Consultancy looks to aggressive weight reduction in major powertrain components for CO2 savings; metal and polymer matrix composites

11 December 2014

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. 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 favors modern hybrid materials such as metal and polymer matrix composites (MMCs and PMCs) over conventional carbon composite solutions.

Continual pressure on the automotive industry to reduce carbon emissions is leading to weight reduction initiatives throughout the vehicle. Currently, several of the heaviest individual components in the powertrain, such as the main casings for the transmission, are still metal (e.g., aluminum alloys, magnesium alloys and iron) castings despite the widespread use of lighter materials elsewhere on the vehicle.

<!——>

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. 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 suggests the next breakthrough in CO₂ emissions reduction will come from more aggressive weight reduction in major powertrain components. Click to enlarge.

DSD 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.

In the automotive industry, MMCs have been used commercially in fibre reinforced pistons and aluminium crank cases with strengthened cylinder surfaces as well as particle-strengthened brake disks. These innovative materials open up unlimited possibilities for modern material science and development. The characteristics of MMCs can be designed into the material, custom-made, dependent on the application. This material group becomes interesting for use as constructional and functional materials, if the property profile of conventional materials either does not reach the increased standards of specific demands, or is the solution of the problem.

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.

If a manufacturer is seeking a component weight reduction whilst minimizing the effect on the supply chain, then it would appear that the adoption of MMCs in some form is the best solution. By redesigning components to accommodate the preformed composite inserts where stresses are high, casing wall thicknesses can be reduced in those areas where stresses are low and the number of casing ribs required can also be minimised. This could result in an estimated overall component weight reduction in the order of 10-15%.
Alternatively, if the manufacturer is looking for maximum reduction in component weight, then the use of a polymer based material is considered to give the biggest gains. To assess which method is most appropriate, a component specific feasibility study would be required.

Both the solutions outlined by DSD avoid the labor 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. It would require the development of new automation techniques to achieve cost-effective cycle times.

DSD presented a paper on ultra-lightweight transmission casings during the FISITA World Automotive Congress at Maastricht in June. That paper, entitled “Composite Transmission Casing for Volume Production” showed the potential of different composite materials to achieve significant weight savings in volume transmission applications.

DSD presented two technical papers at the 13^th annual CTI Symposium in Berlin this week. The first, entitled “Lubrication Efficiency”, describes how a new approach to transmission design can provide dramatic efficiency improvements. The second, entitled “Design Methods for Hybrid Disconnect Clutches” explores the unique challenges faced by clutches in parallel hybrid applications and how these may be overcome.

Resources

• Ian Westall (2014) “Composite Transmission Casing For Volume Production” (FISITA 2014, F2014-TMH-057)