JP6024258B2 - Compression self-ignition engine and control method thereof - Google Patents

Description

  The present invention includes a compression self-ignition engine having a cylinder having a geometric compression ratio set to 14 or more and capable of HCCI combustion in which fuel supplied into the cylinder is self-ignited after mixing with air, and the engine It relates to a control method.

  In general, two types of combustion modes of an engine, premixed combustion and diffusion combustion, are well known. Premixed combustion is a combustion type in which an air-fuel mixture (premixed gas) obtained by previously mixing fuel and air is burned by spark ignition, and is typically employed in gasoline engines that use gasoline as fuel. . Diffusion combustion is a combustion type in which fuel and air are diffused and mixed by supplying fuel to compressed high-temperature and high-pressure air, and is typically used in diesel engines that use light oil as fuel. ing.

  On the other hand, in recent years, research has been advanced to put premixed compression ignition combustion into practical use as a new combustion type that is neither premixed combustion nor diffusion combustion. Premixed compression ignition combustion is a combustion type in which an air-fuel mixture (premixed gas) obtained by previously mixing fuel and air is self-ignited by compression rather than spark ignition. Hereinafter, such premixed compression ignition combustion is referred to as HCCI combustion (Homogeneous-Charge Compression Ignition Combustion).

  HCCI combustion is a mode in which the air-fuel mixture burns simultaneously in the cylinder of the engine. Therefore, compared to conventional premixed combustion using spark ignition, the combustion period can be shortened even under lean air-fuel ratio conditions, and thermal efficiency There is an advantage that stable combustion excellent in the above can be obtained. On the other hand, the range of conditions for establishing proper combustion that does not cause knocking or misfire is narrow, which makes it difficult to apply HCCI combustion to an in-vehicle engine.

  As a prior art that addresses such a problem, for example, Patent Document 1 below is known. The engine disclosed in Patent Document 1 includes a discharge part capable of emitting plasma in a cylinder, and the applied voltage and the application time to the discharge part are controlled, so that the energy input by the plasma is reduced. It is controlled according to the operating state.

JP 2007-309160 A

  According to the technique of the above-mentioned patent document 1, since the distribution of the activated air-fuel mixture containing radicals (active species) is controlled based on the input energy by plasma, proper HCCI combustion is achieved in a wider operating range than before. It is thought that can be performed. Specifically, in this document, when the engine rotational speed is high or the engine load is low, the input energy by plasma is relatively increased. That is, when the engine speed is high or the engine load is low, the ignitability of the air-fuel mixture deteriorates. By supplementing this by activating the air-fuel mixture, an attempt is made to expand the operating range in which HCCI combustion is possible It is.

  However, even if the input energy by the plasma emitted from the discharge part is adjusted as in Patent Document 1 and the activity level of the mixture is changed thereby, the ignition timing of the mixture basically changes. Only. For this reason, there is a limit to the controllability of combustion, and it has not been sufficient to expand the operating range of an engine capable of appropriate HCCI combustion.

  For example, when a large amount of plasma is emitted from the discharge part, the air-fuel mixture is significantly activated and self-ignites at an early stage, and the subsequent combustion proceeds abruptly, which may cause large vibrations and noises in the engine. . This leads to deterioration of NVH (noise, vibration, harshness), and particularly when the engine is an in-vehicle engine, the merchantability of the vehicle is impaired. On the other hand, if it is going to prevent such a situation, the operation area | region of HCCI combustion must be narrowed to a narrow range, and it will become impossible to fully improve the thermal efficiency of an engine.

  The present invention has been made in view of the above circumstances, and achieves HCCI combustion with less vibration and noise in a wider operating range in a compression self-ignition engine that self-ignites after mixing fuel with air. Therefore, it aims at making high thermal efficiency and NVH performance compatible.

In order to solve the above-described problems, the present invention includes a cylinder having a geometric compression ratio set to 14 or more, and HCCI combustion that self-ignites after mixing fuel supplied into the cylinder with air. EGR that is a compression self-ignition type engine that can be opened and closed in an EGR passage that communicates an exhaust passage and an intake passage of the engine, and that can be opened and closed in the EGR passage. an EGR valve for adjusting the amount of gas, and an EGR cooler for cooling EGR gas passing through the EGR passage, and ozone supply means for supplying ozone into the cylinder, the EGR gas to drive the EGR valve and the ozone supplying means And a control means for controlling the supply amount of ozone. The control means is such that the ignition timing of the air-fuel mixture becomes faster as the engine speed is higher, and The amount of ozone supplied from the ozone supply means is increased as the engine speed is increased, and the opening degree of the EGR valve is increased as the engine load is increased so that the combustion period of the gas becomes longer as the engine load is higher. (Claim 1).

