GB2362268A - Stator winding mounting/windage reduction in an electric machine - Google Patents

Abstract

An electrical machine comprises a stator (40) having a plurality of poles (40a - d), a rotor (50) and shaped fillers located between adjacent pole tips so that the fillers and the pole tips together define a substantially continuous circular cylindrical surface. This reduces the losses resulting from drag (windage) and the noise of the machine. Each stator pole (40a - d) carries a bobbin (54a - d) with windings (41a - d) for the pole. Each filler can form an integral part of a bobbin and the bobbins can lock together by way of the co-operating parts (55a, 55b). Alternatively, fillers 101 -104 can be integrally formed on base 110, stator supports 106 - 109 being included.

Description

2362268 Electrical Machine This invention relates to an electrical machine

such as an electrical motor or generator.

Electrical machines are widely used for many different applications and are commonly used in domestic appliances. For example, in a vacuum cleaner a motor is used to drive a fan which causes dirty air to be sucked through a dirty air inlet. The dirty air passes through some form of separation device such as a bag or cyclonic separator which separates dirt and dust from the air flow, and finally the air is exhausted from an air outlet or recycled in some way.

Electrical machines comprise a stator part and a rotor part, each part having a number of poles. Electrical wires are wound around poles of the stator and/or the rotor to form windings. In a motor, current flows through the windings to cause relative movement between the stator and the rotor which is used to drive a load connected to an output drive shaft of the rotor. In a generator, relative movement between the rotor and stator causes a voltage to be generated across the windings, and for a current to flow through a load connected to the windings.

Switched reluctance machines have become increasingly popular in recent years. In a switched re- ictance motor a stator has a set of poles which are sequentially energised to drag a rotor in to line with the energised pair of poles. By rapidly switching between different pairs of poles, it is possible to cause the rotor to rotate at high speed. Switched reluctance machines have an advantage in that they do not use carbon brushes which need to be replaced periodically.

It is desirable to provide a machine that offers high efficiency. Some of the losses in an electrical machine are: electrical resistance of the windings, which results in heat being generated at the windings; friction in the bearings of the shaft, and air resistance, or windage, as the rotor turns.

2 The present invention seeks to provide a machine which offers improved efficiency.

A first aspect of the invention provides an electrical machine comprising a stator having a plurality of poles, a rotor and shaped fillers located between adjacent pole tips so that the fillers and the pole tips together define a substantially continuous circular cylindrical surface.

Use of the fillers to define a substantially continuous surface has the advantage of reducing losses which result from air resistance or drag, also known as windage. This allows the machine to operate with greater efficiency. It also reduces the level of noise and vibration generated by the machine.

Preferably, the fillers are provided as part of bobbins which carry the windings for the stator poles. The use of bobbins has advantages over forming pole windings 'in situ' as it eases assembly and improves packing density for the windings.

Preferably, the fillers serve a function of interlocking adjacent bobbins together so that they remain in place on the stator. The interlocking can be achieved by forming a hook and aperture, or some other co-operating parts, on one of the fillers and an adjacent bobbin. Alternatively, the fillers can be formed as a single or multiple parts with a connecting structure which serves to support the set of fillers in the respective positions in which they are required in the machine. When used with stator pole bobbins, this arrangement also has the advantage of retaining the bobbins in place on the stator.

The stator can surround the rotor, so that the fillers and the pole tips together define a substantially continuous circular cylindrical surface which surrounds the rotor or the rotor can surround the stator, so that the fillers and pole tips together define a substantially continuous circular cylindrical surface around which the rotor can operate.

3 A second aspect of the invention provides an electrical machine comprising a stator having a plurality of poles and a rotor, each stator pole having a bobbin which carries windings for the pole, the bobbin fitting on the pole, and wherein each bobbin has a part for co-operating with another bobbin so as to retain the bobbins on the poles.

The invention is particularly applicable to switched reluctance machines.

While the following embodiments describe the invention as applied to motors which are used to drive a fan in a vacuum cleaner, it will be appreciated that the invention can be applied to both motors and generators, for any type of application, and is not limited to vacuum cleaners or the field of domestic appliances.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figures 1A - 1C show a vacuum cleaner in which the motor can be used; Figure 2 is a section through the central axis of a motor and fan unit; Figure 3 is a section through the motor along the line X-X' of Figure 2; Figures 4A and 4B show the assembly of the bobbins on the motor stator; Figures 5A - 5C show the bobbins in more detail; Figure 5D show an alternative form of the bobbins; Figures 6A - 6D show alternative embodiments of the motor.

