JP2008157093A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To implement a highly accurate air-fuel ratio control regardless of an operational status, in an internal combustion engine. <P>SOLUTION: A plurality of cylinders are arrayed in a right bank 13 and a left bank 12 as cylinder groups. Exhaust pipes 57, 58 are respectively connected to the cylinder groups of the banks 12, 13. Front stage three-way catalyst 59, 60 and control valves 64, 65 are respectively disposed on the exhaust pipes 57, 58. A communicating pipe 63 connects the exhaust pipes 57, 58, and A/F sensors 88, 89 are respectively disposed on the exhaust pipes 57, 58 to the upstream of the front stage three-way catalysts 59, 60. An ECU 81 performs a main air-fuel ratio learning control for each of the cylinder groups in the banks 12, 13, based on detection results of the A/F sensors 88, 89, and performs the main air-fuel ratio learning control depending on opening/closing states of the control valves 64, 65. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention has two cylinder groups in which a plurality of cylinders are divided into left and right banks, a purification catalyst and a control valve are provided in the exhaust passage of each cylinder group, and each exhaust passage is provided with a purification catalyst and a control. The present invention relates to an internal combustion engine communicated by a communication passage on the upstream side of a valve.

  In a general V-type multi-cylinder engine, a cylinder block has two banks inclined upward at a predetermined angle, and a plurality of cylinders are provided in each bank to constitute two cylinder groups. Pistons are movably fitted to a plurality of cylinders provided in each bank, and each piston is connected to a crankshaft that is rotatably supported at the lower part. In addition, each combustion chamber is configured by fastening a cylinder head to the upper part of each bank of the cylinder block, and each combustion chamber is formed with an intake port and an exhaust port, and can be opened and closed by an intake valve and an exhaust valve. It has become. An intake pipe is connected to the intake port of each bank, while an exhaust pipe is connected to each exhaust port of each bank. The exhaust pipes are connected to each other by a communication pipe, and an exhaust valve and a purification catalyst are connected to each exhaust pipe. And the control device controls the opening and closing of each exhaust valve in accordance with the engine operating state.

  In general engines, an A / F (air-fuel ratio) sensor is disposed upstream of the purification catalyst in the exhaust pipe, and the air-fuel ratio is controlled based on the output signal of the A / F sensor. The A / F sensor is an oxygen sensor having an output characteristic linear with respect to the air-fuel ratio. Therefore, the fuel injection amount is feedback-controlled (main feedback control) based on the output signal of the A / F sensor so that the air-fuel ratio (exhaust air-fuel ratio) of the exhaust gas flowing into the purification catalyst becomes the target air-fuel ratio. Yes. The target air-fuel ratio used in the main feedback control is set to an air-fuel ratio (usually the stoichiometric air-fuel ratio) at which the purification catalyst can purify the exhaust gas most efficiently.

  However, the correction range of the main feedback control is limited, and the exhaust air-fuel ratio and the theoretical value may vary depending on individual differences between engines, fuel injection valve injection characteristics, or individual differences in the output characteristics of the airflow sensor for detecting the intake air amount. There may be a steady deviation between the air-fuel ratio. Then, the exhaust air / fuel ratio is biased to the rich side or lean side with respect to the stoichiometric air / fuel ratio, and harmful components such as HC, CO, and NOx in the exhaust gas cannot be properly purified. Therefore, in order to compensate for such steady deviation, the main learning value is statistically calculated based on the deviation between the feedback correction value used in the main feedback control and the control center based on the output signal of the A / F sensor. Then, the control (main A / F learning control) is performed to reflect this in the main feedback control.

In addition to the A / F sensor described above, an O ₂ (oxygen) sensor is disposed on the downstream side of the purification catalyst, and the air-fuel ratio is controlled based on the output signal of the O ₂ sensor. The O ₂ sensor is an oxygen sensor having an output characteristic in which the output changes suddenly between the rich side and the lean side with respect to the air / fuel ratio with reference to the stoichiometric air / fuel ratio. Based on the output signal of the O ₂ sensor, control (sub A / F learning control) for correcting the output signal of the A / F sensor is performed. Since this sub A / F learning control is reflected in the control signal of the main A / F learning control, accurate air-fuel ratio control can be performed.

  Note that the internal combustion engine as described above is described in Patent Document 1 below, and the air-fuel ratio control apparatus is described in Patent Document 2 below.

Japanese Patent Laid-Open No. 08-121153 JP 2001-193521 A

However, in the V-type multi-cylinder engine as described above, an exhaust pipe is connected to each exhaust port of two banks, an exhaust valve and a purification catalyst are attached to each exhaust pipe, and the control device is in an engine operating state. When the exhaust valves are controlled to open and close according to the engine operating conditions, the exhaust gas exhaust paths differ depending on the engine operating state, making it difficult to properly control the air-fuel ratio. That is, when the control device controls the opening and closing of each exhaust valve according to the engine operating state, the exhaust gas joins one exhaust pipe and is purified by one purification catalyst, and the exhaust gas passes through each exhaust pipe. There is a pattern in which the purification treatment is performed by each purification catalyst. Therefore, when there are variations in the intake air amount and the fuel injection amount in the cylinder groups of the two banks, the air-fuel ratio in each bank may be different, and the air-fuel ratio using the A / F sensor or the O ₂ sensor described above may be different. Cannot be corrected with high accuracy.

  An object of the present invention is to provide an internal combustion engine that enables high-precision air-fuel ratio control regardless of the operating state.

  In order to solve the above-described problems and achieve the object, an internal combustion engine of the present invention has two cylinder groups in which a plurality of cylinders are divided into left and right banks, and intake air is supplied to each cylinder group. While the passages are provided, the exhaust passages are provided independently of each other, a control valve for adjusting the flow rate of the exhaust gas is provided in each of the exhaust passages, and a purification catalyst is provided in each of the exhaust passages. In the internal combustion engine, the first air-fuel ratio detection means is provided upstream of the control catalyst and the purification catalyst in the exhaust passage, and upstream of the purification catalyst in the exhaust passage. Control means for performing main air-fuel ratio learning control for each cylinder group based on the detection result of the fuel ratio detection means and for executing main air-fuel ratio learning control according to the open / close state of the control valve is provided. It is an butterfly.

  In the internal combustion engine of the present invention, when only one of the control valves is in an open state, the control means sets the main learning value calculated when both of the control valves are in an open state. The main learning value is calculated in consideration of the back pressure difference of each cylinder group.

  In the internal combustion engine of the present invention, when both of the control valves are in an open state, the control means is configured to calculate each cylinder group calculated when only one of the control valves is in an open state. The main learning value is averaged to calculate the main learning value.

  The internal combustion engine of the present invention is characterized in that the first air-fuel ratio detection means is provided on the upstream side of a connection portion of each exhaust passage with the communication passage.

  In the internal combustion engine of the present invention, second air-fuel ratio detection means is provided downstream of the purification catalyst in each exhaust passage, and the control means is arranged for each cylinder group based on the detection result of the second air-fuel ratio detection means. In addition, the sub air-fuel ratio learning control is executed, and the sub air-fuel ratio learning control is executed in accordance with the open / close state of the control valve.

  In the internal combustion engine of the present invention, when only one of the control valves is in an open state, the control means adds the sub-learning value calculated when both of the control valves are in an open state. The sub-learning value is calculated in consideration of the air-fuel ratio difference between the cylinder groups.

  The internal combustion engine of the present invention is characterized in that the first air-fuel ratio detection means is provided on the downstream side of the connection portion of each exhaust passage with the communication passage and on the upstream side of the purification catalyst.

  In the internal combustion engine of the present invention, the control means performs air-fuel ratio feedback control for each cylinder based on the detection result of the first air-fuel ratio detection means, and only one of the control valves is open. The air-fuel ratio feedback control is executed based on the detection result of the first air-fuel ratio detection means on the cylinder group side in the open state.

  In the internal combustion engine of the present invention, the control means performs air-fuel ratio feedback control for each cylinder based on the detection result of the first air-fuel ratio detection means, and both of the control valves are opened. In some cases, air-fuel ratio feedback control is executed based on a detection result of the first air-fuel ratio detection means for each cylinder group.

  In the internal combustion engine of the present invention, second air-fuel ratio detection means is provided downstream of the purification catalyst in each exhaust passage, and the control means is arranged for each cylinder group based on the detection result of the second air-fuel ratio detection means. In addition, the sub air-fuel ratio learning control is executed, and the sub air-fuel ratio learning control is executed based on the detection result of the second air-fuel ratio detection means for each cylinder group regardless of the open / close state of the control valve. Yes.

  The internal combustion engine of the present invention is characterized in that the first air-fuel ratio detection means is provided in a connection portion of each exhaust passage with the communication passage.

  In the internal combustion engine of the present invention, the control means performs air-fuel ratio feedback control for each cylinder based on the detection result of the first air-fuel ratio detection means, and only one of the control valves is open. The cylinder group in the closed state performs air-fuel ratio feedback control based on the detection result of the first air-fuel ratio detection means on the one cylinder group side, while the cylinder group in the open state The air-fuel ratio feedback control is executed based on the detection result of the first air-fuel ratio detection means of the two cylinder groups.

  In the internal combustion engine of the present invention, the control means performs air-fuel ratio feedback control for each cylinder based on the detection result of the first air-fuel ratio detection means, and both of the control valves are opened. In some cases, air-fuel ratio feedback control is executed based on a detection result of the first air-fuel ratio detection means of each cylinder group.

  In the internal combustion engine of the present invention, when only one of the control valves is in an open state, the control means is in an open state after completion of the main air-fuel ratio learning control on the cylinder group side in the closed state. The main air-fuel ratio learning control on the cylinder group side is executed.

  In the internal combustion engine of the present invention, when both of the control valves are in the open state, the control means simultaneously executes the main air-fuel ratio learning control of the cylinder groups, and sets the learning control update speed to the Only one of the control valves is slower than the learning control update speed of the main air-fuel ratio learning control when the control valve is in the open state.

  In the internal combustion engine of the present invention, when only one of the control valves is in the open state, the control means executes main air-fuel ratio learning control on the cylinder group side in the closed state, and enters this closed state. The main air-fuel ratio learning control on the cylinder group side in the open state is executed by eliminating the main learning value on the cylinder group side.

  In the internal combustion engine of the present invention, second air-fuel ratio detection means is provided downstream of the purification catalyst in each exhaust passage, and the control means is arranged for each cylinder group based on the detection result of the second air-fuel ratio detection means. When the sub air-fuel ratio learning control is executed at the same time and only one of the control valves is in the open state, the control means detects the second air-fuel ratio detection means on the cylinder group side in the open state. The sub-air fuel ratio learning control is executed based on the result.

  According to the internal combustion engine of the present invention, there are two cylinder groups in which a plurality of cylinders are divided into left and right banks, an exhaust passage is provided independently for each cylinder group, and a control valve is provided in each exhaust passage. And a purification catalyst, each control valve in each exhaust passage and the upstream side from each purification catalyst are connected by a communication passage, and an air-fuel ratio detection means is provided upstream from each purification catalyst in each exhaust passage. Control means is provided for executing main air-fuel ratio learning control for each cylinder group based on the detection result of the detection means, and for executing main air-fuel ratio learning control according to the open / close state of the control valve.

  Accordingly, the air-fuel ratio detection means detects the air-fuel ratio of the exhaust gas flowing upstream from the respective purification catalysts in each exhaust passage, and the control means performs main operation for each cylinder group based on the air-fuel ratio detected by this air-fuel ratio detection means. In addition to executing air-fuel ratio learning control, the main air-fuel ratio learning control is executed according to the open / close state of each control valve even if the exhaust path is changed by controlling the open / close of the control valve according to the operating state. Therefore, it is possible to perform highly accurate air-fuel ratio control regardless of the operating state.

  Embodiments of an internal combustion engine according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this Example.

  FIG. 1 is a schematic plan view of a V-type 6-cylinder engine representing an internal combustion engine according to Embodiment 1 of the present invention, FIG. 2 is a schematic cross-sectional view of the V-type 6-cylinder engine of Embodiment 1, and FIG. FIG. 4 is a flowchart showing the main air-fuel ratio learning control in the V-type 6-cylinder engine according to the first embodiment, and FIGS. 5 and 6 are diagrams showing the first embodiment. 7 is a flowchart showing a modification of the main air-fuel ratio learning control in the V-type six-cylinder engine, FIG. 7 is a flowchart showing sub-air-fuel ratio learning control in the V-type six-cylinder engine of the first embodiment, and FIG. 7 is a flowchart showing a modification of sub air-fuel ratio learning control in a V-type 6-cylinder engine.

