JP2018139173A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To locally generate nonequilibrium plasma at a site on a combustion chamber side of an insulator to efficiently use the energy of the nonequilibrium plasma for ignition.SOLUTION: A spark plug includes: a rod-like center electrode extending from a front edge to a tail edge in an axial direction; a bottomed cylindrical insulator surrounding at least the front edge side of the center electrode and having a bottom on a front edge side in the axial direction; and a cylindrical main metal fitting covering around the insulator such that the front edge portion of the center electrode is located closer on the front edge side than the front edge of the main metal fitting. The front edge portion of the center electrode has an outer diameter reduced in diameter toward the front edge side, and, when cross section passing through an axis in the front edge portion of the center electrode is viewed, the front edge portion includes a center electrode step part where a first inflection part expanding radially outward and a second inflection part being narrowed radially inward are continuous.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a spark plug.

  As an ignition device that ignites an air-fuel mixture in a combustion chamber of an internal combustion engine, an ignition device that ignites using non-equilibrium plasma is known (see, for example, Patent Document 1). Such an ignition device includes an ignition plug having an insulator containing a center electrode, and generates an unbalanced plasma on the surface of the insulator by applying an alternating voltage or a plurality of pulse voltages to the center electrode.

  Further, in Patent Document 1, in order to efficiently use the energy of such non-equilibrium plasma for ignition, the tip of the insulator is thinned so that the surface potential is locally increased. It is known to have a structure in which the front end portion is protruded from the metal shell to the combustion chamber side.

JP 2014-123435 A

  In the above-mentioned patent document, as a method for locally increasing the surface potential, the shape of the insulator is examined, but there is room for improvement for shapes other than the insulator.

  The present invention has been made to solve the above-described conventional problems, and generates non-equilibrium plasma locally in the insulator on the combustion chamber side, thereby efficiently igniting the energy of the non-equilibrium plasma. It is intended to be used.

  The solving means includes a rod-shaped center electrode extending from the front end in the axial direction to the rear end, a bottomed cylindrical insulator that surrounds at least the front end side of the center electrode and has a bottom on the front end side in the axial direction, A spark plug comprising a cylindrical metal shell that covers the periphery of the insulator so that the tip of the center electrode is located on the tip side of the tip of the center electrode, and the tip of the center electrode faces the tip side. The outer diameter is reduced, and when the cross-section passing through the axis is viewed at the tip of the center electrode, there are a first inflection portion that swells radially outward and a second inflection portion that constricts radially inward. A spark plug having a series of central electrode step portions.

  Generally, it is known that an electric field tends to concentrate on an inflection part. Therefore, according to the spark plug, the center electrode step portion having the first inflection portion and the second inflection portion is provided at the tip portion of the center electrode, and the tip portion of the center electrode is covered with the insulator. Therefore, a lot of non-equilibrium plasma is generated in the vicinity of the inflection portion of the center electrode on the surface of the insulator as compared with other portions. In addition, by disposing the tip of the center electrode covered with this insulator on the tip side of the metal shell, a lot of non-equilibrium plasma can be generated at a position closer to the combustion chamber. The energy can be efficiently used for ignition.

  The spark plug may include one central electrode step at the tip. According to the spark plug, since the central electrode step portion having the inflection portion that increases the electric field strength is provided in one place, a constant voltage is supplied as compared with the case where a plurality of center electrode step portions are provided. The strength of the electric field concentrated on one central electrode step in the case is maintained without being distributed to the other central electrode step. As a result, it is possible to maintain the amount of non-equilibrium plasma generated on the insulator surface in the vicinity of one central electrode step. As a result, a sufficient amount of non-equilibrium plasma can be generated to ignite a specific portion of the insulator on the tip side of the metal shell, so that, for example, such one central electrode can be generated. By providing the stepped portion closer to the distal end side (more to the combustion chamber side) of the distal end portion of the center electrode, the energy of non-equilibrium plasma can be efficiently used for ignition.

  The spark plug may include a ground electrode having one end connected to the metal shell, and the other end of the ground electrode may form a discharge gap with the insulator at a position where the center electrode step is formed. . A lot of non-equilibrium plasma is generated on the surface of the insulator in the vicinity of the center electrode step, so that the energy can be used for ignition more efficiently by forming a spark gap in the vicinity thereof.

