WO2008029624A1

WO2008029624A1 - Brushless dc motor, brushless dc motor drive system, and hydraulic pump system

Info

Publication number: WO2008029624A1
Application number: PCT/JP2007/066274
Authority: WO
Inventors: Kiyotaka Nishijima
Original assignee: Daikin Industries, Ltd.
Priority date: 2006-09-01
Filing date: 2007-08-22
Publication date: 2008-03-13
Also published as: JP4277889B2; JP2008061444A

Abstract

It is possible to reduce a basic wave component of cogging torque by controlling drive of a brushless DC motor (311). A secondary frequency component of the cogging torque is reduced by improving the structure of the brushless DC motor, especially the structure of the rotor. This reduces the pressure pulsation in a hydraulic pump system.

Description

Specification

Brushless DC motor, brushless DC motor drive system, hydraulic pump system

Technical field

[0001] The present invention relates to a brushless DC motor, for example, a brushless DC motor applied to a hydraulic pump system.

Background art

Reduction of torque ripple is desired in a brushless DC motor. This is because torque ripple causes undesirable phenomena such as vibration and noise. In particular, hydraulic pumps require a function to maintain a constant pressure at a fixed position, so the torque ripple that causes pressure pulsation should be reduced.

By the way, when a constant pressure is maintained at a predetermined fixed position, the load applied to the brushless DC motor may be small and drive at a low speed. In general, the torque ripple at the low speed of a brushless DC motor is dominated by the cogging torque due to the field magnetic flux generated by the magnet provided in the rotor.

[0004] The cogging torque has a fundamental wave component that varies with the number of times of the least common multiple LCM of the number of poles Nr of the rotor and the number of slots Ns of the stator per rotation of the rotor of the brushless DC motor. For example, if the rotor has 6 poles and the stator has 36 slots, the least common multiple of both is 36, so a cogging torque having 36 basic cycles is generated during one rotation of the rotor. The cogging torque further has a higher-order frequency component.

In order to reduce the cogging torque, the shape of the motor has been devised. Generally, a skew is provided, the magnetomotive force of the rotor is made close to a sine wave, the change of magnetic flux in the so-called air gap between the rotor and stator is alleviated, or the frequency of the cogging torque is increased by increasing the number of slots. It is generally known that the effect is reduced by increasing the effect, and the permeance is equalized by devising the shape and interval of the magnetic poles. Examples of Patent Documents 1 to 6 that disclose techniques for reducing cogging torque are shown below.

[0006] Patent Document 1 describes a problem in a motor in which a magnet is embedded in a rotor magnetic body. A technique for dividing a veg motor structure that reduces cogging torque to be divided into a plurality of blocks along the rotation axis direction is disclosed. These blocks are arranged in the direction of the rotation axis at an angle that cancels the cogging torque.

[0007] Patent Document 2 focuses on the angle of the magnetic pole determined by the shape of the magnetic flux barrier that prevents short-circuiting of the field magnetic flux, and by setting the angle to a predetermined value or making the pitch unequal, A technique for reducing cogging torque has been disclosed!

[0008] Patent Document 3 discloses a technique for selecting the value of a parameter that minimizes cogging torque using the angle of a magnetic pole or the like as a shape parameter.

[0009] Patent Document 4 discloses a technique for selecting a predetermined value of the angle of the width of the magnet to reduce the cogging torque without applying a skew to the rotation center axis.

[0010] In Patent Document 5, torque ripple data is stored, and the torque command is corrected using the data. As a result, the current of the sine wave flowing through the armature is corrected and the torque ripple is reduced.

Patent Document 6 shows that torque correction data is obtained by adding a waveform that is an integral multiple of the energization frequency to the armature current to reduce torque fluctuations!

Patent Document 1: Japanese Patent Laid-Open No. 5-236687

Patent Document 2: JP-A-11 98731

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-343861

Patent Document 4: JP-A-11 299199

Patent Document 5: JP-A-11 55986

Patent Document 6: Japanese Patent Laid-Open No. 5 15188

Disclosure of the invention

Problems to be solved by the invention

[0013] Laminating a plurality of blocks in the direction of the rotational axis as in Patent Document 1 complicates the process of assembling the rotor and deteriorates productivity.

