Engine cooling device

Abstract

The diagnosis device of the engine cooling device performs abnormality diagnosis of a thermostat by setting, in a transition period until a difference between a temperature of engine coolant flowing out from a warm-up heat exchanger and an outlet water temperature is reduced to be smaller than a predetermined value after a switching valve is switched from a state in which inflow of the engine coolant from a warm-up water passage to a water jacket is prohibited to a state in which the inflow is allowed, a value smaller than a value in a period other than the transition period as a determination value.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Japanese Patent Application No. 2025-031988 filed on February 28, 2025. The disclosure of the above-identified application, including the specification, drawings, and claims, is incorporated by reference herein in its entirety.BACKGROUNDTechnical Field

[0002] The present disclosure relates to an engine cooling device.Description of Related Art

[0003] As a cooling device applied to an engine mounted in a vehicle or the like, a water-cooled device is known that includes a circulation circuit of an engine coolant that is configured to cool, using a radiator, the engine coolant that has recovered heat after passing through the inside of the engine and to return the engine coolant back to the inside of the engine. A thermostat is provided in the circulation circuit of the engine coolant. The thermostat is configured to stop flow of the engine coolant through the radiator by closing a valve when the engine is cool and to start the flow of the engine coolant through the radiator by opening the valve when the engine is warm.

[0004] Further, an engine cooling device configured to use heat recovered by an engine coolant from an engine for heating a vehicle cabin or a battery is also known, as seen in Japanese Unexamined Patent Application Publication No. 2024-113860 (JP 2024-113860 A). The engine cooling device includes a heater core, a water-to-water heat exchanger, and a switching valve. The heater core is a heat exchanger configured to exchange heat between air blown into the vehicle cabin and the engine coolant. The water-to-water heat exchanger is a heat exchanger configured to exchange heat between a battery coolant that is caused to circulate through the inside of the battery and the engine coolant. The switching valve is a valve that switches between a state in which flow of the engine coolant to the heater core and the water-to-water heat exchanger is prohibited and a state in which the flow of the engine coolant to the heater core and the water-to-water heat exchanger is allowed.SUMMARY

[0005] It is conceivable to diagnose the presence or absence of an abnormality of a thermostat, such as a stuck open valve, based on a temperature change of an engine coolant. In a case of the engine cooling device as seen in JP 2024-113860 A, there is a possibility that the flow of the engine coolant to the heater core or the water-to-water heat exchanger is started during an abnormality diagnosis of the thermostat. In a case where the engine coolant that is cool has stayed inside the heater core and the water-to-water heat exchanger before the flow starts, the engine coolant that is cool flows into the engine after the flow starts. As a result, there is a possibility that diagnostic precision degrades because of a temporary decrease in a detection temperature of the engine coolant used for diagnosing the presence or absence of the abnormality of the thermostat.

[0006] An engine cooling device for solving the above issue is an engine cooling device in which, as flow paths for an engine coolant that circulates from an outlet of a water jacket provided inside an engine to an inlet of the water jacket, a radiator water passage provided through a radiator, a warm-up water passage provided with a warm-up heat exchanger for warming up another fluid with heat of the engine coolant, and a bypass water passage through which the engine coolant flows while the engine coolant bypasses the radiator and the warm-up heat exchanger are provided in parallel, the engine cooling device including a thermostat configured to open and close the radiator water passage and a switching valve configured to switch between a state in which flow of the engine coolant from the warm-up water passage to the water jacket is prohibited and a state in which the flow of the engine coolant from the warm-up water passage to the water jacket is allowed. The engine cooling device includes a diagnosis device configured to perform an abnormality diagnosis of the thermostat based on a comparison result between a rise rate of an outlet water temperature that is a temperature of the engine coolant flowing out of the water jacket and a determination value.

[0007] The diagnosis device is configured to set, during a transition period that is a period until a difference between a temperature of the engine coolant flowing out of the warm-up heat exchanger and the outlet water temperature decreases below a predetermined value after the switching valve switches from the state in which the flow of the engine coolant from the warm-up water passage to the water jacket is prohibited to the state in which the flow of the engine coolant from the warm-up water passage to the water jacket is allowed, a value smaller than a value during a period other than the transition period as the determination value to perform the abnormality diagnosis.

[0008] The engine cooling device has an effect of improving precision of the abnormality diagnosis of the thermostat.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

[0010] FIG. 1 is a diagram schematically showing a configuration of an embodiment of an engine cooling device;

[0011] FIG. 2 is a flowchart of abnormality diagnosis processing executed in the engine cooling device of FIG. 1;

[0012] FIG. 3 is a flowchart of a determination value setting process executed in the engine cooling device of FIG. 1;

[0013] FIG. 4 is a graph showing a relationship between a normality / abnormality determination value and an intake air amount set in the determination value setting process of FIG. 3; and

[0014] FIG. 5 is a time chart showing transitions of an open / close state of a warm-up water passage, an outlet water temperature, and a rise rate of the outlet water temperature in the engine cooling device of FIG. 1, respectively.DETAILED DESCRIPTION OF EMBODIMENTSConfiguration of Engine Cooling Device

[0015] Hereinafter, an embodiment of an engine cooling device will be described in detail with reference to FIGS. 1 to 5. First, a configuration of the engine cooling device according to the present embodiment will be described with reference to FIG. 1. The engine cooling device of the present embodiment is mounted on a hybrid electric vehicle. In the figure, the direction of the flow of a coolant is indicated by an arrow.

