JP2013238130A - 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 executing at the same timing 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 density or lower (S2), if an in-cylinder gas temperature at the time of ignition is a predetermined temperature or lower (S3), or if the rotational speed of the internal combustion engine 1 is a predetermined rotational speed or higher (S4), a first ignition plug 7 and a second ignition plug 8 are controlled so that ignition of an air-fuel mixture in a combustion chamber 2 is carried out by both low temperature plasma and thermal plasma. Thus, since propagation of flame generated by the ignition by the thermal plasma is utilized in operation conditions with ignition of the low temperature plasma deteriorated, deterioration of the ignition by the low temperature plasma is restrained. Thus preferable ignition of the low temperature plasma for igniting an air-fuel mixture is ensured in a relatively wide range in the combustion chamber 2 for a wide range of operation conditions.

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.

  Further, in Patent Document 1, ignition by low temperature plasma and ignition by thermal plasma are used properly, and ignition by low temperature plasma and ignition by thermal plasma are not performed at the same time.

  Therefore, the present invention secures stable ignitability under all operating conditions by performing ignition of the mixture in the cylinder by low temperature plasma and ignition of the mixture in the cylinder by thermal plasma at the same time. However, it aims at realizing stable combustion.

  The ignition control device for an internal combustion engine according to the present invention has an in-cylinder gas density at an ignition timing of a predetermined density or less, an in-cylinder temperature at the ignition timing of a predetermined temperature or less, an internal combustion engine rotation speed of a predetermined rotation speed or more, and an internal combustion engine load. In any case of a predetermined load or less, the air-fuel mixture is ignited by low-temperature plasma after the air-fuel mixture is ignited by thermal plasma.

  According to the present invention, it is possible to suppress deterioration in ignition performance due to low temperature plasma under operating conditions in which ignitability deteriorates only by generating only low temperature plasma, and in a relatively wide range within the combustion chamber under a wide range of operating conditions. Thus, it is possible to ensure good ignitability of the low temperature plasma for igniting the air-fuel mixture.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which showed typically schematic structure of the internal combustion engine to which this invention was applied. The characteristic view which showed the ignition characteristic by a low temperature plasma, and the ignition characteristic by a thermal plasma compared. Explanatory drawing which showed typically the generation | occurrence | production time of low-temperature plasma. 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. 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.

  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.

  The combustion chamber 2 of the internal combustion engine 1 is defined by the lower surface of the cylinder head 3, the inner wall surface of the cylinder 5 of the cylinder block 4, and the crown surface of the piston 6 that reciprocates in the cylinder 5.

The combustion chamber 2 has a first spark plug 7 as a first ignition means for igniting an air-fuel mixture in the combustion chamber 2 by generating a low temperature plasma, and a thermal plasma in the combustion chamber 2. The second spark plug 8 as a second ignition means for igniting the air-fuel mixture is provided separately. The first spark plug 7 is provided at the center of the top of the combustion chamber 2, and the top of the combustion chamber 2. A central electrode 9 disposed so as to protrude from the wall surface into the combustion chamber 2, an outer electrode 10 positioned on the outer peripheral side of the central electrode 9 and having its tip exposed to the combustion chamber 2, and the central electrode 9 and an insulator 11 for holding 9.

  The first spark plug 7 is connected to an ECU (Engine Control Unit) 14 via a distributor 12 and a high voltage generator 13. The high voltage generator 13 is, for example, a high voltage RF power source or a high voltage nano pulse power source that repeatedly generates a nano pulse voltage. The high voltage generator 13 is controlled by the ECU 14 to generate a high voltage at an appropriate time for an appropriate period. The voltage generated by the device 13 is applied by the distributor 12 to the cylinder at the ignition timing.

  The second spark plug 8 is provided on the outer peripheral side of the top of the combustion chamber 2, and is opposed to the center electrode 15 disposed so as to protrude into the combustion chamber 2 from the top wall surface of the combustion chamber 2, and the front end of the center electrode 15. And an outer electrode 16 that discharges between the center electrode 15 and the outer electrode 16 to generate a spark (thermal plasma) to ignite the air-fuel mixture.

