JP4735519B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine that recirculates part of the exhaust gas of the internal combustion engine to an intake system.

  As a technique for reducing the amount of nitrogen oxide (hereinafter also referred to as “NOx”) contained in the exhaust gas of an internal combustion engine, exhaust gas recirculation (hereinafter also referred to as “EGR”) in which a part of the exhaust gas is recirculated to the intake system. The device is known.

  Also, as a technology that enables EGR in a wider operating range, high-pressure EGR means that recirculates the exhaust upstream of the turbine of the turbocharger to the intake passage downstream of the compressor, and recirculates the exhaust downstream of the turbine to the intake passage upstream of the compressor. There is known a technique for performing EGR by providing low-pressure EGR means for circulation and switching or using both high-pressure EGR means and low-pressure EGR means according to the operating state of the internal combustion engine.

  As an exhaust gas recirculation system that employs such a technique, premixed combustion is performed with EGR mainly using high pressure EGR means and auxiliary low pressure EGR means in low to medium speed and low to medium load ranges. Exhaust gas recirculation devices that perform EGR and normal combustion using low pressure EGR means in a high load range, and perform EGR and normal combustion using high pressure EGR means in a high engine speed and low to high load range have been proposed (for example, , See Patent Document 1).

However, in the above technique, there is a case where the amount of NOx generated temporarily increases due to a shortage of the amount of EGR gas in a transient state such as during acceleration from the fuel cut state.
JP 2004-150319 A

The present invention has been made in view of the above circumstances, and is directed to an exhaust gas recirculation device for an internal combustion engine that performs EGR by using or switching high pressure EGR means and low pressure EGR means together. And the objective is to provide the technique which can suppress that the quantity of EGR gas runs short at the time of acceleration from a fuel cut state, and can suppress the generation amount of NOx in a transient state.

The present invention for achieving the above object comprises two systems of EGR means, a low pressure EGR means and a high pressure EGR means, and performs EGR using only the high pressure EGR means or only the low pressure EGR means depending on the operating state of the internal combustion engine. Is an exhaust gas recirculation device for an internal combustion engine that selects whether to perform EGR using a combination of high-pressure EGR means and low-pressure EGR means, and at the time of acceleration from a fuel cut state, If the operating state is in a region where EGR is performed using only the high pressure EGR means or a region where EGR is performed using both the high pressure EGR means and the low pressure EGR means, the opening of the low pressure EGR valve in the low pressure EGR means The greatest feature is that the opening is controlled from the opening required for NOx reduction in the target operating state.

More specifically, a supercharger having a compressor provided in an intake passage of an internal combustion engine and a turbine provided in an exhaust passage of the internal combustion engine,
A low-pressure EGR passage that communicates an exhaust passage downstream from the turbine and an intake passage upstream from the compressor, and a low-pressure EGR valve that controls the amount of exhaust gas passing through the low-pressure EGR passage, and an exhaust passage downstream from the turbine Low pressure EGR means for recirculating the exhaust gas passing through the intake passage upstream of the compressor;
A high-pressure EGR passage that communicates an exhaust passage upstream of the turbine and an intake passage downstream of the compressor, and a high-pressure EGR valve that controls the amount of exhaust gas passing through the high-pressure EGR passage, and an exhaust passage upstream of the turbine High pressure EGR means for recirculating the exhaust gas passing through the intake passage downstream of the compressor;
By changing the opening of the low pressure EGR valve to the target low pressure EGR opening and changing the opening of the high pressure EGR valve to the target high pressure EGR opening according to the operating state of the internal combustion engine, the operating state of the internal combustion engine Is in a predetermined HPL region with a relatively low load or a low rotational speed, the exhaust gas is recirculated using only the high-pressure EGR means, and the operating state of the internal combustion engine is a predetermined medium load or a predetermined rotational speed. The exhaust gas is recirculated using both the low pressure EGR means and the high pressure EGR means, and the operating state of the internal combustion engine is within a predetermined LPL area of a relatively high load or high speed. An exhaust gas recirculation device for an internal combustion engine that recirculates the exhaust gas using only low pressure EGR means,
When the target operating state belongs to the HPL region or the MPL region during acceleration from the fuel cut state of the internal combustion engine, the opening of the low pressure EGR valve is further opened from the target low pressure EGR opening. It is characterized by controlling.

  Here, as described above, in the exhaust gas recirculation apparatus for an internal combustion engine having two systems of EGR means, that is, the low pressure EGR means and the high pressure EGR means, the operating state of the internal combustion engine is a predetermined value with a relatively low load or a low rotational speed. The exhaust gas is recirculated using only the high pressure EGR means. When the operating state of the internal combustion engine belongs to a predetermined MPL region of medium load or medium speed, the low pressure EGR is used. When the exhaust gas is recirculated using both the high pressure EGR means and the high pressure EGR means, and the operating state of the internal combustion engine belongs to a predetermined LPL region with a relatively high load or high speed, only the low pressure EGR means is used. The exhaust gas is recirculated.

