JP2013186999A - Ignition system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable exchange of only a center electrode and an insulator, and thereby, to reduce cost required for exchange and to achieve an excellent economical efficiency.SOLUTION: An ignition system 101 comprises: an AC power supply 51 outputting an AC voltage; a coil housing body 11 having a resonance coil 16 electrically connected with the AC power supply 51; and an ignition plug 21 having a cylindrical insulator 22 with a shaft hole 27 extending in a shaft line CL1 direction, and a center electrode 28 inserted into the shaft hole 27 and electrically connected to the resonance coil 16, and in which at least a part of itself is arranged on a shaft line CL1 direction front end side from the coil housing body 11. The coil housing body 11 is provided with a connector 17 that can electrically connect the resonance coil 16 to a connected part 31 provided at a rear end part of the center electrode 28. The connector 17 is attachable to/detachable from the connected part 31, and the coil housing body 11 is attachable to/detachable from the ignition plug 21.

Description

  The present invention relates to an ignition system that generates corona discharge by applying an alternating voltage.

  Conventionally, a combustion apparatus such as an internal combustion engine uses an ignition plug that ignites an air-fuel mixture by spark discharge (arc discharge). In recent years, in order to further improve the ignitability, a technique has been proposed in which an alternating voltage is applied to the spark plug to generate a corona discharge starting from the center electrode and ignite the air-fuel mixture. (For example, refer patent document 1 etc.).

  Such an ignition system that generates corona discharge generally includes an insulator having a shaft hole, a center electrode inserted through the shaft hole, a cylindrical fitting provided on the outer periphery of the insulator, and the center electrode. A unit having a resonance coil connected in series and disposed in the metal fitting, and an AC power source for applying an AC voltage to the unit are provided.

JP 2009-8100 A

  However, in the above ignition system, when the center electrode or the insulator is damaged due to use or the like, it is necessary to replace the entire unit even if the metal fitting and the resonance coil are normal. Therefore, the cost required for replacement becomes expensive, and the cost is inferior.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible to reduce the cost required for replacement by making it possible to replace only the center electrode and the insulator, and to achieve excellent economic efficiency. To provide a system.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The ignition system of this configuration includes an AC power source that outputs an AC voltage,
A coil housing body having a resonance coil electrically connected to the AC power source;
A cylindrical insulator having an axial hole extending in the axial direction; and a central electrode inserted in the axial hole and electrically connected to the resonant coil, at least a portion of itself being the coil housing A spark plug disposed on the tip end side in the axial direction than
An ignition system that generates a corona discharge starting from the center electrode by applying an AC voltage to the center electrode,
The coil container is provided with a connection portion that can electrically connect the resonance coil to a connection portion provided at a rear end portion of the center electrode, and the connection to the connection portion. Part is removable,
The coil container is detachable with respect to the spark plug.

  According to the configuration 1, the spark plug having the center electrode and the insulator is configured such that the connection portion provided in the coil housing is detachable from the connection portion provided in the rear end portion of the center electrode. On the other hand, a coil housing body having a resonance coil is detachable. Therefore, when the spark plug is damaged due to use or the like, only the damaged spark plug needs to be replaced, and the coil housing can be used as it is. As a result, the cost required for replacement can be reduced, and excellent economic efficiency can be realized.

Configuration 2. The ignition system of this configuration is the above configuration 1, wherein the coil housing is
A cylindrical metal fitting in which the resonance coil is disposed;
An intermediate member made of an insulating material disposed between the outer periphery of the resonance coil and the inner periphery of the metal fitting,
The intermediate member is located closer to the rear end side in the axial direction than the front end of the metal fitting when the coil container is attached to the spark plug.

  According to the configuration 2, the intermediate member made of an insulating material is provided between the resonance coil and the metal fitting disposed on the outer periphery thereof. Therefore, the insulation between the resonance coil and the metal fitting can be enhanced. As a result, an AC voltage can be more reliably applied to the center electrode via the resonance coil, and corona discharge can be more reliably generated.

  In addition, according to the configuration 2, the intermediate member is configured to be positioned on the rear end side (side away from the center of the combustion chamber) from the front end of the metal fitting in a state where the coil housing is mounted on the spark plug. ing. Therefore, damage to the intermediate member due to heat accompanying the operation of the internal combustion engine or the like can be prevented more reliably.

Configuration 3. The ignition system of this configuration is the above configuration 1 or 2, wherein the coil housing is
A cylindrical metal fitting in which the resonance coil is disposed;
An intermediate member disposed between the outer periphery of the resonance coil and the inner periphery of the metal fitting,
In a state where the coil container is mounted on the spark plug, a tip portion of the intermediate member is in contact with the insulator.

  Note that “the tip of the intermediate member is in contact with the insulator” is not only when the intermediate member is in direct contact with the insulator, but also, for example, via a packing or the like to be described later. The case where the front-end | tip part of an intermediate member is indirectly contacting with an insulator is also included.

  According to the configuration 3, the distal end portion of the intermediate member is configured to contact the insulator in a state where the coil container is mounted on the spark plug. Therefore, the heat of the insulator and the center electrode inserted through the intermediate member can be efficiently drawn, and damage to the insulator and the center electrode due to heat can be prevented more reliably. As a result, the life of the ignition system can be extended and the economic efficiency can be further improved.

  Configuration 4. The ignition system of this configuration is characterized in that, in any one of the above configurations 1 to 3, the connection portion is screw-connected to the connected portion.

  According to the configuration 4, the coil container can be attached to the spark plug in a more stable state. Further, the coil container can be easily attached to and detached from the spark plug, and the workability at the time of replacement can be improved.

Configuration 5. The ignition system of this configuration is any one of the above configurations 1 to 4, wherein the coil housing includes a cylindrical fitting in which the resonance coil is disposed,
In the state where the coil container is attached to the spark plug, the coil container is placed on the outer periphery of a portion of the insulator that is located on the distal end side in the axial direction from the distal end of the metal fitting. A tool engaging portion capable of engaging a predetermined tool when mounting is provided.

