Patent ID: 8768590

Claim:
A method for controlling an automatic transmission including a transmission mechanism having an engagement element which is engaged at startup, and a torque converter configured to transmit power from a power source to the transmission mechanism, comprising: performing a neutral control operation which decreases an engaging pressure on the engagement element when a vehicle is stationary in a forward range; measuring temperature of hydraulic oil which operates the engagement element at the start of the neutral control operation; acquiring the rotational speed of the power source and the rotational speed of a turbine of the torque converter; calculating a speed ratio of the torque converter represented by the ratio between the rotational speed of the power source and the rotational speed of the turbine of the torque converter as an actual speed ratio; setting a target speed ratio as a target value for the speed ratio of the torque converter such that the actual speed ratio becomes lower than the speed ratio in the case where the hydraulic oil temperature is normal when the temperature of hydraulic oil measured by a hydraulic oil temperature measuring portion is in a low temperature range that is lower than a predetermined threshold value and a decrease of a hydraulic pressure response is caused by an increase of a viscosity of the hydraulic oil, wherein the target speed ratio is set lower as the temperature of the hydraulic oil becomes lower when the temperature of the hydraulic oil is lower than the predetermined threshold value; adjusting the engaging pressure on the engagement element which brings the actual speed ratio equal to the target speed ratio, wherein when the temperature of the hydraulic oil is in the low temperature range, the engaging pressure becomes higher than the engaging pressure when the temperature of the hydraulic oil is normal; and performing a return control operation which engages the engagement element at the start of the vehicle.