JP2006202684A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug with heat resistance, pollution resistance, and ignitability improved by the regulation of the size of an auxiliary ground electrode and the length of a spark discharge gap. <P>SOLUTION: The auxiliary ground electrode 60 is formed in a bar shape from a precious metal chip with a cross section in a square, and welded to the tip face 57 of a main metal fitting 50 with a direction crossing an axis line O. The opposed part of a tip 61 with an insulator 10 is formed as an in-the-air discharge gap (gap C) which constitutes an auxiliary spark discharge gap together with a creeping discharge gap (gap D) from an insulator-side starting point to a center electrode 20. The sum of the length of the gap C and half the length of the gap D is set at 1.43 times a main spark discharge gap (gap B). Further, a cross section of the tip 61 of the auxiliary ground electrode 60 is to be 1 mm<SP>2</SP>or less with the length of the gap B of 0.3 mm or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a spark plug for an internal combustion engine that can perform self-cleaning in the vicinity of a spark discharge gap.

  Conventionally, spark plugs for ignition are used in internal combustion engines. In this spark plug, generally, a ground electrode is welded to the tip of the metal shell that holds the insulator in which the center electrode is inserted, and the other end of the ground electrode is connected to the tip of the center electrode. A main spark discharge gap is formed so as to face the front end surface of the portion. Then, a spark discharge is performed between the center electrode and the ground electrode, and a flame nucleus is formed by igniting the air-fuel mixture exposed between the two electrodes.

  By the way, so-called fouling in which carbon generated by combustion of the air-fuel mixture adheres may occur on the surface of the insulator of the spark plug exposed in the combustion chamber. When the contamination progresses and the insulation on the surface of the insulator is lowered, a discharge occurs between the metal shell and the insulator, and a spark discharge is not performed between the center electrode and the ground electrode, resulting in a misfire condition. Therefore, the inner peripheral side of the front end surface of the metal shell is projected in a bowl shape toward the insulator, and an auxiliary spark discharge gap (auxiliary spark gap) is formed between the protruding portion (projecting edge) and the center electrode. A so-called auxiliary gap type spark plug in which spark discharge is performed has been proposed (see, for example, Patent Document 1).

  The auxiliary spark discharge gap is defined by the air discharge gap between the protruding edge and the side surface of the insulator tip, and the creeping discharge gap between the center electrode and the origin of the air discharge gap on the side surface of the insulator tip. Become. Normally, spark discharge is performed in the main spark discharge gap that is narrower than the auxiliary spark discharge gap. However, if the insulation on the surface of the insulator decreases due to fouling, the air is formed narrower than the main spark discharge gap. Spark discharge is performed in the discharge gap. Then, sparks run on the surface of the insulator in the creeping discharge gap, and the attached carbon is burned out. When the insulating property of the insulator surface is restored by such a self-cleaning action, spark discharge is again performed in the main spark discharge gap.

  However, in such an auxiliary gap type spark plug, since the inner peripheral side of the front end surface of the metal shell protrudes toward the insulator, there is no gap between the inner peripheral surface of the metal shell and the outer peripheral surface of the insulator. The mixture becomes difficult to enter. For this reason, the cooling effect of the insulator by the air-fuel mixture is lowered, and the heat resistance may be lowered. Further, since the air discharge gap with a narrow gap is formed over the entire circumference of the front end surface of the metal shell, there is a risk that a fuel bridge may be formed between the insulator and the front end surface of the metal shell.

Therefore, by providing a plurality of rod-shaped auxiliary grounding electrodes on the front end surface of the insulator so that the auxiliary grounding electrode is not disposed over the entire outer periphery of the insulator, the inner peripheral surface of the metal shell and the insulator Producing a spark plug that does not hinder the air-fuel mixture from entering the outer peripheral surface is effective in preventing formation of a fuel bridge and improving heat resistance (for example, Patent Document 2). reference.).
JP-A-9-139276 JP-A-49-85428

  However, in the spark plug of Patent Document 2, the dimensions are not defined in consideration of the mutual relationship with the main spark discharge gap, such as the size of the auxiliary ground electrode and the length of the auxiliary spark discharge gap. For this reason, if the air discharge gap is short, there is a risk that spark discharge will occur in the auxiliary spark discharge gap even during normal times, and if the air discharge gap is long, the main metal There is a risk that a so-called side-fire may occur, in which spark discharge is performed between the inner peripheral surface and the outer peripheral surface of the insulator. In addition, if the auxiliary ground electrode is large, the heat of the flame kernel that grows at the time of ignition is taken away, and the ignitability may be lowered.

  The present invention has been made to solve the above-described problems, and by specifying the size of the auxiliary ground electrode and the length of the spark discharge gap, it is possible to improve heat resistance, fouling resistance and ignitability. An object is to provide a spark plug that can be used.

  In order to achieve the above object, a spark plug according to a first aspect of the present invention includes a center electrode, an axial hole extending in the axial direction, an insulator that holds the central electrode in the axial hole, and a tip of the spark plug. In a state where the tip of the insulator is protruded from the surface, the metal shell that surrounds and holds the periphery of the insulator, one end is joined to the tip surface of the metal shell, and one side surface on the other end side is A first ground electrode that is bent so as to face the tip surface of the tip portion of the center electrode and forms a first spark discharge gap between the facing surfaces, and one end are joined to the tip surface of the metal shell, An air discharge gap whose end discharges between its tip and the surface of the insulator, and the insulator between the starting point of the air discharge gap on the surface of the insulator and the tip of the center electrode And a creeping discharge gap that discharges along the surface of the A spark plug configured to have a length of the first spark discharge gap that is longer than a length of the air discharge gap. At least one second ground electrode is provided, the direction from the one end to the other end is orthogonal to the axial direction of the center electrode, and the length of the air discharge gap and the creeping discharge gap are zero. The sum of the length of 5 times and the length of the first discharge gap is 1.43 times or more.

