JP6094231B2 - Internal combustion engine cooling system - Google Patents

Description

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

  In a system that recirculates a part of the exhaust gas of an internal combustion engine to the intake side as EGR gas, a technique for cooling and recirculating EGR gas by an EGR cooler has been put into practical use. Specifically, a water-cooled EGR cooler for exchanging heat of EGR gas with cooling water is provided in an EGR pipe that recirculates EGR gas from the exhaust pipe to the intake pipe. Further, in the circulation path for circulating the cooling water, the EGR cooler is disposed at a position downstream of the cooling passage provided in the internal combustion engine, and the cooling water that has passed through the cooling passage of the internal combustion engine is supplied to the EGR cooler. The structure made into is known (for example, refer patent document 1). Thus, in the configuration in which the EGR cooler is arranged on the downstream side of the cooling passage of the internal combustion engine, the cooling water is supplied to the EGR cooler according to the required flow rate set based on the operating state of the internal combustion engine.

JP 2001-289125 A

  For example, when the temperature of the cooling water is relatively low at the time of cold start of the internal combustion engine, the cooling water flows to the EGR cooler, so that the EGR gas is supercooled in the EGR cooler and condensed water is generated. It is done. Here, when cooling water is supplied to the EGR cooler according to the operating state of the internal combustion engine as described above, it is considered that, for example, priority is given to cooling of the EGR gas, so that condensed water is easily generated. There is a concern that the condensed water may cause corrosion of the EGR cooler and malfunctions due to water scattering downstream (engine water suction, catalyst, exhaust sensor heat shock).

  An object of the present invention is to provide a cooling system for an internal combustion engine that can eliminate the disadvantages caused by the generation of condensed water in an EGR cooler.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  In the present invention, a circulation path (20) for circulating a cooling medium for cooling the internal combustion engine, and a downstream side of the engine cooling passage (13, 14) of the internal combustion engine in the circulation path, the EGR gas is cooled. An EGR cooler (33) that cools with a medium, and a flow rate adjusting means (27) that adjusts the circulation flow rate of the cooling medium that flows to the EGR cooler in the circulation path. And a required flow rate calculation means (40) for calculating a required flow rate of the cooling medium based on an operating state of the internal combustion engine, and a condensation determination means (40) for determining the possibility of generation of condensed water in the EGR cooler. When the condensation determination means determines that there is a possibility of the generation of condensed water, the circulation flow rate of the cooling medium is limited from the required flow rate, and the flow rate by the flow rate adjustment unit is set to the limited flow rate. And control means (40) for performing the control.

  When the internal combustion engine is not at the completion of warm-up but is at a relatively low temperature, there is a concern that the EGR gas is excessively cooled by the EGR cooler, resulting in the generation of condensed water in the EGR cooler. In this regard, according to the above configuration, when it is determined that condensed water is likely to be generated, the flow rate restriction on the required flow rate is performed on the cooling medium flowing through the EGR cooler. Thereby, generation | occurrence | production of condensed water is suppressed in an EGR cooler. As a result, inconvenience due to the generation of condensed water in the EGR cooler can be eliminated.

The block diagram which shows the outline | summary of the cooling system of an engine. The flowchart which shows the procedure of cooling water flow control. The relationship figure used for calculation of basic demand flow. The relationship figure used for calculation of a water temperature coefficient. The relationship figure used for calculation of condensation temperature. The relationship figure used for calculation of a guard flow rate. The relationship figure used for calculation of a guard flow rate. The time chart for demonstrating cooling water flow control more concretely. The flowchart which shows the procedure of cooling water flow control in other embodiment. The related figure used for calculation of the guard flow rate in other embodiments. The block diagram which shows the outline | summary of the cooling system of an engine in other embodiment. The block diagram which shows the outline | summary of the cooling system of an engine in other embodiment. The block diagram which shows the outline | summary of the cooling system of an engine in other embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings. In the present embodiment, a water-cooled multi-cylinder engine (internal combustion engine) mounted on a vehicle is embodied as a cooling system that cools the engine. FIG. 1 is a configuration diagram showing an outline of the present system.

