Patent ID: 8182394

Claim:
A speed change control device of a working vehicle, in which a power of an engine is transmitted as a driving force to wheels through a modulation clutch, a torque converter having a lockup clutch, and a transmission, comprising: a speed change operator; and, a controller that controls at least the modulation clutch and the lockup clutch of the torque converter having the lockup clutch, wherein the controller performs a clutch control so as to: cause a lockup state in which the modulation clutch is engaged while the lockup clutch is engaged, when a vehicle speed becomes a first vehicle speed or lower; cause a lockup and modulation clutch slipping state in which the modulation clutch slips while the lockup clutch remains engaged, when the vehicle speed becomes a second vehicle speed or lower, the second vehicle speed being lower than the first vehicle speed; and cause a torque converter operation state in which the modulation clutch is engaged while the lockup clutch is released, when the lockup and modulation clutch slipping state continues for a prescribed period of time or longer, or when the vehicle speed becomes a third vehicle speed or lower, the third vehicle speed being lower than the second vehicle speed.