Engine

Abstract

To perform lean combustion and clean up nitrogen oxides.SOLUTION: An engine has a first three-way catalytic converter connected to a first combustion chamber via a first upstream exhaust pipe, and a second three-way catalytic converter connected to a second combustion chamber via a second upstream exhaust pipe. The engine has a selective catalytic reduction converter connected to the first three-way catalytic converter and the second three-way catalytic converter via a downstream exhaust pipe. A control system provided on the engine controls an air-fuel ratio in the second combustion chamber to a target air-fuel ratio that is equal to or lower than a stoichiometric air-fuel ratio, when controlling an air-fuel ratio in the first combustion chamber to a target air-fuel ratio that is out of a purification window of the first three-way catalytic converter to the lean side.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to engines. [Background technology]

[0002] To purify engine exhaust gas, a three-way catalytic converter is provided in the engine exhaust system (see Patent Documents 1 and 2). In order for the three-way catalytic converter to function properly, it is necessary to control the air-fuel ratio within a predetermined purification window that includes the stoichiometric air-fuel ratio. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-264341 [Patent Document 2] Japanese Patent Application Publication No. 2017-223162 Summary of the Invention [Problem to be solved by the invention]

[0004] By the way, to improve the fuel economy of an engine, it is necessary to make the mixture leaner. However, the lean combustion of a lean mixture reduces the amount of nitrogen oxides (NO x ) is a factor that increases the NOx emissions. In other words, in lean combustion, the air-fuel ratio deviates from the purification window of the three-way catalytic converter to the lean side, making it difficult for the three-way catalytic converter to purify NOx. For this reason, there is a demand for both lean combustion and purification of NOx. [Means for solving the problem]

[0005] According to the present disclosure, the engine is an engine having a first combustion chamber and a second combustion chamber. The engine has a first injector provided in the first combustion chamber for injecting fuel, and a second injector provided in the second combustion chamber for injecting fuel. The engine has a first three-way catalytic converter connected to an exhaust port communicating with the first combustion chamber via a first upstream exhaust pipe. The engine has a second three-way catalytic converter connected to an exhaust port communicating with the second combustion chamber via a second upstream exhaust pipe. The engine has a selective catalytic reduction converter connected to the first three-way catalytic converter and the second three-way catalytic converter via a downstream exhaust pipe. The engine has a control system including a processor and a memory communicatively connected to each other, and controlling the first injector and the second injector. When the control system controls the air-fuel ratio in the first combustion chamber to a target air-fuel ratio that is outside the purification window of the first three-way catalytic converter to the lean side, the control system controls the air-fuel ratio in the second combustion chamber to a target air-fuel ratio that is equal to or lower than the stoichiometric air-fuel ratio. [Effects of the Invention]

[0006] According to the present disclosure, lean combustion can be performed and nitrogen oxides can be purified. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating an example of a vehicle equipped with an engine according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a view showing the engine along line AA in FIG. [Figure 3] FIG. 3 is a diagram showing an example of the basic structure of an electronic control unit. [Figure 4] FIG. 4 is a diagram showing an example of the purification rate characteristics of a three-way catalytic converter. [Figure 5A] FIG. 5A is a diagram showing an example of the relationship between the catalyst temperature and the ammonia production rate in a three-way catalytic converter. [Figure 5B]FIG. 5B is a diagram showing an example of the relationship between the catalyst temperature, the excess air ratio, and the amount of ammonia produced in a three-way catalytic converter. [Figure 6] FIG. 6 is a diagram showing the state of purification of exhaust gas when stoichiometric combustion is performed. [Figure 7] FIG. 7 is a diagram showing the purification state of exhaust gas when lean combustion and stoichiometric combustion are performed in combination. [Figure 8] FIG. 8 is a flowchart showing an example of a procedure for executing the target air-fuel ratio setting control. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, identical or substantially identical configurations and elements will be designated by the same reference numerals and repeated description will be omitted.

