ST RING TO LIMITS
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When news broke of the longer artic limit, it looked like a useful move. But, as usual, there's a catch: the 16.5m rigs, now due to arrive next month, will have to meet strict turning-circle radii. Thank goodness for self-steering axles... .
• One problem with the 16.5m artic limit is the inability of a 3+2 or 3+3 artic rig of that length to meet the EC's strict turning limits of 5.3m inner and 12.5 outer radii. Initially there were too few tractor units available that would allow the swing clearance needed at 16.5m, and with the deeper pins (up to 1.6m or 2.04m to the outer corners) load distribution with 2+ 3s is too close to the limits for comfort.
Some chassis manufacturers now offer the longer wheelbases necessary, while converters such as Chassis Developments, Southworth Engineering and Vehicle Systems Engineering are busy adding their lifting/trailing axles to spread the load better.
Some trailer manufacturers believe that until the EC relaxes its ruling on turning circles, the use of self-steering axles provides a fairly cost-effective solution, despite their initial extra cost and dead weight. They will also help reduce tyre wear by minimising the increased scrub normally associated with longer outfits. Whatever the outcome, axle makers have a vested interest in the situation and are keen to keep their products bang up to date with as wide a choice of options as is necessary.
BPW
BPW is about to offer a self-tracking axle that is some 90kg lighter than its previous designs. To ensure tyre clearance its spring base is cranked inwards, thus aligning the hanger brackets with the others.
With its distinctive square-sectioned beam and offset trailing arms, the axle has a load-dependent stabiliser that returns the wheels to the straight ahead after cornering. The beam ends have angular split pressure bearings beneath them that allow it to lift when cornering, and with the trailer weight acting downward forces the two sections of the bearing to interlock on straightening.
BPW claims substantial savings in tyre life for the front and rear of a tri-axled system; the new axles are expected to become available in the UK later this year.
The company reduced its axle ratings last year, from 10 to 9.45 tonnes, but without any appreciable loss of strength. It has shaved 40mm off its 120mm square high-tensile steel axle tube, bringing its weight to 325 kg.
SAF
SAF has supplied self-tracking and forcesteer axles throughout Europe for several years. Its self-tracker relies on the simple castoring principle, offsetting the axle spindle to the rear of the tracking knuckle pivot points.
As the vehicle turns the wheels follow the pivot point, to its total turning angle of 400 if necessary. Air-operated damping acting on each knuckle maintains positive control at a system pressure relative to the load condition, and a heavy duty damper on the one-piece tracking bar prevents flutter. Steering pin housings are Teflon coated.
A remote locking device is controlled from the cab to keep the wheels straight when reversing.
For the UK, SAF's RLSM 9042 is rated at 9.0 tonnes and weighs 512kg. Using smaller (419x152mm) brakes in lieu of 420x180mm models saves 15kg on the axle. Its cost, of £1,500 to £1,750, can be recouped quickly via fewer tyre changes, says SAF.
SAF's forced-steer axle has a total steer angle of 80°, needs no lock-up for reversing, and bogie axles can be made to steer if required.
An axle-related project with Voith resulted in the SVR hydrodynamic braking system for two and three-axled trailers which debuted at Frankfurt. It includes a shaft-driven Voith GR116 retarder with a hydrodynamic brake and cooling system set between the rearmost axles, and is integrated with SAF's standard air suspension.
The SVR operates via a truck-mounted retarder or the exhaust brake.
RO-R
RO-R offers a range of self-steer units rated between seven and 10 tonnes.
They have positive air control and hydraulic damping, and can be used with single or twin tyres. All feature Rockwell Stopmaster brakes.
Like other axle manufacturers, RO-R has concentrated on losing dead weight; its most recent TE9000 series axles, with 180mm-wide brakes and outboard drums, weigh around 300kg.
RO-R's Flexair II suspension with its redesigned support springing has a 375450mm ride height and unusual bag profile to allow direct attachment to the frame. Its integral cross-member gives the trailer frame the extra stiffness to carry offset loads. Like all RO-R products, it carries a two-year warranty.
YORK TEC
With the emerging interest in selftrackers, York Trailers TEC group has developed what it believes is the lightest on the market.
Using a 160mm offset wheel and hub, there is a choice of 2,000/2,050mm track with corresponding air spring centres. Spring bases are inset for clearance, and with no need to crank or narrow the chassis rails, York considers its installation to be an easy one too.
The TEC axle, rated at 10.5 tonnes, has its track rod in front of the axle on inward tapering steering arms; twin dampers are designed to prevent flutter. Positive air locking is by the centrallymounted spring brake chamber, giving 600kg of effort on withdrawal and 950kg on lock engagement.
