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CHARGE OF THE LIGHT BRIGADE

11th November 2004
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Developments in axles and suspensions suggest a more high-tech future for trailers. Sharon Clancy caught up with the latest trends at the IAA show.

Less weight equals more payload.That inescapable fact ensures that trimming kilograms off their designs remains a goal for axle and suspension manufacturers. More surprisingly,perhaps.are reports that as reliability increases, electronic controls on trailers are shifting from the exotic to the mainstream, driven by the manufacturers themselves as well as operator demand.

Early doubts about the reliability of integrated axle-suspensions proved unfounded and now a second generation is einerging. DaimlerChrysler, whose Discos axle pioneered the concept, has come up with the Durable Compact Axle.

Unlike Discos, which was developed in collaboration with suspension specialist Hendrickson, the DCA is pure DaimierChrysler. The one-piece fabricated beans axle incorporates the trailing arms to improve stability and roll stiffness.The brakes are Daimlerairysler discs from the Actros range with Knorr Brernse actuators. Daimler Chrysler prefers offset hubs.even on trailer axles. "It delivers more brake area and thus improved wear characteristics than centrenave hubs," says Richard Flackett, MD of DaimlerChrysler's UK trailer axle operation. "Frame centres can be wider, which helps improve stability on tankers and tippers. and for trailer builders it is easier to fit a 22.5in brake."

The DCA is available with centre-nave and offset hubs and a 19.5in brake because, as Flackett admits, some operators prefer it: "Trailer rental companies, for example, already have a lot a centre-nave axles and want to avoid any servicing issues by mixing the two types" Compatico is Renault's answer to the DCA range. It goes into production in 2005 and was developed with ArvinMeritor which, of course, also supplies the French manufacturer's truck axles. The trailer axle has the same wheel end as the truck axle and, as with the DCA range, the advantages to operators are said to include identical parts on tractor and trailer axles and the increased capability of truck dealers to service trailer axles.

Euro angle

Compatico is aimed primarily at those European countries where Renault has a dominant market share, including France. Spain and Portugal.The UK market appeal is still unclear. Tom Ilughes,ArvinMeritor's European trailer engineering director, says sharing axle components keeps costs down and is indicative of ArvinMeritor's design philosophy: "The key questions are how are operators going to benefit and will they pay for it."

He cites the latest pivot-eye tracking as one example of this: "It means there are no problems with axle alignment in trailer manufacturing, which in turn saves tyre wear."

SAF remains the only axle manufacturer confident enough to offer a guarantee against disc cracking on its lntradisc Plus Integral nine-tonne air suspension The company has always believed that the bigger the rotor the better in terms of brake wear: its Integral axle sports a two-piece Wabco PAN brake disc with an adaptor ring that allows the disc to expand radially as it gets hotter.

It's guaranteed for 500,000km or three years with 22.5in discs, and 350,000km or two years with 19.5in discs.The warranty covers continuous cracks—defined as those that rim from the outer circumference of the disk brake through to its inner edge. Networks of cracks, or those running toward the centre of the hub for a short distance, do not count.Trailers must have EBS to qualify and they must be registered with SAF's UK agent, [MS.

Even wear

SAF has extended its Integral concept to its latest self-steer axle, which is designed for nine-tonne applications with a new stub-end and knuckle that saves 45kg. It also features elastic tie rod ends and reinforced thrust washers which contribute to a revised steering angle geometry, ensuring both wheels turn around the centre line to make wear more even.

Most self-steer axles need regular greasing but BPW has developed one with encapsulated pivot bushes.The five-year warranty available on straight axles has been extended to cover the self-steer model.

At Hendrickson trailer axles have taken a back seat.in Europe at least, while the company expands its medium-duty drive axle and mid-lift axle range for truck manufacturers. New MD Andrew Jackson says the European trailer axle market remains overcrowded: "We have had discussions with several potential partners. However, we won't re-enter the market simply to participate in a price war."

Not so niche

Giant may become less of a niche player now it has acquired General Trailers' SMB axle division.TheFB70 has a nine-tonne capacity with ride heights from 240-410mm, a 70mm trailing arm and a simplified axle attachment. This features a single front bracket and bellows, and two types of springs and shock absorbers. Quoted weight is 400kg per axle, excluding the brake actuator.

