WO2009127839A1

WO2009127839A1 - Multiple output transmission systems

Info

Publication number: WO2009127839A1
Application number: PCT/GB2009/001000
Authority: WO
Inventors: John Phillip Chevalier
Original assignee: John Phillip Chevalier
Priority date: 2008-04-17
Filing date: 2009-04-17
Publication date: 2009-10-22
Also published as: GB2474591A; GB201019466D0; GB0807033D0

Abstract

A transmission system for driving a selected one or two of a plurality of drivable devices by a single drive motor (4) includes an input shaft (2) for connection to the drive motor, a plurality of output units (6), each of which includes a drive member (8) which is connected to be driven by the input shaft (2), an output shaft (14) and a clutch mechanism (10, 12), and a clutch engagement actuator (24) arranged to act on a selected one of the clutch mechanisms to connect the drive member (8) with the associated output shaft (14), thereby transmitting rotation from the input shaft to the said output shaft. Only a single clutch engagement actuator (24) is provided and each drive member (8) is connected to rotate with a respective first clutch member (lθ)affording a first engagement surface. Each output shaft (14) is connected to rotate with a respective second clutch member (12) opposed to the first clutch member (10) and affording a second engagement surface. The clutch engagement actuator (24) is arranged to act eccentrically on a selected one of the clutch members to bring its engagement surface into driving engagement with the engagement surface of the opposed clutch member. The second clutch member (12) is connected to rotate with two output shafts (14) extending in opposite directions.

Description

MULTIPLE OUTPUT TRANSMISSION SYSTEMS

The present invention relates to multiple output transmission systems, that is to say transmission systems with a single input shaft and a plurality of output shafts, each of which may be selectively coupled to be rotated by the input shaft. More specifically, the invention relates to a transmission system for driving a selected one or two of a plurality of drivable devices by a single drive motor including an input shaft for connection to the drive motor, a plurality of output units, each output unit including a drive member which is connected to be driven by the input shaft, an output shaft and a clutch mechanism, and a clutch engagement actuator arranged to act on a selected one of the clutch mechanisms to connect the drive member with the associated output shaft, thereby transmitting rotation from the input shaft to the said output shaft.

Such transmission systems have a number of applications, particularly in the automotive field. It is common for automotive seats to be provided with a number of actuators for adjusting the depth, angle and degree of recline of the seat. It is usual for two actuators to be provided for each function, one on each side of the seat. It would of course be possible for each actuator to include a respective electric motor but this is highly undesirable as regards cost and weight and due to the fact that space is at a premium within and below automotive seats. It is therefore known to provide each actuator in the form of an unpowered device which may be selectively connected to a single electric drive motor. The user need simply select the setting which is to be adjusted and the motor is then connected automatically to the desired actuator or actuators and then operated to effect the desired adjustment. A further application for such transmission systems is in automotive door actuators. Thus a single motor coupled to a transmission system may be accommodated in a vehicle door and used selectively to operate one of, for instance, a powered wing mirror, a powered window and a powered door lock.

A transmission system of the type referred to above is disclosed in WO 2006/008663. In this transmission system, each output unit includes a respective solenoid actuator for selective engagement of the respective clutch mechanism. For a transmission system with three output units, this means that three solenoid actuators are required and these are relatively expensive and heavy and take up a lot of space. Although the transmission system in the prior document appears to have four output units, the first unit, to which the drive motor is connected, is in fact only an input unit, which includes a gear wheel in mesh with the gear wheel of the adjacent output unit and it does not have an output. Furthermore, the solenoid actuators are positioned and act axially, that is to say they are positioned at one end of the output unit in line with the axis of rotation of the output shaft and this necessarily means that each output unit only has one output shaft. However, as explained above, in connection with automotive seat adjustment mechanisms, the actuators are normally provided in pairs and this means either that two output units are needed for adjusting each setting or that, if a single output unit is used, some form of power splitter must be used to split the output power from the one output unit into two separate transmission lines for connection to the two actuators. However, both of these options result in an increase in mechanical complexity, cost, weight and space requirement. Furthermore, the clutch mechanisms disclosed in the prior document use a system of plungers, sleeves and jamming balls and are extremely complex. The number of parts in each output unit, particularly in the clutch mechanisms, is extremely high and this adds very considerably not only to the expense of manufacture but also to the cost of assembly and the transmission system disclosed in the prior document is therefore unacceptably expensive. According to the present invention, a transmission system of the type referred to above is characterised in that there is only a single clutch engagement actuator, that each drive member is connected to rotate with a respect first clutch member affording a first engagement surface and each output shaft is connected to rotate with a respective second clutch member opposed to the first clutch member and affording a second engagement surface, that the clutch engagement actuator is arranged to act on a selected one of the clutch members to bring its engagement surface into driving engagement with the engagement surface of the opposed clutch member, that the second clutch member is connected to rotate with two output shafts extending in opposite directions and that the clutch engagement actuator acts eccentrically on the clutch member.

