CROSS-REFERENCE TO RELATED APPLICATION

[0001] Related subject matter is disclosed in International Application No. PCT/US2013/ 048562, filed on June 28, 2013, and in an International Application entitled "Variable Magnetization Machine Controller," Docket No. NS-W0135317 (12-00422), filed concurrently herewith, the entire contents of International Application No.

PCT/US2013/048562 and the International Application entitled "Variable Magnetization Machine Controller," Docket No. NS-WOl 353 1 7 ( 12-00422), being incorporated by reference herein.

BACKGROUND

Field o f the Invention

[0002] The present invention generally relates to a rotor for a variable magnetization machine. More particularly, the present invention relates to a variable magnetization machine rotor which is capable of achieving full magnetization without core saturation and preventing demagnetization under loaded conditions, thus reducing the current required to fully magnetize the magnets in the rotor.

Background Information

[0003] Electric vehicles and hybrid electric vehicles (HEV) include an electric motor that operates as a drive source for the vehicle. In a purely electric vehicle, the electric motor operates as the sole drive source. On the other hand, an HEV includes an electric motor and a conventional combustion engine that operate as the drive sources for the vehicle based on conditions as understood in the art.

[0004] Electric vehicles and HEVs can employ an electric motor having variable magnetization characteristics as understood in the art. For example, the magnetization level of the motor can be increased to increase the torque generated by the motor. Accordingly, when the driver attempts to accelerate the vehicle to, for example, pass another vehicle, the motor controller can change the magnetization level to increase the torque output of the motor and thus increase the vehicle speed.

[0005] Certain techniques exist for increasing the magnetization level of such an electric motor. One technique employs a rotor core structure with a single embedded magnet per pole configuration. In such a configuration, the magnet location is so shallow that the original magnetization level cannot be maintained under loaded condition unless the magnet is thick. However, a larger current is required to fully magnetize this type of thick magnet.

[0006] Another conventional technique employs a rotor core structure with a single embedded magnet per pole configuration. In this configuration, the rotor opening is so narrow that the magnet flux becomes concentrated at only a few stator teeth. As a result, stator core saturation during the magnetization process is severe. Hence, an oversized inverter is required to provide a larger current (e.g., greater than 1 pu) that is necessary to fully magnetize the magnets to higher levels due to the high saturation effect of the stator core.

[0007] In still another conventional technique, two different types of magnets are placed in parallel along a circumferential direction of the rotor. Due to these different types o f magnets in parallel, the total magnet flux during the magnetization process is very high, and the stator and rotor core saturation is severe.

SUMMARY

[0008] Accordingly, it is desirable to provide a rotor for a variable magnetization machine that is capable of achieving full magnetization without core saturation and preventing demagnetization under loaded conditions, thus reducing the current required to fully magnetize the magnets in the rotor.

[0009] In view of the state of the known technology, one aspect of a rotor for a variable magnetization machine according to the disclosed embodiments comprises a rotor core including a circumferential surface that extends about a circumference of the rotor core, at least one rotor pole that extends outward in a radial direction of the rotor core from the circumferential surface along a d-axis, at least one flux barrier that is disposed along a q-axis, and a magnet embedded in the rotor pole at a magnet depth at which the magnet avoids demagnetization by a current applied along the q-axis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Referring now to the attached drawings which form a part of this original disclosure:

[0011] Figure 1 is a partial cross-sectional schematic view of a variable magnetization machine according to a disclosed embodiment;

[0012] Figure 2 is the partial cross-sectional schematic view of the variable magnetization machine shown in Figure 1 further illustrating an exemplary relationship between the magnet depth, the width of a rotor pole, the width of a stator tooth, and the slot pitch between stator teeth according to a disclosed embodiment;

[0013] Figure 3 is the partial cross-sectional schematic view of the variable magnetization machine shown in Figure 1 further illustrating an exemplary relationship between the width of a rotor pole at the base of the rotor pole, the width of the rotor pole at the radially outermost surface of the rotor pole, the width of a stator tooth, and the slot pitch between stator teeth according to a disclosed embodiment;

[0014] Figure 4 illustrates an example of a tapered rotor pole having a uniform taper according to a disclosed embodiment;

[0015] Figure 5 illustrates an example of a tapered rotor pole having a uniform short taper according to a disclosed embodiment;

[0016] Figure 6 illustrates an example of a rotor pole in which the magnet is at too shallow of a magnet depth;

[0017] Figure 7 illustrates an example of a rotor pole in which the magnet is at too deep of a magnet depth;

[0018] Figure 8 illustrates an example of a rotor pole in which the magnet is at a proper magnet depth according to a disclosed embodiment;

