Tribotronics in Electro-Hydraulic Actuator Technology: Improving Durability by Control

A trend in industry and academia is the design of variablespeed pump drives for use in hydraulic supply units, actuation of hydraulic cylinders and so forth, due to the potential of highly limited throttling. A main drawback in existing variable-speed pump drives is the operation of pumps at high loads and low shaft speeds, potentially increasing wear in pump bearings, especially in pumps with journal bearings. Such journal bearings rely on hydrodynamic lubrication films created by the rotation of the pump, which is minimised or removed completely when the pump shaft speed is in the lower range with a high load. The purpose of the study presented is to investigate how these conditions limit the operation of variable-speed pump drives, and how these challenges may be overcome. The study takes offset in the establishment of a wear rate constructed from a risk factor in the form of the Ocvirk number and an impact factor developed from Archard's wear law. With this wear rate, a novel control method targeting the best possible operating conditions for the pump bearings is proposed, when applied to a simple variablespeed drive. Lastly, the consequence of applying the proposed control method on the energy efficiency is investigated. Numerical results demonstrate that the proposed control method reduces the wear rate and hereby the risk of an early pump failure, how-ever, on the cost of a generally reduced energy efficiency.