JP2008121510A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure stable exhaust emission control performance in the left and right groups of cylinders of an internal combustion engine regardless of the presence or absence of a supercharger. <P>SOLUTION: A V-type six cylinder engine comprises groups of cylinders which are classified and disposed on the left and right first and second banks 12, 13. A first exhaust pipe 57 and a second exhaust pipe 58 are connected to the groups of cylinders on the banks 12, 13, respectively. Preceding-stage three-way catalysts 59, 60 and control valves 64, 65 are attached to the exhaust pipes 57, 58, respectively. The exhaust pipes 57, 58 on the upstream side of the preceding-stage three-way catalysts 59, 60 and the control valves 64, 65 are allowed to communicate with each other through a communication pipe 63. A turbosupercharger 67 is mounted on the first bank 12 side. The first bank 12 side first exhaust pipe 57 with the turbosupercharger 67 on the downstream side of a turbine 69 is allowed to communicate with the communication pipe 63 through a bypass pipe 72. A third control valve 73 for regulating the flow of the exhaust gas is attached to the bypass pipe 72. The control valves 64, 65, 73 can be controllably opened and closed by an ECU 81 according to the operating conditions of the engine. <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 that is communicated by a communication passage on the upstream side of a valve and in which a supercharger is provided only in one of two cylinder groups.

  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 the exhaust port of each bank, and a purification catalyst is attached to each exhaust pipe.

  In such a V-type multi-cylinder engine, at the time of cold start of the engine, in order to warm up and quickly activate the purification catalyst provided in each exhaust pipe, each exhaust pipe is arranged upstream of the purification catalyst. There is one that enables bank control by communicating with a communication pipe and providing a control valve in each exhaust pipe. Therefore, when the engine is cold started, the control valve of one exhaust pipe is closed and exhaust gas from the cylinder group of each bank is merged in the other exhaust pipe through the communication pipe, and then the heat of this large amount of exhaust gas Efficiently warm up the purification catalyst for early activation. After that, when the purification catalyst provided in one exhaust pipe is activated, the control valve of the other exhaust pipe is closed and the exhaust gas from the cylinder group of each bank is merged in one exhaust pipe through the communication pipe, The purification catalyst is efficiently warmed up by the heat of this large amount of exhaust gas to achieve early activation.

  In addition, there is such a V-type multi-cylinder engine in which a turbocharger is provided only in one bank. In this case, when the turbocharger is in operation, the control valve of the exhaust pipe without the turbocharger is closed and the exhaust gas from the cylinder group of each bank is merged through the communication pipe in the exhaust pipe with the turbocharger. Thereafter, a turbocharger turbine is driven by this large amount of exhaust gas, and a compressor integrated with the turbine is driven to compress air and introduced into the combustion chamber, thereby enabling high supercharging.

  In addition, there exist some which were described in the following patent documents 1, 2 as such an internal combustion engine.

Japanese Patent Publication No. 01-027246 Japanese Patent Laid-Open No. 08-121153

  As described above, when the engine is provided with a supercharger only in one bank, when the engine is cold-started, the purification catalyst provided in the exhaust pipe of the cylinder group having the supercharger is warmed up and activated. Since the turbocharger turbine is driven by the exhaust gas flowing through the exhaust pipe, a heat loss of the exhaust gas occurs here, and the warm-up property of the purification catalyst is reduced, which takes a long time for activation. The purification performance by the purification catalyst may be reduced.

  An object of the present invention is to provide an internal combustion engine capable of solving such a problem, and capable of ensuring stable exhaust purification performance in two cylinder groups regardless of the presence or absence of a supercharger. To do.

  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 in which the upstream side from each control valve and each purification catalyst in the above is communicated by a communication passage, and a supercharger is provided only in one of the two cylinder groups, the cylinder group having the supercharger The downstream side of the supercharger in the exhaust passage and the communication passage are communicated by a bypass passage, and a bypass valve for adjusting the flow rate of the exhaust gas is provided in the bypass passage, and the internal combustion engine is controlled by the control means. It is characterized in that the control valve and the bypass valve can be opened and closed controlled in accordance with the operating state.

