JP2005135709A - Spark plug device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug device in which crack of an insulator and breakage of a center electrode are reduced by minimizing deformation of the insulator due to heat. <P>SOLUTION: Two center electrodes (130) are arranged inside the insulator (120) provided in a housing (110) and grounding electrodes (115) with a number corresponding to the center electrodes (130) are provided in the housing (110). The insulator (120) has barrel parts (121, 122, 123) having nearly circular cross section supported airtightly by the housing (110) and a leg part (124) of nearly cylindrical shape extending from the barrel parts surrounding the center electrodes (130). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ignition plug device for an internal combustion engine, and more particularly to an ignition plug device for an internal combustion engine suitable for use in a direct injection internal combustion engine capable of stratified combustion.

  Conventionally, as a spark plug device used in such a stratified combustion in-cylinder injection internal combustion engine (hereinafter also referred to as a in-cylinder fuel injection spark ignition internal combustion engine), for example, the one disclosed in Patent Document 1 is known. It has been.

  As schematically shown in FIG. 6, this spark plug has two ground electrodes (side electrodes) B and two center electrodes A, and the ground electrode B and the center electrode A that make a pair, respectively. Form an ignition gap G. Here, the ground electrode B is formed upright at the tip of the housing H screwed into the plug hole of the cylinder head, while the center electrode A is a frustoconical insulator C disposed in the housing H. And the tip end side thereof is bent toward the ground electrode B, and an ignition gap G is formed between each tip portion and the tip portion of the ground electrode B described above.

  In addition, the thing disclosed by patent document 2 is also known as a spark plug which has two center electrodes of the main and auxiliary | assistant. In addition, an auxiliary center electrode opposite to the common ground electrode is provided in the vicinity of the opposing surface of the main center electrode and the ground electrode. And, by forming the ignition gap between the auxiliary center electrode and the common ground electrode smaller than the ignition gap between the main center electrode and the common ground electrode, the pre-discharge and the main discharge are generated, and reliable discharge operation is performed. It is trying to make. Here, the main center electrode and the auxiliary center electrode are not described at all in the specification, but in the drawings, a form surrounded by legs of a tapered insulator is shown.

JP 2001-164940 A Japanese Patent Laid-Open No. 61-42890

  By the way, in the spark plug disclosed in Patent Document 1, since the two center electrodes A are configured to protrude from the frustoconical insulator C, heat generated at the tip of the insulator C is obtained. Due to the expansion, there is a problem that the insulator C is cracked and the center electrode A is likely to break. That is, as shown in FIG. 6 (for the sake of convenience of explanation, the insulator C is exaggerated), the insulator C is heated by the combustion in the combustion chamber and the cooling by the introduction of fresh air or fuel injection. The expansion (represented by a broken line) and contraction (represented by a solid line) are repeated in the extending direction X at the front end of the truncated cone. As a result, there is a high possibility that the insulator C will break or the center electrode A will break.

  As a countermeasure against this, as shown in Patent Document 2, it is conceivable to surround each of the center electrodes with legs of a tapered insulator, but this may cause a new problem. That is, since the spark plug is screwed into the standardized plug hole, the diameter of the housing is limited. When the insulator is a tapered leg, its tip is extremely small. It must be thin. When the thickness of the tip portion is reduced in this way, the heat conduction of the leg portion is deteriorated, and only the temperature of the tip portion becomes extremely high. As a result, the heat escape of the center electrode is hindered and premature ignition occurs, or the temperature difference between the body portion of the insulator and the tip of the leg portion becomes large and is easily broken by thermal strain.

  An object of the present invention is to provide an ignition plug device for an internal combustion engine that can eliminate such conventional problems and reduce cracking of the insulator and breakage of the center electrode by reducing deformation of the insulator due to heat. With the goal.

An ignition plug device for an internal combustion engine according to an embodiment of the present invention that achieves the above object has two or more center electrodes disposed in an insulator provided in a housing, and a number of ground electrodes corresponding to the center electrodes. Is a spark plug device for an internal combustion engine provided in the housing,
The insulator includes a body portion having a substantially circular cross section that is hermetically held in the housing, and a substantially cylindrical leg portion that extends from the body portion and surrounds the center electrode.

  Here, it is preferable that the outer peripheral surface of the substantially cylindrical leg portion is formed in a geometrically inscribed relationship with the outer peripheral surface of the body portion having a substantially circular cross section.

  An ignition plug device for an internal combustion engine according to the present invention is used in an in-cylinder injection internal combustion engine capable of stratified combustion, and two ignition gaps formed between the center electrode and a ground electrode are in the direction of fuel injection. It is preferable that they are arranged side by side in a direction orthogonal to the direction.

