CN112913114A

CN112913114A - Surface magnet type motor and motor module

Info

Publication number: CN112913114A
Application number: CN201980070542.7A
Authority: CN
Inventors: 绵引正伦
Original assignee: Nidec Corp
Current assignee: Nidec Corp
Priority date: 2018-10-26
Filing date: 2019-10-03
Publication date: 2021-06-04
Anticipated expiration: 2039-10-03
Also published as: WO2020085030A1; JP7415938B2; JPWO2020085030A1

Abstract

The disclosed surface magnet motor is provided with: an annular stator (900) having M teeth (911), M being an integer of 3 or more; and a rotor having an outer peripheral surface facing an inner peripheral surface (S) of the stator defined by the tip surfaces of the M teeth with an air gap (950) therebetween, and having N permanent magnets (922) on the outer peripheral surface, wherein N is an integer of 2 or more. The tip surfaces of the M teeth each have a concave-convex structure including two grooves (916A, 916B) arranged at intervals in the circumferential direction of the stator and a ridge (915) located between the two grooves. The two grooves and ridges extend in a direction parallel to a central axis (J1) of rotation of the rotor (920).

Description

Surface magnet type motor and motor module

Technical Field

The present application relates to a surface magnet type motor and a motor module.

Background

A method for reducing both cogging torque and torque ripple at the time of load has been proposed by studying a motor structure. Japanese patent laid-open No. 2001-339921 discloses the following technique: a plurality of auxiliary grooves are provided on the tip end surface of the stator teeth, and a skew corresponding to an electrical angle of 72 DEG is provided between the rotor and the stator, thereby reducing harmonics of an induced voltage. Japanese patent laid-open publication No. 2003-61272 discloses the following technique: a plurality of auxiliary grooves are provided on the tip end surface, and the plurality of auxiliary grooves cause a variation in flux guide that is substantially equivalent to a variation in flux guide that is generated in a groove located between two adjacent teeth.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open gazette: japanese patent laid-open No. 2001-339921

Patent document 2: japanese laid-open gazette: japanese patent laid-open No. 2003-61272

Disclosure of Invention

Problems to be solved by the invention

Further reduction of cogging torque and torque ripple under load is required.

Means for solving the problems

In an exemplary embodiment, a surface magnet motor of the present disclosure includes: an annular stator having M teeth, M being an integer of 3 or more; and a rotor having an outer peripheral surface facing an inner peripheral surface of the stator defined by tip surfaces of the M teeth with an air gap therebetween, the outer peripheral surface having N permanent magnets, N being an integer of 2 or more, the tip surfaces of the M teeth each having a concavo-convex structure including two grooves disposed with a gap therebetween in a circumferential direction of the stator and a ridge located between the two grooves, the two grooves and the ridge extending in a direction parallel to a central axis of rotation of the rotor.

Effects of the invention

Embodiments of the present disclosure provide a novel surface magnet type motor capable of appropriately reducing both cogging torque and torque ripple at the time of load while suppressing a decrease in average torque of the motor, and a motor module having the surface magnet type motor.

Drawings

Fig. 1 is a block diagram schematically illustrating the hardware blocks of a motor module 1000 of the present disclosure.

Fig. 2 is a sectional view of the motor 700 taken along a plane perpendicular to a direction in which a central axis J1 in which the rotor 920 rotates extends.

Fig. 3 is a cross-sectional view of the laminate 910 cut along a plane perpendicular to the direction in which the central axis J1 extends.

Fig. 4 is a schematic diagram schematically illustrating a division core 910D on which a winding 930 is mounted.

Fig. 5 is a plan view of stator 900 having 12 divided cores 910D to which windings 930 are attached.

Fig. 6 is an enlarged view of a part of a cross section of the laminate 910 cut along a plane perpendicular to the direction in which the central axis J1 extends.

Fig. 7 is an enlarged view showing the concave-convex structure of the distal end surface of the tooth 911 in the cross section of the stacked body 910.

Fig. 8 is a perspective view of the division core 910D.

Fig. 9 is a perspective view of a deformation of the division core 910D.

Fig. 10 is a graph showing an analysis result obtained by analyzing the effect of reducing the cogging torque.

Fig. 11 is a graph showing an analysis result obtained by analyzing the effect of reducing the torque ripple.

Fig. 12 is a graph showing the measurement result of the ratio of the amplitudes of the torques.

Fig. 13 is a graph showing the measurement result of the ratio of the amplitudes of the torques.

Detailed Description

Hereinafter, embodiments of the surface magnet motor and the motor module according to the present disclosure will be described in detail with reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid unnecessary redundancy in the following description, which will be readily understood by those skilled in the art.