  As a result, when the operating state of the internal combustion engine belongs to a low load or low rotation speed region, the responsiveness of the entire EGR is secured by preferentially using the low pressure EGR means having excellent responsiveness. Further, when the operating state of the internal combustion engine belongs to a region of a high load or high speed, the recirculation of the low temperature EGR gas from the low pressure EGR means is promoted and the high temperature EGR gas from the high pressure EGR means is recirculated. Is suppressed, and the temperature of the EGR gas is suppressed from becoming excessively high. As a result, the exhaust gas can be recirculated in a wider range of operating conditions.

  Here, consider the case where the internal combustion engine shifts from the fuel cut state to the operating state of the HPL region or the MPL region in response to an acceleration request (during acceleration from the fuel cut state). In this case, exhaust gas is recirculated by the high pressure EGR means. However, since the amount of combustion gas in the high pressure EGR passage itself is reduced by the fuel cut, the exhaust gas that can be recirculated by the high pressure EGR means (EGR gas). The amount of is decreasing. Further, since the capacity of the high pressure EGR passage is smaller than the capacity of the low pressure EGR passage, the amount of EGR gas that can be recirculated by the high pressure EGR means is smaller than the amount of EGR gas that can be recirculated by the low pressure EGR means. Therefore, during the acceleration from the fuel cut state of the internal combustion engine to the HPL region or the MPL region or immediately after the acceleration, the amount of recirculated EGR gas is temporarily insufficient, and the NOx generation amount may increase. there were.

  Therefore, in the present invention, when the internal combustion engine is accelerated from the fuel cut state to the HPL region or the MPL region, the opening of the low pressure EGR valve is set to the opening required for the low pressure EGR valve in the operating state after acceleration. The opening degree is larger than the target low pressure EGR opening degree. As a result, the amount of EGR gas recirculated by the low pressure EGR means during or immediately after acceleration is increased to compensate for the shortage of EGR gas in the transient state.

This makes it possible to increase the amount of EGR gas recirculated by the low pressure EGR means during or immediately after acceleration from the fuel cut state of the internal combustion engine to the HPL region or the MPL region. The EGR gas can be recirculated to reduce the amount of NOx generated.

  In the present invention, when the target operating state belongs to the HPL region during acceleration from the fuel cut state of the internal combustion engine, the amount of EGR gas recirculated to the internal combustion engine is the target You may control the opening degree of the said low pressure EGR valve further to the valve opening side from the said target low pressure EGR opening degree over the period until it becomes the request | requirement EGR gas amount according to a driving | running state.

  Here, when the operation state of the internal combustion engine shifts from the fuel cut state to the low load or low speed HPL region due to the acceleration request, the fluctuation of the fuel injection amount can be small, so the EGR gas during the acceleration or immediately after the acceleration. It's hard to happen that the amount of is drastically short. However, there is still a case where it is difficult to supply sufficient EGR gas. In this case, in the present invention, the low-pressure EGR valve is controlled to be more open than the target low-pressure EGR opening in a pulsed manner during acceleration. It was decided to.

  For example, in the steady state in which the operating state of the internal combustion engine belongs to the HPL region, in the control for closing the low pressure EGR valve, that is, the control in which the target low pressure EGR opening becomes zero, when accelerating from the fuel cut state to the HPL region, The low pressure EGR valve may be opened in a pulse manner.

  In the present invention, the pulse width may be a period from when acceleration starts until the actual amount of EGR gas reaches the required amount of EGR gas corresponding to the requested (after acceleration) operation state. By doing so, the low pressure EGR valve can be opened until the amount of EGR gas required in the operating state after acceleration is satisfied, and the shortage of EGR gas can be more reliably suppressed.

In the present invention, the intake passage is provided upstream of the connection portion with the high pressure EGR passage in the intake passage and downstream of the connection portion with the low pressure EGR passage, and controls the amount of intake air passing through the intake passage. A throttle valve,
At the time of acceleration from the fuel cut state of the internal combustion engine, if the target operating state belongs to the MPL region, the high pressure EGR valve is fully opened and the throttle valve is controlled to the valve closing side. Also good.

  Here, when the operating state after acceleration required for the internal combustion engine belongs to the MPL region, the fuel injection amount fluctuates as compared with the case where the requested operating state after acceleration belongs to the HPL region. The amount of EGR gas deficient during acceleration or immediately after acceleration is large.

  Therefore, in the present invention, when the operating state of the internal combustion engine shifts from the fuel cut state to the MPL region due to an acceleration request, the high pressure EGR valve is fully opened to facilitate the introduction of EGR gas from the high pressure EGR means. Thereby, the responsivity of recirculation of EGR gas can be enhanced as much as possible. In the present invention, the throttle valve is also controlled to the closed side, the amount of fresh air sucked in is suppressed, and the amount of EGR gas recirculated by the high pressure EGR means is further increased. Thereby, the responsiveness of the recirculation of the EGR gas can be further enhanced, and the introduction of the EGR gas in the transient state can be further promoted.