According to a second aspect of the present invention, the spark plug includes a center electrode, an axial hole extending in the axial direction, an insulator that holds the center electrode in the axial hole, and the insulator from the tip end surface of the insulator. A metallic shell that surrounds and holds the periphery of the insulator in a state where the distal end portion is projected, and one end is joined to the distal end surface of the metallic shell, and one side surface of the other end side is the distal end portion of the central electrode. The first ground electrode which is bent so as to face the front end surface of the first ground electrode and forms a first spark discharge gap between the opposing surfaces, one end is joined to the front end surface of the metal shell, and the other end is the front end of itself. And an air discharge gap that discharges between the surface of the insulator and the surface of the insulator between the starting point of the air discharge gap on the surface of the insulator and the tip of the center electrode. A second spark discharge gap consisting of a creeping discharge gap A spark plug configured such that a length of the first spark discharge gap is longer than a length of the air discharge gap, wherein the second ground electrode Is provided with at least one, the direction from the one end to the other end being orthogonal to the axial direction of the center electrode, the cross-sectional area of the other end being 1 mm ² or less, and the air discharge gap Is configured to have a length of 0.3 mm or more.

  According to a third aspect of the present invention, there is provided a spark plug according to the first or second aspect of the present invention, wherein the metal shell is screwed onto the outer periphery of the spark plug into a mounting hole of the engine head of the internal combustion engine. A screw portion is provided, and the outer diameter of the screw portion is M12 or less.

  In a spark plug according to a fourth aspect of the invention, in addition to the configuration of the invention according to any one of the first to third aspects, the second ground electrode is formed of a rod-shaped noble metal tip.

  In the spark plug according to the first aspect of the present invention, the sum of the length of the air discharge gap of the second spark discharge gap and the length of 0.5 times the creeping discharge gap is 1 of the length of the first spark discharge gap. It is composed of 43 times or more. Since the increase in the length of the air discharge gap required to increase the discharge voltage by a predetermined amount corresponds to 0.5 times the increase in the length of the creeping discharge gap, these sums are used as the first spark discharge. If it is configured to be equal to or larger than a constant multiple of the length of the gap, it is possible to prevent the spark discharge from being performed in the second spark discharge gap when the normal spark discharge is performed. If the above-mentioned constant is derived from the relative size relationship between the gaps in order to prevent the occurrence of side fire, the occurrence of side fire can be prevented. In the present invention, the above constant is derived based on an evaluation test, and 1.43 is set, so that spark discharge is surely performed in the first spark discharge gap in normal times and in the second spark discharge gap in the case of fouling. The occurrence of flying fire is prevented. Thereby, the self-cleaning effect of a spark plug can be improved and antifouling property can be improved.

  Further, the second ground electrode is joined to the front end surface of the metal shell, and only the first ground electrode is arranged along the side surface of the insulator protruding from the front end surface. Then, in the combustion chamber, since there are fewer things that obstruct the mixture from entering the clearance between the metal shell and the insulator, the cooling effect of the insulator by the mixture is enhanced, and the heat resistance of the spark plug is improved. . Furthermore, since it becomes difficult to form a fuel bridge at a low temperature start, the low temperature startability of the spark plug can be improved.

In the spark plug of the invention according to claim 2, the second ground electrode has a direction from one end to the other end orthogonal to the axial direction of the center electrode, and a cross-sectional area at the other end of 1 mm ² or less. . For this reason, it is possible to reduce the amount of heat taken by the flame nuclei generated during ignition in contact with the second ground electrode, and to improve the ignitability of the spark plug. If the cross-sectional area of the other end of the second ground electrode is greater than 1 mm ² , the flame extinguishing action of the flame core by the second ground electrode increases, and the ignitability of the spark plug decreases.

  Further, if the length of the air discharge gap is reduced, it is possible to ensure that spark discharge is performed in the air discharge gap at the time of fouling and to prevent side fire. On the other hand, as the air discharge gap becomes narrower, flame nuclei generated at the time of ignition come into contact with the second ground electrode at an early stage of growth, and the volume occupied by the second ground electrode is reduced as described above. Although the effect of improving the ignitability is diminished, the length of the air discharge gap is set to 0.3 mm or more, thereby improving the ignitability of the spark plug, further preventing side-fire, and ensuring the second spark discharge gap when fouling Spark discharge can be performed at. Thereby, the self-cleaning effect of a spark plug can be improved and antifouling property can be improved.

  Further, the second ground electrode is joined to the front end surface of the metal shell, and only the first ground electrode is arranged along the side surface of the insulator protruding from the front end surface. Then, in the combustion chamber, since there are fewer things that obstruct the mixture from entering the clearance between the metal shell and the insulator, the cooling effect of the insulator by the mixture is enhanced, and the heat resistance of the spark plug is improved. . Furthermore, since it becomes difficult to form a fuel bridge at the time of cold start, the cold start property of the spark plug can be improved.

  Further, in the spark plug of the invention according to claim 3, in addition to the effect of the invention according to claim 1 or 2, in the spark plug having an outer diameter of the screw portion of M12 or less, the clearance between the metal shell and the insulator is absolutely Since the dimensions are narrow, it is necessary not to impede the cooling effect of the insulator due to the air-fuel mixture entering the clearance. Therefore, in the spark plug of the present invention, the second ground electrode is joined to the front end surface of the metal shell in a state where the direction from one end to the other end of the second ground electrode is a direction orthogonal to the axial direction of the center electrode. As a result, only the first ground electrode is disposed along the side surface of the insulator protruding from the front end surface of the metal shell, and the mixture does not interfere with the clearance and the heat resistance of the spark plug is improved. can do. Furthermore, since it becomes difficult to form a fuel bridge at a low temperature start, the low temperature startability of the spark plug can be improved.

  Further, in the spark plug of the invention according to claim 4, in addition to the effect of the invention according to any of claims 1 to 3, the second ground electrode is formed from a noble metal tip having excellent spark wear resistance. Even if the ground electrode is made smaller, it is difficult for the spark to be consumed, and the durability of the spark plug can be improved.