In the present invention, both the ignition timing and the combustion period of the air-fuel mixture can be changed by adjusting the supply amounts of the EGR gas and ozone, so that HCCI combustion can be controlled with a higher degree of freedom. For example, the air-fuel mixture ignition timing is early Kunar so the higher the engine rotational speed, the supply amount of the ozone having a function of promoting low temperature oxidation reaction is increased as the high speed side and lowering speed of the piston during the expansion stroke It is possible to reliably prevent misfires in the high rotation speed range where the speed increases. In addition, since the amount of EGR gas that has the effect of slowing the combustion is increased as the engine load increases so that the combustion period of the air-fuel mixture becomes longer as the engine load becomes higher, large combustion energy is generated in a short period of time. Can be avoided, and the level of vibration and noise accompanying combustion can be effectively reduced. As a result, the operating range in which proper HCCI combustion without significant vibration and noise can be performed can be greatly expanded, and the thermal efficiency of the engine can be effectively improved.

In the present invention, preferably, the upper Symbol control means, determined on the basis of the operating state of the engine, and opening degree of the EGR valve to be set, and a target heat generation pattern defining the ignition timing and the combustion period of the air-fuel mixture Then, the amount of ozone to be supplied from the ozone supply means is determined by arithmetic processing using the result ( claim 2 ).

  As described above, when a target heat generation pattern (ignition timing, combustion period) is determined in advance, and the amount of ozone supplied is determined by calculation so that combustion according to the pattern occurs, it depends on the operating state. Therefore, an appropriate amount of ozone can always be supplied, so that proper HCCI combustion without misfire and without significant vibrations and noise can be reliably performed in a wide range of operation.

Further, the present invention provides a cylinder having a geometric compression ratio set to 14 or more, an EGR valve that can be opened and closed to adjust the amount of EGR gas that is recirculated into the cylinder, and ozone in the cylinder. And a method for controlling a compression self-ignition engine capable of HCCI combustion that self-ignites after mixing fuel supplied into a cylinder with air and having an ozone supply means for supplying the same. A first step of determining the opening degree of the engine based on the operating state of the engine, a second step of determining a target heat generation pattern that defines the ignition timing and combustion period of the air-fuel mixture based on the operating state of the engine, A supply process from the ozone supply means is performed by an arithmetic process using the opening degree of the EGR valve obtained in the first step and the target heat generation pattern obtained in the second step. A third step of determining the amount of ozone, wherein the ignition timing of the mixture becomes faster as the engine speed increases and the combustion period of the mixture becomes longer as the engine load becomes higher. in step, set a larger opening degree of the EGR valve as the engine load is high, in the third step, is characterized in that to set a large supply amount of ozone higher engine rotational speed (claim 3 ).

  According to the present invention, the same operational effects as those of the above-described invention of the compression self-ignition engine can be achieved.

  As described above, according to the present invention, in a compression self-ignition engine that self-ignites after mixing fuel with air, HCCI combustion with less vibration and noise can be realized in a wider operating range, and high thermal efficiency. And NVH performance can both be achieved.

It is a figure showing the whole engine composition concerning one embodiment of the present invention. It is a figure which compares and shows the aspect of HCCI combustion when ozone is supplied, and the aspect of HCCI combustion when ozone is not supplied. It is a figure which shows typically the relationship between progress of HCCI combustion, and consumption of ozone. It is a figure which shows how the aspect of HCCI combustion changes with the supply_amount | feed_rate of EGR gas. It is a figure which shows typically how the supply amount of ozone and EGR gas influences the ignition timing and combustion period of air-fuel mixture. It is a figure which shows typically the data of the target heat generation pattern which ECU of the engine has memorize | stored. It is a flowchart which shows the procedure of the process which said ECU performs during operation of an engine.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of an engine according to an embodiment of the present invention. The engine shown in the figure is a compression self-ignition engine capable of HCCI combustion in which fuel is self-ignited after being mixed with air, and is mounted on a vehicle as a power source for traveling. This engine includes a cylinder block 2 in which a cylinder 1 is formed, a cylinder head 3 provided on the upper surface of the cylinder block 2, and a piston 4 that is slidably inserted into the cylinder 1 of the cylinder block 2. Have.

