Cooling system for internal combustion engines

Abstract

To provide a cooling device for an internal combustion engine capable of improving accuracy of an abnormality diagnosis of a thermostat valve.SOLUTION: A cooling device 10a for an internal combustion engine includes: a radiator 40 that discharges heat to outside by causing cooling water from a cooling water passage formed in the internal combustion engine to pass; a radiator circulation passage 50 for circulating the cooling water between the internal combustion engine and the radiator 40; a thermostat valve 70 that is opened in a predetermined condition to perform forced valve opening control for communicating the radiator circulation passage 50 with the cooling water passage; and a control section that performs abnormality diagnosis processing for diagnosing an abnormality of the thermostat valve 70. The control section prohibits the abnormality diagnosis processing from start of the forced valve opening control, and executes the abnormality diagnosis processing when estimating that a temperature difference between a temperature of the cooling water in the cooling water passage and a temperature of the cooling water in the radiator circulation passage 50 becomes a predetermined level or higher after the completion of the forced valve opening control.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a cooling device for an internal combustion engine, and more particularly to a cooling device for an internal combustion engine having a function of diagnosing an abnormality in a thermostat valve. [Background technology]

[0002] An internal combustion engine mounted on a vehicle such as an automobile is provided with a water-cooled cooling device that cools or warms the internal combustion engine by circulating coolant through a water jacket formed inside the internal combustion engine. Such a cooling device is provided with a thermostat valve that switches the coolant path. The thermostat valve is a control valve that opens and closes according to the temperature of the coolant, and maintains the temperature of the coolant at an appropriate temperature by adjusting the flow rate of the coolant flowing to the radiator. For example, Patent Document 1 is an example of a technology for diagnosing an abnormality in such a thermostat valve.

[0003] Patent Document 1 discloses the following cooling device for an internal combustion engine. The ECU of the engine cooling device performs a malfunction diagnosis of the thermostat valve based on the engine side coolant temperature detected by an engine side coolant temperature sensor and the radiator side coolant temperature detected by a radiator inlet side coolant temperature sensor. The thermostat valve performs forced valve opening control when the rise in coolant pressure reaches a forced valve opening pressure. If the rate of change of the radiator side coolant temperature is greater than the rate of change of the engine side coolant temperature, the ECU determines that the thermostat valve is performing forced valve opening control and does not perform a malfunction diagnosis of the thermostat valve. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-81566 A Summary of the Invention [Problem to be solved by the invention]

[0005] In such an internal combustion engine cooling system, when the temperature of the cooling water is relatively low, such as when the internal combustion engine is warming up immediately after starting, the thermostat valve is closed. When the thermostat valve is closed, the circulation of the cooling water to the radiator side is stopped, so that the internal combustion engine is warmed up quickly. In this way, when the thermostat valve is closed, no cooling water flows to the radiator side, so it is expected that the engine side cooling water temperature will be sufficiently higher than the radiator side cooling water temperature.

[0006] On the other hand, when a closed thermostat valve is opened by forced opening control during warming up of an internal combustion engine, the temperature difference between the radiator side cooling water temperature and the engine side cooling water temperature may become smaller due to the flow of cooling water to the radiator side.

[0007] However, in the technology described in Patent Document 1, the thermostat valve fault diagnosis is resumed immediately after the forced opening control by the thermostat valve is terminated, so if the radiator side cooling water temperature indicates a value close to the engine side cooling water temperature, there is a possibility that the thermostat valve may be erroneously diagnosed as having an abnormality (open fault) even though the thermostat valve is operating normally.

[0008] The present invention has been made to solve such problems, and has an object to provide a cooling device for an internal combustion engine that improves the accuracy of abnormality diagnosis of a thermostat valve. [Means for solving the problem]

[0009] A cooling device for an internal combustion engine according to one embodiment includes a radiator that passes cooling water from a cooling water passage formed inside the internal combustion engine to discharge heat to the outside, a radiator circulation passage for circulating the cooling water between the internal combustion engine and the radiator, a thermostat valve that is opened under predetermined conditions to perform forced opening control to connect the radiator circulation passage to the cooling water passage, and a control unit that performs abnormality diagnosis processing to diagnose abnormalities in the thermostat valve, and the control unit prohibits the abnormality diagnosis processing from the start of the forced valve opening control, and executes the abnormality diagnosis processing when it estimates that the temperature difference between the temperature of the cooling water in the cooling water passage and the temperature of the cooling water in the radiator circulation passage will be equal to or greater than a predetermined value after the forced valve opening control ends. Effect of the Invention

[0010] According to the present invention, it is possible to provide a cooling device for an internal combustion engine that improves the accuracy of abnormality diagnosis of a thermostat valve. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram illustrating a configuration of a cooling device according to a first embodiment. [Diagram 2] 4 is a time chart showing a time series change in coolant temperature after the engine is started. [Diagram 3] 5 is a time chart illustrating a time series change in the cooling water temperature accompanying the forced valve opening control. [Figure 4] 4 is a flowchart illustrating an abnormality diagnosis delay control routine executed by an ECU of the cooling device shown in FIG. [Diagram 5] FIG. 11 is a block diagram illustrating a configuration of a cooling device according to a second embodiment. [Figure 6] 6 is a flowchart illustrating an abnormality diagnosis delay control routine executed by an ECU of the cooling device shown in FIG. 5. [Figure 7] 7 is a flowchart illustrating the abnormality diagnosis delay control routine continued from FIG. 6. [Figure 8] 4 is a time chart illustrating time series changes of various parameters accompanying forced valve opening control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In order to clarify the description, the following description and drawings are appropriately simplified. What is shown in the drawings is only a part of the whole, and in reality, many other configurations that are not shown are included. Furthermore, in the following description, the same or equivalent elements are given the same reference numerals, and duplicated descriptions are omitted.

