The spark plug has a configuration satisfying the relationships of B≧0.7A and 0.3 mm≦A≦0.6 mm, where B is an axial thickness along the central axis line Q of the weld portion formed between the base material electrode and the noble-metal chip, and A is an axial distance along the central axis line Q between the intersection points P3 and X. The intersection point P3 is a point at which a phantom axis line radially distant from the central axis line Q by D/2 (D being a diameter of the noble-metal chip) intersects with the boundary line between the weld portion and the noble-metal chip. The intersection point X is a point at which an extension of the contour line of the base material electrode in the vicinity of the weld portion intersects with a boundary line between the weld portion and the base material electrode.
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1. A spark plug for an internal combustion engine comprising:
a center electrode;
an insulator disposed around an outer periphery of the center electrode;
a mounting bracket disposed around an outer periphery of the insulator;
a ground electrode disposed so as to extend from the mounting bracket and form a spark discharge gap with the center electrode; and
a columnar noble-metal chip having a diameter of D and joined, through a weld portion, to a distal end of at least one of the center electrode and the ground electrode as a base material electrode,
wherein, when
Q designates a central axis line of the noble-metal chip,
P0 designates an intersection point in a cross-section of the noble-metal chip passing through the central axis line Q at which the central axis line Q intersects with a boundary line designated by S1 between the weld portion and the noble-metal chip,
P1 designates an intersection point at which a phantom axis line designated by Q1 which is radially distant from the central axis line Q by D/4 intersects with the boundary line S1,
P2 designates an intersection point at which a phantom axis line designated by Q2 which is radially distant from the central axis line Q by 3D/8 intersects with the boundary line S1,
P3 designates an intersection point at which a phantom axis line designated by Q3 which is radially distant from the central axis line Q by D/2 intersects with the boundary line S1,
an angle which a straight line joining the intersection points P0 and P1 makes with the central axis line is θ1,
an angle which a straight line joining the intersection points P1 and P2 makes with the central axis line Q is θ2, and
an angle which a straight line joining the intersection points P2 and P3 makes with the central axis line Q is θ3,
the angle θ1, θ2 and θ3 are all larger than or equal to 70 degrees,
and wherein, when
an axial thickness along the central axis line Q of the weld portion is B,
X designates an intersection point at which an extension of a contour line of the base material electrode in the vicinity of the weld portion intersects with a boundary line designated by S2 between the weld portion and the base material electrode, and
an axial distance along the central axis line Q between the intersection points P3 and X is A,
relational expressions of B≧0.7A and 0.3 mm≦A≦0.6 mm are satisfied, and
wherein when the weld portion is separated into a first region and a second region by a cross-section which passes through a midpoint of the central axis line Q and is perpendicular to the central axis line Q, the first region being closer to the noble-metal chip than to the base material electrode, the second region being closer to the base material electrode than to the noble-metal chip,
and when a content of a chemical composition constituting the noble-metal chip in the first region is C1 mass % and a content of the chemical composition constituting the noble-metal chip in the second region is C2 mass %,
a relational expression of |C1-C2|≦20 mass % is satisfied.
