spark plug

Abstract

Spark plug (10), having: an insulator (11) having an axial hole formed along an axial line (O) extending from a front to a rear side; and a metal connection (30, 60) located on a rear side of the axial hole of the insulator (11), wherein the metal connection (30, 60) at a rear end section (32, 62) having a rearwardly directed bottom surface (33, 63) and a projection (35, 65, 68) which extends rearward from an outer edge (34, 64) of the bottom surface (33, 63), wherein at least a part of the bottom surface (33, 63) is provided with a marking (50), the Vickers hardness of the advantage (35, 65, 68) is 100 HV or more, a rear end surface (37, 67) of the projection (35, 65, 68) is positioned on a rear side in relation to a rear end of the marking (50), an area of ​​the rear end face (37, 67) 3 mm2 or larger, and where a gap (G) is provided between an edge (54) of the marking (50) arranged on the floor surface (33, 63) and the outer edge (34, 64) of the floor surface (33, 63).

Description

Field of the invention

[0001] The present invention relates to a spark plug, particularly to a spark plug in which a mark for a metal terminal is provided. Background of the invention

[0002] DE 10 2014 106 221 A1 discloses a spark plug. DE 10 2011 121 016 A1 discloses a spark plug with a color mark. It is known that a spark plug is provided with a predefined identifier (mark) to prevent incorrect mounting of the spark plug on an engine or to enable tracking of history information about the spark plug. In the disclosed technology of Japanese Patent Application JP 2012 - 128 948 A, a spark plug has a protrusion projecting rearward from the outer edge of the bottom surface of a metal terminal facing the rear side, and a mark is applied to the bottom surface of the metal terminal. Due to the protrusion, an external force that may cause peeling or damage to the mark is less likely to be applied to the bottom surface, thus suppressing peeling or damage to the mark.This can suppress the occurrence of marking reading errors.

[0003] For this type of spark plug, technology is required to further suppress the peeling or damage of the mark.

[0004] The present invention was conceived to meet these needs. One advantage of the present invention is a spark plug that makes it possible to suppress the peeling or damage of the marking. Summary of the invention

[0005] According to the present invention, a spark plug according to claim 1 is provided. It comprises: an insulator having an axial hole formed along an axial line extending from a front side to a rear side; and a metal terminal located on a rear side of the axial hole of the insulator, the metal terminal having, at its rear end portion, a rearward-facing bottom surface and a projection projecting rearward from an outer edge of the bottom surface, at least a part of the bottom surface being provided with a mark, the Vickers hardness of the projection being 100 HV or more, a rear end surface of the projection being positioned on a rear side with respect to a rear end of the mark, and an area of ​​the rear end surface being 3 mm 2 or larger.

[0006] According to a first aspect of the invention, there is provided a spark plug as described above, wherein the Vickers hardness of the projection is 100 HV or higher and the area of ​​the rear end surface of the projection located on the rear side with respect to the rear end of the mark is 3 mm 2 or larger, so that the size and strength of the protrusion can be ensured. The protrusion reduces the likelihood of external forces that may cause the marking to peel off or damage the floor surface, thus enhancing the effect of preventing the marking from peeling off or damaging the floor.

[0007] According to a second aspect of the invention, a spark plug as described above is provided, wherein the protrusion protrudes rearward from the entire circumference of the outer edge of the bottom surface, so that an external force that may cause peeling or damage to the mark is even less likely to be applied to the bottom surface. Thus, in addition to the effect of the first aspect, the effect of suppressing peeling or damage to the mark can be further enhanced.

[0008] According to claim 1, a gap is provided between the edge of the marking arranged on the base surface and the outer edge of the base surface, whereby a reduction in the readability of the marking due to the projection can be suppressed. This can also suppress the occurrence of reading errors of the marking.

[0009] According to another aspect of the invention, there is provided a spark plug as described above, wherein the mark is a code that allows information to be read therefrom using reflected light. The gap between the edge of the code on the bottom surface and the outer edge of the bottom surface is 0.03 mm or more, and the distance along the axial line between the bottom surface and the rear end surface of the projection is 1.5 mm or less. Therefore, in addition to the effect of any of the first to third aspects, the occurrence of mark reading errors can be suppressed. Brief description of the drawings Fig. 1 is a half-sectional view of a spark plug according to the first embodiment. Fig. 2A is a top view of the spark plug. Fig. Figure 2B is a sectional view of a metal terminal taken along line IIb-IIb in Fig. 2A. Fig.3A is a plan view of a spark plug according to the second embodiment. Fig. 3B is a sectional view of a metal terminal taken along line IIIb-IIIb in Fig. 3A. Detailed description of the invention

[0010] In the following, the preferred embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a half-sectional view of a spark plug 10 according to the first embodiment, with an axial line O as a boundary. In Fig. 1, the lower side of the drawing sheet is referred to as the front side of the spark plug 10 and the upper side of the drawing sheet is referred to as the rear side of the spark plug 10. As in Fig. 1, the spark plug 10 includes an insulator 11 and a metal terminal 30.

