JP2010033989A - Spark plug for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent corrosion or the like of an insulator and maintain sufficiently bonding strength of a grounding electrode to a body metal fitting and moreover to surely prevent breakage or the like of the grounding electrode. <P>SOLUTION: The spark plug 1 is provided with a central electrode 5, an insulator 2 holding the central electrode 5 with its top end projecting in a direction of an axial line CL1 from its own top end surface, the body metal fitting 3 having threaded part 15 where threads are formed and having a cylindrical part 42 as well where no threads are formed on its outer circumferential face in a region from the threaded part 15 at least to the top end of the insulator 2 along the axial line CL1 direction, and a grounding electrode 27 with its own base end jointed with a top end part 3a of the body metal fitting 3. On the cylindrical part 42, there is formed a groove part 51 made of a bottom face 52 located nearer the side of the base end than a top end 2a of the insulator 2 and two sidewalls 53, 54 formed in continuation with the bottom face 52 and the top end face 3a of the body metal fitting 3. The base end of the grounding electrode 27 is jointed to the bottom face 52 of the groove part 51. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spark plug used for an internal combustion engine.

  A spark plug used in an internal combustion engine such as an automobile engine includes, for example, a central electrode extending in the axial direction, an insulator provided outside the center electrode, a cylindrical metal shell provided outside the insulator, and a base. And a ground electrode joined to the tip of the metal shell. In addition, the ground electrode is bent back so that the tip of the ground electrode faces the tip of the center electrode, whereby a spark discharge gap is formed between the tip of the center electrode and the tip of the ground electrode. .

  Conventionally, in order to improve the ignitability, it is generally performed that the front end surface of the insulator protrudes from the front end surface of the metal shell, and the spark discharge gap is formed at the center side of the combustion chamber. By the way, if the insulator is disposed so as to protrude from the front end surface of the metal shell, the fuel tends to adhere to the insulator. Here, if the fuel adheres to the insulator, the fouling resistance is lowered, or the fuel adheres to the high-temperature insulator, and the surface of the insulator is swept away. There is a risk of erosion (corrosion). When the insulator is corroded, the corroded portion is heated to a higher temperature and may be ignited before the normal ignition timing, that is, preignition is likely to occur. Particularly in recent years, in direct injection engines, high compression ratio engines, or engines with a supercharger, which are used to improve fuel efficiency and output, fuel is more likely to adhere to the insulator, or the insulator has a higher temperature. Since it is easy to become, corrosion of an insulator is a further concern.

Therefore, a cylindrical cylindrical portion extending toward the distal end side in the axial direction is formed at the distal end portion of the metallic shell, and the distal end surface of the insulator is retracted closer to the proximal side in the axial direction than the distal end surface of the metallic shell (cylindrical portion). A technique has been proposed in which the fuel is prevented from adhering to the insulator by being disposed at the position, and thus the insulator is prevented from corroding (see, for example, Patent Document 1).
JP 2003-59619 A

  By the way, in the case of adopting the above technique, when the base end of the ground electrode is joined to the tip of the metal shell (cylindrical part), the joint between the metal shell and the ground electrode and the tip of the center electrode The distance along the axial direction is relatively short. Therefore, in such a case, in order to ensure a sufficient space for the air-fuel mixture to burn and spread immediately after ignition, while forming a spark discharge gap of a predetermined size with the center electrode, the ground electrode Needs to be bent relatively to the center electrode side (in other words, with a relatively small radius of curvature) and more proximally.

  However, if the ground electrode is bent tightly, stress associated with engine vibration or the like tends to concentrate on the bent portion of the ground electrode, which may cause breakage of the ground electrode. Further, when the ground electrode is bent further on the proximal end side, the stress accompanying the bending process is likely to be applied to the joint portion having a lower strength than the ground electrode itself. As a result, coupled with the fact that the bending stress accompanying the bending process becomes relatively large due to the relatively tight bending of the ground electrode, breakage or the like is likely to occur at the joint, and as a result There is concern about falling off the metal shell.

  On the other hand, as in Patent Document 1, the outer peripheral surface of the front end portion of the metallic shell (cylindrical portion) is formed into a tapered shape that decreases in diameter toward the distal end side, and the tapered metallic shell (cylindrical portion) is formed. A method of joining a straight rod-shaped ground electrode to the tip surface is conceivable. However, in this case, since the side surface on the front end side of the ground electrode faces the front end edge portion of the center electrode, there is a possibility that the ground electrode is partially consumed with spark discharge. In addition, when joining the ground electrode to the metal shell, support the metal shell and perform resistance welding while pressing the ground electrode against the metal shell with a pressing force along the longitudinal direction of the metal shell. Is common. However, if the tip surface of the metal shell is processed into a taper shape, the direction in which the ground electrode is pressed and the tip surface of the metal shell are not orthogonal. Therefore, it becomes difficult to press the ground electrode with a relatively large pressing force, and there is a possibility that sufficient bonding strength cannot be obtained.

  The present invention has been made in view of the above circumstances, and its purpose is to sufficiently secure the bonding strength of the ground electrode to the metal shell while suppressing corrosion of the insulator and the like. An object of the present invention is to provide a spark plug for an internal combustion engine that can more reliably prevent electrode breakage and the like.

