JP6439057B2 - EGR device - Google Patents

Description

  The present invention relates to an EGR (Exhaust Gas Recirculation) apparatus.

  In JP2010-048113A, when high-temperature gas is flowing, water is injected into the EGR cooler to evaporate it, and soot adhering to the surface of the tube is washed away with water vapor to reduce heat exchange efficiency due to soot deposition. An EGR device for preventing the above is disclosed.

  However, in the EGR device of JP2010-048113A, water vapor flows in the tube of the EGR cooler together with the gas, so that the attached soot is washed from the surface side. Therefore, only a small part of the surface of the soot can be washed away, and most of the soot adhering to the tube stays on the surface as it is, and adheres and accumulates. Therefore, in the EGR device of JP2010-048113A, the heat exchange efficiency is lowered. There is a risk.

  An object of this invention is to provide the EGR apparatus which can wash away the soot adhering to the surface of a tube, and can prevent the fall of heat exchange efficiency.

An EGR device according to an aspect of the present invention is an EGR device that recirculates a part of exhaust gas discharged from an engine from an exhaust passage to an intake passage, and is guided from the exhaust passage by a refrigerant flowing through the inside. An EGR cooler that cools the exhaust gas, an EGR inlet pipe that connects the exhaust passage and the EGR cooler, an EGR outlet pipe that connects the EGR cooler and the intake passage, and the EGR outlet pipe An EGR open / close valve that switches an exhaust gas flow, and the EGR cooler includes an EGR gas passage through which exhaust gas guided from the exhaust passage flows, and an exhaust gas in the EGR gas passage; It has a refrigerant channel for coolant flow to perform heat exchange, and the EGR-off valve, the temperature of the refrigerant in the refrigerant passage is opened when it is higher than a predetermined temperature, the EGR inlet The pipe is thicker than the EGR outlet pipe, the refrigerant is cooling water, the EGR on-off valve is closed when the temperature of the cooling water in the EGR cooler is lower than a predetermined temperature, and the EGR cooler And a cooling water on / off valve for switching the flow of the cooling water, and the cooling water on / off valve is closed when the EGR on / off valve is closed .

  According to the above aspect, the exhaust gas that has reached the EGR cooler by natural convection is cooled near the surface of the tube to below the dew point, so that the water by the condensed water generated between the surface of the tube and the attached soot A film is formed. As a result, the tube and soot are separated by the water film, so that the soot adhering to the surface of the tube can be washed away simply by opening the EGR on-off valve and flowing exhaust gas vigorously into the EGR cooler. Can do. Moreover, since the wrinkles adhering to the previous run can be washed away every time cold start, it is possible to prevent the wrinkles from sticking to the surface of the tube over time. Therefore, an EGR device that can prevent a decrease in heat exchange efficiency can be provided.

FIG. 1 is a configuration diagram of an intake / exhaust system of an engine of a diesel vehicle including an EGR device according to an embodiment of the present invention. FIG. 2 is an enlarged configuration diagram of the vicinity of the high pressure EGR cooler attached to the exhaust passage. FIG. 3 is an internal cross-sectional view of the high pressure EGR cooler. FIG. 4 is an enlarged cross-sectional view illustrating the relationship between the tubes and fins of the high-pressure EGR cooler. FIG. 5 is a partial perspective view of the fin of the high pressure EGR cooler. FIG. 6 is a flowchart showing the flow of EGR cooler cleaning control. FIG. 7A is a schematic diagram illustrating a state of wrinkles attached to the tube. Drawing 7B is a mimetic diagram explaining the condensed water generated between a tube and a bowl. FIG. 7C is a schematic diagram for explaining a state in which wrinkles are washed away from the tube. FIG. 8 is a timing chart showing the relationship between the time during which condensed water is generated during a cold start and the EGR outlet water temperature. FIG. 9 is a timing chart illustrating EGR cooler cleaning control when a high load operation is performed at a cold start.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram of an intake / exhaust system of an engine 20 of a diesel vehicle including an EGR device 100 according to an embodiment of the present invention.

  The supply / exhaust system of the engine 20 includes an intake system 10 connected upstream of the engine 20 and an exhaust system 30 connected downstream.

  The intake system 10 includes an air cleaner 11, a compressor wheel 42 of the supercharger 40, an intake shutter valve 63, an intercooler 12, and an intake passage that connects these components so that intake air taken from outside can flow. 13.

  The exhaust system 30 connects the turbine wheel 41 of the supercharger 40, the exhaust purification device 31, the exhaust shutter valve 52, the silencer 32, and these so that the exhaust gas discharged from the engine 20 can flow. And an exhaust passage 33.

