WO2007045319A1

WO2007045319A1 - Self-starting, permanent-magnet synchronous motor

Info

Publication number: WO2007045319A1
Application number: PCT/EP2006/009142
Authority: WO
Inventors: Thomas Heese
Original assignee: Wilo Ag
Priority date: 2005-10-20
Filing date: 2006-09-20
Publication date: 2007-04-26
Also published as: EP1938441A1; CN101292409A; DE102005050643A1

Abstract

The invention relates to a rotor (1) of an electric motor, in particular of a permanent-magnet synchronous motor, comprising a rotor shaft, a cage (2) that is coaxial with the rotor axis and at least one permanent magnet (3). According to the invention, the permanent magnet or magnets is or are situated under the cage (2) and in order to generate a high starting torque for the permanent-magnet synchronous motor, the cage (2) is configured as a solid hollow cylinder.

Description

Self-starting, permanently excited synchronous motor

The invention relates to a rotor of an electric motor, in particular a permanently excited synchronous motor with a rotor shaft, a conductive cage arranged coaxially to the rotor axis and at least one permanent magnet.

Synchronous drives are increasingly used for small drives in industrial applications. These machines are usually operated directly on the AC network without a converter. In nominal operation, they run synchronously with the mains frequency. In order to reach this operating point, the independent startup against the moment of inertia and the load must take place. This is generally not a problem for very small motors, since the moment of inertia is low, but the load torque must also be as low as possible for low speeds. This is the case with pumps and fans, since the load only increases with the speed. This is for _κ -that small, self-starting synchronous motors in these applications use will find the main reason.

Small heating pumps with an output of up to approx. 50 watts are, however, generally implemented today with asynchronous motors and an operating capacitor. These pumps are mainly wet-running machines that have a relatively large air gap, which results in low efficiency. One advantage of asynchronous motors is that the Pump drive on the AC network enables problem-free self-starting.

In order to improve the efficiency of such heating pumps, two-pole permanent-magnet excited excitation synchronous motors with starting electronics have recently been used. These synchronous motors have a better efficiency due to the magnet excitation in nominal operation, whereby the large air gap, due to the wet-running technology, has significantly less effect than with asynchronous motors, since the magnets behave like air in the magnetic circuit and outweigh the mechanical gap.

For heating pumps of this power, however, the synchronous motors require starting electronics, since the tightening torque compared to the moment of inertia and load is not sufficient for a safe self-start under all conditions (e.g. contamination). It should also be mentioned that the start electronics required for the start-up require significant additional costs for the product.

To achieve a high level of efficiency, it is known to combine the advantages of the synchronous motor with the advantages of the asynchronous motor (self-starting). This is done by inserting permanent magnets into the short-circuit cage of an asynchronous motor. The result of this is that the start-up is asynchronous and the nominal operation of the electric motor is synchronous with the mains frequency.

Such a rotor is known, for example, from German published patent application DE 102 54 967. It discloses a rotor of an electric motor with a stack of magnetically conductive sheets through which rods of a short-circuit cage are guided, which ends on both sides with short-circuit rings, into each of which four permanent magnets with a rectangular cross-section are inserted. An electric motor with a rotor of this type runs asynchronously through feeders) of an AC voltage and finally runs at nominal speed in synchronism with the frequency of the AC voltage. A disadvantage of the rotor of DE 102 54 967 is the extremely complex construction and a resultant result high manufacturing costs, combined with correspondingly high manufacturing costs. Furthermore, the fact that the permanent magnets are only embedded in the short-circuit rings on the head side has a negative effect on the magnitude of the starting torque. In addition, such a combination of short-circuit cage and permanent magnet has the disadvantage that the low tightening torque which is present in any case in an asynchronous motor is further reduced in asynchronous motors with an operating capacitor. This disadvantage could be avoided by changing the rod shape of the short-circuit cage or by using a double cage, but this disadvantageously results in a correspondingly higher production and material expenditure.

From international patent application WO 02/061918 a rotor of an electric motor is also known, which has a core made of ferromagnetic material, on the cylindrical outer surface of which thin, narrow permanent magnets are applied, which extend in the axial direction along the axis of rotation. A thin metallic cylindrical sleeve encloses the permanent magnets and presses them against the ferromagnetic material. The disadvantage of this construction is that due to the large number of individual magnets that have to be applied to the cylindrical outer jacket of the ferromagnetic material, there is a high level of production expenditure, which in turn entails high production costs.

