JP2012229679A - Exhaust gas recirculation system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas recirculation system of an internal combustion engine that effectively prevents corrosion on a main component while responding to a request of severe NOx reduction using a low-pressure EGR device.SOLUTION: The exhaust gas recirculation system of the internal combustion includes: the low-pressure EGR device 17; and an ECU 50 that each controls PM regeneration processing of an exhaust purification unit 44 and exhaust gas reflux volume in the low-pressure EGR device 17. The ECU 50 includes: a condensed-water generation determination unit 51 for determining whether condensed water generates in threshold volume or more in a low-pressure-side exhaust recirculation route L2; and a reflux volume control unit 52 for setting an EGR restrictive period contained in a certain time from an execution start point of the PM regeneration processing during an execution period of the regeneration processing, on a condition that the condensed-water generation determination unit 51 determines that the condensed water generates in the threshold volume or more, and restricting the exhaust gas reflux volume in the low-pressure EGR device 17 during the EGR restrictive period, compared with the rest of the period in the execution period of the regeneration processing.

Description

  The present invention relates to an exhaust gas recirculation system for an internal combustion engine, and more particularly to an exhaust gas recirculation system for an internal combustion engine that executes control for suppressing the generation of condensed water in the exhaust gas recirculation passage.

  Engines for vehicles (internal combustion engines) are often equipped with an EGR (exhaust gas recirculation) system that performs exhaust gas recirculation that is effective in reducing NOx (nitrogen oxides), and lean combustion is possible. In an engine having an increased EGR flow rate, an exhaust gas recirculated, that is, an EGR cooler (exhaust cooler) that lowers the temperature of the EGR gas is frequently used. Also, in diesel engines, those equipped with a PM regeneration means that oxidizes and removes PM (particulate matter) deposited on the PM filter by raising the exhaust temperature by post-injection, fuel addition, etc. are widely used. doing. In addition to the HPL (high-pressure loop) -EGR circuit that recirculates a portion of the hot exhaust gas to the intake side, the exhaust gas that has passed through the exhaust aftertreatment device is recirculated upstream from the compressor of the turbocharger. As a result, an apparatus equipped with an LPL (low pressure loop) -EGR circuit which enables a large amount of exhaust gas recirculation at a low temperature has begun to spread.

  As such an exhaust gas recirculation system for an internal combustion engine, for example, an HPL-EGR circuit and an LPL-EGR circuit are provided together. The LPL valve opening is controlled so that the total amount of EGR gas, which is the sum of the amount of internal EGR gas remaining in the cylinder and the amount of external EGR gas over the stroke, is smaller than the total amount of EGR gas under other operating conditions. In addition, there is known one that can ensure sufficient EGR control accuracy even during PM regeneration (see, for example, Patent Document 1).

While NOx reduction control is performed to reduce and release NOx occluded in the NOx occlusion reduction catalyst and the filter to N ₂ , CO ₂ and H ₂ O, the accumulation amount of sulfur compounds, particularly sulfate, on the filter in the catalytic converter Is calculated based on the amount of fuel from the fuel injection valve, catalyst bed temperature, etc., and the catalyst bed temperature is compared by executing intermittent fuel addition from the addition valve with a relatively long time according to the calculation result. It is known that the air-fuel ratio is lowered than stoichiometric or stoichiometric while reducing the PM while purifying PM while at the same time reducing the air-fuel ratio to a low temperature (for example, 250 to 500 degrees Celsius) (for example, patent document) 2).

  In addition, for example, the sulfur estimation degree of the NOx occlusion reduction catalyst is estimated based on the temperature rise of the catalyst bed temperature of the NOx occlusion reduction catalyst detected by a sensor (see, for example, Patent Document 3), or In the PM regeneration mode, the fuel addition from the addition valve is repeated at an air fuel ratio higher than the stoichiometric ratio to increase the catalyst bed temperature to a high temperature (for example, 600 to 700 degrees Celsius). In the S (sulfur) poisoning recovery control mode, the fuel from the addition valve By repeating fuel addition to raise the catalyst bed temperature and setting the air-fuel ratio to a stoichiometric or slightly lower air-fuel ratio than stoichiometric, the S component deposited on the catalyst surface due to excessive S poisoning is removed and removed. (See, for example, Patent Document 4).

JP 2008-261256 A JP 2006-291823 A JP 2009-138525 A Japanese Patent Laying-Open No. 2005-076505

  However, in the conventional exhaust gas recirculation system for an internal combustion engine as described above, the amount of sulfur compound and the like deposited on the catalyst surface can be reduced by increasing the catalyst bed temperature, but the EGR circuit There is a problem that the acidity of the condensed water becomes high at a location where the condensed water is easily accumulated, and corrosion of an oxidation catalyst using an EGR pipe or an alumina-based material is likely to occur.

  That is, when the sulfur compound that adheres and accumulates on the surface of a PM collection filter or the like rises in temperature due to the addition of fuel for the PM regeneration process, the sulfur component (including fine particles) that is easily soluble in water is desorbed from the sulfur compound. A reaction occurs. Since the desorbed sulfur component is easily dissolved in water, acidic condensed water in which the sulfur component is dissolved is generated, and when this condensed water accumulates in a specific location in the EGR circuit, the evaporation of the condensed water proceeds there. At the same time, the acidity of the condensed water increases.

