JP4882878B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to a spark plug used in an internal combustion engine, and more particularly, to an electrode structure of a spark discharge portion of the spark plug.

  In the internal combustion engine, an ignition plug is provided for each cylinder in order to ignite the air-fuel mixture and fuel spray in the cylinder. The spark plug is usually formed in the cylinder by applying a secondary voltage from the secondary coil of the ignition coil to generate an electric spark (spark discharge) in a spark discharge portion that protrudes from the cylinder. Ignition is performed on the air-fuel mixture.

  The spark discharge part of the spark plug is generally electrically connected to the secondary coil of the ignition coil and is grounded (grounded) to the center electrode extending along the center axis of the spark plug and the cylinder head or the like. And a ground electrode provided opposite to the center electrode. A gap (hereinafter referred to as a spark gap) having a predetermined interval is provided between the center electrode and the ground electrode provided to face each other in the spark plug axial direction. When a secondary voltage is applied to the spark discharge portion of the spark plug, an electric spark is generated in the spark gap.

  In the spark plug capable of forming an electric spark between the center electrode and the ground electrode, the center electrode extends in the radial direction of the spark plug having a substantially cylindrical shape, or the center electrode extends in the spark plug radial direction. The thing extended in several different directions among these is proposed (for example, refer patent document 1).

Japanese Utility Model Publication No. 62-142187

  By the way, in a spark plug, in order to make the required dielectric breakdown voltage as low as possible, it is required to set the size of the spark gap as small as possible. By setting the spark gap interval small, the discharge path is shortened and the voltage required for dielectric breakdown can be lowered. On the other hand, by setting the spark gap interval large, the discharge path can be lengthened and the ignitability of the air-fuel mixture can be improved. In particular, in an internal combustion engine equipped with a supercharger or an internal combustion engine that ignites a lean air-fuel mixture, it is required to set a large spark gap interval in order to improve ignitability. That is, an internal combustion engine has an optimal spark gap interval according to its specifications and is required to maintain this.

  However, as shown in FIG. 16, the electrodes constituting the spark discharge portion 151 of the spark plug, that is, the center electrode 164 and the ground electrode 174, are repeatedly ignited to face each other (hereinafter, referred to as facing faces) 164a. , 174a, it is known that the wear gradually proceeds. When the electrodes 164 and 174 are depleted in this way, the gap between the spark gaps increases, causing a problem that the required breakdown voltage increases.

  In particular, when the flow rate of a gas such as an air-fuel mixture is high in the combustion chamber, the electric spark A1 that reaches the breakdown voltage and is linearly formed between the center electrode and the ground electrode is as shown in FIG. In the combustion chamber, a gas such as an air-fuel mixture is flowed in the direction of flow (indicated by an arrow F), and electric sparks mainly flow from the opposing surfaces 164a and 174a of the center electrode 164 and the ground electrode 174, respectively. This causes a problem that the portion on the side to be worn (end surface 164e, 174e side) is unevenly worn.

  Patent Document 1 discloses a spark plug in which a tip portion of a center electrode extends in a radial direction of the spark plug. In this spark plug, since an electric spark is formed between the tip of the center electrode and the external electrode (housing), the gap of the spark gap increases in proportion to the wear of the tip of the center electrode. Occurs.

The present invention was made in view of the above, by delaying the time at which depletion of the electrodes constituting the spark discharge portion is advanced, the spark gap to provide internal combustion engine capable of suppressing to expand prematurely.

In order to achieve the above object, an internal combustion engine according to the present invention includes an intake port and an exhaust port arranged in a crossflow manner, and an ignition plug provided on a ceiling wall that defines the shape of the combustion chamber. The spark plug includes a center electrode center portion provided along the center axis of the spark plug, and at least one center electrode extension extending from the center electrode center portion in a predetermined direction in the spark plug radial direction. A center electrode having a portion, a ground electrode center portion provided opposite to the center electrode center portion in the spark plug axial direction, and at least extending from the ground electrode center portion in the spark plug radial direction. It has a one ground electrode extension, and includes a ground electrode provided to face the center electrode center to the spark plug axis, wherein the spark plug is provided in the ceiling wall central portion of the combustion chamber Cage, the at least one center electrode extension, the center from the electrode central portion in the vicinity of the spark discharge portion of the spark plug gas is extended in the downstream side of the direction of flow, characterized in that.

  In the internal combustion engine according to the present invention, the center electrode extension portion and the ground electrode extension portion can each extend in a plurality of directions with a predetermined angle in the spark plug circumferential direction.

  In the internal combustion engine according to the present invention, the center electrode extension portion and the ground electrode extension portion may be provided alternately in the circumferential direction of the spark plug.

  In the internal combustion engine according to the present invention, the distance between the center electrode extension portion and the ground electrode extension portion in the spark plug axial direction is set so as to increase from the spark plug central axis toward the outside in the spark plug radial direction. be able to.

  In the internal combustion engine according to the present invention, the distance between the center electrode extension and the ground electrode extension in the spark plug axial direction is set to be larger than the distance between the center electrode center and the ground electrode center. be able to.

  In the internal combustion engine according to the present invention, the center electrode extension portion and the ground electrode extension portion may be set to be thinner in the spark plug axial direction than the center electrode center portion and the ground electrode center portion, respectively. .

  According to the present invention, the center electrode of the spark plug extends from the center electrode center portion provided along the spark plug center axis in a predetermined direction (extension direction) in the spark plug radial direction from the center electrode center portion. A center electrode extension, and the center electrode extension extends in the gas flow direction along the ceiling wall in the direction of gas flow mainly in the combustion chamber. The electric spark generated between the center electrode central portion and the ground electrode is caused to flow at a high frequency in the direction in which the extension portion extends, and is maintained in the extension portion until the end of discharge. Thereby, the center electrode is depleted mainly from the extension part, and in the center part of the center electrode where an electric spark is generated at the start of arc discharge, the time at which the depletion proceeds can be delayed. Thereby, the dimension of the spark gap formed between the center electrode central portion and the ground electrode can be prevented from expanding at an early stage.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

  First, the schematic configuration of the internal combustion engine and the arrangement of the spark plug according to the present embodiment will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a schematic configuration around a cylinder of an internal combustion engine. FIG. 2 is a diagram showing the positional relationship between the spark plug and the intake / exhaust valves, and is a diagram of the ceiling wall of the cylinder head viewed from the piston side. FIG. 1 and FIG. 2 schematically show only main parts related to the present invention.

  The internal combustion engine according to this embodiment is a gasoline engine in which a fuel injection valve injects fuel into an intake passage, and is a spark ignition engine that ignites an air-fuel mixture formed in a cylinder with an ignition plug. Hereinafter, one cylinder among the plurality of cylinders of the internal combustion engine will be described.

  As shown in FIG. 1, the internal combustion engine 10 is provided with a cylinder block 12, a cylinder head 20, a piston 30, and a connecting rod and a crankshaft (not shown) as parts of an engine body system in which a cylinder is formed. ing. A cylinder bore 14 is formed in the cylinder block 12, and the piston 30 reciprocates in the cylinder bore 14 along its axis (hereinafter referred to as a bore axis).

  The reciprocating motion of the piston 30 is converted into a rotational motion and output from a crankshaft (not shown). The internal combustion engine 10 is provided with a crank angle sensor (not shown) that detects a rotational angle position of the crankshaft (hereinafter referred to as a crank angle), and sends a signal related to the crank angle to the control device. Yes.

  A cylinder head 20 is coupled to the cylinder block 12 so as to face the piston 30 and close the cylinder bore 14. A combustion chamber 40 is formed in the cylinder head 20, and an intake port 24 that guides intake air to the combustion chamber 40 is disposed on one side of the cylinder bore axis (indicated by a dashed line C in the figure). An exhaust port 26 for discharging exhaust gas from the combustion chamber 40 is formed on the other side.

  The cylinder head 20 is provided with an intake valve 25 and an exhaust valve 27 corresponding to the intake port 24 and the exhaust port 26, respectively. The intake valve 25 and the exhaust valve 27 are driven by receiving mechanical power from the crankshaft via a camshaft. The intake valve 25 and the exhaust valve 27 are configured to be openable and closable at a predetermined timing according to the rotation angle position of the crankshaft (hereinafter referred to as the crank angle).

  When the intake valve 25 is opened, the intake port 24 and the combustion chamber 40 communicate with each other, and air from an intake passage (not shown) can be taken into the combustion chamber 40 in the cylinder from the intake port 24. When the exhaust valve 27 is opened, the exhaust port 26 and the combustion chamber 40 communicate with each other, and the exhaust gas in the combustion chamber 40 in the cylinder can be discharged from the exhaust port 26 to an exhaust passage (not shown).

  As shown in FIG. 2, two intake ports 24 and two exhaust ports 26 are provided, and each includes an imaginary axis including the axis of the cylinder bore 14 and extending in the axial direction of the crankshaft (indicated by an arrow S in the figure). They are arranged so as to face each other across a cylinder row plane (indicated by a dashed line E in the figure) which is a plane. That is, in the internal combustion engine, a plurality of cylinders are arranged in the crankshaft direction, and in each cylinder, the intake port 24 and the exhaust port 26, that is, the intake valve 25 and the exhaust valve 27 are arranged in a so-called “cross flow type”. It has become.