Further, in the present invention, after the high pressure EGR valve is fully opened and the throttle valve is controlled to the closed side, the high pressure EG is determined according to the difference between the amount of EGR gas at that time and the above-mentioned required EGR gas amount.
The R valve may be controlled to the valve closing side and the low pressure EGR valve may be controlled to the valve opening side. Then, the amount of EGR gas recirculated by the high pressure EGR means is decreased, and the amount of EGR gas recirculated by the low pressure EGR means is increased. Finally, the opening of the low pressure EGR valve may be set as the target low pressure EGR opening, and the opening of the high pressure EGR valve may be set as the target high pressure EGR opening.

  Then, the EGR gas is first recirculated using the high-pressure EGR means with high responsiveness, and then the amount of EGR gas recirculated gradually is increased by the low-pressure EGR means, and finally the low-pressure EGR valve is opened. Since the degree can be the target low pressure EGR opening and the opening of the high pressure EGR valve can be the target high pressure EGR opening, the shortage of EGR gas in the transient state can be more reliably suppressed.

  In the present invention, the exhaust passage further includes a second throttle valve that is provided downstream of the connection portion of the exhaust passage with the low pressure EGR passage and controls the amount of exhaust passing through the exhaust passage. When the operation state shifts from the fuel cut state due to an acceleration request and the target operation state (after acceleration) belongs to the MPL region, the low pressure EGR valve is also fully opened and the second throttle valve is closed. You may make it control to the valve side.

  That is, when the internal combustion engine is in an acceleration state from the fuel cut state to the MPL region, the high pressure EGR valve is fully opened, the throttle valve is controlled to the closed side, and the second throttle valve is further controlled to the closed side. In addition, the low pressure EGR valve may be fully opened. By doing this, it is possible to recirculate as much EGR gas as possible by using both the high-pressure EGR means having a relatively high response and the low-pressure EGR means having a large capacity, and the EGR gas in a transient state of the internal combustion engine. Can be more reliably suppressed.

  In the present invention, the opening degree of the low pressure EGR valve and / or the opening degree of the high pressure EGR valve at the time of acceleration from the fuel cut state of the internal combustion engine depends on the required EGR gas according to the target operating state. The actual EGR gas amount deficiency relative to the required EGR gas amount is determined based on the governor fuel injection amount corresponding to the accelerator opening. You may do it.

  That is, an insufficient amount of EGR gas is derived based on the governor fuel injection amount corresponding to the accelerator opening of the accelerator depressed by the driver. Then, the opening degree of the low pressure EGR valve and / or the opening degree of the high pressure EGR valve at the time of acceleration from the fuel cut state of the internal combustion engine is determined based on the actual shortage amount of EGR gas with respect to the required EGR gas amount.

  Here, the fuel injection amount in the process of shifting the operating state of the internal combustion engine due to the acceleration request is such that the fuel injection amount in the original operating state smoothly changes to the fuel injection amount required in the destination operating state. Thus, the fuel injection amount is obtained by adding so-called “smoothing” to the governor fuel injection amount that directly corresponds to the accelerator opening. Therefore, when the actual EGR gas shortage amount with respect to the required EGR gas amount is derived based on the fuel injection amount including this annealing, the EGR gas shortage amount is derived to be less than the actual value. There is a risk of being.

  On the other hand, as in the present invention, when an insufficient amount of EGR gas is derived based on the governor fuel injection amount corresponding to the accelerator opening of the accelerator depressed by the driver at the time of acceleration request, The amount of EGR gas deficiency can be derived based on the fuel injection amount in the target operating state. Therefore, the opening degree of the low pressure EGR valve and / or the opening degree of the high pressure EGR valve at the time of acceleration from the fuel cut state of the internal combustion engine is determined based on a larger amount of EGR gas deficient derived. Thus, the amount of NOx generated in the transient state can be suppressed more reliably.

The present invention further includes an oxygen concentration sensor provided on a downstream side of a connection portion between the intake passage of the internal combustion engine and the high pressure EGR passage, and detects an oxygen concentration in the intake air,
The opening degree of the low pressure EGR valve and / or the opening degree of the high pressure EGR valve at the time of acceleration from the fuel cut state of the internal combustion engine depends on the actual EGR gas amount with respect to the required EGR gas amount corresponding to the target operating state. Determined based on the shortage of quantity,
The shortage of the actual amount of EGR gas relative to the required amount of EGR gas may be derived based on the oxygen concentration of the intake air introduced into the internal combustion engine detected by the oxygen concentration sensor.

