Ceramic valves soon available in series produced cars?
Although ceramic valves have numerous advantages in comparison to metal
valves, the prohibitive cost of their manufacture has prevented their
use in vehicles other than racing cars. Calculation models and tests now
show that series production could be viable after all.
Ceramic valves have been standard components in racing cars for decades. They offer several advantages in comparison with valves made of metal: thanks to their lower weight, higher revs are possible, and thus improved engine performance. They lower fuel consumption and lessen emissions of carbon dioxide. They are also quieter.
The only reason why ceramic valves have not been used in series production cars until now, in spite of these advantages, is their high manufacturing costs. Whereas a steel valve costs around ten marks, the ceramic alternative is 50 times as expensive. Ulrike Brandt of the Fraunhofer Institut für Betriebsfestigkeit LBF (Fraunhofer Institute for Strength of Structures under Operational Conditions) explains: "The manufacturing of ceramic valves is a complex process the surface treatment in particular and this naturally involves substantial cost. But if greater roughness is acceptable in the component, and if the surface treatment is optimized, manufacturing costs can be markedly reduced."
In a joint project with Adam Opel AG, Daimler Benz AG, CeramTec AG, and three further Fraunhofer Institutes (Produktionstechnologie IPT Production Technology, Werkstoffmechanik IWM Mechanics of Materials, and Zerstörungsfreie Prüfverfahren IZFP Non Destructive Testing), the LBF is now working on the development of intake and exhaust valves made of silicon nitride, which are suitable for series production.
The LBF researchers are developing finite element models in order to calculate the stresses exerted on the valves under different engine conditions, and to assess the fatigue life of the components. The empirically ascertained fatigue strength of valves with different degrees of surface roughness has led to the conclusion that cost effective treatment of the ceramic valves meets the necessary strength requirements for use in car engines. Engine and road tests carried out by Opel and Daimler Benz confirm these findings. These high performance new components may therefore soon enter series production.
For further information, please contact:
Cetin Morris Sonsino
Tel. +49 6151/705 244 , Fax +49 6151/705 214
Fraunhofer Institut für Betriebsfestigkeit LBF
Bartningstraße 47, D 64289 Darmstadt
Homepage: http://mm.fhg.de/depts/izfp-e.html
email:
sonsino@lbf.fhg.de