GB2187820A - Shaft coupling for hookes joint - Google Patents

Abstract

A quickly connectable and disconnectable shaft coupling comprises a first element (10) and a second element (11), with inter-engageable dogs (15, 16) for torque transmission. The element (10) supports an angularly movable holding member (17) in the form of a sleeve provided at its end with circumferentially spaced radially extending teeth (28) which are able to pass between complementary teeth (30) provided in the second element (11). Thereafter the holding element (17) is movable angularly within the element (10) by a worm gear drive (22), to draw the elements together axially and provide a secure connection. In a further embodiment, the holding member may be provided with circumferentially spaced rollers (67) mounted on radially outwardly extending trunnions, instead of the teeth (28). <IMAGE>

Description

SPECIFICATION Shaft coupling This invention relates to a coupling for establishing a rapidly disconnectable torque transmitting connection between two shafts or other rotary elements. The coupling comprises a first element and a second element, which are provided with interengaging formations for torque transmission, there being provided means for holding the elements together against axial separation.

One embodiment of such a coupling for connecting two shafts is disclosed in DE-PS 1202074. In that coupling, the two elements have undercut annular grooves which are engaged, in two diametrically opposite regions, by tensioning members movable radially inwardly or outwardly at the same time as one another by means of a common transverse spindle having left-handed and right-handed screw threads. This tensioning device, for holding the elements together against axial separation, has a disadvantage in that the tensioning members only operate at the two diametrically opposed regions, and impose high radial forces on the elements of the coupling.

In addition, there is no safeguard against unintentional loosening of the screw threaded spindle under vibration in use, giving the possibility of accidental disconnection of the coupling.

It is therefore the object of the present invention to provide a shaft coupling which is rapidly disconnectable when required, and yet wherein unintentional disconnection is impossible.

According to the present invention, we provide a coupling assembly comprising a first element and a second element, interengaging formations on said elements for torque transmission about a common axis and tensioning means for holding said elements together against axial separation, said tensioning means comprising:: a holding member, supported by said first element for angular movement relative thereto about said axis and having a number of circumferentially spaced, radially extending, tensioning formations; a number of complementary tensioning formations on said second element, extending in the radially opposite direction to the first said tensioning formations and circumferentially spaced on said second element such that said first tensioning formations can pass axially there between, whereafter opposed tensioning faces of said first and complementary tensioning formations are engagable by angular movement of said holding member; the tensioning faces of at least one of said numbers of tensioning formations comprising portions of a multiple start helical screw thread;; a part of said holding member having circumferential worm wheel teeth and said first element having a chordally mounted worm element engaged therewith, for effecting said angular movement of said holding member.

By arranging the tensioning faces to form parts of a multiple start helical screw thread, it is ensured that, apart from tolerance errors, all the engaged tensioning formations take part in the tensioning process of holding the first and second elements together against axial separation. If the pitch of the notional screw thread is sufficiently small, substantially only axial forces arise between the two elements.

Further, such a small pitch, together with the worm drive for the holding member, means that the holding member is not liable to turn unintentionally and permit disconnection of the coupling in use.

The first element may be provided with a radially movable indicator element, spring biased into engagement with a cam formation on the holding member, so that the radial position of the indicator element shows whether the tensioning formations of the holding member are in their position in which they can pass axially between the formations of the second element.

The advantage of this feature is that it is easier to look at the indicator element, eg. a pin arranged to project outwqrdly of a circumferential surface of the first element, than it is to look at the tensioning formations to see whether the coupling is in the correct condition for it to be connected.

The tensioning formations on the holding member may comprise rollers supported, possibly on roller bearings, on journals extending radially outwardly from the holding member.

The holding member and worm element may each be supported by rolling element bearings, so that tensioning between the two elements of the coupling is very easily carried out.

However, it may then be necessary to provide the worm element with locking means to prevent it turning, thereby to prevent accidental disconnection of the coupling. Such locking means is not absolutely and invariably necessary, however, because the nature of a worm drive is such that the worm element normally cannot be driven by the worm wheel.

The invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a longitudinal section through one embodiment of coupling according to the invention; Figure 2 is a section as Figure 1, but with the two elements of the coupling disconnected from one another; Figure 3 is a transverse section through the coupling of Figure 2; Figure 4 is a transverse section through a further part of the coupling, showing two op erative conditions; Figure 5 is a longitudinal section through a further embodiment of coupling according to the invention; Figure 6 is a longitudinal section through yet a further embodiment of coupling according to the invention; Figure 7 is a composite transverse section through the coupling of Figure 6.

