JP2019003752A - Ignition plug - Google Patents

Abstract

To provide an ignition plug capable of improving ignitability.SOLUTION: An ignition plug includes: a bottomed cylindrical insulator which extends from the tip side to the rear side along an axis and whose tip is closed; a center electrode which is at least included in a tip part of the insulator; and a cylindrical main metal fitting for holding the insulator from the outer peripheral side in a state where the tip part protrudes from the tip of itself. The tip part includes: a first portion located in the tip side in the axial direction than the tip of the central electrode; and a second portion which is recessed up to the rear end of itself on the rear end side of at least itself and adjacent to the first portion. An outer diameter of a large diameter that is the largest of the second portion is bigger than an outer diameter of the first portion.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a spark plug, and more particularly to a spark plug using non-equilibrium plasma.

  Some spark plugs that ignite an air-fuel mixture use non-equilibrium plasma (Patent Document 1). In the spark plug disclosed in Patent Document 1, the metal shell holds the insulator in a state in which the tip of the bottomed cylindrical insulator containing the center electrode protrudes. When an alternating voltage or a plurality of pulse voltages are applied between the metal shell and the center electrode, this spark plug ionizes the gas around the tip of the insulator, and activates an active species such as a radical that becomes a fire. Generate. Increasing the amount of protrusion from the metal shell at the tip and increasing the surface area of the tip increases the amount of active species generated and improves the ignitability.

JP 2014-22341 A

  However, the above-described conventional technique has a problem that when the protruding amount of the tip portion from the metal shell increases, the tip portion is easily broken.

  The present invention has been made to solve the above-described problems, and provides an ignition plug that can increase the amount of active species generated without increasing the amount of protrusion from the metal shell of the tip and improve the ignitability. It is an object.

  In order to achieve this object, the spark plug of the present invention is such that a bottomed cylindrical insulator having a closed end extends along the axis from the front end side to the rear end side, and at least a center electrode is provided at the front end portion of the insulator. Is included. The cylindrical metal shell holds the insulator from the outer peripheral side in a state in which the tip portion protrudes from the tip of itself. The tip portion includes a first portion located on the tip side in the axial direction with respect to the tip of the center electrode, and a second portion adjacent to the first portion that is at least constricted to the back end side of the tip portion. And the outer diameter of the large-diameter portion that is the maximum of the second portion is larger than the outer diameter of the first portion.

  According to the spark plug of the first aspect, the first end portion of the insulator protruding from the metal shell is located closer to the tip end side in the axial direction than the tip end of the center electrode, and the second portion adjacent to the first portion. The portion is constricted to at least the rear end side of the portion up to the rear end of the portion. Since the outer diameter of the large-diameter portion that is the maximum of the second portion is larger than the outer diameter of the first portion, the surface area of the tip portion having a relatively high potential can be increased. As a result, since the surface area of the tip can be increased while suppressing a decrease in the potential of the tip, the amount of active species generated can be increased without increasing the amount of protrusion of the tip from the metal shell, and the ignitability can be improved.

  According to the spark plug of the second aspect, the outer peripheral surface of the front end is curved in a convex shape from the front end of the front end to the outer diameter in the radial direction, and from the large end to the rear end. It curves in a convex shape toward the outside in the radial direction. As a result, since the outer peripheral surface of the tip can hardly hinder the growth of the fire type, in addition to the effect of the first aspect, the ignitability can be further improved.

  According to the spark plug of claim 3, the value D / L obtained by dividing the outer diameter D of the large diameter portion by the distance L in the axial direction from the tip of the metal shell to the tip of the center electrode is 0.3 ≦ D. /L≦1.4 is satisfied. Therefore, in addition to the effect of claim 1 or 2, the amount of active species generated can be increased as compared with the case where D / L exists outside this range.

  According to the spark plug of claim 4, a value H / a value obtained by dividing the axial distance H from the leading end of the metallic shell to the large diameter portion by the axial distance L from the leading end of the metallic shell to the distal end of the center electrode. L satisfies 0.5 ≦ H / L ≦ 0.7. Therefore, in addition to the effect of any one of claims 1 to 3, the amount of active species generated can be increased as compared with the case where H / L exists outside this range.

  According to the spark plug of the fifth aspect, since the outer diameter of the large diameter portion is smaller than the minimum inner diameter of the metal shell, the insulator can be inserted into the metal shell from the front end side. As a result, in addition to the effect of any one of claims 1 to 4, a highly reliable structure in which the metal shell holds the insulator from the outer peripheral side can be easily realized.

