DE69315586T2 - Rotor with a ring-shaped magnet - Google Patents

Description

The invention relates to a rotor used for motors such as an AC servo motor, a brushless motor or the like, and in particular, the invention relates to a rotor provided with a ring-shaped magnet of the rare earth metal-iron type.

Up to now, a rotor with a magnet has been used in motors such as AC servo motors, brushless motors or the like. In these rotors, the magnet has usually been made by combining a plurality of arc-shaped divided magnet segments arranged in the circumferential direction. As the magnet, rare earth metal iron type magnets having good magnetic properties have been primarily used.

When a plurality of such arc-shaped divided magnet segments are arranged on a rotor body to manufacture a rotor, although the assembling efficiency of the divided magnet segments on the rotor body is good, the shape of the magnetic poles depends on the shape of the magnet which is divided into arcs or the like.

Up to now, attempts have been made to fix the magnetic pole using a ring-shaped magnet of the rare earth metal-iron type without division into arcs or the like.

However, when such a ring-shaped rare earth metal-iron type magnet is attached to the rotor body, the thermal expansion coefficient of the rare earth metal-iron type magnet is small, while the thermal Expansion coefficient of the rotor body (e.g. made of S45C, SUS403, Al or the like) is large, so that if the temperature of the rotor rises, the thermal expansion of the rotor body is larger than that of the rare earth metal-iron type ring-shaped magnet, whereby cracking or breakage of the rare earth metal-iron type ring-shaped magnet undesirably occurs.

To solve this problem, it has been proposed to form a large gap between the rotor body and the rare earth metal-iron type ring-shaped magnet or to insert an adhesive into such a large gap. However, in these arrangements, the accuracy of concentricity between the rotor body and the rare earth metal-iron type ring-shaped magnet may be reduced due to the formation of the large gap or aging of the adhesive, so that these arrangements are not effective.

Furthermore, in order to prevent scattering of the broken rare earth metal iron type ring-shaped magnet and to improve the corrosion resistance of the rare earth metal iron type magnet which has poor corrosion resistance per se in a motor requiring high reliability, a coating for preventing scattering and improving corrosion resistance may be arranged around the outer peripheral surface of the ring-shaped magnet. However, if the thermal bonding coefficient of the coating is large and if the rotor is placed in a low temperature environment, the thermal shrinkage of the coating becomes larger than that of the rare earth metal iron type ring-shaped magnet, and as a result, cracking or breakage of the rare earth metal iron type ring-shaped magnet occurs.

GB-A-2151054 discloses a rotor having an outer magnetic ring connected to a shaft by means of a composite interlayer connector. The connector has a low thermal coefficient of volume expansion and includes a metallic element and at least one body of synthetic resin.

JP-A-04008138 discloses a rotor having a rotor body, an annular magnet arranged around the rotor body, and a reinforcing element provided on the outer peripheral surface of the annular magnet.

It is therefore an object of the invention to solve the above-mentioned problems of the known techniques and to provide a rotor which sufficiently maintains the accuracy of concentricity between the rotor body and the ring-shaped rare earth metal-iron type magnet and provides good corrosion resistance of the magnet over a long period without causing cracking or breakage of the magnet even when the temperature of the rotor rises or the rotor is placed in a low temperature environment.

Accordingly, the present invention provides a rotor having a rotor body and a rare earth metal-iron type magnet arranged therearound, characterized in that a low thermal expansion material having a lower thermal expansion coefficient than said rotor body is arranged between said rotor body and said annular magnet.

Preferably, this rotor further comprises a reinforcing element which is attached to the outer peripheral surface of the annular Rare earth metal-iron type magnet, said reinforcing element being made of a low thermal expansion material having a lower thermal expansion coefficient than the rotor body.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Fig. 1 is a schematic cross-sectional view of a first embodiment of a rotor provided with an annular magnet according to the invention;

Fig. 2 is a schematic cross-sectional view of a first comparative embodiment of a rotor provided with an annular magnet;

Fig. 3 is a schematic cross-sectional view of a second embodiment of a rotor provided with an annular magnet according to the invention; and

Fig. 4 is a schematic cross-sectional view of a second comparative embodiment of a rotor provided with an annular magnet.

In the rotor provided with a rare earth metal-iron type ring-shaped magnet according to the invention, carbon steel, low alloy steel, stainless steel and the like are used as a rotor body. For example, S45C can be used as carbon steel and SUS403 as martensitic stainless steel. Furthermore, aluminum material can be used. Most of these materials have a thermal expansion coefficient of about 8 - 25 x 10⁻⁶ / ºC, and more specifically about 10 - 20 x 10⁻⁶ / ºC.

For a rare earth metal-iron type magnet, an R-Fe system, R-Fe-B system, R-Fe-N system or the like (R is one or more of rare earth metal elements) in which Ni, Mn and Co are contained in Fe are used, and an appropriate element may be contained in B or used instead of B, e.g., at least one of C, N, P, Si. A major portion of these systems have a thermal expansion coefficient of not more than about 3 x 10-6 /ºC (including a negative coefficient).