  In particular, in an exhaust gas recirculation system equipped with a low pressure EGR device, it is possible to meet strict NOx reduction requirements by a low temperature and large amount of exhaust gas recirculation, while executing low pressure EGR even during PM regeneration processing. Therefore, both the amount of condensed water generated and the amount of recirculated exhaust gas increase, and a large amount of condensed water in which a sulfur component is dissolved in the LPL-EGR circuit is likely to be generated. Then, when the operation state in which the evaporation of the large amount of condensed water proceeds, the acidity of the condensed water increases, and corrosion of oxidation catalysts using EGR pipes and alumina-based materials is likely to occur at locations where the condensed water tends to accumulate. Become.

  The present invention has been made in view of the above-described problems of the prior art. An internal combustion engine capable of effectively suppressing corrosion of main parts while responding to strict NOx reduction requirements using a low-pressure EGR device. An exhaust gas recirculation system is provided.

  An exhaust gas recirculation system for an internal combustion engine according to the present invention is installed in an internal combustion engine having (1) an intake pipe provided with a supercharging compressor and an exhaust pipe provided with an exhaust purification device. Forming a low-pressure side exhaust recirculation path for returning the low-pressure side exhaust gas after passing through the exhaust purification device of the internal combustion engine from the exhaust pipe downstream from the exhaust purification device to the intake pipe upstream from the compressor The low-pressure EGR device that performs the control, and the control that removes the deposits accumulated in the exhaust purification device by a regeneration process that raises the temperature of the inside to a set temperature, and the control of the recirculation amount of the exhaust gas in the low-pressure EGR device are performed. An exhaust gas recirculation system for an internal combustion engine, wherein the control device is a condensate that is equal to or greater than a preset threshold amount in the low pressure side exhaust gas recirculation path. A condensate generation determination unit that determines whether or not it occurs, and the regeneration within the execution period of the regeneration process, provided that the condensate generation determination unit determines that condensate more than the threshold amount is generated. An EGR limit period included within a certain time from the start of the process execution is set, and during the EGR limit period compared to the remaining period within the regeneration process execution period, the exhaust gas in the low pressure EGR device is And a reflux amount limiting unit for limiting the reflux amount.

  With this configuration, when the regeneration process is started in a state where condensed water of a threshold amount or more is generated in the low pressure side exhaust recirculation path, the low pressure is maintained during the EGR limit period within a certain period from the start of the regeneration process. The amount of exhaust gas recirculation in the EGR device is limited. Therefore, when the concentration of the sulfur component etc. desorbed in the exhaust purification device increases, the recirculation amount of the exhaust gas is limited, and it is suppressed that a large amount of sulfur component etc. dissolves in the condensed water in the low-pressure side exhaust recirculation path, An increase in the acidity of the condensed water is effectively suppressed. In addition, since the limited period of operation of the low-pressure EGR device is limited within a certain period, it is possible to meet strict NOx reduction requirements.

  In the present invention, (2) the EGR restriction period starts while the inside of the exhaust gas purification device is heated from the temperature at the start of execution to the set temperature by the start of execution of the regeneration process. It is preferable to end during the execution period. In this case, when the internal temperature of the exhaust gas purification device rises due to the start of the regeneration process and the reaction rate of desorption of the sulfur component from the deposit increases, the amount of exhaust gas recirculation in the low pressure EGR device is limited. It is possible to effectively prevent a large amount of sulfur component from being dissolved in the condensed water in the side exhaust recirculation path, and to meet a severe NOx reduction requirement by narrowing the operation restriction period of the low-pressure EGR device.

  In the present invention, it is preferable that (3) the control device executes the reproduction processing at a preset reproduction processing cycle, and the EGR limit period is set according to the reproduction processing cycle. In this case, the length of the EGR limit period is accurately controlled depending on whether the regeneration process cycle is long and the amount of deposits is large, or whether the regeneration process cycle is short and the amount of deposits is small. That is, the EGR limit period is set longer when the deposit amount is large, and the EGR limit period is set shorter when the deposit amount is small.

  In the exhaust gas recirculation system for an internal combustion engine according to (3), (4) the control device includes a deposition amount estimation unit that estimates a deposition amount of the deposit during the regeneration processing cycle, and the deposition amount estimation It is preferable to set the EGR restriction period according to the estimation result of the part. In this case, the EGR limit period can be set to an optimum time according to the amount of deposits deposited.

  In the exhaust gas recirculation system for an internal combustion engine according to (4), (5) the control device includes a fuel consumption amount detection unit that detects a fuel consumption amount of the internal combustion engine, and the accumulation amount estimation unit includes: It is preferable that the deposit amount of the deposit is estimated based on detection information of the fuel consumption amount detection unit during the regeneration processing cycle. In this case, the amount of deposits can be accurately estimated, and the EGR limit period can be set to an optimum time.

  In the exhaust gas recirculation system for an internal combustion engine according to (4) or (5), (6) the control device includes a temperature sensor that detects a temperature inside the exhaust gas purification device, and the accumulation amount estimation unit includes: The deposition amount of the deposit is estimated based on detection information of the temperature sensor during the regeneration processing cycle. In this case, it is possible to accurately grasp the desorption concentration of a sulfur component or the like that changes according to the temperature inside the exhaust purification device, and the EGR limit period can be set to an optimum time.

  In the present invention, it is preferable that (7) the control device sets the EGR restriction period as a period during which the concentration value of the sulfur component desorbed from the deposit is estimated to exceed a predetermined concentration value. As a result, the EGR restriction period can be reduced to a short time, and strict NOx reduction requirements can be met.

