pressing process. Therefore, the axis CL1 of the insulator 2 and the central axis of the metal shell 3 supported by the cradle 41 can be aligned with higher accuracy.

  Subsequently, a centering accuracy evaluation test was performed on the insulators in which the angle α and the angle β were variously changed in order to confirm the operational effects achieved by the above embodiment. The outline of the centering accuracy evaluation test is as follows. That is, the insulator was inserted into the metal shell, and the front side packing and talc were placed between the metal shell and the insulator, and then the talc was filled (pressed) with the talc press jig. Then, with respect to the obtained spark plug, as shown in FIG. 8, a deviation amount X between the axis of the insulator and the central axis of the metal shell when measured from the front end side in the axial direction is measured. Was calculated as the amount of eccentricity. Here, when the amount of eccentricity is 0.10 mm or less, the evaluation of “◯” is made because the axis of the insulator can be aligned with the center axis of the metal shell very accurately. . On the other hand, when the amount of eccentricity exceeds 0.10 mm, the evaluation of “x” is made because the accuracy of alignment is slightly low.

  Table 1 shows the test results of the test. In Table 1, the numerical values in parentheses indicate “α + β”. In the test, talc was filled without using the insulator guide (that is, without holding the tip of the insulator) (the same applies to the following tests).

As shown in Table 1, when configured to satisfy 63 ° ≦ α ≦ 73 °, 23 ° ≦ β ≦ 45 °, and 93 ° ≦ α + β ≦ 115 °, the axis of the insulator and the center of the metal shell It became clear that the shaft fits very accurately. This is considered to be because the following reasons (1) to (4) acted synergistically.
(1) By setting 63 ° ≦ α, in addition to the upper side of the talc with which the talc press jig comes into contact with the talc, the lower side of the talc is sufficiently broken, and the particle size of the talc Since it became smaller, the packing density of the talc was made uniform, and the pressing force from the jig was transmitted more reliably to the taper part and step part via the talc.
(2) As shown in FIG. 9 (for convenience of illustration, hatching of the insulator and the metal shell is omitted in FIG. 9 and FIG. 10), the pressing force FA applied to the tapered portion with the talc filling is The force FA1 along the taper portion and the force FA2 that presses the taper portion toward the axis line are decomposed, but by setting α ≦ 73 °, the force FA2 becomes sufficiently large, and the radial direction at the taper portion The movement along is suppressed.
(3) As shown in FIG. 10, the pressing force FB applied to the step portion as the talc is filled is decomposed into a force FB1 orthogonal to the step portion and a force FB2 pressing the step portion toward the axis. 23 ° ≦ β ≦ 45 °, the force FB2 becomes sufficiently large, and movement along the radial direction at the stepped portion is suppressed.
(4) By setting 93 ° ≦ α + β ≦ 115 °, both the force FA2 that presses the taper portion toward the axis side and the force FB2 that presses the step portion toward the axis side with the pressing of the talc are sufficient. Therefore, the movement along the radial direction in both the tapered portion and the step portion is more reliably suppressed, and as a result, the inclination and the movement are suppressed in the entire area of the insulator.

  From the above test results, in order to dramatically improve the alignment accuracy between the insulator axis and the central axis of the metal shell, 63 ° ≦ α ≦ 73 °, 23 ° ≦ β ≦ 45 °, and 93 It can be said that it is preferable to configure so as to satisfy ° ≦ α + β ≦ 115 °.

  Next, the above-described centering accuracy evaluation test was performed on samples in which the ratio of the distance L3 to the length L2 (L3 / L2) was variously changed by changing the contact position of the tip side packing with respect to the tapered portion. . FIG. 11 shows the test results of the test.

  As shown in FIG. 11, when configured to satisfy L3 / L2 ≦ 0.8 (that is, L3 ≦ 0.8 × L2), the eccentricity amount is remarkably reduced, and the alignment accuracy is further improved. I found out that This is considered to be because the talc was in contact with a wider area of the tapered portion, and the movement along the radial direction in the tapered portion was effectively suppressed.

  From the result of the above test, it can be said that it is preferable to configure so that L3 ≦ 0.8 × L2 is satisfied from the viewpoint that the axis of the insulator is aligned with the center axis of the metal shell with higher accuracy.

