WO2008050637A1

WO2008050637A1 - Brushless motor

Info

Publication number: WO2008050637A1
Application number: PCT/JP2007/070173
Authority: WO
Inventors: Masayuki Okubo
Original assignee: Mitsuba Corporation
Priority date: 2006-10-25
Filing date: 2007-10-16
Publication date: 2008-05-02
Also published as: JPWO2008050637A1

Abstract

A brushless motor (3) is provided with a rotor (22) having a magnet (33), and a stator (21) having teeth (27) facing the magnet (33) through an air gap (45). At the leading ends of the teeth (27), a plurality of auxiliary grooves (20) which face the air gap (45) are formed. A ratio W/S of the groove width (S) of the auxiliary groove (20) and the opening width (W) of an opening section (46) between the adjacent teeth (27) satisfies inequalities of 0.9≤W/S≤1.1. A ratio ϑs/ϑw of an angle (ϑw) between the center (M1) of the opening section (46) and the center (M2) of the auxiliary groove (20) and an angle (ϑs) between the centers (M2) of the adjacent auxiliary grooves (20) is set within a range of 0.66≤ϑs/ϑw≤0.965.

Description

Specification

Brushless motor technology

TECHNICAL FIELD [0001] The present invention relates to a brushless motor used for a drive source of an electric power steering apparatus, and more particularly to a brushless motor designed to reduce both inductance and cogging torque.

Background art

In order to assist the steering force of automobiles and the like, many vehicles have been equipped with so-called power steering devices in recent years. As such power steering devices, in recent years, an increasing number of vehicles equipped with electric power steering devices (so-called electric power steering devices, hereinafter abbreviated as EPS as appropriate) from the viewpoint of reducing engine load and weight. is doing. As a power source for such EPS, the power with which brushed motors have been used more than ever in recent years In recent years, the use of brushless motors has increased due to excellent maintainability, small size and high torque. Yes.

[0003] 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 contributes to the deterioration of steering feeling in EPS motors. Therefore, conventionally, a method is known in which the veg stage for reducing the cogging torque is made into multiple slots to subdivide the torque unevenness. 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, there are various countermeasures against cogging, such as providing a groove in the portion where the magnetic flux at the tip of the core teeth is dense and dividing the tip of the tooth into a bifurcated shape, thereby increasing the number of slots in a pseudo manner. Proposed.

[0004] For example, the brushless motor of Patent Document 1 is configured such that an auxiliary groove having a 1/2 slot pitch is provided at the tip of a tooth, and the number of slots is apparently doubled. Further, in the brushless motor of Patent Document 2, overhang portions are provided at both ends of the stator core to suppress the magnetic flux flowing from the end face of the stator core. As a result, the teeth tip to the stator core The amount of magnetic flux flowing in 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 the auxiliary grooves are equally spaced from the center of the slot at angles θ and 2Θ at the tip of the teeth provided at a pitch of 4Θ. An arrangement that reduces cogging is shown!

Patent Document 1: No. 7-47981

Patent Document 2: Japanese Patent Laid-Open No. 10-42531

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-194489

Disclosure of the invention

Problems to be solved by the invention

[0005] However, in the configuration in which the auxiliary groove is provided at the tip of the tooth as described above, the balance of cogging according to the rotational position actually varies depending on the rotation position due to processing distortion of the stator, and the motor characteristics are stabilized. There was a problem that could not be realized. In other words, cogging changes based on variable factors that are difficult to stabilize, such as machining strain, which deteriorates the cogging robustness H4 (stability), and the motor characteristics are not stable.

[0006] On the other hand, when the brushless motor has a concentrated winding configuration, the interval between the teeth becomes narrow. For this reason, the magnetic flux leakage from the teeth increases, and the inductance tends to increase accordingly. 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 occurs, the electron reaction between the stator rotors increases, and there is a risk of so-called torque sagging in which the torque at high loads is reduced.

[0007] 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.

Means for solving the problem

[0008] 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 the air gap is provided at a tip of the teeth. A brushless motor formed with a plurality of auxiliary grooves facing each other, the width S along the circumferential direction of the auxiliary grooves and the circumferential direction of the opening formed at the tip of the adjacent teeth. Ratio with width W along W / S force 0.9≤W / S≤1.1 And the angle between the center along the circumferential direction of the opening and the center axis along the circumferential direction of the auxiliary groove e _w , and the angle between the centers M of the adjacent auxiliary grooves es and

twenty two

Then, the ratio Θ sZ Θ w of the Θ s to the Θ w is 0 · 66≤Θ s / θ w≤0.965.

[0009] In the present invention, W / S is set to 0.9≤W / S≤1.1, and Θ s / Θ w is set to a range of 0.66≤ Θ s w Θ w ≤ 0.965, thereby reducing inductance. Cogging can be kept small while improving the cogging robustness and the effect of armature reaction in the high output range 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 return of steering is improved by reducing cogging. In addition, due to the inductance reduction, torque sagging at high loads is reduced, so that assist force is stabilized and steering feeling is improved.

