JP2008141803A - Brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brushless motor in which generation of loss torque is restrained or suppressed without connecting the winding of each phase in series. <P>SOLUTION: The brushless motor 6 has a rotor 65 including ten permanent magnets 651a-651j, and a stator 61 including twelve tees (salient poles) 611a-611l around which twelve windings 612a-612l are wound one by one. The twelve windings include two winding groups for every phase each consisting of the same number of windings connected in series and connected in parallel such that the magnitude and the phase of respective induced voltages substantially match each other. With such connection, generation of a circulating current can be restrained. Furthermore, generation of loss torque is restrained or suppressed in the brushless motor 6 by reducing the impedance of the motor through an arrangement of ten pole twelve slot, and cogging is also suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a brushless motor including a permanent magnet for forming a field, and more particularly to a brushless motor used in an electric power steering apparatus that applies a steering assist force to a steering mechanism of a vehicle.

  2. Description of the Related Art Conventionally, there has been used an electric power steering device that applies a steering assist force to a steering mechanism by driving an electric motor such as a brushless motor in accordance with a steering torque applied to a steering wheel (steering wheel) by a driver.

  A brushless motor normally used in such an electric power steering apparatus is a permanent magnet electric motor including a stator (stator) provided with windings (coils) and a rotor (rotor) provided with permanent magnets. However, many are driven by three-phase power.

  In addition, a plurality of stator windings are usually provided for each phase. These windings are typically connected in series for each phase. For example, the number of poles of a permanent magnet (hereinafter simply referred to as “the number of poles”) is 8, and the number of salient poles (teeth) provided on the stator (stator) (this number is equal to the number of gaps between salient poles). Some conventional electric motors used in an electric power steering apparatus having 9 (hereinafter also referred to as “slot number”) have a configuration in which three windings are connected in series for each phase (Patent Document) 1).

However, in the configuration in which the windings are connected in series as in the above-described conventional electric motor, since the connecting wire becomes long, the impedance increases, and as a result, the copper loss increases. Therefore, there is a conventional electric motor in which a plurality of windings are connected in parallel for each phase. FIG. 6 is a circuit diagram showing the connection of the U-phase winding in the conventional 10-pole 12-slot electric motor having the windings connected in this manner. As shown in FIG. 6, the first to fourth coils 901 to 904 as four U-phase windings have one end connected to the U-phase terminal 910 and the other end connected to the middle of each phase. It is connected to a neutral point terminal 920 that is a sex point.
JP 2001-275325 A

However, when parallel connections are made as shown in FIG. 6, a loss (loss torque) that does not occur when connecting in series occurs. That is, when the induced voltage in the first coil 901 is Ec1 = sin (θ), the induced voltages Ec2 to Ec4 in the second to fourth coils 902 to 904 are expressed by the following equations (1) to (3). Can be expressed as
Ec2 = sin (θ−π / 6) (1)
Ec3 = sin (θ) (2)
Ec4 = sin (θ−π / 6) (3)

  Thus, since the induced voltage has a phase shift of π / 6 between the first coil 901 and the second coil 902 and between the third coil 903 and the fourth coil 904, these Currents I1 and I2 (that is, circulating currents) shown in FIG. Such circulating current generates a loss torque of the electric motor. As a result, operation feeling such as deterioration of steering wheel return in the electric power steering apparatus is reduced.

  Further, when the number of poles of the permanent magnet is increased as described above, the width of the salient pole (tooth) is relatively narrow, so that the rigidity is lowered and noise and vibration of the electric motor may be generated. Focusing only on this point, it is preferable to increase the width of the salient pole (teeth), but generally the inductance of the electric motor increases as the magnetic flux density of the salient pole (tooth) decreases. A motor with a large inductance has a large copper loss, which causes the electric motor to generate heat and generate a loss torque. As in the case where the circulating current is generated, an operation such as an insufficient assist force in the electric power steering device results. The feeling is reduced.

  Therefore, an object of the present invention is to provide a brushless motor that suppresses or suppresses the generation of loss torque without connecting windings of respective phases in series, and an electric power steering apparatus including the brushless motor.

