JP7655833B2 - Spark plug and method for manufacturing the same - Google Patents

Description

The present invention relates to a spark plug and a method for manufacturing a spark plug.

Spark plugs are used as an ignition means for internal combustion engines such as automobile engines. A spark plug has, for example, an axial center electrode, a roughly cylindrical insulator that holds the center electrode on the inside, and a metal shell that holds the insulator on the inside.

Generally, spark plugs are affixed with marks such as the manufacturer's name, logo, or product number, which are made up of letters, symbols, and other images. For example, Patent Document 1 discloses a spark plug in which a marking layer representing letters, symbols, images, etc. is formed on the surface of the spark plug.

JP 2004-22227 A

The inventors of the present invention believe that there is room for improvement in the accuracy of reading marks on the surface of spark plugs.

The present invention has been made to solve the above problems, and aims to provide a spark plug whose surface markings can be read with high accuracy.

A spark plug according to one aspect of the present invention includes a cylindrical metal shell and an insulator that is held inside the metal shell and protrudes from the axial rear end side of the metal shell, and an identification portion is formed on the outer surface of the metal shell or the insulator, the identification portion is composed of a first layer that is formed on the outer surface, and a second layer that is formed on a part of the surface of the first layer and is distinguishable from the first layer, and the thickness of the portion of the first layer where the second layer is formed on the surface is thicker than the thickness of the exposed portion of the first layer.

According to the above configuration, the identification portion is composed of a first layer and a second layer formed on a part of the surface of the first layer and distinguishable from the first layer, so that it is possible to suppress a decrease in reading accuracy depending on scratches or dirt on the outer surface, as occurs when the identification portion is composed of a single layer. In addition, the identification portion may rub against each other and become partially peeled off during shipping of the spark plug, but when the first layer is peeled off from the outer surface, the reading accuracy decreases significantly compared to when the second layer is peeled off from the first layer in the area where the identification portion is formed. Here, according to the above configuration, the thickness of the part of the first layer on which the second layer is formed is thicker than the exposed part of the first layer, so that it is possible to suppress peeling of the exposed part of the first layer, which is particularly prone to peeling during shipping, and suppress a decrease in reading accuracy.

In one aspect of the spark plug of the present invention, the insulator is formed mainly of alumina, the identification portion is formed on the insulator, and the first layer may have a brightness of 7 or more and the second layer may have a brightness of 5 or less.

With the above configuration, the alumina-based insulator and the first layer with a brightness of 7 or more have the same color scheme, so even if part of the first layer peels off, a significant decrease in reading accuracy can be suppressed. In addition, because there is a difference in brightness between the first and second layers, a contrast is created between the first and second layers, making it easier to read the identification part.

In one aspect of the spark plug of the present invention, the surface roughness Ra of the second layer may be greater than the surface roughness Ra of the first layer.

With the above configuration, the reflectance of the light irradiated for reading on the surface of the second layer, which is located further out than the first layer, can be reduced, thereby preventing a decrease in the readability of the identification section.

In a spark plug according to one aspect of the present invention, the first layer may be opaque.

The above configuration makes it possible to prevent a decrease in the reading accuracy of the identification unit due to the condition of the outer surface.

In another aspect of the present invention, a method for manufacturing a spark plug having an identification portion formed on its outer surface includes a first step of forming a visible first layer on the outer surface, and a second step of forming, after the first step, a second layer on a portion of the first layer that is distinguishable from the first layer and is also visible.

According to the above configuration, the identification unit is composed of a first layer and a second layer that is formed on a part of the surface of the first layer and is distinguishable from the first layer, so that it is possible to prevent the reading accuracy from decreasing due to scratches or dirt on the outer surface, as occurs when the identification unit is composed of a single layer.

In another aspect of the spark plug manufacturing method of the present invention, in the second step, the second layer may be formed by removing a portion of a layer laminated on the first layer.

The above configuration allows for the formation of an identification part with higher shape accuracy.

In another aspect of the spark plug manufacturing method of the present invention, in the second step, when removing a portion of the layer laminated on the first layer, the removal may be performed in such a way that the outer surface is not exposed.

The above configuration makes it possible to prevent damage to the outer surface when removing a portion of the layer stacked on the first layer.

1 is an external view of a spark plug according to a first embodiment; 2 is a schematic diagram showing a cross-sectional configuration of an identification portion forming region in the spark plug shown in FIG. 1 . FIG. 3A to 3C are schematic diagrams showing a process for forming an identification portion in the spark plug shown in FIG. 1 in order of steps.