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

Configuration 1. The spark plug for an internal combustion engine of this configuration includes a rod-shaped center electrode extending in the axial direction,
A substantially cylindrical insulator having an axial hole extending in the axial direction and holding the central electrode by projecting the distal end of the central electrode from the distal end surface thereof in the axial direction;
While having a cylindrical shape and provided on the radially outer side of the insulator, and having a threaded portion formed with a thread on its outer peripheral surface, the space between the threaded portion and at least the tip of the insulator In a region along the axial direction, a metal shell having a cylindrical portion in which no thread is formed on the outer peripheral surface;
An internal combustion engine having a rod-like shape, having a substantially central portion bent by itself, a ground electrode whose own distal end is located on the axis side, and whose proximal end is joined to the distal end portion of the metal shell A spark plug,
The cylindrical portion of the metal shell is formed so as to be continuous with the bottom surface that faces the distal end side in the axial direction and is located on the proximal side of the distal end of the insulator, and the bottom surface and the distal surface of the metal shell. A groove portion that communicates the inside and the outside of the cylindrical portion of the metal shell,
The base end of the ground electrode is joined to the bottom surface of the groove.

  According to the above configuration 1, the metal shell has a thread portion in which the thread is formed, and the thread is formed on the outer peripheral surface in a region along the axial direction from the thread portion to at least the tip of the insulator. It has a cylindrical part that is not formed. In other words, a cylindrical portion is formed at the distal end portion of the metal shell, and the distal end of the insulator is located closer to the proximal end in the axial direction than the distal end of the cylindrical portion (that is, the insulator is , Provided in a retracted state inside the cylindrical portion). For this reason, it is possible to more reliably prevent the fuel from adhering to the insulator. As a result, it is possible to more reliably prevent deterioration of stain resistance and corrosion of the insulator.

  On the other hand, there are concerns about dropout of the ground electrode and a decrease in breakage resistance caused by joining the ground electrode to the tip of the metal shell (cylindrical portion). A groove portion having a bottom surface located on the base end side in the axial direction from the distal end of the insulator is formed, and a ground electrode is bonded to the bottom surface of the groove portion. Therefore, when the ground electrode is bent, the radius of curvature of the bent portion can be made relatively large. As a result, it is possible to prevent the stress accompanying the vibration of the engine from concentrating on the bent portion of the ground electrode, and to make the bending stress generated in the ground electrode accompanying the bending process relatively small. it can. Further, since the distance between the bent portion of the ground electrode and the joint portion of the metal shell and the ground electrode can be secured relatively large, it is possible to suppress the bending stress accompanying the bending process from being applied to the joint portion. . Accordingly, it is possible to more reliably prevent the ground electrode from falling off the metal shell and the deterioration of the breakage resistance of the ground electrode.

  Note that, from the viewpoint of more reliably preventing the corrosion of the insulator, it is preferable to dispose the tip of the insulator at a position where the tip of the cylindrical portion is retracted by about 0.5 mm to the base end side in the axial direction.

  Configuration 2. The spark plug for an internal combustion engine according to this configuration is characterized in that, in the above configuration 1, the tip of the center electrode protrudes further toward the tip in the axial direction than the tip of the cylindrical portion of the metal shell.

  As described above, in order to prevent corrosion of the insulator, it is preferable to dispose the insulator at a position retracted to the proximal end side in the axial direction from the cylindrical portion. However, in this case, the tip of the center electrode can be disposed at a position where the tip of the cylindrical portion is retracted. Here, if the tip of the center electrode is placed at a position where the tip of the cylindrical part is retracted from the tip of the cylindrical part, the spread of flame nuclei generated in the spark discharge gap is hindered by the cylindrical part, leading to a decrease in ignitability. There is a risk of it.

  In this regard, according to the configuration 2, the tip of the center electrode is formed so as to protrude toward the tip in the axial direction from the tip of the cylindrical portion. Therefore, it is possible to more reliably suppress the situation such as the spread of the flame kernel being hindered by the cylindrical portion, and it is possible to improve the ignitability.

  Configuration 3. The spark plug for an internal combustion engine according to the present configuration is characterized in that, in the above configuration 1 or 2, the tip of the center electrode protrudes 1.2 mm or more from the tip of the cylindrical portion of the metal shell toward the tip in the axial direction. Features.

  According to Configuration 3, the tip of the center electrode is formed so as to protrude 1.2 mm or more toward the tip in the axial direction from the tip of the cylindrical portion, so that the ignitability can be further improved.

Configuration 4. The spark plug for an internal combustion engine of this configuration is any one of the above configurations 1 to 3, wherein the center electrode has a cylindrical tip at a tip portion thereof,
The length of the chip along the axial direction is 0.2 mm or more and 1.5 mm or less, and
The protrusion length of the tip of the chip from the tip of the insulator along the axial direction is set to 3.0 mm or less.

  The “chip” is composed of a member that is superior in spark wear resistance than the base material to be joined, and is composed of, for example, a known noble metal material (Ir alloy, Pt alloy, etc.). Can do.

  According to the above configuration 4, since the center electrode has the tip at the tip thereof, it is possible to improve the spark wear resistance.

  On the other hand, when the center electrode has a tip at the tip, the center electrode tends to protrude from the insulator. Here, if the center electrode is disposed so as to protrude from the insulator, the center electrode and the chip become higher in temperature, and as a result, there is a possibility that the effect of improving the spark wear resistance may not be sufficiently achieved.

  In this regard, according to the configuration 4, the length of the chip along the axial direction is set to 0.5 mm or more and less than 1.5 mm, and along the axial direction of the chip with respect to the tip of the insulator. The protruding length is 3 mm or less. Thereby, extreme high temperature of a chip | tip and a center electrode can be suppressed, and the improvement of a spark erosion consumption can be aimed at more reliably.