  In the first embodiment, a V-type 6-cylinder engine is applied as the internal combustion engine. In this V-type six-cylinder engine, as shown in FIGS. 1 and 2, the cylinder block 11 has left and right banks 12 and 13 inclined at a predetermined angle at the upper portion, and a plurality of cylinders are provided in each bank 12 and 13. Are provided to form two cylinder groups. Each of the banks 12 and 13 is formed with three cylinder bores 14 and 15, and pistons 16 and 17 are fitted to the cylinder bores 14 and 15 so as to be vertically movable. A crankshaft (not shown) is rotatably supported at the lower part of the cylinder block 11, and the pistons 16 and 17 are connected to the crankshaft via connecting rods 18 and 19, respectively.

  On the other hand, cylinder heads 20 and 21 are fastened to the upper portions of the banks 12 and 13 of the cylinder block 11, and the combustion chambers 22 and 23 are constituted by the cylinder block 11, the pistons 16 and 17, and the cylinder heads 20 and 21. ing. The intake ports 24 and 25 and the exhaust ports 26 and 27 are formed on the upper portions of the combustion chambers 22 and 23, that is, the lower surfaces of the cylinder heads 20 and 21 so as to face each other. 27, the lower end portions of the intake valves 28 and 29 and the exhaust valves 30 and 31 are located. The intake valves 28 and 29 and the exhaust valves 30 and 31 are supported by the cylinder heads 20 and 21 so as to be movable in the axial direction, and are attached in a direction to close the intake ports 24 and 25 and the exhaust ports 26 and 27. It is supported. Further, intake camshafts 32 and 33 and exhaust camshafts 34 and 35 are rotatably supported on the cylinder heads 20 and 21, and the intake cams 36 and 37 and the exhaust cams 38 and 39 are interposed via a roller rocker arm (not shown). Are in contact with the upper ends of the intake valves 28 and 29 and the exhaust valves 30 and 31.

  Accordingly, when the intake camshafts 32 and 33 and the exhaust camshafts 34 and 35 rotate in synchronization with the engine, the intake cams 36 and 37 and the exhaust cams 38 and 39 operate the roller rocker arm, and the intake valves 28 and 29 and the exhaust valve 30 and 31 move up and down at a predetermined timing to open and close intake ports 24 and 25 and exhaust ports 26 and 27, intake ports 24 and 25 and combustion chambers 22 and 23, combustion chambers 22 and 23, and exhaust port 26. , 27 can communicate with each other.

  In addition, the valve mechanism of this engine is a variable intake valve timing mechanism (VVT) 40 that controls the intake valves 28 and 29 and the exhaust valves 30 and 31 at an optimal opening / closing timing according to the operating state. 41 and an exhaust variable valve mechanism 42, 43. The intake variable valve operating mechanisms 40 and 41 and the exhaust variable valve operating mechanisms 42 and 43 are configured, for example, by providing VVT controllers at the shaft end portions of the intake camshafts 32 and 33 and the exhaust camshafts 34 and 35. The opening / closing timing of the intake valves 28, 29 and the exhaust valves 30, 31 is advanced or retarded by changing the phase of each camshaft 32, 33, 34, 35 with respect to the cam sprocket by a pump (or electric motor). Is something that can be done. In this case, each variable valve mechanism 40, 41, 42, 43 advances or retards the opening / closing timing with the operating angle (opening period) of intake valves 28, 29 and exhaust valves 30, 31 being constant. The intake camshafts 32, 33 and the exhaust camshafts 34, 35 are provided with cam position sensors 44, 45, 46, 47 for detecting their rotational phases.

  A surge tank 50 is connected to the intake ports 24 and 25 of the cylinder heads 20 and 21 via intake manifolds 48 and 49. On the other hand, an air cleaner 52 is attached to an air intake port of an intake pipe (intake passage) 51, and an electronic throttle device 54 having a throttle valve 53 is provided in the intake pipe 51 and is located downstream of the air cleaner 52. It has been. The downstream end of the intake pipe 51 is connected to the surge tank 50.

  The exhaust ports 26 and 27 communicate with collecting passages 55 and 56 in which exhaust gases discharged from the combustion chambers 22 and 23 gather, and exhaust pipe connecting portions 55a and 56a are connected to the collecting passages 55 and 56, respectively. The first and second exhaust pipes (exhaust passages) 57 and 58 are connected to each other. In this case, the exhaust ports 26 and 27, the collecting passages 55 and 56, and the exhaust pipe connecting portions 55a and 56a are integrally formed in the cylinder heads 20 and 21 of the left and right banks 12 and 13, respectively.

  A first front three-way catalyst (purification catalyst) 59 is attached to the first exhaust pipe 57, while a second front three-way catalyst (purification catalyst) 60 is attached to the second exhaust pipe 58. The downstream end portions of the first and second exhaust pipes 57 and 58 are joined and connected to the exhaust collecting pipe 61, and the NOx occlusion reduction type catalyst 62 is attached to the exhaust collecting pipe 61. Each of the preceding three-way catalysts 59 and 60 simultaneously purifies HC, CO, and NOx contained in the exhaust gas by an oxidation-reduction reaction when the exhaust air-fuel ratio is stoichiometric. The NOx occlusion reduction type catalyst 62 can simultaneously purify HC, CO, NOx contained in the exhaust gas by an oxidation-reduction reaction when the exhaust air-fuel ratio is stoichiometric, and the exhaust gas when the exhaust air-fuel ratio is lean NOx contained in the exhaust gas is temporarily stored, and when it is in the rich combustion region or stoichiometric combustion region where the oxygen concentration in the exhaust gas is reduced, the stored NOx is released, and NOx is reduced by the fuel as the added reducing agent. Is.

  Further, the upstream side of the first exhaust pipe 57 and the second exhaust pipe 58 is connected by a communication pipe (communication path) 63 on the upstream side in the flow direction of the exhaust gas from the position where the front three-way catalysts 59 and 60 are mounted. It is communicated. A first control valve 64 and a second control valve 65 are mounted on the first exhaust pipe 57 and the second exhaust pipe 58 on the downstream side of the upstream three-way catalyst 59, 60 in the flow direction of the exhaust gas. Yes. The first and second control valves 64 and 65 are flow control valves, and the flow rate of the exhaust gas flowing through the exhaust pipes 57 and 58 can be adjusted by adjusting the opening degree.

  A turbocharger 67 is provided on the first bank 12 side. The turbocharger 67 is configured such that a compressor 68 provided on the intake pipe 51 side and a turbine 69 provided on the first exhaust pipe 57 side are integrally connected by a connecting shaft 70. In this case, the turbocharger 67 can drive the turbine 69 by the exhaust gas from the first exhaust pipe 57 on the first bank 12 side, and the end of the communication pipe 63 is connected to the turbine 69 in the first exhaust pipe 57. It is connected upstream from the mounting portion. In the turbocharger 67, downstream of the compressor 68 and upstream of the electronic throttle device 54 (throttle valve 53), intake air that has been compressed by the compressor 68 and has risen in temperature is supplied to the intake pipe 51. An intercooler 71 for cooling is provided.

  Therefore, the turbocharger 67 provided in the first bank 12 is turbine-driven by the exhaust gas discharged from the combustion chamber 22 of the first bank 12 through the exhaust port 26 and the collecting passage 55 to the first exhaust pipe 57. 69 is driven, and the compressor 68 connected by the connecting shaft 70 is driven, so that the air flowing through the intake pipe 51 can be compressed. Therefore, the air introduced from the air cleaner 52 into the intake pipe 51 becomes compressed intake air and is cooled by the intercooler 71 and then introduced into the surge tank 50, and the intake manifolds 48 and 49 and the intake ports of the banks 12 and 13. The air is sucked into the combustion chambers 22 and 23 through 24 and 25.

  The cylinder heads 20 and 21 are respectively equipped with injectors 72 and 73 for injecting fuel (gasoline) directly into the combustion chambers 22 and 23. Delivery pipes 74 and 75 are connected to the injectors 72 and 73, respectively. Each of the delivery pipes 74 and 75 can be supplied with fuel at a predetermined pressure from a high-pressure fuel pump 76. The cylinder heads 20 and 21 are provided with spark plugs 77 and 78 that are located above the combustion chambers 22 and 23 and ignite the air-fuel mixture.

  The vehicle is equipped with an electronic control unit (ECU) 81, which can control the fuel injection timing of the injectors 72, 73, the ignition timing of the spark plugs 77, 78, and the like. The fuel injection amount, the injection timing, the ignition timing, and the like are determined based on the engine operation state such as the air amount, the intake air temperature, the throttle opening, the accelerator opening, the engine speed, and the cooling water temperature. That is, an air flow sensor 82 and an intake air temperature sensor 83 are mounted on the upstream side of the intake pipe 51, and the measured intake air amount and intake air temperature are output to the ECU 81. The electronic throttle device 54 is provided with a throttle position sensor 84, and the accelerator pedal is provided with an accelerator position sensor 85, which outputs the current throttle opening and accelerator opening to the ECU 81. Further, a crank angle sensor 86 is provided on the crankshaft, and the detected crank angle is output to the ECU 81. The ECU 81 calculates the engine speed based on the crank angle. The cylinder block 11 is provided with a water temperature sensor 87 and outputs the detected engine cooling water temperature to the ECU 81.

In addition, A / F sensors (first air-fuel ratio detection means) 88, 89 are upstream of the upstream three-way catalysts 59, 60 in the exhaust pipes 57, 58 and upstream of the communication pipe 63. Is provided. The A / F sensors 88 and 89 are oxygen sensors having linear output characteristics with respect to the exhaust air / fuel ratio, and exhaust from the combustion chambers 22 and 23 to the exhaust pipes 57 and 58 through the exhaust ports 26 and 27. The exhaust air / fuel ratio of the exhaust gas thus detected is detected, and the detected exhaust air / fuel ratio is output to the ECU 81. Further, an O ₂ sensor (second air / fuel ratio detecting means) 90 is provided downstream of the upstream three-way catalysts 59 and 60 and upstream of the control valves 59 and 60 in the exhaust pipes 57 and 58. , 91 are provided. The O ₂ sensors 90 and 91 are oxygen sensors having output characteristics in which the output changes suddenly between the rich side and the lean side with respect to the exhaust air / fuel ratio, with the stoichiometric air / fuel ratio as a reference. The stoichiometric air-fuel ratio of the exhaust gas exhausted to the exhaust pipes 57 and 58 through the exhaust ports 26 and 27 is detected, and a stoichiometric detection signal is output to the ECU 81. The ECU 81 performs air-fuel ratio control, which will be described later, based on the exhaust air-fuel ratio and the stoichiometric detection signals detected by the A / F sensors 88 and 89 and the O ₂ sensors 90 and 91.

  The ECU 81 can control the intake variable valve mechanisms 40 and 41 and the exhaust variable valve mechanisms 42 and 43 based on the engine operating state. That is, when the temperature is low, the engine is started, the engine is idling, or when the load is light, the exhaust gas 30 is exhausted from the intake port 24, 31 by eliminating the overlap between the exhaust valve 30, 31 opening timing and the intake valve 28, 29 opening timing. 25 or the amount of air blown back to the combustion chambers 22 and 23 is reduced, and combustion stability and fuel efficiency can be improved. Further, at the time of medium load, by increasing the overlap, the internal EGR rate is increased to improve the exhaust gas purification efficiency, and the pumping loss is reduced to improve the fuel consumption. Further, at the time of high-load low-medium rotation, the closing timing of the intake valves 28 and 29 is advanced to reduce the amount of intake air that blows back to the intake ports 24 and 25, thereby improving volumetric efficiency. At the time of high load and high rotation, the closing timing of the intake valves 28 and 29 is retarded according to the rotational speed, thereby improving the volume efficiency as the timing according to the inertial force of the intake air.

  By the way, in the V-type 6-cylinder engine of this embodiment, as described above, the first exhaust pipe 57 and the second exhaust pipe 58 are connected to the combustion chambers 22 and 23 of the cylinder heads 20 and 21, respectively. First and second front three-way catalysts 59 and 60 and first and second control valves 64 and 65 are attached to the pipe 57 and the second exhaust pipe 58, and the upstream part of each exhaust pipe 57 and 58 is connected to the communication pipe 63. It is communicated by. Therefore, the ECU 81 can change the exhaust gas discharge path by controlling the opening and closing of the control valves 64 and 65 in accordance with the engine operating state.

  For example, when the engine is cold-started, the first control valve 64 is closed, while the second control valve 65 is opened, and the first exhaust pipe 57 is connected from the cylinder group of the first bank 12 through the collecting passage 55. After exhaust gas discharged from the cylinder group of the first and second banks 12 and 13 is merged in the second exhaust pipe 58 by bypassing the exhaust gas discharged to the second exhaust pipe 58 through the communication pipe 63, The second front stage three-way catalyst 60 is warmed up by flowing a large amount of exhaust gas into the second front stage three-way catalyst 60.

