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.

What is claimed is: 
     
         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.