JP2008111371A - Ignition device of reciprocating engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ignition device which can be operated more stably by enabling to change applied voltage of corona discharge in accordance with an operational status of the reciprocating engine in such a case when lean or dilution combustion is performed. <P>SOLUTION: The ignition device of reciprocating engine 20 including a piston 24 which reciprocates inside a cylinder includes: a short-pulse high voltage generator 12 which generates short-pulse high voltage in accordance with the operational status of the reciprocating engine 20; and an electrode 11 which is disposed so as to extend in the cylinder and generates streamer arriving at the piston 24 by the short-pulse high voltage generated at the short-pulse high voltage generator 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ignition device for a reciprocating engine.

For example, the conventional engine ignition device described in Patent Document 1 applies a short rectangular wave-shaped high voltage from a pulse power supply to an electrode disposed in a cylinder head. First, streamer discharge (corona discharge) due to low-temperature plasma is generated on the electrode to which a short pulse high voltage is applied, and then arc discharge due to thermal plasma is generated. The fuel is ignited by such a discharge form. According to such an engine ignition device, it is possible to increase the ignition energy, increase the ignition region, and promote the propagation of flame to the entire combustion chamber as compared with a device using a normal spark plug. Increased capacity.
JP 2000-110697 A

  However, the conventional engine ignition device described above cannot change the applied voltage (input electron energy) of corona discharge. That is, in the conventional engine ignition device, streamer formation becomes unstable if the applied voltage is insufficient, and arc discharge occurs if the applied voltage is excessive, so that the applied voltage cannot be changed.

  However, as a result of diligent research conducted by the present inventors, it has been found that more stable lean or diluted combustion can be realized if the applied voltage of corona discharge can be increased, for example, during lean or diluted combustion.

  The present invention has been made by paying attention to such conventional problems, and allows the applied voltage of corona discharge to be changed according to the operating state of the reciprocating engine, for example, more stable operation during lean or diluted combustion. An object of the present invention is to provide an ignition device for a reciprocating engine.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  The present invention is an ignition device for a reciprocating engine (20) having a piston (24) that reciprocates in a cylinder, and generates a short pulse high voltage corresponding to the operating state of the reciprocating engine (20). A voltage generator (12) and an electrode (11) extending in the cylinder and generating a streamer reaching the piston (24) by the short pulse high voltage generated by the short pulse high voltage generator (12) It is characterized by having.

  According to the present invention, a streamer reaching the piston from the electrode is generated to generate corona discharge. That is, corona discharge is performed using the piston as the negative electrode. Therefore, the distance between electrodes (discharge gap distance) can be easily increased only by the application time. In corona discharge, the applied voltage (input electron energy) can be increased by increasing the distance between the electrodes. Therefore, the applied voltage (input electron energy) can be easily increased by setting the ignition timing at the time of lean or diluted combustion. Stable lean or diluted combustion is possible.

Hereinafter, the best mode for carrying out the present invention will be described in more detail with reference to the drawings.
(First embodiment)
FIG. 1 is a configuration diagram showing a first embodiment of an ignition device for a reciprocating engine according to the present invention.

  The engine ignition device 10 includes a corona discharge electrode 11 and a short pulse high voltage generator 12.

  The corona discharge electrode 11 is formed with a rod-shaped center electrode 11a protruding from the axial center and an insulator 11b for discharging to the piston side without causing the discharge generated at the center electrode 11a to creepage to the root. The

  An insulating layer 241 a is formed near the center of the crown surface 241 of the piston 24 of the engine 20. At least one piston ring 25 is made of a conductor. Other engine configurations are the same as the normal one. That is, the combustion chamber 21 is formed by the cylinder head 22, the cylinder block 23, and the piston 24. The cylinder head 22 is formed with an intake port 22a and an exhaust port 22b. A fuel injector 26 is provided in the intake port 22a. The intake port 22a is opened and closed by an intake valve 51 that responds to engine rotation. The exhaust port 22b is opened and closed by an exhaust valve 61 that responds to engine rotation.

  The short pulse high voltage generator 12 includes a pulse generator 12 a and a high voltage generator 12 b, and applies a short pulse high voltage to the corona discharge electrode 11. The short pulse high voltage generator 12 is controlled by the controller 70. The controller 70 applies the application voltage, application time, and application of the short pulse high voltage generator 12 in accordance with the operating conditions so that the streamer formation does not become unstable due to insufficient voltage and to prevent arc discharge due to excessive voltage. Ignition) timing is controlled. The controller 70 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). The controller 70 may be composed of a plurality of microcomputers.

