GB2047010A

GB2047010A - Collectorless external-rotor direct-current motor

Info

Publication number: GB2047010A
Application number: GB8007516A
Authority: GB
Original assignee: Elektrobau Mulfingen and Co EBM GmbH
Current assignee: Elektrobau Mulfingen and Co EBM GmbH
Priority date: 1979-03-27
Filing date: 1980-03-05
Publication date: 1980-11-19
Also published as: SE8002299L; IT1154713B; DE2911922A1; NL8000420A; CH657239A5; GR74024B; IT8083320A0; FR2452819A1; GB2047010B

Abstract

The stator of the motor comprises a bundle 4 of laminations (Figure 2) with windings 5 located in openings therein, and is surrounded by a rotor bell 1 within which is a permanent magnet in the form of a plastics band 3. A sensor in the form of a Hall generator 15 is mounted upon a printed circuit board 10 which in the case shown in the lower part of the figure is outwardly- disposed on a coil end carrier part 6 and carries its components at the inner side of the board 10, or in the case shown in the upper part of the figure is inwardly disposed on the part 6 and has its components on its outer side. The generator 15 is in register with a coil gap and is adjustable laterally or centrically with said gap. <IMAGE>

Description

SPECIFICATION A collectorless external-rotor direct-current motor The invention relates to a collectorless external-rotor direct-current motor operating with an electromagnetic alternating field and the rotor of which is equipped with at least one permanent magnet, and means to sense voltage which is induced in its windings.

It is generally known that, by using a sensor, such as a Hall generator, a direct-current motor can be constructed so as to be collectorless. In this connection, reference may be had to the various publications, for example German Gebrauchsmusters Nos.

76 09 071, 73 10 863 and 75 16 814, and German published patent applications (Offenlegungsschriften) Nos. 25 14 067, 25 32 551 and 2535411.

An object of the invention is to provide an inexpensive, space-saving, collectorless externalrotor direct-current motor which runs smoothly, especially upon being switched off, which is not excessively stressed, which has a good long-term constancy (i.e. its operating characteristics vary very little with time), which does not need any special transistors for uncoupling, which is usable for all voltage ranges, and the rotative speed of which can be regulated over a specific range with simple regulating means.

With this object in view, the present invention provides a collectorless external-rotor direct-current motor operating with an electromagnetic alternating field and the rotor of which is equipped with at least one permanent magnet, and means to sense voltage induced in its windings, characterised in that at least one Hall generator is arranged in register with a pole-separation gap so as to be adjustable laterally or centrically with regard to the gap and is lockable relative thereto.

In an advantageous embodiment of the invention the Hall generator is fastened to a plate which otherwise serves only to carry a printed circuit of the generator. In this respect, it is particularly material to the invention that use be made of a retaining plate of a specific construction which makes it possible to accommodate the Hall generator with its various leads and/or conductors in a minimum of space.

Preferably use is made of a flux conducting piece in order to improve the effect of the Hall generator.

Of particular significance for the invention is the manner of fastening the flexible magnet, and the quality thereof. This magnet advantageously has on at least one side, and preferably on both sides, a metal plate or the like which serves to intensify the magnetic field.

It is preferable for the stator to have a distributed force line concentration, i.e. the transition should not occur suddenly, because if the concentration of the force lines occurs too suddenly the motor may, for example, run unevenly.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which Figure 1 is a sectional side elevation of a preferred embodiment of the motor of the invention; Figure 2 is an elevation of one of a plurality of laminations which form the stator of the motor of Figure 1; Figure 3a is a plan view of a retaining member forming part of the motor of Figure 1 and serving to mount a Hall generator therein; Figure 3b is a front view of the retaining member of Figure 3a; Figure is an underneath plan of the retaining member of Figure 3a; Figure 3d is a rear view of the retaining member of Figure 3a; Figure 3e is a section taken on the line C-D of Figure 36; Figure 3f is a section taken on the line A-B of Figure 3b;; Figure 3g is a section taken on the line E-F of Figure 3b; and Figure 3b is a diagrammatic section taken on the line G-H of Figure 3c.

