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.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates to a cooling system of an engine (internal combustion engine) and, more particularly, to a coolant temperature sensor abnormality determination apparatus and a coolant temperature sensor abnormality determination method that determine the presence or absence of abnormality of a coolant temperature sensor of the cooling system.[0003]2. Description of Related Art[0004]With regard to an engine mounted in a vehicle or the like, a coolant jacket as a coolant passageway is provided in the engine (a cylinder block or a cylinder head), and the entire engine is cooled (or warmed) by circulating a coolant via the coolant jacket by a coolant pump. In conjunction with such a cooling system, there exists a technology in which a changeover valve that restricts the circulation of the coolant between an engine coolant passageway and a heater system (heater passageway) is provided, and while the engine is cold, the...

AI Technical Summary

Benefits of technology

[0007]The invention provides a coolant temperature sensor abnormality determination apparatus and a coolant temperature sensor abnormality determination method that are capable of precisely determining whether a coolant temperature sensor that detects the temperature of a coolant in a heater system is abnormal without making a false determination, in a cooling system that stops passage of a coolant within an engine.

[0013]As described above, according to the coolant temperature sensor abnormality determination apparatus in accordance with the foregoing aspect, in the case where the amount of increase of the detected bypass coolant temperature value obtained when the bypass coolant temperature is estimated to be equal to or greater than a predetermined value (when the amount of air taken into the engine becomes equal to or greater than a predetermined value) is smaller than the predetermined value, the apparatus opens the control valve to allow the high-temperature coolant from the engine to flow into the bypass passageway so that the temperature of the coolant in the bypass passageway increases, and while such a state of increased coolant temperature is maintained, determination regarding the bypass coolant temperature sensor is performed on the basis of the amount of change in the detected bypass coolant temperature value detected by the bypass coolant temperature sensor. Therefore, even if the bypass passageway does not have a heat source available due to a fault of an exhaust heat recovery device, an EGR cooler, etc., the apparatus is able to precisely determine whether the bypass coolant temperature sensor is abnormal without making a false determination.

[0014]Besides, in the coolant temperature sensor abnormality determination apparatus in accordance with the foregoing aspect, the control valve that restricts the circulation of the coolant between the engine coolant passageway and the bypass passageway may be a temperature-sensitive operation valve that has a temperature sensitive portion that displaces a valve body, and the coolant temperature sensor abnormality determination apparatus may determine that the control valve has opened, when an estimated value of ambient coolant temperature of the control valve becomes equal to or greater than a valve-opening temperature of the control valve. Adoption of this construction makes it possible to shorten the time that is needed for determination whether the control valve has opened. This will be explained below.

[0016]In the case where it is determined that the control valve has opened on the basis of the duration of electrification of the heater, in order to prevent a false determination that the control valve has opened when the valve actually has not opened, an open-valve state criterion value is adapted on the basis of the condition in which it takes the longest time before the control valve is opened. However, as for such an adaptation, the margin is very large, so that there is inevitably a long time before the determination regarding the normality or abnormality of the bypass coolant temperature sensor is performed. However, by adopting a method in which it is determined that the control valve has opened when the estimated value of the ambient coolant temperature of the control valve becomes equal to or greater than the valve-opening temperature, it becomes possible to determine that the control valve has opened according to the actual open state of the valve. Since this eliminates the need to provide the aforementioned margin, only a short time is needed before it is determined that the valve has opened, so that the time prior to the determination regarding the normality or abnormality of the bypass coolant temperature sensor can be shortened.

[0018]According to the coolant temperature sensor abnormality determination apparatus in accordance with the foregoing aspect, if the amount of increase in the detected bypass coolant temperature value obtained when the bypass coolant temperature is estimated to be equal to or greater than a predetermined value is relatively small, the control valve is opened to increase the coolant temperature in the bypass passageway, and then the determination regarding abnormality of the coolant temperature sensor is performed on the basis of the amount of change in the detected bypass coolant temperature value after the control valve has opened. Therefore, the presence of abnormality of the bypass coolant temperature sensor can be precisely determined without making a false determination.

[0021]According to the coolant temperature sensor abnormality determination method in accordance with the second aspect and the engine cooling system in accordance with the third aspect, it is possible to achieve substantially the same effects as those achieved by the coolant temperature sensor abnormality determination apparatus in accordance with the first aspect.

Problems solved by technology

Incidentally, an example of the abnormality of the coolant temperature sensor is a stuck abnormality in which the sensor value is fixed to a certain value.

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