Combustion assist device for internal combustion engine

A combustion assist device is provided in an internal combustion engine provided with a fuel injector for injecting at least a portion of fuel into an intake manifold. Further, the combustion assist device is provided with an electrode element which is provided in the intake manifold and to which a high frequency high voltage is applied. The electrode element includes a dielectric material plate, a first metal conductor, and a second metal conductor. The dielectric material plate includes a first surface and a second surface, and divides a portion of the intake manifold into a first flow path on a first surface side and a second flow path on a second surface side. The first metal conductor is provided on the first surface. The second metal conductor is provided on the second surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a combustion assist device provided in an internal combustion engine, in which at least a portion of fuel is injected into an intake manifold, and assisting combustion of fuel.

2. Description of the Related Art

In conventional internal combustion engines that use gasoline as fuel, air is introduced into a combustion chamber in an amount that is appropriate for an amount of fuel introduced into the combustion chamber. Spark discharge energy is then applied to the mixture of fuel and air formed in the combustion chamber, combustion is induced, and the energy generated as a result is taken out as power.

Further, a technique is known in which temperature and pressure is controlled so that the mixture of fuel and air formed inside the combustion chamber self-ignites without applying spark discharge energy thereto, whereby combustion is induced, and the energy generated as a result is taken out as power.

With either of the combustion modes described above, the combustion state may become unstable due to the influence of the temperature, concentration, flow strength, and so forth of the air-fuel mixture formed in the combustion chamber.

When the combustion state becomes unstable, the traveling speed of a vehicle using the internal combustion engine for power becomes unstable and, in addition, fuel economy decreases, such that it is desirable to make the combustion state as stable as possible.

As a method of making the combustion state more stable, in a conventional method for improving the combustive properties of an internal combustion engine, a high voltage is applied between two discharge electrodes that project into the intake manifold of an internal combustion engine, causing a discharge to be generated between the electrodes. High temperature plasma is generated by this discharge such that ozone is generated from oxygen in the air, and this ozone is added to the air-fuel mixture (see Japanese Patent Application Publication No. H2-191858, for example).

Further, in a conventional engine ignition control device, a portion of injected fuel comes into contact with a discharge electrode, thereby generating an active chemical species having a high reactivity. By adding the generated active chemical species to the air-fuel mixture, ignitability of the air-fuel mixture is improved (see, Japanese Patent Application Publication No. 2013-148098, for example).

SUMMARY OF THE INVENTION

With the conventional technique disclosed in Japanese Patent Application Publication No. H2-191858, if the generated ozone does not move away from the high temperature plasma due to air flow or the like, the ozone state cannot be maintained due to the heat of the plasma, and the ozone reverts back to oxygen.

Ozone generated during an intake stroke moves rapidly away from the high temperature plasma due to the intake flow, however, in internal combustion engines of a type in which fuel is injected into the intake manifold, fuel and air are mixed in a part of the intake manifold during the intake stroke, such that it is necessary to install the electrodes in an upstream portion of the intake manifold that is removed from the combustion chamber in order to prevent ignition of the fuel in the intake manifold. In such a case, a cycle delay occurs while the generated ozone reaches the combustion chamber, hence a problem exists in that control responsiveness cannot be ensured.

Further, with the conventional technique disclosed in Japanese Patent Application Publication No. 2013-148098, a low temperature plasma discharge is generated, such that there is a low possibility of the fuel igniting in the intake manifold and, due to generation of the active chemical species at a location proximate to the combustion chamber, control responsiveness can be ensured. However, as a discharge electrode having a structure similar to that of a conventional spark plug is used, an amount of the active chemical species generated by contact with the low temperature plasma is not necessarily large. Moreover, although ozone is generated when oxygen in the air comes into contact with the low temperature plasma, an amount thereof is, likewise, small.

The present invention has been made to solve the problems described above, and an object thereof is to obtain a combustion assist device for an internal combustion engine that, while ensuring control responsiveness, generates a sufficient amount of ozone and enables a combustion state to be stabilised in a combustion engine in which fuel is injected into an intake manifold.

A combustion assist device for an internal combustion engine according to the present invention is a combustion assist device provided in an internal combustion engine provided with a fuel injector for injecting at least a portion of fuel into an intake manifold, the combustion assist device including an electrode element which is provided in the intake manifold and to which a high frequency high voltage is applied, wherein the electrode element includes a dielectric material plate which has a first surface and a second surface, which is a surface on an opposite side to the first surface, the dielectric material plate dividing a portion of the intake manifold into a first flow path on a side of the first surface and a second flow path on a side of the second surface, a first metal conductor, which is a metal conductor film provided on the first surface, and a second metal conductor, which is a metal conductor provided on the second surface.

