Mechanism of returning to neutral for axle driving apparatus

摘要

A hydrostatic transmission is provided comprising a hydraulic pump and a hydraulic motor fluidly connected with each other through a closed fluid circuit. Pistons press against a control arm connected with a movable swash plate of the hydraulic pump and generate a friction force when the movable swash plate, which has been rotated slantwise, automatically returns toward the neutral position by a neutral return spring. The movable swash plate gradually returns to the neutral position by pressure of the piston. A discharging oil hole is open at the utmost end of each of the pistons for draining a portion of operating oil which operates the piston in the closed fluid circuit to the interior of a housing. Grooves are formed along a surface of the control arm abutting against the pistons. When the movable swash plate is rotated between the neutral position and a predetermined position, the discharging oil holes are connected to the interior of the housing through the grooves so as to release the oil pressure out of the closed fluid circuit. Thus, braking shock can be moderated and the neutral position can be expanded.