JP2012190737A - Spark plug and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability by restraining exfoliation of a center electrode and a noble metal chip in a spark plug obtained by housing a filament body to be a noble metal chip in a recess provided at a tip of the center electrode and welding it with a laser.SOLUTION: A noble metal chip is housed in a recess provided at a tip of a center electrode and welded. When forming a molten portion, at which a component of the center electrode is mixed with a component of the noble metal chip, the tip of the center electrode is positioned nearer a tip in an axial line direction than a tip on an axial line of the molten portion, and a bottom face of the recess is positioned nearer a rear end in the axial line direction than the rear end on the axial line of the molten portion. On a cross section passing through the axial line, the molten portion continues in a radial direction, and a portion A, at which thickness of the molten portion in the axial line direction is 0.1 mm or more, is formed across 0.05 mm or more in the radial direction.

Description

  The present invention relates to a spark plug, and more particularly to a spark plug including a center electrode provided with a noble metal tip as a spark discharge member. The present invention also relates to a method for manufacturing the spark plug.

  A spark plug used in an internal combustion engine has a center electrode fitted into a cylindrical metal shell through an insulator, one end coupled to the metal shell, and the other end opposed to the tip of the center electrode. Generally, it is composed of a ground electrode. In addition, a spark plug in which a noble metal tip made of a noble metal such as Pt, Pd, Ir or the like having excellent heat resistance, thermal shock resistance, or the like or an alloy mainly composed of these is joined to the tip of the center electrode in order to improve ignitability. It is used.

  As a method of manufacturing a center electrode having such a noble metal tip, as schematically shown in FIG. 4A, a recess 51 that is recessed in the axial direction is provided at the tip of the center electrode 50, and a circle is formed in the recess 51. A columnar noble metal tip 60 is embedded, and a laser beam is irradiated from the direction crossing the axis C to the wall surface 52 that forms the recess 51, and as shown in FIG. It has been proposed to form a melted portion 70 by melting (see, for example, Patent Document 1).

  In a spark plug having a noble metal tip on the center electrode, the position where the noble metal tip is attached greatly affects the discharge between the noble metal tip and the ground electrode. Therefore, the alignment of the noble metal tip is an important requirement. If the recess 51 is not formed at the tip of the center electrode 50, the laser is placed on the flat surface of the noble metal tip 60 at a regular position and is held by a holding jig so as not to move the noble metal tip 60. In this case, the noble metal tip 60 is subjected to very strict position control. On the other hand, as described in Patent Document 1, in the method in which the noble metal tip 60 is embedded in the recess 51 and laser welding is performed, such position regulation of the noble metal tip 60 is facilitated. The recess 51 can be formed by drilling at the tip of the center electrode 50. However, since the processing accuracy at that time is high and it is only necessary to insert the noble metal tip 60 into the recess 51 formed with high accuracy, the noble metal The alignment operation of the chip 60 becomes extremely easy.

JP 59-191281 A

  In a spark plug in which a noble metal tip is welded to the center electrode, the tip of the noble metal tip welded has a high temperature, and the higher the temperature, the faster the wear. ) It is desired to make it easier. However, since the melted portion 70 is an alloy of a noble metal alloy that forms the noble metal tip 60 and an electrode material that forms the center electrode 50, the thermal conductivity is lower than that of the noble metal alloy alone. Therefore, as shown in FIG. 4B, the periphery of the axis C inside the noble metal tip 60 is left without melting (hereinafter referred to as the remaining portion 75), and the path of heat from the noble metal tip 60 to the center electrode 50 Is forming. However, since the remaining portion 75 is a noble metal alloy, oxidation due to heat accompanying discharge is unavoidable, and oxidation may proceed from the remaining portion 75 and the noble metal tip 60 may peel off.

  Further, if welding is performed so as to form the remaining portion 75, the alloy composition of the molten portion 70 is likely to vary. Specifically, the closer to the outer periphery of the noble metal tip 60, the greater the proportion of the electrode material that forms the recess 51. Such a variation in the alloy composition may cause a stress difference inside the melted portion 70 and cause cracks in the melted portion 70.