  In the following description, the side on which the intake port 24 and the intake valve 25 are provided with respect to the cylinder row plane E including the axis of the cylinder bore 14 is referred to as “intake side”, and is indicated by the symbol IN in the drawing. On the other hand, the side on which the exhaust port 26 and the exhaust valve 27 are provided with respect to the plane E is referred to as “exhaust side” and is indicated by the symbol EX in the drawing.

  The cylinder head 20 is formed with a ceiling wall 22 that is a wall surface that defines the shape of the combustion chamber 40. The ceiling wall 22 is formed so as to smoothly continue to the cylinder wall 15 which is the wall surface of the cylinder bore 14 at the peripheral edge 22e. A spark discharge portion 51 of a spark plug 50 is disposed at a central portion 22a of the ceiling wall 22 of the combustion chamber 40 formed in the cylinder head 20 (hereinafter referred to as a ceiling wall central portion).

  As shown in FIG. 2, the “ceiling wall central portion” 22 a means the outer edge 24 e of the intake port 24 and the exhaust port 26 in addition to the portion of the ceiling wall 22 of the combustion chamber 40 through which the axis of the cylinder bore 14 passes. A portion sandwiched between the outer edge 26e of the first and second outer edges 26e is included. On the other hand, the “ceiling wall peripheral portion” 22 c is a portion sandwiched between the peripheral edge 22 e of the ceiling wall 22 and the outer edge 24 e of the intake port 24 or the outer edge 26 e of the exhaust port 26 in addition to the peripheral edge 22 e of the ceiling wall 22. Is included.

  In the present embodiment, the spark plug 50 has a substantially cylindrical shape as shown in FIG. 1, and in this embodiment, the center axis of the spark plug (indicated by the alternate long and short dash line C in the figure) is the axis of the cylinder bore 14. Are arranged to match. The spark discharge portion 51 of the spark plug 50 is provided so as to protrude from the combustion chamber 40 of the cylinder head 20. The spark plug 50 is applied with a dielectric breakdown voltage (secondary voltage) required by an ignition coil (not shown) to generate an electric spark (spark discharge) in the spark gap of the spark discharge unit 51, Ignite the mixture. Details of the spark discharge unit 51 will be described later.

  In the following description, the axial center of the cylinder bore 14, that is, the direction along the center axis C of the spark plug is referred to as “ignition plug axial direction”, and is indicated by an arrow P in the figure. Further, the radial direction of the cylinder bore 14, that is, the radial direction of the spark plug 50 is simply referred to as “a spark plug radial direction” and is indicated by an arrow R in the drawing. Further, the circumferential direction of the cylinder bore 14, that is, the circumferential direction around the central axis C of the spark plug 50 is referred to as “piston circumferential direction”, and is indicated by an arrow G in the drawing.

  Also, the direction along the axis C of the cylinder bore 14, that is, the spark plug axial direction P, in which the piston 30 faces the ceiling wall 22 is indicated as "head side" and is indicated by an arrow U in the figure. Further, the direction opposite to the head side in the direction along the bore axis C is referred to as “crank side” and is indicated by an arrow D in the drawing.

  Furthermore, the cylinder bore axis C, that is, the direction perpendicular to the spark plug axis direction P and the direction perpendicular to the crankshaft direction S, that is, the direction in which the thrust force and the thrust reaction force act between the piston 30 and the cylinder wall 15, In the following description, it is indicated as “thrust direction” and indicated by an arrow T in the figure. The thrust direction T is a direction orthogonal to the cylinder row plane E.

  The space surrounded by the cylinder wall 15 of the cylinder block 12, the ceiling wall 22 of the cylinder head 20, and the top surface 32 of the piston 30 described above is a so-called “cylinder”. In the present embodiment, the cylinder includes a combustion chamber 40 formed in the cylinder head 20 in addition to the cylinder bore 14 formed in the cylinder block 12.

  In the cylinder, the air flowing from the intake port 24 and the fuel supplied by a fuel injection device (not shown) are mixed to form an air-fuel mixture. The spark plug ignites the air-fuel mixture formed in the cylinder, and the air-fuel mixture is ignited. The ignition timing of the spark plug and the discharge time are controlled by a control device (not shown).

  Next, the structure of the spark discharge part of the spark plug according to the present embodiment will be described with reference to FIGS. 1, 3, and 4. FIG. 3 is a side view of a spark discharge portion of the spark plug. FIG. 4 is a bottom view of the spark discharge portion of the spark plug. 3 and 4, only the main part related to the present invention is shown.

  As shown in FIGS. 3 and 4, the spark plug 50 is electrically connected to an insulator 56 (insulating) that insulates the center electrode 60 and the ground electrode 70 and a secondary coil (not shown) of the ignition coil. And projecting from the insulator 56 and exposed to the combustion chamber, the exposed portion 61 of the center electrode 60, the exposed portion 61 of the center electrode 60 and the spark plug in the axial direction P. The ground electrode 70 is (grounded), and the housing 58 is connected to the ground electrode 70 and holds the center electrode 60 via the insulator 56. The spark discharge portion 51 of the spark plug 50 includes an exposed portion 61 of the center electrode 60 and a ground electrode 70.

  The housing 58 is a substantially cylindrical metal member, and a male screw 59 is formed on the outer peripheral surface thereof. Corresponding to the male screw 59, the cylinder head 20 is formed with a female screw (not shown). The male screw 59 of the housing 58 is screwed into this female screw, and the spark plug 50 is attached to the cylinder head 20.

  The exposed portion 61 of the center electrode 60 is provided along the center axis of the spark plug, extends from the insulator 56 in the spark plug axial direction P (hereinafter referred to as the center electrode center portion), and the center electrode. It has the extension part 66 (henceforth a center electrode extension part) extended in the predetermined direction outside the spark plug radial direction R from the center part 64. FIG.

  The center electrode center portion 64 extends from the insulator 56 that is an insulator that electrically insulates the ground electrode 70 from the center electrode 60 and extends along the center axis of the spark plug, and is exposed to the combustion chamber 40. It is a columnar part. The center electrode central portion 64 extends from the insulator 56 so as to protrude in the spark plug axial direction P around the spark plug central axis C. The center electrode central portion 64 may have a quadrangular prism shape or a cylindrical shape.

  On the other hand, the center electrode extension 66 is a portion extending from the center of the ground electrode 70 in the spark plug radial direction R, and the boundary between the center electrode center 64 and the center electrode extension 66 is indicated by a dotted line in the drawing. Show. The center electrode extension 66 extends in a predetermined direction (hereinafter referred to as an extension direction and indicated by an arrow X in the drawing) in the spark plug radial direction R, and has a substantially rectangular parallelepiped shape.

  The center electrode center portion 64 and the center electrode extension portion 66 are integrally coupled, and constitute a portion 61 (hereinafter referred to as an exposed portion) of the center electrode 60 that protrudes from the insulator 56 and is exposed to the combustion chamber. ing. The exposed portion 61 of the center electrode 60 has a substantially rectangular parallelepiped shape extending outward from the spark plug radial direction R from the spark plug central axis C. The exposed portion 61 of the center electrode 60 is provided when the cylinder having a height in the spark plug axial direction P is linearly moved outward in the spark plug radial direction R, with the spark plug central axis C being the center. It is good also as the envelope shape of the cylinder group which arises.

  Of the central electrode central portion 64 and the central electrode extension portion 66, the surfaces facing the ground electrode 70 in the spark plug axial direction P are referred to as “opposing surfaces” and are denoted by reference numerals 64a and 66a, respectively. In addition, the end face of the center electrode extension 66 on the outer side in the spark plug radial direction R is referred to as an “outer end face” and is denoted by reference numeral 66 e.

  On the other hand, the ground electrode 70 is provided so as to project the spark plug axial direction P from the housing 58 to the crank side D, and is curved in the middle and extends in the spark plug radial direction R. A ground electrode center portion 74 that protrudes toward the center portion 64 in the spark plug axial direction P, and a ground electrode extension portion 76 that extends from the ground electrode center portion 74 outward in the spark plug radial direction R. Have.

  The leg portion 72 has a substantially L shape, and one end is coupled to the housing 58, and the tip end portion 73 on the opposite side faces the exposed portion 61 of the center electrode 60 in the spark plug axial direction P. The spark plug extends in the radial direction R. A ground electrode central portion 74 is provided so as to protrude in the spark plug axial direction P along the spark plug central axis from the front end 73 facing surface 73a of the front end 73 facing the exposed portion 61 of the center electrode 60. .

  The ground electrode central portion 74 is a columnar portion of the ground electrode 70 that protrudes from the surface facing the tip portion 73 and extends in the spark plug axial direction P about the spark plug central axis C. That is, the ground electrode center portion 74 is provided to face the center electrode center portion 64 in the spark plug axial direction P. The shape of the ground electrode central portion 74 may be a quadrangular prism shape or a cylindrical shape.

  On the other hand, the ground electrode extension portion 76 is a substantially rectangular parallelepiped portion extending outward from the spark plug radial direction R from the above-described ground electrode center portion 74. A boundary between the ground electrode center portion 74 and the ground electrode extension portion 76 is indicated by a dotted line in the figure. The ground electrode extension 76 extends in the same direction as the direction in which the center electrode extension 66 extends out of the spark plug radial direction R, that is, in the extension direction X. That is, the ground electrode extension 76 is provided to face the center electrode extension 66 in the spark plug axial direction P.

