Abstract:
The present invention discloses a generator ( 1 ) able to generate either unidirectional current or bi-directional current. A rotatable disc ( 7 ) has a conductive track ( 9 ) and a ferromagnetic bridge ( 8 ). Brushes ( 12, 13 ) switchingly open circuit a coil ( 16 ) or connect the coil ( 16 ) to a load resistor (R). Movement of the disc ( 7 ) results in bridge ( 8 ) shunting a core ( 15 ) of the coil ( 16 ). This generates an emf in the coil ( 16 ). If the circuit is closed, current flows in the resistor (R). If the circuit is open, no current flows. The arrangement is such that current only flows when the bridge ( 8 ) approaches the magnet ( 14 )—not when the bridge ( 8 ) recedes from the magnet ( 14 ). Thus, only the magnetic attraction for the bridge ( 8 ) by the magnet ( 14 ) impedes the movement of the disc ( 7 ) as the bridge ( 8 ) recedes from the magnet ( 14 ) without the disc&#39;s movement also being impeded by generation of electric current at that time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a National Stage entry of International Application No. PCT/AU02/00081, filed Jan. 25, 2002, the entire specification claims and drawings of which are incorporated herewith by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to electric devices including generators which generate an electric current and electric motors. 
   BACKGROUND ART 
   Most electrical devices include a magnetic field and a magnetically permeable structure which are involved in relative movement. During that movement there is normally a symmetrical motion in which magnetic repulsion during one part of the motion is disadvantageous and magnetic retardation during another part of the motion is also disadvantageous. 
   The object of the present invention is to provide both an electrical device and a method of generating an electric current in which the disadvantageous magnetic retardation is reduced. 
   SUMMARY OF THE INVENTION 
   In accordance with a first aspect of the present invention there is disclosed a method of generating an electric current, said method comprising the steps of:
         1. creating a magnetic field extending from a first magnetic pole to a second magnetic pole,   2. creating a first magnetically permeable path extending from adjacent said first magnetic pole to adjacent said second magnetic pole,   3. winding a coils about said first magnetic path,   4. connecting an electrical load across said coil,   5. connecting a switch means in series with said coil,   6. enabling a second magnetically permeable path to move relative to said poles into a position between said first and second magnetic poles to shunt said first magnetic path,   7. moving said second magnetically permeable path relative to said poles out of said position between said first and second magnetic poles, and   8. opening and closing said switch means so that said switch means is closed when said second magnetic path is moving into said position and opened when said second magnetic path is moving out of said position.       

   In accordance with a second aspect of the present invention here is disclosed an electrical device comprising a magnetic field means having first and second magnetic poles between which a magnetic field extends, a first magnetically permeable path carrying a coil and extending from adjacent said first magnetic pole to adjacent said second magnetic pole, and switch means connected in series with said coil, a second magnetically permeable path mounted for movement relative to said poles into and out of a position between said first and second magnetic poles in which said second path shunts said first path, and means to close said switch means as said second path moves towards said position and open said switch means as said second path moves out of said position. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Two embodiments of the present invention will now be described with reference to the drawings in which: 
       FIG. 1  is a perspective, view of a single coil generator in accordance with a fist embodiment of the present invention, 
       FIG. 2  is a schematic magnetic circuit diagram and current waveform illustrating a first half cycle of operation of the apparatus of  FIG. 1 , 
       FIG. 3  is a diagram similar to  FIG. 2  but illustrating the other half cycle of operation, and 
       FIG. 4  is a plan view of the disc of a multi-coil machine, 
   

   DETAILED DESCRIPTION 
   As seen in  FIG. 1 , a first embodiment of a generator  1  has a base plate  2  on which is mounted a prime mover in the form of an electric motor  3 . Clearly any other form of prime mover such as an internal combustion engine, turbine, hydraulic motor, or the like will suffice. The motor  3  has a shaft  4  which is supported by bearings  5 ,  6 . 