  The piston 4 is connected to a crankshaft 7 that is an output shaft of the engine via a connecting rod 6. A combustion chamber is defined above the piston 4, and the piston 4 is reciprocated in the cylinder 1 by energy of combustion (HCCI combustion of fuel injected from an injector 10 described later) performed in the combustion chamber. (Up-and-down movement) and the crankshaft 7 rotates around the central axis.

  The cylinder block 2 includes an engine speed sensor SW1 that detects the rotation speed of the crankshaft 7 as an engine rotation speed, and a temperature of cooling water (not shown) provided in the cylinder block 2 (not shown). An engine water temperature sensor SW3 for detecting an engine water temperature) is provided.

  The cylinder head 3 is provided with an injector 10 for injecting fuel into the cylinder 1. The injector 10 is provided so that a tip portion thereof faces the upper surface of the piston 4, and fuel is supplied into the cylinder 1 by injecting fuel supplied from a fuel supply pipe (not shown) from the tip portion. The fuel injected from the injector 10 is not limited as long as it is a fuel capable of HCCI combustion, but in this embodiment, gasoline or fuel containing gasoline as a main component (for example, gasoline added with ethanol) ) Is used.

  The engine output torque is controlled by an accelerator pedal 25 provided in the vehicle. That is, the fuel injection amount from the injector 10 is adjusted in accordance with the opening (depression amount) of the accelerator pedal 25, thereby controlling the output torque of the engine. The accelerator pedal 25 is provided with an accelerator opening sensor SW2 for detecting the opening (accelerator opening).

  The cylinder head 3 is provided with an intake port 12 and an exhaust port 13, and an intake valve 14 and an exhaust valve 15 that open and close the ports 12 and 13. The intake valve 14 and the exhaust valve 15 are driven to open and close in conjunction with the rotation of the crankshaft 7 by a valve mechanism (not shown) including a pair of camshafts and the like disposed in the cylinder head 3.

  An intake passage 18 for introducing intake air (fresh air) into the cylinder 1 is connected to the intake port 12, and an exhaust gas (combustion gas) generated in the cylinder 1 is connected to the exhaust port 13. Is connected to the exhaust passage 19.

  The intake passage 18 is provided with an air flow sensor SW4 for detecting the flow rate of air passing through the intake passage 18, that is, the intake air amount. An outside air temperature sensor SW5 for detecting outside air temperature is provided in the engine room near the inlet of the intake passage 18.

  Here, in the engine of this embodiment, in order to realize HCCI combustion, the geometric compression ratio of the cylinder 1 is set to a high value of 14 or more and 30 or less. The geometric compression ratio is a ratio between the combustion chamber volume when the piston 4 is at the bottom dead center and the combustion chamber volume when the piston 4 is at the top dead center.

  Moreover, the engine of this embodiment in which HCCI combustion is performed is operated by the following combustion cycle. First, in the intake stroke, the intake valve 14 is opened, and intake air from the intake passage 18 is introduced into the cylinder 1 (combustion chamber) through the intake port 12. Next, in the compression stroke, fuel is injected from the injector 10, and the injected fuel is mixed with the air in the cylinder 1 to form an air-fuel mixture.・ Increase pressure. Then, the high-temperature and high-pressure mixture starts to combust by self-ignition (HCCI combustion), and in the subsequent expansion stroke, the expansion energy due to the combustion acts on the piston 4 and the piston 4 is pushed down. Next, in the exhaust stroke, the piston 4 starts to rise, the exhaust valve 15 is opened, and the exhaust gas generated by the combustion is discharged to the outside through the exhaust port 13 and the exhaust passage 19. After the exhaust stroke, the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke are repeated by returning to the intake stroke again.