In the brushless motor, the ratio Θ sZ Θ w of Θ s to Θ w may be preferably set to 0.7≤Θ s / θ w≤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. Furthermore, the brushless motor may be used as a drive source for the electric power steering apparatus.

The invention's effect

[0011] According to the brushless motor of the present invention, the rotor includes a magnet, and the stator includes a plurality of teeth facing the magnet through an air gap. In a brushless motor with multiple auxiliary grooves facing each other, 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. The angle Θ w between the opening center Ml and the auxiliary groove center M2 and the angle between the adjacent auxiliary groove centers M2 Θ s ratio Θ s / Θ w is 0.66≤ Θ s / θ w ≤ 0.965 By setting to this range, 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.

[0012] Further, for example, when the brushless motor is used as a drive source of the electric power steering apparatus, the return of the steering is improved by reducing the cogging, and the smooth steering is achieved. Operation becomes possible. In addition, by reducing the influence of the armature reaction in the high output range due to inductance reduction, torque sagging at high loads is reduced, assist force is stabilized, and steering feeling can be improved.

Brief Description of Drawings

FIG. 1 is a cross-sectional view showing a configuration of an electric power steering device using a brushless motor according to the present invention.

FIG. 2 is an axial sectional view showing a configuration of a brushless motor used in the electric power steering apparatus of FIG. 1.

3 is a cross-sectional view of the brushless motor of FIG. 2 in the radial direction.

FIG. 4 is an explanatory diagram showing a configuration of teeth.

[Figure 5] Explanation of Θ sZ Θ w and coggin code when W / S = l in a 6P9S brushless motor

[0014] 1 Electric power steering device

2 Steering shaft

3 Brushless motor

4 Steering wheel

6 Tie rod

7 wheels

8 Assist motor section

9 Deceleration mechanism

11 Torque sensor

12 Control unit

20 Auxiliary groove

21 Stator

22 Rotor

23 Housing 24 Stator core

25 windings

26 Relay section

27 Teeth

28 slots

29 Power supply wiring

30 Bracket

31 Rotating shaft

32 Rotor core

33 Magnet

34 Magnet Honoreda

35 Bearing

36 Bearing

37 Spline

41 Resolver

42 Resolver stator

43 Resolver rotor

44 coils

46 opening

M Center of opening

M Auxiliary groove center

2

S groove width

W opening width

Angle between Θ s M and M

1 2

Angle between Θ w M

2

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is according to the invention. It is sectional drawing which shows the structure of the electric power steering apparatus using a brushless motor. The electric power steering device (EPS) 1 shown in FIG. 1 has a column assist type structure that applies an operation assisting force to the 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) arranged 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 to the left and right via a knuckle arm (not shown).

In EPS 1, the steering shaft 2 is provided with an assist motor unit 8 that is a steering force assist mechanism. In addition to the motor 3, the assist motor unit 8 is provided with a speed reduction mechanism unit 9 and a torque sensor 11. The speed reduction mechanism unit 9 is provided with a worm and a worm hoist 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 unit (ECU) 12.

[0018] 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 operated, 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 the rack 'and' pinion coupling in the steering gear box 5, and the wheel 7 is steered. Operation is performed.

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 having a stator 21 on the outside and a rotor 22 on the inside. 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 synthetic resin bracket 30 is attached to the opening of the housing 23. Stator core 24 is made of steel A large number of the teeth are stacked, and a plurality of teeth protrude from the inner peripheral side of the stator core 24.

FIG. 3 is a cross-sectional view along the radial direction of the motor 3 of FIG. As shown in FIG. 3, the stator core 24 is formed by a ring-shaped yoke portion 26 and a force 27 and a tooth 27 projecting inward from the yoke portion 26. 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 in a concentrated manner. 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.

[0021] 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 disposed on the outer periphery of the rotor core 32. An air gap 45 is formed between the magnet 33 and the teeth 27. The tips of the magnet 33 and the teeth 27 are opposed to each other through an air gap 45. 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.

[0022] 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 be. FIG. 4 is an explanatory view showing the configuration of the tooth 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 tooth 27. It is the gap dimension along the circumferential direction of the opening 46 formed in the section. Also, in the motor 3, unlike the conventional brushless motor, the auxiliary groove 20 is not evenly 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 angle between the center M of the opening 46 and the center M of the auxiliary groove 20 is Θ w

1 2

If the angle between the centers M of the auxiliary grooves 20 is Θ s (see Fig. 4), 0 · 66≤ ds / θ w≤0.96 The auxiliary grooves 20 are formed so that the relationship 5 is established.

[0023] Fig. 5 shows that Θ sZ Θ w and cogging torque amount and inductance (hereinafter referred to as the following) according to the experiment of Θ s / Θ w and co, when W / S = l in a 6P9S brushless motor. (It is abbreviated as cogging torque etc. as appropriate), and it was found that cogging torque etc. increased if Θs / Θw was too large or too small. In this case, if Θ sZ Θ w is small, the magnetic resistance at the center of the tooth 27 increases, and the cogging torque and the like increase as the leakage flux to the adjacent teeth increases. On the other hand, if Θ sZ Θ w is large, the magnetic flux at the tip of the tooth 27 becomes saturated, and it is thought that the cogging torque and the like increase as the magnetic flux easily leaks to the adjacent teeth.

