JP7690933B2 - Engine Cooling System - Google Patents

Description

The present invention relates to an engine cooling device.

Patent document 1 describes an engine cooling device that includes a radiator water passage that passes through a radiator, a bypass water passage that bypasses the radiator, and a switching valve that switches the radiator water passage between a closed state and an open state. The engine cooling device also includes a control unit that controls the switching valve to close the radiator water passage while the engine is warming up, and open the radiator water passage after the warm-up is complete. Furthermore, the control unit opens the radiator water passage when the engine is operating in a state in which the pressure loss of the cooling water flowing through the cooling water circuit is large and cavitation is likely to occur while the radiator water passage is closed. This reduces the pressure loss of the cooling water flowing through the cooling water circuit, thereby suppressing the occurrence of cavitation. The control unit determines whether the engine is in an operating state in which cavitation is likely to occur based on the opening degree of the switching valve, the temperature of the cooling water, and the engine speed.

JP 2018-168755 A

In the cooling system described above, a mechanical pump that operates in response to engine rotation may be used as a water pump for circulating the cooling water. In a cooling system that uses a mechanical water pump, the flow rate of cooling water circulating through the cooling water circuit increases as the engine speed increases. When the radiator water passage is closed, the flow rate of cooling water in the bypass water passage is higher than when it is open. Therefore, if the engine speed increases while the radiator water passage is closed, there is a risk that the water pressure in the bypass water passage will rise beyond the allowable limit.

The engine cooling device that solves the above problem cools an engine that is connected to wheels via a manual transmission that allows manual gear shifting. The engine cooling device has a cooling water circuit that circulates cooling water through the engine, and a control unit. The cooling water circuit includes a mechanical water pump that operates in response to engine rotation, a radiator water passage that passes through a radiator, a bypass water passage that bypasses the radiator, and a switching valve that switches between a state in which water is blocked through the radiator water passage and a state in which water is allowed to pass through the radiator water passage in response to the operation of the valve body. Meanwhile, when the engine speed becomes equal to or greater than the evacuation judgment value while water is blocked through the radiator water passage, the control unit executes an evacuation process that commands the valve body to be driven in the direction in which the switching position is located as viewed from the current operating position, and a change process that changes the evacuation judgment value to a smaller value than when the NV ratio, which is the ratio of the engine speed to the vehicle speed, is large. The above-mentioned switching position is the operating position of the valve body at which the state in which water is blocked and the state in which water is allowed to pass through are switched.

When the valve body is driven in the direction of the switching position from the current operating position, the amount of drive of the valve body required to switch from a state in which water flow through the radiator water passage is blocked to a state in which water flow through the radiator water passage is permitted is reduced. Therefore, by predicting the increase in water pressure in the bypass water passage and performing the evacuation process, it becomes easier to suppress the increase in water pressure in the bypass water passage that exceeds the allowable limit. On the other hand, in a vehicle equipped with a manual transmission, the engine and the wheels are connected and disconnected by the user's operation. When the engine and the wheels are disconnected, the engine speed tends to increase more quickly than when they are connected. Furthermore, when the engine speed is increasing while the engine and the wheels are disconnected, the ratio of the engine speed to the vehicle speed becomes large. When the ratio is large, the control unit of the engine cooling device performs the evacuation process at a lower engine speed than when the ratio is small. Therefore, the engine cooling device has the effect of making it easier to suppress an excessive increase in water pressure in the cooling water circuit.

1 is a diagram illustrating a schematic configuration of a drive system of a vehicle to which an embodiment of an engine cooling device is applied; FIG. 2 is a diagram showing a schematic configuration of the engine cooling device according to the embodiment. 4 is a graph showing the relationship between the operating position of a multifunction valve provided in the engine cooling device and the opening rate of each port. 4 is a flowchart of an evacuation process routine executed by an electronic control unit of the engine cooling device. 11 is a graph showing a relationship between the engine speed and a second evacuation determination value. 13 is a graph showing a relationship between vehicle speed and a third evacuation determination value.