The combustion assist device for an internal combustion engine according to the present invention uses an electrode element that includes a dielectric material plate, a first metal conductor provided on a first surface of the dielectric material plate, and a second metal conductor provided on a second surface of the dielectric material plate, and divides a portion of an intake manifold into a first flow path on a side the first surface and a second flow path on a side of the second surface by means of the dielectric material plate, such that the combustion assist device, while ensuring control responsiveness, generates a sufficient amount of ozone and enables a combustion state to be stabilized in a combustion engine in which fuel is injected into the intake manifold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a configuration diagram showing the main components of an internal combustion engine according to a first embodiment of the present invention. Note that, in internal combustion engines used for driving vehicles and the like, intake manifolds are respectively provided for a plurality of combustion chambers. Here however, the configuration of one intake manifold only is shown in order to simplify explanation of operations.

In the drawing, an internal combustion engine main body1is provided with a combustion space1a, and an intake manifold1band an exhaust manifold1cconnected to the combustion space1a. Further, a spark plug2is provided in the internal combustion engine main body1so as to face the combustion space1a.

A piston3is provided in the combustion space1a. The piston3is coupled to a crank5via a connecting rod4.

The internal combustion engine main body1is provided with an intake valve6that opens and closes between the intake manifold1band the combustion space1aand an exhaust valve7that opens and closes between the exhaust manifold1cand the combustion space1a. The intake valve6opens and closes due to the rotation of an intake cam8. The exhaust valve7opens and closes due to the rotation of an exhaust cam9.

A cam angle signal plate10rotates in synchronization with the intake cam8. The rotation angle of the intake cam8is detected by a cam angle sensor11which faces the cam angle signal plate10. A gap sensor, for example, is used as the cam angle sensor11.

The internal combustion engine main body1is provided with a fuel injector12for injecting at least a portion of fuel into the intake manifold1b. An electrode element13is provided in the intake manifold1bat a position that faces the fuel injector12. The electrode element13is connected to a power supply device15via a pair of power supply conducting wires14aand14b. A throttle valve16is provided upstream from the electrode element13in the intake manifold1b.

A signal from the cam angle sensor11is input to an engine controller17. The engine controller17controls the spark plug2, the fuel injector12, and the power supply device15.

The combustion assist device for an internal combustion engine according to the first embodiment includes the electrode element13, the power supply conducting wires14aand14b, the power supply device15, and the engine controller17.

Next, basic operations of internal combustion engines having a form in which fuel is injected into the intake manifold1bof each cylinder thereof will be described. The piston3respectively provided in each cylinder of the internal combustion engine main body1reciprocates, due to the action of the crank5and the connecting rod4, so as to increase or decrease the volume of the combustion space1a.

In four-stroke internal combustion engines, the intake cam8and the exhaust cam9are set to rotate once with respect to two rotations of the crank5. As a result, during one of two reciprocations of the piston3, the exhaust valve7mainly opens during a stroke in which the volume of the combustion space1adecreases, and the intake valve6mainly opens during a continuing stroke in which the volume of the combustion space1aincreases.

In many cases, in internal combustion engines that use gasoline as fuel, fuel20is injected into the intake manifold1bfrom the fuel injector12provided in each cylinder before the intake valve6starts to open. The engine controller17identifies fuel injection timings on the basis of, for example, the cam rotation angle detected by the cam angle sensor11or information relating to the crank rotation angle, and transmits an injection control signal to the fuel injector12.

When the intake valve6is closed, the injected fuel remains in the intake manifold1b. Thereafter, when the intake valve6starts to open, air, the flow rate of which has been adjusted by the throttle valve16, is sucked into the combustion space1athrough the intake manifold1b, such that the fuel remaining in the intake manifold1bis also sucked into the combustion space1a.

The air and fuel sucked into the combustion space1aare mixed together and compressed by the piston3while forming a homogeneous combustible air-fuel mixture. In the latter half of compression, the spark plug2generates a spark discharge on the basis of a control signal from the engine controller17so as to forcibly ignite the compressed combustible air-fuel mixture.

When the combustible air-fuel mixture begins to combust, pressure in the combustion space1arises and pressure energy thereof pushes back the piston3, whereby rotational energy is taken out to the outside of the engine via the connecting rod4and the crank5.

