WO2002095912A1

WO2002095912A1 - Radial electric motor and control thereof

Info

Publication number: WO2002095912A1
Application number: PCT/NZ2002/000100
Authority: WO
Inventors: Peter Cecil Joseph Parsonage
Original assignee: Peter Cecil Joseph Parsonage
Priority date: 2001-05-21
Filing date: 2002-05-21
Publication date: 2002-11-28

Abstract

An electric motor is disclosed having a number of radially oriented solenoids. Each of the solenoids has a plunger and the plungers are mounted relative to each other and relative to an output shaft. A control methodology is disclosed for energising the solenoids to rotate the output shaft and meet required performance characteristics such as required torque and speed of rotation. The motor is capable of providing high torque at relatively low rotational speeds. It also has relatively small axial dimension, so it is particularly suited for electric vehicle applications.

Description

RADIAL ELECTRIC MOTOR AND CONTROL THEREOF

F1 R[ D OF THE INVENTION

This invention relates to electric motors and control of electric moiors.

5 BACKGROUND OF THE INVENTION

Conventional electric motors operate by establishing electromagnetic forces that attract and/or repel each other between a rotating member (a rotor) and a stationary member (stator). In many existing motor constructions the magnetic flux is generated in a substantially radial direction. Therefore, it is not used optionally to create tangential forces 10 between the stator and the ro r which in turn creates torque.

One- area that is very relevant to electric motor design is that relating to electric vehicles. Electric vehicles have a significant problem that inhibits their widespread use. The energy that can be stored in a battery is very small compared to the energy available from fossil fuels. Although improved batteries are being developed, it is also important to provide more ) 5 efficient electric motors in order to extend the operating range of electric vehicles.

Unfortunately the higher efficiency normally associated with electric motors is typically at one speed, and that speed does not necessarily suit the wheel speed of an electric vehicle. As the speed of a typical electric motor approaches the maximum or minimum speed for that motor, the efficiency in converting electrical energy to mechanical energy falls down 0 towards zero. Therefore, it is desirable to provide an electric motor capable of high efficiency at speeds normally associated with the drive wheels of an electric vehicle.

Speeds thai are associated with drive wheels for a vehicle are usually relatively low compared with conventional electric motor operating speeds. Not only does a motor for this application need to be efficient at these speeds, but it also needs to be capable of providing 5 high torque at these speeds to enable such a motor to directly drive the wheel of an electric \ chicle. Finally, another desirable characteristic of a motor for an electric vehicle application is the "form factor^" of the motor. Most conventional motors have a relatively small diameter and are relatively long in their axial length. In order for a motor to be physically adapted to directly drive the vehicle wheel, the motor needs to be relatively thin in the axial dimension,

OBJECT OF THE INVENTION

It is an object to provide an electric motor which will at least go some way toward overcoming disadvantages of existing motor constructions, or which will at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

In a first aspect the invention provides an electric motor having a plurality of actuators, each actuator acting in response to application of electrical energy to provide a substantially linear mechanical movement, the actuators being mechanically connected to an output of the motor, and control means arranged to selectively energise the actuators to impart rotary motion to the output.

In a preferred embodiment, the control means is able to selectively energise each actuator to prov ide the output of the motor with a desired output characteristic. The required output characteristic may be a required speed, or a required torque, or both a required speed and a required torque.

Selective energisation of the actuators by the control means is such that the control means is capable of energising more than one actuator at the same time. The control means is also capable of energising one or more actuators in advance in order to provide a required electric current in those one or more actuators at a future point in time. This enables the motor to provide greater torque, or to be operated at a higher speed. In a preferred embodiment, the control means is also capable of energising one or more of the actuators to provide an active braking effect Lo the output of the motor. The control means can also be used to provide a regenerative braking effect.

The motor preferably includes a housing and the actuators are mounted on the housing with the motor output comprising an output shaft which can rotate relative to the housing. The housing is preferably sealed and contains a hydraulic fluid such as a lubricating fluid. Each actuator includes a plunger which moves within a actuator housing within which the plunger is sequentially received and expelled, and the hydraulic fluid can enter and leave the actuator housing.

Conveniently, hydraulic fluid which is expelled from an actuator housing upon a plunger entering that housing is forced into one or more other actuators housing to assist in the expulsion of the other plunger or plungers from those one or more housings.

alternatively, the control means comprise one or more switches provided to effect connection of the actuators to a supply of electrical energy to thereby effect the selected energisation of the actuators, and the control means includes communication means to receive control instructions to control the one or more switches. The communication means may include wireless reception means lα receive one or more signals containing the control instructions.

