“AN ELECTRIC MOTOR ROTOR ASSEMBLY HAVING COOLING MEANS, AND AN ELECTRIC ENGINE HAVING SUCH A ROTOR CENTRAL ASSEMBLY”

DESCRIPTION

The present invention is related to an electric motor having suitable cooling means, such cooling means being located in its rotor assembly.

It is known in the art that electric motors are usually built in two main sub-components, namely the stator (which is “fixed”, e.g. with respect to an engine bay of a vehicle) and the rotor, which in turn rotates into the just cited stator: rotors usually bear magnetically active elements, whose interaction with the dynamic magnetic fields generated in cooperation with the stator determine the generation of torque, and this kind of torque generation is created by suitable circulation of electric current within the motor itself.

Current circulation and friction existing between the relatively moving parts of the motor also determines heat generation, which is increasingly becoming an issue in electric motors having a very high torque output (such as the ones applied to electric vehicles): therefore, a need for cooling means arises, and usually such cooling means are, in the known art, realized through various structural architectures of channels transporting a cooling fluid outside or even inside the motors (e.g., conduits running through the motor rotating shaft and through other rotor components, up to the magnetically active pack/stack which is supported around the rotor shaft).

These known-type cooling architectures have, however, drawbacks which are mainly related to complicated developments of the flow paths through which the cooling fluid is conveyed and to the necessity of providing a very accurate and repeatable coolant flow in all the working conditions of the motor itself: these design requirements lead to structural complexity and, consequently, to high building costs and long assembling processes. Having stated the prior art drawbacks, it’s an object of the present invention to provide an electric motor, and in particular, a so-called “rotor assembly” which can be fitted into an electric motor which can overcome the aforementioned drawbacks: for example, one of the aims of the present invention is to provide a rotor assembly insertable in an electric motor which allows for a greater structural simplification, for significantly reduced assembly times and/or shorter machining cycles for the manufacturing of its single components (therefore determining a decrease in production and assembling costs) and also for offering a uniform cooling of the motor itself throughout all its various working conditions (e.g. up to elevated rotations per minute working ranges.)

These aims, along with other technical advantages, will be illustrated and achieved by an electric motor rotor assembly according to the present invention as described and claimed hereinafter, and represented in an exemplificative yet not limiting embodiment in the annexed figures, wherein:

• Figure 1 is a view, in longitudinal cross-section along an ideal plane containing the rotor’s rotation axis, of an electric motor encompassing a first embodiment of the rotor assembly according to the invention;

• Figure 2 is a section view of the first embodiment depicted in figure 1 along the section plane ll-ll;

• Figure 3 is a perspective view of a component of the first embodiment of the invention;

• Figure 4 is a view, in longitudinal cross-section along an ideal plane containing the rotor’s rotation axis, of an electric motor encompassing a second embodiment of the rotor assembly according to the invention;

• Figure 5 is a section view of the second embodiment depicted in figure 4 along the section plane IV-IV; and

• Figure 6 is a perspective view of a component of the second embodiment of the invention.

In the annexed figures, the rotor assembly according to the invention as a whole has been numbered with “1 ” and substantially is defined by a rotor group which in turn comprises:

- a central member (2) extending along an axis (2a);

- at least one extension (3), whose geometry will be exemplified later on, radially protruding from said central member (2) in a plane which can be generally considered as lying “transverse” (e.g. perpendicular) with respect to the axis (2a);

- a drum (4) coaxially developing with respect to the central member (2) and having as a support the extension (3); and

- a magnetically active pack (5) supported by the drum (4).

With regard to the cooling function, the rotor group also comprises at least a radial inlet (6) located in the rotor central member (2) and adapted to receive a coolant flow coming along the axis (2a) (in this regard, the axis (2a) may be provided with an internal axial conduit or having a hollow configuration, as depicted in the non-limiting examples in figures from 1 to 6) and to divert it radially with respect to said axis (2a), and at least one radial conduit (7) connected to the just cited radial inlet (6) and located within the extension (3).

Advantageously, an annular intermediate chamber (8) is also present in the embodiments of the present invention, and such annular intermediate chamber (8) is connected to the radial conduit (7) and is located between the drum (4) and the magnetically active pack (5): in cooperation with the just cited structural feature, the rotor assembly (1 ) further comprises a predetermined number of channels (9) developing in a mutually parallelism relationship and parallel to the axis (2a), so that such channels (9) are connected to the annular intermediate chamber (8) and are located between the drum (4) and the magnetically active pack (5).

In order to have a sufficiently even distribution of the cooling fluid within the rotor assembly, more than one radial outlets (6) and/or radial conduits (7) may be present in the present invention: typically, a predetermined number of radial outlets and conduits may be present in the rotor assembly, and such radial conduits and outlets are uniformly and radially distributed along an ideal plane wherein the extension (3) lies/resides.

