Coolant temperature estimation system for estimating temperature of coolant of internal combustion engine

A coolant temperature estimation system for estimating a temperature of coolant of an internal combustion engine, the system comprising:

• a coolant temperature estimating means, which renews an estimated coolant temperature value based on an operating state of the internal combustion engine during operation of the internal combustion engine, wherein the coolant temperature estimating means includes a fuel cutting period coolant temperature estimating means, which computes the estimated coolant temperature value during a fuel cutting operation, and wherein the fuel cutting period coolant temperature estimating means is selected and used during the fuel cutting operation to renew the estimated coolant temperature value in such a manner that an increase in the estimated coolant temperature value during the fuel cutting operation is reduced in comparison to an increase in the estimated coolant temperature value during a normal operation.

A coolant temperature estimation system for estimating a temperature of coolant of an internal combustion engine, the system comprising:

• a coolant temperature estimating means, which renews an estimated coolant temperature value based on an operating state of the internal combustion engine during operation of the internal combustion engine;
• and
• a coolant temperature estimation prohibiting means, which prohibits renewal of the estimated coolant temperature value upon elapse of a predetermined time period since initiation of a fuel cutting operation until end of the fuel cutting operation.