JP6333210B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug. More specifically, the present invention relates to a spark plug in which convex portions or concave portions are provided on the outer peripheral surface of an insulator.

  Generally, a spark plug used for ignition of an internal combustion engine such as an automobile engine is generally composed of a cylindrical metal shell, a cylindrical insulator disposed in an inner hole of the metal shell, and an inner end of the insulator. A center electrode disposed in the hole, and a ground electrode having one end joined to the distal end side of the metal shell and the other end having a spark discharge gap between the center electrode and the center electrode. The spark plug is subjected to a spark discharge in a spark discharge gap formed between the tip of the center electrode and the tip of the ground electrode in the combustion chamber of the internal combustion engine, and burns the fuel filled in the combustion chamber.

  Incidentally, in recent high-power engines, the impact applied to the insulator due to vibrations caused by pressure fluctuations in the combustion chamber is greater. On the other hand, there is a demand for thinner insulators due to the demand for smaller and smaller diameter spark plugs. That is, even though there is a tendency to cause stress concentration due to an impact applied to the insulator, it is difficult to adopt a method of ensuring strength that can withstand stress by making the insulator thick. Therefore, there is a concern about the occurrence of cracks or the like in a portion of the insulator where stress due to impact or the like is particularly concentrated.

  For example, Patent Document 1 states that “a valley-shaped space is formed in the circumferential direction between the inclined portion (2j) forming the end surface of the diamond portion (2e) and the outer peripheral surface of the middle trunk portion (2g). Therefore, stress concentration tends to occur when a bending moment is applied due to the torsional force of the wrench or other impact force when the plug is attached, but in the present invention, the outer peripheral surface of the inclined portion (2j) Stress concentration is avoided by providing a built-up portion (2k) in a form that fills the valley-like space at each extended intersection with the outer peripheral surface of the trunk portion (2g), and breakage resistance is improved. It can be dramatically improved "(see column 0009 of Patent Document 1).

JP 2003-168540 A

  In the invention described in Patent Document 1, a structure is disclosed in which stress concentration on the insulator due to torsional force by a wrench when attaching the spark plug to the internal combustion engine is disclosed. However, stress on the insulator due to vibration or the like is disclosed. There is no description about the problem of avoiding concentration and its means. On the other hand, in the portion exposed to the combustion gas in the insulator, the vibration due to the pressure fluctuation in the combustion chamber is directly transmitted, so that stress is easily concentrated and easily damaged. In addition, the portion of the insulator that is exposed to the combustion gas is less susceptible to impact than the portion in which the metal shell is fixed to the outer peripheral surface. Therefore, when an impact is applied to the tip of the spark plug when attaching the spark plug to the internal combustion engine, the portion of the insulator that is exposed to the combustion gas is likely to be damaged, and further, the thinner the insulator is, the easier it is to be damaged. Become. Therefore, it is desired to improve the breakage resistance of the part exposed to the combustion gas in the insulator.

  An object of this invention is to provide the spark plug excellent in the fracture resistance of the part exposed to the combustion gas in an insulator.

Means for solving the problems are as follows:
(1) A cylindrical insulator having an axial hole extending in the axial direction and having a stepped portion whose outer diameter decreases toward the tip;
A center electrode provided on the tip side of the shaft hole;
A metallic shell having a cylindrical shape provided on the outer periphery of the insulator and having a receiving portion protruding radially inward on its inner periphery;
An annular packing interposed between the stepped portion and the receiving portion;
A spark plug comprising:
The insulator has at least one reduced-diameter portion between the tip of the insulator and the tip of the portion that contacts the packing when the outer diameter is reduced toward the tip. ,
In at least one of the reduced diameter portions, a convex portion or a concave portion is provided in a part of the outer circumferential surface of the reduced diameter portion in the circumferential direction ,
The convex portion or the concave portion is a spark plug formed in a mesh shape .

Preferred embodiments of the spark plug (1) are as follows.
(2) In the spark plug of (1), the convex portion or the concave portion is provided in all the reduced diameter portions .

  When an impact is applied to the tip of the spark plug due to vibration caused by pressure fluctuation in the combustion chamber during operation of the internal combustion engine, or when an impact is applied to the tip of the spark plug when the spark plug is attached to the internal combustion engine, etc. The stress tends to concentrate on the reduced diameter portion of the portion of the insulator exposed to the combustion gas. Further, the thinner the insulator, the more concentrated the stress is on the reduced diameter portion, and the easier it is to break. In the spark plug according to the present invention, in at least one of the reduced diameter portions, a convex portion or a concave portion is provided in a part of the outer peripheral surface of the reduced diameter portion in the circumferential direction. When an impact is applied, stress concentrated on the reduced diameter portion of the insulator can be dispersed, and as a result, a spark plug provided with an insulator having excellent breakage resistance can be provided.