  The ground electrode center portion 74 and the ground electrode extension portion 76 are integrally coupled to each other and constitute a protruding portion 71 of the ground electrode 70. The protruding portion 71 is a portion that is provided on the center electrode 60 side in the spark plug axial direction P from the front end portion 73 facing surface 73 a of the leg portion 72. The protruding portion 71 has substantially the same shape as the exposed portion 61 of the center electrode 60 and faces the center electrode 60 in the spark plug axial direction P. Note that the protruding portion 71 of the ground electrode 70 is a straight line extending outwardly of the spark plug radial direction R from a cylinder (ground electrode central portion 74) having a height in the spark plug axial direction P, similarly to the exposed portion 61 of the center electrode 60. It is good also as the envelope shape of the cylinder group produced when it moves to a shape. The protruding portion 71 and the leg portion 72 are integrally coupled to constitute the ground electrode 70.

  Of the ground electrode central portion 74 and the ground electrode extension portion 76, the surfaces facing the center electrode 60 are referred to as “opposing surfaces” and are denoted by reference numerals 74 a and 76 a, respectively. In addition, the end face on the outer side of the spark plug radial direction R in the ground electrode extension 76 is referred to as an “outer end face” and is denoted by reference numeral 76 e.

  The center electrode center portion 64 and the ground electrode center portion 74 described above are provided along the spark plug center axis C and are opposed to each other in the spark plug shaft direction P. A gap (hereinafter referred to as a spark gap) with a predetermined interval is set between the facing surface 64a of the center electrode central portion 64 and the facing surface 76a of the ground electrode central portion 74. In the spark gap, when the secondary voltage applied to the spark plug 50 reaches the dielectric breakdown voltage, arc discharge is started, and a substantially linear electric spark is generated along the spark plug center axis C. .

  The exposed portion 61 of the center electrode 60 and the protruding portion 71 of the ground electrode 70 are provided opposite to each other in the spark plug axial direction P with the spark gap interposed therebetween. Specifically, the center electrode center portion 64 and the ground electrode center portion 74 are opposed to each other along the spark plug center axis C, and the center electrode extension portion 66 and the ground electrode extension portion 76 are opposed to the spark plug axial direction P. is doing. That is, the exposed portion 61 of the center electrode 60 and the protruding portion 71 of the ground electrode 70 are mutually opposite to a virtual plane (indicated by a two-dot chain line H in the drawing) that passes through the center of the spark gap and extends in the spark plug radial direction R. It is comprised in the shape used as plane symmetry.

  The width (indicated by a dimension J in the drawing) of the protrusion 71 of the ground electrode 70 in the direction orthogonal to the spark plug center axis C and the extending direction X is set to be the same as the width of the exposed portion 61 of the center electrode 60. The width is set smaller than the width of the leg portion 72 (indicated by a dimension K in the figure). As a result, the heat capacity of the ground electrode 70 adjacent to the spark gap is made smaller than that of a spark plug that does not have the protrusion 71 on the ground electrode 70. As a result, the flame generated in the spark gap due to the ignition of the air-fuel mixture is suppressed from being deprived of heat by the ground electrode 70 and extinguished.

  In the following description, the “spark gap interval” refers to the spark plug axial direction P of the spark gap formed between the facing surface 64 a of the center electrode center portion 64 and the facing surface 74 a of the ground electrode center portion 74. Is the interval. The interval of the spark gap is set in advance to a predetermined length according to the specifications of the internal combustion engine and the usage environment. In the initial state of the spark plug according to the present embodiment, the distance between the facing surface 64a of the center electrode center portion 64 and the facing surface 74a of the ground electrode center portion 74, that is, the gap L of the spark gap, and the facing of the center electrode extension portion 66. The distance between the surface 66a and the opposing surface 76a of the ground electrode extension 76 is set to be the same.

  In the spark plug 50 configured in this way, as shown in FIG. 1, the extension direction X in which the center electrode extension 66 extends from the center electrode center 64 is the exhaust side in the thrust direction T of the internal combustion engine. As described above, the cylinder head 20 of the internal combustion engine is mounted on the central portion 22a of the ceiling wall 22 that defines the shape of the combustion chamber 40.

  Next, an aspect of the electric spark emitted from the ignition plug in the internal combustion engine according to the present embodiment and the wear of the center electrode and the ground electrode will be described with reference to FIGS. 1 and 5 to 7. FIG. 5 is a side view of the spark discharge portion of the spark plug, and shows the state of the electric spark at the start of arc discharge. FIG. 6 is a side view of the spark discharge portion of the spark plug, and shows a state where the electric spark is caused to flow by the gas flow in the cylinder. FIG. 7 is a view showing a state in which wear of the spark plug center electrode and the ground electrode has progressed.

  As shown in FIG. 1, in the internal combustion engine 10, the intake port 24 and the exhaust port 26 of the cylinder head 20 are arranged in a cross-flow type, so that there is a high frequency in the cylinder from the intake stroke to the compression stroke. A tumble flow is formed. Due to this tumble flow, even at the ignition timing of the spark plug 50, in the combustion chamber 40 formed in the cylinder head 20, in the vicinity of the spark discharge portion 51 of the spark plug 50, the exhaust gas is exhausted from the intake side along the ceiling wall central portion 22a. The flow of gas such as air-fuel mixture toward the side occurs frequently.

  Therefore, in the combustion chamber 40, in the vicinity of the spark discharge portion 51 of the spark plug 50, the direction in which the gas such as the air-fuel mixture mainly flows (hereinafter referred to as the gas flow direction) is the internal combustion engine 10 according to the present embodiment. As shown by the arrow F1 in FIG. 5, the exhaust direction in the thrust direction T, that is, the direction from the intake side to the exhaust side. Corresponding to this gas flow direction, the spark plug 50 is arranged such that the center electrode extension 66 and the ground electrode extension 76 face the thrust direction T exhaust side of the internal combustion engine 10.

  When the secondary voltage is applied to the ignition plug by an ignition coil (not shown) and reaches the dielectric breakdown voltage, the internal combustion engine 10 with the ignition plug 50 arranged in this way reaches the dielectric breakdown voltage as shown in FIG. Arc discharge is started between the center electrode 74 and the ground electrode central portion 74, and a substantially linear electric spark A1 is generated along the center axis of the spark plug.

  At this time, since the gas flow from the intake side to the exhaust side exists in the combustion chamber 40 of the internal combustion engine 10 as described above, the substantially linear electric spark A1 is as shown in FIG. The thrust direction T is caused to flow toward the exhaust side, and immediately moves between the center electrode extension 66 and the ground electrode extension 76 to become an electric spark A2. The electric spark A2 is convex and curved in the gas flow direction F, and is maintained between the facing surface 66a of the center electrode extension 66 and the facing surface 76a of the ground electrode extension 76 until the end of the arc discharge. . Specifically, it is maintained between a portion of the opposing surface 66 a of the center electrode extension 66 that is closest to the outer end surface 66 e and a portion of the opposing surface 76 a of the ground electrode extension 76 that is closest to the outer end surface 76 e.

  In the spark plug 50, the electric spark (spark discharge) is generated in this manner, so that the exposed portion 61 of the center electrode 60 is gradually worn from the outer end surface 66 e side of the center electrode extension 66 as shown in FIG. 7. . At the same time, the protrusion 71 of the ground electrode 70 is worn out from the outer end surface 76 e side of the ground electrode extension 76. Thereby, the timing at which the wear proceeds at the center electrode center portion 64 and the ground electrode center portion 74 can be delayed as compared with a spark plug that does not have the center electrode extension portion 66 and the ground electrode extension portion 76, and the spark gap interval is increased. Expansion due to wear of the center electrode center portion 64 and the ground electrode center portion 74 can be suppressed.

  In addition, even if the wear of the center electrode extension 66 and the ground electrode extension 76 progresses and the distance between the opposing surfaces 66a and 76a increases, the arc discharge start in the spark plug is caused by the center electrode center 64 and the ground electrode. Since it is performed between the center part 74, it can suppress affecting the dielectric breakdown voltage requested | required of a spark plug.

  Further, as the wear progresses in this manner, the distance between the facing surface 66a of the center electrode extension 66 and the facing surface 76a of the ground electrode extension 76 is widened, and the discharge path of the electric spark is lengthened. The ignitability of the air-fuel mixture can also be improved.

  In the internal combustion engine according to this embodiment described above, the spark plug 50 is provided on the ceiling wall 22 that defines the shape of the combustion chamber 40, and the spark plug 50 is provided along the spark plug central axis C. A center electrode 60 having a center electrode center portion 64 and a center electrode extension portion 66 extending from the center portion 64 in a predetermined direction (extension direction) in the spark plug radial direction R, the center electrode center portion 64 and the ignition A ground electrode 70 provided to face the plug axis direction P, and the center electrode extension 66 is a gas flow direction in which the gas in the combustion chamber 40 mainly flows along the ceiling wall. It was supposed to be extended.