[0011] The insulator 11 is a substantially cylindrical member made of, for example, alumina, which has excellent mechanical properties and insulation properties at high temperature, and has an axial hole penetrating it along the axial line O. An inner peripheral surface 12 of the insulator 11, through which the axial hole penetrates, has a rearward-facing surface 13 on the front side, the inner diameter of which gradually decreases toward the front side.

[0012] The insulator 11 has a front end portion 14, an engaging portion 15, a small-diameter portion 16, a large-diameter portion 17, and a rear end portion 18, which are continuously formed in this order from the front side to the rear side along the axial line O. The front end portion 14 is a portion located on the front side in the axial line direction, and the outer peripheral surface of the front end portion 14 has a diameter that decreases toward the front side. The outer peripheral surface of the engaging portion 15 has a diameter that widens toward the rear side. The small-diameter portion 16 has a substantially constant outer diameter over the entire length in the axial line direction. The large-diameter portion 17 has a substantially constant outer diameter over the entire length in the axial line direction.The outer diameter of the large-diameter section 17 is larger than the outer diameter of the small-diameter section 16. The outer diameter of the rear end section 18 is smaller than the outer diameter of the large-diameter section 17.

[0013] A center electrode 20 is a rod-shaped member extending along the axial line O and formed by plating, with nickel or a nickel-based alloy, a core material formed of copper or containing copper as a main component. The core material may be omitted. The center electrode 20 has an axial portion 21 and a head portion 22 adjacent to the rear of the axial portion 21 and having a larger outer diameter than the axial portion 21. The center electrode 20 is provided such that the head portion 22 engages with the rearward surface 13 of the insulator 11, and the front of the axial portion 21 protrudes from the front end of the insulator 11.

[0014] A first gasket 23 is a conductive member for sealing and fixing the head portion 22 of the center electrode 20 with respect to the inner peripheral surface 12 of the insulator 11. A conductor 24 is a member for suppressing electric wave noise that occurs during discharge and is provided on the rear side of the first gasket 23 within the inner peripheral surface 12. The conductor 24 is electrically connected to the center electrode 20 via the first gasket 23, which is in contact with the center electrode 20 and the conductor 24. The first gasket 23 is made of a mixture containing conductive powder such as metal powder and glass powder.

[0015] Examples of the conductor 24 include a magnetic body or a resistance body made of a composite material of ferrite and a conductor. The resistance body absorbs components of the discharge current in a frequency band that can cause electrical wave noise. The magnetic body blocks or absorbs components in a frequency band that can cause electrical wave noise through impedance or magnetic loss through the ferrite or the like.

[0016] Examples of the resistance body are an element (resistor) formed by providing a coating of resistance material such as carbon-based material, metal, or metal oxide on the surface of a base material such as porcelain, an element formed by winding a resistance wire such as Ni-Cr wire around a base material such as porcelain, and a mixture containing an aggregate and conductive powder.

[0017] In the resistance body made of a mixture containing an aggregate and conductive powder, the aggregate may be, for example, glass powder or inorganic composite powder. Examples of the glass powder for the aggregate include B2O3-SiO2-based powder, BaO-B2O3-based powder, SiO2-B2O3-CaO-BaO-based powder, SiO2-ZnO-B2O3-based powder, SiO2-B2O3-Li2O-based powder, and SiO2-B2O3-Li2O-BaO-based powder. Examples of the inorganic composite powder for the aggregate include powders of alumina, silicon nitride, mullite, steatite, and the like. Only one of these aggregates may be used, or two or more of these aggregates may be used together.

[0018] Examples of conductive powders include powders made of semiconducting oxides, metals, non-metallic conductive materials, and the like. An example of a semiconducting oxide is SnO2. Examples of metals include Zn, Sb, Sn, Ag, Ni, Fe, and Cu. Examples of non-metallic conductive materials include amorphous carbon (soot), graphite, silicon carbide, titanium carbide, titanium nitride, tungsten carbide, and zirconium carbide. Only one of these conductive powders can be used, or two or more of these conductive powders can be used in combination.

[0019] Examples of the magnetic body include a member formed by providing a conductor on the surface of ferrite porcelain, a member formed by winding a metal wire around ferrite porcelain, and an aggregated body (molded body) of magnetic particles formed by coating ferrite particles with conductive material. In the present embodiment, the conductor 24 is a mixture (resistive body) containing an aggregate and conductive powder.

[0020] A second gasket 25 is a member for electrically connecting the conductor 24 and the metal terminal 30. The second gasket 25 is a mixture of conductive powder, such as metal powder, and glass powder. The conductive powder and glass powder contained in the first gasket 23 and the second gasket 25 are similar to those used in the resistor body. The first gasket 23 and the second gasket 25 may contain semiconductive inorganic composite powder such as TiO2, insulating powder, or the like, as needed.

