Propelling transmission control apparatus for a working vehicle having a hydrostatic stepless transmission

摘要

A propelling transmission control apparatus for a working vehicle having a hydrostatic stepless transmission comprises a variable displacement type hydraulic pump (35), a change speed control mechanism (80) for converting a displacement of a control device (55) to a control displacement for varying a swash plate angle of the hydraulic pump, a fixed displacement main hydraulic motor (36) and a variable displacement auxiliary hydraulic motor (37) connected in series to the hydraulic pump. A common output shaft receives rotational output from both motors. A control piston (35) varies the swash plate angle of the auxiliary hydraulic motor, is connected to a pressure oil supply line (39) for supplying both hydraulic motors with pressure oil, and is operable to vary the swash plate angle of the auxiliary hydraulic motor (37) such that the auxiliary hydraulic motor (37) has an increased volume with a pressure increase applied to the control piston (38).