JPH0458753A - Dc brushless motor having core - Google Patents

Abstract

PURPOSE:To improve energy efficiency and to reduce manufacturing cost by integrally molding the housing sections of core and stator yoke of a composite material in which a resin is admixed with iron powder. CONSTITUTION:When a stator 10 is integrally formed, a composite material is prepared by admixing a resin material such as polyimide with iron powder. When the stator 10 is produced through molding, fixing error is eliminated from each part and the accuracy of the stator 10 depends only on the manufacturing accuracy of mold. Since a highly accurate mold can produce a highly accurate stator 10, fluctuation of rotation or torque can be eliminated positively. Furthermore, manufacturing cost can be reduced through integral molding. When the resistivity of core is increased, eddy current is suppressed and heating is prevented resulting in considerable improvement of energy efficiency.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a DC brushless motor with a core.

<Prior Art> As is well known, DC brushless motors that eliminate brush contact loss and operate efficiently have been put into practical use.

FIG. 4 is a sectional view showing an example of the configuration of a conventional DC brushless motor with a core. In FIG. 4, reference numeral 1 denotes a rotor magnet, and the N pole and S pole are magnetized into eight equal parts alternately. 2 is a rotor yoke, which forms part of a magnetic path through which the magnetic flux generated from the rotor magnet 1 passes.

3 is a three-phase connected armature coil, which is composed of a bobbin 3a and a coil 3b. A core 4 is made of a magnetic material and is fixed to the stator yoke 5.

Next, 6 is a bearing part, which is composed of a ball bearing 6a, a sintered bushing 6b, and a housing 6C, and a shaft 7 to which the rotor yoke 2 is fixed by the ball bearing 6a and the oil-impregnated sintered bushing 6b. is rotatably supported. Reference numeral 8 denotes a Hall element, which detects the magnetic pole position of the rotor magnet l, and selectively switches the current of the three-phase armature coil 3 according to the detected position. The rotational force is obtained by electromagnetic action between the magnetic poles of the rotor magnet 1 and the magnetic poles of the rotor magnet 1.

<Problems to be Solved by the Invention> In the motor configured as described above, the core 4 is the main magnetic path for the magnetic flux generated from the armature coil 3 and the rotor magnet 1, and a large magnetic flux B passes through it. . This magnetic flux B
The direction of flow changes as shown by the arrow in FIG. 5 by switching the current in the armature coil 3 and rotating the rotor magnet 1. Therefore, an electric field is generated inside the core, and an eddy current i as shown in FIG. 5 flows, thereby generating Joule heat and increasing the temperature of the motor.

This temperature rise may cause deformation of the bobbin 3a or
Problems such as melting of the insulating coating material (b) and seizure due to evaporation of the lubricant in the bearing have occurred.

Furthermore, when such Joule heat is generated, the amount of electric power that must be supplied to the motor increases accordingly, resulting in a decrease in energy efficiency.

Further, since the core 4 and the housing 6c are fixed to the stator yoke 5 by press fitting, adhesion, welding, etc., errors in the mounting positions are likely to occur. For this reason, conventionally there has been a limit to reducing rotational unevenness, torque unevenness, etc. based on this error.

In addition, since the stator is constructed by assembling a plurality of parts in this way, the number of manufacturing steps is large (resulting in high costs).

In view of the above-mentioned problems, it is an object of the present invention to improve the energy efficiency of a DC brushless motor with a core and to reduce its manufacturing cost.

Means for Solving the Problems> The core-equipped DC brushless motor of the present invention has a core portion around which an armature coil is wound, through which a current for rotating the rotor is passed, and a stator side portion. A DC brushless motor with a core that includes a stator yoke that forms a magnetic path, and a bearing housing that constitutes a bearing that rotatably supports a shaft to which the rotor is fixed,
The core portion, stator yoke, and housing portion are integrally formed of a composite material made of resin mixed with iron powder.

Effect> By forming the core on the stator side using a composite material in which iron powder is mixed into resin and increasing the resistivity of the core, it is difficult for eddy current to flow. Moreover, the core part, stator yoke, and housing part are integrally formed using the above-mentioned composite material, thereby reducing the number of manufacturing steps for constructing these parts.

