Note: Descriptions are shown in the official language in which they were submitted.
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A STATOR FOR A ROTARY ELECTRIC MACHINE AND A
METHOD FOR MANUFACTURING THEREOF
THE FIELD OF THE INVENTION
The present invention refers to a stator for a rotary electric
machine including a first stator part essentially in the form of a
hollow cylinder with an inner envelope surface and with a
plurality of grooves at least partly running in the axial direction
of the stator, which are intended to receive stator conductors,
wherein each of the grooves in radial direction is delimited
towards the inner envelope surface of the first stator part by a
bridge.
PRIOR ART
By a rotary electric machine is meant a direct as well as an
alternating current machine, and furthermore a synchronous as
well as an asynchronous machine. The rotary electric machine is
especially suited to be utilised as a motor, but may also be
utilised as a generator. In the following, the rotary electric
machine will be explained when it is constituted of an
asynchronous motor, which in its turn is utilised as an electric
motor. This field of application is discussed merely in an
exemplifying objective and not in any way in a restricting sense.
The stator conductors are intended to be connected to a voltage
source. In operation a rotary magnetic flux comes into
existence, the speed of rotation of which is settled by inter alia
the frequency of the supply voltage. The rotor of the machine is
influenced by the rotary magnetic flux and is brought to rotate.
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In a conventional stator, the grooves for receiving of the stator
conductors extend in the axial direction of the stator and are
open towards the inner envelope surface of the stator.
Consequently, the stator conductors in the form of so called
coils are placed in the grooves, in the radial direction, from the
inner space of the stator. However, in the stator in question the
grooves are arranged at a distance from the inner envelope
surface. Thus, each of the grooves is delimited towards the
inner envelope surface by said bridge. A plurality of advantages
can be achieved by such a stator compared with the
conventional stator. For instance, by such a stator, opportunities
are created for a substantially smooth circular-cylindrical inner
surface of the stator. By suitable design of the rotor, a machine
can be accomplished with a substantially uniform gap between
the stator and the rotor in the direction of the circumference of
the rotor, which is advantageous for the achievement of a high
efficiency.
A stator, in which the stator grooves are separated from the
inner envelope surface of the stator, is further advantageous for
applications where a gas, which in direct contact with those
grooves should have a negative effect on the function of the
stator conductors, is intended to be utilised in the gap between
the stator and the rotor.
The stator, in which the stator grooves are open towards an
outer envelope surface of the first stator part is also known. By
reason of this, the stator conductors can be placed in the
grooves from the outside of the first stator part, which is
advantageous for reasons of manufacturing technique.
In order to accomplish a machine with high efficiency, a
magnetic flux through the bridges in the direction of the
circumference should be minimised. This has according to prior
art been achieved by the fact that the grooves are arranged in
such a way that a bottom of respective groove is located in
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close vicinity to the inner envelope surface of the stator.
However, it has turned out, especially when the grooves extend
relatively far in the radial direction of the stator, that a too thin
bridge has a tendency to be deformed and may be ruptured
during manufacturing and handling of the stator.
SUMMARY OF THE INVENTION
An object of the invention is to provide a stator for a rotary
electric machine, which presents bridges that separate
respective stator grooves from an inner envelope surface of the
stator, and which stator provides the conditions for the
achievement of a machine, which in relation to previously known
machines presents a high efficiency in combination with a
relatively high mechanical rigidity of the stator.
This object is achieved in that the first stator part includes at
least one flux influencing stator portion, which is at least partly
arranged in at least one of the bridges and has an interior
material structure that provides it with a magnetic resistance,
which at least in the direction of the circumference of the stator
is larger than the magnetic resistance in the radial direction of
the stator in those portions of the first stator part which surround
said flux influencing portion. Since the stator portion is arranged
in the bridge, occurrence of an undesired stray flux through the
bridge in the direction of the circumference of the stator is
counteracted in the operation of the machine and the magnetic
flux is thus forced to run in the radial direction of the stator to a
great extent. This, in its turn, results in a high concentration of
the magnetic flux in the gap between the stator and the rotor,
resulting in a high efficiency of the machine.
According to an embodiment of the invention, a plurality of said
flux influencing portions are arranged mutually spaced in the
direction of the circumference of the stator between the grooves
and said inner envelope surface. Hereby, the magnetic flux is
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directed to run in the first place in radial direction between the
flux influencing portions, which~~ results in an enhanced
efficiency.
According to a further embodiment of the invention, in the
direction of the circumference of a stator, the stator portion has
substantially the same extension as one of said bridges. Hereby,
the presence of the stator portion will substantially not have any
negative effects on the magnetic flux in the radial direction of
the stator.
