LIGHT AND COMPACT ROTATING ELECTRICAL MACHINE WITH MINIMUM VIBRATIONS AND INTRINSIC REDUTION

TECHNICAL SECTOR

Present invention belongs to rotating electrical machines, specifically belongs to electric motors and generators.

Particularly, present invention relates to a light and compact rotating electrical machine with minimum vibrations, due to its Nonius axial-flux configuration, with a castellated toroidal spiral-rolled stator and double permanent magnet rotor. Its weigh, volume and efficiency make it particularly suitable, for instance, in bicycles and in-wheel motors of vehicles. It can actuate either as a motor or generator, reaching high efficiency in any case and in a wide speed range, improving the use and the recovery of the energy, allowing, for instance, the use of smaller batteries in mobility applications. In the same way, the arrangement of a cooling circuit -specially in two-phase case- keeps the temperature limited and, therefore, a low level of resistive losses. Its low vibration level -and specially in case of Halbach configuration in rotor- makes the ride smooth - without jerks- and makes the current generation originate very low electrical noise, with very low harmonics.

BACKGROUND OF THE INVENTION

Reversible electrical machines, which can function either as motors and generators of electric current, are more in demand every day in the field of mobility and energy generation and storage. The viability of green vehicles depends on the efficiency of these machines -actuating either in motor and generator mode-, their weight and their geometric compatibility. Green vehicles can recover and, in general, manage energy by accumulating it or using it. The sustainability of various energy sources such as wind, hydraulic, etc., also depends on those factors. The performance of any electric machine is intrinsically related to its heat dissipation ability. On the one hand, the more efficient a machine is, the less heat it gives off. On the other hand, the higher the temperature of the machine, the worse its performance -since the conductivity of conducting materials and some magnetic properties of magnetic materials, like magnetization, decrease with temperature-. In addition, other undesirable effects, like dilations, the increase in friction, etc., can increase as the temperature varies.

In many applications -among which robotics, bicycles, skates and other electric vehicles stand out- the use of electrical machines that can develop a high torque with the lowest possible volume, mass and cost is desirable. Also in these cases a high efficiency is desirable for a wide range of speed regimes, whether the electrical machine works as a motor or as a generator. On the other hand, it is advisable to minimize electromagnetic pollution and eddy current induction in the housing, as well as in other internal and external elements of electrical machines.

Another desirable aspect of an electrical machine is making both the torque produced at zero supply current, called “cogging torque”, and the torque ripple as small as possible.

Nonius-type architecture, wrongly called Vernier in French and English literature, in magneto-mechanical circuits like those described by C.H. Lee in ’’Vernier motor and its design”, IEEE Transactions on Power Apparatus and Systems, vol. 82, n 66, pp. 343- 349, June 1963 o Reese in US3301091 for motors and, for instance, by Perez Diaz et al. in WO 2017/050941 A1 in magnetic gearboxes, provides a speed reduction and, consequently, a torque multiplication intrinsic to the magnetic interaction. This multiplication can also be applied to both linear electrical machines -like that described by Ardestani et al. En Physica C, vol 569, 15-2-2020, 1353593- and rotating electrical machines -like, for instance, the one described by Muteba "Performance Evaluation of a Four-Port PM Vernier Motor for Hybrid Electric Vehicles," 2020 IEEE 29th International Symposium on Industrial Electronics (ISIE), Delft, Netherlands, 2020, pp. 345-350 with DOI: 10.1109/ISIE45063.2020.9152481-. The intrinsic multiplication of the Nonius-type architecture makes the ripple smoother compared to conventional configurations, in addition to being able to provide an alternating voltage of frequency 50 or 60 Hz from slower rotations - how it is required, for instance, in wind turbines- but without the need to add any additional reducer/multiplier. In Klassen's invention US10075030B2 - specifically in its claim 1- stator coils -which in said document are called “electromagnetic elements”- are arranged externally to the permanent magnets of the rotor, so that they form a single part with external fins, for a better dissipation of the generated heat. This heat is generated both by Ohmic dissipation in the coil conductors and by hysteresis in the magnetic materials. The Klassen arrangement has the drawback that the generated magnetic field escapes to the outside, thus producing undesirable electromagnetic pollution.

