WO2015181967A1 - Method for manufacturing permanent magnet electric motor - Google Patents

Abstract

　A method for manufacturing an electric motor (1) in which a permanent magnet (53) is included on a rotor (5) or a stator (7), wherein the method for manufacturing an electric motor (1) has: a magnetization step (P4) for magnetizing the permanent magnet; and a demagnetization step (P5) that is carried out after the magnetization step, and incompletely demagnetizes a portion of the permanent magnet magnetized from the magnetization step. In the demagnetization step a phase angle (β) of a demagnetizing electric current that generates a reverse magnetic field around the permanent magnet is controlled to 90º or another predetermined value.

Description

Manufacturing method of permanent magnet type electric motor

The present invention relates to a method for manufacturing a permanent magnet electric motor.

In brushless motors for air conditioner compressors that use permanent magnets such as ferrite magnets, when the external temperature of the air conditioner compressor is low, the room temperature is higher than room temperature to prevent demagnetization that tends to occur at low temperatures. Compared with the case of this, what sets the current limiting threshold value of the electric current which flows into a motor low is known (patent document 1). When using an air conditioner for heating in the winter, the compressor motor at the start is at the same temperature as the low-temperature outside air and easily demagnetizes. The reverse magnetic field is reduced, thereby preventing the demagnetization of the permanent magnet.

Japanese Patent No. 5098599

However, if the current limit threshold value of the current flowing to the electric motor is set low, sufficient output cannot be obtained at the start of the air conditioner that requires the most heating performance, and the intended purpose of the heater is achieved. There is a problem that can not be.

The problem to be solved by the present invention is to provide a method of manufacturing a permanent magnet type electric motor that can suppress a decrease in output due to demagnetization.

According to the present invention, in an electric motor including a permanent magnet in one of a rotor and a stator, after the permanent magnet is magnetized, a demagnetization process is performed in which a part of the permanent magnet is incompletely magnetized. In addition, the above problem is solved by controlling the phase angle β of the demagnetization processing current that generates a reverse magnetic field around the permanent magnet to a predetermined value.

According to the present invention, when a demagnetization process is performed in which a part of the permanent magnet is in an incompletely magnetized state, no demagnetization is performed unless a further magnetic field acts, and the phase angle β of the demagnetization process current Therefore, it is possible to efficiently suppress a decrease in output due to demagnetization when the electric motor is used.

1 is an overall perspective view showing a permanent magnet type electric motor according to an embodiment of the present invention. It is a disassembled perspective view of FIG. 1A. It is a disassembled perspective view of FIG. 1B. It is a fragmentary sectional view which follows the 1D-1D line | wire of the rotor shown to FIG. 1C. It is a fragmentary sectional view (equivalent to a part of section which meets a 1D-1D line) showing a permanent magnet type electric motor concerning other embodiments of the present invention. FIG. 6 is a partial cross-sectional view (corresponding to a part of a cross section taken along line 1D-1D) showing a permanent magnet type electric motor according to still another embodiment of the present invention. It is process drawing which shows the manufacturing method of the permanent magnet type electric motor which concerns on one embodiment of this invention. It is process drawing which shows the manufacturing method of the permanent magnet type electric motor which concerns on other embodiment of this invention. It is a figure which shows the magnetization curve of the permanent magnet in the magnetization process of FIG. 3A and 3B. It is a graph for demonstrating the example of a scene where overcurrent flows into a motor, when this invention is applied as a motor for driving | running | working driving | running | working of an electric vehicle. It is a figure which shows the magnetization curve of a ferrite magnet in case the external magnetic field Hex in cryogenic temperature is large. It is a figure which shows the magnetization curve of a ferrite magnet in case the external magnetic field Hex in cryogenic temperature is small. It is a figure which shows the magnetization curve of the ferrite magnet in normal temperature. It is a graph which shows the no-load induced voltage after applying various drive currents in a low temperature atmosphere and a normal temperature atmosphere, and driving an electric motor. It is a figure for demonstrating the effect | action of this invention using the magnetization curve of the ferrite magnet in cryogenic temperature. It is a graph which shows the no-load induced voltage after applying a various demagnetization process current and carrying out a demagnetization process of the electric motor. It is a graph which shows the mode of a change of a no-load induced voltage with respect to the demagnetization process electric current of an electric motor in four combinations from which the maximum residual magnetic flux density and a holding force become the maximum and the minimum, respectively. It is a graph which shows the no-load induced voltage with respect to the demagnetization process current for demonstrating an example of the demagnetization process of this invention. It is a flowchart which shows an example of the demagnetization process of this invention. It is a flowchart which shows the other example of the demagnetization process of this invention. It is a graph which shows the relationship between the demagnetization process current for demonstrating the effect | action of the demagnetization process example shown in FIG. 15, and a no-load induced voltage. It is a graph which shows the relationship between the demagnetization process current for demonstrating the effect | action of the demagnetization process example shown in FIG. 15, and a no-load induced voltage. It is a flowchart which shows the further another example of the demagnetization process of this invention. It is a graph which shows the relationship between the demagnetization process current for demonstrating the effect | action of the demagnetization process example of FIG. 20, and a no-load induced voltage. It is a flowchart which shows the further another example of the demagnetization process of this invention. It is a graph which shows the relationship between the demagnetization process current and no-load induced voltage for demonstrating the further another example of the demagnetization process of this invention. It is a graph which shows the relationship between the demagnetization process current and no-load induced voltage for demonstrating the further another example of the demagnetization process of this invention. Three-phase AC demagnetizing current when the demagnetizing current is an alternating current that is asynchronous to the rotation of the rotor and demagnetizing processing is performed at a specific frequency obtained by substituting a specific value into Equation 1. It is a graph which shows the rotation angle and current phase angle. Three-phase alternating current demagnetization current when demagnetization processing current is an alternating current that is asynchronous with the rotation of the rotor and demagnetization processing is performed at a specific frequency obtained by substituting other specific values into Equation 1. It is a graph which shows the rotation angle and electric current phase angle of a rotor.

