GB2403516A

GB2403516A - Torque limiting coupling with predetermined re-engagement positions

Info

Publication number: GB2403516A
Application number: GB0412312A
Authority: GB
Inventors: Klaus Kampf
Original assignee: GKN Walterscheid GmbH
Current assignee: Walterscheid GmbH
Priority date: 2003-07-01
Filing date: 2004-06-03
Publication date: 2005-01-05
Anticipated expiration: 2024-06-03
Also published as: DE10329809B4; GB0412312D0; ITMI20041257A1; FR2857069A1; DE10329809A1; FR2857069B1; GB2403516B

Abstract

A torque limiting coupling, for an agricultural implement, comprises a plurality of driving dogs (11, fig 3),12 and 13 mounted in guiding recesses (14), 15, 16 in a coupling hub 1. The driving dogs (11), 12, 13 are radially biassed into engagement with recesses (5), 6, 7 by switching elements 20, 21 that are biassed by springs 22, 23. Driving dogs 12, 13 comprise driving portions 18, 19 having different axial positions which can only engage with corresponding recesses (5), 6, 7 at predetermined re-engagement positions. The driving dogs (11) have axially full length driving portions (17) which cannot engage recesses 6, 7 but can engage full axial length recesses (5) at predetermined re-engagement positions. In the first embodiment the axial position of the recesses (5), 6, 7 are different while in another embodiment the recesses (5), 6, 7 are narrower in a circumferential direction and the driving portions (17), 18, 19 are dimensioned accordingly.

Description

Coupling for Torque Limiting

Description of Invention

The invention relates to a coupling for torque limiting, having a coupling hub and a coupling sleeve which is arranged around the coupling hub so as to be rotatable around an axis of rotation. The coupling sleeve is provided with recesses and the coupling hub with driving dogs, with the driving dogs being guided for movement relative to the coupling hub between a radially outer coupled position in which they engage the recesses for the purpose of transmitting torque between the coupling hub and the coupling sleeve, and a radially inner uncoupled position. The driving dogs are loaded by a switching element to enable same to assume their coupled position, with the switching element permitting the driving dogs to be switched into their uncoupled position when a predetermined torque between the coupling hub and the coupling sleeve is exceeded.

Such a torque limiting coupling is known from DE 197 15 269 C1, but the disadvantage is that after uncoupling the coupling can be reconnected in several rotational positions. However, in some circumstances, particularly when the coupling is used for driving some agricultural implements, it is necessary for the coupling to be reconnectable only in one rotational position or in several predetermined rotational positions.

For this purpose, EP 918954 B1 proposes a coupling which also comprises a coupling hub and a coupling sleeve, with the coupling sleeve being arranged around the coupling hub so as to be rotatable around an axis of rotation and comprising a plurality of recesses. Driving dogs are radially adjustably guided in the coupling hub between a coupled position and an uncoupled position. Each individual driving dog is loaded by a switching element to enable same to assume a coupled position in which the driving dogs engage the recesses, with the switching element permitting the respective driving dog to be transferred into the uncoupled position if a certain torque between the coupling hub and the coupling sleeve is exceeded.

To ensure that reconnection of the coupling can only be effected in a certain rotational position of the coupling hub relative to the coupling sleeve, the recesses are provided with pins which are arranged so as to be flush with an inner face of the coupling sleeve. In each recess, the pins are provided in a different position, with the respective driving dogs comprising recesses corresponding in position to the pins. This means that each driving dog can correctly engage only one recess. However, the disadvantage here is the complicated design and the fact that all the driving dogs have to be designed differently.

It is the object of the present invention to provide a coupling which comprises a plurality of driving dogs which are loaded jointly by at least one switching element towards the coupled position, wherein it is ensured by simple means that reconnection is only possible in certain rotational positions.

In accordance with the invention, the objective is achieved by providing a coupling for torque transmitting purposes, comprising a coupling hub, a coupling sleeve arranged around the coupling hub so as to be rotatable around an axis of rotation, at least one first recess in the coupling sleeve, at least one first driving dog which is guided for movement relative to the coupling hub between a radially outer coupled position for transmitting torque between the coupling hub and the coupling sleeve and a radially inner uncoupled position and which, in the coupled position, by means of a first driving portion, engages a first recess, at least one second recess in the coupling sleeve, at least one second driving dog which is guided for movement relative to the coupling hub between a radially outer coupled position for transmitting torque between the coupling hub and the coupling sleeve and a radially inner uncoupled position and which, in the coupled position, by means of a second driving portion, engages a second recess, a first switching element which is axially force-loaded against first switching faces of the driving dogs and loads the driving dogs to enable same to assume their coupled position and, if a predetermined torque between the coupling hub and the coupling sleeve is exceeded, permits the driving dogs to be switched into their uncoupled position, wherein the at least one first recess is designed in such a way that only a first driving dog is able to engage same, and/or the at least one second recess is designed in such a way that only a second driving dog is able to engage same.