Although Klassen, in the paragraph [0332], mentioned as a possibility (fig 55 of Klassen) an Halbach configuration or the one he calls in semi-Halbach, assumes that the torque density achieved with such a configuration would be less than that achieved with a configuration of permanent magnets placed alternately on a back iron. As indicated, this is because permanent magnets have a lower flux density than iron. The problem of holding permanent magnets -especially in Halbach or semi-Halbach configuration- that are subjected to forces of attraction and repulsion by the stator and the other magnets remains unsolved.

The number of design parameters of electrical machines makes it difficult to identify the relationships of these parameters with the generated torque, density, speed, performance - for each operating condition i.e. speed and torque - as well as other features.

In that sense, Gieras et al. in Axial flux permanent magnet brushless machines, Kluwer Academic Publishers, 2005; describes the advantages of axial machines and describes the type of rolling called “pan cake” in planes perpendicular to the stator iron axis to minimize eddy current losses.

Choppa in PERFORMANCE OF TORUS-TYPE BRUSHLESS DC MOTOR WITH WINDING CONNECTED IN TWO AND THREE-PHASE SYSTEM, Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College, Andhra University, April 2003; studies a theoretical model of a permanent magnet axial toroidal motor with an iron rear yoke (back iron) on the rotor. Choppa teaches that a toroidal stator core without teeth reduces torque ripple, while the presence of teeth increases torque. Hunstable, in US 2016/0020652 A1, describes a toroidal motor with a tunnel-shaped rotor to capture as much as possible of the outgoing magnetic field from the stator teeth. In this way it manages to trap all the flux lines that escape both radially and axially from the toroidal stator, but at the price of adding an appreciable amount of permanent magnets that produce a large penalty in weight and cost of the motor.

T. Zou et al. in "Analysis and design of a dual-rotor axial-flux vernier permanent magnet machine," 2015 IEEE Energy Conversion Congress and Exposition (ECCE), Montreal, QC, Canada, pp. 3906-3913, with DOI: 10.1109/ECCE.2015.7310212 describe a Nonius toroidal motor (which they call Vernier) with double axial rotor of permanent magnets and respective iron yokes behind them. The Nonius configuration allows an intrinsic reduction ratio to be achieved in the motor so that the rotor rotates synchronously but in reduced speed with respect to the electrical frequency of the current in the coils. This is equivalent to having a synchronous motor in series with a magnetic reducer. This provides a multiplication of the available torque and allows to work with high electrical frequencies with relatively slow rotational speeds. Note that many mobility or sustainable energy generation applications require precisely this since they take advantage of slow movements.

Zou uses iron yokes that improve torque and make it easier to hold the permanent magnets, but make the motor wider (in his case in the axial direction) and heavier.

Mobility applications — such as electric bicycles — are very demanding, not only in the density of torque and power supplied when they act as a motor, but also because of the volume and geometry they occupy, as well as the need to produce minimal vibrations. Thus, it is highly desirable to be able to integrate or house a motor with its reduction gear in the drive wheel itself, simplifying the kinematic chain, increasing resilience and reducing the costs of other mechanical transmission elements that are no longer necessary. This requires adjusting to a severe limitation of available space both axially and radially. But there are also other limitations.

In bicycles, for instance, the frame is supported by forks on the hubs of each of the wheels. The frame is a fixed element and the wheels are mobile elements. In order to install the motor inside the wheel, the stator and the wiring of said motor must be kept static, integral with the frame; while the rotor of a wheel motor must rotate transmitting the movement to the wheel itself.

In addition to the fact that the width of the motor is limited by the space between the forks of the frame, and in addition to the fact that the outer diameter must be less than that of the set consisting of the spokes, the rim and the tire, the motor must have an inner hole that allows the placement of a fixed hub integral with the frame and the stator, that is, a hub that is separate from the rotor.

This means that not all electric motors can be installed inside wheels, due to topological and geometric reasons.

For instance, the motor proposed by Zou et al. keeps the casing fixed and rotates the shaft, without being trivial or immediate to make a kinematic inversion. On the other hand, the Zou motor does not fit the space limitations that determine the installation of the motor inside the wheel. In addition, Zou's electric machine is not free of internal structure, constructively preventing the machine from being confined between the forks of the frame (fixed element) and preventing a fixed hub to pass through its interior. Therefore, the limitations of weight, wheel width and geometric requirements make it unfeasible to use the machine proposed by Zou by installing inside the wheel.

