JP2012163060A - Exhaust recirculation system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust recirculation system of an internal combustion engine which prevents generation of condensed water and ensures NOx reduction effect.SOLUTION: An exhaust recirculation system of an internal combustion engine includes a high pressure EGR device 16, a low pressure EGR device 17, a foreign substance capturing filter 74, a LP differential pressure sensor 107 for detecting front and rear differential pressures in an exhaust recirculation direction of a low pressure exhaust recirculation tube 71, and an ECU 50 for controlling both EGR devices 16, 17 based on the detected information. The ECU 50 includes: a condensed water amount estimation part 51 for estimating the amount of condensed water in a low pressure side exhaust recirculation path L2 formed by the low pressure EGR device 16; and a recirculation ratio control part 52 for increasing the high pressure side exhaust recirculation amount so as to reduce a ratio of the low pressure side exhaust recirculation amount to the high pressure side exhaust recirculation amount when an estimated condensed water amount exceeds a threshold value and the detected pressure difference of the differential pressure sensor 107 is increased so as to satisfy a passage blocking determination condition.

Description

  The present invention relates to an exhaust gas recirculation system for an internal combustion engine having both low pressure side and high pressure side exhaust gas recirculation circuits, and more particularly to an exhaust gas recirculation system for an internal combustion engine that suppresses the generation of condensed water in an exhaust gas recirculation path. About.

  In a vehicle engine (internal combustion engine), an exhaust gas recirculation (EGR) system is effective in reducing NOx (nitrogen oxides) and can reduce pumping loss (intake load) of the engine. EGR coolers (exhaust coolers) are used to reduce the temperature of exhaust gas that is recirculated, that is, EGR gas, in engines that are equipped with a large number of systems) and that can perform lean combustion and increase the EGR flow rate. Is frequently used. In addition to the HPL (High Pressure Loop) -EGR circuit that recirculates a portion of the high-temperature exhaust gas to the intake side, the exhaust gas after passing through the exhaust aftertreatment device is upstream of the turbocharger compressor. A device equipped with an LPL (Low Pressure Loop) -EGR circuit, which enables a large amount of exhaust gas recirculation by recirculation, has begun to spread.

  In such an exhaust gas recirculation system of an internal combustion engine, the pumping loss (intake load) of the engine can be reduced by recirculating the exhaust gas to the intake side. However, if a large amount of exhaust gas recirculation is performed, the exhaust gas Cooling of the water inside makes it easy to generate a large amount of acidic condensate containing nitric acid, sulfuric acid, etc., and the condenser of the condensate, the metal parts of the intake system where the condensate easily adheres, and the turbocharger Compressors and the like are easily corroded. Therefore, it is important to enhance the NOx reduction effect while suppressing the generation of condensed water.

  As such a conventional exhaust gas recirculation system, for example, if a large amount of exhaust gas recirculation is performed so that the differential pressure across the low pressure side exhaust gas recirculation passage exceeds a predetermined value in the LPL-EGR circuit, the total pumping loss of the engine increases. If the detected value of the differential pressure sensor for detecting the differential pressure before and after the pressure difference is greater than the predetermined differential pressure, the flow rate of the low-pressure side exhaust recirculation passage is set to a flow rate corresponding to the predetermined differential pressure. The remaining required flow rate is supplemented by the exhaust gas recirculation amount through the high pressure exhaust gas recirculation passage of the HPL-EGR circuit (see, for example, Patent Document 1).

  Further, a foreign matter collecting filter folded zigzag so as to have a plurality of inclined surfaces inclined with respect to the flow direction of the EGR gas and a substantially horizontal plane connecting them is disposed in the low pressure side exhaust gas recirculation passage of the LPL-EGR circuit. Even if the condensed water easily attaches to the inclined surface of the foreign matter collecting filter that is arranged and allows the reflux exhaust gas to pass through, it is known that the condensed water can easily flow down from the inclined surface (for example, Patent Document 2).

  Further, an EGR ratio which is a ratio of a flow rate of the recirculated exhaust gas passing through the LPL-EGR circuit (hereinafter referred to as a low pressure EGR flow rate) and a flow rate of the recirculated exhaust gas passing through the HPL-EGR circuit (hereinafter referred to as a high pressure EGR flow rate). When the value deviates from the value, this is detected as a change in the differential pressure across the exhaust gas recirculation passage, and the smaller one of the low pressure EGR flow rate and the high pressure EGR flow rate is decreased so that the EGR ratio approaches the target value. There is known one that increases the number of cases (see, for example, Patent Document 3).

JP 2007-2111767 A JP 2010-151091 A JP 2008-038627 A

  However, in the conventional exhaust gas recirculation system for an internal combustion engine as described above, when a foreign matter collecting filter as described in Patent Document 2 is arranged upstream of the exhaust gas recirculation passage, Patent Document 1 When the EGR flow rate control using the differential pressure sensor as described in 3 is performed, the following problem may occur.

  That is, if the differential pressure across the exhaust gas recirculation passage is increased due to the deterioration of the EGR cooler of the LPL-EGR circuit over time, the HPL-EGR circuit so as to compensate for the exhaust gas recirculation amount by the LPL-EGR circuit. The required EGR flow rate can be obtained while suppressing the pumping loss of the engine by increasing the exhaust pipe flow rate.

  However, when the condensed water adheres to the foreign matter collecting filter and a water film is formed, and the exhaust gas recirculation passage is blocked by the foreign matter collecting filter or the pressure loss increases, the detection of the differential pressure sensor Since the value increases, the exhaust gas recirculation amount (low pressure EGR flow rate) by the LPL-EGR circuit is reduced, but it is erroneously detected that the exhaust gas recirculation state is large. Therefore, if a water film is formed on the foreign matter collecting filter, the low-pressure EGR flow rate is greatly reduced, and the EGR flow rate of the entire system becomes insufficient, and the NOx reduction effect may not be sufficiently obtained. There is.

  Therefore, it has been difficult to achieve both suppression of condensed water generation and ensuring of NOx reduction effect to the extent that the conventional techniques as described in Patent Documents 1 to 3 are simply gathered together.

  Therefore, the present invention provides an exhaust gas recirculation system for an internal combustion engine that can achieve both suppression of the generation of condensed water and ensuring of an NOx reduction effect.

  In order to solve the above problems, an exhaust gas recirculation system for an internal combustion engine according to the present invention includes: (1) an internal combustion engine having an intake pipe provided with a supercharging compressor and an exhaust pipe provided with a resistance element serving as an exhaust resistance. A high-pressure EGR device having a high-pressure exhaust gas recirculation pipe section for recirculating high-pressure exhaust gas from an exhaust pipe upstream of the resistance element to an intake pipe downstream of the compressor; and downstream of the resistance element of the internal combustion engine A low-pressure EGR device having a low-pressure exhaust gas recirculation pipe section for recirculating low-pressure exhaust gas after passing through the resistance element from the exhaust pipe to an intake pipe upstream of the compressor, and an exhaust pipe downstream of the resistance element A filter disposed on the upstream side in the exhaust gas recirculation direction of the low-pressure exhaust gas recirculation pipe section so as to pass the exhaust gas recirculated from the exhaust gas and collect foreign matter mixed in the exhaust gas, An internal combustion engine comprising: a differential pressure sensor that detects a differential pressure before and after the exhaust gas recirculation pipe portion in the exhaust gas recirculation direction; and a control device that controls the high pressure EGR device and the low pressure EGR device based on detection information of the differential pressure sensor. An exhaust gas recirculation system for an engine, wherein the control device includes a condensed water amount estimating means for estimating an amount of condensed water in a low pressure side exhaust recirculation path formed by the low pressure EGR device, and a condensed water amount estimating means. When the estimated amount of condensed water exceeds a preset threshold water amount and the detected differential pressure of the differential pressure sensor increases to satisfy a predetermined passage blockage determination condition, the return of the high-pressure side exhaust gas is returned. Recirculation ratio control means for increasing the recirculation amount of the high-pressure side exhaust gas so as to reduce the ratio of the recirculation amount of the low-pressure side exhaust gas to the flow rate.