In addition to the use of the cylindrical sleeve as a result of production, it has the result that when the rotor is used within the bore of an electric motor, the stator magnetic field which penetrates the rotor generates local eddy currents in the area in which the stator magnetic field penetrates the cylindrical sleeve , these induced currents in turn resulting in a magnetic field of the same frequency which interacts with the stator magnetic field and generates a torque which accelerates the rotor. Since these eddy currents are locally limited due to the design of the cylindrical sleeve as a thin sheet in the radial direction to the axis of the sleeve and are therefore very small, this results in a low and inadequate starting torque, which makes the use of such a rotor construction unsuitable for a can pump. This very low starting torque is recognized in WO 02/061918 and proposed to insert rods between the permanent magnets, which are connected at both ends with short-circuit rings, this construction being proposed either alternatively or in addition to the cylindrical sleeve. This, in turn, requires considerable manufacturing effort, which results in high manufacturing costs and makes the use of such a rotor unsuitable for pumps of low power.

The object of the invention is to provide a rotor of a synchronous motor which combines a high starting torque and thus a reliable self-start with a high efficiency in rated operation with simple construction and manufacture and at the same time ensures low manufacturing costs and correspondingly low manufacturing costs.

This object is achieved by the features of the characterizing part of claim 1.

The manufacture of a generic rotor can be significantly simplified by replacing the short-circuit cage with a solid, electrically conductive hollow cylinder. For hollow runners, this hollow cylinder can advantageously be made of brass, copper or stainless steel. The resulting solid rotor has a significantly higher tightening torque, which can be used very well for starting up a synchronous motor, especially in the wet-rotor version, in which the rotor rotates in a liquid medium and has to overcome a high load torque when starting. It is advantageous here that the synchronous motor falls into synchronism with a small slip and continues to run with the high synchronous torque and good efficiency in rated operation.

An optimal design of the rotor is achieved in that the solid hollow cylinder is combined with a permanent magnet, the permanent magnet being arranged under the solid hollow cylinder. The permanent magnet can be made of ferrite, a samarium-cobalt compound (SmCo) or a neodymium-iron-boron compound, for example (NdFeB) exist, whereby the permanent magnetic material can be sintered or plastic-bound. Both a synchronous machine stator with concentrated windings and an asynchronous machine stator with diameter windings can be used as the stator of the electric motor.

A particularly advantageous embodiment variant of the present invention results from the fact that the rotor of the permanently excited synchronous motor has a conductive cage arranged coaxially to the rotor axis and a permanent magnet, the cage being designed as a solid hollow cylinder and the permanent magnet being cylindrical in the form of a solid hollow cylinder is formed and extends coaxially along at least part of the cage.

The use of a solid hollow cylinder as a cage instead of a conventional short-circuit cage results in a considerably reduced manufacturing effort on the one hand and the greatest possible starting torque for the synchronous motor on the other.

In a first embodiment variant, the hollow cylindrical permanent magnet can be formed in one piece. Alternatively, the hollow cylindrical permanent magnet can, however, also be composed of several, for example, two, three or four hollow cylindrical sectional parts, the hollow cylindrical sectional parts in this case being firmly connected to one another in such a way that, in their entirety, they form the solid hon (cylindrical permanent magnet of a rotor according to the invention simplified.

Alternatively, it is also possible to introduce two permanent magnets in the rotor instead of the hollow cylindrical permanent magnet, which are diametrically opposite and extend axially parallel over at least part of the cage. This makes it possible to dispense with the manufacture of a hollow cylindrical permanent magnet, which further simplifies the manufacture of the rotor. The combination of the axially parallel permanent magnets with the solid hollow cylinder as a cage produces due to the smaller magnetic air gap also a high starting torque as when using a hollow cylindrical permanent magnet, since the absence of the hollow cylindrical permanent magnet, which acts like air for the magnetic flux, reduces the effective magnetic resistance for the magnetic flux. Alternatively, the axially parallel magnets can also be combined with the hollow cylindrical permanent magnet.

It should be noted that two axially parallel permanent magnets, which are diametrically opposed, are preferably suitable for the use of a two-pole motor, wherein according to the invention, when using 2p-pole electric motors, 2p permanent magnets are to be arranged accordingly within the rotor.

In terms of production technology, it is particularly advantageous if the hollow cylindrical permanent magnet at least partially abuts the inside of the cage. As a result, further fasteners or additional filler material can be avoided. Due to the arrangement of the hollow cylindrical permanent magnet below the cage, the rotor according to the invention is particularly suitable for use in a containment shell pump in which the rotor rotates within a liquid, since the permanent magnet is not directly exposed to the liquid. Alternatively, the hollow cylindrical permanent magnet can also at least partially rest on the outside of the cage, but in this case additional measures are necessary when using a neodymium-iron-boron compound as permanent magnetic material in order to protect the permanent magnet against corrosion.

