The Turbo-Hybrid – An Integral Approach for a Modern Gasoline Hybrid Engine System

Authors

Dr. R. Fischer, Dr. K. Kirsten, AVL List GmbH, Graz

Year

2006

Print Info

Fortschritt-Berichte VDI, Reihe 12, Nr. 622

Summary

For hybrid drives to gain wide acceptance, the decisive features will be not only the customer’s achievable fuel consumption improvement but also, and increasingly, the area of driving pleasure. These requirements can indeed be met many times over through the use of a power split full hybrid, albeit at substantially increased cost. If one analyses the potential fuel savings achievable through hybridizing a gasoline engine, the potential consumption reduction through load shifting specifically is more attractive than that available through recuperation of deceleration energy and idle switchoff. Here, the combination of an exhaust gas turbocharged gasoline direct injection engine with a parallel hybrid in the power range of 15 kW offers a highly costefficientsolution for mid class passenger cars for two reasons: The full load characteristic of a turbocharged gasoline engine in combination with the transient torque boost by the electric motor enables fuel consumption optimised transmission ratios. This in turn leads to a fuel consumption reduction nearly on the level of the power split Hybrid at overall better driving pleasure but much less drive train expense and complexity. The overboost capability of the turbocharged gasoline engine guarantees driving performance and enables recharge of the energy storage system even under worst case driving conditions. This leads to an improved trade off between increased driving pleasure and required energy storage capacity. Contrary to actual proposed systems the dedicated low end torque characteristic of the combustion engine is the key for the advantages of the proposed TurboHybrid drive train. As a result, a comparatively small additional outlay on the engine allows the additional investment necessary on the electrical side to be reduced by a greater proportion yielding for the whole system a significantly better cost / benefit ratio than for other hybrid concepts. Through the application of new dynamic operating strategies, it is already possible to achieve largely the same potential consumption and driving pleasure improvements with a comparatively simple combination of manual transmission, gasoline engine with turbocharger and 15kW motor as those available from a significantly more complex power split full hybrid, and this at a significantly lower cost. The next significant step forward in the direction of further improvements in customers’ driving pleasure and fuel savings can be seen in the combination of the turbo hybrid concept with a dual clutch transmission.

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