[0016] A water jacket 11 is provided in the inside of an engine 10 to which the engine cooling device of the present embodiment is applied. While the engine 10 is being operated, the engine coolant flows from the inlet 12 to the outlet 13 in the water jacket 11. The engine cooling device includes an engine water pump 20 that pumps the engine coolant toward the inlet 12 of the water jacket 11. In the case of the engine cooling device of the present embodiment, an electric pump is adopted for the engine water pump 20. The engine cooling device according to the present embodiment includes the bypass water passage 14, the radiator water passage 15, the first warm-up water passage 16, and the second warm-up water passage 17 as flow paths of the engine coolant that flows from the outlet 13 of the water jacket 11 to the inlet 12. The four water passages including the bypass water passage 14, the radiator water passage 15, the first warm-up water passage 16, and the second warm-up water passage 17 are provided in parallel. The water passages (14 to 17) include a portion shared with each other.

[0017] The bypass water passage 14 is configured to pass through the thermostat 19 and the engine water pump 20 in this order from the outlet 13 of the water jacket 11 and to return to the inlet 12 of the water jacket 11. The radiator water passage 15 is configured to pass through the radiator 21, the reservoir tank 22, the thermostat 19, and the engine water pump 20 in this order from the outlet 13 of the water jacket 11 and to return to the inlet 12 of the water jacket 11. The radiator 21 is a heat exchanger for cooling the engine coolant by heat exchange with the outside air. The reservoir tank 22 is a storage container for the engine coolant. The thermostat 19 opens and closes the radiator water passage 15 according to the temperature of the engine coolant flowing in. Specifically, the thermostat 19 is configured to close the radiator water passage 15 when the temperature of the engine coolant is lower than the set temperature and to open the radiator water passage 15 when the temperature of the engine coolant is equal to or higher than the set temperature. The state in which the radiator water passage 15 is opened here indicates a state in which the engine coolant flows through the radiator water passage 15. In addition, the state in which the radiator water passage 15 is closed indicates a state in which the flow of the engine coolant through the radiator water passage 15 is stopped.

[0018] The first warm-up water passage 16 flows from the outlet 13 of the water jacket 11, passes through the switching valve 18, the heater core 23, the heater water pump 24, the electric heater 25, and the engine water pump 20 in this order, and returns to the inlet 12. The inlet 12 is an inlet of the water jacket 11. The switching valve 18 is a valve for changing a flow rate allocation of the engine coolant in each water passage, and details thereof will be described later. The heater core 23 is a heat exchanger that exchanges heat between the air blown into the vehicle cabin and the engine coolant and is used to warm the air blown with the heat of the engine coolant when the vehicle cabin is heated. The heater water pump 24 is an electric pump. The electric heater 25 generates heat in response to power supply to heat the engine coolant.

[0019] The second warm-up water passage 17 flows from the outlet 13 of the water jacket 11, passes through the switching valve 18, the water-to-water heat exchanger 26, the heater water pump 24, the electric heater 25, and the engine water pump 20 in this order, and returns to the inlet 12. The inlet 12 is an inlet of the water jacket 11. The water-to-water heat exchanger 26 is a heat exchanger that exchanges heat between the battery coolant and the engine coolant. The battery coolant is a coolant that is circulated through the battery water passage 28 and is used for adjusting the temperature of the battery 27. The water-to-water heat exchanger 26 is used to warm the battery coolant with the heat of the engine coolant when the battery 27 is heated. In the engine cooling device of the present embodiment, each of the heater core 23 and the water-to-water heat exchanger 26 corresponds to the warm-up heat exchanger for increasing the temperature of another fluid with the heat of the engine coolant. In the engine cooling device of the present embodiment, the bypass water passage 14 is configured as a water passage that bypasses the radiator 21 and the warm-up heat exchanger (heater core 23, water-to-water heat exchanger 26) to flow the engine coolant.

[0020] The switching valve 18 allocates the flow rate of the engine coolant flowing from the outlet 13 of the water jacket 11 to the first warm-up water passage 16 and the second warm-up water passage 17. The switching valve 18 constitutes four states (A1) to (A4). The state (A1) is a state in which the flow of the engine coolant from the outlet 13 of the water jacket 11 to both the first warm-up water passage 16 and the second warm-up water passage 17 is stopped. The state (A2) is a state in which the engine coolant flows from the outlet 13 of the water jacket 11 to solely the first warm-up water passage 16 among the first warm-up water passage 16 and the second warm-up water passage 17. The state (A3) is a state in which the engine coolant flows from the outlet 13 of the water jacket 11 to solely the second warm-up water passage 17 among the first warm-up water passage 16 and the second warm-up water passage 17. The state (A4) is a state in which the engine coolant flows from the outlet 13 of the water jacket 11 to both the first warm-up water passage 16 and the second warm-up water passage 17.

[0021] In addition, the engine cooling device of the present embodiment is provided with the outlet water temperature sensor 30 and the heater inlet water temperature sensor 31. The outlet water temperature sensor 30 is a sensor that detects the outlet water temperature that is the temperature of the engine coolant flowing out of the outlet 13 of the water jacket 11. The heater inlet water temperature sensor 31 is a sensor that detects a heater inlet water temperature that is a temperature of the engine coolant flowing through a portion of the first warm-up water passage 16 and the second warm-up water passage 17 on a downstream side of the heater water pump 24 and an upstream side of the electric heater 25. The heater inlet water temperature when the engine coolant flows through the first warm-up water passage 16 and the second warm-up water passage 17 corresponds to the temperature of the engine coolant flowing out of the heater core 23 and the water-to-water heat exchanger 26.

