JP2013081311A - Motor, motor control device, and motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor that reduces manufacturing cost, and to provide a motor control device and a motor-driven power steering device.SOLUTION: A motor includes: a rotor yoke; a stator core that is annularly arranged on an outer side of the rotor yoke with a gap between the stator core and the rotor yoke; magnets that have respective low-coercive-force portions and respective high-coercive-force portions, which are higher in coercive force than the low-coercive-force portions, and that are embedded in the rotor yoke with the low-coercive-force portions nearer to the gap than the respective high-coercive-force portions; and excitation coils that excite the stator core and generate magnetic fields for varying magnetic flux content of the respective low-coercive-force portions.

Description

  The present invention relates to an electric motor, an electric motor control device, and an electric power steering device.

  For example, Patent Document 1 discloses a low coercive force with which a magnetic flux density is irreversibly changed by a magnetic field generated by a stator core provided with a stator winding and a current of the stator winding in a rotor core. There is described a permanent magnet type rotating electrical machine including a rotor having a coercive force permanent magnet and a high coercivity permanent magnet having a coercive force twice or more that of the low coercive force permanent magnet.

JP 2006-280195 A

  The technique disclosed in Patent Document 1 requires a low coercivity permanent magnet and a high coercivity permanent magnet, and increases the number of parts of the magnet, resulting in an increase in manufacturing cost. In addition, the technique disclosed in Patent Document 1 has not been studied for application to an electric power steering apparatus.

  This invention is made | formed in view of the above, Comprising: It aims at providing the electric motor which can reduce manufacturing cost, an electric motor control apparatus, and an electric power steering apparatus.

  In order to solve the above-described problems and achieve the object, the electric motor includes a rotor yoke, a stator core arranged in an annular shape with a gap outside the rotor yoke, a low coercive force portion, and the low coercive force portion. A high coercive force portion, a magnet embedded in the rotor yoke such that the low coercive force portion is closer to the gap side than the high coercive force portion, the stator core is excited, and the low coercive force portion And an exciting coil for generating a magnetic field for changing the amount of magnetic flux.

  With the above configuration, the amount of magnetic flux in the low coercive force portion can be changed, so that the amount of magnetic flux interlinked from the rotor yoke embedded with the magnet to the stator core can be varied. Thereby, the induced voltage which arises in an exciting coil can be changed by changing the amount of magnetic flux which acts on an exciting coil. By changing the induced voltage, the electric motor can change the maximum number of rotations determined by the balance between the induced voltage and the power supply voltage. For this reason, the electric motor can change the amount of magnetic flux of the low coercive force portion between the high rotation region and the low rotation region, and obtain a desired rotation speed and torque.

  In addition, the electric motor has a bridging portion formed between a low coercive force magnet and a high coercive force magnet, as compared with a conventional electric motor that combines a low coercive force magnet and a high coercive force magnet. Can be reduced. By embedding the low coercivity part and the high coercivity part in the rotor yoke as one body, leakage of magnet magnetic flux from the bridging part between the low coercivity part and the high coercivity part is suppressed, and the magnetic flux of the magnet is effective. Can be used.

  In addition, the electric motor can reduce the number of parts of the magnet and reduce the machining cost and management cost of the magnet as compared with the conventional electric motor that constitutes a magnet by combining a low coercive force magnet and a high coercive force magnet. it can. Moreover, the magnet of an electric motor can suppress the use of an expensive element and can reduce the unit price of a magnet by reducing the usage-amount of rare earth elements which can raise a coercive force, for example, Dy or Tb. As a result, the electric motor can reduce the manufacturing cost.

  In order to solve the above-described problems and achieve the object, an electric motor control device includes a rotor yoke, a stator core that is annularly arranged with a gap outside the rotor yoke, a low coercive force portion, and the low coercive force portion. A high coercive force portion having a higher coercive force than the high coercive force portion, the magnet being embedded in the rotor yoke such that the low coercive force portion is closer to the gap than the high coercive force portion, and exciting the stator core and the low coercive force portion. An electric motor including an exciting coil that generates a magnetic field for changing the amount of magnetic flux of the magnetic part, and a control unit that controls energization of the exciting coil.

  With the above configuration, the amount of magnetic flux in the low coercive force portion can be changed, so that the amount of magnetic flux interlinked from the rotor yoke embedded with the magnet to the stator core can be varied. Thereby, the induced voltage which arises in an exciting coil can be changed by changing the amount of magnetic flux which acts on an exciting coil. By changing the induced voltage, the electric motor can change the maximum number of rotations determined by the balance between the induced voltage and the power supply voltage. For this reason, the electric motor can change the amount of magnetic flux of the low coercive force portion between the high rotation region and the low rotation region, and obtain a desired rotation speed and torque.

  In addition, the electric motor has a bridging portion formed between a low coercive force magnet and a high coercive force magnet, as compared with a conventional electric motor that combines a low coercive force magnet and a high coercive force magnet. Can be reduced. By embedding the low coercivity part and the high coercivity part in the rotor yoke as one body, leakage of magnet magnetic flux from the bridging part between the low coercivity part and the high coercivity part is suppressed, and the magnetic flux of the magnet is effective. Can be used.

  In addition, the electric motor can reduce the number of parts of the magnet and reduce the machining cost and management cost of the magnet as compared with the conventional electric motor that constitutes a magnet by combining a low coercive force magnet and a high coercive force magnet. it can. Moreover, the magnet of an electric motor can suppress the use of an expensive element and can reduce the unit price of a magnet by reducing the usage-amount of rare earth elements which can raise a coercive force, for example, Dy or Tb. As a result, the motor control device can reduce the manufacturing cost.

  As a preferred aspect of the present invention, it is preferable that the control means controls demagnetization to reduce the amount of magnetic flux of the low coercive force portion when the rotor yoke rotates by an external force without exciting the stator core.

  With the above configuration, the motor control device can suppress an increase in loss torque when the motor runs idle. For example, in a state where the amount of magnetic flux of the low coercive force portion is reduced, the amount of magnetic flux interlinked from the rotor yoke in which the magnet is embedded to the stator core is reduced. For this reason, the hysteresis loss is reduced when the magnetic domains generated in the stator core change direction. Hysteresis loss causes an increase in loss torque when the motor runs idle. In other words, with the above configuration, the motor control device can reduce the frictional force with respect to the rotation of the rotor when the rotor is rotated in a state where the excitation coil is not energized.

  As a desirable mode of the present invention, when the control means is demagnetizing when the demagnetization control is not performed to reduce the amount of magnetic flux of the low coercive force portion, It is preferable to control magnetization to increase the amount of magnetic flux.

  With the above-described configuration, the motor control device can suppress the risk of insufficient magnetic flux due to unintentional demagnetization of the low coercive force portion. For this reason, the motor control device can improve the reliability of driving when torque is required in a so-called low-speed rotation region.

  As a desirable mode of the present invention, it is preferable that the control means periodically increase the amount of magnetic flux of the low coercive force portion.

  With the above-described configuration, the motor control device can suppress the risk of insufficient magnetic flux due to unintentional demagnetization of the low coercive force portion. For this reason, the motor control device can improve the reliability of driving when torque is required in a so-called low-speed rotation region.

  As a desirable mode of the present invention, it is preferable that the control means reduce the amount of magnetic flux of the low coercive force portion when the exciting coil is short-circuited.

  With the above configuration, the electric motor control device can continue to drive the electric motor in a state in which the influence of the short-circuit of the exciting coil is suppressed. For this reason, the relay circuit for suppressing the influence of the short of an exciting coil becomes unnecessary, and the motor control apparatus can reduce manufacturing cost. In addition, when there is a relay circuit, the motor control device can reduce the amount of magnetic flux of the magnet linked to the short coil even in a non-energized state during operation of the relay circuit. For this reason, the motor control device can reduce the electromagnetic brake torque and rotate the motor by an external force.

  As a desirable mode of the present invention, when the induced voltage of the exciting coil is equal to or higher than a threshold value of the rotation speed of the electric motor determined so as not to reach the upper limit of the power supply voltage, the control means is configured to reduce the amount of magnetic flux of the low coercive force portion. Is preferably reduced.

