Patent Publication Number: US-2011049906-A1

Title: Apparatus for converting kinetic energy

Description:
The present invention relates to the conversion of kinetic energy from moving vehicles. 
     Electric rotating machines for the conversion of kinetic energy to electrical energy, such as electric generators and motors generally have an optimum operating speed, at which the electro-magnetic interaction of a moving component with a stationary produces a desired result. For generators and motors described in this specification, the movement of the moving component is a rotation of an armature about an axis of the motor. For an electric generator the desired result is an output of electrical power derived from an input of mechanical power. For an electric motor the desired result is an output of mechanical power derived from an input of electrical power. In such a rotating machine, conversion of mechanical power to or from electrical power is by means of an interaction between a magnetic field and a plurality of electrical wires. The magnetic field may be derived from an electro-magnet or a permanent magnet, or a combination of both. The plurality of electric wires are normally arranged in a number of coils, each coil being wound around a core of a magnetic material. The core of magnetic material is normally shaped so as to direct the flux of a magnetic field within the rotating machine so that it passes through the coil or coils. 
     A problem with known electric machines is that on starting the machine, a high torque is required to accelerate the machine to a suitable operating speed. A part of this torque arises from the mechanical inertia of the machine. In part the this torque arises from a load applied to the machine, which in the case of an electric motor is a driven mechanical load, and in the case of an electric generator is an electrical load. 
     This invention describes as hereinafter set out is by way of example an electrical generator suitable for use with apparatus that is operated on by vehicular traffic passing over it so as to convert a portion of the kinetic energy from each of the passing vehicles into another form of energy. Typically electrical generators operate within a magnetic field which is generally fixed, and either produced as an electro-magnetic field for example by current carrying field coils as a result of relative movement within the generator, or alternatively are constructed with permanent magnets. In both cases, the magnetic field is used to transfer energy from one part of the machine to another, and in the case of a generator thus provides a resistance to rotation which is the consequence of the rotating component moving within the stator, so as to generate an electrical power output and thereby resulting in resistance to rotation. 
     An intention of this invention is to reduce the mechanical inertia of the electrical machine, and in the particular case of an electrical generator, to also reduce the electrical load on the generator. This is advantageous as it also permits the inertia of the drive mechanism to be reduced. 
     According to a first aspect of the present invention, there is provided apparatus for converting kinetic energy into usable power, comprising a frame arranged to be fixed in a vehicle running track and a plurality of plates mounted to the frame so that a vehicle running face of each plate is substantially level with the surrounding track, each plate being movable in relation to the track so as to drive an energy conversion means, wherein the energy conversion means comprises a rotating member having variable inertia. 
     A benefit of the first aspect of the invention is that the energy conversion means is enabled to provide useable power from derived from the kinetic energy of passing vehicular traffic. 
     Preferably the apparatus further comprises at least a first and a second plate being arranged to be moved sequentially in that order by a vehicle passing over the plates, such movement of each plate arranged to cause rotation of a drive mechanism, wherein at least the second plate is arranged to impart a greater degree of rotation to the drive mechanism than the first plate. 
     According to a further aspect of the present invention, there is provided apparatus for converting kinetic energy into usable power, comprising a frame arranged to be fixed in a vehicle running track and a plurality of plates mounted to the frame so that a vehicle running face of each plate is substantially level with the surrounding track, each plate being movable in relation to the track, at least a first and a second plate being arranged to be moved sequentially in that order by a vehicle passing over the plates, such movement of each plate arranged to cause rotation of a drive mechanism, wherein at least the second plate is arranged to impart a greater degree of rotation to the drive mechanism than the first plate. A benefit of the further aspect of the invention is that a vertical force exerted by the first plate upwardly on a passing vehicle may be similar to a vertical force exerted upwardly by the second plate. 
     Preferably the apparatus comprises energy conversion means comprising an electrical generator. 
     A benefit of the energy conversion means comprising an electrical generator is that the power output from the apparatus may be easily utilised. 
     Preferably the energy conversion means further comprises means for storing electrical energy. 
     A benefit of electrical energy storage is that an electrical power output may be maintained during periods when there is no vehicular traffic passing over the apparatus. 
     Preferably the electrical generator comprises a rotating part having variable inertia. 
     A benefit of the generator having a rotating part with a variable inertia, is that a maximum stress on the drive when starting the rotation of the rotating part is reduced. 
     Preferably each plate is arranged to protrude the surrounding surface in a first position when it is not acted on by a vehicle. Preferably at least an edge of the vehicle running face is substantially at the same level as the surrounding surface. In an embodiment, the edge may comprise a surface with a radiused and/or curved and/or bevelled surface. 
     A benefit of the edge being substantially at the same level is that vehicle tyres are not damaged as they contact the plate. 
     Preferably each plate is arranged to move to a second position when it is acted on by a vehicle. Preferably when in the second position a highest portion of the vehicle running face is at least substantially level with the surrounding surface at least the portion where a vehicle is acting on the plate. 
     In an embodiment, when in the second position a highest portion of the vehicle running face is below a level of the surrounding surface at least a portion of the plate. 
     A benefit of the plate being permitted to move so that a portion of the plate is below the surrounding surface is that where a heavy vehicle with large wheels passes over the plate a maximum movement of the plate in the vertical direction can occur. 
     Preferably at least a portion of each of the plates moves in a downwardly substantially vertical direction as a vehicle passes over the plate. A benefit of the plate moving in a vertical direction is that the weight of a passing vehicle may act efficiently on the drive mechanism. 
     Preferably each of the plates is resiliently urged from the second position to the first position. 
     Preferably each of the plates is restrained from moving higher than the first position. 
     Preferably the downwardly substantially vertical direction is an arcuate movement about an axis. 
     Preferably each of the plates is pivotally supported at or adjacent to one end so as to resist vertical movement as a vehicle passes over the plate. More preferably the plate is also arranged to resist horizontal movement. 
     A benefit of the plates being pivotally supported at an end is that construction of the mechanism may be simplified. A benefit of the plate being able to resist horizontal movement is that a vehicle may traverse the plates in a controlled manner. 