First embodiment:
1 is an external view of a spark plug according to a first embodiment. The spark plug 1 includes an insulator 50 and a metallic shell 30.

The insulator 50 is a generally cylindrical member extending in the longitudinal direction of the spark plug 1. The insulator 50 is made of a material with excellent insulating properties, heat resistance, and thermal conductivity. For example, the insulator 50 is made mainly of alumina. A center electrode 21 is provided at one end (tip end 51) of the insulator 50. A terminal fitting 52 is attached to the other end (rear end) of the insulator 50. The insulator 50 may have a glaze layer on its surface. In this case, the glaze layer is also included in the "insulator" of the present invention.

The center electrode 21 is held through an axial hole in the insulator 50 with its tip protruding from the tip 51 of the insulator 50. The center electrode 21 is attached to the insulator 50 so that its tip is located on the axis O of the substantially cylindrical insulator 50. The center electrode 21 has a substantially cylindrical shape, and its tip is tapered. The tip of the center electrode 21 may be made of, for example, a precious metal tip formed into a cylindrical shape.

The metal shell 30 is a generally cylindrical member that is fixed to a screw hole in an internal combustion engine. The metal shell 30 is provided so as to partially cover the insulator 50. The metal shell 30 is formed of a metal material having electrical conductivity, such as low carbon steel or a metal material whose main component is iron. The metal shell may be provided with a plating layer, in which case the "metal shell" according to the present invention includes the plating layer.

The metal shell 30 mainly has a crimping portion 31, a tool engagement portion 32, a curved portion 33, a seat portion 34, and a body portion 35.

The crimping portion 31 and the curved portion 33 are used to attach the metal shell 30 to the insulator 50. The tool engagement portion 32 is used to engage a tool such as a wrench when attaching the metal shell 30 to a screw hole in an internal combustion engine. The seat portion 34 is located between the tool engagement portion 32 and the body portion 35. When the spark plug 1 is attached to the internal combustion engine, an annular gasket is placed on the seat portion 34. The body portion 35 is located on the tip portion 51 side of the insulator 50. When the spark plug 1 is attached to the internal combustion engine, the thread groove formed on the outer periphery of the body portion 35 is screwed into the screw hole of the internal combustion engine.

A ground electrode 41 is attached to the tip side of the metal shell 30 (the side where the body 35 is located). The ground electrode 41 is a plate-like body bent into an L-shape as a whole, and the base end side is joined and fixed to the tip surface of the metal shell 30. The tip of the ground electrode 41 extends to a position where an imaginary extension line of the axis O of the insulator 50 passes through. Although not shown, a convex portion that protrudes toward the center electrode 21 may be formed near the tip of the ground electrode 41.

The center electrode 21 and the ground electrode 41 are formed from a base material made of a metal material such as a Ni-based alloy containing Ni (nickel) as the main component. Examples of alloy elements added to the Ni-based alloy include Al (aluminum). The center electrode 21 and the ground electrode 41 may have a core material made of a metal material with excellent thermal conductivity, such as Cu (copper) or a Cu alloy.

(About spark plug identification)
A two-dimensional code 10, which is an example of an identification portion, is attached to the spark plug 1. The two-dimensional code 10 is, for example, a Datamatrix code, a QR code (registered trademark), etc. The two-dimensional code 10 includes various information for identifying each individual spark plug, such as product information of the spark plug 1 and history information in the manufacturing process.

In the present invention, the identification unit is not limited to a two-dimensional code. Identification units other than two-dimensional codes include, for example, one-dimensional codes such as barcodes, characters, symbols, and images. The identification unit may also be configured by combining some of the one-dimensional codes, two-dimensional codes, characters, symbols, and images.

In one embodiment, as shown in FIG. 1, the two-dimensional code 10 is attached at an arbitrary position on the outer peripheral surface of the insulator 50. The area on the outer surface of the insulator 50 where the two-dimensional code 10 is formed is called the identification portion forming area 10a.

Figure 2 shows a cross-sectional structure of the identification portion forming region 10a of the spark plug 1. The two-dimensional code 10 formed on the insulator 50 has a first layer 11 formed on the insulator 50 and a second layer 12 formed on a part of the first layer 11. The first layer 11 and the second layer 12 are in a distinguishable state. The thickness A of the portion of the first layer 11 on which the second layer 12 is formed is thicker than the thickness B of the portion on which the second layer 12 is not formed. As a result, the portion of the first layer 11 on which the second layer 12 is not formed is deeper from the surface of the identification portion, which makes it possible to prevent the identification portion from peeling off due to external forces during shipping.

