JPH0723975U - 3-phase brushless motor - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce fluctuations in rotational torque. [Structure] The outer peripheral surface of the rotor 7 is a cylindrical surface having no irregularities. Circular holes 16, 16 are formed inside the rotor 7. The positions at which the circular holes 16 are formed are approximately 6 electrical degrees in the same direction in the circumferential direction from the boundary between the adjacent S and N poles.
The part is offset by 0 degrees.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The three-phase brushless motor according to the present invention is used, for example, as a drive source for an electric power steering device.

[0002]

[Prior art]

 Although power steering devices are widely used to reduce the steering force of automobiles, the use of three-phase brushless motors as a drive source for power steering devices for small automobiles such as light automobiles has been studied. FIG. 8 shows a general three-phase brushless motor. In the motor case 1, the front end (upper end of FIG. 8) of the cylindrical tubular portion 2 is closed by a circular ring-shaped front lid 3, and the rear end (lower end of FIG. 8) is opened by a disk-shaped rear lid 4. It is blocking. Bearings 5 and 5 are provided in the central portions of the front lid 3 and the rear lid 4, respectively, and the rotary shaft 6 is rotatably supported by these bearings 5 and 5.

A rotor 7 is supported and fixed on the outer peripheral surface of the intermediate portion of the rotary shaft 6 in the motor case 1. The rotor 7 is composed of permanent magnets, and as shown in FIG. 10, magnetic poles (S pole and N pole) on the outer peripheral surface are alternately arranged in the circumferential direction at different intervals. There is. In such a rotor 7, permanent magnets of the same shape and size each formed in an arc shape are combined in a cylindrical shape, or a magnetizing method of one permanent magnet formed in a cylindrical shape is devised. By doing so, the magnetic poles on the outer peripheral surface are alternately changed.

On the other hand, a three-phase drive coil 8 is supported and fixed to the inner peripheral surface of the cylindrical portion 2. The drive coil 8 is formed into a cylindrical shape by winding a coil 10a, 10b, 10c described below around a core 9 made of a magnetic material, the inner peripheral surface of which is the outer periphery of the rotor 7. It is facing the surface. As shown in FIG. 9, the drive coil 8 is formed by combining three-phase coils 10a, 10b, and 10c of a-phase, b-phase, and c-phase. Then, based on a signal from the Hall element 12 described below, the energization of each of these coils 10a, 10b, 10c is controlled by a control circuit as shown in the figure.

A phase detecting permanent magnet 11 is fixed to a portion of the rear end portion (lower end portion in FIG. 8) of the rotary shaft 6 facing the inner surface 4 a of the rear lid 4. The phase-detecting permanent magnet 11 formed in the shape of a circular ring alternately changes the magnetic poles in the circumferential direction at equal intervals, like the rotor 7 described above. A Hall element 12 for phase detection is provided so as to face the side surface of the permanent magnet 11 for phase detection. In the illustrated example, the three Hall elements 12 are supported by a support plate 13 made of a non-magnetic material and having a ring shape, and the support plate 13 is supported on the inner surface 4a of the rear lid 4 via stays 14 and 14. is doing.

The detection of the phase between the rotor 7 and the drive coil 8 by the Hall element 12 is performed by detecting the direction of the magnetic flux of the magnetic circuit formed by the phase detecting permanent magnet 11 by the Hall element 12. The pitch at which the magnetic poles of the phase detecting permanent magnet 11 change is equal to the pitch at which the magnetic poles on the outer peripheral surface of the rotor 7 change. Therefore, the phase of the rotor 7 and the drive coil 8 is detected by the Hall element 12 described above, and among the three-phase coils 10a, 10b, and 10c of the a-phase, b-phase, and c-phase that form the drive coil 8, The rotor 7 can be rotated in a desired direction by sending a direct current in an appropriate direction to any two-phase coil at an appropriate timing.

That is, when the rotary shaft 6 is rotated, a control circuit as shown in FIG. 9 is constructed based on the phases of the rotor 7 and the drive coil 8 detected by the Hall element 12. Due to the functions of the transistors 15 and 15 and the SCR (silicon controlled rectifier), direct currents in the appropriate directions are sent to the coils 10a, 10b and 10c constituting the drive coil 8 to magnetize the drive coil 8. That is, currents in opposite directions are applied in a rectangular wave to any two-phase coils of the three-phase coils 10a, 10b, and 10c of the a-phase, b-phase, and c-phase, and the remaining one-phase coils are supplied. The state where the coil is not energized is repeatedly realized by changing (switching) the coil which is not energized every 60 degrees in electrical angle. As a result, an attractive force and a repulsive force act between the drive coil 8 and the permanent magnet forming the rotor 7, and the rotor 7 rotates.

