A closed-throttle downshift control adjusts engine torque to raise the
input speed of a transmission to the synchronous speed of the target speed
ratio, and adaptively adjusts clutch control parameters to coordinate the
off-going clutch release and the on-coming clutch apply, and to complete
the shift with minimum driveline torque disturbance. A primary on-coming
clutch control fills the on-coming clutch and then raises the on-coming
pressure when the input speed reaches the synchronous speed of the target
speed ratio. If input synchronization cannot be maintained, a contingent
control increases the on-coming clutch pressure to gradually re-establish
the input speed synchronization and thereupon engage the on-coming clutch
to complete the shift. The fill time or the maintenance pressure of the
on-coming clutch is adaptively decreased for reduced driveline disturbance
in subsequent shifts of the same type if the output shaft jerk during the
primary control exceeds a threshold. Additionally, the fill time or the
maintenance pressure of the on-coming clutch is adaptively increased based
on an integral of the on-coming clutch slip for reduced dependence on the
contingent control in subsequent shifts of the same type if an integral of
the on-coming clutch slip during the contingent control exceeds a
threshold amount.