Claims:WE CLAIM
1. A rotor of an electric machine comprising:
Plurality of sectors 2 placed symmetrically about radial axis across the circular cross section of said rotor 1 wherein;
Each of the said sector 2 comprising of, at least one flux insulators 3 between adjacent direct axes 4, wherein the flux insulator 3 has central part 3a located normal to the quadrature axis 7 and first end and second end 3b located along the direct axis 4, wherein the ends of the flux insulators 3 have extended sides towards direct axis 4 to direct the flux flow in the direction of direct axis 4;
Uniform size cage slots 5 are designed along circumference of the rotor cross section 1, the cage slots 5 at said first end and second end 3b of flux insulator 3 are aligned with the flux insulator end and cage slots 5 across quadrature axis 7 parallel to the centre part of the flux insulator are combined to form extended cage slots 6 wherein, conducting material 11 is die-casted in to the cage slots 5 and/or the extended cage slots 6.

2. The said rotor according to claim 1 comprising a tangential ribs 10 and radial ribs 8 across the flux insulator 3 for improvement of mechanical strength of the said rotor, wherein the said redial ribs 8 are located along the quadrature axis 7 and normal to the central part 3a of the flux insulator 3 of the said rotor, and the said tangential ribs 10 are located between the cage slots 5 and the flux insulator end.
3. The said rotor according to claim 1 wherein the said conducting material 11 dia-casted in the cage slots 5 and/or extended cage slots 6 according to claim 1 is any of aluminium, copper, brass or any conductive material

4. The said rotor according to claim 1 wherein the said end laminations 13 comprising of only cage slots 5 and extended cage slot 6 for die cast the conducting material 11 in to the cage slots 5 and merged cage slots 6.

5. A rotor of an electric machine comprising:
Plurality of sectors 2 placed symmetrically about radial axis across the circular cross section of said rotor 1 wherein;
Each of the said sector 2 comprising of, at least one of the flux insulators 3 between adjacent direct axes 4, wherein the flux insulator 3 has central part 3a located normal to the quadrature axis 7 and first end and second end 3b located along the direct axis 4, wherein the ends of the flux insulators 3 have extended sides towards direct axis 4 to direct the flux flow in the direction of direct axis 4, wherein permanent magnet material 12 can be fixed in the flux insulator 3 and steps 9 provided in the flux insulator 3 helps in fixing the permanent magnet material 12 in the flux insulator 3;
Uniform size cage slots 5 are designed along circumference of the rotor cross section 1, the cage slots 5 at said first end and second end 3b of flux insulator 3 are aligned with the flux insulator 3 end and cage slots 5 across quadrature axis 7 parallel to the centre part of the flux insulator 3 are combined to form extended cage slots 6

6. The said rotor according to claim 5 comprising a tangential ribs 10 and radial ribs 8 across the flux insulator 3 for improvement of mechanical strength of the said rotor 1, wherein the said redial ribs 8 are located along the quadrature axis 7 and normal to the central part 3a of the flux insulator 3 of the said rotor, and the said tangential ribs 10 are located between the cage slots 5 and the flux insulator 3 end.

7. The said rotor according to claim 5 wherein the said permanent magnet material 12 fixed in the flux insulator 3 according to claim5 is any of ceramic magnet or a rare earth magnet or an alnico magnet or samarium cobalt type magnet material.

8. A rotor of an electric machine comprising:
Plurality of sectors 2 placed symmetrically about radial axis across the circular cross section of said rotor wherein;
Each of the said sector 2 comprising of, at least one of the flux insulators 3 between adjacent direct axes 4, wherein the flux insulator 3 has central part 3a located normal to the quadrature axis 7 and first end and second end 3b located along the direct axis 4, wherein the ends of the flux insulators 3 have extended sides towards direct axis 4 to direct the flux flow in the direction of direct axis 4, wherein permanent magnet material 12 can be fixed in the flux insulator 3 and steps 9 provided in the flux insulator 3 helps in fixing the permanent magnet material 12 in the flux insulator 3;
Uniform size cage slots 5 are designed along circumference of the rotor cross section 1, the cage slots 5 at said first end and second end 3b of flux insulator 3 are aligned with the flux insulator 3 end and cage slots 5 across quadrature axis 7 parallel to the centre part of the flux insulator 3 are combined to form extended cage slots 6 wherein, conducting material 11 is die-casted in to the cage slots 5 and/or the extended cage slots 6.