  The intake air is supercharged by the compressor wheel 42 of the supercharger 40 after the foreign matter such as dust and the like is removed by the air cleaner 11 when flowing through the intake flow path 13, and is introduced to the intake shutter valve 63. It is burned. The supercharged intake air changes its flow rate according to the opening degree of the intake shutter valve 63, passes through the intake shutter valve 63, is cooled by the intercooler 12, and then passes through the intake manifold (not shown) to the engine 20. Led to. The intercooler 12 is, for example, a water-cooled type, and is connected to a sub-radiator (not shown) to release heat taken from supercharged intake air to the outside. The intercooler 12 may be an air cooling type.

  The intake air guided to the engine 20 is supplied to the combustion chamber 22 through the intake port 21 and combusted by being compressed together with the fuel injected in the combustion chamber 22. The combustion provides the driving force necessary for the diesel vehicle to travel.

  The exhaust gas generated by the combustion is discharged from the exhaust port 23 to the exhaust passage 33 through the exhaust manifold (not shown) of the exhaust system 30. After the exhaust gas passes through the turbine wheel 41 of the supercharger 40 and is purified by a diesel oxidation catalyst or a particulate collection filter (not shown) in the exhaust purification device 31, the exhaust gas is flowed according to the opening of the exhaust shutter valve 52. Is distributed to the silencer 32. The exhaust gas flowing through the silencer 32 is discharged to the outside with reduced pressure and temperature and reduced exhaust noise. The diesel oxidation catalyst of the exhaust purification device 31 is a catalyst that activates and burns unburned gas in the exhaust gas, and the particulate collection filter is a filter that collects particulates in the exhaust gas. Note that NOx in the exhaust gas is attached to the exhaust purification device 31 by attaching a NOx reduction catalyst for removing nitrogen oxides and a fuel reforming catalyst that generates a reducing agent used in the NOx reduction catalyst. May be reduced.

  For the supercharger 40, for example, a variable capacity turbocharger that controls the flow rate of exhaust gas or intake air according to the rotational speed of the engine 20 is used. When the turbine wheel 41 of the supercharger 40 is rotated by the pressure of the exhaust gas, the rotational force is transmitted to the compressor wheel 42 via the shaft 43 and the intake air is supercharged. A large amount of intake air can be introduced.

  A low pressure EGR device 50 and a high pressure EGR device 60 are connected as an EGR device 100 between the exhaust flow path 33 and the intake flow path 13.

  The low-pressure EGR device 50 includes a low-pressure EGR cooler 51, a low-pressure EGR valve 53, and a low-pressure EGR flow path 54 that connects the exhaust gas recirculated from the exhaust flow path 33 so that the exhaust gas can flow. .

  One end of the low pressure EGR flow path 54 is connected between the exhaust purification device 31 of the exhaust flow path 33 and the exhaust shutter valve 52, and the other end is connected between the air cleaner 11 of the intake flow path 13 and the compressor wheel 42. Is done. Therefore, a part of the exhaust gas in the exhaust passage 33 is returned to the intake passage 13 when the low-pressure EGR valve 53 is opened. Further, the exhaust gas flowing through the low pressure EGR flow path 54 is cooled by the cooling water flowing through the inside when passing through the low pressure EGR cooler 51. In this way, a part of the exhaust gas, which is an inert gas, is recirculated to the intake flow path 13 and recirculated to the combustion chamber 22 of the engine 20, thereby reducing the combustion temperature and reducing NOx and improving fuel consumption. be able to. The amount of exhaust gas to be recirculated is adjusted by changing the opening degree of the low pressure EGR valve 53 according to the operating state of the engine 20. According to the low pressure EGR device 50, a part of the exhaust gas can be recirculated to the intake passage 13 without being affected by the supercharging pressure.

  The high-pressure EGR device 60 includes a high-pressure EGR cooler 61, a high-pressure EGR valve 62, and a high-pressure EGR passage 64 that connects the exhaust gas recirculated from the exhaust passage 33 so that the exhaust gas can flow. . According to the high pressure EGR device 60, as with the low pressure EGR device 50, reduction of NOx and improvement of fuel consumption can be realized. Further, since the high pressure EGR device 60 reduces exhaust gas upstream of the turbine wheel 41 and the exhaust purification device 31 compared to the low pressure EGR device 50, the amount of soot and the like adhering to the turbine wheel 41 and the exhaust purification device 31 is reduced. And durability can be improved.

  The high pressure EGR flow path 64 includes an EGR inlet pipe 64a and an EGR outlet pipe 64b. The EGR inlet pipe 64 a connects the exhaust passage 33 and the high pressure EGR cooler 61. The EGR outlet pipe 64 b connects the high pressure EGR cooler 61 and the intake flow path 13. The EGR inlet pipe 64a is formed shorter than the EGR outlet pipe 64b.

