JP2011081978A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of reducing possibility of failures in confirming a direction of a spark plug. <P>SOLUTION: The spark plug 100 is provided with a mark MK for specifying a direction from a central electrode 20 toward a grounding electrode 30 perpendicular to an axial line OX. The mark MK is provided on a part formed on a face crossing the axial line direction in a rear end BWD of body fittings 50 and is composed of a fluorescent paint. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a spark plug.

  Conventionally, spark plugs have been used for engines. When the spark plug is mounted on the engine, the electrodes (center electrode and ground electrode) of the spark plug are arranged in the combustion chamber of the engine. The arrangement of the electrodes in the combustion chamber affects the flow of gas and flame in the combustion chamber. Engine performance (eg, ignitability) can be affected by the direction of the spark plug in the combustion chamber (eg, the direction of the ground electrode as viewed from the center electrode). In addition, by adjusting the direction of the spark plug to a direction suitable for the engine, good performance of the engine can be obtained. Here, various techniques are known for confirming the direction of the spark plug attached to the engine without removing the spark plug from the engine. For example, a technique for providing an identification part in a hexagonal nut part and a technique for forming a marker on a base of a terminal metal fitting or a cap of a terminal metal fitting are known.

Japanese Patent No. 2010274 JP 2004-92410 A

  However, in some cases, a problem occurs with the confirmation of the direction of the spark plug. For example, when a convex portion as an identification portion is provided on the hexagon nut portion, a dedicated tool may be required for mounting the spark plug. In addition, when forming a marker on the terminal fitting, it is sometimes difficult to confirm the marker because the marker is small.

  The main advantage of the present invention is to provide a technique that can reduce the possibility of problems associated with the confirmation of the direction of the spark plug.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1] An insulator having an axial hole penetrating in the axial direction, a center electrode provided on the tip side of the axial hole, a substantially cylindrical metal shell for holding the insulator, and one end of the main body A spark plug that is attached to a tip of a metal fitting and has a ground electrode that forms a spark gap between the other end and the center electrode, and the ground electrode is perpendicular to the axial direction from the center electrode. The spark plug includes a mark for specifying a direction toward the front, and the mark includes a portion formed on a surface intersecting the axial direction in a rear end portion of the metal shell.

  According to this configuration, since the mark can be easily seen when the spark plug is viewed from the rear end side toward the front end side, it is possible to reduce the possibility of a problem associated with confirmation of the direction of the spark plug.

Application Example 2 The spark plug according to Application Example 1, wherein the mark includes a fluorescent paint.

  According to this configuration, since the mark can be easily confirmed even in a dark place, the possibility of a problem that the mark cannot be confirmed can be reduced. For example, even when a spark plug is installed in a deep plug hole, the mark (that is, the direction) can be easily confirmed.

[Application Example 3] The spark plug according to Application Example 1 or Application Example 2, wherein the metal shell includes an engaging portion with which a tool engages when the spark plug is mounted on an internal combustion engine. Is a spark plug disposed at least partially within a range from an end of the engaging portion on the side of the center electrode to an end of the insulator opposite to the side of the center electrode.

  According to this configuration, since the mark can be easily confirmed, it is possible to reduce the possibility of a problem that it is difficult to confirm the mark. For example, if a mark is arranged on the engaging portion, the mark can be easily confirmed even when the plug cap is attached to the spark plug. Further, if the mark is arranged on the insulator, the mark can be lengthened, so that the mark can be easily confirmed.

Application Example 4 The spark plug according to any one of Application Examples 1 to 3, wherein the mark has a width of 0.8 mm or more.

  According to this configuration, since the mark can be easily confirmed, the possibility of a problem that the mark cannot be confirmed can be reduced.

[Application Example 5] The spark plug according to any one of Application Examples 1 to 4, wherein the mark is based on a center axis of rotation when the spark plug is rotated and mounted on an internal combustion engine. Spark plug that looks at 30 degrees or less.

  According to this configuration, the direction of the spark plug can be confirmed with an accuracy of an error of 30 degrees or less. As a result, the possibility of a problem that the direction of the spark plug cannot be directed to an appropriate direction of the internal combustion engine can be reduced.

[Application Example 6] The spark plug according to any one of Application Examples 1 to 5, wherein the spark plug is rotated with respect to a central axis of rotation when the spark plug is mounted on an internal combustion engine. The angle between the direction toward the center of the mark and the direction toward the center of the portion of the ground electrode that is disposed in a direction perpendicular to the axial direction when viewed from the center electrode is 15 degrees or less. ,Spark plug.

  According to this configuration, since the angle between the mark and the ground electrode is 15 degrees or less, by adjusting the direction of the spark plug according to the mark, the direction of the ground electrode can be adjusted to an accuracy with an error of 15 degrees or less. Can be adjusted. As a result, the possibility of a problem that the direction of the spark plug cannot be directed to an appropriate direction of the internal combustion engine can be reduced.

[Application Example 7] The spark plug according to any one of Application Examples 1 to 6, wherein the insulator includes a ceramic insulating member and a glaze layer covering at least a part of the surface of the insulating member. The spark plug includes: the mark includes a portion formed between the insulating member and the glaze layer.

  According to this configuration, since the mark is protected by the glaze layer, it is possible to reduce the possibility of a problem that the mark is damaged.

