JP2012082723A - Cooling device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling device of an internal combustion engine in which the capacity of a main radiator of a main cooling water passage and the capacity of a sub radiator of a sub cooling water passage are prevented from being increased more than necessary.SOLUTION: A water-cooling type exhaust manifold 16 is connected to both a main cooling water passage 3 and a sub cooling water passage 5 which are cooling water passages independent from each other, and the exhaust manifold 16 and an EGR cooler 13 are connected to each other in parallel in the sub cooling water passage 5. The operating state in which EGR gas is cooled in the EGR cooler 13 is not same as the operating state in which exhaust gas is cooled in the exhaust manifold 16. Thus, the water-cooling type exhaust manifold 16 can be achieved in an optimum state by efficiently using the sub radiator 4 according to the operating state without increasing the capacity of the main radiator 2 and the capacity of the sub radiator 4 more than necessary.

Description

  The present invention relates to a cooling device for an internal combustion engine.

  For example, Patent Document 1 discloses a main radiator that cools cooling water supplied to an EGR cooler and cooling water supplied to a high-temperature portion of the internal combustion engine in order to prevent misfire and improve drivability of the internal combustion engine. There is disclosed a technique in which cooling is performed by a sub-radiator provided in a cooling water path different from the provided path.

  Further, a technology that uses a cooling water that cools the exhaust manifold with cooling water and uses the cooling water that has become high temperature by heat exchange between the exhaust gas and the cooling water is conventionally known. For example, in Patent Document 2, the cooling water is heated by the heat of the exhaust gas by setting a cooling water passage so that the cooling water can flow inside the exhaust manifold or around the exhaust manifold when cold. The heating performance of the hot water heater is improved by allowing the heated cooling water to flow into the hot water heater.

JP 2007-40141 A JP 59-68545 A

  However, in Patent Document 2, if the engine cooling water is allowed to flow in the exhaust manifold or in the periphery of the exhaust manifold after warming up, the exhaust gas temperature is lowered to reduce the thermal deterioration of the catalyst interposed in the exhaust passage. Although it is possible to improve the output of the internal combustion engine while avoiding it, since there is one radiator for cooling the cooling water, there is a problem that the capacity of the radiator must be increased when using in this way is there.

  In addition, the operation region for cooling the EGR gas is limited, and the sub-radiator is not used in the configuration in which the sub-radiator is simply provided in a different route from the route in which the main radiator is provided as in Patent Document 1. There is a problem that an operating region exists and the sub-radiator is not used effectively.

  Therefore, the present invention efficiently uses the sub-radiator provided in the sub-cooling water path that is different from the main cooling water path provided with the main radiator when the water-cooled exhaust manifold is applied to the internal combustion engine. Thus, an object of the present invention is to provide an internal combustion engine cooling device that is optimized without unnecessarily increasing the capacity of the main radiator in the main cooling water path and the capacity of the sub radiator in the sub cooling water path.

  In the cooling apparatus for an internal combustion engine according to the present invention, a water-cooled exhaust manifold is connected to both a main cooling water path and a sub cooling water path which are independent cooling water paths, and the exhaust gas is disposed in the sub cooling water path. The manifold and the EGR cooler are connected in parallel.

  In the EGR cooler, the operation state in which the EGR gas is desired to be cooled is not the same as the operation state in which the exhaust gas is desired to be cooled in the exhaust manifold. Therefore, the water-cooled exhaust manifold is connected to both the main cooling water path and the sub-cooling water path, and the exhaust manifold and the EGR cooler are connected in parallel in the sub-cooling water path, depending on the operating conditions. By efficiently using the sub-radiator, it is possible to make the exhaust manifold a water-cooled exhaust manifold with the main radiator capacity and the sub-radiator capacity optimized without increasing more than necessary.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which showed typically the outline of the cooling device of the internal combustion engine to which this invention was applied. Explanatory drawing which showed typically the driving | operation area | region which can be expanded at the time of high load and can cancel sulfur poisoning. Explanatory drawing which showed typically the driving | operation area | region which can be expanded and the sulfur poisoning cancellation | release is possible at the time of low load.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view schematically showing an outline of a cooling device for an internal combustion engine to which the present invention is applied.

  An internal combustion engine 1 that is a diesel engine has a main cooling water path 3 that cools cooling water in the path by a main radiator 2 and a sub cooling water path 5 that cools cooling water in the path by a sub radiator 4. ing. The main cooling water path 3 and the sub cooling water path 5 are independent cooling water paths, the cooling water circulating in the main cooling water path 3, the cooling water circulating in the sub cooling water path 5, Are formed so as not to mix with each other.

