阅读说明：本技术 火花塞 (Spark plug ) 是由 八木亮树 于 2019-06-19 设计创作，主要内容包括：本发明提供一种火花塞,无论拧紧速度如何都能够抑制主体金属件的断裂。火花塞具备主体金属件,该主体金属件具有在外周面形成有外螺纹的圆筒状的主干部和与主干部的后端邻接并向径向外侧突出的座部。在主干部存在第一区域和第二区域,第一区域在轴线方向上至少包含从主干部的后端至自外螺纹的后端起的第一个螺纹牙的范围,第二区域与第一区域在周向上邻接,第一区域的维氏硬度值比第二区域的维氏硬度值大。(The invention provides a spark plug, which can restrain the breakage of a main metal piece regardless of the tightening speed. The spark plug includes a main body metal fitting having a cylindrical trunk portion with a male screw formed on an outer peripheral surface thereof, and a seat portion adjacent to a rear end of the trunk portion and protruding radially outward. The trunk portion has a first region and a second region, the first region includes at least a range from a rear end of the trunk portion to a first thread ridge from a rear end of the external thread in an axial direction, the second region is adjacent to the first region in a circumferential direction, and a Vickers hardness value of the first region is larger than a Vickers hardness value of the second region.)

1. A spark plug is provided with a main body metal member, and the main body metal member is provided with:

a cylindrical trunk portion extending along an axis from a front end side to a rear end side and having a male screw formed on an outer peripheral surface thereof; and

a seat portion adjacent to a rear end of the trunk portion and protruding radially outward,

there is a first region and a second region in the stem,

the first region includes at least a range from a rear end of the trunk portion to a first thread ridge from a rear end of the external thread in the axial direction and is a range of a part of a circumferential direction,

the second region circumferentially adjoins the first region,

the first region has a vickers hardness value greater than a vickers hardness value of the second region.

2. A spark plug is provided with a main body metal member, and the main body metal member is provided with:

a cylindrical trunk portion extending along an axis from a front end side to a rear end side and having a male screw formed on an outer peripheral surface thereof; and

a seat portion adjacent to a rear end of the trunk portion and protruding radially outward,

there is a first region and a second region in the stem,

the first region includes at least a range from a rear end of the trunk portion to a first thread ridge from a rear end of the external thread in the axial direction and is a range of a part of a circumferential direction,

the second region circumferentially adjoins the first region,

the first region has a different structure from the second region, and martensite is present in the first region.

3. The spark plug according to claim 1 or 2,

the second region is disposed adjacent to both sides of the first region in the circumferential direction.

4. The spark plug of claim 1,

the first region has martensite.

5. The spark plug according to any one of claims 1 to 4,

the first region includes a range from a rear end of the trunk to a front end of the external thread in the axial direction.

Technical Field

The present invention relates to a spark plug, and more particularly to a spark plug including a main metal member having a male screw formed on a part of an outer peripheral surface thereof.

Background

The spark plug is attached to the engine by screwing the male screw of the main body metal fitting into the screw hole of the engine. In order to avoid the breakage of the metal body even if an excessive tightening torque is applied, patent document 1 discloses the following technique: after a male screw is formed in a cylindrical member that is an original shape of a main body metal, the member is subjected to carburizing or quenching, and the screw portion of the main body metal is solidified over the entire circumference.

[ patent document 1 ] Japanese patent application laid-open No. 2007-280942

Disclosure of Invention

Problems to be solved by the invention

However, in the above-described conventional technique, although the fracture load of the body metal can be increased by the solidification of the threaded portion, the toughness of the threaded portion after the solidification is lowered, and therefore, when the tightening speed is high, the body metal may be fractured under a load smaller than the fracture load when the tightening speed is low.

The present invention has been made to solve the above-described problems, and an object thereof is to provide a spark plug capable of suppressing breakage of a main metal fitting regardless of a tightening speed.

Means for solving the problems

In order to achieve the object, a spark plug according to the present invention includes a main body metal member including: a cylindrical trunk portion extending along an axis from a front end side to a rear end side and having a male screw formed on an outer peripheral surface thereof; and a seat portion adjacent to the rear end of the trunk portion and protruding radially outward. The trunk portion has a first region and a second region, the first region includes at least a range from a rear end of the trunk portion to a first thread ridge from a rear end of the external thread in an axial direction and is a range of a part of a circumferential direction, the second region is adjacent to the first region in the circumferential direction, and a Vickers hardness value of the first region is larger than a Vickers hardness value of the second region.

