JP6344966B2 - Spark plug for internal combustion engine - Google Patents

Description

  The present invention relates to a spark plug for an internal combustion engine.

  In an internal combustion engine such as an automobile, a spark plug is used as an ignition means. The spark plug includes an insulator that inserts and holds the center electrode inward, a housing that inserts and holds the tip side of the insulator inward, and a ground electrode that is joined to the housing and forms a spark discharge gap. have. The spark plug applies a high voltage from the ignition coil to break the insulation of the spark discharge gap and generate a discharge spark between the center electrode and the ground electrode.

  When the temperature of the spark plug becomes too high, preignition (premature ignition) occurs, and the center electrode and the ground electrode are easily consumed. An example of a spark plug that suppresses pre-ignition and improves wear resistance is disclosed in Patent Document 1. The spark plug of Patent Document 1 includes a ground electrode having an outer layer made of a metal such as a nickel alloy and an inner layer made of a copper alloy provided inside the outer layer. By forming the inner layer with a copper alloy having high thermal conductivity, the heat of the ground electrode can be efficiently transmitted to the housing, and the temperature rise at the ground electrode can be suppressed.

JP2013-120701A

However, the spark plug disclosed in Patent Document 1 has the following problems.
As described above, the spark plug of Patent Document 1 can improve the wear resistance of the ground electrode by suppressing the temperature rise of the ground electrode. On the other hand, when the internal combustion engine is cold or during low load operation, the temperature of the ground electrode hardly rises. For this reason, the ignition performance of the spark plug may be reduced.

  The present invention has been made in view of such a background, and intends to provide a spark plug for an internal combustion engine that can suppress the temperature rise of the ground electrode at a high temperature and can quickly raise the temperature of the ground electrode at a low temperature. Is.

One embodiment of the present invention includes a center electrode;
An insulator for inserting and holding the center electrode inside;
A housing that inserts and holds the insulator inside while exposing a part of the base end side of the insulator;
A grounding electrode joined to the housing and forming a spark discharge gap with the central electrode;
The ground electrode includes a core part extending from the housing, and a bottomed cylindrical surface layer including an insertion hole made of a material having a smaller linear expansion coefficient than the core part and through which the core part is inserted and disposed. And
A tip side gap is formed between the tip of the core member and the bottom of the insertion hole in the surface layer ,
In the radial direction orthogonal to the axial direction in the core part, a radial gap is formed between the core part and the surface layer part,
At least one positioning portion protruding in the radial direction of the core material portion is formed on the outer peripheral surface of the core material portion, and the size of the partial gap between the positioning portion and the insertion hole in the surface layer portion is large. The length S3 is the spark plug for an internal combustion engine, which is smaller than the size S2 of the radial clearance .

  The ground electrode of the spark plug for an internal combustion engine (hereinafter referred to as a spark plug as appropriate) is made of the core material portion and a material having a smaller linear expansion coefficient than the core material portion, and the core material portion is inserted therethrough. And a bottomed cylindrical surface layer portion having an insertion hole. Furthermore, a front end-side gap is formed between the front end of the core member and the bottom of the insertion hole in the surface layer. Therefore, when the temperature of the spark plug is low, the ground electrode can be quickly heated, and when the temperature of the spark plug is high, the temperature rise of the ground electrode can be suppressed.

  That is, when the temperature of the spark plug is low, the tip side gap is formed inside the ground electrode. Therefore, in the range where the tip side clearance in the ground electrode is formed, the insertion hole is formed and only the hollow surface layer portion becomes a heat transfer path. Therefore, the thermal resistance of the ground electrode is increased, and the amount of heat radiated from the ground electrode to the housing is reduced. Thereby, the temperature of the ground electrode can be quickly raised, and the ignition performance of the spark plug can be improved.

