JP2006211838A - Ferrite permanent magnet motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase an output so as not to cause demagnetization with regard to a small ferrite permanent magnet motor. <P>SOLUTION: The outside diameter (Da) of an armature core (5a) is made to be in the range of 66% to 71% to that (Dy) of a motor casing (1). The ferrite permanent magnet motor comprises casing assembly (3) provided with a ferrite permanent magnet motor (2) on the motor casing (1) formed in the hollow cylindrical shape with a bottom, an armature (5) provided with a commutator (4), and a bracket assembly (7) provided with brushes (6) that slide on the commutator (4) fitted to the opening of the casing assembly (3). The outside diameter of the motor casing (1) is in the range of 35 mmϕ to 45 mmϕ. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ferrite permanent magnet motor.

  Conventionally, in a can type permanent magnet small DC commutator motor corresponding to an outer diameter of 45 mmφ to 35 mmφ, a ferrite magnet is used in order to obtain high performance at low cost. However, as is apparent from the magnetic characteristic diagram of the rare earth magnet and the ferrite magnet shown in FIG. 6, the ferrite magnet has recently been inferior in magnetic characteristics as compared to a rapidly growing rare earth magnet (for example, Patent Documents 1, 2, 3). Therefore, when designing a magnetic circuit for a motor equipped with a ferrite magnet, the armature reaction (acting opposite to the magnetomotive force of the permanent magnet and the amount of magnetic flux of the permanent magnet caused by the current flowing through the winding of the armature is particularly important. Therefore, it is necessary to take care not to demagnetize the permanent magnet. In addition, since a large current flows when starting and restraining the motor, further attention must be paid.

  A permanent magnet placed on the motor's magnetic circuit (yoke, armature core, air gap, permanent magnet) has an operating point (A, A ′ shown in FIG. 6) determined by the magnetic circuit. The density B [T] and the magnetic field strength H [A / m] are determined. Since this operating point moves on the BH curve of the permanent magnet due to the armature reaction, the magnetic flux density B [T] of the permanent magnet changes depending on the load of the motor, and is proportional to the magnetic flux density B [T]. The motor torque to be changed also changes, and the torque decreases due to overload. In addition, when the operating point A falls below the bending point C of the BH curve of the permanent magnet, or when the magnetic flux density B falls below 0 [T], the operating point A does not return to its original position, causing irreversible demagnetization. The motor performance cannot be maintained. In order to prevent such a state, it is necessary to design the magnetic circuit resistance as small as possible and to design the permanent magnet as thick as possible. For this reason, the ferrite magnet is designed to ensure a sufficient thickness so as not to cause demagnetization.

On the other hand, in order to obtain a high output while the motor outer diameter and the motor length are defined in a certain dimension, the relational expression P = k · N · Da ² · La It can be seen that increasing the child core outer diameter Da is effective in improving the motor output. Here, P is the motor output, k is a constant, N is the rotational speed, Da is the outer diameter of the armature core, and La is the armature product thickness.

  In order to increase the armature core outer diameter Da, it is necessary to reduce the thickness of the permanent magnet. Increasing the outer diameter of the armature core can be easily achieved by using a rare earth permanent magnet and reducing its thickness, but using a rare earth magnet increases the cost.

  Therefore, in a conventional can type permanent magnet small DC commutator motor equivalent to an outer diameter of 45 mmφ to 35 mmφ, a ferrite magnet is used in order to obtain high performance at low cost.

JP 2003-235225 A Japanese Patent No. 3480733 Japanese Patent Laid-Open No. 2002-247827

  In motors with ferrite magnets, permanent magnets tend to demagnetize due to the armature reaction caused by the current flowing through the windings of the armature, so the ferrite magnets have sufficient thickness to prevent demagnetization. However, there is a problem that when the outer diameter and the motor length of the motor are limited and the ferrite magnet is made thicker, the outer diameter of the armature core is reduced and the motor output is reduced.