The combusted combustible air-fuel mixture is discharged to the outside of the internal combustion engine through the exhaust manifold1cduring the period in which the exhaust valve7is open.

FIG. 2is a front view showing the electrode element13inFIG. 1, andFIG. 3is a rear view showing the electrode element13inFIG. 1. The electrode element13includes a dielectric material plate21, a first metal conductor22, and a second metal conductor23.

The dielectric material plate21is constituted by a dielectric material such as ceramic. Further, the planar shape of the dielectric material plate21is a rectangular shape having a long side and a short side. Moreover, the dielectric material plate21includes a first surface21a, which is a front surface, and a second surface21bwhich is a surface on an opposite side to the first surface21a, which is a rear surface.

The first metal conductor22is a metal film adhered to the first surface21awithout any gaps therebetween. The first metal conductor22includes a rectangular base end portion22aprovided in the vicinity of one end portion of the dielectric material plate21in the longitudinal direction and a plurality of linear portions22bthat project from the base end portion22atowards the other end portion of the dielectric material plate21in the longitudinal direction.

The linear portions22bare provided in parallel to each other and are separated from each other in a direction perpendicular to the longitudinal direction of the dielectric material plate21by gaps. In other words, the planar shape of the first metal conductor22is a comb shape.

The second metal conductor23is a metal film adhered to the second surface21bwithout any gaps therebetween, and is not in contact with the first metal conductor22. Further, the planar shape of the second metal conductor23is a rectangular shape which is smaller than the dielectric material plate21.

As described above, the planar shape of the first metal conductor22is a comb shape, and the second metal conductor23has a rectangular shape, such that an edge of the first metal conductor22is longer than an edge of the second metal conductor23.

Copper, aluminum, or gold, for example, is used as a material for the first and second metal conductors22and23. In addition, the first and second metal conductors22and23are formed on the dielectric material plate21by, for example, vapor deposition.

First and second connection holes21cand21dare provided at both end portions of the dielectric material plate21in the longitudinal direction. An annular first connecting portion24, to which one of the power supply conducting wires14ais connected, is provided around the periphery of the first connection hole21con the first surface21a. The first connecting portion24is electrically connected to the first metal conductor22.

An annular second connecting portion25, to which the other power supply conducting wire14bis connected, is provided around the periphery of the second connection hole21don the second surface21b. The second connecting portion25is electrically connected to the second metal conductor23.

When high frequency and high voltage energy is output from the power supply device15, low temperature plasma discharges are generated at the respective edge portions of the first metal conductor22and the second metal conductor23.

The electrode element13is disposed at a position that is reached by least a portion of unevaporated fuel particles of the injected fuel20injected from the fuel injector12. The unevaporated fuel particles having reached the electrode element13temporarily adhere to the surface of the electrode element13.

FIG. 4is a cross-sectional view showing an example arrangement of the electrode element13with respect to the intake manifold1binFIG. 1. A portion of the intake manifold1bin which the electrode element13is disposed is divided by the dielectric material plate21into a first flow path1don a first surface21aside and a second flow path1eon a second surface21bside. Further, the electrode element13is disposed so that the second surface21b, on which the second metal conductor23having a short edge distance is provided, faces the fuel injector12.

By disposing the electrode element13in this way, oxygen contained in the air passes through the first flow path1dduring the intake stroke and, at times other than the intake stroke, remains in the first flow path1d, and by coming into contact with a low temperature plasma discharge on a first metal conductor22side, which is more active than a second metal conductor23side, a larger amount of ozone is generated.

Meanwhile, in the second flow path1e, heat generated by a low temperature plasma discharge and the high thermal conductivity of the second metal conductor23are utilized to promote vaporization of unevaporated fuel adhered to the surface of the second metal conductor23, concentration homogenization of the air-fuel mixture formed from the fuel and air introduced into the combustion space1aprogresses, and an improvement in combustion efficiency is realized.

Here, when a high-frequency alternating voltage is applied from the power supply device15to the electrode element13, low temperature plasma discharges occur alternately at both of the edges of the first metal conductor22and the second metal conductor23. For this reason, there is a possibility that the fuel could be ignited by a discharge generated at a contour portion of the second metal conductor23which faces the fuel injector12.

In order to prevent such ignition of the fuel, the power supply device15stops applying the high frequency alternating voltage to the electrode element13before the fuel injected from the fuel injector12during a cycle reaches the electrode element13.

