JP5621638B2 - Exhaust gas recirculation system for internal combustion engines - Google Patents

Description

  The present invention relates to an exhaust gas recirculation system for an internal combustion engine, and more particularly, to a control device that performs EGR control so as to stably stabilize the NOx reduction effect in an exhaust gas recirculation system for an internal combustion engine having a low pressure EGR (Exhaust Gas Recirculation) device, that is, EGR. It relates to the improvement of the control device.

  Engines for vehicles (internal combustion engines) are often equipped with an exhaust gas recirculation system that is effective in reducing NOx (nitrogen oxides) and can reduce pumping loss (intake load) of the engine. In an engine capable of increasing the EGR flow rate, an EGR cooler (exhaust cooler) is frequently used to lower the temperature of exhaust gas recirculated, that is, EGR gas. 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 for an internal combustion engine, if a large amount of exhaust gas recirculation is performed, the water in the exhaust gas recirculated to the intake side is cooled, so that a large amount of acidic condensate is easily generated. Coolers in which water accumulates, intake-type metal parts that easily adhere to condensed water, turbocharger compressors, and the like are susceptible to corrosion. 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, an EGR amount change caused by clogging or gas leakage in an intake / exhaust passage or an EGR circuit, an exhaust gas recirculation passage on the LPL-EGR circuit side (hereinafter referred to as an EGR amount) becomes large. The flow rate of exhaust gas on the low pressure side that passes through the low pressure EGR passage so that the EGR amount becomes a target value (hereinafter also referred to as low pressure EGR flow rate). A correction is known (for example, see Patent Document 1).

  Further, in the operation state of the combined region where the exhaust gas is recirculated through both the high pressure EGR passage and the low pressure EGR passage, the high pressure EGR amount is set so that the detection value of the A / F sensor (the oxygen concentration in the exhaust gas in the lean region) is constant. The feedback control of the metering means and the open control of the low pressure EGR amount metering means, the detection value of the A / F sensor becomes constant in the low pressure EGR region where the high pressure EGR passage is closed and the exhaust gas is recirculated only through the low pressure EGR passage. As described above, there is known one that performs feedback control on the low pressure EGR amount metering means (see, for example, Patent Document 2).

  EGR gas flowing through one of the low pressure EGR passage and the high pressure EGR passage is feedback-controlled according to the fresh air amount measured by the intake fresh air amount measuring means, and the EGR gas flowing through the other EGR passage The amount of the EGR gas flowing through the other EGR passage is controlled by the open loop control based on the operating state of the internal combustion engine, so that the variation due to the open loop control corresponds to the amount of fresh air with respect to the EGR gas flow rate flowing through the one EGR passage. There is also known one that can be corrected by feedback control (for example, see Patent Document 3).

  Further, if a large amount of exhaust gas recirculation is performed so that the differential pressure across the low pressure side exhaust gas recirculation passage in the LPL-EGR circuit exceeds a predetermined value, the total pumping loss of the engine increases, resulting in deterioration of fuel consumption. In view of this, when the detected value of the differential pressure sensor for detecting the differential pressure before and after the pressure is larger than the predetermined differential pressure, the remaining required flow rate is reduced to the HPL while suppressing the flow rate of the low-pressure side exhaust recirculation passage to a flow rate corresponding to the predetermined differential pressure -It is known that the amount of exhaust gas recirculated through the high-pressure exhaust gas recirculation passage of the EGR circuit is compensated (for example, see Patent Document 4).

  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 recirculated exhaust gas to pass through, it is also known that the condensed water can easily flow down from the inclined surface (for example, (See Patent Document 5).

JP 2008-038627 A JP 2007-315371 A JP 2008-002347 A JP 2007-2111767 A JP 2010-151091 A

  However, in the conventional exhaust gas recirculation system for an internal combustion engine as described above, when a foreign matter collecting filter or an EGR filter having both functions is arranged upstream of the exhaust gas recirculation passage, the following There could be a problem.

  In other words, in an exhaust gas recirculation system equipped with an LPL-EGR device, it is possible to meet strict NOx reduction requirements by a low temperature and large amount of exhaust gas recirculation, but since the amount of condensed water generated increases, Condensed water adheres to the filter and a water film is easily formed. For this reason, a state in which the exhaust gas recirculation passage is blocked by the foreign matter collecting filter or the pressure loss thereof is increased easily occurs.

  In this case, since the detection value of the differential pressure sensor that detects the differential pressure at both ends of the low-pressure EGR passage becomes large, it is erroneously detected that the exhaust gas recirculation state is large.

  Therefore, when a water film is formed on the foreign matter collecting filter as described above, control for further reducing the low-pressure EGR flow rate is executed even though the low-pressure EGR flow rate is greatly reduced. And an appropriate ratio (EGR ratio) of the high pressure EGR flow rate cannot be obtained.

  Therefore, in any conventional exhaust gas recirculation system of an internal combustion engine, if a configuration capable of feedback control using a differential pressure sensor is adopted, the amount of condensed water generated increases and the exhaust gas recirculation passage becomes clogged. In such a case, the EGR flow rate of the entire system becomes insufficient, and the NOx reduction effect may not be sufficiently obtained.

  Accordingly, the present invention provides an exhaust gas recirculation system for an internal combustion engine that can ensure the required NOx reduction effect even when the amount of condensed water generated increases and the exhaust gas recirculation passage becomes clogged.

  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 low pressure side exhaust recirculation pipe section for recirculating low pressure side exhaust gas after passing through the resistance element from an exhaust pipe downstream of the resistance element to an intake pipe upstream of the compressor, and the low pressure side exhaust recirculation pipe section The differential pressure between the low pressure EGR device having a low pressure EGR valve that controls the recirculation amount of the low pressure side exhaust gas passing through and the upstream end side and the downstream end side in the exhaust gas recirculation direction in the low pressure side exhaust recirculation pipe section. An exhaust gas recirculation system for an internal combustion engine, comprising: a differential pressure detection unit for detecting; and a control device that feedback-controls the opening degree of the low pressure EGR valve based on the detected differential pressure detected by the differential pressure detection unit The control device includes a clogging determination unit that determines whether or not a clogging that hinders the recirculation of the low-pressure side exhaust gas has occurred in the low-pressure side exhaust gas recirculation pipe unit, and the clogging determination unit by the clogging determination unit When it is determined that the clogging has not occurred in the reflux pipe section, feedback control based on the detected differential pressure of the low pressure EGR valve is executed, and the clogging determination section causes the clogging to occur in the low pressure side exhaust recirculation pipe section. And a control condition setting unit for changing to a control other than the feedback control of the low pressure EGR valve based on the detected differential pressure.

