A hybrid vehicle drive system including (a) an engine, (b) an electric motor, (c) a planetary gear device having a first rotary element connected to the engine, a second rotary element connected to the electric motor and connected through a first clutch to an output member connected to vehicle drive...http://www.google.com.au/patents/US6655485?utm_source=gb-gplus-sharePatent US6655485 - Hybrid drive system wherein clutch in engaged when engine speed has exceeded motor speed upon switching from motor drive mode to engine drive mode