  The high pressure EGR valve 62 is provided in the EGR outlet pipe 64b and adjusts the flow rate of the exhaust gas recirculated to the intake passage 13 according to the opening degree. For example, when the high-pressure EGR valve 62 is closed, the exhaust gas is not recirculated to the intake flow path 13, and thereafter, when the high-pressure EGR valve 62 is opened, the flow of the exhaust gas is switched and the high-pressure EGR valve 62 is switched. Is recirculated to the intake flow path 13 in accordance with the opening degree.

  Next, the high pressure EGR device 60 will be described with reference to FIG. FIG. 2 is an enlarged configuration diagram of the vicinity of the high-pressure EGR cooler 61 attached to the exhaust flow path 33.

  As shown in FIG. 2, the EGR inlet pipe 64 a is routed in a U shape from the exhaust passage 33 and connected to the high pressure EGR cooler 61. An exhaust passage connection portion 64c is formed at a portion of the EGR inlet pipe 64a connected to the exhaust passage 33.

  The exhaust flow path connection portion 64c has an introduction port 64d for introducing the exhaust gas of the exhaust flow path 33 into the EGR inlet pipe 64a, and has an acute angle from the exhaust flow path 33 along the flow direction of the exhaust gas from upstream to downstream. Branches at a certain angle θ. The introduction port 64d is disposed so that a part thereof enters the exhaust passage 33, and opens toward the upstream side of the exhaust gas flow direction in the exhaust passage 33. Since the ram pressure is generated by forming the exhaust flow path connection portion 64c in this way, even when the high pressure EGR valve 62 is closed, a part of the exhaust gas flowing through the exhaust flow path 33 is EGR. It flows to the inlet pipe 64a. The exhaust gas introduced into the EGR inlet pipe 64a is guided to the high pressure EGR cooler 61 by natural convection.

  The high pressure EGR cooler 61 cools the exhaust gas guided from the exhaust flow path 33 by the cooling water flowing through the inside. The cooling water is connected so that the engine 20 can be cooled by a flow path (not shown), and the heat of the high-pressure EGR cooler 61 and the engine 20 is released from a radiator (not shown). The cooling water can cool not only the engine 20 but also various devices that generate heat of the diesel vehicle.

  Here, the high pressure EGR cooler 61 will be described with reference to FIG. FIG. 3 is an internal cross-sectional view of the high pressure EGR cooler 61.

  As shown in FIG. 3, the high-pressure EGR cooler 61 performs heat exchange between the EGR gas passage 61a through which the exhaust gas guided from the exhaust passage 33 circulates and the exhaust gas in the EGR gas passage 61a. It has a plurality of tubes 61b through which the cooling water flows and fins 61c (see FIG. 4) arranged in the EGR gas passage 61a.

  The EGR gas passages 61a are formed between the tubes 61b and the adjacent tubes 61b by alternately stacking a plurality of tubes 61b at intervals. As shown by an arrow A in FIG. 3, the exhaust gas guided from the exhaust passage 33 flows through the EGR gas passage 61a through the EGR inlet pipe 64a. When the high-pressure EGR valve 62 is open, the exhaust gas flowing through the EGR gas passage 61a is recirculated to the intake flow path 13 through the EGR outlet pipe 64b as shown by an arrow B in FIG. On the other hand, the exhaust gas naturally convects around the EGR gas passage 61a and the EGR inlet pipe 64a when the high-pressure EGR valve 62 is closed.

  As shown by the arrow C in FIG. 3, the cooling water flows into the plurality of tubes 61b from the cooling water flow path inlet 61d. When the cooling water flows through the tube 61b, the cooling water exchanges heat with the exhaust gas passing through the adjacent EGR gas passage 61a via the tube 61b, and then, as shown by an arrow D in FIG. It flows out of 61e.

  As shown in FIGS. 4 and 5, the fin 61 c is formed with a protruding plate 61 f that protrudes in a direction that blocks the flow of exhaust gas in the EGR gas passage 61 a.

  FIG. 4 is an enlarged cross-sectional view for explaining the relationship between the tubes 61b and the fins 61c of the high-pressure EGR cooler 61. FIG. 5 is a partial perspective view of the fin 61 c of the high-pressure EGR cooler 61.

  As shown in FIG. 4, the fins 61c are bent so as to have a rectangular corrugated shape, and are disposed so that the bottom surface and the top surface are in contact with two adjacent tubes 61b. Protruding plates 61f are respectively installed on the bottom surface and the top surface of the fin 61c.

