JP2007115537A - Spark plug for internal combustion engine and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug for an internal combustion engine at low cost which has excellent bonding strength between a housing and a ground electrode, and is capable of reducing poor ignition, and to provide a method of manufacturing the same. <P>SOLUTION: This spark plug 1 for the internal combustion engine comprises a central electrode 2 and a ground electrode 3 which form a spark discharge gap G between each other, and a housing 4 to which a base 31 of the ground electrode 3 is welded. In the spark plug, a plating layer 5 having a lower melting point than that of the housing 4 and the ground electrode 3 is plated on the surface of the housing 4, but not plated on the junction interface 11 between the housing 4 and the ground electrode 3 and on the surface of the ground electrode 3. Components of the plating layer 5 are contained in welding burrs 12 formed on places adjacent to the junction interface 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark plug for an internal combustion engine used for automobiles, cogeneration, and the like, and a method for manufacturing the same.

  There is a spark plug for igniting a mixed gas of fuel and air by performing a spark discharge in a combustion chamber of an internal combustion engine used for automobiles, cogeneration and the like. The spark plug includes a center electrode and a ground electrode that form a spark discharge gap therebetween, and a housing in which a proximal end portion of the ground electrode is welded.

  Spark plugs used in environments with severe thermal loads, such as Inconel 600 (trademark of Inconel), which has excellent heat and oxidation resistance, are used as a material for the ground electrode in order to suppress spark consumption due to the progress of oxidation of the ground electrode. Ni-based alloys are generally used. On the other hand, the housing for insulatingly holding the center electrode is usually made of low carbon steel.

  The low carbon steel housing is plated on the surface to prevent corrosion. In forming the plating layer on the surface of the housing, specifically, for example, as described in Patent Document 1, after welding the housing and the ground electrode, the surface of the housing is masked in a state where the ground electrode is masked. Is plated.

  However, in the case of the above plating method, it is difficult to completely cover the ground electrode by masking. Therefore, the plating adheres to the end of the ground electrode on the welding side within a range of about 1 to 2 mm from the base end. There is. Then, the plating on the welding side end of the ground electrode is peeled off due to thermal stress during the operation of the internal combustion engine, and there is a possibility that sparking occurs in the peeled plating (horizontal sparking), resulting in poor ignition. In addition, since the masking is performed, the number of steps is large, which increases the cost.

  Further, when electroless nickel is used as the plating layer, if phosphorus contained as a component remains at the joint interface, solidification cracking may occur in the process of cooling the welded portion. During use of the spark plug, the ground electrode peels off from the solidified crack portion, and there is a risk of misfire.

As a method for solving such a problem, in Patent Document 2, as shown in FIGS. 17 and 18, the plating layer 95 in the welded portion between the housing 94 and the ground electrode 93 is removed in advance by polishing, and then the plating removal portion is removed. 99, a method of welding the ground electrode 93 is described.
That is, in this manufacturing method, as shown in FIG. 17, the ground electrode 93 is welded to the position where the ground electrode 93 is welded on the front end surface 941 of the housing 94 after the plating layer 95 is applied, and then the ground electrode 93 is welded. To do.
However, the problem with this method is that a plating removal step is required, which increases man-hours and increases costs, and further, is inferior in the bonding reliability between the housing 94 and the ground electrode 93.

The latter point will be described in detail below.
The plating removal portion 99 is preferably formed only at a position corresponding to the bonding interface between the ground electrode 93 and the housing 94. However, in order to surely prevent the plating layer 95 from remaining at the bonding interface, the plating removal portion 99 is practical. As shown in FIG. 18, the plating must be removed to the outside of the position corresponding to the bonding interface. Therefore, as shown in FIG. 11, rust is generated unless the plating removal portion 99 existing outside the ground electrode 93 is protected by the welding burr 96. Here, if the plating removal portion 99 cannot be reliably covered with the welding burr 96 or the adhesion degree is not sufficient even if it can be covered, the housing 94 is corroded, and in the worst case, The ground electrode 93 may be peeled off.

On the other hand, if the area for removing the plating layer 95 in advance by polishing is insufficient, there is a problem that the grounding electrode 93 may easily fall off from the joint interface because the welding strength is low. In particular, in electrolytic Ni plating or the like conventionally used as the plating layer 95, the plating layer 95 tends to remain at the bonding interface because the melting point of the plating layer 95 is high, and the above-described problems are likely to occur.
Therefore, since it is necessary to increase the accuracy of plating removal, this method also increases the cost.

