JP2004350384A - Motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reliable motor capable of preventing electric erosion of a bearing by avoiding the oil film of the bearing from dielectrically broken down. <P>SOLUTION: A neutral point P of phase windings Lu, Lv, and Lw in a brushless DC motor 1 is grounded through a capacitor 20. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a motor, for example, a brushless DC motor.
[0002]
[Prior art]
A motor such as a brushless DC motor includes a stator (not shown) having star-connected three-phase windings Lu, Lv, and Lw, and a rotor (not shown) having permanent magnets. The rotor is rotatably supported by bearings, and a rotating shaft is attached to the rotor.
[0003]
The phase windings Lu, Lv, and Lw are connected to a switching circuit (also referred to as an inverter), and each transistor in the switching circuit is controlled to be turned on and off, so that the phase windings are sequentially energized. As a result, the rotor rotates. Further, by controlling the on / off duty of each transistor, the rotation speed of the brushless DC motor changes.
[0004]
In the brushless DC motor that is thus switched and driven, the potential at the neutral point (interconnection point) of the phase windings Lu, Lv, and Lw fluctuates as the on / off duty of each transistor is controlled. It is known that an AC voltage is generated between the bearings during operation due to the fluctuation, and an oil film of each bearing is broken down, and electric current is generated in each bearing by the current flowing along with the breakdown. (For example, see Non-Patent Document 1).
[0005]
[Non-patent document 1]
Masanori Nakamura, Engineering Laboratory, Toyo Electric Manufacturing Co., Ltd.
[0006]
[Problems to be solved by the invention]
The above-described electrolytic corrosion of the bearing of the brushless DC motor accompanying the switching drive significantly shortens the life of the brushless DC motor, and is a problem to be solved.
SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and has as its object to provide a highly reliable motor capable of preventing electric breakdown of a bearing by preventing dielectric breakdown of an oil film of the bearing.
[0007]
[Means for Solving the Problems]
The motor according to the first aspect of the invention has a plurality of phase windings connected in a star shape, and a neutral point of each phase winding is grounded via a capacitor.
[0008]
A motor according to a second aspect of the present invention is a molded motor in which a stator having a plurality of star-connected phase windings is covered with a resin, and a neutral point of each phase winding is connected via a capacitor. Grounded.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
Reference numeral 1 denotes a brushless DC motor using a steel plate as an outer shell, and includes a stator 2 having three-phase windings Lu, Lv, and Lw in a star connection, and a rotor 3 having a permanent magnet 15. The rotor 3 is rotatably supported by bearings 5 and 6, and the rotating shaft 4 is attached to the rotor 3. The control board 16 is housed in the outer shell.
[0010]
Reference numeral 10 denotes a commercial AC power supply. The power supply voltage is rectified by a rectifier circuit 11 and supplied to a switching circuit 12. The switching circuit 12 energizes the phase windings Lu, Lv, and Lw of the brushless DC motor 1 and switches the energization. The switching circuit 12 includes a series circuit of two switching elements on the upstream and downstream sides in the current direction. It has the same amount.
[0011]
That is, for example, transistors Tu + and Tu− as upstream and downstream switching elements for the U phase, transistors Tv + and Tv− as upstream and downstream switching elements for the V phase, and upstream and downstream switching for the W phase. For example, transistors Tw + and Tw- are used as elements.
[0012]
The output voltage (DC voltage) of the rectifier circuit 11 is applied to each series circuit of the switching circuit 12. Note that a damper diode D for preventing back electromotive force is connected in parallel to each transistor.
[0013]
The non-connection end of the phase winding Lu is connected to the interconnection point of the transistors Tu + and Tu-, the non-connection end of the phase winding Lv is connected to the interconnection point of the transistors Tv + and Tv-, and the connection point of the interconnection between the transistors Tw + and Tw-. The non-connection ends of the winding Lw are respectively connected.
[0014]