2. A method of manufacturing a spark plug for an internal combustion engine, the spark plug comprising:
a center electrode;
an insulator disposed around an outer periphery of the center electrode;
a mounting bracket disposed around an outer periphery of the insulator;
a ground electrode disposed so as to extend from the mounting bracket and form a spark discharge gap with the center electrode; and
a columnar noble-metal chip having a diameter of D and joined, through a weld portion, to a distal end of at least one of the center electrode and the ground electrode as a base material electrode,
wherein, when
Q designates a central axis line of the noble-metal chip,
P0 designates an intersection point in a cross-section of the noble-metal chip passing through the central axis line Q at which the central axis line Q intersects with a boundary line designated by S1 between the weld portion and the noble-metal chip,
P1 designates an intersection point at which a phantom axis line designated by Q1 which is radially distant from the central axis line Q by D/4 intersects with the boundary line S1,
P2 designates an intersection point at which a phantom axis line designated by Q2 which is radially distant from the central axis line Q by 3D/8 intersects with the boundary line S1,
P3 designates an intersection point at which a phantom axis line designated by Q3 which is radially distant from the central axis line Q by D/2 intersects with the boundary line S1,
an angle which a straight line joining the intersection points P0 and P1 makes with the central axis line Q is θ1,
an angle which a straight line joining the intersection points P1 and P2 makes with the central axis line Q is θ2, and
an angle which a straight line joining the intersection points P2 and P3 makes with the central axis line is Q is θ3,
the angle θ1, θ2 and θ3 are all larger than or equal to 70 degrees,
and wherein, when
an axial thickness along the central axis line Q of the weld portion is B,
X designates an intersection point at which an extension of a contour line of the base material electrode in the vicinity of the weld portion intersects with a boundary line designated by S2 between the weld portion and the base material electrode, and
an axial distance alone the central axis line Q between the intersection points P3 and X is A,
relational expressions of B≧0.7A and 0.3 mm≦A≦0.6 mm are satisfied; and
wherein the method of manufacturing the spark plug comprises the steps of:
laying the noble-metal chip on a distal end surface of the base material electrode; and
applying a pulsed laser beam to a boundary portion between the base material electrode and the noble-metal chip while shifting a point of application of the pulsed laser bean in a circumferential direction of the boundary portion,
wherein
an angle of application of the pulsed laser beam to the boundary portion is in a range from ±10 degrees from a 90-degree angle with respect to the central axis line Q, and
emission energy of the pulsed laser beam is maximum at a first pulse emission, and thereafter is gradually decreased with the increase of the number of times of pulse emission.
3. The method according to
4. The method according to
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This application claims priority to Japanese Patent Application No. 2012-41452 filed on Feb. 28, 2012, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a spark plug for use in an internal combustion engine of an automobile, a cogeneration apparatus, a gas feed pump, etc., and to a method of manufacturing the spark plug.
2. Description of Related Art
Generally, a spark plug for use in an internal combustion engine includes a center electrode, an insulator disposed around the outer periphery of the center electrode, a mounting bracket disposed around the outer periphery of the insulator, and a ground electrode disposed so as to extend from the mounting bracket and form a spark discharge gap with the center electrode. It is known to provide such a spark plug with a highly durable noble-metal chip at the spark discharge gap thereof. For example, refer to Japanese Patent Application Laid-open No. 2011-34826.
Incidentally, since the joining between the noble-metal chip and the center electrode or ground electrode as a base material electrode is performed by welding, a weld portion is formed therebetween. Accordingly, to achieve high durability thanks to the noble-metal chip, the reliability between the noble-metal chip and the base material electrode through the weld portion has to be sufficiently high.
An exemplary embodiment provides a spark plug for an internal combustion engine comprising:
a center electrode;
an insulator disposed around an outer periphery of the center electrode;
a mounting bracket disposed around an outer periphery of the insulator;
a ground electrode disposed so as to extend from the mounting bracket and form a spark discharge gap with the center electrode; and
a columnar noble-metal chip having a diameter of D and joined, through a weld portion, to a distal end of at least one of the center electrode and the ground electrode as a base material electrode,
wherein, when
Q designates a central axis line of the noble-metal chip,
P0 designates an intersection point in a cross-section of the noble-metal chip passing through the central axis line Q at which the central axis line Q intersects with a boundary line designated by D/4 between the weld portion and the noble-metal chip,
P1 designates an intersection point at which a phantom axis line designated by Q1 which is radially distant from the central axis line Q by D/4 intersects with the boundary line S1,
P2 designates an intersection point at which a phantom axis line designated by Q2 which is radially distant from the central axis line Q by 3D/8 intersects with the boundary line S1,
P3 designates an intersection point at which a phantom axis line designated by Q3 which is radially distant from the central axis line Q by D/2 intersects with the boundary line S1,
an angle which a straight line joining the intersection points P0 and P1 makes with the central axis line Q is θ1,
an angle which a straight line joining the intersection points P1 and P2 makes with the central axis line Q is θ2, and
an angle which a straight line joining the intersection points P2 and P3 makes with the central axis line Q is θ3,
the angle θ1, θ2 and θ3 are all larger than or equal to 70 degrees,
and wherein, when
an axial thickness along the central axis line Q of the weld portion is B,
X designates an intersection point at which an extension of a contour line of the base material electrode in the vicinity of the weld portion intersects with a boundary line designated by S2 between the weld portion and the base material electrode, and
an axial distance along the central axis line Q between the intersection points P3 and X is A,
relational expressions of B≧0.7A and 0.3 mm≦A≦0.6 mm are satisfied.
