Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/01487
A machine and a method therefor
TECHNICAL FIELD
The present invention relates to a rotating electric machine comprising a
stationary part, stator, and a rotatory part, rotor, which is fixedly
journalled in
relation to the stator. More precisely, the invention relates to a rotating
electric
machine which exhibits a stator, the internal limiting surface of which
deviates
from the circular cylindrical surface. The rotating electric machine is
intended
to be manufactured for a plurality of power ranges and for both low voltage
and high voltage. Preferably, the machine is intended to be connected to a
power network and, in particular, the machine is intended to be utilized for
large powers and high voltages. In the following text, the term rotating
electric
machine means such a rotating electric machine which transforms electrical
energy into mechanical energy and vice versa. Thus, the rotating electric
machine may be a motor as well as a generator.
BACKGROUND ART
2 0 The majority of known rotating electric machines comprise a cylindrical
rotor
which rotates in a stator with a cylindrical inside. To obtain a considerable
torque, a rotor with a large diameter is chosen and to obtain a greater
acceleration, a longer rotor with a smaller diameter is chosen. The speed of
rotation and the strength in the material at the outer layer of the rotor
often
2 5 limit the diameter of the rotor. The reason for the cylindrical shape of
the
stator is primarily that the manufacture of an associated stator is so much
simpler if it is designed cylindrically. The fact that the rotor rotates
implies
that only rotationally symmetrical shapes are conceivable for the inside of
the
stator. Likewise, only poles which touch one and the same conceived cylinder,
3 0 housed in the stator, are possible for the rotor. The space between the
inside of
the stator and the mentioned cylinder housed therein is designated air gap.
CA 02342191 2001-02-27
WO 00/13292
PC1'/SE99/01487
2
The typical appearance of an ordinary rotating electric machine is based on
historical reasons. The rotor and the stator are usually manufactured
separately. To be able afterwards to join together the two bodies and obtain
an
even air gap, only two alternative shapes are available: cylindrical or
conical.
A design according to the conical shape has several disadvantages in relation
to the cylindrical shape and has not found any commercial use other than as a
brake motor. The currently most commonly used type of a rotating electric
machine is, therefore, the cylindrical one. Today's winding technology implies
that winding coils are placed in slots in the stator or the rotor. When
manufacturing a motor for high voltage, the coils are first wound onto
fixtures, whereupon they are provided with an insulation. The coils are often
subsequently treated in an autoclave for driving out air bubbles and for
curing
the insulation. The thus "finished" coils are pressed down into the slots and
secured by wedges. Finally, the coil ends are jointed to each other to form
complete windings.
In accordance with established production engineering for large rotating
electric machines, the stator core, and often also the rotor, are composed of
2 0 laminated steel sheet. The laminated sheets, which may be magnetically
oriented, are stacked in the axial direction to reduce losses caused by eddy
currents. To pile up a stator for such a rotating electric machine thus
comprises
building up the stator on edge. Each layer consists of a plurality of punched-
out sheets, which constitute part of a circular segment and which together
2 5 form an axial layer of a hollow cylinder. The sheets contain punched-out
portions which, when the stator is completed, form slots to receive the
winding. Between the slots, teeth are formed, the tip portions of which
constitute the inner limiting surface of the stator.
3 0 However, an evaluation of Maxwell's equations shows that shapes of the
rotor
and the stator which deviate from the cylindrical shape could entail a more
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/01487
3
efficient utilization of the induced forces. A rotating electric machine, the
rotor
of which is rounded at the short ends and the stator of which is drawn down
over the rounded portions of the rotor could thus result in a rotating
electric
machine with higher efficiency. From what is stated above it is realized that
this would also entail a completely new approach and certainly a completely
new mode of working for manufacturing a rotating electric machine.
A so-called "Spherical motor" is described in the specialist literature and in
certain patent documents. The expression indicates that it would relate to a
motor, the rotor of which has a spherical shape and rotates around a shaft.
However, instead it is a question of an operating device for an industrial
robot
or the like, where it is desired to provide a movement in three degrees of
freedom around one and the same point. Such an operating device is described
in patent document US 5,410,232. In the operating device shown, the shaft
fixed to the rotor is not primarily intended to rotate but rather intended to
be
moved in a controlled manner such that it "points" in different directions.
