To provide a transmission of a hydraulic drive device capable of increasing the traveling efficiency, controllability, and reliability of construction machinery and vehicles, agricultural machines, and automobiles by using an open circuit system even in the construction machinery.
This transmission of the hydraulic drive device comprises a hydraulic pump, a variable displacement hydraulic motor, and a closed-center selector valve for switching between forward and backward travelling. The transmission also comprises a shifter select position sensor, a motor rotational speed sensor, a selector valve a two-stage back pressure valve controlling return pressure in a return circuit between the selector valve and an oil tank, and a control device which compares a variation in the selection of a gear shift lever with a motor rotational speed from the motor rotational speed sensor, the minimum allowable rotational speed and the maximum allowable rotational speed of the motor stored therein and, when the rotational speed of the hydraulic motor is between the minimum allowable rotational speed and the maximum allowable rotational speed of the motor, outputs instructions to the closed center selector valve, the two-step back pressure valve, and the variable displacement hydraulic motor.
HIRAKI HIKOSABURO
KANAYAMA NOBORU
MAKITA RYUTARO
