Rotor for rotary electric machine

A rotor for a rotary electric machine includes a rotor core including at least one low-rigidity portion rigidity; a plurality of magnets; a rotary shaft; a washer contacting at least one end surface of the rotor core in an axial direction of the rotor core; and a nut. An outer circumferential end of the washer is disposed more radially inward than the magnet holes, the washer has an outer circumferential shape with recesses and projections in which a distance from a rotation center to the outer circumferential end of the washer periodically varies, and a distance from the outer circumferential end of the washer to each low-rigidity portion is greater than a distance from the outer circumferential end of the washer to each magnet hole.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2017-051869 filed on Mar. 16, 2017 is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present specification discloses a rotor for a rotary electric machine with a washer interposed between a nut screwed onto a rotary shaft and a rotor core.

2. Description of Background Art

In general, a rotor core is composed by stacking a plurality of magnetic steel plates. It has been conventionally proposed that such a rotor core is fastened by a nut screwed onto a rotary shaft so as to apply a compression force in the axial direction to the rotor core. Further, it has also been proposed that a generally annular washer is interposed between this nut and the rotor core. By interposing the washer therebetween, a fastening force by the nut is applied to the rotor core via this washer. Normally, the rotary shaft is inserted through the washer, and an outer circumferential end of the washer is located more radially inward than the magnets so as to prevent magnetic short-circuit.

Meanwhile, usually, a rotor core is formed with a plurality of magnet holes extending through the rotor core in the axial direction so as to insert magnets into these magnet holes. In addition to the magnet holes, the rotor core is also formed with through-holes used for regulating magnetic flux flows and forming magnetic resistance, in some cases. Due to these through-holes, there are low-rigidity portions the rigidities of which are locally decreased in the rotor core. For example, in order to arrange two magnets in a V-shape, two magnet holes in a V-shape are formed in the rotor core. It can be said that a fine gap between these two magnet holes, that is, a portion referred to as a bridge is a low-rigidity portion the rigidity of which is locally decreased. Japanese Patent Application Publication No. 2015-56911 mentions a rotor having such bridges.

SUMMARY

When a washer is pushed against an axial end surface of the rotor core, a stress is generated inside the rotor core due to this pushing force (axial force). If a position pushed by the washer is close to low-rigidity portions, a stress is concentrated onto these low-rigidity portions, so that deterioration or breakage is caused to the low-rigidity portions. Hence, conventionally, a generally annular washer is configured to have a smaller diameter so as not to set its outer circumferential end too close to the low-rigidity portions. Unfortunately, when the washer is configured to have a smaller diameter, a contact area between the washer and the rotor core becomes smaller, and thus there is such a concern that a sufficient axial force cannot be applied to the entire rotor core.

To cope with this, the present disclosure provides a rotor for a rotary electric machine capable of reducing stress applied to low-rigidity portions, while securing a sufficient axial force.

An example aspect of the present disclosure is a rotor for a rotor for a rotary electric machine. The rotor for a rotary electric machine includes: a rotor core being a generally annular shape having a shaft hole at a center, the rotor core having a plurality of magnet holes arranged in a circumferential direction, the rotor core including at least one low-rigidity portion the rigidity of which is locally decreased in the rotor core; a plurality of magnets disposed in the respective magnet holes; a rotary shaft fixedly attached to the shaft hole of the rotor core; a washer tight contacting with at least one end surface in an axial direction of the rotor core; and a nut screwed onto the rotary shaft such that the washer is pushed against the rotor core. An outer circumferential end of the washer is disposed more radially inward than the magnet holes. The washer has an outer circumferential shape with recesses and projections in which a distance from a rotation center to the outer circumferential end of the washer periodically varies. A distance from the outer circumferential end of the washer to each low-rigidity portion is greater than a distance from the outer circumferential end of the washer to each magnet hole.

By configuring the washer to have an outer circumferential shape with recesses and projections in which the distance from the rotation center to the outer circumferential end periodically varies, and by setting a distance from the outer circumferential end of the washer to each low-rigidity portion to be greater than the distance from the outer circumferential end of the washer to each magnet hole, it is possible to apply an axial force in a wide range of the rotor core, while suppressing stress concentration onto the low-rigidity portions. As a result, it is possible to reduce stress applied to the low-rigidity portions, while securing a sufficient axial force.