  An intake passage 6 and an exhaust passage 7 are connected to the internal combustion engine 1. A three-way catalyst 8 and a NOx trap catalyst 9 as exhaust purification catalysts and an exhaust particulate filter (DPF) 10 are interposed in the exhaust passage 7 in series.

  The three-way catalyst 8 purifies the three components of HC, CO, and NOx in the inflowing exhaust when the excess air ratio is substantially “1”, that is, when the exhaust air / fuel ratio is substantially the stoichiometric air / fuel ratio. . The NOx trap catalyst 9 adsorbs NOx in the exhaust gas when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and desorbs and reduces NOx when the exhaust air-fuel ratio is richer than the stoichiometric air-fuel ratio. The NOx trap catalyst 9 traps sulfur contained in the exhaust gas in addition to NOx. The DPF 10 collects PM (particulate matter) in the exhaust gas.

  Connected to the exhaust passage 7 is an EGR passage 11 that recirculates a part of the exhaust gas to the intake passage 6 as EGR gas. The EGR passage 11 is provided with an EGR valve 12 and a water-cooled EGR cooler 13, a bypass passage 14 capable of bypassing the EGR cooler 13 and introducing EGR gas into the intake passage 6, and a bypass passage 14 A bypass passage control valve 15 that opens and closes is provided.

  The bypass passage 14 has one end connected to the EGR passage 11 on the exhaust passage 7 side from the EGR gas inlet side of the EGR cooler 13, and the other end connected to the EGR passage 11 on the intake passage 6 side from the EGR gas outlet side of the EGR cooler 13. Has been. The bypass passage control valve 15 is provided at a connection portion between one end of the bypass passage 14 and the EGR passage 11.

  The EGR valve 12 is of an electronic control type using, for example, a step motor, and controls the amount of exhaust gas recirculated to the intake side according to the opening, that is, the EGR amount sucked into the internal combustion engine 1. . The EGR cooler 13 cools the EGR gas recirculated from the exhaust passage 7 on the downstream side of the exhaust manifold 16 described later.

  Cooling water circulating in the main cooling water path 3 flows through a water jacket (not shown) of the internal combustion engine 1 and cools a cylinder block (not shown) and a cylinder head (not shown). .

  In addition to the main radiator 2, the main cooling water path 3 includes a water-cooled exhaust manifold 16 made of metal such as aluminum, and a first flow rate adjusting valve 17 that adjusts the flow rate of cooling water flowing through the exhaust manifold 16. A water pump (not shown) or the like is interposed.

  In the main cooling water path 3, the exhaust manifold 16 is connected in parallel to the water jacket of the internal combustion engine 1. By opening the first flow rate adjustment valve 17, the exhaust manifold 16 is connected to the exhaust manifold 16 in the main cooling water path 3. It is possible to prevent the cooling water in the main cooling water path 3 from flowing into the exhaust manifold 16 by closing the first flow rate adjusting valve 17 by flowing the cooling water. In the present embodiment, the flow rate of the cooling water in the main cooling water path 3 flowing into the exhaust manifold 16 increases as the valve opening of the first flow rate adjustment valve 17 increases (closer to full opening). The first flow rate adjusting valve 17 is disposed on the downstream side of the exhaust manifold 16 in the main cooling water path 3 in the flow direction of the cooling water in the main cooling water path 3.

  The cooling water circulating in the sub cooling water path 5 flows through the EGR cooler 13 and the exhaust manifold 16.

  In addition to the sub-radiator 4 described above, the sub-cooling water path 5 includes an EGR cooler 13, a water-cooled exhaust manifold 16, an electric water pump 18, a cooling water flow rate flowing through the exhaust manifold 16 and a cooling water flowing through the EGR cooler 13. A second flow rate adjusting valve 19 that adjusts the ratio to the flow rate is interposed.

  The exhaust manifold 16 and the EGR cooler 13 are connected in parallel in the sub-cooling water path 5. In this embodiment, the cooling water in the sub-cooling water path 5 circulates counterclockwise in FIG. 1, and the cooling water discharged from the water pump 18 passes through the exhaust manifold 16 and the EGR cooler 13 and is sub-radiator. 4, and after being cooled by the sub-radiator 4, is introduced into the water pump 18. Further, the cooling water temperature in the sub cooling water passage 5 is set to be lower than the cooling water temperature in the main cooling water passage 3.

