JP2008095535A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve exhaust emission control efficiency by suitably cleaning harmful components in exhaust gas in an internal combustion engine even when an operation state is varied. <P>SOLUTION: In a V-type six-cylinder engine, a cylinder group wherein a plurality of cylinders are divided to left and right first and second banks 12 and 13 is provided, an intake pipe 51 is connected to the cylinder group of the banks 12 and 13, a first exhaust pipe 57 and a second exhaust pipe 58 are connected, downstream ends of the exhaust pipes 57 and 58 are merged in order to be connected to an exhaust collecting pipe 61, first and second front stage three-dimensional catalysts 59 and 60 are respectively disposed on the exhaust pipes 57 and 58, and first and second control valves 65 and 66 are disposed, and the front stage three-dimensional catalysts 59 and 60 of the exhaust pipes 57 and 58 and the upstream sides of the control valves 65 and 66 are communicated through a communicating pipe 64, an intermediate stage three-dimensional catalyst 62 is provided in the vicinity of the merged part where the downstream ends of the exhaust pipes 57 and 58 are merged, and a NOx storage reduction type catalyst 63 is disposed on the downstream side of the exhaust collecting pipe 61. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine having two cylinder groups in which a plurality of cylinders are divided into left and right banks and in which the upstream side of the exhaust passage of each cylinder group is communicated by a communication passage.

  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. A front-stage purification catalyst is attached to the exhaust pipe, and an exhaust collecting pipe into which the exhaust pipes merge is connected. A post-stage purification catalyst is installed.

  In such a V-type multi-cylinder engine, in order to warm up the early stage purification catalyst at the start of the engine and activate it early, the two exhaust pipes communicate with each other on the upstream side of the previous stage purification catalyst, Some exhaust pipes can be controlled by providing a control valve. Therefore, when starting the engine, the control valve of one exhaust pipe is closed and the exhaust gas from the cylinder group of each bank is merged in the other exhaust pipe through the communication pipe, and then the upstream purification is performed by the heat of this large amount of exhaust gas The catalyst can be warmed up efficiently for 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. After that, the turbocharger turbine is driven by this large amount of exhaust gas, the compressor integrated with the turbine is driven to compress the air, and introduced into the combustion chamber, thereby enabling high supercharging. it can.

  As such an internal combustion engine, there is an “exhaust gas purification device for an internal combustion engine” described in Patent Document 1 below.

Japanese Patent Laid-Open No. 08-121153

  In the conventional engine described above, a pre-stage purification catalyst is mounted on both the exhaust pipes of each bank in order to ensure a high exhaust gas purification function. Then, when starting the engine or when the engine is heavily loaded, the control valve in the exhaust pipe of one bank is closed, and the exhaust gas discharged from the cylinder group of this one bank flows through the communication pipe to the other exhaust pipe, By joining the exhaust gas discharged from the cylinder group of each bank, the exhaust gas is introduced into the other upstream purification catalyst for warming up or introduced into the turbocharger for high supercharging. When the warming up of the pre-purification catalyst is completed or the high supercharging of the turbocharger is completed, each control valve is opened so that the exhaust gas discharged from the cylinder group of each bank flows into the respective exhaust pipes. I have to.

  However, when the control valve in the exhaust pipe of one bank is closed and the exhaust gas discharged from the cylinder group of the left and right banks is allowed to flow to the one exhaust pipe through the communication pipe, each control valve is opened and left and right When the operation state is changed so that the exhaust gas discharged from the cylinder group of the other bank flows to the respective exhaust pipes, the pre-purification catalyst attached to the exhaust pipe of the other bank is activated at a low temperature state. There is a risk of not. That is, since the control valve in the exhaust pipe of one bank is closed and operated for a predetermined time, the exhaust gas does not flow in the exhaust pipe of this one bank, and the pre-purification catalyst attached to this exhaust pipe is warmed up. Cannot be performed or fall from the activation temperature range and deviate from the predetermined activation temperature range. Then, the pre-purification catalyst cannot properly purify the harmful substances in the exhaust gas, and the exhaust purification efficiency decreases.

  The present invention is for solving such a problem, and an internal combustion engine that improves exhaust purification efficiency by appropriately purifying harmful components in exhaust gas even when the operating state is changed. The purpose is to provide.

  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 exhaust collecting passages where the downstream ends of the exhaust passages are joined are provided, a pre-stage purification catalyst is provided in the exhaust passages, and the exhaust passages are provided. A control valve that adjusts the flow rate of the exhaust gas is provided in the passage, the upstream side of the upstream purification catalyst and the control valve in each exhaust passage is communicated by a communication passage, and the downstream end portion of each exhaust passage joins A middle stage purification catalyst is provided in the vicinity, and a rear stage purification catalyst is provided in the exhaust collecting passage.

  The internal combustion engine of the present invention is characterized in that the intermediate purification catalyst is provided at the most upstream end in the flow direction of the exhaust gas in the exhaust collecting passage.

  In the internal combustion engine of the present invention, the post-stage purification catalyst is a NOx occlusion reduction type catalyst, and the middle stage purification catalyst is a three-way catalyst having a function of capturing a sulfur component in the exhaust gas.

  The internal combustion engine of the present invention is characterized in that exhaust gas guide means for suppressing mixing of exhaust gas flowing through the exhaust passages is provided at a junction where the downstream ends of the exhaust passages merge.

  In the internal combustion engine of the present invention, the intermediate purification catalyst is provided at the most downstream end in the flow direction of the exhaust gas in any one of the exhaust passages.

  According to the internal combustion engine of the present invention, there are two cylinder groups in which a plurality of cylinders are arranged in left and right banks, and an exhaust passage is provided independently for each cylinder group, and downstream of each exhaust passage. The exhaust gas collecting passages are formed by joining the end portions, the upstream purification catalyst and the control valve are provided in each exhaust passage, the upstream side of the upstream purification catalyst and the control valve in each exhaust passage is connected by the communication passage, and the downstream of each exhaust passage Since the middle purification catalyst is provided near the merged portion where the ends merge, and the rear purification catalyst is provided in the exhaust collecting passage, the exhaust gas discharged from the cylinder group of one bank is communicated by opening and closing each control valve. Installed in the vicinity of the junction with the upstream purification catalyst installed in the other exhaust pipe when in an operating state where it flows through the pipe to the other exhaust pipe and exhaust gas discharged from the left and right bank cylinders flows to the other exhaust pipe. The middle stage purification catalyst was warmed up Therefore, when the operation state is changed to the operation state in which the exhaust gas discharged from the cylinder groups of the left and right banks is passed to the respective exhaust pipes, the pre-purification catalyst attached to one of the exhaust pipes is activated. Even if not, since the intermediate purification catalyst has already been warmed and activated, harmful components in the exhaust gas can be continuously purified appropriately, and the exhaust purification efficiency can be improved.