  That is, in the conventional exhaust gas recirculation device, the amount of fresh air is detected by an air flow meter or the like, and in addition to this fresh air amount, it is based on additional parameters such as fuel injection amount, supercharging pressure, and engine speed. In many cases, an insufficient amount of the actual EGR gas with respect to the required EGR gas amount is derived. However, the error of each parameter may accumulate, and the accuracy of deriving the insufficient amount of EGR gas may be reduced. On the other hand, an oxygen concentration sensor is provided in the intake system of the internal combustion engine to directly detect the A / F of the intake air after the fresh air and the EGR gas merge, and based on the value of this A / F, the required EGR gas If the deficiency of the actual amount of EGR gas with respect to the amount is derived, the accuracy of the derivation can be further improved.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  In the present invention, in an exhaust gas recirculation device for an internal combustion engine that performs EGR by using both the high pressure EGR means and the low pressure EGR means, the shortage of EGR gas is suppressed during acceleration from the fuel cut state, and in a transient state. Generation of NOx can be suppressed.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine, an intake / exhaust system, and a control system to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a diesel engine having four cylinders 2.

An intake manifold 8 is connected to the internal combustion engine 1, and each branch pipe of the intake manifold 8 is communicated with a combustion chamber of each cylinder 2 through an intake port. The intake manifold 8 is provided with an A / F sensor 26 that detects the oxygen concentration of the intake air that passes through the intake manifold 8. In the vicinity of the connection portion between the intake manifold 8 and the intake pipe 9, a throttle valve 12 capable of changing the flow passage cross-sectional area of the intake pipe 9 is provided. The throttle valve 12 is connected to an ECU 22 to be described later via an electrical wiring, and the flow rate of the intake air flowing through the intake pipe 9 can be adjusted by controlling the valve opening degree based on a control signal from the ECU 22. it can. An intercooler 13 that cools the gas flowing through the intake pipe 9 is provided upstream of the throttle valve 12. A compressor housing 6 in which a compressor of the centrifugal supercharger 10 that operates using exhaust energy as a drive source is provided upstream of the intercooler 13. A second throttle valve 17 capable of changing the flow passage cross-sectional area of the intake pipe 9 is provided further upstream of the compressor housing 6. The second throttle valve 17 is also connected to the ECU 22 and adjusts the flow rate of the intake air flowing through the intake pipe 9 based on a control signal from the ECU 22. An air flow meter 24 for detecting the amount of intake air passing through the intake pipe 9 and an air cleaner 25 for removing dust floating in the fresh air are provided further upstream of the second throttle valve 17 in the intake pipe 9.

  On the other hand, an exhaust manifold 18 is connected to the internal combustion engine 1, and each branch pipe of the exhaust manifold 18 communicates with the combustion chamber of each cylinder 2 through an exhaust port. A turbine housing 7 in which the turbine of the centrifugal supercharger 10 is stored is connected to the exhaust manifold 18 via a collecting pipe 16. An exhaust pipe 19 is connected to an opening through which the exhaust of the turbine housing 7 flows out. The exhaust pipe 19 is provided with a filter 20 that collects particulate matter in the exhaust. An exhaust throttle valve 11 capable of changing the cross-sectional area of the exhaust pipe 19 is provided downstream of the filter 20. The exhaust pipe 19 is open to the atmosphere downstream of the exhaust throttle valve 11. The exhaust throttle valve 11 is connected to the ECU 22 via electrical wiring, and the flow rate of the exhaust gas flowing through the exhaust pipe 19 can be adjusted by controlling the valve opening degree based on a control signal from the ECU 22. .

  A portion of the exhaust pipe 19 downstream of the filter 20 and upstream of the exhaust throttle valve 11 and a portion of the intake pipe 9 upstream of the compressor housing 6 are communicated by a low pressure EGR passage 23. The low-pressure EGR passage 23 is provided with a low-pressure EGR cooler 14 that cools the exhaust gas flowing through the low-pressure EGR passage 23 and a low-pressure EGR valve 5 that can change the flow passage cross-sectional area of the low-pressure EGR passage 23. The low pressure EGR valve 5 is connected to the ECU 22 via an electric wiring, and the amount of exhaust flowing through the low pressure EGR passage 23 may be adjusted by controlling the valve opening degree based on a control signal from the ECU 22. (Hereinafter, the exhaust gas flowing through the low pressure EGR passage 23 is referred to as “low pressure EGR gas”, and the amount thereof is referred to as “low pressure EGR gas amount”).

  On the other hand, the exhaust manifold 18 and the intake manifold 8 are communicated with each other by a high pressure EGR passage 15. The high-pressure EGR passage 15 is provided with a high-pressure EGR valve 21 that can change the flow path cross-sectional area of the high-pressure EGR passage 15. The high-pressure EGR valve 21 is connected to the ECU 22 via electric wiring, and the amount of exhaust flowing through the high-pressure EGR passage 15 can be adjusted by controlling the valve opening degree based on a control signal from the ECU 22. (Hereinafter, the exhaust gas flowing through the high pressure EGR passage 15 is referred to as “high pressure EGR gas”, and the amount thereof is referred to as “high pressure EGR gas amount”).

  The internal combustion engine 1 is also provided with an ECU 22 that is an electronic control computer that controls the internal combustion engine 1. The ECU 22 includes a ROM, a RAM, a CPU, an input port, an output port, and the like (not shown), and performs known control such as fuel injection according to the operation state of the internal combustion engine 1 detected by the various sensors and a request from the driver. At the same time, an opening degree command signal is output to the high pressure EGR valve 21, the low pressure EGR valve 5, the throttle valve 12, the second throttle valve 17, and the exhaust throttle valve 11.