《Permanent magnet type electric motor》
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1A to 1D are diagrams showing a permanent magnet type electric motor 1 according to an embodiment of the present invention. As an example of a permanent magnet type electric motor, an embedded magnet type synchronous motor (8 poles 24 slots three-phase AC) is shown. The example of a structure of a synchronous motor) is shown. As shown in FIG. 1C, the electric motor 1 of this example includes a housing 2 made of a nonmagnetic material, a front cover subassembly 3 made of the same nonmagnetic material, a rear cover subassembly 4 made of the same nonmagnetic material, and a permanent member. A rotor subassembly 5 and a coil subassembly 6 that employ a ferrite magnet as a magnet are provided. The front cover subassembly 3, the rear cover subassembly 4, the rotor subassembly 5 and the coil subassembly 6 are subassemblies in which various parts are assembled to the respective main bodies. Hereinafter, the front cover 3, the rear cover 4, and the rotor will be described. 5 and coil 6 may be abbreviated.

The rotor 5 is configured by inserting a shaft 52 into the rotor core 51. As shown in FIG. 1D, the rotor core 51 is provided with a hole 511 for inserting and fixing the shaft 52 at the center and a hole 512 for embedding the permanent magnet 53. The plurality of magnetic steel plates are laminated and fixed. 1D is a cross-sectional view showing a part of a cross section of the rotor 5 of FIG. 1C cut along a plane perpendicular to the axis of the shaft 52, and mainly shows one pole portion of the eight poles and 24 slots. Eight holes 512 for inserting the permanent magnets 53 are provided at equal intervals along the outer periphery of the magnetic steel plate, and the holes 512 are formed by laminating and fixing a plurality of magnetic steel plates in the circumferential direction. The permanent magnet 53 extends in the axial direction, and the permanent magnet 53 is inserted therein and fixed to both ends of the rotor 5 with a nonmagnetic end plate 54 or the like, thereby preventing the permanent magnet 53 from coming off.

The coil subassembly 6 includes a stator core 61 and a coil 62. As shown in FIG. 1D, the stator core 61 is formed by laminating and fixing a plurality of annular magnetic steel plates having teeth 63 formed on the inner peripheral side. It consists of Then, after laminating and fixing a plurality of magnetic steel plates with their circumferential positions aligned, a plurality of teeth 63 formed at equal intervals along the circumferential direction are coiled with three-phase AC windings via an insulator or the like 62 is wound. The coil assembly 6 is fixed to the inside of the housing 2 by a method such as shrink fitting, and the front cover 3 is assembled to the housing 2 so that the stator subassembly 7 shown in FIG. 1B (hereinafter also simply referred to as the stator 7). Is configured. One end of the shaft 52 of the rotor 5 is inserted into the hole 31 of the front cover subassembly 3, the other end of the shaft 52 is supported by a hole or a bearing (not shown) of the rear cover 4, and the rear cover 4 is supported by the stator subassembly 7. As a result, the electric motor 1 of this example shown in FIG. 1A is assembled.

The electric motor 1 of this example shown in FIGS. 1A to 1D is of a type in which a permanent magnet 53 is embedded in a rotor 5 and a coil 62 is provided in a stator 7, but the electric motor 1 of the present invention is a stator. 7 may be a type in which a permanent magnet is provided and a coil 62 is provided in the rotor 5. The electric motor 1 of this example shown in the figure is an embedded magnet type motor in which a permanent magnet 53 is embedded in a rotor core 51. However, the electric motor 1 of the present invention has a surface in which a permanent magnet is arranged on the surface of the rotor core 51. A magnet type motor may be used. Further, in the case of an embedded magnet type motor, the main surface of the rectangular parallelepiped magnet 53 is embedded substantially parallel to the side surface of the rotor 5 as shown in FIG. 1D. In addition, as shown in FIG. Another permanent magnet 53a, 53b may be provided, or two permanent magnets 53c, 53d may be provided at a predetermined angle with respect to the side surface of the rotor 5, as shown in FIG. 2B. 2A and 2B are partial cross-sectional views (corresponding to a part of a cross section taken along line 1D-1D) showing a rotor 5 of a permanent magnet type electric motor 1 according to another embodiment of the present invention.

Further, the output suppression effect by the demagnetization process of the present example described later appears remarkably particularly when a ferrite magnet is adopted for the permanent magnet 53, but for the purpose of eliminating heavy rare earth magnets such as neodymium Nd and dysprosium Dy. Absent. This kind of heavy rare earth magnet may be used because the effect of the demagnetization treatment of this example is the same regardless of the magnitude of the effect. In addition, unlike a ferrite magnet, in the case of an electric motor using a magnet whose demagnetization resistance decreases in a high temperature atmosphere, the technology according to this example may be applied on the high temperature side.