  In this exhaust gas recirculation system, if the clogging determination unit does not determine that clogging has occurred in the low pressure side exhaust gas recirculation pipe unit, the control condition setting unit selects feedback control based on the detected differential pressure of the low pressure EGR valve, and clogging occurs. If it is determined by the determination unit that the clogging has occurred in the low-pressure side exhaust gas recirculation pipe unit, the control condition setting unit changes to a control other than the low-pressure EGR valve feedback control based on the detected differential pressure. Therefore, even if the amount of condensed water generated increases and the exhaust gas recirculation passage becomes clogged, and the detected differential pressure of the differential pressure sensor suddenly increases, feedback control based on the detected differential pressure is prohibited, so the low pressure EGR The low pressure EGR flow rate is not further reduced in a state where the flow rate is lowered. In addition, by executing another control that is not based on the detected differential pressure, a NOx reduction effect in accordance with the normal EGR control can be obtained, so that the amount of condensed water generated increases and the exhaust gas recirculation passage increases. Thus, the exhaust gas recirculation system for the internal combustion engine can ensure the required NOx reduction effect even when the engine is clogged.

  In the exhaust gas recirculation system for an internal combustion engine of the present invention, (2) the clogging determination unit estimates the amount of condensed water generated from the recirculated exhaust gas in the low pressure side exhaust recirculation pipe unit, and the estimated amount of condensed water It is preferable to determine that the clogging has occurred when is greater than a predetermined value. Thereby, when the passage in the low-pressure side exhaust recirculation pipe portion is likely to be blocked by the water film of the condensed water, the clogging can be accurately determined. It should be noted that the process of estimating the amount of condensed water is executed only when the detected differential pressure is larger than a predetermined value and there is a possibility that the exhaust gas recirculation passage is clogged with condensed water. It is also possible to accurately determine clogging while reducing the processing load.

  In the exhaust gas recirculation system for an internal combustion engine of the present invention, (3) the clogging determination unit detects a cooling water temperature of the internal combustion engine, and the clogging occurs when the cooling water temperature is lower than a preset low water temperature value. It may be determined that it is. Also in this case, even if the passage in the low-pressure side exhaust recirculation pipe is blocked by the condensed water film, the clogging can be accurately determined.

  When adopting the configuration of (2) or (3) above, the exhaust gas recirculation system for an internal combustion engine according to the present invention is (4) upstream of the low pressure side exhaust recirculation pipe section in the exhaust gas recirculation direction from the low pressure EGR valve. A foreign matter collecting member that is disposed and collects foreign matter that enters the low-pressure side exhaust gas recirculation pipe portion, and the clogging determining portion determines that the foreign matter collecting member is clogged by a water film. Is preferred. With this configuration, even if a water film of condensed water is formed on the foreign matter collecting member and the clogging occurs suddenly in the low-pressure side exhaust recirculation pipe, the control of the low-pressure EGR flow rate is different from the feedback control based on the detected differential pressure. Therefore, the required NOx reduction effect is ensured.

  In the exhaust gas recirculation system for an internal combustion engine of the present invention that employs any one of the above configurations (1) to (4), (5) the control condition setting unit controls the low pressure EGR valve to the detected differential pressure. When the feedback control based on the control is changed to the other control, it is preferable that the control device performs open-loop control on the low-pressure EGR valve. With this configuration, for example, a low-pressure EGR amount corresponding to the operating state of the internal combustion engine, for example, the engine speed and the accelerator opening (required load) is set as a target EGR amount, but the control is not as fine as feedback control based on a normal detected differential pressure. The required NOx reduction effect can be ensured.

  In the exhaust gas recirculation system for an internal combustion engine of the present invention that employs any one of the above configurations (1) to (4), (6) the control condition setting unit controls the low pressure EGR valve to detect the detection difference. When the control is changed from the feedback control based on the pressure to the other control, the control device executes another feedback control for controlling the opening degree of the low pressure EGR valve based on detection information other than the detected differential pressure. It may be. With this configuration, for example, the low pressure EGR flow rate is feedback-controlled based on the LPL flow rate that is the difference between the cylinder intake air amount obtained from the detected values of the boost pressure and the intake air temperature and the detected value of the fresh air intake amount. Thus, the required NOx reduction effect can be ensured.

  In the exhaust gas recirculation system for an internal combustion engine according to the present invention, (7) the turbocharger having an intake air compressor and an exhaust turbine is attached to 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. The resistance element may be an exhaust purification unit that purifies exhaust gas passing through the exhaust pipe, and a turbocharger other than a turbocharger may be used.

  In order to achieve the above object, an EGR control apparatus for an internal combustion engine according to the present invention includes: (8) 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 low pressure side exhaust recirculation pipe section for recirculating low pressure side exhaust gas after passing through the resistance element from an exhaust pipe downstream of the resistance element to an intake pipe upstream of the compressor; and the low pressure side exhaust recirculation pipe section An exhaust gas recirculation system of an internal combustion engine having a low pressure EGR device having a low pressure EGR valve for controlling a recirculation amount of the low pressure exhaust gas passing through the exhaust gas in the exhaust gas recirculation direction in the low pressure exhaust gas recirculation pipe section. A differential pressure detection unit that detects a differential pressure between the upstream end side and the downstream end side, and feedback-controls the opening of the low-pressure EGR valve based on the detected differential pressure detected by the differential pressure detection unit An internal combustion engine EGR control device that can determine whether or not a clogging that hinders the recirculation of the low-pressure side exhaust gas has occurred in the low-pressure side exhaust gas recirculation pipe unit, and the clogging determination unit When it is determined that the clogging does not occur in the low-pressure side exhaust recirculation pipe section, feedback control based on the detected differential pressure of the low-pressure EGR valve is selected, and the clogging determination section enters the low-pressure side exhaust recirculation pipe section into the low-pressure side exhaust recirculation pipe section. A control condition setting unit that changes control of the low pressure EGR valve from feedback control based on the detected differential pressure of the low pressure EGR valve to another control when it is determined that clogging has occurred. Features.

