Drive transmission system for working vehicle

摘要

A drive transmission system for a working vehicle for transmitting power of an engine to running devices through a main clutch, a main change speed device and an auxiliary change speed device is disclosed. The main change speed device includes a first group of hydraulic clutches and a group of control valves for operating these clutches. The auxiliary change speed device includes a second group of hydraulic clutches and control valves for operating these clutches. Pressure oil is supplied to selected clutches of the first and second groups of hydraulic clutches to obtain the desired speed. The drive transmission system includes a shifter mechanism for transmitting a shift command to the main and auxiliary change speed devices; a first controller operable in response to the shift command to operate one of the first control valves to a drain position which was placed in a supply position prior to transmission of the shift command, and to operate to a supply position a different one of the first control valves corresponding to the shift command; and a second controller operable in response to the shift command to operate one of the second control valves to a drain position which was placed in a supply position, and thereafter to operate one of the second control valves gradually to a supply position.