9. The said rotor according to claim 8 comprising a tangential ribs 10 and radial ribs 8 across the flux insulator 3 for improvement of mechanical strength of the said rotor 1, wherein the said redial ribs 8 are located along the quadrature axis 7 and normal to the central part 3a of the flux insulator 3 of the said rotor, and the said tangential ribs 10 are located between the cage slots 5 and the flux insulator 3 end.

10. The The said rotor according to claim 8 wherein the said conducting material 11 dia-casted in the cage slots 5 and/or extended cage slots 6 is any of aluminium, copper, brass or any conductive material
11. The said rotor according to claim 8 wherein the said end laminations 13 comprising of only cage slots 5 and extended cage slot 6 for die cast the conducting material 11 in to the cage slots 5 and/or extended cage slots 6

12. The said rotor according to claim 8 wherein the said permanent magnet material 12 fixed in the flux insulator 3 is any of ceramic magnet or a rare earth magnet or an alnico magnet or samarium cobalt type magnet material.
, Description:FIELD OF THE INVENTION
The present invention relates to field of electric motor and, specifically the invention relates to design of rotor for electric motor, furthermore the invention is related to design of flux insulators and cage slots and its effect on the motor function.

BACKGROUND OF THE INVENTION
Synchronous reluctance motors and line start synchronous reluctance motors are known in the art.

When a rotor attempts to align its most magnetically conductive axis i.e. direct axis with applied stator field, a reluctance torque is generated. The amplitude of reluctance torque is directly proportional to the difference between inductance in the direction of direct axis to that of quadrature axis. The direct axis or magnetically conductive axis is defined as, minimum reluctance axis so maximum flux travels through direct axis. The quadrature axis is defined as maximum reluctance axis, ideally infinite reluctance. Flux flow through quadrature axis is of minimum value. Saliency ratio is defined as the ratio of inductance in the direction of direct axis to inductance in the direction of quadrature axis.

Operation of the synchronous reluctance machine is based on an anisotropic rotor structure in which each rotor pole has a minimum reluctance in the direction of the direct axis, and maximum reluctance in the direction of the quadrature axis. The rotor's direct axis follows the peak value of the stator's rotating magnetic field. To maximize the power and torque of the synchronous reluctance machine, the ratio of the rotor's direct axis inductance Ld and the quadrature axis inductance Lq need to be as high as possible.

Innovations have been carried out to achieve a higher inductance ratio Ld/Lq, for the structure in which well-conducting routes is formed for the flux in the direction of the direct axis and flux barriers are designed to prevent the flow of magnetic flux in the direction of the quadrature axis.

Conventional synchronous reluctance motor requires drive controller to operate. The inclusion of the driving mechanism adds to the cost of the motor.

Mclaughlin H discloses synchronous reluctance motor with cage slots in the rotor. The said rotor design is helpful for improving pull-in torque. The pull-in torque is defined as maximum value of torque at given speeds that the motor can generate while running in synchronism. FIG. 1 of the drawing of the present application shows a rotor design. However Synchronous reluctance motor designed according to the conventional design principles still exhibit a high torque ripple which causes vibration in the motor.

Mike Melfi in his design discloses a line start synchronous reluctance motor with flux insulator and cage slots of different size, shape, and spacing. The rotor structure supports self starting of the motor and at synchronous speed it operates as synchronous machine. Further the cage slots are arranged radially outwards to rotor diameter. FIG. 2 of the drawing of the present application shows a rotor design. Radial arrangement of the cage slots in the line start synchronous reluctance motor increase the leakage flux and hence affect the motor efficiency.
The rotor design with cage slots having different size, shape, and spacing will require high cost for manufacturing the rotor lamination owing to tooling complexity of the die-cast.

As is apparent in the prior art discussed above, the rotor design for a line start synchronous reluctance motor is different from that of a synchronous reluctance motor. Hence for manufacturing purpose different set of die-cast structures and tools would be required. Such limitation increase the manufacturing complexity of these machines

Hence, there is a need for a novel rotor design which obviates the limitations of the prior art.

SUMMARY OF INVENTION
An object of the present invention is to provide improved rotor design of a line start synchronous reluctance motor. Another object of the invention is to provide a line start synchronous reluctance motor rotor having a low torque ripple and low leakage flux to improve the motor performance.
Yet another object of the present invention is to provide a rotor structure for line start synchronous reluctance motor with improved mechanical strength.