  According to the configuration 5, the tool engaging portion capable of engaging a predetermined tool is provided on the outer periphery of the insulator. Therefore, when the coil container is mounted on the spark plug, it is possible to easily rotate the spark plug or restrict the rotation of the spark plug. Therefore, it is possible to more reliably and easily attach the coil container to the spark plug.

Configuration 6. The ignition system of this configuration is any one of the above configurations 1 to 5, wherein the coil housing includes a cylindrical fitting in which the resonance coil is disposed,
An annular packing is provided between the insulator and the front end surface of the metal fitting in a state where the coil container is mounted on the spark plug.

  According to the configuration 6, the annular packing is provided between the front end surface of the metal fitting and the insulator. Therefore, the airtightness between the coil container and the spark plug can be improved.

  Further, by sandwiching the packing between the front end surface of the metal fitting and the insulator, a pressing force from the packing toward the front end side in the axial direction is applied to the spark plug. Therefore, a force directed toward the distal end side in the axial direction is applied to the connecting portion, and when the connecting portion and the connected portion are screw-connected, the thread of the male screw (or female screw) provided in the connecting portion is The frictional force generated between both of the female threads (or male threads) provided in the connected portion is increased in pressure contact with the threads. Accordingly, it is possible to make it difficult for the screws to loosen due to vibration during operation of the internal combustion engine or the like, and to stably connect the connecting portion (coil housing) and the connected portion (ignition plug) over a long period of time. Can be connected.

Configuration 7. In the ignition system of this configuration, in any one of the above configurations 1 to 6, the coil container is
A cylindrical metal fitting in which the resonance coil is disposed;
An intermediate member disposed between the outer periphery of the resonance coil and the inner periphery of the metal fitting,
An annular packing is provided between the insulator and the front end surface of the intermediate member in a state where the coil container is mounted on the spark plug.

  According to the said structure 7, the effect similar to the said structure 6 will be show | played.

Configuration 8. The ignition system of this configuration is any one of the above configurations 1 to 7, wherein the coil housing includes a cylindrical metal fitting in which the resonance coil is disposed,
When a DC voltage is applied to the center electrode in the atmosphere with the coil container attached to the spark plug, an arc discharge is formed across the surface of the insulator between the center electrode and the metal fitting. The voltage when it is generated is 15 kV or more.

  According to the configuration 8, when a DC voltage is applied to the center electrode in the atmosphere, the voltage value when an arc discharge occurs over the surface of the insulator between the center electrode and the metal fitting is 15 kV or more. It is configured. Therefore, even when the AC voltage applied to the center electrode is increased, the occurrence of arc discharge can be effectively suppressed, and corona discharge can be more reliably generated.

  Moreover, since the upper limit of the voltage range in which corona discharge can be generated is increased without generating arc discharge, a larger AC voltage can be applied to the center electrode. As a result, ignitability can be improved.

  In addition, as a method of setting the voltage value when arc discharge occurs to 15 kV or more, for example, a method of increasing the shortest distance (creeping distance) between the center electrode and the metal fitting over the surface of the insulator, An example is a method in which the maximum outer diameter of a portion of the body located on the tip side of the tip of the metal fitting is larger than the inner diameter of the tip of the metal fitting.

Configuration 9 The ignition system of this configuration is any one of the above configurations 1 to 8, wherein the coil housing includes a cylindrical fitting in which the resonance coil is disposed,
In a state in which the coil container is mounted on the spark plug, the tip of the insulator is located closer to the tip in the axial direction than the tip of the metal fitting.
At least a part of the center electrode is disposed on the inner periphery of a portion of the insulator located on the tip side in the axial direction from the tip of the metal fitting,
In a state where the coil housing is mounted on the spark plug, a distance from the tip of the metal fitting to the tip of the insulator along the axial direction is set to 10 mm or less.

  In order to increase the creeping distance, it is conceivable that the protrusion length of the insulator tip relative to the tip of the metal fitting toward the tip end in the axial direction is made relatively large in a state where the coil container is mounted on the spark plug. However, if the protrusion length is excessively increased, the portion of the insulator that protrudes from the tip of the metal fitting is overheated, and the center electrode located on the inner periphery of the insulator may also be overheated. is there. When the center electrode is overheated, the impedance of the spark plug changes, so that the resonance frequency is shifted and the input power to the center electrode may be reduced. As a result, there is a concern that good ignitability cannot be maintained in a high temperature environment.

  In this regard, according to the above-described configuration 9, in the state where the coil container is mounted on the spark plug, the distance from the tip of the metal fitting to the tip of the insulator along the axis is set to 10 mm or less. Therefore, it is possible to more reliably prevent overheating of a portion of the insulator that protrudes from the tip of the metal fitting, and more reliably to prevent overheating of the center electrode located on the inner periphery of the portion. As a result, a change in impedance in the spark plug can be suppressed, and good ignitability can be maintained even in a high temperature environment.

Configuration 10 The ignition system of this configuration is any one of the above configurations 1 to 9, wherein the coil housing includes a cylindrical fitting in which the resonance coil is disposed,
In the state where the coil container is mounted on the spark plug, an outer periphery of a portion of the insulator located closer to the distal end side in the axial direction than the distal end of the metal fitting extends along the circumferential direction of the insulator. At least one of an annular protrusion and an annular groove extending along the circumferential direction of the insulator is provided.

  According to the configuration 10, the annular protrusion or groove extending along the circumferential direction of the insulator is provided on the outer periphery of the portion of the insulator that protrudes from the tip of the metal fitting. Therefore, the creepage distance can be increased, and corona discharge can be generated more reliably.

Configuration 11 In the ignition system of this configuration, in any of the above configurations 1 to 10, the center electrode and the connected portion are fixed by a conductive sealing material,
The spark plug is composed of only the insulator, the center electrode, the connected portion, and the conductive sealing material.