  According to the ignition plug device for an internal combustion engine according to one aspect of the present invention, the two or more center electrodes disposed in the insulator are substantially extended from the body having a substantially circular cross section that is hermetically held in the housing. Since the cylindrical legs are surrounded by substantially the same thickness, the temperature of only the tip portion does not become extremely high, and deformation due to heat can be reduced. As a result, cracking of the insulator and breakage of the center electrode can be reduced.

  According to the embodiment in which the outer peripheral surface of the substantially cylindrical leg portion is formed in a geometrically inscribed relationship with the outer peripheral surface of the body portion having a substantially circular cross section, the housing whose diameter is limited. , The distance between the center electrodes (between the ignition gap) can be increased.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a preferred embodiment of a spark plug device according to the present invention will be described in detail based on an example applied to an in-cylinder fuel injection spark ignition internal combustion engine with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  First, the structure of the spark plug 100 according to the present invention will be described. As shown in FIG. 1, the spark plug 100 includes a metal cylindrical housing 110 and an insulator 120 disposed therein. The housing 110 includes a screw portion 111 for screwing into a plug hole of the cylinder head, a neck portion 113 to which a gasket 112 is attached, and a nut portion 114 for tightening. Two ground electrodes 115 are provided at the front end of the housing 110 so as to face each other in the radial direction. Further, as will be described later, the inside of the housing 110 has a small-diameter hole portion 117 in which an annular rib 116 is formed to ensure airtightness with the insulator, and a large-diameter hole portion 118 that accommodates the large-diameter portion of the insulator. In addition, a thin crimped portion 119 is formed at the rear end portion.

  On the other hand, the insulator 120 includes a circular medium-diameter trunk 121 having the same diameter as that of the small-diameter hole 117 and a circular large-diameter trunk 122 having substantially the same diameter as the large-diameter hole 118 and a medium-diameter trunk 121. A small-diameter trunk portion 123 having an outer diameter slightly smaller than the inner diameter of the annular rib 116 and two parallel substantially cylindrical leg portions 124, 124 extending from the small-diameter trunk portion 123. I have. A crotch portion 125 is formed between the cylindrical leg portions 124 and 124. The large-diameter trunk portion 122 is connected to the head portion 127 via a neck portion 126 with which the above-described caulking portion 119 is engaged.

  Furthermore, two center electrodes 130 and 130 passing through the centers of the parallel cylindrical legs 124 and 124 and the small-diameter body 123 are arranged in parallel on the insulator 120. The center electrodes 130 and 130 pass through the medium diameter body 121 and the large diameter body 122, and are connected to the terminals 132 and 132 via the center shafts 131 and 131 including resistance.

  The center electrodes 130, 130 are surrounded by cylindrical legs 124, 124 having a substantially uniform wall thickness, and their tips protrude from the tips of the cylindrical legs 124, 124, and the ground electrodes 115, 115 are bent. Ignition gap portions 135 and 135 are formed between the tip portions.

  The insulator 120 on which the center electrodes 130 and 130, the middle shafts 131 and 131, and the terminals 132 and 132 are disposed is inserted into the housing 110 and the spark plug 100 is assembled. In addition, a packing 136 for ensuring airtightness (gas seal) is interposed between the curved surface at the boundary of the small-diameter body portion 123 and the annular rib 116, and then the rear end portion of the housing 110 is thin. The crimping portion 119 is crimped to the neck portion 126 of the insulator 120, and the assembly is completed. As a result, an axial force in the axial direction is applied by the crimping portion 119, the packing 136 is compressed, and the insulator 120 is held in the housing 110 in an airtight manner.

  Here, as shown in FIG. 2, the substantially cylindrical leg portions 124 and 124 surrounding the center electrodes 130 and 130 have an outer circumference circle and a small diameter when the spark plug 100 is viewed from the tip end side. The outer circumferential circle of the trunk portion 123 is formed so as to extend from the small-diameter barrel portion 123 so as to be geometrically inscribed. In this way, the distance between the ignition gap portions 135 and 135 determined by the two substantially cylindrical leg portions 124 and 124 in parallel, in other words, the distance L between the center electrodes 130 and 130 is dimensionally limited. The housing 110 can be elongated in the small-diameter body 123.

  In addition, the substantially cylindrical leg portion in the present invention is not limited to the one in which the inner peripheral surface and the outer peripheral surface are geometrically parallel, and the draft from the mold of the insulator formed of porcelain or the like is considered. It is used in the meaning including a slightly tapered form.

