Speed-changing transmission device for vehicles

A speed-changing transmission device for vehicles to impart an engine braking effect on a vehicle in the parked position thereof comprising an engine crankshaft (1) and input shaft (3), a main clutch interposed between said crankshaft (1) and said input shaft (3), a speed-changing shaft (4) for transmitting driving power to the driving wheels of the vehicle, said speed-change shaft (4), being coaxially disposed with said input shaft (3), a counter shaft (8) mounted in parallel with said speed-changing shaft (4), an input gear, a one-way clutch 42 coupling said input gear to said speed-changing shaft 4, said one-way clutch including an outer wheel 42a fitted to the input gear (3a), and an inner wheel 42b fitting the speed-changing shaft which rotates in the same direction as the input shaft in the forward speed of the input shaft whereby the input gear 3(a) and the speed-changing shaft 4 rotate freely of each other in a drive position and whereby said speed-changing shaft (4) and input gear 3(a) rotate as a unit in a parked position, a counter gear 12a connected to said counter shaft (8) disposed always meshing with said input gear 3(a), a forward speed charging gear system provided between said speed changing shaft (4) and said counter shaft (8), and including a forward speed-changing gear (18(b), 18(c) rotatably mounted on said speed-changing shaft 4 and a forward counter meshing gear 12(b), 12(c) connected to said counter shaft (8) meshing with each other so as to transmit the rotation of said counter shaft (8) to said speed-change shaft at a reduced speed as compared to the speed of the input shaft or in the reverse direction to the direction of rotation of said input shaft (3), a backward speed-changing gear system provided between said speed-changing shaft (4) and said counter shaft (8), said backward speed-changing system including a backward speed-changing gear (14) on said speed-change shaft 4, a backward idler gear (15), and a backward counter gear 11 on said counter shaft (8), clutch means disposed in the power transmission path formed by the respective forward and backward changing gear systems adapted to be selectively operated, and a backward one-way clutch 43 cooperatively associated with said backward gear system.