  Next, an insulator sample (with a glaze layer) covering at least the surface of the part where the talc is located on the outer periphery with the glaze layer, and an insulator made up without covering the surface of the part where the talc is located on the outer periphery with the glaze layer Samples (consisting of a glaze layer) were prepared, and the above-described centering accuracy evaluation test was performed on each sample. FIG. 12 shows the test results of the test.

  As shown in FIG. 12, when the surface of the part where the talc is located on the outer periphery of the insulator is covered with the glaze layer, the amount of eccentricity can be further reduced. This is because when the talc is filled, the frictional force generated between the insulator and the talc is reduced, and the talc is more likely to flow downward, so that the density of the talc is more uniform and the force applied to the tapered portion is greater. This is thought to be due to the increase.

  From the results of the above test, it can be said that it is preferable to cover at least the surface of the insulator where the talc is located on the outer periphery with a glaze layer in order to align the axis of the insulator more accurately with the central axis of the metal shell. .

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the stepped portion 14 is indirectly locked to the metal shell 3 (projecting portion 22) via the plate packing 23, but the stepped portion 14 is not provided with the plate packing 23. It is good also as latching to the metal shell 3 directly.

  (B) In the above-described embodiment, the diameter D1 of the front end side packing 24 is configured to be smaller than the diameter D2 of the rear end side packing 25 in the cross section including the axis CL1. May be equal to or larger than the diameter D2 of the rear end side packing 25.

  (C) In the above embodiment, the case where the ground electrode 27 is joined to the tip of the metal shell 3 is embodied. However, a part of the metal shell (or one of the metal tips previously welded to the metal shell is used. The present invention can also be applied to the case where the ground electrode is formed by cutting out the portion (for example, Japanese Patent Laid-Open No. 2006-236906).

  (D) In the above embodiment, the tool engaging portion 20 has a hexagonal cross section. However, the shape of the tool engaging portion 20 is not limited to such a shape. For example, Bi-HEX ( It may be a modified 12-angle) shape [ISO 22777: 2005 (E)] or the like.

1 ... Spark plug 2 ... Insulator (insulator)
3 ... metal shell 4 ... shaft hole 5 ... center electrode 11 ... taper part 14 ... step part 24 ... front end side packing 25 ... rear end side packing 26 ... talc CL1 ... axis

Claims (4)

An insulator having an axial hole extending in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A cylindrical metal shell disposed on the outer periphery of the insulator;
Comprising a talc filled between the insulator and the metal shell,
The insulator is
A taper portion that expands toward the tip end in the axial direction and contacts the talc,
A step portion that is positioned closer to the distal end side in the axial direction than the tapered portion, has a diameter reduced toward the distal end side in the axial direction, and the metallic shell is directly or indirectly locked; and orthogonal to the axial line The distance between the inner periphery of the front end of the metal shell and the insulator along the direction to be 1.5 mm or less,
A spark plug whose distance from the tip of the tapered portion to the rear end of the step portion along the axis is 22.5 mm or more,
In a cross section including the axis,
The acute angle among the angles formed between the outline of the tapered portion and the straight line orthogonal to the axis is α, and the acute angle of the angles formed between the external line of the stepped portion and the straight line orthogonal to the axis is β In this case, the spark plug satisfies 63 ° ≦ α ≦ 73 °, 23 ° ≦ β ≦ 45 °, and 93 ° ≦ α + β ≦ 115 °. Between the insulator and the metal shell, an annular tip side packing that contacts the tapered portion and the talc,
The length of the tapered portion along the axis is L2 (mm), and the distance along the axis from the rear end of the tip-side packing that contacts the tapered portion to the tip of the tapered portion is L3. The spark plug according to claim 1, wherein L3 ≦ 0.8 × L2 when (mm) is satisfied. Between the insulator and the metal shell, provided with an annular rear end side packing arranged with the talc sandwiched between the front end side packing,
3. The cross section including the axis line, wherein the front end side packing and the rear end side packing have a circular cross section, and the diameter of the front end side packing is smaller than the diameter of the rear end side packing. Spark plug as described in.   4. The spark plug according to claim 1, wherein a surface of at least a portion of the insulator where the talc is located on an outer periphery is covered with a glaze layer. 5.

Images