JP2010059879A - Exhaust gas recirculation device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas recirculation device for suppressing deposit accumulation in an exhaust gas recirculation passage of an internal combustion engine where exhaust gas flowing in an exhaust passage is recirculated to an intake passage, while improving fuel consumption with exhaust gas recirculation. <P>SOLUTION: The exhaust gas recirculation passage 30 of the internal combustion engine 10 consists of an upstream side recirculation passage 32 for recirculating exhaust gas from the upstream side of an exhaust emission control device 27 in the exhaust passage 23 to the intake passage 22, and a downstream side recirculation passage 33 for recirculating exhaust gas from the downstream side of the exhaust emission control device 27 to the intake passage 22. An electronic control device 60 controls the ratio of the amount of the exhaust gas to be recirculated through the upstream side recirculation passage 32 to the intake passage 22 to the amount of the exhaust gas to be recirculated through the downstream side recirculation passage 33 to the intake passage 22 in accordance with the generation amount of soot in a combustion chamber 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine having an exhaust gas recirculation passage for recirculating exhaust gas flowing through the exhaust passage to an intake air passage.

2. Description of the Related Art Conventionally, in an internal combustion engine, exhaust gas is recirculated to an intake passage through an exhaust recirculation passage, thereby reducing NOx emission and improving fuel consumption.
For example, an internal combustion engine described in Patent Literature 1 includes an exhaust gas recirculation passage that recirculates exhaust gas from an upstream side of an exhaust purification device provided in the exhaust passage to an intake passage.
JP 2006-46118 A

  Incidentally, the internal combustion engine described in Patent Document 1 is provided with an intake manifold injector that injects fuel into the intake port of the intake manifold and an in-cylinder injector that directly injects fuel into the combustion chamber.

  Here, when fuel injection is performed by the in-cylinder injector, vaporization of the injected fuel and mixing with air tend not to proceed as compared to when fuel injection is performed by the intake manifold injector. For this reason, soot is likely to be generated in the combustion chamber, the amount of particulate matter mainly composed of such soot is increased, and the amount of soot and particulate matter in the exhaust gas is likely to be increased. However, in the internal combustion engine described in the above-mentioned Patent Document 1, the fuel before being processed by the exhaust purification device both when the fuel injection is performed by the in-cylinder injector and when the fuel injection is performed by the intake passage injector. Exhaust gas is returned to the intake passage. Therefore, when fuel injection is performed by the in-cylinder injector, exhaust containing a large amount of soot and particulate matter flows through the exhaust gas recirculation passage, and deposits resulting from these soot and particulate matter accumulate in the recirculation passage. There is a risk of doing.

  Therefore, if an exhaust gas recirculation passage for recirculating exhaust gas from the downstream side to the intake passage instead of the upstream side of the exhaust purification device is provided, the exhaust gas purified by the exhaust gas purification device is introduced into the exhaust gas recirculation passage. Therefore, it is possible to suppress deposit accumulation as described above. However, in this case, when the fuel injection is performed by the intake passage injector, the exhaust after passing through the exhaust purification device is taken into the intake air even though the exhaust does not contain so much soot and particulate matter. Since the fuel is recirculated to the passage, even the unburned fuel contained in the exhaust gas is reduced. Therefore, the fuel efficiency improvement effect that can be obtained by returning the unburned fuel to the intake passage is reduced.

  The amount of soot generated in the combustion chamber varies depending on the combustion state of the air-fuel mixture. For this reason, the above-described problems occur not only in the internal combustion engine including the in-cylinder injector and the intake manifold injector, but also in other internal combustion engines. There is still room for improvement in terms of appropriately recirculating exhaust gas according to the amount.

  The present invention has been made in view of such circumstances, and an object of the present invention is to deposit deposits in the exhaust gas recirculation passage while improving fuel efficiency by exhaust gas recirculation in an internal combustion engine that recirculates exhaust gas flowing through the exhaust passage to the intake air passage. An object of the present invention is to provide an exhaust gas recirculation device that can be suppressed.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
The invention according to claim 1 is applied to an internal combustion engine that includes an exhaust gas recirculation passage that recirculates part of the exhaust gas discharged from the combustion chamber to the exhaust passage to the intake passage, and in which the exhaust gas purification device is provided in the exhaust passage. An exhaust gas recirculation device, wherein the exhaust gas recirculation passage includes an upstream recirculation passage that recirculates exhaust gas from the upstream side of the exhaust purification device to the intake passage in the exhaust passage, and the intake air passage from the downstream side of the exhaust purification device. And a downstream recirculation passage for recirculating exhaust gas, and based on the amount of soot generated in the combustion chamber, the amount of exhaust gas recirculated to the intake passage through the upstream recirculation passage and the intake air through the downstream recirculation passage The gist is to control the ratio of the amount of exhaust gas recirculated to the passage.

  When exhaust contains a large amount of soot generated in the combustion chamber, when exhaust is recirculated to the intake passage through the upstream recirculation passage, deposits resulting from particulate matter mainly composed of soot and soot in the exhaust will be exhaust recirculation passage It becomes easy to deposit on. In addition, when unburned fuel is included in the exhaust gas, if the exhaust gas is returned to the intake passage through the downstream recirculation passage, the unburned fuel in the exhaust gas is reduced by the exhaust purification device. The resulting fuel efficiency improvement effect is reduced.

  In this regard, according to the above-described configuration, of the exhaust gas recirculated from the exhaust passage to the intake passage, the amount of exhaust gas recirculated to the intake passage without being processed by the exhaust purification device and the exhaust gas recirculated to the intake passage after being processed by the exhaust purification device The ratio to the amount of exhaust can be controlled based on the amount of soot generated in the combustion chamber. Therefore, soot in the exhaust gas that causes deposit accumulation in the exhaust gas recirculation passage can be appropriately treated by the exhaust gas purification device, or the exhaust gas appropriately containing unburned fuel can be recirculated to the intake air passage. . In this way, according to the above configuration, deposit accumulation in the exhaust gas recirculation passage can be suppressed while improving fuel efficiency and the like.

