Control device, control method, and control program

Abstract

A control device for a cooling device that cools an internal combustion engine using cooling water includes circuitry configured to: determine boiling of the cooling water; and control a flow rate of the cooling water based on a result of the boiling determination. The circuitry determines the boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water.

Description

TECHNICAL FIELD

[0001] The present invention relates to a control device, a control method, and a control program for a cooling device used for cooling an internal combustion engine.BACKGROUND ART

[0002] In recent years, efforts to realize a low-carbon society or a decarbonized society have become active, and research and development on electrification techniques have been conducted to reduce CO2 emission and improve energy efficiency in vehicles.

[0003] In the related art, in a cooling device that circulates cooling water through a cooling water pipeline and an engine inside by using an electric water pump (EWP) in order to cool the internal combustion engine, a configuration is known in which a water level detection unit that detects a water level of the cooling water is provided in a part of the cooling water pipeline (for example, a reserve tank that stores the cooling water) to detect an increase rate of the water level of the cooling water, and boiling of the cooling water is detected based on the increase rate (Patent Literature 1). Further, a configuration is known in which a target cooling water temperature of a cooling water temperature for an internal combustion engine varies depending on a highland / lowland state, and the cooling water temperature is controlled by a flow rate control valve (Patent Literature 2). In recent years, development of the EWP has progressed, making it possible to control a flow rate of the cooling water to an extremely low flow rate.CITATION LISTPatent Literature

[0004] Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2008-303775A

[0005] Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 2004-156490ASUMMARY OF INVENTIONTechnical Problem

[0006] When the EWP capable of controlling the flow rate of the cooling water to an extremely low flow rate is used in a cooling system of an internal combustion engine, there is an advantage that the internal combustion engine is quickly warmed and fuel efficiency is improved, but it may be difficult to determine whether the cooling water is boiling.

[0007] For example, it is conceivable to determine whether the cooling water is boiling by detecting hunting of the temperature of the cooling water, but when a measurement value of a temperature sensor fluctuates due to convection of the cooling water or the like, it may be erroneously determined that the cooling water is boiling even though the cooling water is not boiling. For example, when it is erroneously determined that the cooling water is boiling and control for increasing the flow rate of the cooling water is performed, cooling of the internal combustion engine may be inappropriate, and the fuel efficiency may deteriorate.

[0008] The present invention provides a control device, a control method, and a control program capable of accurately determining boiling of cooling water and improving fuel efficiency. This contributes to improvement in energy efficiency.Solution to Problem

[0009] The present invention is a control device for a cooling device that cools an internal combustion engine using cooling water, the control device includes a boiling determination unit configured to determine boiling of the cooling water; and a flow rate control unit configured to control a flow rate of the cooling water based on a result of the boiling determination, and the boiling determination unit determines the boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water.

[0010] The present invention is a control method performed by a processor to control a cooling device that cools an internal combustion engine using cooling water, the control method includes the processor determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; and controlling a flow rate of the cooling water based a result of the determination of the boiling.

[0011] The present invention is a control program executed by a processor to control a cooling device that cools an internal combustion engine using cooling water, and the control program causes the processor to perform processing of determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; and controlling a flow rate of the cooling water based a result of the determination of the boiling.Advantageous Effects of Invention

[0012] According to the present invention, it is possible to accurately determine boiling of the cooling water and improve fuel efficiency.BRIEF DESCRIPTION OF DRAWINGS

[0013] FIG. 1 is a diagram showing a cooling device 10 to which a control device according to an embodiment of the present invention is applied.

[0014] FIG. 2 is a flowchart showing an example of boiling determination processing by a processor 11.

[0015] FIG. 3 is a graph showing an example of flow rate correction corresponding to an atmospheric pressure.

[0016] FIG. 4 is a graph showing an example of flow rate control when a load of an internal combustion engine 1 decreases rapidly.DESCRIPTION OF EMBODIMENTS

[0017] Hereinafter, an embodiment of a control device of the present invention will be described with reference to the accompanying drawings. The drawings are viewed from directions of reference numerals.EMBODIMENTS<Cooling Device 10 to which Control Device According to Embodiment of Present Invention is Applied>

[0018] FIG. 1 is a diagram showing a cooling device 10 to which a control device according to an embodiment of the present invention is applied. The cooling device 10 is a device that cools an internal combustion engine 1 using cooling water. The internal combustion engine 1 is, for example, an engine mounted on a vehicle. The cooling device 10 includes a processor 11, a cooling circuit 12, an EWP 13, a temperature sensor 14 (TW), and an atmospheric pressure sensor 15.

[0019] The processor 11 is a control device that performs control in the cooling device 10. For example, the processor 11 is implemented by an electronic control unit (ECU). The processor 11 is an example of a boiling determination unit of the present invention. The processor 11 is an example of a flow rate control unit of the present invention.

[0020] The cooling circuit 12 is a circuit for circulating the cooling water. The cooling circuit 12 is disposed to be able to perform heat exchange with, for example, a cylinder head or a cylinder block of the internal combustion engine 1, and the internal combustion engine 1 is cooled by circulating the cooling water in the cooling circuit 12. The cooling water circulating in the cooling circuit 12 is, for example, cooling water called long life coolant (LLC), but is not limited to the LLC and may be various types of cooling water.

[0021] The cooling circuit 12 shown in FIG. 1 is an example. For example, the cooling circuit 12 is not limited to a simple annular shape, and may include branching or merging, or may include various valves. Further, the cooling circuit 12 may be provided with a heat exchanger such as a radiator for cooling the cooling water. The cooling circuit 12 may be provided with a heater for heating the cooling water.

[0022] The EWP 13 is a pump serving as power for circulating the cooling water in the cooling circuit 12. The EWP 13 circulates the cooling water in the cooling circuit 12 by pumping the cooling water. A flow rate of the EWP 13 is controlled by the processor 11. A flow rate [L / min] of the cooling water circulating in the cooling circuit 12 changes depending on the flow rate of EWP 13.

[0023] The temperature sensor 14 measures a temperature (TW) of the cooling water circulating in the cooling circuit 12. In the example of FIG. 1, the temperature sensor 14 is provided on an output side of the internal combustion engine 1 in the cooling circuit 12, and measures the temperature of the cooling water immediately after cooling the internal combustion engine 1. The temperature sensor 14 outputs temperature information indicating the measured temperature to the processor 11.