Application Example 8 The spark plug according to any one of Application Examples 1 to 7, wherein the mark includes a portion formed on a surface of the insulator.

  According to this configuration, since the mark can be formed after the parts of the spark plug are assembled, it is possible to easily form the mark at an appropriate position.

Application Example 9 The spark plug according to any one of Application Examples 1 to 8, wherein the mark includes a heat resistant paint.

  According to this configuration, it is possible to reduce the possibility of a problem of mark damage due to heat received from the internal combustion engine.

Application Example 10 The spark plug according to any one of Application Examples 1 to 9, wherein the mark includes a portion whose glossiness is different from a glossiness of a peripheral portion of the mark.

  According to this configuration, when the spark plug is illuminated with a light, the mark can be easily confirmed.

Application Example 11 The spark plug according to any one of Application Examples 1 to 10, wherein the mark includes at least one of a concave portion and a convex portion.

  According to this configuration, it is possible to effectively reduce the possibility of a problem of mark damage.

[Application Example 12] The spark plug according to any one of Application Examples 1 to 11, wherein the mark includes a portion whose brightness is different from the brightness of a peripheral portion of the mark.

  According to this configuration, the mark can be easily confirmed.

[Application Example 13] The spark plug according to any one of Application Examples 1 to 12, further comprising a gasket that allows rotation of the spark plug by 120 degrees or more within a predetermined tightening torque range. Including spark plug.

  According to this configuration, it is easy to direct the direction of the spark plug to an appropriate direction of the internal combustion engine.

  The present invention can be realized in various forms, for example, in the form of a spark plug, an internal combustion engine equipped with the spark plug, and the like.

It is explanatory drawing which fractured | ruptured and showed the spark plug 100 as 1st Example of this invention. It is explanatory drawing of the spark plug 100 seen along -X direction (reverse direction of X direction). It is the top view which looked at the spark plug 100 toward the front-end | tip direction FWD (axial direction OD) from the rear-end side. It is a graph which shows the relationship between the width | variety MW of the mark MK, and the automatic recognition rate of the mark MK. It is explanatory drawing which shows the structure of the apparatus utilized for automatic recognition. It is a graph which shows the relationship between AF lean limit and the direction of the spark plug 100. FIG. FIG. 4 is an explanatory diagram showing the direction of a ground electrode 30. It is explanatory drawing which shows the angle | corner which the mark MK anticipates. 3 is a graph showing a relationship between a limit advance angle and a direction of a spark plug 100. It is explanatory drawing of the position (direction) of the mark MK, and the position (direction) of the ground electrode 30 (part 30t). It is explanatory drawing of the surface of the insulator 10. FIG. It is explanatory drawing which shows another structure. It is explanatory drawing which shows the structure of another Example of a spark plug. It is explanatory drawing which shows an example of the gasket 5. FIG.

Next, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
B. Second embodiment:
C. gasket:
D. Variation:

A. First embodiment:
FIG. 1 is an explanatory view showing a spark plug 100 as a first embodiment of the present invention with a part thereof broken. An axis OX in the drawing is the central axis of the spark plug 100. This axis OX is the same as the central axis of rotation for tightening the spark plug 100. The axial direction OD indicates a direction toward the tip side parallel to the axial line OX. FIG. 1 shows a cross section parallel to the axial direction OD of the spark plug 100. A spark plug 100 shown in FIG. 1 includes an insulator 10, a center electrode 20, a ground electrode 30 (also referred to as an outer electrode 30), a terminal fitting 40, and a metal shell 50. The rod-shaped center electrode 20 protruding from one end of the insulator 10 is electrically connected to a terminal fitting 40 provided at the other end of the insulator 10 through the inside of the insulator 10. Hereinafter, a direction from the terminal fitting 40 toward the center electrode 20 in parallel with the axial direction OD is also referred to as a front end direction FWD, and a reverse direction (a direction from the center electrode 20 toward the terminal fitting 40) is also referred to as a rear end direction BWD.

  The outer circumference of the center electrode 20 is insulated by the insulator 10, and the outer circumference of the insulator 10 is held by the metal shell 50 at a position away from the terminal fitting 40. The ground electrode 30 electrically connected to the metal shell 50 forms a spark gap, which is a gap for generating a spark, between the center electrode 20. The spark plug 100 is attached to a mounting screw hole 201 provided in an engine head 200 of an internal combustion engine (not shown) via a metal shell 50, and a high voltage of 20,000 to 30,000 volts is applied to the terminal fitting 40. Then, a spark is generated in a spark gap formed between the center electrode 20 and the ground electrode 30.

  The insulator 10 of the spark plug 100 is an insulator formed by firing a ceramic material such as alumina. The insulator 10 is a cylindrical body in which the shaft hole 12 that accommodates the center electrode 20 and the terminal fitting 40 is formed at the center. The shaft hole 12 extends along the axial direction OD. At the center of the insulator 10 in the axial direction, a flange portion 19 having an increased outer diameter is formed. A rear end side body portion 18 that insulates between the terminal metal fitting 40 and the metal shell 50 is formed on the terminal metal fitting 40 side of the flange portion 19. A front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 is formed on the center electrode 20 side with respect to the flange portion 19, and the front end side body portion 17 is further forward than the front end side body portion 17. The leg length portion 13 is formed with a smaller outer diameter, and the outer diameter decreases toward the center electrode 20 side.