For optimal flow guidance, it is advantageous that the hollow cylindrical permanent magnet has a radial or diametric magnetization and that the magnetization has magnetic poles which are distributed over the circumference of the permanent magnet. The number of magnetic poles should be selected according to the number of poles of the stator.

Alternatively, any magnetization can be impressed on the permanent magnet, for example one over the circumference of the Permanent magnets considered sinusoidal magnetization. It is particularly advantageous here that, compared with the use of individual, spaced-apart permanent magnets, the hollow cylindrical permanent magnet receives a continuous magnetization through the stamping of a magnetization, which enables a steady polarization transition, in particular when changing from one magnetic pole to the next, with an optimal adaptation of the permanent magnet to the stator magnetic field is possible and the cogging torque is reduced, which is also accompanied by noise reduction.

Alternatively, the impressed magnetization can also be carried out in such a way that the poles are arranged circumferentially of the permanent magnet in such a way that there is a polarity which, in particular, changes abruptly over the circumference of the hollow cylindrical permanent magnet.

When using diametrically opposed and axially parallel permanent magnets, it is advantageous from the manufacturing point of view to have a rectangular cross section, but a cylindrical sectional cross section or a cross section in the form of a section of a hollow cylinder is also conceivable, which can also be radially polarized.

The cage, which is designed in the form of a solid hollow cylinder, can, in an advantageous embodiment, be made in one piece from copper, brass or stainless steel, as a result of which particularly simple manufacture is possible.

The cage can preferably have an axial thickness which is between 5% and 30%, preferably between 10% and 20% of the total radius of the rotor, so that a solid cage is formed.

The hollow cylindrical permanent magnet can preferably have an axial thickness which is between 10% and 40%, in particular between 20% and 30% of the total radius of the rotor. Alternatively, when using axially parallel permanent magnets, the volume of the axially parallel - Q -

Permanent magnets together between 10% and 40%, in particular between 20% and 30% of the total radius of the rotor.

The generic rotor is particularly suitable for use within a liquid medium in which it can be rotatably supported, the medium being able to be conveyed by a pump driven by an electric motor, and the pump preferably has a can or a can for receiving the rotor.

Show it

1: cross section of the rotor with a hollow cylindrical cage and hollow cylindrical permanent magnet,

2: cross section of the rotor with a hollow cylindrical cage and axially parallel permanent magnets,

1 shows the cross section of a rotor 1 according to the invention. The rotor 1 has a rotor shaft 5 and a conductive cage 2 which is arranged coaxially to the rotor axis 7 and which is designed as a solid hollow cylinder. Furthermore, the rotor 1 has a permanent magnet 3, which is likewise designed in the form of a solid hollow cylinder and extends coaxially along at least part of the cage 2. The hollow cylindrical permanent magnet has a thickness d2.

The permanent magnet 3 lies inside the cage 2 and on the inside of the cage 2. The cage 2 has a thickness d1, which is preferably between 5% and 30%, in particular between 10% and 20% of the total radius of the rotor 1. The permanent magnet 3, on the other hand, has an axial thickness d2 which is between 10% and 40% of the total radius of the rotor 1. Here, a hollow cylindrical permanent magnet made of a samarium-cobalt or a neodymium-iron-boron compound preferably has an axial thickness d2 between 10% and 25% and a hollow cylindrical permanent magnet made of a ferrite preferably has an axial thickness d2 between 20% and 40%. When using axially parallel permanent magnets, the percentages refer to the total volume of all axially parallel permanent magnets. A preferably ferromagnetic material 4, which conducts the magnetic flux well, can be located below the permanent magnet 3.

2 shows a generic rotor with a solid short-circuit cage 2 in the form of a hollow cylinder, internal block magnets 6 being inserted instead of the hollow cylindrical permanent magnet 3. The magnets 6 lie diametrically opposite one another and extend parallel to the rotor axis 7 of the rotor shaft 5. The axially parallel permanent magnets 6 lie in the ferromagnetic material 4.

When an electric motor starts up with one of the rotors according to the invention, the hollow cylindrical cage 2 first has its effect, whereas the hollow cylindrical or axially parallel permanent magnets 3, 6 develop their effect in synchronous operation. When the rotor 1 is at a standstill, the stator magnetic field passes through the cage 2 and generates eddy currents within the cage 2 along its entire thickness d1, which in turn result in a magnetic field which interacts with the stator magnetic field in such a way that a torque is generated by which the rotor is accelerated. Eddy currents are generated as long as the speed of the rotor is below the synchronous speed.

