ELECTRIC MOTOR, HOISTING MACHINE AND ELEVATOR SYSTEM
Field of the invention
The invention relates to the structures of electric
motors and more particularly to the structures of
permanent -magnet motors.
Background of the invention
It is a general aim to utilize built space as
efficiently as possible. For example, owing to space
requirements, one aim is to make the hoisting machines
of elevators as compact as possible. In order to
achieve this, hoisting machines are designed to be as
flat as possible in their dimensions in the direction
of the axis of rotation, in which case the hoisting
machines fit better in connection with, for instance,
the wall part of the elevator hoistway or into some
other corresponding narrow space. On the other hand,
the aim in some solutions has been to design the
hoisting machine so as to be as small as possible in
its dimensions in the radial direction, such that the
hoisting machine fits better e.g. in connection with
the top end or the bottom end of the elevator
hoistway.
In recent times permanent -magnet motors have started
to be used in the electric motors of hoisting
machines, which permanent -magnet motors comprise a
concentrated stator winding that is wound into two
adjacent slots around the stator tooth. In a
concentrated winding the proportion of the winding
overhang remains shorter than in a conventional
diamond winding, in which case the size of the
hoisting machine also decreases.
The use of a concentrated winding, however, causes
problems. The density distribution of the magnetic
flux produced by a concentrated winding in the air gap
of an electric motor differs significantly from
sinusoidal, and therefore contains a lot of harmonics.
Harmonics, on the other hand, produce vibration and
disturbing noise in a motor.
Summary of the invention
The aim of the invention is to present a permanent -
magnet motor, in which the vibration and noise caused
by the harmonics of the magnetic field is reduced by
developing the placement and the shape of the
permanent magnets. To achieve this aim the invention
discloses an electric motor according to claim 1 , a
hoisting machine according to claim 11, . and also an
elevator system according to claim 13 . The preferred
embodiments of the invention are described in the nonindependent
claims .
The electric motor according to the invention
comprises a stator, which stator comprises slots, into
which slots a concentrated winding is fitted. , The
electric motor also comprises a rotating rotor, which
rotor comprises permanent magnets placed consecutively
in a ring in the direction of the rotational movement.
L „
The ratio —— of the width of a permanent magnet at
Lp
the point L of the center line of the magnet and the
width Lp of the magnetic pole of the rotor is at least
2 4
— and at most — . In degrees of electrical angle this
3 5 -
means that the width of a permanent magnet at the
point LM of the center line of the magnet ranges
between 120 - 144 degrees of electrical angle. The
term degrees of electrical angle refers to the angle
value set by the cycle length of the fundamental
frequency of the magnetic flux circulating in the air
gap between the rotor and the stator. Thus 180 degrees
of electrical angle is obtained for the width Lp of the
magnetic pole of the rotor. The term center line of a
magnet refers to a ring in the direction of rotational
movement of the rotor, which is situated at
essentially the geometrical center point of the
magnet, in other words the length of the magnet in the
direction of a right angle to the center line is the
same on both sides of the center line.
In a preferred embodiment of the invention the
direction of at least one side of a permanent magnet
on the rotor differs from the direction of the stator
s
slot with a slot inclination s , the ratio — of which
Lp
slot inclination s and the width Lp of a magnetic pole
5 1
of the rotor is at least — - and at most — . In degrees
36 5
of electrical angle this means that the slot
inclination ranges between 25 - 36 degrees of
electrical angle.
By means of the placement of the rotor magnets and of
the shaping of the magnet, as presented above, the
vibration and noise caused by the harmonics of the
magnetic flux can be reduced, particularly in those
types of electric motors in which a concentrated
fractional-slot winding is fitted into the stator
slots of the electric motor, the slots per pole and
phase q of which winding is smaller than 0.5, most
preferably 0.3. The aforementioned slot inclination of
a permanent magnet can preferably be implemented by
shaping the permanent magnets of the rotor to be
essentially arrow-shaped.
