JP2010019093A - Exhaust gas recirculation device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas recirculation device for an internal combustion engine capable of suitably reducing fuel consumption. <P>SOLUTION: This device is applied to an internal combustion engine provided with an external EGR mechanism and a valve timing change mechanism, and re-circulates EGR gas to intake air passage by the execution of external EGR control and valve timing control according to the operation state of the internal combustion engine. One of the recirculation of EGR gas through the external EGR control and the recirculation of EGR gas through the valve timing control is selectively executed according to an operation zone of the internal combustion engine. The operation zone of the internal combustion engine (external EGR zone) in which the recirculation of EGR gas through the external EGR control is executed is changed (expanded by an area indicated by a zone A in the figure) based on a degree of the reduction of a quantity of EGR gas actually passing through the EGR passage from a reference quantity thereof. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine.

  In recent years, an exhaust gas recirculation device for recirculating gas burned in a combustion chamber, so-called EGR gas, to an intake passage in order to reduce fuel consumption of an internal combustion engine, such as the device described in Patent Document 1, has been proposed. Has been put to practical use.

  As a mechanism for recirculating the EGR gas to the intake passage, a mechanism for recirculating the combustion gas (exhaust gas) discharged from the combustion chamber of the internal combustion engine to the exhaust passage, the so-called external EGR mechanism is known. ing. This external EGR mechanism includes an EGR passage communicating with an intake passage and an exhaust passage of an internal combustion engine and an EGR valve provided in the EGR passage. In an internal combustion engine provided with such an external EGR mechanism, EGR gas (specifically, exhaust gas) is recirculated from the exhaust passage to the intake passage using the pressure difference between the intake passage and the exhaust passage. The recirculation amount (external EGR amount) is adjusted by changing the passage cross-sectional area of the EGR passage through opening control of the EGR valve based on the operating state of the internal combustion engine.

Further, as a mechanism for recirculating EGR gas to the intake passage, in addition to the external EGR mechanism, a change for changing a valve overlap period of the engine valve (a period in which both the intake valve and the exhaust valve are opened) is changed. The mechanism is known. In an internal combustion engine equipped with such a change mechanism, EGR gas (specifically, combustion gas) flows into the intake passage due to the pressure difference between the combustion chamber and the intake passage and the pressure difference between the exhaust passage and the intake passage during the valve overlap period. Refluxing takes place. The recirculation amount (internal EGR amount) is adjusted by changing the valve overlap period (period during which both the intake valve and the exhaust valve are opened) through the operation control of the change mechanism based on the operating state of the internal combustion engine. Is done by.
JP-A-2005-207285

  Here, both when the EGR gas is recirculated by the external EGR mechanism and when the EGR gas is recirculated by the change mechanism, the pressure in the intake passage (intake air pressure) changes with the recirculation. In an internal combustion engine in which an external EGR mechanism and a change mechanism are mounted, a change in intake pressure by operation control of the external EGR mechanism (specifically, opening degree control of the EGR valve) and intake air by operation control of the change mechanism. Since changes in pressure interfere with each other, it is difficult to control the intake pressure in a manner that anticipates the pressure in advance. As described above, both the external EGR amount and the internal EGR amount change in accordance with the pressure in the intake passage. Therefore, it is difficult for such an internal combustion engine to accurately adjust the external EGR amount and the internal EGR amount. This not only makes it difficult to adjust the amount of air sucked into the combustion chamber of the internal combustion engine, but also makes it impossible to obtain the expected fuel consumption reduction effect.

  In addition, as the internal combustion engine is used, deposits (those that are gradually carbonized due to fuel or oil in the EGR gas) may accumulate on the EGR valve, and this eliminates the need for a cross-sectional area of the EGR passage. May become smaller. Then, if the amount of EGR gas passing through the EGR passage is reduced and the external EGR amount is reduced, there is a possibility that the expected fuel consumption reduction effect cannot be obtained.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an exhaust gas recirculation device for an internal combustion engine that can suitably reduce fuel consumption.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
According to a first aspect of the present invention, there is provided an external EGR mechanism comprising an EGR passage communicating with an intake passage and an exhaust passage and an EGR valve provided in the EGR passage, and a change mechanism for changing a valve overlap period of the engine valve. An exhaust gas recirculation of the internal combustion engine that is applied to the internal combustion engine provided to recirculate EGR gas in the intake passage through execution of opening control of the EGR valve and operation control of the change mechanism according to an operating state of the internal combustion engine. In the circulation device, one of EGR gas recirculation through opening control of the EGR valve and EGR gas recirculation through operation control of the change mechanism is selectively selected according to an operating region of the internal combustion engine. Based on the execution means to be executed and the degree of decrease in the amount of EGR gas actually passing through the EGR passage from the reference amount, the execution means Further comprising a changing means for changing the operating region of the internal combustion engine in which the recirculation of the EGR gas through the opening control of the EGR valve is executed as its gist.

  According to the above configuration, since the opening control of the EGR valve and the operation control of the changing mechanism are not performed simultaneously to recirculate the EGR gas in the intake passage, the change in the intake pressure by the opening control of the EGR valve is performed. And the change in the intake pressure due to the operation control of the change mechanism are prevented from interfering with each other. Therefore, the amount of EGR gas recirculated to the intake passage (EGR amount, specifically, the external EGR amount or the internal EGR amount) can be adjusted with high accuracy, and a fuel consumption reduction effect that is expected in advance can be obtained. become able to.

