Brushless direct current electric motor with reduced cogging torque and production method thereof

Abstract

The invention relates to a brushless direct current motor, having a rotor made up of at least one permanent magnet and a stator having at least three partitions (160) radially extending from a circular based cylindrical main body (170), the partitions (160) together defining at least two volumes for receiving at least three coils generating a magnetic field, wherein each volume is closed by a wall (170) connecting the partitions (160), and in that the wall comprises, on the face thereof oriented toward the rotor, at least one magnetic restriction zone. A sleeve (4) surrounds the stator and the rotor and has at least one deformation zone formed by cutouts (11) adapted to maintain the external geometrical configuration of the sleeve (4) when mounting the constituent elements of the motor. The invention also relates to a method for manufacturing such a motor.

Claims

1. A brushless direct current motor, comprising: a rotor made up of at least one permanent magnet disposed on an outer face of the rotor, wherein the permanent magnet extends over an entire length of the rotor; a stator inside which the rotor is inserted; and a sleeve surrounding an active part of the stator and defining a wall, wherein the active part of the stator is the part of the stator provided with a winding and generating a magnetic field; wherein: said stator has a plurality of partitions extending radially outwardly from a cylindrical main body, said partitions together defining at least two volumes for receiving at least three coils generating a magnetic field, each volume being closed by a second wall formed by a portion of said main body connecting said partitions, wherein each of the at least three partitions includes a flat end face for engaging an inner surface of the sleeve; said sleeve surrounds said stator and said rotor; and said sleeve comprises: a plurality of deformation zones spaced around the circumference of the sleeve, the plurality of deformation zones adapted to maintain an outer circularity of said sleeve when mounting said stator in said sleeve when said end faces of the plurality of partitions of said stator are positioned adjacent associated ones of said plurality of deformation zones, wherein the plurality of deformation zones are formed by a plurality of cutouts provided in the thickness of the wall; and a plurality of counterbores in the inner surface of the sleeve, each of said plurality of counterbores having a rounded bottom and extending over the length of an inner face of the sleeve, wherein only one of said plurality of counterbores is disposed between adjacent ones of said plurality of deformation zones.

2. The motor according to claim 1, wherein said second wall formed by said main body of said stator comprises a thinner zone defined by a grooving provided in said second wall.

3. The motor according to claim 1, wherein said second wall formed by said main body of said stator comprises a magnetic restriction zone formed by at least one wall portion made of at least one slightly magnetic or non-magnetic material.

4. The motor according to claim 1, wherein said second wall formed by said main body of said stator comprises a magnetic restriction zone formed by at least one zone thinner than said second wall.

5. The motor according to claim 4, wherein said magnetic restriction zone is formed on an inner face of said second wall oriented toward said rotor.

6. The motor according to claim 4, wherein said thinner zone is produced by a grooving.

7. The motor according to claim 4, wherein said thinner zone is produced by a groove on an inner face of said main body of said stator and a grooving positioned on an outer face of said main body of said stator.

8. The motor according to claim 1, wherein said rotor is positioned within said stator.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention will be better understood and further advantages thereof will become more clearly apparent upon reading the following description of a plurality of embodiments of the invention, which is provided by way of a non-limiting example and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a perspective view of a brushless motor according to one embodiment of the invention;

(3) FIG. 2 is a cross section view along II-II of the motor of FIG. 1, without the stator and to a different scale;

(4) FIG. 3 is a perspective view, to a different scale, of the constituent sleeve of the stator of the motor of FIG. 1;

(5) FIG. 4 is a perspective view, to a larger scale, of a ring forming, by stacking, the constituent active part of the stator of the motor of FIG. 1;

(6) FIG. 5 is a front view of a ring similar to that of FIG. 4, to a larger scale, according to another embodiment; and

(7) FIG. 6 is a simplified cross section view, to a different scale, of a brushless motor without the rotor, with the ring of FIG. 5 inserted into the sleeve of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 illustrates a brushless direct current motor 1 commonly designated by the term “brushless motor”.

(9) Such a motor is made of metal material and/or composites, at least for the active part. The rest of the motor, typically the constituent elements of the outer covering, can be made of composite materials or polymers.