JP 2001-68250 A JP 2003-059617 A

  The present invention has been made in view of such conventional problems, and is intended to provide an inexpensive spark plug for an internal combustion engine that has excellent bonding strength between a housing and a ground electrode and that has reduced ignition failure, and a method for manufacturing the spark plug. To do.

A first invention is a spark plug for an internal combustion engine having a center electrode and a ground electrode that form a spark discharge gap between each other, and a housing in which a base end portion of the ground electrode is welded.
A plating layer having a lower melting point than the housing and the ground electrode is applied to the surface of the housing,
The plating layer does not exist on the bonding interface between the housing and the ground electrode and the surface of the ground electrode,
The spark plug for an internal combustion engine is characterized in that a component of the plating layer is present in a weld burr formed at a position adjacent to the joint interface (claim 1).

Next, the effects of the present invention will be described.
In the spark plug, no plating layer is present at the joint interface between the housing and the ground electrode. Therefore, it is possible to prevent solidification cracking due to the components contained in the plating layer. As a result, it is possible to prevent the ground electrode from falling off and to secure the bonding strength between the housing and the ground electrode.
In addition, since a plating layer is not formed on the surface of the ground electrode, it is possible to prevent side fire caused by peeling of the plating from the ground electrode due to thermal stress. Therefore, poor ignition can be reduced.

  The plating layer formed on the surface of the housing has a lower melting point than the housing and the ground electrode. For this reason, even when the ground electrode is welded to the housing after the plating layer is formed on the entire surface of the housing, it is possible to prevent the components of the plating layer from remaining at the joint interface between the housing and the ground electrode. That is, by setting the melting point of the plating layer to a lower melting point than the melting points of the housing and the ground electrode, the plating layer is first melted during welding, so that the plating layer can be easily discharged from the joint interface.

  And the component of the discharged | emitted plating layer will exist in the welding burr | flash formed in the position adjacent to the said joining interface. Even if the component of the plating layer exists in this portion, there is no influence on the bonding strength between the housing and the ground electrode.

In this way, a spark having high bonding strength between the housing and the ground electrode without masking the ground electrode during formation of the plating layer or removing the plating only at the weld after forming the plating layer. You can get a plug. Therefore, the manufacturing cost can be reduced and an inexpensive spark plug can be obtained.
Since the ground electrode can be welded to the housing after the plating layer is formed on the entire surface of the housing as described above, adhesion of plating to the ground electrode can be easily and reliably prevented.

  As described above, according to the present invention, it is possible to provide an inexpensive spark plug for an internal combustion engine which has excellent bonding strength between the housing and the ground electrode and which has reduced ignition failure.

A second invention is a method of manufacturing a spark plug for an internal combustion engine having a center electrode and a ground electrode that form a spark discharge gap between each other, and a housing in which a base end portion of the ground electrode is welded.
A plating layer having a melting point lower than that of the housing and the ground electrode is applied to the surface of the housing,
Next, resistance welding is performed in a state where the base end portion of the ground electrode is in contact with the front end surface of the housing from above the plating layer, and the plating layer is discharged from the joint interface between the housing and the ground electrode. However, the present invention resides in a method for manufacturing a spark plug for an internal combustion engine, wherein the housing and the ground electrode are joined.

Next, the effects of the present invention will be described.
In the manufacturing method, the plating layer is discharged from the bonding interface between the housing and the ground electrode. Therefore, it is possible to prevent solidification cracking due to the components contained in the plating layer, to prevent the ground electrode from falling off, and to secure the bonding strength between the housing and the ground electrode.

  Further, after the plating layer is applied to the surface of the housing, welding is performed in a state where the base end portion of the ground electrode is in contact with the distal end surface of the housing from above the plating layer. Therefore, it is not necessary to perform a process of masking the ground electrode when forming the plating layer or removing the plating only at the welded portion after forming the plating layer. Therefore, the manufacturing cost can be reduced and an inexpensive spark plug can be obtained.

  Further, since the plating layer has a melting point lower than that of the housing and the ground electrode, the plating layer existing between the housing and the ground electrode brought into contact with the front end surface of the housing at the time of resistance welding is provided. Since it melts first, the plating layer can be easily discharged from the bonding interface. Then, the bonding strength between the housing and the ground electrode can be ensured by bonding the housing and the ground electrode while discharging the plating layer from the bonding interface.

  Since the ground electrode is welded to the housing after the plating layer is formed on the entire surface of the housing as described above, the adhesion of the plating to the ground electrode can be easily and reliably prevented. Therefore, it is possible to prevent side fire due to peeling of the plating from the ground electrode due to thermal stress, and to obtain a spark plug with reduced ignition failure.

