COOLING DEVICE FOR INTERNAL COMBUSTION ENGINE

Abstract

An ECU performs a failure diagnosis for a thermostat valve after starting of an engine based on an output of an engine-side coolant water temperature sensor and an output of a radiator-side coolant water temperature sensor. When an electric pump operates in accordance with a heating request or the like of an air-conditioning device during stopping of the engine, the thermostat valve attains a closed state. When the electric pump operates during stopping of the engine before the current starting of the engine, starting of the failure diagnosis performed after starting of the engine is delayed as compared to the case where the electric pump does not operate during stopping of the engine. Consequently, erroneous determination can be suppressed in the failure diagnosis for the thermostat valve.

Description

This nonprovisional application is based on Japanese Patent Application No. 2013-250213 filed on Dec. 3, 2013 with the Japan Patent Office, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cooling device for an internal combustion engine, and particularly to a technique of diagnosing a failure of a thermostat valve provided in a cooling device for an internal combustion engine.

2. Description of the Background Art

Japanese Patent Laying-Open No. 2010-196587 discloses an abnormality detecting device for detecting an abnormality of a thermostat valve provided in an engine cooling system of a hybrid vehicle capable of performing EV traveling of stopping an engine and traveling with a drive force of a motor. An increase in the EV traveling reduces an opportunity to operate an engine and in turn reduces an opportunity to detect an abnormality of a thermostat valve. According to this abnormality detecting device, engine coolant water is heated by a heater during the EV traveling, and if a temperature of the engine coolant water rises to be higher than or equal to a determination temperature, it is determined that a thermostat valve operates normally (Japanese Patent Laying Open No. 2010-196587).

Heat of coolant water heated by exhausted heat of an engine can be utilized for heating or the like performed by an air-conditioning device, and even during stopping of the engine, circulation of coolant water by operation of an electric pump in accordance with a heating request or the like of the air-conditioning device may occur. In this case, since the engine is stopped, the thermostat valve is closed, and the coolant water circulates without passing through a radiator. Accordingly, a situation may occur which causes the temperature of the circulating coolant water to be lower than a temperature of coolant water remaining in a radiator circulation passage for allowing coolant water to flow into the radiator.

When the engine is started in such a situation, and a failure diagnosis for the thermostat valve is executed, erroneous determination is possibly made in the failure diagnosis due to the reversed relationship between the temperature of the circulating coolant water and the temperature of the coolant water remaining in the radiator circulation passage.

SUMMARY OF THE INVENTION

The present invention was made to solve the problem described above, and its object is to suppress erroneous determination in a failure diagnosis for a thermostat valve provided in a cooling device for an internal combustion engine.

A cooling device for an internal combustion engine according to the present invention includes a coolant water passage formed in the internal combustion engine, a radiator cooling coolant water, a radiator circulation passage, a bypass passage, a heat exchanger, a thermostat valve, an electric pump, first and second temperature sensors, and a control device. The radiator circulation passage is configured to allow coolant water discharged from the coolant water passage to pass through the radiator and return to the coolant water passage. The bypass passage is configured to allow coolant water discharged from the coolant water passage to return to the coolant water passage without passing through the radiator. The heat exchanger is provided on the bypass passage and utilizes heat of the coolant water. The thermostat valve is connected to the radiator circulation passage and the bypass passage, and switched, in accordance with a temperature of coolant water flowing in the thermostat valve, to either a closed state of intercepting coolant water from the radiator circulation passage and outputting coolant water from the bypass passage to the coolant water passage, or an opened state of outputting coolant water from the radiator circulation passage and coolant water from the bypass passage to the coolant water passage. The electric pump allows coolant water to circulate. The first temperature sensor detects a temperature of coolant water in the coolant water passage. The second temperature sensor detects a temperature of coolant water in the radiator circulation passage. The control device performs a failure diagnosis for the thermostat valve after starting of the internal combustion engine based on an output of the first temperature sensor and an output of the second temperature sensor. When the electric pump operates in accordance with an operation request of the heat exchanger during stopping of the internal combustion engine, the thermostat valve attains the closed state. In a case where the electric pump operates during stopping of the internal combustion engine, the control device delays starting of the failure diagnosis performed after starting of the internal combustion engine as compared to a case where the electric pump does not operate during stopping of the internal combustion engine.

In this cooling device for an internal combustion engine, in the case where the electric pump operates in accordance with the operation request of the heat exchanger during stopping of the internal combustion engine, starting of the failure diagnosis performed after starting of the internal combustion engine is delayed as compared to the case where the electric pump does not operate during stopping of the internal combustion engine. Therefore, starting of the failure diagnosis for the thermostat valve is avoided in a state where the relationship between the temperature of the coolant water in the coolant water passage and the temperature of the coolant water in the radiator circulation passage are inversed. Thus, according to the cooling device for an internal combustion engine, erroneous determination in the failure diagnosis for the thermostat valve can be suppressed.

Preferably, the control device starts the failure diagnosis when a rise quantity (ΔECT) of a coolant water temperature, which is detected by the first temperature sensor, from starting of the internal combustion engine exceeds a predetermined value. A first value indicating the predetermined value for the case where the electric pump operates during stopping of the internal combustion engine is larger than a second value indicating the predetermined value for the case where the electric pump does not operate during stopping of the internal combustion engine.