  The second flow rate adjusting valve 19 is a three-way valve disposed at a portion where the cooling water flowing through the exhaust manifold 16 and the cooling water flowing through the EGR cooler 13 merge (on the downstream side of the exhaust manifold 16 and the EGR cooler 13). The opening degree is controlled between 0 degrees (fully closed) and 90 degrees (fully opened). In the present embodiment, the cooling water does not flow into the exhaust manifold 16 when fully closed, and the cooling water does not flow into the EGR cooler 13, and the cooling water does not flow into the EGR cooler 13 when fully opened, and all the cooling water flows into the exhaust manifold 16. It is set to flow.

  The first flow rate adjusting valve 17, the second flow rate adjusting valve 19 and the bypass passage control valve 15 are electronically controlled using a step motor, for example, and include the EGR valve 12 described above and an ECU (Engine Control Unit) 20. Is controlled to open and close. Further, the discharge amount per unit time of the water pump 18 can be variably controlled by the ECU 20.

  The ECU 20 includes an engine speed sensor 21 for detecting the engine speed, an accelerator opening sensor 22 for detecting the accelerator opening, an air flow meter 23 for detecting the intake air amount, and a three-way catalyst 8 upstream for controlling the internal combustion engine 1. Sensor 24 for detecting the temperature of the exhaust gas in the exhaust passage 7 on the side, temperature sensor 25 for detecting the temperature of the NOx trap catalyst 9, exhaust pressure sensor 26 for detecting the exhaust pressure at the DPF 10 inlet, and exhaust at the inlet of the three-way catalyst 8 An air-fuel ratio sensor 27 for detecting the air-fuel ratio, an air-fuel ratio sensor 28 for detecting the exhaust air-fuel ratio at the outlet of the NOx trap catalyst 9, a temperature sensor 29 for detecting the EGR gas temperature on the outlet side of the EGR cooler 13, and a catalyst for the three-way catalyst 8 A temperature sensor 30 for detecting the temperature, a temperature sensor 31 for detecting the cooling water temperature in the main cooling water path 3, and a cooling water temperature in the sub cooling water path 5 are detected. Detection signals from various sensors of the temperature sensor 32 and the like are inputted that.

  The ECU 20 controls the drive of the fuel injection valve (not shown) by setting the fuel injection amount and the injection timing based on the detection signals from these various sensors, as well as the throttle valve (not shown) and the EGR. The opening degree of the valve 12 is controlled. In particular, as the control according to the present invention, the ECU 20 operates the opening degree of the first flow rate adjustment valve 17 disposed in the main cooling water path 3 and the second flow rate adjustment valve 19 disposed in the sub cooling water path 5. Control according to the state.

  First, from the start of the internal combustion engine 1 until the three-way catalyst 8 and the NOx trap catalyst 9 are activated, cooling water to the extent that the function of the exhaust manifold 16 is ensured flows into the exhaust manifold 16 and the EGR cooler 13 The cooling requirement for EGR gas is low, and the flow rate of cooling water flowing into the EGR cooler 13 is also reduced.

  In the exhaust manifold 16 made of metal, there is a possibility that the expected function cannot be secured unless the cooling water is flown at all. Therefore, it is necessary to flow the cooling water at a flow rate that ensures the expected function. In the scene from the start of the internal combustion engine 1 to the activation of the three-way catalyst 8 and the NOx trap catalyst 9, the EGR gas is recirculated to the intake passage 6. Since it is necessary to activate, the cooling request | requirement with respect to EGR gas is small, and the cooling water flow volume which flows in into the EGR cooler 13 may be small.

  Therefore, from the start of the internal combustion engine 1 until the three-way catalyst 8 and the NOx trap catalyst 9 are activated, the first flow rate adjustment valve 17 is closed in the main cooling water path 3 and the cooling water flows into the exhaust manifold 16. Do not. In the sub cooling water path 5, the opening of the second flow rate adjusting valve 19 is set to half open (45 °), and the discharge amount of the cooling water per unit time of the water pump 18 is relatively reduced. The cooling water flow rate flowing in the exhaust manifold 16 is controlled so that the cooling water does not boil in the exhaust manifold 16. At this time, the bypass passage control valve 15 is opened, and the EGR gas flows through the bypass passage 14.

  Thereby, cooling of both the exhaust manifold 16 and the EGR gas can be suppressed, and the catalyst can be activated at an early stage.

