JP5803622B2 - Abnormality diagnosis device for EGR system - Google Patents

Description

  The present invention relates to an apparatus for diagnosing the presence or absence of an abnormality in an EGR system mounted on, for example, an internal combustion engine of an automobile. In particular, the present invention relates to an improvement in abnormality diagnosis in an EGR system having a plurality of exhaust gas recirculation mechanisms (EGR mechanisms).

  Conventionally, in an engine that performs lean combustion such as a diesel engine, there is a concern that a relatively large amount of nitrogen oxides (hereinafter referred to as NOx) is discharged. As a countermeasure, it is known to provide an exhaust gas recirculation (EGR) system that recirculates a part of the exhaust gas to the intake passage (see, for example, Patent Document 1 below).

  The EGR system includes an EGR passage that allows an engine exhaust passage and an intake passage to communicate with each other, and an EGR valve that is provided in the EGR passage. Then, by adjusting the opening of the EGR valve, the amount of exhaust gas recirculated from the exhaust passage to the intake passage via the EGR passage (EGR gas amount) is adjusted, and the EGR rate during intake is set in advance. The target EGR rate is set. When a part of the exhaust gas is recirculated to the intake passage in this way, the combustion temperature in the combustion chamber is lowered, the generation of NOx is suppressed, and the exhaust emission is improved.

  In addition, this type of EGR system includes a high pressure EGR mechanism (hereinafter referred to as “HPL-EGR mechanism”) and a low pressure EGR mechanism (hereinafter referred to as “LPL-EGR mechanism”) (hereinafter referred to as “MPL-EGR mechanism”). (Referred to as Patent Document 2 below).

  The HPL (High Pressure Loop) -EGR mechanism recirculates exhaust gas from an exhaust passage (for example, an exhaust manifold) upstream of the turbocharger turbine to an intake passage downstream of the turbocharger compressor. ing. In addition, an LPL (Low Pressure Loop) -EGR mechanism recirculates exhaust gas from an exhaust passage downstream of the turbocharger turbine to an intake passage upstream of the turbocharger compressor.

  In addition, as disclosed in Patent Document 2, the MPL (Middle Pressure Loop) -EGR system is used in a low load operation region of an engine by using only the HPL-EGR mechanism. The exhaust gas at the temperature is recirculated to stabilize the combustion and suppress the emission of HC and CO. Further, in the high load operation region of the engine, the exhaust gas having a relatively low temperature is recirculated using only the LPL-EGR mechanism, thereby suppressing the generation of smoke due to the high temperature of the intake air. Further, in the medium load operation region of the engine, the generation of HC, CO, and smoke is suppressed by using both the HPL-EGR mechanism and the LPL-EGR mechanism to recirculate the exhaust gas.

JP 2001-207916 A JP 2011-89470 A

  By the way, in the MPL-EGR system, when the flow area of the EGR passage of the HPL-EGR mechanism or the EGR passage of the LPL-EGR mechanism is reduced or the EGR passage is blocked due to an increase in deposits, etc. Such situations are simply referred to as “blocking”), and it is necessary to take measures such as detecting the situation and replacing parts (replacement of blocked pipes) as necessary.

  In the above-mentioned Patent Document 2, when the engine operating state is low load and low rotation and the exhaust gas is recirculated only by the HPL-EGR mechanism (in the HPL mode), the blockage in the HPL-EGR mechanism is determined. When the operating state of the engine is high load and high rotation and the exhaust gas is recirculated only by the LPL-EGR mechanism (in the LPL mode), the blockage in the LPL-EGR mechanism is determined.

  However, since the HPL mode and the LPL mode are executed in a relatively limited operating region, there is little opportunity to perform an EGR system abnormality diagnosis (EGR passage blockage diagnosis), and an EGR passage blockage diagnosis is performed. There is a possibility that the engine will continue to run in the absence of this.

  As described above, in the conventional MPL-EGR system, the operation region in which the EGR passage blockage diagnosis can be performed is limited, and it is not possible to accurately diagnose the presence or absence of blockage at an early stage.

  Note that, in the above-mentioned Patent Document 1, the EGR valve opening correction amount and the intake throttle valve when the EGR gas amount is adjusted to the target EGR gas amount by feedback control with respect to the EGR system having only the HPL-EGR mechanism. It is disclosed that when the opening correction amount exceeds a threshold value, it is diagnosed that the EGR passage is blocked.

  However, even if the technology of Patent Document 1 is applied to the MPL-EGR system, it is only possible to diagnose a blockage in the HPL-EGR mechanism in a specific operation region (low load / low rotation). All occlusion diagnoses cannot be made.

  In any patent document, when exhaust gas is recirculated using both the HPL-EGR mechanism and the LPL-EGR mechanism (in the MPL mode), the HPL-EGR mechanism and the LPL-EGR mechanism It is not possible to specify which EGR mechanism is causing the blockage.

  As a result, when an obstruction occurs in the EGR system (when it is determined that an obstruction occurs in the EGR system when the opening correction amount of the intake throttle valve exceeds the threshold value as in Patent Document 1). When parts are replaced, the blockage location cannot be specified, so both parts of the HPL-EGR mechanism and the LPL-EGR mechanism must be replaced (pipe parts that are not blocked must be replaced). Will not be).

  The present invention has been made in view of such points, and the object of the present invention is to determine which exhaust gas recirculation mechanism is clogged with respect to an EGR system having a plurality of exhaust gas recirculation mechanisms. An object of the present invention is to provide an abnormality diagnosis device.

-Summary of invention-
The outline of the present invention taken to achieve the above object is that the low-pressure EGR valve of the low-pressure EGR mechanism is maintained in the closed state in the operating region of the internal combustion engine in which only the high-pressure EGR mechanism is used. From the opening of the high pressure EGR valve of the high pressure EGR mechanism, the opening of the low pressure EGR valve of the low pressure EGR mechanism, and the closing degree (closed degree) of the intake throttle valve, It is possible to diagnose whether or not this has occurred.

-Solution-
Specifically, the present invention is provided in an internal combustion engine in which an intake throttle valve is provided in the intake system, and the exhaust gas upstream of the turbocharger in the exhaust system is recirculated to the intake system and its recirculation amount can be adjusted. A high pressure EGR mechanism equipped with a high pressure EGR valve, and a low pressure EGR mechanism equipped with a low pressure EGR valve capable of returning the exhaust gas downstream of the turbocharger turbine in the exhaust system to the intake system and adjusting the recirculation amount. And an EGR system abnormality diagnosis device that selects an EGR mechanism to be used according to the operating state of the internal combustion engine. When the exhaust gas is recirculated from the exhaust system to the intake system, the opening degree of the high-pressure EGR valve of the high-pressure EGR mechanism is increased to a predetermined high-pressure side exhaust gas recirculation amount increase. The low pressure EGR mechanism when the intake throttle valve closing degree (the ratio of the degree of opening change from the fully opened state to the closing direction; the closing degree) is equal to or higher than a predetermined high pressure side exhaust gas recirculation amount increase closing degree. When the opening of the low pressure EGR valve exceeds a predetermined low pressure side exhaust gas recirculation amount increase opening, it is determined that the low pressure EGR mechanism is clogged, while the low pressure EGR valve of the low pressure EGR mechanism is opened. When the degree is equal to or less than the low pressure side exhaust gas recirculation amount increase opening, it is determined that the high pressure EGR mechanism is clogged.

