Engine cooling system

Abstract

To improve the accuracy of thermostat abnormality diagnosis. [Solution] An electronic control unit 32, which diagnoses abnormalities in the thermostat 19 that opens and closes the radiator water passage 15 based on a comparison of the rate of rise of the outlet water temperature of the engine 10's water jacket 11 with a normal / abnormal determination value, is configured to perform abnormality diagnosis of the thermostat 19 by setting a smaller value for the normal / abnormal determination value than in other periods during the transition period from the start of engine coolant flow from the first heating water passage 16 equipped with a heater core 23 or the second heating water passage 17 equipped with a water-water heat exchanger 26 to the water jacket 11 until the difference between the heater inlet water temperature and the outlet water temperature falls below the transition determination value, using a switching valve 18.

Description

[[Technical Field]]

[0001] The present invention relates to an engine cooling device. [[Background Art]]

[0002] As a cooling device applied to on-vehicle or other engines, there is a water-cooled device including a circulation circuit for engine cooling water configured such that after engine cooling water, which has passed through the interior of the engine and recovered heat, is cooled by a radiator, the engine cooling water is returned to the interior of the engine. A thermostat is provided in the engine cooling water circulation circuit. The thermostat is configured to stop water flow through the radiator by closing the valve while the engine is cold, and start water flow through the radiator by opening the valve when the engine warms up.

[0003] Also, as disclosed in Patent Document 1, there is also known an engine cooling device configured to use heat recovered from an engine by engine cooling water for heating a vehicle compartment and raising the temperature of a battery. This 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 perform heat exchange between air blown into the vehicle compartment and engine cooling water. The water-to-water heat exchanger is a heat exchanger configured to perform heat exchange between battery cooling water circulated through the interior of a battery and engine cooling water. The switching valve is a valve that switches between a state in which the flow of engine cooling water to the heater core and the water-to-water heat exchanger is prohibited and a state in which said flow is permitted. [[Prior Art Documents]] [[Patent Documents]]

[0004] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2024-113860 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0005] It is conceivable to diagnose the presence or absence of thermostat abnormalities, such as stuck open, based on changes in engine coolant temperature. In the case of an engine cooling system like the one described in Patent Document 1, there is a possibility that water flow to the heater core and water-water heat exchanger will start during the thermostat abnormality diagnosis. If cold engine coolant is stagnating inside the heater core and water-water heat exchanger before water flow starts, this cold engine coolant will flow into the engine after water flow starts. As a result, the detection temperature of the engine coolant used to diagnose the presence or absence of thermostat abnormalities may temporarily decrease, potentially worsening the diagnostic accuracy. [Means for solving the problem]

[0006] An engine cooling system that solves the above problems comprises, in parallel, a radiator water channel that passes through a radiator, a heating water channel equipped with a heating heat exchanger for heating other fluids with the heat of the engine cooling water, and a bypass water channel that allows the engine cooling water to flow around the radiator and the heating heat exchanger, as a flow path for engine cooling water that returns from the outlet of the water jacket inside the engine to the inlet of the water jacket, and a thermostat that opens and closes the radiator water channel, and a switching valve that switches between a state in which the inflow of the engine cooling water from the heating water channel to the water jacket is prohibited and a state in which it is permitted. The engine cooling system includes a diagnostic device that performs an abnormality diagnosis of the thermostat based on a comparison between the rate of rise of the outlet water temperature, which is the temperature of the engine coolant flowing out of the water jacket, and a determination value. The diagnostic device is configured to perform the abnormality diagnosis by setting the determination value to a smaller value than that for periods other than the transition period during the transition period from when the switching valve switches from a state in which the inflow of the engine coolant from the heating water passage to the water jacket is prohibited to a state in which it is permitted, until the difference between the temperature of the engine coolant flowing out of the heating heat exchanger and the outlet water temperature decreases to less than a predetermined value. [Effects of the Invention]

[0007] The above-mentioned engine cooling system has the effect of improving the accuracy of thermostat malfunction diagnosis. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the configuration of one embodiment of an engine cooling system. [Figure 2] Figure 2 is a flowchart of the abnormality diagnosis process performed in the engine cooling system shown in Figure 1. [Figure 3] Figure 3 is a flowchart of the judgment value setting process performed in the engine cooling system shown in Figure 1. [Figure 4] Figure 4 is a graph showing the relationship between the normal / abnormal judgment values ​​set in the judgment value setting process in Figure 3 and the intake air volume. [Figure 5] In the engine cooling system shown in Figure 1, Figure 5(A) is a time chart showing the transition of the opening and closing state of the heating water channel, Figure 5(B) shows the transition of the outlet water temperature, and Figure 5(C) shows the transition of the rate at which the outlet water temperature rises. [Modes for carrying out the invention]

[0009] Below, one embodiment of the engine cooling system will be described in detail with reference to Figures 1 to 5. <Engine cooling system configuration> First, the configuration of the engine cooling system of this embodiment will be described with reference to Figure 1. The engine cooling system of this embodiment is installed in a hybrid vehicle. In the figure, the direction of the coolant flow is indicated by arrows.