  In the present invention, when the amount of condensed water in the low-pressure side exhaust recirculation path exceeds the threshold water amount and the detected differential pressure of the differential pressure sensor increases to satisfy a predetermined passage blockage determination condition, the high-pressure side exhaust gas Thus, the ratio of the recirculation amount of the low-pressure side exhaust gas to the recirculation amount of the high-pressure side exhaust gas decreases. Therefore, it is possible to accurately detect a state in which the condensed water adhering to the filter forms a water film and the exhaust gas recirculation pipe section is blocked on the upstream side, and the exhaust gas recirculation amount on the high pressure side with respect to the required amount. Therefore, the amount of recirculation of the exhaust gas on the low pressure side becomes smaller as the value of the exhaust gas increases.For example, it is possible to suppress the increase in the condensed water while ensuring the required exhaust gas recirculation amount until the internal combustion engine is warmed up or the cooling water temperature rises. Therefore, it is possible to achieve both suppression of the generation of condensed water and ensuring of the NOx reduction effect.

  In the exhaust gas recirculation system for an internal combustion engine of the present invention, preferably, (2) the recirculation ratio control means has an amount of the condensed water estimated by the condensed water amount estimating means exceeding a preset threshold water amount, In addition, when the detected differential pressure of the differential pressure sensor increases to satisfy a predetermined passage blockage determination condition, the recirculation amount of the low-pressure side exhaust gas is decreased according to the amount of the condensed water, and the exhaust gas The recirculation amount of the exhaust gas on the high pressure side is increased so as to compensate for the decrease in the recirculation amount. As a result, the amount of condensed water generated can be accurately reduced without unnecessarily reducing the recirculation amount of the exhaust gas on the low pressure side, and both the suppression of the generation of condensed water and the securing of the NOx reduction effect can be achieved at the same time. be able to.

  In the exhaust gas recirculation system for an internal combustion engine according to the present invention, (3) the recirculation ratio control means rapidly increases the detected differential pressure of the differential pressure sensor at a rate greater than a preset threshold rate of increase per unit time. It is preferable that when it increases, it is determined that the predetermined passage blockage determination condition has been increased. In this case, if the condensed water adheres to the filter and forms a water film to close the exhaust gas recirculation passage, the detected differential pressure of the differential pressure sensor increases rapidly, so that the occurrence of the closed state can be determined. When the ratio of the low-pressure side exhaust gas recirculation amount is reduced so as to suppress the amount of condensed water generated, the low-pressure side exhaust gas recirculation passage can be restored from the closed state by the water film to the normal open state.

  In the exhaust gas recirculation system for an internal combustion engine according to the present invention, (4) the recirculation ratio control means increases the differential pressure detected by the differential pressure sensor so that the differential pressure detected by the differential pressure sensor is greater than or equal to a predetermined magnification with respect to a preset normal differential pressure. It is also preferable to determine that it has increased so as to satisfy the predetermined passage blockage determination condition. In this case as well, if condensed water adheres to the filter and forms a water film to block the exhaust gas recirculation passage, the detected differential pressure of the differential pressure sensor exceeds the normal differential pressure by a predetermined factor, and the occurrence of the blocked state can be determined. It becomes. When the ratio of the low-pressure side exhaust gas recirculation amount is reduced so as to suppress the amount of condensed water generated, the low-pressure side exhaust gas recirculation passage can be restored from the closed state by the water film to the normal open state.

  In the exhaust gas recirculation system for an internal combustion engine according to the present invention, (5) the control device increases the specific exhaust component in the exhaust gas of the internal combustion engine that increases as the recirculation amount of the exhaust gas on the high pressure side increases. It is preferable to further include constraint condition determining means for selectively restricting the recirculation amount of the high-pressure side exhaust gas based on the concentration of the specific exhaust component so that the concentration of the exhaust gas falls within an allowable range. With this configuration, even if the exhaust gas recirculation amount on the high-pressure side increases, the emission amount of the specific exhaust components associated therewith is suppressed within an allowable range, and other exhaust emissions deteriorate to ensure the NOx reduction effect. Is prevented.

  In the exhaust gas recirculation system for an internal combustion engine of the present invention, (6) the turbocharger having an intake air compressor and an exhaust turbine is mounted on the internal combustion engine, and the compressor is connected to the intake of the turbocharger. It is preferable that the resistance element is constituted by the exhaust turbine of the turbocharger. With this configuration, even when a large amount of exhaust gas recirculation is executed in response to severe NOx reduction requirements, the exhaust gas energy passing through the low pressure side exhaust gas recirculation path ensures a sufficient number of revolutions of the exhaust turbine, and the vehicle travels. Good acceleration response at the time can be obtained.

  In the exhaust gas recirculation system for an internal combustion engine of the present invention, (7) the resistance element may be configured by an exhaust gas purification unit that purifies exhaust gas passing through the exhaust pipe. With this configuration, even when a supercharger other than the turbocharger is used, it is possible to achieve both suppression of the generation of condensed water and securing of an NOx reduction effect.

  According to the present invention, when the amount of condensed water in the low-pressure side exhaust recirculation path exceeds the threshold water amount and the detected differential pressure of the differential pressure sensor increases to satisfy the predetermined passage blockage determination condition, Since the exhaust gas recirculation amount is increased so that the ratio of the low pressure exhaust gas recirculation amount to the high pressure exhaust gas recirculation amount decreases, the condensed water adhering to the filter forms a water film. A state in which the exhaust gas recirculation pipe portion is blocked on the upstream side can be accurately detected, and the recirculation amount of the low pressure side exhaust gas decreases as the recirculation amount of the high pressure side exhaust gas increases with respect to the required amount. Therefore, it is possible to suppress the increase of the condensed water while ensuring the required exhaust gas recirculation amount until the internal combustion engine is in an operation state in which the condensed water is difficult to be generated. To ensure both It is possible to provide an exhaust gas recirculation system of kill internal combustion engine.

1 is a schematic configuration diagram of an exhaust gas recirculation system for an internal combustion engine according to a first embodiment of the present invention. It is a block block diagram of the control system of the internal combustion engine which concerns on 1st Embodiment of this invention. It is explanatory drawing of the map used for calculation of the amount of condensed water taken away performed with the control apparatus in the exhaust gas recirculation system of the internal combustion engine which concerns on 1st Embodiment of this invention. It is explanatory drawing of reduction operation of the low voltage | pressure EGR flow rate at the time of LP clogging in the exhaust gas recirculation system of the internal combustion engine which concerns on 1st Embodiment of this invention. It is explanatory drawing of the conditions which add restrictions to the increase in HP flow volume (high pressure side exhaust gas recirculation amount) in LP flow rate ratio control performed with the control apparatus in the exhaust gas recirculation system of the internal combustion engine which concerns on 1st Embodiment of this invention. . It is a flowchart of the control program for LP flow ratio control performed with the control apparatus in the exhaust gas recirculation system of the internal combustion engine which concerns on 1st Embodiment of this invention. It is explanatory drawing of the state change of the system in LP flow ratio control performed with the control apparatus in the exhaust gas recirculation system of the internal combustion engine which concerns on 1st Embodiment of this invention. It is a flowchart of the control program for LP flow ratio control performed with the control apparatus in the exhaust gas recirculation system of the internal combustion engine which concerns on 2nd Embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
1 to 6 show a first embodiment of an exhaust gas recirculation system for an internal combustion engine according to the present invention. This embodiment is an in-line four-cylinder diesel engine 10 (a multi-cylinder internal combustion engine). Hereinafter, it is simply applied to the engine 10).