  According to the present invention, when the regeneration process is started in a state where condensed water of a threshold amount or more is generated in the low pressure side exhaust gas recirculation path, during the EGR restriction period within a certain period from the start of the regeneration process. Since the recirculation amount of the exhaust gas in the low pressure EGR device is limited, a large amount of condensed water in which sulfur components are dissolved in the low pressure side exhaust recirculation path is generated and accumulated in the low pressure side exhaust recirculation path. While effectively suppressing the increase in the acidity of the condensed water, it is possible to meet the severe NOx reduction requirement by limiting the operation restriction period of the low pressure EGR device within a certain period. As a result, it is possible to provide an exhaust gas recirculation system for an internal combustion engine that can be equipped with a low-pressure EGR device and can effectively suppress corrosion of main parts while meeting severe NOx reduction requirements.

1 is a schematic configuration diagram of an exhaust gas recirculation system for an internal combustion engine according to an embodiment of the present invention. It is a block block diagram of the control system of the internal combustion engine which concerns on one Embodiment of this invention. FIG. 1 is a diagram showing a change in catalyst bed temperature during a regeneration process performed by a control device in an exhaust gas recirculation system for an internal combustion engine according to an embodiment of the present invention; It is a graph which shows the relationship of the prohibition time of exhaust gas recirculation | reflux by LPL), and the vertical axis | shaft has shown the desorption | desorption rate and the catalyst bed temperature, and the horizontal axis has shown time. It is a flowchart which shows the schematic procedure of EGR control performed with the control apparatus in the exhaust gas recirculation system of the internal combustion engine which concerns on one Embodiment of this invention.

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

(One embodiment)
1 to 4 show an embodiment of an exhaust gas recirculation system for an internal combustion engine according to the present invention. This embodiment is an embodiment of an in-line four-cylinder diesel engine 10 (hereinafter referred to as a multi-cylinder internal combustion engine). , Simply referred to as 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 that is a high-pressure EGR device that recirculates and recirculates, and LPL- that is a low-pressure EGR device that recirculates and recirculates a part of the low-pressure side exhaust gas downstream from turbocharger 15 to the intake side EGR equipment 17 and are 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 A fuel injection valve 23 for injecting the fuel supplied through the combustion chamber 22 at a timing and opening degree (duty ratio) corresponding to an injection command signal from an electronic control unit 50 (control device; hereinafter referred to as ECU 50), which will be described later. It is configured to include. 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 (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, and intake air into the engine 10 A throttle valve 36 for adjusting the 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 gas purification unit 44 composed of a known oxidation catalyst 44a and a DPF (diesel particulate filter) 44b mounted on the exhaust pipe 42 on the downstream side of the turbocharger 15, and exhaust gas flowing into the exhaust gas purification unit 44 An A / F sensor 46 that detects the exhaust air-fuel ratio, an exhaust temperature sensor 47 that detects the temperature of the exhaust gas inside the exhaust purification unit 44, and a DPF front-to-back difference that detects the differential pressure across the DPF 44b of the exhaust purification unit 44 A pressure sensor 48 and an exhaust temperature sensor 49 for detecting the temperature of the exhaust gas that has passed through the exhaust purification unit 44. In is configured.

  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 (high pressure EGR valve) that can be used.

  The HPL-EGR pipe 61 includes an upstream exhaust pipe portion 42a upstream of the exhaust turbine 15b in the exhaust passage inside the exhaust manifold 41 or the exhaust pipe 42, and a downstream side of the intake air compressor 15a in the intake pipe 32. The exhaust pipe 15b on the downstream side or the inside of the intake manifold 31 is communicated with the exhaust turbine 15b and the exhaust purification unit 44 as resistance elements. It can be refluxed immediately before or inside. That is, the HPL-EGR pipe 61 can suck the recirculated high-pressure side exhaust gas into the engine 10 together with the air supercharged from the intake 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) 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. Exhaust cooling which can cool the exhaust gas passing through the LPL-EGR valve 71 (low pressure EGR valve) and the LPL-EGR pipe 71 by heat exchange with cooling water or the like in the middle The opening degree of the LPL-EGR cooler 73 serving as a vacuum vessel and the exhaust passage 42w in the downstream exhaust pipe 42 may be reduced so as to reduce the passage cross-sectional area in the exhaust passage portion downstream of the exhaust purification unit 44. And the above-described exhaust throttle valve 43.

  The LPL-EGR pipe 71 can communicate with the downstream side exhaust pipe portion 42b downstream of the exhaust turbine 15b in the exhaust pipe 42 and the upstream side intake pipe portion 32a upstream of the intake air compressor 15a in the intake pipe 32. The exhaust turbine 15b and the exhaust purification unit 44 are connected as resistance elements so that low-pressure exhaust gas having a low pressure downstream can be recirculated into the upstream intake pipe section 32a. The exhaust gas is compressed by the intake air compressor 15a together with the intake air introduced into the upstream side intake pipe portion 32a, and then can be sucked into the engine 10 again.

  Further, the LPL-EGR pipe 71 is 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 side exhaust pipe 42, and the low pressure side exhaust gas recirculation forming the main part of the low pressure side exhaust gas recirculation path L2 therein A passage 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 portion that forms a part of the low-pressure side exhaust recirculation passage 71w and a housing portion that forms a cooling fluid passage 73wp around the gas pipe portion. The 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 causes the low pressure side The recirculated exhaust gas can be cooled.

