JP2008236858A - Brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brushless motor which is improved in heat resistance against a temperature load applied to a motor, caused by a temperature rise by overload drive or the like and heat generated in use in a high-temperature atmosphere, and does not cause the lowering of torque even in the high-temperature atmosphere. <P>SOLUTION: The brushless motor comprises a rare earth magnet which is arranged at a rotor or a stator, and is characterized in that the rare earth magnet is of an Nd-Fe-B system whose surface is cleaned by being immersed into an acid liquid after performing grain boundary reforming by being diffusely immersed with an M element (M is Pr, Dy, Tb or Ho) from the surface into its inside, and by making an ultrasonic wave act on the acid liquid. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a brushless motor, and more particularly to a brushless motor (hereinafter, also simply referred to as “motor”) that increases in temperature during use and a brushless motor that is used in a high temperature environment.

  In a generally used motor, the heat resistance of a permanent magnet (hereinafter also simply referred to as “magnet”) provided in the rotor or stator of the motor is not high, so that it is in use due to overload operation. When the temperature rises or when it is repeatedly used in a high temperature environment, the magnet causes irreversible demagnetization due to heat, and as a result, when it returns to room temperature, the torque of the motor is significantly reduced and does not recover. Note that the ratio of the magnetization decreased by heating to the magnetization before heating of the magnetization that does not recover even after returning to room temperature is called the irreversible demagnetization factor, and as mentioned above, the torque of the motor is significantly reduced and does not recover. This indicates that the irreversible demagnetization factor is large.

  However, in recent years, in equipment such as FA, electrical equipment, H-EV cars, etc., it has excellent heat resistance as a motor that increases in temperature during use or a motor that is used in a high temperature environment, that is, operation at normal temperature and high temperature. There is a demand for a motor in which the torque of the motor does not decrease even if is repeated (as a guide, the irreversible demagnetization rate at 150 ° C. is 2% or less).

For example, in a roller with a built-in motor for conveying goods, even if a normal motor is used, if the motor temperature under the usage environment is 100 ° C or less, the original torque is recovered by returning to normal temperature due to a stop or the like. However, when the temperature exceeds 100 ° C., the irreversible demagnetization rate of the magnet suddenly increases, and a phenomenon occurs in which the torque does not recover even when the temperature returns to room temperature. That is, when the motor repeatedly receives a temperature increase due to the overload operation, the torque is reduced, that is, the conveyance capacity is gradually reduced. As a result, an article that was initially transportable cannot be transported in some cases.
Therefore, it is necessary to provide a motor with excellent heat resistance for the roller with a built-in motor that is forced to be used in an overload operation due to conveyance of heavy articles or in a high temperature environment.

  In order to provide a motor with excellent heat resistance, it has a high coercive force without reducing the maximum energy product of the magnet, and the temperature to the motor due to heat, such as temperature rise due to overload operation or use in a high temperature environment, etc. A magnet that rarely causes irreversible demagnetization with respect to a load, that is, excellent in demagnetization resistance at a high temperature is required.

  Nd-Fe-B rare earth magnets containing heavy rare earth elements such as terbium (Tb) and dysprosium (Dy) are examples of magnets having high coercive force and excellent demagnetization resistance at high temperatures. Can be mentioned.

This magnet has a structure in which the Nd ₂ Fe ₁₄ B compound main phase is surrounded by an Nd-rich grain boundary phase. Conventionally, by utilizing the magnetic properties of a Dy ₂ Fe ₁₄ B or Tb ₂ Fe ₁₄ B compound having a large anisotropic magnetic field compared to the Nd ₂ Fe ₁₄ B compound, several Dy and Tb are contained in the magnet alloy. Increasing the coercive force has been carried out by adding about 10% by mass or more. However, in this case, at the same time, there is a problem that the maximum energy product (BH _max ) and the residual magnetization (Br) represented by the product of the magnetic flux density B and the magnetic field H are significantly reduced.

  In order to cope with such a problem, as a method for improving the coercive force while suppressing the decrease in the residual magnetic flux density, sputtering of Dy metal from the surface of an Nd—Fe—B based sintered magnet not containing Dy element or the like is performed. So-called grain boundary reforming methods such as a method of forming a film by thermal diffusion and thermally diffusing and a method of reducing and diffusing Dy fluoride have been developed (Patent Documents 1 to 3).

