Portal axle on off-road vehicles: effects on drive shaft strength and passenger ride comfort

The portal axle is an off-road technology which is designed to provide higher ground clearance and increased torque at the wheels. The portal axle is typically mounted on the knuckle of the vehicle, allowing both the axle tubing and differential casing to be mounted higher under the vehicle. The usage of the portal axle system brings about two distinctive drawbacks; compromised ride comfort and increased torsional loadings on the drive shaft. In this study, an experimental test was carried out to determine the torsional strength and failure mode of the portal axle drive shaft. The experimental results were then verified using Finite Element Analysis (FEA). Results from both experimental and FEA methods indicate that shaft failure occurs at the gear spline. However, there is a big discrepancy in the torsional stress values, in which the FEA results are significantly higher than the measured experimental values. This is reasonable considering that the shaft simulation analysis is conducted in a static structural manner, in which the flanged side of the shaft is fixed (zero displacement). On the other hand, this study also describes the influence of portal axles on passenger ride comfort. Here, the on road experiment is conducted by placing an accelerometer in the cabin of a portal axle equipped vehicle. The ride comfort experiments are conducted using two vehicles. The first being a normal pickup truck and the second being a pickup truck with the portal axles equipped. Both vehicles are of the same make, model and age. All measurements are performed on normal highways and over regular speed humps. The results from the ride comfort experiment indicate that the use of the portal axles result in significant deterioration of ride comfort. In order to validate the experimental results, a quarter car model representing the portal axle vehicle is simulated using Matlab’s Simulink function. Simulation results also indicate that the use of the portal axles adversely affects the ride comfort. However, when comparing the simulation to the experimental results, there is an 18% discrepancy in the results. This is primarily attributed to the fact that the quarter car model does not take into account the suspension bushings, suspension joints and chassis bending (flex) of the vehicle.