  FIG. 2 is an enlarged view of the vicinity of the tip of the corona discharge electrode, and particularly shows a state during corona discharge.

  When the central electrode 11a of the corona discharge electrode 11 is subjected to corona discharge, a multi-branch streamer S directed around the insulating layer 241a on the crown surface 241 of the piston 24 is generated in a hollow cone shape. As a result, volumetric ignition occurs. As described above, according to the configuration of the present embodiment, corona discharge is generated at the shortest distance from the center electrode 11a to the piston crown surface 241 on which the insulating layer 241a is not formed. As shown in FIG. A streamer S is formed on the surface, and a relatively large ignition region having a hollow cone shape is formed.

  Next, the discharge mode when a voltage is applied to the corona discharge electrode 11 will be described.

  When a high voltage is applied to the corona discharge electrode 11, electrons are released from the negative electrode (piston crown surface 241 in this embodiment) and accelerated toward the positive electrode (center electrode 11a in this embodiment). On the way, the electrons collide with the atmospheric gas, ionize the atmospheric gas, and further generate free electrons (this phenomenon is called “electron avalanche”). Free electrons immediately go to the positive electrode, but large positive ions are left behind.

  Further, an avalanche of electrons is induced by the potential difference generated between the positive ion group and the negative electrode, and a plasma (low temperature plasma) called positive streamer mixed with positive ions and electrons is generated. The discharge form in which the streamer is generated is called corona discharge.

  As shown in FIG. 2, a plurality of streamers are generated on the positive electrode (center electrode 11a). If any of the streamers reaches the negative electrode (piston crown surface 241) and the positive and negative electrodes are electrically short-circuited, the short circuit occurs. A large current flows through the formed part, and a single arc is generated. The form of discharge in a state where an arc is generated is called arc discharge.

  FIG. 3 is a diagram for explaining power consumption by corona discharge and arc discharge.

  As described above, corona discharge occurs in a transient state from the start of voltage application to transition to arc discharge. Since corona discharge accelerates only light electrons without accelerating protons with large mass, it consumes less current than arc discharge. For this reason, as shown in FIG. 3, the corona discharge can apply a higher voltage (about 30 to 100 kV) than the arc discharge, and the combustion reaction can be promoted by the electrons accelerated by the high energy of the corona discharge. Further, in the corona discharge, as shown in FIG. 2, a multi-branch streamer is generated in a wide range between the electrodes, so that there are a plurality of parts that ignite, and as a result, the volume of the part where the ignition occurs increases. Such volumetric ignition makes it possible to realize combustion with high isovolume.

  FIG. 4 is a diagram showing the relationship between the in-cylinder pressure and the streamer forming voltage (corona discharge voltage) when the interelectrode distance (discharge gap distance) is constant. The line in the figure is a constant line having a distance between electrodes (discharge gap distance).

  As shown in FIG. 4, in the corona discharge, the applied voltage (input electron energy) can be increased by increasing the distance between the electrodes (discharge gap distance).

  In this embodiment, since the negative electrode is the piston crown 241, the distance between electrodes (discharge gap distance) can be easily increased, and the applied voltage (charged electron energy) during discharge can be easily increased. Therefore, if the ignition is advanced when the piston is away from the top dead center (while the discharge gap distance is large), the total discharge area and total discharge volume are also large, so the lean combustion range with the same power consumption as the conventional spark plug To increase the thermal efficiency of the engine.

  According to the present embodiment, since the piston crown surface 241 is a negative electrode, the distance between electrodes (discharge gap distance) can be easily increased only by the application timing, and the applied voltage (input electron energy) of corona discharge as shown in FIG. ) Can be easily raised. In addition, a large discharge volume due to corona discharge can be obtained by applying a voltage corresponding to the distance between the electrodes (a limit voltage that does not cause an arc discharge transition). Further, the discharge volume (volume of the streamer forming portion) can be easily expanded, the lean combustion range is expanded, and the thermal efficiency is improved.

  Further, since the distance from the center electrode 11a to the piston crown surface 241 in the crank angle range of the ignition timing is made shorter than the distance from the center electrode 11a to all the conductors in the combustion chamber, as shown in FIG. In addition, corona discharge can be performed from the center electrode 11a to the piston crown surface 241 in the entire ignition range (the most advanced timing to the most retarded timing of the ignition timing).

