JP5817630B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a technical field of a control device for an internal combustion engine that controls an internal combustion engine provided with a device for generating plasma inside a cylinder.

  This type of internal combustion engine is disclosed in Patent Document 1. According to the diesel engine disclosed in Patent Document 1, the conditions for accelerating the fuel reaction in the combustion chamber using plasma are created, and the PM (Particulate Matter) is reduced by shortening the afterburn period. It is supposed to be possible.

  Patent Document 2 proposes a technique for generating plasma in a cylinder before ignition.

  A method for generating plasma is also disclosed in Patent Document 3.

JP 2001-317360 A JP 2009-036211 JP 2009-287549 A

  Japanese Patent Application Laid-Open No. H10-228561 discloses that the application condition to the discharge electrode is that the start of fuel injection is detected with respect to the timing of generating plasma.

  However, when the start of fuel injection is used as a trigger, the time when plasma is actually generated in the combustion chamber is not clear, and the relative relationship with the combustion reaction changes depending on the situation. That is, as disclosed in Patent Document 2, plasma may be generated before the combustion reaction occurs in the combustion chamber, or conversely, the plasma may be generated after the combustion reaction occurs.

  Here, if plasma is generated in the combustion chamber before the combustion reaction occurs, combustion becomes too active, and the amount of NOx produced and combustion noise increase. In addition, when plasma is generated in the second half of the combustion reaction, the in-cylinder temperature and the in-cylinder pressure become too low, the reaction rate between the plasma and PM decreases, and the PM purification efficiency decreases. None of the conventional devices including those disclosed in Patent Documents 1 to 3 assume such a problem, and ultimately, the plasma generated in the combustion chamber does not necessarily function effectively for PM purification. .

  On the other hand, in order to generate plasma, electric power resources are required, and in particular, a high voltage is required for those using corona discharge as disclosed in Patent Document 1. Therefore, from the viewpoint of efficient use of power resources, it is better that the plasma generation period is short, and from this point of view, effective use of plasma is required.

  This invention is made in view of the point which concerns, and makes it a subject to provide the control apparatus of the internal combustion engine which can utilize a plasma efficiently for PM purification.

  In order to solve the above-described problems, an internal combustion engine control apparatus according to the present invention includes an in-cylinder pressure detecting unit capable of detecting an in-cylinder pressure and an internal combustion engine including a plasma generator capable of generating plasma in the cylinder. A control device for an internal combustion engine for controlling an engine, wherein combustion temperature estimation means for estimating a combustion temperature in a cylinder from a stroke volume of the internal combustion engine and the detected in-cylinder pressure, and mixing with a preset engine operating condition Equivalent ratio estimating means for estimating the equivalent ratio from the relationship with the equivalent ratio of gas, PM emission from the estimated combustion temperature and equivalent ratio, and the relationship between the preset combustion temperature and equivalent ratio and PM emission amount An emission amount estimation means for estimating the amount and a control means for controlling the generation time of the plasma based on the estimated PM emission amount (Claim 1).

  The internal combustion engine according to the present invention is a concept that encompasses an engine that can extract thermal energy associated with the combustion of fuel by converting it into kinetic energy, but preferably further includes an injection mechanism that directly injects fuel into the cylinder. It is an equipped organization. For example, such an internal combustion engine refers to a compression self-ignition type diesel engine, an in-cylinder direct injection type gasoline engine, or the like.

  The plasma generating apparatus according to the present invention is an apparatus capable of generating plasma in a combustion chamber formed in each cylinder of an internal combustion engine, and can be constructed under various known practical aspects. The plasma generator includes, for example, a pair of electrodes including an electrically grounded cathode and a positive electrode for applying a high voltage, a voltage applying device that applies a high voltage to the positive electrode, and a control device that controls the applied voltage. And a device that generates plasma by generating corona discharge between the electrodes. Further, for example, an apparatus that generates plasma by irradiating microwaves in the combustion chamber from an antenna serving as a power feeding unit to impart energy to charged particles may be used. Note that the plasma generator is preferably capable of generating plasma independently for each cylinder.

  According to the control apparatus for an internal combustion engine according to the present invention, the relationship between the combustion temperature in the cylinder, the equivalence ratio of the mixture in the cylinder, and the PM emission amount in the cylinder is, for example, experimentally, empirically, or theoretically. For example, it is set in advance as a map that can be referred to for control. Therefore, the emission amount estimation means can estimate the PM emission amount from this set relationship. The “PM emission amount” in which the relationship between the combustion temperature and the equivalence ratio is defined is not limited to a strict quantity concept, but a standardized quantity concept such as concentration (weight or number per unit volume), In other words, a quantity concept that can be appropriately converted into a strict quantity concept can be included depending on the current operating conditions of the internal combustion engine.

  In the control apparatus for an internal combustion engine according to the present invention, the control means is configured to control the generation time of the plasma based on the estimated PM emission amount. Note that “controlling the generation time of plasma” includes the supply time of energy resources that promote the generation of plasma (in the above example, the application time of voltage or the irradiation time of electromagnetic waves). That is, where plasma generation is a kind of chemical phenomenon, it is not always easy to give strict controllability to plasma generation timing. From this point, preferably, the generation timing can be controlled alternatively with various alternative control amounts that can cause the generation of plasma.