  According to the said structure 11, a spark plug is comprised only from the insulator, the center electrode, the to-be-connected part, and the electroconductive sealing material which fixes a center electrode and to-be-connected part. That is, the spark plug having the above-described configuration 11 does not include a metal shell or a ground electrode provided in a general spark plug. Therefore, the manufacturing cost of the spark plug can be reduced, and as a result, the replacement cost of the spark plug can be further reduced.

Configuration 12. The ignition system of this configuration is any one of the above configurations 1 to 11, wherein the coil housing includes a cylindrical fitting in which the resonance coil is disposed,
The metal fitting has a screw portion for attachment on its outer periphery.

  In general, a spark plug is provided with a metal shell having a threaded portion on the outer periphery for attachment to an internal combustion engine or the like. However, according to the said structure 12, since the screw part for attachment is provided in the metal fitting of a coil container, it is not necessary to provide a main metal fitting in a spark plug. Accordingly, the manufacturing cost of the spark plug can be further reduced, and the replacement cost of the spark plug can be further reduced.

It is a block diagram which shows schematic structure of an ignition system. It is a partially broken front view which shows the structure of a spark plug unit. It is explanatory drawing for demonstrating that electric power required when moving particle | grains between electrodes increases by increasing the length along the direction orthogonal to the axis line of a creeping path | route. It is a partially broken enlarged front view showing another example of a spark plug. It is a schematic diagram of the front-end | tip part of the sample for demonstrating discharge length X etc. FIG. It is a graph which shows the discharge length X in each sample from which an arc discharge generation voltage value differs. It is a graph which shows the discharge length maintenance ratio in the sample which changed the distance L variously. (A) is the schematic diagram of the sample which made the front-end | tip part of the insulator flat, (b) is the schematic diagram of the sample which provided the protrusion in the front-end | tip part of the insulator. (A) is a schematic diagram of a sample in which the length along the axis of the creeping path is larger than the length along the direction orthogonal to the axis of the creeping path, and (b) is orthogonal to the axis of the creeping path. It is a schematic diagram of the sample which made the length along the direction to make larger than the length along the axis line of a creeping path. It is a partially broken front view which shows the attachment method of the spark plug in another embodiment. It is a partially broken enlarged front view which shows the connection method of the connection part with respect to the to-be-connected part in another embodiment.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of the ignition system 101. As shown in FIG. 1, the ignition system 101 includes a spark plug unit 1 attached to the internal combustion engine EN, and an AC power source 51. Although only one spark plug unit 1 is shown in FIG. 1, the actual internal combustion engine EN is provided with a plurality of cylinders, and the spark plug unit 1 is provided corresponding to each cylinder. The voltage from the AC power supply 51 is applied to each spark plug unit 1 via a distributor (not shown).

  The AC power supply 51 applies an AC voltage having a relatively high frequency (for example, 50 kHz to 100 MHz) to the spark plug unit 1. In addition, the AC power supply 51 is configured such that the application timing of the AC voltage to the spark plug unit 1 (that is, the generation timing of corona discharge) is controlled by a predetermined electronic control unit (ECU) 71.

  Furthermore, the energization path between the AC power supply 51 and the spark plug unit 1 includes an inner conductor 62 made of a conductive metal and a cylindrical outer conductor 63 made of a conductive metal disposed on the outer periphery of the inner conductor 62. A coaxial cable 61 is used. By connecting the AC power supply 51 and the spark plug unit 1 by the coaxial cable 61, the reflection of power is prevented. In the present embodiment, the inner conductor 62 is electrically connected to a resonance coil 16 described later, and the outer conductor 63 is electrically connected to a metal fitting 12 described later.

  Next, the configuration of the spark plug unit 1 will be described.

  As shown in FIG. 2, the spark plug unit 1 is configured by connecting a coil housing 11 and a spark plug 21 in series. 2, the direction of the axis CL1 of the spark plug unit 1 will be described as the vertical direction in the drawing, the lower side will be the front end side, and the upper side will be the rear end side.

  The coil housing 11 is constituted by a cylindrical metal fitting 12, a resonance coil 16 disposed therein, and the like.

  The metal fitting 12 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 13 for attaching the spark plug unit 1 (metal fitting 12) to the attachment hole of the internal combustion engine on the outer peripheral surface thereof. Is formed. Further, a bowl-shaped seat portion 14 is formed on the rear end side of the screw portion 13, and a predetermined tool (for example, for example, when attaching the metal fitting 12 to the internal combustion engine on the rear end side of the seat portion 14 is formed. An engaged portion 15 having a hexagonal cross section for engaging a wrench or the like is provided.

  Further, inside the metal fitting 12, the resonance coil 16 in which a conductive metal is spirally wound is disposed. The resonant coil 16 is connected in series with the internal conductor 62 and has a predetermined inductance. The ignition plug 21 having a predetermined capacitance and the resonance coil 16 constitute a series resonance circuit. The AC voltage supplied from the AC power supply 51 is boosted by the series resonance circuit, and the boosted voltage is applied to the spark plug 21 so that corona discharge can be generated starting from the center electrode 28 described later. Yes.

  A connection portion 17 having an external thread on the outer periphery is provided at the tip of the resonance coil 16. The coil housing 11 is attached to the spark plug 21 by connecting the connecting portion 17 to a connected portion 31 described later.

  In addition, a cylindrical intermediate member 18 is disposed between the inner periphery of the metal fitting 12 and the outer periphery of the resonance coil 16. The intermediate member 18 is made of an insulating material (for example, a fluororesin) and insulates the metal fitting 12 and the resonance coil 16 from each other. Further, in the present embodiment, the intermediate member 18 is configured to be located on the rear end side in the axis line CL1 direction from the front end of the metal fitting 12 in a state where the coil container 11 is mounted on the spark plug 21. Note that a resin may be further filled between the outer periphery of the resonance coil 16 and the inner periphery of the intermediate member 18.

  The spark plug 21 includes a cylindrical insulator 22, a center electrode 28 inserted through the insulator 22, and the like.