  According to this specific matter, first, the opening degree of the high pressure EGR valve of the high pressure EGR mechanism is equal to or greater than a predetermined high pressure side exhaust gas recirculation amount increase opening degree, and the closing degree of the intake throttle valve is a predetermined high pressure side exhaust gas recirculation amount increase degree of closure. If it is above, it can be determined that a blockage has occurred somewhere in the EGR system. This is a state in which the exhaust gas recirculation amount is insufficient due to this blockage (a state in which the actual EGR rate is lower than the target EGR rate). For this reason, the opening degree of the high pressure EGR valve of the high pressure EGR mechanism is predetermined open. This is because it can be determined that the intake throttle valve is close to a predetermined close degree.

  In this case, the opening of the low-pressure EGR valve of the low-pressure EGR mechanism is detected, and when the opening of the low-pressure EGR valve exceeds a predetermined low-pressure side exhaust gas recirculation amount increase opening, the low-pressure EGR mechanism It is determined that an occlusion has occurred. That is, the high pressure EGR of the high pressure EGR mechanism is caused by the fact that the exhaust gas recirculation amount is insufficient even though the opening amount of the low pressure EGR valve exceeds the predetermined low pressure side exhaust gas recirculation amount increase opening amount. Since it can be determined that the opening degree of the valve is equal to or greater than the predetermined opening degree and the closing degree of the intake throttle valve is equal to or higher than the predetermined closing degree, in this case, it is determined that the low pressure EGR mechanism is clogged. Can do.

  On the other hand, when the opening of the low pressure EGR valve is equal to or less than a predetermined low pressure side exhaust gas recirculation amount increase opening, it is determined that the high pressure EGR mechanism is clogged. That is, the fact that the opening of the low pressure EGR valve is equal to or less than the predetermined opening despite the exhaust gas recirculation amount being insufficient can be determined as an operating state in which the opening of the low pressure EGR valve is limited. The reason why the opening of the high-pressure EGR valve of the high-pressure EGR mechanism is equal to or larger than a predetermined opening and the closing degree of the intake throttle valve is equal to or larger than the predetermined closing degree is that the high-pressure EGR mechanism is closed and the exhaust gas recirculation amount Therefore, in this case, it can be determined that the high pressure EGR mechanism is clogged.

  As described above, the present solution does not limit the operation region in which only the high pressure EGR mechanism is used or the operation region in which only the low pressure EGR mechanism is used. Can be diagnosed. For this reason, the opportunity to perform abnormality diagnosis can be increased and abnormality diagnosis can be performed at an early stage. In addition, when replacing a part that has been clogged, it is possible to identify the part that has been clogged, so that it is possible to replace useless parts (pipe parts that are not clogged). State that must be).

  Specific uses of the high pressure EGR mechanism and the low pressure EGR mechanism include the following. In other words, the low-pressure EGR mechanism is provided with an EGR cooler that cools the exhaust gas recirculated to the intake system, and only the high-pressure EGR mechanism is used during low-load operation of the internal combustion engine. When the internal combustion engine is in a high load operation, only the low pressure EGR mechanism is used to recirculate exhaust gas to the intake system, and in the internal combustion engine is in a medium load operation, the high pressure EGR mechanism and the low pressure EGR mechanism are recirculated. Both are used to recirculate exhaust gas to the intake system.

  In such usage forms of each EGR mechanism, when the internal combustion engine is operating at a low load and only the high-pressure EGR mechanism is used to recirculate exhaust gas to the intake system, And CO may be discharged, and the use of the low pressure EGR mechanism is prohibited in order to prevent the inside of the EGR cooler from being blocked. For this reason, when the use of the low pressure EGR mechanism is prohibited even when the exhaust gas recirculation amount is insufficient, that is, when the opening of the low pressure EGR valve is small or “0”, the high pressure EGR mechanism. In this case, if the exhaust gas recirculation amount is insufficient, it can be determined that the cause is that the high pressure EGR mechanism is clogged.

  On the other hand, since the EGR cooler is not provided in the high pressure EGR mechanism, it can be used regardless of the operating state of the internal combustion engine. When the internal combustion engine is in a high load operation and the exhaust gas should be recirculated to the intake system using only the low pressure EGR mechanism, the high pressure EGR is caused by the shortage of the exhaust gas recirculation amount. If the opening degree of the high-pressure EGR valve of the mechanism is equal to or greater than a predetermined high-pressure side exhaust gas recirculation amount increase opening degree and the closing degree of the intake throttle valve is equal to or greater than the predetermined high-pressure side exhaust gas recirculation amount increase degree of closure, the low-pressure EGR valve It can be determined that the exhaust gas recirculation amount is insufficient even though the opening amount of the exhaust gas exceeds the predetermined low pressure side exhaust gas recirculation amount increase opening amount. In this case, the low pressure EGR mechanism is blocked. It can be judged that it has occurred.

  In this way, by using the fact that the usage forms of the high pressure EGR mechanism and the low pressure EGR mechanism differ depending on the operating state of the internal combustion engine, which of the high pressure EGR mechanism and the low pressure EGR mechanism is clogged? Can be accurately diagnosed.

  Specifically, the high-pressure side exhaust gas recirculation amount increase opening is an opening corresponding to the fully open or substantially fully opened high pressure EGR valve. Further, the high pressure side exhaust gas recirculation amount increase close degree is specifically the close degree of the intake throttle valve set according to the blockage degree as a reference for determining that the blockage has occurred in the system.

  That is, when the high-pressure EGR valve has an opening corresponding to full open or substantially full open, and the intake throttle valve is not fully open (closed to a certain close degree), the exhaust gas recirculation amount is insufficient. Therefore, the operation is shifted to a specific operation of the closed portion (EGR mechanism in which the blockage is generated) according to the opening degree of the low pressure EGR valve. Further, by appropriately setting the high pressure side exhaust gas recirculation amount increase degree of closure, it is possible to accurately perform abnormality diagnosis that conforms to standards defined by laws and regulations. In other words, the regulations can be observed by setting the high pressure side exhaust gas recirculation amount increase degree of closure according to the regulations.

  In the present invention, whether the high pressure EGR mechanism or the low pressure EGR mechanism is blocked is determined based on the opening degree of the high pressure EGR valve of the high pressure EGR mechanism, the opening degree of the low pressure EGR valve of the low pressure EGR mechanism, and the closing degree of the intake throttle valve. Can be diagnosed. For this reason, the opportunity to perform abnormality diagnosis can be increased and abnormality diagnosis can be performed at an early stage.

It is a figure showing a schematic structure of an engine concerning an embodiment. It is a block diagram which shows the structure of control systems, such as ECU. It is a figure which shows the map which sets the mode of an MPL-EGR system at the time of engine warm. It is a figure which shows the map which sets the mode of an MPL-EGR system at the time of engine cold. It is a flowchart figure which shows the procedure of abnormality diagnosis operation | movement of a MPL-EGR system. It is a timing chart figure which shows an example of the opening state of each valve | bulb when the obstruction | occlusion has not generate | occur | produced in the MPL-EGR system. It is a timing chart figure which shows an example of the opening state of each valve | bulb in case obstruction | occlusion has generate | occur | produced in the LPL-EGR mechanism. It is a timing chart figure which shows an example of the opening state of each valve | bulb in case obstruction | occlusion has generate | occur | produced with the HPL-EGR mechanism.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (for example, in-line 4-cylinder) diesel engine (compression self-ignition internal combustion engine) mounted on an automobile will be described.