  In FIG. 1, an engine 10 has a cylinder block 11 and a cylinder head 12, and each is formed with a water jacket for circulating cooling water as a cooling medium. The water jacket of the cylinder block 11 corresponds to a cylinder block cooling passage 13 through which cooling water flows in the cylinder block 11, and the water jacket of the cylinder head 12 performs cylinder head cooling through which cooling water flows through the cylinder head 12. It corresponds to the passage 14.

  In this embodiment, the cylinder block cooling passage 13 and the cylinder head cooling passage 14 are provided in parallel, so that the cylinder block 11 and the cylinder head 12 are cooled by different systems.

  A circulation path 20 for circulating cooling water is connected to the cooling passages 13 and 14 of the engine 10. The circulation path 20 is constituted by a piping member made of metal or synthetic resin, for example. The circulation path 20 is a cooling water inflow path with respect to the engine 10 (the cooling passages 13 and 14), an inlet side path 21 branched into two paths, and the cooling water outflow from the cylinder block cooling path 13. A cylinder block outlet side path 22 which is a side path, and a cylinder head outlet side path 23 which is a path on the cooling water outflow side from the cylinder head cooling passage 14. A water pump 24 is provided at a position before the branching (aggregation portion) of the inlet side path 21. The water pump 24 is a mechanical water pump driven by the rotation of the engine 10, and the coolant is circulated in the circulation path 20 by driving the water pump 24.

  The cylinder block outlet side path 22 is provided with a flow rate adjusting valve 26 that adjusts the flow rate of the cooling water flowing in the outlet side path 22. Further, the cylinder head outlet side path 23 is branched into two paths, and at the branch position, there is a function of adjusting the flow rate of the cooling water flowing in the outlet side path 23 and the two branch paths 23a and 23b. A flow rate adjusting valve 27 having a switching function for switching the cooling water to flow through is provided. One of the two branch paths 23a and 23b is provided with a radiator 28 that cools the cooling water with outside air. The other branch path 23b is provided in series with a heater core 31 serving as a heat source in the in-vehicle air conditioner and an EGR cooler 33 that cools the EGR gas passing through the EGR device 32. The branch path 23 b is a bypass path that bypasses the radiator 28. When the cooling water flows through the branch path 23b, the cooling water flowing out from the cylinder head cooling passage 14 flows in the order of the flow rate adjusting valve 27 → the heater core 31 → the EGR cooler 33.

  In the present embodiment, the cylinder head outlet side path 23 corresponds to a “first path”, and the cylinder block outlet side path 22 corresponds to a “second path”. The flow rate adjustment valve 27 corresponds to a “first adjustment unit”, and the flow rate adjustment valve 26 corresponds to a “second adjustment unit”.

  The heater core 31 is a heat exchanger that warms the blown air by heat exchange between the cooling water passing through the interior and the air blown into the vehicle interior, and corresponds to a heat radiation source that releases heat of the cooling water. In this case, heat exchange (radiation of cooling water) is performed in the heater core 31 in response to a heating request for heating the vehicle interior.

  The EGR device 32 corresponds to EGR means for recirculating a part of the exhaust discharged from the engine 10 to the intake system as EGR gas, and has an EGR pipe for circulating the EGR gas and an EGR valve for adjusting the EGR gas amount. doing. The EGR cooler 33 is provided in the middle of the EGR pipe and functions as a heat exchanger that exchanges heat between the EGR gas and the coolant. The EGR cooler 33 has a configuration in which, for example, a plurality of thin and long tubular heat transfer tubes (heat exchange pipes) are provided in parallel, EGR gas flows in these heat transfer tubes, and cooling water flows outside the heat transfer tubes.

  The cylinder block outlet side path 22 and the cylinder head outlet side path 23 are integrated into one path on the downstream side of the radiator 28, the heater core 31, and the EGR cooler 33, and are connected to the inlet side path 21 on the downstream side. It has become. In the circulation path 20, a water temperature sensor 35 that detects the temperature of the cooling water is provided on the inlet side of the engine 10 (specifically, on the upstream side of the water pump 24).

