Electrification of hydraulic systems has become an important research topic. The cost of the electric energy storage is high and drives the development of new efficient solutions for the system to be of commercial interest. This study is part of a project where the electrification of a loader crane is the main focus. The crane is a versatile machine and the energy efficiency of the hydraulic system is strongly dependent on the working envelope. A representative envelope can be called a drive cycle and is necessary to evaluate new solutions. This paper describes the method of producing such a cycle. A large amount of data from a field crane has been recorded for several weeks. A pattern of movement is found and used to define parameters of the drive cycle. To extract combinations of the parameters that form a good representation of the measurement data a principal component analysis is carried out. Finally, the drive cycle is defined as a sequence of trajectories with different payloads, corner points and cylinder speeds for movements between corner points. The drive cycle is tested and verified on a crane of the same model as the field crane in a laboratory environment. The methodology is found to produce a drive cycle with good variation and representation of geometrical parameters.

The load-sensing system has for a long time been the most energy efficient hydraulic system widely used for mobile machines. When replacing the combustion engine drive with an electric drive with a battery as energy source an incentive for using more energy efficient systems arise. Some promising examples of more energy efficient systems are independent metering systems, pump controlled systems and open flow control systems. Before getting to deeply involved in a specific design, an investigation of the intended application is of importance. The objective of this study is to present a large number of energy efficient designs for the hydraulic system of an electrified loader crane by the means of a loss analysis and a high level concept comparison. To be able to cover a large design space all systems are modeled based on static pressure-flow relations for their components.

Based on measurements, the losses from simultaneous operation, backpressure losses and load holding valve losses are found to be the largest loss contributors in the hydraulic system. If an electrical supply system is added to the reference load sensing system, the overall efficiency is found to be 23 %. The hydraulic system it is found to account for 62 % of the losses and the drive system for 38 %.

The concept comparison shows that a two or four pump system with recuperation possibilities can decrease the energy consumption of the complete system on the studied working pattern by about 50 %.