The cylinder head 3 is provided with a plasma reactor 11 that emits plasma into the cylinder 1. Specifically, the plasma reactor 11 emits plasma into the cylinder 1 to change molecules and ions in the cylinder 1 into radicals (active species) that are chemically reactive, and ozone (O ₃ ). Is generated. That is, the plasma reactor 11 functions as an ozone supply unit according to the present invention. The plasma reactor 11 may be of any type as long as it can emit plasma for generating ozone. For example, the plasma reactor 11 has a needle-like center electrode and a surrounding electrode surrounding the electrode. A device capable of applying a very short pulsed or high frequency high electric field between is used as the plasma reactor 11.

  The intake passage 18 and the exhaust passage 19 are connected to each other through an EGR passage 20. The EGR passage 20 is a passage for performing an operation of returning a part of the exhaust gas discharged from the cylinder 1 to the cylinder 1, that is, EGR (Exhaust Gas Recirculation). That is, when this EGR is performed, a part of the exhaust gas passing through the exhaust passage 19 is returned to the intake passage 18 through the EGR passage 20 and introduced into the cylinder 1 together with the air passing through the intake passage 18. Hereinafter, the exhaust gas recirculated into the cylinder 1 through the EGR passage 20 is referred to as EGR gas.

The EGR passage 20 is provided with an EGR cooler 21 that cools the EGR gas by heat exchange using engine coolant or the like, and an openable EGR valve 22 for changing the passage area of the EGR passage 20. Yes. EGR valve 22, Ru der possible to adjust the amount of EGR gas in accordance with the set opening.

  Each part of the engine configured as described above is centrally controlled by an ECU (engine control unit) 30. As is well known, the ECU 30 is a microprocessor including a CPU, a ROM, a RAM, and the like, and functions as a control unit according to the present invention.

  The ECU 30 is electrically connected to the engine speed sensor SW1, the accelerator opening sensor SW2, the engine water temperature sensor SW3, the air flow sensor SW4, and the outside air temperature sensor SW5, and based on input signals from these sensors, Various information such as engine speed, engine water temperature, intake air amount, accelerator opening, and outside air temperature are acquired.

  The ECU 30 is electrically connected to the injector 10, the plasma reactor 11, and the EGR valve 22, and performs each of the devices 10, while performing calculations based on various information acquired from the sensors. Control signals for driving are output to 11 and 22, respectively. Specifically, the ECU 30 determines the fuel injection timing and injection amount from the injector 10, the ozone supply amount from the plasma reactor 11, the opening degree of the EGR valve 22, and the like according to the operating state of the engine at each time point. Control each to an appropriate value.

(2) Significance of ozone supply Next, the significance of supplying ozone using the plasma reactor 11 will be described. The supply of ozone by the plasma reactor 11 is mainly performed to adjust the start timing of HCCI combustion, that is, the timing at which the air-fuel mixture compressed by the piston 4 self-ignites (ignition timing). The reason why the ignition timing of the air-fuel mixture can be adjusted by supplying ozone is as follows.

  It is known that HCCI combustion is completed through four stages of combustion: a cold flame reaction, a blue flame reaction, a hot flame reaction, and a CO oxidation reaction. However, the three stages from the blue flame reaction to the CO oxidation reaction are generally observed as a series of combustion. Therefore, in this specification, the main combustion part from the blue flame reaction to the oxidation reaction of CO is referred to as “high temperature oxidation reaction”, and the previous cold flame reaction part is referred to as “low temperature oxidation reaction”. The ignition timing of the air-fuel mixture refers to the start timing of the “high temperature oxidation reaction”.

If ozone (O ₃ ) is supplied into the cylinder 1 halfway through the compression stroke, the supplied ozone is decomposed when the compression stroke proceeds and the inside of the cylinder 1 rises to a predetermined temperature (for example, about 500 to 600 K). To produce O radicals. Since the O radical has a strong oxidizing power, the presence of the O radical causes the fuel component to be oxidized and a low-temperature oxidation reaction to occur even under temperature conditions that normally do not cause a low-temperature oxidation reaction. Once the low-temperature oxidation reaction occurs, the temperature inside the cylinder 1 is increased, and the subsequent high-temperature oxidation reaction is also promoted.

  In this way, the supply of ozone activates the low-temperature oxidation reaction, and as a result, brings about the effect of accelerating the high-temperature oxidation reaction. Therefore, it is possible to control the ignition timing of the air-fuel mixture (starting time of the high temperature oxidation reaction) by adjusting the supply amount of ozone.