  Since the center electrode extension 66 extends in the gas flow direction, the electric spark generated between the center electrode center 64 and the ground electrode 70 at the start of arc discharge is in the direction in which the center electrode extension 66 extends. It is flowed at a high frequency and is maintained until the end of discharge in the extension. As a result, the center electrode 60 is depleted mainly from the center electrode extension 66, and in the center electrode center 64 where an electric spark is generated at the start of arc discharge, it is possible to delay the timing of the depletion. For this reason, it can suppress that the space | interval of the spark gap formed between the center electrode center part 64 and the ground electrode 70 expands early.

  In the present embodiment, the ground electrode 70 of the spark plug includes a center electrode center portion 74 provided opposite to the center electrode center portion 64 in the spark plug axial direction P, and a spark plug from the ground electrode center portion 74. A ground electrode extension portion 76 extending in the radial direction R is provided.

  By maintaining the electric spark flowing in the gas flow direction between the center electrode extension 66 and the ground electrode extension 76, the ground electrode 70 can be depleted from the ground electrode extension 76, and the ground electrode 70, the timing at which the wear of the center electrode center portion 74 facing the center electrode center portion 64 and the spark plug axial direction P progresses can be delayed. Thereby, it is possible to prevent the spark gap formed between the center electrode center portion 64 and the ground electrode center portion 74 from being expanded at an early stage.

  In the present embodiment, the intake port 24 and the exhaust port 26 are arranged in a cross-flow manner, and the spark plug 50 is provided in the center portion 22 a of the ceiling wall of the combustion chamber 40, and the center electrode extension portion 66. Is assumed to extend to the exhaust side in the thrust direction T.

  Since the internal combustion engine 10 has a cross flow arrangement, in the internal combustion engine 10 in which the port and the spark plug 50 are thus arranged, a tumble flow is formed at a high frequency from the intake stroke to the compression stroke. . Therefore, at the ignition timing, there is a gas flow from the intake side to the exhaust side along the ceiling wall 22 in the vicinity of the center electrode 60 and the ground electrode 70 disposed in the center part 22a of the ceiling wall of the combustion chamber 40. It will occur at a high frequency. Therefore, in the vicinity of the center electrode 60 and the ground electrode 70 of the spark plug 50, the direction in which the gas in the combustion chamber 40 mainly flows along the ceiling wall 22 (gas flow direction) is the exhaust side in the thrust direction T. ing.

  In this internal combustion engine 10, since the spark plug 50 is disposed so that the center electrode extension 66 extends to the exhaust side in the thrust direction T, when the arc discharge is started, the spark plug 50 is interposed between the center electrode center 64 and the ground electrode 70. The electric spark generated in the step moves in the direction in which the center electrode extension 66 extends due to the gas flow. The electric spark that has moved to the center electrode extension 66 is maintained between the center electrode extension 66 and the ground electrode 70 until the end of the arc discharge, and can be depleted from the center electrode extension 66. Thereby, the time when the wear of the center electrode central part 64 proceeds can be delayed, and the interval between the spark gaps can be prevented from expanding at an early stage.

  In addition, the spark plug 50 according to the present embodiment is provided with a center electrode center portion 64 provided along the spark plug center axis C and a predetermined direction in the spark plug radial direction R extending from the center electrode center portion 64. A center electrode 60 having a central electrode extension 74, and a ground electrode 70 provided to face the center electrode central portion 64 and the spark plug axial direction P.

  The spark plug is such that the predetermined direction in which the center electrode extension 66 extends is a gas flow direction in which the gas mainly flows along the ceiling wall 22 that defines the shape of the combustion chamber 40 of the internal combustion engine 10. 50 is mounted on the internal combustion engine 10 so that the electric spark generated between the center electrode central portion 64 and the ground electrode 70 at the start of arc discharge is in the gas flow direction, that is, the direction in which the center electrode extension 66 extends. The center electrode extension 66 is maintained until the discharge is completed.

  As a result, the center electrode 60 is depleted mainly from the center electrode extension 66, and in the center electrode center 64 where an electric spark is generated at the start of arc discharge, it is possible to delay the timing of the depletion. For this reason, it can suppress that the space | interval of the spark gap formed between the center electrode center part 64 and the ground electrode 70 expands early.

  Further, in the spark plug 50 according to the present embodiment, the ground electrode 70 includes a ground electrode center portion 74 provided opposite to the center electrode center portion 64 in the spark plug axial direction P, and the ground electrode center portion 74. And a ground electrode extension 76 extending in the spark plug radial direction R. By maintaining the electric spark flowing in the gas flow direction between the center electrode extension 66 and the ground electrode extension 76, the ground electrode 70 can be depleted from the ground electrode extension 76, and the ground electrode 70, the timing at which the wear of the center electrode center portion 74 facing the center electrode center portion 64 and the spark plug axial direction P progresses can be delayed. Thereby, it is possible to prevent the spark gap formed between the center electrode center portion 64 and the ground electrode center portion 74 from being expanded at an early stage.

  The structure of the spark plug according to the present embodiment will be described with reference to FIGS. FIG. 8 is a side view of a spark discharge portion of the spark plug. FIG. 9 is a bottom view of the spark discharge portion of the spark plug. In FIGS. 8 and 9, only the main parts related to the present invention are shown. The spark plug according to the present embodiment relates to the first embodiment in that the center electrode extension portion and the ground electrode extension portion each extend in a plurality of directions with a fixed angle in the circumferential direction of the spark plug. Unlike the spark plug, details will be described below. In addition, about the structure which is common in Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIGS. 8 and 9, the exposed portion 61B of the center electrode 60B of the spark plug 50B has a center electrode center portion 64 provided along the spark plug center axis C, and a spark plug diameter from the center electrode center portion 64. Outside the direction R, there are three center electrode extensions 66A, 66B, 66C extending in different directions (in the drawing, the extending directions are indicated by arrows X, Y, Z). The three center electrode extension portions 66A, 66B, 66C are arranged at three angles different from each other in the spark plug radial direction R at an angle (120 °) with respect to each other in the spark plug circumferential direction (indicated by an arrow G in the figure). It extends in the extending direction (direction) X, Y, Z.

  Each of the center electrode extension portions 66A, 66B, 66C is a substantially rectangular parallelepiped portion extending in the spark plug radial direction R of the exposed portion 61B of the center electrode 60B, and illustrates the boundary between the center electrode center portion 64 and the center electrode extension portion 66. Is indicated by a dotted line. Each of the center electrode extension portions 66A, 66B, 66C and the center electrode center portion 64 together constitute an exposed portion 61B of the center electrode 60B. The exposed portion 61B of the center electrode 60B is provided around the spark plug central axis C, and moves in a straight line to the outside of the spark plug radial direction R through a cylinder (center portion) having a height in the spark plug axial direction P. It is good also as the envelope shape of the cylinder group produced when it is made to do.

  On the other hand, the ground electrode 70B includes a ground electrode central portion 74 that protrudes in the spark plug axial direction P from the leg portion 72 toward the central electrode central portion 64, and an outer side of the spark plug radial direction R from the ground electrode central portion 74. And a ground electrode extension 76 extending in the direction.

  The ground electrode center portion 74 is a columnar portion of the ground electrode 70B that is provided so as to protrude from the surface 73a facing the tip portion 73 of the leg portion 72 and extends in the spark plug axial direction P about the spark plug center axis C. The center electrode central portion 64 is provided to face the spark plug axial direction P.

  Three ground electrode extension portions 76 are extended from the ground electrode center portion 74 to the outside of the spark plug radial direction R in different directions, like the center electrode 60B. Similarly to the center electrode 60B, the three ground electrode extensions 76 form an angle of 120 ° with respect to each other in the spark plug circumferential direction G, and three different orientations (extension directions) X, X of the spark plug radial direction R, respectively. It extends to Y and Z.

  Each ground electrode extension portion 76 is a substantially rectangular parallelepiped portion extending in the spark plug radial direction R in the ground electrode 70B, and a boundary with the ground electrode center portion 74 is indicated by a dotted line in the drawing. In the spark plug radial direction R, the three ground electrode extensions 76 extend in the same direction as the extension directions X, Y, and Z in which the three center electrode extensions 66A, 66B, and 66C extend. In other words, the three ground electrode extensions 76 are provided so as to face the three center electrode extensions 66A, 66B, 66C, respectively, in the spark plug axial direction P.

  The ground electrode center portion 74 and the three ground electrode extension portions 76A, 76B, and 76C integrally constitute a protruding portion 71B of the ground electrode 70B. The protruding portion 71B of the ground electrode 70B is opposed to the exposed portion 61B of the center electrode 60B in the spark plug axial direction P across a spark gap described later, and has the same shape as the exposed portion 61B of the center electrode 60B. The protruding portion 71B and the leg portion 72 are integrally coupled to constitute the ground electrode 70B.

  The center electrode central portion 64 and the ground electrode central portion 74 described above are provided along the spark plug central axis C and face the spark plug axial direction P. Between the center electrode center portion 64 and the ground electrode center portion 74, a gap having a predetermined interval (hereinafter referred to as a spark gap) is set. In the spark gap, when the secondary voltage applied to the spark plug 50B reaches the dielectric breakdown voltage, arc discharge is started, and a substantially linear electric spark is generated along the spark plug center axis C.

