US Patent 7267633 Transmission control method for increasing engine idle temperature

The state of a fluid coupling in a motor vehicle powertrain is selectively controlled during neutral idle operation of the engine for increasing the engine temperature to a desired level. The fluid coupling includes an input member connected to the engine and an output member connected to the transmission, and the output member is selectively grounded under specified enable conditions to impose an engine load for raising the engine operating temperature. The output member is released to resume normal operation of the powertrain when the enable conditions are no longer met or an estimate of the fluid temperature in the coupling reaches or exceeds a predefined temperature.