JPH07177719A - Brushless dc motor - Google Patents

Abstract

PURPOSE:To determine appropriate dimensions of a magnet and others which enable attainment of stability of commutation of a logic circuit at the time of start, in a brushless DC motor wherein a wave form of the inductance of a winding relating to the position of a rotor is detected and the commutation is determined in the logic circuit. CONSTITUTION:In a brushless DC motor wherein a magnet 6 of a rotor 5 is disposed outside a stator core 4 having a winding 3, with a gap between them, the dimensional ratio of the outside diameter of the magnet 6 to the inside diameter thereof is made 1.10-1.15 and the dimensional ratio of the gap to the inside diameter of the magnet 6 is made 0.010-0.014, while the dimensional ratio of the length of the magnet 6 to that of the stator core 4 is made 1.45-1.55. Therefore the point of the minimum value of the inductance of a third winding corresponding to the position of the point at which the inductance of adjacent winding intersect each other is flat and logic circuit detects exactly the point at which the inductance of the adjacent winding intersect each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor for driving a magnetic disk or the like, and more particularly to a method for detecting a waveform of an inductance of a winding with respect to a rotor position without providing a rotor position detection sensor. It relates to the dimensions of the magnets and the like of brushless DC motors that are suitable for determining commutation at startup.

[0002]

2. Description of the Related Art Instead of the conventional method of determining the commutation to the winding by detecting the position of the rotor with a position detecting sensor such as a Hall element, the inductance of the winding with respect to the position of the rotor There is an inductance type position detection system in which a waveform is detected and commutation to a winding is determined by a commutation controller composed of a logic circuit and a commutation drive circuit.

FIG. 1 is a sectional view of a general three-phase brushless DC motor. In the figure, the bearing box 2 of the bracket 1
A stator core 4 having a winding 3 is fixed on the outer side of, and a magnet 6 of a rotor 5 is arranged on the outer side thereof with a gap. A shaft 9 of a hub 8 to which a magnet 6 is fixed via a yoke 7 and a magnetic disk (not shown) or the like is mounted is rotatably supported by a bearing box 2 via a bearing 10. This three-phase brushless DC motor has a commutation controller (not shown) including a logic circuit that determines commutation to the winding 3 of three phases and a commutation drive circuit.

The dimensional ratios of the conventional magnet 6 and the like are as follows, for example. (1) The dimensional ratio of the outer diameter to the inner diameter of the magnet 6 is 1.2. (2) The size ratio of the air gap to the inner diameter of the magnet 6 is 0.01
5. (3) The dimensional ratio of the length of the magnet 6 to the length of the stator core 4 is 1.46. FIG. 3 is a waveform diagram of the inductance of the winding with respect to the position of the rotor of this conventional example.

[0005]

According to the above-mentioned conventional example, the operation of the logic circuit of the commutation controller becomes unstable at the time of start-up, the proper commutation to the winding is not performed, and the start-up fails. Become smooth. As a result of various verifications, the instability of the commutation of the logic circuit at the time of start-up shows that the minimum inductance of the third winding corresponding to the position of the point C where the inductances of the adjacent windings intersect in FIG. It was discovered that the value D point was concave. It was found that the logic circuit cannot accurately detect the point C because the minimum value D of the inductance of the winding is concave. In addition, the above (3)
The leakage flux distribution based on also affects that the logic circuit does not accurately detect point C.

An object of the present invention is to determine the commutation by a logic circuit by detecting the waveform of the winding inductance related to the position of the rotor, and to obtain the stability of the commutation of the logic circuit at the time of start-up. Another object of the present invention is to provide a brushless DC motor that can determine the dimensions of various magnets.

[0007]

A brushless DC motor according to the present invention is a brushless DC motor in which a magnet of a rotor is arranged outside a stator core provided with windings with a gap therebetween. Dimension ratio 1.10
1.15, the size ratio of the air gap to the inner diameter of the magnet is 0.010 to 0.014, and the size ratio of the length of the magnet to the length of the stator core is 1.45 to 1.55. .

[0008]

According to this structure, the minimum value D of the inductance of the third winding, which corresponds to the position of the point C where the inductances of the adjacent windings intersect, becomes flat. The points are accurately detected, and the stability of the commutation of the logic circuit at the time of startup can be obtained. Further, the leakage magnetic flux distribution based on the dimensional ratio of the length of the magnet to the length of the stator core also affects the logic circuit to accurately detect the point C.

[0009]

EXAMPLE FIG. 2 is a waveform diagram of the inductance of the winding with respect to the position of the rotor of the example. Such an inductance waveform diagram can be obtained in the general three-phase brushless DC motor shown in FIG. The dimensional ratio of the outer diameter to the inner diameter of the magnet 6 is 1.10.
1.15. The size ratio of the air gap to the inner diameter of the magnet 6 is 0.010
0.014. The dimensional ratio of the length of the magnet 6 to the length of the stator core 4 is 1.45 to 1.55.

By closely observing the embodiment of FIG. 2, it is found that the minimum value D of the inductance of the third winding, which corresponds to the position of the point C where the inductances of the adjacent windings intersect, is flat. . Therefore, the logic circuit accurately detects the point C, and the stability of the commutation of the logic circuit at the time of startup can be obtained. Further, the leakage magnetic flux distribution based on the above also influences that the logic circuit accurately detects the point C. The ratio of the maximum value of the inductance to the minimum value is preferably about 1.5, and (C−D) / C is preferably 0.10.

[0011]

According to the brushless DC motor of the present invention, since the size ratio of magnets and the like is limited, the minimum inductance of the third winding corresponding to the position of the point C where the inductances of adjacent windings intersect. Value D is flat,
Therefore, there is an effect that the logic circuit accurately detects the point C, and the stability of the commutation of the logic circuit at the time of startup can be obtained. Further, the leakage magnetic flux distribution based on the dimensional ratio of the length of the magnet to the length of the stator core also has an effect of affecting the logic circuit to accurately detect the point C.

[Brief description of drawings]

FIG. 1 is a sectional view of a general three-phase brushless DC motor.

FIG. 2 is a waveform diagram of the inductance of the winding with respect to the position of the rotor of the embodiment.

FIG. 3 is a waveform diagram of the inductance of the winding with respect to the position of the rotor in the conventional example.

[Explanation of symbols]

 1 Bracket 2 Bearing box 3 Winding 4 Stator core 5 Rotor 6 Magnet 7 Yoke 8 Hub 9 Shaft 10 Bearing

Claims (1)

[Claims] 1. In a brushless DC motor in which a magnet of a rotor is arranged outside a stator core provided with a winding with a gap, the size ratio of the outer diameter to the inner diameter of the magnet is 1.10 to 1.1.
5, and the size ratio of the air gap to the inner diameter of the magnet is 0.010 to 0.
014, and the dimensional ratio of the length of the magnet to the length of the stator core is 1.
A brushless DC motor characterized in that it is 45 to 1.55.