  In the above configuration, controlling the ratio of the amount of exhaust recirculated to the intake passage through the upstream recirculation passage and the amount of exhaust recirculated to the intake passage through the downstream recirculation passage means that the upstream recirculation passage and the downstream recirculation passage Recirculating exhaust from both sides to the intake passage, controlling the ratio of the amount of exhaust recirculated from the upstream recirculation passage and the downstream recirculation passage, recirculating exhaust to the intake passage only through the upstream recirculation passage, and The case where the air is returned to the intake passage only through the downstream side return passage is included.

  According to a second aspect of the present invention, in the first aspect of the invention, when the amount of soot generated is equal to or greater than a predetermined amount, exhaust gas is recirculated to the intake passage through the downstream side recirculation passage to generate the soot. When the amount is less than a predetermined amount, the gist is to recirculate exhaust gas to the intake passage through the upstream recirculation passage.

  According to the above configuration, when it is determined that the amount of soot generation in the combustion chamber is greater than or equal to the predetermined amount, the exhaust gas processed by the exhaust purification device is recirculated to the intake passage through the downstream recirculation passage. It is possible to suppress deposits from accumulating in the exhaust gas recirculation passage. Further, when the amount of soot generated in the combustion chamber is less than a predetermined amount and the exhaust does not contain much soot, the exhaust is recirculated to the intake passage through the upstream recirculation passage, so that as much unburned fuel as possible is obtained. The exhaust gas can be recirculated to the intake passage in a state including the fuel consumption, and the fuel consumption can be improved. Therefore, according to the above configuration, deposit accumulation in the exhaust gas recirculation passage can be suppressed while improving the fuel consumption by returning the exhaust gas to the intake passage.

Whether the amount of soot generated is equal to or greater than a predetermined amount may be determined by directly detecting the amount of soot in the exhaust, or may be determined by estimating from the engine operating state. .
According to a third aspect of the present invention, in the first aspect of the invention, the internal combustion engine includes an intake manifold injector that injects fuel into the intake manifold and an in-cylinder injector that injects fuel into the combustion chamber. When the fuel injection by the in-cylinder injector is performed, the exhaust gas is recirculated to the intake passage through the downstream recirculation passage. When the fuel injection by the intake passage injection injector is performed, the exhaust is recirculated through the upstream recirculation passage. The gist is to recirculate exhaust gas into the intake passage.

  When fuel injection is performed by the in-cylinder injector, the amount of soot and particulate matter in the exhaust gas is larger than when fuel injection is performed by the intake manifold injector. In this regard, according to the above configuration, when the fuel injection is performed by the in-cylinder injector, the exhaust discharged from the combustion chamber is returned to the intake passage after passing through the exhaust purification device. This exhaust gas can be recirculated to the intake passage after the particulate matter is reduced, and deposits can be prevented from depositing in the exhaust recirculation passage. Further, when fuel injection is performed by the intake passage injector, the exhaust gas does not contain so much soot and particulate matter. The exhaust gas containing as much as possible can be recirculated to the intake passage, and the fuel consumption can be improved.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the internal combustion engine includes normal combustion in which an air-fuel ratio, which is a weight ratio of air to fuel supplied to the combustion chamber, is a stoichiometric air-fuel ratio. Rich combustion that is less than the stoichiometric air-fuel ratio is selectively executed, exhaust gas is recirculated to the intake passage through the downstream recirculation passage when the rich combustion is performed, and the upstream recirculation passage is performed when the normal combustion is performed. The gist is to recirculate exhaust gas into the intake passage.

  When rich combustion is performed, the amount of soot generated in the combustion chamber is larger than when normal combustion is performed, thereby increasing the amount of soot contained in the exhaust gas. In this regard, according to the above configuration, when rich combustion is performed, the exhaust discharged from the combustion chamber is recirculated to the intake passage after passing through the exhaust purification device. Therefore, after reducing soot in the exhaust, Exhaust gas can be recirculated to the intake passage, and deposits can be suppressed from accumulating in the exhaust recirculation passage. In addition, when normal combustion is performed, the exhaust gas does not contain so much soot, and the exhaust gas that has not passed through the exhaust gas purification device is recirculated to the intake passage so that it contains as much unburned fuel as possible. Exhaust gas can be recirculated to the intake passage, and fuel consumption can be improved.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the exhaust gas recirculation passage includes an intake side passage connected to the intake passage, and both ends of the intake side passage. One end is connected to the intake passage, the other end is connected to the upstream recirculation passage and the downstream recirculation passage, and the other end is recirculated through the upstream recirculation passage. The gist of the invention is that an adjustment mechanism is provided for adjusting the ratio between the amount of exhaust gas to be recirculated and the amount of exhaust gas recirculated through the downstream recirculation passage.

  According to the above configuration, by controlling the operation of the adjustment mechanism, the ratio between the amount of exhaust gas recirculated to the intake passage through the upstream recirculation passage and the amount of exhaust gas recirculated to the intake passage through the downstream recirculation passage is controlled. Can do.

(First embodiment)
Hereinafter, an embodiment of an exhaust gas recirculation device for an internal combustion engine according to the present invention will be described with reference to FIGS.

