Hydrostatic transmission with pressure regulation means

Abstract

A hydrostatic transmission comprising a housing formed with a fluid sump, a center section disposed within the fluid sump, a hydraulic pump mounted on the center section, and a hydraulic motor mounted on the center section. A fluid passage is formed in the center section for hydraulically connecting the hydraulic pump with the hydraulic motor. A bore is open at an outer surface of the center section in communication with the fluid passage. An output operation device is provided for controlling discharged fluid of the hydraulic pump. The output operation device is moved to an operational position from a neutral position. A piston having an outer surface is reciprocally inserted into the bore so as to be allowed to project outward from the center section. A valve is disposed within the bore for opening and closing the bore to and from the fluid passage. The valve is biased to be closed by a spring disposed between the valve and the piston. A member interlocks with the output operation device so as to contact with the outer surface of the piston. When the output operation device is adjacent to the neutral position and pressure fluid in the fluid passage forcedly opens the valve and flows into the bore, the member drains the fluid in the bore to a low-pressure area which is either the fluid sump or the fluid passage for returning fluid from the hydraulic motor to the hydraulic pump.