Spark plug and method of manufacturing the same

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

Spark plugs used in combustion devices such as internal combustion engines include, for example, a center electrode extending in the axial direction, an insulator provided on the outer periphery of the center electrode, and a cylindrical main metal fitting assembled to the outside of the insulator. And a ground electrode whose base end portion is joined to the tip end portion of the main metal fitting. The ground electrode is arranged with its substantially intermediate portion bent back so that its tip faces the tip of the center electrode, whereby a spark discharge occurs between the tip of the center electrode and the tip of the ground electrode. A gap is formed.

Further, in recent years, there has been known a technique of joining a noble metal chip to a portion of the tip of the ground electrode that forms the spark discharge gap to improve wear resistance. Here, as a method of joining the precious metal chip to the ground electrode, there is a method of joining the two by irradiating the outer edge of the contact surface between the two with a laser beam to form a molten portion formed by melting the metal materials constituting the two. It is generally used (see, for example, Patent Document 1 and the like).

By the way, from the viewpoint of further improving the wear resistance, it is conceivable to increase the diameter of the noble metal chip and further increase the area of the surface (discharge surface) of the noble metal chip forming the spark discharge gap.

<p><patcit num="1"><text>Japanese Patent Application Laid-Open No. 2005-158323</text></patcit></p>

<p> However, in the noble metal chip having a large diameter, the difference in thermal stress between the noble metal chip and the ground electrode becomes relatively large. Further, when the noble metal chip is bonded to the ground electrode, since the noble metal chip has a large diameter, the penetration depth of the molten portion may become excessively small compared to the size of the noble metal chip. That is, when a large-diameter precious metal chip is used, the thermal stress difference between the ground electrode and the precious metal chip increases, while a molten portion that absorbs the thermal stress difference is formed with a sufficient depth. Difficult to do. Therefore, there is further concern about the development of the oxidation scale at the joint portion between the two, and eventually the peeling of the noble metal chip from the ground electrode.</p><p> On the other hand, it is conceivable to increase the penetration depth of the molten portion by increasing the irradiation energy of the laser beam, but the molten portion reaches or approaches the discharge surface simply by increasing the irradiation energy. Therefore, there is a possibility that the effect of improving the wear resistance due to the provision of the precious metal chip is not sufficiently exhibited.</p><p> It is also conceivable to thicken the noble metal chip to prevent the molten portion from reaching or approaching the discharge surface. However, since the noble metal alloy constituting the noble metal chip is expensive, if the noble metal chip having a larger diameter is made thicker, the cost may increase remarkably. Rather, the reality is that we want to reduce the thickness of precious metal chips in order to suppress the cost increase due to the increase in diameter as much as possible.</p><p> The present invention has been made in view of the above circumstances, and an object of the present invention is to ensure sufficient peeling resistance of a noble metal tip in a spark plug in which a relatively large diameter noble metal tip is bonded to a ground electrode. The present invention is to provide a spark plug and a method for manufacturing the same, which can suppress an increase in cost.</p>