The failure diagnosis of the thermostat valve is performed based on the coolant water temperature. According to the cooling device for an internal combustion engine, starting of the failure diagnosis is adjusted based on the coolant water temperature. Therefore, a start timing of the failure diagnosis can be adjusted with a high accuracy.

Moreover, preferably, the control device integrates an intake air volume to the internal combustion engine from starting of the internal combustion engine, and starts the failure diagnosis when the integrated value of the intake air volume exceeds a predetermined value. A first value indicating the predetermined value for the case where the electric pump operates during stopping of the internal combustion engine is larger than a second value indicating the predetermined value for the case where the electric pump does not operate during stopping of the internal combustion engine.

The integrated amount of the intake air volume to the internal combustion engine may represent a tendency of a rise in the temperature of the internal combustion engine and of the coolant water. Therefore, in this cooling device for an internal combustion engine, starting of the failure diagnosis is adjusted based on the integrated amount of the intake air volume. Thus, this cooling device for an internal combustion engine can also suppress erroneous determination in the failure diagnosis for the thermostat valve.

Moreover, preferably, the control device starts the failure diagnosis when an elapsed time from starting of the internal combustion engine exceeds a predetermined value. A first value indicating the predetermined value for the case where the electric pump operates during stopping of the internal combustion engine is larger than a second value indicating the predetermined value for the case where the electric pump does not operate during stopping of the internal combustion engine.

In this cooling device for an internal combustion engine, starting of the failure diagnosis is adjusted based on the elapsed time from starting of the internal combustion engine. Therefore, a process for capturing a detection signal of a sensor and a calculation process are not required. Thus, according to this cooling device for an internal combustion engine, the process of the control device can be simplified. Moreover, starting of the failure diagnosis can be adjusted without being affected by an abnormality of a sensor and a measurement accuracy

Preferably, the control device calculates an estimation value of the coolant water temperature in the radiator circulation passage based on a leakage flow rate through the radiator circulation passage in the closed state of the thermostat valve and on an output of the first temperature sensor, and diagnoses that the thermostat valve is failed in a case where an output value of the second temperature sensor is larger than the calculated estimation value.

According to this cooling device for an internal combustion engine, the failure diagnosis of the thermostat valve is performed taking into consideration the leakage flow rate through the radiator circulation passage in the closed state of the thermostat valve. Therefore, the failure diagnosis can be performed with a high accuracy.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a schematic configuration of a vehicle including a cooling device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 represents one example of a change in an engine coolant water temperature before and after starting the engine.

FIG. 3 is a flowchart for describing procedures of the thermostat valve failure diagnosis process executed by the ECU shown in FIG. 1.

FIG. 4 is a flowchart representing process procedures for determining the diagnosis precondition shown in FIG. 3.

FIG. 5 is a flowchart representing process procedures for determining a diagnosis precondition in Modified Example 1.

FIG. 6 is a flowchart representing process procedures for determining a diagnosis precondition in Modified Example 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the same or corresponding parts in the drawings have the same reference numerals allotted and description thereof will not be repeated.

FIG. 1 represents a schematic configuration of a vehicle including a cooling device for an internal combustion engine according to the embodiment of the present invention. Referring to FIG. 1, a vehicle 100 includes an engine 20, an engine cooling device 10 for cooling engine 20, and a thermal component 300.

Engine cooling device 10 includes an electric water pump (hereinafter, referred to as “electric pump”) 30, a radiator 40, a radiator circulation passage 50, a bypass passage 60, and a thermostat valve 70. Moreover, engine cooling device 10 further includes an engine-side coolant water temperature sensor 80, a radiator-side coolant water temperature sensor 90, and a control device (hereinafter, also referred to as “ECU (Electronic Control Unit)”) 200.

Engine 20 has a water jacket 24 for cooling engine 20 by means of coolant water. Water jacket 24 is formed around cylinders of engine 20 and constitutes a coolant water passage 25 allowing coolant water to pass therethrough. Coolant water passage 25 is provided between an inlet 27 and an outlet 26, and allows coolant water from inlet 27 to be sent out from outlet 26. The coolant water flowing into coolant water passage 25 performs a heat exchange with engine 20 to cool engine 20. Accordingly, engine 20 is maintained at a temperature which is suitable for combustion.

Electric pump 30 is a pump driven by an electric motor to circulate coolant water of engine 20. Electric pump 30 is mounted to an attachment-side surface portion 22 of an engine main body. Electric pump 30 allows coolant water to be sent out from inlet 27 into coolant water passage 25.

Driving and stopping of electric pump 30 is controlled by a control signal received from ECU 200. Further, a discharge amount of coolant water discharged from electric pump 30 is controlled by a control signal received from ECU 200.

Outlet 26 constitutes a branch portion 120. Branch portion 120 is connected to radiator circulation passage 50 and bypass passage 60. Branch portion 120 separates coolant water from coolant water passage 25 into coolant water directed to radiator circulation passage 50 and coolant water directed to bypass passage 60.

Radiator circulation passage 50 is a passage for circulating coolant water between engine 20, electric pump 30, and radiator 40. Radiator circulation passage 50 is constituted by pipes 50a, 50b and radiator 40. Pipe 50a is provided between branch portion 120 and an inlet 42 of radiator 40. Pipe 50b is provided between an outlet 44 of radiator 40 and thermostat valve 70. Coolant water warmed up in engine 20 passes through radiator 40 and is cooled.

