1. Monorail apparatus adapted for suspension from an overhead monorail comprising: a vehicle having an upper framework extending the substantial length of the upper section of the vehicle; and at least one drive wheel assembly mounted on said vehicle and engageable with the overhead monorail, each drive wheel assembly including a drive wheel and drive motor therefor, suspension means to suspend said vehicle from the rail for advancement therealong with the drive wheel and drive motor pivotally supported centrally within a space provided between the suspension means and underside of the rail, and means associated with the suspension means biasing said drive wheel into contact with the rail, and a hanger extending upwardly from said framework for connection at its upper end to said suspension means whereby said drive wheel assembly is freely and independently tiltable and rotatable with respect to said vehicle.

10. In an overhead monorail carrier system having a rail provided with a horizontal flange portion, a drive unit comprising: load-supporting wheels extending upwardly from said supporting frame for rolling engagement with the upper surface of the horizontal flange portion; a drive wheel supporting frame beneath the horizontal flange portion; a rotatable drive wheel assembly including a drive wheel, said supporting frame including pivot means pivotally supporting said drive wheel to engage the bottom surface of the flange about a pivotal axis spaced above the drive wheel is at rest through the drive wheel axis of rotation and normal to the bottom surface of the flanged portion whereby to cause said drive wheel to undergo upward swinging movement about its pivotal axis in response to rotation of said drive wheel; and drive means operable to rotate said drive wheel for rolling advancement along the bottom surface of said flange portion.

16. In a drive unit for a monorail carrier system and the like, said drive unit having a supporting frame with load-supporting wheels on said frame for rolling engagement with an inner surface of a horizontal flange on the monorail together with lateral stabilizing means associated with said load-supporting wheels, the improvement comprising: a rotatable traction drive wheel assembly pivotally supported independently of said load-supporting wheels for engagement with a surface of the horizontal flange on the side opposite to said load-supporting wheels, said drive wheel assembly including pivot means pivotally supporting said drive wheel about a pivotal axis spaced above the drive wheel axis of rotation and in a reference plane when said drive wheel is at rest through the drive wheel axis of rotation and normal to the bottom surface of the flanged portion whereby to cause said drive wheel to undergo upward swinging movement away from the reference plane against the surface of the flange as it is caused to advance in either direction of travel along the rail.

20. In a monorail system for suspension of a vehicle from an overhead monorail, the monorail characterized by having a lower horizontal flange portion and a vertical web section extending upwardly from and along the midsection of the flange portion, a pair of drive units spaced longitudinally of the vehicle and extending upwardly therefrom for engagement with the monorail, each of said drive units comprising: a suspension member suspended from the vehicle, a yoke secured to the upper end of said suspension member, said yoke being of generally arcuate configuration to define oppositely directed arm portions curving upwardly and outwardly from said suspension member to provide a space between the yoke and the monorail; load wheel-supporting brackets of generally U-shaped configuration each swiveled to the upper ends of said arm portions and having opposite sides extending upwardly in spaced relation to opposite sides of the horizontal flange portion of the monorail, load-supporting wheels carried by opposite sides of each of said load-wheel-support brackets for rolling engagement With the upper surface of the lower horizontal flange portion of the monorail, guide wheels carried on opposite sides of each of said brackets for rotation about axes perpendicular to the axes of rotation of said load-supporting wheels, and means yieldingly urging said guide wheels against the vertical section of the monorail for rolling engagement therealong; a drive wheel in the space provided between the yoke and monorail and a motor drivingly connected to the drive wheel; and a drive wheel-supporting bracket including means pivotally supporting said drive wheel about a pivotal axis spaced above the drive wheel axis of rotation and in a reference plane when said drive wheel is at rest through the drive wheel axis of rotation and normal to the bottom surface of the flanged portion whereby to cause said drive wheel to undergo upward swinging movement about its pivotal axis in response to rotation of said drive wheel, and means on said drive wheel-supporting bracket biasing said drive wheel into tractional engagement with the bottom surface of the horizontal flange.