JP6411433B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug.

  Conventionally, there are spark plugs for internal combustion engines such as automobiles, cogeneration, and gas pumps. The spark plug has a center electrode and a ground electrode, and a spark discharge gap is provided therebetween. The gas mixture is ignited by the spark discharge in the spark discharge gap.

  Such a spark plug requires a longer life due to higher performance of the engine and maintenance-free, and a noble metal such as an Ir alloy is formed in a spark discharge portion which is a portion facing the spark discharge gap in the center electrode. A chip is disposed.

Here, there is a large difference in thermal expansion coefficient between the noble metal tip (Ir alloy or the like) and the center electrode base material (Ni alloy or the like). Therefore, in order to prevent the chip from dropping off due to thermal stress, a molten layer having a thermal expansion coefficient approximately in the middle between the noble metal chip and the center electrode base material is formed by laser welding. Thereby, the bonding property between the noble metal tip and the center electrode base material is ensured by reducing the thermal stress. In addition, in order to ensure good bondability while also ensuring the durability of the igniting portion, it is known that the width relationship in the chip height direction of the molten layer is adjusted. (For example, patent document 1).

JP 2001-15245 A

Although the spark plug described in the above-mentioned patent document has the durability of the ignition part while ensuring good bondability, as a result of the intensive studies by the present inventors, the durability of the ignition part is further increased. There was room for improvement.
Therefore, in view of such a situation, the present invention aims to provide a spark plug in which the durability of the ignition portion is further improved while ensuring good bondability between the center electrode and the noble metal tip.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms.

(1) According to one aspect of the present invention, a rod-shaped center electrode extending in the axial direction, a tubular insulator that holds the center electrode on its tip side, and a tube provided on the outer periphery of the insulator A metal shell, a ground electrode joined to the tip of the metal shell, a noble metal tip joined to the tip of the center electrode and opposed to the end of the ground electrode through a gap, The center electrode and the noble metal tip are spark plugs joined through a melted portion in which a component of the center electrode and a component of the noble metal tip are melted, and in the cross section including the axis, the noble metal The tip-side boundary, which is the boundary between the tip and the melting portion, has a shape in which the shape in the range from the point X on the most rear end side in the axial direction to the outer peripheral end A is convex toward the melting portion side, And the boundary between the melted part and The electrode side boundary is a shape in which the shape in the range from the most distal point Y to the outer peripheral end B in the axial direction is convex toward the center electrode side, and the contour line of the portion exposed to the outer surface of the melted portion There is provided a spark plug having a concave shape on the melting part side. According to this form of the spark plug, both the tip side boundary, which is the boundary between the noble metal tip and the molten part, and the center electrode side boundary, which is the boundary between the center electrode and the molten part, protrude toward the material side having a large thermal expansion coefficient. Therefore, the stress generated by the difference in thermal expansion at each boundary portion is relieved, and separation at each boundary is less likely to occur. In addition, because the tip side boundary, which is the boundary between the noble metal tip and the melted portion, has a convex shape toward the melted portion, the melted portion is exposed to the discharge surface when the discharge surface of the noble metal tip is consumed by spark discharge. It has good durability performance. Furthermore, since the outline of the part exposed on the outer surface of the melted part has a concave shape on the melted part side, it is possible to suppress the possibility of discharging to the melted part.

(2) In the spark plug of the above aspect, in the cross section including the axis, among the tip side boundaries in the range from the point X on the most rear end side in the axis direction to the outer peripheral end A, the rearmost in the axis direction The portion farthest from the straight line passing through the end point X and the outer peripheral end A is located on the outer side in the radial direction from the position inside the outer diameter of the noble metal tip by 1/4 of the outer diameter of the noble metal tip. You may make it do. As a result, when the discharge surface of the noble metal tip is consumed due to spark discharge, the melted portion becomes more difficult to be exposed to the discharge surface, so that it is possible to have better durability performance.

It is explanatory drawing which shows the partial cross section of a spark plug. It is explanatory drawing which expands and shows the principal part cross section of a spark plug. It is explanatory drawing which expands and shows the principal part cross section of a spark plug.

