Inserted permanent magnet rotor for an external rotor electric machine

The external rotor for an electric machine includes a cylindrically shaped receptacle having a peripheral wall and a magnet-receiving assembly including segments assembled to the inner surface of the peripheral wall so as to define a cylindrically shaped stack. The segments are shaped so as to yield magnet-receiving portions in the ring-shaped stack, and permanent magnets are secured to the magnet-receiving portion of the magnet receiving assembly.

FIELD

The present disclosure generally relates to electric machines. More specifically, the present disclosure is concerned with an inserted permanent magnet (IPM) rotor for an external rotor electric machine.

BACKGROUND

The use of inserted permanent magnet (IPM) in electric machines is well known. Such technology allows the reduction of the number and/or size of magnets and has been essentially used in conventional electric machines, i.e. those including a rotor mounted into a stator for rotation coaxially therein.

It has been found desirable to provide the rotor of an external rotor electric machine with IPM.

SUMMARY

The difficulty of providing an external rotor electric machine with IPM is solved by mounting permanent magnets in a ring-shaped assembly secured to the rotor inner wall.

In accordance with an illustrative embodiment, there is provided an external rotor for an electric machine comprising a cylindrically shaped receptacle including a peripheral wall provided with an inner surface and an input/output shaft coaxial therewith. The rotor also comprises a magnet receiving assembly including elements assembled to the peripheral wall inside the receptacle so as to define a cylindrically shaped stack; the lamination elements being shaped so as to yield magnet-receiving portions in the cylindrically shaped stack; and permanent magnets secured to the magnet-receiving assembly in the magnet-receiving portions.

In accordance with another illustrative embodiment, there is provided an external rotor for an electric machine comprising a cylindrically shaped receptacle including a peripheral wall having an inner surface; a magnet receiving assembly including circular laminations assembled to the inner surface of the peripheral wall so as to define a generally cylindrically shaped stack; the laminations being so shaped as to yield magnet-receiving portions in the cylindrically shaped stack; and permanent magnets secured to the magnet-receiving portions of the magnet receiving assembly.

Other objects, advantages and features will become more apparent upon reading of the following non-restrictive description of illustrative embodiments thereof, given by way of example only with reference to the accompanying drawings.

DETAILED DESCRIPTION

The expression “electric machine” should be broadly construed herein and in the appended claims so as to include electric motors, electric generators and the like.

The expression “connected” should be broadly construed herein and in the appended claims so as to include any cooperative or passive association between mechanical parts or components. For example, such parts may be connected together by direct coupling, or indirectly coupled using further parts therebetween.

With reference first toFIGS. 1, 2, 3A and 3Bof the appended drawings, a first illustrated embodiment of an external rotor electric machine10will now be described.

The external rotor electric machine10comprises an external rotor12provided with an integral coaxial hub14, and internal stator16mounted to the rotor12coaxially therein for rotation of the rotor12thereabout, and a generally cylindrical cooling member18secured to the stator16therein.

It is to be noted that the stator16is not limited to the illustrated embodiment. Since stators are believed to be well known in the art, the stator16will not be further described herein for concision purposes.

The external rotor12comprises a cylindrically shaped receptacle20including a peripheral wall22and an integral cap24provided at its longitudinal end26. The hub14is provided in the cap24coaxially with the wall22. The hub14allows receiving an input/output shaft (not shown) internally or externally with respect to the receptacle.

The rotor12further includes i) a magnet receiving assembly28, including segments30that are assembled into a cylindrically shaped stack and secured to the peripheral wall22inside the receptacle20, and ii) permanent magnets32that are secured to the magnet receiving assembly28. For that purpose, the segments30are shaped so as to yield magnet-receiving portions therein.

According to the first illustrative embodiment, the segments30are made of a plurality of laminations, as can be better seen fromFIG. 2. The segments30are in the form of ring sections resulting for example from stamping or cutting strips of magnetically susceptible material. Of course, the segments30may result from other manufacturing processes.

Prior to their mounting onto the inner surface34of the peripheral wall22, the laminations are pre-assembled into the segments30and a permanent magnet32is positioned in each of the two lateral magnet-receiving portions formed in the segment30.

According to the first illustrative embodiment, the segments30have a thickness equivalent to the height of the magnets received therein. According to another embodiment (not shown), each lateral side of a segment30receives two or more abutted permanent magnets.