The rotor core may include a plurality of pairs of magnet holes in the circumferential direction, each pair of the magnet holes arranged in a V-shape opening radially outward. Each bridge as a fine gap may be provided in between each pair of the magnet holes, and the low-rigidity portion may be the bridge.

With such a configuration, also in the rotor including the magnets disposed in a V-shaped arrangement, it is possible to reduce stress applied to the low-rigidity portions, while securing a sufficient axial force.

The rotor core may include the magnet holes, each magnet hole being long in the circumferential direction, and the low-rigidity portion may be the gap between the magnet holes adjacent to each other in the circumferential direction.

With such a configuration, also in the rotor including the magnets disposed in an I-shaped arrangement, it is possible to reduce stress applied to the low-rigidity portions, while securing a sufficient axial force.

The washer may be disposed such that in the same phase as a phase of each low-rigidity portion, a distance from the rotation center to the outer circumferential end becomes minimum.

Through this, the distance from the outer circumferential end of the washer to each low-rigidity portion can be easily greater, to thus more securely suppress stress concentration onto the low-rigidity portions.

The rotor core may have a plurality of sets of through-holes in the circumferential direction, each set of the through-holes including: a pair of the magnet holes arranged circumferentially adjacent to each other in a V-shape opening radially outward; and an intermediate hole being disposed between the pair of the magnet holes. Each low-rigidity portion may be a bridge that is the fine gap between each magnet hole and each intermediate hole.

With such a configuration, even in the rotor formed with the intermediate holes, it is possible to reduce stress applied to the low-rigidity portions, while securing a sufficient axial force.

The washer may be disposed such that in the same phase as a phase of the intermediate hole, the distance from the rotation center to the outer circumferential end becomes minimum.

Through this, the distance from the outer circumferential end of the washer to each low-rigidity portion can easily be greater, to thus more securely suppress stress concentration onto the low-rigidity portions.

The outer circumferential shape of the washer may be a gear-like shape having round corners.

The outer circumferential shape of the washer does not have sharp corners, to thus prevent overconcentration of stress onto a single local position.

One of an inner circumferential surface of the washer and an outer circumferential surface of the rotary shaft may include a key-projection projecting to the other circumferential surface, and the other of the inner circumferential surface of the washer and the outer circumferential surface of the rotary shaft may have a key-groove accepting the key-projection.

With such a configuration, it is possible to securely restrict the phase of the washer relative to the rotor core.

According to the above configuration, it is understood that the washer has an outer circumferential shape with recesses and projections in which the distance from the rotation center to the outer circumferential end periodically varies, and the distance from the outer circumferential end of the washer to each low-rigidity portion is set to be greater than the distance from the outer circumferential end of the washer to each magnet hole. It is possible to apply an axial force in a wide range of the rotor core, while suppressing stress concentration onto the low-rigidity portions. Accordingly, it is possible to reduce stress applied to the low-rigidity portions, while securing a sufficient axial force.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a configuration of a rotor10for a rotary electric machine will be described with reference to drawings.FIG. 1is a schematic longitudinal sectional view of the rotor10.FIG. 2is a view of the rotor10as viewed in a Y direction. InFIG. 2, an outline of a nut20is illustrated by a two-dot chain line.FIG. 3is an enlarged view of a part A ofFIG. 2.

This rotor10is used for a rotary electric machine, for example, a three-phase synchronous rotary electric machine installed in an electric vehicle or the like, as a drive source. The rotor10includes a rotor core12, permanent magnets14embedded in the rotor core12, a rotary shaft16fixedly attached to the rotor10, and a washer18and a nut20applying an axial force to the rotor core12.

The rotor core12is a generally annular shaped body having a shaft hole at a center thereof. The rotor core12is formed by stacking a plurality of electromagnetic steel plates (such as silicon steel plates) in the axial direction. The rotor core12is formed with a plurality of magnet holes22in the vicinity of an outer circumferential end of the rotor core12, and the plurality of magnet holes22are arranged with intervals in the circumferential direction. Each magnet hole22extends through the rotor core12, and a permanent magnet14composing a magnetic pole of the rotor10is disposed in an inside of each magnet hole22.