-Engine configuration-
FIG. 1 is a diagram showing a schematic configuration of an engine (internal combustion engine) 1 according to the present embodiment. The engine 1 shown in FIG. 1 is a diesel engine having four cylinders 11, 11,..., And each cylinder 11 has an injector (fuel injection valve) 2 capable of directly injecting fuel into the cylinder 11. It is attached. For example, these injectors 2 include piezoelectric elements (piezo elements) inside, and are configured by piezo injectors that are appropriately opened to inject and supply fuel into the cylinder 11. Further, the fuel boosted by a high-pressure fuel pump (not shown) is supplied to the injector 2 via a common rail 21.

  Each cylinder 11 is connected to an intake passage 3 constituting an intake system. An air cleaner 31 is provided at the upstream end of the intake passage 3. A compressor 41, an intercooler 32, and an intake throttle valve (diesel throttle) 33 of a turbocharger (centrifugal supercharger) 4 are sequentially provided in the intake passage 3 along the direction of intake air flow. . The intake air introduced into the intake passage 3 is purified by the air cleaner 31, then supercharged by the compressor 41 and cooled by the intercooler 32. Thereafter, the intake air passes through the intake throttle valve 33 and is introduced into each cylinder 11. The intake air introduced into each cylinder 11 is compressed in the compression stroke, and fuel is burned by being injected into the cylinder 11 from the injector 2. As the fuel burns, in each cylinder 11, a piston (not shown) reciprocates in the cylinder, and an engine output is obtained by rotating the crankshaft via the connecting rod.

  The intake throttle valve 33 is fully opened during normal operation. For example, when the vehicle is decelerated, the intake throttle valve 33 is predetermined as necessary (for example, when it is necessary to prevent a temperature drop of the oxidation catalyst 51 described later). It is closed to the opening. In addition, the intake throttle valve 33 is closed to a predetermined opening as necessary even during an abnormality diagnosis of the EGR system described later.

  Each cylinder 11 is connected to an exhaust passage 5 constituting an exhaust system. A turbine 42 of the turbocharger 4 is provided in the middle of the exhaust passage 5. In the exhaust passage 5 downstream from the turbine 42, an oxidation catalyst (DOC) 51 and a particulate filter (DPF) 52, an exhaust throttle valve 53, and a muffler 54 are arranged along the exhaust flow direction. Are provided in order.

  Exhaust gas (burned gas) generated by combustion in each cylinder 11 is discharged to the exhaust passage 5. The exhaust gas discharged into the exhaust passage 5 passes through a turbine 42 provided in the middle of the exhaust passage 5 and is then purified by an oxidation catalyst 51 and a particulate filter 52, and then passes through an exhaust throttle valve 53 and a muffler 54. And released into the atmosphere.

-EGR system-
The engine 1 according to the present embodiment is provided with an MPL-EGR system including an HPL-EGR mechanism (high pressure EGR mechanism) 6 and an LPL-EGR mechanism (low pressure EGR mechanism) 7.

  The HPL-EGR mechanism 6 sends exhaust gas from the exhaust passage 5 (for example, the exhaust manifold) upstream of the turbine 42 of the turbocharger 4 to the intake passage 3 downstream of the intake throttle valve 33 (downstream of the compressor 41). A high-pressure EGR passage 61 that leads a part (high-pressure EGR gas) and a high-pressure EGR valve 62 that can change the flow passage area of the high-pressure EGR passage 61 are provided.

  The amount of high-pressure EGR gas recirculated (recirculated) by the HPL-EGR mechanism 6 is adjusted by the opening degree of the high-pressure EGR valve 62. Further, if necessary, the opening degree of the intake throttle valve 33 is decreased (the degree of closing is increased), and thereby the recirculation amount of the high-pressure EGR gas may be increased.

  On the other hand, the LPL-EGR mechanism 7 exhausts from the exhaust passage 5 downstream of the particulate filter 52 (downstream of the turbine 42) and upstream of the exhaust throttle valve 53 to the intake passage 3 upstream of the compressor 41. A low-pressure EGR passage 71 that guides a part of the gas (low-pressure EGR gas), a low-pressure EGR valve 72 that can change the flow area of the low-pressure EGR passage 71, and a low-pressure EGR gas that cools the low-pressure EGR gas that flows through the low-pressure EGR passage 71 EGR cooler 73 is provided.

  The amount of low-pressure EGR gas recirculated (recirculated) by the LPL-EGR mechanism 7 is adjusted by the opening degree of the low-pressure EGR valve 72. Further, the opening degree of the exhaust throttle valve 53 is reduced as necessary, and thereby the recirculation amount of the low pressure EGR gas may be increased.

-Control system-
As shown in FIG. 2, the injector 2, the intake throttle valve 33, the exhaust throttle valve 53, the high pressure EGR valve 62 and the low pressure EGR valve 72 are electrically connected to an ECU (Electronic Control Unit) 10.

  The ECU 10 includes an A / F sensor 80, an air flow meter 81, an intake air temperature sensor 82, an intake air pressure sensor 83, an exhaust air temperature sensor 84, a water temperature sensor 85, a crank position sensor 86, an accelerator opening sensor 87, and an intake throttle valve opening sensor 88. These are electrically connected to various sensors such as a differential pressure sensor 89, a high pressure EGR valve opening sensor 8H, and a low pressure EGR valve opening sensor 8L.

  The A / F sensor 80 is a sensor that detects the oxygen concentration in the exhaust gas downstream of the particulate filter 52, and outputs a detection signal that continuously changes according to the oxygen concentration. The air flow meter 81 is a sensor that measures the amount of air flowing into the intake passage 3 from the atmosphere. The intake air temperature sensor 82 is a sensor that detects the temperature of the air flowing through the intake passage 3 (the temperature upstream of the intake throttle valve 33). The intake pressure sensor 83 is a sensor that detects the pressure downstream of the intake throttle valve 33 (for example, in the intake manifold). The exhaust temperature sensor 84 is a sensor that detects the temperature of the exhaust gas flowing through the exhaust passage 5 (the temperature on the upstream side of the exhaust throttle valve 53). The water temperature sensor 85 is a sensor that detects the temperature of the cooling water circulating inside the engine 1. The crank position sensor 86 is a sensor that detects the rotational position of the crankshaft of the engine 1. The accelerator opening sensor 87 is a sensor that detects an operation amount (accelerator opening) of the accelerator pedal by the driver. The intake throttle valve opening sensor 88 is a sensor that detects the opening of the intake throttle valve 33. The differential pressure sensor 89 is a sensor that measures a differential pressure between the upstream pressure and the downstream pressure of the low pressure EGR cooler 73 in the LPL-EGR mechanism 7. The high pressure EGR valve opening sensor 8H is a sensor that detects the opening of the high pressure EGR valve 62. The low pressure EGR valve opening sensor 8L is a sensor that detects the opening of the low pressure EGR valve 72.