  As described above, according to the present invention, it is possible to provide an inexpensive spark plug manufacturing method for an internal combustion engine which has excellent bonding strength between the housing and the ground electrode and reduces ignition failure.

In the first invention (invention 1) and the second invention (invention 6), the internal combustion engine may be an internal combustion engine such as an automobile or a cogeneration.
Moreover, it is preferable that the said plating layer has melting | fusing point of 1000 degrees C or less (Claim 2).
In this case, the plating layer can be easily and reliably discharged from the joint interface between the housing and the ground electrode during welding.

Among materials generally used in the spark plug housing and the ground electrode, a material having a low melting point is, for example, copper (melting point: 1083 ° C.). If the melting point of the plating layer is 1000 ° C. or less, for example, even if copper is used for the ground electrode, the plating layer is first dissolved during welding, so that discharge from the weld joint interface is easy, and the plating layer is formed between the housing and the ground electrode. It can prevent remaining in the welding joint interface.
In particular, the plating layer preferably has a difference in melting point between the housing and the ground electrode of 180 ° C. or higher, more preferably 400 ° C. or higher.

The plating layer is preferably made of electroless nickel plating.
In this case, since the plating layer can have a melting point sufficiently lower than the melting points of the housing and the ground electrode, the plating layer can be easily discharged from the bonding interface.
That is, for example, when the housing is made of low carbon steel (melting point 1539 ° C.) and the ground electrode is made of Inconel 600 alloy (melting point 1425 ° C.), the plating layer made of electroless nickel plating (melting point about 890 ° C.) The melting point difference is 500 ° C or higher. For example, even when copper (melting point: 1083 ° C.) is used for the ground electrode, the difference in melting point between the housing and the ground electrode and the plating layer (melting point: about 890 ° C.) is about 180 ° C. or more. Therefore, at the time of welding, the plating layer can be reliably melted before the housing and the ground electrode, and the plating layer can be easily discharged from the joining interface.

Preferably, the housing is made of an iron-based metal, and at least the outermost layer of the ground electrode is made of a nickel-based heat resistant alloy.
In this case, it is possible to obtain a low-cost housing excellent in moldability and to obtain a ground electrode excellent in heat resistance and oxidation resistance.

  Examples of the iron-based metal constituting the housing include low carbon steel and stainless steel. The ground electrode can be made of, for example, Inconel 600 (trademark of Inconel), Ni-based alloy represented by Inconel 601 or the like. Moreover, you may comprise a ground electrode by forming the said nickel-type heat-resistant alloy in the outer layer of highly heat conductive metals, such as copper (Cu).

Further, it is preferable that the ground electrode is welded in a state where it sinks 0.3 mm or more with respect to the housing.
In this case, it becomes easy to sufficiently discharge the plating layer from the joint interface between the housing and the ground electrode, and the welding strength between the housing and the ground electrode can be sufficiently secured.
When the sinking amount of the ground electrode with respect to the front end surface of the housing is less than 0.3 mm, it may be difficult to discharge the plating layer from the bonding interface.
The amount of subsidence is the amount generated by melting of at least one of the housing and the ground electrode, mainly the ground electrode. For example, welding is performed with reference to the state where the housing and the ground electrode are in contact with each other before welding. This is an amount defined by the position of the ground electrode relative to the subsequent housing.

In the second invention (invention 6), a weld burr is formed at a position adjacent to the joint interface between the housing and the ground electrode, and the component of the plating layer is present in the weld burr. Can be resistance welded.
In this case, the components of the plating layer present at the joint interface between the housing and the ground electrode are discharged from the joint interface and are present in the weld burr. Even if the component of the plating layer exists in this portion, there is no influence on the bonding strength between the housing and the ground electrode. Therefore, it is possible to more easily obtain an inexpensive spark plug for an internal combustion engine that has excellent bonding strength between the housing and the ground electrode and reduces ignition failure.

Preferably, a protrusion is formed on the front end surface of the housing, and the ground electrode is resistance-welded to the housing while the base end of the ground electrode is in contact with the protrusion. ).
In this case, it becomes possible to generate heat at the welding portion with a lower current than in the case where there is no protrusion, so that it is possible to prevent the melting region of the ground electrode from being unnecessarily widened. Therefore, it can contribute to the reduction in welding strength variation.

Further, a protrusion can be formed at the base end of the ground electrode, and the ground electrode can be resistance-welded to the housing while the ground electrode is brought into contact with the distal end surface of the housing at the protrusion. (Claim 9).
Also in this case, since it becomes possible to generate heat at the welding portion with a low current, it is possible to contribute to a reduction in variation in welding strength.

