Transmission for tractors

Claim 1

A transmission of the three-system type for a tractor comprising an input system having a main input shaft carrying a plurality of gears for transmitting the torque of an engine, a propelling speed change system and a power takeof speed change system supported on the opposite sides of the input system respectively in parallel thereto, each of the propelling and power takeoff speed change system including a speed change shaft having a power output end and having a plurality of speed change gears freely rotatably mounted thereon side by side and meshing with the gears of the input system respectively at all times, the speed change shaft being a hollow shaft internally formed with an axial bore, each of the speed change gears being formed in its inner peripheral surface with grooves, the speed change shaft incorporating pins movable radially of the speed change shaft and engageable in and disengageable from the grooves in the corresponding speed change shaft and engageable and disengageable from the grooves in the corresponding speed change gear, the speed change shaft accomodating in its axial bore an axially movable speed change rod being axially movable to engage the pins in the grooves of the corresponding speed change gear and said speed change rod partially extending outwardly from said speed change shaft and operating force transmitting means provided at an end opposite to said power output end coupled to said partially extending portion of said speed change rod for axially moving said speed change rod whereby the speed change gear is coupled to the speed change shaft to transmit the torque to rear wheels and a power takeoff shaft with desired speed changes, and a flexible shock-absorbing coupling provided between the engine and the main input shaft, said coupling mediating the impact resulting from engagement of the pins in the grooves for a speed change.