Exhaust purification device of internal combustion engine

Abstract

To suppress overheating of a catalyst part while suppressing deterioration of an emission.SOLUTION: An exhaust purification device 42 comprises an injector 27 that injects fuel directly to a combustion chamber 16 of an engine 10, a catalytic converter 41 provided in an exhaust passage 40 of the engine 10, and an ECU 60 that controls the injector 27. In order to suppress overheating of the catalytic converter 41, the ECU 60 performs overheating prevention control by injecting fuel from the injector 27 so that an air-fuel ratio of the engine 10 becomes stoichiometric, and by injecting fuel from the injector 27 so that a catalyst inflow air-fuel ratio flowing into the catalytic converter 41 during an exhaust stroke becomes rich.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an exhaust gas purification device for an internal combustion engine. [Background technology]

[0002] Conventionally, according to Patent Document 1, for example, fuel injection control is performed to increase the amount of fuel injected so that the air-fuel ratio of exhaust gas discharged from the cylinder (combustion chamber) becomes richer than the stoichiometric air-fuel ratio in order to prevent overheating of exhaust system components such as catalysts due to high vehicle speeds, high-load driving such as climbing hills, etc. To this end, in the case of a port injector engine, fuel is injected into the intake port before the intake valve opens, and in the case of a direct injector engine, fuel is injected into the cylinder during the intake stroke. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-180822 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the conventional example, during fuel increase control (control to prevent overheating of exhaust system components), the amount of injected fuel is increased at the same time as the fuel is injected for combustion, so that the fuel remains in the cylinder during the combustion stroke, resulting in rich combustion. This increases the amount of PM (particulate matter) emitted in the exhaust gas, worsening emissions. In addition, because the heat generated by combustion is absorbed by fuel that is richer than stoichiometric, there are concerns about a decrease in the thermal efficiency of the engine (internal combustion engine) and the cooling efficiency of catalysts, etc.

[0005] The problem to be solved by the technology disclosed in this specification is to suppress overheating of the catalyst portion while suppressing deterioration of emissions. [Means for solving the problem]

[0006] In order to solve the above problems, the technology disclosed in this specification takes the following measures.

[0007] The first means is an exhaust purification device for an internal combustion engine that includes a fuel injection unit that directly injects fuel into the combustion chamber of the internal combustion engine, a catalyst unit provided in the exhaust passage of the internal combustion engine, and a control unit that controls the fuel injection unit, wherein the control unit performs overheat suppression control to suppress overheating of the catalyst unit by injecting fuel from the fuel injection unit so that the air-fuel ratio of the internal combustion engine becomes the stoichiometric air-fuel ratio, and by injecting fuel from the fuel injection unit so that the catalyst inflow air-fuel ratio flowing into the catalyst unit during the exhaust stroke becomes rich.

[0008] According to the first means, during superheat suppression control, stoichiometric combustion is performed by injecting fuel from the fuel injection unit so that the air-fuel ratio of the internal combustion engine is the theoretical air-fuel ratio. This reduces PM emissions and suppresses deterioration of emissions. Furthermore, by injecting fuel from the fuel injection unit so that the catalyst inflow air-fuel ratio flowing into the catalyst unit during the exhaust stroke is rich, the injected fuel cools the catalyst unit and suppresses overheating of the catalyst unit. Therefore, overheating of the catalyst unit can be suppressed while suppressing deterioration of emissions. Furthermore, unlike conventional examples, by injecting fuel during the exhaust stroke and exhausting the fuel from the combustion chamber, it is possible to suppress a decrease in the thermal efficiency of the internal combustion engine and the cooling efficiency of the catalyst unit.

[0009] The second means is an exhaust purification device for an internal combustion engine of the first means, which is equipped with a catalyst temperature detection unit that detects the temperature of the catalyst unit, and the control unit performs the overheating suppression control when the temperature detected by the catalyst temperature detection unit is equal to or higher than a predetermined temperature.