  Therefore, an object of the present invention is to provide a small ferrite permanent magnet motor that does not cause demagnetization and can increase the outer diameter of the armature core.

  In order to solve the above-mentioned problems, the invention according to claim 1 is directed to a case assembly (3) including a ferrite permanent magnet (2) in a motor case (1) formed in a bottomed hollow cylindrical shape, and a commutator ( 4) and a bracket assembly (7) having a brush that is fitted in the opening of the case assembly (3) and has a brush that slides on the commutator (4). In the ferrite permanent magnet motor in which the outer diameter of the case (1) is in the range of 35 mmφ to 45 mmφ, the outer diameter (Da) of the armature core (5a) is set to 66 with respect to the outer diameter (Dy) of the motor case (1). A ferrite permanent magnet motor with a range of% to 71% is adopted.

The invention according to claim 2 is the ferrite permanent magnet motor according to claim 1, wherein the ferrite permanent magnet motor uses a ferrite permanent magnet (2) having a maximum energy product of 25 kJ / m ³ and a coercive force of 250 kA / m or more. Is adopted.

  The invention according to claim 3 is the ferrite permanent magnet motor according to claim 1 or 2, wherein the width (t) of the armature core teeth (9) is set to the outer diameter (Da) of the armature core (5a). The ferrite permanent magnet motor is employed in which the armature core slot (8) has a bottom diameter (Dab) of 40% or more with respect to the outer diameter (Da) of the armature core (5a).

  According to the first aspect of the present invention, the motor case (1) formed in the bottomed hollow cylindrical shape includes the case assembly (3) including the ferrite permanent magnet (2) and the commutator (4). An armature (5), and a bracket assembly (7) having a brush that is fitted in the opening of the case assembly (3) and slides on the commutator (4). In a ferrite permanent magnet motor having an outer diameter of 35 mmφ to 45 mmφ, the outer diameter (Da) of the armature core (5a) is 66% to 71% of the outer diameter (Dy) of the motor case (1). Since the ferrite permanent magnet motor is in the range, the outer diameter (Da) of the armature core (5a) is increased as much as possible so that the ferrite permanent magnet (2) does not demagnetize, thereby achieving high output of the motor. be able to.

According to the invention of claim 2, the ferrite permanent magnet motor according to claim 1, wherein the ferrite permanent magnet motor uses a ferrite permanent magnet (2) having a maximum energy product of 25 kJ / m ³ and a coercive force of 250 kA / m or more. Therefore, by using a magnet having a magnetic characteristic having no bending point (C), it is possible to achieve high output of the motor without causing irreversible demagnetization.

  According to the invention of claim 3, in the ferrite permanent magnet motor of claim 1 or 2, the width (t) of the armature core teeth (9) is set to the outer diameter (Da) of the armature core (5a). ) 5.5% or more with respect to the outer diameter (Dab) of the armature core slot (8) and 40% or more with respect to the outer diameter (Da) of the armature core (5a). Without reducing the cross section of the armature core slot (8) in which the coil is accommodated as the outer diameter (Da) of the armature core (5a) increases, the width (t) of the armature core teeth (9), A large bottom diameter (Dab) of the armature core slot (8) can be secured. As a result, the magnetic resistance of the armature core (5a) can be reduced, so that the operating point A shown in FIG. 6 is improved, the magnetic flux density B [T] of the permanent magnet is increased, and the output of the motor is increased. Can be achieved.

  The best mode for carrying out the invention will be described below with reference to the drawings.

  As shown in FIGS. 1 and 2, this ferrite permanent magnet motor includes a case assembly 3 having a ferrite permanent magnet 2 in a motor case 1 formed in a bottomed hollow cylindrical shape, and an electric machine having a commutator 4. And a bracket assembly 7 having a brush (not shown) that is fitted in the opening of the case assembly 3 and slides on the commutator 4. The ferrite permanent magnet motor 20 is a so-called small motor, and the outer diameter Dy of the motor case 1 is in the dimension range of 35 mmφ to 45 mmφ.

