Device for controlling a CVT

A device for controlling a continuously variable transmission (CVT) (3) driven by a drive unit (1) having a first cone-pulley (10) on an input shaft and a second cone-pulley (12) on an output shaft and a drive-belt (11) which rotates about said first and second cone-pulleys to transit drive therebetween:

• wherein said first cone-pulley (10) comprises a first fixed cone, fixed axially relative to the input shaft and a first movable pulley cone (S1) movable axially to adjust a spacing between the first fixed and first movable cones. said second cone-pulley (12) comprises a second fixed pulley cone fixed axially relative to said output shaft and a second movable pulley cone (S2) movable axially to adjust a spacing between the second fixed and second movable cones, an electronic device (15) which via electromagnetic actuator controlled hydraulic valves determines a magnitude of said spacings and a hydraulic emergency running unit is activated upon breakdown of said electronic control device (15) to provide a desired ratio of said spaces to maintain a desired pressure on said drive belt by said first and second cone pulleys;
• and
• said hydraulic emergency running unit comprises first and second pressure-reducing valves (24, 25) which act to control output pressure from a pump (22), first and second electromagnetic pressure-regulating valves (27, 28) connected to be operated by said first pressure-reducing valve (24), said first electromagnetic pressure-regulating valve (27) is connected to operate first and second emergency valves (30, 31), said first emergency valve (30) being connected to operate primary valve (38), said second emergency valve (31) being connected to operate secondary valve (39), said primary valve (38) and said secondary valve (39) being connected to receive output from said pump (22), the pressure level for said adjustment of said second pulley cone being determined by said secondary valve (39), said primary valve (38) determines the pressure level for said adjustment of said first pulley cone, said second pressure-reducing valve (25) is connected to both emergency valves (30, 31), the switching positions of said first and second emergency valves (30, 31) are determined by said first electromagnetic pressure-regulating valve (27) so that in a first position (B) of both emergency valves (30, 31), said first pressure-regulating valve (28) acts to control said secondary valve (39), and in a second position (A) of both emergency valves (30, 31), the pressure level of said pressure-reducing valve (25) acts to control said primary valve (38) and said secondary valve (39).