Patent Application
20250015653
The present disclosure relates to a rotor for an outrunner motor and to an outrunner motor that has a rotor which surrounds a stator.
Outrunner motors of this type are flat motors with a rather short axial length. The rotor is connected to the motor shaft by the unilateral rotor bell. It has been shown that the bell structure of the rotor housing of an outrunner motor is unfavorable in terms of noise and vibration, as it has low natural frequencies with little damping, a large mass on a large diameter, small bearing spacing and magnetic forces close to the outer diameter.
In order to keep the mass moment of inertia of the rotor low, the rotor bell must be configured with the thinnest possible walls, however this means that the rotor bell has low rigidity, which favors vibrations.
In particular, if these outrunner motors are adapted to high torque, they are subject to strong magnetic forces. In the real system, these magnetic forces lead to resulting force excitations, the amplitude and time course of which depend on imperfections in the geometry and material and other irregularities. In addition to the resulting driving torque, which acts between the rotor and stator, the magnetic forces act primarily in the radial direction, between the poles, i.e. between the magnets of the rotor and the stator teeth.
The natural frequencies of the motor are defined by the rigidity of elastic components and moving masses or inertia in accordance with the laws of physics. If a vibration excitation occurs in any form in the vicinity of the natural frequency, this leads to a strong increase in the vibration amplitude (resonance), wherein the vibration amplitude can only be limited by dissipating the vibration energy (damping).
By construction, the elastic elements of such an outrunner motor, which mainly participate in the vibration, are the rotor bell and the elastic contacts of the bearing, in particular ball bearings, wherein the rotor bell and bearing have very little damping, which is expressed by a strong increase in the vibration amplitude near resonance.
From CN 211266724 U, an end cover for permanent magnet synchronous motors is known, which comprises an end cover body and a plurality of reinforcing ribs arranged on the end cover body. The reinforcing ribs of the end cover of the permanent magnet synchronous motor are arranged asymmetrically. As a result, the problem of electromagnetic force waves resonating with the structural vibration of the motor under electromagnetic excitation of the motor can be solved, and working noise of the permanent magnet synchronous motor can be reduced.
CN 112271852 A also shows an end cover for a permanent magnet synchronous motor for noise reduction. The end cover has inner and outer reinforcing ribs, wherein the inner reinforcing ribs are also distributed asymmetrically.
In these two documents, the end cover, that is, a non-rotating part of the motor housing, is provided with asymmetrically arranged reinforcing ribs. This already leads to a reduction in noise and vibrations, however there is still room for improvement.
Furthermore, DE 10 2017 123085 A1 shows an outrunner motor with a stator having several electronically switchable poles and a rotor which is mounted so as to be rotatable relative to the stator and at least partially surrounds the stator. The rotor is pot-shaped and comprises a plurality of permanent magnets arranged one behind the other in the circumferential direction. The outrunner motor is adapted to compensate for an output imbalance caused by a drive train of the device in which the outrunner motor is installed. For this purpose, the outrunner motor has two counterweights to generate a defined unbalance. The first counter mass is formed on a part of the circumferential surface of the rotor and is formed in one piece with the rotor. The second counter mass can be configured such that partial areas of the end face of the pot-shaped rotor are punched out and bent over onto the remaining partial areas of the rotor end face.
It is therefore the problem of the present disclosure to further improve the difficulties known from the prior art and, in particular, to configure a rotor for an outrunner motor and an outrunner motor having such a rotor so as to be quieter and with lower levels of vibration.
For this purpose, it is provided according to the disclosure that the center of gravity of the rotor bell is located on its axis of rotation.
