GB2353145A

GB2353145A - Multiphase motor with stator phase adjustment

Info

Publication number: GB2353145A
Application number: GB9918768A
Authority: GB
Inventors: Alex Horng; Yin-Nung Horng; Ming-Chi Tsai; Hung-Sen Yen; Chien-Chin Huang
Original assignee: Sunonwealth Electric Machine Industry Co Ltd
Current assignee: Sunonwealth Electric Machine Industry Co Ltd
Priority date: 1999-08-09
Filing date: 1999-08-09
Publication date: 2001-02-14
Also published as: GB9918768D0

Abstract

A multiphase motor includes at least two stator set 1,2 and driving circuits for driving the coil 13,23 of each set. The driving circuit for each phase is controlled by a Hall sensor 51 52. The poles 11,12 and 21,22 of the sets are positioned to have a particular mechanical angular phase difference and have an interposed magnetic shield 3, the shield carrying index holes which receive studs 614,624 formed on the stator winding bobbins. The Hall sensors are also positioned to have a particular mechanical angular phase difference such that the detecting time results in a particular phase shift. As a result, the current waveforms of each phase driving circuit generate a particular electrical phase angle difference, thereby allowing a brushless D.C. motor to act as a multiphase motor.

Description

2353145 1 MULTIPHASE MOTOR

2 Background of the Invention

3 1. Field of the Invention

4 The present invention relates to a structure of a brushless direct current (D.C.) motor, and more particularly to a structure of a brushless D.C. motor having functions of a multiphase 6 motor by means of changing angular positions of a mechanical structure of a stator.

7 2. Description of the Related Art

8 A conventional single phase D.C. motor generally includes a set of coils, two sets of 9 silicon steel plates, and a control circuit for controlling excitation of the coils under coordination of detection by a Hall sensor. The magnet exciting operations can be called single 11 phase/full wave type, since the control circuit can only control single direction of two-phase 12 power sources or two directions of single-phase power sources. Such a structure has a cogging 13 torque problem in addition to a dead zone problem for starting.

14 There are a wide variety of structures for D.C. brushless motors. For example, Taiwan Utility Model publication No. 349711, entitled "STATOR HAVING DUAL LAYER 16 WD;DINGS" and issued on Jan. 1, 1999, discloses a multi-layer magnetic conducting set that 17 utilizes a multi-layer structure to increase the number of coils, thereby increasing the motor 18 torque. Nevertheless, the dead zone problem for starting and the cogging torque problem are 19 not solved.

Taiwan Utility Model Publication No. 314284, entitled "MOTOR STRUCTURE" and 21 issued on Aug. 21, 1997, proposes an auxiliary pole of silicon steel plate between two sets of 22 magnetic conducting sets and the winding directions of the two sets of magnetic conducting 23 sets are made to be the same or contrary to each other to provide different polarities, thereby 24 eliminating the dead zone for starting. Nevertheless, operation of this motor is within the scope of single phase/full wave magnet exciting. Namely, the cogging torque problem and 26 non-smooth rotation resulting from single phase/full wave magnet exciting still remain.

27 Conventional single-phase fall-wave brushless D.C. motors are thus less competitive in I I product application that require high operation precision and stability, e.g., when applied the 2 motors to digital versatile discs (DVD) or compact disc-read only memory (CD-ROM).

3 Different from the above-mentioned single phase motors, a conventional three-phase 4 motor utilizes three-phase magnet exciting coils having a 120' electrical phase angle difference in the time of exciting the coils to avoid the dead zone problem at starting and the 6 cogging torque problem of the above-mentioned single phase motors, thereby providing 7 smooth switching for forward and reverse rotations of the motor. Nevertheless, such technique 8 cannot be applied to sinaIle phase D.C. motors, as the three-phase motor utilizes three-phase 9 power source and a circuit that is largely different from that for single phase D.C. motors.

The present invention is intended to provide a multiphase motor that mitigates and/or I I obviates the above-mentioned problems.

12 Summary of the Invention

13 It is a primary object of the present invention to provide a brushless D.C. motor that is 14 directly modified from the structure of a conventional single phase brushless D.C. motor to provide a brusWess D.C. motor having multiphases.

16 in order to achieve the above object, the invention utilizes two magnetic conducting sets 17 that are separated by a non-magnetic material and that coordinate with a respective driving 18 circuit to form a motor stator structure. Two Hall sensors are provided at particular detecting 19 positions wherein phase angle difference between the detecting positions relates to number of phases and number of poles. By means of the particular detecting positions of the Hall sensors, 21 the exciting times of the coils on the two magnetic conducting sets have a particular phase 22 difference (e.g., 90' electrical phase angle difference), thereby forming a multiphase brushless 23 D.C. motor structure.