  In the above configuration, the air introduced into the intake pipe 9 passes through the air flow meter 24 after dust is removed by the air cleaner 25, and is supercharged by the compressor in the compressor housing 6, and is also intercooler 13, intake manifold 8 is introduced into each cylinder 2 of the internal combustion engine 1.

  The exhaust discharged from each cylinder 2 flows into the turbine housing 7 via the exhaust manifold 18 and the collecting pipe 16 to drive the turbine. Thereafter, it passes through the exhaust pipe 19, and the particulate matter in the exhaust is collected by the filter 20 and finally discharged into the atmosphere.

Here, when the low pressure EGR valve 5 is opened, the low pressure EGR passage 23 becomes conductive, and a part of the exhaust gas passing through the exhaust pipe 19 flows into the intake pipe 9 via the low pressure EGR passage 23. The low-pressure EGR gas that has flowed into the intake pipe 9 is supercharged by the compressor in the compressor housing 6 and is introduced into the cylinder 2 of the internal combustion engine 1 via the intake manifold 8. Here, the amount of low-pressure EGR gas can also be adjusted by adjusting the opening of the second throttle valve 17 to increase or decrease the pressure at the connection portion of the intake manifold 8 with the low-pressure EGR passage 23 (low-pressure EG).
The EGR performed through the R passage 23 is hereinafter referred to as “low pressure EGR”. ).

  When the high-pressure EGR valve 21 is opened, the high-pressure EGR passage 15 becomes conductive, and a part of the exhaust gas flowing through the exhaust manifold 18 flows into the intake manifold 8 via the high-pressure EGR passage 15, and the cylinder of the internal combustion engine 1. Recycle to 2. Here, the amount of high-pressure EGR gas can be adjusted by adjusting the opening of the throttle valve 12 to increase or decrease the pressure at the connection portion of the intake manifold 8 with the high-pressure EGR passage 15 (via the high-pressure EGR passage 15). The EGR performed in this manner is hereinafter referred to as “high pressure EGR”).

  By recirculating a part of the exhaust gas to the cylinder 2 of the internal combustion engine 1 by the low pressure EGR and / or the high pressure EGR, the combustion temperature in the combustion chamber is lowered, and the amount of NOx generated in the combustion process can be reduced.

  In this embodiment, the low pressure EGR means includes the low pressure EGR passage 23 and the low pressure EGR valve 5. The high pressure EGR means includes a high pressure EGR passage 15 and a high pressure EGR valve 21.

FIG. 2 is a graph illustrating a pattern for selectively using the low pressure EGR and the high pressure EGR corresponding to the operating state of the internal combustion engine 1. As shown in FIG. 2, in an ideal use pattern of the low-pressure EGR means and the high-pressure EGR means, only the low-pressure EGR is used in a high load or high-speed operation state. This corresponds to an LPL (Low Pressure Loop) region in the present embodiment. Also, in medium load or medium speed operating conditions, high pressure E
GR and low pressure EGR are used in combination. This corresponds to an MPL (Middle Pressure Loop) region in the present embodiment. Furthermore, only the high pressure EGR is used in the operation state with a low load and a low rotational speed. This corresponds to an HPL (High Pressure Loop) region in the present embodiment.

  Thereby, when the operating state of the internal combustion engine is low load or low speed, the responsiveness of the whole EGR is ensured by preferentially using the low pressure EGR which is excellent in responsiveness. Further, when the operating state of the internal combustion engine is high load or high speed, the recirculation of the low temperature EGR gas by the low pressure EGR is promoted and the recirculation of the high temperature EGR gas by the high pressure EGR is suppressed. The temperature is suppressed from becoming excessively high. As a result, the exhaust gas can be recirculated in a wider range of operating conditions.

  Here, the exhaust gas recirculation state when the internal combustion engine 1 shifts from the fuel cut state to another operation state due to an acceleration request will be considered. In the fuel cut state, since the fuel injection to the internal combustion engine 1 is stopped, the fresh air introduced into the internal combustion engine 1 is discharged as it is, and the combustion gas is not discharged. Therefore, there is almost no EGR gas as combustion gas in the high pressure EGR passage 15 and the low pressure EGR passage 23.

Therefore, in the acceleration state from the fuel cut state, the EGR gas recirculated to the internal combustion engine 1 is temporarily insufficient, and the amount of NOx generated in the internal combustion engine 1 may increase. Also, the amount of EGR gas that is deficient varies depending on the engine load and engine speed in the previous operating state that is shifted by acceleration.

  Therefore, in this embodiment, when the internal combustion engine 1 shifts from the fuel cut state to a new operation state due to an acceleration request, control for suppressing the shortage of EGR gas in the transient state according to the target operation state. It was decided to do.

