JP2013232381A - Ignition device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ignition device using AC power for ignition, which surely supplies AC power required for performing ignition.SOLUTION: An ignition device for a spark plug comprises: a spark plug; an AC power source; and a cable for connecting the spark plug to the AC power source. The cable comprises an inner conductor extending along a center line; an outer conductor on an outer surface of the cable; a cable terminal provided at a tip of the inner conductor and connecting to a plug side terminal; and an insulator in the cable for electrically insulating the outer conductor from the inner conductor. A tip of the outer conductor has a cable side contact part having an incircle being smaller than a circumcircle of the plug side contact part in a main metal fitting and having the elasticity in radial direction in condition before the cable is connected to the spark plug. The main metal fitting is fit into the cable so that the plug side contact part comes into contact with the cable side contact part.

Description

  The present invention relates to an ignition device including a spark plug.

  An ignition device used for ignition of an internal combustion engine includes a spark plug that generates a spark for ignition. In such a spark plug, a gap, which is a space in which a spark is formed, is generally formed between the center electrode and the ground electrode. As a method of forming a spark in the gap of the spark plug, there is known a method of using AC power (high frequency) in addition to a method of applying a high voltage to the center electrode (see, for example, Patent Document 1).

JP 51-77719 A

  When AC power is used, it is more strongly desired to sufficiently maintain the electrical connection between the signal line and the spark plug than when only DC voltage is used. If the contact between the signal line and the spark plug becomes insufficient when using AC power, for example, leakage of radio waves may affect other devices as noise, or reflection may occur, so that sufficient AC power is ignited. This is because the engine could not be supplied to the engine and could cause engine misfire. In addition, if there is a place where the contact between the signal line and the spark plug is insufficient, that part may become a resistance and generate heat, or if the contact is interrupted and a gap is generated, there is a possibility that electric discharge will occur and power loss will increase. Because there is.

  The present invention has been made to solve the above-described conventional problems. In an ignition device that uses AC power for ignition, the electrical connection between the spark plug and the signal line is sufficiently maintained, An object is to reliably supply AC power necessary for ignition.

  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]
A spark plug comprising a cylindrical metal shell, a cylindrical plug insulator disposed on an inner periphery of the metal shell, and a plug-side terminal provided at a rear end of the plug insulator;
An AC power supply for supplying AC power to the spark plug for the formation and / or maintenance of sparks in the spark plug;
A cable connecting the spark plug and the AC power source;
In an ignition device comprising:
The cable is
An inner conductor extending along the center line of the cable;
An outer conductor formed on the outer surface of the cable;
A cable terminal provided at the tip of the inner conductor inside the cable, and a cable terminal connected to the plug-side terminal;
Between the outer conductor and the inner conductor, provided in a portion excluding the tip of the outer conductor, and an in-cable insulator that insulates between the outer conductor and the inner conductor;
With
In a state before the cable is connected to the spark plug, the distal end portion of the outer conductor has an inner diameter smaller than the diameter of the circumscribed circle of the plug-side contact portion of the metal shell that contacts the distal end portion. Cable side contact portion having a circle, comprising a cable side contact portion having elasticity in the radial direction of the outer conductor,
The ignition device is characterized in that the metal shell is fitted into the cable so that the plug-side contact portion and the cable-side contact portion are in contact with each other.

  According to the ignition device described in Application Example 1, when supplying AC power to the spark plug, the outer conductor applies the radially inward force from the outer conductor to the metal shell, Can be held in. For this reason, even if vibration is applied to the ignition device, it is possible to reliably supply AC power necessary for ignition.

[Application Example 2]
In the ignition device according to Application Example 1, the distal end portion of the outer conductor is formed with a plurality of slits from the distal end side with respect to the cable side contact portion to the rear end side with respect to the cable side contact portion. An ignition device characterized by comprising:
According to the ignition device described in Application Example 2, the operation of fitting the spark plug into the cable can be facilitated.

[Application Example 3]
In the ignition device according to Application Example 2, the metal shell extends in an outer peripheral direction, has a polygonal cross-sectional shape perpendicular to the axis, and includes a tool engagement portion in which the plug-side contact portion is formed, and the slit is The ignition device is formed to extend in the axial direction at a position corresponding to each corner of the polygonal shape when the tool engaging portion is fitted into the tip portion of the outer conductor.
According to the ignition device described in Application Example 3, it is possible to ensure more contact points between the outer conductor and the tool engaging portion, and to reliably supply AC power necessary for ignition.

[Application Example 4]
In the ignition device according to Application Example 3, in the tip portion of the outer conductor, a region including at least the cable-side contact portion that is separated from each other by the slit forms a flat surface, and the tool engagement portion The ignition device according to claim 1, wherein the plug-side contact portion and the cable-side contact portion in contact with the plug-side contact portion are formed in a line segment shape.
According to the ignition device described in the application example 4, it is possible to secure a larger portion where the outer conductor and the tool engaging portion are in contact with each other, and to reliably supply the AC power necessary for ignition.

[Application Example 5]
The ignition device according to any one of Application Examples 2 to 4, wherein the slit has a length of 5 mm or more extending from the front end of the outer conductor to the rear end side along the axial direction. Ignition device characterized.
According to the ignition device described in Application Example 5, it is possible to enhance the effect of absorbing vibration in the vicinity of the slit of the outer conductor, and to reliably supply AC power necessary for performing ignition.

[Application Example 6]
6. The ignition device according to any one of Application Examples 1 to 5, wherein the outer conductor is an ignition in which a region from the outer surface tip of the outer conductor to the inner surface of the outer conductor is formed in a curved shape. apparatus.
According to the ignition device described in Application Example 6, the operation of fitting the spark plug into the cable can be facilitated.

[Application Example 7]
The ignition device according to any one of Application Examples 1 to 6, further including a discharge power source for applying a voltage for causing a spark discharge in the spark plug, wherein the insulator in the cable is made of rubber. An annular rubber part formed, the rubber part having an inner diameter smaller than an outer diameter of the insulator in the plug in a state before the cable is connected to the spark plug, and the rubber part The ignition device is characterized in that the insulator in the plug is fitted into a tip portion of the insulator in the cable including the cable.
According to the ignition device described in Application Example 7, since the adhesion between the insulator in the cable and the insulator in the plug can be improved, the plug-side terminal and the external conductor are applied when voltage is applied by the discharge power source. , And short circuit via the surface of the insulator in the plug can be suppressed.

[Application Example 8]
The ignition device according to Application Example 7, wherein the rubber part has an axial length of the spark plug of 5 mm or more.
According to the ignition device described in Application Example 8, when a voltage is applied by the discharge power supply, the effect of suppressing a short circuit via the surface of the plug insulator between the plug-side terminal and the external conductor is achieved. It can be further increased.

[Application Example 9]
7. The ignition device according to any one of application examples 1 to 6, further comprising: a discharge power source that applies a voltage for causing a spark discharge in the spark plug, wherein the cable insulator includes the cable Covering the outer surface including the boundary between the surface of the connecting portion between the terminal and the plug-side terminal, and the plug-side terminal in the plug-in insulator protruding from the rear end of the metallic shell, and on the plug-in insulator The ignition device according to claim 1, wherein the ignition device is formed to cover 50% or more of an axial distance from a rear end of the insulator in the plug to a rear end of the metal shell.
According to the ignition device described in the application example 9, when a voltage is applied by the discharge power source, the effect of suppressing a short circuit passing through the surface of the insulator in the plug between the plug-side terminal and the external conductor is enhanced. Can do.

[Application Example 10]
9. The ignition device according to Application Example 7 or 8, wherein the in-cable insulator includes a surface of a coupling portion between the cable terminal and the plug-side terminal, and the in-plug insulation protruding from a rear end of the metal shell. 50% of the axial distance from the rear end of the insulator in the plug to the rear end of the metal shell on the insulator in the plug, covering the outer surface including the boundary with the plug-side terminal in the body An ignition device characterized by being formed so as to cover the above.
According to the ignition device described in Application Example 10, when a voltage is applied by the discharge power supply, the effect of suppressing a short circuit that passes through the surface of the plug insulator between the plug-side terminal and the external conductor is enhanced. be able to.

[Application Example 11]
7. The ignition device according to any one of application examples 1 to 6, further comprising: a discharge power source that applies a voltage for generating spark discharge in the spark plug, wherein the insulator in the plug and the external conductor The thickness of the insulator in a cable formed between the direction perpendicular to the axial direction of the spark plug is 5 mm or more.
According to the ignition device described in Application Example 11, it is possible to suppress the occurrence of a short circuit that crosses the insulator in the cable in the thickness direction between the plug-side terminal and the external conductor due to voltage application by the discharge power source. The effect can be enhanced.

[Application Example 12]
The ignition device according to any one of Application Examples 7 to 10, wherein the cable insulator formed between the plug insulator and the outer conductor is perpendicular to the axial direction of the spark plug. The ignition device is characterized by having a thickness of 5 mm or more.
According to the ignition device described in Application Example 12, it is possible to suppress occurrence of a short circuit that crosses the insulator in the cable in the thickness direction between the plug-side terminal and the external conductor in accordance with voltage application by the discharge power source. The effect can be enhanced.

