JP4339219B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug.

In Japanese Patent Application Laid-Open No. 2002-319469, a noble metal tip mainly composed of a noble metal is bonded to the center electrode side and the ground electrode side, and the outer diameter of the noble metal tip on the center electrode side and the ground electrode side is 0.8 mm or less and An example in which the protruding amount from the ground electrode base material is 0.3 mm or more and 1.5 mm or less is disclosed. Japanese Patent Laid-Open No. 2002-184551 has a noble metal tip mainly composed of noble metal bonded to the center electrode side and the ground electrode side, and the outer diameter of the noble metal tip on the center electrode side and the ground electrode side is 0.8 mm. Examples in which the protrusion amount from the ground electrode base material is 0.5 mm or more and 1.2 mm or less are disclosed below.
JP 2002-319469 A JP 2002-184551 A

  Among the noble metal tips disclosed in the above publication, in order to further improve the ignitability, when the outer diameter of the noble metal tip on the ground electrode side is thin and protrudes from the electrode base material, the noble metal tip on the ground electrode side Since the temperature is likely to rise, the amount of wear increases compared to the noble metal tip on the center electrode side. For this reason, compared with the durability of the noble metal tip on the center electrode side, the durability of the noble metal tip on the ground electrode side tends to be insufficient.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a spark plug capable of improving the durability of the noble metal tip on the ground electrode side while maintaining high ignitability.

The spark plug of the present invention includes a center electrode 3, an insulator 2 that covers the periphery of the center electrode 3 in a state where the tip 51 disposed on the center electrode 3 is projected, and a main body that holds the insulator 2. The discharge part 52 which is fixed to the metal fitting 1 and the metal shell 1 and forms the discharge gap 6 between the tip surface 51a of the tip part 51 of the center electrode 3 and its own tip surface 52a protrudes from the electrode base material surface 4a. In the spark plug having the ground electrode 4 arranged in such a manner, the diameter of the tip portion 51 made of the noble metal tip (51b) mainly composed of noble metal is φA (mm), and the electric furnace has an air atmosphere of 1000 ° C. The diameter of the discharge part 52 made of a noble metal tip (52b) mainly composed of noble metal having a remaining rate of 90% or more when left for 100 hours is φB (mm), and the protruding amount from the electrode base material surface 4a is C ( mm) And when
φB ≦ 0.8mm
φB / φA ≧ 1.2
0.5mm ≦ C ≦ 1.2mm
The noble metal tip (52b) of the discharge part (52) is an alloy composed mainly of platinum and rhodium which is superior in high-temperature oxidation resistance to the noble metal tip (51b) of the tip part (51). It is characterized by.

Generally, since the temperature on the ground electrode side is higher by 100 to 200 ° C. than the temperature on the center electrode side, the precious metal tip on the ground electrode side is mainly composed of platinum that is superior in high-temperature oxidation resistance than the center electrode side, and By using a noble metal material that is an alloy made of rhodium, the consumption of the noble metal tip on the ground electrode side can be reduced. Even if the ratio between the diameter of the center electrode tip and the diameter of the outer electrode tip is slightly small, the center electrode tip and the outer electrode tip are consumed in a balanced manner. For this reason, higher ignitability can be maintained.

By encapsulating material having good thermal conductivity than the electrode base metal grounding electrode, it is possible to reduce the temperature of the ground electrode. Therefore, the consumption amount of the noble metal tip on the ground electrode side can be further reduced, and the effect can be further maintained.

  Hereinafter, a spark plug which is a preferred embodiment of the present invention will be described.

The spark plug of this embodiment is shown in FIG. As shown in FIG. 1, the spark plug has a cylindrical metal shell 1, and the metal shell 1 includes a mounting screw portion 1 a for fixing to a not-shown engine block. An insulator ₂ made of alumina ceramic (Al ₂ O ₃ ) or the like is fixed inside the metal shell 1, and the center electrode 3 is fixed in the shaft hole 2 a of the insulator 2. The tip 2b of the insulator 2 is provided so as to be exposed from the metal shell 1.

