Patent ID: 7717246

Claim:
A shift device with a synchronizer adapted for a transmission comprising: a shaft for transmitting drive power; a hub having a boss portion splined with the shaft, a ring portion located outwardly away from the boss portion and formed on an outer peripheral surface thereof with splines, and a flange portion connecting the boss portion and the ring portion, the ring portion and the flange portion being formed with a plurality of notch portions having four axial edges, and each of the four axial edges being provided with a slanted surface for changing rotational force to thrust; a sleeve having splines on an inner peripheral surface thereof and having projections on a part of the splines of the sleeve, the sleeve being supported by and slidable along the splines of the hub; a pair of speed gears arranged to sandwich the hub, the gears having splines, which are engageable with the splines of the sleeve, and a friction surface at a hub side; a pair of synchronizer rings respectively arranged between the hub and the speed gears, the synchronizer rings each having a friction surface and chamfers on an outer circumference thereof, and the friction surfaces of each of the synchronizer rings being pressable on the friction surfaces of the speed gears; and thrust pieces that are movable in the notch portions of the hub in an axial direction of the shift device, wherein the thrust pieces are formed with first slanted surfaces pressable on the chamfers of the synchronizer rings and second slanted surfaces contactable with the slanted surfaces of the hub so that the thrust pieces are capable of changing rotational force due to friction torque generated between the friction surfaces to thrust, and wherein the thrust pieces engage and move together with the sleeve in the axial direction of the shift device when the sleeve is moved toward the gear to be engaged and the first slanted surfaces of the thrust pieces press the chamfers of the synchronizer ring, and the thrust pieces are disengaged from the sleeve when the friction torque becomes zero and the splines of the sleeve are engaged with the splines of the speed gear.