JP2007306798A - Permanent magnet type brushless motor for electric power-steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a permanent magnet type brushless motor for an electric power-steering system in which proper sense of steering can be attained, by satisfying both low torque pulsation and reduction in eddy current loss of the rotor, and demagnetization of the magnet or fall of residual flux density can be prevented by suppressing heat generation from the rotor. <P>SOLUTION: The permanent magnet type brushless motor comprises a rotor 20 having a rotating shaft 21 and a plurality of permanent magnets 22, constituted of independent and separate magnets and provided around the rotating shaft 21, to form a plurality of magnetic poles, and stator 10 having a stator core 11 provided opposite to the rotor 20, while having a plurality of tees 11a projecting in the direction of central axis and slots 11b for winding formed between adjoining tees 11a and a concentrated armature winding 12 wound around the tees 11a. If the number of magnetic poles of the rotor 20 is P, and the number of slots between the teeth 11a of the stator 10 is N, relation; 1<N/P≤1.2 is satisfied, as well as the fraction N/P is not an irreducible fraction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a permanent magnet type brushless motor, and in particular, in a permanent magnet type brushless motor for an electric power steering apparatus used in an electric power steering apparatus such as an automobile, the cogging torque is reduced and the eddy current loss generated in the rotor is reduced. It is related to achieving both.

  FIG. 15 is a conceptual diagram of an electric power steering apparatus such as an automobile. The column shaft 32 transmits the steering force from the steering wheel 31, and the worm gear 33 (details are omitted in the figure, only the gear box is shown) transmits the output (torque, rotation speed) of the motor 34 while changing the rotation direction to a right angle. At the same time, decelerate and increase the assist torque. The handle joint 35 transmits the steering force and also changes the direction. A steering gear 36 (details are omitted in the figure, only the gearbox is shown) decelerates the rotation of the column shaft, and at the same time, converts it into a linear motion of the rack 37 to obtain the required transition. The wheels are moved by the linear motion of the rack 37, and the direction of the vehicle can be changed.

  In such an electric power steering apparatus, torque pulsation generated by the motor 34 is transmitted to the steering wheel 31 via the worm gear 33 and the column shaft 32. Therefore, when the motor 34 generates a large torque pulsation, a good steering feeling cannot be obtained. Even when the motor 34 does not generate assist torque, a smooth steering feeling cannot be obtained if the motor generates a large cogging torque.

  Here, the column assist type electric power steering apparatus that assists the column shaft 32 with the torque of the motor 34 is shown, but the same applies to the rack assist type electric power steering apparatus that assists the rack with the torque of the electric motor. .

JP 2001-218439 A Japanese Patent Laid-Open No. 2000-236652 Japanese Patent No. 2955452 Japanese Patent No. 2743918 Japanese Patent Publication No. 8-8764 JP 2001-275325 A

  In such an electric power steering device, a brushed direct current motor has been often used. However, a permanent magnet type brushless motor that can be made small and have high output is advantageous for application to electric power steering in medium-sized and large vehicles. And in order to apply this permanent magnet type brushless motor to an electric power steering apparatus, reduction of torque pulsation caused by cogging torque or the like has been a big problem.

  As a permanent magnet type brushless motor for an electric power steering apparatus, Patent Document 1 discloses a brushless motor in which a stator winding is a wave winding, the number of rotor poles is 6, and the number of stator grooves is 18. ing. However, in such a motor with a combination of the number of poles and the number of grooves, it is necessary to wind the winding across a plurality of stator teeth such as wave winding and lap winding, and the coil end becomes large, and the axial length of the motor Since the coil end is large and the coil end is large, there is a problem that the copper loss is large and the efficiency of the motor is lowered.

  On the other hand, as a winding for reducing the coil end, there is a so-called concentrated winding motor in which the winding is concentrated around one tooth of the stator. As examples of the motor concentratedly wound on the teeth, Patent Document 2 discloses examples of a magnet embedded type and a surface magnet type in which the number of rotor poles is 6 and the number of stator grooves is 9. However, a brushless motor having a 2: 3 ratio of the number of poles to the number of grooves, which has been conventionally used as in the motor disclosed here, generally has a large cogging torque. Therefore, when this motor is incorporated in an electric power steering apparatus, a good steering feeling cannot be obtained due to cogging torque. That is, a brushless motor having a ratio of the number of poles to the number of grooves of 2: 3, which has been often used conventionally, is not suitable as a motor for an electric power steering apparatus.

