JP4295064B2 - Spark plug - Google Patents

Description

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

Many spark plugs used for ignition of internal combustion engines such as automobile engines have a type in which a noble metal tip mainly composed of Pt or Ir is welded to the other end of the ground electrode in order to improve durability. Proposed. On the other hand, when the spark plug is assembled to an engine head or the like, since the ground electrode protrudes into the combustion chamber of the internal combustion engine, the ground electrode tends to become hot. In view of this, a number of ground electrodes using a composite material in which an alloy mainly composed of Cu and Ag is arranged inside an electrode base material made of Ni alloy have been proposed.
JP-A-5-101869 Japanese Patent Laid-Open No. 4-36681

  By the way, in the spark plug of Patent Document 1, when a noble metal tip mainly composed of Ir or Ir alloy is welded to the ground electrode, the distance between the noble metal tip and the core is set to 0 to 0.5 mm. The heat of the tip is transmitted to the metal shell through the core to keep the noble metal tip at a low temperature. In the spark plug of Patent Document 2, when a noble metal tip mainly composed of Pt or Pt alloy is welded to the ground electrode, the distance between the weld surface of the noble metal tip and the core is 0 to 2 mm. The precious metal tip is prevented from peeling off due to the high temperature of the ground electrode.

  However, recently, there is an increasing demand for higher performance of engines, and spark plugs are also required to have further improved ignitability. In order to improve the ignitability, it is effective to increase the protrusion amount of the noble metal tip attached to the ground electrode from the ground electrode body, and a noble metal tip having a large protrusion is joined to the other end of the ground electrode. Many structures are adopted.

  In the case of such a spark plug in which the protruding amount of the noble metal tip of the ground electrode is large, the heat received at the tip of the tip is difficult to escape to the ground electrode, the noble metal tip is further heated, and the wear resistance of the noble metal tip is reduced. There was a risk of doing so.

  An object of the present invention is to provide a spark plug in which a noble metal tip with a large protruding amount is joined to a ground electrode, the temperature of the noble metal tip can be reduced, and the wear resistance of the noble metal tip can be suppressed from being lowered. There is to do.

The spark plug of the present invention comprises an insulator having an axial hole in the axial direction, a center electrode disposed on the distal end side of the axial hole of the insulator, a metal shell surrounding the periphery of the insulator, and one end thereof A spark plug having a noble metal tip bonded to a metal shell and having a noble metal tip facing the center electrode at the other end and forming a spark discharge gap with the center electrode. A base material, a metal core disposed inside the electrode base material and having higher thermal conductivity than the electrode base material, and a core core having a lower coefficient of thermal expansion than the metal core inside the metal core. When the diameter of the noble metal tip is a and the protruding length of the noble metal tip from the central electrode side inner peripheral surface of the ground electrode is b,
b> a / 2
0.4 (mm) ≦ b
Further, the noble metal tip and the metal core are in contact with each other , and the noble metal tip and the middle core are not in contact with each other.

When the noble metal tip bonded to the ground electrode has a diameter of the noble metal tip as a and the protruding length of the noble metal tip from the center electrode side inner peripheral surface of the noble metal tip as b,
b is larger than a / 2 and 0.4 (mm) or more. Thus, the ignitability is improved by increasing the amount of protrusion of the noble metal tip from the inner peripheral surface of the center electrode. In addition, when b is a / 2 or less, the effect of protrusion is reduced, and the effect of improving the ignitability cannot be sufficiently obtained. Moreover, even if b is smaller than 0.4 (mm), the effect of protrusion is reduced and the effect of ignitability cannot be sufficiently obtained.