  Further, when the temperature of the spark plug rises, the core portion and the surface layer portion constituting the ground electrode linearly expand. At this time, since the linear expansion coefficient of the material forming the core material portion is larger than the linear expansion coefficient of the material forming the surface layer portion, the core material portion linearly expands more than the surface layer portion, and the core The tip of the material part comes into contact with the bottom part of the insertion hole. Thus, when the said front end side clearance gap is block | closed with the said core material part, both the said core material part and the said surface layer part can be utilized as a heat-transfer path | route. Accordingly, the thermal resistance of the ground electrode is reduced, and the amount of heat transferred from the ground electrode to the housing can be increased. Thereby, the temperature rise of the ground electrode can be suppressed, the occurrence of pre-ignition can be prevented, and the wear resistance of the ground electrode can be improved.

  As described above, according to the spark plug for an internal combustion engine, the temperature rise of the ground electrode can be suppressed at a high temperature, and the temperature of the ground electrode can be quickly raised at a low temperature.

FIG. 3 is a partial cross-sectional view showing a spark plug in the first embodiment. The elements on larger scale in FIG. 2 is a partial cross-sectional view showing a ground electrode at a low temperature in Example 1. FIG. 2 is a partial cross-sectional view showing a ground electrode at a high temperature in Example 1. FIG. The graph which shows the temperature change of the ground electrode in a confirmation test. FIG. 6 is a partial cross-sectional view showing a spark plug in Example 2. FIG. 6 is a partial cross-sectional view of a ground electrode in Example 2. The fragmentary sectional view which shows the spark plug in a reference example . The fragmentary sectional view of the ground electrode in a reference example .

  The insertion length of the core member into the insertion hole is L, the linear expansion coefficient of the surface layer is a, the linear expansion coefficient of the core is b, and the temperature of the ground electrode before the operation of the internal combustion engine is assumed. When the temperature difference between the reference temperature t0 and the set temperature t1 assuming the temperature of the ground electrode during operation of the internal combustion engine is Δt, the size S1 of the tip side clearance is S1 = L × {(1 + b × Δt ) / (1 + a × Δt) −1}. In this case, when the ground electrode is heated up to the set temperature (t1), the distal end surface of the core member comes into contact with the bottom of the insertion hole of the surface layer portion, and the distal end side gap is filled. As a result, the ground electrode is quickly heated up until the ground electrode reaches the set temperature, and when the ground electrode is heated above the set temperature, the thermal conductivity of the ground electrode is improved. In addition, the temperature rise of the ground electrode can be suppressed. That is, at the start of operation of the internal combustion engine, the ground electrode can be quickly heated to improve the ignitability of the ground electrode. Further, it is possible to prevent the temperature of the ground electrode from becoming too high during operation of the internal combustion engine, and to effectively improve the wear resistance of the ground electrode.

Further, in the radial direction perpendicular to the axial direction of the core part, it is between the core part and the surface layer portion, the radial gap that is formed. When the temperature of the ground electrode is low, the radial gap is formed, so that the contact area between the core portion and the surface layer portion is smaller than when the radial gap is not formed. Therefore, the thermal resistance between the core member and the surface layer can be increased. Therefore, the amount of heat transferred from the surface layer portion to the core material portion is reduced. Thereby, the temperature of the ground electrode can be raised more quickly. Further, when the temperature of the spark plug rises, the core material portion expands and the radial gap is filled. As a result, the contact area between the core member and the surface layer can be increased, and the amount of heat transferred from the ground electrode to the housing can be increased. Therefore, the temperature increase of the ground electrode can be suppressed more effectively.

  Further, the radial dimension of the core part is assumed to be W, the linear expansion coefficient of the surface layer part is assumed to be a, the linear expansion coefficient of the core part is assumed to be b, and the temperature of the ground electrode before the operation of the internal combustion engine is assumed. When the temperature difference between the reference temperature t0 and the set temperature t1 assuming the temperature of the ground electrode during operation of the internal combustion engine is Δt, the size S2 of the radial gap is S2 = W × {(1 + b × Δt ) / (1 + a × Δt) −1} / 2 is preferably satisfied. In this case, when the ground electrode is heated to the set temperature, the distal end surface of the core member abuts against the bottom of the insertion hole of the surface layer portion, and the radial gap is filled. As a result, the ground electrode is quickly heated up until the ground electrode reaches the set temperature, and when the ground electrode is heated above the set temperature, the thermal conductivity of the ground electrode is improved. In addition, the temperature rise of the ground electrode can be suppressed. That is, when the internal combustion engine is started, the temperature of the ground electrode can be quickly raised to further improve the ignitability of the ground electrode. In addition, it is possible to prevent the temperature of the ground electrode from becoming too high during operation of the internal combustion engine, and to more effectively improve the wear resistance of the ground electrode.