  Further, if the remaining portion 75 is thickened to improve heat dissipation, the melted portion 70 becomes relatively thin, and the thin melted portion 70 cannot absorb the difference in thermal expansion between the remaining portion 75 and the melted portion 70, and remains. Cracks may occur at the interface between the portion 75 and the melted portion 70.

  Therefore, the present invention suppresses peeling between the center electrode and the noble metal tip and improves durability in a spark plug obtained by laser welding with a linear body serving as a noble metal tip contained in a recess provided at the tip of the center electrode. The purpose is to let you.

  The inventors of the present invention do not leave the remaining portion when the melted portion penetrates the radial direction of the noble metal tip when the linear body that becomes the noble metal tip is accommodated in the recess provided at the tip of the center electrode and laser welding is performed. It has been found that the occurrence of oxidation and cracks derived from the remaining portion as described above can be suppressed by welding to the above. The present invention is based on such knowledge.

That is, this invention provides the spark plug and its manufacturing method shown below.
(1) an insulator having an axial hole extending in the axial direction;
A center electrode held in the shaft hole;
A metal shell provided on the outer periphery of the insulator;
One end is joined to the metal shell, the other end is a ground electrode facing the center electrode,
A noble metal tip disposed in a recess provided at the tip of the center electrode and bonded to a position facing the ground electrode;
A spark plug that forms a gap between the tip of the noble metal tip and the ground electrode,
A melting portion in which the component of the center electrode and the component of the noble metal tip are mixed, and the tip of the center electrode is located on the tip side in the axial direction from the tip on the axis of the melting portion, and The bottom surface of the recess is located on the rear end side in the axial direction from the rear end on the axial line of the melted portion,
In the cross section passing through the axis, the molten portion is continuous in the radial direction,
A spark plug characterized in that a portion A having a thickness of 0.1 mm or more in the axial direction of the molten portion is formed over 0.05 mm or more in the radial direction.
(2) The diameter of the noble metal tip is R,
The length of the portion A that overlaps the axis is L ₁ , the point O that is L _1/2 on the axis is the origin, and its coordinates (x, y) = (0, 0),
x-coordinate passes through the point x = 3R / 8, and the y-coordinate of the length of the fused portion overlapping the straight line M parallel to the axis L _2, L _2/2 to become a point y _2,
x-coordinate passes through the point x = -3R / 8, and the length of the fused portion which overlaps with a line parallel N to the axis and L _3, L _3/2 and y ₃ and y coordinates of the point where,
_{O (0,0), a (0} , L 1/2), b (0, -L 1/2), c (3R / 8, y 2), d (3R / 8, y 2 + L 2/4 _{), e (3R / 8,} y 2 -L 2/4), f (-3R / 8, y 3), g (-3R / 8, y 3 + L 3/4), h (-3R / 8, y ₃ -L _3/4 maximum value _{X MAX} percentage X of the main component of the material forming the noble metal tip at 9 points), when a minimum value was _{M MIN, (X MAX -X MIN} ) ≦ 30 % Of the spark plug according to (1) above.
(3) The spark plug according to (2) above, wherein (X _MAX -X _MIN ) ≦ 15%.
(4) The minimum value of the length in the axial direction from the boundary between the portion A and the noble metal tip to the tip end face of the noble metal tip is 0.2 mm or more. The spark plug according to any one of 3).
(5) an insulator having an axial hole extending in the axial direction;
A center electrode held in the shaft hole;
A metal shell provided on the outer periphery of the insulator;
One end is joined to the metal shell, and at the other end, a ground electrode is formed with a gap between the center electrode,
A spark plug manufacturing method comprising:
In the recess formed at the tip of the center electrode, the precious metal tip is accommodated, and a side surface of the recess is irradiated with a laser, and a welding process for welding the recess and the noble metal tip is provided.
In the welding step, in a radial direction of the noble metal tip in a joint portion between the recess and the noble metal tip, while leaving a part of the recess in the axial direction tip side and a part of the noble metal tip on the recess side. A portion having a thickness of 0.1 mm or more in the axial direction of the molten portion in a cross section in the axial direction passing through the center of the front end face of the noble metal tip is 0.05 mm or more in the radial direction. A method for manufacturing a spark plug, comprising welding so as to be formed over a wide area.

