Merc S-class gets world’s first rear axle transmission crossbeam made of plastic

The world’s first plastic transmission crossbeam in the rear axle subframe has been developed by ContiTech Vibration Control and BASF for the Mercedes-Benz S-class.

It is made from the engineering plastic Ultramid A3WG10 CR, a specialty polyamide from BASF which is particularly reinforced and optimised to withstand high mechanical loads. Compared to the previous beam made from die-cast aluminum, this highly durable component offers a weight saving of 25%, better acoustics as well as excellent mechanical properties even at high temperatures and conforms to the latest crash requirements. BASF says the design expertise of its simulation tool Ultrasim also made a major contribution to these properties.

The plastic load-bearing structural component meets all the requirements for the static and dynamic loads which act on a transmission beam: As a central component of the rear axle it supports part of the torque which is transferred from the engine to the transmission, and bears a constant share of the load of the differential. This is why, says BASF, the Ultramid crossbeam is used in all the vehicle designs from Mercedes-Benz with all-wheel drive, with the exception of the AMG cars.

In order to replace the aluminum in this demanding, crash-relevant application, the plastic has to meet high mechanical requirements: The plastic Ultramid A3WG10 CR (CR = crash-resistant), which is 50% glass fibre reinforced, shows optimum strength and rigidity and displays a low tendency to creep under constant loading. In addition, the material has to withstand high bending torques. The component shows good NVH performance (NVH= noise, vibration, harshness).

“The new rear axle transmission crossbeam is a milestone in the use of polyamides in the chassis. It has the potential to set a new trend in the automotive industry,” says Kai Fruehauf, head of the ContiTech Vibration Control business unit. “In order to replace metal with high-performance plastics, it is necessary to make optimum use of the material and adapt it to the particular load situations, as BASF has demonstrated in the development of Ultramid for the transmission crossbeam.”

BASF used its Ultrasim simulation tool in the early phase of development of the new crossbeam in order to determine the size of the component, optimise the component geometry and predict how the component would behave in injection molding and in operation: The simulation of ultimate loads, strengths under dynamic loading and crash safety reflected the real component behavior very well. ContiTech Vibration Control used Ultrasim’s Integrative Simulation to model the entire manufacturing chain. Thus it was possible to define the component geometry at an early stage and reduce the number of prototypes.