  Here, PM is a particulate material mainly composed of soot (soot) or the like, and is an unburned component in the in-cylinder combustion reaction. That is, in the control apparatus for an internal combustion engine according to the present invention, the plasma is controlled to be generated after the start of the combustion reaction. Therefore, pre-ignition, NOx increase, combustion noise increase, and the like due to activation of the air-fuel mixture before the combustion reaction do not occur.

  On the other hand, the combustion temperature and the equivalence ratio are estimated in a form associated with a time concept that can be specified with reproducibility. Therefore, the emission amount estimation means can estimate the PM emission amount that can change every moment in the combustion stroke in the cylinder in association with the time concept. In view of the fact that it is appropriate that the concept of time is given by the crank angle in the control of the internal combustion engine, these are preferably estimated in association with the crank angle. At this time, for example, these may be estimated and stored for each detection period of the crank angle sensor, or an appropriate estimation period may be determined.

  For this reason, according to the control apparatus for an internal combustion engine according to the present invention, plasma can be generated in synchronization with a desired PM emission amount. For example, plasma can be generated during a period when the PM emission amount is relatively large or when the PM emission amount is maximum within one cycle, and plasma is generated under a situation where the PM emission amount is relatively small. It is possible to prevent waste of electric power resources due to the occurrence of loss of opportunity and loss of opportunity due to the fact that plasma is not generated under the condition where the amount of PM emission is relatively large. That is, the plasma can be efficiently used for the purification of PM.

  The combustion temperature estimating means estimates the combustion temperature from the detected in-cylinder pressure and stroke volume. Since the stroke volume is an eigenvalue that can be determined according to the crank angle for each internal combustion engine, if the in-cylinder pressure is detected in association with the crank angle, or later in association with the crank angle, the adiabatic change from the compression stroke to the combustion stroke The combustion temperature in can be estimated in a form corresponding to the time concept according to an arithmetic expression that is experimentally, empirically, or theoretically constructed in advance.

  Further, the equivalence ratio estimation means estimates the equivalence ratio of the air-fuel mixture from a predetermined relationship between the engine operating condition and the equivalence ratio. If the air-fuel mixture is homogeneous in the combustion chamber, the equivalence ratio can be obtained from the stoichiometric air-fuel ratio, that is, the stoichiometric weight ratio of fuel to air and the actual air-fuel ratio. On the other hand, in the configuration of the internal combustion engine according to the present invention in which the fuel is directly injected into the cylinder, the fuel spray and the air are mixed with a bias. Here, since the fuel spray diffuses while taking in the atmosphere immediately after being injected from the nozzle hole, a calculation model for estimating the shape or behavior of the fuel spray in the combustion chamber is preferably used in order to accurately obtain the equivalence ratio. The The predetermined relationship preferably includes such a calculation model, and the engine operating conditions include, for example, engine speed, cylinder injection fuel amount, cylinder intake air amount, fuel density, fuel It may include injection pressure, nozzle hole diameter, and the like.

  In one aspect of the control apparatus for an internal combustion engine according to the present invention, the combustion temperature estimating means estimates the combustion temperature in association with a crank angle, and the equivalence ratio estimating means in association with a crank angle. The ratio is estimated (claim 2).

  As described above, if the combustion temperature and the equivalence ratio can be estimated in association with the crank angle, the PM emission amount can inevitably be estimated in association with the crank angle, and the plasma is more efficiently and effectively produced. Because it can be generated automatically, it is useful in practice. In addition, the practical aspect which concerns on matching with combustion temperature and equivalence ratio, and a crank angle is ambiguous. For example, the combustion temperature and the equivalence ratio may be associated with the crank angle on a one-to-one, one-to-many, many-to-one, or many-to-many basis.

  In another aspect of the control device for an internal combustion engine according to the present invention, the control device further includes a determination unit that determines a timing or a period when the estimated PM emission amount is maximum, and the control unit is configured to determine the determined timing or Plasma is generated during the period (claim 3).

  According to this aspect, the determination means determines the time or period when the estimated PM emission amount is maximum. Note that the time or period may be replaced with a crank angle or a range of crank angles, respectively. If plasma is generated during this period or period, it is preferable because high PM purification efficiency by plasma can be obtained.

  In addition, the definition of “maximum” in this aspect is not unambiguous, and “maximum PM emission” means, for example, that it is maximum in one combustion stroke of one cylinder, or PM in one combustion stroke of one cylinder. The emission amount may change from an increasing tendency to a decreasing tendency, the PM emission amount may exceed a preset threshold, the maximum value in the past combustion stroke, and the like.

  In this aspect, the control means may generate the plasma based on a previous value of the determined time or period.

  According to this aspect, the plasma generation time is controlled based on the previous value of the time or period when the PM emission amount becomes maximum. For this reason, the estimation of the PM emission amount in one combustion stroke and the control of the plasma can be performed independently, and there is little fear that the control means falls into a so-called busy state. In addition, since the timing or period when the PM emission amount becomes maximum in one combustion stroke is not strictly determined until the combustion stroke is completed, the real-time estimation result of the PM emission amount is reflected in the plasma generation timing in real time. In this case, it is difficult to generate plasma at a time or period when the PM emission amount becomes maximum in one combustion stroke.

