JP2008231953A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the exhaust emission control performance by collecting particulate matter contained in the exhaust gas and suppress the lowering of the output due to the rise of the back pressure in the exhaust gas passage in an internal combustion engine. <P>SOLUTION: This internal combustion engine comprises cylinder groups in which a plurality of cylinders are selectively arranged on the left and right first and second banks 12, 13, respectively. First and second exhaust pipes 57, 58 are connected to the cylinder groups of the banks 12, 13, respectively. First and second preceding-stage three-way catalytic converters 59, 60 and first and second control valves 65, 66 are installed in the exhaust pipes 57, 58, respectively. A particulate filter 61 is installed in the second exhaust pipe 58. The upstream sides of the preceding-stage three-way catalytic converters 59, 60, the particulate filter 61, and the control valves 65, 66 in the exhaust pipes 57, 58 are made to communicate with each other through a communication pipe 64. An engine ECU 112 can controllably open and close the control valves 65, 66 according to the operating conditions. <P>COPYRIGHT: (C)2009,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.

  By the way, exhaust gas discharged from the engine includes particulate matter such as graphite and unburned fuel, so-called PM (Particulate Matter), in addition to HC, CO, NOx and the like. In particular, when the engine is cold started, the combustion vibration is large, and therefore, it is necessary to burn it as a rich air-fuel ratio for a predetermined period. The amount of oxygen in the mixture in the combustion chamber is insufficient, and unburned fuel that cannot be burned (fuel Unburned residue) is discharged as particulate matter. In addition, in an engine having a NOx occlusion reduction type catalyst that can occlude NOx in the exhaust gas at the lean air-fuel ratio in the exhaust pipe, the occluded NOx is released at the time of rich spike control in which the oxygen concentration in the exhaust gas is reduced. Therefore, at this time, the amount of oxygen in the air-fuel mixture in the combustion chamber is insufficient and the unburned fuel is discharged as particulate matter. Further, even during sulfur poisoning regeneration control for releasing the sulfur component stored in the NOx storage reduction catalyst, the amount of oxygen in the air-fuel mixture in the combustion chamber is insufficient and unburned fuel is discharged as particulate matter.

  Thus, it has been proposed to install a particulate filter in the exhaust pipe in order to process PM discharged from the engine. This particulate filter can collect particulate matter such as black smoke in the exhaust gas exhausted from the engine, and the particulate matter collected by the filter at high temperature when the vehicle is accelerating or traveling at high speed. Re-burn with the exhaust gas.

  In addition, there exists a thing described in the following patent document 1 as an internal combustion engine as mentioned above.

Japanese Patent Laid-Open No. 08-121153

  As described above, in the conventional V-type multi-cylinder engine, since particulate matter (PM) is contained in the exhaust gas, a particulate filter is attached to the exhaust pipe, and particles in the exhaust gas are caused by this particulate filter. The particulate matter is collected, and the collected particulate matter is reburned by exhaust gas that has become hot. However, since the particulate matter in the exhaust gas is collected by the particulate filter, there is a problem that the filter is clogged, the back pressure is increased, and the output performance is lowered. In this case, although the particulate matter collected by the particulate filter is periodically reburned and removed, it is difficult to avoid a decrease in output due to a temporary increase in back pressure.

  The present invention is intended to solve such problems, and it is possible to collect particulate matter contained in exhaust gas so as to improve exhaust purification performance and to increase output due to an increase in back pressure in the exhaust passage. It aims at providing the internal combustion engine which can suppress a fall.

  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, the upstream purification catalyst is provided in each exhaust passage, and the particulate filter is provided in one of the exhaust passages. An exhaust control valve for adjusting the flow rate of the exhaust gas is provided, the upstream purification catalyst, the particulate filter, and the upstream side of each exhaust control valve in each exhaust passage communicate with each other through a communication passage, and the control means is in an operating state. Accordingly, the exhaust control valve can be controlled to open and close.

  In the internal combustion engine of the present invention, a supercharger is provided in the exhaust passage where the particulate filter is not provided in each exhaust passage, between the communication passage and the upstream purification catalyst. It is said.

  In the internal combustion engine of the present invention, the control means closes the exhaust control valve in the exhaust passage of the cylinder group having the supercharger while the internal combustion engine is cold-started, while the cylinder having the particulate filter The exhaust control valve in the exhaust passage of the group is opened.

  In the internal combustion engine of the present invention, the control means retards the ignition timing and changes the air-fuel ratio to a lean air-fuel ratio when the internal combustion engine is cold-started.

  In the internal combustion engine of the present invention, the control means is configured such that the temperature of the post-stage purification catalyst provided in the exhaust collecting passage where the downstream ends of the exhaust passages merge is equal to or higher than a predetermined temperature set in advance, or The exhaust passage of the cylinder group having the supercharger when the particulate matter collected by the particulate filter is equal to or less than a predetermined amount set in advance or the internal combustion engine load is equal to or greater than a predetermined value set in advance. The exhaust control valve is opened while the exhaust control valve in the exhaust passage of the cylinder group having the particulate filter is closed.

  In the internal combustion engine of the present invention, the control means controls the exhaust control in the exhaust passage of the cylinder group having the supercharger when the air-fuel ratio is a rich air-fuel ratio when the internal combustion engine is started from a warm-up state. While the valve is closed, the exhaust control valve in the exhaust passage of the cylinder group having the particulate filter is opened.

  In the internal combustion engine of the present invention, a communication control valve for adjusting the flow rate of the exhaust gas is provided in the communication passage, and a NOx occlusion reduction type purification catalyst is provided in the exhaust collecting passage where the downstream ends of the exhaust passages merge. The control means closes the communication control valve while opening the sulfur poisoning regeneration control for releasing the sulfur component stored in the NOx storage reduction purification catalyst, and opens the exhaust control valves, The air-fuel ratio of the cylinder group having the supercharger is changed to a lean air-fuel ratio, while the air-fuel ratio of the cylinder group having the particulate filter is changed to a rich air-fuel ratio.

  In the internal combustion engine of the present invention, a communication control valve for adjusting the flow rate of the exhaust gas is provided in the communication passage, and a NOx occlusion reduction type purification catalyst is provided in the exhaust collecting passage where the downstream ends of the exhaust passages merge. The control means opens the communication control valve during execution of NOx reduction control for reducing NOx stored in the NOx storage reduction purification catalyst, and the control means opens the communication passage in the exhaust passage of the cylinder group having the supercharger. While the exhaust control valve is closed, the exhaust control valve in the exhaust passage of the cylinder group having the particulate filter is opened, and the air-fuel ratio of each cylinder group is changed to a rich air-fuel ratio.

  In the internal combustion engine of the present invention, a communication control valve for adjusting the flow rate of the exhaust gas is provided in the communication passage, and a NOx occlusion reduction type purification catalyst is provided in the exhaust collecting passage where the downstream ends of the exhaust passages merge. The control means closes the communication control valve, opens the exhaust control valves, and opens the supercharger during execution of NOx reduction control for reducing NOx stored in the NOx storage reduction purification catalyst. The air-fuel ratio of the cylinder group having the particulate filter is changed to a stoichiometric air-fuel ratio, while the air-fuel ratio of the cylinder group having the particulate filter is changed to a rich 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. In addition, a particulate filter is provided in one of the exhaust passages, the purification catalyst, the particulate filter, and the upstream side of each control valve in each exhaust passage communicate with each other through the communication passage, and the control means is in an operating state. Accordingly, the exhaust control valve can be controlled to open and close.

