Abstract: When a road surface gradient is calculated by a wheel driving force and a vehicle acceleration, if the wheel driving force is calculated based on an output torque of an engine, the accuracy of calculating the wheel driving force, i.e., the road surface gradient becomes poor due to deterioration by aging of the engine or the like. In order to solve this kind of disadvantage, a fluid transmission torque of a torque converter is calculated by those torque ratio of the torque converter and an input shaft torque coefficient which correspond to a speed ratio of the torque converter, and an input rotational speed of the torque converter (=engine rotational speed (step S21-3). The road surface gradient is calculated by using a wheel driving force to be calculated by this torque.

Abstract: A shift control system comprises a diameter-change calculation which calculates the difference between the diameters of the contact circles at present and after a shift to a target speed change ratio and a slip prevention thrust calculation which calculates a slip prevention thrust necessary for transmitting the power through a V belt without slip between the V belt and the drive and driven pulleys. A speed ratio maintaining thrust calculation which calculates a speed ratio maintaining thrust that is an addition to the slip prevention thrust for maintaining the current speed change ratio in constant condition and for transmitting the power without any slip of the belt and a additional thrust calculation which calculates a shifting additional thrust that is added for a contact-circle enlarging pulley to achieve a shift to the target speed change ratio.

Abstract: A shift control system comprises belt-speed calculation means, contact-circle enlarging pulley determination means, diameter-change calculation means, slip prevention thrust calculation means, speed ratio maintaining thrust calculation means and additional thrust calculation means. The diameter-change calculation means calculates the difference between the diameters of the contact circles at present and after a shift to a target speed change ratio, and the slip prevention thrust calculation means calculates a slip prevention thrust necessary for transmitting the power through a V belt without slip between the V belt and the drive and driven pulleys.