  In this respect, the previous value of the PM emission amount is used in this aspect. Therefore, plasma can be generated at least at the time or period when the PM emission amount becomes the maximum in the past, and rationality and validity can be given to the generation time of the plasma. The previous value conceptually means a past value, but actually means the previous value or the latest past value that can be referred to without difficulty in control. Therefore, even if the previous value is used, practically, there is no significant deviation from the time when the PM emission amount becomes maximum in the latest combustion stroke in which the generation time of plasma proceeds in real time. Therefore, stable PM purification efficiency is ensured.

  Such an operation and other advantages of the present invention will become apparent from the embodiments described below.

1 is a block diagram conceptually showing a configuration of an engine system according to a first embodiment of the present invention. It is a schematic sectional drawing of the engine in the engine system of FIG. FIG. 3 is a schematic cross-sectional view around a combustion chamber in the engine of FIG. 2. 2 is a flowchart of plasma ignition control executed by an ECU in the engine system of FIG. It is a figure which illustrates the 1 hour transition of the cylinder pressure estimated in control of FIG. 4, and combustion temperature. It is a flowchart of the plasma ignition control which concerns on 2nd Embodiment of this invention. It is a block diagram showing notionally the composition of the engine system concerning a 3rd embodiment of the present invention. It is a schematic sectional drawing of the combustion chamber periphery of the engine in the engine system of FIG. It is a flowchart of the plasma ignition control performed by ECU in the engine system of FIG. FIG. 10 is a schematic cross-sectional view around the combustion chamber illustrating the effect of the control of FIG. 9.

<Embodiment of the Invention>
Hereinafter, various embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
<Configuration of Embodiment>
First, the configuration of the engine system 10 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram conceptually showing the configuration of the engine system 10.

  In FIG. 1, an engine system 10 is mounted on a vehicle (not shown), and includes an ECU 100, an engine 200, and a plasma generator 300.

  The ECU 100 is an electronic control unit that includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM, and the like, and is configured to be able to control the operation of the engine system 10. Is an example. The ECU 100 is configured to execute plasma ignition control, which will be described later, according to a control program stored in the ROM. The ECU 100 is an integrated electronic control that can function as an example of each of the “combustion temperature estimation means”, “equivalence ratio estimation means”, “emission amount estimation means”, “control means”, and “determination means” according to the present invention. Although it is a unit, the physical, mechanical, and electrical configuration of each means according to the present invention is not limited to this, and each means includes, for example, a plurality of ECUs, various processing units, various controllers, You may comprise as various computer systems etc., such as a microcomputer apparatus.

  The engine 200 is a diesel engine as an example of the “internal combustion engine” according to the present invention. Here, a detailed configuration of the engine 200 will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view of the engine 200.

  The engine 200 compresses and ignites an air-fuel mixture of fuel (here, light oil) injected from the direct injection injector 212 and intake air inside a plurality of cylinders 202 accommodated in the cylinder block 201 and combustion thereof. The compression self-ignition internal combustion engine is configured so that the reciprocating motion of the piston 203 accompanying the above can be converted into the rotational motion of the crankshaft 205 via the connecting rod 204. The cylinders 202 are arranged in a direction perpendicular to the paper surface, and the engine 200 is an in-line multi-cylinder engine.

  A crank angle sensor 206 capable of detecting a crank angle θcrk, which is a rotation angle of the crankshaft 205, is installed in the vicinity of the crankshaft 205. This crank angle sensor 206 is electrically connected to the ECU 100, and the detected crank angle θcrk is referred to the ECU 100 at a constant or indefinite period.

  In the engine 200, air sucked from the outside is guided to the intake pipe 207. An SCV (Swirl Control Valve) 208 for adjusting the amount of fresh air (fresh air amount) guided to the intake port 209 is arranged on the upstream side of the intake port 209 formed in the cylinder head CH, which communicates with the intake pipe 207. It is installed. The SCV 208 is configured such that its drive state is controlled by an actuator (not shown) that is electrically connected to the ECU 100.

  Here, the intake port 209 forms a swirling flow of the intake air (hereinafter, referred to as “swirl flow” as appropriate) when fresh air that has passed through the SCV 208 is drawn into the cylinder 202. Is curved. The SCV 208 can change the flow velocity Vsw of the swirl flow according to the valve opening (SCV opening). In addition, this swirl flow is formed along the cross section which followed the paper surface left-right direction substantially. In other words, the swirl flow is formed along the curved inner wall of the substantially cylindrical cylinder 202. The ECU 100 can appropriately calculate the swirl ratio SR, which is the ratio between the angular velocity of the swirl flow and the angular velocity of the crankshaft 205, from the SCV opening, the intake air amount Ga, and the engine speed NE according to a known method.

  The communication state between the cylinder 202 and the intake port 209 is controlled by opening and closing the intake valve 210, and the intake air described above is taken into the cylinder 202 when the intake valve 210 is opened. The intake valve 210 is driven to open and close in accordance with a cam profile of an intake cam 211 having an elliptical shape in section when attached to an intake camshaft connected to the crankshaft 205 via a sprocket (not shown). It has become.

  The fuel injection valve of the direct injection injector 212 is exposed in the cylinder 202, and the fuel spray injected from the direct injection injector 212 and fresh air sucked through the intake port 209 in the cylinder 202 are exposed. It is mixed and becomes the above-mentioned air-fuel mixture. The air-fuel mixture burned in the cylinder 202 becomes exhaust gas, and is led to the exhaust pipe 215 via the exhaust port 214 when the exhaust valve 213 that opens and closes in conjunction with opening and closing of the intake valve 210 is opened. A DPF (Diesel Particulate Filter) (not shown) is installed in the exhaust pipe 215, and PM contained in the exhaust is temporarily captured by the DPF and then purified at an appropriate regeneration timing. The PM purification method in the DPF is not particularly limited. For example, the DPF may be heated by promoting post-combustion by post injection, and the captured PM may be oxidized and burned.

