JP6707404B2 - Spark plug - Google Patents

Description

The present invention relates to a spark plug, and more particularly to a spark plug that can easily release heat.

The spark plug includes a ground electrode connected to the metal shell and a center electrode held by the metal shell by an insulator. A voltage is applied between the ground electrode and the center electrode, a spark discharge is generated between the ground electrode and the center electrode, and a mixture exposed between the electrodes is ignited to form a flame kernel. Patent Document 1 discloses a technique of disposing a plurality of insulating members having different characteristics between a center electrode and a metal shell in order to improve heat resistance and insulating properties of the insulator.

JP, 2005-185286, A

However, in the technique disclosed in Patent Document 1, the seam between the insulating members blocks the movement of heat, so that the heat generated by ignition of the air-fuel mixture is accumulated in the insulating members and may cause abnormal heating. There is.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a spark plug capable of easily releasing heat.

Means for Solving the Problems and Effects of the Invention

To achieve this object, according to the spark plug of claim 1, the central electrode has a shaft portion extending along the axis from the front end side to the rear end side, and extends from the rear end of the shaft portion to the outside in the radial direction. The collar part overhangs. A receiving portion that supports the flange portion is formed in the shaft hole of the insulator formed along the axis, and the step portion has a diameter that increases from the front end side toward the rear end side. In the tubular metal shell, which is arranged on the outer side in the radial direction of the insulator, a shelf portion axially opposed to the step portion is formed on the inner peripheral surface. The ground electrode facing the center electrode is connected to the metal shell, and the packing is arranged between the step and the shelf.

The insulator includes a first insulator and a second insulator arranged radially outside the first insulator. The first insulator is formed with the entire length of the shaft hole and the receiving portion, and the second insulator is formed with a step portion on the outer peripheral surface. The first insulator and the second insulator, at least a portion of the surface opposed to each other, irregularities facing the each other physician are formed. The second insulator is such that the axial position of the inner edge of the rear end surface is from the edge on the tip side of the contact surface with which the packing contacts the step portion, and the rear of the contact surface with which the flange portion contacts the receiving portion of the first insulator. It exists between the edges on the edge side. Since the contact surface of the first insulator contacts the rear end surface of the second insulator, the second insulator is sandwiched and held between the first insulator and the metal shell.

Due to the unevenness of the first insulator and the second insulator, the surface area of the facing surface can be increased as compared with the case where there is no unevenness. Since the first insulator and the second insulator have the irregularities facing each other, it is possible to easily transfer heat from the first insulator to the second insulator with the irregularities serving as heat transfer surfaces. The heat transferred to the second insulator is transferred from the packing to the metal shell, and the heat transferred from the rear end surface of the second insulator to the contact surface of the first insulator is transferred from the first insulator to the metal shell. Be done. Therefore, there is an effect that heat can be easily released.

According to the spark plug of claim 2, the unevenness formed on the second insulator is such that the position of the tip in the axial direction is between the edge on the tip side of the contact surface where the packing contacts the step and the second insulator. It exists between the tip. As a result, in addition to the effect of claim 1, there is an effect that the heat transferred from the unevenness to the second insulator can be more easily transferred from the packing to the metal shell.

According to the spark plug of the third aspect, the filling layer is arranged between the irregularities of the first insulator and the second insulator. Since the filling layer contacts the first insulator and the second insulator, heat can be transferred between the first insulator and the second insulator through the filling layer. Therefore, depending on the characteristics of the filling layer, in addition to the effect of claim 1 or 2, there is an effect that the thermal conductivity between the first insulator and the second insulator can be improved.

It is sectional drawing of the spark plug in 1st Embodiment of this invention. It is sectional drawing of the spark plug which expanded a part. It is sectional drawing of the spark plug in 2nd Embodiment. It is sectional drawing of the spark plug in 3rd Embodiment. It is sectional drawing of the spark plug in 4th Embodiment. (A) is a figure which shows the test result of the spark plug in Examples 1-3, (b) is a figure which shows the test result of the spark plug in Examples 4-6.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. 1 is a sectional view taken along a plane including an axis O of a spark plug 10 according to a first embodiment of the present invention, and FIG. 2 is a partially enlarged sectional view of the spark plug 10. 1 and 2, the lower side of the paper is referred to as the front end side of the spark plug 10 and the upper side of the paper is referred to as the rear end side of the spark plug 10. In FIG. 2, illustration of the rear end side of the spark plug 10 is omitted (same in FIGS. 3 to 5).

As shown in FIG. 1, the spark plug 10 includes a metal shell 20, a ground electrode 30, an insulator 40, and a center electrode 70. The metal shell 20 is a substantially cylindrical member fixed to a screw hole (not shown) of the internal combustion engine, and is made of a conductive metal material (for example, low carbon steel).

The metal shell 20 is connected from the rear end side to the front end side along the axis O in the order of the end portion 21, the tool engaging portion 22, the groove portion 23, the seat portion 24, the body portion 25, the shelf portion 27, and the leg long portion 28. There is. The end portion 21 and the groove portion 23 are portions for crimping the insulator 40, and the tool engaging portion 22 is a portion for engaging a tool such as a wrench when attaching the spark plug 10 to the internal combustion engine. In the present embodiment, the metallic shell 20 is formed by cold forging or the like.

