JP2013238129A - Ignition control device and ignition control method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure stable ignition of an internal combustion engine by using in combination ignition of an air-fuel mixture in the cylinder by low temperature plasma and ignition of an air-fuel mixture in the cylinder by thermal plasma.SOLUTION: If in-cylinder gas density at the time of ignition is predetermined gas density or higher (S2), the in-cylinder gas temperature at the time of ignition is a predetermined temperature or higher (S3), and the rotational speed of the internal combustion engine is a predetermined rotational speed or lower (S4), an ignition plug is controlled so that ignition of an air-fuel mixture is performed by low temperature plasma (S5). Thus, its ignition delay period is shortened compared with ignition of an air-fuel mixture performed by thermal plasma, so that preferable ignition is ensured, variation of initial combustion is restrained, and stable combustion can be achieved.

Description

  The present invention relates to an ignition control device and an ignition control method for an internal combustion engine.

  Comparing the ignition of the air-fuel mixture by corona discharge with the ignition of the air-fuel mixture by arc discharge in spark ignition of the air-fuel mixture in the cylinder, corona discharge is a relatively wide range discharge, whereas arc discharge is a local discharge. Become. Therefore, in the ignition by corona discharge, the combustion speed in the combustion chamber can be increased compared to the ignition by arc discharge.

  Therefore, in Patent Document 1, under an operating condition that requires rapid combustion, for example, an operating condition such as low load and low rotation in which combustion is relatively unstable, the combustion speed is increased by performing ignition by corona discharge. ing. And under operating conditions that should avoid rapid combustion, for example, operating conditions such as high noise and high rotation that may deteriorate driving performance such as combustion noise when the combustion speed becomes excessive, ignition is performed by arc discharge. This prevents the combustion rate from becoming excessive.

JP 2008-121462 A

  However, in the region where the in-cylinder gas density at the ignition timing is relatively high, the inventor of the present invention ignites ignition by a low temperature plasma generated by corona discharge rather than ignition by thermal plasma generated by arc discharge. If the in-cylinder gas density at the ignition timing is less than the predetermined value, the in-cylinder temperature is less than the predetermined value, or the rotational speed of the internal combustion engine is more than the predetermined value, the period can be shortened. It has been found that ignition by low-temperature plasma generated by discharge worsens (cannot be shortened) the ignition delay period compared to ignition by thermal plasma generated by arc discharge.

  Therefore, the present invention uses a combination of ignition of an air-fuel mixture in a cylinder by low-temperature plasma and ignition of an air-fuel mixture in a cylinder by thermal plasma, and ensures stable ignitability under all operating conditions while maintaining stable combustion. It aims to realize.

  An ignition control apparatus for an internal combustion engine according to the present invention has ignition means capable of igniting an air-fuel mixture in a cylinder by generating at least one of low temperature plasma and thermal plasma, and the cylinder gas density at the ignition timing is a first predetermined value. When the operating condition exceeds the value, at least low temperature plasma is generated and the air-fuel mixture in the cylinder is ignited.

  According to the present invention, by igniting the air-fuel mixture with low-temperature plasma under the operating condition where the in-cylinder gas density is equal to or higher than the first predetermined value, the ignition delay period is longer than when the air-fuel mixture is ignited with thermal plasma. It can be shortened, good ignitability is ensured, variation in initial combustion is suppressed, and stable combustion can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which showed typically schematic structure of the internal combustion engine to which this invention was applied. Explanatory drawing which showed the detail of the ignition chamber typically. Explanatory drawing which showed typically the ignition chamber at the time of corona discharge. Explanatory drawing which showed typically the ignition chamber at the time of arc discharge. Explanatory drawing which shows the relationship between an applied voltage and application time, and a discharge form. The characteristic view which showed the ignition characteristic by a low temperature plasma, and the ignition characteristic by a thermal plasma compared. The flowchart which shows the flow of control in the ignition control apparatus of 1st Example of this invention. The flowchart which shows the flow of control in the ignition control apparatus of 2nd Example of this invention. The flowchart which shows the flow of control in the ignition control apparatus of 3rd Example of this invention. Explanatory drawing which shows the other example of a setting of an ignition area | region calculation map. Explanatory drawing which shows the other example of a setting of an ignition area | region calculation map. Explanatory drawing which shows the other example of a setting of an ignition area | region calculation map. Explanatory drawing which expanded and showed the principal part of the ignition control apparatus in 4th Example of this invention. Explanatory drawing which showed typically the outline of the ignition control apparatus in 5th Example of this invention.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view schematically showing a schematic configuration of an internal combustion engine to which the present invention is applied.