[0010] The engine 10 to which the engine cooling system of this embodiment is applied is provided with a water jacket 11 inside. During operation of the engine 10, engine coolant flows through the water jacket 11 from the inlet 12 to the outlet 13 in the figure. The engine cooling system includes an engine water pump 20 that pumps engine coolant towards the inlet 12 of the water jacket 11. In the case of the engine cooling system of this embodiment, an electric pump is used for the engine water pump 20. The engine cooling system of this embodiment has four parallel water channels: a bypass water channel 14, a radiator water channel 15, a first heating water channel 16, and a second heating water channel 17, which serve as the flow path for engine coolant returning from the outlet 13 to the inlet 12 of the water jacket 11. Each water channel (14 to 17) has a portion that is shared with one another.

[0011] The bypass water channel 14 is configured to return to the inlet 12 of the water jacket 11, passing sequentially from the outlet 13 of the water jacket 11 through the thermostat 19 and the engine water pump 20. The radiator water channel 15 is configured to return to the inlet 12 of the water jacket 11, passing sequentially from the outlet 13 of the water jacket 11 through the radiator 21, the reservoir tank 22, the thermostat 19 and the engine water pump 20. 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 channel 15 according to the temperature of the incoming engine coolant. Specifically, the thermostat 19 is configured to close the radiator water channel 15 when the engine coolant temperature is below the set temperature, and to open the radiator water channel 15 when the engine coolant temperature is above the set temperature. In this context, the state where the radiator water passage 15 is open indicates that engine coolant is flowing through the radiator water passage 15. Conversely, the state where the radiator water passage 15 is closed indicates that the flow of engine coolant through the radiator water passage 15 is blocked.

[0012] The first heating water channel 16 is configured to return to the inlet 12 of the water jacket 11, passing sequentially from the outlet 13 of the water jacket 11 through the switching valve 18, heater core 23, heater water pump 24, electric heater 25, and engine water pump 20. The switching valve 18 is a valve for changing the flow rate distribution of engine coolant in each water channel, and its details will be described later. The heater core 23 is a heat exchanger that exchanges heat between the air blown into the passenger compartment and the engine coolant, and is used to warm the air blown in with the heat of the engine coolant when heating the passenger compartment. The heater water pump 24 is an electrically operated pump. The electric heater 25 generates heat in response to the power supply and heats the engine coolant.

[0013] The second heating water channel 17 is configured to return to the inlet 12 of the water jacket 11, passing sequentially from the outlet 13 of the water jacket 11 through the switching valve 18, water-water heat exchanger 26, heater water pump 24, electric heater 25, and engine water pump 20. The water-water heat exchanger 26 is a heat exchanger that performs heat exchange between the battery coolant and the engine coolant. The battery coolant is the coolant circulated in the battery water channel 28 and is used to regulate the temperature of the battery 27. The water-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 system of this embodiment, the heater core 23 and the water-water heat exchanger 26 each correspond to heating heat exchangers that use the heat of the engine coolant to heat other fluids. In this embodiment of the engine cooling system, the bypass waterway 14 is configured as a waterway that allows engine cooling water to flow, bypassing the radiator 21 and the heat exchanger for heating (heater core 23, water-water heat exchanger 26).

[0014] The aforementioned switching valve 18 distributes the flow rate of engine coolant from the outlet 13 of the water jacket 11 to the first heating water channel 16 and the second heating water channel 17. This switching valve 18 forms the following four states (A1) to (A4). State (A1) is a state in which the flow of engine coolant from the outlet 13 of the water jacket 11 to both the first heating water channel 16 and the second heating water channel 17 is blocked. State (A2) is a state in which engine coolant flows from the outlet 13 of the water jacket 11 to only the first heating water channel 16 of the two heating water channels 17. State (A3) is a state in which engine coolant flows from the outlet 13 of the water jacket 11 to only the second heating water channel 17 of the two heating water channels 16 and 17. Condition (A4) is a state in which engine coolant flows from the outlet 13 of the water jacket 11 to both the first heating water passage 16 and the second heating water passage 17.

[0015] Furthermore, the engine cooling system of this embodiment is provided with an outlet water temperature sensor 30 and a heater inlet water temperature sensor 31. The outlet water temperature sensor 30 is a sensor that detects the outlet water temperature, which is the temperature of the engine coolant flowing out from the outlet 13 of the water jacket 11. The heater inlet water temperature sensor 31 is a sensor that detects the heater inlet water temperature, which is the temperature of the engine coolant flowing in the portion of the first heating channel 16 and the second heating channel 17 that is downstream of the heater water pump 24 and upstream of the electric heater 25. When engine coolant is flowing in the first heating channel 16 and the second heating channel 17, the heater inlet water temperature corresponds to the temperature of the engine coolant flowing out from the heater core 23 and the water-water heat exchanger 26.