When the three-phase brushless motor configured and operating as described above is used as a drive source for the power steering device, the rotary drive force is applied from the front end portion (upper end portion in FIG. 8) of the rotary shaft 6. The steering shaft is rotated by this rotation driving force. However, the magnitude T of the rotational driving force is smaller than the force (torque) F required to rotate the steering shaft (T <F), and this rotational driving force is used to operate the steering wheel. It is used to reduce the steering force required for. Further, when the steering angle (generally the front wheels of the automobile) is kept applied to the steered wheels, a force is applied to the steering shaft by the rotating shaft 6 in the direction for holding the steering angle. As a result, the steering force that must be continuously applied to the steering wheel to maintain the steering angle is reduced.

[0009]

[Problems to be solved by the device]

 By the way, in the case of the conventional three-phase brushless motor configured and operating as described above, the torque fluctuation due to the rotation is large, and as it is, it is not preferable as the driving source of the power steering for automobiles.

That is, the magnetic flux density on the surface of the rotor 7 composed of a permanent magnet changes sinusoidally as shown in FIG. Then, based on the energization of the drive coil 8, the torque acting between the coils 10a, 10b, 10c and the rotor 7 in the direction of rotating the rotor 7 changes in proportion to the magnetic flux density. . For example, when the torque acting between the a-phase coil 10a and the rotor 7 changes as shown by the solid line a in FIG. 12, the torque acting between the b-phase coil 10b and the rotor 7 As shown by a chain line b in the figure, the torque acting between the c-phase coil 10c and the rotor 7 changes as shown by a broken line c in the figure. The rotating torque applied to the rotating shaft 6 via the rotor 7 is the total value of the torques acting between the rotors 7 and the coils 10a, 10b, 10c of the respective phases. Therefore, such a rotating torque T changes as shown by the solid line A in FIG. 12 as the rotating shaft 6 rotates.

As is clear from the solid line A, the rotational torque T of the rotary shaft 6 is 60 electrical degrees in one cycle (as shown in FIG. 10, three pairs of S poles and N poles are provided. In this case, the rotation axis 6 changes by 1/3 rotation as one cycle, and the fluctuation width ΔT (torkle ripple) becomes considerably large. According to the calculation by the present inventor, the maximum value T of the rotational torque T _MAX And the minimum value T_MIN Fluctuation range ΔT (= T_MAX -T_MIN ) Is the average value T of the rotation torque T_AVE (= (T_MAX + T_MIN The ratio to) / 2) reaches 14.2%.

As described above, when the three-phase brushless motor in which the rotation torque of the rotating shaft 6 largely changes is used as a drive source of the power steering device, the driver is accompanied by a change in the assist force (rotation torque). Is not preferable because the force required to operate the steering wheel (steering force) fluctuates greatly and gives a strange feeling to the driver.

As described above, the fluctuation of the rotational torque T that causes such an inconvenience occurs as the magnetic flux density on the surface of the rotor 7 changes sinusoidally over the circumferential direction. Therefore, it is possible to suppress the fluctuation of the rotation torque by devising the method of magnetizing the permanent magnets that form the rotor 7. That is, if the magnetic flux density on the surface of the rotor 7 is changed like a trapezoidal wave as shown in FIG. 13, the fluctuation of the rotational torque can be reduced. However, it is technically difficult to set the magnetic flux density on the surface of the rotor 7 as shown in FIG. 13 in order to reduce the fluctuation of the torque, and at present, it cannot be said to be a practical solution.

The three-phase brushless motor of the present invention was devised in view of the above circumstances.

[0015]

[Means for Solving the Problems]

 The three-phase brushless motor of the present invention is similar to the above-described conventional three-phase brushless motor in that it has a rotary shaft, a rotor fixed to the outer peripheral surface of the rotary shaft, and a three-phase surrounding the rotor. And a drive coil. The outer peripheral surface of the rotor is magnetized with S poles and N poles alternately and at equal intervals.