A. Embodiment:
A-1. Spark plug configuration:
FIG. 1 is an explanatory view showing a partial cross section of the spark plug 10. FIG. 1 illustrates the external shape of the spark plug 10 on the right side of the drawing with the axis CA1 being the axis of the spark plug 10 as a boundary, and the cross-sectional shape of the spark plug 10 on the left side of the drawing. The lower side of the spark plug 10 in FIG. 1 is referred to as “front end side”, and the upper side of FIG. 1 is referred to as “rear end side”.

  The spark plug 10 includes a center electrode 100, an insulator 200, a metal shell 300, and a ground electrode 400. In the present embodiment, the axis CA1 of the spark plug 10 is also the axis of each member of the center electrode 100, the insulator 200, and the metal shell 300.

  The spark plug 10 has a gap SG formed between the center electrode 100 and the ground electrode 400 on the tip side. The gap SG of the spark plug 10 is also called a spark gap. The spark plug 10 is configured to be attachable to the internal combustion engine 90 in a state in which the front end side where the gap SG is formed protrudes from the inner wall 910 of the combustion chamber 920. When a high voltage is applied to the center electrode 100 with the spark plug 10 attached to the internal combustion engine 90, a spark discharge is generated in the gap SG. It is possible to ignite the air-fuel mixture in the combustion chamber 920 by the spark discharge generated in the gap SG.

  FIG. 1 shows XYZ axes orthogonal to each other. Of the XYZ axes in FIG. 1, an axis along the axis CA <b> 1 is a Z axis. With respect to the Z-axis direction (axial direction) along the Z-axis, the + Z-axis direction from the rear end side to the front-end side of the spark plug 10 is set, and the opposite is the −Z-axis direction. The + Z-axis direction is a direction in which the center electrode 100 protrudes from the front end side of the metal shell 300 along the axis CA1 together with the insulator 200.

  Of the XYZ axes in FIG. 1, the axis along the direction in which the ground electrode 400 bends toward the axis CA1 is defined as the Y axis. With respect to the Y-axis direction along the Y-axis, the direction in which the ground electrode 400 bends toward the axis CA1 is the −Y-axis direction, and the opposite is the + Y-axis direction.

  Of the XYZ axes in FIG. 1, an axis orthogonal to the Y axis and the Z axis is taken as an X axis. With respect to the X-axis direction along the X-axis, the + X-axis direction is from the back of the sheet of FIG. 1 toward the front of the sheet, and the opposite is the −X-axis direction.

  The center electrode 100 of the spark plug 10 is a conductive electrode body. The center electrode 100 has a rod shape extending about the axis CA1. In the present embodiment, the center electrode 100 is made of a nickel alloy (for example, Inconel (registered trademark)) whose main component is nickel (Ni). The distal end side of the center electrode 100 protrudes from the distal end side of the insulator 200. The center electrode 100 is electrically connected to the terminal fitting 190 through the seal body 160, the ceramic resistor 170, and the seal body 180.

  The noble metal tip 110 is joined to the distal end portion of the center electrode 100 through a melted portion 120 in which the components of the center electrode 100 and the components of the noble metal tip 110 are melted.

  The ground electrode 400 of the spark plug 10 is an electrode body having conductivity. In the present embodiment, the ground electrode 400 has a shape that once extends parallel to the axis CA1 from the metal shell 300 and then bent toward the axis CA1. The base end portion of the ground electrode 400 is joined to the metal shell 300. A gap SG is formed between the tip of the ground electrode 400 and the center electrode 100. In the present embodiment, the ground electrode 400 is made of a nickel alloy (for example, Inconel (registered trademark)) whose main component is nickel (Ni).

  The insulator 200 of the spark plug 10 is an insulator having electrical insulation. The insulator 200 has a cylindrical shape extending about the axis CA1. In this embodiment, the insulator 200 is formed by firing an insulating ceramic material (for example, alumina).

