Permanent magnet motor

A permanent magnet motor in which electromagnetic excitation force of low spatial order is reduced, and influence of a magnetomotive force harmonic of a rotor and torque ripple is reduced. One set of armature windings receives current from a first inverter, and another set of armature windings receives current from a second inverter. Where a pole number of a rotor is M and the number of slots of a stator core is Q, M and Q satisfy M<Q and a greatest common divisor of M and Q is equal to or greater than 3. In the rotor, the iron core is located beyond a radius intermediate the maximum outer radius and the minimum inner radius of the permanent magnets. A phase difference between three-phase currents from the first and second inverters is in a range of electrical angles of 20 to 40 degrees.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2011/079948 filed Dec. 23, 2011, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a permanent magnet motor, and particularly, to a motor used in an electric power steering apparatus for vehicle.

BACKGROUND ART

As a motor of this type, Patent Document 1 discloses a permanent magnet motor of concentrated-winding and surface-magnet type, with 10 poles and 12 slots, having a multi-phased and multiplexed configuration.

In addition, Patent Document 2 discloses a permanent magnet motor for electric power steering apparatus, of interior magnet type, in which more permanent magnets than the number of concentration-wound salient poles (slot number) are provided.

In addition, Patent Document 3 discloses a permanent magnet motor of consequent-pole type with 14 poles and 12 slots, which is driven by a first drive circuit and a second drive circuit.

CITATION LIST

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, the structure of Patent Document 1 has a problem that since a surface magnet motor is used, reluctance torque cannot be obtained and torque during high-speed rotation is small.

The structures of Patent Document 2 and Patent Document 3 have a problem that since an electromagnetic excitation force of a low spatial order is generated, vibration and noise of the electric power steering apparatus are increased.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a permanent magnet motor in which an electromagnetic excitation force of a low spatial order is reduced, and influence of a magnetomotive force harmonic of a rotor is reduced so that torque ripple is reduced.

Solution to the Problems

The present invention is a permanent magnet motor including: a rotor including a rotor iron core and a plurality of permanent magnets provided in the rotor iron core; and a stator including a stator iron core and two sets of three-phase armature windings provided in a plurality of slots formed in the stator iron core. One set of the armature windings is supplied with current from a first inverter, and the other set of the armature windings is supplied with current from a second inverter. In the case where a pole number of the rotor is M and a slot number of the stator iron core is Q, M and Q satisfy a relationship of M<Q and a greatest common divisor of M and Q is equal to or greater than 3. In the rotor, the rotor iron core is located on the stator side beyond a radius intermediate between the maximum outer radius and the minimum inner radius of the permanent magnets. A phase difference between three-phase currents supplied from the first inverter and three-phase currents supplied from the second inverter is controlled to fall within a range of electrical angles of 20 to 40 degrees.

Effect of the Invention

The present invention makes it possible to obtain a permanent magnet motor in which an electromagnetic excitation force of a spatial order of 2 or less is greatly reduced, thereby greatly reducing vibration and noise, and even if a rotor-side magnetomotive force includes a harmonic of fifth order or seventh order on an electrical-angle basis, torque ripple, vibration, and noise are reduced.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of a permanent magnet motor for electric power steering of the present invention will be described with reference to the drawings.

FIG. 1is a sectional view showing a permanent magnet motor10of embodiment 1, which uses planar permanent magnets13and has 8 poles and 48 slots, as an example.

A rotor11is rotatably provided inside a stator21, and has a shaft14, a rotor iron core12provided outside the shaft14, and eight planar permanent magnets13embedded in the rotor iron core12and arranged at regular intervals.

N and S inFIG. 1indicate the polarities of the permanent magnets13. That is, inFIG. 1, magnets having different polarities are alternately arranged. A surface of the rotor iron core12on the outer circumferential side as seen from each permanent magnet13, which opposes to a stator iron core22, has a curved-plane shape.

On the other hand, the stator21has the stator iron core22provided with a core back23, teeth24, and slots25, and armature windings30of distributed winding type provided in the slots25.

Regarding the arrangement of the armature windings30, the armature windings30indicated by U1, U2, W1, W2, V1, and V2are respectively provided in the slots25indicated by1to6inFIG. 1. Similarly, also for the seventh to forty-eighth slots25, the pattern of U1, U2, W1, W2, V1, and V2is repeated seven times. It is noted that the direction of current flow is inverted between windings at positions separated from each other by 6 slots.

Here, U1, U2, W1, W2, V1, and V2indicate that there are two sets of three-phase armature windings30, and specifically, the first U-phase winding is U1, the second U-phase winding is U2, the first V-phase winding is V1, the second V-phase winding is V2, the first W-phase winding is W1, and the second W-phase winding is W2.

U1, V1, and W1form first armature windings30-1, which are connected to a first inverter, and U2, V2, and W2form second armature windings30-2, which are connected to a second inverter.

InFIG. 1, in the rotor11, the rotor iron core12is located on the stator21side beyond a radius intermediate between a maximum outer radius Rmax and a minimum inner radius Rmin of the permanent magnet13.

InFIG. 1, Rmax is based on a rotation center O, and is the length of a straight line connecting the rotation center and a point on the permanent magnet13that is most distant from the rotation center. It is noted that the rotation center O and the point that is most distant from the rotation center are two points on a plane perpendicular to the shaft14. Such a value Rmax is defined as the maximum outer radius of the permanent magnet13.

Rmin is based on the rotation center O, and is the length of a straight line connecting the rotation center and a point on the permanent magnet13that is closest to the rotation center. It is noted that the rotation center O and the point that is closest to the rotation center are two points on a plane perpendicular to the shaft14. Such a value Rmin is defined as the minimum outer radius of the permanent magnet13.

A radius Rc intermediate between the maximum outer radius Rmax and the minimum outer radius Rmin of the permanent magnet13is defined by Rc=(Rmax+Rmin)/2.

In such a configuration, reluctance torque can be obtained by using change in the magnetic resistance of the rotor iron core12. In a motor causing reluctance torque, a d-axis inductance is large and therefore flux weakening control is effectively exerted, whereby torque during high-speed rotation is improved.

However, since the rotor iron core12is present near the stator21, a magnetic gap length is small as compared to the case of surface-magnet type, and therefore an electromagnetic excitation force and torque ripple tend to increase.

