JP6743648B2 - Internal combustion engine and method of controlling internal combustion engine - Google Patents

Description

The present invention relates to an internal combustion engine and a control method for the internal combustion engine.

The main radiator and the pump for the high temperature side cooling water are provided in the high temperature side cooling water passage through which the engine cooling water flows, and the sub radiator and the low temperature side cooling water are provided in the low temperature side cooling water passage through which the cooling water after cooling the water cooling intercooler flows. There has been proposed a cooling device for an internal combustion engine, which is configured to include a pump for use in the engine (for example, refer to Patent Document 1).

JP2012-189063A

By the way, from the viewpoint of improving the fuel efficiency performance and the exhaust gas performance of the vehicle, the temperature reduction of the exhaust gas (EGR gas) recirculated from the exhaust passage to the intake passage has been studied. However, as in the conventional case, if the engine cooling water, which has a relatively high temperature due to the cooling of the internal combustion engine, is used as the cooling medium of the EGR cooler that cools the EGR gas, further lowering of the EGR gas is achieved. It was difficult.

Further, as the temperature of the EGR gas decreases, the amount of water vapor contained in the EGR gas exceeds the amount of saturated water vapor, and there is a greater concern that excess water vapor is liquefied and condensed water is generated. If this condensed water (water mist) mixes with the intake gas and flows into the cylinder (cylinder) in large quantities, the lubricating oil film on the inner surface of the cylinder is washed off, the parts such as the piston are corroded, and carbon is deposited on the parts. There is a possibility that it will lead to the malfunction of. Further, there is a possibility that various pipes such as EGR pipes and EGR valves and valves may be corroded or deteriorated.

An object of the present invention is to avoid generation of condensed water due to liquefaction of water vapor contained in EGR gas, achieve a further lower temperature of EGR gas, and improve vehicle fuel economy performance and exhaust gas performance. An object of the present invention is to provide an internal combustion engine and a method of controlling the internal combustion engine.

The internal combustion engine of the present invention for achieving the above-mentioned object is provided with a high water temperature radiator and a high water temperature water supply device in a high temperature side cooling water passage through which high temperature side cooling water for cooling the internal combustion engine flows, An internal combustion engine including a low water temperature radiator, a low water temperature water supply device, and an EGR cooler in a low temperature side cooling water passage through which low temperature side cooling water that cools intake gas passing through an intake passage of the internal combustion engine flows. In the engine, a branch channel branched from the high temperature side cooling water channel is connected to the low temperature side cooling water channel upstream of the EGR cooler to pass through the low temperature side cooling water channel. While circulating the mixed cooling water in which the low temperature side cooling water and the high temperature side cooling water passing through the branch passage are mixed into the EGR cooler, the low water temperature water supply device is configured as an electric water supply device, and further, An EGR gas temperature detecting device is provided in an EGR passage downstream of the EGR cooler, and an exhaust gas oxygen excess ratio detecting device is provided in an exhaust passage or an exhaust manifold of the internal combustion engine, and a control device for controlling the internal combustion engine is the EGR gas. Based on the detection value of the temperature detection device and the detection value of the exhaust oxygen excess ratio detection device, while performing the condensed water generation determination to determine whether the water vapor contained in the EGR gas is liquefied to generate condensed water When the condensed water generation determination determines that condensed water is generated, the control is performed to reduce the rotation speed of the low water temperature water supply device below a basic rotation speed that is preset according to the operating state of the internal combustion engine. It is configured to perform rotational speed adjustment control.

