AUTOMATIC GEAR CHANGE DEVICE OF WORKING VEHICLE

摘要

PROBLEM TO BE SOLVED: To provide an automatic gear change device of a working vehicle which can automatically perform downshift operation of a transmission at excavation with a small gear change shock.SOLUTION: An automatic gear change device of a working vehicle comprises: a traveling HST circuit; a transmission which is interposed between a traveling motor and wheels, and has a plurality of gear change stages outputting rotational power inputted from the traveling motor by changing the speed of the power; a lift arm cylinder which controls a position of a bucket by driving a lift arm, and increases pressure in a bottom-side chamber by an excavation reaction force of the bucket; an excavation determination part which reads the pressure in the bottom-side chamber of the lift arm cylinder, and determines an excavation state by the bucket; a motor capacity increase control part which outputs a command for increasing a capacity of the traveling motor according to a command received from the excavation determination part; and a downshift control part which controls downshift to the lowest speed stage from a high speed stage of the transmission.