Field

The invention generally relates to an electric motor.

Background

Electric motors are well known in the art. However, generally, it is desired to provide electric motors with one or more improved characteristics.

Summary

According to an aspect of the present invention, there is provided a motor comprising first and second rotors and a stator, wherein the first rotor comprises an arrangement of a plurality of first magnets and the second rotor comprises an arrangement of a plurality of second magnets, wherein each arrangement comprises a sequence of polarity changes, and wherein the first rotor is arranged facing the second rotor such that each first magnet faces a second magnet and sharing a shaft such that rotation of the first rotor and second rotor is synchronised, and wherein each first magnet has an opposite polarity to its respective opposing second magnet, and wherein the stator is located between the first rotor and the second rotor and comprises an arrangement a plurality of coils which are controllably energised complementary to the arrangement of magnets, wherein the rotors are enabled to rotate with respect to the magnets, wherein the coils of the stator are arranged such that, when energised, adjacent coils produce an opposing magnetic field, the motor further comprising a control unit configured to receive feedback regarding a relative position of the rotors with respect to the stator, and to control energisation of the coils such as to produce a rotational force on the rotors in a selected direction.

According to another aspect of the present invention, there is provided a motor comprising first and second stators and a rotor, wherein the first stator comprises an arrangement of a plurality of first magnets and the second stator comprises an arrangement of a plurality of second magnets, wherein each arrangement comprises a sequence of polarity changes, and wherein the first stator is arranged facing the second stator such that each first magnet faces a second magnet, and wherein each first magnet has an opposite polarity to its respective opposing second magnet, and wherein the rotor is located between the first stator and the second stator and comprises an arrangement a plurality of coils which are controllably energised complementary to the arrangement of magnets, wherein the rotor is enabled to rotate with respect to the magnets, wherein the coils of the stators are arranged such that, when energised, adjacent coils produce an opposing magnetic field, the motor further comprising a control unit configured to receive feedback regarding a relative position of the rotor with respect to at least one stator, and to control energisation of the coils such as to produce a rotational force on the rotor in a selected direction.

The magnets may be permanent magnets.

Optionally, the coils are energised for less than 50% of a full rotation of the rotors. The motor may have a duty cycle approximately 48:52. The coils may be energised when a relative position of the first and second magnets with respect to the coils is such as to cause a rotational force in the selected direction.

The motor optionally further comprises an output configured to produce an output current generated by the coils when the coils are deenergised. The output may be connected to an energy storage element. The energy storage element may be configured to provide electrical energy to the coils for at least a portion of the cycle when the coils are energised.

Optionally, feedback is provided by a feedback unit configured to monitor a relative position of the rotor(s) with respect to the stator(s). The feedback unit may comprise an arrangement of position magnets on a secondary rotor, said secondary rotor configured to rotate synchronously with the rotors or stators, and a Hall effect sensor configured to detect the presence or absence of a position magnet within a predefined proximity, and to communicate said detected presence or absence to the control unit. Preferably, the coils are connected in series.

According to yet another aspect of the present invention, there is provided a composite motor comprising a plurality of motors, each according to either of the above aspects.

According to still yet another aspect of the present invention, there is provided a method of operating a motor according to any one of the above aspects, including the steps of energising the coils when a relative position of the coils and magnets produces a rotational force in the selected direction and deenergising the coils at other times. As used herein, the word“comprise” or variations such as“comprises” or

“comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Brief Description of the Drawings

In order that the invention may be more clearly understood, embodiments will now be described, by way of example, with reference to the accompanying drawing, in which:

Figure 1 shows a schematic representation of a motor according to an embodiment;

Figure 2 shows a first rotor and a second rotor according to an embodiment;

Figure 3 shows an arrangement of the first and second rotors and a stator, according to an embodiment;

Figure 4 shows the stator according to an embodiment;

Figure 5 shows a simplified circuit comprising the coils of the stator;

Figure 6 shows an illustration of the duty cycle of the motor;

Figure 7 shows a simplified schematic of the arrangement of motor, motor power supply, and control unit; Figure 8 shows an embodiment of a feedback unit;

Figure 9 shows a simplified schematic of the arrangement of motor, motor power supply, control unit, and output; and

Figure 10 shows a simplified schematic of the arrangement of motor, motor power supply, control unit, and output connected to energy storage.

