Fluid Power Pumps and the Electrification : With a Focus on Discrete Displacement Control in Load Handling Applications

Abstract: More and more vehicles are being electrified. Mobile working machines and heavy trucks are not excluded, and these machines are often hydraulically intense. Electrification entails new requirements for the hydraulic system and its components, and these requirements must be taken into consideration.Hydraulic systems have looked similar for a long time, but now there is an opportunity to advance. Many things change when a diesel engine is replaced with an electric motor. For example, variable-speed control becomes more relevant, electric regeneration becomes possible, and the use of multiple prime movers becomes an attractive alternative. The noise from the hydraulic system will also be more noticeable when the diesel engine is gone. Furthermore, the introduction of batteries to the system makes the energy more valuable, since batteries are heavy and costly compared to a diesel tank. Therefore, it is commercially viable to invest in the hydraulic system.This thesis revolves around the heart of the hydraulic system, that also is the root of all evil. That is the pump. Traditionally, a pump has had either a fixed displacement or a continuously variable displacement. Here, the focus is on something in between, namely a pump with discrete displacement. The idea of discrete displacement is far from unique, but has not been investigated in detail in combination with variable speed before. In this thesis, a novel design for a quiet pump with discrete displacement is presented and analysed. The results show that discrete displacement is relevant from an energy perspective for machines working extensively at high pressure levels and with low flow rates, and that a few discrete values are enough to make a significant difference. However, for other cycles, the possible energy gains are very limited, but the discrete displacement can be a valuable feature if downsizing the electric machine is of interest.