Due to legislative, social, environmental and economical reasons fuel consumption and CO2 emissions, respectively, reduction is and will remain the key challenge for the automotive industry. However, for most vehicle classes, this can’t be the only focus since customers expectations regarding drivability and fun to drive have to be met as well. If two vehicles show the same fuel consumption, in most cases the one will be purchased which offers more fun to drive & comfort.
A detailed analysis of the fuel economy potential offered by hybridisation of a Gasoline engine shows that shifting of operation points of the ICE is the main effect. The “classical” hybrid functions (brake energy recuperation, idle stop) - also used - have less potential.
Downsizing of the combustion engine and downspeeding by wide ratio spread and proper final drive ratio leads to a tremendous increase in fuel efficiency. The impact on drivability due to these measures is compensated or even over-compensated by the additional usage of an electric drive. For not to suffer from a low battery, which would disable the torque support from the e-drive, AVL has developed and patented a special strategy to guarantee always a high level of the battery charge. Energy needed for support at low engine speeds is gained back at higher speeds by using the overboost capability of the turbo-charged combustion engine. Also under full load conditions a reloading of the battery is possible, the Turbo-Hybrid is born.
In 2008 AVL has realized the Turbo-Hybrid powertrain in a BMW 3-series demo vehicle in cooperation with Bosch and LUK. In comparison to a 2008 reference vehicle a fuel reduction in the NEDC of 10% could be demonstrated while the overall driving performance and fun-to-drive is improved. The strategy of recharging the battery by engine overboost operation was successfully demonstrated on the test track and in real life operation. Consequently with moderate add-on costs of the combustion engine, the required add-on costs for the electric components can be reduced significantly resulting in overall lower drive train costs and a better benefit to cost ratio compared to other Hybrid systems.