FIG. 2 is a diagram showing a comparison between an aspect of HCCI combustion when ozone is supplied and an aspect of HCCI combustion when ozone is not supplied. In FIG. 2, the horizontal axis represents the crank angle after compression top dead center (degATDC), and the vertical axis represents the heat generation rate (J / deg). According to this figure, when ozone is supplied at 22 ppm (O ₃ = 22 ppm), it can be seen that the ignition timing of the air-fuel mixture is earlier than when ozone is not supplied (O ₃ = 0 ppm). .

  Specifically, each of the two types of combustion waveforms shown in FIG. 2 has a portion where the heat generation rate slightly rises at a time slightly before the compression top dead center (crank angle = 0 deg). . This indicates that a low-temperature oxidation reaction has occurred. FIG. 2 also shows an enlarged view of this portion. As is clear from this enlarged view, when ozone is supplied, it is faster than when ozone is not supplied. A low-temperature oxidation reaction is occurring at certain times. This promotes the subsequent high-temperature oxidation reaction, and can be said to play a role in accelerating the start time of the high-temperature oxidation reaction, that is, the ignition timing of the air-fuel mixture.

  As described above, it has been found that the supply of ozone affects the ignition timing of the air-fuel mixture. As is also understood from FIG. 2, the combustion period of the air-fuel mixture, that is, the period from the start to the end of the high-temperature oxidation reaction As for, there is not much change between the case of supplying ozone and the case of not supplying ozone. The reason will be described with reference to FIG. Although ozone accelerates the low-temperature oxidation reaction and accelerates its start timing, it disappears in a short period of time after the start of the low-temperature oxidation reaction, so there is almost no ozone at the time when the high-temperature oxidation reaction starts. For this reason, ozone does not affect the progress rate of the high-temperature oxidation reaction, and the period of the high-temperature oxidation reaction is considered not to change so much. That is, ozone promotes the low temperature oxidation reaction, which accelerates the start time (ignition time) of the high temperature oxidation reaction, but does not directly affect the period of the high temperature oxidation reaction (combustion period). In the graph of the combustion waveform in FIG. 2, the combustion period when ozone is supplied is slightly shortened. This is because the ignition timing is advanced and the compression top dead center is approached. This is because combustion has started in the environment and is not directly related to the supply of ozone.

  Here, the effect of the recirculation of EGR gas to the cylinder 1 on the HCCI combustion will be described in contrast to the supply of ozone as described above. FIG. 4 is a diagram showing how the mode of HCCI combustion changes depending on the supply amount of EGR gas. According to this figure, when an operation of recirculating a part of the exhaust gas into the cylinder 1 as EGR gas (EGR) is performed, the larger the supply amount of EGR gas, the later the ignition timing of the air-fuel mixture becomes, and It can be seen that the combustion period of the gas (the period from the start to the end of the high temperature oxidation reaction) is longer. This is because as the EGR gas increases, the oxygen concentration decreases accordingly, so that the oxidation reaction becomes difficult to occur and the progress rate of the oxidation reaction becomes slow. As described above, the supply of EGR gas has the effect of delaying the ignition timing of the air-fuel mixture and slowing down the combustion.

  What can be understood from the above results is that the manner of influence on HCCI combustion differs between the case where the supply amount of EGR gas is adjusted and the case where the supply amount of ozone is adjusted. That is, when the supply amount of ozone is adjusted, only the ignition timing of the mixture can be changed. However, when the supply amount of EGR gas is adjusted, not only the ignition timing of the mixture but also the mixture is mixed. It will also change the burning period.

  From a different point of view, this means that the ignition timing and combustion timing of the air-fuel mixture can be controlled with a higher degree of freedom by adjusting both the ozone supply amount and the EGR gas supply amount. FIG. 5 schematically shows how the supply amounts of ozone and EGR gas affect the ignition timing and the combustion period of the air-fuel mixture. In FIG. 5, the horizontal axis represents the ignition timing, and the vertical axis represents the combustion period. The base line L indicated by a bold line indicates that the ozone supply amount is zero, and the ignition timing and the combustion period are simply increased or decreased. The case where is changed is shown.