[0019] Figure 9 is a graph illustrating an example of the relationship between leakage flux and demagnetization in accordance with magnet depth in a rotor pole; [0020] Figure 10 illustrates an example of a rotor pole having too small of a width;

[0021] Figure 1 1 illustrates an example of a rotor pole having too large of a width;

[0022] Figure 12 illustrates an example of a rotor pole having a proper width according to a disclosed embodiment;

[0023] Figure 13 illustrates an example of large core saturation that occurs with a rotor core pole having a straight shape;

[0024] Figure 14 illustrates an example of lower core saturation that occurs with a rotor core pole having a proper shape according to disclosed embodiments;

[0025] Figure 15 is a chart illustrating an example of core saturation as represented by the patterns shown in Figures 13 and 14;

[0026] Figure 16 illustrates an example of a rotor pole having stepped sides according to a disclosed embodiment;

[0027] Figure 17 illustrates an example of a rotor pole having stepped and tapered sides according to a disclosed embodiment;

[0028] Figure 1 8 illustrates an example of a rotor core having a rotor surface bridge according to a disclosed embodiment;

[0029] Figure 19 illustrates an example of a rotor core having a thicker rotor surface bridge according to a disclosed embodiment;

[0030] Figure 20 is a graph illustrating an example of a relationship between d-axis flux and magnet flux characteristics achieved by the rotor according to the disclosed embodiments;

[0031] Figure 21 is a graph illustrating an example of a relationship between a variable leakage amount and rotor surface bridge thickness according to disclosed embodiments; and

[0032] Figure 22 is a graph illustrating an example of a relationship between i-axis current and rotor surface bridge thickness according to disclosed embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

[0033] Selected embodiments will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0034] As shown in Figure 1 , a variable magnetization machine 10, which can also be referred to as a variable magnetization motor, includes a rotor 12 and a stator 14. The variable magnetization machine 10 can be employed in any type of electric vehicle or HEV such as an automobile, truck, SUV and so on, and in any other type of apparatus as understood in the art. The rotor 12 and the stator 14 can be made of metal or any other suitable material as understood in the art.

[0035] In this example, the rotor 12 includes a rotor core 16 that has a circumferential surface 1 8 that extends about a circumference of the rotor core 16, at least one rotor pole 20 that extends outward in a radial direction of the rotor core 16 from the circumferential surface 18 along a d-axis, and at least one flux barrier 22 that is disposed along a q-axis. Each rotor pole 20 can be made of the same material as the rotor core 16 or of a different material as understood in the art. Also, each rotor pole 20 can be integral with the rotor core 16 or connected to the rotor core 16 in any suitable manner as understood in the art. The flux barrier 22 can be configured as an air gap or can include any suitable type of insulating material as is conventional in the art which can function as a large flux barrier to achieve the effects discussed herein. In addition, the rotor core 16 includes a magnet 24 that is embedded in the rotor pole 20 at a magnet depth at which the magnet avoids demagnetization by a current applied along the q-axis as discussed in more detail below. The magnet 24 can be, for example, a single embedded low-coercive-force magnet as understood in the art, or any other suitable type of magnet that is capable of achieving the effects discussed herein. As discussed below, the current for the magnetization process can be, for example, 10 amps with the configuration of the rotor 12, as opposed to 35 amps with conventional configurations.

Naturally, the rotor 12 can be configured to allow for any suitable current for the

magnetization process.

[0036] Although only two rotor poles 20, one full flux barrier 22 and two partial flux barriers 22 are shown, the rotor core 16 typically includes a plurality of the rotor poles 20 and a plurality of the flux barriers 22 configured such that each of the flux barriers 22 is disposed between adjacent ones of the rotor poles 20. Also, each of the rotor poles 20 includes a magnet 24 embedded at the depth at which the magnet 24 avoids demagnetization by the current applied along the q-axis. In this example, the rotor core 16 can include twelve rotor poles 20 can be spaced at 30 degree angles about the circum ferential surface 18 of the rotor core 16, and twelve flux barriers 22 can be spaced at 30 degree angles about the

circumferential surface of the rotor core 16, with one flux barrier 22 between each adjacent pair of rotor poles 20 as shown. Naturally, the rotor core 16 can include as many rotor poles 20 and flux barriers 22 as deemed appropriate for the environment in which the variable magnetization machine 10 is employed.

[0037] Also, as shown in this example, a d-axis of the variable magnetization machine 10 passes through the center of at least one of the rotor poles 20 or at a location proximate to the center of at least one of the rotor poles 20. Furthermore, a q-axis of the variable

magnetization machine 10 passes through the center of at least one of the flux barriers 22 or at a location proximate to the center of at least one of the flux barriers 22. However, the rotor poles 20 and the flux barriers 22 can be positioned at any suitable location with respect to the d-axis and the q-axis to achieve the operability of the embodiments discussed herein.

