Shift control apparatus and method for automatic transmission

A shift control method for an automatic transmission adapted to transmit a power by engaging any of a plurality of friction-engagement elements in accordance with a shift-step of the transmission, the plurality of friction-engagement elements including

• a first friction-engagement element adapted to be changed from an engaged state to a disengaged state when changing the shift-step, and
• a second friction-engagement element adapted to be changed from the disengaged state to the engaged state when changing the shift-step, the shift control method comprising:
• a first step of adjusting an engagement-control parameter for the first friction-engagement element to bring a rotational speed difference between an input and an output of the first friction-engagement element gradually close to a target differential speed set as a target value antecedent to the change of shift-step, by causing the first friction-engagement element to slip from a start time of the change of shift-step;
• and
• a second step of
• calculating or estimating a total transfer-torque capacity which is required to maintain the rotational speed difference of the first friction-engagement element substantially at the target differential speed,
• setting a distribution ratio between a transfer-torque capacity of the first friction-engagement element and a transfer-torque capacity of the second friction-engagement element, so as to maintain the sum of the transfer-torque capacities of the first and second friction-engagement elements substantially equal to the total transfer-torque capacity and so as to gradually decrease a distribution to the first friction-engagement element and gradually increase a distribution to the second friction-engagement element,
• setting the transfer-torque capacities of the first and second friction-engagement elements on the basis of the calculated or estimated total transfer-torque capacity and the set distribution ratio, and
• adjusting each of the engagement-control parameters for the first and second friction-engagement elements, in accordance with the set transfer-torque capacities of the first and second friction-engagement elements.

A shift control apparatus comprising:

• an automatic transmission adapted to vary and output a rotational speed inputted from an engine by engaging any of a plurality of friction-engagement elements in accordance with a shift-step of the transmission, the plurality of friction-engagement elements including
• a first friction-engagement element adapted to be changed from an engaged state to a disengaged state when changing the shift-step, and
• a second friction-engagement element adapted to be changed from the disengaged state to the engaged state when changing the shift-step;
• and
• friction-engagement element control means for controlling the first and second friction-engagement elements by adjusting each of an engagement-control parameter for the first friction-engagement element and an engagement-control parameter for the second friction-engagement element when changing the shift-step, the friction-engagement element control means including;
• target-value setting means for setting a first target differential speed which is a target value antecedent to the change of shift-step for a rotational speed difference between an input and an output of the first friction-engagement element;
• first control means for carrying out a first control that adjusts the engagement-control parameter for the first friction-engagement element to bring the rotational speed difference between the input and the output of the first friction-engagement element gradually close to the first target differential speed, by causing the first friction-engagement element to slip from a start time of the change of shift-step;
• and
• second control means for carrying out a second control after the first control, the second control means having
• torque-capacity calculating means for calculating or estimating a total transfer-torque capacity which is required to maintain the rotational speed difference of the first friction-engagement element substantially at the first target differential speed, and
• distribution ratio setting means for setting a distribution ratio between a transfer-torque capacity of the first friction-engagement element and a transfer-torque capacity of the second friction-engagement element, so as to maintain the sum of the transfer-torque capacities of the first and second friction-engagement elements substantially equal to the total transfer-torque capacity and so as to gradually decrease a distribution to the first friction-engagement element and gradually increase a distribution to the second friction-engagement element;
• the second control
• setting the transfer-torque capacities of the first and second friction-engagement elements on the basis of the total transfer-torque capacity calculated or estimated by the torque-capacity calculating means and the distribution ratio set by the distribution ratio setting means, and
• adjusting each of the engagement-control parameters for the first and second friction-engagement elements, in accordance with the set transfer-torque capacities of the first and second friction-engagement elements.