[0016] Furthermore, the engine cooling system of this embodiment includes a return water channel 29 that connects the portions of the first heating water channel 16 and the second heating water channel 17 downstream of the electric heater 25 to the switching valve 18. Even in the above state (A1), the switching valve 18 connects the return water channel 29 to at least one of the first heating water channel 16 and the second heating water channel 17, allowing engine cooling water to flow through the first heating water channel 16 and the second heating water channel 17. In this state, by operating the heater water pump 24 and the electric heater 25, it is possible to heat the passenger compartment and raise the temperature of the battery 27 even when the engine 10 is stopped. The engine cooling system of this embodiment is configured to circulate engine cooling water through the return water channel 29 to the first heating water channel 16 or the second heating water channel 17 when heating the passenger compartment or raising the temperature of the battery 27 is required during electric driving of the hybrid vehicle.

[0017] Furthermore, the engine cooling system of this embodiment includes an electronic control unit 32. The electronic control unit 32 comprises a processing unit 33 and a storage device 34. The storage device 34 has a program and data for controlling the engine cooling system pre-stored in it. The electronic control unit 32 is configured to perform various processes for controlling the engine cooling system by having the processing unit 33 read and execute the program from the storage device 34. The electronic control unit 32 receives detection signals X1 and X2 from the outlet water temperature sensor 30 and the heater inlet water temperature sensor 31. The electronic control unit 32 also receives detection signals X3 to X5 from the airflow meter 35 which detects the amount of intake air of the engine 10, the intake air temperature sensor 36 which detects the intake air temperature of the engine 10, and the vehicle speed sensor 37 which detects the vehicle speed of the hybrid vehicle. Based on the detection signals from these sensors, the processing unit 33 calculates the respective operating amounts for the switching valve 18, the engine water pump 20, the heater water pump 24, and the electric heater 25. The electronic control unit 32 controls the engine cooling system by outputting command signals X6 to X9 corresponding to the operation amount calculated by the processing unit 33 to the switching valve 18, the engine water pump 20, the heater water pump 24, and the electric heater 25.

[0018] <Abnormality Diagnosis of Thermostat 19> The electronic control unit 32 performs abnormality diagnosis on the thermostat 19 as part of the control of the engine cooling system. Specifically, the electronic control unit 32 performs abnormality diagnosis on the thermostat 19 based on a comparison result between the rate of increase in outlet water temperature when the valve opening condition of the thermostat 19 is not satisfied and a normal / abnormal determination value. In 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 system of the present embodiment, the electronic control unit 32 that performs such abnormality diagnosis corresponds to a diagnosis device.

[0019] Fig. 2 shows a flowchart of the abnormality diagnosis process for the thermostat 19. The electronic control unit 32 starts the process shown in Fig. 2 when the engine 10 is cold-started. Note that "S" appended before reference signs in the figure represents a step.

[0020] When the electronic control unit 32 starts the process shown in FIG. 2, it determines whether a diagnostic condition is satisfied in step 100. If the electronic control unit 32 determines that the diagnostic condition is not satisfied (NO), it executes the determination of step 100 again after a predetermined control cycle elapses. On the other hand, if the electronic control unit 32 determines that the diagnostic condition is satisfied (YES), it advances the process to step 102. In the present embodiment, the diagnostic condition is set to be satisfied when all of the following requirements (B1) to (B5) are satisfied. Requirement (B1) is that an outlet water temperature at the time of starting the engine 10 is equal to or higher than a predetermined temperature. Requirement (B2) is that an intake air temperature at the time of starting the engine 10 is equal to or higher than a predetermined temperature. Requirement (B3) is that the engine water pump 20 is in operation. Requirement (B4) is that a vehicle speed of the hybrid vehicle is within a predetermined range. Requirement (B5) is that the number of executions of the abnormality diagnosis process in the current trip is equal to or less than a predetermined number. In the present embodiment, the electronic control unit 32 performs abnormality diagnosis of the thermostat 19 based on the rising speed of the outlet water temperature. However, in an extremely low-temperature environment, heat is absorbed by outside air, which slows down the rise of the outlet water temperature, so accurate abnormality diagnosis may not be performed. Requirements (B1) and (B2) are set to avoid such misdiagnosis in an extremely low-temperature environment. Further, if the flow rate of engine cooling water in the water jacket 11 and the heat generation amount of the engine 10 vary greatly, the accuracy of abnormality diagnosis based on the rising speed of the outlet water temperature cannot be ensured. Requirements (B3) and (B4) are set to avoid deterioration of diagnostic accuracy caused by such variations in the flow rate of engine cooling water and the heat generation amount. Requirement (B5) is set to prevent the abnormality diagnosis from being repeated more than necessary during the same trip.

[0021] When the process advances to step 102, the electronic control unit 32 acquires the rising speed of the outlet water temperature. Specifically, the electronic control unit 32 acquires the rising speed by obtaining the increase amount of the outlet water temperature in a predetermined time based on the detection signal X1 from the outlet water temperature sensor 30.