[0022] Further, the engine cooling device of the present embodiment includes a return water passage 29 that connects a portion of the first warm-up water passage 16 and the second warm-up water passage 17 on a downstream side of the electric heater 25 to the switching valve 18. Even in the state (A1), the switching valve 18 can connect the return water passage 29 to at least one of the first warm-up water passage 16 and the second warm-up water passage 17 to flow the engine coolant through the first warm-up water passage 16 and the second warm-up water passage 17. Then, even when the engine 10 is stopped, it is possible to perform heating of the vehicle cabin and heating of the battery 27 by operating the heater water pump 24 and the electric heater 25 in the state. In the electric traveling of the hybrid electric vehicle, the heating of the vehicle cabin or the temperature elevation of the battery 27 is requested. In this case, the engine cooling device according to the present embodiment causes the engine coolant to circulate through the first warm-up water passage 16 or the second warm-up water passage 17 through the return water passage 29.

[0023] In addition, the engine cooling device of the present embodiment includes the electronic control unit 32. The electronic control unit 32 includes a calculation processing device 33 and a storage device 34. The storage device 34 is provided with a program and data for controlling the engine cooling device in advance. The electronic control unit 32 is configured to execute various types of processing for controlling the engine cooling device by reading and executing the program from the storage device 34 by the calculation processing device 33. The detection signals X1, X2 of the outlet water temperature sensor 30 and the heater inlet water temperature sensor 31 are input to the electronic control unit 32. In addition, detection signals X3 to X5 of an air flow meter 35, an intake air temperature sensor 36, and a vehicle speed sensor 37 are also input to the electronic control unit 32. The air flow meter 35 detects the intake air amount of the engine 10. The intake air temperature sensor 36 detects the intake air temperature of the engine 10. The vehicle speed sensor 37 detects the vehicle speed of the hybrid electric vehicle. The calculation processing device 33 calculates an operation amount of each of the switching valve 18, the engine water pump 20, the heater water pump 24, and the electric heater 25 based on the detection signals of these sensors. The electronic control unit 32 outputs command signals X6 to X9 according to the operation amount calculated by the calculation processing device 33 to the switching valve 18, the engine water pump 20, the heater water pump 24, and the electric heater 25. In this manner, the electronic control unit 32 controls the engine cooling device.Abnormality Diagnosis of Thermostat 19

[0024] The electronic control unit 32 performs the abnormality diagnosis of the thermostat 19 as a part of the control of the engine cooling device. Specifically, the electronic control unit 32 performs the abnormality diagnosis of the thermostat 19 based on the comparison result between the rise rate of the outlet water temperature in a state where the valve opening condition of the thermostat 19 is not satisfied and the normality / abnormality determination value. In the case of the present embodiment, the valve opening condition of the thermostat 19 is that the temperature of the engine coolant flowing into the thermostat 19 is equal to or higher than the set temperature of the thermostat 19. In the engine cooling device of the present embodiment, the electronic control unit 32 that performs such an abnormality diagnosis corresponds to the diagnosis device.

[0025] FIG. 2 shows a flowchart of abnormality diagnosis processing of the thermostat 19. The electronic control unit 32 starts the processing of FIG. 2 at the cold start of the engine 10. The "S" added before the reference numerals in the figure indicates a step.

[0026] In a case where the processing of FIG. 2 is started, the electronic control unit 32 determines in step S100 whether the diagnostic condition is established. In a case where the electronic control unit 32 determines that the diagnostic condition is not established (NO), the electronic control unit 32 re-executes the determination of step S100 after the predetermined control cycle elapses. On the other hand, in a case where the electronic control unit 32 determines that the diagnostic condition is established (YES), the processing proceeds to step S102. In the case of the present embodiment, the diagnostic condition is set to be satisfied when all of the following requirements (B1) to (B5) are satisfied. The requirement (B1) is that the outlet water temperature at the time of the start of the engine 10 is equal to or higher than a predetermined temperature. The requirement (B2) is that the intake air temperature at the time of the start of the engine 10 is equal to or higher than a predetermined temperature. The requirement (B3) is that the engine water pump 20 is in operation. The requirement (B4) is that the vehicle speed of the hybrid electric vehicle is within a predetermined range. The requirement (B5) is that the number of times of executing the abnormality diagnosis process in the current trip is equal to or less than a predetermined number of times. In the case of the present embodiment, the electronic control unit 32 performs the abnormality diagnosis of the thermostat 19 based on the rise rate of the outlet water temperature. In an extremely low temperature environment, the outlet water temperature is likely to rise slowly because the heat is taken away by the outside air, and thus, the abnormality diagnosis may not be accurately performed. The requirements (B1), (B2) are set to avoid the misdiagnosis in such an extremely low temperature environment. In addition, when the flow rate of the engine coolant in the water jacket 11 and the heat generation amount of the engine 10 are greatly varied, the precision of the abnormality diagnosis based on the rise rate of the outlet water temperature cannot be ensured. The requirements (B3), (B4) are set to avoid the deterioration of the diagnostic precision due to the variation in the flow rate and the heat generation amount of the engine coolant. The requirement (B5) is set to avoid the abnormality diagnosis from being repeatedly performed more than needed in the same trip.

[0027] In a case where the process proceeds to step S102, the electronic control unit 32 acquires the rise rate of the outlet water temperature. Specifically, the electronic control unit 32 acquires the rise rate by seeking a rise amount of the outlet water temperature at a predetermined time based on the detection signal X1 of the outlet water temperature sensor 30.