  The exposed portion 61B of the center electrode 60B and the protruding portion 71B of the ground electrode 70B face each other in the spark plug axial direction P across the spark gap. Specifically, the center electrode center portion 64 and the ground electrode center portion 74 are opposed to each other along the spark plug center axis C, and the three center electrode extensions 66A, 66B, 66C and the three ground electrode extensions 76A. , 76B, 76C are opposed to each other in the spark plug axial direction P. That is, the exposed portion 61B of the center electrode 60B and the protruding portion 71B of the ground electrode 70B are mutually opposite to a virtual plane (indicated by a two-dot chain line H in the drawing) that passes through the center of the spark gap and extends in the spark plug radial direction R. It is comprised in the shape used as plane symmetry.

  The spark plug 50 </ b> B configured in this manner is attached to the center portion 22 a of the ceiling wall of the combustion chamber 40 in the cylinder head 20. In the internal combustion engine 10 provided with the spark plug 50B, when a secondary voltage is applied to the spark plug 50B and the breakdown voltage is reached, a spark gap between the center electrode center portion 64 and the ground electrode center portion 74 is obtained. Arc discharge is started and a substantially linear electric spark is generated along the center axis C of the spark plug.

  At this time, the substantially linear electric spark A1 flows in any one of the three extending directions X, Y, and Z in which the center electrode extension 66 and the ground electrode extension 76 extend. For example, when the gas flow direction is the direction indicated by F2 in FIG. 9, the electric spark is caused to flow in the closest extension direction X among the three extension directions X, Y, Z, and the center electrode extension 66A. To the ground electrode extension 76 </ b> A facing the surface. The electric spark is maintained between the center electrode extension 66A and the ground electrode extension 76A until the end of the arc discharge.

  In this case, wear of the exposed portion 61B of the center electrode 60B proceeds from the outer end surface 66e side of the center electrode extension portion 66A. At the same time, wear of the ground electrode 70B proceeds from the outer end surface 76e side of the ground electrode extension 76A. As a result, it is possible to delay the timing at which the wear proceeds in the center electrode center portion 64 and the ground electrode center portion 74 as compared with the spark plug 50B that does not have the center electrode extension portion 66 and the ground electrode extension portion 76, and the gap of the spark gap. Can be prevented from expanding due to wear of the center electrode center portion 64 and the ground electrode center portion 74.

  As described above, in this embodiment, the center electrode extension portion and the ground electrode extension portion each extend in a plurality of directions X, Y, and Z with a certain angle in the spark plug circumferential direction G. Therefore, the electric spark flowed in the gas flow direction is moved in any one of a plurality of directions X, Y, and Z, and the center electrode extension portion and the ground electrode extension portion in the moved direction are moved. The electric spark can be maintained until the end of the arc discharge.

  As a result, when the spark plug 50B is mounted on the internal combustion engine 10, the center electrode extension is extended without matching the direction in which the center electrode extension portion and the ground electrode extension portion of the spark plug 50B extend to the gas flow direction of the internal combustion engine. Part and the ground electrode extension part, and the timing at which the wear proceeds at the center electrode center part 64 and the ground electrode center part 74 can be delayed. Thereby, it is possible to prevent the spark gap formed between the center electrode center portion 64 and the ground electrode center portion 74 from being expanded at an early stage.

  The structure of the spark plug according to the present embodiment will be described with reference to FIGS. FIG. 10 is a side view of a spark discharge portion of the spark plug. FIG. 11 is a bottom view of the spark discharge portion of the spark plug. FIG. 12 is a diagram for explaining changes in the discharge path of the electric spark and the sustaining voltage. In FIGS. 10 and 11, for the sake of easy explanation, some of the outline and hide lines are omitted, and the ground electrode extension is displayed by smudging.

  The spark plug according to the present embodiment is different from the spark plug according to the second embodiment in that the center electrode extension portion and the ground electrode extension portion are set so as to alternately extend in the circumferential direction of the spark plug. Details will be described. In addition, about the structure common to Example 1, 2, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIGS. 10 and 11, the three center electrode extension portions 66A, 66B, 66C provided on the center electrode 60C of the spark plug 50C are mutually connected in the spark plug circumferential direction G with the center electrode center portion 64 as the center. Each of them extends in three directions (extension directions) X, Y, and Z in different spark plug radial directions R at an angle of 120 °. On the other hand, the three ground electrode extension portions 76X, 76Y, and 76Z provided on the ground electrode 70C of the spark plug 50C are 120 with respect to each other in the spark plug circumferential direction G around the ground electrode center portion 74, like the center electrode 60B. Each of them extends in three different directions (extension directions) X2, Y2, and Z2 in the spark plug radial direction R with an angle of °.

  Three extension directions X, Y, Z in which the three center electrode extensions 66A, 66B, 66C extend from the center electrode center 64, and three ground electrode extensions 76X, 76Y, 76Z extend from the ground electrode center 74 3 The two extending directions X2, Y2, and Z2 are alternately set every 60 ° in the spark plug circumferential direction G. Specifically, each extending direction (orientation) is set every 60 ° in the order of X2, Y, Y2, Z, and Z2 with reference to X in the spark plug circumferential direction G. As described above, the extension directions X, Y, and Z of the center electrode extension portions 66A, 66B, and 66C and the extension directions X2, Y2, and Z2 of the ground electrode extension portions 76X, 76Y, and 76Z are alternately set, thereby extending the center electrode extension. And the ground electrode extension are necessarily adjacent in the spark plug circumferential direction G.

  In the spark plug 50C configured in this manner, the center electrode center portion 64 and the ground electrode center portion 74 are opposed to each other in the spark plug axial direction P, and a gap (spark gap) having a predetermined interval therebetween. Is set. In the spark gap, when the secondary voltage applied to the spark plug 50C reaches the breakdown voltage, arc discharge is started, and a substantially linear electric spark is generated along the spark plug center axis C.

  At this time, an electric spark generated between the spark gap, that is, the center electrode central portion 64 and the ground electrode central portion 74 is caused to flow outward in the spark plug radial direction R due to the gas flow flowing along the ceiling wall 22 of the combustion chamber 40. . For example, when the gas flow direction is the direction indicated by F3 in FIG. 11, the electric spark A1 has the closest direction to the gas flow direction F3 among the six extending directions X, X2, Y, Y2, Z, and Z2. Between the center electrode extension portion 66A and the ground electrode extension portion 76X, the spark plug moves in the radial direction R outward.

  In this case, as the electric spark moves outward in the spark plug radial direction R, the distance in the spark plug circumferential direction G between the center electrode extension 66A and the ground electrode extension 76X increases, and the discharge path of the electric spark is long. It becomes. The electric spark is maintained until the end of the arc discharge between the outer end surface 66e of the center electrode extension 66A and the outer end surface 76e of the ground electrode extension 76X.

  The spark plug 50C configured in this manner is necessary to maintain the spark discharge as shown in FIG. 12 when the electric spark discharge path becomes longer due to the electric spark flowing outside the spark plug radial direction R. The sustaining voltage Vk, which is a high voltage, is higher as shown by the broken line than when no electric spark is passed (shown by the solid line). The generation of electric sparks, that is, the start of arc discharge, is performed in the spark gap between the center electrode center portion 64 and the ground electrode center portion 74, and therefore does not affect the required dielectric breakdown voltage Vb.

  The electric spark is caused to flow outward in the spark plug radial direction R, and the discharge path becomes longer, so that the center electrode center portion 64 and the ground electrode center portion 74 are between the center electrode extension portion 66A and the ground electrode extension portion 76X. Compared to the above, the ignitability of the air-fuel mixture is improved.

  The center electrode 60B wears from the outer end surface 66e side of the center electrode extension 66A, and the ground electrode 70C wears from the outer end surface 76e side of the ground electrode extension 76X. Thereby, the timing at which the wear proceeds at the center electrode center portion 64 and the ground electrode center portion 74 can be delayed as compared with a spark plug that does not have the center electrode extension portion 66 and the ground electrode extension portion 76, and the spark gap interval is increased. Expansion due to wear of the center electrode center portion 64 and the ground electrode center portion 74 can be suppressed.

  As described above, in the present embodiment, the center electrode extension 66 and the ground electrode extension 76 are oriented so as to alternately extend in the spark plug circumferential direction G. 64, and the electric spark generated between the ground electrode center portion 74 is moved between the center electrode extension portion 66A and the ground electrode extension portion 76X adjacent to each other in the spark plug circumferential direction G by gas flow, for example, The discharge path can be increased. This improves the ignitability of the air-fuel mixture between the center electrode extension portion 66A and the ground electrode extension portion 76X, and at the center electrode center portion 64 and the ground electrode center portion 74, the gap of the spark gap is rapidly expanded. This can be suppressed.

  The configuration of the spark plug according to the present embodiment will be described with reference to FIGS. 1 and 13. FIG. 13 is a side view of a spark discharge portion of the spark plug. In the spark plug according to the present embodiment, the distance in the spark plug axial direction P between the center electrode extension portion and the ground electrode extension portion is set so as to increase from the spark plug central axis C toward the spark plug radial direction R. Unlike the spark plug according to the first embodiment, the details will be described below. In addition, about the structure which is common in Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 13, the exposed portion 61D of the center electrode 60D includes a center electrode center portion 64 provided along the spark plug center axis C and extending from the insulator 56 in the spark plug shaft direction P, and the center portion. And a center electrode extension 66D extending in a predetermined direction (extension direction X) outside the spark plug radial direction R. The boundary between the center electrode center portion 64 and the center electrode extension portion 66D is indicated by a dotted line in the figure. The center electrode extension 66D extends in a predetermined extension direction X in the spark plug radial direction R.