[Application Example 13]
13. The ignition device according to any one of Application Examples 1 to 12, wherein the front end portion of the outer conductor protrudes radially inward from the rear end side of the cable side contact portion and contacts the metal shell. Ignition device comprising a part.
According to the ignition device described in the application example 13, the contact portion between the outer conductor and the metal shell can be increased without making it difficult to fit the metal shell into the cable. Therefore, it is possible to reliably supply the AC power necessary for this.

[Application Example 14]
14. The ignition device according to any one of application examples 1 to 13, further comprising a clamping member that is provided on an outer periphery of the outer conductor and applies a force toward the radially inner side with respect to the outer conductor.
According to the ignition device described in the application example 14, the tightening member can prevent the outer conductor from spreading outward in the radial direction, and can increase the radially inward force acting on the metal shell from the outer conductor. In addition, it is possible to increase the area where the outer conductor and the metal shell contact. As a result, it is possible to reliably supply AC power necessary for ignition.

  The present invention can be realized in various forms other than those described above. For example, the present invention can be realized in the form of a method for manufacturing an ignition device including a spark plug.

It is a block diagram showing schematic structure of an ignition device. It is a fragmentary sectional view of a spark plug. It is explanatory drawing showing the mode of the coupling | bond part of a spark plug and a plug cable. It is a perspective view which represents typically the external appearance of the front-end | tip part of an external conductor. It is explanatory drawing which expands and shows the mode of the connection part of a tool engaging part and an external conductor. It is explanatory drawing showing a mode that a vibration test is performed using a vibration test apparatus. It is explanatory drawing showing the mode of the coupling | bond part of the plug cable and spark plug as a comparative example. It is explanatory drawing showing the mode of a connection of an external conductor and a metal fitting. It is explanatory drawing showing the mode of the connection part A vicinity when slit length (alpha) differs. It is explanatory drawing which shows the content which examined about other conditions. It is explanatory drawing showing the undesirable short circuit phenomenon which may arise between a spark plug and an external conductor. It is explanatory drawing showing the mode of the coupling | bond part of a spark plug and a plug cable. It is explanatory drawing showing the mode of the coupling | bond part of a spark plug and a plug cable. It is explanatory drawing showing the mode of the coupling | bond part of a spark plug and a plug cable. It is explanatory drawing of the modification which concerns on the coupling | bond part of a spark plug and a plug cable. It is explanatory drawing of the modification which concerns on the coupling | bond part of a spark plug and a plug cable. It is explanatory drawing of the modification which concerns on the coupling | bond part of a spark plug and a plug cable. It is explanatory drawing of the modification which concerns on the coupling | bond part of a spark plug and a plug cable.

A. Overall configuration of ignition device:
FIG. 1 is a block diagram showing a schematic configuration of an ignition device 40 as a first embodiment of the present invention. The ignition device 40 includes a spark plug 100, a discharge power source 41, an AC power source 42, and a mixing unit 43.

  The spark plug 100 includes a center electrode 20 and a ground electrode 30, and generates spark discharge between these electrodes and generates alternating current plasma, thereby igniting a fuel of an internal combustion engine (not shown) to which the spark plug 100 is attached. It is a device to do. A detailed configuration of the spark plug 100 will be described later.

  The discharge power supply 41 is a DC power supply that supplies a high voltage (in this embodiment, a high-voltage pulse of tens of thousands of volts) to the spark plug 100 in order to cause a spark discharge between the electrodes of the spark plug 100. . As the discharge power supply 41, for example, an ignition coil can be used.

  The AC power supply 42 supplies AC power to the spark plug 100 in order to generate AC plasma between the electrodes of the spark plug 100 that has generated spark discharge. In the present embodiment, the frequency of the AC power generated by the AC power source 42 is preferably 50 kHz to 100 MHz, and more preferably 500 kHz to 20 MHz in order to generate AC plasma.

  The mixing unit 43 combines the first transmission path 46 connected to the discharge power supply 41, the second transmission path 47 connected to the AC power supply 42, and the first transmission path 46 and the second transmission path 47. In addition, a plug cable 60 that is a third transmission line connected to the spark plug 100 is provided. The first transmission path 46 is provided with a coil (inductor) 44 to suppress the inflow of the current output from the AC power supply 42 to the discharge power supply 41 side. In addition, a capacitor 45 is provided in the second transmission path 47, and the inflow of the current output from the discharge power supply 41 to the AC power supply 42 side is suppressed. In the present embodiment, the second transmission path 47 and the plug cable 60, which are AC power transmission paths from the AC power source 42 to the spark plug 100, have an inner conductor and an outer conductor disposed outside the inner conductor. It is configured as a coaxial cable to prevent AC power from being reflected. A detailed configuration of the plug cable 60 configured as a coaxial cable will be described later. When an ignition coil is used as the discharge power source 41, a secondary coil included in the ignition coil can be used in place of the coil 44, and the coil 44 can be omitted.

  The center electrode 20 of the spark plug 100 is electrically connected to the discharge power source 41 and the AC power source 42 via the mixing unit 43, and the ground electrode 30 of the spark plug 100 is electrically grounded. In the ignition device 40, the discharge power source 41 and the AC power source 42 are controlled so that AC plasma is generated with spark discharge between the electrodes of the spark plug 100.

  In FIG. 1, the ignition device 40 has one spark plug 100. However, when the internal combustion engine to which the spark plug 100 is attached has a plurality of cylinders, the spark plug 100 corresponds to each cylinder. It is provided one by one. In this case, the power from the discharge power supply 41 or the AC power supply 42 may be supplied to each spark plug 100 via a distributor (not shown).

  FIG. 2 is a partial cross-sectional view showing the configuration of the spark plug 100. In FIG. 2, the right side of the axis Ax indicated by a one-dot broken line shows an external front view, and the left side of the axis Ax shows a cross-sectional view of the spark plug 100 cut along a cross section passing through the central axis of the spark plug 100. In the following description, in the direction parallel to the axis Ax, the lower side in FIG. 2 is referred to as the front end side, and the upper side in FIG. 2 is referred to as the rear end side.

  The spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 32, 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 32 provided at the other end of the insulator 10 through the inside of the insulator 10. The outer periphery of the center electrode 20 is held by the insulator 10, and the outer periphery of the insulator 10 is held by the metal shell 50 at a position away from the terminal fitting 32. 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 tip of the center electrode 20. The spark plug 100 is attached to a mounting screw hole 201 provided in the plug hole 202 of the engine head 200 of the internal combustion engine via the metal shell 50. When a high voltage of 20,000 to 30,000 volts is applied to the terminal fitting 32, a spark discharge is generated in a spark gap formed between the center electrode 20 and the ground electrode 30. Note that the rear end portion of the terminal fitting 32 and the portion exposed from the insulator 10 is hereinafter referred to as a plug-side terminal 33.

  The insulator 10 is an insulator formed by firing a ceramic material such as alumina. The insulator 10 is a cylindrical member that is formed around the shaft hole 12 that accommodates the center electrode 20 and the terminal fitting 32. A central body 19 having a large outer diameter is formed at the axial center of the insulator 10. A rear end side barrel portion 18 that insulates between the terminal fitting 32 and the metal shell 50 is formed on the terminal fitting 32 side of the central barrel 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 central body portion 19, and a front end side body portion 17 is provided further ahead of the front end side body portion 17. A leg length portion 13 having a smaller outer diameter and a smaller outer diameter toward the distal end side is formed. The insulator 10 corresponds to “insulator in plug” in the claims.

  The metal shell 50 is a cylindrical metal fitting that surrounds and holds a portion extending from a part of the rear end side body portion 18 of the insulator 10 to the long leg portion 13. In the present embodiment, the metal shell 50 is made of low carbon steel, and is subjected to a plating process such as nickel plating or zinc plating. The metal shell 50 includes a tool engaging portion 51, a mounting screw portion 52, and a gasket receiving portion 54. The tool engaging portion 51 of the metal shell 50 is a portion into which a tool (not shown) for attaching the spark plug 100 to the engine head 200 is fitted, and in this embodiment, a cross section (the shape of a cross section orthogonal to the axis Ax). ) Is formed in a hexagonal shape. 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 gasket receiving portion 54 of the metal shell 50 is formed in a hook shape on the rear end side of the mounting screw portion 52 so as to protrude to the outer peripheral side in the radial direction from the mounting screw portion 52. The metal shell 50 is fitted with a gasket 5 that is a solid substantially annular member so as to be in contact with the end portion on the front end side of the gasket receiving portion 54. The gasket 5 ensures a sealing property between the gasket receiving portion 54 of the spark plug 100 and the engine head 200. In addition, the front end surface 57 of the metal shell 50 is formed in a circular shape having an opening at the center, and the center electrode 20 protrudes from the long leg portion 13 of the insulator 10 at the center.

