Shift control system for automatic transmission

A shift control system for an automatic transmission provided with shift control means for carrying out shifting by engaging at least one or more friction elements as released when the relationship between a throttle opening of a vehicle and a vehicle speed intersects a shift line of a shift schedule, and torque-reduction control means for temporarily reducing engine torque during a period of shift transition, characterized in that it comprises

• shift-command determination means for determining whether or not a shift command is output,
• inertia-phase detection means for detecting start and completion of an inertia phase, and
• shelf-pressure control means for controlling an engagement pressure of said friction elements,
• wherein said shelf-pressure control means include means for increasing the engagement pressure of said friction elements at a first gradient as previously set after output of the shift command, wherein after output of the shift command and when start of the inertia phase is detected by said inertia-phase detection means, a torque-reduction command is output to said torque-reduction control means, and the engagement pressure at detection of the inertia phase is set as an initial shelf pressure to increase the shelf pressure at a second gradient as previously set, and wherein after start of the inertia phase and when completion of the inertia phase is detected by said inertia-phase detection means, a torque-reduction completion command is output to said torque-reduction control means, and the engagement pressure of said friction elements is increased up to a predetermined pressure as previously set.