Turbomachine comprising a speed reducer having attachment flanges coupled by a gear coupling

A speed reducer for a turbomachine, having a longitudinal axis X, the speed reducer comprising a sun gear sprocket, planet gear sprockets, an external ring gear, and a ring gear carrier attached to the external ring gear, the planet gear sprockets being in mesh on the one hand with the sun gear sprocket and on the other hand with the external ring gear, and the external ring gear comprising a first attachment flange extending radially outwards and being attached to a second attachment flange of the ring gear carrier by attachment members, the first attachment flange and the second attachment flange forming an attachment assembly, wherein the attachment assembly comprises at least one gear coupling with axial coupling teeth comprising a first series of axial coupling teeth engaging with a second series of complementary axial coupling teeth, the attachment members being arranged so as to clamp the first and second attachment flanges together and circumferentially hold each tooth of the first series of axial coupling teeth between two teeth of the second series of complementary axial coupling teeth,

• wherein the first flange and the second flange each comprise axial attachment teeth which are passed through by attachment orifices receiving attachment members.