The strength of a lightweight

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You can be forgiven if you automatically assume that bigger and heavier equates to stronger and tougher. It’s drilled into us from the time we’re children, when we first see the comic strip with a bully kicking sand into the face of a 98-lb. weakling. For that matter, could you imagine the same kid playing the role of enforcer on the Toronto Maple Leafs?

But the makers of driveline components continue to prove that they can shave evermore weight from their products without sacrificing durability – even in the face of ever-rising torque forces from modern engine designs. (At least one engine manufacturer is experimenting with 2,250 lb-ft of torque in Australia.)

There’s an obvious need to continue to focus on the weight of such components, says Eric Samuelson, program manager for Eaton’s Lightning transmission series. “There’s a direct correlation in added payload, and that’s a one-to-one return.” There is also the potential to improve fuel economy.

“Lighter weight does not necessarily mean less strength … the way we look at a design is we’re looking for what is the greatest opportunity to reduce weight, but we’re not necessarily looking at the exact design configuration as it exists,” he says. “The general approach is to really understand what the customer is looking for, and also what the customer can afford.”

By using a “clean sheet of paper”, manufacturers are combining components that were once multi-piece assemblies, and rejecting the use of traditional materials in favor of such things as aluminum to save weight.

Some of that comes with the more extensive use of computers in the engineering process. Thinner walls can be considered if a model shows it will still hold. Different gear designs and profiles can be examined, to know with certainty whether they’ll handle the twisting and hammering forces that are sent their way.

The technology allows for more experiments with complex shapes and loads that simply weren’t available before, says Eaton engineer Paul Peterson.

“Things we’ve done (to shed pounds) revolve around integrating components,” says Meritor’s Kurt Burmeister. Traditionally, conventional brakes and torque plates are added separately to the front axle, but with an integrated design, so there’s no need for the torque plate, and the brake can be mounted to the front axle.

“We integrally mount the brake to the knuckle,” he explains of Meritor’s approach. The resulting savings in weight: 86 lb.

Further parts are shed by integrating the tie rod arm into the knuckle.

Unitized hubs are also playing a significant role in shedding weight. Instead of inner and outer bearings, seals and hubs, the unitized designs come as one unit.

On the front axle, the hub is made out of bearing steel. “The human variability of assembly is taken out so the bearing lasts longer,” he says. And where traditional wheel ends are warrantied for 250,000 miles, the unitized versions are good for at least 750,000 miles.

At first glance, a unitized design might seem to have a higher maintenance cost. Instead of replacing a single component, you’re replacing an entire unit.

“If you have to replace it (under warranty), the fleet doesn’t pay anyway.” And while any conventional hubs would have to be replaced for a million-mile tractor, fewer than five per cent of unitized designs would have to be swapped.

In the near future, clutches integrated into transmissions – thanks to the push for automated transmissions – can also be expected, says Burmeister.

“They really operate as one piece anyway,” he says. And there are benefits beyond a longer clutch life.

“Basically, where you’ll see those reductions is if you take and build up the clutch in the transmission housing … you don’t have the two completely separate housings.”

With its Lightning series, Eaton was able to eliminate some of the iron-to-iron flange joints by combining varioius sections, Samuelson notes.

New materials are also playing a key role.

By switching to aluminum in housing components, Meritor’s Freedom Line was able to save much of its weight. Aluminum has also found its way into drive axles, shedding weight from the casting.

Some type of aluminum could also be used for a future main case enclosure, adds Samuelson.

Without a doubt, aluminum is attracting the most attention. While exotic materials such as carbon fibres might offer great weight savings, they often don’t see the light of day because of high prices, officials with both manufacturers say. It’s always a balance.

“I think there’s a trend evolving toward the integration of components and systems, says Burmeister. And by looking at the transmission, driveline and axle combinations as a single unit, vibrations are better handled, particularly since driveline angles play such a key role.

So too can savings be found by thinking beyond the driveline.

Meritor, for example, worked with Cummins in the development of drive axles since high-torque engines can affect the life of the ring, pinion and bearings within the axle. Since most of that damage occurred in lower gears, Cummins engines with SmartTorque capabilities are able to limit torque on start-up, allowing full torque at highway speeds.

Regardless of the approach, engineers continue that balancing act between weight and strength, to ensure they aren’t mutually exclusive. n

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