  The insulator 200 has a shaft hole 290 that is a through hole extending about the axis CA1. In the shaft hole 290 of the insulator 200, the center electrode 100 is held on the axis CA <b> 1 in a state where it protrudes from the tip side (+ Z axis direction side) of the insulator 200. On the outer side of the insulator 200, in order from the front end side to the rear end side, the first cylindrical portion 210, the second cylindrical portion 220, the third cylindrical portion 250, and the fourth cylindrical portion 270 are provided. Is formed.

  The first tubular portion 210 of the insulator 200 is a cylindrical portion that is tapered toward the distal end side, and the distal end side of the first tubular portion 210 protrudes from the distal end side of the metal shell 300. The second tubular portion 220 of the insulator 200 is a cylindrical portion having a larger diameter than the first tubular portion 210. The third cylindrical portion 250 of the insulator 200 is a cylindrical portion that protrudes in the outer peripheral direction from the second cylindrical portion 220 and the fourth cylindrical portion 270. The fourth cylindrical portion 270 of the insulator 200 is a cylindrical portion that forms the rear end side from the third cylindrical portion 250, and the rear end side of the fourth cylindrical portion 270 is the rear end side of the metal shell 300. Protruding from.

  The metal shell 300 of the spark plug 10 is a metal body having conductivity. The metal shell 300 has a cylindrical shape extending about the axis CA1. In the present embodiment, the metallic shell 300 is a metal body obtained by applying nickel plating to a low carbon steel formed into a cylindrical shape. In other embodiments, the metallic shell 300 may be a metal body that is galvanized, or may be a metal body that is not plated (non-plated).

  The insulator 200 is held inside the metal shell 300 in a state of protruding together with the center electrode 100 from the front end side (+ Z-axis direction side) of the metal shell 300. Inside the metal shell 300, a metal fitting inner peripheral surface 392, an annular convex portion 394, and a metal fitting inner peripheral surface 396 are formed in order from the front end side to the rear end side.

  The metal inner peripheral surface 392 of the metal shell 300 is a portion of the inner peripheral surface of the metal shell 300 that is located on the tip side of the annular convex portion 394. The annular protrusion 394 of the metal shell 300 is an annular portion that protrudes inward from the metal inner peripheral surface 392 and the metal inner peripheral surface 396 that are the inner peripheral surface of the metal shell 300. The metal inner peripheral surface 396 of the metal shell 300 is a portion located on the rear end side of the inner peripheral surface of the metal shell 300 with respect to the annular convex portion 394.

  A gap between the metal inner peripheral surface 392 and the insulator 200 is larger than a gap between the annular convex portion 394 and the insulator 200 and a gap between the metal inner peripheral surface 396 and the insulator 200. When the insulator 200 is inserted from the rear end side of the metal shell 300 and assembled to the metal shell 300, the annular protrusion 394 and the metal inner peripheral surface 396 are used for positioning the insulator 200 with respect to the metal shell 300.

  The metal shell 300 is caulked and fixed to the outer surface of the insulator 200 while being electrically insulated from the center electrode 100. On the outer side of the metal shell 300, there are a front end portion 310, a screw portion 320, a body portion 340, a groove portion 350, a tool engagement portion 360, and a caulking lid 380 in order from the front end side to the rear end side. Is formed.

  The distal end portion 310 of the metallic shell 300 is a cylindrical portion that constitutes the distal end side (+ Z axial direction side) of the metallic shell 300. A ground electrode 400 is joined to the tip portion 310. From the center of the tip portion 310, the insulator 200 together with the center electrode 100 protrudes in the + Z-axis direction.

  The threaded portion 320 of the metal shell 300 is a cylindrical portion having a thread formed on the outer surface. In the present embodiment, the spark plug 10 can be attached to the internal combustion engine 90 by screwing the screw portion 320 of the metal shell 300 into the screw hole 930 of the internal combustion engine 90. In this embodiment, the nominal diameter of the screw part 320 is M12. In other embodiments, the nominal diameter of the threaded portion 320 may be smaller than M12 (for example, M8, M9, M10) or larger than M12 (for example, M14, M18).