  The ECU 40 includes a well-known microcomputer including a CPU, a ROM, and a memory such as a RAM, and executes the various control programs stored in the ROM, so that the present system can be used according to the engine operating state each time. Implement various controls. Specifically, in addition to the water temperature sensor 35 described above, the ECU 40 includes a rotation speed sensor 41 that detects the engine rotation speed, a load sensor 42 that detects intake pipe pressure and the like as an engine load, and an EGR cooler 33 in the EGR pipe. A gas temperature sensor 43 that detects the temperature on the outlet side (exit gas temperature), an outside air temperature sensor 44 that detects the outside air temperature, a humidity sensor 45 that detects the humidity of the outside air, and an exhaust sensor 46 that detects the air-fuel ratio of the exhaust are connected. The detection signals of these sensors are sequentially input to the ECU 40. Then, the ECU 40 performs flow rate control by adjusting the opening degree of the flow rate adjusting valves 26 and 27 based on the various detection signals inputted. In particular, in the present embodiment, the cylinder block outlet side path 22 and the cylinder head outlet side path 23 are separate paths, and the ECU 40 controls the flow rate of the cooling water for each of these paths.

  By the way, for example, when the coolant temperature is low, such as when the engine 10 is cold started, if the coolant is circulated through the EGR cooler 33, the EGR gas is excessively cooled by the EGR cooler 33, and the moisture in the EGR gas is condensed. It is possible to do. There is a concern that corrosion of various metal parts such as EGR pipes and EGR valves may occur due to the generation of the condensed water. Therefore, in this embodiment, the possibility of the occurrence of condensed water in the EGR cooler 33 is determined, and when it is determined that there is a possibility of the generation of condensed water, the flow rate of the cooling water to the EGR cooler 33 is limited. The flow rate control by the flow rate adjustment valve 27 is performed so that the flow rate is limited.

  Next, the flow rate control of the cooling water performed by the ECU 40 will be described. FIG. 2 is a flowchart showing a procedure of cooling water flow rate control, and this process is repeatedly performed by the ECU 40 at a predetermined cycle. Here, the flow rate control of the cooling water flowing through the cylinder head outlet side path 23 (the path where the EGR cooler 33 is provided) will be described. Incidentally, the flow rate of the cooling water flowing through the cylinder block outlet side path 22 (the path where the EGR cooler 33 is not provided) is controlled based on the engine operating state such as the cooling water temperature. For example, the cooling water temperature is a predetermined warm-up completion temperature ( For example, in a state where the temperature is 80 ° C. or higher, the flow rate control may be performed such that the higher the cooling water temperature, the larger the flow rate.

  In FIG. 2, in step S11, the required flow rate is calculated based on the engine operating state. At this time, the basic required flow rate is calculated based on the engine rotation speed and the engine load (torque) as the engine operating state, and the required flow rate is calculated as a result of performing the water temperature correction on the basic required flow rate. More specifically, based on the relationship shown in FIG. 3, the basic required flow rate is calculated such that the flow rate increases as the engine rotation speed increases or the engine load (torque) increases. Further, based on the relationship shown in FIG. 4, the water temperature coefficient is calculated so that the numerical value increases as the cooling water temperature increases. Here, there is a desire to perform EGR at an early stage even when the engine 10 is not in the warm-up completion state. For example, in the temperature range of 60 ° C. (temperature before completion of warm-up), the cylinder head outlet side path 23 Cooling water is circulated in the tank. Then, the final required flow rate is calculated by multiplying the basic required flow rate and the water temperature coefficient.

  In the subsequent step S12, a condensing temperature at which condensed water is generated by the EGR gas is calculated based on the outside air temperature and humidity. At this time, based on the relationship shown in FIG. 5, the condensation temperature is calculated such that the higher the humidity or the higher the outside air temperature, the higher the temperature. In step S13, the temperature on the outlet side of the EGR cooler 33 (exit gas temperature) is calculated based on the detection result of the gas temperature sensor 43.

