Lightweight design~A challenge for modern passenger car engines 2000-05-0051

The application of lightweight materials for new crankcase concepts implies comprehensive design considerations to achieve weight reductions as close as possible to the potential of the selected material. A specific approach for inline and V-engine crankcase concepts is discussed in detail. Engine weight reduction can also be achieved through "Downsizing." Modern technologies applied to existing engine concepts increase the power-weight ratio, the engine''s capability and therefore its marketing value. The use of lightweight materials for diesel and gasoline engines within one engine family allows a combined production and a less costly machining.

Aluminum and magnesium alloys are, due to their high relative strength (tensional strength and e-modulus divided by their material densities), suitable for weight-reduced components which need to be designed for a specific target strength. However, the low absolute values of tensional strength and e-modulus must be taken into account by geometric measures to ensure the high structural stiffness required for modern crankcases. One example for an adapted design concept is the AVL-patented trussing concept which employs stiff hollow structures as oil-retaining channels in the stressed outer walls of the crankcase.

Different design concepts were investigated to ensure a stiff integration of the main bearings in the crankcase structure. An FE analysis was conducted on a deep-skirt concept with standard bearing caps and alternatively with a partly cast-in crack concept and on a bed-plate concept with thick main bearing shells and optionally with reinforcing cast-in structures. The analysis takes static, dynamic and thermal loads into account and results in the peak firing pressure limits of each concept. The limits in combination with other relevant parameters are used to define the best-suited lightweight design concept for the specific structural requirements of each engine type.

AVL''s new lightweight design strategies allow a significant reduction of engine mass compared to conventional concepts and represent an important contribution to reduce the overall vehicle weight.