JP2008038866A - Combustion control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion control device for an internal combustion engine capable of effectively suppressing output step which can be produced when switching combustion modes from normal combustion to bank control. <P>SOLUTION: A combustion control device for an internal combustion engine executes control for switching a combustion mode from normal combustion to bank control for poisoning recovery of an exhaust purifying catalyst. In this case, the combustion control device for an internal combustion engine executes the switching to the bank control considering whether or not step is generated in torque in switching from the normal combustion to the bank control. In the concrete, under the condition that step is produced in the torque, the switching to the bank control is prohibited for prescribed time. Under the condition that no step is produced in the torque, the switching to the bank control is executed on a priority basis. By so doing, the device resists to product dispersion and aging deterioration. As a result, the poisoning recovery of the catalyst can be surely executed while torque step which can be produced is effectively suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a combustion control device for an internal combustion engine that performs switching of a combustion mode and the like.

  Conventionally, by increasing or decreasing the air-fuel ratio for each cylinder, the temperature of the exhaust purification catalyst (NOx catalyst or the like) is raised, and the removal of the purification reducing substance such as sulfur oxide (SOx) is performed. For example, Patent Document 1 discloses a purification-reducing substance by performing control (hereinafter also referred to as “bank control”) in which the air-fuel ratio is different between one cylinder group (bank) and the other cylinder group (bank). Techniques for removing are described.

  By the way, in recent years, for example, a technique for switching to a combustion mode such as stoichiometric combustion or lean combustion having different air-fuel ratios has been performed. When such a combustion mode is switched, an output step such as a torque step may occur greatly, and various proposals have been made to suppress this output step. For example, in Patent Document 2, when switching the combustion mode, the ignition timing is retarded until the torque of the internal combustion engine estimated from the intake air amount or the like matches the predetermined torque after switching, that is, by performing torque correction. A technique for suppressing the torque step is proposed.

JP-A-8-189388 Japanese Patent Laid-Open No. 11-22609

  However, in the techniques described in Patent Documents 1 and 2 described above, when the combustion mode is switched from normal combustion (stoichiometric combustion) to bank control, the output level difference due to product variation and aging deterioration is appropriately suppressed. There was a case that could not be done.

  The present invention has been made to solve such problems, and is an internal combustion engine capable of effectively suppressing an output step that can occur when switching the combustion mode from normal combustion to bank control. It is to provide a combustion control device.

  In one aspect of the present invention, an internal combustion engine that performs bank control for recovering poisoning of an exhaust purification catalyst provided on an exhaust passage by making an air-fuel ratio different between one cylinder group and the other cylinder group. The combustion control device includes a switching request determination unit that determines whether or not there is a request to switch from normal combustion to bank control, and a step in torque generated by the internal combustion engine when switching from the normal combustion to the bank control. When it is determined that there is a request for switching to bank control by the torque step determining means for determining whether or not to occur, and when the switching request determining means determines that there is a request to switch to bank control, Switching prohibiting means for prohibiting the time and the switching.

  The combustion control device for an internal combustion engine executes control for switching from normal combustion to bank control for recovering poisoning of the exhaust purification catalyst. In this case, the combustion control device of the internal combustion engine switches to the bank control in consideration of whether or not a step is generated in the torque when switching from the normal combustion to the bank control. Specifically, when it is determined that there is a step in the torque, switching to bank control is prohibited for a predetermined time. As a result, it is possible to effectively suppress a torque step that may occur when switching from normal combustion to bank control.

  In one aspect of the combustion control apparatus for an internal combustion engine, when the torque step determining means determines that there is no step in the torque, switching from the normal combustion to the bank control is performed without changing the throttle opening. First switching control means is provided.

  In this aspect, the first switching control means preferentially switches to bank control in a situation where no torque step occurs. Specifically, since a torque step does not occur, switching to bank control is executed without changing the throttle opening. By executing the switching in such a situation, it becomes difficult to be affected by product variations and aging deterioration, and therefore it is possible to suppress a torque step that may occur at the time of switching with a considerably high probability.

  In another aspect of the combustion control apparatus for an internal combustion engine, when the time during which the switching prohibition unit continues to prohibit the switching exceeds the predetermined time, the throttle opening is changed to change the normal combustion from the normal combustion. Second switching control means for executing switching to bank control is provided.

