JP2021190270A - Spark plug for internal combustion engine - Google Patents

Abstract

To provide a spark plug for an internal combustion engine capable of suppressing reduction of shock resistance while securing a conductive path between an electrode head part and a resistor even in a configuration that the electrode head part of a center electrode is shortened.SOLUTION: A spark plug 1 comprises a conductive sealant 6 and a resistor 11 filling a proximal end side of a center electrode 4 inside of an insulator 2 which is held inside of a housing 3. The center electrode 4 includes: a lock part 42, in a tapered surface shape, which is locked to a step part 21 formed on an inner peripheral surface of the insulator 2; and an electrode head part 43 formed in a columnar shape of a larger diameter than that of a base part 41 and including a longitudinal groove 7 on an outer peripheral side face 44. The longitudinal groove 7 is formed in a plug axis direction X at a plurality of positions on the outer peripheral side face 44 and opened on a proximal end side front face 45 of the electrode head part 43, and a maximum depth position P in a plug diameter direction Y is located outside of an inner lock end position P1 on an abutment surface of the lock part 42 and the step part 21.SELECTED DRAWING: Figure 1

Description

The present invention relates to a spark plug for an internal combustion engine.

Spark plugs for internal combustion engines generally have a center electrode held inside a tubular insulator. The tip of the center electrode projects from the tip side of the insulating insulator into the combustion chamber of the internal combustion engine and faces the ground electrode. The base end portion of the center electrode has a locking portion locked to a step portion formed on the inner peripheral surface of the insulating insulator, and an electrode head formed on the proximal end side of the locking portion. Inside the insulator, a sealing material made of conductive glass and a resistor are housed on the base end side of the center electrode, and the center electrode is connected to the center electrode from the outside via these conductive sealing materials and resistors. It is electrically connected to the stem that serves as the feeding part.

Here, the spark plug is required to have durability of the electrode against repeated spark discharges. On the other hand, Patent Document 1 discloses a technique of shortening the electrode head of the center electrode to reduce the capacitance between the center electrode held inside the insulator and the metal housing. Has been done. The base end portion of the center electrode consists of a brim portion that contacts the step portion and a head projecting toward the base end side of the brim portion. There is. At this time, by shortening the conductive portion following the brim portion, the capacitance is reduced, and it becomes possible to suppress the consumption of the electrode chip due to the capacitance discharge.

Japanese Patent No. 060879090

In the technique of Patent Document 1, in order to prevent the sealing height of the conductive sealing material from being lowered due to the shortening of the conductive portion, the insulating portion bonded to the conductive portion is placed on the proximal end side of the conductive sealing material. It protrudes to and is buried in the resistor. With this configuration, it is possible to suppress a decrease in impact resistance due to the adhesion between the insulating portion and the resistor, but since the base end surface of the conductive portion is in contact with the insulating portion, the conductive portion and the resistor are separated from each other. The conductive path to be connected is greatly restricted.

Therefore, the electrical load of the restricted conductive path becomes high, and for example, if the conductive sealing material or the resistor is damaged, there is a possibility that a spark discharge cannot be formed between the gap between the center electrode and the ground electrode. rice field. Further, for example, when an external force in the rotational direction acts on the center electrode due to the vibration transmitted to the spark plug, there is a possibility that the adhesiveness with the conductive sealing material or the resistor may be lowered.

The present invention has been made in view of the above problems, and even in a configuration in which the electrode head of the center electrode is shortened, impact resistance is provided while ensuring a conductive path between the electrode head and the resistor. It is an attempt to provide a spark plug for an internal combustion engine that can suppress a decrease.

One aspect of the present invention is
A cylindrical insulator (2) held inside the tubular housing (3), and
The tip portion (41a), which is held inside the insulating insulator and protrudes from the tip side of the insulating insulator, has a center electrode (4) facing the ground electrode (5).
Inside the insulator, the conductive sealing material (6) filled on the base end side of the center electrode and the resistor (11) electrically connected to the center electrode via the conductive sealing material. A spark plug (1) for an internal combustion engine having
The center electrode is provided on the base end side of the axial base portion (41), and is locked from the base end side to the step portion (21) formed on the inner peripheral surface of the insulating insulator (42). ), And an electrode head (43) formed in a columnar shape having a diameter larger than that of the base portion on the proximal end side of the locking portion and having a vertical groove (7) on the outer peripheral side surface (44).
The vertical grooves are formed in the plug axial direction (X) at a plurality of locations on the outer peripheral side surface, open to the proximal end side surface (45) of the electrode head, and are at the maximum depth position in the plug radial direction (Y). (P) is in the spark plug for an internal combustion engine, which is outside the inner locking end position (P1) on the contact surface between the locking portion and the stepped portion.

In the spark plug for an internal combustion engine, the center electrode held inside the insulating insulator has vertical grooves extending in the plug axis direction from the surface on the proximal end side at a plurality of locations on the outer periphery of the electrode head, so that the insulating insulator can be used. The contact area with the conductive sealing material filled inside increases. Since the conductive sealing material filled in the vertical groove is integrated with the conductive sealing material filled in the outer peripheral side and the proximal end side of the electrode head, the electrode head is insulated via the conductive sealing material. It adheres well to the inside of the conductor. Further, the conductive sealing material filled in the vertical groove improves the fixing strength in the rotational direction. Since the position of the vertical groove having the maximum depth is outside the position of the inner locking end of the locking portion, it is possible to secure the sealing property between the locking portion and the stepped portion at the position where the vertical groove is formed. Therefore, since the impact resistance can be improved while maintaining the conductivity and the sealing property, the axial length of the electrode head can be shortened, the capacitance can be reduced, and the electrode durability can be improved.

