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Document Type and Number:
WIPO Patent Application WO/2018/130806
Kind Code:
In a motor in hub driveline (fig 2) there is provided a central circular stator mounted with electro magnets (1) with both poles facing outwards in contact with an outer tire (2). The poles of the electro magnets are selectively switched to interact with permanent magnets (3) mounted in or on the surface of the tire to repel the tire locally and move a gap round the stator to produce rotary output of the tire at reduced ratio and without bearings

Application Number:
Publication Date:
July 19, 2018
Filing Date:
January 10, 2018
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1 A motor comprising a first member with a substantially rigid surface and a second compliant member, portions of whose surface may be moved in or out of contact with the surface of the first member and where the second member includes discrete units attached to each other or to the surface or included within the member and where the position of such units relative to the first member is changed when subject to the imposition or removal of electric charge, magnetic fields or any wavelength of electromagnetic radiation. Such movement acts on the second member to create one or more gaps between portions of a contact area between the first and second members and to change and move the gap(s) so that relative movement occurs between the first and second members and is transferred to an output.

2 A motor as in 1 where the surface of the first member is circular, and the second member is endless

3 A motor as in 1, where either the first or second member is tethered or releasably tethered to prevent movement and so make that member a stator and the other member an output.

4 A motor as in 1 where the first member is central and mounted with outward facing and overlapping electro-magnets so as to simultaneously repel and or attract permanent magnets over different portions of the second member or repel by induction suitable units in the second compliant member

5 A motor as in 1 where the first member is linear or non-circular

6 A motor as in 1 or 4 where the units of the second member are flexibly joined or linked in a toggle relationship

7 A motor as in any of 1 to 5 where the first member comprises a sprocket and the second member comprises a flexible chain including units capable of being attracted or repelled as in 1. Such chain to be of fixed length greater than the co-operating length of the sprocket round or within which it extends

8 A motor as in any of the above where output speed change is effected by changing the rate of switching of the input and or changing the force of the input acting on the compliant second member, so as to change the length of the gap(s) and thereby change the reduction ratio.

9 A motor as in any of the above where a second motor is movably mounted within and to a first motor, preferably with gimbals so that the angle of rotary output of the second motor may be adjusted by rotating the first motor

10 A motor as in any of the above where inputs for the time being not actively driving movement are switched on in reverse mode to increase friction between the first and second members

Combined Motor And Reducer


US Patent 7549357 (John P.R.Hammerbeck, Ratio changing method and apparatus. Granted 23 June 2009 now abandoned.) discusses the prior art of harmonic wave geared reducers. Harmonic gears use a rotating outer input to press a non-rotating flexible gear against a circular output, producing a high reduction ratio between the rotating input and the rotating output. US7549357 discloses frictional and geared reducers, but does not disclose the present invention, in which segments (units) are movably connected to their neighbours or to or within a compliant material and individually actuated to create and or move a shallow gap or gaps between a compliant line of segments and a stator and or an output. Moving the gap(s) causes the compliant material and thence the output to rotate with respect to the stator. This is essentially different from Harmonic gears, in which rotary input provided from a rotating shaft is then output at reduced rotation by interaction of substantially circular members over a portion of the available interaction length. In contrast, the present invention provides interaction over almost the entire available interaction length. This is the case whether the driving interaction is by friction or by positive means.

Further-more one embodiment of the present invention (fig 2) relates to a motor in hub, being a total package of motor and drive-line, incorporating power input, speed change, rotary output support without bearings and damping.