  FIG. 1 shows an internal combustion engine 10 to which the exhaust gas recirculation device is applied. As shown in FIG. 1, the internal combustion engine 10 of the present embodiment is a gasoline engine mounted on a vehicle, and includes a combustion chamber 12 formed in each cylinder 11, an intake passage 22 that feeds intake air into the combustion chamber 12, And an exhaust passage 23 through which exhaust gas generated by combustion in the combustion chamber 12 is exhausted. The combustion chamber 12 and the intake passage 22 and the combustion chamber 12 and the exhaust passage 23 are communicated and blocked by an intake valve 24 and an exhaust valve 25, respectively.

  A throttle valve 21 is provided in the intake passage 22, and the throttle valve 21 adjusts the amount of intake air supplied to the combustion chamber 12 by adjusting its opening degree by a throttle motor (not shown). The intake passage 22 is provided with an intake passage injection injector 14 for injecting fuel into the intake port. Further, an exhaust gas recirculation passage 30 for introducing a part of the exhaust gas flowing through the exhaust passage 23 into the intake passage 22 is connected to the downstream side of the throttle valve 21 in the intake passage 22. In more detail, the exhaust gas recirculation passage 30 includes three passages, that is, an intake side passage 31, an upstream recirculation passage 32, and a downstream recirculation passage 33. One end of the side passage 31 is connected. Further, the intake side passage 31 is provided with an exhaust recirculation valve 34 that adjusts the flow rate of the exhaust gas flowing through the intake side passage 31 and an EGR cooler 36 that cools the exhaust gas recirculated to the intake passage 22.

  Each cylinder 11 is provided with an in-cylinder injector 15 that directly injects fuel into the combustion chamber 12 and an ignition plug 16 that ignites an air-fuel mixture of fuel and air. In this way, in the present embodiment, spark discharge from the spark plug 16 is caused by the mixture of the fuel injected by the intake passage injector 14 or the in-cylinder injector 15 and the air flowing through the intake passage 22. Is ignited and the mixture is burned. As a result, the piston 26 reciprocates due to the combustion energy, and the crankshaft 20 rotates.

  An exhaust gas purification device 27 is provided in the exhaust passage 23. The exhaust purification device 27 carries a three-way catalyst for purifying hydrocarbons HC, carbon monoxide CO, and nitrogen oxides NOx contained in the exhaust. Further, in the exhaust passage 23, one end of the upstream recirculation passage 32 of the exhaust recirculation passage 30 is connected to the upstream portion of the exhaust purification device 27, and the downstream portion of the exhaust purification device 27 is connected to the downstream portion of the exhaust purification device 27. One end of the downstream recirculation passage 33 of the exhaust recirculation passage 30 is connected.

  In the exhaust gas recirculation passage 30, the other end of each of the upstream and downstream recirculation passages 32 and 33 is connected to the other end of the intake air passage 31. The amount of exhaust gas recirculated through the upstream recirculation passage 32 and the recirculation through the downstream recirculation passage 33 are connected to a portion where the three passages of the intake side passage 31, the upstream recirculation passage 32 and the downstream recirculation passage 33 are connected. A flow path switching valve 35 is provided as an adjustment mechanism for adjusting the ratio of the amount of exhaust gas to be discharged. The flow path switching valve 35 communicates with the upstream recirculation passage 32 and the intake air passage 31 shown by the solid line in FIG. 1 and with an upstream mode that blocks communication between the intake air passage 31 and the downstream recirculation passage 33. The operation position can be switched to a downstream mode in which the downstream side return passage 33 and the intake side passage 31 shown by the broken line in FIG. 1 are communicated and the communication between the intake side passage 31 and the upstream side return passage 32 is blocked. It is configured. In the state where the exhaust gas recirculation valve 34 provided in the intake side passage 31 is open, when the flow path switching valve 35 is in the upstream mode, the exhaust on the upstream side of the exhaust purification device 27 in the exhaust passage 23 is upstream. When the air flow is returned to the intake passage 22 through the recirculation passage 32 and the intake side passage 31, and the flow path switching valve 35 is in the downstream mode, the exhaust on the downstream side of the exhaust purification device 27 in the exhaust passage 23 becomes the downstream recirculation passage 33 and the intake side. The air is returned to the intake passage 22 through the passage 31.

  Various controls of the internal combustion engine 10 are performed by an electronic control device 60 mounted on the vehicle. The electronic control unit 60 includes a CPU that executes arithmetic processing related to the control of the internal combustion engine 10, a ROM that stores programs and data necessary for the control, a RAM that temporarily stores arithmetic results of the CPU, An input / output port for inputting / outputting a signal between them is provided.

  Detection signals from various sensors that detect the operating state of the internal combustion engine 10 are input to the input port of the electronic control unit 60. Examples of the various sensors include an NE sensor 51 that detects the rotational speed of the crankshaft 20, a water temperature sensor 52 that detects the cooling water temperature of the internal combustion engine 10, an accelerator sensor 53 that detects the amount of accelerator depression by the driver, and the like.

  The output port of the electronic control unit 60 is connected to a drive circuit such as an intake passage injector 14, an in-cylinder injector 15, a spark plug 16, and actuators for driving the various valves 21, 34, and 35. . The electronic control unit 60 grasps the operation state of the internal combustion engine 10 based on detection signals input from various sensors, and outputs command signals to various drive circuits connected to the output port according to the grasped operation state. . Thus, the opening control of the throttle valve 21 and the fuel injection control by the two injectors 14 and 15 are performed.

  Specifically, the electronic control unit 60 is injected by the opening of the throttle valve 21 and the injectors 14 and 15 to adjust the intake air amount based on the accelerator pedal depression amount detected by the accelerator sensor 53, for example. Adjust the fuel injection amount. Further, when a predetermined condition is satisfied in order to improve fuel consumption and reduce NOx, the exhaust gas recirculation valve 34 is opened to perform exhaust gas recirculation control so as to recirculate the exhaust gas in the exhaust gas passage 23 to the intake air passage 22.

