This invention relates in general to a rotary electric machine comprising a stator with permanent magnets and a rotor or armature having an iron core and a winding, whereby the permanent magnets have a mu ber of magnetic poles being different from the number of coils in the armature winding. More particularly the invention is directed to the design of the armature winding.

Electic machines being of interest in this connection can be both DC machines and AC machines. Besides, the prin¬ ciples and solutions to be explained in the following description, are essentially useful in motors as well as in generators. In electric machines according to traditional design throughout a long number of years, the armature winding is located in grooves in the armature iron core. One coil of the winding encloses one or more grooves, where also a coil side of another coil is located. These grooves in the armature core reduce the iron area surrounded by each coil. It is an object of the invention to improve these relation- ships. Moreover, it is an object of the invention to provide an armature design that to a substantial degree improves the cooling of the machine during operation.

According to the invention the rotary electric machine has novel and specific features consisting in the first place in that the armature winding comprises a number of discrete coils each provided with its iron core and so arranged that between the coils there exist generally radial air passages which contribute to the cooling of the machine during operation. The combination of features stated here is considered to be novel and distinguished from relevant prior art, such as e.g. represented by EP 91.125, GB 1.299.057, GB 2.125.635 and perhaps in particular US 4.437.029.

Discrete coils as they are incorporated in the com- bination according to the invention, result in an electric machine being convenient in production, and the coil design is very advantageous with respect to cooling and efficiency.

The latter factor is due to the fact that the winding will be short in relation to the iron area enclosed thereby. The iron area being surrounded by the coil has no grooves and will be comparatively much larger than in traditional machines.

An additional advantage is obtained in that it will be possible to maintain a spacing between the coils. Thus the insulation between the coils will be simple and the cooling improved, since the spaces or air gaps formed between the coils, will have an effect like a centrifugal fan and there¬ by give an efficient cooling.

It is known per se in electric machines to employ a number of coils being different from the number of poles in the stator. In the electric machine described here, there can be provided a number of magnetic poles in the stator, being one higher or smaller than the number of coils in the armature winding. The number of magnetic poles in practice will normally correspond to a number of permanent magnets having the suitable magnetizing direction and orientation. In the following description the invention will be explained more closely with reference to the drawings, in which:

Fig. 1 shows an axial section through one embodiment of a DC machine (axial machine) , based upon the inven- tion, fig. 2 schematically shows the armature and coil system in the machine of fig. 1, fig. 3 in a corresponding manner and schematically shows the magnetic poles in the machine of fig. 1, fig. 4 in axial section shows another embodiment of a machine according to the invention, i.e. a radial machine, and fig. 5 schematically shows the coil system and the mag¬ netic poles in the machine of fig. 4. The machine shown in fig. 1 comprises a stator housing or casing 2 with bearings for an axle l which carries an armature. Supported by a central part of the armature there is shown an iron core 10 with a coil 11, whereby fig. 2 shows that the winding arrangement comprises a number of

separate coils 11A, 11B, lie and so forth, i.e. a total number of coils equal to eleven. The associated iron cores in fig. 2 are denoted 10A, 10B, IOC and so forth, respecti¬ vely. The coils 11 are wound about iron cores 10 being without the conventional grooves, and the cores can be made of common machine sheet or preferably according to the invention by employing iron powder. Powder cores are very advantageous in this connection, because the magnetic field directions do not lie in one and the same plane in the machine according to the invention.

As will be seen in particular from fig. 2 the coils 11A-C with associated iron cores 10A-C and so forth, consti¬ tute separate or discrete coils being so arranged that there are formed radial air passages between the coils, as illu- strated with arrows 19A and 19B between the coils 11A and 11B as well as 11B and lie, respectively. With such radial air passages the rotating armature will have an effect similar to a centrifugal fan, so that the air flowing through will result in a very efficient cooling of both the armature and the surrounding structure. It is expedient in this connection that the stator housing 2 has suitable venting openings (not shown) for the circulation of air to and from the surroundings.

In stator 2 there are mounted permanent magnets as shown at 3A and 3B in fig. 1, namely at either side of the armature iron core 10, the intermediate air gaps being denoted 6A and 6B, respectively, in fig. 1. The magnetizing direction in the two permanent magnets is indicated with arrows in these. In a more or less conventional manner there can be provided an iron circuit in order that the magnetic field can be closed through the stator.

Fig. 3 illustrates how magnetic poles corresponding to a complete set of permanent magnets, can be provided, i.e. in the form of a number of magnetic poles 13A, 13B and 13C and so forth with alternate polarity (N resp. S) as required for a correct function of the electric machine. According to fig. 3 the number of magnetic poles is equal to 10, which is one less than the number of coils 11A, 11B, 11C and so forth, as illustrated in fig. 2. Thus it is a possible

embodiment according to the invention to have a number of magnetic poles being one higher or smaller than the number of coils in the armature winding. Then there will be a favourable number of mutual angular positions between coils and poles, giving the same field pattern between the coils and the poles, and thereby the same reluctance torque. In this way large variations in the reluctance torque are avoided. Accordingly a more smooth rotation will be ob¬ tained. The embodiment of the electric machine shown in fig. 4 and fig. 5 is a DC machine based on the same principles as the machine according to figs. 1, 2 and 3. In fig. 4 there is shown a stator at 22 with bearings for an armature having an axle 21 and discrete armature cores 30 with associated cores 31. There is here the question of a radial machine, where the air gap being indicated at 26, is facing radially. The stator permanent magnets are indicated at 23, with asso¬ ciated pole pieces 24. Moreover fig. 4 shows a commutator with a supporting member 35 for segments and a cooperating brush 25, quite in anology to corresponding elements 15 and

5 in fig. 1, but with a different position.

As will be seen from fig. 5 there is also in the machine of fig. 4, provided a number of discrete coils 31A, 31B and so forth, with associated cores 30A, 30B and so forth. Between adjacent coils there is also here provided for air passages, one air passage being indicated with the arrow 39A between coils 31A and 3IB. The armature according to the embodiment of fig. 5 has altogether 11 cores, which means that the number of magnetic poles in the stator should be either ten or twelve, in order to obtain an optimum of the reluctance relationship. The stator magnet system is also shown schematically in fig. 5, wherein a permanent magnet 23A with associated pole piece 24A are indicated. In the case of a corresponding three-phase machine, the number of coils should be able to be divided by three. Thus it will be suitable to employ e.g. nine coils and eight or ten magnetic poles.

In certain respects the embodiment of figs. 4 and 5 involve more practical design details than the embodiment of

figs, l, 2 and 3, because, inter alia, there will be more space for the permanent magnets and these will be cheaper. With substantial advantage the armature cores 30 in this embodiment can be made as powder cores. The commutator design in the machine described here, can be mainly the same in the two embodiments referred to, and the particular commutator design described in Norwegian patent application No. 96.3687 can be emplόyd with advan¬ tage.