On the competition between fluid and electric automotive drives

The present general lecture gives a view over the relevance and potential of fluid power systems for automotive applications in the present and future, compared to electric drives as their major challengers. In order to address their respective relevance, the classification of automotive vehicles according to ISO/DIN 70010 is shown in the introduction. There are different reasons which stimulate innovations in drive engineering, where the need for saving energy during production and operation of automobiles can be considered as the first order demand for the future.
For assigning the appropriate drive technology, a distinction between traction (“main”) drives and additional drives (“auxiliaries”) is determined. In order to utilise their specific advantages, more and more different energy sources and/or energy converters (drives) have been combined in one vehicle, known as hybrid traction drives having certain topologies. To understand the relationships, the influence of different drive characteristics and efficiencies on the driving and braking performance of the vehicle is discussed. Selected types of drives are compared, where particularly the aspect of energy storage has to be taken into account.
From the engineering point of view, an automobile’s auxiliary drives are of same level of interest as its traction drive(s). In this area a tendency to electric actuation can clearly be identified, which allow a “power on demand” strategy in an appropriate manner. At present, the low voltage board net may considered as the major handicap, however, once having high voltage aboard, a remarkable breakthrough of electric auxiliary drives can be expected. Anyway, due to their specific advantages, fluid power solutions may retain their importance in automotive engineering, e.g. pneumatic springs and servo brakes and hydrodynamic torque converters. In conclusion, the necessity of significant reduction of energy during the whole automotive life cycle should remain in the focus, particularly during the phases of production and utilisation.