Implementing AHSS in Vehicle Structures…and Improving Tomorrow’s Carbon Footprint

a balance of cost and lightweightingOne of the biggest hurdles facing automakers in making electrified vehicles a high volume reality is the cost of the battery. The lighter the vehicle, the less energy required to mobilize, and the smaller the battery needed. Consequently, development emphasis is on small size vehicle classes, where the battery size and ultimate vehicle cost are “manageable.”  As a result, the value of mass reduction has become even more critical since it is a major means to reduce the battery size, and therefore its cost. In order to make the real jump to zero emission vehicles, they have to be affordable. But will lightweighting come at another environmental cost?

When it comes to vehicle emissions with traditional powertrains, the tailpipe is in the spotlight because 80 percent of a vehicle’s life cycle pollutants are attributed to its use phase, or when the vehicle is being driven. Remove the tailpipe from the equation, or change the powertrain to electric or plug-in hybrid, and the emissions from material and vehicle production become significantly more important.

GHG emissions materials comparison of a typical example vehicle component

GHG emissions materials comparison of a typical example vehicle component. Steel produces 7 to 20 times less emissions than other materials.

Low density materials, such as aluminium, magnesium and composites, are currently being used in luxury class vehicles, where their costs are more easily absorbed into the high sales price. These same materials are now finding their way into electrified vehicles aimed at mass production to reach lightweighting goals. Their high costs can be somewhat justified balanced against reductions in battery size and costs. However, they create another significant emissions issue, as the production of these materials is GHG-intensive, and therefore costly to the environment. These alternative materials produce 7 to 20 times more emissions than steel.

Looking at these low-density materials, this means that reductions in use-phase emissions accomplished by the electric vehicle, are negatively offset by higher emissions in the materials production phase of the vehicle life cycle. The use of aluminium, magnesium and composites has two major impacts: their CO2e in absolute quantities is higher then steel, and they front load the environment with harmful greenhouse gases that immediately begin destroying the environment.

Can lightweighting be done another way? Yes, and automakers are doing it using the attributes of the latest generation of Advanced High-Strength Steel and steel technologies. There are fleets of vehicles in the market place today, and more soon to arrive, that are already achieving great success in reducing body structure weight in traditional internal combustion engine (ICE) vehicles. These vehicles are often gaining fuel and emissions efficiencies due to their weight reduction tactics, and the benefits of AHSS are making it into OEM marketing messages. Here are just two examples, but you can find many more examples on the Steel Muscle in New Vehicles page of our website:

The 2016 Chevrolet Malibu is nearly 300 pounds lighter and has wheelbase that’s been stretched nearly 4 inches, making it more fuel efficient, more functional and more agile.

The 2016 Chevrolet Malibu is nearly 300 pounds lighter and has wheelbase that’s been stretched nearly 4 inches, making it more fuel efficient, more functional and more agile.

2016 Chevy Malibu

GM’s Chevrolet introduced an all-new 2016 Malibu – a completely restyled midsize sedan engineered to offer more efficiency, connectivity and advanced safety features. Its wheelbase has been stretched close to four inches (101 mm). Greater use of high-strength steels enabled engineers to design the body structure with thinner components in some areas, delivering comparable crash performance with lower weight. The body structure accounts for more than one-third of the Malibu’s nearly 300-pound weight reduction. A hybrid powertrain, which leverages technology from the Chevrolet Volt, offers an estimated combined fuel economy rating exceeding 45 mpg. The Malibu’s standard 1.5L turbo powertrain is projected to offer 37 mpg highway.

82 lbs lighter, better fuel economy, 25% improvement in torsional rigidity

82 lbs lighter, better fuel economy, 25% improvement in torsional rigidity

2016 Nissan Maxima

The foundation for the new Maxima’s enhanced handling and ride comfort starts with a redesigned platform that features increased use of high strength steels, including the first use of 1.2GPa high strength steel in a Nissan sedan. This allows the 2016 Maxima to not only boast a 25 percent improvement in torsional rigidity, but also contributes to an 82-pound weight reduction (versus the previous generation).

Transparent view of the FutureSteelVehicle Battery Electric Vehicle

FutureSteelVehicle’s BEV body structure weighs in at just 177kg, a result of 95% High-Strength Steel usage.

FutureSteelVehicle 177kg AHSS BEV Body Structure Concept

Many of today’s vehicles are using steel mass reduction technologies similar to these examples to improve performance and reduce the vehicle carbon footprint. As automakers continue to flex High-Strength and Advanced High-Strength Steel muscles in their high-volume vehicles, the steel industry continues to reinvent itself with steel grades that will enable new efficiencies in vehicle applications. FutureSteelVehicle (FSV), a WorldAutoSteel program with global steel manufacturer participation, demonstrates the use of Gigapascal (>1000 MPa) Advanced High-Strength Steels to achieve optimised body structures for battery electric, plug-in hybrid and fuel cell vehicles.

FSV is the first study in the world to date that is applying Life Cycle Assessment (LCA) methodology all along the entire design and development process. This insures that the materials’ environmental consequences are thoroughly analyzed and final solutions are mass-, cost- and emissions-efficient. Through LCA, vehicle engineering can satisfy the quest for a total and integrated future picture.

The result is a very light (177 kg) steel body structure for an electric powertrain vehicle and up to 70% decrease in greenhouse gas emissions, depending on the electric grid where it is driven. Though the program concentrated on electrified vehicles, the lightweight design concepts are equally applicable to conventional powertrains as well.

Solution or Problem Shift?

The work being done today to reduce weight for fuel efficiency is sowing the seeds for more affordable advanced powertrain vehicles in the future by developing these technologies for high- volume production applications. How that mass reduction is being done will determine whether we truly reduce vehicle carbon footprint or whether we create a new problem with highly increased manufacturing phase emissions and high-cost vehicle structures. The material choices made today will be the deciding factor.

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