  The center electrode 3 has a metal material excellent in thermal conductivity such as Cu disposed therein, and is excellent in heat resistance and corrosion resistance such as a nickel-base alloy made of Inconel 600 (trade name) so as to cover the outside. A cylindrical body made of a metal material. And the front-end | tip part 51 is provided so that it may expose from the front-end | tip part 2b of the insulator 2. FIG. Moreover, the front-end | tip part 51 is formed of the noble metal chip | tip 51b which consists of an iridium alloy formed in circular cross section.

  The center electrode 3 is formed with a small-diameter portion 3c at the tip side, and a straight portion is further formed at the tip of the small-diameter portion 3c. After placing a noble metal tip on the tip of the straight portion, the tip 51 is formed by fixing by laser welding. The straight portion has an outer diameter slightly larger than the outer diameter of the noble metal tip 51b. Laser welding is performed at eight spots at 45 ° intervals in the circumferential direction of the outer peripheral portion of the noble metal tip 51b. The noble metal tip 51b is a noble metal alloy mainly composed of iridium. For example, an alloy of 95 mass% iridium and 5 mass% platinum, an alloy of 80 mass% iridium and 20 mass% rhodium, 95 mass% iridium and 5 mass%. Various iridium materials such as alloys with% yttria can be used. In the present specification, “mainly” is defined to mean that the content rate exceeds 50%.

  A ground electrode 4 is fixed to one end of the metal shell 1 by welding. The ground electrode 4 is made of a metal material such as a nickel base alloy made of Inconel 600 (trade name). In addition, a good heat conductive material such as copper or pure nickel having a heat conductivity higher than that of the electrode base material 4b is enclosed. Further, a discharge part 52 is formed by joining a noble metal tip 52b mainly composed of a noble metal to the electrode base material surface 4a by laser welding so as to protrude from the electrode base material surface 4a, and a distal end surface 52a of the discharge part 52 is formed. A discharge gap 6 is formed by the front end surface 51 a of the front end portion 51 of the center electrode 3. In general, the width of the ground electrode 4 is about 2.2 mm to 2.8 mm. The discharge part 52 is a noble metal alloy mainly composed of platinum or iridium having a circular cross section. For example, an alloy of 80% by mass of platinum and 20% by mass of iridium, an alloy of 80% by mass of platinum and 20% by mass of rhodium, Various platinum materials such as an alloy of mass% platinum and 20 mass% nickel can be used.

  In addition, when it is necessary to maintain higher ignitability during the endurance life, it is necessary to use a noble metal alloy having a residual rate of 90% or more when left in an electric furnace at 1000 ° C. for 100 hours. Such noble metal alloys are mainly platinum-based, but even iridium-based alloys can be used as long as these conditions are satisfied. In general, the tip portion 51 on the center electrode 3 side consumes a larger amount of spark discharge than the discharge portion 52 on the ground electrode 4 side. Further, the temperature on the ground electrode 4 side is likely to be higher than that on the center electrode 3 side. Therefore, the tip portion 51 is often made of an iridium alloy having high wear resistance due to spark discharge, and the discharge portion 52 is often made of a platinum alloy that does not cause oxidation and volatilization at a high temperature. In order to satisfy the residual rate of 90% or more as defined above, the alloy is mainly composed of platinum and iridium containing platinum, and may contain nickel, and the total content of iridium and nickel is 20 masses. %, And a noble metal chip made of an alloy having nickel of 10% by mass or less, an alloy made of platinum and rhodium mainly composed of platinum, and may contain nickel in a ratio of 10% by mass or less. A noble metal chip made of an alloy or an alloy that contains at least platinum, iridium and rhodium, and the ratio of rhodium to iridium is 20% or more by mass, and nickel may be contained at a ratio of 10% by mass or less. Any one kind of noble metal tips may be used.