  The ECU 10 controls the injector 2, the intake throttle valve 33, the exhaust throttle valve 53, the high pressure EGR valve 62, and the low pressure EGR valve 72 based on the detection values and measurement values of the various sensors 80 to 89, 8H, and 8L.

  For example, the ECU 10 controls the HPL-EGR mechanism 6 and the LPL-EGR mechanism 7 according to the operating state (engine load or the like) of the engine 1.

  Specifically, when the engine 1 is warm (for example, when the coolant temperature is 60 ° C. or higher), the EGR mechanisms 6 and 7 to be used are selected according to the map of FIG. That is, when the engine 1 is in the low load operation state, the ECU 10 recirculates the exhaust gas by using the HPL-EGR mechanism 6 (recirculation operation in the high pressure EGR region). When the engine 1 is in a high load operation state, the ECU 10 recirculates the exhaust gas by the LPL-EGR mechanism 7 (reflux operation in the low pressure EGR region). When the engine 1 is in the medium load operation state, the ECU 10 performs the exhaust gas recirculation by using the HPL-EGR mechanism 6 and the LPL-EGR mechanism 7 together (reflux operation in the MPL region). These specific controls will be described later. A region X in FIG. 3 is when the required acceleration for the vehicle is high (during transient operation) or the like, and both the high pressure EGR valve 62 of the HPL-EGR mechanism 6 and the low pressure EGR valve 72 of the LPL-EGR mechanism 7 are closed. This is an operating region where the EGR gas is not recirculated.

  In this way, when the usage mode of the HPL-EGR mechanism 6 and the LPL-EGR mechanism 7 is switched according to the operating state of the engine 1, or when the EGR mechanisms 6 and 7 are used in combination, a wide range of the engine 1 is obtained. Therefore, an appropriate amount of EGR gas can be recirculated in a proper operation region, and the NOx concentration in the exhaust gas can be suitably reduced.

  On the other hand, when the engine 1 is cold, the ECU 10 uses the HPL-EGR mechanism 6 to recirculate the exhaust gas in the operating region other than the region X, as shown in the map of FIG. I do. This utilizes the HPL-EGR mechanism 6 that is not provided with an EGR cooler, thereby causing the exhaust gas at a relatively high temperature to recirculate, thereby prematurely warming up the engine 1 and activating the oxidation catalyst 51 early. Because.

-Basic control of MPL-EGR system-
Next, basic control of the MPL-EGR system will be described.

  First, control of the EGR gas amount in the HPL-EGR mechanism 6 and control of the EGR gas amount in the LPL-EGR mechanism 7 will be described. The control of the EGR gas amount in the HPL-EGR mechanism 6 and the control of the EGR gas amount in the LPL-EGR mechanism 7 are independent controls.

  When the EGR gas is recirculated using the HPL-EGR mechanism 6 (including the case where the LPL-EGR mechanism 7 is used together), the target EGR gas recirculation amount (hereinafter referred to as “target high-pressure EGR gas return”). The flow rate ”) and the estimated EGR gas recirculation amount (hereinafter referred to as“ estimated high pressure EGR gas recirculation amount ”), and the high pressure EGR gas recirculation amount approaches the target high pressure EGR gas recirculation amount. The opening degree of the EGR valve 62 and the opening degree of the intake throttle valve 33 are feedback controlled (hereinafter referred to as “EGR feedback control”). The target high-pressure EGR gas recirculation amount in this case is set according to the operating state of the engine 1 (particularly the engine load). The estimated high-pressure EGR gas recirculation amount is determined by the opening of the high-pressure EGR valve 62 detected by the high-pressure EGR valve opening sensor 8H, the intake air temperature detected by the intake air temperature sensor 82, the pressure in the intake manifold, and the exhaust. Using a differential pressure with respect to the pressure in the manifold as a parameter, it is obtained from a predetermined arithmetic expression or map stored in advance in a ROM (Read Only Memory) of the ECU 10. The pressure in the intake manifold is detected by the intake pressure sensor 83. Further, the pressure in the exhaust manifold is obtained from a predetermined arithmetic expression or map stored in advance in the ROM of the ECU 10 using the pressure in the intake manifold, the operating state amount of the engine 1 and the like as parameters.

  On the other hand, when the EGR gas is recirculated using the LPL-EGR mechanism 7 (including the case where the HPL-EGR mechanism 6 is used together), the target EGR gas recirculation amount (hereinafter referred to as “target low pressure EGR”). Gas recirculation amount) and the estimated EGR gas recirculation amount (hereinafter referred to as "estimated low pressure EGR gas recirculation amount"), and the estimated low pressure EGR gas recirculation amount approaches the target low pressure EGR gas recirculation amount. Further, the opening degree of the low pressure EGR valve 72 and the opening degree of the exhaust throttle valve 53 are feedback controlled (EGR feedback control). The target low-pressure EGR gas recirculation amount in this case is set according to the operating state of the engine 1 (particularly the engine load). The estimated low-pressure EGR gas recirculation amount is detected by the opening of the low-pressure EGR valve 72 detected by the low-pressure EGR valve opening sensor 8L, the temperature of the exhaust detected by the exhaust temperature sensor 84, and the differential pressure sensor 89. The differential pressure between the upstream pressure and the downstream pressure of the low pressure EGR cooler 73 is obtained as a parameter from a predetermined arithmetic expression or map stored in advance in the ROM of the ECU 10.

  Hereinafter, the basic operation of the MPL-EGR system according to the load of the engine 1 (basic operation of the HPL-EGR mechanism 6 and the LPL-EGR mechanism 7) will be described.

(During low load operation)
As described above, when the engine load is relatively low (low load region), the EGR gas is recirculated using only the HPL-EGR mechanism 6. This operation region is referred to as an HPL region. Even when the cooling water temperature is low, the EGR gas is recirculated using only the HPL-EGR mechanism 6.

  In the EGR feedback control in the HPL region, the target high-pressure EGR gas return is performed so that the intake air amount detected by the air flow meter 81 matches the target intake air amount set according to the engine load, the engine speed, and the like. The flow rate is set, and as described above, the opening degree of the high pressure EGR valve 62 is feedback controlled so that the estimated high pressure EGR gas recirculation amount matches the target high pressure EGR gas recirculation amount. At this time, the low pressure EGR valve 72 is maintained fully closed.

  For example, when the intake air amount obtained by the air flow meter 81 is smaller than the target value and the actual EGR rate is higher than the target EGR rate (EGR rate determined according to the operating state of the engine 1 or the like), the estimated high pressure Since the EGR gas recirculation amount is larger than the target high pressure EGR gas recirculation amount, the opening degree of the high pressure EGR valve 62 is reduced so as to decrease the EGR gas amount.

  When the intake air amount obtained by the air flow meter 81 is larger than the target value and the actual EGR rate is lower than the target EGR rate, the estimated high pressure EGR gas recirculation amount becomes smaller than the target high pressure EGR gas recirculation amount. Therefore, the opening degree of the high pressure EGR valve 62 is increased so as to increase the amount of EGR gas. If the estimated high pressure EGR gas recirculation amount does not reach the target high pressure EGR gas recirculation amount even if the opening amount of the high pressure EGR valve 62 is increased in this way, the opening amount of the intake throttle valve 33 is decreased ( The amount of EGR gas recirculated through the high pressure EGR passage 61 is increased by decreasing the pressure on the downstream side of the intake throttle valve 33. This brings the actual EGR rate closer to the target EGR rate.