  In the state from the start of the internal combustion engine 1 to the activation of the three-way catalyst 8 and the NOx trap catalyst 9, the first flow rate adjustment valve 17 is closed in the main cooling water path 3, and the sub cooling water path 5 Controls the opening of the second flow rate adjustment valve 19 so that the flow rate of the cooling water flowing in the exhaust manifold 16 becomes a minimum amount in which the cooling water does not boil in the exhaust manifold 16, and further controls the bypass passage control valve 15. If the valve is opened so that the EGR gas flows through the bypass passage 14, the cooling of both the exhaust manifold 16 and the EGR gas is suppressed without controlling the cooling water discharge amount per unit time of the water pump 18. be able to.

  Next, from the activation of the three-way catalyst 8 and the NOx trap catalyst 9 until the warming up of the internal combustion engine 1 is completed, the internal combustion engine 1 is warmed up using the heat of the exhaust manifold 16. Cooling water flows into the exhaust manifold 16 from the main cooling water path 3 side, but cooling water is prevented from flowing from the sub cooling water path 5 side. Further, since the warm-up of the internal combustion engine 1 has not been completed, the EGR gas is recirculated to the intake passage 6, but the cooling request for the EGR gas in the EGR cooler 13 is low, and the flow rate of the cooling water flowing into the EGR cooler 13 is also reduced. Yes.

  Specifically, in the main cooling water path 3, the first flow rate adjustment valve 17 is opened (fully opened) so that the cooling water flows into the exhaust manifold 16. In the sub cooling water path 5, the opening of the second flow rate adjustment valve 19 is set to be fully closed (0 °), and the discharge amount of the cooling water per unit time of the water pump 18 is relatively reduced. To control. At this time, the bypass passage control valve 15 is closed, so that EGR gas does not flow through the bypass passage 14. Moreover, you may make it control so that the discharge amount of the cooling water per unit time of the water pump 18 at this time may become relatively small.

  As a result, the heat of the exhaust manifold 16 is transferred to the internal combustion engine 1 through the cooling water flowing in the main cooling water passage 3, so that warming up of the internal combustion engine 1 is efficiently promoted, and the internal combustion engine 1 is heated. It is possible to improve fuel efficiency and heating performance by reducing friction.

  In the state from when the three-way catalyst 8 and the NOx trap catalyst 9 are activated until the warm-up of the internal combustion engine 1 is completed, the first flow rate adjustment valve 17 is opened (fully opened) in the main cooling water path 3. In the sub-cooling water path 5, the opening of the second flow rate adjustment valve 19 is fully closed (0 °), and the bypass passage control valve 15 is opened so that EGR gas flows through the bypass passage 14. In this case, it is not necessary to control the water pump 18 so that the amount of cooling water discharged per unit time is relatively small.

  In an operation state in which the EGR gas is recirculated to the intake passage 6 after the warm-up of the internal combustion engine 1 is finished, it is necessary to lower the temperature of the EGR gas in order to reduce NOx in the exhaust gas. Therefore, the sub-cooling water path 5 is a scene in which the cooling water flow rate is desired to be increased with respect to both the EGR cooler 13 and the exhaust manifold 16. On the other hand, in the main cooling water path 3, the EGR gas recirculates in the intake passage 6 and the increase in the combustion temperature is suppressed, so that the main radiator 2 cools the cooling water in the main cooling water path 3. The cooling capacity of the main radiator 2 has sufficient capacity.

  Therefore, in an operation state in which the EGR gas is recirculated to the intake passage 6 after the warm-up of the internal combustion engine 1 is finished, the first flow rate adjustment valve 17 is opened (fully opened) in the main cooling water path 3 and the exhaust manifold 16 is opened. Allow cooling water to flow. In the sub cooling water path 5, the opening degree of the second flow rate adjustment valve 19 is set so that the cooling water flow rate flowing through the exhaust manifold 16 is smaller than the cooling water flow rate flowing through the EGR cooler 13. In other words, the opening degree of the second flow rate adjustment valve 19 is set so that most of the cooling water flows to the EGR cooler 13. At this time, the bypass passage control valve 15 is closed, so that EGR gas does not flow through the bypass passage 14. The opening degree of the second flow rate adjustment valve 19 may be set to be fully closed so that the cooling water in the sub cooling water passage 5 does not flow into the exhaust manifold 16.

  Thus, in an operation state in which the EGR gas is recirculated to the intake passage 6 after the warm-up of the internal combustion engine 1 is finished, the exhaust manifold 16 is mainly cooled by the cooling water in the main cooling water path 3 and the sub cooling water path 5 By cooling the EGR gas mainly by the EGR cooler 13, the EGR gas can be effectively cooled in an optimized state without increasing the capacity of the sub radiator 4 more than necessary.