  Hereinafter, an embodiment of a spark plug embodying the present invention will be described with reference to the drawings. First, the structure of a spark plug 100 as an example of the spark plug according to the present embodiment will be described with reference to FIGS. FIG. 1 is a partial cross-sectional view of a spark plug 100. FIG. 2 is an enlarged cross-sectional view of the tip portion of the spark plug 100. FIG. 3 is a view of the distal end portion of the spark plug 100 as viewed from the direction of the arrows along the two-dot chain line A-A ′ in FIG. 2. In FIG. 1, the axis O direction of the spark plug 100 is defined as the vertical direction in the drawing, and the lower side is described as the front end side and the upper side as the rear end side.

  As shown in FIG. 1, the spark plug 100 generally includes an insulator 10 that constitutes an insulator, a metal shell 50 that holds the insulator 10, and a center electrode that is held in the direction of the axis O within the insulator 10. 20, the base 32 is welded to the front end surface 57 of the metal shell 50, and the main ground electrode 30 whose one side faces the front end 22 of the center electrode 20, and the base 62, similar to the main ground electrode 30. One side surface is joined to the front end surface 57 of the metal shell 50, the front end portion 61 is opposed to the outer peripheral surface of the insulator 10, and the terminal metal fitting 40 provided at the rear end portion of the insulator 10. It is composed of

  First, the insulator 10 of the spark plug 100 will be described. The insulator 10 is a cylindrical insulating member that is formed by firing alumina or the like and has an axial hole 12 in the direction of the axis O as is well known. A flange portion 19 having the largest outer diameter is formed substantially at the center in the direction of the axis O, and a rear end side body portion 18 is formed on the rear end side. Further, a front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 on the front end side from the flange portion 19, and a further outer diameter than the front end side body portion 17 on the front end side of the front end side body portion 17. A small leg length 13 is formed. The long leg portion 13 is reduced in diameter toward the distal end side, and is exposed to the combustion chamber when the spark plug 100 is assembled to an internal combustion engine (not shown). Further, a step portion 15 is formed between the leg length portion 13 and the distal end side trunk portion 17.

  Next, the center electrode 20 is formed of a Ni-based alloy such as Inconel (trade name) 600 or 601, and has a metal core 23 made of copper or the like having excellent thermal conductivity. The distal end portion 22 of the center electrode 20 protrudes from the distal end surface of the insulator 10 and is formed so as to become smaller in diameter toward the distal end side. As shown in FIG. 2, the outer diameter of the tip portion 22 is smaller than the inner diameter of the shaft hole 12 of the insulator 10, and the antifouling property is improved between the inner periphery of the shaft hole 12 and the outer periphery of the tip portion 22. A minute gap 25 is formed for the purpose. A columnar noble metal tip 90 is welded to the distal end surface of the distal end portion 22 so that the column axis is aligned with the axis of the center electrode 20. The center electrode 20 is electrically connected to the terminal fitting 40 on the rear end side via the seal body 4 and the ceramic resistor 3 provided in the shaft hole 12. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown) so that a high voltage is applied.

  Next, the main ground electrode 30 will be described. The main ground electrode 30 is made of a metal having high corrosion resistance, and an Ni-based alloy such as Inconel (trade name) 600 or 601 is used as an example. The main ground electrode 30 has a substantially rectangular cross section in the longitudinal direction, and one end (base portion 32) is joined to the front end surface 57 of the metal shell 50 by welding. The other end (tip portion 31) of the main ground electrode 30 is bent so that the inner surface 33 side faces the tip portion 22 of the center electrode 20. A noble metal tip 91 is joined to the inner surface 33 of the tip 31 in accordance with the axis of the center electrode 20, and a main spark discharge gap (gap B in FIG. 2) that performs a spark discharge with the facing noble metal tip 90. Part shown) is formed. The main spark discharge gap corresponds to the “first spark discharge gap” in the present invention, and the main ground electrode 30 corresponds to the “first ground electrode” in the present invention.

  Next, the auxiliary ground electrode 60 will be described. The auxiliary ground electrode 60 is a noble metal tip made of a bar-shaped Ir alloy having a rectangular cross section. As shown in FIG. 2, the auxiliary ground electrode 60 has an axial direction that is orthogonal to the axis O of the center electrode 20, and the tip surface of the other end (tip portion 61) faces the side surface of the leg long portion 13 of the insulator 10. In this state, one side surface of the one end (base portion 62) is welded to the front end surface 57 of the metal shell 50. In the present embodiment, as shown in FIG. 3, three auxiliary ground electrodes 60 are provided, and two straight lines that are orthogonal to each other with the axis O as an intersection, and each orthogonal to the axis O are the front end surface 57 of the metal shell 50. The main ground electrode 30 and the three auxiliary ground electrodes 60 are respectively arranged at the positions intersecting with. The auxiliary ground electrode 60 corresponds to the “second ground electrode” in the present invention.

  Here, when the spark plug 100 is soiled, spark discharge is not performed in the main spark discharge gap, but spark discharge is performed in the auxiliary spark discharge gap formed between the center electrode 20 and the auxiliary ground electrode 60. As shown in FIG. 2, the space between the tip surface of the tip portion 61 of the auxiliary ground electrode 60 and the outer peripheral surface of the leg long portion 13 of the insulator 10 is configured as an air discharge gap (portion indicated by a gap C in the figure). The main spark discharge gap is configured to be shorter than the length of the gap B. Further, from the starting point of the air discharge gap on the insulator 10 side (position where spark discharge is performed from the outer peripheral surface of the leg long portion 13 of the insulator 10 with respect to the tip portion 61 of the auxiliary ground electrode 60), the surface of the insulator 10 A portion (a portion indicated by a gap D in the figure) extending to the center electrode 20 is configured as a creeping discharge gap. That is, the auxiliary spark discharge gap is composed of an air discharge gap and a creeping discharge gap. The auxiliary spark discharge gap corresponds to the “second spark discharge gap” in the present invention.