Thus the transmission system in accordance with the invention includes only a single clutch engagement actuator rather than one per output unit and this clearly constitutes a significant saving in weight, space and cost. Each drive member and each output shaft is connected to rotate with respective clutch members affording respective engagement surfaces and the clutch engagement actuator is arranged to act on a selected one of the clutch members to bring its engagement surface into driving engagement with the engagement surface of the opposed clutch member. The clutch mechanisms in the transmission system of the present invention are therefore much simpler and, in particular, have a much lower part count than the clutch mechanisms in the prior document. Finally, the clutch engagement actuator is arranged to act on the clutch members eccentrically, that is to say at one or more positions which are offset from the axis of rotation of the drive members and output shafts. This means that there is no longer any obstacle in the axial direction at either axial end of each output unit and thus that each unit may have two output shafts. In practice, the two output shafts are likely to constitute portions of a single output member connected to the clutch member which is connected to the input shaft. However, these two portions will extend from the associated output unit in opposite directions and thus effectively constitute two output shafts. This means that the two actuators needed to adjust one of the settings of a car seat may be connected to respective output shafts of a single output unit and thus that it is no longer necessary to use two output units or some form of power splitter for this purpose. However, whilst each output unit includes two output shafts, it is not necessary that both of them be used and it is of course possible that it will sometimes be desirable to leave one of them unused.

Each drive member preferably consists simply of a gear wheel. The gear wheels are all driven by the input shaft and in a simple embodiment the input shaft carries a gear wheel which is in mesh with one of the drive gear wheels of the output units, all the remainder of which are in mesh with at least one further drive gear wheel.

Each clutch mechanism includes two opposed clutch members, one of which is connected to the input shaft of the transmission via the associated drive member and the other of which is connected to two output shafts. The two clutch members may be of conventional plate construction and arranged to be in surface contact with one another. However, such clutches require a substantial contact pressure in order to be able to transmit any significant torque and since it is desired that the clutch mechanisms be as small and light as possible it is preferred that the two clutch members are constructed for positive engagement with one another. In the preferred embodiment the first and second clutch members thus each afford one or more projections and/or recesses which positively engage with one another when the clutch mechanism is engaged. In one embodiment, the two clutch members have portions of complementary castellated shape and in a further embodiment one clutch member carries one or more pegs which are dimensioned and positioned to engage in corresponding apertures in the other clutch member. It will be appreciated that the side surfaces of the castellations or of the pegs and apertures will constitute the engagement surfaces through which drive is transmitted.

The clutch engagement actuator may act on the clutch mechanisms in a variety of different manners. In one embodiment the clutch engagement actuator comprises an electric motor connected to rotate a cam shaft carrying a plurality of angularly offset cams, each of which is associated with a respective output unit and is arranged to contact one of the clutch members of that output unit eccentrically and to press it into drive engagement with the opposed clutch member, whereby rotation of the electric motor through 360° will result in the clutch mechanisms of all the output units being successively pressed by the respective cam into engagement.

Thus in this embodiment, the clutch engagement actuator is connected to a cam shaft carrying a plurality of cams. As the motor is rotated, one clutch member of each output unit will be contacted successively by a cam and moved by it into engagement with the opposed clutch member, thereby engaging that clutch mechanism and enabling the transmission of power from the input of the transmission system to the outputs of that output unit. Whilst the cam shaft may carry a single cam adapted to engage a clutch member of each output unit, it is preferred that it carries two such cams and these will then be positioned to engage the associated clutch member simultaneously and preferably symmetrically with respect to the axis of rotation of the associated output shaft. This embodiment results in a more symmetrical application of force to the clutch members and thus in smoother and more reliable engagement movement of those clutch members. The output units may be positioned side-by-side in a line and the cam shaft may extend along and parallel to that line and in this event the cams are preferably arranged to contact the associated clutch members directly.