<p> Hereinafter, each configuration suitable for solving the above object will be described in terms of terms. In addition, if necessary, the action and effect peculiar to the corresponding configuration will be added.</p><p> Configuration 1. The spark plug of this configuration consists of a tubular insulator with a shaft hole that penetrates in the axial direction, and a tubular insulator. The center electrode inserted on the tip side of the shaft hole and A tubular main metal fitting provided on the outer circumference of the insulator and The ground electrode arranged at the tip of the main metal fitting and It is provided with a precious metal tip that is joined to the tip of the ground electrode and forms a gap with the tip of the center electrode. The area of the surface of the precious metal chip forming the gap is 0.9 mm.²The above is the spark plug The noble metal chip is a fused portion in which the ground electrode and the noble metal chip are fused, which is formed by irradiating at least one surface of the tip surface and the side surface of the ground electrode with a laser beam or an electron beam. It is joined to the ground electrode via On a projection plane in which the precious metal chip and the molten portion are projected onto a projection plane orthogonal to the central axis along the central axis of the precious metal chip. The ratio of the region where the precious metal chip and the molten portion overlap with respect to the region where the precious metal chip is projected is 70% or more.<u style="single">,further,</u><u style="single">The molten portion is formed by irradiating at least the first surface of the tip surface and the side surface of the ground electrode and a second surface different from the first surface with a laser beam or an electron beam. At the same time</u><u style="single">A first molten region formed by irradiating the first surface with a laser beam or an electron beam, and a first formed by irradiating the second surface with a laser beam or an electron beam. An overlapping molten region is formed by overlapping the molten regions of 2.</u>It is characterized by that.</p><p> The term "side surface of the ground electrode" means a surface of the ground electrode that is adjacent to the surface facing the center electrode (excluding the tip surface of the ground electrode).</p><p> As in the above configuration 1, the area of the surface (discharge surface) forming the gap is 0.9 mm.²While the precious metal chip having a relatively large diameter can be expected to have improved wear resistance, as described above, there is a further concern about peeling from the ground electrode.</p><p> In this regard, according to the above configuration 1, the region formed by projecting the precious metal chip on the projection surface in which the precious metal chip and the molten portion are projected onto the projection surface orthogonal to the central axis along the central axis of the precious metal chip. On the other hand, the ratio of the area where the precious metal chip and the molten part overlap is 70% or more. That is, the precious metal tip is joined to the ground electrode via a sufficiently wide melted portion. Therefore, even a relatively large thermal stress difference generated between the large-diameter precious metal chip and the ground electrode can be sufficiently absorbed by the molten portion, and the evolution of the oxidation scale at the junction between the two can be more reliably performed. Can be prevented. As a result, the peeling resistance of the noble metal chip can be improved more reliably.</p><p> Further, the molten portion is formed by irradiating at least one surface of the tip surface and the side surface of the ground electrode with a laser beam or an electron beam instead of the outer edge of the contact surface between the ground electrode and the precious metal chip. .. Therefore, even if a sufficient area of the molten portion is secured as described above, it is unlikely that the molten portion reaches or approaches the discharge surface, and the wear resistance due to the provision of the precious metal tip is provided. It is possible to fully exert the improvement effect of. As a result, the area of the discharge surface of the precious metal chip is 0.9 mm.²Combined with the above and the relatively large size, it is possible to dramatically improve the wear resistance.</p><p> Further, since it is possible to suppress the arrival or approach of the molten portion to the discharge surface, a relatively thin-walled (for example, 0.5 mm or less) noble metal chip can be used. As a result, it is possible to effectively suppress an increase in manufacturing cost due to the use of a noble metal chip having a large diameter.<u style="single">Further, in the melting portion, an overlapping melting region is formed in which the first melting region and the second melting region overlap each other. That is, the molten portion extends between the tip surface of the ground electrode and at least one side surface of the ground electrode, or between the side surfaces of the ground electrode, or on the tip surface and both side surfaces of the ground electrode. It is formed between the faces. Therefore, the bonding strength of the noble metal chip to the ground electrode can be further improved, and the peeling resistance of the noble metal chip can be further improved.</u></p><p> Configuration 2. The spark plug of the present configuration is characterized in that, in the above configuration 1, the molten portion is formed over the entire area between the outer peripheral portion of the base end portion of the precious metal chip and the ground electrode. ..</p><p> According to the above configuration 2, the molten portion is formed so as to cover the boundary portion between the precious metal chip and the ground electrode. Therefore, the presence of the molten portion can effectively prevent the invasion of the corrosive gas into the boundary portion, and more reliably prevent the development of the oxide scale at the joint portion between the noble metal chip and the ground electrode. As a result, the peeling resistance of the noble metal chip can be further improved.</p><p> Constitution<u style="single">3</u>The spark plug of this configuration has the above configuration.<u style="single">1 or 2</u>In a projection plane formed by projecting a straight line extending along the longitudinal direction of the ground electrode, the noble metal chip, and the molten portion along the central axis of the noble metal chip. The overlapping molten region is located on the straight line in the region formed by projecting the noble metal chip.</p><p> Above configuration<u style="single">3</u>According to the above, the thermal stress difference generated between the ground electrode and the noble metal chip can be more reliably absorbed by the molten portion. As a result, the progress of the oxidation scale at the joint portion between the two can be suppressed extremely effectively, and the peeling resistance of the noble metal chip can be further improved.</p><p> Constitution<u style="single">4</u>The spark plug of this configuration has the above configuration.<u style="single">1 or 2</u>In a projection plane formed by projecting the central axis of the noble metal chip and the molten portion along the central axis of the noble metal chip. The overlapping molten region is located on the central axis of the precious metal chip.</p><p> Above configuration<u style="single">4</u>According to the above, the thermal stress difference generated between the ground electrode and the noble metal chip can be more reliably absorbed by the molten portion, and the peeling resistance of the noble metal chip can be dramatically improved.</p><p> Constitution<u style="single">5</u>The spark plug of this configuration has the above configurations 1 to 1.<u style="single">4</u>In any of the above, the molten portion is not exposed on the surface of the noble metal chip forming the gap.</p><p> Above configuration<u style="single">5</u>According to the above, since the molten portion, which is inferior in wear resistance as compared with the precious metal chip, is not exposed on the discharge surface, the effect of improving the wear resistance due to the provision of the precious metal chip can be more reliably exhibited.</p><p> Constitution<u style="single">6</u>The spark plug of this configuration has the above configurations 1 to 1.<u style="single">5</u>In any of the above, the precious metal chip contains at least one of iridium (Ir), platinum (Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), and rhenium (Re). It is characterized by.</p><p> Above configuration<u style="single">6</u>As described above, by using a metal material containing Pt, Ir, or the like as a metal material constituting the noble metal chip, it is possible to further improve the wear resistance.</p><p> Constitution<u style="single">7</u>The manufacturing method of the spark plug of this configuration is described in the above configurations 1 to 1.<u style="single">6</u>The method for manufacturing a spark plug described in any of the above. After placing the noble metal chip on the ground electrode, the laser beam or the laser beam or the laser beam or the contact surface of the noble metal chip and the ground electrode is inclined from a direction opposite to the surface forming the gap of the noble metal chip. It is characterized in that the precious metal chip is bonded to the ground electrode by irradiating the electron beam.</p><p> Above configuration<u style="single">7</u>According to the above, when the noble metal chip is joined to the ground electrode, a laser beam or an electron beam is emitted from a direction inclined from a direction parallel to the surface (discharge surface) forming the gap of the noble metal chip toward the back surface side of the ground electrode. Be irradiated. Therefore, it is possible to reduce the portion of the noble metal chip that melts at the time of joining, and the noble metal chip after joining has a sufficient thickness. As a result, the wear resistance can be further improved.</p><p> Further, since the molten portion formed by irradiating the laser beam or the electron beam may have minute irregularities formed on its surface, the electric discharge is performed between the uneven portion having a relatively high electric field strength and the center electrode at the time of discharge. May occur and the durability may decrease, but the above configuration<u style="single">7</u>According to the above, it is relatively easy to form a molten portion so as not to be exposed on the gap (spark discharge gap) side. Therefore, the above configuration<u style="single">7</u>If the molten portion is not exposed to the gap side, the discharge between the molten portion and the center electrode can be effectively suppressed, and the durability can be improved.</p><p> Constitution<u style="single">8</u>The manufacturing method of the spark plug of this configuration is the above configuration.<u style="single">7</u>The noble metal chip is bonded to the ground electrode by using a fiber laser or an electron beam.</p><p> Above configuration<u style="single">8</u>According to the above, the molten portion can be brought closer to the inner side of the ground electrode or the like while maintaining a relatively thin state of the fused portion. Therefore, even if the molten portion is formed over a relatively large region as described above, the volume of the fused portion can be made relatively small. Therefore, it is possible to further reduce the portion of the precious metal chip that melts during bonding, and even if a thinner precious metal chip is used, the precious metal chip after bonding has a sufficient thickness (volume). Become. As a result, the wear resistance can be further improved.</p>