  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 cools a gas pipe part that forms a part of the third section of the intake passage 32w that forms a part of the low-pressure side exhaust recirculation path L2 and the periphery of the gas pipe part. By a heat exchange between a cooling fluid (for example, engine coolant) introduced into the housing portion and a low-pressure recirculation exhaust gas passing through the gas pipe portion. The low-pressure side recirculated exhaust gas can be cooled.

  The HPL-EGR device 16 and the LPL-EGR device 17 are controlled by the ECU 50 to open and close the HPL-EGR valve 62 and the LPL-EGR valve 72, and the opening degree thereof, to the downstream side intake pipe portion 32b of the intake pipe 32. The high-pressure side exhaust gas recirculation amount (hereinafter also referred to as HP flow rate) and the low-pressure side exhaust gas recirculation amount (hereinafter also referred to as LP flow rate) to the upstream side intake pipe portion 32a of the intake pipe 32 are respectively controlled. It is supposed to be.

  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.

  As shown in FIG. 2, on the output interface circuit side of the ECU 50, for example, a pump control circuit 24 that performs discharge control of the supply pump 21 (for example, control of the electromagnetic spill valve), a fuel injection valve 23, a throttle valve 36, an HPL-EGR valve 62, an LPL-EGR valve 72, an exhaust throttle valve 43 (specifically, these electromagnetic drive units (no reference)) and the like are connected.

  On the input interface circuit side of the ECU 50, in addition to the air flow meter 35, the intake air temperature sensor 37, the A / F sensor 46, the exhaust gas temperature sensors 47 and 49, and the DPF front-rear differential pressure sensor 48, the depression of an accelerator pedal (not shown) is detected. An accelerator opening sensor 101 for performing an operation, a throttle opening sensor 102 for detecting the opening of the throttle valve 36, a crank angle sensor 103 for outputting a crankshaft rotation signal in a predetermined angle unit, a water temperature sensor 104 for detecting a cooling water temperature of the engine 10, An intake pipe pressure sensor 105 that detects the supercharging pressure of the engine 10 near the inlet of the intake manifold 31, an outside air temperature sensor 106 that detects the outside air temperature, and both ends of the low pressure side exhaust recirculation passage 71 w (positions j 1 and j 2 in FIG. 1). The LP differential pressure sensor 107 that detects the differential pressure between the vehicle and the vehicle mounted with the engine 10 A vehicle speed sensor 108 for detecting the speed or wheel speed are connected. The sensor information from these sensor groups 35, 37, 46 to 49, and 101 to 108 is taken into the ECU 50.

  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.

  Further, in the ROM of the ECU 50, in order to keep the PM accumulation amount in the exhaust purification unit 44 within an allowable range, a known post injection or fuel addition from a fuel addition valve (not shown) is executed at a preset repetition cycle and execution condition. A PM regeneration processing program is stored, and unburned HC (hydrocarbon) generated by the post injection or fuel addition is burned by the oxidation catalyst 44a of the exhaust purification unit 44 to increase the internal temperature of the exhaust purification unit 44, The PM deposited on the DPF 44b of the exhaust purification unit 44 can be removed by combustion. The PM regeneration processing program itself is well known and will not be described in detail. However, the PM regeneration processing program may be executed at a preset fixed period, or may be executed in an integrated state of the operating state of the engine 10 and the fuel injection amount or in the exhaust purification unit 44. The map may be referred to based on the differential pressure across the DPF 44b, and the PM regeneration process may be executed when the integrated value of the fuel injection amount or the differential pressure across the DPF 44b reaches a predetermined value. Here, the latter case is assumed.

  On the other hand, in the engine 10, 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 re-intake into the engine 10, and the low pressure. Side exhaust recirculation path L2 is formed, the exhaust gas in the low pressure side exhaust recirculation path L2 is cooled by the LPL-EGR cooler 73, and downstream of the intake air compressor 15a in the intake passage in the intake pipe 32 The supercharged air is cooled by the intercooler 34. Therefore, 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. Condensed water is likely to be generated. In particular, when the sulfur compound adhering to and depositing on the inner surface of the exhaust purification unit 44 rises in temperature due to the PM regeneration process, the catalyst bed temperature, which is the surface temperature of the oxidation catalyst 44a, reaches a predetermined temperature and dissolves in water. The acidity of the condensed water is easily increased during the period in which the rate of the sulfur component removal reaction that is easy to increase suddenly increases.

  Therefore, the ECU 50 that controls the HPL-EGR device 16 and the LPL-EGR device 17 has a ROM so as to exhibit the functions of the condensed water generation determination unit 51 and the reflux amount restriction unit 52 (EGR restriction period setting unit) described below. The control program corresponding to these functional units is built in.

  The condensed water generation determination unit 51 determines whether or not condensed water equal to or more than a preset threshold water amount is generated in the vicinity of the LPL-EGR cooler 73 or in the vicinity of the intercooler 34 in at least the low pressure side exhaust recirculation path L2. The recirculation amount restriction unit 52 determines that the condensate generation determination unit 51 determines that condensate water equal to or greater than the threshold water amount is generated within the regeneration process execution period. An LPL prohibition time TP2 (EGR limit period) included within a certain time from the start of execution is set, and exhaust in the low pressure EGR device is performed during the LPL prohibition time TP2 as compared with the remaining period within the execution period of the regeneration process. The amount of gas recirculation is prohibited (restricted).