[0010] According to the second means, when the temperature detected by the catalyst temperature detection unit is equal to or higher than a predetermined temperature, that is, when the catalyst unit needs to be cooled, overheating prevention control is performed, thereby making it possible to reduce fuel waste.

[0011] The third means is an exhaust gas purification device for an internal combustion engine according to the first or second means, wherein the control unit injects fuel from the fuel injection unit in at least two separate times during the intake stroke and the exhaust stroke in one cycle of the internal combustion engine during the overheat suppression control.

[0012] According to a third aspect, in the superheat suppression control, fuel is injected from the fuel injection unit at least twice during the intake stroke and the exhaust stroke during one cycle of the internal combustion engine. That is, stoichiometric combustion is performed by injecting fuel from the fuel injection unit during the intake stroke. This reduces PM emissions and suppresses deterioration of emissions. Furthermore, by injecting fuel from the fuel injection unit during the exhaust stroke, the injected fuel cools the catalyst unit and suppresses overheating of the catalyst unit. [Effects of the Invention]

[0013] According to the technology disclosed in this specification, it is possible to suppress overheating of the catalyst portion while suppressing deterioration of emissions. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a configuration diagram showing an engine system including an exhaust gas purification device for an internal combustion engine according to one embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment for carrying out the technology disclosed in this specification will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an engine system equipped with an exhaust gas purification device for an internal combustion engine. As shown in FIG. 1, engine 10 is a direct injection gasoline engine, more specifically, a reciprocating in-line four-cylinder four-stroke engine. Engine 10 corresponds to the "internal combustion engine" referred to in this specification.

[0016] The engine 10 includes a cylinder block 11, a cylinder head 12, and a crankcase 13. The cylinder block 11 has four cylinders 14 (one is shown in FIG. 1). Each cylinder 14 is provided with a piston 15 that is capable of reciprocating up and down. A combustion chamber 16 surrounded by the cylinder head 12 and the piston 15 is formed within the cylinder 14. The piston 15 is connected to a crankshaft 18 via a connecting rod 17.

[0017] The cylinder head 12 is formed with an intake port 20 and an exhaust port 21 that communicate with the combustion chamber 16. An intake valve 22 is provided in the intake port 20. The intake valve 22 is driven to open and close via an intake-side valve mechanism 23 that operates in conjunction with the movement of the piston 15. In addition, an exhaust valve 24 is provided in the exhaust port 21. The exhaust valve 24 is driven to open and close via an exhaust-side valve mechanism 25 that operates in conjunction with the movement of the piston 15. In other words, the intake valve 22 and exhaust valve 24 for each cylinder 14 are driven to open and close at predetermined timing in conjunction with a series of operating strokes (intake stroke, compression stroke, expansion stroke, and exhaust stroke) of the engine 10.

[0018] An injector 27 is provided in the cylinder head 12 for each cylinder 14. The injector 27 injects fuel supplied from a fuel tank by a fuel supply system including a fuel pump directly into the cylinder, i.e., into the combustion chamber 16. During the intake stroke, a combustible mixture is formed in the combustion chamber 16 by the fuel injected from the injector 27 and the air taken in from the intake port 20. The injector 27 corresponds to the "fuel injection unit" referred to in this specification.

[0019] A spark plug 28 is provided in the cylinder head 12 for each cylinder 14. The spark plug 28 sparks upon receiving an ignition signal output from an ignition coil 29. A combustible mixture formed in the combustion chamber 16 during the intake stroke is exploded and burned by the spark action of the spark plug 28 during the compression stroke, and the expansion stroke follows. The burned exhaust gas is discharged from the combustion chamber 16 to the exhaust port 21 during the exhaust stroke. In this way, a series of operating strokes progress as the piston 15 reciprocates in accordance with the combustion of the combustible mixture in the combustion chamber 16, causing the crankshaft 18 to rotate.

