Description:FIELD OF THE INVENTION

[0001] The present invention relates to an interior permanent magnet (IPM) of an electric motor. More particularly, the present invention relates to an interior permanent magnet (IPM) rotor assembly of an electric motor.

BACKGROUND

[0002] The fundamental parts of a permanent magnet based motor are the rotor, stator, and the permanent magnets. Given the magnetic strength of the magnets, the position and orientation of the slots in the rotors in which the magnets are positioned and the shape and size of the magnets, affect the torque producing capability of the motor. Different rotor configurations are shown in Figure 1. As shown in Figure 2, the existing interior permanent magnet (IPM) rotor assembly consists of a rotor core, permanent magnets (10), and a drive shaft (50). The rotor core consists of several silicon steel laminates stacked together. The permanent magnets (10) are embedded (with glue) within the rotor core. The drive shaft (50) is fitted onto the rotor core either by fastening or press-fitting. Additionally, some rotors have plates (30) at the end of the core provided for balancing.
[0003] In the state of art IPM rotor assembly the slots for the permanent magnets (10) are formed to suit the dimensions of each magnet type that is to be used for a given type or rating of motor. Thus, a new rotor stamping die must be manufactured each time for manufacturing motors of different torque ratings. This is time consuming and expensive as rotors or rotor stampings of various types or ratings of motors are to be stocked.
SUMMARY
[0004] Therefore, there exists a need for an IPM rotor assembly for an electric motor that can overcome the problems of the state-of-the-art motors mentioned above.
[0005] This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention nor is it intended for determining the scope of the invention.
[0006] To overcome or at least mitigate one of the problems mentioned above in the state of the art, an interior permanent magnet (IPM) rotor assembly for an electric motor is provided.
[0007] In an embodiment of the present invention, an IPM rotor assembly is disclosed. The disclosed IPM rotor assembly comprises a rotor core comprising a plurality of slots for magnets spaced apart from each other and arranged circumferentially. A disc comprising a plurality of pairs of guide members protruding from the plate portion and arranged circumferentially is provided. Each pair of guide members are positioned on the disc to match with the slots for inserting the magnets. The disc with the guide members is referred to hereinafter as detachable plate. The detachable plate is detachably attached to the rotor such that the protrusions fit into the plurality of slots for the magnets. Each of plurality of permanent magnets is disposed between each pair of guide members slots for the magnets. A drive shaft extends through the detachable plate and the rotor core.
[0008] Thus, magnets of smaller dimensions than the dimensions of the slots may be fitted into the same slots with the disclosed discs with appropriate protrusions.
[0009] To further clarify the advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS

[00010] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
[00011] Figure 1 illustrates different rotor configurations in accordance with the state of the art.
[00012] Figure 2 illustrates an IPM rotor assembly for an electric motor in accordance with state of the art.
[00013] Figure 3 illustrates an IPM rotor assembly for an electric motor according to an embodiment of the present invention;
[00014] Figure 4 illustrates the rotor core of the IPM rotor assembly as shown in Figure 1 according to an embodiment of the present invention;
[00015] Figure 5 illustrates the detachable plate of the IPM rotor assembly as shown in Figure 3 according to an embodiment of the present invention;
[00016] Figure 6 illustrates the permanent magnets of the IPM rotor assembly as shown in Figure 3 according to an embodiment of the present invention;
[00017] Figure 7 illustrates the drive shaft of the IPM rotor assembly as shown in Figure 3 according to an embodiment of the present invention;
[00018] Figure 8 illustrates the balancing plate as shown in Figure 3 according to another embodiment of the present invention; and
[00019] Figure 9 illustrates the skewed configuration according to an embodiment of the present invention.
[00020] Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present invention. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
DETAILED DESCRIPTION OF FIGURES