  According to the spark plug of the sixth aspect, the outer diameter of the rear end of the front end portion is larger than the outer diameter of the rear end of the second portion. As a result, compared with the case where the front end of the metal shell surrounds the rear end of the second part, the gap between the front end of the metal shell and the front end can be narrowed. Can be suppressed. Therefore, in addition to the effect of Claim 5, the penetration (dielectric breakdown) of the tip portion can be suppressed.

It is a half sectional view of the spark plug in the first embodiment of the present invention. It is sectional drawing containing the axis line of the spark plug which expanded the front-end | tip. (A) is a figure which shows distribution of the potential of a spark plug, (b) is a figure which shows distribution of the potential of the spark plug in a comparative example. It is a figure which shows the relationship between D / L and H / L, and the production amount of a radical. It is sectional drawing containing the axis line of the ignition plug in 2nd Embodiment. It is sectional drawing containing the axis line of the ignition plug in 3rd Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-side cross-sectional view with the axis O of the spark plug 10 according to the first embodiment of the present invention as a boundary, and FIG. 2 is a cross-sectional view including the axis O of the spark plug 10 with an enlarged tip. 1 and 2, the lower side of the drawing is referred to as the front end side of the spark plug 10, and the upper side of the drawing is referred to as the rear end side of the spark plug 10 (the same applies to FIGS. 5 and 6). 2, illustration of the rear end side of the spark plug 10 is omitted (the same applies to FIGS. 5 and 6). As shown in FIG. 1, the spark plug 10 includes a metal shell 20, an insulator 30, and a center electrode 50.

  The metal shell 20 is a substantially cylindrical member fixed to a screw hole of an internal combustion engine (not shown), and is formed of a conductive metal material (for example, low carbon steel). The metal shell 20 is connected in the order of the caulking portion 21, the tool engaging portion 22, the bending portion 23, the seat portion 24, and the body portion 25 along the axis O from the rear end side to the front end side. The body portion 25 has a thread portion 26 formed on the outer peripheral surface.

  The caulking portion 21 and the bending portion 23 are portions for fixing the metal shell 20 to the insulator 30. The tool engaging portion 22 is a portion for engaging a tool such as a wrench when the screw portion 26 is coupled to an internal combustion engine (not shown). The seat portion 24 is a portion that is located on the rear end side of the body portion 25 and projects annularly outward in the radial direction. An annular gasket 56 is disposed between the seat portion 24 and the body portion 25. When the screw portion 26 is coupled to the internal combustion engine, the gasket 56 is sandwiched between the seat portion 24 and the internal combustion engine and seals a gap between the screw hole (not shown) and the screw portion 26. As for the trunk | drum 25, the shelf part 27 which protrudes to an inner side of radial direction is formed in the inner periphery.

  The insulator 30 is a bottomed cylindrical member formed of alumina or the like that is excellent in mechanical properties and insulation at high temperatures. The insulator 30 is formed with a hole 31 along the axis O that is open at the rear end of the insulator 30 and closed at the front end. The insulator 30 includes a cylindrical body portion 32 extending in the direction of the axis O, an annular projecting portion 33 projecting outward from the center of the body portion 32 in the axis O direction, and a locking portion 34. And a leg portion 35 connected to the distal end side of the body portion 32. The outer diameter of the leg part 35 is set smaller than the outer diameter of the trunk | drum 32, and the latching | locking part 34 is diameter-reduced as it goes to the front end side.

  The insulator 30 is inserted into the metal shell 20. A packing 48 is interposed between the locking portion 34 of the insulator 30 and the shelf portion 27 of the metal shell 20. The packing 48 is an annular plate formed of a metal material such as a mild steel plate that is softer than the metal material constituting the metal shell 20.

  A pair of ring members 54 and a filler such as talc sandwiched between the ring member 54 and the tool engaging portion 22 of the metal shell 20 between the body 32 on the rear end side of the overhanging portion 33 of the insulator 30 and the tool engaging portion 22 of the metal shell 20. 55 is arranged. When the crimped portion 21 of the metal shell 20 is crimped radially inward toward the insulator 30, the insulator 30 is pressed toward the shelf 27 of the metal shell 20 via the ring member 54 and the filler 55. Is done. As a result, the metal shell 20 holds the insulator 30 from the outer peripheral side with the tip 36 of the insulator 30 protruding from the tip 28 of the metal shell 20 via the packing 48, the ring member 54 and the filler 55. To do.