By the way, in the spark plug in which the noble metal tip having a large protrusion is arranged at the other end of the ground electrode, the noble metal tip is heated and the noble metal tip is consumed. Therefore, as in the present invention, a metal core having higher thermal conductivity than the electrode base material is provided in the ground electrode, and the noble metal tip and the metal core are brought into contact with each other. Thereby, the high temperature of the noble metal tip can be suppressed, and consumption of the noble metal tip can be suppressed. In addition, as a metal core, each single-piece | unit, such as Cu, Fe, Ag, Au, etc., the alloy which has this as a main component, etc. are mentioned.
By the way, the ground electrode in which the metal core having higher thermal conductivity than the electrode base material is arranged inside the electrode base material of the ground electrode is bent toward the center electrode side so as to face the tip portion of the center electrode. In this case, due to the difference in thermal expansion coefficient between the metal core and the electrode base material, a phenomenon (hereinafter also referred to as rising) occurs in which the ground electrode moves in a direction away from the center electrode due to a thermal load. When rising occurs in this manner, the discharge gap is widened, and it becomes difficult for spark discharge to occur, causing misfire.
Therefore, in the spark plug of the present invention, the ground electrode has a middle core having a lower coefficient of thermal expansion than the metal core inside the metal core. Thus, by arranging the core having a low coefficient of thermal expansion inside the metal core, it is possible to suppress the occurrence of rising. In addition, examples of the core include Ni and Fe alone, and alloys containing these as main components. The core and the noble metal tip are not in contact with each other. Thereby, when the metal core and the noble metal tip are sufficiently in contact with each other, the temperature rise of the noble metal tip can be suppressed, and consumption of the noble metal tip can be suppressed.

  Furthermore, in the spark plug of the present invention, the diameter a of the noble metal tip and the protruding length b of the noble metal tip may be 0.3 (mm) ≦ a and b ≦ 1.5 (mm), respectively. . Thus, by setting the diameter a of the noble metal tip to 0.3 (mm) or more, the ignitability is improved and the durability of the noble metal tip can be obtained. If the diameter a of the noble metal tip is less than 0.3 (mm), the diameter of the noble metal tip is too small and the durability of the noble metal tip is reduced. On the other hand, when the protrusion length b is 1.5 (mm) or less, the ignitability is improved and the durability of the noble metal tip can be obtained. In addition, when protrusion length b exceeds 1.5 (mm), heat drawing is not enough and durability of a noble metal tip falls.

  Furthermore, in the spark plug of the present invention, it is preferable that the maximum contact distance c between the metal core and the noble metal tip in a cross section including the axis and cut in the longitudinal direction of the ground electrode is c ≦ 1.1 (mm). . When the maximum contact distance is greater than 1.1 mm, when the noble metal tip is welded to the ground electrode, heat is drawn to the metal shell side by the metal core, and the weldability is deteriorated. That is, by setting the thickness to 1.1 mm or less, the weldability of the noble metal tip to the ground electrode can be maintained. The longitudinal direction of the ground electrode refers to a direction from the joint surface of the metal shell of the ground electrode toward the tip surface of the ground electrode. Furthermore, the maximum contact distance c is preferably 0.5 mm or more. When the maximum contact distance c is 0.5 mm or more, the heat of the noble metal tip can be effectively transmitted to the core, the high temperature of the noble metal tip can be suppressed, and the consumption of the noble metal tip can be further suppressed.

  In the spark plug of the present invention, the noble metal tip can be composed mainly of Ir, W, or Pt. These metal elements can improve the wear resistance of the ignition part even in an environment where the temperature of the center electrode is likely to rise.

  Hereinafter, some embodiments of the present invention will be described with reference to the drawings. A spark plug 100 with a resistor as an example of the present invention shown in FIGS. 1 and 2 includes a cylindrical metal shell 1, an insulator 2 fitted into the metal shell 1 so that a tip portion protrudes, and an ignition part 31. The center electrode 3 provided inside the insulator 2 in a projecting state, the ground electrode 4 disposed so as to face the side surface of the ignition portion 31 (center electrode 3), and the like are provided. The ground electrode 4 is bent so that the front end face thereof is substantially parallel to the side surface of the ignition part 31, and an ignition part 41 is formed at a position facing the ignition part 31. A spark gap g is formed between the ignition part 31 and the ignition part 41.