  Next, the in-cylinder fuel injection spark ignition internal combustion engine 200 to which the ignition plug 100 having the above-described configuration is attached will be described with reference to FIG. An in-cylinder fuel injection spark ignition internal combustion engine 200 includes a cylinder head 207 having an intake port 202, an intake valve 203, an exhaust port 204, an exhaust valve 205, and an ignition plug 100, a cylinder block 209 in which a cylinder 208 is formed, and The piston 210 is mainly provided with a piston 210 that is reciprocally movable with respect to the cylinder 208 (cylinder block 209). The combustion chamber 211 is configured by a space defined by the lower surface of the cylinder head 207, the top surface 210a of the piston 210, and the peripheral wall surface 215a and the bottom wall surface 215b of the cavity 215. The piston 210 is provided with a plurality of piston rings 212 on its side surface to prevent gas from being blown out from the combustion chamber 211.

  The fuel injection valve 213 is attached to the cylinder valve 207 on the side of the intake valve 203 so that the nozzle tip 213a is inclined slightly downward toward the center axis of the cylinder 208. In the present embodiment, as shown in FIG. 4A, two intake valves 203 are provided, and the fuel injection valve 213 is positioned between the intake valves 203. The fuel injection valve 213 is arranged so that the center of the fuel spray flow does not directly hit the spark plug 100 but injects the fuel toward the cavity 215.

  The cavity 215 is formed at the top of the piston 210 so as to open to the piston top surface 210a with the nozzle tip 213a of the fuel injection valve 213 and the spark plug 100 as substantially both ends. The cavity 215 has a substantially cylindrical peripheral wall surface 215a and a bottom wall surface 215b smoothly connected to the peripheral wall surface 215a. At the compression top dead center, the ignition gap portions 135 and 135 of the spark plug 100 are cylinders. The lower surface of the head 207 and the bottom wall surface 215b of the cavity 215 are arranged at a position slightly closer to the cylinder head 207 side from the approximate center or center. Here, since the fuel injection valve 213 is attached with the nozzle tip 213a substantially inclined toward the cylinder center axis and inclined slightly downward, the fuel is injected toward the bottom wall surface 215b of the cavity 215.

  Further, assuming that the total width of the cavity 215 in the direction perpendicular to the injection direction from the fuel injection valve 213 is W, the shape of the cavity 215 in plan view is substantially the entire width W as the major axis as shown in FIG. Further, the width of the peripheral wall surface 215a is larger than the width of the spray when the spray tip reaches the center of the cylinder 208. That is, the spray in the combustion chamber 211 is accommodated in the cavity 215 even when the piston 210 moves up. The peripheral wall surface 215a of the cavity 215 has a concave curved surface at least on the spark plug 100 side.

  In the compression stroke of the piston 210 from the bottom dead center to the top dead center, the air in the combustion chamber 211 is compressed, and fuel is injected from the fuel injection valve 213 in the compression process. The spray of injected fuel spreads substantially symmetrically with respect to the spark plug 100 in a fan shape in a plane orthogonal to the central axis of the cylinder 208. The spray flows from the bottom wall surface 215b of the cavity 215 along the connecting portion between the bottom wall surface 215b and the peripheral wall surface 215a, and further flows along with the air along the peripheral wall surface 215a from the connecting portion. As a result, a flow of a stratified air-fuel mixture rising toward the spark plug 100 is formed, and this is combined with the rise of the piston 210, so that the air-fuel mixture having a concentration suitable for ignition before ignition top dead center is ignited by the spark plug 100. It is distributed around the gaps 135 and 135.

  In the spark plug 100, as described above, the ground electrode 115 and the center electrode 130 that form a pair constitute an ignition gap portion 135, and are connected to different ignition coils (not shown). As shown in FIG. 4A, the spark plug 100 is positioned and cylinders so that two ignition gap portions 135 and 135 are arranged side by side in a direction perpendicular to the injection direction of the fuel injection valve 213. It is attached to the head 207.

  In the in-cylinder fuel injection type spark ignition internal combustion engine 200, in order to ignite reliably corresponding to the density of the air-fuel mixture, shorten the flame propagation distance and shorten the combustion time, as shown in FIG. It can be said that the distance D between the ignition gaps is preferably set to approximately half of the full width W of the cavity 215. However, as described above, the outer diameter of the screw portion 111 of the housing 110 is limited in the spark plug 100 in relation to the plug hole diameter, and the distance L between the two ignition gap portions 135 and 135 is outside this distance. The diameter cannot be exceeded. Therefore, in the present embodiment, as described above, the cylindrical leg portions 124 and 124 are geometrically inscribed with the outer circumference circle and the outer circumference circle of the small-diameter trunk portion 123 as shown in FIG. Therefore, the distance L between the ignition gap portions 135 and 135 (between the center electrodes 130 and 130) is made as long as possible, but this is at least 3 mm or more. If so, the in-cylinder fuel injection spark ignition internal combustion engine 200 can be operated stably.