According to a further embodiment of the invention, the interior
material structure in the flux influencing portion provides the
latter with a lower permeability than the permeability of those
parts of the first stator part which surround the flux influencing
portion. Hereby, the flux influencing portion is saturation-
magnetised at an, in relation to the rest of the first stator part,
lower magnetic flux. This implies that the bridge is saturation-
magnetised at a lower magnetic flux in relation to prior art,
which in its turn leads to the magnetic flux to a greater extent
running in the radial direction.
According to a further embodiment of the invention, the interior
material structure in the flux influencing portion presents such a
magnetic domain structure that a magnetic flux through the flux
influencing portion in the direction of the circumference of the
stator is counteracted. The magnetic domains are for instance
arranged with a low mutual mobility. Hereby, the magnetic flux is
forced to run to a great extent in the radial direction of the
stator.
According to a further embodiment of the invention, the flux
influencing portion extends over at least 50% of the radial
extension of the bridge. Hereby, merely very small magnetic flux
will run in the direction of the circumference of the stator
through the bridges, which provides a high efficiency.
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A further object of the invention °is to provide a method for
manufacturing of a stator for a rotary electric machine, by
means of which the stator can be manufactured with a relatively
high mechanical rigidity and which stator furthermore provides
the conditions for the accomplishment of a machine with a high
efficiency.
This object is achieved in that a first stator part is manufactured
essentially in the form of a hollow cylinder with an inner
envelope surface and with a plurality of grooves at least partly
running in the axial direction of the stator, each of which is
delimited towards the inner envelope surface of the first stator
part by a bridge and which are intended to receive stator
conductors, and in that at least one stator portion, which at least
partly is formed by at least one part of one of said bridges, is
treated in such a way that it obtains an interior material
structure that provides it with a magnetic resistance, which at
least in the direction of the circumference of the stator is larger
than the magnetic resistance in the radial direction of the stator
in those portions of the first stator part which surrounds said
stator portion. A magnetic flux, generated by the machine in
operation, will thus run to a less degree in the direction of the
circumference of the stator through the bridges and to a higher
degree in the radial direction of the stator to the air gap, located
between the stator and the rotor, and to the rotor, which results
in an enhanced efficiency of the machine.
According to a further embodiment of the invention, each stator
portion is treated in such a way that it obtains an interior
material structure with a substantially lower permeability than
the permeability in those parts of the first stator part which
surrounds the stator portion. In operation of the machine, the
bridges including the first portions will thus be saturation-
magnetised at a reduced magnetic flux. This results in the
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magnetic flux to a higher degree extending in the radial direction
of the stator.
According to a further embodiment of the invention, each stator
portion is treated in such a way that it obtains an interior
material structure with a larger magnetic resistance in the
direction of the circumference of the stator than in the radial
direction of the stator. Thus, the magnetic characteristics will
after the treatment be directed in such a way that a magnetic
flux through the stator portion in the direction of the
circumference of the stator is counteracted.
According to a further embodiment of the invention, each stator
portion is tooled in such a way that the stator portion is
plastically deformed. Such a tooling is relatively easy to
accomplish and therefore the cost will be moderate. The tooling
may for instance be done by means of a substantially cylinder-
shaped tool, with an outside diameter which is somewhat
smaller than the inside diameter of the stator, and by a number
of portions protruding from the cylindrical surface, wherein the
tool is lead through the inner space of the stator. Consequently,
the protruding portions are intended to at least partly deform the
bridges in such a way that the magnetic domains are affected.
Further embodiments of the stator and the method for
manufacturing thereof according to the invention will more
closely be seen in the claims and in the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
A detailed description of the preferred embodiments of the
invention with reference to the drawings attached, described by
way of example, follows below.
Fig 1 discloses a cross-section view of a stator according to
a first preferred embodiment.
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7
Fig 2 discloses the design of the stator more closely for one
of the grooves of the stator, illustrated in Fig 1.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
OF THE INVENTION
Fig 1 discloses a stator 1 essentially in the form of a hollow
cylinder according to a first preferred embodiment. The stator 1
includes a first part 2 with a number of grooves 3 running in its
axial direction. Each of the grooves 3 is delimited in radial
direction towards an inner envelope surface 4 of the first stator
part by a bridge 5. The bridge 5 forms a part of the first stator
part 2. Thus, the bridges 5 and the portions of the first stator
part, which are located between the grooves 3, form a
continuous part. A plurality of stator conductors 8 are arranged
in the grooves 3, so called coils in the form of a plurality of fine
wires all of electrically well conductive material such as copper.
Since the grooves 3 are open towards an outer envelope surface
6 of the first stator part 2, the stator conductors can easily and
effectively be positioned in the grooves 3.