[0014] With the technique described in Patent Document 2, cogging torque remains, and it is unclear whether the waveform of the remaining cogging torque is smooth.

[0015] In the techniques described in Patent Document 3 and Patent Document 4, higher-order components of cogging torque remain. It seems to be.

[0016] In the methods disclosed in Patent Documents 1 to 4, although attention is paid to the cogging torque amplitude and peak-to-peak values, the frequency distribution is not considered. Therefore, high-order frequency components of cogging torque remain.

[0017] In the techniques described in Patent Documents 5 and 6, it is necessary to accurately detect the position information of the rotor. If there is an error in the position information for correction to reduce the fundamental component of the cogging torque, the higher-order component of the cogging torque may even be deteriorated.

[0018] For example, the position information may be detected with an error of about 1 degree in the mechanical angle. And in the cogging torque with 36 fundamental periods in one rotation of the rotor, the fundamental period corresponds to 10 degrees of machine angle. Therefore, an error of 1 degree in the mechanical angle corresponds to 2π / 10 of the phase of the basic period of cogging torque.

In the correction of the cogging torque, a correction torque obtained by shifting the waveform of the cogging torque by π is added to the DC torque to be output. Therefore, if the phase of the waveform of the correction torque is shifted by 2 π / 10 corresponding to the error of 1 degree mechanical angle, sin) one sin (a + 2 π / ΐ0) = 0 for the fundamental wave component of the cogging torque. 62cos (α + π / 10), and about 60% of the amplitude remains without being cancelled. On the other hand, for the secondary component of cogging torque (frequency component twice the fundamental wave component), an error of 1 degree in mechanical angle corresponds to 2π / 5 of the phase. Therefore, it corresponds to the secondary component of the cogging torque corresponding to the error of 1 degree of mechanical angle! /, And sin (a)-si η (α + 2 π / 5) = 1. 2cos (α + π / 5) In other words, when an error of 1 degree mechanical angle occurs in the secondary component, an amplitude of about 20% is added and the torque ripple deteriorates. Therefore, it is not easy to reduce the secondary component of cogging torque by correcting the DC torque to be output.

[0020] It is not easy to reduce the error in the mechanical angle. When a motor is installed on a device to which the motor is applied, the stator is held on the motor frame by, for example, shrinking, press-fitting, or fastening with bolts. The rotor is held by, for example, shrinking and press-fitting the rotating shaft. The rotating shaft is held by a bearing incorporated in a bracket on the load side and the opposite side of the motor, and the bracket is attached to the frame of the motor. [0021] A rotor position detector such as an encoder is attached to the rotating shaft protruding from the frame of the motor. It is necessary to calibrate the relationship between the rotor position and the rotor position signal obtained from the rotor position detector and indicating the rotor position. By rotating the rotating shaft with external force, the waveform of the induced voltage generated in the motor is measured, and the deviation between the zero cross point and the rotor position signal is obtained as an offset amount. The offset amount of the motor attached to the frame is unique, so record the offset amount on the motor characteristics table or on the nameplate of the frame. When the motor is driven, the controller performs control corrected using the offset amount.

[0022] The measurement of the zero-cross point is affected by noise generated in the waveform of the induced voltage, and thus causes an error. Measuring the waveform of the induced voltage multiple times and averaging them is also a method that is impractical from the viewpoint of force S and productivity.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique for easily reducing the secondary frequency component of cogging torque of a brushless DC motor. The fundamental wave component of the cogging torque can be reduced by external control of the brushless DC motor by a known method as described in Patent Documents 5 and 6.

Means for solving the problem

[0024] A first aspect of the brushless DC motor that is effective in the present invention is a plurality of field magnets arranged annularly in the circumferential direction with a peripheral edge (10), each having a pair of end portions in the circumferential direction. (6) and an air gap provided at each of the end portions and extending toward the center of the field magnet at a predetermined distance (L1) from the periphery on the periphery side of the field magnet. And a rotor (100) rotatable in the circumferential direction and a stator (200) facing the rotor while being spaced apart from each other.