FIG. 1 is a partial cross-sectional explanatory diagram of a spark plug which is an embodiment of a spark plug according to the present invention. FIG. 2 is a main part explanatory view showing an insulator of the spark plug shown in FIG. FIG. 3A is a cross-sectional explanatory view of a main part showing a cut surface when the insulator of FIG. 2 is cut along the plane A ₁ -A ₂ . FIG. 3B is a cross-sectional explanatory view of a main part showing a cut surface when the insulator of FIG. 2 is cut along the plane B ₁ -B ₂ . FIG. 3C is a cross-sectional explanatory view of a main part showing a cut surface when the insulator of FIG. 2 is cut along a C ₁ -C ₂ plane. FIG. 4 is a main part explanatory view showing an embodiment of a convex portion or a concave portion provided on the outer peripheral surface of the insulator of the spark plug according to the present invention. FIG. 5 is a main part explanatory view showing another embodiment of the convex part or the concave part provided on the outer peripheral surface of the insulator of the spark plug according to the present invention.

(First embodiment)
FIG. 1 shows a spark plug as an embodiment of the spark plug according to the present invention. FIG. 1 is a partial cross-sectional explanatory view of a spark plug 1 which is an embodiment of a spark plug according to the present invention. In FIG. 1, the lower side of the paper is described as the front end direction of the axis O and the upper side of the paper is described as the rear end direction of the axis O.

  As shown in FIG. 1, the spark plug 1 includes a substantially cylindrical insulator 3 having a shaft hole 2 extending in the direction of the axis O, and a substantially rod-shaped center electrode 4 provided on the distal end side in the shaft hole 2. A terminal metal fitting 5 provided on the rear end side in the shaft hole 2, a substantially cylindrical metal shell 6 provided on the outer periphery of the insulator 3, and one end joined to the tip of the metal shell 6. And a ground electrode 7 arranged so that the other end faces the tip of the center electrode 4. The ground electrode 7 includes a tip 8, and the tip 8 is disposed with a gap G between the tip of the center electrode 4.

  The insulator 3 has a substantially cylindrical shape and has an axial hole 2 extending in the direction of the axis O. A seal for fixing the center electrode 4 and the terminal fitting 5 in the shaft hole 2 between the center electrode 4 and the terminal fitting 5 between the center electrode 4 and the terminal fitting 5 at the front end side in the shaft hole 2 and the rear end side. The bodies 10 and 11 and the resistor 12 for reducing radio noise are provided. The insulator 3 has a flange 13 projecting radially in the vicinity of the center in the direction of the axis O. The insulator 3 accommodates the terminal fitting 5 on the rear end side of the flange portion 13 and has a rear end side body portion 14 that insulates the terminal fitting 5 from the metal shell 6. The insulator 3 has a distal end side body portion 15 that accommodates the resistor 12 on the distal end side of the flange portion 13, and the central electrode 4 is accommodated on the distal end side of the distal end side body portion 15. It has the leg length part 16 with a small outer diameter. The insulator 3 has a stepped portion 31 between the distal end side body portion 15 and the leg long portion 16 whose outer diameter decreases toward the distal end. The insulator 3 is fixed to the metal shell 6 with the end of the insulator 3 in the distal direction protruding from the tip of the metal shell 6. A convex portion or a concave portion is provided on the outer peripheral surface of the leg long portion 16. As a result, stress concentrated when an impact is applied to the leg length portion 16 can be dispersed to prevent the insulator 3 from being broken. The detail of the leg long part 16 provided with the convex part or the recessed part is mentioned later. The insulator 3 is preferably formed of a material having mechanical strength, thermal strength, and electrical strength. Examples of such a material include a ceramic sintered body mainly composed of alumina.