  In the above spark plug, the covering portion covering the tip portion of the insulator has a partly reduced outer diameter, and when the covering portion is viewed through a cross section passing through the axis, the outer portion expands radially outward of the axis. You may provide the insulator step part which the 3rd inflection part and the 4th inflection part constricted to radial inside become continuous. According to the spark plug, not only the center electrode step provided at the tip of the center electrode but also the insulator step having the third and fourth inflections covers the tip of the center electrode. Since it is provided in the covering portion, a lot of non-equilibrium plasma is generated in the vicinity of the inflection portion of the covering portion in the surface of the insulator as compared with other portions. In addition, since the coating portion is present on the tip side of the metal shell, more non-equilibrium plasma can be generated on the combustion chamber side, and as a result, the energy can be efficiently used for ignition. .

  In the spark plug, the insulator step portion may be disposed at a position where at least a part thereof overlaps the tip portion of the center electrode in the axial direction. Compared to the case where the insulator step does not overlap the center electrode in the axial direction, the insulator step is arranged at a position closer to the center electrode step, so that there is no equilibrium on the surface of the insulator near the center electrode step. The amount of plasma generated can be further increased.

  In the spark plug, the insulator step portion may be disposed at a position where at least a part thereof overlaps the center electrode step portion in the axial direction. Compared to the case where the insulator step does not overlap the center electrode step in the axial direction, the insulator step is disposed closer to the center electrode step, so the surface of the insulator near the center electrode step The amount of non-equilibrium plasma generated in can be further increased.

  In the spark plug, the portion where the thickness of the covering portion is minimum may be disposed at a position overlapping the center electrode step portion in the axial direction. When the insulator is thin, the surface potential of the insulator is high and non-equilibrium plasma is likely to be generated. By placing such a part in a position overlapping the center electrode step, the vicinity of the center electrode step The amount of non-equilibrium plasma generated on the surface of the insulator can be increased.

1 is a half sectional view of a spark plug as a first embodiment of the present invention. FIG. 3 is an enlarged half-sectional view of the vicinity of the tip of a spark plug as the first embodiment. It is the half sectional view to which the tip end vicinity of the ignition plug as a 2nd embodiment was expanded.

A first embodiment will be described.
FIG. 1 is a half cross-sectional view showing a configuration of a spark plug 10 as a first embodiment. FIG. 1 illustrates the external shape of the spark plug 10 on the right side of the drawing with the axis AL of the spark plug 10 as a boundary, and the cross-sectional shape passing through the axis AL of the spark plug 10 on the left side of the drawing. In the description of the present embodiment, the lower side of the spark plug 10 in FIG. 1 is referred to as “front end side”, and the upper side of FIG. The spark plug 10 includes a center electrode 100, an insulator 200, and a metal shell 300. In the present embodiment, the axis AL of the spark plug 10 is also the axis of each member such as the center electrode 100, the insulator 200, and the metal shell 300. In the description of this embodiment, the radial direction of a circle centered on the axis AL is also referred to as “radial direction”. The radial direction is a direction perpendicular to the axis AL, the direction toward the axis AL is called the radial inner side, and the direction away from the axis AL is called the radial outer side. Furthermore, in the description of this embodiment, the circumferential direction of a circle centered on the axis AL is also referred to as “circumferential direction”.

  The center electrode 100 of the spark plug 10 is a conductive rod-shaped member. In the present embodiment, the center electrode 100 is mainly made of a nickel alloy (for example, Inconel 600 (“INCONEL” is a registered trademark)) whose main component is nickel (Ni).

  The center electrode 100 extends from the front end to the rear end in the direction of the axis AL and is provided inside the insulator 200. In the present embodiment, the center electrode 100 is electrically connected to the rear end side of the insulator 200 via the sealing material 160 and the terminal 180. The sealing material 160 is a conductor that is provided inside the insulator 200 and connects between the center electrode 100 and the terminal 180. The terminal 180 is a conductor that protrudes from the insulator 200 to the rear end side and is connected to an external power source (not shown). Center electrode 100 is applied with a voltage from an external power source (not shown) through sealant 160 and terminal 180. Details of the shape of the center electrode 100 in the present embodiment will be described later.

  The insulator 200 of the spark plug 10 is a member having electrical insulation. In this embodiment, the insulator 200 is a ceramic obtained by firing an insulating material (for example, alumina). The insulator 200 has a bottomed cylindrical shape having a bottom portion 210 on the tip end side in the axis AL direction. The insulator 200 surrounds the periphery of the front end side of the center electrode 100. In the present embodiment, the insulator 200 has a shaft hole 290 extending about the axis AL. In this embodiment, the center hole 100, the sealing material 160, and the terminal 180 are provided in the shaft hole 290 in order from the front end side. Details of the shape of the insulator 200 in the present embodiment will be described later.

