Permanent magnet rotor and brushless motor

In a rotor 20 including a plurality of permanent magnet pieces 60 fixed in a plurality of magnet insertion slots 43 provided on the outer periphery of a rotor yoke 40, respectively, and the rotor yoke 40 having concaves 44 each provided between the permanent magnet pieces 60 adjacent to each other and protrusions 46 each provided in each the concaves 44 to protrude outwardly in the radial direction of the rotor yoke 40, between the sandwiching angle α formed by two sides connecting both outer ends A and A′ of each the concaves 44 to the center axis O of the rotor yoke 40 and the sandwiching angle β formed by two sides connecting both outer ends B and B′ of each the protrusions 46 to the center axis O of the rotor yoke 40, the following relationship is satisfied:0.3<β/α<0.5.

BACKGROUND OF THE INVENTION

This invention relates to a permanent magnet rotor having permanent magnets provided at a rotor iron core and a brushless motor equipped with such a rotor.

As a rotor used for a motor, a permanent magnet rotor is known in which permanent magnets are provided at a plurality magnet attaching segments arranged at a rotor iron core. The permanent magnet rotor includes a type of having a convex (convex pole) between adjacent magnets (e.g. Patent Reference 1) and another type of having not the convex but a concave between the adjacent magnets (e.g. Patent Reference 2).

Both types of permanent-magnetic rotors and brushless motors equipped with these rotors have advantages and disadvantages, respectively.

The permanent magnet rotor of a type having the convex and brushless motor equipped with such a rotor have advantages that (1) reluctance torque is relatively large, and (2) the magnetic flux passes through the convex and hence easily passes through the yoke at a more inner side in a radial direction than the magnet so that the magnetic flux is difficult to be saturated, thus giving “senserless position detection” with a high accuracy, but also have disadvantages of more heat generation of the magnet and being fragile to demagnetization. The “senserless position detection” is to estimate the position of the rotor on the basis of the current flowing through each of windings in a multiple phase when a voltage for position detection is applied to the windings of a stator.

On the other hand, the permanent-magnetic rotor of a type having not the convex but the concave and the brushless motor equipped with such a rotor have advantages of less magnet heat generation and being tolerant to demagnetization, but disadvantages that (1) the reluctance torque is relatively small, and (2) because of absence of the convex, the magnetic flux from the stator is difficult to pass through the yoke at a more outer side in a radial direction than the magnet so that the magnetic flux is likely to be saturated, thus giving “senserless position detection” with a low accuracy, and (3) the thickness of the yoke on both sides in a circumferential direction of the magnet is decreased, thereby low strength against the centrifugal force during a high speed rotation.

Proposed are also a rotor in which an auxiliary pole portion is provided through a groove (concave) between permanent magnets adjacent to each other and a brushless motor equipped with such a rotor (e.g. Patent Reference 3). Patent Reference 3 describes that torque pulsation can be suppressed when the pitch of the slots in a stator, open angle of the magnetic pole of the permanent magnet in the rotor and the open angle of the auxiliary pole are set in their dimension so as to satisfy a prescribed relationship.Patent Reference 1: JP-A-Hei5-76146Patent Reference 2: JP-A-Hei10-285849Patent Reference 3: JP-A-2002-305859

Now, it is eagerly demanded to develop a rotor capable of satisfying all the requirements of an increase in reluctance torque, improvement in the sensorless position detection accuracy and suppression of magnet heat generation and a brushless motor equipped with such a rotor. The brushless motor disclosed in Patent Reference 3 cannot solve such a problem.

SUMMARY OF THE INVENTION

In view of this circumstance, this invention intends to provide a permanent magnet rotor with relative large reluctance torque, improved accuracy of sensorless position detection and less magnet heat generation.

The invention described in aspect1is a permanent magnet rotor (e.g. rotor20in the embodiments described later) including a plurality of permanent magnet pieces (e.g., permanent magnet pieces60in the embodiments described later) fixed in a plurality of magnet attaching segments (e.g., magnet insertion slots43and magnet accommodating concave segments71in the embodiments described later) provided on the outer periphery or inner periphery of a rotor iron core, respectively, and the rotor iron core (e.g., rotor yoke40in the embodiments described later) with concaves (e.g. concaves44and72in the embodiments described later) each provided between the permanent magnet pieces adjacent to each other and protrusions (protrusions46and73in the embodiments described later) each provided in each the concaves to protrude outwardly in the radial direction of the rotor iron core, between the sandwiching angle α formed by two sides connecting both outer ends of each the concaves to the center axis of the rotor iron core and the sandwiching angle β formed by two sides connecting both outer ends of each the protrusions to the center axis of the rotor iron core, is satisfied:
0.3<β/α<0.5.