Further, the method for controlling an internal combustion engine of the present invention to achieve the above object, a high water temperature radiator and a high water temperature water supply in the high temperature side cooling water flow path through which the high temperature side cooling water for cooling the internal combustion engine flows. And a low water temperature radiator, an electric low water temperature water supply device, and an EGR in a low temperature side cooling water passage through which low temperature side cooling water that cools intake gas passing through an intake passage of the internal combustion engine is provided. A cooler is further provided, and a branch channel branched from the high temperature side cooling water channel is connected to the low temperature side cooling water channel upstream of the EGR cooler to provide the low temperature side cooling water flow. A method for controlling an internal combustion engine configured to flow mixed cooling water, which is a mixture of low temperature side cooling water passing through a passage and high temperature side cooling water passing through the branch passage, to the EGR cooler. Based on the temperature of the EGR gas passing through the EGR passage on the downstream side and the oxygen excess rate of the exhaust gas passing through the exhaust passage or the exhaust manifold of the internal combustion engine, the water vapor contained in the EGR gas is liquefied to generate condensed water. While performing the condensed water generation determination to determine whether or not, when it is determined that the condensed water is generated in the condensed water generation determination, the rotation speed of the low water temperature water supply device to the operating state of the internal combustion engine Accordingly, the method is characterized by performing rotation speed adjustment control, which is control for reducing the rotation speed below a preset basic rotation speed.

According to the internal combustion engine and the method for controlling the internal combustion engine of the present invention, the engine cooling water (high temperature side cooling water) and the low temperature side cooling water for cooling the intake gas are mixed to cool the mixed cooling water lower than the engine cooling water. Since it is circulated to the EGR cooler as a medium, the EGR gas can be further cooled as compared with the conventional technique in which engine cooling water is used as the cooling medium. As a result, it is possible to reduce the volume of the air-fuel mixture of intake air and EGR gas flowing into the cylinder to improve the fuel efficiency performance of the vehicle, and to lower the temperature of the air-fuel mixture to improve the exhaust gas performance.

Moreover, since the mixed cooling water having a temperature higher than that of the low temperature side cooling water is used as the cooling medium of the EGR cooler, the condensed water (corrosion water) is generated by the condensation of the water vapor contained in the EGR gas. Can be suppressed. As a result, it is possible to suppress corrosion and deterioration of various pipes and valves due to condensed water.

Further, when there is a concern that condensed water will be generated, the number of rotations of the low water temperature water supply device is reduced to reduce the ratio of the low-temperature side cooling water amount to the total amount of the high-temperature side cooling water and the low-temperature side cooling water. By doing so, the temperature of the mixed cooling water is raised, so that it is possible to raise the temperature of the EGR gas that has passed through the EGR cooler using the mixed cooling water as a cooling medium, and it is possible to further suppress the generation of condensed water.

The present inventor has also found that condensed water may be generated when both the EGR gas temperature and the exhaust oxygen excess rate are low. According to the present invention, whether or not condensed water is generated is determined based on the EGR gas temperature and the exhaust gas oxygen excess ratio, so that the accuracy of determination of generation of condensed water can be improved.

It is a figure which shows typically the structure of 1st Embodiment of the internal combustion engine of this invention. It is a figure which shows the relationship of the ratio of the water vapor contained in EGR gas, exhaust gas oxygen excess rate, and EGR gas. It is a figure which shows the low load area|region of an engine. It is a figure which shows typically the structure of 2nd Embodiment of the internal combustion engine of this invention. It is a figure which shows the control method of the internal combustion engine of this invention in the form of a control flow.

Hereinafter, an internal combustion engine of a first embodiment according to the present invention will be described with reference to the drawings. As shown in FIG. 1, in an internal combustion engine of the present invention, an intake passage 2 is connected to an engine body (internal combustion engine body) 1 via an intake manifold 1a, and an exhaust passage 3 is connected via an exhaust manifold 1b. ing. Further, the EGR passage 4 is connected between the exhaust manifold 1b and the intake manifold 1a. In FIG. 1, a dotted line indicates a passage through which a gas such as air (fresh air) A, exhaust gas Ga or EGR gas Ge passes, a thick line indicates a passage through which the high temperature side cooling water HW passes, and a mixed cooling water MW indicates The flow path through which the low temperature side cooling water LW passes is indicated by a thick line, and the flow path through which the low temperature side cooling water LW passes is indicated by a thin line.

