GB2612204A

GB2612204A - Electric machine

Info

Publication number: GB2612204A
Application number: GB2217971.7A
Authority: GB
Inventors: Conway Ash Lloyd
Original assignee: Electrified Automation Ltd
Current assignee: Electrified Automation Ltd
Priority date: 2021-02-19
Filing date: 2021-02-25
Publication date: 2023-04-26
Anticipated expiration: 2041-02-25
Also published as: GB2612204B; GB202217971D0

Abstract

An electric machine comprising a rotor 200 having a coding for a rotary encoder 400; a stator assembly; and a rotary encoder for detecting the coding, where the encoder comprises an encoder PCB fixed relative to the stator and a daughterboard 420 attached to the PCB. The PCB may comprise an internal face abutting the rotor and an opposing external face where the daughterboard is mounted to the external face. The daughterboard may be removably attached to the PCB. The PCB may be attached to an internal surface 520 of a stator cover 500. The daughterboard may be attached to the PCB from an external surface of the cover via a window in the cover. A board-to-board connector may extend through the window in the cover and couple the PCB and daughterboard. The PCB may comprise inductive circuitry for sensing the coding and the daughterboard may include an encoder controller. A method of assembling an electric machine, with the encoder may also be provided that includes the encoder PCB fixed relative to the stator, attaching a cover to the stator assembly enclosing the encoder; and attaching a controller to the PCB from the exterior of the cover, and also may comprise providing an arm on the PCB, the arm carrying a temperature sensor, and fixing the PCB relative to a stator coil.

Description

ELECTRIC MACHINE

Field of Invention

The present invention relates to electric machines and methods of assembly associated therewith.

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) may consist of a stator and a rotor and operate through the interaction of the machines magnetic field.

Electric machines typically include a rotary encoder which monitors the position and movement of the rotor relative to the stator. This is particularly true for modern brushless motors in which position feedback is required for motor control. A rotary encoder may comprise a coding on one moving part and an encoder sensor on the other of the moving part which detects the coding during relative movement. A common form of rotary encoder for use in electric machines may use electro-magnetic interaction between the coding and encoder sensor. Thus, the coding may typically be a target comprising at least one (and usually a plurality of circumferentially distributed) features having a magnetic reluctance which can be detected when in rotational alignment with at least one (and usually a plurality of circumferentially distributed) electro-magnetic sensors of the sensor. The sensor may be conveniently formed on a printed circuit board (PCB) for example as printed induction coils.

There remains a desire to provide further improvements in the ease of manufacture and/or maintenance of electric machines particularly for use in high volume applications.

Summary of Invention

According to one aspect of the invention, there is provided an electric machine comprising: a rotor having a coding for a rotary encoder; and a stator assembly comprising a stator core, a plurality of coils mounted to the core; and a rotary encoder for detecting the coding on the rotor, wherein the encoder comprises an encoder PCB fixed relative to the stator core the PCB further comprising an integral temperature sensor, the temperature sensor mounted on an arm extending from the encoder PCB to position the temperature sensor proximal to one of the plurality of coils.

Providing a temperature sensor integral with the encoder PCB may reduce the need for an additional component and therefore reduce the overall part count and simplify the assembly of the electric machine.

The arm may extend radially from the encoder PCB. The arm may resiliently hold the temperature sensor against an external surface of the coil (for example the arm may provide a spring bias to urge the temperature sensor into position against the coil). Due to the resilient hold provided by the arm of the encoder PCB the temperature sensor may need no direct attachment to the stator (for example it is not necessary to screw or bond the temperature sensor in place).

The arm may have a necked profile, for example the necked portion of the arm may reduce the spacing required for the arm to pass between stator components (for example busbars connecting stator coils). The temperature sensor may be provided on an enlarged head, for example at the radially distal end of the arm.

The rotary encoder may further comprise a daughterboard mounted to the encoder PCB. This may be advantageous in its own right. Accordingly, in another aspect of the invention there is provided an electric machine comprising: a rotor having a coding for a rotary encoder; a stator assembly and a rotary encoder for detecting the coding on the rotor, wherein the encoder comprises an encoder PCB fixed relative to the stator and a daughterboard attached to the encoder PCB.

The encoder PCB may, for example, comprise an internal face abutting the rotor and an opposing external face, the daughterboard may for example be mounted to the external face. The daughterboard may be removably attached to the encoder PCB. The daughterboard may be replaceable. The encoder PCB may be attached to an internal surface of a cover of the stator, for example an end cover. The daughterboard may be attached to the encoder PCB via a window in the stator cover. Thus, the daughterboard may be externally mounted to the stator (in contrast to the internally mounted encoder PCB.

The encoder PCB may comprise the inductive circuitry (for example coils) for sensing the coding on the rotor. The daughterboard may include the encoder controller. The daughterboard may comprise the inductive coding chip connected to the inductive circuitry of the encoder PCB. Thus, the PCB encoder, may for example, passively detect the coding on the rotor whilst the daughterboard may comprise the processor to determine the position and/or movement data of the rotor. The daughterboard may include a communications output for transmitting motor data, for example to a computer.