  As shown in FIG. 5, the protruding plate 61 f is installed so as to incline forward by an angle α toward the upstream in the exhaust gas flow direction. An arrow E in FIG. 5 indicates the flow of exhaust gas passing near the fins 61c. Further, the protruding plate 61f is installed so as to be inclined at an angle β with respect to the orthogonal direction of the exhaust gas flow. For example, the angle α is set to 60 degrees, and the angle β is set to 30 degrees. The protruding plate 61f may be formed only on the tube 61b instead of the fin 61c, or may be formed on both the fin 61c and the tube 61b.

  As shown in FIG. 3, an EGR outlet water temperature sensor 71 is attached to the cooling water passage outlet 61e. The EGR outlet water temperature sensor 71 detects the outlet temperature of the cooling water of the high pressure EGR cooler 61 as the EGR cooler outlet water temperature Tw. Here, the cooling water channel outlet 61e is connected in the vicinity of the tube 61b. Therefore, since the heat of the cooling water in the tube 61b is transmitted by convection even when the EGR cooling water valve 61g is closed, the cooling water in the tube 61b is detected by detecting the outlet temperature of the cooling water in the high pressure EGR cooler 61. The temperature can be determined. Further, an EGR cooler outlet gas temperature sensor 72 is attached in the vicinity of a connection portion connected to the EGR gas passage 61a of the EGR outlet pipe 64b. The EGR cooler outlet gas temperature sensor 72 detects the outlet gas temperature degree of the high pressure EGR cooler 61 as the EGR cooler outlet gas temperature Tg. The EGR cooler outlet gas temperature sensor 72 may be installed at the outlet portion of the EGR gas passage 61a.

  The controller 70 (see FIGS. 1 and 2) is configured by a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and by reading a program stored in the ROM by the CPU, Various functions are exhibited by the engine 20, the low pressure EGR device 50, and the high pressure EGR device 60.

  To the controller 70, for example, signals from an EGR outlet water temperature sensor 71 and an EGR cooler outlet gas temperature sensor 72 are input in order to cause the high-pressure EGR device 60 to perform various functions. The controller 70 may be input with a signal from an engine rotation sensor (not shown) that detects the rotation speed of the engine 20 or an accelerator opening detection sensor (not shown) that detects the accelerator opening.

  The controller 70 controls the high pressure EGR device 60 based on the input signal. That is, the controller 70 performs opening / closing control of the intake shutter valve 63 and the high-pressure EGR valve 62 as shown by a broken line in FIG. 1 according to the load of the engine 20 and the like, and EGR cooling as shown by a broken line in FIG. The opening / closing control of the water valve 61g is executed.

  Next, EGR cooler cleaning control executed by the controller 70 in order to remove the soot C attached to the EGR cooler will be described with reference to FIG. FIG. 6 is a flowchart showing the flow of EGR cooler cleaning control. The controller 70 executes EGR cooler cleaning control when the engine 20 is cold-started. The cold start is to start the engine 20 when the engine 20 or the like is cooled to near the outside temperature. For example, a situation where the engine 20 is started after the diesel vehicle is parked overnight is assumed as the cold start. . Due to the traveling of the diesel vehicle up to the previous time, adhering soot C is deposited on the surface of the tube 61b of the high pressure EGR cooler 61 at the cold start, as shown in FIG. 7A. FIG. 7A is a schematic diagram illustrating the state of the ridge C attached to the tube 61b.

  In step S <b> 101, the controller 70 executes a cold start process of the engine 20. In the cold start process, the high-pressure EGR valve 62 and the EGR cooling water valve 61g are in a closed state.

  In step S102, the controller 70 determines whether or not the EGR cooler outlet water temperature Tw is equal to or higher than a predetermined water temperature T1. The process of the controller 70 proceeds to step S103 when the EGR cooler outlet water temperature Tw is equal to or higher than the predetermined water temperature T1, and proceeds to step S104 when it is lower than the predetermined water temperature T1. The predetermined water temperature T1 is a temperature at which the exhaust gas cannot be cooled below the dew point when the exhaust gas is cooled, and is 60 ° C., for example.

  When the exhaust gas is cooled below the dew point, condensed water W is generated between the tube 61b and the soot C, as shown in FIG. 7B. FIG. 7B is a schematic diagram illustrating the condensed water W generated between the tube 61b and the bowl C. Condensed water W is obtained by condensation of water vapor contained in the exhaust gas by cooling the exhaust gas that has entered the interior of the bag C from the small gap on the surface of the tube C near the surface of the tube 61b. The condensed water W is also generated when the exhaust gas existing in the soot C deposited near the surface of the tube 61b is cooled and the water vapor in the exhaust gas is condensed.

  The soot C is an oily (hydrophobic) property in which hydrocarbons left unburned in the combustion process are aggregated and solidified through various chemical reactions. Therefore, the generated condensed water W forms a water film layer by spreading between the tube 61b and the ridge C without being absorbed by the hydrophobic ridge C. As a result, the bag C is forcibly separated from the surface of the tube 61b by the water film.

