JP2017227164A - Ignitor of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively improve ignitability by suppressing the wear of a center electrode caused by a concentration of high power.SOLUTION: An ignitor of an internal combustion engine in which a piston 13 is reciprocally accommodated in a cylinder 12 of a cylinder block 11, and a cylinder head 14 is arranged at an upper part of the cylinder block 11 comprises: a housing 21 attached to the cylinder head 14; an insulation insulator 22 which is accommodated and held in the housing 21; a columnar center electrode 24 which is accommodated in the insulation insulator 22 at its upper end side, exposed from the insulation insulator 22 at its lower end side, and protruded into the cylinder 12; and a recessed hole 25 which is recessively formed in a piston axial direction from an apex face of the piston 13, receives at least a part of the center electrode 24 at a top dead point of the piston 13 with a prescribed air gap, and generates spark discharge between its internal face and an external face of the center electrode 24 when a voltage is applied to the center electrode 24.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an ignition device for an internal combustion engine, and more particularly to an ignition device for an internal combustion engine provided with an ignition plug.

  In general, this type of spark plug includes a housing attached to a cylinder head, an insulator accommodated and held in the housing, a center electrode protruding from the insulator, a bent shape formed in a substantially L shape, and a center electrode. A ground electrode facing the tip is provided.

  In such a spark plug, a gas mixture is ignited by applying a voltage to the center electrode and generating a spark discharge in a gap (hereinafter also referred to as a gap) between the center electrode and the ground electrode (for example, Patent Documents 1 and 2).

JP 2006-062865 A JP 2014-175094 A

  By the way, in the spark plug, in order to improve the ignitability of the air-fuel mixture, it is necessary to increase the arc energy of the spark discharge in order to promote the formation of a large flame nucleus in the gap. Further, when increasing the EGR rate in order to improve exhaust emission performance, it is necessary to increase the voltage value applied to the center electrode in order to effectively prevent engine misfire.

  However, since the tip of the center electrode that generates spark discharge is minute, if high power concentrates on such a tip, the gap expands due to the progress of wear, and there is a problem that misfire is likely to occur.

  An object of the technology of the present disclosure is to effectively improve ignitability by suppressing wear of the center electrode due to concentration of high power.

  The technology of the present disclosure is an ignition device for an internal combustion engine in which a piston is housed in a cylinder of a cylinder block so as to be reciprocally movable and a cylinder head is disposed on an upper portion of the cylinder block, and is attached to the cylinder head. A housing, an insulator in which at least a part thereof is accommodated and held in the housing, and an upper end side thereof is accommodated in the insulator, and a lower end side thereof is exposed from the insulator and protrudes into the cylinder. A columnar center electrode, and recessed from the top surface of the piston in the axial direction of the piston, and receiving at least a part of the center electrode with a predetermined gap at the top dead center of the piston, A concave hole for generating a spark discharge between the inner surface of the electrode and the outer surface of the central electrode when a voltage is applied to the electrode.

  The concave hole includes a cylindrical hole portion that is recessed from the top surface of the piston in the axial direction of the piston, and the cylindrical hole portion is located at a predetermined crank angle position on the advance side of the piston from the top dead center. Sometimes it is preferable to receive at least a portion of the center electrode and generate a spark discharge between the inner surface of the center electrode and the outer surface of the center electrode when a voltage is applied to the center electrode.

  The concave hole further includes a spherical hole portion that is recessed in a hemispherical shape from the lower end of the cylindrical hole portion, and when the piston reaches top dead center, the lower end of the center electrode is connected to the cylindrical hole portion and the spherical hole. When a voltage is applied to the center electrode, the spark discharge is preferably generated between at least one inner surface of the cylindrical hole portion or the spherical hole portion and the outer surface of the center electrode. .

  In addition, the lower surface of the cylinder head facing the cylinder may be formed flat, and a recess may be formed in the other portion of the top surface of the piston except the recessed hole.

  Moreover, the said recessed part may be recessedly provided in the annular | circular shape in the periphery of the top surface of the said piston.

  According to the technology of the present disclosure, it is possible to effectively improve the ignitability by suppressing wear of the center electrode due to concentration of high power.