  The metal shell 6 has a substantially cylindrical shape, and is formed so as to hold the insulator 3 by incorporating the insulator 3 therein. A threaded portion 17 is provided on the outer peripheral surface in the front end direction of the metal shell 6, and the spark plug 1 is attached to a cylinder head of an internal combustion engine (not shown) using the threaded portion 17. The metal shell 6 has a flange-shaped gas seal portion 18 on the rear end side of the screw portion 17, and a gasket 19 is fitted between the gas seal portion 18 and the screw portion 17. The metal shell 6 has a tool engagement portion 20 for engaging a tool such as a spanner or a wrench on the rear end side of the gas seal portion 18, and a crimping portion 21 on the rear end side of the tool engagement portion 20. Have. In the annular space formed between the inner peripheral surface of the caulking portion 21 and the tool engaging portion 20 and the outer peripheral surface of the insulator 3, annular ring members 22 and 23 and a talc 24 are arranged, and the insulator 3 Is fixed to the metal shell 6. The metal shell 6 has a receiving portion 32 that protrudes radially inward on the inner circumference on the tip side from the gas seal portion 18. An annular packing 33 is interposed between the receiving portion 32 and the stepped portion 31 of the insulator 3. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas is formed in the gap between the receiving portion 32 exposed to the combustion chamber and the stepped portion 31 so as not to leak to the outside. The metal shell 6 can be formed of a conductive steel material, for example, low carbon steel.

  The terminal fitting 5 is a terminal for applying a voltage for performing a spark discharge between the center electrode 4 and the ground electrode 7 to the center electrode 4 from the outside. The terminal fitting 5 has an outer diameter larger than the inner diameter of the shaft hole 2, is exposed from the shaft hole 2, and an exposed portion 25 in which a part of the hook portion comes into contact with a rear end side end surface in the axis O direction, The exposed portion 25 has a substantially cylindrical columnar portion 26 that extends in the distal direction from the distal end side in the axis O direction and is accommodated in the shaft hole 2. The terminal fitting 5 can be formed of a metal material such as low carbon steel.

  The center electrode 4 has a substantially rod shape, and is formed by an outer layer 27 and a core portion 28 formed so as to be concentrically embedded in an axial center portion inside the outer layer 27. The center electrode 4 is fixed in the shaft hole 2 of the insulator 3 with its tip protruding from the tip of the insulator 3, and is insulated and held with respect to the metal shell 6. The core portion 28 is formed of a material having a higher thermal conductivity than the outer layer 27. Examples of such a material include Cu, Cu alloy, Ag, Ag alloy, and pure Ni. The outer layer 27 can be formed of a known material used for the center electrode, and is preferably formed of a Ni alloy such as Inconel 600. The center electrode 4 has the core portion 28, but may not have the core portion.

  The ground electrode 7 is formed in a substantially prismatic shape, one end is joined to the tip of the metal shell 6, bent in a substantially L shape in the middle, and the other end is disposed with a gap between the center electrode 4. Has been. The ground electrode 7 can be formed of a known material used for the ground electrode, and is preferably formed of a Ni alloy such as Inconel 600.

  The tip 9 is provided on the side surface of the tip portion of the ground electrode 7, and is provided so that the tip of the tip 9 and the tip of the center electrode 4 face each other. A gap G is formed between the tip of the chip 9 and the tip of the center electrode 4, and spark discharge occurs in this gap G. The gap G in the spark plug 1 is the shortest distance between the tip of the tip 9 and the tip of the center electrode 4, and this gap G is normally set to 0.3 to 1.5 mm. In this spark plug 1, the chip 9 is provided only on the ground electrode 7 and not on the center electrode 4, but may be provided on both the center electrode and the ground electrode, or the ground electrode and the center It does not need to be provided on both of the electrodes. The tip 9 is made of a noble metal alloy, and examples of the noble metal alloy include Pr alloys, Ir alloys, and the like mainly containing Pt or Ir. The shape of the chip 9 is not particularly limited, and examples thereof include a columnar shape, a disc shape, a polygonal column shape, and a polygonal plate shape.

  Next, the insulator which is a characteristic part of the present invention will be described with reference to the drawings. FIG. 2A is an explanatory view of a main part showing an insulator of the spark plug shown in FIG. The insulator 3 according to this embodiment has a reduced diameter portion in which the reduction ratio is reduced when the outer diameter is reduced toward the tip direction between the tip of the insulator 3 and the tip of the portion in contact with the packing 33. There are three 34a, 34b, and 34c, and convex portions 36a, 36b or concave portions 36c are provided on a part of the outer peripheral surface of all the reduced diameter portions 34a, 34b, 34c in the circumferential direction. The diameter-reduced portions 34a, 34b, and 34c impact the tip of the spark plug 1 when an impact is applied due to vibration caused by pressure fluctuations in the combustion chamber during operation of the internal combustion engine, or when the spark plug is attached to the internal combustion engine. This is a portion where stress is likely to concentrate when, for example, is added. When the convex portions 36a, 36b or the concave portions 36c are provided on the outer peripheral surface of the portion where stress is likely to concentrate, the stress can be dispersed, and as a result, the insulator 3 having excellent breakage resistance is provided. A spark plug 1 can be provided. The diameter-reduced portions 34a, 34b, and 34c are portions where the outer peripheral surface of the insulator 3 is recessed in a concave shape, and can also be referred to as concave portions.