The intake passage 2 is a passage for supplying air (fresh air) A into the cylinder of the engine body 1, and the low pressure supercharger (low pressure turbo) of the low pressure supercharging system 5S is sequentially arranged from the upstream side. A compressor 5b of the charger 5), a low pressure intercooler 7a, a compressor 6b of the high pressure supercharger (high pressure turbocharger) 6 of the high pressure supercharging system 6S, and a high pressure intercooler 7b are provided.

In the exhaust passage 3, the exhaust gas Ga discharged from each cylinder (six cylinders in FIG. 1) of the engine body 1 to the exhaust manifold 1b, excluding the EGR gas Ge recirculated to the intake passage 2, is discharged to the atmosphere. And a turbine 6a of the high pressure supercharger 6, a turbine 5a of the low pressure supercharger 5, an exhaust gas purification treatment device (not shown), a muffler (not shown), and a tail in order from the upstream side. A pipe (not shown) is arranged.

The EGR passage 4 is a passage for returning a part of the exhaust gas G discharged to the exhaust manifold 1b to the intake passage 2 as EGR gas Ge, and an EGR cooler 8 and an EGR valve (not shown) are arranged in order from the upstream side. It is arranged.

The fresh air A introduced from the atmosphere is introduced into each cylinder via the intake manifold 1a and the intake valve (not shown), together with the EGR gas Ge flowing from the EGR passage 4 into the intake passage 2 as necessary. Sent. Further, the exhaust gas G generated in each cylinder is discharged to the exhaust manifold 1b via an exhaust valve (not shown), a part of the exhaust gas G flows as EGR gas Ge in the EGR passage 4, and the remaining exhaust gas Ga (= G-Ge) flows into the exhaust gas purification processing apparatus via the turbines 6a and 5a, is purified, and is then released into the atmosphere via the muffler and the tail pipe.

The high temperature side cooling water passage is a passage through which the high temperature side cooling water (engine cooling water) HW for cooling the engine body 1 flows, and the engine body 1, a thermostat (not shown), and a high water temperature are arranged in order from the upstream side. A radiator 11 and a high water temperature water pump (high water temperature water supply device) 12 are provided. The high water temperature radiator 11 is a device that cools the high temperature side cooling water HW that has passed through the engine body 1 by the air flowing into the inside of the vehicle. The high water temperature water pump 12 is a device that supplies energy for circulating the high temperature side cooling water flow path to the high temperature side cooling water HW. The drive source of the high water temperature water pump 12 may be the power of the engine body 1 or a battery (not shown) may be provided inside the vehicle to supply electric power from the battery. The thermostat sets whether or not to cool the high temperature side cooling water HW by the high water temperature radiator 11 according to the temperature of the high temperature side cooling water HW after passing through the engine body 1, so that the high temperature side cooling water HW An on-off valve device that adjusts the temperature. More specifically, when the temperature of the high temperature side cooling water HW passing through the thermostat is lower than a preset set temperature, the thermostat is closed and the high temperature side cooling water HW after passing through the engine body 1 becomes high. The warm-up of the engine body 1 is promoted by allowing the water to flow into the engine body 1 again via the bypass passage (not shown) without passing through the water temperature radiator 11. On the other hand, when the temperature of the high temperature side cooling water HW is equal to or higher than the set temperature, the thermostat is opened, and the high temperature side cooling water HW that has passed through the engine body 1 passes through the high water temperature radiator 11 again to reopen the engine body. 1, the engine body 1 is cooled while maintaining the temperature of the high temperature side cooling water HW within a certain range. The degree of valve opening of the thermostat is usually set to increase as the difference between the temperature of the thermostat and the set temperature (=temperature of the thermostat-set temperature) increases.