Particularly, in the three-phase brushless motor of the present invention, the outer peripheral surface of the rotor is a cylindrical surface having no irregularities, and a plurality of air gaps extending in the axial direction of the rotor are provided inside the rotor. Has been. The positions of the air gaps in the circumferential direction are positions that are deviated from the boundary between the adjacent S and N poles in the same direction in the circumferential direction by an electrical angle of approximately 60 degrees.

[0017]

[Action]

 In the case of the three-phase brushless motor of the present invention configured as described above, the magnetic flux density on the rotor surface becomes low at the portion where the air gap is provided. Then, as the magnetic flux density decreases, the rotation torque of the rotating shaft also decreases. In this way, the portion where the magnetic flux density becomes low and the rotating torque of the rotating shaft becomes small corresponds to the portion where the rotating torque becomes maximum when the gap is not provided. Therefore, the difference between the maximum value and the minimum value, that is, the fluctuation range of the rotational torque decreases as the maximum value of the rotational torque decreases.

[0018]

【Example】

 1 to 4 show a first embodiment of the present invention. The feature of the present invention is that the magnetic flux density in the circumferential direction of the rotor 7 is adjusted in order to suppress the fluctuation of the rotation torque, and the configuration and operation of the other parts are the same as those of the conventional 3 described above. It is similar to the phase brushless motor. Therefore, the illustration and description of the same parts are omitted, and the characteristic parts of the present invention will be mainly described below.

The outer peripheral surface 7 a of the rotor 7 that is fixed to the outer peripheral surface of the intermediate portion of the rotating shaft 6 (see FIG. 8) and rotates together with the rotating shaft 6 is a cylindrical surface having no irregularities. S poles and N poles are alternately arranged on the outer peripheral surface 7a at equal intervals. Further, inside the rotor 7, a circular hole 16 extending in the axial direction of the rotor 7 is provided at a circumferentially intermediate position of each pole and at a portion which is radially inward from the outer peripheral surface 7a. 16 are formed, and the insides of the circular holes 16 and 16 are voids.

More specifically, the positions where the circular holes 16 and 16 are formed are such that the positions in the circumferential direction inside the respective S poles and N poles are the boundaries between the adjacent S poles and N poles. It is a portion that is deviated in the same direction in the circumferential direction from the electrical angle by approximately 60 degrees.

In the case of the brushless motor of the present invention configured as described above, the magnetic flux density on the outer peripheral surface 7a of the rotor 7 is provided with the voids by the circular holes 16 and 16 as shown in FIG. It becomes low at a position deviated from the boundary by an electrical angle of about 60 degrees. The drive coil 8 facing the outer peripheral surface 7a of the rotor 7 is provided with three-phase coils 10a, 10b, 10c (see FIG. 9), as in the case of the conventional structure described above. Currents having different phases from each other as shown in FIG. 3 are applied to 10b and 10c in a rectangular wave shape.

When the coils 10a, 10b, 10c are energized in this way, the torque in the direction of rotating the rotor 7 is the same as in the case of the conventional structure described above. It changes in proportion to the density. When the torque acting between the a-phase coil 10a and the rotor 7 changes as shown by the solid line a'in FIG. 4, the torque acting between the b-phase coil 10b and the rotor 7 is As indicated by the chain line b'in the figure, the torque acting between the c-phase coil 10c and the rotor 7 changes as indicated by the dashed line c'in the figure. The rotary torque applied to the rotary shaft 6 via the rotor 7 is the total value of the torques acting between the coils 10a, 10b, 10c of the respective phases and the rotor 7. Therefore, such a rotating torque changes as shown by the solid line A'in FIG. 4 as the rotating shaft 6 rotates.

The rotation torque T of the rotary shaft 6 represented by the solid line A ′ is reduced by the lower the magnetic flux density on the outer peripheral surface 7 a of the rotor 7, but the magnetic flux density is reduced in this way. The part where the rotational torque of the rotary shaft 6 becomes small corresponds to the part where the rotational torque becomes maximum when the circular holes 16, 16 are not provided. Therefore, the difference between the maximum value T _MAX ′ and the minimum value T _MIN ′, that is, the fluctuation range ΔT ′ of the rotational torque becomes smaller as the maximum value T _MAX ′ of the rotational torque becomes lower.