  The reduced diameter portion 34a is provided on the most rear end side in the axis O direction among the three reduced diameter portions 34a, 34b, 34c. The reduced diameter portion 34a is a boundary portion between the tapered surface 35a whose outer diameter decreases at a constant rate toward the tip and the cylindrical surface 35b whose outer diameter is constant. Assuming that the angle formed between the axis O and the tapered surface 35a is the taper angle θa, the taper surface 35a has a smaller outer diameter at a constant rate. Therefore, the taper angle θa is predetermined within a range larger than 0 ° and smaller than 90 °. Has a value. Assuming that the angle formed between the axis O and the cylindrical surface 35b is the taper angle θb, the cylindrical surface 35b has a constant outer diameter and does not change, so the taper angle θb is 0 °. The diameter-reduced portion 34a changes from a tapered surface 35a having a taper angle θa greater than 0 ° toward the tip to a cylindrical surface 35b having a taper angle θb of 0 °, thereby reducing the taper angle. It is a part of.

  The reduced diameter portion 34b is provided closer to the distal end side in the axis O direction than the reduced diameter portion 34a. The reduced diameter portion 24b is a boundary portion between the tapered surface 35c and the tapered surface 35d whose outer diameter decreases toward the tip at a constant rate. If the angle between the axis O and the taper surface 35c is the taper angle θc, and the angle between the axis O and the taper surface 35d is the taper angle θd, the outer diameter of the taper surface 35c and the taper surface 35d becomes smaller at a constant rate. Therefore, the taper angle θc and the taper angle θd have predetermined values in a range larger than 0 ° and smaller than 90 °. Further, the taper angle θd is smaller than the taper angle θc. The reduced diameter portion 34b is an annular portion whose taper angle is reduced by changing from the taper surface 35c toward the tip to a taper surface 35d having a taper angle θd smaller than the taper angle θc.

  The reduced diameter portion 34c is provided on the distal end side in the axis O direction from the reduced diameter portion 34b. The reduced diameter portion 34c is a curved surface 35e having an outer diameter that decreases toward the tip, and a reduced diameter ratio of the outer diameter decreases toward the tip. That is, the diameter-reduced portion 34c is obtained when a tangent line T is drawn with an arbitrary point on the contour line indicating the outer peripheral surface of the insulator 3 as a contact P when the insulator 3 is viewed from a direction orthogonal to the axis O. The region where the inclination of the tangent line T at the contact point P changes from the direction perpendicular to the axis line O to the direction along the axis line O as the position of the contact point P approaches the tip. A cylindrical surface 35f having a constant outer diameter is adjacent to the distal end side of the curved surface 35e.

FIG. 3A is a cross-sectional explanatory view of a main part showing a cut surface when the insulator 3 of FIG. 2 is cut along the plane A ₁ -A ₂ . The reduced diameter portion 34 a has eight linear protrusions 36 a extending along the circumferential direction of the insulator 3. The eight convex portions 36a are provided at equal intervals in the circumferential direction of the reduced diameter portion 34a. The convex portion 36a is elliptical hemispherical, but the shape of the convex portion is not particularly limited. The convex portion 36a is provided so as to straddle the reduced diameter portion 34a from the tapered surface 35a to the cylindrical surface 35b. The convex portion 36a swells outward in the radial direction with respect to the tapered surface 35a and the cylindrical surface 35b. The reduced diameter portion 34a is a portion where stress tends to concentrate when an impact is applied to the distal end portion of the spark plug 1, but since the convex portion 36a is provided on the reduced diameter portion 34a, the stress is easily dispersed, Fracture resistance is improved.