<figref num="1">It is a partially broken front view which shows the structure of a spark plug.</figref><figref num="2">(a) is a partially enlarged front view showing the bonding position of the precious metal chip with respect to the ground electrode, and (b) is a partially broken enlarged front view showing the configuration of the tip portion of the spark plug.</figref><figref num="3">(a) is a partially enlarged side view showing the configuration of the molten portion and the like, and (b) is a projection drawing showing the projection surface on which the precious metal chip, the molten portion and the like are projected.</figref><figref num="4">It is a partially enlarged cross-sectional view which shows the cross-sectional shape of a molten part.</figref><figref num="5">It is a figure for demonstrating the method of specifying the shape and the position of the overlap | melting area, (a) is the perspective schematic view of the ground electrode and the like, (b) is the JJ line sectional view of (a), and ( c) is the KK line sectional view of (a), (d) is the LL line sectional view of (a), (e) is the MM line sectional view of (a), and (f) is (a). ) NN line sectional view.</figref><figref num="6">It is a figure for demonstrating the method of specifying the shape and the position of the overlap | melting area, (a) is the perspective schematic view of the ground electrode and the like, (b) is the JJ line sectional view of (a), and ( c) is a sectional view taken along line KK of (a), and (d) is a sectional view taken along line LL of (a).</figref><figref num="7">It is a figure for demonstrating the method of specifying the shape and the position of the overlap | melting area, (a) is the perspective schematic view of the ground electrode and the like, (b) is the JJ line sectional view of (a), and ( c) is a sectional view taken along line KK of (a).</figref><figref num="8">It is a figure for demonstrating the structure of the molten part in 2nd Embodiment, (a) is the partially enlarged side view which shows the tip part of the ground electrode, and (b) is the precious metal chip, the molten part, etc. It is a projection drawing which shows the projected projection plane.</figref><figref num="9">It is a graph which shows the test result of the desk burner test about the sample which changed the fusion part ratio variously.</figref><figref num="10">It is a figure which shows the shape of the molten part in each sample, (a) is the projection drawing which projected the molten part of sample 1, and (b) is the projection drawing which projected the molten part of sample 2. Yes, (c) is a projection drawing on which the molten part of sample 3 and the like are projected, and (d) is a projection drawing on which the melted part and the like of sample 4 are projected.</figref><figref num="11">It is a graph which shows the test result of the ignitability evaluation test.</figref><figref num="12">It is a partially enlarged sectional view for demonstrating the irradiation direction of a laser beam in another embodiment.</figref><figref num="13">It is a partially enlarged side view which shows the structure of the molten part and the like in another embodiment.</figref><figref num="14">(a) and (b) are projection views for explaining the structure of the molten portion in another embodiment.</figref><figref num="15">(a) and (b) are projection views for explaining the structure of the molten portion in another embodiment.</figref><figref num="16">It is a projection drawing for demonstrating the structure of the molten part in another embodiment.</figref>

[First Embodiment] Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a partially broken front view showing the spark plug 1. In FIG. 1, the axis CL1 direction 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 is composed of an insulator 2 as a tubular insulator, a tubular main metal fitting 3 for holding the insulator, and the like.

As is well known, the insulating insulator 2 is formed by firing alumina or the like, and in its outer shape, the rear end side body portion 10 formed on the rear end side and the tip of the rear end side body portion 10 are further formed. A large-diameter portion 11 formed to protrude outward in the radial direction on the side, a middle body portion 12 formed to have a smaller diameter on the tip side than the large-diameter portion 11, and a tip from the middle body portion 12. It is provided with a leg length portion 13 formed to have a smaller diameter on the side. In addition, of the insulating insulators 2, the large diameter portion 11, the middle body portion 12, and most of the leg length portions 13 are housed inside the main metal fitting 3. A tapered step portion 14 is formed at the connecting portion between the middle body portion 12 and the leg length portion 13, and the insulating insulator 2 is locked to the main metal fitting 3 at the step portion 14.

Further, a shaft hole 4 is formed through the insulating insulator 2 along the axis CL1, and a center electrode 5 is inserted and fixed to the tip end side of the shaft hole 4. The center electrode 5 is composed of an inner layer 5A made of copper or a copper alloy having excellent thermal conductivity and an outer layer 5B made of a Ni alloy containing nickel (Ni) as a main component. Further, the center electrode 5 has a rod shape (cylindrical shape) as a whole, the tip surface thereof is formed flat, and the center electrode 5 protrudes from the tip of the insulator 2. Further, a noble metal portion 31 made of a predetermined noble metal alloy (for example, platinum alloy or iridium alloy) is provided at the tip portion of the center electrode 5.

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

Further, a columnar resistor 7 is arranged 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 via conductive glass seal layers 8 and 9, respectively.

In addition, the main metal fitting 3 is formed in a tubular shape by a metal such as low carbon steel, and a spark plug 1 is attached to the outer peripheral surface thereof to attach a combustion device (for example, an internal combustion engine, a fuel cell reformer, etc.). A threaded portion (male threaded portion) 15 for attaching to the hole is formed. A seat portion 16 is formed on the outer peripheral surface of the screw portion 15 on the rear end side, and a ring-shaped gasket 18 is fitted into the screw neck 17 at the rear end of the screw portion 15. Further, on the rear end side of the main metal fitting 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the main metal fitting 3 is attached to the combustion device is provided, and the rear end portion is provided. A crimping portion 20 for holding the insulating insulator 2 is provided in the above.

Further, a tapered step portion 21 for locking the insulating insulator 2 is provided on the inner peripheral surface of the main metal fitting 3. Then, the insulating insulator 2 is inserted from the rear end side of the main metal fitting 3 toward the tip side, and the rear end of the main metal fitting 3 is locked to the step 21 of the main metal fitting 3. It is fixed by crimping the side opening inward in the radial direction, that is, by forming the crimping portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21 of both the insulating insulator 2 and the main metal fitting 3. As a result, the airtightness in the combustion chamber is maintained, and the fuel gas that enters the gap between the leg length portion 13 of the insulating insulator 2 exposed to the combustion chamber and the inner peripheral surface of the main metal fitting 3 is prevented from leaking to the outside.

