JP4893383B2 - 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 exhaust gas passing through an exhaust system of the internal combustion engine to an intake system.

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

  Further, as a technique for enabling EGR in a wider operating range, a low-pressure EGR means for recirculating exhaust gas passing through an exhaust passage downstream of a turbocharger to an intake passage upstream of a compressor, and an exhaust passage upstream of the turbine There is known a technique for performing EGR by providing high pressure EGR means for recirculating exhaust gas passing through an intake passage downstream of a compressor, and switching or using low pressure EGR means and high pressure EGR means according to the operating state of the internal combustion engine. ing.

  In such an exhaust gas recirculation device, the exhaust gas recirculation is caused by a failure of a valve device that controls the flow rate of exhaust gas in the low pressure EGR means or the high pressure EGR means, or a failure such as clogging of a passage due to carbon accumulation in the exhaust gas. It is conceivable that the circulation stops or the flow rate of exhaust gas that is recirculated cannot be adjusted. In order to avoid such a problem, various failure diagnosis apparatuses for detecting a failure of the low pressure EGR means or the high pressure EGR means have been proposed.

  For example, a fresh air temperature detector that detects the temperature of fresh air upstream from the joining portion of the EGR passage and the intake passage, and an intake air temperature that detects the temperature of intake air after mixing EGR gas downstream of the joining portion A new air temperature difference between the two fresh air temperatures when the EGR valve is opened and closed, and an intake air temperature difference between the two intake air temperatures when the EGR valve is opened and closed; A technique (see Patent Document 1) that determines a failure based on the difference between the two has been proposed.

  In addition, an EGR gas temperature sensor for detecting the temperature of the EGR gas is provided in the vicinity of the joining portion of the EGR passage and the intake passage, and an intake air temperature sensor for detecting the intake air temperature in the intake passage is provided, and the EGR gas temperature and the intake air temperature are A technique for diagnosing the presence or absence of a failure of the EGR system based on the difference between the detected values (see Patent Document 2), and the EGR valve opening detected during EGR valve opening feedback control is a reference in a normal DPF state. A technique for determining that the DPF is damaged when the opening of the EGR valve is larger (see Patent Document 3) is also known.

  However, in the exhaust gas recirculation device having the low pressure EGR means and the high pressure EGR means, the amount of exhaust gas recirculated by the low pressure EGR means and the amount of exhaust gas recirculated by the high pressure EGR means are independent of each other depending on the operating state. Be changed. Even when there is an abnormality such as clogging, if the amount of exhaust gas recirculated by each EGR means is different, the degree of influence of the abnormality on the overall intake air temperature changes. Therefore, depending on the method of detecting the intake air temperature in the steady state of the internal combustion engine, it may be difficult to accurately determine an abnormality in each EGR means.

Further, since there is a difference in the responsiveness between the low pressure EGR means and the high pressure EGR means, even if the intake air temperature is detected after the transient state or immediately after the transient state, the correlation between the intake air temperature and the amount of exhaust gas recirculated by each EGR means. In some cases, it was difficult to accurately grasp the relationship. Therefore, it may be difficult to accurately determine an abnormality in each EGR means even by a method of detecting the intake air temperature in a transient state or immediately after the internal combustion engine.
Japanese Patent Laid-Open No. 2005-69202 Japanese Patent Application Laid-Open No. 2005-291056 JP 2001-207828 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a low pressure EGR means or a high pressure in an exhaust gas recirculation apparatus for an internal combustion engine that performs EGR by using or switching low pressure EGR means and high pressure EGR means together. It is to provide a technique capable of more accurately determining that there is an abnormality such as clogging in the exhaust gas recirculation path in the EGR means.

  In order to achieve the above object, the present invention comprises an EGR means of two systems, a low pressure EGR means and a high pressure EGR means, and an internal combustion engine that performs EGR by combining or switching between the low pressure EGR means and the high pressure EGR means according to the operating state. The present invention relates to an exhaust gas recirculation device for an engine. When the amount of exhaust gas recirculated by the low pressure EGR means and the amount of exhaust gas recirculated by the high pressure EGR means change in a predetermined transient state, the difference between the intake air temperatures before and after the change is expressed as the transient intake air temperature difference. Detect as. Based on the difference between the transient intake air temperature difference and the reference transient intake air temperature difference that is the transient intake air temperature difference when there is no abnormality in the exhaust gas recirculation path in the low pressure EGR means and the high pressure EGR means, The greatest feature is to determine the presence of an abnormality in the exhaust gas recirculation path in the high-pressure EGR means.