  The metal shell 1 is made of carbon steel or the like, and as shown in FIG. 1, a threaded portion 12 for attaching the spark plug 100 to an engine block (not shown) is formed on the outer peripheral surface thereof. The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, and has a through hole 6 for fitting the center electrode 3 along its own axial direction. The terminal fitting 8 is inserted and fixed on one end side of the through-hole 6, and the center electrode 3 is inserted and fixed on the other end side. A resistor 15 is disposed between the terminal fitting 8 and the center electrode 3 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 13 via conductive glass seal layers 16 and 17, respectively.

  The center electrode 3 has an electrode base material 3a formed on the surface and a metal core 3b inserted therein. The electrode base material 3a of the center electrode 3 is a Ni alloy such as INCONEL600 (registered trademark of INCO). On the other hand, the metal core 3b is made of Cu or Ag. The metal core 3b has a higher thermal conductivity than the electrode base material. The electrode base material 3a of the center electrode 3 is reduced in diameter at the front end side and has a flat front end surface, and a disc-shaped noble metal tip constituting the ignition part 31 is overlaid on the electrode base material 3a. The ignition part 31 is formed by forming the welded part W along the outer edge part by laser welding, electron beam welding, resistance welding or the like and fixing it. The ignition part 31 is made of a metal mainly composed of Pt, Ir and W. Specific examples include Pt alloys such as Pt—Ir and Pr—Rh, and Ir alloys such as Ir-5 wt% Pt and Ir-20Rh. As used herein, the term “ignition part” refers to a part of the joined chip that is not affected by the composition variation due to welding (for example, a part that is alloyed with the material of the ground electrode or the center electrode by welding). The remaining part).

  One end 42 of the ground electrode 4 is fixed and integrated with the front end surface of the metal shell 1 by welding or the like. On the other hand, the other end portion 43 of the ground electrode faces the front end surface of the center electrode. The ground electrode 4 has an electrode base material 4a formed on the surface thereof, a metal core 4b inserted therein, and a center core 4c inserted therein. (See FIG. 3) The electrode base material 4a of the ground electrode 4 is INCONEL 600, the metal core 4b is Cu, and the center core 4c is Ni. Furthermore, the thermal conductivity of the electrode base material 4a is 13 W / m · K, the thermal conductivity of the metal core 4b is 428 W / m · K, and this metal core 4b is more thermally conductive than the electrode base material 4a. Is expensive. Further, the thermal conductivity 4c of the middle core is 121 W / m · K, and the middle core 4c has a lower thermal conductivity than the metal core 4b. The other end 43 of the ground electrode 4 is provided with an ignition part 41. Then, the ignition part 41 inserts a circular-shaped noble metal tip into a recess provided at a predetermined position of the ground electrode 4, and further performs laser welding, electron beam welding, resistance along the boundary between the ground electrode 4 and the noble metal tip. The ignition part 41 is formed by forming the welded part W by welding or the like and fixing it. The ignition part 41 is made of a metal mainly composed of Pt, Ir and W. Specific examples include Pt alloys such as Pt—Ir and Pr—Rh, and Ir alloys such as Ir-5 wt% Pt and Ir-20Rh.

  The ignition part 41 has a diameter a of φ0.6 mm and a protrusion amount b from the ground electrode body of 0.8 mm. Thus, the ignitability is improved when the protruding length of the noble metal tip from the inner peripheral surface on the center electrode side satisfies b> a / 2 and 0.4 (mm) ≦ b. On the other hand, the durability of the noble metal tip is secured by setting the diameter of the noble metal tip to 0.3 mm ≦ a and b ≦ 1.5 mm.

  Furthermore, the metal core and the noble metal tip are in contact. As described above, the spark plug in which the noble metal tip having a large protrusion is arranged at the other end of the ground electrode, the noble metal tip is heated and the consumption of the noble metal tip is increased. Further, the high temperature of the noble metal tip can be suppressed, and the consumption of the noble metal tip can be suppressed.

  Furthermore, the contact distance c between the noble metal tip and the metal core in a cross section including the axis and cut in the longitudinal direction of the ground electrode is 0.5 mm. Thus, by making the contact distance c 1.1 mm or less, the weldability of the noble metal tip to the ground electrode can be maintained.

