Efficient and load sensitive hydraulic supply unit using multiple switching converters

In hydraulic drive systems with multiple actuators connected to one common pressure supply often a load sensing strategy is used to reduce the throttling losses. In particular, in mobile applications such load sensitive supply units are installed to lower the overall energy consumption, which results in a more economical and ecological operation of the machine. However, so far common load sensing systems are not able to recuperate the energy, which is actually released when a dead load is lowered. In this paper a load sensitive pressure supply unit is presented, which is able to harvest energy from the load and also efficiently return the stored energy to a load sensitive common pressure rail. The operating principle is based on a parallel arrangement of multiple hydraulic switching converters representing a digital hydraulic transformer, which allows to store recuperable energy in a gas-loaded accumulator. The resulting hydraulic buffer module can even be added to an existing pressure supply, at least in certain cases. Furthermore, the presented storage module is able to boost the hydraulic power at the output beyond the maximum power of the primary motor. The concept is investigated by simulations, the major benefits and limitations are discussed and an outlook on further steps in development is provided at the end of the contribution.