  The electronic control unit 60 switches between fuel injection by the intake passage injector 14 and fuel injection by the in-cylinder injector 15 based on the operating state of the internal combustion engine 10. Specifically, the electronic control unit 60 performs fuel injection by the in-cylinder injector 15 when the engine load is equal to or higher than the predetermined load or the engine speed is equal to or higher than the predetermined speed. When the number becomes less than the predetermined number of revolutions, control is performed so that fuel injection by the intake passage injector 14 is executed. The engine load can be grasped based on the detection results of the accelerator sensor 53 and the NE sensor 51, and the engine speed can be detected by the NE sensor 51. As described above, in this embodiment, the fuel injection by the two injectors 14 and 15 is switched and executed.

  By the way, when the fuel injection by the in-cylinder injector 15 is executed, vaporization of the injected fuel and mixing with the air tend not to proceed more easily than when the fuel injection by the intake passage injector 14 is executed. For this reason, soot is likely to be generated in the combustion chamber 12, and the amount of particulate matter mainly composed of such soot is increased, and the amount of soot and particulate matter in the exhaust gas is likely to be increased. Accordingly, if exhaust gas containing a large amount of soot and particulate matter discharged by the fuel injection by the in-cylinder injector 15 is allowed to flow through the exhaust gas recirculation passage 30 as it is, the recirculation passage 30 is caused by soot and particulate matter. There is a risk that deposits will accumulate.

  In this regard, when the fuel injection by the in-cylinder injector 15 is performed, if an exhaust gas recirculation passage that recirculates exhaust gas from the downstream side of the exhaust gas purification device 27 to the intake air passage is provided, the exhaust gas purified by the exhaust gas purification device 27 is discharged. Since the exhaust gas is introduced into the exhaust gas recirculation passage 30, deposit accumulation in the recirculation passage 30 can be suppressed. On the other hand, when the fuel injection is performed by the intake passage injector 14, if the exhaust gas is recirculated to the intake passage 22 through the downstream-side recirculation passage 33, the exhaust gas purification is performed even though the exhaust gas does not contain much particulate matter. Since the exhaust gas after passing through the device 27 is returned to the intake passage 22, the amount of unburned fuel contained in the exhaust gas is also reduced. Therefore, the fuel efficiency improvement effect that can be obtained by returning the unburned fuel to the intake passage 22 is reduced.

  Therefore, in the present embodiment, the electronic control unit 60 controls the flow path switching valve 35 based on the amount of soot generated in the combustion chamber 12 in order to improve fuel consumption while suppressing deposit accumulation in the exhaust gas recirculation passage 30. Switching between the upstream reflux mode and the downstream reflux mode is performed. In other words, in the present embodiment, the exhaust gas recirculation device of the internal combustion engine 10 includes the exhaust gas recirculation passage 30, the exhaust gas recirculation valve 34, the flow path switching valve 35, and the electronic control device 60. Specifically, when the fuel injection is performed by the in-cylinder injector 15, the electronic control unit 60 sets the flow path switching valve 35 to the downstream recirculation mode, assuming that the amount of soot generated is equal to or greater than a predetermined amount, and When fuel injection is performed by the passage injector 14, the flow path switching valve 35 is set to the upstream recirculation mode on the assumption that the amount of soot generated is less than a predetermined amount.

  Hereinafter, the exhaust gas recirculation control executed by the electronic control unit 60 will be described with reference to FIGS. Note that a series of processing shown in the flowchart of FIG. 2 is performed at predetermined intervals, for example, during operation of the internal combustion engine 10.

  As shown in FIG. 2, when the exhaust gas recirculation control is started, first, in step S11, it is determined whether or not a precondition for the exhaust gas recirculation control is satisfied. Specifically, for example, the cooling water temperature is equal to or higher than a predetermined value, and a predetermined time or more has elapsed since the internal combustion engine 10 was started. Note that the precondition is not particularly limited, and the precondition may include that the engine load is in a low load to medium load operation state. If these conditions are not satisfied, a negative determination is made, and since it is not time to execute the exhaust gas recirculation control, the process proceeds to the end, and this process is temporarily terminated. On the other hand, if these conditions are satisfied, an affirmative determination is made and the process proceeds to step S12.

  In step S12, it is determined whether or not fuel injection by the in-cylinder injector 15 is being performed. Specifically, for example, when the load of the internal combustion engine 10 is equal to or higher than the predetermined load or the engine speed is equal to or higher than the predetermined speed, it is determined that the fuel injection by the in-cylinder injector 15 is being executed and the determination is affirmative. A determination is made, the process proceeds to step S13, the flow path switching valve 35 is set to the downstream recirculation mode, and the process proceeds to the end. On the other hand, when the engine load is low and the engine speed is low, for example, when the internal combustion engine 10 is under a low load, it is determined that fuel injection by the intake manifold injector 14 is being executed, and a negative determination is made in step S12. Then, the process proceeds to step S14, where the flow path switching valve 35 is set to the upstream recirculation mode and proceeds to the end. In step S12, it is determined whether or not the fuel injection by the in-cylinder injector 15 is being executed from the command values of the drive circuits of the injectors 14 and 15 instead of the determination based on the engine load and the engine speed. You may make it do.