  Therefore, when the control means controls the opening and closing of the exhaust control valve, when there is a large amount of particulate matter contained in the exhaust gas, the exhaust gas flows into the exhaust passage on one side and the particulate matter is collected by the particulate filter. On the other hand, when the particulate matter contained in the exhaust gas is small, the exhaust gas flows into the exhaust passage on the other side and does not pass through the particulate filter, so that the back pressure does not increase and is contained in the exhaust gas. It is possible to collect particulate matter and improve exhaust purification performance, and it is possible to suppress a decrease in output due to an increase in back pressure in the exhaust passage.

  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 schematic configuration diagram of a hybrid vehicle to which the V-type 6-cylinder engine of the first embodiment is applied.

  In the first embodiment, a V-type 6-cylinder engine is applied as the internal combustion engine, and a hybrid vehicle is configured by the V-type 6-cylinder engine and an electric motor that outputs torque by supplying electric power.

  First, the overall configuration of this hybrid vehicle will be described in detail. In the hybrid vehicle of the first embodiment, as shown in FIG. 4, a V-type 6-cylinder engine (hereinafter referred to as an engine) 101 and an electric motor (motor generator) 102 are mounted on the vehicle as power sources. The vehicle is also equipped with a generator (motor generator) 103 that receives the output of the engine 101 and generates electric power. The engine 101, the electric motor 102, and the generator 103 are connected by a power split mechanism 104. The power split mechanism 104 distributes the output of the engine 101 to the generator 103 and the drive wheel 105, transmits the output from the electric motor 102 to the drive wheel 105, and drives through the speed reducer 106 and the drive shaft 107. It functions as a transmission related to the driving force transmitted to the wheels 105.

  The electric motor 102 is an AC synchronous motor and is driven by AC power. The inverter 108 converts electric power stored in the battery 109 from direct current to alternating current and supplies it to the electric motor 102, and also converts electric power generated by the generator 103 from alternating current to direct current and stores it in the battery 109. It is. The generator 103 has basically the same configuration as the electric motor 102 described above, and has a configuration as an AC synchronous motor. In this case, the electric motor 102 mainly outputs the driving force, whereas the generator 103 mainly receives the output of the engine 101 and generates electric power.

  The electric motor 102 mainly generates driving force, but can also generate electric power (regenerative power generation) by using the rotation of the driving wheel 105, and can also function as a generator. At this time, since a brake (regenerative brake) acts on the drive wheel 105, the vehicle can be braked by using this in combination with a foot brake or an engine brake. On the other hand, the generator 103 generates electric power mainly by receiving the output of the engine 101, but can also function as an electric motor driven by receiving electric power of the battery 109 via the inverter 108.

  A crank position sensor 111 that detects a crank angle is provided on the crankshaft 110 of the engine 101. The crank position sensor 111 is connected to an engine ECU 112. The engine ECU 112 discriminates intake, compression, expansion (explosion), and exhaust strokes in each cylinder based on the detected crank angle, and determines the engine speed. Calculated. The drive shafts 113 and 114 of the electric motor 102 and the generator 103 are provided with rotation speed sensors 115 and 116 for detecting the rotation position and the rotation speed, respectively. The rotational speed sensors 115 and 116 are connected to the motor ECU 117, and output the detected rotational positions and rotational speeds of the drive shafts 113 and 114 to the motor ECU 117.

  The power split mechanism 104 described above is constituted by a planetary gear unit. That is, the power split mechanism (planetary gear unit) 104 includes a sun gear 201, a plurality of planetary gears 202 arranged around the sun gear 201, a gear carrier 203 that holds the planetary gears 202, and a planetary gear 202 on the outer periphery. The ring gear 204 is arranged. The crankshaft 110 of the engine 101 is coupled to the gear carrier 203 via the central shaft 205, and the output of the engine 101 is input to the gear carrier 203 of the planetary gear unit 104. The electric motor 102 has a stator 206 and a rotor 207 inside, and the rotor 207 is coupled to the ring gear 204 via the drive shaft 113, and the rotor 207 and the ring gear 204 are reduced via a gear unit (not shown). 106. The speed reducer 106 transmits the output input from the electric motor 102 to the ring gear of the planetary gear unit 104 to the drive shaft 107, and the electric motor 102 is always connected to the drive shaft 107.

  Similarly to the electric motor 102 described above, the generator 103 has a stator 208 and a rotor 209 inside, and the rotor 209 is coupled to the sun gear 201 via a drive shaft 114 and a gear unit (not shown). Yes. That is, the output of the engine 101 is divided by the planetary gear unit 104 and input to the rotor 209 of the generator 103 via the sun gear 201. The output of the engine 101 is divided by the planetary gear unit 104 and can be transmitted to the drive shaft 107 via the ring gear 204 or the like.

  Then, by controlling the amount of power generated by the generator 103 to control the rotation of the sun gear 201, the entire planetary gear unit 104 can be used as a continuously variable transmission. That is, the output of the engine 101 or the electric motor 102 is output to the drive shaft 107 after being shifted by the planetary gear unit 104. Further, the number of revolutions of the engine 101 can be controlled by controlling the power generation amount of the generator 103 (power consumption when functioning as an electric motor). Note that when the rotation speeds of the electric motor 102 and the generator 103 are controlled, the motor ECU 117 controls the inverter 108 with reference to the outputs of the rotation speed sensors 115 and 116, thereby the engine 101. The number of rotations can also be controlled.

  The various controls described above are controlled by a plurality of electronic control units (ECUs). The driving by the engine 101 and the driving by the electric motor 102 and the generator 103, which are characteristic of a hybrid vehicle, are comprehensively controlled by the main ECU 118. That is, the distribution of the output of the engine 101 and the output of the electric motor 102 and the generator 103 is determined by the main ECU 118 according to the driving state of the vehicle with respect to the driver's requested output, and the engine 101, the electric motor 102, and the generator 103 are determined. Control commands are output to the engine ECU 112 and the motor ECU 117.

  Further, the engine ECU 112 and the motor ECU 117 also output information on the engine 101, the electric motor 102, and the generator 103 to the main ECU 118. The main ECU 118 is also connected to a battery ECU 119 that controls the battery 109 and a brake ECU 120 that controls the brake. The battery ECU 119 monitors the state of charge of the battery 109 and outputs a charge request command to the main ECU 118 when the amount of charge is insufficient. Receiving the charge request, the main ECU 118 controls the generator 103 to generate power so that the battery 109 is charged. The brake ECU 120 controls the vehicle and controls the regenerative braking by the electric motor 102 together with the main ECU 118.

  Since the hybrid vehicle of the first embodiment is configured as described above, the necessary output required for the entire vehicle is distributed to the engine 101 and the electric motor 102 (generator 103) while the hybrid vehicle is operating. By doing so, it is possible to satisfy the output required for the entire vehicle while controlling the operation state of the engine 101 to a desired operation state.

  Next, the configuration of the V-type six-cylinder engine 101 in the hybrid vehicle of the first embodiment described above will be described in detail. In the V-type 6-cylinder engine 101 in the hybrid vehicle of the first embodiment, 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. A plurality of cylinders are provided at 12 and 13 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 (front purification catalyst) 59 is attached to the first exhaust pipe 57, while a second front three-way catalyst (front purification catalyst) 60 and a partition are attached to the second exhaust pipe 58. A curate filter 61 is attached. In this case, in the second exhaust pipe 58, the second front three-way catalyst 60 is disposed upstream in the flow direction of the exhaust gas, and the particulate filter 61 is disposed downstream. The first and second exhaust pipes 57 and 58 are connected at their downstream ends to the exhaust collecting pipe 62, and a NOx occlusion reduction type catalyst (rear stage purification catalyst) 63 is attached to the exhaust collecting pipe 62. Has been.

