JP2010242630A - Control apparatus and control method of multiple cylinder engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control apparatus and control method of a multiple cylinder engine that can avoid a deterioration in operability and exhaust performance of the engine even when EGR is performed at the time of high load operation to realize high power. <P>SOLUTION: When the EGR is performed at the time of high load operation when a load of the engine is a predetermined value or above, dispersion degree of a combustion state between cylinders and/or dispersion degree of an air fuel ratio between the cylinders is determined. When at least one of the dispersion degree of the combustion state and the dispersion degree of the air fuel ratio between the cylinders is the predetermined value or above, quantity of air supplied into the cylinders is controlled to be reduced in advance, and then the EGR ratio is controlled to be reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for a multi-cylinder engine that performs so-called exhaust gas recirculation (hereinafter referred to as EGR) for recirculating a part of exhaust gas to an intake system, and in particular, when performing EGR during high-load supercharging operation. However, the present invention relates to a control device and a control method for a multi-cylinder engine that can achieve both combustion stabilization and knock (abnormal combustion) suppression.

  In a spark ignition engine such as a gasoline engine and some diesel engines, a technique is known in which EGR is performed to reduce the gas temperature in a cylinder during high load operation. In particular, in a spark ignition engine equipped with a supercharger, the intake air amount (supplied into the cylinder) even in a supercharged state, that is, in a state where the inside of the intake pipe (the downstream portion of the throttle in the intake passage) is pressurized to atmospheric pressure or higher. Air amount = air supply amount) and the EGR rate can be controlled independently, so the air supply amount can be greatly increased compared to the case where EGR is not performed, and high torque (high output) can be achieved. can do.

  In addition, if EGR is performed during high-load operation, the exhaust temperature will decrease. Therefore, the supercharging will exceed the upper limit of the exhaust temperature set for protection of the catalyst installed in the exhaust system and the turbine of the turbocharger. A margin (increased air supply) can be secured, contributing to higher torque. That is, by performing EGR as described above, it is possible to achieve both knock suppression and exhaust gas temperature reduction, and it is an advantage of this technology that high torque of the engine can be realized by these two effects ( For example, the following non-patent document 1 describes experimental results and effects of the above technique).

Terry Alger, Thierry Chauvet, Zlatina Dimitrova, "Synergies between High EGR Operation and GDI Systems", SAE paper 2008-01-0134 (2008).

However, the conventional techniques including the above document 1 have the following problems.
That is, for example, when EGR is performed during high-load operation, the EGR gas distribution amount to each cylinder varies particularly in a multi-cylinder engine. In other words, the EGR rate of each cylinder is different. Furthermore, this variation (degree) changes depending on engine operating conditions and aging deterioration. If the EGR rate is different in each cylinder, combustion becomes unstable in a cylinder with a high EGR rate, and knocking may occur in a cylinder with a low EGR rate, so that the EGR effect cannot be sufficiently obtained. Exhaust performance (emission characteristics) may be deteriorated.

  The present invention has been made in view of such problems, and the object of the present invention is to improve engine operability and exhaust gas even when EGR is performed to increase the output particularly during high load operation. It is an object of the present invention to provide a control device and a control method for a multi-cylinder engine that can avoid deterioration in performance.

  In order to achieve the above object, a control device for a multi-cylinder engine according to the present invention basically includes an air supply amount adjusting means for adjusting the amount of air supplied into the cylinder, and a part of the exhaust air. An EGR passage for returning to the system, an EGR gas flow rate adjusting means for adjusting an EGR gas flow rate circulating to the intake system through the EGR passage, and a combustion state estimating means for detecting or estimating the combustion state of the air-fuel mixture And an air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust, and a control means for controlling the air supply amount adjusting means and the EGR gas flow rate adjusting means, wherein the control means is a high engine load higher than a predetermined value. EGR is performed during load operation, and the degree of variation in combustion state between cylinders and / or based on at least one of the estimation result of the combustion state estimation unit and the detection result of the air-fuel ratio detection unit. Is characterized in that the degree of variation in air-fuel ratio between cylinders is obtained and the EGR rate is controlled based on the degree of variation.

  In a preferred aspect, the control means sets both the amount of air supplied to the cylinder and the EGR rate when at least one of the degree of variation in the combustion state between the cylinders and the degree of variation in the air-fuel ratio is equal to or greater than a predetermined value. Control is performed to reduce.