By these methods, as a result of the Dy element selectively diffusing and penetrating into the grain boundary phase rather than the main phase of the Nd ₂ Fe ₁₄ B compound, a decrease in residual magnetization is suppressed and a significant improvement in coercive force is realized. Since these grain boundary modified magnets generate a coercive force equivalent to that of a magnet without grain boundary modification even if the Dy content is halved, they have the effect of saving rare resources and expensive Dy elements.
JP 2004-304038 A WO 2006/064848 A1 publication JP 2005-210876 A

However, the Nd—Fe—B based grain boundary modified magnet manufactured by these methods is subjected to a high temperature heat treatment at 700 to 1000 ° C. in the process of diffusing Dy element into the grain boundary phase, so that Nd In addition, CaF _{2 and the} like are generated by reduction of Dy fluoride. Further, since rare earth elements are generally easily oxidized, if a rare earth magnet is left untreated, an oxide film is formed on the surface of the magnet.

  These oxides and fluorides are impurity residues on the magnet surface. For example, they interfere with the adhesion of the plating when the anti-corrosion Ni plating is applied to the magnet, and also operate for a long time when applied to a motor. In this case, oxygen and fluorine in the oxide film diffuse into the magnet, and the magnetic properties such as demagnetization resistance (hereinafter simply referred to as magnetic properties) gradually decrease, which adversely affects motor torque. Need to be removed.

  As a method for removing these impurity residues, there is a mechanical barrel method. However, when this method is employed, the magnets are likely to be chipped due to collisions with the magnets and the polishing pieces, and noise during operation of the barrel device becomes a problem. Further, there is a shot blasting method in which sand powder or the like is sprayed onto the magnet surface at high speed, but there are problems of chipping and noise of the magnet, and dust and the like in the separation and collection operation of the sand and magnet as described above.

  On the other hand, there is a chemical acid cleaning method as another method for removing residues on the magnet surface. When a chemical acid cleaning method is used, impurity residues firmly adhered to the magnet surface can be removed, and by adjusting the concentration and time of hydrochloric acid, nitric acid, etc., surface impurity residues can be easily adjusted. Can be removed. However, magnets that have undergone acid cleaning have a lower magnetic property than before cleaning, making it difficult to ensure the desired high magnetic properties. It was not possible to obtain a motor that has improved heat resistance against temperature load on the motor due to heat during use, etc., and does not cause torque reduction even in a high temperature environment.

  The cause of the deterioration of the magnetic properties after the acid cleaning described above is presumed as follows. That is, for example, when acid cleaning with hydrochloric acid is performed, hydrogen gas is generated when Nd, which is a main component of the magnet, is ionized and dissolved. This hydrogen gas is absorbed mainly by the Nd-rich grain boundary phase in the Nd-Fe-B magnet, and the grain boundary phase, which plays an important role in developing the coercive force, causes alteration and volume expansion. It is presumed to cause a decrease in magnetic force. In addition, since the acid cleaning is generally a short time treatment of several minutes to several tens of minutes at room temperature, the absorbed hydrogen remains mainly near the surface of the magnet. For this reason, the magnetic properties of the magnet after acid cleaning are a combination of the magnetic properties of the magnet having the original high coercive force and the magnetic properties of the magnet having the reduced coercive force. Particularly, in the case of a small magnet of several mm or less, since the ratio of the surface area to the volume is large, the characteristic deterioration due to hydrogen absorption is large.

  In view of the above problems, the present invention increases heat resistance against a temperature load on a motor due to heat increase due to overload operation or use in a high temperature environment, and reduces torque even in a high temperature environment. The problem is to provide a motor that does not.

The present inventor devised a method of acid cleaning for the above-described Nd—Fe—B-based grain boundary modified magnet, so that the magnetic characteristics do not deteriorate with respect to those before cleaning, and the desired high magnetic characteristics are obtained. It has been found that the above problems can be solved by incorporating a magnet into a motor, and the present invention has been completed.
Hereinafter, the invention of each claim will be described.