     Preferably the apparatus further comprises two similar sets of plates, one on either side of a longitudinal centre line along the vehicle running track. 
     In an embodiment the end pivotally supported is adjacent the centre line along the vehicle running track. Preferably each plate is arranged to move about a common axial centre line, the axial centre line parallel to the longitudinal centre line of the vehicle running track. 
     In another embodiment the end pivotally supported is adjacent a side edge along the vehicle running track. Preferably each plate is arranged to move about a common axial centre line, the axial centre line parallel to the longitudinal centre line of the vehicle running track. 
     Preferably a transverse fixed portion of track is provided between each plate along a line of the vehicle running track. A benefit of the transverse fixed portions is that a disturbance to the vehicle as it traverses the plates is minimised. 
     Preferably a longitudinal fixed portion of track is provided between each set of plates along the longitudinal centre line. A benefit of the longitudinal fixed portion is that two wheeled vehicles may be provided with a safe fixed running path. 
     Preferably the plates of each of the two similar sets of plates are disposed symmetrically about the longitudinal centre line. 
     Preferably the common axial centre line of each set of plates is displaced symmetrically about the longitudinal centre line. In an alternative embodiment, the common axial centre line of each set of plates is preferably common between each set of plates, and is co-incident with the longitudinal centre line. 
     Preferably the energy conversion means further comprises a drive mechanism, the drive mechanism arranged to transmit kinetic energy to the electrical generator. 
     Preferably the drive mechanism comprises a geared mechanism to translate the substantially vertical movement of the plates to a rotary movement to operate the generator. 
     Preferably the geared mechanism comprises at least a rack and pinion arrangement, a rack being mounted to each of the plates at a distance from the pivotally supported end, each of the rack and pinion arrangements being arranged to translate the substantially vertical movement of the plates to a rotary movement to operate the generator. Preferably a diameter of a pinion of a first plate is a larger diameter than a pinion of a second plate. 
     A benefit of the first pinion being larger than the second pinion is that the first pinion will impart more torque to the drive mechanism for the same downward force than the second pinion. 
     In a further embodiment, preferably the drive mechanism comprises a connecting rod and crank-shaft mechanism to translate the substantially vertical movement of the plates to a rotary movement to operate the generator. Preferably the connecting rod and crank-shaft mechanism comprises a connecting rods mounted to each of the plates at a distance from the pivotally supported end. 
     Preferably a length of a crank of a first plate is longer than a length of a crank of a second plate. 
     A benefit of the first crank being longer than the second crank is that the first crank will impart more torque to the drive mechanism for the same downward force than the second pinion. 
     Preferably the plates and drive mechanism further comprises at least a clutch, the clutch or clutches being arranged so that as a particular plate is moved in the substantially vertical direction and energy is imparted to the drive mechanism, the other plates in the same set of plates may remain in the first position. 
     Preferably each of the pinions and or cranks comprises a said clutch. 
     According to the present invention, there is provided an electrical rotating machine, comprising a rotatable armature and a fixed stator, the armature arranged to rotate about an axis, wherein the armature comprises a plurality of sets of each of a plurality of movable portions, each movable portion movable from at least a first position when the armature is stationary to a second position when the armature is rotating, wherein a dimension of a radial gap between each movable portion and the stator decreases when the moveable portion moves from the first position to the second position, the armature and the stator are arranged such that a magnetic flux coupling the armature and the stator crosses the gap when the movable portions are in the second position, and wherein at least a first set is arranged to move to the second position at a first speed of rotation, and at least a second set is arranged to move to the second position at a second speed of rotation, the second speed being higher than the first speed. 
     A benefit of the invention is that by arranging the electrical machine so that it has a larger gap between the armature and the stator when it is starting from rest, than when it has reached an operating speed, is that the electro-magnetic characteristics and or the mechanical characteristics of the electrical machine may be arranged to be different when starting to when operating such that starting is facilitated. 
     Preferably the rotating machine is an electrical generator. 
     Preferably the electrical generator is arranged to convert kinetic energy from passing vehicles into electrical power. 
     In an alternative embodiment, preferably the electrical machine is an electric motor. 
     Preferably the moveable portions each comprise at least in part a magnetic portion. A benefit of the invention is that when the moveable portions are in the first position, any resistance to rotation of the armature due to magnetic losses, for example arising from eddy currents in the armature or stator, are minimised. 
     Preferably the magnetic portion comprises a permanent magnets. 
     Preferably the magnetic portion comprises an electro-magnet. 
     Preferably the magnetic portion comprises a permanent magnet and an electro-magnet. A benefit of the magnetic portion comprising both a permanent magnet and an electro-magnet is that a strength of the magnetic field may be controlled. A further benefit is that a high strength magnetic field may be obtained by combining both a permanent magnet and an electro-magnet. 
     Preferably the moveable portions are arranged to move radially. 
     Preferably in another embodiment the moveable portions move arcuately. 
     Preferably the armature arranged to rotate within the stator. 
     Preferably the moveable portions are urged towards the axis of rotation 
     Preferably the moveable portions are resiliently urged towards the axis of rotation. 
     Preferably a moment of inertia of the armature when the moveable portions are in the first position is less than the moment of inertia when the moveable portions are in the second position. 
     Preferably this invention provides a means of lowering both the inertia and resistance to rotation by means of providing one or more coil windings or magnetic portions incorporated within suitably designed moveable weights or moveable portions so arranged as to be drawn in and/or allowed to move by springs or other suitable mechanism preferably connected to a central shaft or hub, whereby when the mechanism is stationary or rotated at a low speed, the weights will be in close proximity to the centre of rotation thereby minimising the inertia but also will not be in sufficiently close proximity to the stator as to be impeded by any magnetic field and the armature will therefore be capable of reaching a higher rotational speed than would otherwise be possible for a given power input. 
     Preferably the magnetic flux coupling between the armature and the stator when the moveable portions are in the first position is less than half the magnetic flux coupling when the moveable portions are in the second position. 
     Preferably in another embodiment the magnetic flux coupling between the stator and the armature when the moveable portions are in the first position will be less than one quarter that when the moveable portions are in the second position. 
