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DOWNSHIFT CONTROL METHOD BEFORE STOP OF AUTOMATIC TRANSMISSION, FOR REMOVING NOISE AND HIT SHOCK BETWEEN GEARS FOLLOWED BY POWER STATE CHANGE BEFORE AND AFTER SHIFT IN DOWNSHIFT BEFORE STOP OF AUTOMATIC TRANSMISSION
DOWNSHIFT CONTROL METHOD BEFORE STOP OF AUTOMATIC TRANSMISSION, FOR REMOVING NOISE AND HIT SHOCK BETWEEN GEARS FOLLOWED BY POWER STATE CHANGE BEFORE AND AFTER SHIFT IN DOWNSHIFT BEFORE STOP OF AUTOMATIC TRANSMISSION
PURPOSE: A downshift control method before a stop of an automatic transmission is provided to control shift under predetermined input torque without influence even in brake deceleration and engine idle RPM(Revolutions Per Minute) control states after making a shift point always become a power-on state. CONSTITUTION: A downshift control method before a stop of an automatic transmission comprises steps of determining whether a speed range is in an n+1 speed state(S100); determining whether Ne-Nt is greater than Ns-(dNo/dt*To)/Gear Ratio wherein Ne is engine RPM, NT is turbine RPM, Ns is Margin Slip RPM, dNo/dt is an output RPM variation, To is a release-side clutch release time, and Gear Ratio is a gear ratio(S110); determining whether No_upper is greater than No and No is greater than No_lower wherein No_upper is the upper vehicle speed limit and No_lower is the lower vehicle speed limit(S120); determining whether Th is less than Th1 wherein Th is a rear throttle valve value and Th1 is a set throttle valve value(S130); determining whether No is less than No_lower if Th is less than Th1(S140); executing shift control by shift point change control if No is greater than No_lower(S150); executing shift point control in No_lower if No is less than No_lower(S160); executing learning control of the release-side clutch release time in controlling shift by shift point change control(S170); and executing joining-side clutch duty learning control(S180).
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