In a further aspect the invention provides a wheel assembly having a wheel operatively connected to the output of the motor such that the wheel may be driven by the motor.

In a. further aspect the invention provides a wheel including the motor, in a preferred embodiment the motor housing comprises a part of the wheel which would normally remain stationary which respect to the vehicle in use. Tn another embodiment, the motor housing comprises a part of the wheel which would normally rotate relative to the vehicle body in use

In another aspect the invention provides a vehicle including the electric motor set forth above Preferably the electric motor is operatively connected to a wheel of the vehicle Alternatively, the electric motor is provided as part of a wheel of the vehicle. I n another aspect the invention provides a generator having a plurality of actuators, each actuator providing electrical energy in response to a substantially linear input mechanical movement, the actuators being mechanically connected to a generator input and the generator input being adapted to receive energy from a source of rotational motion.

I n a preferred embodiment the actuators comprise solenoids, each solenoid comprising a coil within which a plunger having a permanent magnetic field is provided.

DRAWING DESCRIPTION

Figure 1 is a diagrammatic plan view of a first example of a motor according to the invention using three solenoids,

Figure 2 is a side elevation of one of the solenoids of Figure 1,

Figure 3 is a plan view from below of the solenoid of Figure 2,

Figure 3a is a diagrammatic plan iew of a second example of a motor according to the invention.

Figure 4 is an isometric view of a third example of a motor construction according to the invention, using eight solenoids, only two of which are shown,

Figure 5 is an isometric view of the motor of Figure 4 in an assembled configuration showing the output shaft,

Figure 6 is a plan view of the motor of Figure 4,

Figure 7 is a side elevation in cross section of the motor of Figure 6,

Figure 8 is an elevation of an output shaft for the motor of Figure 6 and 7,

Figure 9 is a plan view of the output shaft of Figure 8,

Figure 10 is a plan view of a connecting wheel for the motor of Figures 4 and 5,

Figure 11 is a side elevation of Figure 10, Figure 12 is a schematic of a control circuit for the invention,

Figure 13 is a graph of Force (Ib.N) against Stroke (in, mm) for a preferred solenoid used in the motor of Figure 4 in response to fields of a number of different ampere-turns, and

Figure 14 is a flow chart illustrating one example of the control method according to the invention.

DETAILED DESCRIPTION

It will be appreciated that the general motor design described in this document provides an efficient means of converting the linear motion generated by one or more electric solenoids imo the circular motion required by the output of an electric motor. It also will be understood that reference in this document to electric solenoids includes any other device which provides mechanical energy in a substantially linear direction as a result of electrical energy input.

The construction has the advantage that the flux generated in the known way in a radial direction by energisation of one or more of the solenoids, is acted on efficiently by the plunger associated with that solenoid to provide a force in a radial direction which is efficiently converted by the mechanical linkages to a rotational force or torque.

Λ. will be seen from the two examples described below, any number of different mechanical linkages may be used.

Motor Example 1

Referring to Figure 1. a simple diagrammatic illustration of one form of a motor 1 according to the invention is shown. A housing 10 is provided, which in Figure 1 is diagrammatical ly illustrated in the form of a disk. At equidistant poinLs around the periphery, solenoids 7, 8 and 9 are provided, each being pivoted about a pivotal axis represented by point 19, which pivotal axis connects each solenoid to the housing 10. The solenoids have plungers 3 (refer to Figures 2 and 3), and each plunger is pivotally connected to a yoke 17. The connection is illustrated by circles 1 1 , 12 and 13. A central point 16 of the yoke 17 is connected to an output shaft (not shown) which rotates about a central poinl 18 (relative to the housing 10) when the motor is operated as will be described further below. The movement of point 16 is illustrated by circle 14 in Figure 1. In Figures 2 and 3 the pivot point 1 is represented by spigot or pin 6 which can be mounted on housing 1 using an aperture for example in housing 10, to allow the solenoid to swivel. The solenoids arc provided on a base plate 5 from which spigot β projects.

The solenoids described above are of a conventional type i.e. having a substantially tubular winding within which a cylindrical plunger of an appropriate substance, for example a soft iron or a permanent magnet material is provided. Energisation of the solenoid winding causes the plunger to be drawn into the coil, or pushed out of the coil depending on the direction of the current provided in the solenoid coil. Those skilled in the an will appreciate that the solenoids arc not restricted to a circular cross-sectional shape and may be different shapes e.g. square in cross section.