More specifically, the compressor of the supercharger of the internal combustion engine is provided in the intake passage of the internal combustion engine and the turbine of the supercharger is provided in the exhaust passage of the internal combustion engine,
A low pressure that has a low pressure EGR path formed by connecting the exhaust passage downstream from the turbine and the intake passage upstream from the compressor by a low pressure EGR passage and controls the amount of exhaust gas passing through the low pressure EGR passage. Low pressure EGR means having an EGR flow rate control device for recirculating exhaust gas passing through the exhaust passage downstream of the turbine to the intake passage upstream of the compressor;
A high-pressure EGR passage formed by connecting the exhaust passage upstream of the turbine and the intake passage downstream of the compressor by a high-pressure EGR passage and controlling the amount of exhaust gas passing through the high-pressure EGR passage. High-pressure EGR means having an EGR flow rate control device for recirculating exhaust gas passing through the exhaust passage upstream of the turbine to the intake passage downstream of the compressor;
Either the amount of exhaust gas recirculated by the low pressure EGR means is changed by the low pressure EGR flow control device, or the amount of exhaust gas recirculated by the high pressure EGR means is changed by the high pressure EGR flow control device. EGR amount control means for performing control according to the operating state of the internal combustion engine;
An exhaust gas recirculation device for an internal combustion engine comprising:
An intake air temperature detecting means provided on a downstream side of a connection portion with the high pressure EGR passage in the intake passage to detect the temperature of the intake air passing through the intake passage;
The amount of exhaust gas recirculated by the low pressure EGR means is changed by the low pressure EGR flow control device or the amount of exhaust gas recirculated by the high pressure EGR means by the EGR amount control means in a predetermined transient state of the internal combustion engine. Or at least one of the control by the high-pressure EGR flow rate control device, before and after the control is performed, a transient intake air temperature difference that is a difference in intake air temperature detected by the intake air temperature detecting means,
An abnormality in the low pressure EGR path and the high pressure EGR path is determined based on a difference from a reference transient intake air temperature difference that is a transient intake air temperature difference when there is no abnormality in the low pressure EGR path and the high pressure EGR path. It is characterized by.

Here, in an exhaust gas recirculation device for an internal combustion engine that performs EGR by using or switching the low pressure EGR means and the high pressure EGR means in accordance with the operating state, for example, the intake air temperature is detected, and the exhaust gas is recirculated from that temperature. When an abnormality such as a path clogging is to be determined, there is a risk that the detection accuracy may be lowered due to a difference in response between the low pressure EGR means and the high pressure EGR means in a transient state or a steady state immediately after the transient state. was there.

  Further, when an abnormality is determined only at the intake air temperature in the steady state, the amount of exhaust gas recirculated by the low pressure EGR means differs from the amount of exhaust gas recirculated by the high pressure EGR means depending on the operating state. Since the influence on the intake air temperature when there is an abnormality is different, an erroneous determination may occur in this case as well.

  In addition, for example, it is conceivable that pressure sensors are arranged at a plurality of locations in the exhaust passage and an abnormality is determined based on the detected values. In this case, however, the cost is increased and the abnormality of the pressure sensor itself needs to be determined. There was a case.

  Therefore, in the present invention, as a criterion for determining the occurrence of abnormality in the low pressure EGR means or the high pressure EGR means, the transient intake air temperature difference that is the difference in intake air temperature before and after a predetermined transient state of the internal combustion engine is used. Pay attention. Here, the predetermined transient state means a state in which the operation state changes from a specific operation state to another specific operation state, for example, a predetermined high load state from a predetermined light load state. The acceleration state may be sufficient. According to this, first, it is possible to eliminate variations in the operation state when detecting the temperature of the intake air, and it is possible to improve the determination accuracy.

  Further, in the present invention, based on the difference between the transient intake air temperature difference at the time of determination and the reference transient intake air temperature difference that is the transient intake air temperature difference when there is no abnormality in the low pressure EGR path and the high pressure EGR path, An abnormality in the EGR pathway and / or the high-pressure EGR pathway was detected.