  Hereinafter, a control mode in which the EGR gas is recirculated using only the HPL-EGR mechanism 6 is referred to as an HPL mode. Note that the target value of the intake air amount and the target value of the EGR gas amount may each have a certain range to be a target range. When the EGR gas amount can be directly measured by a sensor or the like, the opening degree of the high pressure EGR valve 62 may be adjusted so that the EGR gas amount becomes a target value or a target range.

(During high load operation)
As described above, when the engine load is relatively high (high load region), the EGR gas is recirculated using only the LPL-EGR mechanism 7. This operation region is referred to as an LPL region.

  In the EGR feedback control in this LPL region, the target low pressure EGR gas return is performed so that the intake air amount detected by the air flow meter 81 matches the target intake air amount set according to the engine load, the engine speed, and the like. The flow rate is set, and as described above, the opening degree of the low pressure EGR valve 72 is feedback-controlled so that the estimated low pressure EGR gas recirculation amount matches the target low pressure EGR gas recirculation amount. At this time, basically, the high pressure EGR valve 62 is kept fully closed (unless the amount of EGR gas is insufficient).

  For example, when the intake air amount obtained by the air flow meter 81 is less than the target value and the actual EGR rate is higher than the target EGR rate, the estimated low pressure EGR gas recirculation amount becomes larger than the target low pressure EGR gas recirculation amount. Therefore, the opening degree of the low pressure EGR valve 72 is reduced so as to reduce the amount of EGR gas.

  When the intake air amount obtained by the air flow meter 81 is larger than the target value and the actual EGR rate is lower than the target EGR rate, the estimated low pressure EGR gas recirculation amount becomes smaller than the target low pressure EGR gas recirculation amount. Therefore, the opening degree of the low pressure EGR valve 72 is increased so as to increase the amount of EGR gas. If the estimated low pressure EGR gas recirculation amount does not reach the target low pressure EGR gas recirculation amount even if the opening amount of the low pressure EGR valve 72 is increased in this way, the opening amount of the high pressure EGR valve 62 is increased, Alternatively, the opening amount of the exhaust throttle valve 53 is decreased (the degree of closeness is increased), and the amount of EGR gas recirculated through the low pressure EGR passage 71 is increased. This brings the actual EGR rate closer to the target EGR rate.

  Hereinafter, the control mode in which the EGR gas is recirculated using only the LPL-EGR mechanism 7 is referred to as an LPL mode. Note that the target value of the intake air amount and the target value of the EGR gas amount may each have a certain range to be a target range. When the EGR gas amount can be directly measured by a sensor or the like, the opening degree of the low pressure EGR valve 72 may be adjusted so that the EGR gas amount becomes a target value or a target range.

(During medium load operation)
As described above, when the engine is in a medium load operation (medium load region), the EGR gas is recirculated by using the HPL-EGR mechanism 6 and the LPL-EGR mechanism 7 together. A region between the HPL region and the LPL region is referred to as an MPL region.

  This EGR feedback control in the MPL region is based on the target intake air amount and the target EGR rate (= high pressure EGR gas recirculation amount + low pressure EGR gas recirculation amount / high pressure EGR gas recirculation amount + low pressure EGR) according to the engine load, engine speed, etc. Gas recirculation amount + intake air amount) is determined, and the total amount of EGR gas amount is set from these values. Further, the EGR distribution ratio (ratio between the amount of high-pressure EGR gas recirculated by the HPL-EGR mechanism 6 and the amount of low-pressure EGR gas recirculated by the LPL-EGR mechanism 7) is determined according to the engine load and the like. Then, the distribution ratio of the high pressure EGR gas (= high pressure EGR gas recirculation amount / high pressure EGR gas recirculation amount + low pressure EGR gas recirculation amount) and the low pressure EGR gas distribution ratio (= low pressure EGR gas recirculation amount / high pressure EGR gas recirculation amount + low pressure) By multiplying the total amount of the EGR gas by the EGR gas recirculation amount, the target high pressure EGR gas amount (target high pressure EGR gas recirculation amount) and the target low pressure EGR gas amount (target low pressure EGR gas return) Flow rate).

  As the control of the HPL-EGR mechanism 6, the opening degree of the high pressure EGR valve 62 is controlled so that the estimated high pressure EGR gas recirculation amount reaches the target high pressure EGR gas recirculation amount. The opening degree control for the high pressure EGR valve 62 is the same as that in the low load operation described above.

  On the other hand, as the control of the LPL-EGR mechanism 7, the opening degree of the low pressure EGR valve 72 is controlled so that the estimated low pressure EGR gas recirculation amount reaches the target low pressure EGR gas recirculation amount. The opening degree control for the low-pressure EGR valve 72 is the same as in the above-described high-load operation.

  Hereinafter, a control mode for supplying EGR gas using both the HPL-EGR mechanism 6 and the LPL-EGR mechanism 7 is referred to as an MPL mode. Note that the target value of the intake air amount and the target value of the EGR gas amount may each have a certain range to be a target range. When the EGR gas amount can be directly measured by a sensor or the like, the opening degree of one of the low pressure EGR valve 72 and the high pressure EGR valve 62 may be adjusted so that the EGR gas amount becomes a target value or a target range.

-Abnormality diagnosis operation of MPL-EGR system-
When particulate matter in the exhaust gas adheres to the high pressure EGR passage 61 or the low pressure EGR passage 71 and the flow passage area is reduced or the EGR passage is blocked, the high pressure EGR passage 61 or the low pressure EGR passage 71 is used. An abnormality occurs in which the amount of EGR gas flowing through the gas is smaller than normal.

  In the present embodiment, an abnormality diagnosis operation is performed to determine which of the high pressure EGR passage 61 and the low pressure EGR passage 71 is blocked.

  Before describing the abnormality diagnosis operation that characterizes the present embodiment, the operation of the MPL-EGR system, which is a precondition for enabling this abnormality diagnosis operation, will be specifically described.

(Low load area)
As described above, when the engine load is relatively low (low load region) or when the engine 1 is cold, the EGR gas is recirculated using only the HPL-EGR mechanism 6. This is because in such an operating state, the ignitability of the fuel in the cylinder deteriorates and unburned HC and CO may be discharged. Therefore, high temperature EGR gas is recirculated to stabilize the combustion. This is to suppress emissions of HC and CO.

  Further, when the LPL-EGR mechanism 7 is used in such an operating state where HC and CO may be discharged, the amount of deposits in the low-pressure EGR cooler 73 provided in the LPL-EGR mechanism 7 is reduced. There is a possibility that the inside of the low-pressure EGR cooler 73 will be blocked due to the increase. For this reason, in this operation region, only the HPL-EGR mechanism 6 is used to recirculate the EGR gas. In addition, if the LPL-EGR mechanism 7 is used when the engine 1 is cold, condensed water is generated in the low-pressure EGR passage 71, which may cause corrosion of the low-pressure EGR valve 72 and the injector 2. The EGR gas is recirculated using only the HPL-EGR mechanism 6.

