JP7203786B2 - Spark plug - Google Patents

Description

TECHNICAL FIELD The present invention relates to a spark plug, and more particularly to a technique for fixing a center electrode to an insulator with a sealing material.

As a technique for fixing the center electrode of a spark plug to an insulator, Patent Document 1 discloses that a recess is provided in the rear end surface of the head of the center electrode, and the head is fixed to the insulator with a sealing material that seals the shaft hole. Techniques are disclosed. In the technique disclosed in Patent Document 1, the fixing strength of the center electrode is ensured by mechanical bonding (anchor effect) of the sealing material that has entered the recess.

Japanese Patent Application Laid-Open No. 2017-183105

However, in the above technique, the narrower the head of the center electrode, the smaller the recess, so the anchoring effect of the sealing material is poor and the fixing strength is reduced. That is, there is a problem that the fixing strength of the center electrode depends greatly on the thickness of the head.

SUMMARY OF THE INVENTION An object of the present invention is to solve this problem and to provide a spark plug in which the fixing strength of the center electrode is less dependent on the thickness of the head.

In order to achieve this object, the spark plug of the present invention comprises a first face extending in the axial direction, a stepped portion connected to the tip end side of the first face, and a second face connected to the tip end side of the stepped portion and having a diameter smaller than that of the first face. a cylindrical insulator having an inner peripheral surface including two surfaces; a head having a tip end surface in contact with the stepped portion and disposed inside the first surface; and being connected to the head and inside the second surface and a sealing material in contact with the inner peripheral surface and the head, the head having a side surface connected to the rear end side of the tip surface and a rear end side of the side surface A hole extending from the rear end surface to the side surface is formed, and the sealing material enters the hole.

According to the spark plug of claim 1, the head of the center electrode is formed with a hole penetrating from the rear end surface to the side surface of the head, and the sealing material enters the hole. Even if the head is thin, the anchor effect of the sealing material can be ensured by ensuring the length of the hole, so it is possible to reduce the dependency of the fixing strength of the center electrode on the thickness of the head.

According to the spark plug of claim 2, since a plurality of openings of the hole are formed on the side surface of the head, the surface area of the hole can be increased. Therefore, in addition to the effects of claim 1, the fixing strength of the center electrode can be increased.

According to the spark plug of claim 3, since the cross-sectional shape of the hole perpendicular to the extending direction of the hole is circular or elliptical, the hole can be filled with the sealing material without gaps. Therefore, in addition to the effect of claim 1 or 2, the fixing strength of the center electrode can be further increased.

1 is a half sectional view of a spark plug in a first embodiment; FIG. FIG. 2 is a partial cross-sectional view of the spark plug, enlarging the portion indicated by II in FIG. 1; 4 is a perspective view of a center electrode; FIG. FIG. 5 is a partial cross-sectional view of a spark plug in a second embodiment; 5 is a cross-sectional view of the spark plug taken along line VV of FIG. 4; FIG. FIG. 11 is a partial cross-sectional view of a spark plug in a third embodiment;

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a half sectional view of the spark plug 10 of the first embodiment taken along the axis O. As shown in FIG. In FIG. 1, the lower side of the page is referred to as the front end side of the spark plug 10, and the upper side of the page is referred to as the rear end side of the spark plug 10 (the same applies to FIGS. 2, 3, 4 and 6). As shown in FIG. 1, the spark plug 10 includes an insulator 11, a center electrode 20 and a sealing material 40. As shown in FIG.

The insulator 11 is made of alumina or the like, which has excellent mechanical properties and insulating properties at high temperatures. The insulator 11 has a substantially cylindrical shape in which a shaft hole 12 passing through the insulator 11 along the axis O is formed. A cross section of the shaft hole 12 perpendicular to the axis O is circular. A center electrode 20 is arranged on the tip side of the shaft hole 12 of the insulator 11 .

The center electrode 20 is a rod-shaped member extending along the axis O. As shown in FIG. The tip of the center electrode 20 is exposed through the axial hole 12 . The center electrode 20 is fixed to the insulator 11 with a sealing material 40 . The sealing material 40 is conductive and seals the shaft hole 12 . The sealing material 40 is formed by dispersing conductive powder such as Cu or Fe in glass. As the glass, for example, B ₂ O ₃ --SiO ₂ system, BaO--B ₂ O ₃ system, SiO ₂ --B ₂ O ₃ --CaO--BaO system, etc. can be employed.