A second stator part 7 is arranged in radial direction outside the
first stator part 2 and encloses it. A rotor is intended to be
arranged inside the inner envelope surface 4 of the stator. An
air gap is arranged between the stator 1 and the rotor.
The stator will below be explained for the case when it
constitutes a part of a rotary electric machine in the form of an
electric motor. The stator conductors 8, arranged in the grooves
3, are connected to a voltage source. When the stator
conductors 8 are supplied in a suitable way, a magnetic flux
comes into existence in the machine, which runs through a
magnetic circuit that is formed by the first stator part 2, the
rotor, and the second stator part 7. The magnetic flux is
intended to pass the air gap between the stator 1 and the rotor
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in radial direction. In a stator, according to prior art, with said
bridges 5 between the grooves 3 arid the inner envelope surface
4 of the stator, there is a risk that a part of the flux runs through
the bridges in the direction of the circumference of the stator,
which result in a minor part of the flux passing the air gap and
running through the rotor, which in its turn result in a reduced
efficiency. By, according to the invention, at least partly restrain
the magnetic flux from running in the direction of the
circumference of the stator through the bridges, an enhanced
efficiency can be obtained. That can be realized in a number of
different ways. Some of such ways are described below with
reference to both Fig 1 and Fig 2. By arranging a stator portion
9, which at least partly is arranged in a bridge 5, with such an
interior material structure that a magnetic flux is influenced in
such a way that it at least partly is restrained from running
through it, and thanks to the fact that the bridge at load of the
machine within the intended load range of the machine is
saturation-magnetised, a reduced magnetic flux will run through
the bridge and thus the flux is restrained to a higher degree to
run in the radial direction of the stator to the air gap and the
rotor.
The flux influencing stator portion 9 has reduced magnetic
characteristics relatively the surrounding stator material. Such
stator portions 9 are accomplished preferably by a treatment of
the first stator part 2 from its inside. The stator portion 9
extends from the inner surface 4 of the first stator part 2 over at
least 50% of the height of the bridge 5 in the radial direction of
the stator, preferably over at least 75% of the height of the
bridge in the radial direction of the stator and according to a
preferred example over at least 90% of the height of the bridge
in the radial direction of the stator. The extension of the stator
portion 9 in the direction of the circumference of the stator is
substantially shorter than the distance between two adjacent
bridges 5 in the direction of the circumference of the stator. The
extension of the stator portion 9 in the direction of the
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circumference of the stator is, according to a preferred
embodiment, less than 20% of ''the distance between the
adjacent bridges. Preferably the stator portion 9 presents an
extension in the direction of the circumference of the stator,
which substantially corresponds to the length of the bridge 5 in
said direction of the circumference. The extension of the stator
portion 9 in the direction of the circumference of the stator is
thus up to at least 90% of the length of the bridge in the
direction of the circumference and at a maximum to an
extension which is 10% longer than the length of the bridge. In
such a way the stator portion 9 will substantially not have any
negative effect on the magnetic flux in the radial direction of the
stator. The stator portion 9 is according to a preferred
embodiment symmetrically arranged in the bridge 5 in the
direction of the circumference.
Thus, the object of the stator portion 9 is to provide an
enhanced magnetic resistance against magnetic flux in a circuit
which extends through that bridge 5 in which the stator portion 9
is arranged. Preferably, the stator portions 9 are arranged in
each of said bridges 5. The stator 1 is, except for the stator
portions 9, essentially formed of a magnetic core. The magnetic
core is preferably constituted of iron or an iron alloy. The stator
core is according to Fig 1 formed by a first 2 and a second 7
stator part.
According to a first example the stator portion 9 has such an
interior material structure that the permeability is lower in that
portion than in those parts of the first stator part which surround
the stator portion 9. Of course, by permeability is here meant
magnetic permeability. Such a lower permeability can be
achieved by a different material composition or crystal structure
relatively the surrounding stator material. Such a lower
permeability can for instance be achieved by heat treating of the
material. The heat treatment is locally applied on said stator
portions. Such a heat treatment can for instance be in the form
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of laser exposure. By heating to a suitable level of temperature
and thereafter rapid cooling, a desired crystal structure can be
achieved in the material. An example on a structure constituent
part, which presents low permeability to magnetic fields and
which can be achieved by the heat treatment, is constituted by
martensite. For instance, the heat treatment can also be in the
form of an inductive heating or welding. Thus, according to an
example of the accomplishment, the material is heat treated in
such a way that a martensite structure is obtained in said stator
portions.