Advantageously, embodiments of the invention may enable the daughterboard to be replaced or upgraded in use without the need to remove the encoder PCB from the stator. This is beneficial because the positioning of the encoder PCB relative to the stator must be highly precise to ensure that the encoder operates accurately and reliably.

The daughterboard may further comprise secondary processing functions for example safety and motor management functions. Advantageously, this may enable a common encoder PCB to be used in a modular manner with a plurality of alternate daughterboards. For example, a variety of motors with different functionality could be specified by provided by selecting from one of several daughterboards. It may be appreciated that such flexible configuration may be particularly attractive when mass producing motors with a range of possible applications.

A further aspect of the invention comprises a method of assembling an electric machine, the method comprising the steps of: providing a rotor assembly including an encoder coding; providing a stator assembly; providing an encoder PCB fixed relative to the stator, attaching a cover to the stator assembly, the cover enclosing the encoder and attaching a controller to the encoder PCB from the exterior of the cover.

The method may include attaching the encoder PCB to an internal side of the cover prior to attaching the cover to the stator assembly.

The method may further comprise providing an arm on the encoder PCB, the arm carrying a temperature sensor and wherein fixing the encoder PCB relative to the stator assembly positions the temperature relative to one of a plurality of stator coils.

The method may be used in conjunction with the embodiments described above.

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: Figures 1A and 16 show an electrical machine in accordance with an embodiment; Figures 24 and 26 shows an end view of the stator assembly and aligned encoder assembly of figure 1; Figure 3 shows an isolated view of the rotor assembly and aligned encoder assembly of figure 1; Figure 4 is a version of figure 3 showing hidden details of the rotor; Figures SA and 5B show a cross-section and detailed view of the stator assembly and encoder PCB; Figure 6A and 66 show side and end views of the encoder assembly in isolation; Figure 7 shows an end view of the interior face of a cover and encoder for use in embodiments; Figure 8 shows a three-dimensional view of a cover for use in embodiments; and Figures 9A and 9B show internal and external exploded perspectives of the cover, encoder and rotor of an embodiment.

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 1A and 1B (in which the stator is shown in exploded relationship) 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. The stator assembly is completed by electrically connecting the coils via bus bars 101 to connectors 105.

Electric machines often include an encoder to monitor the position and/or movement of the rotor 200 relative to the stator 100. A typical encoder may include a coding on the rotor provided by a plurality of targets. During rotation of the rotor the targets move into (and out of) alignment with the sensor arrangement of the encoder 400. As shown by the hidden features in hashed lines of figure 4, in the illustrated embodiment the targets are provided by five castellations 250 which are circumferentially distributed around the hub 210 of the rotor. The castellations 250 may be formed from a magnetic material such that they can be detected by induced currents in a circuit printed on the PCB board 410 of the encoder 400. The skilled person will appreciate that other encoder configurations may be possible, for example targets could be provided on the rotor by attaching one or more PCB elements.

The encoder 400 of embodiments has a modular configuration consisting of a separate encoder PCB board 410 and daughterboard 420 mounted on the encoder board. The encoder PCB board 410 is a generally annular disk shape extending between an inner opening 412 providing an opening for the shaft of the rotor 200 and an outer edge 414 having a diameter which is less than the inner diameter of the stator assembly 100. As will be explained in further detail below, the encoder 400 is fixed relative to the stator 100 (via attachment to the cover 500). As such, in use, it will be appreciated that the rotor 200 rotates relative to the encoder 400. The encoder PCB board 410 comprises a printed encoder inductive circuitry, for example a printed coil array. The daughterboard 420 is explained in further detail below.

As best seen in figure 2 a further feature of the encoder 400 in embodiments is the provision of an integrated temperature sensor 430. Integrating the temperature sensor 430 with the board 410 of the encoder can reduce the overall part count of the electric machine 1.

The temperature sensor 430 is mounted on an arm 434 which extends radially outwardly from the encoder board 410. The temperature sensor 430 and encoder board 410 are formed on a single integrated substrate. The arm 434 projects radially outwardly from the outer edge 414 of the encoder board 410. As seen in the radial length of the arm 434 is such that the head portion 432 is aligned with the coils 300 of the stator 100 as shown in the cross section of figure 5. Advantageously, this arrangement may enable the temperature sensor 430 to abut a coil 300 without needing to be directly attached thereto. As such the temperature sensor 430 is neither prone to failure from detachment nor does it require removal if maintenance is required to the coil. The arm 434 of the temperature sensor has a reduced width in comparison to the head and may therefore be more easily accommodated between features of the stator such as the busbars 102. The narrowed neck of the arm 434 may reduce the compromise of having a radially extending feature such that it can pass easily between parts of the coil connections such as the ends 102a and 102b shown in figure 2.