<Control during transition from fuel cut state to HPL region>
First, control when the operating state of the internal combustion engine 1 shifts from the fuel cut state to the HPL region due to an acceleration request will be described. In the HPL region, as described above, the exhaust gas is basically recirculated only by the high pressure EGR, so that only the high pressure EGR valve 21 is opened and the EGR gas is recirculated through the high pressure EGR passage 15. However, since there is no EGR gas in the high-pressure EGR passage 15 in the acceleration state from the fuel cut state, the amount of recirculated EGR gas may be temporarily insufficient with respect to the required value.

  However, in this case, since the required operation state is a low load or low rotation speed region, the fuel injection amount fluctuation at the time of transition is small, and the amount of insufficient EGR gas is not so large. And the lack of the amount of EGR gas rather than the responsiveness of EGR becomes a significant problem. In view of these circumstances, in this embodiment, in this case, in addition to opening the high-pressure EGR valve 21, the low-pressure EGR valve 5 is opened in a pulsed manner.

By doing so, when the operation state of the internal combustion engine 1 shifts from the fuel cut state to the HPL region, the amount of EGR gas is insufficient due to the low temperature EGR using the low pressure EGR valve 17 opened in a pulse manner. Can be suppressed, and an increase in the amount of NOx generated can be suppressed. The pulse width is a period from when an acceleration request is issued to the internal combustion engine 1 until the required amount of EGR gas is recirculated in the (target) operating state after acceleration. It is good. Therefore, since the period during which the EGR gas is recirculated by the low pressure EGR is limited, it is possible to suppress the temperature of the entire EGR gas from becoming excessively low.

  Note that the opening degrees of the high pressure EGR valve 21 and the low pressure EGR valve 5 in this control may be fully open or close to fully open.

<Control during transition from fuel cut state to MPL area>
Next, control at the time of transition from the fuel cut state to the MPL region will be described. In the MPL region, the exhaust gas is recirculated using both the high pressure EGR and the low pressure EGR as described above. Specifically, the opening degrees of the high pressure EGR valve 21 and the low pressure EGR valve 5 are adjusted as appropriate so that the required amount of EGR gas can be recirculated according to the operating state of the MPL region. Further, in this case, since the requested operating state is a medium load or medium rotation speed region, the fluctuation of the fuel injection amount at the time of transition is large compared to the case of transition to the HPL region, and there is insufficient EGR. The amount of gas also increases. Therefore, in this case, first, the high-pressure EGR valve 21 is fully opened as the preceding. At the same time, the throttle valve 12 is controlled to the valve closing side to suppress the amount of fresh air. By these two controls, the recirculation of the EGR gas by the high pressure EGR is promoted.

By the above control, the amount of EGR gas recirculated by the high-pressure EGR that is originally highly responsive can be increased as much as possible, and an increase in the amount of NOx generated in the transient state can be suppressed.

  In this control, as described above, after the high pressure EGR valve 21 is fully opened and the throttle valve 12 is controlled to the valve closing side, the actual EGR with respect to the amount of EGR gas required in the operating state after acceleration. The opening degree of the low pressure EGR valve 5 is increased and the opening degree of the high pressure EGR valve 21 is decreased according to the difference from the gas amount (shortage amount of EGR gas). That is, the ratio of the low pressure EGR gas to the total amount of EGR gas is gradually increased to control the opening of the low pressure EGR valve 5 and the opening of the high pressure EGR valve 21 required in the MPL region in the steady state. . At this time, the opening of the low pressure EGR valve 5 and the opening of the high pressure EGR valve 21 required in the MPL region correspond to the target low pressure EGR opening and the target high pressure EGR opening in this case. The same applies to the transition from the fuel cut state to another operating state in this description.

  In this way, first, the amount of the EGR gas in the transient state can be secured by controlling the high pressure EGR valve 21 and the throttle valve 12, and then the amounts of the low pressure EGR gas and the high pressure EGR gas in the operation state of the transition destination can be obtained. .

  In this control, when the opening degree of the low pressure EGR valve 5 is increased and the opening degree of the high pressure EGR valve 21 is decreased, the actual EGR gas with respect to the amount of EGR gas required in the operating state after acceleration. In addition to the difference from the amount (EGR gas shortage), the opening of the low pressure EGR valve 5 is increased according to the intake air temperature in the intake manifold 8 detected by a temperature sensor (not shown), and the high pressure EGR valve 21 The degree of opening may be reduced.

That is, since the temperature of the high pressure EGR gas is high, the amount of NOx generated may increase unless an appropriate amount of the low pressure EGR gas is mixed and recirculated. Therefore, in this embodiment, the amount of high-pressure EGR gas and the amount of low-pressure EGR gas may be determined so that the intake air temperature does not become excessively high, and control for suppressing the NOx generation amount may be performed.

  If it does so, the NOx generation amount in the transition state at the time of the transition from a fuel cut state to a MPL area | region can be suppressed more reliably.