  As described above, in the MPL-EGR system according to the present embodiment, the low-pressure EGR valve 72 of the LPL-EGR mechanism 7 is always used so that the LPL-EGR mechanism 7 is not used during execution of the HPL mode where the engine load is relatively low. Closed state. That is, if the HPL-EGR mechanism 6 is closed, the low pressure EGR valve 72 is closed even if the EGR gas amount is insufficient.

(High load area)
On the other hand, when the engine load is relatively high (high load region), the EGR gas is recirculated using only the LPL-EGR mechanism 7. This is to suppress the generation of smoke due to the high temperature of the intake air by causing the relatively low temperature exhaust gas (exhaust gas cooled by the low pressure EGR cooler 73) to recirculate.

  Further, since the LPL-EGR mechanism 7 is provided with the low-pressure EGR cooler 73 as described above, there is a concern about the possibility of clogging with deposits as described above, but the HPL-EGR mechanism 6 includes the EGR. Since there is no cooler, it is not possible. For this reason, it is possible to use the HPL-EGR mechanism 7 even when the LPL mode is executed (the possibility of blockage is low even if the HPL-EGR mechanism 7 is used). In other words, if the LPL-EGR mechanism 7 is clogged and the amount of EGR gas is insufficient, the high-pressure EGR valve 62 of the HPL-EGR mechanism 6 is opened regardless of the MPL-EGR system mode. The exhaust gas can be recirculated using the high-pressure EGR passage 61.

(Medium load area)
In an operation region where the engine load is medium load, both the HPL-EGR mechanism 6 and the LPL-EGR mechanism 7 are used to achieve both the suppression of HC and CO emission and the suppression of smoke generation. Used to recirculate EGR gas. In this case, since both the high pressure EGR valve 62 and the low pressure EGR valve 72 can be opened, when the amount of EGR gas is insufficient, the opening of at least one of the valves is increased and the exhaust gas is increased. It is possible to increase the reflux amount.

(Abnormal diagnosis operation)
When the operation of the MPL-EGR system is performed as described above, if one of the high pressure EGR passage 61 of the HPL-EGR mechanism 6 or the low pressure EGR passage 71 of the LPL-EGR mechanism 7 is blocked, the other EGR mechanism It is conceivable that the EGR gas is refluxed using

  However, as described above, if the LPL-EGR mechanism 7 is used when the engine load is relatively low or the engine 1 is cold, the inside of the low-pressure EGR cooler 73 may be blocked or the generation of condensed water. It can lead to corrosion. For this reason, even if the high pressure EGR passage 61 of the HPL-EGR mechanism 6 is closed, the LPL-EGR mechanism 7 cannot be used when the HPL mode is executed.

  Conversely, the HPL-EGR mechanism 6 is not provided with an EGR cooler, and high-temperature EGR gas flows through the high-pressure EGR passage 61. For this reason, if the low pressure EGR passage 71 of the LPL-EGR mechanism 7 is closed, it is possible to recirculate the EGR gas using the HPL-EGR mechanism 6 regardless of the mode of the MPL-EGR system. .

  By utilizing such an operation, in the present embodiment, an abnormality diagnosis operation as described below is performed. The outline of the abnormality diagnosis operation will be described below.

  In this abnormality diagnosis operation, an operation for recognizing that a blockage has occurred somewhere in the MPL-EGR system, and which of the HPL-EGR mechanism 6 and the LPL-EGR mechanism 7 has the blockage occurred. The operation of specifying is performed.

  Specifically, as an operation for recognizing that a blockage has occurred somewhere in the MPL-EGR system, the opening of the high-pressure EGR valve 62 of the HPL-EGR mechanism 6 is greater than or equal to a predetermined value, and the intake air When the closing degree of the throttle valve 33 is equal to or greater than a predetermined value, it is determined that a blockage has occurred. That is, when the EGR gas amount is insufficient, the opening of the high-pressure EGR valve 62 is permitted in any mode (HPL mode, MPL mode, LPL mode), so the opening degree is a predetermined value. The EGR gas amount is insufficient on the condition that the intake throttle valve 33 is close to a predetermined value or more, that is, the MPL-EGR system is blocked at some point. to decide. Note that the opening operation of the high pressure EGR valve 62 is prioritized between the opening operation of the high pressure EGR valve 62 and the operation of increasing the closing degree of the intake throttle valve 33. That is, first, the opening operation of the high pressure EGR valve 62 is performed. For example, when the EGR gas amount is insufficient even when the high pressure EGR valve 62 is fully opened (the opening degree is 100%), the closing degree of the intake throttle valve 33 is increased. Move on to enlarge.

  The low-pressure EGR valve 72 is permitted to be opened in the MPL mode and the LPL mode, but is not permitted to be opened in the HPL mode. Therefore, the low-pressure EGR valve 72 is closed. In this case, it can be determined that the HPL mode is currently being executed and the EGR gas amount is insufficient. That is, since it can be determined that the amount of EGR gas is insufficient even though the high pressure EGR valve 62 is largely opened, it can be diagnosed that the HPL-EGR mechanism 6 is clogged.

  On the other hand, when the low pressure EGR valve 72 is open, it can be determined that the amount of EGR gas is insufficient even though the low pressure EGR valve 72 is largely opened (the opening degree of the high pressure EGR valve 62 is Since it is determined that the EGR gas amount is insufficient because the degree of closing of the intake throttle valve 33 is equal to or greater than a predetermined value above a predetermined value), it can be diagnosed that the LPL-EGR mechanism 7 is clogged.

  Hereinafter, a specific procedure of the abnormality diagnosis operation of the MPL-EGR system will be described with reference to the flowchart of FIG. This flowchart is performed at a predetermined timing (for example, once in one trip of the vehicle (a period from when the ignition is turned on until it is turned off)).

  First, in step ST1, it is determined whether or not a precondition for executing the abnormality diagnosis operation is satisfied. Preconditions include, for example, that the intake throttle valve opening sensor 88, the high pressure EGR valve opening sensor 8H, and the low pressure EGR valve opening sensor 8L are operating normally, the high pressure EGR valve 62, and the low pressure EGR valve. 72 that there is no abnormality and that the operation mode of the engine 1 is the normal combustion mode. The determination that the sensors 88, 8H, and 8L are operating normally and the determination that the EGR valves 62 and 72 are operating normally can be performed by a known determination operation. Description of is omitted. Further, the normal combustion mode of the engine 1 is an operation mode in which the EGR gas is recirculated, and is a state that is not when the required acceleration for the vehicle is high or when the particulate filter 52 is being regenerated.

  If any one of these preconditions is not satisfied, a NO determination is made in step ST1, and the abnormality diagnosis operation is disabled and the process returns.

  On the other hand, when all the preconditions are satisfied and YES is determined in step ST1, the process proceeds to step ST2, and it is determined whether or not the condition for starting the abnormality diagnosis operation is satisfied. As a condition for starting the abnormality diagnosis operation, for example, the engine speed is within a predetermined range, the fuel injection amount from the injector 2 is within a predetermined range, the high pressure EGR valve 62, the low pressure EGR valve 72, and the intake throttle For example, the opening degree of the valve 33 is within a predetermined range. That is, since the EGR gas amount is set to “0” during the transient operation of the engine 1, the absence of such a situation is set as a condition for starting the abnormality diagnosis operation. The EGR gas amount is also set to “0” when the opening of the intake throttle valve 33 is reduced to reduce the exhaust amount and suppress the temperature drop of the oxidation catalyst 51 when the vehicle is decelerating. Since it is set, the absence of such a situation is set as a condition for starting the abnormality diagnosis operation.