<Method for manufacturing electric motor>
Next, the manufacturing method of the electric motor 1 of this example is demonstrated. FIG. 3A is a process diagram showing an example of a manufacturing method of the electric motor 1 of this example. The manufacturing method of this example is the same as that shown in FIG. 1C in the same manner as the rotor assembly step P1 for assembling the rotor subassembly 5 shown in FIG. 1C. A stator assembly step P2 for assembling the housing 2, the front cover assembly 3 and the coil subassembly 6 to the stator subassembly 7 as shown in FIG. 1B. In the next motor assembly step P3, as shown in FIG. 1B, the stator subassembly 7, the rotor subassembly 5, and the rear cover subassembly 4 are assembled to complete the electric motor 1 shown in FIG. 1A. In the subsequent basic characteristic test step P6, various characteristics of the electric motor including the initial induced voltage are measured, and the magnetized state and the coil quality are inspected. In the output inspection process P7, a final operation test including output measurement of the manufactured electric motor is performed.

In the rotor assembly process P1, the permanent magnet 53 is not magnetized. Therefore, when the rotor subassembly 5 is assembled to the stator subassembly 7 in the motor assembly process P3, the magnetic force of the permanent magnet 53 causes the rotor subassembly 5 to be assembled. The assembly 5 is not attracted to the coil subassembly 6 and the assembly workability is improved.

In the next magnetizing process P4, the assembly of the electric motor 1 shown in FIG. 1A is completed, and the terminal of the coil 62 is connected to a magnetizing power source to energize the magnetizing current, and the permanent magnet 53 is fully magnetized (saturated magnetizing). Magnetize). When a plurality of magnetization processes are required according to the specifications of the electric motor 1, this magnetization process step is repeated a plurality of times. In addition to the assembled state shown in FIG. 1A, the form of the electric motor 1 when performing the magnetizing process is a state where the rear cover 4 is removed from the state shown in FIG. 1A, that is, the rotor subassembly 5 is assembled to the stator subassembly 7. It may be in the state. Further, instead of the stator subassembly 7, a dedicated magnetizing device having a structure including the same coil assembly may be used.

FIG. 4 shows the intensity H (A / m, horizontal axis) of the magnetic field acting on the permanent magnet 53 by the magnetizing current and the magnetic flux density B (T = Wb / inside) of the permanent magnet 53 in the magnetizing process P4. m ² ) or a magnetization curve showing a relationship with the magnetization J (T = Wb / m ² ) of the permanent magnet 53. In the magnetizing process P4, a positive magnetic field is applied to the rotor subassembly 5 including the permanent magnet 53, so that the first quadrant of the magnetization curve is shown. When a predetermined magnetizing current (for example, a magnetizing current having a current phase angle β = −90 ° at which the positive magnetic field is the strongest) is energized in the magnetizing process P 4, the external magnetic field from the stator 7 is permanently applied to the rotor 5. Acting on the magnet 53, the magnetization J and the magnetic flux density B of the permanent magnet 53 whose initial magnetization J and initial magnetic flux density B were zero (point a) changed from point a → point b → point c, At this point c, a saturated state (fully magnetized state) is reached. An energization current value for bringing the permanent magnet 53 into a saturated state is obtained in advance by theoretical calculation or verification experiment. When the permanent magnet 53 reaches a saturated state, the energization to the stator 7 is stopped and the external magnetic field is made zero. As a result, the magnetization J and the magnetic flux density B of the permanent magnet 53 change from the point c to the point d. The magnetization at this point d is called residual magnetization Jr (= 4πIr), and the magnetic flux density is called residual magnetic flux density Br, which corresponds to the magnetization J and magnetic flux density B when the magnetic field strength H = 0 in FIG. . The electric motor 1 in which the permanent magnet 53 is completely magnetized is obtained by the above magnetizing process P4.

When the permanent magnet 53 is magnetized, the electric motor 1 is ready for driving. However, when this electric motor 1 is mounted on a real vehicle as a driving motor for an electric vehicle, for example, a demagnetization phenomenon may occur during traveling. FIG. 5 is a graph showing a relationship example between a motor current command value when an electric vehicle equipped with the electric motor 1 is traveling, an actual motor current corresponding to the motor current command value, and a motor rotation speed (rotation speed).

For example, until the time t1, the motor current value and the motor rotation speed are normal values with respect to the motor current command value set according to the accelerator opening. If it occurs, control for restoring the grip force of the tire is performed, and a motor current (overcurrent) larger than the motor current command value may flow between times t2 and t3. In general, a rated output and a rated current are determined for the electric motor 1 and are used within the rated output and the rated current during normal use. However, a current exceeding the rated current may flow under the above-described unique circumstances. Due to this overcurrent, a magnetic field from the stator 7 causes a reverse magnetic field to act on the permanent magnet 53 of the rotor 5, which may demagnetize the permanent magnet 53 during use.

This demagnetization phenomenon will be described in more detail. Ferrite magnets AFe ₂ O ₄ (A = Mn, Co, Ni, Cu, Zn) that do not use heavy rare earth elements such as neodymium Nd and dysprosium Dy are low in cost and can avoid resource procurement risks. It is used in many permanent magnet electric motors. However, the ferrite magnet has a problem that it is easy to demagnetize at a low temperature. When demagnetization is performed, the output of the electric motor 1 is reduced and the desired performance cannot be exhibited. First, this demagnetization phenomenon will be described with reference to FIGS.