Owing to the mutual fluid connection between the radial inlet(s) (6), the radial conduit(s) (7), the annular intermediate chamber (8) and the channels (9), a suitable coolant fluid may be circulated in the rotor assembly, therefore it may be evacuated through discharging ports (10) which are located at one end of the channels (9) themselves (e.g. such discharging ports (10) may be located at opposite ends of the channels (9), or more in general they may be located in proximity of an outer face of the rotor assembly (1 )).

Delving deeper into details and looking at possible geometries/structures of the extension (3), it is possible that this structural feature (3) comprises a disc-shaped element or at least one, and typically a multiplicity of spoke-shaped elements developing radially along the central member (2) towards the drum (4): even in this case, the overall structure/geometry of the extension(s) (3) may be determined so as to be in compliance with an optimal radial symmetry and/or with a requirement of static and dynamic balancing of mass around the axis (2a).

Looking at the annexed figures, it can be observed that the drum (4) comprises a supporting face (4a), while the magnetically active pack (5) comprises an inner face (5a): the just cited supporting face (4a) and inner face (5a) are mutually and directly facing each other in an assembled condition of the rotor assembly (1 ), so that they cooperatively define the cavities which essentially define the channels (9).

According to the present invention, at least one channel (9), and typically all the channels

(9) and/or at least one discharging port (10) (or, in case of need, all the discharging ports

(10)) are cooperatively defined at least by the drum (4) and by the magnetically active pack (5): otherwise stated, the structural cooperation between two basic components of the rotor assembly (1 ) allows for an efficient and low-cost definition of the channels (9), which are instantaneously formed when the drum (4) and the magnetically active pack (5) are joined together: otherwise stated, the supporting face (4a) and/or the inner face (5a) comprise a plurality of concavities extending in parallel to the axis (2a), so that the channels (9) are cooperatively defined by the adjacency of the supporting face (4a) and of the inner face (5a).

According to the invention, the annular intermediate chamber (8) is cooperatively defined at least by the drum (4) and by the magnetically active pack (5), and the drum (4) further comprises one (or more) radial outlets (6a) located on said inner face (4a): taking into account the overall structure and geometry of the rotor (1 ) and looking at the annexed figures, the just cited radial outlets (6a) and the inner face (5a) are mutually and directly facing each other in an assembled condition of the rotor assembly (1 ) itself. According the invention, the supporting face (4a) and/or the inner face (5a) may comprise a transverse concavity extending in correspondence of said radial outlets (6a): the size, position and shape of such transverse concavity is such that the annular intermediate chamber (8) is cooperatively defined by the adjacency of the transverse concavity and by the inner face (5a) (or by the adjacency of said transverse concavity and the supporting face (4a) in correspondence of the radial outlets (6a)).

According to one possible embodiment of the invention, the annular intermediate chamber (8) may define a continuous coronal path circumferentially developing throughout a 360 degrees angle around the axis (2a), so that all of the radial outlets (6a) are connected to the just cited continuous coronal path: nevertheless, according to another possible embodiment of the invention which will be explained in greater detail later on, the annular intermediate chamber (8) may define a predetermined number of discrete sub-paths (8a) (e.g. between two and six discrete sub-paths), each of which discrete sub-paths (8a) is circumferentially developing throughout a predetermined angle around the axis (2a).

Otherwise stated, the invention may provide for the presence of two or more discrete subpaths (8a), and in this case each one of such discrete sub-paths (8a) may have an equal length in terms of coronal development (due to reasons of radial symmetry of the rotor assembly (1 )): in this possible structural architecture, discrete sub-groups of radial outlets (6a) are fluidly connected to each of their respective discrete sub-paths (8a).

According to a further (and optional) aspect of the present invention, the rotor assembly (1 ) may also comprise at least one torque transfer element (11 ) interposed between the drum (4) and the magnetically active pack (5): such a torque transfer element (11 ) has a development along a direction substantially parallel to the axis (2a) and is adapted to transmit rotational forces generated by the magnetically active pack (5) to the drum (4) and/or to the central member (2) and/or to the extension (3).

From a structural standpoint, the just cited torque transfer element (11 ) can be protruding, along a radial direction with respect to the axis (2a), from the magnetically active pack (5) into the drum (4) or vice versa (according to operative or design requirements) may be protruding, along a radial direction, from the drum (4) into the magnetically active pack (5): the function of this at least one torque transfer element (11 ) is to prevent relative rotation in between the magnetically active part and drum and central member of the rotor assembly (1 ) during its exchange of electro-induced force with a stator, and therefore to obtain the required torque output at the entire motor’s shaft exit/connection point.

According to the invention and in order to suit the assembly (1 ) to different operating scenarios, the torque transfer element (11 ) may be integrally protruding, along a radial direction with respect to the axis (2a), from the magnetically active pack (5) into the drum (4); as a first alternative to this embodiment, the torque transfer element (11 ) may be integrally protruding, along a radial direction, from the drum (4) into the magnetically active pack (5) or even insertable, e.g. in a removable fashion, between the drum (4) and the magnetically active pack (5) if needed by peculiar design and/or performance requirements.