The rotor bell is a pot-shaped housing that is at least partially closed on one side and has a shell surface and an end face. The tilting rigidity prevents the end face or the shell surface of the rotor bell from tilting in a direction perpendicular to it. The asymmetrical tilting rigidity is neither point-symmetrical nor rotationally symmetrical in relation to the axis of rotation. The rotor poles are preferably configured as permanent magnets. A bearing point is provided on or in the end face for mounting the rotor bell on one side of the motor shaft. The mathematical solution of the eigenvalue problem for solving the vibration differential equations for the main vibration modes in the circumferential direction is not defined. However, force excitations show clear components in the circumferential direction. This leads to the observation that the elastic relative tilting movement between the rotor and stator is associated with a circumferential movement. With this observation, the mechanical rotor structure can be optimized. While hardly any influence can be exerted on the tilting rigidity of the bearing, it is possible to optimize the tilting rigidity of the rotor bell. The bell structure of the rotor bell is therefore configured such that the tilting rigidity of the rotor bell varies irregularly as a function of the torsional angle when turning around the axis of rotation. On the one hand, the asymmetrical configuration of the tilting rigidity of the rotor bell in relation to the axis of rotation means that the tilting natural frequencies, which are usually close to each other in a symmetrical configuration, are strongly separated from each other. On the other hand, a tilting natural mode vibrating near resonance cannot simply rotate, as the tilting rigidity changes greatly depending on the angle around the axis of rotation, which manifests itself in a vibration or noise analysis through a splitting of the resonance peaks and thus through stronger damping with reduced vibration amplitudes. This configuration of the rotor bell thus enables additional damping and a reduction in excitation. Low unbalance and therefore quiet running of the motor is achieved.
According to a preferred embodiment, it can be provided that the rotor bell has areas of different geometry and/or made of different materials. This is a simple way of achieving the desired asymmetrical tilting rigidity of the rotor bell in relation to the axis of rotation. For example, it may be provided that the rotor bell has different thicknesses in the circumferential direction or is made of different materials.
In another preferred embodiment, it can be provided that an end face of the rotor bell that is perpendicular to the axis of rotation is asymmetrical. As a result, the desired asymmetrical tilting rigidity of the rotor bell is achieved in a simple and stable manner. The shell surface of the rotor bell can thereby be symmetrical, in particular axially symmetrical or rotationally symmetrical. This also enables the motor to run with low unbalance, as well as cost-effective production of the rotor bell.
Preferably, the end face of the rotor bell can then be configured such that it has at least one cutout and spokes, wherein the spokes are made of different materials and/or have different thicknesses or widths and/or include different angles between them. This leads to the asymmetrical tilting rigidity of the rotor bell according to the disclosure and thus to a reduction in noise and vibrations. In this case, the spokes extend from a bearing area in the end face of the rotor bell to the circumference of the rotor bell. In this embodiment, the first two tilting modes are strongly separated from each other and the tilting natural frequencies of the first two tilting modes lie between 100-500 Hz, particularly preferably between 300-500 Hz or more apart.
According to yet another embodiment, it may be provided that the spokes are arranged asymmetrically around the axis of rotation such that they are each arranged between two rotor poles. By arranging the spokes between the rotor poles, that is, the permanent magnets of the rotor, an unfavorable magnetic flux through the rotor bell, which could cause additional magnetic excitations, can be avoided. Preferably, the rotor return circuit is not saturated in the transition area to the spokes in order to better decouple the spoke structure from the magnetic circuit.
Preferably, the number of spokes is less than the number of rotor pole pairs formed by two rotor poles in each case, wherein preferably at least four spokes are provided. It is particularly preferred that the number of spokes corresponds to a prime number. This makes it easy to achieve the desired asymmetrical arrangement of the spokes in the end face of the rotor bell. In this case, it is particularly preferred that the number of spokes corresponds to the next two smallest prime numbers in relation to the number of rotor 10 pole pairs. In general, five or seven spokes and in particular five spokes are preferred.