Hereinafter, an embodiment of an engine cooling device will be described in detail with reference to FIGS.
First, the configuration of the drive system of a vehicle equipped with an engine cooling device of this embodiment will be described with reference to Fig. 1. The vehicle having the drive system of Fig. 1 is configured as a part-time four-wheel drive vehicle that can manually switch between two-wheel drive and four-wheel drive.

As shown in FIG. 1, the drive system of the vehicle includes an engine 10, a manual transmission 11, and a transfer 12. Front and rear drive shafts 13, 14 are connected to the transfer 12. The front drive shaft 13 is connected to left and right front wheels 16 via a front differential 15. The rear drive shaft 14 is connected to left and right rear wheels 18 via a rear differential 17. The manual transmission 11 changes the rotation of the engine 10 and outputs it to the transfer 12. The gear ratio of the manual transmission 11 is changed by switching the gear stages manually operated by the user. The transfer 12 is provided with an auxiliary transmission 19. That is, in the drive system of FIG. 1, the auxiliary transmission 19 is interposed between the manual transmission 11 and the wheels. The auxiliary transmission 19 has three gear stages: "2H", "4H", and "4L". The gear of the auxiliary transmission 19 is changed by manual operation by the user. When the gear of the auxiliary transmission 19 is "2H", the transfer 12 transmits the power input from the manual transmission 11 only to the drive shaft 14 on the rear wheel side. When the gear of the auxiliary transmission 19 is "4H" or "4L", the transfer 12 distributes the power input from the manual transmission 11 to both the drive shafts 13 and 14 on the front and rear wheel sides. When the gear is "4L", the gear ratio of the auxiliary transmission 19 is higher than when the gear is "2H" or "4H". In this embodiment, "4L" corresponds to the low gear of the auxiliary transmission 19, and "4H" and "2H" correspond to the high gear.

Next, the configuration of the engine cooling device of this embodiment will be described with reference to FIG.
The engine cooling system shown in Fig. 2 has a coolant circuit C that circulates coolant through the inside of the engine 10. The coolant circuit C includes a radiator 20 and a mechanical water pump 21. The radiator 20 is a heat exchanger that cools the coolant by exchanging heat between the coolant and outside air. The water pump 21 operates in response to the rotation of the engine 10 and sends the coolant to the engine 10. The flow rate of the coolant discharged by the water pump 21, i.e., the flow rate of the coolant circulating through the coolant circuit C, increases as the engine speed NE increases.

The cooling water circuit C also includes a multifunction valve 22. The multifunction valve 22 is installed at the cooling water discharge port of the engine 10. The multifunction valve 22 has three ports, a radiator port P1, a first bypass port P2, and a second bypass port P3, as ports for discharging the cooling water. The multifunction valve 22 also includes a valve body 22A and a motor 22B for driving the valve body 22A. The multifunction valve 22 is configured to vary the opening rates of the radiator port P1, the first bypass port P2, and the second bypass port P3 according to the operation of the valve body 22A. The radiator port P1 is connected to a radiator water passage 23. The radiator water passage 23 is a water passage that flows the cooling water from the radiator port P1 through the radiator 20 to the water pump 21. The first bypass port P2 is connected to a first bypass water passage 24. The first bypass water passage 24 is a water passage through which the cooling water flows from the first bypass port P2 through the oil warmer/cooler 26 to the water pump 21. The oil warmer/cooler 26 is a heat exchanger that warms and cools the oil of the manual transmission 11 by heat exchange with the cooling water. The second bypass water passage 25 is connected to the second bypass port P3. The second bypass water passage 25 is a water passage through which the cooling water flows from the second bypass port P3 to the throttle body 27 of the engine 10 or to the water pump 21 through a heater core 28 of the air conditioning system. The air conditioning system heats the passenger compartment by heating the air to be blown into the passenger compartment through heat exchange with the cooling water in the heater core 28. The second bypass water passage 25 is provided with an electric pump 29 for adjusting the flow rate of the cooling water passing through the heater core 28. The multifunction valve 22 changes the distribution of cooling water flowing through the radiator water passage 23, the first bypass water passage 24, and the second bypass water passage 25. The multifunction valve 22 can switch between a state in which water flow through the radiator water passage 23 is blocked and a state in which water flow is permitted by closing/opening the radiator port P1. In this embodiment, the multifunction valve 22 corresponds to a switching valve.