[0009] <Power unit> FIG. 1 is a diagram showing an example of a vehicle 11 equipped with an engine 10 according to an embodiment of the present disclosure. As shown in FIG. 1, the vehicle 11 has a power unit 13 made up of the engine 10 and a transmission 12. An output shaft 14 of the power unit 13 is connected to wheels 17 via a propeller shaft 15 and a differential mechanism 16. The power unit 13 shown in the figure is a rear-wheel drive power unit, but is not limited to this and may be an all-wheel drive or front-wheel drive power unit.

[0010] <Engine> Figure 2 is a diagram showing the engine 10 taken along line AA in Figure 1. As shown in Figure 2, the engine 10 has a first cylinder bank 20 consisting of a cylinder block 21 and a cylinder head 22, and a second cylinder bank 30 consisting of a cylinder block 31 and a cylinder head 32. The engine 10 also has a crankshaft 18 supported by the pair of cylinder blocks 21, 31. In other words, the engine 10 has the first cylinder bank 20 and the second cylinder bank 30 facing each other with the crankshaft 18 in between.

[0011] Two cylinder bores B1 and B3 are formed in the cylinder block 21. A piston P1 is housed in the cylinder bore B1, and a piston P3 is housed in the cylinder bore B3. A combustion chamber C1 is defined by the cylinder bore B1, the piston P1, and the cylinder head 22, and a combustion chamber C3 is defined by the cylinder bore B3, the piston P3, and the cylinder head 22. The cylinder head 22 also includes an injector 41 that injects fuel into the combustion chamber C1 and a spark plug 51 that ignites the air-fuel mixture in the combustion chamber C1. The cylinder head 22 also includes an injector 43 that injects fuel into the combustion chamber C3 and a spark plug 53 that ignites the air-fuel mixture in the combustion chamber C3.

[0012] Similarly, two cylinder bores B2 and B4 are formed in the cylinder block 31. A piston P2 is housed in the cylinder bore B2, and a piston P4 is housed in the cylinder bore B4. The cylinder bore B2, the piston P2, and the cylinder head 32 define a combustion chamber C2, while the cylinder bore B4, the piston P4, and the cylinder head 32 define a combustion chamber C4. The cylinder head 32 also includes an injector 42 that injects fuel into the combustion chamber C2 and a spark plug 52 that ignites the air-fuel mixture in the combustion chamber C2. The cylinder head 32 also includes an injector 44 that injects fuel into the combustion chamber C4 and a spark plug 54 that ignites the air-fuel mixture in the combustion chamber C4.

[0013] An exhaust system 70 that guides exhaust gas from exhaust ports 61, 62, 63, and 64 is connected to cylinder heads 22 and 32. Exhaust system 70 includes an exhaust manifold (first upstream exhaust pipe) 71 connected to exhaust ports 61 and 62 that communicate with combustion chambers C1 and C2, and a first three-way catalytic converter 72 connected to exhaust manifold 71. Similarly, exhaust system 70 includes an exhaust manifold (second upstream exhaust pipe) 73 connected to exhaust ports 63 and 64 that communicate with combustion chambers C3 and C4, and a second three-way catalytic converter 74 connected to exhaust manifold 73. Furthermore, exhaust system 70 includes a selective catalytic reduction converter 76 connected to both three-way catalytic converters 72 and 74 via exhaust pipes (downstream exhaust pipes) 75. The "TWC" attached to the three-way catalytic converters 72 and 74 stands for three-way catalyst, and the "SCR" attached to the selective catalytic reduction converter 76 stands for selective catalytic reduction.

[0014] An intake system 80 that guides intake air toward an intake port (not shown) is connected to the cylinder heads 22, 32. The intake system 80 is composed of an intake pipe 81, a throttle valve 82, a surge tank 83, a branch 84, etc. The engine 10 also has an EGR pipe 85 that supplies a portion of the exhaust gas from the exhaust system 70 to the intake system 80. The EGR pipe 85 is provided with an EGR valve 86 that controls the flow rate of the exhaust gas returned to the intake system 80.

