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Closed-Center-type Load Sensing Systems for fluid power controls in hydraulic excavators, which had been considered as far back as 1955, were proposed in the U.S.A. in 1975, but were not feasible. In the late of 1980's European-made hydraulic excavators were equipped with load sensing systems, including flow dividing control. In the early 1990's, further improvement of CLSS's were made in Japan. CLSS's are capable of controlling complex motions of multiple actuators with high accuracy against varying loads under varying engine speed conditions, with expectations for improved controllability and compatibility of hydraulic excavators to many kinds of works in which attachments are used. Conversely, operators have made the best use of the characteristics of conventional fluid power systems, in which each actuator speed is varied by inertia or engine speed change.

Hydraulic excavators can work on both powerful and fine jobs, which are executed safely. In conventional hydraulic systems of excavators, exhausted hydraulic energy losses were generated with fine control for attachments or with force limit. Recently, variable displacement axial piston pumps equipped with energy saving controls have been developed and made available for hydraulic excavators. With such energy saving controls which decrease mean fuel consumption of excavators, attachment drifts and noise are diminished, engine start during cold weather is made smoother and life of working fluid may be elongated.