  A surface of the center electrode extension 66D that faces the ground electrode 70C in the spark plug axial direction P is referred to as an “opposing surface” and is denoted by reference numeral 66f. Further, the end face of the extension portion on the outer side of the spark plug radial direction R is referred to as “outer end face” and is denoted by reference numeral 66g. A virtual plane that passes through the center of the spark gap and extends in the spark plug radial direction R is indicated by a two-dot chain line H.

  The opposed surface 66f of the center electrode extension 66F has a planar shape and is formed so as to be positioned on the insulator 56 side as the distance from the center electrode center 64, that is, the spark plug center axis C, to the outside of the spark plug radial direction R increases. ing. That is, it is inclined with respect to the virtual plane H so that the distance from the virtual plane H increases as the distance from the center electrode central portion 64 in the extending direction X of the spark plug radial direction R increases.

  On the other hand, the ground electrode 70D includes a ground electrode central portion 74 that protrudes in the spark plug axial direction P from the leg portion 72 toward the central electrode central portion 64, and an outer side of the spark plug radial direction R from the ground electrode central portion 74. And a ground electrode extension 76D extending in a predetermined direction. The boundary between the ground electrode center portion 74 and the ground electrode extension portion 76D is indicated by a dotted line in the figure. The ground electrode extension portion 76D extends in the same direction as the extension direction X in which the center electrode extension portion 66D extends in the spark plug radial direction R.

  Of the ground electrode extension portion 76D, a surface facing the center electrode 60D is referred to as an “opposing surface” and is denoted by reference numeral 76f. In addition, an end face on the outer side of the spark plug radial direction R in the ground electrode extension portion 76D is referred to as an “outer end face” and is denoted by reference numeral 76g.

  The opposing surface 76f of the ground electrode extension 76D has a planar shape, like the center electrode 60D, and the distance from the virtual plane H as the distance from the ground electrode center 74 in the extension direction X in the spark plug radial direction R increases. Is inclined with respect to the virtual plane H so as to increase.

  The ground electrode center portion 74 and the ground electrode extension portion 76D integrally form a protruding portion 71D of the ground electrode 70D. The protrusion 71 </ b> D is a portion provided on the center electrode 60 </ b> D side in the spark plug axial direction P with respect to the distal end portion 73 facing surface 73 a of the leg portion 72. The protruding portion 71D has substantially the same shape as the exposed portion 61D of the center electrode 60D, and faces the center electrode 60D in the spark plug axial direction P. That is, the protruding portion 71D of the ground electrode 70D and the exposed portion 61D of the center electrode 60D are configured to be symmetrical with each other with respect to a virtual plane (indicated by a two-dot chain line H in the drawing). The projecting portion 71F and the leg portion 72 are integrally coupled to form a ground electrode 70D.

  The spark discharge part 51D of the spark plug 50D configured as described above has a gap (spark gap) between the opposed surface 64a of the center electrode central part 64 and the opposed surface 74a of the ground electrode central part 74. ) Is set. On the other hand, the distance in the spark plug axial direction P (hereinafter referred to as the extension gap) between the facing surface 66f of the center electrode extension 66D and the facing surface 76f of the ground electrode extension 76D is from the spark plug center axis C. Increasing in the extending direction X of the spark plug radial direction R increases.

  As shown in FIG. 1, the spark plug 50D has a direction (extension direction X) in which the center electrode extension 66F extends from the center electrode center portion 64, that is, the ground electrode extension portion 76F extends from the ground electrode center portion 74. The combustion chamber 40 is mounted on the center portion 22a of the ceiling wall so that the direction X faces the exhaust side in the thrust direction T of the internal combustion engine 10. When the internal combustion engine 10 in which the spark plug 50D is disposed in this way reaches the breakdown voltage, arc discharge is started in the spark gap between the center electrode center portion 64 and the ground electrode center portion 74, and ignition is performed. A substantially linear electric spark is generated along the central axis of the plug 50D.

  At this time, as indicated by an arrow F1 in the figure, there is a gas flow in the combustion chamber 40 of the internal combustion engine 10 from the intake side to the exhaust side. Is moved in the extension direction X, and moves to the extension gap between the center electrode extension 66D and the ground electrode extension 76D.

  As the electric spark moves between the central electrode extension 66D and the ground electrode extension 76D in the thrust direction T exhaust side, that is, in the extension direction X, the extension gap becomes larger, and the discharge path of the electric spark becomes longer accordingly. It will be a thing. The electric spark is maintained between the outer end surface 66g of the center electrode extension 66D and the outer end surface 76g of the ground electrode extension 76D until the end of the arc discharge.

  As the electric spark moves in the extension direction X between the center electrode extension 66D and the ground electrode extension 76D, the discharge path becomes longer, so that there is no gap between the center electrode extension 66D and the ground electrode extension 76D. The ignitability of the air-fuel mixture is improved as compared with that between the center electrode center portion 64 and the ground electrode center portion 74. As the electric spark is caused to flow in the extending direction X, the discharge path gradually becomes longer, so that the sustaining voltage does not increase rapidly.

  The center electrode 60D wears from the outer end surface 66g side of the center electrode extension 66D, and the ground electrode 70D wears from the outer end surface 76g side of the ground electrode extension 76D. As a result, it is possible to delay the timing at which the wear proceeds at the center electrode center portion 64 and the ground electrode center portion 74 as compared with a spark plug that does not have the center electrode extension portion 66D and the ground electrode extension portion 76D, and the spark gap interval is increased. Early expansion due to wear of the center electrode center portion 64 and the ground electrode center portion 74 can be suppressed.

  Note that the center electrode extension 66D and the ground electrode extension 76D according to the present embodiment are set so that the extension gap becomes larger as the distance from the extension direction X increases. The volume of the center electrode extension 66D and the ground electrode extension 76D is small for the length of the spark plug radial direction R compared to the exposed portion 61 and the protrusion 71 of the ground electrode 70 having a substantially rectangular parallelepiped shape. It has become a thing. Therefore, the heat capacities of the center electrode extension 66D and the ground electrode extension 76D through which the electric spark moves can be made smaller than that of the spark plug 50 extending in a substantially rectangular parallelepiped shape in the first embodiment, and the flame in the extension gap is reduced. The center electrode extension 66D and the ground electrode extension 76D are prevented from taking heat and extinguishing the flame.

  As described above, in this embodiment, the distance between the center electrode extension 66D and the ground electrode extension 76D in the spark plug axial direction P increases from the spark plug central axis C toward the spark plug radial direction R. It was set to be.

  As a result, the electric spark generated between the center electrode center portion 64 and the ground electrode center portion 74 is caused to flow outside the spark plug radial direction R between the center electrode extension portion 66D and the ground electrode extension portion 76D by gas flow. By moving and gradually increasing the discharge path, the ignitability of the air-fuel mixture can be improved without rapidly increasing the discharge sustaining voltage. While improving the ignitability of the air-fuel mixture between the center electrode extension part 66D and the ground electrode extension part 76D, the center electrode center part 64 and the ground electrode center part 74 are prevented from expanding the gap of the spark gap at an early stage. can do.

  The configuration of the spark plug according to the present embodiment will be described with reference to FIGS. 1 and 14. FIG. 14 is a side view of a spark discharge portion of the spark plug. In the spark plug according to the present embodiment, the distance between the center electrode extension portion and the ground electrode extension portion in the spark plug axial direction P is set larger than the distance between the center electrode center portion and the ground electrode center portion. Thus, unlike the spark plug according to the first embodiment, details will be described below. In addition, about the structure which is common in Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 14, the exposed portion 61E of the center electrode 60E is provided along the spark plug center axis C, and the center electrode center portion 64 provided to protrude from the insulator 56 in the spark plug axial direction P; A center electrode extension portion 66E extending from the center electrode center portion 64 in a predetermined direction (extension direction X) outside the spark plug radial direction R. The boundary between the center electrode center portion 64 and the center electrode extension portion 66E is indicated by a dotted line in the figure. The center electrode extension 66E extends in a predetermined extension direction X in the spark plug radial direction R.

  A surface of the center electrode extension 66E that faces the ground electrode 70E in the spark plug axial direction P is referred to as an “opposing surface” and is denoted by reference numeral 66h. Further, the end face of the extension portion on the outer side in the spark plug radial direction R is referred to as an “outer end face” and is denoted by reference numeral 66i. A virtual plane passing through the spark gap and extending in the spark plug radial direction R is indicated by a two-dot chain line H.

  The opposed surface 66h of the center electrode extension 66E has a planar shape and is offset from the opposed surface 64a of the center electrode central portion 64 on the insulator 56 side. That is, the facing surface 66h of the center electrode extension 66E is set to have a larger distance from the virtual plane H than the facing surface 64a of the center electrode central portion 64, and the spark plug radial direction R, that is, the virtual plane H is set. It extends in parallel to. A step is provided between the facing surface 64 a of the central electrode central portion 64 and the facing surface 64 a of the central electrode central portion 64. The thickness of the center electrode extension 66E in the spark plug axial direction P is smaller than that of the center electrode center 64.

