GB2580604A

GB2580604A - Flexible motor housing

Info

Publication number: GB2580604A
Application number: GB1900533.9A
Authority: GB
Inventors: Geoffrey Richards Bryn
Original assignee: Digipulse Ltd
Current assignee: Digipulse Ltd
Priority date: 2019-01-15
Filing date: 2019-01-15
Publication date: 2020-07-29
Also published as: GB201900533D0

Abstract

An electric motor comprising a vibration damping component disposed between: shaft and housing (404, Fig. 4; 504, Fig. 5; 604, Fig. 6); stator and housing (102, Fig. 1; 202, Fig. 2); and/or integrated into the housing (305, Fig. 3). The motor housing may be formed of a metal, metal alloy or ceramic. The vibration damping component may comprise: a silicon; metal; metal alloy; rubber or synthetic rubber; or a resin such as an epoxy, thermoplastic polyethylene or polycarbonate. Alternatively, the oscillation damping component may comprise a plurality of corrugated springs integrally formed with the housing or stator. The vibration damping component may comprise fibres with a higher thermal conductivity than a surrounding rubber material. The resin layer may be thicker than 0.8mm and provide damping and insulation. The housing may comprise at least two housing components with the damping component provided therebetween as an O-ring. The vibration damping component may be disposed between bearings and the shaft or bearings and the outer housing, possibly as part of a bearing cartridge. The vibration damping component may fill a space between the stator and the outer housing. The stator may comprise one or more voids or channels utilised for cooling or damping.

Description

FLEXIBLE MOTOR HOUSING

Technical Field

The technical field is electrical motors.

Background

There has been a general increase in the speeds of electric motors, including cost-sensitive electric motors, supported both by advances in semiconductor technology allowing more flexible control strategies and by damping of shaft motion provided by the widespread use of plastics for motor housings. An increase in the speed of electric motors is beneficial, in general, because the volume of relatively expensive electromagnetic material inside a motor (permanent magnets, conductive windings, and "iron" conductor material with the capability of minimising hysteresis loss when subjected to an oscillating field) correlates with a motor's torque capability, provided that the capability of dissipating heat is manageable so as not to be a limitation in the design of the motor. Power being equal to torque multiplied by speed, a given power can be delivered by a higher-speed motor with less torque and therefore incorporating less electromagnetic material than a lower-speed motor delivering the same power.

In certain classes of electric motor, particularly motors for consumer goods below 2kW, over-moulded plastic housings have become an extremely popular design choice. The principal benefit of over-moulded plastic housings is the relative cheapness they allow in the manufacture of complex devices in high volume, because over-moulded plastic can connect and integrate several subcomponents and functions into a single part. Fewer, more multifunctional parts lend themselves to mass manufacturing, as in the consumer goods sector, because they are easier to assemble than many functionally distinct parts. This shifts the cost of manufacture from labour and per-unit costs towards tooling and capital investment costs, which in many cases has the effect of reducing overall amortised manufacturing cost.

Another advantage of over-moulded plastic is the provision of electrical insulation and electromagnetic non-emissivity with moderately good thermal conductivity. It should be recognised that insulation and non-emissivity are benefits arising both from the intrinsic material properties of plastic and also from the cheapness of the material and the nature of the manufacturing process allowing good coverage of the motor with few or no seams. The fact of thermal conductivity (and also strength) being only moderately good can be accommodated in part by over-moulded plastic housings being bulky and thus affording lager thermal reservoirs, greater external surface area, and greater average cross-section then other types of housing in general, which bulk is accommodated by the cheapness of the material.

Plastics in general provide a high degree of damping under strain. This property may not have contributed to the adoption of plastics into electric motor housings, but it has allowed or indicated design changes in motors that are correlated with the provision of damping from the housing and that are now considered as beneficial or at any rate sufficiently ubiquitous as to render their preservation desirable in any new housing design. Most importantly, the ability of the housing to accommodate and to damp strain implies the provision of damping of shaft vibration at the motor's bearings. The need to dampen this vibration is linked to the drivers leading to increasing motor speed described above. The widespread use of over-moulded plastic housings has contributed to and correlated with a general trend towards increasing motor speed.

