Marginal Column

The fascinating digger

Hardly any construction machine is as fascinating for men – both young and old – as the excavator.


When the heavy shovel on the arm of the seemingly ungainly tracked vehicle touches the ground, spectators hold their breath. Uniformly and with great precision, this steel behemoth strips away dirt, layer by layer, to dig a construction pit. There a great deal of technology behind the brawny power of this heavy-duty machine, which can handle both rough demolition effort and more delicate work. Powerful drives and the intelligent linkage of highly developed hydraulic components, joined by mature system software, help this colossus reach maximum performance, extreme precision, high efficiencies, and a long service life. Among the construction machines, the excavator is considered to be the “key machine”, in which all the fundamental engineering and working principles are found. Our “transparent excavator” shows and explains more.

Structure of the system

A dual-circuit system is installed in the tracked excavator shown here. Where movements are superimposed, two using units can be operated at differing pressure levels to achieve the optimum energy situation. Power management – the balancing of the power made available by the diesel engine and the power drawn by the hydraulic system – is regulated with the appropriate LLC software. Thus the diesel engine can run at the right speed for ideal fuel use in differing working modes. At the same time, the excavator can achieve its maximum performance. Over and above that, the high-pressure hydraulics in heavy mobile machinery deliver great energy density (maximum system pressure up to 380 bar) and flexible power transmission.

The path taken by the hydraulic fluid

The control signal selected by the operator is reported to a controller with special digging software, setting the desired slewing angle and displacement volume. At the same time the gate valves, responding to the control block, are swung open, passing the oil volume proportionally through the inlets of the using units (motors and/or cylinders). The fluid moved into the motors and cylinders then passes through the outlets in the control block and back into the tank.

Illustration | Bosch Rexroth AG