PURPOSE: To prevent execution of an unwilling down shift and to ensure operability by a method wherein in case, when abnormality of a car speed sensor is detected, an automatic transmission is brought into an orderly shift down, shift down is prohibited when operation of a brake is not detected and a change gear ratio is maintained at a current value.
CONSTITUTION: An output from an engine 10 is transmitted to a pair of drive wheels through a fluid transmission device 11, an automatic transmission 12, and a propeller shaft 14. A shift control device 24 controls the shift of an automatic transmission 12 based on a detected output from at least a car speed sensor 42. Further, the shift control device 24 causes orderly shift down of the automatic transmission 12 with a lapse of a time when abnormality of the car speed sensor 42 is detected. In this case, it is detected by a brake switch 44 whether or not a brake 43 is operated. When operation of the brake 43 is not detected, shift down of the automatic transmission 12 with a lapse of a time is prohibited and control is effected by the shift control device 24 so that a change gear ratio is maintained at a current time.
KATSUTA TOSHIHIRO
TOKORO SETSUO
KUSHIMA TATSUO
TANAKA MASAHARU
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