Working Within the System

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The lines between suspension components will become increasingly blurred as a “systems” approach to suspension design takes hold. “Vertical integration,” as it applies to the manufacture of vehicles as a whole, is now migrating to the suspension component level. The benefits to end-users include ride quality, safety and improved profitability, but integration is also laying the groundwork for the next generation of suspension developments, such as intelligent electronic suspension controls and work on new materials to further reduce weight.

“Increasingly it will be difficult to talk about the axle versus the suspension versus the brake. It’s all one system, one undercarriage that is the axle, the brake, the slider, the suspension, the higher inflation system, the anti-lock brake system,” says Bob Zirlin, director of product planning and development trailer systems North America, ArvinMeritor.

Like the development of air ride 15 years ago, a systems approach to suspension design has changed the paradigm. The first baby steps towards integration started in heavy duty truck and tractor steer axles with integrated wheel hubs, eliminating misadjusted bearings and seal damage. The next step was axle-and-suspension combinations that first appeared on semitrailers, followed by wider integration.

“We make a distinction between what we call modules and systems. Modules are when you take existing components and optimize them to work together. Whereas with a system, you’re starting with a clean sheet of paper and you have performance objectives in mind. The reason for that is to achieve superior ride and handling,” Zirlin says.

Integrated suspension design has a lot to recommend it. Ride quality and handling improvements on the truck side can directly translate into better safety and comfort, which plays into driver retention. On the trailer side, a smoother ride can mean less cargo damage. In vocational truck applications such as cement, fire and aluminum bodied tanker trucks it can mean less wear and tear on the truck and trailer bodies and the expensive equipment that piggyback on these units. Smoother riding trucks also reduce road damage, which is to everyone’s advantage.

But original equipment manufacturers also stand to benefit from a systems approach. Ken Griswold, product manager trailer suspension systems for the Holland Group says, “The OEMs are going to systems integration in order to standardize their production lines.” He adds, “Eighty per cent of the van market is still designed by about six OEMs, but the specialty trailer market in North America has over 200 manufacturers. It’s a very fragmented, regional business with a lot of mom-and-pop shops. So what does an integrated system do for them? You don’t have to engineer the axle into the suspension because it’s all done for you, which saves a lot of time.” Price, quality advantages and extended warranties can also factor in as high volume integrated suspension factories use robotic welding equipment and other state-of-the-art automation that smaller shops may not be able to afford.

From a fleet perspective, suspension integration helps in resolving warranty issues: “For example, the interface between the axle and suspension is a critical component that drives a lot of the integration. People don’t want to call up the suspension supplier and then call the axle supplier if they have a problem or a warranty issue. They want one person to resolve it,” Griswold says.

A systems engineering approach also provides more opportunity for innovation. Hendrickson International, which has been credited with creating the first integrated suspension, is now turning its attention to packaging front steer axle suspensions for Class 8 trucks. Front suspensions have traditionally been leaf spring over an I-beam axle. Hendrickson’s AirTek suspension incorporates a front air spring and a box section steer axle. “Our system is up to 138 pounds lighter and offers reduced maintenance requirements. It also has a higher role stiffness so it is more stable than traditional systems, which improves tire wear. The axle is more stiff so it doesn’t deflect as much during operation,” says Steve Kiefer, director of marketing and program management of Hendrickson International truck suspension systems division.

The pace of suspension advances is speeding up as competing design engineers learn from one another, making one company’s advantage only temporary at best. The Holland Group, for example, has taken the tire wear issue to the next level and announced its Swing-Align suspension system for trailers, which reduces the time it takes to make an axle alignment. With the typical trailer spanning 53 feet, curbs have a way of snapping things out of alignment. “So if it is easier to align, you can end up saving money. We have the only alignment in the industry that doesn’t require the disassembly of the pivot,” Griswold says.