  The metal shell 50 of the spark plug 100 is a cylindrical metal fitting that surrounds and holds a portion ranging from a part of the rear end side body portion 18 to the leg long portion 13 of the insulator 10. In this embodiment, the low-carbon steel is used. Consists of. The metal shell 50 includes a caulking portion 50t, a tool engaging portion 51, a mounting screw portion 52, a seal portion 54, and a tip surface 57. A tool (not shown) for attaching the spark plug 100 to the engine head 200 is fitted into the tool engaging portion 51 of the metal shell 50. The mounting screw portion 52 of the metal shell 50 has a thread that is screwed into the mounting screw hole 201 of the engine head 200. The seal portion 54 of the metal shell 50 is formed in a hook shape at the base of the mounting screw portion 52. An annular gasket 5 formed by bending a plate is fitted between the seal portion 54 and the engine head 200. The front end surface 57 of the metal shell 50 is a hollow circular surface formed at the front end of the mounting screw portion 52. At the center of the distal end surface 57, the center electrode 20 wrapped in the leg length portion 13 protrudes.

  On the rear end side (end in the rear end direction BWD) of the metal shell 50, a caulking portion 50t is formed. Between the inner peripheral surface from the tool engaging portion 51 to the caulking portion 50t and the outer peripheral surface of the rear end side body portion 18 of the insulator 10, annular ring members 6 and 7 are interposed. Between the ring members 6 and 7, powder of talc (talc) 9 is filled. By crimping the caulking portion 50t so as to be bent inward, the insulator 10 is pressed toward the front end side (front end direction FWD) in the metal shell 50 via the ring members 6 and 7 and the talc 9. Thereby, the step portion 15 of the insulator 10 is supported by the step portion 56 formed at the position of the mounting screw portion 52 on the inner periphery of the metal shell 50 via the annular plate packing 8, The insulator 10 is integrated.

  The center electrode 20 of the spark plug 100 is a rod-like electrode having a structure in which a core material 25 having better thermal conductivity than the electrode base material 21 is embedded in an electrode base material 21 formed in a bottomed cylindrical shape. . An electrode tip 22 is joined to the tip portion of the electrode base material 21 by laser welding. In this embodiment, the electrode base material 21 is made of a nickel alloy containing nickel as a main component such as Inconel (registered trademark), and the core member 25 is made of copper or an alloy containing copper as a main component. In addition, the electrode tip 22 is formed with a high melting point noble metal as a main component in order to improve the spark wear resistance. The center electrode 20 is inserted into the shaft hole 12 of the insulator 10 with the tip of the electrode base material 21 protruding from the shaft hole 12 of the insulator 10, and is electrically connected to the terminal fitting 40 via the ceramic resistor 3 and the seal body 4. Connected.

  The ground electrode 30 of the spark plug 100 is an electrode having a structure in which the electrode base material 31 bonded to the front end surface 57 of the metal shell 50 is bent in a direction intersecting the axial direction OD. An electrode tip 32 is joined near the tip of the electrode base material 31. The electrode tip 32 is disposed so as to face the tip of the center electrode 20. In this embodiment, the electrode base material 31 is made of a nickel alloy containing nickel as a main component such as Inconel (registered trademark).

  A portion 30t of the ground electrode 30 in the drawing indicates a portion arranged in the X direction perpendicular to the axial direction OD when viewed from the center electrode 20. The portion 30 t forms one end of the ground electrode 30, and the end is joined to the front end surface 57 of the metal shell 50. That is, in the present embodiment, the part 30t corresponds to a joint part between the metal shell 50 (tip surface 57) and the ground electrode 30, and the joint part (part 30t) is in the X direction when viewed from the center electrode 20. Has been placed.

  FIG. 2 is an explanatory diagram of the spark plug 100 viewed along the −X direction (the reverse direction of the X direction). As shown in FIG. 2, the ground electrode 30 is disposed on the front surface and the center electrode 20 is hidden behind the ground electrode 30. The spark plug 100 is marked with a mark MK. The mark MK is formed using a black paint. In this embodiment, the mark MK is a linear mark extending in parallel with the axial direction OD from the end 50e1 in the front end direction FWD of the tool engaging portion 51 to the end 10e2 in the rear end direction BWD of the insulator 10. The mark MK includes a first mark MK1, a second mark MK2, and a third mark MK3. The first mark MK <b> 1 is formed on the surface of the rear end side body portion 18 of the insulator 10. The second mark MK2 is formed on the surface of the caulking portion 50t. The third mark MK3 is formed on the surface of the tool engaging portion 51. The width MW in the figure indicates the width of the mark MK. The width MW is in a direction (in the -X direction in the example of FIG. 2) passing through the center line (not shown) of the mark MK and the axis OX (same as the central axis of rotation for tightening the spark plug 100). This is the width of the mark MK when the spark plug 100 is viewed.

  FIG. 3 is a top view of the spark plug 100 as viewed from the rear end side toward the front end direction FWD (axial direction OD). As illustrated, the first mark MK1 extends from the end 10e2 of the insulator 10 (rear end side body portion 18) to the boundary position 10e1. The second mark MK2 extends from the boundary position 10e1 to the end of the crimped portion 50t that contacts the end 50e2 in the rear end direction BWD of the tool engaging portion 51 (see FIG. 2). Further, a third mark MK3 extends from the end 50e2 shown in FIG. 3 to the end 50e1 on the back surface side of FIG. In the tool engaging portion 51, the third mark MK3 extends to the surface of the end 50e2 facing in the rear end direction BWD (the surface on the front side in FIG. 3) until the end portion 50te of the crimping portion 50t is reached. Is provided. In the drawing, a part 30t of the ground electrode 30 is shown. When viewed from the axis OX, the mark MK is disposed in the same direction as the portion 30t.