  A thin caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engaging portion 51. Further, a thin compression deformation portion 58 is provided between the gasket receiving portion 54 and the tool engaging portion 51, similarly to the caulking portion 53. Between the inner peripheral surface of the metal shell 50 from the tool engaging portion 51 to the caulking portion 53 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. Further, talc (talc) 9 powder is filled between the ring members 6 and 7. At the time of manufacturing the spark plug 100, a crimping process is performed in which the compression deforming portion 58 is compressed and deformed by pressing the crimping portion 53 inward so as to be bent inward. By performing the caulking process, the insulator 10 is pressed toward the front end side in the metal shell 50 through the ring members 6 and 7 and the talc 9. By this pressing, the talc 9 is compressed in the direction of the axis Ax, and the airtightness in the metal shell 50 is enhanced.

  In addition, on the inner periphery of the metal shell 50, the insulator positioned at the base end of the leg long portion 13 of the insulator 10 via the annular plate packing 8 is connected to the metal inner step portion 56 formed at the position of the mounting screw portion 52. The step portion 15 is pressed. The plate packing 8 is a member that maintains the airtightness between the metal shell 50 and the insulator 10 and prevents combustion gas from flowing out.

  The center electrode 20 is a rod-like member 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. In the present embodiment, the electrode base material 21 is made of a nickel alloy containing nickel as a main component, and the core member 25 is made of copper or an alloy containing copper as a main component. 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 32 via the seal body 4. ing.

  The ground electrode 30 is made of a metal having high corrosion resistance, and a nickel alloy is used as an example. The proximal end of the ground electrode 30 is welded to the distal end surface 57 of the metal shell 50. The tip side of the ground electrode 30 is bent in a direction intersecting the axis Ax, and the tip of the ground electrode 30 faces the tip surface of the center electrode 20 on the axis Ax.

B. Spark plug and cable connection configuration:
FIG. 3 is an explanatory diagram showing the state of the connecting portion between the spark plug 100 and the plug cable 60. In FIG. 3, the plug cable 60 represents a cross section, and the spark plug 100 represents the appearance. As shown in FIG. 3, the plug cable 60 includes an inner conductor 61, an outer conductor 63, a cable terminal 65, and an in-cable insulator 62.

The inner conductor 61 is provided so as to extend along the center line of the plug cable 60. The outer conductor 63 is provided on the outer surface of the plug cable 60. The inner conductor 61 and the outer conductor 63 are made of a conductive material, and can be made of, for example, a material selected from an aluminum alloy, a copper alloy, an iron alloy, and a nickel alloy. Here, since the outer conductor 63 comes into contact with the spark plug 100 as will be described later, the electrical resistance at the contact portion with the spark plug 100 is sufficiently small (for example, 5 × 10 ^{−8) in the} environment where the spark plug 100 is used. It is desirable that it can be maintained at Ωm or less. If the above-described materials are used as the constituent material of the outer conductor 63, such a low resistance can be realized.

  The cable terminal 65 is provided at the tip of the internal conductor 61, and when the plug cable 60 and the spark plug 100 are connected, the rear end portion (plug side terminal 33) of the terminal fitting 32 of the spark plug 100 is fitted. This is a female terminal.

  The in-cable insulator 62 is provided so as to extend in the axis Ax direction so as to fill the space between the inner conductor 61 and the outer conductor 63. That is, the in-cable insulator 62 includes the boundary between the inner conductor 61, the connecting portion of the cable terminal 65 and the plug-side terminal 33, and the plug-side terminal 33 in the insulator 10 of the spark plug 100 in the outer conductor 63. Covering the outer surface. The front end of the in-cable insulator 62 is located on the rear end side in the axis Ax direction with respect to the front end of the external conductor 63 and is separated from the front end of the external conductor 63. In the present embodiment, the in-cable insulator 62 is provided with a rubber portion 64 that is an annular rubber member formed separately from other portions at the tip thereof. In the in-cable insulator 62, the other part than the rubber part 64 is an insulating property selected from, for example, fluorine resin, silicon resin, epoxy resin, ceramic, ethylene propylene rubber (EPDM), acrylic rubber, and nitrile rubber. It can be formed by material.

  As shown in FIG. 3, the outer conductor 63 has a rear end of the tool engaging portion 51 in the metal shell 50 of the spark plug 100 on the inner wall in the vicinity of the tip thereof and not covered with the cable insulator 62. Contact corners. In FIG. 3, a portion where the external conductor 63 and the tool engagement portion 51 are in contact with each other is shown as a connection portion A.

  FIG. 4 is a perspective view schematically showing the appearance of the distal end portion of the external conductor 63. The outer conductor 63 is formed with a plurality of (six in this embodiment) slits 67 extending in parallel to the axis Ax direction from the tip. The plurality of slits 67 are formed to have a slit length α. The plurality of slits 67 correspond to (overlap) the hexagonal corners of the cross section of the tool engaging portion 51 of the spark plug 100 when the spark plug 100 is fitted into the distal end portion of the plug cable 60. Is provided. That is, the same number of slits 67 as the corners are formed at positions corresponding to the corners extending in parallel to the axis Ax direction formed on the side surface of the tool engaging portion 51. Further, the outer conductor 63 has an inner diameter r of a cross section perpendicular to the direction of the axis Ax at least in the vicinity of the tip, which is the longest diameter in the cross section of the tool engaging portion 51 of the spark plug 100 (in this embodiment, tool engagement). Since the cross section of the portion 51 is substantially a regular hexagon, it is a line segment connecting the opposing vertices of the regular hexagon, and the diameter of the circumscribed circle of the cross section of the tool engagement portion 51 (hereinafter referred to as the longest diameter) It is formed to be small.

  In order to manufacture the plug cable 60, first, a cylindrical metal member for forming the outer conductor 63 is prepared. Then, the tip portion is cut to form six slits 67 having a slit length α. As a result, the outer conductor 63 is formed in which the six connection pieces 66 separated by the slits 67 are provided at the tip (see FIG. 4). Thereafter, a separately produced insulating member for constituting the in-cable insulator 62 is fitted into a predetermined position in the outer conductor 63. This insulating member may be formed in advance by, for example, injection molding so as to have a shape corresponding to the inner conductor 61, the cable terminal 65, and the spark plug 100 to be housed inside. Thereafter, the inner conductor 61 with the cable terminal 65 attached to the tip is inserted from the tip side of the outer conductor 63 into which the insulating member is fitted, and the inner conductor 61 and the cable terminal 65 are assembled. Further, a rubber part 64 is fitted into the tip of the insulating member to form an in-cable insulator 62. The rubber portion 64 has an inner diameter that is smaller than the outer diameter of the insulator 10 of the spark plug 100.

  When connecting the spark plug 100 and the plug cable 60, first, the spark plug 100 is attached to the attachment screw hole 201 in the plug hole 202 of the engine head 200 of the internal combustion engine (see FIG. 2). Thereafter, the front end portion of the plug cable 60 is inserted into the plug hole 202, and the rear end portion of the spark plug 100 is fitted into the in-cable insulator 62.

  When the rear end portion of the spark plug 100 is fitted in the plug cable 60 in this manner, the inner diameter of the outer conductor 63 is smaller than the longest diameter of the tool engaging portion 51, so The rear end corner of the joining portion 51 abuts on the tip of the outer conductor 63. Here, since a plurality of slits 67 are formed at the front end portion of the external conductor 63, when the plug cable 60 is further pushed in, the front end portion of the external conductor 63 is expanded and the rear end side of the plug cable 60 is further extended. The spark plug 100 can be inserted. The extent to which the spark plug 100 can be pushed into the rear end side of the plug cable 60 (insertion depth) is the relationship between the inner diameter of the cross section of the outer conductor 63 and the longest diameter of the cross section of the tool engaging portion 51. It is determined by the slit length α. In the present embodiment, the cable terminal 65 is arranged so that the cable terminal 65 and the plug-side terminal 33 are just connected when the spark plug 100 is pushed to the fitting depth determined as described above. In FIG. 3, the length of the slit 67 provided at the tip of the outer conductor 63 is indicated by a bidirectional arrow.

  FIG. 5 is an explanatory diagram schematically showing an enlarged view of the vicinity of the connection portion A between the tool engagement portion 51 and the external conductor 63. In the present embodiment, since the slit 67 is formed at the distal end portion of the external conductor 63, each connection piece 66 separated by the slit 67 has a leaf spring shape having elasticity in the radial direction of the external conductor 63. The inner diameter of the cross section of the distal end portion of the outer conductor 63 is formed smaller than the longest diameter of the tool engaging portion 51. Therefore, by pushing the spark plug 100 into the distal end portion of the outer conductor 63 and expanding the distal end portion of the outer conductor 63, each connection piece 66 has a radially inward force at the connection portion A with the spark plug 100. Occurs. In FIG. 5, the force applied from the external conductor 63 to the tool engagement portion 51 in the connection portion A is indicated by an arrow. In FIG. 5, the contact portion with the external conductor 63 in the tool engagement portion 51 (spark plug 100) is represented as a plug-side contact portion 59, and the contact portion with the tool engagement portion 51 in the external conductor 63 is represented by a cable. The side contact portion 68 is shown.