  The body 340 of the metal shell 300 is a bowl-shaped portion that protrudes from the groove 350 in the outer circumferential direction. With the spark plug 10 attached to the internal combustion engine 90, the gasket 500 is compressed between the body 340 and the internal combustion engine 90.

  The groove portion 350 of the metal shell 300 is a cylindrical portion that is provided between the body 340 and the tool engaging portion 360 and bulges in the outer peripheral direction when the metal shell 300 is caulked and fixed to the insulator 200.

  The tool engagement portion 360 of the metal shell 300 is a bowl-shaped portion projecting in a polygonal shape in the outer peripheral direction from the groove portion 350 and engages with a tool (not shown) for attaching the spark plug 10 to the internal combustion engine 90. Make a shape. In the present embodiment, the outer shape of the tool engaging portion 360 is a hexagonal shape.

  The caulking lid 380 of the metal shell 300 is a part that is formed by bending the rear end side of the metal shell 300 toward the insulator 200 when the metal shell 300 is caulked and fixed to the insulator 200.

  Between the outer side of the third cylindrical part 250 and the fourth cylindrical part 270 of the insulator 200 and the inner side of the tool engaging part 360 and the caulking lid 380 of the metal shell 300, the ring member 610 is located on the rear end side. The ring members 620 are disposed on the distal end side, and the powder 650 is filled between the ring member 610 and the ring member 620. The ring members 610 and 620 are metal (for example, iron (Fe)) annular members. The powder 650 is a sealing powder (for example, powder talc).

The ring members 610 and 620 and the powder 650 seal the gap between the insulator 200 and the metal shell 300 and improve the holding force of the insulator 200 with respect to the metal shell 300. Here, the ring members 610 and 620 that are annular members may have an O-shape that is not cut in the circumferential direction when viewed in a cross section orthogonal to the axis CA1, or a C-shape that has a cut in a part of the circumferential direction. It may be.

  FIG. 2 is an explanatory diagram showing, in an enlarged manner, a cross section including the axis CA1 near the tip of the center electrode 100 to which the noble metal tip 110 is bonded. In FIG. 2, the lower side of the drawing is the “rear end” and the upper side of the drawing is the “leading side”.

  As shown in FIG. 2, the noble metal tip 110 is joined to the distal end portion of the center electrode 100 through a melted portion 120 in which the components of the center electrode 100 and the components of the noble metal tip 110 are melted. With the noble metal tip 110 placed at the tip of the center electrode 100, the boundary between the two is laser welded to form a melted portion 120 in which the components of the center electrode 100 and the noble metal tip 110 are melted. 110 and the center electrode 100 are joined.

  The tip-side boundary 130, which is the boundary between the noble metal tip 110 and the melting portion 120, has a shape in the range from the point X closest to the rear end side in the direction of the axis CA 1 to the outer peripheral end A 1 and from the point X to the outer peripheral end A 2. It has a convex shape. Here, the outer peripheral ends A1 and A2 correspond to the outer peripheral end A in the claims. The “tip-side boundary 130 is convex toward the melted part 120 side” means that the tip-side boundary 130 from the point X to the outer peripheral end A1 is the rear end of a virtual straight line connecting the point X and the outer peripheral end A1. It means to be located on the side. The same applies to the chip side boundary 130 from the point X to the outer peripheral end A2.

  The center electrode-side boundary 140, which is the boundary between the center electrode 100 and the melted portion 120, has a shape in the range from the most distal point Y to the outer peripheral end B1 and the point Y to the outer peripheral end B2 in the direction of the axis CA1 toward the central electrode. It has a convex shape. Here, the outer peripheral ends B1 and B2 correspond to the outer peripheral end B in the claims. Note that “the center electrode side boundary 140 is convex toward the center electrode 100” means that the center electrode side boundary 140 from the point Y to the outer peripheral end B1 is more than the virtual straight line connecting the point Y and the outer peripheral end B1. It means that it is located on the rear end side. The same applies to the center electrode side boundary 140 from the point Y to the outer peripheral end B2.