  Then, even if there is a difference in responsiveness between the low pressure EGR means and the high pressure EGR means, by comparing the reference intake air temperature difference (when there is no abnormality) with the intake air temperature difference at the time of determination under the same conditions. Since an abnormality in the low pressure EGR path and / or the high pressure EGR path can be detected, it is possible to suppress a decrease in detection accuracy due to a difference in responsiveness between the low pressure EGR means and the high pressure EGR means.

  Further, in the present invention, when the absolute value of the transient intake air temperature difference minus the absolute value of the reference transient intake air temperature difference is equal to or less than the first predetermined value, it is determined that the high pressure EGR path is abnormal. You may make it do.

  That is, when there is an abnormality such as clogging in the high pressure EGR path, the ratio of the amount of exhaust gas recirculated by the low pressure EGR means to the amount of exhaust gas recirculated by the high pressure EGR means increases. Further, the temperature of the exhaust gas recirculated by the low pressure EGR means is lower than the temperature of the exhaust gas recirculated by the high pressure EGR means. Therefore, when there is an abnormality such as clogging in the high pressure EGR path, the temperature of the exhaust gas that is recirculated decreases.

  Therefore, if the absolute value of the intake-air temperature difference at the time of transition minus the absolute value of the intake-air temperature difference at the time of the transient is less than or equal to the first predetermined value, the temperature of the exhaust gas that is recirculated is restarted when there is no abnormality. Since it can be determined that the temperature is relatively low compared to the temperature of the entire exhaust gas that circulates, it is determined that abnormality such as clogging in the high-pressure EGR path is determined.

By doing so, it is possible to determine an abnormality in the high-pressure EGR path with higher accuracy. Here, the first predetermined value is a value obtained by subtracting the absolute value of the reference intake air temperature difference from the absolute value of the transient intake air temperature difference below this value. It is a value of a temperature difference that can be determined that there is an abnormality in the high-pressure EGR path, and is usually set to a negative value.

  In the present invention, an exhaust gas purification device that purifies exhaust gas that passes through the exhaust passage is provided between the turbine in the exhaust passage and a connection portion of the low-pressure EGR passage to the exhaust passage, If the value obtained by subtracting the absolute value of the reference intake air temperature difference during transition from the absolute value of the intake air temperature difference during transition is equal to or greater than a second predetermined value, it is determined that the exhaust gas purification device in the low pressure EGR path is abnormal. You may make it do.

  In other words, in this case, the ratio of the amount of exhaust gas recirculated by the high pressure EGR means to the amount of exhaust gas recirculated by the low pressure EGR means is abnormally high and the temperature of the entire exhaust gas being recirculated is reversed. However, it can be determined that the temperature is relatively higher than the temperature of the entire exhaust gas that is recirculated when there is no abnormality. Therefore, it is determined that the exhaust purification device provided in the low pressure EGR path is clogged. By doing so, it is possible to determine the abnormality of the exhaust purification device in the low pressure EGR path with higher accuracy.

  Here, the second predetermined value is a value obtained by subtracting the absolute value of the reference intake air temperature difference from the absolute value of the intake air temperature during the transient, and if the value exceeds this value, the temperature of the entire exhaust gas that is recirculated increases. The value of the temperature difference that can be determined that there is an abnormality in the exhaust purification device in the low pressure EGR path.

  Further, in the present invention, the exhaust purification device further includes a PM regeneration unit that includes a filter that collects particulate matter in the exhaust, and performs PM regeneration processing for oxidizing and removing particulate matter deposited on the filter, When the value obtained by subtracting the absolute value of the reference intake air temperature difference during the transition from the absolute value of the intake air temperature difference during the transition after the PM regeneration process is performed on the filter is equal to or greater than a second predetermined value, the low pressure It may be determined that there is an abnormality in the exhaust gas purification device in the EGR path. That is, when the exhaust purification device provided in the low-pressure EGR path includes a filter, the PM regeneration process of the filter may be performed before determining the abnormality of the exhaust purification device.

  Here, if it is determined that the ratio of the amount of exhaust gas recirculated by the high pressure EGR means to the amount of exhaust gas recirculated by the low pressure EGR means is abnormally large, the amount of particulate matter deposited on the filter is large. In some cases, the amount of exhaust gas passing through the filter may be decreasing, and it is not always clear whether there is an essential abnormality such as clogging in the exhaust gas purification device. Therefore, in the present invention, the PM regeneration process of the filter is performed before the abnormality determination of the exhaust gas purification device provided in the low pressure EGR path is performed.