  The center electrode 50 is a rod-shaped electrode formed of a conductive metal material (for example, a nickel-based alloy). The center electrode 50 is locked in the hole 31 of the insulator 30 and extends along the axis O from the front end side to the rear end side.

  The terminal fitting 53 is a rod-shaped member to which an alternating voltage or a pulse voltage is input, and is formed of a conductive metal material (for example, low carbon steel). The terminal fitting 53 has the distal end side of the terminal fitting 53 disposed inside the hole portion 31 and is connected to the center electrode 50 via a connection portion 52 such as conductive glass.

  As shown in FIG. 2, in the spark plug 10, the distal end portion 36 of the insulator 30 protrudes from the distal end 28 of the metal shell 20. The distal end portion 36 is a part of the leg portion 35 cut by a cutting plane 37 perpendicular to the axis O passing through the distal end 28 of the metal shell 20. The front end portion 36 is surrounded by a curved outer peripheral surface 40 from the front end 38 to the rear end 39 in the axis O direction of the front end portion 36. The distal end portion 36 includes a first portion 41 located closer to the distal end side in the axis O direction than the distal end 51 of the center electrode 50, and a second portion 42 adjacent to the first portion 41. The first portion 41 is a part of the tip portion 36 cut by a cutting plane 43 perpendicular to the axis O passing through the tip 51 of the center electrode 50.

  In the second portion 42, the tip 44 of the second portion 42 is connected to the first portion 41. In the distal end portion 36, the outer diameter D of the large diameter portion 45 having the largest outer diameter in the second portion 42 is set larger than the maximum outer diameter D <b> 1 of the first portion 41. A portion of the second portion 42 on the rear end 46 side of the second portion 42 has the outer peripheral surface 40 narrowed to the rear end 46. Therefore, the surface area of the front end portion 36 can be increased compared to the case where the front end portion of the front end portion 36 is formed linearly with respect to the rear end 46 (when the second portion 42 is not provided).

  In the present embodiment, the outer peripheral surface 40 of the front end portion 36 is curved in a convex shape from the front end 38 to the large diameter portion 45 of the front end portion 36 toward the outside in the radial direction, and has a diameter from the large diameter portion 45 to the rear end 46. Curved convex toward the outside of the direction. That is, in the cross section including the axis O (FIG. 2), the outer peripheral surface 40 has a distance from the axis O (the length of the line perpendicular to the axis O and the axis O with the outer peripheral surface 40 as an end point) from the tip 38. As it goes to the rear end side, it monotonously increases from the tip 38 to the large diameter portion 45 and monotonously decreases from the large diameter portion 45 to the rear end 46.

  In the cross section including the axis O (FIG. 2), the outer peripheral surface 40 has a maximum value at the large diameter portion 45 and an inflection point at the rear end 46. In the cross section including the axis O, the outer peripheral surface 40 is a curved curve that protrudes radially outward in the vicinity of the large-diameter portion 45, and is a curved curve that protrudes radially inward near the rear end 46. The outer peripheral surface 40 has a vertical surface 47 formed perpendicular to the axis O between the rear end 46 of the second portion 42 and the rear end 39 of the front end portion 36.

  In the present embodiment, the outer diameter D of the large diameter portion 45 is set to the same size as the outer diameter of the rear end 39 of the front end portion 36. The rear end 46 of the second portion 42 is located on the front end side (lower side in FIG. 2) of the front end 28 of the metal shell 20, and the outer diameter of the rear end 39 of the front end portion 36 is the rear end of the second portion 42. 46 is larger than the outer diameter D2. The outer diameter D2 of the rear end 46 of the second portion 42 is smaller than the outer diameter D1 of the first portion 41. Further, the outer diameter D of the large diameter portion 45 is set smaller than the minimum inner diameter D3 (in the present embodiment, the inner diameter of the tip of the shelf portion 27) of the metal shell 20.

  The spark plug 10 has a distance L in the axis O direction from the tip 28 of the metal shell 20 to the tip 51 of the center electrode 50, and a value D / L obtained by dividing the outer diameter D of the large diameter portion 45 is 0.3 ≦ D. /L≦1.4 is satisfied. Further, in the spark plug 10, the value H / L obtained by dividing the distance H in the axis O direction from the tip 28 of the metal shell 20 to the large diameter portion 45 by the distance L satisfies 0.5 ≦ H / L ≦ 0.7. Fulfill.

