Patent ID: 7267633

Claim:
A method of operation for a motor vehicle powertrain including a fluid coupling having input and output members, an internal combustion engine coupled to said input member and a power transmission having an input coupled to said output member, comprising the steps of: detecting a neutral idle condition for which a temperature of said engine is lower than desired; activating at least one selectively engageable friction device of said power transmission to prevent rotation of said output member without establishing a drive connection between said output member and an output of said transmission, to thereby load said engine for increasing said temperature; measuring a temperature of fluid in said transmission; measuring a speed of said engine; determining a slip speed between said input member and said output member; estimating said temperature of fluid in said fluid coupling based on the measured temperature of fluid in said transmission, the measured speed of said engine and the determined slip speed; and deactivating said at least one friction device to initiate a cool down mode when a temperature of fluid in said fluid coupling exceeds a threshold value.