  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. 2 is a graph showing a change in temperature of a catalyst at the time of starting a V-type 6-cylinder engine of FIG.

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

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

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

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

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

  The exhaust ports 26 and 27 communicate with collecting passages 55 and 56 in which exhaust gases discharged from the combustion chambers 22 and 23 gather, and exhaust pipe connecting portions 55a and 56a are connected to the collecting passages 55 and 56, respectively. The first and second exhaust pipes 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.

  The first exhaust pipe 57 is equipped with a first front three-way catalyst (front purification catalyst) 59, while the second exhaust pipe 58 is fitted with a second front three-way catalyst (front purification catalyst) 60. Has been. In addition, the first and second exhaust pipes 57 and 58 are joined at their downstream ends, and an exhaust collecting pipe (exhaust collecting passage) 61 is connected to the joining part. A middle three-way catalyst (middle purification catalyst) 62 is attached in the vicinity of the part, and a NOx occlusion reduction type catalyst (rear purification catalyst) 63 is attached downstream of the exhaust collecting pipe 61. In the present embodiment, the middle three-way catalyst 62 is provided at the most upstream end in the exhaust gas flow direction in the exhaust collecting pipe 61.

  Each of the front three-way catalysts 59, 60 and the middle three-way catalyst 62 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 63 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 first exhaust pipe 57 and the second exhaust pipe 58 are communicated by a communication pipe (communication path) 64 on the upstream side in the flow direction of the exhaust gas from the position where each of the upstream three-way catalysts 59 and 60 is mounted. Yes. Specifically, each end portion of the communication pipe 64 is connected to a connection portion between the exhaust pipe connecting portions 55a and 56a and the exhaust pipes 57 and 58. A first control valve 65 and a second control valve 66 are mounted on the first exhaust pipe 57 and the second exhaust pipe 58 on the downstream side of the upstream three-way catalysts 59 and 60 in the exhaust gas flow direction. . 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.

  Incidentally, an electronic control unit (ECU) 79 is mounted on the vehicle, and this ECU 79 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 conditions such as the intake air amount, intake air temperature, throttle opening, accelerator opening, engine speed, and coolant temperature. That is, the air flow sensor 80 and the intake air temperature sensor 81 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 79. The electronic throttle device 54 is provided with a throttle position sensor 82, and the accelerator pedal is provided with an accelerator position sensor 83, which outputs the current throttle opening and accelerator opening to the ECU 79. Further, a crank angle sensor 84 is provided on the crankshaft, and the detected crank angle is output to the ECU 79. The ECU 79 calculates the engine speed based on the crank angle. Further, the cylinder block 11 is provided with a water temperature sensor 85 and outputs the detected engine cooling water temperature to the ECU 79.

  Further, the ECU 79 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.

  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 collecting passages 55 and 56 of the cylinder heads 20 and 21, respectively. First and second front three-way catalysts 59 and 60 and first and second control valves 65 and 66 are attached to the exhaust pipe 57 and the second exhaust pipe 58, and the collecting passages 55 and 56 are connected to the communication pipe 64. It is communicated by. Therefore, various bank control is possible by changing the combustion state of each bank 12 and 13 and the exhaust gas discharge route.

  When the engine is started at a low temperature, for example, the first control valve 65 is closed and the second control valve 66 is opened, and the first exhaust pipe 57 is connected from the cylinder group of the first bank 12 to the first exhaust pipe 57 via the collecting passage 55. By bypassing the discharged exhaust gas 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, and then a large amount This exhaust gas is caused to flow into the second front-stage three-way catalyst 60, so that the second front-stage three-way catalyst 60 is warmed up. Thereafter, when the warm-up of the second pre-stage three-way catalyst 60 is completed and activated, the first and second control valves 65 and 66 are opened, and the exhaust gases from the cylinder groups of the banks 12 and 13 are discharged. Instead of passing through the communication pipe 64, the exhaust gas collecting pipe 61 is joined through the exhaust pipes 57 and 58, and then the exhaust gas is introduced into the middle three-way catalyst 62 and the NOx occlusion reduction type catalyst 63 for purification treatment. Yes.

  Further, in the V-type 6-cylinder engine of the present embodiment, in a high load state, the first control valve 65 is opened, while the second control valve 66 is closed, so that the cylinders in the second bank 13 By exhausting the exhaust gas discharged to the second exhaust pipe 58 through the collecting passage 56 to the first exhaust pipe 57 through the communication pipe 64, the exhaust gas from the cylinder groups of the first and second banks 12 and 13 is made to flow. After merging in the first exhaust pipe 57, a large amount of exhaust gas is caused to flow into the turbocharger 67, whereby the turbocharger 67 can be operated with high efficiency and high turbocharging can be achieved. The thermal deterioration of the second front three-way catalyst 60 attached to the second exhaust pipe 58 of the cylinder group of the second bank 13 that does not have the supercharger is suppressed.

  Further, for example, the exhaust gas from the cylinder group of the first bank 12 has a lean atmosphere, the exhaust gas from the cylinder group of the second bank 13 has a rich atmosphere, and the first control valve 65 and the second control valve 66 are The exhaust gas in the lean atmosphere discharged from the cylinder group of the first bank 12 is made to flow into the first exhaust pipe 57, and the exhaust gas in the rich atmosphere discharged from the cylinder group of the second bank 13 is made into the first exhaust pipe. The NOx occlusion reduction type catalyst 63 is warmed up using the oxidation exothermic reaction in the NOx occlusion reduction type catalyst 63 or accumulated in the NOx occlusion reduction type catalyst 63. The sulfur component is released and regenerated.

  However, for example, the first exhaust pipe 57 is closed by the first control valve 65, and the exhaust gas discharged from the cylinder group of the first bank 12 is bypassed to the second bank 13 side through the communication pipe 64. , 13 in an operation state in which exhaust gas from the cylinder group flows through the second exhaust pipe 58 in a total amount, high-temperature exhaust gas flows through the second front-stage three-way catalyst 60, so that it is maintained in a predetermined activation temperature region. However, since the exhaust gas does not flow through the first front three-way catalyst 59 attached to the first exhaust pipe 57, the temperature drops and falls out of the active temperature region. Therefore, from this operating state, the first exhaust pipe 57 is opened by the first control valve 65, and the exhaust gas discharged from the cylinder groups of the left and right banks 12 and 13 is caused to flow to the respective exhaust pipes 57 and 58. When the state is changed, the first pre-stage three-way catalyst 59 attached to the first exhaust pipe 57 is not in the active temperature range, so that harmful substances in the exhaust gas cannot be properly purified, and the exhaust purification is performed. Efficiency will decrease.