[0025] A tip of the air gap provided at the end of the other field magnet adjacent to the one field magnet on the one field magnet side, and the one of the field magnets The angle (Θ) at which the tip of the air gap provided at the end on the other side of the field magnet expands in the circumferential direction is selected as follows.

[0026] The fundamental wave component of cogging torque per rotation of the rotor varies depending on the least common multiple (LCM) of the number of poles (Nr) of the rotor and the number of slots (Ns) of the stator. . This group The angle that gives the minimum value of the main wave component is the original angle (θ 1). An angle obtained by adding or subtracting an angle obtained by dividing 90 degrees by the least common multiple to the original angle is an angle used for the selection.

[0027] A second aspect of the brushless DC motor according to the present invention is the first aspect thereof, wherein the original angle is obtained as the angle giving the minimum value of the amplitude of the cogging torque.

[0028] A brushless DC motor drive system that is effective in the present invention includes a brushless DC motor (M) according to the present invention, a position measuring unit (501) for determining the position (φ) of the rotor, and the brushless DC motor. From the current detector (502) for determining the current (iM) flowing through the DC motor, the fundamental wave component data (D) of the cogging torque and the position of the rotor, the fundamental wave component of the cogging torque is obtained. A cancellation signal generator (505) for outputting a cancellation signal (Z) for cancellation, and a motor driving unit for driving the brushless DC motor based on the position of the rotor, the current, and the cancellation signal V (506).

[0029] A hydraulic pump system that is powerful to the present invention includes a brushless DC motor drive system that powers the present invention and a hydraulic pump (36) driven by the brushless DC motor. Desirably, the hydraulic pump system drives the injection molding machine (34).

The invention's effect

[0030] According to the first aspect of the brushless DC motor, which is particularly effective in the present invention, the secondary frequency component of the cogging torque can be easily reduced. The force and the fundamental wave component can be reduced by control from the outside of the brushless DC motor by a known method.

[0031] According to the second aspect of the brushless DC motor of the present invention, the original angle can be easily estimated.

[0032] According to the brushless DC motor drive system which is effective in the present invention, the fundamental wave component of the cogging torque can be reduced.

[0033] According to the hydraulic pump system of the present invention, the pressure pulsation is small. In addition, the pressure pulsation in the injection molding machine that reduces the pressure pulsation at low speed and keeps the piston in place can be reduced by J.

[0034] Objects, features, aspects and advantages of the present invention will be apparent from the following detailed description and the accompanying drawings. It becomes more obvious.

Brief Description of Drawings

[0035]

FIG. 2 is a plan view illustrating the structure of a brushless DC motor.

3] It is a plan view showing the structure of the rotor in detail.

[Fig. 8] A graph showing the dependence of the amplitude of the fundamental component of the cogging torque on the angle Θ.

[Fig. 9] A graph showing the dependence of the secondary component of cogging torque on the angle Θ.

FIG. 10 is a graph showing the dependence of cogging torque on angle Θ.

FIG. 11 is a block diagram illustrating the configuration of a brushless DC motor drive system.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a block diagram showing a hydraulic pump system that performs injection molding using a hydraulic pump. The injection molding machine 34 has a molding machine 34a and a hydraulic cylinder 34b. The hydraulic cylinder 34b is hydraulically driven by a hydraulic pump 36. For example, a gear pump, a vane pump, or a piston pump is used as the hydraulic pump 36. A hydraulic pressure gauge 33 is provided between the hydraulic pump 36 and the hydraulic cylinder 34b to monitor the hydraulic pressure.

[0037] The hydraulic pump 36 is driven by a brushless DC motor drive system 35. The brushless DC motor drive system 35 includes a brushless DC motor 311, a rotational position detector 312 that detects the rotational position of the rotor, and a controller 313 that controls the rotation of the brushless DC motor 311. The controller 313 supplies the appropriate armature current to the brushless DC motor 311 based on the rotational position of the rotor of the brushless DC motor 311 !. The controller 313 is supplied with a DC voltage or an AC voltage from the power supply 30.