  In this aspect, the second switching control means switches from a situation in which a torque step can occur to a situation in which a torque step does not occur for a predetermined time in a situation where a torque step can occur. Switching is prohibited until a change is made, and switching to bank control is executed when the time for which the prohibition has continued reaches a predetermined time even though the switching is prohibited in this way. That is, when the time for which the prohibition has continued reaches a predetermined time, switching to bank control is executed in order to prioritize the execution of the poisoning recovery of the exhaust purification catalyst. More specifically, switching is performed by changing the throttle opening. This is to suppress a torque step generated when switching to bank control. As described above, the poisoning recovery of the exhaust purification catalyst can be surely executed while appropriately suppressing the torque step generated when switching to the bank control.

  Preferably, in the combustion control apparatus for an internal combustion engine, the torque step determining means is based on at least one of the rotational speed, intake air amount, intake pipe pressure, throttle opening, and accelerator opening of the internal combustion engine. The determination can be made.

  More preferably, the predetermined time during which the switching prohibiting unit prohibits the switching may be a value of 1 hour or more.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[overall structure]
FIG. 1 is a schematic diagram showing an overall configuration of a vehicle 100 to which a combustion control device for an internal combustion engine according to the present embodiment is applied. In FIG. 1, solid arrows indicate an example of gas flow, and broken arrows indicate input / output of signals.

  The vehicle 100 mainly includes an intake passage 3, a throttle valve 4, an engine (internal combustion engine) 5, an exhaust passage 6, a catalyst 7, and an ECU (Electronic Control Unit) 10.

  The intake air introduced from outside passes through the intake passage 3, and the throttle valve 4 adjusts the flow rate of the intake air passing through the intake passage 3. The intake air is supplied to the engine 5 after being introduced into the surge tank. The throttle valve 4 is controlled to an opening (throttle opening) corresponding to a control signal supplied from the ECU 10.

  The engine 5 is configured as a V-type 6-cylinder engine in which three cylinders (cylinders) 5c are provided in two banks 5a and 5b. One cylinder group is constituted by the three cylinders 5c of the bank 5a, and another cylinder group is constituted by the three cylinders 5c of the bank 5b. In the following, when the bank 5a and the bank 5b are not distinguished, the reference numerals are omitted.

  The engine 5 generates power by causing an air-fuel mixture obtained by mixing the supplied intake air and fuel to explode in the cylinder 5c. The engine 5 performs control of the fuel injection amount, ignition timing, and the like by a control signal supplied from the ECU 10. Specifically, the control signal is supplied to each of the bank 5a and the bank 5b, whereby the control of the fuel injection amount and the control of the ignition timing in each of the bank 5a and the bank 5b are executed. The engine 5 is not limited to using a V-type 6-cylinder engine in which a bank is constituted by three cylinders 5c.

  The exhaust gas discharged from the engine 5 flows through the exhaust passage 6. A catalyst 7 is provided in the exhaust passage 6. The catalyst 7 (exhaust purification catalyst) is composed of a NOx storage catalyst or the like, and purifies NOx and SOx in the exhaust gas. Although FIG. 1 shows an example in which the catalyst 7 is provided on the exhaust passage 6 connected to both the bank 5a and the bank 5b, the exhaust passage is connected to each of the bank 5a and the bank 5b. Each may be provided with a catalyst.

  The ECU 10 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown). The ECU 10 executes “bank control” in order to recover sulfur poisoning of the catalyst 7 (hereinafter also referred to as “S poisoning recovery”). Specifically, the ECU 10 performs control to vary the air-fuel ratio between one bank and the other bank. Specifically, control is performed so that one bank performs rich combustion (hereinafter, this bank is referred to as “rich bank”), and the other bank performs lean combustion (hereinafter, this bank is referred to as “lean bank”). As a result, a gas obtained by mixing a gas containing a large amount of fuel and a gas containing a large amount of oxygen is supplied to the catalyst 7 and the temperature (bed temperature) of the catalyst 7 rises, so that the sulfur poisoning of the catalyst 7 is recovered. . Bank control is executed every several thousand kilometers of travel.

  In the present embodiment, the ECU 10 executes control for switching the combustion mode from normal combustion to bank control (hereinafter referred to as “combustion mode switching control”). Specifically, the combustion mode switching control is executed so that a torque step that may occur when switching the combustion mode is appropriately suppressed. More specifically, the ECU 10 switches from normal combustion to bank control in consideration of the possibility of a torque step occurring when switching to bank control and the elapsed time since the request to switch to bank control is issued. Execute. Thus, the ECU 10 operates as a combustion control device for an internal combustion engine in the present invention. Specifically, the ECU 10 operates as a switching request determining unit, a torque step determining unit, a switching prohibiting unit, a first switching control unit, and a second switching control unit.