The electric motor according to the invention is
preferably an axial flux motor, in which the air gap
between the stator and the rotor is essentially in the
direction of the axis of rotation of the rotor. The
tip of an arrow-shaped permanent magnet on the rotor
of an axial flux motor is preferably disposed farther
from the axis of rotation of the rotor than the center
line of the aforementioned permanent magnet. The
permanent magnet can be shaped such that the width of
the permanent magnet increases when the distance from
the axis of rotation of the rotor increases. In this
case the shaping of the permanent magnet increases the
torque of the motor, because a larger part of the
magnetic flux of the motor in this case travels in a
part of the electric motor that is disposed farther in
the radial direction from the axis of rotation of the
rotor. The electric motor according to the invention
can also be a radial flux motor, in which the air gap
between the stator and the rotor is essentially in the
direction of the radius of the electric motor.
The magnetic poles of consecutive permanent magnets in
the rotor of an electric motor according to the
invention are preferably of opposite directions to
each other.
With regard to the second aspect the invention relates
to a hoisting machine, which comprises an electric
motor of the type disclosed above. In the hoisting
machine the stator of the electric motor is preferably
disposed in a stationary structure of the hoisting
machine, and the rotor of the electric motor is
preferably disposed in a rotating structure of the
hoisting machine. The rotating structure of the
hoisting machine comprises a traction sheave. When
using an electric motor according to the invention,
the vibration and noise of the hoisting machine can be
reduced.
With regard to the third aspect, the invention relates
to an elevator system, which comprises any hoisting
machine of the type disclosed above, for moving an
elevator car in an elevator hoistway. In an elevator
system according to the invention, the hoisting
machine, owing to its smaller size and quieter noise
level, can be disposed preferably in the elevator
hoistway.
In a preferred embodiment of the invention the rotor
is disposed on a first side of the rotating structure
of the hoisting machine, and the traction sheave is
disposed on the opposite side of the rotating
structure of the hoisting machine. The traction sheave
is fixed to the same piece as the rotor. The traction
sheave can be integrated into the same piece as the
rotor; the hoisting machine can also comprise a fixing
means, such as a bolt, for fixing and/or detaching the
traction sheave. This can be, a benefit e.g. if the
traction sheave must be replaced because of wear or
malfunction. Replacement of the traction sheave can be
necessary e.g. owing to wear of the rope grooves in
the surface part of the traction sheave. The
metallization of the grooves or the coating, such as
polyure thane or corresponding, of coated grooves might
wear owing to, inter alia, slipping of the ropes. Also
the geometry of the grooves affects the wearing.
In a preferred embodiment of the invention, the
traction sheave is hollow. The rotating structure of
the hoisting machine can therefore be made to be
extremely rigid, but the structure is simultaneously
light and fits into a small space. The size of the
hoisting machine can also be further reduced by
disposing e.g. the machinery brake and/or the sensor
that measures the movement of the rotating part of the
hoisting machine inside a hollow traction sheave. The
braking surface of the machinery brake can also be
formed on the inner surface of the ring part of the
hollow traction sheave.
The rotating structure of the hoisting machine is
preferably made from a material that conducts magnetic
flux, at least in the immediate proximity of the
permanent magnets. In a preferred embodiment of the
invention the thickness of the permanent magnets in
the direction of the air gap is essentially constant;
the aforementioned thickness of the permanent magnets
in the direction of the air gap can, however, also
vary such that with the variation in thickness it is
endeavored to achieve a density distribution of
magnetic flux that is as sinusoidal as possible in the
air gap of the magnetic circuit.
The aforementioned permanent magnets of the rotor are
preferably fitted into a fixing matrix, which in order
to reduce eddy currents is made from a material that
does not conduct electricity, or conducts electricity
poorly, such as from glass fiber composite, stainless
steel or corresponding. The permanent magnets can,
however, also be fixed e.g. by embedding them into the
rotating structure of the hoisting machine into
recesses to be machined for this purpose.
