JPS62268079A - Spark plug for internal combustion engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a spark plug for internal combustion, and in particular, to a spark plug for internal combustion, in particular, it is possible to ensure that a tip is located at the tip of the base material of at least one of the center electrode and the ground electrode. Concerning fixed spark plugs.

(Summary of the Invention) In a spark plug for an internal combustion engine, the present invention provides a cavity for attaching a tip at the tip of an electrode base material of at least one of a center electrode and a ground electrode, and after inserting the tip into this cavity. Electrically attach the fixing member made of the same material as the base material! i The tip was fixed to the tip of the electrode base material by welding and joining to the tip of the base metal. In this case, since the tip is in contact with the tip of the electrode base material and the fixing member and is not in a welded joint state, the chip attachment due to repeated thermal stress during use, which occurs in welded tips in the conventional technology, may cause cracks in the part. Chips were prevented from falling off.

(Prior Art) Improving the wear resistance of spark plugs is strongly demanded by society as part of the trend of expanding the maintenance of automobile parts. In order to meet this demand, various techniques for joining and fixing chips made of materials with excellent wear resistance, mainly noble metals, have been shown so far. This conventional technology can be broadly classified into two types. The first is a technique for fixing the tip using plastic deformation, and Japanese Patent Publication No. 56-45265 shows a technique for fixing the tip to the tip of the electrode base material by drawing as illustrated in Fig. 8. No. 145929 discloses a technique in which a concave hole is provided at the tip of the material, the tip is inserted into the concave hole, the side wall of the concave hole is plastically deformed toward the tip, and the tip is fixed by caulking. . The second technique is to join the noble metal tip and the electrode base material by resistance welding or laser, as shown in Japanese Patent Publication No. 59-47436 as shown in Fig. 11 and Japanese Patent Application Laid-Open No. 59-94391 as shown in Fig. 12. ing.

(Problems to be Solved by the Invention) Each of the above-mentioned conventional techniques has its own problems. A problem with techniques using drawing is that the chips are limited to ductile materials. Regarding the caulking fixing technique, there was a problem in that the hardness of the plastically deformed part of the electrode base material light part decreased due to high temperature combustion gas, and the caulking fixing force decreased. In addition, there is a problem in that stress remains in the plastically deformed portion, particularly in the portion where the deformation is large, and as a result, corrosion tends to occur intensively due to combustion gas. Furthermore, considering the springback of the plastically deformed part, this fixing method has poor reliability and durability. On the other hand, in the bonding and fixing method by welding, thermal stress is generated on the bonding surface because the linear expansion coefficients of the chip and the electrode base material are different. Since this thermal stress follows the operating conditions of the engine and occurs repeatedly, cracks occur at the joint surface between the chip and the electrode base material, causing the chip to easily fall off, as shown in FIG. For this reason, it is necessary to provide various thermal stress relaxation means 9 and 10 as shown in Figs. There was a problem in that it was not economical in terms of cost including material costs.

Additionally, since welding is used for joining, the chip material is limited to metal.

(Means for Solving the Problems) The present invention provides a method of reliably fixing the tip to the tip of the electrode base material of the spark plug and having durability without the drawbacks of the conventional tip fixing techniques. The purpose is to obtain a spark plug for internal combustion engines.

A spark plug for an internal combustion engine according to the present invention has a center electrode and a ground ffi[i, and at least one of the N electrodes has a tip end portion of an electrode base material provided with a tip fixing hole, and a ground ffi [i]. A fixing member made of the same material as the tip of the electrode base material and welded to the tip of the electrode base material, and a fixing member disposed within the tip fixing hole and connected to the electrode lf! The electrode has a tip fixed to the electrode by both the tip of the base material and the fixing member, and the tip is simply held in contact with the tip of the electrode base material and the fixing member without being welded to them. Features.

(Function) In the spark plug having the above features of the present invention, the fixing member that fixes the tip and the tip of the electrode base material are made of the same material, so both have excellent bonding properties and no thermal stress is generated at the bonding interface. . Further, the tip is not welded to the tip of the electrode base material and the fixing member, and the tip is placed in a hole defined by the tip of the electrode base material and the fixing member welded to the tip. Since it is fixed to the electrode while simply being in contact with these, there is virtually no thermal stress generated on the chip mounting part during use, and it is no longer necessary to consider thermal stress, which was previously included due to the difference in linear expansion coefficient. do not have. Welding of the tip of the electrode base material and the fixing member can be performed by resistance welding, laser welding, diffusion welding, brazing, or the like.