Configuration 5. The spark plug for an internal combustion engine of this configuration is any one of the above configurations 1 to 4, wherein the ground electrode is joined to the bottom surface of the groove portion by resistance welding,
The width of the gap between the side wall of the groove and the ground electrode is set to 1.0 mm or more and 1.5 mm or less.

  The lower limit of the gap width is the smallest of the plurality of gap distances measured, and the upper limit is the largest of the gap distances measured. It is.

  In joining the ground electrode to the metal shell, it is generally performed to join the two by resistance welding as described above. Then, when both are joined by resistance welding, a melted portion (so-called welding sag) is formed on the outer periphery of the joined portion by melting the metal material constituting the ground electrode and the metal material constituting the metal shell. The Here, in the case of adopting the above configuration 1 or the like, the welding sag contacts the side wall of the groove portion, and there is a risk that a sufficient current does not flow between the base end portion of the ground electrode and the bottom surface of the groove portion. There is. That is, sufficient melting energy is not supplied between the base end portion of the ground electrode and the bottom surface of the groove, and the bonding strength of the ground electrode to the metal shell may be reduced.

  In this regard, according to the above-described configuration 5, since the gap width between the side wall of the groove and the ground electrode is relatively large, 1.0 mm or more, the welding sag contacts the side wall of the groove. Can be prevented more reliably. As a result, sufficient melting energy can be supplied between the base end portion of the ground electrode and the bottom surface of the groove portion, and sufficient bonding strength can be ensured.

  On the other hand, if the width of the gap between the side wall of the groove and the ground electrode is made relatively large, it becomes easy for fuel to pass through the gap, and as a result, the fuel tends to adhere to the insulator. Is concerned. In this regard, according to the present configuration 5, the width of the gap is set to 1.5 mm or less, so that it is possible to suppress the fuel from passing through the gap as much as possible. As a result, it is possible to more reliably prevent the fuel from adhering to the insulator.

  That is, according to the present configuration 5, the effect of further improving the bonding strength of the ground electrode and more reliably preventing the corrosion of the insulator can be achieved at once.

  The gap width of 1.5 mm or less means that the fuel that has passed through the gap is likely to adhere to the insulator, that is, the insulator is visible from the outer periphery through the gap. Especially significant.

  Configuration 6. The spark plug for an internal combustion engine according to the present configuration is configured such that, in any one of the configurations 1 to 5, the side surface located on the proximal end side in the axial direction among the distal end portion of the ground electrode and the bottom surface of the groove portion. The distance along the axial direction is 4 mm or more.

  According to the configuration 6, the axial direction between the side surface (for example, the surface facing the distal end portion of the center electrode) located on the proximal end side in the axial direction among the distal end portion of the ground electrode and the bottom surface of the groove portion. The distance along is set to 4 mm or more. Thereby, since the ground electrode can be bent more gently, it is possible to more reliably prevent stress associated with engine vibration or the like from being concentrated on the bent portion of the ground electrode. As a result, the breakage resistance of the ground electrode can be further improved.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially broken front view showing a spark plug (hereinafter referred to as “spark plug”) 1 for an internal combustion engine. In FIG. 1, the direction of the axis CL <b> 1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

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

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes outward in the radial direction on the side, and a middle body portion 12 that has a smaller diameter on the tip side than the large-diameter portion 11 are provided. Further, the insulator 2 has a leg length portion 13 that is tapered toward the tip end side in the direction of the axis CL <b> 1 on the tip end side with respect to the middle body portion 12. The middle body portion 12 and the leg long portion 13 are accommodated inside the metal shell 3. A tapered step portion 14 is formed at the connecting portion between the leg length portion 13 and the middle trunk portion 12, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  Further, the insulator 2 is formed with a shaft hole 4 penetrating 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 has a rod-like shape (cylindrical shape) as a whole, and its tip end surface is formed flat and protrudes from the tip of the insulator 2. The center electrode 5 includes an inner layer 5A made of copper or a copper alloy and an outer layer 5B made of a Ni alloy containing nickel (Ni) as a main component. Further, a cylindrical tip 31 made of a noble metal alloy (for example, iridium alloy) is provided at the tip of the center electrode 5. More specifically, the tip 31 is provided by forming a melting portion 41 on the outer periphery of the contact surface between the outer layer 5A and the tip 31 by laser welding or the like.

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

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

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

  Further, the metal shell 3 includes a cylindrical cylindrical portion 42 in which the thread is not formed on the outer peripheral surface in a region along the direction of the axis CL1 between the screw portion 15 and at least the tip of the insulator 2. ing. In the present embodiment, the cylindrical portion 42 is formed so as to extend from the distal end of the screw portion 15 toward the distal end side in the direction of the axis CL1 and have an outer diameter that is substantially constant. The cylindrical portion 42 is disposed in a state of protruding from the inner wall of the combustion chamber when the spark plug 1 (screw portion 15) is assembled to the mounting hole (not shown) of the head of the internal combustion engine.

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

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

  In addition, a ground electrode 27 made of Ni alloy or the like is joined to the tip of the metal shell 3 (this will be described in detail later). The ground electrode 27 has a two-layer structure including an outer layer 27A and an inner layer 27B. More specifically, the outer layer 27A is made of a Ni alloy [for example, Inconel 600 and Inconel 601 (both are registered trademarks)]. On the other hand, the inner layer 27B is made of a copper alloy or pure copper, which is a better heat conductive metal than the Ni alloy. Further, the ground electrode 27 is configured such that a substantially central portion of the ground electrode 27 is bent back, and a side surface 27f on the center electrode 5 side of the ground electrode 27 is opposed to a front end surface of the center electrode 5 (chip 31). Has been. A spark discharge gap 33 is formed between the front end surface of the center electrode 5 and the side surface 27f of the ground electrode 27 so as to perform a spark discharge substantially along the axis CL1.