  Next, the metal shell 50 will be described. As shown in FIG. 1, the metal shell 50 is a cylindrical metal fitting for fixing the spark plug 100 to an engine head of an internal combustion engine (not shown), and is held so as to surround the insulator 10. At this time, the distal end portion of the leg long portion 13 of the insulator 10 protrudes forward (lower side in FIG. 1) from the distal end surface 57 of the metal shell 50. The metal shell 50 is made of an iron-based material, and includes a tool engaging portion 51 to which a spark plug wrench (not shown) is fitted, and a screw portion 52 to be screwed into an engine head provided on an internal combustion engine (not shown). I have. As an example of the standard of the threaded portion 52, M12 is used.

  Further, a caulking portion 53 is provided on the rear end side from the tool engaging portion 51. Then, by crimping the caulking portion 53, the step portion 15 of the insulator 10 is supported by the step portion 56 formed in the metal shell 50 via the annular packing 80, and the metal shell 50, the insulator 10, Is united. In order to maintain the airtightness between the step portion 15 and the step portion 56 and to prevent the outflow of combustion gas, and complete sealing by caulking, the tool engagement portion 51 and the caulking portion 53 are covered. Annular ring members 6, 7 are interposed between the metal shell 50 and the rear end body 18 of the insulator 10, and talc (talc) 9 powder is filled between the ring members 6, 7. The Further, a flange 54 is formed between the tool engaging portion 51 and the screw portion 52, and the gasket 5 is inserted into the vicinity of the rear end side of the screw portion 52, that is, the seat surface 55 of the flange 54. ing.

  In the spark plug 100 having such a configuration, it is effective to further define heat resistance, fouling resistance, and ignitability to define by paying attention to the length relationship between the main spark discharge gap and the auxiliary spark discharge gap. is there. Therefore, in the spark plug 100 of the present embodiment, the relative lengths of the main spark discharge gap and the air discharge gap and the creeping discharge gap forming the auxiliary spark discharge gap can be improved. In order to achieve this, the size and arrangement position of each part were specified.

First, the length relationships of the main spark discharge gap (gap B), the air discharge gap (gap C), and the creeping discharge gap (gap D) shown in FIG. Stipulated.
(Length of gap C) + (length of gap D) × 0.5 ≧ (length of gap B) × 1.43
That is, in the spark plug 100 of the present embodiment, the sum of the length of the air discharge gap and the length of 0.5 times the creeping discharge gap is not less than 1.43 times the length of the main spark discharge gap. It is configured. By setting the length relationship between the main spark discharge gap and the auxiliary spark discharge gap in this way, spark discharge is actively performed in the auxiliary spark discharge gap at the time of fouling, and by increasing the self-cleaning effect, It is possible to improve the performance. On the other hand, if the relationship between the gaps B, C, and D does not satisfy the above formula, there is a risk that spark discharge will be performed in the auxiliary spark discharge gap during normal times, or side fire may occur.

In the present embodiment, at the tip 61 of the rod-shaped auxiliary ground electrode 60, the cross-sectional area perpendicular to the axial direction is 1 mm ² or less, and the length of the air discharge gap (gap C) is 0.3 mm. That's it. If the length of the gap C is less than 0.3 mm, a fuel bridge may be formed between the auxiliary ground electrode 60 and the insulator 10. Furthermore, it becomes difficult for the air-fuel mixture to enter between the inner periphery of the metal shell 50 and the outer periphery of the leg long portion 13 of the insulator 10, and there is a possibility that the cooling effect cannot be obtained and the heat resistance is lowered. Further, if the cross-sectional area of the tip portion 61 of the auxiliary ground electrode 60 is larger than 1 mm ² , the volume of the auxiliary ground electrode 60 becomes large, and the ignitability may be deteriorated because the heat of flame nuclei that grow during ignition is taken away. is there.

  In order to confirm the effect of this invention about the spark plug comprised in this way, each evaluation test shown below was done.

[Example 1]
First, an evaluation test was performed on the relationship between the discharge voltage and the atmospheric pressure in the creeping discharge gap and the air discharge gap. In this evaluation test, a spark plug in which an auxiliary ground electrode is joined to the front end surface of the metal shell so that the creeping discharge gap (gap D in FIG. 2) is 1.0 mm is disposed in the chamber. The discharge voltage was measured under each atmospheric pressure of “0.4”, “0.6”, “0.8”, and “1” (MPa). The discharge voltages under each atmospheric pressure were “7”, “10”, “13”, “15.5”, and “17.5” (kV) in this order. Further, the discharge voltage at each atmospheric pressure was also measured for the spark plug having a creeping discharge gap of 1.1 mm. The discharge voltages at each atmospheric pressure were “7.51” and “10.52 in order. ], "13.49", "15.98", "18.01" (kV). A graph of this is shown in FIG.

  Next, a similar evaluation test was performed on the air discharge gap. A spark plug in which an auxiliary ground electrode is joined to the front end surface of the metal shell is arranged in the chamber so that the air discharge gap (gap C in FIG. 2) is 0.5 mm. .4 "," 0.6 "," 0.8 "," 1 "(MPa), and the discharge voltage was measured under each atmospheric pressure. The discharge voltages under each atmospheric pressure were “9”, “14”, “19.02”, “23.9”, and “26.5” (kV) in this order. Further, when the discharge voltage at each atmospheric pressure was measured in the same manner for the spark plug with an air discharge gap of 0.6 mm, “10.01”, “15.1”, “20.04” were sequentially measured. , “25.04”, “27.49” (kV). A graph of this is shown in FIG.

  As a result of this evaluation test, it was found that the discharge voltage was increased by about 0.5 kV uniformly when the creeping discharge gap was increased by 0.1 mm under any atmospheric pressure. Similarly, it was found that the discharge voltage increases by about 1.0 kV when the air discharge gap is increased by 0.1 mm. Therefore, in order to increase the discharge voltage by 1 kV, the length of the creeping discharge gap may be increased by 0.2 mm. However, in the case of an air discharge gap, the length is 0.5 times the creeping discharge gap. It was found that it was sufficient to widen 0.1 mm.