Alternatively, the cam shaft may extend perpendicular to the line and in this event the system may include a plurality of levers, each of which cooperates with a respective cam and a respective clutch member. In this event, the cams are of course arranged to contact the associated clutch members indirectly rather than directly.

In the above embodiments it is convenient if the input shaft is connected to rotate one of the drive members and if all the drive members are in driving engagement with at least one further drive member, whereby all the drive members are driven, directly or indirectly by the input shaft. However, in a modified embodiment, the input shaft is connected to rotate a worm and the drive members constitute worm wheels, the drive members each constituting one of the clutch members and being movable by engagement by the cams into driving engagement with the worm and with the opposed clutch member. In a modification of this, the worm wheels are in constant mesh with the worm and when they are moved into engagement with the respective opposed clutch member they remain in mesh with the worm. In this event, all of the worm wheels are driven at all times whilst in the preceding embodiment only the engaged worm wheel and clutch are driven .

In a further embodiment, the clutch engagement actuator, which could be a manually operable lever but preferably comprises an electric motor, is connected to rotate a pinion gear which is in mesh with a rack gear, either the unit comprising the electric motor and the pinion gear or the rack gear being stationary and the other being movable, on actuation of the electric motor, and carrying a clutch engagement member arranged to contact a clutch member of a selected output unit, on actuation of the motor, to press it into engagement with the opposed clutch member, thereby connecting the drive member of that output unit to the associated output shafts.

Thus in this embodiment, it is again likely that the output units will again be arranged side-by-side in a line. Extending along and parallel to that line is a rack in mesh with a pinion gear connected to be rotated by an electric motor. Either the rack or the unit comprising the motor and the pinion gear carries a clutch engagement member. It is in fact preferred that the clutch engagement member is carried by the motor/pinion gear. When the motor is operated, it will move along the stationary rack and is arranged to contact and displace a clutch member of the output units sequentially. When a clutch member is contacted by the clutch engagement member, it is pressed into engagement with the opposed clutch member, thereby connecting the drive member of that output unit to the associated output shafts. It is preferred that the clutch engagement member includes two oppositely-inclined ramp surfaces and that it is so positioned that, regardless of the direction in which the motor/pinion gear is moving, one of the ramp surfaces will come into engagement with a clutch member and as the motor/pinion gear unit continues to move, the inclination of the ramp surface will result in progressive movement of the clutch member in question until it is in drive engagement with the opposed clutch member. Further movement of the clutch engagement member will result in the clutch member sliding down the other, oppositely inclined ramp surface and in progressive disengagement of the two clutch members under the action of the clutch spring that will in practice be provided. In a modified but similar embodiment, the clutch engagement actuator, which again preferably comprises an electric motor, is connected to rotate a threaded spindle, which is in mesh with a clutch engagement member arranged to contact a clutch member of a selected output unit on actuation of the motor to press it into engagement with the opposed clutch member, thereby connecting the drive member of that output unit to the two associated output shafts. This embodiment is therefore similar to that with a rack and pinion but the rack is replaced by a worm. The clutch engagement member is in mesh with the worm gear and is moved up and down the line of output units, when the electric motor is actuated. The clutch engagement member will again preferably have two opposed ramp surfaces arranged to engage one clutch member of each output unit sequentially as the clutch engagement member moves along the length of the worm gear.

In all of the embodiments described above, each of the clutch members which is acted on by the clutch engagement actuator is positively moved by that actuator from the disengaged position to the engaged position, in which it is in driving engagement with the opposed clutch member, and a return spring or the like will in practice be necessary to return the clutch member which has been moved back to its original, disengaged position. However, in yet a further embodiment, the clutch members acted on by the clutch engagement actuator are moved positively in both directions, that is to say both into the engaged position, in which they are in driving engagement with the opposed clutch member, and from the engaged position to the disengaged position and in this event no clutch return spring or the like will be necessary. In this embodiment, the clutch engagement actuator is connected to rotate a plurality of cam discs, two cam discs being associated with each output unit, each cam disc affording a cam track, a respective follower member being retained in the cam tracks of the two cam discs associated with each output unit and connected to one of the clutch members of the associated output unit, the cam tracks being so shaped and arranged that as the cam discs are rotated through 360° the follower members are constrained to move such that the clutch mechanisms are engaged and then disengaged sequentially. Whilst there could be two separate cam discs associated with each output unit, it is preferred that the number of cam discs is one greater than the number of output units and that two of the cam discs have a cam track in one surface only whilst the remaining cam discs have a cam track in both surfaces. It will be appreciated that this will result in there being two cam tracks associated with each output unit and this is all that is required. The follower members are connected to a respective one of the clutch members of all the output units and the cam tracks are so shaped that as the cam discs rotate the follower members and thus the clutch members connected to them will be constrained to move in a pattern dictated by the shape of the tracks and the shape of the tracks is so selected that as the cam discs are rotated through 360°, each clutch mechanism is disengaged for the majority of the time but is moved once into the engaged position. The cam tracks associated with each output unit will be angularly offset from one another so that each clutch mechanism is moved into the engaged position at a different angular position of the cam discs. In practice, it is desirable that the cam tracks associated with the different clutch mechanisms are equiangularly offset. This means in practice that if there are four output units, the cam tracks associated with them will be offset from one another by 90°.