[0021] The metal terminal 30 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is formed of a conductive metal material (e.g., low-carbon steel). The metal terminal 30 has an axial portion 31 inserted into the axial hole of the insulator 11, and a rear end portion 32 located at the rear end of the insulator 11, wherein the axial portion 31 and the rear end portion 32 are integrally formed. The axial portion 31 is electrically connected to the center electrode 20 via the first gasket 23, the conductor 24, and the second gasket 25 within the axial hole of the insulator 11. The rear end portion 32 has a rearward-facing bottom surface 33 and a projection 35 formed from an outer edge 34 (see Fig.2B) of the bottom surface 33. The projection 35 is formed integrally with the rear end portion 32 by cold forging or the like. The metal terminal 30 is coated as required (e.g., nickel-plated).

[0022] A metal shell 40 is a substantially cylindrical member made of a conductive metal material (e.g., low-carbon steel). The metal shell 40 supports the engaging portion 15 and the large-diameter portion 17 of the insulator 11 from both sides in the axial direction to support the insulator 11. A ground electrode 41 is a rod-shaped metal member (e.g., made of a nickel-based alloy) connected to the metal shell 40. The ground electrode 41 has a front end opposite the center electrode 20 across a gap (spark gap).

[0023] Next, an example of a method for manufacturing the spark plug 10 will be described. First, a portion from the front end portion 14 to the small-diameter portion 16 of the insulator 11 is inserted into a support body (not shown) made of substantially the same material as the insulator 11 and formed into a tubular shape. The front surface of the large-diameter portion 17 of the insulator 11 is supported by one end surface of the support body. Subsequently, the center electrode 20 is inserted into the axial hole of the insulator 11, and the head portion 22 of the center electrode 20 is engaged with the rearward surface 13.

[0024] In the subsequent filling step, raw material powder for the first gasket 23 (part of the terminal portion) is first introduced into the axial hole to be filled around the head portion 22. The raw material powder around the head portion 22 is pre-compacted with a pressure rod (not shown). Then, raw material powder for the conductor 24 (part of the terminal portion) is inserted into the axial hole to be filled on the back side of the raw material powder of the first gasket 23. The filled raw material powder is pre-compacted with the pressure rod (not shown). Then, raw material powder for the second gasket 25 (part of the terminal portion) is introduced into the axial hole to be filled on the back side of the conductor 24. The filled raw material powder is pre-compacted with the pressure rod (not shown).

[0025] In a heating step, the insulator 11 supported by the support body is transferred to a heating furnace (not shown) and heated to a temperature (800 to 1000°C) that is, for example, higher than the softening point of a glass component contained in the raw material powder. Next, in a bonding step, an upper punch (not shown) of a press is pressed against the rear end portion 32 of the metal terminal 30, whose axial portion 31 is inserted into the axial hole of the insulator 11, to apply a load (e.g., approximately 1000 N) in the axial direction to a lower punch (not shown) that supports the insulator 11 via the support body. Thus, the axial portion 31 of the metal terminal 30 is strongly pressed against the softened raw material powder of the second gasket 25, so that the softened raw material powder is compacted in the axial direction.

[0026] When the compressed material is cooled for hardening, the first gasket 23, the conductor 24, and the second gasket 25 (connecting portion) are formed within the inner peripheral surface 12 of the insulator 11, and the second gasket 25 is fixed to the axial portion 31 of the metal terminal 30. Thus, the metal terminal 30 and the center electrode 20 are electrically connected. Next, the metal shell 40, with the ground electrode 41 previously connected thereto, is fixed to the outer periphery of the insulator 11, and then the ground electrode 41 is bent so that the front end portion of the ground electrode 41 is opposed to the center electrode 20, thereby obtaining the spark plug 10.

[0027] With reference to the Fig. 2A and Fig. 2B, the metal terminal 30 is described. Fig. 2A is a plan view of the spark plug 10 in the direction of the axial line and Fig.2B is a sectional view of the metal terminal 30 along the line IIb-IIb in Fig. 2A. In Fig. 2A, the insulator 11 and the metal housing 40 are not shown. In Fig. 2B, the front side of the rear end portion 32 of the metal terminal 30 and the middle side portion of the bottom surface 33 are not shown.

[0028] The metal terminal 30 has so far received heat through processes such as heating to form the first seal 23, the conductor 24 and the second seal 25 and therefore has an oxide film 42 formed by oxidation of the surface of the rear end portion 32, as shown in Fig. 2A. The thickness and density of the oxide layer 42 are uneven, and therefore, it can be seen with the naked eye that the oxide layer 42 has a shade of gray to black gray according to the thickness or density. In Fig. 2A and Fig.2B, the oxide layer 42 formed on a rear end surface 37 of the projection 35 is not shown.

[0029] A mark 50 is formed in the center of the bottom surface 33 of the rear end portion 32, on which the oxide layer 42 is formed. The information marked with the mark 50 is, for example, an identification indicator of an engine (not shown) on which the spark plug 10 is mounted, and / or history information specific to the spark plug 10, the metal terminal 30, or the like, and is designed as needed. In the present embodiment, the mark 50 is a two-dimensional code. However, the mark 50 is not limited to a two-dimensional code. A figure such as a circle or a triangle, a one-dimensional code (barcode), or the like can be used as the mark 50 as appropriate. The bottom surface 33 on which the mark 50 is provided is a flat surface perpendicular to the axial line O.In the present embodiment, the bottom surface 33 has a round shape centered on the axial line O.

