Patent Application
20180278106
The present invention relates to a rotor for an induction motor and an induction motor.
In recent years, needs for rotating an induction motor for a machine tool at a higher speed are increasing. An end ring provided in a rotor of an induction motor is deformed by a centrifugal force during high-speed rotation of the rotor. Therefore, every time start-up and stop of the induction motor are repeated or every time a rotational speed of the rotor changes, stress is applied to a point of connection between the end ring and a conductor bar, so that a fatigue life of the rotor is shortened.
A rotor for an induction motor disclosed in Patent Literature 1 includes a rotor core that is a stacked iron core, a shaft penetrating through the rotor core, a conductor bar that penetrates through the rotor core and is a cage bar, an end ring that is an annular short-circuit ring provided at a position away from an end of the rotor core by a certain distance, a first reinforcing member that is an annular support ring provided between the end ring and the shaft, and a second reinforcing member that is an annular shrink-fit ring provided on an outer circumferential portion of the end ring. Because of shrink-fitting of the second reinforcing member on the end ring, a compressive force from the second reinforcing member is applied to the end ring. Due to this, deformation of the end ring during rotation of the rotor is suppressed.
Patent Literature 1: Japanese Patent Application Laid-open No. H9-103054
However, the rotor for an induction motor disclosed in Patent Literature 1 has a problem that, because the conductor bar between the end of the rotor core and the end ring is deformed when the rotor is rotated, an effect of suppressing deformation of the end ring connected to the conductor bar is not expected, so that the rotor has to be replaced with a new one in a shorter period of time than a designed lifetime.
The present invention has been achieved in view of the above problems, and an object of the present invention is to provide a rotor for an induction motor that can suppress reduction in the lifetime thereof.
To solve the above problems and achieve the object, a rotor for an induction motor according to the present invention includes a rotor core, a conductor bar that penetrates through the rotor core in an axial direction along a center axis of the rotor core, an end ring having an annular shape, which is provided at an end of the rotor core and is connected to the conductor bar projecting from the end of the rotor core, and a first reinforcing member that is provided between the rotor core and the end ring and is in contact with the end ring. The first reinforcing member has an insertion hole formed therein to which the conductor bar projecting from the end of the rotor core is to be inserted.
An effect is obtained where the rotor for an induction motor according to the present invention can suppress reduction in the lifetime thereof.
Exemplary embodiments of a rotor for an induction motor and an induction motor according to the present invention will be described in detail below based on the drawings. The present invention is not limited by the embodiments.
An induction motor 300 illustrated in
The rotor 100 includes the rotor core 1 that is cylindrical and a shaft 2 penetrating through a through hole 1a of the rotor core 1. The rotor core 1 includes a plurality of core slots 5 that are provided in a portion of the rotor core 1 close to an outer circumferential surface of the rotor core 1 and are arranged in an axis-surrounding direction D2 of the center axis AX of the rotor core 1, and a conductor bar 6 that is provided for each of the core slots 5 and penetrates through the rotor core 1 in the axial direction D1.
The rotor 100 also includes an end ring 3-1 having an annular shape, provided at one end 1b1 that is one end of the rotor core 1 in the axial direction D1, a first reinforcing member 4-1 having an annular shape, which is provided between the rotor core 1 and the end ring 3-1 and is in contact with the end ring 3-1, an end ring 3-1 having an annular shape provided on the other end 1b2 that is the other end of the rotor core 1 in the axial direction D1, and a first reinforcing member 4-2 having an annular shape, which is provided between the rotor core 1 and the end ring 3-2 and is in contact with the end ring 3-2.
One end 6a of the conductor bar 6 projecting from the one end 1b1 of the rotor core 1 is connected to the end ring 3-1. An inner circumferential portion 3a of the end ring 3-1 is in contact with the first reinforcing member 4-1. As illustrated in
In the first reinforcing member 4-1, an insertion hole 4a is formed to which the conductor bar 6 projecting from the one end 1b1 of the rotor core 1 is to be inserted.