  In the present embodiment, the fuel injected from the fuel injection valve 213 toward the bottom wall surface 215b of the cavity 215 rises from the bottom wall surface 215b of the cavity 215 toward the spark plug 100 along the peripheral wall surface 215a. A mixture is formed. At this time, the air-fuel mixture is contained in the cavity 215 due to the squish flow caused by the cavity 215 and the top surface 210 a of the piston 210. The flame formed by being ignited by the spark plug 100 develops in the cavity 215 due to flame propagation. The spark plug 100 includes two spark gap portions 135 and 135 that are provided at a predetermined distance L so as to be able to ignite an ignitable mixture that rises toward the spark plug 100. Therefore, the probability that the concentration of the air-fuel mixture existing in the vicinity of both of the two ignition gap portions 135 and 135 exceeds the range of the air-fuel mixture concentration that can be properly ignited at the same time is extremely small. Therefore, even if a misfire occurs in any one of the ignition gap portions 135, the other ignition gap portions 135 can be ignited normally, so that normal combustion is performed for that cylinder. As a result, the occurrence of misfire is greatly suppressed.

  Further, if ignition is performed in two ignition gap portions 135 and 135 that are spatially separated, the combustion speeds in the respective ignition gap portions 135 and 135 are the same, but the combustion is accelerated as viewed in the entire cylinder. It becomes a state. Therefore, the injected fuel can be burned before it overspreads to the periphery, and the occurrence of torque fluctuation can be greatly suppressed. In addition, the fuel efficiency can be improved by a synergistic effect of increasing the combustion efficiency and increasing the isovolume of the cycle.

  Note that the spark plug 100 in the embodiment of the present invention also expands due to the heat load caused by the combustion in the cavity 215 or the combustion chamber due to ignition, the introduction of fresh air from the intake port 202, and the cooling caused by the fuel injection from the fuel injection valve 213. And repeat contraction. This situation is shown in FIG. 5 (for the sake of convenience, it is exaggerated in the figure). By the way, in the spark plug 100 according to the embodiment of the present invention, the insulator leg portions 124, 124 exposed in the combustion chamber have a substantially cylindrical shape surrounding the center electrodes 130, 130 with a substantially uniform thickness. Since it is formed, even when it is affected by the thermal cycle described above, its expansion (shown by a broken line) and contraction (shown by a solid line) occur substantially evenly, and no excessive force is generated in the stretching direction X. As a result, the possibility of cracking of the insulator and breakage of the center electrodes 130 and 130 is reduced.

(A) is a longitudinal sectional view showing a preferred embodiment of a spark plug device according to the present invention, and (B), (C) and (D) are crossings at the neck portion, medium diameter portion and leg portion of the insulator, respectively. FIG. It is a bottom view of the insulator of the spark plug device by this invention. 1 is a longitudinal sectional view showing an in-cylinder fuel injection spark ignition internal combustion engine to which a spark plug device according to the present invention is applied. (A) is a bottom view transparently showing the piston cavity and the lower surface of the cylinder head, and (B) is a top view of the piston. It is sectional drawing for demonstrating the mode of the thermal deformation of the spark plug apparatus by this invention. It is sectional drawing for demonstrating the mode of the thermal deformation of the conventional spark plug apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Spark plug 110 Housing 115 Ground electrode 120 Insulator 121 Medium diameter trunk part 122 Large diameter trunk part 123 Small diameter trunk part 124 Cylindrical leg part 130 Center electrode 135 Ignition gap part

Claims (3)

An ignition plug device for an internal combustion engine in which two or more center electrodes are arranged in an insulator provided in a housing, and a number of ground electrodes corresponding to the center electrodes are provided in the housing,
The insulator has an approximately circular body section that is hermetically held in the housing, and a substantially cylindrical leg section that extends from the body section and surrounds the center electrode. Spark plug device.   2. The ignition of the internal combustion engine according to claim 1, wherein an outer peripheral surface of the substantially cylindrical leg portion is formed in a geometrically inscribed relationship with an outer peripheral surface of the trunk portion having a substantially circular cross section. Plug device.   Used in a cylinder injection type internal combustion engine capable of stratified combustion, wherein two ignition gaps formed between the center electrode and the ground electrode are arranged side by side in a direction perpendicular to the direction of fuel injection. An ignition plug device for an internal combustion engine according to claim 1 or 2.

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