  In this EGR control device, if it is not determined by the clogging determination unit that clogging has occurred in the low-pressure side exhaust recirculation pipe unit, the control condition setting unit selects feedback control based on the detected differential pressure of the low-pressure EGR valve, If it is determined by the clogging determination unit that the clogging has occurred in the low-pressure side exhaust recirculation pipe unit, the control condition setting unit changes the control to a control other than the feedback control of the low-pressure EGR valve based on the detected differential pressure. Therefore, even if the amount of condensed water generated increases and the exhaust gas recirculation passage becomes clogged and the detected differential pressure of the differential pressure sensor suddenly increases, feedback control based on the detected differential pressure is prohibited. There is no further decrease in the low-pressure EGR flow rate when the EGR flow rate is reduced. In addition, by executing another control that is not based on the detected differential pressure, a NOx reduction effect in accordance with the normal EGR control can be obtained, so that the amount of condensed water generated increases and the exhaust gas recirculation passage increases. Even when clogging occurs, the required NOx reduction effect can be ensured.

  According to the present invention, if there is no clogging in the low-pressure side exhaust recirculation pipe section, feedback control based on the detected differential pressure of the low-pressure EGR valve is selected, and if clogging occurs in the low-pressure side exhaust recirculation pipe section, it is detected. Since control other than the feedback control of the low pressure EGR valve based on the differential pressure is executed, the amount of condensed water generated increases and the exhaust gas recirculation passage is clogged, and the detected differential pressure of the differential pressure sensor is reduced. Even if it suddenly increases, the low pressure EGR flow rate is not reduced further in the state where the low pressure EGR flow rate is reduced, and other control that is not based on the detected differential pressure is executed. A NOx reduction effect according to EGR control can be obtained. As a result, it is possible to provide an exhaust gas recirculation system for an internal combustion engine that can ensure the required NOx reduction effect even when the amount of condensed water generated increases and the exhaust gas recirculation passage becomes clogged.

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 the HP flow rate (high pressure side exhaust gas recirculation amount) in the low pressure EGR flow rate control executed by the control device in the exhaust gas recirculation system for the internal combustion engine according to the first embodiment of the present invention. . It is a flowchart of the control program for low-pressure EGR flow 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 the low pressure EGR flow 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 low-pressure EGR flow 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 7 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 FIGS. 1 and 2, 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 shown in FIG. 1). (Not shown) a common rail type fuel injection device 12 for injecting fuel, an intake device 13 for sucking air into the combustion chamber, an exhaust device 14 for exhausting exhaust gas from the combustion chamber, and exhaust in the exhaust device 14 The turbocharger 15 that compresses the intake air in the intake device 13 by using energy and supercharges the air into the combustion chamber, and a part of the exhaust gas on the high-pressure side upstream from the turbocharger 15 is taken in. HPL-EGR device 16 (high pressure EGR device) that recirculates and recirculates to the side, and LPL-EGR device that recirculates and recirculates part of the low-pressure side exhaust gas downstream from the turbocharger 15 to the intake side 17 (low pressure GR apparatus) and 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 the air-fuel ratio in the exhaust gas that has passed through the exhaust purification unit 44 (the oxygen concentration in the exhaust gas in the lean region and the unburned gas concentration in the exhaust gas in the rich region) can be detected. / F sensor 48.

  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 includes an HPL-EGR pipe 61 (a high-pressure side exhaust gas recirculation pipe portion) interposed between the exhaust manifold 41 and the intake pipe 32, and an exhaust gas that is mounted in the middle of the HPL-EGR pipe 61. And an HPL-EGR valve 62 capable of adjusting the amount of reflux of the gas.

  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 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. LPL-EGR valve 72 (low pressure EGR valve) capable of adjusting the recirculation amount of the gas, and LPL-EGR cooler 73 (exhaust cooler) capable of cooling the exhaust gas passing through the LPL-EGR pipe 71 in the middle thereof A foreign matter collecting filter 74 disposed upstream of the LPL-EGR valve 72 and the LPL-EGR cooler 73 (exhaust cooler) in the exhaust gas recirculation direction of the low pressure side exhaust gas recirculation passage 71w in the LPL-EGR pipe 71; The opening degree of the exhaust passage 42w in the exhaust pipe 42 on the downstream side is reduced so that the cross-sectional area of the exhaust passage 42w on the downstream side of the exhaust purification unit 44 is reduced. And a, an exhaust throttle valve 43 described above that can be.

  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 that forms the main part of the low-pressure side exhaust gas recirculation path L2 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 LPL-EGR valve 72 or the intake air compressor 15a of the turbocharger 15 and causing damage, the LPL-EGR valve 72 and LPL-EGR cooler 73 are collected upstream in the exhaust gas recirculation direction 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), or 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. 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, the exhaust gas temperature sensor 47, and the A / F sensor 48, the ECU 50 includes an accelerator opening sensor 101 that detects depression of an accelerator pedal (not shown), A throttle opening sensor 102 that detects the opening of the throttle valve 36, a crank angle sensor 103 that outputs a crankshaft rotation signal in a predetermined angle unit, a water temperature sensor 104 that detects the cooling water temperature of the engine 10, and the vicinity of the inlet of the intake manifold 31. An intake pipe pressure sensor 105 that detects the supercharging pressure of the engine 10, an outside air temperature sensor 106 that detects the outside air temperature, and a differential pressure between both ends of the low pressure side exhaust gas recirculation passage 71w (positions j1 and j2 in FIG. 1). LP differential pressure sensor 107 (differential pressure detector) that detects the traveling speed or wheel rotation speed of the vehicle on which the engine 10 is mounted. A vehicle speed sensor 108, etc. are respectively connected, sensor information from these sensors 35,37,47,48 and 101 to 108 are adapted to be incorporated into the ECU 50. On the other hand, the ECU 50 has a supply pump 21 (for example, its electromagnetic spill valve), a plurality of fuel injection valves 23, a throttle valve 36, an HPL-EGR valve 62, and 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. The path L1 and the low pressure side exhaust recirculation path L2 are formed, and the low pressure side exhaust gas passing through the low pressure side exhaust recirculation path L2 is cooled by the LPL-EGR cooler 73. Therefore, in particular, acidic condensed water is likely to be generated in the low-pressure side exhaust gas recirculation passage 71w that forms the main part of the low-pressure side exhaust gas recirculation path L2.