  As shown in FIG. 1, the engine 10 of the present embodiment has a plurality of cylinders 11 in a main body block 10M. The engine 10 includes combustion chambers (details are not shown) in each cylinder 11. A common rail fuel injection device 12 for injecting fuel into the combustion chamber, an intake device 13 for inhaling air into the combustion chamber, an exhaust device 14 for exhausting exhaust gas from the combustion chamber, and exhaust energy in the exhaust device 14 Then, the turbocharger 15 that compresses the intake air in the intake device 13 and supercharges the air into the combustion chamber, and returns a part of the high-pressure side exhaust gas upstream from the turbocharger 15 to the intake side. HPL-EGR device 16 (high pressure EGR device) that is recirculated and recirculated, and LPL-EGR device 17 (low pressure) that recirculates a part of the exhaust gas on the low pressure side downstream from the turbocharger 15 to the intake side. EGR device Door is equipped with.

  The fuel injection device 12 includes a supply pump 21 that pumps fuel from a fuel tank (not shown), pressurizes the fuel to a high fuel pressure (fuel pressure), and discharges the fuel, a common rail 22 into which fuel from the supply pump 21 is introduced, and the common rail And a fuel injection valve 23 for injecting fuel supplied through the combustion chamber 23 at a timing and opening degree (duty ratio) corresponding to an injection command signal from an ECU (electronic control unit) 50 described later. . The supply pump 21 is driven using, for example, the rotational power of the engine 10, and the common rail 22 distributes and supplies the high-pressure fuel supplied from the supply pump 21 to the plurality of fuel injection valves 23 while maintaining a uniform pressure. . The fuel injection valve 23 is composed of a known needle valve that is electromagnetically driven, and burns an amount of fuel (for example, light oil) according to the injection command signal by controlling the valve opening time according to the injection command signal. Can be injected and supplied indoors.

  The intake device 13 includes an intake manifold 31, an intake pipe 32 upstream of the intake manifold 31, an air cleaner 33 that cleans intake air by a filter at the most upstream portion of the intake pipe 32, and a downstream side of the turbocharger 15. An intercooler 34 (intermediate cooler) that cools the supercharged air heated by compression by the intake air compressor 15a in the intake pipe portion 32b, an air flow meter 35 that detects the intake flow rate of fresh air, A throttle valve 36 for adjusting the intake air amount and an intake air temperature sensor 37 (see FIG. 2) for detecting the intake air temperature upstream of the intake manifold 31 are mounted.

  The exhaust device 14 includes an exhaust manifold 41, an exhaust pipe 42 downstream from the exhaust manifold 41, an exhaust throttle valve 43 that can increase the exhaust temperature during idling and can control the back pressure of the LPL-EGR device 17, An exhaust purification unit 44 comprising a known oxidation catalytic converter and a diesel particulate filter (DPF) mounted on an exhaust pipe 42 downstream of the turbocharger 15 and the temperature of exhaust gas that has passed through the exhaust purification unit 44 are detected. And an exhaust gas temperature sensor 47.

  The turbocharger 15 includes an intake air compressor 15a and an exhaust turbine 15b that are integrally coupled to each other in the rotational direction. The intake air compressor 15a is rotated by rotating the exhaust turbine 15b and exhaust air compressor 15a by exhaust energy. The intake air can be compressed by the compressor 15 a to supply positive pressure air into the engine 10.

  The HPL-EGR device 16 is mounted between the HPL-EGR pipe 61 and the HPL-EGR pipe 61 interposed between the exhaust manifold 41 and the intake pipe 32, and adjusts the recirculation amount of the exhaust gas. HPL-EGR valve 62 that can be used.

  The HPL-EGR pipe 61 includes an upstream exhaust pipe portion 42a upstream of the exhaust turbine 15b or the exhaust manifold 41 in the exhaust passage in the exhaust pipe 42, and a downstream side of the intake air compressor 32a in the intake pipe 32. The downstream side intake pipe portion 32b or the interior of the intake manifold 31 is communicated, and the exhaust gas on the high pressure side, which has a high pressure upstream from the exhaust turbine 15b as a resistance element, is recirculated immediately before or inside the intake manifold 31 of the engine 10. The recirculated exhaust gas can be sucked into the engine 10 together with the air supercharged from the suction air compressor 15a side. The HPL-EGR pipe 61 and the intake manifold 31 and the exhaust manifold 41 form a high-pressure side exhaust recirculation path L1 for recirculating the high-pressure side exhaust gas to the engine 10 and the high-pressure side exhaust recirculation path L1 therein. The high-pressure side exhaust gas recirculation passage 61w is formed. The HPL-EGR valve 62 has an open state in which the high-pressure side exhaust gas recirculation passage 61w in the HPL-EGR pipe 61 is opened, and a closed state in which the opening of the high-pressure side exhaust gas recirculation passage 61w is restricted (for example, shut off). It is possible to switch to.

  The LPL-EGR device 17 includes an LPL-EGR pipe 71 (low-pressure side exhaust gas recirculation pipe portion) interposed between the exhaust pipe 42 and the intake pipe 32 and an exhaust gas that is mounted in the middle of the LPL-EGR pipe 71. An LPL-EGR valve 72 capable of adjusting the recirculation amount of the gas, an LPL-EGR cooler 73 as an exhaust cooler capable of cooling the exhaust gas passing through the LPL-EGR pipe 71, and an LPL- The foreign substance collection filter 74 located upstream of the EGR cooler 73 in the exhaust gas recirculation direction and the cross-sectional area of the exhaust gas passage 42w in the exhaust pipe 42 downstream of the exhaust gas purification unit 44 in the downstream thereof. The above-described exhaust throttle valve 43 that can reduce the opening degree so as to throttle is provided.

  The LPL-EGR pipe 71 communicates a downstream exhaust pipe portion 42b downstream of the exhaust turbine 15b in the exhaust pipe 42 and an upstream intake pipe portion 32a upstream of the intake air compressor 15a in the intake pipe 32, With the exhaust turbine 15b as a resistance element, low-pressure exhaust gas having a low pressure downstream can be recirculated into the upstream intake pipe portion 32a, and the recirculated exhaust gas can be recirculated to the upstream intake pipe. After being compressed by the intake air compressor 15a together with the intake air introduced into the portion 32a, the engine 10 can be re-inhaled.

  Further, the LPL-EGR pipe 71 is located upstream of the intake pipe 32 downstream of the position J1 where the LPL-EGR pipe 71 is connected to the intake pipe 32 and the position J2 where the LPL-EGR pipe 71 is connected to the exhaust pipe 42. The low-pressure side exhaust gas recirculation path L2 for recirculating the low-pressure side exhaust gas to the engine 10 is formed together with the exhaust pipe 42, and the low-pressure side exhaust gas recirculation path forming the main part of the low-pressure side exhaust gas recirculation path L2 therein. 71w is formed.

  The LPL-EGR valve 72 is a valve that is disposed between the LPL-EGR cooler 73 and the upstream side intake pipe portion 32a of the intake pipe 32 and controls the recirculation amount of the low-pressure side exhaust gas, and can be opened / closed and opened. Thus, it is possible to switch between a valve-opening state in which the low-pressure side exhaust gas recirculation passage 71w is opened and a valve-closing state in which the opening of the low-pressure side exhaust gas recirculation passage 71w is restricted (for example, shut off).

