Analysis of Improving Automatic Transmission Upshift Performance by Using Off-Going Clutch During Inertia Phase

The paper presents a detailed numerical and algebraic analysis of potential for improving the step ratio automatic transmission (AT) upshift performance by means of modulating the off-going clutch during the inertia phase. The numerical analysis is based on Pareto optimal frontiers obtained by using the previously developed methods for AT shift control trajectory optimization and piecewise-linear control profile parameter optimization, where the control objectives include minimization of shift time, vehicle RMS jerk, and clutch dissipated energy. The analysis concerns the following control scenarios related to inertia phase: 1) oncoming clutch control only, 2) combined action of oncoming and off-going clutch; 3) oncoming clutch control extended with engine torque reduction control, and 4) combining all three control actions. The numerical results relate to an advanced 10-speed AT and various single-step and double-step upshifts, with emphasis on 1-3 shift. The numerical analysis results are proven algebraically based on a simplified AT model represented in bond graph form. The presented analysis shows that the off-going clutch can reduce either shift time or RMS jerk index by introducing power recirculation via the two clutches, which is in turn paid for by certain increase of AT energy loss.