[Combustion mode switching control]
Hereinafter, the combustion mode switching control executed when the ECU 10 switches the combustion mode from the normal combustion to the bank control will be specifically described.

  In the present embodiment, the combustion mode switching control is executed so that a torque step that may occur when switching the combustion mode from normal combustion to bank control is effectively suppressed. Specifically, the ECU 10 switches from normal combustion to bank control in consideration of the possibility of a torque step occurring when switching to bank control and the elapsed time since a request to switch to bank control is issued. Execute. For example, the ECU 10 determines whether or not a torque step is generated when switching to bank control based on at least one of engine speed, intake air amount, intake pipe pressure, throttle opening, and accelerator opening. Make a decision.

  Specifically, the ECU 10 preferentially switches to bank control in a situation where no torque step occurs. In this case, since a torque step does not occur, the ECU 10 performs switching to bank control without changing the throttle opening. By executing the switching in such a situation, it becomes difficult to be affected by product variations and aging deterioration, and thus it is possible to effectively suppress a torque step that may occur at the time of switching. Accordingly, in the present embodiment, switching to bank control is executed preferentially in a situation where no torque step occurs.

  On the other hand, in a situation where a torque step may occur, the ECU 10 prohibits switching to bank control for a predetermined time after a request to switch to bank control is issued. That is, in the situation described above, switching is prohibited until a change from a situation where a torque level difference can occur to a situation where no torque level difference occurs during a predetermined time. Nevertheless, switching to bank control is executed when the time during which prohibition has continued (elapsed time since the request was issued) reaches a predetermined time. That is, when the time during which the prohibition is continued reaches a predetermined time, switching to bank control is executed in order to give priority to the execution of S poison recovery. In this case, the ECU 10 performs switching by changing the throttle opening. This is to suppress a torque step generated when switching to bank control.

  As described above, in this embodiment, in a situation where a torque step does not occur, the torque step can be suppressed with a considerably high probability because it is less affected by product variations and aging deterioration. Switch to bank control. On the other hand, in a situation where a torque step can occur, switching to bank control is prohibited until a predetermined time elapses, and priority is given to the execution of S poison recovery when the prohibited time reaches the predetermined time. Therefore, the control for suppressing the torque step is appropriately performed to switch to the bank control. Thereby, S poison recovery can be reliably performed while effectively suppressing a torque step that may occur when switching from normal combustion to bank control.

  Here, the combustion mode switching control will be specifically described with reference to FIGS.

(Control when engine speed is high)
First, a situation where a torque step does not occur when switching from normal combustion to bank control, that is, a situation where switching can be performed without changing the throttle opening will be described with reference to FIGS. Specifically, a case where the engine speed is a high speed will be described.

  FIG. 2 is a diagram showing torque generated when the engine speed is high. FIG. 2A is a diagram showing the relationship between the air amount (horizontal axis) and the torque (vertical axis). Further, the graph indicated by the solid line 40 indicates the torque characteristic at the time of stoichiometry (during normal combustion), and the graph indicated by the alternate long and short dash line 41 indicates the torque characteristic at the time of bank control when the engine speed is high. Specifically, the torque characteristic during the bank control is based on the difference in the air-fuel ratio between the two banks, which can raise the bed temperature of the catalyst 7 to the temperature to be set when performing the S poison recovery. It is determined. From FIG. 2A, it can be said that there is almost no difference between the torque during bank control and the torque during normal combustion. This is because when the engine speed is high, the exhaust temperature tends to be high. Therefore, even if the air-fuel ratio difference between the rich bank and the lean bank at the time of bank control is small, the bed temperature of the catalyst 7 is sufficiently high. This is because it can be raised.

  FIG. 2B shows the relationship between the air-fuel ratio (horizontal axis) and the torque (vertical axis), and the graph shown by the curve 60 shows the characteristic of torque with respect to the air-fuel ratio. As described above, since the exhaust temperature tends to be high at a high engine speed, even when the air-fuel ratio difference between the rich bank and the lean bank during the bank control is small, it is set when performing S poison recovery. It can be said that the bed temperature of the catalyst 7 can be sufficiently raised to the desired temperature. Therefore, for example, as indicated by reference numeral 61 in FIG. 2B, a relatively small air-fuel ratio difference is determined as the air-fuel ratio difference between the rich bank and the lean bank during bank control. In this case, using the graph indicated by the curve 60, the torque to be generated from the rich bank is the torque indicated by reference numeral 51, and the torque to be generated from the lean bank is the torque indicated by reference numeral 52. Note that the torque denoted by reference numeral 50 indicates the torque generated during stoichiometry.

