JP5625716B2 - Cooling device for internal combustion engine - Google Patents

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.

The cooling apparatus for an internal combustion engine according to the present invention is characterized in that an exhaust manifold and an EGR cooler are connected in parallel to a sub cooling water path which is a path different from the main cooling water path provided with the main radiator. . In addition, when performing sulfur poisoning release in the NOx trap catalyst during low-load operation, the flow rate adjustment valve interposed in the sub-cooling water path reduces the flow rate of the cooling water flowing to the exhaust manifold and Gas is introduced into the intake passage, bypassing the EGR cooler.

  Since the operation state in which the EGR gas is desired to be maximally cooled in the EGR cooler is not the same as the operation state in which the exhaust gas is maximally cooled in the exhaust manifold, the sub-radiator functions to cool the cooling water in a wide range of operation states.

  Further, since the exhaust manifold is cooled by the cooling water circulating in the sub cooling water path, it is not necessary to increase the capacity of the main radiator in the main cooling water path in order to cool the exhaust manifold.

  According to the present invention, it becomes possible to efficiently use the sub-radiator provided in the sub-cooling water path, and 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 are more than necessary. The manifold can be a water-cooled exhaust manifold in an optimized state without being increased.

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. The characteristic view which showed the correlation with the EGR gas temperature and cooling water flow rate of an EGR cooler exit. 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. The timing chart which shows an example of the control at the time of high load. The flowchart which shows the flow of control of the flow regulating valve which concerns on this invention. Area determination map in normal operation mode. The 1st operation map which determines the opening degree to a flow regulating valve. The 2nd operation map which determines the opening degree to a flow control valve. The area | region determination map in sulfur poisoning cancellation | release operation mode.

  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.

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

  An intake passage 6 and an exhaust passage 7 are connected to the internal combustion engine 1. In the exhaust passage 7, a three-way catalyst 8, a NOx trap catalyst 9, and an exhaust particulate filter (DPF) 10 are interposed 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 in the present embodiment 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.

  Further, the EGR cooler 13 described above is interposed in the sub-cooling water path 5 when viewed in the cooling system. In addition to the EGR cooler 13 and the sub-radiator 4 described above, the sub-cooling water path 5 adjusts the ratio between the cooling water flow rate flowing through the water-cooled exhaust manifold 16 and the exhaust manifold 16 and the cooling water flow rate flowing through the EGR cooler 13. A flow rate adjusting valve 17 and a water pump 18 are 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 flow rate adjusting valve 17 is a three-way valve disposed at a portion where the cooling water flowing in the exhaust manifold 16 and the cooling water flowing in the EGR cooler 13 merge, and is 0 ° (fully closed) to 90 ° ( The degree of opening is controlled between fully open). In the present embodiment, the cooling water does not flow into the exhaust manifold 16 when fully closed, all the cooling water flows 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 flow rate adjusting valve 17 and the bypass passage control valve 15 are electronically controlled, for example, using a step motor, and are opened and closed by an ECU (engine control unit) 20 including the EGR valve 12 described above.

  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 the main cooling water path 3 Detection sensors from various sensors such as a temperature sensor 30 for detecting the cooling water temperature and a temperature sensor 31 for detecting the cooling water temperature in the sub-cooling water path 5 It has been input.

  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 controls the opening degree of the flow rate adjusting valve 17 disposed in the sub cooling water path 5 according to the operating state. In other words, in this embodiment, the opening degree of the flow rate adjustment valve 17 is controlled so that the cooling water flow rate flowing through the EGR cooler 13 increases relatively as the EGR gas cooling request in the EGR cooler 13 increases.

  In the operation state in which the EGR gas is recirculated to the intake passage 6, when the internal combustion engine 1 is in a high load operation, the flow rate of the coolant flowing through the exhaust manifold 16 and the EGR cooler 13 are set so that the EGR gas temperature at the outlet of the EGR cooler 13 is the lowest. The ratio with the flow rate of the flowing cooling water is controlled. In other words, the opening degree of the flow rate adjusting valve 17 is set so that the ratio of the coolant flow rate flowing through the exhaust manifold 16 and the coolant flow rate flowing through the EGR cooler 13 is the lowest rate of the EGR gas temperature at the outlet of the EGR cooler 13. Is controlled. Note that when the internal combustion engine 1 is operating at a high load in an operation state in which the EGR gas is recirculated to the intake passage 6, the amount of EGR gas recirculated to the intake passage 6 is set so that the EGR rate is about 30%. .

