JP6069082B2 - Spark plug and manufacturing method thereof - Google Patents

Description

  The present invention relates to a spark plug used for an internal combustion engine or the like and a manufacturing method thereof.

  A spark plug used for an internal combustion engine or the like includes, for example, an insulator having an axial hole extending in the axial direction, a center electrode inserted on the tip end side of the axial hole, and a cylindrical shape provided on the outer periphery of the insulator A metal shell and a bar-shaped ground electrode fixed to the tip of the metal shell are provided. Further, a gap is formed between the tip of the ground electrode and the tip of the center electrode, and a spark discharge is generated by applying a voltage to the gap.

  Further, in order to improve wear resistance against spark discharge, a tip made of a metal having excellent durability such as a noble metal alloy is joined to a portion of the ground electrode facing the tip of the center electrode, and the tip and the center electrode There is known a technique for forming the gap between the front end portion of each of them (for example, see Patent Document 1).

JP 2012-89353 A

  By the way, in recent years, in order to improve the fuel efficiency, etc., the compression of the internal combustion engine or the like has been advanced, and in such an internal combustion engine or the like, the tip tends to be extremely hot. For this reason, the difference in thermal expansion (thermal stress) generated between the ground electrode and the chip tends to be larger, and the chip may fall off the ground electrode.

  In particular, when the outer diameter of the chip is made relatively large in order to improve wear resistance [for example, the ratio of the outer diameter B of the chip to the width A of the ground electrode (B / A) is 0.5 or more. In some cases, the tip is likely to be very hot, and there is a greater concern about tipping off.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a spark plug capable of sufficiently increasing the bonding strength of the chip to the ground electrode and more reliably preventing the chip from falling off. It is to provide a manufacturing method.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The spark plug of this configuration includes a cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A cylindrical metal shell provided on the outer periphery of the insulator;
A rod-shaped ground electrode whose base end is fixed to the tip of the metal shell;
A spark plug comprising: a chip that is bonded to a surface of the ground electrode that is located on the center electrode side in a state where a part of the ground electrode is buried and that forms a gap with the center electrode. And
In a cross section including the central axis of the chip and parallel to the central axis of the ground electrode,
The area S1 (mm ² ) of the buried portion of the chip with respect to the ground electrode on the tip end side of the ground electrode with respect to the center axis of the chip is greater than the center axis of the chip on the base end side of the ground electrode. area of immersed part of said tip for the ground electrode S2 (mm ²⁾ much larger than the,
The tip end surface of the tip in the axial direction embedded in the ground electrode is inclined with respect to the surface of the ground electrode located on the center electrode side .

  According to the configuration 1, the area S1 corresponding to the tip burying amount on the distal end side of the ground electrode is configured to be larger than the area S2 corresponding to the tip burying amount on the proximal end side of the ground electrode. . Accordingly, since the portion of the chip that is buried in the ground electrode has a so-called wedge shape, a force in the direction of sandwiching the chip can be applied from the ground electrode to the chip. Further, at a high temperature, a large pinching force can be applied from the tip end side of the ground electrode having a large thermal expansion amount to a portion of the chip located closer to the tip end side of the ground electrode than the central axis. As a result, the bonding strength of the chip to the ground electrode can be sufficiently increased, and the chip can be more reliably prevented from falling off.

  Configuration 2. The spark plug of this configuration is characterized in that, in the above configuration 1, S1 / S2 ≧ 1.05 is satisfied.

  According to the configuration 2, it is possible to further increase the sandwiching force applied to the chip from the ground electrode. Therefore, the bonding strength can be further improved, and the chip can be more reliably prevented from falling off.

  Configuration 3. The spark plug of this configuration is characterized in that, in the above configuration 1 or 2, S1 / S2 ≦ 1.50 is satisfied.

  If S1 / S2 is excessively large, a lot of minute spaces are formed in the portion of the ground electrode where the chip is bonded. According to the above configuration 3, S1 / S2 ≦ 1.50. Therefore, the formation of the space can be prevented more reliably. Therefore, it is possible to suppress a decrease in mechanical strength of the ground electrode, and it is possible to increase the bonding strength of the chip to the ground electrode (especially against mechanical load). As a result, the chip drop prevention effect can be further improved.