  In the internal combustion engine of the present invention, the control means closes the control valve in the exhaust passage of the cylinder group having the supercharger at the time of cold start of the internal combustion engine, but does not have the supercharger. The control valve in the exhaust passage of the group is opened, and the bypass valve is opened.

  In the internal combustion engine of the present invention, the control means opens each of the control valves and opens the bypass valve during idle operation of the internal combustion engine.

  In the internal combustion engine of the present invention, the control means opens the control valve in the exhaust passage of the cylinder group having the supercharger while the high-pressure operation of the internal combustion engine, while the cylinder not having the supercharger The control valve in the exhaust passage of the group is closed, and the opening degree of the bypass valve is controlled according to the supercharging pressure.

  In the internal combustion engine of the present invention, the downstream end portions of the exhaust passages merge to provide an exhaust collecting passage, a NOx storage reduction catalyst is provided in the exhaust collecting passage, and the air-fuel ratio of the two cylinder groups is set. Air-fuel ratio changing means for changing is provided, and the control means opens each control valve and opens the bypass valve when the NOx storage reduction catalyst is warmed up. The air-fuel ratio of the group is changed to a rich air-fuel ratio, while the air-fuel ratio of the other cylinder group is changed to a lean air-fuel ratio.

  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 a supercharger is provided only in one of the two cylinder groups. A bypass valve that connects the downstream side of the turbocharger in the exhaust passage of the cylinder group and the communication passage by a bypass passage and adjusts the flow rate of the exhaust gas is provided in the bypass passage, and the control means responds to the operating state of the internal combustion engine. The control valve and bypass valve can be controlled to open and close.

  Therefore, according to the operating state of the engine, each exhaust passage is opened and closed by the control valve, and by opening and closing the bypass passage by the bypass valve, the exhaust passage in the cylinder group having the supercharger is discharged from the cylinder group. Exhaust gas bypasses the turbocharger by the bypass passage and flows to the exhaust pipe and the communication passage, reducing the pressure of exhaust gas in the cylinder group having the supercharger and equalizing the back pressure in the two cylinder groups Thus, stable exhaust purification performance in each cylinder group can be ensured.

  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 an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view of the V-type 6-cylinder engine of this embodiment, and FIG. It is a flowchart showing the operation control in an example V type 6 cylinder engine.

  In this 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 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 temporarily occludes NOx contained in the exhaust gas when the exhaust air-fuel ratio is lean, and occludes when it is in the rich combustion region or stoichiometric combustion region where the oxygen concentration in the exhaust gas is reduced. The released NOx is released, and NOx is reduced by the added fuel as a reducing agent.

  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.

  Further, a portion of the first exhaust pipe 57 on the first bank 12 side having the turbocharger 67 on the downstream side of the turbine 69 and upstream of the first front three-way catalyst 59 and the communication pipe 63 are bypass pipes (bypass pipes). The bypass pipe 72 is provided with a third control valve (bypass valve) 73. The third control valve 73 is an electric flow control valve, and the flow rate of the exhaust gas flowing through the bus bus pipe 72 can be adjusted by adjusting the opening degree. The third control valve 73 functions as a wastegate valve of the turbocharger 67 and can adjust the supercharging pressure. When the turbocharger 67 is operated, the third control valve 73 is provided with a surge tank 50. The opening degree is adjusted according to the detection result of the pressure supply sensor (not shown).

  The cylinder heads 20 and 21 are respectively equipped with injectors 74 and 75 for injecting fuel (gasoline) directly into the combustion chambers 22 and 23. Delivery pipes 76 and 77 are connected to the injectors 74 and 75, respectively. Each of the delivery pipes 76 and 77 can be supplied with fuel of a predetermined pressure from a high-pressure fuel pump 78. The cylinder heads 20 and 21 are equipped with spark plugs 79 and 80 that are located above the combustion chambers 22 and 23 and ignite the air-fuel mixture.