  The EGR gas temperature at the outlet of the EGR cooler 13 can be lowered even if the exhaust gas is cooled in the exhaust manifold 16 or the EGR gas is cooled in the EGR cooler 13, but the exhaust manifold 16 and the EGR cooler 13 as heat exchangers As shown in FIG. 2, the heat exchange efficiency is saturated when the flow rate of the cooling water exceeds a certain flow rate. That is, when the required cooling degree of the EGR gas exceeds a predetermined required degree, the heat exchange efficiency is saturated. Therefore, according to the total amount of water that is the amount of cooling water discharged per unit time of the water pump 18 in the sub-cooling water path 5, the EGR gas having the lowest temperature is obtained at the outlet of the EGR cooler 13, that is, The cooling water flow rate flowing through the exhaust manifold 16 and the cooling water flow rate flowing through the EGR cooler 13 are set so that the EGR gas is cooled with the best efficiency. That is, in FIG. 2, among the characteristic lines indicating the EGR gas temperature at the outlet of the EGR cooler 13 intersecting with the characteristic line representing the total water amount shown by the one-dot chain line, the temperature of the characteristic line having the lowest EGR gas temperature is obtained. The cooling water flow rate flowing through the exhaust manifold 16 and the cooling water flow rate flowing through the EGR cooler 13 are set. In other words, in FIG. 2, the flow rate of the cooling water flowing through the exhaust manifold 16 and the EGR cooler 13 at the intersection of the characteristic line representing the total water amount indicated by the one-dot chain line and the best efficiency line indicated by the solid line. The opening degree of the flow rate adjusting valve 17 is controlled so that the cooling water flow rate is obtained. That is, the ratio of the coolant flow rate flowing through the exhaust manifold 16 and the coolant flow rate flowing through the EGR cooler 13 is controlled so that the EGR gas temperature at the outlet of the EGR cooler 13 is the lowest. It is possible to control the flow rate of the cooling water flowing through the exhaust manifold 16 and the flow rate of the cooling water flowing through the EGR cooler 13 by changing the total water amount that is the discharge amount of the cooling water per unit time of the water pump 8. is there.

  As described above, in this embodiment, the EGR gas recirculated to the intake passage 6 is cooled not only by the EGR cooler 13 in the sub-cooling water passage 5 but also by the water-cooled exhaust manifold 16. Therefore, even during high-load operation when the exhaust gas is at a high temperature, the EGR gas can be efficiently cooled by both the exhaust manifold 16 and the EGR cooler 13, and the EGR gas can be recirculated to the intake passage 6 in a large amount. Is possible.

  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, this point is also advantageous for cooling the EGR gas, and is advantageous in recirculating the EGR gas to the intake passage 6 in a large amount.

  Further, in the operation state in which the EGR gas is recirculated to the intake passage 6, when the internal combustion engine 1 is operated at a low load, the temperature of the EGR gas recirculated to the intake passage 6 is cooled in consideration of the hydrocarbon (HC) in the exhaust gas. Is not desirable. This is because if the EGR gas is cooled too much, the combustion temperature decreases and HC is easily generated.

  Therefore, in an operation state in which the EGR gas is recirculated to the intake passage 6, when the internal combustion engine 1 is in a low load operation, the bypass passage control valve 15 is set so that the EGR gas does not flow through the EGR cooler 13 and the EGR gas flows through the bypass passage 14. Control. The flow rate adjusting valve 17 is controlled so that the flow rate of the cooling water flowing in the exhaust manifold 16 becomes a minimum amount that does not cause the cooling water to boil in the exhaust manifold 16. That is, the opening degree of the flow rate adjustment valve 17 is controlled so that most of the cooling water flows to the EGR cooler 13.

  Even when the sulfur poisoning of the NOx trap catalyst 9 is released, the opening degree of the flow rate adjustment valve 17 is controlled according to the load state (torque) of the internal combustion engine 1 at that time.

  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, in order to suppress an increase in the bed temperature of the NOx trap catalyst 9, the flow rate of the cooling water flowing through the exhaust manifold 16 is increased. The opening degree of the flow regulating valve 17 is controlled. Specifically, the opening degree of the flow rate adjusting valve 17 is controlled so that the cooling water does not flow through the EGR cooler 13 and all the cooling water flows through the exhaust manifold 16.

  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, by controlling the opening degree of the flow rate adjustment valve 17 so that all the cooling water flows through the exhaust manifold 16, the flow rate of the cooling water flowing through the exhaust manifold 16 increases, and the exhaust gas temperature can be reduced to the maximum. it can.