In the first reinforcing member 4-2, an insertion hole 4a is formed to which the conductor bar 6 projecting from the other end 1b2 of the rotor core 1 is to be inserted. An inner diameter of the insertion hole 4a formed in each of the first reinforcing member 4-1 and the first reinforcing member 4-2 is equal to an outer diameter of the conductor bar 6. A through hole 4b is formed in a center portion of each of the first reinforcing member 4-1 and the first reinforcing member 4-2. The shaft 2 penetrates through the through hole 4b of each of the first reinforcing member 4-1 and the first reinforcing member 4-2, and the through hole 1a of the rotor core 1.
The rotor 100 also includes a second reinforcing member 5-1 provided on an outer circumferential portion 3b of the end ring 3-1, and a second reinforcing member 5-2 provided on an outer circumferential portion 3b of the end ring 3-2. An inner circumferential portion 5a of the second reinforcing member 5-1 is in contact with the outer circumferential portion 3b of the end ring 3-1, and an inner circumferential portion 5a of the second reinforcing member 5-2 is in contact with the outer circumferential portion 3b of the end ring 3-2.
In the following description, the end ring 3-1 and the end ring 3-2 may be simply referred to as “end ring(s) 3-1 and/or 3-2”, the first reinforcing member 4-1 and the first reinforcing member 4-2 may be simply referred to as “first reinforcing member(s) 4-1 and/or 4-2”, and the second reinforcing member 5-1 and the second reinforcing member 5-2 may be simply referred to as “second reinforcing member(s) 5-1 and/or 5-2”.
In the present embodiment, outer diameters of the first reinforcing members 4-1 and 4-2, the second reinforcing members 5-1 and 5-2, and the rotor core 1 are equal to one another.
As illustrated in
In the present embodiment, the outer diameters of the first reinforcing members 4-1 and 4-2, the second reinforcing members 5-1 and 5-2, and the rotor core 1 are set to be equal to one another. However, the outer diameters may be different from one another. In this case, the same effects as those described above can be obtained when the inner circumferential portions 5a of the second reinforcing members 5-1 and 5-2 are located within the insertion holes 4a of the first reinforcing members 4-1 and 4-2, respectively. In other words, it suffices to employ an arrangement in which the first reinforcing members 4-1 and 4-2 are pressed by the second reinforcing members 5-1 and 5-2, respectively.
The rotor core 1 is formed by stacking a plurality of thin plates, punched out from an electromagnetic steel plate (not illustrated) as a base material to have an annular shape, in the axial direction D1. The thin plats are fixed to each other by swaging, welding, or bonding.
Each of the core slots 5 extends in the axial direction D1 through the rotor core 1 from the one end 1b1 to the other end 1b2. Also, each of the core slots 5 is skewed towards the axis-surrounding direction D2, as illustrated in
As materials for the end ring 3-1, the end ring 3-2, and the conductor bar 6, a conductor material, such as aluminum, aluminum alloy, copper, or copper alloy, can be used for example. The end rings 3-1 and 3-2 and the conductor bar 6 can be formed by die casting or brazing, which uses the conductor material.
A centrifugal force acting on an object depends not only on a radius and an angular velocity of the object but also on a mass of the object. In order to suppress deformation of the end rings 3-1 and 3-2 caused by a centrifugal force and thermal expansion, the first reinforcing members 4-1 and 4-2 and the second reinforcing members 5-1 and 5-2 have to be designed so as to be hardly deformed by the centrifugal force. Therefore, a material that has a higher tensile strength per unit mass than the material for the end rings 3-1 and 3-2 is used for the first reinforcing members 4-1 and 4-2 and the second reinforcing members 5-1 and 5-2. As the material for the first reinforcing members 4-1 and 4-2 and the second reinforcing members 5-1 and 5-2, iron, titanium, or carbon-fiber reinforced plastic can be used, for example.
As illustrated in
In fabrication of the rotor 100, first, the first reinforcing member 4-1 and the first reinforcing member 4-2 are attached to one end 1b1 and the other end 1b2 of the rotor core 1, respectively. Thereafter, the conductor bar 6 and the end rings 3-1 and 3-2 are cast by die casting using the conductor material described above.