  Thereafter, when the warm-up of the second pre-stage three-way catalyst 60 is completed and activated, the first control valve 64 is opened, while the second control valve 65 is closed, and the cylinders in the second bank 13 are closed. By exhausting the exhaust gas discharged from the group to the second exhaust pipe 58 through the collecting passage 56 to the first exhaust pipe 57 through the communication pipe 63, the exhaust from the cylinder groups of the first and second banks 12 and 13 is bypassed. After the gases are merged in the first exhaust pipe 57, a large amount of exhaust gas flows into the first front-stage three-way catalyst 59, so that the first front-stage three-way catalyst 59 is warmed up.

  Further, when the engine is idling, the first control valve 64 and the second control valve 65 are opened, and the exhaust gas discharged from the cylinder group of the first bank 12 to the collecting passage 55 is discharged to the first exhaust pipe 57. On the other hand, exhaust gas discharged from the cylinder group of the second bank 13 to the collecting passage 56 is discharged to the second exhaust pipe 58, so that the exhaust gas is transferred to the first front-stage three-way catalyst 59 and the second front-stage three-way catalyst 60. By making it flow, each front stage three-way catalyst 59, 60 is kept warm.

  Further, in a low / medium load state of the engine, the first control valve 64 is closed, while the second control valve 65 is opened, and the first exhaust from the cylinder group of the first bank 12 through the collecting passage 55. By exhausting the exhaust gas discharged to the pipe 57 to the second exhaust pipe 58 through the communication pipe 63, the exhaust gases from the cylinder groups of the first and second banks 12 and 13 are merged in the first exhaust pipe 57. I try to discharge it later. On the other hand, when the engine is in a high load state, the first control valve 64 is opened, while the second control valve 65 is closed, and the second exhaust pipe passes from the cylinder group of the second bank 13 through the collecting passage 56. After exhaust gas discharged to 58 is bypassed to the first exhaust pipe 57 through the communication pipe 63, exhaust gas from the cylinder groups of the first and second banks 12 and 13 is merged in the first exhaust pipe 57. By flowing a large amount of exhaust gas into the turbocharger 67, the turbocharger 67 is operated with high efficiency to enable high supercharging, and the output is improved.

  Further, the ECU 81 makes the exhaust gas from the cylinder group of the first bank 12 a lean atmosphere, makes the exhaust gas from the cylinder group of the second bank 13 a rich atmosphere, and the first control valve 64 and the second control valve 65. Is opened, the lean atmosphere exhaust gas discharged from the cylinder group of the first bank 12 is caused to flow to the first exhaust pipe 57, and the rich atmosphere exhaust gas discharged from the cylinder group of the second bank 13 is the first exhaust. The NOx occlusion reduction type catalyst 62 is warmed up using the oxidation exothermic reaction in the NOx occlusion reduction type catalyst 62 or accumulated in the NOx occlusion reduction type catalyst 62. The sulfur component is released and regenerated.

  Here, the operation of the V-type 6-cylinder engine of this embodiment will be briefly described.

  In the V-type six-cylinder engine of this embodiment, the air introduced into the intake pipe 51 through the air cleaner 52 is compressed by the compressor 68 of the turbocharger 67 provided on the first bank 12 side, After being metered by the throttle valve 53, it flows into the surge tank 50, reaches the intake ports 24, 25 via the intake manifolds 48, 49, and opens the intake ports 24, 25 when the intake valves 28, 29 are opened. Air is drawn into the combustion chambers 22,23. During this intake stroke or during the compression stroke in which the pistons 16 and 17 rise and compress the intake air, the injectors 74 and 75 inject a predetermined amount of fuel into the combustion chambers 22 and 23. Then, high-pressure air and mist-like fuel are mixed in the combustion chambers 22 and 23, and the ignition plugs 79 and 80 ignite and explode in the air-fuel mixture, whereby the pistons 16 and 17 are pushed down. While the driving force is output, when the exhaust valves 30 and 31 are opened, the exhaust gas in the combustion chambers 22 and 23 is collected from the exhaust ports 26 and 27 through the collecting passages 55 and 56 and then the first exhaust pipe 57 and the second exhaust pipe. It is discharged to the tube 58. The exhaust gas discharged to the first exhaust pipe 57 drives the turbine 69 of the turbocharger 67, and the compressor 68 connected to the turbine 69 by the connecting shaft 70 drives to be introduced into the intake pipe 51. Compress the air.

  In the first bank 12, the exhaust gas discharged from the combustion chamber 22 through the exhaust port 26 and the collecting passage 55 to the first exhaust pipe 57 warms up and activates the first three-way catalyst 59. The harmful substances contained are purified and flow into the exhaust collecting pipe 61. On the other hand, in the second bank 13, the exhaust gas discharged from the combustion chamber 23 through the exhaust port 27 and the collecting passage 56 to the second exhaust pipe 58 warms up and activates the second front three-way catalyst 60. The harmful substances contained are purified and flow into the exhaust collecting pipe 61. The exhaust gas flowing into the exhaust collecting pipe 61 warms and activates the NOx occlusion reduction type catalyst 62, and is released to the atmosphere after the remaining harmful substances are appropriately purified.

  Here, the opening / closing control of the control valves 64 and 65 in the V-type 6-cylinder engine of this embodiment will be described based on the flowchart of FIG.

  In the V-type 6-cylinder engine of the present embodiment, as shown in FIG. 3, in step S11, it is determined whether or not the ignition key switch (IG) is turned on. Determine if is a cold start. Specifically, the ECU 81 determines that the engine is cold-started when the engine coolant temperature detected by the water temperature sensor 87 is lower than a predetermined temperature set in advance. If it is determined that the engine is cold-started, the ECU 81 closes the first control valve 64 and opens the second control valve 65 in step S13.

  Then, the exhaust gas discharged from the cylinder group of the first bank 12 to the first exhaust pipe 57 is bypassed to the second exhaust pipe 58 through the communication pipe 63, and the exhaust gas from the cylinder group of the first and second banks 12 and 13 is bypassed. After the gases are merged in the second exhaust pipe 58, a large amount of exhaust gas is caused to flow into the second pre-stage three-way catalyst 60, thereby warming up the second pre-stage three-way catalyst 60. In step S14, it is determined whether the second pre-stage three-way catalyst 60 is activated by warming up. Specifically, a temperature sensor (not shown) is provided in the second upstream three-way catalyst 60 or the second exhaust pipe 58 immediately upstream of the second upstream three-way catalyst 60, and the temperature of the catalyst detected by the temperature sensor is determined. It is determined whether or not the catalyst activation temperature range is set in advance. Here, the catalyst temperature of the second front three-way catalyst 60 is raised to the catalyst activation temperature region.

  Then, if it is determined in step S14 that the catalyst temperature of the second front-stage three-way catalyst 60 has been raised to the catalyst activation temperature range and activated, the process proceeds to step S15, where the ECU 81 The first control valve 64 is opened and the second control valve 65 is closed. Then, the exhaust gas discharged from the cylinder group of the second bank 13 to the second exhaust pipe 58 is bypassed to the first exhaust pipe 57 through the communication pipe 63, and the exhaust gas from the cylinder group of the first and second banks 12 and 13 is exhausted. After the gases are merged in the first exhaust pipe 57, a large amount of exhaust gas is caused to flow into the first front-stage three-way catalyst 59, thereby warming up the first front-stage three-way catalyst 59. In step S16, it is determined whether or not the first front three-way catalyst 59 has been activated by warming up. Specifically, in the same manner as described above, a temperature sensor (not shown) is provided in the first upstream three-way catalyst 59 or the first exhaust pipe 57 immediately upstream of the first front three-way catalyst 59. It is determined whether or not the detected catalyst temperature is in a preset catalyst activation temperature region. Here, the catalyst temperature of the first front-stage three-way catalyst 59 is raised to the catalyst activation temperature region.

  When the warm-up of each of the preceding three-way catalysts 59 and 60 is completed and activated as described above, it is determined in step S12 that the engine is not cold-started, and in step S17, the engine is in idle operation. Determine whether or not. Specifically, the ECU 81 determines that the engine is idling when the engine speed calculated based on the crank angle detected by the crank angle sensor 86 is lower than a predetermined speed set in advance. If it is determined that the engine is idling, the ECU 81 opens the first control valve 64 and opens the second control valve 65 in step S18.

  Then, the exhaust gas discharged from the combustion chamber 22 of the first bank 12 flows to the first exhaust pipe 57, while the exhaust gas discharged from the combustion chamber 23 of the second bank 13 flows to the second exhaust pipe 58. Thus, the exhaust gas flows into the first front-stage three-way catalyst 59 and the second front-stage three-way catalyst 60, and the activated states of the front-stage three-way catalysts 59, 60 are maintained.

  On the other hand, if it is determined in step S17 that the engine is not in idle operation, in step S19, the ECU 81 causes the sulfur component stored in the NOx storage reduction catalyst 62 to be a first predetermined value of the sulfur adhesion amount set in advance. Judge whether or not. In this case, the sulfur component stored in the NOx storage reduction catalyst 62 may be estimated based on the travel distance or time of the vehicle after the sulfur poisoning regeneration control is executed. Here, if it is determined that the sulfur component stored in the NOx storage reduction type catalyst 62 exceeds the first predetermined value of the amount of sulfur adhesion, in step S20, the engine operating state such as the engine load and the engine speed is determined. Judge whether it is within the bank controllable range. In this case, for example, determination is made using a map of the engine load with respect to the engine speed, and it is determined that the current engine load and the engine speed are within a bank controllable range (for example, low / medium speed / low / medium load region). If so, the process proceeds to step S21.

  In this step S21, it is determined whether or not the temperature of the NOx occlusion reduction type catalyst 62 is within a predetermined temperature range set in advance. In this case, a temperature sensor (not shown) is provided in the NOx occlusion reduction type catalyst 62 or the exhaust collecting pipe 61 immediately upstream of the NOx occlusion reduction type catalyst 62, and the exhaust gas temperature detected by this temperature sensor is set to a predetermined value. Determine if it is within the temperature range. When the temperature of the NOx occlusion reduction type catalyst 62 is lower than the low temperature (for example, 300 ° C.), the unburned HC cannot be purified by the rich exhaust gas, so the bank control is not executed. Further, when the temperature of the NOx storage reduction catalyst 62 is higher than a high temperature (for example, 700 ° C.), the sulfur component is easily desorbed, but the NOx storage agent (noble metal) supported on the NOx storage reduction catalyst 62 is hot. The bank control is not executed because it deteriorates.

  When it is determined in step S21 that the temperature of the NOx storage reduction catalyst 62 is within the predetermined temperature range, in step S22, the ECU 81 opens the first control valve 64, and the second control valve. 65 is opened. Subsequently, in step S23, in order to execute the bank control, the air-fuel ratio in each cylinder group of each bank 12, 13 is changed, the exhaust gas from the cylinder group in the first bank 12 is set to a lean atmosphere, and the second The exhaust gas from the cylinder group of the bank 13 is set to a rich atmosphere. Then, the exhaust gas in the lean atmosphere and the exhaust gas in the rich atmosphere flow into the exhaust pipes 57 and 58 and merge with each other in the NOx occlusion reduction type catalyst 62 through the exhaust collecting pipe 61, and the oxidation exothermic reaction at that time Is used to heat the NOx occlusion reduction catalyst 62 to regenerate sulfur poisoning.

  In step S24, it is determined whether or not the sulfur component stored in the NOx storage reduction type catalyst 62 is equal to or lower than a second predetermined value (first predetermined value> second predetermined value) of a predetermined sulfur adhesion amount. To do. Here, when the NOx occlusion reduction catalyst 62 is heated to perform sulfur poisoning regeneration over a predetermined period, and it is determined that the sulfur component occluded in the NOx occlusion reduction catalyst 62 has become equal to or less than the second predetermined value, step In S25, in order to cancel the bank control, the air-fuel ratio in each cylinder group of each bank 12, 13 is changed, and the exhaust gas from the cylinder group of each bank 12, 13 is made a stoichiometric atmosphere.

  On the other hand, in step S19, it is determined that the sulfur component stored in the NOx storage reduction catalyst 62 does not exceed the first predetermined value, or in step S20, the engine load and the engine speed can be bank controlled. If it is determined that the temperature of the NOx storage reduction catalyst 62 is not within the predetermined temperature range in step S21, the ECU 81 determines in step S26 whether the engine is in a high load operation state. Determine if. If it is determined that the engine is not in a high load operation state, the ECU 81 closes the first control valve 64 and opens the second control valve 65 in step S27.