  Specifically, the condensate generation determination 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, the time when the exhaust pipe temperature is lower than a predetermined value continues. The approximate amount of condensed water is estimated according to the low temperature duration (see JP 2007-205303 A), and the condensed water amount is calculated in consideration of the LPL-EGR cooler 73 and the tube wall temperature of the EGR pipe. It is possible to use an estimation model (see JP 2009-228564 A), but it is more preferable to use an estimation model that can estimate the amount of condensed water with a certain degree of accuracy and stability while suppressing the processing load and apparatus cost of the ECU 50. .

  That is, the condensed water generation determination unit 51 accurately calculates the amount of condensed water using a calculation model corresponding to the engine 10, for example, intake air temperature (outside air temperature), atmospheric pressure, intake air near the inlet of the intake manifold 31. Based on the temperature and pressure, etc., the amount of moisture in the intake air (steam / air) and dew point temperature are calculated, and the composition of the intake air (molar ratio of each gas molecule and water) is obtained while being obtained as sensor information. Based on the air-fuel ratio obtained from the intake air amount and the fuel injection amount known as the control value and the molecular weight of known fuel and intake air composition components, the composition of the gas before and after combustion and the molecular weight of the burned gas are calculated. Based on the calculation result and the temperature and pressure of the burned gas (EGR gas), the amount of water in the burned gas ( By calculating the absolute humidity) of the gas, as the difference between the moisture content and moisture content of 100% relative humidity of burned gas during the cooling is such as to calculate the amount of condensed water.

  The condensed water generation determination unit 51 determines the moisture concentration in the exhaust gas calculated based on, for example, the exhaust air / fuel ratio detected by the A / F sensor 46, and the refrigerant temperature (for example, in the LPL-EGR cooler 73 and the intercooler 34). , The temperature of the cooling water supplied to the LPL-EGR cooler 73, the temperature of the atmosphere supplied to the intercooler 34) and the gas temperature, etc., the LPL-EGR rate in the LPL-EGR device 17 is further increased for the intercooler 34. (The amount of condensed water can be calculated based on the intercooler 34. That is, since the moisture in the exhaust gas can be calculated by approximately A / F, the moisture concentration is calculated from the sensor information of the intake air temperature and pressure, Based on the calculated value and the saturated water vapor concentration stored in advance as part of the reference information M1, it is possible to determine whether condensed water is generated. Kill.

  The condensate generation determination unit 51 also estimates the amount of condensed water to be taken downstream from the amount of condensate generated per unit time, based on a map created based on the results of previous experiments and sensor information serving as its argument. Then, the amount of condensed water actually generated may be calculated and estimated by subtracting the estimated value of the amount of condensed water taken away from the estimated value of the amount of condensed water generated.

  The condensed water generation determination unit 51 further determines the amount of condensed water [g / s] generated within a preset unit period for each calculation cycle or the total amount of condensed water including the generated amount and the remaining amount in the calculation target passage section. A calculation process to be estimated is executed, and the calculated condensate amount is a reference generation amount or a reference remaining amount (hereinafter simply referred to as a reference amount) corresponding to the upper limit value of the water amount to be suppressed for preventing corrosion of intake system parts. By comparing, it may be determined whether or not condensed water of a reference amount or more is present in the low-pressure side exhaust gas recirculation path L2.

  As shown in FIG. 3, the recirculation amount restriction unit 52 is within the execution period of the PM regeneration process on the condition that the condensate generation determination unit 51 determines that condensate more than the reference amount that is the determination threshold water amount is generated. Is set to the LPL prohibition time TP2 (EGR limit period) included in the fixed time from the execution start point p1 of the PM regeneration process, and compared with the remaining periods TP1 and TP3 in the execution period of the PM regeneration process. During the LPL inhibition time TP2, the exhaust gas recirculation amount in the low pressure EGR device is limited, for example, the exhaust gas recirculation is prohibited.

  Here, the LPL prohibition time TP2 starts during the temperature raising period in which the inside of the exhaust purification unit 44 is heated from the temperature th0 at the execution start time point p1 to the set temperature th1 by the start of execution of the PM regeneration process, and from the execution start time point p1. It is set to end during the reproduction processing execution period TP3 after a certain time (TP1 + TP2) has elapsed.

More specifically, the LPL inhibition time TP2 is determined in advance so that the separation reaction rate and the separation concentration [mol / m ³ ] of the sulfur component from the deposit such as the sulfur compound deposited inside the oxidation catalyst 44a of the exhaust purification unit 44 are preliminarily determined. The separation concentration decrease starts from the separation concentration increase start time point p2 at which the concentration starts to exceed a certain fixed concentration value (hereinafter referred to as the predetermined concentration value), and the sulfur component separation rate rd begins to decrease below the predetermined concentration value. It ends at time p3. Here, the desorption reaction rate of the sulfur component from the deposit such as the sulfur compound is, for example, a sulfur component desorption rate rd calculated by the following equation (1), and the desorption reaction rate value increases as the catalyst bed temperature T increases. Will increase.

rd = k1 · σ · exp (−Ed / RT) (1)
In this equation (1), k1 is a frequency factor of the sulfur component desorption reaction, σ is the amount of sulfur component deposited, and Ed is the activation energy necessary for desorption of the sulfur component. is there. In the formula (1), R is a gas constant, and T is a temperature inside the exhaust purification unit 44 as a catalyst bed temperature. The frequency factor k1 and the activation energy Ed are each set based on a previous experimental result, and are stored in advance in the ROM of the ECU 50. The departure concentration rising start point p2 can also be determined as the catalyst bed temperature tha at which the concentration of the sulfur component is close to the predetermined concentration value.

