WHEEL DRIVE

Abstract: A wheel drive for a boat steering wheel (2) comprises a front drivable ring (11) for clamping to the spokes of the wheel, and a driving part including an autopilot-controlled motor (30) supported on a rear ring (12) that is itself supported on the front ring (11) by a series of circumferential rollers (35) engaging a grooved path (32) around the front ring (11). A torque reaction engagement (25,26) between the rear ring (12) and an adjacent object (4) prevents rotation of the driving part, so that the motor can drive the front ring (11) and the wheel (2) in rotation by means of a drive belt (40) to steer the boat. The engagement (25,26) does not carry the weight of the driving part, which forms a self-contained unit with the drivable part.

Description: This invention relates to a motor drive for driving a steering wheel, particularly that of a boat such as a yacht or motor boat. It is known to drive a steering wheel from e.g. an automatic pilot by means of a belt passing round a pulley connected coaxially to the wheel and around a drive pulley driven by the motor of the automatic pilot, which is mounted on some fixed object adjacent the wheel e.g. a bulkhead or the steering column. This system has the disadvantage that it is essentially not self-­ contained, the driven pulley and belt being separate from the driving components. The invention addresses this problem by providing a wheel drive including a drivable part, preferably a circular member such as a ring, that can be fixed to the steering wheel so as to rotate with it, and a driving part including a drive motor that is supported by the drivable part fixed to the steering wheel but has means for engaging a torque reaction point provided on an adjacent object in order to prevent it from rotating with the drive. A drive coupling such as a belt enables the motor to drive the drivable part and hence the wheel in rotation. The drivable part and driving part may thus constitute a self-­ contained unit that is substantially entirely supported on the wheel with the torque reaction engagement allowing the wheel to be driven but not bearing the weight of the drive. In a preferred version both the driving part and the drivable part comprise respective rings, secured together coaxially by securing means with retaining engagements adapted to allow relative rotation. This may be achieved by having the two rings of substantially the same diameter, with a rolling or sliding engagement between them around the ring to permit the relative rotation while holding them together axially. A plurality of rollers or sliders on one or both the rings may perform these functions; preferably a set of rollers spaced around one ring engages a circular groove path around the other. The driving motor, and also preferably an automatic pilot comprising a direction-finding sensor, is part of the driving part. It is then necessary to secure only the drivable part to the wheel by appropriate securing means and the driving part will be supported on it. Since in most boats the wheel is held to its axle by a single nut, the whole of the wheel drive may readily be removed from the boat by the removal of the wheel; alternatively the wheel drive may be removed by unshipping the wheel, releasing the wheel drive from it and then replacing the wheel on its axle. The drive coupling from the motor to the driven part preferably comprises a belt driven by the motor and passing around a drum surface of the driven ring. The belt may be toothed and engage corresponding teeth on a drive pulley, the drum surface however being substantially smooth so that slipping can occur under excessive loading of the drive. Means, e.g. comprising a clutch mechanism, may also be provided for manually disengaging the drive belt from the motor in order that, for example, steering may temporarily be done manually. Particularly when the driving and drivable parts comprise respective rings mounted coaxially together, they may define between them a cavity enclosing the drive coupling or a substantial part thereof. Where the drive is by belt, for example, the drum surface engaged by the belt, the belt itself and also a drive pulley of the motor that drives the belt, are preferably all in the cavity between the two parts and substantially enclosed to protect them from fouling and damage. It is preferred that the torque reaction engagement with the reaction point on an adjacent object, to prevent rotation of the drive part with the wheel and to provide reaction for the drive, is adapted to allow a degree of radial movement of the drive part relative to the wheel axis. This is because there may not always be perfect axial alignment between the drive assembly and the wheel itself. The radial freedom may be achieved by having a projection on the adjacent object received in a radially-extending slot provided on the drive part, or vice versa. To provide the necessary torque the reaction point or points should be spaced from the wheel axis. By way of example embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 is a side view of a wheel drive installed on the wheel helm of a boat (shown partially); Figure 2 is a face view of the wheel drive; Figure 3 is a side view similar to Figure 1, but showing the wheel drive sectioned along the line A-A of Figure 2; Figure 4 is a sectional view of the wheel drive taken at Y-Y of Figure 2; Figure 5 is a view along arrow B in Figure 2 of a motor arrangement of the wheel drive; and Figures 6 and 7 are cutaway details showing a drive engagement, in disengaged and engaged positions respectively. Looking firstly at Figures 1 and 2, the wheel helm of a boat comprises a