(10) In this case, the motor 1 is a motor according to an embodiment of the invention in which a rotor 2 is inserted into a stator 3. An outer sleeve 4 surrounds the active part of the stator 3 and defines the outer wall of the motor 1. Such a motor 1 is used in various technical fields, for example, in the aeronautical, space, medical, automotive, marine, agri-foodstuff or other industry for operating a movable component either rotationally or translationally. In this case, a rotational drive shaft 5 is directly fixed on one end of the rotor 2 and extends said rotor.

(11) The rotor 2 is provided, on the outer face thereof, with at least two permanent magnets. The magnets are, for example, glued on the outer face, with a glue bridge being provided between two neighboring magnets. The magnets extend over the entire length of the rotor 2. The magnets, the number of which is adapted to the size of the rotor and the motor, are disposed so that the north and south poles of two neighboring magnets are alternately oriented toward the outside and toward the inside of the rotor 2. In one embodiment, not shown, the rotor 2 is hollow. As a variant, as shown in FIG. 2, the rotor 2 is solid. The magnets, under the effect of the magnetic field generated by the stator 3, ensure the rotation of the rotor 2 and therefore of the shaft 5.

(12) FIG. 3 illustrates the outer sleeve 4 ensuring the protection of the active parts of the stator 3, and therefore of the rotor when said rotor is introduced into the stator opening. The sleeve 4 has a flat and unified outer face 7. As a variant, it has a different appearance and/or it comprises an informative marking. The inner face 6 of the sleeve 4 comprises longitudinal grooves 8 or counterbores, with a rounded bottom, extending over the entire length of the face 6 of the sleeve 4. The sleeve 4 is also provided, on the outside of one of the ends thereof, with at least one lug 9 and at least one notch 10 defining an indexing and guiding component when positioning the sleeve 4 on the active part of the stator 3.

(13) Moreover, a deformation zone is provided on the sleeve 4. In this case, it is formed by a plurality of cutouts 11 provided in the thickness of the wall 12 of the sleeve 4. This deformation zone is adapted to absorb the deformation of the active part of the stator 3 in the shape of a star, which is inserted into the sleeve, and thus maintain the outer circularity of the sleeve 4.

(14) The active part of the stator 3 is the part of the stator 3 provided with the winding and generating the magnetic field. The active part of the stator is formed by the active parts of the constituent rings 15 by stacking the stator. Such an active part is, by analogy with FIG. 4, cylindrical, hollow and has a circular base. The dimensions and the shape of the inner opening 14 of each ring 15 are adapted to accommodate a portion of the rotor 2, while ensuring its free rotation, with a minimum amount of friction.

(15) Several partitions 16 radially extend toward the outside of each ring 15 from the annular body 17 of the ring 15. These partitions 16 are configured as a rectangular and flat tab. The length of the partitions 16 is equal to the length L of the ring 15 and they are parallel to this length. The partitions 16 are evenly disposed on the annular body 17. In this case, the space between two neighboring partitions 16 is constant. As will become more clearly apparent in FIG. 6, two neighboring partitions are thus connected by a wall formed by a portion of the annular body. Thus, a portion of the volume for receiving the coil is defined between the partitions and the portion of the annular body.

(16) A longitudinal groove 18 is provided, on the inner face 21 of the annular body 17, between two neighboring partitions 16. The opening of this groove 18 is oriented toward the inside of the body 17. A grooving or counterbore 19 is positioned on the outer face 20 of the annular body 17, facing the groove 18. The groove 18 and the counterbore 19 produce a thinner zone.

(17) As is apparent from FIG. 4, the grooves 18 and the counterbore 19 are evenly distributed on the body 17, along the entire length L of the ring 15. The grooves 18 and the counterbore 19 are produced by removing material on the body 17. This reduction in the nominal thickness of the body 17 in a given zone, and therefore once the stacked rings 15 have decreased the active part of the stator 3, results in a magnetic restriction.

