The application of automotive engineering plastics continues to expand, with Mercedes-Benz using what is described as the world’s first plastic engine support for its new GL Class. The highly reinforced specialty polyamide replaces an aluminum component used for the previous GL and delivers required improvements in weight reduction, thermal insulation, and, notably, acoustics.
Supporting the engine together with the engine mounts, the structure uses BASF’s Ultramid A3WG10CR that has been optimized for high mechanical loads. Joma-Polytec designed the injection mold and produces the support.
Stefan Milimonka, a Key Account Manager with BASF Engineering Plastics Europe, said the material had to meet demanding safety and mechanical requirements, including low tendency to creep when subjected to continuous loads in the confined area of the engine compartment: “And depending on the conditions in the engine compartment, the plastic engine support must also withstand high bending moments.”
Engine supports are subject to the continuous load of the engine’s weight but also have to absorb the engine’s torque.
Milimonka underlined the significance of plastic’s contribution to reducing noise and to creating a more acceptable in-cabin sound: “The good acoustic characteristics are the primary benefit of the Ultramid support. Thanks to the damping behavior specific to plastic, the new engine support contributes to a more balanced sound. An additional benefit is that the heat conduction of the plastic is considerably less than that of aluminum.”
As a result, the new support provides better protection from the engine’s heat for the natural rubber engine mounts; this provides lengthened service life. Weight saving for the use of plastic instead of aluminum is put at 30% by BASF.
A design and development challenge for the use of plastic was to meet the combination of very serious head-on offset crash safety criteria as well as “repair crash” events, the latter specifying that the support has to remain undamaged. But for the energy-absorbing offset crash, it has to fail quickly and in a specific manner to obviate the risk of the engine being forced into the passenger cabin.
Said Milimonka: “In addition to checking these requirements in crash tests, BASF incorporated them into the very early development phase of the complex-shaped support, through use of its Ultrasim simulation tool.”
The values of the aluminum part that it was replacing had to be reached; ultimate loads, strength values under dynamic pulsed loads, and crash loads each met requirements during a rigorous test program.
“Therefore, it was possible to incorporate ribbing both to withstand the high loads and to satisfy acoustic requirements early in the development process, so reducing the number of required prototypes,” added Milimonka.