  Furthermore, the ignition timing is set to advance during lean or diluted combustion, but as shown in FIG. 5, the distance between the electrodes (discharge gap distance) becomes longer and the discharge volume (volume of the streamer forming portion) increases. To do. Accordingly, the applied voltage (input electron energy) of the corona discharge can be increased, and further, the discharge volume is expanded, so that stable lean or diluted combustion can be realized.

  Furthermore, since the insulating layer 241a is formed in the vicinity of the center of the piston crown surface 241, even when the piston is near the top dead center as shown in FIG. ) Can be secured.

  Further, since the piston ring 25 is made of a conductor, the electricity charged in the piston 24 can flow smoothly in the ground direction.

(Second Embodiment)
FIG. 6 is a diagram showing a second embodiment of an ignition device for a reciprocating engine according to the present invention. 6A is a longitudinal cross-sectional view, FIG. 6B is a view taken along the line BB in FIG. 6A, and FIG. 6C is a diagram showing a discharge volume.

  In the following description, the same reference numerals are given to portions that perform the same functions as those in the above-described embodiment, and overlapping descriptions are omitted as appropriate.

  In the center of the piston crown surface 241, a cavity 242 formed by a circular bottom surface 242a and an inner wall surface 242b upstanding from the periphery of the circular bottom surface is provided. An insulating layer 242c is formed at least near the center of the circular bottom surface 242a. In FIG. 6, the insulating layer 242c is formed over the entire circular bottom surface 242a.

  The length of the center electrode 11a is such that at least the tip of the center electrode 11a is located in the cavity when the piston is at the most advanced position of the ignition timing, and the tip of the center electrode 11a is at the top dead center position. Is a length that does not hit the bottom of the cavity.

  With such a configuration, as shown in FIGS. 6A and 6B, corona discharge occurs between the center electrode 11a and the inner wall surface 242b. As shown in FIG. 6C, the streamer S is formed in a cylindrical shape.

  According to this embodiment, the streamer S is formed in a cylindrical shape, and a relatively large volume ignition region is formed. As shown in FIG. 7 (A), if the piston is ignited when near the top dead center, the volume ignition region is large, and as shown in FIG. 7 (B), if the piston moves away from the top dead center. The volume ignition area becomes smaller.

  Further, the distance between the electrodes (discharge gap distance) can be easily increased, and a large discharge (ignition) region can be secured in the center of the combustion chamber. Since the cavity shape is simple, processing is easy, and by devising the cavity shape, it is possible to perform a desired corona discharge in relation to the application time.

  Further, since the insulating layer 242c is formed on the cavity bottom surface 242a, as shown in FIG. 7A, the center electrode 11a discharges to the inner wall surface 242b even near the top dead center, and a relatively long interelectrode distance (discharge) Gap distance) can be ensured, and the applied voltage can be made higher than the relationship of FIG.

  Furthermore, discharge can be performed in the same portion (from the center electrode 11a to the inner wall surface 242b) in a wide ignition timing range.

  In the above description, the length of the center electrode 11a is described as that at least the tip of the center electrode 11a is located in the cavity when the piston is at the most advanced angle position of the ignition timing. ), Corona discharge may be performed in a hollow conical shape between the center electrode 11a and the piston crown surface 241 so that the tip of the center electrode 11a is outside the cavity.

(Third embodiment)
FIG. 8 is a diagram showing a third embodiment of an ignition device for a reciprocating engine according to the present invention. 8A is a longitudinal sectional view, FIG. 8B is a view taken along the line BB in FIG. 8A, and FIG. 8C is a diagram showing a discharge volume.

  In the crown surface 241 of the piston 24 of the present embodiment, a cavity 243 recessed in a hemispherical shape is formed.

  In this way, corona discharge is generated from the tip of the center electrode 11a to the entire surface of the cavity 243 at the time of ignition, and a streamer is generated in a hemispherical region as shown in FIG. Therefore, a large hemispherical ignition volume region can be obtained.

  If the tip of the center electrode 11a is hemispherical, the distance from the tip of the center electrode 11a to the cavity surface becomes equal, and a more uniform streamer can be generated, and the isovolume can be increased.

(Fourth embodiment)
FIG. 9 is a view showing a fourth embodiment of an ignition device for a reciprocating engine according to the present invention. FIG. 9A shows a state where the piston is in the vicinity of the top dead center, and FIG. 9B shows a state where the piston is in front of the top dead center.