Configuration 4. The spark plug manufacturing method according to the present configuration is the spark plug manufacturing method according to any one of claims 1 to 3,
A bonding step of bonding the chip to the ground electrode;
In the bonding step, a surface to be bonded of the chip to be bonded to the ground electrode is inclined by 2 ° or more and 12 ° or less with respect to a bonding planned surface of the chip to which the chip is bonded, By contacting the ground electrode with a portion disposed on the tip side of the ground electrode, while pressing the chip against the ground electrode, by energizing between the ground electrode and the chip, A chip is bonded to the ground electrode.

  According to the configuration 4, the area S1 is excessively larger than the area S2 while the area S1 is larger than the area S2 (that is, S1 / S2> 1.50). This can be prevented more reliably. That is, according to the configuration 4, a spark plug satisfying the configuration 1 and the configuration 3 (that is, the chip bonding strength is extremely excellent) can be obtained by a simple method.

  Configuration 5. In the spark plug manufacturing method according to the present configuration, in the configuration 4, in the bonding step, the surface to be bonded to the ground electrode of the chip is bonded to the planned bonding surface of the ground electrode to which the chip is bonded. The joining surface is inclined by 3 ° or more and 12 ° or less.

  According to the above configuration 5, the manufactured spark plug can more reliably satisfy S1 / S2 ≧ 1.05. That is, it is possible to easily obtain a spark plug in which the chip bonding strength is further improved.

It is a partially broken front view which shows the structure of a spark plug. It is a partially broken expanded front view which shows the structure of the front-end | tip part of a spark plug. It is the elements on larger scale which show a ground electrode and a ground electrode side chip | tip. It is an expanded sectional view for demonstrating the embedding state of the ground electrode side chip | tip with respect to a ground electrode. It is a schematic diagram for demonstrating the relative positional relationship of a ground electrode and a ground electrode side chip | tip in a joining process. (A), (b) is a schematic diagram for demonstrating the method of an electrode bending test.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the direction of the axis CL <b> 1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

  The spark plug 1 includes an insulator 2 as a cylindrical insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. The leg length part 13 formed in diameter smaller than this on the side is provided. In addition, of the insulator 2, the large diameter portion 11, the middle trunk portion 12, and most of the leg long portions 13 are accommodated inside the metal shell 3. A tapered step portion 14 is formed at the connecting portion between the middle body portion 12 and the long leg portion 13, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  Further, a shaft hole 4 is formed through the insulator 2 along the axis CL <b> 1, and a center electrode 5 is inserted on the tip side of the shaft hole 4. The center electrode 5 includes an inner layer 5A made of a metal (for example, copper or copper alloy) excellent in thermal conductivity, and an outer layer 5B made of an alloy containing nickel (Ni) as a main component. Further, the tip portion of the center electrode 5 is a cylindrical shape made of a metal with excellent wear resistance (for example, a metal containing one or more of Pt, Ir, Pd, Rh, Ru, Re, etc.). A center electrode side tip 31 is provided. The center electrode 5 has a rod shape (cylindrical shape) as a whole and protrudes from the tip of the insulator 2.

  In addition, a terminal electrode 6 is inserted and fixed on the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2.

  Further, a cylindrical resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seal layers 8 and 9, respectively.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a spark plug 1 is attached to the outer peripheral surface of the metal shell 3 such as an internal combustion engine or a fuel cell reformer. A threaded portion (male threaded portion) 15 for attachment to the hole is formed. Further, a seat portion 16 projecting radially outward is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. Further, on the rear end side of the metal shell 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the combustion device is provided. 1 is provided with a caulking portion 20 for holding the insulator 2.

  A tapered step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the step 14 of the metal shell 3 is locked to the step 21 of the metal shell 3. It is fixed to the metal shell 3 by caulking the rear end side opening portion radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  In addition, as shown in FIG. 2, a base end portion of a rod-like ground electrode 27 is fixed to the distal end portion 26 of the metal shell 3. The ground electrode 27 is formed of an alloy containing Ni as a main component, and is bent back at a substantially middle portion thereof. In the present embodiment, the ground electrode 27 has a rectangular cross section and is configured to have a constant width along its longitudinal direction.