In this configuration, since the rotor is provided with the protrusions, the reluctance torque can be made large; since the rotor is provided with the concaves, magnet heat generation can be suppressed, thereby making demagnetization difficult. Further, in a brushless motor combined with a stator, the magnetic flux emitted from the stator passes through the protrusion and also passes through a yoke area located at a more inner side than the permanent magnet piece in the radial direction. For this reason, the magnetic flux is difficult to be saturated, thereby extremely increasing the accuracy of the sensorless position detection. Particularly, since the sandwiching angles α and β are set in the angular relationship satisfying, the improvement of the sensorless position detection accuracy and the suppression of the magnet heat generation can be reconciled.

The invention described in aspect2is a brushless motor comprising: a permanent magnet rotor (e.g. rotor20in the embodiments described later) including a plurality of permanent magnet pieces (e.g., permanent magnet pieces60in the embodiments described later) fixed in a plurality of magnet attaching segments (e.g., magnet insertion slots43and magnet accommodating concaves71in the embodiments described later) provided on the outer periphery or inner periphery of a rotor iron core, respectively, and the rotor iron core (e.g., rotor yoke40in the embodiments described later) with concaves (e.g. concaves44and72in the embodiments described later) each provided between the permanent magnet pieces adjacent to each other and protrusions (protrusions46and73in the embodiments described later) each provided in each the concaves to protrude outwardly in the radial direction of the rotor iron core; and a stator (e.g. stator10in the embodiments described later) arranged oppositely to the permanent magnet rotor, wherein the position of the rotor can be estimated on the basis of the current flowing through each winding in a multiple phase when a voltage for detecting the position of the rotor is applied to the windings (e.g. windings12in the embodiments described later) of the stator, characterized in that between the sandwiching angle α formed by two sides connecting both outer ends of each the concaves to the center axis of the rotor iron core and the sandwiching angle β formed by two sides connecting both outer ends of each the protrusions to the center axis of the rotor iron core, is satisfied:
0.3<β/α<0.5.

In this configuration, since the rotor is provided with the protrusions, the reluctance torque can be made large. Further, the magnetic flux emitted from the stator passes through the protrusion and further can reach a yoke area located at a more inner side than the permanent magnet piece in the radial direction. For this reason, the magnetic flux is difficult to be saturated, thereby extremely increasing the accuracy of the sensorless position detection. In addition, since the rotor is provided with the protrusions, an alternate magnetic flux change in the vicinity of the protrusions is reduced, thereby reducing the magnetic flux change in the magnet itself. If the magnetic flux change in the magnet is little, an eddy current is also little, thereby suppressing the magnet heat generation and making its demagnetization difficult.

Particularly, since the sandwiching angles α and β are set in the angular relationship satisfying, the improvement of the sensorless position detection accuracy and the suppression of the magnet heat generation can be reconciled.

The invention described in aspect3is a brushless motor according to aspect2, characterized in that the distance between the outer end of each the protrusions and the outer end of each the concaves located oppositely thereto is larger than that in the radial direction of the gap formed between the rotor and the stator.

In this configuration, it is possible to realize that the magnetic flux of the permanent magnet piece easily passes from the outer periphery of the magnet attaching segment toward the stator, the magnetic flux is difficult pass to the area where the protrusion and concave are arranged, and the short-circuiting of the magnetic flux between the adjacent permanent magnet pieces is difficult to occur.

In accordance with the permanent magnet rotor described in aspect1, the reluctance torque can be made large and magnet heat generation can be suppressed, thereby making demagnetization difficult. In a brushless motor combined with a stator, the senserless position detection accuracy can be increased extremely. Particularly, since the sandwiching angles α and β are set in the angular relationship satisfying, the improvement of the sensorless position detection accuracy and the suppression of the magnet heat generation can be reconciled.

In accordance with the brushless motor described in aspect2, the reluctance torque can be made large, and the senserless position detection accuracy can be increased extremely. In addition, the magnet heat generation can be suppressed, thereby making demagnetization difficult. Particularly, since the sandwiching angles α and β are set in the angular relationship satisfying, the improvement of the sensorless position detection accuracy and the suppression of the magnet heat generation can be reconciled.

In accordance with the invention described in aspect3, it is possible to realize that the magnetic flux of the permanent magnet piece easily passes from the outer periphery of the magnet attaching segment toward the stator, and the short-circuiting of the magnetic flux between the adjacent permanent magnet pieces is difficult to occur. Thus, since the magnetic flux between the rotor and the stator can be usefully employed, the torque can be produced effectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring to the drawings fromFIG. 1toFIG. 7, an explanation will be given of a permanent magnet rotor according to this invention and a brushless motor equipped with such a rotor.

As seen fromFIG. 1, a brushless motor1includes a stator10fixed to a casing2and a rotor (permanent magnet rotor)20rotatably supported by the casing2. The stator10and rotor20are arranged concentrically and so as to be opposite in a radial direction.

