Driving a sustainable world - vehicle emissions, footprint and fuel economy

Materials World magazine
1 Aug 2013

The US Corporate Average Fuel Economy regulations are challenging North American car manufacturers to reduce fuel consumption, vehicle weight, and emissions like never before. Ronald Krupitzer from the Steel Market Development Institute, USA, looks at how steel will fare in this new era.

In the USA, car manufacturers have never faced the challenge of improving fuel economy as rapidly as they do now. The US fleet, rich in large vehicles such as pickup trucks and sport utility vehicles (SUVs), was in a period of suspended animation for 25 years from 1985–2010, when fuel economy requirements were essentially frozen. However, since 2012, the revised Corporate Average Fuel Economy (CAFE) regulations have changed dramatically. The new format has eliminated the weight–class metric, in which car companies could achieve compliance simply by selling more smaller vehicles to offset the larger ones and, therefore, comply with the fleet average requirement for passenger cars or light trucks. The new regulations are based on vehicle footprint – the area defined by the contact points of the four tyres, meaning smaller vehicles now have higher fuel economy requirements. As such, selling more small cars is no longer a workable strategy and instead, manufacturers are being forced to make each platform more fuel-efficient every year.

The aggressive change in slope of the regulation (see graph below), from nearly flat since 1986 to one requiring an improvement of about 4% a year in 2012 in order for car manufacturers to comply, means that companies must now double their average mileper-gallon of fuel by 2025.

According to a study by the International Council for Clean Transportation, the new CAFE regulation puts the USA at a similar pace with the rest of the world in projected rate of improvement. The global automotive industry is united in its efforts to provide more fuel-efficient, sustainable and reduced-emissions vehicles for the future.

New technologies, new materials
The NHTSA and the EPA have issued reports detailing many of the technologies available to car companies that will make such dramatic fuel economy improvements. For example, in 2012, Ford Motor Company explained their approach in a published presentation to the National Academy of Science. This sustainability blueprint identified potential technical options through to 2030. While it is not claimed to be complete, the list does demonstrate the breadth of technical options at the disposal of car manufacturers today. Engine and transmission technologies are important, and other approaches such as electrification, aerodynamics and fuel technologies will also play a role. Weight reduction is another strategy considered critical by Ford, as well as most other car manufacturers. So, what materials will play central roles in providing lighter vehicles for the future?

The US steel industry is no stranger to materials competition. Since the 1980s, US car companies have been lightweighting, although to varying degrees. Most programmes, including the plastic-skinned Fiero sports car, Lumina minivan and Saturn car line, and various aluminium-intensive vehicles such as the Audi A2 and A8, and the Jaguar Range Rover, have not endured or have been relegated to small volumes. However, now all structural materials are contenders for lightweighting.

In the USA, one dominant trend for vehicle materials has been the significant increase in highstrength steels, particularly the newest grades, called advanced high-strength steels (AHSS). These are often more than four times stronger than traditional mild steel and have been termed the fastest growing material in modern vehicles today.

The rapid growth of AHSS can be attributed in part to work by the global UltraLight Steel Auto Body (ULSAB) and its advanced vehicle concepts projects – a series of engineering studies completed in 2002 that demonstrated the potential for lightweighting with AHSS. In these projects, 33 steel companies from around the world collaborated to determine if steel could be competitive against low-density alternatives. These new steels included dual-phase (DP) and transformation-induced-plasticity (TRIP) steels, both containing mixtures of hard and soft phases. Because of the exceptional forming properties of AHSS, higher strength parts could be manufactured and, therefore, body weight could be reduced by up to 25%. These results were achieved with no cost increases and without sacrificing safety or structural stiffness. Car companies began working with these AHSS concepts in the early 2000s, not only to reduce weight but also to address the ever-increasing improvements in crashworthiness required in the last 20 years.