[0022] Next, in step 104, the electronic control unit 32 performs a judgment value setting process. In the judgment value setting process, two judgment values ​​are set: an abnormal judgment value and a normal judgment value. Details of the judgment value setting process will be described later. In this process, the normal judgment value is set to a value greater than the abnormal judgment value. Then, in the following step 106, the electronic control unit 32 determines whether the rate of rise of the outlet water temperature is less than or equal to the abnormal judgment value. If the electronic control unit 32 determines that the rate of rise is less than or equal to the abnormal judgment value (YES), it proceeds to step 108; if it determines that the rate of rise exceeds the abnormal judgment value (NO), it proceeds to step 118.

[0023] If the process proceeds to step 108, the electronic control unit 32 increments the abnormality counter in step 108. The value of the abnormality counter is reset to "0" at the start of the abnormality diagnosis process. The value of the abnormality counter represents the number of times in the current abnormality diagnosis process that the rate of increase was determined to be less than or equal to the abnormality determination value. Next, in step 110, the electronic control unit 32 determines whether the value of the abnormality counter is greater than or equal to the predetermined abnormality determination value. If the electronic control unit 32 determines that the value of the abnormality counter is greater than or equal to the abnormality determination value (YES), in step 112, the electronic control unit 32 confirms the diagnosis result that there is an abnormality in the thermostat 19 and then terminates the abnormality diagnosis process. On the other hand, if the electronic control unit 32 determines that the value of the abnormality counter is less than the abnormality determination value (NO), the electronic control unit 32 proceeds to step 114.

[0024] In step 114, the electronic control unit 32 determines whether the outlet water temperature is above a predetermined diagnostic completion temperature. The diagnostic completion temperature is set to a temperature slightly lower than the set temperature of the thermostat 19. If the electronic control unit 32 determines that the outlet water temperature is above the diagnostic completion temperature (YES), in step 116, it confirms that there is no abnormality in the thermostat 19, or in other words, that the thermostat 19 is normal, and then terminates the abnormality diagnosis process. That is, in this embodiment, if the value of the abnormality counter does not exceed the abnormality confirmation judgment value before the conditions for opening the valve of the thermostat 19 are met, the thermostat 19 is diagnosed as normal. On the other hand, if the electronic control unit 32 determines that the outlet water temperature is below the diagnostic completion temperature (S114:NO), it returns to step 102 after a predetermined control cycle.

[0025] On the other hand, if the electronic control unit 32 determines that the rate of rise is below the abnormal threshold (S106: NO) and proceeds to step 118, it determines in step 118 whether the rate of rise of the outlet water temperature is equal to or greater than the normal threshold. If the electronic control unit 32 determines that the rate of rise is equal to or greater than the normal threshold (YES), it proceeds to step 120; if it determines that the rate of rise is below the normal threshold (NO), it proceeds to step 114 as described above.

[0026] If the process proceeds to step 120, the electronic control unit 32 increments the normal counter in step 120. The value of the normal counter, like the abnormal counter, is reset to "0" at the start of the abnormal diagnosis process. The value of the normal counter represents the number of times in the current abnormal diagnosis process that the rate of increase was determined to be equal to or greater than the normal judgment value. Next, in step 122, the electronic control unit 32 determines whether the value of the normal counter is equal to or greater than the predetermined normal confirmation judgment value. If the electronic control unit 32 determines that the value of the normal counter is equal to or greater than the normal confirmation judgment value (YES), it confirms the diagnosis result that the thermostat 19 is normal in step 116 above, and then terminates the abnormal diagnosis process. On the other hand, if the electronic control unit 32 determines that the value of the normal counter is less than the normal confirmation judgment value (NO), it proceeds to step 114 above.

[0027] In the abnormality diagnosis process described above, after the diagnostic conditions are met, the electronic control unit 32 repeatedly acquires the rate of rise of the outlet water temperature and compares the acquired rate of rise with the abnormality judgment value and the normal judgment value at predetermined control cycles. When the number of times the electronic control unit 32 determines that the rate of rise of the outlet water temperature is below the abnormality judgment value reaches the abnormality confirmation judgment value, it diagnoses that there is an abnormality in the thermostat 19. On the other hand, when the number of times the electronic control unit 32 determines that the rate of rise of the outlet water temperature is above the normal judgment value reaches the normal confirmation judgment value, or when an abnormality is not diagnosed before the outlet water temperature reaches the diagnosis end temperature, it diagnoses that the thermostat 19 is normal.

[0028] <Setting the judgment value> Next, with reference to Figure 3, the details of the judgment value setting process performed by the electronic control unit 32 in step 104 of Figure 2 will be explained. Figure 3 shows the processing procedure of the electronic control unit 32 in the judgment value setting process.

[0029] In the judgment value setting process, the electronic control unit 32 first calculates the temperature difference between the outlet water temperature and the heater inlet water temperature in step 200. Specifically, the electronic control unit 32 subtracts the heater inlet water temperature from the outlet water temperature and calculates the resulting subtracted value as the temperature difference value.

[0030] In the next step 201, the electronic control unit 32 determines whether or not it is in a transition period. If it determines that it is in a transition period (YES), the electronic control unit 32 proceeds to step 210; if it determines that it is not in a transition period (NO), it proceeds to step 202. As will be described later, in this process the electronic control unit 32 determines the start and end of the transition period, and the period from when it is determined that the transition period has started until when it is determined that it has ended is the transition period.

