HYDRAULIC DRIVE DEVICE AND SPEED CHANGE METHOD IN HYDRAULIC DRIVE DEVICE

摘要

A hydraulic pump connected to a drive source and a hydraulic motor are connected to a closed circuit via oil paths. A hydraulic pump-motor connected to each oil path is connected to the hydraulic pump through a first clutch. The hydraulic pump-motor and the hydraulic motor are connected through a second clutch. At the time of starting the drive source, the capacity of the hydraulic pump is set to zero, the capacity of the hydraulic pump-motor to the maximum, the first clutch to OFF, and the second clutch to ON. The capacity of the hydraulic pump is increased to the maximum to increase the rotation speed of an output shaft connected to the hydraulic motor. After the capacity of the hydraulic pump is at the maximum, the hydraulic pump-motor is caused to perform motor function to reduce the capacity from the maximum to zero and the rotation speed of the output shaft is further increased. After the capacity of the hydraulic pump-motor reaches zero, the first clutch is set to ON and the second clutch is set to OFF. This causes the hydraulic pump-motor to perform pump function to increase the capacity from zero to the maximum, further increasing the rotation speed of the output shaft. A hydraulic drive device that has high efficiency in high speed traveling, that has excellent acceleration characteristics both in low and high speeds, and in which the output shaft can be rotated at a high speed is provided.