JP2018091270A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce emission of hydrocarbon.SOLUTION: An exhaust emission control device for an internal combustion engine includes: a catalyst provided in an exhaust passage of the internal combustion engine to purify exhaust gas; an electric supercharger that has a compressor provided in an intake passage on the upstream side of a throttle valve and is operated electrically; an exhaust gas recirculation passage having one end connected to the intake passage on the downstream side of the compressor and the upstream side of the throttle valve and the other end connected to the exhaust passage on the downstream side of the internal combustion engine and the upstream side of the catalyst to enable exhaust gas to recirculate from the exhaust passage to the intake passage; a flow control valve for controlling a flow rate of gas flowing in the exhaust gas recirculation passage; and a control section for operating the electric supercharger and opening the flow control valve to introduce air to the exhaust passage via the exhaust gas recirculation passage from cranking start of the internal combustion engine until completion of warming-up of the catalyst.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  In order to purify harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) discharged from internal combustion engines such as automobiles simultaneously and efficiently, A catalyst is provided.

  When air is supplied to the catalyst, reburning of unburned hydrocarbons can be promoted. Therefore, an exhaust purification system that introduces air compressed by a supercharger into the exhaust passage and supplies air to the catalyst has been proposed. (For example, patent document 1).

JP 2005-42604 A

  The most exhausted hydrocarbons in an internal combustion engine are from the start of the internal combustion engine to the completion of catalyst warm-up, and this is caused by misfire due to poor fuel vaporization at the start, and injection fuel for stabilizing combustion. Increased amount and low reduction rate of hydrocarbons by catalyst.

  The exhaust gas purification system of Patent Document 1 can introduce air compressed by the supercharger into the exhaust passage only when the operation condition of the internal combustion engine is an operation condition (high load operation) that can ensure back pressure. Therefore, there is a possibility that the exhaust of hydrocarbons cannot be sufficiently reduced before the start of the internal combustion engine to the completion of catalyst warm-up, in which back pressure cannot be ensured even though the most hydrocarbons are discharged.

  Accordingly, an object of the exhaust gas purification apparatus for an internal combustion engine disclosed in the present specification is to reduce hydrocarbon emissions.

  In order to solve such a problem, an exhaust purification device for an internal combustion engine disclosed in the present specification is provided in an exhaust passage of the internal combustion engine, and in a catalyst for purifying exhaust, and an intake passage upstream of a throttle valve. An electrically operated supercharger comprising an installed compressor, one end connected to the intake passage downstream of the compressor and upstream of the throttle valve, and the other end downstream of the internal combustion engine and An exhaust gas recirculation passage that is connected to the exhaust passage upstream of the catalyst and that can recirculate exhaust gas from the exhaust passage to the intake passage; a flow rate adjustment valve that adjusts a flow rate of gas flowing through the exhaust gas recirculation passage; From the start of cranking of the internal combustion engine to the completion of warming up of the catalyst, the electric supercharger is operated, the flow rate adjustment valve is opened, and the exhaust passage is emptied through the exhaust gas recirculation path. And a control unit for introducing a.

  The exhaust gas purification apparatus for an internal combustion engine disclosed in this specification can reduce hydrocarbon emissions.

FIG. 1 is a schematic diagram illustrating a configuration of an engine system to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment is applied. FIG. 2 is a flowchart illustrating an example of secondary air supply control executed by the ECU. FIG. 3 is a schematic diagram illustrating another example of the configuration of the engine system to which the exhaust gas purification apparatus for an internal combustion engine according to the embodiment is applied. FIG. 4 is a schematic diagram illustrating another example of the configuration of the engine system to which the exhaust gas purification apparatus for an internal combustion engine according to the embodiment is applied. FIG. 5 is a schematic diagram illustrating another example of the configuration of the engine system to which the exhaust gas purification apparatus for an internal combustion engine according to the embodiment is applied.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, and the like of each part may not be shown so as to completely match the actual ones. In some cases, details are omitted in some drawings.

  First, an engine system to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment is applied will be described with reference to FIG. FIG. 1 is a schematic diagram showing a configuration of an engine system 100 to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment is applied.

  As shown in FIG. 1, the engine system 100 includes an internal combustion engine 20, an intake passage 10, and an exhaust passage 30.

  The internal combustion engine 20 generates power by burning a mixture of fuel and air in a combustion chamber 23 formed in the cylinder block 21 and reciprocating a piston 24 in the combustion chamber 23. The internal combustion engine 20 is a vehicular multi-cylinder engine (only one cylinder is shown). In this embodiment, the internal combustion engine 20 is a four-cylinder engine including cylinders # 1 to # 4. Note that the number of cylinders included in the internal combustion engine 20 is not limited to this embodiment.

