GB2071236A - Overload coupling - Google Patents

Abstract

An overload coupling which normally couples together two rotary parts (1, 2) but which releases on excessive torque comprises a series of entrainment bodies (e.g. balls 3) which are urged by springs (4) into matching recesses (8, 9) in the parts (1, 2) to cause those parts to rotate together. Circulation tracks (10, 11) on one or each of the parts connect the recesses of the respective part. When the torque becomes excessive, the entrainment bodies are forced out of the recesses (8, 9), thus breaking the coupling, and relative movement of the parts (1, 2) occurs, with the entrainment bodies rolling on the circulation tracks between successive recesses. Either or both sets of recesses (8, 9) may be specially contoured to give a particular overload characteristic or to allow overload release in either direction of relative rotation (Figures 2 to 4 (not shown)). In further embodiments the balls 3 may be caged and the cage may be connected to a planet carrier of a planetary gear system driven by the parts 1 and 2, one set of recesses may be formed by a plurality of rotary cams, the entrainment bodies may be caged rollers, or one set of recesses may be formed by grooves inclined to the axial direction and the other set by radial projections (Figures 6 to 10 (not shown)). <IMAGE>

Description

SPECIFICATION Overload coupling The invention relates to an overload coupling consisting of two coupling parts rotatable relative to one another and a number of entrainment bodies distributed over a periphery and serving to couple together the parts for torque transmission, each entrainment body being urged by spring action into recesses in the coupling parts, which recesses face each other on opposite sides of the plane of separation between the parts.

Overload couplings with entrainment bodies of spherical shape, for example, which are secured by the force of one or more springs in the torque transmission position in hemispherical recesses and which escape from the recesses when a certain preselected torque is exceeded, are already known from German Patent Specification No.

1 101059, for example.

That specification describes an overload coupling in which the entrainment bodies secured in the torque transmission position in hemispherical recesses by spring force move out of their recesses, in opposition to the spring force, when overload conditions occur, and are transferred to sliding paths axially or radially offset in relation to the said hemispherical recesses.

in order to minimise the friction occurring in the free-flow position, the depth of the sliding path in the direction of the spring force is greater than that of the recess for the entrainment position.

A particular disadvantage of the construction described is the fact that in order to re-engage the overload coupling the drive has to be rendered inoperative, the two halves of the coupling only being restorable to the entrainment position in relation to each other by means of a reverse rotation in opposition to the torque prevailing.

Overload couplings which re-engage automatically are likewise knuwn and frequently operate on the ratchet principle. These known ratchet coupings, however, suffer from the drawback that after overload conditions have occurred the overload coupling must absorb considerable impact and friction energy until it comes to a complete stop. This often causes unacceptable heating, in addition to which overload couplings of this type suffer serious wear.

In order to surmount these drawbacks it has been suggested, for example, that overload couplings, after being switched over to free-flow conditions, should be shut off by an electrical contact breaking operation (DL Patent 39404). Such solutions, however, can only be adopted in the case of electrical driving systems.

The purpose of the invention is to provide an overload coupling which operates on the ratchet principle and in which, when the drive continues to run at the rated speed, the converted energy, after an overload occurs, can be reduced to such an extent that the resulting harmful effects on the overload couplings are largely avoided. The magnitude of the torque following the commencement of the overlaod conditions is also to be determinable by the design adopted for the coupling.

The overload coupling according to the invention may also be capable of re-engaging automatically by reducing the speed, below a fixed speed which is lower than the rated speed. In addition, the overload coupling may be designed in such a way that it can only be re-engaged by manual operations.

It is also possible to construct it as a reversing overload coupling, in certain cases with wideiy varying torques. The coupling is also to be capable of including, in the range up to the overload torque, the function of a rotationally elastic coupling.

By the invention it is possible to provide a coupling which can be manufactured in a simple manner and which will thus be strong and economical.

