AXIAL-FLUX ELECTRIC MOTOR

The object of the present invention is a so-called axial-flux electric motor, i.e. an electric motor with a relative arrangement of its stator and rotor such that the magnetic circulation is determined according to a peculiar spatial/volumetric pattern that is quite different from more traditional radialflux electric motors; such a motor may be used in various application fields such as (but not limited to) portable agricultural machinery as shakers and the like.

As known, axial-flux electric motors consist of two elements: a “stationary” one (the stator) and a “moving” one (the rotor) which generally rotates relative to the stationary element.

The rotation effect of the rotor is suitably induced by powering the stator in such a way that it produces a variable electromagnetic field, which in turn induces suitable phenomena in the rotor leading to the onset of a magnetic field (induced, in fact) that exerts suitable forces/torques on the rotor itself.

The term "axial-flux" used to define this type of electric motor derives from the fact that the lines of the resulting magnetic field that develop in the motor during its operation have a significant geometric/topological component developing parallel to the rotation axis of the rotor, and thus “longitudinally” relative to the development of the entire motor along such rotation axis: such geometry is in turn a result of the peculiar arrangement of the magnetically active elements of the rotor relative to those of the stator, and by virtue of this peculiarity, axial-flux electric motors may generally offer a higher motor torque output (compared to radial-flux electric motors) and have a particularly small longitudinal size.

Nevertheless, axial-flux electric motors of the known type are not free from drawbacks and criticalities, both from a manufacturing and engineering perspective.

One of the most critical aspects of axial-flux electric motors is represented by the assembly and retention of the magnets on the rotor, which tend to be subject to considerable centrifugal forces during operation: generally, these magnets are either glued to the so-called “rotor plate” (thus suffering from the inherent sealing limitations of the adhesive material) or, though more rarely, they are retained by means of mechanical constraints such as screws or radial “dovetail” (or similar geometries) fittings, which in any case compromise the magnetic field circulation consequently reducing the maximum performance of the entire motor, while increasing its structural complexity.

In the light of the prior art set forth above, the object of the present invention is to manufacture an axial-flux electric motor which is capable of overcoming the drawbacks just mentioned, and which in particular is capable of ensuring a rapid and robust fastening of the magnetically active elements (e.g., permanent magnets) on the rotor while minimising the number of necessary components and screws, and at the same time ensuring an optimal design of the magnetic profiles of the motor (thereby maximising its performance in terms of at least the maximum torque that can be output and/or the minimum electrical current absorption to produce such maximum torque).

These and other objects are obtained by an axial-flux electric motor according to the present invention, having the characteristics shown in the appended claims and shown hereinafter in an exemplary (but not limiting) embodiment as well as in the accompanying drawings, wherein:

Fig. 1 shows an exploded perspective view of an axial-flux electric motor according to the invention;

Fig. 2 shows a perspective view of a rotor of the electric motor in Figure 1 ;

Fig. 3 shows a sectioned perspective view of the rotor along track III - Ill in Figure 2; and

Fig. 4 shows a detailed perspective view of a magnetically active element that can be associated with the rotor in Figures 2 and 3. With reference to the figures, the axial-flux electric motor according to the invention is generally denoted by number (1) and basically comprises a rotor (2), a stator (3) circumscribed to the rotor (2) (therefore the rotor (2) is rotatably engaged to the stator (3)) and suitable power means that are active on the rotor (2) and/or the stator (3) to induce a rotation of the rotor (2) relative to the stator (3).

Advantageously, according to the present invention the rotor (2) comprises a rotor plate (4), which is designed to house a plurality of magnetically active elements (5) angularly equally-spaced in the rotor plate (4), and in particular comprises coronal retaining means: said coronal retaining means are connected to the rotor plate (4) and are shaped and arranged to rest on the magnetically active elements (5) along a minimum circumference (6) and/or along a maximum circumference (7).

In other words, the coronal retaining means are arranged, structurally and functionally, in such a way that the magnetically active elements (5) are positioned - and thus stably retained in their position even during highspeed rotations of the rotor (2) - within the minimum (6) and maximum (7) circumferences; this peculiar constraint insisting between the rotor plate (4) and the magnetically active elements (5) makes the entire rotor assembly (2) very efficient and at the same time extremely simplified, and allows the magnetically active elements (5) to be shaped according to geometries or volumes that do not compromise their efficiency in terms of the resulting magnetic flux during the motor (1) operation.

In more detail and referring to the accompanying figures, it is possible to notice that the minimum circumference (6) and/or the maximum circumference (7) protrude from the rotor plate (4) and respectively define at least one perimeter undercut (which, for the sake of clarity of disclosure, may be defined as “inner coronal undercut” and “outer coronal undercut”), which in turn is designed to rest on suitable edges of the magnetically active elements (5), as will be seen below.