  That is, by increasing the flow rate of the cooling water flowing through the exhaust manifold 16, as shown in FIG. 3, a characteristic line indicating the bed temperature upper limit of the NOx trap catalyst 9 estimated from the relationship between torque (load) and engine speed. 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 by the region P1 indicated by the oblique line in FIG.

  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, in order to suppress a decrease in the bed temperature of the NOx trap catalyst 9, the flow rate of the cooling water flowing through the exhaust manifold 16 is reduced. The opening degree of the flow regulating valve 17 is controlled. Specifically, the flow rate adjusting valve 17 is controlled 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. That is, the opening degree of the flow rate adjustment valve 17 is controlled so that most of the cooling water flows to the EGR cooler 13. Further, in order not to lower the temperature of the EGR gas returning to the intake passage 6, the bypass passage control valve 15 is controlled so that the EGR gas does not flow through the EGR cooler 13 and the EGR gas flows through the bypass passage 14.

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

  That is, by reducing the flow rate of the cooling water flowing through the exhaust manifold 16, as shown in FIG. 4, 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 the 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.

  In this embodiment, since the exhaust manifold 16 is water-cooled, the exhaust gas temperature is likely to be lower than that of a system having an exhaust manifold that is not water-cooled. And the bypass passage control valve 15 can be controlled to suppress the exhaust gas temperature drop.

  When the exhaust particulate matter (PM) collected in the DPF 10 is burned to regenerate the DPF 10, it is important to raise the exhaust gas temperature, so that the flow rate of the cooling water flowing through the exhaust manifold 16 is reduced. The opening degree of the flow regulating valve 17 is controlled. Specifically, the flow rate adjusting valve 17 is controlled 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. That is, the opening degree of the flow rate adjustment valve 17 is controlled so that most of the cooling water flows to the EGR cooler 13. Further, during the regeneration of the DPF, the EGR valve 12 is closed because of a deposit problem, and the EGR gas is not recirculated to the intake passage 6.

  As a result, when the DPF 10 is regenerated, the exhaust gas temperature can be suppressed from decreasing due to the decrease in the flow rate of the cooling water flowing through the exhaust manifold 16, so that the combustion of the exhaust particulates collected in the DPF 10 can be promoted. it can.

  In an operating state in which EGR gas is not recirculated to the intake passage 6, the exhaust system is controlled by controlling the opening degree of the flow rate adjusting valve 17 so that all the cooling water flows through the exhaust manifold 16 when the internal combustion engine 1 is operating at a high load. The output of the internal combustion engine 1 can be improved while ensuring the upper limit of the exhaust gas temperature set for preventing the thermal deterioration of the parts.

  The exhaust passage 7 is attached with an exhaust purification catalyst such as the above-mentioned NOx trap catalyst 9 and exhaust system parts such as a supercharger. The heat of these exhaust system parts exposed to high-temperature exhaust gas. From the viewpoint of suppressing deterioration, an exhaust gas upper limit temperature is set as the exhaust gas temperature. Therefore, since the fuel injection amount cannot be set so that the exhaust gas temperature becomes equal to or higher than the exhaust gas upper limit temperature, the output generated by the internal combustion engine 1 is naturally limited.

  However, in the present embodiment, the flow rate of the cooling water flowing through the exhaust manifold 16 can be increased at the time of high load. Therefore, as shown in FIG. 5, fuel injection is performed while maintaining the exhaust gas temperature at the exhaust gas upper limit temperature. The amount can be increased, and the output of the internal combustion engine 1 can be improved.

  Further, as described above, the operation state in which the EGR gas is desired to be cooled as much as possible in the EGR cooler 13 and the operation state where the exhaust gas is desired to be cooled as much as possible in the exhaust manifold 16 are not the same. By connecting the exhaust manifold 16 and the EGR cooler 13 in parallel, the sub-radiator 4 provided in the sub-cooling water path 5 can be used efficiently, and the main radiator 2 of the main cooling water path 3 can be used. The exhaust manifold 16 can be a water-cooled exhaust manifold in a state in which the capacity and the capacity of the sub-radiator 4 in the sub-cooling water path 5 are optimized without increasing more than necessary.

  FIG. 6 is a flowchart showing a flow of control of the flow rate adjusting valve 17 in the present embodiment.

  In S1, it is determined whether or not the current operation mode is the normal operation mode. That is, if the sulfur accumulation amount in the NOx trap catalyst 9 is less than the predetermined amount and the exhaust particulate accumulation amount in the DPF 10 is less than the predetermined amount, the process proceeds to S2 and proceeds to S3 after determining the normal operation mode. Advances to S8.