  Thereafter, in step S14, it is determined whether or not the outlet gas temperature calculated in step S13 is lower than the condensation temperature calculated in step S12. If the outlet gas temperature is smaller than the condensation temperature, the process proceeds to step S15 to calculate the guard flow rate. Here, as the guard flow rate, an upper limit guard flow rate (upper limit guard value) for limiting the required flow rate calculated in step S11 on the high flow rate side, and a lower limit guard flow rate (lower limit guard value) for limiting on the low flow rate side. These guard flow rates are calculated using water temperature, outside air temperature, and humidity as calculation parameters.

  Specifically, the upper limit guard flow rate and the lower limit guard flow rate are calculated using the relationship shown in FIGS. 6A and 6B for the water temperature and the relationship shown in FIG. 7 for the outside air temperature and humidity. According to FIG. 6A, the lower limit guard flow rate is set to a smaller value as the water temperature is lower, and according to FIG. 6B, the lower limit guard flow rate is set to a larger value as the water temperature is lower. This means that the lower the water temperature (that is, the higher the degree of coldness of the engine 10), the stronger the restriction on the high flow rate side and the low flow rate side. Further, according to FIG. 7, the guard correction value is calculated as a larger value as the outside air temperature is higher or the humidity is higher. This means that the higher the outside air temperature or the higher the humidity, the stronger the restriction on the high flow rate side and the low flow rate side.

  Thereafter, in step S <b> 16, it is determined whether or not the cooling water is being radiated in the heater core 31. If the heater core 31 is in a heat dissipation state, the process proceeds to step S17, and if the heater core 31 is not in a heat dissipation state, the process proceeds to step S19.

  In step S17, it is determined whether the required flow rate calculated in step S11 is larger than the upper limit guard flow rate calculated in step S15, or whether the required flow rate calculated in step S11 is smaller than the lower limit guard flow rate calculated in step S15. Then, if the required flow rate ≦ the upper limit guard flow rate and the required flow rate ≧ the lower limit guard flow rate, this processing is terminated as it is. In this case, the flow rate control of the cooling water is performed with the required flow rate calculated in step S11. If the required flow rate is greater than the upper limit guard flow rate, or if the required flow rate is less than the lower limit guard flow rate, the process proceeds to step S18, and the required flow rate is limited by the upper limit guard flow rate or the lower limit guard flow rate. In this case, the flow rate control of the cooling water is performed at a limited flow rate.

  In step S19, it is determined whether or not the required flow rate calculated in step S11 is larger than the upper limit guard flow rate calculated in step S15. Then, if the required flow rate ≦ the upper limit guard flow rate, this processing is terminated as it is. In this case, the flow rate control of the cooling water is performed with the required flow rate calculated in step S11. Further, if the required flow rate> the upper limit guard flow rate, the process proceeds to step S20, and the required flow rate is limited by the upper limit guard flow rate. In this case, the flow rate control of the cooling water is performed at a limited flow rate.

  FIG. 8 is a time chart for more specifically explaining the cooling water flow rate control when the engine 10 is cold-started. In FIG. 8, only the upper limit guard flow rate is shown as the guard flow rate of the cylinder head side flow rate.

  In FIG. 8, the IG switch (start switch) of the vehicle is turned on at timing t1, and the engine 10 is started. At this time, the water temperature is, for example, 10 ° C., and gradually increases with the start of operation of the engine 10. When the water temperature reaches a predetermined value (60 ° C. in the present embodiment), the flow rate adjusting valve 27 is opened to start the circulation of the cooling water in the cylinder head outlet side passage 23 (timing t2). At this timing t2, it is assumed that the outlet gas temperature of the EGR cooler 33 is smaller than the condensation temperature, and the upper limit guard flow rate is calculated. Since the required flow rate is higher than the upper limit guard flow rate, restriction on the high flow rate side of the cylinder head side flow rate is implemented (shaded portion of t2 to t3).