  As shown in the above line L, when only the EGR gas is supplied, the ignition timing is delayed and the combustion period becomes longer as the EGR gas supply amount is increased, and conversely, the EGR gas supply amount is increased. The smaller the decrease, the earlier the ignition timing and the shorter the combustion period. On the other hand, when ozone is supplied in addition to EGR gas, only the ignition timing changes independently with the addition of ozone. Therefore, the ignition timing and the combustion period are based on the above-mentioned base line L. It changes over the area S shown in the figure translated to the left. That is, when only the supply amount of EGR gas is adjusted, the ignition timing and the combustion period can be changed only one-dimensionally, whereas when the supply amount of ozone in addition to EGR gas is adjusted, The ignition timing and the combustion period can be changed two-dimensionally, and HCCI combustion can be controlled with a higher degree of freedom.

(3) Specific Control Using Ozone and EGR Gas Next, how to control the supply amount of ozone and EGR gas to the cylinder 1 according to the operating state of the engine will be specifically described. The control described below is performed based on the processing of the ECU 30 described above. The ECU 30 stores the data of the target heat generation pattern as shown in FIG. 6, and controls the supply amounts of ozone and EGR gas so that the HCCI combustion becomes the combustion according to the target heat generation pattern of FIG. To do.

  As shown in FIG. 6, the target heat generation pattern defines the ignition timing and the combustion period of the air-fuel mixture, and is set according to the engine speed and load. The ignition timing is set to be faster (advanced side) as the engine speed is higher, and slower (retarded side) as the engine speed is lower, and the combustion period is longer as the engine load is higher. The lower it is, the shorter it is set. The reason why the ignition timing is made earlier as the rotation speed is higher is that if the rotation speed is faster, the piston 4 quickly descends during the expansion stroke, and there is a risk of misfire if the combustion is not started earlier. Also, the reason why the combustion period is increased as the load is increased is that if the load is high, the total energy generated by the combustion is large, and therefore, if the combustion is not slowed down, large vibrations and noise may occur. . In FIG. 6, four target heat generation patterns are shown as representative examples. Actually, however, data on a large number of target heat generation patterns that are finely determined according to the values of the rotational speed and the load are prepared. Has been.

  FIG. 7 is a flowchart showing a procedure of processing performed by the ECU 30 during engine operation. When the processing of this flowchart starts, the ECU 30 executes processing for reading various sensor values (step S1). Specifically, the respective detection signals are read from the engine speed sensor SW1, the accelerator opening sensor SW2, the engine water temperature sensor SW3, the airflow sensor SW4, and the outside air temperature sensor SW5, and based on these signals, the engine speed, Various information such as required torque (load), engine water temperature, intake air amount, and outside air temperature is acquired.

  Next, the ECU 30 determines the opening of the EGR valve 22 to be set based on the information acquired in step S1, and executes a process of driving the EGR valve 22 with the opening as a target (step S2). Specifically, in this step S2, the opening degree of the EGR valve 22 is set larger as the engine load (the required torque based on the accelerator opening degree) is higher. This is because it is necessary to slow down the combustion as the load increases in accordance with the target heat generation pattern of FIG.

  Next, the ECU 30 executes a process for determining the amount of fuel to be injected from the injector 10 and the timing for starting fuel injection based on the information acquired in step S1 (step S3). Specifically, in this step S3, the higher the engine load is, the larger the target injection value from the injector 10 is set. The higher the engine speed, the target injection timing (fuel injection should start from the injector 10). Time) is set earlier. The target injection timing is set within a predetermined crank angle range during the compression stroke.

  Next, the ECU 30 refers to the target heat generation pattern data shown in FIG. 6 and executes a process of determining a target heat generation pattern that matches the current engine operating state (rotation speed, load) (step). S4). Specifically, the engine rotational speed and load acquired in step S1 are applied to the target heat generation pattern data shown in FIG. 6, and an appropriate pattern corresponding to the rotational speed and load is targeted. Determine the target heat generation pattern.