The shelf portion 27 is located at the boundary between the inner circumference of the body portion 25 and the inner circumference of the long leg portion 28, and projects inward in the radial direction from the tip of the body portion 25. The shelf portion 27 is formed to have an inner diameter smaller than the inner diameter of the inner peripheral surface 26 of the body portion 25, and the diameter is reduced from the rear end side toward the front end side. A threaded portion 29 is formed on the outer peripheral surface of the body portion 25 and the leg portion 28 on the tip side of the seat portion 24. An annular gasket 98 is fitted between the seat portion 24 and the screw portion 29. The gasket 98 is sandwiched between the seat portion 24 and the internal combustion engine (engine head) and seals the gap between the metal shell 20 and the internal combustion engine when the screw portion 29 is fitted into the screw hole of the internal combustion engine.

The ground electrode 30 includes a metal (for example, nickel-based alloy) electrode base material 31 joined to the tip of the metal shell 20 (end surface of the leg portion 28 ), and a tip 32 joined to the tip of the electrode base material 31. Is equipped with. The electrode base material 31 is a rod-shaped member that bends toward the axis O so as to intersect with the axis O. The tip 32 is a member formed of a noble metal such as platinum, iridium, ruthenium, or rhodium or an alloy containing any of these as a main component, and is joined at a position intersecting the axis O.

The insulator 40 is a member that is held by the metal shell 20 and holds the center electrode 70 in an insulating manner, and includes a first insulator 50 and a second insulator 60. In the present embodiment, the first insulator 50 is a substantially cylindrical member whose main component is alumina, which is excellent in mechanical characteristics and insulation at high temperatures. The second insulator 60 is a substantially cylindrical member formed of aluminum nitride, silicon carbide, or the like having high thermal conductivity. However, the materials of the first insulator 50 and the second insulator 60 are not limited to this, and can be appropriately set according to the purpose.

The first insulator 50 is formed with a shaft hole 51 penetrating along the axis O. In the first insulator 50, the rear portion 52, the protruding portion 53, and the tubular portion 54 are connected in order from the rear end side to the distal end side along the axis O, and the tubular portion 54 (see FIG. 2) has a large diameter portion 56, The small diameter portion 57 and the leg portion 58 are connected along the axis O from the rear end side to the front end side in order. The receiving portion 55 (see FIG. 2) is located at the boundary between the inner circumference of the tubular portion 54 and the inner circumference of the large diameter portion 56, and projects radially inward from the tip of the tubular portion 54. The receiving portion 55 is reduced in diameter from the rear end side toward the front end side.

The second insulator 60 is arranged radially outside the first insulator 50. The second insulator 60 is connected from the rear end side to the front end side along the axis O in the order of the annular portion 61 and the tubular portion 63. The annular portion 61 is arranged radially outside the small diameter portion 57 of the first insulator 50, and the tubular portion 63 is arranged radially outside the leg portion 58 of the first insulator 50. The step portion 62 (see FIG. 2) is located at the boundary between the outer circumference of the annular portion 61 and the outer circumference of the tubular portion 63, and the diameter thereof decreases from the rear end side toward the tip end side.

The metal shell 20 is fixed to the outer periphery of the first insulator 50 and the second insulator 60. In the first insulator 50, the rear end of the rear portion 52 and the tips of the legs 58 are exposed from the metal shell 20. The leg portion 58 is arranged radially inside the leg portion 28 of the metal shell 20 and the tubular portion 63 of the second insulator 60. The leg portion 58 faces the long leg portion 28 with a predetermined gap. The protruding portion 53 is a portion that projects outward in the radial direction of the rear portion 52, and is arranged inside the groove portion 23 of the metal shell 20 in the radial direction.

The center electrode 70 is a rod-shaped electrode in which a core material 73 having a higher thermal conductivity than the electrode base material is embedded inside an electrode base material formed in a bottomed tubular shape. The core material 73 is formed of copper or an alloy containing copper as a main component. The center electrode 70 is disposed inside the leg portion 58 of the first insulator 50 and extends axially outward from the rear end side of the shaft portion 71 and the shaft portion 71 that extends toward the tip side along the axis O. 1 the insulator 50 and the collar portion 72 arranged in the receiving portion 55 (see FIG. 2).

The tip of the shaft portion 71 is exposed from the shaft hole 51, and the tip 74 is joined thereto. The tip 74 is a columnar member formed of a noble metal such as platinum, iridium, ruthenium, or rhodium, or an alloy containing these as the main components, and faces the tip 32 of the ground electrode 30 via a spark gap.

The packing 80 is an annular plate member formed of a metal material such as a mild steel plate that is softer than the metal material forming the metal shell 20. The packing 80 is carburized or carbonitrided as necessary. The packing 80 hermetically closes the metal shell 20 and the second insulator 60.

The terminal fitting 90 is a rod-shaped member to which a high voltage cable (not shown) is connected, and is made of a conductive metal material (for example, low carbon steel). The tip side of the terminal fitting 90 is arranged in the shaft hole 51 of the first insulator 50.

The resistor 93 is a member for suppressing radio noise generated during sparking, and is arranged in the shaft hole 51 between the terminal fitting 90 and the center electrode 70. Glass seals 94 and 95 having conductivity are arranged between the resistor 93 and the center electrode 70 and between the resistor 93 and the terminal fitting 90, respectively. The glass seal 94 contacts the resistor 93 and the center electrode 70, respectively, and the glass seal 95 contacts the resistor 93 and the terminal fitting 90, respectively. As a result, the center electrode 70 and the terminal fitting 90 are electrically connected via the resistor 93 and the glass seals 94 and 95.