Designed and tested to survive 35 tonnes of immediate loading, TEC's selftracker uses nitrided alloy steel king pins and allu-bronze main pivot bearings.
The new design — patents have been applied for — includes an anti-lock braking facility. York's TEC XL axles are for trailers using low profile tyres. Their 335x210mm S-cam brakes are claimed to be the most powerful for 17.5 and 19.5in rims and the axles are rated at 13.25 tonnes, in accordance with EC annex 7 ruling. Its LM range of general-purpose axles have the same load rating, but with 420mm-diameter brakes. Kevlar nonasbestos linings are standard.
CRANE FRUEHAUF
Not all UK manufacturers are rushing to offer self-tracking axles.
Crane Fruehauf, for example, has access to Fruehauf designs through its European group, but, although more and more operators are looking at full-length tri-axled semis on air, it does not sense any significant interest in self-trackers.
C-F is likely to mark time until the situation clears, especially after the knocks it suffered over last year's innovative convertible 12-13.6m trailer design, and workforce reductions.
With its 127mm square-section beam, C-F's 11-tonne axle has a 1.82m track for twin tyres and 2.03m for singles, weighing 319 and 330kg respectively. Heavy duty S-cam brakes of 419x178mm have sturdier spiders and camshafts.
With their in-built sensors for antilock, slotted rings are eliminated, thus speeding up repair times. Crane Fruehauf fits its own axles to around 40% of its trailer output, according to customer preference: F-Series mechanical and Tair suspension with its single-height control valve goes on to 99% of its production. Lifting axles are optional.
GRANNING
Several companies produce primary and auxiliary air suspensions and axles for OE and refurbishment use.
Granning, for example, offers its ST suspension syustem with or without air lift for axles between 8.0 and 10.17 tonnes. They allow ride heights of between 165 and 432mm, while weights range from 192 and 288kg per axle system (lift kits add 27kg).
Single-leaf spring beams are mounted outboard for maximum roll stiffness with air springs, and their internal bumper pads are offset to clear the tyre.
Granning's lighter T-series is a roll-free design for add-on purposes with a cast torque arm welded to the axle. Air springs are set between frame and axle, assisted by outboard shock absorbers. There is no effect on the trailer's dynamics, so its positioning on the frame is not critical, Granning's Stemfast division produces three-piece beam axles for trailers with 15-24in wheels. Track widths of 1,820, 1,880 and 2.045mm are available with its 100 Series, which can be integrated with the ST17/18 suspension within a steel channel frame and ready for mounting.
DANA SPICER
Dana Spicer lists self-steering trailer axles in its catalogue, and should there be a sufficient surge of interest will no doubt conjure them up.
In world terms, DS is still one of the largest powertrain manufacturers, but having sensed a slackening of the UK trailer market it is placing its sales emphasis on drivelines.
GIGANT
Gigant Suspensions UK of Market Harborough, which supplies companies such as King Trailers and Trailmaster, also distributes Hosta (BV) systems for forced-steering multi-axled trailers.
Shown at the TCS&D exhibition last November on a GRP Massey 13.5m triaxled chassis, it demonstrated yet another solution to the current turningcircle dilemma. Seen with its SAF 10tonne axles and lifting front, the trailer chassis had jig-built I-beams on 1.2m centres, reduced to 800mm over the rear to permit a 25° steer angle.
Hosta's dual-circuit powered system is hydraulically controlled from the fifth wheel with the steering head set in the 125mm-deep trailer neck moving the Ackermann linkage on the axle.
Being positively steered, the 480kg device not only resists lateral forces, but enhances directional control.
GKN TAIDCHURCH
The renowned Tadchurch rubber suspension system is well suited to most artic trailer bogies.
Using rubber bolsters in torsion, its walking beam arrangement allows articulation between the axles and gives well balanced load equalisation. It can be supplied for axle spreads of 1,372 and 1,524mm.
Like other suspension builders, the company is also looking at other composite systems, including air.
That the industry has been manoeuvred into even considering such a complicated option, however, speaks volumes for the way that the transport infrastructure has been neglected.
Stir the high interest rates into the industry mixture and it is easy to see why there were no tanners (2.5p to you, sonny) in the hauliers' Christmas pud this year. At best, the industry must continue to press EC for concessions on turningcircle requirements, but if the best turns out to be the worst, then one way out of the dilemma will be to use a self-tracker, so take your pick. . .
El Bryan Jarvis