  Furthermore, in this embodiment, as shown in FIGS. 2, 3, and 4, the distal end 2a of the insulator 2 is closer to the proximal end side in the axis CL1 direction than the distal end 3a of the metal shell 3 (cylindrical portion 42). It is disposed in a state of being retracted by a predetermined distance (for example, 0.5 mm).

  The cylindrical portion 42 communicates with the inside and outside of the cylindrical portion 42, and includes a bottom surface 52 and two groove portions 53, 54 formed continuously with the bottom surface 52 and the front end surface of the metal shell 3, respectively. A groove 51 having a concave shape in side view is formed. Here, the bottom surface 52 of the groove 51 is directed to the distal end side in the direction of the axis CL <b> 1, and is located on the proximal end side relative to the distal end 2 a of the insulator 2. The base end portion of the ground electrode 27 is joined to the bottom surface 52 of the groove portion 51 by resistance welding. In addition, the metal material composing the metal shell 3 and the metal material composing the ground electrode 27 (outer layer 27A) are melted on the outer periphery of the joint portion between the ground electrode 27 and the bottom surface 52 of the groove 51 due to resistance welding. A welding sag D (not shown in FIGS. 1 and 2, etc.) is formed. The width W1 of the groove 51 is formed to be larger than the width W2 of the ground electrode 27 by 2 mm or more and 3 mm or less.

  In addition, the widths G1 and G2 of the gaps formed between the side walls 53 and 54 of the groove 51 and the side surfaces 27s1 and 27s2 of the ground electrode 27 are 1.0 mm to 1.5 mm, respectively.

  In addition, the protrusion length LA of the center electrode 5 (chip 31) from the tip 31a of the metal shell 3 (cylindrical portion 42) toward the tip side in the direction of the axis CL1 (the protrusion length of the metal fitting) is 1.2 mm or more. It is said that.

  At the same time, the length of the chip 31 along the axis CL1 (the distance between the tip 31a of the chip 31 and the melting portion 41 along the axis CL1 and hereinafter referred to as “chip length”) LB is 0. .2 mm or more and 1.5 mm or less. Further, the protrusion length (opposite insulator protrusion length) LC of the tip 31 with respect to the tip 2a of the insulator 2 along the axis CL1 is set to 3.0 mm or less.

  In addition, the distance (inner electrode inner circumferential height) LD between the side surface 27f of the ground electrode 27 and the bottom surface 52 in the direction of the axis CL1 is 4 mm or more.

  Next, the manufacturing method of the spark plug 1 comprised as mentioned above is demonstrated. First, the metal shell 3 is processed in advance. That is, a cylindrical metal material (for example, an iron-based material such as S17C or S25C or a stainless steel material) is formed by forming a through-hole by cold forging to produce a rough shape. Then, the metal shell intermediate body is obtained by adjusting the outer shape by cutting. Then, the threaded portion 15 is formed by rolling the predetermined portion of the metal shell intermediate body, and the cutting process is performed on the tip portion (the portion corresponding to the cylindrical portion 42) of the metal shell intermediate body. By applying, the groove part 51 is formed. Thereby, the metal shell 3 including the cylindrical portion 42, the groove portion 51, and the like is obtained. In forming the groove 51, the width W1 of the groove 51 is formed to be larger than the width W2 of the ground electrode 27 by 2 mm or more and 3 mm or less.

  Subsequently, the ground electrode 27 having a two-layer structure made of a Ni alloy and a copper alloy is resistance-welded to the bottom surface 52 of the groove 51 of the metal shell 3. More specifically, after positioning so that the center of the bottom surface 52 and the center of the base end surface of the ground electrode 27 substantially coincide with each other, the base end of the ground electrode 27 is moved with the pressing force along the axis CL1. The ground electrode 27 is resistance-welded by passing a current between the two while pressing against the bottom surface 52. As a result, the widths G1 and G2 of the gaps between the side walls 53 and 54 of the groove 51 and the side surfaces 27s1 and 27s2 of the ground electrode 27 are 1.0 mm or more and 1.5 mm or less, respectively. In the welding, the welding sag D is generated, but the inner sag protruding to the inner peripheral side and the outer sag protruding to the outer peripheral side of the welding sag D are subjected to shearing or cutting. Removed. Next, the metal shell 3 to which the ground electrode 27 is welded is subjected to zinc plating or nickel plating. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

  On the other hand, the insulator 2 is formed separately from the metal shell 3. For example, by using a raw material powder mainly composed of alumina and containing a binder or the like, a green granulated material for molding is prepared, and rubber press molding is used to obtain a cylindrical molded body. The obtained molded body is ground and shaped. Then, the shaped one is put into a firing furnace and fired, whereby the insulator 2 is obtained.

  Separately from the metal shell 3 and the insulator 2, the center electrode 5 is manufactured. That is, the Ni alloy is forged, and an inner layer 5A made of a copper alloy is provided at the center of the Ni alloy to improve heat dissipation. Next, the tip 31 is provided on the tip of the center electrode 5 by laser welding. More specifically, after the front end surface of the outer layer 5B and the base end surface of the columnar chip 31 are overlapped, a laser beam is irradiated to the outer periphery of the contact surface of both to form the melted portion 41. Thus, the tip 31 is provided at the tip of the center electrode 5.