Resistor 41 is a member for suppressing radio noise generated during discharge, and is arranged on the rear end side of sealing material 40 . The resistor 41 absorbs frequency band components that cause radio noise in the discharge current.

The connector 42 is conductive and arranged on the rear end side of the resistor 41 . The connection body 42 is formed by dispersing conductive powder such as Cu or Fe in glass. As the glass, for example, B ₂ O ₃ --SiO ₂ system, BaO--B ₂ O ₃ system, SiO ₂ --B ₂ O ₃ --CaO--BaO system, etc. can be employed.

The terminal fitting 43 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is made of a conductive metal material (for example, low carbon steel). The terminal fitting 43 is fixed to the rear end of the insulator 11 in a state in which the tip side thereof is inserted into the shaft hole 12 . At least the tip surface of the terminal fitting 43 is in contact with the connector 42 within the shaft hole 12 . The terminal fitting 43 is electrically connected to the center electrode 20 inside the shaft hole 12 via the sealing material 40 , the resistor 41 and the connector 42 .

The metal shell 44 is a substantially cylindrical member made of a conductive metal material (for example, low-carbon steel). The metal shell 44 holds the front end side portion of the insulator 11 from the outer peripheral side of the insulator 11 . A portion of the center electrode 20 , the entire resistor 41 , and a portion of the terminal fitting 43 are arranged inside the metal shell 44 with the insulator 11 interposed therebetween. The ground electrode 45 is a rod-shaped metal (for example, nickel-based alloy) member that is joined to the metal shell 44 . The tip of the ground electrode 45 axially faces the center electrode 20 with the spark gap therebetween.

FIG. 2 is a partial cross-sectional view including the axis O of the spark plug 10 in which the portion indicated by II in FIG. 1 is enlarged. The inner peripheral surface 13 formed by the shaft hole 12 of the insulator 11 includes a first surface 14 extending in the axial direction, a stepped portion 15 connected to the tip side of the first surface 14, and a second surface connected to the tip side of the stepped portion 15. 16 and. The diameter of the second surface 16 is smaller than the diameter of the first surface 14 . The stepped portion 15 has a conical surface or a spherical band, and the diameter decreases toward the tip side. In the center electrode 20, a core material 21 containing copper or copper as a main component is covered with a base material 22 made of nickel or a nickel-based alloy. It is possible to omit the core material 21 .

FIG. 3 is a perspective view of the center electrode 20. FIG. 3, illustration of part of the shaft portion 23 of the center electrode 20 is omitted. The center electrode 20 includes a substantially cylindrical shaft portion 23 and a substantially cylindrical head portion 24 connected to the rear end side of the shaft portion 23 . Head 24 is thicker than shaft 23 .

The head 24 has a tip surface 25 in contact with the stepped portion 15 and is arranged inside the first surface 14 of the insulator 11 . The shaft portion 23 is arranged inside the second surface 16 of the insulator 11 . A side surface 26 of the head 24 connects the front end surface 25 and the rear end surface 27 . The rear end surface 27 is a substantially flat surface. In this embodiment, the diameter of side surface 26 of head 24 is slightly smaller than the diameter of first surface 14 of insulator 11 . Therefore, the gap between the first surface 14 and the side surface 26 of the head 24 is extremely small.

The head portion 24 is formed with holes 28 and 31 penetrating from the rear end surface 27 of the head portion 24 to the side surface 26 . The sealing material 40 is embedded in the holes 28,31. The hole 28 is provided on the axis O from the rear end surface 27 of the head 24 toward the tip side. The opening 29 of the hole 28 is formed in the rear end face 27 and the bottom 30 of the hole 28 is provided in the head 24 . The cross-section of the hole 28 perpendicular to the axial direction through which the hole 28 extends is circular. Holes 28 and 31 intersect. A plurality of (two in this embodiment) openings 32 of the hole 31 are formed in the side surface 26 . A cross section of the hole 31 perpendicular to the direction in which the hole 31 extends is circular.

