Brushless motor

[0001] The present invention relates to the brushless motor having a magnetic pole according to claim 1 or 4.

[0002] Usually, the stator teeth are distributed into periodic groups depending on the number of phases of the motor. Each tooth has a concentric winding (single tooth winding).

[0003] The first or fourth aspect of claim 1 or 4, wherein the rotor has a radially magnetized permanent magnet, the stator has an electromagnetic pole, and each electromagnetic pole has at least one rectangular ridge. Brushless motors corresponding to parts 1, 3 and 4 are known from the abstracts of the US RE35763E or Japanese JP 60 142240A patent specifications, where the above ridges reduce the air gap and thus the cogging torque. Is reduced. Figure 1 shows a motor from the prior art, where the stator contains nine stator teeth, where it is divided into three periodic groups. The stators are concentrically arranged around the rotor. The rotor has six magnetic poles, each extending at a pitch of one slot. In addition, each magnetic pole has a radius of curvature smaller than the radius of curvature of the cylindrical surface surrounding the rotor itself, thereby ensuring that the induced electromotive force is as sinusoidal as possible.

[0004] The above-mentioned type of brushless motor has a defect caused by so-called cogging torque, and various technical solutions have been used so far in order to correct or reduce the defect. However, these solutions give rise to a variety of other drawbacks. That is, for example, when the same active material is used, magnetic flux is lost; the design is complicated; airborne noise and vibration arise from geometric discontinuities; resulting in Negative effect on active torque, generation of electromotive harmonics; drawbacks such as inconsistent geometry / shape due to the desire to form a virtually sinusoidal electromotive force It is.

[0005] An object of the present invention is to provide a brushless motor in which the cogging torque is smaller than 1/100 of the rated torque, and at the same time, the above-mentioned drawbacks can be minimized.

[0006] This problem is solved by a brushless motor having the following functions.

[0007] The motor has rotors that can rotate around a rotating shaft and have a predetermined number of magnetic poles, where these magnetic poles are evenly distributed around the rotating shaft and spread at a slot pitch. Exists. In addition, the motor has a stator that is concentric with the rotor and has three stator teeth for each of the two magnetic poles, where the stator teeth are evenly distributed around the axis of rotation. The center points of the stator teeth adjacent to each other are separated by one slot pitch from each other. The stator teeth have a free surface facing the magnetic poles, and each stator tooth has a single protruding element, which protrudes from the corresponding free surface towards the rotor. Extends in the radial direction<u style="single">Each protruding element (14) is in the form of an equilateral trapezoid, with the smaller bottom of the trapezoid facing the rotor (2) and its circumferential length (L) being smaller. Measured by the centerline between the bottom of the side and the bottom of the larger side</u>。<u style="single">In yet another embodiment, the motor of the present invention has a number of rotors that can rotate around a rotating shaft and have a predetermined number of magnetic poles and are bundled together in the axial direction to form sectors as magnetic poles. It has a laminate and a stator that is concentrically arranged with respect to the rotor and has three stator teeth for each of the two magnetic poles, the magnetic poles being evenly distributed around the rotating shaft. The center points of the stator teeth adjacent to each other are separated by one slot pitch from each other, and two of the above magnetic poles are magnetized in the circumferential direction. The stator teeth have a free surface facing the magnetic poles, the stator teeth have a single protruding element, and the protruding elements have a corresponding free surface. Extending radially from to the rotor, the protruding element defines a cylindrical stator surface, which is interrupted between the stator teeth and is substantially provided by the stator surface. A quasi-line having a cosine wave shape is drawn, and the quasi-line vibrates around a reference circle concentrically extending around the rotation axis.</u>[0008] In the following, exemplary embodiments of the present invention will be described in more detail with reference to the drawings. It should not be considered here that restrictions are made by this embodiment.

FIG. 1 shows a cross-sectional view of a prior art brushless motor having a permanent magnet, FIG. 2 shows a partial cross-sectional view of a first brushless motor having a permanent magnet, FIGS. 3a-3d. Schematically shows the four different operating conditions of the motor shown in FIG. 2 and the associated diagram of the cogging torque for each operating condition, and FIG. 4 shows a second brushless motor having a permanent magnet. FIG. 5 shows a schematic diagram of the waveforms of the electromotive force and associated phase currents in the motors shown in FIGS. 2 and 4.

[0010] An example according to the prior art shows a brushless motor 1 having a permanent magnet 3, and the brushless motor 1 has a radius of R._rCylindrical rotor surface S_xIt has a rotor 2 that is radially surrounded by and rotates around the axis of rotation A, and a predetermined number of N1 permanent magnets 3 (see FIG. 1).