  Therefore, the ECU 50 that controls the HPL-EGR device 16 and the LPL-EGR device 17 can exhibit the functions of the clogging determination unit 51, the control condition setting unit 52, and the EGR control unit 53 as described below. Control programs corresponding to these functional units are built in the ROM.

  The clogging determination unit 51 also has a function of condensate amount estimation means for estimating the amount of condensate in the low-pressure side exhaust recirculation path L2 formed by the LPL-EGR device 17, and the low-pressure side exhaust recirculation path. The amount of condensed water generated in at least a specific passage section of L2 is estimated.

  Further, the clogging determination unit 51 estimates the amount of condensed water generated from the recirculated exhaust gas in the specific passage section in the low-pressure side exhaust recirculation path L2, and the estimated amount of condensed water is larger than a predetermined value (predetermined value). And the estimated amount of condensed water is determined to be clogged in the low-pressure side exhaust gas recirculation passage 71w in the LPL-EGR pipe 71 to prevent recirculation of the low-pressure side exhaust gas. Is not larger than the predetermined value (below the predetermined value or less than the predetermined value), it is determined that there is no clogging in the LPL-EGR pipe 71 that hinders the recirculation of the exhaust gas on the low pressure side. Yes.

  The specific passage section here means that when the amount of condensed water generated in the low pressure side exhaust recirculation path L2 increases and a water film is formed on the foreign matter collecting filter 74, the amount of condensed water rapidly increases. A passage section, for example, a passage section in the vicinity of the foreign matter collection filter 74 in the low pressure side exhaust recirculation passage 71w in the LPL-EGR pipe 71 and in the vicinity of the LPL-EGR cooler 73 that cools the recirculated exhaust gas. The total amount of condensed water at a plurality of locations (a plurality of passage sections) of the side exhaust recirculation path L2 may be used.

  In addition, the predetermined value here means that the amount of condensed water in the low-pressure side exhaust recirculation path L2 formed by the LPL-EGR device 17 increases, and foreign matter trapped on the upstream side of the LPL-EGR valve 72 is captured. When a water film is formed by the condensed water adhering to the collecting filter 74 and clogging occurs in the low pressure side exhaust recirculation passage 71w in the LPL-EGR pipe 71 such that a pressure loss exceeding a preset allowable pressure loss level occurs. Of the amount of condensed water (corresponding to a threshold water amount α described later).

  Specifically, the estimation of the amount of condensed water in the clogging determination unit 51 is performed by estimating the approximate value of the amount of condensed water generated in the low-pressure side exhaust recirculation path L2 by a known method. One that determines the operating state of the engine 10 that has a high probability of reaching the amount of water that can form a water film on the filter 74 (described later), or a low temperature that continues for a period when the exhaust pipe temperature is lower than a predetermined value. One that estimates according to the duration (see, for example, JP-A-2007-205303), and one that calculates and estimates the amount of condensed water in consideration of the tube wall temperature, etc. (see, for example, JP-A-2009-228564) However, in this embodiment, the amount of condensed water can be accurately and stably estimated while suppressing the processing load of the ECU 50 and the device cost.

  That is, the clogging determination unit 51 calculates / estimates, for example, the amount of condensed water generated in the specific passage section, which is a target section for calculating the condensed water amount, using a calculation model stored in the ROM in advance, and unit in the target section. Of the amount of condensed water Qw1 generated every time (estimated amount generated; see FIG. 3), the amount of condensed water Qw2 taken away downstream is created based on a map M1 created based on the previous experimental results and sensor information serving as its argument. Estimate and calculate / estimate the amount of condensed water (hereinafter referred to as condensed water amount Qwa) that has been taken away from the estimated amount of condensed water generation amount Qw1 and subtracted the estimated value of condensed water amount Qw2 Yes.

  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 preliminary experiment for a specific passage section, or is configured by a map that can estimate the amount of condensed water more accurately by including the low-pressure EGR gas temperature as an argument. Here, the recirculation amount (hereinafter referred to as LP flow rate) of the exhaust gas on the low pressure side per unit time can be calculated from the detection value of the LP differential pressure sensor 107, for example. Alternatively, the recirculation amount (hereinafter referred to as HP flow rate) of exhaust gas on the high pressure side per unit time from the total cylinder intake air amount per unit time obtained from the temperature and pressure of the supercharged air immediately before entering the cylinder 11 and the new It can also be calculated as a value obtained by subtracting the air intake flow rate (the detected intake air amount of the air flow meter 35).

In the calculation of the condensate generation amount Qw1 by the calculation model in the clogging determination unit 51, first, the intake air is based on the outside air temperature, the atmospheric pressure, the temperature and pressure of the intake air near the inlet of the intake manifold 31, and the like. While calculating the amount of water (steam / air (mol%) = water vapor pressure / atmospheric pressure) and dew point temperature, the composition of the intake air (respective gas molecules (N ₂ , O ₂ , Ar) and water (H ₂ O) ), And based on the mass of known fuel and intake air composition components and the air-fuel ratio obtained 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 is expressed as the sum of the product of the molar ratio of each component in the gas and the mass (indicated by the value and symbol 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) · H 2 O 2, the molecular weight of burned gas, that is, the gas after combustion = (1) · CO 2+ (x / 2 + d) · H 2 O + (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 moisture in the fuel gas (absolute humidity of the burnt gas). Then, the clogging determination unit 51 has a moisture content in the burned gas and a relative humidity of 100% under a cooling condition in a specific passage section (here, a section in the vicinity of the LPL-EGR cooler 73 and the foreign matter collecting filter 74). As a difference from the amount of moisture in the burned gas, the amount of condensed water generated Qw1 in the vicinity of the gas outlet of the foreign matter collecting filter 74 is calculated.

