F04C 2/1071

Rotary-piston machines or pumps of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of internal-axis type with the outer member having more teeth or tooth-equivalents, e.g. rollers, than the inner member with helical teeth {the inner and outer member having a different number of threads and one of the two being made of elastic materials, e.g. Moineau type}