  The insulator 22 is formed by firing an insulating ceramic (for example, alumina or the like), and in its outer portion, a rear end side body portion 23 formed on the rear end side, and the rear end side body portion 23. The middle barrel portion 24 having a larger diameter than the middle barrel portion 24 on the distal end side, the large diameter portion 25 bulging radially outward on the distal end side with respect to the middle barrel portion 24, and the large diameter portion 25 And a leg long portion 26 formed on the distal end side. In addition, in the state where the coil housing 11 is mounted on the spark plug 21, the rear end side body portion 23 and the middle body portion 24 of the insulator 22 are accommodated inside the metal fitting 12, while The diameter portion 25 and the leg length portion 26 are exposed from the tip of the metal fitting 12. That is, in the state where the coil housing 11 is mounted on the spark plug 21, the tip of the insulator 22 is located on the tip side in the axis CL <b> 1 direction with respect to the tip of the metal fitting 12.

  Furthermore, in this embodiment, it is comprised so that the front-end | tip part of the said intermediate member 18 may contact with the middle trunk | drum 24 arrange | positioned in the metal fitting 12. As shown in FIG. Further, the rear end side body portion 23 is configured to enter the front end portion of the intermediate member 18.

  In addition, the large-diameter portion 25 is configured such that the outer diameter thereof is larger than the inner diameter of the tip end of the metal fitting 12. In other words, the maximum outer diameter of a portion of the insulator 22 that is located on the distal end side in the axis CL1 direction with respect to the distal end of the metal fitting 12 is made larger than the inner diameter of the distal end of the metal fitting 12. In the present embodiment, insulating grease is applied between the outer peripheral surface of the rear end side body portion 23 and the inner peripheral surface of the intermediate member 18, so that the current flowing through the resonance coil 16 and the center electrode 28 can be reduced. Leak prevention is achieved.

  Further, at least one annular protrusion 26A (one in the present embodiment) extending along the circumferential direction of the insulator 22 is provided on the outer periphery of the long leg portion 26, and the surface of the insulator 22 is sandwiched. The length (creeping distance) of the path (creeping path) connecting the tip of the metal fitting 12 and the tip of the center electrode 28 in the shortest is relatively large (for example, 12 mm or more). As a result, in the atmosphere, when a DC voltage is applied to the center electrode 28, a voltage value (arc discharge generation voltage value) when an arc discharge occurs across the surface of the insulator 22 between the center electrode 28 and the metal fitting 12 is generated. Is set to 15 kV or more.

  In order to increase the arc discharge generation voltage value, as described above, the maximum outer diameter of the portion of the insulator 22 located on the front end side in the axis CL1 direction from the front end of the metal fitting 12 is set to be larger than the inner diameter of the front end of the metal fitting 12. It is particularly effective to increase the length along the direction orthogonal to the axis CL1 of the creeping path. This is due to the following reason. For example, as shown in FIG. 3, when the insulator IN having a step formed on the surface is disposed between the electrodes ER1 and ER2, between the electrodes ER1 and ER2 sandwiching the surface of the insulator IN. The creeping route CR is a creeping route CR1 (a portion indicated by a thick line in FIG. 3) extending in a direction intersecting with a direction in which the line segment forming the shortest distance between the electrodes ER1 and ER2 extends (in other words, an axis CL1 direction). Will have. Here, when particles (electrons and ions) having a charge move along the creeping path CR along with the voltage application between the electrodes ER1 and ER2, the creeping path CR1 is caused by collision between the particles. Friction will occur. Therefore, when moving the particles along the creeping path CR1, compared to moving the particles along the direction in which the line segment forming the shortest distance between the electrodes ER1 and ER2 extends (in the direction of the axis CL1). , More power (energy) is required. Therefore, by increasing the length along the direction perpendicular to the axis CL1 of the creeping path, it is possible to further increase the arc discharge generation voltage value and make it difficult to generate arc discharge.

  As shown in FIG. 4, an annular groove 26 </ b> B extending along the circumferential direction of the insulator 22 may be provided on the outer periphery of the leg long portion 26 instead of the protrusion 26 </ b> A. Further, both the protrusion 26A and the groove 26B may be omitted, and the leg long part 26 may be flat.

  Returning to FIG. 2, in the present embodiment, in the cross section orthogonal to the axis CL <b> 1, the protrusion 26 </ b> A has a hexagonal cross section, and when the coil container 11 is attached to the spark plug 21, a predetermined tool ( For example, a wrench or the like can be engaged. That is, the protrusion 26A corresponds to a “tool engaging portion” in the present invention.

  In addition, while the arc discharge generation voltage value is set to 15 kV or more as described above, in this embodiment, the distance L from the tip of the metal fitting 12 to the tip of the insulator 22 along the axis CL1 is set to 10 mm or less. The insulator 22 and the center electrode 28 are configured not to protrude excessively toward the center side of the combustion chamber.

  Further, a shaft hole 27 extending along the axis line CL1 is formed through the insulator 22, and the center electrode 28 is inserted on the tip side of the shaft hole 27. The center electrode 28 has a rod-like shape as a whole, and the tip thereof has a tapered shape that tapers toward the tip in the direction of the axis CL1. The center electrode 28 includes an inner layer 28A made of a metal having excellent thermal conductivity (for example, copper, copper alloy, pure nickel (Ni), etc.), and an outer layer made of an alloy containing Ni as a main component and covering the inner layer 28A. 28B.

  In addition, the distal end portion of the center electrode 28 protrudes from the distal end of the insulator 22 toward the distal end side in the axis CL1 direction. As a result, a part of the central electrode 28 is more than the distal end of the metal fitting 12 in the insulator 22. Is also arranged on the inner periphery of the part located on the tip side in the direction of the axis CL1. Further, the tip of the center electrode 28 is made of Ni, platinum (Pt), iridium (Ir), palladium (Pd), tungsten (W), or an alloy containing at least one of these metals as a main component. The tip 29 is provided to improve the durability.