Radiator 40 performs a heat exchange between coolant water flowing in radiator 40 and outside air to thereby radiate heat of the coolant water. Radiator 40 is provided with cooling fans 46. Cooling fan 46 accelerates a heat exchange through ventilation to improve a heat-radiation efficiency of the coolant water in radiator 40. Coolant water cooled in radiator 40 is sent out from outlet 44.

Bypass passage 60 is a passage for circulating coolant water without passing through radiator 40. Bypass passage 60 is constituted by pipes 60a, 60b and thermal component 300. Pipe 60a is provided between branch portion 120 and thermal component 300. Pipe 60b is provided between thermal component 300 and thermostat valve 70.

Thermal component 300 includes an EGR (Exhaust Gas Recirculation) cooler 28, a pipe 29, an exhaust heat recovery unit 32, a heater core 36, a throttle body 35, and an EGR valve 34.

EGR cooler 28 cools EGR gas by means of coolant water. Throttle body 35 is warmed up by coolant water to prevent occurrence of adhesion and the like. EGR valve 34 is cooled by the coolant water. Exhaust heat recovery unit 32 warms up the coolant water by heat of exhaust gas to thereby improve an engine mobility during a low temperature.

Heater core 36 is used as a heater of an air-conditioning device, and performs a heat exchange between coolant water and blast air of the air-conditioning device to heat the blast air. It should be note that the air-conditioning device may operate even during stopping of engine 20. When a heating request is given by the air-conditioning device during stopping of engine 20, electric pump 30 operates to circulate coolant water through bypass passage 60, so that a heat exchange is performed by heater core 36 between the coolant water and the blast air of the air-conditioning device. This lowers the temperature of the coolant water flowing through bypass passage 60.

Thermostat valve 70 is arranged at a merging portion 110 which merges coolant water having passed through radiator circulation passage 50 and coolant water having passed through bypass passage 60. Merging portion 110 is connected to radiator 40 through pipe 50b and connected also to pipe 60b. The coolant water from merging portion 110 returns to a suction port of electric pump 30. Thermostat valve 70 is configured to be switched to either a closed state or an opened state in accordance with a temperature of coolant water flowing in thermostat valve 70 (in the vicinity of the valve body).

In the case where a temperature of coolant water in the vicinity of the valve body of thermostat valve 70 is less than a predetermined valve-opening temperature (for example, 70° C.), thermostat valve 70 attains a closed state. In this case, coolant water on the side of bypass passage 60 passes through thermostat valve 70 and is outputted to water jacket 24, but coolant water on the side of radiator circulation passage 50 is intercepted by thermostat valve 70 and not outputted to water jacket 24. Accordingly, coolant water having taken heat from engine 20 flows back to engine 20 (water jacket 24) without being cooled by radiator 40, so that engine 20 is warmed up.

Meanwhile, in a case where a temperature of coolant water in the vicinity of the valve body of thermostat valve 70 is equal to or higher than the valve-opening temperature described above, thermostat valve 70 is attains an opened state. In this case, coolant water from radiator circulation passage 50 and coolant water from bypass passage 60 pass through thermostat valve 70 and are outputted to water jacket 24. Moreover, an opening degree of thermostat valve 70 is adjusted in accordance with a temperature of coolant water. Accordingly, a mixture ratio between the coolant water from radiator circulation passage 50 and the coolant water from bypass passage 60 is adjusted, so that the temperature of the coolant water passing through water jacket 24 is maintained at an appropriate temperature.

Engine-side coolant water temperature sensor 80 is provided at branch portion 120. Engine-side coolant water temperature sensor 80 detects a temperature of coolant water sent out from outlet 26 (hereinafter, referred to as “engine outlet water temperature ECT” or simply as “ECT”) and outputs a detection result (ECT detection value) to ECU 200. It should be noted that engine-side coolant water temperature sensor 80 is all necessary to be provided on a passage through which coolant water always circulates, and it may be provided for example on coolant water passage 25.

Radiator-side coolant water temperature sensor 90 is provided on pipe 50a. Radiator-side coolant water temperature sensor 90 detects a temperature of coolant water flowing into pipe 50a of radiator circulation passage 50 (hereinafter, referred to as “radiator inlet water temperature RCT” or simply as “RCT”) and outputs a detection result (RCT detection value) to ECU 200. It should be noted that radiator-side coolant water temperature sensor 90 is all necessary to be provided on radiator circulation passage 50, and it may be provided for example on pipe 50b.

In vehicle 100 having such a configuration as described above, when thermostat valve 70 is failed, abnormalities may occur including a close failure in which the valve body does not open even if a coolant water temperature in the vicinity of the valve body rises beyond the valve-opening temperature, and an open failure in which the valve body does not close even if a coolant water temperature in the vicinity of the valve body is lowered to be less than the valve-opening temperature. In the state where such a failure occurs, coolant water at an appropriate water temperature cannot be supplied to coolant water passage 25 of engine 20, so that an operation efficiency of engine 20 is lowered. Therefore, it is preferable to continuously perform a failure diagnosis on whether or not thermostat valve 70 functions normally during operation of engine 20 to thereby find a failure in an early stage.