  If any one of these abnormality diagnosis operation start conditions is not satisfied, NO is determined in step ST2, and the abnormality diagnosis operation is returned to be impossible.

  On the other hand, if the condition for starting the abnormality diagnosis operation is satisfied and YES is determined in step ST2, the process proceeds to step ST3, and the opening degree of the high pressure EGR valve 62 and the closing degree of the intake throttle valve 33 (from the fully open state to the closing direction). The ratio of the amount of change in opening to The opening degree of the high pressure EGR valve 62 is detected by the high pressure EGR valve opening degree sensor 8H. Further, the closing degree of the intake throttle valve 33 is detected by an intake throttle valve opening sensor 88.

  Thereafter, the process proceeds to step ST4, where the opening degree of the high pressure EGR valve 62 is equal to or greater than a predetermined value α (“high pressure side exhaust gas recirculation amount increase opening degree” in the present invention) and the closing degree of the intake throttle valve 33 is a predetermined value β (main It is determined whether or not it is “high pressure side exhaust gas recirculation amount increase degree of closure”) or more (closed by a predetermined amount or more). Examples of the predetermined value α used for the opening degree determination of the high pressure EGR valve 62 include an opening degree of 100% (fully open). That is, it is determined whether or not the high pressure EGR valve 62 is fully opened to increase the EGR gas amount due to the lack of the EGR gas amount. The predetermined value β used for determining the closing degree of the intake throttle valve 33 includes, for example, a closing degree of 90% (closed to 90%). That is, even if the opening of the high pressure EGR valve 62 is 100% (fully opened), the amount of EGR gas is insufficient, and the intake throttle valve 33 is closed to a predetermined closing degree in order to increase the amount of EGR gas. It is determined whether or not.

  The predetermined value β used for determining the closing degree of the intake throttle valve 33 is set as appropriate. That is, when the closing degree of the intake throttle valve 33 has reached the predetermined value β, it is assumed that the MPL-EGR system is blocked (the blockage is occurring somewhere in the MPL-EGR system). Since the determination is performed, the predetermined value β is set according to the degree of blockage to be determined as abnormal. For example, when it is determined that any EGR passage in the MPL-EGR system is completely blocked, the predetermined value β is set to 90%, and any passage in the MPL-EGR system is 50%. In the case where it is determined that there is an abnormality when the blockage is% closed (the passage is narrowed), the predetermined value β is set to 40%, for example. These values are not limited to this.

  If NO is determined in step ST4, that is, if the opening degree of the high pressure EGR valve 62 is less than the predetermined value α or the closing degree of the intake throttle valve 33 is less than the predetermined value β, the process proceeds to step ST5. Execute normal judgment. That is, it is determined that there is no blockage in the MPL-EGR system, normality is determined, and the process returns.

  On the other hand, if YES is determined in step ST4, that is, if the opening degree of the high pressure EGR valve 62 is equal to or larger than the predetermined value α and the closing degree of the intake throttle valve 33 is equal to or larger than the predetermined value β, the process proceeds to step ST6. , Perform abnormality determination. That is, an abnormality determination is performed on the assumption that a blockage has occurred somewhere in the MPL-EGR system.

  Then, it moves to step ST7 and acquires the opening degree of the low pressure EGR valve 72. The opening degree of the low pressure EGR valve 72 is detected by the low pressure EGR valve opening degree sensor 8L.

  Thereafter, the process proceeds to step ST8, and it is determined whether or not the opening degree of the low pressure EGR valve 72 exceeds a predetermined value γ (“low pressure side exhaust gas recirculation amount increase opening degree” in the present invention). As the predetermined value γ used for the opening degree determination of the low pressure EGR valve 72, for example, an opening degree of 70% is cited. That is, it is determined whether the opening degree of the low pressure EGR valve 72 is set to be large in order to increase the EGR gas amount due to the lack of the EGR gas amount. The value of the predetermined value γ is not limited to the above value and is set as appropriate.

  If the opening degree of the low pressure EGR valve 72 exceeds the predetermined value γ and a YES determination is made in step ST8, the process proceeds to step ST9, where it is determined that the LPL-EGR mechanism 7 is blocked. Accompanying this abnormality determination, for example, abnormality information (information indicating that a blockage has occurred in the LPL-EGR mechanism 7) is written in the diagnosis provided in the ECU 10. In addition, a warning is issued to the driver as necessary.

  That is, although the opening degree of the low pressure EGR valve 72 exceeds the predetermined value γ, the EGR gas amount is insufficient, so that the opening degree of the high pressure EGR valve 62 is equal to or larger than the predetermined value α and the intake air. Since it can be determined that the closing degree of the throttle valve 33 is equal to or greater than the predetermined value β, in this case, it can be determined that the LPL-EGR mechanism 7 is blocked.

  On the other hand, when the opening degree of the low pressure EGR valve 72 is equal to or less than the predetermined value γ and NO is determined in step ST8, the process proceeds to step ST10, where it is determined that the HPL-EGR mechanism 6 is blocked. Accompanying this abnormality determination, for example, abnormality information (information indicating that the HPL-EGR mechanism 6 is blocked) is written in the diagnosis provided in the ECU 10. In addition, a warning is issued to the driver as necessary.

  In other words, the fact that the opening of the low pressure EGR valve 72 is equal to or less than the predetermined value γ despite the exhaust gas recirculation amount being insufficient means that the opening of the low pressure EGR valve 72 is limited, for example, HPL. It can be determined that the mode is the mode, the opening degree of the high pressure EGR valve 62 is equal to or greater than the predetermined value α, and the closing degree of the intake throttle valve 33 is equal to or greater than the predetermined value β, the HPL-EGR mechanism 6 is blocked. Therefore, it can be determined that the EGR gas amount is insufficient. In this case, it can be determined that the HPL-EGR mechanism 6 is blocked.

  When the above operation is performed every predetermined period (for example, one trip) and the MPL-EGR system is blocked, the blockage point (blocked by either the HPL-EGR mechanism 6 or the LPL-EGR mechanism 7) It is possible to diagnose whether or not

(Specific valve opening states)
FIG. 6 is a timing chart showing the opening states of the respective valves (the high pressure EGR valve 62, the intake throttle valve 33, and the low pressure EGR valve 72) when no blockage occurs in the MPL-EGR system. FIG. 7 is a timing chart showing the opening state of each valve when the LPL-EGR mechanism 7 is closed. Further, FIG. 8 is a timing chart showing the opening state of each valve when the HPL-EGR mechanism 6 is closed. Hereinafter, each operation will be described.

