Before the end of the year, Audi will be replacing the standard steel suspension springs with new lightweight versions made of glass fibre-reinforced polymer composite materials in its upper mid-sized models.
The new spring, which Audi developed in collaboration with an unnamed Italian supplier is thicker than the standard steel spring and has a slightly larger overall diameter with a lower number of coils.
What the spring gains in size it dramatically looses in weight. Where a steel spring for an upper mid-size Audi weights nearly 2.7 kilograms, the new composite spring with the same properties weights around 1.6 kilograms. Together the four GFRP springs thus reduce the weight by roughly 4.4 kilograms (9.7 lb), half of which pertains to the unsprung mass.
Dr. Ulrich Hackenberg, Member of the Board of Management for Technical Development at Audi said;
The GFRP springs save weight at a crucial location in the chassis system. We are therefore making driving more precise and enhancing vibrational comfort.
The core of the springs consists of long glass fibres twisted together and impregnated with an epoxy resin system. 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 100 degrees Celsius.
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. Last but not least, production requires far less energy than the production of steel springs.