  Therefore, in the engine of the first embodiment, as described above, the first front-stage three-way catalyst 59 is attached to the first exhaust pipe 57, while the second front-stage three-way 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 to connect the exhaust collecting pipe 61, and in the vicinity of the joining portion of each exhaust pipe 57 and 58, at the most upstream end of the exhaust collecting pipe 61. A middle three-way catalyst 62 is mounted.

  Accordingly, when the engine is started at a low temperature, as shown in FIGS. 1 and 3, the first exhaust pipe 57 is closed by the first control valve 65 and the second exhaust pipe 58 is opened by the second control valve 66. The exhaust gas discharged from the cylinder group of the bank 12 bypasses to the second bank 13 side through the communication pipe 64, and the exhaust gas from the cylinder group of each bank 12 and 13 flows to the second exhaust pipe 58 in total. In such an operating state, the high-temperature exhaust gas is heated by flowing into the second front-stage three-way catalyst 60, and the temperature is rapidly increased to the activation temperature or higher. On the other hand, since the exhaust gas does not flow through the first front three-way catalyst 59 attached to the first exhaust pipe 57, the temperature hardly rises. Further, the exhaust gas that has passed through the second front-stage three-way catalyst 60 from the second exhaust pipe 58 flows into the exhaust collecting pipe 61 and flows into the middle-stage three-way catalyst 62 and the NOx occlusion reduction type catalyst 63 to be heated and gradually. The temperature is raised.

  From this operating state, when the first exhaust pipe 57 is opened by the first control valve 65 at time t1, the exhaust gas discharged from the cylinder groups of the left and right banks 12 and 13 does not flow into the communication pipe 64. When the operation state is changed to such an operating state, the high-temperature exhaust gas is heated by flowing into the first three-way catalyst 59, and the temperature is rapidly increased. The activation temperature is exceeded. Further, the exhaust gas that has passed through the respective upstream three-way catalysts 59 and 60 from the respective exhaust pipes 57 and 58 continuously flows into the exhaust collecting pipe 61 and flows into the middle three-way catalyst 62 and the NOx occlusion reduction type catalyst 63. It is heated and gradually heated.

  After this operating state is changed at time t1, the high-temperature exhaust gas starts to flow into the first exhaust pipe 57, whereby the first front three-way catalyst 59 attached to the first exhaust pipe 57 is heated and rises. At time t2, the first front-stage three-way catalyst 59 reaches the activation temperature or higher, and during a predetermined time ta from time t1 to time t2, the first front-stage three-way catalyst 59 opens the first exhaust pipe 57. The flowing exhaust gas cannot be properly purified.

  However, since the middle three-way catalyst 62 is at or above the activation temperature at a time t0 prior to the time t1 when the operating state is changed, until the time t2 at which the first front-stage three-way catalyst 59 is at or above the activation temperature. During the predetermined time ta, the exhaust gas flowing through the first exhaust pipe 57 is appropriately purified by the middle three-way catalyst 62 at the junction of the exhaust pipes 57 and 58.

  Here, the opening / closing control of the control valves 65 and 66 and the exhaust gas purification action of the catalysts 59, 60, 62, and 63 in the V-type six-cylinder engine of the first embodiment will be described.

  In the V-type 6-cylinder engine of the first embodiment, as shown in FIGS. 1 and 2, the air introduced into the intake pipe 51 through the air cleaner 52 is supplied to the turbocharger 67 provided on the first bank 12 side. The air is compressed by the compressor 68 to become supercharged intake air, which is metered by the throttle valve 53 and then flows into the surge tank 50, reaches the intake ports 24 and 25 through the intake manifolds 48 and 49, and the intake valves 28 and 29. Is opened, the air in the intake ports 24 and 25 is sucked into the combustion chambers 22 and 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 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 up and activates the middle three-way catalyst 62, and after the remaining harmful substances are appropriately purified, warms up the NOx storage reduction catalyst 63. The NOx is appropriately purified and released into the atmosphere.

  Further, when the engine is started, the first control valve 65 is closed and the second control valve 66 is opened, and the exhaust gas discharged from the cylinder group of the first bank 12 to the first exhaust pipe 57 is communicated. By bypassing to the second exhaust pipe 58 through the pipe 64, exhaust gas from the cylinder groups of the first and second banks 12, 13 is merged in the second exhaust pipe 58, and then a large amount of exhaust gas is supplied to the second front stage. The second upstream three-way catalyst 60 is warmed up by flowing into the three-way catalyst 60. At this time, the exhaust gas that has passed through the second front-stage three-way catalyst 60 flows into the middle three-way catalyst 62 through the exhaust collecting pipe 61 and warms up the middle-stage three-way catalyst 62.

  Thereafter, when the warming-up of the second front three-way catalyst 60 and the middle three-way catalyst 62 is completed and activated, the first and second control valves 65 and 66 are opened, and the first bank 12 The exhaust gas from the cylinder group is set to a lean atmosphere, the exhaust gas from the cylinder group of the second bank 13 is set to a rich atmosphere, and the exhaust gas in the lean atmosphere and the exhaust gas in the rich atmosphere are not passed through the communication pipe 64. The NOx occlusion reduction type catalyst 63 is joined to the NOx occlusion reduction type catalyst 63 through the exhaust collecting pipe 61, and the NOx occlusion reduction type catalyst 63 is warmed up using the oxidation exothermic reaction at that time.

  When the warming-up of the NOx storage reduction catalyst 63 is completed and activated, the exhaust gas from the cylinder groups of the banks 12 and 13 is stoichiometrically maintained with the first and second control valves 65 and 66 open. Then, after being merged in the exhaust collecting pipe 61 through the exhaust pipes 57 and 58, the exhaust gas is caused to flow into the NOx occlusion reduction type catalyst 63 for purification treatment.

  When the engine is under high load and high speed, the first control valve 65 is opened, the second control valve 66 is closed, and the exhaust gas discharged from the cylinder group of the second bank 13 to the second exhaust pipe 58 is discharged. By bypassing the first exhaust pipe 57 through the communication pipe 64, exhaust gas from the cylinder groups of the first and second banks 12 and 13 is merged in the first exhaust pipe 57, and then a large amount of exhaust gas is turbocharged. By introducing the turbocharger 67, the supercharging pressure by the turbocharger 67 is increased, and the output is improved.