  In addition, when the reduction effect of the fuel consumption due to the recirculation of the EGR gas through the opening control of the EGR valve is reduced due to the decrease of the external EGR amount due to the deposit attached to the EGR valve, such a reduction effect. The operating region of the internal combustion engine in which the recirculation of the EGR gas through the opening control of the EGR valve can be changed in a manner corresponding to the change of the EGR valve. Therefore, it is possible to appropriately select and execute one of the EGR gas recirculation based on the opening control of the EGR valve and the EGR gas recirculation based on the operation control of the change mechanism, which has the larger effect of reducing the fuel consumption. As a result, the fuel consumption can be suitably reduced.

  According to a second aspect of the present invention, in the exhaust gas recirculation device for an internal combustion engine according to the first aspect, the changing means recirculates EGR gas through opening degree control of the EGR valve as the degree of decrease is larger. The gist of the invention is to expand the operating range of the internal combustion engine.

  According to the above configuration, the effect of reducing the fuel consumption due to the recirculation of the EGR gas through the opening control of the EGR valve in a specific operation region of the internal combustion engine is reduced due to the adhesion of the deposit to the EGR valve. In this case, instead of executing the recirculation of the EGR gas by the opening control of the EGR valve in the specific operation region, the recirculation of the EGR gas by the operation control of the change mechanism is executed, and the fuel consumption amount thereby Can be reduced.

  According to a third aspect of the present invention, in the exhaust gas recirculation apparatus for an internal combustion engine according to the first or second aspect, the execution means has a low rotational speed of the output shaft of the internal combustion engine and a small load on the internal combustion engine. In the operation region, recirculation of EGR gas through the opening control of the EGR valve is executed, and in the operation region where the output shaft has a high rotation speed and the operation region where the load is large, EGR is performed through operation control of the change mechanism. The main point is to perform gas recirculation.

  According to the above configuration, in an operating region where the rotational speed of the output shaft of the internal combustion engine (engine rotational speed) is low and the load of the internal combustion engine (engine load) is small, the EGR gas is introduced into the intake passage through the opening degree control of the EGR valve. Is recirculated, the pumping loss of the internal combustion engine is reduced, and the fuel consumption rate can be reduced. In addition, the valve overlap period can be controlled so that a large output can be obtained from the internal combustion engine through operation control of the change mechanism in an operation region where the engine speed is high or an engine load is large. It is also possible to recirculate EGR gas to the intake passage during the period.

  When the temperature of the internal combustion engine is low, the operating state of the internal combustion engine tends to become unstable because the combustion state of the fuel is poor and the friction is large. In particular, when the engine load is small, such an operating state is likely to be unstable. Therefore, when the temperature of the internal combustion engine is low and the engine load is small, the operation state is likely to become unstable, and the execution state in which the EGR gas is recirculated through the operation control of the change mechanism and the opening degree control of the EGR valve When switching to the execution state in which the EGR gas is recirculated, it can be said that the operation state of the internal combustion engine is likely to become unstable.

  In this regard, the invention according to claim 4 is the exhaust gas recirculation device for an internal combustion engine according to claim 3, wherein the changing means is configured to change the change mechanism when the temperature of the internal combustion engine is equal to or lower than a predetermined temperature. The gist of the invention is to prohibit the expansion of the operating region in which the EGR gas is recirculated through the operation control to the side where the load of the internal combustion engine is small.

  According to the above configuration, in the operating region where the temperature of the internal combustion engine is low and the engine load is low, the EGR gas is recirculated through the execution state in which the EGR gas is recirculated through the operation control of the changing mechanism and the opening degree control of the EGR valve. It is possible to suppress the switching to the execution state, and to suppress the instability of the operation state of the internal combustion engine.

  According to a fifth aspect of the present invention, in the exhaust gas recirculation device for an internal combustion engine according to any one of the first to fourth aspects, the rotational speed of the output shaft of the internal combustion engine is equal to or lower than a predetermined speed and The boundary between the operation region in which EGR gas is recirculated through the opening control of the EGR valve and the operation region in which EGR gas is recirculated through the operation control of the change mechanism is set in the operation region where the load of the engine is not more than a predetermined value The gist is to prohibit the change of the operation region by the changing means in the changed mode.

  In an operating region where the engine speed is low and the engine load is low, the output of the internal combustion engine (engine output) is small, so the operating state of the internal combustion engine tends to become unstable. Therefore, in such an operation region, switching between an execution state in which the EGR gas is recirculated through the operation control of the change mechanism and an execution state in which the EGR gas is recirculated through the opening degree control of the EGR valve is performed. Therefore, it can be said that the operating state of the internal combustion engine is likely to be unstable.

  In this regard, according to the above configuration, in an operation region where the engine speed is low and the engine load is small, the EGR gas is recirculated through the execution state in which the EGR gas is recirculated through the operation control of the changing mechanism and the opening degree control of the EGR valve. It is possible to suppress switching from the execution state to be circulated, and it is possible to suppress instability of the operation state of the internal combustion engine.

  According to a sixth aspect of the present invention, in the exhaust gas recirculation device for an internal combustion engine according to any one of the first to fifth aspects, the changing means forcibly changes the opening of the EGR valve and changes the opening. The gist thereof is to obtain a change amount of the pressure in the intake passage and to estimate the degree of decrease based on the obtained change amount.

  When the opening degree of the EGR valve is changed, the external EGR amount changes by an amount corresponding to the change amount, and the pressure in the intake passage (intake pressure) changes accordingly. According to the above configuration, the degree of decrease in the external EGR amount from the reference amount can be estimated based on the relationship between the change amount of the opening degree of the EGR valve and the change amount of the intake pressure.

