Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1997-10-16
1999-01-26
Ramirez, Nestor
Electrical generator or motor structure
Dynamoelectric
Rotary
310 68B, 310261, H02K 2112
Patent
active
058641920
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a brushless motor which has a rotor having field permanent magnets inserted into a rotor yoke made of laminated steel plates and a magnetic sensor disposed to oppose to the end face of the rotor.
BACKGROUND ART
Generally known conventional brushless motors consist of a rotor which has a plurality of field permanent magnets inserted into a rotor yoke made of laminated steel plates, and a stator which has a magnetic pole portion opposed to the outer peripheral face of the magnet portion of the rotor with a small gap therebetween.
This type of brushless motor is proposed, to detect a rotational position of the rotor, to adhere to an end face of the rotor a magnet piece to be detected for specifying a rotational position of the rotor, to dispose a magnetic sensor near the trajectory of rotation of the magnet piece to be detected, and to use the magnetic sensor to detect magnetism of the magnet piece to be detected, thereby detecting the rotational position of the rotor.
FIG. 37 shows a vertical sectional view of the above brushless motor having the magnet pieces. A brushless motor 51 has a pair of housing members 53, 54 fastened with bolts 52, and these housing members 53, 54 rotatably support a rotatable shaft 57 with ball bearings 55, 56. To the rotatable shaft 57, a rotor 58 is fixed, and one end of the rotatable shaft 57 is structured to protrude from the end face of the housing member 53 to externally transmit a rotary force of the rotor 58. A stator 59 is disposed around the rotor 58 and held between the housing members 53, 54.
The rotor 58 consists of a rotor yoke 50 which has many steel plates laminated, and a plurality of field permanent magnets 61 which are inserted into the rotor yoke 50. The stator 59 consists of a stator yoke 62 made of laminated steel plates, and stator coils 63 wound on the stator yoke 62. A part of the inner peripheral face of the stator yoke 62 forms a magnetic pole portion 59a of the stator, and the stator magnetic pole portion 59a is opposed to the outer peripheral face of a magnetic pole portion 58a of the rotor 58 with a small distance therebetween.
A magnet piece 64 to be detected is adhered to an end face 58b of the rotor 58. A magnetic sensor board 66 having a plurality of magnetic sensors 65 disposed is fixed to the housing member 53 near the trajectory of rotation of the magnet piece 64 to be detected.
In the above structure, when the rotor 58 of the brushless motor 51 rotates, the magnet piece 64 to be detected is also rotated and approached to the magnetic sensors 65 when it is rotated 360 degrees. The magnetic sensors 65 detect magnetism of the magnet piece 64 to be detected to detect the rotational position of the rotor 58. But, it is known that since this brushless motor 51 has a large distance between the field permanent magnets 61 and the stator magnet pole portion 59a, a magnetic flux is attracted in the rotating direction by an interaction with the stator magnetic pole portion 59a when rotating, and the position of a magnetic flux density peak point in an outside space of the rotor 58 does not agree with the actual rotational position of the rotor 58.
FIG. 38 shows a difference between a change of the magnetic flux density in the outside space of the rotor end face 58b of the brushless motor 51 and the rotational position of the rotor 58 detected by the magnet piece 64 to be detected. In FIG. 38, the horizontal axis shows a lapse of time, and the vertical axis shows the magnitude of an electric signal. Curve L1 shows a change of the magnetic flux density in the outside space of the rotor end face 58b, and kinked line L2 shows the rotational position of the rotor 58 detected by the magnet piece 64 to be detected. It is seen from the drawing that in a brushless motor having field permanent magnets in a rotor yoke and a relatively large distance between the field permanent magnets and a stator magnetic pole portion, a magnetic flux during rotation is attracted in the rotating direction by the stator magnetic pole por
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Ishiguro Akiyoshi
Nagate Takashi
Enad Elvin G.
Ramirez Nestor
Seiko Epson Corporation
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