ENGINEER'S
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NOTEBOOK
out" when negotiating rough ground. A single shock absorber on each side and an anti-roll bar characterise both Volvo and Scania FAS installations, which add 50 and 60kg respectively, to chassis tare weight.
The weight penalty comes largely from additional air reservoirs.
Chassis prices on Scania 93 and 113 drawbar models go up in list price by £2,100 when FAS is specified, or £2,380 for the higher 7.5-tonne axle plating. In left-hand-drive markets Volvo offers parallel-link FAS on the FL7 through to the F16. Last November Volvo introduced FAS in the UK as a £1,950 option on its 14-tonne FL6, primarily for demount applications The geometry is simpler and lighter than on Volvo's heavier chassis version, closely following the Mercedes design with light semi-elliptic leaf springs for axle location. Raise and lower travel of 200mm is available — tare weight is increased by 90kg.
Late last year Daf introduced its own novel design of front air suspension for its 95 Series, though it has yet to be homolegated for the UK. The Dutch company has used the simplicity of a two-leaf semi-elliptic locator spring which takes about 20% of the full 7.5-tonne axle load, leaving the air bags to take the rest.
No Panhard rod is needed but an extra longitudinal radius rod above the front half of each leaf spring effectively completes a Swedish-style brake torque reacting parallelogram linkage. Daf's shock absorber and anti-roll bar layout follows the Swedish pattern. Extra kerb weight, compared with an all-steel sprung front axle, is kept down to 45kg.
With UK availability scheduled for January 1993, Iveco Ford is to offer front axle air springs on its New Cargo range at lighter gross weights than anyone else — from 7.5 through to 15 tonnes. The design for the middleweight New Cargos is simple: an air bag interposed between each frame longitudinal and a soft, though positively axle locating, semi-elliptic spring.
The total installation includes a mandatory torsion bar stabiliser which is designed to combat roll. The extra cost will be £2,000, says Iveco Ford, and the estimated tare weight penalty is just 35kg.
D Alan Bunting