As described above, according to the above aspect, even in the configuration in which the electrode head of the center electrode is shortened, the decrease in impact resistance is suppressed while ensuring the conductive path between the electrode head and the resistor. It is possible to provide a spark plug for an internal combustion engine which can provide a spark plug for an internal combustion engine.
The reference numerals in parentheses described in the scope of claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments described later, and limit the technical scope of the present invention. It's not a thing.

In the first embodiment, a plan view of an electrode head as seen from the proximal end side of a center electrode which is a main part of a spark plug for an internal combustion engine, a side view of the center electrode near the electrode head, and an enlarged view of the main part thereof. The whole sectional view of the spark plug for an internal combustion engine in the plug axis direction in Embodiment 1. FIG. The cross-sectional view in the plug radial direction and the plug axial direction which shows the state of the center electrode held inside the insulating insulator of a spark plug in Embodiment 1. FIG. A cross-sectional view in the direction of the plug axis showing the state of the center electrode held inside the insulator in the spark plug of the conventional configuration. 2 is a plan view of the center electrode, which is the main part of the spark plug, as seen from the proximal end side, and a side view of the vicinity of the electrode head in the second embodiment. FIG. 3 is a plan view, a cross-sectional view, and a side view of the vicinity of the electrode head as viewed from the proximal end side of the central electrode, which is the main part of the spark plug, in the third embodiment. FIG. 3 is a process diagram illustrating a method of caulking and assembling the center electrode in the third embodiment. A plan view, a cross-sectional view, and a side view of the vicinity of the electrode head as seen from the base end side of the center electrode, which is the main part of the spark plug, in the modified example of the third embodiment. FIG. 3 is a process diagram illustrating a method of caulking and assembling the center electrode in the modified example of the third embodiment. FIG. 4 is a plan view, a cross-sectional view, and a side view of the vicinity of the electrode head as viewed from the proximal end side of the central electrode, which is the main part of the spark plug, in the fourth embodiment. FIG. 6 is a process diagram illustrating a method of caulking and assembling the center electrode in the fourth embodiment. FIG. 5 is a plan view of the center electrode, which is the main part of the spark plug, as seen from the proximal end side, and a side view of the vicinity of the electrode head in the fifth embodiment. A plan view of the center electrode, which is the main part of the spark plug, as seen from the proximal end side, and a side view of the vicinity of the electrode head in the modified example of the fifth embodiment. A plan view of the center electrode, which is the main part of the spark plug, as seen from the proximal end side, and a side view of the vicinity of the electrode head in the modified example of the fifth embodiment. A plan view of the center electrode, which is the main part of the spark plug, as seen from the proximal end side, and a side view of the vicinity of the electrode head in the modified example of the fifth embodiment.

(Embodiment 1)
An embodiment of a spark plug for an internal combustion engine will be described with reference to FIGS. 1 to 3. As shown in FIGS. 1 and 2, the spark plug 1 of the present embodiment has an insulating insulator 2, a housing 3, a center electrode 4, a ground electrode 5, a conductive sealing material 6, and a resistor 11.
In the present specification, the extending direction of the spark plug 1 is defined as the plug axial direction X, and the direction orthogonal to the plug axial direction X is defined as the plug radial direction Y. Further, in the plug axial direction X, the side inserted into the combustion chamber of the internal combustion engine is referred to as the distal end side, and the opposite side thereof is referred to as the proximal end side.

The tubular insulating insulator 2 is held inside the tubular housing 3, and the center electrode 4 is held inside the insulating insulator 2. In the center electrode 4, the tip portion 41a of the axial base portion 41 projects toward the tip end side of the insulating insulator 2 and faces the ground electrode 5. Inside the insulator 2, the conductive sealing material 6 is filled on the base end side of the center electrode 4, and the resistor 11 is electrically connected to the center electrode 4 via the conductive sealing material 6. ..

The center electrode 4 has a locking portion 42 and an electrode head 43. The locking portion 42 is provided on the base end side of the base portion 41, and is locked to the stepped portion 21 formed on the inner peripheral surface of the insulating insulator 2 from the base end side. The electrode head 43 is formed in a columnar shape having a diameter larger than that of the base 41 on the base end side of the locking portion 42, and has a vertical groove 7 on the outer peripheral side surface 44.

The flutes 7 are formed in the plug axial direction X at a plurality of locations on the outer peripheral side surface 44, and open to the base end side surface 45 of the electrode head 43. Further, the vertical groove 7 is formed so that the maximum depth position P in the plug radial direction Y is outside the inner locking end position P1 on the contact surface between the locking portion 42 and the step portion 21.

The step portion 21 of the insulating insulator 2 has a shape in which the inner peripheral angle portion 21a is located with a gap on the outside of the base portion 41 and extends from the inner peripheral angle portion 21a toward the base end side in a tapered surface shape. The inner locking end position P1 is the innermost position where the locking portion 42 having a tapered surface extending toward the base end side and the step portion 21 abut.

The maximum depth position P of the vertical groove 7 is a position where the recessed portion forming the vertical groove 7 is the deepest and is closest to the plug shaft A in the plug radial direction Y. Preferably, the maximum depth position P is inside the outer locking end position P2 on the contact surface between the locking portion 42 and the stepped portion 21. The outer locking end position P2 is the outermost position where the locking portion 42 and the step portion 21 abut.