  Such a spark plug 100 is manufactured as follows. However, the manufacturing method of the main part of the spark plug 100 will be mainly described, and the description of the known part will be omitted or simplified.

  First, the insulator 2 is formed by using alumina as a main raw material and firing it into a predetermined shape at a high temperature. Moreover, the metal shell 1 is formed by using a steel material and plastic processing into a predetermined shape. Next, a rod-shaped center electrode 3 and a ground electrode 4 made of a Ni heat-resistant alloy are prepared. Then, the ground electrode 4 is electrically resistance welded to the front end surface of the metal shell 3. Thereafter, the threaded portion 7 is formed on the outer peripheral surface of the distal end portion of the metal shell 1. On the other hand, the diameter of the tip of the center electrode 3 is reduced, and the first noble metal tip 31 is fixed to the tip surface by electrical resistance welding, laser welding, or the like. At this time, the welded portion W1 is formed.

  Then, the center electrode 3 is inserted into the shaft hole 6 of the insulator 2 so that the tip side protrudes from the insulator 2, and then the conductive seal layer 16, the resistor 15, and the conductive seal layer 17 are sequentially arranged on the rear end side. Further, the terminal fitting 8 is inserted on the rear end side of the insulator 2 so that the rear end side of the terminal fitting 5 protrudes from the rear end of the insulator 2 and fixed using a known method. . Then, after assembling the insulator 2 to which the center electrode 3 and the terminal fitting 8 are fixed and the metal shell 1 to which the ground electrode 4 is fixed, the second noble metal tip 41 is electrically connected to the tip of the ground electrode 4. Secure by resistance welding, laser welding, etc. At this time, the welded portion W2 is formed. Then, the ground electrode 4 is bent so that the tip surface 41a of the second noble metal tip 41 of the ground electrode 4 faces the tip surface 31a of the first noble metal tip 31 of the center electrode 3, and the internal combustion engine as shown in FIG. The engine spark plug 100 is completed.

In order to confirm the effect of the present invention, the following various experiments were conducted.
Various test pieces of spark plugs having the shapes shown in FIGS. 1, 2 and 3 were prepared as follows. First, sintered alumina ceramic is used as the material of the insulator 2, INCONEL 600 is used as the electrode base material of the center electrode 3, Cu is used as the metal core, Ni is used as the center core, and noble metal tips for forming the ignition portions 31 and 32 are formed. Pt-20 wt% Ni was selected as the material. The diameter a of the noble metal tip is set to 0.6 mm, and the protruding length b from the inner peripheral surface of the ground electrode is set to 0.1 mm, 0.3 mm, 0.4 mm, 0.6 mm, and 0.8 mm, respectively. did. Note that the length of the gap between the center electrode and the ground electrode is 1.1 mm. The width of the ground electrode is 2.8 mm, the height is 1.5 mm, and the center axis of the chip is 0.8 mm from the tip surface of the ground electrode.

  Each spark plug set as described above was attached to a 2000 cc, 6-cylinder DOHC gasoline engine and operated at an engine speed of 750 rpm. A / F is 14.5. Then, the ignition advance angle was advanced during operation, and the ignition advance angle at which the variation in pressure in the engine at 20 times of ignition was 20% was confirmed. It can be seen that the ignitability improves as the ignition advance proceeds. The results are shown in Table 1. A spark advance angle of 45 ° or more was judged as ◯, and a spark advance angle of less than 45 ° was judged as ×.

  According to Table 1, when the protrusion length b from the inner peripheral surface of the insulator of the noble metal tip was 0.4 mm or more, the ignition advance angle was 45 ° or more. On the other hand, when the protrusion length b is 0.3 mm or less, the ignition advance angle is 45 ° or less. That is, when the diameter of the noble metal tip is a and the protruding length of the noble metal tip from the inner peripheral surface of the center electrode side is b, the protruding length from the inner peripheral surface of the insulator is b> a / By setting it to 2, ignitability improves. Furthermore, in the present embodiment, the protruding length b is 0.4 mm or more. Therefore, the ignitability is sufficiently maintained.