  In this way, by connecting the plug cable 60 and the spark plug 100, a DC voltage is applied and AC power is supplied to the spark plug 100 via the internal conductor 61 and the cable terminal 65. Further, by connecting the plug cable 60 and the spark plug 100, the metal shell 50 of the spark plug 100 comes into contact with the external conductor 63 and is grounded.

  At this time, a spark discharge can be generated in the spark gap between the electrodes by applying a DC voltage from the discharge power supply 41 to the spark plug 100. Further, by supplying AC power from the AC power source 42 to the spark plug 100, plasma is generated in the spark gap, and further energy is supplied to the spark generated by application of the DC voltage using AC power. Can do. In this manner, by supplying further energy using alternating current power to the spark generated using the direct current power supply, ignition in the spark plug 100 is performed as compared with the case where ignition is performed using only the direct current power supply. The ignition performance can be stabilized and the ignition operation can be stabilized.

  As shown in FIG. 5, in the outer conductor 63, a curved surface portion 69 having no corners is formed from the outer surface tip to the inner surface of the outer conductor 63. Therefore, when the spark plug 100 is fitted into the plug cable 60, the spark plug 100 can be guided by the curved surface portion 69 and the operation of inserting the spark plug 100 can be facilitated. In addition, the structure which provides the curved surface part 69 in the front-end | tip of the external conductor 63 is applicable similarly also in other embodiment and modification which are mentioned later.

  According to the ignition device 40 of the present embodiment configured as described above, the plug cable 60 is used to apply a DC voltage and supply AC power to the spark plug. The cable-side contact portion 68 of the leaf spring-like connection piece 66 is in contact with the metal shell of the spark plug 100. Therefore, the plug cable 60 can hold the spark plug 100 while applying a radially inward force to the spark plug 100. As a result, even if vibration is applied to the spark plug 100 and the plug cable 60, it is possible to reliably supply AC power necessary for ignition.

  Along with the fact that AC power necessary for ignition can be reliably supplied, malfunctions caused by poor connections, for example, leakage of radio waves may affect other devices as noise or reflection will cause sufficient AC power. Can be prevented from being supplied for ignition, causing engine misfire. In addition, it is possible to suppress heat generation due to connection failure and power loss due to disconnection and discharge.

  At this time, since the plug cable 60 is a coaxial cable and the area of the loop composed of the forward path and the return path of the alternating current flow is reduced, the inductance in the plug cable 60 can be reduced and consequently the impedance can be suppressed. . Furthermore, in this embodiment, the outer skin portion of the plug cable 60 for fitting the spark plug 100 is used as the outer conductor 63 for grounding directly in contact with the metal shell 50. In this way, the plug cable for connecting the spark plug to apply a DC voltage, the coaxial cable for supplying AC power to the spark plug, and the contact portion of the coaxial cable with the spark plug are integrated, so the whole The structure can be simplified. Further, according to the present embodiment, by using the plug cable 60, it is possible to obtain an ignition device that further supplies AC power using a spark plug that is normally used by applying only a DC voltage. . Further, according to the present embodiment, the distal end portion of the outer conductor 63 opens with an inner diameter that is larger than the outer diameter of the insulator 10 and smaller than the longest diameter of the tool engaging portion 51, and elastic inward in the radial direction. have. Therefore, the connection part A can be formed simultaneously with the operation of fitting the spark plug 100 into the plug cable 60 in the direction of the axis Ax.

  FIG. 6 is an explanatory view schematically showing a state in which a vibration test is performed using the vibration test apparatus 70 in order to confirm the effect of the present embodiment. The vibration test apparatus 70 is an apparatus for causing vibration under arbitrarily set conditions (vibration frequency, acceleration, vibration direction, vibration time, etc.). A simulated engine head 72 was fixed on a pedestal 73 formed horizontally in the vibration test apparatus 70 using a fixing jig 71. The simulated engine head 72 is a block-shaped member having a substantially rectangular parallelepiped shape, and a simulated plug hole having the same shape as the plug hole 202 having the mounting screw hole 201 is formed on the upper surface thereof. In addition, the internal space where the simulated plug hole is opened can be sealed by setting an arbitrary pressure. In the vibration test, the spark plug 100 was attached to the simulated plug hole, and the plug cable 60 was connected to the attached spark plug 100 to reproduce the ignition device 40 similar to FIG. Then, while applying vibration using the vibration test apparatus 70, DC voltage was applied to the spark plug 100 and AC power was supplied, and the behavior related to ignition of the spark plug 100 at that time was observed with an oscilloscope. In the plug cable 60 subjected to the vibration test, the slit length α of the slit 67 provided in the external conductor 63 is 5 mm, and a sample including such a plug cable 60 is hereinafter referred to as a sample S01.

  In addition to the plug cable 60 (sample S01), a plug cable 160 was produced for comparison. The plug cable 160 was connected to the spark plug 100 instead of the plug cable 60, and subjected to a vibration test while applying a DC voltage and supplying AC power under the same conditions.

  FIG. 7 is an explanatory view showing the state of the connecting portion between the plug cable 160 and the spark plug 100 in the same manner as FIG. Portions common to the plug cable 60 are denoted by the same reference numerals, and detailed description thereof is omitted. The plug cable 160 is different from the plug cable 60 in that an external conductor 163 is provided instead of the external conductor 63. The outer conductor 163 has an inner diameter that is larger than the outer diameter of the cross section of the insulator 10 and smaller than the longest diameter of the tool engaging portion 51, as with the outer conductor 63, but has a slit 67 at the tip. Not formed. Therefore, the plug cable 160 is coupled to the spark plug 100 in a state where the tip of the external conductor 163 is in contact with the rear end side of the tool engaging portion 51 as shown in FIG. Hereinafter, a sample including such a plug cable 160 is referred to as a sample S02.

  The vibration conditions using the vibration test apparatus 70 are as follows. The vibration frequency was gradually increased from 50 Hz to 2000 Hz over 5 minutes. Then, it was gradually lowered over 5 minutes from 2000 Hz to 50 Hz. The acceleration of vibration is 30 G. In this way, the operation of reciprocating the vibration frequency over 10 minutes is performed in the X direction parallel to the pedestal portion 73 of the vibration test apparatus 70 and in the X direction parallel to the pedestal portion 73. The measurement was performed for each of three directions, ie, the vertical Y direction and the Z direction perpendicular to the pedestal 73.

  The conditions for supplying AC power using the AC power source 42 were a frequency of 13 MHz and a power of 400 W. The pressure in the internal space of the simulated engine head 72 was 0.2 MPa. The DC voltage application frequency was 10 Hz. That is, during 10 minutes of vibrating in the directions of X, Y, and Z, application of a DC voltage for spark discharge was performed 6000 times while continuously supplying AC power under the above conditions. With the oscilloscope, the waveform of the current applied by the AC power source 42 was observed. By observing the above waveform, when DC voltage is applied, plasma is generated by AC power and ignition is performed without any problem, and there was spark discharge due to DC voltage application, but AC application was insufficient and stable ignition. Can be distinguished from the case where the spark formation failed due to a short circuit or the like. Therefore, based on the waveform of the oscilloscope, the number of times that ignition was performed without any trouble among the application of DC voltage 6000 times was counted. The results are shown in Table 1 below. According to the waveform of the oscilloscope, in the vibration test whose results are shown in Table 1, in all cases where the ignition could not be performed successfully, the AC application was insufficient. Therefore, in Table 1, the number of times that ignition was performed without any problem is described as “the number of plasma generations”, and the ratio that ignition was performed without any problem is described as “plasma generation rate”. In Table 1, the result of vibrating in the Z direction among the three directions is shown as a representative.

  As shown in Table 1, by using the plug cable 60 (sample S01) of the first embodiment, it was possible to increase the number of plasma generations and the plasma generation rate. That is, it was confirmed that the AC power necessary for ignition can be reliably supplied even under vibration conditions. Since the outer conductor 63 is structured to support the tool engaging portion 51 from the side surface, the outer conductor 63 is particularly easily affected by vibration in the Z direction, but is necessary for performing the above-described ignition against vibration in the Z direction. It was shown that the effect of supplying reliable AC power is high. In addition, when vibrations in other directions (X direction and Y direction) were applied, the plasma generation rate could be increased similarly (data not shown).

C. Second embodiment:
FIG. 8 is an explanatory diagram illustrating a state of connection with the metal shell in the outer conductor included in the plug cable of the second embodiment. In the following description, each part of the ignition device of the second embodiment is denoted by the same reference numeral as that of the first embodiment, and detailed description thereof is omitted. FIG. 8A shows a part of the cross section including the connection portion A between the outer conductor 63 and the metal shell 50 in the second embodiment, and FIG. 8B shows the state in the first embodiment. A part of the cross section including the connection portion A between the outer conductor 63 and the metal shell 50 is shown.

  As shown in FIG. 8A, in the second embodiment, each of the connection pieces 66 provided at the distal end portion of the outer conductor 63 and separated by the slit 67 is formed as a flat surface. In order to obtain such an outer conductor 63, for example, the cylindrical outer conductor of the first embodiment shown in FIG. 4 is prepared, the connecting piece 66 at the tip is pressed, and each connecting piece 66 is fixed. What is necessary is just to planarize. Alternatively, the tip of the cylindrical member for forming the outer conductor is pre-pressed so as to be a hexagonal column, and then the six sides on the side of the hexagonal column are cut to form the slit 67. May be.