  Thus, the mark MK is formed on the portion of the spark plug 100 (FIG. 2) outside the engine head 200. Therefore, the direction of the spark plug 100 (that is, the direction of the ground electrode 30 (part 30t) as viewed from the axis OX) can be confirmed without removing the spark plug 100 from the engine head 200. Therefore, the direction of the spark plug 100 can be easily adjusted to a direction suitable for the engine.

  As shown in FIGS. 1 and 2, the portion of the insulator 10 that is visible from the outside (the portion from the boundary position 10e1 to the end 10e2 of the rear end side body portion 18) is the tool engaging portion 51 and the caulking portion. It is long compared to each of 50t. Accordingly, the size (length) of the first mark MK1 formed on the rear end side body portion 18 can be easily increased (lengthened). As a result, when the spark plug 100 is viewed along a direction intersecting the axis OX (for example, the X direction), the mark MK (first mark MK1) can be easily confirmed.

  An enlarged view of the caulking portion 50t is shown in the lower right of FIG. In the drawing, a point P on the surface of the caulking portion 50t and an axial direction OD viewed from the point P are shown. As described above, the caulking portion 50t is processed to be bent inward. That is, by gradually tracing the surface of the caulking portion 50t toward the rear end direction BWD, the surface gradually approaches the axis OX. Thus, the surface of the caulking portion 50t is inclined with respect to the axial direction OD. That is, the surface of the caulking portion 50t intersects the axial direction OD. This means that when the spark plug 100 is observed from the rear end side toward the front end direction FWD, the surface of the crimped portion 50t is visible (FIG. 3). The surface of such a caulking portion 50t can also be described as follows. The normal line NL in the figure is a normal line at the point P, and the vertical direction VD is a direction perpendicular to the axial direction OD viewed from the point P. A normal line NL at a point P on the surface of the caulking portion 50t is inclined from the vertical direction VD toward the rear end direction BWD.

  As described above, the second mark MK2 is arranged in the crimped portion 50t that is visible when the spark plug 100 is observed from the rear end side toward the front end direction FWD. Therefore, even when the spark plug 100 is mounted in a deep plug hole, the mark (second mark MK2) can be easily confirmed.

  The third mark MK3 is disposed on the side surface (surface parallel to the axis OX) of the tool engaging portion 51. Some plug cords attached to the terminal fitting 40 of the spark plug 100 have a cap that covers the insulator 10 (rear end side body portion 18). Even when such a plug cap is attached to the spark plug 100, the tool engaging portion 51 is visible from the outside. Therefore, the mark MK (third mark MK3) can be confirmed without removing the plug cap from the spark plug 100.

  FIG. 4 is a graph showing the relationship between the width MW of the mark MK and the automatic recognition rate of the mark MK. FIG. 5 is an explanatory diagram showing the configuration of the apparatus used for automatic recognition. A spark plug 100 is mounted in the plug hole PH. As the spark plug 100, a so-called M14 size plug is used. The outer diameter of the terminal fitting 40 is 6 mm. The distance between one side of the hexagonal shape of the tool engaging portion 51 and the side facing the side is 16 mm. The plug hole PH accommodates the entire spark plug 100 (specifically, from the seal portion 54 to the rear end (the rear end of the terminal fitting 40) of the spark plug 100). A digital still camera 300 is arranged at a position away from the spark plug 100 by a distance D in the rear end direction BWD. Here, as the digital still camera 300, a digital still camera having a total number of pixels of 300,000 pixels is used. The distance D is 50 cm. In this state, the digital still camera 300 photographs the spark plug 100. Image data obtained by photographing represents an image similar to that shown in FIG. An image processing device (computer) (not shown) automatically recognizes the mark MK by analyzing image data obtained by photographing. In this embodiment, since the mark MK is a straight line, the image processing apparatus recognizes (detects) a straight line pattern. For straight line detection, image data obtained by binarizing captured image data is used. Then, when the deviation between the detected direction of the straight line and the direction of the actual mark MK is 3 degrees or less, it is determined that the automatic recognition is successful.

  As shown in FIG. 4, when the width MW of the mark MK is 0.8 mm or more, the recognition rate is 100%. The recognition rate is 98% when the width MW is 0.7 mm and when the width MW is 0.6 mm. When the width MW is 0.5 mm, the recognition rate is 92%. Accordingly, the width MW of the mark MK is preferably 0.8 m or more. In this way, the direction of the spark plug 100 can be automatically recognized using the image processing apparatus. Also, the mark MK can be easily confirmed visually. In this way, it is possible to reduce the possibility of a problem that the mark cannot be confirmed. It should be noted that various methods such as pattern matching can be employed as a method for automatic recognition (automatic detection) of the mark MK.