FIG. 6 is a diagram showing a magnetization curve (also referred to as a magnetic history curve or a hysteresis loop) of a ferrite magnet at a predetermined low temperature (for example, an extremely low temperature of −20 ° C. or lower), and is shown in the second quadrant. It shows the demagnetization curve to be performed. The horizontal axis in FIG. 6 is the magnetic field strength H (A / m) acting on the magnet, and the vertical axis is the magnetic flux density B (T = Wb / m ² ) inside the magnet or the magnetization J (T = Wb / m ² ) of the magnet. ) And shows both the JH curve and the BH curve. When expressing the demagnetization characteristics when used as the electric motor 1, a reverse magnetic field acts on the magnet, and the strength H of the magnetic field on the horizontal axis becomes a negative value, so the second quadrant is drawn. These JH curve and BH curve are obtained by using magnetic flux density B inside the magnet, magnetic field strength H, magnetization J, and permeability μ ₀ (= 4π × 10 ⁻⁷ H / m) in vacuum, The relationship B = μ ₀ · H + J is established. Therefore, when the magnetic field strength H = 0, B = J.

In FIG. 6, the intersection of the BH curve and the straight line of the inclination of the permeance coefficient pc (= B / H) determined by the shape of the magnet or magnetic path is defined as a point a, and a perpendicular passing through the point a and a JH curve The point a, b represents the state of the magnet in the non-operating state (= the external magnetic field H is zero), and is generally referred to as the “magnet operating point”. Further, when an external magnetic field Hex (corresponding to the reverse magnetic field caused by the overcurrent described in FIG. 5) is applied to drive the motor, a straight line pc ′ passing through the origin O and the point b is applied to the applied external magnetic field. The operating point of the magnet moves to the intersection c with the JH curve when translated to the left by Hex. The operating point on the BH curve is the intersection d of the perpendicular passing through the point c and the BH curve.

When the external magnetic field Hex is weakened from this state, the operating point moves to the right on a straight line having the recoil permeability μr passing through the point d. In the absence of the external magnetic field Hex, the intersection point a 'with the straight line pc becomes the operating point, and the permanent magnet is demagnetized by the decrease ΔB of the magnetic flux density with respect to the initial point a described above. The operating point b 'of the magnet on the JH curve is the intersection of a straight line parallel to the perpendicular passing through the point a' and the straight line pc '.

On the other hand, FIG. 7 is a magnet characteristic diagram showing demagnetization ΔB when an external magnetic field Hex smaller than the external magnetic field Hex shown in FIG. 6 is applied. As the external magnetic field Hex increases as shown in FIG. The degree of demagnetization ΔB is large, and it can be seen that almost no demagnetization ΔB occurs when the external magnetic field Hex is relatively small as shown in FIG.

Also, the magnet characteristics change with temperature, and ferrite magnets tend to demagnetize at lower temperatures. FIG. 8 shows an example of the magnetization curve of the ferrite magnet at room temperature (room temperature, the same applies hereinafter). In this case, it can be seen that the amount of decrease ΔB in the magnetic flux density is smaller than that at the low temperature in FIG. This is because since the residual magnetic flux density Br has a negative coefficient with respect to temperature, the absolute value of the magnetic flux density B becomes smaller at room temperature than at low temperature.

Next, how the demagnetization of the magnet affects the characteristics of the electric motor when a ferrite magnet having such characteristics is applied to the rotor 5 or the stator 7 of the electric motor 1 will be described. In general, the greater the current that drives the electric motor, the greater the torque and output that can be obtained. However, as the drive current increases, the external magnetic field Hex that acts on the magnet also increases, and the magnet demagnetizes from a current above a certain value. . As an index representing the degree of demagnetization of the magnet, a no-load induced voltage is generally used in an electric motor. The no-load induced voltage is a terminal voltage generated when the rotor is rotated by an external force at a predetermined speed in a non-energized state where the motor terminal is opened, and the generated voltage is proportional to the magnetic flux of the magnet.

FIG. 9 is a graph showing an example of no-load induced voltage measured after driving the electric motor 1 by applying various driving currents in a low temperature atmosphere and a normal temperature atmosphere, and the horizontal axis represents driving of the electric motor. The current indicates the no-load induced voltage. The drive current on the horizontal axis is a relative value when the rated drive current value of the electric motor is 1, and the vertical axis is a relative value when the no-load induced voltage in the initial state is 1. As shown in FIG. 9, when an electric motor is driven by applying a drive current smaller than the rated current, the no-load induced voltage does not change from the initial state, but at a certain value exceeding the rated current, It can be seen that as the drive current increases, the magnet is demagnetized and the no-load induced voltage decreases. Further, the lower the temperature of the magnet, there is a tendency to demagnetize with a smaller current. At the same current, the lower the temperature of the magnet, the greater the degree of demagnetization. For example, when the drive current is 1 or less, the induced voltage is almost equal to the initial state even at a low temperature at which demagnetization is likely to occur. However, if a drive current of 1.4 times the rated current is applied, Demagnetization corresponding to a decrease in induced voltage of about 3% occurs.

Such a decrease in the magnetic flux of the magnet directly leads to a decrease in the torque and output of the electric motor 1. That is, in the surface magnet type motor, the generated torque is all the magnet torque due to the interaction between the magnet magnetic flux and the current, so the rate of decrease of the magnetic flux of the magnet directly becomes the rate of decrease of the torque / output of the motor. In the case of the embedded magnet type, there is a ratio of reluctance torque in addition to the magnetic flux of the magnet, so although the motor torque / output does not decrease as much as the decrease of the magnetic flux of the magnet, it is ignored depending on the degree of demagnetization. It is thought that performance degradation that cannot be done will occur.