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

Further, a substantially intermediate portion is bent back to the tip portion 26 of the main metal fitting 3, and a ground electrode 27 whose front end side surface faces the tip portion (precious metal portion 31) of the center electrode 5 is joined. The ground electrode 27 is made of a Ni alloy, and a columnar noble metal chip 32 is bonded to a portion facing the noble metal portion 31. The noble metal chip 32 is formed of a noble metal alloy containing at least one of iridium, platinum, rhodium, ruthenium, palladium, and rhenium. Further, a spark discharge gap 33 as a gap is formed between the tip surface (discharge surface) of the precious metal chip 32 and the precious metal portion 31, and sparks are formed in the spark discharge gap 33 in the direction along the axis CL1. Discharge is being performed.

In addition, the noble metal chip 32 has a relatively large diameter in order to improve wear resistance, and in the present embodiment, the surface (discharge surface) of the noble metal chip 32 forming the spark discharge gap 33. Area is 0.9mm²It is said that it is over. However, in order to suppress the increase in cost due to the increase in diameter, the precious metal chip 32 is made relatively thin (for example, 0.5 mm or less in thickness).

Further, although the ground electrode 27 is formed relatively thin in order to improve the ignitability, as shown in FIG. 2 (a) from the viewpoint of sufficiently maintaining the bonding area of the precious metal chip 32 with respect to the ground electrode 27. The width of the ground electrode 27 is larger than the outer diameter of the precious metal chip 32, and the precious metal chip 32 is joined so that the central axis CL2 of the precious metal chip 32 is located at the center of the ground electrode 27 in the width direction. ing. Therefore, the distance from the side surface 27S1 of the ground electrode 27 to the precious metal chip 32 along the direction orthogonal to the central axis CL2 of the precious metal chip 32 and the straight line SL extending along the longitudinal direction of the ground electrode 27 is defined as A (mm). When the width of the noble metal chip 32 is B (mm) and the distance from the noble metal chip 32 to the side surface 27S2 of the ground electrode 27 is C (mm), A + B + C 3.0 is satisfied.

In addition, as shown in FIG. 2B and the like, the noble metal chip 32 is a molten portion formed by melting the metal material constituting the ground electrode 27 and the metal material constituting the noble metal chip 32 with respect to the ground electrode 27. It is joined via 35 [Note that in FIG. 2 (a) above, the molten portion 35 is omitted]. In the present embodiment, the molten portion 35 is formed over the entire area between the outer peripheral portion of the base end portion of the precious metal chip 32 and the ground electrode 27.

Further, in the present embodiment, as shown in FIGS. 3 (a), 3 (b) and 4, the molten portion 35 has a laser beam or an electron beam with respect to the front end surface 27F and both side surfaces 27S1 and 27S2 of the ground electrode 27. Is formed by being irradiated with. More specifically, the molten portion 35 is composed of molten regions 35a, 35b, 35c, 35d, 35e, and the molten regions 35a, 35b are spark discharge gaps among the precious metal chips 32 with respect to the side surface 27S1 of the ground electrode 27. By irradiating two laser beams or electron beams along the direction parallel to the plane forming 33 (discharge plane) and orthogonal to the longitudinal direction of the ground electrode 27 (in the direction of the white arrow in FIG. 4). It is formed. Further, the molten regions 35c and 35d are in the direction parallel to the discharge surface of the precious metal chip 32 with respect to the portion of the side surface 27S2 of the ground electrode 27 located on the back surface of the molten regions 35a and 35b, and the ground electrode 27. By irradiating two laser beams or electron beams along a direction orthogonal to the longitudinal direction, the molten regions 35a and 35b are formed on the back surface side. Further, the molten region 35e is irradiated with a laser beam or an electron beam in a direction parallel to the discharge surface of the noble metal chip 32 with respect to the tip surface 27F of the ground electrode 27 and along the longitudinal direction of the ground electrode 27. It is formed by gradually moving the irradiation position along the width direction of the ground electrode 27. Further, by irradiating the tip surface 27F and the side surfaces 27S1 and 27S2 of the ground electrode 27 with a laser beam or an electron beam in this way, the molten portion 35 is not exposed on the discharge surface of the precious metal chip 32.

When the side surface 27S1 of the ground electrode 27 is the "first surface" in the present invention, the tip surface 27F and the side surface 27S2 of the ground electrode 27 correspond to the "second surface" in the present invention. .. When the side surface 27S1 of the ground electrode 27 is the "first surface" in the present invention, the molten regions 35a and 35b formed by irradiating the side surface 27S1 with a laser beam or an electron beam are the "first surface" in the present invention. The molten regions 35c, 35d, 35e formed by irradiating the tip surface 27F and the side surface 27S2 with a laser beam or an electron beam correspond to the "melted region" of the present invention. ..

Further, in the present embodiment, as shown in FIG. 3B, the projection of the precious metal chip 32 and the molten portion 35 projected onto the projection plane orthogonal to the central axis CL2 along the central axis CL2 of the precious metal chip 32. In the plane, the region AP1 [the region surrounded by the thick line in FIG. 3 (b)] on which the precious metal chip 32 is projected, and the region AO1 [FIG. 3 (b) where the precious metal chip 32 and the molten portion 35 overlap]. ), The shaded area] is said to occupy 70% or more (for example, 100%).

In addition, as shown in FIGS. 3 (b) and 4, in the melting portion 35, the overlapping melting region 37a in which the melting regions 35a and 35c overlap and the overlapping melting region 37a in which the melting regions 35b and 35d overlap are overlapped and melted. The overlapping melting region 37c where the regions 37b and the melting regions 35b and 35e overlap, the overlapping melting region 37d where the melting regions 35d and 35e overlap, and the overlapping melting region 37e where the melting regions 35b, 35d and 35e overlap each other. Is formed. In the present embodiment, when a straight line SL extending along the longitudinal direction of the ground electrode 27 passing through the central axis CL2 of the precious metal chip 32 is projected onto the projection plane along the central axis CL2 of the precious metal chip 32. In the region AP1 on which the precious metal chip 32 is projected, the formation positions of the molten region 35a and the like are set so that the overlapping molten regions 37a, 37b, 37e are located on the straight line SL.

The "overlapping and melting region" is formed by irradiating one of the front surface 27F and the side surfaces 27S1 and 27S2 (first surface) of the ground electrode 27 with a laser beam or an electron beam. A molten region formed by irradiating a laser beam or an electron beam on a surface different from the first surface (second surface) of the tip surface 27F and the side surfaces 27S1 and 27S2. Refers to the overlapping part of. Therefore, for example, the portion where the molten region 35a and the molten region 35b formed by irradiating the same side surface 27S1 with a laser beam or an electron beam do not correspond to the overlapping molten region in the present invention.