In view of the fact that only two different shapes of recesses and driving dogs have to be provided, it is possible to provide the recesses and driving members as standard elements. For example, the coupling can comprise a plurality of first recesses and a plurality of first driving dogs which are designed to correspond to one another. Furthermore, there can be provided a second recess and a second driving dog which deviate from the design of the first recesses and of the first driving dogs. The production complications are therefore reduced considerably.

As all the driving dogs are loaded jointly by at least one switching element to enable same to assume their coupled position and as the first driving dogs cannot engage the second recesses and/or the second driving dogs cannot engage the first recesses, it is ensured that in all the rotational positions of the coupling hub relative to the coupling sleeve, which rotational positions deviate from the switching position, at least one driving dog cannot engage a recess, with the switching element, in consequence, being prevented by said driving dog of transferring the remaining driving dogs into the recesses.

To ensure that only a second driving dogs can engage the or each second recess, it is proposed that the recesses are provided in an inner face of the S coupling sleeve so as to start from same and form an aperture in said inner face, that the aperture of the at least one first recess is greater than the aperture of the at least one second recess and that the driving portions are designed so as to correspond to the respective recesses.

In a preferred embodiment, the recesses are provided in the form of grooves which extend parallel to the axis of rotation and which each afford a first torque transmitting face. Accordingly, the driving portions are provided in the form of projections which extend parallel to the axis of rotation and each afford a second torque transmitting face. In the coupled position of the driving portions, the first torque transmitting faces come into contact with the second torque transmitting faces, so that torque can be transmitted between the coupling hub and the coupling sleeve.

The at least one first recess and the at least one second recess can comprise different lengths in the axial direction.

This can be achieved in that the coupling sleeve may comprise a sleeve portion which is arranged around the coupling hub, and in whose inner face the recesses are provided, that the at least one first recess extends over the entire axial length of the sleeve portion and that the at least one second recess starts from a first axial longitudinal end of the sleeve portion and extends over part of the length of the sleeve.

It can also be proposed that the at least one first recess, in the circumferential direction, is narrower than the at least one second recess.

Furthermore, there can be provided at least one third recess in the coupling sleeve. Accordingly, there would then be provided at least one third driving dog which is movably guided relative to the coupling hub between a radially outer coupled position for transmitting torque between the coupling hub and the coupling sleeve and a radially inner uncoupled position and which, in the coupled position, by means of a third driving portion, engages a third recess, with the at least one third recess being designed in such a way that no second driving dog is able to engage same.

According to a preferred embodiment it is proposed that there may be provided a second recess, a second driving dog, a third recess and a third driving dog, with the second recess and the third recess as well as the second driving dog and the third driving dog being offset relative to one another by 180 .

It is thus ensured that in the rotational positions in which coupling is prevented, two opposed driving dogs cannot engage the second and third recess, so that the switching element is supported in two diametrically opposed positions on the driving dogs and prevented from transferring the remaining driving dogs into the coupled position. There are thus achieved good supporting conditions which prevent the switching element from tilting.

With reference to a coupling with third recesses and third driving dogs it is proposed that the recesses may be provided in the form of grooves which extend parallel to the axis of rotation and which each afford a first torque transmitting face, the driving portions may be provided in the form of projections which extend parallel to the axis of rotation and which each afford a second torque transmitting face, the coupling sleeve may comprise a sleeve portion which is arranged around the coupling hub and in whose inner face the recesses are provided, the at least one first recess may extend over the entire axial length of the sleeve portion, the at least one second recess may start from a first axial longitudinal end of the sleeve portion and extends over part of the length of the sleeve portion and the at least one third recess may start from a second axial longitudinal end of the sleeve portion, which second end faces away from the first axial longitudinal end and extends over part of the length of the sleeve portion.

The first switching element can be provided in the form of a ring which is arranged around the coupling sleeve and which is axially loaded by first spring means towards the driving dogs.