Further, a spark plug according to the present invention includes a main body metal fitting including: a cylindrical trunk portion extending along an axis from a front end side to a rear end side and having a male screw formed on an outer peripheral surface thereof; and a seat portion adjacent to the rear end of the trunk portion and protruding radially outward. The stem portion includes a first region and a second region, the first region including at least a range from a rear end of the stem portion to a first thread ridge from a rear end of the male thread in an axial direction and being a partial range in a circumferential direction, the second region being adjacent to the first region in the circumferential direction, a structure of the first region being different from a structure of the second region, and the first region having martensite.

Effects of the invention

According to the spark plug described in the first aspect, the first region and the second region which is adjacent to the first region in the circumferential direction and has a smaller vickers hardness value than the first region are present in the range from the rear end of the trunk portion, which is a portion of the trunk portion where a large tightening shaft force acts when the spark plug is tightened, to the first thread ridge from the rear end of the male thread. Since the second region having a smaller vickers hardness value than the first region is juxtaposed to the first region in the direction in which the tightening shaft force is applied, the tightening shaft force is distributed to the first region and the second region so that the elongation of the first region is equal to the elongation of the second region when the external thread is tightened. As a result, the main metal fitting can be suppressed from breaking under a load smaller than the breaking load when the tightening speed is slow when the tightening shaft force is fast, as compared with the case where the second region is not present. Thereby, the breakage of the body metal fitting can be suppressed regardless of the tightening speed.

According to the spark plug of the second aspect, the trunk portion of the main metal fitting includes a first region including a range from the rear end of the trunk portion to the first thread from the rear end of the male screw, and a second region circumferentially adjacent to the first region. The first region has a structure different from that of the second region, and martensite having a high hardness is not present in the second region. The second region, which is softer than the first region, is juxtaposed with the first region along the direction in which the tightening axial force is applied, and therefore has the same effect as the first aspect.

According to the spark plug of the third aspect, the second region is disposed adjacent to both sides of the first region in the circumferential direction, and therefore, in addition to the effects of the first aspect or the second aspect, the breakage of the body metal fitting can be further suppressed regardless of the tightening speed.

According to the spark plug of the fourth aspect, since martensite is present in the first region, the main body metal member can be manufactured from carbon steel in addition to the effects of the first aspect.

According to the spark plug of the fifth aspect, the first region includes a range from the rear end of the trunk portion to the front end of the male screw in the axial direction. Thereby, in addition to the effects of any one of the first to fourth aspects, the strength from the rear end of the trunk portion to which the tightening shaft force is applied to the front end of the male screw can be increased.

Drawings

Fig. 1 is a cross-sectional side view of a spark plug according to a first embodiment.

FIG. 2(a) is a side view of the body metal, FIG. 2(b) is a cross-sectional view of the body metal at line IIb-IIb of FIG. 2(a), and FIG. 2(c) is a cross-sectional view of the body metal at line IIc-IIc of FIG. 2 (a).

Fig. 3 is a schematic diagram showing a relationship between elongation of the male screw of the main metal fitting and a tightening axial force.

Fig. 4(a) is a side view of a main body metal member of a spark plug according to a second embodiment, fig. 4(b) is a side view of a main body metal member of a spark plug according to a third embodiment, and fig. 4(c) is a side view of a main body metal member of a spark plug according to a fourth embodiment.

Description of the reference numerals

10 spark plug

15. 40, 50, 60 body metal piece

16 trunk part

16a rear end of the trunk portion

16b range

17 external screw thread

17a rear end of the external thread

17b thread

17c front end of external thread

18 seat part

31. 41, 51, 61 first region

32. 42, 52, 62 second region

O axis

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional side view of a spark plug 10 of the first embodiment, bounded by an axis O. In fig. 1, the thread ridge of the male thread 17 is simplified (the same applies to fig. 2(a), 4(a) to 4 (c)). The lower side of the drawing in fig. 1 is referred to as the front end side of the spark plug 10, and the upper side of the drawing is referred to as the rear end side of the spark plug 10.