Preferably, in the center electrode 4, the electrode head 43 is embedded in the conductive sealing material 6. The electrode head 43 is electrically connected to the resistor 11 via a conductive sealing material 6 filled on the outer peripheral side and the proximal end side thereof. Specifically, the conductive sealing material 6 is in close contact with the outer peripheral side surface 44 and the proximal end side surface 45 of the electrode head 43, and is filled in the vertical groove 7.

With such a configuration, the axial length of the electrode head 43 can be shortened, the adhesiveness thereof can be enhanced, and the impact resistance can be improved, and the sealing property at the locking portion 42 and the conductive path to the outside can be improved. It can be secured and made into a highly reliable spark plug 1.

Hereinafter, the configuration of the spark plug 1 of the internal combustion engine will be described in detail.
In this embodiment, the internal combustion engine is, for example, an automobile engine. As shown in FIG. 2, the spark plug 1 has a housing 3 attached to an engine combustion chamber (not shown), and coaxially holds the center electrode 4 inside the housing 3 via an insulator 2. The center electrode 4 is formed in a substantially cylindrical shape extending in the plug axial direction X, and the housing 3 and the insulating insulator 2 are formed in a substantially cylindrical shape having a cylindrical hole penetrating in the plug axial direction X.

The center electrode 4 has a tip portion 41a having a small diameter continuous with a base portion 41 having a substantially constant diameter, and the tip portion 41a protrudes from the tip end side of the tubular hole of the insulating insulator 2 and is attached to the tip end side of the housing 3. A spark discharge gap G is formed between the electrode 5 and the electrode 5. Here, the plug axial direction X is the axial direction of the spark plug 1 and coincides with the axial direction of the center electrode 4. Similarly, the plug shaft A coincides with the central shaft of the center electrode 4.

Inside the insulator 2, the base end side of the center electrode 4 is filled with a resistor 11 made of conductive ceramics via a conductive sealing material 6 made of conductive glass. On the base end side of the resistor 11, a stem 12 having a substantially cylindrical shaft shape is arranged via a conductive sealing material 60 made of conductive glass. The large-diameter base end portion of the stem 12 projects toward the base end side of the insulating insulator 2 and serves as a feeding terminal connected to an external power source. The center electrode 4 is electrically connected to the stem 12 via the conductive sealing material 6, the resistor 11, and the conductive sealing material 60.

As shown in FIG. 3, the center electrode 4 is integrally provided with a locking portion 42 and an electrode head 43 in this order on the base end side of the base portion 41. The locking portion 42 has a tapered surface shape that expands in diameter toward the proximal end side, and is locked by contacting the tapered planar step portion 21 formed inside the insulating insulator 2 from the proximal end side. To. The electrode head 43 is located on the base end side of the locking portion 42, is formed in a substantially cylindrical shape having a diameter larger than that of the base 41, and is entirely embedded in the conductive sealing material 6.

As shown in the upper and middle views of FIG. 1, the center electrode 4 includes an electrode core material 4A from the base 41 to the electrode head 43, and a covering material 4B that covers the outer peripheral surface thereof with a predetermined thickness. It has a two-layer structure. The electrode core material 4A is made of a metal material having good conductivity (for example, Cu or the like), and the coating material 4B is made of a metal material having good heat resistance (for example, Ni-based alloy or the like). In the present embodiment, the surface 45 on the base end side of the electrode head 43 is a flat surface without unevenness, and the end faces of the electrode core material 4A and the covering material 4B are exposed.

In the electrode head 43, vertical grooves 7 having substantially the same shape are formed at four locations in the circumferential direction of the outer peripheral side surface 44 at equal intervals. Each of the four vertical grooves 7 is formed in the plug axis direction X and has a predetermined width parallel to the plug axis A. One end side opens to the base end side surface 45 of the electrode head 43 and the other end. The side is open to the tapered surface that serves as the locking portion 42. In the plug radial direction Y, the vertical groove 7 has a shape that is recessed in a substantially semicircular shape from the outer peripheral side surface 44 toward the plug shaft A.

As a result, the electrode head 43 has a rotationally symmetric shape (that is, a quadruple symmetric shape) about the plug shaft A. The outer peripheral contour of the electrode head 43 alternates between the contour of the outer peripheral side surface 44 having an outward arc shape, which is a part of the virtual circle C centered on the plug axis A, and the contour of the vertical groove 7 having an inward arc shape. It becomes an uneven arc shape that appears in. Here, the inward arc shape is an arc that is convex on the side toward the plug shaft A, and the outward arc shape is an arc that is convex on the side away from the plug shaft A. In the present embodiment, both the covering material 4B forming the outer peripheral contour of the electrode head 43 and the electrode core material 4A located inside the covering material 4B have an uneven arcuate contour.

In the plug radial direction Y, the groove width W of the vertical groove 7 is the maximum width of the vertical groove 7 opened in the outer peripheral side surface 44, and is preferably smaller than the width W1 (that is, the diameter) of the base 41. .. Here, for example, it is set to about ½ or less of the width W1 of the base 41. The width of the electrode head 43 at the formation site of the vertical groove 7 is smaller than the diameter of the virtual circle C, and the minimum width W2 of the electrode head 43 is larger than the width W1 of the base 41. It is desirable that the contour length A1 of the virtual circle C corresponding to the groove width W of the vertical groove 7 is smaller than the contour length A2 of the outer peripheral side surface 44 between the two vertical grooves 7.

As described above, the groove width W and the groove depth of the vertical groove 7 may be appropriately set within a range in which the outer shape of the electrode head 43 on which the vertical groove 7 is formed does not greatly deviate from the virtual circle C. At this time, the deeper the vertical groove 7, the smaller the minimum width W2, and the farther away from the contour of the virtual circle C. Further, the wider the groove width W, the larger the contour length A1 and the smaller the contour length A2, and the farther away from the contour of the virtual circle C.