The inventors of the present invention have carried out simulations of different motor configurations to optimize not only the torque and power density, but also the actual geometry of the casing and maintain efficiency, both acting as a motor and acting as an electrical energy generator in a wide speed range. In addition, they have achieved the geometric compatibility of the motor for its possible installation inside the wheel, so that the internal axis of the motor remains fixed and integral with the frame, while the casing rotates with the wheel.

EXPLANATION OF THE INVENTION

In the present invention, an optimized and light Nonius-type axial flux rotary motor/generator is described, with a rotor composed of two disks provided with permanent magnets, said discs structurally joined by their part closest to the axis of rotation and confining between them a toroidal stator. The stator is spirally laminated and provided with axial battlements that is supported externally, leaving its interior free of structural elements. This configuration of the stator simplifies its manufacture by facilitating its winding and, more importantly, it allows the use of the entire inner perimeter of the stator to be occupied by the coils - accommodating more turns- with which it is possible to increase the volumetric torque density for the same electric current.

The design of the present invention allows the installation of the motor inside the wheel of an electric vehicle, such as a bicycle, since the radial and axial restrictions of the wheel installation are met, confining the machine axially between the frame forks and confining it radially between the wheel hub and the set formed by the spokes, the rim and the tire.

The rotating electrical machine of the present invention therefore comprises a toroidal stator composed of a castellated toroidal core of soft ferromagnetic material -with the highest magnetic permeability possible and with a hysteresis loop that is as closed as possible- in a toroidal shape provided with a number N _a of battlements that protrude symmetrically in the axial direction in both directions; so that, around the sections of the toroidal core, electrically insulated conductors are winded forming N _a coils, whose axis and core are the toroid itself and are connected in consecutive pairs - either in series or in parallel - in f phases in consecutive alternating order in what we call an elementary motor unit or basic sequence of phases repeating this sequence an integer n _u of times, so that they make up n _u elementary motor units, the number of coils being N _a — 4 f n _u .

There is a special interest, not only in optimizing performance and weight, but also in maximizing torque without compromising thickness - axial dimension - of the motor, which can be the most limiting dimension in in-wheel motor applications, especially bicycles. In this sense, a preferred realization is proposed in which the magnets are arranged in a Halbach configuration. Although, if we could freely vary all dimensions of the motor without further constraint, the Halbach configuration may not be optimal in terms of mass torque density if there are no volume constraints; but it is for those motors with a geometric restriction that is very limited axially, such as, for instance, those that must be housed in wheels, especially bicycles. The Halbach configuration also provides other advantages such as minimizing torque ripples and anharmonicities. (“ripple” and “cogging”) reducing the generation of torsional vibrations in the axis, thus making the ride more comfortable, natural and pleasant. Asi, por ejemplo, en una bicicleta no se perturba la perception de ejercicio fisico en el pedaleo.

An axial configuration combined with a Halbach arrangement of the permanent magnets concentrates and confines the magnetic fields towards the stator, increasing their gradients and making the electrical machine more powerful for the same thickness, more efficient for the same electrical current supplied and, above all, with less torque ripple. In addition, it drastically reduces electromagnetic pollution in the casing and/or on the outside, which translates into greater real efficiency.

In a preferred realization, the toroidal core of the stator is formed with a spirally winded sheet of electrical sheet metal -typically Silicon steel- varnished or electrically insulated, with machining of its double battlements, which are axially symmetrical and angularly equally spaced, which gives it a double crown shape. The consecutive battlements thus guide the winding of the cable around each toroidal section.

In a preferred realization, one or more cooling tubes for conduction of cooling fluid are arranged along the perimeter of the toroidal core. The winding of each coil embraces both the toroidal part of the core and the cooling tubes, each of said windings being clamped and guided laterally by said battlements. In an option of this preferred realization, said cooling tubes are divided into two complementary circumferential sections so that each fluid inlet is arranged at a lower end -located at the lowest possible height- while each outlet is arranged at an upper end -located at the highest possible height-, and a two-phase fluid is used -with liquid-vapor phase change- for cooling. In this case, liquid enters through the lower part and steam escapes through the upper part, for which it will have absorbed the latent heat of the walls of the corresponding tube. The steam is conducted to an external radiator in which the condensation of the two-phase fluid takes place and the heat is dissipated by convection towards the surrounding air.

