There's not a lot of glamour in trailer axles and
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suspension units, but the right choices can boost efficiency, and thus profits. Sharon Clancy reports on running gear innovations...
Competition in the trailer axle and suspension market is hotting up. BPW, SAF and S MB have all increased production capacity. Discos Trailer Systems. the Da itrilerChrysler axle and suspension division, is ambitiously aiming for leadership of the disc-braked trailer axle market by 2005 with a sales target of 3o,000 units.
Some of those sales will have to be made at the expense of its competitors. Long-life warranties, better axle-corrosion protection, low or no-maintenance products and lighter weights are all key factors in the bid to win sales.
Meanwhile, the truck axle conversion business is thriving. Tax breaks for three-axle tractors at 41 tonnes have boosted demand for higher powered 4x25, while late model, lightly Bearing life on trailer axles has increased considerably over the past few years. Mentor was the first axle manufacturer to introduce cartridge-style bearings two years ago on LMC axles; now Discos is to start offering axles with cartridge hubs. Twinned taper-roller bearings run inside inner and outer races that keep both bearings precisely located in a sealed cartridge. There is no end-float adjustment and a spindle end nut prevents overloading of the bearings.
The 1 MC hub costs around f5oo more than a standard LM axle, but whole-life costs should be lower as the axle needs no maintenance for the life of the warranty: one million kilometres, or seven years. tised hub, popularised by SAF and now adopted by Granning Lynx, is similar, but in this design the hub and bearing cassette are a single unit that cannot be removed under normal workshop conditions.
IMS, the UK importer for SAF, says that while this may seem expensive, operators should balance the cost against a million maintenancefree kilometres. Grartning already plans to offer serviceexchange hubs for its Timken Un i pac cassette bearings.
German axle manufacturer BPW disagrees with this philosophy. One of the features or its Eco axles has been the use of widely available D1N-standard tapered roller bearings, and this practice extends to the new Eco Plus axles, which are sold with a
five-year unlimited-distance warranty. Axles can be fixed or steered and drum or disc braked. Eco Plus
axles feature larger bearings, a new multi-seal dirtprotection arrangement and a spindle nut that incorporates a torque limiter—the 41k, torque limiter nut
slips as soon as the preset
torque is achieved, preventing overloading of the bearings. Bearing play for either disc or drum brakes is always set at the optimum clearance. The nut is reusable, so the hub can. still be removed for servicing.
BPW and Mentor are both adamant that trailer axles and suspensions should be designed specifically for their role. The bearings in a towed vehicle, they point out, are subject to significantly greater lateral forces than a truck during turning manoeuvres. On a triaxle trailer the trailer pivots around its middle axle, dragging the fixed front and rear tyres sideways. Because truck axles steer, they do not suffer the same stresses.
Discos, whose axle is the same as that used on the Actros front steer axle, points Out that the axle was designed from the outset for both truck and trailer fitment, and there is plenty of spare capacity to handle the extra load on the bearings. Whereas trailer axles tend to have an 8-9-tonne rating, on a typical Discos axle it is to tonnes.
There does, however, seem to have been a rethink on discbrake policy at both Discos and SAF. The two manufacturers
have long
argued that large (22.5in) disc brakes on offset 22.5in wheels deliver better braking performance and run cooler, and that offset rims provide better protection for the caliper. However, both firms are now introducing smaller (19.5in) brakes for fitment on 22.5in as well as 19.5in wheels.
The need to cut weight appears to have influenced this change of heart. An SAF Intradisc Plus axle with 19.5in brakes, for example, is quoted as 425kg, saving 135kg. On Discos ' the saving is about 38kg per axle.
To help it reach its sales target, Discos is offering operators more choice.
There is now
a zero-offset hub and a choice of Haldex, Perrot or Wabco disc brakes as well as the standard Knorr Bremse brake. Gigant remains cautious about longevity claims for disc brakes but nonetheless continues to explore new applications for this technology. For rigids and centre-axle draw .L1 bars it has intro' duced a disc braked 17.5in wheel on a Protec.5 tonne axle. Gigant says that because the axle capacity is lower than on trailers, the issue of srnaller
rotors overheating is not a factor.
SMB (Societe Mechanique Bernon), the axle manufacturer in the General Trailers group, is taking the low-maintenance rather than no-maintenance approach. Its latest hub is sold with a three-year, 500,000krn warranty: the bearing pack is now retained with circlips to simplify maintenance; and the hub has a new seal.
Meanwhile, technical improvements are still being made to drum brakes.
Hendrickson Europe. for example. has developed a 335x15ornm drum brake for low-weight/high-volume drawbar applications. It's suitable for 17.5in or 19.5in wheels and there is more distance between the wheel and drum so there is less risk of the glazing that can be a problem where axles are lightly laden.
SM B has developed a newgeneration 1.1 drum brake which is said to save 20kg per axle. It says that narrower drums, a two-piece brake spider, and less metal in the hub face are responsible for most of the
weight-saving.