JP2017111960A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the shape of a ground electrode to further improve the ignition performance of a spark plug.SOLUTION: A ground electrode base material has a base material base end portion, a base material tip portion, and a base material bent portion. At an intersection of an axis of a spark plug and a tip end surface of an insulator, when assuming a first imaginary straight line intersecting perpendicularly with the axis and a second imaginary straight line intersecting perpendicularly with the axis at an intersection of the axis and an inner surface of the base material tip portion, within a range of an axial height between the first imaginary straight line and the second imaginary straight line, a concave groove is formed in at least one of two side faces of the base material bent portion. The groove has a tapered shape in which the width of the groove measured along a direction of the axis gradually narrows from an outer surface side to an inner surface side of the ground electrode base material.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a spark plug.

  In recent years, various technological developments aimed at reducing fuel consumption and emission of automobiles have been advanced from the viewpoint of protecting the global environment. For example, in the development of an engine, a technique is adopted in which combustion is efficiently performed with less fuel by enhancing a so-called tumble flow and increasing a flow velocity in the combustion chamber.

  On the other hand, spark plugs with further improved ignition performance are required in the context of such technological development. For example, in the spark plug described in Patent Document 1, a technique for improving the ignition performance by thinning a part of the ground electrode and shaping the air-fuel mixture into a shape that does not inhibit the ground electrode is disclosed. .

JP 2008-112608 A

  However, the inventors of the present application have found that there is room for further improvement of the ground electrode, and in particular, it has been found that the ignition performance of the spark plug can be further improved by improving its shape.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, a cylindrical insulator having an axial hole extending in the direction of the axis, and the inner side of the insulator is held so that the front end protrudes from the front end of the axial hole. A spark plug having a center electrode, a metal shell that accommodates the insulator, and a ground electrode having a base end portion joined to a tip portion of the metal shell and a tip portion facing the tip surface of the center electrode. Provided. The ground electrode includes an inner surface having a facing portion facing the front end surface of the center electrode, a first side surface and a second side surface adjacent to the inner surface and extending from the front end portion to the base end portion, and opposite to the inner surface. An outer surface extending from the distal end portion to the proximal end portion. In this spark plug, the first imaginary straight line passing through the tip of the insulator and perpendicular to the axis, and the second imaginary straight line passing through the facing portion of the ground electrode and perpendicular to the axis are between the first imaginary straight line. Within the range of the direction of the axis, a concave groove extending from the outer surface side to the inner surface side of the ground electrode is formed on at least one of the first side surface and the second side surface. The width of the groove measured along the direction is gradually narrowed from the outer surface side to the inner surface side of the ground electrode.
According to this spark plug, since the groove is provided on at least one of the first side surface and the second side surface of the ground electrode, the width of the groove gradually decreases from the outer surface side to the inner surface side of the ground electrode. The air-fuel mixture can be rectified by the groove and efficiently guided to the spark gap, improving the ignition performance.

(2) In the spark plug, the groove may be formed on both the first side surface and the second side surface.
According to the spark plug, since the grooves are provided on both side surfaces of the ground electrode, the ignition performance can be further improved.

(3) In the spark plug, the depth of the groove may increase as the distance from the outer surface side of the ground electrode approaches the inner surface side.
According to this spark plug, since the groove depth increases as it approaches the inner surface side from the outer surface side, the rectifying effect of the air-fuel mixture by the groove is increased, and the ignition performance can be further improved.

(4) In the spark plug, the groove has a first width center of the groove on the outer surface of the ground electrode and a second width center of the groove on the inner surface of the ground electrode. A third imaginary straight line to be connected may be formed so as to pass through a range in the direction of the axis between the front end surface of the center electrode and the facing portion of the ground electrode.
According to this spark plug, the rectification effect of the air-fuel mixture by the groove is increased, and the ignition performance can be further improved.

(5) In the spark plug, the groove may be formed on the projection of the third imaginary straight line, the tip surface of the center electrode, and the facing portion of the ground electrode along the direction of the axis. Three imaginary straight lines may be formed so as to pass through a range in which the tip surface of the center electrode and the facing portion of the ground electrode overlap.
According to this spark plug, the rectification effect of the air-fuel mixture by the groove is increased, and the ignition performance can be further improved.