  Although not shown in detail, the LPL-EGR cooler 73 has a gas pipe part that forms a part of the low-pressure side exhaust recirculation passage 71w, and a housing part that forms a cooling fluid passage around the gas pipe part. The low-pressure side recirculation is achieved by heat exchange between the cooling fluid (for example, engine cooling water) introduced into the housing portion and the recirculated exhaust gas passing through a part of the low-pressure side exhaust recirculation passage 71w in the gas pipe portion. The exhaust gas can be cooled.

  The foreign matter collecting filter 74 is a fine mesh mesh called a FOD (Foreign Object Damage) filter. The foreign matter collecting filter 74 is a foreign matter contained in the recirculated exhaust gas that has passed through the exhaust purification unit 44, such as spatter (scattering material during welding), In order to prevent foreign matter such as falling pieces from the exhaust purification unit 44 from entering the intake air compressor 15a of the turbocharger 15 and causing damage, the foreign matter is removed from the LPL-EGR cooler 73 in the exhaust gas recirculation direction. It is collected on the upstream side and removed from the recirculated exhaust gas.

  The intercooler 34 is provided with supercharged air (ascended by compression) in the third section downstream of the intake air compressor 15a in the low pressure side exhaust recirculation path L2 formed by the LPL-EGR device 17. (Warm air) is cooled. Although not shown in detail, the intercooler 34 is provided with a gas pipe part that forms a part of the third section of the intake passage 32w that becomes a part of the low-pressure side exhaust gas recirculation path L2, and a cooling pipe around the gas pipe part. And a heat exchange between a cooling fluid (for example, engine coolant) introduced into the housing portion and a low-pressure side recirculated exhaust gas passing through the gas pipe portion, The reflux exhaust gas on the low pressure side can be cooled.

  The HPL-EGR device 16 and the LPL-EGR device 17 are controlled by the ECU 50 (control device), which is an electronic control unit, to control the opening / closing operation and the opening degree of the HPL-EGR valve 62 and the LPL-EGR valve 72. The recirculation amount of the high-pressure side exhaust gas to the side intake pipe portion 32b (hereinafter also referred to as HP flow rate) and the recirculation amount of the low-pressure side exhaust gas to the upstream side intake pipe portion 32a of the intake pipe 32 (hereinafter also referred to as LP flow rate). ) And to be controlled by each.

  Although the detailed hardware configuration is not illustrated, the ECU 50 is a nonvolatile memory such as a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an EEPROM (Electronically Erasable and Programmable Read Only Memory), An input interface circuit having an A / D converter, a buffer, and the like, and an output interface circuit having a drive circuit and the like are included. The ECU 50 controls the operation of the engine 10, for example, discharge control of the supply pump 21 (for example, control of the electromagnetic spill valve), fuel injection amount control by the fuel injection valve 23, opening control of the throttle valve 36, HPL- The opening degree (EGR rate) control of the EGR valve 62 and the LPL-EGR valve 72, the opening degree control of the exhaust throttle valve 43, and the like are executed.

  As shown in FIG. 2, in addition to the air flow meter 35, the intake air temperature sensor 37, and the exhaust gas temperature sensor 47, the ECU 50 includes an accelerator opening sensor 101 that detects depression of an accelerator pedal (not shown), and the opening of the throttle valve 36. A throttle opening sensor 102 that detects a crank angle, a crank angle sensor 103 that outputs a crankshaft rotation signal in a predetermined angle unit, a water temperature sensor 104 that detects a cooling water temperature of the engine 10, and a supercharging pressure of the engine 10 near the inlet of the intake manifold 31 An intake pipe pressure sensor 105 for detecting the outside air temperature sensor 106 for detecting the outside air temperature, a differential pressure sensor 107 for detecting a differential pressure between both ends (positions j1 and j2 in FIG. 1) of the low pressure side exhaust recirculation passage 71w, A vehicle speed sensor 108 or the like that detects the traveling speed or wheel rotation speed of the vehicle on which the engine 10 is mounted is provided. Is connected, sensor information from these sensors 35,37,47 and 101-108 is adapted to be incorporated into the ECU 50. On the other hand, the ECU 50 has a supply pump 21 (for example, an electromagnetic spill valve), a plurality of fuel injection valves 23, a throttle valve 36, an HPL-EGR valve 62, an LPL-EGR valve 72 ( Specifically, these electromagnetic drive units (no reference) are connected to each other. Further, the ECU 50 reads the acceleration request from the accelerator opening sensor 101 taken into the input interface circuit, the engine speed from the crank angle sensor 103, and the like at predetermined time intervals to inject fuel into the combustion chamber of the engine 10. An arithmetic processing program, a map and the like for calculating the quantity and the like are stored.

  By the way, in the engine 10 of this embodiment, the HPL-EGR device 16 and the LPL-EGR device 17 cause the exhaust gas to recirculate from the exhaust pipe 42 side to the intake pipe 32 side and be sucked into the engine 10 again. A path L1 and a low-pressure side exhaust recirculation path L2 are formed, and the exhaust gas in the low-pressure side exhaust recirculation path L2 is cooled by the LPL-EGR cooler 73, and an intake air compressor in the intake passage in the intake pipe 32 The supercharged air downstream from 15a is cooled by the intercooler 34. Therefore, in particular, the LPL-EGR cooler 73 and the intercooler 34 cool the recirculated exhaust gas and the intake air mixed therewith (hereinafter referred to as both EGR gas), and the water in the EGR gas is cooled. Acidic condensed water is likely to be generated.

  Therefore, the ECU 50 that controls the HPL-EGR device 16 and the LPL-EGR device 17 exhibits the functions of a condensed water amount estimation unit 51 (condensed water amount estimation unit) and a reflux ratio control unit 52 (reflux rate control unit) described below. As described above, control programs corresponding to these functional units are incorporated in the ROM.

  The condensate amount estimation unit 51 estimates the amount of condensate in the low-pressure side exhaust recirculation path L2 formed by the LPL-EGR device 17, and specifically, of the low-pressure side exhaust recirculation path L2. The amount of condensed water is estimated at least in the vicinity of the foreign matter collecting filter 74 and in the vicinity of the gas outlet of the LPL-EGR cooler 73 that cools the recirculated exhaust gas.

  This condensate amount estimation unit 51 estimates a rough value of the amount of condensate generated in the low-pressure side exhaust recirculation path L2 by a known method, for example, according to a low temperature continuation time during which the exhaust pipe temperature is lower than a predetermined value. (For example, refer to Japanese Patent Laid-Open No. 2007-205303), or to calculate / estimate the amount of condensed water in consideration of the tube wall temperature or the like (for example, refer to Japanese Patent Laid-Open No. 2009-228564). However, it is preferable that the amount of condensed water can be estimated accurately and stably while suppressing the processing load of the ECU 50 and the device cost.

  Specifically, the condensate amount estimation unit 51 calculates and estimates, for example, the amount of condensate generated using a calculation model stored in advance in the ROM, and at each unit time in the target section of the first to third sections. Out of the amount of condensed water Qw1 generated (see FIG. 3), the amount of condensed water Qw2 taken away downstream is estimated from the map M1 created based on the previous experimental results and the sensor information as its argument to generate condensed water A condensed water amount (hereinafter referred to as a condensed water amount Qwa) that is actually generated by subtracting the estimated value of the amount Qw2 from the estimated value of the amount Qw1 is calculated and estimated.

  More specifically, as shown in FIG. 3, the map M1, for example, is the amount of condensed water taken away that tends to increase corresponding to an increase in the recirculation amount of the low-pressure side exhaust gas that exclusively passes through the target section every unit time. Qw2 is obtained by a prior experiment for each of the first to third sections, or is configured with a map that can estimate the amount of condensed water more accurately by including the low-pressure EGR gas temperature as an argument, or The map is made up of a combination of calculation formulas for calculating the amount of condensed water taken away in other sections based on the map created from the experimental results for a specific section. Here, the low-pressure side exhaust gas recirculation amount (LP flow rate) per unit time can be calculated from the detection value of the differential pressure sensor 107, for example.

