JP2014154307A - Ignition plug and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ignition plug that is able to achieve extremely satisfactory airtightness, and to provide a manufacturing method therefor.SOLUTION: An ignition plug 1 comprises: an insulator 2; and a main-body metal fitting 3 having a projection part 21 projecting radially inside. The projection part 21 has a reduced diameter part 21A, the insulator 2 has a lock part 14, and the lock part 14 is locked in the reduced diameter part 21A via a lock member 22. In a cross-section including an axial line CL1, if the angle of the lock part 14 is θp(°) and the angle of the reduced diameter part 21A is θs(°), θs≤θp is satisfied. If the Vickers hardness of the lock member 22 at the center point CP1 of a first line segment SL1 is Hvo(Hv), the Vickers hardness of the lock member 22 at the center point CP2 of the second line segment is Hvi(Hv), and the Vickers hardness of the lock member 22 at the center point CP3 of the third line segment SL3 is Hvm(Hv), Hvi>Hvm>Hvo and (Hvi-Hvm)/(Hvi-Hvo)≤0.5 are satisfied.

Description

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

  The spark plug is attached to a combustion apparatus such as an internal combustion engine (engine), and is used to ignite an air-fuel mixture in the combustion chamber. In general, the spark plug is provided at the tip of the metal shell, the insulator having an axial hole extending in the axial direction, the center electrode inserted through the tip of the shaft hole, the metal shell provided on the outer periphery of the insulator, And a ground electrode that forms a gap with the center electrode. Further, the metallic shell has a projecting portion that protrudes inward in the radial direction and has an annular shape around the axis on the inner periphery thereof. The insulator is inserted into the inner periphery of the metal shell, and the locking portion provided on the front end side of the insulator is locked to the reduced diameter portion that is the rear end side surface of the protrusion. A load is applied to the rear end portion of the metal fitting, and the rear end portion of the main metal fitting is bent and deformed to be caulked and fixed to the main metal fitting. In addition, an annular locking member is interposed between the locking portion and the reduced diameter portion in order to improve airtightness (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-289777

  However, in the configuration in which the locking member is simply interposed between the locking portion and the reduced diameter portion, the contact pressure and adhesion of the locking member to the locking portion and the reduced diameter portion are insufficient, and good airtightness is achieved. May not be secured.

  Particularly in recent years, in order to improve the degree of freedom in design of internal combustion engines and the like, there has been a demand for smaller spark plugs (smaller diameters). It is difficult to ensure a sufficient contact area between the diameter portion and the locking member. Therefore, there is a greater concern about a decrease in airtightness.

  This invention is made | formed in view of the said situation, The objective is to provide the ignition plug which can implement | achieve very favorable airtightness, and its manufacturing method.

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

Configuration 1. The spark plug of this configuration includes a cylindrical insulator having an axial hole extending in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A projecting portion protruding radially inward, and a cylindrical metal shell provided on the outer periphery of the insulator;
The protrusion has a reduced diameter portion whose inner diameter decreases toward the tip side,
The insulator has a locking portion whose outer diameter decreases toward the tip side,
An ignition plug in which the locking portion is locked to the reduced diameter portion via an annular locking member,
In a cross section including the axis,
Of the angles formed by the straight line orthogonal to the axis and the outline of the locking portion, the acute angle is θp (°), and the angle formed by the straight line orthogonal to the axis and the outline of the reduced diameter portion is When the acute angle is θs (°), θs ≦ θp is satisfied, and
The locking member is disposed at a position including a first line segment extending in the axial direction connecting the rear end of the locking portion to the reduced diameter portion,
The Vickers hardness of the locking member at the midpoint of the first line segment is Hvo (Hv), and the axial direction connecting the tip of the portion of the reduced diameter portion that contacts the locking member to the locking portion The Vickers hardness of the locking member at the midpoint of the second line segment extending in the direction H is Hvi (Hv), and the Vickers hardness of the locking member at the midpoint of the third line segment connecting both the midpoints is Hvm (Hv). When
Hvi>Hvm> Hvo
(Hvi-Hvm) / (Hvi-Hvo) ≦ 0.5
It is characterized by satisfying.

  According to the said structure 1, it is comprised so that (theta) s <= thetap may be satisfy | filled. Therefore, in a state where the metal shell and the insulator are fixed, a larger load can be applied to the portion of the locking member from the center to the inner peripheral side. In addition, according to the configuration 1, the configuration is such that (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5. Therefore, the high hardness site | part provided over the wide range from the center to the inner peripheral side of a latching member can be pinched | interposed with a big load by a latching | locking part and a reduced diameter part. Thereby, the wide range from the center to the inner peripheral side of the locking member can be brought into contact with the locking portion and the reduced diameter portion with very large pressure. As a result, airtightness can be improved.

  Further, since θs ≦ θp, the load applied to the outer peripheral side portion of the locking member is relatively small. However, according to the configuration 1, the configuration is such that Hvi> Hvm> Hvo is satisfied. It is comprised so that the hardness of the outer peripheral side site | part of a stop member may become comparatively small. Therefore, even when the load is small, the outer peripheral side portion of the locking member can be more closely attached to the locking portion or the like. As a result, the airtightness can be further improved.