The engine cooling system also includes an ECU (Electronic Control Unit) 30 as a control unit. The ECU 30 includes an arithmetic processing unit 31 and a memory 32. The memory 32 stores programs and data for controlling the engine cooling system. The arithmetic processing unit 31 reads and executes the programs stored in the memory 32 to perform various processes for controlling the engine cooling system. The ECU 30 receives detection results from various sensors installed in various parts of the vehicle. The detection results input to the ECU 30 include the engine speed NE, vehicle speed V, water temperature THW, and intake air temperature THA.

Next, the operation of the multi-function valve 22 will be described with reference to FIG. 3. FIG. 3 shows the relationship between the operating position of the valve body 22A of the multi-function valve 22 and the opening ratios of the radiator port P1, the first bypass port P2, and the second bypass port P3. In the figure, "L1" represents the opening ratio of the radiator port P1, "L2" represents the opening ratio of the first bypass port P2, and "L3" represents the opening ratio of the second bypass port P3. The opening ratio represents the ratio of the flow path area to the maximum flow path area of the corresponding port. Thus, when the opening ratio is "0", each port is closed, blocking the flow of water through the connected water passage. When the opening ratio is greater than "0", each port is open, allowing the flow of water through the connected water passage.

The multifunction valve 22 is set to a reference position A0, which is the reference operating position of the valve body 22A. The operating range of the valve body 22A in the multifunction valve 22 is divided into a summer use range and a winter use range, with the reference position A0 as the boundary. The summer use range is the operating range of the valve body 22A used when it is not expected that the vehicle cabin will be heated. The winter use range is the operating range of the valve body 22A used when it is expected that the vehicle cabin will be heated. The ECU 30 selects the operating range to be used for controlling the multifunction valve 22, for example, based on the outside air temperature. In the following explanation, summer and winter represent the selection of the summer use range and the winter use range, respectively.

In FIG. 3, the operating range of the valve body 22A is shown divided into six regions R1 to R6. Region R3 includes the reference position A0. In region R3, the radiator port P1, the first bypass port P2, and the second bypass port P3 are all closed. Region R3 is divided into a summer use region and a winter use region, with the reference position A0 as the boundary. Regions R1 and R2 to the left of region R3 in the figure are included in the summer use region, and regions R4 to R6 to the right of region R3 in the figure are included in the winter use region. In region R2, only the first bypass port P2 is open. In region R1, the radiator port P1 and the first bypass port P2 are open. In region R4, only the second bypass port P3 is open. In region R5, the first bypass port P2 and the second bypass port P3 are open. In region R6, the radiator port P1, the first bypass port P2, and the second bypass port P3 are all open. When the valve body 22A is located in region R2 to region R5, the multifunction valve 22 blocks the flow of water through the radiator water passage 23. When the valve body 22A is located in region R1 or region R6, the multifunction valve 22 allows the flow of water through the radiator water passage 23. In the following description, the operating position of the valve body 22A at which the state of blocking the flow of water through the radiator water passage 23 and the state of allowing the flow of water are switched over to each other will be referred to as the switching position. When the summer use range is selected, "A1" shown in FIG. 3 is the switching position. On the other hand, when the winter use range is selected, "A2" shown in FIG. 3 is the switching position.