  Here, the amount of sulfur deposition in the NOx trap catalyst 9 can be estimated from, for example, the integrated value of the engine speed and the vehicle travel distance, and is calculated in the ECU 20. Also, the amount of exhaust particulate accumulation in the DPF 10 is, for example, the exhaust pressure on the inlet side of the DPF 10 detected by the exhaust pressure sensor 26 and the reference exhaust pressure corresponding to the current operating state (engine speed and fuel injection amount). It can be estimated by comparison and is calculated in the ECU 20.

  In S3, the normal operation mode region determination map shown in FIG. 7 stored in advance in the ECU 20 is used to determine which operation region of the normal operation mode is in the current torque (load) and engine speed, When the internal combustion engine 1 is in the operating region of the region 1-1 where the EGR gas is recirculated to the intake passage 6 and is in the high load operation, the process proceeds to S4. Otherwise, the process proceeds to S5.

  In S4, the opening degree of the flow rate adjustment valve 17 is calculated with reference to the first operation map shown in FIG. 8 stored in advance in the ECU 20, and the flow rate adjustment valve 17 is controlled so as to be the calculated opening degree. . This first operation map is set so that the EGR gas temperature at the outlet of the EGR cooler 13 is the lowest, and the higher the exhaust gas becomes hotter from the rotation of the protection (heat resistance) of the intake valve (not shown) (the higher the The flow rate adjustment valve 17 is set to the closed side (the side on which the flow rate of the coolant flowing through the EGR cooler 13 increases) as the output increases.

  In S5, using the normal operation mode region determination map shown in FIG. 7, the internal combustion engine 1 is in the low load operation state in the operation state in which the EGR gas is recirculated to the intake passage 6 from the current torque (load) and the engine speed. If it is in the operation region of the region 1-2, the process proceeds to S6. If not, that is, in the operation state in which the EGR gas is not recirculated to the intake passage 6, the operation region of the region 1-3 in which the internal combustion engine 1 is in the high load operation is If there is, the process proceeds to S7.

  In S6, the opening degree of the flow rate adjustment valve 17 is calculated with reference to the second operation map shown in FIG. 9 stored in advance in the ECU 20, and the flow rate adjustment valve 17 is controlled so as to be the calculated opening degree. . This second operation map is set so that the flow rate of the cooling water flowing through the exhaust manifold 16 is the minimum amount that the cooling water does not boil in the exhaust manifold 16, and the lower the exhaust gas becomes, the lower the output power becomes. In fact, the flow rate adjustment valve 17 is set to the closed side (the side on which the flow rate of the cooling water flowing through the EGR cooler 13 increases).

  In S7, since it is necessary to cool the exhaust gas temperature as much as possible, the opening of the flow rate adjustment valve 17 is fully opened so that the cooling water does not flow through the EGR cooler 13 and all the cooling water flows through the exhaust manifold 16. Control.

  In S8, it is determined whether or not the current operation mode is the sulfur poisoning release mode. That is, if the amount of accumulated sulfur in the NOx trap catalyst 9 is equal to or greater than the predetermined amount and the operation region is within the operation region in which sulfur poisoning can be removed, the process proceeds to S9, and after determining the sulfur poisoning release mode, the process proceeds to S10. If the amount of sulfur accumulation in the trap catalyst 9 is less than the predetermined amount, the process proceeds to S13, and after determining that the DPF regeneration mode is in which the amount of exhaust particulate accumulation in the DPF 10 is equal to or greater than the predetermined amount, the process proceeds to S14. If the sulfur accumulation amount in the NOx trap catalyst 9 is equal to or greater than the predetermined amount, but the operation region is outside the operation region where sulfur poisoning can be released, the operation proceeds to S9 after the operation region becomes the operation region where sulfur poisoning can be removed. It progresses to S10 after determining with sulfur poisoning cancellation | release mode. Note that if the NOx trap catalyst 9 has a sulfur accumulation amount of a predetermined amount or more, but the operation region is outside the sulfur poisoning releaseable operation region and the exhaust particulate accumulation amount in the DPF 10 is less than the predetermined amount, the process proceeds to S2. You may make it determine with sulfur poisoning cancellation | release mode, after advancing operation area | region becomes a sulfur poisoning cancellation | release possible operation area | region. In addition, when the sulfur accumulation amount in the NOx trap catalyst 9 is equal to or larger than the predetermined amount but the operation region is outside the operation region where sulfur poisoning can be released and the exhaust particulate accumulation amount in the DPF 10 is equal to or larger than the predetermined amount, the process proceeds to S13. The process may proceed to S14 after determining the advance DPF regeneration mode.