In a preferred realization, for the external fastening of the stator, there is a crown of wedges securely fastened to the toroidal core and a support member comprising a set of fixing fingers, arranged around the perimeter, in correspondence with the wedges, so that the stator is held by the support member by the radial pressure exerted by the fixing fingers on the wedges of the crown which, at the same time, press it, reinforcing the fastening of the toroidal core. In this case, the coils are winded around the castellated toroidal core with the crown of wedges already fitted, so that each one of the wedges corresponds to the position of one of the battlements.

The crown of wedges preferably has axial clamping wedges and tangential clamping wedges alternately arranged. The axial clamping wedges have at least one groove arranged tangentially with respect to said crown, while the tangential clamping wedges have at least one axially arranged groove. The ends of the fixing fingers of the support member fit into said grooves, so that both rotation and axial sliding are restricted with great precision. The precision in fixing the axial position allows the distance or "gap" between the stator battlements and the rotor permanent magnets to be made smaller with a great improvement in efficiency and torque provided.

In another preferred realization, the crown of wedges has radial holes for fixing it to the toroidal core by means of screws or other fixing means.

Preferably, in addition, the crown of wedges has an internal recess to house the perimeter cooling conduit, keeping it also pressed and in intimate contact against the toroidal core -improving heat evacuation-.

The crown of wedges plays a key role in ensuring that the interior of the motor remains hollow, o that a fixed hub attached to a vehicle frame can be installed in the inner hollow of the motor.

In a preferred realization, the stator coils are made with an aluminum conductor due to its better electrical current versus weight ratio.

In a preferred realization, each rotor disc is provided with a continuous perimeter housing for the series of magnets, comprising two main functional surfaces, one axial and the other radial, the latter being limited axially on the outer side by the main axial functional surface and on the inner side by a perimeter continuous flange that helps hold the series of magnets. Said axial functional surface further comprises a slight axial recess, and said radial functional surface comprises a continuous radial recess; both recesses with calibrated depths so that an adhesive layer of calibrated thickness can be applied to them without this escaping or flowing under pressure between the magnets and the main functional surfaces and guaranteeing that the thickness of the adhesive layer is optimal for its mechanical function. The perimeter housing, in the same way as the Halbach configuration, helps to minimize the axial width of the rotor, since the continuous perimeter flange helps to hold the magnets without compromising the axial width of the motor.

In a preferred realization that is especially useful for bicycles, the support member is rigidly attached to a hollow shaft that is fixed to the bicycle frame and on which the different rotating parts are mounted through bearings. In addition, in the present invention, preferably, the rotor is connected integrally with the sun of a reduction stage of the planetary type, in which the planet carrier is fixed integrally to said hollow shaft, while a ring attached integrally to a casing in turn jointly attached to the rim of a wheel, preferably by means of the well-known technique of wire spokes, for which the outer U- shaped section is arranged in said casing with the holes corresponding to the spokes, accordingly distributed. It is convenient that the planet carrier remains fixed to achieve the maximum speed reduction in the wheel and, therefore, the maximum increase in torque, which can be done with the design of the present rotating electrical machine.

The geometry of this preferred realization of this in-wheel motor also makes it possible to have a gear change sprocket cassette and to install everything like a conventional bicycle wheel, so that it can be easily assembled and disassembled. Thanks to the hollow characteristic of said axle, it can be done through the pin technique -“thru axle”- usually used in bicycles.

BRIEF DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, a set of drawings is attached as an integral part of said description where, for illustrative and non-limiting purposes, the following has been represented:

Figure 1.- Shows a quarter section in axonometric projection of a preferred realization of the compact light electrical machine with minimal vibrations of the present invention. Figure 2.- Shows a quarter section in axonometric projection of the stator of the electrical machine of the present invention in which only some of the winded coils are shown.

Figure 3.- Shows an exploded view with the assembly of the castellated toroidal core, the perimeter conduit including some sections of inlet tubes and outlet tubes and the crown of wedges, all of them part of the stator.

Figure 4 Shows an exploded view with the assembly of the parts of the stator of figure 2 once winded and a support member.