  Then, the clogging determination unit 51 calculates the actual amount of condensed water Qwa [g / s] that has been taken away from the calculated amount of condensed water generated Qw1 and subtracted the amount of condensed water Qw2 [g / s], and the amount of condensed water Qwa is calculated. The low-pressure side exhaust recirculation passage 71w is connected to the foreign matter collecting filter 74 depending on whether or not the condensate water amount Qwa exceeds the threshold water amount α. It is determined whether or not the amount of condensed water that can be clogged by the adhered condensed water film is generated.

  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 the surface tension causes the surface water amount on the foreign matter collecting surface of the foreign matter collecting filter 74. The amount of condensed water that can form a water film having a certain area or more is equivalent to the predetermined value. 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 clogging determination unit 51 further sets a preset threshold increase rate β per unit time (for example, 0.4 kPa) when the current condensed water amount Qwa calculated and estimated as described above exceeds the threshold water amount α. / 60 sec), the low pressure side exhaust gas recirculation passage 71w detects the foreign matter by determining whether it has increased rapidly at an increase rate greater than (60 sec) or whether the rapid increase time has continued for a certain time (for example, 60 seconds). It may be determined with higher accuracy that the clogging is caused by being clogged with a water film or the like formed on the collecting filter 74.

  When the clogging determination unit 51 determines that the clogging has not occurred in the low-pressure side exhaust gas recirculation passage 71w in the LPL-EGR pipe 71, the control condition setting unit 52 presets the detected differential pressure of the LP differential pressure sensor 107. The feedback control of the LPL-EGR valve 72 based on the detected differential pressure of the LP differential pressure sensor 107 is executed so as to maintain the target differential pressure, and the flow rate of the recirculated exhaust gas passing through the low pressure side exhaust recirculation passage 71w, that is, LP The flow rate is set to the optimum value. The target differential pressure here corresponds to the optimum value of the LP flow rate, and is, for example, a fixed differential pressure value corresponding to a constant LP flow rate in a combined region where both the HP flow rate and the LP flow rate are not zero. The differential pressure value selected from a plurality of different values depending on whether it is a low pressure EGR region where the HP flow rate is zero, a combined region where both the HP flow rate and the LP flow rate are not zero, or a high pressure EGR region where the LP flow rate is zero It may be.

  On the other hand, when the clogging determination unit 51 determines that the clogging is occurring in the low-pressure side exhaust gas recirculation passage 71w in the LPL-EGR pipe 71, the control condition setting unit 52 determines the detected differential pressure of the LP differential pressure sensor 107. The feedback control of the based LPL-EGR valve 72 is prohibited, and the control is changed to another control other than the feedback control based on the detected differential pressure of the LP differential pressure sensor 107. Here, the other control is open loop control based on the operating state of the engine 10 for the LPL-EGR valve 72. For example, according to the operating state of the engine 10 so that the EGR amount of the low pressure EGR becomes substantially constant. The target opening degree of the LPL-EGR valve 72 is calculated based on a map M2 set by a previous experiment, and the target opening degree of the LPL-EGR valve 72 is controlled. The map M2 here is obtained by presetting, as a target value, an optimal LP flow rate or valve opening corresponding to, for example, the engine speed or the accelerator opening (required load). The crank angle sensor 103 or the accelerator opening sensor The stored data can calculate the target value based on the detection information 101.

  The control condition setting unit 52 also executes the ratio of the LP flow rate in the low pressure side exhaust recirculation passage 71w to the HP flow rate in the high pressure side exhaust recirculation passage 61w (EGR ratio) when executing open loop control based on the operating state of the engine 10. (Hereinafter referred to as the LP flow rate ratio), the LP flow rate is decreased according to the condensed water amount Qwa (see FIG. 4), and the decrease in the LP flow rate is determined based on the detection information of the A / F sensor 48. The HP flow rate is increased to compensate.

  That is, when the condensate water amount Qwa is in an LP clogged state where the condensate water amount Qwa exceeds the threshold water amount α, the control condition setting unit 52 suppresses the condensate water amount Qwa to the threshold water amount α to 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. 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.

  Further, when the control condition setting unit 52 selects at least the open-loop control of the LPL-EGR valve 72, the intake air amount detected by the air flow meter 35 based on the air / fuel ratio detected by the A / F sensor 43 or at least. Based on the above, the control conditions for feedback control of the high pressure EGR valve 62 are set so that the total EGR amount decreases as the load of the engine 10 increases.

  For example, the control condition setting unit 52 is configured so that 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 falls within the allowable range. The HP flow rate can be selectively reduced based on the operating condition of the engine 10 when the concentration of the specific emission component reaches a preset limiting value in accordance with the limiting condition of performing.

  That is, for example, as shown in FIG. 5, the control condition setting unit 52 increases as the intake air temperature in the intake manifold 31 increases 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 every predetermined time by using a map M3 (which may be a known simple soot model) shown in FIG. 2 so that the smoke component concentration value (FSN: Filter Smoke Number) indicating the tendency falls within the allowable range. The intake air temperature in the intake manifold 31 is set to the high-pressure side exhaust gas under the constraint that the calculated value does not exceed the intake air temperature when the calculated value reaches a constraint value (for example, smoke FSN = 1). The reflux amount 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 control condition setting unit 52 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 is set according to the constraint condition. The exhaust gas recirculation amount is selectively reduced.

  The EGR control unit 53 operates the HPL-EGR valve 62, the LPL-EGR valve 72, the throttle valve 36, and the exhaust throttle valve 43 in accordance with the control conditions set by the control condition setting unit 52, whereby the HP flow rate and the LP flow rate are controlled. The LP flow rate ratio (EGR ratio), the total recirculation exhaust gas amount (total EGR amount) and the EGR rate corresponding to the HP flow rate and the LP flow rate, respectively, can be controlled. It has a set value for each valve, a control program for calculating a control amount, a map M4, set value information, and the like.

  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, and is disposed in the low pressure side exhaust gas recirculation passage 71w. There is also a possibility that the other member is fine (individual gas passage hole diameter is small). In this case, the clogging determination unit 51 forms a water film on the other member, and in the low pressure side exhaust recirculation passage 71w. It is determined whether or not the pressure loss has increased.