The inner circumferential portion 3a of each of the end rings 3-1 and 3-2 is in contact with an outer circumferential portion 41a of the first annular portion 41 illustrated in
Subsequently, the outer circumferential portion 3b of each of the end rings 3-1 and 3-2 is subjected to cutting, and the outer circumferential portions 3b of the end rings 3-1 and 3-2 after cutting are respectively interference-fitted to the second reinforcing members 5-1 and 5-2 illustrated in
Before shrink-fitting of the end rings 3-1 and 3-2 to the second reinforcing members 5-1 and 5-2, X-ray is radiated from an outer circumferential portion 3b side of the end rings 3-1 and 3-2, so that a flaw inspection is performed. The reason why the flaw inspection is performed at this timing is that X-ray that is a suitable energy for inspecting the end rings 3-1 and 3-2 can be hardly penetrated through the second reinforcing members 5-1 and 5-2 in a state where the end rings 3-1 and 3-2 are respectively shrink-fitted to the second reinforcing members 5-1 and 5-2 because of a difference of a specific gravity between materials respectively forming the second reinforcing members 5-1 and 5-2 and the end rings 3-1 and 3-2. By X-ray radiation from the outer circumferential portion 3b side of the end rings 3-1 and 3-2 before the end rings 3-1 and 3-2 are shrink-fitted to the second reinforcing members 5-1 and 5-2, it is possible to inspect the inside of the end rings 3-1 and 3-2 with high accuracy.
A force that spreads outward in the radial direction D3 due to a centrifugal force acts on the end rings 3-1 and 3-2 during rotation. In the present embodiment, the one end 6a of the conductor bar 6 projecting from the one end 1b1 of the rotor core 1 is inserted into the insertion hole 4a of the first reinforcing member 4-1, and the other end 6b of the conductor bar 6 projecting from the other end 1b2 of the rotor core 1 is inserted into the insertion hole 4a of the first reinforcing member 4-2. Therefore, when a centrifugal force acts on the end rings 3-1 and 3-2, both ends of the conductor bar 6 projecting from the rotor core 1 come into contact with the insertion holes 4a of the first reinforcing members 4-1 and 4-2. This contact suppresses deformation of both ends of the conductor bar 6 and also suppresses deformation of the end rings 3-1 and 3-2. Accordingly, because a stress amplitude generated in the end rings 3-1 and 3-2 each time start-up and stop of the rotor 100 are repeated is reduced, or the stress amplitude generated in the end rings 3-1 and 3-2 each time a rotational speed of the rotor 100 changes is reduced, improvement of a fatigue life of the end rings 3-1 and 3-2 can be achieved. In the following description, a reinforcing effect of the end rings 3-1 and 3-2 by the first reinforcing members 4-1 and 4-2 is described specifically.
(1) Each of the first reinforcing member 4-1A and 4-2A includes a second annular portion 42A in place of the second annular portion 42 illustrated in
(2) The insertion hole 4a illustrated in
In
while the rotor 100A is stopped, the inner circumferential portion 3a of the end ring 3-1 is in contact with the outer circumferential portion 41a of the first annular portion 41. Because the second reinforcing member 5-1 is shrink-fitted to the end ring 3-1, a compressive force from the second reinforcing member 5-1 is applied to the end ring 3-1. Therefore, a friction force is generated between the outer circumferential portion 41a of the first annular portion 41 and the inner circumferential portion 3a of the end ring 3-1. This friction force works to suppress deformation of the end ring 3-1 during rotation and during thermal expansion of the rotor 100A.
A force that spreads outward in the radial direction D3 acts on the end ring 3-1 during rotation of the rotor 100A because of a centrifugal force. This force increases with increase of a rotational speed of the rotor 100A, and therefore the end ring 3-1 is deformed with the point of connection to the conductor bar 6 as a fulcrum. In this deformation, the end ring 3-1 resists the friction force generated between the inner circumferential portion 3a of the end ring 3-1 and the outer circumferential portion 41a of the first annular portion 41 to spread outward in the radial direction D3 as illustrated in
Because an amount of positional deformation of the end ring 3-1 increases with increase of the rotational speed of the rotor 100A, a stress amplitude generated in the end ring 3-1, that is, an amount of positional deformation before rotation in which the rotor 100A is stopped and after the rotation of the rotor 100A becomes larger, as compared with that when the rotational speed of the rotor 100A is low. Every time rotation and stopping of the rotor 100A are repeated or every time the rotational speed of the rotor 100A changes, the inner diameter and the outer diameter of the end ring 3-1 repeat expansion and reduction, so that metal fatigue progresses in the end ring 3-1. Meanwhile, the one end 6a of the conductor bar 6 connected to the end ring 3-1 is deformed outward in the radial direction D3 with the one end 1b1 of the rotor core 1 as a fulcrum with positional deformation of the end ring 3-1. Therefore, each time rotation and stop of the rotor 100A are repeated or each time the rotational speed of the rotor 100A changes, stress is applied to the one end 6a of the conductor bar 6, and therefore metal fatigue in the one end 6a of the conductor bar 6 progresses. Consequently, the rotor 100A may have to be replaced with a new one in a shorter period of time than a designed lifetime.
