JPH0369819A - Bearing device for electric motor - Google Patents

Abstract

PURPOSE:To support a rotor sufficiently even at the time of low speed revolution by connecting an exciting coil of an electric magnet to a motor driving power supply so as to make same the poles the facing magnetic poles of a permanent magnet provided on the bottom end of a rotary member of a dynamic pressure bearing and of the electric magnet. CONSTITUTION:The bottom end face of a bearing rotary member 8 is in contact with the upper end face of a bearing stationary member 2 under the stopping state of an electric motor, in a bearing device 1. When the motor is started under this condition, large acceleration current flows in a stator coil 23 of the motor and an exciting coil 16 of an electric magnet 15. As a result, a permanent magnet 13 o the bottom end of the rotary member 8 receives a strong repelling force by the electric magnet 15, and thus the rotary member 8 is floated and supported by the magnetic force. According as the revolution speed of the motor rises, exciting current of the stator coil 23, that is, the electric magnet 15 becomes less while dynamic pressure generated in dynamic pressure generating channels 4, 5, 10 11 formed in the bearing becomes higher. When the motor reaches the rated revolution speed, the rotary member 8 is almost supported with the dynamic pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bearing device for an electric motor including a hydrodynamic bearing.

[Prior Art] Dynamic pressure bearings are widely used as bearings in high-speed, small-sized electric motors. A hydrodynamic bearing has a large number of grooves cut into the surfaces of its rotating and stationary parts.

The high-speed rotation of the rotor (rotating shaft) forces gas or liquid into the grooves, creating dynamic pressure within the grooves. Due to the generated dynamic pressure, the one-rotation part receives support in the radial direction and the thrust direction.

[Problems to be Solved by the Invention] As is clear from its operating principle, a hydrodynamic bearing cannot support a rotating part unless the rotating part reaches a certain rotational speed or higher. That is, when the electric motor is accelerating from a stopped state to rated rotation, sufficient dynamic pressure is not generated within the groove of the dynamic pressure bearing. As a result, the rotating part bearing surface and the stationary part bearing surface come into contact, which accelerates the wear of the bearing surfaces and causes seizure.

Therefore, it is an object of the present invention to provide a bearing device for an electric motor that can sufficiently support the rotor even when the electric motor rotates at low speed.

[Means for Solving the Problems] A bearing device for an electric motor according to the present invention includes a permanent magnet fixed to a lower end of a rotating portion of a dynamic pressure bearing, and an electromagnet whose magnetic pole faces the permanent magnet. The excitation coil of the electromagnet is connected to the motor drive power source so that the opposing magnetic poles of the permanent magnet and the electromagnet have the same polarity. for example,
In the case of a brushless DC motor, an excitation coil is inserted between the motor drive DC power source and the motor control drive device. In the case of an AC motor, a rectifier is inserted between the motor drive power source and the motor control drive device, and the rectifier supplies DC excitation current to the excitation coil.

[Operation] When the motor is accelerating from a stopped state to its rated rotation, a large accelerating current flows through the armature windings due to the current characteristics of the motor. Since the excitation coil of the electromagnet is connected to the motor drive power source, a large current also flows through the excitation coil. As a result, the permanent magnet at the lower end of the rotating part of the hydrodynamic bearing receives a large repulsive force from the electromagnet, and the rotor is supported by the magnetic force. When the motor reaches its rated rotational speed, the excitation current of the armature winding and therefore the electromagnet is small, so the repulsive force due to the electromagnet is small. However, at this time, high dynamic pressure is generated in the grooves of the bearing due to the high speed rotation of the rotor, and most of the supporting force of the rotor is due to the dynamic pressure.

That is, the magnetic force and dynamic pressure act complementary to each other to support the rotor.

[Example] An example in which the bearing device of the present invention is applied to a brushless DC motor will be described as an example.

As shown in FIG. 1, the bearing device 1 includes a stationary part 2 in the form of a force and a rotor and a rotating part 8 inserted into the stationary part 2. As shown in FIG. The flange 3 of the stationary part 2 and the flange 9 of the rotating part 8 are opposed to each other, and axial dynamic pressure generating grooves 4 and IO are cut in the opposing flange surfaces of both flanges 3.9, respectively. Further, radial dynamic pressure generating grooves 5.11 are cut in the inner circumferential surface of the stationary part 2 and the circumferential surface of the rotating part 8 facing thereto, respectively.

- A ferrite permanent magnet I3 is embedded in the lower end of the rotating part 8. The lower surface of the permanent magnet 13 has a north pole. A through hole 6 is provided at the bottom of the stationary part 2, into which an electromagnet 15 is inserted.

One end of the excitation coil 16 of the electromagnet 15 is connected to a DC power supply 19,
The other end is connected to the input end of the control disturbance device 21. The output side of the control drive 21 is connected to the stator winding 23 of the motor. The excitation coil 16 is wound around the iron core 17 so that one end of the iron core 17 of the electromagnet +5 becomes the north pole. The stator (not shown) is equipped with a three-phase winding.
The control drive device 21 switches the excitation current of the stator winding 23 based on the position of the rotor detected by a Hall element (not shown).

In the bearing device I configured as described above, when the electric motor is stopped, the lower end surface of the rotating part 8 of the bearing is connected to the stationary part 2.
is in contact with the top surface of the bottom. When the motor is started in this state, the stator winding 23 and electromagnet of the motor]5
A large accelerating current flows through the excitation coil 16. As a result, the permanent magnet 13 at the lower end of the rotating part 8 receives a large repulsive force from the electromagnet 15, and the rotating part 8 is levitated and supported by the magnetic force. As the rotational speed of the motor increases, stator winding 2
3. Therefore, the exciting current of the electromagnet 15 becomes smaller and the dynamic pressure generated in the bearing groove 4.5.10.11 becomes higher. Then, when the electric motor reaches its rated rotational speed, the rotating part 8 is almost supported by dynamic pressure.

Although the brushless DC motor has been described above, the present invention can also be applied to AC motors, as is clear from its operation. Further, the electromagnet may have only an exciting coil without an iron core.

[Effects of the Invention] In the bearing device of the present invention, the electromagnet is energized by the motor drive power source to levitate the rotating portion of the hydrodynamic bearing. Therefore, when the motor rotates at low speed, a large current flows through the excitation coil, and the permanent magnet at the lower end of the rotating part of the hydrodynamic bearing receives a large repulsive force from the electromagnet, so it provides sufficient support for the rotor even when the motor rotates at low speed. can,
It is possible to prevent wear and seizure of hydrodynamic bearings. Furthermore, since the rotating part of the hydrodynamic bearing floats up immediately after the motor is started, the acceleration time of the motor is shortened.

[Brief explanation of drawings]

FIG. 1 shows a -1 example of the bearing device 1 of the present invention.
It is a device configuration diagram. 1...Bearing device, 2...Bearing stationary part, 4.5...
Dynamic pressure generation groove, 8... Bearing rotation part, 10.11... Dynamic pressure generation groove, 13... Permanent magnet, 15... Electromagnet, 1
9... DC power supply, 21... Control drive device, 23...
・Stator winding.

Claims (1)

[Claims] 1. A bearing device equipped with a thrust hydrodynamic bearing that supports a rotor in a vertical position of an electric motor, comprising a permanent magnet fixed to the lower end of the rotating part of the hydrodynamic bearing, and an electromagnet whose magnetic poles face the permanent magnet. A bearing device for an electric motor, characterized in that an excitation coil of the electromagnet is connected to a motor drive power source so that opposing magnetic poles of the permanent magnet and the electromagnet have the same polarity.