1.  Field of the Invention
The invention relates to transmissions, and in particular for the drive of generators by turbines, in which the transmission casing is under a partial vacuum and the operation of the transmission is monitored and protected by special devices. 
2.  Description of the Related Art
It is generally known that in high-speed transmissions, the aerodynamic losses, compared with the friction, are greater.  To reduce these windage losses, the air surrounding the rotating gears is completely or partly removed from this region.  For this purpose, DE 295 17 964 U1 proposes an inner casing which closely surrounds the gears and is kept under partial vacuum by means of a pump.  The installation of an inner casing involves additional effort which results in high costs.  The feeds for lubricating and cooling oil must be passed through the inner casing in a complicated manner and the lubricating-oil sprinklers must be fastened in the interior of the inner casing.  In the event of malfunctions at the scavenge pump, due to the small distance between the inner casing and the gears, the oil sump may rise rapidly up to the tooth flanks and lead to sudden braking of a gear, which results in considerable damage to the entire plant.  A special dedicated inner casing is to be provided for every variation in the transmission ratio of the transmission and the accompanying change in the gear diameters. 
It is therefore an object of the invention is to provide a transmission casing in which, at a low cost of the casing, a partial vacuum of predetermined size can be maintained and which ensures a high degree of operational safety. 
This and other objects of the invention are achieved by dispensing with the additional inner casing in an advantageous manner and such that the technical outlay otherwise associated therewith does not apply.  Due to the unobstructed interior space, the optimum arrangement of lubricating-oil sprinklers and scavenge devices in the configuration of the casing according to the invention is possible without extra technical outlay. 
The variation of different transmission ratios in a transmission casing according to the invention is possible due to the omission of the close-fitting inner casing. 
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure.  For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.