In FIG. 3, on the inner peripheral surface of the insulating insulator 2, a tapered surface-shaped step portion 21 whose diameter is expanded toward the proximal end side is provided at the connection portion between the large diameter portion on the proximal end side and the small diameter portion on the distal end side. The locking portions 42 of the center electrodes 4 which are formed and have a similar tapered surface are in close contact with each other. The outermost peripheral edge of the locking portion 42 is connected to the electrode head 43 on the proximal end side thereof, and the insulating insulator is provided by the conductive sealing material 6 filled on the outer peripheral side and the proximal end side of the electrode head 43. The space between the large-diameter portion and the small-diameter portion of 2 is sealed. At this time, since the gap between the base 41 of the center electrode 4 and the small diameter portion of the insulating insulator 2 is open to the engine combustion chamber (not shown), it is important to secure the sealing property by the conductive sealing material 6.

As shown in the lower part of FIG. 1, the locking portion 42 of the center electrode 4 has an R shape in which the inner peripheral edge portion 42a is convex inward, and is connected to the base portion 41 on the distal end side thereof. The outer peripheral edge portion of the locking portion 42 has an R shape that is convex outward. The inner peripheral angle portion 21a of the step portion 21 is located on the outer peripheral side of the inner peripheral edge portion 42a, and the inner peripheral edge portion 21a has an R shape corresponding to the inner peripheral edge portion 42a. As a result, the locking portion 42 is locked on the tapered surface of the step portion 21 with the annular tapered surface extending from the inner peripheral edge portion 42a to the outer outer peripheral edge portion as a substantial contact surface. The innermost position of the contact surface is the inner locking end position P1, and the outermost position is the outer locking end position P2. The effective length L0 of the contact surface is the length obtained by excluding the portion corresponding to the inner peripheral edge portion 42a and the outer peripheral edge portion from the apparent slope length L1, and the inner locking end position P1 and the outer locking end position P2. The slope length between.

At this time, in order to secure the sealing property at the forming position of the vertical groove 7, the vertical groove 7 is formed so that the maximum depth position P, which is the maximum depth, is outside the inner locking end position P1. .. The larger the distance between the maximum depth position P and the inner locking end position P1, the longer the seal length L at the position where the vertical groove 7 is formed. Therefore, at the time of assembly, the conductive sealing material 6 softened by heating can be prevented from leaking into the gap between the small diameter portion of the insulating insulator 2 and the base 41, and the sealing property is improved. Preferably, the seal length L is appropriately set so as to be about 1/4 to 3/4 times (for example, 1/2 times) the effective length L0 of the contact surface.

In the middle view of FIG. 1, the electrode head 43 has a flat shape whose axial length (that is, height H) is shorter than the radial length. In the plug axial direction X, the height H of the electrode head 43 is shorter than the shortest radial length (that is, the minimum width W2 in the plug radial direction Y), and is, for example, about the same as the width W1 of the base 41. There is. The height H1 of the locking portion 42 is lower than the height H of the electrode head 43. The height H of the electrode head 43, the height H1 of the locking portion 42, and the taper angle can be appropriately set within a range in which the desired fixing property and sealing property can be secured.

The number and size of the vertical grooves 7 formed in the electrode head 43 are not necessarily limited, but the plug shaft A is provided at two or more locations, preferably three or more locations in the circumferential direction of the outer peripheral side surface 44. It is desirable that they are evenly distributed in a rotationally symmetric shape centered on them. As a result, the conductive sealing material 6 is evenly filled around the electrode head 43, suppressing the deviation of the central axis of the central electrode 4 and facilitating the position coaxially with the plug shaft A.

In FIG. 3, the inside of the insulating insulator 2 is filled with the conductive sealing material 6 on the outer peripheral side and the proximal end side of the electrode head 43. The conductive sealing material 6 is made of glass containing a conductor such as copper, for example. When assembling the spark plug 1, the center electrode 4 is first inserted from the base end side inside the insulating insulator 2, and the locking portion 42 of the center electrode 4 is locked to the step portion 21 of the insulating insulator 2. Next, the powder material to be the conductive sealing material 6 is filled and arranged so as to cover the electrode head 43 of the center electrode 4, and the powder material to be the resistor 11 is filled on the base end side thereof. A powder material to be a conductive sealing material 60 and a stem 12 are sequentially arranged on the base end side of the resistor 11 (see, for example, FIG. 2).

Then, the insulating insulator 2 on which the stem 12 is arranged is heated to a high temperature to soften the glass layer of the filled powder material and impart fluidity, and then the stem 12 is pressed against the insulating insulator 2 toward the tip side. Then, the softened material is assembled while being compressed. After that, by cooling, each powder material becomes conductive sealing materials 6, 60 and a resistor 11, and is fixed inside the insulating insulator 2. In this process, the conductive sealing material 6 filled around the electrode head 43 enters the inside of the vertical groove 7 between the outer peripheral side surface 44 and the inner peripheral surface of the insulating insulator 2, and is pushed from the base end side. The pressure causes the electrode head 43 and the insulating insulator 2 to come into close contact with each other. At this time, since the vertical groove 7 opens on both the base end side surface 45 and the outer peripheral side surface 44 of the electrode head 43, the conductive sealing material 6 filled inside the vertical groove 7 is the electrode head 43. It is integrated with the conductive sealing material 6 filled on the outer peripheral side and the base end side.

