Engine cooling system

Abstract

The objective is to provide an engine cooling system that suppresses the decrease in control accuracy based on the temperature of the coolant that has passed through the engine. [Solution] The engine cooling system includes a cooling circuit having a circulation path through which coolant circulates between the engine and the heater core by an engine water pump that circulates coolant to the engine and a heater water pump that circulates coolant to the heater core for heating, and a bypass path connected to the circulation path through which the coolant that has passed through the engine bypasses the heater core and flows back into the engine; a temperature sensor provided in the bypass path that detects the temperature of the coolant that has passed through the engine; and a control device that performs control based on the temperature detected by the temperature sensor.

Description

Technical Field

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

Background Art

[0002] There is an engine cooling system provided with a cooling circuit including 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] An engine water pump and a heater water pump for circulating cooling water through the engine and the heater core, respectively, may be provided. Further, a bypass path may be provided that is connected to the circulation path and through which the cooling water that has passed through the engine bypasses the heater core and flows back into the engine again, and a temperature sensor for detecting the temperature of the cooling water that has passed through the engine may be provided in the bypass path. Predetermined control is executed based on the detected temperature of the temperature sensor. Here, depending on the rotational speeds of the engine water pump and the heater water pump, there is a risk that the cooling water may flow backward in the bypass path. When the cooling water in the bypass path flows backward, the temperature sensor detects the temperature of the cooling water that has passed through the heater core instead of the temperature of the cooling water that has passed through the engine. As a result, the accuracy of the control based on the detected temperature of the temperature sensor may decrease.

[0005] Therefore, an object of the present invention is to provide an engine cooling system that suppresses a decrease in the accuracy of control based on the temperature of the cooling water that has passed through the engine.

Means for Solving the Problems

[0006] The above objective can be achieved by an engine cooling system comprising: a cooling circuit having a circulation path through which coolant circulates between the engine and the heater core by an engine water pump that circulates coolant to the engine and a heater water pump that circulates coolant to the heater core for heating, and a bypass path connected to the circulation path through which the coolant that has passed through the engine bypasses the heater core and flows back into the engine; a temperature sensor provided in the bypass path for detecting the temperature of the coolant that has passed through the engine; and a control device that performs control based on the temperature detected by the temperature sensor, wherein the control device includes an acquisition unit for acquiring the rotational speed of the heater water pump, a setting unit that sets a higher lower limit for the rotational speed of the engine water pump as the rotational speed of the heater water pump increases in order to suppress backflow of coolant in the bypass path, and a control unit that controls the rotational speed of the engine water pump to be above the lower limit.

[0007] The control device may include a determination unit that determines whether the temperature of the coolant before it passes through the engine and flows into the heater core is equal to the temperature of the coolant before it passes through the heater core and flows into the engine when the engine is intermittently stopped, and a stop unit that stops the engine water pump when the determination unit makes a positive determination.

[0008] The control device includes a calculation unit that calculates an integrated value of the flow rate of the coolant passing through the engine water pump, and the determination unit may determine, when the integrated value is equal to or greater than a threshold, that the temperature of the coolant before it passes through the engine and flows into the heater core is equal to the temperature of the coolant before it passes through the heater core and flows into the engine.

[0009] The cooling circuit includes an on-off valve that blocks or connects the circulation path between the engine and the heater core, and the calculation unit may calculate the cumulative value after the on-off valve has opened the circulation path. [Effects of the Invention]

[0010] This system provides an engine cooling system that suppresses the decrease in control accuracy based on the temperature of the coolant that has passed through the engine. [Brief explanation of the drawing]

[0011] [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 the lower limit of the EWP rotation speed according to the HWP rotation speed. [Figure 6] Figure 6 is a flowchart illustrating the drive control of the EWP during intermittent engine shutdown. [Modes for carrying out the invention]

[0012] [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 water pump (hereinafter referred to as HWP) 22, a heating element 24, a thermostat 30, a four-way valve 40, and a heat exchanger 50.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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).