  By doing so, it is possible to more accurately determine that the exhaust gas purification apparatus including the filter provided in the low pressure EGR path has an essential abnormality such as clogging due to a cause other than the accumulation of particulate matter. .

  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 or switching between low pressure EGR means and high pressure EGR means, the exhaust gas recirculation path in the low pressure EGR means or the high pressure EGR means is clogged or the like. It is possible to more accurately determine that there is an abnormality.

  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. 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 which will be described later via an electric 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. Here, the intake pipe 9 and the intake manifold 8 constitute an intake passage in this embodiment.

  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 as an exhaust purification device 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. . Here, the exhaust manifold 18, the collecting pipe 16, and the exhaust pipe 19 constitute an exhaust passage in this embodiment.

  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 valve opening degree is controlled based on a control signal from the ECU 22.
The amount of exhaust flowing through the high pressure EGR passage 15 can be adjusted (hereinafter, the exhaust 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”). Note that an intake air temperature sensor 26 as an intake air temperature detecting means for detecting the temperature of the intake air passing through the intake manifold is provided in the intake manifold 8 on the downstream side of the connection portion with the high pressure EGR passage 15. The intake air temperature sensor 26 is connected to the ECU 22 via electrical wiring, and a detection signal from the intake air temperature sensor 26 is input to the ECU 22.

  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 flowing into the intake pipe 9 is supercharged by the compressor in the compressor housing 6 and introduced into the cylinder 2 of the internal combustion engine 1 via the intake manifold 8 (EGR performed via the low pressure EGR passage 23). 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 internal combustion engine 1. Is recirculated to the second cylinder. Here, the amount of high-pressure EGR gas can also be adjusted by adjusting the opening of the throttle valve 12 to increase or decrease the pressure at the branch point of the high-pressure EGR passage 15 in the intake manifold 8 (via the high-pressure EGR passage 15). Hereinafter, the EGR performed is referred to as “high pressure EGR”).

  Thus, by recirculating a part of the exhaust gas to the cylinder 2 of the internal combustion engine 1 by the low pressure EGR and the high pressure EGR, the combustion temperature in the combustion chamber is lowered, and the amount of NOx generated in the combustion process is lowered. Can do.

  In the present embodiment, the low pressure EGR valve 5 corresponds to a low pressure EGR flow control device. In this embodiment, the low pressure EGR passage 23, the intake pipe 9, the intake manifold 8, the internal combustion engine 1, the exhaust manifold 18, the collecting pipe 16, and the exhaust pipe 19 form a low pressure EGR loop. This low pressure EGR loop corresponds to a low pressure EGR path. The low pressure EGR valve 5 and the low pressure EGR loop constitute a low pressure EGR means. The high pressure EGR valve 21 corresponds to a high pressure EGR flow control device. The high pressure EGR passage 15, the intake manifold 8, the internal combustion engine 1 and the exhaust manifold 8 form a high pressure EGR loop. This high-pressure EGR loop corresponds to a high-pressure EGR path. The high pressure EGR valve 21 and the high pressure EGR loop constitute high pressure EGR means.

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, only the low pressure EGR is used in a high load or high speed operation state. In this embodiment, this region is referred to as an LPL (Low Pressure Loop) region. Further, the high pressure EGR and the low pressure EGR are used in combination in an operation state at a medium load or a medium rotation speed. In this embodiment, this region is referred to as an MPL (Middle Pressure Loop) region. Furthermore, only the high pressure EGR is used in the operation state with a low load and a low rotational speed. In this embodiment, this region is referred to as an HPL (High Pressure Loop) region.

  Thereby, when the operating state of the internal combustion engine is low load and low speed, the responsiveness of the whole EGR is ensured by preferentially using the high pressure EGR having excellent responsiveness. Further, when the operating state of the internal combustion engine is a high load or a high rotation speed, the recirculation of the low-temperature low-pressure EGR gas by the low-pressure EGR is promoted and the re-circulation of the high-temperature high-pressure EGR gas by the high-pressure EGR is suppressed. The gas temperature is prevented from becoming excessively high. As a result, the exhaust gas can be recirculated in a wider range of operating conditions. These controls are performed by command signals issued from the ECU 22 to the low pressure EGR valve 5 and the high pressure EGR valve 21. As described above, the ECU 22 that changes the low-pressure EGR gas amount and the high-pressure EGR gas amount according to the operating state corresponds to the EGR amount control means in this embodiment.