[0020] An intake passage 30 is connected to the intake port 20. In the intake passage 30, an air cleaner 31, an electronic throttle device 32, and a surge tank 33 are provided from the upstream side. The air cleaner 31 filters the air taken into the intake passage 30. The electronic throttle device 32 has a motor 32a and a throttle valve 32b that is driven to open and close by the motor 32a. The electronic throttle device 32 adjusts the amount of intake air (intake amount) taken into the combustion chamber 16.

[0021] An exhaust passage 40 is connected to the exhaust port 21. Exhaust gas discharged from the combustion chamber 16 to the exhaust port 21 during the exhaust stroke is discharged to the outside via the exhaust passage 40. A catalytic converter 41 is provided in the exhaust passage 40. The catalytic converter 41 incorporates a three-way catalyst for capturing PM in the exhaust gas from the engine 10. The catalytic converter 41 corresponds to the "catalytic section" as referred to in this specification.

[0022] A water temperature sensor 50 is disposed in the cylinder block 11. The water temperature sensor 50 detects the temperature (coolant temperature) of the cooling water flowing through the cylinder block 11 (more specifically, the water jacket). In addition, a rotational speed sensor 51 is provided in the crankcase 13. The rotational speed sensor 51 detects the rotational speed (engine 10 rotational speed) of a timing rotor 18a fixed to the crankshaft 18.

[0023] An air flow meter 52 is provided in the intake passage 30. The air flow meter 52 is arranged between the air cleaner 31 and the throttle device 32. The air flow meter 52 detects the amount of intake air flowing through the intake passage 30. The electronic throttle device 32 is also provided with a throttle sensor 53. The throttle sensor 53 detects the opening degree of the throttle valve 32b (throttle opening degree). The surge tank 33 is also provided with an intake pressure sensor 54. The intake pressure sensor 54 detects the intake pressure inside the surge tank 33.

[0024] An air-fuel ratio sensor 55 is provided in the exhaust passage 40. The air-fuel ratio sensor 55 is arranged upstream of the catalytic converter 41. The air-fuel ratio sensor 55 detects the air-fuel ratio in the exhaust gas. In addition, an oxygen sensor 56 is provided in the exhaust passage 40. The oxygen sensor 56 is arranged downstream of the catalytic converter 41. The oxygen sensor 56 detects the oxygen concentration Ox in the exhaust gas.

[0025] A temperature sensor 57 is disposed in the catalytic converter 41. The temperature sensor 57 detects the temperature of the three-way catalyst of the catalytic converter 41. If a temperature sensor is not installed, a catalyst temperature estimation system can be employed that estimates the catalyst temperature from the driving conditions (engine load, etc.). The temperature sensor 57 and the catalyst temperature estimation system correspond to the "catalyst temperature detection unit" in this specification. An accelerator sensor 58 provided at the driver's seat of the vehicle detects the depression angle of an accelerator pedal 70 as the accelerator opening.

[0026] The ECU 60 is an electronic control unit that manages various controls. In addition to the various sensors 50 to 58, the ECU 60 is connected to the motor 32a of the electronic throttle device 32, the injectors 27, and the ignition coils 29. The ECU 60 controls the throttle opening of the electronic throttle device 32, the fuel injection of the injectors 27, and the ignition timing of the ignition coils 29 based on electrical signals corresponding to the detected values ​​output from the various sensors 50 to 58. The ECU 60 also executes well-known learning control to learn parameters related to these controls. The ECU 60 corresponds to the "control unit" in this specification.

[0027] The injector 27, catalytic converter 41, ECU 60, etc. constitute an exhaust purification device 42. The injector 27, air flow meter 52, air-fuel ratio sensor 55, oxygen sensor 56, temperature sensor 57, ECU 60, etc. constitute an air-fuel ratio control device that executes air-fuel ratio feedback control.

