JPH027843A - Rotor for motor - Google Patents

Abstract

PURPOSE:To prevent breakdown of a magnet or peel-off of an adhesive layer due to temperature variation by composing a tubular spacer of such material as having thermal expansion coefficient approximately same as that of a tubular magnet. CONSTITUTION:A shaft 1 is pressure inserted into the central hole of a tubular spacer 2. Then a tubular magnet 3 having inner diameter slightly larger than the outer diameter of the spacer 2 is fitted onto the outer circumference of the spacer 2 and adhered thereto. The tubular spacer 2 is composed of such material as having thermal expansion coefficient approximately same as that of the tubular magnet 3. By such arrangement, breakdown of the magnet or peeling off of the adhesive layer from the spacer or the magnet due to temperature variation can be prevented.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to the structure of a rotor in a small stepping motor, etc., and particularly to a structure in which a shaft is attached to the center of a cylindrical magneto through a slot. This invention relates to improvements in motor rotors.

(Prior Art) A typical rotor structure of a permanent magnet stepping motor is shown in the figure. In the figure, 1 is the shaft, 2
is a cylindrical spacer, and 3 is a cylindrical magnet. The shaft 1 is press-fitted into the center hole of the cylindrical spacer 2, and the cylindrical magnet 3, which has an inner diameter slightly larger than the outer diameter of the spacer 2, is fitted onto the inner periphery of the spacer 2 and bonded. For example, for a cylindrical magnet 3 whose inner diameter is 18.8 mm, the outer diameter of the cylindrical spacer 2 is 18+am (both diameters).
, an adhesive layer is interposed in a slight gap between the two.

The material of the magnet 3 is ferrite. The material of the spacer 2 is typically aluminum or PBT (polybutylene terephthalate).

(Problems to be Solved by the Invention) In the conventional rotor structure described above, when used as a motor for a long period of time, the magnet 3 may crack and fall off from the spacer 2, or the adhesive portion between the magnet 3 and the spacer 2 may peel off. Occasionally, problems such as rattling occurred. Through research conducted by the present inventors, it has been found that this type of failure occurs due to the following causes.

When a motor is operating, heat is generated from the stator coil and rotor support, and the temperature of the motor becomes very high. If the motor is stopped, the temperature will gradually drop. Heat generated from the stator coil and bearing portion is conducted from the rotor shaft 1 to the spacer 2 and magnet 3, increasing their temperature.

The thermal expansion coefficient of the ferrite magnet 3 is 9 to 15X
10-6, the aluminum spacer 2 has a thermal expansion coefficient of 23.6810-8, and the PBT spacer 2 has a thermal expansion coefficient of 20 to 40×10-6. As described above, the coefficient of thermal expansion of the spacer 2 is much larger than that of the magnet 3, and heat is transferred to the spacer 2 first. Therefore, when the motor is generating heat, the magnet 3 receives a strong force in the radial direction due to the expansion of the spacer 2, and conversely, when the motor cools down, the contraction of the spacer 2 causes the magnet 3 to receive a strong force in the radial direction.
A peeling force acts on the adhesive layer between the two.

When the motor is used for a long period of time, stress due to the above-mentioned temperature changes is repeatedly applied to the magnet 3 and the adhesive layer. Therefore, depending on the product, magnet 3
may break or the adhesive layer may peel off.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to prevent failures such as magnet breakage and adhesive layer peeling even when the motor is used for a long period of time and temperature changes are repeated. The object of the present invention is to provide a highly reliable motor rotor.

Therefore, in the present invention, the cylindrical spacer is made of a material having approximately the same coefficient of thermal expansion as the cylindrical magnet.

(Function) Since the coefficients of thermal expansion of the spacer and the magnet are almost equal, stress due to thermal expansion becomes extremely small even if temperature changes are repeated as described above, improving durability against temperature changes and improving the rotor's performance. This will extend the life of the motor.

(Example) As is already clear from the above explanation, the cylindrical spacer 2
The illustrated rotor structure, in which the shaft 1 is press-fitted into the center hole of the spacer 2, and a cylindrical magnet 3 having an inner diameter slightly larger than the outer diameter of the spacer 2 is fitted and bonded to the outer periphery of the spacer 2, is similar to the conventional rotor structure in the case of the present invention. is the same as

What differs from the conventional one is the material of the cylindrical spacer 2. The cylindrical magnet 3 is made of ferrite, and its coefficient of thermal expansion is 1.
5×10=. A material for the spacer 2 having a coefficient of thermal expansion almost equal to this is, for example, heat-resistant unsaturated polyester BMC (bulk molding compound) Premiglass #900 manufactured by Ota Pharmaceutical Co., Ltd., which is an FRP molding material.
0 is used to form a cylindrical spacer 2. The coefficient of thermal expansion of the FRP molded product in this example is 14.3×10 −6 , which is extremely close to that of the ferrite magnet 3.

FRP molding material called BMC is generally made by adding a thermoplastic polymer, a hardening material, a filler, a mold release agent, etc. as a low shrinkage agent to an unsaturated polyester resin, and adding glass fiber to the matrix which is sufficiently kneaded in a kneader. It is a thermosetting molding material with excellent electrical properties, mechanical properties, dimensional stability, heat resistance,
Excellent water resistance. Any of compression molding, transfer molding, and injection molding can be used as the molding method.

Further, as a BMC suitable for the molding material of the spacer 2, there is RNC-841D-BK3 manufactured by Showa Kobunshi.

This BMC consists of 20% by weight of unsaturated polyester and 17% by weight of glass fiber, l! It contains 63% by weight of (OH)3, and its coefficient of thermal expansion is 15X10-6, which is almost the same as that of a ferrite magnet.

(Effects of the Invention) As explained above in detail, in the present invention, the spacer is made of a material having approximately the same coefficient of thermal expansion as the magnet, so that it can withstand repeated temperature changes when used as a motor. The durability of the rotor is increased, failures such as breakage of the magnet and peeling of the adhesive layer between the spacer and the magnet hardly occur, and the life of the motor is extended. In addition, since the coefficients of thermal expansion of the spacer and the magnet are almost the same, there is no need for the adhesive that joins them to have large elasticity to absorb the difference in thermal expansion between the two parts, resulting in greater adhesive strength. You can use any hard adhesive that gives you

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a rotor structure common to the prior art and the embodiment of the present invention. 1... Shaft 2... Cylindrical spacer 3... Cylindrical magnet

Claims (2)

[Claims] (1) A motor rotor in which a shaft is press-fitted into the center hole of a cylindrical spacer, and a cylindrical magnet with an inner diameter slightly larger than the outer diameter of the spacer is fitted and bonded to the outer periphery of the spacer, in which the spacer is A rotor for a motor, characterized in that it is made of a material having a coefficient of thermal expansion substantially equal to that of the magnet. (2) The motor rotor according to claim 1, wherein the spacer is a molded FRP product whose base material is unsaturated polyester.