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More than 80% of recent passenger cars have automatic transmissions (ATs), many of which are controlled by microcomputers. Their control algorithm still consists of a predetermined process with shift schedule maps following the example of a mechanically controlled AT.
A shift schedule map creates regions of gear ratio, with boundaries defined as functions of vehicle speed and throttle valve angle.
In compliance with the shift schedule map, shift control is carried out uniformly in spite of various slopes, so the driver feels strange according to circumstances.
Hitachi, Ltd. has developed an estimation technology of drive torque as applied to shift control to select the most suitable gear according to the drive force.
Several control algorithms have been developed for this application: adaptive control of shift schedule and hydraulic pressure as a function of drive torque, feedback control of shift transients to reduce tuning troubles and adaptive control of up-shift during coasting as a function of estimated road gradient.