As can be seen from Figure I , selected energisation of the solenoids can be effected to create rotational movement of central point 16 about point 18 to thereby turn an output shaft. This pattern of energisaiion will typically be sequential, but in certain modes of operation only a single solenoid may be intermittently or periodically energised. This is discussed further below.

In Figure I . solenoid 9 is shown in a fully retracted position in which the plunger has been drawn into that solenoid and solenoids 7 and 8 have plungers in extended positions. From the position as shown in Figure 1. if solenoid 9 is de-energised and solenoid 8 is energised, it will be seen that the central point 16 will be drawn i.e. "pulled" in a direction toward solenoid 8 to thereby create the required turning effect.

Motor Example 2

In Figure 3a a similar, but alternative, arrangement to the example described above is shown whereby solenoids do not pivot, but instead have their plungers attached pivotally to ;orjιecling rods 6a, 7a and 8a which are in turn pivotally connected at the other ends to the ke. The operation of this motor is otherwise substantially the same as that described above with reference to example I .

Motor Example 3

A third example of a motor according to the invention will now be described below with ? reference to Figures 4 to 9.

Referring lo Figure 4, the motor is shown having a housing 50 arranged to accommodate eight solenoids. For ease of illustration only two solenoids are shown and these are referenced 52 and 54, It will be appreciated that any number of solenoids could be used, but the preferred minimum number is 2 (for example oriented at 180 degrees apart) and using a 10 combination of "pull" and/or ''push^" energisations of the solenoids to achieve rotary motion.

Solenoids 52 and 54 are preferably pull type tubular solenoids model 5-41-300 available from Solenoid City of Van Nuys, California. The overall dimensions of the coil for this model of solenoid are approximately 76mm in diameter by 105mm in length. The plunger has a stroke of approximately 100mm of which 50mm is used, and the overall weight of the 15 solenoid and plunger is approximately 4.3kg,

In Figure 5, the motor (again with only two solenoids) is shown assembled illustrating an output shaft 56. It is apparent from Figure 4 and 5 that the housing 50 can be made from any suitable material, for example aluminium or plastics. Aluminium has the advantage of prov iding good heat dissipation while being light and sufficiently strong and not being 20 substantially magnetically permeable and thus also being efficient in a magnetic sense. The housing 50 can be provided in a single piece and machined or otherwise formed so as to allow end plates 38 to be attached on one or both sides. Apertures 60 are provided in the housing and are threaded in the preferred form with an internal thread which engages with an external thread provided at the base of each solenoid. In this way, solenoids are easily

? s attached to the housing, and may easily be detached if they need to be repaired i.e the motor does not need to be completely disassembled if one solenoid coil fails for example, In conventional electric motor constructions, individual coils are not usually accessible.

Turning lo Figure 6, the embodiment of Figures 4 and 5 is shown in plan view, again with only two solenoids shown, Each of the solenoids has a connecting rod 62 which is pivotally atrachcd at one end to the solenoid plunger 64 and is pivotally attached at the other end to a connecting wheel 66 as will be described further below. Further details of the construction can be seen in Figure 7.

Referring to Figure 7, it can be seen that the connecting wheel 66 is connected by a crank pin 68 to an output shaft 70 that is journalcd in bearings relative to housing 50.

In Figure 8. the output shaft is shown in elevation having an aperture 72 for receiving the crank pin and a key 74 for connection to apparatus, such as a vehicle wheel or a washing machine agitator, to be driven by the motor. In figure 8 the shaft 70 is shown in plan view in which it can be seen that the shaft is appropriately counter-balanced.

fuming now to Figure 10, the connecting wheel is shown in greater detail. Holes 80 are used to pivotally mount the connecting rods 62 to the wheel. Apertures 82 are optionally provided to reduce weight of the connecting wheel. In Figure 1 1 the wheel is shown in cross-section in which it can be seen thai il consists of two separate parts (although one skilled in the art will appreciate that an alternative design could be machined from a unitary piece of material). The construction, as shown in Figure 11, allows the connecting rod to be conveniently pivotally connected between the upper or lower faces of the connecting wheel, Similarly, the other end of each connecting rod is pivotally connected to the plunger of the relevant solenoid by providing the remote ends of each plunger with a recess adapted to receive each connecting rod.