24 Other objects, specific advantages, and novel features of the invention will become more apparent from the following detailed description and preferable embodiments when

26 taken in conjunction with the accompanying drawings.

2 I Brief Description of the Drawing

2 Fig. I is an exploded perspective view of a stator and a rotor of a multiphase motor in 3 accordance with the present invention; 4 Figs. 2A through 2D are schematic views illustrating relative positions between the polar plates, Hall sensors, and the magnet poles of the rotor, wherein t-to in Fig. 2A, t--to + T/4 Z2 6 in Fig. 2B, t---to + T/2 U'l Fig. 2C, and t--to + 3T/4 in Fig. 2D; 7 Fig. 3 is a sequence chart of a driving current at different positions of the rotor magnet; 8 Fig. 4 is an exploded perspective view of a preferred embodiment of the multiphase 9 motor in accordance with the present invention; and Fig. 5 is a perspective view of a stator of the multiphase motor in accordance with the I I present invention.

12 Detailed Description of the Preferred Embodiment

13 Referring to Fig. 1, a multiphase motor in accordance with the present invention 14 generally includes two magnetic conducting sets I and 2, a magnetic shielding plate 3, a rotor magnet 4, and a circuit board 5. Each magnetic conducting sets 1, 2 includes upper and lower 16 polar plates I I and 12, 21 and 22 made from silicon steel plates and windings 13, 23. The 17 magnetic conducting sets I and 2 are separated by the magnetic shielding plate 3 to ensure 18 proper magnetic circuit loops of the magnetic conducting sets I and 2. The circuit board 5 19 includes a driving circuit for magnet exciting the coils 13 and 23 respectively. The driving circuit includes independent Hall sensors 51, 52 that act as detectors. Each coil 13, 23 is 21 wound in a manner that the normal extends along an axial direction thereof, thereby 22 generating axial magnetic flux which is then guided by the polar plates 11, 12, 21, 22 and thus 23 becomes radial magnetic flux so as to enter air gap. Alternatively, the coil 13, 23 may be 24 wound in a manner that the normal extends along the radial direction. The rotor magnet 4 is mounted coaxially with the magnetic conducting sets I and 2 and can be driven to rotate by 26 the rotational torque provided by the excited polar plates 11, 12, 21, 22.

3 I Figs. 2A through 2D illustrate relative positions between the Polar plates, Hall sensors 2 51 and 52, and the poles of the rotor magnet 4. There are three (3) protruded poles in each 3 magnetic conducting sets 1, 2. The rotor magnet 4 has three pairs of N- S poles. The Hall 4 sensors 51 and 52 control the drive circuits for the magnetic conducting sets 1 and 2, respectively. Referring to Figs. 2A and 2B, the time required for an N pole rotating to an 6 adjacent N pole is defined as "T". The excited magnet pole change of the polar plates 7 corresponding to different positions of the rotor magnet 4 is as follows:

8 (1) Fig. 2A illustrates position of the rotor magnet 4 when time t--to. At this moment, the 9 two upper polar plates I I and 21 are both excited as north (N) poles while the two tower polar plates 12 and 22 are both excited as south (S) poles.

11 (2) Fig. 2B illustrates position of the rotor magnet 4 when time t--to + T/4. At this moment, 12 Hall sensor 51 is at a position closest to the N pole of the rotor magnet that generates a 13 maximum magnetic field. A signal is thus sent out to proceed with changing of polarities of

14 the polar plates I I and 12 such that the polar plates 12 and 21 are excited as N poles while the polar plates 11 and 22 are excited as S poles.

16 (3) Fig. 2C illustrates position of the rotor magnet 4 when time t--to + T/2. At this moment, 17 Hall sensor 52 is at a position closest to the S pole of the rotor magnet that generates a maximum magnetic field. A signal is thus sent out to proceed with changing of polarities of

19 the polar plates 21 and 22 such that the polar plates 12 and 22 are excited as N poles while the polar plates 11 and 21 are excited as S poles.

21 (4) Fig. 2D illustrates position of the rotor magnet 4 when time t--to + 3T/4. At this moment, 22 Hall sensor 51 is at a position closest to the S pole of the rotor magnet that generates a 23 maximum magnetic field. A signal is thus sent out to proceed with changing of polarities of

24 the polar plates 11 and 12 such that the polar plates 11 and 22 are excited as N poles while the polar plates 12 and 21 are excited as S poles.