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

  Thereafter, the insulator 2 provided with the center electrode 5 and the terminal electrode 6 and the metal shell 3 provided with the ground electrode 27 are assembled as described above. More specifically, it is fixed by caulking the opening on the rear end side of the metal shell 3 formed relatively thin inward in the radial direction, that is, by forming the caulking portion 20. Finally, a process is performed in which the ground electrode 27 is bent toward the center electrode 5 and the size of the spark discharge gap 33 between the center electrode 5 (chip 31) and the ground electrode 27 is adjusted. A plug 1 is obtained.

  As described above in detail, according to the present embodiment, the front end portion of the metal shell 3 is formed with the cylindrical portion 42 extending toward the front end side in the direction of the axis CL1, and the front end 2a of the insulator 2 is It is located closer to the base end side in the direction of the axis CL1 than the tip 3a of the cylindrical portion 42. That is, the insulator 2 is provided in a state of being retracted into the cylindrical portion 42. For this reason, the adhesion of fuel to the insulator 2 can be prevented more reliably. As a result, it is possible to more reliably prevent deterioration of the stain resistance and corrosion of the insulator 2.

  Further, the cylindrical portion 42 is provided with a groove portion 51 having a bottom surface 52 located on the proximal end side in the axis CL1 direction with respect to the distal end 2a of the insulator 2, and the ground electrode 27 is bonded to the bottom surface 52. Has been. Therefore, when the ground electrode 27 is bent, the radius of curvature of the bent portion can be made relatively large. As a result, it is possible to prevent stress due to engine vibration or the like from being concentrated on the bent portion of the ground electrode 27, and to make the bending stress generated in the ground electrode 27 accompanying the bending process relatively small. be able to. Further, since a relatively large distance can be ensured between the bent portion of the ground electrode 27 and the joint portion of the metal shell 3 and the ground electrode 27, bending stress accompanying the bending process is applied to the joint portion. Can be suppressed. As a result, it is possible to more reliably prevent the ground electrode 27 from falling off the metal shell 3 and the breakage resistance of the ground electrode 27 from being lowered.

  In addition, since the protrusion length LA of the metal fitting along the direction of the axis CL1 at the tip of the center electrode 5 from the tip 3a of the cylindrical portion 42 is 1.2 mm or more, the ignitability can be dramatically improved. it can.

  Furthermore, in the present embodiment, the center electrode 5 has the tip 31 at the tip thereof, and the length LB of the tip 31 along the direction of the axis CL1 is 0.5 mm or more and less than 1.5 mm, The protrusion length LC to the insulator along the direction of the axis CL1 of the chip 31 with respect to the tip 2a of the insulator 2 is 3 mm or less. Thereby, extreme high temperature of the chip 31 and the center electrode 5 can be suppressed, and improvement of the spark wear resistance can be achieved more reliably.

  In addition, since the gap widths G1 and G2 between the side walls 53 and 54 of the groove 51 and the ground electrode 27 are relatively large as 1.0 mm or more, the welding sag D is the side walls 53 and 54 of the groove 51. It can prevent more reliably that it contacts. As a result, sufficient melting energy can be supplied between the base end portion of the ground electrode 27 and the bottom surface 52 of the groove portion 51, and the bonding strength of the ground electrode 27 can be further improved.

  Moreover, since the widths G1 and G2 of the gap are 1.5 mm or less, it is possible to suppress the fuel from passing through the gap as much as possible. As a result, it is possible to more reliably prevent fuel from adhering to the insulator 2.

  At the same time, the distance (the ground electrode inner peripheral height) LD between the side surface 27f located on the base end side in the axis CL1 direction and the bottom surface 52 of the groove 51 in the axis CL1 direction of the tip portion of the ground electrode 27. Is 4 mm or more. Thereby, since the ground electrode 27 can be bent more gently, it is possible to more reliably prevent stress accompanying engine vibration and the like from being concentrated on the bent portion of the ground electrode 27. As a result, the breakage resistance of the ground electrode 27 can be further improved.

  Next, a pre-ignition resistance evaluation test was performed in order to confirm the effects achieved by the present embodiment. The outline of the pre-ignition resistance evaluation test is as follows. That is, by fixing the tip position of the insulator and changing the length along the axial direction of the cylindrical portion, the protrusion length of the insulator tip from the tip of the metal shell along the axis (insulator exposure) A plurality of spark plug samples having various lengths of 0 mm, 1.5 mm, and 3 mm were prepared. And, by assembling a predetermined number of samples among a plurality of samples having the same insulator exposure length to a predetermined engine and operating the engine under the high-speed simulated durability condition described later, A sample used for engine operation under the high-speed simulated durability condition (sample after use) and a sample not used for engine operation (unused sample) were obtained. Next, whether or not preignition occurred after each sample obtained was assembled in an engine whose ignition angle was set to a predetermined initial value and the engine was operated for 2 minutes in a fully open state (5500 rpm). If preignition does not occur, the ignition angle is advanced by 1 degree and the engine is operated again for 2 minutes in the fully open state. The ignition angle when the preignition occurs (° CA) was identified. In addition, for the samples having the same insulator exposure length, an angle (deterioration angle) obtained by subtracting the ignition angle at which the pre-ignition occurred in the sample after use from the ignition angle at which the pre-ignition occurred in the unused sample was calculated.