     Preferably when a sufficient rotational speed is reached, the resulting centrifugal force will act upon the weights or moveable portions containing the electrical coil windings or magnetic portions and when sufficient angular velocity is achieved, the weights are designed to come into close proximity to the stator. The magnetic coupling with the stator thereby resulting in the excitation of the magnetic field, creating the generation of an electric current output. An embodiment of this invention is designed to be particularly suitable for utilisation in any situation when the force causing it to rotate is intermittent or when a given rotational speed is required before the magnetic field is activated. 
     Preferably such a sufficient rotational speed or angular velocity of the armature is more than forty percent of an intended optimum operating speed. More preferably the sufficient rotational speed or angular velocity of the armature is less than ninety percent of the intended optimum operating speed. 
     Preferably at least two of the moveable portions are arranged to move in such a way that an out of balance moment arising from the rotation of the one moveable portion is counterbalanced by the out of balance moment arising from the other moveable portion or other moveable portions, as the moveable portions move from the first position to the second position. A benefit of the moveable portions being arranged to counter-balance each other is that as the speed of rotation of the armature increases from rest to a designed operation speed there are substantially no out-of balance forces transmitted to the bearings supporting the armature. 
     Preferably the moveable portions have an outwardly facing surface, facing away from the axis of rotation, the outwardly facing surface of each moveable portion having a radius of curvature, substantially that of the radius of the surface from the axis when the moveable portion is in the second position. A benefit of a the radiused surface is that the moveable portion may rotate in close proximity to an inside surface of the stator when the electrical machine is operating at the designed speed. 
     The said weights or moveable portions described herein, in one convenient embodiment may be designed to have a hole through the centre or in any convenient position to have a round or suitably shaped bar or tube to be inserted through the hole to facilitate the movement of the weights towards or away from the shaft or hub referred to, or in any alternative convenient direction. The weights referred to may be of any suitable shape, size or material. The bar or bars in turn may be so arranged as to, in one further convenient embodiment be attached to a central boss or shaft and any suitable number of bars, shafts or bosses may be fixed and arranged to radiate out from the hub(s) or shaft(s) resulting in a form similar to that of spokes in a wheel or any other suitable shape(s). 
     At the outside edge of these bars or shafts, abutments may be provided or a circular ring manufactured from any suitable material, such as a circlip may be fitted to an end of the bar remote from the axis of rotation so as to contain the weights or moveable portions. 
     In an alternative embodiment, the weights or moveable portions may simply rotate within a tube(s) containing the stator(s) or other suitable electrical wiring arrangement to enable the electrical machine to act as a generator, motor or other rotating mechanism resulting in an effective means of maximising energy utilization as described herein. 
    
    
     
       Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:— 
         FIG. 1  is a perspective view of a first embodiment of an electrical machine according to the invention that is suitable for use with the apparatus shown in  FIG. 18 ; 
         FIG. 2  is an exploded view of the first embodiment shown in  FIG. 1 ; 
         FIG. 3  is a scrap perspective view of the first embodiment shown in  FIG. 1  showing a portion of the armature with moveable portions in a first position; 
         FIG. 4  is a scrap perspective view of the first embodiment shown in  FIG. 1  showing a portion of the armature with moveable portions in a second position; 
         FIG. 5  is a partly sectioned end view along an axis of rotation of the armature of the first embodiment, with moveable portions in a first position; 
         FIG. 6  is a partly sectioned end view along an axis of rotation of the armature of the first embodiment, with moveable portions in an intermediate position; 
         FIG. 7  is a partly sectioned end view along an axis of rotation of the armature and stator of the first embodiment, with moveable portions in the second position; 
         FIGS. 8 ,  8 A,  8 B and  8 C are end views along an axis of rotation of alternative embodiments of armatures according to the invention. 
         FIG. 9  is a side view of a second embodiment according to the invention; 
         FIG. 10  is an end view of the second embodiment shown in  FIG. 9 . 
         FIG. 11  is a perspective view of a stator winding and a stator support plate; 
         FIG. 12  is an end view of the armature for the second embodiment, when the moveable portions are in a first position; 
         FIG. 13  is an end view of the armature for the second embodiment, when a first set of moveable portions are in an intermediate position and a second set of moveable portions are still in the first position; 
         FIG. 14  is an end view of the armature for the second embodiment, when the first set of moveable portions are in a second position and the second set of moveable portions are in an intermediate position; 
         FIG. 15  is an end view of the armature for the second embodiment, when the moveable portions are in a second position; 
         FIG. 16  is an exploded view of a section through a moveable portion together with a support bar, a hub and the ancillary parts forming a part of the armature of either the first or the second embodiments described herein; 
         FIG. 17  is an enlarged scrap view of a stator and a moveable portion according to either the first or second embodiments of the invention; 
         FIG. 18  is a perspective view from above of an embodiment of the present invention, showing apparatus for converting kinetic energy into usable power fixed in a vehicle running track, but with a cover removed to show hidden features; 
         FIG. 19  is a perspective view from below of the apparatus shown in  FIG. 18 , with a motor vehicle traversing the apparatus shown in  FIG. 18 ; 
         FIG. 20  is a view along a longitudinal direction of an alternative drive mechanism; 
         FIG. 20A  is a sectioned view of an alternative connecting rod for use in the mechanism shown in  FIG. 20 ; 
         FIG. 21  is a view of a vehicle wheel acting on one plate of the apparatus shown in  FIG. 18 ; 
         FIG. 22  is a longitudinal cross section of an alternative embodiment of a frame suitable for apparatus similar to that shown in  FIG. 18 ; and 
         FIG. 23  is a transverse cross section of the alternative frame shown in  FIG. 22 . 
     
    
    
     From  FIG. 1  an electrical rotating machine  1  according to the invention is shown, having a rotatable armature  2  and a fixed stator  3 . The armature  2  is arranged to rotate in the direction of arrow  2 R (shown in  FIG. 2 ) about an axis  1 X. The armature  2  has a plurality of movable portions  11  to  22  inclusive, which in  FIGS. 1 and 2  and  4  are shown in a second position, and in  FIG. 3  are shown in a first position. Each movable portion is movable from the first position when the armature is stationary to the second position when the armature is rotating as shown in  FIGS. 1 and 2 , when a dimension  1 D of a radial gap  1 G between each movable portion and the stator is small. From the description of  FIGS. 5 ,  6  and  7  below, it can be seen that the gap decreases when the moveable portion moves from the first position to the second position. The armature and the stator are arranged as shown in  FIG. 17  such that a magnetic flux coupling the armature and the stator crosses the gap when the movable portions are in the second position. 