  When the EGR gas is cooled to the maximum in an operation state in which the EGR gas is recirculated to the intake passage 6 after the warm-up of the internal combustion engine 1 is finished, the water pump 18 has a maximum cooling water discharge amount per unit time. It will be driven to become.

  In an operation-oriented operation state in which EGR gas is not recirculated into the intake passage 6 after the warm-up of the internal combustion engine 1 is finished, it is required to reduce the temperature of the exhaust gas in order to improve the output of the internal combustion engine 1. Therefore, in order to cool the exhaust gas with the exhaust manifold 16, it is a scene where it is desired to increase the coolant flow rate with respect to the exhaust manifold 16.

  Here, in the main cooling water path 3, the internal combustion engine 1 is in an operation state in which output is emphasized, and the demand for cooling the cylinder block and the cylinder head of the internal combustion engine 1 is high. If the cooling water is caused to flow into the exhaust manifold 16, the cylinder block and the cylinder head of the internal combustion engine 1 may not be sufficiently cooled unless the capacity of the main radiator 2 is increased in advance. On the other hand, since it is not necessary to cool the EGR gas in the sub-cooling water path 5, the sub-radiator 2 has sufficient capacity for cooling the cooling water in the sub-cooling water path 5 by the sub-radiator 4.

  Therefore, in an operation state in which the EGR gas is not recirculated to the intake passage 6 after the warm-up of the internal combustion engine 1 is finished, the first flow rate adjustment valve 17 is closed (fully closed) in the main cooling water path 3 to the exhaust manifold 16. Prevent cooling water from flowing in. In the sub cooling water path 5, the opening degree of the second flow rate adjusting valve 19 is set so that the cooling water flow rate flowing through the exhaust manifold 16 is larger than the cooling water flow rate flowing through the EGR cooler 13. In other words, the opening degree of the second flow rate adjustment valve 19 is set so that most of the cooling water flows into the exhaust manifold 16. At this time, the bypass passage control valve 15 is closed, and the EGR gas does not flow through the bypass passage 14 but flows through the EGR cooler 13. Note that the opening of the second flow rate adjustment valve 19 is fully open (90 °), and in the sub-cooling water path 5, the cooling water does not flow into the EGR cooler 13 but all the cooling water flows into the exhaust manifold 16. Is also possible.

  As described above, in the operation state in which the EGR gas is not recirculated to the intake passage 6 after the warm-up of the internal combustion engine 1 is completed, the temperature of the exhaust gas is decreased in order to improve the output of the internal combustion engine 1. By efficiently using the cooling water, the exhaust gas can be effectively cooled in an optimized state without increasing the capacity of the main radiator 2 more than necessary.

  When the exhaust gas is cooled to the maximum in an operation state in which the EGR gas is not recirculated into the intake passage 6 after the warm-up of the internal combustion engine 1 is finished, the water pump 18 has a maximum discharge amount of cooling water per unit time. It will be driven to become.

  Next, when the sulfur poisoning of the NOx trap catalyst 9 is released, the opening degree of the first flow rate adjustment valve and the second flow rate adjustment valve 19 is controlled according to the load state (torque) of the internal combustion engine 1 at that time. To do.

  The sulfur poisoning releaseable operation region (S poisoning releaseable region) is basically set by the engine speed and torque (load), but is limited by the temperature of the NOx trap catalyst 9. The actual sulfur poisoning releasable operation region is limited so that the bed temperature of the NOx trap catalyst 9 does not exceed a predetermined upper limit temperature (for example, 750 ° C.) in order to protect the NOx trap catalyst 9 from thermal degradation. If the temperature of the NOx trap catalyst 9 is too low, the sulfur poisoning cannot be released. Therefore, the bed temperature of the NOx trap catalyst 9 is limited so as not to be lower than a predetermined lower limit temperature (for example, 650 ° C.). That is, even in the sulfur poisoning releaseable operation region set by the engine speed and torque (load), the region where the bed temperature of the NOx trap catalyst 9 is equal to or higher than a predetermined upper limit temperature (for example, 750 ° C.), NOx In the region where the bed temperature of the trap catalyst 9 is equal to or lower than a predetermined lower limit temperature (for example, 650 ° C.), sulfur poisoning cannot be released.