  A cooling water temperature sensor for detecting a cooling water temperature Tw related to the cooling water (LLC) circulated and supplied to cool the engine 200 is provided in a water jacket stretched around the cylinder block 201 containing the cylinder 202. 216 is provided. Further, in the combustion chamber, which is a space defined by the upper surface portion of the piston 203 and the inner wall portion of the cylinder 202 in a state where the piston 203 is positioned at TDC (Top Death Center), the pressure inside the cylinder 202 is increased. A sensor terminal of an in-cylinder pressure sensor 217 capable of detecting a certain in-cylinder pressure Pcyl is exposed. Further, the intake pipe 207 is provided with an intake pressure sensor 218 that can detect an intake pressure Pin that is the pressure of intake air, and an air flow meter 219 that can detect an intake air amount Ga.

  Each of these sensors is electrically connected to the ECU 100, and the detected coolant temperature Tw, in-cylinder pressure Pcy, intake pressure Pin, and intake air amount Ga are respectively referred to by the ECU 100 at a constant or indefinite period. It is the composition which becomes.

  Here, the direct injection injector 212 will be supplemented. The direct injection injector 212 is a part of a high-pressure fuel supply device (not shown), and is configured to be able to inject fuel as a fuel spray into a high-temperature and high-pressure combustion chamber. This high-pressure fuel supply device includes a fuel tank that stores fuel, a low-pressure pump that pumps fuel from the fuel tank and supplies it as a low-pressure fuel with a feed pressure Pfd, a high-pressure pump that boosts the supplied low-pressure fuel, a common rail, and the like. Supply system.

  The common rail is a fuel buffer for accumulating high-pressure fuel supplied from a high-pressure pump and stably supplying it to the direct injection injector 212 provided for each cylinder. Rail pressure Pcr (Pcr> Pfd), which is the pressure of the high-pressure fuel stored in the common rail, is detected by a rail pressure sensor. The rail pressure sensor is electrically connected to the ECU 100, and the detected rail pressure Pcr is referred to by the ECU 100 at a constant or indefinite period. The ECU 100 can maintain the rail pressure Pcr at a desired target pressure by controlling the driving load of the high-pressure pump by controlling the driving of the electromagnetic metering valve provided in the high-pressure pump. Each direct injection injector 212 is connected to a common rail.

  The fuel injection valve of the direct injector 212 is exposed to the combustion chamber of each cylinder 202 as described above. The direct injection injector 212 is configured to be able to inject an amount of fuel determined by the valve opening period of the fuel injection valve and the rail pressure Pcr into the cylinder 202 as spray. The direct injection injector 212 is a so-called porous injection device, and a plurality of injection holes for fuel injection in the fuel injection valve are formed circumferentially along the inner wall (side wall) of the cylinder 202 formed in a circumferential shape. Has been.

  To supplement the configuration of the direct injection injector 212, the direct injection injector 212 includes an electromagnetic valve that operates based on a command supplied from the ECU 100, and a nozzle that injects fuel when the electromagnetic valve is energized (both not shown). Is provided. The solenoid valve is configured to be able to control the communication state between the pressure chamber to which the high-pressure fuel accumulated in the common rail is applied and the low-pressure side low-pressure passage connected to the pressure chamber. The pressure chamber and the low-pressure passage are communicated with each other, and the pressure chamber and the low-pressure passage are blocked from each other when energization is stopped.

  On the other hand, the nozzle has a built-in needle for opening and closing the nozzle hole, and the fuel pressure in the pressure chamber urges the needle in the valve closing direction (direction in which the nozzle hole is closed). Therefore, when the solenoid valve is energized, the pressure chamber communicates with the low-pressure passage, and when the fuel pressure in the pressure chamber decreases, the needle rises in the nozzle and opens (opens the nozzle hole) to supply from the common rail. The high-pressure fuel thus injected is injected from the injection hole. In addition, when the energization of the solenoid valve is stopped, the pressurization chamber and the low pressure passage are cut off from each other and the fuel pressure in the pressure chamber rises, and the needle is lowered in the nozzle to close the valve, thereby terminating the injection. It has become. In the present embodiment, fuel in one cycle is divided and injected into pilot injection for stabilizing combustion and main injection for injecting the remaining fuel.

  Returning to FIG. 1, the plasma generator 300 is an example of the “plasma generator” according to the present invention that can generate plasma in the combustion chamber of the engine 200. The plasma generator 300 includes a high frequency power source 310, a transmission path 320, and an antenna 330.

  The high frequency power supply 310 is a power supply capable of applying a microwave band (eg, 2.45 GHz band) high frequency signal to the transmission line 320.

  The transmission line 320 is a high-frequency coaxial cable in which transmission loss in the microwave band is sufficiently reduced. The transmission path 320 is inserted into a through hole that penetrates the cylinder head CH.

  The antenna 330 is a discharge means that is electrically connected to the transmission path 320 and has a discharge end exposed in the combustion chamber. The antenna 330 is configured to resonate with a microwave high-frequency signal supplied from the transmission line 320 and to generate a high-frequency electric field by radiating electromagnetic waves into the combustion chamber.

