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To alleviate vibration of power-train system in hybrid electric vehicle (HEV) is one of the most difficult obstacles that most of engineers would face. The vibration of gear-shifting would be hider by precise synchronization of applied members in gear-shifting process; however, improvement of the vibration by calibrating conventional hydraulic control was limited. To transcend the limitation of hydraulic method, we developed a combined gear-shifting method assisted by motor speed feedback control to synchronize an input speed of transmission with a target input speed exactly. We divided a whole gear-shifting process into the following five phases to combined hydraulic control with motor speed control. In addition, to prevent the additional vibration, motor speed feedback control starts at the second phase and parameters of motor feedback control are categorized by each phases.

Recently, in accordance with the increased interest of consumer in fuel efficiency due to the phenomenon of high oil price, complaints against actual fuel efficiency in the road in comparison with the certified fuel efficiency have been raised frequently. Especially in case of the hybrid vehicle which is highly popular for the reason of its high fuel efficiency compared with that of existing gasoline car, deviation in the fuel efficiency will be higher compared with that of gasoline car in accordance with the driving mode (downtown/highway), driver's driving style (wild/mild) and external environmental condition (gradient/temperature/altitude). To solve them, this paper developed a method so that the SOC (State Of Charge), EV/HEV mode transition point can be controlled variably in accordance with the driving mode, driver's driving style and external environmental condition by making the most of characteristics of hybrid.