  First, when the MPL mode is executed when no blockage has occurred in the MPL-EGR system, the opening degree of each valve is constant as shown in FIG. Specifically, the intake throttle valve 33 is fully open (the degree of closure is 0%), and the opening degrees of the high pressure EGR valve 62 and the low pressure EGR valve 72 are the target high pressure set according to the distribution ratio as described above. It is set so that the EGR gas recirculation amount and the target low-pressure EGR gas recirculation amount can be obtained. In the case shown in FIG. 6, the opening degree of the high pressure EGR valve 62 and the opening degree of the low pressure EGR valve 72 are set to 50%, respectively. In this case, if the total amount of EGR gas is insufficient, the control of the HPL-EGR mechanism 6 is given priority. That is, when the opening of the high pressure EGR valve 62 of the HPL-EGR mechanism 6 is increased and the total amount of EGR gas is insufficient even when the opening reaches 100%, the opening of the intake throttle valve 33 is increased. The amount of reflux of the EGR gas is increased, for example, by reducing the gas flow rate.

  Next, when the MPL mode is executed or the LPL mode is executed when the LPL-EGR mechanism 7 is blocked, the opening of the low pressure EGR valve 72 of the LPL-EGR mechanism 7 is set as shown in FIG. Even if it is 100%, the total amount of EGR gas is insufficient. In this case, when the opening degree of the high pressure EGR valve 62 of the HPL-EGR mechanism 6 is increased so that the EGR rate approaches the target EGR rate, and the target EGR rate is not reached even when the opening degree reaches 100%. The opening degree of the intake throttle valve 33 is reduced (the degree of closing is increased), thereby increasing the recirculation amount of the high-pressure EGR gas. In such a situation, YES is determined in step ST4 in the flowchart of FIG. 5 described above, and YES is determined in step ST8. In step ST9, it is diagnosed that the LPL-EGR mechanism 6 is blocked. Will do. In this case, the intake throttle valve 33 is not fully closed (for example, 90% is the limit). This is because if the intake throttle valve 33 is fully closed, a misfire or an engine stall is caused due to an insufficient intake amount.

  Next, when the MPL mode is executed when the HPL-EGR mechanism 6 is closed, as shown in FIG. 8, even if the opening degree of the high-pressure EGR valve 62 of the HPL-EGR mechanism 6 is set to 100%, EGR The total amount of gas is in short supply. In this case, the opening degree of the intake throttle valve 33 is reduced so as to bring the EGR rate closer to the target EGR rate, thereby increasing the recirculation amount of the high-pressure EGR gas. If the target EGR rate is not reached even by performing such opening control, the opening of the low pressure EGR valve 72 of the LPL-EGR mechanism 7 is not increased as described above, and the low pressure EGR valve 72 is not increased. The opening is maintained below a predetermined value. FIG. 8 shows a case where the target EGR rate is obtained when the opening degree of the low pressure EGR valve 72 reaches 50%. In the case of the HPL mode, the opening degree of the low pressure EGR valve 72 is maintained at 0%. In such a situation, YES is determined in step ST4 in the flowchart of FIG. 5 described above, and NO is determined in step ST8. In step ST10, it is diagnosed that the HPL-EGR mechanism 6 is blocked. Will do. In this case as well, the closing degree of the intake throttle valve 33 is not fully closed (for example, the closing degree is 90% as a limit).

  As described above, according to the present embodiment, it is limited to an operation region (low load region) where only the HPL-EGR mechanism 6 is used or an operation region (high load region) where only the LPL-EGR mechanism 7 is used. Without being performed, it is possible to diagnose which of the HPL-EGR mechanism 6 and the LPL-EGR mechanism 7 is blocked. For this reason, the opportunity to perform abnormality diagnosis can be increased and abnormality diagnosis can be performed at an early stage. In addition, when replacing a blocked part, it is possible to identify the blocked part. Therefore, useless part replacement (pipe parts that are not blocked) can be replaced. State that must be).

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to an in-line four-cylinder diesel engine mounted on an automobile has been described. The present invention is applicable not only to automobiles but also to engines used for other purposes. Further, the number of cylinders and the engine type (separate type engine, V-type engine, horizontally opposed engine, etc.) are not particularly limited.

  In the above-described embodiment, the case where the present invention is applied to the engine 1 including the two EGR mechanisms 6 and 7 has been described. The present invention is not limited to this and can be applied to an engine including three or more EGR machines. In this case, what recirculates the exhaust gas upstream of the turbine 42 of the turbocharger 4 to the intake system is treated as the HPL-EGR mechanism 6, and what recirculates the exhaust gas downstream of the turbine 42 to the intake system is LPL- An abnormality diagnosis similar to the above is performed by treating as the EGR mechanism 7.

  The present invention is applicable to blockage diagnosis of an MPL-EGR system mounted on a diesel engine.

1 engine (internal combustion engine)
3 Intake passage (intake system)
33 Inlet throttle valve 4 Turbocharger (supercharger)
42 Turbine 5 exhaust passage (exhaust system)
6 HPL-EGR mechanism (high pressure EGR mechanism)
61 High pressure EGR passage 62 High pressure EGR valve 7 LPL-EGR mechanism (Low pressure EGR mechanism)
71 Low pressure EGR passage 72 Low pressure EGR valve 73 Low pressure EGR cooler 10 ECU

Claims (3)

A high pressure equipped with an internal combustion engine provided with an intake throttle valve in the intake system and provided with a high-pressure EGR valve capable of returning the exhaust gas upstream of the turbocharger turbine in the exhaust system to the intake system and adjusting the return amount An operating state of the internal combustion engine having an EGR mechanism and a low-pressure EGR mechanism having a low-pressure EGR valve that recirculates exhaust gas downstream of the turbocharger turbine in the exhaust system to the intake system and adjusts the recirculation amount In the EGR system abnormality diagnosis device that selects the EGR mechanism to be used according to
When the exhaust gas is recirculated from the exhaust system to the intake system, the opening of the high-pressure EGR valve of the high-pressure EGR mechanism is equal to or greater than a predetermined high-pressure side exhaust gas recirculation amount increase opening and the intake throttle valve is closed. When the degree is equal to or higher than the predetermined high-pressure side exhaust gas recirculation increase degree of closure,
When the opening of the low pressure EGR valve of the low pressure EGR mechanism exceeds a predetermined low pressure side exhaust gas recirculation amount increase opening, it is determined that the low pressure EGR mechanism is clogged, while the low pressure of the low pressure EGR mechanism An abnormality diagnosis device for an EGR system, characterized in that when the opening degree of the EGR valve is equal to or less than the low pressure side exhaust gas recirculation amount increase opening degree, it is determined that the high pressure EGR mechanism is clogged. . The abnormality diagnosis apparatus for an EGR system according to claim 1,
The low-pressure EGR mechanism is provided with an EGR cooler that cools the exhaust gas recirculated to the intake system.
At the time of low load operation of the internal combustion engine, only the high pressure EGR mechanism is used to recirculate exhaust gas to the intake system, and at the time of high load operation of the internal combustion engine, only the low pressure EGR mechanism is used to exhaust to the intake system. The EGR is characterized in that gas is recirculated and exhaust gas is recirculated to the intake system using both the high-pressure EGR mechanism and the low-pressure EGR mechanism during medium load operation of the internal combustion engine. System abnormality diagnosis device. The abnormality diagnosis device for an EGR system according to claim 1 or 2,
The high pressure side exhaust gas recirculation amount increase opening is an opening corresponding to the fully open or substantially fully open high pressure EGR valve,
The high pressure side exhaust gas recirculation amount increase close degree is a close degree of the intake throttle valve set in accordance with a closing degree which is a reference for determining that a blocking has occurred in the system. Abnormality diagnosis device.

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