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Study of Vibration from Steering Wheel of an Agricultural Tractor
Abstract:
Steering wheel vibration is one of the major factors in determining the operator comfort in agricultural tractors. Main sources of steering wheel vibration are engine imbalance, resonance of steering system, lesser damping, road / field induced vibration, etc. The European Council directive 2002/44/EC recommendations are taken as guidelines in this work.
Steering vibration study was conducted on various tractor models (40 - 50 kW range) and one tractor was identified for improvement. Upon detailed analysis on that particular tractor, it was found that the resonance of steering system with engine excitation is the root cause for excessive vibration. Various methods to reduce vibration due to resonance were considered, such as shifting the natural frequency away from the second order engine frequency and increasing damping coefficient to reduce the vibration amplitude at resonance. Six different concepts were generated and analyzed using the design assessment matrix. Two concepts were selected, namely radial damper and axial damper concepts for further processing. These concepts were tested and a significant reduction in vibration levels was achieved. Axial damper concept offers higher vibration reduction when compared to radial damper concept.
These new design concepts were modeled as a 2 degree of freedom (2-DOF) system with support motion from engine vibration as input. Expressions were derived for vibration transmissibility from engine to steering wheel and coded in MATLAB. A simulation was done in ADAMS software. It was observed that steering vibration predicted by the mathematical model matched well with the measured values. Furthermore, this model could be employed as a tool in selection of optimal suspension parameters for the steering system.