Sun Je Kim

Feasibility Assessment and Design Optimization of a Clutchless Multimode Parallel Hybrid Electric Powertrain

The fuel economy (FE) of the parallel hybrid electric vehicle (HEV) suffers due to significant energy losses from the wet clutches of the automatic transmission and limited engine operations. To overcome these limitations, a novel clutchless multimode parallel HEV (CMP-HEV) was proposed previously, but its operational feasibility was not proven. In this study, we propose a systematic methodology that can assess the feasibility of the CMP-HEV and efficiently optimize FE and acceleration performance of the design, simultaneously. Using the dynamic models, we assess the feasibility over the entire design spaces under two conditions: full acceleration (for drivability) and moderate acceleration (for fuel efficiency). An instantaneous optimization method is used to rapidly evaluate the full acceleration performance, and the designs with poor acceleration are considered infeasible. For the fuel efficiency, the feasibility is determined by the violation of electric motor constraints under the assumption of efficient engine operations. The feasible design sets from the assessment are used for the design optimization. Dynamic programming is applied over only the feasible design space, and the Pareto front is obtained to show the tradeoff between FE and acceleration performance. The selected final design is found superior to a comparable parallel HEV in both FE and acceleration performance perspectives.

Verification of the Shifting Mechanism of Clutchless Geared Smart Transmission Using the Compact Car Size Test Bench

The existing transmissions have limitations related to driving comfort, manufacturing price, or driveline efficiency. To satisfy the complex demands of users, the clutchless geared smart transmission (CGST) is proposed. The CGST has a distinctive structure combining the geared transmission and planetary gear system. Especially, its pseudo-clutch system including a planetary gear system and an electric motor acts as a clutch to change the gears smoothly. In this research, the shifting mechanism of the CGST was focused to verify their feasibility. To realize its sequential shifting steps including a speed control phase and a torque control phase of CGST operation, the compact car size test bench containing CGST as transmission was developed and tested. From the test, starting flywheel with 1st gear engaging by speed synchronization of carrier gear to output shaft was shown to be possible, and up shifting from 1st gear to 2nd gear was also performed with continuous power delivery to the flywheel. Based on the experimental result, the shifting mechanism was verified. In the future, we will quantify the shifting smoothness by using modified test bench.