[0024] The atmospheric pressure sensor 15 measures an outside air pressure (atmospheric pressure) of the vehicle on which the internal combustion engine 1 is mounted. The atmospheric pressure sensor 15 outputs atmospheric pressure information indicating the measured outside air pressure to the processor 11. The atmospheric pressure sensor 15 may be a sensor outside the cooling device 10, which is provided in the vehicle equipped with the cooling device 10, instead of a sensor provided in the cooling device 10.

[0025] For example, the processor 11 controls the flow rate of the EWP 13 based on load information indicating a load of the internal combustion engine 1. The load of the internal combustion engine 1 is, for example, at least one of an engine speed NE [rpm] and an intake air amount Gair [g]. The load information is acquired by, for example, a drive device that controls driving of the internal combustion engine 1. The drive device may be the processor 11 or a device different from the processor 11.

[0026] For example, the processor 11 performs control such that the flow rate of EWP 13 increases as the load of the internal combustion engine 1 increases. Thus, it is possible to limit a temperature increase of the internal combustion engine 1 accompanying a rise in the load of the internal combustion engine 1.

[0027] Specifically, a memory of the cooling device 10 accessible by the processor 11 stores a control table indicating the flow rate of the cooling water for each load of the internal combustion engine 1 (for example, a combination of the engine speed NE and the intake air amount Gair). In the control table, a higher flow rate is associated with a higher engine speed NE. Further, in the control table, a larger flow rate is associated with a larger intake air amount Gair. The processor 11 controls the flow rate of the EWP 13 based on a flow rate derived from the load of the internal combustion engine 1 indicated by the load information and the control table stored in the memory.

[0028] The control table is stored for each temperature range of the cooling water. For example, a temperature range of the cooling water of 75° C. or lower is referred to as “cold time”, a temperature range of the cooling water between 75° C. and 110° C. is referred to as “after warm-up”, and a temperature range of the cooling water of 110° C. or higher is referred to as “high water temperature”. In this case, the control table is stored for each state including the “cold time”, the “after warm-up”, and the “high water temperature”. In this case, a lower flow rate is associated with a control table of a lower temperature range.

[0029] The control tables for the “cold time”, the “after warm-up”, and the “high water temperature” may not have the same data structure. For example, the control table for the “cold time” may indicate the flow rate of the cooling water for each combination of the engine speed NE and the intake air amount Gair, and the control tables for the “after warm-up” and the “high water temperature” may each indicate the flow rate of the cooling water for each engine speed NE.

[0030] The control table for the “cold time” includes an extremely low flow rate (for example, 7.7 [L / min]). That is, in the “cold time” in which the temperature of the cooling water is 75° C. or lower, the cooling water in the cooling circuit 12 is controlled to an extremely low flow rate.

[0031] In order to control the flow rate of the EWP 13, the processor 11 determines boiling of the cooling water in the cooling circuit 12 in addition to referring to the load information. Here, in a state in which the cooling water in the cooling circuit12 is controlled to an extremely low flow rate, in a method of determining the boiling of the cooling water only by detecting hunting of the temperature of the cooling water which is based on a measurement value of the temperature sensor 14, the measurement value of the temperature sensor 14 fluctuates due to convection of the cooling water, and it may be erroneously determined that the cooling water is boiling even though the cooling water is not boiling.<Boiling Determination Processing Performed by Processor 11>

[0032] FIG. 2 is a flowchart showing an example of boiling determination processing performed by the processor 11. The processor 11 performs processing shown in FIG. 2 to determine the presence or absence of boiling of the cooling water in the cooling circuit 12.

[0033] First, the processor 11 calculates magnitude of a difference between a maximum value and a minimum value of the temperature of the cooling water in the cooling circuit 12 during a predetermined time based on the temperature information output from the temperature sensor 14 (step S11). The predetermined time is, for example, 10 seconds.

[0034] Next, the processor 11 determines whether the magnitude of the difference calculated in step S11 is equal to or greater than a first threshold (step S12). That is, the processor 11 determines whether the hunting of the temperature information occurs. The first threshold is a preset value, and is, for example, 2° C.

[0035] In step S12, when the magnitude of the difference is not equal to or greater than the first threshold (step S12: No), that is, when the hunting of the temperature information does not occur, the processor 11 determines that the boiling does not occur (no boiling) (step S13), and ends the series of boiling determination processing.

[0036] In step S12, when the magnitude of the difference is equal to or greater than the first threshold (step S12: Yes), that is, when the hunting of the temperature information occurs, the processor 11 determines whether the state is the “cold time” based on the temperature information output from the temperature sensor 14 (step S14). Specifically, the processor 11 determines whether the temperature indicated by the temperature information is 75° C. or lower. In other words, the processor 11 determines whether the state is a state in which the cooling water in the cooling circuit 12 is controlled to an extremely low flow rate. For example, the processor 11 determines whether a representative value (for example, an average value) of the temperature of the cooling water in the cooling circuit 12 during the predetermined time is 75° C. or less.

[0037] In step S14, when the state is not the “cold time” (step S14: No), even though the cooling water in the cooling circuit 12 is not controlled to an extremely low flow rate, the hunting of the temperature information occurs and there is a high possibility that the cooling water is boiling. In this case, the processor 11 determines that the boiling has occurred (boiling) (step S15), and ends the series of boiling determination processing.

[0038] In step S14, when the state is the “cold time” (step S14: Yes), the hunting of the temperature information occurs, but the cooling water in the cooling circuit 12 is controlled to an extremely low flow rate, and the hunting of the temperature information may be caused by the convection of the cooling water. In this case, the processor 11 calculates a subcooling degree based on the temperature information output from the temperature sensor 14 and the atmospheric pressure information output from the atmospheric pressure sensor 15 (step S16). For example, the memory of the cooling device 10 accessible by the processor 11 stores, for each atmospheric pressure (pressure), saturation temperature information indicating a saturation temperature (boiling point) Ts of the cooling water at the atmospheric pressure (pressure). The processor 11 derives the saturation temperature Ts from the atmospheric pressure (for example, an average value during a predetermined time) indicated by the atmospheric pressure information and the saturation temperature information stored in the memory. Then, the processor 11 calculates the subcooling degree ΔT=Ts−T based on the derived saturation temperature Ts and a current temperature T (for example, an average value during the predetermined time) of the cooling water indicated by the temperature information.