  An intake passage 4 is connected to the combustion chamber 2 of the internal combustion engine 1 via an intake valve 3, and an exhaust passage 6 is connected via an exhaust valve 5.

  The combustion chamber 2 is defined by the lower surface of the cylinder head 7, the inner wall surface of the cylinder 9 of the cylinder block 8, and the crown surface of the piston 10 that reciprocates in the cylinder 9. An ignition plug 11 as an ignition means for igniting the air-fuel mixture in the combustion chamber 2 is disposed at the center top of the combustion chamber 2.

  As shown in FIGS. 1 and 2, the spark plug 11 in the present embodiment includes a rod-shaped center electrode 12, a cylindrical side electrode 13 that covers the entire periphery of the center electrode 12, and a center electrode. And an insulator 14 for holding 12. The ignition plug 11 is attached to the cylinder head 7 so that one end of the side electrode 13 opens at the center top of the combustion chamber 2, and the ignition chamber 15, which is the space inside the side electrode 13, is the combustion chamber. In communication with the central top of the two.

  As shown in FIG. 2, the center electrode 12 has a plurality of protrusions 16 formed on the outer periphery. This protrusion 16 protrudes in the direction perpendicular to the axis of the center electrode 12 and makes the electric field strength in the ignition chamber 15 nonuniform, so that the tip of the protrusion 16 and the side electrode 13 as shown in FIG. A streamer, which will be described later, is generated.

  The spark plug 11 is connected to an ECU (Engine Control Unit) 20 via a distributor 17, a high voltage generator 18, and a pulse generator 19. The pulse generator 19 is controlled by the ECU 20 so that a pulse is generated at an appropriate time, and the voltage generated by the high voltage generator 18 in response to this pulse is applied by the distributor 17 to the cylinder at the ignition timing.

  The ECU 20 incorporates a microcomputer and performs various controls of the internal combustion engine 1, and includes a rotational speed sensor 21 that detects the rotational speed (engine rotational speed) of the internal combustion engine 1 and an air flow meter 22 that detects the intake air amount. The cooling water temperature sensor 23 for detecting the cooling water temperature, the intake pressure sensor 24 for detecting the intake pressure in the intake passage 4, the intake air temperature sensor 25 for detecting the intake air temperature in the intake passage 4, and the accelerator opening degree Signals from various sensors such as an accelerator pedal sensor 26 that detect a required load on the vehicle are input.

  The ECU 20 controls the fuel injection timing and fuel injection amount by the fuel injection valve 27 and the ignition timing by the spark plug 11 according to the operating conditions. The ECU 20 controls the discharge mode of the spark plug 11 in accordance with the rotational speed, load, etc. of the internal combustion engine 1. More specifically, the ECU 20 can switch the discharge form to corona discharge or arc discharge by controlling the voltage applied to the spark plug 11 and the pulse width of the voltage to be applied.

  When a high voltage is applied between the electrodes of the spark plug 11, electrons accidentally released from the negative electrode proceed while accelerating toward the positive electrode, and in the process, the atmosphere gas is ionized by collision to generate free electrons ( This is called electronic avalanche). Electrons ionized in the process of reaching the positive electrode quickly move to the positive electrode, leaving only large positive ions, and further avalanche is induced by the potential difference between the positive ion group and the negative electrode, which is called a streamer. A plasma in which positive ions and electrons are mixed is formed. This process is called low-temperature plasma, and the discharge mode in which the streamer is generated is called corona discharge. The low temperature plasma is generated in a relatively wide range. Therefore, in the ignition by the low temperature plasma, the air-fuel mixture is ignited in a relatively wide range.