  With the above configuration, the amount of magnetic flux interlinked from the rotor yoke embedded with the magnet to the stator core is suppressed, and the amount of magnetic flux acting on the exciting coil is reduced. For this reason, the amount of magnetic flux acting on the exciting coil is reduced, so that there is a margin of increase in the induced voltage. In the permanent magnet rotary motor, the induced voltage increases in proportion to the rotational speed of the rotor. Therefore, the electric motor can increase the maximum rotation speed determined by the balance between the induced voltage and the power supply voltage. As a result, the electric motor can suppress the possibility that the induced voltage reaches the power supply voltage in the high rotation region, and can expand the variable speed region of the rotor.

  As a desirable mode of the present invention, it is preferable that the control means reduce the amount of magnetic flux of the low coercive force portion before the motor is reversely rotated.

  When the motor is reversely rotated, an induced voltage (counterelectromotive voltage) is instantaneously applied to the motor drive circuit, which may cause a load on the drive circuit or a reverse operation torque on the rotor. With the above configuration, the induced voltage can be reduced by the amount of magnetic flux acting on the exciting coil, so that the induced voltage (counterelectromotive voltage) may be instantaneously applied to the motor drive circuit and cause a load on the drive circuit. The possibility of causing reverse operating torque in the rotor can be suppressed.

  As a desirable aspect of the present invention, the electric motor is preferably an electric power steering electric motor that obtains an auxiliary steering torque.

  With the above configuration, it is possible to suppress an influence on the steering feeling received by the steering person.

  In order to solve the above-described problems and achieve the object, an electric power steering apparatus includes an electric power steering motor that obtains an auxiliary steering torque, and a control unit that controls the electric power steering motor. The electric motor includes a rotor yoke, a stator core that is annularly arranged with a gap outside the rotor yoke, a low coercive force portion, and a high coercive force portion that has a higher coercive force than the low coercive force portion. Excitation that excites the stator core and the stator core so that the coercive force portion is closer to the gap than the high coercive force portion and generates a magnetic field for changing the amount of magnetic flux of the low coercive force portion And a coil.

  With the above configuration, the amount of magnetic flux in the low coercive force portion can be changed, so that the amount of magnetic flux interlinked from the rotor yoke embedded with the magnet to the stator core can be varied. Thereby, the induced voltage which arises in an exciting coil can be changed by changing the amount of magnetic flux which acts on an exciting coil. By changing the induced voltage, the electric power steering motor can change the maximum number of rotations determined by the balance between the induced voltage and the power supply voltage. For this reason, the electric power steering motor can change the amount of magnetic flux of the low coercive force portion between the high rotation region and the low rotation region, and can obtain a desired rotation speed and torque.

  In addition, the electric power steering motor is generated between a low coercive force magnet and a high coercive force magnet, as compared with a conventional electric motor that combines a low coercive force magnet and a high coercive force magnet. The bridge part can be reduced. By embedding the low coercivity part and the high coercivity part in the rotor yoke as one body, leakage of magnet magnetic flux from the bridging part between the low coercivity part and the high coercivity part is suppressed, and the magnetic flux of the magnet is effective. Can be used.

  In addition, the electric power steering motor reduces the number of parts of the magnet and reduces the machining cost and management cost of the magnet compared to the conventional electric motor that combines a low coercivity magnet and a high coercivity magnet. Can be reduced. In addition, the magnet of the electric power steering motor can reduce the amount of rare earth elements that can increase the coercive force, such as Dy or Tb, thereby suppressing the use of expensive elements and reducing the unit price of the magnet. it can. As a result, the electric power steering device can reduce the manufacturing cost.

  As a desirable aspect of the present invention, the control means is configured to reduce the amount of magnetic flux of the low coercive force portion when the rotor yoke rotates without the auxiliary steering torque being required and without exciting the stator core. It is preferable to perform control.

  With the above configuration, the electric power steering apparatus can suppress an increase in loss torque when the electric power steering motor is idled. For example, in a state where the amount of magnetic flux of the low coercive force portion is reduced, the amount of magnetic flux interlinked from the rotor yoke in which the magnet is embedded to the stator core is reduced. For this reason, the hysteresis loss is reduced when the magnetic domains generated in the stator core change direction. Hysteresis loss causes an increase in loss torque when the electric power steering motor runs idle. That is, with the above configuration, the electric power steering electric motor control device can reduce the frictional force against the rotation of the rotor when the rotor is rotated in a state where the excitation coil is not energized.

  As a desirable mode of the present invention, when the control means is demagnetizing when the demagnetization control is not performed to reduce the amount of magnetic flux of the low coercive force portion, It is preferable to control magnetization to increase the amount of magnetic flux.

  With the above-described configuration, the electric power steering apparatus can suppress the risk of insufficient magnetic flux due to unintentional demagnetization of the low coercive force portion. For this reason, the electric power steering apparatus can improve the driving reliability when torque is required in a so-called low-speed rotation region.

  As a desirable mode of the present invention, it is preferable that the control means periodically increase the amount of magnetic flux of the low coercive force portion.

  With the above-described configuration, the electric power steering apparatus can suppress the risk of insufficient magnetic flux due to unintentional demagnetization of the low coercive force portion. For this reason, the electric power steering apparatus can improve the driving reliability when torque is required in a so-called low-speed rotation region.

  As a desirable mode of the present invention, it is preferable that the control means reduce the amount of magnetic flux of the low coercive force portion when the exciting coil is short-circuited.

  With the above configuration, the electric power steering apparatus can continue to drive the electric motor in a state where the influence of the short-circuit of the exciting coil is suppressed. For this reason, the relay circuit for suppressing the influence of the short of the exciting coil becomes unnecessary, and the electric power steering apparatus can reduce the manufacturing cost. Further, when there is a relay circuit, the electric power steering device can reduce the amount of magnetic flux of the magnet interlinked with the short coil even in a non-energized state during operation of the relay circuit. Therefore, the electric power steering apparatus can reduce the electromagnetic brake torque and rotate the motor by an external force.

  As a desirable mode of the present invention, the control means is configured to reduce the low coercive force when the induced voltage of the exciting coil is equal to or higher than a threshold value of the rotational speed of the electric power steering motor determined so as not to reach an upper limit of a power supply voltage. It is preferable to reduce the amount of magnetic flux in the part.

  With the above configuration, the amount of magnetic flux interlinked from the rotor yoke embedded with the magnet to the stator core is suppressed, and the amount of magnetic flux acting on the exciting coil is reduced. For this reason, the amount of magnetic flux acting on the exciting coil is reduced, so that there is a margin of increase in the induced voltage. In the permanent magnet rotary motor, the induced voltage increases in proportion to the rotational speed of the rotor. Therefore, the electric power steering motor can increase the maximum number of rotations determined by the balance between the induced voltage and the power supply voltage. As a result, the electric power steering motor can suppress the possibility that the induced voltage reaches the power supply voltage in the high rotation region, and can expand the variable speed region of the rotor.

  As a desirable mode of the present invention, it is preferable that the control means reduce the amount of magnetic flux of the low coercive force portion before the motor is reversely rotated.

  When the rotation of the electric power steering motor is reversed, an induced voltage (counterelectromotive voltage) is instantaneously applied to the motor drive circuit, which may cause a load on the drive circuit or a reverse operation torque on the rotor. There is. With the above configuration, the induced voltage can be reduced by the amount of magnetic flux acting on the exciting coil, so that the induced voltage (counterelectromotive voltage) may be instantaneously applied to the motor drive circuit and cause a load on the drive circuit. The possibility of causing reverse operating torque in the rotor can be suppressed.

  The present invention can provide an electric motor, an electric motor control device, and an electric power steering device that can reduce manufacturing costs.