  An electronic control unit (ECU) 81 is mounted on the vehicle. The ECU 81 can control the fuel injection timing of the injectors 74 and 75, the ignition timing of the spark plugs 79 and 80, 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 88 and 89 are provided upstream of the upstream three-way catalysts 59 and 60 in the exhaust pipes 57 and 58, respectively. The A / F sensors 88 and 89 detect the exhaust air / fuel ratio of the exhaust gas exhausted to the exhaust pipes 57 and 58 through the exhaust ports 26 and 27 from the combustion chambers 22 and 23, respectively. It is output to the ECU 81. The ECU 81 corrects the fuel injection amount by feeding back the exhaust air / fuel ratio detected by the A / F sensors 88 and 89 and comparing it with the target air / fuel ratio set according to the engine operating state.

  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. The turbocharger 67 is attached to the first bank 12, and the downstream side of the turbine 69 in the first exhaust pipe 57 and the communication pipe 63 are communicated by a bypass pipe 72. A third control valve 73 is mounted on the front. Therefore, the ECU 81 can change the exhaust gas discharge path by controlling the opening and closing of the control valves 64, 65, 73 according to the engine operating state.

  For example, when the engine is cold started, the first control valve 64 is closed, the second control valve 65 is opened, the third control valve 73 is opened, and the cylinder group of the first bank 12 is opened. The exhaust gas discharged from the first exhaust pipe 57 to the second exhaust pipe 58 through the communication pipe 63 through the collecting passage 55 is bypassed to the second exhaust pipe 58, thereby exhaust gas from the cylinder groups of the first and second banks 12 and 13. Are combined in the second exhaust pipe 58, and then a large amount of exhaust gas is allowed to flow into the second front-stage three-way catalyst 60, whereby the second front-stage three-way catalyst 60 is warmed up. At this time, the exhaust gas discharged from the cylinder group of the first bank 12 moves to the second exhaust pipe 58 through the communication pipe 63, but the turbo excess in the first exhaust pipe 57 connected linearly from the collecting passage 55. It is easy to flow to the turbine 69 side of the feeder 67 and the exhaust pressure immediately upstream of the first control valve 64 tends to be high, but the exhaust gas here is discharged to the communication pipe 63 through the bypass pipe 72, It is possible to appropriately flow to the second bank side.

  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, the second control valve 65 is closed, and the third control valve 73 is opened, and the exhaust gas discharged from the cylinder group of the second bank 13 through the collecting passage 56 to the second exhaust pipe 58 is bypassed to the first exhaust pipe 57 through the communication pipe 63, whereby the first and first After the exhaust gases from the cylinder groups of the two banks 12 and 13 are merged in the first exhaust pipe 57, a large amount of exhaust gas flows into the first front three-way catalyst 59, whereby the first front three-way catalyst 59 is obtained. To warm up. At this time, the exhaust gas discharged from the cylinder group of the second bank 13 is discharged to the second exhaust pipe 58 through the bypass pipe 72, thereby bypassing the turbine 69 of the turbocharger 67. This turbine 69 can flow a large amount of exhaust gas into the first front three-way catalyst 59 without causing exhaust resistance.

  Further, when the engine is idling, the first control valve 64 and the second control valve 65 are opened and the third control valve 73 is opened, and the cylinders in the first bank 12 are discharged to the collecting passage 55. The exhaust gas is discharged to the first exhaust pipe 57, while the 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 discharged to the first front stage three. By flowing into the original catalyst 59 and the second previous three-way catalyst 60, the respective previous three-way catalysts 59, 60 are kept warm. At this time, the exhaust gas discharged from the cylinder group of the first bank 12 is discharged to the first exhaust pipe 57 through the bypass pipe 72, thereby bypassing the turbine 69 of the turbocharger 67. The turbine 69 can flow an appropriate amount of exhaust gas into the first front three-way catalyst 59 without causing exhaust resistance.