  Here, in the second embodiment, the cross section of the distal end portion of the outer conductor 63 and the cross section of the tool engaging portion 51 of the metal shell 50 are both substantially regular hexagons. The length of one side of the hexagon formed by the cross section of the distal end portion of the outer conductor 63 is shorter than the length of one side of the hexagon formed by the cross section of the tool engaging portion 51 of the metal shell 50. . Therefore, by inserting the spark plug 100 into the distal end portion of the plug cable 60, the connection piece 66 of the outer conductor 63 is pushed outward and the direction from the connection piece 66 to the metal shell 50 toward the inside of the outer conductor 63. The power of work.

  As shown in FIG. 8A, according to the second embodiment, the connection portion A between the connection piece 66 and the tool engagement portion 51 is formed in a linear shape. On the other hand, as shown in FIG. 8B, when the cross section of the distal end portion of the outer conductor 63 is circular, the connection portion A of the connection piece 66 and the tool engagement portion 51 has a slit 67 in the connection piece 66. In the side part which comprises, it is formed in dot shape. As described above, by flattening the connection piece 66 of the outer conductor 63, it is possible to secure a wider area in contact with the tool engaging portion 51. As in the second embodiment, also in the first embodiment, the slit 67 is formed along the axis Ax direction at a position corresponding to each corner in the cross section of the tool engaging portion 51. ing. Therefore, as compared with the case where the slits 67 are provided at positions that do not correspond to the corners of the tool engaging portion 51, it is possible to secure more connection portions between the external conductor 63 and the tool engaging portion 51.

  The effect of flattening the connection piece 66 was confirmed by a vibration test similar to that of the first embodiment. The configuration of the vibration test apparatus 70 used, the conditions of the vibration test, and the evaluation method are the same as those in the first embodiment. In the plug cable 60 of the second embodiment, the slit length α of the slit 67 provided in the external conductor 63 is 5 mm, and a sample including such a plug cable 60 is hereinafter referred to as a sample S12. The results are shown in Table 2 below. According to the waveform of the oscilloscope, in the vibration test whose results are shown in Table 2, in all cases where the ignition could not be performed successfully, the AC application was insufficient. Therefore, in Table 2, the number of times that ignition was performed without any problem is described as “the number of plasma generations”, and the ratio that ignition was performed without any problem is described as “plasma generation ratio”. In Table 2, the result of vibrating in the Z direction among the three directions is shown as a representative. In Table 2, the vibration test result of the sample S01 shown in Table 1 is also shown as a sample S11, and the result of the sample S02 is also shown as a sample S13.

  As shown in Table 2, the number of plasma generations and the rate of plasma generation can be reduced by forming the connection portion A in a line segment (sample S12), compared to the case where the connection portion A is formed in a dot shape (sample S11). It was confirmed that it was further increased. That is, it was confirmed that even under vibration conditions, the effect of reliably supplying the AC power necessary for ignition can be obtained. Similarly, when the vibrations in other directions (X direction and Y direction) were applied, the plasma generation rate could be increased as compared with the first embodiment (data not shown).

D. Examination of slit length:
FIG. 9 is an explanatory view schematically showing the state in the vicinity of the connection portion A when the slit lengths α of the slits 67 provided in the external conductor 63 are different. 9A shows a state where the slit length α is longer, and FIG. 9B shows a state where the slit length α is shorter. When the slit length α is varied, the length of the leaf spring-like connection piece 66 changes, and the magnitude of the elastic force acting in the radial direction of the cross section of the outer conductor 63 changes from the outer conductor 63 to the metal shell 50. To do. Therefore, the effect of absorbing the vibration and maintaining the contact changes. Therefore, a plurality of types of external conductors 63 having different slit lengths α are prepared, and the ignition device 40 is assembled using each of the external conductors 63 in the same manner as in the first embodiment, and the vibration test shown in FIG. The effect of length α was examined. The vibration conditions, the DC voltage application conditions, and the AC power supply conditions were the same as those in the vibration test described above. Of the three directions, the results when vibrating in the Z direction are shown in Table 3 below as a representative. According to the waveform of the oscilloscope, in the vibration test whose results are shown in Table 3, in all cases where the ignition could not be performed successfully, the AC application was insufficient. Therefore, in Table 3, the number of times that ignition was performed without any problem is described as “plasma generation number”, and the ratio that ignition was performed without any problem is described as “plasma generation ratio”.

  In each sample shown in Table 3, as shown in the second embodiment, the outer conductor 63 is formed so that each connection piece 66 becomes a flat surface, and the connection portion A is formed in a line segment shape. ing. In Table 3, sample S21 represents a sample having a slit length α of 1 mm, sample S22 represents a sample having a slit length α of 3 mm, and sample S23 represents a sample having a slit length α of 5 mm. That is, the sample S23 is the same as the sample S12 in Table 2.

  As shown in Table 3, by setting the slit length α to 5 mm, the number of plasma generations and the plasma generation rate could be extremely high (the plasma generation rate was 100%). Although Table 2 only shows the results when the slit length α is up to 5 mm, the plasma generation rate was 100% even when the slit length α was increased to more than 5 mm, specifically 20 mm. (Data not shown). Similarly, when vibrations in other directions (X direction and Y direction) were applied, the plasma generation rate could be increased by setting the slit length α to 5 mm or more (data not shown). . Furthermore, when using the plug cable 60 including the outer conductor 63 having a circular cross section according to the first embodiment, the plasma generation ratio can be reduced by setting the slit length α to 5 mm or more as in the result of Table 3. It could be enhanced effectively (data not shown).

E. Examination of short-circuit suppression during DC voltage application:
FIG. 10 is an explanatory diagram showing the contents examined in addition to the slit length α, regarding the conditions related to short-circuit suppression when a DC voltage is applied. Specifically, each condition of the length of the rubber part 64 in the axis Ax direction, the ratio of the length in the axis Ax direction covered with the insulator in cable 62 in the insulator 10, and the thickness of the insulator in cable 62 Was examined.

  As shown in FIG. 10, the length of the rubber portion 64 in the axis Ax direction is hereinafter referred to as a rubber length β. The ratio of the length in the axis Ax direction covered by the in-cable insulator 62 in the insulator 10 is the distance in the axis Ax direction from the rear end of the insulator 10 to the rear end of the metal shell 50. This is the ratio (percentage) of 1 / L, where l is the distance in the axis Ax direction from the rear end to the tip of the in-cable insulator 62. The thickness of the in-cable insulator 62 is the thickness of the in-cable insulator 62 in the direction perpendicular to the direction of the axis Ax, and is hereinafter referred to as the insulator thickness γ.

  FIG. 11 is an explanatory diagram showing an undesired short-circuit phenomenon that may occur between the spark plug 100 and the outer conductor 63 when a DC voltage for spark formation is applied to the spark plug 100. As indicated by an arrow B in FIG. 11, when a short circuit occurs between the plug-side terminal 33 of the spark plug 100 and the outer conductor 63 via the surface of the insulator 10, A flashover occurs between the spark plug 100 and the outer conductor 63. In addition, as indicated by an arrow C in FIG. 11, a short circuit occurs between the plug-side terminal 33 of the spark plug 100 and the external conductor 63 via the surface of the insulator 10 and the inside of the cable insulator 62. There is. Such a phenomenon is hereinafter referred to as “penetration”.

  In order to investigate the influence of the rubber length β on the short circuit, the plug cable 60 was manufactured by varying the rubber length β in four stages of 1 mm, 3 mm, 5 mm, and 7 mm. Further, in order to investigate the influence of 1 / L on the short circuit, the plug cable 60 was manufactured by changing l / L in four stages of 35%, 40%, 45%, and 50%. Further, in order to investigate the influence of the insulator thickness γ on the short circuit, the plug cable 60 was manufactured by varying the insulator thickness γ in three stages of 1 mm, 3 mm, and 5 mm. Here, the diameter of the insulator 10 was further varied, and the ignition device 40 was assembled using a spark plug with an insulator diameter of 9.5 mm and a spark plug with a 10.5 mm.

