CN114830493A - Electric motor - Google Patents

Abstract

The electric motor (112) includes a housing (205), a stator assembly (198) disposed within the housing, and a rotor assembly (116, 119) mounted within the housing (205) for rotation within the stator assembly (198). The stator assembly (198) includes a stator core (199) comprising a first steel having a silicon content in excess of 3.5%, and the rotor assembly (116, 119) includes a rotor core (116) comprising a second steel having a silicon content less than or equal to 3.5%.

Description

Electric motor

Technical Field

The present invention relates to an electric motor.

Background

An interior permanent magnet electric motor has a rotor assembly including a rotor core having a set of circumferentially spaced magnets that create magnetic poles around the circumference of the rotor core. Current is supplied to the stator windings to generate electromagnetic poles on the stator teeth that interact with the magnetic poles of the rotor core to cause rotation of the rotor core. Such motors and associated circuitry are typically reversible in order to allow them to be used for regenerative braking.

It would be desirable to improve the performance (such as power and/or efficiency) and/or reduce the cost of manufacturing such motors.

Disclosure of Invention

According to an aspect of the present invention, there is provided a connector including:

a housing;

a stator assembly disposed within the housing; and

a rotor assembly mounted within the housing for rotation within the stator assembly;

wherein the stator assembly comprises a stator core comprising a first steel having a silicon content exceeding 3.5% and the rotor assembly comprises a rotor core comprising a second steel having a silicon content less than or equal to 3.5%.

The combination of such steels with different silicon contents may allow improved switching performance, especially at high switching frequencies, while also reducing production costs.

In particular, by utilizing a stator core with a relatively high silicon content, a more efficient switching may be achieved. However, such relatively high silicon content steels may be more expensive than relatively low silicon content steels. Surprisingly, the use of steel having a relatively high silicon content in both the stator core and the rotor core of an electric motor provides a small efficiency gain compared to an electric motor using steel having a relatively high silicon content in the stator core alone. Accordingly, the inventors of the present application have found that a stator core of an electric motor having a first steel with a silicon content exceeding 3.5% and a rotor core of an electric motor having a second steel with a silicon content of less than or equal to 3.5% may provide improved efficiency without unduly increasing costs.

The first steel may have a silicon content of more than 4% or more than 6%. In a particular embodiment, the first steel may have a silicon content of 6.5%, which may provide good switching performance, in particular at high switching frequencies.

The stator core may include a plurality of circumferentially spaced stator teeth, wherein at least the teeth are formed from a first steel. This may provide good switching performance, especially at high switching frequencies.

The stator core may include a plurality of circumferentially adjacent segments, each segment including one or more teeth. The use of multiple sections may allow for more efficient use of materials in the production process.

Each segment may have circumferentially spaced ends, each end defining a key that interlocks with a corresponding key defined by the end of an adjacent segment. Such an arrangement may facilitate assembly of the stator core and/or may improve structural strength and/or rigidity.

Each segment may have exactly one, two, three or ten teeth. Depending on the implementation, these numbers of teeth per segment may provide a good compromise between performance and production cost.

The electric motor may comprise exactly six sections.

The electric motor may comprise at least one yoke supporting one or more segments. The or each yoke may form part of one or more sections. In some embodiments, the yoke may surround the segments.

Each segment may include a segment feature that interlocks with a corresponding yoke feature at a radially inner region of the yoke. The use of such segment features may facilitate assembly of the stator core and/or may improve structural strength and/or rigidity.

Each segment feature and its corresponding yoke feature may form a dovetail joint. For example, each segment feature may take the form of a dovetail, and each yoke feature may take the form of a recess of complementary shape to the dovetail. The use of such dovetail joints may improve structural strength and/or rigidity.

The yoke may comprise a third steel. For example, the third steel may be the same as the second steel. Alternatively, the third steel may be different from the first and second steels. The particular steel selected may be optimized for the particular electrical, magnetic, and/or mechanical requirements of each component.

Each section may comprise a stack of steel laminations. For example, the thickness of each stack may be between 0.05 and 0.25 mm. The use of a stack reduces eddy currents in use.

The electric motor may be an internal permanent magnet electric motor.

According to another aspect, an electric vehicle is provided comprising the electric motor of the foregoing aspect.

Drawings

In order that the invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic top view of a vehicle including two Electric Drive Units (EDUs);

FIG. 2 is a perspective view of an electric motor forming part of the EDU of FIG. 1;

FIG. 3 is a plan view of the rotor of the electric motor of FIG. 2;

FIG. 4 is a simplified schematic perspective view of the rotor of FIG. 3 with features omitted for clarity;

fig. 5 is a plan view of the rotor of fig. 3 and 4 together with a stator core.