The plating layer is preferably formed by electroless nickel plating.
In this case, since the plating layer can have a melting point sufficiently lower than the melting points of the housing and the ground electrode, the plating layer can be easily discharged from the bonding interface.

Further, it is preferable that the ground electrode is welded in a state where it sinks 0.3 mm or more with respect to the housing.
In this case, it becomes easy to sufficiently discharge the plating layer from the joint interface between the housing and the ground electrode, and the welding strength between the housing and the ground electrode can be sufficiently secured.

Example 1
A spark plug for an internal combustion engine according to an embodiment of the present invention and a manufacturing method thereof will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the spark plug 1 for the internal combustion engine of the present example includes a center electrode 2 and a ground electrode 3 that form a spark discharge gap G therebetween, and a base end portion 31 of the ground electrode 3. And a housing 4 welded thereto.

As shown in FIG. 1, a plating layer 5 having a melting point lower than that of the housing 4 and the ground electrode 3 is applied to the surface of the housing 4.
The plating layer 5 does not exist on the bonding interface 11 between the housing 4 and the ground electrode 3 and on the surface of the ground electrode 3.
And the component of the said plating layer exists in the welding burr | flash 12 formed in the position adjacent to the joining interface 11. FIG.

Further, the plating layer 5 has a melting point of 1000 ° C. or lower. Specifically, the plating layer 5 is made of electroless nickel plating and has a melting point of 890 ° C.
The housing 4 is made of an iron-based metal, and the ground electrode 3 is made of at least the outermost layer of a nickel-based heat resistant alloy. In this example, the housing 4 is made of low carbon steel, and the ground electrode is made of Inconel 600 (trademark of Inconel).

  The spark plug 1 is disposed in an internal combustion engine such as an automobile engine. And the housing 4 which has the attachment screw part 44 for attaching to an internal combustion engine, the insulator 13 penetrated inside this housing 4, the center electrode 2 penetrated and hold | maintained inside this insulator 13, and the said housing 4 and the above-mentioned ground electrode 3 welded to the tip surface 41. A spark discharge gap G is formed between the tip of the center electrode 2 and the ground electrode 3. Precious metal tips 22 and 32 such as Pt and Ir are disposed on the tip of the center electrode 2 and the surface of the ground electrode 3 facing the center electrode 2.

Next, the manufacturing method of the spark plug 1 for the internal combustion engine of this example will be described with reference to FIG.
First, as shown in FIG. 3A, a plating layer 5 (having a lower melting point than the housing and the ground electrode) is applied to the surface of the housing 4. Specifically, the plating layer 5 is formed by performing electroless nickel plating with a melting point of 890 ° C. on the surface of the housing 4 made of low carbon steel S25C having a melting point of 1539 ° C.

Next, as shown in FIG. 3B, resistance welding is performed in a state where the base end portion 31 of the ground electrode 3 is in contact with the front end surface 41 of the housing 4 from above the plating layer 5. At this time, the housing 4 and the ground electrode 3 are joined while discharging the plating layer 5 from the joint interface 11 between the housing 4 and the ground electrode 3. The ground electrode 3 is made of Inconel 600 alloy having a melting point of 1425 ° C.
As shown in FIGS. 5 and 6, phosphorus (P), which is a component of the plating layer 5, is present in the weld burr 12 formed at a position adjacent to the bonding interface 11.

  In the resistance welding, as shown in FIG. 4, the housing 4 is fitted into the lower electrode 61, and the ground electrode 3 sandwiched between the pair of upper electrodes 62 is brought into contact with the distal end surface 41 of the housing 4 at the base end portion 31, Press. In this state, resistance welding is performed by setting current and pressure conditions so that P (phosphorus) is discharged from the bonding interface 11. In this example, when welding the ground electrode 3 having a substantially rectangular shape with a cross-sectional shape of 1.6 × 4.1 mm to the housing 4, the conditions were set such that the current value was 2.9 kA, the number of cycles was 20, and the applied pressure was 45 kgf. .

  Next, as shown in FIG. 3C, the ground electrode 3 is bent and the center electrode 2 held by the insulator 13 is inserted inside the housing 4 so that the center electrode 2 and the ground electrode 3 are inserted. A spark discharge gap G is formed.

Next, the function and effect of this example will be described.
In the manufacturing method, the plating layer 5 is discharged from the bonding interface 11 between the housing 4 and the ground electrode 3. Therefore, solidification cracking due to the component (phosphorus) contained in the plating layer 5 can be prevented, the ground electrode 3 can be prevented from falling off, and the bonding strength between the housing 4 and the ground electrode 3 can be ensured.