[0031] If the process proceeds to step 202, the electronic control unit 32 determines whether or not water has started flowing through the heater core 23 or the water-water heat exchanger 26. Specifically, the electronic control unit 32 determines that the switch from state (C1) to state (C2) is the start of water flowing through the heater core 23 or the water-water heat exchanger 26. State (C1) is a state in which the inflow of engine coolant into the water jacket 11 from both the first heating water channel 16 and the second heating water channel 17 is prohibited. State (C2) is a state in which the inflow of engine coolant into the water jacket 11 from at least one of the first heating water channel 16 and the second heating water channel 17 is permitted. The switch from state (C1) to state (C2) is performed by the switching valve 18. In this embodiment, the electronic control unit 32 makes the determination in step 202 based on the amount of operation commanded to the switching valve 18.

[0032] If the electronic control unit 32 determines that water has not started flowing through the heater core 23 or the water-water heat exchanger 26 (NO), it proceeds to step 204. In step 204, the electronic control unit 32 sets the values ​​for the normal judgment value and the abnormal judgment value using the normal map pre-stored in the memory device 34, and then terminates the judgment value setting process. After terminating the judgment value setting process, the electronic control unit 32 resumes the abnormality diagnosis process from step 106 in Figure 2.

[0033] On the other hand, if the electronic control unit 32 determines in step 202 that water has started flowing through the heater core 23 or the water-water heat exchanger 26 (YES), then in step 203 it determines whether the water temperature difference is greater than or equal to a predetermined transition determination value. If the electronic control unit 32 determines that the water temperature difference is less than the transition determination value (NO), it proceeds to step 204 described above. On the other hand, if the electronic control unit 32 determines that the water temperature difference is greater than or equal to the transition determination value (YES), then in step 206 it determines that the transition period has started. Then, in step 208, the electronic control unit 32 sets the values ​​for the normal determination value and the abnormal determination value using the transition time map pre-stored in the memory device 34, and then terminates the current determination value setting process.

[0034] Furthermore, if the electronic control unit 32 determines in step 200 that it is in a transition period and proceeds to step 210, it determines in step 210 whether the water temperature difference is less than the transition determination value. If the electronic control unit 32 determines that the water temperature difference is less than the transition determination value (YES), it proceeds to step 212; if it determines that the water temperature difference is greater than or equal to the transition determination value (NO), it proceeds to step 208 as described above. If the electronic control unit 32 proceeds to step 212, it determines in step 212 that the transition period has ended, and then proceeds to step 204 as described above.

[0035] In the judgment value setting process described above, the electronic control unit 32 determines that the period during which the difference between the outlet water temperature and the heater inlet water temperature is greater than or equal to the transition judgment value after switching from state (C1) to state (C2) using the switching valve 18 is the transition period. The electronic control unit 32 then sets the normal judgment value and the abnormal judgment value using the transition map during the transition period and the normal map during periods other than the transition period.

[0036] The normal mode map and the transition mode map are configured as functions that take the intake air volume of the engine 10 and the difference in outlet water temperature relative to the ambient temperature as arguments, and return a normal judgment value and an abnormal judgment value, respectively. The electronic control unit 32 acquires the intake air volume of the engine 10 based on the detection signal X3 of the airflow meter 35. The electronic control unit 32 also acquires the ambient temperature based on the detection signal X4 of the intake air temperature sensor 36 when the engine 10 is started.

[0037] As the engine coolant passes through the water jacket 11, it absorbs heat from the engine 10. When the engine 10 is under heavy load, the amount of heat generated by the engine 10 increases, and therefore the amount of heat absorbed by the engine coolant from the engine 10 also increases. As a result, the rate at which the outlet water temperature rises is higher when the engine load is high than when it is low. The amount of intake air for the engine 10 increases with increasing engine load. Furthermore, after the engine coolant flows out from the outlet 13 of the water jacket 11, it loses heat to the outside air as it returns to the inlet 12 of the water jacket 11 through the bypass waterway 14, etc. The amount of heat lost to the engine coolant by the outside air increases as the difference between the outlet water temperature and the ambient temperature increases. As a result, the rate at which the outlet water temperature rises is lower as the difference between the outlet water temperature and the ambient temperature increases.

[0038] On the other hand, if the thermostat 19 is open before the valve opening condition is met, the engine coolant that has passed through the radiator water passage 15 flows into the water jacket 11, and the rate at which the outlet water temperature rises slows down due to cooling by the radiator 21.

[0039] The relationship between the intake air volume, the difference between the ambient temperature and the outlet water temperature, and the range of possible values ​​for the rate of increase of the outlet water temperature, both when the thermostat 19 is open and when it is closed, can be determined in advance through experiments or simulations. In the following explanation, the lower limit of the range of possible values ​​for the rate of increase of the outlet water temperature when the thermostat 19 is closed will be referred to as the normal rate of increase, and the upper limit of the range of possible values ​​for the rate of increase of the outlet water temperature when the thermostat 19 is open will be referred to as the abnormal rate of increase. The normal map is configured to return a value slightly larger than the normal rate of increase as the normal judgment value, and a value slightly smaller than the abnormal rate of increase as the abnormal judgment value. Furthermore, the transition map is configured to return values ​​smaller than the normal judgment value and abnormal judgment value of the normal map when the intake air volume and the difference between the ambient temperature and the outlet water temperature are the same as the normal judgment value and abnormal judgment value.