[0013] First, the configuration of an internal combustion engine cooling device (cooling device 10a) according to this embodiment will be described with reference to Fig. 1. In this embodiment, the cooling device 10a for cooling or warming up an engine 20 equivalent to an internal combustion engine mounted on a vehicle 100 will be described as an example. For example, the cooling device 10a can be applied to a vehicle equipped with a gasoline engine, an engine using alcohol fuel or gas fuel, and a vehicle equipped with a diesel engine. The cooling device 10a can also be applied to a hybrid vehicle equipped with a motor for running together with the engine 20.

[0014] Fig. 1 is a block diagram illustrating the configuration of a cooling device according to the first embodiment. Fig. 1 shows a main part of a vehicle 100 related to a cooling device 10a, and a black arrow indicates a flow direction of cooling water.

[0015] 1, the cooling device 10a includes a control unit (ECU 120), a radiator circulation passage 50, a bypass passage 60, a water pump 30, a radiator 40, and a thermostat valve 70. The cooling device 10a also includes an engine side coolant temperature sensor 80 and a radiator side coolant temperature sensor 90.

[0016] The cooling device 10a has an ECU (Electronic Control Unit) 120 as a control unit. The ECU 120 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a storage device, etc. The CPU loads various control programs stored in the ROM and maps referenced when executing the various control programs, etc., into the RAM to perform calculation processing.

[0017] The radiator 40 is provided in the radiator circulation passage 50. The radiator circulation passage 50 is a passage through which the cooling water circulates between the engine 20 and the radiator 40.

[0018] The bypass passage 60 is provided with a heater core, which is a heat exchanger for heating the vehicle interior by utilizing the heat of the coolant. The bypass passage 60 is a passage for circulating the coolant that does not pass through the radiator 40 between the engine 20 and the heater core and returning it to the engine 20. The bypass passage 60 is configured to branch off from the radiator circulation passage 50 at the outlet 27 of the water jacket 25 of the engine 20, pass through the heater core, and then be connected to a thermostat valve 70 to join the radiator circulation passage 50. Note that instead of or in addition to the heater core, a device other than the heater core may be provided in the bypass passage 60.

[0019] Inside the engine 20, a water jacket 25 is formed as a cooling water passage through which cooling water flows.

[0020] The water pump 30 is provided between the inlet 26 of the water jacket 25 and the thermostat valve 70. The water pump 30 discharges the cooling water that has been returned toward the inside of the water jacket 25 when driven. In this way, the water pump 30 supplies the cooling water into the water jacket 25. The cooling water discharged from the water pump 30 and supplied from the inlet 26 is passed through the water jacket 25 and circulated therein, where it exchanges heat with the engine 20, and is then sent out from the outlet 27 of the water jacket 25.

[0021] Here, a configuration using a mechanical water pump that is rotated in response to the rotation of engine 20 is adopted, but a configuration using an electric water pump that is rotated in response to a control signal from ECU 120 may also be adopted.

[0022] The radiator 40 passes the cooling water from the water jacket 25 to discharge heat to the outside. The radiator 40 dissipates heat from the cooling water by exchanging heat between the cooling water flowing inside the radiator 40 and the outside air. The cooling water supplied from an inlet 41 of the radiator 40 is cooled by the radiator 40 and then discharged from an outlet 42 of the radiator 40.

[0023] The engine-side coolant temperature sensor 80 is provided at the outlet portion 27. The engine-side coolant temperature sensor 80 detects the temperature of the coolant in the water jacket 25, and outputs the detected value as the engine-side coolant temperature ECT to the ECU 120. The engine-side coolant temperature sensor 80 shown in FIG. 1 detects the temperature of the coolant discharged from the outlet portion 27.

[0024] The position of the engine side coolant temperature sensor 80 may be any position that can detect the temperature of the coolant passing through the water jacket 25 near the outlet portion 27. For example, the engine side coolant temperature sensor 80 is not limited to being provided at the outlet portion 27, but may be provided in the water jacket 25, the bypass passage 60, or the radiator circulation passage 50.

[0025] The radiator side coolant temperature sensor 90 is provided in the radiator circulation passage 50. The radiator side coolant temperature sensor 90 detects the temperature of the coolant in the radiator circulation passage 50, and outputs the detected value as the radiator side coolant temperature RCT to the ECU 120. The radiator side coolant temperature sensor 90 shown in FIG. 1 detects the temperature of the coolant before the inlet portion 41.

[0026] The radiator-side coolant temperature sensor 90 may be capable of detecting the temperature of the coolant passing through the radiator circulation passage 50 at a position separated from the engine-side coolant temperature sensor 80. For example, the radiator-side coolant temperature sensor 90 may be provided upstream of the radiator 40 or downstream of the radiator 40.

[0027] The thermostatic valve 70 is provided between the water pump 30 and the radiator 40 on the inlet portion 26 side of the water jacket 25, and is connected to the radiator 40 via the radiator circulation passage 50. In the example shown in FIG. 1, the thermostatic valve 70 is disposed at a portion where the cooling water that has passed through the radiator circulation passage 50 and the cooling water that has passed through the bypass passage 60 join together. The position of the thermostatic valve 70 is not limited to the position shown in FIG. 1, but may be provided at any position at least capable of adjusting the flow rate of the cooling water in the radiator circulation passage 50. For example, the thermostatic valve 70 may be provided at a position on the outlet portion 27 side (e.g., the outlet portion 27) and connected to the radiator circulation passage 50 and the bypass passage 60. In addition, the thermostat valve 70 may be further connected to another passage provided separately from the radiator circulation passage 50 and the bypass passage 60 (a passage for passing cooling water, for example, a passage connected to the water jacket 25 via the water pump 30 so as to bypass both the radiator 40 and the heater core).