The invention described in claim 1
A brushless motor having a rare earth magnet in a rotor or a stator,
The rare earth magnet is subjected to grain boundary modification treatment by diffusing and infiltrating M element (where M is Pr, Dy, Tb or Ho) from the surface to the inside, and then immersed in an acid solution and the acid The brushless motor is an Nd—Fe—B rare earth magnet whose surface is cleaned by applying an ultrasonic wave to the liquid.

  In the invention of this claim, as the rare earth magnet provided in the rotor or stator, the grain boundary modification is performed by diffusing and penetrating M element (where M is Pr, Dy, Tb, or Ho) from the surface to the inside. After the treatment, the Nd-Fe-B rare earth magnet whose surface is cleaned by immersing in the acid solution and applying ultrasonic waves to the acid solution is used, as described below. It is possible to obtain a motor that increases heat resistance against temperature load on the motor due to heat rise due to temperature rise due to operation or use in a high temperature environment and does not cause a torque decrease even in a high temperature environment.

In the present invention, an Nd—Fe—B rare earth magnet is used. For example, a solid sintered magnet made of Nd ₂ Fe ₁₄ B compound, a hot plastic working magnet, and a powder are hardened with a resin. Can be mentioned bonded magnets.

In the present invention, the M element (however, M is Pr, Dy, Tb, or Ho) is diffused and penetrated from the surface to the inside of the Nd-Fe-B rare earth magnet, and the grain boundary is improved. Quality processing is performed.
As a specific method of grain boundary modification treatment, for example, a method of thermally diffusing Dy metal by sputtering from the surface of a Nd—Fe—B based sintered magnet not containing Dy element or the like, A method of reducing and diffusing fluoride can be used.

By these methods, the Dy element selectively diffuses and penetrates into the grain boundary phase rather than the main phase of the Nd ₂ Fe ₁₄ B compound, and as a result, a decrease in residual magnetization is suppressed and a significant improvement in coercive force is realized. be able to. Magnets modified by grain boundaries by these methods generate a coercive force equivalent to that of commercially available sintered magnets even if the Dy content is halved.

As described above, by diffusing and penetrating the M element from the surface of the rare earth magnet to the grain boundary phase, a rare earth magnet having excellent magnetic properties and enhanced coercive force can be obtained. This rare earth magnet contains M element because M element selectively diffuses and penetrates into the grain boundary phase rather than the Nd ₂ Fe ₁₄ B compound main phase, compared with the conventional commercially available Nd—Fe—B based magnet. Decrease in magnetization due to the formation of the (Nd, M) ₂ Fe ₁₄ B compound can be avoided, and the coercive force can be greatly improved with respect to commercially available magnets. In addition, since a large coercive force can be obtained even if M element is hardly taken into the main phase, there is an effect that the rare elements and expensive M elements such as Dy and Tb can be reduced to 50% or less than the conventional one. As a result, it is possible to reduce the manufacturing cost of a motor including such a magnet.

  In the present invention, the Nd-Fe-B rare earth magnet subjected to the grain boundary modification treatment is immersed in an acid solution, and an ultrasonic wave is applied to the acid solution to thereby surface the surface. Wash. By subjecting the surface to acid cleaning while applying ultrasonic waves, impurity residues on the magnet surface such as oxides and fluorides generated on the magnet surface can be removed. Also, by applying ultrasonic waves to the acid solution, a cavitation phenomenon occurs in the acid solution, so that the generated hydrogen gas is hardly absorbed in the rare earth magnet. As a result, the rare earth magnet is subjected to acid cleaning. However, the high magnetic characteristics obtained by the grain boundary modification treatment can be maintained without causing a decrease in coercive force.

  As the frequency of the ultrasonic wave, 20 to 1000 kHz generally used in industry can be applied. If it is less than 20 Hz, the operation noise becomes large, and if it exceeds 1000 kHz, it is difficult for the substance to be removed by cleaning to follow the frequency, and the cleaning ability is reduced.

  The acid solution to be used is not particularly limited, but a strong inorganic acid such as hydrochloric acid, nitric acid, sulfuric acid or hydrofluoric acid diluted with water several tens to several hundred times, or oxalic acid, formic acid, acetic acid Organic acid aqueous solutions such as benzoic acid and benzenesulfonic acid can be used.