  On the other hand, if it is determined in step S26 that the engine is in the high load operation state, the ECU 81 sets the first control valve 64 to the open state and sets the second control valve 65 to the closed state in step S28. To do. Then, the exhaust gas discharged from the cylinder group of the second bank 13 to the second exhaust pipe 58 is bypassed to the first exhaust pipe 57 through the communication pipe 63, so that the combustion chambers of the first and second banks 12, 13 are bypassed. After exhaust gases from 22 and 23 are merged in the first exhaust pipe 57, a large amount of exhaust gas is introduced into the turbocharger 67, whereby the supercharging pressure by the turbocharger 67 is increased and output is increased. Will improve.

In the V-type six-cylinder engine of this embodiment, as described above, the ECU 81 performs air-fuel ratio control based on the detection results of the A / F sensors 88 and 89 and the O ₂ sensors 90 and 91. That is, the ECU 81 compares the exhaust air / fuel ratio detected by the A / F sensors 88 and 89 with the target air / fuel ratio set in accordance with the engine operating state, calculates the fuel injection correction value, and corrects the fuel injection amount. Main feedback control is being executed. The ECU 81 uses the main learning value based on the detection signals (exhaust air / fuel ratio) detected by the A / F sensors 88 and 89, the feedback correction value (fuel injection correction value) used in the main feedback control, and its control center. The main air-fuel ratio learning control is executed to statistically learn based on the difference between the two and reflect this in the main feedback control, thereby compensating for steady deviations of various devices. Further, the ECU 81 executes the sub A / F learning control for correcting the detection signals of the A / F sensors 88 and 89 based on the stoichiometric detection signals detected by the O ₂ sensors 90 and 91, so that the main A / F learning is performed. The detection signals of the A / F sensors 88 and 89 used in the control are corrected.

  The V-type 6-cylinder engine of the present embodiment has a cylinder group in which a plurality of cylinders are divided into a first bank 12 and a second bank 13 on the left and right sides. The first exhaust pipe 57 and the second exhaust pipe 58 are coupled to each other, and the first front-stage three-way catalyst 59 and the second front-stage three-way catalyst 60, the first control valve 64, and the second control valve 65 are connected to the exhaust pipes 57 and 58, respectively. The upstream sides of the upstream three-way catalysts 59 and 60 and the control valves 64 and 65 in the exhaust pipes 57 and 58 are communicated by the communication pipe 63, and the ECU 81 controls the control valves 64 and 65 according to the engine operating state. The exhaust gas discharge route is changed by opening and closing.

  Therefore, the ECU 81 executes the main air-fuel ratio learning control for each cylinder group of the banks 12 and 13 based on the detection results of the A / F sensors 88 and 89, and according to the open / closed states of the control valves 64 and 65. The main air-fuel ratio learning control is executed. Although specifically described below, the first bank 12 is expressed as an L bank and the second bank 13 is expressed as an R bank.

  In the main air-fuel ratio learning control in the V-type 6-cylinder engine of the first embodiment, as shown in FIG. 4, it is determined in step S31 whether or not the first control valve 64 is in the closed state, and the first control valve 64 Is determined to be in the closed state, in step S32, the exhaust gas exhaust path is identified as the pattern A in which the second exhaust pipe 58 is opened by the second control valve 65. In step S33, it is determined in which region of the regions 1 to 4 the engine operating state is. In this case, for example, the area representing the engine load (intake air amount, fuel injection amount, throttle opening, etc.) with respect to the engine speed is divided into four regions, and based on the current engine speed and engine load, It suffices to determine in which region the current engine operating state is.

  When the engine operating state region is set in step S33, the main learning value is determined for each cylinder group in each bank 12 and 13 based on the detection results of the A / F sensors 88 and 89 in step S34. Is calculated. That is, the main learning value AL (n) in the cylinder group of the first bank 12 is calculated based on the detection result of the first A / F sensor 88, and the second bank is calculated based on the detection result of the second A / F sensor 89. The main learning value A-R (n) in the 13 cylinder groups is calculated. In step S35, the calculated main learned value AL (n) and main learned value AR (n) are used as the main learned values L (n) and R (n) for the cylinder groups of the banks 12 and 13, respectively. ).

  On the other hand, if it is determined in step S31 that the first control valve 64 is not in the closed state, it is determined in step S36 whether or not the second control valve 65 is in the closed state, and the second control valve 65 is closed. If determined to be in the state, in step S37, the exhaust gas exhaust path is identified as the pattern B in which the first exhaust pipe 57 is opened by the first control valve 64. When it is determined in step S38 which of the regions 1 to 4 is in the operating state of the engine, in step S39, each bank 12 is determined based on the detection results of the A / F sensors 88 and 89. The main learning value is calculated for each of the 13 cylinder groups. That is, the main learning value BL (n) in the cylinder group of the first bank 12 is calculated based on the detection result of the first A / F sensor 88, and the second bank is calculated based on the detection result of the second A / F sensor 89. The main learning value BR (n) in the 13 cylinder groups is calculated. In step S40, the calculated main learning value B-L (n) and main learning value B-R (n) are used as main learning values L (n) and R (n) for the cylinder groups of the banks 12 and 13, respectively. ).

  If it is determined in step S36 that the second control valve 65 is not closed, the exhaust gas exhaust path is opened in step S41, and both exhaust pipes 57 and 58 are opened by the control valves 64 and 65, respectively. Specified pattern C. When it is determined in step S42 which of the regions 1 to 4 the engine operating state is, in step S43, each bank 12 is determined based on the detection results of the A / F sensors 88 and 89. The main learning value is calculated for each of the 13 cylinder groups. That is, the main learning value CL (n) in the cylinder group of the first bank 12 is calculated based on the detection result of the first A / F sensor 88, and the second bank is calculated based on the detection result of the second A / F sensor 89. The main learning value C-R (n) in the 13 cylinder groups is calculated. In step S44, the calculated main learning value CL (n) and main learning value CR (n) are used as the main learning values L (n) and R (n) for the cylinder groups of the banks 12 and 13, respectively. ).

  Accordingly, canceling the exhaust pressure difference (intake air amount difference) in patterns A, B, and C having different exhaust gas exhaust paths enables highly accurate main air-fuel ratio learning control.

  Note that the control method of the main air-fuel ratio learning control in the V-type six-cylinder engine of the present embodiment is not limited to this method. For example, when only one of the control valves 64 and 65 is in the open state, the ECU 81 sets the bank 12 and the main learning value calculated when both of the control valves 64 and 65 are in the open state. The main learning value is calculated in consideration of the back pressure difference of the cylinder group at 13.

  In the main air-fuel ratio learning control in the V-type 6-cylinder engine according to the modification of the first embodiment, as shown in FIG. 5, it is determined in step S51 that the first control valve 64 is not closed, and in step S56. If it is determined that the second control valve 65 is not closed, in step S61, the exhaust gas exhaust path is opened in step S61, and both the exhaust pipes 57, 58 are opened by the control valves 64, 65. Pattern C is specified. When it is determined in step S62 which of the regions 1 to 4 is in the operating state of the engine, in step S63, each bank 12 is determined based on the detection results of the A / F sensors 88 and 89. The main learning value is calculated for each of the 13 cylinder groups. That is, the main learning value CL (n) in the cylinder group of the first bank 12 is calculated based on the detection result of the first A / F sensor 88, and the second bank is calculated based on the detection result of the second A / F sensor 89. The main learning value C-R (n) in the 13 cylinder groups is calculated. In step S64, the calculated main learning value CL (n) and main learning value CR (n) are used as the main learning values L (n) and R (n) for the cylinder groups of the banks 12 and 13, respectively. ).

  When the main learning values CL (n) and CR (n) in the cylinder groups of each bank 12 are calculated and it is determined in step S51 that the first control valve 64 is in the closed state, in step S52. The exhaust gas exhaust path is specified as the pattern A in which the second exhaust pipe 58 is opened by the second control valve 65. When it is determined in step S53 which of the regions 1 to 4 is in the operating state of the engine, the main learning values CL (n) and CR (n) are determined in step S54. The main learning value is calculated in consideration of the back pressure difference between the cylinder groups in the banks 12 and 13. That is, the main learning values AL (n) and AR (n) in the cylinder groups of the banks 12 and 13 are the ratio of the back pressure to the main learning values CL (n) and CR (n) or Since the ratio depends on the air-fuel ratio α, the calculated main learning value C−L (n) × (2−α) and main learning value C−R (n) × α are calculated in step S55. The main learning values L (n) and R (n) in the cylinder groups of the banks 12 and 13 are reflected.

  On the other hand, if it is determined in step S51 that the first control valve 64 is not in the closed state, and it is determined in step S56 that the second control valve 65 is in the closed state, the exhaust gas is exhausted in step S57. The path is specified as the pattern B in which the first exhaust pipe 57 is opened by the first control valve 64. When it is determined in step S58 which of the regions 1 to 4 is in the engine operating state, in step S59, the main learning values CL (n) and CR (n) are set. The main learning value is calculated in consideration of the back pressure difference between the cylinder groups in the banks 12 and 13. That is, the main learning values BL (n) and BR (n) in the cylinder groups of the banks 12 and 13 are the ratio of the back pressure to the main learning values CL (n) and CR (n) or Since the ratio depends on the air-fuel ratio β, the calculated main learning value C−L (n) × (2−β) and main learning value C−R (n) × β are calculated in step S60. The main learning values L (n) and R (n) in the cylinder groups of the banks 12 and 13 are reflected.

  Therefore, in the patterns A, B, and C having different exhaust gas exhaust paths, the learning time can be shortened by obtaining the main learning values of the patterns A and B based on the main learning value of the pattern C. Since the back pressure difference between the cylinder groups in each of the banks 12 and 13 is taken into account, highly accurate main air-fuel ratio learning control can be performed.

  Further, the ECU 81 calculates each cylinder in each bank 12 and 13 calculated when only one of the control valves 64 and 65 is open when both of the control valves 64 and 65 are open. The main learning value is calculated by averaging the main learning values of the group.

  In the main air-fuel ratio learning control in the V-type 6-cylinder engine of the modified example in the first embodiment, if it is determined in step S71 that the first control valve 64 is in the closed state as shown in FIG. 6, the process proceeds to step S72. Thus, the exhaust gas exhaust path is specified as the pattern A in which the second exhaust pipe 58 is opened by the second control valve 65. When it is determined in step S73 which of the regions 1 to 4 the engine operating state is in, in step S74, each bank 12 is determined based on the detection results of the A / F sensors 88 and 89. The main learning value is calculated for each of the 13 cylinder groups. That is, the main learning value AL (n) in the cylinder group of the first bank 12 is calculated based on the detection result of the first A / F sensor 88, and the second bank is calculated based on the detection result of the second A / F sensor 89. The main learning value A-R (n) in the 13 cylinder groups is calculated. In step S75, the calculated main learning value A-L (n) and main learning value A-R (n) are used as main learning values L (n) and R (n) for the cylinder groups of the banks 12 and 13, respectively. ).

  On the other hand, if it is determined in step S71 that the first control valve 64 is not in the closed state, and it is determined in step S76 that the second control valve 65 is in the closed state, the exhaust gas is exhausted in step S77. The path is specified as the pattern B in which the first exhaust pipe 57 is opened by the first control valve 64. When it is determined in step S78 which of the regions 1 to 4 is in the operating state of the engine, in step S79, each bank 12 is determined based on the detection results of the A / F sensors 88 and 89. The main learning value is calculated for each of the 13 cylinder groups. That is, the main learning value BL (n) in the cylinder group of the first bank 12 is calculated based on the detection result of the first A / F sensor 88, and the second bank is calculated based on the detection result of the second A / F sensor 89. The main learning value BR (n) in the 13 cylinder groups is calculated. In step S80, the calculated main learning value B-L (n) and main learning value B-R (n) are used as main learning values L (n) and R (n) for the cylinder groups of the banks 12 and 13, respectively. ).

  If it is determined in step S76 that the second control valve 65 is not closed, the exhaust gas exhaust path is opened in step S81, and both exhaust pipes 57 and 58 are opened by the control valves 64 and 65, respectively. Specified pattern C. Then, in step S82, when it is determined which of the regions 1 to 4 is in the operating state of the engine, in step S83, the main learning value A-L (n) of pattern A, main learning value A The main learning value is calculated by averaging -R (n), the main learning value B-L (n) of pattern B, and the main learning value B-R (n). That is, the main learning value A-L (n) and the main learning value B-L (n) are added and divided by 2 to calculate the main learning value C-L (n), and the main learning value A-R ( n) and the main learning value B-R (n) are added and divided by 2 to calculate the main learning value C-R (n). In step S84, the calculated main learning value CL (n) and main learning value CR (n) are used as main learning values L (n) and R (n) for the cylinder groups of the banks 12 and 13, respectively. ).