  In addition, a metal having excellent wear resistance by resistance welding (for example, a metal containing one or more of Pt, Ir, Pd, Rh, Ru, Re, etc.) is provided at the tip of the ground electrode 27. A cylindrical ground electrode side chip 32 (corresponding to the “chip” of the present invention) is joined. A spark discharge gap 33 is formed as a gap between the tip of the center electrode 5 (center electrode side tip 31) and the ground electrode side tip 32, and the spark discharge gap 33 has an axis CL1. It is comprised so that a spark discharge may arise in the direction along substantially. The ground electrode side chip 32 may be made of Pt or an alloy containing Pt as a main component (“main component” means a component having the highest mass ratio in the material). preferable. The alloy preferably contains Ni, more preferably 30% by mass or less, still more preferably 5% by mass or more and 25% by mass or less, and more preferably 10% by mass or more and 20% by mass. More preferably, it is less than or equal to mass%.

  Further, the ground electrode side chip 32 is bonded to the central portion along the width direction of the ground electrode 27. The ground electrode side chip 32 is bonded to the ground electrode 27 in a state where at least a part of the ground electrode 27 along the thickness direction of the inner peripheral side surface 27S located on the center electrode 5 side of the ground electrode 27 is buried. Has been.

  In the present embodiment, as shown in FIG. 3, the width of the ground electrode 27 at the portion where the ground electrode side chip 32 is joined is A (mm), and the outer diameter of the ground electrode side chip 32 is B (mm). In this case, B / A ≧ 0.5 is satisfied. That is, during the operation of the internal combustion engine or the like, the amount of heat received by the ground electrode side tip 32 is relatively large, but the heat of the ground electrode side tip 32 is not easily conducted to the metal shell 3 side via the ground electrode 27. The electrode side chip 32 is configured to be easily heated.

In addition, in this embodiment, the buried portion of the ground electrode side chip 32 with respect to the ground electrode 27 is configured to be in the following manner. That is, as shown in FIG. 4 (in FIG. 4, for convenience of illustration, the hatching attached to the ground electrode 27 and the ground electrode side chip 32 in FIG. 1 etc. is omitted), the center of the ground electrode side chip 32 is shown. The cross section includes the axis CL2 (in the present embodiment, the central axis CL2 coincides with the axis CL1) and takes a cross section parallel to the central axis CL3 of the ground electrode 27. At this time, the area S1 (mm ² ) of the buried portion BR1 (the hatched portion in FIG. 4) of the ground electrode side chip 32 with respect to the ground electrode 27 on the tip side of the ground electrode 27 with respect to the central axis CL2 is the center. More than the area S2 (mm ² ) of the buried portion BR2 of the ground electrode side chip 32 with respect to the ground electrode 27 (portion with a dotted pattern in FIG. 4) on the base end side of the ground electrode 27 than the axis CL2. It is said that. In the present embodiment, the end surface of the ground electrode side chip 32 buried in the ground electrode 27 is configured to be inclined with respect to the inner peripheral side surface 27S of the ground electrode 27.

Furthermore, in this embodiment, it is configured to satisfy 1.05 ≦ S1 / S2 ≦ 1.50. Note that in the cross section, the area of the portion buried in the ground electrode 27 of the ground electrode tip 32 (the sum of the areas S1 and area S2) is a 0.295Mm ² or 0.55 mm ² or less.

  Note that the buried portions BR1 and BR2 have a virtual line VL formed by extending a straight line located on the base end side of the ground electrode 27 out of the outline of the inner peripheral side surface 27S to the distal end side of the ground electrode 27 in the cross section. It can also be said that the portion is located inside the ground electrode 27.

  Next, the manufacturing method of the spark plug 1 comprised as mentioned above is demonstrated.

  First, the metal shell 3 is processed in advance. That is, a rough shape is formed by performing a cold forging process or the like on a cylindrical metal material (for example, an iron-based material or a stainless steel material), and a through hole is formed. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, a straight bar-shaped ground electrode 27 is resistance-welded to the front end surface of the metal shell intermediate. When the welding is performed, so-called “sag” is generated. After the “sag” is removed, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 3 to which the ground electrode 27 is welded is obtained. The metal shell 3 to which the ground electrode 27 is welded is galvanized or nickel plated. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

  On the other hand, the insulator 2 is formed separately from the metal shell 3. That is, by using raw material powder mainly composed of alumina and containing a binder or the like, a green compact for molding is prepared, and by performing rubber press molding using the green granule for molding, a cylindrical molded body Get. And the insulator 2 is obtained by shaping | molding the obtained molded object by baking, and baking the shape | molded thing with a baking furnace.

  Separately from the metal shell 3 and the insulator 2, the center electrode 5 is manufactured. That is, the center electrode 5 is produced by forging a Ni alloy in which a copper alloy or the like for improving heat dissipation is arranged at the center. Further, the center electrode side tip 31 is joined to the tip of the center electrode 5 by laser welding or the like.