  The part exposed to the outer surface of the melting part 120 has a concave shape on the melting part 120 side. That is, the outer surface of the melting part 120 is depressed, and in FIG. 2, which is a cross section including the axis CA <b> 1, the outline of the part exposed on the outer surface of the melting part 120 has a concave shape on the melting part 120 side. .

  FIG. 3 is an explanatory view showing an enlarged cross section including the axis CA1 in the vicinity of the tip of the central electrode 100 to which the noble metal tip 110 is joined, as in FIG. The side is the “tip side”.

  In FIG. 3, a reference straight line or the like is shown so that the shape of the melting part 120 as a more preferable form can be specified. The straight line L1 is a straight line passing through the point X and the outer peripheral end A1, and the straight line L2 is a straight line passing through the point X and the outer peripheral end A2. The straight line RL1 is a straight line that is parallel to the axis CA1 that passes through a position that is 1/4 of the outer diameter D of the noble metal tip 110 from the outer peripheral surface of the noble metal tip 110. The line RL2 is a straight line parallel to the axis CA1 that passes through a position that is inside the outer diameter D of the noble metal tip 110 by 1/4 of the outer diameter D of the noble metal tip 110.

  As shown in FIG. 3, the position T1 farthest from the straight line L1 in the chip-side boundary 130 between the point X and the outer peripheral end A1 is radially outward from the straight line RL1. Similarly, a position T2 farthest from the straight line L2 in the chip-side boundary 130 between the point X and the outer peripheral end A2 is radially outside of the straight line RL2. In this way, the position of the chip-side boundary 130 that is most convex on the melted part 120 side is located relatively outside in the radial direction. As a result, when the volume of the noble metal tip 110 is reduced due to the consumption of sparks, the melting portion 120 is discharged when compared with the tip side boundary 130 where the most convex portion on the melting portion 120 side is radially inward. It becomes difficult to be exposed to the surface. That is, durability is good. In addition, a part of the melted part 120 may extend to the outer peripheral surface of the noble metal tip 110 during laser welding. In such a case, the contact point between the rear end point of the outer peripheral edge of the noble metal tip 110 and the melting portion 120 is regarded as the outer peripheral end A (A1, A2). For example, when the noble metal tip 110 having a constant outer diameter is used, the contact point between the rear end point of the portion having the constant outer diameter of the noble metal tip 110 and the melting portion 120 is regarded as the outer peripheral end A (A1, A2).

A-2. effect:
According to the embodiment described above, the tip side boundary 130, which is the boundary between the noble metal tip 110 and the melting portion 120, from the point X on the most rear end side in the axis CA1 direction to the outer peripheral end A1 and from the point X to the outer peripheral end A2. The shape in the range is convex to the melted part 120 side. That is, the chip-side boundary 130 has a convex shape toward the melted part 120 having a large thermal expansion coefficient. As a result, the stress generated due to the difference in thermal expansion at the boundary between the noble metal tip 110 and the melting part 120 is relieved, and peeling at the boundary between the noble metal tip 110 and the melting part 120 is less likely to occur.

  Furthermore, the shape of the tip side boundary 130, which is the boundary between the noble metal tip 110 and the melting portion 120, in the range from the point X on the most rear end side in the axis CA1 direction to the outer peripheral end A1 and from the point X to the outer peripheral end A2 is the melting portion. Since it has a convex shape toward the 120 side, when the discharge surface of the noble metal tip is consumed due to spark discharge, the melted portion is difficult to be exposed to the discharge surface, so that it has good durability performance.

  Further, the center electrode side boundary 140, which is the boundary between the center electrode 100 and the melted portion 120, is centered in the range from the point Y on the most rear end side in the axis CA1 direction to the outer peripheral end B1 and the point Y to the outer peripheral end B2. The shape is convex toward the electrode 100 side. That is, the center electrode side boundary 140 has a convex shape toward the center electrode 100 having a large thermal expansion coefficient. As a result, the stress generated by the difference in thermal expansion at the boundary between the center electrode 100 and the melted part 120 is relieved, and peeling at the boundary between the center electrode 100 and the melted part 120 is less likely to occur.