In a preferred embodiment of the invention, the
rotating structure of the hoisting machine is
supported on the stationary shaft of the hoisting
machine via bearings. The shaft can also be made
hollow, in which case the hoisting machine lightens
without essentially weakening the rigidity of the
hoisting machine. The hollow structure of the shaft
and/or of the traction sheave also means that the
amount of raw material needed for manufacturing the
hoisting machine decreases. The sensor that measures
the movement of a rotating structure of the hoisting
machine can also be disposed inside the hollow shaft.
Drum brakes or disc brakes, for example, can be used
as machinery brakes of the hoisting machine according
to the invention. The braking surface is preferablyformed
into a rim- like ring as an extension of the
outermost ring of the rotating structure of the
hoisting machine, e.g. into the brake disc of a disc
brake or into the brake ring of a drum brake .
The aforementioned summary, as well as the additional
features and advantages of the invention presented
below, will be better understood by the aid of the
following description of some embodiments, said
description not limiting the scope of application of
the invention.
Brief explanation of the figures
Fig. 1 illustrates the placement of permanent
magnets on the surface of the rotor
Fig. 2 illustrates a rotor of an axial flux motor
according to the invention as viewed from the
direction of the axis of rotation
Fig. 3 illustrates a stator of an axial flux motor
according to the invention as viewed from the
direction of the axis of rotation
Fig. 4 illustrates a permanent magnet of an axial
flux motor according to the invention as
viewed from the direction of the air gap
Fig. 5 illustrates a radial flux motor according to
the invention as viewed from the direction of
the axis of rotation
Fig. 6 presents a part of one hoisting machine
according to the invention, sectioned open
upwards from the axis of rotation of the
hoisting machine in the direction of the
radius
Fig. 7 presents an elevator system according to the
invention, as a block diagram
More detailed description of preferred embodiments of
the invention
Fig. 1 presents permanent magnets disposed
consecutively on the surface of a rotor of a
permanent -magnet synchronous motor according to the
invention in a ring 12 in the direction of the
rotational movement, presented from the direction of
the air gap. In Fig. 1 the ring 12 in the direction of
rotational movement is, for the sake of clarity,
presented when straightened out, in which case the
permanent magnets are disposed in a ring in the
direction of rotational movement consecutively in a
straight line. The permanent magnets are essentially
arrow-shaped. The dimensions and placement of the
permanent magnets 3a, 3b on the rotor are selected
L such that the ratio u- of the width of each permanent
magnet 3a, 3b at the point LM of the center line 12 of
the magnet and the width Lp of the magnetic pole of the
rotor is at least — 2 and at most — 4 . In degrees of
3 5
electrical angle this means that when the width L of a
magnetic pole is 180 degrees of electrical angle, the
width of a permanent magnet at the point LM of the
center line 12 of the magnet ranges between 120 144
degrees of electrical angle. The motor also comprises
a stator (not shown in figure) , which comprises slots
for the stator winding. The stator slots are disposed
at a right angle with respect to the ring 12 in the
direction of the rotational movement. The direction of
the sides of a permanent magnet that end in a tip 11,
as likewise of the sides 7 disposed on the opposite
side of the permanent magnet, differs from the
direction of the stator slots with a slot inclination
s
s , the ratio — of which slot inclination s and the
Lp
width Lp of a magnetic pole of the rotor is at least
5 1
— and at most — . In degrees of electrical angle this
36 5
means that the slot inclination s ranges between 25 -
36 degrees of electrical angle. A concentrated
fractional-slot winding is fitted into the stator
slots, the slots per pole and phase q of which winding
is smaller than 0.5. The slots per pole and phase q
indicates the number of stator slots per phase and per
pole of the motor. When the slots per pole and phase
is less than 0.5, with the shaping and placement of a
permanent magnet- that are presented above the
harmonics of the magnetic flux circulating in the air
gap of a motor can be reduced, in which case the
torque ripple of the motor that is produced byvibration
also decreases; and at the same time
disturbing noise caused by operation of the motor also
decreases .