  In contrast, Patent Documents 3 to 5 disclose various combinations of the number of poles and the number of grooves so as to realize a low cogging torque. If a combination of the number of poles and the number of grooves disclosed in these is used, a suitable brushless motor for an electric power steering apparatus was obtained.

  However, as will be described later, the asynchronous component of the armature magnetomotive force varies greatly depending on the combination of the number of poles and the number of grooves, and eddy current loss occurs in the rotor due to the magnetomotive force. Further, the magnitude of eddy current loss generated in the rotor differs depending on the combination of the number of poles and the number of grooves, and the temperature rise of the rotor also differs. And when the temperature of a rotor rose, the temperature of a permanent magnet will also rise in connection with it, and the subject that it might lead to an irreversible demagnetization occurred.

  Moreover, even if irreversible demagnetization does not occur, there is a problem that the residual magnetic flux density decreases due to the temperature rise of the magnet, the magnetic flux generated by the magnet decreases, and as a result, the torque decreases.

  Furthermore, in order to generate the same torque as when there is no increase in temperature, there is a problem that a large armature current is required, the copper loss increases, and the temperature of the stator increases. In particular, rare earth magnets with a high energy product have high electrical conductivity, so eddy currents flow easily. Further, when a stainless steel ring is provided between the magnet and the gap to hold the magnet, eddy currents are further generated. It was easy and heat generation was a problem.

  On the other hand, there is one disclosed in Patent Document 6 as a motor for an electric power steering device. This motor is a brushless motor with 8 poles and 9 grooves and a small cogging torque, but the number of grooves / poles is an irreducible fraction (the denominator and numerator can be reduced without a common divisor other than 1). In other words, the electromagnetic excitation force in mode 1 (spatial order 1), that is, the excitation force that decenters the rotor is constantly generated. For this reason, there has been a problem that the life of the bearing is shortened, torque pulsation increases due to eccentricity, and vibration and noise increase.

  Moreover, although the case where the number of poles is 8 and the number of grooves is a multiple of 9 is disclosed, if the irreducible fraction is not obtained, for example, the number of poles is 8 and the number of grooves is 72 or 128, the number of grooves is too large. It is not suitable for mass production because it lacks workability. Therefore, there is a problem that it is not realistic as a motor for an electric power steering apparatus.

  The present invention has been made to solve the above-described problems. By appropriately selecting the number of poles and the number of grooves, both low torque pulsation and reduction of rotor eddy current loss can be achieved. An object of the present invention is to obtain a permanent magnet type brushless motor for an electric power steering apparatus which can prevent a demagnetization of a magnet and a decrease in a residual magnetic flux density by suppressing a heat generation of a rotor at the same time as obtaining a steering feeling. . Another object of the present invention is to obtain a permanent magnet type brushless motor for an electric power steering apparatus that can reduce the cost of the rotational position sensor and reduce torque pulsation caused by a detected position error of the rotational position sensor.

A permanent magnet type brushless motor for an electric power steering device according to the present invention is a permanent magnet type brushless motor used in an electric power steering device, and is provided with an independent and separate rotary shaft and a plurality of magnetic poles provided around the rotary shaft. A rotor having a plurality of permanent magnets composed of magnets, and a stator provided with a plurality of teeth projecting in the central axis direction so as to face the rotor, and a winding groove formed between adjacent teeth A stator having a core and an armature winding wound around the teeth intensively, when the number of magnetic poles of the rotor is P and the number of grooves between the teeth of the stator is N,
1 <N / P ≦ 1.2
And the fraction N / P is not an irreducible fraction.

  In this invention, by appropriately selecting the number of poles and the number of grooves, both low torque pulsation and reduction of eddy current loss of the rotor can be achieved, and good steering feeling can be obtained, and at the same time, heat generation of the rotor can be suppressed. By doing so, it is possible to provide a permanent magnet type brushless motor for an electric power steering apparatus that can prevent demagnetization of the magnet and a decrease in residual magnetic flux density. Further, it is possible to provide a permanent magnet type brushless motor for an electric power steering apparatus that can reduce the cost of the rotational position sensor and reduce torque pulsation caused by a detection position error of the rotational position sensor.