  The amount of heat received by the sample increases as the ignition angle is advanced, and the amount of heat received by the sample decreases as the ignition angle is delayed. Further, it can be said that the larger the amount of heat received by the sample, the higher the temperature of the sample and the more likely pre-ignition occurs. Therefore, in a sample in which an insulator that is susceptible to pre-ignition is corroded, when the sample is subjected to a heat amount that is relatively smaller than the amount of heat received when pre-ignition occurs in the unused sample (i.e. Pre-ignition occurs at an ignition angle that is relatively later than the ignition angle when the ignition occurs. In other words, when the ignition angle at which pre-ignition occurs in the sample after use and the ignition angle at which pre-ignition occurs in the unused sample are substantially equal (that is, the deterioration angle is 0 ° CA), the sample after use is In spite of being used for engine operation under simulated endurance conditions, it can be said that there was almost no corrosion of the insulator that causes pre-ignition. On the other hand, in the post-use sample, when there is a delay in the ignition angle at which pre-ignition occurred compared to the unused sample, the post-use sample was used for engine operation under high-speed simulated endurance conditions. It can be said that the insulator has been corroded, which causes pre-ignition. In short, when the deterioration angle is 0 ° CA, it can be said that the insulator is hardly corroded. On the other hand, when the deterioration angle is 1 ° CA or more, the insulator It can be said that it is a structure which is easy to produce corrosion.

  The high-speed simulated durability condition is a simulated engine operation pattern assuming that an automobile or the like travels under a high-speed condition. Specifically, while the average speed is 160 km / h and the temperature of the center electrode is within a range of 400 ° C. to 750 ° C., the sample is cooled and the engine speed is increased to 2500 rpm in a predetermined pattern. The cycle is continuously repeated for 300 hours with one cycle being changed to ˜5500 rpm. FIG. 5 is a graph showing the relationship between the insulator exposure length and the deterioration angle.

  As shown in FIG. 5, when the insulator exposure length is 1.5 mm or 3.0 mm, the post-use sample has a delay in the ignition angle where pre-ignition occurs compared to the unused sample. It was found that the insulator was easily corroded.

  On the other hand, for the sample with an insulator exposure length of 0 mm, the ignition angle at which pre-ignition occurred in the sample after use is equal to the ignition angle at which pre-ignition occurred in the unused sample, resulting in corrosion of the insulator. It became clear that it was difficult to do. This is considered to be due to the fact that the adhesion of fuel to the insulator could be more reliably prevented by arranging the insulator at a position retracted from the metal shell.

  Next, a groove portion is formed in the cylindrical portion, and samples in which the width of the gap (gap width) between the side wall of the groove portion and the side surface of the ground electrode is variously changed are prepared, and the pre-ignition resistance test described above for each sample. Went. Note that the widths of both gaps formed between the side wall of the groove and the side surface of the ground electrode were set to be equal to each other, and the insulator exposed length of each sample was set to 0 mm. Moreover, each sample was arrange | positioned so that a groove part might be located between a fuel-injection port and an insulator when it assembled | attached to the engine. FIG. 6 is a graph showing the relationship between the gap width and the deterioration angle.

  As shown in FIG. 6, for the sample having a gap width of 1.5 mm or less, the ignition angle at which pre-ignition occurred in the sample after use is equal to the ignition angle at which pre-ignition occurred in the unused sample, It was revealed that corrosion of the insulator was extremely difficult to occur. This is presumably because the gap width was made relatively small so that it was difficult for the fuel to pass through the gap, and as a result, the fuel was less likely to adhere to the insulator.

  Next, while changing the width | variety of the groove part of a cylindrical part variously, the sample of the metal shell formed by joining a ground electrode with the bottom face of the said groove part by resistance welding was produced, and the bending strength test was done about each sample. The outline of the bending strength test is as follows. That is, after fixing the metal shell, as shown in FIG. 7, the ground electrode was bent 90 ° in the axial direction, and then the ground electrode was repeatedly bent back in the direction opposite to the axial direction. And about the sample in which the fracture did not occur at the joint portion between the bottom surface of the groove and the ground electrode by the end of the third bending back of the ground electrode, it is assumed that the sample has very excellent joint strength. On the other hand, the sample in which the fracture occurred in the joint portion was evaluated as “Δ” because it had a sufficient joint strength but there was a slight decrease in the joint strength. Note that the widths SG1 and SG2 of the gaps formed between the side wall of the groove and the side surface of the ground electrode were changed by changing the width of the groove while keeping the width of the ground electrode constant. Table 1 shows the relationship between the widths SG1 and SG2 of both gaps and the evaluation in the bending strength test.

  As shown in Table 1, for the samples having gaps SG1 and SG2 of 1.0 mm or more respectively, even at the end of the third bending back of the ground electrode, no breakage occurs in the joined portion, and extremely excellent joining strength. It became clear to have. This is because the gap between the side wall of the groove and the ground electrode is made relatively large, so that welding sag generated by resistance welding can be prevented from adhering to the side wall of the groove, and as a result, the bottom of the groove and the ground are grounded. This is considered due to the fact that sufficient melting energy could be supplied between the base end portion of the electrode.

  Next, spark plug samples were prepared with various changes in the length of the projecting portion along the axial direction from the tip of the metal shell (cylindrical portion) to the tip of the center electrode (projection length of the metal fitting), and the ignition rate for each sample An evaluation test was conducted. The outline of the ignition rate evaluation test is as follows. That is, after assembling each sample to the engine, the engine was operated in an idling state (1500 rpm) to obtain a discharge waveform for 100 discharges. And based on the obtained discharge waveform, the ratio (normal ignition rate) at which normal spark discharge was generated between the center electrode tip and the ground electrode during 100 discharges was measured. FIG. 8 is a graph showing the relationship between the protrusion length of the metal fitting and the normal ignition rate. Although not shown in the figure, in a sample in which the tip of the center electrode is retracted 0.5 mm from the tip of the metal shell to the rear end side in the axial direction (that is, a sample with a metal fitting protrusion length of −0.5 mm) The normal ignition rate was about 10%.