[0017] The ECU 100 is an electronic control unit including an arithmetic processing circuit that performs various arithmetic processes related to the vehicle's driving control, and a memory that stores control programs and data. The ECU 100 acquires the temperature of the cooling water based on the temperature sensor 18. The ECU 100 controls the rotational speeds of the EWP 12 and the HWP 22, the energization amount of the heater 24, and the communication state of the four-way valve 40 according to the operating state of the engine 10, the heating requirement, and the battery cooling requirement. The ECU 100 functionally realizes an acquisition unit, a setting unit, a control unit, a determination unit, a stop unit, and a calculation unit, which will be described in detail later.

[0018] In the path 61, the thermostat 30 is arranged at the upstream end, the downstream end is connected to the four-way valve 40, and the EWP 12 and the engine 10 are arranged in the middle. In the path 62, the upstream end is connected to the four-way valve 40, the downstream end is connected to the thermostat 30, and the heater core 20, the HWP 22, and the heater 24 are arranged in the middle. The paths 61 and 62 are an example of a circulation path in which the cooling water circulates between the engine 10 and the heater core 20 when they are in communication with each other by the four-way valve 40. In the path 63, the upstream end is connected between the heater 24 and the thermostat 30 of the path 62, and the downstream end is connected to the four-way valve 40. In the path 64, the upstream end is connected between the engine 10 and the four-way valve 40 of the path 61, and the downstream end is connected between the 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 64 is an example of a bypass path that connects the paths 61 and 62 and allows the cooling water that has passed through the engine 10 to bypass the heater core 20 and flow back into the engine 10 again. In the path 65, the upstream end is connected to the four-way valve 40, the downstream end is connected between the heater core 20 and the HWP 22 of the path 62, and the heat exchanger 50 is arranged in the middle. In the path 66, the upstream end is connected between the engine 10 and the temperature sensor 18 of the path 61, the downstream end is connected to the thermostat 30, and the radiator 14 and the reserve tank 16 are arranged in the middle.

[0019] [Four-way valve] Next, the four-way valve 40 will be described. FIGS. 2A to 2F are explanatory diagrams of the communication states of the four-way valve 40. As the rotor of the four-way valve 40 rotates in one direction, the communication states are 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 EWP12 is stopped and the HWP22 is driven. The cooling water circulates through a part of the path 62 and the path 63 to the heater core 20 and the heating heater 24. The opening ratio of the opening that connects the path 63 and the path 62 in the four-way valve 40 is the maximum. In FIG. 2A, the rotor of the four-way valve 40 is in the initial position. As 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.

[0020] In FIG. 2B, the path 63 is in communication with the paths 62 and 65, and the path 61 is blocked. In this state, the EWP12 is stopped and the HWP22 is driven. The cooling water circulates through a part of the path 62 and the path 63 to the heater core 20 and the heating heater 24, and circulates through the heat exchanger 50 via the path 65. As the rotor rotates in one direction from FIG. 2B, the opening ratio of the opening that connects the path 63 and the path 62 decreases to zero, and the opening ratio of the opening that connects the path 63 and the path 65 increases to the maximum as shown in FIG. 2C.

[0021] In FIG. 2C, the path 63 and the path 65 are in communication, and the paths 61 and the path 62 are blocked. In this state, the EWP12 is stopped and the HWP22 is driven. The cooling water circulates through a part of the path 62, the path 63, and the path 65 to the heat exchanger 50 and the heating heater 24. The opening ratio of the opening that connects the path 63 and the path 65 in the four-way valve 40 is the maximum. As the rotor rotates in one direction from FIG. 2C, the opening ratio of the opening that connects the path 63 and the path 65 decreases, and the opening ratio of the opening that connects the path 61 and the path 62 increases as shown in FIG. 2D.

[0022] In Figure 2D, paths 63 and 65 are connected, and paths 61 and 62 are connected. Paths 63 and 65 are not connected to paths 61 and 62. In this state, EWP12 and HWP22 are operating. Coolant circulates through part of path 62, paths 63 and 65 to the heat exchanger 50 and heating heater 24, and through paths 61 and 62 to the engine 10, heater core 20, and heating heater 24. Therefore, paths 61 and 62 correspond to paths through which 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, coolant also circulates through path 66 to the radiator 14 and reserve tank 16. As the rotor rotates in one direction, as shown in Figure 2D, the opening ratio of the opening connecting path 63 and path 65 decreases to zero, and the opening ratio of the opening connecting path 61 and path 62 increases to its maximum, as shown in Figure 2E.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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 and paths 62 and 65 gradually decreases to the state shown in Figure 2F. The ECU 100 obtains the opening ratio of these paths by referring to a map defined according to the target rotation position of the rotor.