  As described above, according to the above-described configuration 1, the effects of satisfying θs ≦ θp, Hvi> Hvm> Hvo, and (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5 are synergistic. By doing so, very good airtightness can be realized.

  Configuration 2. The spark plug of this configuration is characterized in that, in the above configuration 1, (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.4 is satisfied.

  According to the configuration 2, the portion from the center to the inner peripheral side of the locking member can be brought into contact with the locking portion and the reduced diameter portion with a larger pressure. As a result, the airtightness can be further improved.

Configuration 3. The spark plug manufacturing method of this configuration is the spark plug manufacturing method according to the above configuration 1 or 2,
An arrangement step of arranging the insulator on an inner periphery of the metal shell in a state where the locking member is arranged between the reduced diameter portion and the locking portion;
By applying a load toward the front end side in the axial direction with respect to the rear end portion of the metal shell, the rear end portion of the metal shell is bent and deformed radially inward, so that the reduced diameter portion and the locking portion A caulking step for fixing the metal shell and the insulator in a state of sandwiching the locking member,
In the cross-section including the central axis of the locking member in the arranging step, the Vickers hardness Hwm (Hv) at the center in the thickness direction at the center in the width direction is only 1/8 of the width of the own than the outermost peripheral part. Vickers hardness Hwo (Hv) at the center in the thickness direction on the inner peripheral side, and Vickers hardness Hwi (Hv) at the center in the thickness direction on the outer peripheral side by 1/8 of its width from the innermost peripheral part It is large.

  According to the configuration 3, the locking member in the arrangement step (before the caulking step) is configured such that the hardness Hwm of the central portion is larger than the hardness Hwo of the outer peripheral portion and the hardness Hwi of the inner peripheral portion. Has been. By sandwiching the locking member configured in this way between the locking portion and the reduced diameter portion configured to satisfy θs ≦ θp in the caulking step, in the central portion of the locking member originally having high hardness While maintaining the hardness, the hardness can be remarkably increased in the inner peripheral side portion of the locking member. That is, according to the above configuration 3, the manufactured spark plug can satisfy Hvi> Hvm> Hvo and (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5 with more certainty. A spark plug having good airtightness can be easily obtained.

  Configuration 4. The spark plug manufacturing method of this configuration is the above configuration 3, wherein the locking member in the arranging step includes a tip side surface arranged on the reduced diameter side in the cross section including its center axis, and the engagement member. It is characterized by providing a recessed part in at least one of the rear end side surfaces arrange | positioned at a stop part side.

  According to the said structure 4, in a caulking process, a locking member will bend and deform | transform centering on the formation position of a recessed part. Therefore, in the manufactured spark plug, a reaction force due to bending deformation is applied from the locking member to the locking portion and the reduced diameter portion. Therefore, even if the spark plug is vibrated and the adhesion of the locking member to the locking portion or the reduced diameter portion is likely to be reduced, the locking member is more securely attached to the locking portion or the reduced diameter portion. Can be adhered to. As a result, good ignitability can be maintained over a long period of time.

  Configuration 5. The spark plug manufacturing method of this configuration is characterized in that, in the above configuration 4, the recess is provided at least on the side surface of the tip.

  According to the configuration 5, in the caulking step, a portion of the distal end side surface of the locking member that is located on the outer peripheral side of the recess can be brought into contact with the reduced diameter portion with a very large pressure. Thereby, in the manufactured spark plug, the part located on the outer peripheral side with respect to the concave portion of the tip side surface can be brought into a state of deeply entering the reduced diameter portion. As a result, the airtightness can be further improved.

It is a partially broken front view which shows the structure of a spark plug. It is an expanded sectional view which shows the angle of a reduced diameter part, the angle of a latching | locking part, etc. It is a cross-sectional schematic diagram for demonstrating how to obtain | require the angle of a latching | locking part in case the external line of a latching | locking part is curved or bent. It is a cross-sectional schematic diagram for demonstrating how to obtain | require the angle of a reduced diameter part in case the external line of a reduced diameter part is curving or bending. It is a graph for showing the relationship of hardness Hvi, Hvm, Hvo. It is sectional drawing which shows the metal shell hold | maintained at the receiving type in the arrangement | positioning process. It is sectional drawing which shows the structure of a locking member. It is an expanded sectional view which shows the securing member etc. in an arrangement | positioning process. It is an expanded sectional end view which shows the structure of a locking member. It is sectional drawing which shows the press die etc. which are used in a caulking process. It is sectional drawing which shows the state which is applying the load to the rear-end part of a main metal fitting in a caulking process. It is a graph which shows the result of an airtightness evaluation test. It is a graph which shows the result of a vibration resistance evaluation test. (A) is an expanded sectional end view of the metal member in a cross section including the central axis of the metal member, and (b) is an illustration of the locking member in a cross section including the central axis of the locking member in another embodiment. It is an expanded sectional end view. It is an expanded sectional view which shows the formation position of the recessed part in another embodiment. It is an expanded sectional view showing a locking member of an arrangement process in another embodiment.