  Next, various test products of the spark plug having the same shape as in Example 1 were prepared as follows. The protruding length b from the inner peripheral surface of the ground electrode is 0.8 mm, and the diameter a of the noble metal tip is 0.2 mm, 0.3 mm, 0.6 mm, 1.0 mm, 1.5 mm, and 1.6 mm. Set. Note that the length of the gap between the center electrode and the ground electrode is 1.1 mm, the width of the ground electrode is 2.8 mm, the height is 1.5 mm, and the center axis of the chip is 0. It is at 8mm.

  Each spark plug set as described above was attached to a 2000 cc, 6-cylinder DOHC gasoline engine in the same manner as in Example 1 and was operated at an engine speed of 750 rpm. A / F is 14.5. In the same manner as in Example 1, the ignition advance was advanced during operation, and the ignition advance at which the variation in the pressure in the engine at the number of ignitions of 500 was 20% was confirmed. The results are shown in Table 2. A spark advance angle of 45 ° or more was judged as ◯, and a spark advance angle of less than 45 ° was judged as ×.

  According to Table 2, when the diameter a of the noble metal tip is 1.5 mm or less, the ignition advance angle is 45 ° or more. On the other hand, when the diameter a of the noble metal tip is 1.6 mm, the ignition advance angle is less than 45 °. That is, also from this, when the diameter of the noble metal tip is a and the protruding length of the noble metal tip is b, the ignitability is improved by setting b> a / 2.

  Next, various test products of spark plugs similar to those in Examples 1 and 2 were prepared. The contact length between the metal core and the noble metal tip was 0 mm (not in contact), 0.1 mm, 0.3 mm, 0.5 mm, 0.7 mm, and 1.0 mm. The diameter of the noble metal tip was 0.6 mm, and the protruding length of the noble metal tip from the inner peripheral surface of the ground electrode was 0.8 mm. Note that the length of the gap between the center electrode and the ground electrode is 1.1 mm, the width of the ground electrode is 2.8 mm, the height is 1.5 mm, and the center axis of the chip is 0. It is at 8mm.

  The above-mentioned various test products were attached to a 2000 cc, 6-cylinder DOHC type gasoline engine, and operated for 500 hours with the engine fully rotated at 5000 rpm. And the amount of gap increase after the end of operation was measured. Less than 0.1 mm was evaluated as ◯, 0.1 mm or more and less than 0.15 mm was evaluated as Δ, and 0.15 or more was determined as ×. The results are shown in Table 3.

  According to Table 5, when the contact length between the metal core and the noble metal tip is 0 mm, the gap length is 0.15 mm or more, whereas the contact length between the metal core and the noble metal tip is 0.1 mm. , 0.3 mm, 0.5 mm, 0.7 mm, and 1.0 mm have a gap amount of less than 0.15 mm. Furthermore, when the contact length between the metal core and the noble metal tip is 0.5 mm, 0.7 mm, or 1.0 mm, the gap increase is less than 0.1 mm. That is, by bringing the metal core and the noble metal tip into contact with each other, the precious metal tip is prevented from being heated at high temperatures and the durability is improved. Furthermore, when the maximum contact distance between the noble metal core and the noble metal tip in the cross section including the axis and cut in the longitudinal direction of the ground electrode is 0.5 mm or more, the improvement in durability is more effective.

  Next, various test products of the spark plug having the same shape as in Example 1 were prepared as follows. And the protrusion length from the inner peripheral surface of the ground electrode was 0.8 mm, and the diameter of the noble metal tip was set to 0.2 mm, 0.3 mm, 0.6 mm, 1.0 mm, 1.5 mm, and 1.6 mm. . Note that the length of the gap between the center electrode and the ground electrode is 1.1 mm.

  Each spark plug was attached to a 2000 cc, 6-cylinder, DOHC gasoline engine, and operated for 500 hours with the engine rotating at 5000 rpm and the throttle fully opened. And the gap increase amount after completion | finish of an operation was measured, and less than 0.1 mm was set as (circle) and 0.1 mm or more was judged as x. The results are shown in Table 4.