Fig. 2 illustrates a rotor 2 of an axial flux motor
according to the invention as viewed from the
direction of the axis of rotation. The rotor 2 can be
formed e.g. in the rotating piece 16 of the hoisting
machine 14 of Fig. 6 such that permanent magnets 3a,
3b are fixed onto the surface of the rotating piece 16
of the hoisting machine 14 consecutively at regular
intervals in a ring 12 in the direction of the
rotational movement. The permanent magnets 3a, 3b are
arrow-shaped; additionally, all the permanent magnets
have the same width at the point LM of the center line
of the magnet. The magnetic poles of two consecutive
permanent magnets 3a, 3b are of opposite directions to
each other, such that the strength vectors of the
magnetic field produced by the consecutive permanent
magnets are of opposite directions to each other. The
dimensions and placement of the permanent magnets, as
likewise the slot inclination of the permanent
magnets, are according to the embodiment of Fig. 1 .
The stator 4 of the hoisting machine of Fig. 6
comprises a concentrated fractional-slot winding, the
slots per pole and phase of which winding is smaller
than 0.5. The stator 4 is disposed in the stationary
frame part 15 of the hoisting machine. The rotating
piece 16 of the hoisting machine also comprises a
traction sheave 17, which comprises rope grooves for
the traction ropes. The stator and the rotor are
disposed facing each other in the hoisting machine 14
such that an air gap 8 in the direction of the axis of
rotation 9 remains between them. The magnetic flux of
the motor passes over the air gap 8 when it rotates
between the rotor 2 and the stator 4 .
Fig. 3 presents one possible stator 4 of the hoisting
machine 14 of Fig. 6 . The stator 4 of Fig. 3 comprises
12 slots, and there are three phases in the stator
winding. The rotor according to Fig. 2 , on the other
hand, comprises 10 poles, because each permanent
magnet forms a magnetic pole in the rotor. Therefore,
when using a rotor according to Fig. 2 and also a
stator according to Fig. 3 , 0.4 is obtained as the
slots per pole and phase of the motor. In a preferred
embodiment of the invention the slots per pole and
phase is 0.3. In this case the motor most preferably
comprises 36 stator slots, and the number of magnetic
poles of the rotor is 40. There are 40 permanent
magnets, i.e. as many as there are magnetic poles.
The permanent magnets 3a, 3b of the rotor of Fig. 2
are fitted into a fixing matrix, which is in turn
fixed to the surface of a rotating piece 16 of the
hoisting machine. The thickness of the permanent
magnets in the direction of the air gap 8 is
essentially constant. The rotating piece 16 is made
from ferromagnetic material in the proximity of the
permanent magnets 3a, 3b, in which material the
magnetic flux flowing in the magnetic circuit
circulates.
With the shaping and placement according to the
invention of the permanent magnets 3a, 3b, the torque
ripple of the motor is reduced by reducing the
harmonics of the magnetic flux circulating in the air
gap of the motor. Harmonics could also be reduced with
shapes, such as polygons, that differ from or are
adapted from the shape of an arrow, the width of which
shapes at the point of the center line of the magnet,
and the slot inclination of which shapes, are however
within the scope of the limit values specified in the
invention. One possible shape of a permanent magnet is
a quadrangle, the direction of at least one side of
which differs from the direction of the stator slot
within the limits of slot inclination 2 presented in
the invention. On the other hand one or more corners
of a permanent magnet can also be rounded.