  The waiting time TP1 from the execution start time point p1 of the regeneration process shown in FIG. 3 to the release concentration rise start time point p2 is determined based on the change in the sulfur component release speed rd after the execution start time point p1 every predetermined time. This is the time until the withdrawal concentration reaches a predetermined concentration value obtained every time. The setting of the LPL prohibition time TP2 will be described later.

  The ECU 50 further includes a deposition amount estimation unit 53 that estimates the deposition amount σ of the sulfur component deposit during the PM regeneration process by a control program stored in advance in the ROM, and a fuel injection device 12 of the engine 10. A function with the fuel consumption calculation unit 54 (fuel consumption detection unit) for detecting the fuel consumption is exhibited.

  The deposition amount estimation unit 53 uses the deposition amount estimation unit 53 to deposit a deposit such as a sulfur compound based on the detection information of the fuel consumption calculation unit 54 and the detection information of the exhaust temperature sensor 47 during the PM regeneration process. σ is estimated.

  Then, the reflux amount limiting unit 52 estimates the accumulation amount σ by, for example, the accumulation amount estimation unit 53 on the condition that the condensed water generation determination unit 51 determines that condensed water equal to or greater than the reference amount that is the determination threshold water amount is generated. The LPL prohibition time TP2 is set with reference to a map M2 in which the LPL prohibition time TP2 corresponding to the result is set to an optimum value by an experiment or the like. In this case, the larger the deposition amount σ (the amount of adsorption of the sulfur component, etc.) and the higher the catalyst bed temperature T, the greater the sulfur component desorption rate rd and desorption amount [mol]. The higher the T, the greater the sulfur component removal amount and concentration, so the LPL inhibition time TP2 is set longer. That is, if the accumulation amount σ is large, the LPL inhibition time TP2 is set to be long, and if the accumulation amount of deposit is small, the LPL inhibition time TP2 is set to be short. The accumulation amount σ tends to increase if the period for executing the PM regeneration process is long, and decreases if the period for executing the PM regeneration process is short. Therefore, the accumulation amount σ is not estimated by the accumulation amount estimation unit 53. In addition, the LPL prohibition time TP2 may be set according to the reproduction processing cycle.

  Next, the operation will be described.

  FIG. 4 is a flowchart showing a schematic processing procedure of a control program executed by the ECU 50 every predetermined time. In parallel with the control program for causing the ECU 50 to perform the control of the fuel injection amount and the like described above, the ECU 50 causes the ECU 50 to respectively determine the condensed water generation determination unit 51, the recirculation amount restriction unit 52, and the accumulation amount estimation unit 53. To execute the function, it is repeatedly executed every predetermined time.

  As shown in FIG. 4, in this control, first, sensor information from the various sensor groups 35, 37, 46 to 49, and 101 to 108 is taken into the ECU 50, and the operating state of the engine 10 is acquired (step). S11).

  Next, it is determined whether or not the conditions for PM regeneration processing are satisfied (step S12). For example, when the integrated value of the fuel injection amount or the differential pressure across the DPF 44b reaches a predetermined value in a certain operating state of the engine 10, The PM regeneration condition is satisfied.

  In this case (in the case of YES in step S12), whether or not condensed water above the reference value is generated in the vicinity of the LPL-EGR cooler 73 in at least the low pressure side exhaust recirculation path L2 by the condensed water generation determination unit 51. Is determined (step S13), and if the determination result is YES, the catalyst bed temperature T is then detected from the temperature detected by the exhaust temperature sensor 47 (step S14).

  If the determination result is NO in either step S12 or S13, the process returns to step S11.

  When the catalyst bed temperature T is detected, the accumulation amount estimation unit 53 then detects the sulfur compound or the like based on the detection information of the fuel consumption calculation unit 54 and the detection information of the exhaust temperature sensor 47 during the PM regeneration process cycle. The deposit amount σ of the deposit is calculated, and the LPL prohibition time TP2 having a length corresponding to the calculated value of the deposit amount σ of the deposit such as a sulfur compound and the detected value of the catalyst bed temperature T is set (step S15). ).

  Next, the sulfur component desorption rate rd is calculated based on the calculated value of the accumulation amount σ and the detected value of the catalyst bed temperature T, and the value of the frequency factor k1 and the activation energy Ed stored in advance in the ROM. At the same time, the sulfur component desorption concentration is determined from the change in the sulfur component desorption rate rd after the start point p1 of the PM regeneration process (step S16).

  Next, it is determined whether or not the sulfur component separation concentration has reached a predetermined concentration value (step S17), and the waiting time TP1 has elapsed until the determination result is YES, that is, from the start point p1 of the PM regeneration process. Until this is done, the processes from the detection of the catalyst bed temperature T to the calculation of the sulfur component desorption concentration are repeated (steps S14 to S17).

  Next, when the waiting time TP1 elapses from the execution start time point p1 of the PM regeneration process, the LPL-EGR valve 72 is closed (step S18), and the closed state is maintained until the LPL prohibition time TP2 elapses from the valve closing time point. When the LPL prohibition time TP2 has elapsed (in the case of YES in step S19), the LPL-EGR valve 72 is opened again (step S20), and the current process ends.

