Abstract: A rotary energy-transmitting mechanism, according to the present invention, concerns a mechanical structure having inner and outer relatively movable elements that are combined in a mechanism of rotary nature. The inner and outer elements may be combined with other mechanical structure to facilitate utilization of the general mechanical form of the invention for a number of mechanical purposes, all involving transmission of energy which may be between the relatively movable inner and outer elements and/or between the elements and a fluid. The mechanical structure, depending on the arrangement of the relatively movable parts and depending on the inclusion of other specific parts, may take the form of various energy-transmitting mechanisms, such as a mechanical coupling, a universal joint, a rotary shock absorber, a rotary pump, a rotary compressor and a rotary engine.