[0040] Figure 4 shows the relationship between the normal / abnormal judgment values ​​and the intake air volume for both the normal and transition maps, assuming a constant difference between the ambient temperature and the outlet water temperature. In both maps, the normal / abnormal judgment values ​​are set such that they are larger when the intake air volume is high than when it is low, and the normal judgment value is larger than the abnormal judgment value. Furthermore, if the intake air volume is the same, the normal / abnormal judgment values ​​in the transition map are set to be smaller than those in the normal map.

[0041] <Effect of the Embodiment> Immediately after the engine 10 is cold-started, the flow of engine coolant in the radiator water passage 15 is blocked by the thermostat 19. After the engine 10 starts, the outlet water temperature gradually rises due to heat absorption from the engine 10. When the water temperature of the engine coolant flowing into the thermostat 19 reaches the set temperature, the thermostat 19 opens and water flow to the radiator water passage 15 begins. In the engine cooling system of this embodiment, the electronic control unit 32 performs an abnormality diagnosis process for the thermostat 19 based on the comparison result between the rate of rise of the outlet water temperature and the normal / abnormal judgment value during the period from when the engine 10 starts until the conditions for opening the thermostat 19 are met.

[0042] Figure 5(A) shows the changes in the open / closed state of the heating water channel during the abnormality diagnosis process, Figure 5(B) shows the changes in the outlet water temperature and heater inlet water temperature during the abnormality diagnosis process, and Figure 5(C) shows the changes in the rate of increase of the outlet water temperature during the abnormality diagnosis process. Here, the open state of the heating water channel refers to the state in which engine coolant flowing out from the water jacket 11 flows through the switching valve 18 into at least one of the first heating water channel 16 and the second heating water channel 17. Here, the closed state of the heating water channel refers to the state in which the inflow of engine coolant flowing out from the water jacket 11 into both the first heating water channel 16 and the second heating water channel 17 is blocked by the switching valve 18.

[0043] First, let's explain the case where the heating water channel is held closed, as shown by the solid line in Figure 5(A). In Figure 5(B), the change in outlet water temperature is shown by the solid line, and the change in heater inlet water temperature is shown by the dashed line. Also, in Figure 5(C), the change in the rate of increase of the outlet water temperature is shown by the solid line. In this case, the engine coolant circulates between the water jacket 11 and the bypass water channel 14 until the thermostat 19 opens. Therefore, the outlet water temperature rises smoothly. If the thermostat 19 is stuck open in this case, the engine coolant is cooled by the radiator 21, so the rate of increase of the outlet water temperature is lower compared to when the thermostat 19 is operating normally. The electronic control unit 32 diagnoses that there is a problem with the thermostat 19 when it has determined that the rate of increase of the outlet water temperature is below the abnormality threshold a predetermined number of times. Furthermore, since no engine coolant flows through the first heating water channel 16 and the second heating water channel 17 at this time, the heater inlet water temperature hardly changes from the time the engine 10 is started.

[0044] Next, as shown by the dashed line in Figure 5(A), we will explain the case where the heating water channel is opened by the switching valve 18 at time t1 during abnormality diagnosis due to a request for heating the passenger compartment or a request for raising the temperature of the battery 27. In Figure 5(B), the change in outlet water temperature is shown by the dashed line, and the change in heater inlet water temperature is shown by the dashed line. Also, in Figure 5(C), the change in the rate of increase of the outlet water temperature is shown by the dashed line. Before time t1, cold engine coolant is stagnant in the heating water channel. When water flow to the heating water channel begins at time t1, the cold engine coolant that was stagnant in the heating water channel flows into the water jacket 11. Therefore, the rise in outlet water temperature temporarily stagnates after time t1. In the following explanation, the phenomenon in which the rise in outlet water temperature temporarily stagnates after water flow to the first heating water channel 16 or the second heating water channel 17 begins will be referred to as a water temperature drop. When a drop in water temperature occurs, even if thermostat 19 is functioning normally, the rate at which the outlet water temperature rises will be slower. Therefore, if the same diagnostic procedures as before are followed, there is a possibility of mistakenly diagnosing a problem with thermostat 19.

[0045] In contrast, the electronic control unit 32 in the engine cooling system of this embodiment determines the period during which the difference between the outlet water temperature and the heater inlet water temperature is greater than or equal to a transition determination value, after the start of water flow in the first heating water passage 16 or the second heating water passage 17 by the switching valve 18, is a transition period. The electronic control unit 32 then sets normal determination values ​​and abnormal determination values ​​for the transition period to be smaller than those for periods other than the transition period.