In addition, in an interior magnet type, magnetomotive force harmonics caused on the rotor side tend to include larger amounts of fifth and seventh components (in the case where a component having an electrical angle cycle of 360 degrees is defined as first order) than in a surface-magnet type, thereby causing a problem of increasing an electromagnetic excitation force and torque ripple.

The present invention is to solve such problems and provide a configuration that can reduce both torque ripple and an electromagnetic excitation force, in which a permanent magnet motor10includes: the rotor11including the rotor iron core12and the plurality of permanent magnets13provided in the rotor iron core12; and the stator21including the stator iron core22and the two sets of three-phase armature windings30provided in the plurality of slots25formed in the stator iron core22, wherein one set of armature windings30-1is supplied with current from the first inverter, and the other set of armature windings30-2is supplied with current from the second inverter, wherein in the case where the pole number of the rotor11is M and the number of the slots25of the stator iron core22is Q, M and Q satisfy a relationship of M<Q and a greatest common divisor of M and Q is equal to or greater than 3, wherein in the rotor11, the rotor iron core12is located on the stator21side beyond a radius intermediate between the maximum outer radius and the minimum inner radius of the permanent magnet13, and wherein a phase difference between three-phase currents supplied from the first inverter and three-phase currents supplied from the second inverter is controlled to fall within a range of electrical angles of 20 to 40 degrees.

FIG. 2is a circuit configuration diagram showing a driving circuit of the motor10of embodiment 1.

The motor10is a permanent magnet motor of distributed winding type in which the pole number is8and the slot number is48as described inFIG. 1. InFIG. 2, the details are omitted for the purpose of simplification, and only the armature windings30of the motor10are shown.

The armature windings30of the motor10include the first armature windings30-1composed of the first U-phase winding U1, the first V-phase winding V1, and the first W-phase winding W1, and the second armature windings30-2composed of the second U-phase winding U2, the second V-phase winding V2, and the second W-phase winding W2. The details of an ECU (control unit)101are also omitted for the purpose of simplification, and only a power circuit part of the inverter is shown.

The ECU101includes two inverters102, i.e., inverters102-1and102-2, which respectively supply three-phase currents to the first and second armature windings30-1and30-2.

The ECU101is supplied with DC power from a power supply103such as a battery, to which a power supply relay105is connected via a coil104for noise removal.

InFIG. 2, the power supply103appears to be present inside the ECU101, but actually, power is supplied via a connector from an external power supply such as a battery. The power supply relay105includes two power supply relays105-1and105-2each composed of two MOS-FETs. Upon failure or the like, the power supply relay105is opened to prevent excessive current from flowing.

It is noted that although the power supply103, the coil104, and the power supply relay105are connected in this order inFIG. 2, as a matter of course, the power supply relay105may be provided closer to the power supply103than the coil104is.

The inverter102-1and the inverter102-2are each composed of a bridge using six MOS-FETs. In the inverter102-1, a MOS-FET107-1and a MOS-FET107-2are connected in series, a MOS-FET107-3and a MOS-FET107-4are connected in series, and a MOS-FET107-5and a MOS-FET107-6are connected in series, and the three pairs of MOS-FETs are connected in parallel.

Further, one shunt resistor is connected to the GND (ground) side of each of the three lower-side MOS-FETs107-2,107-4, and107-6, and the shunt resistors are represented as a shunt109-1, a shunt109-2, and a shunt109-3, respectively. These shunt resistors are used for detection of a current value.

It is noted that although an example of using three shunts is shown, current detection can be performed even by two shunts or one shunt, and therefore, as a matter of course, such a configuration may be employed.

Regarding current supply to the motor10side, as shown inFIG. 2, current is supplied from between the MOS-FETs107-1and107-2through a bus bar or the like to U1phase of the motor10, current is supplied from between the MOS-FETs107-3and107-4through a bus bar or the like to V1phase of the motor10, and current is supplied from between the MOS-FETs107-5and107-6through a bus bar or the like to W1phase of the motor10.

The inverter102-2also has the same configuration. In the inverter102-2, a MOS-FET108-1and a MOS-FET108-2are connected in series, a MOS-FET108-3and a MOS-FET108-4are connected in series, and a MOS-FET108-5and a MOS-FET108-6are connected in series, and the three pairs of MOS-FETs are connected in parallel.

Further, one shunt resistor is connected to the GND (ground) side of each of the three lower-side MOS-FETs108-2,108-4, and108-6, and the shunt resistors are represented as a shunt110-1, a shunt110-2, and a shunt110-3, respectively.

These shunt resistors are used for detection of a current value. It is noted that although an example of using three shunts is shown, current detection can be performed even by two shunts or one shunt, and therefore, as a matter of course, such a configuration may be employed.

Regarding current supply to the motor10side, as shown inFIG. 2, current is supplied from between the MOS-FETs108-1and108-2through a bus bar or the like to U2phase of the motor10, current is supplied from between the MOS-FETs108-3and108-4through a bus bar or the like to V2phase of the motor10, and current is supplied from between the MOS-FETs108-5and108-6through a bus bar or the like to W2phase of the motor10.

The two inverters102-1and102-2perform switching by a signal sent from a control circuit (not shown) to the MOS-FETs in accordance with a rotation angle detected by a rotation angle sensor111provided on the motor10, thereby supplying desired three-phase currents to the first and second armature windings30-1and30-2, respectively.

It is noted that a resolver, a GMR sensor, an MR sensor, or the like are used as the rotation angle sensor111.

When three-phase currents are made to flow in the armature windings30-1and the armature windings30-2by the first inverter102-1and the second inverter102-2, if the phase difference between the armature windings30-1and the armature windings30-2is set to be an electrical angle of 20 to 40 degrees, or desirably, an electrical angle of 30 degrees, a sixth order component (in the case where a component having an electrical angle cycle of 360 degrees is defined as first order) of torque ripple is greatly reduced.

The reason is as follows. That is, even if magnetomotive force harmonics caused on the rotor11side include fifth order and seventh order components (in the case where a component having an electrical angle cycle of 360 degrees is defined as first order), the fifth order and seventh order components disappear or are greatly reduced in a magnetomotive force waveform on the armature side by changing the phases of currents in the armature windings30-1and the armature windings30-2.

This phase difference may be changed in accordance with the driving state of the motor10, or may be fixed at an electrical angle of 30 degrees, for example.

It is noted that in the case where the phase difference is fixed at an electrical angle of 30 degrees, the winding factor is improved in an equivalent sense, and torque is also improved. Therefore, large torque can be obtained with a small amount of permanent magnets13, thus providing an effect of contribution to cost reduction of the motor10.