  Further, in a low / medium load state of the engine, the first control valve 64 is closed, the second control valve 65 is opened, the third control valve 73 is opened, and the first bank 12 By bypassing the exhaust gas discharged from the cylinder group to the first exhaust pipe 57 through the collecting passage 55 to the second exhaust pipe 58 through the communication pipe 63, the exhaust gas from the cylinder group of the first and second banks 12, 13 is bypassed. The exhaust gas is discharged after being merged by the first exhaust pipe 57. On the other hand, in the high load state of the engine, the first control valve 64 is opened, the second control valve 65 is closed, and the opening of the third control valve 73 is controlled according to the supercharging pressure. By bypassing the exhaust gas discharged from the cylinder group of the two banks 13 through the collecting passage 56 to the second exhaust pipe 58 to the first exhaust pipe 57 through the communication pipe 63, the first and second banks 12, 13 After the exhaust gas from the cylinder group is merged in the first exhaust pipe 57, a large amount of exhaust gas is caused to flow into the turbocharger 67, thereby operating the turbocharger 67 with high efficiency and high supercharging. It is possible to improve the output. Note that the ECU 81 prevents the turbocharger 67 from being damaged by adjusting the opening of the third control valve 73 in accordance with the supercharging pressure.

  Further, the ECU 81 functions as an air-fuel ratio changing means capable of changing the air-fuel ratio of the engine, makes the exhaust gas from the cylinder group of the first bank 12 a lean atmosphere, and enriches the exhaust gas from the cylinder group of the second bank 13. At the same time, the first control valve 64, the second control valve 65, and the third control valve 73 are opened, and the lean exhaust gas discharged from the cylinder group of the first bank 12 is supplied to the first exhaust pipe 57. The exhaust gas in the rich atmosphere discharged from the cylinder group of the second bank 13 is caused to flow into the first exhaust pipe 57 and merged in the exhaust collecting pipe 61, and the oxidation exothermic reaction in the NOx occlusion reduction type catalyst 62 is utilized. The NOx occlusion reduction type catalyst 62 is warmed up, and the sulfur component accumulated in the NOx occlusion reduction type catalyst 62 is released and regenerated. At this time, the exhaust gas discharged from the cylinder group of the second bank 13 is discharged to the second exhaust pipe 58 through the bypass pipe 72, thereby bypassing the turbine 69 of the turbocharger 67. This turbine 69 does not become exhaust resistance, and exhaust gas does not flow into the communication pipe 63, and an appropriate amount of exhaust gas can flow into the first front-stage three-way catalyst 59.

  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.

  In the V-type 6-cylinder engine of this embodiment configured as described above, the opening / closing control of the control valves 64, 65, 73 will be specifically described below 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. Here, if it is determined that the engine is cold-started, in step S13, the ECU 81 closes the first control valve 64, opens the second control valve 65, and opens the third control valve 73. State.

  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.

  At this time, the exhaust gas discharged from the combustion chamber 22 of the first bank 12 to the first exhaust pipe 57 flows to the second exhaust pipe 58 side through the communication pipe 63, but the turbo in the first exhaust pipe 57 from the collecting passage 55. Since the turbine 69 of the supercharger 67 is connected substantially linearly in consideration of the turbine efficiency, the exhaust gas discharged to the first exhaust pipe 57 flows more easily to the turbine 69 side than the communication pipe 63. . Therefore, the exhaust pressure in the region from the turbine 69 to the closed first control valve 64 in the first exhaust pipe 57 becomes high, and the exhaust gas easily leaks from the first control valve 64 to the downstream side. However, in this embodiment, the exhaust gas in the region where the high pressure tends to be high in the first exhaust pipe 57 flows into the communication pipe 63 through the bypass pipe 72, and the exhaust gas leaks downstream from the first control valve 64. It can suppress and can flow to the 2nd bank 13 side appropriately.

  Therefore, the exhaust gas from the combustion chamber 22 of the first bank 12 flows not to the activated first front three-way catalyst 59 but to the activated second front three-way catalyst 60, so that exhaust purification performance is achieved. Is suppressed. Further, by reducing the back pressure in the first exhaust pipe 57, the exhaust pressure difference between the left and right banks 12, 13 is reduced, and the output torque difference is reduced to prevent the occurrence of engine vibration. Further, a part of the exhaust gas discharged from the combustion chamber 22 of the first bank 12 flows through the turbine 69 from the bypass pipe 72 to the communication pipe 63, and the turbine 69 is warmed up.

  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, the second control valve 65 is closed, and the third control valve 73 is opened. 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.