Note that the number of openings 32 on the side surface 26 is not limited to two. Of course, it is possible to provide three or more openings 32 connected to the holes 28 in the side surface 26 as long as the strength of the head 24 can be ensured.

The spark plug 10 is manufactured by, for example, the following method. First, holes 28 and 31 are made in the head 24 of the center electrode 20 . Examples of processing means for forming the holes 28 and 31 in the head 24 include cutting using a drill or the like, shearing processing using a punch or the like, and drilling using laser light irradiation, water jet, or the like.

After inserting the center electrode 20 with the holes 28 and 31 into the shaft hole 12 of the insulator 11 , the raw material powder of the sealing material 40 is put into the shaft hole 12 and filled around the head 24 of the center electrode 20 . Next, after filling the raw material powder of the resistor 41 into the axial hole 12 , the raw material powder of the connector 42 is filled into the axial hole 12 . After inserting the terminal fitting 43 into the shaft hole 12 , while heating the insulator 11 , the terminal fitting 43 is used to axially compress the raw material powders of the connector 42 , the resistor 41 and the sealing material 40 . This pushes the sealing material 40 through the opening 29 into the holes 28 and 31 . Next, after the metal shell 44 to which the ground electrode 45 is connected in advance is assembled to the insulator 11, the ground electrode 45 is bent to obtain the spark plug 10. As shown in FIG.

Since the sealing material 40 is inserted into the holes 28 and 31 penetrating from the rear end surface 27 of the head 24 of the center electrode 20 to the side surface 26, the length of the holes 28 and 31 is ensured even if the head 24 is thin. Therefore, the anchor effect of the sealing material 40 can be ensured. Therefore, the degree of dependence of the fixing strength of the center electrode 20 by the sealing material 40 on the thickness of the head portion 24 can be reduced. As a result, even if the head portion 24 of the center electrode 20 is made thinner as the diameter of the spark plug 10 is reduced, the contact area of the seal member 40 can be secured, and the fixing strength of the center electrode 20 can be secured.

Since the center electrode 20 has a plurality of openings 32 of the holes 31 formed on the side surface 26 of the head 24, the surface area of the hole 31 can be increased compared to the case where the side surface 26 has one opening. Therefore, the fixing strength of the center electrode 20 can be increased.

Since the cross-sectional shape of the holes 28 and 31 perpendicular to the direction in which the holes 28 and 31 of the head 24 extend is circular, the corners or corners where two surfaces intersect are the corners of the holes 28 and 31 except for the portions where the holes 28 and 31 intersect. It can be made not to exist inside. Therefore, the openings 29 and 32 of the holes 28 and 31 can be filled with the sealing material 40 without gaps. Since the contact area of the sealing material 40 with the holes 28 and 31 can be increased, the cross-sectional area of the sealing material 40 can be ensured. Therefore, the fixing strength of the center electrode 20 can be further increased.

In addition, since the opening 29 is provided in the rear end surface 27 of the head 24, the holes 28 and 31 can be easily filled with the sealing material 40 compared to the structure in which the opening is formed only in the side surface 26 of the head 24. be able to.

_When the area of the rear end surface 27 of the head portion 24 is S1 and the area of the opening 29 formed in the rear end surface 27 is _S2 , the _{opening satisfies 0.3S1≤S2≤0.6S1} . Setting the area _S2 of the head 29 is preferable because the strength of the head 24 is easily ensured.

The opening 32 of the hole 31 is formed on the side surface 26 of the head 24 but does not open on the tip surface 25 of the head 24, so that the stepped portion 15 of the insulator 11 and the tip surface 25 of the head 24 are not open. can reduce the amount of sealing material 40 supplied between . As a result, the distal end face 25 of the head 24 is maintained in close contact with the stepped portion 15 of the insulator 11, so that variations in the amount of projection of the shaft portion 23 of the center electrode 20 from the distal end of the insulator 11 are reduced. can.

Holes 28 and 31 are formed in the head 24 of the center electrode 20 to increase the contact area of the sealing material 40 with the head 24, so that the gap between the first surface 14 of the insulator 11 and the side surface 26 of the head 24 can be increased. It is not necessary to increase the surface area of the side surface 26 of the head 24 with which the sealing material 40 contacts by increasing the size or lengthening the axial length of the side surface 26 of the head 24 . Since it is not necessary to increase the gap between the first surface 14 of the insulator 11 and the side surface 26 of the head 24, the diameter of the first surface 14 of the insulator 11 can be reduced. As a result, the radial distance between the head 24/sealing material 40 and the metal shell 44 can be increased, so that the parasitic capacitance between the head 24/sealing material 40 and the metal shell 44 can be reduced.