  Next, the ECU 30 executes processing for estimating the actual amount of EGR gas recirculated into the cylinder 1 (hereinafter referred to as the true EGR amount) and the temperature and pressure in the cylinder 1 near the compression top dead center. (Step S5). Specifically, in step S5, whether the opening degree of the EGR valve 22 is in an increasing process or a decreasing process, what is the increase / decrease rate of the opening degree, what is the engine speed, etc. Based on various factors that affect the difference between the originally expected EGR amount (EGR amount obtained when the opening degree of the EGR valve 22 is maintained at a constant value) and the true EGR amount, An operation for estimating the EGR amount is performed. Further, based on the true EGR amount and the intake air amount, engine water temperature, and outside air temperature acquired in step S1, the in-cylinder temperature / pressure near the compression top dead center, that is, the piston 4 is compressed. Calculation is performed to estimate the temperature and pressure in the cylinder 1 when it is raised by motoring to a specific time near the dead point.

  Next, the ECU 30 executes a process for determining how much ozone should be supplied by the plasma emission from the plasma reactor 11 (step S6). Specifically, in this step S6, first, based on the fuel injection amount and injection timing determined in step S3 and the true EGR amount and in-cylinder temperature / pressure estimated in step S5, ozone is temporarily assumed. A heat generation pattern generated when no supply is made is estimated. Then, the heat generation pattern (heat generation pattern when the ozone supply amount is zero) is compared with the target heat generation pattern determined in step S4. Whether the combustion closest to the generation pattern can be obtained is obtained by calculation, and the amount is determined as the target ozone supply amount. In order to perform such a calculation process, the ECU 30 stores the influence of the ozone supply on the HCCI combustion (mainly the relationship between the ozone supply amount and the change in the ignition timing) as data.

  In step S6, as a result of determining the target supply amount of ozone aiming at the target heat generation pattern shown in FIG. 6, the supply amount increases as the engine speed increases, and conversely, the supply amount decreases as the rotation speed decreases. Is set less. That is, according to the target heat generation pattern of FIG. 6 in which the ignition timing is set earlier as the rotation speed is higher, the supply amount of ozone is increased as the rotation speed is higher, and the low temperature oxidation reaction is promoted.

  Next, the ECU 30 drives the plasma reactor 11 so that ozone is supplied in accordance with the supply amount determined in step S6, and the injector 10 so that fuel is injected in accordance with the injection amount and injection timing determined in step S3. Is executed (step S7). Since the amount of ozone supplied is determined by the amount of plasma emitted from the plasma reactor 11, the ECU 30 adjusts the amount of ozone supplied by changing at least one of the voltage applied to the plasma reactor 11 and the application time. Further, the ozone supply timing may be a timing at which a required amount of ozone is supplied by the latter stage of the compression stroke at which the low temperature oxidation reaction starts, and is set to an appropriate timing such as the middle of the compression stroke.

(4) Operation, etc. As described above, in this embodiment, the following characteristic configuration is adopted in the compression self-ignition engine capable of HCCI combustion in which fuel is self-ignited after being mixed with air.

Engine, the EGR valve 2 2 for adjusting the amount of EGR gas is an exhaust gas recirculated into the cylinder 1, for supplying ozone into the cylinder 1 plasma reactor 11 (ozone supply means), EGR valve 22 and plasma ECU 30 (control means) for driving the reactor 11 and controlling the supply amount of the EGR gas and ozone. The ECU 30 controls the supply amounts of the EGR gas and ozone so that the ignition timing of the air-fuel mixture becomes faster as the engine rotation speed becomes higher and the combustion period of the air-fuel mixture becomes longer as the engine load becomes higher (see FIG. 6). To do. According to such a configuration, HCCI combustion with less vibration and noise can be realized in a wider operating region, and there is an advantage that both high thermal efficiency and NVH performance can be achieved.

  That is, in the above embodiment, since both the ignition timing and the combustion period of the air-fuel mixture can be changed by adjusting the supply amounts of EGR gas and ozone, HCCI combustion can be controlled with a higher degree of freedom. For example, since the ignition timing of the air-fuel mixture is advanced as the engine rotational speed increases, it is possible to reliably prevent misfire from occurring in a high rotational speed range where the descending speed of the piston 4 during the expansion stroke increases. Further, since the combustion period of the air-fuel mixture is increased as the engine load is higher, generation of large combustion energy in a short period can be avoided, and the level of vibration and noise associated with combustion can be effectively reduced. As a result, the operating range in which proper HCCI combustion without significant vibration and noise can be performed can be greatly expanded, and the thermal efficiency of the engine can be effectively improved.

