Patent ID: 6874319

Claim:
A hydrostatic transmission apparatus comprising: a variable displacement type hydraulic pump, wherein a pump shaft of said hydraulic pump mounts a charge pump for the hydrostatic transmission apparatus, and a rear end of said pump shaft protrudes outwardly to define a live PTO shaft; a variable displacement type first hydraulic motor operable by pressure oil from said hydraulic pump; a fixed displacement type second hydraulic motor operable by the pressure oil from said hydraulic pump; a parallel circuit for interconnecting pressure oil input ports of said first and second hydraulic motors to allow them to communicate with each other, and interconnecting oil drain ports of said first and second hydraulic motors to allow them to communicate with each other, wherein a passage for interconnecting the hydraulic oil input ports of said first and second hydraulic motors to allow them to communicate with each other and a passage for interconnecting the oil drain ports of said first and second hydraulic motors to allow them to communicate with each other are formed in one common oil passage block, said hydraulic pump and said fixed displacement type second hydraulic motor being arranged on a front surface of the oil passage block, and said variable displacement type first hydraulic motor being arranged on a rear surface of the oil passage block; an output confluence mechanism for converging a rotational output of said first hydraulic motor and a rotational output of said second hydraulic motor; a switching cylinder for switching over a cam plate angle of said first hydraulic motor; and an electromagnetic switching valve for selectively switching said switching cylinder to a first position or a second position. wherein said switching cylinder includes a piston rod for hydraulically pushing a cam operating section of said first hydraulic motor, and a return spring for returning said piston rod, when said electromagnetic switching valve is switched over to said first position, said piston rod pushes said cam operating section against the force of said return spring so that the hydrostatic transmission apparatus is forcibly switched over to a first speed state in which state the cam plate angle of said first hydraulic motor is equal with a cam plate angle of said fixed displacement type second hydraulic motor, and when said electromagnetic switching valve is switched over to said second position, the hydrostatic transmission apparatus is switched over to a second speed state under the force of said return spring in which state said cam plate angle of said first hydraulic motor is zero.