Another operating device of this kind is described in patent document US
5,413,010. The task of the shown motors is thus not primarily to rotate but to
constitute an operating device which directs an operating arm in different
2 0 directions. In the examples shown, it is thus not a question of a rotating
electric machine, where the rotor rotates with one degree of freedom, but a
motor which, in a controlled manner, may rotate its shaft in different
directions around a common point.
2 5 Additional examples of a so-called "Spherical motor" are disclosed in
patent
documents US 4,739,241 and US 4,661,737. In these cases, it is a question of a
motor, known per se, with a rotating shaft which is fixed to a suspension
system. The suspension permits the rotary shaft to be rotated, in a controlled
manner, in various directions around a centre.
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/01487
4
Another example of a rotating motor, the rotor of which deviates from the
circular-cylindrical shape are pump motors. In these applications, such a
rotor
is often almost spherical. tJne half houses an impeller which implements
kinetic energy to the liquid passing through. The other half contains the
rotor
itself, which is brought to rotate by magnetic forces from a similarly
hemispherical stator. The magnetic field between the rotor and the stator is
unbalanced, which results in unwanted axial forces acting on the axle bearing.
Usually, a rotor for such a pump motor does not rotate around a stationary
shaft, but instead the rotor is journalled on a ball, which eliminates a shaft
bearing which has to be sealed and which allows the rotor to "wag" to a
certain
extent around a centre. Examples of a pump motor of the kind described are
shown, for example, in patent documents US 4,580,335 and in US 4,352,646.
A rotating electric machine with a rotor in the form of a thick slice cut out
from
a sphere is previously known from an article in Electrical Times, 9 June 1960,
"Design of Spherical Motors", by E. R. Laithwaite. The motor discussed in the
article has an associated stator which, with an air gap of even thickness, is
attached to the rotor. The stator is made from radially arranged plates with
punched-out pockets, which form slots for the stator winding. The stator is
2 0 arranged rotatable around an axis which perpendicularly intersects the
rotor
shaft, such that parts of the stator may be turned outside the rotor. The
stator
winding is angled in relation to a plane intersecting its axis. By turning the
stator, the induction forces are reduced and the rotor and stator windings are
angled in relation to each other. The task of the machine shown is to achieve
a
2 5 possibility of controlling speed and torque by turning the stator.
From patent document US 5,204,570, a rotating electric machine is known, the
rotor of which deviates from the cylindrical shape. The object of the machine
is
to manufacture a miniaturized motor for use where the smallest building
3 0 volume is at a premium. As examples of use of such a machine, a motor for
fans and a motor for driving disc or tape recorders are stated. The machine is
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/01487
said to be inexpensive and still surprisingly efficient, even when being
manufactured in miniaturized form. The machine has a rotor in the form of a
spheroid comprising one or more permanent magnets. The stator comprises
spirally wound coils, the axes of which intersect the motor shaft. The coils
5 have no iron core and are slightly curved. It is stated in the document that
in
relation to weight it is advantageous to use air-wound coils as stator. The
manufacture of a laminated iron core is said to be expensive owing to
expensive tools and, in addition, eddy-current losses are obtained.
To collect the magnetic field on the outside of the stator, a dome-shaped
shell
of ferromagnetic material is connected to the rotor. The fact that this dome
rotates together with the rotor means that no eddy-current losses arise.
However, in practice the dome constitutes a disadvantage since the motor in
this way has an outer limitation which rotates.
At least at higher powers, the stator winding generates large quantities of
heat
which have to be cooled away. From the air-wound coil, heat can only be
discharged by convection into the surrounding air. For an efficient cooling,
however, the surrounding air must circulate such that cold air permanently
2 0 circulates around the coil. This causes the dome arranged outside to
prevent
the surrounding air from circulating. In this way, the cooling becomes
exceedingly inefficient and probably results in the insulating material of the
winding melting, with an ensuing short circuit. For an effective cooling, a
heat
carrier is usually required, which is in thermal contact with the winding and
2 5 which efficiently carries away heat for cooling by a cooling agent. Metal
is
such a heat carrier.