[0028] For example, when the engine 20 is in a cold state, and the temperature of the cooling water passing through the thermostat valve 70 is relatively low (for example, less than 75° C.), the thermostat valve 70 is closed. When the thermostat valve 70 is closed, the cooling water on the radiator circulation passage 50 side is blocked from passing through the water jacket 25, while the cooling water returned from the bypass passage 60 side is passed through the water jacket 25. After the engine 20 is started, the cooling water warmed in the water jacket 25 by the heat generated by the engine 20 is circulated to the bypass passage 60 side, thereby warming up the engine 20.

[0029] The thermostatic valve 70 restricts or allows the flow of cooling water between the radiator circulation passage 50 and the water jacket 25 by moving the valve body in response to a rise in temperature of the cooling water passing through. When the thermostatic valve 70 is opened by the movement of the valve body, the relatively low-temperature cooling water circulated from the radiator circulation passage 50 passes through the thermostatic valve 70 and is mixed with the return cooling water returned from the bypass passage 60. At this time, the mixture ratio of the cooling water circulated from the radiator circulation passage 50 and the return cooling water returned from the bypass passage 60 is controlled by the open / close state of the valve body of the thermostatic valve 70. As a result, the temperature of the cooling water supplied to the water jacket 25 is maintained at an appropriate temperature.

[0030] Further, the thermostat valve 70 is forced to open under a predetermined condition to communicate the radiator circulation passage 50 with the water jacket 25. For example, when the engine 20 is rotating at high speed, the discharge pressure of the water pump 30 increases and the flow rate of the cooling water increases. Therefore, in the cooling device 10a, when it is expected that the water pressure applied to the valve body of the thermostat valve 70 will be a high water pressure equal to or higher than a predetermined water pressure, the thermostat valve 70 is opened by the forced valve opening control to pass the cooling water to the radiator circulation passage 50 side. In this way, in the cooling device 10a, the thermostat valve 70 is opened by the forced valve opening control to release the pressure, so that it is possible to prevent the hose (the hose forming each passage) from coming off or the heater core from being damaged due to high water pressure.

[0031] On the other hand, if the thermostatic valve 70 malfunctions, it will cause anomalies such as a closed malfunction where the valve does not open even when the temperature of the cooling water passing through rises, or an open malfunction where the valve does not close even when the temperature of the cooling water passing through drops. When such a malfunction occurs in the thermostatic valve 70, cooling water at an appropriate temperature cannot be supplied to the water jacket 25, which reduces the operating efficiency of the engine 20.

[0032] For this reason, it is preferable to perform an abnormality diagnosis of whether the thermostat valve 70 is operating normally every time before the vehicle 100 is driven or after the engine 20 is started, in order to find an open valve failure or other such failure at an early stage.

[0033] In this embodiment, the abnormality diagnosis process for diagnosing an abnormality in the thermostat valve 70 is configured to determine the presence or absence of an open-circuit malfunction of the thermostat valve 70 based on the engine-side coolant temperature ECT and the radiator-side coolant temperature RCT. Fig. 2 is a time chart showing the time-series change in the coolant temperature after the start of the engine 20. Fig. 2 shows the temperature behavior of the engine-side coolant temperature ECT and the radiator-side coolant temperature RCT in a normal state where the thermostat valve 70 is operating normally and in an abnormal state where the thermostat valve 70 is experiencing an open-circuit malfunction.

[0034] 2, during the period until time t1 when the thermostat valve 70 is opened by the forced valve opening control, the engine-side coolant temperature ECT rises significantly as the engine 20 warms up, whereas the radiator-side coolant temperature RCT remains low because the thermostat valve 70 is closed. As a result, the engine-side coolant temperature ECT becomes sufficiently higher than the radiator-side coolant temperature RCT.

[0035] Then, when the thermostatic valve 70 is opened by the forced valve opening control at time t1 when a forced valve opening request is made, the radiator side coolant temperature RCT rises and approaches the engine side coolant temperature ECT as coolant flows through the radiator circulation passage 50. In this way, when the thermostatic valve 70 is operating normally, the temperature difference ECT-RCT between the radiator side coolant temperature RCT and the engine side coolant temperature ECT becomes small while the forced valve opening control is being executed.

[0036] On the other hand, as shown on the right side of Fig. 2, in the event of an abnormality, the thermostatic valve 70 is kept open, so that the coolant flows through the radiator circulation passage 50 without forced valve opening control. In this way, when the thermostatic valve 70 is experiencing an open failure, the coolant circulated from the radiator circulation passage 50 and the return coolant returned from the bypass passage 60 are mixed, and the temperature difference ECT-RCT between the radiator side coolant temperature RCT and the engine side coolant temperature ECT continues to decrease from the time the engine 20 begins to start. In other words, the state remains such that ECT ≒ RCT.