On the other hand, in the rotor 100 according to the present embodiment, outward deformation in the radial direction D3 of the conductor bar 6 projecting from the one end 1b1 of the rotor core 1 is suppressed by the first reinforcing member 4-1 during rotation, because the one end 6a of the conductor bar 6 is inserted into the insertion hole 4a of the first reinforcing member 4-1. Due to this, deformation of the one end 6a of the conductor bar 6 is suppressed, as compared with that in the rotor 100A illustrated in
Next, the reason why a width ADW3 in the axial direction D1 of a portion of the inner circumferential portion 3a of each of the end rings 3-1 and 3-2 of the rotor 100 according to the present embodiment, which is in contact with the outer circumferential portion 41a of the first annular portion 41, is narrower than a width ADW5 in the axial direction D1 of the outer circumferential portion 3b of each of the end rings 3-1 and 3-2 is described, referring to
Even when the rotor 100B of
Differences between the rotor 100B illustrated in
(1) The rotor 100B illustrated in
(2) The first reinforcing member 4-1B includes a first annular portion 41A in place of the first annular portion 41 illustrated in
(3) Regarding the rotor 100 illustrated in
In the rotor 100B illustrated in
On the other hand, in the rotor 100 illustrated in
In the rotor 100B in a stop state illustrated in a first diagram from top of
When a rotor is driven to rotate, the temperature rises due to heat generation, so that members of the rotor are thermally expanded. Because the end rings 3-1 and 3-2 and the conductor bar 6 are formed from a member having a large coefficient of thermal expansion, shape deformation is caused by thermal expansion. When the rotor is stopped, the temperature decreases. Therefore, because of shape change caused by heat cycle, the lifetime of the rotor may be shortened. In
In the rotor 100B, because the temperature rises with increase of a rotational speed, the conductor bar 6 thermally expands in the axial direction D1, and the end ring 3-1A moves in the axial direction D1 while resisting a friction force between the outer circumferential portion 41a of the first annular portion 41A and the inner circumferential portion 3a of the end ring 3-1A, as illustrated in a second diagram from top in
Thereafter, because the temperature decreases with decrease of the rotational speed of the rotor 100B, the end ring 3-1A moves in the axial direction D1 to come close to the second annular portion 42 by thermal shrinkage of the conductor bar 6, as illustrated in a third diagram from top in
Regarding the friction force between the end ring 3-1 and the first reinforcing member 4-1, there is actually a non-linear relation between a load and the friction force, and therefore the friction force tends to be smaller as an area of contact between two objects is narrower. Because the width ADW3 of the inner circumferential portion 3a of the end ring 3-1 in
In the rotor 100 in a stop state illustrated in the first diagram from top in
As the rotational speed of the rotor 100 increases, the end ring 3-1 resists the friction force between the outer circumferential portion 41a of the first annular portion 41 and the inner circumferential portion 3a of the end ring 3-1 to move in the axial direction D1 because of thermal expansion of the conductor bar 6, as illustrated in the second diagram from top in
Thereafter, as the rotational speed of the rotor 100 decreases, the end ring 3-1 moves in the axial direction D1 by the shrinking force of the conductor bar 6, as illustrated in a third diagram from top in
Because the first friction force in the rotor 100 is smaller than the second friction force in the rotor 100B illustrated in
Even in a case where the width ADW3 of the inner circumferential portion 3a of the end ring 3-1 illustrated in
(1) The rotor 100C includes an end ring 3-1B in place of the end ring 3-1 illustrated in
(2) In the end ring 3-1B, the inclined surface 3e illustrated in
Because the end ring 3-1B is connected to the one end 6a of the conductor bar 6 provided in a portion of the rotor core 1 which is close to an outer circumferential surface of the rotor core 1, the end ring 3-1B during rotation of the rotor 100C is deformed with a point of connection to the one end 6a of the conductor bar 6 as a fulcrum. Therefore, the largest stress amplitude larger than those generated in any portion other than a corner 3f is generated in the corner 3f between the inner circumferential portion 3a and an end 3d of the end ring 3-1B.