[ 1. Motor Module 1000 ]

In the non-limiting exemplary embodiment, the motor module 1000 includes a motor control device 100, a drive circuit 200, an inverter 300, a current sensor 400, an analog-to-digital conversion circuit (hereinafter referred to as an "AD converter") 500, an angle sensor 600, and a motor 700. The motor module 1000 is modularized, and can be manufactured and sold as an electromechanical integrated motor having a motor, a sensor, a driver, and a motor control device, for example.

The motor 700 is, for example, a surface magnet type synchronous motor having three-phase windings (not shown) of U-phase, V-phase, and W-phase. The three-phase windings are electrically connected to the inverter 300. The wiring of the motor may be any of Y wiring and Δ wiring. The construction of the motor 700 will be described in detail later.

The motor control device 100 typically has a processor 110 and a memory 120. The processor 110 may be, for example, an Integrated Circuit (IC) chip such as a Digital Signal Processor (DSP) or a Micro Control Unit (MCU). Alternatively, the processor 110 may be implemented by a Field Programmable Gate Array (FPGA) incorporating a core of a Central Processing Unit (CPU), for example.

The Memory 120 includes, for example, a writable Memory (e.g., PROM), a rewritable Memory (e.g., flash Memory), or a read-only Memory, and a RAM (Random Access Memory). The memory 120 stores a control program having a command set for causing the motor control device 100 to control the motor 700. For example, the control program is loaded once in a RAM (not shown) at the time of startup.

The motor control device 100 controls the switching operation of the switching elements included in the inverter 300. For example, the motor control device 100 sets a target current value based on a signal indicating an actual current value and a rotation angle of the rotor, generates a PWM (Pulse Width Modulation) signal, and outputs the PWM signal to the drive circuit 200.

The driving circuit 200 is typically a gate driver (or pre-driver). The drive circuit 200 generates a control signal for controlling the switching operation of the switching element included in the inverter 300 based on the PWM signal, and outputs the control signal to the inverter 300. As will be described later, the switching elements of the inverter 300 are, for example, MOS-type field effect transistors (MOSFETs). The control signal generated by the drive circuit 200 is a gate control signal supplied to the gate of the MOSFET.

The inverter 300 is, for example, a half-bridge circuit having 3 low-side switching elements SW _ L1, SW _ L2, SW _ L3 and 3 high-side switching elements SW _ H1, SW _ H2, SW _ H3. As the switching element, a semiconductor switching element such as a MOSFET or an Insulated Gate Bipolar Transistor (IGBT) can be used. The inverter 300 converts dc power supplied from an external dc power supply (not shown) into ac power, for example. The inverter 300 converts the dc power into three-phase ac power, which is pseudo sine waves of U-phase, V-phase, and W-phase.

The current sensor 400 includes at least two current sensors that detect at least two phase currents flowing through the U-phase, V-phase, and W-phase windings of the motor 700. Fig. 1 illustrates two

current sensors

400A and 400B that detect currents flowing in the U-phase and the V-phase. Each of the

current sensors

400A and 400B includes, for example, a shunt resistor Rs and a current detection circuit (not shown) that detects a current flowing through the shunt resistor Rs.

The AD converter 500 samples the analog signal output from the current sensor 400, converts the analog signal into a digital signal, and outputs the digital signal after the conversion to the motor control device 100.

The angle sensor 600 is, for example, a resolver or a hall IC. Alternatively, the angle sensor 600 may be implemented by a combination of an MR sensor having a Magnetoresistive (MR) element and a sensor magnet. The angle sensor 600 detects a rotation angle of the rotor (referred to as a "rotor angle") and outputs the rotation angle to the motor control device 100.

In a surface magnet motor having a rotor and a stator, the outer peripheral surface of the rotor faces the inner peripheral surface of the stator defined by the tip surfaces of the stator teeth with an air gap therebetween. The magnetic flux through the air gap flows mainly in the radial and circumferential directions. As a result, a circumferential force (torque) and a radial force (radial force) are generated between the stator and the rotor. These forces are referred to as "electromagnetic forces". The interlinkage magnetic flux that generates the electromagnetic force includes interlinkage magnetic flux based on the permanent magnet of the rotor and interlinkage magnetic flux formed by energizing the winding of the stator. The magnitude of the magnetic flux component (interlinkage magnetic flux) penetrating each tooth changes spatially and temporally, and thus the electromagnetic force also changes spatially and temporally. This becomes a cause of torque fluctuation. Generally, the causes of torque fluctuation are roughly classified into the following two.