The exemplary embodiment also provides a method of manufacturing the spark plug recited in claim 1, comprising the steps of:
laying the noble-metal chip on a distal end surface of the base material electrode; and
applying a pulsed laser beam to a boundary portion between the base material electrode and the noble-metal chip while shifting a point of application of the pulsed laser bean in a circumferential direction of the boundary portion,
wherein
an angle of application of the pulsed laser beam to the boundary portion is in a range from ±10 degrees from a 90-degree angle with respect to the central axis line Q, and
emission energy of the pulsed laser beam is maximum at a first pulse emission, and thereafter is gradually decreased with the increase of the number of times of pulse emission.
According to the exemplary embodiment, there is provided a spark plug including a noble-metal chip joined to abase material electrode which is excellent in the reliability in the joining between the noble-metal chip and the base material electrode, and can be manufactured at low cost.
Other advantages and features of the invention will become apparent from the following description including the drawings and claims.
In the accompanying drawings:
As shown in
The mounting bracket 2 includes a mounting thread section 20 at its outer periphery. The insulator 3 accommodated in the mounting bracket 2 includes an insulator distal end portion 30 projecting more toward the front side of the spark plug 1 than the mounting bracket 2. A noble-metal chip 40 of a columnar shape having a diameter of D (mm) is joined to the distal end of the center electrode (base material electrode) 4 held inside the insulator 3 so as to project from the insulator distal end portion 30.
The ground electrode 5 disposed extending from the mounting bracket 2 is bent in an L-shape so as to face the noble-metal chip 40 of the center electrode 4 at its distal end. The ground electrode 5 is formed with a projecting portion 50 at a position facing the noble-metal chip 40 of the center electrode 4. The gap between the noble-metal chip 4 and the projecting portion 50 makes a spark discharge gap G. In this embodiment, the projecting portion 50 is made of the same material as the ground electrode 5. Alternatively, the projecting portion 50 may be made of a noble-material chip joined to the ground electrode 5.
The center electrode 4 and the ground electrode 5 are made of a Ni-based alloy having good heat resistance. The noble-metal chip 40 is made of an alloy containing Ir, Rh or Ru.
In this embodiment, the noble-metal chip 40 is joined by welding to the distal end of the center electrode 4 as a base material electrode. That is, as shown in
In
In
Returning to
In
Next, a method of manufacturing the spark plug 1 having the above described structure is explained with reference to
First, the noble-metal chip 40 is laid on and pre-joined to the distal end of the center electrode 4 as shown in
Next, a pulsed laser beam 8 is applied to the boundary portion between the center electrode 4 and the noble-metal chip 40, while rotating the center electrode 4 around its central axis so that the point of application of the pulsed laser beam 8 shifts in the circumferential direction. The emission angle of the laser beam 8 is kept perpendicular (90 degrees) to the central axis line Q.
The laser beam 8 is emitted such that the emission energy is the highest at the first pulse emission, and is gradually decreased with the increase of the number of times of the pulse emission. More specifically, as shown in
The time duration of each pulse emission is 6 ms, and the cooling time from the end of one pulse emission to the start of the next pulse emission is 44 ms. The rotational speed of the center electrode 4 and the noble-metal chip 40 relative to the laser beam is 80 rpm so that the first to fifteenth pulse emissions are applied to fifteen points evenly spaced along the circumference of the center electrode 4 and the noble-metal chip 40.