  Thereafter, the upper limit guard flow rate increases as the water temperature increases, and the flow rate restriction is released when the required flow rate ≦ the upper limit guard flow rate at timing t3.

  At timing t4, the water temperature reaches the warm-up completion temperature (for example, 80 ° C.), and the flow rate adjusting valve 26 is opened, so that the flow of the cooling water in the cylinder block cooling passage 13 is started. After timing t4, the flow rate of the cooling water flowing through the cylinder block outlet side path 22 is controlled based on the cooling water temperature so that the flow rate increases as the cooling water temperature increases.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  According to the above configuration, when it is determined that condensed water is likely to be generated, the flow rate restriction on the required flow rate is performed on the cooling water flowing through the EGR cooler 33. Thereby, generation | occurrence | production of condensed water in the EGR cooler 33 is suppressed. As a result, inconvenience due to the generation of condensed water in the EGR cooler 33 can be solved.

  Set the upper limit guard flow rate (flow rate limit value) for cooling water, and if it is determined that there is a possibility of condensate water generation, limit the flow rate on the high flow rate side based on the comparison between the required flow rate and the upper limit guard flow rate The configuration. If the flow rate of the cooling water with respect to the EGR cooler 33 is excessively large, condensed water is likely to be generated. In this respect, since the flow rate is restricted on the high flow rate side based on the comparison between the required flow rate and the upper limit guard flow rate, the generation of condensed water can be suitably suppressed. Supplementally, the higher the circulating flow rate, the larger the heat capacity of the cooling water, and the smaller the temperature difference between the inlet side and the outlet side of the engine 10 (the temperature rise in the engine 10 becomes smaller). Therefore, the temperature of the cooling water at the EGR cooler inlet is lowered, and there is a concern about the generation of condensed water due to overcooling in the EGR cooler 33. However, as described above, the flow rate is restricted on the high flow rate side, and the temperature rise in the engine 10 The width can be increased and the coolant temperature at the EGR cooler inlet can be increased. Thereby, generation | occurrence | production of condensed water can be suppressed suitably.

  When it is determined that there is a possibility of condensed water generation and the heater core 31 is determined to be in a heat dissipation state, the high flow rate side and the low flow rate side are compared based on a comparison between the required flow rate and the upper limit guard flow rate and the lower limit guard flow rate. The flow rate is limited. In the circulation path 20, the heater core 31 is provided on the downstream side of the engine cooling passage (cylinder head cooling passage 14), and the EGR cooler 33 is further provided on the downstream side thereof. When the heat capacity is small, the temperature increase width in the engine 10 increases, while the temperature decrease width in the heater core 31 serving as a heat radiation source increases. Therefore, depending on the balance between the heat received by the engine 10 and the heat radiation by the heater core 31, the cooling water temperature at the EGR cooler inlet becomes too low, and the EGR cooler 33 may be overcooled. In this regard, in the above configuration, when the heater core 31 is in a heat radiating state, both the high flow rate side and the low flow rate side are limited, so that not only the circulation flow rate becomes excessive, but also the circulation flow rate is excessive. It is possible to regulate the decrease in the number of times. Thereby, generation | occurrence | production of condensed water can be suppressed suitably again.

  The colder the engine 10 (the greater the coldness), the lower the upper guard flow rate and the higher flow rate limit, and the lower limit guard flow rate and the lower flow rate limit. I tried to do it. In this case, the cooling water temperature at the EGR cooler inlet becomes lower as the engine 10 is cooled. However, by limiting the circulation flow rate, it is possible to suppress a decrease in the cooling water temperature at the EGR cooler inlet.

  Since the possibility of the generation of condensed water is determined by comparing the outlet gas temperature of the EGR cooler 33 and the condensation temperature, an appropriate condensation determination can be performed in accordance with the actual state of the EGR gas. Moreover, since it was set as the structure which calculates a condensation temperature based on external temperature and humidity, a condensation temperature can be calculated | required appropriately and by extension, the presence or absence of generation | occurrence | production of condensed water can be determined appropriately.