   An insulative, non-permeable disc  7  is mounted on the shaft  4  for rotation therewith. Set into the disc  7  is a ferromagnetic bridge  8  and a curved conductive track  9 . Mounted on an insulative support  11  are a pair of carbon brushes  12 ,  13 . Mounted to the rear side of the disc  7 , and thus indicated by broken lines in  FIG. 1 , is a U-shaped permanent magnet  14  having a north pole N and a south pole S ( FIG. 2 ). Opposite the magnet  14  is a U-shaped magnetically permeable core  15  formed from steel laminations or the like and upon which is wound a coil  16 . 
   The coil  16 , brushes  12 ,  13  and an electrical load in the form of resistor R are connected in series. It will be apparent to those skilled in the art that the track  9  and brushes  12 ,  13  function as a rotary switch which open circuits the the coil  16  or connects the resistor R across it in accordance with the position of the disc  7 . The track  9  and brushes  12 ,  13  are so arranged that the coil  16  is connected to the resistor R whilst the bridge  8  is approaching the core  15  and whilst the bridge  8  and core  15  are aligned. However, as the bridge  8  begins to leave the core  15  with continued rotation of the disc  7 , the brushes  12 ,  13  are open circuited by the departure of the track  9  from underneath the brushes  12 ,  13 . 
   Turning now to  FIGS. 2 and 3 , the magnetic circuit formed by the core  15 , magnet  14  and bridge  8  is schematically illustrated. Although the bridge  8  is very thin in the direction perpendicular to the plane of the disc  7 , it has an appreciable extent in the plane of the disc  7  and thus a low reluctance. This is indicated in  FIG. 2  by the bridge  8  being drawn larger than it would appear in cross-section. 
   When the bridge  8  is absents as illustrated in  FIG. 3 , the magnetomotive force of the magnet  14  causes a certain level of flux Φ 2  to be present in the core  15 . Because of the relatively large air gaps in the absence of the bridge  8 , the magnetic circuit as illustrated in  FIG. 3  has a relatively him reluctance. However, as seen in  FIG. 2 , with the bridge  8  shunting the core  15 , a relatively low reluctance path is available from the north pole N to the south pole S of the magnet  14  via the bridge  8  and two relatively small air gaps. Thus essentially most of the magnetic flux firm the magnet  14  is present as flux Ø 1  in the bridge  8 . Almost no flux passes through the core  15 . 
   Largely because of the change in air gap sizes, the reluctance of the magnetic circuit in the configuration illustration in  FIG. 2  is less than the reluctance of the magnetic circuit in the configuration illustrated in  FIG. 3 . That is, Φ 1  is larger than Φ 2 . 
   As a consequence, the magnetic potential energy of the circuit in the configuration of  FIG. 2  is less than that of the circuit in the configuration illustrated in  FIG. 3 . This may be illustrated by gently spinning the disc  7  by hand. The disc  7  will come to rest (normally after a few oscillations as the disc  7  slows) with the bridge  8  positioned in line with the magnet  14  and core  15 . That is, in the configuration illustrated in  FIG. 2 . 
   Expressed another way, as the bridge  8  approaches the magnet  14 , the lower magnetic energy state of  FIG. 2  will cause the bridge  8  to be drawn towards the magnet  14 . Similarly, as the rotation continues and the bridge  8  moves away from the magnet  14  an effort is required to maintain the rotation as the higher magnetic potential energy state(s) are attained. For each revolution the effort of removing bridge  8  from the magnet  14  is substantially equal to the impetus gained by the disc  7  as the bridge  8  approaches the magnet  14 . 
   As the bridge  8  approaches the magnet  14 , defining a first half cycle, a steady flux Ø 2  is in the core  15  and links the coil  16 . As the bridge  8  progressively shunts the flux in the core  15 , the magnetic field in the coil  16  collapses. Thus an electromotive force is generated in the coil  16 . Since the coil  16  is connected to the load resistor R via the brushes  12 ,  13  and the track  9 , a current flows in the coil  16  as illustrated in  FIG. 2 . 