26 (5) The rotor magnet 4 returns to a position shown in Fig. 2A when time t--to + T. At this 27 moment, Hall sensor 52 is at a position closest to the N pole of the rotor magnet that generates 4 1 a maximum magnetic field. A signal is thus sent out to proceed with changing of polarities of

2 the polar plates 21 and 22 such that the polar plates I I and 21 are excited as N poles while the 3 polar plates 12 and 22 are excited as S poles.

4 The above five stages form a cycle having a period T that is exactly the period of square pulse waves (Fig. 3) of the exciting current of either coil 13, 23. The electrical phase angle 6 difference between the exciting of the two magnetic conducting sets I and 2 is 90' (1/4 7 electrical phase angle), while the mechanical angular phase difference is 90'/number of rotor 8 poles (3) = 30'. There are four times of electrical phase changes in each complete cycle, 9 thereby acting as a two-phase full wave motor. The dead zone problem for starting is avoided, since the invention utilizes two-phase full wave type driving circuit to control 1 C7 11 exciting of the two magnetic conducting sets I and 2. In addition, effective control of forward 12 and reverse rotation as well as smooth rotations can be achieved, since the electrical phase 13 angle difference is 90' between the driving circuit.

14 Fig. 4 is an exploded perspective view of a preferred embodiment of the multiphase motor in accordance with the present invention. The motor includes a stator coil assembly 6, a 16 rotor magnet 64, a circuit board 65, an axle tube 66, and a base 67.

17 Still referring to Fig. 4 and further to Fig. 5, the stator coil assembly 6 includes two 18 magnetic conducting sets 61 and 62 and a magnetic shielding plate 63. Each magnetic 19 conducting set 61, 62 includes two sets of polar plates 611 and 612, 621 and 622 with a bobbin 613, 623 sandwiched therebetween. Each polar plate is integrally formed or includes a 21 plurality of stacked thin silicon steel plates. The polar plates are intended to guide axial 22 magnetic flux generated by the winding which is wound therearound to pass through radial air 23 gap between the polar plates and the rotor magnet 64. The polar plates may be formed by other 24 magnetic conducting material to achieve the flux guiding function. Each magnetic conducting set 61, 62 includes six radially protruded poles. Nevertheless, the number of the protruded 26 poles may be other positive integer. The number (K) of the protruded poles must be in 27 proportion to the number of the poles of the pe=anent magnet of the rotor. The ratio may be a I particular positive integer or a reciprocal of a particular positive integer. The spacing between 2 the angular positions of the magnetic conducting sets 61 and 62 relates to the poles of the rotor 3 magnet 64. The bobbin 613, 623 is wound with coils to generate axial magnetic flux. The 4 bobbin 613, 623 is made of non-magnetic material and includes pegs 614, 624 for engagement with corresponding holes 631 of the magnetic shielding plate 63. Preferably, the bobbins 613, 6 623 are formed by plastic molding injection. The magnetic shielding plate 63 is mounted 7 between the bobbins 613 and 623 for'separating magnetic circuits and includes holes 631 for 8 engaging with pegs 614, 624 of the bobbins 613, 623, as mentioned above. The magnetic 9 shielding plate 63 may be formed by copper, aluminum, rubber or other non-magnetic material for separating the magnetic circuits on the two magnetic conducting sets I and 2.

I I In this embodiment, a rotor magnet having three pairs of poles is used. Namely, the 12 number of poles of each magnetic conducting sets 61, 62 is the same as that of the poles of the 13 rotor magnet (i.e., the ratio is 1). Nevertheless, the ratio may be a fraction if it is intended to 14 lower the cogging torque of the motor for obtaining better operating characteristics. Since the mechanical full phase for each magnetic conducting set 61, 62 having six poles is 30' (90/the 16 number (3) of pole pairs of rotor). Thus, the polar plates 611 and 612 of the magnetic 17 conducting sets 61 must be positioned relative to the polar plates 621 and 622 of the magnetic 18 conducting sets 62 by a mechanical angular phase difference of 30'.

