Ignition device for spark-ignition internal combustion engine

It is configured such that plasma generated at a time of ignition should diffuse over an entire combustion chamber in a spark ignition type internal combustion engine in order to improve fuel efficiency. An ignition device for a spark ignition type internal combustion engine is provided including an ignition plug and a transmission antenna provided in the vicinity of the ignition plug and adapted to transmit an electromagnetic wave to a combustion chamber. The ignition device allows a spark discharge generated between a central electrode and a ground electrode of the ignition plug to react with an electric field created via the transmission antenna in the combustion chamber so as to generate plasma and ignite fuel air mixture. A receiving antenna is arranged on a combustion chamber-facing surface of at least one of an intake valve and an exhaust valve, and is adapted to receive the electromagnetic wave transmitted from the transmission antenna.

TECHNICAL FIELD

The present invention relates to an ignition device that is attached to a spark ignition type internal combustion engine that allows a spark discharge by an ignition plug to react with an electric field created in a combustion chamber so as to generate plasma, thereby igniting fuel air mixture.

BACKGROUND ART

Conventionally, in a spark ignition type internal combustion engine that is installed in a vehicle, especially an automobile, a spark discharge between a central electrode and a ground electrode of an ignition plug is employed to ignite fuel air mixture in a combustion chamber at each ignition timing. In recent years, plasma generated by a microwave in combination with the spark discharge is employed so as to improve ignition efficiency of the spark discharge as disclosed in, for example, Japanese Unexamined Patent Application, Publication No. 2010-1827.

In the ignition device disclosed in Japanese Unexamined Patent Application, Publication No. 2010-1827, an antenna is arranged in the vicinity of the ignition plug so as to emit a microwave to the combustion chamber, thereby forming a plasma generation region. A magnetron is connected to the antenna so as to emit the microwave toward the vicinity of a discharge gap of the ignition plug, thereby forming the plasma generation region in the vicinity of the discharge gap.

With such configuration, fuel air mixture is ignited due to spark discharge occurred in the plasma generation region during the expansion stroke, and thereby enlarging a flame kernel. Furthermore, the flame kernel reacts with radicals in the plasma to promote combustion. However, with the ignition device disclosed in Japanese Unexamined Patent Application, Publication No. 2010-1827, the plasma generation region can be formed only in the vicinity of the ignition plug. As a result, a good combustion may be attained only in the vicinity of the ignition plug. This means that the propagation process of combustion to the entire combustion chamber is almost same to that of the conventional spark ignition type internal combustion engine in which plasma is not employed. Therefore, it has been difficult to expect the improvement of the fuel efficiency by the plasma.

THE DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

The present invention has been made in view of the above described circumstances, and it is an object of the present invention to improve fuel efficiency by configuring such that plasma should diffuse over the entire combustion chamber.

Means for Solving the Problems

In accordance with the present invention, there is provided an ignition device for a spark ignition type internal combustion engine, including: an ignition plug; and a transmission antenna that is provided in the vicinity of the ignition plug and is adapted to transmit an electromagnetic wave to an combustion chamber, wherein the ignition device allows a spark discharge generated between a central electrode and a ground electrode of the ignition plug to react with an electric field created via the transmission antenna in the combustion chamber so as to generate plasma and ignite fuel air mixture, characterized in that the ignition device further includes receiving antenna arranged on a combustion chamber-facing surface of at least one of an intake valve and an exhaust valve, and is adapted to receive the electromagnetic wave transmitted from the transmission antenna.

According to the configuration described above, the receiving antenna receives the electromagnetic wave transmitted from the transmission antenna. As a result of this, the electromagnetic wave creates the electric field expanding from the vicinity of the ignition plug up to a location where the receiving antenna is arranged. As a result of the expansion of the electric field, a generation range of the plasma also expands, and thus, the combustion is promoted in the entire combustion chamber. Accordingly, it is possible to improve fuel efficiency.

Effect of the Invention

Since the present invention is configured as described above, it is possible to expand the generation range of the plasma by expanding the electric field toward the receiving antenna, and thus it is possible to improve fuel efficiency.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1is an enlarged view of a part of an engine100which an ignition plug1is mounted to. The engine100is of a DOHC (Double OverHead Camshaft) type. In each cylinder, a pair of openings3for intake ports2and a pair of openings5for exhaust ports4are formed and arranged in face-to-face relationship with each other in relation to the ignition plug1as the center. The ignition plug1is attached approximately at a center of a ceiling part of a combustion chamber6. The engine100is mounted to a cylinder block7. Camshafts9and10are respectively attached on the intake side and the exhaust side of a cylinder head8that forms the ceiling part of the combustion chamber6. The intake port2of the cylinder head8is opened and closed by an intake valve11which reciprocates by a rotation of the camshaft9. Likewise, the exhaust port4of the cylinder head8is opened and closed by an exhaust valve12which reciprocates by a rotation of the camshaft10. The ignition plug1is attached to the ceiling part of the combustion chamber6. The intake port2includes a fuel injection valve (not shown) for producing fuel air mixture to be supplied to the combustion chamber6. According to the present embodiment, the ignition plug1is attached to a location sandwiched between the two intake valves11and the two exhaust valves12, i.e., approximately at the center of the ceiling part of the combustion chamber6. As the engine100itself, except for the ignition plug1, a spark ignition type engine which is known in the art may be employed.

