US Patent 7216724 Coupling for dual member pipe

A coupling assembly to interconnect an inner member and an outer member of a dual member drill string in torque transmitting engagement is disclosed. The coupling assembly is adapted to transmit torque input from both members to a downhole tool. In one embodiment, the coupling assembly comprises a connector sub that fixedly and non-fixedly couples both members. In another embodiment, the coupling assembly comprises a clutch mechanism to interconnect both members when the rotational speed of the outer member exceeds the rotational speed of the inner member. In another embodiment, the coupling assembly comprises a mechanism to couple both members by axial downhole movement of the inner member relative to the outer member. In another embodiment, the coupling assembly comprises a planetary gear system that interconnects both members to provide high torque to the downhole tool at relatively low output speed of the dual member drill string.