Referring firstly to Figures 1-4 of the drawings there is shown a coupling assembly which provides a torque transmitting connection between a first element 10 and a second element 11. The first element 10 is in the form of a yoke member of a Hookes universal joint, having spaced parallel axially extending limbs 12 with aligned appertures for receiving bearing cups to support, in known manner, a Hookes joint cross member. The second element 11 is in the form of a sleeve having a central aperture 13 for receiving an end part, indicated in outline at 14, of a drive shaft.

Although not illustrated the aperture 13 and drive shaft end portion 14 would be splined for torque transmission.

The first and second elements 10, 11 have formations for torque transmission therebetween. These are in the form of circumferentially spaced dogs 15 on element 10, engagable in recesses in the element 11, and dogs 16 on element 11 engagable with recesses in the element 10.

Inside the element 10, there is supported, for angular movement about an axis which is the rotary axis of the element 10 in use, a holding member in the form of a sleeve 17.

The sleeve 17 is retained in the element 10 by a washer 18 and circlip 19 so that the sleeve cannot move axially relative to the element 10. A circumferentially extending region 20 of the sleeve 1 7 within the element 10 is toothed as a worm wheel (indicated at 21 in Figure 4), and meshes with a worm gear 22 disposed in a recess 23 extending chordally of the element 10. The worm gear 22 is on a shaft 24 supported in bearing assemblies 25 plugging the ends of recess 23, the shaft 24 having squared ends 26 which are accessible to a suitable key for turning the shaft and worm gear 22, thereby effecting angular movement of the sleeve 17 relative to the element 10.

The sleeve 17 has an end portion 27 which protrudes from the element 10 towards the element 11 and is provided with three circumferentially spaced radially outwardly extending tensioning formations in the form of teeth 28.

Each tooth 28 has a rear surface, facing element 10, which is helically inclined as indicated at 29, each surface 29 forming a respective part of a relatively shallow pitched multi-start screw thread. Viewed axially, each tooth 28 is of part annular configuration.

The element 11 is provided, at its end facing the element 10, with three radially inwardly extending teeth 30 which are disposed at a circumferential spacing corresponding to the teeth 28, so that the teeth 28 are able to pass axially between the teeth 30. Teeth 30 have rear surfaces 38, facing the hollow interior of element 11, which may be helically inclined as are the opposing rear surfaces 29 of teeth 28.

In order to establish the torque transmitting and axially secure coupling between the elements 10, 11, therefore, the sleeve 17 must first be set in the angular position relative to element 10 at which teeth 28 can pass axially between the teeth 30, so that dogs 15, 16 can be engaged for torque transmission.

Thereafter, sleeve 17 is moved angularly by use of a suitable key on either of the shaft ends 26, turning the sleeve by way of worm gear 22 so that the teeth 28 move behind the teeth 30 and their complementary helical surfaces 29, 30 engage with one another to draw the elements 10, 11 firmly together.

When the connection is thus established, the relatively shallow helical angle of the engaging surfaces of teeth 28, 30, and the worm gear operation of sleeve 17, together prevent the sleeve 17 moving under vibration in use. Thereby accidental disconnection of the coupling is prevented.

To provide an indication of the angular position of sleeve 17 relative to element 10, the element 10 is provided with a radially extending recess 31 in which is disposed an indicator pin 32. The indicator pin 32 is retained within the recess 31 by a screwed-in plug 33, and a compression spring 34 acts between the plug 33 and an abutment flange 35 on the pin, to bias the latter radially inwardly to a limit position determined by abutment of the flange 35 with a step in the recess 31. At this position, a nose portion 36 of the pin projects inwardly to the region 20 of sleeve 1 7 provided with the worm wheel gear toothing, which region is provided with cam formations 37 engagable with the nose 36 of the indicator pin. The cam formations 37 are preferably arranged so that, when the sleeve 17 is in the angular position wherein teeth 28 can pass between teeth 30, the pin 32 is caused to stand proud of the surface of element 10.

Thereby a ready indication of the condition of the coupling is provided, without having to examine carefully the teeth 28. When the coupling has been safely connected by angular movement of the sleeve 17, the head of indicator pin 32 lies flush with the surface of element 10.

In Figure 4 of the drawings, the left hand side shows diagramatically the position wherein sleeve 1 7 is disposed to enable connection and disconnection of the coupling, with the indicator pin 32 protruding from the element 10. The right hand side shows the condition when the coupling is connected, with pin 32 lying flush with the surface of element 10.

Referring now to Figure 5 of the drawings, this shows a coupling whose parts which operate to establish a connection are identical to those of the embodiment of Figures 1-4.

Therefore such parts will not be further described. In this embodiment, however, the first and second elements of the coupling, corresponding to the elements 10, 11, are provided with flanges 40, 41 respectively. The flanges have circumferentially spaced apertures for receiving bolts for connection to any appropriate shaft parts or rotary members between which the quickly detachable torque transmitting connection is required.

