Patent ID: 7926373
Filing Date: 2011-04-19
Classification: F16H,Y10T

Abstract:
1. A vehicular transmission, comprising: first and second main shafts, to which power drive from an engine is to be transmitted; a countershaft connected to a drive wheel; gear trains of a plurality of gear positions, disposed between the main shafts and the countershaft and to be selectively established; shifters disposed between idle gears, each forming part of two of the gear trains of the plurality of gear positions and supported rotatably on the main shafts or the countershaft, the shifters being relatively unrotatable on, and slidable along, the main shafts and the countershaft; and a shift drum including a pair of lead grooves formed adjacent to opposite outer peripheries thereof, each of the lead grooves having a shift fork engaged therein which rotatably holds a corresponding one of the shifters, the shift drum being rotatable about an axis extending in parallel with the main shafts and the countershaft, the power drive from the engine to the main shafts being shut down when the shifters are slidably moved between a first position, at which the shifters are engaged with one of the idle gears, and a second position, at which the shifters are engaged with the other of the idle gears; wherein each of the lead grooves includes: a first gear train establishment portion extending circumferentially along the shift drum such that the corresponding shifter is engaged with one of the idle gears; second gear train establishment portion extending circumferentially along the shift drum at a position offset axially of the shift drum from the first gear train establishment portion such that the corresponding shifter is engaged with the other of the idle gears; a communication portion connecting between the first and second gear train establishment portion, the communication portion having a half neutral portion disposed at a central portion thereof, the half neutral portion being formed to extend circumferentially along the shift drum for holding the corresponding shifter at a position, at which the corresponding shifter is disengaged from the corresponding idle gear; and a first clutch associated with the first main shaft; and a second clutch associated with the second main shaft, the first and second clutches enabling power of the engine to be transmitted to one of the first and second main shafts while the other of the first and second main shafts is disconnected during a preliminary gear shift operation, wherein the half neutral portion in each of the lead grooves is arranged between the first gear train establishment portion and the second gear train establishment portion, so that during the preliminary gear shift operation, rotation of the shift drum is temporarily stopped as the shift fork engaged therein passes through the half neutral portion, thereby retarding a timing at which the corresponding shifter is engaged with the corresponding idle gear, and reducing an associated engagement noise.