Abstract Present automobile development is keenly focused on measures to reduce the CO2 output of vehicles. Plug-in hybrid electric vehicles (PHEVs) enable grid electricity, which is clean in tail-pipe emissions terms, to be utilised whilst the on-board electrical storage has sufficient charge. MAHLE Powertrain and Protean have jointly developed a plug-in hybrid demonstrator vehicle based on a C-segment passenger car. The vehicle features Protean’s compact direct drive in-wheel motors with integrated inverters on the rear axle and retains the standard gasoline engine, and manual transmission, on the front axle. To support this one-off prototype, a flexible vehicle control unit has been developed, which is easily re-configurable and adaptable to any hybrid vehicle architecture. The unit operates using software developed by MAHLE Powertrain to achieve a fully configurable vehicle control unit (VCU), intended to provide a rapid and cost effective platform for the development of demonstrator and niche volume vehicle fleets. This paper describes some of the challenges, and solutions, associated with the vehicle conversion, including key vehicle integration topics, such as the CAN interface, vehicle control strategy, and the cooling system. Introduction The UK government has set, in the 2008 Climate change Act [1], the target that the net UK carbon account for the year 2050 is at least 80 % lower than the 1990 baseline. This target is for all sources of carbon dioxide (CO 2) emissions, however, the transport sector accounts for almost 24 % of the UK national CO2 emissions, of which cars and road haulage vehicles account for nearly 80 % [ 2]. Because electric vehicles (EVs) do not generate pollutants during usage, and they can potentially rely on energy provided by a selection of renewable sources, they are the focus of much current interest. However, due to the present capabilities of battery cell technology, the overall range of such a vehicle is limited in comparison to an equivalent gasoline or diesel fuelled vehicle. Furthermore, once the battery is depleted, relatively long recharging times are currently required before the vehicle is available for use again. Plug-in hybrid electric vehicles (PHEVs) overcome many of the short-comings of EVs. Retaining a standard driveline, along with the EV driveline enables the traction battery storage capacity to be reduced, though still maintaining an acceptable vehicle driving range. For long journeys, when the battery and fuel tank are both depleted, the driver can simply refuel the gasoline tank in a matter of minutes. However, it is desirable that for the majority of time the vehicle will operate in a purely electric only mode, from the battery, and that the user recharges the vehicle when it is not in use (e.g. over-night). Thus, the battery should be sized to cope with the majority of daily usage that the vehicle will encounter, and only rely on the range extender for infrequent, longer, journeys. MAHLE Powertrain and Protean Electric have collaborated to construct and develop a PHEV demonstrator to investigate the benefits and challenges provided by the adoption of in-wheel electric motors in such a platform. Wheel Motors Integrating electric drivetrain components is often a significant challenge for vehicle designers and the Protean Electric PD18 inwheel motor offers innovative solutions to many of those problems. The greatest advantage is the elimination of the need to find space to package electric drivetrain components within the vehicle and use instead the available space within, and around, the wheels. In a new vehicle design this gives the designers the flexibility to create cars of a sub-compact footprint and mass but the wheelbase and interior passenger space of luxury cars. In a retro-fit design, such as this one, it removes the burden of finding a location in an already tight engine Through-the-Road Parallel Hybrid with In-Wheel Motors