     From  FIG. 1 , it can be seen that the electrical machine  1  also comprises a mounting plate  30 , to which bearing supports  31  and  32  are mounted. The bearing supports support bearings  33  and  34 , in which the armature  2  is free to rotate within the stator  2 , which is also mounted by means of support block  35  and clamp  36  to the mounting plate  30 . 
     Terminal block  40  is electrically connected to stator windings  42 . The stator windings  42  comprise a plurality of coils  43 ,  44 ,  45 ,  46 , the coils interconnected so as to optimise the electrical performance of the machine, and the coils being terminated at the terminal block. 
     While only four stator coils are shown in these figures, it will be appreciated that the number of coils may be varied in a particular embodiment according to the particular application intended for that embodiment. For example, in a three phase generator it would be convenient for the number of coils to be a multiple of three, and in this case at least three terminals would need to be provided to allow for connection to the stator windings. In another example, where a generator was to be used for a single phase alternating current output, it would be convenient for the number of coils to be a multiple of two. 
     Likewise in the particular case, where the electrical machine is an electric motor for connection to a three phase supply, it would again be convenient for the number of coils to be a multiple of three, and in this case at least three terminals would need to be provided to allow for connection to the stator windings. 
     Each of the moveable portions  11  to  22  comprise a magnet  51  to  62  inclusive respectively (note for clarity not all are labelled in  FIG. 2 ). Each of the moveable portions is mounted slidably on a bar  6  (only one labelled) and is resiliently urged towards the axis of rotation  1 X by a resilient member  7 . As a result of the rotation of the armature at or above a particular speed, as shown in  FIGS. 1 and 2 , the moveable portions have each moved outwardly away from the axis  1 X, as shown for example by moveable portion  11  which has moved in the direction of arrow  2 W against the tensile force exerted on it by the resilient member  7 . 
     In the case of these figures, the resilient member  7  is shown as a wire tension spring, but in alternative embodiments could be a leaf spring, or a pressurised gas spring, of some other resilient arrangement. 
     A pulley or gear wheel  4  is mounted to shaft  5  of the armature  2 . 
     In the case of an electric generator the pulley or gear wheel  4  is used to provide an input of mechanical power, and in the case of an electric motor, the pulley or gear wheel  4  is used to provide an output of mechanical power from the electrical machine. 
     In  FIGS. 1 and 2 , the stator windings  42  are shown to comprise a plurality of coils  43 ,  44 ,  45 ,  46  each of which extend axially substantially the whole length of the stator. However, where the movable portions as shown in  FIGS. 1 and 2  are arranged in sets, that is portions  11 ,  17 ,  16  and  20  are arranged in a first set, and moveable portions  12 ,  18 ,  16  and  21  are arranged as a second set, and moveable portions  13 ,  19 ,  14 ,  22  are arranged as a third set, the stator winding preferably comprises three sets of coils along the length of the stator. Hence each set of coils is arranged to primarily interact with one of the sets of moveable portions. 
     From  FIG. 3 , which is a scrap perspective view of the first embodiment  1  shown in  FIG. 1 , a portion of the armature  2  is shown with moveable portions  11 ,  20 ,  16  and  17  in a first position. The moveable portions would be in this first position when the armature is not rotating, or when it is rotating a low speed such that a centrifugal force acting on each of the moveable portions urging them away from the axis  1 X, is less than the tensile force exerted by resilient member  7 . Each moveable portion has a curved outer face  70 , having a radius of curvature  16 C (shown in  FIG. 16 ) substantially the same as the radius of the face  70  from the axis  1 X when the moveable portions are in the second position. The moveable portions  11 ,  20 ,  16  and  17  are each slidably mounted to a bar  71 ,  72 ,  73  and  74  respectively, each bar securely mounted to a hub  75  at an inner end  76  by means of a threaded portion  78 . At an outer end  77 , each bar is provided with a head  79  having a radiused outer face  80 , having substantially the same radius  16 C as face  70 . Each head  79  has a diameter  83  and an abutting face  81 , arranged to abut a stop surface  87  (only one labelled) of each of the moveable portions. Each moveable portion also has a recess  82  to receive head  79 . 
     From  FIG. 4 , which shows the same portion of the armature  2  as shown in  FIG. 3 , but with moveable portions  11 ,  20 ,  16  and  17  shown in a second position due to rotation of the armature  2  in the direction of arrows  4 R, shaped receiving portions  86 , which abut an inward face  85  of the respective moveable portion when the moveable portions are in the first position. In the first position the moveable portions have a minimum overall diameter  5 D (see  FIG. 5 ). When the armature is rotating, the abutting face  81  abuts the stop surface  87  to prevent further movement of the moveable portion in the radial direction of arrow  2 W. In the second position, the face  80  is preferably substantially flush or below face  70 . 
       FIG. 16  shows an exploded view of a section through a part of the armature  2  having the moveable portion  11  as a typical example of the arrangement of the first and second embodiments. The bar  71  has a means to prevent rotation of the moveable portion about the bar, which in this embodiment is a longitudinal protrusion  90  (only shown in  FIG. 16 ) which extends along the length of the bar. The protrusion  90  co operates with a detent (not shown) in a bearing  92  arranged to fit within bore  93  of the moveable portion  11 . The moveable portion  11  has a large bore  94  to receive an end  95  of the resilient member  7 . The large bore  94  has a location  96  to securely retain the end  95  to the moveable portion. The bar  71  has a location  97  to retain an end  98  of the resilient member. Hence when assembled, the resilient member may urge the moveable portion  11  towards the hub  75  so that face  85  abuts receiving portion  86 . The hub  75  is provided with threaded holes  99  to receive the threaded end  76  of the bar  71 . 
