System and method of controlling automatic transmission

An automatic transmission for an internal combustion engine, comprising:

• a fluid coupling;
• a gear shift mechanism to which motive force of the engine is transferred through the fluid coupling, the mechanism comprising first and second friction engaging elements, wherein a shifting from a first gear ratio to a second gear ratio is carried out by releasing a first hydraulic pressure of the first friction engaging element for disengagement thereof and supplying a second hydraulic pressure to the second friction engaging element for engagement thereof, the second hydraulic pressure being subjected to a feedback control;
• a sensor that senses a parameter on a vehicle cruising condition;
• and
• an electronic control unit (ECU) that is operative in response to the sensed parameter. the ECU being programmed to:
• calculate, in accordance with the sensed parameter, a difference in output-side rotational speed of the fluid coupling before and after the shifting:
• and
• set, when the shifting is carried out with an output of the engine being smaller than a predetermined value, the second hydraulic pressure immediately before a start of the feedback control in accordance with the calculated difference,
• wherein the second hydraulic pressure has an initial value that is determined in accordance with torque acting on the output side of the fluid coupling immediately before the start of the feedback control,
• wherein the initial value is corrected in accordance with the calculated difference in output-side rotational speed, and
• wherein the corrected initial value of the second hydraulic pressure decreases with an increase in the calculated difference in output-side rotational speed.

A method of controlling an automatic transmission for an internal combustion engine, the transmission comprising a gear shift mechanism to which motive force of the engine is transferred through a fluid coupling, the mechanism comprising first and second friction engaging elements, wherein a shifting from a first gear ratio to a second gear ratio is carried out by releasing a first hydraulic pressure of the first friction engaging element for disengagement thereof and supplying a second hydraulic pressure to the second friction engaging element for engagement thereof, the second hydraulic pressure being subjected to a feedback control, the method comprising the steps of:

• sensing a parameter on a vehicle cruising condition;
• calculating, in accordance with the sensed parameter, a difference in output-side rotational speed of the fluid coupling before and after the shifting;
• and
• setting, when the shifting is carried out with an output of the engine being smaller than a predetermined value, the second hydraulic pressure immediately before a start of the feedback control in accordance with the calculated difference,
• wherein the second hydraulic pressure has an initial value determined in accordance with torque acting on the output side of the fluid coupling immediately before the start of the feedback control,
• wherein the initial value is corrected in accordance with the calculated difference in output-side rotational speed, and
• wherein the corrected initial value of the second hydraulic pressure decreases with an increase the calculated difference in output-side rotational speed.