As a result, the electrode head 43 is fixed to the inside of the insulating insulator 2 in a state of being embedded in the conductive sealing material 6 filled around the electrode head 43. Since the electrode head 43 has a plurality of substantially arcuate vertical grooves 7 on the outer periphery, the bonding area with the conductive sealing material 6 is increased to improve the adhesiveness, and the electrode head 43 is combined with the conductive sealing material 6 on the outer peripheral side. The shape is such that it fits unevenly, and the fixing force in the rotational direction is improved. That is, the conductive sealing material 6 filled in the vertical groove 7 of the electrode head 43 receives the force in the rotational direction applied to the center electrode 4 due to the impact force such as combustion gas pressure, heat, and vibration in the engine combustion chamber. , The loosening of the electrode head 43 is suppressed, and the fixing force is maintained.

As shown as a reference form, in the conventional structure shown in FIG. 4, for example, the electrode head 10 of the center electrode 100 has a two-stage structure of a large diameter portion 10A and a small diameter portion 10B on the proximal end side thereof. In that case, although the bonding area with the conductive sealing material 6 can be increased, the structure does not reduce the impact force in the rotational direction. Therefore, a space may be formed due to peeling or breakage of the conductive sealing material 6 in contact with the electrode head 10, and the electrical connection with the conductive sealing material 6 may be poor. Further, as the axial length of the electrode head 10 becomes longer, the capacitance between the electrode head 10 and the housing 3 increases, and the electric charge easily accumulates in the insulating insulator 2, so that the current due to the capacitance discharge is superimposed at the time of ignition. Therefore, it tends to be a factor of electrode wear.

According to the configuration of this embodiment, even in a shape in which the height H of the electrode head 43 is lower than that of the conventional one, it has strong adhesiveness, and it is possible to secure sealing property and conductivity. Further, the capacitance between the electrode head 43 held by the insulator 2 and the housing 3 is reduced, the electrode wear is suppressed, and the life of the spark plug 1 can be extended. Alternatively, it becomes possible to increase the discharge energy at the time of ignition, and by expanding the engine control condition range, it is possible to contribute to the improvement of emissions or the improvement of fuel efficiency.

(Embodiment 2)
As shown in FIG. 5, the present embodiment is a form in which the shape of the electrode head 43 of the center electrode 4 is different from that of the first embodiment. The basic configuration of the spark plug 1 is the same as that of the first embodiment, and the differences will be mainly described below.
In addition, among the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the above-mentioned embodiments represent the same components and the like as those in the above-mentioned embodiments, unless otherwise specified.

Also in this embodiment, the electrode head 43 of the center electrode 4 is formed with vertical grooves 7 extending in the plug axial direction X at four locations in the circumferential direction of the outer peripheral side surface 44. Further, on the surface 45 on the base end side of the electrode head 43, a concave groove 71 having a + groove (that is, a plus groove) shape extending in the plug radial direction Y is formed so as to communicate with the four vertical grooves 7. There is. The concave groove 71 is a groove extending in four directions from the central portion of the proximal end side surface 45 toward the four vertical grooves 7 opening in the proximal end side surface 45, and has a rotationally symmetric shape centered on the plug shaft A. (That is, it has a 4-fold symmetrical shape).

The concave groove 71 is a groove that is recessed in a substantially U shape from the surface 45 on the proximal end side to the distal end side, and the groove width W3 on the surface 45 on the proximal end side is larger than the groove width W of the vertical groove 7 having a substantially semicircular arc shape. It's getting narrower. As described above, by forming the concave groove 71 continuous with the vertical groove 7 in the electrode head 43, the joint area between the electrode head 43 and the conductive sealing material 6 is improved. Further, since the concave groove 71 is integrally formed with the vertical groove 7, the conductive sealing material 6 supplied to the base end side surface 45 of the electrode head 43 at the time of assembly is passed through the concave groove 71. It flows into the vertical groove 7. As a result, the softened conductive sealing material 6 spreads in the space inside the insulating insulator 2, and the residual air inside is expelled, so that a sufficient amount of the conductive sealing material 6 is surely introduced into the vertical groove 7. can do. Then, the conductive sealing material 6 filled in the concave groove 71 and the vertical groove 7 is integrated to improve the adhesiveness.

As a result, the electrode head 43 is more firmly fixed to the inside of the insulating insulator 2 via the conductive sealing material 6 filled around the electrode head 43. Further, in addition to the vertical groove 7 arranged on the outer peripheral side of the electrode head 43, the concave groove 71 arranged on the proximal end side has a rotationally symmetric shape centered on the plug shaft A, so that a force in the rotational direction is obtained. On the other hand, the adhesive strength between the electrode head 43 and the conductive sealing material 6 is improved, and the effect of suppressing peeling or breakage of the conductive sealing material 6 is enhanced. Therefore, it is possible to obtain a highly reliable spark plug 1 by highly achieving both suppression of electrode wear by reducing capacitance and improvement of impact resistance.

The arrangement and shape of the concave groove 71 are not particularly limited, and can be appropriately changed according to the arrangement and shape of the vertical groove 7. For example, when the vertical grooves 7 are formed at six locations in the circumferential direction, the vertical grooves 7 can be radial grooves extending in six directions instead of the + groove shape extending in four directions.

(Embodiment 3)
As shown in FIGS. 6 to 9, the present embodiment is a form in which the structure of the center electrode 4 is different from that of the first embodiment, and the electrode head 43 and the locking portion 42 are configured as separate bodies from the base portion 41. However, it is integrated by assembling. The arrangement and shape of the flutes 7 can be the same as in the first embodiment. The basic configuration of the spark plug 1 is the same as that of the first embodiment, and the differences will be mainly described below.

