阅读说明：本技术 用于无槽永磁同步电动机的开放式定子绕组和定子芯布置 (Open stator winding and stator core arrangement for a slotless permanent magnet synchronous motor ) 是由 M·拉马努贾姆 S·洛哈卡 V·诺伯特 于 2021-06-02 设计创作，主要内容包括：无槽永磁同步(SPMS)电动机包括具有向外突出的线圈前头端(302)和线圈后尾端(306)的开放式定子绕组(300)。因为线圈前头端(302)向外突出,故前转子平衡环(308)被移出开放式定子绕组的有效部外。通过将前转子平衡环(308)移出有效部外,开放式定子绕组(300)的有效部的长度被增大,因此由SPMS电动机产生的转矩增大。定子芯包括带有锁定机构的两个半圆形环(502,504；602,604),该锁定机构具有阶梯形设计以减小由电动机产生的定位转矩。(A Slotless Permanent Magnet Synchronous (SPMS) motor includes an open stator winding (300) having an outwardly protruding coil leading end (302) and a coil trailing end (306). Because the coil front tip (302) protrudes outward, the front rotor balancing ring (308) is moved out of the active portion of the open stator winding. By moving the front rotor balancing ring (308) out of the active portion, the length of the active portion of the open stator winding (300) is increased, and therefore the torque generated by the SPMS motor is increased. The stator core includes two semi-circular rings (502, 504; 602,604) with a locking mechanism having a stepped design to reduce cogging torque produced by the motor.)

1. A Slotless Permanent Magnet Synchronous (SPMS) motor, comprising:

a shaft (312) centered and along a length of the SPMS motor;

a stator winding present around the shaft (312) and having a coil leading end (302) and a coil trailing end (306) on opposite ends and an active portion (304) between the coil leading end (302) and the coil trailing end (306), wherein the coil leading end (302) and the coil trailing end (306) have a flat inner surface;

a rotor magnet (310) disposed above the shaft (312) and below the stator winding, wherein the rotor magnet (310) is present along the entire length of the active portion (304) of the stator winding:

an open stator winding (300) disposed around the rotor magnet (310), wherein the open stator winding (300) has a flat inner surface and a coil leading end (302) and a coil trailing end (306) as protrusions at both ends of the outer surface:

a lamination stack (404) disposed in the active portion (304) between the coil leading end (302) and the coil trailing end (306);

and a stator outer frame (402) disposed outside as a housing of the open stator winding (300).

2. The SPMS motor as set forth in claim 1, further comprising a front rotor balancing ring (308) located below the front head end (302) of the coil and a rear rotor balancing ring (314) located below the rear tail end (306) of the coil to hold the rotor magnet (310) in place, wherein the front rotor balancing ring (308) and the rear rotor balancing ring (314) are located outside the bottom region of the active portion (304) to increase the effective length, thereby increasing the motor torque constant.

3. SPMS motor according to claim 1, characterised in that the lamination stack (404) is made of two semi-circular stator cores (502, 504; 602,604) provided with locking means for mutual locking.

4. The SPMS motor as set forth in claim 3, wherein the two semi-circular stator cores (502, 504; 602,604) engage each other with a stepped design or a ramped surface to reduce variation in reluctance with respect to rotor position, thereby reducing cogging torque of the SPMS motor.

5. The SPMS motor as set forth in claim 3, where the two semi-circular stator cores (502, 504; 602,604) are made from a compacted Soft Magnetic Composite (SMC) material.

6. The SPMS motor according to claim 1, where the effective portion (304) of the winding has an outer diameter that is smaller than the outer diameters of the coil leading end (302) and the coil trailing end (306) that define the shape of the stator winding.

7. The SPMS motor as set forth in claim 1, in which the two semi-circular stator cores (502, 504; 602,604) are placed on the open stator winding (300), are co-inserted into the stator housing, and are cemented in an axial position.

8. SPMS-motor according to claim 1, characterised in that the open stator winding (300) is made of self-supporting non hygroscopic thermo-bonded QT litz wire, and where the litz wire allows to facilitate the formation of an open stator winding shape.

Technical Field

The present invention generally relates to stator winding and stator core arrangements for electric motors. More particularly, the present invention relates to a stator winding and stator core arrangement for a slotless permanent magnet synchronous motor.

Background

The subject matter discussed in the background section should not be assumed to be prior art merely because it was mentioned in the background section. Also, the problems mentioned in the background section are associated with the subject matter of the background section and should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which may themselves also correspond to implementations of the claimed technology.