FIG. 3B is a cross-sectional explanatory view of a main part showing a cut surface when the insulator of FIG. 2 is cut along the plane B ₁ -B ₂ . The reduced diameter portion 34 b has four linear protrusions 36 b extending along the axis O direction of the insulator 3. The four convex portions 36b are provided at equal intervals in the circumferential direction of the reduced diameter portion 34b. The convex portion 36b is provided so as to straddle the reduced diameter portion 34b from the tapered surface 35c to the tapered surface 35d. The convex portion 36b is formed so as to fill the reduced diameter portion 34b that is recessed in a concave shape, and the radially outer surface thereof is a flat surface. Since the convex portion 36b is provided so as to fill the reduced diameter portion 34b, in the portion where the convex portion 36b is provided, there is no portion where the diameter reduction ratio changes rapidly from the tapered surface 35c to the tapered surface 35d. A surface having a taper angle smaller than the taper angle θc and larger than the taper angle θd is interposed between the taper surface 35c and the taper surface 35d, and the diameter is gradually reduced toward the tip. The convex portion 36a swells outward in the radial direction with reference to the tapered surface 35c and the tapered surface 35d. The reduced diameter portion 34b is a portion where stress tends to concentrate when an impact is applied to the tip of the spark plug 1. However, since the convex portion 36b is provided on the reduced diameter portion 34b, the stress is easily dispersed, and the Breakability is improved. Further, since the protrusion 36b of the line extends in the direction along the axis O, the direction orthogonal to the axis O compared to the case where the protrusion extending in the direction orthogonal to the axis O is provided. Resistant to shock from

FIG. 3C is a cross-sectional explanatory view of a main part showing a cut surface when the insulator of FIG. 2 is cut along a C ₁ -C ₂ plane. The reduced diameter portion 34 c has three linear recesses 36 c extending along the axis O direction of the insulator 3. The three concave portions 36c are provided at equal intervals in the circumferential direction of the reduced diameter portion 34c. The recess 36c has a shape that is wound in a spoon shape, but the shape of the recess is not particularly limited. The recess 36c is provided from the curved surface 35e to a part of the cylindrical surface 35f. The recess 36c is wound radially inward with respect to the curved surface 35e and the cylindrical surface 35f. The reduced diameter portion 34c is a portion where stress tends to concentrate when an impact is applied to the tip end portion of the spark plug 1. However, since the recessed portion 36c is provided in the reduced diameter portion 34c, the stress is easily dispersed and breakage resistant. Improves.

  When an impact is applied to the tip of the spark plug 1 due to vibration caused by pressure fluctuations in the combustion chamber during operation of the internal combustion engine, or when the spark plug 1 is attached to the internal combustion engine, the impact is applied to the tip of the spark plug 1. In such a case, stress concentrates on the diameter-reduced portions 34a, 34b, and 34c in the portion exposed to the combustion gas in the insulator 3, that is, from the tip of the insulator 3 to the tip of the portion that contacts the packing 33. Easy to do. Further, as the insulator 3 becomes thinner, the stress concentrates on the reduced diameter portions 34a, 34b, and 34c, and breaks easily. The spark plug 1 of this embodiment has a circumferential direction on all the outer peripheral surfaces of the three reduced diameter portions 34a, 34b, 34c provided between the tip of the insulator 3 and the tip of the portion in contact with the packing 33. Convex parts 36a, 36b and a concave part 36c are provided in the part. Therefore, when an impact is applied to the tip of the spark plug 1, the stress concentrated on the reduced diameter portions 34a, 34b, 34c of the insulator 3 can be dispersed, and as a result, the insulator having excellent breakage resistance. The spark plug 1 with 3 can be provided.

  A spark plug 1 as an embodiment of the spark plug according to the present invention can be manufactured, for example, as follows.

  The insulator 3 can be produced by firing a molded body molded from the raw material powder. Specifically, raw material powder is prepared by blending alumina as a main component and a compound of an element such as Si, Mg, Ca, Ba that functions as a sintering aid. A slurry for molding is prepared by adding and mixing a hydrophilic binder such as polyvinyl alcohol and a solvent such as water to the raw material powder. Next, the molding slurry is spray-dried by a spray drying method or the like to prepare a molding granule. The molded granule is obtained by pressure molding or injection molding to obtain a molded body.

