BACKGROUND TO THE INVENTION Dog clutches or the like find application in manually operable gearboxes and in other applications in which the coupling of two shafts is required while one or both shafts are rotating or stationary.

Synchromesh rings are generally used to facilitate the mesh of the interengaging formations on the clutch plates in manual automotive and other gear boxes with the rings being used to force the two shafts to rotate at the same angular velocity before engagement of the clutch plates is commenced. In situations where the two shafts are stationary, the shafts need to be rotated separately to achieve synchronisation of the clutch plate formations prior to engagement of the plates. In all known clutches of the above type a certain degree of engaging formation interference takes place in the formation meshing process.

SUMMARY OF THE INVENTION A synchronised clutch according to the invention comprises first and second clutch plates which are rotatable about a common clutch axis and include interengageable male and female formations, an actuator for moving the clutch plates from a first position in which their interengageable formations are separated from each other to a second position in which the formations and so the clutch plates are engaged for rotation with each other, characterised in that the clutch includes a synchronisation arrangement which is adapted on operation of the actuator to sense the relative positions of the male and female formations on the clutch plates, and if necessary, partially to rotate one of the clutch plates relatively to the other to bring the formations into register for perfect interference free engagement prior to the actuator moving the clutch plates from their first to second position of operation. The clutch conveniently includes a spring which biases the clutch plates to their second position of operation.

Preferably, the interengageable formations on the clutch plates are rings of dog clutch teeth which are located on the facing faces of the clutch plates.

The synchronisation arrangement may include a first synchronising device on the first clutch plate which is co-axial with the ring of dog clutch teeth on the plate, a second synchronising device which is co-axial with the ring of dog clutch teeth on the second clutch plate and is movable by the actuator in a first stage of operation from a position spaced from the first synchronisation device onto the first synchronisation device to sense the position of the clutch plate formations relatively to each other prior to the actuator moving the clutch plates from their first to second positions of operation in a second stage of operation. In a preferred form of the invention both synchronising devices are synchronising rings which each carry on their facing faces radially extended serrated teeth which are saw-toothed shaped in cross-section and on each ring are opposite inclined to be engageable with each other.

The synchronisation arrangement may include a synchronisation unit comprising a sleeve which carries the second synchronising ring and which, in use, is slidable on and engaged for rotation with a drive shaft for rotating the second clutch plate. Preferably, the bore of the synchronisation sleeve is shaped for slidable engagement with linear splines on the drive shaft, in use.

The synchronisation unit may be located in an inner coupling hub which includes a hub member which faces and is parallel to the untoothed rear face of the second synchronising ring, a sleeve which is fixed to the rear face of the hub member to surround the synchronisation unit sleeve to enable the synchronisation unit and the hub member to be moved in the axial direction in the clutch towards and away from each other, means for causing the inner coupling hub and the synchronisation unit to be partially rotated relatively to each other as they are moved, a spring which surrounds the synchronisation unit sleeve to bias the hub member and the second synchronisation ring apart and a stop on the synchronisation sleeve to limit relative movement between the inner coupling hub and the synchronisation unit in the axial direction of the clutch.

Conveniently the rotating means are slidably engaged helical spline formations on and between the sleeves of the synchronisation unit and the inner coupling hub.

The second clutch plate ring of dog clutch teeth may be fixed to the rim of a cup shaped outer coupling hub which has an opening in its base, the inner coupling hub is located in the outer coupling hub by formations which enable the coupling hubs to be moved relatively to each other in only the axial direction of the clutch with the clutch including a spring in the outer coupling hub which biases the two coupling hubs away from each other in the axial direction of the clutch.

The free end of the inner coupling hub sleeve may be concentrically located in the outer coupling hub opening and the free end of the sleeve and the outer coupling hub opening surround each carry a pressure ring with the outer surfaces of the rings being normal to the clutch axis.