The stator10is formed in a cylindrical shape and has a plurality of teeth iron cores11projected inwardly in the radial direction. A winding12is wound around each teeth iron core11.

The brushless motor1also includes a control device for estimating the position of the rotor20on the basis of the current flowing through each of windings in a multiple phase when a voltage for detecting the position of the rotor20is applied to the windings12of the stator10, thereby being capable of detecting the position of the rotor20with “senserless”. The method of senserless position detection is a known technique and hence will not be described in detail.

As seen fromFIG. 3, the rotor20includes a rotor shaft30, a rotor yoke (rotor iron core)40, a pair of end plates50A,50B and a plurality of magnetic pieces60. Incidentally, the brushless motor1according to this embodiment is a motor with six pairs of poles with 12 (twelve) permanent magnets60.

The rotor shaft30is integrally formed in a hollow-cylindrical shape by casting or forging. The rotor shaft30has an extending-out segment32which is formed at the one end in an axial direction on an outer periphery31and extends out outwardly in a radial direction. The rotor shaft30has also three grooves33extending in the axial direction which are formed on the outer periphery31at regular intervals in a circumferential direction.

The endplate50A,50B is ring-shaped. In order that the end plate is pressed into the outer periphery31, a hole51formed at the center has an inner diameter slightly smaller than the outer diameter of the outer periphery31. Incidentally, the end plate50A,50B is made of a non-magnetic material such as austenitic stainless steel.

The rotor yoke40is formed in a ring-shape by stacking a large number of electromagnetic steel plates45each having the same shape and size. At the center of the rotor yoke40, a through-hole41into which the rotor shaft30is inserted is formed. On the inner periphery of the rotor yoke40, three projections42extending in the axial direction are formed at regular intervals in the circumferential direction.

On the outer periphery of the rotor yoke40, a plurality of magnet insertion slots43in which permanent magnets60are inserted are formed at regular intervals in the circumferential direction. Each magnet insertion slot43penetrates the rotor yoke40in the axial direction.

Further, as seen fromFIG. 4, between the adjacent magnet insertion slots43on the outer periphery of the rotor40, concaves44each opening outward in the radial direction are formed to extend in the axial direction of the rotor yoke40over the entire length thereof. The bottom44aof the concave44is located in the middle of the magnet insertion slot43in the radial direction.

In each of the concaves44, a protrusion46protruding outwardly in the radial direction from the center of the bottom44ais formed. These protrusion46are also formed to extend in the axial direction of the rotor yoke40over the entire periphery thereof. The tip face of each protrusion46and the portion located more outer position than the magnet insertion slot43in the radial direction of the rotor yoke40, i.e. the outer periphery of a magnet covering portion47are arranged on substantially the same virtual circle.

The rotor20is assembled through the following procedure, for example.

First, the end plate50A is fit over the outer periphery31of the rotor shaft30by pressing from the other end34of the rotor30.

Next, the rotor yoke40including a large number of stacked electromagnetic steel plates45is fit over the outer periphery31of the rotor shaft30by pressing from the other side34of the rotor shaft30. In this case, pressing is carried out while the protrusions42of the rotor yoke40are engaged with the grooves33on the outer periphery31of the rotor shaft30.

Subsequently, the permanent magnetic pole pieces60are inserted in the magnet insertion slots43of the rotor yoke40, by one by, respectively. Thereafter, the end plate50B is fit over the outer periphery31of the rotor shaft30from the other end34of the rotor shaft30.

By assembling the rotor20through the procedure described above, the rotor shaft30, rotor yoke40, permanent magnetic pole pieces60and end plates50A and50B are integrated to complete the rotor20. In this rotor20, openings at both ends of each magnet insertion slot are closed by the end plates50A and50B, thereby preventing the permanent magnetic pole piece60from coming off from the rotor yoke40.

In accordance with the brushless motor1, since the rotor20is provided with the protrusions46, the reluctance torque can be made larger than the case with no protrusion.

Further, as seen fromFIG. 2, the magnetic flux G emitted from the stator10passes through the protrusion and also passes through a yoke area40located at a more inner side than the permanent magnetic pole piece in the radial direction. For this reason, the magnetic flux is difficult to be saturated so that the accuracy of the sensorless position detection of the rotor20is extremely high.

In addition, the rotor20is provided with the concaves44so that the grooves48are formed on both sides of each of the protrusions46. This permits magnet heat generation to be suppressed, thereby making demagnetization difficult.

Thus, in the rotor20and brushless motor1, the reluctance torque can be effectively used, the sensorless position detection accuracy of the rotor20can be improved and the magnet heat generation can be suppressed to make demagnetization difficult.