The physical motor construction 50 includes the housing 52 being filled with a hydraulic fluid such as oil, This has several potential benefits. Firstly, it helps disburse heat being generaied. It also provides lubrication for the moving parts and quietens the motor by preventing direct contact between the moving components. The use of oil also provides a hydraulic effect, This effect can be described as follows. When a solenoid plunger is pulled into its respective solenoid coil, oil is displaced from the solenoid through spaces between the solenoid plunger and the coil (or in a specially made hole or groove in the plunger). Because the housing between solenoids is a sealed system, the oil expelled from one solenoid would be forced into another (for example through the hole or groove provided in one of the other solenoid plungers) which is coming out of the solenoid coil. Therefore the 11} draulic effect insists on forcing the other plunger out. Mo tor Control

Turning now to Figure 12, a diagrammatic representation of a motor control system is shown in which a motor according to the invention is generally referenced 1. A control means, for example microprocessor 90 is provided, and a microprocessor actuated switch array (which could be electronic, electrical or electromechanical) 92 is provided which energises one oτ more selected solenoids at varying time intervals for varying durations by connecting the power supply 94 to those solenoids. In the preferred embodiment, the switches comprise power electronic switches such as FETs.

A significant advantage of the invention is that the power supply 94 can comprise a DC suppl> i.e, a supply provided by a battery, Furthermore, it will be appreciated that solenoids can be provided (and are readily available such as the model 5-41-300 referred to in example 3 above) to operate off low voltages such as a 12 voll supply provided by a car battery or a number of parallel connected car batteries. Therefore, the invention is particularly applicable to electric vehicle designs. A motor (or more than one motor) of the present invention may be provided directly connected to a wheel so that no transmission is required. Accordingly, the efficiency of the energy conversion from the battery or other electric power supply to a vehicle wheel is greatly increased. Alternatively, a wheel could be designed incorporating the motor of the present invention. As can be seen from the drawings relating to example 3, the axial length or "thickness" of the motor is relatively small. Therefore the housing 50 referred to above can form a wheel hub for direct connection to the chassis of the motor vehicle and the output shaft 76 may be directly connected to a rotational part of the wheel which extends about the periphery of the housing 50 (and solenoids), It will be readily apparent to one skilled in the art that an alternative wheel design that incorporates the motor o ^' the invention may be provided by arranging the solenoids within the housing 50 rather than externally o the housing. In this way. the solenoid plungers may be connected to a yoke that is eccentrically mounted on a wheel rim which in turn is directly mounted on bearings about the periphery of the housing 50. In this construction, the exterior or periphery of the housing 50 will preferably be circular rather than having discreet walls as shown in the Figures.

It will be seen that ihe controller could control one or more motors, and if one controller is provided for each motor, these may be effectively networked into one central control system. Arcordingly. the invention provides for individual wheels of a vehicle to be controlled in such a way as to provide required performance characteristics for the vehicle. Therefore for example, if a four-wheel vehicle has two driving wheels, each wheel being directly driven by one of the motors of the present invention, then the mechanical differential gear system whic is used to distribute energy to vehicles driven with a single source can be disposed with and instead implemented in the control system of this invention, This is because the control system of the present invention can be used to drive each wheel individually at a required speed. Those skilled in the art will appreciate that individual wheel speed control also allows the control system to be used to actively steer the vehicle.

Furthermore, the motor of the present invention lends itself to easy and precise control (as will be described further below) so that any desired braking effect can be achieved without requiring a vehicle, for example, to have a separate braking system. For example, in order to provide a braking effect, selected solenoids can be energised to oppose the direction of the motion of the driven wheel, Due to the mechanical linkage arrangement a highly resistive force can be provided to the vehicle wheel and if, for example, all the solenoids are energised to restrain the output shaft in a particular position, a vehicle wheel may be effectively locked.

Since the control system of the invention is very effective, an equivalent to "ABS'^* vehicle braking systems may be provided by the control system. Therefore, by deteciing, using known means, whether the vehicle wheel is about to slide relative to the surface over which it is travelling under braking, the braking effect can be reduced slightly to prevent wheel slip and therefore provide the user with control over the vehicle in a sudden braking situation.

