Patent ID: 7721974

Claim:
A thermostat device comprising: a valve housing provided with a cooling water passage that constitutes a cooling water channel of an internal combustion engine; a built-in thermally expansive body that is thermally expanded or contracted by change of temperature of the cooling water; a piston rod that is slid by thermal expansion/contraction of the thermally expansive body; and a valve body which is subjected to opening/closing operation with respect to a valve seat formed within said valve housing by sliding of said piston rod in accordance with change of volume of said thermally expansive body, wherein a valve seat shape further on the downstream side in the direction of flow of the cooling water than the valve seat where said valve body is seated, which is an internal wall face forming the cooling water passage within said valve housing, is formed in a shape such that, in the valve open condition, the cross-sectional area of the passage that is formed between an inlet seal of the valve seat on which said valve body is seated and a top face of the valve body gradually decreases on the cooling water inlet side with reference to the maximum passage cross-sectional area on the upstream side in the direction of flow of the cooling water, and such that the cross-sectional area of the passage at the face perpendicular to the top face gradually increases on the cooling water outlet side so that cooling water flows along the top face of said valve body.