  A streamer is generated at a plurality of parts of the positive electrode. When one of the streamers reaches the negative electrode and the positive and negative electrodes are electrically short-circuited, a large current flows through the short-circuited part, as shown in FIG. Arc is generated. This arc generates a high temperature, and the process of forming this arc is called thermal plasma. The discharge form in which this thermal plasma is generated is called arc discharge. That is, corona discharge occurs in a transient state from the start of voltage application to transition to arc discharge.

  When the discharge form transitions from corona discharge to arc discharge, a large current flows through a portion short-circuited by the arc, resulting in a voltage drop, resulting in an increase in power consumption. Further, in the arc discharge, since discharge occurs in a limited part of the electrode, the ignition of the air-fuel mixture becomes local, and the distance (flame propagation distance) required for the flame to spread over the entire combustion chamber 2 is relatively become longer.

  On the other hand, if the applied voltage is reduced in order to suppress the power consumption, the amount of streamer generation is reduced, or a dark current state is generated in which no streamer is generated.

  If transition to arc discharge can be prevented and the electron temperature of the air-fuel mixture can be increased by the streamer until ignition occurs, a plurality of streamers are generated around the center electrode 12, so that there are a plurality of parts to be ignited. That is, if the air-fuel mixture is ignited by low-temperature plasma in corona discharge, which is a relatively wide range of discharge, the air-fuel mixture is ignited in the combustion chamber 2 in comparison with the case where the air-fuel mixture is ignited by thermal plasma in arc discharge that is local discharge. The burning rate can be increased.

  The correlation between applied voltage, applied time (pulse width), and discharge mode will be described with reference to FIG. Here, the arc region is a region that has transitioned to arc discharge, the corona region is a region that maintains corona discharge before transitioning to arc discharge, and the dark current region is a region in which streamers are not generated.

  As shown in FIG. 5, the dark current region shifts to the corona region and arc region as the applied voltage increases. Further, as the application time becomes longer, the dark current region shifts to the corona region and the arc region. However, when the applied voltage is equal to or lower than a predetermined voltage (E0 in FIG. 5), it is a dark current region regardless of the application time, and does not shift to the corona region or the arc region.

  As described above, even when the distance between the electrodes and the electrode shape are the same, there are cases where arc discharge is caused by high voltage application time and corona discharge is caused. That is, if the high voltage application time is shortened and the electric field is interrupted before the transition to the arc region, the arc discharge does not occur and a high voltage can be applied between the electrodes while maintaining the corona discharge. For example, when the applied voltage is E, the dark current region is applied if the applied time is less than tc, the corona region is applied if the applied time is not less than tc and not more than ta, and the arc region is formed if the applied time is greater than ta. Therefore, for example, when corona discharge is performed with the applied voltage E, as shown in FIG. 5A, when the application time is t1 (tc ≦ t1 ≦ ta) and arc discharge is performed with the applied voltage E, As shown in FIG. 5B, the application time t2 (t2> ta) may be set.

  Further, a switch mechanism (not shown) capable of switching the polarity of the voltage applied to the center electrode of the spark plug 11 is provided between the distributor 17 and the spark plug 11, and by switching the polarity of the applied voltage, It is also possible to switch between corona discharge and arc discharge with the same pulse waveform. A streamer generated when a positive voltage is applied to the side electrode 13 of the spark plug 11 and a negative voltage is applied to the center electrode 12 is defined as a negative streamer, and a negative voltage is applied to the side electrode 13 of the spark plug 11. If a streamer that is applied and a positive voltage is applied to the center electrode 12 is a positive streamer, the positive streamer has a faster development speed than a negative streamer in terms of plasma characteristics.