  The spark plug of the present invention is excellent in ignitability because it has a noble metal tip on the ground electrode, and welds without leaving a remaining portion when the noble metal tip is accommodated in the recess provided at the tip of the center electrode and laser welding is performed. As a result, the occurrence of oxidation and cracks derived from the remaining portion is suppressed, and the durability is excellent.

It is sectional drawing of the spark plug which concerns on this invention. It is sectional drawing along the axis line for demonstrating the method of laser-welding a center electrode and a noble metal tip according to this invention. It is a figure for demonstrating distribution of the alloy composition of a molten part. It is a figure for demonstrating the method of laser-welding the conventional center electrode and a noble metal tip.

  Hereinafter, preferred embodiments of the spark plug according to the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a spark plug according to the present invention. A spark plug 100 is fitted into a cylindrical metal shell 11 and the metal shell 11, and the tip portion 11 a of the metal shell 11 is connected to the tip of the spark plug 100. A cylindrical insulator 12 from which 12a is exposed, a center electrode 13 disposed in the insulator 12 so that its tip portion 13a is exposed from the tip portion 12a of the insulator 12, and a metal shell 11 One end portion is coupled to the distal end portion 11a, and the other end portion is mainly provided with a ground electrode 14 or the like disposed opposite to the distal end portion 13a of the center electrode 13.

  The metal shell 11 is made of carbon steel or the like, and on the outer peripheral surface of the metal shell 11, for example, a mounting screw portion 15 for mounting on a cylinder head of an internal combustion engine is formed in the circumferential direction. In the insulator 12 made of a ceramic sintered body such as alumina, the terminal fitting 17 is exposed at the end on the rear side (upper side in the drawing) of the through hole 16 formed in the axial direction. The center electrode 13 is inserted and fixed at the front end (downward in the figure) with the tip 13a exposed.

  In addition, a resistor 18 is disposed in an intermediate portion between the terminal fitting 17 and the center electrode 13 in the through-hole 16, and conductive glass seal layers 19, 20 is arranged. That is, the center electrode 13 and the terminal fitting 17 are electrically connected through the resistor 18 and the conductive glass seal layers 19 and 20. The conductive glass seal layers 19 and 20 and the resistor 18 form a conductive coupling layer. The resistor 18 may be omitted, and the terminal fitting 17 and the center electrode 13 may be joined with a single conductive glass seal layer.

  The ground electrode 14 is configured by providing a noble metal tip 22 via a pedestal 23 at a position facing the center electrode 13 of the ground electrode main body portion 14A. The ground electrode main body portion 14A is a prismatic member made of a Ni alloy having excellent heat resistance and corrosion resistance, and a base portion 14a is fixed to the metal shell 11 by welding, and an intermediate portion thereof so that the tip end portion 14b faces the center electrode 13. Has a bent portion 14c and is bent into a substantially L shape.

The pedestal 23 is made of, for example, an alloy containing Ni as a main component and containing Fe, Cr, or the like. Cr has an action of suppressing oxidation by forming a Cr ₂ O ₃ film on the surface.

The noble metal tip 22 includes an alloy containing Ir as a main component and at least one additive such as Pt, Rh, Ru, Ni, and Y ₂ O ₃ , and Ir, Rh, Ru, Pd containing Pt as a main component. A material having high oxidation resistance and excellent spark wear resistance, such as an alloy containing at least one additive such as Ni, is used. Among these, a Pt alloy is preferable.

  The pedestal 23 and the noble metal tip 22 are welded by irradiating a laser.

The center electrode 13 is formed in a cylindrical shape from a Ni alloy having excellent heat resistance and corrosion resistance, and the tip portion 13a of the center electrode 13 is excellent in resistance to spark consumption. An alloy containing at least one additive such as Pt, Rh, Ru, Ni, Y ₂ O ₃ or at least one additive such as Ir, Rh, Ru, Pd, Ni containing Pt as a main component. A material such as an alloy having high oxidation resistance and excellent spark wear resistance is used. Among these, an Ir alloy is preferable.

  In the present invention, the center electrode 13 and the noble metal tip 21 are welded by irradiating a laser as shown in FIG.