The low temperature side cooling water flow path is a flow path through which the low temperature side cooling water LW, which is a cooling medium that cools the intake gas in the low pressure stage intercooler 7a and the high pressure stage intercooler 7b, flows in order from the upstream side. A low-water temperature radiator 21, a low-water temperature water pump (low-water temperature water supply device) 22, and an intercooler 7 (low-pressure stage intercooler 7a and high-pressure stage intercooler 7b) are provided. The low-pressure stage intercooler 7a and the high-pressure stage intercooler 7b are arranged in parallel in the low-temperature side cooling water passage downstream of the low-water temperature water pump 22. The low water temperature radiator 21 is a device that cools the low temperature side cooling water LW that has passed through the intercooler 7 by the air flowing into the vehicle interior. The low water temperature water pump 22 is a device that supplies energy for circulating the low temperature side cooling water passage to the low temperature side cooling water LW. The low water temperature water pump 22 is an electric water supply device, and is provided with, for example, a battery (not shown) inside the vehicle and is driven by the electric power of the battery. A hose is connected to the inflow/outflow port of the cooling water for each of the above-mentioned devices 7, 8, 11, 12, 21, 22 and a pipe made of steel, for example, is connected to the hose to form a cooling water circuit. There is.

An EGR gas temperature sensor (EGR gas temperature detection device) 31 is provided in the EGR passage 4 on the downstream side of the EGR cooler 8, and an exhaust lambda sensor (exhaust oxygen excess ratio detection) is provided in the exhaust passage 3 or the exhaust manifold 1b (exhaust manifold 1b in FIG. 1). The exhaust gas temperature sensor 33 is provided in the exhaust passage 3 on the downstream side of the turbine 5a.

Further, the internal combustion engine of the present invention is provided with the control device 40. The control device 40 controls the high water temperature water pump 12 according to the detected value of the temperature by the thermostat, or detects or estimates a parameter indicating an engine operating state such as the engine speed or the fuel injection amount into the cylinder. It is a device that controls the low water temperature water pump 22 according to the value or the detection values of the sensors 31, 32, and 33.

In the internal combustion engine of the present invention, the EGR cooler 8 is configured so that the low temperature side cooling water flow passage passes, and the high temperature side cooling water flow passage is provided in the low temperature side cooling water flow passage upstream of the EGR cooler 8. The branch flow passage 30 that is further branched is connected, and the mixed cooling water MW in which the low temperature side cooling water LW passing through the low temperature side cooling water flow passage and the high temperature side cooling water HW passing through the branch flow passage 30 are mixed is EGR. Distribute to cooler 8. Then, the control device 40 determines whether or not the water vapor contained in the EGR gas Ge is liquefied to generate condensed water, based on the detection values of the EGR gas temperature sensor 31 and the exhaust lambda sensor 32. When the condensed water generation determination is performed and the condensed water generation determination determines that condensed water is generated, the rotation speed Nlp of the low water temperature water pump 22 is set to a basic rotation speed that is preset according to the operating state of the engine. It is configured to perform a rotation speed adjustment control that is a control for lowering it below Nlpc.

The mixed cooling water MW after passing through the EGR cooler 8 has a low water temperature radiator 21 in order to maintain the amount of cooling water passing through each of the high temperature side cooling water flow path and the low temperature side cooling water flow path, It is returned to both the high temperature side cooling water flow path between the high water temperature radiator 11 and the high water temperature water pump 12. Further, the temperature of the high temperature side cooling water HW is about 80°C to 100°C, the temperature of the mixed cooling water MW is about 50°C to 70°C, and the temperature of the low temperature side cooling water LW is about 30°C to 40°C.

The lower the temperature of the EGR gas Ge, the lower the maximum value of the amount of water vapor that can be contained in the EGR gas Ge (the amount of saturated water vapor). Further, as shown in FIG. 2, the smaller the exhaust oxygen excess ratio λ, the larger the amount of water vapor contained in the EGR gas Ge. Therefore, the region where the water vapor contained in the EGR gas Ge is liquefied to generate condensed water (condensed water generation region, shaded portion) has a low temperature of the EGR gas Ge, and the magnitude of the exhaust oxygen excess ratio λ (see FIG. 2 is set according to λ1<λ2). In the condensed water generation determination, a region corresponding to the condensed water generation region of FIG. 2 is set on a map based on the EGR gas temperature and the exhaust oxygen excess ratio, and the detected value of the EGR gas temperature sensor 31 and the exhaust lambda sensor 32 are set. It is determined that the condensed water is generated when the combination of the detected values is included in the region on the map, and is determined that the condensed water is not generated when the combination of the detected values is not included.

