Engine cooling system

Abstract

The objective is to provide an engine cooling system that can appropriately control the flow rate of coolant passing through the engine water pump. [Solution] An engine cooling system comprising: a cooling circuit having an engine water pump for circulating coolant to the engine and a heater core water pump for circulating coolant to the heater core, a circulation path for circulating coolant between the engine and the heater core, and an on / off valve provided in the circulation path between the engine and the heater core with an adjustable opening ratio, and a control device for controlling the engine water pump.

Description

Technical Field

[0001] The present invention relates to an engine cooling system.

Background Art

[0002] There is an engine cooling system including a cooling circuit having a circulation path in which cooling water circulates by a water pump between an engine and a heater core for heating (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There may be provided an engine water pump and a heater core water pump for circulating cooling water through the circulation path to the engine and the heater core, respectively. Further, an on-off valve with an adjustable opening ratio may be provided in the circulation path between the engine and the heater core. For example, it is conceivable to control the heater core water pump based on a target flow rate of cooling water passing through the heater core water pump (hereinafter referred to as the heater target flow rate) calculated according to a heating requirement. In this case, if the target flow rate of cooling water passing through the engine water pump (hereinafter referred to as the engine target flow rate) is calculated without considering the heater target flow rate or the opening ratio of the on-off valve, there is a possibility that the flow rate of cooling water passing through the engine water pump cannot be appropriately controlled.

[0005] Therefore, an object of the present invention is to provide an engine cooling system capable of appropriately controlling the flow rate of cooling water passing through an engine water pump.

Means for Solving the Problems

[0006] The above objective is to provide a cooling circuit having an engine water pump that circulates cooling water to the engine and a heater core water pump that circulates cooling water to the heater core for heating, a circulation path through which cooling water circulates between the engine and the heater core, and an on / off valve provided in the circulation path between the engine and the heater core that can adjust the opening ratio, and a control device that controls the engine water pump, wherein the control device includes an acquisition unit that acquires the heater target flow rate, which is the target flow rate of cooling water flowing to the heater core water pump, and the rotational speed of the heater core water pump, a correction unit that calculates a corrected heater target flow rate by multiplying the heater target flow rate by a correction coefficient between 0 and 1, which takes smaller values ​​as the opening ratio decreases, and the rotational speed of the engine water pump This can be achieved by an engine cooling system that includes: a calculation unit that calculates the distribution ratio based on the acquired rotational speed of the heater core water pump by referring to the correlation between the rotational speed ratio, the distribution ratio, and the opening ratio, such that as the rotational speed ratio, which is the ratio of the rotational speed of the heater core water pump to the rotational speed of the heater core water pump, increases, the distribution ratio, which is the ratio of the flow rate of coolant passing through the engine water pump to the flow rate of coolant passing through the engine water pump, increases, and as the opening ratio decreases, the distribution ratio decreases; and a control unit that calculates the engine target flow rate, which is the target flow rate of coolant flowing through the engine water pump, by dividing the corrected heater target flow rate by the calculated distribution ratio, and controls the rotational speed of the engine water pump according to the engine target flow rate.

[0007] The cooling circuit includes a radiator path that communicates with the circulation path and through which coolant flows from the engine to the radiator without passing through the heater core, and a thermostat provided in the radiator path, and the correlation may be defined such that the distribution ratio increases as the opening of the thermostat decreases.

[0008] The acquisition unit may acquire the rotational speed of the engine water pump, and the calculation unit may calculate the distribution ratio based on the acquired rotational speed of the heater core water pump and the acquired rotational speed of the engine water pump, referring to the correlation. [Effects of the Invention]

[0009] This system provides an engine cooling system that can appropriately control the flow rate of coolant passing through the engine water pump. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is an explanatory diagram of the engine cooling system. [Figure 2] Figures 2A to 2F are explanatory diagrams illustrating the communication state of the four-way valve. [Figure 3] Figure 3A is an explanatory diagram of the coolant flow path when the thermostat is fully closed, and Figure 3B is an explanatory diagram of the coolant flow path when the thermostat is fully open. [Figure 4] Figure 4 is a flowchart illustrating the EWP rotation speed control performed by the ECU. [Figure 5] Figure 5 is a map that defines correction coefficients according to the aperture ratio. [Figure 6] Figure 6 is an example of a map that defines the correlation between rotational speed ratio and distribution ratio. [Modes for carrying out the invention]