  This is because, in a negative streamer in which the streamer travels toward the positive electrode, the electron avalanche generated as the electron progresses causes the electron charge accumulation portion to spread due to diffusion, whereas in the positive streamer, the streamer moves toward the negative electrode. This is because the avalanche itself advances toward the inside of the streamer, so that the streamer tip is thin and the electric field is maintained, so that the advancing speed is increased. Due to this difference in the development speed, it is possible to switch between corona discharge and arc discharge by switching the polarity of the applied voltage even with the same applied voltage and applied time.

  Here, in the region where the in-cylinder gas density at the ignition timing is relatively high, ignition by low-temperature plasma generated by corona discharge may shorten the ignition delay period compared to ignition by thermal plasma generated by arc discharge. Although it is possible, low temperature plasma generated by corona discharge when the in-cylinder gas density at the ignition timing is below a predetermined density, the in-cylinder temperature is below a predetermined temperature, or when the internal combustion engine rotational speed is above a predetermined rotational speed. It has been found by the inventor that the ignition delay period cannot be shortened (ignitability deteriorates) as compared with ignition by thermal plasma generated by arc discharge.

  FIG. 6 is a characteristic diagram showing, as an example, a comparison between ignition characteristics by low-temperature plasma and ignition characteristics by thermal plasma, with the vertical axis representing the ignition delay period and the horizontal axis representing the in-cylinder gas density during ignition. As shown in FIG. 6, in the region where the in-cylinder gas density at the time of ignition is relatively high, ignition by low-temperature plasma can shorten the ignition delay period compared to ignition by thermal plasma. When the gas density is small, the ignitability with respect to the thermal plasma deteriorates. If the cylinder gas density at which the ignition performance of the low-temperature plasma and the ignition performance of the thermal plasma are the same is ρ1, this ρ1 tends to increase as the rotational speed of the internal combustion engine increases.

  Therefore, in the ignition control apparatus according to the first embodiment, when the cylinder gas density at the time of ignition is equal to or higher than the predetermined density, the cylinder gas temperature at the time of ignition is equal to or higher than the predetermined temperature, and the rotation speed of the internal combustion engine 1 is the predetermined rotation. If it is below the speed, the spark plug 11 is controlled so that the air-fuel mixture is ignited by the low temperature plasma. When the in-cylinder gas density at the time of ignition is smaller than the predetermined density, or when the in-cylinder gas temperature at the time of ignition is lower than the predetermined temperature, or the rotational speed of the internal combustion engine 1 is larger than the predetermined rotational speed. In this case, the spark plug 11 is controlled so that the air-fuel mixture is ignited by thermal plasma.

  This makes it possible to shorten the ignition delay period by igniting the air-fuel mixture with thermal plasma by performing ignition with low-temperature plasma at the operating conditions where the ignitability by low-temperature plasma is better than thermal plasma. Good ignitability is ensured, variation in initial combustion is suppressed, and stable combustion can be realized.

  And, under the operating conditions where the ignitability is worse in the ignition by the low temperature plasma than in the ignition by the thermal plasma, the ignition delay period is shortened by performing the ignition by the thermal plasma rather than the ignition of the air-fuel mixture by the low temperature plasma. Can do.

  In addition, with the single spark plug 11, it is possible to realize the ignition of the air-fuel mixture using low-temperature plasma and the ignition of the air-fuel mixture using thermal plasma.

The in-cylinder gas density is prepared in advance through experiments, for example, and a map in which the in-cylinder gas density is calculated from the ignition timing, the intake air amount, and the rotational speed of the internal combustion engine 1 is stored in the ROM in the ECU 20. Thus, it can be estimated with reference to this map. However, the method for calculating the in-cylinder gas density is not limited to this method. For example, the in-cylinder gas density may be calculated from the in-cylinder gas pressure and the in-cylinder gas temperature using a gas state equation. The in-cylinder gas pressure Pign at the ignition timing is Pign = P1 × εignk, ^where the intake pressure is P1, the effective compression ratio at the ignition timing is εsign, and the specific heat ratio k. The in-cylinder gas temperature Tign at the ignition timing is calculated as follows: Tign = (T1 + α) × εign ^{(k -1)} .