  By the way, with the long-term use of the internal combustion engine, the intake pipe 9, the exhaust pipe 19, the low pressure EGR passage 23, the high pressure EGR passage 15 and the like may be clogged due to accumulation of dirt. In such a case, the low-pressure EGR gas amount and the high-pressure EGR gas amount may change from the target values according to the operation state due to the cause.

  Specifically, for example, consider a case where the filter 20 in the exhaust pipe 19 is clogged. In such a case, even if the opening of the low pressure EGR valve 5 is the same, the amount of low pressure EGR gas may decrease. Similarly, for example, when the high pressure EGR passage 15 is clogged, the amount of the high pressure EGR gas may be decreased even if the opening degree of the high pressure EGR valve 21 is the same.

  Therefore, it is necessary to detect that an abnormality such as clogging has occurred in the low pressure EGR loop or the high pressure EGR loop as described above. As this detection method, for example, detection using a pressure sensor in either the low pressure EGR loop or the high pressure EGR loop may be considered, but in this case, it is necessary to provide a pressure sensor, leading to an increase in cost.

  Further, clogging in the low pressure EGR loop or the high pressure EGR loop may be determined by a transient state such as during acceleration or the intake air temperature detected by the intake air temperature sensor 26 immediately thereafter.

  However, in this case, a difference in response between the low pressure EGR and the high pressure EGR becomes a problem. For example, as shown in FIG. 3, when it is determined based on the output of the intake air temperature sensor 26 at the time of acceleration or immediately after the acceleration, the response of the low pressure EGR is low, so that the intake air temperature is detected higher than the actual intake air temperature. On the other hand, when it is determined at the time of deceleration, there is a case where it is detected lower than the actual intake air temperature. As a result, it may be difficult to accurately determine clogging in the low pressure EGR loop or the high pressure EGR loop.

Furthermore, even when an attempt is made to determine when the operating state of the internal combustion engine 1 is a steady state, the opening degrees of the low pressure EGR valve 5 and the high pressure EGR valve 21 depend on the operating state of the internal combustion engine 1 as shown in FIG. Due to the difference, it may be difficult to accurately determine an abnormality in the low pressure EGR loop or the high pressure EGR loop. This is because the degree of influence of abnormalities such as clogging on the intake air temperature varies depending on the opening degrees of the low pressure EGR valve 5 and the high pressure EGR valve 21.

  In contrast, in this embodiment, the difference in intake air temperature before and after acceleration from the idle state of the internal combustion engine 1 to the high load region where both the low pressure EGR valve 5 and the high pressure EGR valve 21 are closed is detected. Then, by comparing this difference with the value when there is no abnormality in the low-pressure EGR loop and the high-pressure EGR loop, it is determined whether or not there is an abnormality in the low-pressure EGR loop or the high-pressure EGR loop.

  FIG. 5 is a graph illustrating a change in the intake air temperature with respect to a change in the operating state of the internal combustion engine 1 when there is an abnormality in the low pressure EGR loop or the high pressure EGR loop. Here, consider a case where the load of the internal combustion engine 1 is accelerated from an idle state to a high load region where both the low pressure EGR valve 5 and the high pressure EGR valve 21 are closed. In this case, when the low pressure EGR loop and the high pressure EGR loop are in a normal state, the intake air temperature decreases as the load increases in the situation shown by the solid line in the upper graph of FIG.

  That is, since the high-pressure EGR valve 21 is fully opened in the idle state, the high-temperature high-pressure EGR gas is recirculated to the intake manifold 8 and the intake air temperature is relatively high. As the load of the internal combustion engine 1 increases, the opening degree of the high pressure EGR valve 21 changes to the closing side and the opening degree of the low pressure EGR valve 5 changes to the opening side, so that the recirculation amount of the low temperature low pressure EGR gas Increases and the overall intake air temperature gradually decreases. When the load of the internal combustion engine 1 further changes to the high load side, both the low pressure EGR valve 5 and the high pressure EGR valve 21 are closed, so that the total amount of EGR gas becomes substantially zero, The intake air temperature is at its lowest level.