  The plasma generating apparatus 300 according to the present embodiment has a mode in which plasma is formed by applying energy to charged particles in the acidified gas atmosphere by an electric field formed by the antenna 330, but the plasma according to the present invention. The aspect which a generator can take is not limited to this. For example, a pair of electrodes consisting of a positive electrode and a cathode are installed in the combustion chamber, the cathode is electrically grounded (for example, electrically connected to a cylinder head), and a high voltage is applied to the positive electrode to corona between the electrodes. You may have the aspect which produces discharge and forms plasma.

  Here, with reference to FIG. 3, a state around the combustion chamber in the cylinder 202 of the engine 200 will be described. FIG. 3 is a schematic cross-sectional view of the periphery of the combustion chamber. In the figure, the same reference numerals are given to the same portions as those in FIGS. 1 and 2, and the description thereof is omitted as appropriate.

  3, a part of the combustion chamber of the cylinder 202 sandwiched between the upper surface portion of the piston 203 and the lower surface portion of the cylinder head CH is represented. The fuel injection valve of the direct injection injector 212 is generally exposed at the center of the combustion chamber (in the figure, since one side half of the combustion chamber is shown, the fuel injection valve is shown at the right end). The fuel spray injected from the fuel injection valve of the direct injection injector 212 is injected along a fuel spray line indicated by a chain line in the drawing.

  On the other hand, the upper surface portion of the piston 203 is curved in a ω shape in a sectional view. The fresh air sucked into the cylinder through the intake port 209 proceeds in the direction of the broken line shown in the figure along the curved upper surface portion, and is mixed with the fuel spray in the process of traveling.

<Operation of Embodiment>
In the engine system 10 according to the present embodiment, plasma is appropriately formed in the combustion chamber by plasma ignition control executed by the ECU 100. This plasma promotes the purification reaction of PM, which is a kind of unburned component.

  Here, the details of the plasma ignition control will be described with reference to FIG. FIG. 4 is a flowchart of the plasma ignition control. The plasma ignition control is a control that is repeatedly executed at a predetermined cycle during the operation period of the engine 200.

  In FIG. 4, the ECU 100 determines whether or not the current situation corresponds to the plasma generation condition (step S110).

  The plasma generation condition according to the present embodiment means a condition that requires PM purification promotion by plasma. In order to generate plasma, it is necessary to operate a high-frequency power source 310 that is a power resource. Therefore, from the viewpoint of saving power resource consumption, it is desirable that the plasma be used to supplement the PM purification function that the engine 200 normally has. The plasma generation conditions are conditions set in advance from such a viewpoint. The plasma generation conditions are set in advance and stored as control information in the ROM. If the current situation does not correspond to the plasma generation condition (step S110: NO), the ECU 100 ends the plasma ignition control.

  The plasma generation condition may be essentially any condition, but may be associated with, for example, the amount of PM trapped by the DPF. For example, the purification of PM by plasma may be performed when the PM discharge amount needs to be controlled so that the PM trapping amount of the DPF is maintained within a predetermined range. Alternatively, it may be executed under operating conditions in which the PM emission amount tends to be relatively large, such as at high rotation and high load.

  When the current situation corresponds to the plasma generation condition (step S110: YES), the process branches into two systems. That is, a first processing system configured by steps S120 to S180 and a second processing system configured by steps S190 to S210.

  In the first processing system, the ECU 100 first acquires engine operating conditions (step S120). In the present embodiment, the engine speed NE, the cylinder intake air amount Gacyl, and the cylinder fuel injection amount Qcyl are acquired as the engine operating conditions. The engine speed NE is obtained by differentiating the crank angle θcrk with time. The in-cylinder intake air amount Gacyl is obtained from the intake air amount Ga of the entire engine detected by an air flow meter (not shown in FIG. 2) installed in the intake pipe 207. Further, the in-cylinder fuel injection amount Qcyl is known as a control amount of the direct injection injector 212.

  When these engine operating conditions are acquired, the ECU 100 acquires the in-cylinder pressure Pcyl (step S130). The in-cylinder pressure Pcyl is acquired in association with the crank angle θcrk.

  Next, the ECU 100 acquires the combustion temperature Tcom based on the acquired in-cylinder pressure Pcyl and the stroke volume Vcyl uniquely determined by the crank angle θcrk (step S140). The combustion temperature Tcom is calculated according to the following equation (1).

Tcom = (Pcyl * Vcyl) / (Wg * Rg) (1)
In the above equation (1), Wg is the gas weight (kg), and Rg is the gas constant (J / kg · K). The gas weight Wg is the sum of the in-cylinder intake air amount Gacyl and the in-cylinder fuel injection amount Qcyl.

  Here, with reference to FIG. 5, the time transition of the in-cylinder pressure Pcyl and the combustion temperature Tcom will be described. FIG. 5 is a diagram exemplifying a one-time transition of the in-cylinder pressure Pcyl and the combustion temperature Tcom estimated in the plasma ignition control.

  In FIG. 5, the upper part of FIG. 5A is a time transition of the in-cylinder pressure Pcyl, and the lower part of FIG. 5B is a time transition of the combustion temperature Tcom. The time axis is indicated by the post-TDC crank angle, and a range of 40 degrees before and after the compression TDC (that is, 0) is illustrated.