  FIG. 3 shows a change in the fuel injection mode by the two injectors 14 and 15 and a change in the recirculation mode of the flow path switching valve 35. As shown in FIG. 3, since the fuel injection by the intake manifold injector 14 is executed until time t1, the flow path switching valve 35 is set to the upstream recirculation mode. Thus, the exhaust gas is recirculated to the intake passage 22 from the upstream side of the exhaust gas purification device 27 in a state where the fuel injection by the intake passage injector 14 is executed and the exhaust gas does not contain much soot and particulate matter. As a result, the unburned fuel contained in the exhaust gas is recirculated to the intake passage 22 together with the exhaust gas, thereby obtaining a fuel efficiency improvement effect. At time t1, for example, when the engine load is increased and the fuel injection by the intake passage injector 14 is switched to the fuel injection by the in-cylinder injector 15, the flow path switching valve 35 enters the downstream recirculation mode. Switch. As a result, when fuel injection is performed by the in-cylinder injector 15 that is likely to generate soot, the exhaust gas is purified by the exhaust gas purification device 27 and then introduced into the exhaust gas recirculation passage 30 to deposit deposits in the exhaust gas recirculation passage 30. Suppress.

As described in detail above, according to the present embodiment, the following operational effects can be achieved.
(1) In the present embodiment, the internal combustion engine 10 includes the intake passage injector 14 and the in-cylinder injector 15, and the exhaust gas recirculation passage 30 extends from the upstream side of the exhaust purification device 27 in the exhaust passage 23 to the intake passage 22. An upstream recirculation passage 32 that recirculates exhaust gas and a downstream recirculation passage 33 that recirculates exhaust gas from the downstream side of the exhaust purification device 27 to the intake passage 22. The electronic control unit 60 then determines the amount of exhaust gas recirculated to the intake passage 22 through the upstream recirculation passage 32 and the exhaust gas recirculated to the intake passage 22 through the downstream recirculation passage 33 based on the amount of soot generated in the combustion chamber 12. I am trying to control the ratio with the amount. Specifically, the electronic control unit 60 sets the flow path switching valve 35 to the downstream recirculation mode when the fuel injection by the in-cylinder injector 15 is performed, and flows when the fuel injection by the intake passage injector 14 is performed. The path switching valve 35 is set to the upstream recirculation mode.

  Therefore, when the fuel injection by the in-cylinder injector 15 is executed, the exhaust discharged from the combustion chamber 12 passes through the exhaust purification device 27 and then returns to the intake passage 22, so that soot and particulate matter in the exhaust is removed. After the reduction, the exhaust gas can be recirculated to the intake passage 22, and deposits can be suppressed from being accumulated in the exhaust recirculation passage 30. Further, when the fuel injection by the intake passage injector 14 is performed, the exhaust does not contain so much soot and particulate matter, so that the exhaust that has not passed through the exhaust purification device 27 is recirculated to the intake passage 22, Exhaust gas containing as much unburned fuel as possible can be recirculated to the intake passage 22 and fuel consumption can be improved. Therefore, in the present embodiment, deposit accumulation in the exhaust gas recirculation passage can be suppressed while improving fuel efficiency and the like.

  (2) In the present embodiment, the exhaust gas recirculation passage 30 includes an intake side passage 31 connected to the intake passage 22, and one end of the both ends of the intake side passage 31 is connected to the intake passage 22, and the other Is connected to the upstream reflux passage 32 and the downstream reflux passage 33. A flow path switching valve 35 is provided at the other end of the intake side passage 31. The operation position of the flow path switching valve 35 is switched between the upstream reflux mode and the downstream reflux mode. Therefore, by controlling the operation of the flow path switching valve 35, switching between the state in which the exhaust gas is recirculated to the intake passage 22 through the upstream recirculation passage 32 and the state in which the exhaust gas is recirculated to the intake passage 22 through the downstream recirculation passage 33 is performed. Can do.

(Second Embodiment)
Next, a second embodiment of the exhaust gas recirculation apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS.

  In the first embodiment, instead of switching the flow path switching valve 35 between the upstream recirculation mode and the downstream recirculation mode in accordance with the switching of the injectors 14 and 15, in the second embodiment, the combustion chamber The flow path switching valve 35 is switched between the upstream recirculation mode and the downstream recirculation mode in accordance with the air-fuel ratio of the air-fuel mixture combusted in the above.

  FIG. 4 shows an internal combustion engine 70 to which the exhaust gas recirculation apparatus of the second embodiment is applied. Note that in the internal combustion engine 70 of the second embodiment, the same reference numerals as those of the first embodiment are used for portions having the same configuration as the internal combustion engine 10 of the first embodiment, and the description thereof is omitted.

  As shown in FIG. 4, the internal combustion engine 70 of this embodiment differs from that of the first embodiment in that the injector for injecting fuel is not provided in the intake passage 22 as an injector for injecting fuel. Fuel injection is performed by the in-cylinder injector 15 having only the injector 15 for injection. In the present embodiment, an air-fuel ratio sensor 54 is provided in a portion of the exhaust passage 23 upstream of the exhaust purification device 27. The air-fuel ratio sensor 54 outputs a linear detection value corresponding to the air-fuel ratio of the air-fuel mixture in the combustion chamber 12 based on the exhaust component flowing through the exhaust passage 23.

  In the present embodiment, the detection signal of the air-fuel ratio sensor 54 is input to the input port of the electronic control unit 80 in addition to the detection signals of the various sensors 51, 52, 53 similar to those of the first embodiment. In the present embodiment, the electronic control unit 60 performs normal combustion in which the air-fuel ratio, which is the weight ratio of air to fuel supplied to the combustion chamber 12 in the internal combustion engine 10, is the stoichiometric air-fuel ratio, and the air-fuel ratio is the stoichiometric sky. Control is performed so that rich combustion, which is in a rich state smaller than the fuel ratio, is selectively executed. Specifically, when it is determined that the internal combustion engine 10 is accelerating based on the detection signals of the accelerator sensor 53 and the NE sensor 51, the electronic control unit 80 increases the fuel injection amount and executes rich combustion. The control is performed so that the normal combustion in which the air-fuel mixture burns at the stoichiometric air-fuel ratio is executed except during acceleration. The control of the fuel injection amount by the in-cylinder injector 15 is performed by feedback control based on the detection value of the air-fuel ratio sensor 54.