     Hub  75  may itself be magnetic, so as to exert an attractive force on the moveable portions. Such a hub arrangement would prevent the movement of the moveable portions until such time as the speed of rotation had increased sufficiently. Such a non linear relationship between rotational speed of the armature and the displacement of the moveable portions would be advantageous in certain applications where starting torque was particularly low. 
     In a further embodiment of the invention similar in all respects to the present embodiment, other than the movement of the moveable portions is controlled, so as to prevent the moveable portions from moving up or down the bars should the speed of the armature fluctuate slightly. Such fluctuation could occur, say, in the case of a generator by a pulsing of an input of power to the pulley  4 . The movement may be controlled by arranging bearing  92  so that it lightly grips the bar, giving rise to mechanical frictional. Alternatively, the control of the movement may be obtained by the use of a viscous coating or lubrication between the bearing and the bar. In a further alternative arrangement, the control may be provided by an additional damping mechanism, such as a dash pot positioned between the moveable portion and the rest of the armature. 
     In a further alternative embodiment, control of the movement of the moveable portions may be effected by a hydraulic mechanism. 
     In a yet further alternative embodiment, control of the movement of the moveable portions may be effected by a spiral thread such as a screw thread on a rotatable part. The rotatable part may have an axis co-axial with the respective bar, or it may have an axis co-axial with the axis of the armature. 
     It will be appreciated that alternative mechanical arrangements to that shown in  FIG. 16  would provide the same constraints and degree of freedom of the moveable portions to move from the first position to the second position. 
     While the resilient member  7  has been described with reference to the first embodiment as a tension spring, a similar effect would be obtained if the resilient member were a compression spring mounted between the abutting face  81  and the stop surface  87 . 
     In an alternative embodiment not shown herein, the resilient member may be a pneumatic or gas spring. 
       FIG. 17  is an enlarged scrap view of a typical moveable portion  170  and stator  172  according to the invention and similar to those described with reference to the first and second embodiments, when the moveable portion is substantially in the second position. A gap  17 G between an inner radiused surface  173  of the stator and an outer radiused face  174  of the moveable portion is small and is bridged by the magnetic flux  17 M (shown by dotted lines in  FIG. 17 ) that couples the armature and the stator. 
     When the moveable portions are in the first position, they are sufficiently remote from the stator that a magnetic coupling between the armature and stator is significantly reduced. 
     From  FIG. 5  a partly sectioned end view along an axis of rotation  1 X of the armature  2  of the first embodiment  1 , with moveable portions in a first position, where they are held close to the axis of rotation. The moveable portions  11 ,  20 ,  16  and  17  are urged inwards in the direction of arrows  5 P by the resilient members  7 . Hence the armature has a minimum moment of inertia, and it is easy to start the armature to rotate about axis  1 X. 
     Known generators have an inherently high inertia which is substantially reduced by having the movable portions shown in this invention. Hence a starting torque for a generator according to this invention is substantially lower than for known generators of a comparable output. 
     Known generators also inherently have a resistance to rotation as a result of the magnetic field present. In this invention, the resistance to rotation when starting arising from the magnetic field is reduced because the armature pole pieces are at a substantially reduced diameter, thereby reducing the magnetic coupling with the stator, and hence the resistance to rotation. This reduced resistance to rotation is maintained as the generator starts to rotate until the speed of rotation has increased such that the centrifugal force on the magnets has caused them to move outwards to a position where the generator reaches excitation. 
     The minimum overall diameter  5 D when the moveable portions are in the first position, is less than the maximum overall diameter  7 D (see  FIG. 7 ) when the moveable portions are in the second position. 
       FIG. 6  is the same partly sectioned end view as shown in  FIG. 5 , but with the moveable portions in an intermediate position between the first position and the second position. As the speed  6 R of the armature increases the moveable portions move from the first position shown in  FIG. 5  through the intermediate position shown in this  FIG. 6  to the second position shown in  FIG. 7 . While in this position there is substantially an equilibrium between the centrifugal forces causing the moveable portions  11 ,  20 ,  16  and  17  to move outwards in the direction of arrows  6 W (which are in the same direction as arrows  2 W) and the tensile force exerted by the resilient members  7 . 
     Any imbalance in the forces will have an effect of causing the moveable portions to move inwards or outwards so as to tend to a position where the forces are balanced. When the forces are balanced, there is no net force acting on the moveable portions so as to cause them to move. 
       FIG. 7  shows the same partly sectioned end view along an axis of rotation  1 X of the armature  2  as shown in  FIGS. 5 and 6  but with the moveable portions  11 ,  20 ,  16  and  17  in the second position, this figure also includes the stator  3 . The speed of rotation  7 R of the armature in this figure is greater than the speed of rotation  6 R of the armature in  FIG. 6 . Since the speed of rotation  7 R has reached or exceeds a desired minimum operating speed, the moveable portions have fully moved in the direction of arrows  7 W to the second position. 
       FIGS. 8 ,  8 A,  8 B and  8 C are end views along an axis of rotation of alternative embodiments of armatures according to the invention, where most features are identical with those already described with reference to the first embodiment. In these figures, armature  802 ,  822 ,  842  and  862  each comprise a hub  875  and four identical bars  874  extending from the hub, at regular angular spacings so as to form a substantially rigid assembly. In operation, each of the embodiments is arranged so that the armatures are each mounted rotatably to a stator, and the moveable portions moves from a first position as shown through intermediate positions to a second position as a speed of the armature increases. The electrical machine may in each case be arranged to operate as an electrical generator or as an electrical motor. 
     A desired operational characteristic of the electrical machine may be obtained by careful selection of magnetic materials and the other materials used for the moveable portions, so as to obtain a desired combination of weight and magnetic properties. 
     The armature  802  has four identical moveable portions  804 , each having an electrical winding  806  arranged to be connected when the armature is mounted within a stator by means of a commutator or slip rings (not shown) to a source of electrical energy. The windings  806  are arranged so that when the windings are energised they each create a magnetic field about a curved pole face  808  of their respective moveable portion. In an embodiment using an armature with the moveable portions  804 , the armature could comprise permanent magnets. 
