US Patent 7429231 Rotary drive for a belt tensioner

A rotary drive for a belt tensioner includes a housing, a pinion rotatably mounted therein, and at least one driving gear coupled to the pinion, the driving gear being mounted in the housing and being adapted to be driven by pressurized gas introduced into a pressure chamber. Formed in the driving gear is a cavity having a substantially radially extending wall which, in the installed state, is opposite to a protrusion which projects into the cavity and is rigidly connected to the housing, the wall of the cavity and the protrusion forming part of a wall of the pressure chamber.