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Foden's twin-steer choice
Page 13
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• Foden, long time advocate of the 6x4 axle configuration, has finally succumbed to market pressure and now offers a twin-steer 38-tonne tractive unit. The new 6x2 has been under development for the past two years with tests in the UK and at Paccar's Technical Centre in the USA. Computer aided engineering was used with braking, ride and handling analysis to establish stability and frame integrity.
With the exception of the centre section the steering mechanism follows the standard eight-wheeler layout and incorporates the 4000 Series GKN S63 steering axles rated at 6.7 and 6.1 tonnes.
The single reduction S160E Rockwell drive unit is rated at 11.5 tonnes. A trailing arm, consisting of a monoleaf asymetric spring and air bag, is used for the second steer axle suspension, with a double shackle restricting side movement to ensure the load is applied vertically on to the air bag. Shock absorbers are fitted with rebound stops and the air bags include integral bump stops, while all of the shackle pins are threaded.
Preferential load control is achieved using two valves giving a 10:6 ratio bias to the fully laden drive axle, but changes when part laden. A cabmounted driver-operated axle load control is also included in the system so that traction can be improved still further for a short period.
A 3.46m wheelbase gives the 4000 Series 6x2 a GVW rating of 20.33 tonnes while at 3.8m it is rated at 22.36 tonnes with a gross combination design weight of up to 48 tonnes.
Two rectangular fuel tanks have been developed, offering capacities of 332 and 468 litres (73 and 103gal) to match the two primary wheelbase dimensions. An offside auxiliary tank increases overall capacity up to 636 litres (140gal) but round aluminium tanks can be specified for weight-sensitive applications.
The rear of the chassis has been ramped, saving 55mm, to maximise trailer compatibility.
Foden claims to have the lightest unladen weight in its class. The 4000 Series twinsteer base model, specified with the Cummins LTAA10, rated at 242kW (325hp), and Eaton nine-speed overdrive transmission, weighs in at 6,550 kg with 23 litres of fuel. Aluminium air tanks and alumi nium wheels give a further reduction of 184kg.
A brief test drive, of the Caterpillar 3406B ATAAC — 425 powered 4000 Series 6x4 and Caterpillar 3406B ATAAC350 powered 6x2 twin steer, highlighted two differences in vehicle handling. The softer suspension of the twin steer allowed the chassis to roll to a greater degree while giving a slightly improved ride.
The long 3.8m wheelbase chassis was almost devoid of any pitching moment. The cab trim is both lighter and brighter and the bunk has been raised to provide extra stowage. Outside a new compact air intake stack meets the increased demands of the large air-to-air charge-cooled engines.
For the first time Foden is also offering the ZF Ecosplit 16S 130 16-speed synchromesh transmission as a limited option in the 4000 Series.