     The armature  822  has four identical moveable portions  824 , each having a permanent magnet  825  and an electrical winding  826  arranged to be connected when the armature is mounted within a stator by means of a commutator or slip rings (not shown) to a source of electrical energy. The windings  826  are arranged so that when the windings are energised they each create a magnetic field about a curved pole face  828  of their respective moveable portion. The permanent magnets are arranged to provide a magnetic field about the curved pole face  829 . The electro-magnetic field is preferably arranged to be additive to the field from the permanent magnets. 
     The armature  842  has four identical moveable portions  844 , each having an cylindrical permanent magnet  846  mounted within the moveable portion. The magnets  846  are arranged to provide a magnetic field about each side  870  (only one side visible) of their respective moveable portion, rather than the curved faces  848 . This embodiment is particularly suited to an arrangement such as that shown in the second embodiment described with reference to  FIG. 9 , where the stator is positioned alongside a disc like armature. 
     The armature  862  has four identical moveable portions  864 , each comprising a magnet  866 . Each moveable portion is magnetised so that a magnetic field preferably extends principally from or about the desired pole face, either the sides  870  where the stator is arranged axially alongside the armature, or the curved pole face  868  where the stator is arranged radially about the armature. 
     While in the embodiments described with respect to the drawings, the moveable portions are constrained to move in a radial direction with respect to the axis of rotation of the armature, alternative arrangements where the moveable portions are constrained to move away from the axis in a direction other than radially as the speed of rotation of the armature increased would provide the same benefits as the embodiments described. For example, the moveable portions could move in a tangential direction along a slide similar to the bar described above. In a further example, the moveable portions could be pivotably mounted to the armature, arranged so that they move in an arcuate manner from a first position close to the axis of rotation to a second position away from the axis of rotation, the second position being closer to the stator than the first position. In this example, an axis about which the moveable portions pivot could be parallel to the axis of rotation or perpendicular to the axis of rotation or at an intermediate angle between these. 
       FIG. 9  shows a side view of a second embodiment  900  according to the invention, which has a stator  903  and an armature  902 . The stator has two sets of windings  942  and  944  arranged alongside the armature  902 , and a support plate  935  and a base mounting plate  930 . As shown in  FIG. 9 , the armature  902  has moveable portions  911 ,  912 ,  913  and  914  arranged in one plane  9 P perpendicular to an axis of rotation  9 X, and a further set of moveable portions  915 ,  916 ,  917  and  918  arranged in another plane  9 Q perpendicular to the axis of rotation  9 X. The armature  902  has a shaft  905  which is arranged to rotate in bearings  933  and  934 . 
     Support plate  935  may be used to provide an insulating or an earthed barrier between the two sets of windings  942  and  944  and their respective armature portions  946  and  948  respectively. 
     A benefit of the support plate  935  being non-conductive is that losses arising from eddy currents may be eliminated. 
     In a further embodiment, the support plate  935  is of a non-magnetic material. 
     In an alternative embodiment, not shown herein, support plate  935  may carry additional windings, so that the windings are disposed symmetrically about the armature portions  946  and  948 . 
     An electrical connection  940  is provided to connect the windings, in the case of a generator to an electrical load, and in the case of a motor, to an electrical supply. 
     The moveable portions are arranged so that side faces  968  and  969  are closely adjacent to their respective coil faces  945  and  943 . Hence a magnetic coupling between the armature and the stator when the moveable portions are in the second position can be optimised. Each moveable portion has a curved face  970  having a recess similar to the first embodiment for receiving an end  980  of a bar  971  on which the moveable portion may move away from the axis of rotation as the speed of rotation of the armature increases. As in the first embodiment the bars are mounted rigidly to a hub  975 , and resilient members  907  are provided to urge the moveable portions towards the axis  9 X. 
       FIG. 10  is an end view along the axis  9 X of the second embodiment  900 , where for clarity support plate  935  has been omitted from this view. As in  FIG. 9  the moveable portions  911 ,  912 ,  913  and  914  are in a second position where they are closely positioned adjacent to the stator windings  944 . The moveable portions can be seen to be similar to those shown in  FIG. 8B , and each have permanent magnets  951  to  958  mounted to them, such that the magnetic field is directed to the side facing the stator coils. 
     From  FIG. 10  it can be seen that a maximum diameter  10  E of the armature across the moveable portions when they are in the second position, is less than a maximum diameter  10 F of the stator winding  944 . 
       FIG. 11  is a perspective view of the stator winding  944  and a stator support plate  904  which is arranged to support the winding. The winding  944  may comprise an even or an odd number of coils  946  depending on the requirements for the electrical machine. The coils can be seen to have a substantially flat face  945  arranged to face the moveable portions  911 ,  912 ,  913  and  914 . 
     A centre portion  906  of the support plate  904  is of such a material or construction that there is a negligible magnetic coupling between the centre portion and the moveable portions when in the first position. 
       FIGS. 12 ,  13   14  and  15  are an end view of the armature  902  as shown in  FIG. 10 , but with the moveable portions in different positions. It can be seen from these Figures that this embodiment has a symmetrical arrangement of the moveable portions and the bars supporting them. An angular spacing between each is substantially identical. Each moveable portion in an opposed pair of moveable portions is of substantially identical mass, for example  911  is the same mass as  913 , and  916  is the same mass as  918 . An advantage of this is that the armature may be easily maintained in balance. It should be noted that moveable portion  911  is heavier than moveable portion  915 . 
     However, in an alternative embodiment, not shown, the angular spacing between at least some of the bars is different. In this embodiment balance of the armature may be obtained by careful selection of the masses of the moveable portions. 
     In  FIG. 12  the armature is stationary or only rotating slowly and hence all the moveable portions are in a first position, where the resilient members  907  have drawn the moveable portions up against the hub  975 . Hence an overall diameter  12 D across the moveable portions is at a minimum. 