FIG. 1 is a configuration diagram of an electric power steering apparatus including a brushless motor according to the first embodiment. FIG. 2 is a front view for explaining an example of a speed reducer included in the electric power steering apparatus according to the first embodiment. FIG. 3 is a cross-sectional view schematically showing the configuration of the motor of the first embodiment on a virtual plane including the central axis. FIG. 4 is a cross-sectional view schematically showing the configuration of the motor according to the first embodiment, taken along a virtual plane orthogonal to the central axis. FIG. 5 is an explanatory diagram schematically illustrating the rotor according to the first embodiment. FIG. 6 is a flowchart for explaining a magnet manufacturing method according to the first embodiment. FIG. 7 is a flowchart for explaining control steps of the brushless motor according to the first embodiment. FIG. 8 is a flowchart for explaining control steps of the brushless motor according to the second embodiment. FIG. 9 is an explanatory diagram illustrating a relationship between the rotation speed and torque of the brushless motor according to the second embodiment. FIG. 10 is a flowchart for explaining control steps of the brushless motor according to the third embodiment. FIG. 11 is a flowchart for explaining control steps of the brushless motor according to the fourth embodiment. FIG. 12 is a flowchart for explaining control steps of the brushless motor according to the fifth embodiment. FIG. 13 is a flowchart for explaining control steps of the brushless motor according to the sixth embodiment.

  DESCRIPTION OF EMBODIMENTS Embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

(Embodiment 1)
FIG. 1 is a configuration diagram of an electric power steering apparatus including a brushless motor according to the first embodiment. First, an outline of an electric power steering apparatus including the brushless motor according to the present embodiment will be described with reference to FIG.

  The electric power steering device 80 includes a steering wheel 81, a steering shaft 82, a steering force assist mechanism 83, a universal joint 84, a lower shaft 85, a universal joint 86, in the order in which the force applied from the steering wheel is transmitted. A pinion shaft 87, a steering gear 88, and a tie rod 89 are provided. The electric power steering device 80 includes an ECU (Electronic Control Unit) 90, a torque sensor 91a, and a vehicle speed sensor 91b.

  The steering shaft 82 includes an input shaft 82a and an output shaft 82b. The input shaft 82a has one end connected to the steering wheel 81 and the other end connected to the steering force assist mechanism 83 via the torque sensor 91a. The output shaft 82 b has one end connected to the steering force assist mechanism 83 and the other end connected to the universal joint 84. In the present embodiment, the input shaft 82a and the output shaft 82b are made of a magnetic material such as iron.

  The lower shaft 85 has one end connected to the universal joint 84 and the other end connected to the universal joint 86. The pinion shaft 87 has one end connected to the universal joint 86 and the other end connected to the steering gear 88.

  Steering gear 88 includes a pinion 88a and a rack 88b. The pinion 88a is connected to the pinion shaft 87. The rack 88b meshes with the pinion 88a. The steering gear 88 is configured as a rack and pinion type. The steering gear 88 converts the rotational motion transmitted to the pinion 88a into a linear motion by the rack 88b. The tie rod 89 is connected to the rack 88b.

  The steering force assist mechanism 83 includes a speed reducer 92 and the brushless motor 10. The reduction gear 92 is connected to the output shaft 82b. The brushless motor 10 is an electric motor that is connected to the reduction gear 92 and generates auxiliary steering torque. In the electric power steering device 80, a steering column is constituted by the steering shaft 82, the torque sensor 91a, and the speed reducer 92. The brushless motor 10 gives auxiliary steering torque to the output shaft 82b of the steering column. That is, the electric power steering apparatus 80 of this embodiment is a column assist system.

  FIG. 2 is a front view for explaining an example of a speed reducer included in the electric power steering apparatus according to the first embodiment. FIG. 2 shows a part in cross section. The speed reducer 92 is a worm speed reducer. The reduction gear 92 includes a reduction gear housing 93, a worm 94, a ball bearing 95 a, a ball bearing 95 b, a worm wheel 96, and a holder 97.

  The worm 94 is coupled to the shaft 21 of the brushless motor 10 by a spline or an elastic coupling. The worm 94 is held in the speed reducer housing 93 so as to be rotatable by a ball bearing 95 a and a ball bearing 95 b held by the holder 97. The worm wheel 96 is rotatably held by the speed reducer housing 93. The worm teeth 94 a formed on a part of the worm 94 mesh with the worm wheel teeth 96 a formed on the worm wheel 96.

  The rotational force of the brushless motor 10 is transmitted to the worm wheel 96 through the worm 94 to rotate the worm wheel 96. The reduction gear 92 increases the torque of the brushless motor 10 by the worm 94 and the worm wheel 96. Then, the reduction gear 92 gives an auxiliary steering torque to the output shaft 82b of the steering column shown in FIG.

  The torque sensor 91a shown in FIG. 1 detects the driver's steering force transmitted to the input shaft 82a via the steering wheel 81 as a steering torque. The vehicle speed sensor 91b detects the traveling speed of the vehicle on which the electric power steering device 80 is mounted. The ECU 90 is electrically connected to the brushless motor 10, the torque sensor 91a, and the vehicle speed sensor 91b.

  The ECU 90 controls the operation of the brushless motor 10. Moreover, ECU90 acquires a signal from each of the torque sensor 91a and the vehicle speed sensor 91b. That is, the ECU 90 acquires the steering torque T from the torque sensor 91a, and acquires the traveling speed V of the vehicle from the vehicle speed sensor 91b. The ECU 90 is supplied with electric power from a power supply device (for example, a vehicle-mounted battery) 99 with the ignition switch 98 turned on. The ECU 90 calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value X supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The ECU 90 acquires the information on the induced voltage from the brushless motor 10 or the information on the rotation of the rotor from the resolver described later as the operation information Y.

  The steering force of the driver (driver) input to the steering wheel 81 is transmitted to the speed reduction device 92 of the steering force assist mechanism 83 via the input shaft 82a. At this time, the ECU 90 acquires the steering torque T input to the input shaft 82a from the torque sensor 91a, and acquires the traveling speed V from the vehicle speed sensor 91b. The ECU 90 controls the operation of the brushless motor 10. The auxiliary steering torque created by the brushless motor 10 is transmitted to the speed reducer 92.

  The steering torque (including auxiliary steering torque) output via the output shaft 82 b is transmitted to the lower shaft 85 via the universal joint 84 and further transmitted to the pinion shaft 87 via the universal joint 86. The steering force transmitted to the pinion shaft 87 is transmitted to the tie rod 89 via the steering gear 88 to steer the steered wheels. Next, the brushless motor 10 will be described.

  FIG. 3 is a cross-sectional view schematically showing the configuration of the motor of the first embodiment on a virtual plane including the central axis. FIG. 4 is a cross-sectional view schematically showing the configuration of the motor according to the first embodiment, taken along a virtual plane orthogonal to the central axis. As shown in FIG. 3, the brushless motor 10 includes a housing 11, a bearing 12, a bearing 13, a resolver 14, a rotor 20, and a stator 30 as a brushless motor stator.

  The housing 11 includes a cylindrical housing 11a and a front bracket 11b. The front bracket 11b is formed in a substantially disc shape and is attached to the cylindrical housing 11a so as to close one open end of the cylindrical housing 11a. The cylindrical housing 11a is formed with a bottom 11c at the end opposite to the front bracket 11b so as to close the end. The bottom part 11c is formed integrally with the cylindrical housing 11a, for example. As a magnetic material forming the cylindrical housing 11a, for example, a general steel material such as SPCC (Steel Plate Cold Commercial), electromagnetic soft iron, or the like can be applied. The front bracket 11b serves as a flange when the brushless motor 10 is attached to a desired device.

  The bearing 12 is provided inside the cylindrical housing 11a and at a substantially central portion of the front bracket 11b. The bearing 13 is provided inside the cylindrical housing 11a and at a substantially central portion of the bottom portion 11c. The bearing 12 rotatably supports one end of a shaft 21 that is a part of the rotor 20 disposed inside the cylindrical housing 11a. The bearing 13 rotatably supports the other end of the shaft 21. Thereby, the shaft 21 rotates around the central axis Zr.

  The resolver 14 is supported by a terminal block 15 provided on the front bracket 11b side of the shaft 21. The resolver 14 detects the rotational position of the rotor 20 (shaft 21). The resolver 14 includes a resolver rotor 14a and a resolver stator 14b. The resolver rotor 14a is attached to the circumferential surface of the shaft 21 by press fitting or the like. The resolver stator 14b is disposed to face the resolver rotor 14a with a predetermined gap.