(1) Spatial higher harmonics

The interlinkage magnetic flux number of the magnetic poles of the rotor formed in the stator winding varies periodically according to the rotational position of the rotor. Hereinafter, the rotation angle (or angular position) of the rotor is represented by an angle θ formed with respect to the reference direction in the fixed coordinate system. The number of interlinkage magnetic fluxes formed in each stator winding when a current flows through the stator winding also depends on an inductance that can be periodically changed in accordance with the rotation angle θ of the rotor. The magnetic poles and the inductance of the rotor may contain not only a fundamental wave component having the rotation angle θ of the rotor as a variable but also a harmonic component (spatial harmonic component) that cannot be ignored. Such a spatial harmonic component causes a fluctuation in torque generated when a current flows through the stator winding.

(2) Cogging torque

Even in a state where no current flows through the stator winding (no-load state), magnetic flux due to the magnetic poles of the rotor exists in the air gap between the rotor and the stator, and magnetic energy is accumulated. The air gap varies periodically according to the rotation angle θ of the rotor due to the presence of the plurality of slots of the stator, so the magnetic energy is a function of the rotation angle θ of the rotor. When the magnetic energy accumulated in the air gap in a state where no current flows through the stator winding is represented by W (θ), a torque having a magnitude represented by δ W (θ)/δ θ is generated. This is referred to as "cogging torque". The cogging torque is independent of the current (drive current) with or without the stator winding. Therefore, when a current is applied to the stator winding to operate the motor (in a load state), torque ripple occurs in which a component due to the spatial harmonics and a component due to the cogging phenomenon are superimposed.

According to the studies of the present inventors, in the case where the groove is provided on the leading end surface of the stator tooth, generally, the average torque of the motor is reduced. As the number of slots increases, the higher the spatial harmonics of the magnetic flux in the load state when the motor is energized becomes. Therefore, it is difficult to generate variation in the permeance for canceling the vibration of the low time frequency.

The present inventors have conceived a surface magnet motor capable of suppressing a decrease in the average torque of the motor and appropriately reducing cogging torque and torque ripple during loading based on the above findings. Hereinafter, the structure of the surface magnet motor will be described in more detail.

[ 2. Structure of Motor 700 ]

Fig. 2 is a sectional view of the motor 700 taken along a plane perpendicular to a direction in which a central axis J1 in which the rotor 920 rotates extends. Fig. 3 is a cross-sectional view of the laminated annular core 910 cut along a plane perpendicular to the direction in which the central axis J1 extends. Fig. 4 is a schematic diagram schematically illustrating a division core 910D on which a winding 930 is mounted. Fig. 5 is a plan view of stator 900 having 12 divided cores 910D to which windings 930 are attached.

The motor 700 has a stator 900 and a rotor 920. In a non-limiting exemplary embodiment, the motor 700 is an 8-pole, 12-slot surface magnet type motor (SPM).

The annular stator 900 is an annular laminated body (sometimes referred to as a "laminated annular core") 910 and a winding (sometimes referred to as a "coil") 930. To avoid complicating the drawing, fig. 2 illustrates the winding 930 attached to only 1 of the divided cores 910D. The stator 900 generates magnetic flux according to the driving current. The laminated body 910 is formed of laminated steel plates in which a plurality of steel plates (referred to as "annular core pieces") are laminated in a direction parallel to the central axis J1 of rotation of the rotor 920. The laminated body 910 may include an annular laminated core back 912 and M (M is an integer of 3 or more) laminated teeth (hereinafter, referred to as "teeth") 911. A stack 910 having 12 teeth 911 is illustrated in fig. 2. Between the adjacent 2 teeth 911 there is a slot 940. That is, the stacked body 910 has 12 grooves 940. The laminated core back 912 is fixed to an inner wall of a housing (not shown) of the motor.

The inner circumferential surface S of the stator 900 shown in fig. 3 is defined by the respective tip end surfaces of the 12 teeth 911. Hereinafter, the inner peripheral surface may be referred to as a distal end surface S.

The rotor 920 includes a rotor core 921 and N (N is an integer of 2 or more) permanent magnets 922. The rotor 920 has an outer peripheral surface facing the inner peripheral surface S of the stator 900 with an air gap 950 therebetween. The N permanent magnets 922 are arranged uniformly on the outer peripheral surface. For example, the permanent magnet 922 is fixed to the outer peripheral surface of the rotor core 921 in a state of being supported by a magnet holder (not shown). Fig. 2 illustrates a rotor 920 having 8 permanent magnets 922. For example, the size of the air gap 950 is about 0.5 mm.

The ratio of the number N of permanent magnets 922 to the number M of teeth 911 (or grooves 940) in the motor 700 as a surface magnet type motor may be N: m is 2: 3. in an embodiment of the present disclosure, the motor 700 is an 8 pole, 12 slot SPM.

