JP2010121566A - Ignition plug structure used under high frequency electric field - Google Patents

Abstract

An adverse effect of applying a voltage higher than a power supply voltage to an electronic device through an ignition coil connected to an ignition plug by preventing a back electromotive force from being generated in the ignition coil by a high-frequency electric field through a center electrode. To avoid.
A spark plug 1 of a spark ignition type internal combustion engine 100 according to the present invention includes a housing 13 made of a conductive material, a center electrode 14 insulated and attached in the housing 13, and a housing 13 apart from the center electrode 14. A spark ignition type comprising a ground electrode 15 provided at the lower end of the gas chamber and reacting a spark discharge generated between the center electrode 14 and the ground electrode 15 with a plasma generated in the combustion chamber 6 to ignite an air-fuel mixture. When the spark plug 1 of the internal combustion engine 100 is attached to the spark ignition internal combustion engine 100, the center electrode 14 is electromagnetically cut off by the housing 13 maintained at a ground potential capable of spark discharge.
[Selection] Figure 3

Description

  The present invention relates to a spark plug of a spark ignition type internal combustion engine mounted on a vehicle, particularly an automobile.

  Among the internal combustion engines mounted on vehicles, particularly automobiles, in a spark ignition internal combustion engine, that is, an engine that uses gasoline as fuel, the air-fuel mixture in the combustion chamber is ignited by the spark discharge of the ignition plug, and the air-fuel mixture is combusted. ing. For this reason, an ignition device including an ignition plug is required to reliably generate a spark discharge that burns the air-fuel mixture. For this reason, in order to compensate the spark discharge of the spark plug, a plasma atmosphere is generated in the discharge region of the spark plug, for example, as described in Patent Document 1, and arc discharge is performed in the plasma atmosphere. It is known that the air-fuel mixture in the combustion chamber is surely ignited and a stable flame can be obtained without applying a high voltage as compared with the above.

Incidentally, the spark plug generally includes a housing made of a metal such as iron, a center electrode that is insulated and attached in the housing, and a ground electrode that is provided at the lower end of the housing apart from the center electrode. In order to improve ignitability, such a spark plug has a structure in which the center electrode protrudes from the lower end of the housing and jumps into the combustion chamber when attached to the combustion chamber. Such an electrode structure is the same in Patent Document 1, and the main electrode corresponding to the center electrode protrudes from the lower end of the housing.
JP 2007-032349 A

  By the way, in order to improve the combustion, attempts have been made to increase the spark discharge of the spark plug. In this case, plasma is generated around the center electrode of the spark plug by forming a spark discharge in a high-frequency electric field formed by radiating a high-frequency electromagnetic wave from an antenna provided in the combustion chamber, specifically, a microwave output from a magnetron. To increase the number of radicals contained in the plasma, thereby improving the propagation of ignition and combustion.

  However, when the spark plug having the main electrode protruding from the lower end described in Patent Document 1 is used in the above configuration, the protruding portion of the main electrode can be an antenna. And when it becomes an antenna, the electric current by a microwave flows into the secondary winding of the ignition coil connected to the ignition plug, and a high voltage arises. As a result, a voltage is generated on the primary winding side of the ignition coil in accordance with the winding ratio, which is sufficiently higher than the power supply system (for example, the voltage is 12 V) of the electronic control device that controls the engine. In some cases, the IC and other electronic components constituting the electronic control device may be adversely affected.

  Therefore, a method using an isolator is conceivable in order to prevent an abnormal voltage generated in the ignition coil from being applied to the electronic control device by such a microwave, but an increase in system cost due to the introduction of the isolator is inevitable.

  Therefore, the present invention focuses on the above-described problems. By adopting a structure in which the center electrode does not function as an antenna without using an isolator, an electron is connected via an ignition coil connected to a spark plug. The purpose is to avoid the adverse effect that a voltage higher than the power supply voltage is applied to the device.

  The spark plug of the spark ignition type internal combustion engine according to the present invention made to solve the above-described problems includes a housing made of a conductive material, a center electrode that is insulated and attached in the housing, and a distance from the center electrode. Ignition of a spark ignition internal combustion engine having a ground electrode provided at the lower end of the housing and igniting an air-fuel mixture by reacting a spark discharge generated between the center electrode and the ground electrode with a plasma generated in the combustion chamber The plug is characterized in that when the center electrode is attached to the spark ignition internal combustion engine, the plug is electromagnetically cut off by a housing maintained at a ground potential capable of spark discharge.

  If it is such, it will become difficult to function as an antenna in the case where plasma is generated by, for example, microwaves, because the central electrode is electromagnetically cut off. Therefore, it is possible to avoid the adverse effect that a voltage higher than the power supply voltage is applied to the electronic device via the ignition coil connected to the ignition plug.

  In the above configuration, if the ground electrode is formed integrally with the housing at the lower end of the housing, the number of parts and the number of processing steps can be reduced.

  In addition, if the ground electrode extends from the lower end of the housing to a position facing the lower end of the center electrode, a spark discharge can be generated outside the housing, so that it easily reacts with the microwaves in the combustion chamber and is mixed. Easy to ignite.