It should be noted that performance degradation such as a decrease in torque and output of the electric motor 1 due to demagnetization of the permanent magnet 53 can occur during use of the electric motor 1 as a product. That is, compared to immediately after purchasing the product, for example, when used for a compressor motor of an air conditioner, there is a concern about a decrease in heating capacity, and when used for a driving motor of an electric vehicle, acceleration performance There is concern about the decline. In addition, the change in the state of the magnetic flux increases the electromagnetic excitation force, which worsens the noise of the electric motor, increases the electricity bill when using the air conditioner due to the deterioration of efficiency, and the range of the electric vehicle. There is also a risk of spilling over.

As described above, in this example, before the electric motor 1 is shipped as a product, that is, before the initial drive as the product, the demagnetization process is performed in advance on the electric motor production line (demagnetization process step in FIG. 3A). P5).

As explained in FIG. 6, in the JH curve of FIG. 6, the operating point of the magnet when the initial ferrite magnet type motor is not operating is the point b, but the external magnetic field Hex exceeding the demagnetization resistance of the magnet is When acting, the magnet is demagnetized, and the operating point of the magnet when the motor is not operating after removing the external magnetic field Hex is b ′. However, at this time, as shown in FIG. 10, even if the external magnetic field Hex is applied again thereafter, the operating point of the magnet becomes the same point c as when the external magnetic field Hex was applied from the initial state, and the external magnetic field Hex was removed. The later operating point is b ′. That is, once the external magnetic field Hex is applied and demagnetized, the demagnetization of the magnet does not proceed as long as a magnetic field not exceeding the external magnetic field Hex is applied thereafter. Strictly speaking, the characteristic is a minor loop characteristic having some hysteresis as shown in FIG. 10, but it can be regarded as a minute range in view of the entire demagnetization characteristic.

For example, as described above, when the electric motor 1 of this example is driven at a predetermined low temperature with a current 1.4 times the rated drive current, the no-load induced voltage is reduced by about 3% with respect to the initial state (FIG. 9). reference). However, even if it is driven with a current of 1.4 times after the second time, the demagnetization of the magnet does not proceed, so that the reduction is only about 3% with respect to the initial state. Further, even when the driving is performed again with a current smaller than this, since the demagnetization is already performed with the driving current of 1.4 times, the induced voltage is reduced by about 3% with respect to the initial state. Therefore, when the electric motor 1 having the characteristics at the low temperature of FIG. 9 (shown by the dotted line in FIG. 11) is driven once with 1.4 times the current, the induced voltage characteristics are as shown by the solid line in FIG. Become. That is, although the induced voltage is reduced by about 3% with respect to the initial state, the magnetization J of the magnet does not change up to 1.4 times the current. The characteristics remain unchanged up to 1.4 times the current. In this example, by carrying out such a demagnetization process in the manufacturing process of the electric motor 1 (demagnetization process P5 in FIGS. 3A and 3B), the demagnetization resistance can be increased to 1.4 times the rated current. An improved electric motor 1 can be provided.

However, when the drive current of the electric motor 1 is increased without limit in the demagnetization process P5 of this example and the reverse magnetic field acting on the permanent magnet 53 is extremely increased, the entire permanent magnet 53 is almost entirely changed depending on the portion. Is demagnetized from the fully magnetized state, and demagnetization proceeds rapidly to significantly reduce the magnetic flux. In FIG. 9 and FIG. 11, the state where the no-load induced voltage rapidly decreases in the region where the current value is large indicates that state. However, depending on the design of the electric motor 1, the permanent magnet is usually demagnetized if the current is 20 to 40% higher than the rated current, as indicated by the broken-line circles in FIGS. 1D, 2A and 2B. It has been confirmed by the present inventors that it remains in a local part such as the edge part 53e of 53. In other words, it remains at the edge 53e of the permanent magnet 53 on the side facing the gap G with the stator 7 to which the external magnetic field Hex is applied. For this reason, even if the demagnetization process is performed, the rate of decrease in the magnetic flux of the permanent magnet 53 is small, and the induced voltage is only reduced by about 3% in the electric motor 1 of this example.

The torque T of the permanent magnet type synchronous motor is expressed by the following formula 1 as the number of pole pairs Pn, the interlinkage magnetic flux Φa of the magnet, the current Ia, the current phase angle β, the d-axis inductance Ld, and the q-axis inductance Lq.
[Equation 1]
T = Pn · {Φa · Ia · cosβ + 1/2 · (Lq−Ld) · Ia ² · sin2β} Equation 1
The second term on the right side of Equation 1 is called reluctance torque, and is an effective term for an embedded magnet type synchronous motor, and is zero for a surface magnet type motor. The interlinkage magnetic flux Φa and the current Ia of the magnet are both values in the dq axis coordinate system of the electric motor, but the interlinkage magnetic flux Φa is proportional to the magnet magnetic flux, and the current Ia is proportional to the alternating current that drives the electric motor. The output of the electric motor 1 is a product of torque and the number of revolutions. From the above, if the allowable value of the driving current can be increased by about 40% of the rated current value, a large output can be obtained even if the magnetic flux decreases by 3% due to the effect of the demagnetization process. I understand.

In the present invention, the permanent magnet 53 is a single magnet, and is made slightly demagnetized from the fully magnetized state, and can be inserted into the rotor core 51. However, even in that case, the external magnetic field Hex acting on the permanent magnet 53 must be matched with the conditions for driving the actual electric motor 1 as a product. This may cause performance degradation by demagnetizing unnecessary parts, or a demagnetization process may be inadequate because the reverse magnetic field does not act on the necessary parts, and demagnetization proceeds while the product is driving. This is in order to prevent clogging.