  In order to confirm the effect of the preferred embodiment of the present invention described above, the following experiment was conducted. First, an alloy having a composition of 80 mass% iridium-20 mass% rhodium was prepared by blending and dissolving a predetermined amount of iridium and rhodium. By subjecting this alloy to predetermined processing, a noble metal tip 51b on the side of the center electrode 3 having a diameter of 0.3 mm (= φA) and a length of 0.8 mm was obtained. Similarly, an alloy having a composition of 80% by mass of platinum-20% by mass of rhodium was prepared by blending and dissolving a predetermined amount of platinum and rhodium. By performing predetermined processing on this alloy, noble metal tips 52b on the ground electrode 4 side having various diameters and lengths were obtained.

Using these tips, the spark plug tip 51 and the discharge gap 6 were set to 0.8 mm to form opposing discharge portions 52. For the diameter B and the protruding amount C of the discharge part 52 shown in FIG. 2, test spark plugs having respective dimensions shown in FIG. And the ignitability test of each of these test spark plugs was performed under the following conditions. That is, this ignitability test was performed by the load / load lean burn method . For the test, an in-line 6-cylinder, 2-liter, DOHC engine that can change the air-fuel ratio (A / F) was used. The test conditions were set to conditions equivalent to 2000 rpm and 60 km / h running on a constant land . And when it becomes 50% or less with respect to the average value of the indicated mean effective pressure (IMEP) of 0 cycle in various air-fuel ratios, it is judged as misfire, and A / F where misfire occurs 10 times is set as an ignition limit. . The results are shown in FIG.

  From this result, it can be seen that when the diameter B of the discharge part 52 is 1.0 mm, the ignition limit A / F is significantly lower than in the case of other outer diameters B. Moreover, when the protrusion amount C is 0.5 mm or more, it can be seen that the ignition limit A / F is greatly improved as compared with the case where the protrusion amount C is less than 0.5 mm. That is, it can be seen that the ignition limit A / F is greatly improved by setting the diameter B of the discharge part 52 to 0.8 mm or less and further setting the protrusion C to 0.5 mm or more.

  Next, a high temperature oxidation resistance test was performed. The noble metal tips 51b and 52b were manufactured in the same manner as described above, but the diameter A of the noble metal tip 51b on the center electrode side was 0.5 mm. First, a high temperature oxidation resistance test was performed on a test spark plug in which the noble metal tip 52b on the ground electrode 4 side was 80% by mass platinum-20% by mass nickel.

  That is, for this test, an inline 6 cylinder, 2 liter, DOHC engine was used. The test condition was 4900 rpm, and the endurance test was performed for 250 hours with the valve fully open. In this condition, the base material temperature of the ground electrode 4 is about 1000 ° C. And about each spark plug for a test, the increase amount of the discharge gap 6 after completion | finish of a test was measured. The results are shown in FIG.

  From this result, when the ratio B / A of the diameter A of the tip portion 51 and the diameter B of the discharge portion 52 is 1.0 and 1.2, the discharge gap is larger than in the case of other B / A. It can be seen that increases. Moreover, when the protrusion amount C is larger than 1.5 mm, it turns out that the increase amount of the discharge gap 6 is increasing. That is, it can be seen that the high-temperature oxidation resistance is greatly improved by setting B / A to 1.4 or more and the protrusion amount C to 1.2 mm or less.

  Next, a high-temperature oxidation resistance test similar to that described above is performed on a test spark plug in which the noble metal tip 52b on the side of the ground electrode 4 is a platinum-based noble metal alloy, specifically, 80 mass% platinum-20 mass% rhodium. went. The results are shown in FIG.

  From this result, when the ratio B / A of the diameter A of the tip 51 and the diameter B of the discharge part 52 is 1.0, the discharge gap is greatly increased as compared with other B / A. I can see that Moreover, when the protrusion amount C is larger than 1.5 mm, it turns out that the increase amount of the discharge gap 6 is increasing. That is, it can be seen that the high-temperature oxidation resistance is greatly improved by setting B / A to be 1.2 or more and the protrusion amount C to be 1.2 mm or less.

  Furthermore, the high temperature oxidation characteristics of various precious metal alloys mainly composed of iridium and precious metal alloys mainly composed of platinum were investigated. This test is not a test using a spark plug as described above, but a residual ratio is calculated by measuring the weight of a noble metal alloy chip after being left in an electric furnace at 1000 ° C. for 100 hours. The results are shown in FIG.