  In the above curve, first, consider a case where there is an abnormality such as clogging in the high-pressure EGR loop. In this case, even when the high pressure EGR valve 21 is opened, the amount of the high pressure EGR gas recirculated by the high pressure EGR is relatively reduced. Accordingly, the intake air temperature in the idle state is lower than that in the normal state. Therefore, the intake air temperature difference ΔT between the intake air temperature in the idle state in this case and the intake air temperature in the high load state in which both the low pressure EGR valve 5 and the high pressure EGR valve 21 are closed becomes small.

  Next, consider a case where there is an abnormality such as clogging in the filter 20 in the low pressure EGR loop. In this case, conversely, the amount of low-pressure EGR gas that is recirculated by low-pressure EGR decreases. Then, the intake air temperature in the idle state becomes higher than that in the normal state. Therefore, the intake air temperature difference ΔT between the intake air temperature in the idle state in this case and the intake air temperature in the high load state in which both the high pressure EGR valve and the low pressure EGR valve are closed increases.

  In this embodiment, the intake air temperature difference between the intake air temperature in the normal idle state and the intake air temperature in the high load state in which both the high pressure EGR valve and the low pressure EGR valve are closed is defined as a reference value ΔTbase, and the intake air temperature difference ΔT is On the other hand, when it is larger than the threshold value α, it is determined that the filter 20 has an abnormality such as clogging. In addition, when the threshold value β is smaller than the reference value, it is determined that there is an abnormality such as clogging in the high-pressure EGR loop.

  FIG. 6 shows a flowchart of an EGR abnormality determination routine in the present embodiment. This routine is a program stored in the ROM of the ECU 22, and is executed by the ECU 22 at predetermined intervals while the internal combustion engine 1 is in operation.

  When this routine is executed, the operation state is first acquired in S101. Specifically, the engine speed is acquired from a crank position sensor (not shown), and the engine load is acquired from an accelerator position sensor. When the processing of S101 ends, the process proceeds to S102.

  In S102, the intake air temperature is acquired. Specifically, the output signal of the intake air temperature sensor 26 is acquired by being read by the ECU 22. When the process of S102 ends, the process proceeds to S103.

  In S103, it is determined whether the operating state of the internal combustion engine 1 is in an abnormal determination transient state. In other words, from the engine load value acquired in the current processing of S101 and the engine load value acquired in the processing of S101 in the past execution of this routine, from the idle state, the low pressure EGR valve 5 and the high pressure EGR It is determined whether or not the engine is in a transient state in which the operating state shifts to a high load state in which both valves 21 are closed. Here, when it is determined that the operating state of the internal combustion engine 1 is not the abnormality determination transient state, the present routine is temporarily ended as it is. On the other hand, if it is determined that the operating state of the internal combustion engine 1 is in the abnormality determination transient state, the process proceeds to S104.

  In S104, the difference between the intake air temperature acquired by the intake air temperature sensor 26 in the initial idle state in the abnormality determination transient state confirmed in S103 and the intake air temperature acquired in the processing of S102 in the current execution of this routine. It is determined whether or not a value obtained by subtracting a predetermined reference intake air temperature difference ΔTbase from the absolute value ΔT is α or more. If the determination is affirmative, the process proceeds to S105. On the other hand, if a negative determination is made, the process proceeds to S108.

  In S105, it is determined whether or not the filter 20 is in a state after PM regeneration at this time. Specifically, the determination may be made based on whether or not the PM regeneration process has been performed in the past and the subsequent travel distance of the vehicle is within a predetermined distance at which the effect of the PM regeneration process is maintained. If it is determined that the PM regeneration process has not been completed, the process proceeds to S106. On the other hand, if it is determined that the PM regeneration process has been completed, the process proceeds to S107.

  In S106, PM regeneration processing is executed. Specifically, for example, when an oxidation catalyst is supported on the filter 20, sub-injection is executed in the internal combustion engine 1, and fuel as a reducing agent is supplied to the filter 20 to increase the temperature of the filter 20. The deposited particulate material may be removed by oxidation. In this case, the ECU 22 that executes this process and a fuel injection valve (not shown) constitute PM regeneration means. When the process of S106 ends, this routine is temporarily ended.