The windings 930 are formed of a conductive wire (typically a copper wire), typically mounted to each of the 12 teeth 911 of the stack 910. The winding method of the stator winding may be concentrated winding or distributed winding.

An example of a method of manufacturing the stator 900 and the rotor 920 will be briefly described. For example, the laminated body 910 may be divided into 12 divided cores 910D at the time of manufacturing. In the case of concentrated winding, the laminated body 910 is divided so that each of the divided cores 910D has 1 tooth 911 in principle. After the laminated body 910 is divided, as shown in fig. 4, the windings 930 are attached to the 12 divided cores 910D, respectively. The 12 divided cores 910D to which the windings 930 are respectively attached are returned to a ring shape by using a jig, thereby obtaining a ring-shaped stator 900 shown in fig. 5.

For example, the rotor core 921 and the magnet holder (not shown) are integrated by insert molding. The permanent magnet 922 is inserted into the integrated rotor core 921 and magnet holder, and thereby 8 permanent magnets 922 are fixed to the outer peripheral surface of the rotor 920. Thereby, the rotor 920 is obtained.

Fig. 6 is an enlarged view of a part of a cross section of the laminate 910 cut along a plane perpendicular to the direction in which the central axis J1 extends. Fig. 7 is an enlarged view showing the concave-convex structure of the distal end surface of the tooth 911 in the cross section of the stacked body 910. Fig. 8 is a perspective view of the division core 910D.

The front end surface of the tooth 911 has a concave-convex configuration. The concave-convex structure includes two

grooves

916A and 916B arranged at intervals in the circumferential direction of the stator 900 or the inner circumferential surface S, and a ridge 915 located between the two

grooves

916A and 916B. In the drawing, two grooves located on the leading end surface S are denoted by

reference numerals

916A, 916B in the circumferential direction in clockwise order. Similarly, two adjacent teeth in the stacked body 910 are denoted by

reference numerals

911A and 911B, respectively, in the clockwise order.

A reference line (one-dot chain line in the figure) L1 and a reference plane R are defined. The reference line L1 is a straight line passing through the center point o on the center axis J1 and approximately bisecting the tooth 911 in plan view. The reference plane R is a plane including the openings a of the two

grooves

916A and 916B, respectively. The reference surface R is a part of the inner peripheral surface S, and includes a surface between the ridge 915 and the groove 916A and a surface between the ridge 915 and the groove 916B.

In the concave-convex structure of the distal end surface S, the ridge 915 is a portion that protrudes relative to the reference surface R, and the two

grooves

916A and 916B are portions that are recessed relative to the reference surface R.

The ridge 915 protrudes from the reference surface R toward the outer circumferential surface of the rotor 920. The ridge 915 extends in a direction parallel to the central axis J1 of rotation of the rotor 920 on the front end surface S of the tooth 911. The ridge 915 bisects the front face S of the tooth 911 and is located between the two grooves 916, 916B. In a cross section of the laminate 910 cut along a plane perpendicular to the direction in which the central axis J1 extends (hereinafter referred to as "cross section C"), the ridge 915 is located on the reference line L1. The height h1 (see fig. 7) of the ridge 915 from the reference surface R is, for example, about 0.1 mm. For example, the ridge 915 may be a column such as a quadrangular prism or a convex portion having a semi-cylindrical shape. Where the ridge 915 is cylindrical in shape, the corners may have a slight rounded corner R.

The two

grooves

916A, 916B are each a recess dug in the front end surface S of the tooth 911. The two

grooves

916A, 916B extend in parallel with the central axis J1 along with the ridge 915. The two

grooves

916A, 916B are provided on the leading end surface S substantially line-symmetrically with respect to the ridge 915. The two

slots

916A, 916B typically have substantially the same shape. The corners of the grooves may have slight rounded corners R. The depth h2 (see fig. 7) of each of the two

grooves

916A, 916B from the reference surface R is, for example, about 0.1 mm.

In the circumferential direction of the inner peripheral surface S, the distance between the groove 916A and the ridge 915 is equal to the distance between the groove 916B and the ridge 915. As explained in further detail with reference to fig. 6, in the section C, the angle (i.e., the center angle) made by the line segment connecting the center of the groove 916A and the center point o with the reference line L1 is equal to the angle made by the line segment connecting the center of the groove 916B and the center point o with the reference line L1. The angle is θ 1.

The width w1 of the ridge in the circumferential direction of the inner peripheral surface S and the width w2 of each of the two

grooves

916A, 916B preferably satisfy the relationship of 0.5 < (w2/w1) < 1.5. The reason is described later.

