US Patent 8989935 Method and system for engine control

Methods and systems are provided for extending an engine-off period of a hybrid vehicle while reducing engine cold-start emissions. During an engine pull-up to meet operator demand, the engine is held at a higher power for a longer duration to aggressively heat the exhaust catalyst. Subsequently, the engine is pulled up to a lower power and held at the lower power for shorter bursts of time to activate the exhaust catalyst.