JP6399474B2 - Flow control device in combustion chamber - Google Patents

Description

  The present invention relates to a flow control device in a combustion chamber, and in particular, a cavity recessed downward is formed in a central portion of a piston top surface, and between a peripheral portion surrounding a radially outer side of the cavity and a ceiling surface of the combustion chamber. The present invention relates to a flow control device in a combustion chamber that controls the flow of gas in the combustion chamber in an engine in which a squish area is formed.

  Conventionally, improvement of engine combustion is performed by controlling the flow of gas in a combustion chamber. For example, in a spark ignition engine, a squish flow that flows along the combustion chamber ceiling surface and the piston crown surface is generated from the intake side and exhaust side squish areas at the end of the compression stroke, and the air-fuel mixture is collected in the center of the combustion chamber. Thus, a technique for improving the ignitability of fuel is known (for example, see Patent Document 1).

JP 2013-194561 A

  By the way, in order to improve the efficiency of the engine, it is necessary to reduce the cooling loss. However, when a squish flow or a reverse squish flow that flows along the ceiling surface of the combustion chamber and the piston crown surface is generated as in the engine described in Patent Document 1, the hot gas in the combustion chamber and the combustion are generated by these flows. Convective heat transfer between the chamber ceiling surface and the piston crown surface is promoted, resulting in an increase in cooling loss.

  The present invention has been made to solve the above-described problems of the prior art, and in an engine in which a squish area is formed between the peripheral edge of the piston top surface and the ceiling surface of the combustion chamber, An object of the present invention is to provide a flow control device in a combustion chamber that can reduce a cooling loss due to a reverse squish flow.

In order to achieve the above object, a flow control device in a combustion chamber according to a first invention of the present invention is formed with a cavity recessed downward in the center of a piston top surface and surrounding a radially outer side of the cavity. An engine in which a squish area is formed between a ceiling surface of a combustion chamber and a flow control device in the combustion chamber for controlling the flow of gas in the combustion chamber, wherein the cavity formed on the piston top surface includes a side wall surface and a cavity surface The cavity has a bottom surface, and both the squish flow and the reverse squish flow flow along the side wall surface of the combustion chamber at a predetermined time in the second half of the compression stroke and the first half of the expansion stroke before and after the compression top dead center of the engine. a shape as to generate a vertical vortex including a flow in the same direction towards the has a plasma actuator disposed in the combustion chamber, the plasma actuator , Including a dielectric disposed along the side wall surface of the cavity, an exposed electrode disposed on the combustion chamber side of the dielectric, and an embedded electrode disposed on the opposite side of the exposed electrode across the dielectric electrodes, to counteract the flow in the same direction toward the ceiling surface of the combustion chamber by the squish flow and the reverse squish flow is disposed on the bottom side of the cavity than the exposed electrode, it is characterized.
In the present invention configured as described above, the exposed electrode of the plasma actuator is disposed on the combustion chamber side of the dielectric disposed along the side wall surface of the cavity, and the buried electrode is disposed between the exposed electrode and the dielectric. Since it is arranged on the bottom side of the cavity from the exposed electrode on the opposite side, by applying a high frequency and high voltage AC voltage to the exposed electrode and the embedded electrode at the time when the squish flow or reverse squish flow occurs, Plasma is generated in the discharge space between the end face and the dielectric, and a flow toward the bottom surface of the cavity along the side wall surface of the cavity can be induced by the volume force generated by the plasma. As a result, the flow can be generated in the direction to cancel the longitudinal vortex generated in the cavity by the squish flow or the reverse squish flow, and the flow velocity of the gas in the vicinity of the side wall surface of the cavity can be suppressed. Convection heat transfer with the wall surface can be suppressed, and cooling loss due to squish flow or reverse squish flow can be reduced.