The 12 teeth 911 of the stacked body 910 include

adjacent teeth

911A and 911B. A slotted opening SA is formed between the front end faces of

teeth

911A and 911B. The positions at which the two

grooves

916A, 916B are arranged on the inner circumferential surface S satisfy the following condition between the

adjacent teeth

911A and 911B.

A line segment connecting the center of the slot SA and the center point o is referred to as a 1 st line segment. The 1 st line segment corresponds to a reference line L2 (the two-dot chain line shown in fig. 6) passing through the center of the slot opening SA and the center point o. A line segment connecting the center of the groove 916B on the groove opening SA side of the two

grooves

916A, 916B arranged on the distal end surface of the tooth 911A and the center point o is referred to as a 2 nd line segment. A line segment connecting the center of the groove 916A on the groove opening SA side of the two

grooves

916A, 916B arranged on the distal end surface of the tooth 911B and the center point o is referred to as a 3 rd line segment, as in the 2 nd line segment.

The angle (central angle) formed by the 1 st line segment (or the reference line L2) and the 2 nd line segment is equal to the angle formed by the 1 st line segment and the 3 rd line segment. The angle is θ 2. In other words, in the circumferential direction of the inner circumferential surface S, the distance from the center of the groove opening SA to the center of the groove 916A is equal to the distance from the center of the groove opening SA to the center of the groove 916B. The angle theta 2 preferably satisfies the relationship of 5.0 DEG < theta 2 < 6.5 deg. The reason is described later.

Fig. 9 is a perspective view of a deformation of the division core 910D.

As described above, the laminated body 910 is formed by laminating a plurality of ring-shaped core pieces. Fig. 8 and 9 illustrate 1 divided core 910D included in a laminated body 910 in which 19 annular core pieces 910s are laminated. However, the number of laminated blocks is not limited to this, and can be appropriately determined according to the necessary characteristics required for the motor, for example.

The terms "ridge" and "groove" in the present specification include not only ridges and grooves formed by continuously providing a concavo-convex structure on all the laminated annular core sheets but also ridges and grooves formed by discontinuously providing a concavo-convex structure on several of the laminated annular core sheets. Fig. 8 shows a concave-convex structure including ridges 915 and

grooves

916A and 916B continuously formed on the front end surface S of the divided core 910D. Fig. 9 shows a concave-convex structure including ridges 915 and

grooves

916A and 916B discontinuously formed on the front end surface of the divided core 910D. For example, the laminated body 910 may be formed by alternately laminating a ring-shaped core piece 910s having a convex portion for forming the ridge 915 and a concave portion for forming the

grooves

916A and 916B and a ring-shaped core piece 910s having no convex portion and no concave portion.

The discontinuous uneven structure appearing on the end surface S of the divided core 910D shown in fig. 9 belongs to the category of the uneven structure including ridges and grooves of the present disclosure. For example, a concave-convex structure having ridges continuously formed on the front end surface S of the divided core 910D and grooves discontinuously formed, a concave-convex structure having ridges discontinuously formed on the front end surface of the divided core 910D and grooves continuously formed, or other irregular concave-convex structures are also included in the scope of the present disclosure.

In the embodiment of the present disclosure, in order to generate cogging torque of opposite phase, the ridge 915 of the concavo-convex structure is used, and in order to generate torque ripple of opposite phase, the two

grooves

916A, 916B of the concavo-convex structure are used. The width w1 of the ridge 915 is set to an optimum value for the cogging torque, and the width w2 of each of the two

grooves

916A, 916B is set to an optimum value for the torque ripple. By adjusting the widths w1, w2 in the uneven structure, it is possible to suppress a decrease in the average torque of the motor and appropriately reduce both the cogging torque and the torque ripple at the time of loading. To explain the effect of reducing cogging torque and torque ripple at the time of load, an approximation equation of cogging torque is derived. The results of investigation of the optimum range of the ratio (w2/w1) of the width w2 of each of the two

grooves

916A and 916B to the width w1 of the ridge 915 and the optimum range (range of the angle θ 2) of the position where the two

grooves

916A and 916B are disposed on the distal end surface S of the tooth 911 will be described using this approximate expression.

Before deriving the approximation of the cogging torque, the symbols used in the approximation are defined. Mechanical angle: θ [ rad ], mechanical angular velocity: ω [ rad/s ], time: t [ s ]]Amplitude of k-th order component of magnetomotive force on the rotor side: f_{rt_k}Amplitude of 1-th order component of magnetomotive force on the stator side: f_{st_l}The number of pole pairs: pn, phase current amplitude: i, current advance angle: β, mean permeance: lambda₀Magnetic conductance s, amplitude of m-th order component: lambda_s、Λ_mMagnetic conductance s, phase of m-th order component: theta_s、θ_mThe number of grooves: s, number of concavities and convexities: and m is selected.