Example 1
Examples of the spark plug for the internal combustion engine will be described with reference to FIGS.
As shown in FIG. 1, the spark plug 1 for an internal combustion engine includes a center electrode 2, an insulator 3 through which the center electrode 2 is inserted and held, and a part of the base end side of the insulator 3 while exposing the insulator. And a ground electrode 11 which is joined to the housing 4 and forms a spark discharge gap G between the housing 4 and the center electrode 2. As shown in FIGS. 2 and 3, the ground electrode 11 includes a core part 12 extending from the housing 4 and a bottomed cylindrical surface layer part 13 having an insertion hole 14 through which the core part 12 is inserted. And have. A front end side gap S <b> 1 is formed between the front end portion of the core member 12 and the bottom portion 141 of the insertion hole 14 in the surface layer portion 13.

This will be described in more detail below.
As shown in FIG. 1, the spark plug 1 of this example is used for ignition of an air-fuel mixture in an internal combustion engine. In the axial direction of the spark plug 1, one end of the spark plug 1 is connected to an ignition coil (not shown), and the other end on the opposite side is arranged in a combustion chamber (not shown) of the internal combustion engine. In this example, the side connected to the ignition coil in the axial direction is referred to as the base end side, and the side disposed in the combustion chamber is referred to as the front end side.

  The spark plug 1 includes a cylindrical insulator 3, a cylindrical housing 4 that holds the insulator 3 inside, a center electrode 2 that is held inside the insulator 3 so that a tip portion protrudes, and a center A stem 5 disposed on the proximal end side of the electrode 2 and a ground electrode 11 connected to the housing 4 are provided.

The insulator 3 is formed of alumina in a substantially cylindrical shape, and is formed so as to hold the center electrode 2 and the stem 5 inside thereof.
The stem 5 has a stem body 51 inserted and held inside the insulator 3 and a terminal 52 exposed from the insulator 3 on the proximal end side of the stem body 51 and connected to the ignition coil.
A resistor 6 is disposed between the stem 5 and the center electrode 2. This register 6 is for suppressing ignition noise in the spark plug 1.

The center electrode 2 connected to the stem 5 via the resistor 6 has an electrode base material 21 and a center discharge tip 22 joined to the tip of the electrode base material 21.
The electrode base material 21 has an inner layer member made of a copper alloy and an outer layer member made of a nickel alloy and covering the inner layer member.
The center discharge chip 22 is joined to the tip of the electrode base material 21 so as to be exposed from the tip of the insulator 3. As the material of the center discharge chip 22, a noble metal such as iridium, platinum, rhodium or an alloy thereof is used. The center discharge chip 22 is not necessarily a noble metal, and may be a high melting point material made of tungsten, rhenium, tantalum, niobium, or an alloy thereof, for example.

  The housing 4 is formed in a substantially cylindrical shape, and the insulator 3 is inserted and held therein. The housing 4 exposes the proximal end side of the insulator 3 and covers the distal end side of the insulator 3. A screw thread for screwing with a cylinder head (not shown) of the internal combustion engine is formed on the outer peripheral side surface of the housing 4, and a ground electrode 11 is disposed on the front end surface of the housing 4.