Further features and details of the invention will be apparent from the following description of certain specific embodiments which is given by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a first embodiment of transmission system in accordance with the invention; Figure 2 is a side view of the transmission of Figure 1;

Figure 3 is a perspective view of the transmission of Figure 1;

Figure 4 is a perspective view of the two clutch members of the embodiment in Figures 1 to 3;

Figure 5 is a perspective view similar to Figure 3 of a second embodiment;

Figure 5A is a partly cut-away perspective view similar to Figure 5 of a modified version of the second embodiment;

Figure 5B is a partly cut-away side view of the modified embodiment of Figure 5 A;

Figure 6 is a perspective sectional view of the modified clutch mechanism in the embodiment of Figure 5;

Figure 7 is a perspective view of a third embodiment;

Figure 8 is a plan view of the embodiment of Figure 7;

Figure 9 is a perspective view of a fourth embodiment;

Figure 10 is a perspective view of a fifth embodiment;

Figure 11 is a plan view of the embodiment of Figure 10; Figure 12 is a perspective view of a sixth embodiment;

Figure 13 is a perspective view of the clutch actuation mechanism of a seventh embodiment;

Figure 14 is a plan view of the mechanism of Figure 13; and

Figure 15 is a sectional view on the line B-B in Figure 14.

Referring firstly to Figures 1 to 3, a multiple output transmission system includes an input 2, which is shown in this case connected to a drive motor 4, which may be of electrical, hydraulic, pneumatic or any other type. The transmission system includes an input/output unit 5 and a number, in this case 3, of output units 6, each of which includes an input drive member 8 in the form of a pinion gear. The input 2 is connected axially to the pinion gear 8 of the input/output unit 5, which is in mesh with the gear 8 of the adjacent output unit 6. The gears 8 of all the output units are all in mesh with at least one further gear such that rotation of the input 2 will result in rotation of all the gears 8, though necessarily in alternately opposite directions, when the motor 4 is operated. The gear 8 of each output units 6 is connected to rotate with a respective first clutch member 10. The clutch member 10 is opposed to a second clutch member 12, which is connected to rotate with an output member which extends outwardly from the output unit at the lower end, as seen in Figure 1, where it constitutes a first output shaft 14, and rotatably projects also through a hole in the gear 8 and beyond it, upwardly as seen in Figure 1, to constitute a second output shaft 14. Situated between the two clutch members 10 and 12 and extending around the output member is a return spring 16. The gear 8 of the input/output unit 5 could act simply as the means for causing rotation of the gears 8 of the output units 6 but in this case it forms part of a unit very similar to the output units 6 and thus also includes two clutch members. However, the unit 5 differs from the units 6 in that it only has a single output and not two outputs. This is the consequence of the fact that the input shaft 2 is connected axially to one end of the unit 5.

As best seen in Figure 4, the two clutch members 10, 12 are of generally cup shape, the side walls of the cups terminating in complementary series of projections 18 and recesses 20. The ends of the projections 18 and the corresponding portions of the recesses 20 are defined by two oppositely inclined ramp surfaces. The dimensions of the projections and recesses and the inclination of the ramp surfaces is such that when the two clutch members are moved towards one another, the projections 18 on the two clutch members will automatically be received in the recesses 20, if necessary with a small amount of relative rotational movement caused by the engagement of the ramp surfaces on the two clutch members, which rotational movement is generally permitted by dimensional tolerances and backlash in the output unit. As may be seen, the clutch member 12 has a non-circular hole, in this case a hexagonal hole 22, formed in it, which receives a complementarily shaped portion of the output member and thus ensures that the output member and the clutch member 12 are rotationally fixedly connected to one another.