  In a more preferred aspect, the control means reduces the amount of air supplied to the cylinder first when at least one of the degree of variation in the combustion state and the degree of variation in the air-fuel ratio between the cylinders is equal to or greater than a predetermined value. Thereafter, control is performed to reduce the EGR rate.

  In another preferred aspect, the control means performs control to increase both the amount of air supplied into the cylinder and the EGR rate when the required torque for the engine is larger than the actual torque.

  In this case, in a more preferable aspect, when the required torque for the engine is larger than the actual torque, the control means performs control to increase the amount of air supplied into the cylinder first and then increase the EGR rate. To be.

  In another preferred aspect, the control means uses, as at least an initial value of the EGR rate at the time of high load operation after restart, an EGR rate at the time of high load operation under the same previous conditions set before restart. To be used.

  In another preferred aspect, the control means is configured to set the control amount for the air supply amount adjusting means and / or the control amount for the EGR flow rate adjusting means set during the high load operation under the same conditions after restart. It is used as at least an initial value of the control amount during high load operation.

  In another preferred embodiment, the control means controls the ignition timing in addition to the EGR rate.

  In another preferred aspect, an EGR gas flow rate estimating means for detecting or estimating a flow rate of EGR gas recirculated to the intake system through the EGR passage is provided.

  In another preferred aspect, the EGR gas flow rate estimation means includes a flow rate sensor disposed in the EGR passage or a temperature sensor disposed in either the EGR passage or the intake passage, and a signal obtained from the sensor is provided. Based on this, the EGR gas flow rate is detected or estimated.

  In this case, the control means changes the EGR rate based on the detection or estimation result of the EGR gas flow rate estimation means.

  In another preferred aspect, the control means performs EGR during the high load operation when the EGR gas temperature or the gas temperature in the intake passage is equal to or higher than a predetermined value based on the detection or estimation result of the EGR gas flow rate estimating means. Not to be.

  On the other hand, according to the control method for a multi-cylinder engine according to the present invention, when performing EGR during a high load operation in which the engine load is a predetermined value or more, the degree of variation in the combustion state between cylinders and / or the variation in air-fuel ratio between cylinders. Control that obtains the degree, and when at least one of the degree of variation in the combustion state and the degree of variation in the air-fuel ratio among the cylinders is equal to or greater than a predetermined value, the amount of air supplied into the cylinder is first reduced, and then the EGR rate is reduced To be done.

  In a preferred aspect of the engine control apparatus and method according to the present invention, when performing EGR during high load operation, the degree of variation in combustion state between cylinders and the degree of variation in air-fuel ratio between cylinders are obtained in real time, and the degree of variation is determined. When the value exceeds a predetermined value, the amount of air supplied into the cylinder is first reduced, and then the EGR rate is controlled to be reduced, so that both combustion stabilization and knock suppression can be achieved. Regardless of deterioration and operating conditions, it is possible to operate the engine with as high output as possible while avoiding engine operability and exhaust deterioration.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows 1st Example of the control apparatus which concerns on this invention with the multicylinder engine to which it is applied. The figure used for description of the relationship between exhaust temperature and engine torque. The figure used for description of the relationship between the intake pipe pressure and the target EGR rate. The figure used for description of the relationship between the heat generation rate and the crank angle in each cylinder. The flowchart which shows an example of control routines, such as an EGR rate, a supercharging pressure, and ignition timing, in 1st Example. The flowchart which shows the other example of control routines, such as an EGR rate, a supercharging pressure, and ignition timing, in 1st Example. The flowchart which shows some control routines, such as an EGR rate, a supercharging pressure, and ignition timing, in 2nd Example. The figure used for description of the relationship between supply air (EGR gas) temperature and target EGR rate. The schematic block diagram which shows 2nd Example of the control apparatus which concerns on this invention with the multicylinder engine to which it is applied. The flowchart which shows an example of the EGR gas flow control routine in 2nd Example. The schematic block diagram which shows 3rd Example of the control apparatus which concerns on this invention with the multicylinder engine to which it is applied.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing a first embodiment of a control device according to the present invention together with a multi-cylinder engine to which the control device is applied.