The ignition plug1according to the present embodiment includes a housing13made of an electrically conductive material, a central electrode14accommodated in the housing13in an insulated manner, a ground electrode15arranged at a lower end of the housing13spaced apart from the central electrode14, and a transmission antenna16for transmitting a microwave, which is an electromagnetic wave. Except for the transmission antenna16, the ignition plug1may be configured the same as an ignition plug known in the art.

The transmission antenna16is provided with a tip end protruded from an insulator (not shown) in the vicinity of the central electrode14via a through hole provided in the insulator. The insulator supports the central electrode14in the housing13in an electrically insulated manner. The transmission antenna16is arranged in face-to-face relationship with the ground electrode15across the central electrode14. The transmission antenna16has a length corresponding to a wavelength of the microwave so as not to function as a ground electrode.

As against the transmission antenna16described above, a receiving antenna17for receiving the microwave transmitted from the transmission antenna16is provided on a surface of the intake valve11, the surface facing toward the combustion chamber6, i.e., a lower surface of the intake valve11. As the receiving antenna17, any type of an antenna may be applicable as long as the antenna is excellent in electric conductivity and made of highly durable metal material. In the present embodiment, the receiving antenna17is made of the same material as the intake valve11.

As shown inFIG. 3, the receiving antenna17protrudes approximately from a central part of the lower surface of the intake valve11toward an extension line of the central electrode14of the ignition plug1in the combustion chamber6. This means that the receiving antenna17is directed toward a direction in which an axis line of the receiving antenna17intersects with the extension line of the central electrode14at a location downward from the ignition plug1. This makes it possible to minimize the peel of a tumble flow at a time of combustion, which will be described later. The shape of the receiving antenna17is not limited to a specific shape and may be cuspidate, planar, or the like.

A protrusion length of the receiving antenna17of the shape described above is set to, for example, a quarter wavelength of the microwave. The length of the receiving antenna17is determined for the purpose of maximizing the reception efficiency of the microwave. The receiving antenna17does not necessarily have a metal part exposed therefrom, and may be covered by an insulator such as ceramic to improve durability.

In the configuration described above, the transmission antenna16is connected to a magnetron, which is a microwave generation device that outputs the microwave. Meanwhile, the ignition plug1is connected to an igniter. The engine100itself is electrically maintained to a ground potential. The ground electrode15of the ignition plug1is maintained to the ground potential, and the receiving antenna17is constantly maintained to the ground potential.

When fuel air mixture in the combustion chamber6is ignited by means of the ignition plug1, the engine100is designed to allow the spark discharge of the ignition plug1to react with an electric field created in the combustion chamber6so as to generate plasma. In this manner, an ignition region is enlarged in comparison with an ignition by spark discharge in a case in which the plasma is not generated. By way of the microwave outputted from the magnetron, the transmission antenna16creates the electric field in a space including a discharge gap formed between the central electrode14and the ground electrode15of the ignition plug1. The electric field expands toward a lower side of the intake valve11by the microwave progressing toward the receiving antenna17. By allowing the spark discharge to react with the electric field thus expanded, the plasma is generated, and a flame kernel is generated.

This means that the spark discharge is caused to occur at the ignition plug1by an ignition coil (not shown), and the electric field is created by the microwave approximately at the same time as or immediately before/after the start of the spark discharge. By allowing the spark discharge to react with the electric field, the plasma is generated so that the fuel air mixture is rapidly combusted in the combustion chamber6. Here, “immediately after the start of the spark discharge” is preferably at the latest by the start of inductive discharge, which constitutes the spark discharge”.

More specifically, the spark discharge by the ignition plug1generates the plasma in the electric field, and the fuel air mixture is ignited under the presence of the plasma. Consequently, the flame kernel that initiates flame propagation combustion is enlarged in comparison with the ignition by the spark discharge alone. Furthermore, owing to the presence of the plasma, a large amount of radicals are produced in the combustion chamber6so as to promote the combustion. The plasma does not stay in the vicinity of the ignition plug1alone, but expands up to the vicinity of the intake valve11. Owing to the receiving antenna17provided on the lower surface of the intake valve11, the microwave emitted from the transmission antenna16propagates through the space of the combustion chamber6toward the receiving antenna17and is received by the receiving antenna17while, on the other hand, a part of the microwave is reflected and diffuses in the combustion chamber6. As a result of this, the electric field is widely created by the microwave in the combustion chamber6including the space from the transmission antenna16up to the receiving antenna17. Accordingly, the plasma expands, as described above.

Under the presence of the plasma described above, flows of electrons by the spark discharge and ions and radicals produced by the spark discharge are caused to vibrate and meander under the influence of the electric field, consequently, increase their travel lengths, and thus, dramatically increase the number of times of collision with ambient molecules of water and nitrogen, thereby promoting the combustion. The molecules of water and nitrogen having collided with the ions and radicals become OH radicals and N radicals, and ambient gas having collided with the ions and radicals are ionized, i.e., brought into the plasma state, thereby the ignition region of the fuel air mixture is dramatically enlarged and the flame kernel that initiates the flame propagation combustion is also enlarged.