Patent Document 1 discloses an example in which the pole number is10and the slot number is12, and in this case, an electromagnetic excitation force of second spatial order occurs. Patent Document 2 discloses an example in which the pole number is10and the slot number is9, an example in which the pole number is20and the slot number is18, and an example in which the pole number is22and the slot number is21. In these cases, electromagnetic excitation forces of second spatial order, first spatial order, and second spatial order occur, respectively.

In addition, Patent Document 3 discloses a consequent-pole type in which the pole number is14(the number of magnets is 7) and the slot number is12. In this case, the magnetic circuit is not rotationally symmetric, and therefore an electromagnetic excitation force of first spatial order occurs.

Thus, in the conventional examples, electromagnetic excitation forces of first spatial order and second spatial order occur, thereby causing a problem of vibration and noise on electric power steering apparatuses.

An electromagnetic excitation force of first spatial order serves as an electromagnetic force that vibrates a rotor always in the radial direction, and therefore especially large vibration and noise occur. An electromagnetic excitation force of second spatial order deforms the stator21into elliptic shape, and therefore, as compared to the case of third or higher spatial order under the same value of electromagnetic excitation force, deformation amount of a stator or a frame is large, so that vibration and noise may be caused.

Further, in a motor of interior magnet type, a rotor iron core is located on a stator side beyond a radius intermediate between the maximum outer radius and the minimum inner radius of a permanent magnet, and therefore a problem arises that an electromagnetic excitation force in this case also increases.

However, in the configuration inFIG. 1, an electromagnetic excitation force of second or lower spatial order does not occur. InFIG. 1, the pole number is8and the slot number is48, and the armature windings30are arranged so as to have symmetry at six-slot intervals, i.e., mechanical angle intervals of 45 degrees as described above. In the rotor11, there is rotational symmetry at one-pole intervals, i.e., mechanical angle intervals of 45 degrees though polarities are opposite to each other.

Therefore, the spatial distribution of an electromagnetic force has symmetry at one-pole and six-slot intervals, and the spatial order of the electromagnetic excitation force is as high as 8, so that vibration and noise can be greatly reduced. Here, the spatial order 8 of the electromagnetic excitation force is equal to a greatest common divisor of the pole number and the slot number.

In the motor with the pole number of10and the slot number of9disclosed in the conventional example, a greatest common divisor of the pole number and the slot number is1, and therefore, in order to cause the spatial order of an electromagnetic excitation force to be 3 or higher, the pole number and the slot number need to be tripled, i.e., 30 poles and 27 slots, respectively.

Similarly, in the example in which the pole number is20and the slot number is18, 30 poles and 27 slots are needed, and in the example in which the pole number is22and the slot number is21, 44 poles and 42 slots are needed. In the consequent-pole type in which the pole number is14(the number of magnets is 7) and the slot number is12, a greatest common divisor of the pole number and the slot number is2. Therefore, in order to cause the spatial order of an electromagnetic excitation force to be 3 or higher, a consequent-pole type in which the pole number is28(the number of magnets is 14) and the slot number is24is needed.

In the motors of these conventional examples, M and Q satisfy M>Q, where M is the pole number of a rotor composed of permanent magnets and a rotor iron core, and Q is the number of slots in which armature windings are provided in a stator iron core. In such motors that satisfy this condition, a greatest common divisor of the pole number and the slot number is small. Therefore, the pole number needed in order to cause the spatial order of an electronic excitation force to be 3 or higher is excessively large.

If the pole number is large, the frequency becomes higher under the same rotation rate, and therefore load of computing (microcomputer) for control increases, resulting in high cost.

In addition, if the pole number is large, a value obtained by converting positional error of a rotational angle sensor into electrical angle becomes large, thereby causing a problem of increasing torque ripple, vibration, and noise.

However, in the configuration inFIG. 1, a small pole number may be used, so that an effect of reducing load of computing for control is obtained.

In addition, an electromagnetic excitation force of second or lower spatial order can be greatly reduced, whereby an effect of also greatly reducing vibration and noise is obtained.

Further, even if the rotor-side magnetomotive force includes a harmonic of fifth order or seventh order on an electrical-angle basis, a motor with small torque ripple, small vibration, and small noise can be obtained.

In the conventional examples, the pole number is large, the frequency is higher under the same rotation rate, and therefore load of computing (microcomputer) for control increases, resulting in high cost. However, in the configuration inFIG. 1, a small pole number may be used, so that load of computing for control is reduced.

In addition, since a small pole number can be used, a value obtained by converting positional error of a rotational angle sensor into electrical angle becomes small, whereby torque ripple, vibration, and noise can be reduced.

Further, reluctance torque is obtained, whereby torque during high-speed rotation can be increased.

Here, an effect obtained in the case of providing two inverters102as shown inFIG. 2will be described.

In the case of providing two inverters, the capacitance and the heat dissipation area of the inverters increase, so that large current can be applied to the armature windings. That is, the rated current of the motor10can be increased. Therefore, in the case of designing a motor10with the same torque, the rated rotation rate can be increased by reduction of winding resistance.

This will be described with reference toFIG. 13.

C1indicates NT curve of a motor having a rated torque of T0and driven by one inverter. The rated rotation rate is N10and the no-load rotation rate is N11.

On the other hand, C2indicates NT curve of a motor also having a rated torque of T0but driven by two inverters, and having a larger rated current than that of the above motor driven by one inverter. Its rated rotation rate N20is larger than N10, and thus high output can be realized. Its no-load rotation rate N21is also larger than N11, and thus a motor having high torque even in a high rotation region can be obtained.

If the heat dissipation area increases by providing two inverters, temperature increase in the inverters can be suppressed even if a driver repeats steering for a long time. Therefore, a motor can continue to assist a steering force for a long time. This contributes to improvement in performance as an electric power steering apparatus.

In the permanent magnet motor10inFIG. 1, the shape of the permanent magnet13is planar. Therefore, an effect of improving material yield of permanent magnet and reducing the cost is obtained. A normal semi-cylindrical magnet has a thin portion, thereby causing a problem that demagnetization is likely to occur in such a portion. However, the planar magnet has a uniformed thickness, thereby providing an effect of suppressing demagnetization.

