Abnormality determination apparatus and abnormality determination method for coolant temperature sensor, and engine cooling system

Abstract

A coolant temperature sensor abnormality determination apparatus opens a changeover valve to increase the temperature of a coolant in a heater passageway if the amount of increase of the detected heater inlet coolant temperature value obtained when the intake air amount of an engine becomes equal to or greater than a predetermined value is small. Then, if the amount of increase in the detected heater inlet coolant temperature value after the changeover valve opens is greater than or equal to the predetermined value, the apparatus determines that the heater inlet coolant temperature sensor is normal. If the amount of increase in the detected heater inlet coolant temperature value is smaller than the predetermined value, the apparatus determines that the heater inlet coolant temperature sensor is abnormal.

1 . A coolant temperature sensor abnormality determination apparatus which is applied to an engine cooling system that includes a coolant passageway comprising an engine coolant passageway and a bypass passageway that bypasses an engine, a control valve that can be in an open state to allow mixing of coolant from the engine coolant passageway and coolant from the bypass passageway at a confluence between the engine coolant passageway and the bypass passageway and that can be in a closed state to restrict the mixing of the coolant from the engine coolant passageway and the coolant from the bypass passageway at the confluence between the engine coolant passageway and the bypass passageway, and a bypass coolant temperature sensor that is arranged in the coolant passageway, downstream of the confluence between the engine coolant passageway and the bypass passageway, and that detects a bypass coolant temperature, and which determines whether the bypass coolant temperature sensor is abnormal, the coolant temperature sensor abnormality determination apparatus comprising
 a determination portion that opens the control valve if an amount of increase of a detected value of the bypass coolant temperature obtained when the bypass coolant temperature is estimated to be equal to or greater than a first predetermined value is smaller than a second predetermined value, and that determines whether the bypass coolant temperature sensor is abnormal based on an amount of change in the detected value of the bypass coolant temperature obtained after the control valve opens.   
     
     
         2 . The coolant temperature sensor abnormality determination apparatus according  claim 1 , wherein:
 the determination portion determines that the bypass coolant temperature sensor is normal, if the amount of increase in the detected value of the bypass coolant temperature becomes equal to or greater than the second predetermined value after the control valve opens; and   the determination portion determines that the bypass coolant temperature sensor is abnormal, if the amount of increase in the detected value of the bypass coolant temperature is smaller than the second predetermined value after the control valve opens.   
     
     
         3 . The coolant temperature sensor abnormality determination apparatus according to  claim 1 , wherein the bypass passageway is provided with at least one of an exhaust heat recovery device and an EGR cooler. 
     
     
         4 . The coolant temperature sensor abnormality determination apparatus according to  claim 1 , wherein:
 the control valve is a temperature-sensitive operation valve that has a temperature sensitive portion that displaces a valve body; and   the coolant temperature sensor abnormality determination apparatus includes an open-valve state determination portion that determines that the control valve has opened, when an estimated value of an ambient coolant temperature of the control valve becomes equal to or greater than a valve-opening temperature of the control valve.   
     
     
         5 . The coolant temperature sensor abnormality determination apparatus according to  claim 1 , wherein after a predetermined time elapses following opening of the control valve, the determination portion executes determination regarding the bypass coolant temperature sensor. 
     
     
         6 . A coolant temperature sensor abnormality determination method which is for use in an engine cooling system that includes a coolant passageway comprising an engine coolant passageway and a bypass passageway that bypasses an engine, a control valve that can be in an open state to allow mixing of coolant from the engine coolant passageway and coolant from the bypass passageway at a confluence between the engine coolant passageway and the bypass passageway and that can be in a closed state to restrict the mixing of the coolant from the engine coolant passageway and the coolant from the bypass passageway at the confluence between the engine coolant passageway and the bypass passageway, and a bypass coolant temperature sensor that is arranged in the coolant passageway, downstream of the confluence between the engine coolant passageway and the bypass passageway, and that detects a bypass coolant temperature, and which determines whether the bypass coolant temperature sensor is abnormal, the coolant temperature sensor abnormality determination method comprising:
 detecting the bypass coolant temperature by using the bypass coolant temperature sensor when the bypass coolant temperature is estimated to be equal to or greater than a first predetermined value,   determining that the bypass coolant temperature sensor is normal if an amount of increase in the bypass coolant temperature detected is greater than or equal to a second predetermined value; and   opening the control valve if the amount of increase in the bypass coolant temperature detected is smaller than the second predetermined value, and detecting the bypass coolant temperature again by using the bypass coolant temperature sensor after the control valve opens, and determining whether the bypass coolant temperature sensor is abnormal on the basis of an amount of change in the bypass coolant temperature between before and after the control valve opens.   
     
     
         7 . An engine cooling system comprising:
 a coolant passageway comprising an engine coolant passageway and a bypass passageway that bypasses an engine;   a control valve that can be in an open state to allow mixing of coolant from the engine coolant passageway and coolant from the bypass passageway at a confluence between the engine coolant passageway and the bypass passageway and that can be in a closed state to restrict the mixing of coolant from the engine coolant passageway and the coolant from the bypass passageway at the confluence between the engine coolant passageway and the bypass passageway;   a bypass coolant temperature sensor that is arranged in the coolant passageway, downstream of the confluence between the engine coolant passageway and the bypass passageway, and that detects a bypass coolant temperature; and   a coolant temperature sensor abnormality determination portion that opens the control valve if an amount of increase of a detected value of the bypass coolant temperature obtained when the bypass coolant temperature is estimated to be equal to or greater than a first predetermined value is smaller than a second predetermined value, and that determines whether the bypass coolant temperature sensor is abnormal based on an amount of change in the detected value of the bypass coolant temperature obtained after the control valve opens.