  Next, the results of the plasma simulation will be described with reference to FIG. Plasma generation for dielectric barrier discharge was calculated using CFD-ACE + (Multiphysics based on Computational Fluid Dynamics) as software. The calculation model is a two-dimensional symmetric model, and ionization / attachment between atoms and electrons was calculated for a half region with the axis O as a symmetric boundary. FIG. 3A is a diagram showing the potential distribution of the spark plug 10, and FIG. 3B is a diagram showing the potential distribution of the spark plug 80 in the comparative example.

  The dimensions of each part of the modeled spark plug 10 were as follows (see FIG. 2). The outer diameter of the center electrode 50 = Φ1.7 mm, the inner diameter D3 of the metal shell 20 = Φ7.9 mm, the outer diameter of the rear end 39 of the tip portion 36 = Φ7.4 mm, and the outer diameter D2 of the rear end 46 of the second portion 42 = Φ4.1 mm, outer diameter D of the large diameter portion 45 = Φ7.4 mm, axial length from the tip 28 of the metal shell 20 to the tip 38 of the tip 36 = 12.7 mm, center from the tip 28 of the metal shell 20 The distance L in the axial direction to the tip 51 of the electrode 50 is 11.29 mm, the distance H in the axial direction from the tip 28 of the metal shell 20 to the large diameter portion 45 is 6.774 mm, and the vertical surface 47 from the tip 28 of the metal shell 20. The length in the axial direction until M = 1.0 mm, D / L = 0.66.

  On the other hand, portions other than the tip 81 of the spark plug 80 in the comparative example are the same as the respective portions of the spark plug 10. The front end portion 81 is formed such that a portion closer to the front end than the rear end 46 (see FIG. 2) is linear, and D = D2 = Φ4.1 mm.

In the spark plugs 10 and 80, the dielectric constant of the insulator 30 was set to 9.5. The size of the boundary where the electric potential surrounding the tip portions 36 and 81 is zero was 62.7 mm and Φ104 mm from the tip 28 to the tip side. The gas species in the gas phase is N ₂ , the initial pressure of the gas is 0.2 MPa, the initial temperature of the gas is 300 K, and the reaction of electrons, radicals, and ions when an AC voltage is applied to the center electrode 50 is calculated. The distribution of was obtained.

  In FIG. 3A and FIG. 3B, the distribution of the potential is illustrated by a curve (equipotential line) connecting points having the same potential. The closer to the center electrode 50, the higher the potential, and the lower the potential from the center electrode 50, the lower the potential. Since the energy for ionizing the gas is higher as the potential is higher, the amount of active species such as radicals serving as fire species increases as the distribution of the distribution with higher potential increases.

  As shown in FIG. 3B, the equipotential line at the tip 81 has a distance from the axis O in the direction perpendicular to the axis O as the distance from the tip of the tip 81 approaches the center of the tip 81 in the axial direction. The length increases and decreases from the vicinity of the center in the axial direction of the distal end portion 81 toward the rear end of the distal end portion 81. Therefore, the spark plug 10 increases the surface area of the tip portion 36 by increasing the thickness near the center in the axial direction of the tip portion 36 where the distance between the equipotential line and the axis O is long.

  As shown in FIG. 3A, the spark plug 10 forms a second portion 42 (see FIG. 2), and the radial thickness (wall thickness) near the center in the axial direction of the tip portion 36 is set to the tip portion. It is larger than the wall thickness near the center in the axial direction of 81 (see FIG. 3B). Specifically, as shown in FIG. 2, the outer diameter D of the large diameter portion 45 having the largest outer diameter in the second portion 42 is made larger than the largest outer diameter D1 of the first portion 41, Out of the portion 42, the outer peripheral surface 40 on the rear end 46 side of the second portion 42 is narrowed to the rear end 46. Thereby, the surface area of the portion having a relatively high potential in the tip portion 36 can be increased. As a result, the spark plug 10 can increase the generation amount of active species such as radicals without increasing the protruding amount of the distal end portion 36 from the metal shell 20 in the axial direction, thereby improving the ignitability.