As shown in FIGS. 6 and 8, in the present embodiment, the center electrode 4 is composed of a base portion 41 having a constant diameter and a large diameter portion 40 fitted to one end side of the base portion 41. The base 41 has a two-layer structure in which the outer periphery of the electrode core material 4A having a predetermined diameter is covered with a covering material 4B having a predetermined thickness, and the large diameter portion 40 serving as the electrode head 43 and the locking portion 42 has a structure. , It is composed of only the electrode core material 4A and is not covered with the covering material 4B. The electrode core material 4A is made of a good conductive material such as Cu, and the coating material 4B is made of a heat resistant material such as a Ni-based alloy.

The large-diameter portion 40 can be, for example, a cylindrical body having a through hole in the plug axial direction X and having the base portion 41 exposed on the base end side surface 45 of the electrode head 43 (see FIG. 6). Alternatively, as a columnar body having a fitting hole on the locking portion 42 side, the base portion 41 may be configured not to be exposed on the base end side surface 45 of the electrode head 43 (see FIG. 8). In either case, as shown in FIGS. 7 and 9, by caulking, the recess 7 can be formed on the outer peripheral side surface 44 of the large diameter portion 40 and can be assembled to the base 41.

At this time, since the large diameter portion 40 is in a position not exposed to the combustion gas with respect to the base 41 exposed to the combustion gas from the engine combustion chamber, it is not necessary to cover the surface with the heat-resistant coating material 4B. .. On the other hand, the Ni-based alloy or the like used as the coating material 4B has a high hardness, whereas the Cu or the like used as the electrode core material 4A has a lower hardness and higher workability. Therefore, by forming the large diameter portion 40 with the electrode core material 4A, caulking assembly can be easily performed. At that time, since the base portion 41 coated with the high-hardness coating material 4B is arranged inside the large-diameter portion 40, it is possible to maintain the strength of the electrode head 43 and withstand hot compression and pressurization. .. Therefore, it is possible to suppress excessive deformation of the large diameter portion 40, and it is possible to suppress deterioration of the sealing property and the fixing property of the electrode head 43 and the locking portion 42.

Specifically, as shown in FIG. 7A, first, the tubular body to be the large diameter portion 40 of FIG. 6 is preformed using the electrode core material 4A, and is coated with the electrode core material 4A. The base 41 of the two-layer structure made of the material 4B is preformed. After that, one end side of the base 41 is press-fitted into the through hole of the large diameter portion 40 to integrate the base 41. In that case, for example, one end side of the base portion 41 to be press-fitted into the through hole of the large-diameter portion 40 may be formed to have a slightly larger diameter than the other portion in anticipation of the reduced diameter in the press-fitting process. desirable.

As shown in FIG. 7B, after integrating the large diameter portion 40 and the base portion 41, a plurality of caulking molds D are arranged around the outer periphery of the large diameter portion 40 to perform caulking processing. The mold surface of the caulking mold D is formed, for example, in a columnar shape having an inward semicircular contour corresponding to the shape of the vertical groove 7 of the first embodiment, and corresponds to the formation position of the vertical groove 7. Placed in place. At this time, the four caulking molds D are positioned so that their respective mold surfaces surround the large diameter portion 40, and are driven in a direction approaching the plug shaft A by a drive unit (not shown) to face the large diameter portion 40. Is pressed against the surface of.

As a result, as shown in FIG. 7 (c), vertical grooves 7 extending in the plug axial direction X are formed at four locations on the outer peripheral side surface 44 of the large diameter portion 40. At the same time, the outer surface of the base 41 is closely fixed to the inside of the through hole of the large diameter portion 40, and the tubular base end side surface of the large diameter portion 40 and the base end side surface of the base 41 exposed inside the tubular base end side surface. Form the base end side surface 45 of the electrode head 43. By forming the base 41 of the center electrode 4 and the large diameter portion 40 separately in this way, the large diameter portion 40 is further processed while maintaining the heat-resistant structure in which the base portion 41 is covered with the covering material 4B. It can be easily assembled by forming it with a highly high-performance electrode core material 4A and caulking it.

As shown in FIG. 9, even when the columnar body having the large diameter portion 40 of FIG. 8 is used, caulking is performed in the same step. Specifically, as shown in FIG. 9A, a large-diameter portion 40 having a fitting hole on the locking portion 42 side and a base portion 41 having a two-layer structure are preformed using the same material. .. Next, the base 41 is fitted into the fitting hole of the large diameter portion 40, integrated by resistance welding, for example, and then, as shown in FIG. 9B, a plurality of caulking is performed around the outer periphery of the large diameter portion 40. The mold D is arranged and the same caulking process is performed.

As a result, as shown in FIG. 9C, vertical grooves 7 extending in the plug axial direction X are formed at four locations on the outer peripheral side surface 44 of the large diameter portion 40. In this case, the base end side surface of the large diameter portion 40 forms the base end side surface 45 of the electrode head 43, and the base end side surface of the base portion 41 is not exposed. Even in this way, the base 41 and the large diameter portion 40 of the center electrode 4 are formed as separate bodies, and the electrode head 43 having the vertical groove 7 can be relatively easily formed by caulking. ..

In the present embodiment, the vertical groove 7 is formed on the outer peripheral side surface 44 of the large diameter portion 40 which is the electrode head 43, but as shown in the second embodiment, the surface 45 on the proximal end side is further formed. It may be configured to have a concave groove 71. In that case, the vertical groove 7 and the concave groove 71 are formed at the same time by arranging a caulking mold having a shape corresponding to the concave groove 71 on the base end side of the large diameter portion 40 and caulking in the same manner. can do.