  At this time, most of the exhaust gas discharged from the combustion chamber 22 of the first bank 12 to the first exhaust pipe 57 flows into the first exhaust pipe 57 through the turbine 69 of the turbocharger 67, and the second bank 13. Most of the exhaust gas flowing from the combustion chamber 23 to the communication pipe 63 flows through the bypass pipe 72 to the first exhaust pipe 57. Therefore, the exhaust gas discharged from each combustion chamber 22, 23 of each bank 12, 13 can flow properly to the first exhaust pipe 57. Since the turbine 69 is warmed up by the exhaust gas discharged from the first bank 12 when the second pre-stage three-way catalyst 60 is warmed up, the exhaust gas is discharged from the combustion chambers 22 and 23 of the banks 12 and 13. The exhaust gas thus exhausted is not deprived of heat by the turbine 69, and the first front three-way catalyst 59 is efficiently heated. If it is determined in step S16 that the catalyst temperature of the first front-stage three-way catalyst 59 has been raised to the catalyst activation temperature region and activated, the control at the cold start is terminated.

  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, opens the second control valve 65, and opens the third control valve 73 in step S18. And

  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. At this time, part of the exhaust gas discharged from the combustion chamber 22 of the first bank 12 bypasses the turbine 69 of the turbocharger 67 and is discharged to the first exhaust pipe 57 through the bypass pipe 72. Therefore, an appropriate amount of exhaust gas flows into the first front three-way catalyst 59 without the turbine 69 becoming exhaust resistance.

  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, and the third control valve 73 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. At this time, part of the exhaust gas discharged from the combustion chamber 22 of the first bank 12 bypasses the turbine 69 of the turbocharger 67 and is discharged to the first exhaust pipe 57 through the bypass pipe 72. Therefore, an appropriate amount of exhaust gas flows into the first exhaust pipe 57 without the turbine 69 becoming exhaust resistance.

  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, opens the second control valve 65, and opens the third control valve 73 in step S27. State.

  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 in the open state and the second control valve 65 in the closed state in step S28. The opening of the third control valve 73 is controlled according to the supercharging pressure. 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.

  At this time, the first control valve 64 is in an open state, and the opening degree of the third control valve 73 is adjusted according to the supercharging pressure, so that the exhaust gas from the cylinder groups of the first and second banks 12 and 13 Almost all the turbocharger 67 is introduced into the turbocharger 67, and the supercharging pressure by the turbocharger 67 is surely increased, resulting in higher output.

  Thus, in the internal combustion engine of the present embodiment, in the V-type 6-cylinder engine, a cylinder group in which a plurality of cylinders are divided and arranged in the first bank 12 and the second bank 13 on the left and right sides 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 turbocharger 67 is mounted on the first bank 12 side, and the downstream side of the turbine 69 and the communication pipe 63 in the first exhaust pipe 57 on the first bank 12 side having the turbocharger 67 are configured. And communicating with the bypass pipe 72 The third control valve 73 for adjusting the flow rate of the exhaust gas to the bypass pipe 72 is provided, and the respective control valves 64,65,73 in accordance with the engine operating condition-off controllable by ECU 81.

  Accordingly, the first and second exhaust valves 57 and 58 are opened and closed by the first and second control valves 64 and 65 and the bypass pipe 72 is opened and closed by the third control valve 73 according to the operating state of the engine. In the first exhaust pipe 57 in the cylinder group of the first bank 12 having the turbocharger 67, the exhaust gas discharged from the combustion chamber 22 bypasses the turbine 69 by the bypass pipe 72 and communicates with the first exhaust pipe 57. By flowing into the pipe 63, the pressure of the exhaust gas in the cylinder group of the first bank 12 having the turbocharger 67 is reduced, and the back pressure in the cylinder group of the left and right banks 12, 13 is made uniform, The stable exhaust purification performance of the front three-way catalyst 59, 60 in the cylinder group of each bank 12, 13 can be ensured.

  Specifically, the ECU 81 closes the first control valve 64 in the first exhaust pipe 57 of the cylinder group of the first bank 12 having the turbocharger 67 during the cold start of the engine, while turning the turbocharger on. The second control valve 65 in the second exhaust pipe 58 of the cylinder group of the second bank 13 that is not provided is opened, and the third control valve 73 is opened. Therefore, the exhaust gas discharged from the cylinder group of the first bank 12 to the first exhaust pipe 57 flows to the second exhaust pipe 58 through the communication pipe 63 and is discharged from the cylinder group of the second bank 13 to the second exhaust pipe 58. By joining the exhaust gas and flowing into the second front-stage three-way catalyst 60, the second front-stage three-way catalyst 60 can be efficiently warmed up by a large amount of exhaust gas.

