JPWO2008050637A1 - Brushless motor - Google Patents

Abstract

The brushless motor 3 includes a rotor 22 having a magnet 33 and a stator 21 having a plurality of teeth 27 facing the magnet 33 with an air gap 45 therebetween. A plurality of auxiliary grooves 20 are formed at the tip of the teeth 27 so as to face the air gap 45. While the ratio W / S between the groove width S of the auxiliary groove 20 and the opening width W of the opening 46 between adjacent teeth 27 is set to 0.9 ≦ W / S ≦ 1.1, the center M1 of the opening 46 The ratio θs / θw between the angle θw between the center M2 of the auxiliary grooves 20 and the angle θs between the centers M2 of the adjacent auxiliary grooves 20 is set in the range of 0.66 ≦ θs / θw ≦ 0.965.

Description

  The present invention relates to a brushless motor used as a drive source for an electric power steering apparatus, and more particularly to a brushless motor that reduces both inductance and cogging torque.

  In recent years, many vehicles have been equipped with so-called power steering devices for assisting steering force of automobiles and the like. As such power steering devices, in recent years, vehicles equipped with electric power steering devices (so-called electric power steering devices, hereinafter abbreviated as EPS as appropriate) have increased in view of reducing engine load and weight. ing. As a power source of such EPS, a motor with a brush has been used more than ever. However, in recent years, the use of a brushless motor has increased because it is excellent in maintainability and can be obtained with a small size and high torque. Yes.

  However, in a brushless motor, a so-called cogging torque tends to occur due to the attractive force between the rotor-side magnet and the stator-side core teeth. Such cogging torque not only causes noise and vibration, but also causes a deterioration in steering feeling in the EPS motor. Therefore, conventionally, a method is known in which the stator is multi-slotted and torque unevenness is subdivided in order to reduce the cogging torque. However, it is impossible to increase the number of slots indefinitely, and the increase in the number of slots is naturally limited in terms of motor size. For this reason, various cogging countermeasures have been proposed, such as a method in which a groove is provided in the portion where the magnetic flux at the tip of the core teeth is dense and the tip of the teeth is divided into two forks, thereby realizing pseudo-multiple slots. Yes.

For example, in the brushless motor of Patent Document 1, an auxiliary groove having a 1/2 slot pitch is provided at the tip of the tooth so that the number of slots apparently doubles. Moreover, in the brushless motor of patent document 2, an overhang part is provided in the both ends of a stator core, and the magnetic flux which flows in from a stator core end surface is suppressed. As a result, the amount of magnetic flux flowing into the stator core from the tooth tip is increased, and the pseudo multi-slot effect by the auxiliary groove is improved. Furthermore, in the electric motor of Patent Document 3, the rotor has a 2P structure and the stator has a 3P structure, and auxiliary grooves are arranged at equal intervals from the slot center at angles θ and 2θ at the tips of teeth provided at a pitch 4θ. A configuration for reducing cogging is shown.
No. 7-47981 Japanese Patent Laid-Open No. 10-42531 JP2004-194489

  However, in the configuration in which the auxiliary groove is provided at the tip of the teeth as described above, the balance of cogging according to the rotational position varies depending on the rotation position due to the processing distortion of the stator, and the motor characteristics cannot be stabilized. There was a problem. That is, since cogging changes based on a variable factor that is difficult to be fixed, such as machining strain, there is a problem that the robustness (stability) of cogging is deteriorated and the motor characteristics are not stabilized.

  On the other hand, when the brushless motor has a concentrated winding configuration, the interval between the teeth is narrowed. For this reason, the magnetic flux leakage from the teeth increases, and the inductance tends to increase correspondingly. When the inductance increases, the electric time constant of the motor increases, and accordingly, a phase difference occurs between the drive voltage applied to the stator coil and the current flowing through the stator coil. When such a phase difference is generated, there is a possibility that a so-called torque sag in which the torque at the time of high load is reduced due to an increase in the reaction between the stator and the rotor.