On the outer periphery of the rear portion 52 of the first insulator 50, ring members 96, 96 and a powder layer 97 of talc or the like sandwiched between the ring members 96, 96 are arranged. When the end portion 21 of the metal shell 20 is swaged radially inward toward the first insulator 50, the ring member 96 and the powder layer 97 are sandwiched between the protruding portion 53 and the end portion 21, and the first insulation is formed. The body 50 is pressed toward the distal end side in the axial direction. As a result, the packing 80 comes into close contact with the shelf portion 27 of the metal shell 20 and the step portion 62 (see FIG. 2) of the second insulator 60.

As shown in FIG. 2, the first insulator 50 has a contact surface 56a formed at the boundary between the large diameter portion 56 and the small diameter portion 57. The small diameter portion 57 is a portion whose outer diameter is set smaller than the outer diameter of the large diameter portion 56 and larger than the outer diameter of the leg portion 58. The contact surface 56a is a surface formed in a step shape toward the inner side in the radial direction with respect to the outer peripheral surface of the large diameter portion 56.

In the second insulator 60, the stepped portion 62 formed at the boundary between the annular portion 61 and the tubular portion 63 is supported by the shelf portion 27 of the metal shell 20 via the packing 80. The annular portion 61 is formed in an annular shape, and the tubular portion 63 is formed in a cylindrical shape whose outer diameter is smaller than the outer diameter of the annular portion 61 by the amount of the step portion 62. The outer peripheral surfaces of the large-diameter portion 56 of the first insulator 50 and the annular portion 61 of the second insulator 60 are arranged on the same curved surface.

The stepped portion 62 of the second insulator 60 is pressed against the shelf portion 27 of the metal shell 20 via the packing 80, and the position in the axial direction is regulated. When the contact surface 56a of the first insulator 50 is pressed against the rear end surface 64 of the second insulator 60, the axial position of the first insulator 50 is regulated via the second insulator 60. Since the second insulator 60 is held in a state of being sandwiched between the shelf portion 27 of the metal shell 20 and the contact surface 56a of the first insulator 50, the second insulator 60 is retained with respect to the first insulator 50 by the second insulator. 60 can be firmly fixed.

In the second insulator 60, the tip of the tubular portion 63 is arranged inside the leg elongated portion 28 of the metal shell 20 in the radial direction. The tip end side (lower side in FIG. 2) of the leg portion 58 of the first insulator 50 projects in the axial direction from the leg long portion 28 of the metal shell 20. The first insulator 50 has irregularities 59 formed on the outer peripheral surface of the boundary between the leg portion 58 and the small diameter portion 57. The second insulator 60 has the unevenness 66 formed on the inner peripheral surface of the cylindrical portion 63 at a position facing the unevenness 59.

The irregularities 59 and 66 have a surface intersecting a straight line L passing through the inner edge 63a of the tip of the second insulator 60 (the tubular portion 63) and the inner edge 65 of the rear end surface 64 in the cross section including the axis O (FIG. 2). I have it. As a result, the surface area of the surface where the first insulator 50 and the second insulator 60 face each other can be increased by the unevenness 59, 66 as compared with the case where the unevenness 59, 66 does not exist.

In the present embodiment, the unevenness 59 is a male screw formed on the outer peripheral surface of the small diameter portion 57, and the unevenness 66 is a female screw formed on the inner peripheral surface of the tubular portion 63. In the first insulator 50 and the second insulator 60, when the concavities and convexities 59 and 66 are engaged with each other and screwed in, the rear end surface 64 of the second insulator 60 abuts on the contact surface 56 a of the first insulator 50. The positions of the contact surface 56a and the irregularities 59 and 66 are set.

Positions P1, P2, P3 and P4 indicate axial positions of each part in a cross section (FIG. 2) including the axis O. The positions P1 of the tips and the positions P2 of the rear ends of the irregularities 59 and 66 are the edge position P3 on the tip side (lower side in FIG. 2) of the contact surface with which the packing 80 contacts the step 62 and the tip of the second insulator 60. And the position (the position of the inner edge 63a). In the second insulator 60, the inner edge 65 of the rear end face 64 is between the position P3 and the position P4 of the edge on the rear end side of the contact surface where the collar portion 72 contacts the receiving portion 55 of the first insulator 50. Exists.

The spark plug 10 is manufactured by the following method, for example. First, the leg portion 58 of the first insulator 50 is inserted from the rear end surface 64 side of the second insulator 60, the concavities and convexities 59 and 66 are engaged with each other, and the first insulator 50 is attached to the rear end surface 64 of the second insulator 60. The abutting surface 56a is pressed to assemble the insulator 40. Next, the center electrode 70 is inserted from the rear portion 52 side of the shaft hole 51 of the first insulator 50. The tip 74 of the center electrode 70 is joined to the tip of the shaft 71. The center electrode 70 is arranged such that the flange portion 72 is supported by the receiving portion 55 and the tip of the shaft portion 71 is exposed to the outside from the tip of the shaft hole 51.

