Patent ID: 8327729

Claim:
A shift drive mechanism for a multi-speed transmission comprising: a plurality of drive gears supported on a first gear shaft and a plurality of driven gears supported on a second gear shaft which extends parallel to the first gear shaft, the plurality of drive gears being in a state of constant mesh on a gear speed basis, respectively, with the plurality of driven gears fixed to the second gear shaft; an engagement switch-over mechanism being provided by which engagement between the second gear shaft and each of the plurality of drive gears on the first gear shaft is switched over on a gear basis, and the engagement switch-over mechanism being driven by a shift drive mechanism so as to perform a shift, wherein the shift drive mechanism includes: a shift rod inserted on an inner side of a plurality of cam rods along a center axis of an inner cavity of the gear shaft, the shift rod being moved in an axial direction to thereby move the cam rods; a shift pin moved in the axial direction together with the shift rod; a shift drum having a center axis of rotation parallel to the shift rod, the shift drum having an outer peripheral surface formed with a shift guide groove with which an end portion of the shift pin is engaged; and a shift actuator for turning the shift drum; wherein the shift guide groove has a configuration in which gear speed groove portions being formed at axial-direction positions determined on the gear speed basis and being oriented in a circumferential direction so as not to move the shift pin in the axial direction attendant on turning of the shift drum are sequentially connected to each other through spirally shaped shift groove portions operable to move the shift pin in the axial direction attendant on turning of the shift drum; and wherein the gear speed groove portions are each set to be longer than a distance the shift drum travels idly from a moment of stop of driving of the shift actuator.