Accordingly, ECU 200 performs a failure diagnosis for thermostat valve 70 based on an ECT detection value received from engine-side coolant water temperature sensor 80 and an RCT detection value received from radiator-side coolant water temperature sensor 90. This ECU 200 is configured by a CPU (Central Processing Unit), a storage device, an input/output buffer, and the like (none of these are illustrated).

As one example, ECU 200 implements a failure diagnosis with a high diagnosis accuracy as will be described in the following. In other words, in a water temperature region where thermostat valve 70 essentially does not open (in a water temperature region lower than the valve-opening temperature), thermostat valve 70 is in the closed state. Therefore, theoretically, the coolant water flows into bypass passage 60, and the coolant water does not flow into radiator circulation passage 50. Therefore, a difference equal to or greater than a predetermined value occurs between the ECT detection value and the RCT detection value. Thus, in the water temperature region where thermostat valve 70 essentially does not open, when the difference between the ECT detection value and the RCT detection value is less than the predetermined value, it is determined that thermostat valve 70 is opened, in other words, an open failure occurs in thermostat valve 70.

However, indeed, even when thermostat valve 70 is normally closed, a rise in the water pressure in radiator circulation passage 50 by driving of electric pump 30 causes the coolant water in radiator circulation passage 50 to leak out from thermostat valve 70 to coolant water passage 25. In this case, even though thermostat valve 70 is in the closed state, coolant water of the amount corresponding to the leakage flow rate of thermostat valve 70 flows from coolant water passage 25 into radiator circulation passage 50 and is mixed with the coolant water present in radiator circulation passage 50, so that radiator inlet water temperature RCT comes close to engine outlet water temperature ECT. Since it causes the temperature difference between the ECT detection value and the RCT detection value to be small, it may lower an accuracy of the failure diagnosis.

Therefore, ECU 200 performs a failure diagnosis for thermostat valve 70 taking into consideration that the coolant water leaks out from thermostat valve 70 even when thermostat valve 70 is in a normal state. Specifically, ECU 200 performs a process of calculating an estimation value of radiator inlet water temperature RCT based on the ECT detection value and the leakage flow rate of thermostat valve 70, and diagnosing whether or not thermostat valve 70 is failed based on a result of comparing the calculated RCT estimation value and the RCT detection value (hereinafter, referred to as “thermostat valve failure diagnosis process”). This thermostat valve failure diagnosis process will be described later in detail with reference to a flowchart.

Meanwhile, as described above, the heat of the coolant water heated by the exhaust heat of engine 20 can be utilized for heating and the like by the air-conditioning device. In this embodiment, the heat is used for heating by the air-conditioning device with use of heater core 36 provided on bypass passage 60. Here, the heat of the heated coolant water can be used even during stopping of engine 20, and the coolant water may be circulated by operating electric pump 30 in accordance with a heating request or the like during stopping of engine 20. In this case, since engine 20 is stopped, thermostat valve 70 is closed, and the coolant water does not flow into radiator circulation passage 50 but circulate through coolant water passage 25 of engine 20 and bypass passage 60. In that case, the coolant water circulating through coolant water passage 25 and bypass passage 60 is deprived of heat by heater core 36, and on the other hand the coolant water remaining in radiator circulation passage 50 radiates heat only in a natural manner. Therefore, it is likely to cause a situation in which the temperature of the coolant water circulating though coolant water passage 25 and bypass passage 60 becomes lower than the temperature of the coolant water in radiator circulation passage 50. Accordingly, although engine outlet water temperature ECT is generally higher than radiator inlet water temperature RCT, the relationship between engine outlet water temperature ECT and radiator inlet water temperature RCT is inversed, so that erroneous determination may be made in the failure diagnosis.

FIG. 2 represents one example of a change in the engine coolant water temperature before and after starting of engine 20. Referring to FIG. 2, it is assumed that, before time t1, engine 20 is stopped, and use of a heater and the like during stopping of the engine causes a situation of ECT detection value <RCT detection value. It should be noted that the failure diagnosis for thermostat valve 70 is not performed during stopping of engine 20.

It is assumed that engine 20 is started at time t1. In that case, the engine coolant water is heated by the exhaust heat of engine 20, and the ECT detection value indicating the temperature of the coolant water at the engine outlet starts to rise. It should be noted that, immediately after starting of engine 20, the temperature of the coolant water is lower than the valve-opening temperature of thermostat valve 70, and thermostat valve 70 is closed, so that no rise in the RCT detection value can be seen. Then, until time t2, the ECT detection value <RCT detection value continues, and it attains the ECT detection value >RCT detection value on or after time t2.

As can be seen, even when engine 20 is started at time t1, the ECT detection value <RCT detection value continues until time t2. Therefore, if the failure diagnosis is started before time t2, erroneous determination is made since the relationship of ECT detection value >RCT detection value which should be essentially provided is inversed. Therefore, in this embodiment, taking into consideration the erroneous determination region between times t1 and t2, in the case where electric pump operates in accordance with a heating request or the like of the air-conditioning device during stopping of engine 20 (thermostat valve 70 is in the closed state), ECU 200 delays starting of the failure diagnosis process for thermostat valve 70 performed after starting of engine 20 as compared to the case where electric pump 30 does not operate during stopping of engine 20. Accordingly, the failure diagnosis is avoided in the state where the relationship between the ECT detection value and the RCT detection value is inversed, so that the erroneous determination in the failure diagnosis is suppressed.