Furthermore, there can be provided a second switching element which is axially force-loaded against second switching faces of the driving dogs and loads the driving dogs to enable same to assume their coupled position, and which, if a predetermined torque between the coupling hub and the coupling sleeve is exceeded, permits the driving dogs to be transferred into their uncoupled position and which is arranged at a driving dog end which faces away from the first switching element.

Three preferred embodiments will be explained in greater detail with reference to the drawings wherein: Figure 1 is a cross-section through a first embodiment of a coupling according to the invention, in the coupled position; Figure 2 is a longitudinal section through the coupling according to Figure 1 along sectional line II-II; Figure 3 is a longitudinal section through the coupling according to Figure 1 along sectional line III-III; Figure 4 is a cross-section through the coupling according to Figure 1 in the uncoupled position; Figure 5 is a longitudinal section through the coupling according to Figure 4 along the sectional line V-V Figure 6 is a longitudinal section through the coupling according to Figure 4 along sectional line VI-VI; Figure 7 is a cross-section through the coupling according to Figure 1 in a further rotational position; Figure 8 is a longitudinal section through the coupling according to Figure 7 along sectional line VII-VII; Figure 9 is a cross-section through a second embodiment of coupling according to the invention in the coupled position; Figure 10 is a cross-section through the coupling according to Figure 9 in the uncoupled position; Figure 11 is a cross-section through a third embodiment of coupling according to the invention, in the coupled position; Figure 12 shows a tractor with an attached implement which is driven, with an inventive coupling being connected between the tractor and the implement.

Figures 1 to 8 show a first embodiment of coupling in different views and with the driving dogs being in different positions; they will be described jointly below.

The coupling comprises a coupling hub 1 and a coupling sleeve 2 arranged around the latter, with the coupling sleeve 2 being rotatably supported around an axis of rotation 3. The coupling sleeve 2 comprises an inner face 4 which is arranged coaxially relative to the axis of rotation 3. The inner face 4 is provided with four first recesses 5, one second recess 6 and one third recess 7.

The recesses 5, 6, 7 are provided in the form of grooves and extend parallel to the axis of rotation 3. Furthermore, the recesses 5, 6, 7 start from the inner face 4 and together with same, each form an aperture 8, 9, 10.

In accordance with the recesses 5, 6, 7, four first driving dogs 11, one second driving dog 12 and one third driving dog 13 are arranged in the coupling hub 1 and are movably guided in four guiding recesses 14, one second guiding recess 15 and one third guiding recess 16, respectively, between a radially outer coupled position and a radially inner uncoupled position. The first driving dogs 11 comprise a first driving portion 17 which is arranged on the radial outside of the first driving dogs 11 and faces the inner face 4. Accordingly, the second driving dog 12 comprises a second driving portion 18 and the third driving dog 13 a third driving portion 19. In their coupled position (Figures 1, 2 and 3), the driving dogs 11, 12, 13 radially pass with their driving portions 17, 18, 19 through the apertures 8, 9, 10 into the recesses 5, 6, 7, so that the transmission of torque between the coupling hub 1 and the coupling sleeve 2 becomes possible.

A first switching element 20 and a second switching element 21 which are each provided in the form of a ring are arranged around the coupling hub 1.

The first switching element 20 is axially supported by first spring means 22 against the driving dogs 11, 12, 13. At an end of the driving dogs 11, 12, 13 which faces away from the first switching element 20, the second switching element 21 is axially supported by second spring means 23 against the driving dogs 11, 12, 13. Because the switching elements 20, 21 are supported against the driving dogs 11, 12, 13, the latter are force-loaded to enable same to assume their coupled position.

The coupling sleeve 2 comprises a first coupling sleeve element 24, a second coupling sleeve element 25 and a sleeve portion 26. The sleeve portion 26 is cylindrical in shape and arranged around the axis of rotation 3. The first coupling sleeve element 24 and the second coupling sleeve element 25 are connected to opposed axial ends of the sleeve portion 26. The first coupling sleeve element 24 comprises a connecting portion 27 with a bore 28. The bore 28 is provided with longitudinal teeth 29 to be able to connect the coupling sleeve 2 to a first shaft in a rotationally fast way.

The coupling hub 1 comprises a through-bore 32 which is arranged coaxially relative to the bore 28 of the coupling sleeve 2. In the through-bore 32, there are also arranged longitudinal teeth 33, for connecting the coupling hub 1 to a second shaft in a rotationally fast way.

