Patent ID: 7366601

Claim:
An automatic transmission system for a vehicle, comprising: an automatic transmission including a torque converter provided with a lockup clutch; and a controller that controls, while the vehicle is coasting in a fuel-cut state, an oil pressure of the lockup clutch through a feedback control using a hydraulic device so that a slip rotation speed of the lockup clutch matches a target slip rotation speed, wherein the controller includes a calculation portion that calculates the slip rotation speed of the lockup clutch, and a control portion configured to control the hydraulic device so that the oil pressure of the lockup clutch becomes constant if the slip rotation speed calculated by the calculation portion is greater than a predetermined rotation speed during a downshift of the automatic transmission, and controls the hydraulic device so that the slip rotation speed matches the predetermined slip rotation speed if the slip rotation speed calculated by the calculation portion is less than the predetermined slip rotation speed during the downshift of the automatic transmission.