FIG. 3 is a flowchart for describing procedures of the thermostat valve failure diagnosis process executed by ECU 200 shown in FIG. 1. The process shown in this flowchart is executed at the time of starting engine 20, for example, at the time of starting engine after idling stop. In the case where vehicle 100 is a hybrid vehicle, the process is executed further at the time of starting an engine when switched from EV traveling with use of a drive force of a motor after stopping engine 20 to HV traveling with operation of engine 20. This flowchart is achieved by executing a program stored in ECU 200 at predetermined cycles, and the process of some steps can be achieved by constructing a dedicated hardware (electronic circuit).

Referring to FIG. 3, ECU 200 calculates an estimation value of radiator inlet water temperature RCT (RCT estimation value) based on the ECT detection value received from engine-side coolant water temperature sensor 80, and a leakage flow rate into radiator circulation passage 50 when thermostat valve 70 is in the closed state (Step S10). Specifically, ECU 200 can calculate the RCT estimation value with use of the following expression as one example.

RCT estimation value=(ECT detection value×leakage flow rate+RCT estimation value (previous value)×(pipe volume−leakage flow rate))/pipe volume  (1)

In Expression (1), the RCT estimation value is calculated based on the assumption that the coolant water with the ECT detection value and the coolant water with the RCT estimation value (previous value) are evenly mixed in accordance with a ratio of the leakage flow rate with respect to the pipe volume.

Herein, the leakage flow rate may be a fixed value determined in advance based on an experimental result or the like, or it may be a variable value set to have a larger value as the flow rate of electric pump 30 for example is larger. The pipe volume is a volume of the pipe through which the coolant water flows from engine-side coolant water temperature sensor 80 to radiator-side coolant water temperature sensor 90. It should be noted that the calculation accuracy can be improved by dividing the pipe into any number of regions and applying the expression of (1) described above to each divided region.

Next, ECU 200 executes the process of determining whether or not a precondition for executing an open failure diagnosis process for thermostat valve 70 (hereinafter, simply referred to as “diagnosis precondition”) is met (Step S20). The contents of this process will be described in detail in FIG. 4 which will be described later.

Then, ECU 200 determines whether or not the thermostat open failure diagnosis process will be performed based on the process result of Step S20 (Step S30). When it is determined that the diagnosis precondition is not met (NO in Step S30), ECU 200 terminates the process without executing the thermostat open failure diagnosis process (processes of Steps S40 to S60). In other words, ECU 200 prohibits the thermostat open failure diagnosis process in the case where the diagnosis precondition is not met.

On the other hand, when it is determined in Step S30 that the diagnosis precondition is met (YES in Step S30), ECU 200 executes the thermostat open failure diagnosis process (the processes of Steps S40 to S60).

In other words, ECU 200 determines whether or not the RCT detection value received from radiator-side coolant water temperature sensor 90 is higher than the RCT estimation value calculated in Step S10 (Step S40). Then, when the RCT detection value is higher than the RCT estimation value (YES in Step S40), ECU 200 determines that thermostat valve 70 is in the open failure state (Step S50). This is because when thermostat valve 70 is in the open failure state, the heated coolant water of the amount larger than the expected leakage flow rate flows into radiator circulation passage 50, and a situation in which the RCT detection value is higher than the RCT estimated value occurs. On the other hand, when the RCT detection value is equal to or lower than the RCT estimation value (NO in Step S40), ECU 200 determines that thermostat valve 70 is normal (Step S60).

FIG. 4 is a flowchart representing the process procedures for the diagnosis precondition determination executed in Step S20 of FIG. 3. Referring to FIG. 4, ECU 200 determines whether or not the monitoring precondition is met. The monitoring precondition is a condition set as a precondition for monitoring a water temperature rise quantity ΔECT indicating a rise in the coolant water temperature from starting of the engine in Steps S130 and S160 which will be described later. As one example, ECU 200 determines that the monitoring precondition is met when all of the following conditions (a) to (f) are met.

(a) After current starting of an engine, the thermostat failure diagnosis is not completed.

(b) The ECT detection value is less than the valve-opening temperature (for example, 70° C.) of thermostat valve 70.

(c) The ECT detection value at the time of starting the engine is included in the range of −10° C. to +56° C.

(d) The engine is started.

(e) The time change quantity of the ECT detection value is equal to or greater than a predetermined value (for example, 0.1° C./second).

(f) Engine-side coolant water temperature sensor 80 and radiator-side coolant water temperature sensor 90 are normal.

Condition (a) provides the premise that the thermostat failure diagnosis is performed once between starting of engine 20 and stopping next. Condition (b) is a condition for assuring that thermostat valve 70 is essentially (if it is normal) closed. Conditions (c) and (d) are conditions for assuring that the ECT detection value increases in a manner capable of performing the thermostat failure diagnosis after starting the engine. Condition (e) is a condition for assuring a rise in the engine water temperature after starting the engine. Condition (f) is a condition for assuring a reliability of the ECT detection value or the RCT detection value. It should be noted that, as the monitoring precondition, conditions (a) to (f) described above may be selected as needed.