The transmission system includes a single clutch engagement actuator, in this case a stepper motor 24. The output of the motor 24 is connected to a cam shaft 26. This shaft carries eight cams 28. These cams are associated in pairs and the cams of pair are angularly aligned with one another and cooperate with the clutch member 12 of a respective unit 5, 6. However, each pair of cams is angularly offset from the or each adjacent pair of cams by 90°. The cams are constructed and arranged to contact the external surface of the associated clutch member 12 at two spaced eccentric positions, that is to say positions which are remote from the axis of rotation of the clutch members. The lift or displacement induced by each pair of cams on the associated clutch member 12 is sufficient to press it into driving engagement with the associated clutch member 10 with the projections 18 on the two clutch members received in the recesses 20 in the opposed clutch member. When the clutch member 10 of an engaged clutch mechanism is rotated, the side surfaces of the projections 18 will be forced into engagement with the corresponding side surfaces of the recesses 20 on the opposed clutch member and rotation will therefore be transmitted between the two clutch members via these engaging surfaces. If the stepper motor 24 is caused to rotate the cam shaft 26 through a full revolution, the clutch mechanisms of the four output units will be caused to move into and out of engagement sequentially at positions which are spaced 90° apart.

By means of conventional feedback positional control, the angular position of the stepper motor 24 will be known to the control system which will in practice be provided but is not illustrated. In use, the outputs of some or all of the output units will be connected to respective drivable devices, such as seat adjustment actuators, and if it is desired to operate a specific actuator or pair of actuators, an appropriate command is input via the control system. The stepper motor 24 is then caused to rotate to the angular position necessary to produce engagement of the clutch mechanism of the appropriate output unit. The electric motor 4 is then operated and this will result in rotation of the inputs of all the output units but of the output shafts of only the selected output unit. Once the necessary adjustment has been effected, operation of the motor 4 is terminated and, if desired, the stepper motor 24 may then be operated to cause the clutch mechanism of a different output unit to be engaged in order to operate a different pair of actuators. If one of the output units 6 is selected, two rotating output shafts will be available and the single output shaft of the input/output unit 5 will rotate at all times, though this, in practice, may not be used.

Once the stepper motor 24 has been rotated to the position necessary to produce engagement of the clutch mechanism of the desired output unit, the control system will operate to maintain it stationary, that is to say in the position desired to maintain engagement of the desired clutch mechanism. Stepper motors are, however, relatively expensive and Figure 5 shows a modified embodiment in which the stepper motor is replaced by a cheaper, conventional electric motor. In this case, the output of the motor 24' is connected to rotate a worm 30, in mesh with a worm wheel 32 carried by the cam shaft 36. The inherent low mechanical efficiency of such a worm drive means that once the cam shaft has been rotated to the desired angular position, the motor 24' may be simply de-energised and will nevertheless remain in the correct position because worm drives are not capable of being operated in the reverse direction.

The embodiment of Figure 5 is otherwise substantially the same as that of Figures 1 to 3 but does differ from it in one further important respect. Thus the clutch mechanisms are not of the type illustrated in Figure 4 but are instead as illustrated in Figure 6. In this case, the drive gear 8 constitutes the first clutch member 10 and formed in its side surface opposed to the other clutch member 12 is an annular array of circular holes or apertures 34. Integrally formed on the opposing side surface of the other clutch member 12 is a complementary annular array of projections 36 with substantially hemispherical ends. The arrangement and spacing of the holes 34 and projections 36 is again such that, when the clutch member 12 is pressed by the associated cams towards the clutch member 10, the projections 36 will be accommodated in the holes 34, if necessary with a slight relative rotation of the two clutch members caused by engagement of the hemispherical ends of the projections 36 with the opposing surface of the clutch member 10. Torque may then again be transmitted between the clutch members 10 and 12 via their engaging surfaces, that is to say the side surfaces of the projections 36 and of the holes 34.

The drive motor 4 is not shown in Figure 5, and whilst it is in fact intended to be connected to the unit adjacent the motor 24, it could in fact be connected to any of the units. It will be appreciated that, in the input/output unit to which the drive motor is to be connected, it is essential that the shafts 14, one of which will in fact constitute the input shaft, be locked to rotate with the first clutch member so that the drive member 8 will rotate the drive members of the other units. This is achieved by the use of a peg 27, seen in Figure 5, which may be passed through a hole 29 in the output member, seen in Figure 6, and a hole in the second clutch member 12 to hold the clutch members 10, 12 in engagement. This will result in continuous rotation of the one shaft 14, which is available for use as an output. If the peg 27 is removed, the input unit will operate as an output unit and the peg 27 may then be positioned in any of the other units, which will then operate as the input unit.