Specifically, the stress amplitude generated in a portion close to the inner circumferential portion 3a of the end ring 3-1B is larger than the stress amplitude generated in a portion close to the outer circumferential portion 3b of the end ring 3-1B. Further, the stress amplitude generated in a portion of the end ring 3-1B close to the end 3d that is on an opposite side to the rotor core 1 is larger than the stress amplitude generated in a portion of the end ring 3-1B close to an end 3c on a rotor core 1 side. Therefore, because the largest amplitude of the stress in the entire end ring 3-1B is generated in the corner 3f between the inner circumferential portion 3a and the end 3d of the end ring 3-1B, which is located at a farthest position from the fulcrum during rotation, the corner 3f is deteriorated earliest in the entire end ring 3-1B, and deterioration of the end ring 3-1B progresses from the corner 3f as a start point.
In the end ring 3-1 of the rotor 100 illustrated in
(1) The first reinforcing members 4-1C and 4-2C each include a first annular portion 41B in place of the first annular portion 41 illustrated in
(2) An end 41b of the first annular portion 41B, on an opposite side to the rotor core 1, has a plurality of screw holes 41c that are formed therein and are arranged in the axis-surrounding direction D2.
Because a plurality of the insertion holes 4a are formed in the second annular portion 42, the weight of the rotor 100 may become unbalanced due to positions and sizes of the insertion holes 4a. The imbalance means that the distances between the insertion holes 4a adjacent in the axis-surrounding direction D2 are not even, or the distances from centers of the insertion holes 4a arranged in the axis-surrounding direction D2 to the center axis AX are not even. Due to this imbalance, vibration occurs during rotation of the rotor 100. In the rotor 100 provided with the first reinforcing members 4-1C and 4-2C, a screw (not illustrated) is tightened into part of the screw holes 41c formed in the first annular portion 41B, so that the imbalance of the weight is improved. Examples of a method for improving the imbalance of the weight are a method for cutting out a portion of the first reinforcing member(s) 4-1C and/or 4-2C to improve the imbalance of the weight and a method for applying a ballast material typified by epoxy resin onto the first reinforcing member(s) 4-1C and/or 4-2C to improve the imbalance of the weight, other than the method for providing the screw holes 41c. However, in the first reinforcing members 4-1C and 4-2C illustrated in
Although the rotor 100 including the second reinforcing members 5-1 and 5-2 is described in the present embodiment, the second reinforcing members 5-1 and 5-2 may be omitted. Even in a case where the second reinforcing members 5-1 and 5-2 are omitted, deformation of the end rings 3-1 and 3-2 can be suppressed at a rotational speed lower than a certain rotational speed, because the first reinforcing members 4-1 and 4-2 are provided in the rotor 100. With the second reinforcing members 5-1 and 5-2, deformation of the end rings 3-1 and 3-2 can be also suppressed in a range of a rotational speed higher than the certain rotational speed.
Further, although an example where the conductor bar 6 is formed by die casting in the first reinforcing members 4-1 and 4-2 that are manufactured in advance is described in the present embodiment, the first reinforcing members 4-1 and 4-2 may be formed by shrink-fitting after the conductor bar 6 is formed by brazing. In a case where the first reinforcing members 4-1 and 4-2 are shrink-fitted to the conductor bar 6, it is likely that a portion of the plural conductor bars 6 expands because of contact with the first reinforcing members 4-1 and 4-2, to cause the first reinforcing members 4-1 and 4-2 in the middle of fitting to be stopped at unintended positions. Forming the first reinforcing members 4-1 and 4-2 by die casting can suppress reduction of a yield caused by a failure of manufacturing of the first reinforcing members 4-1 and 4-2.
The configuration described in the above embodiment are only an example of the content of the present invention. The configuration can be combined with other well-known techniques, and a part the configuration can be omitted or modified without departing from the gist of the present invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/077862 | 9/21/2016 | WO | 00 |