Further, the presence or absence of the overlapping molten region can be determined as follows. That is, in the molten region generally irradiated with the laser beam or the electron beam, the portion located inside the ground electrode 27 or the like (that is, the portion of the molten region excluding the portion melted toward the precious metal chip 32 side) is It has a tapered shape from the outer surface toward the inner side of the ground electrode 27 and the like. Therefore, for example, as shown in FIGS. 5A to 5F, when the overlapping melting regions are not formed, the laser beam for forming the melting regions MA1 and MA2 for each melting region MA1 and MA2. Alternatively, when a plurality of cross sections are taken along the irradiation direction of the electron beam (in the direction of the white arrow in the figure) and the central axis CL2 of the precious metal chip (not shown in FIGS. 5 to 7), each of them melts. The cross-sectional shape of the regions MA1 and MA2 is such that the width decreases toward the inside.

On the other hand, when overlapping molten regions are formed, for example, as shown in FIGS. 6 (a) to 6 (d) and 7 (a) to 7 (c), the respective molten regions MA3, When the cross-sections of MA4, MA5, and MA6 are taken, the cross-sectional shape of any of the molten regions MA3 to MA6 has a shape in which the width is constant or expands toward the inside at least in a part. Therefore, by utilizing this point, it is possible to determine the presence or absence of the overlapping molten region.

Further, the formation position of the overlapping molten region can be specified as follows. That is, in the cross-sectional shape of the molten region, a molten region (for example, the molten region MA3 in FIG. 6) having a portion (curved portion) having a constant or expanding width is specified, and the portion of the molten region located on the outer surface. Based on the cross-sectional shape from to the curved portion, the continuous cross-sectional shape of the molten region [for example, FIGS. 6 (b) to 6 (d)] is estimated when it is assumed that there is no overlapping molten region. To do. Then, the shape of the three-dimensional molten region is derived based on the estimated continuous cross-sectional shape, and the relative position of the molten region with respect to the ground electrode or the like is specified. The work of deriving the shape of the melted region and the work of specifying the relative position of the melted region with respect to the ground electrode or the like are performed for all the melted regions having the inflection point, and for each melted region, the three-dimensional shape and the three-dimensional shape thereof and , Obtain the relative position with respect to the ground electrode, etc. Then, by arranging each melting region corresponding to each relative position, the formation position of the overlapping melting region can be three-dimensionally specified.

Next, a method of manufacturing the spark plug 1 configured as described above will be described. First, the main metal fitting 3 is processed in advance. That is, a rough shape is formed from a columnar metal material (for example, an iron-based material or a stainless steel material) by cold forging or the like, and a through hole is formed. After that, the outer shape is adjusted by cutting to obtain the main metal fitting intermediate.

Subsequently, a straight rod-shaped ground electrode 27 made of Ni alloy is resistance welded to the tip surface of the main metal fitting intermediate. Since so-called "sagging" occurs during the welding, after removing the "sagging", a threaded portion 15 is formed by rolling at a predetermined portion of the main metal fitting intermediate. As a result, the welded main metal fitting 3 of the ground electrode 27 is obtained. Further, the welded main metal fitting 3 of the ground electrode 27 is galvanized or nickel-plated. In addition, in order to improve the corrosion resistance, the surface thereof may be further subjected to chromate treatment.

On the other hand, the insulating insulator 2 is molded separately from the main metal fitting 3. For example, a tubular molded product is prepared by preparing a base granule for molding using a raw material powder mainly composed of alumina and containing a binder or the like, and performing rubber press molding using the base granulated product for molding. Is obtained. Then, the obtained molded body is ground and shaped, and the shaped insulator is fired in a firing furnace to obtain an insulating insulator 2.

Further, the center electrode 5 is manufactured separately from the main metal fitting 3 and the insulating insulator 2. That is, the center electrode 5 is manufactured by forging a Ni alloy in which a copper alloy or the like is arranged in the central portion to improve heat dissipation. Next, the noble metal portion 31 made of a noble metal alloy is joined to the tip end portion of the center electrode 5 by laser welding or the like.

Next, the insulating insulator 2 and the center electrode 5 obtained as described above, the resistor 7, and the terminal electrode 6 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 glass is injected into the shaft hole 4 of the insulating insulator 2 so as to sandwich the resistor 7. After that, it is baked and hardened by heating in a firing furnace while pressing it from the rear with the terminal electrode 6. At this time, the glaze layer may be fired at the same time on the surface of the rear end side body portion 10 of the insulating insulator 2, or the glaze layer may be formed in advance.

After that, the insulator 2 having the center electrode 5 and the terminal electrode 6 produced as described above and the main metal fitting 3 having the ground electrode 27 are assembled. More specifically, the opening on the rear end side of the main metal fitting 3 formed to be relatively thin is crimped inward in the radial direction, that is, it is fixed by forming the crimping portion 20.

Next, the precious metal chip 32 is joined to the tip of the ground electrode 27 that has been plated off by laser beam or electron beam welding.

More specifically, the precious metal tip 32 is supported by a predetermined holding pin in a state where the precious metal tip 32 is placed on a predetermined portion of the ground electrode 27. Then, a high-energy laser beam such as a fiber laser or an electron beam is irradiated to a predetermined portion of the side surfaces 27S1 and 27S2 of the ground electrode 27, and the ground electrode 27 and the noble metal chip 32 are fused to form a molten region 35a, 35b. , 35c, 35d are formed. Further, the molten region 35e is formed by moving the irradiation position of the laser along the width direction of the ground electrode 27 while irradiating the tip surface 27F of the ground electrode 27 with the high energy laser beam. As a result, the molten portion 35 composed of the molten regions 35a, 35b, 35c, 35d, and 35e is formed, and the precious metal chip 32 is joined to the ground electrode 27.

