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Vehicle transmission which has discrete gear-stages inevitably produces torque drop during shifting gears. This torque drop should be minimized because it may lead to uncomfortable driving feeling and degradation of acceleration performance. In accordance with the spread of electric-powered vehicle technology, this study proposes novel transmission architecture to eliminate torque drop during shifting gears by using one electric motor and verifies its operating concept through experiments with a test-bench. The proposed transmission, called CGST (clutchless geared smart transmission) can synchronize the gear-shaft to be engaged for the next gear-stage with the output shaft by using a planetary gear-set and an electric motor. The CGST has a dual input gear-box with even and odd gear-stages on different input shafts, and the planetary gear-set and the electric motor control the speeds of each input shafts to smoothly engage the next gear-stage. This idea was verified by the simplified test-rig in this study. Three distinct scenarios for gear-shift including starting from engine idling, odd to even gear-shift, and even to odd gear-shift were conducted in the experiment. The shifting performance of the CGST was evaluated by comparing it with the results of the manual transmission (MT). As a result, the CGST shows only 24% of torque drop of the MT, and torque oscillation followed after gear-shifting is reduced by 26%. Although the developed test bench was of limited size, the possibility and expected performance of the CGST have been confirmed as the solution for seamless transmission.

Experimental Investigation of the Seamless Gearshift Mechanism Using an Electric Motor and a Planetary Gear-Set