Hereinafter, an embodiment of an exhaust gas recirculation device for an internal combustion engine according to the present invention will be described.
FIG. 1 shows a schematic configuration of an internal combustion engine to which an exhaust gas recirculation device according to the present embodiment is applied.

  As shown in FIG. 1, a throttle valve 12 is provided in the intake passage 11 of the internal combustion engine 10. A throttle motor 13 is connected to the throttle valve 12. Then, the opening degree of the throttle valve 12 (throttle opening degree TA) is adjusted through the drive control (throttle control) of the throttle motor 13, thereby adjusting the amount of air taken into the combustion chamber 14 through the intake passage 11. The The intake passage 11 is provided with a fuel injection valve 15. Fuel is injected into the intake passage 11 through drive control (fuel injection control) of the fuel injection valve 15.

  The internal combustion engine 10 is provided with a spark plug 16 for igniting an air-fuel mixture composed of intake air and injected fuel inside the combustion chamber 14. An igniter 17 is connected to the spark plug 16. The spark plug 16 operates when a high voltage output from the igniter 17 is applied. Through the operation control (ignition timing control) of the igniter 17, the air-fuel mixture burns at an appropriate timing, the piston 18 reciprocates, and the crankshaft 19 as the output shaft of the internal combustion engine 10 rotates. The air-fuel mixture after combustion is sent out from the combustion chamber 14 to the exhaust passage 20 as exhaust.

  In the internal combustion engine 10, the intake passage 11 and the combustion chamber 14 are communicated and blocked by the opening / closing operation of the intake valve 21. The intake valve 21 opens and closes with the rotation of the intake camshaft 22 to which the rotation of the crankshaft 19 is transmitted. On the other hand, the combustion chamber 14 of the internal combustion engine 10 and the exhaust passage 20 are communicated and blocked by the opening / closing operation of the exhaust valve 23. The exhaust valve 23 opens and closes with the rotation of the exhaust camshaft 24 to which the rotation of the crankshaft 19 is transmitted.

  The intake camshaft 22 is provided with a valve timing changing mechanism 25. The valve timing changing mechanism 25 adjusts the relative rotation angle of the intake camshaft 22 with respect to the rotation angle (crank angle) of the crankshaft 19 to advance or retard the valve timing VT of the intake valve 21. The valve timing changing mechanism 25 operates through operation control (valve timing control) of a VVT actuator 26 such as a hydraulic control valve.

  FIG. 2 shows how the valve timing of the intake valve 21 is changed by the operation of the valve timing changing mechanism 25. As can be seen from FIG. 2, when the valve timing VT is changed, the intake valve 21 is opened while the operating angle of the intake valve 21 (the crank angle from when the valve is opened until the valve is closed) is kept constant. Both the valve timing and the valve closing timing are advanced or retarded.

  Such valve timing control is executed to adjust a period (valve overlap period) during which both the intake valve 21 and the exhaust valve 23 are opened in order to increase the intake efficiency and improve the fuel consumption rate. Further, when the valve overlap period changes, the amount of combustion gas (EGR gas) returned from the combustion chamber 14 to the intake passage 11 (internal EGR amount) changes, so that the internal EGR amount can be reduced by adjusting the valve overlap period. It is metered.

  The internal combustion engine 10 is also provided with an external EGR mechanism 27 for returning a part of the exhaust gas flowing through the exhaust passage 20 to the intake passage 11. The external EGR mechanism 27 adjusts the opening degree of the EGR passage 28 that connects the exhaust passage 20 and the portion of the intake passage 11 downstream of the throttle valve 12, the EGR valve 29 provided in the middle thereof, and the opening degree of the EGR valve 29. An EGR actuator 30 is provided. In the operation control of the external EGR mechanism 27 (external EGR control), the operation of the EGR actuator 30 is controlled according to the engine operating state, the opening degree of the EGR valve 29 (EGR opening degree) is controlled, and recirculation is performed through the EGR passage 28. The amount (external EGR amount) of exhaust (EGR gas) to be performed is adjusted.

  The apparatus according to the present embodiment includes various sensors. Examples of such various sensors include a crank sensor 41 for detecting the rotational speed of the crankshaft 19 (engine rotational speed NE) of the internal combustion engine 10 (FIG. 1), and the amount of intake air passing through the intake passage 11 (intake air). An intake air amount sensor 42 for detecting the amount GA) and an accelerator sensor 43 for detecting the depression amount AC of the accelerator pedal 31 are provided. Further, a throttle sensor 44 for detecting the throttle opening degree TA, a pressure sensor 45 for detecting the intake pressure (intake pressure PM) downstream of the throttle valve 12 in the intake passage 11, and the temperature of the engine coolant ( A temperature sensor 46 for detecting the coolant temperature THW) is provided. In addition, a position sensor 47 for detecting the valve timing VT of the intake valve 21, an opening degree sensor 48 for detecting the EGR opening degree, and the like are also provided.

  In addition, the apparatus according to the present embodiment includes an electronic control unit 40 that includes, for example, a microcomputer. The electronic control unit 40 takes in detection signals from various sensors and performs various calculations. Based on the calculation results, the electronic control unit 40 performs various controls such as throttle control, fuel injection control, ignition timing control, valve timing control, and external EGR control. Execute. In the present embodiment, the electronic control device 40 functions as an execution unit.

  The throttle control is executed as follows. That is, first, the target throttle opening degree Tta is calculated based on the depression amount AC of the accelerator pedal 31 and the engine rotational speed NE at that time. Then, the drive of the throttle motor 13 is controlled so that the target throttle opening degree Tta and the actual throttle opening degree TA coincide with each other. Through such throttle control, the amount of air taken into the combustion chamber of the internal combustion engine 10 is adjusted to an amount suitable for the operating state.