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

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

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. The leg length part 13 formed in diameter smaller than this on the side is provided. In addition, of the insulator 2, the large diameter portion 11, the middle trunk portion 12, and most of the leg long portions 13 are accommodated inside the metal shell 3. The connecting portion between the middle body portion 12 and the long leg portion 13 is formed with a tapered locking portion 14 whose outer diameter decreases toward the distal end side. Is locked to the metal shell 3.

  Further, the insulator 2 is formed with a shaft hole 4 extending along the axis CL <b> 1, and a center electrode 5 is inserted and fixed to the tip side of the shaft hole 4. The center electrode 5 includes an inner layer 5A made of a metal having excellent thermal conductivity (for example, copper, copper alloy, pure nickel (Ni), etc.) and an outer layer 5B made of an alloy containing Ni as a main component. The center electrode 5 has a rod shape (cylindrical shape) as a whole, and a tip portion of the center electrode 5 projects from the tip of the insulator 2. In the present embodiment, in order to improve the durability, the tip of the center electrode 5 is provided with a cylindrical tip 31 made of a metal having excellent wear resistance (for example, an iridium alloy or a platinum alloy). Yes.

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

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

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel (for example, S25C), and a spark plug 1 is attached to an outer peripheral surface of the metal shell 3 such as an internal combustion engine or a fuel cell reformer. A threaded portion (male threaded portion) 15 is formed for attachment to the apparatus. Further, a seat portion 16 is formed on the rear end side of the screw portion 15 so as to protrude toward the outer peripheral side, and a ring-shaped gasket 18 is fitted into the screw neck 17 at the rear end of the screw portion 15. Further, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the combustion device is provided on the rear end side of the metal shell 3. A caulking portion 20 that bends inward in the radial direction is provided at the rear end portion of the metal shell 3. In the present embodiment, in order to reduce the diameter of the spark plug 1, the metal shell 3 is reduced in diameter, and the screw diameter of the screw portion 15 is relatively small (for example, M12 or less).

  Furthermore, the inner periphery of the metal shell 3 is provided with a projecting portion 21 that has an annular shape centered on the axis line CL1 and projects radially inward. The protrusion 21 has a tapered reduced diameter portion 21A (which is the rear end side surface of the protrusion 21) whose inner diameter decreases toward the tip side. The insulator 2 is inserted into the metal shell 3 from the rear end side to the front end side, and its own locking portion 14 is an annular shape made of a predetermined metal (for example, copper, iron, SUS, etc.). By subjecting the rear end side opening of the metal shell 3 to the inside in the radial direction while being locked to the reduced diameter portion 21 </ b> A via the locking member 22, that is, by forming the crimped portion 20. It is fixed to the metal fitting 3. Note that the locking member 22 provided between the locking portion 14 and the reduced diameter portion 21A maintains the airtightness in the combustion chamber, and the length of the leg portion 13 of the insulator 2 exposed to the combustion chamber and the metal shell 3 is increased. The fuel gas entering the gap with the peripheral surface is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 23 , 24 is filled with talc 25 powder. That is, the metal shell 3 holds the insulator 2 via the locking member 22, the ring members 23 and 24, and the talc 25.

  In addition, a ground electrode 27 is joined to the distal end portion 26 of the metal shell 3 so that the side surface of the distal end side of the metal shell 3 faces the distal end portion (chip 31) of the center electrode 5. . In addition, a gap 28 is formed between the tip of the center electrode 5 (chip 31) and the tip of the ground electrode 27, and spark discharge is generated in the gap 28 in a direction substantially along the axis CL1. To be done.

  Subsequently, the structure of the latching | locking part 14 and the diameter reduction part 21A which are the characterizing parts of this invention, and the latching member 22 located between both is demonstrated.

  In the present embodiment, as shown in FIG. 2 (in FIG. 2, for convenience of illustration, hatching of the insulator 2 and the metal shell 3 is omitted), the angle of the locking portion 14 is set in the cross section including the axis CL1. When θp (°) is assumed and the angle of the reduced diameter portion 21A is θs (°), it is configured to satisfy θs ≦ θp.

  Note that the angle θp is an acute angle among the angles formed by the straight line XL1 perpendicular to the axis CL1 and the outline of the locking portion 14 in the cross section. In addition, the angle θs is an acute angle among the angles formed by the straight line XL2 orthogonal to the axis CL1 and the outline of the reduced diameter portion 21A in the cross section.

  Further, in the case where the outer contour line of the locking portion 14 is curved or bent, the angle θp is obtained as follows. That is, as shown in FIG. 3, on one side across the axis CL1, from the radius of the middle trunk 12 (the radius at the rear end of the locking portion 14) to the rear end of the long leg portion 13 using a projector. A radius difference D1 obtained by subtracting the radius (the radius at the tip of the locking portion 14) is obtained. When the middle body portion 12 is tapered, the radius (from the axis) at the intersection of the extension line of the outer shape line at the tip of the middle body portion 12 and the extension line of the outer shape line of the locking portion 14. A value obtained by subtracting the radius at the rear end of the leg length 13 from the distance to the intersection) is obtained as the radius difference D1. Next, seven virtual lines VL1 to VL7 that extend along the axis CL1 and equally divide the radius difference D1 into eight along the direction orthogonal to the axis CL1 are drawn. Then, using the projector, of the seven virtual lines VL1 to VL7, the five virtual lines VL2 to VL6 excluding the virtual line VL1 located on the outermost side and the virtual line VL7 located on the innermost side. And the coordinate in intersection P1-P5 with the outline of the said latching | locking part 14 is calculated | required. Next, an acute angle α is obtained from angles formed by the approximate straight line AL1 and the straight line XL1 orthogonal to the axis line CL1 with respect to the obtained five coordinates. Further, on the other side across the axis CL1, the angle α formed by the approximate straight line with respect to the obtained five coordinates and the straight line XL1 orthogonal to the axis CL1 is obtained by the same method as described above, and the two obtained angles α The average value of is calculated. In the present embodiment, the average value of the two angles α is the angle θp.