<Embodiment> FIG. 1 is a sectional view of a DC brushless motor with a core showing an embodiment of the present invention, and FIG. 2 is a perspective view of a stator. Note that in FIG. 1, parts common to those in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As is clear from FIGS. 1 and 2, the core-equipped DC brushless motor of this embodiment has a core section 10 of the stator IO.
a, the housing portion 10b and the yoke portion 10c are integrally formed. In this way, when the stator 10 is integrally formed, a composite material may be prepared by mixing iron powder into a resin material such as polyamide, and molding may be performed using this composite material. When the stator 10 is manufactured by molding, there is no error in the attachment of each part, so the accuracy of the stator 10 is limited only to the manufacturing accuracy of the mold. Therefore, if the mold is made with high precision, the stator 10 can be made with high precision, and rotational unevenness, torque unevenness, etc. can be reliably eliminated. Also,
Since integral molding eliminates the need for man-hours for installation, manufacturing costs can be reduced compared to conventional methods.

FIG. 3 is a diagram showing general characteristics of iron loss and copper loss when a core is formed from a molded product of a composite material in which iron powder is mixed into polyamide resin. In FIG. 3, the horizontal axis indicates the volume ratio of iron in the core, which takes a value from 0 to 100% by changing the ratio of polyamide resin and iron powder.

Further, the vertical axis indicates the amount of loss, which is obtained when the DC brushless motor is driven with a constant load and rotation speed. The characteristic curve A shown by a solid line shows the iron loss, the curve B shown by a dashed-dot line shows the copper loss, and the curve C shown by a two-dot chain line shows the total loss, which is the sum of the iron loss and the copper loss.

As is clear from Fig. 3, in the range where the volume ratio is high, the rate of change of magnetic flux density with respect to time (δB/δ
t) is large and, in this case, the resistivity is small, so a large eddy current flows, resulting in a large loss. On the other hand, in this case, since the magnetic flux density is high, a predetermined output torque can be obtained with a small armature coil current, so the copper loss is small.

Further, in a range where the volume ratio of iron powder is small, the rate of change of magnetic flux density with respect to time is small, and the resistivity is large, so iron loss is small. In this case, the copper loss is large because the magnetic flux density is small.

In this way, the loss characteristics at the iron powder volume ratio are contradictory for iron loss and copper loss, and the total loss that is the sum of both losses is:
The minimum value is reached at a volume ratio of 54%, where they are well balanced.

This minimum point moves depending on the load conditions, rotation speed, etc., but under the general usage conditions of the motor in the example, the rotation speed is 300 to 5.00 Orpm, and the motor temperature rise is 60.
When experimented with a load within the range of ``C, the volume ratio was 45 ~
It was found that a minimum value exists in the range of 7596. Therefore, if the usage conditions of the motor are determined, the energy usage efficiency can be further improved by determining the mixing ratio of the composite material so that the total loss (iron loss + copper loss) is minimized under those conditions.

<Effects of the Invention> As described above, the present invention improves the resistivity by forming the core part of the stator, the stator yoke, and the bearing housing part from a composite material in which iron powder is mixed into resin. Therefore, heat generation due to eddy current can be prevented and energy efficiency can be greatly improved.

In addition, the core part and the stator yoke are made of the composite material.
Since the housing portion of the bearing is integrally molded, it is possible to reduce manufacturing man-hours and reduce costs, and also to reduce these positional errors and rotational unevenness and torque unevenness.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a DC brushless motor with a core showing an embodiment of the present invention, FIG. 2 is a perspective view showing the overall structure of a stator, and FIG.
A characteristic diagram showing the relationship between iron powder volume ratio and loss. Figures 4 and 5 show a conventional DC brushless motor with a core. Figure 4 is a cross-sectional view of the DC brushless motor with a core. , a plan view of a DC brushless motor with a core, and FIG. 6 is a diagram showing the relationship between magnetic flux and thin current. l...Rotor magnet, 2...Rotor yoke. 7...Shaft, 1o-...Stator. 10a...core part, IOb...housing part. 10c -- Yoke part. Patent applicant: Oki Electric Industry Co., Ltd.
Evening pities Figure 1 j r whip's fZ force 17 Figure 2 ftNMn Bu 28 Figure 3! i$ f) 7'752-X f -9(7)111
K) El Fig. 4 C Kisu 60〉-〉Moon stone - 1fΔhB Fig. 5 Uy'view 7 De to each other in a bow dadata η Fig. 6

Claims (1)

[Claims] A core part around which an armature coil is wound around which current flows to rotate the rotor, a stator yoke that forms a magnetic path on the stator side, and a shaft to which the rotor is fixed. In a DC brushless motor with a core, the core part, the stator yoke, and the bearing housing part constitute a bearing part for rotatably supporting the motor. A DC brushless motor with a core characterized in that it is integrally formed of a material.