  FIG. 2 is a cross-sectional view showing the vicinity of the recess 30 of the center electrode 13 along the axis C. First, as shown in FIG. 2A, the recess recessed at the tip of the center electrode 13 along the axis C. 30, the noble metal tip 21 is accommodated in the recess 30, and the laser beam is irradiated from the direction crossing the axis C to the wall surface 31 forming the recess 30.

  By this laser irradiation, as shown in FIG. 2B, a melted portion 40 formed by melting and mixing the components of the center electrode 13 and the components of the noble metal tip 21 penetrates the noble metal tip 21 in the radial direction. To form. Further, the upper end surface 31a that is the front end in the axial direction of the wall surface 31 of the concave portion 30 and a part on the bottom surface side of the concave portion 30 from the upper end surface 31a remain. Furthermore, a part of the bottom surface side of the recess 30 of the noble metal tip 21 is left.

  The melted portion 40 is formed so that the thickness in the axial direction becomes thinner toward the axis C, but as described above, by melting while leaving a part of the upper end surface side of the wall surface 31 of the recess 30, The upper end surface 31 a of the wall surface 31 is positioned on the front end side in the axial direction (upward in the drawing) with respect to the axial upper end 40 a of the melting portion 40. Further, by melting while leaving a part of the bottom surface side of the concave portion 30 of the noble metal tip 21, the bottom surface 31 b of the concave portion 30 is closer to the axial rear end side (lower side in the drawing) than the rear upper end 40 b of the melting portion 40. Come to be located.

  Further, as shown in FIG. 2B, the melted portion 40 has a portion 41 (hereinafter referred to as “penetrating portion”) having a thickness (T) on the axial line of 0.1 mm or more having a width ( W) It should be formed over 0.05 mm or more. Laser irradiation is performed through the wall surface 31 of the recess 30, and the laser irradiation portion of the wall surface 31 melts into the melted portion 40. Therefore, if the melted portion 40 is not formed so as to penetrate the noble metal tip 21 in the radial direction, the amount of Ni that is the main component of the wall surface 31 in the melted portion 40 is excessively large relative to the amount of noble metal in the melted noble metal tip 21. Therefore, the noble metal tip 21 may be peeled off due to the difference in thermal expansion between the unmelted noble metal tip 21 and the molten portion 40. Therefore, it is necessary to make the thinnest portion (that is, the through portion 41) of the melted portion 40 have a thickness of 0.1 mm or more and a radial width of 0.05 mm or more.

Furthermore, as the alloy composition is not different in each part of the melted portion 40, the mechanical strength is not biased, and the occurrence of cracks and the like can be suppressed. Specifically, as shown in FIG. 3, the diameter of the noble metal tip 21 is R, the length of the portion of the penetrating portion 41 that overlaps the axis C is L ₁ , and the point O that is L _1/2 on the axis C is the origin. The coordinate (x, y) = (0, 0) is set, and the length of the melted portion 40 that overlaps the straight line M that passes through the point where the x coordinate is x = 3R / 8 and is parallel to the axis C is L _2. , _L 2/2 become y-coordinate of a point of _y 2, x coordinate x = point through the -3R / 8, and the length of the fused portion 40 overlapping with the straight line parallel N the axis C _L 3, L _When the y coordinate of the point that becomes 3/2 is y ₃ , the maximum value X _MAX and the minimum value M _MIN of the ratio X of the main component (for example, Pt) of the material forming the noble metal tip 41 at the following nine points: Is preferably 30% or less, and more preferably 15% or less.

O point (0,0): the origin a point _{(0, L 1/2)} : on the axis C, than the origin O _L 1/2 only in that position in the noble metal tip side point b (0, _-L 1 / 2): A point located on the center electrode side by L _1/2 from the origin O on the axis C point c (3R / 8, y ₂ ): a point located on the straight line M at the point y ₂ d point (3R _{/ 8, y 2 + L 2} /4): on the straight line M, than _{y 2 L 2/4} only in located on the noble metal tip side e point _{(3R / 8, y 2 -L} 2/4): linear M above, _{y 2} points f point located only center electrode side _L 2/4 than _{(-3R / 8, y 3)} : on a straight line N, the position points point g _{y 3} (-3R / 8, _{y 3 + L 3/4)} : on the straight line N, _L 3/4 only noble metal tip point h point located side than _{y 3 (-3R / 8, y} 3 -L 3/4); on the line N in , L ₂ than y ₃ / 4 Points located on the center electrode side

  In irradiating the laser, the irradiation position and the irradiation intensity are adjusted so that the melting portion 40 and the penetration portion 41 as described above are formed.