  In addition, a metal connected portion 31 fixed by a conductive sealing material 30 containing a glass component or a conductive metal is provided at the rear end portion of the center electrode 28. The connected portion 31 is inserted into the shaft hole 27, and at least the rear end portion thereof has a cylindrical shape, and a male screw formed on the outer periphery of the connecting portion 17 can be screwed to the inner periphery of the rear end portion. An internal female screw is formed. The connecting portion 17 is screw-connected to the connected portion 31 by the male screw being screwed into the female screw of the connected portion 31. Therefore, the connecting portion 17 can be attached to and detached from the connected portion 31, and the coil housing 11 can be attached to and detached from the spark plug 21.

  In this embodiment, when attaching the spark plug unit 1 to the internal combustion engine EN, the coil housing 11 is attached to the spark plug 21 and the screw portion 13 of the metal fitting 12 is provided in the mounting hole of the internal combustion engine EN. The spark plug unit 1 is attached to the internal combustion engine EN by being screwed into a female thread portion (not shown).

  In addition, in the present embodiment, the spark plug 21 is configured only by the insulator 22, the center electrode 28, the connected portion 31, and the conductive sealing material 30. That is, the spark plug 21 of the present embodiment is configured not to include a ground electrode that is generally provided in a spark plug of a type that ignites an air-fuel mixture by spark discharge.

  In addition, in the present embodiment, a ring made of a predetermined metal (for example, an iron-based metal) is formed between the insulator 22 and the front end surface of the metal fitting 12 in a state where the coil housing 11 is mounted on the spark plug 21. The packing 32 is disposed. The packing may be disposed between the insulator 22 and the front end surface of the intermediate member 18.

  Further, in the present embodiment, from the viewpoint of enhancing the ease of insertion of the intermediate member 18 and the insulator 22 into the metal fitting 12, the outer peripheral surface of the intermediate member 18, the outer peripheral surface of the insulator 22 (middle body portion 24), and the metal fitting 12. A slight gap (air layer) is formed between the inner peripheral surface. And in this embodiment, the part which forms a clearance gap between the insulators 22 and the intermediate member 18 between the metal fittings 12 is the metal layers 33 and 34 made of a predetermined metal material (in FIG. 2, the metal layer 33 and 34 are shown thicker than actual). More specifically, the metal layer 33 is provided on the outer peripheral surface of the intermediate member 18, and the metal layer 34 is provided on the outer peripheral surface of the insulator 22. The two metal layers 33 and 34 are electrically connected to the metal fitting 12 and are equipotential with the metal fitting 12. By providing the metal layers 33 and 34, it is possible to prevent dielectric barrier discharge from occurring in the gap (air layer) between the insulator 22 and the intermediate member 18 and the metal fitting 12, and the center electrode 28 is the starting point. Corona discharge can be generated more reliably.

  As described above in detail, according to the present embodiment, the connection portion 17 is detachable from the connected portion 31, and the resonance coil is connected to the spark plug 21 having the center electrode 28 and the insulator 22. A coil housing 11 having 16 is detachable. Accordingly, when the spark plug 21 is damaged due to use or the like, only the damaged spark plug 21 needs to be replaced, and the coil housing 11 can be used as it is. As a result, the cost required for replacement can be reduced, and excellent economic efficiency can be realized.

  In addition, an intermediate member 18 is provided between the resonance coil 16 and the metal fitting 12 disposed on the outer periphery thereof. Therefore, the insulation between the resonance coil 16 and the metal fitting 12 can be enhanced. As a result, an AC voltage can be more reliably applied to the center electrode 28 via the resonance coil 16, and corona discharge can be more reliably generated.

  Further, in the present embodiment, the intermediate member 18 is configured to be located on the rear end side (side away from the center of the combustion chamber) from the front end of the metal fitting 12 in a state where the coil housing 11 is mounted on the spark plug 21. Has been. Therefore, damage to the intermediate member 18 due to heat accompanying the operation of the internal combustion engine or the like can be prevented more reliably.

  At the same time, the distal end portion of the intermediate member 18 is configured to come into contact with the insulator 22 (the middle barrel portion 24) in a state where the coil container 11 is mounted on the spark plug 21. Therefore, heat of the insulator 22 and the center electrode 28 inserted through the intermediate member 18 can be efficiently drawn, and damage to the insulator 22 and the center electrode 28 due to heat can be prevented more reliably. . As a result, the life of the ignition system 101 can be extended, and the economic efficiency can be further improved.

  Furthermore, in the present embodiment, the connecting portion 17 is screw-connected to the connected portion 31. Therefore, the coil container 11 can be mounted on the spark plug 21 in a more stable state. In addition, the coil housing 11 can be easily attached to and detached from the spark plug 21, and workability at the time of replacement can be improved.

  In addition, a protrusion 26 </ b> A capable of engaging a predetermined tool is provided on the outer periphery of the insulator 22. Therefore, when the coil container 11 is mounted on the spark plug 21, it is possible to easily rotate the spark plug 21 or restrict the rotation of the spark plug 21. For this reason, it is possible to more reliably and easily attach the coil container 11 to the spark plug 21.

  Further, a packing 32 is provided between the front end surface of the metal fitting 12 and the insulator 22 (large diameter portion 25). Therefore, the airtightness between the coil housing 11 and the spark plug 21 can be improved. Further, by sandwiching the packing 32 between the front end surface of the metal fitting 12 and the insulator 22, a pressing force from the packing 32 toward the front end side in the axis line CL <b> 1 direction is applied to the spark plug 21. Therefore, a force directed toward the distal end side in the axis CL1 direction is applied to the connecting portion 17, and the thread of the male screw provided in the connecting portion 17 is in pressure contact with the thread of the female screw provided in the connected portion 31. The frictional force generated between the two increases. Accordingly, it is possible to make it difficult for the screw to loosen due to vibration or the like, and to stably connect the connecting portion 17 (coil housing) and the connected portion 31 (ignition plug 21) over a long period of time. it can.