Fig. 4 presents one such permanent magnet, slightly
adapted from the shape of an arrow, that is applicable
e.g. to any of the axial flux motors described above,
wherein the tip 11 of the arrow-shaped permanent
magnet is disposed farther from the axis of rotation 9
of the rotor than the center line 12 that runs via the
geometrical center point of the permanent magnet 3a
and that is disposed in a ring in the direction of the
rotational movement of the rotor. The center line 12
refers to such a ring in the direction of rotational
movement of the rotor that is 'situated at essentially
the geometrical center point of the magnet, in other
words the length of the magnet in the direction A of a
right angle to the center line is the same on both
sides of the center line 12. In addition, the width 1
of the permanent magnet increases when the distance 10
from the axis of rotation 9 of the rotor increases in
the direction of the arrow 10, in which case a larger
part of the magnetic field produced by a permanent
magnet is situated farther from the axis of rotation
of the rotor. With this type of shaping of the
permanent magnet, the torque production of a motor can
be improved .
Fig. 5 illustrates a radial flux motor according to
the invention as viewed from the direction of the axis
of rotation. The permanent magnets 3a, 3b are on the
surface of the rotor 2 . The permanent magnets 3a, 3b
are fixed to a fixing matrix and disposed
consecutively on the surface of the rotor in a ring in
the direction of the rotational movement. The
permanent magnets 3a, 3b are essentially arrow-shaped.
The dimensions and placement of the permanent magnets
3a, 3b on the rotor 2 are selected such that the ratio
of the width of each permanent magnet 3a, 3b at
the point LM of the center line 12 of the magnet and
the width L of the magnetic pole of the rotor is at
2 4
least — and at most — . In degrees of electrical angle
3 5
this means that when the width Lp of a magnetic pole is
180 degrees of electrical angle, the width of the
permanent magnet at the point L of the center line 12
of the magnet ranges between 120 - 144 degrees of
electrical angle. The motor also comprises a stator 4 ,
which comprises slots 5 for the stator winding 6 . The
stator slots 5 are disposed at a right angle with
respect to the ring in the direction of the rotational
movement. The stator in Fig. 5 comprises open slot
apertures, but the motor can also have semi -open or
closed slot apertures. The direction of the sides of a
permanent magnet that end in a tip, as likewise of the
sides disposed on the opposite side of the permanent
magnet, differs from the direction of the stator slots
5
5 with a slot inclination s , the ratio — of which
LP
slot inclination s and the width L of a magnetic pole
5 1
of the rotor is at least — and at most — . In degrees
36 5
of electrical angle this means that the slot
inclination s ranges between 25 - 36 degrees of
electrical angle. A concentrated fractional-slot
winding is fitted into the stator slots, the slots per
pole and phase q of which winding is smaller than 0.5.
When the slots per pole and phase is less than 0.5,
with the shaping and placement of a permanent magnet
that are presented above the harmonics of the magnetic
flux circulating in the air gap of a radial flux motor
can be reduced, in which case the torque ripple of the
motor that is produced by vibration also decreases;
and at the same time disturbing noise caused byoperation
of the motor also decreases.
Fig. 7 presents as a block diagram an elevator system,
in which the elevator car 18 and the counterweight 20
are suspended in the elevator hoistway 19 with
elevator ropes passing via the traction sheave 17 of
the hoisting machine 14 of the elevator. The elevator
car is moved by exerting a force effect on the
elevator car via the hoisting ropes with the hoisting
machine 14 of the elevator. The power supply to the
hoisting machine 1 of the elevator occurs with a
frequency converter (not shown in figure) connected
between the electricity network and the hoisting
machine 14 of the elevator. The frequency converter
and the hoisting machine 14 of the elevator are
disposed in the elevator hoistway, in connection with
a wall of the elevator hoistway 19 outside the path of
movement of the elevator car 18. The hoisting machine
14 of the elevator is of the type presented in Fig. 6 .
A s a result of the concentrated fractional -slot
winding, the hoisting machine 14 of the elevator can
therefore be made flatter in its dimension in the
direction of the axis of rotation 9 than a prior-art
one. As can be observed from Fig. 7 , a flatter
hoisting machine 14 of an elevator enables increasing
the width of the elevator car 18 in the direction of
the axis of rotation 9 of the hoisting machine 1 of
the elevator, in which case a more spacious elevator
car 18 than before can be fitted into the same
elevator hoistway. Likewise the placement and shaping
of the rotor magnets of a hoisting machine 14
according to the invention reduces the torque ripple
of the motor and makes the hoisting machine extremely
quiet .