[Example 2]
Next, an evaluation test was conducted on the heat resistance of the spark plug. In this evaluation test, as shown in FIG. 6, the test was performed under the same conditions using the spark plug 100 of the present embodiment and four types of spark plugs as comparison targets. The parallel electrode type spark plug is a general spark plug having no self-cleaning action. A four-pole semi-creeping spark plug is such that four ground electrodes are provided on the tip surface of the metal shell and each tip is bent toward the center electrode so that self-cleaning is always performed. This is a spark plug. A three-pole hybrid type spark plug is a parallel electrode type spark plug with two auxiliary grounding electrodes joined to the tip of the metal shell, and the tip of each auxiliary grounding electrode is centered in the same way as the four-pole semi-surface type It is a spark plug that has a self-cleaning action by the auxiliary ground electrode when fouled by being bent toward the electrode. Auxiliary gap type spark plug is a spark plug that facilitates self-cleaning at the time of fouling by extending the end face of the metal shell of the parallel electrode type spark plug inward and reducing the distance from the insulator. .

  In the heat resistance evaluation test, each of the various spark plugs described above was assembled in a 4-cylinder gasoline engine with a displacement of 1600 cc and driven at 5500 rpm WOT (abbreviation for Wide Open Throttle, meaning throttle fully open). Then, when the ignition timing of the spark plug was advanced, the advance angle (ignition timing) at which preignition (premature ignition) occurred was measured. As a result, in the spark plug of the present embodiment, the pre-ignition generation advance angle was 45 ° BTDC. Further, the pre-ignition generation advance angles of the parallel electrode type, the 4-pole semi-surface type, the 3-pole hybrid type, and the auxiliary gap type spark plugs as comparative examples are “45”, “35”, “38”, “ 35 "(° BTDC). A graph of this is shown in FIG.

  As a result of this evaluation test, it was confirmed that the spark plug of the present embodiment has a higher preignition generation temperature and is less likely to cause preignition, as with the parallel electrode type spark plug. . In the 4-pole semi-creeping type and 3-pole hybrid type spark plug, the auxiliary ground electrode is large and is disposed so as to surround the tip of the insulator, and the tip is bent toward the center electrode. For this reason, the air-fuel mixture hardly enters the clearance between the metal shell and the insulator in the combustion chamber. Similarly, in the auxiliary gap type spark plug, the air-fuel mixture hardly enters the clearance because the front end surface of the metal shell protrudes toward the center electrode. For this reason, these spark plugs cannot sufficiently obtain the cooling effect by the air-fuel mixture, and heat is easily trapped in the clearance, so that the heat resistance is lower than that of the parallel ground electrode type spark plug. However, in the spark plug of the present embodiment, the size of the auxiliary ground electrode and the length of the air discharge gap are defined, so that only the main ground electrode is disposed along the tip of the insulator. There is a configuration in which it is difficult to prevent the mixture from entering the clearance. Thus, it was confirmed that the spark plug of the present embodiment was able to obtain the same heat resistance as the parallel electrode type spark plug.

[Example 3]
Next, an evaluation test was conducted on the antifouling property of the spark plug. In this evaluation test, the four types of spark plugs shown in FIG. 6 described in the heat resistance evaluation test (Example 2) were used as comparative examples with the spark plug 100 of the present embodiment, and the test was performed under the same conditions. It was.

  In the anti-fouling evaluation test, each spark plug was assembled in a 4-cylinder direct-injection gasoline engine with a displacement of 1800 cc, and a pre-delivery fouling test defined in JIS standard D1606 was performed in a test room at a room temperature of −10 ° C. Specifically, after starting the engine several times, the engine is driven for 3 seconds at 35 km / h for 40 seconds, idling is performed for 90 seconds, and then driven again for 3 seconds at 35 km / h for 40 seconds. To stop. Then, complete cooling is performed until the temperature of the cooling water reaches room temperature, the engine is started again, and the engine is blown, and the 15-second drive at the first speed of 15 km / h and the engine stop for 30 seconds are performed twice. Drive again for 15 seconds at h to stop the engine. This series of test patterns was taken as one cycle, and a plurality of cycles were repeatedly tested. Then, at the end of each cycle, the insulation resistance value between the metal shell of the spark plug and the connection terminal was measured, and the number of cycles when the value was less than 10 MΩ was confirmed.

  As a result, in the spark plug of the present embodiment, the insulating property was not lost for 10 cycles or more. Further, in the parallel electrode type, the 4-pole semi-creeping type, and the 3-pole hybrid type spark plug, the insulation was lost at the “4”, “9”, and “8” cycles, respectively. Further, in the auxiliary gap type spark plug, the insulating property was not lost for 10 cycles or more. A graph of this is shown in FIG.

  As a result of this antifouling resistance evaluation test, the 4-pole semi-creeping type and 3-pole hybrid type spark plugs have a larger number of startable cycles than the parallel electrode type spark plugs that cannot perform self-cleaning. Although it is favorable in terms of surface, it can be seen that the auxiliary gap type and the spark plug of the present embodiment are further advantageous in terms of antifouling properties. As shown in FIG. 6, in the four-pole semi-creeping type and three-pole hybrid type spark plug, an air discharge gap and a creeping discharge gap are formed at the tip of the insulator opposite to the tip of the auxiliary ground electrode. In the spark plug according to the present embodiment, the creeping discharge gap is formed longer than those spark plugs. In other words, the formation position of the air discharge gap is far from the center electrode compared to the 4-pole semi-creeping type and 3-pole hybrid type spark plugs, and it is difficult to fly between the auxiliary ground electrode and the center electrode at the time of non-staining. In addition, the length of the air discharge gap can be further reduced. As a result, spark discharge is generated in the insulator in the metal shell, so-called side fire can be suppressed, and when the spark plug is soiled, the spark discharge is surely generated in the auxiliary spark discharge gap and self-cleaned. be able to.

[Example 4]
Next, an evaluation test was performed on the ignitability of the spark plug. In this evaluation test, as the auxiliary ground electrode of the spark plug of the present embodiment, the cross-sectional areas orthogonal to the axial direction are “0.64”, “1.00”, “1.44”, “3.50”. ”,“ 4.50 ”(mm ² ). Then, an auxiliary ground electrode is joined to the front end surface of the spark plug main metal fitting so that the length of the air discharge gap becomes “0.1” to “0.7” (mm) for each of the various types. A sample was made. Each of these samples was started by assembling a 6-cylinder gasoline engine with a displacement of 2000 cc, and idling was performed at an intake pressure of −550 mmHg and 750 rpm. Then, the ignition timing of the spark plug was advanced, and the stable combustion limit at which misfire did not occur was measured.

