A Digital Hydraulic Full-Bridge Oscillation Transformer

As emission standards around the world grow more stringent, construction equipment manufacturers are looking towards electrification. A variety of electrified machines are being brought to market, dramatically reducing emissions of carbon dioxide, nitrogen oxide and acoustic noise. However, electrification comes with challenges as the machine’s ability to perform a full day’s work on a single charge is imperative. OEMs must balance battery cost with the power and range requirements of the machine without creating price-prohibitive products. Adding extra battery power to enable longer runtime adds expense, and therefore in the pursuit to balance extended runtime, without excessive battery costs, the inefficiency of hydraulics is the prime target. In this paper we present a novel linear transformer based on the digital displacement technology. The transformer differs from other linear topologies in that the piston is free-floating and the chambers are operated similar to digital displacement unit chambers, where switching losses are minimized with timely operation of the low- and high-pressure manifold valves in relation to the compression and decompression of the displacement chamber. While exhibiting the disadvantage of a single piston machine in terms of vibrations, the mechanical construction of the transformer is simple compared to rotational piston-type displacement units, however the simplicity comes with the cost of complicated control. The research target is to develop a small, efficient, high-frequency transformer, which can replace the inefficient control valves in common-pressure-rail systems. A prototype designed for operation of the boom in an electrified wheel loader is presented.