As a low thermal expansion material, Fe-Ni system, Fe-Ni-Co system, Fe-B system, Fe-Cr-B system or the like are used. A major proportion of these systems have a thermal expansion coefficient of not more than about 5 x 10-6 /ºC (including a negative coefficient). In particular, Fe-36% Ni (Invar), Fe-29% Ni-17% Co (Kovar), Fe-42% Ni and the like are present.

In the rotor according to the invention, a low thermal expansion material is arranged between the rotor body and the annular magnet, so that the magnetic pole can be easily set at a desired position, while even if the temperature of the rotor rises and a difference in thermal expansion occurs between the rotor body and the annular magnet, this thermal expansion difference is absorbed by the low thermal expansion material. Therefore, cracking or breakage of the annular magnet based on the difference in thermal expansion coefficient between the rotor body and the annular magnet is prevented.

In a preferred embodiment of the invention, further, a low thermal expansion material is disposed on the outer peripheral surface of the ring-shaped magnet so that even when the rotor is in a low temperature environment, the difference in thermal shrinkage between the ring-shaped magnet and the outside low thermal expansion material is small. Therefore, cracking and breakage of the ring-shaped magnet can be prevented. Even if the ring-shaped magnet is broken, scattering of the broken magnet is further prevented by the outside low thermal expansion material. In addition, the corrosion resistance of the ring-shaped magnet, which per se has poor corrosion resistance, can be satisfactorily maintained over a long period.

The following examples are given as an illustration of the invention and are not intended to limit the invention.

example 1

Fig. 1 shows a first embodiment of a rotor provided with an annular magnet according to the invention, wherein numeral 1 denotes a rotor, numeral 2 denotes a rotor body, numeral 3 denotes an annular magnet of the rare earth metal-iron type and numeral 4 denotes an internally arranged low thermal expansion material arranged between the rotor body 2 and the annular magnet 3.

The rotor body 2 is made of carbon steel S45C, with a large diameter section having a Width of 30 mm and an outer diameter of 42.95 mm.

Furthermore, the ring-shaped magnet 3 of the rare earth metal iron type is made of 28 wt% Nd, up to 2 wt% Dy, up to 0.9 wt% B, up to 3 wt% Co, the balance being Fe, and has a width of 30 mm, an outer diameter of 60 mm and an inner diameter of 54 mm.

In addition, the internally arranged low thermal expansion material 4 is made of 36 wt% Ni, the remainder being Fe, and has a width of 30 mm, an outer diameter of 53.95 mm and an inner diameter of 43 mm.

The internally arranged low thermal expansion material 4 is bonded to the rotor body 2 by means of an adhesive (trade name: Locktite 325UV), while the ring-shaped magnet 3 of the rare earth metal-iron type is bonded to the internally arranged low thermal expansion material 4 by means of the same adhesive already mentioned above, thereby forming a rotor 1 according to the invention.

No cracking of the rare earth metal-iron type ring-shaped magnet 3 was observed after heating the rotor 1 to 200°C.

Comparison example 1

Fig. 2 shows a first comparative embodiment of the rotor, in which the number 11 represents a rotor, the number 12 a rotor body and the number 13 denotes a ring-shaped magnet of the rare earth metal-iron type.

The rotor body 12 is made of a carbon steel according to S45C, with a large diameter section having a width of 30 mm and an outer diameter of 53.95 mm.

Furthermore, the ring-shaped magnet 13 of the rare earth metal iron type is made of 23 wt% Nd, up to 2 wt% Dy, up to 0.9 wt% B, up to 3 wt% Co, the balance being Fe, and has a width of 30 mm, an outer diameter of 60 mm and an inner diameter of 54 mm.

The ring-shaped rare earth metal-iron type magnet 13 is adhered to the rotor body 12 with an adhesive (trade name: Locktite 325UV) to form the rotor 11.

When the rotor 11 was heated to 200°C, cracking of the rare earth metal-iron type ring-shaped magnet 13 was observed when it reached 110°C.

Example 2

Fig. 3 shows a second embodiment of a rotor provided with an annular magnet according to the invention, in which numeral 21 designates a rotor, numeral 22 a rotor body, numeral 23 a rare earth metal-iron type annular magnet, numeral 24 an internally arranged low thermal expansion material arranged between the rotor body 22 and the annular magnet 23, and numeral 25 an externally arranged low thermal expansion material arranged at the outer edge surface of the annular magnet 23.

The rotor body 22 is made of carbon steel according to S45C, with a large diameter section having a width of 20 mm and an outer diameter of 23 mm.

Furthermore, the ring-shaped rare earth metal iron type magnet 23 is made of 28 wt% Nd, up to 2 wt% Dy, up to 0.8 wt% B, up to 3 wt% Co, up to 0.5 wt% Mo, up to 0.1 wt% Ta, up to 0.1 wt% C, the balance being Fe, and has a width of 20 mm, an outer diameter of 40 mm and an inner diameter of 33 mm.

In addition, the internally disposed low thermal expansion material 24 is made of 42 wt% Ni, the remainder being Fe and has a width of 20 mm, an outer diameter of 33 mm and an inner diameter of 23 mm.