[0039] Next, the processor 11 determines whether the subcooling degree calculated in step S16 is equal to or smaller than a second threshold (step S17). The second threshold is a preset value, and is, for example, 28° C.

[0040] In step S17, when the subcooling degree is equal to or smaller than the second threshold (step S17: Yes), there is a high possibility that the hunting of the temperature information is caused by the boiling of the cooling water. In this case, the processor 11 determines that the boiling has occurred (boiling) (step S18), and ends the series of boiling determination processing.

[0041] When the subcooling degree is not equal to or smaller than the second threshold in step S17 (step S17: No), there is a high possibility that the hunting of the temperature information is caused by something other than the boiling of the cooling water, such as the convection of the cooling water. In this case, the processor 11 determines that the boiling has not occurred (no boiling) (step S19), and ends the series of boiling determination processing.

[0042] The processor 11 controls the flow rate of the EWP 13 based on the control table and the load information of the internal combustion engine 1, and repeatedly performs, for example, the boiling determination processing shown in FIG. 2 (for example, every predetermined time). When it is determined that the boiling of the cooling water has occurred, the processor 11 performs control to increase the flow rate of the EWP 13 as compared with when it is determined that the boiling of the cooling water has not occurred. Thus, the boiling of the cooling water can be prevented.<Flow Rate Correction Corresponding to Atmospheric Pressure>

[0043] FIG. 3 is a graph showing an example of flow rate correction corresponding to the atmospheric pressure. In the graph of FIG. 3, a horizontal axis represents the atmospheric pressure [Pa], and a vertical axis represents a flow rate addition amount. The atmospheric pressure is an example of a use environment of the internal combustion engine 1. An addition characteristic 30 is an example of the flow rate addition amount corresponding to the atmospheric pressure. In the addition characteristic 30, the flow rate addition amount linearly increases as the atmospheric pressure decreases. The memory of the cooling device 10 accessible by the processor 11 stores an addition table indicating the addition characteristic 30. The processor 11 derives the flow rate addition amount based on the atmospheric pressure indicated by the atmospheric pressure sensor 15 and the addition characteristic 30 indicated by the addition table.

[0044] For example, when controlling the flow rate of the EWP 13 based on the control table, the processor 11 adds the derived flow rate addition amount to the flow rate that is based on the control table and controls the flow rate of the EWP 13 based on the flow rate obtained by the addition.

[0045] Thus, the flow rate of the EWP 13 can be controlled in consideration of the atmospheric pressure in addition to the load of the internal combustion engine 1 and the temperature of the cooling water. Specifically, for example, even when the boiling point of the cooling water decreases as the atmospheric pressure decreases, the flow rate of the cooling water is increased accordingly to decrease the temperature of the cooling water, and the boiling of the cooling water can be prevented.

[0046] <Flow Rate Control at the Time of Rapid Decrease of Load of Internal Combustion Engine 1>

[0047] FIG. 4 is a graph showing an example of flow rate control when the load of the internal combustion engine 1 decreases rapidly. In FIG. 4, a horizontal axis represents passage of time, and a vertical axis represents the flow rate of cooling water controlled by the EWP 13. In the example of FIG. 4, it is assumed that the load of the internal combustion engine 1 rises at a time t1 and the load of the internal combustion engine 1 decreases rapidly at a time t2.

[0048] A flow rate progress 41 is an example of the flow rate control corresponding to the load of the internal combustion engine 1 using the above control table. In the flow rate progress 41, the processor 11 increases the flow rate of EWP 13 from the time t1 and rapidly decreases the flow rate of EWP 13 from the time t2 in response to the change in the load of the internal combustion engine 1. In this way, when the flow rate of the EWP 13 rapidly decreases according to the rapid decrease of the load of the internal combustion engine 1, a cooling capacity for cooling the internal combustion engine 1 rapidly decreases. However, since the temperature of the internal combustion engine 1 does not rapidly decrease even if the load of the internal combustion engine 1 rapidly decreases, the cooling capacity for cooling the internal combustion engine 1 is temporarily insufficient, the cooling is delayed, and the temperature of the internal combustion engine 1 may become too high.

[0049] On the other hand, when the load of the internal combustion engine 1 rapidly decreases, the processor 11 may perform control to slow down the decrease in the flow rate of the EWP 13 as compared with the control using the control table. In this case, the change in the flow rate of the EWP 13 is, for example, a flow rate progress 42. For example, the processor 11 can perform such control by setting an upper limit for a decrease amount of the flow rate of the EWP 13 per unit time. In this way, when the load of the internal combustion engine 1 rapidly decreases, the processor 11 can prevent the cooling delay by performing control to slow down the decrease in the flow rate of the EWP 13.

[0050] The control method performed by the processor 11 described in the above embodiment may be implemented by executing a control program prepared in advance on a computer. The control program is stored in a computer-readable storage medium and executed by being read from the storage medium. Further, the control program may be provided in a form stored in a non-transitory storage medium such as a flash memory, or may be provided via a network such as the Internet. The computer that executes the control program may be provided in a processing device, may be provided in an electronic device such as a smartphone, a tablet terminal, or a personal computer that can communicate with the processing device, or may be provided in a server device that can communicate with the processing device and the electronic device.

[0051] Although an embodiment of the present invention has been described above with reference to the accompanying drawings, it is needless to say that the present invention is not limited to the embodiment. It is apparent to those skilled in the art that various changes or modifications can be conceived within the scope described in the claims, and it is understood that the changes or modifications naturally fall within the technical scope of the present invention. In addition, respective constituent elements in the above embodiment may be freely combined without departing from the gist of the invention.

[0052] For example, the vehicle equipped with the internal combustion engine 1 may be a hybrid electrical vehicle (HEV) that includes an electric motor in addition to the internal combustion engine 1 and travels by a driving force of the electric motor and / or the internal combustion engine according to a traveling state of the vehicle.