[0011] Further, the motor 1 has a stator 4, which is concentrically attached to the outside around the rotor 2. This rotor has three stator teeth 5 for each of the two permanent magnets 3. The stator teeth 5 are evenly distributed around the axis of rotation A. The stator teeth 5 are separated from each other, which forms the slot 6. The center points of the stator teeth adjacent to each other are separated from each other by one slot pitch. The stator tooth 5 has a free surface S_s, Which is the surface S_rFacing. Free surface S_s And surface S_rAre separated from each other and form a gap T having a constant width.

[0012] The motor 1 is designed as a three-phase motor having six permanent magnets 3, with nine stator teeth 5 corresponding to these six permanent magnets, and these nine stator teeth are phase-wound. It is divided into groups F1, F2, and F3 that are evenly distributed around the axis of rotation A based on.

[0013] Each stator tooth 5 has a phase winding. Each stator tooth 5 is substantially T-shaped and has an extension 7 arranged along a line of radius and two wings 8 at the ends, where these wings are: It extends from two regions on opposite sides of the extension 7 so as to intersect it with respect to the extension 7 itself, and inwardly in the radial direction, the corresponding surface S._sBounded by .

Cogging torque C_cIn order to reduce , each stator tooth 5 of the motor 1 has a corresponding surface S._s Has two slots 9. As already mentioned, this means not only increases manufacturing costs, but also increases harmonics in active torque and increases airborne noise in motors with "lacuna" at rotational speed.

[0015] In FIG. 2, the same reference numerals are used to represent the same parts and parts already described.

[0016] In one exemplary embodiment, a brushless three-phase motor 10 with a permanent magnet 3 is shown, the motor 10 having a rotor 2 mounted inside a stator 4. However, it is also within the scope of the present invention to use the reverse geometric arrangement in which the rotor 2 is arranged around the stator 4.

[0017] The rotor 2 contains a number of laminations 11, which are axially packed or bundled together to form sectors. These sectors form a seat 13 with respect to the permanent magnet 3, and these seats are arranged between the sectors. Each sector is magnetized by a permanent magnet 3 in two adjacent seats 13 and thus forms a magnetic pole 12 with respect to the rotor 2. Magnetic pole 12 is in the radial direction, the associated surface S_rBounded by , its radius of curvature R_r Is the surrounding surface S around which the rotor 2 is itself surrounded._rRadius R_rSmaller than Each magnetic pole 12 has a 1-slot pitch P_CIn two areas on the opposite side of the perimeter, the surface S_rIt has longitudinal teeth 12a along the'. The opposing axial teeth 12a of the two adjacent magnetic poles 12 radially block the permanent magnet 3 located between them.

[0019] Instead of having to provide sectors, it is also possible to have the magnetic poles in the form of permanent magnets, as in the examples from the prior art. In this case, these permanent magnets are placed directly opposite the stator and have a rotor surface S._rBounds in the radial direction.

The ratio between the number N1 of the permanent magnets 3 and the number N2 of the stator teeth 5 in the motor 10 and the corresponding ratio of the examples of the prior art are consistent with each other and are constant 2/3.

[0021] Each stator tooth 5 has a protruding element 14, which is the associated surface S._s To rotor surface S_rIt extends in the radial direction toward. Element 14 has a radial size optimized by a computer using a magnetic optimization program, which minimizes cogging torque. In such a program, for example, the finite element method can be used. The output obtained from the optimization process is a unique minimum size, which corresponds to the minimum size of the gap T. This minimum size of the gap is an empirically determined standard size, which is about 0.5 mm in the field of automotive technology. The circumferential size of element 14 is L, which corresponds to the distance Z between the two stator teeth 5. The expression "circumferential size" in this case means the length of the element 14 in the circumferential direction of the stator 4 (see FIG. 2). Each element 14 is an equilateral trapezoid with the smaller bottom facing the rotor 2. The circumferential size L is measured at the center line between the smaller bottom surface and the larger bottom surface.

The size and shape of each element 14 is computer-optimized using a magnetic optimization program, thereby cogging torque C due to the interaction between the magnetic pole 12 and the particular element 14._cIs formed, where the magnitude of this cogging torque is the cogging torque C formed by another pole 12 and a particular slot 6._cIs substantially equal to. This cogging torque has the opposite sign. This means that the left edge 12 of the axial tooth 12a of the magnetic pole 12_uAlso on the right edge 12_eAlso applies to both.

As shown in FIGS. 3a to 3d, the cogging torque C_cIs formed under the following four basic conditions. That is, a) the side edge 12 of the magnetic pole 12_eEnters the area of slot 6 (see Figure 3a), b) Side edge 12 of the same magnetic pole 12_uComes out of the slot area (see Figure 3b), c) Side edge 12 of pole 12_eEnters the region of element 14 (see Figure 3c), d) c) side edge 12 of pole 12_uComes out of the area of element 14 (see Figure 3d).