As shown in fig. 1, the spark plug 10 holds the insulator 11 to the main metal 15. The insulator 11 is a substantially cylindrical member formed of alumina or the like having excellent insulation properties at high temperatures and mechanical properties. The insulator 11 passes through the shaft hole 12 along the axis O.

The center electrode 13 is a rod-shaped electrode inserted into the axial hole 12 and held by the insulator 11 along the axis O. The center electrode 13 is disposed in the axial hole 12 so as to protrude from the front end of the insulator 11. The center electrode 13 has a core member having excellent thermal conductivity embedded in an electrode base member. The electrode base material is formed of an alloy mainly containing Ni or a metal material composed of Ni, and the core material is formed of copper or an alloy mainly containing copper. The core material may be omitted.

The terminal fitting 14 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and the distal end side is disposed in the insulator 11. The terminal fitting 14 is electrically connected to the center electrode 13 in the axial hole 12. A metal body 15 is fixed to the front end side of the outer periphery of the insulator 11.

The metal shell 15 is a substantially cylindrical member formed of a conductive metal material (for example, mild steel). The body metal fitting 15 includes a cylindrical trunk portion 16, a seat portion 18 adjacent to a rear end of the trunk portion 16 and protruding radially outward, and a rear end portion 19 adjacent to a rear end of the seat portion 18. The rear end portion 19 includes a thin portion 20 having a smaller thickness than the seat portion 18, and a tool engagement portion 21 protruding radially outward from the thin portion 20.

The trunk portion 16 is a portion surrounding a portion on the distal end side of the insulator 11, and has a male screw 17 formed on the outer periphery thereof. The male screw 17 engages with a screw hole 25 of the engine 24 to fix the body metal 15 to the engine 24. The seat portion 18 is a portion for limiting the amount of screwing of the male screw 17 into the engine 24 and for plugging a gap between the male screw 17 and the threaded hole 25. In the present embodiment, a pad 23 is attached to the front end of the seat 18. A gasket 23 sandwiched between the seat portion 18 and the engine 24 seals a gap between the external thread 17 and the threaded hole 25.

The thin portion 20 is a portion to be fastened and fixed by plastically deforming the body metal 15 when the body metal is assembled to the insulator 11. The tool engagement portion 21 is a portion for engaging a tool such as a wrench when the male screw 17 is screwed into the threaded hole 25 of the engine 24.

The ground electrode 22 is a rod-shaped metal (for example, made of a nickel-based alloy) member joined to the trunk portion 16 of the metal shell 15. A spark gap is formed between the ground electrode 22 and the center electrode 13. In the present embodiment, the ground electrode 22 is bent.

The spark plug 10 is manufactured by the following method, for example. First, the center electrode 13 is inserted into the axial hole 12 of the insulator 11, and the tip of the center electrode 13 is disposed so as to protrude from the tip of the insulator 11. Next, the terminal fitting 14 is inserted into the axial hole 12 of the insulator 11, and the terminal fitting 14 and the center electrode 13 are electrically connected. Next, the insulator 11 is inserted into the metal shell 15 to which the ground electrode 22 is joined in advance, and the rear end of the metal shell 15 is bent to assemble the metal shell 15 to the insulator 11. The ground electrode 22 is bent and the gasket 23 is fitted to obtain the spark plug 10.

Referring to fig. 2, the main body metal 15 is explained. Fig. 2(a) is a side view of the main body metal piece 15, fig. 2(b) is a sectional view of the main body metal piece 15 taken along line IIb-IIb of fig. 2(a), and fig. 2(c) is a sectional view of the main body metal piece 15 taken along line IIc-IIc of fig. 2 (a). The main body metal fitting 15 shown in fig. 2(a) illustrates a state before being assembled to the insulator 11. The lower side of fig. 2(a) is referred to as the front end side of the metal shell 15, and the upper side of the figure is referred to as the rear end side of the metal shell 15 (the same applies to fig. 4(a) to 4 (c)).