  Specifically, in the above embodiment, the plasma reactor 11 is driven so that the supply amount of ozone increases as the engine speed increases. As described above, when the supply amount of ozone having the action of promoting the low-temperature oxidation reaction is increased toward the higher rotation side, misfiring can be reliably prevented by increasing the ignition timing in the higher rotation region.

  In the above embodiment, the EGR valve 22 is driven so that the supply amount of EGR gas increases as the engine load increases. As described above, when the supply amount of EGR gas that has the effect of slowing down combustion is increased as the load becomes higher, the combustion period in the high load region is lengthened to reliably reduce vibration and noise. be able to.

  Moreover, in the said embodiment, the opening degree of the EGR valve 22 which should be set and the target heat generation pattern (FIG. 6) which prescribes | regulates the ignition timing and combustion period of air-fuel | gaseous mixture are determined based on the engine operating state, The amount of ozone to be supplied from the plasma reactor 11 is determined by arithmetic processing using the result (S7 in FIG. 7). As described above, when a target heat generation pattern (ignition timing, combustion period) is determined in advance, and the amount of ozone supplied is determined by calculation so that combustion according to the pattern occurs, it depends on the operating state. Therefore, an appropriate amount of ozone can always be supplied, so that proper HCCI combustion without misfire and without significant vibrations and noise can be reliably performed in a wide range of operation.

  In the above-described embodiment, the plasma reactor 11 is provided at a position where the plasma can be directly emitted into the cylinder 1 of the engine. However, the plasma reactor 11 can supply ozone generated by the emission of the plasma into the cylinder 1. For example, the plasma may be emitted toward the intake port 12.

  In the above embodiment, the plasma reactor 11 that supplies ozone by plasma discharge is provided as the ozone supply means. However, the ozone supply means may be any means that can supply ozone, and is not necessarily limited to those using plasma. I can't.

1 cylinder 11 plasma reactor (ozone supply means)
18 Intake passage 19 Exhaust passage 20 EGR passage 22 EGR valve
30 ECU (control means)

Claims (3)

A compression self-ignition engine having a cylinder with a geometric compression ratio set to 14 or more and capable of HCCI combustion that self-ignites after mixing fuel supplied into the cylinder with air,
An EGR passage communicating the engine exhaust passage and the intake passage;
Openably provided in the EGR passage, an EGR valve for adjusting the amount of EGR gas is an exhaust gas recirculated into the cylinder through the EGR passage,
An EGR cooler for cooling EGR gas passing through the EGR passage;
Ozone supply means for supplying ozone into the cylinder;
A control means for driving the EGR valve and the ozone supply means to control the supply amount of the EGR gas and ozone,
The control means increases the ozone from the ozone supply means as the engine speed increases so that the ignition timing of the air-fuel mixture increases as the engine speed increases and the combustion period of the air-fuel mixture increases as the engine load increases. And increasing the opening of the EGR valve as the engine load increases .
A compression self-ignition engine characterized by that. The compression self-ignition engine according to claim 1 ,
Upper Symbol control means, based on operating conditions of the engine, and opening degree of the EGR valve to be set, the ignition timing and the combustion period of the mixture was determined and the target heat generation pattern defining, with the result The amount of ozone to be supplied from the ozone supply means is determined by arithmetic processing.
A compression self-ignition engine characterized by that. A cylinder whose geometric compression ratio is set to 14 or more, an EGR valve which can be opened and closed to adjust the amount of EGR gas which is exhaust gas recirculated into the cylinder, and an ozone supply means for supplying ozone into the cylinder And a method for controlling a compression self-ignition engine capable of HCCI combustion that self-ignites after mixing fuel supplied into a cylinder with air,
A first step of determining an opening of the EGR valve to be set based on an operating state of the engine;
A second step of determining a target heat generation pattern that defines the ignition timing and combustion period of the mixture based on the operating state of the engine;
The amount of ozone to be supplied from the ozone supply means is determined by a calculation process using the opening degree of the EGR valve obtained in the first step and the target heat generation pattern obtained in the second step. And a third step to
In the first step, the opening degree of the EGR valve is increased as the engine load increases so that the ignition timing of the mixture becomes faster as the engine speed increases and the combustion period of the mixture becomes longer as the engine load increases. In the third step, the ozone supply amount is set larger as the engine speed is higher.
A control method of a compression self-ignition engine characterized by the above.

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