Energy Saving in a Hydraulic Servomechanism System – Theory and Examples of Laboratory Verifi cation

A control system with a directional control servo valve or a roportional directional throttling control valve, controlling a linear hydraulic motor (cylinder) is used in the ship steering gear drive, in the controllable pitch propeller control, in the variable capacity pump control system for hydraulic deck equipment motors or fi xed pitch propellers in small ships (e.g. ferries). The most popular solution is a system where a throttling control valve is fed by a constant capacity pump cooperating with an overfl ow valve. This system, working with a constant pressure, achieves a high energy effi ciency value η only at the point of maximum motor load coefficient MM and maximum motor speed coeffi cient ωM. Energy savings in a constant capacity pump operation may be achieved by means of an overfl ow valve controlled by the oil outlet point pressure between the directional control valve and the cylinder. Although structural volumetric losses cannot be eliminated in such a system, it is possible to reduce considerably structural pressure losses, mechanical losses and volumetric losses in the pump, and also mechanical losses in the cylinder. The paper discusses these energy savings using an earlier developed mathematical model of losses in elements, the energy effi ciency of the system and the operating range of the cylinder [9]