Figures IA to IC show one example of a vacuum cleaner 10 in which the motor may be used. Dirty air can be drawn into the cleaner via a cleaner head 12, if on-the-floor 4 cleaning is required, or via a hose and wand assembly 11, if above-the- floor or manual cleaning is required. Dirty air is drawn into the cleaner along path A or B. The dirty air is carried along path C before entering a separator 15 which serves to separate dirt and dust from the dirty air (path D). The separator can be a cyclonic separator, as shown here, or some other separator, such as a bag. Cleaned air leaves the separator along paths E, F before entering (G) a fan and motor housing 20 at the base of the cleaner. The fan and motor housing 20 supports a fan 24 and a motor 25 to drive the fan. In use, the motor 25 rotates the fan at a very high speed (of around 50,000rpm) to draw air along the paths A - H through the cleaner. A pre- motor filter 22 is usually placed in the airflow path before the fan to filter any fine dust particles which were not separated by separator 15. A post-motor filter 28 is usually placed in the air flow path after the motor 25 to filter any carbon particles which enter the airflow from the brushes on the motor 25. In a brushless motor of the kind described below, the post-motor filter is not required. Alternatively, where there is insufficient space for the pre-motor filter 22, the pre-motor filter 22 can be removed and the post motor filter 28 can perform the job of the pre-motor filter 22. Air is exhausted from the cleaner (path H) via a suitable outlet.

Figure 2 shows the fan 24 and motor 25 used in the cleaner of Figures 1A IC. A housing 35 supports a first set of bearings 44. The bearings 44 support a central shaft 42 which is rotatable about an axis 46. An impeller 30 is coaxially mounted on the shaft 42 at the upstream end of the shaft 42. Blades extend radially outwardly from the main body of the impeller towards the housing 35 within a channel 48 and, in use, serve to draw air into the housing 35 in the direction 55 shown. Motor 25 is mounted downstream of fan 24. The main components of the motor are stator 40 and rotor 50.

The stator 40 is secured to the downstream side of housing 35. Rotor 50 is mounted on the shaft 42 and can rotate within the stator 40. A small airgap exists between the outer surface of the rotor and the inner surface of the stator to allow the rotor to move while minimising losses. The outer surface of the rotor 50 is not of constant radius; the leading edge of the rotor 50 is of a smaller radius than the trailing edge to provide a tapered air gap which is less noisy than a gap which is uniform across its surface.

An end cover 38 is secured to the downstream face of the stator 40 and supports the second set of bearings 43. A control system (not shown) is also provided. In use, the control system sequentially energises the stator poles to cause the rotor 40 and hence the impeller 30 to rotate about axis 46, drawing air into the housing 35 and exhausting air in direction 56, across the outside of the stator 40, or in direction 57, through the core of the stator 40 and across the rotor 50. This helps to cool the motor. The housing 35 and end cover 38 are made of metal, such as aluminium, and assist in the cooling of the motor. Other materials could be used, such as a suitable engineering polymer.

The motor also comprises an encoding system for allowing the control system to detect the position of the rotor and therefore decide when to energise the phases of the motor. Encoding systems are well known and will not be described further. An output from the encoding system allows the control system to determine the position of the rotor 40 and to switch the windings 41 a - 4 1 d on or off to control movement of the rotor.

Figure 3 is a section through the motor along X - X' of Figure 2. Motor 25 is a four pole, two-phase switched reluctance motor. It comprises a stator 40 having four salient poles 40a, 40b, 40c and 40d (only 40a and 40b are visible in Figure 2.) Each pole 40a - 40d has an associated winding 41a 41d which comprises a large number of turns (e.g. 100 turns) of an insulated electrical conductor around the pole. The electrical conductor forming the winding 41a - 41d for each pole 40a - 40d is pre wound on a respective electrically insulated bobbin 54a - 54d. The stator 40 comprises a stack of stamped thin laminations which are insulated from each other and held together as a stack by welding, key tacks or some other suitable means. The rotor 50 is solid and is also made from a stack of stamped laminations each insulated from the other and secured to the shaft 42.