[0027] [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.

[0028] 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.

[0029] [EWP rotation speed control] Figure 4 is a flowchart illustrating the rotational speed control of the EWP12 performed by the ECU100. The ECU100 determines whether or not paths 61 and 62 are in communication (step S1). The communication state in which paths 61 and 62 are in communication is the state of the four-way valve 40 shown in Figures 2D to 2F, where coolant that has passed through the engine 10 can pass through the heater core 20, and coolant that has passed through the heater core 20 can pass through the engine 10. If the answer in step S1 is No, this control is terminated.

[0030] If the answer in step S1 is Yes, the ECU 100 acquires the rotational speed of the HWP22 (step S2). The rotational speed of the HWP22 may be, for example, the target rotational speed of the HWP22, or it may be the actual rotational speed of the HWP22 detected by the sensor. Step S2 is an example of the processing performed by the acquisition unit.

[0031] Next, the ECU 100 sets a lower limit for the rotational speed of the EWP 12 based on the rotational speed of the HWP 22 (step S3). Figure 5 is a map that defines the lower limit for the rotational speed of the EWP 12 according to the rotational speed of the HWP 22. As shown in Figure 5, the higher the rotational speed of the HWP 22, the higher the lower limit for the rotational speed of the EWP 12 is set to. Here, the lower limit is set to a value that suppresses the backflow of coolant passing through path 64. If the rotational speed of the EWP 12 is too low compared to the rotational speed of the HWP 22, the flow rate of coolant flowing from the HWP 12 to path 64 via path 62 may increase more than the flow rate of coolant flowing from the EWP 12 to path 64 via path 61. As a result, there is a risk of coolant backflow in path 64. If the coolant passing through path 64 backflows, the temperature sensor 18 will detect the temperature of the coolant that has passed through the heater core 20, rather than the temperature of the coolant that has passed through the engine 10. Therefore, the lower limit of the rotational speed of the EWP12 is defined in the map shown in Figure 5 to suppress backflow of cooling water in path 64. Step S3 is an example of a process performed by the setting unit.

[0032] Next, the ECU 100 controls the rotation speed of the EWP 12 so that it is equal to or greater than the lower limit value mentioned above (step S4). This suppresses the backflow of coolant in the aforementioned path 64 and prevents a decrease in the accuracy of the control based on the temperature detected by the temperature sensor 18. Step S4 is an example of a process performed by the control unit.

[0033] Here, control based on the temperature detected by the temperature sensor 18 refers to, for example, the control of the fuel injection amount and ignition timing of the engine 10. For example, the lower the temperature detected by the temperature sensor 18, the more the fuel injection amount is increased to compensate for the unburned fuel adhering to the inner wall of the cylinder. Also, the lower the temperature detected by the temperature sensor 18, the more the ignition timing is advanced to compensate for the decrease in the output torque of the engine 10. Furthermore, the target rotational speed of the EWP 12 is calculated based on the target flow rate of the coolant flowing through the EWP 12, the opening degree of the thermostat 30, the rotational speed of the HWP 22, and the opening ratio of the path 61 by the four-way valve 40. If the target rotational speed of the EWP 12 is below the lower limit, the rotational speed of the EWP 12 is controlled to the lower limit.

[0034] [EWP drive control during intermittent engine shutdown] Figure 6 is a flowchart illustrating the drive control of the EWP 12 during intermittent shutdown of the engine 10. The ECU 100 determines whether or not paths 61 and 62 are in communication (step S11). The communication state in which paths 61 and 62 are in communication means that the four-way valve 40 is in the state shown in Figures 2D to 2F, and that the coolant that has passed through the engine 10 can pass through the heater core 20, and the coolant that has passed through the heater core 20 can pass through the engine 10. If the answer in step S11 is No, this control is terminated.

