The 'first plastic engine support'.
Daimler is installing what has been claimed to be the world’s first plastic engine support for the six-cylinder diesel engine used in the new Mercedes GL Class. Compared to the previous aluminium support, the plastic part is said to offer improved acoustical properties, better thermal insulating characteristics and a definite weight advantage, while being able to withstand the same load. The part, which supports the engine with the aid of the engine mounts, is moulded from Ultramid A3WG10 CR, a highly reinforced specialty polyamide from BASF that has been optimised for high mechanical loads. Joma-Polytec in Bodelshausen designed the injection mould and produced the plastic engine support.
Engine supports are subject to a permanent load – the engine's weight – while also absorbing the entire engine torque.
To replace aluminum in this application, the plastic needed to fulfill demanding mechanical requirements. While Ultramid A3WG10 CR is very rigid, it was also necessary to demonstrate that it exhibited sufficiently low tendency to creep in the confined space of the engine compartment when subjected to a continuous load. Furthermore, depending on the installation conditions in the engine compartment, the plastic engine support must also withstand high bending moments. The good acoustic characteristics are the primary benefit of the Ultramid engine support over its aluminium counterpart. Thanks to the damping behaviour 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 aluminium. As a consequence, the Ultramid engine support provides better protection from the engine’s heat for the natural rubber engine mounts connected to it, increasing their service life. In the context of the CO2 discussion, a weight saving of over 30% for the plastic part versus the aluminium version is an achievable.
The multitude of tests that the plastic part needed to pass included the repair crash, which replicates smaller crashes, and the massive offset crash (offset head-on crash). In the first test, the support needed to remain undamaged; in the second test, it needed to fail quickly and in a specific manner to prevent the engine from entering the passenger compartment.
In addition to checking these requirements in crash tests, BASF incorporated both cases into the very early development phase of the complex-shaped engine support through use of its Ultrasim universal simulation tool and predicted the part’s behaviour: Ultimate (breaking) loads, strength values under dynamic pulsed loads and crash loads are reported to have matched up well with the test results and achieved the values required. It was then possible to incorporate ribbing to withstand the high loads and satisfy acoustic requirements early on and reduce the number of prototypes.