  The second spark plug 8 is connected to the ECU 14 via a distributor 17, an ignition coil 18, and a power source 19. The ignition coil 18 is controlled by the ECU 14 to turn on and off the primary current of the ignition coil 18, thereby generating a high voltage at an appropriate time on the secondary side of the ignition coil 18. The high voltage generated on the secondary side of the ignition coil 18 is applied by the distributor 17 to the cylinder at the ignition timing.

  The ECU 14 incorporates a microcomputer and performs various controls of the internal combustion engine 1. The ECU 14 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. A cooling water temperature sensor 23 for detecting the cooling water temperature, an intake pressure sensor 24 for detecting the intake pressure in the intake passage, an intake air temperature sensor 25 for detecting the intake air temperature in the intake passage, and the accelerator opening to the internal combustion engine 1 Signals from various sensors such as an accelerator pedal sensor 26 for detecting the required load are input.

  The first spark plug 7 generates a non-uniform electric field around the tip of the center electrode 9 by applying a high voltage from an RF power source or a nano pulse power source, and generates low-temperature plasma due to corona discharge 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. Low temperature plasma is a thermally non-equilibrium state in which only the electron temperature in the plasma is very high.

  The second spark plug 8 generates thermal plasma by arc discharge between the center electrode 15 and the outer electrode 16. In the arc discharge, the center electrode 15 and the outer electrode 16 are electrically short-circuited, a large current flows through the short-circuited portion, and a single arc is generated. This arc generates a high temperature, and the process of forming this arc is called thermal plasma. Therefore, in the ignition by the thermal plasma, the ignition of the air-fuel mixture becomes local, and the distance (flame propagation distance) required until the flame spreads over the entire combustion chamber 2 becomes relatively long.

  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. 2 is a characteristic diagram showing, as an example, a comparison between ignition characteristics by low-temperature plasma and ignition characteristics by thermal plasma, where the vertical axis is the ignition delay period and the horizontal axis is the in-cylinder gas density at the time of ignition. As shown in FIG. 2, 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 device according to the first embodiment, when the in-cylinder gas density at the time of ignition is higher than the predetermined density, the in-cylinder gas temperature at the time of ignition is higher than the predetermined temperature, and the rotation speed of the internal combustion engine 1 is When the rotational speed is lower than the predetermined rotational speed, the first spark plug 7 is controlled so that the air-fuel mixture in the combustion chamber 2 is ignited only by the low temperature plasma. When the in-cylinder gas density at the time of ignition is equal to or lower than the predetermined density, the in-cylinder gas temperature at the time of ignition is equal to or lower than the predetermined temperature, or the rotational speed of the internal combustion engine 1 is equal to or higher than the predetermined rotational speed. The first spark plug 7 and the second spark plug 8 are controlled so that the air-fuel mixture in the combustion chamber 2 is ignited by both low temperature plasma and thermal plasma.

  When the mixture in the combustion chamber 2 is ignited by both the low temperature plasma and the thermal plasma, the space (in which the low temperature plasma is generated in the combustion chamber 2 at the timing when the low temperature plasma is generated by the first spark plug 7 ( Prior to generating the low temperature plasma, the second spark plug 8 generates thermal plasma so that the state of the discharge region of the low temperature plasma is easily ignited by the low temperature plasma, and ignites the mixture by the thermal plasma. .

  Here, the generation timing of the low temperature plasma in the case where the air-fuel mixture in the combustion chamber 2 is ignited by both the low temperature plasma and the thermal plasma will be described in detail with reference to FIG.

  If the air-fuel mixture is ignited by thermal plasma before generating low-temperature plasma, the air-fuel mixture in the portion ignited by thermal plasma expands as burned gas, and the gas density of the air-fuel mixture in the unburned region increases accordingly. Thus, the state of the space where the low temperature plasma is generated becomes easy to ignite with the low temperature plasma.

  However, if the time from the ignition by the thermal plasma to the ignition by the low temperature plasma is too short, the active chemical species formed by the low temperature plasma disappears before the gas density in the unburned region is sufficiently increased. Ignition does not improve. Therefore, the gas density in the space where the low temperature plasma is generated increases due to the propagation of the flame formed by the ignition by the thermal plasma, and the active chemical species formed when the low temperature plasma is generated does not disappear and the ignition of the air-fuel mixture After the time when it is effectively used for (oxidation reaction), low temperature plasma is generated and ignition by low temperature plasma is performed.