The sleeve portion 26 affords the inner face 4 of the coupling sleeve 2 in which there are provided the recesses 5, 6, 7. In the cross-sections according to Figures 1, 4 and 7, all the recesses 5, 6, 7 have the same shape and will be explained in greater detail with reference to the second recess 6.

The second recess 6 forms a first torque transmitting face 34 which, in the coupled position of the second driving dog 12, rests against a second torque transmitting face 35 of the second driving dog 12. The second torque transmitting face 35 is formed by the second driving portion 18 of the second driving dog 12. In the cross-sectional view, the first torque transmitting face 34 encloses an angle with a radius extending centrally through the second recess 6, which angle is open towards the axis of rotation 3. It is thus ensured that, when a predetermined torque is exceeded, the inclined torque transmitting faces 34, push the driving dogs 11, 12 radially inwards out of the recesses 5, 6, 7 until the coupling hub 1 is rotatable relative to the coupling sleeve 2.

Furthermore, the second recess 6 forms a first guiding face 36 which, in the coupled position of the second driving dog 12, rests against a second guiding face 37. The first guiding face 36 also encloses an angle with a radius extending centrally through the second recess 6, which angle is open towards the axis of rotation 3, with said latter angle being greater than the angle enclosed between the first torque transmitting face 34 and the radius. It is thus ensured that a greater torque is transmitted in one direction of rotation than in the other direction of rotation. The guiding faces 36, 37 do not primarily have the function of transmitting torque; their purpose is to facilitate the engagement of the driving portions 17, 18, 19 of the driving dogs 11, 12, 13 in the recesses 5,6,7.

To ensure that the second recess 6 can only be engaged by the second driving dog 12 and the third recess only by the third driving dog 13, in the first embodiment of coupling shown in Figures 1 to 8, if viewed in the axial direction, the recesses 5, 6, 7 and the driving portions 17, 18, 19 are of different lengths. The first recesses 5 extend along the entire axial length of the sleeve portion 26 (Figures 3 and 5). This means that the first recesses 5 start from a first longitudinal end 38 to which the coupling sleeve element 24 is secured and extend as far as a second longitudinal end 39 to which the second coupling sleeve element 25 is secured. The second recess 6 starts from the first longitudinal end 38 and extends only over part of the length of the sleeve portion 26 (Figures 2, 6 and 8). This means that the second recess 6 ends in front of the second longitudinal end 39. The second driving portion 18 of the S second driving dog 12 is designed accordingly. It does not extend over the entire width of the second driving dog 12, which width extends parallel to the axis of rotation 3; at its end facing the second longitudinal end 39, the driving dog comprises a recess 40.

The third recess 7 starts from the second longitudinal end 39 of the lO sleeve portion 26 and also extends along only part of the length of the sleeve portion 26. This means that the third recess 7 ends in front of the second longitudinal end 39. The third driving dog 13 comprises a recess 41 at the end facing the first longitudinal end 3 8.

As the second driving portion 18 and the third driving portion 19 are shorter than the first recesses 5, they are able to engage the first recesses (Figure 5). However, the second driving dog 12 cannot engage the third recess 7 by means of its second driving portion 18 because the second driving dog 12 is not provided with a recess at the end at which the third recess 7 does not continue (Figure 8). This applies to the third and to the first driving dog 13, 11 (Figure 6). Figures 7 and 8 show the rotational position in which the second driving dog 12 is arranged opposite the third recess and the third driving portion 13 opposite the second recess 6. In consequence, in each of the rotational positions of the coupling hub 1 relative to the coupling sleeve 2, which rotational positions deviate from that according to Figures 1 to 3, it is ensured that no driving dog is able to engage the second recess 6 and the third recess 7. This means that in these regions the switching elements 20, 31 are held in their respective positions and cannot transfer the remaining driving dog 11 into the recesses 5.

The two switching elements 20, 21 are identical in design and will be described in greater detail below with reference to the first switching element and the third driving dog 13.

In the coupled position as illustrated in Figures 2 and 3, the first switching element 20, by means of its first supporting element 43, rests against a first switching face 45 of the third driving dog 13. In the uncoupled position as shown in Figure 4, the first switching element 20, by means of its second supporting face 44, rests against a second switching face 46 of the third driving dog 13.