[0046] After the water flow begins, engine coolant, warmed by the heat of the engine 10 after passing through the water jacket 11, flows into the first heating channel 16 or the second heating channel 17. As a result, the heater inlet water temperature gradually rises from time t1 onward, and the difference between the outlet water temperature and the heater inlet water temperature also decreases. In the case of Figure 5, at time t2, the difference between the outlet water temperature and the heater inlet water temperature has decreased to less than the transition judgment value. At this time t2, the electronic control unit 32 determines that the transition period has ended and returns the normal judgment value and abnormal judgment value to the values ​​before time t1.

[0047] In this way, the electronic control unit 32 performs a diagnostic check of the thermostat 19 by setting the normal judgment value and abnormal judgment value to smaller than usual during the transition period when the rate of increase of the outlet water temperature temporarily decreases. Therefore, even if the rate of increase of the outlet water temperature temporarily decreases after the start of water flow to the heating channel, it becomes less likely that the thermostat 19 will be misdiagnosed as having an abnormality. In this embodiment, the amount of decrease in the rate of increase of the outlet temperature after the start of water flow to the heating channel is determined in advance by experiments or simulations. Then, the transition map is set to return values ​​for the normal judgment value and abnormal judgment value that are smaller than those in the normal map by the amount of that decrease.

[0048] Furthermore, since the engine coolant is also cooled by the heater core 23 and the water-water heat exchanger 26, the rate of increase in outlet water temperature after the transition period will be lower than when water is not flowing through the heating water channel. However, the heater core 23 and the water-water heat exchanger 26 have a smaller volume than the radiator 21, and therefore have a smaller impact on the rate of increase in outlet water temperature than the radiator 21. For this reason, after the transition period, it is possible to perform a malfunction diagnosis of the thermostat 19, just as before the start of water flow.

[0049] <Effects of the Embodiment> The engine cooling system of this embodiment provides the following effects. (1) The electronic control unit 32 determines the period from when water is started to flow into the first heating water channel 16 or the second heating water channel 17 by the switching valve 18 until the difference between the heater inlet water temperature and the outlet water temperature decreases to a predetermined value (transition judgment value) or less as the transition period. The electronic control unit 32 then sets a value smaller than that for periods other than the transition period as the normal / abnormal judgment value and performs abnormal diagnosis of the thermostat 19. As a result, even if a drop in water temperature occurs when water is started to flow into the first heating water channel 16 or the second heating water channel 17, it becomes less likely that the thermostat 19 will be mistakenly diagnosed as having an abnormality. Thus, the engine cooling system of this embodiment has the effect of improving the accuracy of abnormal diagnosis of the thermostat 19.

[0050] (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, it can accurately determine the period during which a water temperature drop occurs as the transition period.

[0051] (3) The electronic control unit 32 calculates a normal / abnormal judgment value based on the difference in outlet water temperature relative to the ambient temperature and the intake air volume, which is an indicator value of the engine load. Furthermore, the electronic control unit 32 is configured to calculate a normal / abnormal judgment value that is smaller than that for periods other than the transition period, even if the above difference and engine load are the same. The rate at which the outlet water temperature rises changes not only depending on whether there is a malfunction in the thermostat 19, but also on the difference in outlet water temperature relative to the ambient temperature and the engine load. Therefore, by reflecting these effects in the normal / abnormal judgment value, the diagnostic accuracy of the thermostat 19 can be further improved.

[0052] (4) The electronic control unit 32 repeatedly determines whether the rate of increase of the outlet water temperature is below an abnormality threshold during the period until the conditions for opening the thermostat 19 are met. The electronic control unit 32 is configured to diagnose a malfunction in the thermostat 19 if it has determined that the rate of increase of the outlet water temperature is below an abnormality threshold a predetermined number of times or more. The rate of increase of the outlet water temperature changes due to various factors, so even if the thermostat 19 is functioning normally, the rate of increase may temporarily drop below an abnormality threshold. Therefore, the diagnostic accuracy can be improved by diagnosing a malfunction in the thermostat 19 based on multiple determinations that the rate of increase is below an abnormality threshold.

[0053] <Other Embodiments> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0054] The diagnostic criteria used to determine whether the condition is met in step 100 of Figure 2 may be modified as appropriate. • In the abnormality diagnosis process, it is also possible to diagnose whether there is an abnormality due to the thermostat 19 being stuck closed after the valve opening condition is met. When the thermostat 19 is stuck closed, the rate of increase in the outlet water temperature after the valve opening condition is met is lower compared to when the thermostat 19 is normally open. Therefore, by changing the content of the abnormality diagnosis process as follows, it is possible to diagnose whether there is an abnormality due to the thermostat 19 being stuck closed after the valve opening condition is met. First, in the judgment value setting process in Figure 3, both judgment values ​​are set so that the normal judgment value is a smaller value than the abnormal judgment value. Then, in step 106 in Figure 2, it is determined whether the rate of increase is greater than or equal to the abnormal judgment value, and in step 118 in Figure 2, it is determined whether the rate of increase is less than or equal to the normal judgment value. Even in such cases, the accuracy of abnormality diagnosis can be improved by setting the normal / abnormal judgment values ​​so that they are smaller during the transition period than during periods other than the transition period.

