Patent ID: 6336880
Filing Date: 2002-01-08
Classification: F16H

Abstract:
A device for controlling a continuously variable transmission, said transmission havinga first pair of conical disks rotationally fixed to an input shaft of the transmission and a second pair of conical disks rotationally fixed to an output shaft of the transmission, each of the pairs having an axially movable disk and an axially fixed disk, an endless chain-belt arranged to transmit torque between the first and second pair of disks, a first piston/cylinder unit assigned to the first pair of disks and a second piston/cylinder unit assigned to the second pair of disks, said first and second piston/cylinder units serving to generate a belt-tightening pressure to press the first and second pairs of disks against the chain-belt, a third piston/cylinder unit assigned to the first pair of conical disks and a fourth piston/cylinder unit assigned to the second pair of conical disks, said third and fourth piston/cylinder units effecting a ratio change of the transmission when pressure medium is added to one and simultaneously removed from the other of the third and fourth piston/cylinder units, and a control valve device directing pump-circulated pressure medium to flow into the first and second piston/cylinder units, and to flow into one of the third and fourth piston/cylinder unit and simultaneously out of the other of the third and fourth piston/cylinder units, wherein said control valve device comprises a pressure-reducing valve to produce the belt-tightening pressure for the first and second piston/cylinder units and a ratio-shifting valve device to add pressure medium to one of the third and fourth piston/cylinder unit and simultaneously remove pressure medium from the other of the third and fourth piston/cylinder units, said pressure-reducing valve and said ratio-shifting valve device working in a cascade arrangement where at least a first offset pressure valve directs the pump-circulated pressure medium first to the pressure-reducing valve to produce the belt-tightening pressure and subsequently, but only after the belt-tightening pressure has been established, to the ratio-shifting valve device.