  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 EGR control. This control program exhibits the functions of the clogging determination unit 51, the control condition setting unit 52, and the EGR control 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, 48 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 condensate amount Qwa that has been taken away from the condensate generation amount Qw1 for each unit period and subtracted the condensate amount Qw2 by the clogging determination unit 51 is preset and calculated at a calculation cycle (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 calculated condensate water amount Qwa does not exceed the threshold water amount α (NO in step S13), it is determined that the low-pressure side exhaust gas recirculation passage 71w is not clogged, and the LP differential pressure sensor 107 detects it. By performing feedback control of the LPL-EGR valve 72 based on the detected differential pressure of the LP differential pressure sensor 107 so as to maintain the differential pressure at a preset target differential pressure, the LP flow rate is controlled to an optimal value ( Step S14).

  On the other hand, if the calculated condensed water amount Qwa exceeds the threshold water amount α (YES in step S13), it is determined that the low pressure side exhaust gas recirculation passage 71w is clogged, and the detection difference of the LP differential pressure sensor 107 is detected. The feedback control of the LPL-EGR valve 72 based on the pressure is prohibited, and open loop control which is another control is started (step S15). At this time, the LPL-EGR valve 72 is controlled to a target opening corresponding to the engine speed of the engine 10 and the accelerator opening so that the EGR amount of the low pressure EGR becomes substantially constant.

  When the calculated condensate water amount Qwa exceeds the threshold water amount α, the detected differential pressure of the LP differential pressure sensor 107 rapidly increases at an increase rate larger than the threshold increase rate β per unit time, or rapidly increases. When the clogging determination is executed based on whether or not the duration of the period of time exceeds a certain time, the differential pressure feedback control and the open loop control of the LPL-EGR valve 72 are switched according to the final determination result.

  On the other hand, during this time, at least when the LPL-EGR valve 72 is open-loop controlled, the high-pressure EGR valve 62 is based on the air / fuel ratio detected by the A / F sensor 48 or the intake air amount detected by the air flow meter 35. Based on the above, feedback control is performed so that the total EGR amount decreases as the load of the engine 10 increases, and further, the smoke component and the concentration value of HC in the exhaust gas are appropriately limited so as not to exceed the constraint values.

  Here, an example of the operating state of the system when the clogged state with the condensed water occurs in the low-pressure side exhaust gas recirculation passage 71w will be described with reference to FIG.

  First, as indicated by a solid line in FIG. 7B, when the LPL-EGR valve 72 is gradually opened to a certain opening every predetermined time t (for example, about 20 seconds) and the LP flow rate increases, the low pressure side The EGR amount 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. A clogging state occurs in which the differential pressure across the collection filter 74 increases rapidly.

  In the present embodiment, occurrence of such clogging is determined by the above-described processing, and when clogging occurs in the low-pressure side exhaust gas recirculation passage 71w, the LPL-EGR valve 72 based on the detected differential pressure of the LP differential pressure sensor 107 is used. The feedback control is prohibited and the control is switched to another control, open loop control. In addition, by this open loop control, the LP flow rate that suppresses the condensed water amount Qwa to a value up to the threshold water amount α is reduced, and so that the NOx reduction effect is reduced due to the decrease in the LP flow rate up to the threshold LP flow rate X. The HP flow rate will be increased. Accordingly, in this case, the opening degrees of the HPL-EGR valve 62 and the LPL-EGR valve 72 are changed to opening degrees Vb and Va indicated by thick dotted lines in FIGS. 7A and 7B, for example.

  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.

  Thus, in the exhaust gas recirculation system of the present embodiment, if it is not determined by the clogging determination unit 51 that clogging has occurred in the low pressure side exhaust gas recirculation passage 71w in the LPL-EGR pipe 71, the control condition setting unit 52, feedback control based on the detected differential pressure of the LPL-EGR valve 72 is selected, and if the clogging determination unit 51 determines that clogging has occurred in the LPL-EGR pipe 71, the control condition setting unit 52 detects the detection difference. A control other than the feedback control of the LPL-EGR valve 72 based on the pressure is selected.

  Therefore, even if a water film is formed on the foreign matter collecting filter 74 and the low pressure side exhaust gas recirculation passage 71w is clogged, the feedback control based on the detected differential pressure is prohibited, so that the LP flow rate (low pressure EGR flow rate) decreases. In this state, the LP flow rate is not further reduced, and the open loop control not based on the detected differential pressure is executed, so that the NOx reduction effect according to the normal EGR control can be obtained. As a result, an exhaust gas recirculation system for an internal combustion engine that can ensure the required NOx reduction effect even when the amount of condensed water generated increases and the low pressure side exhaust gas recirculation passage 71w becomes clogged.

  Further, in this embodiment, the amount of condensed water generated in the specific passage section can be calculated with high accuracy, so that the clogging can be accurately determined when the passage in the LPL-EGR pipe 71 is likely to be blocked by the water film of the condensed water. It becomes. In addition, since it is possible to accurately determine whether or not the foreign matter collecting filter 74 is clogged with the water film, a water film of condensed water is formed on the foreign matter collecting filter 74 and suddenly becomes clogged in the LPL-EGR pipe 71. Even if this occurs, the control of the LP flow rate is accurately switched to the above-described open loop control, and the required NOx reduction effect is ensured.

  In the open loop control, the LP flow rate corresponding to the engine speed and the required load of the engine 10 is set as the target value EGR amount. Therefore, although the control is not as fine as the feedback control based on the normal detected differential pressure, it is relatively good. A NOx reduction effect can be secured.

  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 and its EGR control device according to the present embodiment, the amount of condensed water generated increases and the low pressure side exhaust gas recirculation passage 71w is clogged, and the detected differential pressure of the LP differential pressure sensor 107 is reduced. Even if it suddenly increases, the low-pressure EGR flow rate does not decrease further in the state where the low-pressure EGR flow rate is reduced, and the open loop control that is not based on the detected differential pressure is executed. A NOx reduction effect according to EGR control can be obtained. As a result, the required NOx reduction effect can be ensured even when the amount of condensed water increases and the low pressure side exhaust gas recirculation passage 71w becomes clogged.
(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 an EGR control program 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 control condition setting 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 control condition setting unit 52, which is a difference, will be described below while using the components of the first embodiment and the reference numerals of the processing steps shown in FIGS.