  Further, the fuel injection control is executed as follows. First, based on the intake air amount GA and the engine rotational speed NE at that time, a target fuel injection amount Tq (an amount corresponding to the fuel injection amount at which the air-fuel ratio of the air-fuel mixture becomes a desired ratio (for example, 14.5)). Calculated. Then, the fuel injection valve 15 is driven to open so that the target fuel injection amount Tq matches the actual fuel injection amount Q.

  The ignition timing control is basically executed as follows. That is, first, the base ignition timing Abse is calculated based on the intake air amount GA and the engine rotational speed NE at that time, and the knock correction amount Kn is calculated according to the occurrence of knocking. Then, the required ignition timing Acal is calculated by adding the knock correction amount Kn to the base ignition timing Abse. At the crank angle corresponding to the required ignition timing Acal set in this way, the igniter 17 is driven and ignition by the spark plug 16 is performed. Through such ignition timing control, the ignition timing of the internal combustion engine 10 is set to a timing at which it is possible to reduce fuel consumption while appropriately suppressing the occurrence of knocking.

  The valve timing control is executed as follows. First, a control target value (target valve timing Tvt) for the valve timing VT is calculated based on the intake air amount GA and the engine rotational speed NE at that time. Then, the operation of the VVT actuator 26 is controlled so that the target valve timing Tvt matches the actual valve timing VT. Through such valve timing control, the amount of air taken into the combustion chamber of the internal combustion engine 10 and the internal EGR amount are adjusted to an amount commensurate with the operating state of the internal combustion engine 10.

  The external EGR control is executed as follows. That is, first, a control target value (target EGR opening) for the EGR opening is calculated based on the intake air amount GA and the engine rotational speed NE at that time. Then, the operation of the EGR actuator 30 is controlled so that the target EGR opening degree matches the actual EGR opening degree. Through such external EGR control, the external EGR amount is adjusted to an amount commensurate with the operating state of the internal combustion engine 10.

  The apparatus according to the present embodiment has a structure capable of recirculating EGR gas to the intake passage 11 by either valve timing control or external EGR control. In this embodiment, one of EGR gas recirculation through external EGR control and EGR gas recirculation through valve timing control is selectively executed in accordance with the operating region of the internal combustion engine 10. ing.

  As a result, when the EGR gas is recirculated to the intake passage 11, the external EGR control and the valve timing control are not executed at the same time. Therefore, the change in the intake pressure PM accompanying the external EGR control and the intake by the valve timing control are eliminated. Interference with changes in the pressure PM can be suppressed. Therefore, the deviation between the actual transition of the intake pressure PM and the transition expected in advance can be suppressed, and the external EGR amount or the internal EGR amount can be accurately adjusted. Accordingly, an effect expected in advance by the recirculation of the EGR gas to the intake passage 11 (specifically, an effect of reducing the fuel consumption) can be appropriately obtained, and is further sucked into the combustion chamber 14 of the internal combustion engine 10. It becomes possible to accurately adjust the amount of air.

  FIG. 3 shows the boundary between the operation region (external EGR region) of the internal combustion engine 10 where EGR gas is recirculated by external EGR control and the operation region (VVT region) where EGR gas is recirculated by valve timing control. Show.

  As shown in FIG. 3, in the present embodiment, recirculation of EGR gas by external EGR control is executed in an operation region where the engine speed NE is low and the load of the internal combustion engine 10 (engine load KL) is small. In an operation region where the engine rotational speed NE is high and an operation region where the engine load KL is large, the EGR gas is recirculated by valve timing control.

  In the present embodiment, the amount of air actually sucked into the combustion chamber 14 of the internal combustion engine 10 (R) is the amount of air sucked into the combustion chamber 14 during full load (WOT) operation of the internal combustion engine 10 ( A value corresponding to a value (= R / Rwot) calculated by Rwt) is calculated based on the intake air amount GA and the engine rotational speed NE, and the same value is used as the engine load KL.

  In the present embodiment, in an operation region where the engine speed NE is low and the engine load KL is small, EGR gas is recirculated to the intake passage 11 through external EGR control, and the intake pressure PM increases accordingly. As a result, the pumping loss of the internal combustion engine 10 is reduced, and the fuel consumption rate is reduced. In addition, in an operation region where the engine rotational speed NE is high or an operation region where the engine load KL is large, the valve overlap period is controlled so that a large output can be obtained from the internal combustion engine 10 through valve timing control. During the valve overlap period, an appropriate amount of EGR gas is recirculated to the intake passage 11 to reduce the fuel consumption rate.

  Here, when deposits adhere to the EGR valve 29 and the passage cross-sectional area of the EGR passage 28 becomes smaller, the amount of external EGR decreases accordingly. As a result, the amount of air sucked into the combustion chamber 14 of the internal combustion engine 10 and the fuel injection amount increase, so that the amount of heat generated with combustion of the air-fuel mixture increases and knocking is likely to occur. .

  For this reason, in the present embodiment, when the external EGR amount decreases due to deposits attached to the EGR valve 29, the occurrence of knocking is suppressed by correcting the ignition timing by retarding the ignition timing. This retardation correction is performed as follows.