BPW has expanded the applications for its Airlight Direct suspension, originally developed to prevent airbag damage on intermoclal operations. The design saves 28kg per axle and is said to offer an improved ride. The air bags are located directly over the axle beam and are fastened directly to the frame • rather than the trailing arms.

As a result the vertical axle load is channelled through the air bags into the frame; the hanger brackets only have to cope with the residual stabilisation forces.The vertical forces on the axle are lower than in conventional systems, reducing the stress on the cargo and improving driver comfort.

The air bag is integrated into the axle connection so there is a minimal height increase. It is currently available on 380inm disc-braked axles with a 120mm offset, but early next year Airlight Direct, a 430mm brake centre-nave and a drum-braked model, will be added.

Hughes admits that European operators have been wary about ArvinMeritor's Litellex composite trailer leaf spring, but he adds: "Liteflex has a clear payload advantage, weighing 10.45kg compared to 29.55kg fora comparable steel spring. If steel prices continue to rise it may soon have a price advantage too and requires no major design changes to accommodate it." • The next generation of disc brakes will start appearing on new trailers from 2005, and disc brake manufacturers are confident that they will resolve a lot of operator concerns over premature wear and failures.

The market remains split between 19.5in and 22.5in wheel sizes but John Hibbert, CV technical sales manager for Ferodo, says there is a distinct shift towards 22.5in brakes as lighter brake components become available.

SAF plans to start fitting Wabcds second-generation single-tappet PAN disc brakes next summer. There is a new brake caliper with an offset pad, which eliminates the brake carrier on one side. This saves 4kg in weight and is said to improve the pressure distribution on the pad. Wabco explains that this gives improved resistance to cracking while reducing radial and tangential wear. Other features include a spread plate to protect the tappet from high thermal stress.

Haldex has launched a lighter version of its 22.5in DB22LT brake, which weighs just 34,8kg including pads. Like other brakes in the ModulX range, it can befitted on nearside or offside wheels.

Haldex, Knorr Bremse and Wabco are all vying for sales in the booming market for trailer electronic control systems, *Third-generation disc brakes will feature including EBS, a fixed caliper EBS has proven benefits for trailer manufacturers. Volumes are high enough to keep costs low; and EBS is quicker to fit and set up than conventional ABS which is why some, like Schmitz, are fitting it as standard.

Having an electronic control unit on the trailer opens up other possibilities for brake manufacturers. These extend from integrated electronic suspension control and brake pad-wear indicators to rollstability, advanced diagnostics and even telematics capability. And for operators, devices such as Knorr Bremse's Trailer Information Module (TIM) save workshop time by simplifying fault-finding.

The latest version of Haldex's EB+ system allows for independent load sensing on the front and rear axles not currently possible.

You won't see third-generation brakes until 2007 at the earliest, but common to them all is a shift from sliding calipers to fixed calipers. The sliding-caliper design helps maintain the correct clearance between discs and pads, but in third-generation brakes, this will be achieved by 'mechatronics' a combination of electrical and mechanical actuation Cynical operators might say this sounds like a recipe for in-service trouble, but the manufacturers stress that this need not be the case. "The advantages outweigh any disadvantages," says Roger Thorpe, BPW's customer service manager. "Fixed calipers are more reliable because there are no moving parts. Good performance is less dependent on good maintenance and wear is improved because the correct clearance between the disc and the pad is maintained at all times."

Having put its all-electric Eco Dlstronic hub into hibernation, BPVV is likely to be the first axle manufacturer to fit Knorr Bremse's thirdgeneration brake, the S3G. The caliper has one-sided actuation. While actuation is still pneumatically controlled the gap between the caliper and disc is now controlled by two electric motors, one each side of the disc. The electronic motor control system is also included in the brake housing and can communicate with the vehicle electronics.

The adjusting system in the S3G compensates for thermal expansion of the pads and disc the air gap can be kept small which improves response times.

Haldex's next-generation design features a fixed caliper and two sliding discs, although the company is also developing an all-electric brake. The two-discs design gives a larger friction surface, says Haldex, so less clamping force is needed for the same performance.

Drums are not obsolete, however: there are still applications for which they represent the best technical solution; especially 17.5in wheels. "Small wheels mean a small space for discs and often more than one disc per wheel is required," says Hibbert.

ArvinMeritor's latest drum brake applications feature improved cam head bearings, better tolerances on anchor pins and cam rollers, and 20% thicker brake linings.


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