  An object of the present invention is to provide a brushless motor capable of efficiently exhibiting effects such as cogging torque reduction by an auxiliary groove while reducing inductance.

The brushless motor of the present invention includes a rotor including a magnet and a stator including a plurality of teeth facing the magnet via an air gap, and faces the air gap at a tip portion of the teeth. A brushless motor formed with a plurality of auxiliary grooves, wherein the auxiliary groove has a width S along the circumferential direction and a width W along the circumferential direction of the opening formed at the tip of the adjacent teeth. The ratio W / S is 0.9 ≦ W / S ≦ 1.1, and the center M ₁ along the circumferential direction of the opening and the center M ₂ along the circumferential direction of the auxiliary groove. .theta.w the angle between the, when the angle between the center _{M 2} of the auxiliary groove adjacent to the [theta] s, the ratio [theta] s / .theta.w of the said [theta] s .theta.w is, 0.66 ≦ θs / θw ≦ 0.965 It is characterized by being.

  In the present invention, while setting W / S to 0.9 ≦ W / S ≦ 1.1 and setting θs / θw within the range of 0.66 ≦ θs / θw ≦ 0.965, the inductance can be reduced. While reducing the cogging, the cogging can be kept small, the cogging robustness can be improved, and the influence of the armature reaction in the high output region can be reduced. For this reason, for example, when the brushless motor is used as a drive source of the electric power steering apparatus, the returnability of the steering is improved by reducing the cogging. Further, the inductance reduction reduces torque sagging at high loads, so that the assist force is stabilized and the steering feeling is improved.

  In the brushless motor, the ratio θs / θw between the θs and the θw may be preferably set to 0.7 ≦ θs / θw ≦ 0.9. The brushless motor may have a 6-pole 9-slot configuration in which the magnet has 6 poles and the number of slots formed between the teeth is 9. Further, the brushless motor may be used as a drive source for the electric power steering apparatus.

  According to the brushless motor of the present invention, the rotor includes a magnet and a stator including a plurality of teeth facing the magnet via an air gap, and a plurality of the teeth face the air gap at the tip of the teeth. In the brushless motor in which the auxiliary groove is formed, the ratio W / S between the auxiliary groove width S and the opening width W between adjacent teeth is 0.9 ≦ W / S ≦ 1.1, and the opening between the teeth The ratio θs / θw between the angle θw between the center M1 and the center M2 of the auxiliary groove and the angle θs between the adjacent auxiliary groove centers M2 is set in the range of 0.66 ≦ θs / θw ≦ 0.965. As a result, it is possible to reduce cogging while reducing inductance. Therefore, it is possible to improve the cogging robustness and reduce the influence of the armature reaction in the high output range.

  Further, for example, when the brushless motor is used as a drive source of the electric power steering device, the return of the steering is improved due to the reduction of cogging, and a smooth steering operation is possible. In addition, due to the reduced influence of the armature reaction in the high output range due to the inductance reduction, torque sagging at high loads is reduced, the assist force is stabilized, and the steering feeling can be improved.

It is sectional drawing which shows the structure of the electric power steering apparatus using the brushless motor by this invention. It is sectional drawing of the axial direction which shows the structure of the brushless motor used with the electric power steering apparatus of FIG. It is sectional drawing of the radial direction of the brushless motor of FIG. It is explanatory drawing which shows the structure of teeth. It is a graph which shows the relationship between (theta) s / (theta) w, cogging torque amount (N * m), and inductance (H) at the time of setting W / S = 1 in the brushless motor of 6P9S structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering shaft 3 Brushless motor 4 Steering wheel 5 Steering gear box 6 Tie rod 7 Wheel 8 Assist motor part 9 Deceleration mechanism part 11 Torque sensor 12 Controller 20 Auxiliary groove 21 Stator 22 Rotor 23 Housing 24 Stator core 25 Winding 26 yoke portion 27 teeth 28 slot 29 power supply wiring 30 bracket 31 rotating shaft 32 rotor core 33 magnet 34 magnet holder 35 bearing 36 bearing 37 spline portion 41 resolver 42 resolver stator 43 resolver rotor 44 coil 45 air gap 46 opening M ₁ opening Center M ₂ Auxiliary groove center S Groove width W Opening width θs Angle between M _{1 and} M ₂ θw Angle between M ₂

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing a configuration of an electric power steering apparatus using a brushless motor according to the present invention. An electric power steering apparatus (EPS) 1 shown in FIG. 1 has a column assist type structure that applies an operation assisting force to a steering shaft 2, and a brushless motor 3 (hereinafter abbreviated as a motor 3) according to the present invention. Used as a power source.

