Hybrid electric propulsion for military vehicles - overview and status of the technology

In the civilian market the hybrid electric vehicle (HEV) is receiving increasing attention due to its reduced fuel consumption. The HEV is basically a combination of the common internal combustion engine (ICE) powered vehicle and the battery powered electric vehicle (EV). The purpose of the electric motor and battery is to shift the operation of the ICE closer to its optimum operating condition, and enable regenerative braking. There is also a great interest in HEV technology for military vehicles. An important advantage is the possibility to generate additional onboard electric power. This is important in meeting the ever increasing demand for electric power onboard modern military vehicles. Other potential advantages are improved fuel economy, extended silent watch capability, silent mobility, a modular vehicle design and reduced life cycle cost (LCC). However, there are important technical challenges that need to be solved before we will see the successful fielding of a mass produced military HEV. A number of military HEVs have been successfully demonstrated, but there are still important limitation related to key technologies such as electric motors, power electronics and energy storage systems (e.g. batteries). The maturity of the technology, depends on the vehicle type (role, weight, tracked or wheeled etc) and the HEV drivetrain architecture opted for (series, parallel etc.) This report aims to describe the HEV technology and the advantages and technical challenges of different key technologies. How the technology affects the overall vehicle design, is also discussed. In doing so, the different key technologies are described in some detail. The different programs and efforts related to the development of military HEVs are also presented. The first military HEV is expected to be fielded in approximately 5-7 years. Based on the maturity of the technology this will likely be a wheeled multirole vehicle, weighing 5.000-10.000 kg, implementing a parallel drivetrain. This claim is however based on the assumption that an HEV demonstrator is selected, in June 2008, to participate in the demonstration phase of the US Joint Light Tactical Vehicle (JLTV) program. The US Future Combat System (FCS) program is committed to the development of a series drivetrain technology for tracked vehicles. If the FCS program is completed as planned, a family of tracked HEVs will be fielded in approximately 7 years. In recent years, military vehicle requirements have changed considerably. This is likely to continue in the future, with features such as flexibility, transportability and cost becoming increasingly important. To meet these requirements, it is expected that HEV technology will become important, due to the features and advantages enabled by the technology.