Efficiency improvements in mobile hydraulic systems

Regulations such as TIER IV Final and STAGE IIIb force manufacturers of mobile construction machinery to reduce special exhaust elements. As this requirement is unattainable solely through measures inside the engine and exhaust gas treatment is extensive, engines with reduced power seem to be a good compromise to meet the requirements. But then, a higher overall hydraulic efficiency is essential to fulfil same tasks with the machine. In addition, decreasing energy resources lead to raising fuel costs. Customers require higher productivity without changes in the handling characteristics of the machine. This situation provided the motivation to define ways that assist developers to accommodate these conflicting requirements. This thesis deals with efficiency improvements in mobile hydraulic systems. It demonstrates a methodology for investigating different system designs, even in case of insufficient cycle data. As the results do not provide general information valid for all tasks of a machine, cycle-based data can be utilized to reflect the machine use or to discover potential power reserves of a new hydraulic system design. The investigations are based on hydraulic system simulations. A crawler excavator was chosen as an example to represent conventional work hydraulic systems. This application also utilizes many subsystems that are typically found in mobile hydraulics. A main focus is the interaction between engine and work hydraulics. The methodology is applied to a load-sensing system, so that fifteen new designs are compared to each other. Besides the reference system, three new system designs based on a throttle-free working principle are discussed in detail. The results are illustrated using plot-diagrams that show the cumulated energy for each operation point in the efficiency map of each component. Statistical data is used to present the correlation between engine and hydraulic efficiencies as well as to point out efficiency with respect to the machine use. In addition to the energetic aspects of all investigated designs, system-specific issues as well as the quality and weakness of the simulation type are also focuses of the investigations.