  As shown in FIG. 2, in the spark plug 10, the outer peripheral surface 40 of the distal end portion 36 is curved in a convex shape outward from the distal end 38 to the large diameter portion 45 in the radial direction. The rear end 46 is curved in a convex shape toward the outside in the radial direction. As a result, compared to the case where the outer circumferential surface 40 has irregularities in order to increase the surface area, the dents in the outer circumferential surface 40 can be prevented from hindering the growth of the fire type, so that the ignitability can be further improved. Further, compared to the case where the outer circumferential surface 40 has irregularities, heat conduction from the tip portion 36 to the center electrode 50, the metal shell 20 and the like can be improved, so that the tip portion 36 is prevented from being overheated. 36 can be prevented from becoming an ignition source.

  Since the outer diameter D1 of the first portion 41 is larger than the outer diameter D2 of the rear end 46 of the second portion 42 (D1> D2), the surface area of the first portion 41 can be increased compared to the case of D1 <D2. As a result, the potential distribution can be spread to the tip end side of the spark plug 10 in the axis O direction. Therefore, the active species generated by the tip portion 36 can be supplied to the center side of the combustion chamber of the internal combustion engine (not shown).

  Since an alternating voltage or a plurality of pulse voltages are applied to the spark plug 10, when the plasma is superimposed between the tip 28 and the tip 36 of the metal shell 20, the tip 36 penetrates (breaks down). There is a risk. On the other hand, in the spark plug 10, the rear end 46 of the second portion 42 is positioned on the front end side of the front end 28 of the metal shell 20, and the outer diameter of the rear end 39 of the front end portion 36 is the rear end of the second portion 42. The outer diameter of the end 46 is made larger. Thereby, compared with the case where the front-end | tip 28 of the metal shell 20 surrounds the rear end 46 of the 2nd part 42, the clearance gap between the front-end | tip 28 and the front-end | tip part 36 of the metal shell 20 can be narrowed. As a result, since plasma generated between the tip 28 and the tip 36 of the metal shell 20 can be suppressed, penetration of the tip 36 can be suppressed.

  Since the outer diameter D of the large diameter portion 45 of the distal end portion 36 is set smaller than the smallest inner diameter D3 (the inner diameter of the distal end of the shelf portion 27) of the metal shell 20, the insulator 30 is inserted from the distal end portion 36 side. It can be inserted into the metal shell 20. Therefore, it is possible to easily realize a highly reliable structure in which the latching portion 34 of the insulator 30 is latched by the shelf 27 of the metal shell 20 and the metal shell 20 holds the insulator 30 from the outer peripheral side.

  Next, with reference to FIG. 4, the result of calculating the radical generation amount of the spark plug 10 will be described. As the software, CFD-ACE + was used in the same manner as in FIG. Dimensions of each part modeled, etc. (the outer diameter of the center electrode 50, the inner diameter D3 of the metal shell 20, the outer diameter of the rear end 39 of the tip 36, the outer diameter of the rear end 46 of the second portion 42, the tip of the metal shell 20) 28, the length in the axial direction from the tip 28 of the tip 36, the axial distance L from the tip 28 of the metal shell 20 to the tip 51 of the center electrode 50, and the axis from the tip 28 of the metal shell 20 to the vertical plane 47. The length M in the direction, the relative dielectric constant of the insulator 30, the size of the boundary where the potential is zero, the gas species in the gas phase, the initial pressure and the initial temperature of the gas) are the same as in FIG. did.

By changing the outer diameter D of the large diameter portion 45 and the axial distance H from the tip 28 of the metal shell 20 to the large diameter portion 45, D / L and H / L and radicals (nitrogen molecule radical and nitrogen molecule ion) ) Was calculated. FIG. 4 is a diagram showing the relationship between D / L and H / L and the amount of radicals generated. In FIG. 4, the horizontal axis represents D / L, and the vertical axis represents the amount of radical generation [× 10 ⁻²⁷ ] (g).

  As shown in FIG. 4, when 0.4 ≦ H / L ≦ 0.8, when D / L <0.9, the amount of radicals generated increases as D / L increases (increase in surface area). With the peak at L≈0.9, the amount of radicals generated decreased with an increase in D / L> 0.9. As a result, it was found that 0.3 ≦ D / L ≦ 1.4 is preferable and 0.4 ≦ D / L ≦ 1.3 is more preferable to secure the amount of radicals generated. Further, it was found that when 0.5 ≦ H / L ≦ 0.7, the amount of radicals generated can be increased more than when H / L = 0.4 or H / L = 0.8. Therefore, it was found that 0.5 ≦ H / L ≦ 0.7 is preferable in order to ensure the amount of radical generation.

