Direct-Driven Hydraulic Drive Without Conventional Oil Tank

In the past few years, direct-driven hydraulic drive (DDH) has synthesized the advantages of compact high power of the hydraulic system and flexible control of the electric motor. This paper investigates the direct-driven hydraulic setup for the non-road mobile machinery (NRMM) application. In the proposed setup, the speed and position control of a double-acting cylinder is implemented directly with a Synchronous Torque Motor drive in a close-loop system without conventional control valves and oil tank. In relation to this, hydraulic accumulator is employed as a replacement of the conventional oil tank. For position and speed control of this closed-loop system, only single feedback is applied from motor’s rotor encoder. As a result, excellent control capabilities of a modern electric drive brings along safety functions and monitoring capabilities of the motor and controller to benefit the hydraulic system. Functionalities of motor controllers offer opportunities to duplicate conventional sensors based on either safety or reliability demands. The system is investigated by means of measurements and also simulation models.