  The stator 30 is provided in a cylindrical shape so as to surround the rotor 20 inside the cylindrical housing 11a. The stator 30 is attached, for example, by being fitted to the inner peripheral surface 11d of the cylindrical housing 11a. The central axis of the stator 30 coincides with the central axis Zr of the rotor 20. The stator 30 includes a cylindrical stator core 31 and an excitation coil 37. In the stator 30, an exciting coil 37 is wound around the stator core 31.

  As shown in FIG. 4, the stator core 31 includes a plurality of divided cores 32. The plurality of split cores 32 are arranged at equal intervals in the circumferential direction around the central axis Zr (the direction along the inner peripheral surface 11d of the cylindrical housing 11a shown in FIG. 3). Hereinafter, the circumferential direction around the central axis Zr is simply referred to as the circumferential direction. The stator core 31 is configured by combining a plurality of divided cores 32. The stator core 31 is press-fitted into the cylindrical housing 11a, so that the stator 30 is provided in the cylindrical housing 11a in an annular state. The stator core 31 and the cylindrical housing 11a may be fixed by adhesion, shrink fitting, welding or the like in addition to press-fitting.

  The split core 32 is formed by stacking and bundling a plurality of core pieces formed in substantially the same shape in the central axis Zr direction. The split core 32 is formed of a magnetic material such as an electromagnetic steel plate. The split core 32 has a back yoke 33 and teeth 34. The back yoke 33 includes an arc-shaped portion. The back yoke 33 forms an annular shape when the plurality of divided cores 32 are combined. The teeth 34 are portions extending from the inner peripheral surface of the back yoke 33 toward the rotor 20.

  The exciting coil 37 shown in FIG. 4 is a linear electric wire. The exciting coil 37 is concentratedly wound around the outer periphery of the tooth 34 of the split core 32 via an insulator 37a. The insulator 37a is a member for insulating the exciting coil 37 and the split core 32, and is formed of a heat resistant member. By combining a plurality of stator cores 31 thus configured as shown in FIG. 4, the stator 30 has a shape that can surround the rotor 20. The stator core 31 is annularly disposed outside the rotor yoke 22 with a gap Lg having a predetermined interval.

  The rotor 20 is provided inside the cylindrical housing 11a so as to be rotatable about the central axis Zr with respect to the cylindrical housing 11a. The rotor 20 includes a shaft 21, a rotor yoke 22, and a magnet 23. The shaft 21 is formed in a cylindrical shape. The rotor yoke 22 is formed in a cylindrical shape.

  The rotor yoke 22 is manufactured by laminating electromagnetic steel plates by means such as adhesion, boss, caulking and the like. The rotor yoke 22 is sequentially stacked in the mold and discharged from the mold. The rotor yoke 22 is fixed to the shaft 21 by press-fitting the shaft 21 into, for example, a hollow portion thereof. The shaft 21 and the rotor yoke 22 may be integrally formed.

  A plurality of magnets 23 are embedded along the outer circumferential direction of the rotor yoke 22. The magnet 23 is a permanent magnet, and S poles and N poles are alternately arranged at equal intervals in the circumferential direction of the rotor yoke 22. As a result, the number of poles of the rotor 20 shown in FIG. 4 is 14 poles in which N poles and S poles are alternately arranged on the outer circumferential side of the rotor yoke 22 in the circumferential direction of the rotor yoke 22.

  The magnet 23 is accommodated in the magnet accommodation hole 24 of the rotor yoke 22 and attached by, for example, a magnetic force. In the present embodiment, the magnet 23 has a divided shape (segment structure). FIG. 5 is an explanatory diagram schematically illustrating the rotor according to the first embodiment.

  As shown in FIG. 5, the magnet accommodation hole 24 is a through hole formed in the rotor yoke 22. A plurality of magnet housing holes 24 are provided on the outer peripheral portion and arranged at equal intervals. The magnet 23 in which the outer peripheral side of the rotor yoke 22 is magnetized with an N pole includes a pair of segment magnets 23A and a segment magnet 23B. The pair of segment magnets 23 </ b> A and the segment magnets 23 </ b> B are housed in the magnet housing holes 24 and are arranged in a V shape extending on the outer periphery of the rotor yoke 22 as viewed from the central axis Zr.

  Further, the magnet 23 in which the outer peripheral side of the rotor yoke 22 is magnetized to the S pole includes a pair of segment magnets 23C and a segment magnet 23D. The pair of segment magnets 23C and the segment magnets 23D are housed in the magnet housing holes 24, and are arranged in a V shape that spreads on the outer periphery of the rotor yoke 22 as viewed from the central axis Zr.

  The flux barrier 25 is, for example, a through hole provided in the rotor yoke 22 and can prevent a magnetic flux short circuit between the S pole and the N pole. The flux barrier 25 only needs to be capable of suppressing or blocking the passage of magnetic flux, and may be a gap or a non-magnetic insulating material.

  By providing the flux barrier 25 in the rotor yoke 22, a partial magnetic resistance difference occurs in the outer circumferential direction of the rotor yoke 22. For example, a magnetic concave portion is formed between the pair of segment magnets 23A and the segment magnet 23B, and the vicinity of the flux barrier 25 is a magnetic convex portion called a bridge.

  Similarly, a magnetic concave portion is formed between the pair of segment magnets 23C and the segment magnet 23D, and the vicinity of the flux barrier 25 is a magnetic convex portion called a bridge. For this reason, magnetic concave portions and magnetic convex portions are alternately arranged on the outer periphery of the rotor yoke 22, and the magnetic concave portion is called the q axis and the magnetic convex portion is called the d axis.

  The segment magnet 23A, the segment magnet 23B, the segment magnet 23C, and the segment magnet 23D include a low coercive force portion 26 and a high coercive force portion 27 that are regions having relatively different coercive forces in one magnetic body. As shown in FIG. 5, the low coercive force portion 26 is embedded in the rotor yoke 22 so as to be closer to the gap Lg of the rotor yoke 22 than the high coercive force portion 27. FIG. 6 is a flowchart for explaining a magnet manufacturing method according to the first embodiment.

  As shown in FIG. 6, the manufacturing apparatus manufactures a low coercivity magnet using a magnetic material having a coercive force corresponding to the low coercive force portion 26 for the entire segment magnet 23A, segment magnet 23B, segment magnet 23C, and segment magnet 23D. (Step S1). For example, the magnetic material is an Nd—Fe—B magnet.

  The coercive force of the magnetic material is preferably such that it is not demagnetized by the exciting magnetic field generated by the exciting coil 37 rotating the rotor 20. The coercive force of the magnetic material is preferably such that the exciting coil 37 can be demagnetized or magnetized when a demagnetizing magnetic field or a magnetizing magnetic field that is larger than the above-described exciting magnetic field is applied.

  Next, the manufacturing apparatus performs grain boundary diffusion processing on the magnetic material manufactured in step S1 (step S2). For example, the manufacturing apparatus diffuses at least one kind of Dy or Tb, which is a rare earth element, on a predetermined surface of a magnetic body of an Nd—Fe—B based magnet. In the grain boundary diffusion treatment, at least one kind of Dy or Tb, which is a rare earth element, is introduced into the grain boundary of the magnetic body of the Nd—Fe—B based magnet.

  Thereby, in the magnetic body, a region in which at least one of Dy or Tb is diffused in one magnetic body and a region in which at least one of Dy or Tb is not diffused are formed. In the region where at least one of Dy or Tb is diffused, the coercive force can be improved by diffusing Dy or Tb into the grain boundary of the Nd—Fe—B magnet. As a result, the segment magnet 23A, the segment magnet 23B, the segment magnet 23C, and the segment magnet 23D are formed with a low coercive force portion 26 and a high coercive force portion 27 that have relatively different coercive forces.

  For this reason, the magnet 23 can reduce a number of parts compared with the magnet which combined the magnet of the low coercive force and the magnet of the high coercive force, and can reduce processing cost and management cost. Moreover, the magnet 23 can improve the mass per unit volume of a magnet compared with the magnet which combined the magnet of a low coercive force and the magnet of a high coercive force, and can reduce the unit price of a magnet. As a result, the brushless motor 10 of this embodiment can reduce cost.