As mentioned above, if the two clutch members which are to be engaged are not perfectly aligned, slight relative rotation of them will be required to permit engagement. This rotation may be permitted by backlash and tolerances in the system, but this may not necessarily be enough to permit sufficient relative rotation. This potential problem is solved in the modified embodiment shown in Figures 5A and 5B in which the output member is keyed to rotate with the clutch member 12 by a coupling constructed to permit limited relative rotation. As may be seen, the clutch members 12 have an aperture defined by four sides, two of which are opposed and of circular arcuate shape and the other two of which are also opposed and are straight and parallel. The output member has a portion 15, which is received in that hole and has a cross-sectional shape which is again defined by four sides. Two of them are again of circular arcuate shape and match and are in sliding contact with the arcuate sides of the hole in the clutch member. The other two sides are, however, not straight but are defined by two straight lines which define an obtuse angle, whereby those sides are convex with a central apex. If relative rotation of the clutch member 12 is necessary to permit engagement with the opposed clutch member, the opposed engaging circular surface will slide relative to one another until two of the flat surfaces on opposed sides of the portion 15 are in surface engagement with the flat surfaces of the hole in the clutch member 12, whereafter the clutch member 12 and the output member will rotate as a solid body.

Figure 7 illustrates a further modified embodiment, which is again generally similar to that illustrated in Figures 1 to 3. However, in Figure 3, the cam shaft 26 extends along and parallel to the line of output units whereas in Figure 7 it extends perpendicular to the line of output units. Furthermore, whilst in Figures 1 to 3, the cams 28 engage the clutch members 12 directly, in the embodiment of Figure 7 they engage the clutch members 10 indirectly, that is to say via respective levers 38. In this case, the cam shaft 26 carries only a single cam 28 for each of the output units. Positioned adjacent the cam shaft 26 is one end of four L-shaped levers 38, each of which is mounted to pivot about a vertical axis 40. On end of each lever 38 is positioned so as to be engaged by a respective one of the cams 28 and the other end of each lever is in engagement with a respective one of the clutch members 10. The angular positions at which the cams engage the associated levers are again angularly offset from one another by 90°. The operation of the embodiment of Figure 7 is substantially as described above and the motor 24 may again be a stepper motor, though a conventional electric motor connected to a worm drive would again be possible, as in Figure 5. If the cam shaft 26 is rotated through a full revolution, the four cams will each contact their associated lever once and result in engagement of the clutch mechanism with which it is associated. In order to permit the necessary movement of the clutch member 10, it is mounted on the shaft with which the associated gear rotates so as to be non-rotatable but linearly movable with respect to it.

In the embodiments described above, the input drive gears 8 are all connected to be rotated by the input shaft 2 by virtue of being in mesh with one another. However, in the further embodiment illustrated in Figure 9, the input drive gears 8 are spaced apart from one another and are all of worm wheel type. These gears 8 are all adjacent to but not normally in mesh with a worm 42 connected to the transmission input 2. Rotation of the input 2 by a drive motor 4, which is not shown, will result in rotation of the worm 42 about its longitudinal axis. The clutch mechanisms are again actuated by respective pairs of cams 28 carried by a cam shaft 26, which is operated by a motor 24' via a worm drive, as described in connection with Figure 5. However, the transmission of Figure 9 differs further from that of Figure 5 in that the cams 28 are positioned to act directly on the side surface of the worm gears 8, which therefore constitute one of the clutch members. However, a worm drive inherently permits a certain degree of relative lateral movement whilst nevertheless maintaining driving engagement and when the worm gears 8 are moved into engagement with the respective opposed clutch member, they also start to mesh with the worm 42 and are thus driven by it. Alternatively, the worm gears may be in mesh with the worm 42 at all times. In other respects, the transmission of Figure 9 is substantially the same as that of the preceding embodiments.