  In the above case, when switching from normal combustion to bank control, the torque change in the rich bank (difference between torque 50 and torque 51) becomes “Tr1”, and the torque change in the lean bank (difference between torque 50 and torque 52). ) Becomes “Tl1”. In this case, the relationship “Tr1≈Tl1” is established between the torque change Tr1 in the rich bank and the torque change Tl1 in the lean bank. That is, it can be said that the torque generated during bank control is substantially equal to the torque generated during normal combustion. That is, when the engine speed is high, it can be said that there is almost no torque step even when switching from normal combustion to bank control. Therefore, when the engine speed is high, it is not necessary to control the throttle opening when switching from normal combustion to bank control. As described above, in this embodiment, when the engine speed is a high engine speed, switching to bank control is preferentially executed.

  Next, control executed when switching from normal combustion to bank control when the engine speed is high will be described with reference to FIG. 3 (a) shows the throttle opening, FIG. 3 (b) shows the air amount, FIG. 3 (c) shows the ignition timing, and FIG. 3 (d) shows the target air-fuel ratio. In addition, the horizontal axis of FIG. 3 has shown time.

  In this case, at time t1, the ECU 10 starts switching from normal combustion to bank control. At this time, since the engine speed is high, the ECU 10 does not change the throttle opening (see FIG. 3A) and does not change the air amount (see FIG. 3B). Further, at the start of switching at time t1, the ECU 10 performs control to change the ignition timing and the target air-fuel ratio to values used in the rich bank and the lean bank, respectively (see FIGS. 3C and 3D). That is, when the engine speed is high, the ECU 10 performs control to change the control value at a time at the start of switching at time t1 without performing control for shifting from normal combustion to bank control. Since the combustion mode is switched without changing the throttle opening and the like in this way, it is less susceptible to product variations and aging deterioration, so that it is possible to effectively suppress the torque step that can occur when switching the combustion mode. it can.

(Control when the engine speed is low)
Next, a situation in which a torque step can occur when switching from normal combustion to bank control, that is, a situation where switching is performed by changing the throttle opening will be described with reference to FIGS. Specifically, a case where the engine speed is a low speed will be described.

  FIG. 4 is a diagram showing the torque generated when the engine speed is low. FIG. 4A shows the relationship between the air amount (horizontal axis) and the torque (vertical axis). Further, the graph indicated by the solid line 40 indicates the torque characteristic at the time of stoichiometry (during normal combustion), and the graph indicated by the alternate long and short dash line 42 indicates the torque characteristic at the time of bank control when the engine speed is low. Specifically, the torque characteristic during the bank control is based on the difference in the air-fuel ratio between the two banks, which can raise the bed temperature of the catalyst 7 to the temperature to be set when performing the S poison recovery. It is determined. From FIG. 4A, it can be said that the difference between the torque during bank control and the torque during normal combustion is large. This is because, when the engine speed is low, the exhaust temperature tends to be relatively low. Therefore, in order to sufficiently increase the bed temperature of the catalyst 7, the rich bank and the lean bank at the time of bank control This is because the difference in air-fuel ratio needs to be increased.

  FIG. 4B shows the relationship between the air-fuel ratio (horizontal axis) and torque (vertical axis), and the graph shown by the curve 60 shows the characteristics of torque with respect to the air-fuel ratio. As described above, since the exhaust temperature tends to be low at a low engine speed, in order to sufficiently raise the bed temperature of the catalyst 7 to the temperature to be set when performing the S poison recovery, the bank control is performed. It is necessary to increase the difference in air-fuel ratio between the rich bank and the lean bank. Therefore, for example, as indicated by reference numeral 63 in FIG. 4B, a relatively large air-fuel ratio difference is determined as the air-fuel ratio difference between the rich bank and the lean bank at the time of bank control. In this case, using the graph indicated by the curve 60, the torque to be generated from the rich bank is the torque indicated by reference numeral 53, and the torque to be generated from the lean bank is the torque indicated by reference numeral 54. Note that the torque denoted by reference numeral 50 indicates the torque generated during stoichiometry.