As a result, the stable combustion limit when the cross-sectional area of the auxiliary ground electrode is 0.64 mm ² is that the length of the air discharge gap is “0.1”, “0.2”, “0.3”, “ In each of 0.4, “0.5”, “0.6”, “0.7” (mm), “23”, “25”, “42”, “45”, “48”, “ 50 ”and“ 52 ”(° BTDC). Similarly, when the cross-sectional area of the auxiliary ground electrode is 1.00 mm ² , the stable combustion limits with respect to the length of each air discharge gap are “22”, “24”, “40”, “44”, “47.5”, “50”, and “52” (° BTDC). When the cross-sectional area of the auxiliary ground electrode is 1.44 mm ² , the stable combustion limits with respect to the length of each air discharge gap are “22”, “23”, “28.3”, “40.1”, respectively. , “45”, “49”, “52” (° BTDC). When the cross-sectional area of the auxiliary ground electrode is 3.50 mm ² , the stable combustion limits with respect to the length of each air discharge gap are “22”, “22.5”, “25”, “27”, “ 30 ”,“ 35 ”, and“ 40 ”(° BTDC). When the cross-sectional area of the auxiliary ground electrode is 4.50 mm ² , the stable combustion limits with respect to the length of each air discharge gap are “22”, “22.5”, “24”, “26”, “ 28.5 ”,“ 32.5 ”,“ 36 ”(° BTDC). A graph of this is shown in FIG. In FIG. 9, the stable combustion limit is indicated as Adv.Limit.

From the results of this ignitability evaluation test, it is understood that the ignitability improves as the cross-sectional area of the auxiliary ground electrode (area of the cross section perpendicular to the axis) decreases. This is because the flame extinguishing action in which the flame nucleus generated by igniting the air-fuel mixture comes into contact with the auxiliary ground electrode and heat is taken away decreases as the volume of the auxiliary ground electrode in contact decreases. It can also be seen that the ignitability improves as the length of the air discharge gap increases. This is because in the growth process of the flame kernel, the longer the gap in the air, the more the flame kernel can grow before it comes into contact with the auxiliary ground electrode. In Example 3, it has been described that the smaller the length of the air discharge gap is, the better the anti-fouling property of the spark plug is. However, based on the result of this evaluation test, the cross-sectional area of the auxiliary ground electrode is 1 mm ² or less, In addition, it was found that if the length of the air discharge gap is 0.3 mm or more, the ignitability is good.

[Example 5]
Next, an evaluation test was performed on the low temperature startability of the spark plug. In this evaluation test, the four types of spark plugs shown in FIG. 6 described in the heat resistance evaluation test (Example 2) were used as comparative examples with the spark plug 100 of the present embodiment, and the test was performed under the same conditions. It was.

  In the low temperature startability evaluation test, the above various spark plugs were assembled in a 4-cylinder direct injection gasoline engine with a displacement of 1800 cc, respectively, and the engine was started for 15 seconds with the gear set to N after starting the engine in a test room at room temperature -30 ° C. The engine was stopped after the gear was put in D and driven for 15 seconds, and complete cooling was performed until the temperature of the cooling water reached room temperature. The test was repeated for a plurality of cycles with this as one cycle, and the number of cycles until the engine could not be started was confirmed.

  As a result, with the spark plug of the present embodiment, the engine could be started up to 11 cycles. The parallel electrode type, 4-pole semi-creeping type, 3-pole hybrid type, and auxiliary gap type spark plugs can start the engine up to "12", "6", "7", and "3" cycles, respectively. It was. A graph of this is shown in FIG.

  From the results of this low temperature startability evaluation test, in the auxiliary gap type spark plug, the entire front end surface of the metal shell protrudes toward the insulator, so the distance between the front end surface and the insulator is short. It can be seen that a fuel bridge is easily formed when an unvaporized air-fuel mixture adheres at the time of starting the engine, and the engine cannot easily be started. In the 4-pole semi creepage type and 3-pole hybrid type spark plug, the auxiliary grounding electrode is arranged so as to surround the tip of the insulator exposed from the tip of the metal shell, followed by the auxiliary gap type spark plug. A bridge is easily formed. However, a parallel electrode type spark plug without an auxiliary ground electrode hardly forms a fuel bridge, which is better in terms of low temperature startability than the above spark plugs. In the spark plug of the present embodiment, since the auxiliary ground electrode is small and there are few portions facing the insulator, it has been found that the performance is almost the same as that of the parallel electrode type spark plug in terms of low temperature startability.

[Example 6]
Next, an evaluation test was conducted on the occurrence of side fire. First, this embodiment in which the lengths of the main spark discharge gap, the air discharge gap, and the creeping discharge gap are adjusted to be “1.1”, “0.3”, and “1.5” (mm), respectively. A spark plug was prepared. This spark plug is placed in the chamber, and a side fire is generated under each pressure of “0.2”, “0.4”, “0.6”, “0.8”, “1” (MPa). Was measured, and the occurrence rate was determined from the number of occurrences. The occurrence rates of side fire under each atmospheric pressure were “14”, “31.7”, “48”, “59.5”, and “60” (%), respectively. A graph of this is shown in FIG. From this, when the atmospheric pressure in the chamber increased, the rate of occurrence of side fire increased, and when it was 0.8 MPa or more, the following test was conducted assuming that a sufficient environment could be obtained for evaluating the occurrence of side fire.