[0037] Therefore, in this embodiment, an abnormality of the thermostat valve 70 is determined based on the temperature difference ECT-RCT between the engine-side cooling water temperature ECT and the radiator-side cooling water temperature RCT after the engine 20 is started. For example, the ECU 120 determines that the thermostat valve 70 is operating normally when the temperature difference ECT-RCT is equal to or greater than the abnormality determination threshold, and determines that an abnormality (open malfunction) has occurred in the thermostat valve 70 when the temperature difference ECT-RCT is less than the abnormality determination threshold. In this way, in the cooling device 10a, the abnormality diagnosis process is repeatedly executed by the ECU 120 every time the condition for executing the abnormality diagnosis process is satisfied after the engine 20 is started.

[0038] Next, Fig. 3 is a time chart for explaining the time series change in the coolant temperature accompanying the forced valve opening control. Fig. 3 shows the relationship between the engine speed Ne, the valve phase of the valve body of the thermostatic valve 70, the engine side coolant temperature ECT, and the radiator side coolant temperature RCT. As shown in Fig. 3, when the engine speed Ne becomes equal to or higher than a reference speed Ne0 preset in the ECU 120, the ECU 120 executes the forced valve opening control to open the thermostatic valve 70.

[0039] 3 shows an example in which forced valve-opening control is started when the engine speed Ne reaches a reference speed Ne0 at time t1, and ends when the engine speed Ne falls below the reference speed Ne0 at time t2. The thermostat valve 70 is closed until time t1 when the forced valve-opening control is started, and during the period from time t1 to t2 during which the forced valve-opening control is in progress, the valve phase of the valve disc of the thermostat valve 70 changes according to the engine speed Ne.

[0040] The reference rotation speed Ne0 is a threshold value for determining whether or not to execute the forced valve opening control. The reference rotation speed Ne0 is appropriately set in consideration of the rotation speed of the engine 20 at which a malfunction such as a hose coming off may occur, and in this embodiment, the reference rotation speed Ne0 is set to 4500 rpm.

[0041] When the engine speed Ne becomes equal to or higher than the reference speed Ne0 and thus the forced valve-opening control is executed, the thermostatic valve 70 is opened, and the coolant circulating from the radiator circulation passage 50 is passed into the water jacket 25. Then, as the thermostatic valve 70 opens, the radiator circulation passage 50 is connected to the water jacket 25, and the radiator-side coolant temperature RCT rises and approaches the engine-side coolant temperature ECT. Thus, at time t2 when the forced valve-opening control ends, the temperature difference ECT-RCT becomes small, and the temperature behaves similarly to when an abnormality (opening failure) occurs in the thermostatic valve 70.

[0042] Therefore, if the abnormality diagnosis process is executed immediately after the forced valve-opening control is ended, a state in which the temperature difference ECT-RCT is small (ECT≒RCT) due to the forced valve-opening control may be detected, leading to a possibility of erroneously diagnosing that an abnormality has occurred in the thermostatic valve 70. For this reason, after the forced valve-opening control is executed, it is preferable to postpone the abnormality diagnosis process until a temperature difference ECT-RCT (e.g., 6.6°C) at which the abnormality diagnosis process can be executed occurs. In the example shown in Fig. 3, since a temperature difference ECT-RCT at which the abnormality diagnosis process can be executed occurs at time t3 after the forced valve-opening control is executed, the period from time t2 to t3 is the delay time required to execute (restart) the abnormality diagnosis process.

[0043] Therefore, the ECU 120 prohibits abnormality diagnosis processing from the start of the forced valve opening control, and performs abnormality diagnosis delay control to execute (resume) abnormality diagnosis processing when it estimates that the temperature difference ECT-RCT between the cooling water temperature in the water jacket 25 and the cooling water temperature in the radiator circulation passage 50 will be a predetermined value or more after the forced valve opening control ends.

[0044] The abnormality diagnosis delay control makes it possible to avoid performing the abnormality diagnosis process in a state in which the radiator-side cooling water temperature RCT has not sufficiently deviated from the engine-side cooling water temperature ECT after the forced valve-opening control ends. As a result, the possibility of misdiagnosing an abnormality in the thermostat valve 70 can be reduced compared to a case in which the abnormality diagnosis process is restarted immediately after the forced valve-opening control by the thermostat valve 70 ends.

[0045] In addition to the engine-side coolant temperature sensor 80 and the radiator-side coolant temperature sensor 90, various sensors including a rotation speed sensor 110 are connected to the ECU 120 of the cooling device 10a to detect the operating state of the engine 20 and the traveling conditions of the vehicle 100. The rotation speed sensor 110 detects the rotation speed of a crankshaft, which is the output shaft of the engine 20, and outputs the detected value as an engine rotation speed Ne to the ECU 120. The ECU 120 executes various controls of the engine 20 and abnormality diagnosis delay control based on signals input from the various sensors.

[0046] Furthermore, the ECU 120 includes a counter C. This counter C is a water temperature counter that accumulates the amount of change (°C / sec) per unit time of the engine side cooling water temperature ECT after the forced valve opening control is ended. Hereinafter, the amount of change per unit time of the engine side cooling water temperature ECT after the forced valve opening control is ended is referred to as the ECT change amount.

[0047] With reference to Fig. 4, the following will mainly describe the contents related to the abnormality diagnosis delay control among various controls executed by the ECU 120. Fig. 4 is a flowchart illustrating an abnormality diagnosis delay control routine executed by the ECU of the cooling device shown in Fig. 1. The cooling device 10a determines whether or not to execute the abnormality diagnosis process according to the process flow shown in Fig. 4.

[0048] 4 is implemented by repeatedly executing a program stored in advance in the ECU 120 at predetermined intervals. Alternatively, the processing can be implemented by constructing some or all of the steps of the program using dedicated hardware.