In this embodiment, the raw materials of the first layer 11 and the second layer 12 are not particularly limited, but the first layer 11 is made of, for example, a white ink having a brightness of 7 or more, and the second layer 12 is made of, for example, an ink of a different color from the first layer 11 having a brightness of 5 or less. If the first layer 11 has a brightness of 7 or more, even if the first layer 11 peels off, the alumina-based insulator 50 and the first layer 11 have the same color, so that the reading accuracy of the two-dimensional code 10 is prevented from significantly decreasing. In addition, if the second layer 12 has a brightness of 5 or less, a contrast is created between the first layer 11 and the second layer 12 due to the difference in brightness with the first layer 11 having a brightness of 7 or more, making it easier to read the identification part.

Furthermore, it is preferable that the surface roughness of the second layer 12 is greater than that of the first layer 11. Note that the "surface roughness" according to the present invention refers to the average arithmetic surface roughness. This makes it possible to suppress the reflectance of the irradiated light for reading on the surface of the second layer 12, which is located further outward than the first layer 11, and thus to suppress a decrease in the readability of the two-dimensional code 10.

In addition, it is preferable that the first layer 11 is opaque. As a result, even if the portion of the insulator 50 on which the first layer 11 is formed is scratched or dirty, the first layer 11 covers the scratch or dirt, thereby preventing a decrease in the reading accuracy of the two-dimensional code 10.
(Spark plug manufacturing method)

Next, a method for manufacturing the spark plug 1 will be described. Here, the process for forming marks such as the two-dimensional code 10 will be mainly described. For the other manufacturing processes in the method for manufacturing the spark plug 1, the same manufacturing methods as those for conventional spark plugs can be applied.

Figures 3(a) to (c) show the process of forming the two-dimensional code 10 in the order of steps included in the manufacturing method of the spark plug 1. The following describes an example in which the two-dimensional code 10 is formed on the finished spark plug 1. However, the two-dimensional code 10 may also be formed on the components of the spark plug 1 during manufacturing in a manner similar to that described below.

First, a spark plug is prepared without the two-dimensional code 10. Then, the first layer 11 is formed on the surface of the insulator 50 (see FIG. 3(a)). The first layer 11 can be formed, for example, by printing the white ink as described above on the surface of the insulator 50.

Next, a layer (hereinafter referred to as intermediate formation layer 13) that will later become second layer 12 is formed on the formed first layer 11 (see FIG. 3(b)). Intermediate formation layer 13 can be formed, for example, by printing an ink of a color different from that of first layer 11 as described above on the surface of first layer 11.

After forming the intermediate formation layer 13 on the first layer 11, a laser L is irradiated to a predetermined area of the intermediate formation layer 13, and the intermediate formation layer 13 is partially removed so as to expose the first layer, thereby forming the second layer 12 (see Figs. 3(b) and (c)). At this time, the first layer 11 is not removed until the surface of the metal shell 30 is exposed in the laser irradiated area. The type of laser L is not particularly limited, and for example, a YAG laser or a fiber laser can be used for pulse irradiation or continuous irradiation.

Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment, and can be embodied in various forms without departing from the gist of the present invention.

In the above embodiment, the two-dimensional code 10 is formed on the surface of the insulator 50, but it can also be formed on the metal shell 30.

1: Spark plug 10: Two-dimensional code 11: First layer 12: Second layer 13: Intermediate layer 21: Center electrode 30: Metal shell 41: Ground electrode 50: Insulator

Claims (3)

a cylindrical metal shell; and an insulator that is held inside the metal shell and protrudes from a rear end side in an axial direction of the metal shell,
A spark plug having an identification portion formed on an outer surface of the insulator ,
The insulator is formed mainly of alumina,
the distinguishing portion comprises a first layer formed on the outer surface, and a second layer formed on a part of the surface of the first layer and distinguishable from the first layer;
the first layer has a brightness of 7 or more, and the second layer has a brightness of 5 or less;
a thickness of a portion of the first layer on which the second layer is formed is greater than a thickness of an exposed portion of the first layer. 2. The spark plug according to claim 1 , wherein the second layer has a surface roughness Ra greater than a surface roughness Ra of the first layer. 3. The spark plug of claim 1, wherein said first layer is opaque.

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