  In the case of pressure molding, the granulated material for molding is pressure-molded by a die press molding method, a rubber press method, or the like to form a cylindrical molded body having a hole that becomes the shaft hole 2. Next, the outer peripheral surface of the obtained molded body is ground so as to have the shape described above. At the time of grinding, the convex portions 36a, 36b and the concave portion 36c are formed while forming the three reduced diameter portions 34a, 34b, 34c in the leg length portion 16. Regarding the recess 36c, after forming the reduced diameter portion 34c in the leg length portion 16, the surface of the reduced diameter portion 34c can be ground to form the recess 36c. Thus, three reduced diameter portions 34a, 34b, 34c are provided on the outer peripheral surface of the leg length portion 16, and the reduced diameter portions 34a, 34b, 34c are provided with convex portions 36a, 36b or concave portions 36c, respectively. The body is obtained.

  In the case of injection molding, injection molding is performed using a mold from which the insulator 3 having the shape described above can be obtained. A pattern capable of forming the convex portions 36a, 36b or the concave portion 36c is provided in advance on the inner peripheral surface of the mold. Therefore, in one step, the leg length portion 16 is provided with three reduced diameter portions 34a, 34b, 34c, and the reduced diameter portions 34a, 34b, 34c are respectively provided with convex portions 36a, 36b or concave portions 36c. The body is obtained. According to injection molding, a convex part or a concave part can be easily formed only by providing a desired pattern on the inner peripheral surface of the mold. Therefore, the injection molding method has a smaller number of steps than the compression molding method in which the molded granule is pressure molded to obtain a molded body, and then the outer peripheral surface of the molded body is ground. A molded body in which the convex portions 36a, 36b or the concave portion 36c are respectively provided on the diameter portions 34a, 34b, 34c can be easily manufactured.

  Next, the molded body formed into a desired shape is fired at 1450 ° C. to 1700 ° C. for 1 to 24 hours in an air atmosphere. The insulator 3 can be obtained by applying a glaze after firing and performing finish firing if desired.

  The center electrode 4 formed in a predetermined shape is inserted into the shaft hole 2 of the obtained insulator 3, further glass powder forming the seal bodies 10, 11, resistor composition forming the resistor 12, Glass powder is filled in the shaft hole 2 in this order while being pre-compressed. Next, the resistor composition and the glass powder are compressed and heated while the terminal fitting 5 is press-fitted from the end in the shaft hole 2. Thus, the resistor composition and the glass powder are sintered to form the resistor 12 and the seal bodies 10 and 11. The insulator 3 in which the center electrode 4 and the terminal metal fitting 5 are inserted is inserted into the metal shell 6 formed in a predetermined shape, and the stepped portion 31 and the receiving portion 32 are engaged with each other via the annular packing 33. By attaching, the insulator 3 is attached to the metal shell 6. The ground electrode 7 is joined to the vicinity of the tip of the metal shell 6 by electrical resistance welding or the like before or after the insulator 3 is attached to the metal shell 6. Further, the chip 9 is joined to the side surface of the front end portion of the ground electrode 7 by electrical resistance welding and / or laser welding before or after joining the ground electrode 7 to the metal shell 6. Finally, the tip of the ground electrode 7 is bent toward the center electrode 4, and the spark plug 1 is manufactured such that the tip 8 provided at the tip of the ground electrode 7 faces the tip of the center electrode 4.

(Second Embodiment)
FIG. 4 is a main part explanatory view showing an embodiment of a convex portion or a concave portion provided on the outer peripheral surface of the insulator of the spark plug according to the present invention. The insulator 203 in the spark plug of this embodiment has one reduced diameter portion 234, and the shape and arrangement of the projections 236 provided on the reduced diameter portion 234 are different, the spark of the first embodiment. It has basically the same structure as the plug 1.

The reduced diameter portion 234 is a boundary portion between a tapered surface 235a whose outer diameter decreases toward the tip at a constant rate and a cylindrical surface 235b whose outer diameter is constant. The reduced diameter portion 234 has twelve linear protrusions 236 on the outer peripheral surface thereof, and the protrusions 236 extend along a direction inclined with respect to the axis O ₂ . The inclination angle θ _{2 with} respect to the plane perpendicular to the axis O ₂ of the projection 236 of the filament is not particularly limited, but is preferably 20 ° or more, more preferably 45 ° or more, and 75 ° or more. Is particularly preferable, and the closer to 90 °, the more preferable. When the protrusions 236 are arranged on the outer peripheral surface of the insulator 203 so as to extend along the direction inclined with respect to the axis O _2, compared to the case where the protrusions 236 extend in the direction orthogonal to the axis O _2. Thus, the breakage resistance of the insulator 203 is improved.