  The cylinder block outlet side path 22 and the cylinder head outlet side path 23, which are different from each other, are provided, and the flow rate control of the cooling water is individually performed. In the engine 10, in the configuration in which the cylinder block cooling passage 13 and the cylinder head cooling passage 14 are provided independently, it is desirable from the viewpoint of suppressing knocking that the cylinder head 12 side is kept at a relatively low temperature. In the configuration in which the EGR cooler 33 is provided in the cylinder head outlet side passage 23 connected to the cylinder head cooling passage 14, overcooling in the EGR cooler 33 easily occurs as the temperature of the cylinder head 12 decreases. In this respect, as described above, the flow rate control of the cooling water is independently performed for the cylinder block cooling passage 13 and the cylinder head cooling passage 14, and further the cylinder head cooling passage 14 (the cooling to which the EGR cooler 33 is connected) is controlled. Since the supercooling in the EGR cooler 33 is suppressed with respect to the passage), it is possible to suppress inconvenience due to the generation of condensed water while suppressing knocking.

(Other embodiments)
You may change the said embodiment as follows, for example.

  In the above embodiment, the flow rate of the cooling water is limited when the engine 10 is cold-started. In addition to this, for example, when the cylinder head 12 is lowered in temperature to suppress knocking in the engine 10 The flow rate of the cooling water may be limited. Specifically, even after the warm-up period of the engine 10 ends, the ECU 40 performs a temperature reduction control that maintains the cooling water temperature (engine outlet water temperature) at, for example, about 60 ° C. And when implementing the low temperature control, the supercooling in the EGR cooler 33 is suppressed. The control procedure by the ECU 40 is shown in FIG.

  In FIG. 9, in step S21, it is determined whether or not the low temperature control of the cylinder head 12 is being performed. The state where the temperature reduction control is performed corresponds to a “predetermined low temperature state”. If the temperature reduction control is not in the implementation state, the process proceeds to step S22 to calculate the required flow rate for normal control based on the engine operation state (engine speed, load, water temperature, etc.), and the temperature reduction control implementation state. If so, the process proceeds to step S23, and the required flow rate for low temperature control is calculated based on the engine operating state (engine speed, load, water temperature, etc.). Note that the required flow rate for low temperature control is larger than the required flow rate for normal control.

  After the execution of step S22, this process is terminated as it is, and after the execution of step S23, the process proceeds to step S12. Step S12 and subsequent steps are the same as those in FIG. 2 described above, and will not be described.

  When the engine 10 is in a predetermined low temperature state, the water temperature at the EGR cooler inlet tends to be low, and it is necessary to suppress overcooling in the EGR cooler 33. In this regard, since it is configured to limit the circulation flow rate when it is determined that the engine 10 is in a predetermined low temperature state, the flow rate limitation can be performed as necessary.

  The guard flow rate (flow rate limit value) may be set based on the air-fuel ratio of the engine 10. Specifically, as shown in (a) of FIG. 10, the upper limit guard flow rate is set to a smaller value as the air-fuel ratio detected by the exhaust sensor 46 is richer, and as shown in (b) of FIG. The lower limit guard flow rate is set to a larger value as the air-fuel ratio is richer. In other words, when the air-fuel ratio is rich, the amount of water vapor in the exhaust gas increases and the possibility of generation of condensed water increases, so the upper limit guard flow rate is reduced or the lower limit guard flow rate is increased. Increase the limit. Thereby, generation | occurrence | production of condensed water can be suppressed appropriately.

  -The structure of a cooling system is not restricted to what is shown in FIG. 1, It can be changed and embodied as follows.

  (1) In FIG. 1, the heater core 31 and the EGR cooler 33 are provided in the cylinder head outlet side path 23, but in FIG. 11, this configuration is changed, and the heater core 31 and the EGR cooler 33 are disposed in the cylinder block outlet side path 22. Is provided. In this case, the flow rate of the cooling water flowing through the EGR cooler 33 is controlled by adjusting the opening degree of the flow rate adjustment valve 26.