[0028] Next, in step S104, the electronic control unit 32 performs the determination value setting processing. In the determination value setting process, two determination values, that is, an abnormality determination value and a normality determination value are set. The details of the determination value setting process will be described later. In the process, a value larger than the abnormality determination value is set as the normality determination value. Then, in step S106, the electronic control unit 32 determines whether the rise rate of the outlet water temperature is equal to or less than the abnormality determination value. In a case where the determination is made that the rise rate is equal to or less than the abnormality determination value (YES), the electronic control unit 32 proceeds to step S108, and in a case where the determination is made that the rise rate exceeds the abnormality determination value (NO), the electronic control unit 32 proceeds to step S118.

[0029] In a case where the process proceeds to step S108, the electronic control unit 32 performs the count-up of the abnormality counter in step S108. The value of the abnormality counter is reset to zero at the start of the abnormality diagnosis process. The value of the abnormality counter indicates the number of times of determining that the rise rate is equal to or less than the abnormality determination value in the current abnormality diagnosis process. Next, in step S110, the electronic control unit 32 determines whether the value of the abnormality counter is equal to or greater than a predetermined abnormality confirmation determination value. When the electronic control unit 32 determines that the value of the abnormality counter is equal to or greater than the abnormality confirmation determination value (YES), the electronic control unit 32 ends the abnormality diagnosis process after confirming the diagnosis result that the thermostat 19 is abnormal in step S112. On the other hand, in a case where the determination is made that the value of the abnormality counter is less than the abnormality confirmation determination value (NO), the electronic control unit 32 proceeds to step S114.

[0030] In step S114, the electronic control unit 32 determines whether the outlet water temperature is equal to or higher than a predetermined diagnosis end temperature. A temperature slightly lower than the set temperature of the thermostat 19 is set as the diagnosis end temperature. When the electronic control unit 32 determines that the outlet water temperature is equal to or higher than the diagnosis end temperature (YES), the electronic control unit 32 ends the abnormality diagnosis process after determining that the abnormality diagnosis result of the thermostat 19 is normal in step S116. The diagnosis results that the thermostat 19 is normal is, in other words, the diagnosis results that the thermostat 19 is normal. That is, in the case of the present embodiment, when the value of the abnormality counter is not equal to or greater than the abnormality confirmation determination value until the valve opening condition of the thermostat 19 is satisfied, the thermostat 19 is diagnosed as normal. On the other hand, in a case where the electronic control unit 32 determines that the outlet water temperature is less than the diagnosis end temperature (S114: NO), the electronic control unit 32 returns the process to step S102 after the default control cycle.

[0031] On the other hand, in a case where the determination is made that the rise rate is less than the abnormality determination value (S106: NO) and the processing proceeds to step S118, the electronic control unit 32 determines whether the rise rate of the outlet water temperature is equal to or higher than the normality determination value in step S118. Then, when the electronic control unit 32 determines that the rise rate is equal to or higher than the normality determination value (YES), the electronic control unit 32 progresses the process to step S120, and when the electronic control unit 32 determines that the rise rate is lower than the normality determination value (NO), the electronic control unit 32 progresses the process to step S114.

[0032] In a case where the processing proceeds to step S120, the electronic control unit 32 performs the count-up of the normality counter in step S120. The value of the normality counter is reset to zero at the start of the abnormality diagnosis process, as in the abnormality counter. The value of the normality counter indicates the number of times of determining that the rise rate is equal to or higher than the normality determination value in the current abnormality diagnosis process. Next, in step S122, the electronic control unit 32 determines whether the value of the normality counter is equal to or higher than the predetermined normality confirmation determination value. When the electronic control unit 32 determines that the value of the normality counter is equal to or greater than the normality confirmation determination value (YES), the electronic control unit 32 ends the abnormality diagnosis process after confirming the diagnosis result that the thermostat 19 is normal in step S116. On the other hand, when the electronic control unit 32 determines that the value of the normality counter is less than the normality confirmation determination value (NO), the electronic control unit 32 progresses the process to step S114.

[0033] In the abnormality diagnosis process described above, the electronic control unit 32 repeats the acquisition of the rise rate of the outlet water temperature and the comparison between the acquired rise rate and the abnormality determination value and the normality determination value at a predetermined control cycle after the diagnostic condition is satisfied. Then, when the number of times of determining that the rise rate of the outlet water temperature is equal to or less than the abnormality determination value reaches the abnormality confirmation determination value, the electronic control unit 32 diagnoses that the abnormality is present in the thermostat 19. In addition, in a case where the number of times in which the determination is made that the rise rate of the outlet water temperature is equal to or higher than the normality determination value reaches the normality confirmation determination value, the electronic control unit 32 diagnoses that the thermostat 19 is normal. Alternatively, in a case where the thermostat 19 is not diagnosed as having an abnormality before the outlet water temperature reaches the diagnosis end temperature, the electronic control unit 32 diagnoses that the thermostat 19 is normal.Determination Value Setting Process

[0034] Next, details of the determination value setting processing executed by the electronic control unit 32 in step S104 of FIG. 2 will be described with reference to FIG. 3. FIG. 3 shows a processing procedure of the electronic control unit 32 in the determination value setting process.

[0035] In the determination value setting processing, the electronic control unit 32 first calculates the water temperature difference between the outlet water temperature and the heater inlet water temperature in step S200. Specifically, the electronic control unit 32 subtracts the heater inlet water temperature from the outlet water temperature and calculates a value of the subtraction as the water temperature difference.