  In addition, after the plating layer 5 is applied to the surface of the housing 4, welding is performed in a state where the base end portion 31 of the ground electrode 3 is in contact with the distal end surface 41 of the housing 4 from above the plating layer 5. Therefore, it is necessary to adopt a step of masking the ground electrode 3 before forming the plating layer 5 or a step of removing the plating only at the welded portion after forming the plating layer 5 instead. Absent. Therefore, the manufacturing cost can be reduced and an inexpensive spark plug 1 can be obtained.

  In addition, since the plating layer 5 has a lower melting point than the housing 4 and the ground electrode 3, the resistance between the housing 4 and the ground electrode 3 brought into contact with the front end surface 41 of the housing 4 during resistance welding. Since the existing plating layer 5 is melted first, the plating layer 5 can be easily discharged from the bonding interface 11. Then, the bonding strength between the housing 4 and the ground electrode 3 can be ensured by bonding the housing 4 and the ground electrode 3 while discharging the plating layer 5 from the bonding interface 11.

  Since the ground electrode 3 is welded to the housing 4 after the plating layer 5 is formed on the entire surface of the housing 4 as described above, the adhesion of the plating to the ground electrode 3 can be easily and reliably prevented. Therefore, it is possible to prevent side fire due to peeling of the plating from the ground electrode 3 due to thermal stress, and to obtain the spark plug 1 with reduced ignition failure.

Further, since the plating layer 5 is made of electroless nickel plating, the plating layer 5 can have a melting point sufficiently lower than the melting points of the housing 4 and the ground electrode 3. Therefore, the plating layer 5 can be easily discharged from the bonding interface 11.
That is, there is a difference in melting point between the housing 4 made of low carbon steel (melting point 1539 ° C.) and the ground electrode 3 made of Inconel 600 alloy (melting point 1425 ° C.) and the plating layer 5 made of electroless nickel plating (melting point about 890 ° C.). It is 500 ° C or higher. Therefore, the plating layer 5 can be easily discharged from the bonding interface 11.

  In addition, for example, copper having a high thermal conductivity (melting point: 1083 ° C.) may be used as the core material of the ground electrode 3. The melting point difference is about 180 ° C. or more. Therefore, the plating layer 5 can be easily discharged from the bonding interface 11.

  The housing 4 is made of low-carbon steel that is an iron-based metal, and the ground electrode 3 is made of Inconel 600 that is a nickel-based heat-resistant alloy. Therefore, it is possible to obtain the housing 4 having excellent moldability and low cost, and it is possible to obtain the ground electrode 3 having excellent heat resistance and oxidation resistance.

  As described above, according to this example, it is possible to provide an inexpensive spark plug manufacturing method for an internal combustion engine, which has excellent bonding strength between the housing and the ground electrode and reduces ignition failure.

(Example 2)
In this example, as shown in FIGS. 7 and 8, after welding the housing 4 and the ground electrode 3, in order to confirm that P (phosphorus) is discharged from the joint interface 11, a cross-sectional sample of the welded portion is used. The component analysis was performed by EDS at a magnification of 350 times, and mapping was performed to relatively indicate the contained mass for each element contained in each part. As the EDS, JSM-5300LV manufactured by JEOL Ltd. was used.

  FIG. 7A is an enlarged view in the dotted line frame A in FIG. 6, that is, an enlarged view on the interface side with the housing 4 in the vicinity of the end of the welding burr 12 on the side far from the ground electrode 3. 7 (B), (C), and (D) show the distribution (mapping) of the corresponding phosphorus (P), nickel (Ni), and iron (Fe) components. FIG. 7 schematically shows the SEM photograph and mapping image of the dotted line frame A portion in FIG. 7 (B), (C), and (D), the relative concentrations of the components (P, Ni, Fe) are hatched and displayed in four stages, and the relative values of the hatched display portions are relative to each other. The concentration follows the legend shown in FIG.

  Further, FIG. 8A is an enlarged view inside the dotted frame B in FIG. 6, that is, an enlarged view of the bonding interface 11, and the corresponding components of phosphorus (P), nickel (Ni), and iron (Fe) are shown in FIG. Each of the distributions (mappings) is shown in FIGS. 8B, 8C, and 8D. FIG. 8 also schematically shows the SEM photograph and mapping image of the dotted line frame B portion in FIG. 6, and the hatched portions in FIGS. 8B, 8 </ b> C, and 8 </ b> D are also shown in FIG. Represents the relative concentration of each component according to the legend.

