| description abstract | Abstract. The trailer trains for the transport of freight in sites where people are present proceed rather slowly along tortuous paths and roll on stiffer wheels compared with the common road vehicles, whence their motion is ruled by the wheel rolling constraint with no transverse slip. These trailers must be equipped with proper steering devices, generating point paths with very large curvature and containing all these paths within very narrow bands. The present analysis proposes front-back symmetric steering systems, which turn all the wheels of each trailer together so that the perpendiculars to their median planes intersect at a single point of the transverse symmetry axis through the trailer barycenter: the instantaneous center of rotation of the trailer. This requisite implies a projective correspondence between the pencils of the straight prolongations of the steering arms integral with the wheel hubs, whence the correct steering may be generated by the motion along a conic of a particular guidance point of the steering mechanism. Choosing the geometry of the links so that this conic is an ellipse, the desired elliptic path may be generated by a suitable Cardan motion mechanism. Hence, the motion of the whole train may be calculated starting from the first trailer up to the last one, and the results show a very good fulfillment of the desired requisites when the minor semiaxis of the ellipse is equal to the golden section of the major one. At last, the inertial and traction forces are also calculated, starting from the last trailer up to the first one and the tractor. | |