Yet another object of the present invention is to provide a universal rotor design that can be used for construction of rotor for variety of synchronous reluctance based rotating machines

Yet another object of the present invention is to provide a rotor design that requires minimal tooling cost and thereby reduces the manufacturing cost and improving the manufacturability

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the scope of the claims wherein;

FIG. 1 shows a rotor cross section design as illustrated in the invention by Mclaughlin H implemented in synchronous reluctance rotor;

FIG. 2 shows a rotor cross section design as illustrated in the invention by Mike Melfi implemented in line start synchronous reluctance motor;
FIG. 3 shows a cross section of the rotor according to one embodiment of the present invention with flux insulators and uniform size uniformly distributed cage slot;

FIG. 4 shows a cross section of the rotor according to one embodiment of the present invention with uniform size uniformly distributed cage slot and flux insulator along with the steps to hold permanent magnet material in the flux insulator to improve the motor stability;

FIG. 5 shows a cross section of the rotor according to another embodiment of the present invention with uniform size cage slots and flux insulator along with steps to hold permanent magnet material in the flux insulator to improve the motor stability where the cage slots at end of flux insulator are aligned with flux insulator in order to improve the flux flow across direct axis;

FIG. 6 shows a cross section of the rotor according to yet another embodiment of the present invention with flux insulator having steps and uniform size cage slots and merged cage slots. The merged cage slots are hereafter referred as extended cage slots for better clarity in understanding;

FIG. 7 shows a cross section of the rotor according to yet another embodiment of the present invention with flux insulator having steps and conductive material die casted inside the cage slots and extended cage slots;
FIG. 8 shows a cross section of the rotor according to yet another embodiment of the present invention with flux insulator having steps wherein permanent magnet material fixed in the flux insulator with the support of the steps and further having uniform size cage slots and extended cage slots;

FIG. 9 shows a cross section of the rotor according to yet another embodiment of the present invention with flux insulator having steps wherein permanent magnet material fixed in the flux insulator and conductive material die casted inside the cage slots and extended cage slots; and

FIG. 10 shows the cross section of the rotor end lamination according to one of the embodiment of the present invention where the end laminations only comprising of cage slots and extended cage slots

DETAILED DESCRIPTION OF THE OF THE ACCOMPANYING DRAWING
As used in the specification, the singular forms “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “an article” may include a plurality of articles unless the context clearly dictates otherwise.

Those with ordinary skill in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated, relative to other elements, in order to improve the understanding of the present invention.

There may be additional components described in the foregoing application that are not depicted on one of the described drawings. In the event such a component is described, but not depicted in a drawing, the absence of such a drawing should not be considered as an omission of such design from the specification.

The purpose of the invention is to create a new rotor structure of the synchronous reluctance machine which has a high inductance ratio Ld/Lq, which is mechanically strong and can withstand mechanical stress created due to centrifugal force at high speed and which is economical to manufacture.

Proposed rotor design can provide high saliency ratio with the design to accommodate maximum flux flow across the direct axis 4 and minimum flux flow across the quadrature axis 7. The direct axis 4 or magnetically conductive axis is defined as, minimum reluctance axis so maximum flux travels through direct axis 4. The quadrature axis 7 is defined as maximum reluctance axis, ideally infinite reluctance. Flux flow through quadrature axis 7 is of minimum value. Saliency ratio is defined as the ratio of inductance in the direction of direct axis 4 to inductance in the direction of quadrature axis 7.
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.

FIG. 3 shows rotor cross section 1 of the rotor according to one of the embodiment of the present invention. The rotor cross section 1 can be further comprises of plurality of sectors 2 placed radially symmetrically along the rotor cross section 1.

Each of the sectors 2 comprises of plurality of uniformly distributed slots 5 designed along the circumference of the rotor. Each of the uniformly distributed cage slots 5 are of uniform shape, size and geometry and further each of the cage slots 5 have notched end 5’. The cage slot 5 allows a squirrel cage winding to be provided on the rotor, thereby allowing motor starting motor direct on line without the requirement of drive.

Each of the sectors 2 further comprises of multiple flux insulators 3 between two adjacent direct axes 4 as shown in FIG.3. The flux insulator 3 has one central part 3a located normal to the quadrature axis 7 whereas first end and second end 3b are located along the direct axis 4.