<Control 2 during transition from the fuel cut state to the MPL area>
Next, another aspect of control at the time of transition from the fuel cut state to the MPL region will be described. In this embodiment, both the high-pressure EGR valve 21 and the low-pressure EGR valve 5 are fully opened as a precedent. At the same time, the throttle valve 12 is controlled to the closed side to control the amount of intake air, and the second throttle valve 17 is also controlled to be closed to suppress the amount of fresh air. These controls facilitate both high pressure EGR gas recirculation and low pressure EGR gas recirculation.

  By the above control, the amount of the high-pressure EGR gas recirculated by the high-pressure EGR that is originally highly responsive can be increased as much as possible, and the low-pressure EGR recirculated by the high-pressure EGR having a large EGR gas volume. The amount of gas can be increased as much as possible, and an increase in the amount of NOx generated in a transient state can be suppressed.

  Then, the opening degree of the low-pressure EGR valve 5 and the high-pressure EGR valve 21 according to the difference between the amount of EGR gas required in the operating state after acceleration and the actual amount of EGR gas (shortage amount of EGR gas). Gradually decrease both of the opening. Then, the opening degree of the low pressure EGR valve 5 and the opening degree of the high pressure EGR valve 21 required in the MPL region in the steady state are controlled.

  In this way, first, the total amount of the EGR gas that can be recirculated from the high pressure EGR and the low pressure EGR is maximized, and then the amounts of the low pressure EGR gas and the high pressure EGR gas in the operation state of the transfer destination can be obtained. As a result, the amount of EGR gas in the transient state can be ensured more reliably, and the amount of NOx generated can be suppressed.

<EGR gas deficiency determination method>
Here, when the operating state of the internal combustion engine shifts from the fuel cut state to another operating state due to the acceleration request to the internal combustion engine 1, as described above, the amount of EGR gas required in the operating state after acceleration is reduced. The opening degree of the low pressure EGR valve 5 and the opening degree of the high pressure EGR valve 21 are determined according to the difference from the actual amount of EGR gas (EGR gas shortage amount). In this case, the difference between the amount of EGR gas required in the operating state after acceleration and the actual amount of EGR gas (shortage amount of EGR gas) is directly from the accelerator opening detected by an accelerator position sensor (not shown). It is derived from the determined governor injection amount.

  Normally, when a change in the operating state of the internal combustion engine 1 occurs, in the transient state, the fuel injection amount in the internal combustion engine 1 is not directly controlled to the fuel injection amount according to the target operating state, In order to smoothly change from the current fuel injection amount, control in consideration of so-called annealing is performed. When the amount of EGR gas deficiency is calculated based on the fuel injection amount while taking this annealing into account, the amount of EGR gas deficiency may appear small. In contrast, in this embodiment, the EGR gas deficiency is directly derived from the governor fuel injection amount in the target operating state, which is determined from the accelerator opening, so that the EGR gas relative to the final EGR gas amount is derived. A deficiency of can be obtained. As a result, the amount of EGR gas that is recirculated more quickly can be increased, and the amount of NOx generated can be more reliably suppressed.

<Determining EGR gas deficiency 2>
In the conventional exhaust gas recirculation device, the intake air amount Gn is detected by the air flow meter 24, the amount of fresh air obtained from the detected intake air amount, the fuel injection amount in the target operating state, the supercharging pressure, the engine rotation The required amount of EGR gas is determined based on the number and the like, and an insufficient amount of EGR gas is often derived from the required amount of EGR gas and the actual amount of EGR gas. However, in this case, when the required amount of EGR gas is determined, the oxygen concentration of the intake air including both EGR gas and fresh air is estimated from the amount of fresh air. There is a possibility that the required amount of EGR gas is not necessarily an optimum value. Moreover, the accuracy of the required amount of EGR gas derived may deteriorate due to the accumulation of parameter errors.

  On the other hand, in this embodiment, an A / F sensor 26 is provided in the intake manifold 8, and EGR required based on the A / F of the intake air introduced into the internal combustion engine 1 detected by the A / F sensor. The amount of gas was determined, and the shortage of EGR gas was derived from the required amount of EGR gas and the actual amount of EGR gas. Then, since the required amount of EGR gas can be determined based on the actual oxygen concentration after the fresh air and the EGR gas merge, the deficiency of the EGR gas can be calculated more accurately. be able to.

It is a figure which shows schematic structure of the internal combustion engine in the Example of this invention, its intake / exhaust system, and a control system. It is a graph which shows the relationship between the driving | running state of the internal combustion engine which concerns on the Example of this invention, and the usage aspect of low pressure EGR and high pressure EGR.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 5 ... Low pressure EGR valve 6 ... Compressor 7 ... Turbine 8 ... Intake manifold 9 ... Intake pipe 10 ... Centrifugal supercharger 11. ..Exhaust throttle valve 12 ... Throttle valve 13 ... Intercooler 14 ... EGR cooler 15 ... High pressure EGR passage 16 ... Collecting pipe 17 ... Second throttle valve 18 ... Exhaust manifold DESCRIPTION OF SYMBOLS 19 ... Exhaust pipe 20 ... Filter 21 ... High pressure EGR valve 22 ... ECU
23 ... Low pressure EGR passage 24 ... Air flow meter 25 ... Air cleaner