In order to obtain a magnetic field distribution similar to that of the actual electric motor 1 when the permanent magnet 53 is magnetized and demagnetized by a single product, the permanent magnet 53 is formed on the same soft magnetic body as the electric motor 1 of the product. It is necessary to apply a reverse magnetic field Hex to the permanent magnet 53 using a yoke having the same stator shape as the electric motor 1 of the product. Therefore, it is preferable to demagnetize the rotor 5 by assembling the rotor 5 and the stator 7 and then applying a predetermined current in the product state of the electric motor 1 to simplify the manufacturing process.

Further, if the permanent magnet 53 is somewhat magnetized, the assembly workability of the rotor 5 is deteriorated by the magnetic force. For this reason, it is preferable that the electric motor 1 is assembled with a non-magnetized permanent magnet 53 to the rotor 5 and magnetized in the state of the rotor 5 or the electric motor 1 as in this example. The magnetizing process includes a method of magnetizing the electric motor 1 by energizing the electric motor 1 after being incorporated into the stator 7 as a product, and a method of magnetizing with a magnetizing yoke which is a production facility in the state of the rotor 5. . For this reason, there is a merit when the demagnetization process is performed in the assembled state as the rotor 5 or the electric motor 1 even when the demagnetization process is performed as in this example.

In addition, it is preferable that the permanent magnet 53 is once completely magnetized before demagnetizing the permanent magnet 53. The purpose of the demagnetization process of the present invention is to energize the maximum current that can be used when the product is used, demagnetize the portion of the permanent magnet 53 that is likely to be demagnetized during the manufacturing process, and further demagnetize it. This is because the magnetized magnetic field is larger in the part where the demagnetization is likely to occur than in other parts. If this part is magnetized from a non-magnetized state to an incomplete state (a state in which complete magnetization is not reached), a sufficient magnetizing magnetic field will not be generated in other parts, and the desired performance will be obtained. The necessary magnetized state of the permanent magnet 53 cannot be created. Therefore, it is preferable to demagnetize a portion where a reverse magnetic field is likely to be generated by demagnetization processing after the permanent magnet 53 is completely magnetized with a sufficiently strong magnetic field.

In the manufacturing process example shown in FIG. 3A, the magnetizing process P4 and the demagnetizing process P5 are performed after the electric motor 1 is assembled as shown in FIG. 1A in the motor assembling process P3. P5 will not be specifically limited if it is a post process of the magnetization process P4. FIG. 3B is a process diagram showing a method of manufacturing a permanent magnet electric motor according to another embodiment of the present invention. In this example of the manufacturing process, a rotor assembly process P1 for assembling the rotor subassembly 5 shown in FIG. 1C is shown. Immediately after that, a magnetizing process P4 for magnetizing the permanent magnet 53 of the rotor 5 is provided, and immediately thereafter, a demagnetizing process P5 of this example is provided. Then, the rotor subassembly 5 that has been subjected to the demagnetization process and the stator subassembly 7 assembled together in the stator assembly process P2 are assembled in the next motor assembly process P3. Thereby, the electric motor 1 shown in FIG. 1A is completed.

Next, the magnetization processing current when performing the demagnetization processing P5 will be described. In this example, in order to execute the demagnetization process most effectively and efficiently, the phase angle β of the demagnetization process current supplied from the AC power supply or the DC power supply is controlled to a predetermined value. For example, if the d-axis inductance is Ld, the d-axis current is Id, and the current phase angle is β (−90 ° ≦ β ≦ 90 °), the magnetic flux Ψd of the d-axis magnetic pole axis of the electric motor 1 is Ψd = −Ld · Since it is expressed by Id · sin β, the reverse magnetic field becomes maximum (the magnetic field is minimum) when β = 90 °. Therefore, in the demagnetization process P5, the AC power supply device is controlled in a state where the rotational direction positions of the rotor 5 and the stator 7 are relatively fixed (both non-rotating or both rotating speed and rotating direction are the same). Then, the demagnetization process is performed after setting the phase angle β of the demagnetization process current flowing through the coil 62 of the stator 7 to 90 °. Thereby, since the maximum reverse magnetic field acts on the permanent magnet 53, the demagnetization process can be performed efficiently.

As another example of controlling the phase angle β of the demagnetization processing current to a predetermined value, the following example can be given in addition to setting the phase angle β = 90 °.

The purpose of the demagnetization process in this example is to suppress the occurrence of a demagnetization phenomenon for some reason when the electric motor 1 is used as a product. Therefore, it can be said that it is preferable to carry out the demagnetization process according to the usage state of the electric motor 1 in advance on the production line of the electric motor. For example, when the maximum phase angle βmax of the drive current is set for the electric motor 1 as a product, the demagnetization processing in the demagnetization processing step P5 of this example is the position of the rotor 5 and the stator 7 in the rotational direction. In a relatively fixed state (both non-rotating or both rotating speed and rotating direction are the same), the phase angle β of the demagnetizing process current flowing through the coil 62 of the stator 7 by controlling the AC power supply is maximized. The phase angle β is set equal to or larger than the phase angle βmax (≧ βmax). As a result, compared to the example in which the phase angle β of the demagnetization processing current is set to 90 °, when the maximum phase angle βmax in use is smaller than 90 °, the demagnetization processing is not performed more than necessary, and the output torque Can be suppressed.