Another way that US steel companies have addressed the potential problems in the use of much stronger steels early in the development cycle, and enabled their new products to be so rapidly accepted by car manufacturers, is by collaboration. One such collaborative group, the Auto/Steel Partnership (A/ SP), has been doing this since 1987 and continues to address the complications of manufacturing with AHSS by studying forming limits, springback, joining and tool wear. These factors need to be placed under control before new steel products can grow successfully in automotive manufacturing. Members of A/SP include Chrysler Group LLC, Ford, General Motors Company and the major automotive steel suppliers organised under the Steel Market Development Institute (SMDI). Since 2000, much of the A/SP research has been supported by project funding through the US DoE’s office of automotive technologies.

Steel, weight reduction and sustainability
While the introduction of AHSS during 2002–2012 has served the automotive industry well, helping to achieve vehicle crashworthiness improvements without significant structural weight gain, the challenge of substantially reducing vehicle weight remains.

Recent studies by Dr Blake Zuidema of ArcelorMittal USA LLC and the SMDI have made use of the published Volpe model, a tool used by NHTSA and EPA to assess the relative contributions of technologies towards successful achievement of the CAFE targets by the US vehicle fleet. Zuidema’s analysis takes into account the recent work of WorldAutoSteel in its FutureSteelVehicle project. Together with assumptions based on the achievement of technical goals ascribed to engine, transmission and other technologies to achieve fuel economy improvement, it determines whether or not a gap will exist by 2025 in the achievement of CAFE targets should AHSS be used as the primary source of weight reduction.

Will AHSS products give car companies the sufficient weight reduction needed to satisfy the fuel economy targets? Results of the Volpe analysis show that projected AHSS products available between now and 2025 will suffice for car manufacturers to make CAFE targets under reasonable technical scenarios.

Car companies clearly need to achieve the CAFE targets, but they need to do it affordably while maintaining other vehicle attributes such as crashworthiness, durability and performance, all of which have kept steel in the game in previous years. AHSS technologies make steel a strong contender to remain the dominant material in vehicles for many years to come.

What is CAFE?
CAFE regulations have been in force since 1975 and require vehicle manufacturers to comply with fuel economy standards set by the US Department of Transportation (DoT). CAFE values are determined using city and highway fuel economy test results along with the average vehicle sales figure. Fuel economy data are generated via laboratory tests using operating vehicles on a dynamometer, as part of a programme administered by the US Environmental Protection Agency (EPA). The National Highway Traffic and Safety Administration (NHTSA), part of DoT, is responsible for modifying the criteria and for assessing penalties based on the information supplied by the EPA. Failure to meet the standards incurs a penalty charge (currently US$5.50 per 0.1mpg under standard, multiplied by the manufacturer’s total production in the US market), in addition to a tax levy on individual passenger car models.  




Short term
Leverage existing technologies at high volume

✔ Significant number of vehicles with EcoBoost engines

✔ Stop-start systems (micro-hybrids) introduced

✔ Electric power steering – begin global migration

✔ Dual clutch and 6-speed transmissions replace 4 and 5 speeds

✔ Add hybrid applications

✔ Battery management systems – begin global migration

✔ Aero improvements

✔ Flex-fuel vehicles

✔ CNG/LPG prep engines available where select markets demand



Mid term 
Substantial weight reduction and expand electrification

• EcoBoost engines available in nearly all vehicles

• Engine displacement reduction aligned with weight-save

• Increased application of stop-start

✔ Electric power-steering – high volume

✔ 6-speed transmissions – high volume

• 8+ speed transmissions

• Weight reduction of 250–750lb

• Increased use of hybrid technologies

• Introduction of PHEV and BEV

• Additional aero improvemnts

• Diesel use as market demands

• Vehicle capability to fully leverage available renewable fuels



Long term
High-volume electrification and alternative energies

• Continue improving efficiency of internal combustion engines

• Volume expansion of hybrid and PHEV technologies

• Continued weight reduction actions via advanced materials

• Continued leverage of BEV

• Continue to develop fuel cells – implementation timing aligned with fuels and infrastructure

For further information, contact Ronald Krupitzer rkrupitzer@steel.org