THE 4P LINK
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ZF is developing the 4P four-link rear suspension for medium and heavy trucks. The bottom of the drive axle is connected to the chassis by a pair of conventional trailing arms which can incorporate steel or air suspension.
The top of the drive axle Is located at two points on either side of the diff housing, connected to two points on the chassis by an X-shaped member This is a precision-made steel forging (mounted at each corner on compliant bushes) which twists as it pivots, acting as an antiroll bar as well as a suspension link— rather like the semi-independent trailing-arm suspension fitted to some small cars.
The new design will be suitable for 4x2 and 6x4 on-road applications with axle loads of 11.5 tonnes or more; its first production appearance is likely to be on a MAN. It will be shown at Frankfurt an a concept chassis.
The system has the advantages of lower weight (about 20kg per axle, according to 71) with fewer components, better ground clearance and easier assembly (and replacement) than a conventional setup. The X-member can be a standardised component, its roll characteristics "tuned" by varying the compliance of the bushes.
The system has just been patented; while the design looks simple it requires sophisticated computer-aided design to make it work properly, and the forging has to withstand considerable stress—ZF is working on a cheaper, cast version.