When the drive current for the electric motor 1 as a product is not the maximum phase angle βmax but a predetermined range (βs ≦ β ≦ βe) is set, in the demagnetization processing step P5 of this example, In a state where the positions of the rotor 5 and the stator 7 in the rotational direction are relatively fixed (both are non-rotating or both the rotational speed and rotational direction are the same), the AC power supply is controlled to flow through the coil 62 of the stator 7. Demagnetization processing is performed while discretely or continuously changing the phase angle β of the demagnetization processing current within the range of the phase angle (βs ≦ β ≦ βe). For example, since the optimal operating phase angle β corresponding to the operating point (torque and rotation speed) may be stored in the control device of the electric motor 1, the minimum value of the optimal phase angle is set to βs and the maximum value is set to βe. Then, a demagnetization process is performed. Thereby, the demagnetization process more than necessary is not performed, and the decrease in output torque can be suppressed. In particular, by performing the demagnetization process while continuously changing the phase angle β of the demagnetization process current from βs to βe, the process can be completed at a time, which is efficient.

In the above-described example, an alternating current is used as the demagnetization processing current in the demagnetization processing step P5 of this example, and the rotational positions of the rotor 5 and the stator 7 are relatively fixed (both non-rotating or both Although the demagnetization process is performed at the same rotational speed and rotation direction, the demagnetization process may be performed using a direct current. However, it is necessary to consider the rotational position of the rotor 5 and the stator 7. For example, when the phase angle β of the demagnetization processing current is set to a fixed value such as 90 °, the demagnetization processing is performed after setting the relative position of the rotor 5 and the stator 7 to the target demagnetization processing position. Further, when the demagnetization process is performed while changing the phase angle β of the demagnetization process current in a predetermined range (βs ≦ β ≦ βe), the demagnetization process is performed while rotating the rotor 5 at a predetermined rotation speed. . In this case, the phase angle β of the DC demagnetization processing current is within the phase angle range of the drive current of the electric motor 1 (βs ≦ β ≦ βe), and the rotation speed is changed discretely or continuously. A direct current is applied while rotating the rotor 5. Although it is easiest to rotate the rotor 5, the stator or the demagnetizing device may be rotated, or both may be rotated. Thereby, like the demagnetization process using an alternating current, the demagnetization process more than necessary is not performed, and the decrease in output torque can be suppressed.

Further, in the example of demagnetizing using the above-described alternating current, the demagnetizing process is performed in a state where the rotational positions of the rotor 5 and the stator 7 are relatively fixed. The demagnetization process can also be performed while relatively rotating the rotational position of the stator 5 and the stator 7. In this case, the demagnetization processing current may be an alternating current synchronized with the rotation of the rotor 5 or may be an asynchronous alternating current. When the demagnetization processing current is an alternating current synchronized with the rotation of the rotor 5, the phase angle β of the demagnetization processing current can be set to a fixed value such as 90 ° or a predetermined range (βs ≦ β ≦ βe) can also be changed. In this case, in order to suppress demagnetization unevenness, it is desirable that the rotor 5 is physically rotated at least once.

When the demagnetization processing current is an alternating current that is asynchronous with the rotation of the rotor 5, it is desirable to set the frequency of the alternating current to a value obtained by the following equation 1. In this case, it is desirable to physically rotate the rotor 5 at least n times in order to suppress the demagnetization unevenness.
fs = (Nr / 60) · [{(βe−βs) / 360n} + P]...
Where fs is the frequency of the alternating current, Nr is the mechanical angular rotation speed (rpm) of the electric motor, βs is the current phase angle (deg) at the start of the demagnetization process, and βe is the current phase angle (deg) at the end of the demagnetization process. ), N is an integer of 1 or more, and P is the number of pole pairs of the electric motor.

FIG. 22A shows an AC current that is asynchronous with the rotation of the rotor 5 as the demagnetization processing current, the mechanical angle rotation speed Nr = 60 rpm, the current phase angle βs = 30 deg at the start of the demagnetization processing, and the current phase angle at the end of the demagnetization processing. It is a graph explaining the effect | action at the time of setting to the frequency fs (= 2.083Hz) of an alternating current when it is set as (beta) e = 60deg, n = 1, and pole pair number P = 2, The above figure is a demagnetization of a three-phase alternating current The processing current, the middle diagram shows the rotation angle of the rotor, and the lower diagram shows the current phase angle with respect to the same time. When the demagnetization process is performed by applying a three-phase alternating current of frequency fs = 2.083 Hz as shown in the upper diagram, the current phase is changed as shown in the lower diagram while the rotor 5 makes one revolution as shown in the middle diagram. It can be seen that the angle β continuously varies from βs to βe, and the demagnetization process is performed in this state.

In FIG. 22B, similarly, the demagnetization processing current is an AC current asynchronous with the rotation of the rotor 5, the mechanical angular rotation speed Nr = 600 rpm, the current phase angle βs = 30 deg at the start of the demagnetization processing, and the current phase at the end of the demagnetization processing. It is a graph explaining the effect | action at the time of setting to the frequency fs (= 20.027Hz) of alternating current when it is set as angle | corner (beta) e = 60deg, n = 30, and the number of pole pairs P = 2, The above figure is reduction of three-phase alternating current. The magnetic processing current, the middle figure shows the rotation angle of the rotor, and the lower figure shows the current phase angle with respect to the same time. When a demagnetization process is performed by applying a three-phase alternating current having a frequency fs = 20.027 Hz as shown in the upper diagram, the current phase is changed as shown in the lower diagram while the rotor 5 rotates 30 times as shown in the middle diagram. It can be seen that the angle β continuously varies from βs to βe, and the demagnetization process is performed in this state. In particular, in this example, since the rotor 5 makes one rotation while β changes every 1 deg, a reverse magnetic field can be applied uniformly. In addition, the time required for the demagnetization process can be shortened by increasing the mechanical angular rotation speed of the rotor 5, and in addition to the reduction of the manufacturing cost, the temperature generated by supplying a large current called the demagnetization process current to the stator coil. The rise can also be suppressed.

