Aleksandar M. Egelja

Positive flow control of closed-center electrohydraulic implement-by-wire systems for mobile equipment applications

Digitally controlled electrohydraulic (EH) closed-center valves and load sensing hydraulic pump systems have been quickly replacing the older generation of hydro-mechanically controlled (pilot actuated, mechanically controlled) open-center valves and fixed displacement pump systems in mobile equipment applications such as earth moving and construction equipment (i.e. wheel loaders, excavators, harvesters). With carefully designed and coordinated motion control systems, the power efficiency of the hydraulic system can be improved using closed-center EH systems to the point that significant fuel savings can be achieved. Furthermore, the machine behavior can be optimized for different applications via real-time control software. Such capabilities were not possible in hydro-mechanically controlled systems. Energy efficiency, high performance, software based re-configurability and reliability are the main objectives in design of EH systems for mobile equipment applications.

Wear Problem in a Linear Hydraulic Actuation System and Solution Using Forced Lubrication

The subject of this paper is early hours wear problem of a hydraulic actuator. Material transfer from the actuator housing to the actuator surface was observed after short time of component testing. A general case, where the actuator is tilted in the bore due to side load, is examined. The mechanism of local scuffing (micro-welding) is discussed. The paper describes the theoretical analysis combined with practical experience in solving common wear problems related to poor material pair and lack of lubrication between sliding surfaces. A validated solution is also discussed.Copyright