The control unit 13 performs control for sequentially switching the multi-phase energization in which the upstream switching element of at least one series circuit and the downstream switching element of another at least one series circuit among the series circuits of the switching circuit 12 conduct. . The energization includes rectangular wave energization and sine wave energization. In the case of rectangular wave energization, the upstream transistor of one series circuit and the downstream transistor of another series circuit in each series circuit of the switching circuit 12 are connected. Control for sequentially switching the conducting two-phase conduction is performed.
[0015]
At the time of two-phase conduction, a current flows through two of the phase windings Lu, Lv, and Lw, and a magnetic field is generated from the two phase windings. Due to the interaction between the magnetic field and the magnetic field generated by the permanent magnet of the rotor 3, a rotational torque is generated in the rotor 3, and the rotor 3 starts rotating. The rotation of the rotor 3 is continued by repeating the so-called commutation in which the two-phase energization is sequentially switched.
[0016]
On the other hand, the on / off duty of each transistor is controlled by the control unit 13. Thereby, the period of the two-phase energization to the phase windings Lu, Lv, Lw is adjusted, and the rotation speed of the brushless DC motor 1 changes.
[0017]
The rectifier circuit 11, the switching circuit 12, and the control unit 13 are provided on the control board 16.
[0018]
In the brushless DC motor 1 thus switched and driven, the potential of the neutral point (interconnection point) P of the phase windings Lu, Lv, Lw fluctuates as the on / off duty of each transistor is controlled. I do. With this change, an alternating voltage is generated between the bearings 5 and 6 during operation, and the oil film of the bearings 5 and 6 is broken down, and the current flowing along with the dielectric breakdown causes electrolytic corrosion in the bearings 5 and 6. I will.
[0019]
Therefore, as shown, the neutral point P of the phase windings Lu, Lv, Lw in the brushless DC motor 1 is grounded via the capacitor 20. This ground line conducts to the negative output terminal (−) of the rectifier circuit 11 and is led out of the outer shell of the brushless DC motor 1.
[0020]
As described above, the neutral point P of the phase windings Lu, Lv, Lw is grounded via the capacitor 20, so that the fluctuation of the potential of the neutral point P, that is, the ripple component is suppressed. Due to this suppression, it is possible to avoid electric breakdown of the bearings 5 and 6 by avoiding dielectric breakdown of the oil films of the bearings 5 and 6. Therefore, the life of the brushless DC motor 1 is greatly improved, and high reliability as the motor can be secured.
[0021]
In the above embodiment, the case where the switching element is a transistor has been described as an example, but an FET, an IGBT, or the like can be used.
[0022]
Further, the brushless DC motor 1 is covered with the outer shell made of a steel plate, but the stator coil portion of the brushless DC motor 1 is covered with resin, and the resin is used as the outer shell of the motor. May be adopted. FIG. 3 shows an example of this molded motor. That is, the stator 2 and the phase windings Lu, Lv, Lw are covered with the resin 30, and the resin 30 forms an outer shell. A resin-molded plastic magnet 31 is attached to the rotor 3.
[0023]
In addition, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements in an implementation stage without departing from the scope of the invention. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment. Further, components of different embodiments may be appropriately combined.
[0024]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a highly reliable motor capable of avoiding dielectric breakdown of an oil film of a bearing and preventing electrolytic corrosion of the bearing.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an embodiment and a switching circuit.
FIG. 2 is a view schematically showing a cross section of the configuration of the embodiment.
FIG. 3 is an exemplary sectional view schematically showing the configuration of a modification of the embodiment;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Brushless DC motor, Lu, Lv, Lw ... Phase winding, 10 ... Commercial AC power supply, 12 ... Switching circuit, Tu +, Tu-, Tv +, Tv-, Tw +, Tw -... Transistor (switching element), P ... Neutral point, 13: control unit (control means), 20: condenser, 30: resin, 31: plastic magnet

Claims (2)

In a motor having a plurality of phase windings star-connected,
A motor wherein the neutral point of each phase winding is grounded via a capacitor. In a mold-type motor in which a stator having a plurality of star-connected phase windings is covered with resin,
A molded motor, wherein the neutral point of each phase winding is grounded via a capacitor.

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