Next, the raw material powder of the glass seal 94 is put in through the shaft hole 51 and filled around the collar portion 72 and the rear end side. The raw material powder of the glass seal 94 filled in the shaft hole 51 is pre-compressed using a compression rod (not shown). The raw material powder of the resistor 93 is filled on the molded raw material powder of the glass seal 94. The raw material powder of the resistor 93 filled in the shaft hole 51 is pre-compressed using a compression rod (not shown). Next, the raw material powder of the resistor 93 is filled with the raw material powder of the glass seal 95. The raw material powder of the glass seal 95 filled in the shaft hole 51 is pre-compressed using a compression rod (not shown).

Then, the tip 81 of the terminal fitting 90 is inserted from the rear end side of the shaft hole 51, and the terminal fitting 90 is arranged so that the tip 81 contacts the raw material powder of the glass seal 95. Next, for example, while heating to a temperature higher than the softening point of the glass component contained in each raw material powder, the front end surface of the overhanging portion 92 provided on the rear end side of the terminal fitting 90 becomes the rear end surface of the first insulator 50. The terminal fitting 90 is press-fitted until they come into contact with each other, and an axial load is applied to the raw material powder of the glass seals 94 and 95 and the resistor 93 by the tip portion 91. As a result, each raw material powder is compressed and sintered, and the glass seals 94 and 95 and the resistor 93 are formed inside the first insulator 50 (insulator 40).

Next, the packing 80 is arranged on the shelf 27 of the metal shell 20 to which the ground electrode 30 has been joined in advance, and then the insulator 40 is axially inserted from the end 21 side of the metal shell 20. After inserting the ring member 96 and the powder layer 97 between the end portion 21 and the first insulator 50, the end portion 21 is fixed by a jig (not shown) having a recess corresponding to the crimped shape of the end portion 21. The end portion 21 is bent radially inward by pressing in the axial direction.

Thereby, the metal shell 20 and the first insulator 50 are fixed. The groove 23 is buckled and bent by the load applied to the metal shell 20. As a result, the protruding portion 53 of the first insulator 50 is pressed by the end portion 21 toward the tip end side in the axial direction via the ring member 96 and the powder layer 97. As a result, the packing 80 is sandwiched between the step portion 62 of the second insulator 60 and the shelf portion 27 of the metal shell 20 via the first insulator 50, and the packing 80 is in close contact.

Then, the tip 32 is bonded to the electrode base material 31 of the ground electrode 30, and the electrode base material 31 is bent so that the tip 32 of the ground electrode 30 and the tip 74 of the center electrode 70 are axially opposed to each other. To get

When the screw portion 29 of the metal shell 20 is attached to the screw hole of the internal combustion engine (not shown), the spark plug 10 exposes the portion protruding from the metal shell 20 to the air-fuel mixture. When a spark discharge is generated between the ground electrode 30 and the center electrode 70 of the spark plug 10 and the ignited mixture explodes, the legs 58 of the first insulator 50 are heated. Since the first insulator 50 and the second insulator 60 have the concavities and convexities 59 and 66 facing each other, the concavities and convexities 59 and 66 are used as a heat transfer surface to conduct heat conduction or heat transfer from the first insulator 50 to the second insulator 60. The heat can be easily transmitted.

Part of the heat transferred from the irregularities 59 and 66 to the second insulator 60 is transferred from the packing 80 to the metal shell 20 by heat conduction. Further, a part of the heat transferred to the second insulator 60 is transferred from the annular portion 61 to the body portion 25 of the metal shell 20 by heat conduction or heat transfer, or from the rear end surface 64 to the first insulator 50. It is also transmitted to the contact surface 56a. The heat transferred to the first insulator 50 is transferred to the metal shell 20 by heat conduction or heat transfer. Since the heat of the legs 58 of the first insulator 50 can be easily released to the metal shell 20, it is possible to prevent the heat from being accumulated in the legs 58 and to easily release the heat. As a result, abnormal heating of the first insulator 50 can be suppressed, and early ignition of the air-fuel mixture can be prevented.

A position P1 on the tip end side in the axial direction of the irregularities 59 and 66 exists between the position P3 of the packing 80 and the position of the tip end of the second insulator 60. As a result, the heat transferred from the irregularities 59 and 66 to the second insulator 60 can be easily transferred from the packing 80 to the metal shell 20. Therefore, the heat of the leg portion 58 of the first insulator 50 can be easily released.

In the second insulator 60, the inner edge 65 of the rear end surface 64 exists between the position P3 of the packing 80 and the position P4 of the receiving portion 55. As a result, the contact surface 56a of the first insulator 50, which faces the rear end surface 64 of the second insulator 60, can be provided closer to the tip end side of the first insulator 50 than the tubular portion 54. Thereby, the area of the contact surface 56a can be secured without affecting the radial thickness of the tubular portion 54.

On the other hand, when the contact surface 56a is provided on the cylindrical portion 54, the protruding portion 53, or the like, the radial thickness of the cylindrical portion 54, the protruding portion 53, or the like is reduced by the contact surface 56a. As a result, the cylindrical portion 54, the protruding portion 53, and the like may be damaged when the spark plug 10 that applies an axial load to the raw material powder of the glass seals 94 and 95 and the resistor 93 filled in the shaft hole 51 is damaged. According to the present embodiment, this can be prevented, and both the radial thickness of the tubular portion 54 and the area of the contact surface 56a can be secured.

Since the unevenness 59 is a male screw and the unevenness 66 is a female screw, the first insulator 50 and the second insulator 60 can be integrated by engaging the unevenness 59 and 66. As a result, when the spark plug 10 is manufactured, the first insulator 50 and the second insulator 60 can be handled as the integrated insulator 40, so that the manufacturing process of the spark plug 10 can be simplified.