Meanwhile, in order to improve the sensorless position detecting accuracy, it is preferred that the circumferential size of the protrusion46is large and that of the groove48is small. On the other hand, in order to suppress heat generation of the magnet, it is preferred that the circumferential size of the groove48is large. In short, in determining the size of the groove38, the improvement of the sensorless position detection accuracy and the suppression of the magnet heat generation are contradictive propositions. So it is very difficult to reconcile these two propositions.

The rotor yoke40according to this embodiment, however, can reconcile the improvement of the sensorless position detection accuracy and the suppression of the magnet heat generation by setting a predetermined angular relationship between the concave44and the protrusion46.

Referring toFIGS. 2 and 5, an explanation will be given of the angular relationship between the concave44and the protrusion36. Assuming that the sandwiching angle formed by two sides of virtual lines connecting both outer ends A and A′ in the radial direction of the concave44to the center axis O of the rotor yoke40(hereinafter referred to as the sandwiching angle of the concave44) is α, and the sandwiching angle formed by two sides of virtual lines connecting both outer ends B and B′ in the radial direction of the protrusion46to the center axis O of the rotor yoke40(hereinafter referred to as the sandwiching angle of the protrusion46) is β, using as a parameter the ratio (β/α) of the sandwiching angle β of the protrusion46to the sandwiching angle α of the concave44, relationships between the quantity of generated heat (W) for each of the permanent magnet pieces60and the probability (%) of erroneous detection in the sensorless position detection have been experimentally calculated.FIG. 5illustrates an example of the experimental result. This example is an experimental result when the sandwiching angle a of the concave44is set at 4.5 deg.

From the experimental result shown inFIG. 5, it has been found that if β/α is larger than 0.3, the probability of erroneous detection in the sensorless position detection is 0, and if β/α is smaller than 0.5, the magnet heat generation is greatly suppressed.

In view of this fact, in the brushless motor1according to this embodiment, β/α is set to be within a range of Equation 3, and preferably within a range of Equation 4.
0.3<β/α<0.5
0.3<β/α<0.4

By setting the range of β/α as described above, the improvement of the sensorless position detection accuracy of the brushless motor1and the suppression of the magnet heat generation can be reconciled.

Further, in the brushless motor according to this embodiment, the distance between the outer end A (or A′ of the protrusion46and the outer end B (or B′) of the concave44located oppositely thereto is set to be larger than that in the radial direction of the gap formed between the rotor20and the stator10.

By setting these dimensions, it is possible to realize that the magnetic flux of the permanent magnet piece easily passes from the outer periphery of the magnet attaching segment toward the stator, the magnetic flux is difficult pass through the area where the protrusion and concave are arranged and the short-circuiting of the magnetic flux between the permanent magnet pieces adjacent to each other is difficult to occur. Thus, since the magnetic flux between the rotor and the stator can be usefully employed, the torque can be produced effectively.

Additionally, in the embodiment described above, a permanent magnet rotor with the permanent magnets embedded in the rotor iron core was explained. This invention, however, can be applied to the permanent magnetic rotor with the permanent magnets fixed to the outer periphery of the rotor iron core as shown inFIGS. 6 and 7.

The rotor20shown inFIGS. 6 and 7will be explained briefly. On the outer periphery of the rotor yoke40, magnet accommodating concaves (magnet attaching segments)71are provided in place of the magnet insertion slots43. A concave72is formed between the magnet accommodating concaves71adjacent to each other. A protrusion73is formed at the center of the concave72. The concave71corresponds to the concave44in the previous embodiment. The protrusion73corresponds to the protrusion46in the previous embodiment. Incidentally, the rotor yoke40is provided with magnet securing segments75each located between the magnet accommodating concave71and concave72so that the permanent magnet piece60is secured by the magnet securing segment75, thereby preventing the permanent magnet piece from coming off outward in the radial direction. The remaining configuration, which is the same as that of the previous embodiment (FIGS. 1 to 5), will not be explained here with like reference numerals referring to like parts.

In this invention, the magnet attaching segments include not only the magnet insertion slots43shown inFIGS. 1 to 4but also the magnet accommodating concaves71shown inFIGS. 6 and 7.

Incidentally, the embodiments described above were directed to an inner rotor type of motor in which the rotor is located inside the stator and a plurality of permanent magnet pieces are arranged on the outer periphery of the rotor. This invention, however, can be likewise applied to an outer rotor type of motor in which the rotor is located outside the stator and the plurality of permanent magnet pieces are arranged on the inner periphery of the rotor, thereby achieving the same effect.

This invention can be used as, for example, the motor generator of a hybrid motor vehicle which can run by the driving force of an internal combustion engine and a motor generator, and also used as the motor generator directly linked with the internal combustion engine. Further, this invention can also be applied to the other motor or generator than the motor generator for the hybrid motor vehicle.