Raydan Manufacturing of Edmonton, on the other hand, has modernized Hendrickson’s 80-year-old walking beam suspension by adding an air spring. As a result, its Air Link walking beam for front twin steer trucks has not only made major inroads into the US vocational truck market, it has also landed the company the Northern Alberta Transportation Club’s 2004 Award of Achievement. “What Air Link does is give you the articulation you need for off-highway application. The air springs give you the air ride smoothness. The walking beam basically cuts your bump in half. It has very high roll stability – in fact, the highest of any air ride suspension. It’s more like a rigid suspension. It was built to go off-road. Other air ride suspensions were never meant to be off -highway suspensions,” says Rick Nissen, sales and marketing manager at Raydan.

Nissen says the Air Link is now the standard suspension on all the major crane manufacturers in North America and nine out of 10 major fire truck manufacturers. It is 450 lbs. lighter than a spring suspension and allows vocational trucks to travel at highway speeds without fear for their expensive equipment.

Despite a Raydan patent on its walking beam/air bag combination, the competition isn’t far behind. Hendrickson has just launched its own patented walking beam air suspension called AR-2. “In many ways it’s similar to what Raydan has done, however this is a patented Hendrickson system, fully compatible with our walking beam suspension,” Kiefer says.

If it seems that the decade-long trend towards air suspension is alive and well, that is because it is. “Air suspension gives excellent ride quality, as compared to spring or rubber block, especially over a wide range of loads. By varying the pressure within the air spring you can accommodate various loads without adversely affecting the ride quality. In addition, the suspension mounting height (axle to chassis frame dimension) stays constant at various loads and does not vary, as would a leaf spring version. The improved ride quality often results in less cargo damage, vehicle structure damage and improved operator comfort,” says Bruce Barton, director of engineering, Ridewell Corp.

But some applications, such as in hostile environments, do not lend themselves to air suspension. A refuse truck, for example, may back into objects that could puncture the air spring. Still, Barton notes that even here air springs are making headway. Building tougher air bags is one step. But an integrated, application specific approach to suspension design allows engineers to locate the air springs out of harm’s way.

For Barton, though, integration of product components primarily represents an opportunity for weight and cost optimization: “Weight is a major factor in trailer purchase decisions. Our industry is under constant pressure to reduce weight in suspensions and to maximize payload. Over the lifespan of a trailer, the revenues in additional payload can be very significant. An added benefit of reducing suspension unsprung weight is that it will also improve ride quality.”

In the quest to shed suspension pounds, Ridewell is also employing higher strength low carbon alloys – low carbon so it can readily be welded. At ArvinMeritor, materials are also under scrutiny. “We got together with LiteFlex, which used to be a part of Delphi, about a year ago. Delphi composite springs are in Corvettes, for example. On the commercial vehicle side, the performance benefits of using composites go beyond just the reduction in weight. There’s the ability to utilize and manage sprung versus unsprung weight. Now with our integration approach, composite materials truly bring some benefits that weren’t there in the past,” says Nelson Goncalves, director of business development and product management for commercial vehicle suspensions.

Integrated suspensions should also be safer, which stands to reason if there are gains in road handling. But the potential for more consistent quality in the manufacture of fully integrated bogeys should also help in this area. For Kiefer the biggest contribution to ensuring the safe operation of the truck is “that the customer gets the right product for their applications.”

Integrated suspensions also make it easier to incorporate the next generation of electronics. Apart from tire inflation, anti-lock brakes and the other electronic and pneumatic offerings that are currently tied into suspensions, “smart technologies” are still in the early stages according to most suspension engineers. But the fact that engineers are now taking a wider view of the truck and trailer undercarriage opens the door to incorporating electronic controls as they become available.

So it appears there are very few sour notes in the march towards suspension integration. One concern may be the costs of repairing an integrated suspension system. But the suggestion that it might become cheaper to replace a whole system rather than repair it is dismissed by Goncalves: “The integration process has us look at component replacement within that system. A large consideration in the process is life expectancy. It all comes down to the value proposition that we can deliver to the manufacturers and to the end users.”

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