  That is, first, the degree of decrease of the external EGR amount from the reference amount (in this embodiment, the external EGR amount when no deposit is attached to the EGR valve 29) is estimated. Here, when the opening degree of the EGR valve 29 is changed, the external EGR amount changes by an amount corresponding to the change amount, and the intake pressure PM changes accordingly. In the present embodiment, paying attention to this point, the EGR opening is forcibly changed, the change amount ΔPM of the intake pressure PM accompanying the change is obtained, and the degree of decrease is estimated based on the obtained change amount ΔPM. I have to.

Specifically, when an execution condition for determining that the operating state of the internal combustion engine 10 is stable is established, the EGR valve 29 is opened from a state where the EGR valve 29 is turned off to a predetermined opening degree. Operated. Then, a change amount ΔPM of the intake pressure PM accompanying the valve opening operation (specifically, a difference between the intake pressure PM immediately before the opening of the EGR valve 29 and the intake pressure PM when the change is stabilized after the valve opening) is calculated. And stored in the electronic control unit 40. The execution condition is determined to be satisfied when, for example, the following conditions are satisfied.
・ The engine speed NE is medium.
-The change speed of the engine speed NE is small.
・ The engine load KL is moderate.
-The change speed of the intake pressure PM is small.

  Then, an estimated value (estimated EGR amount) for the external EGR amount is calculated based on the degree of deviation between the change amount ΔPM of the intake pressure PM and the standard change amount (specifically, the difference between the change amounts). And stored in the electronic control unit 40. The standard change amount is a change amount when no deposit is attached to the EGR valve 29 and is stored in the electronic control unit 40 in advance. As the amount of change in the intake pressure PM is smaller than the standard amount of change, a smaller amount is calculated as the estimated EGR amount.

  When the ignition timing is corrected, the ignition timing correction amount (deposit correction amount Kdp) is calculated from the map on the basis of the engine speed NE, the engine load KL, and the estimated EGR amount. The required ignition timing Acal is corrected by adding the deposit correction amount Kdp. The map is stored in advance in the electronic control unit 40, and the map accurately suppresses the operating range of the internal combustion engine 10 determined by the engine speed NE and the engine load KL, the estimated EGR amount, and the occurrence of knocking. The relationship with the possible correction amount (deposit correction amount Kdp) is obtained and set in advance based on experimental results and the like.

  By correcting the ignition timing in this way, the occurrence of knocking can be accurately suppressed. However, at this time, since the amount of air sucked into the combustion chamber 14 of the internal combustion engine 10 and the fuel injection amount increase, the amount of fuel consumption increases accordingly. When the deposit amount of the EGR valve 29 increases, depending on the operation region of the internal combustion engine 10, the valve in the operation region where the EGR gas is recirculated through external EGR control when no deposit is adhered. It has been confirmed that fuel consumption is reduced by recirculating EGR gas through timing control.

  In view of this point, in the present embodiment, the operating range of the internal combustion engine 10 in which the recirculation of EGR gas through the external EGR control is executed based on the degree of reduction of the external EGR amount from the reference amount (the external The EGR area) is changed. As a result, when the reduction effect of the fuel consumption due to the recirculation of the EGR gas through the external EGR control is reduced due to the reduction of the external EGR amount due to the adhesion of the deposit to the EGR valve 29, the reduction effect is reduced. The external EGR area can be changed according to the change. For this reason, it is possible to appropriately select and execute a fuel consumption reduction effect that is greater between EGR gas recirculation by external EGR control and EGR gas recirculation by valve timing control. In addition, fuel consumption can be reduced.

  In the present embodiment, specifically, the external EGR region is expanded when the degree of decrease in the external EGR amount from the reference amount becomes large. Accordingly, when the deposit on the EGR valve 29 is attached, the effect of reducing the fuel consumption due to the recirculation of the EGR gas through the external EGR control in the specific operation region of the internal combustion engine 10 is reduced. In the same operation region, EGR gas recirculation can be executed by valve timing control instead of executing EGR gas recirculation by external EGR control, thereby reducing fuel consumption. .

  When the temperature of the internal combustion engine 10 is low, the combustion state of the fuel is bad and the friction is large, so that the operation state of the internal combustion engine 10 tends to become unstable. In particular, when the engine load KL is small, such an operating state tends to become unstable. Therefore, when the temperature of the internal combustion engine 10 is low and the engine load KL is small, the operation state is likely to be unstable, and the EGR gas recirculation by the valve timing control and the EGR gas recirculation by the external EGR control If switching is performed, it can be said that the operation state of the internal combustion engine 10 is likely to become unstable.

  Therefore, in the present embodiment, when the temperature of the internal combustion engine 10 (specifically, the coolant temperature THW that is the index value) is equal to or lower than a predetermined temperature (for example, 80 ° C.), the EGR gas is recirculated through valve timing control. The operation range (the VVT region) to be performed is prohibited from expanding to the side where the load of the internal combustion engine 10 is small.

  Thereby, in an operation region where the temperature of the internal combustion engine 10 is low and the engine load KL is small, switching between an execution state in which EGR gas is recirculated through valve timing control and an execution state in which EGR gas is recirculated through external EGR control. Is suppressed, and instability of the operating state of the internal combustion engine 10 is suppressed.

  Further, in an operating region where the engine rotational speed NE is low and the engine load KL is small, the output of the internal combustion engine 10 is small, and therefore the influence when the same output fluctuates easily increases. Tends to be unstable. Therefore, in such an operation region, when switching between an execution state in which the EGR gas is recirculated through the valve timing control and an execution state in which the EGR gas is recirculated through the opening degree control of the EGR valve, the internal combustion is performed accordingly. It can be said that there is a high possibility that the operating state of the engine 10 becomes unstable.