  Therefore, the learning time can be shortened by obtaining the main learning value of the pattern C based on the main learning value of the patterns A and B in the patterns A, B, and C having different exhaust gas exhaust paths. , B can be simplified, control of the air-fuel ratio at the start of pattern C learning can be suppressed, and high-accuracy main air-fuel ratio learning control can be performed.

In the V-type 6-cylinder engine of the present embodiment, the A / F sensors 88 and 89 are provided on the upstream side of the connection portions of the exhaust pipes 57 and 58 with the communication pipe 63, and O ₂ sensors 90 and 91 are provided downstream of the first front-stage three-way catalysts 59 and 60 and upstream of the control valves 64 and 65. The ECU 81 is based on the detection results of the O ₂ sensors 90 and 91. The sub air / fuel ratio learning control is executed for each cylinder group of the banks 12 and 13 and the sub air / fuel ratio learning control is executed according to the open / closed state of the control valves 64 and 65.

In the sub air-fuel ratio learning control in the V-type six-cylinder engine of the first embodiment, as shown in FIG. 7, if it is determined in step S91 that the first control valve 64 is in the closed state, the exhaust is determined in step S92. The gas exhaust path is specified as the pattern A in which the second exhaust pipe 58 is opened by the second control valve 65. Then, in step S93, when it is determined which of the regions 1 to 4 is in the operating state of the engine, in step S94, based on the detection result of each O ₂ sensor 90, 91, each bank 12, A sub-learning value is calculated for each of the 13 cylinder groups. That is, in the 1O ₂ calculates a sub learning value Asub-L in the cylinder group of the first bank 12 based on the detection result of the sensor 90 cylinder group of the second bank 13 based on the detection result of the 2O ₂ sensor 91 A sub-learning value Assub-R is calculated. In step S95, the calculated sub-learning value Asub-L and sub-learning value Assub-R are reflected as the sub-learning values L and R in the cylinder groups of the banks 12 and 13, respectively.

On the other hand, if it is determined in step S91 that the first control valve 64 is not in the closed state, and it is determined in step S96 that the second control valve 65 is in the closed state, the exhaust gas is exhausted in step S97. The path is specified as the pattern B in which the first exhaust pipe 57 is opened by the first control valve 64. When it is determined in step S98 which of the regions 1 to 4 is in the engine operating state, in step S99, each bank 12, 12 is determined based on the detection results of the O ₂ sensors 90, 91. A sub-learning value is calculated for each of the 13 cylinder groups. That is, the sub-learning value Bsub-L in the cylinder group in the first bank 12 is calculated based on the detection result of the first O ₂ sensor 90, and in the cylinder group in the second bank 13 based on the detection result of the second O ₂ sensor 91. A sub-learning value Bsub-R is calculated. In step S100, the calculated sub-learning value Bsub-L and sub-learning value Bsub-R are reflected as the sub-learning values L and R in the cylinder groups of the banks 12 and 13, respectively.

If it is determined in step S96 that the second control valve 65 is not closed, the exhaust gas exhaust path is opened in step S101, and both exhaust pipes 57 and 58 are opened by the control valves 64 and 65, respectively. Specified pattern C. Then, in step S102, when it is determined which of the regions 1 to 4 is in the operating state of the engine, in step S103, based on the detection result of each O ₂ sensor 90, 91, each bank 12, A sub-learning value is calculated for each of the 13 cylinder groups. That is, in the 1O ₂ calculates a sub learning value Csub-L in the cylinder group of the first bank 12 based on the detection result of the sensor 90, the cylinder group of the second bank 13 based on the detection result of the 2O ₂ sensor 91 A sub-learning value Csub-R is calculated. In step S104, the calculated sub-learning value Csub-L and sub-learning value Csub-R are reflected as sub-learning values L and R in the cylinder groups of the banks 12 and 13, respectively.

  Therefore, in the patterns A, B, and C having different exhaust gas exhaust paths, the highly accurate sub air-fuel ratio learning control can be performed by canceling the exhaust pressure difference (intake air amount difference).

  Note that the control method of the sub air-fuel ratio learning control in the V-type six-cylinder engine of the present embodiment is not limited to this method. For example, when only one of the control valves 64 and 65 is in an open state, the ECU 81 sets each bank 12, 12 to the sub-learning value calculated when both of the control valves 64 and 65 are in an open state. The sub-learning value is calculated in consideration of the air-fuel ratio difference of the cylinder group at 13.

In the sub air-fuel ratio learning control in the V-type 6-cylinder engine of the modified example in the first embodiment, as shown in FIG. 8, it is determined in step S111 that the first control valve 64 is closed, and in step S116. If it is determined that the second control valve 65 is not closed, the exhaust gas exhaust path is a pattern C in which both the exhaust pipes 57 and 58 are opened by the control valves 64 and 65 in step S121. Is identified. Then, in step S122, when it is determined which of the regions 1 to 4 is in the operating state of the engine, in step S123, based on the detection result of each O ₂ sensor 90, 91, each bank 12, A sub-learning value is calculated for each of the 13 cylinder groups. That is, in the 1O ₂ calculates a sub learning value Csub-L in the cylinder group of the first bank 12 based on the detection result of the sensor 90, the cylinder group of the second bank 13 based on the detection result of the 2O ₂ sensor 91 A sub-learning value Csub-R is calculated. In step S124, the calculated sub-learning value Csub-L and sub-learning value Csub-R are reflected as the sub-learning values L and R in the cylinder groups of the banks 12 and 13, respectively.

  The sub-learning values Csub-L and Csub-R in the cylinder groups of each bank 12 are calculated, and if it is determined in step S111 that the first control valve 64 is in the closed state, the exhaust gas exhaust is determined in step S112. The path is specified as the pattern A in which the second exhaust pipe 58 is opened by the second control valve 65. When it is determined in step S113 which of the regions 1 to 4 is in the engine operating state, the sub-learned values Csub-L and Csub-R are stored in the banks 12 and 13 in step S114. The sub-learning value is calculated in consideration of the air-fuel ratio difference of the cylinder group. That is, since the sub-learning values Asub-L and Assub-R in the cylinder groups of the banks 12 and 13 correspond to the air-fuel ratio difference γ with respect to the sub-learning values Csub-L and Csub-R, in step S115. The calculated sub-learning value Csub−L + γ and the sub-learning value Csub−R + γ are reflected as the sub-learning values L and R in the cylinder groups of the banks 12 and 13.

  On the other hand, if it is determined in step S111 that the first control valve 64 is not in the closed state, and it is determined in step S116 that the second control valve 65 is in the closed state, the exhaust gas is exhausted in step S117. The path is specified as the pattern B in which the first exhaust pipe 57 is opened by the first control valve 64. When it is determined in step S118 which of the regions 1 to 4 the engine operating state is in, in step S119, the sub-learned values Csub-L and Csub-R are stored in the banks 12 and 13, respectively. The sub-learning value is calculated in consideration of the air-fuel ratio difference of the cylinder group. That is, since the sub-learned values Bsub-L and Bsub-R in the cylinder groups of the banks 12 and 13 correspond to the air-fuel ratio difference δ with respect to the sub-learned values Csub-L and Csub-R, in step S120. The calculated sub-learning values Csub−L + δ and sub-learning values Csub−R + δ are reflected as the sub-learning values L and R in the cylinder groups of the banks 12 and 13.

If it is determined in step S116 that the second control valve 65 is not closed, in step S121, the exhaust gas exhaust path is opened, and the control valves 64 and 65 open both the exhaust pipes 57 and 58. Specified pattern C. Then, in step S122, when it is determined which of the regions 1 to 4 is in the operating state of the engine, in step S123, based on the detection result of each O ₂ sensor 90, 91, each bank 12, A sub-learning value is calculated for each of the 13 cylinder groups. That is, in the 1O ₂ calculates a sub learning value Csub-L in the cylinder group of the first bank 12 based on the detection result of the sensor 90, the cylinder group of the second bank 13 based on the detection result of the 2O ₂ sensor 91 A sub-learning value Csub-R is calculated. In step S124, the calculated sub-learning value Csub-L and sub-learning value Csub-R are reflected as the sub-learning values L and R in the cylinder groups of the banks 12 and 13, respectively.

  Therefore, the learning time can be shortened by obtaining the sub-learning values of the patterns A and B based on the sub-learning values of the pattern C in the patterns A, B, and C having different exhaust gas exhaust paths. Since the air-fuel ratio difference between the cylinder groups in each of the banks 12 and 13 is taken into consideration, highly accurate sub air-fuel ratio learning control can be performed.

  Thus, in the internal combustion engine of the first embodiment, in the V-type 6-cylinder engine, a cylinder group in which a plurality of cylinders are divided and arranged in the left and right first banks 12 and second banks 13 is provided, and each bank is provided. While the intake pipe 51 is connected to the 12 and 13 cylinder groups, the first exhaust pipe 57 and the second exhaust pipe 58 are connected, and the first front three-way catalyst 59 and the second front stage are connected to the exhaust pipes 57 and 58, respectively. The three-way catalyst 60 is provided, and the first control valve 64 and the second control valve 65 are provided. The upstream three-way catalysts 59 and 60 and the control valves 64 and 65 in the exhaust pipes 57 and 58 are connected to the upstream side by the communication pipe 63. The A / F sensors 88 and 89 are provided upstream of the upstream three-way catalysts 59 and 60 in the exhaust pipes 57 and 58, respectively. The ECU 81 detects the detection results of the A / F sensors 88 and 89. In each bank 12, 13 And it executes the main air-fuel ratio learning control for each cylinder group, so that to execute the main air-fuel ratio learning control in accordance with the opening and closing states of the control valves 64 and 65.

  Accordingly, the A / F sensors 88 and 89 detect the air-fuel ratio of the exhaust gas flowing upstream from the front three-way catalysts 59 and 60 in the exhaust pipes 57 and 58, and the ECU 81 detects the A / F sensor 88, Even if the main air-fuel ratio learning control is executed for each cylinder group based on the air-fuel ratio detected by 89 and the control valves 64 and 65 are controlled to open and close according to the engine operating state, The main air-fuel ratio learning control is executed according to the open / closed state of the control valves 64 and 65, and high-precision air-fuel ratio control can be performed regardless of the operating state.

  In the present embodiment, the A / F sensors 88 and 89 are provided on the upstream side of the connection portions of the exhaust pipes 57 and 58 with the communication pipe 63. Therefore, the air-fuel ratio of the exhaust gas discharged from the cylinder group of each bank 12 and 13 can be detected at an early stage, and mixing with the exhaust gas of the other cylinder group is prevented to perform highly accurate air-fuel ratio control. Can be possible.

In this embodiment, O ₂ sensors 90 and 91 are provided in the exhaust pipes 57 and 58 downstream of the first front-stage three-way catalysts 59 and 60 and upstream of the control valves 64 and 65, respectively. Performs sub air-fuel ratio learning control for each cylinder group of the banks 12 and 13 based on the detection results of the O ₂ sensors 90 and 91, and sub air-fuel ratio learning according to the open / close state of the control valves 64 and 65. Control is executed.

Accordingly, the O ₂ sensors 90 and 91 detect the air-fuel ratio of the exhaust gas flowing downstream from the front three-way catalysts 59 and 60 in the exhaust pipes 57 and 58, and the ECU 81 detects that the O ₂ sensors 90 and 91 Even if sub-air-fuel ratio learning control is executed for each cylinder group based on the detected air-fuel ratio, and the control valves 64 and 65 are controlled to open and close according to the engine operating state, each control valve The sub air-fuel ratio learning control is executed in accordance with the open / closed state of 64, 65, so that highly accurate air-fuel ratio control can be performed regardless of the operating state.

  9 is a schematic plan view of a V-type 6-cylinder engine representing an internal combustion engine according to Embodiment 2 of the present invention, FIG. 10 is a flowchart showing main feedback control in the V-type 6-cylinder engine of Embodiment 2, and FIG. 4 is a flowchart showing sub air-fuel ratio learning control in a V-type 6-cylinder engine according to Embodiment 2.

