Automatic transmission control apparatus

An automatic transmission control apparatus comprising:

• shift control means for issuing instructions to selectively engage and disengage a combination of a plurality of frictionally engaging elements of a planetary gear mechanism to establish a corresponding one of a plurality of gear ratios;
• first rotary-speed detecting means for detecting a rotational speed of a first rotary member of the planetary gear mechanism which rotates at a different speed from an input shaft of the planetary gear mechanism;
• second rotary-speed detecting means for detecting a rotational speed of a second rotary member of the planetary gear mechanism which rotates at a different speed from the input shaft of the planetary gear mechanism;
• input shaft speed calculation means for calculating a rotational speed of the input shaft using values detected by the first and second rotary-speed detecting means;
• output shaft speed detecting means for detecting a rotational speed of an output shaft of the planetary gear mechanism;
• gear ratio calculation means for calculating a gear ratio from the rotational speed of the input shaft calculated by the input shaft speed calculation means and the rotational speed of the output shaft detected by the output shaft speed detection means;
• neutral determination means for determining if the automatic transmission has failed and a neutral state has been established due to an occurrence of an engagement malfunction of one the frictionally engaging elements, based on the gear ratio calculated by the gear ratio calculation means;
• and
• neutral control means for conducting a neutral control by forcing the automatic transmission to shift to a non-malfunctioning gear ratio upon the neutral determination means determining that the automatic transmission has failed and is in the neutral state when the shift control section issues instructions to establish an appropriate one of the gear ratios for driving.

A method of controlling an automatic transmission comprising:

• issuing instructions to selectively engage and disengage a combination of a plurality of frictionally engaging elements of a planetary gear mechanism to establish a corresponding one of a plurality of gear ratios;
• detecting a first rotational speed of a first rotary member of the planetary gear mechanism which rotates at a different speed from an input shaft of the planetary gear mechanism;
• detecting a second rotational speed of a second rotary member of the planetary gear mechanism which rotates at a different speed from the input shaft of the planetary gear mechanism;
• calculating a rotational speed of the input shaft using values of the first and second rotational speeds that were detected;
• detecting a rotational speed of an output shaft of the planetary gear mechanism;
• calculating a gear ratio from the rotational speed of the input shaft that was calculated and the rotational speed of the output shaft that was detected;
• determining if the automatic transmission has failed and a neutral state has been established due to an occurrence of an engagement malfunction of one the frictionally engaging elements, based on the gear ratio that was calculated;
• and
• conducting a neutral control by forcing the automatic transmission to shift to a non-malfunctioning gear ratio upon determining that the automatic transmission has failed and is in the neutral state when instructions are issues to establish an appropriate one of the gear ratios for driving.