[0015] <Control System> 2, engine 10 has a control system 90 consisting of an electronic control unit 91 for controlling throttle valve 82, injectors 41-44, spark plugs 51-54, etc. Sensors connected to electronic control unit 91 include an accelerator sensor 92 that detects the amount of accelerator pedal operation and a brake sensor 93 that detects the depression of the brake pedal. Sensors connected to electronic control unit 91 also include a vehicle speed sensor 94 that detects vehicle speed and an engine rotation sensor 95 that detects engine speed, which is the rotation speed of crankshaft 18. Furthermore, a power switch 96 that is operated when activating the control system or starting the engine is connected to electronic control unit 91.

[0016] The sensors connected to the electronic control unit 91 include a throttle opening sensor 97 that detects the opening of the throttle valve 82, and an air flow sensor 98 that detects the intake air amount. The sensors connected to the electronic control unit 91 also include an O2 sensor 99 that detects the oxygen concentration in the exhaust gas flowing through the exhaust manifold 71, and an O2 sensor 100 that detects the oxygen concentration in the exhaust gas flowing through the exhaust manifold 73. The sensors connected to the electronic control unit 91 also include a temperature sensor 101 that detects the temperature of the second three-way catalytic converter 74, and a NOx sensor 102 that detects the nitrogen oxide concentration in the exhaust gas that has passed through the selective catalytic reduction converter 76. X There is a sensor 102 .

[0017] Fig. 3 is a diagram showing an example of the basic structure of the electronic control unit 91. As shown in Fig. 3, the electronic control unit 91 has a microcontroller 112 incorporating a processor 110 and a main memory (memory) 111. A predetermined program is stored in the main memory 111, and the program is executed by the processor 110. The processor 110 and the main memory 111 are connected to each other so that they can communicate with each other. Note that a plurality of processors 110 may be incorporated into the microcontroller 112, and a plurality of main memories 111 may be incorporated into the microcontroller 112.

[0018] The electronic control unit 91 also includes an input circuit 113, a drive circuit 114, a communication circuit 115, an external memory 116, and a power supply circuit 117. The input circuit 113 converts signals input from various sensors into signals that can be input to the microcontroller 112. The drive circuit 114 generates drive signals for devices such as the injectors 41 to 44 based on signals output from the microcontroller 112. The communication circuit 115 converts signals output from the microcontroller 112 into communication signals directed to other electronic control units, etc. The communication circuit 115 also converts communication signals received from other electronic control units, etc. into signals that can be input to the microcontroller 112. The power supply circuit 117 supplies a stable power supply voltage to the microcontroller 112, the input circuit 113, the drive circuit 114, the communication circuit 115, the external memory 116, etc. The external memory 116, which is a non-volatile memory, etc., stores programs, various data, etc.

[0019] <Three-way catalytic converter> 4 is a diagram showing an example of the purification rate characteristics of three-way catalytic converters 72, 74. As shown in FIG. 4, when the air-fuel ratio is controlled to be within a predetermined purification window W1, three-way catalytic converters 72, 74 purify hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO). X In other words, the three-way catalytic converters 72, 74 convert hydrocarbons (HC) into carbon dioxide (CO2) and water (H2O), convert carbon monoxide (CO) into carbon dioxide (CO2), and convert nitrogen oxides (NO) into non-harmful components. X In addition, as shown by the symbol α in FIG. 4, when the air-fuel ratio becomes larger and deviates from the purification window W1, the oxygen becomes excessive and suppresses the reduction reaction, resulting in the conversion of nitrogen oxides NO X In other words, in order to improve the fuel economy of the engine 10, it is necessary to make the mixture in the combustion chambers C1 to C4 lean. However, the leaning of the mixture causes the air-fuel ratio to move out of the purification window W1 to the lean side, and the purification rate of nitrogen oxides NO XThe control system 90 controls the injectors 41 to 44 based on the output voltage V1 of the O2 sensors 99, 100 to keep the air-fuel ratio within the purification window W1.