The segments30are assembled for example by using a partial and local deformation (not shown) of the laminations achieved by punching. The permanent magnets32are secured to the segments30using an adhesive. The resulting segment is secured to the inner surface34of the receptacle20using an adhesive. Other fastening means can also be used, such as other mechanical or chemical fastening, including soldering.

According to another embodiment, the permanent magnets32are directly positioned onto the segments30without an adhesive.

As can be seen fromFIG. 2, the ring segments30are so shaped as to define a central protrusion38that is shaped so as to yield two rounded notches40between the central protrusion and respective lateral magnet-receiving portions33. Within a segment30, the notches40together define a channel42between the central protrusion and respective magnets32that prevents the magnetic field to directly go from the magnets32to the central protrusions38. Each notch40defines, with the magnet-receiving portion33, a small shoulder that helps positioning and maintaining in place the magnet32.

The segments30are dimensioned so as to yield a small angular gap36between adjacent segments30when they are assembled on the inner surface34of the receptacle20. This eases their mounting onto the receptacle20from a radial direction (see arrow48inFIG. 3B).

Caps46are provided onto adjacent magnets32of two adjacent segments30(see arrow49inFIG. 3B). The caps46are made of magnetic powder, which allows a functional magnetic permeability and a low electric conductivity. A person skilled in the art will also appreciate that there is no direct connection between the caps46and the segments30, thereby preventing magnetic short circuit. It will also be apparent to one skilled in the art that the caps46could be made of stacks of laminations or of other soft magnetic material (SMC).

The thickness and configuration of the magnets32, caps46, and segments30are such that the resulting assembly28yields a generally evenly rounded surface of the rotor12, with the exception of the channels42, thereby improving the electric machine efficiency.

Both the inner surface34of the receptacle20and the facing contacting side of the segments30can be provided with cooperating guiding elements such as tongues and grooves (not shown) to help position and assemble the segments30within the receptacle20.

Since the permanent magnets32are mounted to the receptacle20of the rotor12via a magnet receiving assembly made of magnetically susceptible material, the receptacle20itself is not limited to being made from magnetically susceptible metals and can be made of other materials such as plastics, other metals such as aluminum and fiber reinforced plastics, amongst others.

FIG. 4shows an external rotor for an external rotor electric machine according to a second illustrative embodiment wherein the caps46are omitted.

FIG. 5shows an external rotor50for an electric machine according to a third illustrative embodiment. Since the rotor50is similar to the rotor12, only the differences therebetween will be described hereinbelow in more detail for concision purposes. It is to be noted that some of the caps46have been omitted only to alleviate the drawing.

According to this embodiment, a first row of segments35is assembled to the receptacle20inside thereof and the next adjacent row is similarly assembled to the receptacle20so as to be angularly shifted with regards to the previous adjacent row. While this angular shift is of three (3) degrees according to the third embodiment, other angular shift angles can also be foreseen.

This shifting from one row of segments to the next has been found to cancel harmonics and to reduce cogging torque.

FIG. 6shows an external rotor60for an electric machine according to a fourth illustrative embodiment. Since the rotor60is similar to the rotor12, only the differences therebetween will be described herein in more detail for concision purposes.

According to this fourth embodiment, each segment64is provided with a central magnet-receiving portion63and with two lateral protrusions65,67.

The angular gap62between two consecutive segments64is minimized by providing segments64that have complimentary abutting surfaces. More specifically, the lateral sides of the segments are cut at non-orthogonal complimentary angles or curves. This allows positioning a segment64onto the peripheral wall22of the cylindrically shaped receptacle20by abutting a first end of a segment64with the opposite end of the adjacent segment, and then by pivoting the segment in place with the already positioned end thereof as a pivot.

With reference now toFIGS. 7A-7B, an external rotor70for an electric machine according to a fifth illustrative embodiment will now be described. Since the rotor70is similar to the rotor12, only the differences therebetween will be described herein in more detail for concision purposes.

The permanent magnet-receiving portions of the segments72are in the form of generally rectangular cuts74opened on each lateral side76of the segments72defining magnet-receiving grooves therein. With this configuration, a permanent magnet32is inserted in such a groove from the side. This has been found as requiring less adhesive grating after mounting the magnet32in the groove. However, as can be seen inFIG. 7B, the lamination segments72cannot be mounted radially. Lamination segments72are assembled by tilting (see arrow77) and then pushing thereon (see arrows78). It is to be noted that the caps46are integral with the segments72and that the gap between two adjacent magnets32is increased.