  In this small ferrite permanent magnet motor, the outer diameter of the armature 5, that is, the outer diameter Da of the armature core 5 a is in the range of 66% to 71% with respect to the outer diameter Dy of the motor case 1. In the illustrated example, the outer diameter Da of the armature core 5 a is 68% of the outer diameter Dy of the motor case 1.

  Further, the width t of the armature core teeth 9 is 6.5% of the outer diameter Da of the armature core 5a, and the bottom diameter Dab of the armature core slot 8 is 43.7% of the outer diameter Da of the armature core 5a. The

  This Da (outer diameter of the armature core 5a) / Dy (outer diameter of the motor case) = 0.66 to 0.71 is determined based on the data shown in FIGS. 3, 4 and 5 as described below. The

  FIG. 3 shows a motor whose outer diameter Dy of the motor case 1 is equivalent to 36 mmφ, where the outer diameter and inner diameter of the motor case 1 are constant, the thickness of the ferrite permanent magnet 2, the outer diameter Da of the armature core 5a, the armature core teeth. 9 shows a change in the amount of magnetic flux when the width t of 9 and the bottom diameter Dab of the armature core slot 8 are changed.

  As described above, the ferrite permanent magnet 2 of the present invention tries to make the outer diameter Da of the armature core 5a as large as possible while ensuring a thickness that does not cause demagnetization. Therefore, the data of FIG. 3 is a conventional small ferrite permanent magnet motor (ratio of armature core outer diameter Da to motor case outer diameter Dy is about 63%), and almost no current is passed through the winding of armature 5. The magnet thickness is reduced from here, and the armature core outer diameter Da, the armature core teeth width t, and the armature core slot 8 bottom diameter Dab are increased with reference to the state of no flow (no load). It is obtained by changing. Also, in order to confirm the degree of demagnetization of the ferrite permanent magnet when a large current flows through the winding of the armature 5 and the armature reaction occurs, the change in the amount of magnetic flux when the motor is restrained (when locked) is also shown. Yes.

  As apparent from FIG. 3, first, the conventional armature core outer diameter / motor case outer diameter ratio (hereinafter referred to as the Da / Dy ratio) is about 63%, and the unloaded magnetic flux amount ratio is 1. Then, the magnetic flux amount ratio at the time of motor restraint with a Da / Dy ratio of 63% is about 0.96 times and decreased by 0.04 times. This is presumably because the permanent magnet demagnetizes due to the armature reaction and the amount of magnetic flux is reduced by 4%. Next, the magnetic flux amount ratio when the Da / Dy ratio is about 66% increases by 1.02 times, and 0.02 times that when no load is applied when the Da / Dy ratio is about 63%. Moreover, at the time of restraint, it is 0.98 times, and it has decreased 0.04 times compared with the time of no load. This is because the ferrite permanent magnet thickness is thin with a Da / Dy ratio of about 66%, and the outer diameter of the armature core is increased without causing demagnetization of the ferrite permanent magnet more than the conventional motor. This means that the amount of magnetic flux itself can be increased.

  Thereafter, similarly, the Da / Dy ratio is 68%, 70%, and 74%, and the ferrite permanent magnet thickness is reduced, and when the armature core outer diameter is increased, the magnetic flux amount ratio becomes 1, 0, and 0 in order at no load. 97, 0.92 times, and when restrained, they change in order 0.95, 0.92, 0.86 times. From this, in the no-load state, the Da / Dy ratio is about 68% or more and the amount of magnetic flux is reduced compared to the conventional motor. In the restrained state, the Da / Dy ratio is about 68% and the conventional motor is restrained. It means that the demagnetization becomes larger than the current state below the amount of magnetic flux. From this result, it can be determined that the Da / Dy ratio is optimal at about 66%, and that it is lower than the conventional motor at about 68% or more.

  However, on the other hand, increasing the outer diameter of the armature core can increase the output of the motor, so it is possible to improve the characteristics of the motor in the end without paying attention only to the change in the amount of magnetic flux. There is a need to pay attention.