The bobbins 54a - 54d can be more clearly seen in Figure 4A. Stator windings 41a to 41d are firstly wound onto their respective bobbins 54a 54d before being fitted to the stator poles 40a - 40d. Looking at bobbin 54a, it has an inner core 61 which is 6 dimensioned so as to fit around pole 40a. A flat rear face 64 of the bobbin 54a fits against the inner flat surface 67 of the stator and a pair of arms 65, 66 on bobbin 54a fit around the side faces 68, 69 of the stator 40. The bobbin 54a also has an outer flange 62 and an inner flange 63 which extend perpendicularly outward from the inner core 61 for retaining windings on the bobbin. The outer flange 62 includes a slot 70 and a post 72 (best seen on bobbin 54b) which serve to secure the two ends of the conductor used for the winding. The use of bobbins allows a more efficient and compact winding to be achieved than would be the case when winding the bobbins in situ on the stator. Figure 4B shows the bobbins assembled on the stator 40.

The two opposed bobbins 54a and 54b have a first shape while the other two bobbins 54c and 54d have a second shape. The designs are complimentary so that when fitted on the stator 40 they define a substantially cylindrical space around the rotor 44. The tips of the poles 40a to 40d are part-cylindrical in shape and the cylindrical space in which the rotor 50 operates is delimited partly by the arcuate pole tips and partly by ears' or fillers 55 of the bobbins 54a - 54d. The ears and the pole tips have the same radius of curvature.

Figures 5A - 5C show the bobbins in more detail. Figure 5A is a section through one of the first type of bobbins 54a, 54b. Figure 5B is a plan view of one of the second type of bobbins 54c, 54d, showing the face of the bobbin which faces inwardly into the rotor space, and Figure 5C is a section through one of the bobbins 54c, 54d.

Referring to Figure 5A, 'ears' or 'fillers' 55 are integrally moulded with the bobbin cheek. The fillers 55 extend arcuately outwards from the cheek of the bobbin 54 with the same radius of curvature as the pole tip. The pole is received in the aperture 59 within each bobbin. Each ear 55 has a tongue 56 which locates in a complimentary recess 57 in the cheek of one of the complimentary bobbins 54c, 54d. Bobbins 54c, 54d have a pair of recesses or apertures 57, one on each side of the bobbin. When assembled in the manner shown in Figure 4B, the ear serves the dual purpose of delimiting the rotor space and retaining the adjacent bobbin in place on the stator, since the shape of ear 55 and tongue 56 provide an outward force on the adjacent bobbin in a direction towards the outside of the stator 40 which keeps the bobbin 7 firmly in place on the stator 40. Where the motor has a different number of poles, the first and second types of bobbins are used alternately around the poles of the motor.

For example, if the poles are sequentially numbered from 1 to 8 around the stator, poles 1, 3, 5, 7 use the two-eared bobbins of the type shown in Figure 5A and poles 2, 4, 6, 8 use the two-holed bobbins of the type shown in Figures 5B and 5C.

An alternative arrangement for the bobbins 54a to 54d is shown in Figure 5D. This differs from the arrangement shown in Figures 5A - 5C in that all four bobbins 54a - 54d are of identical shape. One side of the bobbin has an ear 55 and tongue 56 and the other side of the bobbin has a complimentary mating recess 57. This alternative arrangement may provide cost savings in tooling over providing two different designs of bobbin.

In the above embodiments each pole of the stator 40 carries a bobbin 54. In alternative embodiments some of the poles do not have windings and therefore do not have a windings bobbin. Poles adjacent to the pole without the windings bobbin do carry a bobbin, and the bobbins on these adjacent poles have fillers integrally formed with them which extend towards the tip of the pole which lacks a bobbin.

Figures 6A - 6D show an alternative embodiment of the motor in which the fillers are not provided as part of the winding bobbins but as a separate part. In this embodiment the windings can be retained on bobbins, as shown in Figures 6A - 61), or the windings can be wound 'in situ' on the poles, with the poles being covered by a suitable electrically insulative material before the windings are applied to the poles.

As before, fillers 101 - 104 are provided for filling in the gap between adjacent poles so as to define a substantially continuous surface within which the rotor can operate.