For each of the first region R1 and the second region R2 constituting the weld portion 45, the chemical compositions were measured at three different points, and the average value was calculated. As a result, it was found that the first region R1 contains Ir, which is the composition of the noble-metal chip, by 55 mass % on average, and the second region R2 contains Ir by 38 mass % on average. Accordingly, it was confirmed that |C1−C2|=17 mass % which is lower than 20 mass %.
As described above, the spark plug 1 according to this embodiment satisfies the first requirement that the angles θ1, θ2 and θ3 are all greater than 70 degrees, and the second requirement of B≧0.7A where B is the axial thickness and A is the axial distance. Accordingly, the thickness variation along the radial direction of the spark plug 1 can be made small. More specifically, although the axial thickness of the weld portion 45 becomes smaller in the direction from its outer periphery to its axial center, it is possible to prevent the thickness variation from becoming excessively abrupt. Since this makes it possible to lessen the thermal stress applied between the weld portion 45 and the noble-metal chip 40 or the center electrode 4, the reliability of the joining between them can be increased.
Further, since the weld portion 45 satisfies that the difference between C1 and C2 is smaller than 20 mass %, it is possible to prevent cracks from being formed by the thermal stress due to non-uniformity of the chemical compositions of the weld portion 45.
The spark plug 1 satisfies, in addition to the first and second requirements, the third requirement of 0.3 mm≦A≦0.6 mm where A is the axial distance A. Accordingly, since the volume of the weld portion 45 can be limited within an appropriate value, it is possible to reduce an amount of the noble-metal chip necessary to form the weld portion 45. Since this makes it possible to reduce a use amount of the expensive noble-metal chip 45, the manufacturing cost of the spark plug 1 can be reduced.
In the method of manufacturing the spark plug 1 described above, the angle of application of the pulsed laser beam 8 to the boundary portion between the center electrode 4 and the noble-metal chip 40 is set substantially perpendicular to the central axis line Q. This makes it possible to suppress the shape of the weld portion 45 from suffering due to the effect of the angle of application of the laser beam.
As described in the foregoing, the laser beam 8 is emitted such that the emission energy is the highest at the first pulse emission, and is gradually decreased with the increase of the number of times of the pulse emission. This makes it possible to prevent the weld portion from becoming excessively large due to overlap of the heat brought by one emission of the laser beam and the succeeding emission of the laser beam. Hence, according to this embodiment, it is easy to form the weld portion 45 having the above described specific shape.
Further, since the laser beam emission apparatus 7 used in this embodiment excels in beam collection, and is capable of forming a laser beam spot of a very small diameter, shape control of the weld portion 45 can be performed accurately.
An example of the weld portion formed between the center electrode 4 and the noble-metal chip 40 not satisfying the requirements 1 to 3 is shown in the following as comparative Example 1.
In this comparative Example 1, the pulsed laser beam is applied at an angle of 90 degrees with respect to the central axis line Q (see
TABLE 1
model No.
model shape
dimension of a or b (mm)
stress (MPa)
a1
M1 (FIG. 11)
0.2
2662
a2
M1 (FIG. 11)
0.4
3345
a3
M1 (FIG. 11)
0.6
3248
b1
M2 (FIG. 12)
0.2
1367
b2
M2 (FIG. 12)
0.4
1248
b3
M2 (FIG. 12)
0.6
1236
As seen from Table 1 and
Incidentally, noble-metal chip 40 is joined to the center electrode 4 in the above described embodiment, however, the noble metal-chip 40 may be joined to the ground electrode 5.
As seen from
In the above described Embodiment 1, the emission energy of the pulsed laser beam is decreased with the increase of the number of times of the pulse emission to remove the effect of heat accumulation. However, the way to remove the effect of heat accumulation may be achieved by increasing the interval of the pulse emission or by provision of a cooling means. In these cases, the emission energy of the pulsed laser beam can be constant.
The above explained preferred embodiments are exemplary of the invention of the present application which is described solely by the claims appended below. It should be understood that modifications of the preferred embodiments may be made as would occur to one of skill in the art.
Nakamura, Masaya, Ishiguro, Hiroya
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