[0038] The stator 14 includes a plurality of stator teeth 26 and other components such as windings (not shown) which can be configured in any conventional manner. In this example, the stator teeth 26 are configured as wide stator teeth as known in the art. However, the stator teeth 26 can have any suitable size, and the stator 14 can include any number of stator teeth 26 to achieve the operability of the embodiments discussed herein. The slots 28 between the stator teeth 26 can be any suitable size as discussed below to achieve the effects described herein. In this example, the stator teeth 26 are open to the inner circumference 30 of the stator 14, but can be closed if desired. Also, an air gap 32 is present between the radially outer surface 34 of each of the rotor poles 20 as discussed herein to enable the rotor 12 to rotate unrestrictedly or substantially unrestrictedly about an axis (not shown). The size of the air gap 32, which represents a distance between the inner surface of the inner circumference 30 of the stator 14 surrounding the rotor core 16 and the radially outer surface 34 (i.e., an outermost surface) of the rotor pole 20 in the radial direction of the rotor core 16 is based on a shape of the rotor pole 20 as will now be discussed.

[0039] Examples of the configurations and relationships between the rotor poles 20, the magnets 24 and the stator teeth 26 are shown in Figures 2 and 3. For example, the magnet depth D _pm can be defined according to

_ W _open x W _f00ih

Dpm -

2 ^x ^sloLpitch

where D _pm represents the magnet depth, W _open represents a width of the tapered pole 20 taken along a circumferential direction of the rotor core 16 at a widest location of the tapered rotor pole 20, Wsi _ot _p _itC h represents a pitch of the slots 28 between adjacent teeth 26 of the stator 14 surrounding the rotor 12, and W _t00t h represents a respective width of the teeth 26 of the stator 14. Furthermore, any or all of the rotor poles 20 can be configured as a tapered rotor pole 20 to provide a tapered flux path. The tapered rotor pole 20 can be configured according to

^open Bmag ^slot_pitc

W _pm Sfooi/i Wiooil

where W _open represents a width of the tapered pole taken along a circumferential direction of the rotor core 16 at a widest location of the tapered rotor pole 20, W _pm represents a width of the tapered pole 20 taken along the circumferential direction of the rotor core 16 at a base 36 of the tapered rotor pole 20 at the circumferential surface of the rotor core 1 6, W _s \ _{oi p c} h represents a pitch of slots 28 between adjacent teeth of a stator 14 surrounding the rotor 12, Wtooth represents a respective width of the teeth 26 of the stator 14, B _t00 th represents a saturation flux density for each of the teeth 26 of the stator 14, and B _mag represents a magnet flux density during a full magnetization process of the rotor core 16. The value of B _iool h can typically be in the range of 1 .7-2. I T, and the value of B _mag can typically be in the range of 1 .3-1 ,7T. However, the values of B _t00 th and B _mag can have any suitable value for achieving the effects discussed herein. [0040] Each side 38 and 40 of the tapered rotor pole 20 facing a circumferential direction of the rotor core 16 (e.g., opposite circumferential directions) has a taper 42 and 44, respectively, extending from respective outer edges 46 and 48 at the radially outer surface 34 of the tapered rotor pole 20 that faces the stator 14 surrounding the rotor 12 toward the circumferential surface 18 of the rotor core 16 such that the base 36 of the tapered rotor pole 20 proximate to the circumferential surface 1 8 has a width W _pm along the circumferential direction smaller than the width W _open of the radially outer surface 34 at the outer edges 46 and 48 of the tapered rotor pole 20 along the circumferential direction. The taper 42 and 44 on each side 38 and 40 of the tapered rotor pole 20 can be a uniform taper as shown, for example, in Figure 4. Also, the taper 42 and 44 on each side 38 and 40 of the tapered rotor pole 20 can end before reaching the magnet depth D _pm as shown, for example, in Figure 5.

[0041] As can be appreciated from Figures 6 through 8, if the magnet depth D _pm is too shallow as in Figure 6, the q-axis flux will cause the magnet 24 to become demagnetized. Also, if the magnet depth D _pm is too deep as in Figure 7 (e.g., the rotor poles 20 extend too far from the circumferential surface 1 8 of the rotor core 1 6), too much leakage flux will occur even though there may be very little demagnetization of the magnet 24 However, when the magnet depth D _pm is proper according to the disclosed embodiments, little or no

magnetization of the magnet 24 will occur, and the leakage flux will be at the proper amount as shown in the graph of Figure 9.