In addition, since the permanent magnet13is embedded in the rotor iron core12, an effect is obtain that it becomes unnecessary to take a measure to prevent magnet scattering, such as providing a metallic cover made of SUS, aluminum, etc., thereby reducing the cost.

It is noted that althoughFIG. 1shows the case where the planar permanent magnet13is embedded in the rotor iron core12and the width of the permanent magnet13in the circumferential direction is larger than the thickness thereof in the radial direction, the present invention is not limited thereto.

FIG. 3shows another example of the permanent magnet motor10, in which the permanent magnets13having a rectangular sectional shape and having a greater length in the radial direction than the length thereof in the circumferential direction are embedded in the rotor iron core12. The magnetization directions of the permanent magnets13are such that N and S inFIG. 3indicate N pole and S pole, respectively.

That is, the permanent magnets13are magnetized such that surfaces facing to each other of the adjacent permanent magnets13have the same pole. By thus setting the magnetization directions, an effect of converging magnetic flux on the rotor iron core12and thereby increasing the magnetic flux density is obtained.

In addition, the rotor iron core12is interposed between the adjacent permanent magnets13. The rotor iron core12has a curved surface portion15on its surface facing to the stator21side. The shape of the curved surface portion15is formed to be such a convex curved surface that the gap length from the stator21is shortened toward the midpoint between the adjacent permanent magnets13.

The outer side of the curved surface portion15in the radial direction protrudes toward the stator21side beyond a radius intermediate between the maximum outer radius and the minimum inner radius of the permanent magnet13, which is defined in the same manner as inFIG. 1.

This shape smoothens the waveform of the magnetic flux density occurring in the gap, thereby reducing cogging torque and torque ripple.

Further, a non-magnetic portion16ais provided in contact with an end surface of the permanent magnet13on the inner circumferential side. This portion may be air or may be filled with resin, or a non-magnetic metal such as stainless or aluminum may be interposed in this part.

Thus, flux leakage of the permanent magnet13can be reduced, whereby torque of the motor10can be increased.

A joint portion17is provided between the rotor iron core12between the adjacent permanent magnets13and the rotor iron core12provided so as to surround the outer circumference of the shaft14. The joint portion17functions to mechanically join both rotor iron cores12.

In the above example, the length of the permanent magnet13in the radial direction is longer than the length in the circumferential direction, magnetic flux is converged on the rotor iron core12, resulting in high torque.

Conventionally, a structure in which the permanent magnet13is embedded in the rotor iron core12has a problem that torque ripple increases and vibration and noise increase as compared to the case of surface magnet type. However, by driving with the two three-phase inverters shown inFIG. 2such that the phase difference between the armature windings30-1and the armature windings30-2is an electrical angle of 20 to 40 degrees, or desirably, an electrical angle of 30 degrees, the sixth order torque ripple can be reduced.

In addition, as in the case ofFIG. 1, the spatial order of the electromagnetic excitation force is as high as 8, so that vibration and noise can be greatly reduced.

Although the case where the slot number for each pole for each phase is 2 has been shown inFIGS. 1 and 3, the slot number is not limited thereto.

AlthoughFIG. 5(a)shows an example in which the slot number for each pole for each phase is2, the slot number for each pole for each phase may be4as shown inFIG. 5(b).

In the case where the slot number for each pole for each phase is an even number equal to or greater than 4, harmonics of the armature winding magnetomotive force are reduced, whereby an effect of further reducing torque ripple is obtained.

Here, the reason for employing an even number is that two sets of armature windings are needed for driving by two inverters.

Generally, if the value of Q/(3M) which is the slot number for each pole for each phase is an integer, and further, the value of Q/(3M) is an even number equal to or greater than 2, magnetomotive force harmonics caused by the armature windings do not include an even-number order component (in the case where a component having an electrical angle cycle of 360 degrees is defined as first order), and therefore, torque ripple does not occur even if a magnetomotive force on the rotor11includes even-number order harmonics (in the case where a component having an electrical angle cycle of 360 degrees is defined as first order), so that a motor with small torque ripple, small vibration, and small noise can be obtained.

Further, another effect in the case where Q/(3M) is an even number equal to or greater than 2 is that the slot pitch becomes an electrical angle of 30 degrees or smaller, whereby structuring of two sets of three-phase armature windings is facilitated.

FIG. 4is an explanation diagram of a cross-section of a permanent magnet motor10of embodiment 2, showing an example in which concentrated winding is employed and 20 poles and 24 slots are provided.

A rotor11is rotatably provided inside a stator21, and has a shaft14, a rotor iron core12provided outside the shaft14, and twenty permanent magnets13provided at regular intervals around the outer circumference of the rotor iron core12.

The stator21has a ring-shaped core back23, a total of twenty-four teeth24extending radially inward from the core back23, a stator iron core22in which a slot25is provided between the adjacent two teeth24, and an armature winding30wound on each tooth24in a concentrated manner.

It is noted that inFIG. 4, for the purpose of simplification, an insulator provided between the armature winding30and the stator iron core22, and a frame provided on the outer circumference of the stator iron core22, are not shown. In addition, for convenience sake, numbers of1to24are assigned to the teeth24. Further, for convenience sake, numbers are assigned to the armature windings (coils)30wound on the respective teeth24in a concentrated manner, in order to identify three phases of U, V, and W of the coils.

In addition, regarding the winding directions of the windings, U11and U12are opposite to each other, U21and U22are opposite to each other, U31and U32are opposite to each other, and U41and U42are opposite to each other. The winding directions of the other phases V and W are also configured in the same manner. These coils are connected in a Y-connection fashion or in a Δ-connection fashion to form two sets of three-phase armature windings30.

The armature windings30-1and the armature windings30-2are connected to two inverters102-1and102-2, respectively, as shown inFIG. 2.

A protruding portion18is present between the adjacent permanent magnets13of the rotor11. The protruding portion18is made of magnetic material as in the rotor iron core12. In addition, the outer side of the protruding portion18in the radial direction protrudes toward the stator21side beyond a radius intermediate between the maximum outer radius and the minimum inner radius of the permanent magnet13, which is defined in the same manner as inFIG. 1.

In such a configuration, reluctance torque can be obtained by using change in the magnetic resistance of the rotor iron core12. In a motor causing reluctance torque, a d-axis inductance is large and therefore flux weakening control is effectively exerted, whereby torque during high-speed rotation is improved.