The synchronisation arrangement may include a radial displacer member including an annular disc which is interposed between the first and second synchronising rings and carries on each face a ring of serrated saw tooth shaped teeth which are engageable with those on the first and second synchronising rings, a plurality of male and female formations which connect the displacer to the first clutch plate and which are relatively dimensioned to enable the displacer to be rotated by engagement with the second synchronising ring by no more than the circumferential width of one saw tooth on the first synchronisation ring, and means biasing the radial displacer, relatively to the first clutch plate, in a direction of rotation opposite to that of the clutch, in use.

In one form of the invention the actuator may include first and second pusher members which are movable in the axial direction of the clutch and respectively bear on the inner and outer coupling hub pressure rings and actuator means for sequentially operating the pusher members to cause a first and second stage of operation of the actuator.

A method of operating the above synchronised clutch may include the steps of rotating the drive shaft, operating the actuator in its first stage of operation to cause the first pusher member to move the inner coupling hub towards the first clutch plate to bring the second synchronising ring into contact with the first synchronising ring and if a perfect mesh of the teeth on the two rings occurs, allowing the actuator in its second stage of operation to cause the second pusher member to move the outer coupling hub towards the first clutch plate to bring their rings of dog clutch teeth into coupling mesh.

Should the contact of the teeth of the first and second synchronising rings result in an incomplete mesh of the teeth to prevent further movement of the second ring onto the first, the method may include the steps of causing the first actuator pusher to compress the spring between the inner coupling hub member and the second synchronising ring to cause the inner coupling hub and the outer coupling hub which it carries to be partially rotated on the helical spline formations to bring the dog clutch teeth on the clutch plates into mating register and then allowing the actuator in its second stage of operation to cause the second pusher member to move the outer coupling hub to bring the clutch plate rings of dog clutch teeth into coupling mesh.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now described by way of example only with reference to the drawings in which: Figure 1 is an exploded isometric view of the clutch of the invention, Figure 2 is a perspective view including some of the Figure 1 components as seen from the opposite side, Figure 3 is side elevation of the assembled synchronised clutch of the invention, Figure 4 is a perspective view of an actuator cam unit of the clutch, Figure 5 is a half-sectioned side elevation of the assembled clutch, Figure 6 is a perspective view illustrating the function of the synchronisation unit of the clutch, Figure 7 is an enlarged fragment of the zone marked A in Figure 6, Figure 8 is a perspective view from above of the dog clutch rings of the clutch, Figure 9 is an enlarged fragment B of Figure 8, Figures 10 and 11 are perspective views from opposite sides of the clutch components of a second embodiment of the clutch, and Figure 12 is a half-sectioned side elevation of the second clutch embodiment.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS The first embodiment of the clutch 10 of the invention is shown in Figures 1 to 5 to include first and second clutch plates 12 and 14 respectively, inner and outer coupling hubs 16 and 18 respectively, a synchronisation unit 20 and an actuator arrangement 22.

The first clutch plate 12, in this embodiment of the invention, is composed of a circular body which carries on its periphery a ring of gear teeth 24, a ring of dog clutch teeth 26 which face the second clutch plate 14, a recess in the rear face of the body and a synchronising ring 28 which is fixed in the recess.

The synchronising ring 28 carries on its rear face a ring of radially extending teeth which, as is seen in the drawings, are saw tooth shaped in cross-section.

The synchronisation unit 20 consists of a second synchronising ring 30 which carries on its front face a ring of serrated saw teeth which are oppositely shaped to and have the same pitch as those on the synchronising ring 28, and a sleeve 32 which is fixed to and projects from its rear face and carries helical male splines 34. The bore of the sleeve, as shown in Figure 2, is, in this embodiment, linearly splined.

The inner coupling hub 16 includes a dish-shaped hub member 38 with the forwardly projecting rim 40 of the member being circumferentially slotted and a rearwardly projecting sleeve 42. The inner surface of the sleeve 42 carries female helically splined formations, as best seen in Figure 2, in which the splines 34 on the sleeve 32 of the synchronisation unit 20 are slidably engageable. The free end of the inner coupling hub sleeve carries a pressure ring 44.