  In the figure, an air cleaner 17, an air flow sensor 2, an impeller (compressor) 6 b of a supercharger (turbocharger) 6, an intercooler 16, A throttle 13 for adjusting the amount of intake air, an intake port 20, and a fuel injection valve (hereinafter referred to as an injector) 5 are arranged. The air supply amount adjusting means in the present embodiment is the supercharger 6, the intercooler 16, and the throttle 13 capable of adjusting the air amount supplied into the cylinder 19, and the intake air amount detecting means is the air flow sensor 2. is there.

  The engine control unit (hereinafter referred to as ECU) 8 determines the combustion mode of the engine 30 according to the user request such as the accelerator opening α and the brake state, the vehicle state such as the vehicle speed, and the engine operating conditions such as the engine cooling water temperature and the exhaust temperature. The control amount is determined. The injector 5 is of a type that injects fuel into the intake port 20, and a predetermined amount of fuel is injected at a predetermined fuel injection timing in accordance with a target engine torque calculated from an opening signal of the accelerator opening sensor 1 or the like. The However, this fuel injection is not particularly limited to the injection into the intake port 20, and it may be arranged to inject fuel directly into the combustion chamber 18. The injection parameter is appropriately corrected according to the opening signal θtp of the throttle 13, the opening signal θegr of the EGR valve 11, the supercharging pressure Ptin by the supercharger 6, the output value of the air-fuel ratio sensor 3, and the like.

The air-fuel ratio sensor 3 is a sensor that measures the air-fuel ratio of the engine-out, but any sensor that can estimate the air-fuel ratio and oxygen concentration of exhaust gas, such as an oxygen sensor or a CO ₂ sensor, may be used. Absent. The throttle 13 is preferably an electronically controlled throttle, and the throttle valve is driven by an electric actuator. An intake pressure sensor 14 and an intake temperature sensor 12 are disposed in the intake port 20 and are used as means for detecting a gas state in the intake port 20. There is no problem even if the intake air temperature sensor 12 is arranged in the EGR passage 9 to detect the EGR gas temperature and calculate the intake air temperature based on the result. The exhaust passage 40 is provided with an exhaust temperature sensor 21, an EGR passage 9 for circulating a part of the exhaust to the intake port 20, an EGR cooler 10, and an EGR valve 11. In this case, a pressure sensor (not shown) may be arranged in order to grasp the pressure state before the turbine 6b of the supercharger.

  Next, engine operating characteristics such as exhaust temperature, engine torque, and combustion state when EGR is performed during high-load operation of the engine will be described with reference to FIGS.

  First, FIG. 2A shows the relationship between the exhaust temperature and the engine torque at each ignition timing in a certain engine speed, intake port pressure (hereinafter referred to as intake pipe pressure), and air-fuel ratio. The intake pipe pressure is equal to or higher than atmospheric pressure (supercharging state), and the air-fuel ratio is set to be equal to or lower than the theoretical air-fuel ratio. At this time, when the EGR rate is increased to 5% and 10%, the intake pipe pressure is constant, the engine air amount is reduced, and the air-fuel ratio is constant, so the fuel amount is also reduced. However, the trace knock point (ignition timing at which a weak knock starts) is advanced by the aforementioned EGR effect. Due to this effect, the ignition timing approaches the MBT point (the time when torque is generated most), so that the engine torque at the trace knock point becomes substantially constant under each EGR condition even though the air amount / fuel amount decreases.

  Further, the exhaust gas temperature also decreases due to a decrease in the gas temperature in the combustion chamber. The upper limit value of the exhaust gas temperature in the figure is a value set for protection of the turbine 6b and the catalyst 7 of the supercharger 6, and normally the improvement in engine output is limited by this value and the occurrence of trace knock. However, as shown in FIG. 2A, since the exhaust gas temperature is lowered by the introduction of EGR, the possibility that high output can be realized by setting the intake pipe pressure (supercharging pressure) higher is shown.

  FIG. 2B shows engine torque characteristics when the intake pipe pressure is increased from the condition of FIG. 2A until the exhaust gas temperature reaches the set upper limit value. The ignition timing is advanced as much as possible so that no trace knock occurs. As can be seen from FIG. 2B, exhaust gas temperature can be reduced and knocking can be avoided by performing EGR during high-load operation, so that high torque (high output) can be obtained as a result.

