Gear box with gears shiftable under load

A gearbox comprising two shafts disposed in a housing with their axes parallel to one another;

• at least two pairs of gear wheels, each pair comprising a wheel on one of the shafts permanently in mesh with a wheel on the other shaft;
• the wheels on one of the shafts being connectable to the shaft for torque transmission by respective friction clutches;
• and an actuating means disposed between two adjacent friction clutches for selectively causing engagement thereof, the actuating means comprising:
• two pressure rings respectively operable axially on the friction clutches by way of thrust bearings, the pressure rings being rotatable and movable axially relative to the associated shaft;
• an adjusting ring disposed between the pressure rings, the adjusting ring being rotatable and axially fixed relative to the associated shaft;
• adjusting means for causing relative angular movement, about the shaft axis, between the adjusting ring and the pressure rings;
• each side of the adjusting ring and the adjacent pressure ring having opposed faces provided with circumferentially extending grooves, arranged as at least three opposed pairs of grooves, including portions of varying depth;
• and
• rolling members disposed one in each opposed pair of grooves;
• the grooves on one side of the adjusting ring and the adjacent pressure ring being arranged so that relative angular movement of the adjusting ring and pressure ring in one direction, from a starting position thereof, causes axial movement of the pressure ring away from the adjusting ring to operate on the adjacent friction clutch, whilst relative angular movement of the rings in the opposite direction from the starting position does not cause said axial movement of the pressure ring;
• and the grooves on the other side of the adjusting ring and the other pressure ring being arranged so that said relative angular movement in the opposite direction from the starting position causes axial movement of said other pressure ring away from the adjusting ring to operate on the other friction clutch whilst relative movement in the first direction from the starting position does not cause said axial movement of said other pressure ring.