It is notable that the softness of plastic (i.e. the high elasticity of plastic) contributes to its ability to damp movement and vibration. Complementing its intrinsic property of damping rather than re-releasing strain energy elastically, the softness of plastic allows a greater range of movement. Since the phenomenon of damping is an absorption of energy and energy is a force acting over a distance, there must be movement in the first place before a material can dampen or elastically return that energy. Thus softness contributes to the ability of plastic over-moulded housings to damp vibrations such as the vibrations from motor bearings, which damping is desirable provided the resulting heat can be dissipated.

The desire to reduce waste has led to new directives and research, particularly in Europe, towards an increase in plastics recycling and a reduction in the use of plastics in consumer goods. Over-moulded plastic housings are large in terms of total volume of housing per motor power output as compared to other forms of motor housing, and they are thus wasteful of material. Furthermore, over-moulded housings can be difficult to recycle because they integrate several motor parts into a single, complex component, this being one principal advantage they provide towards the cheapening of motor manufacturing. This means that over-moulded plastic housings often incorporate non-plastic parts into a single moulding. Finally, over-moulded plastic housings sometimes use non-recyclable thermoset plastics which offer properties generally favourable to motor applications, including inelasticity, thermal conductivity, and thermal tolerance.

Summary

Aspects of the invention are set out in the appended independent claims. Details of embodiments are provided in the dependent claims.

Brief Description of the Drawings

Figure 1 is a cutaway view of the internal arrangement of a motor within a housing according to an embodiment whereby a soft material such as rubber may be incorporated between the motor's outer diameter (stator outer diameter) and the housing; Figure 2 is cutaway view of the internal arrangement of a motor within a housing according to an embodiment whereby a spring and damping arrangement made up of corrugated material may be incorporated between the motor's outer diameter (stator outer diameter) and the housing; Figure 3 is a cross-sectional view of a motor with damping according to an embodiment whereby two halves of a motor's housing, each half housing locating and retaining the outer race of one of the motor shaft's bearings, may be separated from each other by a soft material such as rubber, thereby providing damping; Figure 4 is a cross-sectional view of a structure surrounding a bearing according to an embodiment whereby a soft material such as plastic may be inserted between the bearing's outer race and the housing that locates and may retain the bearing's outer race; Figure 5 is a cross-sectional view of a structure surrounding a bearing according to an embodiment whereby a soft material such as plastic may be inserted between the bearing's inner race and the motor's shaft; Figure 6 is a cross-sectional view of an embodiment in which a bearing may be located and retained within a bearing cartridge which in turn may be located and retained within the housing with at least one degree of movement allowed with respect to the housing and whereby a soft material such as rubber may be inserted between the cartridge and the housing; and Figure 7 is a cross sectional view of a stator comprising cut-outs in the stator's, 700, iron.

Detailed Description

The embodiments presented here are intended to accommodate flexibility in the motor housing to allow thermal expansion and the accommodation or damping of vibrations.

The embodiments are suited in particular to housings formed of a rigid or semi-rigid material that is easily or relatively easily recycled. Example materials are ceramic, metal, and metal alloys. Embodiments make use of a damping component whose purpose is specifically to provide damping by allowing movement. This is distinct from motors with over-moulded plastic housings whereby all of the housing is somewhat flexible and provides some damping 'naturally'.

Figure 1 is a cutaway view of an electric motor 100 according to an embodiment. There is provided a motor 101, a damping component 102 and a generally cylindrical housing 103. The motor comprises a stator and a rotor (not shown). The stator surrounds the rotor and is attached to the damping component. In an embodiment, the damping component comprises resin. The resin may comprise one of epoxy or a thermoplastic polyethylene or polycarbonate material. In an embodiment, the stator stack of the motor is pressed or baked into a housing with additional resin at the outer diameter of the stator stack, between the stator stack and the housing. This additional resin is additional in the sense that it is more than the thickness of resin required for electrical insulation, and acts as a spring and damping medium in respect of radial motions of the stator within the housing. In an embodiment the thickness of the resin component is greater than 0.8 mm. The resin may comprise, for example, epoxy or thermoplastic polyethylene or polycarbonate materials. Other materials than resin may be used in place of resin, or in addition to resin, the additional materials being added between the motor stator and the housing, as inserts or linings. Typical materials include silicon based materials, rubber, and metals. In an embodiment, the damping may comprise a surrounding material containing fibres with a higher heat conductivity than the surrounding material. In an embodiment, the surrounding material is rubber.