  Next, the insulator 2 and the center electrode 5, the resistor 7, and the terminal electrode 6 obtained as described above are sealed and fixed by the glass seal layers 8 and 9. The glass seal layers 8 and 9 are generally prepared by mixing borosilicate glass and metal powder, and the prepared material is injected into the shaft hole 4 of the insulator 2 with the resistor 7 interposed therebetween. After being done, it is baked and hardened by heating in the firing furnace while pressing with the terminal electrode 6 from the rear. At this time, the glaze layer may be fired simultaneously on the surface of the rear end body portion 10 of the insulator 2 or the glaze layer may be formed in advance.

  Thereafter, the insulator 2 provided with the center electrode 5 and the terminal electrode 6 and the metal shell 3 provided with the ground electrode 27 are fixed. More specifically, after the insulator 2 is inserted through the metal shell 3, the rear end side opening of the metal shell 3 formed relatively thin is crimped radially inward, that is, the crimp portion 20 is formed. By doing so, the insulator 2 and the metal shell 3 are fixed.

  Next, in the joining step, the ground electrode side chip 32 is joined to the tip of the ground electrode 27. Specifically, first, after removing zinc plating and the like at the tip of the ground electrode 27, the ground electrode 27 is slightly inclined toward the axis CL1 side with respect to the metal shell 3 as shown in FIG. . As a result, the surface to be joined 32S of the ground electrode side chip 32 to be joined to the ground electrode 27 with respect to the inner peripheral side surface 27S to be joined to the ground electrode side chip 32 of the ground electrode 27 is angle θ. Just tilt. In the present embodiment, the inclination angle of the ground electrode 27 with respect to the metal shell 3 is set so that the angle θ is 2 ° or more and 12 ° or less (more preferably, 3 ° or more and 12 ° or less). Note that the ground electrode side chip 32 before joining has a certain thickness.

  Next, after the ground electrode side tip 32 is brought into contact with the ground electrode 27, the ground electrode 27 and the ground electrode 27 are pressed while pressing the ground electrode side tip 32 against the ground electrode 27 with a predetermined welding electrode rod WR. The side chips 32 are energized with a predetermined current value. Thereby, the ground electrode side chip 32 is welded to the ground electrode 27 in a state in which a part along the thickness direction is buried in the ground electrode 27.

  As described above, since the bonded surface 32S is inclined with respect to the inner peripheral side surface 27S, only the portion of the ground electrode side chip 32 disposed on the tip side of the ground electrode 27 is in contact with the ground electrode 27. Welding is started in the state. For this reason, due to energization, the contact portion between the ground electrode 27 and the portion disposed on the tip side of the ground electrode 27 in the ground electrode side tip 32 becomes particularly high temperature, and the tip of the ground electrode 27 in the ground electrode side tip 32 is placed on the tip side. The part to be disposed is buried relatively deeply with respect to the ground electrode 27. In addition, when the site | part arrange | positioned in the front end side of the ground electrode 27 among the ground electrode side chips | tips 32 is deeply buried, the site | part adjacent to the said site | part of the ground electrode 27 bulges and deforms.

  When the ground electrode 27 is buried in the ground electrode 27 to some extent, the ground electrode 27 comes into contact with a portion of the ground electrode chip 32 disposed on the base end side of the ground electrode 27. In this state, the ground electrode 27 is in contact with the ground electrode 27. The contact area between 27 and the ground electrode side chip 32 is sufficiently large. Therefore, the portion of the ground electrode side chip 32 that is disposed on the proximal end side of the ground electrode 27 and the contact portion between the ground electrode 27 are unlikely to become high temperature, and the ground electrode side chip 32 is disposed on the proximal end side of the ground electrode 27. The buried amount of the portion to be grounded with respect to the ground electrode 27 is relatively small. Thereby, the area S1 can be easily made larger than the area S2.

  Further, a portion of the ground electrode side chip 32 that is disposed on the proximal end side of the ground electrode 27 is crushed and deformed by being pressed, and as a result, the maximum thickness of the portion is that of the ground electrode side chip 32. Of these, the thickness is smaller than the maximum thickness of the portion disposed on the tip side of the ground electrode 27. The area S1, S2 and thus S1 / S2 can be changed by changing the load and energizing current when pressing the ground electrode side tip 32, the shape of the ground electrode side tip 32 before welding, and the angle θ. it can.