  Note that the present invention can be realized in various modes. For example, it is realizable with forms, such as a manufacturing method of a spark plug.

The front view which shows the spark plug of 1st Embodiment. Explanatory drawing which expands and shows the front-end | tip part of the spark plug of 1st Embodiment. Explanatory drawing which expands and shows the front-end | tip part of the spark plug of 2nd Embodiment. Explanatory drawing which expands and shows the front-end | tip part of the spark plug of a comparative example.

  FIG. 1 is a front view showing a spark plug 100 as an embodiment of the present invention. In FIG. 1, the lower side where the ignition part of the spark plug 100 exists is defined as the front end side of the spark plug 100, and the upper side is defined as the rear end side. The spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a metal shell 50. The insulator 10 is a cylindrical body having an axial hole extending along the axis O. The axis O is also referred to as “center axis”. The center electrode 20 is a rod-shaped electrode extending along the axis O, and is held inside the insulator 10 so that its tip protrudes from the tip of the shaft hole of the insulator 10. The ground electrode 30 is an electrode whose base end is fixed to the front end 52 of the metal shell 50 and whose front end faces the front end surface of the center electrode 20. A noble metal tip 22 is provided at the tip of the center electrode 20, and a noble metal tip 32 is also provided on the inner surface of the tip of the ground electrode 30. However, these noble metal tips 22 and 32 can be omitted. The terminal fitting 40 is a terminal for receiving power supply, and is electrically connected to the center electrode 20. The metal shell 50 is a cylindrical member that covers the periphery of the insulator 10 and accommodates the insulator 10. The outer periphery of the metal shell 50 is screwed. The screw part 4 is a part where a screw thread is formed, and is screwed into a screw hole of the engine head when the spark plug 100 is attached to the engine head.

  In this specification, the phrase “center electrode 20” is used to include both the center electrode having the noble metal tip 22 and the center electrode not having the noble metal tip 22. Similarly, the phrase “ground electrode 30” is used to encompass both a ground electrode having a noble metal tip 32 and a ground electrode not having the noble metal tip 32. As for the ground electrode 30, the portion excluding the noble metal tip 32 is also referred to as a “ground electrode base material 38”. In the example of FIG. 1, the ground electrode 30 includes a proximal end portion 35, a distal end portion 37, and a bent portion 36 formed therebetween. The proximal end portion 35 is joined to the distal end portion 52 of the metal shell 50 and has a substantially straight bar shape. The distal end portion 37 extends in a direction substantially perpendicular to the axis O of the spark plug 100 and has a substantially straight bar shape. The bent portion 36 is shaped so that the inner surface of the distal end portion 37 is positioned on the axis O so as to face the distal end surface of the center electrode 20. The ground electrode 30 has a substantially rectangular shape in cross section, and has an outer surface 39, an inner surface 33, and two side surfaces 31a and 31b. The outer side surface 39 is a surface facing the outer side (opposite to the axis O) of the spark plug 100 and extends from the distal end portion 37 to the proximal end portion 35. The inner surface 33 is a surface opposite to the outer surface 39. The inner surface of the tip portion 37 has a facing portion 32 op that faces the tip surface of the center electrode 20. In this example, since the noble metal tip 32 is provided at the tip portion 37 of the ground electrode 30, the facing portion 32 op is the surface of the noble metal tip 32. The first side surface 31 a and the second side surface 31 b are adjacent to the inner surface 33 and extend from the distal end portion 37 to the proximal end portion 35.

  Concave grooves 34 are provided on the side surfaces 31 a and 31 b of the ground electrode 30. In the first embodiment, the groove 34 is provided in the bending portion 36. The groove 34 has a function of rectifying the air-fuel mixture and guiding the air-fuel mixture to the spark gap between the center electrode 20 and the ground electrode 30. The feature of the shape of the groove 34 will be described in detail below. In FIG. 1, the grooves 34 are hatched for convenience of illustration. The same applies to the other figures.