  FIG. 7 is a flowchart showing a control flow in the ignition control apparatus of the first embodiment. In S1, a target torque, engine rotation speed (rotation speed of the internal combustion engine 1), and ignition timing are calculated based on various information input to the ECM 20. In S2, the in-cylinder gas density at the time of ignition is calculated by a known method as described above, and it is determined whether or not the calculated in-cylinder gas density is equal to or higher than the predetermined density set in advance. If the in-cylinder gas density is equal to or higher than the predetermined density, the process proceeds to S3, and if not, the process proceeds to S6. In S3, the in-cylinder gas temperature at the time of ignition is calculated by a known method as described above, and it is determined whether or not the calculated in-cylinder gas temperature is equal to or higher than the predetermined temperature set in advance. If the in-cylinder gas temperature is equal to or higher than the predetermined temperature, the process proceeds to S4, and if not, the process proceeds to S6. In S4, it is determined whether or not the current engine speed is equal to or less than the predetermined speed set in advance. If the engine speed is equal to or lower than the predetermined speed, the process proceeds to S5, and if not, the process proceeds to S6. In S5, the air-fuel mixture is ignited by low-temperature plasma. In S6, the air-fuel mixture is ignited by thermal plasma.

  Hereinafter, other embodiments of the present invention will be described. The same components as those of the first embodiment of the present invention described above are denoted by the same reference numerals, and redundant description will be omitted.

  The ignition control device according to the second embodiment of the present invention has substantially the same configuration as the ignition control device according to the first embodiment described above, but the in-cylinder gas is used for switching between ignition by low-temperature plasma and ignition by thermal plasma. Only the density and the rotational speed of the internal combustion engine 1 are taken into account.

  FIG. 8 is a flowchart showing a control flow in the ignition control apparatus of the second embodiment. In S11, a target torque, an engine rotational speed (the rotational speed of the internal combustion engine 1), and an ignition timing are calculated based on various information input to the ECM 20. In S12, the in-cylinder gas density at the time of ignition is calculated by a known method as described above, and it is determined whether or not the calculated in-cylinder gas density is equal to or higher than the predetermined density set in advance. If the in-cylinder gas density is equal to or higher than the predetermined density, the process proceeds to S13, and if not, the process proceeds to S15. In S13, it is determined whether or not the current engine speed is equal to or less than the predetermined speed set in advance. If the engine rotation speed is equal to or lower than the predetermined rotation speed, the process proceeds to S14, and if not, the process proceeds to S15. In S14, the air-fuel mixture is ignited by low-temperature plasma. In S15, the air-fuel mixture is ignited by thermal plasma.

  In the second embodiment as described above, it is possible to obtain substantially the same operational effects as those of the first embodiment described above.

  Next, an ignition control apparatus according to a third embodiment of the present invention will be described. The ignition control device according to the third embodiment has substantially the same configuration as the ignition control device according to the first embodiment described above, but in-cylinder gas density is used to determine whether to switch between ignition by low-temperature plasma and ignition by thermal plasma. Instead of the engine load (target torque) is used. That is, the third embodiment is an example in which the engine load (target torque) is used as the in-cylinder gas density at the time of ignition. The in-cylinder gas density at the time of ignition may be simply represented by the engine load.

  FIG. 9 is a flowchart showing a control flow in the ignition control apparatus of the third embodiment. In S21, a target torque, an engine rotational speed (the rotational speed of the internal combustion engine 1), and an ignition timing are calculated based on various information input to the ECM 20. In S22, the in-cylinder gas temperature at the time of ignition is calculated by a known method as described above, and it is determined whether or not the calculated in-cylinder gas temperature is equal to or higher than the predetermined temperature set in advance. If the in-cylinder gas temperature is equal to or higher than the predetermined temperature, the process proceeds to S23, and if not, the process proceeds to S25. In S23, using the ignition region calculation map in which the ignition region by the low temperature plasma and the ignition region by the thermal plasma are assigned according to the engine load and the engine speed, whether the current operating condition is the ignition region by the low temperature plasma or the heat A determination is made as to whether or not the ignition region is caused by plasma.