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/01487
6
SUMMARY OF THE INVENTION
The object of the invention is to suggest methods for the manufacture of a
rotating electric machine which, in a more efficient way than previously
known, utilizes the induction forces between the rotor and the stator. The
rotating electric machine, which may be a motor as well as a generator, shall
be cost-efficient and be capable of being manufactured for high as well as low
voltage ranges within a wide power range. In comparison with a conventional
machine for the same power range, the machine in question shall permit a
considerable saving of material, both with regard to the stator and rotor
cores
as well as with regard to winding material. The machine in question shall also
be capable of being manufactured with a greater efficiency than a conventional
machine of the same size. The machine shall also be capable of efficiently
carrying off heat generated in the machine.
The rotating electric machine shall be capable of being manufactured for low
as well as high power ranges. Among the fields of use which the machine is
intended to cover within the high-voltage range are primarily hydro- and
turbogenerators which may be directly connected to a high-voltage network
2 0 for 36 kV or a higher voltage. In such applications, the machine shall be
capable of being manufactured for powers higher than 10 kW. Also machines
for connection to a power network shall be capable of being manufactured.
Within the low-voltage range, there are examples of a plurality of fields of
use
where an energy-saving machine according to the invention may be utilized as
2 5 a motor or a generator. Thus, the machine may be used as a generator in
conveyances which are driven by an internal-combustion engine. It may also
be used as a drive means for a conveyance. The concept conveyance in this
connection is to be interpreted in a broad sense. The word conveyance
includes vehicles for ground transport on roads or on rails as well as craft
for
3 0 travelling in space and in water. Another field of use within the low-
power
range for a machine according to the invention is as a prime mover in
electrical
CA 02342191 2001-02-27
WO 00/13292
PCT/SE99/01487
7
domestic appliances as, for example, refrigerators and freezers, vacuum
cleaners, kitchen machines, etc.
This and other objects are achieved with a rotating electric machine with the
characteristic features described in the characterising portion of the
independent claims I,17 and 19 and with a method with the characteristic
features described in the characterizing portion of the independent claims 12
and 16. Advantageous embodiments are described in the characterizing
portions of the dependent claims.
The rotating electric machine in question, which in the following text is
referred to as a motor, a generator or a machine, has a stator comprising a
core
of a magnetizable material, the inner limiting surface of which has a
rotationally symmetrical shape which, in at least some part, exhibits a cup
shape. By a magnetizable material is to be understood a material which has a
relative permeability which is greater than one. The inner limitation of the
stator may thus comprise a cavity defined by a solid of revolution formed by
rotation of a curve. Such curve has a continuous rate of change, which, in at
least the end parts, is different from zero. Likewise, the rotor deviates from
a
2 0 circular-cylindrical body and may have the same shape as the inner
limiting
surface of the stator, such that an air gap with a substantially even
thickness is
formed between the rotor and the stator. It is essential for the machine in
question that an active magnetic field is directed three-dimensionally towards
the centre of the rotor. Such an active magnetic field would intersect the
stator
2 5 winding substantially at right angles and surrounds the rotor, or at least
parts
of the rotor, in a cup-shaped manner.
While a traditionally cylindric type motor has an active magnetic field formed
as a wedge the magnetic field of the motor in question has conical or
3 0 pyramidal form. The cup-shaped magnetic field thereby amplifies the
induction forces between the stator and the rotor. The magnetic field
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/01487
8
according to the present invention could be described as containing magnetic
vectors, having an active component parallel to the rotor axle and pointing
towards the centre of the rotor. When the magnetic field is in balance the sum
of the components parallel to the axle is zero. The most efficient embodiment
would seem to be a machine with a stator which has a spherical inner limiting
surface, in which a spherical rotor rotates. The difficulty of designing the
stator
winding close to the shaft of the machine, however, indicates that other
solids
of revolution may be preferable.
The common shape which is aimed at in both the rotor and the stator is
achieved by a so-called spheroid. A spheroid is a surface generated when an
ellipse rotates around one of its symmetry lines. It may thus have both an
oblate, flattened, and a prolate, extended, shape. As the ellipse includes the
circle the spheroid includes the sphere. The common rotational shape is not,
however, limited to a spheroid but may be composed of several solids of
revolution. Thus, the invention also comprises a circular cylinder with half a
spheroid attached to each end thereof. In certain applications, the shape may
be determined by the practical arrangement of the stator winding.