  A steering wheel 4 is attached to the steering shaft 2. The steering force of the steering wheel 4 is transmitted to the tie rod 6 via a pinion and a rack shaft (not shown) disposed in the steering gear box 5. Wheels 7 are connected to both ends of the tie rod 6. As the steering wheel 4 is operated, the tie rod 6 is actuated, and the wheel 7 is steered left and right via a knuckle arm (not shown).

  In EPS1, the steering shaft 2 is provided with an assist motor unit 8 that is a steering force assisting mechanism. The assist motor unit 8 includes a motor 3 and a speed reduction mechanism unit 9 and a torque sensor 11. The deceleration mechanism unit 9 is provided with a worm and a worm wheel (not shown). The rotation of the motor 3 is decelerated and transmitted to the steering shaft 2 by the deceleration mechanism 9. The motor 3 and the torque sensor 11 are connected to a control device (ECU) 12.

  When the steering wheel 4 is operated and the steering shaft 2 rotates, the torque sensor 11 is activated. The ECU 12 appropriately supplies electric power to the motor 3 based on the torque detected by the torque sensor 11. When the motor 3 is actuated, the rotation is transmitted to the steering shaft 2 via the speed reduction mechanism unit 9 and a steering assist force is applied. The steering shaft 2 is rotated by the steering assist force and the manual steering force, and this rotational motion is converted into a linear motion of the rack shaft by rack-and-pinion coupling in the steering gear box 5, and the steering operation of the wheels 7 is performed. Is done.

  FIG. 2 is a sectional view in the axial direction showing the configuration of the motor 3. As shown in FIG. 2, the motor 3 is an inner rotor type brushless motor in which a stator 21 is disposed on the outer side and a rotor 22 is disposed on the inner side. The stator 21 includes a housing 23, a stator core 24 fixed to the inner peripheral side of the housing 23, and a winding 25 wound around the stator core 24. The housing 23 is formed in a bottomed cylindrical shape with iron or the like. A bracket 30 made of synthetic resin is attached to the opening of the housing 23. The stator core 24 has a structure in which a large number of steel plates are laminated, and a plurality of teeth protrude from the inner peripheral side of the stator core 24.

  FIG. 3 is a cross-sectional view taken along the radial direction of the motor 3 of FIG. As shown in FIG. 3, the stator core 24 is formed of a ring-shaped yoke portion 26 and teeth 27 that protrude from the yoke portion 26 in an inward direction. Nine teeth 27 are provided. Slots 28 (9) are formed between the teeth 27, and the motor 3 has a 9-slot configuration. An auxiliary groove 20 is formed at the tip of each tooth 27. A winding 25 is wound around each tooth 27 by concentrated winding. The winding 25 is accommodated in each slot 28. Winding 25 is connected to a battery (not shown) via power supply wiring 29. The winding 25 is supplied with trapezoidal phase currents (U, V, W) including harmonic components.

  The rotor 22 is disposed inside the stator 21 and has a configuration in which a rotating shaft 31, a rotor core 32, and a magnet 33 are arranged coaxially. A cylindrical rotor core 32 in which a large number of steel plates are stacked is attached to the outer periphery of the rotating shaft 31. A segment type magnet 33 is arranged on the outer periphery of the rotor core 32. An air gap 45 is formed between the magnet 33 and the teeth 27. The magnet 33 and the tip of the tooth 27 face each other with an air gap 45 interposed therebetween. The auxiliary groove 20 is formed facing the air gap 45. The magnets 33 are attached to a magnet holder 34 fixed to the rotating shaft 31, and six magnets 33 are arranged along the circumferential direction. That is, the motor 3 has a 6-pole 9-slot (6P9S) configuration.