  In the center of the piston crown surface 241 of the present embodiment, a cavity 242 formed by a circular bottom surface 242a, a first inner wall spherical surface 242d, and a second inner wall spherical surface 242e is provided. The first inner wall spherical surface 242d continues around the circular bottom surface 242a and gradually increases in diameter as the inner diameter proceeds upward. The second inner wall spherical surface 242e continues around the first inner wall spherical surface 242d, gradually increases in diameter as the inner diameter proceeds upward, and has a larger diameter expansion rate than the first inner wall spherical surface 242d. An insulating layer 242c is formed at least near the center of the circular bottom surface 242a. In FIG. 9, an insulating layer 242c is formed over the entire circular bottom surface 242a.

  In this way, when the piston is near the top dead center, corona discharge is generated from the tip of the center electrode 11a to the first inner wall spherical surface 242d. When the distance from the vicinity of the top dead center is reached, a corona discharge is generated from the tip of the center electrode 11a to the second inner wall spherical surface 242e.

  Although the ignition timing is set to advance during lean or diluted combustion, the discharge volume increases when advanced as shown in FIG. 9, so that stable lean or diluted combustion can be realized.

(Fifth embodiment)
FIG. 10 is a view showing a fifth embodiment of an ignition device for a reciprocating engine according to the present invention. FIG. 10A shows a state where the piston is in the vicinity of the top dead center, and FIG. 10B shows a state where the piston is in front of the top dead center.

  A cavity 242 formed by a circular bottom surface 242a, a first inner wall spherical surface 242d, an opening reduced diameter surface 242f, and a second inner wall spherical surface 242e is provided at the center of the piston crown surface 241 of the present embodiment. The first inner wall spherical surface 242d continues around the circular bottom surface 242a and gradually increases in diameter as the inner diameter proceeds upward. The opening diameter-reducing surface 242f is continuous with the opening of the first inner wall spherical surface 242d and is formed in parallel with the circular bottom surface 242a to narrow the opening area of the first inner wall spherical surface 242d. The second inner wall spherical surface 242e is continuous around the opening of the opening diameter-reducing surface 242f and gradually increases in diameter as the inner diameter proceeds upward. An insulating layer 242c is formed at least near the center of the circular bottom surface 242a. In FIG. 10, the insulating layer 242c is formed over the entire circular bottom surface 242a. An insulating layer 242g is formed on the opening reduced diameter surface 242f.

  In this way, when the piston is near the top dead center, corona discharge is generated from the tip of the center electrode 11a to the first inner wall spherical surface 242d. When the distance from the vicinity of the top dead center is reached, a corona discharge is generated from the tip of the center electrode 11a to the second inner wall spherical surface 242e.

(Sixth embodiment)
FIG. 11 is a view showing a sixth embodiment of an ignition device for a reciprocating engine according to the present invention. FIG. 11A shows a state where the piston is in the vicinity of the top dead center, and FIG. 11B shows a state where the piston is in front of the top dead center.

  In the present embodiment, an insulating layer 241a is further formed on the piston crown surface 241 as compared with the second embodiment.

  The length of the center electrode 11a is such that at least the tip of the center electrode 11a is located outside the cavity when the piston 24 is at the most advanced position of the ignition timing, and the center electrode 11a is at the top dead center position. This length is such that the tip does not hit the bottom of the cavity.

  With such a configuration, when the piston 24 is near the top dead center, as shown in FIG. 11A, corona discharge occurs between the center electrode 11a and the inner wall surface 242b, and the streamer S has a small diameter circle. It is formed in a column shape. When the piston 24 is in front of the top dead center, corona discharge is generated between the center electrode 11a and the cylinder block wall surface 231 as shown in FIG. 11B, and the streamer S is formed in a large-diameter columnar shape. The

  Without being limited to the embodiments described above, various modifications and changes are possible within the scope of the technical idea, and it is obvious that these are also included in the technical scope of the present invention.

  For example, in the above embodiment, the piston position at the time of ignition is changed by the advance / retarded angle of the ignition timing, but in addition to this, a multi-link variable compression ratio as disclosed in, for example, JP-A-2001-227367 is used. It is also suitable for a device that changes the piston position by a mechanism.

  Also in the third to fifth embodiments, an insulating layer may be formed on the piston crown surface 241 as in the sixth embodiment. By doing so, when the piston 24 is in front of the top dead center, a corona discharge can be generated between the center electrode 11a and the cylinder block wall surface 231 to form a large-diameter columnar streamer.

