Compact Electrohydraulic Energy Converter for Off-Road Machines

Abstract

A novel electrohydraulic energy converter for hybrid off-road machines is presented. The converter is utilized as a power source for hydraulic actuators enabling electrical energy recuperation. The authors have designed, built and tested a device which combines a 7 kW S3 70% electric motor, a planetary gear and a bent-axis hydraulic pump. The integration aims for a power dense small volume device, which can perform the load cycles e.g. of a log stacker. The load cycles are first simulated to define design boundaries for the motor design. The motor uses a moderate amount of oil inside motor chamber as heat transfer medium bringing the motor losses to the converter outer surfaces to be then dissipated in the ambient. The converter is attached to a log loader and real load-cycle performance is investigated. Real load cycles for a log loader are recorded, the converter performance and thermal behaviour are studied. Motor thermal behaviour and losses are studied with no oil or with a moderate amount of oil in the motor. The converter prototype cleared well the requirements in the load cycles tested.