Moreover, since the length of the side surface 26 of the head 24 in the axial direction does not need to be increased, the length of the head 24 in the axial direction can be shortened. As a result, the distance in the axial direction from the boundary between the first surface 14 of the insulator 11 and the stepped portion 15 to the rear end of the sealing member 40 can be shortened. As a result, the parasitic capacitance between the head 24 and the sealing material 40 and the metal shell 44 can be reduced.

When the parasitic capacitance between the head 24/sealing material 40 and the metal shell 44 is reduced, the amount of charge stored in the parasitic capacitance is reduced when a voltage is applied between the terminal metal fitting 43 and the metal shell 44. can. Therefore, when the insulation between the center electrode 20 and the ground electrode 45 is broken, the wear of the center electrode 20 and the ground electrode 45 caused by the charge stored in the parasitic capacitance flowing into the spark gap can be reduced. Therefore, the wear resistance of the center electrode 20 and the ground electrode 45 can be improved while securing the fixing strength of the center electrode 20 .

A second embodiment will be described with reference to FIGS. 4 and 5. FIG. In the first embodiment, one opening 29 of the hole 28 is provided on the rear end surface 27 of the head 24, the hole 28 branches in the head 24, and a plurality of openings 32 of the holes 31 are provided on the side surface 26. Electrode 20 has been described. In contrast, in the second embodiment, a center electrode 50 in which a plurality of openings 52 of holes 51 are provided on the rear end surface 27 of the head 24 and a plurality of openings 53 of the holes 51 are provided on the side surface 26 will be described. The same reference numerals are given to the same parts as those described in the first embodiment, and the following description is omitted.

FIG. 4 is a partial cross-sectional view of a spark plug according to the second embodiment. 5 is a cross-sectional view of the spark plug taken along line VV of FIG. 4. FIG. The center electrode 50 is arranged in place of the center electrode 20 of the spark plug 10 in the first embodiment. As in FIG. 2, FIG. 4 illustrates the portion indicated by II in FIG. 1 (the same applies to FIG. 6).

A head portion 24 of the center electrode 50 is formed with a plurality of (two in this embodiment) holes 51 penetrating from the rear end surface 27 to the side surface 26 of the head portion 24 . Sealing material 40 enters hole 51 . The hole 51 is obliquely provided from the rear end surface 27 of the head 24 toward the side surface 26 . Two openings 52 of the hole 51 are formed on the rear end surface 27 and two openings 53 of the hole 51 are formed on the side surface 26 . The shape of the opening 52 of the hole 51 is elliptical (see FIG. 5). A cross section of the hole 51 perpendicular to the direction in which the hole 51 extends is circular.

Note that the number of holes 51 provided in the head 24 is not limited to two. Of course, it is possible to provide three or more holes 51 within a range in which the strength of the head 24 can be ensured. The holes 51 may cross each other. The lengths of the plurality of holes 51 may be the same or different. _When the area of the rear end surface 27 of the head portion 24 is S1 and the _total area of the plurality of openings 52 formed in the rear end surface 27 is _S2 , _{0.3S1≤S2≤0.6S} . If the area _S2 of the opening 52 is set so as to satisfy ₁ , the strength of the head 24 can be easily ensured, which is preferable. According to the spark plug of the second embodiment, it is possible to achieve the same effects as those of the first embodiment.

A third embodiment will be described with reference to FIG. In the first embodiment and the second embodiment, the cases where the thicknesses of the head portions 24 of the center electrodes 20 and 50 are substantially the same in the axial direction have been described. On the other hand, in the third embodiment, the head portion 61 of the center electrode 60 includes a first portion 62 and a second portion 63 having different thicknesses. The same reference numerals are given to the same parts as those described in the first embodiment, and the following description is omitted.

FIG. 6 is a partial cross-sectional view of a spark plug according to the third embodiment. The center electrode 60 is arranged in place of the center electrode 20 of the spark plug 10 in the first embodiment.

