JPS6216790Y2 - - Google Patents

Description

[Detailed description of the invention] The brushless DC motor has a rotor rotational position detection means, and when the N pole or S pole of the rotor magnet is at an appropriate position with respect to the stator coil, the stator coil is detected. Current is passed through it to obtain rotational torque.

In this case, as a method of detecting the rotational position of the rotor, a method of detecting a magnetic field from a rotor magnet is generally used because it does not require a power source and does not cause positional deviation.

By the way, in the drive circuit of this type of brushless DC motor, there are two methods: unidirectional energization in which a current flows in one direction through the stator coil by detecting only one of the N pole or S pole of the rotor magnet; S
There are two two-way energization methods that detect both poles and send current to the stator coil in the opposite direction, but the unidirectional energization method is generally used because the drive circuit configuration is simple. Ru.

FIG. 1 shows an example of a drive circuit in the case of unidirectional current supply, where A, B and C are stator coils, 1, 2 and 3 are stator coils A, 3 and 3, respectively.
These are saturable coils provided corresponding to B and C as rotor rotational position detection means.

Also, 5A, 6A, 5B, 6B and 5C, 6C
are transistors for switching stator coils A, B, and C, respectively.

Then, a Colpitts oscillator 7 consisting of a transistor 7T is oscillated at a constant frequency, for example, 500 kHz, and this is connected to a series circuit of a resistor 9A and a saturable coil 1 through a transistor 8 having an emitter follower configuration for a damper.
is supplied to the series circuit of the resistor 9C and the saturable coil 3, respectively.

When the N pole of the rotor magnet is detected in the saturable coil 1, for example, the saturable coil 1 becomes saturated, its impedance becomes smaller than that when it is not saturated, and the voltage across it becomes 0.6V.
and the transistor 5A turns off, which causes the capacitor 11A to connect to this and the resistor 10
The charging voltage turns on the transistor 6A, and a current flows through the stator coil A from the terminal 12 where a positive DC voltage is obtained.

Similarly, transistors 6A, 6B,
6C are sequentially switched, stator coils A,
Current flows through B and C sequentially. This generates rotational torque and rotates the rotor.

By the way, in this case, as mentioned above, in the saturable coils 1, 2 and 3, it is necessary to detect only one magnetic pole of the rotor magnet, but the rotor magnet has an N pole and an S pole. Since the magnets are alternately magnetized in the circumferential direction, it is not possible to detect only one pole as is.

This invention is intended to provide a brushless DC motor in which only one pole of the rotor magnet can be detected satisfactorily.

An example of the brushless DC motor according to this invention will be described below with reference to the drawings.

In FIG. 2, 13 is a rotor shaft, 14 is a rotor yoke, and the rotor yoke 14 is a rotor pedestal 15.
It is fixed to the rotor shaft 13 by.

16 and 17 are annular rotor magnets, each having N and S poles alternately in the circumferential direction, for example.
It is magnetized with 12 poles. These rotor magnets 16 and 17 are arranged at a predetermined distance so that their opposite magnetic poles face each other, and the stator coil block 18 is arranged between them. That is, in this case, the rotor magnet 16
The surface of the stator coil opposite to the surface facing the block 18 is attached to the rotor yoke 14 and fixed to the rotor, and the rotor magnet 17 is fixed to the rotor yoke 14.
A yoke 19 is attached to the surface of the stator coil opposite to the surface facing the block 18, and this yoke 19 is fixed to the rotor pedestal 15, thereby being fixed to the rotor.

Further, the block 18 of the stator coil 6 is mounted on an annular printed circuit board 20, and this printed circuit board 20 is fixed to the stator frame 21.

In this example, a portion of the circumferential end of the yoke 19 attached to the rotor magnet 17, which is magnetized to the N pole, for example, is cut out and missing as shown in FIG. A portion 19a is formed.

Then, the yoke 19 of the stator frame 21
Saturable coils 22, the number of which corresponds to the number of stator coils, are attached to predetermined angular positions of the annular band portion facing the missing portion 19a.

Note that 23 is a bearing molded integrally with the stator frame, and 24 is a thrust bearing.

Therefore, in this invention, leakage magnetic flux is generated only in the missing portion 19a of the yoke 19, rather than in the rotor magnet 17, with respect to the saturable coil 10. Since the speed is detected, only the north pole can be reliably detected. In addition, since only the N pole is directly detected by the missing portion 19a, a shield plate that shields only the magnetic flux from the S pole, for example, is attached over the entire annular plane of the rotor magnet 17. Compared to the conventional case, detection sensitivity is better, and the magnitude of the magnetic flux can be determined better, making detection more reliable. In addition, the structure can be as simple as just cutting out a part of the yoke, and there is no need to use a special shield plate as described above, which has the advantage that it can be manufactured at low cost.

In addition, as shown in FIG. 4, in the case of a DC motor using a rotor in which a rotor magnet 26 is attached to the inside of the side peripheral surface of the rotor yoke 25, as shown in FIG. For example, a portion of the rotor magnet 26 on the side circumferential surface that covers the magnetized portion of the N pole is cut out to form a cutout portion 25a;
A rotational position detecting means may be provided at a position on the outside of the rotor yoke facing the cutout portion 25a.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an example of a drive circuit of a brushless DC motor, Fig. 2 is a sectional view of an example of a brushless DC motor according to this invention, Fig. 3 is a perspective view of an example of its essential parts, and Fig. 4 is a circuit diagram of an example of a drive circuit of a brushless DC motor. 5 and 5 are diagrams for explaining the main parts of another example of the brushless DC motor according to this invention. A, B, and C are stator coils, 1, 2, 3, and 22 are saturable coils, 13 is a rotor shaft, 16 and 17 are rotor magnets, 18 is a stator coil block, 19 is a yoke, and 21 is a stator frame. be.

Claims (1)

[Scope of utility model registration request] The rotor magnet has a rotor magnet in which N poles and S poles are alternately magnetized to N poles, a stator coil, and a rotational position detection means using a saturable coil for detecting the rotational position of the rotor magnet. A position detecting means detects only one of the north pole and the south pole of the rotor magnet to cause current to flow through the stator coil, wherein a surface of the rotor magnet facing the stator coil and A yoke is attached to different surfaces, and a portion of the yoke corresponding to the portion magnetized by the one pole of the rotor magnet is cut out, and the rotational position detection sensor is placed at a position opposite to the cutout portion. A brushless DC motor is provided with means for detecting leakage magnetic flux generated from the notched portion.