  In addition, if the time from ignition by thermal plasma to ignition by low temperature plasma becomes too long, the flame generated by ignition by thermal plasma reaches the space where low temperature plasma is generated, and the air-fuel mixture in the space where low temperature plasma is generated Becomes burnt gas. Therefore, before the time when the flame generated by the ignition by the thermal plasma arrives and the mixture in the space where the low temperature plasma is generated becomes burned gas, the low temperature plasma is generated and the low temperature plasma is ignited. I do.

  Therefore, when the mixture in the combustion chamber 2 is ignited by both the low temperature plasma and the thermal plasma, the gas density in the space where the low temperature plasma is generated is increased by the propagation of the flame formed by the ignition by the thermal plasma, and the low temperature plasma is After the time when the active chemical species formed when it is generated does not disappear and is used effectively for ignition (oxidation reaction) of the air-fuel mixture, the flame generated by ignition by the thermal plasma arrives and low temperature plasma is generated Low temperature plasma is generated by the first spark plug 7 within a period (for example, the low temperature plasma generation period in FIG. 3) before the time when the air-fuel mixture in the space becomes burnt gas.

  Note that the target ignition timing calculated by the ECU 14 from the operating conditions is an ignition timing by low-temperature plasma. That is, the reference ignition timing is the ignition timing of the low temperature plasma by the first spark plug 7, and when the mixture in the combustion chamber 2 is ignited by both the low temperature plasma and the thermal plasma, this reference ignition is performed. The ignition timing of the second spark plug 8 is set so that the air-fuel mixture is ignited by the low temperature plasma at the timing.

  In such an ignition control device of the first embodiment, under the operating conditions in which the ignitability due to the low temperature plasma deteriorates, the deterioration of the ignitability due to the low temperature plasma is obtained by utilizing the propagation of the flame generated by the ignition due to the thermal plasma. Therefore, it is possible to ensure good ignitability of the low temperature plasma that ignites the air-fuel mixture in a relatively wide range in the combustion chamber 2 under a wide range of operating conditions.

  Further, from the start to the end of the generation of the low temperature plasma, the air-fuel mixture can be ignited in a relatively wide region by the low temperature plasma by the ignition by the low temperature plasma.

The in-cylinder gas density is prepared in advance through experiments, for example, 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 and stored in the ROM in the ECU 14. 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. 4 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 14. 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 less than the predetermined density set in advance. If the in-cylinder gas density is equal to or lower than the predetermined density, the process proceeds to S6, and if not, the process proceeds to S3. 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 lower than the predetermined temperature set in advance. If the in-cylinder gas temperature is equal to or lower than the predetermined temperature, the process proceeds to S6, and if not, the process proceeds to S4. In S4, it is determined whether or not the current engine rotation speed is equal to or higher than the predetermined rotation speed set in advance. If the engine rotational speed is equal to or higher than the predetermined rotational speed, the process proceeds to S6, and if not, the process proceeds to S5. In S5, the air-fuel mixture is ignited by low-temperature plasma. In S6, both ignition of the air-fuel mixture using thermal plasma and ignition of the air-fuel mixture using low-temperature plasma are performed.

  In determining whether to perform ignition by low temperature plasma, or both ignition by thermal plasma and ignition by low temperature plasma, as in the second embodiment shown in FIG. 5, the engine load (target torque) and the engine 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 both thermal plasma and low-temperature plasma are assigned according to the rotation speed.

  FIG. 5 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 14. In S12, 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 lower than the predetermined temperature set in advance. If the in-cylinder gas temperature is equal to or lower than the predetermined temperature, the process proceeds to S13, and if not, the process proceeds to S14. In S14, the current operating condition is ignited by the low temperature plasma using the ignition region calculation map in which the ignition region by the low temperature plasma and the ignition region by both the thermal plasma and the low temperature plasma are assigned according to the engine load and the engine speed. It is determined whether the region is an ignition region by both thermal plasma and low-temperature plasma.

  The ignition region calculation map used in S14 is such 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. Is set to be an ignition region by both thermal plasma and low-temperature plasma when the engine speed is extremely high and the engine load is low and medium load.