  By the way, when performing rich combustion, the amount of soot generated in the combustion chamber is larger than when performing normal combustion, thereby increasing the amount of soot contained in the exhaust and particulate matter mainly composed of such soot. . Therefore, if exhaust containing a large amount of soot and particulate matter discharged during rich combustion is passed through the exhaust gas recirculation passage 30 as it is, deposits resulting from soot and particulate matter may accumulate in the recirculation passage 30. In this regard, if the exhaust gas recirculation passage for recirculating the exhaust gas from the downstream side of the exhaust gas purification device 27 to the intake passage is provided during rich combustion, the exhaust gas purified by the exhaust gas purification device 27 is introduced into the exhaust gas recirculation passage 30. Therefore, deposit accumulation in the exhaust gas recirculation passage 30 can be suppressed. On the other hand, when performing normal combustion in which the air-fuel mixture burns at the stoichiometric air-fuel ratio in the combustion chamber 12, if the exhaust gas is recirculated to the intake passage 22 through the downstream-side recirculation passage 33, the exhaust gas does not contain much particulate matter. Nevertheless, since the exhaust gas after passing through the exhaust gas purification device 27 is recirculated to the intake passage 22, the amount of unburned fuel contained in the exhaust gas is also reduced. Therefore, the fuel efficiency improvement effect that can be obtained by returning the unburned fuel to the intake passage 22 is reduced.

  Therefore, in the present embodiment, the electronic control unit 80 controls the flow path switching valve 35 based on the amount of soot generated in the combustion chamber 12 in order to improve fuel efficiency while suppressing deposit accumulation in the exhaust gas recirculation passage 30. Switch between upstream reflux mode and downstream reflux mode. Specifically, the electronic control unit 80 sets the flow path switching valve 35 to the downstream recirculation mode on the assumption that the amount of soot generated is greater than or equal to a predetermined amount when performing rich combustion, and when performing normal combustion, Assuming that the generated amount is less than the predetermined amount, the flow path switching valve 35 is set to the upstream recirculation mode. Hereinafter, the exhaust gas recirculation control executed by the electronic control unit 80 will be described with reference to FIGS. 5 and 6. A series of processes shown in the flowchart of FIG.

  As shown in FIG. 5, when the exhaust gas recirculation control is started, first, in step S21, it is determined whether or not a precondition for the control is satisfied. The determination in step S21 is the same as the determination in step S11 in the flowchart shown in FIG. When it is determined in step S21 that the preconditions for exhaust gas recirculation control are not satisfied, the process proceeds to the end, and this process is temporarily terminated. In step S21, it is determined that the exhaust gas recirculation execution conditions are satisfied. Then, the process proceeds to step S22.

  In step S <b> 22, it is determined whether or not rich combustion is being executed in which the ratio of the fuel occupying the mixture is higher than the stoichiometric air-fuel ratio. Specifically, the electronic control unit 80 determines whether or not the air-fuel ratio of the air-fuel mixture in the combustion chamber 12 is rich based on the detection signal detected by the air-fuel ratio sensor 54. If it is determined by the detection signal of the air-fuel ratio sensor 54 that the current time is the execution of rich combustion, an affirmative determination is made in step S22, the process proceeds to step S23, and the flow path switching valve 35 is set to the downstream recirculation mode. To the end. On the other hand, if the air-fuel ratio detected by the air-fuel ratio sensor 54 is the stoichiometric air-fuel ratio, it is determined that the current combustion is being performed, a negative determination is made in step S22, the process proceeds to step S24, and the flow path switching valve 35 is set. Set to upstream reflux mode and move to end.

  In the present embodiment, in step S22, it is determined based on the detection signal of the air-fuel ratio sensor 54 whether or not rich combustion is being performed. However, for example, it may be determined whether or not the current time is the rich combustion by determining whether or not the current time is the acceleration based on the detection signal of the accelerator sensor 53 or the NE sensor 51. Based on the command value of the fuel injection amount to the injector 15 for injection, it may be determined whether or not the present time is rich combustion.

  FIG. 6 shows the combustion state and change in the combustion chamber 12 and the change in the recirculation mode of the flow path switching valve 35. As shown in FIG. 6, until the time t2, normal combustion at the stoichiometric air-fuel ratio is executed, so that the flow path switching valve 35 is set in the upstream recirculation mode. In this way, when normal combustion is performed, since the exhaust gas does not contain much particulate matter, the exhaust gas is recirculated from the upstream side of the exhaust purification device 27, whereby the unburned fuel is recirculated to the intake passage 22 and the fuel consumption is improved. An improvement effect is obtained. At time t2, when the internal combustion engine 10 is accelerated and switches to rich combustion, the flow path switching valve 35 switches to the downstream recirculation mode. As a result, when rich combustion is likely to generate soot, exhaust is purified by the exhaust purification device 27 and then introduced into the exhaust recirculation passage 30 to suppress deposit accumulation in the exhaust recirculation passage 30.

According to this embodiment described in detail above, the effect (2) of the first embodiment and the following effect can be achieved.
(3) In the internal combustion engine 70 of the present embodiment, rich combustion and normal combustion are selectively executed. The electronic control unit 80 sets the flow path switching valve 35 to the downstream recirculation mode when the rich combustion is performed, and selects the flow path switching valve 35 in the upstream recirculation mode when the normal combustion is performed. As a result, when rich combustion in which soot in the exhaust gas tends to increase is performed, exhaust gas exhausted from the combustion chamber 12 is returned to the intake passage 22 after passing through the exhaust gas purification device 27, so that soot in the exhaust gas is reduced. This exhaust gas can be recirculated to the intake passage 22 and the accumulation of deposits in the exhaust recirculation passage 30 can be suppressed. In addition, when normal combustion is performed, the exhaust gas does not contain so much soot, and the exhaust gas that has not passed through the exhaust gas purification device 27 is returned to the intake passage 22 to contain as much unburned fuel as possible. The exhaust in the state can be recirculated to the intake passage 22 and fuel consumption can be improved.