  Further, the brushless motor 10 according to the present embodiment has a low coercivity magnet and a high coercivity magnet, as compared with a conventional electric motor that combines a low coercivity magnet and a high coercivity magnet. Can reduce the bridging part. By embedding the low coercive force portion 26 and the high coercive force portion 27 in the rotor yoke 22 as one body, leakage of magnet magnetic flux from the bridging portion generated between the low coercive force portion 26 and the high coercive force portion 27 is suppressed, The magnetic flux of segment magnet 23A, segment magnet 23B, segment magnet 23C, and segment magnet 23D can be used effectively.

  The coercive force of the high coercive force portion 27 is increased to such an extent that the magnetic flux amount of the high coercive force portion 27 does not change even if the excitation coil 37 generates a magnetic field that can demagnetize or magnetize the low coercive force portion 26. Is preferred.

  Next, in the manufacturing apparatus, the low coercive force portion 26 is more rotor rotor yoke than the high coercive force portion 27 with respect to the segment magnet 23A, the segment magnet 23B, the segment magnet 23C, and the segment magnet 23D that are the magnetic bodies subjected to the grain boundary diffusion treatment in step S2. It accommodates in the magnet accommodation hole 24 so that it may become the outer peripheral side of 22, and arrangement | positioning to the rotor yoke 22 is performed (step S3).

  In the manufacturing apparatus, the segment magnet 23A, the segment magnet 23B, the segment magnet 23C, and the segment magnet 23D may be accommodated in the magnet accommodation hole 24 after being magnetized. Alternatively, the manufacturing apparatus may magnetize after the segment magnets 23A, the segment magnets 23B, the segment magnets 23C, and the segment magnets 23D that are not magnetized are accommodated in the magnet accommodation holes 24.

  As described above, the brushless motor 10 according to the first embodiment is a permanent magnet rotary motor in which a permanent magnet is embedded in the rotor yoke 22. The brushless motor 10 is annularly arranged with a rotor yoke 22, a magnet 23 including a low coercive force portion 26 and a high coercive force portion 27 having relatively different coercive forces, and a gap Lg outside the rotor yoke 22. It includes a stator core 31 and an exciting coil 37 that excites the stator core 31 and generates a magnetic field for changing the amount of magnetic flux of the low coercive force portion 26. The magnet 23 is embedded in the rotor yoke 22 so that the low coercive force portion 26 is closer to the gap Lg of the rotor yoke 22 than the high coercive force portion 27 is.

  The ECU 90 described above serves as a control unit that controls the brushless motor 10. The ECU 90 can energize the exciting coil 37 via the drive circuit. That is, the brushless motor 10 and the ECU 90 described above constitute an electric motor control device. The energized exciting coil 37 generates a magnetic field. The ECU 90 can excite the stator core 31 by generating a magnetic field in the excitation coil 37. Further, the ECU 90 can generate a demagnetizing magnetic field that demagnetizes the amount of magnetic flux of the low coercive force portion 26 by energizing the exciting coil 37 in the form of a pulse wave. Alternatively, the ECU 90 can generate a magnetized magnetic field that increases the amount of magnetic flux of the low coercive force portion 26 by energizing the excitation coil 37 in the form of a pulse wave.

  Since the brushless motor 10 according to the first embodiment can change the amount of magnetic flux of the low coercive force portion 26, the amount of magnetic flux interlinked from the rotor yoke 22 in which the magnet 23 is embedded to the stator core 31 can be varied. Thereby, by changing the amount of magnetic flux acting on the exciting coil 37, the induced voltage generated in the exciting coil 37 can be changed. By changing the induced voltage, the brushless motor 10 can change the maximum rotational speed determined by the balance between the induced voltage and the power supply voltage. For this reason, the brushless motor 10 can change the amount of magnetic flux of the low coercive force portion between the high rotation region and the low rotation region to obtain a desired rotation speed and torque.

  The brushless motor 10 described above is an electric power steering motor that obtains an auxiliary steering torque. For this reason, it is necessary for the brushless motor 10 to suppress the influence on the steering feeling received by the steering person. For example, when the vehicle on which the electric power steering device 80 is mounted goes straight, the ECU 90 described above may not need to add an auxiliary steering force to the force given by the steering person. Since the auxiliary steering torque is unnecessary, the brushless motor 10 is in a state where the excitation coil 37 is not energized.

  Even in this case, the force (self-aligning torque) in the direction in which the steering wheel 81 returns to the straight traveling state acts on the steering force assist mechanism 83 from the output shaft 82b. For this reason, as for the brushless motor 10, the rotor 20 rotates in the state where electric power is not supplied. When the rotor 20 rotates in a state where power is not supplied, the rotor 20 receives a loss torque from the stator 30 in a direction in which the rotation is inhibited. Since this loss torque affects the steering feeling received by the steering wheel, it is preferable that the loss torque be small.

  FIG. 7 is a flowchart for explaining control steps of the brushless motor according to the first embodiment. As shown in FIG. 7, when there is an assist command (step S11, Yes), the ECU 90 advances the process to step S15. ECU90 advances a process to step S12, when there is no assist instruction | command (step S11, No).

  In step S12, the ECU 90 supplies power to the brushless motor 10 so that the exciting coil 37 generates a demagnetizing magnetic field so as to reduce the magnetic flux amount of the low coercive force portion 26 described above. Thereby, the ECU 90 executes a demagnetizing magnetic field control step for controlling the demagnetizing magnetic field (step S12). The demagnetizing magnetic field is preferably a magnetic field that does not reduce the amount of magnetic flux of the high coercive force portion 27 but reduces the amount of magnetic flux of the low coercive force portion 26.

  As shown in FIG. 5, the pair of segment magnets 23A and segment magnets 23B (segment magnets 23C and segment magnets 23D) are accommodated in the magnet accommodation holes 24 and spread in the outer periphery of the rotor yoke 22 as viewed from the central axis Zr. Is arranged. The exciting coil 37 forms a demagnetizing magnetic field exceeding the coercive force of the low coercive force portion 26 in the direction opposite to the polarity of the low coercive force portion 26.

  Further, the low coercive force portion 26 is closer to the outer periphery side of the rotor yoke 22 than the high coercive force portion 27. For this reason, the exciting coil 37 can cause the demagnetizing magnetic field to be applied by the low coercive force portion 26 rather than the high coercive force portion 27. As a result, the amount of power supplied to the exciting coil 37 can be suppressed in order to generate a demagnetizing magnetic field.

  Next, when there is no assist command (step S13, No), the ECU 90 sets the brushless motor 10 to a state where no electric power is supplied, and enters a standby state for the assist command. A force (self-aligning torque) in a direction in which the steering wheel 81 returns to the straight traveling state acts on the steering force assist mechanism 83 from the output shaft 82b.

  For example, when the amount of magnetic flux of the low coercive force portion 26 shown in FIG. 5 is reduced, the segment magnet 23A, the segment magnet 23B, the segment magnet 23C, and the segment magnet 23D can reduce the amount of magnetic flux that affects the stator core 31. When the amount of magnetic flux in the closed magnetic path of the rotor yoke 22 is reduced, the hysteresis loss of the rotor yoke 22 that causes a loss torque can be reduced.

  For this reason, the brushless motor 10 can reduce the loss torque received from the stator 30 in a direction in which the rotor 20 is prevented from rotating even when the rotor 20 rotates in a state where no electric power is supplied. As a result, it is possible to suppress the influence of the steering on the feeling of steering.

  Further, when the amount of magnetic flux of the low coercive force portion 26 shown in FIG. 5 is reduced, the amount of magnetic flux in the vicinity of the flux barrier 25 can be reduced. As a result, the difference in the amount of magnetic flux between the magnetic convex portion and the magnetic concave portion generated on the outer periphery of the rotor yoke 22 is suppressed, and the loss torque ripple can be reduced. And the electric power steering device 80 can suppress the influence which it has on the feeling of steering which a steering person receives.

  Next, ECU90 advances a process to step S14, when there exists an assist command (step S13, Yes). If the brushless motor 10 supplies power to the brushless motor 10 in a state where the amount of magnetic flux of the low coercive force portion 26 is reduced, the starting torque of the rotor 20 may be reduced.