  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 particulate filter 61 captures graphite, unburned fuel (SOF: flammable organic components), engine oil burnout (oil ash), etc. as particulate matter (PM), which is particulate matter in the exhaust gas. To collect. Then, the particulate matter collected by the particulate filter 61 is reburned by spontaneous ignition or forced regeneration of the particulate filter 61, and the particulate filter 61 is regenerated. In this case, the spontaneous ignition of the particulate filter 61 is performed when the engine 101 is operated in a high rotation and high load state, the exhaust gas temperature becomes the ignition temperature of the particulate matter (for example, 600 ° C.), and the particulate matter spontaneously Ignite and burn. On the other hand, forced regeneration of the particulate filter 61 is performed by heating the particulate filter 61 by changing the air-fuel ratio to rich when the amount of accumulated particulate matter exceeds a predetermined amount, and forcibly igniting the deposited particulate matter. And burn.

  The NOx occlusion reduction type catalyst 63 is a NOx occlusion reduction type three-way catalyst, and simultaneously purifies HC, CO, and NOx contained in the exhaust gas by an oxidation reduction reaction when the exhaust air-fuel ratio is stoichiometric. NOx contained in the exhaust gas is temporarily stored when the exhaust air-fuel ratio is lean, and the stored NOx is released when it is in the rich combustion region or stoichiometric combustion region where the oxygen concentration in the exhaust gas is reduced In addition, NOx is reduced by the added fuel as a reducing agent.

  The upstream side of the first exhaust pipe 57 and the second exhaust pipe 58 is connected by a communication pipe (communication path) 64 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. The first exhaust pipe 57 and the second exhaust pipe 58 have a first control valve 65 and a second control valve as exhaust control valves on the downstream side of the upstream three-way catalysts 59 and 60 in the exhaust gas flow direction. 66 is attached. The first and second control valves 65 and 66 are flow rate 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 thereof.

  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 64 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 a main ECU 118 in addition to the engine ECU 112 described above. The engine ECU 112 can control the fuel injection timing of the injectors 72 and 73, the ignition timing of the spark plugs 77 and 78, and the like. The fuel injection amount, the injection timing, the ignition timing, and the like are determined based on the engine operating state such as the intake air amount, the intake air temperature, the throttle opening, the accelerator opening, the engine speed, and the cooling water temperature.

  That is, an airflow sensor 81 and an intake air temperature sensor 82 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 engine ECU 112. The electronic throttle device 54 is provided with a throttle position sensor 83, which outputs the current throttle opening to the engine ECU 112. Further, the crankshaft 110 is provided with a crank angle sensor 111, which outputs the detected crank angle to the engine ECU 112. The engine ECU 112 calculates the engine speed based on the crank angle. Further, the cylinder block 11 is provided with a water temperature sensor 84 and outputs the detected engine cooling water temperature to the engine ECU 112. The accelerator pedal is provided with an accelerator position sensor 85 and outputs the current accelerator opening to the main ECU 118.

  Therefore, as shown in FIG. 4, the main ECU 118 controls the engine 101 via the engine ECU 112 and the electric motor 102 and the generator 103 via the motor ECU 117 in response to a driver's request. That is, the main ECU 118 sets a required output based on the accelerator opening, and the distribution of the output of the engine 101 and the output of the electric motor 102 is determined so as to achieve the maximum efficiency according to the travel stop state of the vehicle. 101, and the motor ECU 117 controls the electric motor 102.

  For example, when the vehicle starts or travels at low and medium speeds, the fuel is cut or the engine 101 is stopped in a region where the engine efficiency deteriorates, and the driving wheels 105 are driven only by the electric motor 102 (eco-run traveling). During normal running, the output of the engine 101 is divided into one system path by the power split mechanism 104, one of them is sent to the generator 103 to generate power, and the electric motor 102 is driven by the power to drive the driving wheels 105, while the other The driving wheel 105 is directly driven by the engine 101 and the electric motor 102 travels. At the time of sudden acceleration (at the time of high load), in addition to the control at the time of normal traveling, the electric motor 102 receives power from the battery 109 and drives the drive wheels 105 to travel. At the time of deceleration or braking, the electric motor 102 is driven by the driving wheel 105, and the electric motor 102 is operated as a generator and also acts as a regenerative brake, and the collected electric power is charged in the battery 109. When the battery is charged, the output of the engine 101 is sent to the generator 103 via the power split mechanism 104 to generate power, and the power is stored in the battery 109.

  The engine ECU 112 distributes the fuel injection amount, the injection timing, and the ignition timing based on the engine operation state such as the intake air amount, the intake air temperature, the throttle opening, the engine speed, and the cooling water temperature in addition to the engine output distribution from the main ECU 118. The injectors 72 and 73 and the spark plugs 77 and 78 are controlled.

  In addition, A / F sensors 86 and 87 are provided upstream of the upstream three-way catalysts 59 and 60 in the exhaust pipes 57 and 58, respectively. The A / F sensors 86 and 87 are oxygen sensors having a linear output characteristic 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 engine ECU 112. The engine ECU 112 executes air-fuel ratio feedback control based on the exhaust air-fuel ratio detected by the A / F sensors 86 and 87.

  Further, the engine ECU 112 can control the intake variable valve mechanism 40, 41 and the exhaust variable valve mechanism 42, 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.

  In the V-type six-cylinder engine 101 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. The exhaust pipe 57 and the second exhaust pipe 58 are provided with the first and second upstream three-way catalysts 59 and 60, the particulate filter 61, and the first and second control valves 65 and 66. The upstream portion is communicated by a communication pipe 64. Therefore, the engine ECU 112 can change the exhaust gas discharge path by controlling the opening and closing of the control valves 65 and 66 according to the engine operating state.

  For example, when the engine 101 is cold-started, the first control valve 65 is closed, while the second control valve 66 is opened, and the first exhaust pipe passes from the cylinder group of the first bank 12 through the collecting passage 55. After exhaust gas discharged to 57 is bypassed to the second exhaust pipe 58 through the communication pipe 64, exhaust gas from the cylinder groups of the first and second banks 12 and 13 is merged in the second exhaust pipe 58. 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. Further, at this time, exhaust gas discharged from the cylinder groups of the first and second banks 12 and 13 is passed through the particulate filter 61 of the second exhaust pipe 58, so that the exhaust gas generated in the cold start is increased. PM is collected by the particulate filter 61. At the cold start, the air-fuel ratio is changed to a slightly lean state so that the exhaust gas discharged from the cylinder groups of the banks 12 and 13 becomes an oxygen surplus state, and the PM accumulated in the particulate filter 61 is burned. is doing.

  Thereafter, when the warm-up of the second pre-stage three-way catalyst 60 is completed and activated, the first control valve 65 is opened, the second control valve 66 is closed, and the cylinders of 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 64, the exhaust from the cylinder groups of the first and second banks 12 and 13 is performed. 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. At this time, the exhaust gas discharged from the cylinder groups of the first and second banks 12 and 13 is passed through the first exhaust pipe 57 without the particulate filter, but the engine 101 has already been warmed up and the exhaust gas is exhausted. There is almost no PM in the gas.

  Similarly, after the warm-up of the engine 101 and each of the preceding three-way catalysts 59 and 60 and in a high load state of the engine 101, the first control valve 65 is similarly opened while the second control valve 66 is closed. State. Then, the exhaust gas discharged from the cylinder group of the second bank 13 to the second exhaust pipe 58 via the collecting passage 56 is bypassed to the first exhaust pipe 57 through the communication pipe 64, so that 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. High supercharging is possible and output is improved.

