JP2024048426A - Squirrel cage rotor and induction motor - Google Patents

Abstract

A cage rotor that suppresses damage to end rings and the like during high-speed rotation is provided.
[Solution] The squirrel-cage rotor includes a rotor shaft having a conductor holding portion on its outer periphery, and a squirrel-cage conductor attached to the conductor holding portion of the rotor shaft. The conductor holding portion is formed integrally with the rotor shaft by cutting out the outer periphery of the rotor shaft. The squirrel-cage conductor is arranged in the circumferential direction of the rotor shaft and has a plurality of rotor bars each extending in the axial direction, and a pair of end rings arranged at both axial ends of the rotor bars and electrically connecting the plurality of rotor bars. The axial ends of the end rings are supported by flange-shaped steps of the conductor holding portion formed by being recessed radially from the outer periphery of the rotor shaft.
[Selected Figure] Figure 1

Description

The present invention relates to a cage rotor and an induction motor.

Conventionally, induction motor rotors use cage rotors that are constructed by assembling cage conductors to a rotor core. The cage conductors have multiple rotor bars that are inserted into slots in the rotor core and extend in the axial direction, and a pair of end rings that are disposed on both ends of the rotor bars and electrically connect the ends of each rotor bar.

When applying the induction motor described above to electric vehicles and the like, there is a strong demand for increasing the rotation speed of the induction motor in order to achieve higher output. When this type of induction motor is rotated at high speed, the mechanical stress acting on the rotor increases. In addition, the increased losses caused by the higher current frequency cause the squirrel cage conductor to thermally expand, and the effect of thermal stress on the rotor also increases.

For example, Patent Document 1 proposes a structure in which reinforcing rings with eaves-shaped protrusions are attached to both axial ends of the rotor, and the outer periphery and axial ends of the end rings are covered with the reinforcing rings to protect them.

Patent No. 2838896

In the configuration of Patent Document 1, a reinforcing ring, which is a separate part, is attached to the shaft to hold the end rings, so the reinforcing ring, which receives loads from centrifugal force and thermal expansion, needs to be firmly fixed to the shaft so that it does not come off in the axial direction. Furthermore, in the configuration of Patent Document 1, when the rotating electric machine rotates at high speed, centrifugal force causes stress to concentrate on the ends and radially outer parts of the reinforcing ring, which may damage the reinforcing ring or end ring.

The present invention was made in consideration of the above situation, and provides a cage rotor that prevents damage to end rings and other components during high-speed rotation.

The cage rotor of one aspect of the present invention comprises a rotor shaft having a conductor holding portion on its outer periphery, and a cage conductor attached to the conductor holding portion of the rotor shaft. The conductor holding portion is formed integrally with the rotor shaft by cutting out the outer periphery of the rotor shaft. The cage conductor has a number of rotor bars arranged in the circumferential direction of the rotor shaft, each extending in the axial direction, and a pair of end rings arranged at both axial ends of the rotor bars and electrically connecting the rotor bars. The axial ends of the end rings are supported by flange-shaped steps of the conductor holding portion formed by recessing radially from the outer periphery of the rotor shaft.

The conductor holding portions may each be disposed between the rotor bars and have a plurality of protrusions extending in the axial direction, and the end rings may be supported in the axial direction by the protrusions and the steps.
The squirrel cage conductor may be accommodated in the conductor holding portion so as to be flush with the outer circumferential surface of the rotor shaft.
Moreover, an induction motor according to another aspect of the present invention includes the above-mentioned squirrel cage rotor and a stator.

According to one aspect of the present invention, it is possible to provide a cage rotor that prevents damage to end rings and other components during high-speed rotation.

FIG. 2 is a perspective view showing a configuration example of a squirrel-cage rotor according to the present embodiment. FIG. 2 is a cross-sectional view of the squirrel cage rotor shown in FIG. 1 . FIG. FIG. 2 is a vertical cross-sectional view showing an example of the configuration of a squirrel-cage rotor and an induction motor.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the embodiments, in order to make the description easier to understand, structures and elements other than the main parts of the present invention will be described in a simplified or omitted manner. In addition, in the drawings, the same elements are given the same reference numerals. Note that the shapes, dimensions, etc. of each element shown in the drawings are shown only for illustrative purposes, and do not represent the actual shapes, dimensions, etc.

In the following description, the direction parallel to the extension direction of the rotation axis Ax is referred to as the axial direction, the circumferential direction centered on the rotation axis Ax is simply referred to as the circumferential direction, and the radial direction centered on the rotation axis Ax is simply referred to as the radial direction. In the following description, "extending in the axial direction" includes not only extending strictly in the axial direction, but also extending in a direction tilted by less than 45° with respect to the axial direction. In this specification, "extending in the radial direction" includes not only extending strictly in the radial direction, i.e., extending in a direction perpendicular to the axial direction, but also extending in a direction tilted by less than 45° with respect to the radial direction. In addition, "parallel" includes not only strictly parallel, but also tilted by an angle of less than 45°.