  The metal shell 300 of the spark plug 10 is a conductive member. In the present embodiment, the metallic shell 300 is mainly made of low carbon steel. The metal shell 300 has a cylindrical shape extending in the direction of the axis AL. The metal shell 300 holds the insulator 200 in a state where the insulator 200 protrudes from the tip side. Further, the metal shell 300 covers the periphery of the insulator 200 so that the tip portion 110 of the center electrode 100 included in the insulator 200 is located on the tip side of the tip of itself. In the present embodiment, the metal shell 300 holds the insulator 200 from the front end side via the packing 410. The metal shell 300 holds the insulator 200 from the rear end side via two rings 420 and 440 and talc powder 430 sandwiched between them. In the present embodiment, the metal shell 300 includes a tip portion 310, a male screw portion 320, a body portion 330, and a tool engagement portion 340.

  The tip 310 of the metal shell 300 constitutes the tip of the metal shell 300. From the center of the tip portion 310, the insulator 200 protrudes toward the tip side. At that time, the distal end portion 110 of the center electrode 100 is located on the distal end side with respect to the distal end portion 310.

  The male threaded portion 320 of the metal shell 300 is a cylindrical portion that is formed on the rear end side from the distal end portion 310 and has a male thread formed on the outer periphery. The spark plug 10 is fixed to the internal combustion engine by fitting the male screw portion 320 to a female screw (not shown) formed in the internal combustion engine. In the present embodiment, the nominal diameter of the male screw portion 320 is M14. In other embodiments, the nominal diameter of the male screw portion 320 may be smaller than M14 (for example, M8, M10, M12), or may be larger than M14 (for example, M18).

  The body portion 330 of the metal shell 300 is a portion that is formed on the rear end side from the male screw portion 320 and projects outward in the radial direction from the male screw portion 320. With the spark plug 10 attached to the internal combustion engine, the body 330 presses the gasket 500 against the internal combustion engine.

  The tool engaging portion 340 of the metal shell 300 is a portion that is formed on the rear end side from the body portion 330 and projects in a polygonal shape outward in the radial direction. The tool engaging portion 340 has a shape that engages with a tool (not shown) for attaching the spark plug 10 to an internal combustion engine (not shown). In this embodiment, the outer periphery shape of the tool engaging part 340 forms a hexagon.

  FIG. 2 shows a detailed configuration of the spark plug 10 on the tip side. The center electrode 100 of the spark plug 10 includes a tip portion 110 that is located on the tip side of the tip of the metal shell 300. The distal end portion 110 has an outer diameter that decreases toward the distal end side. As a result, one center electrode step 120 is formed at the tip 110.

  The center electrode step portion 120 is configured by a first inflection portion 121 that swells radially outward and a second inflection portion 122 that constricts radially inward. In this embodiment, the center electrode step 120 is formed by directly connecting the first inflection part 121 and the second inflection part 122.

  The insulator 200 of the spark plug 10 includes a covering portion 220 that is located on the front end side of the front end of the metal shell 300 and covers the front end portion 110 of the center electrode 100. The outer diameter of the covering portion 220 is reduced toward the distal end side. The outer diameter of a part of the covering portion 220 is reduced. As a result, an insulator step 230 is formed in the cover 220. The insulator step portion 230 is formed by connecting a third inflection portion 231 that swells outward in the radial direction of the axis and a fourth inflection portion 232 that constricts inward in the radial direction. In this embodiment, the insulator step portion 230 is formed by directly connecting the third inflection portion 231 and the fourth inflection portion 232.

In the present embodiment, the insulator step portion 230 is disposed at a position overlapping the center electrode step portion 120 in the axis AL direction. The insulator step portion 230 is disposed at a position overlapping the tip portion 110 of the center electrode 100 in the axis AL direction.

Further, in this embodiment, the covering portion 220 is compared with other portions in the insulator step portion 230 (specifically, the fourth inflection portion 232) that overlaps the center electrode step portion 120 in the axis AL direction. The thickness is getting smaller. That is, the part where the thickness of the covering part 220 is the minimum is arranged at a position overlapping the center electrode step part 120 in the axis line AL direction.

