A Modified Brush Tyre Model and LP Tyre Force Allocation for 4WIS/4WID Vehicles Motion Control

The over-actuated characteristic of four-wheelindependent-steering-and-driving vehicle opens a new dimension to reduce the dynamic inversion error, as the preferred tyre operating region used in the control allocation can be defined as the region where the tyre model has higher accuracy. Motivated by this, this paper proposes a modified brush tyre model in concert with tyre force allocation using linear programming. Contrasting with the existing brush tyre models which have magnitude error and direction error simultaneously, the proposed model only has tyre force direction error, and also achieves higher overall accuracy. The error pattern analysis of the proposed model shows that the use of tyre force near 45° direction (i.e., equal longitudinal and lateral force) should be avoided. Thus, the tyre force is allocated with the cost function defined using 1-norm, as it penalises the tyre force usage in certain directions. The effectiveness of the proposed method is validated by Simulation. Results demonstrate good tracking of a path with varying curvature and speed. Comparisons to a run using 2-norm as the cost function to allocate tyre forces highlight the importance of accounting for the low-level tyre model inversion error in the mid-level tyre force allocation.