Effect of Torsion Bar Size and Rotary Valve Type on Steering Correction Requirements for Heavy Truck Power Steering

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.