In the present invention, preferably, the exposed electrode and the buried electrode are arranged so as to surround the cavity along the side wall surface of the cavity.
In the present invention configured as described above, since the exposed electrode and the buried electrode are arranged so as to surround the cavity along the side wall surface of the cavity, the high frequency and high frequency are generated when the squish flow or the reverse squish flow is generated. By applying an alternating voltage of the voltage to the exposed electrode and the embedded electrode, the vertical vortex generated in the cavity due to the squish flow or the reverse squish flow can be suppressed on the entire side wall surface of the cavity. Cooling loss can be reduced more effectively.

In the combustion chamber flow control device according to the second aspect of the present invention, a cavity recessed downward is formed in the central portion of the piston top surface, and a peripheral portion that surrounds the radially outer side of the cavity and the ceiling surface of the combustion chamber. In an engine in which a squish area is formed, a flow control device in a combustion chamber for controlling the flow of gas in the combustion chamber , wherein the cavity formed on the top surface of the piston has a side wall surface and a bottom surface, Both the squish flow and the reverse squish flow flow in the same direction toward the ceiling surface of the combustion chamber along the side wall surface of the cavity at predetermined times in the second half of the compression stroke and the first half of the expansion stroke before and after the compression top dead center of the engine. a shape as to generate a vertical vortex including controls a plasma actuator disposed along the side wall surface of the cavity, the plasma actuators It comprises a control means, the control means, along the side wall surface of the cavity during the expansion stroke from the compression stroke of the engine for controlling the plasma actuators to generate a flow towards the bottom of the cavity, and wherein the To do.
In the second invention of the present invention configured as described above, the control means moves the plasma actuator disposed along the side wall surface of the cavity between the compression stroke and the expansion stroke where the squish flow and the reverse squish flow are generated. The flow is controlled to generate a flow toward the bottom surface of the cavity along the side wall surface of the cavity. The gas flow velocity in the combustion chamber can be suppressed, thereby suppressing the convective heat transfer between the hot gas in the combustion chamber and the side wall surface of the cavity, thereby reducing the cooling loss due to the squish flow or the reverse squish flow. .

  According to the flow control device for a combustion chamber according to the present invention, in an engine in which a squish area is formed between the peripheral portion of the piston top surface and the ceiling surface of the combustion chamber, the cooling loss due to the squish flow or the reverse squish flow is reduced. be able to.

1 is a schematic configuration diagram of an engine to which a flow control device in a combustion chamber according to an embodiment of the present invention is applied. It is a block diagram which shows the electrical structure regarding the flow control apparatus in the combustion chamber by embodiment of this invention. It is a conceptual diagram which shows the basic composition of the plasma actuator by embodiment of this invention. 1 is a partial cross-sectional view of a piston and a cylinder head of an engine according to an embodiment of the present invention. It is a partial expanded sectional view of the squish area vicinity of the engine by embodiment of this invention. It is a top view of the piston by which the plasma actuator by embodiment of this invention is arrange | positioned. It is a partial expanded sectional view of the squish area vicinity of the engine by embodiment of this invention, (a) is a figure which shows operation | movement of the plasma actuator in a compression stroke, (b) is a figure which shows operation | movement of the plasma actuator in an expansion stroke. It is.

  Hereinafter, a flow control device in a combustion chamber according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  First, an apparatus configuration of an engine according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic configuration diagram of an engine to which a flow control device in a combustion chamber according to an embodiment of the present invention is applied, and FIG. 2 shows an electrical configuration related to the flow control device in the combustion chamber according to an embodiment of the present invention. It is a block diagram.

  In FIG. 1, reference numeral 1 denotes an engine. The engine 1 is a gasoline engine that is mounted on a vehicle and supplied with a fuel containing at least gasoline. The engine 1 includes a cylinder block 4 provided with a plurality of cylinders 2 (only one cylinder 2 is shown in FIG. 1, but four cylinders 2 are provided in series, for example), and the cylinder block 4 And an oil pan 8 disposed below the cylinder block 4 and storing lubricating oil. A piston 14 connected to the crankshaft 12 via a connecting rod 10 is fitted in each cylinder 2 so as to be able to reciprocate. The cylinder head 6, the cylinder 2, and the piston 14 define a combustion chamber 16. The shape of the combustion chamber 16 is not limited to the shape illustrated. For example, the shape of the top surface of the piston 14 and the shape of the ceiling surface of the combustion chamber 16 can be appropriately changed.

