Patent ID: 8775036

Claim:
A control device for a vehicle drive train equipped with a torque converter, comprising: a controller that is configured to calculate a speed ratio of the torque converter on the basis of an actual power transmission efficiency of the torque converter by referring to a predetermined relationship between a power transmission efficiency and speed ratio of the torque converter when a capacity coefficient of the torque converter is larger than or equal to a predetermined threshold, wherein: a relationship exists between the speed ratio and capacity coefficient of the torque converter, such that: the capacity coefficient increases from a predetermined value to a local maximum as the speed ratio increases from zero; then the capacity coefficient decreases from the local maximum to a value smaller than the predetermined value as the speed ratio further increases; a single value for the speed ratio is determined when the capacity coefficient is smaller than the predetermined value; no single value for the speed ratio is determined when the capacity coefficient is larger than or equal to the predetermined value; and the predetermined threshold is set to the predetermined value in advance.