  (2) In FIG. 12, a cooling passage 51 for flowing cooling water from the cylinder block 11 to the cylinder head 12 is provided as a cooling passage for the engine 10. That is, in the engine 10, the cylinder block cooling passage and the cylinder head cooling passage are provided in series. An outlet side path 52 is connected to the passage outlet of the cylinder head 12, and a flow rate adjusting valve 53 is provided in the outlet side path 52. The heater core 31 and the EGR cooler 33 are provided in the outlet side path 52, and the flow rate of the cooling water flowing through the EGR cooler 33 is controlled by adjusting the opening degree of the flow rate adjustment valve 53. The order in which the cooling water flows in the cooling passage of the engine 10 may be in the order of the cylinder head 12 → the cylinder block 11, contrary to FIG. 12.

  (3) In FIG. 1, the heater core 31 and the EGR cooler 33 are provided in the cylinder head outlet side path 23, but in FIG. 13, this configuration is changed to provide the heater core 31 in the cylinder block outlet side path 22 and the cylinder An EGR cooler 33 is provided in the head outlet side path 23.

  In the above embodiment, the heater core 31 is used as a heat exchanger that releases heat of the cooling water (cooling medium). However, an oil warmer that warms the lubricating oil may be used as the heat exchanger. . In this case, for example, an oil warmer is provided in place of the heater core 31 in the cylinder head outlet side path 23 shown in FIG.

  In the above embodiment, the temperature on the outlet side of the EGR cooler 33 (outlet gas temperature) is calculated based on the detection result of the gas temperature sensor 43, but this may be changed. For example, the outlet gas temperature can be calculated based on calculation parameters such as the engine inlet water temperature, the engine rotation speed, the load, the EGR gas amount, and the required flow rate of the cooling water. In this case, the outlet gas temperature may be calculated to be higher as the engine inlet water temperature is higher, the engine rotational speed is higher, the load is larger, the EGR gas amount is larger, or the required flow rate of cooling water is smaller. In the configuration in which the heater core 31 is provided on the upstream side of the EGR cooler 33 in the cooling water circulation path, the outside air temperature may be added as the calculation parameter. The higher the outside air temperature, the higher the outlet gas temperature. In the configuration in which an oil warmer is provided on the upstream side of the EGR cooler 33 in the cooling water circulation path, the oil temperature may be added as the calculation parameter. The higher the oil temperature, the higher the outlet gas temperature.

  In the above embodiment, the water pump is a mechanical water pump, but this may be changed and an electric water pump may be used. It is good also as a structure which uses a water pump as a flow volume adjustment means, and controls flow volume by controlling the drive of the water pump.

  In the above embodiment, cooling water is used as the cooling medium, but other fluids such as oil may be used as the cooling medium instead.

  DESCRIPTION OF SYMBOLS 10 ... Engine (internal combustion engine), 13 ... Cylinder block cooling passage (engine cooling passage), 14 ... Cylinder head cooling passage (engine cooling passage), 20 ... Circulation route, 27 ... Flow rate adjusting valve (flow rate adjusting means), 32 ... EGR device (EGR means), 33 ... EGR cooler, 40 ... ECU (required flow rate calculation means, condensation determination means, control means).

Claims (7)