In this example, the permanent magnets14are disposed in a V-shape arrangement. That is, a single magnetic pole15is composed by a pair of permanent magnets14arranged in a V-shape opening radially outward. In an example ofFIG. 2, the rotor10has sixteen permanent magnets14composing eight magnetic poles15. Each permanent magnet14has a flat and generally rectangular shaped cross section, and is magnetized in its short-axial direction (substantially a rotor-radial direction). Of the permanent magnets14, permanent magnets14composing S-magnetic poles are arranged such that S poles are located radially outward, and permanent magnets14composing N-magnetic poles are arranged such that N poles are located radially outward.

The magnet holes22are also disposed in a V-shape arrangement so as to accept the permanent magnets14disposed in a V-shape arrangement. That is, the rotor core12is provided with multiple pairs (eight pairs in the illustrated example) of the magnet holes22with equal intervals in the circumferential direction, each pair of the magnet holes22being arranged in a V-shape opening radially outward. Each magnet hole22has a generally rectangular shape a long axial dimension of which is greater than that of each permanent magnet14. Hence, when each permanent magnet14is inserted into each corresponding magnet hole22, voids are formed on both sides in the long-axial direction of this permanent magnet14. Such a void is called a flux barrier, and functions as a magnetic resisting portion so as to regulate magnetic characteristics of the rotor core.

Two magnet holes22belonging to the same magnetic pole are close to each other in the circumferential direction, and a bridge24that is a fine gap portion is formed between the both magnet holes22. It can be said that this bridge24is a low-rigidity portion rigidity of which is locally decreased in the rotor core12. To such bridges24(low-rigidity portions), stress is likely to be concentrated, so that deterioration or breakage is likely to be caused thereto. Hence, in order to reduce stress concentration onto the bridges24, the washer18is configured to be in a special shape, and this will be described later.

In this example, each bridge24is configured as a part of the rotor core12, but the bridge24may be composed by using a member different from the stacked steel plates composing the rotor core12. For example, as shown inFIG. 4, it may be configured that a through-hole in a generally V-shape continued in a single line is formed, and a bridge member25as indicated by a two-dot line inFIG. 4may be interposed in a valley portion of this V-shape. In this case, a material of the bridge member25is not limited to a specific one, but it is preferable to use a non-magnetic one for this material.

The rotary shaft16is inserted into the shaft hole of the rotor core12, and is fixedly attached thereto. The rotary shaft16is rotatably supported via a not-illustrated bearing, and integrally rotates with the rotor core12. A flange26protruding radially outward is formed in the middle of the rotary shaft16. The rotor core12through which the rotary shaft16is inserted is pushed against this flange26.

An outer circumferential surface of the rotary shaft16, which is located in the vicinity of the opposite side to the flange26with the rotor core12interposed therebetween, is formed with a male screw. Bold lines inFIG. 1indicate a position where the male screw is formed. As described later, the nut20is screwed onto this male screw. In this drawing, the rotary shaft16is illustrated in a hollow cylindrical shape, but the configuration of the rotary shaft16is not limited to a specific one as far as the rotary shaft16is concentric to the rotor core12, and has an outer circumferential surface having a circular cross section. Hence, the rotary shaft16may be as a solid round bar shape, or may be formed with a coolant flow passage therein.

The washer18and the nut20, together with the flange26, restrict movement of the rotor core12in the axial direction, and also applies a compression force in the axial direction to the rotor core12. The rotary shaft16is inserted through the washer18from its end portion opposite to the flange26so that the washer18comes into contact with an axial end surface of the rotor core12. The nut20is mounted onto the rotary shaft16from its end portion opposite to the flange26so as to be screwed with the male screw formed on the rotary shaft16. By being fastened with this nut20, the rotor core12is held between the washer18and the flange26so as to restrict the movement in the axial direction, and also receive a compression force (axial force) in the axial direction.

Here, in the rotor10disclosed in the present specification, for the purpose of preventing local deterioration of the rotor core12, or the like while sufficiently securing the axial force applied to the rotor core12, the washer18is configured to have a special shape. This will be described in comparison with the background art.FIG. 9is an example of the rotor10of the background art.