  When performing the above-mentioned acid cleaning, if the magnet and the acid solution for grain boundary modification are forcibly moved relative to each other, or if the pressure in the cleaning tank system in which the acid solution is stored is reduced or evacuated, the hydrogen gas is moved into the magnet. This is more preferable because it is more difficult to absorb.

  As described above, by using the Nd—Fe—B rare earth magnet, the grain boundary modification treatment, and the acid cleaning under the action of ultrasonic waves, the heat resistance is high and the torque is reduced even in a high temperature environment. No motor can be provided.

The invention described in claim 2
2. The brushless motor according to claim 1, wherein the rare earth magnet is an Nd—Fe—B rare earth magnet having a hydrogen content of 50 ppm or less.

  In the invention of this claim, as the rare earth magnet provided in the rotor or the stator, an Nd—Fe—B rare earth magnet having a hydrogen content of 50 ppm or less after the acid cleaning is used. The effect of the acid cleaning treatment, and hence the effect of the grain boundary modification treatment, appears more remarkably, and it is possible to provide a motor that has high heat resistance and does not cause torque reduction even in a high temperature environment.

According to the present invention, it is possible to provide a motor that has improved heat resistance against a temperature load on the motor due to heat, such as a temperature rise due to overload operation or the like, and is used in a high temperature environment, and does not cause a torque decrease even in a high temperature environment.
Moreover, since the permanent magnet which can reduce the usage-amount of rare and expensive elements (Dy, Tb, etc.) is provided, the increase in the cost required for motor manufacture can be suppressed.

  Hereinafter, the present invention will be described based on the best mode. In addition, this invention is not limited to the following embodiment. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

(Permanent magnet production)
A sintered magnet obtained by pulverizing, forming and sintering a raw material alloy having a composition represented by Nd _12.5 Fe _79.5 B ₈ is cut to obtain a plate-like Nd—Fe having a size of 30 mm × 8 mm × 2 mm. -A plurality of B-based sintered magnet pieces were produced. Next, 1 g of DyF ₃ powder and 0.6 g of CaH ₂ powder were slurried with ethanol, applied to the surface of the magnet piece, and dried. Subsequently, these magnet pieces are loaded into a crucible made of SUS, held in an Ar gas atmosphere at 900 ° C. for 2 hours, and subjected to a heat treatment for reducing DyF ₃ to Dy metal and simultaneously diffusing into the magnet, thereby changing the grain boundary. A quality magnet was produced. The magnet sample was taken out from the crucible, and the CaF ₂ powder on the sample surface was lightly removed with a brush and loaded into a mesh basket made of SUS304.

  Next, the net basket is immersed in an acid aqueous solution in which nitric acid with a concentration of 70% is diluted 100 times with pure water while applying ultrasonic waves with an oscillation frequency of 28 kHz and an output of 100 W, and an acid cleaning treatment is performed. An Fe-B sintered magnet (hereinafter referred to as a treated magnet) was obtained.

  An inner rotor type IPM (Interior Permanent Magnet) type brushless in which the obtained processed magnet 1 is embedded in a rotor core 2 of a brushless motor whose conceptual diagram is shown in FIG. A motor 22 was manufactured.

Hereinafter, the configuration of the brushless motor 22 will be described with reference to FIG.
The rotor core 2 in which the processed magnets 1 are evenly embedded every 90 ° on the circumference and the position detection magnet 3 magnetized with four poles are rotationally fixed to the rotor shaft 4. Both ends of the rotor shaft 4 are held by a motor case 7 via a bearing 5 and a motor frame 6 that holds the bearing 5, and have the same axis as a stator 8 that is press-fitted and fixed by the motor case 7. .

  The rotor (four poles: parallel circumferential direction) is arranged at the same position in the thrust direction with respect to the stator 8 around which the magnet wire 13 is wound, and the motor passes through the bearing 5 and the motor frame 6 so as to be rotatable. It is fixed to the case 7.

  The Hall IC 9 is disposed on the Hall substrate 10 at three positions every 60 ° with respect to the axis, detects the magnetic pole of the position detection magnet 3 disposed on the rotor, and moves the Hall substrate 10 and the hollow shaft 19. A signal is sent to the control board 12 connected separately through the cable 11 which penetrates. The separately connected control board 12 receives the signal and appropriately sends a current to the magnet wire 13 wound around the stator 8 to rotate the rotor shaft 4.