  Further, the engine ECU 112 sets the exhaust gas from the cylinder group of the first bank 12 to a lean atmosphere and the exhaust gas from the cylinder group of the second bank 13 to a rich atmosphere, and the first control valve 65 and the second control valve. 66, the exhaust gas in the lean atmosphere exhausted from the cylinder group of the first bank 12 is caused to flow to the first exhaust pipe 57, and the exhaust gas in the rich atmosphere exhausted from the cylinder group of the second bank 13 is made into the second state. The exhaust gas is allowed to flow through the exhaust pipe 58, and is joined by the exhaust collecting pipe 62 so as to flow into the NOx occlusion reduction type catalyst 63. Then, the NOx occlusion reduction catalyst 63 is warmed up using the oxidation exothermic reaction in the NOx occlusion reduction catalyst 63, or the sulfur component accumulated in the NOx occlusion reduction catalyst 63 is released and regenerated. .

  Further, the engine ECU 112 brings the exhaust gas from the cylinder groups of the first and second banks 12 and 13 into a rich atmosphere, closes the first control valve 65, and opens the second control valve 66, By bypassing the exhaust gas discharged from the cylinder group of one bank 12 through the collecting passage 55 to the first exhaust pipe 57 to the second exhaust pipe 58 through the communication pipe 64, the first and second banks 12, 13 After exhaust gas from the cylinder group is merged in the second exhaust pipe 58, a large amount of exhaust gas is caused to flow into the NOx occlusion reduction type catalyst 63 through the exhaust collecting pipe 62. When the air-fuel ratio is in the rich combustion region, the stored NOx is released, and NOx is reduced by the added fuel as a reducing agent.

  Further, when the engine ECU 112 operates the exhaust gas from the cylinder groups of the first and second banks 12 and 13 in a rich atmosphere, the engine ECU 112 closes the first control valve 65 and opens the second control valve 66. The exhaust gas discharged from the cylinder group of the first bank 12 through the collecting passage 55 to the first exhaust pipe 57 is bypassed to the second exhaust pipe 58 through the communication pipe 64, whereby the first and second banks 12 , 13 after the exhaust gas from the cylinder group is merged in the second exhaust pipe 58, a large amount of exhaust gas is allowed to flow into the particulate filter 61.

  Here, the operation of the V-type 6-cylinder engine applied to the hybrid vehicle 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 72 and 73 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 77 and 78 are ignited 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 contained harmful substances are purified and flow into the exhaust collecting pipe 62. 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 contained harmful substances are purified and flow into the exhaust collecting pipe 62. The exhaust gas flowing into the exhaust collecting pipe 62 warms and activates the NOx occlusion reduction type catalyst 63 and releases the remaining harmful substances to the atmosphere after being appropriately purified.

  Here, the opening / closing control of the control valves 65 and 66 in the V-type 6-cylinder engine applied to the hybrid vehicle 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 the ignition key switch (IG) is turned on and the engine is stopped. In this case, the engine ECU 112 determines IG-ON based on the ignition key signal from the main ECU 118, and determines engine stop based on the engine speed calculated based on the crank angle detected by the crank position sensor 111. Here, if the engine is IG-ON and the engine is stopped, the hybrid vehicle is driven by the electric motor 102.

  Therefore, in step S12, the first control valve 65 is closed and the second control valve 66 is opened. In step S13, it is determined whether or not there is a request for starting the engine 101. In this case, the main ECU 118 outputs the output of the engine 101 and the output of the electric motor 102 in accordance with the driver's request (accelerator opening detected by the accelerator opening selection 5) so that the traveling stop state of the vehicle becomes maximum efficiency. Therefore, the engine ECU 112 determines whether or not the engine 101 has been requested to start based on the engine start command from the main ECU 118. Here, if there is no request for starting the engine 101, the system waits in this state.

  If it is determined in step S13 that the engine 101 has been requested to be started, the engine 101 is started in step S14. Then, in the engine 101, 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 64, and the first and second banks 12, 13 After exhaust gas from the cylinder group is merged in the second exhaust pipe 58, this large amount of exhaust gas flows into the second front three-way catalyst 60 and the particulate filter 61. When the engine 101 is started, combustion in the combustion chambers 22 and 23 becomes unstable and a large amount of PM is generated. Exhaust gas containing this PM passes through the particulate filter 61 of the second exhaust pipe 58. Thus, PM in the exhaust gas is collected by the particulate filter 61.

  In step S15, it is determined whether or not there is a request for rapid warm-up control of the second front-stage three-way catalyst 60. In this case, when the engine 101 is cold-started, since the second pre-stage three-way catalyst 60 is in a low temperature state and does not reach the activation temperature of the exhaust gas, the ignition timing is greatly retarded and the ignition plug By igniting with 77, 78, the combustion energy of the fuel is reduced from being consumed for driving the engine 101, and the second front-stage three-way catalyst 60 is caused by flowing the exhaust gas to the second exhaust pipe 58 at a high temperature. Need to warm up quickly. Therefore, the engine ECU 112 determines that the engine is cold-started when the engine coolant temperature detected by the water temperature sensor 84 is lower than a predetermined temperature, and determines that there is a request for rapid warm-up control.

  If it is determined that the engine 101 is cold-started and there is a request for rapid warm-up control of the second front-stage three-way catalyst 60, the engine ECU 112 determines that the second front-stage three-way catalyst 60 is in step S16. Start rapid warm-up control. That is, the engine ECU 112 significantly retards the ignition timing of the spark plugs 77 and 78. Then, in the engine 101, the injectors 72, 73 inject fuel near the top dead center in the compression stroke, and the ignition plugs 77, 78 ignite in the expansion stroke. Less is consumed to drive. High-temperature exhaust gas discharged from the cylinder groups of the banks 12 and 13 flows into the second front-stage three-way catalyst 60 through the second exhaust pipe 58, and the second front-stage three-way catalyst 60 is rapidly warmed up.

  Further, when executing the rapid warm-up control of the second front-stage three-way catalyst 60, the engine ECU 112 changes the air-fuel ratio to lean. Then, the exhaust gas discharged from the cylinder groups of the banks 12 and 13 is in a high temperature and oxygen surplus state, and the PM deposited on the particulate filter 61 is burned and regenerated.

  Subsequently, in step S17, the current bed temperature in the NOx storage reduction catalyst 63 is estimated. In other words, after the engine 101 is started, the first control valve 65 is closed and the second control valve 66 is opened, so that the exhaust gas from the cylinder groups of the first and second banks 12 and 13 is completely exhausted. The exhaust gas flows through the second exhaust pipe 58, passes through the second front-stage three-way catalyst 60 and the particulate filter 61, flows from the exhaust collecting pipe 62 to the NOx occlusion reduction type catalyst 63, and the first front-stage three-way catalyst 59 of the first exhaust pipe 57. Remains in a cold state. Therefore, when the exhaust gas path is changed from the second exhaust pipe 58 to the first exhaust pipe 57 side, the exhaust gas flowing through the first exhaust pipe 57 is purified by the NOx occlusion reduction type catalyst 63, so that the NOx occlusion is performed. It is necessary to grasp the bed temperature of the reduction catalyst 63.

  Specifically, the engine ECU 112 estimates the bed temperature Tc of the NOx storage reduction catalyst 63 based on the integrated air amount calculated from the engine start calculated based on the intake air amount detected by the air flow sensor 81 and the engine load factor. To do. The engine load factor is calculated based on the intake air amount and the engine speed. F is a function caused by the bed temperature Tc of the NOx storage reduction catalyst 63.