[0053] Further, although a configuration has been described in which the atmospheric pressure information output from the atmospheric pressure sensor 15 is used to perform the control corresponding to the outside air pressure of the internal combustion engine 1, the present invention is not limited to the configuration. For example, since the outside air pressure of the internal combustion engine 1 varies depending on an altitude at a position of the internal combustion engine 1, information on the altitude at the position of the internal combustion engine 1 may be used to perform the control corresponding to the outside air pressure of the internal combustion engine 1. The information on the altitude at the position of the internal combustion engine 1 can be acquired from, for example, a global navigation satellite system (GNSS) such as a global positioning system (GPS) provided in a vehicle equipped with the internal combustion engine 1.

[0054] In the present description, at least the following matters are described. In the parentheses, the corresponding constituent elements and the like in the above embodiment are shown as an example, but the present invention is not limited thereto.

[0055] (1) A control device (processor 11) for a cooling device (cooling device 10) that cools an internal combustion engine (internal combustion engine 1) using cooling water, the control device including:

[0056] a boiling determination unit (processor 11) configured to determine boiling of the cooling water; and

[0057] a flow rate control unit (processor 11) configured to control a flow rate of the cooling water based on a result of the boiling determination, in which

[0058] the boiling determination unit determines the boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water.

[0059] According to the above (1), by using the subcooling degree of the cooling water in addition to hunting of the temperature of the cooling water, the boiling of the cooling water can be accurately determined. As a result, efficiency of cooling the internal combustion engine can be improved, and fuel efficiency can be improved.

[0060] (2) The control device according to the above (1), in which

[0061] the boiling determination unit determines that the cooling water is boiling when magnitude of the difference between the maximum value and the minimum value of the temperature of the cooling water is equal to or greater than a predetermined value and the subcooling degree is at a predetermined position or lower.

[0062] According to the above (2), even if the temperature of the cooling water is hunting, it is not determined that the cooling water is boiling when the subcooling degree is large, and thereby it is possible to prevent erroneous determination that the cooling water is boiling even though the cooling water is not boiling.

[0063] (3) The control device according to the above (1) or (2), in which

[0064] the cooling device includes an electric water pump (EWP 13) that circulates the cooling water, and

[0065] the flow rate control unit controls the flow rate of the cooling water by controlling the electric water pump.

[0066] According to the above (3), the cooling water can be controlled to an extremely low flow rate, and the boiling of the cooling water can be accurately determined even in a state where the cooling water is controlled to an extremely low flow rate.

[0067] (4) The control device according to any one of the above (1) to (3), in which

[0068] the flow rate control unit controls the flow rate of the cooling water based on a use environment of the internal combustion engine.

[0069] According to the above (4), the flow rate of the cooling water can be controlled such that the cooling water is less likely to boil, according to the use environment of the internal combustion engine such as an outside air pressure.

[0070] (5) The control device according to any one of the above (1) to (4), in which

[0071] the subcooling degree is a difference between the temperature of the cooling water and a temperature corresponding to a use environment of the internal combustion engine.

[0072] According to the above (5), by not determining that the cooling water is boiling when the cooling water is less likely to boil, it is possible to prevent erroneous determination that the cooling water is boiling even though the cooling water is not boiling.

[0073] (6) The control device according to the above (4) or (5), in which

[0074] the use environment of the internal combustion engine is an outside air pressure of the internal combustion engine.

[0075] According to the above (6), the flow rate of the cooling water can be appropriately controlled according to a boiling point of the cooling water.

[0076] (7) A control method performed by a processor to control a cooling device that cools an internal combustion engine using cooling water, the control method including:

[0077] determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; and

[0078] controlling a flow rate of the cooling water based a result of the determination of the boiling.

[0079] According to the above (7), by using the subcooling degree of the cooling water in addition to the hunting of the temperature of the cooling water, the boiling of the cooling water can be accurately determined. As a result, the efficiency of cooling the internal combustion engine can be improved, and the fuel efficiency can be improved.

[0080] (8) A control program executed by a processor to control a cooling device that cools an internal combustion engine using cooling water, the control program causing the processor to perform processing including:

[0081] determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; and

[0082] controlling a flow rate of the cooling water based a result of the determination of the boiling.

[0083] According to the above (8), by using the subcooling degree of the cooling water in addition to the hunting of the temperature of the cooling water, the boiling of the cooling water can be accurately determined. As a result, the efficiency of cooling the internal combustion engine can be improved, and the fuel efficiency can be improved.REFERENCE SIGNS LIST1 internal combustion engine

[0085] 10 cooling device

[0086] 11 processor (boiling determination unit, flow rate control unit)

[0087] 13 electric water pump (EWP)

Examples

embodiments

10 to which Control Device According to Embodiment of Present Invention is Applied>

[0018]FIG. 1 is a diagram showing a cooling device 10 to which a control device according to an embodiment of the present invention is applied. The cooling device 10 is a device that cools an internal combustion engine 1 using cooling water. The internal combustion engine 1 is, for example, an engine mounted on a vehicle. The cooling device 10 includes a processor 11, a cooling circuit 12, an EWP 13, a temperature sensor 14 (TW), and an atmospheric pressure sensor 15.

[0019]The processor 11 is a control device that performs control in the cooling device 10. For example, the processor 11 is implemented by an electronic control unit (ECU). The processor 11 is an example of a boiling determination unit of the present invention. The processor 11 is an example of a flow rate control unit of the present invention.

[0020]The cooling circuit 12 is a circuit for circulating the cooling water. The cooling circuit...

TECHNICAL FIELD

[0001] The present invention relates to a control device, a control method, and a control program for a cooling device used for cooling an internal combustion engine.BACKGROUND ART

[0002] In recent years, efforts to realize a low-carbon society or a decarbonized society have become active, and research and development on electrification techniques have been conducted to reduce CO2 emission and improve energy efficiency in vehicles.

