Apparatus and method of determining failure in thermostat

1. An apparatus of determining a failure in a thermostat for controlling the flow of a coolant into a radiator in response to an actual water temperature of the coolant for an engine in a vehicle, the apparatus comprising:

a water temperature detector that detects the actual water temperature; and

a controller including:

a water temperature estimator that calculates an estimated water temperature of the coolant; and

a failure determining unit that compares the actual water temperature detected by the water temperature detector with the estimated water temperature calculated by the water temperature estimator under cold start of the engine and determines whether the thermostat is valve-open failure,

wherein in an automatic stop state of the engine, the water temperature estimator applies a behavior of the actual water temperature to an estimated water temperature calculated immediately before automatic stop of the engine to calculate, based on a temperature gradient of the actual water temperature such that a temperature gradient of an estimated water temperature in the automatic stop state of the engine varies identical to the temperature gradient of the actual water temperature, the estimated water temperature in the automatic stop state of the engine.

2. The apparatus of determining a failure in the thermostat according to claim 1 , further comprising:

an engine speed sensor that detects an engine speed of the engine,

the controller further includes:

a mode determiner that determines whether the vehicle is in the automatic stop state as an engine nonoperating mode based on the detected actual water temperature and the detected engine speed,

wherein the mode determiner also determines that a period from a restart of the automatically stopped engine until a lapse of a predetermined time to be included in the engine nonoperating mode.

3. The apparatus of determining a failure in the thermostat according to claim 2 , wherein

the mode determiner revises the predetermined time in response to a variation in the actual water temperature in the automatically stopped engine.

4. The apparatus of determining a failure in the thermostat according to claim 3 , wherein

the failure determining unit stops comparison between the actual water temperature and the estimated water temperature in the engine nonoperating mode and restarts the comparison at the termination of the engine nonoperating mode.

5. The apparatus of determining a failure in the thermostat according to claim 4 , wherein

at the termination of the engine nonoperating mode, the water temperature estimator adds a variation in the actual water temperature during a period between a time immediately before the automatic stop and the termination to the estimated water temperature calculated immediately before the automatic stop.

6. The apparatus of determining a failure in the thermostat according to claim 2 , wherein

the failure determining unit stops comparison between the actual water temperature and the estimated water temperature in the engine nonoperating mode and restarts the comparison at the termination of the engine nonoperating mode.

7. The apparatus of determining a failure in the thermostat according to claim 6 , wherein

at the termination of the engine nonoperating mode, the water temperature estimator adds a variation in the actual water temperature during a period between a time immediately before the automatic stop and the termination to the estimated water temperature calculated immediately before the automatic stop.

8. The apparatus of determining a failure in the thermostat according to claim 1 , wherein

the failure determining unit stops comparison between the actual water temperature and the estimated water temperature in the engine nonoperating mode and restarts the comparison at the termination of the engine nonoperating mode.

9. The apparatus of determining a failure in the thermostat according to claim 8 , wherein

at the termination of the automatic stop state of the engine, the water temperature estimator adds a variation in the actual water temperature during a period between a time immediately before the automatic stop and the termination to the estimated water temperature calculated immediately before the automatic stop.

10. A method of determining a failure in a thermostat for controlling the flow of a coolant into a radiator in response to an actual water temperature of the coolant for an engine in a vehicle, the method comprising:

determining whether the engine is cold-started;

detecting the actual water temperature, if the engine is cold-started, and applying a behavior of the actual water temperature to an estimated water temperature calculated immediately before automatic stop of the engine in an engine automatic stop state of the engine to calculate, based on a temperature gradient of the actual water temperature such that a temperature gradient of an estimated water temperature varies in the automatic stop state of the engine varies identical to the temperature gradient of the actual water temperature, the estimated water temperature in the automatic stop state of the engine; and

comparing the actual water temperature with the estimated water temperature to determine whether the thermostat is valve-open failure.