GB2604042A

GB2604042A - Rotor and electric machine

Info

Publication number: GB2604042A
Application number: GB2202288.3A
Authority: GB
Inventors: Conway Ash Lloyd
Original assignee: Electrified Automation Ltd
Current assignee: Electrified Automation Ltd
Priority date: 2021-02-19
Filing date: 2022-02-21
Publication date: 2022-08-24
Anticipated expiration: 2042-02-21
Also published as: GB2603969A; GB2603926A; GB202202288D0; GB2604034B; GB2604034A; GB2604033B; GB2604042B; GB2603969B; GB2603926B; GB2604033A; GB202102330D0; GB202102697D0

Abstract

An interior permanent magnet electric machine rotor assembly comprising an integrally cast shaft (220, fig 5B) and hub (210, fig 5B), the hub comprising over-cast iron and circumferentially distributed slots for permanent magnets 250. The hub may comprise integral targets 214 for a rotary encoder, where the targets are cast features of the hub. The targets may be circumferentially distributed around an axial end face 212 of the hub, where the targets may comprise castellations. A cooling passageway 230 may be disposed between the shaft and hub, where the passageway comprises an annular array of passageways separated by support spokes 236. Each passageway may be a through passageway extending between first 212 and second 213 axial faces on opposing sides of the hub, where the passageway may comprise an inlet 232 on one axial face and an outlet 233 on the other face the outlet being radially outward of the inlet such that flow through the passageway is induced during rotor rotation. The passageway may have a divergent cross-sectional profile. The over-cast iron may comprise a lamination stack 240 with slots formed in the stack. The rotor may be pre-balanced prior to the magnet installation. A method of the manufacturing comprises providing a lamination stack; over-casting an integral shaft and hub; balancing the rotor assembly; and mounting the magnets in the assembly.

Description

Rotor and Electric Machine

Field of Invention

The present invention relates to a rotor and an electric machine including a rotor.

Background

Electric machines (which it will be appreciated is used as a general term for a machine which uses electromagnetic forces such as an electric motor or generator) typically consist of a stator and a rotor and operate through the interaction of the machines

magnetic field.

One form of electric machine is a permanent magnet motor in which typically use a stator comprising a plurality of electric windings in combination with an array of permanent magnets in the rotor. Permanent magnet rotors are generally categorised as either a surface permanent magnet ("SPM") arrangement in which permanent magnets are attached at an outer surface of the rotor or an interior permanent magnet (IPM) rotor in which the permanent magnets are embedded within the rotor. IPM motors in particular may have high power density, good efficiency and wide speed range performance and as such there is high demand for IPM motors for applications such as Electric Vehicles (EVs).

There is a need for electric machines and electric machine rotors which are designed to enable efficient manufacture, for example to aid volume manufacture. For example, it is desirable to provide assemblies for electric machines, including rotors, with a reduced part count and which may be suitable for automated assembly.

Summary of Invention

According to a first aspect of the invention, there is provided an interior permanent magnet electric machine rotor assembly comprising an integrally cast shaft and hub, the hub comprising over-cast iron and a plurality of circumferentially distributed slots for permanent magnets.

The integrally cast shaft and hub may be an aluminium casting. The integrally cast shaft and hub may be cast and machined to provide a required finish. The aluminium casting may for example be over-cast onto the iron which forms the ferro-magnetic part of the rotor (which provides the magnetic function of the rotor in conjunction with the permanent magnets received in the slots). The iron may for example be a laminated steel stack. The plurality of circumferentially distributed slots for permanent magnets may be formed in the over cast iron portion of the rotor.

Advantageously, embodiments of the invention provide a rotor assembly which can be balanced during the initial casting and machining steps. A such the rotor may requires only minor subsequent adjustment when the permanent magnets are inserted prior to final assembly of an electric machine. This may simplify and streamline rotor manufacturing.

In embodiments the hub further comprises a plurality of integral targets for a rotary encoder. Electric machines may include an encoder to monitor the position and/or movement of the rotor relative to the stator. A plurality of targets on the rotor may form a coding for the rotary encoder. In use, rotation of the rotor causes the targets move into (and out of) alignment with a sensor arrangement of the encoder. The targets may be formed of a magnetic material such that they can be detected by induced currents in a circuit printed on a PCB board of the encoder.

The targets may be cast features of the hub. The targets may be circumferentially distributed around axial end face the hub. The targets may comprise a plurality of castellations. Providing an integral targets may reduce the need for an additional component (and therefore reduce the overall part count) and simplify the assembly of the electric machine. Further, an integrally formed target requires may remove the need for an additional alignment or calibration when assembling the the rotary encoder of the electric machine.