An overload coupling, according to this invention, comprises a driving coupling part and a driven coupling part having a plane of separation therebetween and provided-with recesses which face one another across the plane of separation; a number of entrainment bodies capable of entering the recesses in order to couple the coupling parts together; bias means urging the entrainment bodies towards the recesses; a circulation track on at least one of the coupling parts interconnecting successive recesses; and contacting surfaces on at least one of the coupling parts, so inclined with respect to the perpendicular to the radius of the recesses that, when an overload occurs in use, the entrainment bodies are subjected to a force component opposed to the force of the bias means and urging the entrainment bodies out of the recesses and on to the circulation tracks.The invention has the advantage that the entrainment bodies, at all events in non-coupling condition, are able to serve as bearing structures for the purpose of centering the coupling parts in relation to one another. The properties of a rotationally elastic coupling are obtained as a result of the fact that some of the recesses are constructed with an approximately constant angle of contact in the direction of the thrust track.

The overload coupling can be constructed in such a way that the coupling parts are rotatable in one another. This renders a rotation-saving design possible. Alternatively, if a coupling of extremely limited width is required, coupling parts may be mounted so that they can rotate side by side.

To ensure that the separate entrainment bodies will be automatically driven when an overload occurs, a compartment for engaging the entrainment bodies may in each case be provided at the end of the displacement paths of the entrainment bodies of one coupling parts, in the zone of the circulation tracks of the second coupling part.

If a reversing coupling with an equal torque in each direction is to be provided, the angle of contact of the recesses in respect of the entrainment bodies is to be made the same for both direction of rotation. If the drag moments are to be kept constant, the angles of contact of the compartments are likewise to be made equal.

For applications in which a reversing coupling with a different slip moment and/or drag moment on the basis of one and the same spring system is required, different angles of contact are to be adopted for the two directions of rotation.

To reduce the harmful impact of the entrainment bodies on the surfaces between the recesses and the circulation track, the pressure surface of the circulation track is in each case to be designed to ascend in a straight line or in a curve in the direction of rotation of the entrainment bodies.

To reduce the torque after the commencement of an overload the angle of contact of recesses of the coupling parts with securing compartments is to be made greater than the angle of contact of the compartments in respect of the entrainment body in the direction of rotation. The smaller the angle of contact of the compartments, the lower the residual torque. With a coupling in which the re-engagement takes place automatically after the drive has been put out of operation the angle of contact of the compartment is to be made greater than the friction losses of the coupling, so that the entrainment bodies can roll or slip backwards into the recesses as a result of the spring force. If the angle of contact is made smaller than the resultant angle of friction, equal to 00, the coupling can only be re-engaged by rotating the driving shaft in the reverse direction.

In many applications it is desirable for the reengagement to be possible only by reverse rotation and slight braking of the driven shaft. This object can be achieved by providing a suitably hump-like elevation between the recess and the compartment.

According to a subsidiary feature of the invention it is possible to construct a unilaterally operating or double-acting overload coupling in which the recesses are provided in the form of guide paths along the plane of separation between the coupling parts, the paths of at least one coupling part being oblique to the direction of rotation. If the oblique paths all take one direction, the entrainment bodies will be displaced in one direction or in the other, according to the direction of rotation, so that a separate coupling can almost be said to be formed for each direction of rotation at each end of the displacement track, with a corresponding subdivision of the load, the wear and the heat developed.At all events, however, the coupling characteristics including the spring force can be provided separately, so that a reversing overload coupling with widely varying torques can be produced without difficulty. If the separate paths are oblique but in alternating directions, the entrainment bodies, when the torque takes one direction, will be displaced in the other, so that the torque likewise will be subdivided. Furthermore. the supporting and centering properties provided by the entrainment bodies are greatly improved by the formation of two groups of such bodies, while finally the best possible equilibration of the internal forces and mass forces is achieved.

