EXPERIMENTAL INVESTIGATION OF HYDRAULIC POWER SHARING POTENTIAL IN A DUAL CYLINDER ELECTRO-HYDRAULIC VARIABLE-SPEED DRIVE NETWORK

Variable-speed drive networks (VDN) constitute novel energy efficient drive architectures for hydraulic actuators used in industrial and mobile applications. VDN architectures control the power flows by the variable-speed control of electric machines which are driving hydraulic pump/motor units. These hydraulic units may be connected in various ways to the hydraulic actuators. Additionally, some actuator chambers may be hydraulically short circuited to allow free fluid flow between the connected chambers. This paper presents an experimental investigation of a dual cylinder VDN focusing on the hydraulic power sharing potential and energy efficiency. The VDN architecture is compared to an electro-hydraulic single axis cylinder drive system, also tested experimentally under equivalent load conditions. The applied VDN architecture includes three rotary pump/motor units and one hydraulic short circuit connection between the rod side chambers of the cylinders. The two hydraulic cylinders are made to follow a sinusoidal trajectory with varying phase shift. The more phase shift that is introduced between the cylinder trajectories, the more hydraulic power sharing is ascertained for the VDN architecture. This confirms the expectation that VDN architectures may be realized with lower power installations than electro-hydraulic single axis drive systems, and with higher energy efficiency when exploiting the hydraulic short circuit connection between cylinders.