  As shown in the figure, the in-cylinder pressure Pcyl gradually increases during the compression stroke, and reaches a maximum at a position slightly advanced from the compression TDC. The combustion temperature Tcom also has a waveform that conforms to the in-cylinder pressure Pcyl, and is generally maximum at a position where the in-cylinder pressure Pcyl is maximum.

  Next, the ECU 100 calculates the equivalence ratio φ of the in-cylinder mixture based on a preset spray model (step S150). The spray model is a calculation model for analyzing the behavior of the fuel spray in the cylinder, which is theoretically constructed in advance, and is stored in the ROM. Various known models can be applied to this type of calculation model.

  For example, the ECU 100 calculates the equivalence ratio φ of the air-fuel mixture according to the following formulas (2) to (5). Each of these formulas is an example of formulating a spray model. Formula (2) is a formula for determining penetration (spray reach distance) Lsp, Formula (3) is a formula for determining an injection angle θ, and Formula (4) is a spray volume. Equation (5) for obtaining Vsp is an equation for obtaining the equivalence ratio φ.

Lsp = 0.39 * (2 * ΔP / ρ _f ) ^0.5 * t (2)
Lsp = 2.9 * (ΔP / ρ _a ) ^0.25 * (d * t) ^0.5 (2)
In the above formula (2), the upper formula is applied when the elapsed time t from the fuel injection timing satisfies (0 ≦ t ≦ tb), and the lower formula is similarly used when the elapsed time t is (t> tb). Applicable when meeting. tb is a threshold value set in advance. ΔP is a pressure difference between the fuel spray and the atmosphere (fresh air), ρ _a is the air density, and ρ _f is the fuel density. Further, d is the diameter of the injection hole in the fuel injection valve of the direct injection injector 212.

θ = 0.05 * (ρ _a * ΔP * d ² / μ _a ² ) ^0.25 (3)
Mu _a in the above equation (3) is a viscosity coefficient of the atmosphere (fresh air).

Vsp = 1/3 * π * tan ² θ * Lsp ³ (4)
φ = M / Vsp (5)
In the above equation (5), M is a fresh air volume corresponding to a stoichiometric ratio with respect to the in-cylinder fuel injection amount Qcyl. That is, the fuel spray gradually diffuses into the combustion chamber as time elapses, and is mixed with fresh air taken into the combustion chamber in the diffusion process. As the elapsed time is shorter, the spray volume Vsp becomes smaller than the stoichiometric equivalent value for the injected fuel, so the fuel spray equivalent ratio (equivalent ratio of the mixture) φ is large, that is, the fuel is rich.

  Note that such a spray model is merely an example of various known simulation models or calculation models. Like the calculation formula for deriving the combustion temperature Tcom from the in-cylinder pressure Pcyl, there are various modes for obtaining the equivalent ratio φ. Applicable. The calculated equivalent ratio φ and the combustion temperature Tcom acquired in step S140 are stored in the RAM in association with the crank angle.

  When the equivalence ratio φ is calculated, the ECU 100 calculates the PM discharge amount in the cylinder (step S160). The PM emission amount is calculated by referring to a PM emission amount map stored in advance in the ROM. The PM emission amount map is a control map in which the equivalence ratio φ, the combustion temperature Tcom, and the PM emission amount are associated in advance experimentally, empirically, or theoretically. The ECU 100 acquires the PM emission amount from the PM emission amount map for each crank angle corresponding to the equivalence ratio φ and the combustion temperature Tcom. The acquired PM discharge amount is temporarily stored in the RAM.

  Next, the ECU 100 determines whether or not the maximum value of the PM emission amount in one combustion stroke has been detected (step S170). When the maximum value of the PM emission amount is not detected (step S170: NO), that is, when the estimated PM emission amount tends to increase in the transition period from the compression stroke to the combustion stroke, the processing is performed. It returns to step S120. That is, the process from step S120 to step S160 is repeated until the maximum value of the PM emission amount is detected.

  When the maximum value of the PM emission amount is detected (step S170: YES), the ECU 100 sets the crank angle corresponding to the maximum value as the next plasma ignition timing (step S180).

  When the plasma ignition timing in the next combustion stroke is set, the first processing system ends. As described above, since the plasma ignition control is repeatedly executed, when the first and second processing systems are completed in one control routine, the process is repeated again from step S110.

  Here, the crank angle corresponding to the maximum value of the PM emission amount is set as the next plasma ignition timing. However, when the region where the PM emission amount is greater than or equal to a predetermined value is widened in the vicinity of the maximum value, A range of the crank angle where the PM emission amount is equal to or greater than a predetermined value may be set as a plasma ignition period in the next combustion stroke.

  Next, the second processing system will be described. When the second processing system is started, ECU 100 determines whether or not the current crank angle θcrk corresponds to the plasma ignition timing set in step S180 in the previous control routine (step S190). When it does not correspond to the set plasma ignition timing (step S190: NO), the process is set to a standby state.

  On the other hand, when the set plasma ignition timing is met (step S190: YES), the ECU 100 controls the high-frequency power source 310 to radiate microwave band electromagnetic waves from the antenna 330 via the transmission path 320, and Plasma is generated (step S200).

  When the plasma is generated, ECU 100 determines whether or not the next plasma ignition timing has been set in the first processing system (step S210), while the next plasma ignition timing has not been set. (Step S210: NO), the process is set to a standby state. When the setting of the next plasma ignition timing is completed (step S210: YES), the ECU 100 ends the second processing system.