However, since the rotor iron core12is present near the stator21, a magnetic gap length is small as compared to the case of surface-magnet type. Therefore, magnetomotive force harmonics caused on the rotor11side include larger amounts of fifth and seventh components (in the case where a component having an electrical angle cycle of 360 degrees is defined as first order), whereby an electromagnetic excitation force and torque ripple tend to increase. In the case where Q is the number of the slots25in which the armature windings30are provided in the stator iron core22, M and Q satisfy a relationship of M<Q, and a greatest common divisor of M and Q is4. Therefore, the spatial order of the electromagnetic excitation force becomes 4, so that vibration and noise are reduced.

Also in the present embodiment, when three-phase currents are made to flow in the armature windings30-1and the armature windings30-2by the first inverter102-1and the second inverter102-2, if the phase difference between the armature windings30-1and the armature windings30-2is set to be an electrical angle of 20 to 40 degrees, or desirably, an electrical angle of 30 degrees, a sixth order component (in the case where a component having an electrical angle cycle of 360 degrees is defined as first order) of torque ripple is greatly reduced.

The reason is as follows. That is, even if magnetomotive force harmonics caused on the rotor11side include fifth order and seventh order components (in the case where a component having an electrical angle cycle of 360 degrees is defined as first order), the fifth order and seventh order components disappear or are greatly reduced in a magnetomotive force waveform on the armature side by changing the phases of currents in the armature windings30-1and the armature windings30-2.

This phase difference may be changed in accordance with the driving state of the motor, or may be fixed at an electrical angle of 30 degrees, for example.

FIG. 6is an example of a consequent-pole motor10of surface-magnet type with a stator21of distributed winding type and with 8 poles and 48 slots.

The stator21is the same as inFIG. 1, that is, the stator21has a stator iron core22provided with a core back23, teeth24, and slots25, and armature windings30provided in the slots25.

Regarding the arrangement of the armature windings30, the armature windings30indicated by U1, U2, W1, W2, V1, and V2are respectively provided in the slots25indicated by1to6inFIG. 6. Similarly, also for the seventh to forty-eighth slots25, the pattern of U1, U2, W1, W2, V1, and V2is repeated seven times. It is noted that the direction of current flow is inverted between windings at positions separated from each other by 6 slots.

Here, U1, U2, W1, W2, V1, and V2indicate that there are two sets of three-phase armature windings30, and specifically, the first U-phase winding is U1, the second U-phase winding is U2, the first V-phase winding is V1, the second V-phase winding is V2, the first W-phase winding is W1, and the second W-phase winding is W2.

U1, V1, and W1form first armature windings30-1, which are connected to a first inverter102-1, and U2, V2, and W2form second armature windings30-2, which are connected to a second inverter102-2.

The rotor11is different from that inFIG. 1, that is, four permanent magnets13are arranged along the circumferential direction, and the magnetization directions are such that N and S inFIG. 6indicate N pole and S pole, respectively.

That is, the four permanent magnets13are all magnetized in the same direction. The rotor iron core12is present between the permanent magnets13, and a portion indicated as a salient pole Sc corresponds to an S pole of a normal motor.

In addition, the outer side of the salient pole Sc in the radial direction protrudes toward the stator21side beyond a radius intermediate between the maximum outer radius and the minimum inner radius of the permanent magnet13, which is defined in the same manner as inFIG. 1.

FIG. 7is an example of a consequent-pole motor10of surface-magnet type with 10 poles and 60 slots. The armature windings30indicated by U1, U2, W1, W2, V1, and V2are respectively provided in the slots25indicated by1to6inFIG. 7. Similarly, also for the seventh to sixtieth slots25, the pattern of U1, U2, W1, W2, V1, and V2is repeated nine times. It is noted that the direction of current flow is inverted between windings at positions separated from each other by 6 slots.

Here, U1, U2, W1, W2, V1, and V2indicate that there are two sets of three-phase armature windings30, and specifically, the first U-phase winding is U1, the second U-phase winding is U2, the first V-phase winding is V1, the second V-phase winding is V2, the first W-phase winding is W1, and the second W-phase winding is W2.

U1, V1, and W1form first armature windings30-1, which are connected to a first inverter102-1, and U2, V2, and W2form second armature windings30-2, which are connected to a second inverter102-2.

In the example in which the pole pair number is an odd number disclosed in Patent Document 3, that is, in the consequent-pole type in which the pole number is14(the number of magnets is 7) and the slot number is12, the magnetic circuit is not rotationally symmetric, and therefore an electromagnetic excitation force of first spatial order occurs, resulting in a problem of increasing vibration and noise on an electric power steering apparatus.

However, the structures inFIGS. 6 and 7cause no electromagnetic excitation force of a low spatial order in spite of the consequent-pole type. The principle will be described.

The rotors11inFIGS. 6 and 7are formed in a consequent-pole type, and configured to have a periodicity on a 2-pole basis (corresponding to an electrical angle of 360 degrees) on the rotor11side.

On the other hand, the stator21is configured to have a periodicity on a 6-slot basis (corresponding to an electrical angle of 180 degrees) as described above. It is noted that since currents in opposite directions flow in armature windings30at positions separated by an electrical angle of 180 degrees, the periodicity is such that the direction of the magnetic flux density inverts.

In view of the above description and the fact that an electromagnetic force is proportional to the square of the magnetic flux density, the electromagnetic force has a periodicity on a 2-pole basis which corresponds to an electrical angle of 360 degrees.

Therefore, if electromagnetic forces in regions R1, R2, R3, R4, and R5between lines OA, OB, OC, OD, and OE connecting the rotation center O and a total of five points A, B, C, D, and E at electrical angle intervals of 360 degrees inFIG. 7are summed, they are balanced, so that an electromagnetic excitation force of first spatial order does not occur.

Further, since the electromagnetic force has a periodicity on a 2-pole basis which corresponds to an electrical angle of 360 degrees, the spatial order of an electromagnetic excitation force is 5.

Thus, in the structure of the present embodiment, an electromagnetic excitation force of third or lower spatial order does not occur in spite of a consequent-pole type with an odd pole pair number, and therefore a motor with small vibration and small noise is obtained.

In addition, inFIGS. 6 and 7, the permanent magnet13is provided at the surface of the rotor iron core12, and therefore flux leakage to an iron core is reduced, whereby an effect of enhancing usage efficiency of magnetic flux of the permanent magnets13is obtained. In the consequent-pole type, an effect of reducing the component number of the permanent magnets13is obtained.