In the reduced diameter portion 234, twelve convex portions 236 are provided at equal intervals in the circumferential direction of the reduced diameter portion 234, but the number and arrangement of the convex portions 236 are not particularly limited. For example, fewer than 12 protrusions or more than 12 protrusions may be provided randomly in the circumferential direction of the reduced diameter portion 234. However, it is preferable that the convex portions 236 are disposed rotationally symmetrically about the axis O ₂ along the outer periphery of the reduced diameter portion 234. Further, the outer peripheral surface of the reduced diameter portion 234 shown in FIG. 4 is provided with a convex portion 236 that swells in the radial direction with respect to the tapered surface 235a and the cylindrical surface 235b. However, a concave portion may be provided. Moreover, both the convex part and the recessed part may be provided. In this case, as in the case where the convex portion 236 is provided, the inclination angle theta ₂ is breakage resistance is improved closer to 90 °.

The diameter-reduced portion 234 of this embodiment extends along the direction in which the linear protrusion 236 is inclined with respect to the axis O ₂ , and thus extends in the direction perpendicular to the axis on the outer peripheral surface of the insulator. Compared with the case where the convex part or recessed part to be provided is provided, it is excellent in breakage resistance. Furthermore, since the reduced diameter portion 234 of this embodiment is provided with a large number of twelve convex portions 236, it is more resistant to breakage than when there are fewer than twelve convex portions or concave portions. Excellent.

(Third embodiment)
FIG. 5 is a main part explanatory view showing another embodiment of the convex part or the concave part provided on the outer peripheral surface of the insulator of the spark plug according to the present invention. The insulator 303 in the spark plug of this embodiment has two reduced-diameter portions, the first reduced-diameter portion 334 is provided with a recess 336, and the shape and arrangement of the recess 336 are different except for the first. The spark plug 1 of the embodiment has basically the same structure.

The reduced diameter portion 334 is a curved surface 335a having an outer diameter that decreases toward the tip and a reduced diameter ratio of the outer diameter decreases toward the tip. Adjacent to the distal end side of the curved surface 335a is a tapered surface 335b whose outer diameter decreases at a constant rate toward the distal end. The reduced diameter portion 334 has a mesh-like recess 336 on the outer peripheral surface thereof. The mesh-shaped recess 336 of this embodiment is an Aya knurled, but is not particularly limited as long as it is a mesh. The knurled line in the knurled knurl is formed by a groove group A in which a plurality of linear grooves are arranged in parallel and a groove group B in which a plurality of linear grooves are arranged in parallel so as to intersect the groove group A. Is done. Assuming that the inclination angle of the groove group A with respect to the plane orthogonal to the axis O ₃ is the knurled angle θ ₃ , the inclination angle of the groove group B with respect to the plane orthogonal to the axis O ₃ is 180 ° −θ ₃ . The knurled angle θ ₃ is in the range of more than 0 ° and less than 90 °, preferably 15 ° or more, more preferably 45 ° or more, and particularly preferably 75 ° or more. Knurled angle theta ₃ is breakage resistance is improved closer to 90 °. The pitch d of the knurls is not particularly limited, but is preferably 0.2 mm to 3 mm, more preferably 0.2 mm to 1.0 mm, and particularly preferably 0.2 to 0.5 mm. The smaller the knurled pitch d, the better the breakage resistance.

  The mesh-shaped recess 336 shown in FIG. 5 is formed as a recess 336 with respect to the peak among the peaks and valleys in the knurl, but if the center of the peak and valley in the knurl is used as a reference, the mesh It can also be said that the concave and convex portions are formed, and when the valley is the reference among the peaks and valleys in the knurled eyes, rhombic convex portions arranged in a staggered manner are formed. You can also. In addition, a mesh-like convex portion may be provided on the outer peripheral surface of the reduced diameter portion 334 instead of the mesh-like concave portion 336. In this case, as in the case where the mesh-shaped concave portion 336 is provided, the breakage resistance is improved as the inclination angle of the mesh-shaped convex portion is closer to 90 °.

  Since the diameter-reduced portion 334 of this embodiment is provided with a mesh-like concave portion 336, it is more resistant to breakage than a case where a linear convex portion or a linear concave portion is provided on the outer peripheral surface of the insulator. Excellent.