[0036] In following step S201, the electronic control unit 32 determines whether the transition period is progress. Then, in a case where the electronic control unit 32 determines that the transition period is progress (YES), the electronic control unit 32 proceeds to step S210, and in a case where the electronic control unit 32 determines that the transition period is not ongoing (NO), the electronic control unit 32 proceeds to step S202. As will be described later, in the present process, the electronic control unit 32 determines the start and the end of the transition period, and the period from the determination that the transition period is started to the determination that the transition period is ended is the transition period.

[0037] In a case where the processing proceeds to step S202, the electronic control unit 32 determines in step S202 whether the water passage of the heater core 23 or the water-to-water heat exchanger 26 is started. Specifically, the electronic control unit 32 determines the switching from the following state (C1) to the state (C2) as the start of the flow of the engine coolant to the heater core 23 or the water-to-water heat exchanger 26. The state (C1) is a state in which the flow of the engine coolant from both the first warm-up water passage 16 and the second warm-up water passage 17 to the water jacket 11 is prohibited. The state (C2) is a state in which the flow of the engine coolant from at least one of the first warm-up water passage 16 and the second warm-up water passage 17 to the water jacket 11 is allowed. The switching from the state (C1) to the state (C2) is performed by the switching valve 18. In the present embodiment, the electronic control unit 32 performs the determination in step S202 based on the operation amount of the switching valve 18.

[0038] When the electronic control unit 32 determines that the flow of the engine coolant through the heater core 23 or the water-to-water heat exchanger 26 is not started (NO), the electronic control unit 32 progresses the process to step S204. In step S204, the electronic control unit 32 sets the values of the normality determination value and the abnormality determination value by using the normal time map stored in the storage device 34 in advance and ends the current determination value setting process. In a case where the determination value setting process is ended, the electronic control unit 32 resumes the abnormality diagnosis process from step S106 of FIG. 2.

[0039] On the other hand, in a case where the electronic control unit 32 determines that the water passage of the heater core 23 or the water-to-water heat exchanger 26 is started in step S202 (YES), the electronic control unit 32 proceeds to step S203. In step S203, the electronic control unit 32 determines whether the water temperature difference is equal to or higher than a predetermined transition determination value. In a case where the electronic control unit 32 determines that the water temperature difference is smaller than the transition determination value (NO), the electronic control unit 32 proceeds to the processing in step S204. On the other hand, in a case where the electronic control unit 32 determines that the water temperature difference is equal to or higher than the transition determination value (YES), the electronic control unit 32 determines that the transition period is started in step S206. Then, in step S208, the electronic control unit 32 sets the values of the normality determination value and the abnormality determination value by using the transition time map stored in the storage device 34 in advance, and ends the current determination value setting process.

[0040] In addition, in a case where the electronic control unit 32 determines that the transition period is in progress in step S200 and proceeds to step S210, the electronic control unit 32 determines whether the water temperature difference is smaller than the transition determination value in step S210. In a case where the electronic control unit 32 determines that the water temperature difference is smaller than the transition determination value (YES), the electronic control unit 32 proceeds to step S212, and in a case where the electronic control unit 32 determines that the water temperature difference is equal to or higher than the transition determination value (NO), the electronic control unit 32 proceeds to step S208. In a case where the electronic control unit 32 proceeds to step S212, the electronic control unit 32 determines that the transition period is ended in step S212 and then proceeds to the processing in step S204.

[0041] In the above-described determination value setting processing, the electronic control unit 32 determines a period in which the difference between the outlet water temperature and the heater inlet water temperature is equal to or higher than the transition determination value after switching from the state (C1) to the state (C2) via the switching valve 18 as the transition period. The electronic control unit 32 sets the normality determination value and the abnormality determination value by using the transition time map during the transition period and by using the normal time map during a period other than the transition period.

[0042] Each of the normal time map and the transition time map is configured as a function that takes the intake air amount of the engine 10 and the difference between the outlet water temperature and the outside air temperature as arguments and returns the normality determination value and the abnormality determination value as return values. The electronic control unit 32 acquires the intake air amount of the engine 10 based on the detection signal X3 of the air flow meter 35. In addition, the electronic control unit 32 acquires the outside air temperature based on the detection signal X4 of the intake air temperature sensor 36 at the time of the start of the engine 10.

[0043] The engine coolant receives heat from the engine 10 while passing through the water jacket 11. When the load of the engine 10 is high, the heat generation amount of the engine 10 is increased, and thus the heat amount that the engine coolant receives from the engine 10 is also increased. Therefore, the rise rate of the outlet water temperature is higher when the engine load is high than when the engine load is low. The intake air amount of the engine 10 is increased as the engine load is increased. In addition, the engine coolant is taken away heat by the outside air while flowing from the outlet 13 of the water jacket 11 to the inlet 12 of the water jacket 11 through the bypass water passage 14 or the like. The amount of heat taken away from the engine coolant by the outside air is increased as the difference between the outlet water temperature and the outside air temperature is increased. Therefore, the rise rate of the outlet water temperature is lower as the difference between the outlet water temperature and the outside air temperature is larger.

[0044] On the other hand, in a case where the thermostat 19 is opened before the valve opening condition is satisfied, the engine coolant that flows through the radiator water passage 15 flows into the water jacket 11, and thus the cooling in the radiator 21 causes the rise rate of the outlet water temperature to be slow.