[0003] In the related art, in a cooling device that circulates cooling water through a cooling water pipeline and an engine inside by using an electric water pump (EWP) in order to cool the internal combustion engine, a configuration is known in which a water level detection unit that detects a water level of the cooling water is provided in a part of the cooling water pipeline (for example, a reserve tank that stores the cooling water) to detect an increase rate of the water level of the cooling water, and boiling of the cooling water is detected based on the increase rate (Patent Literature 1). Further, a configuration is known in which a target cooling water temperature of a cooling water temperature for an internal combustion engine varies depending on a highland / lowland state, and the cooling water temperature is controlled by a flow rate control valve (Patent Literature 2). In recent years, development of the EWP has progressed, making it possible to control a flow rate of the cooling water to an extremely low flow rate.CITATION LISTPatent Literature

[0004] Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2008-303775A

[0005] Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 2004-156490ASUMMARY OF INVENTIONTechnical Problem

[0006] When the EWP capable of controlling the flow rate of the cooling water to an extremely low flow rate is used in a cooling system of an internal combustion engine, there is an advantage that the internal combustion engine is quickly warmed and fuel efficiency is improved, but it may be difficult to determine whether the cooling water is boiling.

[0007] For example, it is conceivable to determine whether the cooling water is boiling by detecting hunting of the temperature of the cooling water, but when a measurement value of a temperature sensor fluctuates due to convection of the cooling water or the like, it may be erroneously determined that the cooling water is boiling even though the cooling water is not boiling. For example, when it is erroneously determined that the cooling water is boiling and control for increasing the flow rate of the cooling water is performed, cooling of the internal combustion engine may be inappropriate, and the fuel efficiency may deteriorate.

[0008] The present invention provides a control device, a control method, and a control program capable of accurately determining boiling of cooling water and improving fuel efficiency. This contributes to improvement in energy efficiency.Solution to Problem

[0009] The present invention is a control device for a cooling device that cools an internal combustion engine using cooling water, the control device includes a boiling determination unit configured to determine boiling of the cooling water; and a flow rate control unit configured to control a flow rate of the cooling water based on a result of the boiling determination, and the boiling determination unit determines the boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water.

[0010] The present invention is a control method performed by a processor to control a cooling device that cools an internal combustion engine using cooling water, the control method includes the processor determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; and controlling a flow rate of the cooling water based a result of the determination of the boiling.

[0011] The present invention is a control program executed by a processor to control a cooling device that cools an internal combustion engine using cooling water, and the control program causes the processor to perform processing of determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; and controlling a flow rate of the cooling water based a result of the determination of the boiling.Advantageous Effects of Invention

[0012] According to the present invention, it is possible to accurately determine boiling of the cooling water and improve fuel efficiency.BRIEF DESCRIPTION OF DRAWINGS

[0013] FIG. 1 is a diagram showing a cooling device 10 to which a control device according to an embodiment of the present invention is applied.

[0014] FIG. 2 is a flowchart showing an example of boiling determination processing by a processor 11.

[0015] FIG. 3 is a graph showing an example of flow rate correction corresponding to an atmospheric pressure.

[0016] FIG. 4 is a graph showing an example of flow rate control when a load of an internal combustion engine 1 decreases rapidly.DESCRIPTION OF EMBODIMENTS

[0017] Hereinafter, an embodiment of a control device of the present invention will be described with reference to the accompanying drawings. The drawings are viewed from directions of reference numerals.EMBODIMENTS<Cooling Device 10 to which Control Device According to Embodiment of Present Invention is Applied>

[0018] FIG. 1 is a diagram showing a cooling device 10 to which a control device according to an embodiment of the present invention is applied. The cooling device 10 is a device that cools an internal combustion engine 1 using cooling water. The internal combustion engine 1 is, for example, an engine mounted on a vehicle. The cooling device 10 includes a processor 11, a cooling circuit 12, an EWP 13, a temperature sensor 14 (TW), and an atmospheric pressure sensor 15.

[0019] The processor 11 is a control device that performs control in the cooling device 10. For example, the processor 11 is implemented by an electronic control unit (ECU). The processor 11 is an example of a boiling determination unit of the present invention. The processor 11 is an example of a flow rate control unit of the present invention.

[0020] The cooling circuit 12 is a circuit for circulating the cooling water. The cooling circuit 12 is disposed to be able to perform heat exchange with, for example, a cylinder head or a cylinder block of the internal combustion engine 1, and the internal combustion engine 1 is cooled by circulating the cooling water in the cooling circuit 12. The cooling water circulating in the cooling circuit 12 is, for example, cooling water called long life coolant (LLC), but is not limited to the LLC and may be various types of cooling water.

[0021] The cooling circuit 12 shown in FIG. 1 is an example. For example, the cooling circuit 12 is not limited to a simple annular shape, and may include branching or merging, or may include various valves. Further, the cooling circuit 12 may be provided with a heat exchanger such as a radiator for cooling the cooling water. The cooling circuit 12 may be provided with a heater for heating the cooling water.

[0022] The EWP 13 is a pump serving as power for circulating the cooling water in the cooling circuit 12. The EWP 13 circulates the cooling water in the cooling circuit 12 by pumping the cooling water. A flow rate of the EWP 13 is controlled by the processor 11. A flow rate [L / min] of the cooling water circulating in the cooling circuit 12 changes depending on the flow rate of EWP 13.

[0023] The temperature sensor 14 measures a temperature (TW) of the cooling water circulating in the cooling circuit 12. In the example of FIG. 1, the temperature sensor 14 is provided on an output side of the internal combustion engine 1 in the cooling circuit 12, and measures the temperature of the cooling water immediately after cooling the internal combustion engine 1. The temperature sensor 14 outputs temperature information indicating the measured temperature to the processor 11.

[0024] The atmospheric pressure sensor 15 measures an outside air pressure (atmospheric pressure) of the vehicle on which the internal combustion engine 1 is mounted. The atmospheric pressure sensor 15 outputs atmospheric pressure information indicating the measured outside air pressure to the processor 11. The atmospheric pressure sensor 15 may be a sensor outside the cooling device 10, which is provided in the vehicle equipped with the cooling device 10, instead of a sensor provided in the cooling device 10.

[0025] For example, the processor 11 controls the flow rate of the EWP 13 based on load information indicating a load of the internal combustion engine 1. The load of the internal combustion engine 1 is, for example, at least one of an engine speed NE [rpm] and an intake air amount Gair [g]. The load information is acquired by, for example, a drive device that controls driving of the internal combustion engine 1. The drive device may be the processor 11 or a device different from the processor 11.

