JP5199704B2 - Brushless motor - Google Patents

Description

  The present invention relates to a brushless motor having a skew structure, and more particularly to a brushless motor having a low torque ripple and a high output using a ring magnet.

Conventionally, in order to improve the silent performance of a brushless motor, a control method is known in which the switching of energization is smoothed by sinusoidal driving and the torque cripple is reduced. In such a sine wave drive, by supplying a current whose current value changes in a sine wave shape to a motor whose induced voltage waveform has a sine wave shape, compared to a normal 120 ° rectangular wave drive, Torque ripple is reduced. As a method for reducing torque ripple, a skew structure in which rotor magnetic poles and the like are inclined in the axial direction is also widely known. In a motor employing this skew structure, since the harmonic component of the induced voltage waveform is reduced, the induced voltage waveform can be made a smooth sine waveform, and the torque ripple reduction effect during sine wave driving is further improved.
Japanese Unexamined Patent Publication No. 2006-174692

  However, in the skew structure motor, when the skew angle is increased, the fundamental wave component of the induced voltage is reduced along with the harmonic component. Since the output torque of the motor is approximately the product of the induced voltage and the motor current, the magnitude of the torque depends exclusively on the fundamental wave component. For this reason, when the skew angle is increased in order to reduce torque ripple, the motor torque is reduced and the voltage utilization rate is lowered. On the other hand, if the motor specification is set in a state where the skew is reduced and the decrease in the induced voltage is suppressed in order to secure the motor torque, the harmonic component increases accordingly, and the torque ripple increases. For this reason, in a brushless motor, it is difficult to satisfy both a reduction in torque ripple and an improvement in output, and countermeasures have been demanded.

  On the other hand, for example, in a brushless motor for an electric power steering apparatus, the use of a segment magnet that can be magnetized at a high magnetic flux density is increasing as a rotor magnet due to a demand for miniaturization and high output. However, the segment magnet needs to set the angle of the magnet during magnetization, and it is difficult to perform skew magnetization. For this reason, in a motor using segment magnets, so-called step skew is performed by stacking magnets in order to realize a skew structure. However, in the step skew structure motor, there is actually a variation in the assembled state, physical property value, processing accuracy, and the like, and there is a problem that the motor performance is likely to vary.

  An object of the present invention is to provide a brushless motor that satisfies both high output and low torque ripple, is easily skew magnetized, and has little variation in performance.

A brushless motor according to the present invention is a brushless motor including a rotor having 2n (n is a positive integer) magnetic poles and a stator having 3n slots, and a magnet that forms the magnetic poles has a circumferential shape. A ring magnet having magnetic poles arranged in a direction is used, and a coil wound around the stator is Δ-connected , and a ratio θr / θp between the magnetized angle θr of the magnet and the pole pitch angle θp of the magnetic pole Is set to 0.5 ≦ θr / θp ≦ 0.9 and the skew angle θskew of the rotor is set to an electrical angle of 39 ° ≦ θskew ≦ 54 °, the fundamental of the fifth harmonic component contained in the induced voltage of the brushless motor The content ratio with respect to the wave is set to 4.5% to 6.5%, and the line-to-line induced voltage is trapezoidal .

In the present invention, the use of the ring magnet facilitates skew magnetization and reduces the number of steps required for the magnetization operation. Further, the skew angle variation can be suppressed as compared with the step skew structure, and the motor performance variation can be suppressed. Further, a Δ connection is adopted , the ratio θr / θp between the magnet magnetization angle θr and the pole pitch angle θp of the magnetic pole is 0.5 ≦ θr / θp ≦ 0.9, and the skew angle θskew of the rotor is electrically The angle 39 ° ≦ θskew ≦ 54 ° is set, the content ratio of the fifth harmonic component contained in the induced voltage of the brushless motor to the fundamental wave is set to 4.5% to 6.5%, and the induced voltage between lines is trapezoidal. As a result , the peak current value can be suppressed.

In the brushless motor, the content of the fifth harmonic component contained in the induced voltage with respect to the fundamental wave is set to 4.5% to 6.5%, so that the torque and the rotational speed are effective for the sine wave drive. To increase. Further, by setting the skew angle θskew of the rotor to an electrical angle of 39 ° ≦ θskew ≦ 54 °, the content of the fifth harmonic component with respect to the total harmonic component in the induced voltage is increased. Furthermore, by setting the ratio θr / θp between the magnetized angle θr of the magnet and the pole pitch angle θp of the magnetic pole to be 0.5 ≦ θr / θp ≦ 0.9, in a brushless motor of 2P3S × n configuration, While the skew angle is set to an electrical angle of 39 ° ≦ θskew ≦ 54 °, the content of the fifth harmonic component contained in the induced voltage of the brushless motor with respect to the fundamental wave can be approximately 4.5% to 6.5%. .