In the calculation of the condensate generation amount Qw1 by the calculation model in the condensate amount estimation unit 51, first, based on the outside air temperature and atmospheric pressure, the temperature and pressure of the intake air near the inlet of the intake manifold 31, etc. The amount of moisture in the air (steam / air (mol%) = water vapor pressure / atmospheric pressure) and dew point temperature are calculated, and the composition of the intake air (each gas molecule (N ₂ , O ₂ , Ar) and water (H ₂ ) O) molar ratio), and based on the mass of known fuel and intake air composition components and the air-fuel ratio determined from the intake air amount obtained as sensor information and the fuel injection amount grasped as the control value, A model in which the molecular weight of the gas before and after combustion is expressed as the sum of the product of the molar ratio of each component in the gas and the mass (indicated by the values and symbols in parentheses in the following formula), for example, the molecular weight of the gas before combustion = (1) ・ CHx (1 + x / 4 + a) .O2 + (b) .N2 + (c) .Ar + (d) .H2O. The molecular weight of the burned gas, that is, the gas after combustion. = (1) .CO2 + (x / 2 + d) .H2O + ( a) · O2 + (b) · N2 + (c) · Ar, and based on the vapor pressure, molecular weight, density, etc. of the burned gas obtained from the calculation results and the detected values of the temperature and pressure of the burned gas, Calculate the amount of water in the burnt gas (absolute humidity of the burnt gas). The condensed water amount estimation unit 51 collects foreign matter as a difference between the amount of moisture in the burned gas and the amount of moisture in the burned gas having a relative humidity of 100% under the cooling condition in the LPL-EGR cooler 73. The amount of condensed water generated Qw1 in the vicinity of the gas outlet of the filter 74 is calculated.

  The recirculation ratio control unit 52 is preset by the condensate amount estimation unit 51 and is taken away from the condensate generation amount calculation value Qw1 for each unit period in a calculation cycle, and the actual condensate amount Qwa [g] is obtained by subtracting the condensate amount Qw2. / S] is calculated, the condensed water amount Qwa is compared with a threshold water amount α set based on a previous experimental result, and whether the condensed water amount Qwa exceeds the threshold water amount α or not. Accordingly, it is determined whether or not the low pressure side exhaust gas recirculation passage 71w is an amount of condensed water that may cause a clogged state in which the water film of the condensed water adhering to the foreign matter collecting filter 74 is blocked.

  Here, the threshold water amount α is such that condensed water adheres when the recirculated exhaust gas flows into the low pressure side exhaust recirculation passage 71w through the foreign matter collecting filter 74, and due to the surface tension, the foreign matter collecting filter 74 collects the foreign matter. It is set as the amount of condensed water when a water film of a certain area or more is formed on the surface. This threshold water amount α may be a fixed value based on a previous experimental result, or may be a map value corresponding to the rotational load of the engine 10. When the condensed water amount Qwa exceeds the threshold water amount α, the LPL-EGR device 17 of the engine 10 is in a state where the opening degree of the LPL-EGR valve 72 is exclusively large or the opening degree of the exhaust throttle valve 43 is small.

  The reflux ratio control unit 52 also determines that the detected differential pressure of the LP differential pressure sensor 107 satisfies a predetermined passage blockage determination condition when the current condensed water amount Qwa calculated and estimated by the condensed water amount estimation unit 51 exceeds the threshold water amount α. It is determined whether or not it has been increased to satisfy.

  The predetermined passage blockage determination condition mentioned here is, for example, a rapid increase with a rate of increase in which the differential pressure detected by the LP differential pressure sensor 107 is greater than a preset threshold increase rate β (eg, 0.4 kPa / 60 sec) per unit time. Clogged state in which the low pressure side exhaust recirculation passage 71w is blocked by a water film or the like formed on the foreign matter collecting filter 74 and the pressure loss is increased when the time to increase is continued for a certain time (for example, 60 seconds) or longer This is a determination condition for determining that it is (hereinafter also referred to as an LP clogged state).

  In addition, what increases the pressure loss in the low-pressure side exhaust gas recirculation passage 71w by adhering condensed water or forming a water film is not limited to the foreign matter collecting filter 74. Other members arranged may be used. The reflux ratio control unit 52 is not based on the detected differential pressure of the LP differential pressure sensor 107 but based on the detected differential pressure of the differential pressure sensor that can directly detect the differential pressure across the foreign matter collecting filter 74. It may be determined whether or not the pressure has increased to satisfy a predetermined passage blockage determination condition.

  The recirculation ratio control unit 52 further determines that the current condensate amount Qwa exceeds the threshold amount of water α, and the detected differential pressure of the LP differential pressure sensor 107 satisfies a predetermined passage blockage determination condition when the LPL-EGR valve 72 is open. When it is determined that the increase has been satisfied, the return of the low-pressure side exhaust gas in the low-pressure side exhaust recirculation passage 71w with respect to the recirculation amount of the high-pressure side exhaust gas in the high-pressure side exhaust recirculation passage 61w (hereinafter also referred to as HP flow rate). In order to reduce the LP flow rate ratio, which is the ratio of the flow rate (hereinafter also referred to as LP flow rate), the LP flow rate is reduced according to the condensed water amount Qwa (see FIG. 4), and the decrease in the LP flow rate is compensated. The HP flow rate is increased.

  That is, when the condensed water amount Qwa is in an LP clogged state where the condensed water amount Qwa exceeds the threshold water amount α, the reflux ratio control unit 52 suppresses the condensed water amount Qwa to the threshold water amount α so that the threshold LP flow rate X ( 4), and the reduction in the NOx reduction effect in the LPL-EGR device 17 and the HPL-EGR device 16 due to the decrease in the LP flow rate up to the threshold LP flow rate X is reduced to the threshold LP flow rate X. The increase amount of the HP flow rate is changed according to the decrease amount of the LP flow rate, and the LP flow rate ratio, which is the ratio of the LP flow rate to the HP flow rate, is variably controlled to a suitable reduction ratio. When the LP flow rate is decreased to the threshold LP flow rate X, the opening degree of the LPL-EGR valve 72 is reduced, the exhaust throttle valve 43 is opened, or both are executed. Further, the threshold LP flow rate X is fixed at, for example, the base opening of the LPL-EGR valve 72, which is an appropriate value during steady running, or is fixed at the fully closed position. The base opening here is, for example, a cylinder intake gas amount calculated from the detected pressure of the intake pipe pressure sensor 105, which is a supercharging pressure sensor, and an estimated intake temperature, and an intake air amount obtained from a detected value of the air flow meter 35. (The amount of fresh air) can be estimated by calculating the LP flow rate value that is the difference between the two, or can be estimated by pre-mapped data as a decrease value of the LP flow rate corresponding to the condensed water amount Qwa. Good.

  The ECU 50 further incorporates a control program corresponding to this function unit in the ROM so as to exhibit the function of the next constraint condition determination unit 53 (constraint condition determination means).

  For example, the constraint condition determination unit 53 causes the concentration value of the specific exhaust component in the exhaust gas of the engine 10 that shows an increasing tendency as the recirculation amount of the exhaust gas on the high pressure side increases to be within the allowable range. According to the constraint condition, the recirculation amount of the exhaust gas on the high pressure side can be selectively reduced based on the operating condition of the engine 10 when the concentration of the specific exhaust component reaches a preset constraint value. Yes.