[0042] Furthermore, as can be appreciated from Figures 10 through 12, if the width W _ope „ of the radially outer surface 34 of the tapered rotor pole 20 is too small as in Figure 10, saturation will occur in the stator teeth 26. Also, if the width W _open of the radially outer surface 34 of the tapered rotor pole 20 is too large as in Figure 1 1 , although no saturation will occur in the stator teeth 26, the q-axis flux path will be too large. However, if the width W _open of the radially outer surface 34 of the tapered rotor pole 20 is at the proper dimension according to the disclosed embodiment as shown, for example, in Figure 12, no saturation will occur in the stator teeth 26 and the q-axis flux path will be at the proper amount. [0043] Figures 13 through 15 illustrate a comparison of the flux patterns for a salient- shaped rotor design with a straight rotor core shape (e.g., straight rotor poles 20) as shown in Figure 13 versus a salient-shaped rotor design with wider rotor opening tips (i.e., radially outer surfaces 34 having a larger width W _open ) according to the disclosed embodiments. As indicated, a larger saturation of the rotor core 16 occurs for the configuration shown in Figure 13 as compared to the lesser saturation of the rotor core that occurs for the configuration shown in Figure 14. Figure 15 illustrates a grid representing an amount of saturation by the different patterns shown in Figures 13 and 14 that correspond to the indicated amount of saturation.

[0044] In addition, the rotor poles 20 can have different shapes according to the disclosed embodiments. For example, each side 38 and 40 of the tapered rotor pole 20 facing a circumferential direction of the rotor core 16 can include a stepped portion 50 and 52 as shown in Figure 16. Furthermore, as shown, for example, in Figure 17, each side 38 and 40 of the tapered rotor pole 20 facing the circumferential direction of the rotor core 1 6 can have a stepped portion 54 and 56 and a tapered portion 58 and 60, with the tapered portions 58 and 60 extending from the stepped portions 54 and 56, respectively, toward the circumferential surface 1 8 of the rotor core 16 such that the base 36 of the tapered rotor pole 20 proximate to the circumferential surface 1 8 has a width W _pm along the circumferential direction smaller than the width W _open of the stepped portion along the circumferential direction, which corresponds to the width W _open of the radially outer surface 34 at the outer edges 46 and 48 of the tapered rotor pole 20 along the circumferential direction.

[0045] In addition, as shown, for example, in Figures 18 and 19, the rotor core 16 can include a rotor surface bridge 62 that extends between adjacent ones of the rotor poles 20 and defines an outer circumference 64 of the rotor 12. The rotor surface bridge 62 can be made of the same material as the rotor core 16, the rotor pole 20, or both, or of any suitable type of material capable of achieving the effects discussed herein. Furthermore, the rotor surface bridge 62 can be integral with the rotor poles 20 or connected to the rotor poles 20 in any suitable manner as known in the art. The thickness of the rotor surface bridge 62 in the radial direction of the rotor core 16 is less than a length of each of the rotor poles 20 in the radial direction of the rotor core 16. For instance, in the configuration shown in Figure 1 7, the rotor surface bridge 62 has a thickness of at or about 1 mm. In the configuration shown in Figure 1 8, the rotor surface bridge 62 has a thickness of at or about 4 mm. Naturally, the thickness of the rotor surface bridge 62 can be any suitable thickness capable of achieving the effects discussed herein. The graphs shown in Figures 20 through 22 illustrate examples of the effect on the d-axis flux, magnetic flux characteristic, variable leakage amount and i-axis current in relation to the thickness of the rotor surface bridge 62.

[0046] Accordingly, as can be appreciated from the above, the configuration of the rotor 12 can achieve full magnetization without saturation of the rotor core 16 and can prevent demagnetization of the magnets 24 under loaded condition to reduce the required current to fully magnetize the magnets 24. Furthermore, the rotor 12 discussed herein allows for magnetizability in variable flux machines within an inverter current rating of as little as, for example, 1 pu.

GENERAL INTERPRETATION OF TERMS

[0047] In understanding the scope of the present invention, the term "comprising" and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, "including", "having" and their derivatives. Also, the terms "part," "section," "portion," "member" or "element" when used in the singular can have the dual meaning of a single part or a plurality of parts. The terms of degree such as "substantially", "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed.

[0048] While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, the size, shape, location or orientation of the various components can be changed as needed and/or desired. Components that are shown directly connected or contacting each other can have intermediate structures disposed between them. The functions of one element can be performed by two, and vice versa. The structures and functions of one embodiment can be adopted in another

embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such features. Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.