Patent ID: 8596228

Claim:
A thermostat located on the downstream side of an engine in a cooling water circuit in which cooling water is circulated through the inside of the engine by driving a pump, the thermostat comprising: a valve body for inhibiting or permitting passage of the cooling water flowing through the thermostat; a thermoelement for driving the valve body based on a temperature of the cooling water, wherein if the temperature of the cooling water is lower than a determination value, the valve body is closed to inhibit passage of the cooling water through the inside of the engine, and if the temperature of the cooling water is higher than or equal to the determination value, wherein the thermoelement, which receives heat transferred from the cooling water, opens the valve body to permit passage of the cooling water through the inside of the engine; and a heat generator for heating the thermoelement in order to open the valve body forcedly if the temperature of the cooling water in the cooling water circuit is lower than the determination value, wherein the temperature of the cooling water in the cylinder head of the engine is estimated by a control unit based on an accumulated amount value of air taken into the engine since its start-up and a value of the temperature of the cooling water actually measured by the water temperature sensor at the outlet of the engine in the cooling water circuit, and wherein, when the estimated cooling water temperature is higher than or equal to a predetermined value, the valve body is opened by an external device independently of operation of the thermostat based on the temperature of the cooling water in the cooling water circuit.