(Confirmation of heat resistance)
First, the dynamic characteristics of a motor are measured using a motor analyzer at room temperature (25 ° C.).
The measuring method is as follows.
(Dynamic characteristic measurement elements): Rotational speed, torque, input voltage, input current, input, output, efficiency (motor alone and control board included)

(Measuring method)
A specimen (brushless motor incorporating a processed magnet) is attached to a dedicated fixing base, and the rotor shaft 4 is rotationally fixed to the motor analyzer via the coupling. The power line and signal line of the motor and control board 12 are connected to the motor analyzer dedicated terminal so that the measurement element can be measured. The motor analyzer uses a pre-installed software to set the necessary test conditions for PC operation. Characteristic measurement can be performed based on the rotational speed or torque, and this time the rotational speed standard was selected. Other elements can be measured for each set number of revolutions, and each element can be plotted on the screen and left as data in CSV format, so evaluation is performed based on the data.

(Measurement condition)
First, the measurement is performed at room temperature and humidity.

Next, the whole motor is wrapped with a mantle heater to virtually create a high temperature environment.
A thermocouple is attached to the motor coil section, the temperature is monitored by a PC card type data collection system, heated to each predetermined temperature (60/100/120/150/180 ° C.), held for 1 hour, and then air-cooled. After returning to room temperature, the dynamic characteristics are measured again.

Using the normal temperature torque as a reference, the rate of change in torque after heating to a predetermined temperature was determined.
The results are shown in FIG.
As shown in FIG. 2, the torque decreases drastically when the temperature exceeds 100 ° C. before the treatment, but after the treatment, the decrease in the torque is gradually reduced (less than 2%) even at 180 ° C. You can see that it is obtained.

(Example of motor use)
FIG. 3 is a cross-sectional conceptual diagram of a roller incorporating the IPM brushless motor.
The sun gear 14 that engages with the tip of the rotor shaft 4 of the motor shown in FIG. 1 by rotation is output to the output shaft 16 that has been decelerated through the planetary reduction mechanism 15, and the output shaft 16 rotates to the pipe 17. The pipe 17 is rotated by engaging with the fixed output plate 18 by rotation and transmitting the output to the pipe 17. Further, the shaft 19 is fixed to the motor case 7 so as to rotate and be fixed to the pipe 17 and is fixed to the mounting frame 20 via a fixing fitting 21. By attaching the shaft 19 to the attachment frame 20 and rotating and fixing it, the pipe 17 rotates and the article can be conveyed.

  Conventionally, when used in a high-temperature environment or overloaded with heavy transported objects, the motor built-in roller gradually decreases in torque each time it is heated, and in some cases, it may not be able to transport articles. . By incorporating the brushless motor of the present invention using a treated magnet in the roller, the motor torque does not decrease even after use under high temperature conditions or overload operation due to heavy transported objects, resulting in poor conveyance. Absent.

It is a conceptual diagram of the vertical and horizontal cross section of the brushless motor which concerns on this invention. It is a figure which shows the relationship between motor temperature and a torque change rate. It is a cross-sectional conceptual diagram of the roller incorporating the brushless motor according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processed magnet 2 Rotor core 3 Position detection magnet 4 Rotor shaft 5 Bearing 6 Motor frame 7 Motor case 8 Stator 9 Hall IC
10 Hall board 11 Cable 12 Control board 13 Magnet wire 14 Sun gear 15 Planetary speed reduction mechanism 16 Output shaft 17 Pipe 18 Output plate 19 Shaft 20 Mounting frame 21 Fixing bracket 22 Motor

Claims (2)

A brushless motor having a rare earth magnet in a rotor or a stator,
The rare earth magnet is subjected to grain boundary modification treatment by diffusing and infiltrating M element (where M is Pr, Dy, Tb or Ho) from the surface to the inside, and then immersed in an acid solution and the acid A brushless motor, which is a Nd-Fe-B rare earth magnet whose surface is cleaned by applying ultrasonic waves to the liquid.   The brushless motor according to claim 1, wherein the rare earth magnet is an Nd—Fe—B rare earth magnet having a hydrogen content of 50 ppm or less.

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