Epicyclic change-speed gearbox casing with a spiral partition wall

A gearbox casing for an epicyclic change-speed gearbox, comprising two casing wall parts branching off upwards from a base part open towards a bottom thereof in an installed position and arranged on both sides of a casing longitudinal axis coinciding with a central main axis of rotation of rotating gearbox parts and extending in a direction of the casing longitudinal axis so as to enclose therebetween a casing interior accommodating the rotating gearbox parts of the epicyclic change-speed gearbox, in which the rotating gearbox parts define an outer rotating boundary, and forming a unitary cylindrical casing outer part, and a casing inner part arranged in the casing interior in a rotationally fixed manner relative to the base part and extending along a lower portion of the outer rotating boundary of the rotating gearbox parts, and one region of the casing interior enclosed by the base part said casing inner part being configured as an intermediate solid wall extending from one of the two casing wall parts toward the other of the two casing wall parts to partition off another region of the casing interior which accommodates the rotating gearbox parts from the one region of the casing interior enclosed by the base part and is open towards the bottom, the casing inner part being cylindrical and lying centrally with respect to the casing longitudinal axis, and the casing outer part and the casing inner part constituting a one-piece casing cylinder, and at least one outlet opening for lubricating oil arranged to connect the another region of the casing interior which accommodates the rotating gearbox parts to the one region of the casing interior and one wall surface of the casing cylinder contains an inner mouth of the at least one outlet opening, said inner mouth lying in the another region of the casing interior which accommodates the rotating gearbox parts at an upper free end of the casing inner part, wherein the wall surface containing the inner mouth is opposite a casing bulge defined by an inner wall surface which starts from a point on an inner wall of the cylindrical casing outer part lying ahead of the inner mouth in relation to a forward rotation direction of the rotating gearbox parts, and follows a spiral curve away from the casing longitudinal axis in a circumferential direction of the central main axis of rotation corresponding to the forward rotation direction.