Abstract:
The goodness-of-fit analysis performed over the results provided by a model presented in
a previous paper proved that the theoretical data were very well correlated with the experimental
data with regard to the traction force (with Pearson coefficient r2 over 0.9); however, the model was
less accurate in predicting traction efficiency, with r2 = 0.203. In order improve the model and obtain
a better fit between the theoretical and experimental data (especially for the traction efficiency), the
model was updated and modified by taking into account the geometry of the tire cross section, which
was considered to be a deformable ellipse. Due to the deformable cross section, the minor axis of
the tire–ground contact super ellipse decreased compared with the previous model (from 0.367 m
to 0.222 m), while the major axis increased (from 0.530 m to 0.534 m). As a result, different data
for the traction force and traction efficiency were obtained. The effect of the wheel travel reduction
(wheel slip) over the tire–soil shear area was also investigated, and the hypothesis of a constant shear
area (independent of wheel slip) provided the most accurate results. The goodness-of-fit analysis
performed using the data predicted by the modified model showed that the Pearson coefficient
increased significantly with regard to the traction efficiency (from 0.203 to 0.838), while it decreased
by only 2.7% with regard to the data for the traction force, still preserving a high value (r2 = 0.896).