  The ignition region calculation map used in S23 indicates that the engine speed is low and the engine load is low, medium and high, the engine speed is medium and the engine load is medium and high, and the engine speed is high. When the engine load is high and the engine load is high, it is set to be an ignition region by low-temperature plasma. When the engine load is extremely low, the engine speed is medium and the engine load is low. When the engine load is low, the engine load is low, and the medium load is set, the ignition region is set to be the thermal plasma ignition region when the engine rotation speed is extremely high.

  If the determination result in S23 is the ignition region by the low temperature plasma, the process proceeds to S24, and if the determination result is the ignition region by the thermal plasma, the process proceeds to S25. In S24, the air-fuel mixture is ignited by low-temperature plasma. On the other hand, in S25, the mixture is ignited by thermal plasma.

  Also in the third embodiment, it is possible to obtain substantially the same operational effects as those of the first embodiment described above.

  In the third embodiment, instead of the in-cylinder gas temperature at the time of ignition, the coolant temperature at the time of ignition or the oil temperature of the engine oil may be used. That is, in S22 of FIG. 9, for example, when the cooling water temperature is equal to or higher than a predetermined water temperature or when the oil temperature is equal to or higher than a predetermined oil temperature, the process proceeds to S23. You may make it progress to S25.

  Further, the ignition region calculation map used in the third embodiment is changed according to the ignition performance of the air-fuel mixture by the low temperature plasma. For example, the ignition region calculation map as shown in FIGS. 10 and 11 is used. It is also possible to use it.

  In each of the ignition region calculation maps described above, the ignition region due to the low temperature plasma and the ignition region due to the thermal plasma are assigned according to the engine load and the engine speed, but as shown in FIG. It is also possible to use an ignition region calculation map in which an ignition region by low-temperature plasma and an ignition region by thermal plasma are assigned according to the density and the engine rotation speed. If an ignition region calculation map as shown in FIG. 12 is used, it is possible to more accurately estimate whether the ignition region is a low-temperature plasma ignition region or a thermal plasma ignition region.

  The ignition region calculation map shown in FIG. 12 is when the engine speed is low and the in-cylinder gas density is low, medium, and high, and when the engine speed is medium and the in-cylinder gas density is medium and high, When the engine speed is high and the in-cylinder gas density is high, it is set to be an ignition region by low-temperature plasma. When the in-cylinder gas density is extremely low, the engine speed is in the cylinder at medium speed. When the gas density is low, the engine rotation speed is high, and the in-cylinder gas density is low and medium density. When the engine rotation speed is extremely high, the ignition region is set by thermal plasma. .

  Further, when switching between ignition by low-temperature plasma and ignition by thermal plasma with a single ignition plug, it is possible to use an ignition plug 31 as shown in FIG. 13 instead of the ignition plug 11 described above.

  FIG. 13 is an explanatory view showing, in an enlarged manner, main portions of the ignition control device according to the fourth embodiment of the present invention.

  The ignition control device in the fourth embodiment has substantially the same configuration as the ignition control device in the first embodiment described above, but the spark plug 31 in the fourth embodiment is more than the top wall surface of the combustion chamber 2. A center electrode 32 disposed so as to protrude into the combustion chamber 2, an outer electrode (earth) 33 located on the outer peripheral side of the center electrode 32 and disposed so that the tip is exposed to the combustion chamber 2, and the center electrode And an insulator 34 for holding 32.