Referring now to Figures 6 and 7 of the drawings, the coupling there illustrated is similar in principle to those of Figures 1-5 and therefore only the significant features of difference will be described in detail. Broadly, the coupling comprises a first element 50 and second element 51, which have annular connection surfaces 52, 53 to which drive flanges on shafts or other rotary elements can be connected. The elements 50, 51 have interengaging torque transmitting dogs 54, 55, the element 51 having a collar 56 which covers the region of the interengaging dogs to exclude dirt once the connection is made. Element 50 supports a sleeve 57, moveable angularly by a worm drive arrangement indicated generally at 58 in Figure 6. Element 50 also has an indicator pin assembly 59.

Sleeve 57 is supported relative to element 50 for angular movement, by angular contact ball bearings 60. Shaft 61 of the worm gear drive arrangement for rotating sleeve 57 is supported in needle roller bearing assemblies 62 in its chordal recess 63 in element 57. A key 64 is indicated diagramatically, engaged with a squared end portion of shaft 61.

Instead of teeth 28, sleeve 57 has an end portion 65 provided with three radially extending trunnions on which are supported, with the intermediary of rolling element bearings, rollers 67. Element 51 has three circumferentially spaced radially inwardly extending tensioning formations in the form of teeth 68 between which the rollers 67 are able to pass axially when the sleeve 57 is in the appropriate angular position relative to element 50, and the teeth 68 have rear surfaces 69 which form helical portions of a notional multi-start fine pitched screw thread. Therefore, after the rollers 67 have been passed axially between the teeth 68, angular movement of sleeve 57 will cause the rollers to engage the rear surfaces 69 of the teeth 68 and, because of the helical inclination thereof, draw the elements 50, 51 together and hold them firmly against axial separation.

In this embodiment, because of the support of the sleeve 57, worm gear shaft 61, and rollers 67 by rolling element bearings, there is not as much friction as in the embodiment of Figures 1-4. Therefore, under vibration in use and despite the normal irreversibility of a worm drive as illustrated, the sleeve 57 may move angularly within the the element 50, possibly as far as to permit unintentional disconnection of the coupling. To prevent this, a locking arrangement is provided for shaft 61.

This comprises a locking plate 70 which has a square aperture fitting on the squared end of shaft 61, and a square periphery. A spring 71 biases the locking plate 70 along the shaft 61 so that its square periphery is engagable with an abutment 72 fitted to the element 50, thereby preventing the locking plate 70 and the shaft 61 with it from turning. When key 64 is applied to the end of shaft 61, it pushes the locking plate 70, against the action of spring 71, to a position in which it is disengaged from the abutment 72 and therefore is able to turn. In Figure 7, key 64 is shown in contact with the locking plate 70, immediately prior to pushing the locking plate along the shaft to disengage it from the abutment 72.

Claims (9)

1. A coupling assembly comprising a first element and a second element, interengaging formations on said elements for torque transmission about a common axis and tensioning means for holding said elements together against axial separation, said tensioning means comprising: a holding member, supported by said first element for angular movement relative thereto about said axis and having a number of circumferentially spaced, radially extending, tensioning formations;; a number of complementary tensioning formations on said second element, extending in the radially opposite direction to the first said tensioning formations and circumferentially spaced on said second element such that said first tensioning formations can pass axially therebetween, whereafter opposed tensioning faces of said first and complementary tensioning formations are engagable by angular movement of said holding member; the tensioning faces of at least one of said numbers of tensioning formations comprising portions of a multiple-start helical screw thread; a part of said holding member having circumferential worm wheel teeth and said first element having a chordally mounted worm element engaged therewith, for effecting said angular movement of said holding member.

2. A coupling assembly according to Claim 1 wherein said first element is provided with a radially movable indicator element, spring biased into engagement with a cam formation on said holding member.

3. A coupling assembly according to Claim 2, wherein said indicator element projects outwardly of a circumferential surface of said first element when said holding member is in a position such that its tensioning formations are able to pass axially between said complementary tensioning formations.

4. A coupling assembly according to any one of the preceding claims wherein the tensioning faces of both said tensioning formations and said complementary formations comprise portions of respective multiplestart helical screw threads.

5. A coupling assembly according to any one of Claims 1 to 3 wherein said tensioning formations on said holding member comprise rollers supported on trunnions extending outwardly from said holding member.

6. A coupling assembly according to Claim 5 wherein said holding member and said worm element are supported relative to said first element by rolling element bearings.

7. A coupling assembly according to Claim 6 further comprising locking means operable to prevent turning of said worm element.

8. A coupling according to any one of the preceding claims wherein one of said elements comprises a member of a universal joint.

9. A coupling assembly substantially as hereinbefore described with reference to Figures 1 to 4, Figure 5, or Figures 6 and 7 of the accompanying drawings.