  The brushless motor may have a 6-pole 9-slot structure having 6 (n = 3) magnetic poles and 9 slots, and the brushless motor is used as a drive source for electric power steering. Also good. Since the brushless motor according to the present invention satisfies both low torque ripple and high output, it is particularly useful as a motor for electric power steering that requires strict requirements for torque ripple and requires small size and high output.

  The brushless motor of the present invention is a so-called 2P3S × n brushless motor, which uses a ring magnet for the magnetic pole and uses a Δ connection for the stator coil, so that skew magnetization is easy and man-hours required for the magnetizing operation. Reduction is planned. Also, variations in skew angle can be suppressed, and variations in motor performance can be suppressed. Furthermore, by adopting the Δ connection, the line-to-line induced voltage can be trapezoidal, the peak current value can be suppressed, and the motor output can be increased.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a brushless motor according to an embodiment of the present invention. As shown in FIG. 1, a brushless motor 1 (hereinafter abbreviated as “motor 1”) is an inner rotor type brushless motor having a stator (stator) 2 on the outside and a rotor (rotor) 3 on the inside. Yes. The motor 1 is used, for example, as a power source of a column assist type electric power steering device (EPS), and applies an operation assisting force to a steering shaft of an automobile. The motor 1 is attached to a speed reduction mechanism provided on the steering shaft, and the rotation of the motor 1 is transmitted to the steering shaft by being decelerated by the speed reduction mechanism.

  The stator 2 includes a bottomed cylindrical case 4, a stator core 5, a stator coil 6 wound around the stator core 5 (hereinafter abbreviated as coil 6), and a bus bar unit (terminal unit) 7 attached to the stator core 5. It is configured. The case 4 is formed in a bottomed cylindrical shape with iron or the like, and an aluminum die cast bracket 8 is attached to an opening of the case 4 with a fixing screw (not shown). As shown in FIG. 2, the stator core 5 has a configuration in which a plurality (9 in this case) of divided cores 9 are assembled in the circumferential direction. The stator core 5 is provided with nine teeth 5a projecting radially inward. The split core 9 is formed by stacking core pieces made of electromagnetic steel plates, and an insulator 11 made of synthetic resin is attached around the core.

  A coil 6 is wound around the outside of the insulator 11, and an end portion 6 a of the coil 6 is drawn out in the radial direction on one end side of the stator core 5. A bus bar unit 7 in which a copper bus bar is insert-molded in a synthetic resin main body is attached to one end side of the stator core 5. Around the bus bar unit 7, a plurality of power feeding terminals 12 project in the radial direction, and when the bus bar unit 7 is attached, the coil end 6 a is welded to the power feeding terminal 12. In the bus bar unit 7, the number of bus bars corresponding to the number of phases of the motor 1 (here, three for the U phase, V phase, and W phase) is provided. Each coil 6 is connected by Δ connection, and each coil 6 is electrically connected to a power supply terminal 12 corresponding to the phase. The stator core 5 is press-fitted and fixed in the case 4 after the bus bar unit 7 is attached.

  A rotor 3 is inserted inside the stator 2. The rotor 3 has a rotor shaft 13, and the rotor shaft 13 is rotatably supported by bearings 14a and 14b. The bearing 14 a is fixed to the center of the bottom of the case 4, and the bearing 14 b is fixed to the center of the bracket 8. A cylindrical rotor core 15 is fixed to the rotor shaft 13, and a cylindrical ring magnet (permanent magnet) 16 (hereinafter abbreviated as magnet 16) is bonded and fixed to the outer periphery thereof. A bottomed cylindrical magnet cover 17 is attached to the outside of the magnet 16.

  The magnet 16 is skew-magnetized, and a magnetic pole is provided so as to be inclined along the axial direction. The magnetic poles of the magnet 16 are provided in 6 poles along the circumferential direction, whereby the motor 1 has a 6 pole 9 slot (6P9S) structure. In the motor 1 of the present invention, since the ring magnet 16 is used as the magnetic pole, skew magnetization is easier than the segment magnet, and the man-hours required for the magnetization work can be reduced. In addition, the skew angle variation can be suppressed as compared with the step skew structure, and the motor performance variation can be suppressed.