The motor can provide a regenerative braking effect if the plungers are magnetised. Therefore, as the plunger is dragged out of a coil or pushed into the solenoid coil, a voltage is generated across ihe coil, and if the coil is connected to the power supply in the correct fashion, energy may be returned to the supply. Therefore, the invention also provides a generator,

Although a number of different mechanical linkage arrangements between each solenoid and the output shaft are illustrated in the foregoing figures and description, it will be appreciated thai the invention includes a large number of different linkage arrangements including linkage systems that arc similar to those used in rotary internal combustion engines, Furthermore, with reference to Figure 12, it will be understood that the controller 90 may be provided remote from the motor or motors which it controls and that communication between the controller and the switch array 92 can be wireless i.e. appropriate control instructions may be provided by radio frequency signals or optical signals for example. Therefore, a motor could be controlled remotely by an infrared link for example, or by wireless communication protocols such as that referred to under the trade mark Bluetooth. Also, the invention envisages the motor being provided with switching network 92 physically incorporated within the motor. For example, electronic switches could be provided mounted on the housing 52, or on each solenoid.

A characteristic of the energisation of the solenoid is that the solenoid winding has inductance which results in an exponential increase in current in the solenoid coil after it has been connected to a power supply. Also, the inductance will vary depending upon the position of the plunger relative to the coil. Thus, when the motor is operating at low speeds, there is typically sufficient time for a significant current to be established in each solenoid coil, and therefore a significant attraction of repulsion force can be provided to the solenoid plunger. The time for which the current is allowed to have effect can be used to control the torque or speed of the motor. However, when high speeds of operation are desired, the current in each solenoid coil may noi be able to reach a desired magnitude before the physical position of the output shaft dictates that the next successive solenoid must be energised. A novci aspect of the present invention is the energisation of one or more solenoids in advance of a solenoid which is, or would be, required at a particular point in time.

Therefore, initialising the energisation of a solenoid in advance allows time for current to build up in the coil of that solenoid, so that a pushing or pulling effect of a required magnitude can be provided at the required time during high speed operation. This same methodology is also applied during active (for example regenerative) braking. A further aspect of the control system involves energising more than one solenoid at any point in time in order to provide increased torque if required. Therefore, even if the motor is operating at low speed but a sudden increase in torque is required (for example to accelerate a vehicle) the solenoid which will nomially be operating can be augmented by energising a number of adjacent solenoids to provide the sudden increase in torque necessary to accelerate the vehicle.

Smooth controlled acceleration from a standstill is another important aspect that a control system needs to address. If the motor output is heavily loaded, then a smooth acceleration is unlikely to be a problem, However, if the motor output is lightly loaded then the control system may need to take into account any sudden change in acceleration due lo energisation of one or more solenoids at start up, In many applications this may not be important, but in an electric vehicle application acceleration will change the nature of the ride provided by the vehicle. One approach that the control system may implemeni is to initially energise the solenoids or solenoids which exert the least torque. This solenoid will be the one which has an armature that is near full extent. As can be seen with reference to Figure 13, the force exerted by the solenoid reduces as the stroke of the solenoid increases. In this way, some control can be exercised upon the start up torque.

Another method of controlling the start up torque, and for controlling the energy applied to each solenoid, is to effect pulse width modulation to the solenoid coils. Therefore, the output of the microprocessor may be modulated, for example in a square wave having a variable duly cycle. The square wave can then be applied to the switching device for any one of particular solenoids that is being energised. As the duty cycle increases the effect of the voltage applied to the solenoid coil increases correspondingly. Therefore, the duty cycle and time period for the energisation of any particular solenoid can be chosen (for example from a lookup table in the microprocessor) to control the force applied by each solenoid and the length of time for which that force is applied. Variation in the duty cycle can also be used to compensate for the force/stroke non-linearity shown in Figure 13.

In Figure 14. a flow chart for control of the electric motor described above is shown, Firstly, beginning at step 100 the control inputs are defined. As can be seen, photo-interrupters provide an indication of when each solenoid plunger is in or out. An analog voltage is used in this example to provide a desired speed where 2 '/. volts represents the motor being stationary, zero volts is the motor going at maximum speed in reverse (approximately 1000 rpm in this exa ple) and the five volt signal represents the motor going in a forward direction at maximum speed, (again 1000 rpm). The output signals are also defined in this case being an on or off signal to each of the solenoid coils. The process starts at step 102 and the first step is to measure the value of the input voltage (i.e. required speed and direction) at step 104, In step 106 the actual speed of rotation is calculated. This is performed by bridging the time between adjacent activations of the solenoids and measuring the order of activation of the solenoids to obtain an indication as to whether the motor is travelling forward or reverse i.e. clockwise or counter clockwise.