  The cylinder head of the internal combustion engine 20 is provided with an intake valve 25 for opening and closing the intake port and an exhaust valve 26 for opening and closing the exhaust port for each cylinder. Each intake valve 25 and each exhaust valve 26 are opened and closed by a camshaft. A spark plug 27 for igniting the air-fuel mixture in the combustion chamber 23 is attached to the top of the cylinder head for each cylinder.

  An injector 22 for injecting fuel into the intake port is installed at the intake port of each cylinder. The fuel injected from the injector 22 is mixed with intake air to form an air-fuel mixture, which is sucked into the combustion chamber 23 when the intake valve 25 is opened, compressed by the piston 24, and ignited and burned by the spark plug 27. It is done.

  In the intake passage 10, an air cleaner 19, an intercooler 14, an electronically controlled throttle valve 13, and a surge tank 18 are provided in order from the upstream side. The air cleaner 19 is provided with an air flow meter 15 for detecting the amount of intake air. The surge tank 18 is provided with an intake pressure sensor 16 that detects intake pressure. The intake port of each cylinder is connected to a surge tank 18 via an intake manifold 17.

  Further, in the intake passage 10 upstream of the throttle valve 13, a compressor 12a of an electrically operated supercharger (electric supercharger) 12 is disposed, and the intake air is compressed by the rotation of the compressor 12a. (Supercharged).

  An exhaust port of each cylinder is connected to the exhaust passage 30 via an exhaust manifold 32. The exhaust passage 30 is provided with a catalyst 31 for purifying the exhaust gas. An air-fuel ratio sensor 35 that detects the air-fuel ratio of the exhaust gas is provided on the upstream side of the catalyst 31.

  Further, the exhaust passage 30 is provided with a turbine 12 b of the electric supercharger 12. When the turbine 12 b is rotated by the exhaust gas discharged from the internal combustion engine 20, energy regeneration is performed in the electric supercharger 12.

  The engine system 100 also includes an external EGR (Exhaust Gas Recirculation) passage 40 that recirculates a part of exhaust gas (EGR gas) to the intake passage 10. The external EGR passage 40 is an example of an exhaust gas recirculation passage. One end 40 a of the external EGR passage 40 is connected to the intake passage 10 on the downstream side of the compressor 12 a of the electric supercharger 12 and on the upstream side of the throttle valve 13. The other end 40 b of the external EGR passage 40 is connected to the exhaust passage 30 downstream of the internal combustion engine 20 and upstream of the catalyst 31. Hereinafter, the exhaust gas recirculated through the external EGR passage 40 is referred to as “external EGR gas”.

  In the middle of the external EGR passage 40, an EGR cooler 42 for cooling the external EGR gas is provided. An EGR valve 44 is provided downstream of the EGR cooler 42 in the external EGR passage 40. The EGR valve 44 is an example of a flow rate adjustment valve. By changing the opening degree of the EGR valve 44, the amount of exhaust gas passing through the external EGR passage 40, that is, the amount of external EGR can be adjusted.

  The engine system 100 includes an ECU (Electronic Control Unit) 50. The ECU 50 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and a storage device. The ECU 50 performs various controls by executing a program stored in the ROM or the storage device. The ECU 50 is an example of a control unit.

  The ECU 50 is electrically connected to the ignition plug 27, the throttle valve 13, the injector 22, and the like. In addition to the above-described air flow meter 15, intake pressure sensor 16, air-fuel ratio sensor 35, crank angle sensor that detects the crank angle of the internal combustion engine 20, the ECU 50 includes an accelerator opening sensor that detects the accelerator opening, and various other types. The sensor is electrically connected via an A / D converter (not shown) or the like. The ECU 50 controls the ignition plug 27, the throttle valve 13, the injector 22 and the like so as to obtain a desired output based on the detection values of various sensors and the like, and performs ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc.

  In addition, the ECU 50 executes secondary air supply control for supplying air to the catalyst 31 by operating the electric supercharger 12 to introduce air into the exhaust passage 30.

  FIG. 2 is a flowchart showing an example of secondary air supply control executed by the ECU 50. The process of FIG. 2 is started when the internal combustion engine 20 starts cranking.

  The ECU 50 operates the electric supercharger 12 to increase the intake pressure to the target supercharging pressure (step S101).