Applied to an internal combustion engine system comprising EGR means (32) for recirculating a part of the exhaust discharged from the internal combustion engine (10) to the intake system as EGR gas;
A circulation path (20) for circulating a cooling medium for cooling the internal combustion engine;
An EGR cooler (33) provided on the downstream side of the engine cooling passage (13, 14) of the internal combustion engine in the circulation path and cooling the EGR gas with the cooling medium;
A flow rate adjusting means (27) for adjusting a circulating flow rate of the cooling medium flowing through the EGR cooler in the circulation path;
A required flow rate calculation means (40) for calculating a required flow rate of the cooling medium based on an operating state of the internal combustion engine;
Condensation determination means (40) for determining the possibility of generation of condensed water in the EGR cooler;
When it is determined by the condensation determination means that condensed water is likely to be generated, the circulation flow rate of the cooling medium is limited from the required flow rate, and the flow rate control means by the flow rate adjustment means is set to the limited flow rate. Control means (40) for implementing
Low temperature determination means (40) for determining whether or not low temperature control is performed to lower the temperature of the cooling medium after the internal combustion engine is warmed up;
With
The required flow rate calculation means increases the required flow rate when it is determined that the low temperature control is being performed, compared to when the low temperature control is not being performed,
The internal combustion engine is characterized in that the control means limits the circulation flow rate when the condensation determination means determines that there is a possibility of the generation of condensed water under the situation where the low temperature control is being performed. Engine cooling system. The control means includes
Means for setting an upper limit guard value as a flow rate limit value for the circulating flow rate of the cooling medium;
When it is determined by the condensation determination means that there is a possibility of the generation of condensed water, based on the comparison between the required flow rate calculated by the required flow rate calculation means and the upper limit guard value, Means to enforce the restrictions;
The cooling system for an internal combustion engine according to claim 1, comprising: A cooling system in which a heat exchanger (31) for releasing heat of the cooling medium is provided on the downstream side of the engine cooling passage in the circulation path, and the EGR cooler is further provided on the downstream side thereof;
The heat exchanger comprises a heat release determining means (40) for determining whether the cooling medium is in a state where heat is released.
The control means includes
Means for setting an upper limit guard value and a lower limit guard value as a flow rate limit value for the circulating flow rate of the cooling medium;
The required flow rate calculated by the required flow rate calculation means when the condensation determination means determines that there is a possibility of the generation of condensed water, and the heat dissipation determination means determines that the heat exchanger is in a heat dissipation state. And means for performing a restriction on the high flow rate side and the low flow rate side of the circulating flow rate based on a comparison between the upper limit guard value and the lower limit guard value;
The cooling system for an internal combustion engine according to claim 1, comprising:   The cooling system for an internal combustion engine according to claim 2 or 3, wherein the control means sets the flow rate limit value based on a cold degree of the internal combustion engine. Air-fuel ratio detection means (46) for detecting the air-fuel ratio of the combustion gas in the internal combustion engine,
5. The internal combustion engine cooling system according to claim 2, wherein the control unit sets the flow rate limit value based on an air-fuel ratio detected by the air-fuel ratio detection unit. Condensation temperature calculation means (40) for calculating a condensation temperature at which condensed water is generated by the EGR gas;
Gas temperature calculating means (40) for calculating the temperature of the EGR gas;
With
The said condensation determination means determines the possibility of generation | occurrence | production of the said condensed water by comparison with the gas temperature calculated by the said gas temperature calculation means, and the condensation temperature calculated by the said condensation temperature calculation means. The internal combustion engine cooling system according to any one of the preceding claims. The internal combustion engine has a cylinder block cooling passage (13) for cooling the cylinder block (11) and a cylinder head cooling passage (14) for cooling the cylinder head (12) as the engine cooling passage,
The circulation path is connected to the cylinder block cooling path and the cylinder head cooling path, respectively, and has a block side path (22) and a head side path (23) which are different paths.
The EGR cooler is provided in one of the block side path and the head side path, and a first flow rate adjustment unit serving as the flow rate adjusting means is provided in the first route of the two routes in which the EGR cooler is provided. A second flow rate adjusting valve (26) for adjusting a circulating flow rate of the cooling medium in the path is provided in the second path where the valve (27) is provided and the EGR cooler is not provided,
The control means controls the first flow rate adjusting valve as the flow rate control of the cooling medium flowing through the first path, while the control unit controls the flow rate of the cooling medium flowing through the second path based on the operating state of the internal combustion engine. The internal combustion engine cooling system according to any one of claims 1 to 6 , wherein the second flow rate adjusting valve is controlled.

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