  When releasing the sulfur poisoning of the NOx trap catalyst 9 during a high load operation, the exhaust gas temperature rises, so the bed temperature of the NOx trap catalyst 9 rises. Therefore, when the sulfur poisoning of the NOx trap catalyst 9 is released during high load operation, the temperature of the exhaust gas is lowered in the exhaust manifold 16 in order to suppress the rise in the bed temperature of the NOx trap catalyst 9. Specifically, when the sulfur poisoning of the NOx trap catalyst 9 is released during high load operation, the first flow rate adjusting valve 17 is opened (fully opened) in the main cooling water path 3, and the cooling water is supplied to the exhaust manifold 16. To flow in. In the sub cooling water path 5, the opening degree of the second flow rate adjusting valve 19 is set so that the cooling water flow rate flowing through the exhaust manifold 16 is larger than the cooling water flow rate flowing through the EGR cooler 13. In other words, the opening degree of the second flow rate adjustment valve 19 is set so that most of the cooling water flows into the exhaust manifold 16. At this time, the bypass passage control valve 15 is closed, so that EGR gas does not flow through the bypass passage 14.

  When the sulfur poisoning is released, it is necessary to control the air-fuel ratio to be the stoichiometric air-fuel ratio, so the EGR gas is recirculated to the intake passage 6, but if the recirculation amount of the EGR gas is too large, smoke in the exhaust increases. Therefore, the amount of EGR gas recirculated to the intake passage 6 is set to be a small amount of about 5% to 10% in terms of the EGR rate. Therefore, in order to expand the operation range where sulfur poisoning can be released at high loads, it is more effective to cool the exhaust gas directly in the exhaust manifold 16 than to cool the temperature of the EGR gas returning to the intake passage 6. Decreases and contributes to protection against thermal deterioration of the NOx trap catalyst 9.

  Therefore, the opening degree of the first flow rate adjustment valve 17 and the second flow rate adjustment valve 19 is controlled so that a large amount of cooling water flows from both the main cooling water path 3 and the sub cooling water path 5 to the exhaust manifold 16. By doing so, the exhaust gas temperature can be reduced to the maximum.

  That is, by increasing the flow rate of the cooling water flowing into the exhaust manifold 16, as shown in FIG. 2, the characteristic indicating the bed temperature upper limit of the NOx trap catalyst 9 estimated from the relationship between torque (load) and engine speed. The line A becomes the characteristic line A ′, and the operation region in which sulfur poisoning can be released can be expanded to the high load side and the high frequency side for the region P1 indicated by the oblique line in FIG.

  In addition, when exhaust gas is cooled to the maximum when releasing the sulfur poisoning of the NOx trap catalyst 9 during high load operation, the water pump 18 is operated so as to maximize the discharge amount of the cooling water per unit time. Will be.

  When the sulfur poisoning of the NOx trap catalyst 9 is released during low load operation, the exhaust gas temperature decreases, so the bed temperature of the NOx trap catalyst 9 decreases. Although there is a method of raising the exhaust gas temperature such as retarding the injection timing, the bed temperature of the NOx trap catalyst 9 may be lower than a predetermined lower limit temperature (for example, 650 ° C.) due to the misfire limit of the internal combustion engine 1. Therefore, when the sulfur poisoning of the NOx trap catalyst 9 is released during low load operation, the temperature decrease of the exhaust gas is positively suppressed in order to suppress the decrease in the bed temperature of the NOx trap catalyst 9.

  Specifically, when the sulfur poisoning of the NOx trap catalyst 9 is released during low load operation, the first flow rate adjustment valve 17 is closed (fully closed) in the main cooling water path 3 to cool the exhaust manifold 16. Keep water out. In the sub cooling water path 5, the opening degree of the second flow rate adjustment valve 19 is set so that the cooling water flow rate flowing through the exhaust manifold 16 is smaller than the cooling water flow rate flowing through the EGR cooler 13. At this time, the bypass passage control valve 15 is opened, and the EGR gas flows through the bypass passage 14 and bypasses the EGR cooler 13.

  As described above, since it is necessary to flow a minimum amount of cooling water to the exhaust manifold 16 so as to ensure the desired function, the opening degree of the second flow rate adjustment valve 19 is set to the exhaust manifold 16. The flow rate of the cooling water flowing in the exhaust manifold 16 is not set below the opening at which the cooling water does not boil in the exhaust manifold 16. It is most advantageous to set the flow rate of the cooling water flowing to the opening so that the cooling water does not boil in the exhaust manifold 16. For this reason, when the water pump 18 controls the discharge amount of the cooling water per unit time, the energy loss is reduced by controlling the discharge amount of the cooling water per unit time to be relatively small.

  As a result, the flow rate of the cooling water flowing into the exhaust manifold 16 is reduced, and a decrease in the exhaust gas temperature is suppressed. Further, when the EGR gas recirculated to the intake passage 6 flows through the bypass passage 14, the temperature decrease of the EGR gas is suppressed, which also contributes to the suppression of the temperature decrease of the exhaust gas.