[0038] The speed of the piston J of the hydraulic cylinder 34b determines the flow rate of the oil used for the hydraulic drive. It is determined by the value divided by the cross-sectional area of the motor 34b. The force that can be generated in the piston J is determined by the product of the hydraulic pressure and the cylinder cross-sectional area. When piston J is displaced, the flow rate of oil is required, so brushless DC motor 311 must rotate to flow oil against the hydraulic pressure.

On the other hand, the hydraulic pump is required to have a function of maintaining a constant pressure at a predetermined fixed position. For example, in the molding machine 34a, although not shown in detail, a plastic resin is injected into the mold. After filling the mold with the plastic resin, a constant pressure is maintained without injecting the plastic resin. In this case, it is not necessary to displace the piston J, but oil leaks from the hydraulic pump 36, for example. Therefore, since some oil flow is generated in the hydraulic pump 36, the brushless DC motor 311 rotates at a slightly low speed / rotation speed in order to drive the hydraulic pump 36.

[0040] The oil leakage tends to increase as the hydraulic pressure increases. The higher the hydraulic pressure, the higher the rotational speed of the brushless DC motor 311. In other words, hydraulic pumps are used at higher speeds as torque load increases. Therefore, the torque ripple has little effect on the hydraulic pressure fluctuation due to the inertia of the motor rotor and hydraulic pump at high speeds, but the effect is large at low speeds, and torque ripple correction is important. Since the load is light at low speed, the cogging torque is dominant in the torque ripple where the current supplied to the brushless DC motor 311 is also small. Therefore, to reduce the pressure pulsation in the hydraulic pump system, it is important to reduce the cogging torque.

FIG. 2 is a plan view illustrating the structure of the brushless DC motor 311. The brushless DC motor 311 has a rotor 100 and a stator 200 facing the rotor 100 while being spaced apart. A plane perpendicular to the rotation axis of the rotor 100 is shown in FIG. 2 as a plan view.

[0042] In the stator 200, teeth 201 and slots 202 are alternately arranged in the circumferential direction. Actually, the armature winding wound around the teeth 201 is accommodated in the slot 202. In FIG. 2, the drawing of the armature winding is omitted in order to avoid complexity of the drawing. In this example, the number of slots 202 is 36!

FIG. 3 is a plan view showing the structure of the rotor 100 in detail. The rotor 100 is rotatable about a rotation axis Z0 and has a peripheral edge 10 on the outer peripheral side thereof. And in the circumferential direction A plurality of field magnets 6 that are arranged in a shape and each have a pair of end portions in the circumferential direction are embedded in a direction perpendicular to the rotation axis Z0. Each of the field magnets 6 is provided with a gap 31 for preventing a magnetic flux short circuit. The air gap 31 extends toward the center of the field magnet 6 at a predetermined distance L1 on the peripheral edge 10 side of the field magnet 6.

Further, the rotor 100 is provided with a through hole 5 through which a rotary shaft (not shown) passes, and a plurality of fastening holes 4 are provided on the outer peripheral side thereof. The fastening hole 4 is used when the core of the rotor 100 in which the field magnet 6 is embedded is formed by laminating a plurality of steel plates. For example, when these steel plates are laminated and fixed with bolts and nuts, the bolts penetrate through the fastening holes 4. Other methods for laminating and fixing steel plates without using the fastening holes 4 are also well known, and of course, the fastening holes 4 are not necessary.

FIG. 3 illustrates the case where six field magnets 6 are provided and the number of poles is six. The force that the number of fastening holes 4 is also 6 is not necessary to match the number of field magnets.

[0046] The tips of the air gaps 31 provided at the ends of different field magnets adjacent to each other are directed to the opposite sides in the circumferential direction. The angle at which the pair of tips expands in the circumferential direction is depicted as an angle Θ in FIG.