Still referring to the figures, it is possible to notice that each perimeter/coronal undercut (inner and/or outer) continuously extends either along the minimum circumference (6) or along the maximum circumference (7): this makes it possible to obtain, on the one hand, an exceptional geometric regularity of the rotor components and, on the other hand, to install magnetically active elements (5) having different dimensions in terms of “width”.

Focusing the attention on the minimum circumference (6), it is possible to notice that it is cooperatively defined by the rotor plate (4) and a discoidal element (8) which may be reversibly connected to the rotor plate (4) near a central portion thereof: in turn, the aforementioned discoidal element (8) also includes reversible active constraining means (9) between the discoidal element (8) itself and the rotor plate (4), so as to allow a correct insertion and assembly of the magnetically active elements (5).

Depending on the current requirements, the above-mentioned reversible constraining means (9) may comprise suitable mechanical devices, also of the known type: for example, this may be a predetermined number of screws that are radially equally-spaced relative to the rotation axis of the rotor (2) (referring to a rotation axis of the rotor (2), in the language of the invention, as an axis placed at said central portion of the rotor (2) itself).

As regards the maximum circumference (7), it integrally extends from the rotor plate (4) and typically develops at a maximum diameter of the rotor (2) relative to its rotation axis: the fact that the maximum circumference (7) is made in a “single piece” or integrally, as you may call it, greatly simplifies the construction of the rotor (2) and implements a considerable degree of retention and holding in position of the magnetically active elements (5), even opposing very high centrifugal forces and thus making it possible to achieve a higher rotational speed for the entire axial-flux electric motor (1) according to the invention.

Still referring to the attached figures, it is possible to notice that at least one, and preferably all, the magnetically active elements (5) comprise prismatic bodies perimetrically defined by the following set of sides: - an inner edge (5a) counter-shaped to the undercut defined by the inner circumference (6);

- two intermediate sides (5b) radially projecting from the suitable ends of the inner edge (5a) (and e.g. arranged radially relative to the rotation axis of the rotor (2), so as to attain a pseudo-trapezoidal plan shape of the magnetically active elements (5)); and

- a counter-shaped outer edge (5c) subtended between the two above- mentioned intermediate sides (5b) and counter-shaped to the undercut defined by the outer circumference (7).

Conveniently, in order to maximise the geometric/structural interconnection between the various components of the rotor (2), the inner edge (5a) and the undercut (inner coronal) defined by the inner circumference (6) have a mutually counter-shaped geometric pattern: this geometric pattern, when viewed “in section” may conveniently comprise one or more rectilinear and/or curvilinear segments that are mutually complementary in the motor (1) assembled conditions.

Similarly, the outer edge (5c) and the (outer coronal) undercut defined by the outer circumference (7) have a mutually counter-shaped geometric pattern which, when still viewed “in section”, may comprise one or more mutually complementary curvilinear segments in the motor (1) assembled condition.

Returning finally to the rotor (2), it is also possible to notice that the invention may possibly include the presence of ventilation vanes (10), which may project from one or both faces of the rotor plate (4): these ventilation vanes (10) may be integrally formed in a single piece with the rotor plate (4) or may be connected to and/or mounted on the rotor plate (4) itself by means of suitable mechanical constraints, as illustrated in Figure 1.

It is also an object of the present invention to provide a machinery or device (which, by way of a non-limiting example, may be a portable agricultural tool), which comprises at least one drive unit as well as at least one operating tool moved by said drive unit: advantageously, said drive unit comprises at least one axial-flux electric motor according to the foregoing and/or according to what hereinafter claimed.

The invention allows to obtain important advantages.

First of all, it should be noted how the peculiar constructional architecture of the present axial-flux electric motor makes it possible to obtain a high degree of retention and positional stability of the magnets in the rotor plate (or “rotor disc”, as you may call it), without introducing “interposed” complex mechanical constraints such as screws or the like, without interrupting or making the magnetic flux lines discontinuous, and without being limited by the sealing performance of the adhesive materials.

Thanks to the peculiar way in which the magnets are retained, it is also possible to achieve an overall rotor shape with a very high geometric regularity, to the benefit of the (static and dynamic) balance of the rotor masses and thus to the benefit of the reliability of the motor itself.

It should also be noted that the peculiar structure of the invention described so far, and claimed below, may be applied to numerous variants and may be “dimensionally scaled” according to wide quantitative ranges, to the benefit of the possible applications of the present motor in various fields that require the output of drive torques equally variable in terms of maximum quantity and/or in terms of compactness of the motor that may be installed.