  More specifically, as shown in FIG. 5, for example, the constraint condition determination unit 53 determines the intake air temperature in the intake manifold 31 under operating conditions in which the engine speed, the fuel injection amount, and the oxygen concentration in the intake air are constant. The smoke component concentration value is determined by the map M2 shown in FIG. 2 (which may be a known simple soot model) so that the smoke component concentration value (FSN: Filter Smoke Number) showing a tendency to increase as the value increases. The intake air temperature in the intake manifold 31 is set to the high-pressure side under the constraint that the calculated value is calculated every predetermined time and the calculated value does not exceed the intake air temperature when reaching the constraint value (for example, smoke FSN = 1). The recirculation amount of the exhaust gas is appropriately limited.

  Of course, the specific emission component mentioned here may be HC (hydrocarbon) instead of smoke, or may include both (multiple types of emission components). In the following description, the constraint condition determination unit 53 sets a constraint condition that the concentration values of both smoke and HC are within the allowable range as the specific emission component, and the high pressure side according to the constraint condition. The exhaust gas recirculation amount is selectively reduced.

  Next, the operation will be described.

  FIG. 6 is a flowchart showing a schematic processing procedure of a control program executed by the ECU 50 at predetermined time intervals for the LP flow rate control. This control program demonstrates the functions of the condensate amount estimation unit 51, the recirculation ratio control unit 52, and the constraint condition determination unit 53 in parallel with the control program for causing the ECU 50 to execute the control of the fuel injection amount described above. Therefore, it is repeatedly executed every predetermined time or every predetermined time during the period when the coolant temperature of the engine 10 is equal to or lower than the predetermined temperature.

  As shown in FIG. 6, in this control, first, sensor information from the various sensor groups 35, 37, 47 and 101 to 108 is taken into the ECU 50, and the operating state of the engine 10 is acquired (step S11). .

  Next, the actual amount of condensed water Qwa generated this time is calculated by subtracting the amount of condensed water Qw2 that is taken away from the amount of condensed water generated Qw1 for each unit period and calculated in advance by the condensed water amount estimation unit 51 (step S12).

  Next, this condensate water amount Qwa is compared with a threshold water amount α set based on the result of a previous experiment, and according to the result, a clogged state in which a water film of condensate water is formed on the foreign matter collecting filter 74 occurs. It is determined whether or not to obtain (step S13).

  At this time, if the condensed water amount Qwa does not exceed the threshold water amount α (NO in step S13), the process returns to the first step and the above-described processing is started again.

  On the other hand, if the condensed water amount Qwa exceeds the threshold water amount α (in the case of YES in step S13), then, the detected differential pressure of the LP differential pressure sensor 107 is rapidly increased at a rate greater than the threshold rate increase rate β per unit time. It is determined whether or not it has increased, and it is determined whether or not the pressure loss in the low-pressure side exhaust recirculation passage 71w is suddenly rising due to a water film or the like formed on the foreign matter collecting filter 74 (step) S14).

  At this time, if the increase rate per unit time of the differential pressure detected by the LP differential pressure sensor 107 does not exceed the threshold increase rate β (in the case of NO in step S14), the process returns to the first step and the above processing is performed again. Start.

  On the other hand, if the increase rate per unit time of the differential pressure detected by the LP differential pressure sensor 107 exceeds the threshold increase rate β (in the case of YES in step S14), a water film or the like formed on the foreign matter collecting filter 74 Thus, it is determined that an LP clogged state has occurred in the low pressure side exhaust gas recirculation passage 71w (step S15), and control of the LP flow rate ratio with the following steps is started.

  Here, an example of the operating state of the system when the LP clogging state occurs will be described with reference to FIG.

  First, as shown by a solid line in FIG. 7B, the LPL-EGR valve 72 is gradually opened to a certain opening degree every predetermined time t (for example, about 20 seconds), and the LP flow rate is increased. Then, the amount of EGR on the low pressure side increases, and the amount of condensed water Qwa generated in the low pressure side exhaust gas recirculation passage 71w increases. The amount of condensed water adhering to the foreign matter collecting filter 74 increases, and the surface tension of the condensed water is relatively short (for example, about 1 to 2 minutes) from the increase in the LP flow rate due to the opening of the LPL-EGR valve 72. As a result, a water film starts to stick to the foreign matter collecting filter 74. At this time, as indicated by a solid line in FIG. 7C, the temperature of the exhaust gas in the low-pressure side exhaust recirculation passage 71w has increased due to a decrease in the HP flow rate or as the engine 10 warms up. The temperature rapidly drops from the temperature T1 (the gas temperature after passing through the exhaust purification unit 44) to the gas temperature T2 after passing through the foreign matter collecting filter 74 covered with a water film.

  In such a state, a water film gradually stretches on the foreign matter collecting surface of the foreign matter collecting filter 74, so that the differential pressure across the foreign matter collecting filter 74 (see FIG. 7D) as indicated by an arrow A1. In the figure, the FOD differential pressure) starts to increase, and when a water film is formed on almost the entire surface of the foreign matter collecting surface of the foreign matter collecting filter 74, as shown by arrows A2 and A3 in FIG. The differential pressure across the collection filter 74 increases rapidly.

  When the differential pressure across the foreign matter collecting filter 74 increases rapidly as indicated by an arrow A1 or A2, the detected differential pressure of the LP differential pressure sensor 107 shows a similar upward trend, so that the detection of the LP differential pressure sensor 107 is performed. It is determined that the increase rate of the differential pressure per unit time exceeds the threshold increase rate β, and the LP clogged state has occurred in the low pressure side exhaust recirculation passage 71w (step S15).

  In the present embodiment, after such an LP clogging occurrence determination (step S15), the control of the LP flow rate ratio with the following steps is executed.

  First, the opening degree of the LPL-EGR valve 72 that has been operated to generate the condensed water amount Qwa exceeding the threshold water amount α is fixed (step S16). If the opening degree of the exhaust throttle valve 43 is reduced while the opening degree of the LPL-EGR valve 72 is fixed, the opening degree of the exhaust throttle valve 43 is fixed.

  Next, in order to suppress the condensed water amount Qwa to a value up to the threshold water amount α, a threshold LP flow rate X corresponding to the threshold water amount α is calculated, and a decrease amount of the LP flow rate from the current LP flow rate is calculated (step S17). In order to suppress the decrease in the NOx reduction effect in the LPL-EGR device 17 and the HPL-EGR device 16 due to the decrease in the LP flow rate up to the threshold LP flow rate X, this is compensated according to the decrease amount (decrease amount) in the LP flow rate. An increase amount of the HP flow rate is calculated (step S18). Then, according to these calculated values, the ECU 50 indicates the opening degrees of the HPL-EGR valve 62 and the LPL-EGR valve 72 by the opening degrees Vb, indicated by thick dotted lines in FIGS. 7 (a) and 7 (b). Change to Va.

  In this state, the foreign matter collecting filter 74 is heated by heat received from the case of the exhaust purification unit 44 having a large heat capacity, and the gas temperature in the vicinity of the foreign matter collecting filter 74 is as shown in FIG. It shows a rising tendency like a gas temperature T3 that gradually increases from the gas temperature T2 until then.

  Then, due to such a rise in exhaust gas temperature, a rise in the temperature of the foreign matter collecting filter 74, a decrease in the amount of condensed water generated in the low pressure side exhaust recirculation passage 71w, etc., as shown by a thick dotted line in FIG. The differential pressure across the collection filter 74 starts to decrease, and the clogged state of the low pressure side exhaust recirculation passage 71w begins to be eliminated.

  Next, the restriction condition determination unit 53 determines whether the smoke component or the concentration value of HC in the exhaust gas does not exceed the restriction value (step S19). If the smoke component or the concentration value of HC in the exhaust gas does not exceed the restriction value (YES in step S19), the current process is terminated.