(Embodiment 4)
As shown in FIGS. 10 to 11, the present embodiment is a form in which the shape of the vertical groove 7 formed on the outer peripheral side surface 44 of the large diameter portion 40 in the center electrode 4 is different from that of the first to third embodiments. .. The electrode head 43 and the locking portion 42 are separated from the base portion 41, and the configuration integrated by assembly is the same as that of the third embodiment. The basic configuration of the spark plug 1 is the same as that of the first embodiment, and the differences will be mainly described below.

As shown in FIG. 10, the center electrode 4 of the present embodiment has a configuration in which a large diameter portion 40 made of a tubular body is fitted to one end side of a base portion 41 having a constant diameter, and becomes a large electrode head 43. A vertical groove 7 is formed on the outer peripheral side surface 44 of the diameter portion 40 so as to open to the surface 45 on the proximal end side of the electrode head 43. The flutes 7 are formed in the plug axial direction X at four locations on the outer peripheral side surface 44, and the end portion on the tip end side extends to a position near the connection portion with the locking portion 42. In that case, for example, at the end portion on the distal end side, the groove width W of the vertical groove 7 becomes narrower toward the distal end side, and the groove depth becomes shallower toward the distal end side, so that the vertical groove 7 can be formed in a hemispherical shape.

In this way, the vertical groove 7 can be shaped so as not to open in the locking portion 42, and the filling amount of the conductive sealing material 6 can be secured by making the axial length as long as possible. At that time, since the cross-sectional area of the vertical groove 7 becomes smaller toward the tip end side, compression at the time of filling the conductive sealing material 6 is improved. Further, since the vertical groove 7 does not open in the locking portion 42, the effect of suppressing the leakage of the conductive sealing material 6 into the gap between the locking portion 42 and the inner base portion 41 is enhanced, and the locking portion 42 increases the effect. Since the sealing area is larger, the sealing property is improved. The axial length of the vertical groove 7 (that is, the maximum length from the surface 45 on the proximal end side to the end portion on the distal end side of the vertical groove 7) is, for example, 1/2 times the height H of the electrode head 43. As described above, the length can be preferably about 3/4 times or more.

As shown in FIG. 11, such a vertical groove 7 can also be formed by the same caulking assembly step. In that case, in FIG. 11A, a large-diameter portion 40 made of a tubular body having a through hole and a base portion 41 having a two-layer structure are previously molded and integrated by press fitting, and then FIG. 11 In (b), the shape of the caulking mold D is changed to correspond to the shape of the vertical groove 7, and caulking is performed. In the caulking type D, the surface shape facing the large diameter portion 40 is formed in an inward arc shape, and at the end portion on the tip side, the surface shape is formed so as to be a hemispherical shape.

As a result, as shown in FIG. 11C, vertical grooves 7 extending in the plug axial direction X and reaching the vicinity of the locking portion 42 are formed at four locations on the outer peripheral side surface 44 of the large diameter portion 40. Here, the large-diameter portion 40 is a cylindrical body having a through hole (see, for example, FIG. 6), but of course, it can also be configured as a columnar body having a fitting hole (see, for example, FIG. 8). ..

(Embodiment 5)
In this embodiment, as shown in FIGS. 12 to 15, the shape and arrangement of the vertical grooves 7 formed on the outer peripheral side surface 44 of the large diameter portion 40 in the center electrode 4 are different from those in the first to fourth embodiments. Is. Here, the configuration in which the electrode head 43 and the locking portion 42 are provided integrally with the base 41 as in the first and second embodiments is illustrated, but as in the third embodiment, the electrode head 43 and the locking portion 42 are separated from the base 41. It can also be installed in. The basic configuration of the spark plug 1 is the same as that of the first embodiment, and the differences will be mainly described below.

In the example shown in FIG. 12, the shape of the vertical groove 7 is a V-shaped recess inward from the outer peripheral side surface 44. The flutes 7 are formed at four locations on the outer peripheral side surface 44 in the plug axial direction X, and are open to the base end side surface 45 of the electrode head 43 and to the locking portion 42 on the tip end side. The shape of the vertical groove 7 may be changed in this way, and a desired effect can be obtained by appropriately setting the groove width W, the depth, and the like of the vertical groove 7.

In the example shown in FIG. 13, instead of forming the vertical grooves 7 at four locations on the outer peripheral side surface 44, they are formed at two locations facing each other with the plug shaft A interposed therebetween. The shape of the vertical groove 7 is an inward semicircular arc. As described above, it is sufficient that the vertical grooves 7 are evenly arranged at at least two places or more on the outer peripheral side surface 44, and the groove width W and the depth of the vertical grooves 7 can be appropriately set. The desired effect is obtained.

In the example shown in FIG. 14, the vertical grooves 7 are arranged at eight locations on the outer peripheral side surface 44. In that case, in addition to the four inwardly semicircular vertical grooves 7 as in the first embodiment, inwardly from the outer peripheral side surface 44 between the two inwardly semicircular vertical grooves 7. It has four vertical grooves 7a that are recessed in a substantially U-shape. The inward U-shaped vertical groove 7a is formed, for example, with a narrower groove width and a deeper groove depth than the inward semicircular vertical groove 7. Even in that case, the vertical groove 7a has the maximum depth position P in the plug radial direction Y outside the inner locking end position P1 on the contact surface between the locking portion 42 and the step portion 21 (for example,). , See FIG. 1), it is desirable to be formed.