When it is determined in Step S110 that the monitoring precondition is not met (NO in Step S110), ECU 200 shifts the process to Step S180 and determines that the diagnosis precondition is not met (Step S180).

When it is determined in Step S110 that the monitoring precondition is met (YES in Step S110), ECU 200 determines whether or not electric pump 30 operates during previous stopping of the engine (from previous stopping of the engine to the current starting of the engine) (Step S120).

In the case where electric pump 30 operates during stopping of the engine (YES in Step S120), ECU 200 determines whether or not the water temperature rise quantity ΔECT indicating a rise in the quantity of the ECT detection value after starting of engine 20 is larger than a predetermined value A (>predetermined value B) (Step S130). This predetermined value A is a determination value of the diagnosis precondition for the case where electric pump 30 operates during stopping of the engine, and it is larger than a determination value B (default value) of the diagnosis precondition for the case where electric pump 30 does not operate during stopping of the engine. As one example, predetermined value B is 1° C., and predetermined value A is 3° C. Accordingly, starting of the failure diagnosis for the case where electric pump 30 operates during stopping of the engine can be delayed as compared to the case where electric pump 30 does not operate during stopping of the engine.

Then, when it is determined in Step S130 that water temperature rise quantity ΔECT is larger than predetermined value A (YES in Step S130), ECU 200 determines that the diagnosis precondition is met (Step S140). When it is determined in Step S130 that water temperature rise quantity ΔECT is less than or equal to predetermined value A (NO in Step S130), it is determined that the diagnosis precondition is not met (Step S150).

On the other hand, when it is determined in Step S120 that electric pump 30 does not operate during previous stopping of the engine (NO in Step S120), ECU 200 determines whether or not water temperature rise quantity ΔECT is larger than predetermined value B (Step S160). When it is determined in Step S160 that water temperature rise quantity ΔECT is larger than predetermined value B (YES in Step 160), ECU 200 determines that the diagnosis precondition is met (Step S170). When it is determined in Step S160 that water temperature rise quantity ΔECT is less than or equal to predetermined value B (NO in Step S160), ECU 200 determines that the diagnosis precondition is not met (Step S180).

As described above, in this engine cooling device 10, in the case where electric pump 30 operates in accordance with a heating request or the like of the air-conditioning device during stopping of engine 20, starting of the failure diagnosis performed after starting of engine 20 is delayed as compared to the case where electric pump 30 does not operate during stopping of engine 20, so that starting of the failure diagnosis of thermostat valve 70 in the state where the relationship between engine outlet water temperature ECT and radiator inlet water temperature RCT is inversed can be avoided. Thus, according to this engine cooling device 10, erroneous determination can be suppressed in the failure diagnosis of thermostat valve 70.

Moreover, while the failure diagnosis for thermostat valve 70 is performed based on the temperature of the coolant water, according to this engine cooling device 10, starting of the failure diagnosis is adjusted based on the coolant water temperature, so that the start timing of the failure diagnosis can be adjusted with a high accuracy.

Moreover, according to this engine cooling device 10, the failure diagnosis of thermostat valve 70 is performed taking into consideration the leakage flow rate through radiator circulation passage 50 in the closed state of thermostat valve 70, so that the failure diagnosis can be performed with a high accuracy.

Modified Example 1

In the embodiment described above, starting of the thermostat valve failure diagnosis process after starting of the engine (the diagnosis precondition is met) is delayed based on the rise quantity (ΔECT) of the engine coolant water temperature (ECT detection value) after starting of engine 20. In place of water temperature rise quantity ΔECT, an integrated amount of the intake air volume into engine 20 from starting of engine 20 may be used. This is because the integrated intake air volume from starting of engine 20 may represent a tendency of the rise in temperatures of engine 20 and the coolant water.

The overall configuration of the vehicle in this Modified Example 1 is the same as vehicle 100 shown in FIG. 1. Moreover, the procedures of the overall process of the thermostat valve failure diagnosis executed by ECU 200 of this Modified Example 1 is the same as the process procedures shown in FIG. 3.

FIG. 5 is a flowchart representing process procedures of the diagnosis precondition determination (the process executed in Step S20 of FIG. 3) in this Modified Example 1. Referring to FIG. 5, this flowchart includes, in the flowchart shown in FIG. 4, Steps S132 and S136 in place of Steps S130 and S160.

In other words, when it is determined in Step S120 that electric pump 30 operates during previous stopping (YES in Step S120), ECU 200 determines whether or not an integrated intake air volume indicating an integrated amount of the intake air volume into engine 20 from starting of engine 20 is greater than a predetermined value C (>predetermined value D) (Step S132). It should be noted that predetermined value C is a determination value of the diagnosis precondition for the case where electric pump 30 operates during stopping of the engine, and it is larger than determination value D (default value) for the case where electric pump 30 does not operate during stopping of the engine. As one example, predetermined value C is 50 g, and predetermined value D is 20 g. It should be noted that the intake air volume into engine 20 can be detected with use of an air flow meter. With predetermined value C >predetermined value D, starting of the failure diagnosis for the case where electric pump 30 operates during stopping of the engine can be delayed as compared to the case where electric pump 30 does not operate during stopping of the engine.