[0020] The purification window W1 of the three-way catalytic converters 72, 74 is set to a range including the stoichiometric air-fuel ratio and its vicinity. When the fuel is gasoline, the stoichiometric air-fuel ratio is "14.7." Furthermore, when expressed using an air excess ratio λ that is independent of the fuel, the purification window W1 is set, for example, to a range where the air excess ratio λ is 0.97 or more and 1.03 or less. Furthermore, the purification window W1 is set ... X If it is possible to neutralize the excess air ratio λ, the purification window W1 may be set in a range where the excess air ratio λ is 0.96 or more and 1.04 or less, or the purification window W1 may be set in a range where the excess air ratio λ is 0.95 or more and 1.05 or less. The excess air ratio λ is a value obtained by dividing the actual air-fuel ratio by the stoichiometric air-fuel ratio. In other words, when the air-fuel ratio is controlled at the stoichiometric air-fuel ratio, the excess air ratio λ is "λ=1", when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, the excess air ratio λ is "λ<1", and when the air-fuel ratio is larger than the stoichiometric air-fuel ratio, the excess air ratio λ is "λ>1".

[0021] <Ammonia production> FIG. 5A shows an example of the relationship between catalyst temperature and ammonia production rate in a three-way catalytic converter 74. As shown in FIG. 5A, in the three-way catalytic converter 74, the production rate of ammonia (NH3) increases as the excess air ratio λ decreases, and the production rate of ammonia (NH3) increases as the catalyst temperature increases. In other words, as indicated by the symbol β in FIG. 5A, when the three-way catalytic converter 74 reaches a predetermined activation temperature, a large amount of ammonia (NH3) is produced when the air-fuel ratio is slightly richer than the stoichiometric air-fuel ratio. In other words, when the three-way catalytic converter 74 reaches its activation temperature, ammonia (NH3) can be produced as long as the air-fuel ratio is controlled to or near the stoichiometric air-fuel ratio. It is believed that ammonia (NH3) is produced by the reaction of nitrogen monoxide (NO) produced by the combustion of the air-fuel mixture with hydrogen (H2) produced by the water-gas shift reaction.

[0022] Figure 5B is a diagram showing an example of the relationship between catalyst temperature, excess air factor λ, and the amount of ammonia produced in three-way catalytic converter 74. The lines shown in Figure 5B connect points where the amount of ammonia produced is the same. Note that line L1 in Figure 5B connects points where the amount of ammonia produced is small, and line L2 in Figure 5B connects points where the amount of ammonia produced is large.

[0023] As shown by arrow Xa in Fig. 5B, in the three-way catalytic converter 74, the amount of ammonia NH3 produced increases as the excess air ratio λ decreases, and the amount of ammonia NH3 produced increases as the catalyst temperature increases. For example, when the catalyst temperature is equal to or higher than 200°C and lower than 350°C, a predetermined amount of ammonia NH3 can be produced by controlling the excess air ratio λ to 1.01 or less. Furthermore, when the catalyst temperature is equal to or higher than 350°C, a predetermined amount of ammonia NH3 can be produced by controlling the excess air ratio λ to 1.00 or less.

[0024] <Stoichiometric combustion> Fig. 6 is a diagram showing the purification status of exhaust gas when stoichiometric combustion is performed. As shown in Fig. 6, the control system 90 controls the air-fuel ratio in the combustion chambers (first combustion chambers) C1 and C2 toward a target air-fuel ratio set within the purification window W1 by controlling the fuel injection amount of the injectors (first injectors) 41 and 42. The control system 90 also controls the air-fuel ratio in the combustion chambers (second combustion chambers) C3 and C4 toward a target air-fuel ratio set within the purification window W1 by controlling the fuel injection amount of the injectors (second injectors) 43 and 44. In other words, when the control system 90 controls the air-fuel ratio in the combustion chambers C1 and C2 to a target air-fuel ratio within the purification window W1, the control system 90 also controls the air-fuel ratio in the combustion chambers C3 and C4 to a target air-fuel ratio within the purification window W1.