  In the cylinder head 6, an intake port 18 and an exhaust port 20 are formed for each cylinder 2. The intake port 18 and the exhaust port 20 have an intake valve 22 and an exhaust for opening and closing the opening on the combustion chamber 16 side. Each valve 24 is disposed.

  The cylinder head 6 is also provided with an injector 26 (fuel injection valve) for directly injecting fuel into the cylinder 2 for each cylinder 2. The injector 26 is disposed so that the nozzle hole faces the inside of the combustion chamber 16 from the central portion of the ceiling surface 16 a of the combustion chamber 16. The injector 26 directly injects an amount of fuel into the combustion chamber 16 at an injection timing set according to the operating state of the engine 1 and according to the operating state of the engine 1.

  A spark plug 30 for forcibly igniting the air-fuel mixture in the combustion chamber 16 is also attached to the cylinder head 6. In the present embodiment, two spark plugs 30 are disposed between the intake valve 22 and the exhaust valve 24.

  A plasma actuator 28 is disposed in the cavity 34 formed on the top surface of the piston 14. Details of the plasma actuator 28 will be described later.

  The engine 1 is controlled by a powertrain control module (hereinafter referred to as PCM) 32. The PCM 32 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. The PCM 32 constitutes a controller.

  As shown in FIGS. 1 and 2, various signals including a detection signal of a crank angle sensor SW 12 that detects a rotation angle of the crankshaft 12 are input to the PCM 32.

  The PCM 32 determines the state of the engine 1 and the vehicle by performing various calculations based on these detection signals, and in response thereto, the injector 26, the spark plug 30, the plasma actuator 28, and various valves (throttle valve and EGR). A control signal is output to the actuator of the valve. Thus, the PCM 32 operates the engine 1. Although details will be described later, the plasma actuator 28 and the PCM 32 correspond to the flow control device in the combustion chamber in the present invention, and the PCM 32 functions as a control means for controlling the plasma actuator 28.

Next, a basic configuration of the plasma actuator 28 according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a conceptual diagram showing a basic configuration of the plasma actuator 28 according to the embodiment of the present invention.
As shown in FIG. 3, the plasma actuator 28 includes a thin film-like dielectric 38, and an exposed electrode 40 and a buried electrode 42 arranged with the dielectric interposed therebetween. The exposed electrode 40 and the buried electrode 42 are arranged with their positions shifted along the planar direction of the dielectric 38. In FIG. 3, the exposed electrode 40 and the buried electrode 42 are arranged so as not to overlap in the normal direction of the dielectric 38, but the exposed electrode 40 and the buried electrode 42 are arranged so as to partially overlap. May be. An AC power supply 44 is connected to the exposed electrode 40 and the embedded electrode 42.

When an AC voltage of high frequency and high voltage (for example, several kHz, several tens of kV) is applied to the exposed electrode 40 and the embedded electrode 42 by the AC power supply 44, as shown in FIG. Plasma P is generated in the discharge space between. The plasma P generates a volume force from the exposed electrode 40 toward the embedded electrode 42, and the volume force induces a gas flow (indicated by an arrow in FIG. 3) along the surface of the dielectric 38.
The magnitude of the volume force generated by the plasma P can be controlled by the voltage and frequency applied to the exposed electrode 40 and the embedded electrode 42.

