Patent ID: 6895832

Claim:
A power transmission system for transmitting a driving force of a prime mover to driving wheels via a stepped transmission, said stepped transmission including: a main clutch, an input shaft connected to the prime mover via said main clutch, an output shaft connected to the driving wheels, a plurality of gear pairs for at least three speed positions of said stepped transmission, each formed by an input gear arranged on said input shaft, and an output gear arranged on said output shaft and in mesh with said input gear, with one gear of said input gear and said output gear being rotatably supported on said input shaft or said output shaft, a connecting/disconnecting clutch of a meshing engagement type, for selectively connecting and disconnecting said one gear of said input gear and said output gear of each of said plurality of gear pairs to and from said input shaft or said output shaft rotatably supporting said one gear, to thereby establish a speed position of said stepped transmission by a connected one of said gear pairs including said connected one gear, and a driving force assist mechanism for supplying the driving force of the prime mover to said output shaft when a shift in speed position is carried out by said connecting/disconnecting clutch, wherein said driving force assist mechanism comprises: an auxiliary shaft arranged in parallel with said input shaft and said output shaft and connected to the prime mover; a plurality of transmission paths provided on said auxiliary shaft and connected to said output shaft, for transmitting the driving force of the prime mover to said output shaft at respective different gear ratios; and an assist clutch for selecting one of said plurality of transmission paths during the shift in speed position to thereby supply the driving force of the prime mover to said output shaft via said auxiliary shaft and the selected one of said plurality of transmission paths.