According to a trial calculation by the present inventor, by forming the circular holes 16 and 16, the magnetic flux density at a position deviated by 60 degrees from the boundary is obtained when the circular holes 16 and 16 are not formed. When the density is reduced to 70%, the fluctuation width ΔT ′ (= T _MAX ′ −T _MIN ′), which is the difference between the maximum value T _MAX ′ and the minimum value T _MIN ′ of the rotational torque, is the rotational torque. It was found that the ratio to the average value T _AVE ′ (= (T _MAX ′ + T _MIN ′) / 2) can be reduced to 1%.

Next, FIGS. 5 to 7 show a second embodiment of the present invention. In the above-described first embodiment, inside each S pole and N pole, only the position where the position in the circumferential direction deviates from the boundary between the adjacent S poles and N poles by an electrical angle of about 60 degrees, While the circular holes 16 and 16 are formed, in the case of the present embodiment, the circular holes 16 and 16 are formed in the portion deviated by approximately 60 degrees and the portion deviated by approximately 120 degrees. Therefore, in the case of the present embodiment, the magnetic flux density on the surface of the rotor 7 is deviated from the boundary, which is formed by the circular holes 16 and 16 as shown in FIG. It becomes low at two points, the position and the position shifted by about 120 degrees.

As in the case of the first embodiment described above, the torque acting between the coils 10a, 10b, 10c of each phase and the rotor 7 is shown by the solid line a ', the chain line b', and the broken line in FIG. It changes as shown by c ', and the fluctuation range of the rotation torque of the rotary shaft 6 becomes extremely small as shown by the solid line A'in the figure.

[0027]

[Effect of device]

 Since the three-phase brushless motor of the present invention is configured and operates as described above, the torque unevenness applied to the rotating shaft is reduced, and the driver feels uncomfortable when used as a drive source of a power steering device, for example. You can prevent giving. Further, since the outer peripheral surface of the rotor is a cylindrical surface having no unevenness, a failure such as clogging with foreign matter between the outer peripheral surface and the inner peripheral surface of the drive coil is unlikely to occur.

[Brief description of drawings]

FIG. 1 is an end view of a rotor showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a change in magnetic flux density in a circumferential direction of an outer peripheral surface of the rotor shown in FIG.

FIG. 3 is a diagram showing an energized state of a drive coil.

FIG. 4 is a diagram showing torque fluctuations of the three-phase brushless motor of the first embodiment.

FIG. 5 is an end view of a rotor showing a second embodiment of the present invention.

6 is a diagram showing a change in magnetic flux density in a circumferential direction of an outer peripheral surface of the rotor shown in FIG.

FIG. 7 is a diagram showing torque fluctuations of a three-phase brushless motor according to a second embodiment.

FIG. 8 is a cross-sectional view showing an example of the structure of a three-phase brushless motor to which the present invention is applied.

FIG. 9 is a circuit diagram showing a drive circuit of a drive coil.

FIG. 10 is an end view of a rotor incorporated in a conventional three-phase brushless motor.

FIG. 11 is a diagram showing a change in magnetic flux density over the outer circumferential surface of the rotor shown in FIG. 10 in the circumferential direction.

FIG. 12 is a diagram showing torque fluctuation of a conventional three-phase brushless motor.

FIG. 13 is a diagram showing changes in magnetic flux density on the outer peripheral surface of the rotor capable of suppressing torque fluctuations.

[Explanation of symbols]

 1 Motor Case 2 Cylindrical Part 3 Front Lid 4 Rear Lid 4a Inner Surface 5 Bearing 6 Rotating Shaft 7 Rotor 7a Outer Surface 8 Drive Coil 9 Cores 10a, 10b, 10c Coil 11 Phase Detection Permanent Magnet 12 Hall Element 13 Support Plate 14 Stay 15 Transistor 16 circular hole

Claims (1)

[Scope of utility model registration request] 1. A rotary shaft, a rotor fixed to an outer peripheral surface of the rotary shaft, and a three-phase drive coil provided around the rotor, the outer peripheral surface of the rotor having an S pole and an N pole. In a three-phase brushless motor in which the poles are magnetized alternately and at equal intervals, the outer peripheral surface of the rotor is a cylindrical surface having no irregularities, and the inside of the rotor is axially oriented in the rotor. A plurality of air gaps are provided, and the positions of the air gaps in the circumferential direction are in the same direction in the circumferential direction from the boundary between the adjacent S poles and N poles, and at positions that are deviated by approximately 60 degrees in electrical angle. A three-phase brushless motor that is characterized.