[0025] 6, each combustion chamber C1 to C4 of the engine 10 performs stoichiometric combustion in which the air-fuel ratio is controlled within a window W1, that is, stoichiometric combustion in which the air-fuel ratio is controlled to the stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio. When stoichiometric combustion is performed in the combustion chambers C1 and C2 in this manner, the first three-way catalytic converter 72 reduces hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO) in the exhaust gas. X Similarly, when stoichiometric combustion is performed in the combustion chambers C3 and C4, the second three-way catalytic converter 74 neutralizes hydrocarbons HC, carbon monoxide CO, and nitrogen oxides NO in the exhaust gas. X The detoxified exhaust gas is then guided from an exhaust pipe 75 through a selective catalytic reduction converter 76 to a muffler (not shown).

[0026] <Lean combustion and stoichiometric combustion> 7 is a diagram showing the state of purification of exhaust gas when lean combustion and stoichiometric combustion are performed in combination. As shown in FIG. 7, in order to improve the fuel economy of the engine 10, the control system 90 controls the air-fuel ratio in the combustion chambers (first combustion chambers) C1 and C2 toward a target air-fuel ratio that is outside the purification window W1 and on the lean side by controlling the fuel injection amount of the injectors (first injectors) 41 and 42. In this way, when lean combustion is performed in the combustion chambers C1 and C2, the first three-way catalytic converter 72 reduces nitrogen oxides NO X In other words, the exhaust gas that has passed through the first three-way catalytic converter 72 contains a large amount of nitrogen oxides NO. X When performing lean combustion in the combustion chambers C1 and C2, the target air-fuel ratio may be set to, for example, "λ=2" or "λ=1.5".

[0027] Therefore, the nitrogen oxides NO emitted from the first three-way catalytic converter 72 are XTo purify the exhaust gas, the control system 90 controls the air-fuel ratio in the combustion chambers C3 and C4 (second combustion chambers) toward a target air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio by controlling the fuel injection amount of the injectors (second injectors) 43 and 44. In other words, the control system 90 controls the air-fuel ratio in the combustion chambers C3 and C4 toward a target air-fuel ratio that is within the purification window W1 and equal to or lower than the stoichiometric air-fuel ratio. When stoichiometric combustion is performed in the combustion chambers C3 and C4 in this manner, ammonia (NH3) is generated when the exhaust gas passes through the second three-way catalytic converter 74. In other words, ammonia (NH3) can be contained in the exhaust gas discharged from the second three-way catalytic converter 74, and ammonia (NH3) can be supplied to the selective catalytic reduction converter 76.

[0028] That is, since lean combustion is performed in the combustion chambers C1 and C2, nitrogen oxides NO are transferred from the first three-way catalytic converter 72 to the selective catalytic reduction converter 76. X On the other hand, since stoichiometric combustion is performed in the combustion chambers C3 and C4, ammonia NH3 is supplied from the second three-way catalytic converter 74 to the selective catalytic reduction converter 76. Here, the selective catalytic reduction converter 76 converts nitrogen oxides NO X It has the function of reducing nitrogen oxides NO to nitrogen N2 and water H2O. X By combining lean combustion that produces nitrogen oxides NO and stoichiometric combustion that produces ammonia NH3, the selective catalytic reduction converter 76 X This allows lean combustion to be actively utilized, thereby improving the fuel economy of the engine 10.

[0029] In addition, since ammonia NH3 is produced by stoichiometric combustion, nitrogen oxides NO are not produced by using a selective catalytic reduction converter 76 without providing an injector for injecting urea water. X In addition, by performing stoichiometric combustion in conjunction with lean combustion, nitrogen oxides (NO) generated by lean combustion can be purified. XSince it can immediately purify LNT (Lean NO x Trap: NO X Without using a storage reduction catalyst, nitrogen oxides NO X This allows for the purification of nitrogen oxides NO X Since the selective catalytic reduction converter 76 contains iron zeolite, etc., the selective catalytic reduction converter 76 can reduce the purification cost of the nitrogen oxides NO. X In this way, the selective catalytic reduction converter 76 can capture small amounts of nitrogen oxides NO. X Therefore, it is not necessary to start lean combustion and stoichiometric combustion at the same time, and stoichiometric combustion may be started after the start of lean combustion.