4 to 7 are graphs showing the cogging torque at electrical angles of 0 to 60 degrees when the configuration shown in FIG. 3 is adopted for the rotor. The horizontal axis is the electrical angle. Here, the number of poles of the rotor is assumed to be 6! /, And so the example is! /, So the electrical angle is 3 (= 6/2) times the mechanical angle. The fundamental wave component of cogging torque is equivalent to the number of the least common multiple LCM for the mechanical angle of 360 degrees, here 36 cycles, so one period corresponds to a mechanical angle of 10 degrees. Therefore, one period of the fundamental component of cogging torque corresponds to an electrical angle of 30 degrees.

[0048] FIG. 4, FIG. 5, FIG. 6, and FIG. 7 show cases where the angle Θ force is 17 degrees, 20 degrees, 22 degrees, and 25 degrees, respectively. In Fig. 6, it can be seen that the cogging torque has the smallest amplitude, but its higher order components remain.

FIG. 8 is a graph showing the dependence of the amplitude of the fundamental component of the cogging torque on the angle Θ. Since the fundamental wave component of the cogging torque is dominant, it can be seen that the amplitude of the cogging torque is minimized when the angle Θ is around 22 degrees, corresponding to Figs. The angle Θ that gives the minimum amplitude of the fundamental component of the cogging torque is the original angle Θ1. [0050] For example, Patent Document 3 suggests that an integer multiple of a value obtained by dividing 360 degrees by the least common multiple LCM is adopted as the angle Θ for reducing the cogging torque, which is described here. For example, the angle θ 1 will appear every 360 degrees / 36 = 10 degrees. In FIG. 8, one of the original angles θ 1 appears in the vicinity of 22 degrees, so the other values of the original angle θ 1 are estimated to be 12 degrees and 32 degrees, and the prediction is based on the shape of the graph in FIG. Inferred to be reasonable.

[0051] FIG. 9 is a graph showing the dependency of the amplitude of the secondary component of the cogging torque on the angle Θ. The angle Θ that minimizes the amplitude of the secondary component appears at intervals of 15 degrees, 20 degrees, 25 degrees, 30 degrees, and 5 degrees.

That is, the angle Θ that minimizes the amplitude of the secondary component of the cogging torque may exist at a plurality of original angles θ 1 with a minimum interval of 360 degrees / half of LCM, 360 degrees / LCM / 2. Recognize. In other words, the angle Θ is selected by adding or subtracting the angle obtained by dividing 90 ° by the least common multiple LCM to the original angle θ 1 that gives the minimum value of the fundamental component of the cogging torque. Thus, the amplitude of the secondary component of the cogging torque can be minimized.

[0053] Figure 10 shows the dependence of the cogging torque on the P-P (peak 'to-peak') value, its primary component (fundamental wave component) amplitude value, and secondary component amplitude value on the angle Θ. It is a graph showing. The original angle Θ 1 is the angle Θ that gives the minimum value of the amplitude of the fundamental component of the cogging torque, but can be easily calculated as the angle that gives the minimum value of the amplitude of the cogging torque. This is because the fundamental wave component of the cogging torque is dominant as described above. Note that the third and higher harmonics of the cogging torque are practically small enough not to cause a problem.

In this embodiment, the amplitude of the secondary component of the cogging torque is minimized by using one of the parameters of the motor shape such as the angle Θ. Unlike the angle Θ 1, the angle Θ does not minimize the amplitude of the fundamental component of the cogging torque. However, since the angle Θ does not maximize the amplitude of the fundamental component of the cogging torque, the well-known technique exemplified in Patent Documents 5 and 6 is used to correct the armature current. Therefore, it is easy to reduce the fundamental component (not the secondary component of cogging torque).

FIG. 11 is a block diagram illustrating the configuration of a brushless DC motor drive system. Mo Data M corresponds to the brushless DC motor 311 in Fig. 1. The rotational position detector 501a corresponds to the rotational position detector 312 in FIG. The rotational position detector 501 detects the position of the rotor of the motor M as a position signal φ0, which is corrected with the offset value φ1 of the angular position, and the position Φ is measured. In other words, the rotational position detector 501a and the adder / subtractor 50 lb for adjusting the offset value φ1 can be combined to be understood as the position measuring unit 501 for measuring the position φ.