In the base region, i.e. in the radially inner region, the third driving dog 13 comprises a first switching face 45 which faces the first switching element and which extends in a planar way with reference to the axis of rotation 3, i.e. it encloses a small angle with the axis of rotation 3. As all the remaining driving dogs 11, 12, 13 are identical with reference to the switching faces 45, 46, all the first switching faces 45 enclose a small angle between each other.

The first supporting face 43 of the first switching element 20 is arranged at the same angle.

The first supporting face 43, towards the third driving portion 19, is followed by a second switching face 46 which extends at a steeper angle relative to the axis of rotation 3. This means that the second switching faces 46 of all the driving dogs 11, 12, 13, between one another, enclose a large angle.

The second supporting face 44 is arranged at a corresponding angle and follows the first supporting face 43 towards the axis of rotation.

The different angles of the first switching face 45 and the second switching face 46 ensure that, in the coupled position, first a high radial force has to be transmitted by the driving dogs 11, 12, 13 to the switching rings 20, 21 until these can be axially displaced against the spring force of the spring means 22, 23. The first switching faces 45 of the driving dogs 11, 12, 13 slide on the first supporting faces 43 of the switching elements 20, 21 until the second switching faces 46 come to rest against the second supporting faces 44.

As these are arranged more steeply relative to the axis of rotation 3, thereafter a lower force is sufficient to move the driving dogs 11, 12, 13 inwardly out of the recesses 5, 6, 7. Because a lower force is required in the uncoupled position in order to hold the driving dogs 11, 12, 13 in the uncoupled position, it is ensured that the speed differential between the coupling hub 1 and the coupling sleeve 2 has to be considerably reduced until the driving dogs 11, 12, 13 can be pushed back into the recesses 5, 6, 7.

Figures 9 and 10 show a second embodiment of a coupling whose functioning mode corresponds to that of the coupling according to Figures 1 to 8. Identical components have been given reference numbers which are increased by the value 100 and which are described in connection with Figures 1 to 8.

The second embodiment of a coupling according to Figures 9 and 10 also comprises four first driving dogs 111 as well as first recesses 105, a second driving dog 112 as well as a second recess 106 and a third driving dog 113 as well as a third recess 107. In the circumferential direction, the first recesses are narrower than the second recess 106 and the third recess 107. The driving portions 117, 118, 119 are designed accordingly. It is thus ensured that the first recesses 105 can only be engaged by the first driving portions 117 of the first driving dogs 111. As can be seen in Figure 10, the second driving portion 118 and the third driving portion 119 cannot engage the first recesses 105, so that the coupling is held in its uncoupled position.

In the axial direction, the recesses 105, 106, 107 can be of identical lengths. It is also possible for the length of the recesses 105, 106, 107 and of the respective driving dogs 117, 118, 119 to be formed in accordance with the first embodiment of the coupling according to Figures 1 to 8. This means that the second recess 106 and the second driving portion 118 can be shorter than the first recess 105 and the first driving portion 117. Equally, the third driving portion 110 and the third recess 107 can be correspondingly shorter. It would therefore be ensured in addition that the first driving portions 117 of the first driving dogs 111 cannot engage the second recess 106 or the third recess 107 which are wider in the circumferential direction.

Figure 11 shows a third embodiment of an inventive coupling wherein the first driving dogs 211 have a smaller diameter than the second driving dogs 212 and the third driving dogs 213. This means that the first driving portions 217 are shorter than in the previous embodiments. The second driving dog 212 and the third driving dog 213 are designed in accordance with the driving dogs in the first embodiment, i.e. they each comprise a recess towards the longitudinal end of the coupling sleeve.

Furthermore, the first recesses, in the circumferential direction, are narrower than the second recess 206 and the third recess 207.

As the driving portions 218, 219 of the first driving dog 211 and of the second driving dog 212, in the circumferential direction, are wider than the first recesses 205, they cannot engage the first recesses 205. Furthermore, because of the opposed recesses 240, 341, the driving portions 218, 219 of the second driving dog 212 and of the third driving dog 213 cannot engage the respective other recess 206, 207. This means that in this embodiment, too, reconnection can only take place after a rotation of 360 .