FIG. 3 shows the relationship between the intake pipe pressure and the target EGR rate under certain operating conditions of the engine. If the intake pipe pressure is increased, that is, the air is supercharged, the temperature pressure in the cylinder increases, so that knocking is likely to occur. Therefore, in order to avoid this, in the control device for a multi-cylinder engine of the present invention, the target EGR rate is increased as the intake pipe pressure is increased. However, when the EGR rate is increased, combustion tends to become unstable due to an inert gas (CO ₂ or the like) in the EGR gas. Therefore, in this multi-cylinder engine control device, the EGR rate of the combustion stability limit obtained in the pre-engine shipment conforming process or the like is set in advance, and within this range, the engine Control the EGR rate.

  FIG. 4 is a heat release rate chart of each cylinder of the engine 30 at the target EGR rate near the combustion stability limit set value of FIG. In this embodiment, an example of a four-cylinder engine is shown. The EGR rate is controlled to reach the target EGR rate using the EGR valve 11, the supercharger 6, the throttle 13, and the like, but due to the shape of the intake port 20, variation occurs for each cylinder. Particularly in the vicinity of the combustion stability limit, the degree of variation greatly affects the combustion in each cylinder. In FIG. 4, the EGR rate of the # 4 cylinder is higher than the target EGR rate, and as a result, the combustion speed of this cylinder Is delayed and the combustion (operation) state of the engine is getting worse. That is, in an engine that performs EGR during high-load operation, it is necessary to control the EGR rate so that both combustion deterioration and knock avoidance are compatible.

  Hereinafter, the processing contents executed by the ECU of the present embodiment that controls the EGR rate so as to achieve both the above-described combustion deterioration and knock avoidance will be sequentially described with reference to a flowchart and the like.

  FIG. 5 is a flowchart showing an example of an EGR rate, supercharging pressure, and ignition timing control routine in the first embodiment of the present invention. In particular, in FIG. 5, when the EGR is performed during operation under a high load condition where the engine 30 is fully opened or in the vicinity thereof, that is, the pressure in the intake port 20 is near or above atmospheric pressure, The control flowchart when stability is detected is shown.

  First, in step (hereinafter abbreviated as “S”) 1001, the accelerator opening sensor 1 determines the operation state of the engine 30, the operation state of the vehicle equipped with the engine 30, and the user intention of the user of the vehicle or engine 30. It is estimated by reading the output value and brake state (not shown). Since the engine is in a high load state close to full throttle, the target EGR rate, the target boost pressure (air amount), the target air-fuel ratio, the target ignition timing, etc. are read or calculated in the ECU 8 in S1002, and these values are obtained. Thus, the fuel injection amount / injection timing from the EGR valve 11, the throttle 13, the supercharger 6, and the injector 5, the ignition timing by the spark plug 15 and the like are controlled (S1003).

  Next, in order to estimate the current combustion state, the output value of the air-fuel ratio sensor 3 is read (S1004), and further, the output value of the cylinder-specific combustion state estimation sensor, here, the knock sensor 22 is read (S1005). The reading of the output value of the air-fuel ratio sensor 3 in S1004 is performed not only for the total air-fuel ratio state of all cylinders but also by calculating the output value of at least one air-fuel ratio sensor 3 installed in the exhaust port 40 for each cylinder. Since the air-fuel ratio state can also be estimated, the EGR distribution state between the cylinders can be estimated from this value, and it can be indirectly estimated whether the combustion is unstable as shown in FIG. Further, by calculating the output value of the knock sensor 22 read in S1005, it is possible to calculate the combustion stability (or instability) based on the degree of variation in the in-cylinder pressure between the cylinders. From the values read in S1004 and S1005, if the degree of air-fuel ratio variation between cylinders is equal to or greater than a predetermined value, or the combustion instability is equal to or greater than a predetermined value, the combustion state becomes unstable by performing EGR. Determination is made and the process proceeds to S1007 to S1009.