The resultant force of the cogging torque and the circumferential electromagnetic force of the torque ripple is obtained by the magnetic flux density B in the air gap_gThe square of (θ, ω t) is obtained by angular integration, and is expressed by the following expression of number 1. Magnetic flux density B_gThe (θ, ω t) is expressed by a product of magnetomotive force F (θ, ω t) and permeance Λ (θ) expressed by the following equation of number 2.

[ number 1]

[ number 2]

B_g(θ，ωt)＝F(θ，ωt)·Λ(θ)

Suppose that magnetomotive force F (θ, ω t) has component F of magnetomotive force on the rotor side_{r_rt}(θ, ω t) and component F of magnetomotive force on the stator side_{r_st}(θ, ω t). Magnetomotive force F (θ, ω t) is a resultant force of these components,expressed by the following equation of number 3. Magnetomotive force F on stator side in equation 3_{r_st}(θ, ω t) is U, V and the resultant magnetomotive force of the W phase. The permeance Λ (θ) represents the resultant permeance through the air gap between the rotor and the stator, expressed by the following equation of number 4.

[ number 3]

[ number 4]

Λ(θ)＝{Λ₀+Λ_ssin(sθ+θ_s)+Λ_mSin(mθ+θ_m)}

When the concave-convex structure is provided on the front end surface of the tooth, the number m of the concave-convex is m ≠ 0. The number m of the irregularities is the number of one of the grooves and ridges included in the irregular structure. For example, in the case of an 8-pole 12-slot motor, m-12 indicates the number of ridges of the uneven structure, and m-24 indicates the number of slots of the uneven structure.

[ 3. approximation of cogging torque in no-load state ]

A cogging torque T is derived for a 8-pole 12-slot concentrated winding motor in which the front end surfaces of the teeth do not have a concave-convex structure_co_gThe approximate expression of (c). Pn (number of pole pairs) is 4, s (number of grooves) is 12, and m is 0 (number of projections and depressions m) is substituted into the expression of the number 3. When no load is applied, the phase current amplitude is set to I equal to 0, and therefore the following equation of number 5 is obtained as the cogging torque T_cogThe approximate expression of (c). Cogging torque T_cogThe main component of (2) is a torque ripple of a harmonic component of a degree determined by the least common multiple of the number of poles (2 × Pn) and the number of slots s per rotation of the rotor. According to the equation of the number 5, the 24 th harmonic component having the vibration frequency 24 times as high as the fundamental wave component of the torque is the cogging torque T_cogThe main component (c).

[ number 5]

Next, it is considered to provide a concave-convex structure on the tip end surface of the tooth to make the cogging torque T_cogThe minimum case. When m is 12, the following number 6 is obtained as the cogging torque T_cogThe approximate expression of (c). m-12 indicates a concave-convex structure including 1 ridge.

[ number 6]

Compare the equations of

numbers

5 and 6. In the equation of number 6, when Λ is satisfied_s＝Λ_mAnd theta_s＝θ_mAt + π condition, cogging torque T_cogAnd in the equation of number 5_sThe case of 0 is equal. As a result, the cogging torque T_cogApproximately considered to be 0.

When m is 24, the following equation of number 7 is obtained as the cogging torque T_cogThe approximate expression of (c). The "m" 24 indicates a concave-convex structure including 2 ridges. In the equation of the number 7, when 4 Λ is satisfied_s＝Λ₀Λ_mAnd 2 theta_s+π/2＝θ_mCondition (2), cogging torque T_cogAnd in the equation of number 5_sThe case of 0 is equal. As a result, the cogging torque T represented by the equation of the number 7_cogApproximately considered to be 0.

[ number 7]

In the case of the expansion of m-36, 48, and.. it is assumed that the cogging torque T is also the same as that in the case of m-12 and 24_cogIs approximately 0. By providing the projections and depressions (specifically, ridges) having an appropriate size and a number that is an integral multiple of the number of grooves s at an appropriate position on the distal end surface, the cogging torque T can be made to be equal to or larger than the total number of grooves s_cogIs approximately 0. In this case, the condition of the flux guide corresponding to the value of m is satisfied as in the expressions of the number 6 and the number 7.