[0011] [Engine Cooling System] Figure 1 is an explanatory diagram of the engine cooling system 1. The engine cooling system 1 is installed, for example, in a vehicle. The engine cooling system 1 has an engine cooling circuit 2 and an ECU (Electronic Control Unit) 100. The engine cooling circuit 2 includes an engine 10, an engine water pump (hereinafter referred to as EWP) 12, a radiator 14, a reserve tank 16, a temperature sensor 18, a heater core 20, a heater core water pump (hereinafter referred to as HWP) 22, a heating heater 24, a thermostat 30, a four-way valve 40, and a heat exchanger 50.

[0012] Engine 10 is the power source for the vehicle's movement. EWP 12 is an electric water pump that circulates coolant to engine 10 by pressurizing and sending coolant towards engine 10 in the direction of the arrow in Figure 1. Radiator 14 cools the coolant by exchanging heat between the coolant and the air outside the vehicle. Reserve tank 16 stores excess coolant. Heater core 20 heats the passenger compartment using the heat from the coolant. HWP 22 is an electric water pump that circulates coolant to heater core 20 by drawing coolant from heater core 20 in the direction of the arrow in Figure 1. Heating heater 24 heats the coolant when the temperature of the coolant is insufficient for heating the passenger compartment by heater core 20.

[0013] Thermostat 30 is fully closed when the temperature of the coolant flowing into it is below the first temperature, and fully open when the temperature of the coolant flowing into it is above the first temperature (second temperature or higher). Furthermore, when the temperature of the coolant flowing into it is above the first temperature but below the second temperature, the opening of the thermostat 30 increases as the coolant temperature increases. For example, before the engine 10 is fully warmed up, the temperature of the coolant flowing into thermostat 30 is below the first temperature, and after the engine is fully warmed up, the temperature of the coolant flowing into thermostat 30 is above the second temperature. The coolant flow path in the fully closed and fully open states of thermostat 30 will be described in detail later.

[0014] The four-way valve 40 circulates cooling water through predetermined paths, which will be described in more detail later, by switching the communication state of the four paths. The four-way valve 40 is equipped with a rotor rotatably housed within the housing and an actuator that drives the rotor. The communication state of the four paths is switched according to the rotational position of the rotor, which is controlled by the actuator.

[0015] The heat exchanger 50 exchanges heat between the coolant flowing through the engine cooling circuit 2 and the coolant flowing through the battery cooling circuit for cooling a battery (not shown).

[0016] The ECU100 is an electronic control unit comprising an arithmetic processing circuit that performs various calculations related to vehicle driving control, and a memory that stores control programs and data. The ECU100 acquires the temperature of the coolant based on the temperature sensor 18. The ECU100 controls the rotational speeds of the EWP12 and HWP22, the amount of current supplied to the heating heater 24, and the communication state of the four-way valve 40 in accordance with the operating status of the engine 10, heating requests, and battery cooling requests. The ECU100 functionally implements an acquisition unit, a correction unit, a calculation unit, and a control unit, as will be described in more detail later.

[0017] The path 61 has a thermostat 30 arranged at its upstream end, its downstream end connected to the four-way valve 40, and an EWP 12 and an engine 10 arranged therein midway. The path 62 has its upstream end connected to the four-way valve 40, its downstream end connected to the thermostat 30, and a heater core 20, a HWP 22, and a heating heater 24 arranged therein midway. The path 63 has its upstream end connected between the heating heater 24 and the thermostat 30 of the path 62, and its downstream end connected to the four-way valve 40. The path 64 has its upstream end connected between the engine 10 and the four-way valve 40 of the path 61, and its downstream end connected between the heating heater 24 and the thermostat 30 of the path 62. The temperature sensor 18 is provided at the connected part of the path 61 and the path 64. The path 65 has its upstream end connected to the four-way valve 40, its downstream end connected between the heater core 20 and the HWP 22 of the path 62, and a heat exchanger 50 arranged therein midway. The path 66 has its upstream end connected between the engine 10 and the temperature sensor 18 of the path 61, its downstream end connected to the thermostat 30, and a radiator 14 and a reserve tank 16 arranged therein midway.