Figure 5.- Shows a preferred realization of the double permanent magnet rotor of the present invention.

Figure 6.- Shows a detail of the fixation of the permanent magnets in the rotor.

Figure 7.- Shows a sectional view of a preferred embodiment of the machine of the present invention connected to a planetary gearbox without the side covers.

Figure 8.- Shows the sectional view of the assembly of figure 7 with the side covers on. Figure 9.- Shows a sectional view of the machine of the present invention connected on one side to a bicycle gear cassette and on the other to a bicycle brake disc.

Figure 10.- Shows a perspective view of an arrangement of the machine of the present invention on the rear wheel of a bicycle together with the heat dissipation elements of a two-phase circuit.

Figure 11.- Shows a perspective view of the machine of the present invention connected to the heat dissipation elements of a two-phase fluid circuit.

Figure 12.- Shows a perspective view of the heat dissipation circuit by means of a two- phase fluid circuit.

PREFERRED REALIZATION OF THE INVENTION

The rotating electrical machine of the present invention comprises a toroidal stator (1) composed of a castellated toroidal core (2) of soft ferromagnetic material in toroidal shape provided with a N _a number of double battlements (3) protruding symmetrically in both the axial directions; so that electrically insulated conductors are winded around the sections of the toroidal core (2) -typically with varnish- forming N _a coils (4) whose axis and core is the toroid itself and are electrically connected by consecutive pairs in f phases in consecutive alternating order in what we call an elementary motor unit or basic sequence of phases -this is, for instance, for a three-phase series they would be arranged as +A+A-B-B+C+C-A-A+B+B-C-C- repeating this sequence an integer number n _u of times, so that they make up n _u elementary motor units, the number of coils being N _a = 4 f- n _u .

It also comprises a rotor (56) composed of two disks (5) and (6) preferably integral with each other in which two respective series of permanent magnets are arranged grouped and arranged in a Halbach configuration (7) and (8) facing axially with the battlements (3) and in such a way that the number N _d of Halbach groups of permanent magnets (7) and (8) each one -also called magnetic teeth- has a relation N _d =n _u (4 f±1), obtaining the reduction ratio between the frequency of the electrical wave and the mechanical turning frequency of the rotor i = ±1/(n _u (4 f±1)).

This allows forming multiple configurations of synchronous electrical machines with a number f of phases. The particular triphasic case with N _a =24, N _d =22 is especially useful, for instance, in the case of bicycles due to the ratio offered, geometry and ease of manufacturing.

The castellated toroidal core (2) is preferably laminated into spiral or annular sheets to minimize losses due to eddy currents generated by variable magnetic fluxes, both in the tangential direction (in the toroidal core) and axial direction (in the battlements of said core).

The hollows between battlements (3) are preferably formed with parallel faces to facilitate the winding of the coils (4). Similarly, the section of the core (2) is preferably square or rectangular with blunt edges or, in general, rounded to avoid sectioning the conductors and facilitate winding.

The symmetry with respect to the central axial plane causes the axial forces that the bearings must support to be balanced and their resultant to be cancelled -this being very advantageous from the mechanical point of view-. In addition, it causes the magnetic fields to be confined thanks to the Halbach configuration of the magnets, reducing magnetic contamination and losses due to externally induced currents.

The efficiency of the motor is strongly related to the distance or gap between the series of magnets (7) and (8) and the heads of the battlements (3) of the toroidal stator (1). This series of magnets during the operation of the machine suffers alternately attractive and repulsive axial forces. It is, therefore, necessary that they remain precisely and firmly attached. The precision in the angular position is, likewise, important since an angular misalignment would create a lack of coordination of the Nonius geometry and a consequent loss of efficiency.

To do this, in the present invention, each rotor disc (5, 6) is provided with a continuous perimeter housing for the series of magnets (7, 8) comprising two main functional surfaces, one axial and one radial, the latter being axially limited, on the outer side, by the main axial functional surface and, on the inner side, by a peripherally continuous flange (9) that helps hold the corresponding series of magnets. Said axial functional surface further comprises a slight axial recess (10), and the radial functional surface comprises a continuous radial recess (11); both recesses (10, 11) with depths calibrated in such a way that they allow an adhesive layer of optimal thickness to be applied in them without this escaping or flowing due to pressure between the magnets and the main functional surfaces or being too thick.