In the assembly of the inner coupling hub 16 a spring 46 is located over the synchronisation unit sleeve 32 and the helical splines on the sleeves 32 and 42 are rotatably engaged with the free end of the spring on the sleeve 32 being located in and bearing against the blind end of a slot 48 in the coupling hub member 38 to bias the synchronisation unit from the coupling hub. A stop disc 50 is attached by screws to the end of the synchronisation unit sleeve and is located in a recess at the end of the coupling hub sleeve to hold the two components together against the bias of the spring 46.

The second clutch plate 14 consists of the cup-shaped outer coupling hub 18 which carries on its rim a second ring 52 of dog clutch teeth. The outer coupling hub carries, on its inside, four hub springs 54 and keying formations 56, shown only in Figure 2, which are equally numbered to and slidably engaged in the slots in the rim 40 of the inner coupling hub. With the inner coupling hub located in the outer hub 18 the two hubs are movable relatively to each other in only the axial direction of the clutch with and against the bias of the hub springs 54. The base of the coupling hub is open with the surround to the opening carrying a pressure ring 58.

The actuator arrangement 22, in this embodiment of the invention, consists, as shown in Figure 1, of two cam rings 60 and 62 and a cam displacer 64.

The outer actuator cam ring 60 includes two diametrically opposite cam lobes 66 and a control arm 68 by means of which the actuator is operated. The cam ring 62 is concentrically engaged in the ring 60 by diametrically opposite keying formations 70 on the ring 62 which are slidably engageable in slots 72 in the ring 60 to enable the two rings to be moved in the axial direction of the clutch axis independently of each other while being rotatably coupled for concomitant rotational movement by the formations 70 and 72. The cam ring 62 includes two opposite cam lobes 74. The front faces of both cam rings are smooth.

The cam displacer 64 is shown in Figure 4 to include radially inner and outer cam lobes 76 and 78 with the lobes 76 having a smaller circumferential dimension than that of the lobes 78.

In the assembled clutch all of the clutch components are, in this embodiment of the invention, located over a common drive shaft 80 with the only clutch component which is directly coupled to the shaft for rotation with the shaft being the inner coupling hub 16 through the synchronisation unit 20. The shaft 80 is splined, as shown in Figure 1 over a short portion of its length with the linearly splined sleeve 32 of the synchronisation unit 20 being slidably engaged with the shaft 80, in the axial direction of the clutch, on the drive shaft spines.

The cam displacer 64 is fixed to fixed structure over the drive shaft 80 which projects from the structure. The cam rings 60 and 62, while engaged with each other, are pressed up against the )' cam displacer 64 with their cam lobes up against the flat face of the displacer between its lobes.

With rotation of the drive shaft 80 in the anticlockwise direction of the arrow in Figure 1 the cam lobes 66 and 74 of the cam rings are situated on the anticlockwise side of the displacer lobes.

The outer coupling hub 18, with the inner coupling hub 16 and the synchronisation unit 20 which it carries are pressed up against the cam rings 60 and 62, over the shaft 80, with their pressure rings 44 and 58 bearing on the smooth front faces of the cam rings 62 and 60 respectively.

A spring 82, for biasing the clutch plates 12 and 14 apart, is located over the shaft 80 to act between the front face of the second synchronising ring 30 radially inward of the ring of teeth which it carries and the rear face of the recess in the clutch plate 12 when the assembled clutch plate is pressed against the bias of the spring 82. The clutch plate 12 is located on the shaft 80 and held pressed against the bias of the various springs in the clutch against the fixed cam displacer 64 and the inner race of a bearing 84, on which the clutch plate 12 is journaled for rotation, is locked to the shaft 80 by a circlip 86 or by some other suitable fastening arrangement. With the clutch components locked together the dog clutch rings of the clutch plates 12 and 14 are held biased apart by the spring 82, as shown in Figure 5.