  Next, the plasma actuator 28 according to the embodiment of the present invention will be described in detail with reference to FIGS. 4 is a partial cross-sectional view of the piston 14 and the cylinder head 6 according to the embodiment of the present invention, and FIG. 5 is a partially enlarged cross-sectional view of the vicinity of the squish area of the engine 1 according to the embodiment of the present invention. FIG. 6 is a plan view of the piston 14 in which the plasma actuator 28 according to the embodiment of the present invention is arranged. FIG. 4 shows a view when the piston 14 is positioned at 10 ° before the compression top dead center.

  In the engine 1 according to the present embodiment, the combustion chamber 16 in which the combustion chamber ceiling surface 16a on the cylinder head 6 side is formed in a gable roof shape (pent roof shape) is applied. FIG. 4 is a cross-sectional view of a part of the piston 14 and the cylinder head 6 and the like cut along a plane along a line perpendicular to the pent roof-shaped ridge line constituting the combustion chamber 16.

  A cavity 34 recessed downward is formed at the center of the top surface of the piston 14. The cavity 34 is formed so that the planar shape when viewed from the axial direction of the cylinder 2 is substantially circular. An injector 26 is disposed immediately above the center of the cavity 34, and two spark plugs 30 are disposed in the recess of the cavity 34.

  Further, on the top surface of the piston 14, a peripheral edge portion 36 that extends from the outer edge of the cavity 34 to the outer edge of the upper surface of the piston 14 and surrounds the radially outer side of the cavity 34 is provided. A squish area SA is formed between the peripheral edge 36 of the top surface of the piston 14 and the combustion chamber ceiling surface 16a.

The plasma actuator 28 is annularly arranged so as to surround the cavity 34 along the side wall surface 34 a of the cavity 34.
Specifically, as shown in FIGS. 5 and 6, the dielectric 38 of the plasma actuator 28 is annularly formed so as to surround the cavity 34 along the side wall surface 34 in the vicinity of the upper end of the side wall surface 34 a of the cavity 34. Has been placed.

  An exposed electrode 40 is arranged on the combustion chamber 16 side (right side in FIG. 5) of the dielectric 38, and a buried electrode 42 is placed on the opposite side of the exposed electrode 40 (that is, on the piston 14 side and on the left side in FIG. 5) across the dielectric 38. Is embedded.

  In the present embodiment, the two exposed electrodes 40 are arranged in the axial direction of the piston 14 along the side wall surface 34 a of the cavity 34, and the embedded electrode 42 is more in the cavity 34 than the exposed electrode 40 for each exposed electrode 40. It arrange | positions so that it may be located in the bottom face 34b side.

  Next, the operation of the plasma actuator 28 according to the embodiment of the present invention will be described with reference to FIG. FIG. 7 is a partially enlarged cross-sectional view in the vicinity of the squish area SA of the engine 1 according to the embodiment of the present invention. FIG. 7A is a diagram showing the operation of the plasma actuator 28 during the compression stroke, and FIG. 7B is the expansion stroke. It is a figure which shows operation | movement of the plasma actuator 28 in it.

As shown in FIG. 7A, in the compression stroke, when the piston 14 moves up and the volume of the squish area SA decreases as the piston 14 approaches the combustion chamber ceiling surface 16a, the combustion chamber ceiling surface 16a and the piston top surface are reduced. A squish flow S from the squish area SA toward the cavity 34 is generated along the peripheral surface portion 36, and the squish flow S descends the central portion of the cavity 34, and radially outwards the combustion chamber 16 along the bottom surface 34 b. A vertical vortex (indicated by a dotted arrow in FIG. 7A) is formed that faces and then rises along the side wall surface 34a of the cavity 34.
At a time when the vertical vortex is strongest (for example, around 10 ° before compression top dead center), the PCM 32 applies an AC voltage of high frequency and high voltage to the exposed electrode 40 and the embedded electrode 42 by the AC power supply 44. Thereby, plasma is generated in the discharge space between the end face of the exposed electrode 40 and the dielectric 38, and the volume force generated by the plasma travels along the side wall surface 34 a of the cavity 34 toward the bottom surface 34 b of the cavity 34. Flow is induced. That is, in the vicinity of the side wall surface 34 a of the cavity 34, a flow is generated in a direction that cancels the vertical vortex generated by the squish flow S. Thereby, the flow velocity of the gas in the vicinity of the side wall surface 34a of the cavity 34 can be suppressed, and the convective heat transfer between the high temperature gas in the combustion chamber 16 and the side wall surface 34a can be suppressed to reduce the cooling loss. .

