Patent ID: 7229372

Claim:
A slippage prevention apparatus of a belt-drive continuously variable transmission for an automotive vehicle, which employs a primary variable-width pulley of an input side, a secondary variable-width pulley of an output side, and a drive belt running in the primary and secondary pulleys, and whose downshift is made by an increase in a V-groove width of the primary pulley arising from a drop in a primary pulley pressure supplied to the primary pulley and a decrease in the V-groove width of the secondary pulley occurring in synchronism with the drop in the primary pulley pressure, or by a decrease in a V-groove width of the secondary pulley arising from a rise in a secondary pulley pressure supplied to the secondary pulley and an increase in the V-groove width of the primary pulley occurring in synchronism with the rise in the secondary pulley pressure, comprising: a speed-change control valve being responsive to a relative-position relationship between a position of a movable flange of the primary pulley and a position of a ratio-change control actuator for switching its valve position among a neutral position, a pressure build-up position in which the primary pulley pressure is supplied to a primary pulley actuation chamber of the primary pulley, and a pressure reduction position in which the primary pulley pressure is drained from the primary pulley actuation chamber; a belt slippage foretelling section that foretells that a slippage between the drive belt and each of the primary and secondary pulleys tends to occur when the primary pulley pressure is dropping during the downshift; and a primary-pulley-pressure drop inhibition section that inhibits the primary pulley pressure from dropping by switching the speed-change control valve to either one of the neutral position and the pressure build-up position, when the belt slippage foretelling section foretells that the slippage between the drive belt and each of the primary and secondary pulleys tends to occur during the downshift.