Each of the fillers 101 - 104 is joined by a connecting structure 110 which supports the fillers 101 - 104 in the position in which they are needed in the motor. The connecting structure is a planar base 110 from which the fillers 101 - 104 extend perpendicularly outwardly. Supports 106 - 109 are also provided on the planar base 110. A support 106 - 109 is associated with each filler 101 - 104 and is located radially outwardly from the filler 101 - 104. Each bobbin 105 has a pair of arms for 8 embracing the stator; one arm fits over the stator and the other arm fits underneath the stator. The supports 106 - 109 have a height which is substantially equivalent to the height of the arm; this allows the assembled stator and bobbins to lie flat against the planar base 110. The bobbins 105a - 105d are standard bobbins which lack any co- operating parts to hold them together. Instead, the fillers, by virtue of the connecting structure 110, hold the bobbins in place on the poles. The full set of fillers can be provided with a connecting structure I 10 as one part, as shown in Figure 6A, or two or more connecting parts can fit alongside one another, each connecting part carrying one or more of the fillers.

In Figures 6A - 6C a single planar base 110 is provided from which the set of fillers 101 - 104 extend for a sufficient distance to provide a smooth surface surrounding the rotor and to hold the bobbins 105 in place. Figure 6D shows an alternative to this. A second planar base 115 lies on the opposite side of the stator 40' to the first planar base 110, the two planar bases 110, 115 sandwiching the stator 40'. Each of the fillers 101 - 104 comprises two portions, each portion extending outwardly from one of the bases 110, 115. In Figure 61), filler 103 is formed by part 103' which extends from base 110 and part 103 " which extends from base 115. Each planar base 110, 115 also has a set of supports 106 - 109 and 106' - 109' which serve to support the stator 40'.

When assembled, the ends of the two filler portions abut one another at some midpoint between the two bases. The filler portions 103' and 103" can be of equal height or can differ in height.

Variations to the described embodiments will be apparent to a skilled person and are intended to fall within the scope of the invention. For example, while a four pole stator, two pole rotor machine has been described, the invention can be equally applied to machines having other numbers of poles on its stator and rotor and with motors having other dimensions.

9

Claims (19)

Claims:

1. An electrical machine comprising a stator having a plurality of poles, a rotor and shaped fillers located between adjacent pole tips so that the fillers and the pole 5 tips together define a substantially continuous circular cylindrical surface.

2. A machine according to claim 1, wherein at least some of the stator poles carry a bobbin, the bobbin carrying windings for the pole, and wherein the fillers form an integral part of the bobbins.

3. A machine according to claim 2, wherein each bobbin is shaped to be fitted onto a stator pole after construction of said stator.

4. A machine according to claim 2 or 3 wherein the filler has a first part for co- operating with a second part on another bobbin so that, in use, the bobbins are secured together.

5. A machine according to claim 4 wherein the first and second parts are a hook and an aperture.

6. A machine according to any one of the preceding claims wherein the bobbin has a flange for retaining windings on the bobbin.

7. A machine according to any one of claims 2 to 6, wherein some of the bobbins have two fillers integral therewith, the fillers being located on the bobbin so as to lie, in use, on opposite sides of the pole on which the bobbin is carried.

8. A machine according to any one of claim 2 to 6, wherein each bobbin has one filler formed integrally with the bobbin and located on the bobbin so as to lie, in use, on one side of the pole on which the bobbin is carried.

9. A machine according to claim I wherein a set of the fillers are formed as a single part with a connecting structure which serves to support the set of fillers in the respective positions in which they are required in the machine.

10. A machine according to claim 9 wherein each stator pole carries a bobbin, the bobbin carrying windings for the pole, and the set of fillers serve to retain the bobbins on the stator poles.

11. A machine as claimed in any one of the preceding claims and having four 10 stator poles.

12. A machine according to any one of the preceding claims wherein the stator surrounds the rotor, the fillers and the pole tips together defining a substantially continuous circular cylindrical surface which surrounds the rotor. 15

13. A machine according to any one of claims 1 to 11 wherein the rotor surrounds the stator.

14. A machine according to any one of the preceding claims which operates in 20 excess of 20,000rpm.

15. A machine according to any one of the preceding claims in the form of a motor.

16. A machine according to claim 15 in the form of a switched reluctance motor.

17. A machine according to any one of claims 1 to 14 in the form of a generator.

18. An electrical machine comprising a stator having a plurality of poles and a rotor, each stator pole having a bobbin which carries windings for the pole, the bobbin fitting on the pole, and wherein each bobbin has a part for co-operating with another bobbin so as to retain the bobbins on the poles.

19. A machine substantially as described herein with reference to the accompanying drawings.