PUB - Hybrid module for electrohydraulic drive systems of excavators

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Authors: Leifeld, Robert; Murrenhoff; Hubertus; Schmitz; Katharina

To this day, mobile machines largely consist of drive systems that are primarily powered by a diesel engine. A large proportion of the mechanical power available at the engine shaft is usually converted into hydraulic power by hydrostatic pumps. The advantages of hydraulics as a robust and compact drive technology for operating many parallel, primarily linear, actuators will continue to lead to its use in mobile machinery in the future. For a long time, increasing machine efficiency or productivity was based on improving individual drive subsystems. However, a holistic view of the mobile machine, which considers the interaction of all subsystems in the machine as well as the external influences on the machine, is promising. With respect to the interaction between subsystems, the primary goal is to shift the load collective of each subsystem to its optimal operating point. The focus of this work is the development of a hydraulic hybrid system, which is to be understood as an additional module supplementing the regular valve system of a hydraulic excavator. In addition to a purely static power balancing, this system also includes the limitation of dynamic torque changes on the diesel engine. Transient load conditions of the ICE in particular are responsible for an increase in both fuel consumption and engine emissions. The hydraulic hybrid system developed, which is used as a supplement to a ICE, is thus able to prevent abrupt torque loads on the ICE through dynamic support. The static power balancing of the ICE consists of actively charging the storage in phases with power surplus, which corresponds to an increase of the base load, and being supported by the storage of the hybrid system in phases with power shortage. In the form of volume flow support, the hybrid system together with the main pump provides the required power for the electrohydraulic LS system. The hybrid system is compared with the standard/LS system based on three load cycles, whereby the measurements were carried out in each case with the same machine, on the same day, with the same machine operator, in order to ensure a high degree of comparability of the measurement results. On average of all cycles, a fuel saving of approx. 16 % and a reduction in cycle time of approx. 4 % is determined with the hybrid system.