The body metal fitting 15 is manufactured by, for example, the following method. First, a cylindrical workpiece (not shown) that is the original shape of the metal master 15 is formed by cold forging, cutting, or the like. The engaging portion 30 of the workpiece abuts the front end of the seat portion 18. The engaging portion 30 is a portion with which the gasket 23 (see fig. 1) engages.

As shown in fig. 2(a), after a ground electrode 22 (a straight bar material before bending) is joined to a trunk 16 of a work, a male screw 17 is formed on the trunk 16 by rolling, cutting, or the like. The engagement portion 30 abuts the rear end 17a of the male screw 17. As shown in fig. 2(b), the groove diameter of the male screw 17 is substantially the same as the outer diameter of the engagement portion 30. After the male screw 17 is formed in the trunk portion 16, a first region 31 and a second region 32 are formed in the trunk portion 16, and the metal shell 15 is obtained. The main metal fitting 15 is plated or the like as necessary.

The first region 31 is a region having a vickers hardness value greater than the vickers hardness value of the second region 32. In the present embodiment, the body metal member 15 is made of mild steel, and is hardened by heating and irradiating a laser beam to a part of the surface of the external thread 17, thereby forming the first region 31. The insufficiently heated region becomes the second region 32. After quenching, tempering is performed as necessary. The structure of the first region 31 contains martensite due to quenching, and the structure of the second region 32 contains at least one of austenite and pearlite. By using the main metal material 15 made of carbon steel, the first region 31 and the second region 32 having different hardness can be formed by heat treatment.

The formation of the first region 31 is not limited to laser hardening. The first region 31 may be formed by electron beam quenching, electric discharge curing, shot peening, as a matter of course. Since the structure is not solidified by solid solution of carbon in the electric discharge solidification and shot peening, the material of the metal master 15 may not be carbon steel. In this case, the material of the main metal fitting may be appropriately selected from various metal materials in consideration of thermal conductivity, heat resistance, and the like.

The first region 31 is not limited to the case where a part of the male screw 17 is solidified. It is of course possible to soften a portion of the external thread 17 to form the second region 32 and the remaining portion to form the first region 31. For example, the second region 32 can be formed by hardening the main body metal 15 formed with the male screw 17 by quenching and tempering, then irradiating a part of the surface of the male screw 17 with a laser beam or an electron beam, and heating and annealing. The region where annealing is insufficient becomes the first region 31.

As shown in fig. 2(c), the first region 31 is a region of a part of the trunk portion 16 in the circumferential direction, and the second region 32 is adjacent to the first region 31 in the circumferential direction. The first region 31 and the second region 32 are present in a range 16b from a rear end 16a (see fig. 2(b)) of the trunk portion 16 on which a large tightening shaft force acts when the male screw 17 of the spark plug 10 is tightened to the screw hole 25 of the engine 24 to the first thread ridge 17b from the rear end 17a of the male screw 17. The first thread 17b may be a complete thread portion or an incomplete thread portion. In the present embodiment, the first region 31 and the second region 32 include a range from the rear end 16a of the trunk portion 16 to the front end 17c of the male screw 17. The second regions 32 are disposed adjacent to both sides of the first region 31 in the circumferential direction, and the first region 31 and the second region 32 are respectively provided at three positions.

The vickers hardness of the first region 31 and the second region 32 is in accordance with JIS Z2244: 2009. The trunk portion 16 is cut by a plane perpendicular to the axis O, and the cut surface is mirror-polished to measure vickers hardness. In the vickers hardness test, indenters are pressed into a plurality of measurement points separated from each other in the circumferential direction of a test piece (trunk portion 16) to make indentations. The distance from the outer peripheral surface of the trunk portion 16 to each measurement point is constant, and the test force and the holding time applied to the indenter at each measurement point are the same.

In the present embodiment, since the entire body of the first region 31 in the thickness direction (radial direction) of the trunk portion 16 is solidified by laser quenching, the center of the thickness of the trunk portion 16 is set as a measurement point. However, when the first region 31 is formed by shot peening or the like, and when the first region 31 and the second region 32 are present in a very small portion of the surface of the male thread 17, the vickers hardness of the hardened (or softened) portion is measured.

Since the vickers hardness values in the first region 31 and the second region 32 are different by about ± 50HV, the regions having the difference of the vickers hardness values of 100HV or more are defined as the first region 31 and the second region 32. For example, the first region 31 has a vickers hardness value of 500HV or more, and the second region 32 has a vickers hardness value of less than 400 HV.