  After joining the ground electrode side chip 32, the ground electrode 27 is bent toward the center electrode 5 side, and the size of the spark discharge gap 33 formed between the center electrode 5 (center electrode side chip 31) and the ground electrode side chip 32 is increased. By adjusting the above, the above-described spark plug 1 is obtained.

  As described above in detail, according to the present embodiment, the area S1 is configured to be larger than the area S2. Therefore, since the portion embedded in the ground electrode 27 of the ground electrode side chip 32 has a so-called wedge shape, a force in a direction to sandwich the ground electrode side chip 32 is applied from the ground electrode 27 to the ground electrode side chip 32. Can do. Further, under high temperature, the ground electrode 27 having a large thermal expansion amount is larger than the buried portion BR1 located on the tip side of the ground electrode 27 with respect to the center axis CL2 in the ground electrode side chip 32 from the tip side of the ground electrode 27. A pinching force can be applied. As a result, the bonding strength of the ground electrode side chip 32 to the ground electrode 27 can be sufficiently increased, and the ground electrode side chip 32 can be more reliably prevented from falling off.

  In particular, in the present embodiment, since S1 / S2 ≧ 1.05, the pinching force applied from the ground electrode 27 to the ground electrode side chip 32 can be further increased. Accordingly, the bonding strength can be further improved, and the ground electrode side chip 32 can be more reliably prevented from falling off.

  Further, since S1 / S2 ≦ 1.50, it is possible to more reliably prevent a minute space from being formed in the ground electrode 27 due to the joining of the ground electrode side chip 32. Accordingly, it is possible to suppress a decrease in the mechanical strength of the ground electrode 27 and to increase the bonding strength of the ground electrode side chip 32 to the ground electrode 27 (particularly to a mechanical load). As a result, the drop prevention effect of the ground electrode side chip 32 can be further improved.

  In addition, in the joining step, the angle θ is configured to be 2 ° or more and 12 ° or less. Therefore, the area S1 is made larger than the area S2 while the area S1 is excessively larger than the area S2 (that is, S1 / S2> 1.50). Can be prevented. That is, the spark plug 1 with extremely excellent bonding strength of the ground electrode side chip 32 can be obtained by a simple method.

  In particular, in the present embodiment, the angle θ is configured to be 2 ° or more and 12 ° or less by a simple method of inclining the ground electrode 27 with respect to the metal shell 3. Therefore, the above-described spark plug 1 can be obtained more easily.

  Next, in order to confirm the effects achieved by the above embodiment, the area S1 and S2 are adjusted after the width A of the ground electrode is set to 2.7 mm and the outer diameter B of the tip on the ground electrode side is set to 1.6 mm. As a result, the spark plug samples with various changes of S1 / S2 and the width A of the ground electrode are set to 4.4 mm and the outer diameter B of the tip of the ground electrode side is set to 2.2 mm. By adjusting, a plurality of spark plug samples in which S1 / S2 were variously changed were produced, and a desktop cooling test was performed on each sample.

  The outline of the desk cooling test is as follows. That is, with a predetermined high-frequency heating device, the tip of the ground electrode was heated for 30 seconds so that the temperature became 1000 ° C., and then allowed to cool for 2 minutes, and then 5000 cycles were performed. After the end of 5000 cycles, the ground electrode side chip is separated from the ground electrode at the boundary portion between the ground electrode and the ground electrode side chip while taking a cross section including the central axis of the ground electrode side chip and parallel to the central axis of the ground electrode. The length of the part (peeling part) which has been measured was measured. And the ratio (peeling ratio) of the length of the said peeling part with respect to the length of the said boundary part was computed. Here, a sample having a peeling ratio of more than 30% and not more than 40% is less likely to cause oxide scale at the boundary portion under high temperature, and is evaluated as “◯” because it has good peeling resistance against thermal load. The sample having a peeling ratio of 30% or less was evaluated as “◎” as having very good peeling resistance against a thermal load. On the other hand, a sample having a peeling ratio of more than 40% is evaluated as “x” because an oxide scale is likely to be formed at the boundary portion at a high temperature and the peeling resistance against a thermal load is insufficient. I decided to give it.