In some embodiments the rotor may further comprise a cooling passageway disposed between the integrally cast shaft and hub. Thus, the cooling feature may be integrally formed in the rotor. The cooling passageway may comprise an array of passageways, for example an annular array each separated by support spokes. The support spokes may extend substantially radially. The, or each, cooling passageway may be a through passageway, for example the passageway(s) may extending between first and second axial faces on opposing sides of the hub. The, or each cooling passageway may extend generally axially through the rotor.

The, or each, passageway may comprise an inlet on one axial face and an outlet on the other axial face. The outlet may be radially outward of the inlet such that coolant flow through the passageway is induced during rotation of the rotor. For example centrifugal flow will occur during rotation of the rotor. Advantageously, such an induced coolant flow may both help to cool the rotor via the passageway and also encourage coolant flow around the electric machine outside of the passageway.

The, or each, passageway may have a divergent cross-sectional profile. For example, the, or each passageway may diverge (for example radially) along its axial length.

Thus, the passageway may provide a nozzle effect to accelerate coolant flow thereth rough.

The over-cast iron may comprise a lamination stack. The plurality of circumferentially distributed slots may be formed in the lamination stack.

In embodiments the rotor may be pre-balanced prior to installation of a plurality of magnets.

The rotor assembly may further comprise a plurality of permanent magnet. Each permanent magnet of the plurality may be mounted in one of the plurality of circumferentially distributed slots.

According to a further aspect of the invention there is provided an electric machine comprising a stator assembly and a rotor assembly in accordance with embodiments.

In another aspect of the invention there is provided a method of manufacturing an interior permanent magnet electric machine rotor assembly, the method comprising: providing a lamination stack; over-casting an integral shaft and hub; balancing the rotor assembly; and mounting a plurality of permanent magnets in the rotor assembly.

It will be appreciated that the method may be used in combination with one or more features in accordance with embodiments of the rotor assembly.

Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description or drawings.

Description of the Drawings

Embodiments of the invention may be performed in various ways, and embodiments thereof will now be described by way of example only, reference being made to the accompanying drawings, in which: Figure 1 shows an electric motor assembly in accordance with an embodiment; Figures 2 shows a partial exploded view of a rotor assembly in accordance with an embodiment; Figure 3A and 3B shows a perspective and end view of the rotor of figure 3 from a first axial direction; Figure 4A and 4B shows a perspective and end view of the rotor of figure 3 from a second axial direction; and-Figure 5A and 5B shows a side view and cross-section of the rotor of figure 3.

Detail Description of Embodiments

It may be noted that directional/orientational terms such as radial, circumferential and axial may be used herein to refer to the general directions of the assembly or components thereof relative to their in-use configuration. The general directions are shown, by way of example only, by arrow R showing a radial direction, C showing a circumferential direction and A showing an axial direction in Figure 1. However, the skilled person will appreciate that (unless expressly indicated otherwise) such directions are used broadly and do not imply strict mathematical conformance with a particular orientation. Likewise, the use of such terminology does not exclude a component or feature having a non-circular or irregular form.

An electric machine 1 is shown in figure 1 and comprises a stator 100 surrounding a rotor 200. The stator comprises a stator core 110 and a plurality of coils 300 mounted on poles of the stator core 110. As will be explained further below, the rotor 200 is an internal permanent magnet (IPM) rotor. The electric machine 1 further comprises an encoder 400 to monitor the position and movement of the rotor 200 relative to the stator 100. The encoder 400 includes inductive circuitry on a PCB board 410 arranged to pick up position data from the rotor 200 by detecting at least one target (discussed further below).

Figures 2 illustrates a partially exploded view of a rotor assembly 200 in accordance with an embodiment. The rotor assembly comprises a hub 210 and axle 220 which are an integrally formed body. The hub 210 and axle 220 are cast and machined to provide a high tolerance integral component. The axle 220 has a hollow bore 222. As best seen in figure 4, at either axial end of the rotor assembly the shaft 220 is provided with a seat 224 and 225 for front and back bearings (not shown) such that the rotor assembly can be supported rotationally with respect to the stator 100.

The outer portion of the rotor assembly 200 comprises a lamination stack 240 which includes a plurality (in this embodiment ten) slots 245 each of which receives a permanent magnet 250. The lamination stack 240 may be cast into the integrated hub 210 and axle 220 to reduce the effective part count and number of subsequent manufacturing steps. This may also ensure that the rotor assembly can be pre-balanced when machining the hub/axle casting so that only minimal minor adjustment balancing of the assembly is required once the magnets are installed (for example during final assembly of the electric machine).