In addition, as shown in FIG. 1, the connection point CP between the low temperature side cooling water flow path and the branch flow path 30 is arranged in the low temperature side cooling water flow path between the intercooler 7 and the EGR cooler 8 and If it is configured to generate the mixed cooling water MW on the downstream side of the cooler 7, since the low temperature side cooling water on the downstream side has a higher water temperature than the low temperature side cooling water on the upstream side of the intercooler 7, the upstream side of the intercooler 7 The temperature range of the mixed cooling water MW flowing into the EGR cooler 8 can be made higher than in the case where the mixed cooling water MW is generated on the side. As a result, the generation of condensed water can be suppressed more reliably.

Further, when the engine has a low load (in the low load region shown in FIG. 3), the temperature of the EGR gas Ge tends to be a low temperature at which condensed water may be generated. Therefore, when the control device 40 is configured to perform the rotational speed adjustment control of the low water temperature water pump 22 only when the engine has a low load, when the engine has a medium load or a high load, Since it is only necessary to set the rotation speed Nlp of the water temperature water pump 22 to the basic rotation speed Nlpc, the control can be simplified.

Further, the control device 40 performs the condensed water generation determination for each preset control time when the engine is in the operating state. When the condensed water generation determination determines that the condensed water is generated, the rotation speed Nlp of the low water temperature water pump 22 is set to the basic rotation until the condensed water generation determination thereafter determines that the condensed water is not generated. The rotation speed is reduced to a value lower than the number Nlpc.

Regarding the reduction of the rotation speed, for example, there are the following two methods. In the first method, when it is first determined that condensed water is generated, the rotation speed Nlp of the low water temperature water pump 22 is reduced to a rotation speed Nlp1 lower than the basic rotation speed Nlpc, and then the condensed water is generated. This is the method of maintaining the rotational speed Nlp1 until it is determined that condensed water is not generated. The rotation speed Nlp1 is set to an optimum value in advance by experiments or the like. In this method, since it is only necessary to maintain the rotation speed Nlp1, control can be simplified.

In the second method, when it is first determined that condensed water is generated, the rotation speed Nlp of the low water temperature water pump 22 is reduced to a rotation speed Nlp1 lower than the basic rotation speed Nlpc, and then the condensed water is generated. A method of lowering the rotation speed of the low water temperature water pump 22 below the rotation speed at the time of the previous determination each time the determination is made that condensed water is generated, until the determination is made that condensed water is not generated. Is. In this method, since the ratio of the low temperature side cooling water LW contained in the mixed cooling water MW flowing into the EGR cooler 8 is gradually decreased to raise the temperature of the mixed cooling water MW, the EGR gas Ge is heated. The generation of condensed water due to the liquefaction of water vapor contained in the EGR gas Ge can be more reliably suppressed.

The amount of decrease in the rotation speed between the determinations may be a fixed amount or a variation amount according to the number of determinations. If the amount of decrease in the rotation speed between the determinations is set to a constant amount, the control can be simplified. When the amount of decrease in the number of revolutions between the determinations is set to a variation amount according to the number of determinations, the cooling capacity of the EGR cooler 8 is finely adjusted to optimize the temperature of the EGR gas Ge. It is possible to suppress the generation of condensed water due to the liquefaction of the water vapor contained in the EGR gas Ge while minimizing the influence.

Then, when it is determined that the condensed water is not generated in the subsequent condensed water generation determination, the control device 40 performs the control of returning the rotation speed Nlp of the low water temperature water pump 22 to the basic rotation speed Nlpc, and changes the EGR gas Ge to the EGR gas Ge. The temperature of the EGR gas Ge is optimized by setting the temperature of the inflowing mixed cooling water MW to the optimum value according to the operating state of the engine.

Even when the rotational speed adjustment control of the low water temperature water pump 22 is performed only when the engine is under a low load, the engine is low while the condensed water generation determination is determined to generate the condensed water. Even if the load shifts to a medium load or a high load, it is more preferable to continuously perform the condensed water generation determination until the condensed water generation determination determines that the condensed water is not generated.