[0018] [Four-way valve] Next, the four-way valve 40 will be described. FIGS. 2A to 2F are explanatory diagrams of the communication state of the four-way valve 40. When the rotor of the four-way valve 40 rotates in one direction, the communication state is switched in the order of FIGS. 2A to 2F. In FIG. 2A, the path 63 and the path 62 are in communication, and the paths 61 and 65 are blocked. In this state, the EWP 12 is stopped and the HWP 22 is driven. The cooling water circulates through the heater core 20 and the heating heater 24 via a part of the path 62 and the path 63. The opening ratio of the opening that connects the path 63 and the path 62 of the four-way valve 40 is the maximum. In FIG. 2A, the rotor of the four-way valve 40 is in the initial position. When the rotor rotates in one direction from the initial position, the opening ratio of the opening that connects the path 63 and the path 62 decreases, and the opening ratio of the opening that connects the path 63 and the path 65 increases as shown in FIG. 2B.

[0019] In FIG. 2B, path 63 communicates with paths 62 and 65, and path 61 is blocked. In this state, EWP12 is stopped and HWP22 is driven. The cooling water circulates through part of path 62 and path 63 to the heater core 20 and the heating heater 24, and circulates through path 65 to the heat exchanger 50. When the rotor rotates in one direction from FIG. 2B, as shown in FIG. 2C, the opening ratio of the opening that communicates path 63 and path 62 decreases to zero, and the opening ratio of the opening that communicates path 63 and path 65 increases to the maximum.

[0020] In FIG. 2C, path 63 communicates with path 65, and paths 61 and 62 are blocked. In this state, EWP12 is stopped and HWP22 is driven. The cooling water circulates through part of path 62, path 63, and path 65 to the heat exchanger 50 and the heating heater 24. The opening ratio of the opening that communicates path 63 and path 65 of the four-way valve 40 is the maximum. When the rotor rotates in one direction from FIG. 2C, as shown in FIG. 2D, the opening ratio of the opening that communicates path 63 and path 65 decreases, and the opening ratio of the opening that communicates path 61 and path 62 increases.

[0021] In FIG. 2D, path 63 communicates with path 65, and path 61 communicates with path 62. Note that paths 63 and 65 do not communicate with paths 61 and 62. In this state, EWP12 and HWP22 are driven. The cooling water circulates through part of path 62, path 63, and path 65 to the heat exchanger 50 and the heating heater 24, and circulates through paths 61 and 62 to the engine 10, the heater core 20, and the heating heater 24. Therefore, paths 61 and 62 correspond to the paths through which the cooling water that has passed through the engine 10 passes through the engine 10 again without passing through the radiator 14. Note that when the thermostat 30 is fully open, the cooling water also circulates through the radiator 14 and the reserve tank 16 via path 66. When the rotor rotates in one direction from FIG. 2D, as shown in FIG. 2E, the opening ratio of the opening that communicates path 63 and path 65 decreases to zero, and the opening ratio of the opening that communicates path 61 and path 62 increases to the maximum.

[0022] In Figure 2E, paths 61 and 62 are connected, while paths 63 and 65 are blocked. In this state, at least the EWP 12 is driven. Coolant circulates through paths 61 and 62 to the engine 10, heater core 20, and heating element 24. The opening ratio of the opening of the four-way valve 40 connecting paths 61 and 62 is at its maximum. When the thermostat 30 is fully open, coolant also circulates through path 66 to the radiator 14 and reserve tank 16. As the rotor rotates in one direction from Figure 2E, the opening ratio of the opening connecting paths 61 and 62 decreases, and the opening ratio of the opening connecting paths 61 and 65 increases, as shown in Figure 2F.

[0023] In Figure 2F, paths 61, 62, and 65 are connected, while path 63 is blocked. The coolant circulates through at least the EWP 12 via paths 61, 62, and 65 to the engine 10, heater core 20, heating heater 24, and heat exchanger 50. Therefore, paths 61, 62, and 65 correspond to paths through which the coolant that has passed through the engine 10 passes through the engine 10 again without going through the radiator 14. When the thermostat 30 is fully open, the coolant also circulates through path 66 to the radiator 14 and the reserve tank 16.

