| 摘要 |
The present invention relates to a speed changing device for a hydraulic driving apparatus and a speed change control method thereof, which provide excellent controllability, traveling efficiency, and reliability without occurrence of cavitation. To this end, the device comprises a shifter selected position sensor (63a) for detecting a shift lever change, a motor rotational speed sensor (52) for detecting a rotational speed of a hydraulic motor (50), and a control device (60); and the control device (60) judges and controls either a powering control or a brake control, based on the change of the shift lever selection and on the comparison of the detected motor rotational speed with a memorized motor rotational speed. In addition, a two-stage back pressure valve (23) can be provided between a directional control valve (21) and an oil tank.
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