Next, an internal combustion engine of the second embodiment according to the present invention will be described. As shown in FIG. 4, the internal combustion engine of the second embodiment differs from the internal combustion engine of the first embodiment shown in FIG. 1 in that the second EGR cooler 9 is arranged in the EGR passage 4 upstream of the EGR cooler 8. 2 and the high temperature side cooling water HW is used as a cooling medium for the EGR gas Ge in the second EGR cooler 9, and the other points have the same configuration.

Like the internal combustion engine of the second embodiment, by disposing the second EGR cooler 9 using the high temperature side cooling water HW as the cooling medium on the upstream side of the EGR cooler 8, the EGR gas Ge that has been cooled by the second EGR cooler 9 is provided. Since this flows into the EGR cooler 8, the cooling capacity required for the EGR cooler 8 can be reduced. As a result, the rotational speed adjustment control of the low water temperature water pump 22 can reliably suppress the generation of condensed water due to the liquefaction of the water vapor contained in the EGR gas Ge.

Next, a method of controlling the internal combustion engine based on the configuration of the internal combustion engine of the present invention will be described by taking the control flow shown in FIG. 5 as an example. The control flow shown in FIG. 5 is a flow executed every time a preset control time elapses when the engine is in the operating state.

When the control flow of FIG. 5 starts, it is determined in step S10 whether the engine has a low load. If it is determined that the engine has a low load (YES), the process proceeds to step S20. When it is determined that the engine is not under a low load but is under a medium load or a high load (NO), the process proceeds to return and the control flow is ended.

When the process proceeds from step S10 to step S20, it is determined in step S20 whether or not condensed water is generated by the liquefaction of the water vapor contained in the EGR gas Ge. If it is determined that condensed water is generated (YES), the process proceeds to step S30. When it is determined that the condensed water is not generated (NO), the process returns to step S10 and the determination of step S10 is performed again.

Note that the generation of condensed water may be determined by using a map based on the EGR gas temperature and the exhaust oxygen excess rate as described above, or alternatively, the EGR gas temperature and the exhaust oxygen excess rate may be set respectively. You may perform using the comparison result with a threshold value. More specifically, the method using the comparison result means that condensed water is generated only when the EGR gas temperature is lower than a preset temperature threshold value set in advance and the exhaust oxygen excess ratio is lower than a preset concentration concentration threshold value set in advance. If the EGR gas temperature is equal to or higher than the set temperature threshold value or if the exhaust oxygen excess rate is equal to or higher than the set concentration threshold value, it is determined that condensed water is not generated.

When the process proceeds from step S20 to step S30, control is performed in step S30 to reduce the rotation speed Nlp of the low water temperature water pump 22 to a rotation speed Nlp1 lower than the basic rotation speed Nlpc. The rotation speed Nlp1 is set to an optimum value in advance by experiments or the like. After performing the control of step S30, the process proceeds to step S40.

In step S40, it is determined whether or not condensed water is generated by the liquefaction of the water vapor contained in the EGR gas Ge from the second time onward. If it is determined that condensed water is generated (YES), the process proceeds to step S50, and in step S50, the rotation speed Nlp of the low water temperature water pump 22 is maintained at the basic rotation speed Nlp1, or Control is performed to reduce the rotation speed to a speed lower than the rotation speed. After performing the control of step S50, the process returns to step S40, and the determination of step S40 is performed again.

On the other hand, if it is determined in step S40 that condensed water is not generated (NO), the process proceeds to step S60, and in step S60, the control for returning the rotation speed Nlp of the low water temperature water pump 22 to the basic rotation speed Nlpc. I do. After performing the control of step S60, the process proceeds to return and the present control flow ends.