  While varying the above-described conditions, a simulated ignition device 40 is assembled using a simulated engine head 72 similar to that in FIG. 6, a DC voltage is applied and AC power is supplied, and ignition of the spark plug 100 at that time is performed. The behavior according to was observed with an oscilloscope. The conditions for supplying AC power using the AC power supply 42 are set to a frequency of 13 MHz and power of 400 W, as in the vibration test described above, and the pressure in the internal space of the simulated engine head 72 is 0.8 to 2.0 MPa. did. Moreover, the gap of the spark plug 100 was 1.3 mm, and the applied DC voltage was changed in four stages of 20 kV, 25 kV, 30 kV, and 35 kV. The DC voltage was applied at a frequency of 10 Hz, and the evaluation test was performed on two sets for each condition, with the operation of applying DC voltage for 1 minute at such a frequency as one set. Whether or not the ignition operation was possible was determined based on the waveform observed with an oscilloscope, as in the vibration test described above. With the above application frequency, 600 ignition operations are performed during one set. If it is determined that ignition has failed even once during one set of tests, Evaluated as failure. According to the waveform of the oscilloscope, any case where ignition could not be performed successfully was a case where spark formation failed due to a short circuit or the like. Therefore, when ignition failed, it was confirmed whether the cause of ignition failure was due to flashover or penetration. Specifically, at the time of ignition failure, the spark plug was disassembled and the in-cable insulator 62 was observed, and if a penetrating burn mark was confirmed, it was determined that the cause of the ignition failure was penetration. If no burn mark passing through the in-cable insulator 62 was confirmed, the cause of the ignition failure was determined to be flashover.

  The results of evaluation for each of the above conditions are shown in Tables 4 to 9 below. Tables 4 to 6 show the results using spark plugs having an insulator diameter of 9.5 mm, and Tables 7 to 9 show results using spark plugs having an insulator diameter of 10.5 mm. Tables 4 and 7 show the results when the insulator thickness γ is 1 mm, Tables 5 and 8 show the results when the insulator thickness γ is 3 mm, and Tables 6 and 9 show the insulators. The results when the thickness γ is 5 mm are shown. In each table, the result of varying the rubber length β, the result of varying l / L, and the result of varying the applied DC voltage are shown. In each table, if there was no ignition failure in both of the two sets, “XX” was indicated. When only one set fails in ignition, “◯ ×” is shown. When both sets failed in ignition, “XX” was indicated. In the case of ignition failure, the case where the cause is due to flashover and the case where it is due to penetration are distinguished by the attached hatch. In each sample whose results are shown in Tables 4 to 9, as the external conductor 63, the external conductor 63 having a circular cross section at the tip is used as in the first embodiment.

  Usually, the DC voltage applied to the spark plug is about 20 kV. As shown in Tables 4 to 9, by setting the rubber length β to 5 mm or more, even when the applied voltage is set to 25 kV higher than the above 20 kV, a short circuit at the time of applying the DC voltage is effectively performed. It was able to be suppressed (becomes “XX”). This is presumably because the action of closing the gap between the in-cable insulator 62 and the insulator 10 is increased by increasing the rubber length β. Actually, when the rubber length β was less than 5 mm and the applied voltage was 25 kV or 30 kV, the cause of ignition failure was mostly due to flashover. From the above, it has been confirmed that by setting the rubber length β to 5 mm or more, it is possible to particularly enhance the effect of suppressing the flashover and performing the ignition operation without any trouble.

  Further, as shown in Tables 4 to 9, by setting l / L to 50% or more, even when the applied voltage is set to 25 kV higher than the above 20 kV, a short circuit at the time of applying DC voltage is effectively prevented. It was able to be suppressed (when the rubber length β was 3 mm or more, it became “◯◯”). Here, under the condition where the rubber length β is 1 mm, even if l / L is 50%, it may be “Ox” instead of “Ox”. By changing L from 45% to 50%, the ignition performance was improved from “xx” to “Ox” (see Tables 4 and 7). This is because the ratio of 1 / L is increased to increase the axial length of the surface of the insulator 10 covered by the in-cable insulator 62, thereby suppressing the short circuit via the surface of the insulator 10. It is thought to increase. Actually, when l / L was less than 50% and the applied voltage was 25 kV or 30 kV, the cause of ignition failure was mostly due to flashover (see Tables 4 to 9). From the above, it has been confirmed that by setting l / L to 50% or more, it is possible to particularly enhance the effect of suppressing the flashover and performing the ignition operation without any trouble.

  Moreover, as shown in Tables 4-9, the short circuit at the time of a DC voltage application was effectively suppressed by making insulator thickness (gamma) 5 mm or more. For example, when the rubber length β is 5 mm or more and l / L is 50% or more, even if the applied voltage is increased to 35 kV, the insulator thickness γ is set to 5 mm or more, and “◯◯” is obtained. (See Tables 6 and 9). This is presumably because the effect of suppressing a short circuit penetrating through the in-cable insulator 62 is increased by increasing the insulator thickness γ. Actually, when the insulator thickness γ was less than 5 mm and the applied voltage was 35 kV, the cause of ignition failure was due to penetration (see Tables 4, 5, 7, and 8). From the above, it was confirmed that by making the insulator thickness γ 5 mm or more, in particular, the effect of suppressing the penetration and performing the ignition operation without hindrance can be enhanced.

  As described above, by setting the rubber length β to 5 mm or more, 1 / L to 50% or more, or the insulator thickness γ to 5 mm or more, the ignition operation with AC voltage application can be stabilized. It was confirmed that In particular, when all the above three conditions were satisfied, even if the applied DC voltage was increased to 35 kV, it became “◯◯” (see Tables 6 and 9). With respect to spark plugs, with the recent downsizing of engines (high compression, high supercharging), there is an increasing demand for higher applied DC voltage. By satisfying at least one of the above-mentioned conditions, even if the applied voltage is increased, it is considered that the effect of suppressing the short circuit and performing the ignition operation without any trouble can be enhanced.

  Similarly, flashover could be suppressed when the rubber length β was 7 mm or when 1 / L was 55% or 60% (data not shown). Similarly, when the insulator thickness γ was 10 mm or more, penetration could be suppressed (data not shown).

F. Third embodiment:
FIG. 12 is an explanatory view showing the state of the connecting portion between the spark plug and the plug cable in the ignition device of the third embodiment, similar to FIG. In the third embodiment, parts common to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The ignition device of the third embodiment is different from the first embodiment in that a plug cable 260 is provided instead of the plug cable 60. The plug cable 260 includes a fastening member 269 in addition to the same configuration as the plug cable 60.

  As shown in FIG. 12, the fastening member 269 is a member extending in the direction of the axis Ax, and is disposed outside the external conductor 63 so as to be in contact with the outer surface on the distal end side of the external conductor 63. In the present embodiment, the tightening member 269 is a cylindrical member, and the distal end portion of the plug cable 260 reaches the vicinity of the lower end of the tool engaging portion 51 of the spark plug 100 fitted in the outer conductor 63. The outer conductor 63 is fitted from the rear end side to the front end side. Further, the fastening member 269 is formed such that the inner diameter of the transverse section thereof is slightly smaller than the outer diameter of the transverse section at the connection portion A in the outer conductor 63 when the spark plug 100 is fitted therein. Thereby, the fastening member 269 can suppress the outer conductor 63 from spreading outward in the radial direction, and can apply a pressing force inward in the radial direction from the fastening member 269 to the outer conductor 63.

  As a result, the pressing force applied from the outer conductor 63 to the tool engaging portion 51 at the connection portion A becomes larger, and the effect of reliably supplying AC power necessary for performing ignition can be enhanced. Further, by providing such a tightening member 269, the area of the connection portion A where the outer conductor 63 and the tool engagement portion 51 come into contact with each other is increased, and the supply of AC power necessary for ignition is ensured. The effect to be performed can be further enhanced.

  Here, the fastening member 269 only needs to apply a radially inward pressing force to the outer conductor 63 at least at a position corresponding to the connection portion A (outside of the connection portion A). Various shapes such as a ring shape having a shorter length in the axis Ax direction and a C ring shape having slits in the axis Ax direction can be used. Such a fastening member 269 can be formed of, for example, a metal material.

G. Fourth embodiment:
FIG. 13 is an explanatory diagram illustrating a state of a connection portion between a spark plug and a plug cable in the ignition device of the fourth embodiment. In the fourth embodiment, portions common to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The ignition device of the fourth embodiment differs from the first embodiment in that a plug cable 360 is provided instead of the plug cable 60. The plug cable 360 includes an outer conductor 363 instead of the outer conductor 63. In addition, a pleat portion 366 is provided at the tip of the external conductor 363 instead of the slit 67 and the connection piece 66.

  FIG. 13A is an explanatory diagram showing the appearance of the vicinity of the joint between the plug cable 360 and the spark plug 100. FIG. 13B is a diagram schematically illustrating a cross-sectional state in the connection portion A where the plug cable 360 and the tool engagement portion 51 are in contact with each other. In FIG. 13A, the position of the cross section shown in FIG.

  The pleat portion 366 is formed with six convex portions and six concave portions extending alternately in the direction of the axis Ax, and has a shape that gradually increases in diameter toward the distal end side. The plug cable 360 having such a pleat portion 366 can be formed, for example, by pressing a tip portion of a substantially cylindrical metal member for producing the plug cable 360.