As described above, in embodiment 3, a M/2 number of permanent magnets13are arranged along the circumferential direction of the rotor11in the case where M is the pole number of the rotor11, and the permanent magnets13are provided at the surface of the rotor iron core12, so that effects are obtained that the component number is reduced, usage efficiency of magnets is improved by reduction in flux leakage, reduction in torque ripple, vibration, and noise is realized even if a magnetomotive force waveform on the rotor side includes an even-number order component.

Embodiment 3 has shown an example in which the consequent-pole type is employed and permanent magnets are provided at the surface of the rotor iron core12. However, an IPM (Interior Permanent Magnet) type may be employed in which permanent magnets are embedded in the rotor iron core12.

FIG. 10shows an example of an IPM with 10 poles and 60 slots in which the stator21is of a distributed winding type and the rotor11is of a consequent-pole type. The armature windings30indicated by U1, U2, W1, W2, V1, and V2are respectively provided in the slots25indicated by1to6inFIG. 10. Similarly, also for the seventh to sixtieth slots25, the pattern of U1, U2, W1, W2, V1, and V2is repeated nine times. It is noted that the direction of current flow is inverted between windings at positions separated from each other by 6 slots.

Here, U1, U2, W1, W2, V1, and V2indicate that there are two sets of three-phase armature windings30, and specifically, the first U-phase winding is U1, the second U-phase winding is U2, the first V-phase winding is V1, the second V-phase winding is V2, the first W-phase winding is W1, and the second W-phase winding is W2.

U1, V1, and W1form first armature windings30-1, which are connected to a first inverter102-1, and U2, V2, and W2form second armature windings30-2, which are connected to a second inverter102-2.

In the rotor11, a M/2 number of, i.e., five planar permanent magnets13are arranged along the circumferential direction in the case where M is the pole number of the rotor11, and the permanent magnets13are embedded in the rotor iron core12. Regarding polarities, the permanent magnets13are magnetized such that N and S inFIG. 6indicate N pole and S pole, respectively. A salient pole Sc of the rotor iron core12provided between the permanent magnets13serves the same role as an S pole of a normal motor.

Thus, in the consequent-pole type, an N pole and a salient pole Sc due to the permanent magnet13are magnetically asymmetric. For understanding of this magnetic asymmetry,FIGS. 8 and 9show magnetomotive force waveforms and results of frequency analysis thereof, in which the order of a component having an electrical angle cycle of 360 degrees is defined as first order.

An upper diagram inFIG. 8is a magnetomotive force waveform of a rotor of a normal motor in which both an N pole and an S pole are formed by the permanent magnet13. A lower diagram inFIG. 8is a frequency analysis result thereof. The waveform has symmetry in which positive and negative are inverted between an electrical angle range of 0 to 180 degrees and an electrical angle range of 180 to 360 degrees. In this case, only odd-number order harmonics are included (lower diagram).

On the other hand, in the case of consequent-pole type, the waveform is not symmetric between an N pole and a salient pole Sc (or in another case, an S pole and a salient pole Nc corresponding to an N pole of a normal motor). An upper diagram inFIG. 9shows a magnetomotive force waveform of a rotor of consequent-pole type, and a lower diagram shows a frequency analysis result thereof. It is found that since the magnetomotive force waveform is asymmetric, harmonics of even-number orders such as second order and fourth order are included. In a conventional configuration, there is a problem that if a magnetomotive force waveform of a rotor includes even-number order harmonics, cogging torque and torque ripple increase, so that such a configuration is not suitable for a motor for electric power steering apparatus.

However, unlike the case of concentrated winding in Patent Document 3, in the configuration of the present embodiment shown inFIG. 10, the armature windings30are wound in a distributed manner, and the armature windings30of U1, U2, W1, W2, V1, and V2are provided in the slots25indicated by1to6, respectively. Similarly, also for the seventh to sixtieth slots25, the pattern of U1, U2, W1, W2, V1, and V2is repeated nine times. It is noted that the direction of current flow is inverted between windings at positions separated from each other by 6 slots. In such a configuration, no magnetomotive force harmonic of even-number order appears in principle.

Therefore, as in embodiment 3, effects are obtained that the component number is reduced, usage efficiency of magnets is improved by reduction in flux leakage, reduction in torque ripple, vibration, and noise is realized even if a magnetomotive force waveform on the rotor side includes an even-number order component.

Further, slits19ato19dare provided in the rotor iron core12inFIG. 10. Their shapes are symmetric with respect to a magnetic pole center indicated by a dotted line, and the slits approach the magnetic pole center as approaching the outer circumferential side of the rotor11.

Such shapes provide an effect of converging magnetic flux on the magnetic pole center, thereby improving torque, and at the same time, provide an effect of reducing asymmetry of the magnetomotive force waveform shown inFIG. 9so that the magnetomotive force waveform at the salient pole comes close to the magnetomotive force waveform at the magnetic pole of the permanent magnet13.

That is, an effect of reducing even-number order harmonics inFIG. 9is obtained, whereby an effect of reducing cogging torque and torque ripple is obtained.

FIG. 10has shown an example in which four slits are provided for each salient pole Sc. However, as a matter of course, the number of slits is not limited thereto, and the same effect is obtained even in the case of providing four or less slits or providing six or more slits.

FIG. 11is another example of the arrangement of the permanent magnets13and the shape of the rotor iron core12in the configuration inFIG. 3. The rotor11is rotatably provided inside the stator21. The rotor11is provided with the shaft14as a rotational shaft, and the rotor iron core12outside the shaft14.

The permanent magnets13have a rectangular sectional shape having a greater length in the radial direction than the length thereof in the circumferential direction. A M/2 number of, i.e., five permanent magnets13are arranged at regular intervals along the circumferential direction in the case where M is the pole number of the rotor11.

The magnetization directions of the permanent magnets13are such that N and S inFIG. 11indicate N pole and S pole, respectively. That is, the surfaces facing to each other of the adjacent permanent magnets13are magnetized to have different polarities.

Further, a non-magnetic portion16bis provided between the adjacent permanent magnets13. The non-magnetic portion16bmay be air or may be filled with resin, or a non-magnetic metal such as stainless or aluminum may be interposed in this part. By setting the magnetization direction as described above and further providing the non-magnetic portion16b, an effect is obtained that magnetic flux is converged on the rotor iron core12, thereby increasing the magnetic flux density.

