(Mech Eng) A shaft or spindle about which or with which a wheel rotates. (Transp) An automotive under-carriage assembly, including housings, gearing, differential, bearings, and mounting appurtenances. Also called: Axle Assembly. Note: A bogie is an assembly of two or more automotive-type axles mounted in tandem in a frame so as to divide the load between them and permit vertical oscillation of the wheels