An abnormality diagnosis device of a thermostat includes: a temperature detection module that detects a temperature of cooling water on the basis of a sensor signal of a cooling water temperature sensor; an abnormality determination module that detects an abnormality of the thermostat, when the temperature of the cooling water reaches a first reference temperature and thereafter becomes lower than an abnormality determination reference temperature that is lower than the first reference temperature; and a cooling water temperature adjustment module that executes a control for preventing temperature decrease of the cooling water, when the temperature of the cooling water reaches the first reference temperature and thereafter becomes lower than a second reference temperature that is lower than the first reference temperature and is higher than the abnormality determination reference temperature.

A valve for use in a coolant flow. The valve comprises a valve housing with an inlet and at least one outlet, a valve body which is rotatably received by the valve housing, an actuator for rotating the valve body, and a fail-safe mechanism which can be pretensioned rotationally. The valve body is in rotational engagement with an axially moveable coupling element, via which the valve body is releasably connected indirectly to the actuator shaft. In the event of a fault, the valve body can be decoupled from the actuator shaft by an axial movement of the coupling element. The axial movement of the coupling element also causes the fail-safe mechanism to come into rotational engagement with the coupling element in order to rotate the valve body to a predefined fail-safe position.

Disclosed herein is a fault diagnosis method of a thermostat including: confirming, by a controller, whether a flow stop valve is equipped in a vehicle; if it is determined that the flow stop valve is equipped in the vehicle, diagnosing the flow stop valve; and if it is determined that the diagnosis on the flow stop valve ends, diagnosing the thermostat to determine whether the thermostat is faulty.

When both a position sensor and a motor malfunction, an ECU limits the engine rotation speed to such a speed range that the pressure inside a circulation route remains at or below a predetermined value even when the opening degree of a control valve is a minimum opening degree. When the position sensor is malfunction but the motor is not malfunction, the ECU relaxes the limits on the engine rotation speed, compared with when both the position sensor and the motor are malfunction, by driving the motor to an end of a motion range thereof and increasing the opening degree of the control valve to an opening degree larger than the minimum opening degree.

A system includes an internal combustion engine having a thermostat provided to selectively allow coolant flow through the engine, and a coolant temperature determination device that provides a coolant temperature value. The system further includes a controller structured to functionally execute operations to diagnose the thermostat. The controller determines whether the engine is providing a high output operation. When the engine is providing a high output operation, the controller determines the thermostat is passed in response to the coolant temperature value exceeding a first threshold temperature value.

A thermostat is diagnosed as open failure when a specified time variation in radiator inflow water temperature from a temperature sensor mounted in a first flow path running through a radiator at a time of starting an electric water pump at a cold start of an engine is equal to or greater than a predetermined variation. In the case of open failure of the thermostat, starting the electric water pump causes cooling water from a cooling water flow path of the engine to be flowed to the first flow path, as well as to a second flow path. The radiator inflow water temperature detected by the temperature sensor mounted in the first flow path is raised by the cooling water from the cooling water flow path of the warmed engine.

An ECU that is a diagnostic device includes a calculation unit that is a water temperature obtaining unit obtaining the temperature of a discharge coolant which is a coolant discharged from an engine, a diagnostic unit that diagnoses a thermostat which is a temperature adjusting valve by comparing the temperature of the discharge coolant and a threshold, and a suspending unit that suspends a diagnosis performed by the diagnostic unit. The suspending unit suspends a diagnosis performed by the diagnostic unit in a case where the temperature of the discharge coolant is estimated to be lower than the threshold according to an operating condition of the vehicle even though the thermostat is normal.

Disclosed herein is a fault diagnosis method of a thermostat including: confirming, by a controller, whether a flow stop valve is equipped in a vehicle; if it is determined that the flow stop valve is equipped in the vehicle, diagnosing the flow stop valve; and if it is determined that the diagnosis on the flow stop valve ends, diagnosing the thermostat to determine whether the thermostat is faulty.

A thermostat failure detection device sequentially calculates a normal-time minimum water temperature on an assumption that a thermostat is normal and an internal combustion engine is operated in a state where the engine water temperature is less likely to rise, sequentially calculates a failure-time maximum water temperature on an assumption that the thermostat is in a stuck-open failure state and the internal combustion engine is operated in a state where the engine water temperature is likely to rise, determines the failure of the thermostat if the engine water temperature is lower than the normal-time minimum water temperature, determines the normality of the thermostat if the engine water temperature is higher than the failure-time maximum water temperature, and determines neither the normality nor the failure if the engine water temperature is between the normal-time minimum water temperature and the failure-time maximum water temperature.