2 0 A machine according to the invention may be wound in a plurality of
different
ways, both as regards the rotor and the stator. Each winding type which is
used in a conventional machine may also be applied to a machine according to
the invention. The rotor thus also comprises a squirrel-cage winding whereas
both the stator and the rotor comprise both a lap winding and a wave
2 5 winding. The machine may also be wound for connection to a power network.
This comprises, among other things for alternating current, such single-phase
and polyphase windings for both the rotor and the stator as are normally used
for conventional machines. A conventional machine in this context means a
machine with a cylindrical rotor and a stator with a corresponding cylindrical
3 0 inner limiting surface.
CA 02342191 2001-02-27
WO 00/13292
9
PCT/SE99/01487
In the same way as for conventional machines, slots for receiving a winding
are arranged in the rotor and/or the stator in the machine in question. In
conventional machines, this is commonplace, since in these machines the
winding slots are straight. In the machine referred to here, the slots are
curved,
and therefore normal winding technology cannot be applied in a simple
manner. The winding is thus not suitable for manufacture in a fixture for
subsequent placement in the slots. In the machine in question, the winding
most likely has to be wound "in situ". To this end, the winding may
advantageously be manufactured from a cable. By cable is to be understood
here a flexible, insulated electric conductor, which may contain several
conductor strands.
For direct connection to a high-voltage network, a machine according to the
invention is adapted to comprise a winding of a high-voltage cable. Powers of
up to 20 MW or more may thus be obtained. Such a cable usually comprises a
semiconducting even layer around the conductor which may be divided into
strands. The semiconducting layer is intended to distribute the electric field
strength such that no field concentrations arise which may cause a flashover.
Such a cable may also comprise a semiconducting layer surrounding the
2 0 insulation and intended to contain the electric field in the cable.
Usually, the
outer semiconducting layer is connected to ground. A suitable cable and a
suitable method of manufacturing the winding in question fox high voltage are
described in patent document WO 97/45919.
2 5 In a conventional machine with a cylindrical rotor which rotates in a
cylindrical stator, the end walls constitute ineffective 'surfaces. No
effective
magnetic fields are created here but instead leakage fields, which deteriorate
the efficiency, arise here. To joint the coils using the conventional winding
technology, a large volume is required at the end pieces of the stator. The
3 0 space-demanding coil ends also imply that the bearing locations for the
rotor
shafts will be situated far away from the centre of the rotor. This results in
an
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/O1487
increased risk of unbalance of the rotor, in which case the bearings must be
oversized. It is then realized that the end walls of a traditional machine
entail
both a lower efficiency and a lower utilization of the total volume of the
machine. Rounding of the end walls of the rotor and surrounding the stator in
5 a cup-shaped manner would thus seem to be advantageous. In this way the
entire rotor is surrounded by a concentrated magnetic field, whereby the
efficiency of the machine may be increased.
It may be demonstrated that a rotating electric machine according to the
10 invention possesses advantages in relation to a conventional machine with
only a cylindrical rotor and a corresponding stator. Based on the volume of a
rotor associated with a conventional machine, the weight of a machine
according to the invention may be reduced by about 30% in spite of the fact
that the machine yields the same power. For a machine according to the
invention with the same weight as a conventional machine, the machine in
question may yield about 50% more power.
If a conductor loop surrounds a magnetic flux which varies in time, a voltage,
electromotive power, is induced in the loop. The voltage which is induced is
2 0 described by the product of the number of turns in the loop and the time
rate
of change of the magnetic flux. The magnetic flux is dependent on the
magnetic field multiplied by the area of, for example, the field enclosed in
the
stator winding. Since the magnetic field is dependent on the material, it is
realized that the area is the sole variable. When optimizing the area in
relation
2 5 to the circumference, a surface of a circle, or rather a sphere, is
obtained since a
volume is formed during rotation of a loop. This implies that the rotor should
be spherical and that the inner surface of the stator shall describe a sphere.
For a conventional machine, the coil ends constitute a problem area. In a
3 0 machine according to the invention, there are practically no coil ends.