   Conversely, as the bridge  8  moves away from the magnet  14 , defining a second half cycle, at first there is a small amount of flux in the core  15 , and the flux progressively increases to Ø 2 . Thus an electromotive force is generated in the coil  16 . If the coil  16  were not open circuit, a current indicated by broken lines in  FIG. 3  would flow (with reverse polarity to the current in  FIG. 2 ). However, the brushes  12 ,  13  and track  9  are open circuit, so no current flows. 
   Thus, at this time, the disc  7  is only impeded by the attraction of the magnet  14  for the bridge  8 . As a result, the impediment to continued rotation of the disc  7  is at a minimum and the efficiency of the generator  1  is increased. 
   The current flowing in the coil  16  generates an induced magnetic flux in the core  15  which increases the magnetic flux in the core  15 . This induced magnetic flux increases with increasing speed of the disc  7 . The speed of the disc  7  reaches a critical speed, at which the magnitude of the induced flux is equal to the magnitude of the flux supplied by the magnet  14 . Thereafter, increasing speed causes increased induced flux in the core  15  and the device runs as a motor. 
   It will be appreciated that the current generated by the arrangement in  FIG. 1  is unidirectional in that current is generated only intermittently. However, with the duplicated arrangement, as illustrated in  FIG. 4 , two bridges  8 ,  108  are provided together with two tracks  9 ,  109 , two pairs of brushes  12 ,  13  and  112 ,  113  and two pairs of coils  16 ,  116  each with its corresponding magnet ( 14 ,  114 ). Thus with the arrangement of the disc  107  of  FIG. 4 , two pulses are generated for each revolution of the disc  107 . Depending upon the relative phasing of the coils  16 ,  116 , the current supplied to the resistor R can be either 2 pulses of the same polarity (i.e. unidirectional current) or 2 pulses of opposite polarity (i.e. bi-directional current or AC). 
   That is, either DC current or single phase alternating current can be generated. By providing 3 discs  107  rotates by 120° to each other on the same shaft  4 , three phase alternating current can be generated with the 3 resistors being connected in either Y or delta configuration as is well known to those skilled in the electric generating arts. 
   The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto without departing from the present invention. For example, the permanent magnet(s)  14 ,  114  can be replaced by an electromagnet having a magnetic field generating current. The magnitude of the current generated or the speed of the motor, can be controlled by controlling the magnetic field of the device. For example, the field current of an electromagnet replacing magnet  14  can be controlled. Other ways of controlling the magnetic field include adjusting the size of air gaps in the magnetic circuit or other arrangements to adjust the reluctance of the magnetic path by, for example, changing the size of the core  15 . Alternatively, a small winding can be wound about the magnet  14  to increase or decrease its magnetic field. 
   Furthermore, control can also be effected by utilizing a control resistor in series with the coil  16  instead of the open circuit as described above. As the resistance of such a control resistor is progressively decreased from an initial very high value, so the current generated, or motor speed, is decreased. Other control methods include electronically clipping the voltage in coil  16  and/or electronically controlling the current in coil  16 . 
   Similarly, rather than use a mechanical switch in the form of tracks  9 ,  109  and brushes  12 ,  13 ,  112 ,  113 , a solid state switch utilizing SCRs, thyristors, transistors, or even diodes can be employed. Such SCRs and thyristors can be triggered by stationary sensing coils in which trigger currents can be generated by small auxiliary magnets carried by the discs  7 ,  107 . Also rather than a closed circuit/open circuit being used as the switch means, a low resistance/high resistance circuit can be used instead. 
   Finally, although the disc  7 ,  107  is preferably rote in one direction as described above, it will be apparent to those skilled in the art that the disc  7 ,  107  can be oscillated (as indicated by the broken line arrow in  FIG. 1 ) rather than rotated. In one such embodiment, the stationary end point of the oscillation would see the bridge  8  fully inserted between the magnet  14  and core  15 . 
   The tern “comprising” (and its grammatical variants thereof) is used in the inclusive sense of “having” or “including” and not in the exclusive sense of “consisting only of”.