Patent ID: 7291078

Claim:
A gear change control system of a belt-type continuously variable transmission, comprising: I) a movable pulley piston chamber for causing a thrust force to a movable pulley which varies a groove width of each of a primary pulley and a secondary pulley, the movable pulley piston chamber having a double-piston constitution including: a) a clamp chamber including a primary clamp chamber and a secondary clamp chamber, for causing a clamp force for clamping a belt, and b) a cylinder chamber including a primary pulley cylinder chamber and a secondary pulley cylinder chamber, for causing a differential thrust force at a gear change; II) a communication passage communicating the primary clamp chamber with the secondary clamp chamber, a clamp chamber's applied pressure area on a primary side being substantially equal to a clamp chamber's applied pressure area on a secondary side; III) a gear change control valve for controlling an oil pressure of the cylinder chamber; IV) a clamping force setting valve disposed between an oil pressure source and the communication passage, the clamping force setting valve setting an oil pressure of the clamp chamber; and V) a gear change control section for achieving a certain gear change ratio by outputting an instruction signal to the gear change control valve and the clamping force setting valve in accordance with a sensed traveling state, the gear change control section including: a) a primary thrust force calculating section for calculating a primary thrust force of the movable pulley on the primary side, b) a secondary thrust force calculating section for calculating a secondary thrust force of the movable pulley on the secondary side, c) a thrust force selecting section for selecting one of the primary thrust force and the secondary thrust force that is greater than the other, and d) a clamp chamber oil pressure setting section for setting up a clamp chamber oil pressure by a following calculation: dividing the selected one of the primary thrust force and the secondary thrust force by an addition of: the clamp chamber's applied pressure area of one of the primary clamp chamber and the secondary clamp chamber, and a cylinder chamber's applied pressure area of the cylinder chamber on a selected side.