  Moreover, the site | part exposed to the outer surface among the fusion | melting parts 120 has a concave shape at the fusion | melting part 120 side. That is, the outer surface of the melting part 120 is depressed, and in FIG. 2, which is a cross section including the axis CA <b> 1, the outline of the part exposed on the outer surface of the melting part 120 has a concave shape on the melting part 120 side. Therefore, it is possible to suppress the possibility of discharging to the melting part 120. As a result, abnormal consumption of the melted part 120 due to discharge is suppressed.

  Furthermore, since the most convex position on the melt side 120 of the chip side boundary 130 is located on the relatively outer side in the radial direction, when the volume of the noble metal chip 110 is reduced due to spark consumption, the chip side boundary 130 Compared to a case where the position convex to the melt part 120 side of 130 is radially inward, the melt part 120 is less likely to be exposed on the discharge surface. As a result, the durability is good.

B. Other embodiments:
The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the above-described effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Spark plug 90 ... Internal combustion engine 100 ... Center electrode 110 ... Precious metal tip 120 ... Melting part 130 ... Chip side boundary 140 ... Center electrode side boundary 160 ... Sealing body 170 ... Ceramic resistance 180 ... Sealing body 190 ... Terminal metal fitting 200 ... Insulation Body 210 ... 1st cylindrical part 220 ... 2nd cylindrical part 250 ... 3rd cylindrical part 270 ... 4th cylindrical part 290 ... Shaft hole 300 ... Metallic body 310 ... Tip part 320 ... Screw part 340 ... Trunk part 350 ... groove portion 360 ... tool engaging portion 380 ... caulking lid 392 ... metal fitting inner peripheral surface 394 ... annular convex portion 396 ... metal fitting inner peripheral surface 400 ... ground electrode 500 ... gasket 610 ... ring member 620 ... ring member 650 ... powder 910 ... inner wall 920 ... Combustion chamber 930 ... Screw hole SG ... Gap CA1 ... Axis A (A1, A2) ... Outer peripheral edge B (B1, 2) Outer peripheral edge of center electrode side boundary X: Point on the most rear end side in chip side boundary Y: Point on the most distal side in center electrode side boundary L (L1, L2) ... Point X and outer peripheral end A ( A straight line passing through A1, A2) T: a part of the chip side boundary farthest from the straight line L D: outer diameter of the noble metal tip RL (RL1, RL2): 1 / out of the outer diameter of the noble metal tip from the outer peripheral surface of the noble metal tip A straight line that passes through a position that is 4 inward

Claims (2)

A rod-shaped center electrode extending in the axial direction;
A cylindrical insulator holding the center electrode on its tip side;
A cylindrical metal shell provided on the outer periphery of the insulator;
A ground electrode joined to the tip of the metal shell;
A noble metal tip bonded to the tip of the center electrode and facing the end of the ground electrode via a gap;
The center electrode and the noble metal tip are spark plugs that are joined through a melted portion in which a component of the center electrode and a component of the noble metal tip are melted,
In a cross section including the axis,
The tip side boundary, which is the boundary between the noble metal tip and the melting portion, is a shape in which the shape in the range from the point X on the most rear end side in the axial direction to the outer peripheral end A is convex toward the melting portion side,
The center electrode side boundary, which is the boundary between the center electrode and the melted portion, is a shape in which the shape in the range from the most distal end point Y to the outer peripheral end B in the axial direction is convex toward the center electrode side,
A spark plug in which an outline of a portion exposed to the outer surface of the melted portion has a concave shape on the melted portion side. The spark plug according to claim 1,
In a cross section including the axis,
Of the tip-side boundary in the range from the point X closest to the rearmost end in the axial direction to the outer peripheral end A, it is farthest from a straight line passing through the point X closest to the rearmost end in the axial direction and the outer peripheral end A. The spark plug is located on the outer side in the radial direction than the position where the part is located inside the outer diameter of the noble metal tip by 1/4 of the outer diameter of the noble metal tip.

Images