STERLING HEIGHTS, MI – Lotus Engineering’s lightweight-vehicle concept has passed another hurdle – virtual crash-testing, with the next likely step construction of a rolling chassis, as the engineering consultant looks to prove a 38% reduction in mass is both technically and commercially feasible.
Virtual testing of the body-in-white shows the design meets or exceeds federal standards in all front-, side- and rear-impact tests, plus roof-crush testing, officials tell WardsAuto in outlining study results at the firm’s U.S. operations here.
Lotus first developed its lightweight concept as part of research funded by the International Council on Clean Transportation and undertaken with the California Air Resources Board, U.S. Environmental Protection Agency and National Highway Traffic Safety Admin.
It features strategic use of advanced materials and bonding techniques and clever design ideas that eliminate more than half the components of a conventional competitive model. Fuel economy can improve 6%-8% for every 10% of weight reduction, Lotus officials say, so the 38% lower mass could equate to a 24% gain or more in gas mileage.
Details on the first phase of the project, which models a 2020 multi-passenger vehicle based on specifications of a current Toyota Venza, were released in a March 2010 report that pegged potential weight savings at 1,097 lbs. (497.8 kg), not including the powertrain, and put the manufacturing cost-penalty at just 3% above the estimated tab for the Venza.
Results of this second phase to determine whether the design potentially could meet crash-protection standards just now are being made public in a 450-page report meant to convince an often skeptical industry that big fuel-efficiency gains are possible without seriously adding to the cost of a vehicle, if new design methods are employed.
“What we’re saying here is if you approach the design of the vehicle in a holistic manner at the system level, a lot of those fuel-efficiency gains and emissions reductions (needed to meet upcoming U.S. regulations) are absolutely achievable at no extra cost,” says Lotus Engineering CEO Darren Somerset. “And that’s a very powerful message for us.”
The Lotus concept vehicle body-in-white weighs 531 lbs. (241 kg), compared with the Venza’s 844 lbs. (383 kg). Three-quarters of the structure is made from aluminum, with 12% consisting of magnesium (mostly in the front section), 8% high-strength steel (key load-bearing components) and 5% composite materials (primarily floor sections). That compares with 100% steel (49% high-strength steel) for the production Venza.
The concept is envisioned as a parallel hybrid, ultimately to be powered by a 1.0L 3-cyl. turbocharged direct-injected gasoline engine, with output approaching 160 hp. The baseline production Venza is offered with a standard 181-hp 2.7L 4-cyl. engine or optional 268-hp 3.5L V-6 in the U.S.
Lotus began the body design around bending and torsion bogeys, rather than crash loads, allowing it to make the structure as light as possible, then reinforce where needed to deliver desired crash-test scores.
“It’s a philosophical difference from some OEMs in terms of optimizing the weight of the vehicle,” says Gregory E. Peterson, senior technical specialist.
The Lotus body consists of less than 170 parts, compared with more than 260 for the Venza, and is held together with structural adhesive bonding, friction spot welding and a variety of rivets and fasteners, much of the technology already in use, officials says.
Foam inserts in some structural parts, such as the B-pillars, help reduce the amount of steel needed, cutting weight and cost, Peterson says.
The floor consists of polyethylene terephthalate (PET), the same type of plastic used in water bottles, borrowing a concept from a company Lotus stumbled upon that makes scaffolding from glass-fiber-reinforced recycled plastic.
“We wanted to be as green as we could with this vehicle, so we looked at recycled materials,” Peterson says, noting the material is safer in a hybrid application because it won’t conduct electricity into the passenger compartment in the event of a collision.
Use of adhesive bonding helped reduce required welding and the number of fasteners. A typical SUV has about 5,000 resistance-spot welds, Peterson says, while the Lotus design uses less than half that.
The virtual body’s torsional stiffness is said to exceed the benchmark target, a BMW X5, by 20%. “And you could argue, it doesn’t have to be that stiff,” Peterson says.
In the virtual front-impact test conducted, intrusion by the upper dashboard into the passenger compartment is limited to 0.8 ins. (2.0 cm) and footwell intrusions held to less than 0.4 ins. (1.0 cm). Front wheels of the concept do not impact the A-pillar.
“This is a solid performance,” Peterson says, pointing out that the vehicle’s crash pulse is conventional enough to allow standard airbags and sensors to be employed.
In side-impact pole testing, the worst-case intrusion at the vehicle’s door is 6.3 ins. (16.0 cm), a full 5.5 ins. (14.0 cm) away from the outer edge of the driver’s seat, a “performance that is equivalent or better than most vehicles that are out there today,” he says.
In a roof-crush simulation, the Lotus design withstood six times its curb weight, bettering the performance of the current Venza, which already exceeds federal standards and even tougher bogeys set by the Insurance Institute for Highway Safety.
“That says we probably over-engineered it, but we like the performance of this,” Peterson notes.
In virtual 50-mph (80-km/h) rear-impact offset crash tests, there is no evidence of intrusion into the fuel tank or battery pack, and the strains placed on the plastic fuel tank are under 10%.
Lotus says the crash-simulation tools it used are the same as employed by the industry worldwide. Even if applying a 10% margin of error, the concept data falls well within industry crash standards, Peterson says.
Many of the proposed manufacturing processes, material uses and design philosophies already are a reality today, Peterson says, pointing to the vehicle’s magnesium front structure, which is similar to that of a production Ford Flex.
“Although we targeted 2020, a lot of this is already in production. There’s nothing here that says you can’t start doing this tomorrow.”
Further weight could be cut by using advanced noise cancellation systems to quiet interiors, rather than sound-absorbing mastic, a trend Lotus says could emerge by 2020.
“We have evidence from some programs we have in-house that we can save 20 kg (44 lbs.) of mastic using an active noise-cancellation system,” Peterson says. “High-end cars will get it first, of course, but we see it certainly for 2020 as a pretty big player in mass reduction.”
The next logical step is to produce a rolling chassis, which would allow developers to optimize the suspension design to further cut weight and cost, Somerset says, followed by a physical prototype to prove out the entire design.
“Ultimately, it would be good to produce a vehicle with the four major mass systems in a physical model,” he says. “We’re already talking to a number of potential collaborators, suppliers that would potentially build a vehicle of this kind and governmental institutions to try and find the funding to build it.
“There’s no substitute for a physical model,” Somerset adds. “But we have a high degree of confidence in the analysis work.”
In the meantime, Lotus Engineering is working to perfect its development software, which it ultimately envisions licensing to auto makers. The next phase calls for folding in cost-analysis algorithms, allowing developers to not only sort out the best materials and designs but determine which solutions are the most cost effective.