[0024] The sum of the opening ratios of the openings connecting paths 61 and 62 and the opening ratio of the openings connecting paths 61 and 65 in Figure 2F is lower than the maximum opening ratio of the openings connecting paths 61 and 62 in Figure 2E. For example, let's assume the opening ratio of the openings connecting paths 61 and 62 in Figure 2E is 100%. In Figure 2F, the opening ratio of the openings connecting paths 61 and 62 is 40%, and the opening ratio of the openings connecting paths 61 and 65 is 40%. Therefore, the total opening ratio of path 61 in Figure 2F is 80%, which is lower than the 100% opening ratio in Figure 2E.

[0025] Therefore, the opening ratio of the opening connecting path 61 and path 62 in Figure 2C increases from zero to the state shown in Figure 2D. Next, the opening ratio of the opening connecting path 61 and path 62 reaches its maximum, resulting in the state shown in Figure 2E. Then, the opening ratio of the opening connecting path 61 with paths 62 and 65 gradually decreases to the state shown in Figure 2F. In this way, the four-way valve 40 adjusts the opening ratio of the path through which the coolant that has passed through the engine 10 passes through the engine 10 again without passing through the radiator 14. The four-way valve 40 is an example of an on-off valve. The ECU 100 obtains the opening ratio of such a path by referring to a map defined according to the target rotational position of the rotor.

[0026] [thermostat] Next, the fully closed and fully open states of the thermostat 30 will be explained. Figure 3A is an explanatory diagram of the coolant flow path when the thermostat 30 is in the fully closed state. Figure 3A shows the state in which the four-way valve 40 connects paths 61 and 62 and blocks paths 63 and 65. The coolant flows in the following order: EWP 12, engine 10, four-way valve 40, heater core 20, HWP 22, heating heater 24, and thermostat 30. Coolant flows from the temperature sensor 18 to path 62 in path 64. Since the thermostat 30 is in the fully closed state, coolant does not flow to the radiator 14, and the engine 10 is warmed up.

[0027] Figure 3B is an explanatory diagram of the coolant flow path when the thermostat 30 is fully open. Similar to Figure 3A, Figure 3B shows the state in which the four-way valve 40 connects paths 61 and 62 and blocks paths 63 and 65. A portion of the coolant that has passed through the engine 10 flows to the heater core 20 via path 62, and the remaining coolant that has passed through the engine 10 flows to the radiator 14 via path 66. In addition, the coolant that has passed through the heater core 20, HWP 22, and heating heater 24 via path 62 flows into the thermostat 30. Furthermore, the coolant that has passed through the radiator 14 and reserve tank 16 via path 66 also flows into the thermostat 30. In this way, the coolant that has flowed into the thermostat 30 from both directions circulates through the EWP 12 and engine 10 via path 61. In this way, a portion of the coolant also circulates to the radiator 14, which suppresses the overheating of the coolant.

[0028] [EWP rotation speed control] Figure 4 is a flowchart illustrating the rotational speed control of the EWP12 performed by the ECU100. As described above, the EWP12 is stopped in the states shown in Figures 2A to 2C, and is driven in the states shown in Figures 2D to 2F. In the states shown in Figures 2D and 2E, the target engine flow rate is calculated based on the target heater flow rate, and the rotational speed of the EWP12 is controlled based on the target engine flow rate. In the state shown in Figure 2F, the rotational speed of the EWP12 is controlled based on the target flow rate of the cooling water flowing to the heat exchanger 50. Figure 4 illustrates the case where the rotational speed of the EWP12 is controlled based on the target heater flow rate.

[0029] The ECU100 acquires the heater target flow rate and the rotational speeds of EWP12 and HWP22 (step S1). The heater target flow rate is calculated according to the heating request. Here, the rotational speeds of EWP12 and HWP22 may be command values ​​for EWP12 and HWP22, or values ​​detected by sensors may be used. Step S1 is an example of the processing performed by the acquisition unit.

[0030] Next, 100 corrects the heater target flow rate based on the opening ratio of the opening connecting path 61 and path 62 in order to calculate the engine target flow rate described later (step S2). Figure 5 is a map that defines the correction coefficient K according to the opening ratio. The corrected heater target flow rate is calculated by multiplying the heater target flow rate by the correction coefficient K. The correction coefficient K is a value between 0 and 1, and becomes smaller as the opening ratio decreases. When the opening ratio is 0%, the correction coefficient K is 0. When the opening ratio is 100%, the correction coefficient K is 1. Therefore, for example, when the opening ratio is 10%, the correction coefficient K is 0.1. When the opening ratio is 80%, the correction coefficient K is 0.8. Step S2 is an example of the processing performed by the correction unit.