1 is a configuration diagram showing a first embodiment of an ignition device for a reciprocating engine according to the present invention. FIG. It is an enlarged view near the front-end | tip of a corona discharge electrode, and shows the state at the time of a corona discharge especially. It is a figure explaining the power consumption by corona discharge and arc discharge. FIG. 6 is a diagram showing the relationship between in-cylinder pressure and streamer formation voltage (corona discharge voltage) when the distance between electrodes (discharge gap distance) is constant. It is a schematic diagram which shows the mode of the corona discharge in the whole ignition range of 1st Embodiment (the most advanced angle timing-the most retarded timing of ignition timing). It is a figure which shows 2nd Embodiment of the ignition device of the reciprocating engine by this invention. It is a schematic diagram which shows the mode of the corona discharge in the whole ignition range of 2nd Embodiment (the most advanced timing-the most retarded timing of ignition timing). It is a figure which shows 3rd Embodiment of the ignition device of the reciprocating engine by this invention. It is a figure which shows 4th Embodiment of the ignition device of the reciprocating engine by this invention. It is a figure which shows 5th Embodiment of the ignition device of the reciprocating engine by this invention. It is a figure which shows 6th Embodiment of the ignition device of the reciprocating engine by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine ignition device 11 Corona discharge electrode 11a Center electrode 12 Short pulse high voltage generator 20 Reciprocating engine 21 Combustion chamber 23 Cylinder block 231 Cylinder block wall surface 24 Piston 241 Crown surface 241a Insulating layer 242 243 Cavity 25 Piston ring 70 Controller

Claims (11)

An ignition device for a reciprocating engine having a piston that reciprocates in a cylinder,
A short pulse high voltage generator for generating a short pulse high voltage according to the operating state of the reciprocating engine;
An electrode extending into the cylinder and generating a streamer reaching the piston by a short pulse high voltage generated by the short pulse high voltage generator;
An ignition device for a reciprocating engine. The short pulse high voltage generator generates a short pulse high voltage according to the operating state of the reciprocating engine so that the electrode maintains the streamer formation without transitioning to arc discharge.
The ignition device for a reciprocating engine according to claim 1. The electrode is disposed near the center of the combustion chamber ceiling,
An insulating layer formed near the center of the crown surface of the piston and preventing the streamer from reaching the electrode;
The ignition device for a reciprocating engine according to claim 1 or 2, wherein the ignition device is a reciprocating engine. The piston has a cavity whose crown surface is recessed and a streamer generated from the electrode reaches and ignites volume.
The reciprocating engine ignition device according to any one of claims 1 to 3, wherein the ignition device is a reciprocating engine. The cavity is formed in a hemispherical shape,
The ignition device for a reciprocating engine according to claim 4. The cavity is formed by a circular bottom surface and an inner wall surface upright from the periphery of the circular bottom surface.
The ignition device for a reciprocating engine according to claim 4. The cavity includes a circular bottom surface, a first inner wall spherical surface that continuously extends around the circular bottom surface and gradually increases in diameter as the inner diameter progresses upward, and continues around the first inner wall spherical surface and progresses upward along the inner diameter. The diameter is gradually increased, and the second inner wall spherical surface has a larger diameter change rate than the first inner wall spherical surface.
The ignition device for a reciprocating engine according to claim 4. The cavity is formed in parallel with the circular bottom surface, the first inner wall spherical surface that is continuous around the circular bottom surface and gradually increases in diameter as the inner diameter progresses upward, and the opening of the first inner wall spherical surface. In addition, an opening diameter-reducing surface that narrows the opening area of the first inner wall spherical surface, and a second inner wall spherical surface that continuously extends around the opening of the opening diameter-reducing surface and gradually increases in diameter as the inner diameter proceeds upward. ,
The ignition device for a reciprocating engine according to claim 4. The electrode is disposed near the center of the combustion chamber ceiling,
An insulating layer that is formed near the center of the circular bottom surface and prevents a streamer from reaching the electrode;
The reciprocating engine ignition device according to any one of claims 6 to 8, wherein the ignition device is a reciprocating engine. An insulating layer that is formed on the crown of the piston and prevents the streamer from reaching the electrode;
The electrode generates a streamer that reaches the inner wall surface of the cylinder when the tip is above the crown surface of the piston and the tip is outside the cavity.
The ignition device for a reciprocating engine according to any one of claims 6 to 9, wherein the ignition device is a reciprocating engine. The piston is provided with a piston ring that is formed of a conductor and releases the electric charge charged to the piston to the ground.
The ignition device for a reciprocating engine according to any one of claims 1 to 10, wherein the ignition device is a reciprocating engine.