As shown in FIGS. 2 and 3, the ground electrode 11 has a core member 12 extending from the housing 4 and a surface layer 13 covering the core member 12.
The core member 12 is formed in a straight quadrangular prism shape extending in the axial direction of the spark plug 1, and its base end is joined to the housing 4. The core material part 12 consists of copper alloys, and the magnitude | size b of the linear expansion coefficient is 16.8 * 10 < ^-6 > micrometer / m ( ^degreeC ). In addition, the magnitude | size b of a linear expansion coefficient is determined by the material which forms the core part 12, the temperature conditions of preset temperature, etc.

The surface layer portion 13 is formed in the same shape as the outer shape of the ground electrode 11, and the extending portion 132 extending from the housing 4 to the distal end side in the axial direction, and the facing portion disposed to face the distal end of the center electrode 2 133 and a bent portion 134 that connects the extended portion 132 and the facing portion 133 are formed. The surface layer portion 13 is made of a nickel alloy, and the linear expansion coefficient size a is 14 × 10 ⁻⁶ μm / m ° C. The magnitude a of the linear expansion coefficient is determined by the material forming the surface layer portion 13, the temperature condition of the set temperature, and the like.
The facing portion 133 is disposed so as to face the center electrode 2, and the ground electrode chip 111 is disposed coaxially with the center electrode 2. As a material of the ground electrode tip 111, a noble metal such as iridium, platinum, rhodium or an alloy thereof is used as the material of the center discharge tip 22. The center discharge chip 22 is not necessarily a noble metal, and may be a high melting point material made of tungsten, rhenium, tantalum, niobium, or an alloy thereof, for example. Further, a spark discharge gap G is formed between the ground electrode tip 111 and the center electrode 2.

  An insertion hole 14 for inserting the core member 12 is formed inside the extended portion 132. The insertion hole 14 is formed to be slightly larger than the core member 12 in the cross section orthogonal to the axial direction, and a radial clearance S2 is formed between the inner surface of the insertion hole 14 and the core member 12. Yes. Further, the total length in the axial direction of the insertion hole 14 is longer than the total length of the core member 12, and a front end side gap S <b> 1 is formed between the front end of the core member 12 and the bottom 141 of the insertion hole 14. Is formed.

In this example, the insertion length of the core member 12 into the insertion hole 14 is L, the radial dimension of the core member 12 is W, the linear expansion coefficient of the surface layer 13 is a, and the linear expansion coefficient of the core member 12 is b. Let Δt be the temperature difference between the reference temperature t0 and the set temperature t1. The reference temperature t0 is a temperature that assumes the temperature of the ground electrode 11 before the operation of the internal combustion engine, and is set to about 15 ° C to 25 ° C. The set temperature t1 is a temperature that assumes the temperature of the ground electrode 11 during operation of the internal combustion engine, and is set to about 450 to 800 ° C. In this example, the linear expansion coefficient of the surface layer portion 13 is a = 14 × 10 ⁻⁶ μm / m ° C., and the linear expansion coefficient of the core material portion 12 is b = 16.8 × 10 ⁻⁶ μm / m ° C. It is. The reference temperature was t0 = 25 ° C., and the set temperature was t1 = 650 ° C. The magnitude | size of front end side clearance gap S1 is calculated | required so that the relationship of S1 = Lx {(1 + bx (DELTA) t) / (1 + ax (DELTA) t) -1} may be satisfy | filled. Further, the size of the radial dimension S2 is determined so as to satisfy the relationship of S2 = W × {(1 + b × Δt) / (1 + a × Δt) −1} / 2.

Next, the effect of this example is demonstrated.
The ground electrode 11 of the spark plug 1 for an internal combustion engine includes a core part 12 and a bottomed cylindrical shape including an insertion hole 14 made of a material having a smaller linear expansion coefficient than that of the core part 12 and through which the core part 12 is inserted. And the surface layer portion 13. Further, a front end side gap S <b> 1 is formed between the front end portion of the core portion 12 and the bottom portion 141 of the insertion hole 14 in the surface layer portion 13. Therefore, when the temperature of the spark plug 1 is low, the ground electrode 11 can be quickly heated, and when the temperature of the spark plug 1 is high, an increase in the temperature of the ground electrode 11 can be suppressed.