In addition, the externally arranged low thermal expansion material 25 is made of 36 wt% Ni, the remainder being Fe, and has a width of 20 mm, an outer diameter of 42 mm and an inner diameter of 40 mm.

The inside low thermal expansion material 24 is bonded to the rotor body 22 with an adhesive (trade name: Locktite 334UV). The ring-shaped magnet 23 of the rare earth metal-iron type is bonded to the inside low thermal expansion material 24 with the same adhesive as mentioned above. The outside low thermal expansion material 25 is also bonded to the ring-shaped magnet 24 via the same adhesive as mentioned above. glued, thereby forming a rotor 21 according to this invention.

After the rotor 21 was kept in a thermostatic chamber heated to 200ºC for one hour and then cooled in a thermostatic chamber at minus 40ºC for one hour, no cracking of the rare earth metal-iron type ring-shaped magnet 23 was observed.

Comparison example 2

Fig. 4 shows a second comparative embodiment of the rotor, in which numeral 31 denotes a rotor, numeral 32 a rotor body, numeral 33 a ring-shaped magnet of the rare earth metal-iron type, and numeral 35 a coating disposed on the outside of the ring-shaped magnet 33 for preventing straying and improving corrosion resistance.

The rotor body 32 is made of a carbon steel according to S45C, with a large diameter section having a width of 20 mm and an outer diameter of 33 mm.

Furthermore, the ring-shaped rare earth metal iron type magnet consists of 28 wt% Nd, up to 2 wt% Dy, up to 0.8 wt% B, up to 3 wt% Co, up to 0.5 wt% Mo, up to 0.1 wt% Ta, up to 0.1 wt% C, with the balance being Fe, and has a width of 20 mm, an outer diameter of 40 mm and an inner diameter of 33 mm.

In addition, the coating 35 is made of a ferritic stainless steel according to SUS430 and has a Width of 20 mm, an outer diameter of 42 mm and an inner diameter of 40 mm.

The ring-shaped magnet 33 of the rare earth iron type is adhered to the rotor body 32 with an adhesive (trade name: Locktite 334UV), while the coating 35 is adhered to the ring-shaped magnet 33 with the same adhesive already mentioned above to form the rotor 31.

After the rotor 31 was kept in a thermostatic chamber heated to 200°C for one hour and then cooled to minus 40°C in a thermostatic chamber for one hour, cracking of the rare earth-iron type ring-shaped magnet 33 was observed at three positions in a cylindrical axial direction.

As mentioned above, according to the invention, the internally arranged low thermal expansion material is arranged between the rotor body and the rare earth iron type annular magnet in the rotor so that the magnetic pole can be easily set at a desired position, while even if the temperature of the rotor rises and a difference in thermal expansion occurs between the rotor body and the annular magnet, this thermal expansion difference is absorbed by the internally arranged low thermal expansion material. Therefore, no cracking or breakage of the annular magnet occurs due to the difference in thermal expansion coefficient between the rotor body and the annular magnet, and consequently the accuracy of the concentricity of the annular magnet with the rotor body can be fully maintained over a long period of time.

When an externally arranged low thermal expansion material is arranged on the outer peripheral surface of the ring-shaped magnet, the difference in thermal shrinkage between the ring-shaped magnet and the externally arranged low thermal expansion material is small even when the rotor is arranged in a low temperature environment. Therefore, cracking and breakage of the ring-shaped magnet can be prevented. Even if the ring-shaped magnet is broken, scattering of the broken magnet can be prevented by the externally arranged low thermal expansion material. In addition, the corrosion resistance of the ring-shaped magnet, which has poor corrosion resistance per se, can be satisfactorily maintained over a long period of time.

As a result, the rotors according to the invention can be used in AC servo motors and the like, while satisfactorily utilizing the advantages of an annular magnet which can fix the magnetic pole as desired.

Claims (4)

1. Rotor with a rotor body (2;22) and a magnet (3;23) of the rare earth metal-iron type arranged around it; characterized in that a material (4;24) with low thermal volume expansion, which has a lower thermal volume expansion coefficient than this rotor body (2;22), is arranged between this rotor body (2;22) and this ring-shaped magnet (3;23). 2. A rotor according to claim 1, further comprising a reinforcing member (25) arranged on the outer peripheral surface of the ring-shaped magnet (23) of the rare earth metal-iron type, said reinforcing member (25) being made of a low thermal volume expansion material having a lower thermal volume expansion coefficient than the rotor body (22). 3. Rotor according to claim 1 or 2, wherein said rotor body (2;22) has a thermal volume expansion coefficient of 8-25 x 10-6/°C, said ring-shaped magnet (3;23) has a thermal volume expansion coefficient of not more than 3 x 10-6/°C and said low thermal volume expansion material (4;24) has a thermal volume expansion coefficient of not more than 5 x 10-6/°C. 4. Rotor according to claim 1 or 2, wherein said rotor body (2;22) has a thermal volume expansion coefficient of 10-20 x 10-6/°C, said ring-shaped magnet (3;23) has a thermal volume expansion coefficient of not more than 3 x 10-6/°C and said low thermal volume expansion material (4;24) has a thermal volume expansion coefficient of not more than 5 x 10-6/°C.