  In addition, when the outline of the reduced diameter portion 21A is curved or bent, the angle θs is obtained as follows. That is, as shown in FIG. 4, on one side across the axis CL <b> 1, a projection is used to project from the radius of a portion 3 </ b> A extending from the rear end to the rear end side of the reduced diameter portion 21 </ b> A of the metal shell 3. 21 is obtained by subtracting the radius of the portion 21B extending from the tip of the reduced diameter portion 21A to the tip side (more specifically, the radius of the portion located on the innermost side of the portion 21B). Next, seven virtual lines VL11 to VL17 that extend along the axis CL1 and equally divide the radius difference D2 into eight along the direction orthogonal to the axis CL1 are drawn. Then, using the projector, of the seven virtual lines VL11 to VL17, the five virtual lines VL12 to VL16 excluding the virtual line VL11 located on the outermost side and the virtual line VL17 located on the innermost side are excluded. And coordinates at intersections P11 to P15 with the outline of the reduced diameter portion 21A. Next, an acute angle β is obtained from the angles formed by the approximate straight line AL2 and the straight line XL2 orthogonal to the axis CL1 with respect to the obtained five coordinates P11 to P15. Further, on the other side across the axis CL1, the angle β formed by the approximate straight line with respect to the obtained five coordinates and the straight line XL2 orthogonal to the axis CL1 is obtained by the same method as described above, and the two obtained angles β The average value of is calculated. In the present embodiment, the average value of the two angles β is the angle θs.

  Returning to FIG. 2, in the cross section, the locking member 22 is disposed at a position including a first line segment SL1 extending in the direction of the axis CL1 connecting the rear end 14B of the locking portion 14 to the reduced diameter portion 21A. In other words, the locking member 22 is disposed over the entire area between the rear end 14B of the locking portion 14 and the portion of the reduced diameter portion 21A facing the rear end 14B along the axis CL1. Yes.

  Further, in the cross section, the locking member 22 includes a second line segment SL2 extending in the direction of the axis CL1 connecting the tip 21AF of the portion of the reduced diameter portion 21A that contacts the locking member 22 to the locking portion 14. Is arranged. In other words, the locking member 22 is disposed over the entire area between the tip 21AF and the portion of the locking portion 14 that faces the tip 21AF along the axis CL1.

  Furthermore, in this embodiment, in the cross section, the Vickers hardness of the locking member 22 at the midpoint CP1 of the first line segment SL1 is Hvo (Hv), and the locking member 22 at the midpoint CP2 of the second line segment SL2 is When the Vickers hardness is Hvi (Hv) and the Vickers hardness of the locking member 22 at the midpoint CP3 of the third line segment SL3 connecting both the midpoints CP1 and CP2 is Hvm (Hv), Hvi> Hvm> Hvo It is configured to meet. That is, the locking member 22 is configured such that the hardness increases from the outer peripheral side toward the inner peripheral side.

  In the present embodiment, (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5 [more preferably, (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.4] is satisfied. Yes. That is, as shown in FIG. 5, Hvm is sufficiently large so that (Hvi-Hvm) is 0.5 times or less of (Hvi-Hvo), and the locking member 22 It is comprised so that the hardness of the site | part from an inner peripheral side may become comparatively large.

  In this embodiment, for example, Hvo is 111 Hv or more and 210 Hv or less, Hvi is 115 Hv or more and 275 Hv or less, and Hvm is 113 Hv or more and 244 Hv or less. Moreover, in this embodiment, it is comprised so that 0.1 <= (Hvi-Hvm) / (Hvi-Hvo) may be satisfy | filled. The hardness of the locking member 22 can be measured, for example, by a technique based on JIS Z2244. Specifically, the diagonal length of the indentation formed on the locking member 22 when a predetermined load (for example, 1.961 N) is applied to the locking member 22 with a diamond indenter having a square square shape. Based on the above, the hardness of the locking member 22 can be measured.

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

  First, the insulator 2 is molded. For example, a green body granulation material is prepared using a raw material powder mainly composed of alumina and containing a binder and the like, and a rubber compact is used to obtain a cylindrical molded body. Then, after the outer shape is shaped by grinding the obtained molded body, the insulator 2 is obtained by firing the shaped body.

  Further, the center electrode 5 is manufactured separately from the insulator 2. That is, the center electrode 5 is produced by forging a Ni alloy in which a copper alloy or the like for improving heat dissipation is arranged at the center. Further, the tip 31 is joined to the tip of the center electrode 5 by laser welding or the like.