(Embodiment) FIG. 1 is an enlarged sectional view of the ignition part of an embodiment of the spark plug for internal combustion of the present invention, and FIG. 2 is an overall view of this spark plug. Reference numeral 1 designates the tip of the center electrode base material, which is made of a Ni alloy (e.g. 93 wt.
%xr -2%Cr -3%Mn-2%Sl) M epidermis 1
It has b. 2 is @1t! It is the tip of the electric rod base material,
It has a tip fixing hole 2C, and the center electrode is made of the same material as the skin 1b at the tip of the material. The discharging facing part of each electrode base material tip 1.2 has a 70 to 90
wt%Pt-30~10%lr alloy tip 3a, 3
b is the chip fixing hole 1c.

It is located within 2C. 5a and 5b are fixing members welded to the tip of the electrode base material within the chip fixing holes 1G and 2C, respectively. The electrode base material tip 1.2 and the fixing members 5a, 5b cooperate to fix the tips 3a, 3b to the electrode base material tip 1, 2, respectively. The fixing member 5a is made of the same material as the skin 1b at the tip of the center electrode base material, and the fixing member 5b is made of the same material as the tip 2 of the grounding electrode ff1ffl material. The tips 3a, 3b are not welded to either the electrode base material tips 1, 2 or the fixing members 5a, 5J, but are welded to the tip fixing holes 1c, 2c and the fixing members 5a, 5b welded thereto. The chips 3a and 3b are fixed to the tip of the electrode base material by placing the T-shaped tips in the T-shaped holes defined by the T-shaped holes. That is, one of the main features of the present invention is that the tips 3a and 3b are simply in contact with the tip of the electrode base material and the fixing member, respectively.
It is one.

Next, a method of machining and assembling an embodiment of the spark plug shown in FIGS. 1 and 2 will be explained with reference to FIGS. 3a to 4d. As shown in Figure 3a, the ground electrode has holes 4a and 4b with a T-shaped cross section and a hole 4C with a truncated cone shape at the tip of the base material.
A chip fixing hole is provided, which is a through hole 4 having a shape in which the two sides meet.

Among the through holes 4, the hole 4a on the discharge part side has a smaller diameter than the center hole 4b, and the truncated conical hole 4C on the opposite side from the discharge part has a shape that widens toward the surface. Next, most of this 4a,
A chip 3b having a shape that can be inserted and placed in 4b is provided, and this chip 3b is inserted and placed in the holes 4a and 4b from the hole 4C side as shown in FIG. 3b. In this case, the distal end of the tip on the side of the discharge section is on the same plane as the surface of the distal end of the ground electrode base material. Next, a fixing member 5b in the shape of a truncated cone, which corresponds to the shape of the hole 4C and has an external dimension slightly larger than the hole 4C, is fitted into the hole 4C and pressed into the hole 4C while applying pressure and using predetermined welding conditions. By resistance welding, the fixing member 5b is substantially welded only to the ground electrode base material tip 2 forming the hole 4C (3C).
(FIG. 3D), As a result, the tip 3b is simply held in contact with the ground electrode base material tip 2 and the fixing member 5b, and is securely fixed to the tip 2. Since the ground electrode base material tip 2 and the fixing member 5b are made of the same material, they have excellent bonding properties to each other, and no thermal stress is generated at the bonding interface 6b due to a difference in linear expansion coefficient.

The assembly and processing method for the center electrode is shown in Figures 4a-4d. First, on the epidermis 1b at the tip of the center electrode base material,
A hole for fixing a knob is provided, which is comprised of a truncated conical major portion 7b located on the surface side and a cylindrical major portion 7a located inside. Most of the truncated cone shape has a larger diameter on the surface side. Next, a T-shaped tip 3a having an insertable flange portion and a cylindrical portion extending vertically from the flange portion is provided in the major portion 7a, and the tip 3a is provided in the major portion 7a as shown in FIG. 4b. Insert and place the flange part. In this case, the tip end of the tip on the discharge section side is made to protrude outward from the surface of the tip end of the center electrode base material. Next, a fixing member 5a having a truncated conical shape corresponding to the shape of the major portion 7b and having slightly larger dimensions is fitted into the major portion;
By applying pressure to the fixing member 5a and pushing it into the main part 7b, resistance welding is performed using predetermined welding conditions, so that the center electrode of the fixing member 5a is substantially welded only to the skin 1b of the front end of the material. It is joined (Fig. 40, Fig. 4d). Thereby, the tip 3a is reliably fixed to the tip 1 while being held in substantially contact with the center electrode base material tip 1 and the fixing member 5a. Since the skin at the tip of the center cylinder ff1fn material and the fixing member are made of the same material, they have excellent bonding properties to each other, and the thermal stress that conventionally occurs due to the difference in linear expansion coefficient is generated at the bonding interface 6a. do not.