Embodiment 1 FIG.
Before describing the embodiment of the present invention, let us consider the mechanism of eddy current loss of the rotor in a permanent magnet type brushless motor. When the rotating magnetic field generated by the current flowing through the armature winding is synchronized with the rotor, a steady torque is generated in the rotor and the rotor rotates. The rotating magnetic field synchronized with the rotor is stationary when viewed in a coordinate system fixed to the rotor. The fact that it appears to be stationary means that it does not cause a change in magnetic flux and therefore does not cause eddy current loss in the rotor.

  However, the rotating magnetic field generated by the armature current includes a component that is not synchronized with the rotor. For example, there is a magnetic field that rotates in the opposite direction to the rotor. Such a component that is not synchronized with the rotor is not stationary when viewed from the coordinate system fixed to the rotor, and thus has an effect of changing the magnetic flux. An eddy current is generated in the rotor to cancel the change in magnetic flux.

  In the rotating magnetic field generated by the armature current, the amplitude and spatial order of components that are not synchronized with the rotor differ depending on the number of poles and the number of grooves. FIGS. 1 to 5 show what kind of rotating magnetic field is generated by the armature current when the stator winding is concentrated. FIG. 1 is a graph showing components of a rotating magnetic field when N / P = 1.5, where P is the number of poles and N is the number of grooves. 2 is N / P = 1.2, FIG. 3 is N / P = 1.125, FIG. 4 is N / P = 0.9, and FIG. 5 is N / P = 0. 7 is a graph showing components of a rotating magnetic field at 75. In each figure, the horizontal axis indicates the spatial order, and the electrical angle of 360 degrees is the primary. The vertical axis indicates the amplitude of the rotating magnetic field and is normalized with the synchronization component, that is, the fundamental wave as 1. In each figure, when the amplitude of the rotating magnetic field is positive, it is a magnetic field that rotates in the same direction as the rotor, that is, a positive-phase rotating magnetic field. On the other hand, when the amplitude is negative, it indicates that the rotating magnetic field rotates in the opposite direction to the rotor, that is, the rotating magnetic field has a reverse phase. Of course, the rotating magnetic fields of opposite phase are all asynchronous components. Further, among the positive-phase rotating magnetic fields, those other than the spatial primary rotating magnetic field are all non-synchronous components because they are not stationary magnetic fields when viewed from the coordinate system fixed to the rotor.

  1 to 5, it can be seen that the rotating magnetic field generated by the armature current differs depending on the combination of the number of poles and the number of grooves. In particular, when the ratio N / P between the number of poles P and the number of grooves N is N / P <1, it can be seen that there is an asynchronous component having an amplitude larger than the synchronous component. For example, when N / P = 0.9, there is an asynchronous component with an amplitude of 1.25 in the space 4/5, and when N / P = 0.75, an asynchronous component with an amplitude of 2.0 in the space 1/2. Exists. When the asynchronous component is larger than the synchronous component in this way, the eddy current loss generated in the rotor is larger than when there is no asynchronous component larger than the synchronous component (when N / P> 1). Conceivable.

  Therefore, in order to know how the eddy current loss generated in the rotor changes depending on the number of poles P and the number of grooves N, various combinations of permanent magnet type brushless motors are designed and magnetic fields using the finite element method are used. The eddy current loss of the rotor was calculated by analysis. FIG. 6 shows the number of poles P, the number of grooves N, and N / P of the five types of permanent magnet brushless motors designed. Moreover, sectional views of the stator and rotor of each motor are shown in FIGS.

  7 to 11, the permanent magnet type brushless motor stator 10 has a stator core 11 and an armature winding 12. The stator core 11 has a substantially cylindrical shape, a plurality of teeth 11a projecting in the central axis direction, and a winding groove 11b is formed between adjacent teeth 11a. The armature windings 12 are so-called concentrated windings that are intensively wound around the teeth 11 a of the stator core 11. Here, the concentrated winding refers to a case where a conductive wire is wound around a certain tooth 11a a plurality of times to form a coil for the tooth 11a. The other teeth 11a are similarly wound with a plurality of turns to form coils for the teeth 11a, and these coils are connected in parallel or in series to form a multi-phase (for example, three-phase) armature winding 12. It is formed.