The ECU 30 drives the motor 22B to adjust the operating position of the valve body 22A according to the cooling requirements of the engine 10 and the heating requirements of the vehicle interior. For example, the ECU 30 promotes the warming up of the engine 10 by maintaining the operating position of the valve body 22A within the range of regions R2 to R5 and blocking the flow of water to the radiator 20 until the warming up of the engine 10 is complete. Then, when the warming up of the engine 10 is complete, the ECU 30 transitions the operating position of the valve body 22A to region R1 or region R6 and starts cooling the engine 10 by passing water through the radiator 20.

As described above, the engine cooling system of this embodiment employs a mechanical water pump 21 that operates in response to the rotation of the engine 10. The amount of cooling water discharged from the water pump 21 increases as the engine speed NE increases. Meanwhile, while the engine 10 is warming up, the flow of water through the radiator water passage 23 is stopped. At this time, the cooling water flows concentratedly through the first bypass water passage 24 and the second bypass water passage 25. If the engine speed NE increases while the flow of water through the radiator water passage 23 is cut off, there is a risk that the water pressure in the first bypass water passage 24 and the second bypass water passage 25 will exceed the pressure limit of the hose connectors and heater core 28 that make up these water passages.

When the engine speed NE becomes equal to or exceeds the preset emergency opening speed LIM while the water flow through the radiator water passage 23 is cut off, the ECU 30 opens the radiator port P1 to lower the water pressure in the first bypass water passage 24 and the second bypass water passage 25. The emergency opening speed LIM is set to the upper limit of the engine speed NE at which the water pressure in the first bypass water passage 24 and the second bypass water passage 25 does not exceed the allowable upper limit when the water flow through the radiator water passage 23 is cut off. However, it takes a certain amount of time to change the operating position of the valve body 22A of the multi-function valve 22. Therefore, when the rate of increase ΔNE of the engine speed NE is high, even if the radiator port P1 is commanded to be opened when the engine speed NE reaches the emergency opening speed LIM, the water pressure may not be lowered in time. Therefore, the ECU 30 performs a retreat process to start driving the preliminary valve body 22A while the water pressure is within the allowable range.

Figure 4 shows the procedure for the evacuation processing routine executed by the ECU 30 for the evacuation process. The ECU 30 repeatedly executes this routine at each predetermined control period while the water flow through the radiator water passage 23 is cut off. Incidentally, the "S" before the three-digit number in Figure 4 and the following description indicates the step.

When this routine starts, the ECU 30 first determines in S100 whether the gear stage of the sub-transmission 19 is set to "4L", which is a low gear stage. If it is set to "4L" (YES), the ECU 30 proceeds to S200, and if it is set to any other gear stage, i.e., a high gear stage (NO), the ECU 30 proceeds to S110.

In S110, the ECU 30 determines whether the NV ratio is equal to or greater than the predetermined neutral determination value X0. The NV ratio represents the ratio of the engine speed NE to the vehicle speed V. If the NV ratio is equal to or greater than the neutral determination value X0 (YES), the ECU 30 sets the predetermined low-speed side determination value LO as the value of the evacuation determination value X1 in S120. On the other hand, if the NV ratio is less than the neutral determination value X0 (NO), the ECU 30 sets the predetermined high-speed side determination value HI as the value of the evacuation determination value X1 in S130. The high-speed side determination value HI is set to a rotation speed that is higher than the low-speed side determination value LO and lower than the emergency release rotation speed LIM described above. After processing S120 or S130, the ECU 30 proceeds to S150.

In S150, the ECU 30 calculates the value of the second evacuation judgment value X2 based on the engine speed NE. The ECU 30 calculates the second evacuation judgment value X2 by referring to the map MAP1 stored in the memory 32. The map MAP1 is configured as a hash table in which the engine speed NE is the input value and the second evacuation judgment value X2 is the return value. FIG. 5 shows the relationship between the engine speed NE and the second evacuation judgment value X2 in the map MAP1. As shown in FIG. 5, the second evacuation judgment value X2 is calculated as a value that gradually decreases as the engine speed NE increases. More specifically, the second evacuation judgment value X2 is calculated to be a value proportional to the difference between the engine speed NE and the emergency release speed LIM. Next, in S160, the ECU 30 determines whether the engine speed NE is equal to or greater than the evacuation judgment value X1 and whether the rising speed ΔNE is equal to or greater than the second evacuation judgment value X2. If the ECU 30 judges S160 as positive (YES), it proceeds to S200, and if the ECU 30 judges S160 as negative (NO), it proceeds to S170.