  The spark plug according to the present invention is used as an ignition plug for an internal combustion engine for automobiles such as a gasoline engine, and the screw portion is provided in a screw hole provided in a head (not shown) that defines a combustion chamber of the internal combustion engine. It is screwed and fixed at a predetermined position. The spark plug according to the present invention can be used for any internal combustion engine, but a convex portion is formed on the outer peripheral surface of the reduced diameter portion of the insulator where stress is likely to concentrate when an impact is applied to the tip of the spark plug. Alternatively, since the spark plug is provided with an insulator excellent in breakage resistance by having a recess, it can be suitably used for an internal combustion engine that has a high compression ratio in the combustion chamber and easily generates vibrations.

  The spark plug according to the present invention is not limited to the above-described embodiment, and various modifications can be made within a range in which the object of the present invention can be achieved.

  The shape, number, arrangement, and the like of the reduced diameter portion formed between the tip of the insulator in this invention and the tip of the portion that contacts the packing are not particularly limited to the above-described embodiment, and are required for the spark plug. It is set as appropriate according to the performance and the like.

The shape, number, arrangement, and the like of the protrusions or recesses provided on the outer peripheral surface of the insulator in the present invention are not particularly limited to the above-described embodiment.
For example, the convex portion or the concave portion only needs to be provided in a part of the circumferential direction on the outer peripheral surface of the reduced diameter portion, and it is sufficient that at least one convex portion or concave portion is provided, and ten or more convex portions. Or it is preferable that the recessed part is provided.
The convex portion or the concave portion only needs to be provided on a part of the outer circumferential surface of the reduced diameter portion, and is adjacent to the outer peripheral surface of the reduced diameter portion and the reduced diameter portion so as to straddle the reduced diameter portion in the axial direction. It is preferably provided on a part of the outer peripheral surface, and further preferably provided so as to be gently connected to the outer peripheral surface adjacent to the reduced diameter portion.
Moreover, it is not limited to the case where only one convex portion or only a concave portion is provided in one reduced diameter portion as in the above-described embodiment, and both the convex portion and the concave portion are provided in one reduced diameter portion. Also good.
In the case where the insulator has a plurality of reduced diameter portions from the tip thereof to the tip of the portion in contact with the packing, it is sufficient that the convex portion or the concave portion is provided in at least one of the plurality of reduced diameter portions. Of the portions, a convex portion or a concave portion may be provided only on the reduced diameter portion where stress is particularly concentrated.
Moreover, a convex part or a recessed part may be provided in a different shape and arrangement | positioning in each of several diameter reduction parts, and a convex part or a recessed part may be provided in the same shape and arrangement | positioning.
Further, as in the above-described embodiment, the present invention is not limited to the case where each of the plurality of reduced diameter portions is provided with a separate convex portion or concave portion, and the convex portion or the concave portion extends in the axial direction so as to straddle the plurality of reduced diameter portions. For example, a convex portion or a concave portion may extend from the tip of the insulator to the tip of the portion in contact with the packing.

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Shaft hole 3,203,303 Insulator 4 Center electrode 5 Terminal metal fitting 6 Main metal fitting 7 Grounding electrode 8 Tip | Leg portion 17 Screw portion 18 Gas seal portion 19 Gasket 20 Tool engagement portion 21 Clamping portion 22, 23 Ring member 24 Talc 25 Exposed portion 26 Column portion 27 Outer layer 28 Core portion 31 Stepped portion 32 Receiving portion 33 Packing 34a, 34b , 34c, 234, 334 Reduced diameter portion 35a, 35c, 35d, 235a, 335b Tapered surface 35b, 35f, 235b Tubular surface 35e, 335a Curved surface 36a, 36b, 236 Convex portion 36c, 336 Concavity G Gap

Claims (2)

A cylindrical insulator having an axial hole extending in the axial direction and having a stepped portion whose outer diameter decreases toward the tip;
A center electrode provided on the tip side of the shaft hole;
A metallic shell having a cylindrical shape provided on the outer periphery of the insulator and having a receiving portion protruding radially inward on its inner periphery;
An annular packing interposed between the stepped portion and the receiving portion;
A spark plug comprising:
The insulator has at least one reduced-diameter portion between the tip of the insulator and the tip of the portion that contacts the packing when the outer diameter is reduced toward the tip. ,
In at least one of the reduced diameter portions, a convex portion or a concave portion is provided in a part of the outer circumferential surface of the reduced diameter portion in the circumferential direction ,
The spark plug, wherein the convex portion or the concave portion is formed in a mesh shape .   The spark plug according to claim 1, wherein the convex portion or the concave portion is provided in all the reduced diameter portions.

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