  Therefore, in the present embodiment, when the VVT region is changed (enlarged), the engine speed NE is not more than a predetermined speed (for example, 1500 rpm) and the engine load KL is not more than a predetermined value (for example, 40%). When the boundary between the external EGR area and the VVT area is set in the area, the change of the VVT area is prohibited.

  As a result, in an operation region where the engine rotational speed NE is low and the engine load KL is small, switching between an execution state in which EGR gas is recirculated through valve timing control and an execution state in which EGR gas is recirculated through external EGR control is performed. This is suppressed, and instability of the operating state of the internal combustion engine 10 is suppressed.

Hereinafter, the process of changing the VVT area (change process) will be described in detail.
FIG. 4 is a flowchart showing a specific processing procedure of the change processing, and a series of processing shown in the flowchart is executed by the electronic control unit 40 as processing at predetermined intervals. In the present embodiment, this changing process functions as a changing means.

As shown in FIG. 4, in this process, when any one of the following (Condition A) to (Condition F) is not satisfied (“NO” in any of Steps S101 to S106), the VVT region is The normal control is executed as control for recirculating the EGR gas in the intake passage 11 without being changed (step S107). In other words, one of EGR gas recirculation by external EGR control and EGR gas recirculation by valve timing control is selectively executed based on the relationship shown in FIG.
“Condition A” When the VVT area is not expanded, it is an external EGR area (step S101 in FIG. 4: YES). Specifically, it is an EGR region in the relationship shown in FIG.
“Condition B” The degree of decrease in the external EGR amount from the reference amount is greater than a predetermined value (step S102: YES in FIG. 4). Specifically, the change amount ΔPM of the intake pressure PM described above is not more than a predetermined value. As the predetermined value, the EGR gas is recirculated by the external EGR control by executing the recirculation of the EGR gas by the valve timing control in the external EGR region (see FIG. 3) when no deposit is attached. A value capable of appropriately determining that the degree of decrease is large to the extent that the fuel consumption is reduced compared to the case of execution is set in advance.
“Condition C” Compared with the case where the EGR gas is recirculated through the external EGR control, the fuel consumption is reduced when the EGR gas is recirculated through the valve timing control (step S103 in FIG. 4). : YES) Specifically, the operation region of the internal combustion engine 10 determined by the engine speed NE and the engine load KL is determined in advance according to a predetermined operation region (based on the results of experiments and simulations and stored in the electronic control unit 40). Area).
“Condition D” Cooling water temperature THW is higher than a predetermined temperature (step S104: YES).
“Condition E” The engine rotational speed NE is higher than a predetermined speed (step S105: YES).
“Condition F” The engine load KL is larger than a predetermined value (step S106: YES).

  On the other hand, when all of the above (condition A) to (condition F) are satisfied (“YES” in all of steps S101 to S106), the VVT region is expanded and the EGR gas is recirculated through the valve timing control. (Step S108).

  FIG. 5 shows the boundary between the external EGR region and the VVT region when the VVT region is enlarged as described above. As shown in FIG. 5, in the present embodiment, the VVT region is expanded only in the portion indicated by the slanted line A in FIG. 5, that is, the operating region where the engine rotational speed NE is low and the operating region where the engine load KL is small. Is done.

  When switching from a state where EGR gas recirculation is performed through external EGR control to a state where EGR gas recirculation is performed through valve timing control, execution of recirculation of EGR gas by external EGR control is performed. After a predetermined delay period has elapsed since the stop, execution of recirculation of EGR gas by valve timing control is started. As the delay period, a period (for example, several hundred milliseconds) in which deterioration of combustion is accurately suppressed based on the results of experiments and simulations is set in advance. By setting such a delay period, most of the EGR gas remaining in the intake passage 11 when the recirculation of the EGR gas by the external EGR control is stopped is sucked into the combustion chamber 14, and then the EGR gas by the valve timing control is used. Can start recirculation execution. Therefore, when switching from a state in which recirculation of EGR gas is performed through external EGR control to a state in which recirculation of EGR gas is performed through valve timing control, the amount of EGR gas recirculated into the intake passage 11 is unnecessary. Increase can be suppressed, and deterioration of the combustion state of the air-fuel mixture can be suppressed.

As described above, according to the present embodiment, the effects described below can be obtained.
(1) Depending on the operating region of the internal combustion engine 10, one of EGR gas recirculation through external EGR control and EGR gas recirculation through valve timing control is selectively executed, and the EGR passage 28 is The EGR region is changed based on the degree of decrease in the amount of EGR gas that actually passes from the reference amount. Therefore, since the external EGR control and the valve timing control are not executed simultaneously to recirculate the EGR gas to the intake passage 11, the change in the intake pressure PM by the external EGR control and the change in the intake pressure PM by the valve timing control are performed. Can be prevented from interfering with each other. As a result, the EGR amount can be adjusted with high accuracy, and a fuel consumption reduction effect expected in advance can be obtained. In addition, when the reduction effect of the fuel consumption due to the recirculation of the EGR gas through the external EGR control is reduced due to the reduction of the external EGR amount due to the adhesion of the deposit to the EGR valve 29, the change of the reduction effect is changed. Accordingly, it is possible to change the operating range of the internal combustion engine 10 in which the recirculation of the EGR gas through the external EGR control is executed. For this reason, it is possible to appropriately select and execute a fuel consumption reduction effect that is greater between EGR gas recirculation by external EGR control and EGR gas recirculation by valve timing control. In addition, fuel consumption can be reduced.