  FIG. 6 is a graph showing the relationship between the AF lean limit and the direction of the spark plug 100. The vertical axis indicates the AF lean limit, and the horizontal axis indicates the direction of the ground electrode 30. The AF lean limit is a lean limit value of the air-fuel ratio at which no misfire occurs. A large AF lean limit indicates good ignitability. In this graph, an in-line 4-cylinder, DOHC (Double OverHead Camshaft) type, 2L engine is used as the engine. The AF lean limit indicates a value when the partial throttle and the engine rotational speed are 2000 rpm.

  FIG. 7 is an explanatory diagram showing the direction of the ground electrode 30. In the drawing, a schematic view of the upper surface (end surface) of the cylinder (combustion chamber) of the engine is shown. A spark plug 100 is attached to a substantially central portion of the upper surface F1 of the cylinder. An angle (−180 degrees to +180 degrees) is assigned around the axis OX of the spark plug 100. Two intake ports In1 and In2 are arranged side by side in an approximately half region of −90 degrees to +90 degrees on the upper surface F1. Further, two exhaust ports Ex1 and Ex2 are arranged side by side in the remaining half of the upper surface F1. The direction of 0 degrees indicates a direction toward the space between the two intake ports In1 and In2. +180 degrees (−180 degrees) indicates a direction toward the space between the two exhaust ports Ex1 and Ex2. The horizontal axis of FIG. 6 represents the position of the portion 30t of the ground electrode 30 by the angle of FIG.

  As shown in FIG. 6, in the angle range R1 (−60 degrees to +60 degrees) in which the ground electrode 30 faces the intake port, AF is compared with the other angle ranges R2 (+60 to +180, −60 to −180). Lean limit (ignitability) decreases. This is because when the ground electrode 30 (part 30t) is within the angle range R1, the gas flowing in from the intake ports In1 and In2 is blocked by the ground electrode 30 and hardly reaches the spark gap of the spark plug 100. It is estimated that

  In the range from +60 degrees to +45 degrees (−60 degrees to −45 degrees), the decrease in AF lean limit is not so serious as compared to the range from +45 degrees to 0 degrees (−45 degrees to 0 degrees). . Accordingly, it is allowed that the ground electrode 30 (part 30t) approaches 0 degrees by 15 degrees from the limit (+60 degrees, −60 degrees) of the appropriate angle range R1 (+60 to +180, −60 to −180). The Therefore, when adjusting the direction of the spark plug 100, it is preferable to confirm the direction of the spark plug 100 with an error of 15 degrees or less (the allowable range of deviation in direction is 30 degrees from -15 degrees to +15 degrees). Is).

  FIG. 8 is an explanatory diagram showing the angle at which the mark MK is expected. FIG. 8 shows the same top view as FIG. An angle AG in the figure indicates an angle at which the mark MK is estimated with respect to the axis OX. In this embodiment, the axis OX coincides with the central axis of rotation when the spark plug 100 (FIG. 1) is rotated and mounted on the engine head 200. The central axis of this rotation is the same as the central axis of the mounting screw portion 52 (FIGS. 1 and 2). As shown in the figure, the expected angle AG is a range in a direction that can pass through the mark MK as viewed from the axis OX.

  As described with reference to FIGS. 6 and 7, it is preferable to confirm the direction of the spark plug 100 with an accuracy of an error of 15 degrees or less. Therefore, it is preferable to form the mark MK so that the expected angle AG is 30 degrees or less (30 degrees = −15 degrees to +15 degrees). In this way, the possibility of a problem that the direction of the spark plug cannot be directed to an appropriate direction of the internal combustion engine can be reduced.

  FIG. 9 is a graph showing the relationship between the limit advance angle and the direction of the spark plug 100. The vertical axis indicates the direction of the spark plug 100, and the horizontal axis indicates the limit advance angle. The direction of the spark plug 100 is represented by the angle described in FIG. The limit advance angle is a limit value of the advance angle at which so-called preignition does not occur. A large advance angle indicates that preignition is unlikely to occur. The unit of the limit advance angle is degree (crank angle). The limit advance angle indicates a value when the wide open throttle (fully open) and the engine rotational speed are 6000 rpm.

  As shown in the figure, the limit advance angle becomes smaller as the direction of the ground electrode 30 (part 30t) is closer to 0 degrees. The reason is estimated as follows. When the ground electrode 30 (part 30t) faces the exhaust ports Ex1, Ex2 (FIG. 7), the gas flowing in from the intake ports In1, In2 flows into the spark gap of the spark plug 100. Since the spark plug 100 is cooled by this gas, the temperature of the spark plug 100 is lowered. As a result, pre-ignition is unlikely to occur. On the other hand, when the ground electrode 30 faces the intake ports In1 and In2 (FIG. 7), the gas flowing in from the intake ports In1 and In2 is blocked by the ground electrode 30 and reaches the spark gap of the spark plug 100. Hateful. Therefore, cooling of the spark plug 100 becomes insufficient, and the temperature of the spark plug 100 increases. As a result, pre-ignition is likely to occur.

  Therefore, if the direction of the spark plug 100 (the direction of the ground electrode 30) is set to an angle close to +180 degrees (−180 degrees) in the appropriate angle range R2 (FIG. 6), the occurrence of preignition is prevented. Can be suppressed.