[0030] The mark 50 (code) includes a first portion 51 formed by a collection of rectangular cells, and a second portion 52 formed by a collection of rectangular cells with a higher reflectance than the first portion 51. In the present embodiment, the first portion 51 is set as a dark module, and the second portion 52 is set as a light module. Various types of information are displayed by combining the first portion 51 and the second portion 52. The mark 50 has, at one edge thereof, a margin (quiet zone) 53 for distinguishing between the mark 50 and a portion (oxide layer 42) adjacent to the periphery of the mark 50, and the margin 53 is a portion of the second portion 52 that has a higher reflectance than the first portion 51.

[0031] To form the mark 50, a laser beam is first applied to the bottom surface 33, scanned along the bottom surface 33 with the laser beam, and thereby formed a rectangular base (background) by removing the oxide layer 42 at a portion where the mark 50 is to be formed. The laser power, scanning speed, focus diameter, and depth of field of the laser beam, and the like, are adjusted to prevent re-oxidation of the bottom surface 33 as much as possible. This reduces shading variations on the background of the mark 50 while increasing the reflectance.

[0032] A laser beam is then applied to the base surface to partially heat the base surface. This promotes the formation of an oxide layer on the component to which the laser beam is applied. By scanning the laser beam along the base surface 33, the first section 51 is formed. The part to which the laser beam was not applied becomes the second section 52.

[0033] Furthermore, a laser beam may be applied to the part corresponding to the second portion 52 to remove an oxide layer generated on the contour part of the second portion 52 due to thermal influences when the first portion 51 is formed. In this case, the laser power, scanning speed, focus diameter, and depth of field of the laser beam, and the like, are adjusted so that the applied energy corresponds to the energy applied during the formation of the base (background). This improves the dimensional accuracy of the first portion 51 and the second portion 52 and enhances the contrast between the first portion 51 and the second portion 52.

[0034] The mark 50 is formed on the metal terminal 30 at any time during the manufacturing process of the spark plug 10. For example, the time at which the mark 50 is formed on the metal terminal 30 is before the heating step of heating the insulator 11 into which the raw material powder is filled, after the heating step, after applying the metal shell 40 to the insulator 11, or after bending the ground electrode 41 and completing the spark plug 10.

[0035] The mark 50 is read by irradiating the mark 50 with illumination light and detecting the reflected light reflected by the mark 50 with a light-receiving element (not shown). The light-receiving element is part of an imaging element such as a CCD or CMOS with a condenser lens, a color filter, and the like. Since the first portion 51 absorbs more illumination light than the second portion 52, the light-receiving element receives more reflected light from the second portion 52 than from the first portion 51.

[0036] As in Fig. 2B, the metal terminal 30 has the projection 35 projecting rearwardly (in Fig.2B). In the present embodiment, the projection 35 projects rearward from the entire circumference of the outer edge 34. An inner peripheral surface 36 of the projection 35 is smoothly adjacent to the bottom surface 33 of the rear end portion 32, and the entire inner peripheral surface 36 is located on the rear side with respect to the bottom surface 33. The thickness of the projection 35 in the radial direction gradually decreases toward the rear end surface 37 from the bottom surface 33. In the present embodiment, the entire rear end surface 37 of the projection 35 is included in a plane perpendicular to the axial line O (see Fig. 1).

[0037] Thus, in the joining step of manufacturing the spark plug 10, the upper punch (not shown) of the press is pressed onto the entire rear end surface 37 of the projection 35. The rear end surface 37 has an area of ​​3 mm 2or more. Note that the upper limit of the area of ​​the rear end surface 37 of the projection 35 is a value obtained by subtracting the area of ​​the bottom surface 33, which is essential for the formation of the mark 50, from the cross-sectional area of ​​the rear end portion 32 along the direction perpendicular to the axial line O.

[0038] The Vickers hardness of the projection 35 at normal temperature (15 to 25°C) is 100 HV or more. The Vickers hardness of the projection 35 is measured according to JIS Z2244:2009. The projection 35 is cut along a plane including the axial line O, and the cut surface is mirror-polished to serve as a test piece whose Vickers hardness is to be measured. In a test piece (cut surface), the projection 35 appears at two parts on both sides with respect to the axial line O. Therefore, an indenter is inserted into the center of each part of the projection 35 (parts above the dashed line in Fig.2B) to form an indentation, the Vickers hardness of the two parts was measured, and the average of these values ​​was calculated. The test force applied to the indenter was 980 mN, and the dwell time was 15 seconds. Preferably, the Vickers hardness of the projection 35 at normal temperature was 400 HV or lower. This is to prevent deterioration of processability during production.

[0039] The rear end surface 37 of the protrusion 35 is positioned on the rear side in the axial direction of the mark 50, opposite the rear end. In the present embodiment, an edge 54 (boundary between the edge 53 and the oxide layer 42) of the mark 50 is formed by removing the oxide layer 42, and therefore, the rear end of the mark 50 refers to the surface of the oxide layer 42 present at the edge 54 of the mark 50.