Claims (7)

A compressor provided in the intake passage of the internal combustion engine and a turbocharger having a turbine provided in the exhaust passage of the internal combustion engine;
A low-pressure EGR passage that communicates an exhaust passage downstream from the turbine and an intake passage upstream from the compressor, and a low-pressure EGR valve that controls the amount of exhaust gas passing through the low-pressure EGR passage, and an exhaust passage downstream from the turbine Low pressure EGR means for recirculating the exhaust gas passing through the intake passage upstream of the compressor;
A high-pressure EGR passage that communicates an exhaust passage upstream of the turbine and an intake passage downstream of the compressor, and a high-pressure EGR valve that controls the amount of exhaust gas passing through the high-pressure EGR passage, and an exhaust passage upstream of the turbine High pressure EGR means for recirculating the exhaust gas passing through the intake passage downstream of the compressor;
By changing the opening of the low pressure EGR valve to the target low pressure EGR opening and changing the opening of the high pressure EGR valve to the target high pressure EGR opening according to the operating state of the internal combustion engine, the operating state of the internal combustion engine Is in a predetermined HPL region with a relatively low load or a low rotational speed, the exhaust gas is recirculated using only the high-pressure EGR means, and the operating state of the internal combustion engine is a predetermined medium load or a predetermined rotational speed. The exhaust gas is recirculated using both the low pressure EGR means and the high pressure EGR means, and the operating state of the internal combustion engine is within a predetermined LPL area of a relatively high load or high speed. An exhaust gas recirculation device for an internal combustion engine that recirculates the exhaust gas using only low pressure EGR means,
When the target operating state belongs to the HPL region or the MPL region during acceleration from the fuel cut state of the internal combustion engine, the opening of the low pressure EGR valve is further opened from the target low pressure EGR opening. An exhaust gas recirculation device for an internal combustion engine, characterized by being controlled.   At the time of acceleration from the fuel cut state of the internal combustion engine, if the target operating state belongs to the HPL region, the amount of EGR gas recirculated to the internal combustion engine is a request EGR corresponding to the target operating state. 2. The exhaust gas recirculation device for an internal combustion engine according to claim 1, wherein the opening degree of the low pressure EGR valve is controlled further to the valve opening side than the target low pressure EGR opening degree over a period until the gas amount is reached. . A throttle valve that is provided on the upstream side of the connection portion with the high-pressure EGR passage in the intake passage and downstream of the connection portion with the low-pressure EGR passage, and that controls the amount of intake air that passes through the intake passage;
During acceleration from the fuel cut state of the internal combustion engine, when the target operating state belongs to the MPL region, the high pressure EGR valve is fully opened and the throttle valve is controlled to the valve closing side. The exhaust gas recirculation device for an internal combustion engine according to claim 1.   At the time of acceleration from the fuel cut state of the internal combustion engine, if the target operating state belongs to the MPL region, the high pressure EGR valve is fully opened and the throttle valve is controlled to the closed side, By controlling the EGR valve to the valve closing side and controlling the low pressure EGR valve to the valve opening side, the opening of the low pressure EGR valve is changed to the target low pressure EGR opening and the opening of the high pressure EGR valve is targeted. 4. The exhaust gas recirculation device for an internal combustion engine according to claim 3, wherein the opening is changed to a high pressure EGR opening degree. A second throttle valve provided on the upstream side of the connection portion of the intake passage with the low-pressure EGR passage, for controlling the amount of fresh air passing through the intake passage;
When accelerating from the fuel cut state of the internal combustion engine, if the target operating state belongs to the MPL region, the low pressure EGR valve is also fully opened and the second throttle valve is controlled to the valve closing side. The exhaust gas recirculation device for an internal combustion engine according to claim 3. The opening degree of the low pressure EGR valve and / or the opening degree of the high pressure EGR valve at the time of acceleration from the fuel cut state of the internal combustion engine depends on the actual EGR gas amount with respect to the required EGR gas amount corresponding to the target operating state. Determined based on the shortage of quantity,
6. The internal combustion engine according to claim 1, wherein the shortage of the actual amount of EGR gas with respect to the required EGR gas amount is derived based on a governor fuel injection amount corresponding to an accelerator opening. Engine exhaust gas recirculation device. An oxygen concentration sensor provided on a downstream side of a connection portion between the intake passage of the internal combustion engine and the high pressure EGR passage, and detecting an oxygen concentration in the intake air;
The opening degree of the low pressure EGR valve and / or the opening degree of the high pressure EGR valve at the time of acceleration from the fuel cut state of the internal combustion engine depends on the actual EGR gas amount with respect to the required EGR gas amount corresponding to the target operating state. Determined based on the shortage of quantity,
The deficiency of the actual amount of EGR gas with respect to the required amount of EGR gas is derived based on an oxygen concentration of intake air introduced into the internal combustion engine detected by the oxygen concentration sensor. The exhaust gas recirculation device for an internal combustion engine according to any one of 1 to 6.

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