When the axial force applied to the rotor core12becomes decreased, a fixing force for the rotor core12becomes naturally decreased. When the axial force is decreased, gaps between the electromagnetic steel plates composing the rotor core12become greater, so that leakage of the coolant from the gaps occurs. Hence, it is desired to apply a sufficient axial force to the rotor core12.

In order to enhance the axial force applied to the rotor core12, naturally, a fastening force by the nut20may be increased. However, in the configuration of the background art, the washer18is configured to have an annular shape the diameter of which is substantially the same as that of the nut20, so that the washer18is in contact with the rotor core12by a radially inward area one third as large as the rotor core12. Hence, if the fastening force by the nut20is increased, a great fastening force (axial force) is applied to only this radially inward area one third as large as the rotor core12; consequently, it is difficult to apply a sufficient axial force to the entire rotor core12.

To cope with this, it is natural to consider to increase the area of the washer18. However, in order to prevent a magnetic short-circuit and heat radiation of the permanent magnet14, as well as other considerations, it is preferable that the washer18does not cover the permanent magnet14. To cope with this, for example, it can be considered that the outer diameter of the washer18in an annular shape is enlarged to the vicinity of the inner circumferential ends of the magnet holes22. With such a configuration, a fastening force by the nut20can be distributed in a wider area, and thus it is possible to apply a sufficient axial force to the entire rotor core12.

However, if the outer diameter of the annular washer18is simply enlarged, force is applied to the vicinities of the bridges24the rigidities of which are locally decreased. In this case, a stress caused in the rotor core12by applying the fastening force is likely to be concentrated on the bridges24the rigidities of which are decreased. Consequently, other problems, such as deterioration and breakage of the bridges24, are caused.

To cope with this, in the rotor10disclosed in the present specification, the washer18is configured to have a special shape. That is, as shown inFIG. 2andFIG. 3, the outer circumferential shape of the washer18of this example is located more radially inward than the magnet holes22, and a distance from a rotation center O to the outer circumferential end of the washer18periodically varies in the circumferential direction so as to have a shape with recesses and projections. In addition, as shown inFIG. 3, the washer18has such a shape that a distance D1from the outer circumferential end of the washer18to each bridge24is not less than a distance D2from the outer circumferential end of the washer18to each magnet hole22. Here, each of the distance D1and the distance D2means a minimum distance. For example, the “distance D2from the outer circumferential end of the washer18to each magnet hole22” means a width of the gap at a position where the width of the gap between the outer circumferential end of the washer18to this magnet hole22becomes the smallest. Similarly, the “distance D1from the outer circumferential end of the washer18to each bridge24” means a width of the gap at a position where the width of the gap between the outer circumferential end of the washer18and this bridge24becomes the smallest.

The shape of the washer18is more specifically described as follows. The outer circumferential shape of the washer18is a generally flower-like shape or a generally gear-like shape having round corners. The generally flower-like shape and the generally gear-like shape each include projecting portions18a, each in an arc shape projecting radially outward, and recessed portions18b, each in an arc shape recessed radially inward, the projecting portions18aand the recessed portions18bbeing arranged alternately with each other in the circumferential direction. Such a variable period of the recesses and projections of the outer circumferential shape of the washer18coincides with an arrangement pitch of the magnetic poles15, or an arrangement pitch of the bridges24as the low-rigidity portions. In the present example, there are eight magnetic poles15and eight bridges24, and each arrangement pitch thereof is 360/8=45°; therefore, the projections and the recesses of the outer circumferential shape of the washer18vary with a period of 45°.

In addition, the washer18is disposed such that a center point (hereinafter, referred to as a “recess point19”) of each recessed portion18b, where a distance from the rotation center to the outer circumferential end of the washer18becomes minimum, is located in the same phase as that of each bridge24. In other words, the washer18is disposed such that each recess point19and each bridge24are aligned in a straight line in the radial direction.

Hence, the outer circumferential shape of the washer18is similar to a shape formed by connecting lines obtained by offsetting inner circumferential ends of the magnet holes22disposed in a generally V-shape arrangement toward a radially inward direction. However, the washer18has an opening angle α1at a position corresponding to the V-shape that is smaller than an opening angle α2at this position of each magnet hole22, so that the washer18has a V-shape deeper radially inward than that of the magnet hole22. As a result, the distance D1from the outer circumferential end of the washer18to the bridge24is not less than a distance D2from the outer circumferential end of the washer18to the magnet hole22.

