This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. TO2010A000022 filed in Italy on Jan. 15, 2010.
This invention relates to an electric motor and in particular, to a rotor for an electric motor and an electric motor having such a rotor.
The present invention has particular application in an electric motor of the type with an external rotor and an internal stator, in particular a permanent magnet direct-current brushless type motor. More specifically the invention is directed to a rotor of the type comprising a carrier structure including a disc portion to which is centrally connected a hub, and the periphery of which is joined to a basically annular cylindrical skirt portion which in use extends coaxially around the stator.
This type of rotor for a brushless D.C. motor typically carries, in the annular skirt part, a plurality of permanent magnets, and an associated structure for linking up the magnetic flux produced by these magnets.
In a brushless electric motor of this construction, the stator has a magnetically conducting structure in a star geometry, with a plurality of radial expansions or teeth, supporting coils that form the stator windings. Typically at least one card or board containing the components of an electronic control circuit are attached to the stator, usually on the opposite side from the rotor. These components generate heat during use and add to the heat generated by the stator windings.
There is a desire to provide a rotor of the type specified above, capable of contributing significantly to the cooling of the stator windings and of the electronic control circuit connected to the motor.
Accordingly, in one aspect thereof, the present invention provides a rotor for an electric motor of the type with an internal stator, the rotor comprising a carrier structure including a disc portion to which is centrally connected a shaft, and the periphery of which is joined to an essentially cylindrical annular skirt portion which in use extends coaxially around the stator; wherein the disc portion of the carrier structure has a plurality of slots between which there is defined a corresponding plurality of spokes, at least some of which have, in a circumferential direction, a transverse cross-section shaped in a manner such to induce, at least when the rotor rotates in one sense, an at least approximately axial air flow through corresponding slots.
Preferably, the slots of the disc portion are essentially radial.
Preferably, at least some of the spokes have, in a circumferential direction, a transverse cross-section having an essentially planar external surface, and an internal surface which has a symmetrical profile which, proceeding from one end to the other, is concave, then convex, then once again concave, like a double-wing profile.
Alternatively, at least some of the spokes have, in a circumferential direction, a transverse cross-section having an essentially planar internal surface, and an external surface which has a symmetrical profile which, proceeding from one end to the other, is concave, then convex, then once again concave, essentially like a double-wing profile disposed upside down.
Preferably, the spokes have, in a circumferential direction, alternately an aerodynamically inactive cross-section and an aerodynamically active cross-section.
Preferably, the spokes having, in a circumferential direction, an aerodynamically active cross-section, have transverse-sections shaped as wing profiles having the same orientation.
Preferably, the spokes having, in a circumferential direction, an aerodynamically active cross-section, have crescent shaped transverse-sections.
According to a second aspect, the present invention provides an electric motor having an outer rotor and an inner stator, wherein the rotor is as defined in any one of the preceding claims.
Preferably, the motor is a permanent magnet brushless D.C. motor.
The axial air flow set up as a rotor of this construction spins can have an effective cooling action on the stator windings and on the components of the control circuitry connected to the motor.
A preferred embodiment of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below.
In
In a manner also known per se, the stator 3 comprises a magnetic field conducting structure, which in the embodiment illustrated by way of example comprises a plurality of radial expansions or teeth 4, around each of which a coil 5 is wound.
The rotor 2 comprises a carrier structure 6 made of molded plastic. This structure 6 includes an essentially disc-shaped portion 7, which has a plurality of essentially radial slots 8 arranged at equal angular intervals. The carrier structure 6 is overmolded on a central hub or shaft 9 (
In the disc portion 7 of the rotor 2, between pairs of consecutive slots 8, corresponding spokes 11 are defined, their width increasing radially from the centre towards the periphery of the rotor. The spokes 11 have, in a circumferential direction, a transverse cross-section shaped, for example as seen in
In the embodiment shown by way of example in
When a rotor 2 of this construction rotates, in either direction, it draws an air flow from the region inside it to the region outside it, as indicated by the arrows in
In another alternative embodiment, shown diagrammatically in
The cross-sections shown by way of example in
In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items.
Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow.
Number | Date | Country | Kind |
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TO2010A0022 | Jan 2010 | IT | national |
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Number | Date | Country | |
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20110175494 A1 | Jul 2011 | US |