  Therefore, in the spark plug in which the atmospheric pressure in the chamber was set to 0.8 MPa and the length of the main spark discharge gap was 1.1 mm, the length of the air discharge gap, the length of the creeping discharge gap, and the occurrence of a side fire A test was conducted for the relationship with the rate. In this test, when joining the auxiliary ground electrode to the front end surface of the metal shell of the spark plug of the present embodiment, an intermediate member is disposed between the two, and the length of the creeping discharge gap is “1.0”, “ 1.5 ”,“ 2.0 ”,“ 2.5 ”(mm), and adjustment so that the length of the air discharge gap is“ 0.1 ”to“ 0.9 ”(mm) Thus, a spark plug sample was produced. The intermediate member is a metal member made of the same material as the main ground electrode, welded to the front end surface of the metal shell, and joined so that the auxiliary ground electrode is in conduction with the metal shell via the intermediate member. The length of each creeping discharge gap is adjusted by adjusting the length of the intermediate member in the direction of the axis O.

  When the length of the creeping discharge gap is 1.0 mm, the length of the air discharge gap is set to “0.1”, “0.2”, “0.3”, “0.4”, “0.5”. ”,“ 0.6 ”,“ 0.7 ”,“ 0.8 ”,“ 0.9 ”(mm), the occurrence rates of side fire of the spark plug are“ 99 ”,“ 98 ”,“ 95 ”,“ 87.3 ”,“ 60 ”,“ 40 ”,“ 20 ”,“ 8 ”,“ 0 ”(%). Similarly, when the length of the creeping discharge gap is 1.5 mm, the length of the air discharge gap is set to “0.1”, “0.2”, “0.3”, “0.4”, “ The occurrence rates of side fire of the spark plugs set to 0.5, 0.6, and 0.7 (mm) are “98”, “80”, “59”, “35”, and “18”, respectively. ”,“ 3 ”,“ 0 ”(%). When the length of the creeping discharge gap is 2.0 mm, the length of the air discharge gap is set to “0.1”, “0.2”, “0.3”, “0.4” (mm). The occurrence rates of sparks from the spark plug were “45”, “22.4”, “9”, and “0” (%), respectively. And when the length of the creeping discharge gap is 2.5 mm, the rate of occurrence of side fire of the spark plug with the length of the air discharge gap being “0.1”, “0.2” (mm), respectively, “4” and “0” (%). A graph of this is shown in FIG.

  As a result, when the creeping discharge gap lengths are “1.0”, “1.5”, “2.0”, and “2.5” (mm), respectively, the air in which side fire does not occur The lengths of the discharge gaps were found to be “0.9”, “0.7”, “0.4”, and “0.2” (mm), respectively. Although not shown in the drawing, the same evaluation test was conducted for each case where the length of the main spark discharge gap was set to “1.3”, “0.9”, “0.7” (mm). The relationship between the length of the creeping discharge gap and the length of the air discharge gap when no longer occurred was confirmed (Table 1).

  On the other hand, in a spark plug in which the length of the creeping discharge gap was 1.5 mm, the length of the main spark discharge gap and the relationship between the length of the air discharge gap and the occurrence rate of side-fire were tested. In this test, the length of the main spark discharge gap is “0.7”, “0.9”, “1.1”, “1.3” (mm), and the length of the air discharge gap is the same as above. Samples of spark plugs adjusted to be each combination of “0.1” to “1” (mm) were produced.

  When the length of the main spark discharge gap is 1.3 mm, the length of the air discharge gap is set to “0.1”, “0.2”, “0.3”, “0.4”, “0. The occurrence rates of side fires of the spark plugs “5”, “0.6”, “0.7”, “0.8”, “0.9”, “1” (mm) are “100”, “99”, “98”, “84”, “63.6”, “48”, “31.1”, “19”, “9”, “0” (%). Similarly, when the length of the main spark discharge gap is 1.1 mm, the length of the air discharge gap is set to “0.1”, “0.2”, “0.3”, “0.4”, The occurrence rates of side fire of spark plugs set to “0.5”, “0.6”, and “0.7” (mm) are “98”, “80”, “59”, “35”, “ 18 ”,“ 3 ”,“ 0 ”(%). When the length of the main spark discharge gap is 0.9 mm, the length of the air discharge gap is set to “0.1”, “0.2”, “0.3”, “0.4”, “0. The occurrence rates of side fires of the spark plug with 5 ”(mm) were“ 51 ”,“ 30 ”,“ 12 ”,“ 2 ”, and“ 0 ”(%), respectively. And when the length of the main spark discharge gap is 0.7 mm, the occurrence rate of the horizontal spark of the spark plug with the length of the air discharge gap being “0.1” and “0.2” (mm) is respectively , “11”, “0” (%). A graph of this is shown in FIG.

  As a result, when the length of the main spark discharge gap is “1.3”, “1.1”, “0.9”, “0.7” (mm), respectively, there is no tendency for side sparks to occur. It was found that the lengths of the middle discharge gap were “1”, “0.7”, “0.5”, and “0.2” (mm), respectively. Although not shown in the drawing, the same evaluation test was conducted when the creeping discharge gap lengths were set to “1.0”, “2.0”, “2.5” (mm), respectively, and a side fire occurred. The relationship between the length of the main spark discharge gap and the length of the air discharge gap when the failure occurred was confirmed (Table 1).

  Based on the results of the evaluation test, the relationship between the lengths of the main spark discharge gap, the creeping discharge gap, and the air discharge gap when no side fire occurs is summarized as shown in the table below. was gotten.

Next, based on the results of the evaluation tests of Example 1 and Example 6, the following relational expression was derived.
(Length of air discharge gap) + (length of creeping discharge gap) × 0.5 ≧ (length of main spark discharge gap) × K (where K is a constant)
From Example 1, when the discharge voltage is increased by a predetermined amount, 0.5 times the increase in the length of the creeping discharge gap and the increase in the length of the air discharge gap are approximately the same increase in the discharge voltage. It is confirmed that it corresponds. Therefore, if the sum of these is equal to or greater than K times the length of the main spark discharge gap, it can be said that no side fire occurs. Therefore, when the values of Table 1 were substituted into the above equation to determine the value of the constant K, the main spark discharge gap was 0.7 mm, the creeping discharge gap was 1.0 mm, and the air discharge gap was 0.5 mm. It was found that the largest value was 1.43.