In the present embodiment, irradiation conditions such as a laser beam are used so that the ratio of the region AO1 where the precious metal chip 32 and the molten portion 35 overlap is 70% or more with respect to the region AP1 on which the precious metal chip 32 is projected. Is set. If the outer diameter of the precious metal chip 32 and the materials that make up the precious metal chip 32, etc. are different, the output of the laser beam, etc., the irradiation time, and the method of striking the laser beam, etc. By appropriately adjusting the pulse) and the like, it is possible to form the molten portion 35 in which the ratio of the region AO1 to the region AP1 is 70% or more.

After joining the precious metal tip 32, the intermediate portion of the ground electrode 27 is bent toward the center electrode 5. Then, by adjusting the size of the spark discharge gap 33 between the noble metal portion 31 and the noble metal chip 32, the above-mentioned spark plug 1 can be obtained.

As described in detail above, according to the present embodiment, on the projection plane in which the precious metal chip 32 and the molten portion 35 are projected onto the projection plane orthogonal to the central axis CL2 along the central axis CL2 of the precious metal chip 32. The ratio of the region AO1 where the precious metal chip 32 and the molten portion 35 overlap with the region AP1 on which the precious metal chip 32 is projected is 70% or more. That is, the precious metal tip 32 is joined to the ground electrode 27 via a sufficiently wide melted portion 35. Therefore, the area of the discharge surface is 0.9 mm.²Even a relatively large thermal stress difference between the above and the large-diameter precious metal chip 32 and the ground electrode 27 can be sufficiently absorbed by the molten portion 35, and the development of the oxidation scale at the junction between the two can be sufficiently absorbed. It can be prevented more reliably. As a result, the peeling resistance of the precious metal chip 32 can be improved more reliably.

Further, the molten portion 35 is formed by irradiating the tip surface 27F and the side surfaces 27S1 and 27S2 of the ground electrode 27 with a laser beam or an electron beam instead of the outer edge of the contact surface between the ground electrode 27 and the precious metal chip 32. There is. Therefore, even if a sufficient area of the molten portion 35 is secured as described above, it is unlikely that the molten portion 35 reaches or approaches the discharge surface of the precious metal chip 32, and the precious metal chip 32 is used. It is possible to fully exert the effect of improving the wear resistance due to the provision. As a result, the area of the discharge surface of the precious metal chip 32 is 0.9 mm.²Combined with the above and the relatively large size, it is possible to dramatically improve the wear resistance.

Further, since it is possible to suppress the arrival or approach of the molten portion 35 to the discharge surface, a relatively thin-walled precious metal chip 32 can be used. As a result, it is possible to effectively suppress an increase in manufacturing cost associated with the use of the noble metal chip 32 having a large diameter.

Further, the molten portion 35 is formed over the entire area between the outer peripheral portion of the base end portion of the precious metal chip 32 and the ground electrode 27, and the fused portion 35 forms a boundary portion between the precious metal chip 32 and the ground electrode 27. It is located so as to cover it. Therefore, the presence of the molten portion 35 can effectively prevent the intrusion of corrosive gas into the boundary portion, and more reliably prevent the development of the oxidation scale at the joint portion between the precious metal chip 32 and the ground electrode 27. Can be done. As a result, the peeling resistance of the precious metal chip 32 can be further improved.

In addition, the molten portion 35 is formed between the front end surface 27F of the ground electrode 27 and the side surfaces 27S1 and 27S2, respectively. Therefore, the bonding strength of the noble metal chip 32 with respect to the ground electrode 27 can be further improved, and the peeling resistance can be further improved.

At the same time, on the projection plane, the overlapping fusion regions 35a, 35b, 35e are located on the straight line SL in the region AP1 on which the precious metal chip 32 is projected. Therefore, the thermal stress difference generated between the ground electrode 27 and the noble metal chip 32 can be more reliably absorbed by the molten portion 35, and the peeling resistance of the noble metal chip 32 can be further improved.

Further, a fiber laser or an electron beam is used when joining the precious metal chip 32 to the ground electrode 27. Therefore, even if the molten portion 35 is formed over a relatively large region as described above, the volume of the molten portion 35 can be made relatively small, and the precious metal chips 32 are melted at the time of joining. The portion can be further reduced. Therefore, the volume of the precious metal chip 32 can be secured more reliably, and the wear resistance can be further improved. [Second Embodiment] Next, the second embodiment will be described focusing on the differences from the first embodiment with reference to the drawings. In the second embodiment, as shown in FIGS. 8 (a) and 8 (b), the irradiation positions of the laser beam or the electron beam, especially when the noble metal chip 32 is bonded to the ground electrode 27, are different, and as a result, The structure of the molten portion 45 to be formed is different.

In detail, the melting portion 45 has a melting region 45a, 45b, 45c, 45d, 45e, 45. It is composed of f, 45g, 45h, and the molten regions 45a, 45b, 45c, 45d are in the direction parallel to the discharge surface of the precious metal chip 32 with respect to the side surface 27S1 of the ground electrode 27, and the length of the ground electrode 27. It is formed by irradiating four laser beams or electron beams along a direction orthogonal to the direction. Further, the molten regions 45e, 45f, 45g, 45h are in directions parallel to the discharge surface of the noble metal chip 32 with respect to the portion of the side surface 27S2 of the ground electrode 27 located on the back surface of the molten regions 45a, 45b, 45c, 45d. It is formed by irradiating four laser beams or electron beams along a direction orthogonal to the longitudinal direction of the ground electrode 27. In the same manner as in the first embodiment, the precious metal tip 32 is projected on the projection plane orthogonal to the central axis CL2 along the central axis CL2 of the precious metal tip 32. The projected area AP2 [the area surrounded by the thick line in Fig. 8 (b)] is shaded in the area AO2 [the area surrounded by the thick line in Fig. 8 (b)] where the precious metal chip 32 and the molten portion 45 overlap. Area] is said to occupy 70% or more.

In addition, in the melting portion 45, the overlapping melting region 47a in which the melting regions 45a and 45e overlap, the overlapping melting region 47b in which the melting regions 45b and 45f overlap, and the overlapping melting region 47b in which the melting regions 45c and 45g overlap each other A region 47c and an overlapping fusion region 47d formed by overlapping the fusion regions 45d and 45h are formed. In the present embodiment, the straight line SL extending along the longitudinal direction of the ground electrode 27 passing through the central axis CL2 of the precious metal chip 32 and the central axis CL2 of the precious metal chip 32 are projected along the central axis CL2 of the precious metal chip 32. When projected onto a surface, each melting region 45a is located so that the overlapping melting regions 47a, 47b, 47c, 47d are located on the straight line SL and the overlapping melting regions 47c are located on the central axis CL2. Etc. are set.