  Then, one exhaust pipe 57 (58) of each cylinder group of the left and right banks 12 and 13 is closed at a low temperature start of the engine, a high load and a high rotation, and the exhaust gas discharged from this cylinder group is connected to the communication pipe. In the operation state of joining the exhaust pipe 58 (57) of the other cylinder group through 64 and discharging through the exhaust pipe 58 (57), the front three-way catalyst 60 (59) and the middle three-way catalyst 62 are warmed up. Can do. Thereafter, from this operating state, the exhaust pipes 57 and 58 of each cylinder group of the left and right banks 12 and 13 are opened, and the exhaust gas discharged from each cylinder group is exhausted from the respective exhaust pipes 57 and 58. When the change is made, the exhaust gas passing through one exhaust pipe 57 (58) is appropriately purified by the middle three-way catalyst 62 until the warm-up of the front three-way catalyst 59 (60) is completed by the exhaust gas. The

  Thus, in the internal combustion engine of the first embodiment, in the V-type 6-cylinder engine, a cylinder group in which a plurality of cylinders are divided and arranged in the left and right first banks 12 and second banks 13 is provided, and each bank is provided. While the intake pipe 51 is connected to the 12 and 13 cylinder groups, the first exhaust pipe 57 and the second exhaust pipe 58 are connected, and the downstream ends of the exhaust pipes 57 and 58 are joined together to connect the exhaust collecting pipe 61. Are connected to each of the exhaust pipes 57, 58, and the first front-stage three-way catalyst 59 and the second front-stage three-way catalyst 60 are 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 65 and 66 are connected to each other by a communication pipe 64, and a middle three-way catalyst 62 is provided in the vicinity of the junction where the downstream ends of the exhaust pipes 57 and 58 are joined. A NOx occlusion reduction type catalyst 63 is provided downstream of the exhaust collecting pipe 61. There.

  Therefore, by opening and closing the first and second control valves 65 and 66, the exhaust gas discharged from one cylinder group of the left and right banks 12 and 13 passes through the communication pipe 64 and the exhaust pipe 58 of the other cylinder group. (57) and in the operation state in which all exhaust gases discharged from the cylinder groups of the left and right banks 12 and 13 are discharged through the exhaust pipe 58 (57), the front three-way catalyst 60 (59) and the middle The three-way catalyst 62 is warmed up, and this operating state is changed to an operating state in which exhaust gas discharged from the cylinder groups of the left and right banks 12 and 13 is discharged from the respective exhaust pipes 57 and 58. At this time, even if the warming-up of the front three-way catalyst 59 (60) is not completed, the middle three-way catalyst 62 has already been warmed up, so that the exhaust gas passing through the exhaust pipe 57 (58) is transferred to the middle three-way catalyst 62. Purify properly Is the thing now, be changed operating conditions, it is possible to purification treatment proper harmful components in the exhaust gas continuously, it is possible to improve the exhaust purification efficiency.

  FIG. 4 is a schematic plan view of a V-type 6-cylinder engine that represents an internal combustion engine according to a 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 V-type six-cylinder engine of the second embodiment, as shown in FIG. 4, a plurality of cylinders are provided in the left and right first and second banks 12 and 13 to constitute a cylinder group. An air cleaner 52 is attached to the air intake port of the intake pipe 51, and an electronic throttle device 54 having a throttle valve 53 is provided on the downstream side of the air cleaner 52. A surge tank 50 is connected to the downstream end of the intake pipe 51, and the surge tank 50 is connected to intake ports 24 and 25 of the banks 12 and 13 via intake manifolds 48 and 49.

  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. A first front three-way catalyst 59 is attached to the first exhaust pipe 57, while a second front three-way catalyst 60 is attached to the second exhaust pipe 58, and the first and second exhaust pipes 57, 58 are attached. The downstream end of the exhaust gas is joined and an exhaust collecting pipe 61 is connected to the joining part, and a middle three-way catalyst (medium purification catalyst) 91 is attached to the most upstream end of the exhaust collecting pipe 61 in the flow direction of the exhaust gas. The NOx occlusion reduction type catalyst 63 is mounted on the downstream side of the exhaust collecting pipe 61.

  Further, the first exhaust pipe 57 and the second exhaust pipe 58 are communicated by a communication pipe 64 on the upstream side in the flow direction of the exhaust gas from the position where each of the preceding three-way catalysts 59 and 60 is mounted. A first control valve 65 and a second control valve 66 are attached to the first exhaust pipe 57 and the second exhaust pipe 58 on the downstream side of the upstream three-way catalysts 59 and 60 in the exhaust gas flow direction. Yes. The first and second control valves 65 and 66 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 according to the engine operating state. it can. That is, various bank controls are possible by changing the combustion state of each bank 12, 13 and the exhaust gas discharge route. A turbocharger 67 is provided on the first bank 12 side.

  By the way, the fuel contains a sulfur component. When the fuel containing the sulfur component is combusted and discharged as exhaust gas to the exhaust pipes 57 and 58, the sulfur component in the exhaust gas is converted into a NOx occlusion reduction type catalyst. As a result, the NOx purification efficiency decreases.

  Therefore, in the engine of the second embodiment, the first front three-way catalyst 59 is attached to the first exhaust pipe 57, while the second front three-way catalyst 60 is attached to the second exhaust pipe 58, and the first and second The downstream end portions of the exhaust pipes 57 and 58 are joined to connect the exhaust collecting pipe 61, and the middle three-way catalyst 91 is located in the vicinity of the joining part of the exhaust pipes 57 and 58 at the most upstream end of the exhaust collecting pipe 61. Wearing. The middle three-way catalyst 91 is provided with a function of capturing sulfur components in the exhaust gas.

  Therefore, for example, when the engine is cold started, if the first exhaust pipe 57 is closed by the first control valve 65 and the second exhaust pipe 58 is opened by the second control valve 66, the cylinders in the first bank 12 are discharged. The exhaust gas is bypassed to the second bank 13 side through the communication pipe 64, and the exhaust gas from the cylinder groups of the banks 12 and 13 flows to the second exhaust pipe 58 in a whole. The exhaust gas flows into the second front stage three-way catalyst 60 and is warmed up to be activated. Further, the exhaust gas that has passed through the second front-stage three-way catalyst 60 from the second exhaust pipe 58 flows into the exhaust collecting pipe 61 and flows into the middle-stage three-way catalyst 91 and the NOx occlusion reduction type catalyst 63. The middle three-way catalyst 91 is activated over time.

  Then, when the first exhaust pipe 57 is opened by the first control valve 65 from this operating state, the exhaust gas discharged from the cylinder groups of the left and right banks 12 and 13 does not flow into the communication pipe 64 but the respective exhaust pipes 57. , 58, and when the operation state is changed to this, the high-temperature exhaust gas flows into the first front-stage three-way catalyst 59 to be warmed up and activated. It is difficult for the first front-stage three-way catalyst 59 to properly purify the exhaust gas from when this operating state is changed until the first front-stage three-way catalyst 59 is activated. The middle stage three-way catalyst 91 is appropriately purified.