Then, when it is determined in Step S132 that the integrated intake air volume is larger than predetermined value C (YES in Step S132), the process is shifted to Step S140, and it is determined that the diagnosis precondition is met. When it is determined that the integrated intake air volume is equal to or less than predetermined value C in Step S132 (NO in Step S132), the process is shifted to Step S150, and it is determined that the diagnosis precondition is not met.

On the other hand, when it is determined in Step S120 that electric pump 30 does not operate during previous stopping of the engine (NO in Step S120), ECU 200 determines whether or not the integrated intake air volume is larger than predetermined value D (Step S162). Then, when it is determined that the integrated intake air volume is larger than predetermined value D (YES in Step S162), the process is shifted to Step S170, and it is determined that the diagnosis precondition is met. When it is determined in Step S162 that the integrated intake air volume is less than or equal to predetermined value D (NO in Step S162), the process is shifted to Step S180, and it is determined that the diagnosis precondition is not met.

Also by this Modified Example 1, in the case where electric pump 30 operates in accordance with a heating request or the like of the air-conditioning device during stopping of engine 20, starting of the failure diagnosis performed after starting of engine 20 can be delayed as compared to the case where electric pump 30 does not operate during stopping of engine 20. Accordingly, similarly to the embodiment described above, erroneous determination can be suppressed in the failure diagnosis of thermostat valve 70.

Modified Example 2

While starting of the thermostat valve failure diagnosis from starting of engine 20 (the diagnosis precondition is met) is delayed based on the integrated intake air volume from starting of engine 20 in Modified Example 1 described above, time from starting of engine 20 can be measured to use an elapsed time after starting of the engine. Accordingly, the process of capturing a detection signal of a sensor and the calculation process are not required, so that the process of ECU 200 is simplified. Moreover, starting of the failure diagnosis can be adjusted without being affected by an abnormality of the sensor and a measurement accuracy.

The overall configuration of the vehicle in this Modified Example 2 is the same as that of vehicle 100 shown in FIG. 1. Moreover, the procedures of the overall process of the thermostat valve failure diagnosis executed by ECU 200 in this Modified Example 2 are the same as the process procedures shown in FIG. 3.

FIG. 6 is a flowchart representing the process procedures for determining the diagnosis precondition (the process executed in Step S20 of FIG. 3) in this Modified Example 2. Referring to FIG. 6, this flowchart includes, in the flowchart shown in FIG. 4, Steps S134 and S164 in place of Steps S130 and S160.

In other words, when it is determined in Step S120 that electric pump 30 operates during previous stopping of the engine (YES in Step S120), ECU 200 determines whether or not an elapsed time from starting of engine 20 exceeds a predetermined value T1 (>predetermined value T2) (Step S134). It should be noted that predetermined value T1 is a determination value of the diagnosis precondition for the case where electric pump 30 operates during stopping of the engine, and it is larger than determination value T2 (default value) of the diagnosis precondition for the case where electric pump 30 does not operate during stopping of the engine. As one example, predetermined value T1 is 5 seconds, and predetermined value T2 is 2 seconds. It should be noted that the elapsed time from starting of engine 20 can be measured by means of a timer or the like not illustrated in the drawings. With predetermined value T1>predetermined value T2, starting of the failure diagnosis for the case where electric pump 30 operates during stopping of the engine can be delayed as compared to the case where electric pump 30 does not operate during stopping of the engine.

Then, when it is determined in Step S134 that the elapsed time exceeds predetermined value T1 (YES in Step S134), the process is shifted to Step S140, and it is determined that the diagnosis precondition is met. When it is determined in Step S134 that the elapsed time is less than or equal to predetermined value T1 (NO in Step S134), the process is shifted to Step S150, and it is determined that the diagnosis precondition is not met.

On the other hand, when it is determined in Step S120 that electric pump 30 does not operate during previous stopping of the engine (NO in Step S120), ECU 200 determines whether or not the elapsed time exceeds predetermined value T2 (Step S164). Then, when it is determined that the elapsed time exceeds predetermined value T2 (YES in Step S164), the process is shifted to Step S170, and it is determined that the diagnosis precondition is met. When it is determined in Step S164 that the elapsed time is less than or equal to predetermined value T2 (NO in Step S164), the process is shifted to Step S180, and it is determined that the diagnosis precondition is not met.

Also by this Modified Example 2, in the case where electric pump 30 operates in accordance with a heating request or the like of the air-conditioning device during stopping of engine 20, starting of the failure diagnosis performed after starting of engine 20 can be delayed as compared to the case where electric pump 30 does not operate during stopping of engine 20. Accordingly, similarly to the embodiment described above, erroneous determination can be suppressed in the failure diagnosis of thermostat valve 70.

Moreover, in this Modified Example 2, starting of the failure diagnosis is adjusted based on the elapsed time from starting of engine 20. Therefore, the process of capturing a detection signal of a sensor and the calculation process are not required. Thus, according to this Modified Example 2, the process of ECU 200 can be simplified. Moreover, starting of the failure diagnosis can be adjusted without being affected by an abnormality of the sensor and the measurement accuracy.