In addition, the rotor iron core12is present on both sides in the circumferential direction of the permanent magnet13. In accordance with the magnetization direction of the permanent magnet13, the salient pole Nc forms a magnetic pole corresponding to an N pole, and the salient pole Sc forms a magnetic pole corresponding to an S pole. Therefore, the rotor11operates as a rotor with 10 poles.

The outer sides of the salient poles Nc and Sc in the radial direction protrude toward the stator21side beyond a radius intermediate between the maximum outer radius and the minimum inner radius of the permanent magnet13, which is defined in the same manner as inFIG. 1.

Further, a non-magnetic portion16ais provided in contact with end surfaces of the permanent magnet13and the non-magnetic portion16bon the inner circumferential side. This portion may be air or may be filled with resin, or a non-magnetic metal such as stainless or aluminum may be interposed in this part.

Thus, flux leakage of the permanent magnet13can be reduced, whereby torque of the motor10can be increased. A joint portion17is provided between the rotor iron core12between the adjacent permanent magnets13and the rotor iron core12provided so as to surround the outer circumference of the shaft14. The joint portion17functions to mechanically join both rotor iron cores12.

Such a rotor structure conventionally has a problem that, since the number of the permanent magnets13is reduced by half, distribution of the magnetic flux density is uneven as compared to the structure of the rotor shown inFIG. 3, resulting in increase in torque ripple.

Besides, since the stator iron core22has a closed slot structure, there is a problem that increase in the torque ripple is also caused by magnetic saturation of the iron core due to flux leakage between the teeth24.

However, according to the configuration of the present embodiment, by driving with the two three-phase inverters as shown inFIG. 2such that the phase difference between the armature windings30-1and the armature windings30-2is an electrical angle of 20 to 40 degrees, or desirably, an electrical angle of 30 degrees, the sixth order component of torque ripple is greatly reduced.

Further, slits19eto19hare provided in the rotor iron core12. These slits are provided at all magnetic poles. In addition, the slits19eto19hare located symmetrically with respect to the center line of the permanent magnet13indicated by a dotted line passing through the rotation center O inFIG. 11.

Further, the shapes of the slits are such that the slits become away from the center line of the permanent magnet13as approaching the outer side in the radial direction of the rotor11.

Such shapes provide an effect of guiding magnetic flux to the salient pole Nc side and the salient pole Sc side to converge the magnetic flux on the vicinity of the salient pole Nc and the salient pole Sc, thereby improving torque of the motor10.

Further, by forming the rotor iron core12in the vicinity of the salient pole Nc and the salient pole Sc into a shape not being rotationally symmetric, even-number order components of magnetomotive force harmonics due to asymmetry shown inFIG. 9which cause a problem in the case of consequent-pole type, can be reduced, whereby an effect of reducing cogging torque and torque ripple is obtained.

In addition, the armature windings30are the same as inFIG. 10. In this configuration of the armature windings30, as described in embodiment 4, no magnetomotive force harmonics of even-number orders appear in a magnetomotive force of the armature winding30in principle. Therefore, naturally, an effect is obtained that even if magnetomotive force harmonics of even-number orders are present on the rotor11side, torque ripple hardly increases.

FIG. 11has shown an example in which a total of four slits are provided on both sides of each permanent magnet13. However, as a matter of course, the number is not limited thereto, and the same effect is obtained even in the case of providing four or less slits or providing six or more slits.

FIG. 12is another example of the arrangement of the permanent magnets13and the shape of the rotor iron core12in the configuration inFIG. 3. The rotor11is rotatably provided inside the stator21. The rotor11is provided with the shaft14as a rotational shaft, and the rotor iron core12outside the shaft14.

The permanent magnets13have a rectangular sectional shape having a greater length in the radial direction than the length thereof in the circumferential direction. Five of the permanent magnets13are arranged at regular intervals along the circumferential direction.

The magnetization directions of the permanent magnets13are such that N and S inFIG. 12indicate N pole and S pole, respectively. That is, the surfaces facing to each other of the adjacent permanent magnets13are magnetized to have different polarities.

Further, a non-magnetic portion16bis provided between the adjacent permanent magnets13. The non-magnetic portion16bmay be air or may be filled with resin, or a non-magnetic metal such as stainless or aluminum may be interposed in this part. By setting the magnetization direction as described above and further providing the non-magnetic portion16b, an effect is obtained that magnetic flux is converged on the rotor iron core12, thereby increasing the magnetic flux density.

In addition, the rotor iron core12is present on both sides in the circumferential direction of the permanent magnet13. In accordance with the magnetization direction of the permanent magnet13, the salient pole Nc forms a magnetic pole corresponding to an N pole, and the salient pole Sc forms a magnetic pole corresponding to an S pole. Therefore, the rotor11operates as a rotor with 10 poles.

The outer sides of the salient poles Nc and Sc in the radial direction protrude toward the stator21side beyond a radius intermediate between the maximum outer radius and the minimum inner radius of the permanent magnet13, which is defined in the same manner as inFIG. 1.

Further, a non-magnetic portion16ais provided in contact with end surfaces of the permanent magnet13and the non-magnetic portion16bon the inner circumferential side. This portion may be air or may be filled with resin, or a non-magnetic metal such as stainless or aluminum may be interposed in this part.

Thus, flux leakage of the permanent magnet13can be reduced, whereby torque of the motor10can be increased. A joint portion17is provided between the rotor iron core12between the adjacent permanent magnets13and the rotor iron core12provided so as to surround the outer circumference of the shaft14. The joint portion17functions to mechanically join both rotor iron cores12.

Such a rotor structure conventionally has a problem that, since the number of the permanent magnets13is reduced by half, distribution of the magnetic flux density is uneven as compared to the structure of the rotor shown inFIG. 3, resulting in increase in torque ripple.

Besides, since the stator iron core22has a closed slot structure, there is a problem that increase in the torque ripple is also caused by magnetic saturation of the iron core due to flux leakage between the teeth24.

However, according to the configuration of the present embodiment, by driving with the two three-phase inverters as shown inFIG. 2such that the phase difference between the armature windings30-1and the armature windings30-2is an electrical angle of 20 to 40 degrees, or desirably, an electrical angle of 30 degrees, the sixth order component of torque ripple is greatly reduced.

Further, slits19iand19jare provided in the rotor iron core12. These slits are provided at all magnetic poles. In addition, the slits19iand19jare located symmetrically with respect to the center line of the permanent magnet13indicated by a dotted line passing through the rotation center O inFIG. 12. Further, the shapes of the slits are such that the slits become away from the center line of the permanent magnet13as approaching the outer side in the radial direction of the rotor11.

