Experimental and analytical evaluations of a torsio-elastic suspension for off-road vehicles

The ride performance potentials of a prototype torsio-elastic axle suspension for an off-road vehicle were investigated analytically and experimentally. A forestry vehicle was fitted with the prototype suspension at its rear axle to assess its ride performance benefits. Field measurements of ride vibration along the vertical, lateral, fore-aft, roll and pitch axes were performed for the suspended and an unsuspended vehicle, while traversing a forestry terrain. The measured vibration responses of both vehicles were evaluated in terms of unweighted and frequency-weighted rms accelerations and the acceleration spectra, and compared to assess the potential performance benefits of the proposed suspension. The results revealed that the proposed suspension could yield significant reductions in the vibration magnitudes transmitted to the operator's station. The field evaluations revealed that suspended vehicle could yield 35%, 43% and 57% lower frequency-weighted rms accelerations in the x -, y - and z -axis, respectively, compared to the unsuspended vehicle, when loaded. A 13-degrees-of-freedom model of the suspended vehicle was subsequently developed and validated using the measured data, which could serve as a design tool for deriving optimal suspension designs for a wide range of vehicles. The model results revealed reasonably good agreements with the measured vibration spectra. From the simulation results, it was further concluded that a reduction in the vertical stiffness of the torsio-elastic member would yield beneficial effects on the overall weighted vertical and pitch rms acceleration magnitudes

Investigating the Relationship between Coupling Forces and Hand-Transmitted Vibration under Varying Excitation Levels

In this study, the vibration total value of the acceleration transmitted to the wrist and elbow was measured in the laboratory with a group of 13 male subjects holding a cylindrical handle while modifying the coupling force under varying levels of vibration. The results were used to establish the relationship between hand-transmitted vibration and coupling forces and to compare with the relations proposed as part of an ISO Technical Specification, ISO/TS 15230-2. This was done to determine the suitability of the proposed relationships when variations are introduced on the level of vibration on the handle. While tracing back the origins of the relations proposed in ISO/TS 15230-2, this paper further brings in evidence of the importance of considering the role of coupling forces when evaluating the exposure to hand-transmitted vibration and provides additional evidence to support the relationships which are proposed as part of the ISO Technical Specification. Irrespective of the level of broadband random vibration excitation considered, the agreement with these relationships was found to be best when setting the reference coupling force at 50, 75, 100 and 125 N and whenever the coupling forces applied on the handle were maintained below 150 N