IN coordination with announcements by Freightliner at the Great American Trucking Show in Dallas, Hendrickson introduced its new air suspension and axle for the steering axle of heavy trucks. The new system combines air and leaf springs and uses a fabricated axle instead of a forged I-beam. Hendrickson's AirTek front suspension and axle gives fleets the opportunity to run a full suite of air suspension including the steering axle, drive axles, and trailer axles.
Previous attempts to use air suspension on the front axle of heavy trucks ran into engineering problems that required designers to sacrifice ride comfort to gain vehicle stability. The paradox inherent in front axle suspension design is that roll stability requires stiff springs, while comfortable ride characteristics argue for soft springs. The compromises required to produce stability in a front air suspension added stabilizers and reinforced structures to the suspension that degraded ride quality and made the suspensions too heavy and complex for widespread fleet adoption.
The new suspension utilizes an integrated system of asymmetric steel leaf springs, air springs, and a fabricated axle beam. A patent is pending on the new box-shaped axle beam, which is stiffer than conventional I-beam axles. The steel leaf springs in AirTek use a smooth conventional curve in the front limb between the front frame brackets and the axle clamps. The axle beam and the front limbs of the leaf springs form a torsion system that enhances vehicle roll stability and improves truck handling. Improved steering geometry and the torsion system reduce bump steer, wheel kick, and vibration.
The fabricated axle is known as SteerTek. It resists vertical and longitudinal loads more effectively than traditional axle beams, thus reducing variations in dynamic camber and toe for improved steering geometry.
The leaf spring assembly is patented. It shares vehicle loads equally with the associated air springs, which are engineered to support 50% of the vertical load while providing a low spring rate for smooth ride. Lab and field tests of roll stiffness and dynamic roll gradients show that the AirTek suspension improves roll stability more than 20% compared to other conventional front suspensions.
The basic AirTek suspension consists of a suspension assembly that weighs 238 lb and an axle assembly weighing 274 lb. This is more than 100 lb lighter than other suspension and axle systems. Hendrickson also supplies other fabricated axles for AirTek that weigh 277 lb or 279 lb. Weights are based on the suspension components including frame hangers, main springs, bushings, air bags and attachments, height control system, shock dampers, upper shock damper brackets, and axle attachment hardware. Components included in the axle weights are the axle beam, knuckle and steering arm assemblies, and tie rod assemblies. The axle and suspension are each rated at 12,000-lb capacity.
Steering and tie rod arms are integrated for increased strength and reduced weight. The steering knuckle design is capable of a 50 wheel cut. It can be disassembled without removing the kingpin during kingpin bearing service. The knuckles use high quality, low friction bushings and thrust bearings with integrated seals for long service life.
The suspension is designed for low maintenance. Quick snap features and a push-to-connect air supply allow rapid removal and replacement of the air springs. Front and rear bushings on the leaf springs are maintenance-free. Four-sided clamping at the axle attachment points eliminates the need to retorque the axle clamp groups.
The first versions of AirTek were designed for Freightliner and will be available on Freightliner's Coronado, Century S/T, and Columbia conventional tractors after April 1, 2001. After a period of exclusive availability to Freightliner ending in 2003, Hendrickson will release AirTek designs for other highway tractors.
For more information, visit www.hendrickson-intl.com.