     In  FIG. 13  the armature has begun to rotate to a sufficient speed  13 R where the lighter set of moveable portions  915 ,  916 ,  917  and  918  have moved to an intermediate position. The heavier set of moveable portions  911 ,  912 ,  913  and  914  are still in the first position since the resilient members  907  holding them close to the axis  9 X exert a proportionately greater force than the resilient members  908  acting on the moveable portions  915  to  918 . As the speed continues to increase, in the case of an electrical generator, the winding  942  will commence production of electrical power. 
     In  FIG. 14  the speed  14 R of rotation has increased to or beyond the speed at which the first or lighter set of moveable portions are in the second position and the second set of moveable portions have moved to an intermediate position. Hence, as the speed increases further, in the case of an electrical generator, the winding  944  will commence generation of electrical power. 
       FIG. 15  illustrates the condition where the speed  15 R of rotation of the armature has increased sufficiently that all the moveable portions have moved to their second position. Hence in the case of an electrical generator, the output is at a maximum for the particular speed of the armature. 
     From  FIG. 18 , a perspective view of apparatus  200  for converting kinetic energy into usable power according to the present invention, shown fixed in a vehicle running track  202 , but with a cover removed to show hidden features. The apparatus  200  has a frame  204  arranged to be fixed in the vehicle running track  202  and a plurality of plates  211  to  219  inclusive and  221  to  229  inclusive. Each of the plates is moveably mounted to the frame, so that a vehicle running face  220 ,  230  (only two labelled) of each plate is substantially level with the surrounding track  202 . Each plate is arranged to drive an energy conversion means  232  or  234 . The energy conversion means has a rotating member  293  (see  FIG. 19 ) having variable inertia as described with reference to  FIGS. 1 to 17  above. Since the frame is fixed in the track, each plate  211  to  219  inclusive and  221  to  229  inclusive is movable in relation to the frame  204  and in relation to the track  202 . The plates  211  to  219  inclusive and  221  to  229  inclusive are arranged as two sets of plates  501  and  502  respectively. Each of the plates is pivotally mounted to the frame  204 , at a pivoted end  505  and  507 . In the embodiment shown in  FIG. 1  the pivoted ends are adjacent the longitudinal centre line  200 C. Each plate is pivotally mounted about a pivot axis  515  and  517 , which are symmetrically disposed about axis  200 C, by distance  516 . 
     An intention of the invention is that the energy conversion means  232  and or  234  is enabled to provide useable power derived from the kinetic energy of passing vehicular traffic. Vehicles approach the apparatus along a direction of arrow  200 A. In the special case of two wheeled vehicles, a level uninterrupted path  236  is provided along a centre of the apparatus. For normal four wheeled vehicles, or indeed those with more axles, the wheels will be disposed about either side of a longitudinal centre line  200 C along a centre of the apparatus. The wheel tracks will normally be expected to fall within off-side track  240  and near-side track  242 . A kerb  244  is provided alongside the apparatus to encourage vehicles to traverse the apparatus as intended. Although not shown, it may be preferred to have a kerb on each side of the apparatus. 
     While in the embodiment shown the plates have a common pivotal axis, in a particular embodiment it may be convenient for them to have different pivotal axes, in effect providing different effective plate lengths. In another embodiment (not shown) the end pivotally supported end is adjacent a side edge  511 ,  512  along the vehicle running track. 
     As a vehicle approaches the apparatus, the front wheels of the vehicle will first contact the first plates  211  and  221  on each side of the apparatus, and then after the front wheels pass over these plates the wheels will then run onto the second plates  212  and  222 . Hence the first and second plates are moved sequentially in that order by a vehicle passing over the plates. 
     From  FIG. 19 , it can be seen that the movement of each plate  211  to  219  inclusive is arranged to cause rotation of a drive mechanism  250 . In operation, as the vehicle drives across the apparatus, the plates  211  to  219  are acted on by the vehicle wheels is sequence. A diameter of the pinions decreases from those on plate  211  to those on plate  219 , and hence as the vehicle reaches the end of the ramp and the speed of rotation of the shaft  252  increases, for the same vertical movement  289  of the plate  219  as the movement  281  of plate  211 , the racks  279  and  279 ′ will rotate the pinions  269  and  269 ′ by a greater angular movement, which given the speed of the vehicle will have remained substantially the same, effectively results in a greater speed of rotation of the shaft  252  than was the case for the substantially identical movement  281  of plate  211 . 
     A gearbox  290  is provided to couple the shaft  252  to an electrical generator  292 . The electrical generator  292  is an energy conversion means  232 . 
     Coil springs  291  are provided under each plate to resiliently return the plates to the first positions. All the plates are shown in the first positions in this figure, since the car tyres are at the instant shown, traversing transverse portions of the cover plate between two consecutive plates. 
     The electrical generator  292  preferably is provided with an armature that changes in effective diameter according to the speed of rotation, as described herein with reference to  FIGS. 1 to 17 . Hence when starting the generator to rotate, there is a minimum inertia and magnetic resistance to be overcome, reducing stress on the drive mechanism. From  FIG. 1 , a battery  294  and  294 ′ can be seen to be connected to the generator output in this particular embodiment. 
     From  FIG. 21  a pair of vehicle wheels  402  and  404  of vehicle  400  can be seen acting on a pair of plates  215  and  225  (not visible in this view) of the apparatus shown in  FIG. 1 . The vehicle  400  is travelling in the direction of arrow  400 A. The previously traversed plate  214  can be seen to have already been resiliently returned to its first position  414  where the plate protrudes the surrounding surface  420  of the cover plate  421  which effectively forms a part of the vehicle track  202 . Plate  214  protrudes the surrounding surface  420  by a small distance  416 . Meanwhile plate  215  which is being acted on by the tyre tread  407  of tyre  406  has been moved to the second position  415  where it is a small distance  417  below the surrounding surface. 
     In a practical embodiment, the distances  416  and  417  depend on the type of vehicular traffic likely to pass over the apparatus and its speed. Typically in a low speed location  416  could be, for example 50 mm, but in a high speed location would be less, for example 25 mm. The distance  417  would typically be less than the distance  416 . In a particular example distance  416  would conveniently be 25 mm, but could be more where vehicles with larger wheels were traversing the apparatus. In a low speed location, where only heavier vehicles with larger wheels would pass over the apparatus a larger height  416  would be possible, for example 75 mm, or greater. 