  In step S18, the amount of particulate matter deposited on the particulate filter 61 is estimated. That is, when the engine 101 is cold-started, a lot of PM is contained in the exhaust gas, and the particulate filter 61 collects PM in the exhaust gas, while the subsequent rapid warm-up of the second front three-way catalyst 60 is performed. In the machine control, the PM deposited on the particulate filter 61 is burned and regenerated, and it is necessary to grasp the amount of PM deposited on the particulate filter 61 in order to reduce the flow resistance of the second exhaust pipe.

  Specifically, the engine ECU 112 estimates the PM accumulation amount Qp in the particulate filter 61 based on the fuel injection amount injected by the injectors 72 and 73 and the exhaust air-fuel ratio detected by the A / F sensors 86 and 87. . Note that F is a function resulting from the PM accumulation amount Qp in the particulate filter 61.

  In step S19, it is determined whether the estimated bed temperature Tc of the NOx storage reduction catalyst 63 is equal to or higher than a predetermined value (for example, catalyst activation temperature). Here, if it is determined that the bed temperature Tc of the NOx storage reduction catalyst 63 is equal to or higher than a predetermined value, it is estimated that the NOx storage reduction catalyst 63 is in an activated state, and the process proceeds to step S20. In step S20, it is determined whether or not the PM accumulation amount Qp in the estimated particulate filter 61 is equal to or less than a predetermined value set in advance. Here, if it is determined that the PM accumulation amount Qp is equal to or less than the predetermined value, it is estimated that the PM accumulated on the particulate filter 61 is almost burned and regenerated, and the process proceeds to step S21.

  On the other hand, in step S19, it is determined that the estimated bed temperature Tc of the NOx storage reduction catalyst 63 is not equal to or higher than a predetermined value, or in step S20, the estimated PM accumulation amount Qp in the particulate filter 61 is equal to or lower than a predetermined value. If determined not, the process returns to step S17 to repeat the process.

  In step S21, the engine ECU 112 ends the rapid warm-up control of the second front-stage three-way catalyst 60 and changes the air-fuel ratio to stoichiometric. In step S22, the engine ECU 112 opens the first control valve 65 and closes the second control valve 66. 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 64, and the exhaust gas from the cylinder group of the first and second banks 12 and 13 is exhausted. After the gases merge in the first exhaust pipe 57, a large amount of exhaust gas passes through the turbocharger 67, passes through the first front three-way catalyst 59, and flows through the exhaust collecting pipe 62 to the NOx occlusion reduction type catalyst 63.

  At this time, a large amount of exhaust gas from the cylinder groups of the first and second banks 12 and 13 is introduced into the turbocharger 67, so that the supercharging pressure by the turbocharger 67 is increased and the engine output is increased. Will improve. Further, exhaust gas discharged from the cylinder groups of the first and second banks 12 and 13 passes through the first exhaust pipe 57 without the particulate filter, but the engine 101 has already been warmed up, Since there is almost no PM, a large amount of PM is not discharged to the outside. Further, the first front three-way catalyst 59 of the first exhaust pipe 57 is in a low temperature state, but the NOx occlusion reduction type catalyst 63 has already been activated, so the exhaust gas is purified by the NOx occlusion reduction type catalyst 63. be able to.

  On the other hand, in step S11, even if the ignition key switch is in the OFF state or the ignition key switch is in the ON state, if the engine 101 has already been started, the process proceeds to step S22, and the engine ECU 112 The control valve 65 is opened and the second control valve 66 is closed.

  Further, if it is determined in step S15 that there is no request for the rapid warm-up control of the second pre-stage three-way catalyst 60, the engine 101 is already warmed up, not cold started, so only the electric motor 102 is used. It is determined that the vehicle has shifted from the eco-run traveling to the normal traveling using the engine 101 and the electric motor 102. In step S23, engine ECU 112 determines whether the air-fuel ratio is rich.

  That is, in the hybrid vehicle, when the engine 101 is started from the eco-run traveling to the normal traveling, the air-fuel ratio is made rich to improve the startability. When the engine 101 is driven at a rich air-fuel ratio, unburned fuel discharged from the combustion chambers 22 and 23 increases and a large amount of PM is generated. Therefore, when it is determined in step S23 that the air-fuel ratio is rich, the exhaust gas from the cylinder groups of the first and second banks 12 and 13 is maintained by maintaining the open / close state of the control valves 65 and 66. Flows into the second exhaust pipe 58, and the PM in the exhaust gas is collected by the particulate filter 61 when the exhaust gas containing PM passes through the particulate filter 61 of the second exhaust pipe 58.

  Thereafter, the air-fuel ratio of the engine 101 is changed to stoichiometric or lean, and when it is determined in step S23 that the air-fuel ratio is not rich, the process proceeds to step S22, and the engine ECU 112 opens the first control valve 65. Then, the second control valve 66 is closed.

  While the first control valve 65 is closed, the second control valve 66 is opened, and the exhaust gas from the cylinder groups of the first and second banks 12 and 13 is allowed to flow through the second exhaust pipe 58 in its entirety. When the engine 101 is driven, the turbocharger 67 cannot be operated and the output of the hybrid vehicle may be insufficient. In this case, the exhaust purification control of the engine 101 is preferentially executed, and the output (assist amount) of the electric motor 102 is increased to compensate for the insufficient output.

  As described above, in the first embodiment, in the hybrid vehicle equipped with the V-type six-cylinder engine 101 and the electric motor 102, a plurality of cylinders are divided and arranged in the first bank 12 and the second bank 13 on the left and right. A cylinder group is provided, and the intake pipe 51 is connected to the cylinder groups of the banks 12 and 13, while the first exhaust pipe 57 and the second exhaust pipe 58 are connected. The original catalyst 59 and the second front three-way catalyst 60 are provided, the first control valve 65 and the second control valve 66 are provided, the particulate filter 61 is provided in the second exhaust pipe 58, and the front stages in the exhaust pipes 57 and 58 are provided. The upstream side of the three-way catalyst 59, 60, the particulate filter 61, and the control valves 65, 66 communicates with the communication pipe 64 to constitute the engine 101, and the engine ECU 112 controls each control valve according to the operating state. 5,66 are you open and close control.

  Therefore, when the amount of PM contained in the exhaust gas is large, the first control valve 65 is closed, while the second control valve 66 is opened, and the exhaust gas from the cylinder groups of the banks 12 and 13 is secondly discharged. By flowing through the exhaust ring 58, PM can be collected by the particulate filter 61. On the other hand, when the PM contained in the exhaust gas is small, the first control valve 65 is opened, while the second control valve 66 is closed, and exhaust gas from the cylinder groups of the banks 12 and 13 is caused to flow through the first exhaust ring 57, so that the exhaust gas does not pass through the particulate filter 61, so that the back pressure does not increase. As a result, it is possible to efficiently collect PM contained in the exhaust gas and improve the exhaust purification performance, and it is possible to suppress a decrease in output due to an increase in the back pressure of the exhaust gas. .

  In the engine 101 according to the first embodiment, the particulate filter 61 is provided only on the second exhaust pipe 58 side, and the turbocharger 67 is provided only on the first exhaust pipe 57 side. Accordingly, when the exhaust gas contains a large amount of PM, the exhaust gas from the cylinder groups of the banks 12 and 13 can be caused to flow through the second exhaust ring 58 so that the particulate filter 61 can properly collect the PM. On the other hand, when the amount of PM contained in the exhaust gas is small, the turbocharger 67 is operated to generate a predetermined output by flowing the exhaust gas from the cylinder groups of the banks 12 and 13 to the first exhaust ring 57. Can be secured.