PCB base materials (for example glass epoxy compounds) are generally resilient. As such, the position of the encoder board 400 and the temperature sensor 430 may be selected such that the head 432 of the sensor is spring biased into engagement with the coil 300 as shown by arrow S in figure 5B. It may be appreciated that the bias at the head 432 can be readily tailored when designing an electric machine by selecting the width and thickness of the arm 434 and the relative in use alignment positions of the PCB board 410 and the temperature sensor 430.

The configuration of the daughterboard 420 and the assembly of the electric machine 1 with the encoder 400 will now be described in further detail with reference to figures 6 to 9. Figure 6 shows the encoder 400 in isolation. It may be noted that the main PCB board 410 includes connection features such as a plurality of attachment holes 415 and an alignment feature 416 which helps ensure correct and accurate alignment of the encoder PCB Board 410 within the stator assembly 100 of the electric machine 1. The daughterboard 420 is connected to the PCB board 410 via a board-to-board connector 422 which provides a removable physical and electrical connection between the boards. The connector 422 may for example include a snap fit type resilient connection.

The daughterboard 420 includes the controller. The encoder board 410 includes the inductive circuitry required to pick up the position data from the coding on the rotor 200 (for example provided by the targets 250). The encoder board 410 must be precisely aligned within the electric machine to ensure accurate encoder function. The provision of a separate daughterboard 420 enables the controller to be replaceable without the encoder board 410 being removed from the electric machine 1 (for the example for repair or upgrading). This provides an advantage since it does not require the encoder board 410 to be re-aligned when a change (for example maintenance or upgrade) is required on the daughterboard.

In particular, the end cover 500 of the electric machine 1 may be used for attachment of the encoder 400. The cover 500 may be an axial end plate which attaches to the stator 100 enclosing the coils 300 and rotor 200. The cover has an axially internal face 520, shown in Figure 7, and an axially external face 510 shown in figure 8. It will be appreciated that the cover SOO may seal the electric machine 1 to provide environmental and electrical protection and includes an opening 530 through which the shaft 220 or the rotor can project.

The encoder board 410 is affixed to the interior face 520 of the cover 500 via screws or other fixings passing through the holes 415. At this stage, the daughterboard 420 is not connected to the encoder board 410. The cover 500 with the encoder PCB board 410 is then connected to the stator 100 with the rotor 200 captive within the electric machine 1. Attachment of the cover SOO aligns both the PCB encoder board 410 and the temperature 430. The daughterboard 420 may then be attached to the PCB encoder board 410 by positioning the connector 422 through a window 515 which extends axially through the cover SOO. The daughterboard 420 may be enclosed in a protective casing 421. With the electric machine 1 assembled the daughterboard 420 may be readily accessed from the exterior 510 (for example by removal of its cover 421) of the cover 500. The PCB encoder board 410 can remain internal to the case 500 and does not, therefore, need to be realigned during maintenance.

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, whilst the illustrated embodiment described above comprises an internal rotor and external stator embodiments of the invention need not be limited to such an arrangement. In this regard the skilled person will appreciate that some motors use a stator having an internal annular stator core with outwardly projecting pole teeth. It will be appreciated that embodiments of the present disclosure can easily be adapted to such an arrangement without the departing from the scope of the invention.

Claims

Claims 1. An electric machine comprising: a rotor having a coding for a rotary encoder; a stator assembly; and a rotary encoder for detecting the coding on the rotor, wherein the encoder comprises an encoder PCB fixed relative to the stator and a daughterboard attached to the encoder PCB.
2 The electric machine of claim 1 wherein, the encoder PCB comprises an internal face abutting the rotor and an opposing external face and the daughterboard is mounted to the external face.
3. The electric machine of claim 1 or 2 wherein, the daughterboard is removably attached to the encoder PCB.
4. The electric machine of any of claims 1 to 3 wherein, encoder PCB is attached to an internal surface of a cover of the stator.
5 The electric machine of claim 4 wherein, the daughterboard is attached to the encoder PCB from an external surface of the cover via a window in the stator cover.
6. The electric machine of claim 5, further comprising a board-to-board connector extending through the window in the stator cover and coupling the encoder PCB and daughterboard.
7. The electric machine of any preceding of claim wherein, the encoder PCB comprise the inductive circuitry for sensing the coding on the rotor and the daughterboard includes the encoder controller.
8. A method of assembling an electric machine, the method comprising the steps of: providing a rotor assembly including an encoder coding; providing a stator assembly; providing an encoder PCB fixed relative to the stator; attaching a cover to the stator assembly, the cover enclosing the encoder; and attaching a controller to the encoder PCB from the exterior of the cover.
9. The method of claim 8, wherein the controller is a daughterboard attached to the encoder PCB.
10. The method of claim 8 or 9, further comprising attaching the encoder PCB to an internal side of the cover prior to attaching the cover to the stator assembly.
11 The method of any of claims 8 to 10, further comprise providing an arm on the encoder PCB, the arm carrying a temperature sensor and wherein fixing the encoder PCB relative to the stator assembly positions the temperature relative to one of a plurality of stator coils.
12. The method of any of claims 8 to 10 further comprising enclosing the daughterboard in a protective casing on the exterior of the cover.