  In the V-type 6-cylinder engine of the second embodiment, as shown in FIG. 9, a plurality of cylinders have a cylinder group that is divided into a first bank 12 and a second bank 13 on the left and right sides. The first exhaust pipe 57 and the second exhaust pipe 58 are connected to the cylinder group, and the first front three-way catalyst 59, the second front three-way catalyst 60, the first control valve 64, and the like are connected to the exhaust pipes 57, 58, respectively. A second control valve 65 is provided, and upstream sides of the upstream three-way catalysts 59, 60 and the control valves 64, 65 in the exhaust pipes 57, 58 are communicated by the communication pipe 63, and the ECU 81 controls each control according to the engine operating state. The exhaust gas discharge path is changed by opening and closing the valves 64 and 65.

  A / F sensors 88 and 89 are provided downstream of the connecting portions of the exhaust pipes 57 and 58 with the communication pipe 63 and upstream of the upstream three-way catalysts 59 and 60, respectively. Performs air-fuel ratio feedback control for each cylinder of the banks 12 and 13 based on the detection results of the A / F sensors 88 and 89, and performs air-fuel ratio feedback control according to the open / closed state of the control valves 64 and 65. I am trying to do it.

  Specifically, the ECU 81 executes air-fuel ratio feedback control for each cylinder based on the detection results of the A / F sensors 88 and 89, and only one of the control valves 64 and 65 is in an open state. Air-fuel ratio feedback control is executed based on the detection results of the A / F sensors 88 and 89 on the cylinder group side in the open state. The ECU 81 executes air-fuel ratio feedback control for each cylinder based on the detection results of the A / F sensors 88 and 89, and for each cylinder group when both of the control valves 64 and 65 are in the open state. The air-fuel ratio feedback control is executed based on the detection results of the A / F sensors 88 and 89.

  In the air-fuel ratio feedback control in the V-type 6-cylinder engine of the second embodiment, as shown in FIG. 10, if it is determined in step S201 that the first control valve 64 is in the closed state, the exhaust gas in step S202. Is specified as the pattern A in which the second exhaust pipe 58 is opened by the second control valve 65. In step S203, based on the detection result of the second A / F sensor 89, feedback correction values, that is, fuel injection amount correction values f () for all the cylinders (# 1 to # 6) of the banks 12 and 13 are obtained. AFS-R) is calculated.

  On the other hand, if it is determined in step S201 that the first control valve 64 is not in the closed state, and it is determined in step S204 that the second control valve 65 is in the closed state, the exhaust gas is exhausted in step S205. The path is specified as the pattern B in which the first exhaust pipe 57 is opened by the first control valve 64. In step S206, based on the detection result of the first A / F sensor 88, feedback correction values, that is, fuel injection amount correction values f (for each cylinder (# 1 to # 6) in each of the banks 12 and 13 are provided. AFS-L) is calculated.

  If it is determined in step S204 that the second control valve 65 is not closed, the exhaust gas exhaust path is opened in step S207, and both the exhaust pipes 57 and 58 are opened by the control valves 64 and 65, respectively. Specified pattern C. In step S208, based on the detection result of the second A / F sensor 89, the feedback correction value, that is, the fuel injection amount correction value f (AFS−) is determined for each of the # 1, # 3, and # 5 cylinders of the second bank 13. R) is calculated, and based on the detection result of the first A / F sensor 88, the feedback correction value, that is, the fuel injection amount correction value f (AFS-L) for each of the # 2, # 4, and # 6 cylinders of the first bank 12 is calculated. ) Is calculated.

  Therefore, in the patterns A and B in which only one of the exhaust pipes 57 and 58 is opened, the air / fuel ratio on the side where the exhaust gas flows is detected by the A / F sensors 88 and 89 and fed back, thereby providing high accuracy. By feeding back the air-fuel ratio detected by the A / F sensors 88 and 89 corresponding to the exhaust pipes 57 and 58 in the pattern C in which the air-fuel ratio feedback control becomes possible and both the exhaust pipes 57 and 58 are opened, Highly accurate air-fuel ratio feedback control becomes possible.

Further, in the V-type six-cylinder engine of this embodiment, in addition to the A / F sensors 88 and 89, each exhaust pipe 57 and 56 is downstream of the first front three-way catalyst 59 and 60 and each control valve. O ₂ sensors 90 and 91 are provided upstream of 64 and 65, and the ECU 81 executes sub air-fuel ratio learning control for each cylinder group of the banks 12 and 13 based on the detection results of the O ₂ sensors 90 and 91. At the same time, the sub air-fuel ratio learning control is executed in accordance with the open / close state of the control valves 64 and 65. Specifically, the ECU 81 executes the sub air-fuel ratio learning control based on the detection results of the O ₂ sensors 90 and 91 provided for each cylinder group regardless of whether the control valves 64 and 65 are opened or closed.

In the sub air-fuel ratio learning control in the V-type 6-cylinder engine of the second embodiment, as shown in FIG. 11, if it is determined in step S211 that the first control valve 64 is in the closed state, the exhaust is determined in step S212. The gas exhaust path is specified as the pattern A in which the second exhaust pipe 58 is opened by the second control valve 65. Then, when it is determined in step S213 which of the regions 1 to 4 is in the operating state of the engine, in step S214, based on the detection result of the _second O ₂ sensor 91, each bank 12, 13 is stored. A sub-learning value is calculated for each cylinder group. That is, based on the detection result of the second O ₂ sensor 91, the sub-learning value Asub-L in the cylinder group in the first bank 12 and the sub-learning value Asb-R in the cylinder group in the second bank 13 are calculated. In step S215, the calculated sub-learning value Assub-L and sub-learning value Assub-R are reflected as the sub-learning values L and R in the cylinder groups of the banks 12 and 13, respectively.

On the other hand, if it is determined in step S211 that the first control valve 64 is not in a closed state, and it is determined in step S216 that the second control valve 65 is in a closed state, exhaust of exhaust gas is determined in step S217. The path is specified as the pattern B in which the first exhaust pipe 57 is opened by the first control valve 64. Then, when it is determined in step S218 which of the regions 1 to 4 is in the operating state of the engine, in step S219, based on the detection result of the first O ₂ sensor 90, each bank 12, 13 is stored. A sub-learning value is calculated for each cylinder group. That is, based on the detection result of the first O ₂ sensor 90, the sub-learning value Bsub-L in the cylinder group of the first bank 12 and the sub-learning value Bsub-R in the cylinder group of the second bank 13 are calculated. In step S220, the calculated sub-learning value Bsub-L and sub-learning value Bsub-R are reflected as the sub-learning values L and R in the cylinder groups of the banks 12 and 13, respectively.

If it is determined in step S216 that the second control valve 65 is not closed, the exhaust gas exhaust path is opened in step S221, and both the exhaust pipes 57 and 58 are opened by the control valves 64 and 65, respectively. Specified pattern C. Then, in step S222, when it is determined which of the regions 1 to 4 is in the operating state of the engine, in step S223, based on the detection result of each O ₂ sensor 90, 91, each bank 12, A sub-learning value is calculated for each of the 13 cylinder groups. That is, in the 1O ₂ calculates a sub learning value Csub-L in the cylinder group of the first bank 12 based on the detection result of the sensor 90, the cylinder group of the second bank 13 based on the detection result of the 2O ₂ sensor 91 A sub-learning value Csub-R is calculated. In step S224, the calculated sub-learning value Csub-L and sub-learning value Csub-R are reflected as sub-learning values L and R in the cylinder groups of the banks 12 and 13, respectively.

Therefore, in the patterns A, B, and C having different exhaust gas exhaust paths, the first A / F sensor 88, the first O ₂ sensor 90, the second A / F sensor 89, and the like regardless of whether the control valves 64 and 65 are opened or closed. The combination of the _second O ₂ sensor 91 is not changed, and the main air-fuel ratio learning control can be performed with high accuracy.

When the O ₂ sensor is provided before and after the NOx occlusion reduction type catalyst, in the patterns A and B, the sub air-fuel ratio learning control is performed with the A / F sensor and the O ₂ sensor in a one-to-one relationship as described above. However, in the pattern C, since the air-fuel ratio difference cannot be detected, the sub air-fuel ratio learning control is executed as an average value of both. In this case, the sub air / fuel ratio learning control is executed using the sub learning value at the time of the sub air / fuel ratio learning control executed in the patterns A and B as a reference value.

  As described above, in the internal combustion engine of the second embodiment, in the V-type 6-cylinder engine, a cylinder group in which a plurality of cylinders are divided and arranged in the left and right first banks 12 and second banks 13 is provided. While the intake pipe 51 is connected to the 12 and 13 cylinder groups, the first exhaust pipe 57 and the second exhaust pipe 58 are connected, and the first front three-way catalyst 59 and the second front stage are connected to the exhaust pipes 57 and 58, respectively. The three-way catalyst 60 is provided, and the first control valve 64 and the second control valve 65 are provided. The upstream three-way catalysts 59 and 60 and the control valves 64 and 65 in the exhaust pipes 57 and 58 are connected to the upstream side by the communication pipe 63. An A / F sensor 88, 89 is provided on the downstream side of the connecting portion of the exhaust pipes 57, 58 with the communication pipe 63 and on the upstream side of the front three-way catalysts 59, 60, respectively. , Detection result of each A / F sensor 88, 89 And executes the air-fuel ratio feedback control for each cylinder in each bank 12, 13 on the basis of, and to execute the air-fuel ratio feedback control in accordance with the opening and closing states of the control valves 64 and 65.

  Therefore, the A / F sensors 88 and 89 detect the air-fuel ratio of the exhaust gas flowing immediately upstream of the front three-way catalysts 59 and 60 in the exhaust pipes 57 and 58, and the ECU 81 detects the A / F sensor 88, Even if air-fuel ratio feedback control is executed for each cylinder based on the air-fuel ratio detected by the engine 89 and the control valves 64 and 65 are controlled to open and close according to the engine operating state, The air-fuel ratio feedback control is executed in accordance with the open / closed state of 64, 65, so that highly accurate air-fuel ratio control can be performed regardless of the operating state.

  In this case, in this embodiment, the A / F sensors 88 and 89 are provided on the downstream side of the connection portions of the exhaust pipes 57 and 58 with the communication pipe 63 and on the upstream side of the upstream three-way catalysts 59 and 60, respectively. Yes. Therefore, the A / F sensors 88 and 89 detect the air-fuel ratio of the exhaust gas flowing into the front-stage three-way catalysts 59 and 60, and the front-stage three-way catalysts 59 and 60 regardless of the open / closed state of the control valves 64 and 65. The air-fuel ratio of the exhaust gas flowing into the exhaust gas can be appropriately detected, and the exhaust gas purification performance can be improved by easily controlling the air-fuel ratio of the exhaust gas to stoichiometric.

In this embodiment, O ₂ sensors 90 and 91 are provided in the exhaust pipes 57 and 56 downstream of the first front-stage three-way catalysts 59 and 60 and upstream of the control valves 64 and 65, respectively. Performs sub air-fuel ratio learning control for each cylinder group of the banks 12 and 13 based on the detection results of the O ₂ sensors 90 and 91, and sub air-fuel ratio learning according to the open / close state of the control valves 64 and 65. Control is executed.

Accordingly, the O ₂ sensors 90 and 91 detect the air-fuel ratio of the exhaust gas flowing downstream from the front three-way catalysts 59 and 60 in the exhaust pipes 57 and 58, and the ECU 81 detects that the O ₂ sensors 90 and 91 Even if sub-air-fuel ratio learning control is executed for each cylinder group based on the detected air-fuel ratio, and the control valves 64 and 65 are controlled to open and close according to the engine operating state, each control valve The sub air-fuel ratio learning control is executed in accordance with the open / closed state of 64, 65, so that highly accurate air-fuel ratio control can be performed regardless of the operating state.

  FIG. 12 is a schematic plan view of a V-type 6-cylinder engine representing an internal combustion engine according to Embodiment 3 of the present invention, FIG. 13 is a flowchart showing main feedback control in the V-type 6-cylinder engine of Embodiment 3, and FIG. FIG. 15 is a flowchart showing main air-fuel ratio learning control in the V-type 6-cylinder engine of the third embodiment, FIG. 15 is a time chart showing main air-fuel ratio learning control in the V-type 6-cylinder engine of the third embodiment, and FIG. 6 is a time chart showing a modification of main air-fuel ratio learning control in a V-6 engine of No. 3; In addition, the same code | symbol is attached | subjected to the member which has the same function as what was demonstrated in the Example mentioned above, and the overlapping description is abbreviate | omitted.

  In the V-type 6-cylinder engine of the third embodiment, as shown in FIG. 12, a plurality of cylinders have a cylinder group divided into left and right first banks 12 and second banks 13. The first exhaust pipe 57 and the second exhaust pipe 58 are connected to the cylinder group, and the first front three-way catalyst 59, the second front three-way catalyst 60, the first control valve 64, and the like are connected to the exhaust pipes 57, 58, respectively. A second control valve 65 is provided, and upstream sides of the upstream three-way catalysts 59, 60 and the control valves 64, 65 in the exhaust pipes 57, 58 are communicated by the communication pipe 63, and the ECU 81 controls each control according to the engine operating state. The exhaust gas discharge path is changed by opening and closing the valves 64 and 65.