[0049] 4 is started after the engine 20 is started, the ECU 120 determines whether or not the forced valve-opening control is being executed (step S1). Specifically, the ECU 120 determines whether or not the current engine speed Ne obtained from the speed sensor 110 is equal to or greater than a preset reference speed Ne0.

[0050] When the engine speed Ne is equal to or higher than the reference speed Ne0, the ECU 120 determines that the forced valve-opening control is being executed (step S1: YES). If the forced valve-opening control is being executed, the ECU 120 clears the counter C to set the count value cnt to zero (initial value) (step S2). Then, the process proceeds to step S4.

[0051] On the other hand, when the engine speed Ne is less than the reference speed Ne0, the ECU 120 determines that the forced valve-opening control is not being executed (step S1: NO). If the forced valve-opening control is not being executed, the ECU 120 starts integrating the ECT change amount by the counter C and calculates the count value cnt of the counter C (step S3). Then, the process proceeds to step S4.

[0052] Here, the ECT change amount can be obtained by using a map in which suitable values ​​(amount of change in the coolant temperature) are mapped by experiments, simulations, etc., using the heater core flow rate (flow rate of the coolant passing through the heater core), vehicle speed, engine heat generation amount (engine intake amount), fuel cut (F / C) and other operating conditions of the engine 20 as parameters. The map used here is stored in advance in the ROM of the ECU 120. The ECU 120 calculates the count value cnt corresponding to the engine side coolant temperature ECT by referring to the map.

[0053] The count value (integrated value) cnt calculated in this manner is an estimate of the temperature difference ECT-RCT. When the thermostat valve 70 is closed, no coolant flows through the radiator circulation passage 50, suppressing an increase in the radiator-side coolant temperature RCT, so the radiator-side coolant temperature RCT remains at a substantially constant temperature. Therefore, the counter C can estimate the temperature difference ECT-RCT based on the engine-side coolant temperature ECT. In this manner, the cooling device 10a can use the counter C to estimate that the temperature difference ECT-RCT will be equal to or greater than a predetermined value after the forced valve-open control ends.

[0054] Next, the ECU 120 determines whether the count value cnt is equal to or greater than an abnormality diagnosis execution threshold (step S4). The abnormality diagnosis execution threshold is a threshold value of the temperature difference ECT-RCT at which the abnormality diagnosis process can be executed. In addition, it is preferable that the abnormality diagnosis execution threshold is repeatedly changed for each cycle of the forced valve opening control according to the period during which the engine speed Ne is equal to or greater than the reference speed Ne0.

[0055] During execution of the forced valve opening control, the extent to which the radiator side cooling water temperature RCT approaches the engine side cooling water temperature ECT varies depending on the period during which water is supplied to the radiator circulation passage 50. The period during which water is supplied to the radiator circulation passage 50 is the duration during which the thermostat is open from the start to the end of one cycle of the forced valve opening control, and corresponds to the period during which the engine speed Ne is equal to or higher than the reference speed Ne0.

[0056] That is, the delay time required from the execution of the forced valve-opening control until the execution (resumption) of the abnormality diagnosis process is determined according to the period during which the engine speed Ne is equal to or higher than the reference speed Ne0. For example, the shorter the period during which water is passed through the radiator circulation passage 50, i.e., the shorter the period during which the thermostat valve is open due to the forced valve-opening control, the larger the temperature difference ECT-RCT immediately after the forced valve-opening control ends, and therefore the delay time of the abnormality diagnosis process can be shortened.

[0057] Therefore, by setting the abnormality diagnosis execution threshold according to the period during which the engine speed Ne is equal to or higher than the reference speed Ne0 for each cycle of the forced valve opening control, the abnormality diagnosis process can be resumed promptly with the minimum required delay time. As a result, it is possible to ensure the frequency of abnormality diagnosis of the thermostatic valve 70 while suppressing erroneous diagnosis of an abnormality of the thermostatic valve 70.

[0058] Next, if the count value cnt is equal to or greater than the abnormality diagnosis execution threshold (step S4: YES), the ECU 120 determines that the conditions for executing the abnormality diagnosis process are satisfied, and performs control to execute the abnormality diagnosis process (step S5). Then, the process returns to step S1 (RETURN). If the count value cnt is less than the abnormality diagnosis execution threshold (step S4: NO), the ECU 120 determines that the conditions for executing the abnormality diagnosis process are not satisfied, and performs control to prohibit the abnormality diagnosis process (step S6). Then, the process returns to step S1 (RETURN).

[0059] The timing of the abnormality diagnosis will be described with reference to the time chart in Fig. 3. Until time t1 when the forced valve-opening control is started, the thermostat valve 70 is closed and the abnormality diagnosis process is executed. Then, at time t1 when the forced valve-opening control is started, the thermostat valve 70 opens and the abnormality diagnosis process is simultaneously prohibited. Then, during the period from time t1 to t2 when the forced valve-opening control is being executed, the thermostat valve 70 remains open and the abnormality diagnosis process is continued to be prohibited. Furthermore, at time t2 when the forced valve-opening control ends, the thermostat valve 70 is closed.

[0060] On the other hand, the inhibition of the abnormality diagnosis process continues during the period from time t2 to t3. That is, the inhibition of the abnormality diagnosis process continues during the period from time t1 when the forced valve opening control is started to time t3 when a temperature difference ECT-RCT that allows the abnormality diagnosis process to be executed is generated between the engine side cooling water temperature ECT and the radiator side cooling water temperature RCT after the forced valve opening control is executed. Therefore, when the period from time t2 to t3, which is the delay time for executing (resuming) the abnormality diagnosis process after the forced valve opening control is executed, has elapsed, the abnormality diagnosis process is executed.