The advantage of a high starting torque is increased in particular by continuous magnetization of the hollow cylindrical permanent magnet 3 instead of discrete magnetic poles, which are formed by individual permanent magnets, since this reduces the cogging torque, i.e. the desire of the rotor to align itself with a pole of the permanent magnet towards a stator pole, this likewise reducing noise when the rotor is running.

Due to the four-part design of the rotor 1 in the embodiment variant with a hollow cylindrical permanent magnet 3 and the coaxiality of the Components a particularly simple and fast manufacture, in particular an inexpensive manufacture of the rotor is possible. In this case, the ferrite material 4 is first applied to the rotor shaft 5, the outer diameter of the ferrite material 4 just corresponding to the inner diameter of the hollow cylindrical permanent magnet 3. Alternatively, the ferrite material 4 can also first be made in the shape of a hollow cylinder and then pushed over the rotor shaft 5.

The permanent magnet 3 is then pushed over the ferrite material 4 and finally the short-circuit cage 2 is pushed over the permanent magnet 3. At both ends of the rotor there may also be an end plate, which closes the rotor at the front and rear, so that the permanent magnet 3 is airtight and watertight and is inserted below the cage 2. Such a rotor is particularly suitable for use within a can or a can of an electric motor-driven pump.

The manufacturing method described can essentially be transferred to the second embodiment variant of the rotor according to the invention, but here the permanent magnets 6 according to FIG. 2 are first introduced into the material 4 when producing the hollow cylinder from the ferromagnetic material 4. The hollow cylinder thus produced, made of ferrite material 4 and permanent magnet 6, is pushed with its inner cavity onto the rotor shaft 5 and then the massive short-circuit ring 2 is pushed over the ferromagnetic material 4. Here, too, an end plate can be used on both sides of the rotor, which seals the rotor airtight and watertight, so that it is particularly suitable for use within an electromotive canned or canned pump.

Claims

Expectations

1. rotor (1) of an electric motor, in particular a permanently excited synchronous motor with a rotor shaft (5), an electrically conductive cage (2) arranged coaxially to the rotor axis and at least one permanent magnet (3, 6), characterized in that the cage ( 2) has the shape of a solid one-piece hollow cylinder and the permanent magnet (3) is cylindrical in the form of a solid hollow cylinder and extends coaxially along at least part of the cage (2) and / or the rotor (1) has at least two permanent magnets (6) has diametrically opposite and axially parallel over at least part of the cage (2).

2. Rotor according to claim 1, characterized in that the hollow cylindrical permanent magnet is formed in one piece.

3. Rotor according to claim 1, characterized in that the hollow cylindrical permanent magnet consists of at least two hollow cylindrical sectional parts.

4. Rotor according to one of the preceding claims, characterized in that the hollow cylindrical permanent magnet (3) at least partially abuts the cage (2) inside and / or outside.

5. Rotor according to one of the preceding claims, characterized in that the hollow cylindrical permanent magnet (3) has a radial or diametric magnetization.

6. Rotor according to one of the preceding claims, characterized in that the poles are arranged circumferentially in such a way that there is a sectionally changing polarity over the circumference of the hollow cylindrical permanent magnet.

7. Rotor according to one of the preceding claims, characterized in that two or more one- or multi-part hollow cylindrical permanent magnets are arranged axially one behind the other.

8. Rotor according to claim 1, characterized in that the axially parallel permanent magnets (6) have a rectangular or a cylindrical or hollow-cylindrical cross-section.

9. Rotor according to one of the preceding claims, characterized in that the hollow cylindrical or the axially parallel permanent magnets (3, 6) is / are arranged within the cage (2).

10. Rotor according to one of the preceding claims, characterized in that the cage (2) consists of copper, brass or stainless steel.

11. Rotor according to one of the preceding claims, characterized in that it is rotatable within a liquid medium which is conveyed by a pump driven by the electric motor, wherein the electric motor has a can or can for receiving the rotor.

12. Rotor according to one of the preceding claims, characterized in that the cage (2) has an axial thickness (d1) which is between 5% and 30%, preferably between 10% and 20% of the total radius of the rotor (1).

13. Rotor according to one of the preceding claims, characterized in that the hollow cylindrical permanent magnet (3) has an axial thickness (d2) which is between 10% and 40%, preferably between 20% and 30% of the total radius of the rotor 1 and / or that the volume of the axially parallel permanent magnets (6) together is between 10% and 40%, preferably between 20% and 30% of the total radius of the rotor 1.