  First, in order to avoid instability of the combustion state, it is necessary to lower the EGR rate. In this case, if the EGR rate is lowered simply by controlling the EGR valve 11, the characteristics shown in FIG. First, in order to reduce the supercharging pressure (the amount of air supplied into the cylinder) in S1007, the throttle 13 and the supercharger 6 (a) ( b) is controlled. Whether the pressure has reached a predetermined pressure is determined based on the value of the intake pressure sensor 14 (S1008). If it is determined that the pressure is equal to or lower than the predetermined value, the process proceeds to S1009 and the EGR valve 11 is controlled to reduce the EGR rate. To do. If the combustion state can be stabilized through the control flow from S1004 to S1009, the process proceeds to S1010 to detect the presence or absence of knock from the output of the knock sensor 22 and the like, and if it is determined that there is a knock, ignition retard control is performed. Thus, knocking is avoided (S1011). After that, when an exhaust temperature sensor is provided immediately before or immediately after the turbocharger turbine 6 (a) (not shown), whether the temperature is detected and is below the set upper limit value described above. It is determined whether or not (S1012). If the value is equal to or greater than the upper limit (predetermined value), the process proceeds to S1013 to control to reduce the supercharging pressure (air amount) in order to avoid damage and deterioration of the supercharger 6 and the catalyst 7. With this control, in a system that performs EGR to achieve high-load operation of the engine, it is possible to prevent deterioration of the operating state and exhaust deterioration due to unstable combustion and realize suitable high torque (high output) operation It is.

  Next, the flowchart shown in FIG. 6 is a high load state in which the engine 30 is almost fully open, that is, in the intake port 20, as an example of a control routine for the EGR rate, the boost pressure, and the ignition timing in the first embodiment. The processing contents when EGR is introduced until immediately before the combustion becomes unstable during operation under conditions where the pressure is near atmospheric pressure or higher are shown. This control routine is applied in the following situation, for example. As a result of executing the control routine as shown in FIG. 5 above, when the engine is stopped while a relatively low EGR rate (including 0%) is set during high load operation, the engine is operated under the same high load condition after restart. In order to avoid combustion instability, the EGR rate or each control parameter set before restart is applied. In this case, since the engine torque is lower than the initial set value, it is possible to achieve both high torque (high output) and combustion stability by raising the EGR rate to a value at which combustion instability occurs.

  Hereinafter, a specific control routine will be described. First, steps S2001 to 2003 are the same as those in steps S1001 to S1003 of FIG. Next, when the user-requested torque of the engine 30 or a vehicle equipped with the engine 30 is larger than the actual torque (currently estimated torque) of the engine that is currently operating, for example, when the output value of the accelerator opening sensor 1 is greater than or equal to a predetermined value. In order to further increase the torque, steps S2005 to S2007 are executed, and control is performed to raise the EGR rate within the limits of the limit boost pressure and the combustion stability limit shown in FIG. At this time, if the supercharging pressure (air amount) is first increased, an excessive increase in exhaust temperature or occurrence of knocking is feared. Therefore, in step S2005, the EGR valve 11 is first controlled to increase the EGR rate. It is preferable that the EGR rate to be raised is written in advance in the ECU 8 as the degree of raising.

  Thereafter, based on the characteristics shown in FIG. 2, the ignition timing advance control (S2006) and the boost pressure (air amount) increase control are performed (S2007) to achieve the target torque. Although the torque (output) of the engine is improved by these controls, there is a concern that the combustion may become unstable due to an increase in the EGR rate. Therefore, the steps from S2008 to S2017 are executed to avoid the combustion instability as much as possible. Maintain high torque. Since the steps from S2008 to S2017 are the same as S1004 to S1013 in FIG. 5, the description is omitted here. As described above, in the system that performs EGR during engine high-load operation by the control described with reference to the flowchart of FIG. 6, even when the initial EGR rate is set low, the operating state deteriorates or the exhaust gas deteriorates due to unstable combustion. Thus, a suitable high torque (high output) operation can be realized.

  FIGS. 7 to 10 show an example of the second embodiment of the present invention in which a flowchart and a configuration for detecting or estimating the EGR gas state are added to the first embodiment.

  FIG. 7 shows a flowchart in which EGR gas detection and estimation steps are added to the control routine of FIGS. 5 and 6 of the present embodiment. In the case of the system of the present invention in which EGR is introduced to avoid knocking and torque (output) is improved, the occurrence of knocking, the presence or absence of combustion instability, etc. are affected by the flow rate and temperature of the actually flowing EGR gas. Therefore, by detecting or estimating whether or not the set EGR rate is within the predetermined range and whether or not the EGR gas temperature is within a predetermined range, a more suitable control can be performed by selecting a control amount corresponding to this. Can be implemented. The flowchart of FIG. 7 is obtained by providing S3002 of EGR estimation between S1001 and S1002 of FIG. 5 and between S2001 and S2002 of FIG. The estimation of the EGR gas state can be realized, for example, by providing a temperature sensor in the EGR passage 9 or estimating the EGR gas temperature from the output of the intake air temperature sensor 12 installed in the intake port 20.