As can be seen from FIG. 8B, phosphorus (P) does not exist at the weld joint interface 11 between the ground electrode 3 and the housing 4. On the other hand, as can be seen from FIG. 7B, phosphorus (P) is thinly concentrated and distributed on the interface side with the housing 4 near the end of the welding burr 12 far from the ground electrode 3. It could be confirmed. In the figure, two phosphorus (P) layers are distributed vertically, but the lower layer represents phosphorus in the plating layer 5 on the surface of the housing 4 and has a thickness of 6 ± 2 μm. . The phosphorus (P) distributed on the upper side is phosphorus in the welding burr 12.
When quantitative analysis was performed on an area having a size of 5 × 5 μm to 10 × 10 μm obtained by further enlarging a plurality of portions in this portion, 5 to 15% by mass of phosphorus was detected.
On the other hand, the other parts in FIG. 7B were similarly quantitatively analyzed. As a result, the phosphorus content was 0.01% by mass or less. In addition, the quantitative analysis result of phosphorus in FIG. 8B was 0.01% by mass or less.

  As described above, according to this example, it was confirmed that the plating layer 5 at the joint interface 11 was melted and discharged in a concentrated manner near the tip of the weld burr 12 while being caught in the weld burr 12.

(Example 3)
In this example, as shown in FIGS. 9 to 13, a protruding tip 43 is provided at a part of the tip of the housing 4, and the ground electrode 3 is orthogonal to the axial direction of the housing 4 at the protruding tip 43. It is an example of the spark plug 1 which has the structure joined in the state which laid down in the direction.
The protruding tip portion 43 is formed by forming a convex portion 431 having a smaller cross-sectional area at the tip.

  In the spark plug 1 of this example, as shown in FIG. 11, the ground electrode 3 is welded to the housing 4 in a state where it sinks 0.3 mm or more. The sinking amount H is an amount defined by the position of the ground electrode 3 with respect to the housing 4 after welding with reference to a state in which the housing 4 and the ground electrode 3 are in contact with each other before welding.

  When welding, as shown in FIG. 10, the housing 4 is fitted into the lower electrode 61, the ground electrode 5 is placed on the protruding tip 43 of the housing 4, and the ground electrode 5 is sandwiched between the housing 4 and the upper electrode. After pressing 62, resistance welding was performed at a current value of 2.4 kA, a cycle number of 20, and a pressure of 45 kgf.

In addition, the convex part 431 of the said protrusion front-end | tip part 43 is width | variety w = 1.0mm and protrusion amount u = 0.2mm. The ground electrode 5 has a thickness t = 1.6 mm, and a distance s = 6.0 mm from the base end surface of the ground electrode 5 to the convex portion 431.
Others are the same as in the first embodiment. 9 to 12, the plating layer 5 is not shown, but the plating layer 5 is formed in the same manner as in the first embodiment.

In the case of this example, the welding current at the time of resistance welding is concentrated on the convex portion 431 of the protruding tip portion 43 having a small area, so that the current density is increased and the plating layer 5 existing on the tip surface 41 of the housing 4 can be easily formed. It can be dissolved and discharged.
By providing the convex portion 431, heat is generated at a certain place first, so that variation in welding strength between the housing 4 and the ground electrode 3 can be reduced. That is, by forming the position of the convex portion 431 at a position where the load is most likely to be applied, it is possible to sufficiently secure the welding strength at the position and improve the welding reliability.

  Further, by welding the ground electrode 3 in a state where it sinks 0.3 mm or more with respect to the front end surface 41 of the housing 4, the plating layer 5 can be sufficiently discharged from the joint interface 11 between the housing 4 and the ground electrode 3. Thus, the welding strength between the housing 4 and the ground electrode 3 can be sufficiently secured.

  That is, the ground electrode 3 is sunk by 0.3 mm or more with respect to the front end surface 41 of the housing 4 so that the plating existing on the front end surface 41 of the housing 4 as shown in FIGS. The layer 5 is pushed outward while being resistance-welded between the housing 4 and the ground electrode 5 while being wound around the molten welding burr 12. Then, as shown in FIG. 12C, the weld burr 12 is discharged around the joint interface 11, and the component (phosphorus) of the plating layer 5 is distributed in the weld burr 12.

  The reason why the plating layer 5 is smoothly discharged outward in this way is that the ground electrode 3 is placed on the convex portion 431 and resistance welding is performed. That is, as shown in FIGS. 12A and 12B, the gap 15 between the housing 4 and the ground electrode 3 formed on the side of the convex portion 431 becomes the discharge path of the welding burr 12. As the ground electrode 5 sinks, the welding burr 12 is easily discharged out of the bonding interface 11 through the gap 15.