The flux insulator 3 design provides high flux flow in the direction of direct axis 4 and minimum flux flow in the direction of quadrature axis 7.

In yet another embodiment of the invention the flux insulators 3 are separated by thin redial ribs 8. Wherein the radial rib 8 is located along the quadrature axis 7 and across the central part 3a of the flux insulator 3

In an another embodiment of the present invention FIG. 4 shows the step 9 in the flux insulator 3 to hold any material in the flux insulator 3 and to improve the motor stability

After simulation of the rotor of the FIG. 3 and FIG. 4, it is identified that the cage slots 5 being hollow can also affect the direction of the flux flow while the rotor is in operation by affecting the maximum flux flow in direction of the direct axis 4 and minimum flux flow in the direction of the quadrature axis 7 during synchronous speed of the rotation. This may oppose the flux flow and hence the motor efficiency gets affected.
As an improvement to the previous design, the FIG. 5 shows rotor according to one of the embodiment of the invention. Each of the sectors 2 comprises of flux insulator 3 aligned across two adjacent direct axes 4 and cage slots 5 are designed on the circumference of the rotor. The Cage slots 5 are of uniform size and the cage slots 5 at the end of the flux insulators 3 are aligned in the direction of flux insulator 3 ends separated by tangential ribs 10 as shown in FIG. 5.

In yet another embodiment of the invention the flux insulators 3 are separated by thin redial ribs 8. Wherein the radial rib 8 is located along the quadrature axis 7and across the central part 3a of the flux insulator 3

The cage slots 5, aligned to the end of the flux insulators 3 are parallel to the flux conducting path as shown in FIG. 5. The notched end 5’ in the direction of the flux insulators 3 end are aligned towards flux insulator 3 axis in order to minimize the leakage flux as compared to conventional radial notched end design. This design helps to improve the flux flow in the direction of the direct axis 4.

The cage slots 5 near quadrature axis 7 other than the cage slots 5 aligned with the flux insulator 3 ends are in close proximity to each other in order to improve the flux flow and in turn it improves the motor efficiency as shown in FIG. 5.

The tangential rib 10 may be provided to enhance the mechanical strength of the rotor.
Optionally the tangential ribs 10 can be left out if the mechanical structure of the rotor cross section 1 is ensured by other means.

As an improvement to the previous design, the FIG. 6 shows rotor according to one of the embodiment of the invention. Each of the sectors 2 comprises flux insulator 3 aligned across two adjacent direct axes 4 and cage slots 5 are designed on the circumference of the rotor. Cage slots 5 are of uniform size and the cage slots 5 at the end of the flux insulators 3 are aligned in the direction of flux insulator 3 ends separated by a tangential ribs 10 as shown in FIG. 6. A tangential rib 10 may be provided to enhance the physical strength of the rotor.

In yet another embodiment of the invention the flux insulators 3 are separated by thin redial ribs 8. Wherein the radial rib is located along the quadrature axis 7 and across the central part 3a of the flux insulator 3

Cage slots 5 across quadrature axis 7 other than the cage slots 5 aligned with the outer end of the flux insulator 3 are merged to form a merged cage slot 6 as illustrated in the FIG. 6. The merged cage slots 6 hereafter referred as extended cage slots 6 for the clarity of understanding. The extended cage slot 6 can also act as a flux insulator 3 across the quadrature axis 7 in order to reduce the leakage along the quadrature axis 7 and it further improves the flux flow across the direct axis 4 and in turn it improves the motor efficiency.
The rotor cross section 1 shows the design of cage slots 5 aligned in the direction of the flux insulators 3 ends, which provides the smooth flux flow and thereby reducing the leakage flux across the cage slots 5. The notched end 5’ in the direction of the flux insulators 3 end are aligned towards flux insulator 3 axis in order to minimize the leakage flux as compared to conventional radial notched end design. This design helps to improve the flux flow in the direction of the direct axis 4.

This design under the simulation test indicates improvement in the maximum flux flow in direction of the direct axis 4 and minimum flux flow in the direction of the quadrature axis 7 during synchronous speed of the rotation.