  FIG. 8 shows the relationship between the intake (EGR gas) temperature and the target EGR rate in the second embodiment of the present invention. If the intake air (EGR gas) temperature is high, the in-cylinder temperature is raised by EGR, and it becomes easy to knock, so it is necessary to lower the target EGR rate. Therefore, in the configuration of the second embodiment, the ECU 8 is set in advance with the target EGR rate corresponding to the characteristic as shown by the line L02, that is, the EGR gas state (temperature), and based on this, the EGR rate and supercharging are set. Control pressure (air volume).

  FIG. 9 shows a configuration of the second embodiment of the present invention when the EGR flow sensor 23 is installed in the EGR passage 9, and FIG. 10 shows an EGR flow control when the EGR gas flow sensor 23 is used. An example of a flowchart is shown.

  The EGR gas flow rate sensor 23 is a sensor that can directly detect the mass flow rate of EGR gas flowing through the EGR passage 9. As an effect, for example, when the EGR gas amount is set to an amount corresponding to the target EGR rate, the deterioration state of the engine 30 is detected by detecting and controlling the EGR gas flow rate according to the flowchart shown in S4001 to S4003 of FIG. In addition, appropriate and smooth EGR rate control can be realized regardless of the control responsiveness of the supercharger 6 or the like. The detection principle of the EGR flow rate is not limited within the scope of the present invention, but a sensor having a hot wire type or hot plate type measuring element is preferable as a structure for avoiding contamination by EGR gas. In addition, an EGR flow rate estimation method based on charging efficiency estimation using, for example, the output values of the intake pressure sensor 14, the intake air temperature sensor 12, and the air flow sensor 2 may be used without directly detecting the EGR flow rate.

  FIG. 11 shows a configuration example of a control device for a multi-cylinder engine in the third embodiment of the present invention. This embodiment differs from the engine configuration of the embodiment so far in that the EGR passage 9 is arranged as a passage connecting the exhaust catalyst 7 in the exhaust passage 40 and the impeller 6 b of the supercharger 6. The throttle 13 for adjusting the intake air amount is disposed immediately downstream of the air cleaner 17 and upstream of the intake side communication port of the EGR passage 9. In this configuration, since the EGR gas after passing through the exhaust catalyst 7 can be input from the upstream side, it is possible to return a large amount of EGR gas with little fouling into the engine. In this configuration, the distance from the engine combustion chamber 18 to the air flow sensor 2 and the distance to the EGR sensor 12 are substantially the same, so the effect of improving the control accuracy of the EGR rate during transient operation is reduced. Since the deterioration of the EGR flow sensor 12 due to contamination is suppressed, it is possible to estimate the EGR rate and the in-cylinder oxygen concentration with high accuracy in cooperation with the air flow sensor 2. In the case of this configuration, since a large amount of EGR gas can be introduced, if the gas flow rate is mainly sensed, the air flow sensor 2 may be removed from the system and the cost may be reduced. However, since this content is not a problem intended by the present invention, details are omitted.

  The arrangement of the EGR flow sensor 23 shown in the second and third embodiments of the present invention has the same effect as that of the present embodiment even if it is downstream of the EGR valve 11 or upstream of the EGR cooler 10. Therefore, it should be noted that these are not limited to the installation locations described in the drawings of the embodiments, and may be anywhere in the EGR passage 9.

