Experimental approach to unsteady characteristics of a hydraulic motor in low-speed range.

Unsteady characteristics of a hydraulic motor are examined experimentally in the speed range where negative resistance appears in a friction torque-rotational speed diagram. When the rotational speed is fluctuating around a mean value during continuous rotation of the motor, the friction torque takes a constant value and negative resistance does not appear even in the negative resistance speed range of the steady characteristic. On the other hand, in the case where the motor stops intermittently, as in the case of stick-slip or inching operation, the friction torque shows hysteresis between the accelerating and decelerating periods. The effects of the stop time, the magnitude of speed fluctuation, and the reverse of rotational speed on the unsteady friction torque are also clarified. The friction torque changes quasi-steadily while the pressure changes.