[0026] For example, the processor 11 performs control such that the flow rate of EWP 13 increases as the load of the internal combustion engine 1 increases. Thus, it is possible to limit a temperature increase of the internal combustion engine 1 accompanying a rise in the load of the internal combustion engine 1.

[0027] Specifically, a memory of the cooling device 10 accessible by the processor 11 stores a control table indicating the flow rate of the cooling water for each load of the internal combustion engine 1 (for example, a combination of the engine speed NE and the intake air amount Gair). In the control table, a higher flow rate is associated with a higher engine speed NE. Further, in the control table, a larger flow rate is associated with a larger intake air amount Gair. The processor 11 controls the flow rate of the EWP 13 based on a flow rate derived from the load of the internal combustion engine 1 indicated by the load information and the control table stored in the memory.

[0028] The control table is stored for each temperature range of the cooling water. For example, a temperature range of the cooling water of 75° C. or lower is referred to as “cold time”, a temperature range of the cooling water between 75° C. and 110° C. is referred to as “after warm-up”, and a temperature range of the cooling water of 110° C. or higher is referred to as “high water temperature”. In this case, the control table is stored for each state including the “cold time”, the “after warm-up”, and the “high water temperature”. In this case, a lower flow rate is associated with a control table of a lower temperature range.

[0029] The control tables for the “cold time”, the “after warm-up”, and the “high water temperature” may not have the same data structure. For example, the control table for the “cold time” may indicate the flow rate of the cooling water for each combination of the engine speed NE and the intake air amount Gair, and the control tables for the “after warm-up” and the “high water temperature” may each indicate the flow rate of the cooling water for each engine speed NE.

[0030] The control table for the “cold time” includes an extremely low flow rate (for example, 7.7 [L / min]). That is, in the “cold time” in which the temperature of the cooling water is 75° C. or lower, the cooling water in the cooling circuit 12 is controlled to an extremely low flow rate.

[0031] In order to control the flow rate of the EWP 13, the processor 11 determines boiling of the cooling water in the cooling circuit 12 in addition to referring to the load information. Here, in a state in which the cooling water in the cooling circuit12 is controlled to an extremely low flow rate, in a method of determining the boiling of the cooling water only by detecting hunting of the temperature of the cooling water which is based on a measurement value of the temperature sensor 14, the measurement value of the temperature sensor 14 fluctuates due to convection of the cooling water, and it may be erroneously determined that the cooling water is boiling even though the cooling water is not boiling.<Boiling Determination Processing Performed by Processor 11>

[0032] FIG. 2 is a flowchart showing an example of boiling determination processing performed by the processor 11. The processor 11 performs processing shown in FIG. 2 to determine the presence or absence of boiling of the cooling water in the cooling circuit 12.

[0033] First, the processor 11 calculates magnitude of a difference between a maximum value and a minimum value of the temperature of the cooling water in the cooling circuit 12 during a predetermined time based on the temperature information output from the temperature sensor 14 (step S11). The predetermined time is, for example, 10 seconds.

[0034] Next, the processor 11 determines whether the magnitude of the difference calculated in step S11 is equal to or greater than a first threshold (step S12). That is, the processor 11 determines whether the hunting of the temperature information occurs. The first threshold is a preset value, and is, for example, 2° C.

[0035] In step S12, when the magnitude of the difference is not equal to or greater than the first threshold (step S12: No), that is, when the hunting of the temperature information does not occur, the processor 11 determines that the boiling does not occur (no boiling) (step S13), and ends the series of boiling determination processing.

[0036] In step S12, when the magnitude of the difference is equal to or greater than the first threshold (step S12: Yes), that is, when the hunting of the temperature information occurs, the processor 11 determines whether the state is the “cold time” based on the temperature information output from the temperature sensor 14 (step S14). Specifically, the processor 11 determines whether the temperature indicated by the temperature information is 75° C. or lower. In other words, the processor 11 determines whether the state is a state in which the cooling water in the cooling circuit 12 is controlled to an extremely low flow rate. For example, the processor 11 determines whether a representative value (for example, an average value) of the temperature of the cooling water in the cooling circuit 12 during the predetermined time is 75° C. or less.

[0037] In step S14, when the state is not the “cold time” (step S14: No), even though the cooling water in the cooling circuit 12 is not controlled to an extremely low flow rate, the hunting of the temperature information occurs and there is a high possibility that the cooling water is boiling. In this case, the processor 11 determines that the boiling has occurred (boiling) (step S15), and ends the series of boiling determination processing.

[0038] In step S14, when the state is the “cold time” (step S14: Yes), the hunting of the temperature information occurs, but the cooling water in the cooling circuit 12 is controlled to an extremely low flow rate, and the hunting of the temperature information may be caused by the convection of the cooling water. In this case, the processor 11 calculates a subcooling degree based on the temperature information output from the temperature sensor 14 and the atmospheric pressure information output from the atmospheric pressure sensor 15 (step S16). For example, the memory of the cooling device 10 accessible by the processor 11 stores, for each atmospheric pressure (pressure), saturation temperature information indicating a saturation temperature (boiling point) Ts of the cooling water at the atmospheric pressure (pressure). The processor 11 derives the saturation temperature Ts from the atmospheric pressure (for example, an average value during a predetermined time) indicated by the atmospheric pressure information and the saturation temperature information stored in the memory. Then, the processor 11 calculates the subcooling degree ΔT=Ts−T based on the derived saturation temperature Ts and a current temperature T (for example, an average value during the predetermined time) of the cooling water indicated by the temperature information.

[0039] Next, the processor 11 determines whether the subcooling degree calculated in step S16 is equal to or smaller than a second threshold (step S17). The second threshold is a preset value, and is, for example, 28° C.

[0040] In step S17, when the subcooling degree is equal to or smaller than the second threshold (step S17: Yes), there is a high possibility that the hunting of the temperature information is caused by the boiling of the cooling water. In this case, the processor 11 determines that the boiling has occurred (boiling) (step S18), and ends the series of boiling determination processing.

[0041] When the subcooling degree is not equal to or smaller than the second threshold in step S17 (step S17: No), there is a high possibility that the hunting of the temperature information is caused by something other than the boiling of the cooling water, such as the convection of the cooling water. In this case, the processor 11 determines that the boiling has not occurred (no boiling) (step S19), and ends the series of boiling determination processing.