  Needless to say, the present invention can be modified in various ways. For example, although three auxiliary ground electrodes 60 are provided in the present embodiment, the number of auxiliary earth electrodes 60 may be one or four, and at least one or more may be provided. For example, as in the spark plug 200 shown in FIG. 14, four auxiliary groundings are provided at each position where two straight lines perpendicular to each other with the axis O as an intersection and also perpendicular to the axis O intersect the tip surface 57 of the metal shell 50. The electrode 260 may be disposed, and the main ground electrode 30 may be disposed at an intermediate position between the two. In this case, the number of the auxiliary ground electrodes 260 is not limited to four. Note that the auxiliary ground electrode does not necessarily have to overlap with the main ground electrode in the direction of the axis O.

Further, although the auxiliary ground electrode 60 is formed from an Ir alloy, it may be formed from a Pt alloy or an Rh alloy. In addition, although the auxiliary ground electrode 60 has a bar shape with a rectangular cross section, the cross sectional shape may be a rectangle, a circle, or a polygon. Moreover, although the cross-sectional area of the front-end | tip part 61 of the auxiliary | assistant ground electrode 60 was 1 mm < ² > or less, this means that the cross-sectional area of the base 62 is not necessarily 1 mm < ² > or less. That is, the shape from the base portion 62 to the distal end portion 61 may be formed in a taper shape or may be formed in a step shape.

  In the present embodiment, the outer diameter is M12 as an example of the standard of the screw portion 52, but the effect of the present invention can be achieved in a small-diameter spark plug of M12 or less. In such a small-diameter spark plug, the clearance between the inner periphery of the metal shell and the outer periphery of the insulator is inevitably reduced. However, in the spark plug 100 of the present embodiment, the auxiliary ground electrode is the insulator. Therefore, it is difficult to inhibit the air-fuel mixture from entering the clearance in the combustion chamber, and the heat resistance of the spark plug can be improved without reducing the cooling effect of the air-fuel mixture.

  The present invention can be applied to a spark plug for an internal combustion engine.

1 is a partial cross-sectional view of a spark plug 100. FIG. FIG. 3 is an enlarged cross-sectional view of the tip portion of the spark plug 100. It is the figure which looked at the front-end | tip part of the spark plug 100 from the arrow direction in the dashed-two dotted line A-A 'of FIG. It is a graph which shows the relationship between the discharge voltage in a creeping discharge gap, and atmospheric pressure. It is a graph which shows the relationship between the discharge voltage in an air discharge gap, and atmospheric pressure. It is a figure which shows the difference between the spark plug of this Embodiment, and the spark plug as a comparative example of an evaluation test. It is a graph which shows the result of the evaluation test about heat resistance. It is a graph which shows the result of the evaluation test about stain resistance. It is a graph which shows the result of the evaluation test about ignitability. It is a graph which shows the result of the evaluation test about low temperature startability. It is a graph which shows the result of the evaluation test about generation | occurrence | production of side fire. It is a graph which shows the result of the evaluation test about generation | occurrence | production of side fire. It is a graph which shows the result of the evaluation test about generation | occurrence | production of side fire. It is the figure which looked at the front-end | tip part of the spark plug 200 as a modification from the axial direction front end side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Insulator 12 Shaft hole 20 Center electrode 22 Tip part 30 Main ground electrode 31 Tip part 32 Base part 33 Inner surface 50 Metal fitting 52 Screw part 57 Tip surface 60 Auxiliary ground electrode 61 Tip part 62 Base part 100 Spark plug

Claims (4)

A center electrode;
An insulator having an axial hole extending in the axial direction and holding the center electrode in the axial hole;
A metal shell that surrounds and holds the periphery of the insulator in a state where the tip of the insulator protrudes from the tip surface of itself,
One end is joined to the front end surface of the metal shell, and one side surface on the other end side is bent so as to oppose the front end surface of the front end portion of the center electrode, and a first spark discharge gap is formed between the opposing surfaces. A first ground electrode that
One end is joined to the front end surface of the metal shell, and the other end is an air discharge gap that discharges between its front end and the insulator surface, and an origin of the air discharge gap on the insulator surface And a second ground electrode that forms a second spark discharge gap comprising a creeping discharge gap that discharges along the surface of the insulator between the tip of the central electrode and the center electrode,
A spark plug configured such that the length of the first spark discharge gap is longer than the length of the air discharge gap,
The second ground electrode is
At least one is provided, and the direction from the one end to the other end is orthogonal to the axial direction of the center electrode,
In addition, the sum of the length of the air discharge gap and the length of 0.5 times the creeping discharge gap is configured to be not less than 1.43 times the length of the first discharge gap. And spark plug. A center electrode;
An insulator having an axial hole extending in the axial direction and holding the center electrode in the axial hole;
A metal shell that surrounds and holds the periphery of the insulator in a state where the tip of the insulator protrudes from the tip surface of itself,
One end is joined to the front end surface of the metal shell, and one side surface on the other end side is bent so as to oppose the front end surface of the front end portion of the center electrode, and a first spark discharge gap is formed between the opposing surfaces. A first ground electrode that
One end is joined to the front end surface of the metal shell, and the other end is an air discharge gap that discharges between its front end and the insulator surface, and an origin of the air discharge gap on the insulator surface And a second ground electrode that forms a second spark discharge gap comprising a creeping discharge gap that discharges along the surface of the insulator between the tip of the central electrode and the center electrode,
A spark plug configured such that the length of the first spark discharge gap is longer than the length of the air discharge gap,
The second ground electrode is
At least one or more are provided, the direction from the one end to the other end is orthogonal to the axial direction of the center electrode, and the cross-sectional area of the other end is 1 mm ² or less,
And the spark plug characterized by the length of the said air discharge gap being set to 0.3 mm or more. The metal shell is provided with a threaded portion on its outer periphery for screwing into a mounting hole of an engine head of an internal combustion engine,
The spark plug according to claim 1 or 2, wherein an outer diameter of the thread portion is M12 or less. The spark plug according to any one of claims 1 to 3, wherein the second ground electrode is formed of a rod-shaped noble metal tip.

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