GKN leaf springs
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GKN remains coy about revealing who the first customer for its composite leaf spring CM, December 17, 1983) will be, saying only that it will be "a major British vehicle manufacturer", but Freight Rover seems the most likely contender, despite earlier denials.
Composite leaf springs suitable for vehicles ranging from car-derived vans to 16-ton gvw rigids have been designed by GKN, and volume production will begin in its Telford factory next February. According to GKN, this means its new GKN Composites UK company will have a two-year lead over its nearest competitors, and that it will be the first independent manufacturer to mass produce composite springs.
All the GKN composite springs have a similar structure based on unidirectional glass fibres embedded in a matrix of epoxy resin. Bushes at the ends are projection-welded to simple metal pressings, which are attached to the spring by pressed straps.
One of the major problems facing designers of composite springs has been finding a satisfactory means of bonding steel bushes to the composite.
Apart from the composite spring's main advantage of light weight (typically 50 per cent of the weight of an equivalent steel tapered leaf spring) it also offers good noise-damping characteristics and can reduce the transmission of axle noise to the chassis — a particularly significant feature for van applications.
Moreover, the new GKN spring will fail safe; that is, unlike steel springs, when severely overloaded the composite component will fail along its length thus maintaining axle location and not immobilise the vehicle.
But GKN is confident that spring failure will be less likely with the composite component anyway. In a typical vehicle manufacturer specified test a spring is cycled over 70 per cent of its deflection from bump to rebound. GKN says that the new spring withstood one million cycles compared to the 200,000 normally specified.
To support its rig testing GKN has fitted several of its composite springs to 2.5 tonne gvw vehicles (again not specified) in service in a variety of fleets, and it is reported that over 250,000 miles of field trials have now been accumulated.