In a first architecture (fig 1) where the output lies encircled by a stator there is provided a circle of electro magnets (2) whose core surfaces define the inner surface of a circular stator. Pressing against the inner surface of the stator there is provided a member (3) comprising a compliant material. Close to, or on, the surface of the compliant member (3) are provided multiple permanent magnets (4) aligned so that their repulsive or attractive poles all face the magnetic coils (2). The compliant member may be the final output i.e. integrated with a tyre or wheel or attached to an output by known means, such as those employed in flexible shaft connectors. Ducts to circulate coolant may be provided round and between the coils and stator or within and around the compliant material. In operation the magnetic coils are switched on and off successively around the stator. More than one may be activated at a time. Switching on one or more coils causes a mutually repulsive field to be established between the coil cores and the permanent magnets, causing the compliant member to yield away from the stator and away from contact with the stator. This creates a gap (5) between the stator and the compliant member which can then be caused to rotate round the stator by switching appropriate coils on and off. Rotating the gap causes the compliant member to rotate by the difference in lengths between that part of the surface of the stator that is out of contact with the surface of the compliant member and the length of the surface of the compliant member that is out of contact with the surface of the stator. The difference may be extremely small giving rise to a very high reduction ratio for each rotation of switching of coils round the stator. The displacement of the compliant material to create a gap may be so small and the switching so rapid that the mechanism appears to be merely resonating. Friction between the compliant material and the stator can be increased by switching on, with reversed current, a number coils that are not momentarily creating gaps. This causes the neighbouring magnets in the compliant member to be attracted to the coils and press harder on the stator to increase the friction. Additionally, or alternatively, a fluid channel may be incorporated in the compliant member and inflated to increase the pressure between the member and the stator or such a channel may be incorporated in the stator supports for the electro magnets. Because the device may resonate when operating at specific speeds, changing the fluid pressure will change the resonance. Increasing the pressure in the fluid channel compensates for wearing of the compliant material to stator interface. In normal operation as an electric vehicle drive, the vehicle may be slowed by slowing the cycle of coil activation However, failure of the electrical supply or controls will result in the drive locking up. Deflating a fluid channel in either the stator or output will lower the friction between stator and output. This serves to partially free the drive and provide friction braking. A further method of emergency free-wheel and braking is to mount the drive and associated wheel into a braking system that acts on the stator. The brake system is normally locked to the stator and provides a locked connection to the suspension. When the drive fails the brake is partially released, allowing the drive unit to rotate at whatever rate is optimal for maximum safe braking of the vehicle. All wheels must be released

simultaneously. In the event of electrical power failure brake release should be initiated by other means such as a localised permanent electric power source, springs or vacuum systems as used in trains.

Input speed is controlled by the switching rate of the coils. A further method of control is changing the actuating power supplied to the coils and so increasing the repulsive force and thereby changing the length of the gap. This option allows a degree of continuously variable output.

One significant advantage of this invention is that no bearings are required. To improve this aspect, the surface of the output may be provided with ridges or other surface features, as used in belt driven pulleys, which conform to features on the compliant member so as to maintain alignment and prevent relative axial displacement between the compliant material and the stator. The different elements of the drive can be re-arranged so that the stator is innermost and the output ring is on the outside.

In a preferred layout of a motor in hub driveline (fig 2) there is provided a central circular stator with mounted with electro magnets (1) with both poles facing outwards in contact with an outer tire (2) . The poles of the electro magnets are selectively switched to interact with permanent magnets (3) mounted in or on the surface of the tire to repel the tire locally. The repulsive effect can also be provided by induction means using non-magnetic units backed with steel as the units in the tire. The other pole of each electro-magnet, when switched on, may be used to attract the units in the tire and increase friction between the tire and the stator. Layouts such as overlapping electromagnets will facilitate this.

In a third embodiment (Fig 3 - shows the actuating sequence with actuated segments shaded) multiple rectangular linked piezo segments (1) are butted together and mounted in, or, on compliant material (2) such as rubber and sandwiched between a radially outer stator ring (3) and an inner output ring. The compliant material presses the piezo segments against the output (4), which increased friction on the output, holds the segments in place by compliantly anchoring them to the stator and prevents the segments from rotating. Additionally it provides pre-loading to the piezo segments.

The total length of the piezo segments provided is greater than the circumference of the output, therefore at least two of the piezo segments and neighbouring compliant material initially cannot lie flat on the output and consequently stick up as a shallow triangular arch (5) and are out of contact with the output rotor. By actuating these two segments forming the triangle and the next segment in sequence, (Fig 3), the triangular arch substantially becomes a trapezium and a gap between the piezos and the output rotates around the output. Relative movement of the piezos 95 can be assisted by angling and curving the abutting ends of the segments to create a toggle

relationship so that they naturally snap upwards when actuated and momentarily form an unstable arch with three segments out of contact with the output. It will also be helpful to have a ridge on top of the piezo to act as a fulcrum with increased pressure from the compliant material. During the rotation of the arch, deflection of the piezo elements stores force in the compliant

100 member, which is gradually released as the output rotates. Bending piezo segments may also be used. Actuating them to bend them from a curve around the output to a straight line has the same effect as lengthening the segments, but with an additional outwards vector. Bending the piezos to conform with the curve of the output also evens and increases the friction with the output. Fig 3 shows how the switching sequence of piezos causes a gap to rotate round the inner circular

105 output. As in any rotary embodiment, the stator may be the outermost member or the innermost member and with the power supplied to the piezos from the appropriate direction. Because it requires no bearings or gears, this drive can be manufactured in the form of a very thin ring with a large central opening and either the outer or inner member can be the output. Torque (friction) capacity can be scaled up by increasing the axial length

110 This type of embodiment is appropriate for uses such as humanoid robot arms because it holds position when the power is off and it can be compliant, lightweight and quiet. The large central opening means that a second ring can be installed inside the first on an optionally locking gimbal and thereby the joint can closely mimic the action of the ball and socket in the human shoulder. In employing this mechanism in low temperature applications where the compliant material may

115 become too rigid, compliance may be provided by springs between the piezos and stator that are rotationally locked to the stator and which also press the piezos against the output.