In use, with the drive shaft 80 rotating in an anticlockwise direction and with a gear, not shown, connected to a second shaft which is to be driven by the clutch, and which is held against rotation by the load of whatever it is to drive, meshed in a desirable ratio with the clutch gear 24 the control arm 68 in Figure 1 is moved in a clockwise direction to actuate the clutch.

As the control arm is moved the lobes 74 on the cam ring 62 first come into contact with and ride onto the lobes 76 of the cam displacer 64 to move the cam ring 62 and so the inner coupling hub 16, against which it bears, forwardly on the splines on the rotating drive shaft, against the bias of the spring 82 until the teeth on the synchronising ring 30 come into contact with the teeth of the synchronising ring 28. The bias of the spring 82 is less than the bias of the spring 46.

Should the positions of the saw teeth on the synchronising rings be such that when they contact each other a complete mesh of the teeth occurs i. e. the parallel edges of the saw teeth of the two rings abut each other, the dog teeth of the clutch plates 12 and 14 will be in register for perfect mesh while the hub springs hold the dog teeth of the clutch plates 12 and 14 out of engagement. Continued movement of the control arm 68 will now bring the cam lobes on the cam ring 60 into contact with and ride onto the lobes 78 of the cam displacer 64 to move the outer coupling hub forwardly to bring the synchronised dog teeth on the clutch plates 12 and 14 into perfect mesh to drive the gear which is meshed with the clutch gear 24 and the shaft which it carries.

If, however, the engagement of the teeth of the tooth rings of the synchronising rings 28 and 30 result in an incomplete mesh i. e. the sloping ramps of the teeth are engaged and not their parallel saw tooth driving faces, as shown in Figures 6 and 7, the dog teeth of the clutch plates 12 and 14 will not be synchronised in engaging register, as shown in Figures 8 and 9, and the forward motion of the synchronisation unit 20 will tend to be arrested. The forward cam induced force on the inner coupling hub pressure ring 44 will, however, override the compression force of the spring 46. This will cause the synchronisation unit 20 to be moved forwardly and simultaneously to be twisted in rotation in an anticlockwise direction by the helical spline arrangement on the sleeves 32 and 42 to bring the dog teeth of the clutch plates into meshing register. The angular displacement of this twisted motion which is required to bring the dog teeth of the clutch plates into meshing register is related to the magnitude of the incomplete mesh of the teeth on the synchronising rings 28 and 30 and is sufficient to bring the dog teeth on the clutch plates into synchronised register for clean mating on further rotation of the control arm 68.

The above synchronisation of the clutch plates is illustrated with reference to Figures 6 to 9.

Figures 6 and 7 spatially illustrate the synchronising ring 30 on the synchronisation unit 20 as its teeth come into contact, in an incomplete mesh, with those on the clutch plate 12 synchronising ring 28 on actuation of the inner coupling hub 16.

Figures 8 and 9 illustrate the resulting relative out of mesh positions of the dog teeth on the clutch plates 12 and 14.

In the above situation the forward movement of the synchronisation unit 20 is halted and, as described above, the continued forward cam induced movement of the inner coupling hub 16 will override the bias of the spring 82. This will cause the synchronisation unit 20 and so the clutch plate 14 with it to be moved forwardly with the twisting motion of the synchronisation unit 20 until the dog teeth on the two clutch plates are in synchronised register prior to the actuation of the outer coupling hub 18.