Fig. 6 is a plan view of a stator core including a plurality of segments.

FIG. 7 is a plan view of a portion of the stator core and rotor;

FIG. 8 is a plan view of a portion of an alternative stator core and rotor;

FIG. 9 is a plan view of a portion of another alternative stator core and rotor;

FIG. 10 is a plan view of a portion of yet another alternative stator core and rotor;

FIG. 11 is a plan view of a portion of yet another alternative stator core and rotor;

FIG. 12 is a plan view of a portion of yet another alternative stator core and rotor; and is

Fig. 13 is a plan view of a portion of yet another alternative stator core and rotor.

Detailed Description

Unless the specific context indicates otherwise, the word "axial" as used in this specification refers to the axis about which the rotor rotates when mounted in an electric motor.

Referring to the drawings, FIG. 1 shows a vehicle in the form of an automobile 100. The automobile 100 includes a front Electric Drive Unit (EDU)102 and a rear EDU 104. The front EDU102 drives a pair of front wheels 106 and the rear EDU104 drives a pair of rear wheels 108. In other embodiments, only a single EDU is employed to drive any desired number of wheels. In other embodiments, more than two EDUs may be employed, each EDU driving any desired number of wheels.

The front EDU102 includes a gearbox 110. An electric motor 112 is mounted to the gearbox 110 and is configured to provide drive to an input shaft (not shown) of the gearbox 110. A drive electronics unit in the form of an inverter 114 is mounted to the gearbox 110 and is configured to provide drive current to the electric motor 112. In the illustrated embodiment, the electric motor 112 is mounted to a first lateral side of the gearbox 110, and the inverter 114 is mounted to a second lateral side of the gearbox 110 opposite the first lateral side.

Rear EDU104 has a similar combination of components, including gearbox 111, electric motor 113, and inverter 115.

Fig. 2 shows electric motor 112 of front EDU102 (electric motor 113 from rear EDU104 is identical and will not be separately described). Electric motor 112 is an Interior Permanent Magnet (IPM) electric motor that includes an IPM rotor core 116 having interior permanent magnets embedded within a steel lamination stack, as described below. The rotor core 116 is mounted to an output shaft 119, and when the EDU102 is assembled, the output shaft 119 is mated with an input shaft (not shown) of the gearbox 110.

Turning to fig. 3 and 4, in the illustrated embodiment, the rotor core 116 is formed from a plurality of bodies. Each body takes the form of an axial stack 118. Each axial stack 118 is formed from a stack of electrical steel laminations 120. For example, in the illustrated embodiment, the rotor core 116 includes six axial stacks 118, each axial stack 118 being formed of approximately one thousand laminations 120 of electrical steel, each lamination being approximately 0.1mm thick.

The stacks 118 may be angularly aligned with one another. Alternatively, at least some of the stacks 118 may be angularly offset relative to one another, which may facilitate torque transfer.

Those skilled in the art will appreciate that in other embodiments, only a single body may be provided. Furthermore, the or each body may be formed from a different number of laminations 120, or may be formed from a single layer of material.

As best shown in fig. 3 and 5, each stack 118 includes a plurality of axially extending bores 122. In the illustrated embodiment, the aperture 122 extends through the entire stack 118, but in alternative embodiments, the aperture 122 may only partially extend through the stack 118. For example, where laminates 120 are used, holes are only through some of the laminates 120.

The holes 122 may be formed by any suitable process. For example, prior to assembling the stack 120 to form the stack 118, the individual stacks 120 may be cut, stamped, machined, or otherwise processed to form the corresponding portion of each hole 122. Alternatively, each hole 122 may be cut, stamped, machined, or otherwise formed in the stack 118 after assembly of the laminates 120.

In the axial plane, each hole 122 includes parallel sides with parallel sides. The apertures 122 are disposed in a plurality of aperture pairs 124 that are circumferentially spaced about the stack 118, as described in more detail below. Each hole pair 124 is configured such that its holes 122 are disposed on either side of a radius 130 of the rotor core 116. In the illustrated embodiment, there are exactly ten hole pairs 124.

In the axial plane, the holes 122 of each hole pair 124 define a mechanical angle that can be selected to provide a desired magnetic pole.

Each aperture 122 receives a magnet 136. The holes 122 and the magnets 136 they receive are arranged and configured such that the magnetic field generated by the magnets 136 of each hole pair 124 generates a magnetic pole at the radially outer surface 138 of the rotor core 116 that is circumferentially centered at the point 121 where the radius 130 intersects the outer edge of the rotor core 116. In the presence of ten pairs of holes 124, ten poles are created around the outer surface 138 of the rotor core 116.