The invention may also use contraction or withdrawal of segments to provide a friction or geared output motor. (Fig 4 ) There is provided a circular output (1) onto which is mounted a tight

120 fitting compliant member (2) which is connected by multiple lengths of smart material (3) to a stator. The smart material changes shape so as to contract lengthwise when stimulated by electric current or magnetic field. Successive lengths of the smart material are switched on and off to create a moving gap ((4) between the compliant member and the output and so rotate the output. The contracting material is preferably embedded in compliant material, which preferably holds

125 the contracting segments in place, presses on the output and also anchors them to a stator (5).

While the transfer of power at the interface between output and compliant member will usually be frictional, it may be provided with complementary features to provide a positive transfer of power. Such a device is capable of employing any material that can be made to contract and so pull back against the force of the compliant member. Thus carbon nanotube muscles, other bio

130 muscles and even the classic frog's legs would operate this rotary motor.

An advantage of some polymers over piezos is that the voltage required is much lower and the material will change shape with the application of a few volts and change back again when the voltage is removed. This gives an opportunity to overcome the problem mentioned in the first embodiment i.e. that the device will lock when power is turned off. Thus, a device using

135 segments of smart material pulling towards the axis on a slightly compliant member will be in free wheel before power is supplied. If power is then supplied to all segments bar a few, a gap will be created that can be moved switching of units, so to create relatives movement between the output and stator 140 Turning to linear embodiments using non-endless stator and compliant surfaces, a new gap should be initiated at the starting end before the gap moves. This is facilitated In a magnetic version by employing a stronger coil and or spring assistance to the starting end coil(s) to increase friction and avoid slippage. In operation sufficient adjacent coils at the starting end of the motor are activated to create a longer than usual gap that is open at the start end. The first

145 coil is then switched off thereby closing the gap and creating a gap of the usual size for moving along the non-endless member. It may prove helpful if the stator converges slightly with the output at the start point. In a linear embodiment the compliant members may be rings arranged successively round a rod. Successively activating and deactivating the polymer members creates a moving gap and relative movement between the polymer members and the rod.


For rotating or slewing large structures such as cranes, diggers, turrets and buildings, the slew rings and bearings are high precision and are necessarily expensive because of their large diameter. Further such rings are liable to impact damage shearing a tooth in operation. A further

155 embodiment takes advantage of the compliance and bearing-less aspect of the invention. There is provided a large inflatable tire or inflatable segments bonded to provide a torus. The outside of the torus fits within a conforming stator support. If the structure is to support a building or non- moveable structure, the conforming support may be cast in position round the torus. The conforming support is provided with endless electrically conducting rails. A small electric

160 locomotive is inserted between the torus and the support and runs on the rails, picking up electric power. The locomotive may be driven as a rack railway. The stator support may also be provided with a trench reaching radially outwards to accommodate the locomotive. The locomotive supports a bar set at right angles to the locomotive. The bar conforms to the curve of the torus and is provided with rollers conforming to the curve of the torus. In operation the locomotive is

165 powered to move along the rail. This causes the gap between the torus and the support to move as the locomotive moves. The torus is supported by the rollers mounted on the bar between the torus and the support. As with other embodiments, moving the gap causes the torus to rotate at a deep reduction ratio compared with the rotational speed of the locomotive. Employed as a mechanism for rotating turrets in military vehicles, the torus can be attached to and support the

170 turret. The locomotive can be withdrawn and the torus will then be completely sealed against the support to prevent gas entry or water entry during river crossings. The inflated torus provides vibration attenuation and reduces noise. The turret can be quickly lifted off for change of engine by deflating the torus and any members employed to further hold it in position. The reduction in mass compared with a slew ring bearing is significant. This embodiment may also be employed

175 as a lightweight winch or similar mechanism. Any of the features, layouts and methods described above may be used in combination to suit the application.

In any of the described embodiments, compliance may be introduced by flexibly linking units, mounting the units to or within compliant material or providing springy connection to the

180 appropriate member.

Those skilled in the art will appreciate that the various features described in the description above may be used in different combinations without departing from the spirit of the invention.