It should be noted that, while the failure diagnosis of thermostat valve 70 is performed taking into consideration the leakage flow rate through radiator circulation passage 50 in the closed state of thermostat valve 70 in the embodiment described above and Modified Examples 1 and 2 thereof, the method of the failure diagnosis is not limited to such methods. For example, the present invention is applicable for the case where the failure diagnosis is performed based on the comparison between ECT detection value and the RCT detection value in more simple manner.

It should be noted that this invention is applicable also to a hybrid vehicle provided with a traveling motor in addition to engine 20 and a vehicle not provided with the traveling motor. In the vehicle not provided with the traveling motor, this invention is applicable to starting of the engine after idling stop or after IG-on operation by a user. In the hybrid vehicle, this invention is further applicable to starting of engine when switching from the EV traveling to the HV traveling.

It should be noted that, in the description above, engine 20 corresponds to one example of the “internal combustion engine” of this invention, and heater core 36 corresponds to one example of the “heat exchanger” of this invention. Moreover, engine-side coolant water temperature sensor 80 corresponds to one example of the “first temperature sensor” of this invention, and radiator-side coolant water temperature sensor 90 corresponds to one example of the “second temperature sensor” of this invention.

Although the present invention has been described and illustrated in detail, it should be understood that the same is by way of illustration and example only and is not to be taken by way of limitation. The scope of the present invention is indicated by the scope of claims, and includes meaning equivalent to that of the scope of claims and all the modification within the scope.

Claims

1. A cooling device for an internal combustion engine, comprising:

a coolant water passage formed in said internal combustion engine;

a radiator configured to cool coolant water;

a radiator circulation passage configured to allow coolant water discharged from said coolant water passage to pass through said radiator and return to said coolant water passage;

a bypass passage configured to allow coolant water discharged from said coolant water passage to return to said coolant water passage without passing through said radiator;

a heat exchanger provided on said bypass passage and utilizing heat of said coolant water; and

a thermostat valve connected to said radiator circulation passage and said bypass passage,

said thermostat valve being switched, in accordance with a temperature of coolant water flowing in said thermostat valve, to either a closed state of intercepting coolant water from said radiator circulation passage and outputting coolant water from said bypass passage to said coolant water passage, or an opened state of outputting coolant water from said radiator circulation passage and coolant water from said bypass passage to said coolant water passage,

said cooling device further comprising:

an electric pump configured to allow coolant water to circulate;

a first temperature sensor configured to detect a temperature of coolant water in said coolant water passage;

a second temperature sensor configured to detect a temperature of coolant water in said radiator circulation passage; and

a control device configured to perform a failure diagnosis for said thermostat valve after starting of said internal combustion engine based on an output of said first temperature sensor and an output of said second temperature sensor, wherein

when said electric pump operates in accordance with an operation request of said heat exchanger during stopping of said internal combustion engine, said thermostat valve attains the closed state, and

in a case where said electric pump operates during stopping of said internal combustion engine, said control device delays starting of said failure diagnosis performed after starting of said internal combustion engine as compared to a case where said electric pump does not operate during stopping of said internal combustion engine.

2. The cooling device for an internal combustion engine according to claim 1, wherein said control device starts said failure diagnosis when a rise quantity of a coolant water temperature, which is detected by said first temperature sensor, from starting of said internal combustion engine exceeds a predetermined value, and

a first value indicating said predetermined value for the case where said electric pump operates during stopping of said internal combustion engine is larger than a second value indicating said predetermined value for the case where said electric pump does not operate during stopping of said internal combustion engine.

3. The cooling device for an internal combustion engine according to claim 2, wherein said control device calculates an estimation value of the coolant water temperature in said radiator circulation passage based on a leakage flow rate through said radiator circulation passage in the closed state of said thermostat valve and on an output of said first temperature sensor, and diagnoses that said thermostat valve is failed in a case where an output value of said second temperature sensor is larger than the calculated estimation value.

4. The cooling device for an internal combustion engine according to claim 1, wherein said control device integrates an intake air volume to said internal combustion engine from starting of said internal combustion engine, and starts said failure diagnosis when the integrated value of said intake air volume exceeds a predetermined value, and

a first value indicating said predetermined value for the case where said electric pump operates during stopping of said internal combustion engine is larger than a second value indicating said predetermined value for the case where said electric pump does not operate during stopping of said internal combustion engine.

5. The cooling device for an internal combustion engine according to claim 4, wherein said control device calculates an estimation value of the coolant water temperature in said radiator circulation passage based on a leakage flow rate through said radiator circulation passage in the closed state of said thermostat valve and on an output of said first temperature sensor, and diagnoses that said thermostat valve is failed in a case where an output value of said second temperature sensor is larger than the calculated estimation value.

6. The cooling device for an internal combustion engine according to claim 1, wherein said control device starts said failure diagnosis when an elapsed time from starting of said internal combustion engine exceeds a predetermined value, and

a first value indicating said predetermined value for the case where said electric pump operates during stopping of said internal combustion engine is larger than a second value indicating said predetermined value for the case where said electric pump does not operate during stopping of said internal combustion engine.

7. The cooling device for an internal combustion engine according to claim 6, wherein said control device calculates an estimation value of the coolant water temperature in said radiator circulation passage based on a leakage flow rate through said radiator circulation passage in the closed state of said thermostat valve and on an output of said first temperature sensor, and diagnoses that said thermostat valve is failed in a case where an output value of said second temperature sensor is larger than the calculated estimation value.