  And in this 4th Example, the ignition by a low temperature plasma and the ignition by a thermal plasma are switched by changing the voltage which generate | occur | produces by high frequency LC resonance. When the air-fuel mixture in the combustion chamber 2 is ignited by low-temperature plasma, the voltage applied to the spark plug 31 is relatively lowered, so that the streamer is provided around the center electrode 32 as shown in FIG. Is generated. When the air-fuel mixture in the combustion chamber 2 is ignited by thermal plasma, the voltage applied to the spark plug 31 is relatively increased, so that as shown in FIG. One arc (arc channel) that short-circuits the electrode 33 is generated.

  In the ignition control apparatus of the fourth embodiment as well, as in the first embodiment described above, the ignition by the low temperature plasma and the thermal plasma are performed in consideration of the in-cylinder gas density, the in-cylinder gas temperature, and the engine rotation speed. By switching between ignition by the above-mentioned, it is possible to obtain substantially the same operational effects as in the first embodiment described above. In the ignition control apparatus of the fourth embodiment, only the in-cylinder gas density and the engine rotational speed are considered in switching between ignition by low temperature plasma and ignition by thermal plasma as in the second embodiment described above. Alternatively, as in the third embodiment described above, the in-cylinder gas temperature, the engine rotation speed, and the engine load may be considered.

  Then, as in the fifth embodiment shown in FIG. 14, an ignition plug for ignition by low-temperature plasma and an ignition plug for ignition by thermal plasma may be provided separately.

  The ignition control device in the fifth embodiment has substantially the same configuration as the ignition control device in the first embodiment described above, but in this fifth embodiment, mixing is performed by low-temperature plasma at the center of the top of the combustion chamber 2. A first spark plug 41 for igniting the gas is disposed, and a second spark plug 51 for igniting the air-fuel mixture by thermal plasma is disposed on the outer periphery of the top of the combustion chamber 2. That is, in the fifth embodiment, the first spark plug 41 and the second spark plug 51 correspond to the ignition means.

  The first spark plug 41 is positioned so as to protrude from the top wall surface of the combustion chamber 2 into the combustion chamber 2, and is positioned on the outer peripheral side of the center electrode 42 so as to be exposed to the combustion chamber 2. An outer electrode (earth) 43 disposed and an insulator 44 for holding the center electrode 42 are provided. The first spark plug 41 ignites the air-fuel mixture by low-temperature plasma when a voltage is applied from a high-voltage RF power source.

  The second spark plug 51 has a center electrode 52 disposed so as to protrude into the combustion chamber 2 from the top wall surface of the combustion chamber 2, and an outer electrode 53 facing the tip of the center electrode 52. And the outer electrode 53 are discharged to generate sparks (thermal plasma) to ignite the air-fuel mixture.

  In the ignition control apparatus of the fifth embodiment as well, as in the first embodiment described above, in consideration of the in-cylinder gas density, the in-cylinder gas temperature, and the engine rotation speed, the ignition by the low temperature plasma and the thermal plasma are performed. By switching between ignition by the above-mentioned, it is possible to obtain substantially the same operational effects as in the first embodiment described above. Also in the ignition control device of the fifth embodiment, only the in-cylinder gas density and the engine speed are taken into account when switching between ignition by low-temperature plasma and ignition by thermal plasma, as in the second embodiment described above. Alternatively, as in the third embodiment described above, the in-cylinder gas temperature, the engine rotation speed, and the engine load may be considered.