  In the above case, when switching from normal combustion to bank control, the torque change in the rich bank (difference between torque 50 and torque 53) is “Tr2”, and the torque change in the lean bank (difference between torque 50 and torque 54). Becomes “Tl2”. In this case, the relationship “Tr2 <Tl2” is established between the torque change Tr2 in the rich bank and the torque change Tl2 in the lean bank. That is, it can be said that the difference between the torque generated during bank control and the torque generated during normal combustion is large. Therefore, when the engine speed is low, it can be said that a torque step occurs when switching from normal combustion to bank control. Specifically, the torque generated during bank control is lower than the torque generated during normal combustion. Therefore, in this embodiment, when the engine speed is low, when switching from normal combustion to bank control, control of the throttle opening is executed in order to suppress such a torque step.

  Next, the control executed when switching from normal combustion to bank control when the engine speed is low will be described with reference to FIG. FIG. 5A shows the throttle opening, FIG. 5B shows the air amount, FIG. 5C shows the ignition timing, and FIG. 5D shows the target air-fuel ratio. In addition, the horizontal axis of FIG. 5 has shown time.

  In this case, at time t21, the ECU 10 starts switching from normal combustion to bank control. At this time, since the engine speed is low, the ECU 10 changes the throttle opening (see FIG. 5A) and changes the air amount (see FIG. 5B). Specifically, the ECU 10 obtains an air amount to be set so that the torque after switching to bank control is approximately equal to the torque before switching, and adjusts the throttle opening so that this air amount can be obtained.

  Further, the ECU 10 performs the retard control of the ignition timing in a state where the target air-fuel ratio is maintained stoichiometrically (see FIG. 5 (d)) so that the torque generated when the air amount changes becomes equal torque. Execute (see FIG. 5C). Further, the ECU 10 calculates (estimates) torque that can be generated by the bank control when the air amount changes, and ends the switching when the estimated torque reaches the target torque. Specifically, since the estimated torque reaches the target torque at time t22, the ECU 10 changes the ignition timing and the target air-fuel ratio to values used in the rich bank and the lean bank, respectively (FIG. 5 (c), ( d)). When the engine speed is thus low, the ECU 10 performs control for shifting from normal combustion to bank control from time t21 to time t22 so that the occurrence of a torque step is suppressed. Thereby, the torque level difference which can be generated by switching the combustion mode from the normal combustion to the bank control can be appropriately suppressed.

  In the above description, an example is shown in which whether or not a torque step can occur is defined by the engine speed, but is not limited thereto. In another example, whether or not a torque step can occur is defined based on at least one of the engine speed, intake air amount, intake pipe pressure, throttle opening, and accelerator opening. Can do.

[Combustion mode switching process]
Next, the combustion mode switching process according to the present embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing the combustion mode switching process. This process is repeatedly executed by the ECU 10 at a predetermined cycle.

  First, in step S101, the ECU 10 determines whether or not there is a request to switch from normal combustion to bank control. Specifically, the ECU 10 determines whether or not the amount of sulfur deposited on the catalyst 7 is within a predetermined range. In this case, the ECU 10 obtains the amount of sulfur deposition by estimation or the like. If there is a request to switch to bank control (step S101; Yes), the process proceeds to step S102. If there is no request to switch to bank control (step S101; No), the process exits the flow.

  In step S102, the ECU 10 counts an elapsed time Tbank after a request to switch to bank control is issued. Then, the process proceeds to step S103.

  In step S103, the ECU 10 determines whether or not the elapsed time Tbank is less than the predetermined time Tbank_max. Here, the determination using the predetermined time Tbank_max is performed to determine whether or not the S poison recovery should be immediately executed. The predetermined time Tbank_max generally corresponds to the time required from when the request for switching to bank control is issued until S poisoning in the catalyst 7 becomes a problem. For example, the predetermined time Tbank_max is set to a value of 1 hour or more. When the elapsed time Tbank is less than the predetermined time Tbank_max (step S103; Yes), the process proceeds to step S104. In this case, it can be said that it is not a situation where the S poison recovery should be executed immediately.

  In step S104, the ECU 10 determines whether or not a condition for starting bank control (hereinafter also referred to as “bank control start condition”) is satisfied. Here, the determination using the bank control start condition is performed to determine whether or not the torque step is not generated when switching from the normal combustion to the bank control. Specifically, the ECU 10 determines whether or not a bank control start condition is satisfied based on at least one of the engine speed, the intake air amount, the intake pipe pressure, the throttle opening, and the accelerator opening. . For example, the bank control start condition is satisfied when the engine speed is high (see FIG. 2), and the bank control start condition is not satisfied when the engine speed is low (see FIG. 4). If the bank control start condition is satisfied (step S104; Yes), the process proceeds to step S105.