[0030] <Target air-fuel ratio setting control> Fig. 8 is a flowchart showing an example of the execution procedure of target air-fuel ratio setting control for setting the target air-fuel ratio in the combustion chambers C3, C4. Each step of the target air-fuel ratio setting control shown in Fig. 8 is executed by the processor 110 constituting the control system 90. The target air-fuel ratio setting control is executed by the control system 90 at predetermined intervals.

[0031] As shown in Fig. 8, the control system 90 proceeds to step S10 and determines whether lean combustion is being performed in the combustion chambers C1 and C2. If the control system 90 determines in step S10 that lean combustion is being performed, the control system 90 proceeds to step S11 and calculates the combustion temperatures in the combustion chambers C1 and C2 based on the engine load and ignition timing. Next, the control system 90 proceeds to step S12 and calculates the nitrogen oxides NO associated with lean combustion based on the combustion temperatures in the combustion chambers C1 and C2. X The control system 90 also proceeds to step S13, where it calculates the amount of nitrogen oxides NO X Based on the amount of nitrogen oxides produced, X Calculate the amount of ammonia NH3 produced that is required for purification.

[0032] The control system 90 then proceeds to step S14 and sets a target air-fuel ratio for performing stoichiometric combustion in the combustion chambers C3 and C4 based on the amount of ammonia NH3 produced and the temperature of the second three-way catalytic converter 74. For example, as shown in FIG. 5B, when the amount of ammonia NH3 produced is along line Lx and the temperature of the second three-way catalytic converter 74 is 350°C, the control system 90 sets "λx" as the excess air ratio λ corresponding to the target air-fuel ratio. Furthermore, because the amount of ammonia NH3 produced varies depending on the catalyst temperature, the control system 90 sets the excess air ratio λ corresponding to the target air-fuel ratio to 1.01 or less when the temperature of the second three-way catalytic converter 74 is 200°C or higher but lower than 350°C. Furthermore, the control system 90 sets the excess air ratio λ corresponding to the target air-fuel ratio to 1.00 or less when the temperature of the second three-way catalytic converter 74 is 350°C or higher.

[0033] In this way, the control system 90 sets the target air-fuel ratio in the combustion chambers C3, C4 based on the temperature of the second three-way catalytic converter 74. This makes it possible to appropriately set the target air-fuel ratio in the combustion chambers C3, C4, and appropriately control the amount of ammonia (NH3) produced. In addition, since the amount of ammonia (NH3) produced can be appropriately controlled, the amount of nitrogen oxides (NO) in the selective catalytic reduction converter 76 can be reduced. X It is possible to properly neutralize the

[0034] <Engine vibration> However, since the combustion pressure differs between lean combustion and stoichiometric combustion, it is necessary to suppress engine vibration caused by the difference in combustion pressure. Therefore, as shown in Figure 7, lean combustion is performed in combustion chamber C1 in one cylinder bank 20, and lean combustion is performed in combustion chamber C2 in the other cylinder bank 30. Furthermore, stoichiometric combustion is performed in combustion chamber C3 in one cylinder bank 20, and stoichiometric combustion is performed in combustion chamber C4 in the other cylinder bank 30.

[0035] That is, combustion chambers C1 and C2 that perform lean combustion are provided in both cylinder banks 20 and 30, and combustion chambers C3 and C4 that perform stoichiometric combustion are provided in both cylinder banks 20 and 30. In this way, lean combustion is performed in both cylinder banks 20 and 30, and stoichiometric combustion is performed in both cylinder banks 20 and 30, so the difference in combustion pressure can be sufficiently canceled out and engine vibration can be effectively suppressed.