Figure 12 shows a tractor 47 with an attached implement 48. A power takeoff shaft 49 of the tractor 47 serves to drive the implement 48 by means of a driveshaft 50. The driveshaft 50 comprises a coupling 51 which can be designed in accordance with one of the previously described embodiments and which is arranged towards the power take-off-shaft. Furthermore, the driveshaft 50 is connected to the driveshaft 52 at the implement end. The coupling 51 serves to interrupt the drive if, for example due to any blocking in the region of the tools of the implement 48, an overload occurs. The power take-off shaft 49 can continue to rotate whereas the transmission of torque to the driveshaft 50 is interrupted.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A coupling for torque limiting, comprising a coupling hub, a coupling sleeve arranged around the coupling hub so as to be rotatable around an axis of rotation, at least one first recess in the coupling sleeve, at least one first driving dog which is guided for movement relative to the coupling hub between a radially outer coupled position for transmitting torque between the coupling hub and the coupling sleeve and a radially inner uncoupled position and which, in the coupled position, by means of a first driving portion, engages a first recess, at least one second recess in the coupling sleeve, at least one second driving dog which is guided for movement relative to the coupling hub between a radially outer coupled position for transmitting torque between the coupling hub and the coupling sleeve and a radially inner uncoupled position and which, in the coupled position, by means of a second driving portion, engages a second recess, a first switching element which is axially force-loaded against first switching faces of the driving dogs and loads the driving dogs to enable same to assume their coupled position and, if a predetermined torque between the coupling hub and the coupling sleeve is exceeded, permits the driving dogs to be switched into their uncoupled position, wherein the at least one first recess is designed in such a way that only a first driving dog is able to engage same, and/or the at least one second recess is designed in such a way that only a second driving dog is able to engage same.

2. A coupling according to Claim 1, wherein the recesses are in the form of grooves which extend parallel to the axis of rotation and which each afford a first torque transmitting face, and that the driving portions are provided in the form of projections which extend parallel to the axis of rotation and which each form a second torque transmitting face.

3. A coupling according to Claim 2, wherein the at least one first recess and the at least one second recess are of different lengths in the axial direction.

4. A coupling according to Claim 3, wherein the coupling sleeve comprises a sleeve portion which is arranged around the coupling hub and in whose inner face the recesses are provided, the at least one first recess extends over the entire axial length of the sleeve portion, and the at least one second recess starts from a first axial longitudinal end of the sleeve portion and extends over part of the length of the sleeve portion.

S. A coupling according to any one of Claims 1 to 4, wherein the at least one first recess is narrower in the circumferential direction than the at least one second recess.

6. A coupling according to any one of Claims 1 to 5, wherein there is provided at least one third recess in the coupling sleeve, there is provided at least one third driving dog which is guided for movement relative to the coupling hub between a radial outer coupled position for transmitting torque between the coupling hub and the coupling sleeve and a radially inner uncoupled position and, in the coupled position, by means of a driving portion, engages a third recess, and the at least one third recess is designed in such a way that no second driving dog is able to engage same.

7. A coupling according to Claim 6, wherein there are provided a second recess, a second driving dog, a third recess and a third driving dog, wherein the second recess and the third recess as well as the second driving dog and the third driving dog are arranged so as to be angularly offset relative to one another by 180 .

8. A coupling according to Claim 6 or 7, wherein the recesses are in the form of grooves which extend parallel to the axis of rotation and which each form a first torque transmitting face, the driving portions are in the form of projections which extend parallel to the axis of rotation and which each form a second torque transmitting face, the coupling sleeve comprises a sleeve portion which is arranged around the coupling hub and in whose inner face recesses are formed, the at least one first recess extends over the entire axial length of the sleeve portion, the at least one second recess starts from an axial first longitudinal end of the sleeve portion and extends along part of the length of the sleeve portion, and that the at least one third recess starts from an axial second longitudinal end of the sleeve portion, which end faces away from the axial first longitudinal end and extends over part of the length of the sleeve portion.

9. A coupling according to any one of Claims 1 to 8, wherein the first switching element is in the form of a ring which is arranged around the coupling sleeve and is axially loaded by first spring means towards the driving dogs.

10. A coupling according to any one of Claims 1 to 9, wherein there is provided a second switching element which is axially force-loaded against second switching faces of the driving dogs and loads the driving dogs to enable same to assume their coupled position and which, when a predetermined torque between the coupling hub and the coupling sleeve is exceeded, allows the driving dogs to be switched into their uncoupled position and which is arranged at an end of the driving dogs which faces away from the first switching element.

1 1. A coupling according to Claim 10, wherein the second switching element is in the form of a ring which is arranged around the coupling sleeve and is axially loaded by second spring means towards the driving dogs.

12. A coupling substantially as hereinbefore described with reference to the accompanying drawings.

13. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.