  A / F sensors 88 and 89 are provided at the connection portions of the exhaust pipes 57 and 58 with the communication pipe 63, respectively. The ECU 81 determines the banks 12 based on the detection results of the A / F sensors 88 and 89. The air-fuel ratio feedback control is executed for each of the cylinders 13 and 13, and the air-fuel ratio feedback control is executed according to the open / closed state of the control valves 64 and 65.

  Specifically, the ECU 81 executes air-fuel ratio feedback control for each cylinder based on the detection results of the A / F sensors 88 and 89, and only one of the control valves 64 and 65 is in an open state. The cylinder group in the closed state executes air-fuel ratio feedback control based on the detection results of the A / F sensors 88 and 89 on the cylinder group side, while the cylinder group in the open state has each A in each of the two cylinder groups. The air-fuel ratio feedback control is executed based on the detection results of the / F sensors 88 and 89. The ECU 81 executes air-fuel ratio feedback control for each cylinder based on the detection results of the A / F sensors 88 and 89, and when both of the control valves 64 and 65 are in the open state, the two cylinder groups The air-fuel ratio feedback control is executed based on the detection results of the A / F sensors 88 and 89.

  In the air-fuel ratio feedback control in the V-type six-cylinder engine of the third embodiment, as shown in FIG. 13, if it is determined in step S301 that the first control valve 64 is in the closed state, the exhaust gas is determined in step S302. Is specified as the pattern A in which the second exhaust pipe 58 is opened by the second control valve 65. In step S303, based on the detection results of the A / F sensors 88 and 89, the feedback correction value, that is, the fuel injection amount correction value f () for each of the # 1, # 3, and # 5 cylinders of the second bank 13. AFS-R, AFS-L) is calculated, and feedback correction values, that is, fuel injection amount corrections are performed for the cylinders # 2, # 4, and # 6 of the first bank 12 based on the detection result of the first A / F sensor 88. The value f (AFS-L) is calculated.

  On the other hand, if it is determined in step S301 that the first control valve 64 is not in the closed state, and it is determined in step S304 that the second control valve 65 is in the closed state, the exhaust gas is exhausted in step S305. The path is specified as the pattern B in which the first exhaust pipe 57 is opened by the first control valve 64. In step S306, based on the detection result of the second A / F sensor 89, the feedback correction value, that is, the fuel injection amount correction value f (AFS−) for each of the # 1, # 3, and # 5 cylinders of the second bank 13 is obtained. R) is calculated, and the feedback correction value, that is, the fuel injection amount correction value f (AFS) is calculated for each of the # 2, # 4, and # 6 cylinders of the first bank 12 based on the detection results of the A / F sensors 88 and 89. -R, AFS-L).

  In the case of these patterns A and B, the detection value of the cylinder group on the open side is doubled, and the detection value of the cylinder group on the close side is subtracted from this, so that the cylinder group on the open side is subtracted. The air-fuel ratio can be obtained.

  If it is determined in step S304 that the second control valve 65 is not closed, the exhaust gas exhaust path is opened in step S307, and both exhaust pipes 57 and 58 are opened by the control valves 64 and 65, respectively. Specified pattern C. In step S308, based on the detection result of the second A / F sensor 89, the feedback correction value, that is, the fuel injection amount correction value f (AFS−) for each of the # 1, # 3, and # 5 cylinders of the second bank 13. R) is calculated, and the feedback correction value, that is, the fuel injection amount correction value f (AFS-L) is calculated for each of the # 2, # 4, and # 6 cylinders of the first bank 12 based on the detection result of the first A / F sensor 88. ) Is calculated.

  Accordingly, in the patterns A and B in which only one of the exhaust pipes 57 and 58 is opened, the air-fuel ratio of the cylinder group on the closed side is detected by the one A / F sensor 88 and 89 and the opened side is opened. The air-fuel ratio of each cylinder group is detected by both of the A / F sensors 88 and 89 and feedback control is performed, so that the air-fuel ratio of the cylinder group on the open side is equal to the air-fuel ratio of the cylinder group on the closed side. The A / F sensors 88 and 89 corresponding to the exhaust pipes 57 and 58 detect the pattern C in which both of the exhaust pipes 57 and 58 are opened, with high accuracy air-fuel ratio feedback control being possible by eliminating the influence. By feeding back the air-fuel ratio, highly accurate air-fuel ratio feedback control becomes possible.

  In the V-type 6-cylinder engine of this embodiment, the ECU 81 executes main air-fuel ratio learning control for each cylinder group of the banks 12 and 13 based on the detection results of the A / F sensors 88 and 89, and The main air-fuel ratio learning control is executed according to the open / closed state of the control valves 64 and 65. Specifically, when only one of the control valves 64 and 65 is in the open state, the ECU 81 completes the main air-fuel ratio learning control on the cylinder group side in the closed state, and then closes the cylinder group side in the open state. The main air-fuel ratio learning control is executed. On the other hand, when both of the control valves 64 and 65 are open, the ECU 81 simultaneously executes the main air-fuel ratio learning control of each cylinder group, and updates the learning control update speed among the control valves 64 and 65. Only one of them is slower than the learning control update speed of the main air-fuel ratio learning control when it is in the open state.

  In the main air-fuel ratio learning control in the V-type six-cylinder engine according to the third embodiment, as shown in FIG. 14, if it is determined in step S311 that the first control valve 64 is in the closed state, the exhaust is determined in step S312. The gas exhaust path is specified as the pattern A in which the second exhaust pipe 58 is opened by the second control valve 65. In step S313, when it is determined and set in which of the regions 1 to 4 the operating state of the engine, the main air-fuel ratio learning control of the first bank 12 is started in step S314. In this case, the main learning value A−L (n) is calculated based on the detection result of the first A / F sensor 88 and reflected in the main learning value L (n).

  In step S315, it is determined whether or not the main air-fuel ratio learning control of the first bank 12, that is, the main learning value AL (n) has been calculated, and until the main learning value AL (n) is calculated. Wait for the start of the main air-fuel ratio learning control of the second bank 13. Here, if it is determined that the main learning value AL (n) of the first bank 12 has been calculated, the main air-fuel ratio learning control of the second bank 12 is executed in step S316. In this case, the main learning value A-R (n) is calculated based on the detection results of the A / F sensors 88 and 89, and is reflected in the main learning value R (n). Specifically, the air / fuel ratio of the cylinder group in the second bank 13 can be obtained by doubling the detection value of the second A / F sensor 89 and subtracting the detection value of the first A / F sensor 88 therefrom. it can.

  On the other hand, if it is determined in step S311 that the first control valve 64 is not in the closed state, and it is determined in step S317 that the second control valve 65 is in the closed state, exhaust of the exhaust gas is determined in step S318. The path is specified as the pattern B in which the first exhaust pipe 57 is opened by the first control valve 64. When it is determined in step S319 which of the regions 1 to 4 is in the engine operating state, the main air-fuel ratio learning control of the second bank 13 is started in step S320. In this case, the main learning value B−R (n) is calculated based on the detection result of the second A / F sensor 89 and is reflected in the main learning value R (n).

  In step S321, it is determined whether or not the main air-fuel ratio learning control of the second bank 13, that is, the main learning value BR (n) has been calculated, and until the main learning value BR (n) is calculated. Wait for the start of the main air-fuel ratio learning control of the first bank 11. Here, if it is determined that the main learning value BR (n) of the second bank 13 has been calculated, the main air-fuel ratio learning control of the first bank 13 is executed in step S322. In this case, the main learning value B−L (n) is calculated based on the detection results of the A / F sensors 88 and 89, and is reflected in the main learning value L (n). Specifically, the air-fuel ratio of the cylinder group in the first bank 12 can be obtained by doubling the detection value of the first A / F sensor 88 and subtracting the detection value of the second A / F sensor 89 from this. it can.

  If it is determined in step S317 that the second control valve 65 is not closed, the exhaust gas exhaust path is opened in step S323, and both the exhaust pipes 57 and 58 are opened by the control valves 64 and 65, respectively. Specified pattern C. When it is determined in step S324 which of the regions 1 to 4 is in the engine operating state, in step S325, the first bank 12 is checked based on the detection result of the first A / F sensor 88. The main learning value CL (n) in the cylinder group is calculated, and the main learning value CR (n) in the cylinder group of the second bank 13 is calculated based on the detection result of the second A / F sensor 89. It is reflected in the learning values L (n) and R (n). At this time, the learning control update speed of the main learning values L (n) and R (n) is set to the learning control update speed of the main air-fuel ratio learning control when only one of the control valves 64 and 65 is in the open state. Make it slower.

  Accordingly, in the patterns A and B in which only one of the exhaust pipes 57 and 58 is opened, after calculating the main learning value of the cylinder group on the closed side, the main learning value of the cylinder group on the opened side is calculated. In this case, the main learning value of the cylinder group on the closed side is calculated based on one of the A / F sensors 88 and 89, and the main learning value of the cylinder group on the opened side is calculated for both A / F sensors 88 and 89 are calculated, and the main air-fuel ratio learning control is executed to eliminate the influence of the air-fuel ratio of the closed cylinder group on the open cylinder group. Thus, highly accurate main air-fuel ratio learning control can be performed. Further, in the pattern C in which both the exhaust pipes 57 and 58 are opened, the main learning value of each cylinder group is calculated based on the A / F sensors 88 and 89 corresponding to the exhaust pipes 57 and 58, and each cylinder group is calculated. The main air-fuel ratio learning control is simultaneously executed, and the learning control update speed is made slower than the learning control update speed of the main air-fuel ratio learning control when only one of the control valves 64, 65 is open. As a result, the main air-fuel ratio learning control can be executed in a wide range of operation to reduce errors generated in accordance with the update.

  Specifically, as shown in FIG. 15, in the case of a pattern A in which the first exhaust pipe 57 is closed by the first control valve 64 while the second exhaust pipe 58 is opened by the second control valve 65, the first A The sensor output AFS-L of the / F sensor 88 and the sensor output AFS-R of the second A / F sensor 89 are shifted. At this time, if the main air-fuel ratio learning control of the banks 12 and 13 is executed at the same time, in the second bank 13 in which the second exhaust pipe 58 is open, as shown by a two-dot chain line in FIG. Under the influence of the sensor output AFS-L of the sensor 88, erroneous learning is performed, the main learning value A-R increases, and as a result, the actual air-fuel ratio fluctuates and the exhaust purification performance deteriorates. On the other hand, when the main air-fuel ratio learning control of the second bank 13 is executed after the main air-fuel ratio learning control of the first bank 12 is completed, the second bank 13 in which the second exhaust pipe 58 is opened is the first bank. During execution of the main air-fuel ratio learning control No. 12, the main learned value A-R becomes constant, and as a result, the actual air-fuel ratio does not fluctuate and deterioration of the exhaust purification performance is prevented.

  Note that the control method of the main air-fuel ratio learning control in the V-type six-cylinder engine of the present embodiment is not limited to this method. For example, the ECU 81 executes main air-fuel ratio learning control on the cylinder group side in the closed state when only one of the control valves 64 and 65 is in the open state, while on the cylinder group side in the open state, The main air-fuel ratio learning control is executed while considering the update effect of the main air-fuel ratio learning control on the cylinder group side in the closed state. Specifically, the ECU 81 executes main air-fuel ratio learning control on the cylinder group side in the closed state, excludes the main learning value on the cylinder group side in the closed state, and removes the main air-fuel ratio side on the cylinder group side in the open state. The fuel ratio learning control is executed.

  As a result, as shown in FIG. 16, in the case of the pattern A in which the first exhaust pipe 57 is closed by the first control valve 64 while the second exhaust pipe 58 is opened by the second control valve 65, the first A / F sensor is used. The sensor output AFS-L of 88 and the sensor output AFS-R of the second A / F sensor 89 are shifted. At this time, the main air-fuel ratio learning control of the first bank 12 is executed and the main air-fuel ratio learning control of the second bank 13 is executed. At this time, the main learning value calculated in the first bank 12 is excluded. Therefore, in the second bank 13 in which the second exhaust pipe 58 is open, the main learning value A-R does not fluctuate greatly during execution of the main air-fuel ratio learning control of the first bank 12, and the actual air-fuel ratio does not change. The fluctuation is suppressed and the exhaust purification performance is prevented from deteriorating.