When performing resistance welding, each of the fixing members 5a and 5b is welded only to the tip of the electrode base material by applying pressure to the fixing members 5a and 5b and pushing the fixing members into the tip fixing hole while welding under predetermined welding conditions.・It is joined, but is not substantially welded to the chips 3a and 3b. Furthermore, even if the welding of the tips 3a and 3b occurs partially due to variations in welding conditions, repeated thermal stress during subsequent use will cause cracks to occur at the interface between the tips and the electrode base material and fixing member, resulting in the chips being welded together. is in mere contact with the tip of the electrode base material and the fixing member. In the case of resistance welding, an insulating coating may be applied to the chip surface to increase the reliability of the welded joint. Since the applied voltage during resistance welding is as low as 2 to 6 V, this film can be made very thin and does not affect workability during spark plug manufacturing. This coating is unnecessary when the fixing member and the tip of the electrode base material are joined by brazing or laser welding.

Other embodiments of the invention are shown in FIGS. 5, 6 and 7. In these embodiments, the shape of the chip fixing hole provided at the tip of the electrode base material is different from that of the first embodiment. 5 and 6 show the tip of the ground electrode base material, and FIG. 7 shows the tip of the center electrode base material.

It goes without saying that the present invention may be applied to both the center electrode and the ground electrode, or either of these electrodes may be applied to one of the electrodes.

(Effects of the Invention) In the spark plug for an internal combustion engine of the present invention, the tip is fixed to the tip of the electrode base material by joining the fixing member made of the same material as the tip of the electrode base material to the tip of the electrode base material. The tip itself is not welded to either the fixing member or the tip of the electrode base material, but is simply held in contact with them. Therefore, the thermal stress that occurs in the welded joint between the tip and the tip of the electrode base material in the case of conventional tip-joint spark plugs does not occur in this invention, so cracking due to generation of thermal stress does not occur. It is now possible to prevent chips from falling off. In addition, the present invention can prevent the problem of conventional tip-caulking type spark plugs in which the hardness of the plastically deformed portion decreases due to heat during use and the caulking mechanism that fixes the tip decreases. Furthermore, since only the tip of the electrode base material is connected to the fixing member, there is an advantage that the tip can be selected regardless of the material of the electrode base material. For example, as the chip material, metals such as cermets, transition metal carbides, borides, and nitrides can be selected.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the main parts of an embodiment of the spark plug for an internal combustion engine of the present invention, FIG. 2 is a plan view showing the entire spark plug of FIG. 1, and FIG. 3a is a , Fig. 3b, Fig. 3C, Fig. 3d are grounded Ti.
Figures 4a, 4b, 4c, and 4d are cross-sectional views sequentially showing the steps for assembling the pole; 6 and 7 are cross-sectional views showing other embodiments of the spark plug of the present invention, and FIG. 8 shows tip fixation by drawing as shown in the prior art Japanese Patent Publication No. 56-45265. Fig. 9 is a diagram showing the tip caulking fixing method shown in the prior art, Utility Model Application Publication No. 50-145929, and Fig. 10 shows the tips of the electrode base material having different linear expansion coefficients. 11 and 12 are diagrams showing conventional means for solving the problem shown in FIG. 10, and FIG. 59-4
An example is shown in which the diffusion layer 9 shown in No. 7436 is provided,
FIG. 12 is a diagram showing an example in which the thermal stress relaxation layer 10 shown in Japanese Patent Publication No. 59-94391 is provided. 1 is the tip of the center electrode base material, 2 is the tip of the ground electrode base material, 3
A and 3b are chips, and 5a and 5b are fixing members.

Claims (1)

[Claims] In a spark plug for an internal combustion engine that includes a center electrode and a ground electrode, at least one of the electrodes has a tip end portion of an electrode base material provided with a tip fixing hole; A fixing member made of the same material as the tip of the electrode base material and welded to the tip of the electrode base material within the tip fixing hole; and a tip fixed to the electrode, wherein the tip is not substantially welded to the tip of the electrode base material and the fixing member, but is held in contact with them. Spark plug.