Figure 1 is a perspective view showing an example of the configuration of a squirrel cage rotor of this embodiment. Figures 2(a) to (c) are cross-sectional views taken along lines A-A, B-B, and C-C of the squirrel cage rotor shown in Figure 1. Figure 3 is a perspective view of the rotor shaft. Figure 4 is a longitudinal cross-sectional view showing an example of the configuration of a squirrel cage rotor and an induction motor.

As shown in FIG. 4, the induction motor 10 of this embodiment is an inner rotor type motor and includes a cage rotor 11, a stator 12, and a housing 13. The cage rotor 11 and the stator 12 are housed in the housing 13.

As shown in FIG. 1, the cage rotor 11 has a cage conductor 15 and a rotor shaft 16. The cage conductor 15 includes a number of rotor bars 17 and a pair of end rings 18.

The rotor bars 17 are rod-shaped members made of conductive metals such as aluminum or copper, and pass induced currents (secondary currents) in the rotor due to the rotating magnetic field. As shown in FIG. 2(a), the rotor bars 17 are arranged in an annular shape at equal intervals around the rotor's circumference, and extend in the axial direction as shown in FIG. 1. The cross-sectional shape of the rotor bars 17 perpendicular to the axial direction is rectangular, but may be other shapes such as circular.

The end rings 18 are annular members made of a conductive metal such as aluminum or copper, and are arranged on both axial ends of the rotor bars 17. Each end ring 18 is joined to an end of the rotor bar 17, and electrically connects the multiple rotor bars 17 arranged in a ring.

The rotor shaft 16 is a cylindrical member that serves as both the shaft and the core of the rotor, and extends axially along the rotation axis Ax. As shown in FIG. 4, one end side and the other end side of the rotor shaft 16 are rotatably supported by bearings 14 provided in the housing 13.

The rotor shaft 16 is made of a metal material, such as stainless steel or titanium, that is more rigid than the cage conductor 15. The rotor shaft 16 serves to increase the torque of the induction motor 10 by increasing the magnetic flux density around the rotor bars 17, and to hold the cage conductor 15.

As shown in FIG. 3, the rotor shaft 16 has an outer peripheral surface cut out to match the shape of the cage conductor 15, and has a groove-shaped conductor holding portion 19 that accommodates the cage conductor 15. The conductor holding portion 19 has a first region 19a that accommodates the end ring 18, and a second region 19b that accommodates the rotor bar 17. The conductor holding portion 19 is formed integrally with the rotor shaft 16, for example, by cutting the rotor shaft 16.

The first regions 19a of the conductor holding portion 19 are formed in pairs on the outer periphery of the rotor shaft 16 with a gap in the axial direction. In each of the first regions 19a, a groove that accommodates the end ring 18 is formed in an annular shape along the circumferential direction of the rotor shaft 16. The second region 19b of the conductor holding portion 19 is formed between the pair of first regions 19a. In the second region 19b, a plurality of protrusions 19b1 that protrude radially and extend axially are formed at equal intervals in the circumferential direction. A groove that accommodates the rotor bar 17 is formed between each of the protrusions 19b1. Both ends of each groove in the second region 19b are connected to the groove in the first region 19a.

The cage conductor 15 is attached to the conductor holding portion 19 so that the surface of the rotor shaft 16 is almost flush with the conductor holding portion 19. The cage conductor 15 is attached to the rotor shaft 16 so that it is in close contact with the groove of the conductor holding portion 19. The rotor bar 17 is held in the circumferential direction by being sandwiched between the protrusions 19b1 of the second region 19b, and is positioned in the axial direction by a pair of end rings 18 joined to both ends.

Each end ring 18 is supported in the axial direction by being sandwiched between a protrusion 19b1 of the second region 19b and a flange-shaped step 19a1 formed by being recessed radially from the outer periphery of the rotor shaft 16.

When the cage rotor 11 rotates, the rotor bars 17 thermally expand due to current flow, and extend in the axial direction, with each end ring 18 being pressed against the flange-shaped step 19a1. As a result, when the cage rotor 11 rotates, both axial ends of the end rings 18 are in surface contact with the flange-shaped step 19a1, and the cage conductor 15 is supported on both sides, resulting in a doubly supported structure.

The above-mentioned cage conductor 15 is assembled, for example, by the following process. First, the rotor bars 17 are fitted into the grooves of the second region 19b of the conductor holding portion 19. Then, the half-shaped (bisected) parts of the end ring 18 are attached to the first region 19a of the conductor holding portion 19. Then, the rotor bars 17 and the end ring 18, and the parts of the end ring 18 are joined by welding, respectively, to form the cage conductor 15.

