Elasto-Kinematic and Structure Design of the Multi-Link Torsion Axle and Its Full-Vehicle Evaluation

In times of increasing electrification in all vehicle segments, one of the main challenges is to provide high driving range in combination with a smart battery pack design. Especially for A and B Vehicle-segments the torsion beam of the twist beam axle (TBA) is the main limiting factor regarding package space in the rear end.

Based on this problem, a new axle concept, the so called Multi Link Torsion Axle (MLTA), was developed as a part of a research project in collaboration with Ford, VW and other project partners. The basic idea is to reverse the installation direction of the TBA to create additional package for the battery. To compensate the kinematic drawbacks caused by reversed installation, namely anti-lift and wheel recession behavior, the twist beam structure was integrated in a longitudinally oriented Watt’s linkage. This new arrangement leads to a battery volume increase of up to 30%. At the same time, the longitudinal kinematic behavior can be varied nearly independently from the torsion beam position by modifying the Watt’s linkage hard points.

The basic kinematic concept and design process was presented at Chassis.Tech 2021. Based on this prior work, the elasto-kinematic design was carried out further. To achieve the elasto-kinematic performance close to a conventional TBA, the orientation and stiffness of the toe-correcting bushings were optimized using a method developed in this work. Furthermore, a new bushing for the Watt’s Linkage was developed in collaboration with Vorwerk-Autotec. Additionally, side-force springs developed by Mubea were implemented to further improve the lateral compliance and the steering response behavior.

Following the concept development, the CAD was conducted. The design process was mainly driven by structural stiffness and strength performance, evaluated with CAE Methods. Finally, the whole axle-module was manufactured and mounted by CP Auto to a modified Ford Fiesta body, which was done with a tubular frame work design. To rate the overall performance, handling, ride and KnC Test with the full-vehicle were performed by Ford and finally compared to the original and a mass modified Ford Fiesta.