  FIG. 2 is an explanatory diagram showing an enlarged front end portion of the spark plug 100. In FIG. 2A, two virtual straight lines X and Y are drawn. The first virtual straight line X is a virtual straight line that passes through the tip 12 of the insulator 10 and intersects the axis O perpendicularly. The second virtual straight line Y is a virtual straight line that passes through the facing portion 32op of the ground electrode 30 and intersects the axis O perpendicularly. The groove 34 is formed on both of the two side surfaces 31a and 31b within a range in the direction of the axis O between these two virtual straight lines X and Y. However, the groove 34 may be formed only on one of the two side surfaces 31a and 31b.

  Here, the dimension of the groove 34 measured along the direction of the axis O is referred to as “the width of the groove 34”. The width Win of the groove 34 on the inner surface 33 of the ground electrode 30 is smaller than the width Wout of the groove on the outer surface. In other words, the width of the groove 34 gradually decreases from the outer surface 39 side of the ground electrode 30 toward the inner surface 33 side. By providing such a tapered groove 34 in the ground electrode 30, the air-fuel mixture can be rectified by the groove 34 and efficiently guided to the spark gap SG, and the ignition performance can be improved. In particular, if such a spark plug 100 is used in an internal combustion engine having a structure that generates a tumble flow in the combustion chamber, the air-fuel mixture is rectified by the rectifying action of the groove 34 while utilizing the flow velocity of the air-fuel mixture increased by the tumble flow. Furthermore, since it can guide | induce to the spark gap SG efficiently, the improvement of ignition performance is remarkable. The width Wout of the groove 34 on the outer surface 39 of the ground electrode 30 is preferably in the range of 0.5 mm to 1.0 mm, for example. The width Win of the groove 34 in the inner surface 33 of the ground electrode 30 is preferably in the range of 0.2 mm to 0.5 mm, for example.

  FIG. 2B shows a BB cross section of FIG. 2A, which corresponds to a projection view in which the groove 34 is projected along the direction of the axis O. FIG. In this figure, the dimension of the groove 34 measured along the direction perpendicular to the center line 30o of the ground electrode 30 is referred to as “depth of the groove 34”. The depth Din of the groove 34 on the inner surface 33 of the ground electrode 30 is larger than the depth Dout of the groove on the outer surface 39. In other words, the groove 34 has a shape in which an inclination angle θ is given to the bottom surface 34 m of the groove 34 so that the depth of the groove 34 gradually increases as it approaches the inner surface 33 side from the outer surface 39 side of the ground electrode 30. Have. As described above, if not only the widths Wout and Win (FIG. 2A) of the grooves 34 are tapered, but the depths Dout and Din of the grooves 34 are also tapered, the air-fuel mixture by the grooves 34 is obtained. The rectifying effect increases, and the ignition performance can be further improved. In addition, it is preferable that the depth Dout of the groove | channel 34 in the outer surface 39 of the ground electrode 30 shall be 0.1 mm or more and 0.3 mm or less, for example. In addition, the inclination angle θ of the bottom surface 34m of the groove 34 is preferably in the range of 8 ° to 12 °, for example.

  FIG. 2C shows the same shape as FIG. 2A, and a third virtual straight line Lab is drawn as another shape feature of the groove 34. The third virtual straight line Lab is a virtual straight line that connects the center 34o of the width of the groove 34 on the outer surface 39 of the ground electrode 30 and the center 34i of the width of the groove 34 on the inner surface 33 of the ground electrode 30. That is, the third virtual straight line Lab corresponds to the center line of the width of the groove 34. The groove 34 is such that the third imaginary straight line Lab passes through a range in the direction of the axis O (that is, a range of the spark gap SG) between the tip surface of the center electrode 20 and the facing portion 32op of the ground electrode 30. Is formed. This further increases the rectification effect of the air-fuel mixture by the grooves 34, so that the ignition performance can be further improved.

  The third virtual straight line Lab is preferably formed so as to pass through the range of the spark gap SG in FIG. The range of the spark gap SG in FIG. 2B is a projection in which the tip surface of the center electrode 20 (here, the lower surface of the noble metal tip 22) and the facing portion 32op of the ground electrode 30 are projected along the direction of the axis O. In the drawing, it means a range where the tip surface of the center electrode 20 and the facing portion 32op of the ground electrode 30 overlap. If the groove 34 is shaped in this way, the effect of rectifying the air-fuel mixture by the groove 34 is increased, and the ignition performance can be further improved.