However, the person skilled in the art will appreciate the other materials, including those discussed above, may be used as the surrounding material. In an embodiment, the fibres may be used to increase the conduction of heat through the damping material.

In alternative embodiment, the damping component comprises a plurality of spring elements. Figure 2 is a cutaway view of an embodiment which uses corrugated sections as the spring elements, where the corrugations extend generally parallel to the motor axis. As in Figure 1, there is provided a motor 201 and a housing 203. In this embodiment, the damping component comprises at least one corrugated section 202.

The corrugated section 202 is disposed between the motor 201 and the housing 203. In an embodiment, the corrugated section may be integrally formed with the housing. In an embodiment, the damping component comprises a plurality of corrugated sections disposed circumferentially around the motor 201. In another embodiment, the damping component comprises a plurality of springs disposed between the motor and the housing.

In an embodiment, the housing surrounding the stator stack is corrugated, such that the housing incorporates channels running axially along the length of the stator stack and through which air, water, or another cooling medium may pass. The corrugated structure provides spring and damping properties, particularly if the angle of the corrugation and its thickness are correctly chosen in respect of the elastic modulus of the spring material using engineering mechanics. If the corrugated material is broken or bent over itself in the circumferential direction, it will have room to flex and will display a lower spring rate and be softer. In an embodiment, the corrugated material is placed directly inside of and outside of rings that provide a controlled friction surface and allow flex. In this embodiment, the spring rate, k (the reacting force per unit displacement) provided by one segment of a corrugated spring with a free edge is found by the equation: k - 3E1 1,3 cos U where: E is the modulus of elasticity of the material; I is the sectional moment of inertia of the spring; a L is the length of the segment; and e is the angel of the segment with respect t the motor housing.

Any reacting force from the spring on the opposing side of the motor must be subtracted from the net spring force. Taking the opposing springs on both sides of the motor into account, the net spring rate is likely to be near zero as deflection begins and then increase in value (the reaction force increasing) as the angle, 6 becomes smaller on the compressing side and larger on the decompressing side.

In an embodiment, bearings within the motor arrangement may be allowed movement with respect to each other by dividing the housing into two parts, one part surrounding each bearing. Figure 3 is a cross-sectional view of such a motor arrangement with two housing sections 303a and 303b. The arrangement has a rotor 301 and a stator 302. The two housing sections are generally cylindrical and are connected by means of a flexible interface 304. In an embodiment, the flexible interface comprises overlapping sections. In an alternative embodiment, the flexible interface comprises flange interfaces. The person skilled in the art will recognise that other arrangements are possible and the invention is not limited to any one arrangement for the flexible interface. The housing sections are connected to each other with a damping component 305 such as an 0-ring. In an embodiment, the damping component comprises a soft material capable of providing spring and damper characteristics, such as rubber or silicon materials. In alternative embodiments, springs or corrugated sections are used. The first housing section 303a surrounds a first bearing 306a and the second housing section surrounds a second bearing 306b. The bearings 306a, 306b are disposed between the respective housing sections 303a, 303b and the shaft 307, the latter having an axis of rotation 308.

In an embodiment, the motor bearings are allowed movement relative to the stator by surrounding them by means of a damping component between the bearings and the (substantially rigid) housing. Figure 4 is a cross-sectional view of a structure 400 surrounding a bearing 401, the bearing being disposed between a shaft 402 and a housing 403, which allows movement between the bearing 401 and the housing 403. A damping component 404 such as an 0-ring is disposed between the bearing 401 and the housing 403. In an embodiment, the damping component comprises soft material.

In alternative embodiments, the damping component may comprise corrugated sections or springs, as described above.

In yet another embodiment, a damping component is disposed between the bearings and the shaft, allowing the damping of shaft vibrations without the need for the bearings to be movable with respect to each other or with respect to the stator. Figure 5 is a cross-sectional view of a structure 500 surrounding a bearing according to an embodiment. The structure comprises a shaft 501, a bearing 502, a housing section 503, and a damping component 504 such as an 0-ring. In this embodiment, the damping component is disposed between the shaft 501 and the bearing 502. In an embodiment, the damping component comprises soft material. In alternative embodiments, the damping component may comprise corrugated sections or springs, as described above.