  In S10, when the sulfur poisoning release mode region determination map as shown in FIG. 10 stored in advance in the ECU 20 is used and the operation region is the region 2-1 during the high load operation in the sulfur poisoning release mode. The process proceeds to S11, and in the case of the operation area 2-2 in the low load operation in the sulfur poisoning release mode, the process proceeds to S12.

  In S11, since it is necessary to cool the exhaust gas temperature as much as possible, the opening of the flow rate adjustment valve 17 is fully opened so that the cooling water does not flow through the EGR cooler 13 and all the cooling water flows through the exhaust manifold 16. Control.

  In S12, the opening degree of the flow rate adjustment valve 17 is calculated with reference to the second operation map shown in FIG. 9, and the flow rate adjustment is performed so that the opening amount becomes a minimum amount in which the cooling water does not boil in the exhaust manifold 16. The valve 17 is controlled.

  Even when the DPF regeneration mode is determined and the routine proceeds to S14, the opening degree of the flow rate adjusting valve 17 is calculated with reference to the second operation map shown in FIG. 9, and the cooling water does not boil in the exhaust manifold 16. The flow rate adjusting valve 17 is controlled so that the opening amount becomes the minimum amount.

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 ... Flow control valve 18 ... Water pump 20 ... ECU

Claims (7)

Exhaust gas recirculation means for recirculating a part of the exhaust gas to the intake passage through a water-cooled EGR cooler;
A main cooling water path through which the cooling water cooled by the main radiator and flowing through the water jacket of the internal combustion engine circulates;
A sub-cooling water path that is cooled by a sub-radiator and through which cooling water flowing through the water-cooled exhaust manifold and the EGR cooler circulates;
An NOx trap catalyst in the exhaust passage ,
The exhaust gas recirculation means includes a bypass passage that is connected in parallel to the EGR cooler, can bypass the EGR cooler, and can introduce exhaust gas into the intake passage, and a bypass passage control valve that opens and closes the bypass passage,
A flow rate adjusting valve for adjusting a ratio of a cooling water flow rate flowing through the exhaust manifold and a cooling water flow rate flowing through the EGR cooler is interposed in the sub cooling water path;
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,
When performing sulfur poisoning release in the NOx trap catalyst during low load operation,
The degree of opening of the flow rate adjustment valve is controlled so that the flow rate of cooling water flowing through the exhaust manifold decreases.
The internal combustion engine cooling device , wherein an opening of the bypass passage control valve is controlled so that exhaust gas bypasses the EGR cooler and flows through the bypass passage .   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. Claim 1 or 2, characterized in that the opening of the flow control valve so that the cooling water flow through the EGR cooler as the cooling requirements of the EGR gas before Symbol EGR cooler becomes larger relative increase is controlled A cooling apparatus for an internal combustion engine according to claim 1. Before Symbol flow regulating valve, with increases or decreases the cooling water flow rate to the EGR cooler in accordance with the cooling requirements of the EGR gas in the EGR cooler, if cooling demand degree of the EGR gas reaches a predetermined cooling demand degree than The cooling device for an internal combustion engine according to claim 1 or 2, wherein an increase in the flow rate of cooling water to the EGR cooler is limited, and cooling water is preferentially flowed to the exhaust manifold. Under the operating conditions in which the EGR gas is recirculated to the intake passage, during a high load operation, the cooling water flow rate flowing through the exhaust manifold and the cooling water flowing through the EGR cooler so that the EGR gas temperature at the outlet of the EGR cooler becomes the lowest. The cooling device for an internal combustion engine according to any one of claims 1 to 4 , wherein a ratio with the flow rate is controlled. When performing sulfur poisoning release in the NOx trap catalyst during high load operation,
The cooling device for an internal combustion engine according to any one of claims 1 to 5, wherein an opening degree of the flow rate adjusting valve is controlled so that a flow rate of the cooling water flowing through the exhaust manifold increases. The exhaust passage has an exhaust particulate filter that collects exhaust particulates in exhaust gas, and at the time of exhaust particulate filter regeneration that burns the exhaust particulates collected by the exhaust particulate filter,
The cooling device for an internal combustion engine according to any one of claims 1 to 6 , wherein an opening degree of the flow rate adjusting valve is controlled so that a flow rate of the cooling water flowing through the exhaust manifold decreases.

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