T'he
CA 02342191 2001-02-27
WO 00/13292
11
PCT/SE99/01487
losses in the end regions of the machine will thus be considerably lower than
the corresponding losses for a conventional machine
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in greater detail by description of an
embodiment with reference to the accompanying drawings, wherein
Figure 1 shows half a cross section of a rotating electric machine according
to the invention,
Figure 2 shows, in a longitudinal section, the principle of one embodiment
of such a machine,
Figure 3 shows a stator element cut out from a machine according to the
invention,
Figure 4 shows a part cut out from the stator element, and
Figure 5 shows three different shapes (a, b and c) of a rotor associated
2 0 with a rotating electric machine according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The rotating electric machine shown in Figure 1 has a rotor 1 and a stator 2.
2 5 The rotor is adapted to rotate with one degree of freedom in relation to
the
stator. The stator is composed of, for example, laminated sheets which may be
magnetically oriented to a core which surrounds the rotor. The stator is made
with a plurality of teeth 3 and an equally large number of stator slots 4. A
plurality of insulated conductors 5, which may comprise a plurality of
3 0 conductor strands, are arranged in the stator slots. In the example shown,
the
winding is made from a cable and the machine shown is intended to be used at
CA 02342191 2001-02-27
WO 00/13292
12
PCT/SE99/01487
high voltage. The conductors together form one or more main windings. At
the furthest end in a radial direction, a plurality of smaller, insulated
conductors 6 are arranged, which in the example shown are adapted to
constitute a winding for auxiliary power or other voltage, such as in a so-
y called mufti-voltage machine which is connected to a plurality of voltages.
Figure 2 is an embodiment showing the principle of a~rotating electric machine
according to the invention. A rotor 1 is fixed to a rotor shaft 7 around which
it
rotates. The rotor is surrounded by a stator 2,which is made of a magnetizable
material, for example soft iron which may be magnetically oriented. The stator
has an inner cavity 9 which surrounds the rotor 1 and the outer surface of
which constitutes the inside of the stator. In the example shown the cavity is
limited by a sphere. The outside of the stator is limited by a spheroid. In
the
example shown, the surface is formed from an ellipse which rotates with its
shorter symmetry line coinciding with the rotor axis. The outside of the
stator
may, however, have an arbitrary shape. The rotor is a solid of revolution
which, in the example shown, also has a shape which Iis limited by a spheroid.
In the example shown, both the stator and the rotor are limited by surfaces of
revolution, the symmetry axes of which coincide. The symmetry axes may,
2 0 however, also cross each other.
The figure also schematically shows four stator winding 8, which penetrate the
stator core. Three of the windings leave the stator core at the rotor ends
whereas one is enclosed in the stator. The stator winding is threaded through
2 5 slots in the stator core. A comparison between cross sections through the
stator
in a normal plane to the rotor axis shows that the largest cross-section
diameter is obtained in a normal plane to the centre of the rotor axis. The
cross-section diameter then decreases towards the ends of the stator. In the
example shown, also the cross-section area of the stator decreases towards the
3 0 ends. However, the winding area is constant through all the cross
sections, so
the proportion of core area decreases towards the ends. It is thus realized
that,
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/01487
13
at some distance from the central normal plane, the core area between the
winding turns ceases. At this distance from the central normal plane, the
windings may be disposed in the same slots or be placed across one another.
At some further distance from the symmetry plane, only the winding area
remains, and therefore the windings here leave the stator core and pass into
the open. On the other side of the rotor shaft, the windings again penetrate
in
the same way into the stator core. To illustrate the winding technique more
closely, it may be compared to winding a ball which is rotated in one degrees
of freedom only. This implies that a winding turn lies in a plane which
intersects the rotor axis.
Figure 3 shows a stator element 10 cut out from a stator, which stator element
constitutes a body which is obtained at two plane mutually intersecting
sections through a hollow sphere, whereby the intersection line coincides with
a symmetry line through the hollow sphere. To better illustrate the appearance
of the body, it may be likened to a slice cut out from, for example, a melon.
The stator element is limited by an inner cup-shaped surface 11, which
coincides with the cavity 9, and an outer surface 12 (concealed) which is
bulging. In the lateral direction, the body is limited by a first side 13
which is a
2 0 plane and a second side 14 (concealed) which is also plane: The stator
element
is oriented with its longest extent in a plane coinciding with the rotor axis.
To
provide space for the rotor shaft, a first cupped chamfer 15 and a second
cupped chamfer 16 are arranged in the stator element in the edge line between
the first side and the second side. The figure also shows the contour of a
part
2 5 17 which is integrated into the body and which is described in more detail
in
Figure 4.