  In step S12, the ECU 90 supplies power to the brushless motor 10 so that the exciting coil 37 generates a magnetizing magnetic field so as to increase the amount of magnetic flux of the low coercive force portion 26 described above. Thereby, ECU90 performs the magnetization magnetic field control step which controls a magnetization magnetic field (step S14).

  As shown in FIG. 5, the pair of segment magnets 23A and segment magnets 23B (segment magnets 23C and segment magnets 23D) are housed in the magnet housing holes 24 and spread toward the gap Lg of the rotor yoke 22 as viewed from the central axis Zr. It is arranged in a letter shape. The exciting coil 37 forms a magnetizing magnetic field exceeding the coercive force of the low coercive force portion 26 in the polarity direction of the low coercive force portion 26 shown in FIG.

  Further, the low coercive force portion 26 is closer to the gap Lg of the rotor yoke 22 than the high coercive force portion 27. For this reason, the exciting coil 37 can cause the magnetizing magnetic field to act on the low coercive force portion 26 rather than the high coercive force portion 27. As a result, the amount of power supplied to the exciting coil 37 can be suppressed in order to generate a magnetizing magnetic field.

  Next, the ECU 90 advances the process to step S15. The ECU 90 calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted electric power generates an exciting magnetic field, and the ECU 90 controls the exciting magnetic field (step S15). Thereby, the brushless motor 10 transmits the produced auxiliary steering torque to the speed reducer 92.

  As described above, the ECU 90 as the control means performs demagnetization magnetic field control that controls demagnetization to reduce the amount of magnetic flux of the low coercive force portion 26 when the rotor yoke 22 rotates by external force without exciting the stator core 31. Perform steps.

  For example, in a state where the amount of magnetic flux of the low coercive force portion 26 is reduced, the amount of magnetic flux interlinking from the rotor yoke 22 in which the magnet 23 is embedded to the stator core 31 is reduced. For this reason, the hysteresis loss is reduced when the magnetic domain generated in the stator core 31 changes its direction. The hysteresis loss becomes a factor of increase in loss torque when the brushless motor 10 runs idle. That is, with the above configuration, the electric power steering device 80 can reduce the frictional force with respect to the rotation of the rotor 20 when the rotor 20 is rotated in a state where the excitation coil 37 is not energized. As a result, the electric power steering apparatus 80 according to the first embodiment can suppress an increase in loss torque when the brushless motor 10 is idling.

(Embodiment 2)
FIG. 8 is a flowchart for explaining control steps of the brushless motor according to the second embodiment. In the brushless motor 10 according to the second embodiment, the ECU 90 controls the demagnetizing magnetic field according to the rotational speed of the rotor 20. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 8, the ECU 90 described above calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted electric power generates an exciting magnetic field, and the ECU 90 executes a first exciting magnetic field control step for controlling the exciting magnetic field (step S21).

  FIG. 9 is an explanatory diagram illustrating a relationship between the rotation speed and torque of the brushless motor according to the second embodiment. In FIG. 9, the rotational speed of the rotor 20 is plotted on the horizontal axis and the torque of the rotor 20 is plotted on the vertical axis, and the torque rotational speed curve Tn1 in which the low coercive force portion 26 is magnetized and the low coercive force portion 26 are demagnetized. A torque rotation speed curve Tn2 is illustrated. For example, the rotation speed at the intersection of the torque rotation speed curve Tn1 and the torque rotation speed curve Tn2 is set as a threshold value P, a region where the rotation is lower than the threshold value P is MN, and a region where the rotation is higher than the threshold value P is NF.

  In step S21 described above, the low coercive force portion 26 is magnetized. For this reason, when the rotational speed increases as shown in the torque rotational speed curve Tn1, the induced voltage generated in the excitation coil 37 and the power supply voltage due to the rotation of the rotor 20 reach the upper limit of the balanced rotational speed. Therefore, the ECU 90 calculates the rotational speed based on the detection information of the rotational position of the rotor 20 from the resolver 14, and monitors whether the rotor 20 is equal to or higher than the predetermined threshold value P shown in FIG.

  When the rotor 20 rotates at a rotation speed lower than the rotation speed of the predetermined threshold value P shown in FIG. 9 (step S22, No), the ECU 90 returns the process to step S21 and continues the control of the excitation magnetic field. When the rotor 20 rotates at a high rotational speed equal to or higher than the rotational speed of the predetermined threshold P shown in FIG. 9 (step S22, Yes), the ECU 90 advances the process to step S23.

  In step S23, the ECU 90 supplies power to the brushless motor 10 so that the exciting coil 37 generates a demagnetizing magnetic field so as to reduce the magnetic flux amount of the low coercive force portion 26 described above. Thereby, the ECU 90 executes a demagnetizing magnetic field control step for controlling the demagnetizing magnetic field (step S23). The demagnetizing magnetic field is preferably a magnetic field that does not reduce the amount of magnetic flux of the high coercive force portion 27 but reduces the amount of magnetic flux of the low coercive force portion 26.

  Next, the ECU 90 calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted electric power generates an exciting magnetic field, and the ECU 90 executes a second exciting magnetic field control step for controlling the exciting magnetic field (step S24).

  As shown in FIG. 9, when the amount of magnetic flux of the low coercive force portion 26 is reduced, the rotor 20 shows the behavior of the torque rotation speed curve Tn2. For this reason, the possibility that the induced voltage reaches the upper limit of the power supply voltage is suppressed, and the possibility that the torque as the output is significantly reduced can be reduced. Next, the ECU 90 calculates the rotational speed based on the detection information of the rotational position of the rotor 20 from the resolver 14 and monitors whether the rotor 20 is equal to or higher than the predetermined threshold value P shown in FIG. .

  When the rotor 20 rotates at a high rotational speed equal to or higher than the rotational speed of the predetermined threshold P shown in FIG. 9 (No at Step S25), the ECU 90 returns the process to Step S23 and continues the control of the excitation magnetic field. The ECU 90 advances the process to step S25 when the rotor 20 rotates at a rotation speed lower than the rotation speed of the predetermined threshold P shown in FIG. 9 (step S25, Yes).

  In step S26, the ECU 90 supplies power to the brushless motor 10 so that the exciting coil 37 generates a magnetizing magnetic field so as to increase the amount of magnetic flux of the low coercive force portion 26 described above. Thereby, ECU90 performs the magnetization magnetic field control step which controls a magnetization magnetic field (step S26).

  Next, the ECU 90 proceeds with the process to step S27. The ECU 90 calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted electric power generates an exciting magnetic field, and the ECU 90 executes a third exciting magnetic field control step for controlling the exciting magnetic field (step S27). As shown in FIG. 9, when the amount of magnetic flux of the low coercive force portion 26 is increased, the rotor 20 shows the behavior of the torque rotation speed curve Tn1. Thereby, the brushless motor 10 transmits the produced auxiliary steering torque to the speed reducer 92.

  As described above, the ECU 90 serving as the control means, when the induced voltage of the exciting coil 37 is equal to or higher than the threshold value P of the rotational speed of the brushless motor 10 determined so as not to reach the upper limit of the power supply voltage, the low coercive force portion 26. A demagnetizing magnetic field control step for performing demagnetizing control for reducing the magnetic flux amount of the magnetic field is executed.

  With the above configuration, the amount of magnetic flux interlinked from the rotor yoke 22 in which the magnet 23 is embedded to the stator core 31 is suppressed, and the amount of magnetic flux acting on the exciting coil 37 is reduced. For this reason, the amount of magnetic flux acting on the exciting coil 37 is reduced, so that there is a margin of increase in the induced voltage. In a permanent magnet rotary motor such as the brushless motor 10 described above, the induced voltage increases in proportion to the rotational speed of the rotor 20. Therefore, the brushless motor 10 can increase the maximum rotation speed determined by the balance between the induced voltage and the power supply voltage. As a result, the electric power steering device 80 of the second embodiment can suppress the possibility that the induced voltage reaches the power supply voltage in the high rotation region, and can expand the variable speed region of the rotor.