[ 4. approximate expression of Torque under load ]

A case of a concentrated winding motor with 8 poles and 12 slots is considered as in the case of no load. Component F of magnetomotive force on stator side_{r_st}The 2 nd term in the expression of (θ, ω t), i.e., the number 2, is represented by the following expression of the number 8. Further, the approximate expression of the torque at the time of load is expressed by an expression of number 9 including the phase current amplitude I, based on an expression of number 8. Torque T from tooth space_cogSimilarly, according to the equation of the number 9, a 24 th harmonic component having a vibration frequency 24 times as high as a fundamental wave component of the torque is a main component of the torque.

[ number 8]

[ number 9]

Next, a case where torque ripple is minimized by providing a concave-convex structure on the tip end surface of the stator tooth is considered. When m is 12, the following expression of number 10 is obtained as an approximate expression of torque. m-12 indicates a concave-convex structure including one groove.

[ number 10]

The equations of numbers 9 and 10 are compared. In the equation of number 10, when Λ is satisfied_s＝Λ_mAnd theta_s＝θ_m+ π, torque and Λ in the equation of number 9_sThe case of 0 is equal. As a result, the torque ripple converges to a value represented by the following expression of number 11.

[ number 11]

T(ωt)→AπIΛ₀ ²{F_{rt_5}F_{st_5}sin(24ωt+β)-F_{rt_7}F_{st_7}sin(24ωt-β)}

Although the description of the approximate expression of the torque in the case where m is 24 is omitted, it is assumed that the torque ripple converges to the value shown in the expression of the number 11 as in the case where m is 12.

By providing 1 ridge on the front end face, the cogging torque T can be made_co_gApproximately 0 (corresponding to m-12). As a result, the cogging torque is effectively reduced. Further, by providing two grooves on the tip end surface, the torque ripple converges to a value expressed by the equation of 11 (equivalent to m equal to 24). As a result, torque ripple is effectively reduced. The concave-convex configuration of the embodiment of the present disclosure includes a ridge and two grooves. By providing the ridge and the two grooves on the front end surface, a composite effect of reducing both the cogging torque and the torque ripple at the time of loading is obtained.

According to the concave-convex structure of the present disclosure, by providing the concave-convex including the ridges and the grooves whose number is an integral multiple of the number of the grooves s, which has an appropriate size, at an appropriate position of the front end surface, not only the cogging torque but also the torque ripple can be reduced at the same time. In this case, the condition of the flux guide according to the value of m is satisfied as in the expression of the number 6, the number 7, or the number 10. This is true when the primary vibration frequency of the cogging torque and the torque ripple is equal, as in an 8-pole 12-slot motor.

[ 5. examples ]

The tooth gap torque and the torque ripple were simulated and analyzed by a finite element method for the SPM700 having the 8-pole 12-slot of the embodiment of the present disclosure, which has the concavo-convex structure including the ridge 915 and the two

slots

916A and 916B on the leading end surface S of the tooth. The land 915 included in the concave-convex structure of the front end face is used to generate cogging torque of opposite phase, and the two

grooves

916A, 916B included in the concave-convex structure are used to generate torque ripple of opposite phase. Thus, the effect of reducing cogging torque and torque ripple was measured.

Fig. 10 is a graph showing a simulation analysis result obtained by analyzing an effect of reducing the cogging torque. Fig. 11 is a graph showing the results of simulation analysis by analyzing the effect of reducing torque ripple. In fig. 10 and 11, the horizontal axis represents the motor mechanical angle ω t [ degrees ], and the vertical axis represents the amplitude ratio of the torque. Fig. 10 and 11 show the results of simulation analysis of the torque in the case where the uneven structure is not provided on the distal end surface, as a comparative example. From the measurement results, it is found that the cogging torque and the torque ripple can be effectively reduced by providing the uneven structure on the tip surface.

Further, in order to appropriately reduce cogging torque and torque ripple, widths of ridges and grooves required for the concave-convex configuration of the present disclosure are specifically studied.

Reference is again made to fig. 7. The front face S of the tooth 911 has a concave-convex configuration including a ridge 915 and two

grooves

916A, 916B. The depth h2 of each of the two

slots

916A, 916B is closely related to the average torque. If the groove is deep, the average torque decreases. Therefore, the depth h2 of the groove is set to 0.1 [ mm ]. By providing the ridge 915 in this manner, the depth h2 of the opposing groove from the reference surface R can be reduced. As a result, the average torque can be suppressed from decreasing.

The height h1 of the ridge 915 is set to 0.1 [ mm ] in consideration of the contact with the rotor 920. An optimum of the width w2 of each of the two

grooves

916A, 916B relative to the width w1 of the ridge 915 was determined. The positions of the two

grooves

916A and 916B on the distal end surface S are fixed, and the ratio of the torque amplitudes is measured using the torque amplitude when the two grooves are not provided, that is, when w2 is 0, as a reference value.