[0055] The engine cooling system of the above embodiment included a first heating water channel 16 equipped with a heater core 23 and a second heating water channel 17 equipped with a water-water heat exchanger 26, which served as heating water channels equipped with a heating heat exchanger. The system may also be configured to include only one of the first heating water channel 16 and the second heating water channel 17 as the heating water channel. Furthermore, the system may be configured to include a water channel equipped with a heat exchanger separate from the heater core 23 and the water-water heat exchanger 26, as long as the heat exchanger is used to heat another fluid using the heat of the engine cooling water.

[0056] In the above embodiment, the normal / abnormal determination value was calculated based on the engine load and the difference in outlet water temperature relative to the ambient temperature, but it may be calculated using only one of these. Alternatively, other parameters that affect the rate of increase in outlet water temperature may be used to calculate the normal / abnormal determination value. Furthermore, each of the normal / abnormal determination values ​​may have only two values: a value for the transition period and a value for the other periods.

[0057] In the above embodiment, the temperature of the engine coolant flowing out of the heating heat exchanger (heater inlet water temperature) was detected in the first heating water channel 16 and the second heating water channel 17, downstream of the heater water pump 24 and upstream of the electric heater 25. This temperature detection location may be changed as appropriate. 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 of the heating heat exchanger.

[0058] • The abnormality diagnosis process may be performed using only one of the normal judgment values ​​or abnormal judgment values. For example, if only the normal judgment value is used, the thermostat 19 will be diagnosed as abnormal if a normal diagnosis result cannot be confirmed.

[0059] In the above embodiment, the intake air volume was used as an indicator value for engine load to calculate the normal / abnormal determination value, but other parameters such as intake air charge rate and fuel injection amount may also be used as indicator values ​​for engine load.

[0060] A mechanical pump that operates using power from the engine 10 may be used as the water pump 20 for the engine. The engine cooling system of the above embodiment may be applied to a conventional engine vehicle that is not a hybrid vehicle. [Explanation of symbols]

[0061] 10...Engine, 11...Water jacket, 12...Inlet, 13...Outlet, 14...Bypass water channel, 15...Radiator water channel, 16...First heating water channel, 17...Second heating water channel, 18...Switching valve, 19...Thermostat, 20...Engine water pump, 21...Radiator, 22...Reservoir tank, 23...Heater core (heat exchanger for heating), 24...Heater water pump, 25...Electric heater, 26...Water-water heat exchanger (heat exchanger for heating), 27...Battery, 28...Battery water channel, 29...Recirculation water channel, 30...Outlet water temperature sensor, 31...Heater inlet water temperature sensor, 32...Electronic control unit (diagnostic device), 33...Calculation processing unit, 34...Memory device, 35...Airflow meter, 36...Intake air temperature sensor, 37...Vehicle speed sensor.

Claims

1. An engine cooling system comprising: a radiator water channel passing through a radiator as a flow path for engine coolant that flows from the outlet of a water jacket located inside the engine back to the inlet of the water jacket; a heating water channel equipped with a heating heat exchanger for heating other fluids using the heat of the engine coolant; and a bypass water channel that allows the engine coolant to flow around the radiator and the heating heat exchanger, all arranged in parallel; a thermostat for opening and closing the radiator water channel; and a switching valve for switching between a state in which the inflow of engine coolant from the heating water channel to the water jacket is prohibited and a state in which it is permitted; The system includes a diagnostic device that diagnoses abnormalities in the thermostat based on a comparison between the rate of increase of the outlet water temperature, which is the temperature of the engine coolant flowing out of the water jacket, and a determination value. Furthermore, the diagnostic device is configured to perform the abnormality diagnosis by setting the determination value to a smaller value than the value for the period other than the transition period during the transition period from when the switching valve switches the state in which the engine coolant flows from the heating water channel to the water jacket is prohibited to when it is permitted, until the difference between the temperature of the engine coolant flowing out of the heating heat exchanger and the outlet water temperature decreases to less than a predetermined value. Engine cooling system.

2. The engine cooling device according to claim 1, wherein the diagnostic device calculates the determination value based on the difference in outlet water temperature with respect to the ambient temperature and the engine load, and is configured to calculate a value smaller than that for periods other than the transition period as the determination value during the transition period, even if the difference and the engine load are the same.

3. The engine cooling device according to claim 1, wherein the diagnostic device is configured to diagnose an abnormality in the thermostat if it has determined a specified number of times or more that the rate of rise of the outlet water temperature is less than or equal to the determination value during the period until the conditions for opening the thermostat are met.

4. The engine cooling device according to claim 1, wherein the heat exchanger for raising the temperature is a heater core that performs heat exchange between the air supplied to the passenger compartment and the engine coolant.

5. The engine cooling device according to claim 1, wherein the heat exchanger for raising the temperature is a water-water heat exchanger that performs heat exchange between battery cooling water used for temperature control of the battery and the engine cooling water.

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