  FIG. 10 is an explanatory diagram of the position (direction) of the mark MK and the position (direction) of the ground electrode 30 (part 30t). A center direction MKc in the drawing indicates a direction from the axis OX toward the center of the mark MK, and a center direction 30 tc indicates a direction from the axis OX toward the center of the portion 30 t of the ground electrode 30. The center direction MKc indicates the center direction of an angle (angle range) MKa in which the mark MK viewed from the axis OX is viewed. The center direction 30tc indicates the center direction of an angle (angle range) 30ta at which a portion 30t is viewed from the axis OX. The angle AGd indicates an angle between the central direction MKc and the central direction 30tc. This angle AGd represents a deviation in the direction between the portion 30t of the ground electrode 30 and the mark MK. As described with reference to FIGS. 6 and 7, it is preferable to confirm the direction of the spark plug 100 with an accuracy of an error of 15 degrees or less. Therefore, the angle AGd is preferably 15 degrees or less. In this way, by adjusting the direction of the spark plug 100 according to the mark, the direction of the ground electrode 30 (part 30t) can be adjusted with an accuracy of 15 degrees or less. As described above, the direction of the mark MK viewed from the axis OX does not have to coincide with the direction of the ground electrode 30 (part 30t).

  FIG. 11 is an explanatory diagram of the surface of the insulator 10. FIG. 11 shows a part including the rear end side body 18 of the insulator 10 in the same explanatory view as FIG. FIG. 11 also shows an enlarged view of a cross section of the insulator 10 (rear end side body portion 18). In the present embodiment, the rear end side body portion 18 (insulator 10) has a ceramic insulating member 10c and a glaze layer 10g covering the surface thereof. A first mark MK1 is formed on the surface of the glaze layer 10g. Thus, since the 1st mark MK1 is formed in the surface of the insulator 10 (rear end side trunk | drum 18), after the assembly | attachment of the components of the spark plug 100, the 1st mark MK1 can be formed. As a result, it is possible to easily form the first mark MK1 at an appropriate position. In addition, such a rear end side trunk | drum 18 can be obtained by apply | coating a glaze on the surface of the insulating member 10c and baking it. And the 1st mark MK1 can be formed by apply | coating a coating material on the surface of the rear end side trunk | drum 18 after baking.

  FIG. 12 is an explanatory diagram showing another configuration. The only difference from the configuration shown in FIG. 11 is that the first mark MK1 is formed between the insulating member 10c and the glaze layer 10g. According to this configuration, since the first mark MK1 is protected by the glaze layer 10g, the possibility of damage to the first mark MK1 can be reduced. For example, it is possible to reduce the possibility of damage to the first mark MK1 when removing the plug cap or in the process of manufacturing the spark plug 100. Such a first mark MK1 is formed by, for example, applying a paint to the surface of the insulating member 10c before firing to form the first mark MK1, and applying a glaze to the surface of the insulating member 10c including the first mark MK1. It can be obtained by firing. In addition, the glaze layer 10g does not need to cover the whole surface of the rear end side trunk | drum 18, but should just cover at least one part of the surface of the rear end side trunk | drum 18.

  In any case, the mark MK may be formed of a material including a fluorescent paint. In this way, the mark MK can be easily confirmed even in a dark place. For example, the mark MK can be easily confirmed even when the spark plug 100 is mounted in a deep plug hole PH that accommodates the entire spark plug 100 as shown in FIG.

  The mark MK may include a heat resistant paint. This can reduce the possibility of damage to the mark MK due to heat received from the engine. In addition, as a heat-resistant coating material, the coating material currently utilized for coatings, such as a muffler and a chimney, can be utilized. For example, a silicon-based or fluorine-based heat-resistant paint can be used for forming the mark MK.

  Further, the mark MK may include a portion whose glossiness is different from the peripheral portion of the mark MK. For example, the glossiness of the second mark MK2 formed on the crimping portion 50t (FIG. 2) may be smaller than the glossiness of the crimping portion 50t. Specifically, the second mark MK2 may be formed by using a matte black paint whose glossiness is smaller than the metallic glossiness of the caulking portion 50t. In this way, when the spark plug 100 is illuminated with a light, the mark MK can be easily confirmed. In addition, what is necessary is just to employ | adopt the specular glossiness prescribed | regulated to JISZ8741 as glossiness. For the measurement of specular gloss, a sample obtained using the same material may be used. For example, when measuring the specular gloss of the caulking portion 50t, a sample formed of the same metal material may be used. When measuring the specular gloss of the second mark MK2, a sample may be formed using the material (for example, paint) used for forming the second mark MK2. Note that the glossiness of the mark MK may be higher than the glossiness of the peripheral portion of the mark MK.

  Further, the mark MK may include a part whose brightness is different from the peripheral part of the mark MK. For example, the brightness of the first mark MK1 formed on the insulator 10 (rear end side body portion 18) may be darker (smaller) than the brightness of the insulator 10. Specifically, when the color of the insulator 10 is bright white, the first mark MK1 may be formed using a darker black paint than the color of the insulator 10. In this way, the first mark MK1 can be easily confirmed. In addition, what is necessary is just to employ | adopt the value measured with the colorimeter as lightness. For lightness measurement, a sample obtained using the same material may be used. For example, when measuring the brightness of the insulator 10, samples formed of the same ceramic material may be used. Further, when measuring the brightness of the first mark MK1, a sample may be formed using a material (for example, paint) used for forming the first mark MK1. Note that the lightness of the mark MK may be higher than the lightness of the peripheral portion of the mark MK. The hue and saturation may be the same or different between the mark MK and the peripheral part of the mark MK.

