Patent ID: 7357047

Claim:
A power unit comprising an engine and a vehicle-use automatic transmission device, said engine having a crank case with a crank shaft supported by the crank case, said power unit further including a torque converter mounted on the crank shaft, said transmission device including a main shaft and a counter shaft, said crank shaft, said main shaft, and said counter shaft being arranged in parallel to each other and being rotatably supported by said crank case, said transmission device also including power receiving means for receiving power from said torque converter to drive said main shaft and power output means for transferring power from said counter shaft to a driven member; the transmission device further comprising: a first group of driving gears which are fixed to a tubular auxiliary main shaft which is concentrically and rotatably mounted on the main shaft; a first group of follower gears which are rotatably mounted on the counter shaft and are constantly meshed with the first group of driving gears so as to be selectively joined to the counter shaft; a first and only clutch which performs the power engagement and power disengagement between the main shaft and the tubular auxiliary main shaft; a second group of driving gears which are rotatably mounted on the main shaft and are selectively jointed to the main shaft; a second group of follower gears which are fixed to a tubular auxiliary counter shaft which is concentrically and rotatably mounted on the counter shaft and are constantly meshed with the second group of driving gears; and a second and only clutch which performs the power connection and disconnection between the counter shaft and the tubular auxiliary counter shaft; wherein the first and second clutches are the only clutches in said automatic transmission device so that said device is multi-stage, but light weight.