FIGS. 8A-8Bshow a sixth embodiment of an external rotor80for an electric machine. The external rotor80is very similar to the rotor70with, as differences, that the lamination segments82are shorter, leaving a gap84therebetween facilitating their mounting to the receptacle20from a radial direction (see arrows86). However the greater gap84is to the detriment to the ease of positioning. To cope with this additional challenge, circular holes88are provided at a same position in all lamination segments82, which can be used to align all stacked segment82. The holes82can be used as visual guides or to receive pins (not shown) to force the alignment of the segments82when they are abutted to the peripheral wall22.

An external rotor90according to a seventh embodiment is shown inFIGS. 9A-9B. Compared to the embodiment shown inFIGS. 1, 2, 3A-3B, the permanent magnets32on facing sides of two adjacent segments92are secured in respective magnet-receiving portions94so that the permanent magnets are in contact. A cap96is secured onto the pair of contacting adjacent magnets92as described hereinabove. The cap96includes two lateral shoulders98that are shaped and positioned so as to force the two facing magnets32into contact and prevent their displacement within the magnet-receiving portions94. Similarly to the embodiment shown inFIGS. 8A-8B, the segments include holes99for alignment. The holes99are oval-shaped. The shape of the lamination segments92allows their mounting to the peripheral wall22from the radial direction (see arrows97).

An external rotor100according to an eighth embodiment, which is shown inFIGS. 10A-10B, differs from the first embodiment by including lamination segments102whose central protrusion104includes two (2) small lips106, each extending within a respective magnet-receiving portion107. The lips106are contacted by the caps109. As illustrated by the arrows108, the lamination segments are positioned radially.

The ninth illustrative embodiment of an external motor110shown inFIGS. 11A-11Bis similar to the first embodiment, and only the differences therebetween will be described herein in more detail for concision purposes.

As a first difference, each lamination segment112includes a bulge114that cooperates with a complementary groove116in the peripheral wall118of the receptacle to fix the position of the segments112relative to the peripheral wall118and to helps transfer the torque to the rotor.

The magnet-receiving portions120are defined by two pairs of shoulders122in the lamination segments112on respective lateral side thereof.

The caps124are so configured as to be snapped to adjacent lamination segments over consecutive permanent magnets32. For this purpose, the caps124include tongues126on each lateral side thereof that cooperate with corresponding notches128provided on the segments112between the portions120and the central protrusion129. Of course, the notches128define grooves within a stack of segments112. No adhesive is used to secure the caps124to the segments112.

An external rotor130for an electric machine according to a tenth illustrative embodiment will now be described with reference toFIGS. 12A-12B. Since the rotor130is similar to the rotor110, only the differences therebetween will be described herein in more detail for concision purposes.

In addition to the tongue and groove arrangements shown inFIGS. 11A-11B, the external rotor130includes biasing members in the form of pre-loaded springs132that are positioned in secondary notches134provided in the main notches129. The tongues136, which are similar to the tongues126, are arcuate, thereby defining spring-receiving recesses therein that come into contact with the springs132when the caps138are mounted to the stack of segments140.

Finally, an external rotor140or an electric machine according to an eleventh illustrative embodiment will now be described with reference toFIG. 13. Since the rotor140is similar to the various rotors described above, only the differences therebetween will be described herein in more detail for concision purposes.

The main difference between the rotor140and the above-described rotors relates to the laminations142that are circular and fitted in the cylindrically shaped receptacle144. Glue (not shown) may be used to secure the stack of laminations142in the receptacle144.

The stack of laminations142include longitudinal apertures146configures and sized to receive permanent magnets148therein.

Grooves150are provided in the laminations142to allow room for excess adhesive.

One skilled in the art will understand that other configurations of an inserted permanent magnet rotor for an external rotor electric machine using some of the various features of the above-described illustrative embodiments can be designed.

One skilled in the art will also understand that while the segments forming the magnet-receiving assembly have been described hereinabove as being made of a stack of laminations, these segments could be made of blocks of compressed magnetic powders that have suitable magnetic properties. Or course, other soft magnetic materials (SMC) could be used to form the magnet receiving assembly.

It is to be understood that the inserted permanent magnet rotor for an external rotor electric machine is not limited in its applications to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. The inserted permanent magnet rotor for an external rotor electric machine is capable of other embodiments and of being practiced in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation. Hence, although the inserted permanent magnet rotor for an external rotor electric machine has been described hereinabove by way of illustrative embodiments thereof, it can be modified, without departing from the spirit, scope and nature of the subject invention.