  That is, as shown in FIG. 3, the tip side gap S <b> 1 is formed inside the ground electrode 11 when the temperature of the spark plug 1 is low. Therefore, in the range where the front end side gap S1 in the ground electrode 11 is formed, the insertion hole 14 is formed and only the hollow surface layer portion 13 becomes a heat transfer path. Therefore, the thermal resistance in the ground electrode 11 increases, and the amount of heat radiated from the ground electrode 11 to the housing 4 decreases. Thereby, the temperature of the ground electrode 11 can be quickly raised, and the ignition performance of the spark plug 1 can be improved.

  As shown in FIG. 4, when the temperature of the spark plug 1 rises, the core material portion 12 and the surface layer portion 13 constituting the ground electrode 11 undergo linear expansion. At this time, since the linear expansion coefficient of the material forming the core part 12 is larger than the linear expansion coefficient of the material forming the surface layer part 13, the core material part 12 linearly expands more than the surface layer part 13, and the core material The tip of the portion 12 comes into contact with the bottom 141 of the insertion hole 14. Thus, when the front end side gap S1 is closed by the core member 12, both the core member 12 and the surface layer 13 can be used as a heat transfer path. Therefore, the thermal resistance in the ground electrode 11 is reduced, and the amount of heat radiated from the ground electrode 11 to the housing 4 can be increased. Thereby, the temperature rise of the ground electrode 11 can be suppressed, the occurrence of pre-ignition can be prevented, and the wear resistance of the ground electrode 11 can be improved.

  Further, the insertion length of the core material portion 12 into the insertion hole 14 is L, the linear expansion coefficient of the surface layer portion 13 is a, the linear expansion coefficient of the core material portion 12 is b, and the temperature of the ground electrode 11 before the operation of the internal combustion engine. When the temperature difference between the assumed reference temperature t0 and the set temperature t1 assuming the temperature of the ground electrode 11 during operation of the internal combustion engine is Δt, the size of the tip side clearance S1 is S1 = L × {(1 + b × The relationship of [Delta] t) / (1 + a * [Delta] t) -1} is satisfied. Therefore, when the temperature of the ground electrode 11 is increased to the set temperature (t1), the distal end surface of the core member portion 12 comes into contact with the bottom portion 141 of the insertion hole 14 of the surface layer portion 13 to fill the distal end side gap S1. Thus, until the ground electrode 11 reaches the set temperature, the temperature of the ground electrode 11 is quickly increased, and when the ground electrode 11 is heated to the set temperature or higher, the thermal conductivity in the ground electrode 11 is improved. The temperature rise of the ground electrode 11 can be suppressed. That is, at the start of operation of the internal combustion engine, the ground electrode 11 can be quickly heated to improve the ignitability at the ground electrode 11. Further, it is possible to prevent the temperature of the ground electrode 11 from becoming too high during the operation of the internal combustion engine, and to effectively improve the wear resistance of the ground electrode 11.

  Further, a radial gap S <b> 2 is formed between the core material portion 12 and the surface layer portion 13 in the radial direction orthogonal to the axial direction of the core material portion 12. When the temperature of the ground electrode 11 is low, the radial gap S2 is formed, so that the contact area between the core member 12 and the surface layer part 13 is smaller than when the radial gap S2 is not formed. Therefore, the thermal resistance between the core part 12 and the surface layer part 13 can be increased. Accordingly, the amount of heat transferred from the surface layer portion 13 to the core material portion 12 is reduced. Thereby, the temperature of the ground electrode 11 can be raised more quickly. Moreover, if the temperature of the spark plug 1 rises, the core part 12 will expand | swell and the radial direction clearance S2 will be filled. Thereby, the contact area of the core part 12 and the surface layer part 13 can be increased, and the amount of heat transferred from the ground electrode 11 to the housing 4 can be increased. Therefore, the temperature rise of the ground electrode 11 can be more effectively suppressed.