  (2) The EGR region is expanded when the amount of EGR gas actually passing through the EGR passage 28 is greatly reduced from the reference amount. Therefore, when the deposit reduction on the EGR valve 29 causes the reduction in fuel consumption due to the recirculation of EGR gas through the external EGR control in a specific operation region of the internal combustion engine 10 to be reduced, Instead of executing the recirculation of the EGR gas by the external EGR control in a specific operation region, the recirculation of the EGR gas by the valve timing control can be executed to thereby reduce the fuel consumption. .

  (3) In an operation region where the engine speed NE is low and the engine load KL is small, EGR gas recirculation is executed through external EGR control, and in an operation region where the engine speed NE is high and the engine load KL is large. Performed EGR gas recirculation through valve timing control. Therefore, in an operation region where the engine rotational speed NE is low and the engine load KL is small, the EGR gas is recirculated to the intake passage 11 through the external EGR control, thereby reducing the pumping loss of the internal combustion engine 10 and the fuel consumption rate. Can be reduced. In addition, in an operation region where the engine rotational speed NE is high or an operation region where the engine load KL is large, the valve overlap period can be controlled through valve timing control so that a large output can be obtained from the internal combustion engine 10. It is also possible to recirculate an appropriate amount of EGR gas to the intake passage 11 during the overlap period.

  (4) When the coolant temperature THW is equal to or lower than the predetermined temperature, the VVT region is prohibited from expanding to the side where the load of the internal combustion engine 10 is small. Therefore, in an operation region where the temperature of the internal combustion engine 10 is low and the engine load KL is small, switching between an execution state in which EGR gas is recirculated through valve timing control and an execution state in which EGR gas is recirculated through external EGR control is performed. This can be suppressed, and instability of the operating state of the internal combustion engine 10 can be suppressed.

  (5) When changing the VVT region, if the boundary between the external EGR region and the VVT region is set in the operation region where the engine speed NE is equal to or lower than the predetermined speed and the engine load KL is equal to or lower than the predetermined value, VVT The change of the area was prohibited. Therefore, in an operation region where the engine rotational speed NE is low and the engine load KL is small, switching is performed between an execution state in which EGR gas is recirculated through valve timing control and an execution state in which EGR gas is recirculated through external EGR control. The instability of the operating state of the internal combustion engine 10 can be suppressed.

  (6) Forcibly changing the EGR opening and obtaining a change amount ΔPM of the intake pressure PM accompanying the change, and based on the obtained change amount ΔPM, a reference for the amount of EGR gas that actually passes through the EGR passage 28 The degree of decline from the amount was estimated. Therefore, the degree of decrease in the external EGR amount from the reference amount can be estimated based on the relationship between the change amount of the EGR opening and the change amount ΔPM of the intake pressure PM.

The embodiment described above may be modified as follows.
The intake air amount sensor 42 may be omitted. In this case, the intake air amount may be obtained based on the intake pressure PM and the engine speed NE and used for various controls.

  The execution condition for calculating the change amount ΔPM of the intake pressure PM can be arbitrarily changed as long as it can be determined that the operating state of the internal combustion engine 10 is stable at a low change speed. It is.

  The delay period is not limited to a predetermined period, and the delay period is an index value (eg, engine speed NE or intake air amount GA) regarding the flow velocity of the air flowing through the intake passage 11 of the internal combustion engine 10. Etc.) may be variably set according to the above. By setting a delay period in accordance with the flow velocity of the air flowing through the intake passage 11 of the internal combustion engine 10, an EGR gas recirculation execution state through valve timing control and an EGR gas recirculation execution state through external EGR control It is possible to accurately prevent the operating state of the internal combustion engine 10 from becoming unstable during the switching.

  -The calculation method of the estimated EGR amount can be arbitrarily changed. For example, the estimated EGR amount can be calculated based on the ratio between the change amount ΔPM of the intake pressure PM and the standard change amount. Further, an estimated EGR amount is calculated based on the change amount ΔPM of the intake pressure PM and the intake pressure PM immediately before the forced change, or the intake air when the change is stable after the change amount ΔPM of the intake pressure PM and the forced change is made. It is also possible to calculate the estimated EGR amount based on the pressure PM.

The deposit correction amount Kdp can be arbitrarily changed as long as it is a method calculated based on the estimated EGR amount.
The process for calculating the deposit correction amount Kdp can be omitted. In this case, the process of calculating the estimated EGR amount based on the change amount ΔPM of the intake pressure PM may be omitted.

  The predetermined value of “condition b” may be variably set based on the operating state of the internal combustion engine 10 (for example, the engine speed NE, the engine load KL, etc.) when the change amount ΔPM of the intake pressure PM is calculated. Good.

  Instead of the change amount ΔPM of the intake pressure PM in “condition b”, a ratio between the change amount ΔPM and a standard change amount or an estimated EGR amount may be used. The point is that the value has a high correlation with the degree of decrease in the external EGR amount from the reference amount.

  ・ As a predetermined operating area of “Condition C”, a plurality of areas determined according to the degree of decrease in the external EGR amount from the reference amount are set, and the area according to the degree of decrease at that time is determined in “Condition C” You may make it use for. In this case, a plurality of regions may be set such that a wider region is set as the predetermined operation region as the degree of decrease in the external EGR amount from the reference amount is larger. As a result, the external EGR region is enlarged as the degree of decrease is larger.

  In “Condition D”, instead of using the coolant temperature THW, an index value of the temperature of another internal combustion engine 10 (for example, the temperature of the lubricating oil) may be used. Also, a temperature sensor for detecting the temperature of the internal combustion engine 10 can be newly provided, and the temperature detected by the sensor can be used in the “condition d”.