As described above, according to the second embodiment, since the overlapping molten region 47c is located on the central axis CL2 of the noble metal chip 32 on the projection surface, the heat generated between the ground electrode 27 and the noble metal chip 32 by the melting portion 45 is generated. The stress difference can be absorbed more reliably. As a result, the peeling resistance of the precious metal chip 32 can be dramatically improved.

Next, by changing the irradiation conditions of the laser beam in order to confirm the action and effect produced by the above embodiment, the noble metal chip and the molten portion are formed on the projection surface in the region where the noble metal chip is projected. Samples of spark plugs in which the ratio of overlapping regions (ratio of molten parts) were variously changed were prepared, and a desk burner test was performed on each sample. The outline of the desk burner test is as follows. That is, 1000 cycles of heating the sample with a burner so that the temperature of the precious metal chip becomes 1050 ° C and then slowly cooling for 1 minute in an air atmosphere are carried out as one cycle, and after 1000 cycles, the sample is sampled. By observing the cross section, the ratio of the length of the oxide scale formed at the interface to the length of the interface between the molten portion, the ground electrode and the precious metal chip (oxidation scale ratio) was measured. FIG. 9 shows a graph showing the relationship between the melted portion ratio and the oxidation scale ratio. As a precious metal chip, the outer diameter is 1.2 mm (the area of the discharge surface is about 1.1 mm).²), The one with a thickness of 0.4 mm was used. As the ground electrode, one having a width of 2.8 mm and a thickness of 1.5 mm was used. In addition, it was decided to form a molten region in each sample so that an overlapping molten region would not be formed.

As shown in FIG. 9, it was clarified that in the sample in which the melted portion ratio was less than 70%, the oxidation scale ratio increased and the peel resistance of the noble metal chip became insufficient. This is because the fused portion is relatively narrow, so that the thermal stress difference generated between the large-diameter precious metal chip and the ground electrode cannot be sufficiently absorbed, and as a result, the development of the oxidation scale cannot be sufficiently prevented. It is thought that this is because of the fact.

On the other hand, it was found that the sample in which the melted portion ratio was 70% or more had an oxidation scale ratio of 50% or less and had sufficient peeling resistance. Further, it was confirmed that the peeling resistance can be further improved as the ratio of the molten portion is increased. Therefore, in order to prevent peeling of the precious metal chip, the melted portion ratio is preferably 70% or more, the melted portion ratio is more preferably 80% or more, and the melted portion ratio is further set to 100%. It can be said that it is preferable.

Next, as shown in FIG. 10 (a), a sample (sample 1) in which the molten portion M1 is formed so that the overlapping molten region OM1 is located on the central axis CL2 of the precious metal chip 32 on the projection plane, and FIG. 10 As shown in (b), a sample (sample 2) in which the molten portion M2 was formed so that the overlapping molten region OM2 was located on the straight line SL on the projection plane, and as shown in FIG. 10 (c). As shown in FIG. 10 (d), the overlapping molten region is not formed with the sample (sample 3) in which the molten portion M3 is formed so that the molten region OM3 is located at a position shifted from the straight line SL on the projection surface. Samples (Sample 4) on which the molten portion M4 was formed were prepared as described above, and the above-mentioned desk burner test was performed on each sample. Table 1 shows the test results for each sample. The melted portion ratio was set to 70% for each sample, and the precious metal chips and ground electrodes of the same size as those in the above test were used.

<tables num="1"><img file="JP4928596B2_D0001.tif" /></tables>

As shown in Table 1, it was found that the samples (samples 1 to 3) in which the overlapping molten regions OM1, OM2, and OM3 were formed each had a further reduced oxidation scale ratio and further excellent peeling resistance. It is considered that this is because the bonding strength of the noble metal chip to the ground electrode is further improved due to the formation of the overlapping molten region.

Further, the samples (samples 1 and 2) in which the molten regions OM1 and OM2 are formed on the straight line SL on the projection surface have more excellent peeling resistance, and in particular, on the projection surface on the central axis CL2 of the precious metal chip. It was found that the sample (Sample 1) on which the molten region OM1 was formed was excellent in peeling resistance. This is because the overlapping fusion region is formed so as to be located on the straight line SL or the central axis CL2 on the projection surface, so that the thermal stress difference generated between the ground electrode and the precious metal chip by the fusion portion is more effectively absorbed. As a result, it is considered that the progress of the oxidation scale was suppressed very effectively.

From the above test results, it can be said that it is preferable to form the molten portion so that the overlapping molten region is formed from the viewpoint of further improving the peeling resistance. Further, in order to further improve the peel resistance, it is more preferable to form the overlapping fusion region on the projection surface on the straight line SL, and the overlap fusion region on the projection surface is formed on the central axis CL2 of the precious metal chip. Is even more preferable.

Next, by changing the irradiation energy and irradiation position of the laser beam, a sample (sample 5) in which the molten part is exposed on the surface (discharge surface) of the precious metal chip that forms the spark discharge gap, and the molten part on the discharge surface. Samples (Sample 6) that were not exposed were prepared, and both samples were subjected to a desktop spark test. The outline of the desk spark test is as follows. That is, with the frequency of the voltage applied to the sample set to 100 Hz (that is, with 6000 discharges per minute), each sample was subjected to an atmospheric atmosphere of 0.4 MPa for 100 hours. And discharged. Then, after 100 hours had passed, the consumed volume of the precious metal chip (melted portion) due to the spark discharge was measured. Table 2 shows the test results of the test. As the precious metal chip and the ground electrode, the same size as in the above test was used for both samples.

<tables num="2"><img file="JP4928596B2_D0002.tif" /></tables>

As shown in Table 2, it was clarified that the sample (Sample 5) in which the molten portion was not exposed on the discharge surface had a relatively small consumption volume and was excellent in wear resistance. Therefore, in order to improve the wear resistance, it is preferable to configure the molten portion so that it is not exposed on the discharge surface.

