VALVE SPECIFICATION REQUIREMENTS FOR DIGITAL HYDRAULIC WINCH DRIVES

Digital Displacement Machines (DDM) have been shown to improve energy efficiency for various applications such as wind turbine and automotive transmission systems. A DDM’s performance depends heavily on the digital valves that it utilizes. This paper investigates the required digital valve flow coefficient and switching time for realizing a digital offshore winch drive. The proposed drive improves system efficiency and reliability by replacing the winch’s conventional hydraulic motors with DDMs and removing the gearboxes. A commercially available winch system of an offshore knuckle-boom crane is used as an example when deriving the parameters of the DDM. The valve specifications are derived conservatively based on simulations to ensure a motor efficiency of at least 90 % throughout the operating range of the winch. A partial-stroke strategy is used to control the motor displacement where the highpressure valve can be closed at any given shaft angle before the cylinder reaches the top dead center. It is concluded that commercially available valves will require a DDM with a high number of cylinders, resulting in a complex system with high cost. On the contrary, certain prototype valves have shown promise for enabling the use of DDM with as few as seven pistons. However, further experimental work is required to verify the performance of these valves.