  Further, when the exhaust gas contains a sulfur component, when the exhaust gas passes through the middle three-way catalyst 91, the middle three-way catalyst 91 captures the sulfur component in the exhaust gas. The storage reduction catalyst 63 is not poisoned by sulfur and NOx purification efficiency does not decrease.

  As described above, in the internal combustion engine of the second embodiment, the first exhaust pipe 57 and the second exhaust pipe 58 are connected to the cylinder groups of the left and right banks 12 and 13, and the downstream ends of the exhaust pipes 57 and 58 are connected. The exhaust collecting pipe 61 is connected to each other, the upstream three-way catalysts 59, 60 and the control valves 65, 66 are provided in the exhaust pipes 57, 58, and the upstream three-way catalysts 59, 60 in the exhaust pipes 57, 58 are provided. 60 and the upstream side of the control valves 64, 65 are communicated by a communication pipe 64, a middle three-way catalyst 91 having a sulfur component trapping function is provided at the most upstream end of the exhaust collecting pipe 61, and the downstream side of the exhaust collecting pipe 61 Is provided with a NOx occlusion reduction type catalyst 63.

  Therefore, when the exhaust gas discharge path is changed by opening and closing the first and second control valves 65 and 66, the warming of the front three-way catalyst 59 (60) attached to one exhaust pipe 57 (58). Even if the machine is not completed, the middle three-way catalyst 91 has already been warmed up, so the exhaust gas passing through the exhaust pipe 57 (58) will be appropriately purified by the middle three-way catalyst 91, and Even if the state is changed, it is possible to properly purify harmful components in the exhaust gas continuously and to improve the exhaust purification efficiency.

  Further, since the middle three-way catalyst 91 provided on the upstream side of the NOx storage reduction catalyst 63 has a sulfur component capturing function, when the exhaust gas passes through the middle three-way catalyst 91, this middle three-way catalyst. 91 can capture the sulfur component in the exhaust gas, and can prevent sulfur poisoning in the NOx occlusion reduction type catalyst 63 to ensure high NOx purification efficiency.

  FIG. 5 is a schematic plan view of a V-type 6-cylinder engine representing an internal combustion engine according to Embodiment 3 of the present invention, and FIGS. 6-1 to 6-4 are the exhaust passages in the V-type 6-cylinder engine of Embodiment 3. It is the schematic showing the modification of the exhaust-gas guide means provided in a confluence | merging part. In addition, the same code | symbol is attached | subjected to the member which has the same function as what was demonstrated in the Example mentioned above, and the overlapping description is abbreviate | omitted.

  In the V-type six-cylinder engine of the third embodiment, as shown in FIG. 5, a plurality of cylinders are provided in the left and right first and second banks 12 and 13 to constitute a cylinder group. An air cleaner 52 is attached to the air intake port of the intake pipe 51, and an electronic throttle device 54 having a throttle valve 53 is provided on the downstream side of the air cleaner 52. A surge tank 50 is connected to the downstream end of the intake pipe 51, and the surge tank 50 is connected to intake ports 24 and 25 of the banks 12 and 13 via intake manifolds 48 and 49.

  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. A first front three-way catalyst 59 is attached to the first exhaust pipe 57, while a second front three-way catalyst 60 is attached to the second exhaust pipe 58, and the first and second exhaust pipes 57, 58 are attached. Are connected to each other, and an exhaust collecting pipe 61 is connected to the joining section. A middle three-way catalyst 62 is attached to the most upstream end of the exhaust collecting pipe 61 in the flow direction of the exhaust gas. A NOx occlusion reduction type catalyst 63 is mounted downstream of 61.

  Further, the first exhaust pipe 57 and the second exhaust pipe 58 are communicated by a communication pipe 64 on the upstream side in the flow direction of the exhaust gas from the position where each of the preceding three-way catalysts 59 and 60 is mounted. A first control valve 65 and a second control valve 66 are attached to the first exhaust pipe 57 and the second exhaust pipe 58 on the downstream side of the upstream three-way catalysts 59 and 60 in the exhaust gas flow direction. Yes. The first and second control valves 65 and 66 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 according to the engine operating state. it can. That is, various bank controls are possible by changing the combustion state of each bank 12, 13 and the exhaust gas discharge route. A turbocharger 67 is provided on the first bank 12 side.

  By the way, the fuel contains a sulfur component. When the fuel containing the sulfur component is combusted and discharged as exhaust gas to the exhaust pipes 57 and 58, the sulfur component in the exhaust gas is converted into a NOx occlusion reduction type catalyst. As a result, the NOx purification efficiency decreases. Therefore, the exhaust gas from the cylinder group of the first bank 12 is set to a lean atmosphere, the exhaust gas from the cylinder group of the second bank 13 is set to a rich atmosphere, and the exhaust gas of the lean atmosphere and the exhaust gas of the rich atmosphere are each exhaust pipe. The NOx storage reduction catalyst 63 is made to flow at a high temperature and rich by utilizing the oxidation exothermic reaction at that time by flowing into the exhaust collecting pipe 61 from 57 and 58 and joining the NOx storage reduction catalyst 63. The catalyst is regenerated by releasing the accumulated sulfur component.

  However, the exhaust gas collecting pipe 61 is provided with a middle three-way catalyst 62 on the upstream side of the NOx occlusion reduction type catalyst 63, and the exhaust gas in the lean atmosphere and the exhaust gas in the rich atmosphere discharged from the banks 12 and 13. When the gas flows into the exhaust collecting pipe 61 from the exhaust pipes 57 and 58, it mixes in the vicinity of the middle three-way catalyst 62 to generate an oxidation exothermic reaction, and the NOx occlusion reduction type catalyst 63 can be sufficiently heated. The sulfur poisoning regeneration cannot be properly executed.

  Therefore, in the engine of the third embodiment, the first front three-way catalyst 59 is attached to the first exhaust pipe 57, while the second front three-way catalyst 60 is attached to the second exhaust pipe 58, and the first and second The downstream end portions of the exhaust pipes 57 and 58 are joined to connect the exhaust collecting pipe 61, and the middle three-way catalyst 62 is located near the joining part of the exhaust pipes 57 and 58 and at the most upstream end of the exhaust collecting pipe 61. The NOx occlusion reduction type catalyst 63 is mounted on the downstream side, and exhaust gas guide means for suppressing mixing of the exhaust gas is provided at the junction where the downstream ends of the exhaust pipes 57 and 58 merge.

  Specifically, in the exhaust gas guiding means of the third embodiment, when the length of the exhaust collecting pipe 61 from the junction of the exhaust pipes 57 and 58 to the middle three-way catalyst 62 is L, and the inner diameter is D, both Is set so that L <2D.