[0061] As described above, the cooling device 10a according to the first embodiment includes the radiator 40 that passes the cooling water from the cooling water passage formed inside the internal combustion engine to discharge heat to the outside, the radiator circulation passage 50 that circulates the cooling water between the internal combustion engine and the radiator 40, the thermostat valve 70 that is opened under a predetermined condition to perform a forced valve opening control that connects the radiator circulation passage 50 to the cooling water passage, and a control unit that performs an abnormality diagnosis process to diagnose an abnormality in the thermostat valve 70. The control unit prohibits the abnormality diagnosis process from the start of the forced valve opening control, and executes the abnormality diagnosis process when it estimates that the temperature difference ECT-RCT between the temperature of the cooling water in the cooling water passage and the temperature of the cooling water in the radiator circulation passage 50 becomes equal to or greater than a predetermined value after the forced valve opening control ends.

[0062] The cooling device 10a according to the present embodiment temporarily suspends the abnormality diagnosis process during execution of the forced valve-opening control, and delays the execution of the abnormality diagnosis process so that the abnormality diagnosis process is executed (resumed) at a time when a temperature difference ECT-RCT at which the abnormality diagnosis process can be executed occurs after the forced valve-opening control ends. With this configuration, it is possible to suppress erroneous diagnosis of an abnormality in the thermostat valve 70 and improve the accuracy of the abnormality diagnosis of the thermostat valve 70.

[0063] Furthermore, in the cooling device 10a according to the present embodiment, the shorter the duration of the thermostat valve open state due to the forced valve opening control, the shorter the delay time of the abnormality diagnosis process. With this configuration, it is possible to ensure the frequency of abnormality diagnosis of the thermostat valve 70 while suppressing erroneous diagnosis of abnormality of the thermostat valve 70. As a result, it is possible to further improve the accuracy of abnormality diagnosis of the thermostat valve 70.

[0064] Embodiment 2 The configuration of an internal combustion engine cooling device (cooling device 10b) according to this embodiment will be described with reference to Fig. 5. In this embodiment, the cooling device 10b for cooling or warming up an engine 20 equivalent to an internal combustion engine mounted on a vehicle 200 will be described as an example. For example, the cooling device 10b is suitable for a vehicle that performs stop-and-start control (S&S control) that automatically stops and automatically restarts the engine 20 depending on the driving situation, and a hybrid vehicle that alternately drives the engine 20 and a motor.

[0065] Fig. 5 is a block diagram for explaining the configuration of a cooling device according to the second embodiment. Fig. 5 is a diagram corresponding to Fig. 1. Fig. 5 shows the main parts of a vehicle 200 related to the cooling device 10b, and the black arrow indicates the direction in which the cooling water flows.

[0066] 5, the cooling device 10b has an ECU 130 as a control unit. The ECU 130 executes various controls of the engine 20 and abnormality diagnosis delay control based on signals input from various sensors. Since the other configurations except for the abnormality diagnosis delay control process in the EUC are the same as those of the cooling device 10a according to the first embodiment, detailed descriptions will be omitted and differences from the first embodiment will be mainly described.

[0067] When the engine 20 of the vehicle 200 equipped with an automatic stop function for the engine 20, such as a vehicle that performs S&S control or a hybrid vehicle, is automatically stopped, the time until the temperature difference ECT-RCT at which the abnormality diagnosis process can be executed is generated after the forced valve opening control is executed becomes long. If the time until the temperature difference ECT-RCT at which the abnormality diagnosis process can be executed is generated becomes long, the frequency of abnormality diagnosis decreases.

[0068] Therefore, the ECU 130 of the cooling device 10b prohibits abnormality diagnosis processing from the start of the forced valve-opening control, and executes (resumes) abnormality diagnosis processing if it estimates that the temperature difference ECT-RCT will be equal to or greater than a predetermined value after the forced valve-opening control ends. Furthermore, the ECU 130 performs abnormality diagnosis delay control that prohibits automatic stopping (intermittent stopping) of the engine 20, which automatically stops and automatically restarts depending on the driving conditions, until a predetermined time (engine stop permission delay time) has elapsed since the prohibition of the abnormality diagnosis processing.

[0069] With reference to Figures 6 and 7, the following will mainly describe the contents related to the abnormality diagnosis delay control among various controls executed by the ECU 130. Figure 6 is a flowchart illustrating the abnormality diagnosis delay control routine executed by the ECU of the cooling device shown in Figure 5. Figure 7 is a flowchart illustrating the abnormality diagnosis delay control routine following Figure 6. The cooling device 10b determines whether or not to execute each of the engine stop processing and the abnormality diagnosis processing according to the processing flows shown in Figures 6 and 7.

[0070] 6 and 7 is started after the engine 20 is started, the ECU 130 determines whether or not the forced valve-opening control is being executed (step S11). Specifically, the ECU 130 determines whether or not the current engine speed Ne acquired from the speed sensor 110 is equal to or greater than a preset reference speed Ne0.

[0071] When the engine speed Ne is equal to or higher than the reference speed Ne0, the ECU 130 determines that forced valve-opening control is being executed (step S11: YES). If forced valve-opening control is being executed, the ECU 130 turns off the abnormality diagnosis permission flag (step S21). This prohibits (temporarily stops) the abnormality diagnosis process. The abnormality diagnosis permission flag is a flag that is turned on when the abnormality diagnosis process is executed.

