With the launch of the new Mercedes-Benz GL Class, Daimler AG has installed in the six-cylinder diesel model a world first: an engine bracket made of plastic. The noise in the vehicle interior originating from combustion processes in the engine and from inertial forces in the powertrain, made it necessary to look for new ways of improving driving comfort. This unwanted noise lay in frequency ranges which the relatively stiff aluminum engine bracket and the multifunctional engine mountings were not able to reduce effectively. Minor improvements were achieved by filling the aluminum engine bracket with a polymer embedding compound. The only moderate improvement and its disproportionately high cost gave rise to the idea of developing an engine bracket made entirely of plastic so as to deliberately employ the high damping of the engine bracket in the path taken by structure-borne sound. With the support of BASF SE, polyamide prototypes for the Mercedes-Benz R Class were made by injection molding and subjected to acoustic measurements in Daimler's NVH Center. The idea was only feasible in practice with the aid of BASF SE's comprehensive and realistic analytical methods (Ultrasim in conjunction with structural analysis) for mechanical strength and its validation on Daimler's static and dynamic test stands. The requirements made of the plastic components represent a great challenge for thermoplastic materials. Not only static loads (engine weight, setting) but also dynamic loads (inertial forces under poor roadway conditions, crash requirements) must be permanently sustainable at operating temperatures up to 130 °C and peak temperatures as high as 150 °C. Here it was necessary to deliberately exploit the anisotropic properties arising from the fiber orientation in order to optimize strength. This means aligning the glass fibers in the direction of high loading. To achieve this, the fiber orientation required was determined in structural analyses by means of FEM calculations and, using suitable mold-filling simulation calculations, the injection mold was designed such that fiber orientation in areas under heavy loading ran in parallel with the transmission of forces. The constitutive relationships required for this and the calculations are held by BASF SE. For production release, strength and acoustics trials were carried out on Daimler's test stands. The components were tested under operating conditions - in other words, static and cyclic strength at both low and high temperatures, and also rough-road testing on a tri-axial servo hydraulic test stand with a constant ambient temperature using load collectives from rough-road testing of the real vehicle. In parallel with this, in-vehicle tests were conducted with test vehicles and here crash testing played a key role. Acoustic testing took place not only in the vehicle on the external-noise test stand but also on engine test beds at the NVH Center. The acoustic measurements are taken under all possible customer-related loading states such as acceleration, constant speed, full power, idling and thrust.
Development of a new plastic engine mount and its influence in vehicle NVH
2013
8 Seiten, Bilder
Conference paper
English
Motorträger , statische Prüfung , Kunststoff , Spritzgießform , Fahrzeuginnenausstattung , Verbrennungsprozess , Geräuschmessung , Strukturanalyse , Aluminium , Trägheitskraft , Polyamid , Polymerverbindung , Antriebsstrang , plastische Komponente , Fahrkomfort , Rauschen , Körperschall , Faserorientierung , Probefahrt , Arbeitstemperatur , Krafteinleitung , Fahrzeugtest , Crash-Test , akustische Prüfung , Motorprüfstand , Beschleunigung
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