The electric motor 1 and hoisting machine 14 according
to the invention are suited for use e.g. in different
conveying systems and lifting systems; in addition to
a passenger elevator and freight elevator system, the
electric motor 1 and hoisting machine 14 can be used
e.g. in mine elevators, drum drive elevators, and also
in cranes. On the other hand, the electric motor
according to the invention is also suited for use in
e.g. escalator systems and travelator systems.
The invention is not only limited to be applied to the
embodiments described above, but instead many
variations are possible within the scope of the
inventive concept defined by the claims below.
CLAIMS
1 . Electric motor (1), which comprises a stator (4) ;
which stator comprises slots (5) , into which slots a
concentrated winding (6) is fitted;
and which electric motor comprises a rotating rotor
(2);
which rotor (2) comprises permanent magnets (3a, 3b)
placed consecutively in a ring (12) in the direction
of the rotational movement;
characterized in that the ratio (-^-) of the width of
L
a permanent magnet (3a, 3b) at the point (LM) of the
center line (12) of the magnet and the width (L ) of
2
the magnetic pole of the rotor s at least — and at
4
most — .
5
2 . Electric motor according to claim 1 , characterized
in that the direction of at least one side of at least
one permanent magnet (3a, 3b) on the rotor differs
from the direction of the stator slot (5) with a slot
s
inclination (s) , the ratio (— ) of which slot
L
inclination (s) and the width (L p) of a magnetic pole
5 1
of the rotor is at least — and at most — .
36 5
3 . Electric motor according to claim 1 or 2 ,
characterized in that the concentrated winding is a
concentrated fractional -slot winding (6) .
4 . Electric motor according to claim 3 , characterized
in that the slots per pole and phase (q) of the
concentrated fractional -slot winding (6) is smaller
than 0.5.
5 . Electric motor according to any of claims 1 - 4 ,
characterized in that the air gap (8) between the
stator (4) and the rotor (2) is essentially in the
direction of the axis of rotation (9) of the rotor.
6 . Electric motor according to claim 5 , characterized
in that the width (1) of the permanent magnet (3a, 3b)
increases when the distance (10) from the axis of
rotation (9) of the rotor increases.
7 . Electric motor according to any of the preceding
claims, characterized in that the permanent magnet
(3a, 3b) of the rotor is essentially arrow-shaped.
8 . Electric motor according to claim 7 , characterized
in that the tip (11) of the arrow-shaped permanent
magnet (3a, 3b) on the rotor is disposed farther from
the axis of rotation (9) of the rotor than the center
line (12) of the aforementioned permanent magnet (3a,
3b) .
9 . Electric motor according to any of the preceding
claims, characterized in that the magnetic poles of
consecutive permanent magnets (3a, 3b) are of opposite
directions to each other.
10. Electric motor according to any of the preceding
claims, characterized in that the thickness of a
permanent magnet (13) in the direction of the air gap
is essentially constant.
11. Hoisting machine (14), characterized in that the
hoisting machine comprises an electric motor (1)
according to any of claims 1 - 10.
12. Hoisting machine according' to claim 11,
characterized in that the stator (4) of the electric
motor is disposed in a stationary structure (15) of
the hoisting machine;
and in that the rotor (2) of the electric motor is
disposed in a rotating structure (16) of the hoisting
machine;
and in that the rotating structure (16) of the
hoisting machine comprises a traction sheave (17) .
13 . Elevator system, characterized in that the
elevator system comprises a hoisting machine (14)
according to claim 13 or 14, for moving an elevator
car (18) in an elevator hoistway (19) .
14. Elevator system according to claim 13,
characterized in that the hoisting machine (14) is
disposed in the elevator hoistway (19) .