  On the other hand, the ground electrode 70E includes a ground electrode center portion 74 that protrudes in the spark plug axial direction P from the leg portion 72 toward the center electrode center portion 64, and an outer side of the spark plug radial direction R from the ground electrode center portion 74. And a ground electrode extension 76E extending in a predetermined direction. A boundary between the ground electrode center portion 74 and the ground electrode extension portion 76E is indicated by a dotted line in the drawing. The ground electrode extension portion 76E extends in the same direction as the extension direction X in which the center electrode extension portion 66E extends in the spark plug radial direction R.

  A surface of the ground electrode extension 76E that faces the center electrode 60E is referred to as an “opposing surface” and is denoted by reference numeral 76h. In addition, the end face on the outer side of the spark plug radial direction R in the ground electrode extension portion 76E is referred to as an “outer end face” and is denoted by reference numeral 76i.

  The opposing surface of the ground electrode extension portion 76E has a planar shape, similar to the center electrode 60E, and is offset from the opposing surface 74a of the ground electrode center portion 74 toward the distal end portion 73 side of the leg portion 72. ing. That is, the facing surface 76 h of the ground electrode extension 76 </ b> E is set to have a greater distance from the virtual plane H than the facing surface 74 a of the ground electrode center portion 74. The opposing surface 76h of the ground electrode extension 76E extends in the spark plug radial direction R, that is, parallel to the virtual plane H. A step is provided between the facing surface 74a of the ground electrode central portion 74 and the facing surface 76h of the ground electrode extension 76E. The thickness of the ground electrode extension 76 </ b> E in the spark plug axial direction P is thinner than that of the ground electrode center 74.

  The ground electrode center portion 74 and the ground electrode extension portion 76E integrally form a protruding portion 71E of the ground electrode 70E. The protruding portion 71E has substantially the same L shape as the exposed portion 61E of the center electrode 60E, and faces the center electrode 60E in the spark plug axial direction P. That is, the protruding portion 71E of the ground electrode 70E and the exposed portion 61E of the center electrode 60E are configured to be symmetrical with each other with respect to a virtual plane (indicated by a two-dot chain line H in the drawing). The exposed portion 61E of the center electrode 60E and the protruding portion 71E of the ground electrode 70E can be configured by bending a wire. The protruding portion 71E and the leg portion 72 are integrally coupled to form a ground electrode 70E.

  In the spark discharge portion 51E of the spark plug 50E configured as described above, a spark gap having a predetermined interval is set between the facing surface 64a of the center electrode center portion 64 and the facing surface 74a of the ground electrode center portion 74. ing. In contrast, the gap in the spark plug axial direction P (hereinafter referred to as the extension gap) between the facing surface 66h of the center electrode extension 66E and the facing surface 76h of the ground electrode extension 76E is larger than the spark gap. It has become.

  As shown in FIG. 1, the spark plug 50E has a direction (extension direction) in which the center electrode extension 66E extends from the center electrode central portion 64, that is, a direction in which the ground electrode extension 76E extends from the ground electrode central portion 74. Is mounted on the center portion 22 a of the ceiling wall of the combustion chamber 40 so as to face the exhaust side in the thrust direction T of the internal combustion engine 10. When the internal combustion engine 10 in which the spark plug 50E is arranged in this way reaches the dielectric breakdown voltage, arc discharge is started between the center electrode central portion 64 and the ground electrode central portion 74, and the spark plug 50E A substantially linear electric spark is produced along the central axis.

  At this time, since the gas flow from the intake side to the exhaust side in the thrust direction T exists in the combustion chamber 40 of the internal combustion engine 10 as indicated by an arrow F1 in the drawing, the electric spark is generated in the thrust direction T. Is moved in the extension direction X, and moves to an extension gap between the center electrode extension 66E and the ground electrode extension 76E.

  At this time, when the electric spark moves from between the center electrode center portion 64 and the ground electrode center portion 74 to between the center electrode extension portion 66E and the ground electrode extension portion 76E, the interval in the spark plug axial direction P increases. The electric spark discharge path is long. The electric spark is maintained between the outer end surface of the center electrode extension 66E and the outer end surface of the ground electrode extension 76E until the end of the arc discharge.

  The electric spark generated between the center electrode center portion 64 and the ground electrode extension portion 76E (spark gap) moves between the center electrode extension portion 66E and the ground electrode extension portion 76E (extension portion gap), and discharges. As the path becomes longer, the ignitability of the air-fuel mixture is improved in the electric spark in the extension gap than in the spark gap. The electric spark between the central electrode central portion 64 and the ground electrode central portion 74 is slightly flowed in the extending direction X, and the discharge path becomes long. Therefore, the gas flowing along the ceiling wall 22 of the combustion chamber 40 The ignitability can be improved reliably by using the flow.

  The center electrode 60E wears from the outer end surface 66i side of the center electrode extension 66E, and the ground electrode 70E wears from the outer end surface 76i side of the ground electrode extension 76E. As a result, it is possible to delay the timing at which the wear proceeds at the center electrode center portion 64 and the ground electrode center portion 74 as compared with a spark plug that does not have the center electrode extension portion 66E and the ground electrode extension portion 76E, and the spark gap interval is increased. Expansion due to wear of the center electrode center portion 64 and the ground electrode center portion 74 can be suppressed.

  The center electrode extension 66E and the ground electrode extension 76E according to the present embodiment are thinner in the spark plug axial direction P than the center electrode center 64 and the ground electrode center 74, respectively. Therefore, as compared with the first embodiment in which the exposed portion 61 of the center electrode 60 and the protruding portion 71 of the ground electrode 70 have a substantially rectangular parallelepiped shape, the center electrode is extended for the length of the spark plug radial direction R. The volume of the portion 66E and the ground electrode extension portion 76E is small. Accordingly, the heat capacities of the center electrode extension 66E and the ground electrode extension 76E through which the electric spark moves can be reduced as compared with the above-described spark plug 50 extending in a substantially rectangular parallelepiped shape, and the flame in the extension gap This prevents the electrode extension 66E and the ground electrode extension 76E from taking heat and extinguishing the flame.

  As described above, in this embodiment, the distance between the center electrode extension 66E and the ground electrode extension 76E in the spark plug axial direction P is larger than the distance between the center electrode center 64 and the ground electrode center 74. It was assumed that it was set large.

  As a result, the electric spark generated between the center electrode center portion 64 and the ground electrode center portion 74 is caused to flow outside the spark plug radial direction R between the center electrode extension portion 66E and the ground electrode extension portion 76E by gas flow. By moving and increasing the discharge path, the ignitability of the air-fuel mixture can be improved. While improving the ignitability of the air-fuel mixture between the center electrode extension part 66E and the ground electrode extension part 76E, the center electrode center part 64 and the ground electrode center part 74 are prevented from expanding the gap of the spark gap at an early stage. can do.

  The structure of the spark plug according to the present embodiment will be described with reference to FIGS. FIG. 15 is a side view of a spark discharge portion of the spark plug. In the spark plug according to the present embodiment, the distance between the center electrode extension portion and the ground electrode extension portion in the spark plug axial direction P is set larger than the distance between the center electrode center portion and the ground electrode center portion. Thus, unlike the spark plug according to the first embodiment, details will be described below. In addition, about the structure which is common in Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 15, the exposed portion 61F of the center electrode 60F is provided along the spark plug center axis C and protrudes from the insulator 56 in the spark plug axial direction P, and the center electrode center. A center electrode extension 66F extending from the portion 64 in a predetermined direction (extension direction X) outside the spark plug radial direction R. The boundary between the center electrode center portion 64 and the center electrode extension portion 66F is indicated by a dotted line in the figure. The center electrode extension 66F extends in a predetermined extension direction X in the spark plug radial direction R. Of the center electrode extension 66F, the end surface on the outer side of the spark plug radial direction R is referred to as an “outer end surface” and is denoted by reference numeral 66k.

  The opposed surface 66h of the center electrode extension 66F has a planar shape, is continuous with the opposed surface 64a of the center electrode central portion 64, and extends in the spark plug radial direction R, that is, parallel to the virtual plane H. Yes. The thickness of the center electrode extension 66F in the spark plug axial direction P is set to be thinner than that of the center electrode center 64.

  On the other hand, the ground electrode 70F includes a ground electrode central portion 74 that protrudes in the spark plug axial direction P from the leg portion 72 toward the central electrode central portion 64, and an outer side of the spark plug radial direction R from the ground electrode central portion 74. A ground electrode extension portion 76F extending in a predetermined direction. The boundary between the ground electrode center portion 74 and the ground electrode extension portion 76F is indicated by a dotted line in the figure. The ground electrode extension portion 76F extends in the same direction as the extension direction X in which the center electrode extension portion 66F extends in the spark plug radial direction R. An end surface of the ground electrode extension portion 76F on the outer side in the spark plug radial direction R is referred to as an “outer end surface” and is denoted by reference numeral 76k.

  The facing surface 76a of the ground electrode extension portion 76F is continuous with the facing surface 74a of the ground electrode center portion 74 and extends in parallel to the spark plug radial direction R, that is, the virtual plane H, like the center electrode 60F. . The thickness of the ground electrode extension 76 </ b> F in the spark plug axial direction P is set to be thinner than that of the ground electrode center 74.