In a Permanent Magnet Synchronous (PMS) motor, permanent magnets are located on the rotor and phase windings are located on the stator. A controller is used to sequentially energize the phase windings to produce a rotating magnetic field. The permanent magnets interact with the rotating magnetic field to generate a torque for rotating the rotor.

Typically, the stator is made of steel laminations that are stamped and stacked to form a cylindrical shape with a central opening to accommodate the rotor. The steel laminations of the stator have a slotted design or a non-slotted design. The toroidal stator core and the windings placed in the air gap exhibit slotless, i.e. slotless stators have a low winding inductance and low core losses and can therefore be operated at very high speeds. Slotless Permanent Magnet Synchronous (SPMS) motors are generally suitable for use in small D/L ratios, i.e., ratio of outer diameter to axial length, low torque, and high speed applications. The lack of stator core teeth in SPMS motors allows for the absence of cogging torque as compared to slotted motors that produce cogging torque.

Typically, self-supporting coil windings are used in SPMS motors. Fig. 1 shows an axial cross-sectional view 100 of a conventional SPMS motor with an axial-type self-supporting coil winding. The stator winding of the SPMS motor has an inwardly projecting leading end 102, an active portion 104 of the stator winding (also referred to as the stator active portion 104), and a trailing end 106 having a flat inner surface and a convex protrusion on its outer surface. The forward balancing ring 108 and the aft balancing ring 110 are located at the ends of the rotor magnets 112 and surround the rotor shaft 114. The stator active portions 104 of the stator windings may be aligned parallel to correspond to the length of the rotor magnets 112.

Fig. 2 shows another axial cross-sectional view 200 of a conventional SPMS motor. Axial cross-sectional view 200 shows stator outer frame 202, stack of laminations 204 disposed over stator active portion 104, and lamination stack 206. Lamination holders 206 are positioned on both ends of lamination stack 204 to hold lamination stack 204 in place. The length of the stator active portion 104 is responsible for generating torque in the SPMS motor. In the conventional configuration shown in fig. 1 and 2, the length of the rotor magnet 112 is limited by the inward protrusion of the leading end 102 and the presence of the rotor leading balancing ring 108 below the stator active portion 104. This limited length of the rotor magnet 112 results in a limited amount of torque being generated in a small brushless direct current (SBLDC) motor when the D/L ratio of the motor is high. Furthermore, if a forced air cooling arrangement is considered, the inward projection of the front head end 102 of the assembly 100 also impedes air flow, resulting in poor heat dissipation.

Applications such as medical drills and saws require SBLDC motors with better torque density, higher autoclave, reliability, and better heat dissipation.

Disclosure of Invention

It is a general object of the present invention to increase torque density in a Slotless Permanent Magnet Synchronous (SPMS) motor.

It is another object of the present invention to improve the autoclaving, reliability and heat dissipation of SPMS motors.

It is a further object of the present invention to develop a stator assembly to provide for easy installation of the rotor into the stator assembly.

It is a further object of the present invention to improve the performance and reliability of SPMS motors.

It is a further object of the present invention to provide a stator core arrangement that reduces cogging torque associated with the proposed SPMS motor stator winding arrangement.

Disclosure of Invention

The summary is provided to introduce aspects related to stator winding and stator core arrangements for Slotless Permanent Magnet Synchronous (SPMS) motors for increased torque density, and these aspects are further described in the detailed description below. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used to identify or limit the scope of the claimed subject matter.

In one embodiment, the SPMS motor includes a shaft located centrally and along the length of the SPMS motor. The stator winding is present around the axis and has a coil leading end and a coil trailing end at opposite ends, and an effective portion is present between the coil leading end and the coil trailing end. The coil leading end and the coil trailing end both have flat inner surfaces. The rotor magnets are positioned above the shaft and below the stator windings. The rotor magnets are present along the entire length of the stator winding active portion. An open stator winding is disposed around the rotor magnets. The open stator winding has a flat inner surface and has coil leading and trailing ends as projections on the outer surface ends. The lamination stack is disposed in the active portion between the leading and trailing coil ends. The stator outer frame is located on the outside as a housing for the open stator winding.

In one embodiment, the front rotor balancing ring is located below the front head end of the coil and the rear rotor balancing ring is located below the rear tail end of the coil to hold the rotor magnets in place. The front rotor balancing ring and the rear rotor balancing ring are located outside the bottom region of the effective portion to increase the effective length, thereby increasing the motor torque constant.