For the coupling variants described it is important to preserve a certain accuracy in the pitch and shape of the recesses, compartments and entrainment bodies. Furthermore, local differences in the nature of the material or surface may cause variations in the wear occurring, so that the forces and distances distributed over the periphery cause the couplings to operate unevenly and jerkily. These conditions can be greatly improved if the entrainment bodies are secured in approximately the same plane and/or in a given pitch by means of a cage. The latter is situated in principle in or along the plane of separation.

Indirectly, therefore, the adoption of the cage can lead to higher manufacturing tolerances.

In the case of couplings with a high ratchet moment and without compartments the impact energy and friction energy can be greatly reduced if the cage receives its drive from the coupling parts via planet wheels of a planetary gearing, for instance, at a rotation speed corresponding to the average speed of the two coupling parts. The entrainment bodies are thus automatically controlled, so that despite inaccuracy or different friction conditions they will always engage the next recess gently at each stage around the pitch.

The planetary gearing, however, can equally well be designed to cause the cage to assume a different speed, so that the full ratchet action takes place at longer intervais.

The frequency of the ratchet action can thus be increased as needed by making the number of recesses of a coupling part equal to the number of entrainment bodies or to a whole multiple thereof.

This may under certain circumstances enable the cause of the overload to be eliminated more rapidly, as in the case of the drive of agricultural machines, for example, when the material is enabled to free itself from an obstruction.

The frequency of the ratchet action, however, can also be reduced by giving the entrainment bodies an unequal pitch over the periphery. In the case of a coupling with four entrainment bodies and a pitch of 800--10000-8000-1000, for instance, the re-engagement and thus the impact frequency, despite four entrainment bodies, can be reduced to two per rotation, the impact energy and friction energy being reduced accordingly.

By the use of suitable cams on the periphery of a coupling part, the recesses being mainly formed between them, the manufacture of this coupling structure can be simplified, particularly in the case of small quantities, especially since the cams can be made of a more noble metal. If the cams are made rotatable, the proportion accounted for by the sliding friction can be greatly reduced by comparison with the rolling friction between the entrainment bodies and coupling parts on the one hand and the spring supporting rings on the other.

The cams are particularly advantageous for overload couplings of the reversing or doubleacting type.

The aforementioned reduction in the part played by the sliding friction can also be effected by the introduction, between the entrainment body and the spring supporting ring, of two thrust bearings one inside the other. The entrainment bodies, which may be balls, can thus rotate mainly about an axis parallel to the main axis of the coupling.

Furthermore, the aforementioned sliding friction can be reduced by adopting for the entrainment bodies a particular arrangement in which each of these latter consists of two roiling structures which are mounted on a cage and one inside the other. The axis of rotation of the rolling structures is preferably perpendicular to the plane of separation.

A further method of a general but nevertheless effective kind for reducing the impact energy and the drag moment at the same time is the inclusion of a damping system for the spring-back resilience by pneumatic, hydraulic, electrical or mechanical means of the type known per se.

The invention will be more readily understood by way of example from the following description of couplings in accordance therewith, reference being made to the accompanying drawings, in which Figure 1 is a schematic diagram illustrating the principle of the overload coupling in the overload position, Figure 2 is a schematic part-development of the coupling parts, Figure 3 is a schematic part-development of the coupling parts of a reversing overload coupling, in which the recesses and compartments, as well as the pressure surfaces, are of symmetrical design, Figure 4 is a part-development corresponding to Figure 3 but with differently designed recesses, compartments and pressure surfaces, Figure 5 is a longitudinal section through an overload coupling in which the coupling parts rotate within one another, the entrainment bodies being controlled by planetary gearings, Figure 6 is a longitudinal section through an overload coupling having cams on one of the coupling parts, Figure 7 is a longitudinal section through an overload coupling having two cylindrical rollers serving as an entrainment body and mounted in a cage, Figure 8 is a longitudinal section through an overload coupling having two partly spherical rollers mounted in one another and on a cage and serving as an entrainment body, Figure 9 is a schematic part-diagram of a bilaterally acting overload coupling, and Figure 10 is a longitudinal section through a bilaterally acting overload coupling having a builtin damping device for the return resilience.