  Further, since the melted portion where the melted portion 40 is formed through the noble metal tip 21 is more easily consumed than the noble metal tip, the noble metal tip is not melted to a certain extent at the tip portion in order to ensure the durability of the plug. It is necessary to secure a part. Specifically, as shown in FIG. 2B, the distance (H) from the upper end 40a on the axis of the penetrating portion 41 to the upper end surface 21a of the noble metal tip 21 is preferably 0.2 mm or more.

  Hereinafter, the present invention will be further described with reference to test examples, but the present invention is not limited thereto.

(Test-1)
A concave portion is formed in the center of the upper surface of the Ni alloy base that is regarded as the center electrode, and a columnar body made of Pt alloy having a diameter of 0.6 mm and a length of 0.8 mm as a noble metal tip is accommodated, and perpendicular to the wall surface of the concave portion The base and the noble metal tip were welded by irradiating a laser so that Welding was performed by changing the laser irradiation conditions, and the thickness (T) and width (W) of the penetrating portion were controlled as shown in Table 1.

  Then, the base to which the noble metal tip is welded is attached to a cold heat test machine, and the thermal cycle of heating at 1000 ° C. for 2 minutes and then gradually cooling for 1 minute is repeated 3000 times, and after completion, cut along the axis of the noble metal tip. The molten part was observed. The test was performed 10 times each, and if any crack of 1/4 or more of the tip diameter or a gap between the noble metal tip and the melted part was recognized, “X” was added to Table 1 as not possible, and the others were acceptable. As shown in Table 1, “◯” is attached.

  As shown in Table 1, cracks and gaps are eliminated by forming the melted portion so that the thickness (T) of the penetrating portion is 0.1 mm or more and the width (W) is 0.05 mm or more. It can be seen that the weld strength between the noble metal tip and the center electrode is increased.

(Test-2)
Using a base and a columnar body equivalent to Test-1, the thickness (T) of the penetrating portion was controlled to be 0.1 mm or more and a width of 0.05 mm or more, and laser irradiation was performed for welding.

  Then, a cooling test was performed in the same manner as in Test 1, and after completion, the composition was analyzed by cutting along the axis of the noble metal tip and sampling the melted portion. Sampling was performed by sampling the nine points shown in FIG. 3 and analyzing the composition at each measurement point to determine the Pt content as the main component of the noble metal tip. The spot diameter at each sampling point is 10 μm. Moreover, the test was performed 10 times and the composition was taken as the average value.

Then, to calculate the maximum value of the Pt content in 9 points _{(X MAX)} and the minimum value the difference between _{(X MIN) (X MAX -X} MIN). Then, this _(X MAX _{-X MIN),} obtained relation between cold test results. The results are shown in Table 2. In Table 2, “x” indicates a case where 5 or more cracks occurred, or a crack having a length of 1/4 or more of the diameter of the columnar body, and “◯” represents 4 or less cracks. And the crack length is less than ¼ of the diameter of the columnar body, and “◎” indicates the case where the number of cracks is 1 or less and the crack length is less than ¼ of the diameter of the columnar body.

As shown in Table 2, as (X _MAX -X _MIN ) is smaller, the noble metal tip and the center electrode in the melted portion are more homogeneously melted, and the generation of cracks and gaps is reduced. Preferably, 15% or less is more preferable.

(Test-3)
The relationship between the distance (H) from the upper end of the penetrating portion to the upper end surface of the noble metal tip (see FIG. 2B) and the gap increase amount was verified by a desktop spark durability test. That is, the noble metal tip is a Pt alloy having a diameter of 0.6 mm, the recess material is a Ni alloy, the thickness (T) of the through portion is 0.1 mm or more, the width is 0.05 mm or more, and the distance (H) is Table 3. The amount of increase in the gap when welded so as to have the value shown in Fig. 6 was obtained by simulation. The test conditions were 0.4 MPa, 250 hours, and 100 Hz.