It is a typical fragmentary sectional view showing the ignition device of the internal-combustion engine concerning one embodiment of the present invention. It is a typical fragmentary sectional view explaining the principal part of the ignition device of the internal combustion engine which concerns on one Embodiment of this invention. In the ignition device for an internal combustion engine according to an embodiment of the present invention, it is a schematic diagram illustrating a state in which the air-fuel mixture in the combustion chamber is ignited at a predetermined crank angle position on the advance side. In the ignition device for an internal combustion engine according to one embodiment of the present invention, it is a schematic diagram illustrating a state in which an air-fuel mixture in a combustion chamber is ignited near the compression top dead center of a piston. It is a typical fragmentary sectional view which shows the ignition device of the internal combustion engine which concerns on other embodiment. It is a typical fragmentary sectional view which shows the ignition device of the internal combustion engine which concerns on other embodiment.

  Hereinafter, an ignition device for an internal combustion engine according to an embodiment of the present invention will be described with reference to the accompanying drawings. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  As shown in FIG. 1, in a cylinder block 11 of the engine 10, a piston 13 is accommodated in a cylinder 12 so as to be reciprocally movable. A cylinder head 14 is fixed to the upper part of the cylinder block 11 with a head bolt (not shown).

  The cylinder head 14 is provided with an intake port 15 and an exhaust port 16. The cylinder block 14 is provided with an injector 30 for injecting fuel (gasoline or natural gas such as LPG, LNG, CNG) into the intake port 15. The cylinder head 14 includes an intake valve 18 that introduces an air-fuel mixture from the intake port 15 into the combustion chamber 17 by an opening / closing operation, and an exhaust valve that extracts exhaust gas from the combustion chamber 17 into the exhaust port 16 by an opening / closing operation. 19 is provided. The lower surface of the cylinder head 14 that forms the upper wall of the combustion chamber 17 is substantially flat, and a female screw hole 14A for attaching the spark plug 20 is formed in the center thereof.

  Next, a detailed configuration of the spark plug 20 will be described with reference to FIG. The spark plug 20 of the present embodiment includes at least a housing 21, an insulator 22, a connection terminal 23, and a center electrode 24.

  The housing 21 is formed in a substantially cylindrical shape, and a hexagonal portion 21 </ b> A having a larger diameter than the female screw hole 14 </ b> A of the cylinder head 14 is provided on the upper end side thereof. Further, a male screw portion 21B that is screwed into the female screw hole 14A is provided on the lower end side of the housing 21. Further, a gasket (not shown) that seals the gap between the cylinder head 14 and the housing 21 is provided between the hexagonal portion 21 </ b> A and the male screw portion 21 </ b> B of the housing 21.

  The insulator 22 is formed in a substantially cylindrical shape. With the upper end portion 22B and the lower end portion 22A exposed from the housing 21, the other portions excluding the upper end portion 22B and the lower end portion 22A are the cylinders of the housing 21. It is housed and held inside. A lower end 22 </ b> A of the insulator 22 protrudes into the combustion chamber 17. A connection terminal 23 is held at the upper end 22B of the insulator 22.

  The connection terminal 23 is housed in the cylinder of the insulator 22 at the lower end side and protrudes from the insulator 22 at the upper end side. An external power source is connected to the upper end side of the connection terminal 23 via a cable (not shown). Further, the lower end side of the connection terminal 23 is electrically connected to the upper end side of the center electrode 24 via a middle shaft (not shown).

  The center electrode 24 is formed in a substantially cylindrical shape having a diameter larger than that of a general spark plug electrode, and other portions except for the lower end portion 24 </ b> A are accommodated and held in the cylinder of the insulator 22. That is, the lower end portion 24 </ b> A of the center electrode 24 is provided so as to protrude in the axial direction of the cylinder 12 from the lower end portion 22 </ b> A of the insulator 22 toward the substantially central portion of the top surface of the piston 13 in the combustion chamber 17.