In a preferred realization of the present invention, the magnets of series (7) and (8) are laminated - preferably forming sectors- to minimize eddy current losses. It is understood by lamination forming sectors that each permanent magnet is sectioned in a sequence of planes containing axis and radii.

In the present invention, there is also a perimeter conduit (12) in the stator that is in close contact with the toroidal core (2) through which a cooling fluid can circulate, further characterized by being, together with the toroidal core (2), embraced by the windings of the coils (4). In this way, the heat generated in the coils is dissipated, minimizing the heating of the ferromagnetic material of the toroidal core (2) and maximizing its efficiency and properties. In a preferred realization of the present invention, aluminum conductors will be used for the windings of the coils so that, although they do not accept as much current as conventional copper conductors, they weigh much less and the torque density is maximized.

This perimeter conduit (12) is preferably further divided into two symmetrical semicircular parts (12A, 12B) so that the fluid inlets (121 A, 121 B) and outlets (122A, 122B) line up at the lower and upper points of the stator. Thus, in a preferred embodiment, a biphasic fluid is used - with liquid-vapor phase change - for cooling. In this case, liquid enters through the lower part through some liquid tubes (123A, 123B) and vapor escapes through the upper part through some vapor tubes (124A, 124B). The steam tubes (124A, 124B) are joined in a single steam collector (122C) which, after a downward radial section, curves axially through a widening (171) of the hollow shaft (17) through an upper hole (172) until exiting to the outside at the top of the widening (171). The steam is conducted by the steam collector (122C) to the upper part of an external radiator (13) -preferably fixed to the frame of the bicycle at a certain height- in which the biphasic fluid condensates. The liquid thus condensed in the lower part of the radiator (13) is conducted by gravity through a liquid collector (123C) that axially crosses the widening (171) of the hollow shaft (17) at its lower part through a hole lower (173); to then curve down and unfold into the two liquid tubes (123A.123B). The height at which the radiator (13) is arranged must be sufficient to provide the pressure that makes a sufficient flow of liquid flow towards the inlets (121 A, 121 B) overcoming fluid dynamic friction. The simple design of the curves and the sustained slopes make it possible to avoid siphoning or embolism due to the formation of bubbles in the circuit.

In a preferred realization, the stator (1) also comprises a crown of wedges (16), so that the stator is held by a support member (14) characterized by having a series of fixing fingers (15) peripherally arranged that exert radial pressure on said crown of wedges (16) which in turn hold the toroidal core (2). The coils (4) are winded in this case around the castellated toroidal core (2) and the crown of wedges (16) together and in such a way that each of the wedges corresponds to the position of one of the battlements (3).

The crown of wedges (16) preferably has axial clamping wedges (22) and tangential clamping wedges (23). The axial clamping wedges (22) have at least one groove arranged tangentially with respect to said crown, while the tangential clamping wedges (23) have at least one groove arranged axially. The ends of the fixing fingers (15) of the support member (14) fit into said grooves, so that both rotation and axial sliding are restricted. The support member (14) thus presses, by means of the fixing fingers (15), the crown of wedges (16) against the toroidal core (2), making them all solidly united.

Preferably, furthermore, the crown of wedges (16) has an internal perimeter recess to house the perimeter conduit (12), also keeping it pressed and in close contact against the toroidal core (2).

In a preferred realization that is especially useful for bicycles, the support member (14) is rigidly mounted attached to a hollow shaft (17) that is fixed to the bicycle frame and on which the different rotating parts are mounted through bearings. The hollow shaft (17) also has flat faces to be housed in the cradles of the frame and prevent its rotation with respect to it.

In the present invention, moreover, the rotor is preferably connected integrally with the planet (18) of a planetary reduction stage, in which the planet carrier (19) is fixed integrally to the hollow shaft (17) while the ring (20) is integrally attached to a casing (21) which, in turn, is integrally attached to the rim of the wheel, preferably by means of spokes, for which the outer U-section is arranged in said casing (21) with the corresponding holes.

The geometry of this preferred realization of this motor also makes it possible to have a gear change sprocket cassette (22) on one side and a brake disc (23) on the other and install everything inside of a bicycle wheel.