Optionally, and as shown in the illustrated embodiment, each magnet 136 may be mounted in a holder 137, which holder 137 in turn is inserted into one of the holes 122. Each holder 137 may be formed of an elastic material (e.g., an elastomeric material). In use, each holder 137 covers the end of its corresponding magnet 136 and extends beyond it. Each magnet 136 and keeper 137 pair is a friction fit within its bore 122.

Optionally, each holder 137 may extend radially inward and/or outward from its corresponding magnet 136. For example, in the illustrated embodiment (and as best shown in fig. 3), each holder 137 includes a radially inner portion 139 that extends beyond its magnet 136 and a radially outer portion 141 that extends beyond its magnet 136. The radially inner portion 139 and the radially outer portion 141 of each retainer 137 help retain the corresponding magnet 136 in its predetermined position within bore 122.

In the illustrated embodiment, each hole pair 124 is symmetrically positioned about its corresponding radius 130. In other embodiments, the hole pairs 124 may be positioned asymmetrically about their corresponding radii. Different forms of asymmetry may provide improvements in the performance of the electric motor, whether as a motor drive, or for generating electricity in a regenerative mode. For example, such asymmetry may provide improved efficiency when the motor is rotating in one direction, while reducing efficiency in the other direction. A more efficient rotational direction may be used to propel the vehicle forward, with a less efficient rotational direction being used for reverse.

Fig. 5 and 6 illustrate a stator (or stator assembly) 198 mounted within and supported by a housing 205 of the electric motor 112 illustrated in fig. 2 (the windings of the stator assembly 198 are omitted for clarity). The rotor core 116 is mounted within a housing 205 for rotation relative to the stator assembly 198. The stator assembly 198 includes a stator core 199. 60 circumferentially spaced axially extending slots 200 are formed in the stator core 199 to define 60 circumferentially spaced axially extending teeth 201.

Typically, the stator comprises a stator core comprising a first steel having a silicon content exceeding 3.5%, and the rotor assembly comprises a rotor core comprising a second steel having a silicon content of less than or equal to 3.5%.

The stator core 199 may take many different forms as will now be described with reference to fig. 6-13.

For example, fig. 6 shows stator core 199 having six circumferentially adjacent segments 300 that form a ring 301. Each segment 300 is arcuate in plan view and includes a slot 200, the slot 200 defining ten radially extending teeth 201 in each segment 300. Each segment 300 has circumferentially spaced ends 302, each end defining a key 304 that interlocks with a corresponding key defined by the end of an adjacent segment 300. In this context, "interlocking" means engaging each other by overlapping or by fitting the protrusion and recess together. The key 304 may take any suitable form to effect this interlocking. For example, one end 302 of each segment 300 may have a protrusion and the other end may have a recess complementary in shape to the protrusion.

In other embodiments, each end 302 may have a plurality of protrusions and/or recesses that are complementary to corresponding protrusions and/or recesses on an adjacent end 302. The projections and/or recesses need not be identical on each segment, but in many cases keeping them the same will simplify the design, manufacture, and assembly of the stator core 199.

Alternatively or additionally, the key 304 may include a lap region (not shown) of the end 302.

The keys 304 may be used primarily to position the segments 300 relative to one another during assembly. However, in other embodiments, the keys 304 may be configured to interlock more securely, which may increase the mechanical integrity of the stator core as a whole.

The sections may comprise steel with a silicon content of more than 4%, or in other embodiments more than 6%. In the illustrated embodiment, the segment 300 comprises steel having a silicon content of 6.5%. This relatively high silicon level results in lower switching losses, especially at high switching frequencies.

Each segment 300 comprises an axial stack of steel laminations. In general, each stack thickness may be between 0.05 and 0.25 mm. In the embodiment shown, each stack is 0.1mm thick. The individual laminations may be cut, stamped, machined or otherwise processed to form the corresponding sections 300. Alternatively, stamping, machining, cutting, or other forming processes may be performed after the laminations are stacked.

It should be appreciated that the stator core 199 may include any suitable number of segments. Generally, six or more sections may be required due to manufacturing loss reduction, but this must be balanced against the reduction in stiffness caused by the large number of sections.

Although the embodiment of fig. 6 uses sections that are entirely made of steel having a silicon content greater than 3.5%, in other embodiments only a portion of each section may be formed of such steel. For example, the portion (i.e., one or more teeth) around which the conductor in each section is positioned may be formed from such steel, while at least some of the remaining portions of the sections may be formed from one or more other steels having a lower silicon content. The two (or more) types of steel may be joined in any suitable manner, such as by welding, interlocking, or using suitable fasteners. This principle can also be applied to any other embodiments, including those described specifically above and below.