  Further, as shown in FIG. 13, in the configuration of this example, the relationship between the sinking amount H of the ground electrode 3 and the remaining position L of phosphorus (P) which is a component of the plating layer 5 was confirmed. Here, the remaining position L of phosphorus is P (when the base end portion (right end) of the ground electrode 5 is the zero point (L = 0) and the distance to the front end side (left side) is + (plus). The existing region of the welding burr 12 containing the (phosphorus) component is shown.

As shown in FIG. 13, when the sinking amount H is less than 0.3 mm, phosphorus is present at the bonding interface 11, but the existence region becomes smaller as the sinking amount H increases. However, if the sinking amount H is 0.3 mm or more, phosphorus does not exist at the bonding interface 11.
Thus, by setting the sinking amount H to 0.3 mm or more, it is possible to prevent the component (phosphorus) of the plating layer 5 from remaining on the bonding interface 11 and to secure the bonding strength of the ground electrode 3.
In addition, the same effects as those of the first embodiment are obtained.

(Claim 4)
In this example, as shown in FIG. 14, a protrusion 45 is formed on the distal end surface 41 of the housing 4, and the ground electrode 3 is placed on the housing 4 while the base end 31 of the ground electrode 3 is brought into contact with the protrusion 45. 3 is an example of resistance welding.
The protrusion 45 in this example has a triangular shape.
Others are the same as in the first embodiment.

In the case of this example, since the protrusion 45 has a triangular shape, the electroless nickel plating melted along the slope of the protrusion 45 is easily discharged while being caught in the welding burr.
Thus, since this example has a structure in which the plating layer 5 is easily discharged, it is particularly effective when the area of the weld interface between the housing 4 and the ground electrode 3 is large.

Moreover, since it becomes possible to heat a welding location with a lower current than the case where there is no projection 45, it is possible to prevent the melting region of the ground electrode 3 from being unnecessarily widened. Therefore, it is possible to contribute to a reduction in welding strength variation.
In addition, the same effects as those of the first embodiment are obtained.
Even if the protrusion 45 has another shape such as a semicircular shape or a rectangular shape, the above effect can be obtained.

(Claim 5)
In this example, as shown in FIG. 15, a protrusion 311 is formed at the base end portion 31 of the ground electrode 3, and the ground electrode 3 is brought into contact with the distal end surface 41 of the housing 4 at the protrusion 311. 4 shows an example in which the ground electrode 3 is resistance-welded.
The protrusion 311 in this example also has a triangular shape.
Others have the same configuration as the fourth embodiment, and have the same operation and effect.

(Comparative example)
In this example, as shown in FIG. 16, after the ground electrode 3 is welded to the housing 4, the spark plastic 9 is manufactured by forming a plating layer 50 by electrolytic nickel plating on the surface of the housing 4.
That is, first, as shown in FIG. 16A, the ground electrode 3 made of Inconel 600 alloy is resistance-welded to the housing 4 made of low carbon steel.
Next, as shown in FIG. 16B, masking 91 is applied to the surface of the ground electrode 3.

Next, as shown in FIG. 16C, the surface of the housing 4 is subjected to electrolytic nickel plating to form a plating layer 50, and then the masking 91 is peeled off.
Next, as shown in FIG. 16 (D), the ground electrode 3 is bent, and after the center electrode 2 held by the insulator is inserted into the housing 4, the ground electrode 3 is bent, and the center electrode A spark discharge gap G is formed between 2 and the ground electrode 3.
Thus, the spark plug 9 is manufactured.

In the manufacturing method of the spark plug 9 of this example, since it is necessary to perform the masking 91 as described above, the number of processes is large, which causes an increase in cost.
Further, in the case of the above plating method, it is difficult to completely cover the ground electrode 3 with the masking 91. Therefore, the welding side end portion (base end portion 31) of the ground electrode 3 is about 1 to 2 mm from the base end. Plating may adhere to the range up to. And the plating of the welding side end part (base end part 31) of the ground electrode 3 is peeled off due to thermal stress during operation of the internal combustion engine, and the peeled plating may generate sparks (horizontal sparks), resulting in poor ignition. There is.

On the other hand, according to the present invention, as described above, since the masking to the ground electrode is not performed, man-hours can be reduced and an inexpensive spark plug can be obtained.
Further, since the ground electrode is welded after the plating layer is formed on the housing, plating does not adhere to the ground electrode. Therefore, there is no risk of the side fire.