Such shapes provide an effect of guiding magnetic flux to the salient pole Nc side and the salient pole Sc side to converge the magnetic flux on the vicinity of the salient pole Nc and the salient pole Sc, thereby improving torque of the motor10.

Further, by forming the rotor iron core12in the vicinity of the salient pole Nc and the salient pole Sc into a shape not being rotationally symmetric, even-number order components of magnetomotive force harmonics due to asymmetry shown inFIG. 9which cause a problem in the case of consequent-pole type, can be reduced, whereby an effect of reducing cogging torque and torque ripple is obtained.

Further, a surface20aand a surface20bof the rotor iron core12have curved-plane shapes symmetric with respect to the center line of the permanent magnet13indicated by a dotted line. By providing such curved surfaces, harmonics of a magnetomotive force waveform are reduced and a magnetic flux density waveform is smoothed, whereby cogging torque and torque ripple can be reduced.

In addition, the armature windings30are the same as inFIG. 10. In this configuration of the armature windings30, as described in embodiment 4, no magnetomotive force harmonics of even-number orders appear in a magnetomotive force of the armature winding30in principle. Therefore, naturally, an effect is obtained that even if magnetomotive force harmonics of even-number orders are present on the rotor11side, torque ripple hardly increases.

FIG. 12has shown an example in which a total of two slits are provided on both sides of each permanent magnet13. However, as a matter of course, the number is not limited thereto, and the same effect is obtained even in the case of providing two or more slits.

Since the length of the permanent magnet13in the radial direction is greater than the length thereof in the circumferential direction as shown inFIGS. 11 and 12, magnetic flux is converged on the rotor iron core12, whereby a gap magnetic flux density can be increased. Therefore, a motor10with high torque can be formed even with a magnet having a small residual magnetic flux density.

For example, even in the case of using an inexpensive permanent magnet13having a residual magnetic flux density of 1 T or smaller, e.g., 0.7 T to 0.9 T, the same torque can be obtained with the same size as in the case of using neodymium sintered magnet having a residual magnetic flux density of about 1.2 T to 1.3 T, whereby an effect of reducing the cost of the permanent magnet13is obtained.

FIG. 16is an explanation diagram of an electric power steering apparatus of an automobile.

A driver steers a steering wheel (not shown), and the resultant torque is transmitted to a shaft201via a steering shaft (not shown).

At this time, the torque detected by a torque sensor202is converted into an electric signal and then the electric signal is transmitted through a cable (not shown) to an ECU101via a connector203.

Meanwhile, information about the automobile such as the velocity thereof is converted into an electric signal and then the electric signal is transmitted to the ECU101via a connector204. The ECU101calculates required assist torque from the above torque and the information about the automobile such as the velocity thereof, and thereby supplies current to a permanent magnet motor10through inverters102-1and102-2as shown inFIG. 4. The motor10is provided in parallel to the movement direction (indicated by an arrow) of a rack shaft.

In addition, power is supplied from a battery or an alternator to the ECU101via a power supply connector205. Torque generated by the permanent magnet motor10is decelerated by a gear box206containing a belt (not shown) and a ball screw (not shown), and generates thrust for moving the rack shaft (not shown) provided inside a housing207in the direction of the arrow, thereby assisting a steering force for the driver.

As a result, a tie rod208is moved and a wheel is turned, whereby the automobile can be turned. Owing to the assist by the torque of the permanent magnet motor10, the driver can turn the automobile with a less steering force.

It is noted that a rack boot209is provided for preventing a foreign material from entering the inside of the apparatus.

In such electric power steering apparatuses, since cogging torque and torque ripple caused by the motor10are transmitted to a driver via a gear, it is desirable that the cogging torque and torque ripple are small in order to obtain a preferable steering feeling.

In addition, it is also desirable that vibration and noise upon operation of the motor10are small.

Considering the above, by applying the motors10described in embodiments 1 to 5, the effects described in these embodiments can be obtained.

In addition, since vibration and noise can be reduced even in a large-output motor, by applying the motors described in embodiments 1 to 5, an effect is obtained that an electric power steering apparatus can be applied also to a large vehicle and fuel efficiency can be reduced.

As a matter of course, although not shown, the motor of the present invention is also applicable to a steer-by-wire type, so that the same effect can be obtained.

FIG. 14is an example of the permanent magnet motor10, in which the ECU is integrally provided in back of the permanent magnet motor. In a rotational angle sensor50of the motor10, a permanent magnet52is provided at an end of the shaft14. The permanent magnet52rotates along with the shaft14.

A magnetic field detecting element is disposed at a position facing to the permanent magnet52. A magnetic field is detected by the magnetic field detecting element, and then a rotational angle is detected from the direction of the magnetic field. By magnetizing the permanent magnet52at two polarities, the magnetic field rotates one revolution while the shaft14, i.e., the rotor11rotates one revolution, thereby realizing a sensor with a shaft angle multiplier of 1×. Thus, in the case of using a sensor of 1×, even if the pole pair number of the motor10is increased to, for example, 3 or more, the frequency of sensor error is constant, and therefore the frequencies of vibration and noise due to angle error of the sensor remain small, so that an effect of reducing noise in an auditory sense is obtained.

Since operation is possible under any pole pair number, there is an advantage in terms of system that the rotational angle sensor can be commonly applied to the motors10with various pole numbers.

FIG. 15is another example of the permanent magnet motor10, in which the ECU is integrally provided in back of the permanent magnet motor. A rotor61of a VR (variable reluctance) resolver60with a shaft angle multiplier of NX is provided at an end of the shaft14, and a stator62of the resolver60is provided on the outer side in the radial direction of the rotor61of the resolver60.

Since a VR resolver of NX is an inexpensive rotational angle sensor having an excellent environment resistance, an effect is obtained that an inexpensive electric power steering system having an excellent environment resistance can be structured.

It is noted that, within the scope of the present invention, the above embodiments may be freely combined with each other, or each of the above embodiments may be modified or abbreviated as appropriate.

DESCRIPTION OF THE REFERENCE CHARACTERS

12rotor iron core

15curved surface portion

22stator iron core

51magnetic field detecting element

61rotor of resolver

62stator of resolver

105power supply relay

105-1first power supply relay

105-2second power supply relay

205power supply connector