In yet another embodiment, the damping component may be disposed in a cartridge or similar modular component. This enables the flexible interface to be insulated from the surrounding housings by damping comprising a soft material or corrugated housing. Figure 6 is a cross sectional view of an embodiment in which the damping component is disposed within a bearing cartridge. The structure 600 comprises a shaft 601, a bearing 602, a housing 603 and a bearing cartridge 604, comprising a flexible interface or damping material 605. A bracket, flange, or a piece of the housing 603 may extend to touch the bearing cartridge 604, constraining its movement. For example, a flange may prevent the bearing cartridge from moving in the axial direction while allowing it to move in the radial direction, compressing or decompressing the damping material 605 and rubbing against the flange as it moves.

In an embodiment, the stator incorporates voids or channels where otherwise there would be an electrical conductor (e.g. copper) or an electromagnetic flux permitter (e.g. iron). Figure 7 is a cross sectional view of a stator comprising cut-outs in the stator's, 700, iron 701, 702, 703. These voids or channels are used, for example, for cooling. In an embodiment, the voids and channels can also be configured so that they allow movement between one or more motor parts, such as to allow movement of those parts with respect to other parts. Such an arrangement may provide damping between those parts.

Each of the above embodiments may be used in conjunction with any other embodiment or combination of embodiments. For example, a motor arrangement may comprise a damping component between the housing and the stator in addition to damping between the shaft and the bearing, and/or between the bearing and the housing. All combinations of damping component locations are contemplated and are within the scope of the invention.

Claims

CLAIMS: 1. An electric motor comprising an outer housing and within the outer housing a stator, a rotor having a shaft extending through the outer housing, one or more bearings for supporting the shaft, and at least one damping component disposed between the shaft and the housing, the stator and the housing, and/or integrated into the housing.
2. An electric motor according to claim 1, wherein said motor housing is formed substantially of metal, a metal alloy, or ceramic.
3. An electric motor according to claim 1 or 2, wherein the damping component comprises a silicon based material, a metal or metal alloy, or a rubber or synthetic rubber.
4. An electric motor according to claim 1 or claim 2, wherein the damping component comprises a resin.
5. An electric motor according to claim 4, wherein the resin comprises one of epoxy or a thermoplastic polyethylene or polycarbonate material.
6. An electric motor according to any preceding claim, wherein the damping component further comprises fibres with a higher thermal conductivity than a surrounding material.
7. An electric motor according to claim 6, wherein the surrounding material comprises rubber.
8. An electric motor according to claim 1 or claim 2, wherein the damping component comprises a spring component or components.
9. An electric motor according to claim 8, wherein the damping component comprises one or more corrugated spring components disposed between the stator and the outer housing.
10. An electric motor according to claim 9, wherein the corrugated spring components are integrally formed with said outer housing or with said stator.
11. An electric motor according to claim 4, wherein a single resin layer provides damping and insulation.
12. An electric motor according to claim 11, wherein the single resin layer has a thickness greater than 0.8 mm.
13. An electric motor according to any one of the preceding claims, wherein the outer housing comprises at least two axially discrete housing components and said damping component is provided between these two housing components.
14. An electric motor according to claim 13, wherein said axially spaced housing components are in a telescopically overlapping configuration or comprises substantially abutting flanges.
15. An electric motor according to any one of claims 1 to 11, wherein the damping component is disposed between the one or more bearings and the shaft.
16. An electric motor according to any one of claims 1 to 11, wherein the damping component is disposed between the one or more bearings and the outer housing.
17. An electric motor according to claim 15 or 16, wherein said damping component comprises one or more 0-rings.
18. An electric motor according to any one of claims 15 to 17, wherein the damping component and the or at least one of the bearings form part of a bearing cartridge that is secured between the outer housing and the shaft.
19. An electric motor according to claim 18, further configured such that it is free to move in one or more directions and in doing so acts to compressor decompress a damping material.
20. An electric motor according to claim 19, wherein the damping material is one of: epoxy or a thermoplastic polyethylene or polycarbonate material, a silicon based material, a metal or metal alloy, or a rubber or synthetic rubber.
21. An electric motor according to any of claims 3 to 11, wherein said damping component substantially fills an annular space between the stator and the outer housing.
22. An electric motor according to any preceding claim, wherein the stator comprises one or more voids or channels.
23. An electric motor according to claim 22, configured to use the one or more voids of channels for cooling the motor.
24. An electric motor according to claim 22 or claim 23, wherein the one or more channels or voids is configured to provide damping.