[0072] Next, the ECU 130 turns on the valve opening history flag (step S22). The valve opening history flag is a flag that is turned on when there is a history of the forced valve opening control being executed. Then, the process proceeds to step S41.

[0073] On the other hand, when the engine speed Ne is less than the reference speed Ne0, the ECU 130 determines that the forced valve-opening control is not being executed (step S11: NO). When the forced valve-opening control is not being executed, the ECU 130 determines whether the valve-opening history flag is ON (step S31).

[0074] If the valve opening history flag is ON (step S31: YES), the ECU 130 prohibits engine stop processing that automatically stops the engine 20 while it is running (step S32). This allows the engine 20 to continue running after the forced valve opening control ends. If the valve opening history flag is OFF (step S31: NO), steps S32 to S34 are skipped and the process proceeds to step S35.

[0075] When the engine stop process is prohibited in step S32, the ECU 130 starts measurement by the counters C1 and C2 to calculate the count values ​​TM1 and TM2 of the counters C1 and C2 (step S33). The counters C1 and C2 are timers that measure the elapsed time from the time when the engine stop process was prohibited. Next, the ECU 130 turns off the valve opening history flag (step S34). Then, the process proceeds to step S35.

[0076] When the valve opening history flag is in the OFF state, the ECU 130 determines whether the count value TM1 (measured time) of the counter C1 is equal to or greater than the engine stop permission delay (step S35). The engine stop permission delay is a delay time from when the engine stop process is prohibited to when it is executed (restarted). Here, the engine stop permission delay is set to the same delay time as the abnormality diagnosis permission delay, which will be described later. If the count value TM1 is equal to or greater than the engine stop permission delay (step S35: YES), the ECU 130 permits the engine stop process (step S36). Then, the process proceeds to step S37. If the count value TM1 is less than the engine stop permission delay (step S35: NO), the process proceeds to step S37 while the engine stop process remains prohibited.

[0077] Next, the ECU 130 judges whether the count value TM2 (measurement time) of the counter C2 is equal to or greater than the abnormality diagnosis permission delay (step S37). The abnormality diagnosis permission delay is an estimate of the time required for the temperature difference ECT-RCT between the engine side coolant temperature ECT and the radiator side coolant temperature RCT to become equal to or greater than the threshold value (e.g., 6.6°C) of the temperature difference ECT-RCT at which the abnormality diagnosis process can be executed. Therefore, when the count value TM2 is less than the abnormality diagnosis permission delay, it can be estimated that the temperature difference ECT-RCT at which the abnormality diagnosis process can be executed has not occurred. On the other hand, when the count value TM2 is equal to or greater than the abnormality diagnosis permission delay, it can be estimated that the temperature difference ECT-RCT at which the abnormality diagnosis process can be executed has occurred. When the ECU 130 includes the counter C described in the first embodiment, the time from when the counter C starts accumulating the ECT change amount until the count value cnt becomes equal to or greater than the abnormality diagnosis execution threshold becomes the abnormality diagnosis permission delay. Since the amount of change in ECT varies depending on the operating conditions of the engine 20, such as the heater core flow rate (the flow rate of cooling water passing through the heater core), vehicle speed, engine heat generation (engine intake volume), and fuel cut (F / C), the abnormality diagnosis permission delay is variable depending on the operating conditions of the engine 20.

[0078] In this way, the cooling device 10b can use the counters C1 and C2 to estimate that the temperature difference ECT-RCT will be equal to or greater than a predetermined value after the forced valve-open control ends. In addition, since the engine stop permission delay and the abnormality diagnosis permission delay are set to the same delay time, the engine 20 is allowed to operate while the abnormality diagnosis process is not being executed. Note that the period during which the abnormality diagnosis process is not being executed refers to the period from when the execution of the abnormality diagnosis process is prohibited until it is executed (restarted).

[0079] If the count value TM2 is equal to or greater than the abnormality diagnosis permission delay (step S37: YES), the ECU 130 turns on the abnormality diagnosis permission flag (step S38). Then, the process proceeds to step S41. If the count value TM2 is less than the abnormality diagnosis permission delay (step S37: NO), the process proceeds to step S41 while keeping the abnormality diagnosis permission flag in the OFF state.

[0080] 7, the ECU 130 determines whether the abnormality diagnosis permission flag is ON or not (step S41). If the abnormality diagnosis permission flag is ON (step S41: YES), the ECU 130 determines that the condition for executing the abnormality diagnosis process is satisfied, and performs control to execute the abnormality diagnosis process (step S42). Then, the process returns to step S11 (RETURN). If the abnormality diagnosis permission flag is OFF (step S41: NO), the ECU 130 determines that the condition for executing the abnormality diagnosis process is not satisfied, and performs control to prohibit the abnormality diagnosis process (step S43). Then, the process returns to step S11 (RETURN).

[0081] Fig. 8 is a time chart for explaining the time series changes of various parameters accompanying the forced valve opening control. Fig. 8 shows the relationship between the engine speed Ne, the open / closed state of the thermostat valve 70, the permission / prohibition state of the abnormality diagnosis process, the engine side cooling water temperature ECT, and the radiator side cooling water temperature RCT.

[0082] In the example shown in Fig. 8, similarly to Fig. 3, the forced valve-opening control is started when the engine speed Ne reaches the reference speed Ne0 at time t1, and ends when the engine speed Ne falls below the reference speed Ne0 at time t2. As for the temperature behavior of the coolant temperature at this time, as the thermostat valve 70 opens, the radiator-side coolant temperature RCT rises and approaches the engine-side coolant temperature ECT, and at time t2 when the forced valve-opening control ends, the temperature difference ECT-RCT becomes small.