In one embodiment, the lamination stack is made of two semi-circular stator cores provided with locking means for mutual locking. The two semi-circular stator cores are engaged using a stepped design or ramp to reduce variation in reluctance with respect to rotor position, thereby reducing cogging torque of the SPMS motor. The two semi-circular stator cores are made of compacted Soft Magnetic Composite (SMC) material. The two semi-circular stator cores are placed on the open stator windings and bonded to each other, inserted into the stator housing and cemented in one axial position. The open stator winding is made of self-supporting non-hygroscopic thermally bonded QT litz wire. Litz wire allows for the easy formation of open stator winding shapes.

Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

Drawings

The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification.

Fig. 1 shows an axial cross-sectional view of a conventional Slotless Permanent Magnet Synchronous (SPMS) motor including stator windings and a rotor assembly according to the prior art.

Fig. 2 shows another axial cross-sectional view of a conventional SPMS motor including a stator and rotor assembly according to the prior art.

Fig. 3 shows an axial cross-sectional view of a proposed assembly of an SPMS motor including stator windings and a rotor assembly according to an embodiment of the present invention.

Fig. 4 shows an axial cross-sectional view of a proposed assembly of an SPMS motor including a stator and rotor assembly according to an embodiment of the present invention.

Fig. 5 illustrates a lamination stack arrangement for a two-piece stator core of an SPMS motor in accordance with an embodiment of the present invention.

Fig. 6 illustrates an exemplary representation of a two-piece stator Soft Magnetic Composite (SMC) core of an SPMS motor in accordance with an embodiment of the invention.

Fig. 7 shows the back emf generated as a function of SPMS motor rotor position in accordance with another embodiment of the present invention.

FIG. 8 illustrates detent torque as a function of proposed SPMS motor rotor position according to an embodiment of the present invention.

Detailed Description

The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described herein is provided merely as an example or illustration of the present invention and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details.

In one embodiment, an open stator winding and stator core arrangement for a Slotless Permanent Magnet Synchronous (SPMS) motor is provided herein to overcome problems associated with performance, reliability, torque density, heat transfer capability, and cogging torque of SPMS motors. Next, the structure and arrangement of the stator winding and the stator core of the SPMS motor are explained in turn with reference to the drawings.

Fig. 3 shows an axial cross-sectional view of the open stator winding 300 and rotor assembly of the SPMS motor. Open stator winding 300 includes a coil front end 302 having a flat inner surface and a protrusion on an outer surface. Open stator winding 300 also includes a coil tail end 306 having projections on its outer surface. The effective portion 304 exists between the coil leading end 302 and the coil trailing end 306. The open stator winding 300 further includes a front rotor balancing ring 308, a rotor magnet 310 present on a shaft 312, and a rear rotor balancing ring 314. The front rotor balancing ring 308 may be located below the coil front head end 302 and the rear rotor balancing ring 314 may be located below the coil rear tail end 306. Front rotor balancing ring 308 and rear rotor balancing ring 314 may be used to balance rotor magnets 310 and hold rotor magnets 310 in place in view of high speed motor operation. The front rotor balancing ring 308 and the rear rotor balancing ring 314 may be non-magnetic and non-productive components. The front rotor balancing ring 308 and the rear rotor balancing ring 314 may not contribute to generating torque in the SPMS motor. Front rotor balancing ring 308 and rear rotor balancing ring 314 exist outside the bottom region of active portion 304 to increase the effective length, thereby increasing the motor torque constant.

Since the coil front head end 302 has a flat inner surface and protrudes outward, the front rotor balancing ring 308 is moved out of the bottom area of the effective portion 304. By shifting the front rotor balancing ring 308, the length of the effective portion 304 is increased. As the length of the open stator winding active portion 304 increases, the torque generated by the SPMS motor also increases. Thus, the torque density and performance of the SPMS motor is improved when using the open stator winding 300. Further, the open stator windings may include straight conductors in the active portion 304 to increase the torque constant of the SPMS motor. The open stator windings also provide better autoclave sterilization of the SPMS motor by transfer molding the stator assembly.

According to this embodiment, the ball bearings may be press fit onto the shaft 312 and the rotor assembly may pass through the open stator winding assembly. This allows for better assembly of the ball bearing, thus resulting in longer motor life.

The open stator winding may employ self-supporting and non-hygroscopic thermal bonded QT litz wire to provide improved stator transfer molding capability and high pressure sterilization of the SPMS motor with higher operating temperatures of about 200 ℃. The reliability of SPMS motors can be improved due to the implementation of thermally bonded QT litz wire. Furthermore, litz wire allows for easy formation of open stator winding shapes.