B. Second embodiment:
FIG. 13 is an explanatory view showing the configuration of another embodiment of the spark plug. The only difference from the spark plug 100 shown in FIGS. 1 and 2 is that in this spark plug 100a, a convex portion formed on the crimping portion 50t is used as the mark MKa. The other structure of the spark plug 100a is the same as the structure of the spark plug 100 of FIGS. Such a mark MKa is less susceptible to damage than a mark formed on the surface of the spark plug by painting. Therefore, if the mark MKa is used, the possibility of damage to the mark MKa can be reduced. For example, the direction of the spark plug 100a can be easily confirmed over a long period of time such as ten or more years.

  As a method for forming the mark MKa, any method can be adopted. For example, you may fix a convex part to the metal shell 50 (caulking part 50t) by welding. Further, the mark MKa may be formed by pressing the metal shell 50. Moreover, as a mark, you may employ | adopt not only a convex part but a recessed part. Any method can be adopted as a method for forming the recess. For example, the mark may be formed by laser marking. Further, the mark including at least one of the convex portion and the concave portion may be formed at an arbitrary location on the metal shell 50. For example, a mark including a recess may be formed in the tool engaging portion 51. Further, a mark including at least one of a convex portion and a concave portion may be formed on the insulator 10. Moreover, you may form both the mark MK of FIG. 2, and the mark containing at least one of a convex part and a recessed part in a spark plug. In this way, the mark can be easily confirmed under various conditions.

C. gasket:
FIG. 14 is an explanatory view showing an example of the gasket 5. As described with reference to FIG. 6, it is preferable to set the direction of the spark plug outside the 120-degree angle range R1 (−60 degrees to +60 degrees). On the other hand, it is often recommended to use a torque within a predetermined range for tightening the spark plug for mounting on the engine. Therefore, it is preferable that the gasket 5 allows the spark plug to rotate 120 degrees or more within a predetermined tightening torque range. Various configurations can be adopted as the configuration of such a gasket 5. For example, you may employ | adopt the structure described in Unexamined-Japanese-Patent No. 2000-266186. FIG. 14 shows an example of such a gasket 5.

  FIG. 14A is an explanatory view showing a part of the gasket 5 in a broken state. An axial direction OD (axial line OX) in the drawing indicates the axial direction OD (axial line OX) of the spark plug in a state where the gasket 5 is attached to the spark plug (for example, the spark plug 100 in FIG. 1). A cross section of the gasket 5 is shown on the left side of FIG. FIG. 14B is a top view of the gasket 5. An axis OX in the figure indicates the axis OX of the spark plug in a state where the gasket 5 is attached to the spark plug. FIG. 14C is an enlarged view of the cross section shown in FIG. The gasket 5 is formed by bending a circular metal plate a plurality of times. A radial direction RD in the drawing is a radial direction of the gasket 5 and is a direction outward from the central axis (same as the axis OX) of the gasket 5. The cross section shown is parallel to this radial direction RD. The gasket 5 has two bent portions C1 and C2. These bent portions C1 and C2 are portions where the metal plate is bent. The first bent portion C1 is a portion that curves from the inside to the outside in the radial direction RD and then toward the inside again. The second bent portion C2 is a portion that curves from the outside in the radial direction RD to the inside and then toward the outside again. When the spark plug is tightened, such a curved portion is crushed. Thereby, the increase in the tightening torque accompanying the tightening of the spark plug is mitigated. In other words, the rotation angle of the spark plug within a predetermined tightening torque range can be increased.

  By using such a configuration of the gasket 5, it is possible to obtain a gasket that allows rotation of the spark plug by 120 degrees or more within a predetermined tightening torque range. Here, the detailed dimensions and shape of the gasket 5 may be determined experimentally.

  In addition, as a structure of the gasket 5, not only the structure shown in FIG. 14 but various structures are employable. For example, you may employ | adopt the various structure described in Unexamined-Japanese-Patent No. 2000-266186. Further, the total number of bent portions is not limited to 2, and may be 3 or more. In any case, as in the embodiment shown in FIG. 14C, the positions of the plurality of bent portions in the radial direction RD may be different from each other. By doing so, each of the plurality of bent portions is crushed by tightening the spark plug, and thus the increase in torque can be moderated appropriately. Such a gasket 5 can be applied to the above-described embodiments.

D. Variation:
In addition, elements other than the elements claimed in the independent claims among the constituent elements in each of the above embodiments are additional elements and can be omitted as appropriate. The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

Modification 1:
As a structure of a spark plug, not only the structure of each above-mentioned Example but various structures are employable. For example, in the embodiment shown in FIG. 1, the ground electrode 30 may be bent toward the side surface of the center electrode 20. In this case, the end of the ground electrode 30 and the side surface of the center electrode 20 form a spark gap. The total number of ground electrodes is not limited to 1 and may be 2 or more. In this case, a plurality of marks corresponding to a plurality of ground electrodes may be provided on the spark plug. Instead, one mark for specifying the position (direction) of one predetermined ground electrode may be provided on the spark plug. In any case, it is preferable that the mark includes a portion formed on a surface intersecting the axial direction in the rear end portion of the metal shell. In this way, since the mark can be easily seen even when the spark plug is viewed from the rear end side toward the front end side, it is possible to reduce the possibility of a problem associated with confirmation of the direction of the spark plug. In particular, with respect to a spark plug that is assumed to be used in a state where the entire spark plug is housed in the plug hole PH as shown in FIG. 5, it is difficult to confirm the mark from the side. For this reason, in the configuration in which the mark can be seen even when viewed from the rear end side toward the front end side, the effect of reducing the possibility of malfunction associated with the confirmation of the direction of the spark plug is remarkable.