Fig. 12 is a graph showing the measurement result of the ratio of the amplitudes of the torques. The horizontal axis in the graph of fig. 12 represents the ratio w2/w1 of the width w2 to the width w1, and the vertical axis represents the amplitude ratio of the torque. The measurement results of the amplitude ratio of the cogging torque and the torque ripple are shown in the graph. The amplitude ratio when w2 is 0, that is, when w2/w1 is 0, is 1. The range of the slot width w2 for which the amplitude ratio of both the cogging torque and the torque ripple is 0.5 × w1 < w2 < 1.5 × w1 is 0.5 × w. Therefore, by setting the width w2 of the two grooves to an appropriate value within this range, both the cogging torque and the torque ripple can be reduced to half or less, as compared with the case where no grooves are provided.

Next, the width w2 of each of the two

grooves

916A, 916B is fixed, and the optimum position for disposing these grooves on the distal end surface S is measured. With the ratio w2/w1 fixed at 1, the amplitude of the torque when the width w2 is 0 is used as a reference value. The change in the amplitude ratio of the torque when the angle θ 2 with respect to the reference value was varied was measured.

Fig. 13 is a graph showing the measurement result of the ratio of the amplitudes of the torques. The horizontal axis in the graph indicates the value of the groove angle θ 2 shown in fig. 6, and the vertical axis indicates the amplitude ratio of the torque. The graph shows the measurement results of the amplitude ratio of the cogging torque and the torque ripple. The amplitude ratio when θ 2 is 0 is 1. The range of the angle theta 2 in which the amplitude ratio of both the cogging torque and the torque ripple is 0.5 or less is 5.0 DEG < theta 2 < 6.5 deg. Therefore, by arranging the two slots within this range, both the cogging torque and the torque ripple can be reduced to less than half.

Industrial applicability

Embodiments of the present disclosure can be widely applied to various motors used in a dust collector, a dryer, a ceiling fan, a washing machine, a refrigerator, an electric power steering device, and the like.

Description of the reference symbols

900: a stator; 910: a laminate; 911: teeth; 915: a ridge; 916A, 916B: a groove; 920: a rotor; 930: a winding; 940: a groove.

Claims

1. A surface magnet type motor includes:

an annular stator having M teeth, M being an integer of 3 or more; and

a rotor having an outer peripheral surface facing an inner peripheral surface of the stator defined by tip surfaces of the M teeth with an air gap therebetween, and having N permanent magnets on the outer peripheral surface, N being an integer of 2 or more,

each of the M teeth has a concave-convex structure on a distal end surface thereof, the concave-convex structure including two grooves arranged at an interval in a circumferential direction of the stator and a ridge located between the two grooves, the two grooves and the ridge extending in a direction parallel to a central axis of rotation of the rotor.

2. The surface magnet type motor according to claim 1,

the dominant number of oscillations of the torque ripple is equal to the dominant number of oscillations of the cogging torque.

3. The surface magnet type motor according to claim 1 or 2,

N：M＝2：3。

4. the surface magnet type motor according to claim 3,

n is 8 and M is 12.

5. The surface magnet type motor according to claim 4,

the ridge is located at a position that bisects the front end surface of each tooth.

6. The surface magnet type motor according to claim 5,

the distance between one of the two grooves and the ridge is equal to the distance between the other of the two grooves and the ridge.

7. The surface magnet type motor according to claim 6,

when w1 is the width of the ridge in the circumferential direction and w2 is the width of each of the two grooves in the circumferential direction, the relationship of 0.5 < (w2/w1) < 1.5 is satisfied.

8. The surface magnet type motor according to claim 6 or 7,

the M teeth include adjacent 1 st tooth and 2 nd tooth, the 1 st tooth and the 2 nd tooth form a slot opening between the front end surfaces, in a cross section perpendicular to a direction in which the central axis extends, a 1 st angle formed by a 1 st line segment connecting a center of the slot opening and a center point on the central axis and a 2 nd line segment connecting a center of a slot on the slot opening side and the center point of two slots arranged on the front end surface of the 1 st tooth is equal to a 2 nd angle formed by a 3 rd line segment connecting a center of a slot on the slot opening side and the center point of two slots arranged on the front end surface of the 2 nd tooth and the 1 st line segment.

9. The surface magnet type motor according to claim 8,

when the 1 st angle and the 2 nd angle are set to theta 1, the relation of 5.0 DEG < theta 1 < 6.5 DEG is satisfied.

10. A motor module having:

the surface magnet type motor of any one of claims 1 to 9;

an inverter that converts electric power from an external power source into electric power supplied to the surface magnet type motor; and

and a motor control device that controls the inverter.