  Since the melted portion is a mixture of the Pt alloy of the noble metal tip and the Ni alloy of the base, it is consumed faster than the noble metal tip. Therefore, it can be said that the durability increases as the gap increase amount increases. In consideration of practicality, the criterion was less than 0.3 mm. The results are shown in Table 3.

  As shown in Table 3, it can be seen that the durability of the noble metal tip can be maintained by setting the distance (H) to 0.2 mm or more.

DESCRIPTION OF SYMBOLS 11 Metal body 12 Insulator 13 Center electrode 14 Ground electrode 21 Precious metal tip 30 Recessed part 31 Wall surface 40 Melting part 41 Through part 100 Spark plug

Claims (5)

An insulator having an axial hole extending in the axial direction;
A center electrode held in the shaft hole;
A metal shell provided on the outer periphery of the insulator;
One end is joined to the metal shell, the other end is a ground electrode facing the center electrode,
A noble metal tip disposed in a recess provided at the tip of the center electrode and bonded to a position facing the ground electrode;
A spark plug that forms a gap between the tip of the noble metal tip and the ground electrode,
A melting portion in which the component of the center electrode and the component of the noble metal tip are mixed, and the tip of the center electrode is located on the tip side in the axial direction from the tip on the axis of the melting portion, and The bottom surface of the recess is located on the rear end side in the axial direction from the rear end on the axial line of the melted portion,
In the cross section passing through the axis, the molten portion is continuous in the radial direction,
A spark plug characterized in that a portion A having a thickness of 0.1 mm or more in the axial direction of the molten portion is formed over 0.05 mm or more in the radial direction. The diameter of the noble metal tip is R,
The length of the portion A that overlaps the axis is L ₁ , the point O that is L _1/2 on the axis is the origin, and its coordinates (x, y) = (0, 0),
x-coordinate passes through the point x = 3R / 8, and the length of the molten partially-overlapping with the straight line M parallel to the axis L _2, L _2/2 become y-coordinate of a point of y _2,
x-coordinate passes through the point x = -3R / 8, and the y-coordinate of the length of the molten partially-overlapping with the straight line parallel N to the axis L _3, L _3/2 and becomes a point and y _{3,
O (0,0), a (0} , L 1/2), b (0, -L 1/2), c (3R / 8, y 2), d (3R / 8, y 2 + L 2/4 _{), e (3R / 8,} y 2 -L 2/4), f (-3R / 8, y 3), g (-3R / 8, y 3 + L 3/4), h (-3R / 8, y ₃ -L _3/4 maximum value _{X MAX} percentage X of the main component of the material forming the noble metal tip at 9 points), when a minimum value was _{M MIN, (X MAX -X MIN} ) ≦ 30 The spark plug according to claim 1, wherein the spark plug is%. The spark plug according to claim 2, wherein (X _MAX −X _MIN ) ≦ 15%.   The minimum value of the length in the axial direction from the boundary between the portion A and the noble metal tip to the tip end surface of the noble metal tip is 0.2 mm or more. The spark plug according to item. An insulator having an axial hole extending in the axial direction;
A center electrode held in the shaft hole;
A metal shell provided on the outer periphery of the insulator;
One end is joined to the metal shell, and at the other end, a ground electrode is formed with a gap between the center electrode,
A spark plug manufacturing method comprising:
In the recess formed at the tip of the center electrode, the precious metal tip is accommodated, and a side surface of the recess is irradiated with a laser, and a welding process for welding the recess and the noble metal tip is provided.
In the welding step, in a radial direction of the noble metal tip in a joint portion between the recess and the noble metal tip, while leaving a part of the recess in the axial direction tip side and a part of the noble metal tip on the recess side. A portion having a thickness of 0.1 mm or more in the axial direction of the molten portion in a cross section in the axial direction passing through the center of the front end face of the noble metal tip is 0.05 mm or more in the radial direction. A method for manufacturing a spark plug, comprising welding so as to be formed over a wide area.

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