[0040] Since the Vickers hardness of the projection 35 is 100 HV or higher and the area of ​​the rear end surface 37 of the projection 35 positioned on the rear side with respect to the rear end of the mark 50 is 3 mm 2 or larger, the size and strength of the protrusion 35 can be ensured. Due to the protrusion 35, an external force (e.g., frictional force between the metal terminals 30) that may cause peeling or damage to the mark 50 is less likely to be applied to the bottom surface 33, so that peeling or damage to the mark 50 can be suppressed.

[0041] Furthermore, since the strength of the protrusion 35 is ensured, deformation of the protrusion 35 caused by the load applied to the rear end surface 37 of the protrusion 35 by the upper punch (not shown) of the press can be suppressed in the bonding step of manufacturing the spark plug 10. This can prevent the upper punch of the press from being pressed against the bottom surface 33, thereby suppressing peeling or damage to the mark 50.

[0042] It should be noted that the external force that may cause peeling or damage to the mark 50 is not limited to an external force applied to the rear end portion 32 after the mark 50 is formed on the bottom surface 33. An external force applied to the rear end portion 32 before the mark 50 is formed is also included. If an external force is applied to the bottom surface 33 before the mark 50 is formed, the bottom surface 33 may be damaged. If the mark 50 is formed on the damaged bottom surface 33, the mark 50 becomes defective or unclear at the damaged part of the bottom surface 33, resulting in the occurrence of a reading error of the mark 50.

[0043] Since the projection 35 protrudes rearward from the entire circumference of the outer edge 34 of the bottom surface 33, it is even less likely that an external force that may cause peeling or damage to the mark 50 will act on the bottom surface 33. Thus, the effect of suppressing peeling or damage to the mark 50 can be further enhanced.

[0044] At the rear end portion 32 of the metal terminal 30, a gap G is formed between the edge 54 of the mark 50 and the outer edge 34 of the bottom surface 33. The presence of the gap G can suppress the impairment of the readability of the mark 50 by the projection 35. The size of the gap G is 0.03 mm or more. A distance D along the axial line O (see Fig.1) between the bottom surface 33 and the rear end surface 37 of the projection 35 is 1.5 mm or less. This can suppress the occurrence of errors in reading the mark 50 (code) by the light-receiving element (not shown).

[0045] Note that the distance D is greater than the thickness of the mark 50 formed on the bottom surface 33. Thus, the projection 35 can prevent an external force from being applied to the mark 50. In the present embodiment, the distance D is greater than the thickness of the oxide layer 42 at the edge 54 of the mark 50. This is because the oxide layer 42 forms the edge 54 of the mark 50.

[0046] With reference to Fig.3, the second embodiment will be described. In the first embodiment, the case where the protrusion 35 is formed on the entire circumference of the outer edge 34 of the bottom surface 33 of the metal terminal 30 was described. In the second embodiment, on the other hand, the case where protrusions 65, 68 are formed on parts of an outer edge 64 of a bottom surface 63 of a metal terminal 60 will be described. Note that the metal terminal 60 is replaced by the metal terminal 30 of the spark plug 10 described in the first embodiment. Accordingly, the same parts as described in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted below.

[0047] Fig. 3A is a plan view of a spark plug according to the second embodiment, and Fig. 3B is a sectional view of the metal terminal 60 taken along the line IIIb-IIIb in Fig. 3A. In Fig. 3A, the insulator 11 and the metal housing 40 are not shown. In Fig. 3B, the front side of the rear end portion 32 of the metal terminal 60 is not shown. The axial portion 31 (see Fig. 1) is adjacent to the front of the rear end portion 32.

[0048] The metal terminal 60 has projections 65 projecting rearwardly (upwardly in Fig. 3B), and projections 68 projecting rearward from two positions on the outer edge 64 of the bottom surface 63. Each set of projections 65, 68 is aligned with the axial line O (see Fig. 1) are positioned opposite each other therebetween. The marking 50 is formed in the center of the bottom surface 63, within the inner area surrounded by the projections 65, 68.

[0049] An inner peripheral surface 66 of each projection 65 is smoothly adjacent to the bottom surface 63 of the rear end portion 62, and the entire inner peripheral surface 66 is arranged on the rear side with respect to the bottom surface 63. An inner peripheral surface 69 of each projection 68 is smoothly adjacent to the bottom surface 63 of the rear end portion 62, and the entire inner peripheral surface 69 is arranged on the rear side with respect to the bottom surface 63. The rear end surfaces 67 of the projections 65 and the rear end surfaces 70 of the projections 68 are positioned on the rear side with respect to the rear end of the marker 50. The thicknesses of the projections 65, 68 in the radial direction gradually decrease toward the rear end surfaces 67, 70 from the bottom surface 63.