DESCRIPTION OF SYMBOLS 1 ... Accelerator opening sensor, 2 ... Air flow sensor, 3 ... Air-fuel ratio sensor, 5 ... Injector, 6 ... Supercharger, 6a ... Impeller, 6b ... Turbine, 7 ... Catalyst, 8 ... ECU, 9 ... EGR passage, 10 DESCRIPTION OF SYMBOLS EGR cooler, 11 EGR valve, 12 Intake temperature sensor, 13 Throttle, 14 Intake pressure sensor, 15 Spark plug, 16 Intercooler, 17 Air cleaner, 18 Combustion chamber, 19 Cylinder, 20 Intake port, 21 ... Pressure sensor, 22 ... Knock sensor, 23 ... EGR gas flow sensor, 24 ... EGR valve, 25 ... EGR piping, 26 ... EGR cooler 30 ... Multi-cylinder engine, 32 ... Intake passage, 40 ... Exhaust passage

Claims (13)

An air supply amount adjusting means for adjusting the amount of air supplied into the cylinder, an EGR passage for returning a part of the exhaust gas to the intake system, and an EGR gas flow rate recirculated to the intake system through the EGR passage EGR gas flow rate adjusting means for adjusting, combustion state estimating means for detecting or estimating the combustion state of the air-fuel mixture, air / fuel ratio detecting means for detecting the air / fuel ratio of the exhaust, said air supply amount adjusting means and EGR gas flow rate Control means for controlling the adjusting means,
The control means performs EGR during high load operation when the engine load becomes a predetermined value or more, and based on at least one of the estimation result of the combustion state estimation means and the detection result of the air-fuel ratio detection means A control device for a multi-cylinder engine, which obtains a degree of variation in combustion state between the cylinders and / or a degree of variation in air-fuel ratio between cylinders and controls the EGR rate based on the degree of variation.   The control means performs control to reduce both the amount of air supplied into the cylinder and the EGR rate when at least one of the degree of variation in combustion state and the degree of variation in air-fuel ratio between the cylinders is equal to or greater than a predetermined value. The control apparatus for a multi-cylinder engine according to claim 1.   When at least one of the degree of variation in the combustion state and the degree of variation in the air-fuel ratio between the cylinders is greater than or equal to a predetermined value, the control means first reduces the amount of air supplied into the cylinder, and then the EGR rate The control device for a multi-cylinder engine according to claim 1, wherein control for reducing the engine is performed.   4. The control unit according to claim 1, wherein when the required torque for the engine is larger than the actual torque, the control unit performs control to increase both the amount of air supplied into the cylinder and the EGR rate. 5. A control device for a multi-cylinder engine as described in 1.   2. The control unit according to claim 1, wherein when the required torque for the engine is larger than the actual torque, the control means increases the amount of air supplied into the cylinder first and then increases the EGR rate. 5. The control device for a multi-cylinder engine according to any one of 4 above.   The control means uses, as at least an initial value of an EGR rate at the time of high load operation after restart, an EGR rate at the time of high load operation under the same previous conditions set before restart. The control apparatus for a multi-cylinder engine according to any one of claims 1 to 5.   The control means controls the control amount for the air supply amount adjusting means and / or the control amount for the EGR flow rate adjusting means set during the high load operation at the time of high load operation under the same conditions after restart. The multi-cylinder engine control device according to any one of claims 1 to 5, wherein the control device is used as at least an initial value of the quantity.   The control device for a multi-cylinder engine according to any one of claims 1 to 7, wherein the control means controls an ignition timing in addition to an EGR rate.   The multi-cylinder engine according to any one of claims 1 to 8, further comprising EGR gas flow rate estimating means for detecting or estimating a flow rate of EGR gas recirculated to the intake system through the EGR passage. Control device.   The EGR gas flow rate estimating means has a flow rate sensor arranged in the EGR passage or a temperature sensor arranged in either the EGR passage or the intake passage, and calculates the EGR gas flow rate based on a signal obtained from the sensor. The control device for a multi-cylinder engine according to claim 9, wherein detection or estimation is performed.   The control device for a multi-cylinder engine according to claim 10, wherein the control means changes an EGR rate based on a detection or estimation result of the EGR gas flow rate estimation means.   The control means prohibits EGR during the high load operation when the EGR gas temperature or the gas temperature in the intake passage is equal to or higher than a predetermined value based on the detection or estimation result of the EGR gas flow rate estimating means. The control device for a multi-cylinder engine according to any one of claims 9 to 11.   When performing EGR during high load operation where the engine load is a predetermined value or more, the degree of variation in combustion state between cylinders and / or the degree of variation in air-fuel ratio between cylinders is determined, and the degree of variation in combustion state between the cylinders A control method for a multi-cylinder engine, wherein when at least one of the degrees of variation in the air-fuel ratio is equal to or greater than a predetermined value, control is performed to first reduce the amount of air supplied into the cylinder and then reduce the EGR rate.

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