  Therefore, for example, when the engine is cold started, if the first exhaust pipe 57 is closed by the first control valve 65 and the second exhaust pipe 58 is opened by the second control valve 66, the cylinders in the first bank 12 are discharged. The exhaust gas is bypassed to the second bank 13 side through the communication pipe 64, and the exhaust gas from the cylinder groups of the banks 12 and 13 flows to the second exhaust pipe 58 in a whole. The exhaust gas flows into the second front stage three-way catalyst 60 and is warmed up to be activated. Further, the exhaust gas that has passed through the second front-stage three-way catalyst 60 from the second exhaust pipe 58 flows into the exhaust collecting pipe 61 and flows into the middle-stage three-way catalyst 62 and the NOx occlusion reduction type catalyst 63. The middle three-way catalyst 62 is activated over time.

  Then, when the first exhaust pipe 57 is opened by the first control valve 65 from this operating state, the exhaust gas discharged from the cylinder groups of the left and right banks 12 and 13 does not flow into the communication pipe 64 but the respective exhaust pipes 57. , 58, and when the operation state is changed to this, the high-temperature exhaust gas flows into the first front-stage three-way catalyst 59 to be warmed up and activated. It is difficult for the first front-stage three-way catalyst 59 to properly purify the exhaust gas from when this operating state is changed until the first front-stage three-way catalyst 59 is activated. The intermediate stage three-way catalyst 62 is appropriately purified.

  If the exhaust gas contains a sulfur component, when the exhaust gas passes through the NOx storage reduction catalyst 63, the sulfur component in the exhaust gas adheres to the NOx storage reduction catalyst 63 and is covered. You will be poisoned. When the amount of sulfur adhering to the NOx occlusion reduction catalyst 63 exceeds a predetermined value set in advance, the exhaust gas from the cylinder group of the first bank 12 is set to a lean atmosphere, and from the cylinder group of the second bank 13 The exhaust gas is set to a rich atmosphere, and the exhaust gas in the lean atmosphere and the exhaust gas in the rich atmosphere are caused to flow from the exhaust pipes 57 and 58 to the exhaust collecting pipe 61, and are passed through the middle three-way catalyst 62. Merge.

  At this time, in each cylinder group of the left and right banks 12 and 13, explosions occur at predetermined intervals and exhaust gas is discharged to the exhaust pipes 57 and 58. This confluence is reached alternately through 58. Since the relationship between the length L and the inner diameter D of the exhaust collecting pipe 61 from the junction of the exhaust pipes 57 and 58 to the middle three-way catalyst 62 is set to L <2D, the exhaust pipes 57 and 58 are alternately connected. The exhaust gas that reaches the gas flows into the NOx occlusion reduction type catalyst 63 in a laminar flow that is difficult to mix, and is easily mixed here. Therefore, the lean exhaust gas and the rich exhaust gas are merged in the NOx occlusion reduction type catalyst 63, and an oxidation exothermic reaction occurs here, and sulfur poisoning in the NOx occlusion reduction type catalyst 63 is eliminated and the exhaust gas is efficiently regenerated.

  In the above description, the relationship between the length L and the inner diameter D of the exhaust collecting pipe 61 from the junction of the exhaust pipes 57 and 58 to the middle three-way catalyst 62 is set to L <2D. However, the exhaust gas guiding means of the present invention is not limited to this configuration.

  For example, as shown in FIG. 6A, the exhaust gas guiding means extends into the exhaust collecting pipe 61 at the junction of the downstream end of the first exhaust pipe 57 and the downstream end of the second exhaust pipe 58. A partition plate 101 is provided to divide the inside of the exhaust collecting pipe 61 from the junction of the exhaust pipes 57 and 58 to the middle three-way catalyst 62 into upper and lower passages or left and right passages. Further, as shown in FIG. 6B, the downstream end of the first exhaust pipe 57 and the downstream end of the second exhaust pipe 58 are joined to the junction between the downstream end of the second exhaust pipe 58 and the exhaust collecting pipe 61. An extension pipe 102 is provided to extend to the inner and outer passages from the junction of the exhaust pipes 57 and 58 to the middle three-way catalyst 62.

  Accordingly, the exhaust gas in the lean atmosphere flowing through the first exhaust pipe 57 and the exhaust gas in the rich atmosphere flowing through the second exhaust pipe 58 are separated at the upstream end of the exhaust collecting pipe 61 by the partition plate 101 or the extension pipe 102. The NOx occlusion reduction type catalyst 63 passes through the middle three-way catalyst 62 without mixing, and is mixed with the NOx occlusion reduction type catalyst 63 to cause an oxidative exothermic reaction, thereby properly eliminating and regenerating sulfur poisoning. Is done.

  Further, as shown in FIG. 6-3, the exhaust gas guiding means is an extended portion between the downstream end portion of the first exhaust pipe 57 and the downstream end portion of the second exhaust pipe 58 and the exhaust collecting pipe 61. 103 is provided. In addition, as shown in FIG. 6-4, the expansion portion 103 is provided at the junction between the downstream end of the first exhaust pipe 57 and the downstream end of the second exhaust pipe 58, and the first exhaust pipe 57 and the second exhaust pipe are provided. A predetermined exhaust gas incident angle θ is provided at the connecting portion of the pipe 58.

  Therefore, the exhaust gas in the lean atmosphere flowing through the first exhaust pipe 57 and the exhaust gas in the rich atmosphere flowing through the second exhaust pipe 58 have an inertia effect by the expansion portion 103 and pass through the middle three-way catalyst 62 without being mixed. To the NOx occlusion reduction type catalyst 63, and the exhaust gas in the lean atmosphere flowing through the first exhaust pipe 57 and the exhaust gas in the rich atmosphere flowing through the second exhaust pipe 58 enter the expansion portion 103 at a predetermined exhaust gas incident angle θ. By flowing in, due to its inertial effect, it passes through the middle three-way catalyst 62 without mixing and reaches the NOx occlusion reduction type catalyst 63, which mixes with this NOx occlusion reduction type catalyst 63 to cause an oxidative exothermic reaction. It is regenerated by properly eliminating the poison.

  As described above, in the internal combustion engine of the third embodiment, the first exhaust pipe 57 and the second exhaust pipe 58 are connected to the cylinder groups of the left and right banks 12 and 13, and the downstream ends of the exhaust pipes 57 and 58 are connected. The exhaust collecting pipe 61 is connected to each other, the upstream three-way catalysts 59, 60 and the control valves 65, 66 are provided in the exhaust pipes 57, 58, and the upstream three-way catalysts 59, 60 in the exhaust pipes 57, 58 are provided. 60 and the upstream side of the control valves 64, 65 are communicated by a communication pipe 64, a middle three-way catalyst 62 is provided at the most upstream end of the exhaust collecting pipe 61, and the NOx occlusion reduction type catalyst 63 is provided downstream of the exhaust collecting pipe 61. The exhaust gas guide means for suppressing the mixing of the exhaust gas is provided at the junction where the downstream ends of the exhaust pipes 57 and 58 are joined.