  In S107, although the filter 20 is in the state immediately after the PM regeneration process is performed, the intake air temperature in the initial idle state in the abnormality determination transient state and the processing of S102 in the current execution of this routine are performed. Since the value obtained by subtracting a predetermined reference intake air temperature difference ΔTbase from the absolute value ΔT of the difference from the acquired intake air temperature is equal to or larger than α, it is determined that an abnormality such as clogging has occurred in the filter 20. When the process of S107 ends, this routine is temporarily ended.

  In S108, the absolute difference between the intake air temperature acquired by the intake air temperature sensor 26 in the initial idle state in the abnormality determination transitional state and the intake air temperature acquired in the processing of S102 at the time of the current execution of this routine. It is determined whether or not a value obtained by subtracting the reference intake air temperature difference ΔTbase from the value ΔT is −β or less. If a negative determination is made here, this routine is once terminated. On the other hand, if a positive determination is made, the process proceeds to S109.

  In S109, it is determined that there is an abnormality such as clogging in the high pressure EGR loop. When the process of S109 is completed, this routine is temporarily ended.

As described above, in the present embodiment, in a specific abnormality determination transient state, the difference in intake air temperature in the steady state before and after the transient state is an abnormality determination in a state where the low pressure EGR loop and the high pressure EGR loop are normal. Whether or not an abnormality such as clogging has occurred in the low pressure EGR loop or the high pressure EGR loop is determined depending on how much the intake air temperature changes before and after the transient state.

  Therefore, it can be suppressed that a difference in response between the low pressure EGR and the high pressure EGR becomes a problem. Further, it is possible to suppress the opening degree of the low pressure EGR valve 5 or the high pressure EGR valve 21 from affecting the determination result. Therefore, it is possible to more accurately determine abnormality in the low pressure EGR loop and the high pressure EGR loop.

  In this embodiment, when the value obtained by subtracting ΔTbase from ΔT is equal to or larger than α, the PM regeneration process is performed first, and the value obtained by subtracting ΔTbase from ΔT even though the PM regeneration process is completed. Is greater than α, the abnormality determination of the filter 20 is performed. Therefore, the influence of the particulate matter deposited on the filter 20 can be removed, and the accuracy of the filter abnormality determination can be improved.

  In the above, the value of ΔT corresponds to the absolute value of the transient intake air temperature difference, and the value of ΔTbase corresponds to the absolute value of the reference transient intake air temperature difference. In this embodiment, the transient intake air temperature difference is acquired from the intake air temperature acquired by the intake air temperature sensor 26 in the initial idle state in the abnormal determination transient state in the processing of S102 in the execution of the EGR abnormality determination routine at the time of determination. This is the value obtained by subtracting the intake air temperature.

  Whether the change in intake air temperature in the abnormality determination transient state is an increase or a decrease, the absolute value of the difference is ΔT, and similarly, the abnormality determination transient when the low pressure EGR loop and the high pressure EGR loop are normal The abnormality determination may be performed based on a result obtained by subtracting ΔTbase that is an absolute value of the change in intake air temperature in the state.

  Further, in the above-described embodiment, the abnormality determination transient state employs a state in which acceleration is performed from an idle state to a high load region where both the low pressure EGR valve 5 and the high pressure EGR valve 21 are closed. Another state may be adopted as the state. For example, you may employ | adopt the state which decelerated from the high load area | region where both the low pressure EGR valve 5 and the high pressure EGR valve 21 close to an idle state.

  Further, based on the difference between the intake air temperature before and after the abnormal determination transient state and the difference between the intake air temperatures in the abnormal determination transient state when the low pressure EGR loop and the high pressure EGR loop are normal, the low pressure EGR loop and / or the high pressure As long as it is based on the idea of performing an abnormality determination in the EGR loop, another specific method may be adopted as a specific calculation method.

  In the above embodiment, the example in which the filter 20 is provided as the exhaust purification device has been described. However, as the exhaust purification device, an exhaust purification catalyst, an oxidation catalyst, a configuration in which the catalyst is supported on the filter, or the like is adopted. Of course.