  On the other hand, when the exhaust gas is not cooled below the dew point, the water vapor contained in the exhaust gas passes through the EGR gas passage 61a of the high-pressure EGR cooler 61 without being condensed.

  In step S <b> 103, the controller 70 executes a cleaning process for the high pressure EGR cooler 61. In the cleaning process, the controller 70 opens the high-pressure EGR valve 62 and the EGR cooling water valve 61g.

  When the high pressure EGR valve 62 is opened, EGR is started, and exhaust gas passes through the EGR gas passage 61a vigorously. Therefore, the soot C separated from the surface of the tube 61b is blown downstream together with the condensed water W by the exhaust gas as shown in FIG. 7C. FIG. 7C is a schematic diagram illustrating a state in which the ridge C is washed away from the tube 61b. At that time, since the temperature of the exhaust gas when the EGR cooler outlet water temperature Tw exceeds the predetermined water temperature T1 is normally a high temperature of 100 ° C. or higher, the blown-off condensed water W evaporates when blown off. Thus, it does not flow into the engine 20 as a liquid.

  Moreover, since the EGR cooling water valve 61g is opened, the cooling water in the tube 61b flows, so that the high-temperature exhaust gas passing through the EGR gas passage 61a can be continuously cooled.

  After the soot C and the condensed water W are blown off, the controller 70 ends the EGR cooler cleaning control and executes normal EGR control.

  In step S104, the controller 70 determines whether or not the EGR cooler outlet gas temperature Tg is equal to or higher than a predetermined gas temperature T2. The processing of the controller 70 proceeds to step S105 when the EGR cooler outlet gas temperature Tg is equal to or higher than the predetermined gas temperature T2, and proceeds to step S106 when it is lower than the predetermined gas temperature T2. The predetermined gas temperature T2 is a temperature at which the condensed water W boils and evaporates, and is 100 ° C., for example.

  In step S105, the controller 70 determines that the engine 20 is in a high load state, and executes a high load process. In the high load process, the controller 70 opens the high pressure EGR valve 62 while closing the EGR cooling water valve 61g. As a result, the high-temperature exhaust gas passes through the EGR gas passage 61a of the high-pressure EGR cooler 61 vigorously, and the separated soot C is blown off together with the condensed water W by the exhaust gas. Thereafter, the controller 70 terminates the EGR cooler cleaning control when the EGR cooler outlet water temperature Tw becomes equal to or higher than the predetermined water temperature T1, and executes normal EGR control.

  In step S <b> 106, the controller 70 executes a condensed water generation process in order to generate more condensed water W. In the condensed water generation process, the controller 70 keeps the high pressure EGR valve 62 and the EGR cooling water valve 61g closed. As a result, the exhaust gas can be introduced into the high-pressure EGR cooler 61 little by little by natural convection while suppressing the temperature of the high-pressure EGR cooler 61 from rapidly flowing due to high-temperature exhaust gas flowing. As a result, the exhaust gas that has entered the interior of the eaves C through the gaps on the surface of the eaves C is cooled by the cooling water, and a water film is formed by the condensed water W on the surface of the tube 61b. Thereafter, the controller 70 executes normal EGR control after executing the EGR cooler cleaning process after the EGR cooler outlet water temperature Tw becomes equal to or higher than the predetermined water temperature T1.

  Next, referring to FIG. 8, the state of the temperature change of the cooling water in the high-pressure EGR cooler 61 when the controller 70 executes the EGR cooler cleaning control when the engine 20 is cold started will be described. FIG. 8 is a timing chart showing the relationship between the time during which the condensed water W is generated at the cold start and the EGR cooler outlet water temperature Tw. The horizontal axis of FIG. 8 is time, and the vertical axis is the EGR cooler outlet water temperature Tw. In addition, the EGR cooler outlet water temperature Tw of the present embodiment is indicated by a solid line, and as a comparative example, the EGR cooler outlet water temperature Tw when the high pressure EGR valve 62 is opened from the beginning is indicated by a broken line.

  Time t0 is the time when the engine 20 has started cold. At time t0, the EGR cooler outlet water temperature Tw of the present embodiment and the EGR cooler outlet water temperature Tw of the comparative example are both in a low temperature state.

  The controller 70 of the comparative example starts normal EGR control at time t0 and opens the EGR cooling water valve 61g. In normal EGR control, the exhaust gas temperature is low at the cold start and EGR cannot be started, so the high pressure EGR valve 62 is closed, and the exhaust gas flowing through the exhaust passage 33 is guided to the high pressure EGR cooler 61 by natural convection. It is burned.