  In the first embodiment, when the engine 101 is cold started, the exhaust gas from the cylinder groups of the first and second banks 12 and 13 is caused to flow to the second exhaust pipe 58, so that a large amount is generated during the cold start. PM in the exhaust gas can be collected by the particulate filter 61, and the exhaust purification performance can be improved.

  Further, when the engine 101 is cold started, the ignition timing is retarded and the air-fuel ratio is changed to a lean air-fuel ratio. Accordingly, when the engine 101 is cold-started, the ignition timing of the spark plugs 77 and 78 is greatly retarded, thereby increasing the exhaust gas temperature discharged from the cylinder groups of the banks 12 and 13 and increasing the temperature of the exhaust gas. By flowing into the second front-stage three-way catalyst 60 from the second exhaust pipe 58, the second front-stage three-way catalyst 60 can be quickly warmed up. At this time, by changing the air-fuel ratio to weak lean, the exhaust gas discharged from the cylinder groups of the banks 12 and 13 becomes a high-temperature and oxygen surplus state, and accumulates on the particulate filter 61. The PM that is present can be burned early, and the particulate filter 61 can be reliably regenerated.

  Further, in the first embodiment, the estimated bed temperature Tc of the NOx occlusion reduction type catalyst 63 is predetermined from the state in which the exhaust gas from the cylinder groups of the first and second banks 12 and 13 is flowing into the second exhaust pipe 58. When the PM accumulation amount Qp in the particulate filter 61 becomes equal to or less than a predetermined value and the regeneration is completed, the first control valve 65 is opened while the second control valve 66 is closed. The exhaust gas from the cylinder groups of the first and second banks 12 and 13 is caused to flow through the first exhaust pipe 57.

  Therefore, after the estimated bed temperature Tc of the NOx occlusion reduction type catalyst 63 reaches a predetermined value or higher and is activated, all the exhaust gas flows through the first exhaust pipe 57, whereby the exhaust path is changed from the second exhaust pipe 58 to the second exhaust pipe 58. When the first exhaust pipe 57 is changed, the exhaust gas can be purified by the already activated NOx storage reduction catalyst 63 even if the first front three-way catalyst 59 is not activated. Further, after the PM accumulation amount Qp in the particulate filter 61 becomes equal to or less than a predetermined value and the regeneration is completed, all exhaust gas is caused to flow through the first exhaust pipe 57, thereby depending on the PM accumulated in the particulate filter 61. An increase in the back pressure of the second exhaust pipe 58 can be suppressed.

  In Example 1 described above, when the estimated bed temperature Tc of the NOx storage reduction catalyst 63 is equal to or higher than a predetermined value and the PM accumulation amount Qp in the particulate filter 61 is equal to or lower than the predetermined value, the exhaust gas is exhausted. Although the path is changed from the second exhaust pipe 58 to the first exhaust pipe 57, it is not limited to this configuration. For example, the exhaust path is changed when the estimated bed temperature Tc of the NOx storage reduction catalyst 63 becomes a predetermined value or more, or the exhaust path is changed when the PM accumulation amount Qp in the particulate filter 61 becomes a predetermined value or less. Also good. Further, when the load on the engine 101 exceeds a predetermined value set in advance, the exhaust path is changed from the second exhaust pipe 58 to the first exhaust pipe 57, and the turbocharger 67 is driven to ensure the output. You may make it do.

  In the first embodiment, when the air-fuel ratio is rich when the engine 101 is started from the warm-up state, the exhaust gas from the cylinder groups of the first and second banks 12 and 13 is caused to flow to the second exhaust pipe 58. As a result, PM in the exhaust gas frequently generated during operation at this rich air-fuel ratio can be collected by the particulate filter 61, and the exhaust purification performance can be improved.

  FIG. 5 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, and FIG. 6 is a flowchart showing control valve switching control in the V-type 6-cylinder engine of Embodiment 2. . 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 second embodiment, a V type 6 cylinder engine is applied as the internal combustion engine. In the V-type 6-cylinder engine of the second embodiment, as shown in FIG. 5, a plurality of cylinders have a cylinder group that is 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 particulate filter 61, the first exhaust pipe 57, 58 are connected to the exhaust pipes 57, 58, respectively. The first control valve 65 and the second control valve 66 are provided, and upstream sides of the upstream three-way catalysts 59 and 60 and the control valves 65 and 66 in the exhaust pipes 57 and 58 are communicated by a communication pipe 64. A third control valve (communication control valve) 91 is provided in the middle of the direction, and the engine ECU 112 can control the opening and closing of the control valves 65, 66, 91 according to the engine operating state.

  Here, the opening / closing control of each control valve 65, 66, 91 in the V-type 6-cylinder engine of this embodiment will be described based on the flowchart of FIG.

  In the V-type six-cylinder engine of this embodiment, as shown in FIG. 6, in step S31, the engine ECU 112 determines whether or not the NOx storage reduction catalyst 63 is under sulfur poisoning regeneration control. In this case, the engine ECU 112 estimates the sulfur storage amount stored in the NOx storage reduction catalyst 63 based on the integrated value of the sulfur content in the fuel and the fuel injection amount from the injector, and this NOx storage reduction catalyst 63. The sulfur poisoning regeneration control is executed when the sulfur occlusion amount occluded in exceeds the predetermined value set in advance. Note that the sulfur storage amount estimation method is not limited to this method, and may be estimated based on, for example, the travel distance or travel time of the vehicle.

  In the sulfur poisoning regeneration control of the NOx occlusion reduction type catalyst 63, the exhaust gas from the cylinder group of the first bank 12 flows as a lean atmosphere to the first exhaust pipe 57, and the exhaust gas from the cylinder group of the second bank 13 flows. The gas is flowed to the second exhaust pipe 58 as a rich atmosphere and joined by the NOx occlusion reduction type catalyst 63, so that the oxidation exothermic reaction in the NOx occlusion reduction type catalyst 63 is utilized and the occluded sulfur component is released and regenerated. To do.

  If it is determined in step S31 that the NOx storage reduction catalyst 63 is under sulfur poisoning regeneration control, the first control valve 65 and the second control valve 66 are opened in step S32, and the third The control valve 91 is closed. Then, the exhaust gas in the lean atmosphere exhausted from the cylinder group of the first bank 12 flows to the first exhaust pipe 57, and the exhaust gas in the rich atmosphere exhausted from the cylinder group of the second bank 13 enters the second exhaust pipe 58. The NOx occlusion reduction type catalyst 63 flows into the NOx occlusion reduction type catalyst 63 and flows into the NOx occlusion reduction type catalyst 63. The NOx occlusion reduction type catalyst 63 regenerates by releasing the sulfur component occluded by utilizing an exothermic oxidation reaction. can do.

  On the other hand, if it is determined in step S31 that the NOx storage reduction catalyst 63 is not under sulfur poisoning regeneration control, the engine ECU 112 determines in step S33 whether the NOx storage reduction catalyst 63 is under NOx reduction control. Determine. In this case, the engine ECU 112 estimates the NOx occlusion amount stored in the NOx occlusion reduction type catalyst 63 based on the lean burn operation time, and the NOx occlusion amount occluded in the NOx occlusion reduction type catalyst 63 is preset. When the predetermined value is exceeded, NOx reduction control is executed.

  The NOx reduction control (rich spike control) of the NOx storage reduction catalyst 63 supplies the exhaust gas from the cylinder groups of the first and second banks 12 and 13 to the NOx storage reduction catalyst 63 as a rich atmosphere. Therefore, the NOx occluded and reduced by the NOx occlusion reduction catalyst 63 is released, and NOx is reduced by the added fuel as a reducing agent.