19 In order to precisely and reliably fix the mechanical angular phase difference between the magnetic conducting sets 61 and 62, the bobbin 613, 623 is provided with grooves for 21 positioning the polar plates 611 and 612, 621 and 622 in addition to the pegs 614, 624 on the 22 bobbins 613, 623, and the holes 631 in the magnetic shielding plate 63. It is appreciated that, 23 provision of holes in the bobbins 613, 623 and pegs on two faces of the magnetic shielding 24 plate 63 may achieve the same effect.

The circuit board 65 includes a drive circuit for respectively exciting the coils 613 and 26 623. Hall sensors are used as detectors for controffing two sets of transistors, which is identical 27 to the drive circuit for conventional brushless D.C. motors, wherein the driving circuit utilizes 6 I two Hall sensors to proceed with simultaneous phase change. A particular angular position 2 difference exists between the two Hall sensors such that the time difference of each excited 3 phase is 90' of electrical phase angle.

4 In assembly, the stator coil assembly 6 is engaged with the circuit board 65 via the axle tube 66 and then coaxially mounted to the base 67. Next, the rotor magnet 64 is coaxially 6 mounted by a shaft 641 thereof and thus rotatable relative to the stator when subjected to 7 magnetic torque. Accordingly, a multiphase motor is formed.

8 According to the above description, it is appreciated that a brushless D.C. motor is

9 capable of acting as a multiphase motor.

Although the invention has been explained in relation to its preferred embodiment as I I mentioned above, it is to be understood that many other possible modifications and variations 12 can be made without departing from the spirit and scope of the invention. It is, therefore, 13 contemplated that the appended claims will cover such modifications and variations that fall 14 within the true scope of the invention.

7

Claims

I What is claimed is:
2 1. A multiphase motor, comprising:
3 two magnetic conducting sets each including two sets of polar plates and a set of coils, a
4 magnetic shielding plate being provided between the two magnetic conductinor sets, the polar plates of the two magnetic conducting sets being positioned to have a fixed mechanical 6 angular phase difference; 7 a rotor is coaxial with the two magnetic conducting sets and including a plurality of 8 pairs of poles; and 9 a control circuit including two-phase current waveform output and two sets of detecting elements for respectively controlling exciting currents of the two magnetic conducting sets, I I the two detecting elements being positioned to have the fixed mechanical angular phase 12 difference such that the two magnetic conductin sets have a fixed electrical phase angle 9 C7 13 difference.

14 2. The multiphase motor as claimed in claim 1, wherein the coils are wound in a bobbin along an axial direction.

16 3. The multiphase motor as claimed in claim 1, wherein the fixed mechanical angular phase 17 difference of the positions of the polar plates of the two magnetic conducting sets is 18 determined by an expression as follows:

19 3600 X 1 the number of pairs of rotor poles 4 21 4. The multiphase motor as claimed in claim 1, wherein the ratio of protruded poles of the 22 stator to the number of rotor poles is a positive integer or a positive fraction.

23
5. The multiphase motor as claimed in claim 1, wherein the polar plates are formed by a 24 plurality of stacked thin silicon steel plates.
6. A multiphase motor, comprising:

26 two magnetic conducting sets each including a bobbin, the bobbin including two side 27 faces for mounting polar plates thereon, the polar plates of the two magnetic conducting sets 28 being positioned to have a fixed mechanical angular phase difference; 8 a magnetic shielding plate provided between the two magnetic conducting sets to separate the magnetic circuit of the two magnetic conducting sets; 3 a rotor is coaxial with the two magnetic conductincr sets and including a plurality of 4 pairs of poles; and a control circuit including, two detecting elements and a driving circuit for controlling 6 excitina currents of the two magnetic conducting sets.

I.; C)
7 7. The multiphase motor as claimed in claim 6, wherein the magnetic shielding plate includes 8 a plurality of holes to engage with the pegs which are provided on the side faces of the two 9 bobbins in contact with the magnetic shielding plate.
8.. A multiphase motor, comprising:

I I at least two magnetic conducting sets each including two sets of polar plates and a set of 12 coils, a magnetic shielding plate being provided between two adjacent said magnetic 13 conducting sets, the polar plates of two adjacent said magnetic conducting sets being 14 positioned to have a fixed mechanical angular phase difference; a rotor is coaxial with the magnetic conducting sets and including a plurality of pairs of 16 poles; and 17 a control circuit including at least two two-phase current waveform, output and at least 18 two sets of detecting elements corresponding to the number of the magnetic conducting set for 19 respectively controlling exciting currents of multiphase coils, each of said detecting elements being positioned to have the fixed mechanical angular phase difference such that an output of 21 each said exciting current form. a fixed electrical phase angle difference.

9