  Then, the insulator 2 and the center electrode 5, the resistor 7, and the terminal electrode 6 obtained as described above are sealed and fixed by the glass seal layers 8 and 9. The glass seal layers 8 and 9 are generally prepared by mixing borosilicate glass and metal powder, and the prepared material fills the shaft hole 4 of the insulator 2 with the resistor 7 interposed therebetween. After being done, it is baked and hardened by heating in the firing furnace while pressing with the terminal electrode 6 from the rear. At this time, the glaze layer may be fired simultaneously on the surface of the rear end body portion 10 of the insulator 2 or the glaze layer may be formed in advance.

  Next, the metallic shell 3 is processed. That is, a through-hole is formed by subjecting a cylindrical metal material (for example, an iron-based material such as S17C or S25C or a stainless material) to a cold forging process, and an approximate shape is formed. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, a straight bar-shaped ground electrode 27 made of Ni alloy or the like is resistance-welded to the front end surface of the metal shell intermediate. When the welding is performed, so-called “sag” is generated. After the “sag” is removed, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 3 to which the ground electrode 27 is joined is obtained. In order to improve the corrosion resistance, the metal shell 3 to which the ground electrode 27 is welded may be plated.

  Thereafter, the insulator 2 provided with the center electrode 5 and the terminal electrode 6 and the metal shell 3 provided with the ground electrode 27 are fixed.

  Specifically, as shown in FIG. 6, first, in the arrangement step, the distal end side of the metal shell 3 is inserted into a cylindrical receiving mold 51 made of a predetermined metal (for example, hard steel such as hardened steel). Thus, the metal shell 3 is held by the receiving mold 51. Next, the locking member 22 is inserted into the metal shell 3, and the locking member 22 is disposed on the reduced diameter portion 21A. Then, by inserting the insulator 2 into the metal shell 3, the insulator 2 is placed on the inner periphery of the metal shell 3 with the locking member 22 disposed between the reduced diameter portion 21A and the locking portion 14. Deploy.

  As shown in FIGS. 7 and 8, the locking member 22 in the arranging step includes a front end side surface 22 </ b> F arranged on the reduced diameter portion 21 </ b> A side and a rear end side surface 22 </ b> B arranged on the engaging portion 14 side. At least one is provided with a recess, and in the present embodiment, an annular recess 22D is provided at the center of the tip side surface 22F. In addition, the locking member 22 is such that the rear end side surface 22B and the surface of the front end side surface 22F located on the inner peripheral side and the outer peripheral side with respect to the concave portion 22D extend in a direction orthogonal to the central axis CL2. It is configured.

  The recess 22D is formed by pressing the locking member 22. Therefore, the locking member 22 in the arranging step has a hardness at the center portion larger than the hardness at the outer peripheral side portion and the inner peripheral side portion. More specifically, as shown in FIG. 9, the locking member 22 in the arranging step has a Vickers hardness Hwm (Hv) at the center X1 in the thickness direction at the center in the width direction, as shown in FIG. Vickers hardness Hwo (Hv) at the thickness direction center X2 on the inner peripheral side by 1/8 of its own width W from the outer peripheral portion, and outer peripheral side by 1/8 of its own width W from the innermost peripheral portion It is comprised so that it may become larger than the Vickers hardness Hwi (Hv) in thickness direction center X3.

  The caulking portion 20 is formed in the caulking step after the locking member 22 is arranged. More specifically, first, as shown in FIG. 10, a cylindrical pressing die 53 is mounted from above the metal shell 3. The cylindrical pressing die 53 has a curved surface portion 53 </ b> A corresponding to the shape of the caulking portion 20 on the inner peripheral surface of the opening portion. After the pressing mold 53 is mounted, a predetermined load (for example, 30 kN or more and 50 kN or less) is applied to the metallic mold 3 by the pressing mold 53 toward the receiving mold 51 while the metal shell 3 is sandwiched between the receiving mold 51 and the pressing mold 53. Press at. As a result, as shown in FIG. 11, the rear end side opening of the metal shell 3 is bent radially inward (that is, the caulking portion 20 is formed), and the insulator 2 and the metal shell 3 are connected to each other. Fixed.

  By applying a load from the pressing die 53, the locking member 22 is bent and deformed around the position where the recess 22D is formed, and after the caulking step, a reaction force due to the bending deformation is applied from the locking member 22 to the locking portion. 14 and the reduced diameter portion 21A. Further, since the recess 22D is provided on the distal end side surface 22F of the locking member 22, when a load is applied from the pressing die 53, the outer peripheral portion of the distal end side surface 22F with respect to the reduced diameter portion 21A with respect to the recess 22D. Contact with high pressure. Therefore, although illustration is omitted, after the caulking step, a portion of the distal end side surface 22F on the outer peripheral side with respect to the concave portion 22D enters a reduced diameter portion 21A.

  Furthermore, since θs ≦ θp, in the caulking process, a larger load is applied particularly to the inner peripheral side portion of the locking member 22, and therefore, after the caulking process, the locking member 22 The hardness of the inner peripheral portion is remarkably increased. And since the center part of the locking member 22 is made into high hardness, the locking member 22 after a caulking process is Hvi> Hvm> Hvo, and (Hvi-Hvm) / (Hvi-Hvo) <= 0 .5 is satisfied.