  As described above, in the present embodiment, when the PM regeneration process is started in a state where condensed water having a reference value (threshold amount) or more is generated in the low pressure side exhaust recirculation path L2, the execution of the PM regeneration process is started. During the LPL prohibition time TP2 within a certain period (TP1 + TP2) from the time point p1, the recirculation amount of the exhaust gas in the low pressure EGR device 17 is limited. Therefore, it is suppressed that a large amount of sulfur components are dissolved in the condensed water in the low-pressure side exhaust recirculation path L2, and the acidity of the condensed water is effectively suppressed from increasing. In addition, since the restriction period of operation of the low-pressure EGR device 17 is restricted within a certain relatively short period TP2, it is possible to meet strict NOx reduction requirements.

  Further, the LPL prohibition time TP2, which is the limit period of the low pressure EGR, starts while the inside of the exhaust purification unit 44 is heated from the temperature th0 at the execution start time point p1 to the set temperature th1 by the start of execution of the PM regeneration process, and Since the PM regeneration process ends during the execution period of the PM regeneration process, the internal temperature of the oxidation catalyst 44a of the exhaust purification unit 44 rises due to the start of the PM regeneration process, and the rate of separation reaction of sulfur components from deposits such as sulfur compounds increases. The exhaust gas recirculation amount in the low pressure EGR device 16 is limited. Therefore, it is possible to effectively prevent a large amount of sulfur component from being dissolved in the condensed water in the low-pressure side exhaust recirculation path L2, and to meet a severe NOx reduction requirement by narrowing the operation restriction period of the low-pressure EGR device 16. it can.

  Moreover, since the LPL prohibition time TP2, which is the EGR limit period, is set according to the PM regeneration processing cycle, the PM regeneration processing cycle is long and the amount of deposits such as sulfur compounds is large, or the PM regeneration processing cycle is The EGR limit period is accurately controlled depending on whether the deposit amount is short or short.

  Further, since the LPL prohibition time TP2 is set according to the estimation result of the accumulation amount estimation unit 53 that estimates the accumulation amount of the deposit during the PM regeneration processing cycle, the LPL is determined according to the accumulation amount of the deposit such as a sulfur compound. The prohibition time TP2 can be set to an optimum time.

  Furthermore, since the accumulation amount estimation unit 53 estimates the accumulation amount of the deposit such as the sulfur compound based on the detection information of the fuel consumption calculation unit 54 during the PM regeneration processing cycle, the accumulation amount of the deposit is accurately determined. The LPL prohibition time TP2 can be set to an optimum time.

  In addition, the accumulation amount estimation unit 53 estimates the accumulation amount of the deposit based on the detection information of the exhaust temperature sensor 47 during the PM regeneration processing cycle, and changes according to the temperature inside the exhaust purification unit 44. The desorption rate and concentration of sulfur components and the like can be accurately grasped, and the EGR limit period can be set to an optimum time.

  Further, since the ECU 50 sets the LPL prohibition time TP2 as a period during which the concentration value of the sulfur component desorbed from the deposit is estimated to exceed the predetermined concentration value, the LPL prohibition time TP2 can be suppressed to a short time. Strict NOx reduction requirements can be met.

  As described above, in the exhaust gas recirculation system of the present embodiment, when the PM regeneration process is started in a state where condensed water of a threshold amount or more is generated in the low pressure side exhaust gas recirculation path L2, the PM regeneration process is performed. The exhaust gas recirculation amount in the low pressure EGR device 16 is limited during the EGR restriction period within a certain period from the execution start time point p1, and the exhaust gas having a high concentration of sulfur components or the like is difficult to enter the low pressure side exhaust recirculation path L2. Therefore, it is effective that a large amount of condensed water in which the sulfur component is dissolved in the low-pressure side exhaust recirculation path L2 is generated and the acidity of the condensed water accumulated in the low-pressure side exhaust recirculation path L2 is increased. Can be suppressed. In addition, since the restriction period for the operation of the low-pressure EGR device 16 is restricted within a certain period, it is possible to meet strict NOx reduction requirements. As a result, it is possible to provide an exhaust gas recirculation system for an internal combustion engine that is capable of effectively suppressing corrosion of main parts while being equipped with the low pressure EGR device 16 and meeting strict NOx reduction requirements.

  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.

  In each of the above-described embodiments, the turbocharger 15 is mounted on the engine 10, and the resistance element that divides the exhaust passage in the exhaust pipe 42 into the high-pressure side and the low-pressure side is the exhaust of the turbocharger 15. Although the turbine 15b and the exhaust purification unit 44 are configured, the present invention is also applicable to an internal combustion engine having a supercharger other than a turbocharger. For example, the present invention is also applicable 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 does not have the exhaust turbine 15b. Even when such a configuration is adopted, if the amount of condensed water during PM regeneration is large, the low pressure EGR is accurately limited when the concentration of desorbed components that increase the acidity of condensed water, such as sulfur components, increases. Therefore, it is possible to effectively suppress an increase in the acidity of the condensed water and to sufficiently secure the NOx reduction effect by the low pressure EGR.

  In the above-described embodiment, the LPL prohibition time TP2 for closing the LPL-EGR valve 72 is set as the EGR limit period for limiting the recirculation amount of the exhaust gas by the low pressure EGR device 17. Rather than fully closing the EGR valve 72, the opening of the LPL-EGR valve 72 is smaller than that of other PM regeneration processing periods when the concentration of desorbed components that increase the acidity of the condensed water increases. Of course, it can be limited to.