Description of Embodiments

Referring to Figure 1, generally, embodiments of the invention relate to a motor 10 controllable by a controller 11— in particular, the controller 11 is configured to control electrical power supplied to the motor 10. This relationship is shown schematically in the figure.

According to an embodiment, as shown in Figure 2, the motor includes a first rotor 20 and a second rotor 30, each comprising respective arrangements of permanent magnets 21 and 31. Each rotor 20, 30 comprises a substantially circular disk 27, 37 having a thickness 24, 34, and a first side 28, 38 and a second side 29, 39 (respectively). In the embodiment shown, each disk is identical in size and shape— however, it is expected other dimensions can be utilised.

For the purposes of this disclosure, a general feature of the drawings is denoted with a numerical reference. When necessary to refer to specific instances of a general feature, a letter suffix may be appended to the numerical reference. For example, Figure 2 shows an arrangement of magnets 21, comprising magnets 21a, 21b, 21c, 2 Id, 21e, 2 If, 21g, and 21h.

Referring still to Figure 2, as can be seen, each rotor 20, 30 comprises an equally spaced arrangement of eight magnets 2 la-2 lh and 3 la-3 lh. The magnets 21, 31 may be permanent magnets and may comprise rare Earth magnets. The magnets 21, 31 are arranged about the circumference of imaginary rings 22, 32, respectively (where each ring has the same radius). Generally, it is preferred that the magnets 21, 31 are located near the edge of the respective motor 20, 30. This may advantageously provide improved torque production. According to the described embodiment, the magnets 21, 31 are cylindrical magnets having a first polarity (herein“north” polarity) at one base of the cylinder and having a second, opposite, polarity (herein“south” polarity) at the opposite base. Other shapes of magnet 21, 31 are anticipated.

In an embodiment, each magnet 21, 31 extends from one side 28 to the opposite side 29 of the respective rotor 27a, 27b. However, generally, it may only be required that the first sides 28, 38 of each rotor 27a, 27b include exposed magnet 21, 31 surfaces. In fact, it is anticipated that some embodiments may not include exposed magnet surfaces (for example, including a protective covering). Generally, it is required that respective magnet forces (represented as fields) extend into an area above the respective first surfaces 28, 38.

Both arrangements of magnets 21, 31 comprise alternative polarities of the magnets 21, 31. Referring to the first rotor 20, the magnets are arranged according to the following sequence (with respect to first surface 28):

(Table 1)

The second rotor 30 includes, effectively, the same arrangement of its magnets 31, with respect to its first surface 38, as shown in the following table:

(Table 2)

Referring to Figure 3, in use, the two rotors 20, 30 are arranged facing one another (i.e. with respective first surfaces 28, 38 facing one another), such that each magnet 21, 31 is facing its respective magnet 31, 21 (e.g. magnet 21a is facing magnet 3 la, etc.). Therefore, in use, the opposing polarities face one another at each respective magnet position. It should be noted in the figure that rotor 20 shows its second side (which is of opposite polarity to that facing the second rotor 30).

As shown in Figure 3, arranged between the two rotors 20, 30 is stator 40. The figure also exaggerates the typical distance between rotors 20, 30 and stator 40. The stator 40 is fixed in position (e.g. with reference to a base to which it is mounted (not shown)) and the two rotors 20, 30 are rotatably mounted with respect to the stator 40. Generally, the rotors 20, 30 are mounted to shaft 14 at a centre of the imaginary rings 22, 32 (not shown in this figure)— i.e., such that the respective magnets 21, 31 rotate about a common centre. The two rotors 20, 30 are therefore fixed with respect to one another and rotate together. The shaft 14 extends through aperture 43 of stator 40.

Figure 4 shows an embodiment of the stator 40. The stator 40 comprises an arrangement of wire coils 41 (“coils 41”). The stator 40 comprises a body 47 having a first side 48 and a second side 49. Relevantly, the body 47 is sized such that the arrangement of coils 41 can mirror the arrangement of magnets 21, 31 of the two rotors 20, 30. That is, there are eight coils 41a-41h arranged around an imaginary ring 42 having the same radius as the rings 22, 32 of the rotors 20, 30. For convenience, the centres of the magnets 21, 31 and the coils 41 are arranged on the respective rings 22, 32, 42. The coils 41 may have an inner diameter smaller than a corresponding diameter of the magnets 21, 31.

