GB2190977A - Coupling device - Google Patents

Abstract

The invention concerns a substantially frictionless coupling device which can be used as a clutch, brake or torque limiter. A rotatable input shaft 12 carries a flywheel divided into six separate pieces 15 each individually movable radially of the shaft and each carrying a roller. A housing extends co-axially around the flywheel and carries a profiled track with indentations 25. The rollers engaged the track which guides the pieces 15 for in and out movement. The centrifugal force on the pieces 15 is converted to a turning force on the housing. When the housing is free to rotate the device acts as a substantially frictionless clutch or when the housing is fixed the device can act as a low friction brake. <IMAGE>

Description

SPECIFICATION Coupling device This invention relates to a coupling device in corporating a flywheel.

An object of the invention is to provide a substantially frictionless coupling.

In its broadest aspect the invention provides a substantially frictionless coupling between a first part carrying a flywheel and a second part, in which the flywheel is formed in a plu rality of pieces which can move independently of one another and are guided in their radial movements by rolling engagement with the second part. The rolling engagement provides a substantially frictionless coupling and the de vice can be arranged as a gradual engagement clutch where the second part is also free to rotate or a brake where the second part is restrained from movement. The device can also act as a torque limiter.

In a preferred form the invention provides a coupling device comprising a flywheel mounted for rotation with a first part about a first axis, the flywheel being composed of a plurality of separate pieces mounted for radial movement relative to the first part and inde pendently of one another, the pieces engaging a second part mounted co-axially with the first part and the pieces being guided in their movement by engagement with a profiled track on a second part.

Preferably each piece includes a roller which engages the track with a rolling contact. This minimises friction between the first and second parts so that little energy is wasted in heat generation.

Preferably the second part is mounted for rotation about the axis and the track is shaped such that the centrifugal force on the flywheel pieces is translated into a turning force on the second part.

Preferably the track surrounds the flywheel and is annular and formed with a plurality of indentations, each indentation having a substantially radial portion joined to the substantially radial portion of the next indentation by a gradual concave curve and a convex peak.

In use as a clutch, with the first part driving the second part, as the first part rotates, the flywheel pieces tend to move outwards under centrifugal force. When the roller connected to a piece is opposite a substantially radially extending part of the track it can travel freely outwards, then (unless the parts are rotating at the same speed) as it engages the gradually curved convex portion it is forced inwards against the action of the centrifugal force and the opposite reaction tends to rotate the second part.

As an alternative use, the outer part may be fixed and act as a substantially frictionless brake on the inner part. For this use, preferably the flywheel and first part are coupled to the device to be braked through a variable speed coupling so that as the part to be braked slows down the flywheel's rotational speed can be maintained.

Embodiments of coupling device, in accordance with the invention, will now be described, by way of example only with reference to the accompanying drawings of which: Figure 1 is a transverse sectional view of a first form of coupling taken on the line l-l of Fig. 2, Figure 2 is a section on the line ll-il of Fig.

1 (partly exploded).

Figure 3 is a transverse sectional view of an alternative coupling.

In the exploded view of Fig. 2 the three C/L indications will coincide in the assembled coupling.

An input shaft 12, mounted for rotation about its axis 13 carries a flywheel 14 divided into 6 separate sector shaped pieces 15. Each flywheel piece 15 is mounted on a pin 16 slidably located in radially extending slots 17 in opposed, spaced, side cheeks 18 keyed to the shaft 12. The slots allow the pieces 15 to slide radially relative to the drive shaft and independently of one another. Each piece 15 has included therein a roller 20 rotatable on the pin 16.

A housing 22 (omitted in Fig. 1) extends co-axially around the flywheel and carries a profiled, internally facing, annular track 23, substantially co-planar with the rollers 20. The housing is mounted for rotation about the axis 13 independently of the drive shaft 12 and is coupled to a sleeve 24 which may be connected to an output shaft (not shown). Alternatively the housing can be fixed. The track is symmetrical having four indentations 25, each having a first substantially radially extending portion 26, a second gradually concave curved portion 27 and a convex peak 28.

When the coupling is to be used as a gradual engagement, low friction clutch, the housing is allowed to rotate. Initially the drive shaft and fiywheel will be rotating with the pieces constrained by a suitable clip in their innermost positions within the peaks 28 and therefore exerting no turning forces on the housing. When the pieces are released, as the drive shaft rotates anti-clockwie as seen in Fig. 1, a piece will come opposite a radially extending portion 26 of the track and will move outwards under centrifugal force, as it engages the part 27 of the track, the track will force it inwards and in return the piece will exert a turning action on the housing.

Eventually the housing will rotate at the same speed as the shaft and the pieces will not be forced in and out. It will be appreciated that the contact between the rollers and the track is a rolling contact with little frictional force and thus the clutch is a gradual engagement clutch with little friction and thus little dissipa tion of energy as heat.

The device can also be used as a brake by restraining the housing from rotation when the force exerted on the flywheel pieces as they ride up the curved parts 27 will then act as a braking force. Since this force will be smaller the lower the speed, a variable speed coupling is preferably interposed between the drive shaft and the device to be braked.

Fig. 3 shows a modified coupling device having a twelve lobe ring with a ten sector fiywheel (only some sectors are illustrated).

Since the greatest torque is exerted by any flywheel sector when it is at its maximum radius this is more efficient.

The torque exerted under slip conditions is proportional to the tangential force exerted on any segment on the rising (towards the centre) arc of the profiled outer rim. This force results from the deceleration of the segment as it is constrained to move towards the centre of the flywheel. The tangential force is, of course, proportional to the rotational speed of the coupling.

If the input shaft speed is maintained constant and insufficient torque is being generated to accelerate the outer ring (coupled to the load) slip will continue to occur.

Claims (10)

1. A substantially frictionless coupling between a first part carrying a flywheel and a second part, in which the flywheel is formed in a plurality of pieces which can move independently of one another and are guided in their movement by rolling engagement with the second part.

2. A coupling device comprising a flywheel mounted for rotation with a first part about a first axis, the flywheel being composed of a plurality of separate pieces mounted for radial movement relative to the first part and independently of one another, the pieces being arranged for engagement with a second part mounted co-axially with the first part and the pieces being guided in their movement by engagement with a profiled track on a second part.

3. A coupling device according to Claim 2 in which each piece includes a roller which engages the track with a rolling contact.

4. A coupling device according to Claim 2 or Claim 3 in which the track is annular and is formed with a plurality of indentations.

5. A coupling device according to Claim 4 in which the number of indentations is different from the number of pieces of flywheel.

6. A coupling device according to Claim 4 or Claim 5 in which each indentation has a substantially radially extending portion joined to the adjacent substantially radially extending portion of the next indentation by a gradually concavely curved portion and a convex peak.

7. A coupling device according to any of Claims 2 to 6 in which each flywheel piece is mounted on a pin slidably located in radially extending slots in opposed spaced cheeks coupled to a drive shaft forming the first part and each piece includes a roller rotatable on the pin.

8. A coupling device according to any of Claims 1 to 7 in which the second part is mounted for rotation co-axially with the first part.

9. A coupling device according to any of Claims 1 to 7 in which the second part is fixed.

10. A coupling device substantially as described herein with reference to or as illustrated in the accompanying drawings.