[0050] The distance along the axial line O between the rear end surface 67 of each projection 65 and the lower surface 63 is greater than the distance along the axial line O between the rear end surface 70 of each projection 68 and the lower surface 63. The rear end surfaces 67 of the projections 65 are arranged in a plane perpendicular to the axial line O (see Fig. 1). Thus, in the joining step of manufacturing the spark plug 10, the upper punch (not shown) of the press is pressed against the rear end surfaces 67 of the projections 65. The rear end surfaces 67 of the projections 65 have an area of ​​3 mm 2or more, and the Vickers hardness of the protrusions 65 at normal temperature (15 to 25°C) is 100 HV or more. This ensures the size and strength of the protrusions 65. Due to the protrusions 65, an external force that may cause peeling or damage to the mark 50 is less likely to be applied to the bottom surface 63, thereby suppressing peeling or damage to the mark 50.

[0051] Furthermore, since the strength of the protrusions 65 is ensured, deformation of the protrusions 65 caused by the loading of the upper punch (not shown) of the press against the rear end surfaces 67 of the protrusions 65 during the bonding step of manufacturing the spark plug 10 can be suppressed. This can prevent the upper punch of the press from being pressed against the bottom surface 63, thereby suppressing peeling or damage to the mark 50.

[0052] It should be noted that the Vickers hardness of the protrusions 68 is also 100 HV or higher at normal temperature. Therefore, due to the protrusions 68, external forces that may cause peeling or damage to the mark 50 are less likely to be applied to the bottom surface 63. This can suppress peeling or damage to the mark 50. Examples

[0053] The present invention will be further described using examples. However, the present invention is not limited to the examples. Test 1

[0054] Various samples 1 to 6 were prepared in which the protrusion 35 protruded rearward from the entire circumference of the outer edge 34 of the bottom surface 33 of the rear end portion 32, as in the metal terminal 30 according to the first embodiment, and the strength of the protrusion 35 was evaluated. Each prepared sample (metal terminal 30) was made of low-carbon steel, and the Vickers hardness of the protrusion 35 at normal temperature was 100 HV (test load 980 mN, dwell time 15 seconds). The shape of the bottom surface 33 in each sample was a round shape, and the height of the protrusion 35 from the bottom surface 33 (distance D along the axial line O between the bottom surface 33 and the rear end surface 37 of the protrusion 35) was 1.0 mm. In these samples, the outer diameters of the projections 35 were the same, but the inner diameters were designed differently so that the rear end surfaces 37 of the projections 35 had different areas.

[0055] The test was conducted on each sample heated in a heating furnace to 900°C (furnace internal temperature) by pressing the upper punch of the press against the rear end surface 37 of the protrusion 35 to apply a load of 1000 N in the axial direction to the protrusion 35 between the upper punch (die) and the lower punch (die). The sample was removed from the heating furnace, and after the sample cooled to normal temperature, the height (distance D) of the protrusion 35 from the bottom surface 33 of the sample was measured. The sample in which the height of the protrusion 35 was reduced by 0.1 mm or more after the test was evaluated as subject to deformation of the protrusion 35 (Poor), and the sample in which the height change of the protrusion 35 between before and after the test was less than 0.1 mm was evaluated as sufficiently strong (Good). The results are shown in Table 1. Table 1 No. Range (mm 2 ) Evaluation 1 2.00 Bad 2 2.25 Bad 3 2.50 Bad 4 2.75 Bad 5 3.00 Good 6 3.25 Good

[0056] As shown in Table 1, in Samples 1 to 4 in which the area of ​​the rear end surface 37 of the projection 35 was less than 3 mm 2 was deformed. On the other hand, in samples 5, 6, in which the area of ​​the rear end surface 37 of the projection 35 was 3 mm 2 or larger, the projection 35 was hardly deformed. Thus, it was found that in the case where the Vickers hardness of the projection 35 is 100 HV, when the area of ​​the rear end surface 37 of the projection 35 is 3 mm 2 or more, the projection 35 is hardly deformed even if a load of 1000 N is applied to the projection 35 under the condition of 900°C (furnace internal temperature). Test 2

[0057] Various samples 7 to 11 were prepared in which the protrusion 35 protrudes rearward from the entire circumference of the outer edge 34 of the bottom surface 33 of the rear end portion 32, as in the metal terminal 30 according to the first embodiment, and the strength of the protrusion 35 was evaluated. Each prepared sample (metal terminal 30) was made of low-carbon steel, and the rear end surface 37 of the protrusion 35 in each sample had an area of ​​3 mm. 2 In each sample, the shape of the bottom surface 33 was round, and the height of the protrusion 35 from the bottom surface 33 (distance D along the axial line O between the bottom surface 33 and the rear end surface 37 of the protrusion 35) was 1.0 mm. The samples were subjected to quenching or annealing, so that the protrusions 35 varied in Vickers hardness (test load 980 mN, dwell time 15 seconds) at normal temperature.

