Large-torque overdrive twin-countershaft transmission

Disclosed is a large-torque overdrive twin-countershaft transmission. The technical scheme includes that spindle gear retainers, spindle gear spacers, spline retainers, flattened steel wire check rings for holes, various spindle gears and a hexagonal key are matched with a spindle so that the large-torque overdrive twin-countershaft transmission is axially positioned, and a spindle assembly is provided with the single flat hexagonal key; and the spindle gears and auxiliary shaft gears are meshed mutually so that the large-torque overdrive twin-countershaft transmission is radially positioned. The large-torque overdrive twin-countershaft transmission is simple in structure, high in carrying capacity and short in axial length. For the twin-countershaft transmission, the various spindle gears radially float on the spindle, the axis of the spindle and the axis of an auxiliary shaft are positioned in the same plane, radial force generated when the gears are meshed is offset mutually, namely the spindle only transfers torque, and resultant force of the radial force of the spindle is zero. The carrying capacity of the large-torque overdrive twin-countershaft transmission in the positioning mode is increased to 2300Nm from the original 1900Nm as compared with an existing transmission with double hexagonal keys while the weight and the cost of the spindle assembly are hardly changed.