  Normally, determination of the maximum value of the PM emission amount in the first processing system is continued after the plasma ignition control in the second processing system. Strictly speaking, whether or not the PM emission amount is maximum is not determined until the combustion stroke is completed. Therefore, when the first processing system ends, step S210 of the second processing system also branches to the “YES” side, and both of them end approximately at the same time.

  As described above, according to the plasma ignition control according to the present embodiment, the crank angle at which the PM discharge amount is maximized or the PM discharge amount is greater than or equal to a predetermined value, which is determined in the previous control routine, Plasma can be generated in the combustion chamber as the plasma ignition timing in the next combustion stroke. Since the combustion state of the engine 200 hardly changes in one cycle, when the plasma is ignited at a crank angle corresponding to the previous maximum value in this way, efficient PM purification can be expected. Thus, it is possible to obtain a sufficient PM purification effect while reducing power resources as much as possible. Further, according to the technical idea that the PM emission amount is estimated and used for the plasma ignition control in this way, the plasma can be generated at the time when the purification of PM is required. In the point that plasma can be reliably used for PM purification while preventing an increase in noise or an increase in NOx emission amount, it is sufficiently effective even if it is not associated with the maximum value of the PM emission amount.

Second Embodiment
Next, PM purification control according to the second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a flowchart of the PM purification control according to the second embodiment. In the figure, the same reference numerals are given to the same portions as those in FIG. 4, and the description thereof will be omitted as appropriate.

  In FIG. 6, when the PM emission amount is estimated (step S160), the ECU 100 determines whether or not the PM emission amount has changed from an increasing tendency to a decreasing tendency (step S171). When the PM emission amount does not change or tends to increase (step S171: NO), the ECU 100 returns the process to step S120 and repeats a series of processes. When it is detected that the PM emission amount has changed from an increasing tendency to a decreasing tendency (step S171: YES), the ECU 100 generates plasma in the combustion chamber (step S200) and ends the plasma ignition control.

  Thus, unlike the first embodiment, the second embodiment uses a real-time estimated value of the PM emission amount for controlling the plasma ignition timing. Therefore, effective PM purification based on the real-time PM emission amount in the current combustion stroke can be realized.

  In addition, the effectiveness of using the trigger for control that the PM emission amount has changed from the increasing tendency as the decreasing tendency is that the combustion temperature Tcom, the equivalence ratio φ, and the PM emission amount are defined in the PM emission amount map. Supported by relationships.

  That is, during the period from the compression stroke to the combustion stroke, the equivalence ratio gradually decreases while the fuel spray diffuses and the combustion temperature rises. When such a qualitative tendency is associated with the PM emission amount, the trajectory drawn by the point on the coordinates defined by the equivalence ratio φ and the combustion temperature Tcom passes through the region where the PM emission amount is small to the high region again. Return to a small area. Therefore, the maximum value of the PM emission amount almost coincides with the time when the PM emission amount has changed from the increasing tendency to the decreasing tendency.

<Third Embodiment>
Next, a third embodiment of the present invention provided with a plasma generator different from the first and second embodiments will be described.

  First, the configuration of the engine system 11 according to the third embodiment will be described with reference to FIG. FIG. 7 is a block diagram conceptually showing the configuration of the engine system 11. In addition, in the same figure, the same code | symbol is attached | subjected to the location which overlaps with FIG.

  In FIG. 7, the engine system 11 is different from the engine system 10 according to the first and second embodiments in that a plasma generator 301 is provided instead of the plasma generator 300. The plasma generator 301 includes an antenna 331 and an antenna driver 340, and is different from the plasma generator 300 in that the three-dimensional position of the antenna 331 in the combustion chamber is variable.

  Here, the plasma generator 301 will be described in more detail with reference to FIG. FIG. 8 is a schematic sectional view around the combustion chamber. In the figure, the same reference numerals are given to the same portions as those in FIG. 3, and the description thereof will be omitted as appropriate.

  In FIG. 8, the antenna 331 is supported by the antenna driving unit 340 in which the cylinder head CH is embedded in such a manner that one end thereof can be extended and rotated (see broken line). That is, the antenna 331 can freely change the position of its discharge end in the combustion chamber, starting from the embedded position of the antenna driving unit 340 in the cylinder head CH. The antenna drive unit 340 is an electrically driven actuator such as a servo motor, for example, and the position of the antenna 331 in the combustion chamber can be controlled quickly and accurately.

  When the plasma generator 301 having such a variable antenna position is provided, the plasma ignition control can be further refined. The plasma ignition control according to the third embodiment based on such a purpose will be described with reference to FIG. FIG. 9 is a flowchart of the plasma ignition control. In the figure, the same reference numerals are given to the same portions as those in FIG. 4, and the description thereof will be omitted as appropriate.

  In FIG. 9, when the plasma generation condition is satisfied (step S110: YES), the process branches to the first processing system and the second processing system as described above.

  In the first processing system, the ECU 100 first acquires engine operating conditions (step S121). Here, in step S121, in addition to the engine operating conditions (NE, Qcyl, Gacyl) according to the first and second embodiments, the in-cylinder pilot injection amount Qpcyl, the fuel injection pressure Pinj, and the swirl ratio SR are acquired. The The in-cylinder pilot injection amount Qpcyl is constantly grasped by the ECU 100 as information necessary for the control of the direct injection injector 212, and the rail pressure Pcr of the common rail described above is used as the fuel injection pressure Pinj. The swirl ratio SR can be appropriately calculated by the ECU 100 as described above.