  In addition, as a structure of a metal shell, not only the structure which has the crimping part 50t (FIG. 1, FIG. 2) but various structures are employable. A surface intersecting the axial direction in the rear end portion of the metal shell (that is, a surface visible when the spark plug is observed from the rear end side toward the front end direction FWD) is formed on the surface of the caulking portion 50t. Not limited to this, various surfaces suitable for the structure of the metal shell can be adopted. For example, an end surface in the rear end direction BWD of the metal shell may be employed.

Modification 2:
In each of the above-described embodiments, the mark of each of the above-described embodiments may be combined as the mark, or a part of the mark of the above-described embodiment may be employed. For example, in the embodiment of FIG. 2, the first mark MK1 may be formed only in a part of the range from the boundary position 10e1 to the end 10e2 of the insulator 10. Similarly, the third mark MK3 may be formed only in a part of the range from the end 50e1 in the front end direction FWD to the end 50e2 in the rear end direction BWD of the tool engaging portion 51. Similarly, the second mark MK2 may be formed only in a part of the range from the end 50e2 of the caulking portion 50t to the boundary position 10e1. Further, in the embodiment of FIG. 2, some marks arbitrarily selected from the three marks MK1, MK2, and MK3 may be adopted.

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 6 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 10c ... Insulating member 10g ... Glaze layer 12 ... Shaft hole 13 ... Leg long part 15 ... Step part 17 ... Tip side Body 18 ... Rear end side body 19 ... Gutter 20 ... Center electrode 21 ... Electrode base material 22 ... Electrode tip 25 ... Core material 30 ... Ground electrode 30t ... Part 30tc ... Center direction 31 ... Electrode base material 32 ... Electrode tip DESCRIPTION OF SYMBOLS 40 ... Terminal metal fitting 50 ... Main metal fitting 50t ... Clamping part 51 ... Tool engaging part 52 ... Mounting screw part 54 ... Sealing part 56 ... Step part 57 ... End face 100, 100a ... Spark plug 10e1 ... Boundary position 200 ... Engine head 201 ... Mounting screw hole 300 ... Digital still camera 50e1 ... End 10e2 ... End 50e2 ... End F1 ... Upper surface C1, C2 ... Bending part PH ... Plug hole MK, MKa ... mark MK1 ... first mark MK2 ... second mark MK3 ... third mark OX ... axis FWD ... tip end direction BWD ... rear end direction In1, In2 ... intake port Ex1, Ex2 ... exhaust port

Claims (13)

An insulator having an axial hole penetrating in the axial direction;
A center electrode provided on the tip side of the shaft hole;
A substantially cylindrical metal shell for holding the insulator;
One end is attached to the tip of the metal shell, and the other end is a ground electrode that forms a spark gap with the center electrode,
A spark plug comprising:
A mark for specifying a direction from the center electrode toward the ground electrode perpendicular to the axial direction;
The mark includes a portion formed on a surface intersecting the axial direction in a rear end portion of the metal shell,
Spark plug. The spark plug according to claim 1,
The mark includes a fluorescent paint;
Spark plug. The spark plug according to claim 1 or 2, wherein
The metal shell includes an engaging portion with which a tool engages when the spark plug is mounted on an internal combustion engine,
The mark is disposed in at least a part of a range from an end of the engaging portion on the side of the center electrode to an end of the insulator on the side opposite to the center electrode.
Spark plug. The spark plug according to any one of claims 1 to 3,
The width of the mark is 0.8 mm or more.
Spark plug. The spark plug according to any one of claims 1 to 4, wherein
The angle at which the mark with reference to the central axis of rotation when the spark plug is rotated and attached to the internal combustion engine is 30 degrees or less,
Spark plug. The spark plug according to any one of claims 1 to 5,
A direction toward the center of the mark when the spark plug is rotated and mounted on the internal combustion engine as a reference, and the axial direction as viewed from the center electrode of the ground electrode. The angle between the direction toward the center of the portion arranged in the vertical direction and 15 degrees or less,
Spark plug. The spark plug according to any one of claims 1 to 6,
The insulator includes a ceramic insulating member and a glaze layer covering at least a part of the surface of the insulating member,
The mark includes a portion formed between the insulating member and the glaze layer.
Spark plug. The spark plug according to any one of claims 1 to 7,
The mark includes a portion formed on a surface of the insulator,
Spark plug. The spark plug according to any one of claims 1 to 8,
The mark includes a heat resistant paint,
Spark plug. The spark plug according to any one of claims 1 to 9,
The mark includes a portion whose glossiness is different from the glossiness of the peripheral portion of the mark,
Spark plug. The spark plug according to any one of claims 1 to 10,
The mark includes at least one of a concave portion and a convex portion,
Spark plug. The spark plug according to any one of claims 1 to 11, wherein
The mark includes a portion whose brightness is different from the brightness of the peripheral portion of the mark.
Spark plug. The spark plug according to any one of claims 1 to 12, further comprising:
Including a gasket that allows rotation of the spark plug by 120 degrees or more within a predetermined tightening torque range,
Spark plug.

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