  That is, by reducing the flow rate of the cooling water flowing into the exhaust manifold 16, as shown in FIG. 3, a characteristic line indicating the bed temperature lower limit of the NOx trap catalyst 9 estimated from the relationship between torque (load) and engine speed. B becomes a characteristic line B ′, and an operation region in which sulfur poisoning can be released can be expanded to the low load side and the low rotation speed side by the region P2 indicated by the oblique line in FIG.

  When sulfur poisoning is released, the air-fuel ratio is controlled to be the stoichiometric air-fuel ratio, so the air-fuel ratio becomes relatively rich and hydrocarbon (HC) is likely to be generated, but the EGR rate is also low, so EGR Even when the EGR gas is cooled by the cooler 13 at a high load, the EGR cooler 13 is also prevented from being clogged with hydrocarbons in the exhaust gas. In addition, when the load is low, the EGR gas bypasses the EGR cooler 13 in the first place, so that the hydrocarbon in the exhaust gas is not clogged in the EGR cooler 13.

  As described above, in the EGR cooler 13, the operation state in which the EGR gas is desired to be cooled is not the same as the operation state in which the exhaust gas is desired to be cooled in the exhaust manifold 16. Therefore, the water-cooled exhaust manifold 16 is connected to both the main cooling water path 3 and the sub cooling water path 5, and the exhaust manifold 16 and the EGR cooler 13 are connected in parallel in the sub cooling water path 5. Then, by controlling the valve opening degree of the first flow rate adjusting valve 17 and the second flow rate adjusting valve 19 according to the operating state and using the sub radiator 4 efficiently, the capacity of the main radiator 2 and the sub radiator 4 are increased. The exhaust manifold can be the water-cooled exhaust manifold 16 in an optimized state without increasing the capacity of the exhaust manifold more than necessary.

  The sub cooling water path 5 is provided for the purpose of cooling the exhaust gas (EGR gas), and the cooling water temperature in the sub cooling water path 5 is set lower than the cooling water temperature of the main cooling water path 3. Therefore, the exhaust manifold 16 and the EGR cooler 13 can be efficiently cooled by the cooling water in the sub-cooling water passage 5, and this is an advantageous configuration for returning a large amount of EGR gas to the intake passage 6. ing.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Main radiator 3 ... Main cooling water path 4 ... Sub radiator 5 ... Sub cooling water path 6 ... Intake passage 7 ... Exhaust passage 8 ... Three-way catalyst 9 ... NOx trap catalyst 10 ... Exhaust particulate filter 11 ... EGR Passage 12 ... EGR valve 13 ... EGR cooler 14 ... Bypass passage 15 ... Bypass passage control valve 16 ... Exhaust manifold 17 ... First flow rate adjustment valve 18 ... Water pump 19 ... Second flow rate adjustment valve 20 ... ECU

Claims (10)