[0045] The relationship between the intake air amount in a case where the thermostat 19 is in an open state, the difference between the outlet water temperature and the outside air temperature, and the range of values that can be taken by the rise rate of the outlet water temperature can be obtained in advance by an experiment, a simulation, or the like. The relationship between the intake air amount in a case where the thermostat 19 is in a closed state, the difference between the outlet water temperature and the outside air temperature, and the range of values that can be taken by the rise rate of the outlet water temperature can be obtained in advance by an experiment, a simulation, or the like. In the following description, a lower limit value of a range of values that the rise rate of the outlet water temperature can take in a state where the thermostat 19 is closed is referred to as a normal time rise rate. Then, an upper limit value of a range of values that the rise rate of the outlet water temperature can take in a state where the thermostat 19 is opened is referred to as an abnormal time rise rate. The normal time map is configured to return a value slightly larger than the normal time rise rate as the normality determination value, and a value slightly smaller than the abnormal time rise rate as the abnormal time determination value. Further, the transition time map is configured to return, as the normality determination value and the abnormality determination value, a value smaller than the normality determination value and a value smaller than the abnormality determination value of the normal time map when the difference between the outlet water temperature and the outside air temperature is the same as the intake air amount.

[0046] FIG. 4 shows a relationship between a normality / abnormality determination value and an intake air amount of each of a normal time map and a transition time map when a difference between an outlet water temperature and an outside air temperature is constant. In any of the maps, a normality / abnormality determination value is set to be larger when the intake air amount is larger than when the intake air amount is smaller, and is set such that the normality determination value is a larger value than the abnormality determination value. Then, in a case where the intake air amount is the same, the normality / abnormality determination value is set to a smaller value in the transition time map than in the normal time map.Action of Embodiment

[0047] Immediately after the cold start of the engine 10, the flow of the engine coolant through the radiator water passage 15 is stopped by the thermostat 19. After the start of the engine 10, the outlet water temperature gradually increases due to the heat received from the engine 10. Then, when the temperature of the engine coolant flowing into the thermostat 19 reaches the set temperature, the thermostat 19 is opened and the flow of the engine coolant to the radiator water passage 15 is started. In the present embodiment, the electronic control unit 32 performs the abnormality diagnosis process of the thermostat 19 based on the comparison result between the rise rate of the outlet water temperature and the normality / abnormality determination value in a period from the start of the engine 10 to the establishment of the opening valve condition of the thermostat 19.

[0048] A top portion of FIG. 5 shows a transition of an opening and closing state of the warm-up water passage during the abnormality diagnosis process. A center portion of FIG. 5 shows a transition of the outlet water temperature and the heater inlet water temperature during the abnormality diagnosis process. A bottom portion of FIG. 5 shows a transition of the rise rate of the outlet water temperature during the abnormality diagnosis process. The state in which the warm-up water passage is opened here refers to a state in which the engine coolant flowing out of the water jacket 11 flows into at least one of the first warm-up water passage 16 and the second warm-up water passage 17 through the switching valve 18. In addition, the state in which the warm-up water passage is closed here refers to a state in which the flow of the engine coolant that flows out of the water jacket 11 to both the first warm-up water passage 16 and the second warm-up water passage 17 is stopped by the switching valve 18.

[0049] First, a case where the warm-up water passage is held in a closed state will be described as shown by a solid line in the upper portion of FIG. 5. In the center portion of FIG. 5, a transition of the outlet water temperature in this case is shown by a solid line, and a transition of the heater inlet water temperature is shown by a two-dot chain line. In addition, in the lower portion of FIG. 5, a transition of the rise rate of the outlet water temperature in this case is shown by a solid line. The engine coolant in this case circulates between the water jacket 11 and the bypass water passage 14 until the thermostat 19 is opened. Therefore, the outlet water temperature rises smoothly. In a case where the thermostat 19 is stuck open in this case, the engine coolant is cooled by the radiator 21, so that the rise rate of the outlet water temperature is lower than that in a case where the thermostat 19 operates normally. In a case where a determination that the rise rate of the outlet water temperature is equal to or less than the abnormality determination value is made a predetermined number of times, the electronic control unit 32 diagnoses that the thermostat 19 is abnormal. In this case, since the engine coolant does not flow in the first warm-up water passage 16 and the second warm-up water passage 17, the heater inlet water temperature hardly changes from the start of the engine 10.

[0050] Next, as shown by a one-dot chain line in the upper portion of FIG. 5, a case will be described where, at time t1 during the abnormality diagnosis, the warm-up water passage is opened by the switching valve 18 for a request for heating of the vehicle cabin or a request for temperature rise of the battery 27. In the center portion of FIG. 5, a transition of the outlet water temperature in this case is shown by a one-dot chain line, and a transition of the heater inlet water temperature is shown by a broken line. In addition, in the lower portion of FIG. 5, a transition of the rise rate of the outlet water temperature in this case is shown by a one-dot chain line. Cold engine coolant is retained in the warm-up water passage before time t1. When the flow of the engine coolant to the warm-up water passage is started at time t1, the cold engine coolant that stays in the warm-up water passage flows into the water jacket 11. Therefore, the outlet water temperature temporarily stops rising after time t1. In the following description, the phenomenon in which the outlet water temperature temporarily stops rising after the water flow start of the first warm-up water passage 16 or the second warm-up water passage 17 will be referred to as a water temperature drop. In a case where the water temperature drop occurs, even in a case where the thermostat 19 normally functions, the rise rate of the outlet water temperature decreases, so that, in a case where the abnormality diagnosis is continued as it is, there is a possibility that the abnormality of the thermostat 19 is erroneously diagnosed.

