Transmission control method of belt type continuously variable transmission

A transmission control method of a belt type continuously variable transmission, in which a metal belt (15) is wound on a drive pulley (13) and a driven pulley (14) and a gear ratio is changed by changing axial thrusts of the drive pulley (13) and the driven pulley (14), comprising:

• a first process of estimating a relationship between a tangential friction coefficient and a ratio of a non-slippage side pulley according to a relationship between a tangential friction coefficient and a ratio of a slippage side pulley, wherein one of the drive pulley (13) and the driven pulley (14) is the non-slippage side pulley and another one of the drive pulley (13) and the driven pulley (14) is the slippage side pulley,
• a second process of calculating transmission torque transmitted by the metal belt (15) from the tangential friction coefficient and a winding diameter of the slippage side pulley,
• a third process of calculating a required axial thrust for suppressing slippage of the non-slippage side pulley from the transmission torque and the winding diameter of the non-slippage side pulley, and
• a fourth process of changing the gear ratio by reducing a ratio holding axial thrust of the non-slippage side pulley toward the required axial thrust.