[0031] Next, the ECU 100 refers to the map in Figure 6, which predefines the correlation between the rotational speed ratio and the distribution ratio, and calculates the distribution ratio based on the rotational speeds of EWP12 and HWP22 obtained in step S1 (step S3). Step S3 is an example of the process performed by the calculation unit. The rotational speed ratio is the ratio of the rotational speed of HWP22 to the rotational speed of EWP12, as shown in equation (1) below. The distribution ratio is the ratio of the flow rate of coolant passing through HWP22 to the flow rate of coolant passing through EWP12, as shown in equation (2) below. Speed ​​ratio = (HWP22 speed) / (EWP12 speed) ... (1) Distribution ratio = (Flow rate of cooling water passing through HWP22) / (Flow rate of cooling water passing through EWP12) ... (2)

[0032] Figure 6 is an example of a map that defines the correlation between rotational speed ratio and distribution ratio. The map in Figure 6 defines the above correlation in the engine cooling circuit 2 shown in Figure 1, based on experimental and simulation results. Therefore, the correlation in the map in Figure 6 can be considered as the actual distribution ratio that changes in accordance with the rotational speed ratio in the engine cooling circuit 2.

[0033] As shown in Figure 6, the distribution ratio increases as the rotational speed ratio increases. This is because an increase in the rotational speed ratio indicates an increase in the rotational speed of HWP22 relative to the rotational speed of EWP12, and consequently, the flow rate of coolant passing through HWP22 also increases relative to the flow rate of coolant passing through EWP12. Figure 6 shows the cases where the thermostat 30 is fully closed and fully open with solid lines. The distribution ratio increases as the opening degree of the thermostat 30 decreases. This is because as the opening degree of the thermostat 30 decreases, the flow rate of coolant passing through EWP12 increases relative to the rotational speed of EWP12. The opening degree of the thermostat 30 is estimated by the ECU 100 based on the coolant temperature detected by the temperature sensor 18, for example.

[0034] The solid line in Figure 6 shows the case where the opening ratio of the opening connecting path 61 and path 62 is 100%. As the opening ratio of the opening connecting path 61 and path 62 decreases, the distribution ratio decreases. When the opening ratio is near 0%, the distribution ratio also becomes a small value near 0, which is less than 1. This is because in the engine cooling circuit 2, when the opening ratio is small, the flow rate of coolant passing through HWP22 becomes a minute amount compared to the flow rate of coolant passing through EWP12. The opening ratio is estimated by the ECU100 according to, for example, the target rotation position of the rotor of the four-way valve 40.

[0035] Next, the ECU100 calculates the engine target flow rate by dividing the corrected heater target flow rate by the calculated distribution ratio (step S4). Specifically, the engine target flow rate is calculated using the following formula. Engine target flow rate = (Corrected heater target flow rate) / (Calculated distribution ratio) ... (3)

[0036] Next, the ECU 100 calculates the target rotational speed of the EWP 12 based on the calculated target engine flow rate and controls the rotational speed of the EWP 12 to match the target rotational speed (step S5). By repeating steps S1 to S5 as described above, the rotational speed of the EWP 12 is controlled while controlling the flow rate of the coolant passing through the HWP 22 to the heater target flow rate. Steps S4 and S5 are examples of processes performed by the control unit.

[0037] As described above, the engine target flow rate is calculated based on the corrected heater target flow rate and the rotational speeds of HWP22 and EWP22, by referring to a map that pre-defines the correlation between the rotational speed ratio and the distribution ratio based on experimental results. Therefore, an engine target flow rate is calculated that allows the flow rate of the coolant passing through HWP22 to be controlled to the heater target flow rate. This enables appropriate control of the coolant flow rate passing through HWP22 to the heater target flow rate. Thus, the calculated heater target flow rate can be achieved according to the heating requirements.

