FLEXIBLE SHAFT COUPLING The present invention relates to a flexible shaft coupling, comprising a first coupling member attached to a first shaft, a second coupling member attached to a second shaft, which two coupling members are arranged directly opposite each other and spaced apart in the direction of the shaft, one or more flexible members in engagement with the two coupling members for transmission of a torque between the coupling members, and a ball joint disposed between the two coupling halves.

Flexible shaft couplings of this type are used when it is desirable to have a certain flexibility between the two interconnected shafts, while the coupling should, at least to a certain extent, be capable of taking axial forces.

It is an object of the invention to provide a flexible shaft coupling, especially for rather large, so-called heavy drive mechanisms, for example, for driving pinions in rack- drilling rigs, which shaft coupling can serve to assure flexibility and straightness and transmission of compressive and tensile forces with minimal movement in the torque part of the coupling, and especially when using standard components to provide the ball joint.

According to the invention, there is therefore proposed a flexible shaft coupling as mentioned above in the introduction, characterised in that the ball joint comprises two spherical bearings so arranged that their bearing faces each form a part of a spherical surface the centre of which is centrally positioned between the two coupling halves.

It is of particular advantage if one of the spherical bearings can be arranged in the bottom of a cup-shaped body the rim of which is attached to the first coupling half, the two spherical bearings being held apart from one another within the cup part by means of a sleeve aligned in the direction of the shaft between the convex bearing portions of the two spherical bearings, which bearing portions are held together by a bolt running through the sleeve and attached to the second coupling half.

In a flexible shaft coupling of this kind it is advantageous to use standard spherical bearings which, with some simple adjustments, can be utilised to provide the ball joint centrally in the coupling.

The invention will now be explained in more detail with reference to the drawing which shows a section through a preferred embodiment of the new flexible shaft coupling.

The two shafts that are to be connected by means of the flexible shaft coupling are indicated by the reference numerals 1 and 2 respectively. The first shaft 1 has an end flange 3 and the second shaft 2 has an end flange 4. The coupling itself consists of a first coupling half 5 and a second coupling half 6, the first coupling half 5 being connected to the first end flange 3 and the second coupling half 6 being connected to the second end flange 4. In order to provide the connection between the end flanges and the coupling halves, bolt holes 7 that are aligned with threaded bores 8 in the respective coupling half are made in a known way per se in the end flanges 3,4. The threaded bolts that are used for the connections between the end flanges and the coupling halves have not been included in the drawing.

Rubber members 9, shown in broken lines on the drawing, are disposed between the two coupling halves 5,6 in a known way. These rubber members 9 serve to transmit torque. Of course, many torque-transmitting members that are known per se could be used here.

As shown, the two coupling halves 5,6 are hollowed out 10,11, so that a space is formed between them to provide room for the ball joint, which in this case is formed of two spherical bearings 12 and 13. The spherical bearing 12 is made of a bearing ring 14 having a concave bearing face and of a spherical segment 15 which constitutes the convex bearing portion. Similarly, the spherical bearing 13 is made of a bearing ring 16 and a spherical segment 17. The two bearing rings 14,16 are alike and thus are interchangeable, and the same is true of the spherical segments 15,17.

The bearing ring 14 lies in the first coupling half 5, whilst the bearing ring 16 lies in the bottom of a cup-shaped part 18. On its opening side, the cup-shaped part 18 is connected to the first coupling half 5 by means of screw bolts 19 (the screw holes 8 and the bolts 19 are shown in the same plane in the drawing, but are of course offset in the practical embodiment so that they do not overlap). Cut out in the bottom of the cup- shaped part 18 is an opening 20, for the insertion of a bolt 21 the head 22 of which rests against the spherical segment 15, and the shank of which is passed through the bottom opening 20 of the cup body and through a washer 23, and is tensioned by means of a nut 24. Disposed between the two spherical segments 15,17 is a spacer sleeve 25 that is machined with exactitude so that the two spherical segments 15,17 screwed together as

shown form parts of an ideal sphere. Placed around the bolt 21 is an inner sleeve 26 which centres the spacer sleeve 25.

From the drawing and accompanying description, it will be understood that the theoretical sphere is composed of two spherical, preferably standard bearings that are spaced apart by a spacer sleeve in such manner that the bearing faces of the two spherical bearings each form a part of a spherical surface. The coupling can transmit thrust load in both directions, and at the same time it is self-aligning. The couplings are made so that the centre of the"sphere"is also the centre of the torque transmission.

This means that there is minimal movement in the torque part of the coupling, which in turn serves to reduce wear in the coupling.