[0051] On the other hand, the electronic control unit 32 in the present embodiment determines a period during which the difference between the outlet water temperature and the heater inlet water temperature is equal to or larger than the transition determination value after the water flow start of the first warm-up water passage 16 or the second warm-up water passage 17 by the switching valve 18 as a transition period. Then, the electronic control unit 32 sets the normality determination value and the abnormality determination value to be smaller in the transition period than in a period other than the transition period.

[0052] The engine coolant warmed by the heat of the engine 10 by passing through the water jacket 11 flows into the first warm-up water passage 16 or the second warm-up water passage 17 after the water flow start. As a result, the heater inlet water temperature gradually increases after time t1, so that the difference between the outlet water temperature and the heater inlet water temperature also decreases. In a case of FIG. 5, at time t2, the difference between the outlet water temperature and the heater inlet water temperature is reduced to be smaller than the transition determination value. The electronic control unit 32 determines that the transition period ends at time t2 and restores the normality determination value and the abnormality determination value to the values before time t1.

[0053] As described above, the electronic control unit 32 sets a value smaller than the normal value in the normality determination value and the abnormality determination value in the transition period in which the rise rate of the outlet water temperature temporarily decreases and performs the abnormality diagnosis of the thermostat 19. Therefore, even when the rise rate of the outlet water temperature temporarily decreases after the start of the flow to the warm-up water passage, the abnormality of the thermostat 19 is less likely to be mistakenly diagnosed. In the case of the present embodiment, the decrease amount of the rise rate of the outlet temperature after the start of the flow through the warm-up water passage is obtained in advance by an experiment, a simulation, or the like. Then, the transition time map is set to return a value smaller than the value of the normal time map by the decrease amount as the normality determination value and the abnormality determination value.

[0054] Since the engine coolant is also cooled by the heater core 23 and the water-to-water heat exchanger 26, the rise rate of the outlet water temperature after the end of the transition period is lower than the rise rate of the outlet water temperature when the flow of the engine coolant through the warm-up water passage is not performed. Note that the volume of the heater core 23 and the water-to-water heat exchanger 26 is smaller than the volume of the radiator 21, and the influence on the rise rate of the outlet water temperature is also smaller than the influence of the radiator 21. Therefore, it is possible to perform the abnormality diagnosis of the thermostat 19 after the end of the transition period, as before the flow start.Effect of Embodiment

[0055] The engine cooling device of the present embodiment has the following effects.

[0056] (1) The electronic control unit 32 determines a period from the start of the water flow to the first warm-up water passage 16 or the second warm-up water passage 17 by the switching valve 18 until the difference between the heater inlet water temperature and the outlet water temperature is reduced to a predetermined value (transition determination value) or less as the transition period. Then, the electronic control unit 32 sets the normality / abnormality determination value to a value smaller than the value in the period other than the transition period in the transition period and performs the abnormality diagnosis of the thermostat 19. Therefore, even in a case where the water temperature drop occurs due to the start of the water flow to the first warm-up water passage 16 or the second warm-up water passage 17, the abnormality of the thermostat 19 is less likely to be erroneously diagnosed. As described above, the engine cooling device of the present embodiment has an effect of improving the precision of the abnormality diagnosis of the thermostat 19.

[0057] (2) The electronic control unit 32 determines the transition period based on the difference between the heater inlet water temperature and the outlet water temperature. Therefore, the period in which the water temperature drop occurs can be accurately determined as the transition period.

[0058] (3) The electronic control unit 32 calculates the normality / abnormality determination value based on the difference between the outlet water temperature and the outside air temperature and the intake air amount that is an index value of the engine load. Further, the electronic control unit 32 is configured to calculate a value smaller than a value of a period other than the transition period as the normality / abnormality determination value even when the difference between the outlet water temperature and the outside air temperature and the engine load are the same during the transition period. The rise rate of the outlet water temperature is also changed by the difference between the outlet water temperature and the outside air temperature and the engine load in addition to the presence or absence of the abnormality of the thermostat 19. Therefore, by reflecting the influence of the difference between the outlet water temperature and the outside air temperature and the engine load on the normality / abnormality determination value, the diagnostic precision of the thermostat 19 can be further improved.

[0059] (4) The electronic control unit 32 repeatedly performs a determination of whether the rise rate of the outlet water temperature is equal to or less than the abnormality determination value until the valve opening condition of the thermostat 19 is satisfied. The electronic control unit 32 is configured to diagnose that the abnormality is present in the thermostat 19 when the determination that the rise rate of the outlet water temperature is equal to or less than the abnormality determination value is made a predetermined number of times or more. Since the rise rate of the outlet water temperature is changed by various factors, there is a possibility that the rise rate temporarily decreases to or below the abnormality determination value even when the thermostat 19 is normal. Therefore, by diagnosing that the abnormality is present in the thermostat 19 based on the fact that the rise rate is equal to or less than the abnormality determination value for a plurality of times, the diagnostic precision can be improved.Other Embodiments

[0060] The embodiment described above can be modified and carried out as follows. The embodiment described above and the following modifications can be carried out in combination within a technically consistent range.