In S170, the ECU 30 determines whether the engine 10 is idling. Idle operation is an operation of the engine 10 in a state where the shaft torque output by the engine 10 to the outside is "0". If the engine 10 is idling (YES), the ECU 30 proceeds to S180. On the other hand, if the engine 10 is not idling (NO), the ECU 30 ends the processing of this routine in the current control cycle. In S180, the ECU 30 calculates the third evacuation determination value X3 based on the vehicle speed V. The ECU 30 calculates the third evacuation determination value X3 by referring to the map MAP2 stored in the memory 32. The map MAP2 is configured as a hash table in which the vehicle speed V is used as a subtraction value and the third evacuation determination value X3 is used as a return value, for example. FIG. 6 shows the relationship between the vehicle speed V and the third evacuation determination value X3 in the map MAP2. In this embodiment, a value that is inversely proportional to the vehicle speed V is calculated as the third evacuation determination value X3. More specifically, a value equal to the quotient of a preset rotation speed NX, which will be described later, divided by the vehicle speed V is calculated as the third evacuation determination value X3. Next, in S190, the ECU 30 determines whether the engine speed NE is equal to or greater than the third evacuation determination value X3. If the engine speed NE has remained equal to or greater than the third evacuation determination value X3 for more than the preset time (YES), the ECU 30 proceeds to S200. On the other hand, if the engine speed NE is less than the third evacuation determination value X3 (NO), the ECU 30 ends the processing of this routine in the current control cycle.

On the other hand, in S200, the ECU 30 commands the multifunction valve 22 to drive the valve body 22A to the switching position A1 or A2. That is, in summer, the ECU 30 commands the valve body 22A to be driven to the switching position A1, and in winter, the ECU 30 commands the valve body 22A to be driven to the switching position A2. After the command, the ECU 30 ends the processing of this routine for the current control cycle. In this embodiment, the processing of S200 corresponds to a retreat process that commands the valve body 22A to be driven in the direction of the switching positions A1 and A2 from the current operating position. When the retreat process is started, the amount of movement of the valve body 22A up to the switching positions A1 and A2 approaches "0". By performing the retreat process, the ECU 30 shortens the time required to open the radiator port P1 in advance in preparation for an increase in water pressure.

<Effects of the embodiment>
The operation and effects of this embodiment will be described.
1, the torque transmission path between the engine 10 and the drive shafts 13, 14 is connected and disconnected by the user's operation of the shift lever or clutch pedal. In the following description, the state in which the torque transmission path is disconnected is referred to as the neutral state of the drive system, and the state in which the torque transmission path is connected is referred to as the connected state of the drive system.

When the accelerator pedal is depressed and the engine output increases, the engine speed NE increases. When the drive system is in a neutral state, the engine speed NE increases more easily than when it is in a connected state. Therefore, when the drive system is in a neutral state, it is necessary to start the retraction operation of the multi-function valve 22 earlier than when it is in a connected state. On the other hand, the gear ratio of the drive system when the drive system is in a connected state is determined by the respective gear stages of the manual transmission 11 and the auxiliary transmission 19. In other words, the NV ratio when the drive system is in a connected state is determined by the respective gear stages of the manual transmission 11 and the auxiliary transmission 19. On the other hand, since the NV ratio when the drive system is in a neutral state is indefinite, it may be a large value that cannot be taken when the drive system is in a connected state. Therefore, if the NV ratio is larger than a certain value, it can be determined that the drive system is highly likely to be in a neutral state. In response to this, in steps S110 to S130 of the evacuation processing routine, when the NV ratio is equal to or greater than the neutral determination value X0, the ECU 30 sets the evacuation determination value X1 to a lower rotation speed than when the NV ratio is less than the neutral determination value X0.