(18) FIG. 5 illustrates another embodiment of a ring 150 similar to the ring 15. In this case, only the grooves 180 are present, the grooving or the counterbore on the outer face of the body 170 are absent. In all cases, the grooves 180 ensure, like the grooves 18, a reduction in the thickness of the active portion of the stator when the rings 150 are stacked, and therefore define a magnetic restriction zone.

(19) In another embodiment, not shown, the stack is made from rings that are equivalent, for example, to the combined features of a ring 15 and 150.

(20) As is apparent from FIG. 6, when the stator 3 is mounted, and therefore when the active part is wound and is inserted into the sleeve 4, the grooves 180 are substantially located in a central position between two neighboring partitions 160, with the winding, not shown, being in place. As shown in FIG. 6, the presence of grooves 180, due to the smaller amount of magnetic material at this point, directs the magnetic field so that it does not pass directly from one partition 160 to another, but follows a circuit through one of the magnets of the rotor, with said rotor being introduced into the volume V defined for the opening of the stacked rings 150. The rotor is then set into rotation, with its magnets attempting to align with the magnetic field. Due to the presence of the grooves 180, and therefore of the magnetic restriction zone over the entire circumference of the body 170, an even and constant circuit is brought about that enables cogging to be avoided. Moreover, the presence of cutouts 11 in the sleeve 4 provides a perfectly circular configuration for the inside of the sleeve, thus avoiding any deformation of the stacked rings, in particular in the vicinity of the partitions. This also helps to ensure even rotation of the rotor.

(21) It is understood that the operation is identical with the rings 15 stacked according to the embodiment shown in FIG. 4.

(22) As a variant, in another embodiment, the magnetic restriction zone is obtained by a change of material. Typically, one or more materials are used with magnetic conductivity that is lower than that of the rest of the body 17; 170 and partitions 16; 160. It is also possible to use non-magnetic materials.

(23) Moreover, the grooves 18; 180 allow, due to the method for producing the stator 3, a precise adjustment to be achieved, with optimum contact between the parts to ensure thermal and magnetic conductivity, without deformation of the constituent parts.

(24) The mounting of such a motor will now be described with reference to the various figures. To this end, a stack of rings 15; 150 is initially made that constitutes the active part of the stator 3. These rings 15; 150 were previously machined and configured, according to the cross section of the stator to be obtained. The number of rings to be stacked depends on the desired length of the stator 3. Once the stack is made, the winding is carried out by winding the copper wire around the partitions 16; 160 from the open zone. Such winding is easy to produce, since there is no obstacle hindering handling.

(25) Once the winding is carried out, a stack of circular rings, not illustrated, constituting the sleeve 4 is produced. It is understood that the stack for the sleeve is independent of the rest of the method and that it advantageously can be carried out at another location and/or at another time than simultaneously with the winding. In other words, it is possible to produce the sleeve 4 by stacking a number of rings that is defined according to the length of the sleeve to be obtained, independently of the mounting of the active part and the winding. It is understood that, when the winding is carried out, it is important that the volumes receiving the coils are closed quickly by installing the stack of rings constituting the sleeve.

(26) The previously obtained active part is then inserted into the sleeve 4 using the lacing technique. By way of a reminder lacing refers to the assembly of two parts with a tight fit. Assembly is carried out by heating the outer part or hoop, which allows the cold part to be laced to be introduced into the hoop or into a housing provided in the hoop. The adjustment between the parts is made by cooling the parts to the same temperature. Such a technique allows a homogeneous and similar adjustment at any point in the zone for assembling the parts together.

(27) Positioning the parts during lacing is facilitated by the presence of the lugs 9 and notches 10, which allow indexed positioning of the parts.

(28) The grooves 18; 180 also allow, during temperature variations, the parts of each ring 15; 150 to deform, and thus adjust, independently of each other, in a resilient manner.

(29) The deformation zones 11 of the sleeve 4 mentioned above also help to define resilient behavior of the sleeve 4. This results in reduced stresses and deformations on the entire stator 3.

(30) The mounting of the motor is finalized by shaping the copper wire portions of the winding that appear on the ends. This step is referred to as coil production.

(31) A final step involves overmolding all the elements of the stator and of the rotor with a protective resin.