According to a first aspect of the present invention, there is provided an annular stator including a plurality of Y-connected windings driven by three-phase power, and an inner side of the stator that is rotatably supported with respect to the stator. A brushless motor comprising a rotor including a permanent magnet that forms a plurality of poles in the circumferential direction,
The stator is
The plurality of windings are provided one by one, and a plurality of teeth portions of the same size disposed at equal intervals along the circumferential direction so as to protrude toward the rotor,
An annular yoke portion to which the plurality of teeth portions are coupled,
The plurality of windings are a plurality of winding groups composed of the same number of windings connected in series, and the plurality of winding groups selected so that the magnitudes and phases of the induced voltages substantially coincide with each other. Connected in parallel and included for each phase,
The number of poles of the permanent magnet is less than the number of the tooth portions provided with a multiple of 3 that is 9 or more and more than 2/3 of the number of the tooth portions.

According to a second invention, in the first invention,
The plurality of winding groups are provided in the same number as one of the divisors of the absolute value of the difference between the number of the tooth portions and the number of poles formed by the permanent magnet.

According to a third invention, in the first invention,
Twelve teeth portions are provided,
The permanent magnet forms ten poles.

4th invention is equipped with the brushless motor as described in 1st invention,
Thus, a steering assist force is applied to the steering mechanism of the vehicle.

  According to the first aspect of the present invention, the number of poles of the permanent magnet is less than the number of teeth portions, so that the impedance can be reduced, and the number of poles of the permanent magnet is greater than 2/3 of the number of teeth portions. Thus, cogging can be suppressed. In addition, the plurality of windings is a winding group composed of the same number of windings connected in series, and the plurality of winding groups selected so that the magnitudes and phases of the respective induced voltages substantially coincide with each other. By connecting and including for each phase, generation of circulating current can be suppressed. As described above, generation of loss torque can be suppressed or suppressed, and cogging can be suppressed.

  According to the second aspect of the invention, the winding group is provided in the same number as one of the divisors of | (number of teeth portions−number of poles of permanent magnet) |, so that generation of circulating current is suppressed. And the generation of loss torque can be suppressed or suppressed.

  According to the third aspect of the present invention, in a practical brushless motor, the generation of loss torque can be particularly suppressed or suppressed, and cogging can be suppressed.

  According to the fourth aspect, it is possible to provide an electric power steering apparatus including a brushless motor that exhibits the same effect as the first aspect.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
<1. Overall configuration>
FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus according to an embodiment of the present invention, together with a vehicle configuration related thereto. This electric power steering apparatus includes a steering shaft 102 having one end fixed to a handle (steering wheel) 100 as an operation means for steering, a rack and pinion mechanism 104 connected to the other end of the steering shaft 102, a handle The steering angle sensor 2 for detecting the steering angle indicating the rotational position of 100, the torque sensor 3 for detecting the steering torque applied to the steering shaft 102 by the operation of the handle 100, and the driver's load in the steering operation (steering operation). A brushless motor 6 that generates a steering assist force to reduce, a reduction gear 7 that transmits the steering assist force to the steering shaft 102, and a power supply from an in-vehicle battery 8 via an ignition switch 9, and a steering angle sensor 2, torque sensor 3, vehicle speed sensor Based on the sensor signals from and an electronic control unit (ECU) 5 for controlling the driving of the brushless motor 6.

  When the driver operates the steering wheel 100 in a vehicle equipped with such an electric power steering device, the steering torque by the operation is detected by the torque sensor 3 and the steering angle is detected by the steering angle sensor 2, and the detected steering is detected. The brushless motor 6 is driven by the ECU 5 based on the torque and the steering angle and the vehicle speed detected by the vehicle speed sensor 4. As a result, the brushless motor 6 generates a steering assist force, and this steering assist force is applied to the steering shaft 102 via the reduction gear 7, thereby reducing the driver's load in the steering operation. That is, the sum of the steering torque applied by the steering operation and the torque due to the steering assist force generated by the brushless motor 6 is given to the rack and pinion mechanism 104 via the steering shaft 102 as the output torque. Thus, when the pinion shaft rotates, the rotation is converted into a reciprocating motion of the rack shaft by the rack and pinion mechanism 104. Both ends of the rack shaft are connected to a wheel 108 via a connecting member 106 composed of a tie rod and a knuckle arm, and the direction of the wheel 108 changes according to the reciprocating motion of the rack shaft.

<2. Configuration of brushless motor>
FIG. 2 is a vertical sectional view with respect to the rotation axis of the brushless motor 6. As shown in FIG. 2, the brushless motor 6 has a rotor (rotor) 65 that rotates around a motor shaft 66 that is a rotating shaft and a narrow gap (air gap) that surrounds the rotor 65. And a stator (stator) 61 provided.