Referring to Figure 5, the wires of each coil 41 are connected in series, creating a single electrical circuit 50 between each of the coils 41. Figure 5 shows a schematic representation of this circuit 50. This is also shown in Figure 4, where the coils are connected in series as shown. Motor power supply 17 is a controllable power supply, as discussed below. The coils 41 are arranged so that adjacent coils 41 create opposite magnetic fields when energised by motor power supply 17. Therefore, when energised (for example), the fields generated by the coils 41 can be considered to follow the pattern exemplified in the following table:

(Table 3) Figure 6 shows four illustrative arrangements, corresponding to positions I,

II, III, IV, of the two rotors 20, 30 and the stator 40. The illustrations show the relative positions of magnet 21a (with north pole facing the stator 40) and magnet 31a (with south pole facing the stator 40) with respect to coil 41a and coil 41b during a single duty cycle. The pattern is repeated for each magnet 21, 31 with respect to each coil 41 during an entire rotation of the rotors 20, 30. In this illustration, the coil 41a is arranged to generate a north field directed towards the first rotor 20 and a south field directed towards the second rotor 30— in order to show this, the coil is shown as a cylinder, and is labelled“N” and“S” when energised.

At position I, magnets 31a and 31a are approaching coil 41a. As coil 41a produces a magnetic field which would repulse magnets 21a and 31a, it is deenergised at this point in the cycle. At position II, magnets 21a and 31a have just passed coil 41a. Coil 41a is therefore energised. The resulting magnetic field from coil 41a causes a repulsive force with respect to the magnets 21a, 31a. At position

III, the magnets 21a and 31a are approaching coil 41b (which has opposite polarity to coil 41a), and are therefore being attracted to the coil 41b. Just before coil 41b is aligned with magnets 21a, 31a, the coil is deenergised— this is shown in position

IV Therefore, the coils 41 are only energised when configured to repulse or attract magnets 21, 31 in a particular direction, and deenergised to avoid applying a force to the magnets 21, 31 in an opposite direction.

Referring to Figure 7, power supply from the motor power unit 17 to coils 41 is controlled by control unit 15. The control unit 15 receives feedback from a feedback unit 16 as to a relative position of the rotors 20, 30 with respect to stator 40. Generally, the voltage applied by the motor power supply 17 will be dependent on the application— larger motors 10 may draw higher currents and/or receive higher voltages than smaller motors.

Referring to Figure 8, in an embodiment, feedback unit 16 comprises a Hall effect sensor 60 and an arrangement of permanent position indicator magnets 61 (“position magnets 61”) coupled to a secondary rotor 62. Secondary rotor 62 is positioned on shaft 14 (shaft 14 is shown extending into the figure) and therefore configured for synchronised rotation with rotors 20, 30. The Hall effect sensor 60 can be configured as a switch, producing a signal when a position magnet 61 is close and, optionally, a second signal when a position magnet 61 is not close— this can be represented as a logical TRUE when a position magnet 61 is close. Typically, the position magnets 61 are selected with relatively low field strength— it is sufficient that the position magnet 61 strength and Hall sensor 60 sensitivity are selected to enable the described operation. The output of the Hall effect sensor 60 is provided to the control unit 15. The locations of the positions magnets 61 can be selected to reflect the duty cycle illustrated in Figure 6.

Other embodiments of feedback unit 16 are envisaged. For example, an optical encoding may be utilised to enable determination of current motor position. Generally, feedback unit 16 is configured for identifying relevant points in the duty cycle of the motor 10.

Referring to Figure 9, the motor power supply 17 provides an electrical power supply with fixed polarity— e.g. via positive terminal 71a and negative terminal 71b. The motor power supply 17 can provide a DC supply (i.e. fixed voltage) or a variable DC supply (e.g. by providing full wave rectification of a mains AC supply). In the latter case, the voltage changes over time but the polarity of terminals 71a, 71b remains consistent. In the latter case, a smoothing capacitor can be provided in order to provide a more consistent voltage output of the motor power supply 17.