According to a second example, which forms a complement or
an alternative to the first example, the magnetic domains in the
stator portion are arranged in such a way relatively each other
that they are restrained to move relatively each other. This can
for instance be accomplished by defects, in the form of
dislocation, core boundaries, point defects, etc, being
introduced in the lattice structure. Such defects fix the domain
boundaries and thus prevent movement or growing of the
domains. When a magnetic field is applied, the domains will
therefore not be able to be aligned in the direction of the field,
which reduces the magnetic characteristics of the stator portion.
Such defects can for instance be accomplished by a plastic
deformation. At such a plastic deformation of the bridges can for
instance a tool, with a cylindrical shape and with a plurality of
portions which are protruding from the tool in its radial direction,
be utilised. The deformation is achieved by the tool having such
a form that the protruding portions deform the bridges at the
positions of said stator portions when the tool is moved through
the stator.
According to a further example, foreign elements in the form of
for instance carbon and nickel are supplied to said stator portion
at an enhanced temperature. Hereby, the foreign elements are
forced into the lattice and disturb the regularity in it, which has a
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negative effect on the magnetic characteristics of the stator
portion.
According to a further example, ions in the form of nitrides,
carbides, etc. are supplied to the stator portion during the
heating. Such ions disturb the regularity in metal lattice and
have a reducing effect on the magnetic characteristics of the
stator portion.
It is also possible to provide said stator portions 9 with an
interior structure with aligned magnetic characteristics. In order
to counteract a magnetic flux in the direction of the
circumference of the stator, the stator portion can be provided
with such an interior material structure that it presents a larger
magnetic resistance in the direction of the circumference than in
the radial direction. Hereby, in the stator portion, conditions are
created for obtaining a relatively high maximal magnetic flux
density in the radial direction and a relatively low maximal
magnetic flux density in the direction of the circumference. This,
in its turn, provides the conditions for allowing the stator portion
9 to have a relatively large extension in the direction of the
circumference and to extend around the entire inner envelope
surface 4 without the efficiency of the machine being negatively
affected to a substantial degree. This is advantageous for the
achievement of the stator portion 9, since a large part, and up to
the whole, of the inner envelope surface 4 can be treated.
It is accentuated that the embodiments described above and
illustrated in the drawings merely are to be considered as
exemplifying. Consequently, the invention may be realized in
other ways, while maintaining of the fundamental idea of the
invention. In particular, it is pointed out that persons skilled in
this field, after having received knowledge about the solution
according to the invention, of course, are capable to perform
different re-constructions of the exemplified embodiments
without leaving the scope of the patent protection.
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The grooves 3 of the stator ~~fisclose in the figures
a
substantially flat bottom faced towards the inner envelope
surface 4 of the stator. The 3 may be
bottom of
the grooves
presented in other as a rounded form,which of
forms, such
course is within the scope of the claims according
to the
invention.
According to the illustrated embodiment, the stator 1 is
constituted of two stator parts. However, it is also possible to
design the stator as one piece. In that case the stator
conductors have to be led into and through the grooves in the
axial direction of the stator.
The stator portions 9 may, of course, also be treated by a
combination of two or more of the above said treatments.
For instance, the first stator part 2 may be build of a plurality of
adjacent plates. These plates are lying in planes which are
perpendicular to the axial direction of the stator and form a plate
package. The treatment of the stator portions 9 can, of course,
within the scope of the claims according to the invention, be
done before the assembling of the plates to the plate package
as well as after the assembling. The treatment may further be
accomplished from the inner surface 4 of the stator as well as
from the grooves 3, or from the both directions.
The denote cylinder should be considered in a wide sense and
the term cylinder does not necessarily mean that the cylinder
has a circle as base surface. However, the base surface may be
defined by any closed curve. The stator, disclosed in Fig 1, has
the form of a circular cylinder. However, that is only one
example of a cylinder within the scope of the invention.
The denote bridge is above concerning the portion of the stator
which is located in radial direction between each of the grooves
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3 and the inner envelope surface 4. The length of the bridge 5 in
the direction of circumference of the stator is defined
substantially by the width of the groove 3 in the direction of
circumference of the stator.
It should be noted that the interior material structure in the flux
influencing stator portion 9 is different from the interior material
structure in those portions of the first stator part which surround
the flux influencing portion.
It should also be noted that the flux influencing portion
advantageously has an interior material structure that provides it
with a magnetic resistance which also in other directions than in
the direction of the circumference is larger than the magnetic
resistance in the radial direction in those stator portions which
surround the flux influencing portion. According to a preferred
accomplishment, the magnetic resistance in the flux influencing
portion is substantially equal in all directions.
It should also be noted that those stator portions which surround
the flux influencing portion 9 generally have an interior material
structure that provides a substantially equal magnetic resistance
in all directions.
