HYDRAULIC PUMP UNIT

The invention relates to a hydraulic pump unit comprising a hydrostatic system pump which is used to provide a hydraulic working system with hydraulic fluid via a pressure connection, also comprising a second pump which is used to suction hydraulic fluid via an inlet and feed said fluid to a low pressure area of the system pump, further comprising an electric motor provided with an outer casing and which is used to drive both pumps. The aim of the invention is to provide a hydraulic pump unit enabling power losses to be kept to a minimum and which can be permanently operated without causing the temperature of the hydraulic fluid to rise to values resulting in increased leakage or rapid ageing of the hydraulic fluid. To achieve this aim, the system pump is an especially pressure-regulated variable displacement pump and the hydraulic fluid can be pumped by the second pump into a return opening in such a way that it by-passes the system during circulation from the inlet via a cooling circuit.