Clamped, not screwed: The BPW cast trailing arm axle has set standards

When the development team at BPW Bergische Achsen was given the task of designing new running gear around 15 years ago, it had to meet numerous requirements: “We had to make technical optimisations, achieve weight and maintenance benefits for customers and, in particular, significantly reduce the previously-existing range of trailing arm and spring running gear variants,” explains Thomas Borlinghaus. A long-standing BPW employee, he was the responsible project manager and is named as one of the inventors on the patent specification for the cast trailing arm axle.

The development team literally started with a blank sheet of paper: they developed completely new ideas and put alternative materials through their paces in tests. When switching to cast running gear components, we also had to consider how this would affect manufacturing processes and assembly lines. “We carried out a comprehensive technical study between 2008 and the end of 2009, on the basis of which the management then made the fundamental decision in favour of the cast trailing arm running gear,” continues Borlinghaus. The implementation phase commenced at the start of 2010, where the team worked intensively with customers to test the prototypes until the cast trailing arm axle finally went into series production in spring 2012.

We succeeded in optimising the trailing arm range, as summarised by the project manager: “New development allowed us to use a modular system with significantly fewer components and variants to produce all of the desired assemblies according to customer requirements. Less variety of parts and simplified handling led to sustainable benefits, including assembly and warehousing on the part of our customers.” The decision to use the patented, two-part cast trailing arm, which is clamped directly onto the vehicle axle with diagonal bolting, was crucial in this respect: it saves on components, such as the spacers of the “spring pads” and “axle plate”, and thus considerably reduces weight. “Maintenance-free integration therefore reduces operating expenses,” explains Borlinghaus.

Another important feature of the invention is the steel-rubber bush that connects the rigid cast-iron system to the chassis in such a way that it can be moved, but at the same time remains directionally stable and resilient to lateral swaying of the vehicle. “As part of the same development project, we also designed and implemented a new axle lift to protect the tyres when the payload is low,” explains Borlinghaus. “Here, a considerable advantage is that the axle lift with its air cylinder is particularly easy to install by simply attaching it to its mounting bracket and using a hole pattern to adjust it.”

The creativity and work that the development team has put into the design of the cast trailing arm has all been worthwhile, concludes the project manager: “It makes me quite proud to realise, after more than a decade, that the development team’s ideas have proven themselves in practice over such a long period of time and that the running gear meets the requirements placed on it.” There is a direct line of descent from the original invention, based on a square axle beam, to today’s running gear generations with round axles. After all, the current BPW ECO Air running gear generation continues to employ the principle of directly clamped integration without additional clamping components – more than 15 years after the developers had conceived of this brilliant idea.