  Subsequently, the ECU 50 adjusts the opening degree of the EGR valve 44 so that the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio (step S103). At this time, the ECU 50 uses, for example, the command value of the fuel injection amount of the ECU 50 and the air flow rate acquired from the flow rate map with respect to the supercharging pressure and the valve opening of the EGR valve 44, and the air-fuel ratio of the exhaust gas. Calculate

  By the processing in steps S101 and S103, air (secondary air) is introduced into the exhaust passage 30 via the external EGR passage 40 by the electric supercharger 12 and air is supplied to the catalyst 31. Thereby, since the recombustion of unburned hydrocarbons can be promoted in the catalyst 31, hydrocarbon emissions can be reduced.

  Subsequently, the ECU 50 determines whether or not a catalyst warm-up control request for requesting execution of catalyst warm-up control for warming up the catalyst 31 is ON (step S105). In this step, it is determined whether or not catalyst warm-up has been completed. When the catalyst warm-up control request is ON, the catalyst warm-up has not been completed yet.

  When the catalyst warm-up control request is ON (step S105 / YES), the ECU 50 feedback-controls the fuel injection amount to each cylinder so that the air-fuel ratio detected by the air-fuel ratio sensor 35 matches the stoichiometric air-fuel ratio. It is determined whether an air-fuel ratio feedback control request for requesting execution of the fuel ratio feedback control is ON (step S107). In this step, it is determined whether air-fuel ratio feedback control has been started. When the air-fuel ratio feedback control request is not ON (when OFF), this means that the air-fuel ratio feedback control has not yet started.

  If the air-fuel ratio feedback control request is not ON (step S107 / NO), the ECU 50 returns to step S105. On the other hand, when the air-fuel ratio feedback control request is ON (step S107 / YES), the ECU 50 stops supercharging by the electric supercharger 12 and closes the EGR valve 44 (step S109). That is, the ECU 50 stops introducing the secondary air into the exhaust passage 30 via the external EGR passage 40 by the electric supercharger 12. When the air-fuel ratio feedback control is started, the introduction of the secondary air is stopped because the catalyst 31 is assumed to be warmed up to some extent at the start of the air-fuel ratio feedback control. This is to prioritize. When priority is given to recombustion of hydrocarbons or the like, even if the start of air-fuel ratio feedback control is started, air is introduced into the exhaust passage 30 by the electric supercharger 12 until the catalyst warm-up is completed. You may continue.

  By the way, even when the catalyst warm-up control request is not ON (step S105 / NO), that is, when the catalyst warm-up control request is turned OFF and the catalyst warm-up control request is turned OFF, the ECU 50 The supercharging by the container 12 is stopped, and the EGR valve 44 is closed (step S109). That is, the introduction of secondary air into the exhaust passage 30 via the external EGR passage 40 by the electric supercharger 12 is stopped.

  After the processing of step S109, the ECU 50 performs so-called external EGR control in which a part of the EGR gas flowing through the exhaust passage 30 is returned to the intake passage 10 via the external EGR passage 40.

  More specifically, the ECU 50 determines the opening degree of the EGR valve 44 from the EGR request map based on the requested external EGR amount, and adjusts the opening degree of the EGR valve 44 (step S111). The ECU 50 may determine the opening degree of the EGR valve 44 from the EGR request map based directly on the engine speed and the engine load.

  Subsequently, the ECU 50 determines whether or not supercharging is necessary (step S113). Specifically, the ECU 50 calculates a supercharging pressure for realizing the required torque, and determines that supercharging is necessary when the current intake pressure is less than the calculated supercharging pressure.

  When supercharging is necessary (step S113 / YES), the ECU 50 operates the electric supercharger 12 so as to achieve the required torque (step S115). On the other hand, when supercharging is not necessary (step S113 / NO), the ECU 50 drives the electric supercharger 12 with the energy of exhaust gas to regenerate energy (step S117).

  After the processes of steps S115 and S117, the process returns to step S113.

  As described above in detail, the engine system 100 is provided in the exhaust passage 30 of the internal combustion engine 20, the catalyst 31 for purifying exhaust gas, and the compressor installed in the intake passage 10 upstream of the throttle valve 13. 12a, and electrically operated supercharger 12, one end 40a is connected to the intake passage 10 on the downstream side of the compressor 12a and upstream of the throttle valve 13, and the other end 40b is on the downstream side of the internal combustion engine 20. An external EGR passage 40 that is connected to the exhaust passage 30 upstream of the catalyst 31 and can recirculate the exhaust gas from the exhaust passage 30 to the intake passage 10; an EGR valve 44 that adjusts the flow rate of gas flowing through the external EGR passage 40; The electric supercharger 12 is operated and the EGR valve 44 is opened until the warming-up of the catalyst 31 is completed after the internal combustion engine 20 starts cranking. Via the GR passage 40 is provided with a ECU50 for introducing air into the exhaust passage 30. As a result, air is introduced into the exhaust passage 30 from the start of the internal combustion engine 20 to the completion of warming up of the catalyst 31 in which the back pressure cannot be ensured even though the largest amount of hydrocarbons is discharged. Air is supplied. Therefore, recombustion of unburned hydrocarbons in the catalyst 31 can be promoted, and hydrocarbon emissions can be reduced. In addition, by utilizing an electric supercharger with an electric motor mechanism attached to the supercharger of the current engine system and an external EGR passage for introducing EGR gas, it is not necessary to make a major change to the engine system. .