  In addition, the radial dimension in the core member 12 is W, the linear expansion coefficient of the surface layer 13 is a, the linear expansion coefficient of the core member 12 is b, and the temperature of the ground electrode 11 before the operation of the internal combustion engine is assumed. When the temperature difference between the temperature t0 and the set temperature t1 assuming the temperature of the ground electrode 11 during operation of the internal combustion engine is Δt, the size of the radial gap S2 is S2 = W × {(1 + b × Δt) / The relationship of (1 + a × Δt) −1} / 2 is satisfied. Therefore, until the ground electrode 11 reaches the set temperature, the temperature of the ground electrode 11 is quickly increased. When the ground electrode 11 is heated to the set temperature, the end surface of the core member 12 is inserted into the surface layer portion 13. Abutting against the bottom 141 of the hole 14, the radial gap S2 is filled. Therefore, at the set temperature, the thermal conductivity of the ground electrode 11 can be improved, and the temperature rise of the ground electrode 11 can be suppressed. That is, at the start of operation of the internal combustion engine, the ground electrode 11 can be quickly heated to improve the ignitability at the ground electrode 11. Further, it is possible to prevent the temperature of the ground electrode 11 from becoming too high during the operation of the internal combustion engine, and to effectively improve the wear resistance of the ground electrode 11.

  As described above, according to the spark plug 1 for the internal combustion engine of this example, the temperature rise of the ground electrode 11 can be suppressed at a high temperature, and the ground electrode 11 can be quickly heated at a low temperature.

(Confirmation test)
In this test, as shown in FIG. 5, the transition of the temperature change in the ground electrode 11 when the spark plug 1 of Example 1 was heated was confirmed.
In this test, the temperature of the spark plug 1 was changed by changing the rotational speed of the internal combustion engine between 1200 rpm to 3600 rpm and the load between 55 and 156 Nm, and the temperature change of the ground electrode 11 was confirmed.
As a sample, one example and two conventional examples were used.
The spark plug 1 as an embodiment is the spark plug 1 shown in the first embodiment.
In the spark plug 1 of Conventional Example 1, the ground electrode 11 is not divided into the core portion 12 and the surface layer portion 13 and is formed by one member. In the spark plug 1 of Conventional Example 2, the ground electrode 11 is divided into the core member 12 and the surface layer 13, and the front end side clearance S 1 and the radial clearance S 2 are between the core member 12 and the surface layer 13. Not formed. Other configurations are the same as those of the first embodiment.

  FIG. 5 is a graph showing the temperature change of the ground electrode 11 with the vertical axis representing the temperature (° C.) of the ground electrode 11 and the horizontal axis representing the temperature (° C.) of the spark plug 1. In addition, as the temperature of the spark plug 1, the temperature in the insulator 3 is shown. A solid line L1 indicates a temperature change of the ground electrode 11 in the spark plug 1 of the embodiment. A broken line B1 and a broken line B2 indicate changes in the temperature of the ground electrode 11 in the spark plugs 1 of Conventional Example 1 and Conventional Example 2, respectively.

  As indicated by the broken line B1, the temperature of the ground electrode 11 in the spark plug 1 of the conventional example 1 changes in proportion to the temperature increase of the spark plug 1. Further, as shown by the broken line B2, the temperature of the ground electrode 11 in the spark plug 1 of the conventional example 2 changes in proportion to the temperature rise of the spark plug 1 in a temperature range lower than that of the spark plug 1 of the conventional example 1. Yes.

  As shown by the solid line L1, the temperature of the ground electrode 11 in the spark plug 1 of the embodiment is the ground in the spark plug 1 of the conventional example 1 and the conventional example 2 in the temperature range T1 where the temperature of the insulator 3 is about 410 ° C. or less. It was confirmed that the temperature was higher than the temperature of the electrode 11. Further, in the spark plug 1 of the embodiment, when the temperature of the ground electrode 11 reaches around the set temperature when the temperature of the spark plug 1 is between about 380 ° C. and about 530 ° C., the temperature rise of the insulator 3 It was confirmed that the temperature rise of the ground electrode 11 was moderate and the temperature rise was suppressed. In the spark plug 1 of the example, it was confirmed that the temperature of the ground electrode 11 increased in proportion to the temperature increase of the spark plug 1 in the temperature range where the temperature of the spark plug 1 exceeded about 530 ° C.