From Figures 6 to 9, as an example, the following are derived: where: a = mm/revolution (Helix specification) b = tooth height c = circumferential width of one tooth d = circumferential length of an adjacent pair of clutch dog teeth e = degree of radial incomplete mesh of the synchronisation teeth (complete mesh e = c) f = degree of incomplete mesh of synchronisation teeth in an axial direction (complete mesh f = o) g = degree of radial incomplete mesh of dog clutch teeth (complete mesh g = o). a = mm/revolution (1) b a = d#360° (2) b#(c - e/c) f = c (3) C sothatiff=bthene=Oandiff=Othene=c f d g = b (4) so that if f = b then g = d Using 3 and 4 <BR> <BR> <BR> <BR> <BR> <BR> (C--) d<BR> <BR> <BR> <BR> <BR> 9 = C 5)<BR> <BR> <BR> c The above will ensure that the dog teeth are always synchronised after action of the inner cam ring 62. It is to be noted that because of this synchronisation of the positions of the dog teeth on the clutch rings that the meshing of the teeth will be clean and will not cause any rotational movement of either of the shafts connected to the clutch.

As an example of the operation of the above, consider the input shaft 80 of the clutch to be rotating at 3000 rpm or 50 rev/sec. Assume the depth of the saw tooth teeth, b, to be 3mm as well as the depth (engage distance) of the dog clutch teeth to be 3mm. Assume further that the ramp up on both the inner and outer cams 62 and 60 to be 5° to fully perform the synchronisation (move the inner hub 16) and 5° to move the outer hub 18 (engaging the dog clutch teeth). In both cases the cams 62 and 60 have a 3mm lift. Assume that the radial length of one saw tooth, c, is 6° and that the radial length of a pair of dog clutch teeth, d, is 6°. i Using equation 2, a is calculated as: b 3. 3600 a--360'=-= 180mm/rev d 6° Assume that the time duration t1 to actuate the synchroniser is 0.27ms and the time t2 to engage the dog clutch rings is 26 and 52.

Since the synchroniser and outer hub travels the same distance, 3mm, the average velocity during engagement will be 3mm/0.27ms = 11 m/s which is slow if compared to engine valve movement or average piston speed.

In the second embodiment of the invention which is illustrated in Figures 10 to12 the clutch of the previous embodiment includes a radial displacer 88 which is interposed between the synchronisation rings 28 and 30 and serves, in selected clutch applications, only to compensate in the synchronisation process of the synchronising rings 28 and 30 for the time lag between the operation of the outer and inner cam rings 60 and 62.

The radial displacer is essentially a disc which carries on each of its faces a ring of saw teeth which are complementally shaped to and are of opposite inclination to the teeth of the synchronising rings 28 and 30. The disc includes four forwardly directed locating formations 90 which each carry on one edge a spigot-like formation which is engaged with a displacer spring 92.

The clutch plate 12 is modified, as shown in Figure 11, to accommodate the displacer 88 in a recess in the rear face of the clutch plate. The clutch plate separating spring 82 of the previous embodiment is replaced by a spring 89 which acts between the front face of the inner coupling hub and the body of the clutch plate 12. The wall of the recess carries four spacer members 94 which are slightly upwardly inclined on their clockwise edges which carry spigot formations which are engageable in the free ends of the displacer springs 92 when the displacer is located in the clutch plate recess. The circumferential spacing between the edges of the spacers 94 is larger in dimension than the circumferential dimension of the locating formations 90 on the radial displacer by a dimension which will allow the displacer to be rotated relatively to the synchronising ring 28 by no more than the circumferential width of one tooth on the ring 28. In operation, because of the above time lag, even though in practice the control arm 68 will be operated in a single motion, probably by some suitable electronic means, a situation may arise where, during the time lag, the teeth of the synchronising ring 30 and those of the tooth ring on the back face of the displacer 88 might become fully engaged and tend to drive one another.

When this situation does arise the tooth ramps of the toothed ring on the front face of the displacer and the tooth ramps of the synchronising ring 28 will sit on each other out of full mesh and cause the displacer 88 springs 92 to be compressed as torque is applied to the clutch plate 12 in the direction of rotation of the shaft 80 to keep the dog teeth of the clutch plates synchronised and ready for complete mesh on operation of the outer cam ring 60.

Other special applications include the coupling of two stationary shafts that cannot be rotated during coupling.

However this invention is not limited to the above examples but may be used in any application where coupling between two mechanical components is required.