SHIFT CONTROL METHOD IN POWER OFF DOWNSHIFT OF 2-SHAFT AUTOMATIC TRANSMISSION FOR VEHICLE

摘要

PURPOSE: A shift control method in power off downshift of a 2-shaft automatic transmission for a vehicle is provided to reduce the development cost by achieving 6-speed without development of a new power train and reduce the manufacturing cost through sharing a manufacturing line. CONSTITUTION: A shift control method in power off downshift of a 2-shaft automatic transmission for a vehicle comprises a first step of beginning shift control of a second shaft while preparing beginning of control of friction elements of first and second shafts according to the running conditions of the vehicle at a point of time when a shift command is given(S100¯S130), beginning shift of the first shaft while setting up feedback control and a desired input rotational-speed variable ratio of the second shaft if the beginning of shift of the second shaft is detected(S140¯S160), and setting up a variable ratio for desired input/output feedback control of the first shaft if beginning of shift of the first shaft is detected(S170¯S180); a second step of executing feedback control of each shaft, according to a desired value of the first shaft followed by the variable ratio by the difference between the input rotation frequency and the output rotation frequency, and according to a desired value of the second shaft followed by the variable ratio of the turbine rotation frequency while outputting shift-initial duty of the first and second shafts; and a third step of finishing shift of the second shaft if the shift of the first shaft is finished through the second step.