[0038] Furthermore, the reason for calculating the engine target flow rate using the corrected heater target flow rate rather than the heater target flow rate is as follows. For example, if the opening ratio of the opening connecting path 61 and path 62 is around 0%, the distribution ratio is calculated as a very small value according to the map in Figure 6. As a result, if the uncorrected heater target flow rate is used instead of the corrected heater target flow rate in equation (3), the calculated engine target flow rate will be excessive. If the EWP12 is controlled according to the excessively calculated engine target flow rate in this way, the engine 10 will be cooled more than necessary, and the power consumption of the EWP12 will also increase. Therefore, in this embodiment, the engine target flow rate is calculated using equation (3) with the corrected heater target flow rate, which is calculated by multiplying the heater target flow rate by a correction coefficient K that is between 0 and 1, and whose value decreases as the opening ratio decreases. This avoids the calculated engine target flow rate being excessive, and suppresses overcooling of the engine 10 and an increase in the power consumption of the EWP12.

[0039] Furthermore, if EWP12 is stopped, its rotational speed is zero, and therefore the engine target flow rate is calculated as zero based on equation (1), the map in Figure 6, and equation (3). Consequently, when EWP12 is stopped, the engine target flow rate may be calculated as follows. For example, if the rotational speed of EWP12 is zero, the rotational speed ratio is calculated using a predetermined upper limit. This results in the engine target flow rate being calculated as a small value other than zero, and the rotational speed of EWP12 is controlled accordingly. Alternatively, the rotational speed ratio may be calculated by substituting a predetermined expected rotational speed of EWP12 (other than zero) based on the heater target flow rate into the rotational speed of EWP12 in equation (1). Alternatively, the engine target flow rate may be calculated by substituting a predetermined fixed value into the rotational speed of EWP12 in equation (1), and the engine target flow rate may be repeatedly calculated by substituting the target rotational speed of EWP12 corresponding to the engine target flow rate into the rotational speed of EWP12 in equation (1).

[0040] In the above embodiment, a map defining the correlation between the rotation speed ratio and the distribution ratio was referred to, but a calculation formula defining this correlation may also be referred to. The calculation formula may take the opening degree of the thermostat 30 and the opening ratio of the path 61 by the four-way valve 40 as arguments. Figure 4 illustrates the case in which the rotation speed of the EWP 12 is controlled based on the heater target flow rate. When the rotation speed of the EWP 12 is controlled based on the target flow rate to the heat exchanger 50, the target flow rate of the cooling water passing through the heat exchanger 50 is used instead of the heater target flow rate.

[0041] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0042] 1. Engine Cooling System 2. Engine cooling circuit 10 Engines 12. Engine water pump 14 Radiator 20 Heater Cores 22 Heater core water pump 30 Thermostats 40 4-way valve (on / off valve) 100 Control device (acquisition unit, correction unit, calculation unit, control unit)

Claims

1. A cooling circuit comprising an engine water pump for circulating coolant to the engine and a heater core water pump for circulating coolant to the heater core, a circulation path for circulating coolant between the engine and the heater core, and an on / off valve provided in the circulation path between the engine and the heater core with an adjustable opening ratio, The system includes a control device for controlling the engine water pump, The control device is An acquisition unit that acquires the target flow rate of the cooling water flowing through the heater core water pump, which is the target flow rate of the heater, and the rotational speed of the heater core water pump. A correction unit calculates a corrected heater target flow rate by multiplying the heater target flow rate by a correction coefficient between 0 and 1, which takes smaller values ​​as the aperture ratio decreases. A calculation unit calculates the distribution ratio based on the rotational speed of the heater core water pump obtained by referring to the correlation between the rotational speed ratio, the distribution ratio, and the opening ratio, wherein the distribution ratio increases as the rotational speed ratio, which is the ratio of the rotational speed of the heater core water pump to the rotational speed of the engine water pump, increases, and the distribution ratio decreases as the opening ratio decreases. An engine cooling system comprising: a control unit that calculates an engine target flow rate, which is the target flow rate of cooling water flowing to the engine water pump, by dividing the corrected heater target flow rate by the calculated distribution ratio, and controls the rotational speed of the engine water pump according to the engine target flow rate.

2. The cooling circuit includes a radiator path that communicates with the circulation path and through which coolant flows from the engine to the radiator without passing through the heater core, and a thermostat provided in the radiator path. The engine cooling system according to claim 1, wherein the correlation is defined such that the distribution ratio increases as the opening of the thermostat decreases.

3. The acquisition unit acquires the rotational speed of the engine water pump, The engine cooling system according to claim 2, wherein the calculation unit calculates the distribution ratio based on the acquired rotational speed of the heater core water pump and the acquired rotational speed of the engine water pump, by referring to the correlation.

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