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Measures for reducing engine friction within the powertrain are assessed in this paper. The included measures work in combination with several new technologies such as new combustion technologies, downsizing and alternative fuels. The friction reduction measures are discussed for a typical gasoline vehicle. If powertrain friction could be eliminated completely, a reduction of 15% in CO2 emissions could be achieved. In order to comply with more demanding CO2 legislations, new technologies have to be considered to meet these targets. The additional cost for friction reduction measures are often lower than those of other new technologies. Therefore, these measures are worth following up in detail.

The challenge to reduce fuel consumption in S.I. engines is leading to the application of new series production technologies: including direct injection and, recently, the variable valve train, both aiming at unthrottled engine operation. In addition to these technologies, turbo- or mechanical supercharging is of increasing interest because, in principle, it offers a significant potential for improved fuel economy. However, a fixed compression ratio normally leads to a compromise, in that the charged engine is more of a performance enhancement than an improver of fuel economy. Fuel efficient downsizing concepts can be realized through the application of variable compression ratio. In this paper, a variable compression ratio design solution featuring eccentric movement of the crankshaft is described. Special attention is given to the integration of this solution into the base engine.

Downsizing is an effective way to further improve the efficiency of SI engines. To make most of this concept, the compression ratio has to be adjusted during engine operation. Thus, the efficiency disadvantages during part load can be eliminated. A fuel consumption reduction of up to 30% can be realized compared to naturally aspirated engines of the same power. After the assessment of several known concepts it turned out that the eccentric crankshaft positioning represents an appropriate solution which meets the requirements of good adjustability, unaltered inertia forces, low power demand of the positioning device and reasonable design effort. The basic challenges posed by the eccentric crankshaft positioning have been tackled, namely the crankshaft bearing and the integration of the newly developed power take-offs which have almost no influence on the base design.

Beside the traditional prediction of stresses and verification by mechanical testing the optimization of cylinder liner bore distortion is one of today's most important topics in crankcase structure development. Low bore distortion opens up potentials for optimizing the piston group. As the piston rings achieve better sealing characteristics in a low deformation cylinder liner, oil consumption and blow-by are reduced. For unchanged oil consumption and blow-by demands, engine friction and subsequently, fuel consumption could be reduced by decreasing the pre-tension of the piston rings. From the acoustical point of view an optimization of piston-slap noise is often based on an optimized bore distortion behavior. Apart from basics to the behavior of liner bore distortion the paper presents advanced analytical and empirical methods for detailed prediction, verification and optimization of bore distortion taking into account the effective engine operation conditions.

Over the last few years, engine development has succeeded in reducing friction by up to 30 %. This corresponds to a reduction of fuel consumption in urban traffic of around 10 %, thus, making friction reduction - aside from the introduction of Otto DI engine and the transition from IDI to DI Diesel engines - an effective measure to reduce fuel consumption. Investigations of engines and engine components show that even today's “Best in Class” engines still harbor a reduction potential of least 20 %. Possible ways to realize this potential lie in: Adapted dimensioning of the friction relevant engine parameters Lightweight design of dynamic components Optimized layout of the timing drive (especially in valve train designs with roller followers and chain drives) Optimization of the piston group (up to 50 % of the parasitic losses can occur here) The investigations are based on detailed friction measurements of over 100 sample engines and their components.

Due to the future application of combustion engines in small and hybrid vehicles, the demand for high efficiency with low mass and compact engine design is of prime importance. The diesel engine, with its outstanding thermal efficiency, is a well suited candidate for such applications. In order to realize these targets, future diesel engines will need to have increasingly higher specific output combined with increased power to weight ratios. This is therefore driving the need for new designs of 3 and/or 4 cylinder, small bore engines of low displacement, sub 1.5l. Recent work on combustion development, has shown that combustion systems, ports, valves and injector sizes are available for bore sizes down to 65 mm.

In the early design stage a 16-cylinder V-engine is optimized with respect to its vibrational and acoustic behavior. The objectives of the development are: (1) to minimize vibrations of the crankcase with special focus on the structure-borne noise transmission via the engine mounts, and (2) in this context, to identify the appropriate locations for the engine mounts. The NVH behavior of the engine structure is simulated using the Finite Element Method (FEM). The dynamic FE-model of the engine is excited via synthesized cylinder pressure force spectra. The corresponding vibrations of the sound emitting surface are calculated, thereby revealing structural weaknesses. By calculation of the crankcase modal vibrations, the noise relevant modes are identified. Based on these results the influence of structural modifications on the NVH behavior is predicted.

The IDI diesel engine still offers a substantial development potential. One major advantage is its low fuel consumption and, hence, its low CO2 emission compared to gasoline engines. The disadvantage of its higher noise emission, however, requires particular attention in the development stage. By means of modern signal analysing and signal processing methods in combination with computer simulation methods new tools for the development of low noise Diesel engines are available. The noise emission of IDI diesel engines has on average been reduced by about 5 to 8 dBA within the last 15 years. This trend will continue further despite the introduction of more and more light weight design components. Today's IDI diesel engine is mainly dominated by high noise levels in the frequency range about 1600 to 2000 Hz. In-depth measurements show that this is generally caused by a high combustion excitation (Helmholtz-resonance) and, in addition, structure weaknesses of the crankcase.