As described above, the control method of the internal combustion engine of the present invention includes the high water temperature radiator 11 and the high water temperature water supply device 12 in the high temperature side cooling water flow path through which the high temperature side cooling water HW for cooling the internal combustion engine flows. , A low-water temperature radiator 21, an electric low-water temperature water supply device 22, and an EGR cooler in a low-temperature side cooling water flow path through which low-temperature side cooling water LW that cools intake gas passing through an intake passage 2 of an internal combustion engine flows. 8, and a branch flow passage 30 branched from the high temperature side cooling water flow passage is connected to the low temperature side cooling water flow passage upstream of the EGR cooler 8 to provide a low temperature side cooling water flow passage. In the control method for the internal combustion engine, the mixed cooling water MW in which the low temperature side cooling water LW passing through the high temperature side cooling water HW passing through the branch flow passage 30 is mixed is circulated in the EGR cooler 8. Based on the temperature of the EGR gas Ge passing through the EGR passage 4 downstream of 8 and the oxygen excess ratio of the exhaust gas G passing through the exhaust passage 3 of the internal combustion engine or the exhaust manifold 1b. When the condensed water generation determination is performed to determine whether or not condensed water is generated by liquefaction, and when it is determined that condensed water is generated in this condensed water generation determination, the rotation speed Nlp of the low water temperature water supply device 22. The method is characterized by performing rotational speed adjustment control, which is control for lowering the basic rotational speed Nlpc from a preset basic rotational speed Nlpc according to the operating state of the internal combustion engine.

As described above, according to the internal combustion engine and the method of controlling the internal combustion engine of the present invention, the engine cooling water (high temperature side cooling water) HW and the low temperature side cooling water LW for cooling the intake gas are mixed to be lower than the engine cooling water HW. Since the mixed cooling water MW of 1 is circulated to the EGR cooler 8 as a cooling medium, the EGR gas Ge can be further cooled as compared with the conventional technique in which the engine cooling water HW is used as the cooling medium. As a result, it is possible to reduce the volume of the air-fuel mixture of intake air and EGR gas flowing into the cylinder to improve the fuel efficiency performance of the vehicle, and to lower the temperature of the air-fuel mixture to improve the exhaust gas performance.

Further, since the mixed cooling water MW having a higher temperature than the low temperature side cooling water LW is used as the cooling medium of the EGR cooler 8 without using the low temperature side cooling water LW, the condensed water (corrosion caused by the condensation of the water vapor contained in the EGR gas Ge (corrosion) is used. Water) can be suppressed. As a result, it is possible to suppress corrosion and deterioration of various pipes and valves due to condensed water.

Further, when there is a concern that condensed water will be generated, the rotation speed of the low water temperature water supply device 22 is reduced to reduce the amount of the low temperature side cooling water LW relative to the total amount of the high temperature side cooling water HW and the low temperature side cooling water LW. Is decreased to raise the temperature of the mixed cooling water MW, the EGR gas Ge after passing through the EGR cooler 8 using the mixed cooling water MW as a cooling medium can be raised, and the generation of condensed water is further suppressed. can do.

Further, since it is determined whether or not the condensed water is generated based on the EGR gas temperature and the exhaust gas oxygen excess rate, the accuracy of the condensed water generation determination can be improved.

1 Engine Body 1a Intake Manifold 1b Exhaust Manifold 2 Intake Passage 3 Exhaust Passage 4 EGR Passage 7 Intercooler 7a Low Pressure Intercooler 7b High Pressure Intercooler 8 EGR Cooler 9 Second EGR Cooler 11 High Water Temperature Radiator 12 High Water Temperature Water Pump (water supply device for high water temperature)
21 Low water temperature radiator 22 Low water temperature water pump (low water temperature water supply device)
30 branch flow path 31 EGR gas temperature sensor (EGR gas temperature detection device)
32 Exhaust gas lambda sensor (exhaust oxygen excess rate detection device)
40 Controller Nlp Number of revolutions of low water temperature water pump Nlpc Basic number of revolutions of low water temperature water pump CP Connection point HW High temperature side cooling water (engine cooling water)
MW Mixed cooling water LW Low temperature side cooling water

Claims (6)