By measuring the vickers hardness values of a plurality of measurement points separated from each other in the circumferential direction and comparing them, the first region 31 and the second region 32 adjacent to each other in the circumferential direction of the trunk portion 16 can be specified. Further, by measuring the vickers hardness values of a plurality of test pieces having different distances from the rear end 16a of the trunk portion 16 to the cut surface, the ranges of the first region 31 and the second region 32 extending from the rear end 16a of the trunk portion 16 to the front end side can be specified. By combining these, the circumferential and axial extents of the first region 31 and the second region 32 of the trunk portion 16 can be determined.

Further, the trunk portion 16 is cut off on a plane perpendicular to the axis O, the trunk portion 16 is polished so that a flat cross section appears, and the martensite in the first region 31 can be confirmed by a structure observation of a group image by a metal microscope or SEM. In the observation of the structure, electrolysis by an etchant, electroless etching, or the like is performed as necessary. Further, by performing tissue observation of a plurality of cross sections having different distances from the rear end 16a of the trunk portion 16 to the cut surface, the range in which the first region 31 and the second region 32 extend from the rear end 16a of the trunk portion 16 to the distal end side can be specified. By combining these, the circumferential and axial extents of the first region 31 and the second region 32 in the trunk portion 16 can be determined.

Fig. 3 is a schematic diagram showing the relationship between the elongation of the male thread 17 of the body metal member 15 and the tightening axial force. Fig. 3 shows, in addition to the line drawing of the body metal 15 of the present embodiment, a line drawing of a body metal (hereinafter referred to as "metal 31") of a comparative example in which the first region 31 is formed over the entire circumference of the male screw 17, and a line drawing of a body metal (hereinafter referred to as "metal 32") of a comparative example in which the second region 32 is formed over the entire circumference of the male screw 17.

When an excessive tightening torque is applied to the external thread 17, the yield point is exceeded and the fracture occurs. The metal member 32 is elongated more than the metal member 31, but has a smaller breaking load than the metal member 31. On the other hand, although the metal fitting 31 has a larger breaking load than the metal fitting 32 due to solidification of the male screw 17, the toughness of the male screw 17 is reduced, and the elongation until the breaking is small. Therefore, when the tightening speed is high, the metal fitting 31 may be broken by a smaller load than that when the tightening speed is low due to the impact.

In contrast, the body metal fitting 15 has a first region 31 and a second region 32 adjacent to the first region 31 in the circumferential direction and having a vickers hardness value smaller than that of the first region 31 in a range 16b from the rear end 16a of the trunk portion 16 to the first thread ridge 17b from the rear end 17a of the male thread 17. The range 16b is a portion where stress concentration is likely to occur at the time of tightening. Since the second region 32 is present in parallel with the first region 31 along the direction in which the tightening shaft force is applied (axial direction), when the male screw 17 is tightened, the tightening shaft force is distributed to the first region 31 and the second region 32 so that the extension of the first region 31 is equal to the extension of the second region 32. As a result, the main body metal fitting 15 can be suppressed from breaking under a load smaller than the breaking load when the tightening speed is slow, as compared with the case where the second region 32 is not present (the case of the metal fitting 31). Thereby, the breakage of the body metal fitting can be suppressed regardless of the tightening speed.

In addition, the main metal 15 is solidified in the first region 31 with martensite. The first region 31 has a structure different from that of the second region 32, and no martensite is present in the second region 32. Since the second region 32, which is softer than the first region 31, is arranged in parallel with the first region 31 in the direction in which the tightening axial force is applied, the breakage of the body metal fitting can be suppressed regardless of the tightening speed as described above.

Since the second regions 32 are disposed adjacent to both sides of the first region 31 in the circumferential direction, the second regions 32, which are softer than the first region 31, can be disposed in a dispersed manner in the circumferential direction. Thereby, the breakage of the body metal fitting 15 can be further suppressed regardless of the tightening speed.