When the groove width of the vertical groove 7a is narrowed in this way, the outer shape of the electrode head 43 does not change significantly even if the number of formed portions of the vertical groove 7 is increased, and the groove depth is deepened. , The filling amount of the conductive sealing material 6 can be increased to improve the fixing strength against the force in the rotational direction. It should be noted that all of the eight vertical grooves 7 may have the same shape, for example, an inward semicircular shape or an inward U-shape such as the vertical groove 7a.

In the example shown in FIG. 15, the vertical groove 7 is recessed inward from the outer peripheral side surface 44 into a substantially rectangular groove shape having a predetermined depth. The vertical grooves 7 are formed at four locations on the outer peripheral side surface 44 in the plug axial direction X, and have, for example, a shape having wide openings in which the groove width W is larger than the groove depth. The groove width W can be appropriately set, but is preferably the same as in the first embodiment (see, for example, FIG. 1) with respect to the contour length A2 of the outer peripheral side surface 44 between the two adjacent vertical grooves 7. Therefore, it is preferable that the contour length A1 of the virtual circle C corresponding to the groove width W of the vertical groove 7 has a size equal to or less than the same.

As described above, the shape of the vertical groove 7 may be a shape having a plurality of corners, and can be arbitrarily selected. At this time, for example, by making the groove width W relatively wide and the groove depth relatively shallow, a sufficient amount of the conductive sealing material 6 can be surely filled in the corners of the rectangle, and similarly. The effect of is obtained.

The present invention is not limited to each of the above embodiments, and can be applied to various embodiments without departing from the gist thereof. For example, the concave groove 71 shown in the second embodiment is combined with the vertical groove 7 shown in the first embodiment, but may be combined with the vertical groove 7 having the shape and arrangement shown in the third and subsequent embodiments. Further, in the above embodiment, the vertical groove 7 is arranged in parallel with the plug shaft A, but it may be formed along the plug shaft direction X. For example, the longitudinal direction of the vertical groove 7 is the plug shaft A. On the other hand, it may be slightly inclined.

In the above embodiment, the groove width W of the vertical groove 7 is substantially constant, but the groove width W may be gradually changed in the plug axial direction X. In that case, if the groove width W is formed so as to be narrower toward the tip side, a force in the compression direction acts on the conductive sealing material 6 filled in the vertical groove 7, and the adhesiveness can be improved. preferable. Further, the shape of the vertical groove 7 is not limited to the shape exemplified in the above embodiment, but may be a shape having corners such as an arc shape, a V shape or a U shape, or a rectangle forming a part of a circle or an ellipse, or a shape thereof. Any shape such as a similar shape or a combination thereof can be used.

1 Spark plug 2 Insulator 21 Steps 3 Housing 4 Center electrode 42 Base 42 Locking part 43 Electrode head 44 Outer peripheral side surface 45 Base end side surface

Claims (7)

A cylindrical insulator (2) held inside the tubular housing (3), and
The tip portion (41a), which is held inside the insulating insulator and protrudes from the tip side of the insulating insulator, has a center electrode (4) facing the ground electrode (5).
Inside the insulator, the conductive sealing material (6) filled on the base end side of the center electrode and the resistor (11) electrically connected to the center electrode via the conductive sealing material. A spark plug (1) for an internal combustion engine having
The center electrode is provided on the base end side of the axial base portion (41), and is locked from the base end side to the step portion (21) formed on the inner peripheral surface of the insulating insulator (42). ), And an electrode head (43) formed in a columnar shape having a diameter larger than that of the base portion on the proximal end side of the locking portion and having a vertical groove (7) on the outer peripheral side surface (44).
The vertical grooves are formed in the plug axial direction (X) at a plurality of locations on the outer peripheral side surface, open to the proximal end side surface (45) of the electrode head, and are at the maximum depth position in the plug radial direction (Y). (P) is a spark plug for an internal combustion engine, which is outside the inner locking end position (P1) on the contact surface between the locking portion and the stepped portion. The step portion has a shape that extends in a tapered surface shape from the inner peripheral angle portion (21a) located outside the base portion with a gap to the base end side.
The spark for an internal combustion engine according to claim 1, wherein the inner locking end position is the innermost position where the locking portion having a shape extending in a tapered surface shape toward the base end side and the step portion abut on each other. plug. The maximum depth position is a position where the recessed portion forming the vertical groove is deepest.
The vertical groove according to claim 1 or 2, wherein the maximum depth position (P) is inside the outer locking end position (P2) on the contact surface between the locking portion and the stepped portion. Spark plugs for internal combustion engines. The electrode head is embedded in the conductive sealing material, and is electrically connected to the resistor via the conductive sealing material filled on the outer peripheral side and the proximal end side of the electrode head. The spark plug for an internal combustion engine according to any one of claims 1 to 3. The spark plug for an internal combustion engine according to any one of claims 1 to 4, wherein the electrode head has a concave groove (71) communicating with the vertical groove on the surface on the base end side. The center electrode has a two-layer structure in which the base portion, the locking portion, and the electrode head are integrally provided, and the outer peripheral surface of the electrode core material (4A) is coated with a heat-resistant coating material (4B). The spark plug for an internal combustion engine according to any one of claims 1 to 5. The center electrode has a two-layer structure in which the base portion of the outer peripheral surface of the electrode core material (4A) is coated with a heat-resistant coating material (4B), and the locking portion is located on the base end side of the base portion. The spark plug for an internal combustion engine according to any one of claims 1 to 5, which is configured by fitting a large diameter portion (40) including the electrode head.

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