  A rotor (resolver rotor) 22 of a resolver 21 serving as a rotation angle detection unit is attached to the left side of the magnet 16 in FIG. A key groove 22 a is formed on the inner periphery of the rotor 22, and engages with the key 18 attached to the outer periphery of the rotor shaft 13. The key 18 is also used for positioning when the magnet 16 is magnetized, and a magnetic pole is formed on the magnet 16 at a predetermined position on the basis of the position of the key 18. Therefore, by fixing the rotor 22 to the rotor shaft 13 with the key 18, the magnetic poles of the rotor 22 and the magnet 16 are positioned with a predetermined angular relationship.

  A stator (resolver stator) 23 of the resolver 21 is press-fitted into a metal resolver holder 24 and is fixed to the bracket holder unit 25 in this state. A sensor harness (not shown) for transmitting a signal output as the rotor 22 rotates is fixed to the resolver stator 23. The sensor harness is drawn between the bracket 8 and the bracket holder unit 25 along the circumferential direction, and is drawn out of the apparatus from the outer peripheral portion of the bracket 8.

  In the motor 1, the resolver holder 24 is formed in a bottomed cylindrical shape, and is inserted and mounted in the central portion of the bracket holder unit 25. On the other hand, the opening side end portion where the flange portion 24 a is formed is lightly press-fitted into the outer periphery of the end portion of the rib 26 provided in the bracket 8. The rib 26 projects in a cylindrical shape toward the axial direction at the center of the bracket 8, and a bearing 14 b that supports the rotor shaft 13 is fixed to the inside of the rib 26. Therefore, the resolver stator 23 is mounted concentrically with the rotor shaft 13 by lightly press-fitting the resolver holder 24 into the rib 26.

  The bracket holder unit 25 is made of synthetic resin, and a metal female screw portion 27 is insert-molded. A mounting screw 28 is screwed into the female screw portion 27 from the outside of the bracket 8, whereby the resolver holder 24 is fixed to the inside of the bracket 8. The bracket holder unit 25 is also provided with three external power supply terminals 31 (U, V, and W phases) connected to the power supply wiring 29. Each external power feeding terminal (U, V, W) 31 is welded to a bus bar terminal 32 (U, V, W) provided in the bracket holder unit 25.

  The bus bar terminal 32 projects from the bus bar unit 7 in the axial direction. When the motor 1 is assembled, the bus bar terminal 32 and the external power feeding terminal 31 face each other in parallel. In the motor 1, after the bracket 8 is attached to the case 4, the bus bar terminal 32 and the external power feeding terminal 31 are fixed by welding. A work hole 33 is formed in the bracket 8, and a bracket cap 34 is attached to the work hole 33 after the welding process.

  By the way, in the said motor 1, unlike the conventional brushless motor, the coil 6 is connected by (DELTA) connection. This is because the motor 1 uses a ring magnet 16 in which the magnetic flux distribution of the magnet is trapezoidal. Therefore, when the coil 6 is Y-connected as in the prior art, the line-to-line induced voltage waveform does not become a trapezoidal wave, and torque This is because the current waveform in which the ripple is 0 is also not a trapezoidal wave, and the peak current value cannot be suppressed. Since the peak value of trapezoidal wave current can be reduced compared to sine wave current, the peak current value can be lowered. The output also increases. On the other hand, when the current waveform is a non-trapezoidal wave having a convex portion, the peak current value cannot be suppressed, so that a large amount of current cannot flow and the motor output is suppressed.

  Therefore, in the motor 1, an equivalent exchange with the Y connection is possible, and a Δ connection in which the signs of the fifth and seventh harmonics are reversed is adopted for the coil 6, and the induced current between the lines is trapezoidally converted into a peak current. I try to suppress the value. In other words, the motor 1 of the present invention uses the ring magnet 16 that is easily skew magnetized and has little skew angle variation to reduce torque ripple, while the use of the ring magnet increases the peak current value. Is eliminated by adopting Δ connection.

  On the other hand, the induced voltage of a motor having a structure that is an integral multiple of 2P3S (motor 1 is 2P3S × 3 = 6P9S) includes odd-order harmonic components of the fifth or higher order, among which the fifth-order component has Most often included. In the case of 2P3S × n, the third harmonic that becomes a circulating current in the Δ connection is not generated because the short-pitch coefficient Kp = cos {n · (1-β) · π / 2} = 0 ( n: order, β: coil pitch / polar pitch angle, 2P3S becomes β = 2/3, and when n = 3, cos is 0). In addition, if only the 5th harmonic component is included in the fundamental wave, the line induced voltage becomes a substantially trapezoidal wave. At this time, if the motor drive current is a trapezoidal wave, the torque ripple approaches 0 as described above. The peak current value can also be lowered.