The motor power supply 17 is electrically coupled to control unit 15, which in turn is electrically coupled to the motor 10 (specifically, the coils 41 of the motor 15). Therefore, electrical power from the motor power supply 17 can be contra llably provided to coils 41 (via control unit 15)— for example, the control comprises an on (energised) state and an off (non-energised) state. Therefore, when on, coils 41 are receiving electrical power and generating magnetic fields due to the power supply from the motor power supply 17 . When off, the coils 41 are not receiving electrical power and therefore are not generating magnetic fields due to a power supplied from the motor power supply 17.

Figure 9 also shows output 74 and a diode 75 in series with the (or other suitable single current direction element) the two terminals 44a, 44b of the stator 40. The diode 75 is arranged with its cathode end coupled to the output 74 and its anode end coupled to the control unit 15 and the motor 10. The diode 75 can be, in an embodiment, a Zener diode.

When power supply is removed from coils 41, the collapsing magnetic field within the coils 41, which interacts with the surrounding magnetic fields of the magnets 20, 30, produces a voltage at output 74 (and therefore, a corresponding current).

In an embodiment, as shown in Figure 10, the output 74 is coupled to an energy storage element 76. In an embodiment, this energy storage element 76 is a capacitor. In another embodiment, the energy storage element 76 is a battery. In either case, when the coils 41 are energised, there is no current flow towards the energy storage element 76— i.e., there is no charging current applied to the energy storage element 76. The energy storage element 76 generally should be some element in which electrical energy can be converted into potential energy, and then reconverted into electrical energy. For example, the energy storage element 76 may store energy in the form of non-electrical potential energy such as in the form of pressure (e.g. of a gas).

However, when coils 41 are not powered, the voltage due to magnetic field collapse within the coils 41 produces a current which flows in an opposite sense to the current during energisation. Therefore, with switch 73 open, current flow is only directed through energy storage element 76. Diode 75 does not oppose current flow in this direction. Therefore, during the off portion of the duty, energy storage element 76 is effectively charged by the voltage generated by the coils 41.

In one beneficial arrangement, according to an embodiment, electrical energy stored in the energy storage element 76 is enabled to flow through the coils 41 during an on portion of the duty cycle. The voltage difference across energy storage element 76 (Vs) can be larger than the voltage supplied by motor power supply 17 (VM). Therefore, while Vs is greater than VM, current flow can be arranged to flow from the energy storage element 76 through the stator coils 41. Once Vs is below VM, current is arranged to flow from the motor power supply 17 through the coils 41.

It is expected that, in an embodiment, output 74 may be connected to a load— i.e., one that uses the electrical energy generated by the coils 41 rather than storing it. This can have the advantage of directing energy stored within the coils 41 to generate work.

The embodiments described herein can be implemented at various different scales. For example, the motor 10 can be implemented at a scale of 1 to 50 kW (and lower) through to 1.2 MW (and higher). In an embodiment, several (i.e. two or more) motors 10 are arranged in a multi-motor assembly— the design is suitable for parallel arrangements where each pair of rotors 20, 30 and stator 40 share a common shaft 14. Additionally, it is expected that at least two parallel motors 10 share a rotor 20, 30. In this case, it is expected the magnets 21, 31 of said rotor 20, 30 extend from one side of the rotor 20, 30 to the other, thereby enabling interaction with the stators 40 on either side of the rotor 20, 30.

The motor 10 can be constructed from known suitable materials. It may be preferred that the motor components (apart from magnets 21, 31) be formed of a non-ferromagnetic material.

Further modifications can be made without departing from the spirit and scope of the specification.

In a variation, first and second stators are provided, each having embedded magnets. A rotor is provided between the two stators comprising an arrangement of coils. The coils are connected, electrically, in series and arranged with alternating polarity, as per the embodiments described herein. The magnets of the first stator 80 are arranged in a pattern of alternating polarity and the magnets of the second stator 81 are also arranged in a pattern of alternating polarity. The stators face one another such that the facing surface of each magnet of the first stator has a different polarity to the facing surface of its corresponding magnet of the second stator.

In effect, the variation simply swaps the rotors 20, 30 for stators and the stator 40 for a rotor. Known arrangements for providing current to the coils on the rotating rotor can be used— for example, using a commutator.

In another variation, the magnets 21, 31 can be shaped such as to extend from near the edge of the respective rotor 20, 30 towards its centre— for example, the magnets 21, 31 may be substantially wedge-shaped. This variation may advantageously increase the magnetised portion of the rotor 20, 30 surfaces and therefore the magnetic interaction with the coils 21, 31.