[0083] In this example, the thermostat valve 70 is closed and abnormality diagnosis processing is executed until time t1 when the forced valve-opening control is started. Then, at time t1 when the forced valve-opening control is started, the thermostat valve 70 opens and the abnormality diagnosis processing is simultaneously prohibited. Then, during the period from time t1 to t2 when the forced valve-opening control is being executed, the thermostat valve 70 remains open and the abnormality diagnosis processing is continued to be prohibited. Furthermore, at time t2 when the forced valve-opening control ends, the thermostat valve 70 is closed.

[0084] On the other hand, the inhibition of the abnormality diagnosis process continues during the period from time t2 to t3. That is, the inhibition of the abnormality diagnosis process continues during the period from time t1 when the forced valve opening control is started to time t3 when a temperature difference ECT-RCT that allows the abnormality diagnosis process to be executed is generated between the engine side cooling water temperature ECT and the radiator side cooling water temperature RCT after the forced valve opening control is executed. Therefore, when the period from time t2 to t3, which is the delay time for executing (resuming) the abnormality diagnosis process after the forced valve opening control is executed, has elapsed, the abnormality diagnosis process is executed.

[0085] As described above, the cooling device 10b according to the second embodiment includes the radiator 40 that passes the cooling water from the cooling water passage formed inside the internal combustion engine to discharge heat to the outside, the radiator circulation passage 50 that circulates the cooling water between the internal combustion engine and the radiator 40, the thermostat valve 70 that is opened under a predetermined condition to perform a forced valve opening control that connects the radiator circulation passage 50 to the cooling water passage, and a control unit that performs an abnormality diagnosis process to diagnose an abnormality in the thermostat valve 70. The control unit prohibits the abnormality diagnosis process from the start of the forced valve opening control, and executes the abnormality diagnosis process when it estimates that the temperature difference ECT-RCT between the temperature of the cooling water in the cooling water passage and the temperature of the cooling water in the radiator circulation passage 50 becomes a predetermined value or more after the forced valve opening control ends. Furthermore, the control unit prohibits the automatic stop of the internal combustion engine that automatically stops and automatically restarts depending on the driving situation until a predetermined time has elapsed since the prohibition of the abnormality diagnosis process.

[0086] The cooling device 10b according to this embodiment, like the first embodiment, suspends the abnormality diagnosis process while the forced valve-opening control is being executed, and delays the execution of the abnormality diagnosis process so that the abnormality diagnosis process is executed (resumed) when a temperature difference ECT-RCT at which the abnormality diagnosis process can be executed is generated after the forced valve-opening control ends. With this configuration, it is possible to suppress erroneous diagnosis of an abnormality in the thermostat valve 70 and improve the accuracy of the abnormality diagnosis of the thermostat valve 70.

[0087] Furthermore, the cooling device 10b according to the present embodiment increases the load on the engine 20 during the period by prohibiting the automatic stop of the engine 20 until a temperature difference ECT-RCT that allows the abnormality diagnosis process to be executed is generated after the forced valve opening control is terminated. When the load on the engine 20 increases, the rate of increase in the engine-side coolant temperature ECT increases, so that the delay time until the temperature difference ECT-RCT that allows the abnormality diagnosis process to be executed is generated can be shortened. With this configuration, it is possible to ensure the frequency of abnormality diagnosis of the thermostat valve 70 while suppressing erroneous diagnosis of abnormality of the thermostat valve 70. As a result, it is possible to further improve the accuracy of abnormality diagnosis of the thermostat valve 70.

[0088] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit of the present invention. For example, in the above-described second embodiment, the load on the engine 20 is increased by operating the engine 20. However, the load on the engine 20 may be increased by operating an electric load such as an air conditioner mounted on the vehicle 200, not limited to vehicles that perform S&S control or hybrid vehicles.

[0089] Furthermore, the present invention may be implemented by appropriately combining the respective embodiments. [Explanation of symbols]

[0090] 10a, 10b Cooling device 20 Engine 25 Water Jacket 26 Entrance 27 Exit section 30 Water Pump 40 Radiator 41 Entrance 42 Exit section 50 Radiator circulation passage 60 Bypass Passage 70 Thermostatic valve 80 Engine side coolant temperature sensor 90 Radiator side coolant temperature sensor 100, 200 vehicles 110 Rotational speed sensor 120, 130 ECU ECT Engine side coolant temperature RCT Radiator side coolant temperature

Claims

1. a radiator that passes cooling water from a cooling water passage formed inside the internal combustion engine to discharge heat to the outside; a radiator circulation passage for circulating the cooling water between the internal combustion engine and the radiator; a thermostat valve that is forced to open under a predetermined condition to communicate the radiator circulation passage with the cooling water passage; A control unit that performs an abnormality diagnosis process to diagnose an abnormality in the thermostat valve, The control unit is The abnormality diagnosis process is prohibited from the start of the forced valve opening control, the abnormality diagnosis process is executed when it is estimated that a temperature difference between the cooling water in the cooling water passage and the cooling water in the radiator circulation passage will be equal to or greater than a predetermined value after the forced valve opening control is terminated. Cooling system for internal combustion engines.

2. The control unit is prohibiting automatic stopping of the internal combustion engine, which automatically stops and automatically restarts depending on the driving conditions, until a predetermined time has elapsed since the abnormality diagnosis process was prohibited; 2. The cooling system for an internal combustion engine according to claim 1.

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