In this study, mode change and gear shift algorithm for a DCT(dual clutch transmission) based 2-clutch HEV(hybrid electric vehicle) were proposed.
A DCT based 2-clutch HEV performance simulator was developed based on dynamic models of the target HEV powetrain including an engine, engine clutch, motor, DCT, and vehicle. A DCT model was validated by comparing the simulation results with the vehicle test results for WOT(wide open throttle), and kick-down(4th→2nd) cases.
A mode change algorithm was proposed for mode change without kickdown, and mode change with kickdown cases. The proposed mode change algorithm controlled the motor, engine clutch, and DCT clutch to crank up the engine and synchronize the engine speed with the motor speed without ISG(integrated starter and generator). In order to evaluate the mode change algorithm, simulations were conducted for 3 cases: WOT(wide open throttle) launch, 33% hill climbing, kick-down cases, and simulation results were compared with the experiment results of AT(automatic transmission) based TMED(transmission mounted electric device) type HEV which has the same engine and motor with target HEV. It was found from the simulation results that the mode change from EV to HEV mode was performed showing satisfactory acceleration performance with acceptable jerk.
In addition, a gear shift algorithm of the DCT based 2-clutch HEV was proposed, which consists of 4 steps for power upshift: (1)preselect, (2)disengage off-going clutch and engage on-coming clutch, (3)synchronize on-coming clutch speed(torque intervention), (4)on-coming clutch lock up, and 5 steps for power down shift(even→even): (1)release even clutch, (2)disengage even clutch and engage odd clutch, (3)drive vehicle with odd gear, (4)engage odd clutch and disengage even clutch, (5)even clutch lock up. For the power upshift, the proposed gear shift algorithm reduced excessive torque through torque intervention which reduces the engine torque, and generates negative(-) motor torque during inertia phase. For the power downshift(even→even), downshift from an even gear to another even gear was conducted via an odd gear to prevent the torque interruption. To evaluate the gear shift algorithm, simulations were carried out for 3 cases: 1st→2nd upshift, 2nd→3rd upshift, 4th→2nd kick-down shift, and simulation results were compared with the experiment results of AT based TMED type HEV. It was found from the simulation results that power upshifts and power downshift were performed showing better shift quality in comparison to the experiment results of AT based TMED type HEV.