  On the other hand, the rotor 20 includes a rotary shaft 21 and a plurality of permanent magnets 22 provided around the circumference of the rotary shaft 21 in the circumferential direction. The permanent magnet 22 is magnetized so as to constitute a plurality of alternately different magnetic poles. In this embodiment, the ring-shaped magnet 22 is shown as a whole. However, each magnetic pole 22 may be composed of an independent magnet or embedded in the rotor core of the rotor 20. It may be a structure.

  In the motor shown in each figure, the rotor 20 and the stator 10 have the same diameter. That is, the outer diameter (diameter) of the rotor 20 was 40 mm, and the outer diameter (diameter) of the stator 10 was 80 mm. The shaft length and rated current value are the same. This is because the output can be compared with the same motor even if the combination of the number of poles and the number of grooves is changed. Furthermore, the opening width of the groove 11b is the same and designed to be smaller than usual so that the influence of the permeance by the groove 11b of the stator 10 becomes substantially the same. This is because the influence of the permeance due to the groove 11b affects eddy current loss and cogging torque, which will be described later, so it is necessary to design and compare under the same conditions.

FIG. 12 shows an analysis result of eddy current loss generated in the rotor 20 of these five types of permanent magnet brushless motors. This result is an eddy current loss generated in the rotor 20 when the motor rotates at 2000 rpm and the rated current is applied to the armature winding 12. Further, the value of the eddy current loss indicates a ratio with respect to the output as a% value. From FIG. 12, it can be seen that the eddy current loss generated in the rotor 20 greatly depends on the ratio N / P of the number of grooves N and the number of poles P of the motor. Further, as described above, when N / P <1 where the asynchronous component of the rotating magnetic field generated by the armature current includes an amplitude larger than the synchronous component, N / P> 1. It became clear that the eddy current loss was increasing. Therefore, when designing a permanent magnet type brushless motor for an electric power steering device, the ratio N / P of the number of poles P and the number of grooves N is N / P> 1 (1)
If the relational expression is selected to hold, the asynchronous component of the rotating magnetic field generated by the armature current does not include a component larger than the synchronous component, so that the eddy current loss generated in the rotor 20 can be reduced and the heat generated by the magnet It can be seen that there is an effect that it is possible to prevent a decrease in torque due to demagnetization or a decrease in residual magnetic flux density.

  From the examination so far, it has been found that the eddy current loss generated in the rotor 20 can be reduced by selecting N / P> 1 for the number of poles P and the number of grooves N of the permanent magnet brushless motor. However, a permanent magnet brushless motor for an electric power steering apparatus cannot obtain a good steering feeling unless its torque pulsation is reduced. Therefore, it is necessary to reduce the cogging torque that causes torque pulsation. Therefore, the cogging torque was obtained for the five types of brushless motors shown in FIG. The results are shown in FIG. The horizontal axis represents the ratio N / P between the number of grooves N and the number of poles P of the motor, and the vertical axis represents the ratio of the cogging torque to the rated torque in%.

In general, when converted from a gear ratio, a motor for an electric power steering apparatus is a guideline that the torque pulsation should be about 2% or less of the rated torque in order to obtain a smooth steering feeling in the steering wheel. . From the result of FIG. 13, in order to reduce the cogging torque to 2% or less of the rated torque, 0.85 <N / P ≦ 1.2 for the number of poles P and the number of grooves N (2)
You can see that. That is, in order to obtain a brushless motor for an electric power steering apparatus with a small torque pulsation, the number of poles P and the number of grooves N of the brushless motor need only satisfy Equation (2).

From the examination results so far, when formulas (1) and (2) are considered simultaneously, that is, the number of poles P and the number of grooves N are 1 <N / P ≦ 1.2 (3)
Thus, a brushless motor for an electric power steering device with a small eddy current of the rotor 20 and a small torque pulsation can be obtained.

  However, it may not be suitable as a brushless motor for an electric power steering device by merely satisfying the expression (3). When the fraction N / P is an irreducible fraction, the electromagnetic excitation force in mode 1, that is, the excitation force in the direction that causes the rotor 20 to be eccentric exists constantly. The cause of this will be described. When the fraction N / P is not an irreducible fraction, symmetry appears in the magnetic flux density distribution inside the motor, and as a result, the electromagnetic force is balanced. For example, a motor having 6 poles and 9 grooves has symmetry in the magnetic flux density distribution for two poles. That is, in this case, the magnetic flux density is symmetrical at a mechanical angle of 120 degrees, and the electromagnetic force is balanced at a point away from the mechanical angle of 120 degrees, so that the value obtained by integrating the electromagnetic force in the circumferential direction becomes zero. As a result, mode 1 electromagnetic excitation force is not generated. However, when the number of poles is 8 and the number of grooves is 9, the fraction N / P is an irreducible fraction and has no symmetry. In other words, since the electromagnetic force is integrated in the circumferential direction and does not become zero, a mode 1 electromagnetic excitation force is generated.