  In the outer conductor 363, the inner diameter on the rear end side from the pleat portion 366 is formed smaller than the longest diameter of the tool engaging portion 51 and larger than the outer diameter of the insulator 10. The inscribed circle at the tip of the pleat portion 366 is formed to be larger than the longest diameter of the tool engaging portion 51. Therefore, when the spark plug 100 is fitted into the plug cable 360 from the front end side of the plug cable 360, the inner wall of the pleat portion 366 and the rear end corner portion of the tool engaging portion 51 come into contact with each other at a position in the middle of the pleat portion 366. To do. FIG. 13B shows that the concave portion in the pleat portion 366 abuts against the central portion of each side of the hexagonal cross section of the tool engaging portion 51 to form a connection portion A, and the cross section including the connection portion A. In the drawing, the inscribed circle of the pleat portion 366 and the inscribed circle of the cross section of the tool engaging portion 51 are overlapped as an inscribed circle D. By pushing the tool engaging portion 51 into the pleated portion 366 having a plurality of irregularities extending in the axis Ax direction, the connecting portion A is directed radially inward from the pleated portion 366 to the tool engaging portion 51. A pressing force can be generated. In FIG. 13B, the force acting radially inward is represented by an arrow.

  Even in such a configuration, by generating a radially inward force at the connection portion A, the effect of reliably supplying the AC power necessary for ignition is enhanced, and the same as in the first embodiment. The effect is obtained.

H. Fifth embodiment:
FIG. 14 is an explanatory diagram illustrating a state of a coupling portion between a spark plug and a plug cable in the ignition device of the fifth embodiment. In the fifth embodiment, parts common to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The ignition device of the fifth embodiment is different from the first embodiment in that a plug cable 460 is provided instead of the plug cable 60. The plug cable 460 includes an outer conductor 463 instead of the outer conductor 63. In addition, a diameter-enlarged portion 466 having a slit 467 is provided in place of the slit 67 and the connection piece 66 at the distal end portion of the external conductor 463.

  FIG. 14A shows an appearance in which the plug cable 460 and the spark plug 100 are assembled. FIG. 14B shows the appearance of the distal end portion of the plug cable 460 before the spark plug 100 is assembled.

  As shown in FIG. 14B, the diameter-enlarged portion 466 has a substantially frustoconical appearance that gradually increases in diameter toward the distal end side. Further, the enlarged diameter portion 466 has a plurality of line-shaped slits 467 extending in the direction of the axis Ax in the middle thereof. The plug cable 460 having such a diameter-enlarged portion 466 is formed, for example, into a shape that gradually increases in diameter by pressing the tip portion of a substantially cylindrical metal member for producing the plug cable 460. The slit 467 can be formed by cutting.

  In the external conductor 463, the inner diameter on the rear end side with respect to the enlarged diameter portion 466 is formed to be smaller than the longest diameter of the tool engaging portion 51 and larger than the outer diameter of the insulator 10. Further, the inner diameter at the tip of the enlarged diameter portion 466 is formed to be larger than the longest diameter of the tool engaging portion 51. Therefore, when the spark plug 100 is fitted into the plug cable 460 from the distal end side of the plug cable 460, the enlarged diameter portion is located at a position in the middle of the enlarged diameter portion 466, specifically, at the position where the slit 467 is formed. The inner wall of 466 comes into contact with the rear end corner of the tool engaging portion 51. After the inner wall of the enlarged diameter portion 466 and the rear end corner of the tool engaging portion 51 come into contact with each other at the position of the slit 467, when the spark plug 100 is further pushed in, each slit 467 is opened and the rear of the tool engaging portion 51 is opened. The enlarged diameter portion 466 is pushed and widened by the end corner portion. By fitting the spark plug 100 in this way, it is possible to generate a pressing force inward in the radial direction from the enlarged diameter portion 466 to the tool engaging portion 51.

  As described above, even when the slit formed in the line segment shape without reaching the tip is provided in the outer conductor, a force inward in the radial direction can be generated in the connection portion A, which is necessary for performing ignition. The effect of reliably supplying the AC power is enhanced, and the same effect as that of the first embodiment can be obtained.

I. Variations:
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.

I1. Modification 1 (deformation relating to the configuration of the connection part A):
I1-1. Deformation related to the position of the connection part A:
In the first to fifth embodiments, the plug-side contact portion 59 on the metal shell 50 side that constitutes the connection portion A is formed at the rear end corner portion of the tool engagement portion 51, but a different configuration may be used. Below, the modification which concerns on the mode of a coupling | bonding of a spark plug and a plug cable is demonstrated.

  FIG. 15 is an explanatory diagram showing one of the modified examples related to the coupling portion between the spark plug and the plug cable. In the modification shown below, the same reference numerals are given to the portions common to the first embodiment, and detailed description will be omitted. A plug cable 560 shown in FIG. 15 includes an external conductor 563 instead of the external conductor 63. The outer conductor 563 is formed with a contact recess 569 that extends in the circumferential direction and is bent radially inward. The contact recess 569 comes into contact with the compression deformation portion 58 of the metal shell 50 when the spark plug 100 is fitted in the outer conductor 563. That is, in the outer conductor 563, the cable side contact portion 68 is formed on the inner wall of the contact recess 569, and in the metal shell 50, the plug side contact portion 59 is formed on the surface of the compression deformation portion 58.

  FIG. 16 is an explanatory view showing another modification example relating to the joint portion between the spark plug and the plug cable. In FIG. 16A, an external conductor 663A is used instead of the external conductor 63. The outer conductor 663A has a bent portion 669A that is bent radially inward at the tip thereof. The bent portion 669A has an inner diameter smaller than the longest diameter of the tool engaging portion 51, and comes into contact with the side surface of the tool engaging portion 51 when the spark plug 100 is fitted in the outer conductor 663A. .

  In FIG. 16B, an external conductor 663B is used instead of the external conductor 63. The outer conductor 663B is formed with a contact recess 669B that extends in the circumferential direction and is bent radially inward. The contact recess 669B contacts the tip corner of the tool engaging portion 51 when the spark plug 100 is fitted in the external conductor 663B.

  In FIG. 16C, an external conductor 663C is used instead of the external conductor 63. The outer conductor 663C has a contact recess 669C that extends in the circumferential direction and is bent radially inward. The contact recess 669C comes into contact with the rear end corner of the gasket receiving portion 54 when the spark plug 100 is fitted into the outer conductor 663C.

I1-2. A configuration in which a plurality of connection portions A are provided:
FIG. 17 is an explanatory diagram illustrating an example in which a plurality of connection portions A are provided along the axis Ax direction as still another modification of the coupling portion between the spark plug and the plug cable. In FIG. 17, an external conductor 763 is used instead of the external conductor 63. The outer conductor 763 is formed with a contact concave portion 769 that extends in the circumferential direction and is bent radially inward. The contact recess 769 has an inner diameter smaller than the longest diameter of the tool engaging portion 51 and the outer diameter of the gasket receiving portion 54. When the spark plug 100 is fitted into the outer conductor 763, the contact recess 769 is positioned in the vicinity of the compression deformation portion 58, and the outer conductor 763 is mainly formed at two positions on the front end side and the rear end side of the contact recess 769. Contact the bracket. Specifically, the outer conductor 763 is in contact with the tip corner portion (plug side contact portion 59A) of the tool engaging portion 51 at the cable side contact portion 68A on the rear end side of the contact recess 769. Further, the cable-side contact portion 68B on the front end side of the contact recess 769 makes contact with the rear end corner portion (plug-side contact portion 59B) of the gasket receiving portion 54.

  In FIG. 17, the contact recess 769 is provided so that the outer conductor 763 is in contact with the front end corner of the tool engaging portion 51 of the metal shell 50 and the rear end corner of the gasket receiving portion 54. Also good. Regardless of the arrangement of the connecting portion A, the outer conductor includes a cable side contact portion 68 having an inscribed circle whose diameter is smaller than the diameter of the circumscribed circle of the plug side contact portion 59 in the metal shell 50, and the cable side contact portion 68. In this case, it is only necessary to have elasticity in the radial direction of the outer conductor. If a predetermined uneven shape is provided at the tip of the external conductor and a plurality of connecting portions A are provided along the direction of the axis Ax, the effect of reliably supplying AC power necessary for ignition can be enhanced. Can do.

I1-3. Configuration in which a protrusion is provided on the inner wall of the outer conductor:
FIG. 18 is an explanatory diagram showing an example in which a protruding portion for contacting the metal shell is provided so as to protrude from the inner wall of the outer conductor as still another modified example related to the connecting portion of the spark plug and the plug cable. 18A and 18B, external conductors 863A and 863B are used in place of the external conductor 63, respectively. In the outer conductors 863A and 863B, contact recesses 769 similar to the outer conductor 763 in FIG. 17 are formed, and at two positions corresponding to the front end corner of the tool engaging portion 51 and the rear end corner of the gasket receiving portion 54, A connection portion A is formed. Furthermore, the outer conductors 863A and 863B are provided with projecting portions 80 provided so as to project from the inner surface and extend in the circumferential direction. In FIG. 18A, the protrusion 80 comes into contact with the metal shell 50 on the side of the tool engaging portion closer to the rear end than the rear end corner of the tool engaging portion 51. In FIG. 18B, the protrusion 80 contacts the metal shell 50 on the side of the gasket receiving portion closer to the tip than the rear end corner of the gasket receiving portion 54. In FIG. 18, a portion where the protrusion 80 and the metal shell 50 come into contact is shown as a connection portion E. Thus, by providing the protrusion 80 and increasing the number of connecting portions between the outer conductor and the metal shell, it is possible to further enhance the effect of reliably supplying AC power necessary for ignition.