Next, samples of spark plugs in which the width of the ground electrode (that is, the size of "A + B + C" in the above embodiment) were changed were prepared, and an ignitability evaluation test was conducted on each sample. The outline of the ignitability evaluation test is as follows. That is, after each sample was attached to a predetermined engine, spark discharge was performed at a rotation speed of 2000 rpm while gradually increasing the air-fuel ratio (A / F). Then, the air-fuel ratio when the number of times of discharge abnormality (misfire) occurred 10 times or more during 1000 discharges was measured as the limit air-fuel ratio. The larger the critical air-fuel ratio, the better the ignitability. Figure 11 shows a graph showing the relationship between the A + B + C values and the critical air-fuel ratio.

As shown in FIG. 11, it was found that the sample having A + B + C of 3.0 mm or less had a critical air-fuel ratio of more than 20.0 and had excellent ignitability. Therefore, in order to improve the ignitability, it can be said that it is preferable that the ground electrode satisfies A + B + C 3.0 mm.

The content is not limited to the description of the above embodiment, and may be implemented as follows, for example. Of course, other application examples and modification examples not illustrated below are also possible.

(a) In the above embodiment, the irradiation direction of the laser beam or the like is parallel to the discharge surface of the noble metal chip 32, but as shown in FIG. 12, the side opposite to the discharge surface of the noble metal chip 32 (a). The molten portion 55 may be formed by irradiating the laser beam from a direction inclined (in the direction of the white arrow in FIG. 12) toward the ground electrode 27). In this case, the amount of melting of the noble metal chip 32 at the time of joining can be further reduced, and the volume of the noble metal chip 32 can be further increased. As a result, the wear resistance can be further improved. Further, as shown in FIG. 13, it becomes easier to form the molten portion 55 so as not to be exposed on the side of the spark discharge gap 33. Durability can be improved by adopting a configuration in which the molten portion 55 is not exposed on the side of the spark discharge gap 33.

(b) The configuration of the molten portions 35 and 45 in the above embodiment is an example, and the region where the precious metal chip 32 and the molten portion overlap with respect to the region where the precious metal chip 32 is projected on the projection surface occupies. If the ratio is 70% or more, the composition of the molten portion (shape and number of molten regions, etc.) is not limited.

Therefore, for example, as shown in FIG. 14A, the melting portion 65 may be composed of three melting regions 65a, 65b, 65c.

Further, as shown in FIG. 14 (b), by changing the irradiation method of the laser beam on the side surfaces 27S1 and 27S2 of the ground electrode 27, the molten portion has a relatively wide molten region 75a and 75b. It may form 75.

Further, as shown in FIG. 15 (a), the irradiation direction of the laser beam or the like is tilted from the direction orthogonal to the longitudinal direction of the ground electrode 27 toward the tip end side of the ground electrode 27 [white in FIG. 15 (a). By setting the direction of the pull-out arrow], the molten portion 85 may be formed so as to have the molten regions 85a and 85b having a shape inclined toward the base end side of the ground electrode 27.

Further, the irradiation position of the laser beam or the like, the irradiation energy, the irradiation direction, and the like may be changed according to the arrangement position of the precious metal chip 32 with respect to the ground electrode 27. Therefore, as shown in FIG. 15B, the molten portion 95 may be formed by forming the molten regions 95a, 95b, 95c at positions corresponding to the arrangement positions of the precious metal chips 32.

(c) In the above embodiment, the noble metal chip 32 has a columnar shape, but the shape of the noble metal chip 32 is not limited to this. Therefore, for example, as shown in FIG. 16, the precious metal chip 42 may have a rectangular cross section. Even in such a case, the precious metal chip 42 is projected on the projection plane on which the precious metal chip 42 and the molten portion 105 are projected along the central axis CL3 of the precious metal chip 42 on the projection plane orthogonal to the central axis CL3. The ratio of the area AO3 (the area shaded in FIG. 16) where the precious metal chip 42 and the molten portion 105 overlap to the area AP3 (the area surrounded by the thick line in FIG. 16) is 70% or more. Therefore, the peeling resistance of the precious metal chip 42 can be sufficiently improved.

(d) In the above embodiment, the noble metal chip 32 is laser-welded to the ground electrode 27 while being supported by the holding pin. However, prior to laser welding, the noble metal chip 32 is attached to the ground electrode 27. It is also possible to perform resistance welding, temporarily fix both, and then laser weld both.

(e) In the above embodiment, a spark plug 1 of a type in which spark discharge is performed in a direction substantially along the axis CL1 in the spark discharge gap 33 is described, but a spark plug to which the technical idea of the present invention can be applied is described. The type is not limited to this. Therefore, the technical idea of the present invention may be applied to a type of spark plug in which spark discharge is performed along a direction substantially orthogonal to the axis CL1. Further, the technical idea of the present invention may be applied to a type of spark plug in which spark discharge is performed in an oblique direction with respect to the axis CL1.

(f) In the above embodiment, the case where the ground electrode 27 is joined to the tip 26 of the main metal fitting 3 is specified, but a part of the main metal fitting (or the tip metal fitting pre-welded to the main metal fitting 3). It is also applicable to the case where the ground electrode is formed by carving out (a part of) (for example, Japanese Patent Application Laid-Open No. 2006-236906).

(g) In the above embodiment, the tool engaging portion 19 has a hexagonal cross section, but the shape of the tool engaging portion 23 is not limited to such a shape. For example, it may have a Bi-HEX (deformed hexadecimal) shape [ISO22977: 2005 (E)] or the like.

1 ... spark plug 2 ... Insulator (insulator) 3 ... Main metal fittings 4 ... Shaft hole 5 ... Center electrode 27 ... Ground electrode 27F ... Tip surface (of ground electrode) 27S1, 27S2 ... Side (of ground electrode) 32 ... precious metal chips 33 ... Spark discharge gap (gap) 35 ... melted part 35a, 35b, 35c, 35d, 35e ... melting region 37a, 37b, 37c, 37d, 37e ... Overlapping fusion region CL1 ... axis CL2 ... Central axis (of precious metal chips)