Method for controlling switching over of speed stages of transmission with presetting of due period

A method for controlling switching over of speed stages of an automatic transmission for a vehicle of the type having a first and second transmission for a vehicle of the type having a first and second transmission unit each having an input rotational member, an output rotational member, at least one intermediate rotational member operable to transmit rotational power between said input rotational member and said output rotational member and a servo actuator for selectively braking said intermediate rotational member or rotationally connecting said intermediate rotational member with another one of said rotational members and independently operable to provide a plurality of gear ratios between said input rotational member and said output rotational member, said first and said second transmission unit being connected in series so as to provide a plurality of speed stages by various combinations of gear ratios of said first and said second transmission unit, comprising the steps of:

• detecting operating conditions of the vehicle including engine load and vehicle speed by detecting means therefor;
• detecting rotational speed of said intermediate rotational member in said first transmission unit by a detecting means therefor;
• detecting rotational speed of said intermediate rotational member in said second transmission unit by a detecting means therefor;
• determining switching over of speed stages of said transmission based upon the operating conditions of the vehicle including engine load and vehicle speed detected by said vehicle operating condition detecting means;
• determining a period during which the switching over of speed stages of said transmission is to be completed based upon the operating conditions of the vehicle including engine load and vehicle speed detected by said vehicle operating condition detecting means;
• and
• controlling operating of said servo actuators in said first and said second transmission unit based upon a coordination of respective rotational speeds of said intermediate rotational members in said first and said second transmission unit detected by said intermediate rotational member rotational speed detecting means for said first and said second transmission unit and said computed period so that the switching over of said first and second transmission unit are respectively completed with the end of said period.