  When a combination in which the fraction N / P is an irreducible fraction is selected in this way, an excitation force is always generated in the direction in which the rotor 20 is eccentric, so that the life of the bearing is shortened, and torque pulsation increases due to the eccentricity. In addition to not being able to obtain a good steering feeling, vibration noise is also increased. As already described, for example, P = 8 and N = 9. As in the case of P = 8 and N = 9, even when N / P = 1.125, when P = 24 and N = 27, the fraction N / P is 27/24 and does not become an irreducible fraction. No excitation force is generated.

  Therefore, a brushless motor for an electric power steering apparatus that satisfies Equation (3) and has a small eddy current in the rotor 20 and a small torque pulsation when the fraction N / P is not an irreducible fraction can be obtained.

As described above, in the permanent magnet brushless motor for an electric power steering apparatus, the rotor 20 having a plurality of magnetic poles by the permanent magnet 22 and the stator 10 in which the armature winding 12 is intensively wound around the teeth 11a are provided. When the number of magnetic poles of the rotor 20 is P and the number of grooves of the stator is N,
1 <N / P ≦ 1.2 (3)
In addition, by adopting a configuration in which the fraction N / P is not an irreducible fraction, it is possible to achieve both a low cogging torque and a reduction in eddy current loss of the rotor 20 and obtain a good steering feeling. There is an effect that it is possible to prevent demagnetization due to heat generation of the magnet 22 and a decrease in torque due to a decrease in residual magnetic flux density. Further, there is no effect of extending the life of the bearing because there is no electromagnetic excitation force in mode 1, that is, no excitation force for eccentricizing the rotor 20, and a good steering feeling is obtained because torque pulsation due to eccentricity is small. There is also an effect that it is possible.

  In this embodiment, the case where the conductive ring for holding the magnet of the rotor 20 is not provided is described. However, the eddy current generated in the ring for holding the magnet (for example, a ring made of stainless steel metal). Since the loss is also generated by the same mechanism as described above, it is needless to say that the same effect as this embodiment can be obtained even when a conductive ring for holding the magnet is provided.

Embodiment 2. FIG.
FIG. 14 is a sectional view showing an example of a permanent magnet type brushless motor for an electric power steering apparatus according to the present invention. This embodiment shows an example of 16 poles and 18 slots. Number of poles P and number of grooves N are 1 <N / P ≦ 1.2 (3)
This is an example of the case where the fraction N / P is not an irreducible fraction, and the case where N / P = 1.125 is shown. With such a configuration, none of the asynchronous components of the rotating magnetic field generated by the armature current exceeds the amplitude of the synchronous component, and the eddy current of the rotor 20 can be reduced and the cogging torque is small. . Furthermore, since the fraction N / P is not an irreducible fraction, the electromagnetic excitation force of mode 1 is not generated, which contributes to the extension of the bearing life and increases the torque pulsation due to the eccentricity of the rotor 20 and the vibration and noise caused by it. There is also an effect that the increase can be prevented.

  Further, as an index of how to effectively use the air gap magnetic flux generated by the magnet of the rotor 20, there is a winding coefficient. It can be said that the higher the winding coefficient, the more effective the gap magnetic flux generated by the magnet is, and the more efficient the motor. In the conventional example in which the number of poles of the rotor 20 of Patent Document 2 is 6 and the number of grooves of the stator 10 is 9, the winding coefficient is 0.866, whereas N / P = 1. In the case of 125, the winding coefficient is as high as 0.945, and there is an effect that an efficient motor can be configured.

  Furthermore, various combinations are possible where N / P = 1.125 and the fraction N / P is not an irreducible fraction. P = 24, N = 27, P = 32, N = 36, and the like. Of these, the combination with the smallest number of poles is the case of FIG. 14 where P = 16 and N = 18. It will be described that a smaller number of poles is more suitable as a brushless motor for an electric power steering apparatus.

