Light Vehicles and How They Got That Way
The approach that is clearly being taken by engineers to create vehicles is to use the right materials in the right places. The time of a single dominant material is gone and unlikely ever to return.
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Honda Clarity Fuel Cell
When you’re making a hydrogen-powered vehicle, you want to make it as light as possible.
And consequently, it is a multi-material vehicle. For example, there is a lot of steel being used for the structure. They’re using 1,500-MPa hot-stamped steel in the frame and a high-formability 980-MPa steel, as well, with this being what is thought to be the first such application in the world. Those two alloys account for about 40 percent of the frame.
In addition to which, there are 780-, 590-, 440-, 270-MPa steels used for the structure.
All in, the weight of the structure is approximately 15 percent lighter than an Accord.
Aluminum is used, as well. The hood, fenders, doors and trunk lid, for example. The rear parcel shelf and the rear bulkhead. Even the front bumper beam and the door beams are made with a 7000-series aluminum alloy.
While on the subject of bumper beams, the rear bumper beam is a glass-fiber-reinforced plastic component, consisting of layered discontinuous and continuous glass fibers, which is also thought to be a world’s first.
Back to aluminum. There is a die-cast, hollow aluminum front subframe developed using know-how from Honda’s motorcycle manufacturing. This single-piece structure with closed sections and no welding flanges is 20 percent lighter versus conventionally produced components.
The rear subframe is a squeeze-cast aluminum structure that is engineered to handle the loads of the two hydrogen storage tanks (one 24 liters, the other 117 liters). It is 27 percent lighter than the subframe of the previous-generation Clarity.
And aluminum is used in the front and rear suspensions, as well. The front lower arm is forged aluminum is 30 percent lighter than a conventional stamped steel part. There is a hollow knuckle, 10 percent lighter and a solid version. All of the arms of the rear multi-link suspension are forged aluminum; on the previous Clarity they were all steel; this arrangement is 40 percent lighter. The tie rod is produced with what is said to be the “world’s first high-strength aluminum forging method”; it is 20 percent lighter than a conventional component.
BMW 5 Series
BMW has an approach called “EfficientLightweight.” Which, in the case of the new 5 Series, has resulted in a weight reduction of up to 137 pounds from the previous generation car.
This is a multi-material approach. That is, there is the use of high- and ultra-high strength steels for the roof, side members and rear. The trunk, trunk lid, engine cross member, rear side members, roof and doors are made with aluminum. There is a cast magnesium instrument panel support, which is 4 pounds lighter than the steel component used on the previous generation model.
And they’re even using kenaf fiber for the inner trunk lid lining, which provides a weight save of about 1 pound.
Hybrid: 2,996 pounds
Electric: 3,164 pounds
Twenty-six pounds. That’s how much weight is saved in the Ioniq Hybrid because the traditional 12-volt battery has been deleted. This is just one example of how the Hyundai engineers looked at a multiplicity of ways to reduce mass for the Ioniq, a vehicle that will be available as a conventional hybrid, a plug-in hybrid and as an electric vehicle. (The plug-in will be a 2018 model.)
While in the approximate area of the hood, it is worth noting that they’re using an aluminum hood, which, at 16.5 pounds, provides a 14.4-pound weight savings compared with steel.
They’re saving 13.5 pounds through the use of aluminum for the rear hatch (which weighs 16.5 pounds, as well).
There is aluminum used for the Ioniq suspension, as well. They calculate that through the use of things like aluminum control arms, the total weight save is approximately 22 pounds (13 pounds in the front and 9 in the rear).
But this being Hyundai—know that Hyundai Group runs a steel company—there is an extensive use of advanced high-strength steel: 54 percent of the body-in-white is made with these strong-but-light steels.
Because this is an advanced environmental platform that is all about efficiency—using EPA numbers, Hyundai points out that the “Cost to Drive” 25 miles is $0.81 for the Ioniq Electric, $0.92 for the Chevy Bolt and $0.97 for the Nissan Leaf; the cost for driving an Ioniq Hybrid Blue is $1.00, $1.04 for the Toyota Prius Eco and $1.46 for the Ford C-Max—on the interior there is the use of recycled plastic.
Not just regular recycled plastic, but polymers combined with powdered wood and volcanic stone filler materials, resulting in a weight save of 20 percent.
Alfa Romeo Giulia Quadrifoglio
First of all, know that this car is fast thanks to its 2.9-liter 505-hp, twin-turbo V6 that happens to be all-aluminum. But it is more than that. For one thing, while on the subject of aluminum, the material is used for the front and rear vehicle frames, front shock towers, brakes, suspension components, doors and fenders.
In addition to which, there is a significant deployment of carbon fiber materials. There is a carbon-fiber drive shaft, for example. As well as a hood, roof, rocker panel moldings, rear deck-lid spoiler and active aero front splitter.
There is a combined aluminum/composite rear cross member.
And they’ve even cut weight by using carbon-ceramic brake rotors instead of cast iron rotors. They’re said to be 50 percent lighter.
4,144.7 pounds (German spec vehicle)
In 1994 Audi launched the A8 with the “Audi Space Frame,” with was a structure that consisted of aluminum die castings and extrusions that were wrapped with aluminum. But times have changed and the company itself admits that it no longer has an “obsession with using a single material.” That material: aluminum.
So for the new A8, the body structure consists of four materials: aluminum, steel, magnesium and carbon fiber-reinforced polymer (CFRP).
The last-named is rather significant. There is a rear panel made with CFRP that is the largest component for the passenger cell (it is located behind the rear seat) that provides 33 percent to the torsional rigidity of the A8 (which, overall, is 24 percent more rigid than the previous vehicle, which was launched in 2010). The part is engineered with 50-mm wide tapes that are layered; depending on where they need strength, there are from six to 19 layers.
Hot-formed steel is used for the lower section of the front bulkhead, the side sills, the B-pillars and the front section of the hood. Analogous to the layering of the CFRP, the steel stampings are blanked so that there are varying gauges within a given component.
Magnesium is used to connect the front strut tower domes. It weighs 28 percent less than the brace used in the previous-generation A8.
Aluminum is used in a variety of forms: cast nodes, extrusions and sheets. There is more aluminum than any other material, at 58 percent of the body-in-white. They’re using a variety of aluminum alloys, including castings that have a tensile strength of more than 230 MPa and extrusions that are 280 and 320 MPa.
(It is worth noting that in order to put together this structure Audi, at its Neckarsulm plant, is using 14 different joining processes, such as laser welding, grip-punch riveting, roller hemming, adhesive bonding and more.)
The LC 500, which features a five-liter, 471-hp, all aluminum V8 and a 10-speed automatic transmission, can go from 0 to 60 mph in 4.4 seconds. It has a steel body and front and rear steel subframes. It has steel rear fenders. The inner panels of the doors and the trunk are made with carbon fiber reinforced plastic. There is an optional carbon-fiber roof, which is produced with a high-speed resin transfer molding process (raw carbon fiber material is inserted into a mold, the mold is clamped, and the resin is injected) that allows production volumes to be achieved, as well as a visible twill weave.
There is aluminum deployed, too, as for the hood, front fenders and doors.
In places where aluminum and steel have to come together—as in the front suspension towers—self-piercing rivets are used for assembly, which is said to provide an additional advantage of reducing weight.
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