[0036] <Other variations> The present disclosure is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit and scope of the present disclosure. For example, the illustrated engine 10 is a horizontally opposed engine having a pair of cylinder banks 20, 30, but is not limited to this and may be an in-line engine or a V-type engine. Furthermore, the illustrated engine 10 is a four-cylinder engine having four combustion chambers C1 to C4, but is not limited to this. For example, it may be a two-cylinder engine having two combustion chambers, a three-cylinder engine having three combustion chambers, or a multi-cylinder engine having five or more combustion chambers.

[0037] In the above description, when lean combustion is performed in two combustion chambers C1 and C2, stoichiometric combustion is performed in two combustion chambers C3 and C4, but this is not limited to this. For example, in a four-cylinder engine, when lean combustion is performed in one combustion chamber, stoichiometric combustion may be performed in three combustion chambers, and when lean combustion is performed in three combustion chambers, stoichiometric combustion may be performed in one combustion chamber. Also, in the above description, the control system 90 is configured using one electronic control unit 91, but this is not limited to this, and the control system 90 may be configured using multiple electronic control units. [Explanation of symbols]

[0038] 10...engine, 20...cylinder bank (first cylinder bank), 30...cylinder bank (second cylinder bank), 41, 42...injector (first injector), 43, 44...injector (second injector), 61, 62, 63, 64...exhaust port, 71...exhaust manifold (first upstream exhaust pipe), 72...three-way catalytic converter (first three-way catalytic converter), 73...exhaust manifold (second upstream exhaust pipe), 74...three-way catalytic converter (second three-way catalytic converter), 75...exhaust pipe (downstream exhaust pipe), 76...selective catalytic reduction converter, 90...control system, 110...processor, 111...main memory (memory), C1, C2...combustion chamber (first combustion chamber), C3, C4...combustion chamber (second combustion chamber), W1...purification window

Claims

1. An engine having a first combustion chamber and a second combustion chamber, a first injector provided in the first combustion chamber for injecting fuel; a second injector provided in the second combustion chamber for injecting fuel; a first three-way catalytic converter connected to an exhaust port communicating with the first combustion chamber via a first upstream exhaust pipe; a second three-way catalytic converter connected to an exhaust port communicating with the second combustion chamber via a second upstream exhaust pipe; a selective catalytic reduction converter connected to the first three-way catalytic converter and the second three-way catalytic converter via a downstream exhaust pipe; a control system including a processor and a memory communicatively connected to each other, the control system controlling the first injector and the second injector; and The control system includes: When the air-fuel ratio in the first combustion chamber is controlled to a target air-fuel ratio that is deviated from the purification window of the first three-way catalytic converter to the lean side, controlling the air-fuel ratio in the second combustion chamber to a target air-fuel ratio that is equal to or lower than the stoichiometric air-fuel ratio; engine.

2. 2. The engine of claim 1, The control system includes: When the air-fuel ratio in the first combustion chamber is controlled to a target air-fuel ratio that is deviated from the purification window of the first three-way catalytic converter to the lean side, controlling the air-fuel ratio in the second combustion chamber to a target air-fuel ratio that is within a purification window of the second three-way catalytic converter and is equal to or lower than the stoichiometric air-fuel ratio; engine.

3. 2. The engine of claim 1, The control system includes: When the air-fuel ratio in the first combustion chamber is controlled to a target air-fuel ratio within a purification window of the first three-way catalytic converter, controlling the air-fuel ratio in the second combustion chamber to a target air-fuel ratio within a purification window of the second three-way catalytic converter; engine.

4. 2. The engine of claim 1, The control system includes: When the air-fuel ratio in the first combustion chamber is controlled to a target air-fuel ratio that is deviated from the purification window of the first three-way catalytic converter to the lean side, setting a target air-fuel ratio in the second combustion chamber based on the temperature of the second three-way catalytic converter; engine.

5. 2. The engine of claim 1, The engine has a first cylinder bank and a second cylinder bank that face each other across the crankshaft, The first combustion chamber is provided in both the first cylinder bank and the second cylinder bank, The second combustion chamber is provided in both the first cylinder bank and the second cylinder bank. engine.

Images