  Table 1 shows the test results of a sample in which the width A of the ground electrode is 2.7 mm and the outer diameter B of the ground electrode side chip is 1.6 mm. Table 2 shows that the width A of the ground electrode is 4.4 mm. The test result of the sample which made the outer diameter B of the ground electrode side chip 2.2 mm is shown. The ground electrode side chip having an outer diameter B of 1.6 mm has a thickness of 0.4 mm before bonding to the ground electrode, and the ground electrode side chip having an outer diameter B of 2.2 mm is bonded to the ground electrode. The previous thickness was 1.0 mm. The ground electrode side chip with an outer diameter B of 1.6 mm was made of Pt-10Ni, and the ground electrode side chip with an outer diameter B of 2.2 mm was made of Pt-20Ni.

  As shown in Table 1 and Table 2, it was found that the samples in which the area S1 was larger than the area S2 had good peeling resistance. This is because the portion embedded in the ground electrode in the ground electrode side tip has a so-called wedge shape, so that a force in the direction of sandwiching the ground electrode side tip is applied from the ground electrode to the ground electrode side tip. And, under high temperature, a large pinching force was applied from the front end side of the ground electrode having a large thermal expansion amount to a portion of the ground electrode side chip located closer to the front end side of the ground electrode than the center axis thereof. It seems to be due to the point.

  In particular, it was confirmed that the sample satisfying S1 / S2 ≧ 1.05 has very good peeling resistance. This is considered to be because the clamping force applied from the ground electrode to the ground electrode side chip is further increased.

  From the results of the above test, it can be said that the area S1 is preferably larger than the area S2 in order to improve the peel resistance.

  Moreover, it can be said that it is more preferable to satisfy S1 / S2 ≧ 1.05 in order to further improve the peel resistance.

  Next, the width A of the ground electrode is set to 2.7 mm, the outer diameter B of the tip on the ground electrode side is set to 1.6 mm, and the areas S1 and S2 are adjusted so that S1 / S2 is variously changed. A plurality of ground electrodes were prepared, and an electrode bending test was performed on each ground electrode. The outline of the electrode bending test is as follows. That is, as shown in FIGS. 6A and 6B, the ground electrode is bent at a right angle at the position where the center portion of the ground electrode side chip is joined. Then, the ground electrode side chip | tip was observed and it was confirmed whether the ground electrode side chip | tip peeled from the ground electrode. Here, as shown in FIG. 6A, when the chip on the ground electrode side does not peel off, the evaluation of “◯” is given as having excellent peeling resistance against the mechanical load. did. On the other hand, as shown in FIG. 6 (b), when peeling occurs in at least a part of the ground electrode side chip, the evaluation of “x” is given because the peeling resistance against a mechanical load is insufficient. It was decided that Table 3 shows the results of the test. Note that the thickness of the ground electrode side chip before bonding was 0.4 mm.

  As shown in Table 3, it was revealed that excellent peeling resistance with respect to a mechanical load can be realized by satisfying S1 / S2 ≦ 1.50. This is because if S1 / S2 is excessively large, a lot of minute spaces are formed in the ground electrode where the ground electrode side tip is welded, and S1 / S2 ≦ 1.50. This is considered to be because the formation of the space was more reliably prevented and the decrease in mechanical strength of the ground electrode was suppressed.

  From the results of the above test, it can be said that it is more preferable to satisfy S1 / S2 ≦ 1.50 in order to further improve the peel resistance.

  Next, a sample of a spark plug formed by joining the ground electrode side tip to the ground electrode after making the angle θ different from each other was produced. Then, in the prepared sample, the area S1 and the area S2 were measured, the magnitude relationship between S1 and S2 was examined, and it was confirmed whether or not a minute space was formed in the ground electrode as a result of bonding. Here, a sample satisfying S1> S2 and having no space formed in the ground electrode is evaluated as “◯” as having good peeling resistance against a thermal load and a mechanical load. . On the other hand, a sample in which S1 ≦ S2 or a space is formed in the ground electrode indicates that the peel resistance is insufficient with respect to at least one of a thermal load and a mechanical load. It was decided to make an evaluation.

  Table 4 shows the results of the test. In each sample, the width A of the ground electrode was 2.7 mm, and the outer diameter B of the ground electrode side chip was 1.6 mm. Further, the thickness of the ground electrode side chip before bonding was set to 0.4 mm.

  As shown in Table 4, when the angle θ is not less than 2 ° and not more than 12 °, S1> S2 is satisfied and a minute space is hardly formed in the ground electrode, so that the thermal load and the mechanical load are not affected. It was found to have good peel resistance. This is because, by setting the angle θ to 2 ° or more, a portion of the ground electrode side chip located on the tip side of the ground electrode can be deeply inserted into the ground electrode, and the angle θ is 12 ° or less. This is considered to be because it was possible to more reliably prevent the area S1 from becoming excessively large.