  If it is determined in step S33 that the NOx storage reduction catalyst 63 is under NOx reduction control, the first control valve 65 is closed while the second control valve 66 is open in step S34. And the third control valve 91 is opened. 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 64, and the exhaust 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, this large amount of exhaust gas flows into the second front three-way catalyst 60 and the particulate filter 61, and flows into the NOx occlusion reduction type catalyst 63 through the exhaust collecting pipe 62. With this NOx occlusion reduction type catalyst 63, the occluded NOx can be released and NOx can be reduced by the fuel.

  During the sulfur poisoning regeneration control and the NOx reduction control of the NOx occlusion reduction type catalyst 63 described above, exhaust gas in a rich atmosphere from the cylinder group of the second bank 13 or the cylinders of the first and second banks 12 and 13 Exhaust gas in a rich atmosphere from the group flows into the second exhaust pipe 58 and passes through the second front-stage three-way catalyst 60 and the particulate filter 61. Therefore, PM in the exhaust gas that is frequently generated when the air-fuel ratio is rich is collected by the particulate filter 61.

  On the other hand, if it is determined in step S33 that the NOx occlusion reduction type catalyst 63 is not under NOx reduction control, in step S35, the engine ECU 112 opens the first control valve 65 while the second control valve 66 is open. Is closed, and the third control valve 91 is opened. Then, after the exhaust gas from the cylinder groups of the first and second banks 12 and 13 merges in the first exhaust pipe 57, the exhaust gas flows through the turbocharger 67 to the first front three-way catalyst 59, and the exhaust collecting pipe The NOx occlusion reduction catalyst 63 flows through 62. Therefore, the supercharging pressure by the turbocharger 67 is increased, and the engine output is improved.

  Thus, in the V-type 6-cylinder engine of the second embodiment, 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 the cylinders in the banks 12 and 13 are provided. While the intake pipe 51 is connected to the group, 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 three-way catalyst 60 are connected to the exhaust pipes 57 and 58, respectively. The first control valve 65 and the second control valve 66 are provided, the particulate filter 61 is provided in the second exhaust pipe 58, the three-stage catalysts 59, 60 in the front stages in the exhaust pipes 57, 58, the particulate filter 61, The upstream side of the control valves 65, 66 is communicated by a communication pipe 64, a third control valve 91 is provided in the communication pipe 64, and the exhaust pipes 57, 58 are gathered by an exhaust collecting pipe 62 to store the NOx storage reduction type catalyst 63. And configure Jin ECU112 is opening and closing control of the control valves 65,66,91 in accordance with the operating condition.

  During the execution of the sulfur poisoning regeneration control for releasing the sulfur component stored in the NOx storage reduction catalyst 63, the first bank 12 is made lean, the second bank 13 is made rich, and the first and second control valves 65, 66 are made. Is opened and the third control valve is closed, so that the exhaust gas in the rich atmosphere from the banks 12 and 13 and the exhaust gas in the rich atmosphere are not mixed in the communication pipe 64, and immediately before the NOx storage reduction catalyst 63. The NOx occlusion reduction type catalyst 63 is supplied to the NOx occlusion reduction type catalyst 63, and the NOx occlusion reduction type catalyst 63 is able to appropriately release and regenerate the occluded sulfur component using an oxidation exothermic reaction. it can.

  Further, during the execution of the NOx reduction control for reducing the NOx stored in the NOx storage reduction type catalyst 63, the first bank 12 and the second bank 13 are made rich and the first control valve 65 is closed while the second control is closed. By opening the valve 66 and opening the third control valve, the exhaust gas in the rich atmosphere from the cylinder group of the first and second banks 12 and 13 flows to the second exhaust pipe 58, and the second front three-way catalyst 60 and the particulate filter 61, and the PM in the exhaust gas that is generated frequently when the air-fuel ratio is rich can be properly collected by the particulate filter 61.

  FIG. 7 is a flowchart showing the control valve switching control in the V-type 6-cylinder engine representing the internal combustion engine according to the second embodiment of the present invention. 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 third embodiment, a V-type 6-cylinder engine is applied as the internal combustion engine. In the V-type 6-cylinder engine of the second embodiment, as shown in FIG. 5, a plurality of cylinders have a cylinder group that is 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 particulate filter 61, the first exhaust pipe 57, 58 are connected to the exhaust pipes 57, 58, respectively. The first control valve 65 and the second control valve 66 are provided, and upstream sides of the upstream three-way catalysts 59 and 60 and the control valves 65 and 66 in the exhaust pipes 57 and 58 are communicated by a communication pipe 64. A third control valve (communication control valve) 91 is provided in the middle of the direction, and the engine ECU 112 can control the opening and closing of the control valves 65, 66, 91 according to the engine operating state.

  Here, the opening / closing control of each control valve 65, 66, 91 in the V-type 6-cylinder engine of the present embodiment will be described based on the flowchart of FIG.

  In the V-type 6-cylinder engine of this embodiment, as shown in FIG. 7, in step S41, the engine ECU 112 determines whether or not the NOx storage reduction catalyst 63 is under sulfur poisoning regeneration control. Here, if it is determined that the NOx occlusion reduction type catalyst 63 is under sulfur poisoning regeneration control, in step S42, the first control valve 65 and the second control valve 66 are opened, and the third control valve 91 is turned on. Closed state. Then, the exhaust gas in the lean atmosphere exhausted from the cylinder group of the first bank 12 flows to the first exhaust pipe 57, and the exhaust gas in the rich atmosphere exhausted from the cylinder group of the second bank 13 enters the second exhaust pipe 58. The NOx occlusion reduction type catalyst 63 flows into the NOx occlusion reduction type catalyst 63 and flows into the NOx occlusion reduction type catalyst 63. The NOx occlusion reduction type catalyst 63 regenerates by releasing the sulfur component occluded by utilizing an exothermic oxidation reaction. can do.

  On the other hand, if it is determined in step S41 that the NOx storage reduction catalyst 63 is not under sulfur poisoning regeneration control, the engine ECU 112 determines in step S43 whether the NOx storage reduction catalyst 63 is under NOx reduction control. Determine. If it is determined that the NOx occlusion reduction type catalyst 63 is under NOx reduction control, the air-fuel ratio of the cylinder group in the first bank 12 is changed to stoichiometric in step S44, and the cylinder group in the second bank 13 is changed. The air-fuel ratio is changed to rich, and the process proceeds to step S42. In step S42, the first control valve 65 and the second control valve 66 are opened, and the third control valve 91 is closed. Then, the exhaust gas in the stoichiometric atmosphere discharged from the cylinder group of the first bank 12 flows to the first exhaust pipe 57, and the exhaust gas in the rich atmosphere discharged from the cylinder group of the second bank 13 enters the second exhaust pipe 58. The NOx occlusion reduction type catalyst 63 flows into the NOx occlusion reduction type catalyst 63 and flows into the NOx occlusion reduction type catalyst 63. The NOx occlusion reduction type catalyst 63 releases the NOx occluded in a rich atmosphere and reduces NOx by the fuel. Can do.

  During the NOx reduction control of the NOx occlusion reduction type catalyst 63, the exhaust gas in the stoichiometric atmosphere from the cylinder group of the first bank 12 flows to the first exhaust pipe 57 and passes through the first front three-way catalyst 59. Since the fuel ratio is stoichiometric, the amount of PM in the exhaust gas is very small. On the other hand, when the exhaust gas in the rich atmosphere from the cylinder group of the second bank 13 flows into the second exhaust pipe 58 and passes through the second front-stage three-way catalyst 60 and the particulate filter 61, the air-fuel ratio is rich. A large amount of PM in the exhaust gas generated is collected by the particulate filter 61.

