Axial loading device

#This invention relates to a device for applying an axial load to a member and in which the force applied by said device differs under differing operating conditions.

#One example of apparatus in which such axial loading device is used is a variable ratio frictional drive gear of the kind comprising basically two axially spaced torus discs or rotors, one serving as an input and the other an output, between which there is a set of circumferentially spaced drive rollers in frictional rolling contact with part toroidal surfaces on the discs, each roller being rotatably mounted in a bearing structure which can tilt about an axis at right angles to the axis of rotation of each roller so as to vary distances from the gear axis at which the roller engages the two discs respectively, thus varying the drive ratio of the gear. The angle of tilt of the roller bearing structure as it controls the drive ratio of the gear is called the ratio angle. There is furthermore provided means which is normally fluid pressure operated, for loading the discs axially so that there is pressure between the toroidal surfaces and the surfaces of the rollers engaging them.

#One way of changing the ratio angle is to provide means to apply a force to each of the roller bearing structures to move it generally tangentially with respect to the gear axis, and by allowing the rollers then to steer themselves towards a different ratio angle. The rollers are each mounted in their bearing structures in such a way that they are inclined at an angle to a plane perpendicular to the gear axis. This angle is called the caster angle. Gears of this general construction are referred to as gears with tangentially controlled roller bearing structures.

#The invention will now be described by way of example with reference to the accompanying drawings, in which:

#FIG. 1 is a cross-sectional view showing a transmission system constructed in accordance with the invention;

#FIG. 2 is an enlarged view of part of the end loading device of the construction shown in FIG. 1;

#The transmission system is principally designed for use in driving aircraft accessories and in particular an alternator. The alternator is driven from an aircraft main engine but is required to be rotated at constant speed. The transmission is therefore designed for variable input speed, but constant output speed. It is however, to be understood that transmissions incorporating the invention as herein defined can be used in transmissions of this sort with other operating characteristics including constant input and variable output speed and variable input as well as output speeds.

#Referring first to FIG. 1, the general layout of the transmission is illustrated. The system includes a variable ratio drive unit having three rotors 10, 11, 12 which have respective part toroidal surfaces 10a, 11a and 12a and 12b respectively. The rotor 12 is situated mid-way between the rotors 10 and 11, and is provided with its part toroidal surfaces 12a and 12b, on opposite axially presented sides thereof. The rotor 10 has its part toroidal surface 10a presented towards the surface 12a and similarly the surface 11a of the rotor 11 is presented towards the surface 12b of the central rotor 12. The rotors 10, 11 are output rotors and the rotor 12 is an input rotor. However, the system will operate perfectly satisfactorily with the rotors 10, 11 as input and the output as the rotor 12. Situated between the rotors 10, 12 and 11 and 12 are respective sets of flat rollers 13, 14. In this example there are three rollers in each set. These are rotatable in a manner which will be described and are for this purpose carried in respective bearings 15, 16. The rollers are shown in FIG. 1 in positions in which they engage the respective surfaces 10a, 12a and 11a, 12b at the same distances from the axis of rotation of the rotors 10, 11, 12. Such axis is identified at 17. The rotors 10, 11 are carried non-rotatably upon a hollow shaft 18. This is supported on suitable fixed structure by means of bearings. Surrounding one end of this drive unit is a hollow casing 19 which is engaged at one end on the external periphery of the rotor 12 by splines 20. The other end of this casing 19 is journalled co-axially with the shaft 18 in bearings 21, 22 and engages through a clutch 23, a hollow shaft 24. This has gear teeth 25 engaging a gear 26 on an input shaft 27. The clutch 23 is provided to allow reversal of the input shaft rotation.

#The output of the system is in engagement with the shaft 18 at its end remote from the input shaft 27. The connection to the shaft 18 is represented by splines 28 in the end thereof.