In the motor 3 according to the present invention, the ratio W / S between the groove width S of the auxiliary groove 20 and the opening width W of the teeth 27 is 0.9 ≦ W / S ≦ 1.1 while adopting such a 6P9S configuration. It is set to become. FIG. 4 is an explanatory view showing the configuration of the teeth 27. As shown in FIG. 4, the groove width S is the width dimension along the circumferential direction of the auxiliary groove 20, and the opening width W is the tip of the adjacent teeth 27. It is a gap dimension along the circumferential direction of the opening 46 formed in. Also, in the motor 3, unlike the conventional brushless motor, the auxiliary groove 20 is not equally arranged at the tip of the tooth 27, and the auxiliary groove 20 is set as follows while setting W / S within the above-mentioned range. It is provided in a range. That is, the center _{M 1} of the opening 46, .theta.w the angle between the center _{M 2} auxiliary groove 20, the angle between the center _{M 2} adjacent auxiliary groove 20 when the [theta] s (see FIG. 4), 0. The auxiliary grooves 20 are formed so that the relationship of 66 ≦ θs / θw ≦ 0.965 is established.

  FIG. 5 is a graph showing the relationship between θs / θw, cogging torque amount (N · m), and inductance (H) when W / S = 1 in a brushless motor having a 6P9S configuration. According to the experiments by the inventors, there is a correlation between θs / θw and the amount of cogging torque and inductance (hereinafter abbreviated as appropriate cogging torque, etc.), and θs / θw is too large or too small. It was also found that cogging torque and the like increased. In this case, it is considered that when θs / θw is small, the magnetic resistance at the center of the tooth 27 is increased, the leakage magnetic flux to the adjacent teeth is increased, and the cogging torque or the like is increased. On the other hand, if [theta] s / [theta] w is large, the magnetic flux at the tip of the tooth 27 becomes saturated, and the magnetic flux is likely to leak to the adjacent teeth, thereby increasing the cogging torque and the like.

  Therefore, in the motor 3 of the present invention, θs / θw is set in the range of 0.66 ≦ θs / θw ≦ 0.965 (frame A in FIG. 4) in view of the above-described relationship. As shown in FIG. 4, in this range, the cogging torque or the like takes a minimum value (near θs / θw = 0.77), and this makes it possible to reduce the cogging while reducing the inductance. Thus, if cogging is suppressed, the cogging balance change due to processing strain is also suppressed, and the cogging robustness is improved. Further, if the inductance is suppressed, the influence of the armature reaction on the high output side can be reduced, and the torque sag at the time of high load can also be reduced.

  One end of the rotating shaft 31 is rotatably supported by a bearing 35 press-fitted into the bottom of the housing 23. The other end of the rotating shaft 31 is rotatably supported by a bearing 36 attached to the bracket 30. A spline portion 37 is formed at an end portion (left end portion in FIG. 2) of the rotating shaft 31. The rotation shaft 31 is connected to the worm shaft of the speed reduction mechanism portion 9 by a joint member (not shown) attached to the spline portion 37. A worm is formed on the worm shaft. The worm meshes with a worm wheel fixed to the steering shaft 2 at the speed reduction mechanism unit 9.

  A bearing 36 and a resolver 41 that detects the rotation of the rotor 22 are accommodated in the bracket 30. The resolver 41 includes a resolver stator 42 fixed to the bracket 30 side and a resolver rotor 43 fixed to the rotor 22 side. A coil 44 is wound around the resolver stator 42, and an excitation coil and a detection coil are provided. Inside the resolver stator 42, a resolver rotor 43 fixed to the left end of the magnet holder 34 is disposed. The resolver rotor 43 has a structure in which metal plates are laminated, and has convex portions in three directions.