[0024] Cogging torque C_cIs transferred to the diagram as a function of the corresponding positions of the magnetic poles 12 with respect to slot 6 and element 14, which shows the cogging torque C above the opening of slot 6._cIs sufficient, that is, the cogging torque C exceeds the distance between the two stator teeth 5 or the width L of the element 14._cAnd this is not symmetrical with respect to the axis of the slot or the element 14 itself.

Cogging torque C obtained from conditions a), b), c) and d)_cIs added. Cogging torque C obtained from condition a) by the above design of motor 10_cAnd the cogging torque C obtained from the condition c)_cA situation arises in which and the like substantially cancel each other out. The corresponding situation is the cogging torque C obtained from condition b)._cAnd the cogging torque C obtained from the condition d)_cThe same applies to, and as a result, the cogging torque C of the motor 10_cIs about 100 times smaller than the rated torque.

It is easy to see that this result was achieved with minimal changes to the conventional brushless motor 1 and without going into the difficulties faced by conventional solutions in fabrication. It has been achieved.

A second exemplary embodiment, shown in FIG. 4, relates to a motor 20 that is substantially equal to the motor 10 except for the following differences. That is, here, the protruding element 14 causes a cylindrical stator surface S._sIs defined, and this stator surface draws a sine wave D that is interrupted between the stator teeth 5 and has a substantially cosine wave shape. Here, this quasi-line D oscillates around a reference circle B that extends concentrically around the axis of rotation A.

[0028] The quasi-line D is a 1-slot pitch P._cSurface S of the associated stator tooth 5 with a period corresponding to_sDetermine the minimum size of the gap T at the center of . This quasi-line has a radius R in polar coordinates.₀Extends around the reference circle. Radius R₀Is the radius of curvature R surrounding the rotor 2_rIs equal to the sum of the value of, the minimum size of the gap T, and the amplitude λ of the cosine function of the quasi-line D, which is optimized by the magnetic optimization program.

[0029] The above surface S_sThe unique geometry of the stator 4 can be given a given geometry by means of slot 6 and element 14 shown in FIG. 2 as compared to the first exemplary embodiment. The resulting geometric discontinuity is reduced. Further surface S_sThis unique shape of the electromotive force can reduce airborne noise and provide better control over the shape of the electromotive force, which makes the shape of the electromotive force closer to a sinusoidal curve, which is the cogging torque C._cFrom the point of view, the same result will be obtained.

[0030] In addition to the above advantages, the proposed solution provides the following electromotive force. That is, this electromotive force has a sinusoidal waveform mainly containing the 5th harmonic, where the 5th harmonic is opposite to the fundamental wave of the electromotive force and also has the amplitude of the fundamental wave. It has an amplitude of values that is less than or equal to 10%. Typical values for amplitude are advantageously on the order of 6% of the amplitude of the fundamental wave.

It turns out that the above is important to control the motor 10 using the following electronic bridge circuit with block commutation (known but not shown): If you keep in mind what you can do. That is, this electronic bridge circuit forms a sinusoidal current waveform in the phase of the motor, where it has harmonic components that are substantially in phase with the fundamental wave consisting of the fifth harmonic, which is typical. The order of values has an amplitude that is 6% of the magnitude of the fundamental wave.

If the electromotive force is completely sinusoidal, this current waveform forms an undesired ripple, or cogging torque, in the active torque. However, since the 5th harmonic of the electromotive force of the motor 10 and the 5th harmonic in the waveform of the phase current are antiphase and have similar amplitudes up to the percentage term, the negative influence of ripple on the active torque has an effect. It is considerably reduced.

It is clear from this that the motor 10 does not use advanced and costly techniques and sinusoidal feed voltages that form electromotive forces without causing cogging motion in the active torque. Nevertheless, it is possible to achieve cogging motion at active torque, which has a very small percentage value relative to the rated torque, i.e. the torque intended to be output by the motor 1.

To aid understanding, FIG. 5 shows a typical waveform of electromotive force and the corresponding phase current in a motor 10 with bridge control when using a square wave, where the harmonic components and You can see the related phases.

[0035] The present invention is not limited to the forms described and illustrated herein. These embodiments should be regarded as exemplary embodiments of brushless motors with permanent magnets. It is possible to make changes in the shape and arrangement of the members, design details and assembly, as such changes can be combined with the ideas of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a prior art brushless motor having a permanent magnet.

FIG. 2 is a partial cross-sectional view of a first brushless motor having a permanent magnet.

FIG. 3 is a diagram schematically showing four different operating conditions of the motor shown in FIG. 2 and a diagram relating to cogging torque for each operating condition.

FIG. 4 is a partial cross-sectional view of a second brushless motor having a permanent magnet.

5 is a diagram of waveforms of electromotive force and associated phase currents in the motors shown in FIGS. 2 and 4.