Furthermore, for reasons of maximizing the torque transfer, granting a satisfactory level of reliability and allowing for an efficient countering of deformative effects due to high speed rotation, more than one torque transfer elements (11 ) may be present and operative between the drum (4) and the magnetically active pack (5): in this case, these torque transfer elements (11 ) are radially equi-distributed around the axis (2a) (or otherwise stated, they can be equally spaced around the axis (2a) itself) so as to gain the required balancing of rotating masses during the motor’s operating conditions.

In a possible embodiment of the invention, the torque transfer element (11 ) has a length, along a direction parallel to the axis (2a), which is substantially equal to an axial length of the drum (4) (or it can be equal to an axial length of the magnetically active pack (5)): in this configuration, the torque transfer element (11 ) is substantially intersecting said annular intermediate chamber (8) so as to define an interrupted coronal development of the annular intermediate chamber (8) itself.

However, an alternative embodiment of the present invention may have at least two (or, otherwise stated, two or more) torque transfer elements (11 ): according to possible different axial lengths of such torque transfer elements (11 ), there can be an intersection of these elements (11 ) themselves with the annular intermediate chamber (8).

More in particular, if two or more torque transfer elements (11 ) have a length substantially corresponding to the axial length of the drum (4) (or of the magnetically active pack (5)), they will intersect the annular intermediate chamber (8) so as to define at least two adjacent discrete sub-paths (8a) (which in turn cooperatively form the annular intermediate chamber (8) in its entirety): in this case, each of said discrete sub-paths (8a) is circumferentially developing throughout a predetermined angle around the axis (2a), and each of said angles of each discrete sub-paths (8a) is typically of equal length in order to achieve and maintain the required rotational symmetry of the entire assembly (1 ).

Whenever at least one torque transfer element (11 ) intersects the intermediate annular chamber (8), one or more corresponding discrete sub-groups of radial outlets (6a) are respectively connected to each of the just cited discrete sub-paths (8a), while in case of the annular intermediate chamber (8) is developing around the drum (4) and/or the magnetically active pack (5) without being interrupted/intersected by torque transfer elements (11 ), all the radial outlets (6a) are simultaneously connected to the annular intermediate element (8) itself.

Delving deeper into details, the torque transfer element (11 ) may have a length, along a direction parallel to the axis (2a), which is a fraction of the overall length of the drum (4) or of the magnetically active pack (5): for example, at least one (and typically, all) torque transfer element(s) (11 ) may have a length substantially equal to half an axial length of the drum (4) minus an axial width of said annular intermediate chamber (8), so that such torque transfer element(s) (11 ) are not intersecting the annular intermediate chamber (8) (therefore, in this configuration all the radial outlets (6a) are connected to the annular intermediate chamber (8) as in the exemplificative embodiment hereabove stated).

According to the invention, and in order to maximize flexibility and adaptability of the present assembly (1 ) to different conditions, any combination between the following parameters of the torque transfer element(s) (11 ):

- overall number; and/or

- radial/angular positioning; and/or

- axial length; and/or

- presence or absence of geometrical/topological intersection with the intermediate annular chamber (8); and/or

- structural integrity/continuity with the drum (4) or with the magnetically active pack (5); and/or

- capability of being removably inserted between the drum (4) or with the magnetically active pack (5), may be devised, without exiting from the scope of the invention itself.

The present invention scope also encompasses an electric motor comprising a stator assembly, a rotor assembly adapted to be housed and to be rotating in the stator assembly and energy provision means connected to the stator assembly and/or the rotor assembly: advantageously, within such an electric motor the rotor assembly is of a kind as hereabove described and/or herebelow claimed.

The described, illustrated and claimed invention achieves the technical aims and surpasses the shortcomings of the prior art hereabove mentioned, starting but not being limited to the advantage consisting in coolant being fed to a very large/high number of cooling ducts running between the drum (4) and the magnetically active pack (5) throughout a single “distribution volume” which is given by the annular intermediate chamber (8): this geometry/topology/hydraulic connection is substantially non-retrievable in the known art, which is mainly based on architectures wherein for each channel or coolant passage located in the “hot area” of a rotor assembly, a single and corresponding radial feeding channel is required.

Besides, the overall structural architecture of the rotor assembly, and its highly integrated layout of the cooling network, allows for a very fast, reliable and economically convenient realization of the entire rotor assembly, granting at the same time a very even and homogeneous distribution of the coolant throughout the most critical parts of the rotor itself: this leads to a lighter, more reliable and long-lasting electric motor as well.

Furthermore, the cooling architecture according to the invention can be implemented in various embodiments, thereby allowing for the adoption of this architecture to various ranges of torque outputs, maximum rotations per minute values and whatever else operating parameter which may characterize an electric motor (and this leads to the capability of providing this highly efficient cooling architecture to a wide range of electric motors, irrespectively to their maximum performance output level).

Last but not least, the rotor assembly (and the motor comprising such rotor assembly) according to the present invention can also be implemented in any other embodiment enclosed in its inventive concept as claimed, also by way of collateral modifications available to a skilled technician in the technical sector of pertinence of the invention itself, and thus maintaining the functional achievements of the invention along with practicality of production, usage, assembly and maintenance.