When the unevenness 59 (male screw) and the unevenness 66 (female screw) are engaged with each other, the screw flanks of the unevenness 59 and 66 can be brought into close contact with each other. As a result, as compared with the case where heat is transferred between the unevennesses 59 and 66 via air, the heat can move better between the unevennesses 59 and 66, so that the heat of the legs 58 is released to the second insulator 60. It can be done easily.

Next, a second embodiment will be described with reference to FIG. In the first embodiment, the case where the irregularities 59 and 66 of the first insulator 50 and the second insulator 60 are brought into close contact with each other has been described. On the other hand, in the second embodiment, the case where the filling layer 130 is interposed between the unevenness 111 of the first insulator 110 and the unevenness 126 of the second insulator 120 will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 3 is a sectional view of the spark plug 100 according to the second embodiment.

As shown in FIG. 3, the spark plug 100 includes a first insulator 110 and a second insulator 120 that insulate and hold the center electrode 70 with respect to the metal shell 20. The first insulator 110 has a contact surface 56 a formed at the boundary between the large-diameter portion 56 and the leg portion 58, and the outer periphery of the leg portion 58 is provided with the unevenness 111 in which a plurality of annular grooves are arranged in the axial direction. Has been done.

In the second insulator 120, the step portion 122 formed at the boundary between the annular portion 121 and the tubular portion 123 is supported by the shelf portion 27 of the metal shell 20 via the packing 80. The annular portion 121 is formed in an annular shape, and the tubular portion 123 is formed in a cylindrical shape whose outer diameter is smaller than the outer diameter of the annular portion 121 by the amount of the step portion 122.

The position of the first insulator 110 in the axial direction is regulated by the contact surface 56a hitting the rear end face 124 of the second insulator 120. The second insulator 120 has the unevenness 126 formed on the inner peripheral surface of the tubular portion 123 at a position facing the unevenness 111. The unevenness 126 has a shape in which a plurality of annular grooves are arranged in the axial direction. The concavities and convexities 111 and 126 do not have screw-like engagement.

Since the unevenness 126 is formed, in the cross section including the axis O (FIG. 3 ), the second insulating body 120 (cylindrical portion 123) has a first inner edge 123 a and a rear end surface 124 having an inner edge 125 which is larger than a straight line passing through the inner edge 125 a. 2 The contour of the inner peripheral surface of the insulator 120 can be lengthened. Similarly, in the first insulator 110, the contour of the outer peripheral surface of the leg portion 58 can be lengthened by the unevenness 111. As a result, the surface area of the surface where the first insulator 50 and the second insulator 60 face each other can be increased by the unevenness 111, 112 as compared with the case where the unevenness 111, 126 does not exist.

The concavities and convexities 111, 112 are opposed to each other with a proper gap therebetween, and the filling layer 130 is disposed between the inner peripheral surface of the second insulator 120 and the outer peripheral surface of the leg portion 58. The filling layer 130 is a solid having heat resistance and heat conductivity, and is in close contact with the first insulator 110 and the second insulator 120. The filling layer 130 includes an inorganic adhesive (so-called cement) and the same material as the glass seal 94 (see FIG. 1) (for example, glass particles such as B ₂ O ₃ —SiO ₂ system) and metal particles such as Cu and Fe. Composition) and the like are used.

Since heat is transferred between the first insulator 110 and the second insulator 120 via the filling layer 130, it depends on the characteristics of the filling layer 130, but between the first insulator 110 and the second insulator 120. The thermal conductivity of can be improved. Since heat conduction is performed by the filling layer 130 even in the unevennesses 111 and 126 having no meshing, the degree of freedom in designing the shape of the unevenness can be improved. The filling layer 130 is preferably provided in a circular ring shape with the axis O substantially as the center, but is not limited to this. That is, it does not necessarily have to be continuous in an annular shape, and may be formed so as not to be continuous in the circumferential direction.

Positions P1, P2, P3 and P4 indicate axial positions of the respective parts in a cross section (FIG. 3) including the axis O. The positions P1 of the tips of the irregularities 111 and 126 are the edge position P3 on the tip side (the lower side in FIG. 3) of the contact surface where the packing 80 contacts the step 122 and the tip position of the second insulator 120 (the inner edge 123a). Position). The position P2 at the rear end of the irregularities 111 and 126 is located on the rear end side (upper side in FIG. 3) of the second insulator 120 than the position P3. In the second insulator 120, the inner edge 125 of the rear end face 124 is between the position P3 and the position P4 of the edge on the rear end side of the contact surface where the collar portion 72 contacts the receiving portion 55 of the first insulator 110. Exists.

In the spark plug 100, a part of the heat transferred from the irregularities 111 and 126 to the second insulator 120 is transferred to the metal shell 20 from the packing 80 by heat conduction. The position P1 on the tip side in the axial direction of the irregularities 111 and 126 exists between the position P3 of the packing 80 and the position of the tip of the second insulator 120, so that heat can be easily transferred from the packing 80 to the metal shell 20. .. In addition, since the position P2 of the rear end in the axial direction of the unevennesses 111 and 126 is located on the rear end side (upper side of FIG. 3) of the second insulator 120 than the position P3 of the packing 80, The heat transferred to the second insulator 120 can be more easily transferred from the second insulator 120 to the metal shell 20. Therefore, the heat of the first insulator 110 can be easily released to the metal shell 20.