  In the fifth embodiment in which the first ignition plug 41 for ignition by low-temperature plasma and the second ignition plug 51 for ignition by thermal plasma are individually provided, the in-cylinder gas density at the time of ignition is the predetermined value. If the density is higher than the density, the mixture is ignited at least by low-temperature plasma. If the in-cylinder gas density at the time of ignition is smaller than the predetermined density, at least the mixture is ignited by thermal plasma. You may do it. That is, when the in-cylinder gas density at the time of ignition is equal to or higher than the predetermined density, when the air-fuel mixture is ignited by the low temperature plasma using the first spark plug 41, the second spark plug 51 is used at the same time for the thermal plasma. When the in-cylinder gas density at the time of ignition is smaller than the predetermined density, the second spark plug 51 is used to ignite the air-fuel mixture using the thermal plasma. At the same time, the air-fuel mixture may be ignited by the low temperature plasma using the first spark plug 41.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Combustion chamber 3 ... Intake valve 4 ... Intake passage 5 ... Exhaust valve 6 ... Exhaust passage 7 ... Cylinder head 8 ... Cylinder block 9 ... Cylinder 10 ... Piston 11 ... Spark plug 12 ... Center electrode 13 ... Side Electrode 14 ... Insulator 15 ... Ignition chamber 16 ... Projection 17 ... Distributor 18 ... High voltage generator 19 ... Pulse generator 20 ... Engine control unit (ECU)
21 ... Rotational speed sensor 22 ... Air flow meter 23 ... Cooling water temperature sensor 24 ... Intake pressure sensor 25 ... Intake temperature sensor 26 ... Accelerator pedal sensor 27 ... Fuel injection valve

Claims (10)

Ignition means capable of igniting an air-fuel mixture in the cylinder by generating at least one of low temperature plasma and thermal plasma;
In-cylinder gas state detection means capable of estimating the in-cylinder gas density,
An ignition control device for an internal combustion engine, characterized in that, when operating conditions are such that the in-cylinder gas density at the ignition timing is equal to or higher than a first predetermined value, at least low-temperature plasma is generated to ignite an air-fuel mixture in the cylinder.   In the operating condition where the in-cylinder gas density at the ignition timing is smaller than the second predetermined value that is equal to or less than the first predetermined value, at least thermal plasma is generated to ignite the air-fuel mixture in the cylinder. The ignition control device for an internal combustion engine according to claim 1.   When the operating condition is such that the in-cylinder gas density at the ignition timing is equal to or higher than the first predetermined value, only low-temperature plasma is generated to ignite the mixture in the cylinder, and the in-cylinder gas density at the ignition timing is higher than the second predetermined value. 3. An ignition control device for an internal combustion engine according to claim 2, wherein only the thermal plasma is generated and the air-fuel mixture in the cylinder is ignited when the operating condition becomes smaller.   4. The ignition control device for an internal combustion engine according to claim 2, wherein the first predetermined value and the second predetermined value increase as the rotational speed of the internal combustion engine increases.   4. When the rotational speed of the internal combustion engine is larger than a predetermined rotational speed, thermal plasma is generated regardless of the in-cylinder gas density at the ignition timing to ignite the mixture in the cylinder. An ignition control device for an internal combustion engine according to any one of the above.   The in-cylinder gas mixture is ignited by generating thermal plasma regardless of the in-cylinder gas density at the ignition timing when the in-cylinder gas temperature at the ignition timing is lower than a predetermined temperature. An ignition control device for an internal combustion engine according to any one of the above.   4. When the water temperature or oil temperature of the internal combustion engine is lower than a predetermined temperature, thermal plasma is generated regardless of the in-cylinder gas density at the ignition timing to ignite the mixture in the cylinder. An ignition control device for an internal combustion engine according to any one of the above.   The ignition means has one ignition plug that can be switched between a discharge mode for generating low-temperature plasma and a discharge mode for generating thermal plasma by switching the discharge mode by energization control. An ignition control device for an internal combustion engine according to any one of the above.   The ignition means includes a first spark plug capable of generating only low-temperature plasma and a second spark plug capable of generating only thermal plasma. An ignition control device for an internal combustion engine according to claim 1. An ignition means capable of igniting an air-fuel mixture in the cylinder by generating at least one of a low temperature plasma and a thermal plasma; and an in-cylinder gas state detection means capable of estimating an in-cylinder gas density;
When the operating condition is such that the cylinder gas density at the ignition timing is equal to or higher than the first predetermined value, at least low temperature plasma is generated to ignite the mixture in the cylinder,
An internal combustion engine that generates at least thermal plasma and ignites an air-fuel mixture in a cylinder under an operating condition in which an in-cylinder gas density at an ignition timing is smaller than a second predetermined value that is equal to or lower than the first predetermined value. Engine ignition control method.

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