Turning to fig. 7, an alternative embodiment of the stator core 199 is shown, the stator core 199 including a ring yoke 306. A yoke 306 surrounds the annular ring 301 to support the segment 300 it forms. In the embodiment of fig. 7, each segment 300 comprises only a single tooth 201. A plurality of circumferentially spaced recesses 308 are formed along a radially inner region of the yoke 306. Each recess 308 retains one of the segments 300. In this particular embodiment, the segments 300 do not contact each other and therefore do not have the key portions 304 as described with respect to the embodiment of fig. 6. Thus, in this embodiment, the annular ring 301 is not continuous.

The yoke 306 may be formed from a different steel than the steel used for the section 300. For example, the yoke 306 may be formed of a steel having a lower silicon content than the steel used for the section 300. This may reduce the production cost of the stator due to reduced material costs (e.g., less expensive steel may be used for the yoke 306) and/or reduced production costs (e.g., low silicon steel may be cheaper to produce because it causes slower wear of the cutting dies). For example, the yoke may comprise steel having a silicon content of less than or equal to 3.5%.

For example, the yoke 306 may be formed from the same steel used to produce the rotor core 116. In some embodiments, this may allow the rotor and yoke to be produced in a single stamping or cutting operation. The ability to use the same material for multiple components may simplify production and inventory management, if not. Alternatively, the yoke 306, rotor core 116 and segments 300 are all formed from different types of steel, which may be optimized for the specific electrical, magnetic and/or mechanical requirements of each component.

Fig. 8 shows a variation of the embodiment of fig. 7, wherein like reference numerals are used to indicate like features. The main difference is that the section 300 of the embodiment of fig. 8 extends further in the radially outward direction than the embodiment of fig. 7. This increases the radial extent of the segment 300 relative to the radial extent of the yoke 306. Where the yoke 306 is formed of a steel having a lower silicon content than the segment 300, increasing the radial extent of the segment 300 may improve switching performance at the expense of using a steel having a higher relative silicon content.

Fig. 9 shows a variation of the embodiment of fig. 7 and 8, wherein the same reference numerals are used to indicate the same features. The main difference is that the segments 300 of the fig. 9 embodiment do not extend as far in the radially outward direction as in fig. 7 and 8. This reduces the radial extent of the segment 300 relative to the radial extent of the yoke 306. When the yoke 306 is formed of a steel having a lower silicon content than the segment 300, reducing the radial extent of the segment 300 may reduce the amount of steel required having a relatively higher silicon content, at the expense of reduced high frequency switching performance.

Fig. 10 shows an embodiment in which each segment 300 has two teeth 201. Another difference between this embodiment and that shown in fig. 7-9 is that the segments 300 in the embodiment of fig. 10 contact each other to form a continuous annular ring 301 (i.e., there are no gaps between the segments, as there are in the embodiment of fig. 7-9).

In the embodiment of fig. 10, each segment 300 includes a segment feature in the form of a radially extending protrusion, in this case in the form of a dovetail 314. The dovetail 314 interlocks with corresponding yoke features at a radially inner region of the yoke 306. The yoke feature takes the form of a recess 316 in a radially inner region of the yoke 306, the recess 316 being complementary to the dovetail 314. The dovetail joint formed by the dovetail 314 and the recess 316 facilitates positioning of the segment 300 relative to the yoke 306.

Fig. 11 shows a variation of the embodiment of fig. 10, wherein like reference numerals are used to indicate like features. The main difference is that the section 300 of the embodiment of fig. 11 extends further in the radially outward direction than the embodiment of fig. 10. This increases the radial extent of the segment 300 relative to the radial extent of the yoke 306. Where the yoke 306 is formed of a steel having a lower silicon content than the segment 300, increasing the radial extent of the segment 300 may improve switching performance at the expense of using a steel having a relatively higher silicon content.

Fig. 12 shows an embodiment in which each segment 300 has three teeth 201, with like reference numerals being used to indicate like features. As with the embodiment of fig. 10 and 11, the segments 300 contact each other to form an annular ring 301.

Fig. 13 shows a variation of the embodiment of fig. 12, wherein like reference numerals are used to indicate like features. The main difference is that the section 300 of the embodiment of fig. 13 extends further in the radially outward direction than the embodiment of fig. 12. This increases the radial extent of the segment 300 relative to the radial extent of the yoke 306. Where the yoke 306 is formed of a steel having a lower silicon content than the segment 300, increasing the radial extent of the segment 300 may improve switching performance at the expense of using a steel having a higher relative silicon content.