Figure 4 is a circuit diagram of the motor of Figure 1; Figure 5a is an enlarged detached detail, being a rear elevation showing the arrangement of the Hall generator in the motor; Figure 5b is a diagrammatic sectional side view corresponding to Figure 5a; Figure 6 is a sectional side elevation illustrating a modified embodiment of rotor suitable for the motor in accordance with the invention; and Figure 7 is a side elevation of a complete stator which with the rotor of Figure 6 forms a motor is accordance with the invention.

The illustrated collectorless direct-current external-rotor motor can be used as a separate driving motor for a piece of apparatus, but is preferably constructed as an integrated motor, for instance in an axial fan or like piece of equipment. It is designed to have a constant inductance B in the region of its poles and with narrow pole clearances (e.g. from 10 to 20 ).

The external-rotor motor, as shown in Figure 1, comprises a rotor bell 1 having a pressed-in shaft 2.

The rotor bell 1 is made of a mildly-magnetic material or from die-cast aluminium, or aluminium alloy and serves to provide magnetic reflux for an internal magnet, in the form of a strip-like plastics magnet 3 inserted into and fitting snugly within the rotor bell 1. This plastics magnet strip 3 can be fixed with adhesive (not shown) to the inside wall of the rotor bell 1. Associated with the plastics magnetic strip 3 is a dynamo bundle 4 of laminations, preferably without grooves, of which one is shown in Figure 2. Figure 6 shows an alternative arrangement in which the laminations are indicated at 18.

The bundle 4 of laminations may have an axial length (i.e. considered in the direction of the axis of the motor) corresponding to that of the magnet strip 3, or it may be axially shorter or longer than the strip 3, furthermore, it may be thicker than, be of the same thickness as or be of a lesser thickness than the plastics magnet strip 3.

After machining of the motor, more especially to achieve the necessary air gap between the magnet strip 3 and the motor's stator, the magnet strip 3 is magnetised diametrically or radially in accordance with the number of poles and the desired characteristics ofthe motor. In effecting this magnetisation, a fixed pole slope should be taken into consideration, for the purposes of effective start-up of the motor.

The magnetisatiion may be effected, according to the desired motor characteristics, for instance sinusoidally, trapezoidally, of with sharp impulses. The rotor may be laminated with dynamo sheet iron, and the bell may be made from die cast aluminium or aluminium alloy.

Because the dynamo bundle of laminations provides improved magnetic flux in comparison with mildly-magnetic material, improvement in efficiency and more economic production is achieved. Hall generator 15 gets its signal from the magnet which is magnetized in the rotor. This signal may also come from a separate magnet which is accurately posi tidned, being, for instance, fastened on the shaft of the motor or as an extension of the existing magnet.- Moreover it is advantageous if the usual transistors or thyristors of the Hall generator, on its printed circuit board are located in the motor housing or into the fan housing for better heat dissipation.

The arrangement of the specific printed circuit board on the motor may be such that the components are mounted on the outer side, or they may be mounted on the inner side.

The rotor bell 1 may also have a corresponding or appropriate magnetic ring made from strongly-magnetic material. The plastics magnet 3 may be in the form of an injection-moulded mould made, for example from Alnico (i.e. an aluminium/nickel/cobalt alloy), barium ferrite and so on, from isotropes, anisotropes and so on. The rotor may, for example, thus, be designed as a radially-magnetised, permanent part.

The stator consists of individually-punched and stacked dynamolaminations. The form of the iron punching forming each lamination may correspond.

to what is shown in Figure 2, having pronounced stamped-out poles. The pole tips may be opposedly flattened (seex -x in Figure 2). In this way one obtains a preferential position and the Hall generator 15 can be situated in the centre of the pole, without staggering of its corresponding angle. The section shape may have various geometrical configurations.

The Hall generator 15may also be fastened centrally or laterally to a non-conductive strip or cleat 16. This strip or cleat 16, with the appropriate wiring, is then position in register with the gap or introduced into the gap (i.e. the pole separation gap) and fastened from outside (e.g. to the printed circuit board 10). The strip or cleat 16 serves as a flux conducting piece, and, of course, is arranged laterally relative to the magnet 3.