[0042] The processor 11 controls the flow rate of the EWP 13 based on the control table and the load information of the internal combustion engine 1, and repeatedly performs, for example, the boiling determination processing shown in FIG. 2 (for example, every predetermined time). When it is determined that the boiling of the cooling water has occurred, the processor 11 performs control to increase the flow rate of the EWP 13 as compared with when it is determined that the boiling of the cooling water has not occurred. Thus, the boiling of the cooling water can be prevented.<Flow Rate Correction Corresponding to Atmospheric Pressure>

[0043] FIG. 3 is a graph showing an example of flow rate correction corresponding to the atmospheric pressure. In the graph of FIG. 3, a horizontal axis represents the atmospheric pressure [Pa], and a vertical axis represents a flow rate addition amount. The atmospheric pressure is an example of a use environment of the internal combustion engine 1. An addition characteristic 30 is an example of the flow rate addition amount corresponding to the atmospheric pressure. In the addition characteristic 30, the flow rate addition amount linearly increases as the atmospheric pressure decreases. The memory of the cooling device 10 accessible by the processor 11 stores an addition table indicating the addition characteristic 30. The processor 11 derives the flow rate addition amount based on the atmospheric pressure indicated by the atmospheric pressure sensor 15 and the addition characteristic 30 indicated by the addition table.

[0044] For example, when controlling the flow rate of the EWP 13 based on the control table, the processor 11 adds the derived flow rate addition amount to the flow rate that is based on the control table and controls the flow rate of the EWP 13 based on the flow rate obtained by the addition.

[0045] Thus, the flow rate of the EWP 13 can be controlled in consideration of the atmospheric pressure in addition to the load of the internal combustion engine 1 and the temperature of the cooling water. Specifically, for example, even when the boiling point of the cooling water decreases as the atmospheric pressure decreases, the flow rate of the cooling water is increased accordingly to decrease the temperature of the cooling water, and the boiling of the cooling water can be prevented.

[0046] <Flow Rate Control at the Time of Rapid Decrease of Load of Internal Combustion Engine 1>

[0047] FIG. 4 is a graph showing an example of flow rate control when the load of the internal combustion engine 1 decreases rapidly. In FIG. 4, a horizontal axis represents passage of time, and a vertical axis represents the flow rate of cooling water controlled by the EWP 13. In the example of FIG. 4, it is assumed that the load of the internal combustion engine 1 rises at a time t1 and the load of the internal combustion engine 1 decreases rapidly at a time t2.

[0048] A flow rate progress 41 is an example of the flow rate control corresponding to the load of the internal combustion engine 1 using the above control table. In the flow rate progress 41, the processor 11 increases the flow rate of EWP 13 from the time t1 and rapidly decreases the flow rate of EWP 13 from the time t2 in response to the change in the load of the internal combustion engine 1. In this way, when the flow rate of the EWP 13 rapidly decreases according to the rapid decrease of the load of the internal combustion engine 1, a cooling capacity for cooling the internal combustion engine 1 rapidly decreases. However, since the temperature of the internal combustion engine 1 does not rapidly decrease even if the load of the internal combustion engine 1 rapidly decreases, the cooling capacity for cooling the internal combustion engine 1 is temporarily insufficient, the cooling is delayed, and the temperature of the internal combustion engine 1 may become too high.

[0049] On the other hand, when the load of the internal combustion engine 1 rapidly decreases, the processor 11 may perform control to slow down the decrease in the flow rate of the EWP 13 as compared with the control using the control table. In this case, the change in the flow rate of the EWP 13 is, for example, a flow rate progress 42. For example, the processor 11 can perform such control by setting an upper limit for a decrease amount of the flow rate of the EWP 13 per unit time. In this way, when the load of the internal combustion engine 1 rapidly decreases, the processor 11 can prevent the cooling delay by performing control to slow down the decrease in the flow rate of the EWP 13.

[0050] The control method performed by the processor 11 described in the above embodiment may be implemented by executing a control program prepared in advance on a computer. The control program is stored in a computer-readable storage medium and executed by being read from the storage medium. Further, the control program may be provided in a form stored in a non-transitory storage medium such as a flash memory, or may be provided via a network such as the Internet. The computer that executes the control program may be provided in a processing device, may be provided in an electronic device such as a smartphone, a tablet terminal, or a personal computer that can communicate with the processing device, or may be provided in a server device that can communicate with the processing device and the electronic device.

[0051] Although an embodiment of the present invention has been described above with reference to the accompanying drawings, it is needless to say that the present invention is not limited to the embodiment. It is apparent to those skilled in the art that various changes or modifications can be conceived within the scope described in the claims, and it is understood that the changes or modifications naturally fall within the technical scope of the present invention. In addition, respective constituent elements in the above embodiment may be freely combined without departing from the gist of the invention.

[0052] For example, the vehicle equipped with the internal combustion engine 1 may be a hybrid electrical vehicle (HEV) that includes an electric motor in addition to the internal combustion engine 1 and travels by a driving force of the electric motor and / or the internal combustion engine according to a traveling state of the vehicle.

[0053] Further, although a configuration has been described in which the atmospheric pressure information output from the atmospheric pressure sensor 15 is used to perform the control corresponding to the outside air pressure of the internal combustion engine 1, the present invention is not limited to the configuration. For example, since the outside air pressure of the internal combustion engine 1 varies depending on an altitude at a position of the internal combustion engine 1, information on the altitude at the position of the internal combustion engine 1 may be used to perform the control corresponding to the outside air pressure of the internal combustion engine 1. The information on the altitude at the position of the internal combustion engine 1 can be acquired from, for example, a global navigation satellite system (GNSS) such as a global positioning system (GPS) provided in a vehicle equipped with the internal combustion engine 1.

[0054] In the present description, at least the following matters are described. In the parentheses, the corresponding constituent elements and the like in the above embodiment are shown as an example, but the present invention is not limited thereto.