  In addition, the locking member 22 is deformed following the reduced diameter portion 21A and the locking portion 14 during the caulking process. Therefore, the recess 22D does not remain in the locking member 22 after the caulking step, and the front end side surface 22F and the rear end side surface 22B of the locking member 22 are in surface contact with the reduced diameter portion 21A and the locking portion 14. doing.

  In addition, by applying a load from the pressing die 53, the relatively thin cylindrical portion located between the seat portion 16 and the tool engaging portion 19 is curved and deformed outward in the radial direction. As a result, an axial force along the axis CL1 is applied from the metal shell 3 to the insulator 2, and as a result, the insulator 2 and the metal shell 3 are more reliably fixed.

  After fixing the metal shell 3 and the insulator 2, the ground electrode 27 is bent toward the center electrode 5, and the size of the gap 28 formed between the tip portion of the center electrode 5 and the tip portion of the ground electrode 27. By adjusting the above, the spark plug 1 described above is obtained.

  As described above in detail, according to the present embodiment, it is configured to satisfy θs ≦ θp. Therefore, in a state where the metal shell 3 and the insulator 2 are fixed, a larger load can be applied to the portion of the locking member 22 from the center to the inner peripheral side. In addition, the present embodiment is configured to satisfy (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5. Therefore, a high hardness portion provided over a wide range from the center to the inner peripheral side of the locking member 22 can be sandwiched with a large load by the locking portion 14 and the reduced diameter portion 21A. Thereby, a wide range from the center of the locking member 22 to the inner peripheral side can be brought into contact with the locking portion 14 and the reduced diameter portion 21A with a very large pressure. As a result, airtightness can be improved.

  In addition, by setting θs ≦ θp, the load applied to the outer peripheral side portion of the locking member 22 is relatively small, but in the present embodiment, it is configured to satisfy Hvi> Hvm> Hvo. The outer peripheral portion of the member 22 is configured to have a relatively small hardness. Therefore, even in a state where the load is small, the outer peripheral side portion of the locking member 22 can be more closely attached to the locking portion 14 and the like. As a result, the airtightness can be further improved.

  As described above, according to the present embodiment, the operational effects by satisfying θs ≦ θp, Hvi> Hvm> Hvo, and (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5 are synergistic. By doing so, very good airtightness can be realized.

  In particular, in this embodiment, since the screw diameter of the screw portion 15 is small (for example, M12 or less), the airtightness tends to be insufficient. However, the above-described configuration causes the screw portion 15 to have a small screw diameter. Even so, very good airtightness can be obtained. In other words, the above-described configuration is particularly effective in a spark plug in which the screw diameter of the screw portion 15 is small (for example, M12 or less) and airtightness tends to be insufficient.

  Moreover, when it comprises so that (Hvi-Hvm) / (Hvi-Hvo) <= 0.4, the site | part from the center of the latching member 22 to an inner peripheral side may be the latching | locking part 14 and diameter reduction part 21A. Can be brought into contact with a greater pressure. As a result, the airtightness can be further improved.

  In addition, the locking member 22 in the arrangement step (before the caulking step) is configured such that the hardness Hwm of the central portion is larger than the hardness Hwo of the outer peripheral portion and the hardness Hwi of the inner peripheral portion. . Then, in the caulking step, the locking member 22 is sandwiched between the locking portion 14 and the reduced diameter portion 21A configured to satisfy θs ≦ θp, so that the center portion of the locking member 22 originally having high hardness While maintaining the hardness, the hardness can be remarkably increased in the inner peripheral side portion of the locking member 22. As a result, in the manufactured spark plug 1, Hvi> Hvm> Hvo and (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5 can be satisfied more reliably, and a very good airtightness can be achieved. It is possible to easily obtain the spark plug 1 having the same.

  Further, since the recess 22D is formed in the locking member 22 in the arrangement step, in the manufactured spark plug 1, reaction force due to bending deformation is generated from the locking member 22 to the locking portion 14 and the reduced diameter portion 21A. Will be added to. Therefore, even if the spark plug 1 is vibrated and the adhesion of the locking member 22 to the locking portion 14 or the reduced diameter portion 21A is liable to be lowered, the locking member 22 is fixed to the locking portion 14 or the reduced diameter. It can be made to adhere more securely to part 21A. As a result, good ignitability can be maintained over a long period of time.

  In the present embodiment, the recess 22 </ b> D is provided on the tip side surface 22 </ b> F of the locking member 22. Therefore, in the caulking step, a portion of the front end side surface 22F that is located on the outer peripheral side of the recessed portion 22D can be brought into contact with the reduced diameter portion 21A with very large pressure, and the front end side surface 22F can be contacted with the recessed portion 22D. Also, the portion located on the outer peripheral side can be deeply inserted into the reduced diameter portion 21A. As a result, the airtightness can be further improved.