Each copper winding 5 is located into the respective opening in appropriately the bundle laminations, being electrically insulated therefrom.

A coil end carrier 6 comprises tubes or sleeves which have flanges abutting the end faces ofthe coils and which are preferably injection moulded with the flanges, which serve to provide operating insulation, in a single operation, from highly heatresisting thermoplastics material. For accommodating bearings 7, a stator bush 8 is a press fit in an inner bore through the bundle of laminations.

At the rotor side, in orderto protect the winding and to prevent electrical leakage or arcing, a coil end protector 9 is pressed onto the corresponding part of the tubular coil end support 6 and is held thereon by the material of one or the other of the parts being upset or pryed over or by being flanged At the stator side (i.e. the open rotor side), a printed circuit board 10, equipped with appropriate components, is similarly pressed onto the respective coil-end support part. The starts and ends of the leads of the coils are soldered at respective locations on said circuit board 10 which also has the usual supply connection cable (not shown) connected thereto.

Magnetic force lines emanating from the rotor magnet 3 are sensed by the Hall generator 15, of which more than one may be provided. Each Hall generator 15, depending on the sensed magnetic flux, selects which of the further components, pm-.

vided on the printed circuit board 10.

Although sensors in the form of Hall generators are preferably used, other forms of sensor such as magnetic switches, induction coils, filed plates, magnetic diodes, Hall - IC's, or the like, may be used.

Such a sensor has a control part, which produces, on the basis of the magnetic flux and change in direction thereof, a control signal which controls the reversal of current as a function of the rotor position.

The sensor (e.g. the Hall generator 15) is fastened, for example, by means of a retaining plate 17 (the details of which are shown in Figures 3a to 3h) to the printed circuit board 10. The retaining plate 17, in which the sensor is mounted, is of thermoplastics material and has two moulded-on pegs for rivetting to the printed circuit board 10.

Inserted into the retaining plate 17 is a magnetically-conductive yoke which concentrates the force lines and directs the same perpendicularly to the surface to the Hall platelet.

Four connections of the Hall generator 15 are located in the retaining plate 17 on soldering pins.

These pins are in turn soldered at their free ends onto respective tracks of the printed circuit board 10.

The basic circuitry is illustrated in Figure 4. The illustrated components, mounted on the printed circuit boards 10, cause a specific power loss which is converted into heat. This heat can be conducted away by the printed -circuit board 10 itself, especially if use is made of a board, such as a multiwire board, having good heat conductivity. Then, with the same components, better motor performance can be achieved. Moreover, the printed circuit board 10 may be formed into a initary structure with the components mounted thereon, by means of cast synthetic resin, or application of insulation lacquer or varnish.

The embodiments described here can analogously also be used for an internal rotor motor.

Furthemore, the use of a Hall generator giving a digital output is essential to the invention; this ensures that no flux conductor piece is needed. The Hall generator is soldered, without a retaining plate, directly (like any other component) at a specific location of the printed circuit board. As a result of the special characteristics of the Hall generator with digital output, greater tolerances of the positioning can be permitted in the axial and radial directions as well as in the angular position.

Thus, more rational production is possible.

Moreover the advantage is obtained that one can achieve one-hundred percent initial start-up, even with only a single Hall generator.

Shown in Figure 7 is a complete stator, as would be fitted into the rotor bell 1 of Figure 6 to form a second embodiment of the motor of the invention.

The printed circuit board 10 with its soldering points 19, provided by copper tracks, can be seen, as also can the electronic components 21 as well as the Hall generator 15 having a digital output and lying opposite from slot or gap 22 which provides pole separation. Copper windings 20 of the coils are also perceptible.

Referring back to Figure 1, in the drawing, note is to be taken of the fact that the printed circuit board in the case of the lower part of the figure lies outwardly and the electronic components lie inwardly, in contrast to what is shown in the upper region of the figure, so that this figure naturally shows two alternative possibilities.