  According to Table 4, when the diameter of the noble metal tip is 0.2 mm, the gap increase amount is 0.1 mm or more. On the other hand, when the diameter of the noble metal tip is 0.3 mm, 0.5 mm, 1.0 mm, 1.5 mm, and 1.6 mm, the gap increase amount is less than 0.1 mm. That is, the wear resistance of the noble metal tip is improved by setting the diameter a of the noble metal tip to 0.3 mm or more.

  Next, various test products of the spark plug having the same shape as in Example 1 were prepared as follows. Then, the diameter was set to 0.6 mm, and the projecting lengths from the inner peripheral surface of the ground electrode were set to 0.8 mm, 1.2 mm, 1.5 mm, and 1.6 mm, respectively. Note that the length of the gap between the center electrode and the ground electrode is 1.1 mm.

  Each spark plug was attached to a 2000 cc, 6-cylinder, DOHC gasoline engine, and operated for 500 hours with the engine rotating at 5000 rpm and the throttle fully opened. And the gap increase after completion | finish of a driving | operation was measured, and less than 0.1 mm was set to (circle) and 0.1 mm or more was set to x. The results are shown in Table 5.

  According to Table 5, when the diameter of the noble metal tip is 1.6 mm, the gap increase amount is 0.1 mm or more. On the other hand, when the diameter of the noble metal tip is 0.8 mm, 1.2 mm, or 1.5 mm, the gap increase is less than 0.1 mm. That is, the wear resistance of the noble metal tip is improved by setting the protruding length b of the noble metal tip to 1.5 mm or less.

The present invention is not limited to the specific embodiments described above, and various modifications can be made within the scope of the present invention depending on the purpose and application. For example, in the present embodiment, the core 4c is provided on the ground electrode 4, but the ground electrode 4 may be configured by an electrode base material 4a and a metal core 4b.
In the present embodiment, the ground electrode 4 is provided with a recess, and a noble metal tip is inserted into the recess and welded with a laser or the like. However, the present invention is not limited thereto, and the ground electrode 4 is provided with a through hole. A noble metal tip may be provided so as to embed the through hole, and the surface of the ground electrode 4 opposite to the center electrode 3 side may be welded with a laser or the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. Front sectional drawing which shows the principal part of FIG. Front sectional drawing which shows the principal part of the ground electrode of the spark plug of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 3 Center electrode 4 Ground electrode 6 Through-holes 31 and 41 Firing part (precious metal chip)
100 spark plug

Claims (4)

An insulator having an axial hole in the axial direction;
A center electrode disposed on the tip side of the shaft hole of the insulator;
A metal shell surrounding the periphery of the insulator;
In a spark plug comprising: a ground electrode having one end joined to the metal shell, the other end facing the center electrode, and a noble metal tip that forms a spark discharge gap between the center electrode;
The ground electrode includes an electrode base material, a metal core disposed in the electrode base material and having higher thermal conductivity than the electrode base material, and a thermal expansion coefficient in the metal core that is higher than that of the metal core. Has a low core and
The diameter of the noble metal tip is a,
When the protruding length of the noble metal tip from the center electrode side inner peripheral surface of the ground electrode is b,
b> a / 2
0.4 (mm) ≤ b
The spark plug is characterized in that the noble metal tip and the metal core are in contact with each other , and the noble metal tip and the center core are not in contact with each other . The spark plug according to claim 1, wherein
The diameter a of the noble metal tip and the protruding length b of the noble metal tip are each 0.3 (mm) ≦ a
b ≦ 1.5 (mm)
Spark plug characterized by being. The spark plug according to claim 1 or 2,
A maximum contact distance c between the metal core and the noble metal tip in a cross section cut in the longitudinal direction of the ground electrode, including an axis,
c ≦ 1.1 (mm)
Spark plug characterized by being.   The spark plug according to any one of claims 1 to 3,
  The spark plug characterized in that the noble metal tip is mainly composed of Ir, W, or Pt.