Figures 10 and 11 show a further embodiment which is generally similar to that of Figures 1 to 3 but differs from it in that the cam mechanism has been replaced by a rack and pinion mechanism. Extending along and parallel to the line of output units 10 is a stationary rack 44, which is in mesh with a pinion wheel 46 connected to be rotated by a conventional electric motor 24'. The motor 24' and pinion 46 constitute a unit which is mounted so as to be movable on a rail 48 parallel to the rack 44. Also connected to move with the motor 24' is a clutch engagement member 50 which, as best seen in Figure 11, affords two vertically extending, oppositely inclined ramp surfaces 52, which meet at a rounded oblique angle, as seen in plan view. If the motor 24' is operated, it will move together with the pinion 46 and member 50 along the rail 48. The ramp surfaces 52 are positioned and dimensioned so that, as it does so, it will come into engagement with the outer surface of the clutch member 12 of the closest output unit 10. Continued movement of the motor and formation 50 will result in progressive movement of the clutch member 12 in the downward direction, as seen in Figure 11, until it is in driving engagement with the opposed clutch member 10. The member 50 may thus be moved as desired under the control of the control system to engage any selected one of the clutch mechanisms. The provision of the two oppositely-inclined ramp surfaces 52 on the formation 50 means of course that it may approach any of the clutch members 12 from either direction. In other respects, the transmission of Figures 10 and 11 is substantially the same as those of the previous embodiments.

Figure 12 shows yet a further embodiment in which the rack and pinion of Figures 10 and 11 is replaced by a threaded spindle 56, which is in mesh with an internally threaded passage in a clutch engagement member 50. This member is substantially the same as that shown in Figures 10 and 11 and again has two oppositely-inclined ramp surfaces 52. Operation of the motor 24' will of course result in linear movement of the member 50 along the threaded spindle 56. The ramp surfaces 52 are again be positioned to press any desired one of the clutch members 12 into driving engagement with the opposed clutch member 10.

In all of the embodiments described above, one clutch member of a selected one of the output units is pressed, that is to say positively moved, into driving engagement with the opposed clutch member so as to transmit power from the input shaft of the transmission to the output shafts of the selected output unit. The clutch member in question subsequently returns to the disengaged position under the action of a clutch return spring or the like. However, in the further embodiment illustrated in Figures 13 to 15, the movable clutch member of the output units is moved positively both into and out of the engaged position. Figures 13 to 15 show only the clutch engagement mechanism and the output units themselves and the clutch engagement actuator are omitted for the sake of clarity. In this embodiment, a plurality of cam discs 60 is provided in a line, two such discs being associated with each output unit. The two cam discs at the ends of the line are associated with only one output unit and the remaining cam discs are each associated with two adjacent output units. As illustrated in Figures 13 and 14, there are five cam discs 60 in this case and the transmission system therefore has a total of four output units. All the cam discs 60 have a central polygonal hole formed in them, through which a complementary polygonal shaft 62 passes. The shaft 62 is connected to a clutch actuation motor (not shown) and the cam discs are therefore rotated in synchronism by the clutch actuation motor. Formed in each side surface of each cam disc 60 is a recessed cam track 64. As will be apparent from the following description it is not in fact necessary for the outer surfaces of the two cam discs at the ends of the line to be provided with such a cam track. The cam tracks 64 are all of identical elongate generally oval shape. The two cam tracks associated with each output unit are identically orientated, that is to say in phase, but the cam tracks associated with each output unit are angularly offset from the cam tracks associated with the or each adjacent output unit by 90°. Retained in the two cam tracks associated with each output unit is a respective follower member 66, which constitutes a circular rod. Each rod 64 is connected to the clutch member 12 (of which only a part is shown) of a respective output unit. If the clutch actuation motor is rotated, the cam discs 60 will all rotate with it and the followers 60 will be constrained to progressively move around the two oval cam tracks in which they are retained. As they do so, the followers 66 and thus the clutch members 12 attached to them will be caused to remain substantially stationary during the majority of the time but to move horizontally, that is to say substantially perpendicular to the shaft 62, once per revolution. This horizontal movement of the follower member 66 and of the clutch member 12 will result in the clutch member 12 moving into driving engagement with the opposed clutch member 10 of that output unit, thereby resulting in the transmission of torque from the input shaft of the transmission system to the output shafts of that output unit. As rotation of the clutch actuation motor continues, the follower 66 and the associated clutch member 12 will be positively moved back into the disengaged position by the action of the cam tracks on the follower 66. Accordingly, if it is desired to transmit torque to the output shafts of a particular output unit, the clutch actuation motor is rotated to the desired position in which the clutch member 12 of that output unit is moved into engagement with the opposed clutch member. As described above, the clutch actuation motor may be a stepper motor or it may be a simple motor acting on the shaft 62 via a worm drive.