Further, in the V-type 6-cylinder engine of the present embodiment, in addition to the A / F sensors 88 and 89, downstream of the first front-stage three-way catalysts 59 and 60 in the exhaust pipes 57 and 56, and the control valves O ₂ sensors 90 and 91 are provided upstream of 64 and 65, and the ECU 81 executes sub air-fuel ratio learning control for each cylinder group of the banks 12 and 13 based on the detection results of the O ₂ sensors 90 and 91. At the same time, the sub air-fuel ratio learning control is executed in accordance with the open / close state of the control valves 64 and 65. Specifically, when only one of the control valves 64, 65 is in the open state, the ECU 81 performs sub air-fuel ratio learning control based on the detection results of the O ₂ sensors 90, 91 on the cylinder group side in the open state. To calculate the sub-learning values Asub-R and BsubL. In this case, the sub-learned values Asub-R and BsubL on the cylinder group side in the open state are calculated based on the detection results of the O ₂ sensors 90 and 91 when both the control valves 64 and 65 are in the open state. The learning values Csub-R and CsubL are shared.

  As described above, in the internal combustion engine of the third embodiment, in the V-type 6-cylinder engine, a cylinder group in which a plurality of cylinders are divided and arranged in the left and right first banks 12 and second banks 13 is provided. While the intake pipe 51 is connected to the 12 and 13 cylinder groups, the first exhaust pipe 57 and the second exhaust pipe 58 are connected, and the first front three-way catalyst 59 and the second front stage are connected to the exhaust pipes 57 and 58, respectively. The three-way catalyst 60 is provided, and the first control valve 64 and the second control valve 65 are provided. The upstream three-way catalysts 59 and 60 and the control valves 64 and 65 in the exhaust pipes 57 and 58 are connected to the upstream side by the communication pipe 63. The A / F sensors 88 and 89 are provided at the connecting portions of the exhaust pipes 57 and 58 with the communication pipe 63, and the ECU 81 is configured based on the detection results of the A / F sensors 88 and 89. Empty for each cylinder in banks 12 and 13 And executes the ratio feedback control, so as to perform the air-fuel ratio feedback control in accordance with the opening and closing states of the control valves 64 and 65.

  Therefore, the A / F sensors 88 and 89 detect the air-fuel ratio of the exhaust gas flowing immediately upstream of the front three-way catalysts 59 and 60 in the exhaust pipes 57 and 58, and the ECU 81 detects the A / F sensor 88, Even if air-fuel ratio feedback control is executed for each cylinder based on the air-fuel ratio detected by the engine 89 and the control valves 64 and 65 are controlled to open and close according to the engine operating state, The air-fuel ratio feedback control is executed in accordance with the open / closed state of 64, 65, so that highly accurate air-fuel ratio control can be performed regardless of the operating state.

  In this case, in this embodiment, the A / F sensors 88 and 89 are provided at the connection portions of the exhaust pipes 57 and 58 with the communication pipe 63, respectively. Therefore, the A / F sensors 88 and 89 can detect the air-fuel ratio of the exhaust gas discharged from the cylinder groups of the banks 12 and 13 at an early stage, and the exhaust gas flowing into the upstream three-way catalysts 59 and 60 can be detected. The air-fuel ratio is detected, and highly accurate air-fuel ratio feedback control can be executed regardless of the open / closed state of the control valves 64 and 65.

  Further, in this embodiment, when only one of the control valves 64, 65 is in the open state, the ECU 81 causes the cylinder in the open state after completion of the main air-fuel ratio learning control on the cylinder group side in the closed state. The main air-fuel ratio learning control on the group side is executed. Accordingly, the air-fuel ratio of the cylinder group in the open state can be controlled with high accuracy regardless of the operating state by eliminating the influence of the air-fuel ratio of the cylinder group in the closed state. Air-fuel ratio control can be performed.

  In each of the above-described embodiments, the V-type 6-cylinder engine is applied as the internal combustion engine. However, the engine type, the number of cylinders, and the like are not limited to the embodiments. Furthermore, although the fuel injection type of the internal combustion engine is the in-cylinder injection type, it may be a port injection type.

  As described above, the internal combustion engine according to the present invention executes the main air-fuel ratio learning control for each cylinder group based on the exhaust air-fuel ratio, and executes the main air-fuel ratio learning control according to the open / close state of the control valve. Thus, highly accurate air-fuel ratio control is possible regardless of the operating state, and it is useful for any internal combustion engine.

1 is a schematic plan view of a V-type 6-cylinder engine that represents an internal combustion engine according to Embodiment 1 of the present invention. 1 is a schematic cross-sectional view of a V-type 6-cylinder engine according to Embodiment 1. FIG. 3 is a flowchart illustrating control valve switching control in the V-type six-cylinder engine according to the first embodiment. 3 is a flowchart showing main air-fuel ratio learning control in the V-type 6-cylinder engine according to the first embodiment. 7 is a flowchart illustrating a modification of main air-fuel ratio learning control in the V-type six-cylinder engine according to the first embodiment. 7 is a flowchart illustrating a modification of main air-fuel ratio learning control in the V-type six-cylinder engine according to the first embodiment. 3 is a flowchart showing sub air-fuel ratio learning control in the V-type six-cylinder engine according to the first embodiment. 6 is a flowchart illustrating a modification of sub air-fuel ratio learning control in the V-type six-cylinder engine of the first embodiment. It is a schematic plan view of the V type 6 cylinder engine showing the internal combustion engine which concerns on Example 2 of this invention. 6 is a flowchart showing main feedback control in a V-type 6-cylinder engine according to a second embodiment. 6 is a flowchart showing sub air-fuel ratio learning control in a V-type 6-cylinder engine according to Embodiment 2. It is a schematic plan view of the V type 6 cylinder engine showing the internal combustion engine which concerns on Example 3 of this invention. 6 is a flowchart illustrating main feedback control in a V-type 6-cylinder engine according to a third embodiment. 7 is a flowchart showing main air-fuel ratio learning control in a V-type 6-cylinder engine according to Embodiment 3. 6 is a time chart showing main air-fuel ratio learning control in a V-type 6-cylinder engine according to Embodiment 3. 6 is a time chart showing a modification of main air-fuel ratio learning control in the V-type 6-cylinder engine of Embodiment 3.

Explanation of symbols

12 First bank 13 Second bank 22, 23 Combustion chamber 24, 25 Intake port 26, 27 Exhaust port 28, 29 Intake valve 30, 31 Exhaust valve 51 Intake pipe (intake passage)
54 Electronic throttle device 57 First exhaust pipe (exhaust passage)
58 Second exhaust pipe (exhaust passage)
59 First three-way catalyst (purification catalyst)
60 Second front three-way catalyst (purification catalyst)
61 exhaust collecting pipe 62 NOx occlusion reduction type catalyst 63 communication pipe (communication passage)
64 First control valve 65 Second control valve 67 Turbocharger 72, 73 Injector 77, 78 Spark plug 81 Electronic control unit, ECU (control means)
88 1st A / F sensor (1st air fuel ratio detection means)
89 Second A / F sensor (first air-fuel ratio detecting means)
90 1st O ₂ sensor (second air-fuel ratio detecting means)
91 2nd O ₂ sensor (second air-fuel ratio detecting means)

Claims (17)

  There are two cylinder groups in which a plurality of cylinders are divided into left and right banks, and an intake passage is provided for each cylinder group, while an exhaust passage is provided independently. A control valve for adjusting the flow rate of the exhaust gas is provided, and a purification catalyst is provided in each exhaust passage, and each control valve in each exhaust passage and the upstream side of each purification catalyst are communicated by a communication passage, In an internal combustion engine provided with first air-fuel ratio detection means upstream of each purification catalyst in the exhaust passage, main air-fuel ratio learning control is executed for each cylinder group based on the detection result of the first air-fuel ratio detection means And an internal combustion engine characterized by comprising a control means for executing a main air-fuel ratio learning control in accordance with the open / closed state of the control valve.   2. The internal learning engine according to claim 1, wherein when only one of the control valves is in an open state, the control means calculates main learning calculated when both of the control valves are in an open state. An internal combustion engine characterized in that a main learning value is calculated in consideration of a back pressure difference of each cylinder group.   2. The internal combustion engine according to claim 1, wherein when both of the control valves are in an open state, the control means calculates each of the control valves calculated when only one of the control valves is in an open state. An internal combustion engine that calculates a main learning value by averaging main learning values of a cylinder group.   2. The internal combustion engine according to claim 1, wherein the first air-fuel ratio detection means is provided on an upstream side of a connection portion of each exhaust passage with the communication passage.   5. The internal combustion engine according to claim 4, wherein second exhaust air-fuel ratio detection means is provided downstream of the purification catalyst in each exhaust passage, and the control means is based on a detection result of the second air-fuel ratio detection means. An internal combustion engine that performs sub air-fuel ratio learning control for each cylinder group and performs sub air-fuel ratio learning control according to an open / close state of the control valve.   6. The internal combustion engine according to claim 5, wherein when only one of the control valves is in an open state, the control means calculates sub-learning when both of the control valves are in an open state. An internal combustion engine characterized in that a sub-learning value is calculated in consideration of an air-fuel ratio difference between the cylinder groups.   2. The internal combustion engine according to claim 1, wherein the first air-fuel ratio detecting means is provided downstream of a connection portion of each exhaust passage with the communication passage and upstream of the purification catalyst. Internal combustion engine.   8. The internal combustion engine according to claim 7, wherein the control means performs air-fuel ratio feedback control for each of the cylinders based on a detection result of the first air-fuel ratio detection means, and only one of the control valves. An internal combustion engine that performs air-fuel ratio feedback control based on a detection result of the first air-fuel ratio detection means on the cylinder group side in the open state when is in an open state.   8. The internal combustion engine according to claim 7, wherein the control means executes air-fuel ratio feedback control for each cylinder based on the detection result of the first air-fuel ratio detection means, and both of the control valves are An internal combustion engine that performs air-fuel ratio feedback control based on a detection result of the first air-fuel ratio detection means for each cylinder group when in an open state.   8. The internal combustion engine according to claim 7, wherein a second air-fuel ratio detection means is provided downstream of the purification catalyst in each exhaust passage, and the control means is based on a detection result of the second air-fuel ratio detection means. The sub air-fuel ratio learning control is executed for each cylinder group, and the sub air-fuel ratio learning control is executed based on the detection result of the second air-fuel ratio detection means for each cylinder group regardless of the open / close state of the control valve. An internal combustion engine characterized by the above.   2. The internal combustion engine according to claim 1, wherein the first air-fuel ratio detection means is provided at a connection portion of each exhaust passage with the communication passage.   12. The internal combustion engine according to claim 11, wherein the control means performs air-fuel ratio feedback control for each of the cylinders based on a detection result of the first air-fuel ratio detection means, and only one of the control valves. Is in the open state, the cylinder group in the closed state performs air-fuel ratio feedback control based on the detection result of the first air-fuel ratio detection means on the one cylinder group side, while the cylinder group in the open state The internal combustion engine, wherein the cylinder group executes air-fuel ratio feedback control based on a detection result of the first air-fuel ratio detection means of the two cylinder groups.   12. The internal combustion engine according to claim 11, wherein the control means executes air-fuel ratio feedback control for each cylinder based on a detection result of the first air-fuel ratio detection means, and both of the control valves are An internal combustion engine that performs air-fuel ratio feedback control based on a detection result of the first air-fuel ratio detection means of each cylinder group when in an open state.   12. The internal combustion engine according to claim 11, wherein when only one of the control valves is in an open state, the control means opens after completion of the main air-fuel ratio learning control on the cylinder group side in the closed state. An internal combustion engine that performs main air-fuel ratio learning control on the cylinder group side in a state.   12. The internal combustion engine according to claim 11, wherein when both of the control valves are in an open state, the control means simultaneously executes main air-fuel ratio learning control of the cylinder groups and learning control update speed. The internal combustion engine is made slower than a learning control update speed of main air-fuel ratio learning control when only one of the control valves is in an open state.   The internal combustion engine according to claim 11, wherein when only one of the control valves is in an open state, the control means executes a main air-fuel ratio learning control on the cylinder group side in a closed state, An internal combustion engine that executes main air-fuel ratio learning control on the cylinder group side in an open state while excluding a main learning value on the cylinder group side in a closed state.   12. The internal combustion engine according to claim 11, wherein a second air-fuel ratio detecting means is provided downstream of the purification catalyst in each exhaust passage, and the control means is based on a detection result of the second air-fuel ratio detecting means. When the sub air-fuel ratio learning control is executed for each cylinder group and only one of the control valves is in the open state, the control means detects the second air-fuel ratio on the cylinder group side in the open state. An internal combustion engine that performs sub air-fuel ratio learning control based on a detection result of the means.

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