  These engine operating conditions are used for estimating the three-dimensional position of the fuel spray using the space spray model. That is, after steps S130 and S140 are executed, the ECU 100 determines a local rich portion of the fuel spray (step S141). The determination of the local rich portion means that a three-dimensional position in the combustion chamber of a portion where the fuel is locally rich (local rich portion) in the mixture of fuel spray and fresh air is determined.

  For the determination of the local rich portion, a spatial spray model based on the spray model described above is used. The spatial spray model is a calculation model that has been experimentally, empirically, or theoretically formulated in advance in the same manner as the spray model, and takes into account the effects of swirl flow and pilot injection formed in the combustion chamber. An arithmetic expression related to such a spatial spray model is also stored in the ROM in advance as in the spray model. Details of the spatial spray model are not discussed here because known techniques can be applied. In step S141, the above-described fuel injection pressure Pinj, pilot injection amount Qpcyl, and swirl ratio SR are referred to, and an approximate three-dimensional position of the local rich portion is estimated. Note that “substantially” means accuracy that does not exceed the positional accuracy of the antenna unit 331.

  When the local rich portion is determined, it is determined whether the maximum value of the PM emission amount is detected through the estimation of the equivalence ratio φ (step S150) and the estimation of the PM emission amount (step S160) (step S170). ). If the maximum value of the PM emission amount has not yet been detected (step S170: NO), the process returns to step S121. When the maximum value of the PM emission amount is detected (step S170: YES), the ECU 100 sets the control position of the antenna 331 at the next plasma ignition timing in addition to the next plasma ignition timing (step S181). The control position of the antenna 331 is the position of the local rich portion in the crank angle or the crank angle range where the PM emission amount becomes the maximum value (that is, the three-dimensional position of the local rich portion changes every moment).

  On the other hand, in the second processing system, when the plasma ignition timing set in the previous routine has come (step S190: YES), plasma ignition control is executed at the set antenna position (step S201). ). That is, the ECU 100 controls the three-dimensional position of the discharge end of the antenna 331 in the combustion chamber to a position corresponding to the local rich portion via the antenna driving unit 340, and then generates plasma.

  When the plasma is generated, ECU 100 determines whether or not the next plasma ignition timing and antenna position have been set (step S211), and the process is in a standby state until completion (step S211: NO). When the next ignition timing and position are set (step S211: YES), the second processing system is terminated.

  In this embodiment, the position of the discharge end of the antenna 331 is variable. However, a configuration may be adopted in which a plurality of antennas are installed in the combustion chamber and one antenna closest to the local rich portion is used for plasma generation. Good.

  Here, the case where the position control function of the antenna 331 is used for the plasma ignition control according to the first embodiment has been described, but the present invention can be similarly applied to the plasma ignition control according to the second embodiment. Needless to say.

  Here, the effect of this embodiment will be described with reference to FIG. FIG. 10 is a schematic sectional view around the combustion chamber. In the figure, the same reference numerals are given to the same portions as those in FIG. 8, and the description thereof will be omitted as appropriate.

  In FIG. 10, it is assumed that there is a local rich portion in the circular hatching area shown in the figure. In this case, the plasma can be formed at a position very close to the local rich portion by extending the antenna 331 with respect to the position illustrated in FIG. As described above, according to the plasma ignition control according to the present embodiment, plasma is generated at a position where PM is localized in a crank angle or a crank angle range (that is, timing or period) in which the PM emission amount is maximum. I can do it. Therefore, a high PM purification action can be obtained.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification, and the control of the internal combustion engine accompanying such a change. The apparatus is also included in the technical scope of the present invention.

  The present invention is applicable to control of an internal combustion engine provided with a plasma generator.

  DESCRIPTION OF SYMBOLS 10 ... Engine system, 100 ... ECU, 200 ... Engine, 202 ... Cylinder, 208 ... Swirl valve, 217 ... In-cylinder pressure sensor, 300 ... Plasma generator, 330, 331 ... Antenna, 340 ... Antenna drive part.

Claims (3)

In-cylinder pressure detecting means capable of detecting in-cylinder pressure;
A control device for an internal combustion engine for controlling an internal combustion engine comprising a plasma generator capable of generating plasma in a cylinder,
Combustion temperature estimation means for estimating the combustion temperature in the cylinder from the stroke volume of the internal combustion engine and the detected in-cylinder pressure;
Equivalent ratio estimating means for estimating the equivalent ratio from the relationship between the preset engine operating conditions and the equivalent ratio of the air-fuel mixture;
Emission amount estimation means for estimating the PM emission amount from the estimated combustion temperature and equivalent ratio and the relationship between the preset combustion temperature and equivalent ratio and the PM emission amount;
Control means for controlling the generation time of the plasma based on the estimated PM emission amount ;
Determining means for determining a time or period when the estimated PM emission amount is maximum ,
The control device for an internal combustion engine, wherein the control means generates plasma at the determined time or period . The combustion temperature estimating means estimates the combustion temperature in association with a crank angle;
The control apparatus for an internal combustion engine according to claim 1, wherein the equivalence ratio estimation means estimates the equivalence ratio in association with a crank angle. The control device for an internal combustion engine according to claim 1 , wherein the control means generates the plasma based on a previous value of the determined time or period.

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