  In the present embodiment, the clogging determination unit 51 of the ECU 50 determines a low water temperature value β (for example, a preset water temperature (cooling water temperature)) based on the detected water temperature of the water temperature sensor 104 that detects the cooling water temperature of the engine 10. When the temperature is lower than about 30 ° C., it is determined that a clogging is generated such that a water film is formed on the foreign matter collecting filter 74 and a pressure loss exceeding the allowable pressure loss level occurs in the low-pressure side exhaust recirculation passage 71w. It is like that.

  Further, it is determined by the clogging determination unit 51 that clogging has occurred in the low pressure side exhaust recirculation passage 71w, and the control condition setting unit 52 changes the control of the LPL-EGR valve 72 from feedback control based on the detected differential pressure to another control. The control condition setting unit 52 performs LPL-EGR based on sensor information other than the detected differential pressure of the LP differential pressure sensor 107 as control other than feedback control based on the detected differential pressure of the LP differential pressure sensor 107. Another feedback control for controlling the opening degree of the valve 72 is executed.

  Specifically, the control condition setting unit 52 determines the LP flow rate for each unit time from the total cylinder intake air amount for each unit time obtained from the temperature and pressure of the supercharged air immediately before entering the cylinder 11 of the engine 10. The LPL-EGR valve 72 is also calculated as a value obtained by subtracting the HP flow rate and the detected intake air amount (fresh air intake air amount) of the air flow meter 35 so that the calculated value of the LP flow rate becomes the optimum value of the LP flow rate described above. Is controlled at a constant LP flow rate value in a combined region where both the HP flow rate and the LP flow rate are not zero. Further, a target value selected from a plurality of different values depending on whether it is a low pressure EGR region where the HP flow rate is zero, a combined region where both the HP flow rate and the LP flow rate are not zero, or a high pressure EGR region where the LP flow rate is zero. The LP flow rate may be used.

  As shown in FIG. 8, in this embodiment, first, when the operating state of the engine 10 is acquired from the sensor information from the various sensors 35, 37, 47, 48 and 101 to 108 (step S11), then clogging occurs. The determination unit 51 determines whether or not the detected water temperature of the water temperature sensor 104 is lower than a preset low water temperature value β (step S12).

  At this time, if the detected water temperature of the water temperature sensor 104 is lower than the low water temperature value β (in the case of YES in step S12), it is determined that the low pressure side exhaust gas recirculation passage 71w is clogged with condensed water, and then LP While the feedback control of the LPL-EGR valve 72 based on the detected differential pressure of the differential pressure sensor 107 is prohibited, open loop control which is another control is started (step S15). At this time, the LPL-EGR valve 72 is controlled to a target opening corresponding to the engine speed of the engine 10 and the accelerator opening so that the LP flow rate becomes substantially constant.

  On the other hand, when the detected water temperature of the water temperature sensor 104 is equal to or higher than the low water temperature value β (in the case of NO in step S12), it is determined that the low pressure side exhaust gas recirculation passage 71w is not clogged, and the LP differential pressure sensor 107 Feedback control of the LPL-EGR valve 72 based on the detected differential pressure of the LP differential pressure sensor 107 is executed to maintain the detected differential pressure at a preset target differential pressure, and the LP flow rate is controlled to an optimum value (step) S14).

  Also in the exhaust gas recirculation system of this embodiment, if it is not determined by the clogging determination unit 51 that clogging has occurred in the low-pressure side exhaust gas recirculation passage 71w in the LPL-EGR pipe 71, the control condition setting unit 52 performs LPL- When feedback control based on the detected differential pressure of the EGR valve 72 is selected and the clogging determining unit 51 determines that clogging has occurred in the LPL-EGR pipe 71, the control condition setting unit 52 determines the LPL based on the detected differential pressure. A control other than the feedback control of the EGR valve 72 is selected. Therefore, even if a water film is formed on the foreign matter collecting filter 74 and the low pressure side exhaust recirculation passage 71w is clogged, the feedback control of the LPL-EGR valve 72 based on the differential pressure detected by the LP differential pressure sensor 107 is prohibited. As a result, the LP flow rate is not further reduced in a state where the LP flow rate (low pressure EGR flow rate) is reduced, and the LP flow value is made to follow the target value LP flow rate as another control not based on the detected differential pressure. Since feedback control is executed, a NOx reduction effect according to normal EGR control can be obtained. As a result, an exhaust gas recirculation system for an internal combustion engine that can ensure the required NOx reduction effect even when the amount of condensed water generated increases and the low pressure side exhaust gas recirculation passage 71w becomes clogged.

  Moreover, in this embodiment, since clogging determination is performed based on the detected water temperature of the water temperature sensor 104, the processing load for clogging determination of ECU50 can be reduced.

  In each of the above-described embodiments, a control program that is selectively set to any one of the open loop control of the LPL-EGR valve 72 and the feedback control based on the detected differential pressure of the differential pressure sensor 107 is set at predetermined intervals. Alternatively, it is executed every predetermined time when the cooling water temperature of the engine 10 is low. However, when the detected differential pressure of the LP differential pressure sensor 107 is so low that the low pressure side exhaust gas recirculation passage 71w cannot be clogged, the low pressure side The EGR according to the present invention with good accuracy while suppressing the processing load of the ECU 50 by not determining whether or not the exhaust gas recirculation passage 71w is clogged or switching the EGR control condition according to the result of the determination. Control can also be performed. That is, the process of estimating the amount of condensed water is executed only when the detected differential pressure is larger than a predetermined value and there is a possibility that the low pressure side exhaust gas recirculation passage 71w is clogged with condensed water or is likely to occur. It is also possible to accurately determine clogging while reducing the processing load on the control device.

  In the above-described embodiment, the actual condensate amount Qwa is calculated by the clogging determination unit 51 every fixed time. However, the actual amount of accumulated condensate generated in the low pressure side exhaust recirculation path L2 is It may be such that the stored liquid level is detected by a sensor and the amount of condensed water in the target section is calculated / estimated.