Furthermore, in S150, the ECU 30 sets the second evacuation determination value X2 as a value that decreases as the engine speed NE increases. Then, in S160, the ECU 30 commands the evacuation operation of the multi-function valve 22 when it determines that the engine speed NE is equal to or greater than the evacuation determination value X1 and the increasing speed ΔNE is equal to or greater than the second evacuation determination value X2. In this embodiment, the processing of S110 to S130 in the evacuation processing routine corresponds to a change processing that changes the evacuation determination value X1 to a smaller value when the NV ratio, which is the ratio of the engine speed NE to the vehicle speed V, is large compared to when the NV ratio is small. In this embodiment, the processing of S150 in the evacuation processing routine corresponds to a setting processing that sets the second evacuation determination value X2 to a higher speed when the engine speed NE is high than when the engine speed NE is low.

In this embodiment, the NV ratio is a large value, and when the drive system is likely to be in a neutral state, the evacuation operation is more likely to be initiated at a lower engine speed NE than when this is not the case. Therefore, the evacuation operation of the multifunction valve 22 can be initiated at an appropriate timing that matches the difference in the ease with which the engine speed NE increases between the neutral state and the connected state of the drive system. Furthermore, in this embodiment, the higher the rate of increase ΔNE of the engine speed NE, the lower the engine speed NE at which the evacuation operation is initiated. Therefore, the evacuation operation of the multifunction valve 22 can be initiated at an appropriate timing that matches the rate of increase ΔNE of the engine speed NE.

On the other hand, the engine 10 during deceleration of the vehicle is in an idling state in which it does not generate any shaft torque. In addition, the engine 10 during deceleration of the vehicle is further rotated in response to the rotation of the wheels. If the user performs a gear shift operation of the manual transmission 11 during such deceleration of the vehicle, the engine speed NE may suddenly increase. In response to this, in S180 of the evacuation processing routine, the ECU 30 calculates a value equal to the quotient of the above-mentioned default rotation speed NX divided by the vehicle speed V as the value of the third evacuation judgment value X3. The rotation speed NX is set to the maximum value of the normal range of the engine speed NE during vehicle deceleration. The normal range represents the range of values that the engine speed NE can take when the vehicle decelerates while the gear stage of the manual transmission 11 is held. Therefore, if the engine speed NE becomes "NX" or more during deceleration of the vehicle, that is, if the NV ratio becomes the third evacuation judgment value X3 or more, it can be determined that there is a high possibility that the manual transmission 11 has been operated to shift down. The ECU 30 also commands the retraction operation of the multi-function valve 22 when the NV ratio is equal to or greater than the third retraction determination value X3 during idling (S170: YES and S190: YES). Therefore, the retraction operation of the multi-function valve 22 is performed when it is predicted that the engine speed NE may subsequently exceed the emergency release speed LIM due to the user's operation to shift down the manual transmission 11 while the vehicle is decelerating.

When a user of the vehicle described above travels up a steep slope or a rocky mountain, which requires a large driving force, the user sets the gear stage of the sub-transmission 19 to "4L", which is a low-speed gear stage. When traveling in this manner, there is a high possibility that the engine speed NE will increase significantly. In response to this, in the evacuation processing routine, the ECU 30 performs the evacuation operation of the multi-function valve 22 when the gear stage of the sub-transmission 19 is set to a low-speed gear stage (S100: YES).

<Other embodiments>
This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction.

- The process of S100 in the evacuation process routine of FIG. 4 may be omitted. That is, the evacuation operation of the multi-function valve 22 may not be performed when the sub-transmission 19 is set to a low gear stage. Also, the processes of S170 to S190 in the evacuation process routine of FIG. 4 may be omitted. That is, the evacuation operation of the multi-function valve 22 may not be performed when the engine speed NE becomes equal to or higher than a preset speed NX during vehicle deceleration. Furthermore, the processes of S150 and S160 in the evacuation process routine of FIG. 4 may be omitted. That is, the determination of whether to perform the evacuation operation based on the rate of increase ΔNE of the engine speed NE may be omitted.