  At this time, a part of the exhaust gas discharged to the first exhaust pipe 57 of the first bank 12 flows to the turbine 69 side, and the exhaust pressure on the upstream side of the first control valve 64 tends to be high. Since the exhaust gas that has passed through 69 flows to the communication pipe 63 through the bypass pipe 72, it is possible to prevent the back pressure from rising and to prevent the exhaust gas from leaking downstream from the first control valve 64. Therefore, the exhaust gas from the combustion chamber 22 of the first bank 12 properly flows to the second front-stage three-way catalyst 60 side, and it is possible to suppress the deterioration of the exhaust purification performance, and in the first exhaust pipe 57. By reducing the back pressure, the exhaust pressure difference between the left and right banks 12 and 13 can be reduced, and the output torque difference can be reduced to prevent engine vibration.

  The ECU 81 opens the first and second control valves 64 and 65 and also opens the third control valve 73 when the engine is idling. Therefore, 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. Since the exhaust gas flows into the first front-stage three-way catalyst 59 and the second front-stage three-way catalyst 60 and heats appropriately, the front-stage three-way catalysts 59, 60 are kept warm and properly maintained in the activated state. can do. Further, part of the exhaust gas discharged from the combustion chamber 22 of the first bank 12 bypasses the turbine 69 of the turbocharger 67 and is discharged to the first exhaust pipe 57 through the bypass pipe 72. Thus, an appropriate amount of exhaust gas flows into the first front-stage three-way catalyst 59 without the exhaust resistance of the turbine 69, and the exhaust pressure difference between the left and right banks 12, 13 can be reduced.

  Further, the ECU 81 opens the first control valve 64 in the first exhaust pipe 57 of the cylinder group of the first bank 12 having the turbocharger 67 during the high load operation of the engine, but does not have the turbocharger. The second control valve 65 in the second exhaust pipe 58 of the cylinder group of the second bank 13 is closed, and the opening degree of the third control valve 73 is controlled according to the supercharging pressure. Therefore, the exhaust gas discharged from the combustion chamber 23 of the second bank 13 to the second exhaust pipe 58 flows to the first exhaust pipe 57 through the communication pipe 63, and the exhaust gas discharged from the combustion chamber 22 of the first bank 12. As a result, almost the entire amount of exhaust gas is introduced into the turbocharger 67, and the supercharging pressure by the turbocharger 67 is increased, and the output can be reliably improved.

  Further, the ECU 81 opens the first and second control valves 64 and 65 and opens the third control valve 73 when the NOx storage reduction catalyst 62 is warmed up or regenerated, and the cylinder group of the first bank 12 is opened. The air / fuel ratio of the second bank 13 is changed to a lean air / fuel ratio while the air / fuel ratio of the second bank 13 is changed to a lean air / fuel ratio. Therefore, the rich air-fuel ratio exhaust gas discharged from the combustion chamber 22 of the first bank 12 flows to the first exhaust pipe 57, while the lean air-fuel ratio exhaust gas discharged from the combustion chamber 23 of the second bank 13 is the first exhaust gas. 2, the lean air-fuel ratio exhaust gas and the rich air-fuel ratio exhaust gas flow from the exhaust pipes 57, 58 to the exhaust collecting pipe 61, and join in the NOx occlusion reduction type catalyst 62 to generate oxidation heat. When the reaction occurs, the NOx occlusion reduction catalyst 62 can be appropriately heated to perform sulfur poisoning regeneration.

  At this time, part of the exhaust gas discharged from the combustion chamber 22 of the first bank 12 bypasses the turbine 69 of the turbocharger 67 and is discharged to the first exhaust pipe 57 through the bypass pipe 72. Therefore, the turbine 69 does not become exhaust resistance and an appropriate amount of exhaust gas flows into the first exhaust pipe 57. By reducing the difference in exhaust pressure between the left and right banks 12, 13, the lean air in the communication pipe 63 is reduced. Mixing of the exhaust gas of the fuel ratio and the exhaust gas of the rich air-fuel ratio is suppressed, and the NOx storage-reduction catalyst 62 is appropriately joined by combining the lean air-fuel ratio exhaust gas and the rich air-fuel ratio exhaust gas by the NOx storage reduction catalyst 62. The sulfur poisoning regeneration of the type catalyst 62 can be performed efficiently.