Yet another preferred embodiment can provide that the spokes are arranged asymmetrically in relation to the axis of rotation and each include an angle that is as equal as possible. The spokes are thereby arranged as evenly distributed as possible. A preferred embodiment of a motor can provide that 12 rotor poles are arranged in the rotor bell and the end face has five spokes. In this configuration, adjacent spokes are spaced apart from each other by a minimum of two and a maximum of three rotor pole gaps or form an angle of at least 60° and at most 90° with each other. In such a configuration of the rotor bell, the tilting rigidity of the rotor bell, which counteracts tilting of the end face of the rotor bell in relation to this vertical tilting direction, is between 1 and 5 Nm/degree. In this case, the area of the rotor bell with the highest rigidity arranged in relation to the axis of rotation has a rigidity that is between 20-60% higher than the area with the lowest rigidity in relation to the axis of rotation.
Yet another preferred embodiment can provide that the rotor poles are arcuate on the radially outer side and flat on the radially inner side. Preferably, the rotor poles are configured as discrete anisotropic magnetic segments. This configuration of the rotor poles allows the course of the air gap flux density in the outrunner motor to be smoothed and the magnetic flux in the air gap ideally has a sinusoidal course. This avoids erratic and stronger excitations. At the same time, such rotor poles or magnets reduce costs compared to curved magnets, as the smooth surface requires less machining than a curved surface.
According to a further preferred embodiment, a ring-shaped damping element can be provided in the rotor. Preferably, the damping element is configured as a ring made of a plastic with good damping properties, such as glass fiber-reinforced PPA (polyphthalamide), which has high rigidity. The plastic ring comprises webs arranged evenly distributed along its circumferential surface in the circumferential direction. Preferably, the number of webs corresponds to the number of spaces between the rotor poles. The plastic ring is inserted into the rotor bell, preferably in such a way that the webs are positioned in the spaces between the rotor poles. Due to the high rigidity of the plastic ring, the shell surface of the rotor bell is additionally stabilized and the desired damping is achieved.
With regard to an outrunner motor with a motor shaft, a stator with a plurality of stator teeth and a rotor surrounding the stator as described above, the above-mentioned problem is solved in that the number of stator teeth is smaller than the number of rotor poles. Preferably, the outrunner motor is an electronically commutated outrunner motor. An optimized layout of the rotor and stator system also helps to reduce or avoid the noise and vibrations of the motor. It has been shown that a combination of 12 rotor poles to 8 stator teeth or 16 rotor poles to 12 stator teeth is preferred. For rotors with larger diameters, combinations of 28 rotor poles to 24 stator teeth or 40 rotor poles to 36 stator teeth can also be preferred. In general, ratios of 4 rotor poles to 3 stator teeth or 7 rotor poles to 6 stator teeth or 10 rotor poles to 9 stator teeth or multiples of these ratios are particularly suitable.
In another preferred embodiment, each of the stator teeth has a stator tooth head and the tangential distance between the rotor poles is greater than the tangential slot gap width between two stator tooth heads. In particular, the ratio of the tangential slot gap width between two stator tooth heads to the tangential distance between the rotor poles is between 0.5 and 0.85. This configuration also leads to reduced noise and vibration.
Another preferred embodiment can provide that the ratio of the tangential slot gap width between two stator tooth heads to the tangential width of a stator tooth head is <=0.25 and is preferably in a range between 0.11 and 0.2. A stator tooth head that is as wide as possible can reduce a reluctance change from the rotor's point of view over one rotation, which reduces the magnetic excitations. This also leads to a reduction in noise and vibration.
A further reduction in noise and vibration can be achieved by each stator tooth having a stator tooth neck around which a copper winding is arranged, wherein the width of the stator tooth neck is adapted such that the magnetic flux in the stator tooth neck does not reach the saturation range during motor operation.
Yet another preferred embodiment can provide that each of the stator teeth has a stator tooth head and an air gap is formed between the rotor and the stator, wherein the ratio between a width of the air gap and the tangential slot gap width between two stator tooth heads is in a range of 0.25 to 0.5. This resulting reduction in the air gap field can also prevent excitation of the system.