As another method of preventing fuel ignition, a method exists in which a potential of the second metal conductor23is constantly fixed to the zero potential of the power supply device15, and the power supply device15applies a half-wave potential only to the first metal conductor22. With this method, the power supply device15does not need to stop applying a high frequency half-wave voltage to the electrode element13before the fuel injected from the fuel injector12during a cycle reaches the electrode element13.

In such a combustion assist device for an internal combustion engine, the electrode element13which includes the dielectric material plate21, the first metal conductor22provided on the first surface21aof the dielectric material plate21, and the second metal conductor23provided on the second surface21bof the dielectric material plate21is used and a portion of the intake manifold1bis divided into the first flow path1dand the second flow path1eby means of the dielectric material plate21, such that the combustion assist device, while ensuring control responsiveness, generates a sufficient amount of ozone and enables a combustion state to be stabilized in a combustion engine in which the fuel20is injected into the intake manifold1b.

In addition, as the electrode element13is disposed at a position directly reached by at least a portion of the unevaporated fuel particles of the injected fuel20injected from the fuel injector12, vaporization of the unevaporated fuel adhered to the surface of the second metal conductor23can be promoted by utilizing heat generated by a low temperature plasma discharge and the high thermal conductivity of the second metal conductor23. As a result, it is also possible for the second metal conductor23to be cooled.

Further, as the distance of the edge of the first metal conductor22is longer than that of the edge of second metal conductor23, a larger amount of ozone can be generated by a low temperature plasma discharge at the first metal conductor22side.

Second Embodiment

Next,FIG. 5is a configuration diagram showing the main components of an internal combustion engine according to a second embodiment of the present invention. In the second embodiment, an auxiliary element31is provided upstream from the electrode element13and downstream from the throttle valve16in the intake manifold1b. In this example, an element having the same configuration as the electrode element13shown inFIGS. 2 and 3is used as the auxiliary element31. In other words, the auxiliary element31, in the same way as the electrode element13, includes the dielectric material plate21, the first metal conductor22, and the second metal conductor23. However, in the auxiliary element31, the shape of the second metal conductor23may be the same as that of the first metal conductor22.

The auxiliary element31is connected to an auxiliary element power supply device33via a pair of auxiliary conductive wires32aand32b. High frequency high voltage energy from the auxiliary element power supply device33is supplied to the auxiliary element31. As a result, it is possible for ozone to be generated in a portion of the intake manifold1bthat is upstream from the electrode element13.

The combustion assist device of the second embodiment includes, in addition to the combustion assist device of the first embodiment, the auxiliary element31, the auxiliary conductive wires32aand32b, and the auxiliary element power supply device33. Other configurations and operations are similar or identical to those of the first embodiment.

Ozone generation by the auxiliary element31is used to compensate for the insufficiency of ozone generation by the electrode element13. In other words, as the control responsiveness of an amount of ozone supplied to the combustion space1aby the electrode element13, which is proximate to combustion space1a, is good, a required amount of ozone is constantly and quantitatively supplied by the auxiliary element31, and the ozone supply amount is quickly changed in accordance with changes in combustion conditions by the electrode element13. As a result, stabilization of the combustion state can be further improved.

Here, element temperatures of both the electrode element13and the auxiliary element31rise due to the low temperature plasma discharges. In the electrode element13, cooling is performed by utilizing the surrounding air flow and the heat of vaporization of unevaporated fuel adhered to the surface thereof, however, in the auxiliary element31, cooling is performed only by the surrounding air flow. Accordingly, in the auxiliary element31, it is necessary to keep an element heat generation density, which is the amount of heat generated per unit area, lower than that of the electrode element13.

As a method of suppressing the heat generation density of the auxiliary element31, a method exists in which, when a value obtained by dividing an amount of energy input (W), by a total distance (m) of an edge of a metal conductor generating a low temperature plasma discharge, and an energy input time (sec) (W/(m·sec)) is set as an evaluation value, an evaluation value relating to the auxiliary element31is set to be lower than an evaluation value relating to the electrode element13.

Note that, in the first and second embodiments, the shape of the first metal conductor22is a comb shape, however, other shapes may also be adopted as long as an edge length thereof can be made long. For example, a comb shape in which linear portions are parallel to the short side of the dielectric material plate, a spiral shape, or a serpentine shape may be used.

Moreover, the length of the edge of the first metal conductor and the length of the edge of the second metal conductor do not necessarily have to be different from each other.

Further, the position of the electrode element does not necessarily have to be a position directly reached by fuel from the fuel injector.