[0058] The test was conducted on each sample heated in a heating furnace to 900°C (furnace internal temperature) by pressing the upper punch of the press against the rear end surface 37 of the protrusion 35 to apply a load of 1000 N in the axial direction to the protrusion 35 between the upper punch and the lower punch. The sample was removed from the heating furnace, and after the sample cooled to normal temperature, the height (distance D) of the protrusion 35 from the bottom surface 33 of the sample was measured. The sample in which the height of the protrusion 35 was reduced by 0.1 mm or more after the test was evaluated as subject to deformation of the protrusion 35 (Poor), and the sample in which the height change of the protrusion 35 between before and after the test was less than 0.1 mm was evaluated as sufficiently strong (Good). The results are shown in Table 2. Table 2 No. Hardness (HV) Evaluation 7 50 Bad 8 80 Bad 9 100 Good 10 120 Good 11 150 Good

[0059] As shown in Table 2, in samples 7 and 8, where the Vickers hardness of the projection 35 was less than 100 HV, the projection 35 was deformed. On the other hand, in samples 9 to 11, where the Vickers hardness of the projection 35 was 100 HV or higher, the projection 35 was hardly deformed. Thus, it was found that in the case where the area of ​​the rear end surface 37 of the projection 35 was 3 mm 2 When the Vickers hardness of the projection 35 is 100 HV or higher, the projection 35 is hardly deformed even if a load of 1000 N is applied to the projection 35 under the condition of 900°C (furnace internal temperature).

[0060] From tests 1, 2 it is concluded that in case the Vickers hardness of the projection 35 is 100 HV or more and the area of ​​the rear end surface 37 of the projection 35 is 3 mm 2or more, the projection 35 itself is hardly deformed when a force in the axial line direction is applied to the projection 35 in the joining step during manufacture of the spark plug 10. In the case that the mark 50 is formed on the bottom surface 33 of the metal terminal 30 before the joining step, it is possible to suppress peeling of the mark 50 even after the joining step has been passed. In the case that the mark 50 is formed on the bottom surface 33 of the metal terminal 30 after the joining step, it is possible to suppress damage to the bottom surface 33 even after the joining step. Since damage to the bottom surface 33 can be suppressed, occurrence of defects such as loss of the mark 50 can be suppressed when the mark 50 is formed on the bottom surface 33. Test 3

[0061] Samples were prepared in which the protrusion 35 protruded rearward from the entire circumference of the outer edge 34 of the outer edge 33 of the bottom surface 33 of the rear end portion 32, as in the metal terminal 30 according to the first embodiment, and the mark 50 was formed on the bottom surface 33 in each sample. The shape of the bottom surface 33 of each sample (metal terminal 30) was round, and the area of ​​the rear end surface 37 of the protrusion 35 was 3 mm. 2Each mark 50 was a two-dimensional code of the same size, formed by applying a laser beam. The reading performance was evaluated according to ISO / IEC TR29158:2011. The samples differed in the height of the protrusion 35 from the bottom surface 33 (distance D along the axial line O between the bottom surface 33 and the rear end surface 37 of the protrusion 35) and in the gap G (minimum value) between the edge 54 of the mark 50 and the outer edge 34 of the bottom surface 33. The reading result (quality) is shown in Table 3. In Table 3, "U" indicates that reading could not be performed. A large mark 50 is preferable because the amount of information can be increased, but enlarging the mark 50 results in a decrease in the gap G. As shown in Table 3, it was found that when the gap G is smaller than 0.03 mm, the quality is low and reading errors are more likely to occur. On the other hand, when the gap G is 0.03 mm or larger and the distance D is 1.50 mm or smaller, the quality is A or B. Therefore, it was found that when the gap G and the distance D are set to satisfy this condition, the occurrence of reading errors of the mark 50 can be suppressed, while the peeling off or damage of the mark 50 by the projection 35 is suppressed.

[0062] Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments. It is readily understood that various modifications can be made without departing from the gist of the present invention.

[0063] In the above embodiments, the spark plug 10 was described in which the conductor 24 and the second gasket 25 are arranged between the first gasket 23 and the metal terminal 30, 60, but the present invention is not necessarily limited thereto. Of course, it is also possible for the head portion 22 of the center electrode 20 and the axial portion 31 of the metal terminal 30, 60 to be connected via the first gasket 23 without providing the conductor 24 and the second gasket 25.

[0064] In this case, during spark plug manufacturing, after the raw material powder for the first gasket 23 is filled into the axial hole of the insulator 11, the insulator 11 is heated, and the axial portion 31 of the metal terminal 30, 60 is inserted into the axial hole. In the bonding step, the axial portion 31 is pressed against the softened raw material powder of the first gasket 23, and the metal terminal 30, 60 is fixed to the insulator 11 via the hardened first gasket 23.

[0065] Also in this step, an external force is likely to be applied to the rear end portion 32, 62 of the metal terminal 30, 60 due to friction between the metal terminals 30, 60 or the like, or an external force that occurs when the axial portion 31 is pressed against the raw material powder of the first seal 23. In view of this, the Vickers hardness of the projection 35, 65, 68 is set to 100 HV or higher, and the area of ​​the rear end surface 37, 67 of the projection 35, 65 is set to 3 mm. 2 or higher, thereby ensuring the size and strength of the projection 35, 65, 68 and thus making it less likely that such an external force, which may cause detachment or damage to the mark 50, will be exerted on the lower surface 33, 63.