In the embodiment of fig. 10 to 13, each segment 300 has only one projection in the form of a dovetail 314. In other embodiments, any or all of the sections 300 may include two or more protrusions, and/or other positioning and/or reinforcing features. Where one or more projections (and/or other locating and/or reinforcing features) are provided, they may take the form of dovetails, similar to that shown in fig. 10-13. Alternatively, any or all such dovetails may be formed on the yoke and complementary recesses formed on the corresponding segments. Any other shape or configuration of locating and/or reinforcing features may be used in place of or in addition to the dovetail joint shown.

Optionally, at least one annular ring in the stack is angularly offset relative to at least one other annular ring. For example, laminations in a lamination stack forming the stator core may be positioned at an angle such that the abutment between circumferentially adjacent segments is angularly offset relative to the abutment of segments in adjacent laminations in the stack. This may increase the mechanical integrity of the stator core as a whole. Alternatively or additionally, one or more bodies (i.e., a stack of annular rings) may be radially offset relative to one or more other bodies. This may help to smooth torque transfer.

Although in the described embodiment the yoke 306 takes the form of a separate annular element that completely surrounds the segments, in other embodiments a plurality of circumferentially spaced yokes may be provided, each forming part of and/or supporting one or more segments.

Each stator core 199 may form a portion of a stator or stator assembly. In each stator assembly, teeth 201 are wound with a conductor (not shown) in a known manner. The conductors may take the form of insulated wires or pins. In use, the conductors may be driven with current in a controlled manner by the inverter 114 to produce electromagnetic poles that interact with the magnetic poles 121 of the rotor core 116 to produce torque in the rotor core 116. For example, the stator assembly 198, conductor windings, and drive current may be conventional and, therefore, not described in further detail.

Although the invention has been described with reference to a number of specific embodiments, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims (20)

1. An electric motor, comprising:

a housing;

a stator assembly disposed within the housing; and

a rotor assembly mounted within the housing for rotation within the stator assembly;

wherein the stator assembly comprises a stator core comprising a first steel having a silicon content exceeding 3.5% and the rotor assembly comprises a rotor core comprising a second steel having a silicon content less than or equal to 3.5%;

wherein the stator core comprises a plurality of circumferentially spaced stator teeth and a plurality of circumferentially adjacent segments, wherein at least the teeth are formed from the first steel, each segment comprising one or more of the teeth;

and the motor further comprises at least one yoke supporting one or more of the segments, the at least one yoke comprising a third steel.

2. The electric motor of claim 1, wherein the first steel has a silicon content of more than 4%.

3. An electric motor as claimed in claim 1 or 2, wherein the first steel has a silicon content greater than or equal to 6%.

4. An electric motor as claimed in any one of the preceding claims, wherein the first steel has a silicon content of 6.5%.

5. An electric motor as recited in any preceding claim, wherein each segment has circumferentially spaced ends, each end defining a key that interlocks with a corresponding key defined by an end of an adjacent segment.

6. An electric motor as claimed in any one of the preceding claims, wherein each segment has exactly one, two or three teeth.

7. An electric motor as claimed in any one of claims 1 to 5, wherein each segment has exactly 10 teeth.

8. An electric motor as claimed in claim 7, comprising exactly six sections.

9. An electric motor as claimed in any preceding claim, wherein the at least one yoke forms part of one or more of the segments.

10. An electric motor as claimed in any preceding claim, wherein the at least one yoke encircles the section.

11. An electric motor as recited in any preceding claim, wherein each segment comprises a segment feature that interlocks with a corresponding yoke feature at a radially inner region of the yoke.

12. The electric motor of claim 11, wherein each segment feature and its corresponding yoke feature form a dovetail joint.

13. An electric motor as recited in claim 12, wherein each segment feature is in the form of a dovetail, and each yoke feature takes the form of a recess having a complementary shape to the dovetail.

14. The electric motor of any of the preceding claims, wherein the third steel is different from the first steel.

15. An electric motor as claimed in any preceding claim, wherein the third steel is the same as the second steel.

16. The electric motor of any of claims 1-13, wherein the third steel is different from the first and second steels.

17. An electric motor as claimed in any preceding claim, wherein each segment comprises a laminated stack of the steel.

18. An electric motor as claimed in claim 17, wherein each lamination has a thickness of between 0.05 and 0.25 mm.

19. An electric motor as claimed in any preceding claim, wherein the electric motor is an internal permanent magnet electric motor.

20. An electric vehicle comprising the electric motor of any of the preceding claims.

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