Exhaust gas recirculation means for recirculating EGR gas, which is part of the exhaust gas, to the intake passage via a water-cooled EGR cooler;
A main cooling water path through which cooling water that is cooled by the main radiator and flows through the water jacket of the internal combustion engine and the water-cooled exhaust manifold;
A sub-cooling water path that is cooled by a sub-radiator and through which the cooling water flowing through the exhaust manifold and the EGR cooler circulates,
The main cooling water path and the sub cooling water path are independent cooling water paths, and the exhaust manifold and the EGR cooler are connected in parallel in the sub cooling water path. A first flow rate adjustment valve for adjusting the flow rate of cooling water flowing into the exhaust manifold is interposed in the path,
In the sub-cooling water path, a second flow rate adjusting valve for adjusting a ratio between the cooling water flow rate flowing through the exhaust manifold and the cooling water flow rate flowing through the EGR cooler is interposed.
An internal combustion engine characterized in that the flow rate of cooling water flowing through the exhaust manifold and the EGR cooler is adjusted by controlling the valve opening degree of the first flow rate adjustment valve and the second flow rate adjustment valve according to an operating state. Cooling system.   The cooling apparatus for an internal combustion engine according to claim 1, wherein the cooling water temperature in the sub cooling water path is set to be lower than the cooling water temperature in the main cooling water path. An exhaust purification catalyst interposed in the exhaust passage;
An electric water pump for circulating cooling water in the sub-cooling water path,
After starting the internal combustion engine, until the catalyst is activated,
In the main cooling water path, the opening degree of the first flow rate adjustment valve is adjusted so that the cooling water does not flow to the exhaust manifold,
In the sub cooling water path, the second flow rate adjustment valve and the water pump are controlled so that both the cooling water flow rate flowing through the exhaust manifold and the cooling water flow rate flowing through the EGR cooler are reduced.
3. The cooling apparatus for an internal combustion engine according to claim 1, wherein the water pump is controlled so that a discharge amount of the cooling water per unit time is relatively small. 4. An exhaust purification catalyst interposed in the exhaust passage;
The EGR gas bypasses the EGR cooler and recirculates to the intake passage, and after starting the internal combustion engine until the catalyst is activated,
In the main cooling water path, the opening degree of the first flow rate adjustment valve is adjusted so that the cooling water does not flow to the exhaust manifold,
In the sub cooling water path, the opening degree of the second flow rate adjusting valve is adjusted so that the cooling water flow rate flowing through the EGR cooler is larger than the cooling water flow rate flowing through the exhaust manifold,
The cooling apparatus for an internal combustion engine according to claim 1 or 2, wherein the exhaust gas recirculation means is adjusted so that the EGR gas flows through the bypass passage. An exhaust purification catalyst interposed in the exhaust passage;
An electric water pump that circulates cooling water in the sub-cooling water path, and from the activation of the catalyst until the warm-up of the internal combustion engine is completed,
In the main cooling water path, the opening of the first flow rate adjustment valve is adjusted so that a large amount of cooling water flows into the exhaust manifold,
In the sub-cooling water path, the second flow rate adjusting valve and the water pump are controlled so that the cooling water does not flow through the exhaust manifold and the cooling water flow rate flowing through the EGR cooler decreases.
The cooling device for an internal combustion engine according to any one of claims 1 to 4, wherein the water pump is controlled so that a discharge amount of the cooling water per unit time is relatively reduced. An exhaust purification catalyst interposed in the exhaust passage;
A bypass passage in which the EGR gas bypasses the EGR cooler and recirculates to the intake passage, and until the warm-up of the internal combustion engine is completed after the activation of the catalyst,
In the main cooling water path, the opening of the first flow rate adjustment valve is adjusted so that a large amount of cooling water flows into the exhaust manifold,
In the sub cooling water path, the opening of the second flow rate adjustment valve is adjusted so that the cooling water does not flow to the exhaust manifold,
The cooling apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the exhaust gas recirculation means is adjusted so that the EGR gas flows through the bypass passage. When the EGR gas is recirculated to the intake passage after the internal combustion engine has been warmed up,
In the main cooling water path, the opening of the first flow rate adjustment valve is adjusted so that a large amount of cooling water flows into the exhaust manifold,
In the sub cooling water path, the opening degree of the second flow rate adjusting valve is adjusted so that the cooling water flow rate flowing through the exhaust manifold is smaller than the cooling water flow rate flowing through the EGR cooler. The cooling device for an internal combustion engine according to any one of claims 1 to 6. When the EGR gas is not recirculated into the intake passage after the warm-up of the internal combustion engine is completed,
In the main cooling water path, the opening degree of the first flow rate adjustment valve is adjusted so that the cooling water does not flow to the exhaust manifold,
In the sub cooling water path, the opening degree of the second flow rate adjusting valve is adjusted so that the cooling water flow rate flowing through the exhaust manifold is larger than the cooling water flow rate flowing through the EGR cooler. The cooling device for an internal combustion engine according to any one of claims 1 to 7. Having a NOx trap catalyst as an exhaust purification catalyst interposed in the exhaust passage,
When performing sulfur poisoning release in the NOx trap catalyst during high load operation,
In the main cooling water path, the opening of the first flow rate adjustment valve is adjusted so that a large amount of cooling water flows into the exhaust manifold,
In the sub cooling water path, the opening degree of the second flow rate adjusting valve is adjusted so that the cooling water flow rate flowing through the exhaust manifold is larger than the cooling water flow rate flowing through the EGR cooler. The cooling device for an internal combustion engine according to any one of claims 1 to 8. Having a NOx trap catalyst as an exhaust purification catalyst interposed in the exhaust passage,
When performing sulfur poisoning release in the NOx trap catalyst during low load operation,
In the main cooling water path, the opening degree of the first flow rate adjustment valve is adjusted so that the cooling water does not flow to the exhaust manifold,
In the sub cooling water path, the opening degree of the second flow rate adjusting valve is adjusted so that the cooling water flow rate flowing through the exhaust manifold is smaller than the cooling water flow rate flowing through the EGR cooler. The cooling device for an internal combustion engine according to any one of claims 1 to 9.

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