  In “condition”, instead of using the engine load KL, a value corresponding to the load of the internal combustion engine 10 according to the engine parameters such as the intake pressure PM, the intake air amount GA, the throttle opening degree TA, the engine speed NE, etc. May be calculated and used. Of these engine parameters, the throttle opening TA changes early. Therefore, by using such a throttle opening degree TA for calculation of a value corresponding to the load of the internal combustion engine 10, it is possible to determine a change in the load of the internal combustion engine 10 at an early stage, and to perform recirculation of EGR gas through valve timing control. It becomes possible to quickly switch between the state and the execution state of the recirculation of the EGR gas through the external EGR control.

A boundary between the VVT region and the external EGR region may be set in an operation region where the engine speed NE is equal to or lower than a predetermined speed and the engine load KL is equal to or lower than a predetermined value.
-The present invention performs EGR gas recirculation through valve timing control in an operating region where the engine speed is low and the engine load is small, and externally in an operating region where the engine speed is high and the engine load is large. The present invention can also be applied to an exhaust gas recirculation device that performs recirculation of EGR gas through EGR control. In this case, when the degree of decrease in the external EGR amount from the reference amount increases due to deposits on the EGR valve, the operating range is higher on the engine speed side or on the higher engine load side. The VVT area may be changed (enlarged).

  The VVT area and the external EGR area can be arbitrarily changed. The point is that the external EGR area is changed according to the setting mode of the VVT area and the external EGR area when the degree of decrease in the external EGR quantity from the reference quantity increases due to deposits on the EGR valve. do it.

1 is a schematic diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas recirculation apparatus according to an embodiment embodying the present invention is applied. The time chart which shows the change aspect of the valve timing of an intake valve. 6 is a schematic diagram showing a boundary between an external EGR region and a VVT region. The flowchart which shows the specific execution procedure of a change process. 6 is a schematic diagram showing a boundary between an external EGR region and a VVT region when the VVT region is enlarged.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Intake passage, 12 ... Throttle valve, 13 ... Throttle motor, 14 ... Combustion chamber, 15 ... Fuel injection valve, 16 ... Spark plug, 17 ... Igniter, 18 ... Piston, 19 ... Crankshaft, 20 Exhaust passage, 21 ... Intake valve, 22 ... Intake camshaft, 23 ... Exhaust valve, 24 ... Exhaust camshaft, 25 ... Valve timing changing mechanism, 26 ... VVT actuator, 27 ... External EGR mechanism, 28 ... EGR passage, 29 ... EGR valve, 30 ... EGR actuator, 31 ... Accelerator pedal, 40 ... Electronic control device, 41 ... Crank sensor, 42 ... Intake sensor, 43 ... Accelerator sensor, 44 ... Throttle sensor, 45 ... Pressure sensor, 46 ... Temperature sensor , 47... Position sensor, 48.

Claims (6)

Applied to an internal combustion engine having an external EGR mechanism composed of an EGR passage communicating with an intake passage and an exhaust passage and an EGR valve provided in the EGR passage, and a change mechanism for changing a valve overlap period of the engine valve, In an exhaust gas recirculation device for an internal combustion engine that recirculates EGR gas in the intake passage through execution of opening control of the EGR valve and operation control of the change mechanism according to an operating state of the internal combustion engine,
Execution means for selectively executing one of recirculation of EGR gas through opening control of the EGR valve and recirculation of EGR gas through operation control of the change mechanism in accordance with an operating region of the internal combustion engine When,
The recirculation of the EGR gas is executed by the execution means through the opening control of the EGR valve based on the degree of decrease from the reference amount of the amount of the EGR gas that actually passes through the EGR passage. An exhaust gas recirculation device for an internal combustion engine, comprising: changing means for changing an operation region. The exhaust gas recirculation device for an internal combustion engine according to claim 1,
The exhaust gas recirculation device for an internal combustion engine, wherein the change means expands an operating range of the internal combustion engine that performs recirculation of EGR gas through opening degree control of the EGR valve as the degree of decrease increases. The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2,
The execution means executes recirculation of EGR gas through opening control of the EGR valve in an operation region where the rotation speed of the output shaft of the internal combustion engine is low and the load of the internal combustion engine is small, and the output shaft An exhaust gas recirculation device for an internal combustion engine, wherein recirculation of EGR gas is performed through operation control of the change mechanism in an operation region where the rotational speed is high and an operation region where the load is large. The exhaust gas recirculation device for an internal combustion engine according to claim 3,
The changing means prohibits expansion of an operating region in which EGR gas is recirculated through operation control of the changing mechanism to a smaller load side of the internal combustion engine when the temperature of the internal combustion engine is equal to or lower than a predetermined temperature. An exhaust gas recirculation device for an internal combustion engine. The exhaust gas recirculation device for an internal combustion engine according to any one of claims 1 to 4,
The operation region in which EGR gas is recirculated through opening control of the EGR valve to the operation region in which the rotational speed of the output shaft of the internal combustion engine is equal to or lower than a predetermined speed and the load of the internal combustion engine is equal to or lower than the predetermined value An exhaust gas recirculation device for an internal combustion engine, which prohibits change of the operating region by the changing means in a changing mode in which a boundary with an operating region where EGR gas is recirculated is set through operation control of the mechanism. The exhaust gas recirculation device for an internal combustion engine according to any one of claims 1 to 5,
The changing means forcibly changes the opening of the EGR valve, obtains a change amount of the pressure in the intake passage accompanying the change, and estimates the degree of reduction based on the obtained change amount. An exhaust gas recirculation device for an internal combustion engine.

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