  Therefore, when the exhaust gas discharge path is changed by opening and closing the first and second control valves 65 and 66, the warming of the front three-way catalyst 59 (60) attached to one exhaust pipe 57 (58). Even if the machine is not completed, since the middle three-way catalyst 62 has already been warmed up, the exhaust gas passing through the exhaust pipe 57 (58) will be appropriately purified by the middle three-way catalyst 62, and Even if the state is changed, it is possible to properly purify harmful components in the exhaust gas continuously and to improve the exhaust purification efficiency.

  When the amount of sulfur adhering to the NOx storage reduction catalyst 63 exceeds a predetermined value set in advance, the exhaust gas from the cylinder group of the first bank 12 is set to a lean atmosphere, and from the cylinder group of the second bank 13 The exhaust gas of the lean atmosphere and the exhaust gas of the rich atmosphere are caused to flow from the exhaust pipes 57 and 58 to the exhaust collecting pipe 61 and merged by the NOx occlusion reduction type catalyst 63. At this time, as the exhaust gas guiding means, the relationship between the length L and the inner diameter D of the exhaust collecting pipe 61 from the confluence portion of the exhaust pipes 57 and 58 to the middle three-way catalyst 62 is set to L <2D. The exhaust gas that reaches the exhaust collecting pipe 61 through 57 and 58 is difficult to mix and flows into the NOx occlusion reduction type catalyst 63 in a laminar flow, and lean exhaust gas and rich exhaust gas are generated in the middle three-way catalyst 62. Without mixing, the NOx occlusion reduction type catalyst 63 mixes to cause an exothermic oxidation reaction, and sulfur poisoning in the NOx occlusion reduction type catalyst 63 can be eliminated to efficiently regenerate.

  FIG. 7 is a schematic plan view of a V-type 6-cylinder engine that represents an internal combustion engine according to Embodiment 4 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 V-type 6-cylinder engine of the fourth embodiment, as shown in FIG. 7, a plurality of cylinders are provided in the left and right first and second banks 12 and 13 to constitute a cylinder group. An air cleaner 52 is attached to the air intake port of the intake pipe 51, and an electronic throttle device 54 having a throttle valve 53 is provided on the downstream side of the air cleaner 52. A surge tank 50 is connected to the downstream end of the intake pipe 51, and the surge tank 50 is connected to intake ports 24 and 25 of the banks 12 and 13 via intake manifolds 48 and 49.

  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. A first front three-way catalyst 59 is attached to the first exhaust pipe 57, while a second front three-way catalyst 60 is attached to the second exhaust pipe 58, and the first and second exhaust pipes 57, 58 are attached. Are connected to each other, and an exhaust collecting pipe 61 is connected to the joining part. A middle three-way catalyst (medium purification catalyst) 92 is mounted near the joining part of each of the exhaust pipes 57 and 58, and the exhaust collecting pipe is connected. A NOx occlusion reduction type catalyst 63 is mounted downstream of 61. In the present embodiment, the middle three-way catalyst 92 is provided at the most downstream end in the flow direction of the exhaust gas in the first exhaust pipe 57. The middle three-way catalyst 92 may be provided at the most downstream end of the second exhaust pipe 58 in the exhaust gas flow direction.

  Further, the first exhaust pipe 57 and the second exhaust pipe 58 are communicated by a communication pipe 64 on the upstream side in the flow direction of the exhaust gas from the position where each of the preceding three-way catalysts 59 and 60 is mounted. A first control valve 65 and a second control valve 66 are attached to the first exhaust pipe 57 and the second exhaust pipe 58 on the downstream side of the upstream three-way catalysts 59 and 60 in the exhaust gas flow direction. Yes. The first and second control valves 65 and 66 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 according to the engine operating state. it can. That is, various bank controls are possible by changing the combustion state of each bank 12, 13 and the exhaust gas discharge route. A turbocharger 67 is provided on the first bank 12 side.

  Therefore, for example, when the engine is cold started, if the first exhaust pipe 57 is closed by the first control valve 65 and the second exhaust pipe 58 is opened by the second control valve 66, the cylinders in the first bank 12 are discharged. The exhaust gas is bypassed to the second bank 13 side through the communication pipe 64, and the exhaust gas from the cylinder groups of the banks 12 and 13 flows to the second exhaust pipe 58 in a whole. The exhaust gas flows into the second front stage three-way catalyst 60 and is warmed up to be activated. Further, the exhaust gas that has passed through the second front-stage three-way catalyst 60 from the second exhaust pipe 58 flows into the exhaust collecting pipe 61 and is warmed up by flowing into the NOx storage reduction catalyst 63. Further, in each cylinder group of the left and right banks 12 and 13, an explosion occurs at a predetermined interval and exhaust gas is alternately discharged, so that exhaust pulsation is transmitted to the second exhaust pipe 58 and the second exhaust pipe 58. The exhaust gas flowing into the exhaust collecting pipe 61 from here flows back to the first exhaust pipe 57 side by exhaust pulsation, warms up and activates the middle three-way catalyst 92.

  Then, when the first exhaust pipe 57 is opened by the first control valve 65 from this operating state, the exhaust gas discharged from the cylinder groups of the left and right banks 12 and 13 does not flow into the communication pipe 64 but the respective exhaust pipes 57. , 58, and when the operation state is changed to this, the high-temperature exhaust gas flows into the first front-stage three-way catalyst 59 to be warmed up and activated. It is difficult for the first front-stage three-way catalyst 59 to properly purify the exhaust gas from when this operating state is changed until the first front-stage three-way catalyst 59 is activated. The middle stage three-way catalyst 92 is appropriately purified.

  If the exhaust gas contains a sulfur component, when the exhaust gas passes through the NOx storage reduction catalyst 63, the sulfur component in the exhaust gas adheres to the NOx storage reduction catalyst 63 and is covered. You will be poisoned. When the amount of sulfur adhering to the NOx occlusion reduction catalyst 63 exceeds a predetermined value set in advance, the exhaust gas from the cylinder group of the first bank 12 is brought into a lean atmosphere, and from the cylinder group of the second bank 13 The exhaust gas of the lean atmosphere and the exhaust gas of the rich atmosphere are caused to flow from the exhaust pipes 57 and 58 to the exhaust collecting pipe 61 and are combined by the NOx occlusion reduction type catalyst 63.