In this manner, since the distance from the outer circumferential end of the washer18to each bridge24becomes greater, it becomes more difficult to apply force to the vicinity of each bridge24rigidity of which is locally decreased, thus suppressing stress concentration onto the bridge24. Accordingly, it is possible to effectively suppress deterioration and damages of the bridges24. In the meantime, of the washer18, each portion the phase of which deviates from the bridge24extends more radially outward than the rotor10of the background art, and thus an axial force can be applied in a wide range of the rotor core12. Accordingly, according to the washer18of the present example, it is possible to prevent local deterioration of the rotor core12, or the like, while securing a sufficient axial force applied to the rotor core12.

In order to suppress the stress concentration onto the bridges24, it is necessary to align the phase of each recess point19of the washer18with the phase of each bridge24. Hence, in the rotor10disclosed in the present specification, in order to align the phase of the washer18with the phase of the rotor core12, the washer18is key-engaged with the rotary shaft16. Specifically, an inner circumferential surface of the washer18is provided with key-projections30projecting radially inward, and the outer circumferential surface of the rotary shaft16is provided with key-grooves32accepting the key-projections30. The washer18is assembled to the rotary shaft16such that the key-projections30are fitted into the key-grooves32, to thereby restrict the phase of the washer18relative to the rotor core12in a preferable manner.

In the present example, the washer18is provided with the key-projections30, and the rotary shaft16is provided with the key-grooves32, but this combination may be inverted to each other. This means that the rotary shaft16may be provided with the key-projections, and the washer18may be provided with the key-grooves. The number of the key-grooves32and the number of the key-projections30may appropriately be changed.

Next, another example of the rotor10will be described.FIG. 5is a view showing one example of a rotor10according to another exemplary embodiment.FIG. 6is an enlarged view of a part B ofFIG. 5. In this rotor10, each single magnetic pole15is composed by three permanent magnets14a,14barranged in an inverted triangle shape (subscripts are omitted when the permanent magnets14a,14bof two types are not distinguished from each other. This is the same in the magnet holes described later). That is, each single magnetic pole15is composed by a pair of the permanent magnets14aarranged in a V-shape opening radially outward and one permanent magnet14bdisposed between respective outer circumferential ends of the pair of the permanent magnets14a.

The rotor core12is formed with the magnet holes22for accepting the permanent magnets14. Each pair of the magnet holes22aare arranged in a V-shape opening radially outward. Note that these two magnet holes22aare not close to each other in the circumferential direction, but there is an intermediate hole28between respective inner circumferential ends of the two magnet holes22a. Each intermediate hole28is a through-hole extending through the rotor core12in the axial direction. This intermediate hole28functions as a magnetic resisting portion, and by providing the intermediate hole28, magnetic flux flows can be regulated. Here, as apparent fromFIG. 6, the bridge24as a fine gap portion rigidity of which is locally decreased is formed between each intermediate hole28and each magnet hole22a.

In addition, a magnet hole22bextending in the circumferential direction is formed between respective outer circumferential ends of every two magnet holes22a. A pair of void holes29are formed on both circumferential sides of each magnet hole22b. As similar to the intermediate hole28, each void hole29is a through-hole extending through the rotor core12in the axial direction, and functions as a magnetic resisting portion. This void hole29is also provided so as to regulate the magnetic flux flows.

In examples shown inFIG. 5andFIG. 6, the washer18is disposed on the axial end surface of the rotor core12, and the washer18is pushed against the rotor core12with a fastening force by the nut20(not illustrated inFIG. 5andFIG. 6). As similar to the example shown inFIG. 2, the outer circumferential shape of the washer18of this example is located more radially inward than the magnet holes22, and the distance thereof from the rotation center O to the outer circumferential end periodically varies in the circumferential direction so as to have a shape with recesses and projections. In addition, as shown inFIG. 6, the washer18has such a shape that a distance D1from the outer circumferential end of the washer18to each bridge24is not less than a distance D2from the outer circumferential end of the washer18to each magnet hole22.