  Note that the groove 34 does not have to include all of the above-described various shape features described in FIG. 2, and may include only a part of them.

  FIG. 3 is an explanatory view showing, in an enlarged manner, the tip portion of the spark plug 100a of the second embodiment. This spark plug 100a is different from the first embodiment in that two grooves 34a and 34b are formed on the side surfaces 31a and 31b of the ground electrode 30, respectively. These grooves 34a and 34b also preferably have various shape features described in FIG. The number of grooves 34 provided on one side surface of the ground electrode 30 is not limited to 1 or 2, and may be 3 or more. In the case where a plurality of grooves 34 are provided on one side surface of the ground electrode 30, at least one of the grooves 34 includes at least one of the various geometric features described in FIG. Preferably it is.

  FIG. 4 is an explanatory view showing, in an enlarged manner, a tip portion of a spark plug 100c of a comparative example. This spark plug 100c is different from the first embodiment in that the groove 34c provided on the side surfaces 31a and 31b of the ground electrode 30 is not tapered and the width of the groove 34c is substantially constant. The difference in effect between this comparative example and the embodiment is as follows.

Table 1 is a table | surface which shows the experimental result of the ignition performance about various samples. Here, the following four items are shown as the shape of the groove 34 of the ground electrode 30.
(1) Parallel groove / tapered groove: the width of the groove 34 is parallel (FIG. 4) or tapered (FIG. 2) (2) one side / both sides: the groove 34 is formed on the side surfaces 31a, 31b of the ground electrode 30 (3) Cross section inclination presence / absence: Whether or not the bottom face 34m of the groove 34 is inclined in the cross section of the groove 34 (FIG. 2B) (4) Center Line direction: Whether or not the center line (third imaginary straight line Lab) of the width of the groove 34 passes through a range in the direction of the axis O of the spark gap SG (FIG. 2C).

The sample S01 is a sample of the comparative example shown in FIG. 4, and one parallel groove is formed only on one of the side surfaces 31a and 31b of the ground electrode 30. Samples S11 to S14 are samples of the example. Of these, the last sample S14 has all the features of the groove 34 shown in FIG. As the dimensions of the sample S14, the following was used.
(A) The width Wout of the groove 34 on the outer surface 39 of the ground electrode 30 is 0.7 mm.
(B) The width Win of the groove 34 on the inner surface 33 of the ground electrode 30 is 0.3 mm.
(C) Depth Dout of groove 34 in outer surface 39 of ground electrode 30: 0.2 mm
(D) Inclination angle θ of the bottom surface of the groove 34: 10 °

  The sample S13 is different from the sample S14 in that the third virtual straight line Lab passes outside the range of the spark gap SG, and other features are the same as the sample S14. In the sample S12, the depth of the groove 34 is made constant by eliminating the inclination of the bottom surface 34m of the groove 34 from the sample S13. In the sample S11, the groove 34 is further formed on only one of the side surfaces 31a and 31b of the ground electrode 30 from the sample S12.

Using these samples S01 and S11 to S14, an ignition performance test was performed. The test conditions for this ignition performance test are as follows.
(A) Engine specifications: Inline 4 cylinder, displacement 1.5L, DOHC, natural intake, intake port improvement (configured to generate tumble)
(B) Engine operating conditions: The fuel injection amount was adjusted and the air-fuel ratio A / F in the combustion chamber was made leaner at a rotational speed of 1600 rpm and NMEP (average illustrated effective pressure) of 340 kPa.