  Next, a second embodiment will be described with reference to FIG. In the first embodiment, in the cross section including the axis O (FIG. 2), the distance from the axis O of the outer peripheral surface 40 of the tip 36 increases monotonically from the tip 38 to the large diameter 45, and from the large diameter 45. The case of monotonously decreasing toward the rear end 46 has been described. On the other hand, in 2nd Embodiment, the spark plug 60 by which the unevenness | corrugation was formed in the outer peripheral surface of the front-end | tip part 62 is demonstrated. In addition, about the part same as 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. FIG. 5 is a cross-sectional view including the axis O of the spark plug 60 according to the second embodiment.

  As shown in FIG. 5, in the spark plug 60, the distal end portion 62 of the insulator 61 protrudes from the distal end 28 of the metal shell 20. The front end portion 62 is surrounded by a curved outer peripheral surface from the front end 63 to the rear end 64 in the axis O direction of the front end portion 62. The distal end portion 62 includes a first portion 65 located closer to the distal end side in the axis O direction than the distal end 51 of the center electrode 50, and a second portion 66 adjacent to the first portion 65. In the distal end portion 62, the outer diameter D of the large diameter portion 67 having the maximum outer diameter in the second portion 66 is set larger than the maximum outer diameter of the first portion 65. The portion of the second portion 66 on the rear end 68 side of the second portion 66 is narrowed on the outer peripheral surface to the rear end 68. The outer diameter D of the large diameter portion 67 is set smaller than the minimum inner diameter D3 of the metal shell 20.

  In the present embodiment, the irregularities formed in the second portion 66 are continuous in the circumferential direction. The minimum outer diameter of the concave and convex portion formed in the second portion 66 is set larger than the maximum outer diameter of the first portion 65. Thereby, it can prevent that the mechanical strength of the recessed part of an unevenness | corrugation falls remarkably.

  According to the spark plug 60, since the unevenness is formed in the second portion 66, the surface area of the tip portion 62 can be increased while preventing the potential of the tip portion 62 from being lowered. As a result, the generation amount of active species can be increased without increasing the axial protrusion amount of the distal end portion 62 from the metal shell 20, and the ignitability can be improved.

  Next, a third embodiment will be described with reference to FIG. In 1st Embodiment and 2nd Embodiment, the case where the outer diameter D of the large diameter parts 45 and 67 was set smaller than the minimum inner diameter D3 of the metal shell 20 was demonstrated. In contrast, in the third embodiment, a case will be described in which the outer diameter D of the large-diameter portion 77 is set larger than the minimum inner diameter D3 of the metal shell 20. In addition, about the part same as 1st Embodiment, the same code | symbol is attached | subjected and the following description is abbreviate | omitted. FIG. 6 is a cross-sectional view including the axis O of the spark plug 70 in the third embodiment.

  As shown in FIG. 6, the spark plug 70 has a distal end portion 72 of an insulator 71 protruding from the distal end 28 of the metal shell 20. The front end portion 72 is surrounded by a curved outer peripheral surface from the front end 73 to the rear end 74 in the axis O direction of the front end portion 72. The distal end portion 72 includes a first portion 75 located on the distal end side in the axis O direction with respect to the distal end 51 of the center electrode 50, and a second portion 76 adjacent to the first portion 75.

  In the distal end portion 72, the outer diameter D of the large diameter portion 77 having the maximum outer diameter in the second portion 76 is set to be larger than the maximum outer diameter of the first portion 75. A portion of the second portion 76 on the rear end 78 side of the second portion 76 is narrowed on the outer peripheral surface to the rear end 78. The rear end 78 of the second portion 76 is the most rear end portion between the rear end 74 and the large diameter portion 77 of the front end portion 72 and the outer diameter starts to expand.

  Since the outer diameter D of the large diameter portion 77 is set to be larger than the minimum inner diameter of the metal shell 20, the insulator 71 cannot be inserted into the metal shell 20 from the distal end portion 72 side. Therefore, the spark plug 70 inserts the insulator 71 into the metal shell 20 from the rear end side, and holds the rear end side of the insulator 71 with the metal shell 20. Further, the insulator 71 is divided into a portion including the locking portion 34 (see FIG. 1) (hereinafter referred to as “rear end member”) and a portion including the front end portion 72 (hereinafter referred to as “front end member”). The insulator 71 is configured by joining the end member to the end member. According to the spark plug 70, since the second portion 76 is provided, the amount of active species generated can be reduced without increasing the protruding amount in the axial direction of the distal end portion 72 from the metal shell 20, as in the first embodiment. Increase the ignitability.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily guessed.