wheel 1 (shown only partially here) having three spokes 2 extending radially from a hub 3 mounted rotatably with its axis horizontal towards the top of a pedestal 4 which is itself mounted on the deck of the boat (not shown). The pedestal 4 serves to mount the wheel 1 at a convenient height and to house the mechanism connecting it to the rudder of the boat. Between the pedestal 4 and the wheel 1, and clamped to the spokes 2 of the latter so as to be coaxial with it, is a generally ring-shaped wheel drive 10. Referring now also to Figure 3, this comprises a circular front ring 11 and a circular rear ring 12 between which an annular cavity 13 is defined around the drive 10. The front ring 11 is of a shallow Y-shaped cross-section with the inner and outer limbs of the U pointing towards the pedestal 4 and defining a substantially cylindrical inner wall 15 and outer wall 16 of the drive 10. The base of the U includes a flat portion defining a flat front radial wall 17 of the front ring 11. This front wall 17 is clamped against the spokes 2 of the wheel by arched lugs 20 positioned over the spokes 2 and screwed by their ends to the front wall 17 of the front ring 11. The front ring 11 is thus constrained to rotate with the wheel 1. The rear ring 12 has the same general diameter and radial extent as the front ring 11 but has a somewhat shallower cross-section defined by a flat rear radial wall 18, with a short outer circumferential flange 23 that extends slightly forwardly, so as nearly to abut the rearwardly-facing edges of the limbs of the front ring 11, thus defining the internal cavity 13 between the rings. At the lowest point of the rear wall 18 of the rear ring 12 there is a hole around which the material of the ring 12 projects inwardly to form an oval hole or slot 25 in which is received a metal pin 26 that projects axially forwardly from the pedestal 4. Screwed to the front of the pedestal 4, opposite the slot 25 on the rear ring 12, is a cast part 27 with a circular socket in which the metal pin 26 is held to extend axially forwardly into the oval slot 25. The slot 25 is substantially of the same width as the pin 26 so that rear ring 12 cannot move horizontally in relation to the pedestal 4 and is thereby restrained from rotation. Also mounted rigidly on the rear ring 12 towards its lower part is a motor of an autopilot device 30, the cylindrical casing of which projects axially rearwardly from the rear ring 12 past one side of the pedestal 4. The autopilot constitutes a control system for the drive and works on the known autopilot principle, including a direction sensing mechanism coupled to the motor 30 for driving the steering of the boat so as to maintain a predetermined heading. The motor of the autopilot drives a drive pulley 51 (see Figs. 6 and 7) located in the lower part of the cavity 13 between the two limbs of the front ring 11 with its axis parallel to the axis of the wheel 1. The drive pulley functions when necessary to drive the front ring 11 and hence the wheel 1 in rotation relative to the rear ring 12 and pedestal 4. To explain this the engagement between the front and rear rings 11,12 will now be described in more detail. Referring to Figures 2,3 and 4 it will be seen that the outside wall 16 of the front ring 11 has a circumferential groove 32 extending right around its inner surface. At seven positions about its circumference the rear ring 12 has thickened, reinforced portions 33 in its rear wall 18 and on each of these a roller 35 is mounted. Each roller 35 is disc-shaped with a tapering edge and is mounted, with its axis of rotation parallel to the axis of the wheel 1, so that its edge engages and rolls in the groove 32 around the front ring 11. By this arrangement the two rings 11,12 can rotate freely relative to one another because the rollers 35 are free to turn, but the engagement of the rollers in the groove 32 prevents the two rings 11,12 from falling apart axially. With particular reference to Figure 5 it will be seen that one of the three rollers 36 rotates about a hub 38 that is itself eccentric about a pivot mounting 39 in the rear wall 18 of the ring 12. Alternatively one or more of the rollers 35 may be adapted for movement out of engagement with the groove 32 to enable separation of the front and rear rings 11,12 when desired. The drive from the drive pulley of the motor to the front ring 11 is by means of a belt 40 that extends around the cavity 13 between the front and rear rings, making contact with a substantially smooth drum surface 2 on the inner wall 15 of the front ring 11. The belt 40 makes contact with the drum surface 42 of the ring 11 all the way round except immediately adjacent the drive pulley, where it is guided away from the drum surface 42 and around the drive pulley by a pair of guide rollers 52,54 whose axes are indicated at 44 and 45 in Figures 6 and 7. The inner surface of the belt 40 is provided with a series of projections and recesses (not shown) and these engage corresponding recesses and projections on the drive pulley 51. Pivoted into the rear ring 12 adjacent the autopilot is a disengaging handle 50 which, when pivoted from the inner to the outer of the two positions indicated in Figures 2,6 and 7 releases belt tension on the drum surface 42 so that the autopilot can no longer drive the front ring 11 and wheel 1. Details of this are seen in Figures 6 and 7. On one side of the drive pulley 51 a first guide roller 52 is mounted on axis 44 on an eccentric bush 53. Alteration of the angle of this bush moves the roller 52 slightly (see dot-dash lines) causing adjustment in the working tension of the belt 40 to allow for manufacturing