The same applies to what is shown in Figure 7. In Figure 6 a rotor bush, which is a press fit into a hole in the ball 1 has been designated by the numeral 23.

Claims

1. A collectorless external-rotor direct-current motor operating with an electromagnetic alternating field and the rotor of which is equipped with at least one permanent magnet, and means to sense voltage induced in its windings, characterised in that at least one Hall generator is arranged in register with a pole-separation gap so as to be adjustable laterally or centrically with regard to the gap and is lockable relative thereto.

2. A collectorless external-rotor direct-current motor as claimed in claim 1 characterised in that a flux conducting piece is associated with the Hall generator, which flux conducting piece is arranged laterally relative to a permanent plastics magnet.

3. A collectorless external-rotor direct-current motor as claimed in claim 1 or 2 characterised in that the Hall generator is fastened to a printed circuit board carrying a printed circuit of the generator.

4. A collectorless external-rotor direct-current motor as claimed in claim 1,2 or 3 characterised in that a retaining plate is fastened to the printed circuit board and carries the Hall generator.

5. A collectorless external-rotor direct-current motor as claimed in any preceding claim, characterised in that the rotor comprises a bell designed as a reflux elementfcrthe internal magnets.

6. A collectorless external-rotor direct-current motor as claimed in claim 5 characterised in that the inner surface of the rotor bell, is lined, at least over the width of the stator, with a flexible plastics magnet which constitutes the permanent magnet.

7. A collectorless external-rotor direct-current motor as claimed in claim 6 characterised in that the plastics magnet is magnetised only after fixing to the inside wall of the rotor.

8. A collectorless external-rotor direct-current motor as claimed in any preceding claim, characterised in that its stator comprises a lamination bundle providing pole tips which are opposedly flattened.

9. A collectorless external-rotor direct-current motor as claimed in any preceding claim, characterised in that the lamination shape is of symmetrical geometrical configuration.

10. A collectorless external-rotor direct-current motor as claimed in any preceding claim characterised in that the Hall generator is arranged in the pole centre.

11. A collectorless external-rotor direct-current motor as claimed in claim 8, characterised in that the pole tips have a radial spacing with regard to one another.

12. A collectorless external-rotor direct-current motor as claimed characterised in that part of the material of the stator is removed in order to concentrate the magnetic field into an effective region.

13. A collectorless external-rotor direct-current motor as claimed in any preceding claim, characterised in that the Hall generator is secured to a non-conductive strip or cleat whereby it is arranged in the slot.

14. A collectorless external-rotor direct-current motor as claimed in any preceding claim, characterised by at least one metal ring, associated on one side with the magnet, for concentrating the magnet flux.

15. A collectorless external-rotor direct-current motor as claimed in any preceding claim, characterised in that the Hall generator is replaced on alternative sensor, such as magnetic switches, induction coils, filed plates and magnetic diodes.

16. A collectorless external-rotor direct-current motor as claimed in any preceding claim, characterised in that the rotor is formed from dynamo sheet.

17. A collectorless external-rotor direct-current motor as claimed in any preceding claim, characterised in that the rotor has arranged therein at least one magnet serving as signal transmitter for the Hall generator.

18. A collectorless external-rotor direct-current motor as claimed in claim 17, characterised in that the magnet is fastened on the shaft or in extension of the first-mentioned magnet.

19. A collectorless external-rotor direct-current motor as claimed in any preceding claim, charaterised in that components of the circuitry of the generator are embedded on the printed circuit board, for efficient heat abstraction.

20. A collectorless external-rotor direct-current motor as claimed in any preceding claim, characterised in that a dynamo bundle of laminations butts against the permanent magnet.

21. A collectorless external-rotor direct-current motor as claimed in claim 20, characterised in that the dynamo bundle of laminations has a lesser length (considered in the direction of the axis of the motor) than the plastics magnet.

22. A collectorless external-rotor direct-current motor substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 5 or in Figures 6 and 7 of the accompanying drawings.