(Embodiment 3)
FIG. 10 is a flowchart for explaining control steps of the brushless motor according to the third embodiment. In the brushless motor 10 of the third embodiment, the ECU 90 controls the demagnetizing magnetic field according to the change in the rotation direction of the rotor 20. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 10, the ECU 90 described above calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted power generates an exciting magnetic field, and the ECU 90 controls the exciting magnetic field in the forward direction (step S31).

  Further, it may be necessary to reverse the direction of the auxiliary steering torque that assists the output shaft 82b of the steering column in accordance with the rotation direction of the steering shaft 82. When the rotation direction of the rotor 20 in the assist command is the forward direction, that is, not the reverse direction (step S32, No), the ECU 90 returns the process to step S31 and continues the control of the excitation magnetic field in the forward direction. ECU90 advances a process to step S33, when the rotation direction of the rotor 20 in an assist command is a reverse direction (step S32, Yes).

  In step S33, the ECU 90 supplies power to the brushless motor 10 so that the excitation coil 37 generates a demagnetizing magnetic field so as to reduce the magnetic flux amount of the low coercive force portion 26 described above. As a result, the ECU 90 controls the demagnetizing magnetic field (step S33). The demagnetizing magnetic field is preferably a magnetic field that does not reduce the amount of magnetic flux of the high coercive force portion 27 but reduces the amount of magnetic flux of the low coercive force portion 26.

  Since the amount of magnetic flux of the low coercive force portion 26 is reduced, the segment magnet 23A, the segment magnet 23B, the segment magnet 23C, and the segment magnet 23D can reduce the amount of magnetic flux that affects the stator core 31. Then, the back electromotive force generated in the exciting coil 37 is reduced, and the electromagnetic brake shock applied to the rotor 20 by the exciting coil 37 is reduced. As a result, it is possible to suppress the influence of the steering on the feeling of steering. Next, the ECU 90 proceeds with the process to step S34.

  In step S34, the ECU 90 supplies power to the brushless motor 10 so that the exciting coil 37 generates a magnetizing magnetic field so as to increase the amount of magnetic flux of the low coercive force portion 26 described above. As a result, the ECU 90 controls the magnetization magnetic field (step S34).

  Next, the ECU 90 calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted power generates an exciting magnetic field, and the ECU 90 controls the exciting magnetic field in the reverse direction (step S35). Thereby, the brushless motor 10 transmits the produced auxiliary steering torque to the speed reducer 92. The brushless motor 10 according to the third embodiment describes an example in which the ECU 90 controls the demagnetizing magnetic field according to the case where the rotation direction of the rotor 20 changes from the forward direction to the reverse direction. In the brushless motor 10 according to the third embodiment, the ECU 90 can control the demagnetizing magnetic field in accordance with a case where the rotation direction of the rotor 20 changes from the reverse direction to the forward direction.

  As described above, the ECU 90 serving as the control means executes a demagnetizing magnetic field control step for performing demagnetization control for reducing the magnetic flux amount of the low coercive force portion 26 before rotating the brushless motor 10 in the reverse direction.

  When the brushless motor 10 is reversely rotated, an induced voltage (counterelectromotive voltage) is instantaneously applied to the drive circuit of the motor, which may cause a load on the drive circuit. With the above configuration, since the induced voltage can be reduced by the amount of magnetic flux acting on the exciting coil 37, the induced voltage (counterelectromotive voltage) is lowered and applied to the motor drive circuit, causing a load on the drive circuit. Reduce fear.

  Further, when the brushless motor 10 is rotated in the reverse direction, a reverse operation torque may be generated in the rotor 20, which may affect the steering feeling received by the steering person. With the above configuration, the induced voltage can be reduced by the amount of magnetic flux acting on the exciting coil 37, so that the induced voltage (counterelectromotive voltage) is reduced and the reverse operating torque is reduced in the rotor 20. As a result, it is possible to suppress the possibility of affecting the steering feeling received by the steering person.

(Embodiment 4)
FIG. 11 is a flowchart for explaining control steps of the brushless motor according to the fourth embodiment. In the brushless motor 10 according to the fourth embodiment, the ECU 90 periodically controls the magnetizing magnetic field. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 11, the ECU 90 described above calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted electric power generates an exciting magnetic field, and the ECU 90 controls the exciting magnetic field (step S41).

  The ECU 90 measures the elapsed time in step S41. If the elapsed time has not reached the predetermined time (No in step S42), the ECU 90 returns the process to step S41 and continues the control of the excitation magnetic field. If the elapsed time reaches a certain time (step S42, Yes), the ECU 90 advances the process to step S43.

  In step S43, the ECU 90 supplies power to the brushless motor 10 so that the exciting coil 37 generates a magnetizing magnetic field so as to increase the amount of magnetic flux of the low coercive force portion 26 described above. Thereby, ECU90 performs the magnetization magnetic field control step which controls a magnetization magnetic field (step S43). Thereby, the possibility that the coercive force of the low coercive force portion 26 having a relatively low coercive force may cause unintentional demagnetization can be reduced.

  If the process is not terminated (No at Step S44), the ECU 90 returns the process to Step S41 and continues the control of the excitation magnetic field. ECU90 complete | finishes a process, when complete | finishing a process (step S44, Yes).

  As described above, the ECU 90, which is a control unit, periodically executes a magnetization magnetic field control step for performing magnetization control for increasing the amount of magnetic flux of the low coercive force portion 26.

  With the above configuration, the electric power steering device 80 can suppress the risk of insufficient magnetic flux due to unintentional demagnetization of the low coercive force portion 26. For this reason, the electric power steering apparatus 80 can improve the driving reliability when torque is required in a so-called low-speed rotation region.

(Embodiment 5)
FIG. 12 is a flowchart for explaining control steps of the brushless motor according to the fifth embodiment. In the brushless motor 10 of the fifth embodiment, the ECU 90 controls the magnetizing magnetic field when the low coercive force portion 26 performs demagnetization unintentionally. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 12, the ECU 90 described above calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted electric power generates an exciting magnetic field, and the ECU 90 controls the exciting magnetic field (step S51).

  The ECU 90 measures the induced voltage of the exciting coil 37, reaches a predetermined induced voltage, and when the coercive force of the low coercive force portion 26 is not demagnetized unintentionally (No in step S52), processing is performed. Is returned to step S51, and the control of the excitation magnetic field is continued. When the induced voltage of the exciting coil 37 does not reach the predetermined induced voltage and the coercive force of the low coercive force portion 26 is unintentionally demagnetized (step S52, Yes), that is, the ECU 90 When the demagnetization control for reducing the magnetic flux amount of the low coercive force portion 26 is not performed, when the coercive force portion 26 is demagnetized, the process proceeds to step S53.

  In step S53, the ECU 90 supplies power to the brushless motor 10 so that the exciting coil 37 generates a magnetizing magnetic field so as to increase the amount of magnetic flux of the low coercive force portion 26 described above. Thereby, ECU90 performs the magnetization magnetic field control step which controls a magnetization magnetic field (step S53). Thereby, the possibility that the coercive force of the low coercive force portion 26 having a relatively low coercive force may cause unintentional demagnetization can be reduced.

  If the process is not terminated (No at Step S54), the ECU 90 returns the process to Step S51 and continues the control of the excitation magnetic field. ECU90 complete | finishes a process, when complete | finishing a process (step S54, Yes).

  As described above, the ECU 90, which is the control means, controls the magnetization to increase the amount of magnetic flux of the low coercive force portion 26 when the control means determines that the low coercive force portion 26 is unintentionally demagnetized. A magnetizing magnetic field control step is performed.

  With the above configuration, the electric power steering device 80 can suppress the risk of insufficient magnetic flux due to unintentional demagnetization of the low coercive force portion 26. For this reason, the electric power steering apparatus 80 can improve the driving reliability when torque is required in a so-called low-speed rotation region.

(Embodiment 6)
FIG. 13 is a flowchart for explaining control steps of the brushless motor according to the sixth embodiment. In the brushless motor 10 of the sixth embodiment, the ECU 90 controls the demagnetizing magnetic field when there is a possibility that the excitation coil 37 is short-circuited. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 13, the ECU 90 described above calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted electric power generates an exciting magnetic field, and the ECU 90 executes a first exciting magnetic field control step for controlling the exciting magnetic field (step S61).