Figure 1 is a schematic diagram of a coupling showing the contours of coupling parts 1 and 2, which are to be coupled together for joint rotation, by a number of entrainment members, one of which is shown at 3, and which are illustrated as balls. Although other forms of entrainment members may be used as illustrated in Figures 7 and 8, they will be referred to in relation to Figures 1 to 6, 9 and 10 for convenience as "balls". For each ball 3 there is a pressure spring 4 acting on the ball through a pressure disc 5. In the plane of separation 7 between the two coupling parts 1 and 2 there is a ball race represented by a ball bearing 6.The two parts 1 and 2 have recesses 8 and 9 respectively at intervais, successive recesses in each part 1 and 2 being connected by circulation tracks 10 and 11 respectively, on which the balls 3 run during relative rotation between the coupling parts 1 and 2. Figure 1 shows the overload condition prevailing when the two coupling parts occupy a completely "free-flow" position in relation to each other. The ball 3 is engaged by the coupling parts 1 and 2 on the prolongation surface of the circulation tracks, thus producing a supplementary supporting system which serves to stablilize the coupling under overload or "ratchet" conditions.

If the coupling parts are rotatable one inside the other, the axes I or II shown in broken lines are to be added in order to complete the schematic diagram. If the parts rotate side-by-side in the form of rings, the relevant axes are those marked Ill or IV.

The spring 4 abuts against an extension of the coupling part 1. The spring 4 may likewise abut against an extension of the coupling part 2 or against two extensions of the two coupling parts.

In Figure 2 the coupling part 1 is provided with compartments 12 which are designed as radially inward prolongations of the recesses 8, so that the angles of the contact surfaces of the recesses and compartments of the coupling part 1 are the same in the direction of rotation F. The figure again shows the coupling in the "free-flow" overload position, in which the balls 3 rest on pressure surfaces 11 a of the circulation track of the coupling part 2, shown in broken lines. The arrangement also corresponds to a unilaterally operative reversing overload coupling in which the overload torque, i.e. the torque at which relative movement between the parts 1 and 2 starts, is the same for each direction of rotation.

Figure 3 corresponds in principle to the diagram shown in Figure 2 but with the following points of difference: each compartment 12 is constructed with a contact surface 14 at an angle T to the direction of rotation F, that angle being smaller than the contact angle A of the recess 8 to the same direction of rotation. As soon as the coupling part 1 moves farther away from the position shown, i.e. when the ball 3 has left the highest point 13 of the coupling part 2, the ball, as a result of the spring force, starts to roll or slip over the ramp 1 4 into the recess 8.According to the magnitude of the angle T of the compartment and according to the friction conditions prevailing between the ball and the spring system the speed of the spherical body in relation to coupling part 1 is determined, so that the magnitude of the residual "ratchet torque" after the overload is decisively governed by the angle T. Furthermore, by reducing the rotation speed, the spherical bodies are given sufficient time to re-engage the recesses. In addition, the pressure surfaces 1 5 of the coupling part 2 are arranged to ascend in the direction of rotation, so that the effect of the impact of the balls is reduced. The number of recesses 9 of the coupling part 2 is twice as great as the number of balls 3.

Figure 4 shows an overload coupling in which the overload torques differ in the two directions of rotation, as a result of the differences in the angles of the contact surfaces 16R and 1 6L, and 17R and 1 7L, of the coupling parts 1 and 2 respectively.