  In the first embodiment, the case where the outer diameter D of the large diameter portion 45 is the same as the outer diameter of the rear end 39 of the distal end portion 36 has been described, but the present invention is not necessarily limited thereto. Since the outer diameter D of the large diameter portion 45 only needs to be larger than the outer diameter D1 of the first portion 41, it is set as appropriate so as to satisfy the relationship D> D1.

  In the first embodiment, the case where the outer diameter D2 of the rear end 46 of the second portion 42 is smaller than the outer diameter D1 of the first portion 41 (D2 <D1) has been described. However, the present invention is not necessarily limited to this. Absent. Since the second portion 42 only needs to be narrowed to the rear end 46 on the rear end 46 side, it is naturally possible to satisfy D2 ≧ D1 contrary to this relationship.

  In the second embodiment, the case where the minimum outer diameter of the concave and convex portion formed in the second portion 66 is larger than the maximum outer diameter of the first portion 65 has been described. It is not a thing. Of course, it is possible to make the minimum outer diameter of the concave and convex portion formed in the second portion 66 smaller than the maximum outer diameter of the first portion 65. In this case, the surface area of the tip 62 can be increased by deepening the recess.

  In the third embodiment, the distance from the axis O of the outer peripheral surface of the front end portion 72 monotonously increases from the front end 73 to the large diameter portion 77 as it goes from the front end 73 to the rear end side, and from the large diameter portion 77 to the rear end. Although the case of monotonically decreasing toward 78 has been described, the present invention is not necessarily limited thereto. As in the second embodiment, it is naturally possible to provide irregularities on the distal end portion 72.

  In each of the above embodiments, the case where the metal shell 20 is crimped to the insulator 30 via the ring member 54 and the filler 55 has been described, but the present invention is not necessarily limited thereto. Of course, the metal shell 20 can be crimped by omitting the ring member 54 and the filler 55.

10, 60, 70 Spark plug 20 Metal shell 28 Tip of metal shell 30, 61, 71 Insulator 36, 62, 72 Tip of insulator 38, 63, 73 Tip of tip 39, 64, 74 After tip End 40 Outer peripheral surface 41, 65, 75 First portion 42, 66, 76 Second portion 45, 67, 77 Large diameter portion 46, 68, 78 Second portion rear end 50 Central electrode 51 Center electrode tip D Outer diameter of large diameter part H, L Distance

Claims (6)

A bottomed cylindrical insulator extending along the axis from the front end side to the rear end side,
A central electrode contained at least in the tip of the insulator;
A spark plug provided with a cylindrical metal shell that holds the insulator from the outer peripheral side in a state in which the tip portion protrudes from its tip,
The tip portion is a first portion located closer to the tip side in the axial direction than the tip of the center electrode;
A second portion adjacent to the first portion, and having at least a second portion constricted to the rear end on the rear end side of the first portion;
A spark plug in which the outer diameter of the largest diameter portion of the second portion is larger than the outer diameter of the first portion.   The outer peripheral surface of the tip is curved in a convex shape from the tip of the tip to the large-diameter portion toward the outside in the radial direction, and toward the outside in the radial direction from the large-diameter portion to the rear end side. The spark plug according to claim 1, wherein the spark plug is curved in a convex shape.   A value D / L obtained by dividing the outer diameter D of the large diameter portion by the distance L in the axial direction from the tip of the metal shell to the tip of the center electrode is 0.3 ≦ D / L ≦ 1.4. The spark plug according to claim 1 or 2, wherein:   A value H / L obtained by dividing an axial distance L from the tip of the metal shell to the large diameter portion by an axial distance L from the tip of the metal shell to the tip of the center electrode is 0. The spark plug according to any one of claims 1 to 3, wherein .5 ≦ H / L ≦ 0.7 is satisfied.   The spark plug according to any one of claims 1 to 4, wherein an outer diameter of the large diameter portion is smaller than a minimum inner diameter of the metal shell.   The spark plug according to claim 5, wherein an outer diameter of a rear end of the tip portion is larger than an outer diameter of a rear end of the second portion.

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