  In step S105, the ECU 10 performs S poison recovery by performing control to switch from normal combustion to bank control. In this case, since the bank control start condition is satisfied, it can be said that there is almost no torque step at the time of switching to the bank control, so the ECU 10 does not change the throttle opening, and does not change the fuel injection amount (air-fuel ratio) or Control is performed to change the ignition timing to a value necessary for bank control. Then, the process exits the flow.

  On the other hand, when the bank control start condition is not satisfied (step S104; No), the process exits the flow. In this case, since the elapsed time Tbank is less than the predetermined time Tbank_max, it is not a situation where the S poison recovery should be executed immediately, and the bank control start condition is not satisfied. Therefore, control for switching to bank control is not executed. That is, it waits until the bank control start condition is satisfied until the elapsed time Tbank becomes equal to or longer than the predetermined time Tbank_max.

  If the elapsed time Tbank is equal to or longer than the predetermined time Tbank_max (step S103; No), the process proceeds to step S106. This case corresponds to the case where the bank control start condition is satisfied, but the bank control start condition is not satisfied even though the elapsed time Tbank has reached the predetermined time Tbank_max. That is, it can be said that S poison recovery should be executed immediately. Therefore, in step S106, the ECU 10 performs S poison recovery by performing control to switch from normal combustion to bank control. Specifically, in this case, it can be said that a torque step can occur. Therefore, in order to suppress the torque step that occurs when switching to bank control, the ECU 10 changes the throttle opening. Perform switching. When the above process ends, the process exits the flow.

  According to the above combustion mode switching processing, S poison recovery can be reliably performed while effectively suppressing a torque step that may occur when switching from normal combustion to bank control.

  In the above description, the combustion mode switching control performed when the combustion mode is switched from the normal combustion to the bank control has been described. However, the present invention can also be applied to the case where the bank control is switched to the normal control. In this case, when the engine speed is high, the bank control can be switched to the normal control without changing the throttle opening. On the other hand, when the engine speed is low, the throttle opening can be changed to switch from bank control to normal control.

1 is a schematic diagram illustrating an overall configuration of a vehicle to which a combustion control device for an internal combustion engine according to an embodiment is applied. It is a figure which shows the torque produced | generated when it is a high engine speed. It is a figure for demonstrating the control performed when switching from normal combustion to bank control in the case of high engine speed. It is a figure which shows the torque produced | generated when it is a low engine speed. It is a figure for demonstrating the control performed when switching from normal combustion to bank control in the case of low engine speed. It is a flowchart which shows a combustion mode switching process.

Explanation of symbols

3 Intake passage 4 Throttle valve 5 Engine 5a, 5b Bank 6 Exhaust passage 7 Catalyst 10 ECU
100 vehicles

Claims (5)

In a combustion control device for an internal combustion engine that executes bank control for poisoning and recovering an exhaust purification catalyst provided on an exhaust passage by making the air-fuel ratio different between one cylinder group and the other cylinder group,
Switching request determination means for determining whether or not there is a request to switch from normal combustion to bank control;
Torque step determining means for determining whether or not a step is generated in the torque generated by the internal combustion engine when switching from the normal combustion to the bank control;
When it is determined by the switching request determining means that there is a request to switch to bank control, when the torque step determining means determines that a step occurs in the torque, a switching prohibiting means for prohibiting the switching for a predetermined time, A combustion control apparatus for an internal combustion engine, comprising:   When the torque level determining means determines that there is no level difference in torque, the torque level determining means comprises first switching control means for executing switching from the normal combustion to the bank control without changing the throttle opening. The combustion control device for an internal combustion engine according to claim 1.   Second switching control means for executing switching from the normal combustion to the bank control by changing a throttle opening when a time during which the switching inhibition is continued by the switching prohibition means exceeds the predetermined time; The combustion control apparatus for an internal combustion engine according to claim 1, further comprising:   2. The torque step determining means performs the determination based on at least one of the rotational speed, intake air amount, intake pipe pressure, throttle opening, and accelerator opening of the internal combustion engine. The combustion control device for an internal combustion engine according to any one of claims 1 to 3.   The combustion control device for an internal combustion engine according to any one of claims 1 to 4, wherein the predetermined time during which the switching prohibiting unit prohibits the switching is a value of 1 hour or more.

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