A head portion 61 of the center electrode 60 includes a substantially cylindrical first portion 62 having the distal end surface 25 and a substantially cylindrical second portion 63 connected to the rear end side of the first portion 62 . A side surface 64 of the head portion 61 connects the distal end surface 25 and the rear end surface 65 of the second portion 63 . The rear end surface 65 is a substantially flat surface. The second portion 63 is narrower than the first portion 62 . As a result, the gap between the side surface 64 of the head 61 and the first surface 14 of the insulator 11 is wider in the second portion 63 than in the first portion 62 .

The head 61 is formed with holes 66 and 69 extending from the rear end surface 65 of the second portion 63 to the side surface 64 . Sealing material 40 enters holes 66 and 69 . The hole 66 is provided at a position offset from the axis O from the rear end surface 65 of the second portion 63 toward the tip side. An opening 67 of hole 66 is formed in rear end face 65 and a bottom 68 of hole 66 is provided in head 61 . A cross section of the hole 66 perpendicular to the direction in which the hole 66 extends is circular. _When the area of the rear end surface 65 of the _second portion 63 is S1 and the area of the opening 67 formed in the rear end surface 65 is _S2 , _{0.3S1≤S2≤0.6S1} is _satisfied . It is preferable to set the area S2 of the opening 67 in such a manner that the strength of the _second portion 63 is easily ensured.

Holes 66 and 69 intersect. One opening 70 of the hole 69 is formed on the side surface of the second portion 63 among the side surfaces 64 . A cross section of the hole 69 perpendicular to the direction in which the hole 69 extends is circular. According to the third embodiment, among the functions and effects of the first embodiment, functions and effects other than those obtained by forming a plurality of hole openings in the side surface 64 of the head portion 61 can be realized.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above-described embodiments, and it is easily understood that various modifications and improvements are possible without departing from the scope of the present invention. It can be inferred. For example, the shapes and sizes of the center electrodes 20, 50, 60 and the holes 28, 31, 51, 66, 69 are examples and can be set as appropriate. The positions and numbers of the holes 28, 31, 51, 66, 69 provided in the heads 24, 61 are also examples, and can be set as appropriate.

In the embodiment, the hole 28, 31, 51, 66, 69 formed in the head 24, 61 is entirely filled with the sealing material 40, but it is not necessarily limited to this. Naturally, voids not filled with sealing material 40 may exist in holes 28 , 31 , 51 , 66 , 69 .

Although the embodiments describe the case where the rear end surfaces 27, 65 of the heads 24, 61 are substantially flat surfaces, the present invention is not necessarily limited to this. Of course, it is possible to provide recesses in the rear end surfaces 27 and 65 . Of course, it is possible to connect the holes 28, 51, 66 to the recesses.

In the embodiment, the case where the cross-sectional shape of the holes 28, 31, 51, 66, 69 perpendicular to the extending direction of the holes 28, 31, 51, 66, 69 provided in the heads 24, 61 is circular has been described. , but not necessarily limited to this. By performing shearing processing using a punch, the cross-sectional shape of the hole can be made into an arbitrary shape such as a polygon or an ellipse according to the cross-sectional shape of the punch. Even when the cross-sectional shape of the hole is elliptical, the hole can be filled with the sealing material 40 without gaps because the hole can be filled with no corners or corners where two surfaces intersect.

In the embodiment, the case where the corners (openings 29, 32, 52, 67, 70) formed by the intersection of the side surfaces 26, 64 of the heads 24, 61 and the holes 28, 31, 51, 66, 69 are angular will be described. However, it is not necessarily limited to this. Of course, it is possible to round or chamfer the corners.

In the embodiment, the case where the sealing material 40 is electrically connected to the terminal metal fitting 43 through the resistor 41 and the connector 42 has been described, but the present invention is not necessarily limited to this. Of course, it is possible to omit the resistor 41 and the connector 42 and connect the sealing member 40 to the terminal fitting 43 .

In the embodiments, spark plugs are described in which sparks generated by sparks between the center electrodes 20, 50, 60 and the ground electrode 45 grow to ignite the air-fuel mixture in the combustion chamber, but the present invention is not necessarily limited to this. Absent. It is of course possible to employ the center electrodes 20, 50, 60 in other spark plugs. Other spark plugs include, for example, spark plugs having a center electrode and a ground electrode located within the prechamber.