  Next, in order to confirm the operational effects achieved by the above-described embodiment, the spark plug in which θs ≦ θp and Hvi> Hvm> Hvo are satisfied while (Hvi−Hvm) / (Hvi−Hvo) is variously changed. Five samples were prepared, and an airtightness evaluation test was performed on each sample. The outline of the airtightness evaluation test is as follows. That is, after the sample was attached to a predetermined aluminum bush, a pressure of 1.5 MPa was continuously applied by air to the tip of the sample. And the temperature (seat surface temperature) of the part (seat surface) where the gasket contacts in the aluminum bush is gradually increased, and the amount of air leakage per minute from between the insulator and the metal shell is The seating surface temperature (leakage temperature) at 10 cc / min or higher was measured. Subsequently, the minimum value (minimum leakage temperature) of the leakage temperature in five samples with the same (Hvi-Hvm) / (Hvi-Hvo) was specified. A sample with a minimum leakage temperature of 200 ° C. or higher can be said to have good airtightness, and a sample with a minimum leakage temperature of 250 ° C. or higher can be said to have excellent airtightness. .

  FIG. 12 shows the results of the airtightness evaluation test. Note that Hvi, Hvo, and Hvm were changed by changing the hardness of the locking member before the caulking process or adjusting the applied load in the caulking process.

As shown in FIG. 12, a sample satisfying θs ≦ θp and Hvi>Hvm> Hvo and satisfying (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5 has a minimum leakage temperature of 200 ° C. or more. It was revealed that it has good airtightness. This is considered to be because the following (1) to (3) acted synergistically.
(1) Since θs ≦ θp, the portion from the center of the locking member to the inner peripheral side is sandwiched between the locking portion and the reduced diameter portion with a large load.
(2) By setting (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5, the hardness of the portion from the center to the inner peripheral side of the locking member is sufficiently high, and this is formed in a relatively wide range. The high hardness portion is sandwiched with a large load by the locking portion and the reduced diameter portion, so that a wide range of the locking member is in contact with the locking portion or the like with a very large pressure.
(3) Since Hvi>Hvm> Hvo and the hardness of the outer peripheral side portion of the locking member that is relatively small in load is relatively small, the outer periphery of the locking member can be obtained even when the load is small. The side part is more securely attached to the locking part or the like.

  In particular, it was confirmed that the sample satisfying (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.4 had a minimum leakage temperature of 250 ° C. or higher and extremely excellent airtightness.

  From the results of the above test, it can be said that it is preferable to satisfy θs ≦ θp, Hvi> Hvm> Hvo, and (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5 in order to achieve good airtightness.

  From the viewpoint of further improving the airtightness, it is more preferable to satisfy (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.4 while satisfying θs ≦ θp and Hvi> Hvm> Hvo. It can be said.

  Next, a spark plug sample (a sample with a recess) obtained using a locking member having a recess on at least one of the front end side surface and the rear end side surface (the front end side surface in this test), the front end side surface and the rear end Five spark plug samples (samples without recesses) obtained using a locking member configured to be parallel to the side surface were prepared, and a vibration resistance evaluation test was performed on both samples. The outline of the vibration resistance evaluation test is as follows. That is, the minimum leakage temperature in both samples was obtained by the same method as the above-described airtightness evaluation test. Next, vibrations were applied to the samples under predetermined conditions, and after applying vibrations, the minimum leakage temperature in both samples was obtained again. Here, after the vibration is applied, the sample having a minimum leakage temperature of 200 ° C. or higher is less likely to be deteriorated in airtightness due to vibration, and good airtightness can be ensured over a long period of time. I can say that.

  FIG. 13 shows the results of the vibration resistance evaluation test. In both samples, the locking member in the arrangement step was configured such that Hwm was larger than Hwo and Hwi. Both samples were configured to satisfy θs ≦ θp, Hvi> Hvm> Hvo, and (Hvi−Hvm) / (Hvi−Hvo) ≦ 0.5.

  As shown in FIG. 13, it was found that the sample with recesses had a minimum leakage temperature of 200 ° C. or higher even after vibration was applied, and good airtightness could be ensured over a long period of time. This is because the locking member is bent and deformed around the formation position of the recess in the caulking step, and a reaction force due to the bending deformation is applied from the locking member to the locking portion and the reduced diameter portion after the caulking step. It is thought that it was because of it.

  From the results of the above test, the locking member in the placement step is a cross-section including its own central axis from the viewpoint of effectively suppressing the deterioration of the airtightness due to vibration and ensuring good airtightness over a long period of time. Therefore, it can be said that it is preferable that at least one of the front end side surface and the rear end side surface is provided with a recess.

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

  (A) In the above embodiment, the screw diameter of the screw portion 15 is relatively small (for example, M12 or less). However, the present invention is applied to a spark plug having a relatively large screw diameter of the screw portion 15. You may apply.

  (B) In the above embodiment, the recess 22D is formed so that the Hwm is larger than Hwo and Hwi in the locking member 22 in the arrangement step. On the other hand, you may comprise so that Hwm may become larger than Hwo and Hwi, without providing the recessed part 22D. For example, as shown to Fig.14 (a), after obtaining the cyclic | annular metal member ME in which the center part was formed more thickly than the outer peripheral side and the inner peripheral side, the said metal member ME is inserted | pinched and it deform | transforms by pressure. 14B, as shown in FIG. 14B, the front end side surface 32F and the rear end side surface 32B are parallel and are not provided with a recess, while the locking member 32 having Hwm larger than Hwo and Hwi is obtained. Also good.