  The rotor 65 has ten poles in the circumferential direction by arranging ten permanent magnets 651a to 651j in the circumferential direction. These permanent magnets 651a to 651j are rare earth neodymium magnets that are magnetized in the radial direction (direction perpendicular to the rotation axis), and are arranged so that N poles and S poles are alternately arranged in the circumferential direction. It has been. As described above, the number of poles of the permanent magnet is simply referred to as “number of poles”.

  The stator 61 includes a cylindrical yoke 615 and 12 teeth (saliency poles) 611a to 611l provided so as to protrude from the inner peripheral surface of the yoke 615 toward the motor shaft 66. Corresponding windings 612a to 612l are wound around these teeth 611a to 611l, and a predetermined current flows through these windings, so that the stator 61 has 12 poles in the circumferential direction. As described above, the number of teeth (that is, the number of windings) corresponding to the number of poles of the stator 61 is referred to as “slot number”. Therefore, the brushless motor 6 is a 10-pole 12-slot motor and has a feature that the number of slots is larger than the number of poles.

  Here, the windings 612a to 612l are appropriately connected to a three-phase power source (not shown) so that four sets of four windings are specifically driven by U-phase, V-phase, or W-phase power. Yes. Here, as will be described later, the Y connection method is adopted. The three-phase power source controls the rotation of the brushless motor 6 by, for example, outputting a pulse width modulation (PWM) signal that is a voltage signal whose pulse width is controlled corresponding to each phase. In addition, since the structure of such a winding is known except the connection (connection relation) for each phase of the winding devised so as to suppress or suppress the generation of loss torque, Detailed description will be omitted, and the wiring connection specific to the brushless motor 6 will be described below with reference to FIG. The three sets of windings corresponding to the three phases are Y-connected as described above, and the windings of each set are referred to as a U-phase winding, a V-phase winding, and a W-phase winding, respectively. .

  FIG. 3 is a circuit diagram showing the connection of the U-phase winding in the brushless motor 6 having 10 poles and 12 slots. As shown in FIG. 3, among the four first to fourth windings 612a to 612d functioning as U-phase windings, the first and second windings 612a and 612b are connected in series, and The third and fourth windings 612c and 612d are connected in series, and the two windings connected in series are connected in parallel. One end of each of the first and third windings 612a and 612c is connected to a neutral point terminal 614 that is a neutral point of each phase, and one end of each of the second and fourth windings 612b and 612d is U The phase terminal 613 is connected. By connecting the windings in this way, the impedance can be made smaller than the conventional connection in which all the windings are connected in series, and as a result, the copper loss can be reduced.

Moreover, even if it connects in this way, the loss torque by a circulating current does not arise. That is, when the induced voltage in the first winding 612a is E1 = sin (θ), the induced voltages E2 to E4 in the second to fourth windings 612b to 612d are expressed by the following equations (4) to (6). It can be expressed as
E2 = sin (θ−π / 6) (4)
E3 = sin (θ) (5)
E4 = sin (θ−π / 6) (6)

  Accordingly, the magnitude and phase of the voltage (E1 + E2) across the first and second windings 612a and 612b connected in series are the same as both ends of the third and fourth windings 612c and 612d connected in series. Therefore, there is no circulating current between these windings because it matches the magnitude and phase of the voltage (E3 + E4). Therefore, since the loss torque of the brushless motor is not generated by the circulating current, it is possible to prevent a decrease in operation feeling such as deterioration of the steering wheel return in the electric power steering apparatus.

  Next, with reference to FIG. 4, it will be described that the impedance of a brushless motor having a smaller number of poles than the number of slots is smaller than that of a brushless motor having a larger number of poles than the number of slots together with the detailed configuration of the windings.

  FIG. 4 is an enlarged view of main portions of the yoke and teeth in the brushless motor. As shown in FIG. 4, for example, a winding 612a is wound around the teeth 611a. More specifically, a winding 612a is wound around a cylindrical bobbin having a jaw at the bottom, a winding restraining plate is press-fitted into the tip of the bobbin, and the bobbin around which the winding 612a is wound is attached to the teeth 611a. By inserting, the winding 612a is wound around the teeth 611a. In this manner, the windings 612a to 612l are wound around the teeth 611a to 611l. Such a concentrated winding method is also called salient pole winding. In this way, by performing concentrated winding without performing distributed winding that is distributed in a plurality of slots, it is possible to eliminate almost no winding portion that does not form an effective magnetic flux, thereby reducing copper loss.