To be more specific, the outer circumferential shape of the washer18is a generally flower-like shape or a generally gear-like shape having round corners. The generally flower-like shape and the generally gear-like shape each include the projecting portions18a, each in an arc shape projecting radially outward, and the recessed portions18b, each in an arc shape recessed radially inward, the projecting portions18aand the recessed portions18bbeing arranged alternately with each other in the circumferential direction. The variable period of the recesses and projections of the outer circumferential shape of the washer18coincides with the arrangement pitch of the magnetic poles15.

In addition, the washer18is disposed such that each recess point19, where a distance from the rotation center to the outer circumferential end of the washer18becomes minimum, is located in the same phase as that of the circumferential center of the intermediate hole28. In other words, the washer18is disposed such that each recess point19and the circumferential center of each intermediate hole28are aligned in a straight line in the radial direction. With such a configuration, it is possible to reduce the stress concentration onto the bridges24, and it is also possible to apply an axial force in a wide range of the rotor core12.

Note that each recessed portion18bis formed in a generally arc shape recessed radially inward in the examples ofFIG. 5andFIG. 6, but this recessed portion18bmay be a straight shape extending in the generally circumferential direction, as shown inFIG. 7. With such a configuration, compared with the cases ofFIG. 5and theFIG. 6, the distance D1from the outer circumferential end of the washer18to the bridge24can be greater, to thus suppress more stress concentration onto each bridge24.

Next, another exemplary embodiment of the rotor10will be described.FIG. 8is a view showing another exemplary rotor10. In this rotor10, each single magnetic pole15is formed by a single permanent magnet14that is long in the generally circumferential direction. In the example ofFIG. 8, the rotor10includes sixteen magnetic poles15and sixteen permanent magnets14.

The rotor core12is formed with the magnet holes22for accepting these permanent magnets14. Each magnet hole22is a flat rectangular shape that is long in the generally circumferential direction, and a long axial dimension is greater than a long axial dimension of the permanent magnet14. A gap portion36having a thin width is formed between each two magnet holes22adjacent to each other in the circumferential direction. It can be said that this gap portion36is a low-rigidity portion rigidity of which is locally decreased, as with the above described bridge24.

As with the washer18shown inFIG. 2, the washer18in tight contact with this rotor core12has an outer circumferential shape located more radially inward than the magnet holes22, and having recesses and projections in which the distance from the rotation center O to the outer circumferential end periodically varies in the circumferential direction. In addition, as shown inFIG. 8, the washer18has such a shape that the distance D1from the outer circumferential end of the washer18to each gap portion36is not less than the distance D2from the outer circumferential end of the washer18to each magnet hole22.

To be more specific, the outer circumferential shape of the washer18is a generally flower-like shape or a generally star-like shape having round corners. The generally flower-like shape and the generally star-like shape each include projecting portions18a, each in an arc shape projecting radially outward, and recessed portions18b, each in an arc shape recessed radially inward, the projecting portions18aand the recessed portions18bbeing arranged alternately with each other in the circumferential direction. The variable period of the recesses and projections of the outer circumferential shape of the washer18coincides with the arrangement pitch of the magnetic poles15.

In addition, the washer18is disposed such that the circumferential center point of each recessed portion18b(hereinafter, referred to as a “recess point19”), where the distance from the rotation center O to the outer circumferential end of the washer18becomes minimum, is located in the same phase as that of the gap portion36. In other words, the washer18is disposed such that each recess point19and the gap portion36are aligned in a straight line in the radial direction. With such a configuration, it is possible to reduce the stress concentration onto the gap portions36, and it is also possible to apply an axial force in a wide range of the rotor core12.

As apparent from the above description, according to the rotor10disclosed in the present specification, it is possible to reduce stress applied onto the low-rigidity portions. The configurations disclosed in the present specification are exemplary embodiments, and as far as the distance from the outer circumferential end of the washer to each low-rigidity portion is not less than the distance from the outer circumferential end of the washer to each magnet hole, the other configurations may appropriately be changed. For example, in the above description, the washer18is formed in a generally gear-like shape corners of which are all round, but may be formed in a generally gear-like shape having sharp corners. However, in order to avoid overconcentration of stress onto a single local position, it is preferable to avoid sharp corners for the outer circumferential shape of the washer18, as much as possible.