  When the rotating shaft 31 rotates, the resolver rotor 43 also rotates in the resolver stator 42. A high frequency signal is applied to the exciting coil of the resolver stator 42, and the phase of the signal output from the detection coil changes due to the proximity of the convex portion. The rotational position of the rotor 22 is detected by comparing the detection signal with the reference signal. Then, based on the rotational position of the rotor 22, the current to the winding 25 is appropriately switched, and the rotor 22 is rotationally driven.

  In such EPS1, when the steering wheel 4 is operated and the steering shaft 2 is rotated, the rack shaft is moved in a direction corresponding to the rotation, and a steering operation is performed. By this operation, the torque sensor 11 is activated, and electric power is supplied from the battery (not shown) to the winding 25 via the power supply wiring 29 according to the detected torque. When electric power is supplied to the winding 25, the motor 3 operates and the rotating shaft 31 and the worm shaft rotate. The rotation of the worm shaft is transmitted to the steering shaft 2 via the worm wheel, and the steering force is assisted.

  As described above, in the motor 3 according to the present invention, the cogging torque, which is a pulsation when no current is supplied, is reduced as compared with the conventional brushless motor. For this reason, the returnability of the steering is improved, and a smooth steering operation is possible. For example, when turning the steering wheel at the time of a right turn or the like and then returning the steering wheel for straight ahead, the driver generally does not apply force to the steering wheel. At this time, the EPS is in a state in which the steering force is not assisted (not energized), and if the cogging of the motor is large at this time, there is a possibility that the steering stops halfway and does not return smoothly to the straight-ahead position. In that respect, in EPS using the motor 3, since the cogging torque that prevents the return of the steering is suppressed, the return of the steering is improved and the steering operation is also smooth. Further, in the motor 3, since the inductance is suppressed as well as the cogging torque is reduced, the torque sag at the time of high load is reduced, the assist force is stabilized, and the deterioration of the steering feeling is suppressed.

It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.
For example, in the above-described embodiment, an example in which θs / θw is set in the range of 0.66 ≦ θs / θw ≦ 0.965 is shown. However, as can be seen from FIG. , Θs / θw is more preferably set in a range of 0.7 ≦ θs / θw ≦ 0.9 (frame B in FIG. 4). In the above-described embodiment, the motor 3 is described by taking a 6-pole 9-slot motor as an example. However, the motor configuration is not limited to this, and the present invention is applicable to a motor having an integral multiple of 2-pole 3-slot. Is applicable.

  Furthermore, in the above-described embodiment, an example using an inner rotor type brushless motor has been shown. However, the present invention can also be applied to an outer rotor type brushless motor in which a rotor is arranged outside a stator. In addition, in the above-described embodiment, an example in which the control method according to the present invention is applied to a column assist type EPS motor has been shown. The present invention can also be applied to a pinion assist type EPS motor that applies an auxiliary force to the pinion gear.

Claims (4)

A rotor having a magnet and a stator having a plurality of teeth facing the magnet via an air gap, and a plurality of auxiliary grooves are formed at the tip of the teeth so as to face the air gap. A brushless motor,
The ratio W / S of the width S along the circumferential direction of the auxiliary groove and the width W along the circumferential direction of the opening formed at the tip of the adjacent teeth is 0.9 ≦ W / S ≦ 1.1, and
The center M ₁ along the circumferential direction of the opening, .theta.w the angle between the center M ₂ along the circumferential direction of said auxiliary groove, and θs the angle between the center M ₂ of the auxiliary grooves adjacent Then, the ratio θs / θw between θs and θw is 0.66 ≦ θs / θw ≦ 0.965.   2. The brushless motor according to claim 1, wherein a ratio [theta] s / [theta] w between [theta] s and [theta] w is 0.7≤ [theta] s / [theta] w≤0.9.   2. The brushless motor according to claim 1, wherein the brushless motor has a 6-pole 9-slot configuration in which the magnet has 6 poles and nine slots are formed between the teeth.   The brushless motor according to claim 1, wherein the brushless motor is used as a drive source of an electric power steering apparatus.

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