(Other embodiments)
In addition, you may change the said embodiment suitably as follows.
In the second embodiment, the internal combustion engine 70 is provided with only the in-cylinder injector 15, but it may be configured to include only the intake manifold injector instead of the in-cylinder injector.

  In each of the above embodiments, when the injectors 14 and 15 are switched or the air-fuel ratio of the air-fuel mixture combusted in the combustion chamber 12 is changed, the flow path switching valve 35 is immediately switched between the upstream recirculation mode and the downstream recirculation mode. I try to switch. However, when switching the flow path switching valve between the upstream recirculation mode and the downstream recirculation mode, the flow of the exhaust recirculation path, the flow of the exhaust path, and the exhaust component supplied to the combustion chamber caused by the rapid operation of the flow path switching valve In order to suppress a sudden change, the flow path switching valve may be operated slowly.

  That is, in the internal combustion engine in which the switching of the fuel injection by the two injectors as shown in FIG. 1 is executed, as shown in FIG. 7, for example, from the fuel injection by the intake passage injector to the in-cylinder injector Even when switching to fuel injection, the flow path switching valve is operated slowly to gradually change from the upstream reflux mode to the downstream reflux mode. Similarly, when the fuel injection by the in-cylinder injector is switched to the fuel injection by the intake manifold injector, the flow path switching valve is gradually changed from the downstream recirculation mode to the upstream recirculation mode. In this way, when switching the reflux mode of the flow path switching valve, the flow path switching valve is indicated by the state shown by the solid line and the broken line in FIG. 1 from the start to the end of the operation of the flow path switching valve. The exhaust gas is recirculated to the intake passage from both the upstream side and the downstream side of the exhaust purification device in the exhaust passage.

  Similarly, when switching the reflux mode of the flow path switching valve between the rich combustion and the normal combustion, similarly, the flow path switching valve is operated slowly to gradually change the reflux mode of the flow path switching valve. Also good.

  In each of the above embodiments, the flow path switching valve 35 is switched between the upstream recirculation mode and the downstream recirculation mode according to the air-fuel ratio of the air-fuel mixture combusted in the injectors 14 and 15 where the fuel injection is performed and the combustion chamber 12. It is set to either. However, the operating position of the flow path switching valve 35 is maintained between the state shown by the solid line in FIG. 1 and FIG. 4 and the state shown by the broken line, and the upstream side and the downstream side of the exhaust purification device 27 in the exhaust passage 23. It is also possible to be able to set a recirculation mode in which the exhaust gas is recirculated to the intake passage 22 from both sides. Then, the flow path switching valve 35 can be set to any one of the upstream recirculation mode, the downstream recirculation mode, and the both recirculation mode, and in the double recirculation mode, the amount of exhaust gas recirculated to the intake passage through the upstream recirculation passage The ratio of the amount of exhaust gas recirculated to the intake passage through the downstream recirculation passage may be arbitrarily controlled.

  Specifically, in an internal combustion engine in which fuel injection by the intake manifold injector and the in-cylinder injector can be performed simultaneously, as shown in FIG. 8, the higher the ratio of fuel injection by the in-cylinder injector, the higher the ratio. Since the amount of soot increases, when the exhaust gas recirculation control is executed, the amount of exhaust gas that is recirculated to the intake passage through the downstream recirculation passage (downstream recirculation ratio) is increased. That is, when fuel injection is performed only by the intake passage injector (the ratio of fuel injection by the in-cylinder injector is 0%), the flow path switching valve is set to the upstream recirculation mode, and only the in-cylinder injector is used. When the fuel injection is performed by (when the fuel injection ratio by the in-cylinder injector is 100%), the flow path switching valve is set to the downstream recirculation mode. When fuel injection is performed by both the intake manifold injector and the in-cylinder injector, the flow path switching valve 35 is set to the recirculation mode, and the fuel ratio by the in-cylinder injector increases as the fuel ratio increases. Increase the side reflux ratio.

  Further, as shown in FIG. 9, when the internal combustion engine performs rich combustion and normal combustion, the amount of soot increases as the rich degree increases, so that the exhaust gas recirculated to the intake passage through the downstream recirculation passage The amount (downstream reflux ratio) is increased. That is, when the richness is considerably high, the flow path switching valve is set to the downstream recirculation mode, and when the stoichiometric air-fuel ratio is reached, the flow path switching valve is set to the upstream recirculation mode. You may make it make a downstream reflux ratio low, so that a rich degree is low, setting a valve in both return mode.

  In each of the above embodiments, the amount of exhaust gas recirculated to the intake passage through the upstream recirculation passage and the intake passage through the downstream recirculation passage according to the fuel injection ratio by the two injectors that inject fuel and the air-fuel ratio of the air-fuel mixture The ratio to the amount of exhaust gas to be recirculated is controlled. However, the exhaust gas only needs to be recirculated from the upstream and downstream recirculation passages to the intake passage based on the amount of soot generated. For example, the amount of soot detected in the exhaust gas is directly detected by a sensor or the like. The ratio of the exhaust gas recirculated through the upstream and downstream recirculation passages may be controlled based on the amount of generated gas. In this case, this ratio may be arbitrarily controlled. When the amount of soot is not less than a predetermined amount, the exhaust gas is recirculated to the intake passage through the downstream side recirculation passage to generate soot. When the amount is less than the predetermined amount, the exhaust gas may be recirculated to the intake passage through the upstream recirculation passage. Furthermore, the amount of soot generated in the combustion chamber is estimated by estimating the combustion state of the air-fuel mixture in the combustion chamber based on other detection results such as the cooling water temperature of the internal combustion engine, and based on the estimated amount of soot The ratio between the amount of exhaust gas recirculated to the intake passage through the upstream recirculation passage and the amount of exhaust gas recirculated to the intake passage through the downstream recirculation passage may be controlled.