  The protrusion 80 may be provided at a position different from that in FIG. 18 so that the protrusion 80 is in contact with another part of the metal shell 50. However, as shown in FIG. 18A, the spark plug 100 into the external conductor is provided on the rear end side of the connection portion A, particularly on the rear end side of the tool engagement portion 51. This is desirable because it facilitates the operation of inserting.

  The protrusion 80 may be formed as a claw-like protrusion that is separated from each other at a plurality of positions along the inner periphery of the outer conductor 863, in addition to a shape that makes one round of the inner surface of the outer conductor 863. Such a protrusion 80 may be formed by welding, for example, or may be bent toward the inner peripheral side after the outer conductor 863 is cut and nipped. In addition, the structure which provides such a projection part 80 is not combined with the structure of FIG. 17, but can be combined with any structure having a connection portion A having a different shape, including the first to fifth embodiments. it can.

  Further, in each configuration shown in FIGS. 15 to 18, the distal end portion of the outer conductor including the cable side contact portion 68 may have a slit similar to that of the first embodiment. If the slit is provided, the operation of fitting the spark plug and the plug cable can be facilitated. However, the tip of the outer conductor may be elastically deformed to such an extent that the plug cable can be fitted into the spark plug, and the difference between the outer diameter of the region covered with the outer conductor in the metal shell 50 and the inner diameter of the outer conductor. If is sufficiently small, it is good also as not forming a slit in the front-end | tip part of an external conductor.

I2. Modification 2 (Modification related to plug cable):
In the first to fifth embodiments described above, the in-cable insulator 62 included in the plug cable includes the rubber portion 64 at the tip, but may not include the rubber portion 64. It is only necessary to ensure that the adhesion between the cable insulator 62 and the insulator 10 is acceptable in the entire cable insulator 62.

  Further, the connection form of the cable terminal 65 provided at the tip of the inner conductor 61 and the terminal fitting 32 provided in the spark plug 100 may be different. For example, the cable terminal 65 side may be a male terminal, and a female terminal may be formed on the terminal fitting 32 of the spark plug 100. It is sufficient that the internal conductor 61 and the terminal fitting 32 can be connected simultaneously with the operation of fitting the plug cable into the spark plug 100.

I3. Modification 3:
In the first to fifth embodiments, a DC voltage is applied to the spark plug 100 from the discharge power supply 41 and AC power is supplied from the AC power supply 42. However, different configurations may be used. The ignition operation may be performed using only AC power supplied from the AC power source 42. By applying the configuration of the present application to at least an ignition device that supplies electric power from the AC power source 42 to the spark plug 100, the above-described effect relating to securing of AC power necessary for ignition can be obtained.

DESCRIPTION OF SYMBOLS 4 ... Sealing body 5 ... Gasket 6, 7 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 12 ... Shaft hole 13 ... Leg long part 15 ... Insulator step part 17 ... Front end side body part 18 ... Rear end side body part DESCRIPTION OF SYMBOLS 19 ... Central trunk | drum 20 ... Center electrode 21 ... Electrode base material 25 ... Core material 30 ... Ground electrode 32 ... Terminal metal fitting 33 ... Plug side terminal 40 ... Ignition device 41 ... Power source for discharge 42 ... AC power source 43 ... Mixing part 44 ... Coil 45 ... Capacitor 46 ... First transmission path 47 ... Second transmission path 50 ... Metal fitting 51 ... Tool engaging part 52 ... Mounting screw part 53 ... Clamping part 54 ... Gasket receiving part 56 ... Inner metal part 57 ... distal end surface 58 ... compression deformation part 59 ... plug side contact part 60, 160, 260, 360, 460, 560 ... plug cable 61 ... inner conductor 62 ... insulator in cable 63, 163, 363, 463, 5 3, 663, 763, 863 ... external conductor 64 ... rubber part 65 ... cable terminal 66 ... connection piece 67, 467 ... slit 68 ... cable side contact part 69 ... curved surface part 70 ... vibration test apparatus 71 ... fixing jig 72 ... simulation Engine head 73 ... Base part 80 ... Projection part 100 ... Spark plug 200 ... Engine head 201 ... Mounting screw hole 202 ... Plug hole 269 ... Tightening member 366 ... Pleated part 466 ... Diameter expansion part 569, 669B, 669C, 769 ... Contact recess 669A ... bent portion

Claims (14)

A spark plug comprising a cylindrical metal shell, a cylindrical plug insulator disposed on an inner periphery of the metal shell, and a plug-side terminal provided at a rear end of the plug insulator;
An AC power supply for supplying AC power to the spark plug for the formation and / or maintenance of sparks in the spark plug;
A cable connecting the spark plug and the AC power source;
In an ignition device comprising:
The cable is
An inner conductor extending along the center line of the cable;
An outer conductor formed on the outer surface of the cable;
A cable terminal provided at the tip of the inner conductor inside the cable, and a cable terminal connected to the plug-side terminal;
Between the outer conductor and the inner conductor, provided in a portion excluding the tip of the outer conductor, and an in-cable insulator that insulates between the outer conductor and the inner conductor;
With
In a state before the cable is connected to the spark plug, the distal end portion of the outer conductor has an inner diameter smaller than the diameter of the circumscribed circle of the plug-side contact portion of the metal shell that contacts the distal end portion. Cable side contact portion having a circle, comprising a cable side contact portion having elasticity in the radial direction of the outer conductor,
The ignition device is characterized in that the metal shell is fitted into the cable so that the plug-side contact portion and the cable-side contact portion are in contact with each other. The ignition device according to claim 1,
The ignition device according to claim 1, wherein the front end portion of the outer conductor has a plurality of slits formed from a front end side to the cable side contact portion to a rear end side from the cable side contact portion. The ignition device according to claim 2, wherein
The metal shell extends in the outer peripheral direction, the cross-sectional shape orthogonal to the axis is a polygonal shape, and includes a tool engaging portion on which the plug-side contact portion is formed,
The slit is formed to extend in the axial direction at a position corresponding to each corner portion of the polygonal shape when the tool engaging portion is fitted into the distal end portion of the outer conductor. The ignition device according to claim 3, wherein
In the tip portion of the outer conductor, a region that is separated from each other by the slit and includes at least the cable side contact portion forms a flat surface,
The plug-side contact portion in the tool engagement portion and the cable-side contact portion in contact with the plug-side contact portion are formed in line segments. The ignition device according to any one of claims 2 to 4,
The ignition device characterized in that a length of the slit extending from the front end of the outer conductor to the rear end side along the axial direction is 5 mm or more. The ignition device according to any one of claims 1 to 5,
In the external conductor, a region from the outer surface tip of the outer conductor to the inner surface of the outer conductor is formed in a curved shape. The ignition device according to any one of claims 1 to 6, further comprising:
A discharge power source for applying a voltage to cause a spark discharge in the spark plug;
The in-cable insulator is an annular rubber part made of rubber, and has an inner diameter smaller than the outer diameter of the in-plug insulator in a state before the cable is connected to the spark plug. The ignition device is characterized in that the insulator in the plug is fitted into the tip of the insulator in the cable including the rubber portion at the tip. The ignition device according to claim 7, wherein
The rubber part has an axial length of the spark plug of 5 mm or more. The ignition device according to any one of claims 1 to 6, further comprising:
A discharge power source for applying a voltage to cause a spark discharge in the spark plug;
The insulator in the cable has an outer surface including a boundary between the surface of the coupling portion between the cable terminal and the plug-side terminal and the plug-side terminal of the insulator in the plug protruding from the rear end of the metal shell. And covering at least 50% of the axial distance from the rear end of the plug insulator to the rear end of the metal shell on the plug insulator. Ignition device. The ignition device according to claim 7 or 8,
The insulator in the cable has an outer surface including a boundary between the surface of the coupling portion between the cable terminal and the plug-side terminal and the plug-side terminal of the insulator in the plug protruding from the rear end of the metal shell. And covering at least 50% of the axial distance from the rear end of the plug insulator to the rear end of the metal shell on the plug insulator. Ignition device. The ignition device according to any one of claims 1 to 6, further comprising:
A discharge power source for applying a voltage to cause a spark discharge in the spark plug;
The ignition device according to claim 1, wherein a thickness of the insulator in the cable formed between the insulator in the plug and the outer conductor in a direction perpendicular to the axial direction of the spark plug is 5 mm or more. The ignition device according to any one of claims 7 to 10,
The ignition device according to claim 1, wherein a thickness of the insulator in the cable formed between the insulator in the plug and the outer conductor in a direction perpendicular to the axial direction of the spark plug is 5 mm or more. The ignition device according to any one of claims 1 to 12,
The front end portion of the outer conductor includes a protrusion that protrudes inward in the radial direction on the rear end side of the cable-side contact portion and contacts the metal shell. The ignition device according to any one of claims 1 to 13, further comprising:
An ignition device comprising a fastening member that is provided on an outer periphery of the outer conductor and applies a force directed radially inward to the outer conductor.

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