  On the other hand, if it is determined in step S43 that the NOx occlusion reduction type catalyst 63 is not under NOx reduction control, in step S45, the engine ECU 112 opens the first control valve 65 while the second control valve 66 is open. Is closed, and the third control valve 91 is opened. Then, after the exhaust gas from the cylinder groups of the first and second banks 12 and 13 merges in the first exhaust pipe 57, the exhaust gas flows through the turbocharger 67 to the first front three-way catalyst 59, and the exhaust collecting pipe The NOx occlusion reduction catalyst 63 flows through 62. Therefore, the supercharging pressure by the turbocharger 67 is increased, and the engine output is improved.

  As described above, in the V-type 6-cylinder engine according to the third embodiment, the first bank 12 is stoichiometric while the NOx reduction control for reducing the NOx stored in the NOx storage reduction catalyst 63 is performed. By making the second bank 13 rich and opening the first and second control valves 65 and 66 while closing the third control valve 66, the exhaust gas in the stoichiometric atmosphere from the cylinder group of the first bank 12 becomes the first. The exhaust gas in the rich atmosphere from the cylinder group of the second bank 13 flows into the second exhaust pipe 58, flows into the exhaust pipe 57, joins in the exhaust collecting pipe 62, and flows into the NOx occlusion reduction type catalyst 63. The NOx occlusion reduction type catalyst 63 can release the NOx occluded in a rich atmosphere and reduce NOx with fuel. At this time, since the cylinder group of the first bank 12 is stoichiometric, there is almost no PM in the exhaust gas, and even if the exhaust gas flows into the first exhaust pipe 57 without the particulate filter, the exhaust purification performance is lowered. There is no. On the other hand, since the cylinder group of the second bank 13 is rich, a large amount of PM exists in the exhaust gas. However, the PM in the exhaust gas is collected by the particulate filter 61, and the exhaust purification performance. Can be improved.

  In the first embodiment described above, the internal combustion engine of the present invention is described as being mounted on a hybrid vehicle. However, as in the second and third embodiments, the same effects can be achieved even when mounted on a general vehicle. Can do. In each embodiment, a V-type 6-cylinder engine is applied as the internal combustion engine, but the engine type, the number of cylinders, and the like are not limited to the embodiment. 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 can collect particulate matter in the exhaust gas so as to improve exhaust purification performance, and can suppress a decrease in output due to an increase in back pressure in the exhaust passage. 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 section of a V-type 6-cylinder engine according to a first embodiment. 3 is a flowchart illustrating control valve switching control in the V-type six-cylinder engine according to the first embodiment. 1 is a schematic configuration diagram of a hybrid vehicle to which a V-type 6-cylinder engine of Example 1 is applied. 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. 7 is a flowchart showing control valve switching control in a V-type 6-cylinder engine according to Embodiment 2; It is a flowchart showing the switching control of the control valve in the V type 6 cylinder engine showing the internal combustion engine which concerns on Example 2 of this invention.

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 front three-way catalyst (front purification catalyst)
60 Second front three-way catalyst (front purification catalyst)
61 Particulate Filter 62 Exhaust Collecting Pipe 63 NOx Occlusion Reduction Catalyst (Post-Purification Catalyst)
64 communication pipe (communication passage)
65 First control valve (exhaust control valve)
66 Second control valve (exhaust control valve)
67 Turbocharger 72, 73 Injector 77, 78 Spark plug 91 Third control valve (communication control valve)
101 V-6 engine (internal combustion engine)
102 electric motor 112 engine ECU (control means)
118 Main ECU

Claims (9)

  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. While a pre-purification catalyst is provided, a particulate filter is provided in any one of the exhaust passages, an exhaust control valve for adjusting the flow rate of exhaust gas is provided in each exhaust passage, and each of the exhaust passages An internal combustion engine characterized in that the upstream side of the upstream purification catalyst, the particulate filter, and the exhaust control valves are communicated by a communication passage, and the control means can control the opening and closing of the exhaust control valve according to the operating state.   2. The internal combustion engine according to claim 1, wherein a supercharger is provided between the communication passage and the upstream purification catalyst in the exhaust passage where the particulate filter is not provided in each exhaust passage. An internal combustion engine characterized by that.   3. The internal combustion engine according to claim 1, wherein the control unit closes the exhaust 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 exhaust control valve in the exhaust passage of a cylinder group having a curate filter.   4. The internal combustion engine according to claim 3, wherein the control means retards the ignition timing and changes the air-fuel ratio to a lean air-fuel ratio when the internal combustion engine is cold-started.   The internal combustion engine according to claim 4, wherein the control means is configured such that the temperature of the post-purification catalyst provided in the exhaust collecting passage where the downstream end portions of the exhaust passages merge is equal to or higher than a predetermined temperature set in advance. Alternatively, when the particulate matter collected by the particulate filter is equal to or less than a predetermined amount set in advance or the internal combustion engine load is equal to or greater than a predetermined value, the cylinder group having the supercharger An internal combustion engine that opens the exhaust control valve in the exhaust passage and closes the exhaust control valve in the exhaust passage of a cylinder group having the particulate filter.   3. The internal combustion engine according to claim 1, wherein when the air-fuel ratio is a rich air-fuel ratio when the internal combustion engine is started from a warm-up state, the exhaust of the cylinder group having the supercharger is performed. An internal combustion engine that closes the exhaust control valve in the passage and opens the exhaust control valve in the exhaust passage of the cylinder group having the particulate filter.   3. The internal combustion engine according to claim 1, wherein a communication control valve for adjusting a flow rate of exhaust gas is provided in the communication passage, and a NOx occlusion reduction type purification is provided in an exhaust collecting passage where downstream ends of the exhaust passages are joined. A catalyst is provided, and the control means closes the communication control valve during execution of the sulfur poisoning regeneration control for releasing the sulfur component stored in the NOx storage reduction purification catalyst, while the exhaust control valve And changing the air-fuel ratio of the cylinder group having the supercharger to a lean air-fuel ratio, while changing the air-fuel ratio of the cylinder group having the particulate filter to a rich air-fuel ratio.   3. The internal combustion engine according to claim 1, wherein a communication control valve for adjusting a flow rate of exhaust gas is provided in the communication passage, and a NOx occlusion reduction type purification is provided in an exhaust collecting passage where downstream ends of the exhaust passages are joined. A catalyst is provided, and the control means opens the communication control valve during execution of NOx reduction control for reducing NOx stored in the NOx storage reduction purification catalyst, and controls the cylinder group having the supercharger. Closing the exhaust control valve in the exhaust passage, and opening the exhaust control valve in the exhaust passage of the cylinder group having the particulate filter to change the air-fuel ratio of each cylinder group to a rich air-fuel ratio. A featured internal combustion engine.   3. The internal combustion engine according to claim 1, wherein a communication control valve for adjusting a flow rate of exhaust gas is provided in the communication passage, and a NOx occlusion reduction type purification is provided in an exhaust collecting passage where downstream ends of the exhaust passages are joined. A catalyst is provided, and the control means closes the communication control valve and opens the exhaust control valves during execution of NOx reduction control for reducing NOx stored in the NOx storage reduction purification catalyst, An internal combustion engine characterized in that the air-fuel ratio of the cylinder group having the supercharger is changed to a stoichiometric air-fuel ratio, while the air-fuel ratio of the cylinder group having the particulate filter is changed to a rich air-fuel ratio.

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