Research by UK consultancy says weight of vehicle transmissions could be reduced

New research by UK automotive engineering consultancy, Drive System Design (DSD), suggests the next breakthrough in CO₂ emissions reduction will come from more aggressive weight reduction in major powertrain components. Extensive analysis by the company has identified both near-term and medium-term solutions for the manufacture of items such as transmission casings using advanced composite materials, but favours modern hybrid materials over conventional carbon composite solutions.

Continual pressure on the automotive industry to reduce carbon emissions is leading to weight reduction initiatives throughout the vehicle, because lighter cars burn less fuel and emit less CO₂. Currently, several of the heaviest individual components in the powertrain, such as the main casings for the transmission, are still metal castings despite the widespread use of lighter materials elsewhere on the vehicle. The research by DSD may help to change this.

“Experience gained from composite applications for vehicle bodies on the one hand, and small powertrain components on the other, has not led to the kind of production-feasible light weight composites that can replace heavy, structural castings,” explained DSD’s managing director, Mark Findlay. “Our contribution has been to identify the preferred material options for these challenging applications, such as metal or polymer matrices, based on manufacturing costs and the required component properties.”

DSD, which works with vehicle manufacturers and Tier 1s around the world, engineering new technologies and solving problems that make their products more competitive, has identified that, in the short term, the solution requiring least disruption to existing automotive supply chains would be based on metal matrix composites (MMCs) which use filaments, whiskers or particles of high strength materials to enhance the properties of the base matrix. Such materials are already in commercial production and DSD believes that selective reinforcement of a conventional casting by the use of MMC inserts will enable the use of lighter ‘thin wall’ designs with additional strength provided only where necessary. The inserts fuse to the molten aluminium during the casting process, creating a fully integrated component.

A more ambitious solution is possible in the medium term, using polymer matrix composites (PMCs). Light weight polymers are already popular for non-structural covers, often incorporating metal inserts where fasteners generate local clamping forces. To handle the high structural loads found in transmission and axle casings, DSD proposes the inclusion of larger metal inserts into the mould, forming a metallic skeleton to achieve the required strength in specific areas. By injecting the polymer around the metallic inserts, a hybrid structure is created that could be significantly lighter than a traditional design, without incurring additional costs.

Both the solutions outlined by DSD avoid the labour intensive manufacturing processes associated with carbon composites, according to Findlay. “Though the time for resin application can be shortened through increasing injection pressure, we believe the time required for accurate lay-up of the laminated layers will confine carbon composite materials to niche vehicles in the medium term,” he said. “It would require the development of new automation techniques to achieve cost-effective cycle times.”

Effective implementation of these innovative construction methods is made easier by DSD’s ability to predict NVH behaviour, structural stiffness and system performance reliably, using a range of advanced software tools. “The new materials require a very different design approach to traditional castings,” said Findlay. “We have a clear understanding of the fundamental material characteristics and failure modes, backed by well established and proven analytical techniques.”