  Accordingly, the inventors focused on the characteristics of the motor of the 2P3S × n structure, and studied a configuration in which the harmonic component is made only the fifth order component as much as possible and the other order components are reduced. As a result of various experiments, the following conclusions were obtained.

  (1) When the content rate of the fifth harmonic component with respect to the fundamental wave of the induced voltage is set to 4.5% to 6.5%, the torque and the rotational speed effectively increase with respect to the sine wave drive.

  (2) If the skew angle is set to an electrical angle of 39 ° ≦ θskew ≦ 54 °, the content of the fifth harmonic component with respect to the total harmonic component becomes large (90%). The electrical angle of 39 ° ≦ θskew ≦ 54 ° corresponds to the mechanical angle of 13 ° ≦ θskew ≦ 18 ° in the 6P9S motor.

  (3) When the magnetization angle θr in the magnet 16 is 0.5 ≦ θr / θp ≦ 0.9, preferably 0.52 ≦ θr / θp ≦ 0.86, the fifth order is satisfied while satisfying the condition (2). The content rate of the harmonic component is approximately 4.5% to 6.5% (θp: pole pitch angle).

  Hereinafter, each of (1) to (3) will be described based on experimental results. First, regarding (1), FIG. 3 is a graph showing the relationship between the content ratio of the fifth-order harmonic component and the torque increase rate and rotation speed increase rate with respect to sinusoidal drive. As shown in FIG. 3, the torque and the number of rotations increase as the fifth-order harmonic component increases. Further, there is a difference between changes in the torque increase rate and the rotation speed increase rate, with the former peaking at about 5% and the latter at about 6.5%. Then, the range which can ensure the increase rate of 3% or more of both was considered effective, and the conclusion that the content rate 4.5%-6.5% was preferable like (1) was obtained.

  Next, regarding (2), FIG. 4 is a graph showing the relationship between the skew angle (electrical angle) in the 6P9S motor and the content of the fifth harmonic component relative to the total harmonic component. As shown in FIG. 4, the content rate of the fifth harmonic component increases as the skew angle increases, but decreases when it exceeds 54 ° and decreases rapidly when it exceeds 66 °. Therefore, the range in which the content of the fifth harmonic component is 90% or more is considered effective, and the skew angle (electrical angle) 39 ° ≦ θskew (electrical angle) is obtained with a 2P3S × n motor as shown in (2). ) ≦ 54 ° (6P9S: mechanical angle 13 ° ≦ θskew ≦ 18 °) was concluded. Note that FIG. 4 is a motor in which the width of the magnet and the eccentricity of the inner and outer diameters are changed, and the above relationship was examined, but the same tendency was obtained regardless of the magnet configuration. .

  Further, regarding (3), FIG. 5 shows the relationship between θr / θp (magnetization angle / polar pitch angle) in the 6P9S motor and the content of the fifth harmonic component in the induced voltage, and the skew angle as a parameter. It is a graph which shows the result investigated. 6A and 6B are explanatory diagrams showing the relationship between the magnetization angle θr and the pole pitch angle θp. As shown in FIG. 6A, the pole pitch angle θp is the center angle of each magnetic pole with respect to the rotation center O of the rotor 3, and here, θp = 60 ° (mechanical angle) because of the six-pole configuration. . On the other hand, the magnetization angle θr indicates a range having a predetermined magnetic force in each magnetic pole (pitch θp), as shown in FIG. 6B. In the magnet 16, the range of θr extends in a strip shape along the axial direction, and a skew structure is formed by inclining the strip portion.

  As shown in FIG. 5, when the ratio θr / θp between the magnetization angle and the pole pitch angle exceeds 0.4, the content of the fifth harmonic component increases as the ratio increases. In addition, when the skew angle is small, the content ratio of the fifth-order harmonic component also increases. Therefore, when the range in which the skew angle is 39 ° ≦ θskew (electrical angle) ≦ 54 ° and the content ratio of the fifth harmonic component is 4.5% to 6.5% is shown in FIG. The applied part is the range that satisfies it. That is, when 0.5 ≦ θr / θp ≦ 0.9, a motor satisfying both (1) and (2) can be obtained.