Further, as shown in FIG. 7B, in the expansion stroke, when the volume of the squish area SA increases as the piston 14 descends and the piston 14 moves away from the combustion chamber ceiling surface 16a, the combustion chamber ceiling surface 16a and the piston A reverse squish flow RS from the cavity 34 toward the squish area SA is generated along the top peripheral edge 36, and the reverse squish flow RS descends the central portion of the cavity 34, and the diameter of the combustion chamber 16 along the bottom surface 34 b. A longitudinal vortex (indicated by a dotted arrow in FIG. 7B) is formed that goes outward in the direction and then rises along the side wall surface 34 a of the cavity 34.
At the time when the reverse squish flow RS is strongest (for example, around 10 ° after compression top dead center), the PCM 32 applies high-frequency and high-voltage AC voltages to the exposed electrode 40 and the embedded electrode 42 by the AC power supply 44. Thereby, plasma is generated in the discharge space between the end face of the exposed electrode 40 and the dielectric 38, and the volume force generated by the plasma travels along the side wall surface 34 a of the cavity 34 toward the bottom surface 34 b of the cavity 34. Flow is induced. That is, in the vicinity of the side wall surface 34a of the cavity 34, a flow is generated in a direction that cancels out the vertical vortex generated by the reverse squish flow RS. Thereby, the flow velocity of the gas in the vicinity of the side wall surface 34a of the cavity 34 can be suppressed, and the convective heat transfer between the high temperature gas in the combustion chamber 16 and the side wall surface 34a can be suppressed to reduce the cooling loss. .

Next, further modifications of the embodiment of the present invention will be described.
In the above-described embodiment, the case where the plasma actuator 28 is formed in an annular shape so as to surround the cavity 34 along the side wall surface 34a of the cavity 34 has been described as an example. Also good.
For example, the plurality of plasma actuators 28 may be arranged in the circumferential direction of the cavity 34 so as to surround the cavity 34 along the side wall surface 34 a of the cavity 34.

  Next, effects of the flow control device in the combustion chamber according to the above-described embodiment of the present invention and the modification of the embodiment of the present invention will be described.

  First, the exposed electrode 40 of the plasma actuator 28 is disposed on the combustion chamber 16 side of the dielectric 38 disposed along the side wall surface 34 a of the cavity 34, and the embedded electrode 42 is disposed between the exposed electrode 40 and the dielectric 38. Since the opposite side is disposed closer to the bottom surface 34b of the cavity 34 than the exposed electrode 40, a high-frequency and high-voltage AC voltage is applied to the exposed electrode 40 and the embedded electrode 42 when the squish flow S and the reverse squish flow RS are generated. As a result, plasma is generated in the discharge space between the end surface of the exposed electrode 40 and the dielectric 38, and the flow toward the bottom surface of the cavity 34 along the side wall surface 34a of the cavity 34 by the volume force generated by the plasma. Can be induced. As a result, the squish flow S and the reverse squish flow RS can generate a flow in a direction that cancels out the vertical vortex generated in the cavity 34, and the gas flow velocity in the vicinity of the side wall surface 34 a of the cavity 34 can be suppressed. The convective heat transfer between the hot gas and the side wall surface 34a of the cavity 34 can be suppressed, and the cooling loss due to the squish flow S and the reverse squish flow RS can be reduced.