     Plate  215  can be seen to have a smoothly shaped leading edge  422  and trailing edge  423 . The plates also have a smoothly shaped end, for example as  218 E in  FIG. 19 . 
     As the vehicle tyre traverses the plates they are displaced at the end away from the pivotal support by a vertical displacement  424 . Mounted to the end of the plate  215  are two rack gears  275  and  275 ′, which act on pinions  265  and  265 ′ respectively to rotate the shaft  252 . The shaft  252  is supported by the frame  204  by bearings  253 . 
     The movement of the rack gears is substantially linear, although in applications where the plates are relatively short and have a large vertical displacement  424 , they may be made slightly curved to conform to the radius of curvature equal to the distance from the pivotal axis of the plate. 
     Each of the pinions  265  and  265 ′ is provided with a clutch mechanism  435  and  435 ′ to enable the shaft to be rotated by other pinions without the pinions  256  and  256 ′ moving the plate  215 . 
     In  FIG. 20 , an alternative arrangement for the apparatus  300  is shown with a drive mechanism  302  which has a connecting rod  304  coupled between a plate  311  and a crank-shaft  306  mechanism to translate the substantially vertical movement  300 V of the plate to a rotary movement  300 R to operate the generator (not shown in this figure). To obtain the maximum displacement of the connecting rod, it is mounted to each of the plates at a distance  300 D from the pivotally supported end  308 . An alternative embodiment of a connecting rod  304 ′ is shown in  FIG. 20A , having a co-axial slidable piston and cylinder arrangement, to enable the maximum torque applied to the crank to be controlled should the plate be subjected to a sudden downward deflection. The connecting rod  304 ′ has an internal resilient member to return the rod to its normal operating length. To obtain different mechanical advantage so as to maximise the torque available as a vehicle traverses the first few plates, a length  307  of the crank  306  of the first plate  311  is longer than a length of a crank of a second plate (not shown in this figure). Likewise, the length of the second crank is preferably greater than that of the third, and so on. The shortest crank would be the last crank operated by the last plate traversed by a vehicle as it exits or leaves the apparatus. If an installed apparatus is to be traversed from both directions, then it would be preferable to size the cranks so that the shortest cranks are in a middle section of the apparatus, and the longest cranks are at each end, with the intermediate cranks at intermediate lengths. 
     A longer crank will impart more torque to the drive mechanism for the same downward force than a shorter crank. However, the shorter crank will impart greater rotational movement to the shaft  310  for the same vertical movement  312 . 
     It should be noted that a similar result may be obtained by positioning the connecting rod and crank arrangement  302  at different distances  300 D from the pivot axis  314  of the plate  311  on the different plates. To permit the shaft  310  to rotate without rotating the crank  306 , a clutch  313  is provided. Hence as a particular plate is moved in vertically and energy is imparted to the drive mechanism, the other plates in the same set of plates may remain in the first position. This reduces the inertia of the system. 
     The plate  311  is restrained from moving higher than the first position  321  by a stop  320 . The plate  311  is resiliently returned from the second position  322  to the first position  321  by spring  323 . A support  324  is provided to protect against excessive loads applied to the vehicle running surface  325  of the plate  311 . 
     The vertical movement of the plate in the direction of  300 V is limited, so that a desired angular movement of the crank  306  is obtained. Although a rack and pinion arrangement or a crank and connecting rod arrangement have been shown and described, an alternative embodiment which is not shown, uses hydraulic cylinders operated on by the plates and hydraulic oil as the transmission means to power a hydraulic motor to drive the generator. 
     In this embodiment it may be preferred to use different diameter cylinders on the different plates, such that the first plate has the smallest cylinder and on a single direction apparatus, the last plate traversed has the largest cylinder. 
     In another alternative embodiment, pneumatic cylinders and a gaseous transmission media are used. 
     It will be appreciated that for a particular installation it may be advantageous to combine aspects of these embodiments. 
     From  FIG. 22  a longitudinal cross section of an alternative embodiment  350  of a frame  352  which is shown with cross-hatching omitted for clarity.  FIG. 23  is a transverse cross section of the alternative frame  352 , also with the cross hatching omitted. The frame  352  comprises a plurality of compartments  353 ,  354 ,  355  each of which is arranged to receive a plurality of plates, similar to the plates  211  to  219  and  221  to  229  shown and described with reference to  FIG. 18 . 
     In a particular example of the embodiment  350 , the frame comprises a housing structure  359  having three compartments  353 ,  354 , and  355  each of the compartments is arranged to receive four plates. Hence a four wheeled vehicle traversing along the plate in the direction of arrow  358 A will transverse twelve plates on each side, one set with its nearside wheels, the other set with its offside wheels. 
     A vehicle travels along the running track  362  and then onto plate surfaces  363 ,  364  and  365  sequentially. Moveable plates are mounted in each of the plates  363 ,  364  and  365  arranged to drive the energy conversion means, which may be mounted within any one of the compartments or in a separate adjacent compartment. The running track is preferably bounded by a curb  357  or other guideway to ensure vehicles travel over the mechanism. 
     The mechanism is arranged to receive energy from the passing vehicle and convert it into useable power using the energy conversion means described herein. Apertures or communication holes are provided to permit power from each of the compartments to be fed through into the adjacent compartments. The transmission means may be by a rotating shaft in respect of mechanical power, and electrically conductive cables for electrical power. 
     Alternative mechanical transmission means such as axially oscillating transmission shafts could be used. 
     While a frame comprising three compartments is mentioned above, in a particular application, it may be preferable to have only two compartments, or alternatively to have more compartments. 
     The housing structure  359  may comprise a preformed component, or it may be preferable for a particular installation site to construct it in situ using materials such as concrete or blockwork. The load of the passing vehicles is transmitted by the housing structure into the supporting ground  360 . 
     In a further embodiment not shown herein, the frame comprises a plurality of housing structures, each with a compartment each arranged for mounting in a vehicle running track, means being provided between each of the housing structures for the transmission of power between each compartment, so that a power output is obtained from the combined energy received by each of the compartments when a vehicle passes over each compartment in sequence.