[0055] (1) A control device (processor 11) for a cooling device (cooling device 10) that cools an internal combustion engine (internal combustion engine 1) using cooling water, the control device including:

[0056] a boiling determination unit (processor 11) configured to determine boiling of the cooling water; and

[0057] a flow rate control unit (processor 11) configured to control a flow rate of the cooling water based on a result of the boiling determination, in which

[0058] the boiling determination unit determines the boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water.

[0059] According to the above (1), by using the subcooling degree of the cooling water in addition to hunting of the temperature of the cooling water, the boiling of the cooling water can be accurately determined. As a result, efficiency of cooling the internal combustion engine can be improved, and fuel efficiency can be improved.

[0060] (2) The control device according to the above (1), in which

[0061] the boiling determination unit determines that the cooling water is boiling when magnitude of the difference between the maximum value and the minimum value of the temperature of the cooling water is equal to or greater than a predetermined value and the subcooling degree is at a predetermined position or lower.

[0062] According to the above (2), even if the temperature of the cooling water is hunting, it is not determined that the cooling water is boiling when the subcooling degree is large, and thereby it is possible to prevent erroneous determination that the cooling water is boiling even though the cooling water is not boiling.

[0063] (3) The control device according to the above (1) or (2), in which

[0064] the cooling device includes an electric water pump (EWP 13) that circulates the cooling water, and

[0065] the flow rate control unit controls the flow rate of the cooling water by controlling the electric water pump.

[0066] According to the above (3), the cooling water can be controlled to an extremely low flow rate, and the boiling of the cooling water can be accurately determined even in a state where the cooling water is controlled to an extremely low flow rate.

[0067] (4) The control device according to any one of the above (1) to (3), in which

[0068] the flow rate control unit controls the flow rate of the cooling water based on a use environment of the internal combustion engine.

[0069] According to the above (4), the flow rate of the cooling water can be controlled such that the cooling water is less likely to boil, according to the use environment of the internal combustion engine such as an outside air pressure.

[0070] (5) The control device according to any one of the above (1) to (4), in which

[0071] the subcooling degree is a difference between the temperature of the cooling water and a temperature corresponding to a use environment of the internal combustion engine.

[0072] According to the above (5), by not determining that the cooling water is boiling when the cooling water is less likely to boil, it is possible to prevent erroneous determination that the cooling water is boiling even though the cooling water is not boiling.

[0073] (6) The control device according to the above (4) or (5), in which

[0074] the use environment of the internal combustion engine is an outside air pressure of the internal combustion engine.

[0075] According to the above (6), the flow rate of the cooling water can be appropriately controlled according to a boiling point of the cooling water.

[0076] (7) A control method performed by a processor to control a cooling device that cools an internal combustion engine using cooling water, the control method including:

[0077] determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; and

[0078] controlling a flow rate of the cooling water based a result of the determination of the boiling.

[0079] According to the above (7), by using the subcooling degree of the cooling water in addition to the hunting of the temperature of the cooling water, the boiling of the cooling water can be accurately determined. As a result, the efficiency of cooling the internal combustion engine can be improved, and the fuel efficiency can be improved.

[0080] (8) A control program executed by a processor to control a cooling device that cools an internal combustion engine using cooling water, the control program causing the processor to perform processing including:

[0081] determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; and

[0082] controlling a flow rate of the cooling water based a result of the determination of the boiling.

[0083] According to the above (8), by using the subcooling degree of the cooling water in addition to the hunting of the temperature of the cooling water, the boiling of the cooling water can be accurately determined. As a result, the efficiency of cooling the internal combustion engine can be improved, and the fuel efficiency can be improved.REFERENCE SIGNS LIST1 internal combustion engine

[0085] 10 cooling device

[0086] 11 processor (boiling determination unit, flow rate control unit)

[0087] 13 electric water pump (EWP)

Examples

embodiments

10 to which Control Device According to Embodiment of Present Invention is Applied>

[0018]FIG. 1 is a diagram showing a cooling device 10 to which a control device according to an embodiment of the present invention is applied. The cooling device 10 is a device that cools an internal combustion engine 1 using cooling water. The internal combustion engine 1 is, for example, an engine mounted on a vehicle. The cooling device 10 includes a processor 11, a cooling circuit 12, an EWP 13, a temperature sensor 14 (TW), and an atmospheric pressure sensor 15.

[0019]The processor 11 is a control device that performs control in the cooling device 10. For example, the processor 11 is implemented by an electronic control unit (ECU). The processor 11 is an example of a boiling determination unit of the present invention. The processor 11 is an example of a flow rate control unit of the present invention.

[0020]The cooling circuit 12 is a circuit for circulating the cooling water. The cooling circuit...

Claims

1. A control device for a cooling device that cools an internal combustion engine using cooling water, the control device comprising:circuitry, whereinthe circuitry is configured to:determine boiling of the cooling water; andcontrol a flow rate of the cooling water based on a result of the boiling determination, andthe circuitry determines the boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water.

2. The control device according to claim 1, whereinthe circuitry determines that the cooling water is boiling when magnitude of the difference between the maximum value and the minimum value of the temperature of the cooling water is equal to or greater than a predetermined value and the subcooling degree is at a predetermined position or lower.

3. The control device according to claim 1, whereinthe cooling device includes an electric water pump that circulates the cooling water, andthe circuitry controls the flow rate of the cooling water by controlling the electric water pump.

4. The control device according to claim 1, whereinthe circuitry controls the flow rate of the cooling water based on a use environment of the internal combustion engine.

5. The control device according to claim 1, whereinthe subcooling degree is a difference between the temperature of the cooling water and a temperature corresponding to a use environment of the internal combustion engine.

6. The control device according to claim 4, whereinthe use environment of the internal combustion engine is an outside air pressure of the internal combustion engine.

7. A control method performed by a processor to control a cooling device that cools an internal combustion engine using cooling water, the control method comprising:determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; andcontrolling a flow rate of the cooling water based a result of the determination of the boiling.

8. A non-transitory computer-readable medium storing a control program for causing a processor to execute a process to control a cooling device that cools an internal combustion engine using cooling water, the process comprising:determining boiling of the cooling water based on a difference between a maximum value and a minimum value of a temperature of the cooling water during a predetermined time and a subcooling degree that is based on the temperature of the cooling water; andcontrolling a flow rate of the cooling water based a result of the determination of the boiling.

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