  From this result, it can be seen that iridium has a high oxidation volatility, and therefore, when platinum is added in an amount of more than 20% by mass to platinum which hardly causes oxidation volatilization, the residual rate falls below 90%. However, it can be seen that oxidation volatilization can be suppressed by adding rhodium even if the iridium content is 20% by mass or more. This is thought to be due to the fact that rhodium forms an oxide film, thereby suppressing the oxidative volatilization of iridium. From this result, it can be seen that even in the case of a platinum-based noble metal alloy, the residual rate may be less than 90% depending on the type and amount of the added metal. Further, it can be seen that even in the case of iridium-based noble metal alloys, the residual ratio may exceed 90% depending on the type and amount of the added metal.

  From the above test results, the diameter of the tip portion 51 is φB, the diameter of the discharge portion 52 is φA, and the amount of protrusion from the base material surface 4a is φB ≦ 0.8 mm, φB / φA ≧ 1.4, In addition, it can be seen that ignitability and durability can be maintained for a long time by satisfying the relationship of 0.5 mm ≦ C ≦ 1.2 mm.

  In addition, when the precious metal tip 51a on the ground electrode 4 side is left in an electric furnace having an air atmosphere of 1000 ° C. for 100 hours and the remaining rate is 90% or more, for example, 80% by mass platinum-20% by mass rhodium, 75% by mass In the case of platinum-20 mass% iridium-5 mass% rhodium, 80 mass% iridium-20 mass% rhodium, etc., even if the relationship φB / φA ≧ 1.2 is satisfied, the ignitability and durability are It can be seen that it can be maintained for a long time.

It is a front view which shows one Example of the spark plug of this invention. It is a principal part enlarged view of the spark plug of this invention. It is a graph which shows a test result of ignitability. It is a graph which shows the high temperature oxidation resistance test result at the time of using an iridium alloy for the ground electrode side noble metal tip. It is a graph which shows the high temperature oxidation-proof test result at the time of using the platinum alloy whose residual rate is 90% or more for the ground electrode side noble metal tip. It is a graph which shows the result of the high temperature oxidation characteristic test in a noble metal chip simple substance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal shell 1a Mounting screw 2 Insulator 3 Center electrode 4 Ground electrode 4a Electrode base material surface 4b Electrode base material 4c Good heat conductive material 51 Tip part 51a Tip surface 51b Noble metal tip 52 Discharge part 52a Tip surface 52b Noble metal tip 6 Discharge gap A Diameter of the tip on the center electrode side B Diameter of the discharge part on the ground electrode side C Projection amount of the discharge part on the ground electrode side from the surface of the electrode base material

Claims (2)

A center electrode (3);
An insulator (2) covering the periphery of the center electrode (3) in a state in which the tip (51) disposed on the center electrode (3) is projected;
A metal shell (1) for holding the insulator (2);
Discharge fixed to the metal shell (1) and forming a discharge gap (6) between the front end surface (51a) of the front end portion (51) of the center electrode (3) and its front end surface (52a). A ground electrode (4) disposed so that the portion (52) protrudes from the electrode base material surface (4a);
In a spark plug having
The diameter of the tip (51) made of the noble metal tip (51b) mainly composed of noble metal is φA (mm),
The diameter of the discharge part (52) made of a noble metal tip (52b) mainly composed of a noble metal having a residual rate of 90% or more when left in an electric furnace at 1000 ° C. for 100 hours is φB (mm), and the electrode When the amount of protrusion from the base material surface (4a) is C (mm),
φB ≦ 0.8mm
φB / φA ≧ 1.2
0.5mm ≦ C ≦ 1.2mm
Satisfied with the relationship
The noble metal tip (52b) of the discharge part (52) is an alloy composed of platinum and rhodium mainly composed of platinum which is superior in high-temperature oxidation resistance than the noble metal tip (51b) of the tip part (51). Spark plug characterized by   The spark plug according to claim 1, wherein the ground electrode (4) is filled with a material (4c) having better thermal conductivity than the electrode base material (4b).

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