  In this way, in the brushless motor of the present invention, the use of the ring magnet 16 as the magnetic pole of the rotor 3 facilitates skew magnetization and suppresses variations in skew angle, thereby suppressing variations in motor performance. It becomes possible. In addition, with the use of the ring magnet 16, when the coil 6 is Y-connected as in the past, the peak current value increases and the output is reduced. Is trapezoidal to suppress peak current values and increase output.

  Further, focusing on the fifth-order harmonic component from the viewpoint of converting the induced voltage between lines into a trapezoidal wave, the content rate is set to 4.5% to 6.5% and the skew angle is set to an electrical angle of 39 ° ≦ θskew ≦ 54. By setting the angle, the content of the fifth harmonic component is increased, and the torque and the rotational speed are effectively increased. In this case, in the ring magnet 16, when the ratio of the magnetization angle θr and the pole pitch angle θp is 0.5 ≦ θr / θp ≦ 0.9, the fifth harmonic component is contained while satisfying the above condition of the skew angle. The rate is generally in the range of 4.5% to 6.5%. Accordingly, the ring magnet 16 is used to make the coil 6 have Δ connection, and θr / θp is set in the range of 0.5 to 0.9 (preferably 0.52 to 0.86), thereby achieving high output. It is possible to realize a brushless motor that satisfies both the low torque ripple and the ease of skew magnetization and has little variation in performance.

  It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

  For example, in the above-described embodiment, the brushless motor used for the column assist type EPS is shown. However, the present invention can be applied to other types of EPS motors. In addition, the present invention is widely applicable not only to EPS and motors for various on-vehicle electric products, but also to general brushless motors. In the above-described embodiment, an example in which the present invention is applied to a 6-pole 9-slot brushless motor using six magnets has been described. However, the configuration of the magnets and slots of the motor is not limited thereto, and the present invention is not limited thereto. Can be widely applied to brushless motors having a configuration that is an integral multiple of two poles and three slots.

It is sectional drawing of the brushless motor which is one Example of this invention. It is explanatory drawing which shows the structure of the stator in the motor of FIG. It is the graph which showed the relationship between the content rate of the 5th harmonic component in an induced voltage, the torque increase rate with respect to a sine wave drive, and a rotation speed increase rate. It is the graph which showed the relationship between the skew angle (electrical angle) in a 6 pole 9 slot motor, and the content rate of the 5th harmonic component with respect to all the harmonic components. It is a graph which shows the result of having investigated the relationship between (theta) r / (theta) p (magnetization angle / pole pitch angle) in a 6P9S motor, and the content rate of the 5th harmonic component in an induced voltage by using a skew angle as a parameter. It is explanatory drawing which shows the shape of the magnet in the motor of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brushless motor 2 Stator 3 Rotor 4 Case 5 Stator core 5a Teeth 6 Coil 6a End 7 Bus bar unit 8 Bracket 9 Divided core 11 Insulator 12 Feed terminal 13 Rotor shaft 14a, 14b Bearing 15 Rotor core 16 Ring magnet 17 Magnet cover 18 Key 21 Resolver 22 Rotor 23 Resolver stator 24 Resolver holder 24a Flange portion 25 Bracket holder unit 26 Rib 27 Female screw portion 28 Mounting screw 29 Power supply wiring 31 External power supply terminal 32 Bus bar terminal 33 Work hole 34 Bracket cap O Rotor rotation center θskew Skew angle θp Pole pitch angle θr Magnetization angle

Claims (3)

A brushless motor comprising a rotor having 2n (n is a positive integer) magnetic poles and a stator having 3n slots,
As a magnet that forms the magnetic pole, a ring magnet in which the magnetic pole is disposed along the circumferential direction is used, and a coil wound around the stator is Δ-connected ,
The ratio θr / θp between the magnetized angle θr of the magnet and the pole pitch angle θp of the magnetic pole is 0.5 ≦ θr / θp ≦ 0.9, and the skew angle θskew of the rotor is an electrical angle 39 ° ≦ θskew ≦ 54 °. By
A brushless motor characterized in that the content ratio of the fifth harmonic component contained in the induced voltage of the brushless motor to the fundamental wave is set to 4.5% to 6.5%, and the line-to-line induced voltage is trapezoidal. .   2. The brushless motor according to claim 1, wherein the brushless motor has a 6-pole 9-slot structure including six (n = 3) magnetic poles and nine slots.   3. The brushless motor according to claim 1, wherein the brushless motor is a motor used as a drive source for electric power steering.

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