  In the case of the comparative example, since the EGR cooling water valve 61g is open, the heat when the engine 20 or the like is cooled is transmitted to the high pressure EGR cooler 61. Then, the cooling water in the high pressure EGR cooler 61 is rapidly heated by the exhaust gas guided by natural convection and the heat of the engine 20, etc., and the EGR cooler outlet water temperature Tw reaches the predetermined water temperature T1 at time t1 ′. . Thereafter, normal EGR control is started at time t <b> 1 ′, whereby the high pressure EGR valve 62 is opened, and the exhaust gas flows into the high pressure EGR cooler 61.

  On the other hand, the controller 70 of the present embodiment starts the EGR cooler cleaning control at time t0, and the high pressure EGR valve 62 and the EGR cooling water valve 61g are closed by the cold start process as shown in step S101 in FIG. Yes. Therefore, the exhaust gas flowing through the exhaust passage 33 is guided to the high pressure EGR cooler 61 by natural convection. The controller 70 performs the condensed water production | generation process of step S106, when the engine 20 is not high-load.

  Thereafter, the cooling water in the high-pressure EGR cooler 61 is heated only by the exhaust gas guided by natural convection and gradually raised in temperature, so that the EGR cooler outlet water temperature Tw is a time t1 longer than the time t1 ′. The predetermined water temperature T1 is reached. Then, when the controller 70 starts normal EGR control and opens the high pressure EGR valve 62, the exhaust gas flows into the high pressure EGR cooler 61. Here, from time t0 to time t1, a large amount of condensed water W is generated by the condensed water generation process, and a water film is sufficiently formed between the tube 61b and the bowl C. Therefore, the soot C on the water film can be washed away when the exhaust gas vigorously flows through the EGR gas passage 61a of the high-pressure EGR cooler 61. Thus, in the case of this embodiment compared with the case of a comparative example, since the time which can produce | generate condensed water W can be made sufficiently long to time t1, the quantity of the condensed water W to produce | generate is increased and the tube 61b is increased. A water film can be surely formed between 煤 and C.

  Further, as shown by the solid line in FIG. 8, the EGR cooler outlet water temperature Tw of the present embodiment can maintain a temperature lower than that of the comparative example until reaching the time t1. As a result, in the case of this embodiment, a state in which the amount of saturated water vapor is small can be maintained for a long time, so that the amount of condensed water W to be generated can be increased.

  FIG. 9 is a timing chart illustrating EGR cooler cleaning control when a high load operation is performed at a cold start. The horizontal axis in FIG. 9 is time, and the vertical axis is temperature. Further, the EGR cooler outlet water temperature Tw of the present embodiment is indicated by a straight line, and the EGR cooler outlet gas temperature Tg is indicated by a broken line.

  When a high load operation is performed at a cold start, the combustion temperature of the engine 20 rises at a stretch and the temperature of the exhaust gas increases. Therefore, the temperature of the exhaust gas guided into the high-pressure EGR cooler 61 by natural convection also increases, and the EGR cooler outlet gas temperature Tg rises to a predetermined gas temperature T2 or higher at time t2.

  When the EGR cooler outlet gas temperature Tg becomes equal to or higher than the predetermined gas temperature T2, the controller 70 determines that the engine 20 is in a high load state and executes a high load process as shown in step S105 of FIG. In the high load processing, even when the EGR cooler outlet water temperature Tw is lower than the predetermined water temperature T1, the high pressure EGR valve 62 is opened and the exhaust gas is caused to flow into the high pressure EGR cooler 61. Therefore, the soot C adhering to the surface of the tube 61b of the high pressure EGR cooler 61 is immediately washed away by the generated condensed water W.

  Thereafter, when the EGR cooler outlet water temperature Tw becomes equal to or higher than the predetermined water temperature T1 at time t1, the controller 70 starts normal EGR control, opens the EGR cooling water valve 61g, and circulates the cooling water in the high pressure EGR cooler 61.

  According to the above embodiment, there exist the effects shown below.

  The high pressure EGR device 60 recirculates a part of the exhaust gas discharged from the engine 20 from the exhaust passage 33 to the intake passage 13. The high-pressure EGR device 60 includes a high-pressure EGR cooler 61 that cools the exhaust gas guided from the exhaust passage 33 by cooling water that flows through the inside, and an EGR inlet pipe 64 a that connects the exhaust passage 33 and the high-pressure EGR cooler 61. The EGR outlet pipe 64b that connects the high-pressure EGR cooler 61 and the intake passage 13 and the high-pressure EGR valve 62 that is provided in the EGR outlet pipe 64b and switches the flow of the exhaust gas. The high pressure EGR cooler 61 includes an EGR gas passage 61a through which exhaust gas guided from the exhaust passage 33 flows, and a tube 61b through which cooling water as a refrigerant flows so as to exchange heat with the exhaust gas in the EGR gas passage 61a. And having. In the high-pressure EGR cooler 61, the exhaust gas in the EGR gas passage 61a is cooled by the cooling water, so that the gap between the wall C of the EGR gas passage 61a, that is, the surface attached to the outer surface of the tube 61b, and the surface of the tube 61b. Condensed water W is generated. The high pressure EGR valve 62 is opened when the EGR cooler outlet water temperature Tw as the temperature of the cooling water in the tube 61b is equal to or higher than the predetermined water temperature T1.

