Intelligent design enables Meritor’s MT150 detachable and liftable rear tandem axle to feature smaller gears that contribute to reduced weight and improved acceleration. (Meritor)
Meritor pursues lightweighting strategies for drivelines
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As with passenger vehicles, reducing the weight of systems and components in commercial vehicles is a key strategy to improve fuel efficiency. In the commercial-vehicle sector, the extra incentive to slim down is to increase cargo- or passenger-carrying capacity—a significant driver because it directly impacts a fleet’s bottom line.
Downsizing, or what some refer to as “rightsizing,” is an important aspect to achieving weight-loss goals. This is increasingly seen with vehicles running smaller-displacement engines packed with the performance of larger powerplants. This strategy extends to areas throughout a vehicle, including the driveline.
“We’ve been able to take weight out and downsize our gearing in every iteration of axle products, so there’s intelligence just in the way we design our products to begin with, even outside of changing the material,” John Bennett, VP & Chief Technology Officer at Meritor, told Truck & Off-Highway Engineering at the IAA Commercial Vehicles trade show. “In many cases, it’s more cost-effective. We can offer that at the same, if not even lower cost, to our OEMs.”
Balancing weight reduction with cost is a trade-off engineers often face, especially when considering lightweight materials for new applications. This issue sometimes can be avoided via “smart” design, achieving a smaller package and reduced weight at cost parity—even if the weight loss is more incremental than extraordinary.
Take, for example, Meritor’s approach that Bennett described: “Every time we’ve launched a new product that’s replaced a previous generation, the gearsets have been smaller. So we’re increasing what we call the torque density of our products—the same torque-carrying capability in a smaller size and a lighter weight. We’re doing that with more intelligent designs of the gear teeth, better or different materials—better gear steels, for example—better optimization of the castings.”
In his discussion at IAA of axle technology contributing to efficiency gains in commercial vehicles, Chris Villavarayan, Senior VP and President of Global Truck at Meritor, referred to the company’s new detachable tandem axle as “revolutionary,” providing the traction of a 6x4 with the efficiency of a 6x2. By disengaging the forward tandem, turning losses are reduced, resulting in almost a 2.5% fuel efficiency savings, he said.
“What we can also do is provide a blended ratio—a different ratio on the forward vs. the rear,” Villavarayan explained. “By doing this, we can downsize the ratios on the back, therefore reducing the gear size, reducing weight and providing more acceleration. So it’s not only an efficiency story, it’s also a weight-reduction story.”
Exploring carbon fiber
Meritor has developed a proof-of-concept composite driveline made from carbon fibers in a polymer matrix.
“Carbon fiber works great for weight reduction, but it also works great for strength,” Villavarayan said, claiming a potential 100-lb (45-kg) weight reduction over a full drivetrain.
“We can go from three drivelines to two. We can go from two drivelines, in some cases, to one,” he explained. “And by taking out all the complexity of slip yokes, bearings, crosses, center bearings, what we have done is driven complexity reduction that essentially drives a best-in-class vibration performance. Not only do we provide efficiency from a weight perspective, but we can also provide a better balance.”
The composite driveline is ready for field trials, according to Bennett, but he doesn’t have an answer on the cost—other than to say it’s “much more expensive; you’re paying for the weight reduction, obviously.”
Understanding the long-term durability of carbon fiber in such an application, given the demanding environments commercial vehicles can encounter, is another concern. But Bennett and his team currently are performing testing in this regard, and believe this challenge is manageable.
“The real hurdle is not as much technical, it’s cost,” he said flat-out. “It’s a significant premium that most fleets will not be willing to pay, but we’ll see. Some extremely weight-sensitive fleets will do it. The cost-per-pound-saved I know is very high.”
Even so, Meritor’s R&D team is exploring other areas to employ the material. Bennett told TOHE that they’re looking at composites for gearbox housings—“that’s very early R&D,” he said—and in some individual brake components that are traditionally metal, but “not necessarily the structural components,” he noted.
“We are looking for opportunities [for composite materials]. With a lot of the structural components it’s more challenging. That’s why you don’t see more of them and the weight reduction is more focused on aluminum than anything else,” Bennett said.
Lighter for electrification
With the accelerated move to hybrid and electric drives in a variety of trucking applications, lightweighting becomes even more important. It’s an effective strategy to offset the additional weight of batteries and other components while improving the performance and efficiency of such vehicles.
“What will make this market switch [to electric solutions]?” posed Villavarayan. “Cost and weight.”
Meritor had its eCarrier on display at the IAA show. The eCarrier is a simple and flexible design, according to Villavarayan, “with a small two-speed gearbox that enables us to shrink down a motor and fit into a traditional axle. By doing this, we essentially create an axle that almost fits in the same space of a traditional axle. We don’t have to re-engineer your truck in most cases.”
The downsized gearbox and motor help to address the weight aspect. “Integrating this solution with the massive scale that we have in our axle portfolio, can you imagine what that does in cost? And then what we’ve done in weight. Both of these we believe is what will get us to market,” he said.
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