  At the same time, when a DC voltage is applied to the center electrode 28 in the atmosphere, the voltage value when an arc discharge over the surface of the insulator 22 occurs between the center electrode 28 and the metal fitting 12 is 15 kV or more. It is configured. Therefore, even when the AC voltage applied to the center electrode 28 is increased, the occurrence of arc discharge can be effectively suppressed, and corona discharge can be more reliably generated.

  In addition, since the upper limit value of the voltage range in which corona discharge can be generated increases without generating arc discharge, a larger alternating voltage can be applied to the center electrode 28. As a result, ignitability can be improved.

  In addition, in the present embodiment, the distance L is set to 10 mm or less in a state where the coil container 11 is mounted on the spark plug 21. Therefore, overheating of a portion of the insulator 22 that protrudes from the tip of the metal fitting 12 can be more reliably prevented, and by extension, the overheating of the center electrode 28 located on the inner periphery of the portion can be more reliably prevented. . As a result, a change in impedance in the spark plug 21 can be suppressed, and good ignitability can be maintained even in a high temperature environment.

  Further, an annular protrusion 26 </ b> A is provided on the outer periphery of a portion (leg long portion 26) of the insulator 22 that protrudes from the tip of the metal fitting 12. Therefore, the creepage distance can be increased, and corona discharge can be generated more reliably.

  The spark plug 21 is composed only of the insulator 22, the center electrode 28, the connected portion 31, and the conductive sealing material 30, and the mounting screw portion 13 is provided on the metal fitting 12. . Therefore, the spark plug 21 does not include a metal shell having a ground electrode or a threaded portion. Therefore, the manufacturing cost of the spark plug 21 can be reduced, and as a result, the replacement cost of the spark plug 21 can be further reduced.

  In addition, in the present embodiment, the maximum outer diameter of a portion of the insulator 22 that is located on the tip side of the tip of the metal fitting 12 is made larger than the inner diameter of the tip of the metal fitting 12. Accordingly, the creeping path between the metal fitting 12 and the center electrode 28 over the surface of the insulator 22 is a portion (large diameter portion) provided at the tip of the insulator 22 and having an outer diameter larger than the inner diameter of the tip of the metal fitting 12. 25 and the protrusion 26A). Therefore, the creepage distance can be further increased, and corona discharge can be generated more reliably. Furthermore, since the length along the direction orthogonal to the axis CL1 of the creeping path can be increased, it is possible to prevent the occurrence of arc discharge more reliably compared to the case where the creeping path is simply lengthened, thereby further reducing the corona discharge. It can be generated reliably.

  Next, in order to confirm the operational effects achieved by the above embodiment, as shown in FIG. 5, the length K along the axis of the metal coating MC covering the surface of the leg long part, which is electrically connected to the metal fitting, is set. By various changes, the voltage value (arc discharge generation) when arc discharge over the surface of the insulator occurs between the center electrode and the metal fitting (metal coating) when a DC voltage is applied to the center electrode in the atmosphere. Samples of spark plug units having different voltage values were prepared, and discharge length measurement tests were performed on the samples. The outline of the discharge length measurement test is as follows. That is, after the sample was mounted in a predetermined chamber, the maximum AC voltage in a voltage range in which arc discharge did not occur was applied to the sample. Then, the maximum length (discharge length) X (mm) along the axis of the corona discharge CO that originated from the application of the AC voltage and started from the tip of the center electrode was measured. In addition, it can be said that it is excellent in ignitability, so that the discharge length X is large.

  FIG. 6 is a graph showing the discharge length X in each sample having different arc discharge generation voltage values. In addition, the sample made the outer diameter C of the leg long part 2 mm or 3 mm. Moreover, in FIG. 6, the test result of the sample which made the outer diameter C of the leg long part 2 mm is shown by a circle mark, and the test result of the sample which made the outer diameter C of the leg long part 3 mm is shown by a triangle mark. Further, in this test, the AC power supply was set to an oscillation frequency of 5 MHz, an output power (average value of the input electric power per second) of 500 W, and an AC voltage was applied to the spark plug for 1 ms.

  As shown in FIG. 6, it was found that the sample having an arc discharge generation voltage value of 15 kV or higher has a significantly increased discharge length X and extremely excellent ignitability. This is considered to be because the upper limit of the voltage range in which corona discharge can be generated is larger, so that a larger AC voltage can be applied to the spark plug unit.

  From the results of the above test, it is possible to generate corona discharge more reliably without generating arc discharge, and thus to apply a relatively large AC voltage to the spark plug unit, thereby improving ignitability. In the atmosphere, when a DC voltage is applied to the center electrode, it can be said that it is preferable to set the voltage value to 15 kV or more when arc discharge occurs across the surface of the insulator between the center electrode and the metal fitting.

  Next, after setting the outer diameter C of the long leg portion to 2 mm or 3 mm, samples of the spark plug unit were prepared in which the distance L from the tip of the metal fitting along the axis to the tip of the insulator was variously changed. The ignitability test during heating was performed. The outline of the ignitability test during heating is as follows. That is, the maximum voltage in a voltage range capable of generating corona discharge was applied to the sample at room temperature and in an air atmosphere, and the discharge length (discharge length before heating X1) was measured. Next, after attaching the sample to the water-cooled chamber, a portion of the insulator protruding from the tip of the metal fitting was heated with a predetermined burner. Then, immediately after heating, a maximum voltage in a voltage range in which corona discharge can be generated is applied to the sample, a discharge length (discharge length X2 during heating) is measured, and during the heating with respect to the discharge length X1 before heating. The ratio of the discharge length X2 (discharge length maintenance ratio) was calculated. Here, it can be said that the greater the discharge length maintenance ratio, the less the ignitability is lowered under a high temperature environment, and the higher the ignitability can be maintained under a high temperature environment during operation of the internal combustion engine.