Claims

1. A transmission system for driving a selected one or two of a plurality of drivable devices by a single drive motor including an input shaft for connection to the drive motor, a plurality of output units, each output unit including a drive member which is connected to be driven by the input shaft, an output shaft and a clutch mechanism, and a clutch engagement actuator arranged to act on a selected one of the clutch mechanisms to connect the drive member with the associated output shaft, thereby transmitting rotation from the input shaft to the said output shaft, characterised in that there is only a single clutch engagement actuator, that each drive member is connected to rotate with a respective first clutch member affording a first engagement surface and each output shaft is connected to rotate with a respective second clutch member opposed to the first clutch member and affording a second engagement surface, that the clutch engagement actuator is arranged to act on a selected one of the clutch members to bring its engagement surface into driving engagement with the engagement surface of the opposed clutch member, that the second clutch member is connected to rotate with two output shafts extending in opposite directions and that the clutch engagement actuator acts eccentrically on the clutch member.

2. A system as claimed in Claim 1 in which the first and second clutch members are constructed for positive engagement with one another.

3. A system as claimed in Claim 1 or 2 in which the clutch engagement actuator is connected to rotate a cam shaft carrying a plurality of angularly offset cams, each of which is associated with a respective output unit and is arranged to contact one of the clutch members of that output unit eccentrically and to press it into drive engagement with the opposed clutch member, whereby rotation of the clutch engagement actuator will result in the clutch mechanisms of all the output units being successively pressed by the respective cam into engagement.

4. A system as claimed in Claim 3 in which the output units are positioned side-by-side in a line and the cam shaft extends along and parallel to the line and the cams are arranged to contact the associated clutch members directly.

5. A system as claimed in Claim 3 in which the output units are positioned side-by-side in a line and the cam shaft extends perpendicular to the line and the cams are arranged to contact the associated clutch members indirectly via respective levers, each of which cooperates with a respective cam and a respective clutch member.

6. A system as claimed in Claim 4 or 5 in which the input shaft is connected to rotate a worm and the drive members constitute worm wheels meshable with the worm, the drive members each constituting one of the clutch members and being movable by engagement by the cams into driving engagement with the opposed clutch member whilst in mesh with the worm.

7. A system as claimed in Claim 1 or 2 in which the clutch engagement actuator comprises an electric motor connected to rotate a pinion gear which is in mesh with a rack gear, either the unit comprising the electric motor and the pinion gear or the rack gear being stationary and the other being movable, on actuation of the electric motor, and carrying a clutch engagement member arranged to contact a clutch member of a selected output unit on actuation of the motor to press it into engagement with the opposed clutch member, thereby connecting the drive member of that output unit to the two associated output shafts.

8. A system as claimed in Claim 1 or 2 in which the clutch engagement actuator is connected to rotate a threaded spindle which is in mesh with a clutch engagement member arranged to contact a clutch member of a selected output unit on actuation of the clutch engagement actuator to press it into engagement with the opposed clutch member, thereby connecting the drive member of that output unit to the two associated output shafts.

9. A system as claimed in Claim 1 or 2 in which the clutch engagement actuator is connected to rotate a plurality of cam discs, two cam discs being associated with each output unit, each cam disc affording a cam track, a respective follower member being retained in the cam tracks of the two cam discs associated with each output unit and connected to one of the clutch members of the associated output unit, the cam tracks being so shaped and arranged that as the cam discs are rotated through 360°, the follower members are constrained to move such that the clutch mechanisms are engaged and then disengaged sequentially.

10. A system as claimed in Claim 9 in which the number of cam discs is one greater than the number of output units and two of the cam discs have a cam track in one surface only whilst the remaining cam discs have a cam track in both surfaces.

11. A system as claimed in any one of the preceding claims in which the clutch engagement actuator is an electric motor.

12. A system as claimed in any one of the preceding claims in which each output shaft is connected to rotate with the associated second clutch member by a connection constructed to permit limited relative rotation.

13. A system as claimed in any one of the preceding claims in which the input shaft forms part of an input unit substantially the same as the output units and the input unit and all the output units include releasable locking means for locking the two output shafts, to rotate with the associated first clutch member, whereby any of the units may constitute the input unit after being so locked.