  Further, since the exposed electrode 40 and the buried electrode 42 are disposed so as to surround the cavity 34 along the side wall surface 34a of the cavity 34, high frequency and high voltage are generated when the squish flow S and the reverse squish flow RS are generated. By applying an AC voltage to the exposed electrode 40 and the embedded electrode 42, the vertical vortex generated in the cavity 34 due to the squish flow S or the reverse squish flow RS can be suppressed on the entire side wall surface 34a of the cavity 34, and the squish flow The cooling loss due to S or the reverse squish flow RS can be further effectively reduced.

  Further, the PCM 32 moves the plasma actuator 28 disposed along the side wall surface 34a of the cavity 34 along the side wall surface 34a of the cavity 34 during the compression stroke and the expansion stroke in which the squish flow S and the reverse squish flow RS are generated. Since control is performed so as to generate a flow toward the bottom surface of the cavity 34, the flow is generated in a direction to cancel the vertical vortex generated in the cavity 34 by the squish flow S and the reverse squish flow RS, and in the vicinity of the side wall surface 34 a of the cavity 34. The flow rate of the gas can be suppressed, thereby suppressing the convective heat transfer between the high temperature gas in the combustion chamber 16 and the side wall surface 34a of the cavity 34, thereby reducing the cooling loss due to the squish flow S and the reverse squish flow RS. Can be reduced.

1 Engine (Engine body)
14 Piston 16 Combustion chamber 16a Combustion chamber ceiling 28 Plasma actuator 32 PCM
34 Cavity 34a Side wall surface 34b Bottom surface 36 Peripheral portion 38 Dielectric 40 Exposed electrode 42 Embedded electrode SA Squish area

Claims (3)

In an engine in which a cavity recessed downward is formed at the center of the top surface of the piston, and a squish area is formed between the peripheral edge surrounding the radially outer side of the cavity and the ceiling surface of the combustion chamber, the gas in the combustion chamber A flow control device in the combustion chamber for controlling the flow of
The cavity formed in the piston top surface has a side wall surface and a bottom surface,
The cavity has a squish flow and a reverse squish flow on the ceiling surface of the combustion chamber along the side wall surface of the cavity at a predetermined time in the second half of the compression stroke and the first half of the expansion stroke before and after the compression top dead center of the engine. It is shaped to create a vertical vortex that contains the same direction of flow
A plasma actuator disposed in the combustion chamber;
The plasma actuator includes a dielectric disposed along the side wall surface of the cavity, an exposed electrode disposed on the combustion chamber side of the dielectric, and disposed on the opposite side of the exposed electrode across the dielectric. Embedded electrode,
The buried electrode, characterized in order to cancel the flow in the same direction toward the ceiling surface of the combustion chamber by the squish flow and the reverse squish flow, than the exposed electrode is arranged on the bottom side of the cavity, that A flow control device in the combustion chamber.   The flow control device in a combustion chamber according to claim 1, wherein the exposed electrode and the embedded electrode are disposed so as to surround the cavity along a side wall surface of the cavity. In an engine in which a cavity recessed downward is formed at the center of the top surface of the piston, and a squish area is formed between the peripheral edge surrounding the radially outer side of the cavity and the ceiling surface of the combustion chamber, the gas in the combustion chamber A flow control device in the combustion chamber for controlling the flow of
The cavity formed in the piston top surface has a side wall surface and a bottom surface,
The cavity has a squish flow and a reverse squish flow on the ceiling surface of the combustion chamber along the side wall surface of the cavity at a predetermined time in the second half of the compression stroke and the first half of the expansion stroke before and after the compression top dead center of the engine. It is shaped to create a vertical vortex that contains the same direction of flow
A plasma actuator disposed along a side wall surface of the cavity;
And a control means for controlling the plasma actuators,
Said control means, a combustion chamber, wherein along the side wall surface of the cavity for controlling the plasma actuators to generate a flow towards the bottom of the cavity, that between the expansion stroke from the compression stroke of the engine Flow control device.

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