Figure 4 shows a piece of the core,17, cut out from a stator element
belonging,
for example, to a low-voltage machine. For the sake of clarity, the cut-out
core
3 0 piece may be conceived to be cut out from the stator element in Figure 3,
as
indicated by the dashed line. The core piece is limited in the lateral
direction
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/01487
14
by four plane sections which all intersect the same point, such that the core
piece is accommodated in a truncated pyramid. The four plane sections
constitute only conceived limiting planes for the cut-out core piece and shall
only show the three-dimensional shape. A continuous passage 18 is provided
through the core piece and is adapted to receive a winding (not shown). The
side of the hole connects with an opening 19 which separates a first tooth 20
and a second tooth 21 as well as a back portion 25 positioned therebetween.
The core body is limited inwardly by a first tooth surface 22 and a second
tooth surface 23, which are both cup-shaped and, on the outside of the back
portion, by an envelope surface 24 (concealed) which is bulging.
When activating a loop, arranged through the hole 18, a magnetic field is
generated through the core piece. From a rotor (not shown) which is
positioned immediately in front of the teeth, the magnetic field is directed
vertically against the first, cup-shaped tooth surface 22. In the core piece,
the
magnetic field then follows the tooth in a radial direction, the back portion
in a
tangential direction and then along the outer part of the stator. When the
magnetic field reaches a second, cup-shaped tooth surface, the field passes in
a
direction vertically out from the second tooth surface towards the rotor, in
2 0 which the field is closed.
The area of the magnetizable material through which the field penetrates
should in each section be equally large. For a three-dimensionally curved
stator, which is represented by the core piece in Figure 4, the larger width
at
the back portion compensates for the distance between the edge and the hole.
The cut surfaces indicated by dashed lines in the figure are intended to show
this fact. Thus, it is realized from the figure that the first tooth surface
22 has
the same size as a first cut surface 26 on a level with the largest width of
the
passage 18. Finally, it is realized that this area also corresponds to a
second cut
3 0 surface 27 placed at the back portion and which has an extent directed
opposite to the first tooth surface. The three-dimensional curvature therefore
CA 02342191 2001-02-27
WO 00/13292 PC1'/SE99/01487
implies that material may be saved, especially in the back portion of the
stator,
and that the stator may be made smaller.
The rotor belonging to the machine may have a plurality of different shapes.
5 Figure 5 shows three examples of a rotor comprised in a machine. Figure 5a
shows a rotor with a ball shape whereas Figure 5c shows a rotor in the form of
a spheroid. In the example shown, the spheroid is prolate, that is, extended.
Figure 5b, finally, shows a composed shape, which exhibits a cylindrical mid-
portion connected at each end to half a spheroid.
To carry off heat generated in the machine, cooling channels (not shown) for a
cooling agent can be arranged in the stator core. The machine shown in the
example is wound with a high-voltage cable containing a plurality of strands.
Such a cable is completely insulated and therefore contains, inside the
insulation, the entire voltage potential. This is advantageous when, for
example, cooling the machine since the stator is connected to ground
potential.
In this way, thus, also the cooling agent may be maintained at ground
potential. Another great advantage with the wound cable is that the windings
may freely cross each other and even make contact with each other in the end
2 0 regions of the machine.
The present invention is not limited to the machines shown in the
embodiments. The shape of the rotor and the stator may thus vary within a
very wide range. Common to all of them, however, is that the stator core
2 5 surrounds the rotor in a cup-shaped manner such that a three-dimensionally
directed magnetic field is formed around the rotor. Nor is the invention
limited to comprise only a winding disposed in slots in the stator. The
winding
may thus also be arranged as a so-called air-gap winding. Nor must a winding
for a machine according to the invention be arranged in a direction which
3 0 coincides with the motor or stator shaft. Parts of the Winding may thus be
arranged in a free pattern along the curved stator and may thus represent both
CA 02342191 2001-02-27
WO 00/13292 PCT/SE99/01487
16
straight slots and slots crossing the rotor axle. Also, the shafts of the
rotor and
the stator do not have to coincide but a machine with crossing shafts is also
comprised in the invention.
A motor according to the invention can also comprise permanent magnets in
either the rotor or the stator.