  When the brushless motor is controlled by sinusoidal driving, a desired torque cannot be obtained unless a current is supplied with a phase corresponding to the rotor position. If the accuracy of the rotational position sensor is reduced and an accurate rotor position cannot be grasped, a current is supplied with an incorrect phase, and a torque different from a desired torque is generated. Further, in a rotational position sensor such as a variable reluctance resolver, the error has a periodic variation with respect to the rotational position. Therefore, when this error is large, the generated torque is not constant but periodically varies according to the position of the rotor 20 and appears as torque pulsation. This torque pulsation causes a decrease in steering feeling, leading to a decrease in performance as an electric power steering apparatus. Since the error is determined by the electrical angle, the larger the number of poles, the larger the value representing the error in electrical angle. Therefore, the smaller the number of poles, the smaller the error of the rotation sensor, so it can be said that it is suitable as a motor for an electric power steering apparatus.

Therefore, in the motor of P = 16 and N = 18 shown in the present embodiment, the number of poles P and the number of grooves N are 1 <N / P ≦ 1.2 (3)
In addition, since the fraction N / P is not an irreducible fraction, both the low cogging torque and the reduction of the eddy current loss of the rotor 20 can be achieved, and a good steering feeling can be obtained. There is an effect that it is possible to prevent a demagnetization due to heat generation and a torque decrease due to a decrease in residual magnetic flux density. Further, there is no effect of extending the life of the bearing because there is no electromagnetic excitation force in mode 1, that is, no excitation force for eccentricizing the rotor 20, and a good steering feeling is obtained because torque pulsation due to eccentricity is small. There is also an effect that it is possible.

  Furthermore, since it is the combination with the smallest number of poles among those satisfying N / P = 1.125, an inexpensive sensor such as a variable reluctance resolver is used without using an expensive sensor such as an optical encoder. Therefore, the cost of the rotational position sensor can be reduced. Further, since the position detection accuracy of the rotational position sensor is deteriorated, the rotor position cannot be accurately determined, and there is an effect that torque pulsation generated due to a shift in the energization phase of the armature current can be reduced.

  In the present embodiment, the case where the conductive ring for holding the magnet of the rotor 20 is not provided has been described. However, the eddy current loss generated in the magnet holding ring (for example, a stainless steel ring) has also been described so far. Needless to say, the same effect can be obtained even when a conductive ring for holding a magnet is provided because the mechanism is generated by the same mechanism as described.

Embodiment 3 FIG.
Another example of the permanent magnet type brushless motor for an electric power steering apparatus according to the present invention will be described. In the present embodiment, the number of poles P and the number of grooves N are 1 <N / P ≦ 1.2 (3)
As an example in which the fraction N / P is not an irreducible fraction, an example of N / P = 1.2 (example of 10 poles and 12 slots) is shown. FIG. 8 corresponds to this embodiment. With such a configuration, none of the asynchronous components of the rotating magnetic field generated by the armature current exceeds the amplitude of the synchronous component, and the eddy current of the rotor 20 can be reduced and the cogging torque is small. . Furthermore, since the fraction N / P is not an irreducible fraction, the electromagnetic excitation force of mode 1 is not generated, which contributes to the extension of the bearing life and increases the torque pulsation due to the eccentricity of the rotor 20 and the vibration and noise caused by it. There is also an effect that the increase can be prevented.

  Further, as an index of how to effectively use the air gap magnetic flux generated by the magnet of the rotor 20, there is a winding coefficient. It can be said that the higher the winding coefficient, the more effective the gap magnetic flux generated by the magnet is, and the more efficient the motor. In the conventional example in which the number of poles of the rotor of Patent Document 2 is 6 and the number of grooves of the stator is 9, the winding coefficient is 0.866, whereas N / P = 1.2. In this case, the winding coefficient is as high as 0.933, and there is an effect that an efficient motor can be configured.

  Furthermore, various combinations are possible where N / P = 1.2 and the fraction N / P is not an irreducible fraction. P = 20, N = 24, P = 30, N = 36, and the like. Of these, the combination with the smallest number of poles is the case of FIG. 8 where P = 10 and N = 12.