  The ECU 90 measures the resistance value of the exciting coil 37. If the resistance value is within a predetermined range and there is no possibility of short-circuiting of the exciting coil 37 (No in step S62), the process returns to step S61, and the exciting magnetic field Continue control. If the resistance value of the exciting coil 37 is not a resistance value within a predetermined range and there is a possibility that the exciting coil 37 is short-circuited (step S62, Yes), the ECU 90 advances the process to step S63.

  In step S33, the ECU 90 supplies power to the brushless motor 10 so that the excitation coil 37 generates a demagnetizing magnetic field so as to reduce the magnetic flux amount of the low coercive force portion 26 described above. Thereby, the ECU 90 executes a demagnetizing magnetic field control step for controlling the demagnetizing magnetic field (step S63). The demagnetizing magnetic field is preferably a magnetic field that does not reduce the amount of magnetic flux of the high coercive force portion 27 but reduces the amount of magnetic flux of the low coercive force portion 26.

  Since the amount of magnetic flux of the low coercive force portion 26 is reduced, the segment magnet 23A, the segment magnet 23B, the segment magnet 23C, and the segment magnet 23D can reduce the amount of magnetic flux that affects the stator core 31. Then, the back electromotive force generated in the exciting coil 37 is reduced, and the electromagnetic brake shock applied to the rotor 20 by the exciting coil 37 is reduced. As a result, it is possible to suppress the influence of the steering on the feeling of steering. Next, the ECU 90 proceeds with the process to step S64 and step S65.

  In step S64, the ECU 90 warns the driver that there is a possibility that the exciting coil 37 may be short-circuited with a display or a warning sound. The ECU 90 calculates an assist steering command value of the assist command based on the steering torque T and the traveling speed V. Then, the ECU 90 adjusts the power value supplied to the brushless motor 10 based on the calculated auxiliary steering command value. The exciting coil 37 supplied with the adjusted electric power generates an exciting magnetic field, and the ECU 90 executes a second exciting magnetic field control step for controlling the exciting magnetic field (step S65).

  As described above, the ECU 90 serving as the control means executes a demagnetizing magnetic field control step for performing demagnetization control for reducing the magnetic flux amount of the low coercive force portion 26 when the exciting coil 37 is short-circuited.

  With the above configuration, the electric power steering device 80 can continue to drive the brushless motor 10 in a state where the influence of the short circuit of the exciting coil 37 is suppressed. For this reason, the relay circuit for suppressing the influence of the short of the exciting coil 37 becomes unnecessary, and the electric power steering device 80 can reduce the manufacturing cost. Further, when there is a relay circuit, the electric power steering device 80 can reduce the magnetic flux amount of the magnet interlinked with the short coil even in a non-energized state during operation of the relay circuit. For this reason, the electric power steering apparatus 80 can reduce the electromagnetic brake torque and rotate the brushless motor 10 by an external force.

  As described above, the motor control device of the electric power steering apparatus according to the present embodiment has been described by taking the column assist method as an example, but can also be applied to the pinion assist method and the rack assist method.

DESCRIPTION OF SYMBOLS 10 Brushless motor 11 Housing 11a Tubular housing 11b Front bracket 11c Bottom part 11d Inner peripheral surface 12, 13 Bearing 14 Resolver 14a Resolver rotor 14b Resolver stator 15 Terminal block 20 Rotor 21 Shaft 22 Rotor yoke 23 Magnet 30 Stator 31 Stator core 32 Divided core 33 Yoke 34 Teeth 37 Exciting coil 37a Insulator 80 Electric power steering device 81 Steering wheel 82 Steering shaft 82a Input shaft 82b Output shaft 83 Steering force assist mechanism 84, 86 Universal joint 85 Lower shaft 87 Pinion shaft 88 Steering gear 88a Pinion 88b Rack 89 Tie rod 90 ECU
91a Torque sensor 91b Vehicle speed sensor 92 Deceleration device 93 Deceleration device housing 94 Worm 94a Worm tooth 95a, 95b Ball bearing 96 Worm wheel 96a Worm wheel tooth 97 Holder 98 Ignition switch 99 Power supply Zr Central shaft

Claims (16)

Rotor yoke,
A stator core disposed annularly with a gap outside the rotor yoke;
Including a low coercivity portion and a high coercivity portion having a coercivity higher than that of the low coercivity portion, and a magnet embedded in the rotor yoke such that the low coercivity portion is closer to the gap than the high coercivity portion;
An exciting coil that excites the stator core and generates a magnetic field for changing the amount of magnetic flux of the low coercive force portion;
An electric motor comprising: A rotor yoke, a stator core arranged annularly with a gap outside the rotor yoke, a low coercivity portion, and a high coercivity portion having a higher coercivity than the low coercivity portion, and the low coercivity portion A magnet embedded in the rotor yoke so as to be closer to the gap than the high coercive force portion, and an exciting coil that excites the stator core and generates a magnetic field for changing the amount of magnetic flux of the low coercive force portion. Including an electric motor,
Control means for controlling energization of the exciting coil;
An electric motor control device comprising:   3. The motor control device according to claim 2, wherein the control unit performs demagnetization control to reduce a magnetic flux amount of the low coercive force portion when the rotor yoke rotates by an external force in a state where the stator core is not excited.   If the demagnetizing control is not performed when the demagnetizing control is performed to reduce the amount of magnetic flux of the low coercive force portion, the control means may increase the amount of magnetic flux of the low coercive force portion. The electric motor control device according to claim 2 or 3, wherein the control is performed.   The motor control device according to any one of claims 2 to 4, wherein the control unit periodically increases the amount of magnetic flux of the low coercive force portion.   The motor control device according to any one of claims 2 to 5, wherein the control means reduces the amount of magnetic flux of the low coercive force portion when the excitation coil is short-circuited.   The control means reduces the amount of magnetic flux of the low coercive force portion when the induced voltage of the exciting coil is equal to or greater than a threshold value of the rotation speed of the electric motor determined so as not to reach the upper limit of the power supply voltage. The electric motor control device according to claim 6.   The motor control device according to any one of claims 2 to 7, wherein the control means reduces the amount of magnetic flux of the low coercive force portion before the motor is reversely rotated.   The motor control device according to claim 2, wherein the electric motor is an electric power steering electric motor that obtains an auxiliary steering torque. An electric power steering motor for obtaining an auxiliary steering torque, and a control means for controlling the electric power steering motor;
The electric power steering motor includes a rotor yoke, a stator core disposed in an annular shape with a gap outside the rotor yoke, a low coercive force portion, and a high coercive force portion having a higher coercive force than the low coercive force portion. Including a magnet embedded in the rotor yoke such that the low coercive force portion is closer to the gap than the high coercive force portion, and a magnetic field for exciting the stator core and changing the amount of magnetic flux of the low coercive force portion An electric power steering device comprising: an exciting coil for generating   The control means performs demagnetization control for reducing the amount of magnetic flux of the low coercive force portion when the rotor yoke rotates in a state where the auxiliary steering torque is unnecessary and the stator core is not excited. The electric power steering apparatus as described.   If the demagnetizing control is not performed when the demagnetizing control is performed to reduce the amount of magnetic flux of the low coercive force portion, the control means may increase the amount of magnetic flux of the low coercive force portion. The electric power steering apparatus according to claim 10 or 11, wherein the control is performed.   The electric power steering apparatus according to any one of claims 10 to 12, wherein the control unit periodically increases the amount of magnetic flux of the low coercive force portion.   The electric power steering apparatus according to any one of claims 10 to 13, wherein the control means reduces the amount of magnetic flux of the low coercive force portion when the exciting coil is short-circuited.   The control means reduces the amount of magnetic flux of the low coercive force portion when the induced voltage of the exciting coil is equal to or greater than the threshold value of the rotational speed of the electric power steering motor determined so as not to reach the upper limit of the power supply voltage. The electric power steering device according to any one of claims 10 to 14.   The electric power steering apparatus according to any one of claims 10 to 15, wherein the control means reduces the amount of magnetic flux of the low coercive force portion before rotating the electric motor in the reverse direction.

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