  On the other hand, when it is determined that the smoke component or HC concentration value in the exhaust gas exceeds the restriction value (NO in step S19), then the smoke component or HC concentration value in the exhaust gas is the restriction value. The increase amount of the HP flow rate is corrected to a small value so as to become the following. At this time, the total EGR flow rate, which is the sum of the low pressure side exhaust gas recirculation amount and the high pressure side exhaust gas recirculation amount, is reduced, and the NOx reduction effect is somewhat reduced, but the exhaust purification performance is increased by the increase of smoke components and HC in the exhaust gas. It is possible to avoid the damage.

  Thus, in the exhaust gas recirculation system of the present embodiment, the condensed water amount Qwa in the low pressure side exhaust recirculation path L2 exceeds the threshold water amount α, and the detected differential pressure of the LP differential pressure sensor 107 is a predetermined passage blockage. When increased to satisfy the determination condition, the HP flow rate is increased and the LP flow rate ratio is decreased. Therefore, when the condensed water adhering to the foreign matter collecting filter 74 or the like forms a water film and an LP clogged state occurs in the low pressure side exhaust recirculation passage 71w in the LPL-EGR pipe 71, the LP clogged state is accurately detected. It becomes possible. Moreover, since the LP flow rate can be reduced as the HP flow rate is increased with respect to the required exhaust gas recirculation amount according to the operating state of the engine 10, the cooling water temperature at which the engine 10 is warmed up or the amount of condensed water is reduced. The amount of condensed water that keeps the LP clogging state can be suppressed while ensuring the required exhaust gas recirculation amount until reaching the value, and it is possible to achieve both suppression of condensed water generation and ensuring of NOx reduction effect. .

  Further, in the present embodiment, the amount of condensed water generated can be accurately reduced to such an extent that the LP clogging state can be avoided without reducing the LP flow rate (the amount of low-pressure exhaust gas recirculation) more than necessary.

  Further, since the reflux ratio control unit 52 determines that the predetermined passage blockage determination condition is satisfied when the detected differential pressure increase rate per unit time of the differential pressure sensor 107 exceeds the threshold increase rate β, the foreign matter collecting filter 74 is determined. When the condensed water adheres to the water and forms a water film to block the exhaust gas recirculation passage, the detected differential pressure of the differential pressure sensor 107 increases rapidly, so that the occurrence of the blocked state is accurately determined. Then, the LP flow rate ratio is reduced so as to suppress the condensate amount Qwa, so that even if the LP clogged state is prevented or the LP clogged state starts to occur, the low pressure side exhaust recirculation passage 71w is It is possible to quickly recover from a partially blocked state by a water film to a normal open state.

  In addition, in the present embodiment, even if the HP flow rate (exhaust gas recirculation amount on the high-pressure side) increases due to the operation of the constraint condition determination unit 53, the discharge amount of the specific exhaust component associated therewith is suppressed within an allowable range. Further, it is possible to prevent other exhaust emissions from deteriorating in order to ensure the NOx reduction effect.

  Further, in the present embodiment, even when a large amount of exhaust gas recirculation is executed in response to a strict NOx reduction request, the rotational speed [rpm of the exhaust turbine 15b is determined by the energy of the exhaust gas passing through the low pressure side exhaust gas recirculation path L2. ] Is sufficiently ensured, so that a good acceleration response during vehicle travel can be obtained.

As described above, in the exhaust gas recirculation system of the present embodiment, the condensed water amount Qwa generated in the low pressure side exhaust gas recirculation path L2 exceeds the threshold water amount α, and the detected differential pressure of the differential pressure sensor 107 is a predetermined passage. Since the HP flow rate is increased and the LP flow rate ratio is reduced when the blockage determination condition is increased, the condensed water adhering to the foreign matter collecting filter 74 or the like forms a water film to form a low pressure side. The state in which the LP clogging state occurs in the exhaust gas recirculation passage 71w can be accurately detected, and the recirculation amount of the exhaust gas on the low pressure side can be reduced as the recirculation amount of the exhaust gas on the high pressure side increases with respect to the required amount. Therefore, it is possible to suppress the increase in the condensed water while ensuring the required exhaust gas recirculation amount until the engine 10 is in an operation state in which the condensed water is difficult to be generated. As a result, it is possible to provide an exhaust gas recirculation system for an internal combustion engine that can simultaneously suppress the generation of condensed water and ensure the NOx reduction effect.
(Second Embodiment)
FIG. 8 is a diagram showing a second embodiment of the exhaust gas recirculation system for an internal combustion engine according to the present invention, and shows a schematic processing procedure of a control program for LP flow rate control executed by the control device. .

  The exhaust gas recirculation system of the second embodiment is the same as that of the first embodiment, except that a part of the processing of the recirculation ratio control unit 52 in the ECU 50 that is a control device is different from the first embodiment. Therefore, only a part of the processing of the reflux ratio control unit 52, which is a difference, will be described below using the components of the first embodiment and the reference numerals of the processing steps shown in FIGS.

  In the present embodiment, the recirculation ratio control unit 52 of the ECU 50 determines that the differential pressure detected by the LP differential pressure sensor 107 is steady when the condensed water amount Qwa calculated and estimated by the condensed water amount estimating unit 51 exceeds the threshold water amount α. When the differential pressure reaches an increased differential pressure that is greater than or equal to a predetermined magnification γ (detected differential pressure / adapted differential pressure> 1) with respect to the normal differential pressure set in advance as the adaptive value in the operating state of the running engine 10, the LP difference It is determined that the detected differential pressure of the pressure sensor 107 has increased to satisfy a predetermined passage blockage determination condition.

  Specifically, as shown in FIG. 8, in the present embodiment, first, the operating state of the engine 10 is acquired (step S <b> 11), and the condensed water for each unit period is preset by the condensed water amount estimation unit 51 and calculated. After the actual amount of condensed water Qwa that has been taken away from the amount of generated Qw1 and subtracted the amount of condensed water Qw2 is calculated (step S12), this amount of condensed water Qwa is compared with a threshold water amount α that is set based on the results of previous experiments. Thus, it is determined whether or not a clogged state where a water film of condensed water is formed on the foreign matter collecting filter 74 can occur (step S13).

  When the condensed water amount Qwa exceeds the threshold water amount α (in the case of YES in step S13), then the ratio (detection difference) between the detected differential pressure of the LP differential pressure sensor 107 and the adaptive differential pressure that is the adaptive value of the normal differential pressure. It is determined whether or not an increased differential pressure exceeding a predetermined magnification γ is reached with respect to (pressure / adapted differential pressure), and the pressure loss in the low-pressure side exhaust recirculation passage 71w is caused by a water film or the like formed on the foreign matter collecting filter 74. It is determined whether or not the state is suddenly rising (step S34).

  At this time, if the magnification of the detected differential pressure of the LP differential pressure sensor 107 with respect to the adaptive differential pressure does not exceed the predetermined magnification γ (NO in step S34), the process returns to the first step and the above-described processing is started again. .

  On the other hand, if the magnification of the detected differential pressure of the LP differential pressure sensor 107 with respect to the adaptive differential pressure exceeds the predetermined magnification γ (in the case of YES at step S34), the pressure is reduced by a water film or the like formed on the foreign matter collecting filter 74. It is determined that an LP clogged state has occurred in the side exhaust gas recirculation passage 71w (step S15), and the above-described control of the LP flow rate ratio (steps S16 to S20) is executed.

  Also in the exhaust gas recirculation system of the present embodiment, the condensed water amount Qwa in the low pressure side exhaust recirculation path L2 exceeds the threshold water amount α, and the detected differential pressure of the LP differential pressure sensor 107 satisfies a predetermined passage blockage determination condition. When such an increase is made, the HP flow rate is increased and the LP flow rate ratio is lowered, so that the same effect as in the first embodiment can be expected.

