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Modem power steering systems for heavy trucks are available with a variety of hydraulic valve options. Two of these options, port design and torsion bar spring rate, directly influence vehicle handling characteristics. This study focuses on the effects of steering torque requirements and valve response on steering activity, which contributes directly to driver fatigue. A test was performed measuring steering torque and steering position at highway driving conditions to compare long term steering effort and corrections with different valve options. The findings indicate lowered effort in power steering systems does not increase steering corrections, if accompanied by increased valve responsiveness.

Austempered Ductile Iron (A.D.I.) is an engineering material gaining wide acceptance by designers of Automobile Components, Agricultural Equipment, Railroad Parts, Mining Tools, Transportation Equipment, and General Machinery. A.D.I, has a unique microstructure which enables it to display remarkable mechanical properties for a low manufacturing cost. The A.D.I. technology involves two processes: A) A good quality ductile casting, free of shrinkage voids and eutectic carbides, with closely controlled chemistry and graphitic nodule count. B) An austempenng heat treatment cycle which consists of austenitizing and an isothermal quench. The success of austempered ductile iron as an engineering material lies in its unique after heat treatment microstructure which consists of acicular ferrite mixed with high carbon stable austenite. Due to the differences between the metallurgies of cast iron and steel, this structure does not occur in commonly used steels.