Patent ID: 7775134

Claim:
A four wheel drive switching device of a tractor, comprising: a rear wheel drive shaft rotated by receiving power from an engine; a first drive gear coupled to the rear wheel drive shaft to transmit rotational power; a second drive gear rotated by receiving power from the first drive gear and supported by a rear PTO (Power Take Off) shaft to revolve thereon; a third drive gear rotated by receiving power from the second drive gear; an idle shaft for supporting the third drive gear so that the third drive gear can revolve thereon; a sliding gear coupled to the idle shaft to move in a right and left direction thereon so as to make a power transmission or interruption state to the third drive gear; a pressing device having a flow path and a cylinder chamber formed between the sliding gear and the idle shaft, the pressing device exerting pressure of a working fluid through the flow path so that the sliding gear is moved to one side to keep the power transmission state to the third drive gear; a return spring for moving the sliding gear in an opposite side when the pressure of the pressing device is released, so as to keep the power interruption state to the third drive gear; and a front wheel drive gear for operating a front wheel drive shaft by receiving power from the sliding gear.