In the first and second embodiments, the case where the sealing material 40 is hardly present between the first surface 14 of the insulator 11 and the side surface 26 of the head 24 has been described, but the present invention is not necessarily limited to this. Absent. It is naturally possible to provide a gap into which the sealing material 40 can enter between the first surface 14 of the insulator 11 and the side surface 26 of the head 24 . As a result, the contact area of the sealing material 40 with the head 24 is increased by the amount of the sealing material 40 entering between the first surface 14 of the insulator 11 and the side surface 26 of the head 24, so that the head 24 is fixed. Can increase strength.

In the first embodiment, the case where the hole 28 is provided along the axis O of the head 24 has been described, but this is not necessarily the case. It is of course possible to provide the hole 28 at a position substantially parallel to the axis O, to provide the hole 28 so that the axis O obliquely intersects, or to provide the hole 28 so that the axis O is at a twisted position. . Moreover, it is of course possible to provide two or more holes 28 .

In the first embodiment, the hole 31 that intersects the hole 28 is provided substantially perpendicular to the axis O, but the present invention is not necessarily limited to this. It is of course possible to provide the hole 31 so that the axis O intersects obliquely, or to provide the hole 31 so that the axis O is at a twisted position. Moreover, it is naturally possible to make the opening 32 of the hole 31 formed in the side surface 26 of the head 24 one.

In the second embodiment, the case where the head 24 is provided with two holes 51 has been described, but the present invention is not necessarily limited to this. Of course, it is possible to omit one of the two holes 51 .

In the third embodiment, the case where the sealing material 40 hardly exists between the first surface 14 of the insulator 11 and the side surface 64 of the first portion 62 of the head portion 61 has been described, but it is not necessarily limited to this. Absent. It is naturally possible to provide a gap into which the sealing material 40 can enter between the first surface 14 of the insulator 11 and the first portion 62 of the head portion 61 . As a result, the contact area of the sealing material 40 with the head 61 is increased by the amount that the sealing material 40 enters between the first surface 14 of the insulator 11 and the first portion 62 , so the fixing strength of the head 61 is increased. can be high

In the third embodiment, the case where the opening 70 of the hole 69 provided in the head portion 61 is formed in the second portion 63 has been described, but the present invention is not necessarily limited to this. It is of course possible to form the opening 70 of the hole 69 in the first part 62 . This is because the contact area between the seal member 40 and the head portion 61 (hole 69) can be ensured in this case as well.

Although the case where one opening 70 of the hole 69 is formed in the side surface 64 of the head 61 has been described in the third embodiment, it is not necessarily limited to this. It is of course possible to provide a plurality of openings 70 in side 64 of head 61 . For example, the first portion 62 may have a plurality of openings, the second portion 63 may have a plurality of openings, or the first portion 62 and the second portion 63 may each have openings.

10 spark plug 11 insulator 13 inner peripheral surface 14 first surface 15 step portion 16 second surface 20,50,60 center electrode 23 shaft portion 24,61 head portion 25 tip surface 26,64 side surface 27,65 rear end surface 28, 31, 51, 66, 69 hole 32, 53 opening 40 sealing material O axis

Claims (3)

It has an inner peripheral surface including a first surface extending in the axial direction, a stepped portion connected to the tip side of the first surface, and a second surface connected to the tip side of the stepped portion and having a diameter smaller than that of the first surface. a cylindrical insulator;
a center electrode having a head portion having a distal end surface in contact with the stepped portion and arranged inside the first surface; and a shaft portion connected to the head portion arranged inside the second surface;
A spark plug comprising a sealing material in contact with the inner peripheral surface and the head,
The head has a side surface connected to the rear end side of the front end surface and a rear end surface connected to the rear end side of the side surface, and a hole penetrating from the rear end surface to the side surface is formed,
A spark plug in which the sealing material is inserted into the hole. 2. The spark plug according to claim 1, wherein a plurality of openings of said hole are formed in said side surface. 3. The spark plug according to claim 1, wherein a cross-sectional shape of said hole perpendicular to the extending direction of said hole is circular or elliptical.

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