[00021] For the purpose of promoting an understanding of the principles of the present invention, reference will now be made to the various embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the present invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the present invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the present invention relates.
[00022] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the present invention and are not intended to be restrictive thereof.
[00023] Whether or not a certain feature or element was limited to being used only once, it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element.” Furthermore, the use of the terms “one or more” or “at least one” feature or element do not preclude there being none of that feature or element, unless otherwise specified by limiting language including, but not limited to, “there needs to be one or more…” or “one or more elements is required.”
[00024] Reference is made herein to some “embodiments.” It should be understood that an embodiment is an example of a possible implementation of any features and/or elements of the present invention. Some embodiments have been described for the purpose of explaining one or more of the potential ways in which the specific features and/or elements of the proposed invention fulfil the requirements of uniqueness, utility, and non-obviousness.
[00025] Use of the phrases and/or terms including, but not limited to, “a first embodiment,” “a further embodiment,” “an alternative embodiment,” “one embodiment,” “an embodiment,” “multiple embodiments,” “some embodiments,” “other embodiments,” “further embodiment”, “furthermore embodiment”, “additional embodiment” or other variants thereof do not necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or in the context of more than one embodiment, or in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.
[00026] Any particular and all details set forth herein are used in the context of some embodiments and therefore should not necessarily be taken as limiting factors to the proposed invention.
[00027] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by “comprises... a” does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.
[00028] In view of the state of the art, there exist a need for an IPM rotor assembly for an electric motor that can produce different torques out of a given stator and rotor of a certain stack height, say ‘x’, by merely changing the primary dimensions of the magnets (length, breadth, and height).
[00029] In an embodiment of the present invention, an interior permanent magnet (IPM) rotor assembly for an electric motor is disclosed. The IPM rotor assembly comprises a rotor core comprising a plurality of slots for magnets spaced apart from each other and arranged circumferentially. A disc comprising a plurality of pairs of guide members protruding from the plate portion and arranged circumferentially is provided. Each pair of guide members are positioned on the disc to match with the slots for inserting the magnets. The disc with the guide members is referred to hereinafter as detachable plate. The detachable plate is detachably attached to the rotor such that the protrusions fit into the plurality of slots for the magnets. Each of plurality of permanent magnets is disposed between each pair of guide members slots for the magnets. A drive shaft extends through the detachable plate and the rotor core.
[00030] a rotor core comprising a plurality of slots spaced apart from each other and arranged circumferentially. A detachable plate comprising a plate portion and a plurality of pairs of guide members protruding from the plate portion and arranged along the circumferential direction. Each pair of guide members are detachably fitted to the corresponding slot of the plurality of slots. A plurality of permanent magnets, wherein each permanent magnet is disposed between the corresponding pair of guide members within the corresponding slot. A drive shaft extending through the detachable plate and the rotor core.
[00031] Figure 3 illustrates an IPM rotor assembly for an electric motor according to an embodiment of the present invention. The IPM rotor assembly (100) comprises a rotor core (200), a detachable plate (300) as disclosed herein, permanent magnets (400), and a drive shaft (500). In one aspect, the IPM rotor assembly (100) comprises a balancing plate (600), apart from the above said components.
[00032] In one aspect, rotor core (200) comprises a plurality of slots for magnets (202) spaced apart from each other and arranged circumferentially as shown in Figure 4.
[00033] In one aspect, as shown in Figure 4, the rotor core (200) comprises silicon steel laminations and has a plurality of slots for magnets (202) for magnet insertion. The rotor laminations are usually manufactured by laser cutting (for small scale production and prototypes) or by stamping (for large scale production). These laminations are then stacked together either by laser welding or self-stitching. For example, an 8 pole rotor is represented with block slots (202) for magnets for magnet insertion. 3 parameters are important to define the shape of the magnet:
Width of Magnet - WM
Thickness of magnet - TM
Distance between the magnet and the rotor outer circumference - H
As an example, the rotor shown in this example has the following dimensions:
WM = 25 mm
TM = 3 mm
H = 5 mm