  In the present embodiment, the piston 13 is provided with an annular recess 26 formed by obliquely notching the peripheral edge of the top surface toward the outer surface. Further, a ground electrode concave hole 25 that can receive the lower end portion 24 </ b> A of the center electrode 24 protruding into the combustion chamber 17 is formed in a substantially central portion of the piston 13.

  More specifically, the ground electrode concave hole 25 has a cylindrical hole portion 25A that is recessed in a cylindrical shape at a predetermined depth from the substantially central portion of the top surface of the piston 13 and a hemispherical shape from the lower end of the cylindrical hole portion 25A. And a hollow spherical hole 25B.

  When the piston 13 is located at the top dead center, the hole diameter (diameter) D of the cylindrical hole portion 25A is such that the lower end portion 22A of the insulator 22 and the lower end portion 24A of the center electrode 24 are received therein, It is formed slightly larger than the outer diameter of the lower end portion 24A so that a minute gap G is secured between the peripheral surface and the outer peripheral surface of the lower end portion 24A of the center electrode 24. The gap G is preferably set to a value approximately equal to a gap of a general spark plug (gap between the center electrode and the ground electrode). The radius R of the spherical hole portion 25B is preferably set to a value that is half (1/2) the hole diameter D of the cylindrical hole portion 25A.

  The depth L of the cylindrical hole portion 25A is such that the lower end portion 24A of the center electrode 24 is at a predetermined crank angle position (for example, about 25 to 30 degrees) on the advance side before the piston 13 reaches the top dead center. When the piston 13 reaches the top dead center, the tip of the lower end 24A of the center electrode 24 is the boundary between the cylindrical hole 25A and the spherical hole 25B when received at the upper end of the cylindrical hole 25A (see FIG. 3). (See FIG. 4). That is, the lower end 24A of the center electrode 24 is reliably received in the ground electrode recess 25 over a predetermined crank angle range before and after the top dead center of the piston 13.

  Next, based on FIG.3, 4, the effect by the ignition device of the internal combustion engine which concerns on this embodiment is demonstrated.

  FIG. 3 shows a state in which the air-fuel mixture in the combustion chamber 17 is ignited at a predetermined crank angle position (for example, about 25 to 30 degrees) on the advance side when the ignition timing is advanced, such as during high-load operation of the engine 10. FIG. When the piston 13 reaches a predetermined crank angle position (for example, about 25 to 30 degrees) on the advance side with respect to the top dead center, the lower end portion 24A of the center electrode 24 is in the cylindrical hole portion 25A of the ground electrode concave hole 25. It will be in the state received by the upper end side. When a high voltage is applied to the center electrode 24 from an external power source (not shown) through the connection terminal 23 in this state, a plurality of spark discharges are generated between the outer peripheral surface of the center electrode 24 and the inner peripheral surface of the cylindrical hole portion 25A. Thus, the air-fuel mixture is effectively ignited.

  In this way, by generating a plurality of fireworks discharges between the outer peripheral surface of the center electrode 24 having a large area and the inner peripheral surface of the cylindrical hole portion 25A that surrounds the central electrode 24, the electric power concentration at the extreme portion of the center electrode 24 is achieved. Will be prevented. Thereby, the gap expansion due to wear of the center electrode 24 is effectively suppressed, and the ignition performance at the time of advance can be reliably improved.

  FIG. 4 is a diagram illustrating a state in which the air-fuel mixture in the combustion chamber 17 is ignited near the compression top dead center of the piston 13. When the piston 13 reaches the vicinity of the compression top dead center, the lower end portion 24 </ b> A of the center electrode 24 is entirely received in the ground electrode recess 25. When a high voltage is applied to the center electrode 24 from an external power source (not shown) through the connection terminal 23 in this state, the outer peripheral surface of the center electrode 24 and the inner periphery of the ground electrode concave hole 25 (the cylindrical hole portion 25A and the spherical hole portion 25B). A plurality of spark discharges are generated between the surface and the air-fuel mixture to be ignited effectively.