Next, a third embodiment will be described with reference to FIG. In the second embodiment, the case where the irregularities 111 and 126 have no meshing has been described. On the other hand, in the third embodiment, a case will be described in which the irregularities 151 and 166 have surfaces that face each other in the axial direction. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 4 is a sectional view of the spark plug 140 according to the third embodiment.

As shown in FIG. 4, the spark plug 140 includes a first insulator 150 and a second insulator 160 that insulate and hold the center electrode 70 with respect to the metal shell 20. In the first insulator 150, a ring-shaped concavo-convex portion 151 is formed in a step shape at the boundary between the small diameter portion 57 and the leg portion 58. In the second insulator 160, a step portion 162 formed at the boundary between the annular portion 161 and the tubular portion 163 is supported by the shelf portion 27 of the metal shell 20 via the packing 80. The annular portion 161 is formed in an annular shape, and the tubular portion 163 is formed in a cylindrical shape whose outer diameter is smaller than the outer diameter of the annular portion 161 by the step portion 162.

The position of the first insulator 150 in the axial direction is regulated via the second insulator 160 by the contact surface 56a abutting the rear end surface 164 of the second insulator 160. In the second insulator 160, a ring-shaped concavo-convex portion 166 is formed in a step shape on the inner peripheral surface of the tubular portion 163 at a position facing the concavo-convex portion 151.

Since the unevenness 166 is formed, in the cross section including the axis O (FIG. 4 ), the second insulating body 160 (cylindrical portion 163) has a first inner edge 163 a and a rear end surface 164 having an inner edge 165 which is more straight than a straight line passing through. 2 The contour of the inner peripheral surface of the insulator 160 can be lengthened. Similarly, in the first insulator 150, the contour of the outer peripheral surface from the small diameter portion 57 to the leg portion 58 can be lengthened by the unevenness 151. As a result, the surface area of the surface where the first insulator 150 and the second insulator 160 face each other can be increased by the unevennesses 151 and 166 as compared with the case where the unevennesses 151 and 166 do not exist.

The outer peripheral surface of the first insulator 150 from the small-diameter portion 57 to the leg portion 58 and the inner peripheral surface of the second insulator 160 face each other with a proper gap. A filling layer 170 that contacts the first insulator 150 and the second insulator 160 is disposed in the gap.

Positions P1, P2, P3, and P4 indicate axial positions of the respective parts in a cross section (FIG. 4) including the axis O. The irregularities 151 and 166 are provided between the front end position P1 and the rear end position P2. The position P1 exists between the position P3 of the edge on the tip side (lower side in FIG. 4) of the contact surface where the packing 80 contacts the step 162 and the position of the tip of the second insulator 160 (the position of the inner edge 163a). To do. In the second insulator 160, the inner edge 165 of the rear end face 164 exists between the position P3 and the position P4.

Since the spark plug 140 is provided with the irregularities 151 and 166 and the filling layer 170, it is possible to easily release the heat of the leg portion 58 of the first insulator 150 to the metal shell 20, as in the third embodiment. Since the irregularities 151 and 166 have surfaces facing each other in the axial direction, the gap between the irregularities 151 and 166 can be made smaller than in the case where the irregularities do not have meshing (see FIG. 3 ). Since the thickness of the filling layer 170 between the irregularities 151 and 166 can be reduced, the cost required for the filling layer 170 can be reduced. Since the thickness of the filling layer 170 can be reduced, even if the filling layer 170 having a relatively low thermal conductivity is used, it is possible to reduce the influence on the heat transfer from the first insulator 150 to the second insulator 200.

Next, a fourth embodiment will be described with reference to FIG. In the first to third embodiments, the position P1 on the tip end side of the irregularities 59, 111, 151, 66, 126, 166 is the second insulator 60, 120, 160, rather than the position P3 of the packing 80. The case where it exists on the front end side of 200 has been described. On the other hand, in the fourth embodiment, the case where the irregularities 193, 204 are located on the rear end side of the second insulator 200 with respect to the position P3 of the packing 80 will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. FIG. 5 is a sectional view of the spark plug 180 according to the fourth embodiment.

As shown in FIG. 5, the spark plug 180 includes a first insulator 190 and a second insulator 200 that insulate and hold the center electrode 70 with respect to the metal shell 20. In the second insulator 200, the step portion 202 formed at the boundary between the annular portion 201 and the tubular portion 203 is supported by the shelf portion 27 of the metal shell 20 via the packing 80. The annular portion 201 is formed in an annular shape, and the tubular portion 203 is formed in a cylindrical shape whose outer diameter is smaller than the outer diameter of the annular portion 201 by the amount of the step portion 202.

The second end face 200 of the second insulator 200 has a shape in which a plurality of concentric rings centering on the axis O are connected in a stepwise manner. In the rear end surface 204, the positions of the plurality of rings (steps) in the axial direction are located toward the front end side (the lower side in FIG. 5) as the position approaches the axis O. The rear end surface 204 formed in a step shape also serves as unevenness. In a cross section including the axis O (FIG. 5), a straight line connecting the inner edge 205 of the rear end face 204 and the inner edge 203a of the tubular portion 203 is parallel to the axis O.