A high water temperature radiator and a high water temperature water supply device are provided in the high temperature side cooling water flow path through which the high temperature side cooling water for cooling the internal combustion engine is provided, and the intake gas passing through the intake passage of the internal combustion engine is cooled. In an internal combustion engine configured to include a low water temperature radiator, a low water temperature water supply device, and an EGR cooler in a low temperature side cooling water passage through which the low temperature side cooling water flows,
A low temperature side cooling passage that passes through the low temperature side cooling water passage by connecting a branch passage branching from the high temperature side cooling water passage to the low temperature side cooling water passage upstream of the EGR cooler. The mixed cooling water in which the water and the high temperature side cooling water passing through the branch passage are mixed is circulated in the EGR cooler, and the low water temperature water supply device is configured as an electric water supply device.
Further, an EGR gas temperature detecting device is provided in an EGR passage downstream of the EGR cooler, and an exhaust oxygen excess ratio detecting device is provided in an exhaust passage or an exhaust manifold of the internal combustion engine,
A control device for controlling the internal combustion engine,
Condensed water generation determination that determines whether or not water vapor contained in EGR gas is liquefied to generate condensed water based on the detected value of the EGR gas temperature detecting device and the detected value of the exhaust gas oxygen excess ratio detecting device In addition, when determining that condensed water is generated in the condensed water generation determination, the rotation speed of the low water temperature water supply device is made lower than a basic rotation speed that is preset according to the operating state of the internal combustion engine. An internal combustion engine configured to perform a rotational speed adjustment control, which is a control. An intercooler that cools the intake gas with low-temperature side cooling water is provided in the intake passage and the low-temperature side cooling water flow path, and is provided in the low-temperature side cooling water flow path between the intercooler and the EGR cooler. The internal combustion engine according to claim 1, wherein a connection point between the low temperature side cooling water channel and the branch channel is arranged. The control device is
The internal combustion engine according to claim 1, wherein the rotational speed adjustment control is performed only when the internal combustion engine has a low load. The control device is
While performing the condensed water generation determination every preset control time,
When it is determined that condensed water is generated in the condensed water generation determination, it is determined that condensed water is generated in the condensed water generation determination until it is determined that condensed water is not generated in the subsequent condensed water generation determination. Each time the rotation speed of the low water temperature water supply device is reduced, and when it is determined that condensed water is not generated in the subsequent condensed water generation determination, the rotation speed of the low water temperature water supply device is the basic rotation speed. The internal combustion engine according to any one of claims 1 to 3, wherein the internal combustion engine is configured to perform control for returning to the above. The EGR cooler different from the EGR cooler and provided with a second EGR cooler using a high temperature side cooling water as a cooling medium in the EGR passage upstream of the EGR cooler. The internal combustion engine according to claim 1. A high water temperature radiator and a high water temperature water supply device are provided in the high temperature side cooling water flow path through which the high temperature side cooling water for cooling the internal combustion engine is provided, and the intake gas passing through the intake passage of the internal combustion engine is cooled. The low temperature side cooling water flow path through which the low temperature side cooling water flows has a low water temperature radiator, an electric low water temperature water supply device and an EGR cooler, and further, for the low temperature side cooling water upstream of the EGR cooler. A branch flow path branched from the high temperature side cooling water flow path is connected to the flow path, and a low temperature side cooling water passing through the low temperature side cooling water flow path and a high temperature side cooling water passing through the branch flow path. In a method of controlling an internal combustion engine configured to cause the mixed cooling water in which is mixed to flow through the EGR cooler,
Based on the temperature of the EGR gas passing through the EGR passage downstream of the EGR cooler and the oxygen excess rate of the exhaust gas passing through the exhaust passage or the exhaust manifold of the internal combustion engine, the water vapor contained in the EGR gas is liquefied. In addition to performing condensed water generation determination to determine whether condensed water is generated,
When it is determined in the condensed water generation determination that condensed water is generated, a rotation that is a control for lowering the rotation speed of the low water temperature water supply device below a basic rotation speed that is preset according to the operating state of the internal combustion engine. A method for controlling an internal combustion engine, characterized in that a number adjustment control is performed.

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