In the present embodiment, the distal end portion 110 of the center electrode 100 has an outer diameter that decreases toward the distal end side, and a first inflection portion 121 that swells radially outward and a second inflection that constricts radially inward. The center electrode step 120 is connected to the portion 122. Generally, it is known that an electric field tends to concentrate on an inflection part. Therefore, according to the spark plug 10, the center electrode step portion 120 having the first inflection portion 121 and the second inflection portion 122 is provided at the tip portion 110 of the center electrode 100, and the tip portion 110 of the center electrode 100 is provided. Since it is covered with the insulator 200, a lot of non-equilibrium plasma is generated in the vicinity of the inflection portions 121 and 122 of the center electrode 100 on the surface of the insulator 200 as compared with other portions. In addition, by disposing the tip 110 of the center electrode 100 covered with the insulator 200 on the tip side of the metal shell 300, a lot of non-equilibrium plasma can be generated at a position closer to the combustion chamber. As a result, the energy can be efficiently used for ignition.

  In the said 1st Embodiment, the front-end | tip part 110 is provided with one center electrode step part. According to the spark plug 10, since the central electrode step portion 120 including the inflection portions 121 and 122 where the electric field concentrates is one place, a constant voltage is obtained as compared with the case where a plurality of center electrode step portions are provided. The strength of the electric field concentrated on one center electrode step 120 in the case of supplying is maintained without being distributed to other center electrode steps. As a result, it is possible to maintain the amount of non-equilibrium plasma generated on the insulator surface in the vicinity of one central electrode step. As a result, an amount of non-equilibrium plasma sufficient for ignition can be biased and generated in a specific portion of the insulator 200 on the tip side of the metal shell 300. For example, By providing the center electrode step 120 on the more distal end side (more on the combustion chamber side) of the distal end portion 110 of the center electrode 100, the energy of non-equilibrium plasma can be efficiently used for ignition.

  In the first embodiment, the covering portion 220 that covers the distal end portion 110 of the insulator 200 has a partially reduced outer diameter. When the covering portion 220 is viewed through a cross section along the axis, the axis AL There may be provided an insulator step portion 230 in which a third inflection portion 231 that swells radially outward and a fourth inflection portion 232 that constricts radially inward. According to the spark plug 10, not only the center electrode step portion 120 provided at the tip portion 110 of the center electrode 100 but also the insulator step portion 230 having the third inflection portion 231 and the fourth inflection portion 232 is provided at the center. Since it is provided in the covering portion 220 that covers the distal end portion 110 of the electrode 100, a lot of non-equilibrium plasma is generated in the vicinity of the inflection portion of the covering portion 220 in the surface of the insulator 200 as compared with other portions. . In addition, since the covering portion 220 is present on the tip side of the metal shell 300, more non-equilibrium plasma can be generated on the combustion chamber side, and as a result, the energy can be efficiently used for ignition. Can do.

  In the first embodiment, the insulator step portion 230 may be disposed at a position where at least a portion thereof overlaps the tip portion 110 of the center electrode 100 in the axis line AL direction. Compared to the case where the insulator step 230 does not overlap the center electrode 100 in the direction of the axis AL, the insulator step 230 is disposed at a position close to the center electrode step 120, so that the insulation near the center electrode step 120 is insulated. The amount of non-equilibrium plasma generated on the surface of the body 200 can be further increased.

  In the first embodiment, at least a part of the insulator step 230 may be disposed at a position overlapping the center electrode step 120 in the axis AL direction. Compared to the case where the insulator step portion 230 does not overlap the center electrode step portion 120 in the axis AL direction, the insulator step portion 230 is disposed at a position closer to the center electrode step portion 120, and thus the center electrode step portion 120. The amount of non-equilibrium plasma generated on the surface of the nearby insulator 200 can be further increased.

  In the first embodiment, the portion where the thickness of the covering portion 220 is the minimum is disposed at a position overlapping the center electrode step portion 120 in the axial direction. When the insulator is thin, the surface potential of the insulator is high and non-equilibrium plasma is likely to be generated. Therefore, by arranging such a portion at a position overlapping the center electrode step 120, the center electrode step The amount of non-equilibrium plasma generated on the surface of the insulator 200 near 120 can be increased.

Next, a second embodiment will be described.
FIG. 3 shows a half cross-sectional view of the spark plug 10B of the second embodiment on the tip side. The spark plug 10B of the second embodiment has the same configuration as the spark plug 10 of the first embodiment, except that one end 610 includes a ground electrode 600 connected to the tip 310 of the metal shell 300. .

  In the second embodiment, the other end 620 of the ground electrode 600 forms a discharge gap with the insulator 200 at the position where the center electrode step 120 is formed. Since a lot of non-equilibrium plasma is generated on the surface of the insulator 200 in the vicinity of the center electrode step portion 120, the energy of the non-equilibrium plasma is used for ignition more efficiently by forming a discharge gap in the vicinity thereof. Can do.