Under these test conditions, the variation of NMEP in 1000 cycles was measured. In general, when ignition is stable, NMEP does not fluctuate, and a large NMEP means that ignition is unstable. Therefore, the air-fuel ratio A / F at which the fluctuation of NMEP in 1000 cycles is 5% is judged as the lean limit value, and the ignition performance is evaluated. The ignition performance shown in the rightmost column of Table 1 is the performance evaluated as follows according to the difference from the lean limit values of the other samples S11 to S14 on the basis of the lean limit value of the sample S01.
*: Lean limit value improved by 0 to +0.25 with respect to the standard.
★★: Lean limit value improved by +0.26 to +0.50 with respect to the standard.
★★★: Lean limit value improved by +0.51 to +0.75 relative to the standard.
★★★★: Lean limit value improved by +0.76 to +1.00 with respect to the standard.

  As shown in Table 1, the best ignition performance was obtained with the sample S14 having all the shape characteristics of the groove 34 described in FIG. Further, although the other samples S11 to S13 as examples had slightly lower ignition performance than the sample S14, better ignition performance was obtained compared to the sample S01 as a comparative example. Therefore, it was confirmed that all the four items of the groove shape of the ground electrode 30 shown in Table 1 have the effect of improving the ignition performance.

Modification Examples The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the scope of the invention.

・ Modification 1:
As the spark plug, spark plugs having various configurations other than those shown in FIG. 1 can be applied to the present invention. In particular, various modifications can be made to the specific shapes of the terminal fitting and the insulator.

DESCRIPTION OF SYMBOLS 10 ... Insulator 12 ... Tip of insulator 20 ... Center electrode 22 ... Precious metal tip of center electrode 30 ... Ground electrode 3Oo ... Center line of ground electrode 31a ... First side surface 31b of ground electrode ... Second side surface of ground electrode 32 ... Noble metal tip of ground electrode 32op ... opposing portion 33 ... inner surface 34 of ground electrode ... groove 34i ... center of width on inner surface side of groove 34m ... bottom surface of groove 34o ... center of width on outer surface side of groove 35 ... base end portion 36 ... Bending part 37 ... tip part 38 ... ground electrode base material 39 ... outer surface of ground electrode 40 ... terminal metal fitting 50 ... metal shell 52 ... metal metal tip 54 ... screw part of metal shell 100 ... spark plug O ... axis X ... 1st virtual straight line Y ... 2nd virtual straight line SG ... Spark gap Lab ... 3rd virtual straight line

Claims (5)

A cylindrical insulator having an axial hole extending in the direction of the axis, a center electrode held inside the insulator so that its tip protrudes from the tip of the shaft hole, and a main body that houses the insulator In a spark plug having a metal fitting, and a ground electrode whose base end is joined to the tip of the metal shell, and the tip is opposed to the tip surface of the center electrode,
The ground electrode includes an inner surface having a facing portion facing the front end surface of the center electrode, a first side surface and a second side surface adjacent to the inner surface and extending from the front end portion to the base end portion, and opposite to the inner surface. An outer surface extending from the distal end portion to the proximal end portion.
A range in the direction of the axis between the first imaginary straight line passing through the tip of the insulator and perpendicular to the axis and the second imaginary straight line passing through the facing portion of the ground electrode and perpendicular to the axis. Inside, a concave groove extending from the outer surface side to the inner surface side of the ground electrode is formed in at least one of the first side surface and the second side surface,
The spark plug is characterized in that a width of the groove measured along the direction of the axis is gradually narrowed from the outer surface side to the inner surface side of the ground electrode. The spark plug according to claim 1, wherein
The spark plug is characterized in that the groove is formed in both the first side surface and the second side surface. The spark plug according to claim 1 or 2,
The spark plug is characterized in that the depth of the groove increases as it approaches the inner surface side from the outer surface side of the ground electrode. In the spark plug according to any one of claims 1 to 3,
The groove has a third imaginary straight line connecting the center of the first width of the groove on the outer surface of the ground electrode and the center of the second width of the groove on the inner surface of the ground electrode, A spark plug formed so as to pass through a range in a direction of the axis line between a front end surface of a center electrode and the facing portion of the ground electrode. The spark plug according to claim 4, wherein
The groove is formed by projecting the third imaginary straight line, the front end surface of the center electrode, and the facing portion of the ground electrode along the direction of the axis. A spark plug characterized by being formed so as to pass through a range in which a front end surface and the facing portion of the ground electrode overlap each other.

Images