The first insulator 190 includes a large diameter portion 191 connected to the tubular portion 54, and a leg portion 192 having an outer diameter smaller than that of the large diameter portion 191. The leg portion 192 is formed into a cylindrical shape having a diameter smaller than the outer diameter of the large diameter portion 191 by the amount of the contact surface 193. The contact surface 193 is a surface corresponding to the rear end surface 204 of the second insulator 200, and has a shape in which a plurality of concentric rings centering on the axis O are connected in a stepwise manner. The abutment surface 193 is located such that the axial positions of the plurality of rings (steps) are closer to the tip end side (lower side in FIG. 5) toward the axis O. The step-shaped contact surface 103 also serves as unevenness.

Since the rear end surface 204 and the contact surface 193 are formed with irregularities, the rear end surface 204 and the contact surface 193 are compared with a case where the rear end surface and the contact surface are flat surfaces without the irregularities. The surface area of can be increased. As a result, the surface area of the surface where the first insulator 190 and the second insulator 200 face each other can be increased by the amount of the unevenness. Thereby, heat can be easily transferred from the first insulator 190 to the second insulator 200.

Positions P1, P2, P3 and P4 indicate axial positions of the respective parts in the cross section (FIG. 5) including the axis O. The position P1 of the tip and the position P2 of the rear end of the irregularities (the contact surface 193 and the rear end surface 204) are the same as the position P3 of the edge (on the lower side in FIG. 5) of the contact surface with which the packing 80 contacts the step 202. It exists between the position P4. Since the contact surface 193 and the rear end surface 204 of the spark plug 180 also serve as unevenness, it is possible to easily release the heat of the leg portion 58 of the first insulator 190 to the metal shell 20, as in the first embodiment.

The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. In this example, with reference to the spark plug 10 (see FIG. 2) described in the first embodiment, various samples in which the positions of the concavities and convexities 59 and 66 were made different were prepared, and the heat release was examined.

(Example 1)
The first insulator 50 and the second insulator 60 have an axial length of 6 mm from the inner edge 63a at the tip of the second insulator 60 to the position P3 of the packing 80, and the second insulator 60 from the position P3 of the packing 80. The axial length to the rear end face 64 was 6 mm, and the axial length from the rear end face 64 of the second insulator 60 to the position P4 of the collar portion 72 was 2 mm. The screw-shaped irregularities 59 and 66 were provided between the inner edge 63a at the tip of the second insulator 60 and the position P3 of the packing 80 to obtain a spark plug sample in the first embodiment.

(Example 2)
A spark plug sample in Example 2 was obtained in the same manner as in Example 1 except that irregularities 59 and 66 were provided on the inside of the packing 80 in the radial direction so as to overlap the position P3 of the packing 80.

(Example 3)
A spark plug sample in Example 3 was obtained in the same manner as in Example 1 except that irregularities 59 and 66 were provided between the position P3 of the packing 80 and the rear end surface 64 of the second insulator 60.

(Comparative Example 1)
The concavities and convexities 59 and 66 are omitted, and instead, a conical curved surface that connects the inner edge 65 of the rear end surface 64 of the second insulator 60 and the inner edge 63a of the tip is provided in the second insulator and the first insulator. A spark plug sample in Comparative Example 1 was obtained in the same manner as in Example 1 except for the above.

(Example 4)
A spark plug sample in Example 4 was obtained in the same manner as in Example 1 except that the filling layer was provided between the irregularities 59 and 66. For the filling layer, a composition containing B ₂ O ₃ —SiO ₂ based glass particles and metal particles such as Cu and Fe was used. The composition was placed between the irregularities 59 and 66 and heated to a temperature higher than the softening point of the glass component to form a filling layer. The filling layer is the same in Examples 5 and 6 and Comparative Example 2.

(Example 5)
A spark plug sample in Example 5 was obtained in the same manner as in Example 2 except that a filling layer was provided between the irregularities 59 and 66.

(Example 6)
A spark plug sample in Example 5 was obtained in the same manner as in Example 3 except that a filling layer was provided between the irregularities 59 and 66.

(Comparative example 2)
A spark plug sample in Comparative Example 2 was obtained in the same manner as Comparative Example 1 except that the filling layer was provided between the conical curved surfaces where the first insulator and the second insulator face each other.

(Test method)
The screw part 29 of the metal shell 20 of each sample is fitted into the screw hole of the aluminum alloy plate (not shown) having the screw hole penetrating in the thickness direction, and the ground electrode 30 and the first insulator 50 are inserted. The tip end side of the leg portion 58 and the tip end of the center electrode 70 were projected from the plate. The tip of the center electrode 70 was heated with a burner so that the temperature of the tip of the center electrode 70 was 800°C. When the temperature of the tip of the center electrode 70 reached 800° C., the temperature of the leg portion 58 (a point 1 mm away from the tip in the axial direction) of the first insulator 50 was measured.

(result)
FIG. 6A is a diagram showing test results of the spark plugs in Examples 1 to 3, and FIG. 6B is a diagram showing test results of the spark plugs in Examples 4 to 6. The vertical axis represents the temperature (° C.) at the tip of the first insulator. As shown in FIG. 6A, it was found that Examples 1 to 3 can lower the temperature of the first insulator as compared with Comparative Example 1. It was confirmed that by providing unevenness between the first insulator and the second insulator, the heat at the tip of the first insulator can be easily released to the metal shell.