  Further, in each of the above-described embodiments, the turbocharger 15 is attached to 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 selects the feedback control based on the detected differential pressure of the low pressure EGR valve if there is no clogging in the low pressure side exhaust recirculation pipe section, If the exhaust gas recirculation pipe is clogged, control other than the feedback control of the low pressure EGR valve based on the detected differential pressure is executed. Even if clogging occurs and the detected differential pressure of the differential pressure sensor suddenly increases, the low-pressure EGR flow rate is not further reduced in a state where the low-pressure EGR flow rate is reduced, and is not based on the detected differential pressure. By performing the other control, it is possible to obtain the NOx reduction effect in accordance with the normal EGR control. As a result, the amount of condensed water generated increases and the exhaust gas recirculation passage is clogged. It is possible to provide an exhaust gas recirculation system for an internal combustion engine that can ensure the required NOx reduction effect even in such a case, and an exhaust gas recirculation system for an internal combustion engine equipped with a low pressure EGR device, particularly This is useful for all EGR control devices that perform EGR control so as to ensure a stable NOx reduction effect.

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, EGR control device)
51 Clogging determination unit (condensate amount estimation means)
52 Control condition setting section 53 EGR control section 61 HPL-EGR pipe (exhaust gas recirculation pipe section on the high pressure side)
61w High pressure side exhaust recirculation passage 62 HPL-EGR valve (High pressure EGR valve)
71 LPL-EGR pipe (exhaust gas recirculation pipe on the low pressure side)
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 (cooling water temperature detection means)
105 Intake pipe pressure sensor 107 LP differential pressure sensor (differential pressure detector)
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 (predetermined value)
β Low water temperature

Claims (8)

The resistance from the exhaust pipe downstream of the resistance element of the internal combustion engine to the intake pipe upstream of the compressor having an intake pipe provided with a supercharging compressor and an exhaust pipe provided with a resistance element serving as an exhaust resistance Low-pressure EGR device having a low-pressure side exhaust gas recirculation pipe part for recirculating low-pressure side exhaust gas after passing through the element and a low-pressure EGR valve for controlling the recirculation amount of the low-pressure side exhaust gas passing through the low-pressure side exhaust gas recirculation pipe part When,
A differential pressure detector that detects a differential pressure between the upstream end and the downstream end in the exhaust gas recirculation direction in the low-pressure side exhaust recirculation pipe, and based on the detected differential pressure detected by the differential pressure detector An exhaust gas recirculation system for an internal combustion engine comprising: a control device that feedback-controls the opening degree of the low pressure EGR valve;
The controller is
A clogging determination unit that determines whether clogging that hinders recirculation of the low-pressure side exhaust gas occurs in the low-pressure side exhaust recirculation pipe unit;
When the clogging determination unit determines that the clogging is not occurring in the low-pressure side exhaust recirculation pipe unit, feedback control based on the detected differential pressure of the low-pressure EGR valve is executed, and the clogging determination unit performs the low-pressure side exhaust. A control condition setting unit for changing to a control other than the feedback control of the low pressure EGR valve based on the detected differential pressure when it is determined that the clogging is occurring in the reflux pipe unit, An exhaust gas recirculation system for an internal combustion engine.   The clogging determination unit estimates the amount of condensed water generated from the recirculated exhaust gas in the low-pressure side exhaust recirculation pipe unit, and determines that the clogging occurs when the estimated amount of condensed water is greater than a predetermined value. The exhaust gas recirculation system for an internal combustion engine according to claim 1.   The clogging determination unit detects a cooling water temperature of the internal combustion engine, and determines that the clogging occurs when the cooling water temperature is lower than a preset low water temperature value. An exhaust gas recirculation system for internal combustion engines. A foreign matter collecting member that is disposed upstream of the low pressure side exhaust recirculation pipe portion in the exhaust gas recirculation direction from the low pressure EGR valve, and that collects foreign matter that enters the low pressure side exhaust recirculation pipe portion;
4. The exhaust gas recirculation system for an internal combustion engine according to claim 2, wherein the clogging determination unit determines that the foreign matter collecting member is clogged with a water film. 5.   When the control condition setting unit changes the control of the low pressure EGR valve from the feedback control based on the detected differential pressure to the other control, the control device performs open loop control of the low pressure EGR valve. An exhaust gas recirculation system for an internal combustion engine according to any one of claims 1 to 4.   When the control condition setting unit changes the control of the low pressure EGR valve from the feedback control based on the detected differential pressure to the other control, the control device is configured to detect the low pressure based on detection information other than the detected differential pressure. The exhaust gas recirculation system for an internal combustion engine according to any one of claims 1 to 4, wherein another feedback control for controlling an opening degree of the EGR valve is executed. 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 6, wherein the resistance element includes the exhaust turbine of the turbocharger. The resistance from the exhaust pipe downstream of the resistance element of the internal combustion engine to the intake pipe upstream of the compressor having an intake pipe provided with a supercharging compressor and an exhaust pipe provided with a resistance element serving as an exhaust resistance Low-pressure EGR having a low-pressure side exhaust recirculation pipe portion for recirculating low-pressure side exhaust gas after passing through the element and a low-pressure EGR valve for controlling the recirculation amount of the low-pressure side exhaust gas passing through the low-pressure side exhaust recirculation pipe portion A differential pressure detection unit that is provided in an exhaust gas recirculation system for an internal combustion engine equipped with a device and detects a differential pressure between an upstream end side and a downstream end side in the exhaust gas recirculation direction in the low pressure side exhaust recirculation pipe unit An EGR control device for an internal combustion engine capable of feedback-controlling the opening degree of the low-pressure EGR valve based on a detected differential pressure detected by the differential pressure detecting unit,
A clogging determination unit that determines whether clogging that hinders recirculation of the low-pressure side exhaust gas occurs in the low-pressure side exhaust recirculation pipe unit;
When the clogging determination unit determines that the clogging is not occurring in the low pressure side exhaust gas recirculation pipe unit, feedback control based on the detected differential pressure of the low pressure EGR valve is selected, and the clogging determination unit selects the low pressure side exhaust gas. A control condition setting unit that changes the control of the low-pressure EGR valve from feedback control based on the detected differential pressure of the low-pressure EGR valve to another control when it is determined that the clogging has occurred in the reflux pipe unit. An EGR control device for an internal combustion engine, characterized in that:

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