  As can be seen from FIG. 4, the brushless motor 6 has 10 poles and 12 slots and has a smaller number of poles than the number of slots. Therefore, the density of magnetic flux passing through one tooth increases. Therefore, since the magnetic flux density of the teeth increases, the inductance decreases and the impedance decreases. Since the motor having such a small impedance has a small copper loss, loss torque due to heat generation can be suppressed.

  However, to suppress cogging of the permanent magnet motor (specifically, to reduce the magnitude of cogging torque and its fluctuation range), set those values so that the least common multiple of the number of slots and the number of poles increases. It is known to be effective. In this regard, the brushless motor 6 has 10 poles and 12 slots and the least common multiple is sufficiently large, so that cogging can be suppressed. However, it is suitable for suppressing cogging while suppressing or suppressing the generation of loss torque. A combination of the number of slots and the number of poles will be described with reference to FIG.

  FIG. 5 is a diagram showing a combination of the preferred number of poles and number of slots. The crosses shown in FIG. 5 are combinations of the number of poles and the number of slots, which are known to have high efficiency but have a large effect of cogging, and specifically, the ratio between the number of poles and the number of slots (ie, The number of poles: the number of slots) is 2: 3 or 4: 3. Also, the circles shown in FIG. 5 are combinations in a practical brushless motor that is known to have a relatively small cogging. Furthermore, the symbol 印 shown in FIG. 5 is a combination of the number of poles and the number of slots in the brushless motor 6.

  Referring to FIG. 5, the upper limit and the lower limit of the combination indicated by the circles are substantially the same as the combination indicated by the crosses. In other words, the number of poles in the combination indicated by a circle is driven by three-phase power, and is more than 2/3 of the number of slots that is a multiple of 3, and less than 4/3.

  However, in order to suppress or suppress the generation of loss torque due to heat generation by reducing the impedance of the brushless motor, it is preferable to reduce the number of poles as compared with the number of slots as described above. The number of poles in the combination is greater than 2/3 of the number of slots and less than the number of slots. If the number of poles and the number of slots are the same, the rotor does not rotate, so there is no need to consider.

  Here, a combination of the number of poles and the number of slots capable of suppressing the generation of loss torque due to the circulating current flowing between the windings will be considered. First, when the number of slots is 9 (that is, when the ratio is 8: 9), when the phase of the induced voltage generated for one of the three windings in a certain phase is 0 °, The phases of the induced voltages generated for the remaining two windings at -20 are -20 ° and + 20 °, respectively. Therefore, all three windings must be connected in series in order to prevent the generation of circulating current. When the ratio is 10: 9, the number of poles is larger than the number of slots, so it is not considered here.

  Next, when the number of slots is 12 (that is, when the ratio is 10:12), when the phase of the induced voltage generated for one of the four windings in one phase is 0 °, The phases of the induced voltages generated for the remaining three windings in the phase are + 30 °, 0 ° and + 30 °, respectively. Therefore, in order to prevent the generation of circulating current, all these windings are connected in series, or one winding whose phase is 0 ° and one winding whose phase is + 30 ° are connected. It can be considered that one set connected in series is connected in parallel with one set connected in series with the remaining windings. The connection connected in parallel is the connection in the brushless motor 6 as shown in FIG.

  Subsequently, when the number of slots is 15 (that is, when the ratio is 14:15), when the phase of the induced voltage generated for one of the five windings in one phase is 0 °, The phases of the induced voltages generated for the remaining four windings in the phase are + 12 °, −12 °, + 24 ° and −24 °, respectively. Therefore, in order to prevent the generation of circulating current, all these multiple windings must be connected in series.

  When the number of slots is 21 (that is, when the ratio is 20:21), when the phase of the induced voltage generated for one of the seven windings in a certain phase is 0 °, The phases of the induced voltages generated for the remaining six windings at + are + 8.6 °, −8.6 °, + 17.1 °, −17.1 °, + 25.7 °, and −25.7 °, respectively. . Therefore, in order to prevent the generation of circulating current, all these multiple windings must be connected in series.

  Thus, the number of sets of the plurality of windings is to be provided by the same number as one of the divisors of the absolute value of the difference between the number of teeth as the number of slots and the number of poles formed by the permanent magnet. Become. That is, in the case of 8 poles and 9 slots, the divisor is only 1, and the plurality of windings are connected in series, that is, in parallel number 1. The same applies to the case of 14 poles and 15 slots and the case of 20 poles and 21 slots. However, in the case of 10 poles and 12 slots, the above divisors are 1 and 2, and the combinations connected in parallel number 2 all have lower impedance than in the case of connecting in series. Therefore, it can be seen that, among the combinations shown in FIG. 5, the combination in which the number of poles employed in the brushless motor 6 is 10 and the number of slots is 12 is extremely suitable for a practical brushless motor.