Embodiments of the present disclosure are explained in more detail below with reference to drawings.
It is shown by:
A damping element 12 (plastic ring) is arranged in the rotor bell 2 on the inside of the shell surface 3. The damping element 12 comprises webs 15 which connect two circular end sections 13, 14. Rotor poles 5 are arranged between the webs 15 in the recesses of the damping element 12. The rotor poles 5 are arranged evenly around the circumference of the rotor bell on the inside of the shell surface 3. The rotor poles 5 are preferably configured as permanent magnets and preferably as discrete, anisotropic magnetic segments. Two rotor poles 5 each form a rotor pole pair. The rotor poles 5 are described in more detail below with reference to
Outrunner motors of this type are characterized by a rather short axial length. The rotor 1 is connected to the motor shaft by the unilateral rotor bell 2. Such a bell structure for the rotor housing is rather unfavorable in terms of noise and vibration, as it has low natural frequencies with less damping, a large mass on a large diameter, small bearing spacing and magnetic forces close to the outer diameter.
According to the disclosure, the bell structure of the rotor bell 2 is therefore configured such that the tilting rigidity of the rotor bell 2 varies irregularly around the axis of rotation R as a function of the rotor angle. The tilting rigidity of the rotor bell 2 is thus asymmetrical in relation to the axis of rotation R. The asymmetrical tilting rigidity of the rotor bell 2 can be achieved, for example, by the rotor bell having areas of different geometry. These can be, for example, areas of different wall thicknesses or cutouts formed in the rotor bell. Another possibility is that areas of the rotor bell 2 are made of different materials. Advantageously, the asymmetry of the rotor bell 2 is configured such that the center of gravity of the rotor bell 2 is always on the axis of rotation R.
In the embodiment shown in
In contrast to
As already described, the rotor poles 5 are configured as discrete anisotropic magnetic segments. On their radially outer side 9, the rotor poles 5 are arcuate. On their opposite side, that is, on the radially inner side 10, the rotor poles 5 are flat. This allows the air gap flux density curve to be smoothed and the magnetic flux in the air gap between the rotor and the stator of the outrunner motor is ideally sinusoidal. This avoids erratic and stronger excitations. At the same time, the configuration of the rotor poles 5 in such a way reduces costs compared to curved magnets, as the smooth or flat surface, that is, the radially inner surface 10, requires less machining than a curved surface.
Each of the spokes 7 is arranged between two rotor poles 5 of the rotor 1. By arranging the spokes 7 between the rotor poles 5, an unfavorable magnetic flux through the rotor bell 2 can be avoided, which could cause additional magnetic excitations. Preferably, the rotor return circuit is not saturated in the transition area to the spokes in order to better decouple the spokes 7 from the magnetic circuit. The five spokes 7 are therefore distributed asymmetrically along the circumference of the end face 4 of the rotor bell 2. Preferably, the spokes 7 are arranged such that they enclose as equal an angle as possible between them or are arranged as evenly distributed as possible. As can be seen in
Other embodiments of the rotor bell are also possible. Preferably, the rotor bell is configured with a number of at least four spokes. Furthermore, the number of spokes of the rotor bell preferably corresponds to a prime number. The number of spokes is also preferably smaller than the number of rotor pole pairs. It is particularly preferred that the number of spokes corresponds to the next two smallest prime numbers in relation to the number of rotor pole pairs. In general, five or seven spokes and in particular five spokes are preferred.
Outrunner motors with such rotors are subject to strong magnetic forces, especially if they are adapted to high torque. Ideally, these magnetic forces cancel each other out. In the real system, however, they lead to resulting force excitations, the amplitude and time course of which depend on imperfections in the geometry and material and other irregularities. In addition to the resulting driving torque, which acts between the rotor and stator, the magnetic forces act primarily in the radial direction, between the rotor poles of the rotor and the stator teeth.