  The ground electrode center portion 74 and the ground electrode extension portion 76F integrally form a protruding portion 71F of the ground electrode 70F. The protruding portion 71F has substantially the same L shape as the exposed portion 61F of the center electrode 60F, and faces the center electrode 60F in the spark plug axial direction P. That is, the protruding portion 71F of the ground electrode 70F and the exposed portion 61F of the center electrode 60F are configured to be symmetrical with respect to a virtual plane (indicated by a two-dot chain line H in the drawing). The exposed portion 61F of the center electrode 60F and the protruding portion 71F of the ground electrode 70F can be configured by bending a wire. The projecting portion 71F and the leg portion 72 are integrally coupled to form a ground electrode 70F.

  In the spark discharge portion 51F of the spark plug 50F configured as described above, a spark gap having a predetermined interval is set between the facing surface 64a of the center electrode center portion 64 and the facing surface 74a of the ground electrode center portion 74. ing. In contrast, the gap in the spark plug axial direction P (hereinafter referred to as the extension gap) between the facing surface 66h of the center electrode extension 66F and the facing surface 76a of the ground electrode extension 76F is larger than the spark gap. It has become.

  As shown in FIG. 1, the spark plug 50 </ b> F extends in the direction X (extension direction) in which the center electrode extension 66 </ b> F extends from the center electrode center 64, i.e., the ground electrode extension 76 </ b> F extends from the ground electrode center 74. The combustion chamber 40 is attached to the center portion 22a of the ceiling wall so that the direction faces the exhaust side in the thrust direction T of the internal combustion engine 10. When the internal combustion engine 10 in which the spark plug 50F is arranged in this way reaches the dielectric breakdown voltage, arc discharge is started between the center electrode center portion 64 and the ground electrode center portion 74, and the spark plug 50F A substantially linear electric spark is produced along the central axis.

  At this time, since the gas flow from the intake side to the exhaust side in the thrust direction T exists in the combustion chamber 40 of the internal combustion engine 10 as indicated by an arrow F1 in the drawing, the electric spark is generated in the thrust direction T. Is moved in the extension direction X, and moves to an extension gap between the center electrode extension 66F and the ground electrode extension 76F. The electric spark is maintained between the outer end surface 66k of the center electrode extension 66F and the outer end surface 76k of the ground electrode extension 76F until the end of the arc discharge.

  The center electrode 60F is worn out from the outer end surface 66k side of the center electrode extension 66F, and the ground electrode 70F is worn out from the outer end surface 76k side of the ground electrode extension 76F. Thereby, the timing at which the wear proceeds in the center electrode center portion 64 and the ground electrode center portion 74 can be delayed as compared with the spark plug that does not have the center electrode extension portion 66F and the ground electrode extension portion 76F, and the gap of the spark gap is increased. Expansion due to wear of the center electrode center portion 64 and the ground electrode center portion 74 can be suppressed.

  As described above, in the spark plug 50F according to the present embodiment, the center electrode extension portion 66F and the ground electrode extension portion 76F are closer to the spark plug axial direction P than the center electrode center portion 64 and the ground electrode center portion 74, respectively. Since the thickness is set to be thin, the spark plug radial direction is larger than that in which the exposed portion 61 of the center electrode 60 and the protruding portion 71 of the ground electrode 70 are formed in a substantially rectangular parallelepiped shape as in the first embodiment. The volume of the center electrode extension 66F and the ground electrode extension 76F is small for the length of R, and the heat capacities of the center electrode extension 66F and the ground electrode extension 76F through which the electric spark moves extend in the above substantially rectangular parallelepiped shape. It can be made smaller than the spark plug 50. Thereby, it can suppress that the flame in an extension part gap loses heat and is extinguished by the center electrode extension part 66F and the ground electrode extension part 76F.

  In each of the above-described embodiments, the gas flow direction is the exhaust side in the thrust direction T of the internal combustion engine 10, but the gas flow direction is not limited to this. For example, when the internal combustion engine is configured to form a swirl in a specific direction in the cylinder and the spark plug is disposed on the peripheral edge of the ceiling wall of the combustion chamber, the gas flow direction is The direction along the cylinder wall, that is, the circumferential direction of the cylinder bore axis, is preferably disposed in the cylinder head in accordance with this direction.

  As described above, the present invention is useful for an ignition plug that generates an electric spark between a center electrode and a ground electrode, and is suitable for an internal combustion engine in which an ignition plug is provided on a ceiling wall that defines the shape of a combustion chamber. ing.

1 is a cross-sectional view illustrating a schematic configuration around a cylinder of an internal combustion engine according to a first embodiment. It is a figure which shows the arrangement | positioning relationship between the ignition plug and suction / exhaust valve which concerns on Example 1, and is the figure which looked at the ceiling wall of the cylinder head from the piston side. It is a side view of the spark discharge part of the ignition plug which concerns on Example 1. FIG. It is a bottom view of the spark discharge part of the ignition plug which concerns on Example 1. FIG. It is a side view of the spark discharge part of the ignition plug which concerns on Example 1, and is a figure which shows the state of the electric spark at the time of arc discharge start. It is a side view of the spark discharge part of the spark plug which concerns on Example 1, and is a figure which shows the state by which the electric spark was poured by the gas flow in a cylinder. It is a figure which shows the state which the abrasion of the spark plug center electrode which concerns on Example 1 and the ground electrode advanced. 6 is a side view of a spark discharge part of a spark plug according to Embodiment 2. FIG. 6 is a bottom view of a spark discharge part of a spark plug according to Embodiment 2. FIG. 6 is a side view of a spark discharge part of a spark plug according to Embodiment 3. FIG. 6 is a bottom view of a spark discharge part of a spark plug according to Embodiment 3. FIG. It is a figure explaining the change of the discharge path of an electric spark, and a discharge maintenance voltage. 6 is a side view of a spark discharge part of a spark plug according to Embodiment 4. FIG. It is a side view of the spark discharge part of the spark plug which concerns on Example 5. FIG. It is a side view of the spark discharge part of the spark plug which concerns on Example 6. FIG. It is a figure explaining depletion of the center electrode and the ground electrode in the spark discharge part of the spark plug which concerns on a prior art example. It is a figure explaining depletion of a center electrode and a ground electrode when an electric spark is made to flow by gas flow in a spark discharge part of a spark plug concerning a conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Cylinder block 14 Cylinder bore 20 Cylinder head 22 Combustion chamber ceiling wall 22a Ceiling wall center part 22c Ceiling wall peripheral part 24 Intake port 25 Intake valve 26 Exhaust port 27 Exhaust valve 30 Piston 40 Combustion chamber 50, 50B, 50C, 50D, 50E, 50F Spark plug 51, 51B, 51C, 51D, 51E, 51F Spark discharge part 56 Insulator 60, 60B, 60C, 60D, 60E, 60F Center electrode 64 Center electrode center part 66, 66A, 66B, 66C, 66D , 66E, 66F Center electrode extension 70, 70B, 70C, 70D, 70E, 70F Ground electrode 76, 76A, 76B, 76C, 76D, 76E, 76F, 76X, 76Y, 76Z Ground electrode extension Vb Dielectric breakdown voltage (2 Secondary voltage, required voltage)
Vk discharge sustaining voltage (secondary voltage)

Claims (6)

An internal combustion engine in which an intake port and an exhaust port are arranged in a crossflow manner, and an ignition plug is provided on a ceiling wall that defines the shape of the combustion chamber,
Spark plug
A center electrode having a center electrode center portion provided along the center axis of the spark plug, and at least one center electrode extension portion extending from the center electrode center portion in a predetermined direction in the spark plug radial direction; ,
A ground electrode central portion provided opposite to the center electrode central portion in the spark plug axial direction, and at least one ground electrode extension portion extending in the spark plug radial direction from the ground electrode central portion; A center electrode and a ground electrode provided to face the spark plug axial direction;
With
The spark plug is provided at the center of the ceiling wall of the combustion chamber,
The internal combustion engine, wherein the at least one center electrode extension portion extends from the center electrode center portion to a downstream side in a direction in which a gas in the vicinity of a spark discharge portion of the spark plug flows . The internal combustion engine according to claim 1 ,
An internal combustion engine characterized in that the center electrode extension portion and the ground electrode extension portion each extend in a plurality of directions with a predetermined angle in the circumferential direction of the spark plug. The internal combustion engine according to claim 2 ,
The internal combustion engine, wherein the center electrode extension portion and the ground electrode extension portion are alternately provided in the spark plug circumferential direction. The internal combustion engine according to claim 1 or 2 ,
An internal combustion engine characterized in that the distance between the center electrode extension portion and the ground electrode extension portion in the spark plug axial direction is set so as to increase from the spark plug central axis toward the outside in the spark plug radial direction. The internal combustion engine according to claim 1 or 2 ,
An internal combustion engine characterized in that the distance between the center electrode extension and the ground electrode extension in the spark plug axial direction is set larger than the distance between the center electrode center and the ground electrode center. The internal combustion engine according to any one of claims 1 to 5 ,
The internal combustion engine, wherein the center electrode extension and the ground electrode extension are set to be thinner in the spark plug axial direction than the center electrode center and the ground electrode center, respectively.

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