  According to the present invention, by adopting a structure in which the center electrode does not easily function as an antenna, an adverse effect that a voltage higher than the power supply voltage is applied to the electronic device via the ignition coil connected to the ignition plug is avoided.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  An engine 100, which is a spark ignition type internal combustion engine, showing an enlarged mounting portion of the spark plug 1 in FIG. 1, is of a double overhead camshaft (DOHC) type, and has an intake port 2 opening 3 and an exhaust port 4 opening 5. However, they are opposed to each other centering on a spark plug 1 attached to substantially the center of the ceiling portion of the combustion chamber 6 and open at two locations per cylinder. That is, the engine 100 is attached to the cylinder block 7, and the camshafts 9 and 10 are attached to the intake side and the exhaust side of the cylinder head 8 forming the ceiling portion of the combustion chamber 6, respectively. The intake port 2 of the cylinder head 8 is opened and closed by an intake valve 11 that reciprocates when the camshaft 9 rotates, and the exhaust port 4 is opened and closed by an exhaust valve 12 that reciprocates when the camshaft 10 rotates. Is. In addition to the spark plug 1, an antenna 21 for generating plasma is attached to the ceiling portion of the combustion chamber 6.

  As shown in FIGS. 2 and 3, the spark plug 1 of this embodiment includes a housing 13 made of a conductive material, a center electrode 14 that is insulated and attached in the housing 13, and a housing 13 that is separated from the center electrode 14. And a ground electrode 15 provided at the lower end. That is, in the spark plug 1, the housing 13 supports the substantially cylindrical insulator 16, and the connection terminal 17 attached to the upper end of the insulator 16 has a center electrode 14 protruding from the lower end of the insulator 16 and a center shaft (not shown). The ground electrode 15 is integrally provided in the housing 13 at a position that is electrically connected and extends from the lower end of the housing 13 to a position facing the lower end of the center electrode 14. The insulator 16 insulates the center electrode 14 and the housing 13 that is an attachment portion to the engine 100, and also insulates the central shaft that is a connecting member between the center electrode 14 and the connection terminal 17, and has a substantially cylindrical shape. ing.

  The housing 13 has a cylindrical shape with an internal space sufficient to accommodate the insulator 16, and is made of, for example, stainless steel, which is a conductive material. The upper end portion of the housing 13 is squeezed inward in order to keep the insulator 16 in tight contact and maintain airtightness. Further, a male screw portion 18 for attachment to the cylinder head 8 is formed on the outer periphery of the lower portion from the central portion in the longitudinal direction. In addition, between the male screw part 18 and the upper end part, a metal shell 19 serving as a mounting base part when attached is formed with a larger outer diameter than the male screw part 18.

  The center electrode 14 is formed of, for example, a columnar metal material, and the lower end thereof is exposed from the insulator 16 and is set to a length that does not protrude from the lower end opening 20 in a virtual plane including the lower end surface of the housing 13. It is. That is, the center electrode 14 is located in an internal space formed at the lower end of the housing 13 and has a length that does not extend outward from the internal space. This means that when the spark plug 1 is attached to the engine 100, the housing 13 is maintained at the ground potential, so that the center electrode 14 is electromagnetically shielded in the internal space. is there.

  With respect to the center electrode 14, the ground electrode 15 is substantially L-shaped in a side view formed integrally with the lower end surface of the housing 13, and the tip thereof substantially coincides with the center axis of the center electrode 14. Extends to position. Since the ground electrode 15 is integrally provided in the housing 13 as described above, it is maintained at the same potential as the housing 13 during use.

  In such a configuration, the spark plug 1 is attached to each cylinder of the engine 100. In the engine 100, when the air-fuel mixture in the combustion chamber 6 is ignited by using the spark plug 1, the spark discharge of the spark plug 1 is caused to react with the plasma generated in the combustion chamber 6. The discharge is larger than the spark discharge in the case where the discharge does not react with the plasma. For this purpose, the engine 100 includes an antenna 21 in the combustion chamber 6 for generating plasma by microwaves. The antenna 21 is a horn type antenna, for example, and is attached to the ceiling of the combustion chamber 6. The antenna 21 has a conical horn shape, and its tip is closed by a dielectric 22 such as ceramics. A magnetron (not shown) is connected to the antenna 21. The microwave output from the magnetron is applied to the antenna 21. A high-frequency electric field is formed in the combustion chamber 6 by a microwave in a direction orthogonal to the spark discharge generated between the center electrode 14 and the ground electrode 15 of the spark plug 1.

  At the time of ignition, a spark discharge is generated in the spark plug 1 by an ignition coil (not shown), and a high-frequency electric field is generated by microwaves almost simultaneously with or immediately after the spark discharge to generate plasma. In this configuration, the air-fuel mixture is burned rapidly.

  Specifically, the spark discharge by the spark plug 1 becomes plasma in a high-frequency electric field, and the flame becomes large.