Comparing the first and second embodiments with the third embodiment, rather than providing unevenness on the rear end side of the second insulator 60 with respect to the position P3 of the packing 80, the second insulator 60 from the position P3 of the packing 80 is not provided. It has been found that it is preferable to provide unevenness up to the tip. In particular, it was found that it is preferable to provide the unevenness so as to overlap the position P3 of the packing 80 as in the second embodiment. This is because the heat transferred from the unevenness to the second insulator 60 can be easily released from the packing 80 to the metal shell 20.

As shown in FIG. 6B, it was found that the temperatures of Examples 4 to 6 could be lower than those of Comparative Example 2 even when the filling layer was provided. Comparing FIG. 6A and FIG. 6B, it was found that the temperature of the example 4 can be lowered as compared with the example 1. Similarly, it was found that Examples 5 and 6 can lower the temperature as compared with Examples 2 and 3. It was confirmed that the thermal conductivity between the first insulator and the second insulator can be improved by providing the filling layer.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and various improvements and modifications are possible without departing from the spirit of the present invention. It can be easily guessed. For example, the shapes of the metal shell 20 and the ground electrode 30 are examples, and can be set appropriately. Similarly, the shapes and sizes of the first insulator 50 and the second insulator 60, and the shapes and sizes of the concaves and convexes 59, 66, 111, 126, 151, 166, 193, 204 are merely examples and can be set appropriately. ..

In each of the above embodiments, the case where the irregularities 59, 66, 111, 126, 151, 166, 193, 204 are continuous in the circumferential direction has been described, but the present invention is not necessarily limited to this. Since the irregularities of the first insulators 50, 110, 150, 190 and the irregularities of the second insulators 60, 120, 160, 200 may be opposed to each other, appropriate intervals are provided at a plurality of positions in the circumferential direction, It is of course possible to provide the concavities and convexities at the positions facing each other.

In each of the above embodiments, the case where the chips 42 and 74 are provided on the ground electrode 30 and the center electrode 70 respectively has been described, but the present invention is not limited to this, and the chips 42 and 74 can be omitted. .

In each of the above embodiments, the spark plug 10 in which the resistor 93 is incorporated has been described. However, the present invention is not limited to this, and the resistor 93 can be omitted. In this case, the terminal fitting 90 and the center electrode 70 are joined by the glass seal 94.

In each of the above embodiments, the case where the end portion 21 of the metal shell 20 crimps the first insulator 50 via the ring member 96 and the powder layer 97 has been described, but the embodiment is not limited thereto. It is naturally possible to omit the ring member 96 and the powder layer 97 and crimp the end portion 21 of the metal shell 20 to the protruding portion 53 of the first insulator 50.

Although not described in the fourth embodiment, it is naturally possible to provide a filling layer between the rear end surface 204 (unevenness) and the contact surface 193 (unevenness). By providing the filling layer, the heat transfer performance between the first insulator 190 and the second insulator 200 can be improved. Similarly, it is naturally possible to provide a filling layer between the irregularities 59 and 66 of the first embodiment.

10, 100, 140, 180 Spark plug 20 Metal shell 27 Shelf part 30 Ground electrode 40 Insulator 50, 110, 150, 190 First insulator 51 Shaft hole 55 Receiving part 56a Contact surface 59, 111, 151 Concavo-convex 60, 120,160,200 2nd insulator 62,122,202 Step part 64,124,164 Rear end face 65,125,165 Inner edge 66,126,166 Concavo-convex 70 Center electrode 71 Shaft part 72 Collar part 80 Packing 130,170 Filling Layer 193 Abutment surface (uneven)
204 Rear end surface (uneven)
205 Inner edge O axis

Claims (3)

A center electrode that includes a shaft portion that extends along the axis from the front end side to the rear end side, and a flange portion that projects radially outward from the rear end of the shaft portion,
An insulator provided with a receiving portion that is formed in a shaft hole formed along the axis and that supports the collar portion, and a step portion that increases in diameter from the front end side toward the rear end side,
A cylindrical metal shell, in which a shelf portion that axially faces the step portion is formed on the inner peripheral surface and is arranged on the outer side in the radial direction of the insulator,
A ground electrode connected to the metal shell and facing the center electrode;
A spark plug comprising a packing arranged between the step portion and the shelf portion,
The insulator is a first insulator in which the entire length of the shaft hole and the receiving portion are formed,
A second insulator that is arranged radially outside of the first insulator and has the step portion formed on the outer peripheral surface thereof;
In the second insulator, the axial position of the inner edge of the rear end surface is from the edge on the tip side of the contact surface where the packing contacts the step portion, and the flange portion is provided in the receiving portion of the first insulator. It exists between the rear edge of the contact surface that contacts,
A tip end of the second insulator is located inside of the metal shell in a radial direction, and is located axially rearward of a tip end of the metal shell;
The first insulator includes a contact surface that contacts the rear end surface of the second insulator,
The spark plug, wherein the first insulator and the second insulator each have concavities and convexities facing each other on at least a part of surfaces facing each other. The unevenness formed on the second insulator is such that the position of the tip in the axial direction is between the edge on the tip side of the contact surface where the packing contacts the step and the tip of the second insulator. Spark plug according to claim 1, characterized in that it is present. A filling layer disposed between the irregularities of the first insulator and the second insulator,
The spark plug according to claim 1 or 2, wherein the filling layer is in contact with the first insulator and the second insulator.

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