Therefore, in the motor 3 of the present invention, in view of the above-described relationship, Θ s / Θ w is set to 0 · 66≤ Θ s / Θ w

The range was set to ≤0 · 965 (frame A in Fig. 4). As shown in Fig. 4, the cogging torque, etc., takes a minimum value in this range (near Θ s / Θ w = 0.77), which makes it possible to reduce the cogging while reducing the inductance. In this way, if cogging is suppressed, the cogging balance change due to processing strain is suppressed, and the robustness of cogging 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.

[0025] One end of the rotating shaft 31 is supported by a bearing 35 press-fitted into the bottom of the housing 23 so as to rotate. 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 the end of the rotating shaft 31 (left end in FIG. 2). The rotating 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 is engaged with a worm wheel fixed to the steering shaft 2 at the speed reduction mechanism section 9.

[0026] In the bracket 30, a bearing 36 and a resolver 41 for detecting the rotation of the rotor 22 are accommodated. The resolver 41 includes a resolver stator 42 fixed to the bracket 30 side and a resolver rotor 43 fixed to the port 22 side. A coil 44 is wound around the resolver stator 42, and an excitation coil and a detection coil are provided. Resor A resolver rotor 43 fixed to the left end of the magnet holder 34 is disposed inside the stator 42. The resolver rotor 43 has a structure in which metal plates are laminated, and convex portions are formed 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.

[0028] In such EPS1, when the steering wheel 4 is operated and the steering shaft 2 rotates, the rack shaft moves in a direction corresponding to the rotation, and a steering operation is performed. As a result of this operation, the torque sensor 11 is activated, and electric power is supplied to the winding 25 via the power supply wiring 29 by a battery force (not shown) according to the detected torque. When electric power is supplied to the winding 25, the motor 3 operates and the rotary shaft 31 and the worm shaft rotate. The rotation of the worm shaft is transmitted to the steering shaft 2 via the warm wheel, and the steering force is assisted.

[0029] As described above, in the motor 3 according to the present invention, the cogging torque, which is a pulsation when no power is passed, is reduced as compared with the conventional brushless motor. For this reason, the return of the steering is improved, and a smooth steering operation is possible. For example, when turning the steering wheel when turning right and then returning the steering wheel for straight ahead, the driver generally does not apply any force to the steering wheel. At this time, the EPS does not assist the steering force (no power is supplied), and if the cogging of the motor is large at this time, there is a possibility that the steering stops midway and does not return smoothly to the straight position. . On the other hand, in the EPS using the motor 3, since the cogging torque that hinders the return of the steering is suppressed, the return of the steering is improved and the steering operation is smooth. In addition, since the motor 3 can reduce the cogging torque and the inductance, the torque sagging at high loads is reduced, the assist force is stabilized, and deterioration of the steering feeling is suppressed.

[0030] Needless to say, 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-mentioned embodiment, Θ s / Θ w is set in the range of 0 · 66 ≤ Θ s / θ w ≤ 0.965. However, as can be seen from Fig. 4, in order to reduce cogging torque, etc. It is more preferable to set Θ s / 6 w within the range of 0 · 7≤θ s / θ w≤0.9 (frame 枠 in Fig. 4). In the above-described embodiment, a 6-pole 9-slot motor has been described as an example of the motor 3. However, the motor configuration is not limited to this, and the present invention is applicable to a 2-pole 3-slot integral multiple motor. Is applicable.

Further, in the above-described embodiments, the force using an inner rotor type brushless motor has been shown. The present invention can also be applied to an outer rotor type brushless motor in which a rotor is arranged outside the stator. In addition, in the above-described embodiments, the force S shown in the example in which the control method according to the present invention is applied to a column assist type EPS motor, the rack assist type in which the motor is arranged coaxially with the rack shaft, and the rack shaft are combined. It can also be applied to a pinion assist type EPS motor that applies auxiliary force to the pinion gear.

Claims

The scope of the claims

[1] 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 members facing the air gap at the tip of the teeth A brushless motor formed with grooves,

Ratio of width s along the circumferential direction of the auxiliary groove to width W along the circumferential direction of the opening formed at the tip of the adjacent tooth W / S force S, 0.9≤W / S≤1.1 And center M along the circumferential direction of the opening, and center M along the circumferential direction of the auxiliary groove

When the angle between 1 and 2 is Θ w and the angle between the centers M of the adjacent auxiliary grooves is Θ s,

2

The ratio of Θ s to Θ w Θ s / Θ w force 0.66≤ Θ s / θ w ≤ 0.965

[2] The brushless motor according to claim 1, wherein the ratio Θ sZ Θ w of Θ s to Θ w is

A brushless motor characterized by 0.7≤ Θ s / θ w ≤ 0.9.

[3] 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 the number of slots formed between the teeth is 9. Brushless motor.

[4] The brushless motor according to claim 1, wherein the brushless motor is used as a drive source of an electric power steering device.