Fig. 4 shows an axial cross-sectional view of the proposed SPMS motor assembly 400. In addition to the component parts of assembly 300, assembly 400 includes a stator outer frame 402 and a lamination stack 404. The stator outer frame 402 serves as a housing for the open stator winding 300. The lamination stack 404 is positioned in the area defined between the coil leading end 302 and the coil trailing end 306 and between the active portion 304 and the outer frame 402.

The micromotor has a built-in Printed Circuit Board (PCB) assembly. The hall sensor is mounted on such a built-in PCB assembly. These hall sensors are used to find the rotor position for commutation. These hall sensor failures are mainly present in sterilizable SPMS motors. To avoid hall sensor failure, the PCB can be over-molded along with the stator assembly to improve reliability of the SPMS motor.

Fig. 5 illustrates a lamination stack arrangement for a two-piece stator core 500 for an SPMS motor. The two-piece stator core 500 may include two semi-circular ring shaped stator cores 502 and 504. The two semi-circular stator cores 502 and 504 may be made of a stack of laminations and provided with a locking mechanism for locking with each other when assembled to form the stator windings. The two-piece stator core 500 may be manufactured as two semi-circular ring shaped stator cores 502 and 504 to fit on the active portion 304 having an outer diameter smaller than the outer diameters of the coil leading end 302 and the coil trailing end 306 defining the winding shape. The laminations are stacked and laser welded or riveted together at the outer surfaces. The lamination core has an outer diameter greater than the coil leading end 302 and the coil trailing end 306.

Fig. 6 illustrates an exemplary representation of a two-piece stator core 600 for an SPMS motor. In one implementation, to eliminate cogging torque produced by the engagement surfaces, semi-annular stator cores 602 and 604 may be engaged using a stepped design or a ramped surface to reduce variation in reluctance with respect to rotor position, as shown in fig. 6. The detent torque of the SPMS motor decreases as the reluctance decreases. The two semi-circular ring shaped stepped stator cores 602 and 604 may be made of compacted Soft Magnetic Composite (SMC) material.

As a first step in the assembly process, the open coil is formed with a forming tool. Subsequently, the stator core is placed on the stator winding and bonded together. Thereupon, the subassembly is jointly inserted into the stator housing and cemented at a desired axial position. Because of the open winding arrangement, the rotor assembly can be inserted from either side of the stator housing. This feature would allow for modularity of components and analysis of motor failure modes during the manufacturing stage.

Fig. 7 shows the resulting back electromotive force (EMF) as a function of SPMS motor rotor position for two different stator winding implementations. The back electromotive force represents an open circuit voltage generated in the stator winding when the rotor rotates. Further, the back electromotive force is related to a motor torque constant. The higher the motor torque constant, the less current is required to meet the load torque demand. Curve 702 represents the variation in back emf in a conventional stator winding implementation in an SPMS machine. Curve 704 represents the change in back emf in the proposed open stator winding implementation in the SPMS motor. By implementing open stator windings in an SPMS motor, the performance of the SPMS motor may be improved by at least up to 8% over the performance of other SPMS motors implemented with conventional stator windings. Furthermore, the increase in stator winding resistance is negligible compared to prior art coil designs.

Fig. 8 shows detent torque as a function of SPMS motor rotor position for three different stator core implementations. Curve 802 represents the variation in cogging torque in conventional or existing ring stator core and existing stator winding implementations in SPMS motors. Curve 804 represents the variation in cogging torque in an open stator winding with two semi-circular stator cores of flat design. Curve 806 represents the variation in cogging torque in an open stator winding with two half-circle ring stator cores of stepped design. By implementing a flat design in both semi-circular stator cores (i.e., two-piece stator cores), cogging torque can be increased as compared to conventional circular stator cores. By implementing a stepped design/profile in both semi-circular stator cores (i.e., two-piece stator cores), peak cogging torque can be reduced to 1.5 millinewton-meters (mNm) and is negligible. Thus, the stepped core design reduces cogging torque produced by the SPMS motor.

In one embodiment, the open stator windings and stator core/assembly may be implemented in any of two-pole, four-pole, and eight-pole slotless Permanent Magnet (PM) synchronous motors.

As described above, embodiments of stator winding and stator core arrangements used in SPMS motors may provide certain advantages. While not required to practice aspects herein, these advantages can include those provided by the following features.