  In 1st Embodiment and 2nd Embodiment, the coating | coated part 220 of the insulator 200 is diameter-reduced as it goes to the front end side. However, the covering portion 220 may have a corrugation shape. In this case, a pair of convex portions and concave portions of the corrugation correspond to the insulator step portion 230, the convex portion of the corrugation corresponds to the third inflection portion, and the concave portion corresponds to the fourth inflection portion. Further, the insulating step 230 may not be formed on the covering 220.

  The center electrode step portion 120 is formed by directly connecting the first inflection portion 121 and the second inflection portion 122. However, the center electrode step part 120 may be formed by connecting the first inflection part 121 and the second inflection part 122 via a straight line part whose diameter is reduced at a substantially constant rate.

  The insulator step portion 230 is formed by directly connecting the third inflection portion 231 and the fourth inflection portion 232. However, the insulator step part 230 may be formed by connecting the third inflection part 231 and the fourth inflection part 232 through a straight line part having a reduced diameter at a substantially constant rate.

  One center electrode step 120 is formed at the tip 110 of the center electrode 100. However, a plurality of center electrode step portions 120 may be formed at the distal end portion 110. In that case, it is preferable that the plurality of center electrode step portions 120 are not provided uniformly at the distal end portion 110 but are concentrated at a specific location. For example, it is preferable that a plurality are provided only at positions overlapping the insulator step portion 230 in the axis line AL direction.

  In the covering portion 220, the portion having the smallest thickness is provided in the fourth inflection portion 232 in the insulator step portion 230. However, a portion where the thickness of the covering portion 220 is minimized may be provided in the third inflection portion 231. In addition, the portion where the thickness of the covering portion 220 is minimum may be provided at any portion regardless of the shape of the insulator 200 as long as the portion overlaps the center electrode step portion 120 in the axial direction.

  In the second embodiment, only one ground electrode 600 is provided, but a plurality of ground electrodes 600 may be provided. For example, a plurality of ground electrodes 600 may be connected to the distal end portion 310 of the metal shell 300 at equal intervals in the circumferential direction.

  The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit of the present invention. For example, among the technical features in the embodiments, examples, and modifications, those corresponding to the technical features in each embodiment described in the summary section of the invention are for solving some or all of the above-described problems. Alternatively, in order to achieve part or all of the above-described effects, replacement and combination can be performed as appropriate. Further, technical features that are not described as essential in the present specification can be appropriately deleted.

10, 10B ... Spark plug
100: Center electrode
110 ... tip 160 ... sealing material
180 ... terminal
200: Insulator
210 ... Bottom
220 ... covering part
290 ... Shaft hole
300 ... metal shell
310 ... tip
320 ... Male thread
330 ... trunk
340 ... Tool engaging portion
410 ... packing
420 ... Ring
430 ... talc powder
440 ... Ring
500 ... Gasket
600 ... Ground electrode 610 ... One end 620 ... Other end

Claims (7)

A bottomed cylindrical insulator that surrounds at least the front end side of the center electrode and has a bottom on the front end side in the axial direction, and extends from the front end to the rear end in the axial direction;
A spark plug provided with a cylindrical metal shell covering the periphery of the insulator so that the tip of the center electrode is located on the tip side of the tip of the center electrode,
The tip of the center electrode has an outer diameter reduced toward the tip,
A center electrode step portion in which a first inflection portion that swells radially outward and a second inflection portion that constricts radially inward when the cross-section passing through the axis is viewed with respect to the tip portion of the center electrode A spark plug characterized by that. The spark plug according to claim 1, wherein the tip portion includes one central electrode step portion. One end includes a ground electrode connected to the metal shell,
The spark plug according to claim 1 or 2, wherein the other end portion of the ground electrode forms a discharge gap with the insulator at a position where the center electrode step portion is formed. Of the insulator, the covering portion covering the tip portion has a reduced outer diameter in part.
When the cross section passing through the axis of the covering portion is viewed, an insulating step portion is provided in which a third inflection portion bulging radially outward and a fourth inflection portion constricting radially inward are connected. The spark plug according to any one of claims 1 to 3. 5. The spark plug according to claim 4, wherein at least a part of the insulator step portion is disposed at a position overlapping the center electrode in the axial direction. The spark plug according to claim 5, wherein at least a part of the insulator step portion is disposed at a position overlapping with the center electrode step portion in the axial direction. The spark plug according to any one of claims 1 to 6, wherein a portion where the thickness of the covering portion is minimum is disposed at a position overlapping the center electrode step portion in the axial direction.

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