[00034] In one aspect, the detachable plate (300) comprises a plate portion (302) and a plurality of pairs of guide members (304) protruding from the plate portion (302) and arranged circumferentially. Each pair of guide members (304) are fitted into the corresponding slot for magnets of the plurality of slots for magnets (202) of the permanent magnets (400) (shown in Figure 6) while assembling the components as shown in Figure 5.
[00035] In one exemplary aspect, the size of the guide members (304) is within a length ranging between 10 mm and 15 mm.
[00036] In one aspect, the detachable plate (300) comprises a plurality of guide slots (306), wherein each guide slot (306) is disposed between the corresponding pair of guide members (304) as shown in Figure 5.
[00037] In one aspect, as shown in Figure 5, the detachable plate (300) is made of epoxy resin thermoplastic such as PA66, for example. In another aspect, the detachable plate (300) can be made up of any suitable material based on the requirement, preferably a nonmagnetic material. In another aspect, the detachable plate (300) has guide slots (306) for insertion of permanent magnets (400), but unlike the rotor core (200), the dimensions of these guide slots (306) are different.
Out of the three design parameters of the permanent magnets (400), this plate (300) will have different WM and/or TM.
In this example, the detachable plate (300) has slot size of:
WM = 20 mm, while TM remains 3 mm.
This will limit the available space for the permanent magnets (400) and will accommodate a smaller permanent magnet (400) in the rotor core (200) intended originally for larger permanent magnets. This enables accommodating the plurality of permanent magnets (400) of different dimensions.
[00038] In one aspect, each permanent magnet (400) is inserted through the corresponding guide slot of the plurality of guide slots (306) and disposed between the corresponding pair of guide members (304) within the corresponding slot (202).
[00039] In one important aspect, the detachable plate (300) acts as the key component. By means of this detachable plate (300), it is possible to produce motors of different torque ratings out of a given stator and rotor of a certain stack height, say ‘x’, by merely changing the primary dimensions of the magnets (length, breadth, and height). This solves an operational problem where an existing IPM rotor assembly does not allow for varying this dimension and a new rotor die has to be manufactured each time a motor with a different torque rating has to be manufactured.
[00040] In one aspect, a plurality of permanent magnets (400) is provided in the IPM rotor assembly (100). Each permanent magnet (400) is disposed between the corresponding pair of guide members (304) of the detachable plate (300) within the corresponding slot (202) of the rotor core (200) while assembling the components as shown in Figure 6.
[00041] In one aspect, each permanent magnet (400) is inserted through the one end of the rotor core (200) and disposed between the corresponding pair of guide members (304) within the corresponding slot (202). In this aspect of the invention, the detachable plate (300) does not include the guide slots (306).
[00042] In another aspect, as shown in Figure 6, the shape of the permanent magnets (400) and the corresponding slot (202) might be of any configuration such as: a) Block: b) Layered: c) Spoke: and d) V-Shape, etc.
[00043] But regardless of the configuration of the rotor core (200), the detachable plate (300) may correspondingly be modified for different WM and TM parameters of the permanent magnets (400) to accommodate smaller permanent magnets (400) in bigger slot (202) of the rotor core (200).
[00044] In one aspect, a drive shaft (500) is provided in the IPM rotor assembly (100). The drive shaft (500) is extending through the detachable plate (300) and the rotor core (200) as shown in Figure 7. In one aspect, the drive shaft (500) comprises an arresting member (502), slots (504) and protrusions (506). In one aspect, drive shaft (500) may be a cylindrical shape extending through the detachable plate (300) and the rotor core (200). In one aspect, the drive shaft (500) can be made up of steel or plastic. In another aspect, the drive shaft can be made up of any suitable material.
[00045] In one aspect, the arresting member (502) is configured for restricting an axial movement of the detachable plate (300) while assembling the components.
[00046] In one aspect, the IPM rotor assembly (100) comprises a balancing plate (600), apart from the above said components, as shown in Figure 8.
[00047] In one aspect, as shown in Figure 8, the balancing plate (600) comprises an inner periphery (602) having a plurality of protrusions (604) fitted to a plurality of slots (504) formed in the drive shaft (500) while assembling the components.
[00048] In one aspect, the material of the balancing plate (600) is one of aluminum and/or brass.
[00049] In another aspect, the balancing plate (600) is coupled to the one end of the rotor core (200), wherein the drive shaft (500) extends through the balancing plate (600) while assembling the components.
[00050] In one aspect, a quantity of material of the balancing plate (600) is removed from a portion determined by a well-known method of balancing to reduce vibration when the motor runs.
[00051] In one aspect, the IPM rotor assembly (100) has a skewed configuration as shown in Figure 9. In one aspect, the skewed configuration comprises two units (700). In one aspect, the unit (700) comprises a rotor core (200), a detachable plate (300), and a plurality of permanent magnets (400). Each of the two units (700) are radially offset with each other hence called the skewed configuration. In particular, the permanent magnets (400) on the bottom unit (700) are radially offset from the top unit (700) by a predetermined angle. Each unit (700) has its own detachable plate (300). In the present invention, the skewed configuration can be used for reducing cogging torque and torque ripple and to increase the power rating of the electric motor.
[00052] The process of assembling the components of the IPM rotor assembly (100) is described below.
[00053] Initially, the detachable plate is connected to the rotor core (200).
[00054] In the next step, the permanent magnets (400) are inserted and embedded with glue, within the rotor core (200).
[00055] In the next step, the drive shaft (500) is mechanically assembled, by means of rivets or fasteners to the rotor core (200), wherein the arresting member (502) of the drive shaft (500) restricts an axial movement of the detachable plate (300).
In an optional step, the balancing plate (600) is press-fitted to the shaft or mechanically assembled, by means of rivets or fastening to the rotor core (200), if required.
[00056] In this application, unless specifically stated otherwise, the use of the singular includes the plural and the use of “or” means “and/or.” Furthermore, use of the terms “including” or “having” is not limiting. Any range described herein will be understood to include the endpoints and all values between the endpoints. Features of the disclosed embodiments may be combined, rearranged, omitted, etc., within the scope of the invention to produce additional embodiments. Furthermore, certain features may sometimes be used to advantage without a corresponding use of other features.
[00057] List of reference numerals:
Components Reference numerals
10 Permanent magnet
20 Magnet Array
30 Balancing plate
40 Magnet
50 Drive shaft
60 Skewed Lamination Stacks
100 Interior Permanent Magnet rotor assembly
200 Rotor core
202 slot
300 Detachable plate
302 Plate portion
304 Guide member
306 Guide slot
400 Permanent magnet
500 Drive shaft
502 Arresting member
504 Slot
506 Protrusions
600 Balancing plate
602 Inner periphery
700 Unit
, Claims:1. An Interior Permanent Magnet (IPM) rotor assembly (100) for an electric motor, the IPM rotor assembly (100) comprising:

a rotor core (200) comprises a plurality of slots (202) spaced apart from each other and arranged along a circumferential direction;

a detachable plate (300) comprising a plate portion (302) and a plurality of pairs of guide members (304) protruding from the plate portion (302) and arranged along the circumferential direction, wherein each pair of guide members (304) are detachably fitted to the corresponding slot of the plurality of slots (202);

a plurality of permanent magnets (400), wherein each permanent magnet (400) is disposed between the corresponding pair of guide members (304) within the corresponding slot (202); and

a drive shaft (500) extending through the detachable plate (300) and the rotor core (200).

2. The IPM rotor assembly (100) as claimed in claim 1, wherein the detachable plate (300) comprises a plurality of guide slots (306), wherein each guide slot (306) is disposed between the corresponding pair of guide members (304).

3. The IPM rotor assembly (100) as claimed in claim 2, wherein each permanent magnet (400) is inserted through the corresponding guide slot of the plurality of guide slots (306) and disposed between the corresponding pair of guide members (304) within the corresponding slot (202).

4. The IPM rotor assembly (100) as claimed in claim 1, wherein each permanent magnet (400) is inserted through one end of the rotor core (200) and disposed between the corresponding pair of guide members (304) within the corresponding slot (202).

5. The IPM rotor assembly (100) as claimed in claim 1, wherein the detachable plate (300) is replaceable to accommodate the plurality of permanent magnets (400) of different dimensions.

6. The IPM rotor assembly (100) as claimed in claim 1, wherein the slots (202) are arranged in at least one of block configuration, a layered configuration, a spoke configuration, and a V-shaped configuration.

7. The IPM rotor assembly (100) as claimed in claim 1, wherein the drive shaft (500) comprises an arresting member (502) for restricting an axial movement of the detachable plate (300).
8. The IPM rotor assembly (100) as claimed in claim 1, comprising a balancing plate (600) coupled to one end of the rotor core (200), wherein the drive shaft (500) extends through the balancing plate (600).

9. The IPM rotor assembly (100) as claimed in claim 8, wherein the balancing plate (600) comprises an inner periphery (602) having a plurality of protrusions (604) fitted to a plurality of slots (504) formed in the drive shaft (500).

10. The IPM rotor assembly (100) as claimed in claim 8, wherein the material of the balancing plate (600) comprises at least one of aluminum, and brass.

11. The IPM rotor assembly (100) as claimed in claim 1, wherein the IPM rotor assembly (100) is a skewed configuration, wherein the skewed configuration comprises at least two units (700), wherein each unit (700) comprises a rotor core (200), a detachable plate (300), and a plurality of permanent magnets (400), wherein each of the two units (700) are radially offset to each other

12. The IPM rotor assembly (100) as claimed in claim 1, wherein the material of the detachable plate (300) comprises at least one of aluminum, plastic and brass.