US Patent 7841455 Hydraulic control system for automatic transmission

In clutch-to-clutch upshifting, the occurrence of inertia shock is suppressed while racing of the engine is prevented. Corresponding to a first sweep control in which an engaging-side pressure sweeps up toward a target hydraulic pressure PTA, a releasing-side hydraulic pressure PB sweeps down as an initial control. When the releasing-side hydraulic pressure PB becomes a minute torque capacity [fPB(0)+PKEEP+PLS2T], a hold control, which has a very low gradient δPB, is started so that the pressure is substantially held, and, after a rotation change is started, the pressure sweeps down with a low gradient δPE2 until release.