As an improvement to the previous design, the FIG. 7 shows rotor according to one of the embodiment of the invention. Each of the sectors 2 comprises of flux insulator 3 aligned across two adjacent direct axes 4 and cage slots 5 are designed on the circumference of the rotor. The cage slots 5 are of uniform size and the cage slots 5 at the end of the flux insulators 3 are aligned in the direction of flux insulator ends separated by tangential ribs 10. A tangential rib 10 may be provided to enhance the physical strength of the rotor.

In yet another embodiment of the invention the flux insulators 3 are separated by thin redial ribs 8. Wherein the radial rib is located along the quadrature axis 7 and across the central part 3a of the flux insulator 3
The cage slots 5 near quadrature axis 7 other than the cage slots 5 aligned with the outer end of the flux insulator 3 are merged to form extended cage slot 6 as illustrated in the FIG. 7. The extended cage slot 6 can also act as a flux insulator 3 across the quadrature axis 7 in order to reduce the leakage along the quadrature axis 7 and it further improves the flux flow across the direct axis 4 and in turn it improves the motor efficiency.

Conductive material 11 can be die casted/fixed/inserted in the cage slots 5 and the extended cage slots 6 of the rotor cross section 1 as illustrated in the FIG. 7 and the FIG. 9

The conductive material 11 die casted/fixed/inserted in the cage slot 5 as illustrated in the FIG. 7 can be any of aluminium, copper, brass or any conductive material.

Permanent magnet material 12 can be inserted in the flux insulator 3 as illustrated in the FIG. 8 and the FIG. 9. The steps 9 are provided in the flux insulator 3 of the rotor design as illustrated in FIG. 8 and FIG. 9 to fix the permanent magnet material 12 in the flux insulator 3. The steps 9 help in the fixing the permanent magnet material 12 in the rotor 1 to improve the stability of the rotor 1.
The permanent magnet material 12 used in the flux insulator 3 as illustrated in the figure 8 can be any of ceramic magnet or a rare earth magnet or an alnico magnet or samarium cobalt type magnet material.
By adding the permanent magnet material 12 in flux barriers 3, permanent magnet torque component will be added to overall torque so for the same torque to be generated, burden on reluctance torque will be reduced. This improves the power factor of the motor by reducing the magnetizing current requirement
Due to relative motion between stator’s revolving field and conducting material 11 within the cage slots 5 and extended cage slots 6 of the rotor, emf will be induced within the cage slots 5 and extended cage slots 6. The rotor field will be produced due to the current flowing in the cage slots 5 and extended cage slots 6 as their ends are short circuited. Torque will be produced due to the interaction of stator and rotor fields which helps the motor to start.

When motor speed reaches near to synchronous speed, rotor will pull into synchronism with respect to stator field and locked in this position which allows rotor to continuously rotate at synchronous speed. Once motor reaches synchronous speed the relative motion between the stator field and rotor becomes zero (slip) and hence the induced emf in cage slots 5 and extended cage slots 6 also becomes zero. This will nullify the joule loss within the cage slots 5 and extended cage slots 6.

Rotor end laminations 13 as shown in the FIG. 9 are used to disposed/inserted/die-casted conducting material 11 is in to the cage slots 5 and extended cage slots 6 in order to avoid the melted conductive material 11 to escape in to the flux insulator 3 and/or the other part of the rotor other than cage slots 5 and extended cage slots 6.

The embodiment of the present invention is to utilize/use/apply the single rotor design for multiple motor technologies.

The said rotor cross section 1 as illustrated in the FIG. 6 can be utilized for manufacturing of the synchronous reluctance motor rotor.

The said rotor cross section 1 as illustrated in the FIG. 7 with the conductive material 11 in the cage slots 5 as well as in the extended cage slots 6 can be utilized for manufacturing of the line start synchronous reluctance motor.

The said rotor cross section 1 as illustrated in the FIG. 8 with the flux insulator 3 having permanent magnet material 12 can be utilized for manufacturing of the permanent magnet assisted synchronous reluctance motor.

The said rotor cross section 1 as illustrated in the FIG. 9 with the flux insulator 3 having permanent magnet material 12 and further to that conductive material 11 in the cage slots 5 and in the extended cage slots 6 can be utilized for manufacturing of the line start permanent magnet assisted synchronous reluctance motor.

The present invention has a compact mechanism with a simple construction and less moving parts, which reduces the friction amongst the parts

Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention, it is therefore contemplated that such modifications can be made without departing from the spirit or scope of the invention as defined.