Engine cooling apparatus

An engine cooling apparatus comprising:

• a coolant circuit that recirculates coolant that has passed through an engine back to the engine, wherein the coolant circuit includes a first passage, which allows coolant to flow through a radiator, and a second passage, which allows coolant to flow without passing through the radiator, arranged parallel to the first passage;
• a coolant control valve that varies a ratio of a first passage flow rate, which is a flow rate of the coolant flowing through the first passage, and a second passage flow rate, which is a flow rate of the coolant flowing through the second passage;
• an outlet coolant temperature sensor that detects an outlet coolant temperature, which is a temperature of the coolant before the coolant reaches a branching point of the first passage and the second passage in the coolant circuit;
• an inlet coolant temperature sensor that detects an inlet coolant temperature, which is a temperature of the coolant after the coolant has passed through a merging point of the first passage and the second passage in the coolant circuit;
• and
• a coolant temperature estimator that calculates a radiator coolant temperature when the first passage flow rate is greater than or equal to a specified flow rate, wherein the radiator coolant temperature is a temperature of the coolant at a coolant exit of the radiator, and the radiator coolant temperature relative to the first passage flow rate, the second passage flow rate, the outlet coolant temperature, and the inlet coolant temperature satisfies a relationship expressed by an equation of
• Trad
• =
• Tin
• -
• (
• Tout
• -
• Tin
• )
• ×
• Fsec
• Frad
• where Trad represents the radiator coolant temperature, Frad represents the first passage flow rate, Fsec represents the second passage flow rate, Tout represents the outlet coolant temperature, and Tin represents the inlet coolant temperature.