  In the above embodiment, as shown in FIG. 3, an electric compressor 80 may be provided instead of the electric supercharger 12. In this case, the ECU 50 operates the electric compressor 80 and opens the EGR valve 44 from the start of cranking of the internal combustion engine 20 to the completion of warm-up of the catalyst 31 or the start of air-fuel ratio feedback control, thereby opening the external EGR passage 40. Air may be introduced into the exhaust passage 30 via the.

  In the above embodiment, the external EGR passage 40 is used as the air introduction passage to the exhaust passage 30, but as shown in FIG. 4, one end 60 a is on the downstream side of the compressor 12 a and the upstream side of the throttle valve 13. A secondary air passage 60 that is connected to the intake passage 10 and that has the other end 60b connected to the exhaust passage 30 downstream of the internal combustion engine 20 and upstream of the catalyst 31 may be provided. . In this case, the secondary air passage 60 is provided with a secondary air metering valve 61 that adjusts the amount of air flowing through the secondary air passage 60. The ECU 50 operates the electric supercharger 12 from the start of cranking of the internal combustion engine 20 to the completion of warm-up of the catalyst 31 or the start of air-fuel ratio feedback control, closes the EGR valve 44, and the air-fuel ratio of the exhaust gas The opening degree of the secondary air metering valve 61 is adjusted so that the stoichiometric air fuel ratio is obtained. Thereby, since air can be introduced into the exhaust passage 30 via the secondary air passage 60, the same effect as in the above embodiment can be obtained.

  In the above embodiment, the electric supercharger 12 is used to introduce air into the exhaust passage 30 via the external EGR passage 40. However, as shown in FIG. 5, air is introduced into the external EGR passage 40. An air pump 70 may be used. In this case, a check 71 for adjusting the amount of air introduced into the external EGR passage 40 is provided in the passage 71 in which one end 71 a is connected between the EGR valve 44 and the exhaust passage 30 and the other end 71 b is connected to the air pump 70. A valve 72 is provided. The ECU 50 operates the air pump 70 from the start of cranking of the internal combustion engine 20 to the completion of warm-up of the catalyst 31 or the start of air-fuel ratio feedback control, closes the EGR valve 44, and the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio. The opening of the check valve 72 is adjusted so that Thereby, since air can be introduced into the exhaust passage 30 via the external EGR passage 40, the same effect as in the above embodiment can be obtained. In the configuration of FIG. 5, a supercharger 12 </ b> A that operates by the energy of exhaust gas from the internal combustion engine 20 may be used instead of the electric supercharger 12.

  In the above-described embodiment, when the internal combustion engine 20 includes a plurality of cylinders, fuel injection to some cylinders may be stopped and the cylinders may be used as a secondary air supply passage.

  The above-described embodiments are merely examples for carrying out the present invention, and the present invention is not limited to these. Various modifications of these embodiments are within the scope of the present invention, and It is apparent from the above description that various other embodiments are possible within the scope.

DESCRIPTION OF SYMBOLS 10 Intake passage 12 Electric supercharger 13 Throttle valve 12a Compressor 20 Internal combustion engine 30 Exhaust passage 31 Catalyst 40 External EGR passage (exhaust gas recirculation passage)
40a One end of the external EGR passage 40b Other end of the external EGR passage 44 EGR valve (flow adjustment valve)
50 ECU (control unit)
100 engine system

Claims (1)

A catalyst provided in an exhaust passage of the internal combustion engine for purifying exhaust;
An electric supercharger having a compressor installed in the intake passage upstream of the throttle valve and electrically operating;
One end is connected to the intake passage on the downstream side of the compressor and upstream of the throttle valve, and the other end is connected to the exhaust passage on the downstream side of the internal combustion engine and upstream of the catalyst. An exhaust gas recirculation passage capable of recirculation from the exhaust passage to the intake passage;
A flow rate adjusting valve for adjusting the flow rate of the gas flowing through the exhaust gas recirculation path;
From the start of cranking of the internal combustion engine until the warm-up of the catalyst is completed, the electric supercharger is operated, the flow rate adjustment valve is opened, and the exhaust passage through the exhaust gas recirculation passage is opened. A control unit for introducing air;
An exhaust gas purification apparatus for an internal combustion engine.

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