  According to such a high-pressure EGR device 60, the exhaust gas that has reached the high-pressure EGR cooler 61 by natural convection is cooled near the surface of the tube 61b until it falls below the dew point, so that the soot C attached to the surface of the tube 61b A water film is formed by the condensed water W generated during As a result, since the tube 61b and the bag C are separated by the water film, the high pressure EGR valve 62 is opened and the exhaust gas is forced to flow into the high pressure EGR cooler 61. The adhered soot C can be washed away. Further, since the soot C adhering during the previous run can be washed away every time cold start, it is possible to suppress the soot C from adhering to the surface of the tube 61b over time. Therefore, it is possible to provide the high-pressure EGR device 60 that can prevent a decrease in heat exchange efficiency.

  In the high pressure EGR device 60, the EGR inlet pipe 64a is shorter than the EGR outlet pipe 64b. Therefore, the exhaust gas in the exhaust passage 33 can reach the high pressure EGR cooler 61 by natural convection even if the high pressure EGR valve 62 is not opened. As a result, the exhaust gas can be cooled in the vicinity of the surface of the tube 61b until it falls below the dew point, so that condensed water W is generated between the surface of the tube 61b and the attached soot C to form a water film. it can.

  In the high pressure EGR device 60, the EGR inlet pipe 64 a has an exhaust flow path connection portion 64 c connected to the exhaust flow path 33. The exhaust flow path connection portion 64 c branches at an acute angle θ from upstream to downstream along the flow direction of the exhaust gas in the exhaust flow path 33. As a result, the exhaust gas in the exhaust passage 33 is subjected to the ram pressure at the exhaust passage connection portion 64c when flowing toward the downstream, so that a part of the exhaust gas flows into the EGR inlet pipe 64a. .

  Further, in the high pressure EGR device 60, the exhaust flow path connection portion 64 c has an introduction port 64 d formed in the exhaust flow path 33. The introduction port 64d opens toward the upstream of the exhaust gas flow direction in the exhaust passage 33.

  As a result, even if the high pressure EGR valve 62 is closed, the exhaust gas can be naturally convected up to the high pressure EGR cooler 61 using the action of the ram pressure.

  The exhaust flow path connecting portion 64c may be branched from the exhaust flow path 33 at an acute angle θ so that the ram pressure acts, and is arranged so that the entire inlet 64d does not enter the exhaust flow path 33. May be. As a result, the exhaust gas can be naturally convected into the high-pressure EGR cooler 61 by the ram pressure while suppressing an increase in the pressure loss of the exhaust passage 33.

  In the present embodiment, the exhaust flow path connection portion 64c is disposed so that a part of the introduction port 64d enters the exhaust flow path 33. However, the entire introduction port 64d enters the exhaust flow path 33. You may arrange | position so that it may face the upstream of the exhaust flow path 33. FIG. By arranging the exhaust flow path connection portion 64c in this way, the exhaust gas in the exhaust flow path 33 can be easily flowed into the EGR inlet pipe 64a.

  The high pressure EGR valve 62 is closed when the temperature of the cooling water in the high pressure EGR cooler 61 is lower than the predetermined water temperature T1. Therefore, a part of the exhaust gas flowing through the exhaust passage 33 can be guided into the high-pressure EGR cooler 61 by natural convection. As a result, the guided exhaust gas is cooled by the cooling water in the EGR gas passage 61a, whereby the condensed water W can be generated. In addition, since the high-pressure EGR valve 62 is closed and high-temperature exhaust gas does not flow into the high-pressure EGR cooler 61 at a stretch, the cooling water is heated to a high temperature so that the condensed water W cannot be generated. Can be suppressed.

  In the high pressure EGR device 60, the high pressure EGR cooler 61 has an EGR cooling water valve 61g for switching the flow of the cooling water. The EGR cooling water valve 61g is closed when the high-pressure EGR valve 62 is closed. Thus, when the EGR cooler cleaning control is executed, the EGR cooling water valve 61g is closed, so that the cooling water flow path in the high-pressure EGR cooler 61 can be made independent. For this reason, the cooling water in the high-pressure EGR cooler 61 can be suppressed from being rapidly heated by exhaust heat from the engine 20 and the like, and the temperature rise can be moderated. Therefore, the amount of condensed water W generated can be increased. Further, when normal EGR control is executed, the cooling water flows through the tube 61b, so that the exhaust gas flowing through the EGR gas passage 61a can be stably cooled as usual.