  Further, in the above-described embodiment, since the content (ratio) of the sulfur component in the fuel is generally stable, the accumulated amount σ of the sulfur component is determined based on the cycle of the PM regeneration process and the engine 10 during that cycle. Although the estimation is based on the fuel consumption, the content of the sulfur component contained in the fuel is estimated based on a plurality of sensor information during the operation of the engine 10 or the content ratio of the sulfur component in the fuel is a sensor. It is needless to say that the amount of sulfur component deposited can be calculated with higher accuracy by correcting the calculated value of the amount of sulfur component deposited. Of course, instead of the fuel consumption calculation unit 54, the fuel consumption detection unit can be configured by means capable of detecting the fuel consumption.

  As described above, the exhaust gas recirculation system for an internal combustion engine according to the present invention performs the regeneration process when the regeneration process is started in a state where condensed water of a threshold amount or more is generated in the low pressure side exhaust gas recirculation path. Since the exhaust gas recirculation amount in the low-pressure EGR device is limited during the EGR restriction period within a certain period from the start of execution of the engine, a large amount of condensed water in which the sulfur component is dissolved in the low-pressure side exhaust recirculation path This effectively suppresses the increase in the acidity of the condensed water that occurs in the low-pressure side exhaust recirculation path and restricts the operation restriction period of the low-pressure EGR device within a certain period to meet strict NOx reduction requirements. As a result, an exhaust gas recirculation system for an internal combustion engine that can be equipped with a low-pressure EGR device and can effectively suppress corrosion of main parts while meeting strict NOx reduction requirements is provided. It is intended that there is an effect that it is useful for exhaust gas recirculation system in general for an internal combustion engine that performs control to suppress occurrence of condensed water in the exhaust gas recirculation passage in.

10 engines (internal combustion engines, diesel engines)
12 Fuel injection device 15a Intake air compressor (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 32w Intake passage 34 Intercooler (intercooler)
42 exhaust pipe 43 exhaust throttle valve 44 exhaust purification unit (resistance element)
44a Oxidation catalyst 44b DPF (Diesel particulate filter)
46 A / F sensor (air-fuel ratio sensor)
47, 49 Exhaust temperature sensor (temperature sensor)
48 DPF differential pressure sensor 50 ECU (electronic control unit, control device)
51 Condensate Generation Determination Unit 52 Recirculation Amount Limiting Unit 53 Deposit Amount Estimation Unit 54 Fuel Consumption Calculation Unit (Fuel Consumption Detection Unit)
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)
L1 High pressure side exhaust recirculation path L2 Low pressure side exhaust recirculation path p1 Execution start point p2 Departure concentration rise start point p3 Departure concentration fall point T Catalyst bed temperature (temperature inside exhaust purification unit)
TP1 waiting time (remaining period, part of heating period)
TP2 LPL prohibition time (EGR limit period)
TP3 remaining period (regeneration process execution period after temperature increase)
σ deposition amount

Claims (7)

Equipped in an internal combustion engine having an intake pipe equipped with a supercharging compressor and an exhaust pipe provided with an exhaust purification device, the exhaust gas on the low pressure side after passing through the exhaust purification device of the internal combustion engine is exhausted A low-pressure EGR device that forms a low-pressure side exhaust recirculation path that recirculates from an exhaust pipe downstream of the purification device to an intake pipe upstream of the compressor, and deposits accumulated inside the exhaust purification device are set in the interior An exhaust gas recirculation system for an internal combustion engine, comprising: a control device for performing removal control by a regeneration process for raising the temperature; and a control device for controlling the exhaust gas recirculation amount in the low pressure EGR device,
The controller is
A condensed water generation determination unit that determines whether or not condensed water of a predetermined threshold amount or more is generated in the low pressure side exhaust gas recirculation path;
EGR restriction included within a certain period of time from the start of execution of the regeneration process within the execution period of the regeneration process, provided that the condensed water generation determination unit determines that condensed water of the threshold amount or more is generated. A recirculation amount restriction unit that sets a period and restricts the recirculation amount of exhaust gas in the low pressure EGR device during the EGR restriction period as compared with the remaining period in the execution period of the regeneration process. An exhaust gas recirculation system for an internal combustion engine.   The EGR restriction period starts while the inside of the exhaust gas purification apparatus is heated from the temperature at the start of execution to the set temperature by the start of execution of the regeneration process, and ends during the period of execution of the regeneration process. 2. An exhaust gas recirculation system for an internal combustion engine according to 1. The control device executes the reproduction processing at a preset reproduction processing cycle,
The exhaust gas recirculation system for an internal combustion engine according to claim 1 or 2, wherein the EGR limit period is set according to the regeneration processing cycle. The control device includes a deposition amount estimation unit that estimates a deposition amount of the deposit during the regeneration processing cycle,
The exhaust gas recirculation system for an internal combustion engine according to claim 3, wherein the EGR limit period is set according to an estimation result of the accumulation amount estimation unit. The control device includes a fuel consumption amount detection unit that detects a fuel consumption amount of the internal combustion engine,
5. The internal combustion engine exhaust gas recirculation according to claim 4, wherein the accumulation amount estimation unit estimates the accumulation amount of the deposit based on detection information of the fuel consumption amount detection unit during the regeneration processing cycle. Circulation system. The control device has a temperature sensor for detecting the temperature inside the exhaust purification device,
The exhaust amount of the internal combustion engine according to claim 4 or 5, wherein the accumulation amount estimation unit estimates the accumulation amount of the deposit based on detection information of the temperature sensor during the regeneration processing cycle. Recirculation system.   2. The internal combustion engine according to claim 1, wherein the control device sets the EGR limit period as a period during which the concentration value of the sulfur component desorbed from the deposit is estimated to exceed a predetermined concentration value. Exhaust recirculation system.

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