Furthermore, the holding compartments 12 are designed in such a way that between them and the recesses 8 there is in each case a curved elevation with the highest point 1 8 in the direction of the spring. The highest point 1 3 of the coupling part 2 is likewise higher than point 1 8 in the direction of the spring. When the coupling part 1 moves relative to part 2 in the direction of rotation F, as a result of an overload, the balls 3 are moved into the compartments 1 2R. As a result of the further rotation of the coupling part 1 in relation with the coupling part 2 the balls are pressed or lifted in the direction of the spring by the pressure surfaces 13 on the coupling part 2 which follow up, and are then caused to engage the compartments.Accordingly a residual or ratchet torque is produced which in many applications causes a welcome acoustic or vibratory warning to be emitted. After the drive has been rendered inoperative, the spherical bodies remain in their securing compartments 12R. For the coupling to be re-engaged the coupling parts have to be rotated in the opposite direction to a distance approximately equal to one pitch division. This can be done with the coupling direct or by reversing the drive, e.g. of the coupling part 1 , the coupling part 2 being at the same time slightly braked, or by the rapid rotation of one coupling part. The securing compartments for the opposite direction of the arrow F are constructed in such a way that between the latter and the flatter contact surfaces of the recesses a straight pressure surface is provided which is parallel to the direction of rotation.Here again, the coupling cannot be reengaged when the speed of rotation is reduced.

The overload coupling in Figure 5 again consists of an outer coupling part 1 and an inner coupling part 2 with symmetrical recesses 8 and 9 as well as circulation tracks 10 and 1 The balls 3 rest on two correspondingly profiled pressure rings 20 and 21 which are situated one inside the other and on opposite sides of the plane of separation. Between the pressure disc 5 and each of the separate pressure rings 20 and 21 there is a needle thrust bearing 22 or 23. The pressure rings 20,21 which rotate one inside the other and independently of one another ensure that the balls, in the event of an overload, can rotate about an axis approximately situated in the plane of separation and parallel to the main rotation axis.

so that the motion of the balls on all pressure surfaces is mainly that of rolling, thus producing only very little friction due to heat. The superimposed movement of the balls about the main axis is likewise compensated by the thrust bearings. The cups 24 rest on the inner ring 28 of a ball bearing 28, 30 which in its turn is held in the axial direction on the coupling part 2 by means of the check nut 29. The outer ring 30 of the ball bearing is accommodated in a sleeve 31, which is likewise secured in position on the coupling part 1 by screw threading. By adjusting the check nut 29 or sleeve 31 the spring force and thus the overload torque can be varied. The spring force can be taken up by the outer and/or inner coupling part according to the adjustment of the individual screw threadings.A cage 32 is provided on the same side as the balls, with slots 33 serving to locate the spherical bodies 3. The cage also consists of a ring-like part 34 carrying a number of pins 35. Planet wheels 36 mounted on the pins 35 are driven by gear wheels 37 and 38 on the outer and inner coupling part respectively. This causes the cage to rotate at a speed dependent on the number of teeth in the gear wheels, so that the full engagement of the balls 3 in recesses 8 and 9 does not depend on the pitch, as might otherwise be the case, but on the design of the planetary gearing and on the number and pitch of the balls.

Figure 5 shows the position in which the spherical bodies press only on the circulation tracks 10 of the coupling part 1.

If the differential gearing is equipped with pairs of planet wheels, so that these or the cage rotate at a speed corresponding to the average speed of the two coupling bodies, balls 3 will always engage the next recesses after each pitch movement. In this system the coupling is provided, after the overload occurs, with a pulsating or alternating torque which is approximately equal to the overload torque. The cage 32 and the planet wheels 36 are secured in the axial direction by a plate 39 and a spring ring 40.

Figure 6 shows an overload coupling with the outer coupling part 1 containing a sequence of cams 41 defining between them recesses which can receive the balls 3 and which correspond in function to the recesses 8 of Figure 1. The cams 41 are rotatable, in order to reduce the proportion accounted for by the friction in the overload condition. The rotation axes of the cams are in this case perpendicular to the plane of separation. If necessary, the cams can be mounted in roller bearings. In order to render the overload coupling more reliable and more resistant to wear, cages 32 are provided, having suitable holes 42 for the control of the balls 3. The radii of the contact surfaces of the cams and also the recesses, compartments and pressure rings are greater than the corresponding radii of the balls, in order to compensate kinematic differences and manufacturing tolerances.