  In the high pressure EGR device 60, the high pressure EGR cooler 61 further includes fins 61c disposed in the EGR gas passage 61a. At least one of the fin 61c and the tube 61b as the refrigerant flow path is formed with a protruding plate 61f that protrudes in a direction that blocks the flow of exhaust gas in the EGR gas passage 61a. Thus, the protruding plate 61f formed on at least one of the fin 61c and the tube 61b stirs the flow of the exhaust gas in the EGR gas passage 61a, so that the soot C can be washed away vigorously by the turbulent flow.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

  For example, in the high-pressure EGR device 60 of the above-described embodiment, the case where the EGR inlet pipe 64a is shorter than the EGR outlet pipe 64b or the case where the high-pressure EGR device 60 opens toward the upstream in the exhaust gas flow direction has been described. However, the mode in which the ram pressure can be applied is not limited to these embodiments. For example, by forming the EGR inlet pipe 64a with a diameter larger than that of the EGR outlet pipe 64b, the exhaust gas easily convects naturally due to the ram pressure. Therefore, even if the high-pressure EGR valve 62 is closed, the condensed water W The generation of can be promoted. Further, the valve may be stopped halfway so that the flow path is temporarily restricted when the high pressure EGR valve 62 is opened. Further, when the EGR cooling water is excessively cooled, the valve may be stopped halfway so as to temporarily restrict the flow path when the EGR cooling water valve 61g is opened. Moreover, even if the opening / closing valves of the high-pressure EGR valve 62 and the EGR cooling water valve 61g are controlled in a coordinated manner so that the temperature difference between the exhaust gas temperature and the cooling water temperature becomes large so that condensed water is easily generated. Good.

  Further, the same mode and control as the high pressure EGR device 60 of the above embodiment can be applied to the low pressure EGR device 50. Accordingly, it is possible to provide the low pressure EGR device 50 that can prevent a decrease in heat exchange efficiency. In addition to the cooling water, for example, air or other cooling liquid may be used as the refrigerant.

  In addition, the said embodiment can be combined suitably.

  This application claims the priority based on Japanese Patent Application No. 2006-19802 for which it applied to Japan Patent Office on February 4, 2016, and all the content of this application is integrated in this specification by reference.

Claims (5)

An EGR device that recirculates a part of exhaust gas discharged from an engine from an exhaust passage to an intake passage,
An EGR cooler that cools the exhaust gas guided from the exhaust flow path by the refrigerant circulating in the interior;
An EGR inlet pipe connecting the exhaust passage and the EGR cooler;
An EGR outlet pipe connecting the EGR cooler and the intake passage;
An EGR on-off valve provided in the EGR outlet pipe for switching the flow of exhaust gas;
With
The EGR cooler is
An EGR gas passage through which the exhaust gas guided from the exhaust flow path flows;
A refrigerant flow path through which a refrigerant flows so as to exchange heat with the exhaust gas in the EGR gas passage;
Have
The EGR on-off valve is opened when the temperature of the refrigerant in the refrigerant flow path is equal to or higher than a predetermined temperature ,
The EGR inlet pipe is thicker than the EGR outlet pipe,
The refrigerant is cooling water,
The EGR on-off valve is closed when the temperature of the cooling water in the EGR cooler is lower than a predetermined temperature,
The EGR cooler has a cooling water on-off valve that switches the flow of cooling water,
The cooling water on-off valve is closed when the EGR on-off valve is closed.
EGR device. The EGR device according to claim 1,
The EGR inlet pipe is shorter than the EGR outlet pipe.
EGR device. The EGR device according to claim 1 or 2,
The EGR inlet pipe has an exhaust passage connecting portion connected to the exhaust passage,
The exhaust flow path connecting portion branches at an acute angle from upstream to downstream along the flow direction of the exhaust gas in the exhaust flow path.
EGR device. The EGR device according to claim 3,
The exhaust passage connection portion has an inlet formed in the exhaust passage,
The introduction port opens toward the upstream of the exhaust gas flow direction of the exhaust flow path,
EGR device. The EGR device according to any one of claims 1 to 4, wherein:
The EGR cooler further includes fins disposed in the EGR gas passage,
At least one of the fin and the refrigerant flow path is formed with a protruding plate that protrudes in a direction that blocks the flow of exhaust gas in the EGR gas passage.
EGR device.

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