  As described in the present embodiment, a rotational position sensor is widely used to control a brushless motor. However, since the position of the rotor 20 is determined by an electrical angle, the accuracy required for the rotational position sensor increases as the number of poles increases. Get higher. Therefore, even if the cogging torque and the eddy current loss of the rotor 20 can be reduced, if the number of poles becomes too large, the cost of the rotational position sensor increases, and the rotor position cannot be accurately determined due to low accuracy. In some cases, the energization phase of the armature current shifts and torque pulsation occurs. Since the accuracy of the rotation sensor needs to be determined by the electrical angle, the accuracy varies depending on the number of poles of the motor even with the same error, and the error when expressed in electrical angle increases as the number of poles increases. Therefore, it can be said that the smaller the number of poles, the better the motor for the electric power steering apparatus.

Therefore, in the motor of P = 10 and N = 12, shown in the present embodiment, the number of poles P and the number of grooves N are 1 <N / P ≦ 1.2 (3)
In addition, since the fraction N / P is not an irreducible fraction, both the low cogging torque and the reduction of the eddy current loss of the rotor 20 can be achieved, and a good steering feeling can be obtained. There is an effect that it is possible to prevent a demagnetization due to heat generation and a torque decrease due to a decrease in residual magnetic flux density. Further, there is no effect of extending the life of the bearing because there is no electromagnetic excitation force in mode 1, that is, no excitation force for eccentricizing the rotor 20, and a good steering feeling is obtained because torque pulsation due to eccentricity is small. There is also an effect that it is possible.

  Furthermore, since the combination with the smallest number of poles among those satisfying N / P = 1.2, an inexpensive sensor such as a variable reluctance resolver is used without using an expensive sensor such as an optical encoder. Therefore, the cost of the rotational position sensor can be reduced. Further, since the position detection accuracy of the rotational position sensor is deteriorated, the rotor position cannot be accurately determined, and there is an effect that torque pulsation generated due to a shift in the energization phase of the armature current can be reduced.

  In this embodiment, the case where the conductive ring for holding the rotor magnet is not provided has been described. However, the eddy current loss generated in the magnet holding ring (for example, a stainless steel ring) has also been described so far. Needless to say, the same effect can be obtained even when a conductive ring for holding a magnet is provided.

A permanent magnet type brushless motor for an electric power steering apparatus according to the present invention is a permanent magnet type brushless motor used in an electric power steering apparatus, and is provided with a plurality of permanent magnets that are provided around a rotating shaft and a plurality of magnetic poles. Concentrating on the rotor having a magnet, the stator core provided opposite to the rotor, a plurality of teeth projecting in the central axis direction, and a winding groove formed between adjacent teeth, and the teeth A stator having a wound armature winding, where the number of magnetic poles of the rotor is P, and the number of grooves between the teeth of the stator is N,
1 <N / P ≦ 1.2
And the fraction N / P is not an irreducible fraction. With this configuration, both low cogging torque and reduction of rotor eddy current loss can be achieved, and a good steering feeling can be obtained. At the same time, torque due to demagnetization due to magnet heat generation and reduction in residual magnetic flux density There is an effect that it is possible to prevent a decrease in the amount of water. Furthermore, since no electromagnetic excitation force in mode 1 is generated, an increase in vibration and noise can be prevented.

In addition, the number of magnetic poles P of the rotor and the number N of grooves between the teeth of the stator are
N / P = 1.125
It is. With this configuration, both low cogging torque and reduction of rotor eddy current loss can be achieved, and a good steering feeling can be obtained. At the same time, torque due to demagnetization due to magnet heat generation and reduction in residual magnetic flux density There is an effect that it is possible to prevent a decrease in the amount of water. Furthermore, there is an effect that a winding factor is high and an efficient motor can be configured.

In addition, the number of magnetic poles P of the rotor and the number N of grooves between the teeth of the stator are
N / P = 1.20
It is. With this configuration, both low cogging torque and reduction of rotor eddy current loss can be achieved, and a good steering feeling can be obtained. At the same time, torque due to demagnetization due to magnet heat generation and reduction in residual magnetic flux density There is an effect that it is possible to prevent a decrease in the amount of water. Furthermore, there is an effect that a winding factor is high and an efficient motor can be configured.