FIG. 3 is a cross-sectional view of the vicinity of the tip of the spark plug in the first embodiment. The side view of the spark plug in Example 1. FIG. Explanatory drawing of the manufacturing method of a spark plug in Example 1. FIG. FIG. 3 is an explanatory diagram of a resistance welding method between a housing and a ground electrode in the first embodiment. Sectional explanatory drawing of the joining interface vicinity of a housing and a ground electrode in Example 1. FIG. FIG. 3 is a cross-sectional view near a welding burr in Example 1. The schematic diagram of the SEM photograph of the interface vicinity of the welding burr | flash and housing in Example 2. FIG. FIG. 6 is a schematic diagram of an SEM photograph in the vicinity of a bonding interface between a ground electrode and a housing in Example 2. FIG. 6 is a cross-sectional view of the vicinity of a tip portion of a spark plug in Example 3. Explanatory drawing of the method of the resistance welding of the housing and ground electrode in Example 3. FIG. Sectional explanatory drawing which shows the amount of sinking of the ground electrode to the housing in Example 3. FIG. Sectional explanatory drawing which shows the movement of the welding burr | flash at the time of welding with a housing and a ground electrode in Example 3. FIG. FIG. 9 is a diagram showing the relationship between the sinking amount of the ground electrode and the phosphorus remaining position at the bonding interface in Example 3. Explanatory drawing of the manufacturing method of the spark plug in Example 4. FIG. Explanatory drawing of the manufacturing method of the spark plug in Example 5. FIG. Explanatory drawing of the manufacturing method of a spark plug in a comparative example. Explanatory drawing of the manufacturing method of a spark plug in a prior art example. Explanatory drawing which shows the state which the plating removal part in the prior art example exposed. Explanatory drawing which shows the state which covered the plating removal part with the welding burr | flash in a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spark plug 11 Joining interface 12 Welding burr 2 Center electrode 3 Ground electrode 31 Base end part 4 Housing 41 Front end surface 5 Plating layer

Claims (11)

In a spark plug for an internal combustion engine having a center electrode and a ground electrode that form a spark discharge gap between each other, and a housing in which a base end portion of the ground electrode is welded,
A plating layer having a lower melting point than the housing and the ground electrode is applied to the surface of the housing,
The plating layer does not exist on the bonding interface between the housing and the ground electrode and the surface of the ground electrode,
A spark plug for an internal combustion engine, wherein a component of the plating layer is present in a weld burr formed at a position adjacent to the joining interface.   The spark plug for an internal combustion engine according to claim 1, wherein the plating layer has a melting point of 1000 ° C. or less.   3. The spark plug for an internal combustion engine according to claim 1, wherein the plating layer is made of electroless nickel plating.   The spark plug for an internal combustion engine according to any one of claims 1 to 3, wherein the housing is made of an iron-based metal, and at least the outermost layer of the ground electrode is made of a nickel-based heat-resistant alloy.   The spark plug for an internal combustion engine according to any one of claims 1 to 4, wherein the ground electrode is welded in a state where the ground electrode sinks 0.3 mm or more with respect to the housing. In a method of manufacturing a spark plug for an internal combustion engine having a center electrode and a ground electrode that form a spark discharge gap between each other, and a housing in which a base end portion of the ground electrode is welded,
A plating layer having a melting point lower than that of the housing and the ground electrode is applied to the surface of the housing,
Next, resistance welding is performed in a state where the base end portion of the ground electrode is in contact with the front end surface of the housing from above the plating layer, and the plating layer is discharged from the joint interface between the housing and the ground electrode. A method of manufacturing a spark plug for an internal combustion engine, wherein the housing and the ground electrode are joined.   7. The welding according to claim 6, wherein a welding burr is formed at a position adjacent to the joint interface between the housing and the ground electrode, and resistance welding is performed so that the component of the plating layer exists in the welding burr. A method of manufacturing a spark plug for an internal combustion engine characterized by the above.   8. The method according to claim 6, wherein a protrusion is formed on the distal end surface of the housing, and the ground electrode is resistance-welded to the housing while the base end of the ground electrode is brought into contact with the protrusion. A method of manufacturing a spark plug for an internal combustion engine characterized by the above.   8. The ground electrode according to claim 6, wherein a projection is formed at a base end portion of the ground electrode, and the ground electrode is made to resist the housing while the ground electrode is brought into contact with the distal end surface of the housing at the projection. A method of manufacturing a spark plug for an internal combustion engine, characterized by welding.   The method for manufacturing a spark plug for an internal combustion engine according to any one of claims 6 to 9, wherein the plated layer is formed by electroless nickel plating.   The method for manufacturing a spark plug for an internal combustion engine according to any one of claims 6 to 10, wherein the ground electrode is welded in a state where the ground electrode is submerged by 0.3 mm or more with respect to the housing.

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