Steel and automotive carbon dioxide reduction – challenges facing the metal

Materials World magazine
,
1 Jul 2008

The European automobile industry is facing legislation to achieve significant reductions in CO2 levels for new vehicles by 2012. What does this mean for steel, which is used in the construction of 99% of the world’s passenger cars? Professor Jon King of Corus Automotive Engineering, Coventry, UK, explains.

In 1998, the EU and car manufacturers agreed to work together to lower CO2 emissions from the average level of 197g CO2/km to 140g by 2008 – and to reduce this even further to 120g by 2012. By the end of 2006, emissions had reached 160g, but it was apparent that the 2008 target would not be met, even though manufacturers had developed more environmentally friendly technologies and vehicles. Failure to hit the target is due to government leadership and consumer choice.

European governments have, until recently, been slow to spread awareness of the need to conserve energy and resources, introduce (unpopular) fiscal incentives and improve education on efficient driving techniques. European consumers are affluent and desire well-specified, high performance, luxurious and safe vehicles.

Legislation so far

Since early 2007, the EU has been working to develop legislation that will force faster change on the industry. It is proposing a 20% reduction in the emissions target (from the 2006 achieved level of 160g CO2/km), to 130g by 2012, together with a package of other measures (low rolling resistance tyres, introduction of five per cent use of biofuels and mobile air conditioning unit legislation) to gain another 10g – in effect meeting the original 2012 target of 120g. However, the manufacturing industry claims that the targets are impossible to meet in the proposed timeframe and that the EU is putting a disproportionate emphasis on technology. It could therefore be the end of 2008 before the legislation proposal is determined.

The new laws recognise that all cars are not the same and is framed around the average emissions across each carmaker’s model range, seeking an overall European total of 130g. To achieve this, the EU has proposed a ‘limit value curve’ to the average vehicle meaning that lighter (smaller) vehicles need to exceed the target of 130g, but allowing heavier (larger) vehicles to emit more CO2. A sliding scale of tax penalties provides a fiscal incentive for those whose fleet average is worse than the curve to improve.

Makers of smaller, more fuel-efficient vehicles, such as Fiat, have branded this as unfair. The image above right illustrates the current VW Group position as an example, and how their ‘BlueMotion’ products will help the company move towards compliance.

The sting in the tail of the current proposal – and of particular relevance to material suppliers – is that the curve is parallel to CO2 improvement derived from weight reduction, giving no fiscal incentive to reduce weight. The King Review (published in October 2007) makes specific mention of this, referring to the need to monitor trends in average vehicle mass to ‘ensure the legislation does not provide manufacturers with perverse incentives to increase vehicle weight’. In practice, this means weight reduction efforts in vehicle development must focus on cost-effectiveness.

Industry response

In the meantime, the industry is introducing significant new technologies to offer lower CO2 products. Most carmakers have launched medium-sized family cars (Focus/Astra/Golf/Megane) that are just under the 120g mark, and smaller cars that are just over the 100g mark (Mini). These are competing effectively with hybrids like the Toyota Prius. But BMW has taken the limelight in the executive league with its ‘Efficient Dynamics’ technologies, adding new micro-hybrid technology (stop-start) to the 3 Series. Together with other low cost features it has created a 126g product – 20% better than most of its competition – while offering more power and better acceleration.

There are three fundamental ways to improve economy and emissions. In order of effectiveness, these are to – improve powertrain efficiency, reduce weight and increase aerodynamic efficiency. Using currently available technologies, the most cost-effective combination of these will provide 20% improvement over 2006 levels and cost around €1,000 per vehicle. Beyond these levels, costs rise significantly.

The role of steel 

Specialist steels have a major role to play in powertrain efficiency. Ultra-clean engineering steels that can be machined at close tolerances are facilitating higher-pressure fuel injection systems (working at 2,000 Bar and above), which are vital for greater combustion efficiency. More consistent, improved quality forging steels are contributing to design-optimised crankshafts, and new materials for connecting-rods are enabling smaller, more weight-efficient powertrains with higher specific outputs. Cleaner drawing quality wire rod products are supporting tyre cord developments for reduced rolling resistance, and gear steel developments will focus on materials for lightweight seven and eight speed transmissions. The focus of property development will be on better machineability, fatigue and wear resistance. But perhaps the greatest opportunity is in body structures, closures and chassis systems applications.

Last year, around 99% of all cars built had steel-intensive body structures. Steel is the acknowledged benchmark material for these structures, because it is well understood by design and manufacturing engineers, is the world’s most recycled engineering material and produces strong, stiff, safe, relatively lightweight and cost-effective vehicles. ‘Relatively lightweight’, however, will not be good enough in the future – the challenge for steel materials and applications technologists is to retain and enhance all of the other attributes of steel, and find ways to achieve a more radical weight reduction in the end product.

The use of advanced high strength steels (AHSS) has provided cost-effective lightweighting on vehicles over the last 10 years or so, making them up to 60kg lighter, despite significant changes to strengthen and stiffen their structures to enhance handling and crash safety. Further weight savings due to AHSS are being realised, which can equate to savings of over one tonne of CO2 during the vehicle’s lifespan.

A more intelligent use of materials science in product specification and design gives the biggest weight savings overall. ‘Forming to’ technologies (F2X) are an example. Advanced high strength steelsexhibit high strain rate sensitivity, which makes them more resistant to deformation in the vehicle crash structure, improving crash energy management. Using AHSS can allow a five per cent additional mass reduction in crash structure areas by using thinner gauge, higher strength steels. Corus has developed a suite of F2X technologies to improve design optimisation using AHSS, by using ‘as formed’ (instead of just off-coil) material properties inside crash, fatigue and strength computer aided engineering models.

Another example is design optimisation tools. Corus has developed a smart weld optimiser by combining different analysis routines into an integrated sequence of activities. Recently deployed for the first time, the company has proposed a spot-weld count reduction of 50% on a front engine subframe, providing significant cost savings. Value analysis and engineering methodology is being used to identify viable cost and weight reduction ideas while retaining or improving performance of vehicle structures. By collaborating with its customers in the supply chain, Corus has been able to propose significant cost/weight reduction solutions for many years.

To make reduced vehicle emissions a practical reality, legislators, materials suppliers, technology developers, tier suppliers and carmakers all have a part to play. They have a responsibility to be excellent rather than average, and must collaborate even more closely to produce competitive and more environmentally friendly automotive products. Steel materials and applications technologies are well positioned to play an influential role.

BlueMotion

BlueMotion uses technology to improve the standard engine/vehicle. Currently, VW focus in three areas:

Aerodynamics – On the Polo, Golf and Passat, VW has lowered the suspension, redesigned the spoilers and performed additional enhancements underneath each car so the air is better channelled, reducing air stream resistance to improve fuel consumption.
Transmission – On the Polo, Golf and Passat, the last two gear ratios are longer than
standard turbocharged direct injections.
Engine remapping – Remapping the engine and diesel particulate filters has lowered fuel consumption and NOx levels.

Further information:

Corus Automotive

King Review