Further, since the first region 31 is formed so as to include the range from the rear end 16a of the body portion 16 to the front end 17c of the male screw 17 in the axial direction, not only the range 16b in which stress concentration from the rear end 16a of the body portion 16 to the first thread ridge 17b is likely to occur, but also the strength from the rear end 16a of the body portion 16 to the front end 17c of the male screw 17 to which the tightening axial force is applied can be increased.

Referring to fig. 4, the second to fourth embodiments are explained. Fig. 4(a) is a side view of a main body metal member 40 of a spark plug according to a second embodiment, fig. 4(b) is a side view of a main body metal member 50 of a spark plug according to a third embodiment, and fig. 4(c) is a side view of a main body metal member 60 of a spark plug according to a fourth embodiment. The metal fittings 40, 50, and 60 hold the insulator 11 instead of the metal fitting 15 of the spark plug 10 described in the first embodiment. The same portions as those described in the first embodiment are denoted by the same reference numerals, and the following description is omitted.

As shown in fig. 4(a), the body metal 40 has first regions 41 and second regions 42 alternately formed in the circumferential direction of the trunk portion 16. The first region 41 has a vickers hardness value greater than that of the second region 42, and martensite is present in the structure of the first region 41.

The first region 41 is present in a range 16b from the rear end 16a of the trunk portion 16 to the first thread 17b (see fig. 2 (b)). In the axial direction (the vertical direction in fig. 4 (a)), a second region 42 exists from the tip of the first region 41 to the tip 17c of the male screw 17. In the present embodiment, the first region 41 and the second region 42 are present at two positions in the range 16 b. Since the body metal 40 includes the first region 41 and the second region 42 in the range 16b where stress concentration is likely to occur, as described in the first embodiment, the body metal 40 can be prevented from being broken regardless of the tightening speed.

As shown in fig. 4(b), the body metal 50 has first regions 51 and second regions 52 alternately formed in the circumferential direction of the trunk portion 16. The first region 51 has a vickers hardness value greater than that of the second region 52, and martensite is present in the structure of the first region 51.

The first region 51 exists in a range from the rear end 16a of the trunk portion 16 to the front end 17c of the male screw 17. In the present embodiment, the first region 51 and the second region 52 are present at six positions. Since the circumferential widths of the first region 51 and the second region 52 can be made narrower than those of the first embodiment, the processing area of the male thread 17 for forming the first region 51 and the second region 52 can be reduced. As a result, in addition to the operational effects described in the first embodiment, the process for forming the first region 51 and the second region 52 can be simplified.

As shown in fig. 4(c), the body metal 60 has first regions 61 and second regions 62 alternately formed in the circumferential direction of the trunk portion 16. The first region 61 has a vickers hardness value greater than that of the second region 62, and martensite is present in the structure of the first region 61.

The first region 61 and the second region 62 are each formed spirally from the rear end 16a of the trunk portion 16. This can extend the length of the first region 61 and the second region 62, compared to a case where the first region and the second region are parallel to the axis O (see fig. 2 a). Since the first region 61 and the second region 62 can be extended and the extension of the first region 61 and the second region 62 can be increased accordingly, the allowable range of the tightening torque can be expanded in addition to the operational effect described in the first embodiment.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above-described embodiments at all, and it can be easily estimated that various modifications and changes can be made without departing from the scope of the present invention. For example, the number of the first regions 31, 41, 51, 61 and the second regions 32, 42, 52, 62 may be set as appropriate as long as there is at least one of each of the first regions and the second regions.

In the embodiment, the spark plug 10 in which the gasket 23 is disposed at the tip of the seat portion 18 of the metal shell 15, 40, 50, 60 has been described, but the present invention is not necessarily limited to this. Of course, the present invention can be applied to a cone-type spark plug (a main body metal fitting) in which a gasket is omitted, a tip end surface of the seat portion 18 is tapered, and the seat portion 18 is brought into contact with the engine 24 to seal combustion gas.

In the embodiment, the case where the first regions 31, 41, 51, 61 are formed by quenching, electric discharge hardening, shot peening, or the second regions 32, 42, 52, 62 are formed by annealing has been described, but the present invention is not necessarily limited thereto. Of course, 2 raw materials having vickers hardness values different from each other by 100HV or more are prepared, the first region and the second region are formed using the raw materials, and these are joined by welding or the like to manufacture a metal body having the first region and the second region.