Instead of a ball, each entrainment body of the overload coupling shown in Figure 7 consists of two cylindrical rollers 43 and 44 with a spacer disc 49 mounted on a pin 46 which is secured in a cage 45. In this case the cage is subjected to the full spring force. A sliding movement between the rollers 43 and 44 and the relevant surfaces of the recesses 8 and 9 and compartments 12 is largely avoided. A further reduction of the heat generated in use can be achieved by the use of roller bearings between the rollers and the pin 46.

The design for the rollers is to be varied according to requirements, so that they are to be given different diameters, for example, and in extreme cases even constructed in the form of gear wheels.

Each entrainment body of the overload coupling shown in Figure 8 consists of part-spherical rollers 50 and 51 which are mounted one inside the other and between which a cage 52 is accommodated. This ensures that the cage does not receive the spring force.

As in the previous examples, the entrainment bodies serve as bearing structures between the coupling parts 1 and 2, so that only one further supporting system is required, even for very exacting standards of accuracy. In this case a ball bearing 53 is situated, for example, at a suitable distance from the entrainment bodies. The space between the ball bearing and the other coupling parts can be used for other purposes without difficulty, e.g. for the purpose of securing the overload coupling in the axial direction on a suitable shaft with rapid engagement, the attachment means consisting of securing balls 54, a securing disc 55 and a pressure spring 56. The securing disc can be operated through a window 57 provided in a sleeve 58, which corresponds to the sleeve 31 of Figure 5.

Figure 9 schematically illustrates the principle of a double-sided overload coupling. The coupling part 1 has parallel tracks 60 which are oblique to the direction of movement F. The coupling part 2, shown in broken lines, is likewise provided with tracks, situated along surfaces 61 and 62. The entrainment bodies (balls 3) are guided by the tracks of both coupling parts. If the coupling part 1 rotates in the direction shown by the arrow F, the entrainment bodies are loaded by the surfaces 63 and 61, so that the said entrainment bodies move in the direction shown by the arrow A in opposition to a spring force. If the coupling part 1 rotates in the opposite direction, then the entrainment bodies are subjected to a load from the surfaces 64 and 62, so that these latter move in the direction shown by the arrow B, in opposition to the force of a second spring.

Therefore, by selecting the angle of slope or the course taken by the tracks, i.e. straight or curved, and the springs concerned, the overload torques can be rendered equal or varied considerably in the two directions of rotation. In extreme cases the second spring can be made so weak that the coupling, in one direction, functions as a freerunning system.

The bilaterally acting overload coupling shown in Figure 10 is illustrated in the transmission position. The entrainment bodies 3 are situated in grooves 65 of the outer coupling part 1 and also in spiral paths 60 of coupling part 2. Cage 66 with the radial slots 67 for the entrainment bodies is displaceable in the axial direction between the outer and the inner coupling parts. When the coupling is overloaded in one direction of rotation a rubber spring 69 is subjected to force via a piston 68 until the entrainment bodies complete a full revolution in the corresponding circulation track 1 OR. If the overload coupling is subjected to a load in the other direction, the spherical bodies move in the opposite direction, so that a spring 70 is compressed, via the cage 66, until the spherical bodies perform a complete revolution in their corresponding circulation tracks 10L.The grooves 65 may also be produced by the free space between inserted cams (see cams 41 in Figure 6).

The inner coupling part 2 is secured in the axial direction, on the one hand by the piston 68 and the rubber spring 69 and on the other hand by the supporting ring 71 and the spring ring 72. The damping of the spring-back resilience of the piston 68 is effected not only by the hysteresis of the rubber spring 69 but also by inserted packing rings 73 and 74 which, on the return movement of the piston, create a vacuum inside the closed cylinder 75.