  Thus, in the spark plug 1 of the example, it was confirmed that the temperature of the ground electrode 11 was quickly raised in a temperature range where the temperature of the spark plug 1 was relatively low. Further, it has been confirmed that when the temperature of the ground electrode 11 reaches the vicinity of the set temperature t1, the temperature rise of the ground electrode 11 becomes moderate and the temperature rise is suppressed.

(Example 2)
In this example, as shown in FIGS. 6 and 7, the structure of the spark plug of Example 1 is partially changed.
In the spark plug 1 of this example, the insertion hole 14 of the surface layer portion 13 is formed to the inside of the bent portion 134.
The core member 12 is formed so as to follow the shape of the insertion hole 14. The core member extending portion 121 extends in the axial direction from the housing 4, and the bent portion of the surface layer portion 13 extends from the tip of the core member extending portion 121. 134 and a core bending portion 122 formed along the line 134. A positioning portion 123 that protrudes outward in the radial direction of the core material bending portion 122 is formed at the tip of the core material bending portion 122. The positioning part 123 is formed in a bowl shape on the entire circumference of the outer edge at the tip of the core material bending part 122. In this example, the partial gap S3 between the positioning portion 123 and the inner peripheral surface of the insertion hole 14 is set to approximately 0 mm, and the size S3 of the partial gap S3 is greater than the size S2 of the radial gap S2. Is also small.

In addition, the ground electrode 11 of this example prepares the linear core material part 12 and the linear surface layer part 13, and inserts the core material part 12 in the insertion hole 14 of the surface layer part 13, and is then bent. As a result, an extended portion 132, a facing portion 133, and a bent portion 134 of the ground electrode 11 are formed.
Other configurations are the same as those of the first embodiment. Of the reference numerals used in this example or the drawings relating to this example, the same reference numerals as those used in the first embodiment represent the same components as in the first embodiment unless otherwise specified.

  In the spark plug 1 of this example, the core member 12 can be easily positioned in the insertion hole 14 by forming the positioning member 123 in the core member 12. Thereby, the radial clearance S <b> 2 can be easily formed between the core material portion 12 and the surface layer portion 13. Further, when forming the bent portion 134, the radial gap S <b> 2 can be easily formed between the core material portion 12 and the surface layer portion 13.

( Reference example )
In this example, as shown in FIGS. 8 and 9, the structure of the spark plug of Example 1 is partially changed.
In the spark plug 1 of this example, the surface layer portion 13 has a surface layer main body portion 135 and a surface layer front end portion 136.
The surface layer main body 135 forms part of the extended portion 132, the bent portion 134, and the facing portion 133 in the ground electrode 11. The insertion hole 14 is formed so as to penetrate the entire length of the surface layer portion 13.
The surface layer tip portion 136 has a substantially rectangular parallelepiped shape, and has a concave portion 137 that is recessed toward the opposite side of the surface layer main body portion 135 on the surface facing the surface layer main body portion 135. The depth of the concave portion 137 is set to the size of the front end side gap S1. The ground electrode tip 111 is disposed on the surface facing the center electrode 2 at the front end portion 136 of the surface layer.

  The core member 12 is formed so as to follow the shape of the insertion hole 14. The core member extending portion 121 extends in the axial direction from the housing 4, and the bent portion of the surface layer portion 13 extends from the tip of the core member extending portion 121. 134, and a core material bending portion 122 formed along 134, and a core material facing portion 133 disposed inside the facing portion 133. In the present example, the radial gap S <b> 2 is not formed between the core member 12 and the surface layer 13.