  As shown in FIG. 8, the sample with a metal fitting protrusion length exceeding 0 mm has a normal ignition rate exceeding 50%, and the ignitability is significantly higher than that of a sample in which the tip of the center electrode is retracted from the tip of the metal shell. It became clear that it improved. This is considered to be because the expansion of the flame kernel was inhibited by the metal shell (cylindrical portion) by projecting the tip of the center electrode from the tip of the metal shell.

  In addition, the sample with a metal fitting protrusion length of 0.5 mm or more has a normal ignition rate exceeding 80%, and has an even better ignitability, and the sample with a metal fitting protrusion length of 1.2 mm or more is The normal ignition rate was 100%, and it was found that the product had very good ignitability. Therefore, from the viewpoint of further improving the ignitability, it can be said that the protrusion length of the metal fitting is preferably 0.5 mm or more, and more preferably 1.2 mm or more.

  Next, a tip made of a noble metal alloy is provided at the tip of the center electrode, the length of the protruding portion along the axial direction from the tip of the insulator to the tip of the tip (to the insulator protruding length), and the axis of the tip Samples of spark plugs having various lengths (chip lengths) along the surface were prepared and subjected to a wear resistance evaluation test. Here, in the wear resistance evaluation test, each sample was assembled to a predetermined engine, and after the engine was operated for 100 hours in a fully opened state (5500 rpm), it was formed between the chip and the ground electrode. The increase amount of the spark discharge gap (gap increase amount) was measured. FIG. 9 shows the relationship between the protrusion length against the insulator, the chip length, and the gap increase amount. In the figure, the test results when the chip length is 0.5 mm are plotted with black circles, and the test results when the chip length is 1.0 mm are plotted with black squares. The test results when the chip length was 1.5 mm were plotted with black triangles, and the test results when the chip length was 2.0 mm were plotted with cross marks.

  As shown in FIG. 9, it was revealed that the sample with the protrusion length to the insulator of 4 mm had a gap increase amount exceeding 0.2 mm and insufficient wear resistance. This is considered to be because the heat of the chip or the like is not sufficiently drawn to the insulator by causing the chip and the center electrode to protrude relatively large from the insulator. In addition, it was found that the sample with a chip length of 2 mm had a gap increase exceeding 0.2 mm regardless of the protrusion length of the insulator, and the wear resistance was insufficient. This is considered to be due to the fact that the heat of the chip is not sufficiently drawn to the insulator due to the relatively large chip length of 2 mm.

  On the other hand, the sample with the protrusion length to the insulator of 3 mm or less and the chip length of 1.5 mm or less has a gap increase of less than 0.2 mm and has very excellent wear resistance. I understood it. This is considered to be because the heat of the chip and the center electrode is sufficiently drawn through the insulator.

  If the length of the tip is too short, the melted portion will be exposed at the tip of the center electrode at a relatively early stage as the tip is consumed, leading to a reduction in wear resistance and ignitability. There is a risk that. Therefore, the chip length is preferably 0.2 mm or more.

  Next, the spark plug in which the distance (the inner peripheral height of the ground electrode) between the bottom surface of the groove portion along the axis and the side surface (surface facing the center electrode) located on the base end side of the tip portion of the ground electrode is variously changed. These samples were prepared, and a heating vibration test was performed on each sample. The outline of the heating vibration test is as follows. That is, in each sample, while the bent portion of the ground electrode was heated to 900 ° C., vibration with a frequency of 200 Hz was continuously applied, and the time (endurance time) required until the bent portion was broken was measured. And when breakage did not occur for 10 hours or more, it was evaluated as having excellent breakage resistance. FIG. 10 is a graph showing the relationship between the inner peripheral height of the ground electrode and the durability time.

  As shown in FIG. 10, although a sample having a ground electrode inner peripheral height of less than 4 mm has sufficient breakage resistance, a sample having a ground electrode inner peripheral height of 4 mm or more has a durability of 10 hours. It was revealed that the ground electrode did not break even when the thickness reached, and had a very good break strength. This is because the inner peripheral height of the ground electrode is set to 4 mm or more, so that the ground electrode can be bent more gently, and the stress accompanying the vibration of the engine is concentrated on the bent portion of the ground electrode. This is thought to be due to the fact that this could be prevented more reliably.

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

  (A) In the above embodiment, the widths G1 and G2 of the gap between the groove 51 and the ground electrode 27 are 1.0 mm or more and 1.5 mm or less, respectively, but the sizes of the widths G1 and G2 are particularly limited. Is not to be done.

  (B) In the above embodiment, the side wall 53 and the side wall 54 are formed substantially in parallel, and the width of the opening portion of the groove 51 and the width of the bottom surface 52 of the groove 51 are substantially equal. The width of the opening portion of the groove 51 may be different from the width of the bottom surface 52. Therefore, for example, as shown in FIG. 11, the width of the opening portion may be formed larger than the width of the bottom surface 52, and the width of the opening portion is smaller than the width of the bottom surface 52 as shown in FIG. 12. It is good also as forming. Here, by forming the width of the opening portion to be larger than the width of the bottom surface 52, the groove 51 can be formed more easily, and the production efficiency can be improved. On the other hand, by forming the width of the opening portion smaller than the width of the bottom surface 52, the fuel adheres to the insulator 2 through the gap between the side walls 53, 54 of the groove 51 and the ground electrode 27. This can be prevented more reliably. As a result, corrosion of the insulator 2 can be prevented more reliably.