  At this time, the middle three-way catalyst 92 is provided at the most downstream end in the flow direction of the exhaust gas in the first exhaust pipe 57, so that the lean exhaust gas and the rich exhaust gas merge at the middle three-way catalyst 92. However, the NOx occlusion reduction catalyst 63 is appropriately joined, and an oxidation exothermic reaction occurs here, so that sulfur poisoning in the NOx occlusion reduction catalyst 63 is eliminated and the NOx occlusion reduction catalyst 63 is efficiently regenerated.

  As described above, in the internal combustion engine of the fourth embodiment, the first exhaust pipe 57 and the second exhaust pipe 58 are connected to the cylinder groups of the left and right banks 12 and 13, and the downstream ends of the exhaust pipes 57 and 58 are connected. The exhaust collecting pipe 61 is connected to each other, the upstream three-way catalysts 59, 60 and the control valves 65, 66 are provided in the exhaust pipes 57, 58, and the upstream three-way catalysts 59, 60 in the exhaust pipes 57, 58 are provided. 60 and the upstream side of the control valves 65 and 66 are communicated by a communication pipe 64, a middle three-way catalyst 92 is provided at the most downstream end of the first exhaust pipe 57, and a NOx occlusion reduction type catalyst is provided downstream of the exhaust collecting pipe 61. 63 is provided.

  Therefore, when the exhaust gas discharge path is changed by opening and closing the first and second control valves 65 and 66, the warming of the front three-way catalyst 59 (60) attached to one exhaust pipe 57 (58). Even if the engine is not completed, the intermediate three-way catalyst 92 has already been warmed by the backflow of the exhaust gas, so that the exhaust gas passing through the exhaust pipe 57 (58) is appropriately purified by the intermediate three-way catalyst 92. In other words, even if the operating state is changed, it is possible to continuously purify harmful components in the exhaust gas properly and improve the exhaust purification efficiency.

  When the amount of sulfur adhering to the NOx storage reduction catalyst 63 exceeds a predetermined value set in advance, the exhaust gas from the cylinder group of the first bank 12 is set to a lean atmosphere, and from the cylinder group of the second bank 13 The exhaust gas of the lean atmosphere and the exhaust gas of the rich atmosphere are caused to flow from the exhaust pipes 57 and 58 to the exhaust collecting pipe 61 and merged by the NOx occlusion reduction type catalyst 63. At this time, the middle three-way catalyst 92 is provided at the most downstream end of the first exhaust pipe 57, so that the exhaust gas that reaches the exhaust collecting pipe 61 through the exhaust pipes 57, 58 is properly stored in the NOx storage reduction catalyst. 63, the lean exhaust gas and the rich exhaust gas are not mixed by the middle three-way catalyst 62 but mixed by the NOx occlusion reduction type catalyst 63 to cause an oxidation exothermic reaction, and the sulfur in the NOx occlusion reduction type catalyst 63 occurs. It is possible to eliminate poisoning and regenerate efficiently.

  In each of the above-described embodiments, the front three-way catalyst 59, 60 is attached to both the exhaust pipes 57, 58 of the banks 12, 13, but the front three-way catalyst is attached to only one of the exhaust pipes 57, 58. A catalyst may be attached and a three-way catalyst may be provided in the collective exhaust pipe 61. In addition, the turbocharger 67 is provided in the first bank 12 and the first and second banks 12 and 13 are supercharged. However, the turbocharger 67 may be provided in both the banks 12 and 13 or both banks 12 and 13 may be provided. , 13 may be removed from the turbocharger.

  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 aims to improve exhaust purification efficiency by appropriately purifying harmful components in the exhaust gas even when the operating state is changed. Also useful.

1 is a schematic plan view of a V-type 6-cylinder engine that represents an internal combustion engine according to Embodiment 1 of the present invention. 1 is a schematic cross-sectional view of a V-type 6-cylinder engine according to Embodiment 1. FIG. 2 is a graph showing a change in catalyst temperature when the V-type six-cylinder engine of Example 1 is started. 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. It is a schematic plan view of the V type 6 cylinder engine showing the internal combustion engine which concerns on Example 3 of this invention. FIG. 10 is a schematic diagram showing a modification of the exhaust gas guide means provided at the merging portion in the exhaust passage in the V-type 6-cylinder engine of Embodiment 3. FIG. 10 is a schematic diagram showing a modification of the exhaust gas guide means provided at the merging portion in the exhaust passage in the V-type 6-cylinder engine of Embodiment 3. FIG. 10 is a schematic diagram showing a modification of the exhaust gas guide means provided at the merging portion in the exhaust passage in the V-type 6-cylinder engine of Embodiment 3. FIG. 10 is a schematic diagram showing a modification of the exhaust gas guide means provided at the merging portion in the exhaust passage in the V-type 6-cylinder engine of Embodiment 3. It is a schematic plan view of the V type 6 cylinder engine showing the internal combustion engine which concerns on Example 4 of this invention.

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 (exhaust passage)
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 Exhaust collecting pipe (exhaust collecting passage)
62, 91, 92 Middle three-way catalyst (middle purification catalyst)
63 NOx occlusion reduction type catalyst 64 Communication pipe (communication passage)
65 First control valve 66 Second control valve 67 Turbocharger 72, 73 Injector 77, 78 Spark plug 79 Electronic control unit, ECU
101 Partition plate (exhaust gas guide means)
102 Extension pipe (exhaust gas guide means)
103 Expansion part (exhaust gas guide means)

Claims (5)

  A plurality of cylinders have two cylinder groups arranged in left and right banks, and an intake passage is provided for each cylinder group, while an exhaust passage is provided independently. An exhaust collecting passage where downstream ends are joined is provided, a pre-stage purification catalyst is provided in each exhaust passage, and a control valve for adjusting the flow rate of exhaust gas is provided in each exhaust passage, and the exhaust passage in each exhaust passage is A upstream purification catalyst and the upstream side of the control valve are communicated by a communication passage, a middle purification catalyst is provided in the vicinity of a joining portion where downstream ends of the exhaust passages are joined, and a rear purification catalyst is provided in the exhaust collecting passage. An internal combustion engine characterized by that.   2. The internal combustion engine according to claim 1, wherein the intermediate stage purification catalyst is provided at an uppermost stream end portion in a flow direction of exhaust gas in the exhaust collecting passage.   3. The internal combustion engine according to claim 2, wherein the rear purification catalyst is a NOx occlusion reduction catalyst, and the middle purification catalyst is a three-way catalyst having a function of capturing a sulfur component in exhaust gas. An internal combustion engine.   The internal combustion engine according to claim 2 or 3, wherein an exhaust gas guide means for suppressing mixing of exhaust gas flowing through each exhaust passage is provided at a joining portion where downstream ends of the respective exhaust passages merge. A characteristic internal combustion engine.   2. The internal combustion engine according to claim 1, wherein the intermediate purification catalyst is provided at a most downstream end portion in a flow direction of the exhaust gas in any one of the exhaust passages.

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