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 in the Example of this invention, and the pattern of proper use of low voltage | pressure EGR and high voltage | pressure EGR. It is a graph for demonstrating the influence of the response delay of the low voltage | pressure EGR with respect to a detected value when the intake air temperature is detected in the transient state in the Example of this invention. It is a graph which shows the relationship between the engine load in the Example of this invention, and the opening degree of a low pressure EGR valve and a high pressure EGR valve. It is a graph for demonstrating how the change of intake temperature with respect to the change of the engine load in the Example of this invention changes in the state of a low pressure EGR valve and a high pressure EGR valve. It is a flowchart about the EGR abnormality determination routine in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 5 ... Low pressure EGR valve 6 ... Compressor housing 7 ... Turbine housing 8 ... Intake manifold 9 ... Intake pipe 10 ... Centrifugal supercharger DESCRIPTION OF SYMBOLS 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 19 ... Exhaust pipe 20 ... Filter 21 ... High pressure EGR valve 22 ... ECU
23 ... Low pressure EGR passage 24 ... Air flow meter 25 ... Air cleaner 26 ... Intake air temperature sensor

Claims (4)

A compressor of the internal combustion engine supercharger is provided in the intake passage of the internal combustion engine and a turbine of the supercharger is provided in the exhaust passage of the internal combustion engine;
A low pressure that has a low pressure EGR path formed by connecting the exhaust passage downstream from the turbine and the intake passage upstream from the compressor by a low pressure EGR passage and controls the amount of exhaust gas passing through the low pressure EGR passage. Low pressure EGR means having an EGR flow rate control device for recirculating exhaust gas passing through the exhaust passage downstream of the turbine to the intake passage upstream of the compressor;
A high-pressure EGR passage formed by connecting the exhaust passage upstream of the turbine and the intake passage downstream of the compressor by a high-pressure EGR passage and controlling the amount of exhaust gas passing through the high-pressure EGR passage. High-pressure EGR means having an EGR flow rate control device for recirculating exhaust gas passing through the exhaust passage upstream of the turbine to the intake passage downstream of the compressor;
Either the amount of exhaust gas recirculated by the low pressure EGR means is changed by the low pressure EGR flow control device, or the amount of exhaust gas recirculated by the high pressure EGR means is changed by the high pressure EGR flow control device. EGR amount control means for performing control according to the operating state of the internal combustion engine;
An exhaust gas recirculation device for an internal combustion engine comprising:
An intake air temperature detecting means provided on a downstream side of a connection portion with the high pressure EGR passage in the intake passage to detect the temperature of the intake air passing through the intake passage;
The amount of exhaust gas recirculated by the low pressure EGR means is changed by the low pressure EGR flow control device or the amount of exhaust gas recirculated by the high pressure EGR means by the EGR amount control means in a predetermined transient state of the internal combustion engine. Or at least one of the control by the high-pressure EGR flow rate control device, before and after the control is performed, a transient intake air temperature difference that is a difference in intake air temperature detected by the intake air temperature detecting means,
An abnormality in the low pressure EGR path and the high pressure EGR path is determined based on a difference from a reference transient intake air temperature difference that is a transient intake air temperature difference when there is no abnormality in the low pressure EGR path and the high pressure EGR path. An exhaust gas recirculation device for an internal combustion engine. When the value obtained by subtracting the absolute value of the reference transient intake air temperature difference from the absolute value of the transient intake air temperature difference is equal to or less than a first predetermined value, it is determined that the high pressure EGR path is abnormal. The exhaust gas recirculation device for an internal combustion engine according to claim 1. An exhaust purification device for purifying exhaust gas passing through the exhaust passage is provided between the turbine in the exhaust passage and a connection portion of the low pressure EGR passage to the exhaust passage;
If the value obtained by subtracting the absolute value of the reference transient intake air temperature difference from the absolute value of the transient intake air temperature difference is equal to or greater than a second predetermined value, the exhaust purification device in the low pressure EGR path is abnormal. The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2, wherein the determination is made. The exhaust purification device includes a filter that collects particulate matter in the exhaust,
PM regeneration means for performing PM regeneration processing for oxidizing and removing particulate matter deposited on the filter is further provided,
When the value obtained by subtracting the absolute value of the reference intake air temperature difference during the transition from the absolute value of the intake air temperature difference during the transition after the PM regeneration process is performed on the filter is equal to or greater than a second predetermined value, the low pressure The exhaust gas recirculation device for an internal combustion engine according to claim 3, wherein the exhaust gas purification device in the EGR path is determined to have an abnormality.

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