  In each of the above embodiments, the condensate amount estimation unit 51 calculates the actual condensate amount Qwa for every fixed time. However, a partial amount of the actual condensate generated in the low-pressure side exhaust recirculation path L2 is calculated. The accumulated amount and the stored liquid level may be detected by a sensor to calculate / estimate the amount of condensed water in the target section.

  In each of the above-described embodiments, the turbocharger 15 is mounted on the engine 10, and a resistance element that divides the exhaust passage in the exhaust pipe 42 into a high-pressure side and a low-pressure side is an exhaust of the turbocharger 15. Although the turbine 15b is used, the present invention is also applicable to an internal combustion engine that does not have a turbocharger. For example, the present invention can be applied to a case where the resistance element referred to in the present invention is configured by the exhaust purification unit 44 that purifies exhaust gas passing through the exhaust pipe 42 and the engine 10 does not have the exhaust turbine 15b. Even in the case where such a configuration is adopted, the LP flow rate ratio is accurately reduced when the amount of condensed water increases, and the amount of condensed water generated is suppressed. It is possible to achieve both of these.

  As described above, the exhaust gas recirculation system for an internal combustion engine according to the present invention is such that the amount of condensed water in the low pressure side exhaust gas recirculation path exceeds the threshold water volume, and the detected differential pressure of the differential pressure sensor is a predetermined path. When increasing to satisfy the blockage determination condition, the recirculation amount of the high-pressure side exhaust gas is increased, and the ratio of the recirculation amount of the low-pressure side exhaust gas to the recirculation amount of the high-pressure side exhaust gas is decreased. In addition, it is possible to accurately detect a state in which the condensed water adhering to the filter forms a water film and the exhaust gas recirculation pipe section is blocked on the upstream side, and the exhaust gas recirculation amount on the high-pressure side with respect to the required amount can be detected. The higher the increase, the smaller the recirculation amount of the exhaust gas on the low pressure side, and it is possible to suppress the increase of the condensate while ensuring the required exhaust gas recirculation amount until the internal combustion engine is in an operating state where it is difficult to generate condensate. , Suppressing the generation of condensed water An internal combustion engine that has an effect of providing an exhaust gas recirculation system for an internal combustion engine that can achieve both an Ox reduction effect and suppresses the generation of condensed water in the exhaust gas recirculation path. Useful for engine exhaust gas recirculation systems in general.

10 engines (internal combustion engines, diesel engines)
11 cylinder 15 turbocharger 15a intake air compressor 15b exhaust turbine (resistance element)
16 HPL-EGR equipment (high pressure EGR equipment)
17 LPL-EGR device (low pressure EGR device)
32 Intake pipe 35 Air flow meter 37 Intake temperature sensor 42 Exhaust pipe 43 Exhaust throttle valve 44 Exhaust purification unit (resistance element)
47 Exhaust temperature sensor 50 ECU (electronic control unit, control device)
51 Condensate Estimator (Condensate Estimator)
52 Reflux ratio control unit 53 Restriction condition determination unit 61 HPL-EGR pipe (exhaust gas recirculation pipe portion on high pressure side)
61w High-pressure side exhaust recirculation passage 62 HPL-EGR valve 71 LPL-EGR pipe (low-pressure side exhaust recirculation pipe)
71w Low pressure side exhaust recirculation passage 72 LPL-EGR valve (Low pressure EGR valve)
73 LPL-EGR cooler (exhaust cooler, low pressure EGR cooler)
74 Foreign matter collection filter (filter)
104 Water temperature sensor 105 Intake pipe pressure sensor 107 LP differential pressure sensor (differential pressure sensor)
L1 High pressure side exhaust recirculation path L2 Low pressure side exhaust recirculation path Qwa Actual amount of condensed water (condensed water volume)
α Threshold water volume β Threshold increase rate γ Specified magnification

Claims (7)

A high-pressure side from an exhaust pipe upstream of the resistance element to an intake pipe downstream of the compressor of the internal combustion engine having an intake pipe provided with a supercharging compressor and an exhaust pipe provided with a resistance element serving as an exhaust resistance A high-pressure EGR device having a high-pressure exhaust gas recirculation pipe section for recirculating the exhaust gas, and a low pressure after passing through the resistance element from an exhaust pipe downstream of the resistance element of the internal combustion engine to an intake pipe upstream of the compressor A low-pressure EGR device having a low-pressure exhaust gas recirculation pipe section that recirculates the exhaust gas on the side, and the low-pressure EGR device that passes the exhaust gas recirculated from the exhaust pipe downstream from the resistance element and collects foreign matters mixed in the exhaust gas A filter disposed upstream of the exhaust gas recirculation pipe section in the exhaust gas recirculation direction; a differential pressure sensor for detecting a differential pressure before and after the low pressure exhaust gas recirculation pipe section in the exhaust gas recirculation direction; A control device for controlling the high-pressure EGR device and the low-pressure EGR device based on the detection information of the differential pressure sensor, an internal combustion engine exhaust gas recirculation system with a
The controller is
Condensed water amount estimation means for estimating the amount of condensed water in the low pressure side exhaust gas recirculation path formed by the low pressure EGR device;
When the amount of condensate estimated by the condensate amount estimation means exceeds a preset threshold water amount and the detected differential pressure of the differential pressure sensor increases to satisfy a predetermined passage blockage determination condition, the high pressure Recirculation ratio control means for increasing the recirculation amount of the high-pressure side exhaust gas so as to decrease the ratio of the recirculation amount of the low-pressure side exhaust gas to the recirculation amount of the side exhaust gas. An exhaust gas recirculation system for an internal combustion engine.   The reflux ratio control means is configured such that the amount of the condensed water estimated by the condensed water amount estimation means exceeds a preset threshold water quantity, and the detected differential pressure of the differential pressure sensor satisfies a predetermined passage blockage determination condition. The amount of recirculation of the low-pressure side exhaust gas is decreased according to the amount of the condensed water, and the amount of recirculation of the high-pressure side exhaust gas is set so as to compensate for the decrease in the amount of recirculation of the exhaust gas. The exhaust gas recirculation system for an internal combustion engine according to claim 1, wherein the exhaust gas recirculation system is increased.   The recirculation ratio control means increases to satisfy the predetermined passage blockage determination condition when the detected differential pressure of the differential pressure sensor rapidly increases at an increase rate larger than a preset threshold increase rate per unit time. The exhaust gas recirculation system for an internal combustion engine according to claim 1 or 2, wherein   The recirculation ratio control means increases when the detected differential pressure of the differential pressure sensor is increased so as to satisfy the predetermined passage blockage determination condition when the differential pressure detected by the differential pressure sensor is increased to a predetermined magnification or more with respect to a preset normal differential pressure. The exhaust gas recirculation system for an internal combustion engine according to claim 1 or 2, wherein the determination is made. The controller is
Based on the concentration of the specific exhaust component, the concentration of the specific exhaust component in the exhaust gas of the internal combustion engine, which increases as the recirculation amount of the exhaust gas on the high pressure side increases, falls within an allowable range. The exhaust of the internal combustion engine according to any one of claims 1 to 4, further comprising constraint condition determining means for selectively limiting a recirculation amount of the exhaust gas on the side. Recirculation system. The internal combustion engine is equipped with a turbocharger having an intake air compressor and an exhaust turbine,
The compressor is constituted by the intake air compressor of the turbocharger;
The exhaust gas recirculation system for an internal combustion engine according to any one of claims 1 to 5, wherein the resistance element is configured by the exhaust turbine of the turbocharger.   The exhaust of the internal combustion engine according to any one of claims 1 to 5, wherein the resistance element includes an exhaust purification unit that purifies exhaust gas passing through the exhaust pipe. Recirculation system.

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