<3. Effect>
As described above, in the brushless motor 6, the number of poles of the permanent magnet formed by the ten permanent magnets 651a to 651j is equal to the number of the 12 teeth 611a to 611l (equal to the number of the 12 windings 612a to 612l). If the number is less than the number of teeth, the impedance is reduced, and if the number is more than 2/3 of the number of teeth, cogging can be suppressed. In addition, the windings 612a to 612l are connected in parallel so that the magnitudes and phases of the induced voltages substantially coincide with each other, and the first and second windings 612a and 612b and the third and fourth windings 612c, As shown in 612d, two winding groups, each consisting of the same number of windings connected in series, are connected in parallel so that the magnitude and phase of the induced voltages are substantially the same. By including each, generation | occurrence | production of a circulating current can be suppressed.

  Therefore, the electric power steering apparatus according to this embodiment equipped with the brushless motor 6 in which the generation of the loss torque is suppressed or suppressed and the cogging is suppressed in this way suppresses a decrease in operation feeling such as a deterioration in steering wheel return. Can do.

<4. Modification>
In the above embodiment, the first winding 612a is wound around the tooth 611a, the second winding 612b is wound around the tooth 611b, the third winding 612c is wound around the tooth 611c, and the fourth winding 612d. Is wound around the teeth 611d, but is not limited to this correspondence. For example, the third winding 612c is wound around the teeth 611b, and the second winding 612b is wound around the teeth 611d. It may be a configuration. Further, the second winding 612b is wound around the teeth 611d, the third winding 612c is wound around the teeth 611g, and the fourth winding 612d is wound around the teeth 611j, that is, a winding is provided for each phase. A configuration may be adopted in which the three teeth are wound clockwise in order.

It is the schematic which shows the structure of the electric power steering apparatus which concerns on one Embodiment of this invention with the vehicle structure relevant to it. It is a vertical cross section with respect to the rotating shaft of the brushless motor in the said embodiment. In the brushless motor in the said embodiment, it is a circuit diagram which shows the connection of U phase winding. It is the figure which expanded the principal part of the yoke and teeth of the brushless motor in the said embodiment. In the said embodiment, it is a figure which shows the combination of the number of slots and poles suitable in order to suppress cogging, suppressing or suppressing generation | occurrence | production of loss torque. It is a circuit diagram which shows the connection of U phase winding in the conventional 10 pole 12 slot brushless motor.

Explanation of symbols

2 ... Steering angle sensor 3 ... Torque sensor 4 ... Vehicle speed sensor 5 ... Electronic control unit (ECU)
6 ... Brushless motor 61 ... Stator 65 ... Rotor 66 ... Motor shaft 611a-611l ... Teeth 612a-612l ... Winding 613 ... U-phase terminal 614 ... Neutral point terminal 615 ... Yoke 651a-651j ... Permanent magnet

Claims (4)

An annular stator including a plurality of Y-connected windings driven by three-phase power, and a plurality of stators arranged on the inner side of the stator and rotatably supported by the stator. A brushless motor comprising a rotor including a permanent magnet that forms a pole of
The stator is
The plurality of windings are provided one by one, and a plurality of teeth portions of the same size disposed at equal intervals along the circumferential direction so as to protrude toward the rotor,
An annular yoke portion to which the plurality of teeth portions are coupled,
The plurality of windings are a plurality of winding groups composed of the same number of windings connected in series, and the plurality of winding groups selected so that the magnitudes and phases of the induced voltages substantially coincide with each other. Connected in parallel and included for each phase,
The number of poles of the permanent magnet is smaller than the number of the tooth portions provided with a multiple of 3 that is 9 or more and more than 2/3 of the number of the tooth portions.   The plurality of winding groups are provided in the same number as one of the divisors of absolute values of the difference between the number of teeth and the number of poles formed by the permanent magnet. Item 10. A brushless motor according to item 1. Twelve teeth portions are provided,
The brushless motor of claim 1, wherein the permanent magnet forms 10 poles. The brushless motor according to claim 1.
The electric power steering apparatus according to claim 1, wherein the brushless motor is driven in accordance with an operation by an operation means for steering the vehicle to apply a steering assist force to a steering mechanism of the vehicle.

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