  FIG. 7 shows the results of the test. In FIG. 7, the test result of the sample with the outer diameter C of the leg length part of 2 mm is indicated by a circle, and the test result of the sample with the outer diameter C of the leg length part of 3 mm is indicated by a triangle mark. The heating conditions with the burner were such that the tip of the center electrode was 650 ° C. in a sample with an outer diameter C of 3 mm and a distance L of 6 mm.

  As shown in FIG. 7, it was found that the ignitability of the sample with the distance L exceeding 10 mm is slightly lowered in a high temperature environment. This is because the impedance of the spark plug changes and the resonance frequency shifts due to overheating of the insulator and the center electrode inserted through the insulator, and the input power to the center electrode decreases. It is thought that.

  On the other hand, it was confirmed that the sample having the distance L of 10 mm or less has excellent ignitability even in a high temperature environment.

  From the results of the above test, in order to maintain good ignitability in a high temperature environment, the distance L from the tip of the metal fitting to the tip of the insulator along the axial direction in the state where the coil container is mounted on the spark plug. Is preferably 10 mm or less.

  Next, as shown in FIG. 8 (a), the outer diameter C of the leg length portion is 4 mm, the distance L is 8 mm, and the outer peripheral surface of the leg length portion is a flat shape parallel to the axis CL1. As shown in FIG. 8 (b), the sample P and an annular protrusion extending along the circumferential direction of the insulator on the outer periphery of the leg long portion with the outer diameter C being 4 mm and the distance L being 8 mm. A sample Q of a spark plug unit provided with three 26A was prepared. And about each sample, the DC voltage was applied to the center electrode in air | atmosphere, and the voltage value (arc discharge generation voltage value) when the arc discharge over the surface of the insulator generate | occur | produced was measured. In sample Q, the outer diameter E (mm) of the protrusion was set to 5.5 mm.

  When the arc discharge occurrence voltage value was measured for the samples P and Q, the arc discharge occurrence voltage value of the sample Q increased by 3 kV from the arc discharge occurrence voltage value of the sample P, and the arc discharge suppression effect was excellent. I understood. This is considered to be due to a further increase in the creepage distance between the metal fitting and the center electrode. Even when the annular groove extending along the circumferential direction of the insulator is provided, it is considered that the same effect as that provided when the protrusion is provided is obtained.

  From the results of the above test, in order to suppress the occurrence of arc discharge and generate corona discharge more reliably, an insulator is provided on the outer periphery of a portion of the insulator located on the tip side in the axial direction from the tip of the metal fitting. It can be said that it is preferable to provide at least one of an annular protrusion extending along the circumferential direction and an annular groove extending along the circumferential direction of the insulator.

  Providing protrusions and grooves makes the distance L 10 mm or less in order to maintain good ignitability in a high temperature environment, and increases the distance from the tip of the metal fitting to the tip of the insulator along the axis. This is particularly suitable for a spark plug unit in which it is difficult to increase the creepage distance.

  Next, as shown in FIG. 9 (a), the length A of the path extending in the direction perpendicular to the axis among the creeping paths between the metal fittings and the center electrode over the surface of the insulator is 2 mm, and the creeping path 9B, the spark plug unit sample R in which the length B of the path extending in the axial direction is 10 mm, and, as shown in FIG. An ignition plug unit in which the length A is set to 5 mm and the length B is set to 7 mm (that is, the same creepage distance as that of the sample R) by making the outer diameter larger than the inner diameter at the tip of the metal fitting. Sample S was prepared, and arc discharge generation voltage values of both samples R and S were measured.

  When the arc discharge generation voltage value was measured for the samples R and S, the arc discharge generation voltage value of the sample S was larger than the arc discharge generation voltage value of the sample R, and the creeping distance was the same. Nevertheless, it was found that arc discharge is less likely to occur. This means that when particles move along a path along the direction intersecting the axis of the creeping path, more power (energy) is required than when particles move along the axis. It is thought to be caused by.

  From the above results, in order to prevent arc discharge more reliably and to generate corona discharge more reliably, the maximum outer diameter of the portion of the insulator located closer to the distal end side in the axial direction than the distal end of the bracket is It can be said that it is preferable that the length A is larger than the inner diameter of the tip of the surface and the length A along the direction perpendicular to the axis of the creeping path is larger.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, after connecting the coil housing 11 to the spark plug 21, the screw portion 13 of the metal fitting 12 is screwed into the female screw portion provided in the mounting hole of the internal combustion engine EN. The unit 1 is attached to the internal combustion engine EN. On the other hand, as shown in FIG. 10, the threaded portion 13 of the coil housing 11 is screwed into the female threaded portion FS provided in the mounting hole HO of the internal combustion engine EN, and then the ignition plug is connected from the combustion chamber side. 41 may be attached to the coil housing 11. In this case, the outer diameter of the portion of the insulator 42 that is located on the distal end side in the axis CL1 direction with respect to the distal end of the metal fitting 12 can be made larger than the inner diameter of the mounting hole HO. Therefore, the occurrence of arc discharge between the center electrode 28 and the metal fitting 12 over the surface of the insulator 22 can be more reliably prevented.

  (B) In the above embodiment, the connecting portion 17 is configured to be screwed to the connected portion 31, but the connection mode of the connecting portion 17 to the connected portion 31 is not limited to this. Absent. Therefore, for example, as shown in FIG. 11, while providing a hook-like projection 44 projecting radially outward at the rear end of the connected portion 43, the tip of the connecting portion 45 is tubular, A ring spring 46 that is elastically deformable along the radial direction is provided on the outer periphery of the tip portion, and the connection portion 45 is inserted into the inner periphery of the connection portion 45, thereby connecting the connection portion 45 to the connection portion 43. It is good to do. In this case, a force directed radially inward from the ring spring 46 to the connected portion 43 is applied, and the protrusion 44 is locked to the ring spring 46. Therefore, the connecting portion 45 can be easily connected to the connected portion 43, and good connection reliability can be ensured between them.