[0066] In the above embodiment, the case where the entire rear end surface 37 of the protrusion 35 formed on the rear end portion 32 of the metal terminal 30 is located on a plane perpendicular to the axial line O (the case where the height of the protrusion 35 is uniform in the circumferential direction of the rear end portion 32) was described. However, the present invention is not necessarily limited to this. Of course, the height of the protrusion 35 may vary in the circumferential direction of the rear end portion 32. In this case, the area of ​​the rear end surface of the protrusion 35 refers to an area of ​​the highest part of the protrusion 35. This is because the higher the protrusion 35 is, the less likely it is that an external force that may cause peeling or damage to the mark 50 will be applied to the bottom surface 33.

[0067] In the above embodiment, the case where the first portion 51 (dark module) is formed after the ground plane (background) is formed during the formation of the mark 50 was described. However, the present invention is not necessarily limited to this. Of course, in the case where the oxide layer 42 has high brightness (high reflectance), it is also possible to apply a laser beam to the oxide layer 42 during the formation of the mark 50 to form the first portion 51 on the oxide layer 42 without providing the ground plane.

[0068] On the other hand, in the case where the oxide layer 42 has a low brightness (low reflectance), it is of course also possible that, during the formation of the mark 50, a laser beam is applied to the oxide layer 42 and the oxide layer 42 is partially removed to form the second portion 52 without providing the base area.

[0069] Although not described in the above embodiments, the marking 50 in which the light module and the dark module are interchanged may of course be provided on the metal terminal 30, 60. In this case, the edge 53 of the marking 50 is part of the first portion 51 (dark module).

[0070] In the above embodiments, the case of forming the mark 50 by applying a laser beam to the metal terminal 30, 60 was described. However, the present invention is not necessarily limited to this. Of course, the mark 50 may be printed on the metal terminal 30, 60 with ink. The ink used may be an ultraviolet curing type, an electron beam curing type, a thermosetting type, or the like, as needed. In this case, the tail end of the mark 50 refers to the tail end of the cured ink.

[0071] The following invention is also disclosed in the embodiments. Disclosed is a method for manufacturing a spark plug, comprising: an insulator having an axial hole formed along an axial line extending from a front side to a rear side; a center electrode located on a front side of the axial hole of the insulator; a metal terminal located on a rear side of the axial hole of the insulator; and a connecting portion electrically connecting the metal terminal and the center electrode, wherein the metal terminal has, at a rear end portion, a rearward-facing bottom surface and a projection projecting rearward from an outer edge of the bottom surface, at least a part of the bottom surface being provided with a mark, the method comprising: a center electrode placing step of placing the center electrode in the axial hole;a filling step of filling raw material powder for the connecting portion on a rear side of the center electrode; and a joining step of pressing the metal terminal inserted into the axial hole against the raw material powder for the connecting portion in a hot state, wherein the Vickers hardness of the protrusion is 100 HV or higher, the rear end surface of the protrusion is positioned on a rear side with respect to a rear end of the mark, and an area of ​​the rear end surface is 3 mm; 2 or larger.

[0072] This spark plug manufacturing process ensures the strength of the protrusion, preventing damage or deformation of the protrusion during the bonding step. This reduces the likelihood of external force being applied to the bottom surface of the metal terminal, thus preventing peeling or damage to the marking. Description of reference symbols 10 Spark plug 11 Insulator 30, 60 metal connection 32, 62 rear end section 33, 63 floor area 34, 64 outer edge 35, 65, 68 lead 37, 67 rear end face 50 Mark 54 edge D Distance G gap

Claims

[1] Spark plug (10), comprising: an insulator (11) having an axial hole formed along an axial line (O) extending from a front side to a rear side; and a metal terminal (30, 60) located on a rear side of the axial hole of the insulator (11), wherein the metal terminal (30, 60) has, at a rear end portion (32, 62) thereof, a rearwardly directed bottom surface (33, 63) and a projection (35, 65, 68) projecting rearward from an outer edge (34, 64) of the bottom surface (33, 63), at least a part of the bottom surface (33, 63) being provided with a marking (50), the Vickers hardness of the projection (35, 65, 68) is 100 HV or more, a rear end surface (37, 67) of the projection (35, 65, 68) is positioned on a rear side with respect to a rear end of the marker (50), an area of ​​the rear end surface (37, 67) 3 mm 2or greater, and where a gap (G) is provided between an edge (54) of the marking (50) arranged on the bottom surface (33, 63) and the outer edge (34, 64) of the bottom surface (33, 63). [2] The spark plug (10) according to claim 1, wherein the projection (35) projects rearward from an entire circumference of the outer edge (34) of the bottom surface (33). [3] The spark plug (10) according to one of claims 1 or 2, wherein the marking (50) is a code that allows information to be read therefrom using reflected light, a gap (G) between an edge (54) of the code attached to the bottom surface (33) and the outer edge (34) of the bottom surface (33) is 0.03 mm or more, and a distance (D) along the axial line (O) between the bottom surface (33) and the rear end surface (37) of the projection (35) is 1.5 mm or less.

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