  If the determination result in S14 is the ignition region by the low temperature plasma, the process proceeds to S15, and if the determination result is the ignition region by both the thermal plasma and the low temperature plasma, the process proceeds to S13. In S15, the air-fuel mixture is ignited by low-temperature plasma. On the other hand, in S13, the mixture is ignited by both the thermal plasma and the low temperature 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.

  In the second 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 S12 of FIG. 5, for example, when the cooling water temperature is equal to or lower than a predetermined water temperature set in advance or when the oil temperature is equal to or lower than a predetermined oil temperature set in advance, the process proceeds to S13. You may make it progress to S14.

  Further, the ignition region calculation map used in the second 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. 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 both thermal plasma and low-temperature plasma are assigned according to the density and the engine speed. If an ignition region calculation map as shown in FIG. 8 is used, it is possible to more accurately estimate whether it is an ignition region due to low temperature plasma or an ignition region due to both thermal plasma and low temperature plasma.

  The ignition region calculation map shown in FIG. 8 is when the engine rotation speed is low and the in-cylinder gas density is low, medium, and high, and when the engine rotation 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. When the engine rotation speed is extremely high, the ignition region is sent by sending thermal plasma and low-temperature plasma. It is set as follows.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Combustion chamber 3 ... Cylinder head 4 ... Cylinder block 5 ... Cylinder 6 ... Piston 7 ... 1st spark plug 8 ... 2nd spark plug 14 ... ECU

Claims (5)

First ignition means for generating low temperature plasma and igniting an air-fuel mixture in the cylinder;
Second ignition means for generating thermal plasma and igniting the air-fuel mixture in the cylinder;
In-cylinder gas state detection means for detecting an in-cylinder gas state, and an ignition control device for an internal combustion engine,
When the in-cylinder gas density at the ignition timing is equal to or lower than the predetermined density, the in-cylinder temperature at the ignition timing is equal to or lower than the predetermined temperature, the rotation speed of the internal combustion engine is equal to or higher than the predetermined rotation speed, and the load of the internal combustion engine is equal to or lower than the predetermined load, An ignition control apparatus for an internal combustion engine, wherein both the first ignition means and the second ignition means are driven so that the air-fuel mixture is ignited by low-temperature plasma after the air-fuel mixture is ignited by thermal plasma.   The ignition timing of the low temperature plasma is the discharge region of the low temperature plasma, which is an unburned region in the ignition of the thermal plasma, so that the active chemical species formed when the low temperature plasma is generated is used for ignition of the air-fuel mixture. The ignition control device for an internal combustion engine according to claim 1, wherein the ignition control device is set at a time when the gas density of the engine increases.   The ignition timing by the low temperature plasma is set so that the air-fuel mixture in the discharge region of the low temperature plasma becomes the burned gas by the propagation of the flame formed by the ignition by the thermal plasma. The ignition control device for an internal combustion engine according to 1 or 2. The low temperature plasma generation period for generating low temperature plasma by the first ignition means is as follows:
Discharge of the low temperature plasma, which is an unburned region in the ignition by the thermal plasma, from the start of the low temperature plasma generation where the active chemical species formed when the low temperature plasma is generated does not disappear and is used for ignition of the air-fuel mixture From the time when the gas density of the region has increased to the end of the low-temperature plasma generation where the gas-fuel mixture in the discharge region of the low-temperature plasma becomes burnt gas due to the propagation of the flame formed by ignition by thermal plasma The ignition control device for an internal combustion engine according to any one of claims 1 to 3, wherein the ignition control device is an internal combustion engine. First ignition means for generating low temperature plasma and igniting an air-fuel mixture in the cylinder;
Second ignition means for generating thermal plasma and igniting the air-fuel mixture in the cylinder;
In-cylinder gas state detection means for detecting the in-cylinder gas state,
When the in-cylinder gas density at the ignition timing is equal to or lower than the predetermined density, the in-cylinder temperature at the ignition timing is equal to or lower than the predetermined temperature, the rotation speed of the internal combustion engine is equal to or higher than the predetermined rotation speed, and the load of the internal combustion engine is equal to or lower than the predetermined load, An ignition control method for an internal combustion engine, wherein both the first ignition means and the second ignition means are driven so that the air-fuel mixture is ignited by low-temperature plasma after the air-fuel mixture is ignited by thermal plasma.

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