[0061] The diagnostic condition determined in step S100 of FIG. 2 may be appropriately changed. In the abnormality diagnosis process, the presence or absence of the abnormality due to the stuck closed valve of the thermostat 19 after the valve opening condition is satisfied may be diagnosed. When the thermostat 19 is stuck closed, the rise rate of the outlet water temperature after the valve opening condition is satisfied is lower than the rise rate of the outlet water temperature when the thermostat 19 is normally opened. Therefore, by changing the content of the abnormality diagnosis process as follows, it is possible to diagnose the presence or absence of the abnormality due to the stuck closed valve of the thermostat 19 after the valve opening condition is satisfied. First, in the determination value setting process of FIG. 3, both the determination values are set such that the normality determination value is a value smaller than the abnormality determination value. In step S106 of FIG. 2, whether the rise rate is equal to or higher than the abnormality determination value is determined, and in step S118 of FIG. 2, whether the rise rate is equal to or lower than the normality determination value is determined. Even in such a case, the normality / abnormality determination value can be set to be smaller during the transition period than during the period other than the transition period to improve the precision of the abnormality diagnosis.

[0062] The engine cooling device of the embodiment includes the first warm-up water passage 16 in which the heater core 23 is provided and the second warm-up water passage 17 in which the water-to-water heat exchanger 26 is provided as the warm-up water passage in which the warm-up heat exchanger is provided. A configuration in which only one of the first warm-up water passage 16 or the second warm-up water passage 17 is provided as the warm-up water passage may be adopted. In addition, the engine cooling device may have a configuration in which a water passage in which a heat exchanger different from the heater core 23 and the water-to-water heat exchanger 26 is provided is used as a warm-up water passage in a case where the warm-up heat exchanger for increasing the temperature of another fluid with the heat of the engine coolant is used.

[0063] In the embodiment, the normality / abnormality determination value is calculated based on the engine load and the difference between the outlet water temperature and the outside air temperature but may be calculated using only any one of the engine loads or the difference between the outlet water temperature and the outside air temperature. In addition, other parameters that affect the rise rate of the outlet water temperature may be used for calculating the normality / abnormality determination value. Further, each of the normality / abnormality determination values may have solely two values, that is, a value during the transition period and a value during a period other than the transition period.

[0064] In the embodiment, the temperature of the engine coolant flowing out from the warm-up heat exchanger is detected at a portion downstream of the heater water pump 24 in the first warm-up water passage 16 and the second warm-up water passage 17 and upstream of the electric heater 25. The temperature of the engine coolant may be the heater inlet water temperature. The detection position of the temperature may be appropriately changed. For example, the temperature of the engine coolant near the inlet 12 of the water jacket 11 may be detected as the temperature of the engine coolant flowing out from the warm-up heat exchanger.

[0065] The abnormality diagnosis process may be performed using solely any one of the normality determination values and the abnormality determination value. For example, in a case where solely the normality determination value is used, the abnormality is diagnosed in the thermostat 19 when the normal diagnosis result is not confirmed.

[0066] In the embodiment, the intake air amount is used as the index value of the engine load to calculate the normality / abnormality determination value, but other parameters, such as the intake air filling rate and the fuel injection amount, may be used as the index value of the engine load.

[0067] A mechanical pump that operates by receiving the power of the engine 10 may be adopted as the engine water pump 20. The engine cooling device of the embodiment may be applied to a normal engine vehicle that is not the hybrid electric vehicle.

Claims

1. An engine cooling device in which, as flow paths for an engine coolant that circulates from an outlet of a water jacket provided inside an engine to an inlet of the water jacket, a radiator water passage provided through a radiator, a warm-up water passage provided with a warm-up heat exchanger for warming up another fluid with heat of the engine coolant, and a bypass water passage through which the engine coolant flows while the engine coolant bypasses the radiator and the warm-up heat exchanger are provided in parallel, the engine cooling device including a thermostat configured to open and close the radiator water passage, and a switching valve configured to switch between a state in which flow of the engine coolant from the warm-up water passage to the water jacket is prohibited and a state in which the flow of the engine coolant from the warm-up water passage to the water jacket is allowed, the engine cooling device comprising:a diagnosis device configured to perform an abnormality diagnosis of the thermostat based on a comparison result between a rise rate of an outlet water temperature that is a temperature of the engine coolant flowing out of the water jacket and a determination value,wherein the diagnosis device is configured to set, during a transition period that is a period until a difference between a temperature of the engine coolant flowing out of the warm-up heat exchanger and the outlet water temperature decreases below a predetermined value after the switching valve switches from the state in which the flow of the engine coolant from the warm-up water passage to the water jacket is prohibited to the state in which the flow of the engine coolant from the warm-up water passage to the water jacket is allowed, a value smaller than a value during a period other than the transition period as the determination value to perform the abnormality diagnosis.

2. The engine cooling device according to claim 1, wherein the diagnosis device is configured tocalculate the determination value based on a difference between the outlet water temperature and an outside air temperature, and an engine load, andcalculate, during the transition period, a value smaller than a value during the period other than the transition period as the determination value even when the difference and the engine load are the same as the difference and the engine load in the period other than the transition period.

3. The engine cooling device according to claim 1, wherein the diagnosis device is configured to diagnose, during a period until an opening condition of the thermostat is satisfied, the thermostat as abnormal in a case where determination that the rise rate of the outlet water temperature is equal to or lower than the determination value is made at least a predetermined number of times.

4. The engine cooling device according to claim 1, wherein the warm-up heat exchanger is a heater core configured to exchange heat between air blown into a vehicle cabin and the engine coolant.

5. The engine cooling device according to claim 1, wherein the warm-up heat exchanger is a water-to-water heat exchanger configured to exchange heat between a battery coolant that is used for adjusting a temperature of a battery and the engine coolant.

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