  This is because the flow of electrons due to the spark discharge and the ions and radicals generated by the spark discharge oscillate and meander due to the influence of the high-frequency electric field, resulting in a longer path length and the number of collisions with surrounding water and nitrogen molecules. This is due to a dramatic increase. Water molecules and nitrogen molecules that have been struck by ions and radicals become OH radicals and N radicals, and the surrounding gas that has been struck by ions and radicals is ionized, in other words, a plasma state. The flame will increase dramatically.

  As a result, the air-fuel mixture is ignited by the spark discharge increased by reacting with the high-frequency electric field, so that the ignition region is expanded and the two-dimensional ignition of only the spark plug 1 is changed to the three-dimensional ignition. Therefore, the initial combustion is stabilized, and the combustion rapidly propagates into the combustion chamber 6 as the radicals increase, and the combustion expands at a high combustion rate.

  According to this embodiment, the housing 13 made of a conductive material, the center electrode 14 insulated and attached in the housing 13, and the ground electrode 15 provided at the lower end of the housing 13 apart from the center electrode 14 are provided. A spark plug 1 of a spark ignition type internal combustion engine 100 that reacts a spark discharge generated between an electrode 14 and a ground electrode 15 with a plasma generated in a combustion chamber 6 to ignite an air-fuel mixture. 14 is attached to the spark ignition type internal combustion engine 100 with the ground electrode 15 extending into the combustion chamber 6 in a state of being located inside the lower end portion of the housing 13. In such a case, the center electrode 14 is electromagnetically cut off by the housing 13 maintained at a ground potential capable of spark discharge, and therefore is not exposed to a high frequency electric field, so that it becomes difficult to function as an antenna. For this reason, it is possible to avoid the adverse effect that a voltage higher than the power supply voltage is applied to the electronic device via the ignition coil connected to the ignition plug.

  Further, since the ground electrode 15 extends from the lower end of the housing 13 to a position facing the lower end of the center electrode 14 in a side view, even if the center electrode 14 is attached to the inner side of the lower end portion of the housing 13, In other words, since a spark discharge can be generated inside the high-frequency electric field generated by the microwave, the plasma is easily generated in the combustion chamber 6 and the air-fuel mixture can be easily ignited.

  The present invention is not limited to the above embodiment.

  In the above-described embodiment, the ground electrode 15 protrudes from the lower end of the housing 13 and the tip extends to a position directly below the center electrode 14, but the spark plug 1 of the spark ignition internal combustion engine 100 of the present invention is also described. As shown in FIGS. 4 and 5, the ground electrode 15 may be integrated with the housing 13 without protruding. That is, the portion surrounding the center electrode 14 of the housing 13 functions as the ground electrode 15. In such a case, since the ground electrode 15 is provided integrally with the housing 13, it is maintained at the same potential as the housing 13 during use. Further, due to the electrical property that the sharper part is more susceptible to discharge, the spark discharged from the center electrode 14 is discharged toward the inner corner of the lower end surface of the ground electrode 15.

  In addition, these spark plugs 1 of the present invention may be attached so that the lower end of the housing 13 protrudes from the ceiling surface of the combustion chamber 6. In this case, since the housing 13 is maintained at the ground potential, the center electrode 14 is maintained in an electromagnetically cut off state.

  Further, in this embodiment, a horn type antenna in which the tip facing the combustion chamber is covered with a dielectric is used as an antenna for generating plasma by microwaves. It may be made of a dielectric such as. Further, instead of the horn antenna, a monopole antenna such as an inverted L-shaped antenna may be attached to the ceiling of the combustion chamber. In the case of using a monopole antenna as the antenna in the present embodiment, considering the heat resistance of the tip portion facing the combustion chamber, the antenna should be made of high heat resistance such as tungsten or the antenna. It is conceivable to use such as coating with a dielectric.

  In addition to the above-described magnetron, the high frequency generation source may be a traveling wave tube or the like, and may further include a semiconductor microwave oscillation circuit.

  Other specific configurations of the respective parts are not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

1 is an enlarged sectional view showing a main part of an engine to which an embodiment of the present invention is applied. The front view of the ignition plug of the embodiment. Sectional drawing of the ignition plug of the embodiment. The front view of the ignition plug which shows other embodiment of this invention. Sectional drawing of the ignition plug of the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Engine 1 ... Spark plug 13 ... Housing 14 ... Center electrode 15 ... Ground electrode

Claims (3)

A spark discharge generated between the center electrode and the ground electrode, comprising: a housing made of a conductive material; a center electrode insulated from the housing; and a ground electrode provided at a lower end of the housing apart from the center electrode. An ignition plug for a spark ignition internal combustion engine that reacts with plasma generated in a combustion chamber to ignite an air-fuel mixture,
When the center electrode is attached to the spark ignition internal combustion engine, the spark plug of the spark ignition internal combustion engine is electromagnetically cut off by a housing maintained at a ground potential capable of spark discharge. The spark plug of the spark ignition type internal combustion engine according to claim 1, wherein the ground electrode is formed integrally with the housing at a lower end of the housing. The spark plug for a spark ignition type internal combustion engine according to claim 1, wherein the ground electrode extends from the lower end of the housing to a position facing the lower end of the center electrode.

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