In addition, the number of magnetic poles P of the rotor and the number N of grooves between the teeth of the stator are
N = 18 and P = 16
It is. With this configuration, both low cogging torque and reduction of rotor eddy current loss can be achieved, and a good steering feeling can be obtained. At the same time, torque due to demagnetization due to magnet heat generation and reduction in residual magnetic flux density There is an effect that it is possible to prevent a decrease in the amount of water. Furthermore, since the number of poles is not too large, the accuracy of the rotational position sensor is not lowered, so that there is an effect that a motor with low torque pulsation can be realized. In addition, there is an effect that it is more advantageous in terms of noise and torque pulsation because the first-order radial radial excitation force due to eccentricity is less likely to occur than when N = 9 and P = 8.

In addition, the number of magnetic poles P of the rotor and the number N of grooves between the teeth of the stator are
N = 12 and P = 10
It is. With this configuration, both low cogging torque and reduction of rotor eddy current loss can be achieved, and a good steering feeling can be obtained. At the same time, torque due to demagnetization due to magnet heat generation and reduction in residual magnetic flux density There is an effect that it is possible to prevent a decrease in the amount of water. Furthermore, since the number of poles is not too large, the accuracy of the rotational position sensor is not lowered, so that there is an effect that a motor with low torque pulsation can be realized.

It is a graph which shows the component of a rotating magnetic field when the pole number P and the groove number N are N / P = 1.5. It is a graph which shows the component of a rotating magnetic field when the number of poles P and the number of grooves N are N / P = 1.2. It is a graph which shows the component of a rotating magnetic field when the pole number P and the groove number N are N / P = 1.125. It is a graph which shows the component of a rotating magnetic field when the pole number P and the groove number N are N / P = 0.9. It is a graph which shows the component of a rotating magnetic field when the pole number P and the groove number N are N / P = 0.75. It is a table | surface which shows the pole number P, the groove number N, and N / P of each motor. It is sectional drawing of a permanent magnet type brushless motor with the number of poles P = 8 and the number of grooves N = 12. It is sectional drawing of a permanent magnet type brushless motor with the number of poles P = 10 and the number of grooves N = 12. It is sectional drawing of a permanent magnet type brushless motor with the number of poles P = 8 and the number of grooves N = 9. It is sectional drawing of a permanent magnet type brushless motor with the number of poles P = 10 and the number of grooves N = 9. It is sectional drawing of a permanent magnet type brushless motor with the number of poles P = 8 and the number of grooves N = 6. It is a graph which shows the analysis result of the eddy current loss which generate | occur | produces in a rotor. It is a graph which shows the magnitude | size of a cogging torque. It is sectional drawing of a permanent magnet type brushless motor with the number of poles P = 16 and the number of grooves N = 18. It is a conceptual diagram of electric power steering devices, such as a car.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Stator, 11 Stator iron core, 11a Teeth, 11b Groove, 12 Armature winding, 20 Rotor, 21 Rotating shaft, 22 Permanent magnet

Claims (5)

A permanent magnet type brushless motor used in an electric power steering device,
A rotor having a rotating shaft and a plurality of permanent magnets formed of independent independent magnets that are provided around the rotating shaft and form a plurality of magnetic poles;
A stator core provided opposite to the rotor and projecting a plurality of teeth in the direction of the central axis and having a winding groove formed between adjacent teeth, and an electric machine intensively wound around the teeth A stator having a child winding, and
When the number of the magnetic poles of the rotor is P and the number of grooves between the teeth of the stator is N,
1 <N / P ≦ 1.2
And a fraction N / P is not an irreducible fraction. A permanent magnet type brushless motor for an electric power steering apparatus. The number P of the magnetic poles of the rotor and the number N of grooves between the teeth of the stator are
N / P = 1.125
The permanent magnet type brushless motor for an electric power steering apparatus according to claim 1, wherein The number P of the magnetic poles of the rotor and the number N of grooves between the teeth of the stator are
N / P = 1.20
The permanent magnet type brushless motor for an electric power steering apparatus according to claim 1, wherein The number P of the magnetic poles of the rotor and the number N of grooves between the teeth of the stator are
N = 18 and P = 16
The permanent magnet brushless motor for an electric power steering apparatus according to claim 2, wherein the permanent magnet brushless motor is an electric power steering apparatus. The number P of the magnetic poles of the rotor and the number N of grooves between the teeth of the stator are
N = 12 and P = 10
The permanent magnet brushless motor for an electric power steering apparatus according to claim 3, wherein

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