As shown in FIG. 4, the stator 12 is fitted to the inner circumference of the housing 13 and is arranged concentrically with the cage rotor 11 on the outer circumference of the cage rotor 11 with a small air gap between them. The stator 12 has coils (not shown) that carry a primary current arranged in the circumferential direction, and these coils form magnetic poles at equal intervals along the circumferential direction of the stator. In the induction motor 10, a rotating magnetic field is formed in the stator 12 by controlling the current to the coils. As a result, a torque is generated between the rotating magnetic field and the secondary current that is induced by the rotating magnetic field and flows through the cage conductor, causing the cage rotor 11 to rotate around the rotation axis Ax.

As described above, the cage rotor 11 of the induction motor 10 of this embodiment includes the rotor shaft 16 having the conductor holding portion 19 on its outer periphery, and the cage conductor 15 attached to the conductor holding portion 19 of the rotor shaft 16. The conductor holding portion 19 is formed integrally with the rotor shaft 16 by cutting out the outer periphery of the rotor shaft 16. The cage conductor 15 has a plurality of rotor bars 17 arranged in the circumferential direction of the rotor shaft 16, each extending in the axial direction, and a pair of end rings 18 arranged at both axial ends of the rotor bars 17 and electrically connecting the plurality of rotor bars 17. The axial ends of the end rings 18 are supported by the flange-shaped step 19a1 of the conductor holding portion 19 formed by recessing radially from the outer periphery of the rotor shaft 16.

In the cage rotor 11 of this embodiment, the cage conductor 15 is attached to a conductor holding portion 19 formed by cutting out the outer periphery of the rotor shaft 16, and the axial end of the end ring 18 is supported by a flange-shaped step 19a1. As a result, the axial displacement of the cage conductor 15 is restrained by the flange-shaped step 19a1 formed integrally with the rotor shaft 16, and a reaction force is generated against the centrifugal load and thermal expansion load that are directed axially outward from the end ring 18. This reduces stress concentration at the axial end of the end ring 18, making the end ring 18 less likely to break during high-speed rotation.

In addition, in this embodiment, the conductor holding portion 19 is formed integrally with the rotor shaft 16, so the rigidity of the portion facing the axial end of the end ring 18 is increased, resulting in a structure that can adequately support the end ring 18 even if the axial end of the end ring 18 does not cover the end ring 18 from the outer periphery. In other words, according to this embodiment, there is no need to provide a portion that covers the end ring 18 from the outer periphery and receives the load of the centrifugal force toward the radial outward, so the squirrel cage rotor 11 is less likely to be damaged.

The present invention is not limited to the above-described embodiment, and various improvements and design changes may be made without departing from the spirit of the present invention.

For example, in the above embodiment, the induction motor 10 is a motor, but the induction motor 10 may be a generator.
Furthermore, the rotor bars 17 of the cage conductor 15 may be arranged in a skewed manner, inclined obliquely with respect to the axial direction.

The end rings 18 of the cage conductor 15 in the above embodiment may be formed by casting. For example, the rotor bars 17 are fitted into the grooves of the second region 19b of the conductor holding portion 19, and then a mold material (not shown) is attached to the first region 19a of the conductor holding portion 19. The metal material of the end rings 18 may then be cast into the mold material to form the end rings 18 joined to the rotor bars 17. The mold material is removed after the end rings 18 are formed.

In addition, the embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

10...induction motor, 11...squirrel cage rotor, 12...stator, 13...casing, 14...bearing, 15...squirrel cage conductor, 16...rotor shaft, 17...rotor bar, 18...end ring, 19...conductor holder, 19a...first region, 19a1...step, 19b...second region, 19b1...projection

Claims (4)

a rotor shaft having a conductor holding portion on an outer periphery thereof;
a cage conductor attached to the conductor holding portion of the rotor shaft;
the conductor holding portion is formed integrally with the rotor shaft by cutting out an outer periphery of the rotor shaft,
The cage conductor is
A plurality of rotor bars arranged circumferentially around the rotor shaft and each extending in an axial direction;
a pair of end rings disposed on both axial ends of the rotor bar and electrically connecting the rotor bars;
A squirrel-cage rotor in which the axial ends of the end rings are supported by flange-shaped steps of the conductor holding portion that are formed by recessing radially from the outer periphery of the rotor shaft. the conductor holding portions are each disposed between the rotor bars and have a plurality of protrusions extending in the axial direction;
2. The squirrel cage rotor according to claim 1, wherein the end rings are supported in the axial direction by the projections and the steps. 3. The squirrel cage rotor according to claim 2, wherein the squirrel cage conductor is accommodated in the conductor holding portion so as to be flush with an outer circumferential surface of the rotor shaft. A squirrel cage rotor according to any one of claims 1 to 3;
An induction motor comprising: a stator.