  In each of the above-described embodiments, the exhaust gas recirculation passage 30 includes the intake side passage 31 and the upstream recirculation passage 32 and the downstream recirculation passage 33, and a flow path switching valve 35 is provided as an adjustment mechanism at these connection portions. Yes. However, the mode of the adjusting mechanism may be other than the flow path switching valve 35. Further, the exhaust gas recirculation passage has an upstream recirculation passage directly connected to both the exhaust passage and the intake passage, and a downstream recirculation passage 33 is also directly connected to both the exhaust passage and the intake passage. The exhaust gas recirculation valve may be provided in each of the recirculation passages.

1 is a schematic diagram showing an internal combustion engine to which an exhaust gas recirculation device is applied and its peripheral mechanism in a first embodiment according to the present invention. 5 is a flowchart showing an execution procedure of exhaust gas recirculation control in the first embodiment. The timing chart which shows the switching mode of the fuel injection mode by two injectors, and the recirculation | reflux mode of a flow-path switching valve in 1st Embodiment. The schematic diagram which shows the internal combustion engine and its peripheral mechanism to which the exhaust gas recirculation apparatus is applied in the second embodiment according to the present invention. 9 is a flowchart showing an execution procedure of exhaust gas recirculation control in the second embodiment. The timing chart which shows the switching mode of the combustion state in a combustion chamber, and the recirculation | reflux mode of a flow-path switching valve in 2nd Embodiment. The timing chart which shows the switching mode of the recirculation | reflux mode of a flow-path switching valve in other embodiment concerning this invention. The graph which shows the relationship with the downstream recirculation | reflux ratio with respect to the fuel-injection ratio by the in-cylinder injector in other embodiment concerning this invention. The graph which shows the relationship with the downstream recirculation | reflux ratio with respect to an air fuel ratio in other embodiment concerning this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,70 ... Internal combustion engine, 11 ... Cylinder, 12 ... Combustion chamber, 14 ... Intake passage injector, 15 ... In-cylinder injector, 16 ... Spark plug, 20 ... Crankshaft, 21 ... Throttle valve, 22 ... Intake 23: Exhaust passage, 24 ... Intake valve, 25 ... Exhaust valve, 26 ... Piston, 27 ... Exhaust purification device, 30 ... Exhaust recirculation passage, 31 ... Intake side passage, 32 ... Upstream return passage, 33 ... Downstream side Reflux passage, 34 ... exhaust recirculation valve, 35 ... flow path switching valve, 36 ... EGR cooler, 51 ... NE sensor, 52 ... water temperature sensor, 53 ... accelerator sensor, 54 ... air-fuel ratio sensor, 60, 80 ... electronic control device.

Claims (5)

An exhaust gas recirculation device that is applied to an internal combustion engine that includes an exhaust gas recirculation passage that recirculates part of the exhaust gas discharged from the combustion chamber to the exhaust passage to the intake air passage, and is provided with an exhaust gas purification device in the exhaust passage,
The exhaust gas recirculation passage includes an upstream recirculation passage that recirculates exhaust gas from the upstream side of the exhaust purification device to the intake passage in the exhaust passage, and a downstream side that recirculates exhaust gas from the downstream side of the exhaust purification device to the intake passage. A reflux passage,
Based on the amount of soot generated in the combustion chamber, the ratio of the amount of exhaust recirculated to the intake passage through the upstream recirculation passage and the amount of exhaust recirculated to the intake passage through the downstream recirculation passage is controlled. An exhaust gas recirculation device for an internal combustion engine. In claim 1,
When the amount of soot generated is greater than or equal to a predetermined amount, exhaust gas is recirculated to the intake passage through the downstream recirculation passage, and when the amount of soot is less than a predetermined amount, the intake passage through the upstream recirculation passage An exhaust gas recirculation device for an internal combustion engine, characterized in that exhaust gas is recirculated to an internal combustion engine. In claim 1,
The internal combustion engine includes an intake passage injector that injects fuel into the intake passage and an in-cylinder injector that injects fuel into the combustion chamber,
When fuel injection is performed by the in-cylinder injector, exhaust gas is recirculated to the intake passage through the downstream recirculation passage. When fuel injection is performed by the intake passage injection injector, exhaust is discharged to the intake passage through the upstream recirculation passage. An exhaust gas recirculation device for an internal combustion engine, characterized in that In claim 1,
The internal combustion engine selectively executes normal combustion in which an air-fuel ratio, which is a weight ratio of air and fuel supplied to the combustion chamber, becomes a stoichiometric air-fuel ratio and rich combustion in which the air-fuel ratio becomes less than the stoichiometric air-fuel ratio,
Exhaust gas from an internal combustion engine, wherein exhaust gas is recirculated to the intake passage through the downstream recirculation passage when the rich combustion is performed, and exhaust gas is recirculated to the intake passage through the upstream recirculation passage when the normal combustion is performed. Reflux apparatus. In any one of Claims 1-4,
The exhaust gas recirculation passage includes an intake side passage connected to the intake air passage, and one end portion of the intake air side passage is the air intake passage, and the other end portion is the upstream recirculation flow. A passage and the downstream recirculation passage, and the other end adjusts the ratio of the amount of exhaust gas recirculated through the upstream recirculation passage and the amount of exhaust gas recirculated through the downstream recirculation passage An exhaust gas recirculation device for an internal combustion engine, characterized in that an adjusting mechanism is provided.

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