In addition, the ground electrode 11 of this example prepares the linear core part 12 and the linear surface layer main body part 135, and after inserting the core material part 12 into the insertion hole 14 of the surface layer main body part 135, Cutting is performed so that the end surface of the core member 12 disposed on the front end side is aligned with the end surface of the surface layer main body 135. The surface layer tip 136 is joined to the end face that has been subjected to the cutting, and the ground electrode 11 is formed by bending. At this time, the recessed part 137 forms the front end side clearance S1.
Other configurations are the same as those of the first embodiment. Of the reference numerals used in this example or the drawings relating to this example, the same reference numerals as those used in the first embodiment represent the same components as in the first embodiment unless otherwise specified.

According to the spark plug 1 of this example, the front end side clearance S1 can be easily and reliably formed in the ground electrode 11.
Also in this example, the same effects as those of the first embodiment can be obtained.

The above-mentioned Example 1 , Example 2, and the reference example show a part of the aspects, and various other aspects can be adopted. For example, you may combine the structure of Example 1 , Example 2, and a reference example .

DESCRIPTION OF SYMBOLS 1 Spark plug for internal combustion engines 11 Ground electrode 12 Core material part 13 Surface layer part 14 Insertion hole 141 Bottom part 2 Center electrode 3 Insulator 4 Housing

Claims (4)

A center electrode (2);
An insulator (3) for inserting and holding the center electrode (2) inside;
A housing (4) for inserting and holding the insulator (3) inward while exposing a part of the base end side of the insulator (3);
A ground electrode (11) joined to the housing (4) to form a spark discharge gap (G) with the center electrode (2);
The ground electrode (11) has a bottomed cylindrical shape including a core member (12) extending from the housing (4) and an insertion hole (14) through which the core member (12) is inserted. And a surface layer portion (13) of
A clearance on the distal end side is formed between the distal end portion of the core portion (12) and the bottom portion (141) of the insertion hole (14) in the surface layer portion (13) ,
In the radial direction perpendicular to the axial direction of the core material part (12), a radial gap is formed between the core material part (12) and the surface layer part (13).
At least one positioning part (123) projecting in the radial direction of the core part (12) is formed on the outer peripheral surface of the core part (12), and the positioning part (123) and the surface layer part are formed. A spark plug (1) for an internal combustion engine , wherein a size S3 of a partial gap between the insertion hole (14) in (13) is smaller than a size S2 of the radial gap .   The insertion length of the core part (12) into the insertion hole (14) is L, the linear expansion coefficient of the surface layer part (13) is a, the linear expansion coefficient of the core part (12) is b, and the internal combustion engine When the temperature difference between the reference temperature t0 assuming the temperature of the ground electrode (11) before the operation of the engine and the set temperature t1 assuming the temperature of the ground electrode (11) during the operation of the internal combustion engine is Δt, The spark plug (1) for an internal combustion engine according to claim 1, wherein the size S1 of the tip side clearance satisfies a relationship of S1 = L × {(1 + b × Δt) / (1 + a × Δt) -1}. ). The dimension in the radial direction in the core part (12) is W, the linear expansion coefficient of the surface layer part (13) is a, the linear expansion coefficient of the core part (12) is b, and the above before the operation of the internal combustion engine. When the temperature difference between the reference temperature t0 assuming the temperature of the ground electrode (11) and the set temperature t1 assuming the temperature of the ground electrode (11) during operation of the internal combustion engine is Δt, the size of the radial gap is large. The internal combustion engine spark plug (1) according to claim 1 or 2 , wherein the length S2 satisfies a relationship of S2 = W x {(1 + b x Δt) / (1 + a x Δt) -1} / 2. . The ground electrode (11) is opposed to the extending portion (132) extending from the housing (4) in the axial direction of the spark plug (1) for the internal combustion engine and the tip of the center electrode (2). And the bent portion (134) connecting the extended portion (132) and the opposed portion (133), and the core portion (12) The spark plug (1) for an internal combustion engine according to any one of claims 1 to 3, wherein the spark plug (1) extends to a position closer to the facing portion (133) than the bent portion (134).

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