  In each of the above-described embodiments, the turbocharger of the present invention is a general turbocharger, but may be a variable capacity turbocharger. In this case, at the time of supercharging by the variable capacity turbocharger, the first control valve 64 is opened, the second control valve 65 is closed, and the opening degree of the third control valve 73 is controlled according to the supercharging pressure. The boost pressure by the variable capacity turbocharger can be increased, and the output can be improved with certainty. On the other hand, at the time of natural supercharging which does not require supercharging by the variable capacity turbocharger, the first control valve 64 is closed, the second control valve 65 is opened, and the third control valve 73 is opened. It is possible to prevent the exhaust gas from leaking by preventing the back pressure on the side of the exhaust pipe 57 from increasing, and to improve the response of the variable capacity turbocharger when switching to supercharging.

  In each of the above-described embodiments, a 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. Further, the fuel injection type of the internal combustion engine is the in-cylinder injection type, but it may be a port injection type, and the combustion mode may not be a lean combustion type, and in this case, the NOx occlusion reduction type catalyst becomes unnecessary. .

  As described above, the internal combustion engine according to the present invention is provided with three control valves in the exhaust system, and changes the exhaust passage by opening and closing each control valve according to the operating state of the internal combustion engine. This makes it possible to ensure stable exhaust purification performance in the left and right cylinder groups regardless of the presence or absence, and 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 an embodiment of the present invention. It is a schematic sectional drawing of the V type 6 cylinder engine of a present Example. It is a flowchart showing the operation control by the V type 6 cylinder engine of a present Example.

Explanation of symbols

12 First bank 13 Second bank 16, 17 Piston 20, 21 Cylinder head 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 55, 56 Collecting passage 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 Bypass pipe (bypass passage)
73 Third control valve (bypass valve)
74,75 Injector 79,80 Spark plug 81 Electronic control unit, ECU (control means, air-fuel ratio changing means)

Claims (5)

  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, 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 in which a supercharger is provided only in one of the two cylinder groups, the downstream side of the supercharger in the exhaust passage of the cylinder group having the supercharger communicates with the communication passage by a bypass passage. In addition, a bypass valve for adjusting the flow rate of the exhaust gas is provided in the bypass passage, and the control valve and the bypass valve can be controlled to open and close according to the operating state of the internal combustion engine by the control means. Internal combustion engine, characterized in that.   2. The internal combustion engine according to claim 1, wherein the control unit closes the control valve in the exhaust passage of the cylinder group having the supercharger when the internal combustion engine is cold-started. An internal combustion engine characterized by opening the control valve in the exhaust passage of the cylinder group not having the cylinder group and opening the bypass valve.   2. The internal combustion engine according to claim 1, wherein the control means opens the control valves and opens the bypass valves during idle operation of the internal combustion engine.   2. The internal combustion engine according to claim 1, wherein the control unit opens the supercharger while opening the control valve in the exhaust passage of a cylinder group having the supercharger during high load operation of the internal combustion engine. An internal combustion engine characterized in that the control valve in the exhaust passage of a cylinder group that does not have is closed, and the degree of opening of the bypass valve is controlled according to supercharging pressure.   2. The internal combustion engine according to claim 1, wherein downstream ends of the exhaust passages merge to provide an exhaust collecting passage, a NOx occlusion reduction type catalyst is provided in the exhaust collecting passage, and the two cylinder groups are connected to each other. Air-fuel ratio changing means for changing the air-fuel ratio is provided, and the control means opens the control valves and opens the bypass valves when the NOx storage reduction catalyst is warmed up. An internal combustion engine characterized in that the air-fuel ratio of one cylinder group is changed to a rich air-fuel ratio, while the air-fuel ratio of the other cylinder group is changed to a lean air-fuel ratio.

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