  In particular, by setting the angle θ to 3 ° or more, it was possible to satisfy S1 / S2 ≧ 1.05, and it was confirmed that the peel resistance against thermal load could be further improved.

  From the result of the above test, in order to more reliably manufacture a spark plug having good peeling resistance, in the joining process, the ground electrode side of the ground electrode in the joining process is to be joined to the ground electrode side chip to be joined. It can be said that it is preferable that the surface of the chip to be bonded to the ground electrode is inclined by 2 ° or more and 12 ° or less.

  Further, in order to more reliably manufacture a spark plug having superior peeling resistance, in the bonding process, the ground electrode side chip is bonded to the bonding planned surface to which the ground electrode side chip is bonded. It can be said that it is more preferable that the surface to be bonded to the ground electrode is inclined by 3 ° or more and 12 ° or less.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the ground electrode side chip 32 has a cylindrical shape, but the shape of the ground electrode side chip 32 is not particularly limited. Therefore, for example, the ground electrode side chip may be configured to have a rectangular parallelepiped shape or a polygonal column shape. In this case, the outer diameter B means that the ground electrode side chip is projected when the ground electrode side chip is projected along the central axis with respect to a plane orthogonal to the central axis of the ground electrode side chip. The diameter of the smallest circle that includes the projected area of the chip inside.

  (B) In the above embodiment, the case where the ground electrode 27 is joined to the distal end portion 26 of the metal shell 3 is embodied. However, a part of the metal shell (or the tip metal fitting previously welded to the metal shell) The present invention can also be applied to the case where the ground electrode is formed so as to cut out a part of (see Japanese Patent Laid-Open No. 2006-236906, etc.).

  (C) In the above embodiment, the tool engaging portion 19 has a hexagonal cross section, but the shape of the tool engaging portion 19 is not limited to such a shape. For example, it may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)].

  DESCRIPTION OF SYMBOLS 1 ... Spark plug, 2 ... Insulator (insulator), 3 ... Main metal fitting, 4 ... Shaft hole, 5 ... Center electrode, 27 ... Ground electrode, 32 ... Ground electrode side chip | tip (chip), 33 ... Spark discharge gap ( Gap), CL1... Axis, CL2... Center axis (of ground electrode side tip), CL3... Center axis (of ground electrode).

Claims (5)

A cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A cylindrical metal shell provided on the outer periphery of the insulator;
A rod-shaped ground electrode whose base end is fixed to the tip of the metal shell;
A spark plug comprising: a chip that is bonded to a surface of the ground electrode that is located on the center electrode side in a state where a part of the ground electrode is buried and that forms a gap with the center electrode. And
In a cross section including the central axis of the chip and parallel to the central axis of the ground electrode,
The area S1 (mm ² ) of the buried portion of the chip with respect to the ground electrode on the tip end side of the ground electrode with respect to the center axis of the chip is greater than the center axis of the chip on the base end side of the ground electrode. area of immersed part of said tip for the ground electrode S2 (mm ²⁾ much larger than the,
The spark plug according to claim 1, wherein an end surface of the tip in the axial direction embedded in the ground electrode is inclined with respect to a surface of the ground electrode located on the center electrode side .   The spark plug according to claim 1, wherein S1 / S2 ≧ 1.05 is satisfied.   The spark plug according to claim 1, wherein S1 / S2 ≦ 1.50 is satisfied. A method for manufacturing a spark plug according to any one of claims 1 to 3,
A bonding step of bonding the chip to the ground electrode;
In the bonding step, a surface to be bonded of the chip to be bonded to the ground electrode is inclined by 2 ° or more and 12 ° or less with respect to a bonding planned surface of the chip to which the chip is bonded, By contacting the ground electrode with a portion disposed on the tip side of the ground electrode, while pressing the chip against the ground electrode, by energizing between the ground electrode and the chip, A method of manufacturing a spark plug, comprising bonding a chip to the ground electrode.   In the bonding step, a bonding surface of the chip to be bonded to the ground electrode is inclined by 3 ° or more and 12 ° or less with respect to a bonding planned surface of the ground electrode to which the chip is bonded. The method for manufacturing a spark plug according to claim 4.

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