The change of the evacuation determination value X1 according to the NV ratio may be performed in three or more stages. Also, the evacuation determination value X1 may be changed continuously according to the NV ratio.
In the evacuation process, a command may be issued to drive the valve body 22A to a position closer to the current operating position than the switching positions A1 and A2. Also, in the evacuation process, a command may be issued to drive the valve body 22A to a position farther from the current operating position than the switching positions A1 and A2.

The configuration of the coolant circuit C of the engine cooling device may be changed as appropriate. Specifically, the coolant circuit may have a configuration different from that shown in FIG. 2, so long as it includes a mechanical water pump, a radiator water passage that passes through the radiator, a bypass water passage that bypasses the radiator, and a switching valve. In addition, the engine cooling device of the above embodiment can be applied to vehicles having a drive system other than that shown in FIG. 1, so long as the engine and wheels are connected via a manual transmission that allows manual gear shifting.

10...engine, 11...manual transmission, 12...transfer, 13, 14...drive shaft, 15, 17...differential, 16...front wheels, 18...rear wheels, 19...sub-transmission, 20...radiator, 21...water pump, 22...multifunction valve (22A...valve body, 22B...motor), 23...radiator water passage, 24...first bypass water passage, 25...second bypass water passage, 26...oil warmer/cooler, 27...throttle body, 28...heater core, 29...electric pump, 30...ECU, 31...CPU, 32...memory, C...cooling water circuit

Claims (5)

An engine cooling device that cools an engine that is connected to wheels via a manual transmission that allows manual gear shifting,
A cooling water circuit that circulates cooling water through the engine, and a control unit,
the cooling water circuit includes a mechanical water pump that is operated by rotation of the engine, a radiator water passage that passes through a radiator, a bypass water passage that bypasses the radiator, and a changeover valve that switches between a state in which water flow through the radiator water passage is blocked and a state in which water flow is permitted in response to the operation of a valve body;
the control unit executes an evacuation process for instructing the valve body to be driven in a direction toward a switching position as viewed from a current operating position when the engine speed becomes equal to or greater than an evacuation determination value while water flow through the radiator water passage is blocked, and a change process for changing the evacuation determination value when an NV ratio, which is a ratio of the engine speed to a vehicle speed, is large so that the evacuation determination value is smaller than when the NV ratio is small,
The engine cooling device, wherein the switching position is an operating position of the valve body at which the water flow is switched between a state in which the water flow is blocked and a state in which the water flow is permitted. the control unit performs a setting process of setting a higher speed as the second evacuation determination value when the engine rotation speed is high than when the engine rotation speed is low,
2. The engine cooling device according to claim 1, wherein the evacuation process is a process of instructing the valve body to be driven in a direction toward the switching position from a current operating position when the engine speed becomes equal to or greater than the evacuation judgment value and the rate of increase of the engine speed becomes equal to or greater than the second evacuation judgment value. The engine cooling device according to claim 1, wherein the evacuation process is a process that commands the valve body to be driven in the direction toward the switching position from the current operating position even if the NV ratio becomes equal to or exceeds a predetermined value during vehicle deceleration. a vehicle equipped with the engine includes an auxiliary transmission having a low-speed gear stage and a high-speed gear stage, the auxiliary transmission being interposed between the manual transmission and the wheels;
2. The engine cooling device according to claim 1, wherein the evacuation process is a process of instructing the valve body to be driven in a direction toward the switching position as viewed from a current operating position, even when the gear stage of the auxiliary transmission is set to the low gear stage. The engine cooling device according to any one of claims 1 to 4, wherein the evacuation process is a process for issuing a command to drive the valve body to the switching position.

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