  FIG. 4 shows the results of obtaining torque from Maxwell stress for Da / Dy ratios of 63%, 66% and 68%. From this figure, it can be seen that when the Da / Dy ratio is approximately 66% to 68%, the torque characteristic higher than that of the conventional motor having the Da / Dy ratio of 63% is obtained. Although not shown, when 71%, the torque characteristics are the same as in the case of 66%, and when 74%, the torque characteristics are the same as in the case of 63%.

  Further, FIG. 5 shows the torque at the time of restraint up to 74% of the Da / Dy ratio with the torque near the restraint in the conventional motor having a Da / Dy ratio of 63% as 1, in order to clarify the torque difference for each Da / Dy ratio. The ratio is shown. From this figure, it can be seen that the Da / Dy ratio around 68% is the torque peak.

Based on the above results, we prototyped a motor with a Da / Dy ratio of 66% where the amount of magnetic flux is the largest and a motor with a Da / Dy ratio of 68% where the torque is the largest, and a conventional Da / Dy ratio of 63%. As a result of comparison with this motor, both the Da / Dy ratios of 66% and 68% exceeded the characteristics of the conventional motor. That is, even if the outer diameter of the armature core is increased to a Da / Dy ratio of 71% indicating the ratio between the thickness of the ferrite permanent magnet and the size of the armature core, and the ferrite permanent magnet thickness is reduced, the demagnetization of the ferrite permanent magnet is reduced. The motor characteristics also exceed the conventional motor characteristics or remain at the same level, and the armature core outer diameter Da is set as shown by the above-described formula P = k · N · Da ² · La. By making it larger, it is possible to obtain a higher output than before.

In this small ferrite permanent magnet motor, a ferrite magnet having a maximum energy product of 25 kJ / m ³ and a coercive force of 250 kA / m or more is preferably used.

  As a result, the ferrite magnet mounted in the motor case has a magnetic characteristic without the bending point C shown in FIG. 6, and the small ferrite permanent magnet motor achieves high output without causing irreversible demagnetization. Become.

It is sectional drawing which cuts and shows the small ferrite permanent magnet motor based on this invention by the vertical surface containing a motor shaft. FIG. 2 is a cross-sectional view showing the permanent magnet motor shown in FIG. 1 cut along a vertical plane orthogonal to the motor axis. It is the graph which showed the magnetic flux amount ratio with respect to the ratio of an armature core outer diameter and a motor case outer diameter. It is a motor torque curve figure shown for every ratio of armature core outer diameter Da and motor case outer diameter Dy. It is the graph which showed the torque ratio with respect to the ratio of an armature core outer diameter and a motor case outer diameter. It is a magnetic characteristic figure of a rare earth magnet and a ferrite magnet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Motor case 2 ... Ferrite permanent magnet 3 ... Case assembly 4 ... Commutator 5 ... Armature 5a ... Armature core 7 ... Bracket assembly 8 ... Armature core slot 9 ... Armature core teeth C ... Bending point Da ... Armature core outer diameter Dy ... Motor case outer diameter

Claims (3)

  A motor case formed of a bottomed hollow cylinder with a ferrite permanent magnet, an armature with a commutator, and a brush that is fitted into the opening of the case assembly and slides against the commutator. In a ferrite permanent magnet motor having an outer diameter of a motor case in the range of 35 mmφ to 45 mmφ, the outer diameter of the armature core is 66% to 71% with respect to the outer diameter of the motor case. Ferrite permanent magnet motor characterized by being in the range of The ferrite permanent magnet motor according to claim 1, wherein a ferrite permanent magnet having a maximum energy product of 25 kJ / m ³ and a coercive force of 250 kA / m or more is used.   3. The ferrite permanent magnet motor according to claim 1, wherein the width of the armature core teeth is 5.5% or more with respect to the outer diameter of the armature core, and the bottom diameter of the armature core slot is set outside the armature core. A ferrite permanent magnet motor characterized by being 40% or more of the diameter.

Images