tolerances. A guide roller 54 on the other side of the pulley 51 is mounted on axis 45 by another eccentric bush 55, this being of much higher eccentricity than bush 53 and being constrained to rotate with the handle 50. In the condition seen in Figure 6 the minimum radius of the bush 55 lies between the axis 45 and the belt 40. The belt 40 is now essentially slack, although in some cases a slight tension may be maintained on the belt, just enough to continue to urge the handle 50 to the position shown in this Figure. In the condition shown in Figure 7 the handle 50 has been brought to position 50′. This causes the roller 54 to exert substantial tension on the belt 40. It is however some 20° overcentre, that is to say past the attitude at which the maximum radius 56 of the bush 55 would be normal to the relaxed line of the belt 40. Therefore the tension of the belt 40 has the effect of biassing the roller and handle to be held in the engaged position. It will be seen that in this arrangement the entire weight of the drive is taken by the mounting of the wheel 1, since the pin and slot arrangement 25,26 does not take any weight. The operation of the drive is as follows. In response to signals from the direction finder of the autopilot the motor 30 of the autopilot drives the drive pulley in the appropriate direction. The belt 40, led around the drive pulley 51 by the two guide rollers 52,54, drives the front ring 11 and wheel 1 in rotation in the appropriate direction, while the slot 25 provides by engagement with the pin 26 a reaction point to prevent rotation of the rear ring 12. If the drive 10 has not been mounted exactly coaxially with the wheel 1 it will oscillate slightly as the wheel 1 turns; the vertical component of this oscillation can be taken up by movement of the pin 26 along the slot 25, while the horizontal component produces only a slight fluctuation in the speed at which the wheel 1 is driven. The engagement between the toothed surface of the driving belt 40 and the drum surface 42 of the front ring 11 is purely frictional, so that if the drive 10 is subjected to excessive loads e.g. in heavy seas, these parts can slip over one another to prevent excessive stresses and possible damage occurring. Should it be desired to disengage the autopilot and steer manually this can be done by throwing the lever 50. It will be apparent that the particular drive mechanism described is not the only one which can be used. For example, the motor could drive a gear or pinion to engage a corresponding rack provided around the ring clamped to the wheel; in this case it would be desirable to provide a slip clutch in the motor gearbox to allow uncoupling under heavy loads.

Claims: 1. A wheel drive for a vehicle steering wheel (1), the drive having a driving part (12,30) comprising a drive motor for driving in rotation a drivable part (11) constrained to rotate with the wheel (1), characterised in that the drivable part (11) is adapted to be fixed to the wheel (1), and to support the driving part (12,30) while being rotatable relative thereto, and the driving part (12,30) comprises means (25) for making a torque reaction engagement with an adjacent object (4,26) to restrain the driving part (12,30) from rotation with the drivable part (11) and wheel (1). 2. A wheel drive according to claim 1 wherein the drivable part comprises a generally circular member (11) adapted to be fixed to the wheel (1) substantially coaxially to rotate therewith. 3. A wheel drive according to claim 2 wherein the driving and drivable parts (12,30,11) are connected by retaining engagements (34) that engage around a circle to hold the parts together axially while permitting relative rotation of the drivable part (11). 4. A wheel drive according to claim 3 wherein the retaining engagements comprise a plurality of rollers (35) on one said part engaging a circular path (32) on the other part. 5. A wheel drive according to any one of the preceding claims, wherein the driving and drivable parts comprise respective circular rings (11,12) of substantially the same diameter, held together by retaining engagements to oppose one another coaxially. 6. A wheel drive according to any one of the preceding claims, wherein drive coupling (51,40) connecting the drive motor to the drivable part (11) is enclosed in a cavity (13) defined between the driving part (12) and the drivable part (11). 7. A wheel drive according to any one of the preceding claims, wherein the driving part includes an automatic pilot (30) incorporating a direction sensor, for controlling the drive motor. 8. A wheel drive according to any one of the preceding claims, wherein the means for providing a torque reaction engagement comprise an axially projecting pin (26) radially spaced from the wheel axis and adapted to engage a corresponding opening (25). 9. A wheel drive according to any one of the preceding claims, wherein the torque reaction engagement means (25,26) are adapted to accommodate relative radial movements due to eccentricity of mounting of the drive on the wheel (1). 10. A wheel drive according to any one of the preceding claims, wherein the drive motor drives the drivable part (11) through a coupling comprising a belt (40) that engages a drive pulley (51) of the motor and a drum surface (42) of the drivable part (11). 11. A wheel drive according to any one of the preceding claims, wherein a manually operable mechanism (50,52,54) is provided for wholly or partially disengaging drive coupling between the drive motor and the drivable part (11).

Inventors: FAWCETT, DEREK JAMES
Applicants: NAUTECH LIMITED
Application year: 1988
Main classification: B63H25
IPC codes: B63H25