Audi claims to be reinforcing its leading role in automotive lightweight construction by introducing new, lightweight suspension springs made of glass fibre-reinforced polymer (GFRP) which will appear in "an upper mid-size model" before the end of 2014.
The GFRP spring, which the VW group premium car unit developed in collaboration with an Italian supplier, looks different to a steel spring. It is light green, the fibre strand is thicker than the wire of a steel spring, and it has a slightly larger overall diameter with a lower number of coils.
Most importantly, however, it is some 40% lighter. Whereas a steel spring for an upper mid-size model weighs nearly 2.7kg (6lb), a GFRP spring with the same properties weighs approximately 1.6kg (3.5lb). Together the four GFRP springs thus reduce the weight by roughly 4.4kg (9.7lb), half of which pertains to the unsprung mass.
"The GFRP springs save weight at a crucial location in the chassis system. We are therefore making driving more precise and enhancing vibrational comfort," said Ulrich Hackenberg, Audi's technical development chief.
The core of the springs consists of long glass fibres twisted together and impregnated with epoxy resin. A machine wraps additional fibres around this core - which is only a few millimetres in diameter - at alternating angles of plus and minus 45 degrees to the longitudinal axis. These tension and compression plies mutually support one another to optimally absorb the stresses acting on the component. In the last production step, the blank is cured in an oven at temperatures of over 100C.
The GFRP springs can be precisely tuned to their respective task, and the material exhibits outstanding properties. It does not corrode, even after stone chipping, and is impervious to chemicals such as wheel cleaners. Lastly, production requires far less energy than the production of steel springs.
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