As a result of this, since the fuel air mixture is ignited by the plasma generated by the reaction of the spark discharge and the electric field, the ignition region expands, and two-dimensional ignition only by the ignition plug1is transformed into three-dimensional ignition. Accordingly, the initial combustion is stabilized, the combustion rapidly propagates in the combustion chamber6in association with the increase of the radicals described above, and the combustion expands at a high combustion speed.

Thus, owing to the receiving antenna17provided on the intake valve11, it is possible to prevent the combustion from being destabilized in the vicinity of the intake valve11when the tumble flow of the fuel air mixture is generated in the cylinder during the expansion stroke. As described above, owing to the receiving antenna17provided on the lower surface of the intake valve11, the plasma expands up to the vicinity of the intake valve11, and thus, it is possible to secure the combustion, i.e., increase the combustion rate, even if the combustion tends to decrease in speed in the vicinity of the intake valve11under the influence of the tumble flow. Furthermore, according to the present embodiment, since the receiving antenna17is adjusted so that the axial direction of the receiving antenna17is oriented to a location on an extension line of the central electrode14of the ignition plug1, as described above, the fuel air mixture flow peeling around the receiving antenna17is directed toward the ignition plug1. Accordingly, the fuel air mixture concentrates on the ignition plug1without diffusion, and it is possible to increase combustion efficiency, and thus improve fuel efficiency.

The present invention is not limited to the present embodiment described above.

In the present embodiment described above, it has been described that the receiving antenna17is provided on the intake valve11. However, depending on the intensity of the tumble flow, the receiving antenna may be provided on the exhaust valve, or may be provided on both the intake valve and the exhaust valve.

Furthermore, as shown inFIG. 4, the receiving antenna may be in the form of an arc-like shape, and provided on the intake valve, for example. InFIG. 4, an receiving antenna117is constituted by a first straight part117athat extends in an axial direction of an intake valve111from a center of a combustion chamber-facing surface of the intake valve111, i.e., a lower surface111a, a second straight part117bthat extends in a direction perpendicular to the first straight part117afrom a distal end of the first straight part117a, an arc part117cconstituted by an arc centered on the distal end of the first straight part117aand connected to a distal end of the second straight part117b, and a covering part117dthat covers the first and second straight parts117aand117band the arc part117c. The arc part117cis formed on an imaginary plane that passes through the distal end of the first straight part117aand is perpendicular to the first straight part117a. The arc part117cis formed in an arc shape smaller in diameter than the lower surface111aof the intake valve111. Therefore, the arc part117cis not exposed from a side surface of the covering part117d, which is formed by an extension of a side surface of the intake valve111. In the present embodiment, the material of the receiving antenna117may be the same as that of the intake valve111, and may be different electrically-conducting material such as, for example, copper foil. The covering part117dis formed by ceramic, for example. InFIG. 4, the covering part117dis shown as being transparent for a purpose of clearly illustrating the receiving antenna117. However, the covering part117dis not required to be transparent.

According to the configuration described above, although the covering part117dis exposed to the combustion chamber6in a state in which the intake valve111is closed, since the covering part117dis approximately in a shape of a truncated cone, the covering part117dwill not peel the tumble flow. Since the tumble flow is not disturbed, the combustion is promoted even in the vicinity of the intake valve111owing to expansion of the plasma due to expansion of the electric field by the receiving antenna117, and it is possible to increase combustion efficiency, which will contribute to fuel consumption reduction.

As described above, the receiving antenna117may be provided on the exhaust valve, and may be provided on both the intake valve and the exhaust valve.

In place of the magnetron as described above, a source of the microwave may be a travelling wave tube or the like, and may include a microwave oscillation circuit using semiconductors.

Furthermore, unlike the transmission antenna according to the present embodiment described above, a transmission antenna may be provided separately from the ignition plug. In this case, for example, a horn type transmission antenna may be employed. It is preferable that the antenna of this type may be provided in the vicinity of the central electrode14of the ignition plug1.

Furthermore, the central electrode of the ignition plug1may be designed to function as an antenna. In this case, it is preferable that the ignition plug is of a type without resistors. If a microwave of a constant voltage is continuously applied to the central electrode, the temperature of the central electrode will excessively increase. Therefore, it is preferable to control the applied voltage of the microwave so that the temperature of the central electrode should be below an upper limit value determined based on a heat resistant temperature of the central electrode.

Furthermore, in the present embodiment described above, it has been described that the microwave is utilized to create the electric field. However, a high frequency wave of a different frequency such as a frequency lower than that of the microwave may be employed.

Also, particular configurations of other constituent elements are not limited to the present embodiment described above, and various modifications are possible within the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention may be applied to a spark ignition type internal combustion engine that requires a spark discharge by an ignition plug to ignite a fuel such as gasoline and liquefied natural gas.

EXPLANATION OF REFERENCE NUMERALS