  (C) In the above-described embodiment, the metal layers 33 and 34 are provided in a portion of the insulator 22 and the intermediate member 18 that forms a gap with the metal fitting 12. On the other hand, it is good also as providing a metal layer only in a part of site | part which forms the said clearance gap among the insulators 22 and the intermediate members 18. FIG. Further, the metal layer may be omitted.

  (D) In the above embodiment, the relative arrangement position of the resonance coil 16 with respect to the spark plug 21 is an example, and the relative arrangement position of the resonance coil 16 with respect to the ignition plug 21 is not limited to this. Therefore, for example, the resonance coil 16 may be arranged on the rear end side in the axis CL1 direction (side away from the center electrode 28), the opening side of the mounting hole provided in the internal combustion engine, the middle part of the mounting hole, etc. You may arrange in.

  (E) In the above embodiment, the voltage from the AC power source 51 is applied to each spark plug unit 1 via the distributor, but the AC power source 51 may be provided for each spark plug unit 1. .

  (F) In the above embodiment, the tip 29 is provided at the tip of the center electrode 28, but the tip 29 may not be provided.

  (G) In the above embodiment, the protrusion 26A corresponding to the tool engaging portion has a hexagonal cross section, but the shape of the tool engaging portion is not limited to this, for example, a rectangular cross section Or an elliptical cross section.

DESCRIPTION OF SYMBOLS 11 ... Coil container 12 ... Metal fitting 13 ... Screw part 16 ... Resonance coil 17 ... Connection part 18 ... Intermediate member 21 ... Spark plug 22 ... Insulator 26A ... Projection part 26B ... Groove part 27 ... Shaft hole 28 ... Center electrode 30 ... Conductivity 31 ... Connected part 32 ... Packing 51 ... AC power supply 101 ... Ignition system CL1 ... Axis

Claims (12)

An AC power supply that outputs AC voltage;
A coil housing body having a resonance coil electrically connected to the AC power source;
A cylindrical insulator having an axial hole extending in the axial direction; and a central electrode inserted in the axial hole and electrically connected to the resonant coil, at least a portion of itself being the coil housing A spark plug disposed on the tip end side in the axial direction than
An ignition system that generates a corona discharge starting from the center electrode by applying an AC voltage to the center electrode,
The coil container is provided with a connection portion that can electrically connect the resonance coil to a connection portion provided at a rear end portion of the center electrode, and the connection to the connection portion. Part is removable,
The ignition system, wherein the coil housing is detachable from the ignition plug. The coil container is
A cylindrical metal fitting in which the resonance coil is disposed;
An intermediate member made of an insulating material disposed between the outer periphery of the resonance coil and the inner periphery of the metal fitting,
2. The ignition system according to claim 1, wherein the intermediate member is located closer to a rear end side in the axial direction than a front end of the metal fitting in a state in which the coil housing is attached to the ignition plug. The coil container is
A cylindrical metal fitting in which the resonance coil is disposed;
An intermediate member disposed between the outer periphery of the resonance coil and the inner periphery of the metal fitting,
3. The ignition system according to claim 1, wherein a tip portion of the intermediate member is in contact with the insulator in a state in which the coil housing is mounted on the ignition plug.   The ignition system according to any one of claims 1 to 3, wherein the connection portion is screw-connected to the connected portion. The coil container includes a cylindrical metal fitting in which the resonance coil is disposed,
In the state where the coil container is attached to the spark plug, the coil container is placed on the outer periphery of a portion of the insulator that is located on the distal end side in the axial direction from the distal end of the metal fitting. The ignition system according to any one of claims 1 to 4, wherein a tool engaging portion capable of engaging with a predetermined tool when being mounted is provided. The coil container includes a cylindrical metal fitting in which the resonance coil is disposed,
6. The annular packing is provided between the insulator and a front end surface of the metal fitting in a state in which the coil housing body is mounted on the spark plug. Ignition system described in. The coil container is
A cylindrical metal fitting in which the resonance coil is disposed;
An intermediate member disposed between the outer periphery of the resonance coil and the inner periphery of the metal fitting,
7. The annular packing is provided between the insulator and the front end surface of the intermediate member in a state in which the coil container is mounted on the spark plug. Ignition system according to item. The coil container includes a cylindrical metal fitting in which the resonance coil is disposed,
When a DC voltage is applied to the center electrode in the atmosphere with the coil container attached to the spark plug, an arc discharge is formed across the surface of the insulator between the center electrode and the metal fitting. The ignition system according to any one of claims 1 to 7, wherein a voltage when generated is 15 kV or more. The coil container includes a cylindrical metal fitting in which the resonance coil is disposed,
In a state in which the coil container is mounted on the spark plug, the tip of the insulator is located closer to the tip in the axial direction than the tip of the metal fitting.
At least a part of the center electrode is disposed on the inner periphery of a portion of the insulator located on the tip side in the axial direction from the tip of the metal fitting,
The distance from the front-end | tip of the said metal fitting along the said axial direction to the front-end | tip of the said insulator shall be 10 mm or less in the state which mounted | wore with the said coil container with respect to the said spark plug. 9. The ignition system according to claim 1. The coil container includes a cylindrical metal fitting in which the resonance coil is disposed,
In the state where the coil container is mounted on the spark plug, an outer periphery of a portion of the insulator located closer to the distal end side in the axial direction than the distal end of the metal fitting extends along the circumferential direction of the insulator. The ignition system according to any one of claims 1 to 9, wherein at least one of an annular protrusion and an annular groove extending along a circumferential direction of the insulator is provided. The center electrode and the connected portion are fixed by a conductive sealing material,
The ignition system according to any one of claims 1 to 10, wherein the ignition plug includes only the insulator, the center electrode, the connected portion, and the conductive sealing material. . The coil container includes a cylindrical metal fitting in which the resonance coil is disposed,
The ignition system according to any one of claims 1 to 11, wherein the metal fitting has an attaching thread portion on an outer periphery thereof.

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