With particular reference to the axial end views of Figure 3, it may be noted that one end face 212 of the hub 210 is formed with cast-in targets 214 for a rotary encoder 400. The targets 214 comprises an annular castellated array defined by a plurality of axial recesses 215 separating a series of lands 216 formed in the end face 212. The lands 212 of the targets 214 provide a mass of magnetic material which can be detected by inductive features of the PCB board 410 which is positioned in close proximity to the end face 212 and fixed relative to the stator 100. Thus, as the rotor rotates within the stator 100 the lands 212 of the targets 214 are detected moving past the inductive features of the PCB board 410 and can be used to determine the position and/or rotational speed of the rotor 200.

The rotor casting is also provided with integrated cooling features in the form of a cooling passageway 230 disposed between the hub 210 and shaft 220. The cooling passageway 230 generally extends annularly around the full circumference of the rotor 200. The cooling passageway also extends axially through the full axial depth of the hub 210 of the rotor 200. As such, the passageway extends from a first opening 232 at the first axial end face 212 of the rotor hub 210 to a second opening 233 at the second (opposing) axial end face 213 of the rotor hub 210. The passageway 230 may be formed of a plurality of individual passageways (for example passageways 235a, 235b) distributed circumferentially around the rotor 200. The individual passageways may be independent or may be interconnected and may, for example, converge into a common annular mouth at one or both of the openings 232, 233 at the end faces 212, 213. A plurality of spoke members 236 may provide support from the shaft 220 to the hub 210 through the cooling passageway 230 (the spoke members 236 providing radial walls between adjacent individual passageways 235). The series of spoke members 236 may be generally radially extending and may be circumferentially distributed.

As best seen in the cross section of figure 4, as the passageway 230 extends axially through the rotor 200 from the first end face 212 to the second end face 213 it is progresses radially outwardly. As such, the opening 233 in the second end face 213 is radially outward of the opening 232 in the first end face 212. Additionally, the passageway is divergent as it progresses axially (in the same direction from the first opening 232 to the second opening 233). In use, the shape and profile of the passageway 230 causes a centrifugal pump effect upon cooling fluid (for example air) surrounding the rotor 200). Cooling fluid will be drawn into the first opening 232 of the passageway and ejected from the second opening 233. This will not only assist in cooling of the rotor 200 (by thermal interaction with the flow through the passageway) but may also encourage the establishment of an effective coolant flow around the interior of the electric machine 1 (so may, for example, also assist in cooling of the stator 100).

Although the invention has been described above with reference to preferred embodiments, it will be appreciated that various changes or modification may be made without departing from the scope of the invention as defined in the appended claims. For example, it will be appreciated that the position and dimensions of the features described above could be readily altered to optimise the rotor dependent on

the specification of the electric machine.

Claims

Claims 1. An interior permanent magnet electric machine rotor assembly comprising an integrally cast shaft and hub, the hub comprising over-cast iron and a plurality of circumferentially distributed slots for permanent magnets.
2. The rotor assembly of claim 1, wherein the hub further comprises a plurality of integral targets for a rotary encoder.
3. The rotor assembly of claim 2, wherein the targets are cast features of the hub.
4. The rotor assembly of claim 2 or 3, wherein the targets are circumferentially distributed around axial end face the hub.
5. The rotor assembly of any of claims 2 to 4, wherein the cast targets comprise a plurality of castellations.
6. The rotor assembly of any preceding claim, further comprising a cooling passageway disposed between the integrally cast shaft and hub.
7. The rotor assembly of claim 6, wherein the cooling passageway comprises an annular array of passageways separated by support spokes.
8. The rotor assembly of claim 6 or 7, wherein the, or each, cooling passageway is a through passageway extending between first and second axial faces on opposing sides of the hub.
9. The rotor assembly of claim 8, wherein the, or each, passageway comprises an inlet on one axial face and an outlet on the other axial face and wherein the outlet is radially outward of the inlet such that coolant flow through the passageway is induced during rotation of the rotor.
10. The rotor assembly of any of claims 6 to 9, wherein the passage way has a divergent cross-sectional profile.
11. The rotor assembly of any preceding claim, wherein the over-cast iron comprises a lamination stack and wherein the plurality of circumferentially distributed slots are formed in the lamination stack.
12. The rotor assembly of claim 11, wherein the rotor is pre-balanced prior to installation of a plurality of magnets.
13. The rotor assembly of any previous claim, further comprising a plurality of permanent magnets each mounted in one of the plurality of circumferentially distributed slots.
14. An electric machine comprising a stator and a rotor as claimed in any preceding claim.
15. A method of manufacturing an interior permanent magnet electric machine rotor assembly, the method comprising: providing a lamination stack; over-casting an integral shaft and hub; balancing the rotor assembly; and mounting a plurality of permanent magnets in the rotor assembly.