The data D of the primary component of the torque ripple is given to the torque ripple primary component cancellation signal generation unit 505 together with the position φ. The generation unit 505 outputs a cancellation signal Z based on the data D and the position φ. The cancellation signal Z is a signal for canceling the fundamental wave component of the cogging torque.

[0057] The data D of the primary component of the torque ripple can be obtained in advance by driving the motor M, for example, with no load. As described above, when the motor is applied to the hydraulic pump, the data D is collected at a low speed because the speed is low when the load is light. As a result, the fundamental wave component of the cogging torque can be obtained as data D.

The current detector 502 obtains the current value iM of the current flowing through the motor M. Torque command calculation unit 506a calculates torque command τ * based on position φ and current iM. The motor drive waveform generator 506b generates a motor drive waveform based on the position φ, the current value iM, and the torque command τ *, and supplies the current reflecting the waveform to the motor Μ. Therefore, the torque command calculation unit 506a and the motor drive waveform generation unit 506b are combined, based on the rotor position φ, current value i M, and cancellation signal Z! /, And grasped as the motor drive unit 506 that drives the motor M Doing with the power S

[0059] As described above, an error occurs in the offset value φ1, which may cause an error in the position φ. However, in the brushless DC motor drive system, the fundamental value component of the cogging torque is reduced by controlling the current value iM, and the secondary component of the cogging torque is not reduced by controlling the current value iM. Therefore, as described above, a situation in which the secondary component of the cogging torque increases is not caused. As described above, the secondary component of the cogging torque is reduced by devising the shape of the motor! Therefore, the cogging torque can be reduced in consideration of the frequency distribution. [0060] In this way, the fundamental wave component of the cogging torque is reduced by the control during driving of the brushless DC motor 311, and the secondary frequency component is reduced by the structure of the brushless DC motor 311 (in particular, the structure of the rotor 100). This reduces the pressure pulsation in the hydraulic pump system with the force S.

The present invention has been described in detail. The above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that the myriad variations S that are not illustrated can be assumed without departing from the scope of the present invention.

Claims

The scope of the claims

[1] Perimeter (10),

A plurality of field magnets (6) that are annularly arranged in the circumferential direction, each having a pair of ends in the circumferential direction;

A gap (31, 32) provided at each of the end portions and spaced from the peripheral edge by a predetermined distance (L1) on the peripheral side of the field magnet and extending toward the central portion of the field magnet. A rotor (100) rotatable in the circumferential direction,

A stator (200) opposed to the rotor while being spaced apart;

With

A tip of the air gap provided at the end of the other field magnet adjacent to the one field magnet on the one field magnet side, and the other of the one field magnet. The angle at which the tip of the air gap provided at the end on the field magnet side extends in the circumferential direction (Θ) is selected as a predetermined angle,

The fundamental component of the cogging torque varies with the number of times of least common multiple (LCM) of the number of poles of the rotor (Nr) and the number of slots of the stator (Ns) per revolution of the rotor,

An angle obtained by adding or subtracting an angle obtained by dividing 90 degrees by the least common multiple to the original angle (Θ 1) that gives the minimum value of the fundamental wave component is the predetermined angle. Brushless DC motor (311; M).

[2] The brushless DC motor according to claim 1, wherein the original angle is obtained as the angle that gives a minimum value of the amplitude of the cogging torque.

[3] The brushless DC motor (M) according to any one of claims 1 to 2, a position measuring unit (501) for obtaining a position (φ) of the rotor,

From the current detector (502) for obtaining the current (iM) flowing through the brushless DC motor, the fundamental wave component data (D) of the cogging torque and the position of the rotor, the fundamental wave of the cogging torque A cancellation signal generator (505) that outputs a cancellation signal (Z) for canceling the component;

A motor drive unit (506) for driving the brushless DC motor based on the position of the rotor, the current, and the cancellation signal; A brushless DC motor drive system (35).

[4] The brushless DC motor drive system according to claim 3,

A hydraulic pump system comprising: a hydraulic pump (36) driven by the brushless DC motor.

5. The hydraulic pump system according to claim 4, which drives the injection molding machine (34).