The examples shown in Figures 5 to 8 and 10 relate to overload couplings with coupling parts rotatable one inside the other. Overload couplings with coupling parts rotatable side by side can be constructed on the same principles, subject to the appropriate modifications. The teaching provided is likewise fully applicable to overload couplings in which the plane of separation is conical, i.e. of a shape intermediate between cylindrical and discoid.

Claims (19)

1. An overload coupling comprising a driving coupling part and a driven coupling part having a plane of separation therebetween and provided with recesses which face one another across the plane of separation; a number of entrainment bodies capable of entering the recesses in order to couple the coupling parts together; bias means urging the entrainment bodies towards the recesses; a circulation track on at least one of the coupling parts interconnecting successive recesses; and contacting surfaces on at least one of the coupling parts, so inclined with respect to the perpendicular to the radius of the recesses that, when an overload occurs in use, the entrainment bodies are subjected to a force component opposed to the force of the bias means and urging the entrainment bodies out of the recesses and on to the circulation tracks.

2. An overload coupling in accordance with Claim 1, in which the coupling parts have zones engaging one another in the manner of bushings and the entrainment bodies are prestressed axially by the bias means.

3. An overload coupling in accordance with Claim 1, in which the coupling parts have flange like zones facing one another across the plane of separation and the entrainment bodies are prestressed radially.

4. An overload coupling in accordance with Claim 1, in which, in one coupling part, a compartment for holding an entrainment body is provided at the end of each contact surface which forms a displacement track for the entrainment body, in the zone of the circulation track of the second coupling part.

5. An overload coupling in accordance with Claim 4, in which the recesses and/or the compartments have the same angles of contact with the entrainment bodies for both directions of rotation.

6. An overload coupling in accordance with Claim 4, in which the angles of contact of the recesses and/or the compartments with the entrainment bodies are different for the two directions of rotation.

7. An overload coupling in accordance with Claim 1, in which, on the circulation tracks the pressure surfaces in each case ascend in a straight line or in a curve in the direction of rotation of the entrainment bodies.

8. An overload coupling in accordance with Claim 4, in which the angle to the direction of rotation of the contact of the entrainment body with a recess of a coupling part that has the holding compartments is greater than the corresponding angle of the associated compartment.

9. An overload coupling in accordance with Claim 8, in which a hump-like elevation is provided between each recess and its compartment.

10. An overload coupling in accordance with Claim 1, in which the recesses are formed as guide paths along the plane of separation and that the paths of at least one coupling part are oblique to the direction of rotation.

11. An overload coupling in accordance with Claim 1, in which the entrainment bodies are to some extent located, in a certain pitch or in a certain plane, by means of a cage.

12. An overload coupling in accordance with Claim 11, in which the cage has drive means engaged with both coupling structures and including planet wheels of a planetary gearing.

13. An overload coupling in accordance with Claim 1, in which the number of recesses of a coupling part is equal to the number of entrainment bodies or to a whole multiple thereof.

14. An overload coupling in accordance with Claim 1, in which the entrainment bodies are distributed over the periphery at an unequal pitch.

15. An overload coupling in accordance with Claim 1, in which the recesses of one coupling part are formed by the gaps between rigid or rotatable cams on the periphery of that coupling part.

1 6. An overload coupling in accordance with Claim 2, in which there are two thrust bearings engaging each other between the entrainment bodies and the springs.

17. An overload coupling in accordance with Claims 1 or 11, in which each entrainment body consists of two rollers and that the rollers are mounted on one inside the other and on a cage.

18. An overload coupling in accordance with Claim 1, in which damping means is provided, in the known manner, for the bias means.

19. An overload coupling substantially as herein described with reference to the accompanying drawings.