The natural frequencies of the motor are defined by the rigidity of elastic components and moving masses or inertia according to the laws of physics. If a vibration excitation occurs in any form in the vicinity of the natural frequency, this leads to a strong increase in the vibration amplitude (resonance), wherein the vibration amplitude can only be limited by dissipating the vibration energy (damping). Due to the construction, the elastic elements of such an outrunner motor, which mainly participate in the vibration, are the rotor bell and the elastic contacts of the bearing, in particular ball bearings, wherein the rotor bell and bearing have very little damping, which is expressed by a strong increase in the vibration amplitude near resonance. Any additional damping and any reduction in excitation is therefore very welcome in order to make outrunner motors quieter and with a lower level of vibration.
The mathematical solution of the eigenvalue problem for solving the vibration differential equation for the main vibration modes in the circumferential direction is not defined. However, force excitations show clear components in the circumferential direction. From this it can be concluded that the elastic relative tilting movement between rotor and stator is associated with a circumferential movement. With this observation, the mechanical rotor design was optimized as described above.
The rotor 1 therefore comprises a rotor bell 2 with a shell surface 3. The rotor poles 5 are arranged in or on the shell surface 3. The rotor 1 can be configured according to one of the two embodiments mentioned above and is therefore not described in more detail below. Reference is made to
The stator 17 comprises a plurality of stator teeth 18. Each stator tooth 18 comprises a stator tooth head 19 and a stator tooth neck 20. A copper winding 21 is arranged around each stator tooth neck 20. Preferably, the rotor 1 has more rotor poles 5 than stator teeth 18. In particular, a combination of 12 rotor poles to 8 stator teeth or 16 rotor poles to 12 stator teeth is preferred. For rotors with larger diameters, combinations of 28 rotor poles to 24 stator teeth or 40 rotor poles to 36 stator teeth can also be preferred. In general, ratios of 4 rotor poles to 3 stator teeth or 7 rotor poles to 6 stator teeth or 10 rotor poles to 9 stator teeth or multiples of these ratios are particularly suitable.
In a preferred embodiment, the tangential distance T of the rotor poles 5, that is, the width of the rotor pole gaps 11, is greater than the tangential slot gap width NB between two stator tooth heads 19. In particular, the ratio of the tangential slot gap width NB to the tangential distance T of the rotor poles is preferably between 0.5 and 0.85.
Further preferred is the ratio of the tangential slot gap width NB to the tangential width ZB of a stator tooth head 19<=0.25 and is in particular in a range between 0.11 and 0.2. By having a stator tooth head 19 that is as wide as possible, non-linearities due to saturation of the magnetic flux in the stator tooth head 19 can be avoided and thus also resulting excitations.
In order to avoid non-linearities and thus vibration excitation, the stator tooth neck 20, around which the copper winding 21 is arranged, should be adapted with a sufficient width ZHB so that the magnetic flux in the stator tooth neck 20 does not reach the saturation range during motor operation.
An air gap 22 is formed between the rotor 1 and the stator 17. In this case, a width LB of the air gap 22 between rotor 1 and stator 17 is configured to be relatively large, so that a ratio of the width LB of the air gap 22 to the tangential slot gap width NB between two stator tooth heads 19 is between 0.25 and 0.5. This resulting reduction in the air gap field can also prevent excitation of the system.
Depending on, for example, the number of rotor poles, the number of stator teeth 18 or the current applied to the stator teeth 18, the shell surface 3 can be excited to vibrate differently, as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 21205609.7 | Oct 2021 | EP | regional |
This application claims priority to PCT Patent Application No. PCT/EP2022/080174, filed on Oct. 28, 2022, entitled “ROTOR FOR AN OUTRUNNER MOTOR AND OUTRUNNER MOTOR COMPRISING A ROTOR,” then entire contents of which is herein incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/080174 | 10/28/2022 | WO |