[0028] (Characteristic configuration of this embodiment) When the temperature (detected value) detected by the temperature sensor 57 is equal to or higher than a predetermined temperature, i.e., when the catalytic converter 41 overheats, the ECU 60 performs the following overheat suppression control. In the overheat suppression control, in order to suppress overheating of the catalytic converter 41, fuel is injected from the injector 27 so that the air-fuel ratio of the engine 10 becomes the stoichiometric air-fuel ratio, and fuel is injected from the injector 27 so that the catalyst inflow air-fuel ratio flowing into the catalytic converter 41 becomes rich during the exhaust stroke. That is, during the intake stroke of one cycle of the engine 10, fuel is injected from the injector 27 so that the air-fuel ratio of the engine 10 becomes the stoichiometric air-fuel ratio, and fuel is injected from the injector 27 during the exhaust stroke.

[0029] (Advantages of the characteristic configuration of this embodiment) According to this embodiment, during superheat suppression control, stoichiometric combustion is performed by injecting fuel from the injector 27 so that the air-fuel ratio of the engine 10 becomes the stoichiometric air-fuel ratio. This reduces PM emissions and suppresses deterioration of emissions.

[0030] In addition, by injecting fuel from the injector 27 so that the catalyst inflow air-fuel ratio flowing into the catalytic converter 41 is rich during the exhaust stroke, the injected fuel can cool the catalytic converter 41 and prevent the catalytic converter 41 from overheating.

[0031] Therefore, it is possible to suppress deterioration of emissions while also suppressing overheating of the catalytic converter 41. Furthermore, unlike the conventional example, by injecting fuel during the exhaust stroke, the fuel is exhausted from the combustion chamber 16, which also suppresses a decrease in the thermal efficiency of the engine 10 and a decrease in the cooling efficiency of the catalytic converter 41.

[0032] Furthermore, when the temperature (detected value) detected by the temperature sensor 57 is equal to or higher than a predetermined temperature, that is, when the catalytic converter 41 needs to be cooled, the overheating prevention control is performed, thereby making it possible to reduce fuel waste.

[0033] In addition, in the overheat suppression control, fuel is injected from the injector 27 at least twice during the intake stroke and the exhaust stroke in one cycle of the engine 10. That is, stoichiometric combustion is performed by injecting fuel from the injector 27 during the intake stroke. This reduces PM emissions and suppresses deterioration of emissions. In addition, by injecting fuel from the injector 27 during the exhaust stroke, the injected fuel cools the catalytic converter 41 and suppresses overheating of the catalytic converter 41.

[0034] [Other embodiments] The technology disclosed in this specification is not limited to the above-described embodiment and may be embodied in various other forms. For example, the technology disclosed in this specification is not limited to direct injection gasoline engines and may be applied to direct injection diesel engines. [Explanation of symbols]

[0035] 10 Engine (internal combustion engine) 16 Combustion chamber 27 Injector (fuel injection part) 40 Exhaust passage 41 Catalytic converter (catalytic part) 42 Exhaust gas purification device 57 Temperature sensor (catalyst temperature detection section) 60 ECU (Electronic Control Unit)

Claims

1. a fuel injection unit that directly injects fuel into a combustion chamber of the internal combustion engine; a catalyst unit provided in an exhaust passage of the internal combustion engine; a control unit that controls the fuel injection unit; An exhaust gas purification device for an internal combustion engine comprising: The control unit performs overheat suppression control to suppress overheating of the catalyst unit by injecting fuel from the fuel injection unit so that the air-fuel ratio of the internal combustion engine becomes the stoichiometric air-fuel ratio, and by injecting fuel from the fuel injection unit so that the catalyst inflow air-fuel ratio flowing into the catalyst unit during the exhaust stroke becomes rich, in order to suppress overheating of the catalyst unit.

2. 2. An exhaust gas purification device for an internal combustion engine according to claim 1, a catalyst temperature detection unit that detects the temperature of the catalyst unit; The control unit performs the overheat suppression control when the temperature detected by the catalyst temperature detection unit is equal to or higher than a predetermined temperature.

3. 3. An exhaust gas purification device for an internal combustion engine according to claim 1 or 2, In the overheat suppression control, the control unit injects fuel from the fuel injection unit at least twice during an intake stroke and an exhaust stroke in one cycle of the internal combustion engine.

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