Ricardo led the concept generation through to the manufacture and testing of the ultra-lightweight rear drive unit. The unit is based around a lightweight differential mounted within a compact, single-piece skeletal casing with tough, low-density lightweight plastic covers.
The form of the skeletal design originated from finite element-based simulation and topology optimisation. Using this data-driven template, the skeletal design could then be developed in CAD, based on a single integrated aluminium die-cast structure, with closures and fluid seals formed by the lightweight plastic cover assemblies.
Using a systems approach to lightweighting, Ricardo eliminated internal parts and simplified those remaining, while maintaining comparable performance or improving upon the baseline design. The conventional differential carrier has been eliminated with the crownwheel supported in a double-row angular contact bearing, and differential gears supported directly within the crown wheel. A hollow pinion shaft was designed and manufactured, delivering a mass saving of 1kg for this component alone. The overall 8.5kg (24%) mass saving of the complete unit was achieved approximately equally between the gears and shafts, and the casing system.
The TRL-5 prototypes of the rear drive unit manufactured by the project have been evaluated under tests including high torque, lubrication tilt, efficiency, durability and in-vehicle ride and NVH. Through these evaluations, the prototype unit demonstrated its functionality with comparable performance to the current production unit.
Ricardo’s systems approach to lightweighting was also demonstrated with the design of a 6-speed manual transmission casing. In this instance, a weight saving of 1.9kg (16%) was achieved in comparison with the baseline.
“ULTRAN set very ambitious goals by defining as its baseline vehicle a product that in many respects represents the current state of the art in terms of driveline mass reduction,” said Ulf Herlin, head of the Ricardo Driveline and Transmission Systems Product Group. “By applying the methodologies demonstrated in the ULTRAN project, we have shown that significant further mass reductions – with consequent improvements in vehicle efficiency and CO2 savings – are possible at comparable cost and performance to existing production, based on market-ready materials, processes and design technologies.”
ULTRAN lightweight transmission casing designed by Ricardo