  (C) In the above embodiment, the recess 22D is provided on the front end side surface 22F of the locking member 22, but as shown in FIG. 15, the recess 22E is provided on the rear end side surface 22B of the locking member 22. Also good. Moreover, it is good also as providing a recessed part in both the front end side surface 22F and the rear end side surface 22B of the latching member 22. FIG.

  (D) In the above-described embodiment, the locking member 22 in the arranging step has the rear end side surface 22B and the surface located on the inner peripheral side and the outer peripheral side of the front end side surface 22F on the inner peripheral side and the outer peripheral side. It is comprised so that it may extend in the direction orthogonal to the side. On the other hand, as shown in FIG. 16, the surfaces of the rear end side surface 33B and the front end side surface 33F that are located on the inner peripheral side and the outer peripheral side with respect to the concave portion 33D are inclined toward the front end side toward the central axis CL2. In the arrangement step, the locking member 33 may be configured to be in surface contact with the locking portion 14 and the reduced diameter portion 21A. In this case, it is possible to more reliably prevent stress from being concentrated on the part of the insulator 2 from the locking member 33 in the caulking step. As a result, breakage of the insulator 2 in the caulking process can be effectively prevented.

  (E) In the above embodiment, the case where the ground electrode 27 is joined to the distal end portion 26 of the metal shell 3 is embodied. However, a part of the metal shell (or the tip metal fitting previously welded to the metal shell is used. The present invention is also applicable to the case where the ground electrode is formed by cutting out a part of the ground (for example, Japanese Patent Application Laid-Open No. 2006-236906).

  (F) In the above embodiment, the tool engaging portion 19 has a hexagonal cross section, but the shape of the tool engaging portion 19 is not limited to such a shape. For example, it may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)].

  DESCRIPTION OF SYMBOLS 1 ... Spark plug, 2 ... Insulator (insulator), 3 ... Main metal fitting, 4 ... Shaft hole, 5 ... Center electrode, 14 ... Locking part, 21 ... Projection part, 21A ... Reduced diameter part, 22 ... Locking Member, 22B: Rear end side surface, 22D: Recessed portion, 22F ... Front end side surface, CL1 ... Axis line, CL2 ... Center axis of (locking member), CP1 ... (First line segment) midpoint, CP2 ... (Second line) (Min) midpoint, CP3 ... midpoint (third line segment), SL1 ... first line segment, SL2 ... second line segment, SL3 ... third line segment.

Claims (5)

A cylindrical insulator having an axial hole extending in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A projecting portion protruding radially inward, and a cylindrical metal shell provided on the outer periphery of the insulator;
The protrusion has a reduced diameter portion whose inner diameter decreases toward the tip side,
The insulator has a locking portion whose outer diameter decreases toward the tip side,
An ignition plug in which the locking portion is locked to the reduced diameter portion via an annular locking member,
In a cross section including the axis,
Of the angles formed by the straight line orthogonal to the axis and the outline of the locking portion, the acute angle is θp (°), and the angle formed by the straight line orthogonal to the axis and the outline of the reduced diameter portion is When the acute angle is θs (°), θs ≦ θp is satisfied, and
The locking member is disposed at a position including a first line segment extending in the axial direction connecting the rear end of the locking portion to the reduced diameter portion,
The Vickers hardness of the locking member at the midpoint of the first line segment is Hvo (Hv), and the axial direction connecting the tip of the portion of the reduced diameter portion that contacts the locking member to the locking portion The Vickers hardness of the locking member at the midpoint of the second line segment extending in the direction H is Hvi (Hv), and the Vickers hardness of the locking member at the midpoint of the third line segment connecting both the midpoints is Hvm (Hv). When
Hvi>Hvm> Hvo
(Hvi-Hvm) / (Hvi-Hvo) ≦ 0.5
A spark plug characterized by satisfying. (Hvi-Hvm) / (Hvi-Hvo) ≦ 0.4
The spark plug according to claim 1, wherein: A method for producing a spark plug according to claim 1 or 2,
An arrangement step of arranging the insulator on an inner periphery of the metal shell in a state where the locking member is arranged between the reduced diameter portion and the locking portion;
By applying a load toward the front end side in the axial direction with respect to the rear end portion of the metal shell, the rear end portion of the metal shell is bent and deformed radially inward, so that the reduced diameter portion and the locking portion A caulking step for fixing the metal shell and the insulator in a state of sandwiching the locking member,
In the cross-section including the central axis of the locking member in the arranging step, the Vickers hardness Hwm (Hv) at the center in the thickness direction at the center in the width direction is only 1/8 of the width of the own than the outermost peripheral part. Vickers hardness Hwo (Hv) at the center in the thickness direction on the inner peripheral side, and Vickers hardness Hwi (Hv) at the center in the thickness direction on the outer peripheral side by 1/8 of its width from the innermost peripheral part A method of manufacturing a spark plug characterized by being large.   The engaging member in the arranging step is at least one of a front end side surface arranged on the reduced diameter portion side and a rear end side surface arranged on the engaging portion side in a cross section including its own central axis. The method for manufacturing a spark plug according to claim 3, further comprising a recess.   The spark plug manufacturing method according to claim 4, wherein the recess is provided at least on the side surface of the tip.

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