  As described above, a plurality of spark discharges are generated between the outer peripheral surface of the center electrode 24 having a large area and the inner peripheral surface of the ground electrode concave hole 25 (the cylindrical hole portion 25A and the spherical hole portion 25B) surrounding the central electrode 24. Thus, as in the above-described advance angle, the power concentration at the center electrode 24 is prevented from being concentrated, and gap expansion due to wear of the center electrode 24 can be effectively suppressed, and compression top dead center is ignited. The performance can also be improved reliably.

  Further, since the annular recess 26 is provided on the peripheral edge of the top surface of the piston 13, when the piston 13 approaches the compression top dead center, a part of the air-fuel mixture flows into the annular recess 26. Thereby, even in the combustion chamber 17 having a flat ceiling surface, an excessive increase in the compression ratio is suppressed, and the occurrence of knocking can be effectively prevented.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, the shape of the annular recess 26 is not limited to the above embodiment, and may be provided between the peripheral edge of the top surface of the piston 13 and the ground electrode recess 25 as shown in FIG. Moreover, the shape is not limited to an annular shape, and a plurality of recesses may be provided individually.

  In addition, as shown in FIG. 6, the tip side of the center electrode 23 may be projected in a hemispherical shape so as to follow the shape of the spherical hole 25B. By comprising in this way, the space | gap of the center electrode 23 and the ground electrode recessed hole 25 is equalize | homogenized as a whole, and ignitability can be stabilized more.

  Further, the shape of the combustion chamber 17 is not limited to the above embodiment, and may be a combustion chamber having another shape such as a pent roof type.

  Further, the fuel injection type is not limited to the premixing type injected into the intake port 15, and may be a direct injection type injected into the combustion chamber 17.

  The engine 10 is not limited to a gasoline engine or a gas engine, and can be widely applied to other internal combustion engines that use fuel that can be ignited by the spark plug 20 of the above-described embodiment.

DESCRIPTION OF SYMBOLS 10 Engine 11 Cylinder block 12 Cylinder 13 Piston 14 Cylinder head 15 Intake port 16 Exhaust port 17 Combustion chamber 18 Intake valve 19 Exhaust valve 20 Spark plug 21 Housing 22 Insulator 23 Connection terminal 24 Center electrode 25 Ground electrode concave hole 25A Cylindrical hole part 25B Spherical hole 26 Annular recess 30 Injector

Claims (5)

An internal combustion engine ignition device in which a piston is housed in a cylinder of a cylinder block so as to be capable of reciprocating movement, and a cylinder head is disposed above the cylinder block,
A housing attached to the cylinder head;
An insulator in which at least a part thereof is accommodated and held in the housing;
A columnar center electrode whose upper end is accommodated in the insulator and whose lower end is exposed from the insulator and protrudes into the cylinder;
The piston is recessed from the top surface of the piston in the piston axial direction, and at least a part of the center electrode is received with a predetermined gap at the top dead center of the piston, and a voltage is applied to the center electrode. An internal combustion engine ignition device characterized by comprising: and a concave hole for generating a spark discharge between an inner surface thereof and an outer surface of the central electrode. The concave hole includes a cylindrical hole portion that is recessed in the piston axial direction from the top surface of the piston, and the cylindrical hole portion is located at a predetermined crank angle position on the advance side of the top dead center. The ignition device for an internal combustion engine according to claim 1, wherein at least a part of the center electrode is received, and when a voltage is applied to the center electrode, a spark discharge is generated between an inner surface of the center electrode and an outer surface of the center electrode. . The concave hole further includes a spherical hole portion that is recessed in a hemispherical shape from the lower end of the cylindrical hole portion, and when the piston reaches top dead center, the lower end of the center electrode is formed between the cylindrical hole portion and the spherical hole portion. The spark discharge is generated between at least one inner surface of the cylindrical hole portion or the spherical hole portion and an outer surface of the central electrode when a voltage is applied to the central electrode, which is positioned at the boundary. Ignition device for internal combustion engine. The lower surface of the cylinder head that faces the cylinder is formed in a flat shape, and a recess is formed in the other portion of the top surface of the piston except for the recessed hole. Ignition device for internal combustion engine. The ignition device for an internal combustion engine according to claim 4, wherein the recess is annularly provided in a periphery of the top surface of the piston.

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