In step 108 the required speed and direction of rotation is determined. Therefore if the input indicates that the motor should be stopped, the process proceeds to step 110 to see whether the actual direction matches the stop condition. If it doesn't, then the system applies braking in step 1 1 until the motor has stopped.

Similarly, if a clockwise direction is required, then the comparison between actual and required directions is undertaken in step 1 14 and if there is not a match, then braking is again applied in step 1 12 until the motor has stopped. If a counter clockwise direction is required. then the comparison is performed in step 1 16 and again if there is not a match then braking is applied in step 1 12.

If after the comparison in step 1 14 shows that the motor is rotating in a clockwise direction, ihen the desired speed is compared with the actual speed of rotation in step 118 and appropriate control is applied to speed up the motor in step 120 or slow down the motor in step 122. Similarly, after the counter clockwise direction comparison is performed in step 1 16. if the motor is rotating in a counter clockwise direction then a speed comparison is performed in step 124. Again, if the motor is rotating too quickly, then the control system slows down the speed of rotation in step 1 6, or alternatively speeds up the motor in 128. The process flow then returns to step 104.

Increasing the torque (i.e. power into the motor) causes it to accelerate, thereby increasing the motor speed. Therefore, a speed control system is provided in that when the speed increases, the torque (power input) is reduced to hold the speed constant. For the greatest torque (speed) the solenoids are operated in groups of three (in the example where eight solenoids are provided in total) with the longest possible pulse that suits the particular speed as set by the input voltage (which in the preferred embodiment is established by potentiometer). Ft>r lesser speed/tυrque the pulse duration may be reduced and the solenoids operated in groups of two, or individually, As the torque requirement is further reduced solenoids may only be fired occasionally (for example only every second solenoid may be fired, or only one solenoid may be fired every complete motor revolution),

The sysiem described above refers to photo-interrupters being used to provide an indication of solenoid plunger position. A more complex approach, which can save cost, is to instead measure the change in current, over a very short time period, in response to a known applied voltage to each solenoid. This approach can be used since the inductance of each solenoid will depend upon plunger position It can also occur dynamically during motor operation, and be used to determine motor speed,

In an electric vehicle application, anolher important consideration for the control system is the energy available from the power supply. In a simple form, this can take the form of a baste visual indication of the battery state of charge to the user. However, the invention also provides for monitoring of the available energy, such as the battery safe charge, and controlling the energy applied to the motor accordingly. Battery state of charge can be monitored in a number of ways, for example based upon battery terminal voltage and integrating the current delivered by the battery over time beginning when the battery is known to be fully charged and comparing this with a maximum integrated current which may be delivered from a fully charged battery. A lookup table is provided in the microprocessor whereby as the energy available from a power supply reduces to a certain point, then the maximum acceleration and/or maximum speed of the motor are reduced to predefined limits as an energy conservation measure.

The motor control system described aboγe provide a number of advantages, particularly for electric vehicle applications. These advantages include efficient operation over a number of output speeds, the ability to provide high torque at low speeds, and precise control which includes acceleration and braking control.

Although the discussion in the examples provided has made references to electric vehicles, it

AH be appreciated that the invention has other applications, Another example is a washing machine drive, where varying speed characteristics and torque requirements need to be met to provide an agitation action. Tn the case of a vehicle, the invention is also applicable to pcrsonal electric vehicles such as scooters including that commonly referred to as "the S iiwav^".

Claims

π.AlMS:

1. An electric motor having a plurality of actuators, each actuator acting in response to application of electrical energy to provide a substantially linear mechanical movement, the actuators being mechanically connected to an output of the motor, and control means arranged to selectively energise the actuators to impart rotary motion to the output.

2. A moior as claimed in claim 1 wherein the control means can selectively energise each actuator to provide the output with a desired output characteristic.

j . A motor as claimed in claim 2 wherein the required output characteristic comprises a required speed.

4. A motor as claimed in claim 2 wherein the required output characteristic comprises a required torque,

5 A motor as claimed in claim I wherein the control means can energise more than one actuator at the same time.

6. A motor as claimed in claim 1 wherein the control means is capable of energising one or more actuators in advance in order lo provide a required electric current in those one or more actuators at a future point in time.

7 A motor as claimed in claim 1 wherein the control means may energise one or more actuators to provide an active braking effect to the output.

8. A wheel for a vehicle, the wheel including an electric motor according to claim 1 .

9 A vehicle having at least one driven wheel, the wheel being connected to the output of an electric motor according to claim 1 to be driven thereby.

10 Any novel feature or step or combination thereof disclosed herein