[0035] If the answer in step S11 is Yes, the integrated value of the flow rate of the coolant passing through the EWP12 is calculated (step S12). The integrated value of the flow rate of the coolant passing through the EWP12 is, for example, the value obtained by integrating the target flow rate of the coolant passing through the EWP12 with respect to time. Step S12 is an example of the process performed by the calculation unit. The target flow rate of the coolant flowing through the EWP12 is mainly calculated by the ECU100 according to the operating state of the engine 10. The ECU100 controls the rotation speed of the EWP12, taking into account the opening degree of the thermostat 30, the rotation speed of the HWP22, and the opening ratio of the path 61 by the four-way valve 40, so that the flow rate of the coolant flowing through the EWP12 becomes the target flow rate.

[0036] Next, the ECU 100 determines whether the engine 10 is in an intermittent stop state (step S13). The intermittent stop may be, for example, a temporary pause of the engine 10 due to the idle stop function, or a temporary pause of the engine 10 when the driving mode of a hybrid vehicle is switched to motor driving mode. If the answer in step S13 is No, this control ends.

[0037] If the answer in step S13 is Yes, the ECU 100 determines whether the accumulated value is equal to or greater than a threshold (step S14). The threshold is the accumulated value of the flow rate of the coolant that has passed through the EWP 12, which is necessary from the time the system is in contact with the system until the temperature of the coolant in the circulating path in the connected state can be considered uniform. The threshold is set considering the amount of heat exchanged between the engine 10, heater core 20, heat exchanger 50 and the coolant in the connected state described above. Step S14 is an example of the process executed by the determination unit.

[0038] If the answer in step S14 is No, the ECU100 continues to drive the EWP12 (step S15). If the answer in step S14 is Yes, the ECU100 stops driving the EWP12 (step S16).

[0039] As described above, when the engine 10 is intermittently stopped, the EWP 12 stops when the accumulated value exceeds a threshold and the temperature of the coolant circulating in the path described above in the connected state can be considered uniform. As a result, even if coolant flows backward in the path 64 when the engine 10 is restarted after an intermittent stop, the temperature detected by the temperature sensor 18 will be almost the same as if there had been no backflow of coolant in the path 64. This suppresses a decrease in the accuracy of control based on the temperature detected by the temperature sensor 18 when the engine 10 is restarted.

[0040] 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]

[0041] 1. Engine Cooling System 2. Engine cooling circuit (cooling circuit) 10 Engines 12. Engine water pump 14 Radiator 18 Temperature sensor 20 Heater Cores 22 Heater water pump 40 4-way valve (on / off valve) Routes 61 and 62 (Circular Routes) 64 routes (bypass routes) 100 ECUs (Control unit, acquisition unit, setting unit, control unit, determination unit, stop unit, calculation unit)

Claims

1. A cooling circuit having a circulation path through which coolant circulates between the engine and the heater core by an engine water pump that circulates coolant to the engine and a heater water pump that circulates coolant to the heater core for heating, and a bypass path connected to the circulation path through which the coolant that has passed through the engine bypasses the heater core and flows back into the engine, A temperature sensor provided in the bypass path for detecting the temperature of the coolant that has passed through the engine, The system includes a control device that performs control based on the temperature detected by the temperature sensor, The control device is An acquisition unit for acquiring the rotational speed of the heater water pump, A setting unit that sets a higher lower limit for the rotational speed of the engine water pump as the rotational speed of the heater water pump increases, in order to suppress backflow of coolant in the bypass path, Includes a control unit that controls the rotational speed of the engine water pump to be above the lower limit value, Engine cooling system.

2. The control device is When the engine is intermittently stopped, a determination unit determines whether the temperature of the coolant before it passes through the engine and flows into the heater core is equal to the temperature of the coolant before it passes through the heater core and flows into the engine. The determination unit includes a stop unit that stops the engine water pump when it determines to be positive, The engine cooling system according to claim 1.

3. The control device includes a calculation unit that calculates the integrated value of the flow rate of the cooling water passing through the engine water pump. The engine cooling system according to claim 2, wherein the determination unit determines, when the accumulated value exceeds a threshold, that the temperature of the coolant before it passes through the engine and flows into the heater core is equal to the temperature of the coolant before it passes through the heater core and flows into the engine.

4. The cooling circuit includes an on / off valve that blocks or connects the circulation path between the engine and the heater core. The engine cooling system according to claim 3, wherein the calculation unit calculates the accumulated value after the on / off valve opens the circulation path.

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