  Note that the widths g1 and g2 of the gap between the side walls 53 and 54 corresponding to the opening portion of the groove 51 and the ground electrode 27 are from the viewpoint of preventing the fuel from adhering to the insulator 2 through the gap. , 1.5 mm or less is preferable. Further, the widths g3 and g4 of the gap between the side walls 53 and 54 and the ground electrode 27 on the bottom surface 52 side are the side walls of the welding sag D that are generated when the fuel adheres to the insulator 2 and the ground electrode 27 is joined. From the viewpoint of preventing contact with 53 and 54, it is preferable that the thickness is 1.0 mm or more and 1.5 mm or less.

  (C) In the said embodiment, although the metal fitting protrusion length LA shall be 1.2 mm or more, it is good also as a metal fitting protrusion length being less than 1.2 mm. Further, the chip length LB, the protrusion length LC to the insulator, and the inner peripheral height LD of the ground electrode are not limited to the numerical ranges in the above embodiment.

  (D) In the above embodiment, the tip 31 is provided at the tip of the center electrode 5, but the tip 31 may be omitted. In addition, a chip made of a metal material, such as a noble metal alloy, that has better wear resistance than the metal material constituting the ground electrode 27 may be provided on the surface of the ground electrode 27 facing the center electrode 5 (chip 31). . In this case, it is possible to further improve the spark wear resistance.

  (E) In the above embodiment, the ground electrode 27 has a two-layer structure including the outer layer 27A and the inner layer 27B, but the configuration of the ground electrode 27 is not limited to this. Therefore, the ground electrode 27 may be configured by omitting the inner layer 27B, for example, or may have a three-layer structure or a multilayer structure of four or more layers.

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

It is a partially broken front view which shows the structure of the spark plug of this embodiment. It is a partial expanded front view which shows the structure of the front-end | tip part of a spark plug. It is a partial expanded side view which shows the structure of the front-end | tip part of a spark plug. It is a partial enlarged plan view which shows the structure of the front-end | tip part of a spark plug. It is a graph which shows the relationship between the insulator exposure length and deterioration angle in a pre-ignition resistance test. It is a graph which shows the relationship between the gap | interval width | variety and a deterioration part angle in a pre-ignition resistance test. It is an expansion schematic diagram for demonstrating a bending strength test. It is a graph which shows the relationship between a metal fitting protrusion length and a normal ignition rate in an ignition rate evaluation test. It is a graph which shows the relationship between the protrusion length with respect to an insulator, chip | tip length, and the gap increase amount in a wear resistance test. It is a graph which shows the relationship between a ground electrode inner peripheral height and durable time in a heating vibration test. It is a partial expanded side view which shows the shape of the groove part in another embodiment. It is a partial expanded side view which shows the shape of the groove part in another embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Spark plug for internal combustion engines, 2 ... Insulator as insulator, 3 ... Main metal fitting, 4 ... Shaft hole, 5 ... Center electrode, 27 ... Ground electrode, 31 ... Tip, 42 ... Cylindrical part, 51 ... Groove part, 52 ... Bottom, 53, 54 ... Side wall, CL1 ... Axis.

Claims (6)

A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator having an axial hole extending in the axial direction and holding the central electrode by projecting the distal end of the central electrode from the distal end surface thereof in the axial direction;
While having a cylindrical shape and provided on the radially outer side of the insulator, and having a threaded portion formed with a thread on its outer peripheral surface, the space between the threaded portion and at least the tip of the insulator In a region along the axial direction, a metal shell having a cylindrical portion in which no thread is formed on the outer peripheral surface;
An internal combustion engine having a rod-like shape, having a substantially central portion bent by itself, a ground electrode whose own distal end is located on the axis side, and whose proximal end is joined to the distal end portion of the metal shell A spark plug,
The cylindrical portion of the metal shell is formed so as to be continuous with the bottom surface that faces the distal end side in the axial direction and is located on the proximal side of the distal end of the insulator, and the bottom surface and the distal surface of the metal shell. A groove portion that communicates the inside and the outside of the cylindrical portion of the metal shell,
A spark plug for an internal combustion engine, wherein a base end of the ground electrode is joined to a bottom surface of the groove.   2. The spark plug for an internal combustion engine according to claim 1, wherein a distal end of the center electrode protrudes further toward a distal end side in the axial direction than a distal end of a cylindrical portion of the metal shell.   3. The spark plug for an internal combustion engine according to claim 1, wherein the tip of the center electrode protrudes 1.2 mm or more toward the tip in the axial direction from the tip of the cylindrical portion of the metallic shell. The center electrode has a cylindrical tip at its tip,
The length of the chip along the axial direction is 0.2 mm or more and 1.5 mm or less, and
The spark for an internal combustion engine according to any one of claims 1 to 3, wherein a protruding length of the tip of the tip from the tip of the insulator along the axial direction is set to 3.0 mm or less. plug. The ground electrode is joined to the bottom surface of the groove by resistance welding,
The spark plug for an internal combustion engine according to any one of claims 1 to 4, wherein a width of a gap between the side wall of the groove and the ground electrode is set to 1.0 mm or more and 1.5 mm or less. .   The distance along the axial direction between the side surface located on the proximal end side in the axial direction of the distal end portion of the ground electrode and the bottom surface of the groove portion is set to 4 mm or more. The spark plug for an internal combustion engine according to any one of 5.

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