By the way, when the demagnetization process P5 of this example is performed, the error in the output characteristics of each product of the electric motor 1 tends to increase due to variations in magnet characteristics (individual differences in manufacturing the permanent magnet 53). The indices representing the characteristics of the permanent magnet 53 mainly include the maximum residual magnetic flux density Brmax related to the magnetic flux of the magnet and the holding force Hcj representing the strength against demagnetization. There are some variations in the maximum residual magnetic flux density Brmax and the holding force Hcj depending on the 53 production lots.

FIG. 12 shows how the no-load induced voltage changes with respect to the demagnetization processing current of the electric motor 1 in the four combinations in which the maximum residual magnetic flux density Brmax and the holding force Hcj are maximum and minimum due to manufacturing variations. It is the graph which showed whether to do. According to this, it can be seen that the initial induced voltage is higher as the maximum residual magnetic flux density Brmax is larger, and the induced voltage is less likely to decrease with respect to the demagnetization processing current as the coercive force Hcj is larger. In the electric motor 1 of this example, the initial induced voltage has a product individual variation of about ± 3% and a total width of about 6% mainly due to variations in the maximum residual magnetic flux density Brmax of the permanent magnet 53. In the electric motor 1 having such characteristics, when the demagnetization process is performed at a current 1.4 times the original rated current, as shown in FIG. 12, the variation of the induced voltage is expanded to 8%. This is because, in addition to initial induced voltage variations due to individual differences in the maximum residual magnetic flux density Brmax, variations in the degree of demagnetization due to individual differences in the holding force Hcj are added.

As a result, the variation in individual product of output performance with respect to the conventional electric motor increases. This is not preferable from the viewpoint of securing stable performance. Therefore, when performing the demagnetization processing of this example, as shown in FIG. 13, the drive current is set according to the variation in the magnet characteristics so that it falls within the allowable error ± δ with respect to the induced voltage target value Φt. As a result, the product individual variation of the no-load induced voltage is made almost constant. FIG. 14 is a flowchart showing a procedure for setting an optimum demagnetization drive current for the electric motor 1 having individual product differences when performing the demagnetization process.

In FIG. 14, in the first step S1, the minimum current Imin for guaranteeing demagnetization resistance is set as the demagnetization drive current Ide, and in step S2, the electric motor 1 is energized to perform demagnetization processing. In step S3, the induced voltage Φe of the electric motor 1 subjected to the demagnetization process in step S2 is measured. In the subsequent step S4, the measured induced voltage Φe is compared with the target lower limit value Φlow, and if the measured induced voltage Φe is equal to or lower than the target lower limit value Φlow, the process proceeds to step S8, where the components of the electric motor 1 or the magnetization process, After determining that there is some abnormality in the demagnetization process and making an NG determination, this process is terminated.

If the measured induced voltage Φe exceeds the target lower limit value Φlow in step S4, the process proceeds to step S5, and it is determined whether or not the error (absolute value of the difference) between the induced voltage Φe and the target value Φt is less than δ. To do. If the absolute value of the difference between the induced voltage Φe and the target value Φt is δ or more, the process proceeds to step S6, the demagnetization drive current Ide increased by ΔI is set as the demagnetization drive current, and the process returns to step S2. Perform demagnetization again. This process is repeated by increasing the demagnetization drive current Ide by ΔI until the absolute value of the difference between the induced voltage Φe and the target value Φt is less than δ. In step S5, when the absolute value of the difference between the induced voltage Φe and the target value Φt becomes less than δ, the process proceeds to step S7, and this process is terminated assuming that the demagnetization process is appropriately performed. Note that the value of ΔI, which is the amount of increase in the demagnetization drive current, is a value determined in advance by a verification experiment or the like, but ΔI is adjusted according to the magnitude of the error between the induced voltage Φe and the target value Φt. Also good.

By performing such demagnetization processing, it is possible to suppress individual product variation in motor performance that is expanded by demagnetization processing. Further, it is possible to improve the motor output by increasing the drive current while realizing the electric motor 1 with improved demagnetization resistance. In addition, it is possible to extremely reduce individual product variations in motor output caused by variations such as the maximum residual magnetic flux density Brmax, which is unavoidable with conventional electric motors.

FIG. 15 is a flowchart according to another embodiment of the demagnetization processing step P5 of this example. In the range of the allowable error ± δ with respect to the induced voltage target value Φt shown in FIG. 13, the lower limit value of the no-load induced voltage target value after demagnetization processing is Φlow (= Φt−δ), and the upper limit value is Φhigh (= Φt + δ). To do. In this example, the difference Φhigh−Φlow between the upper limit value and the lower limit value of the no-load induced voltage target value is set to 6%, which corresponds to the variation width of a conventional electric motor that does not perform demagnetization processing.

In FIG. 15, in the first step S11, the minimum current Imin for guaranteeing demagnetization resistance is set as the demagnetization drive current Ide, and in step S12, the electric motor 1 is energized to perform demagnetization processing. In step S13, the induced voltage Φe of the electric motor 1 subjected to the demagnetization process in step S12 is measured. In the subsequent step S14, the measured induced voltage Φe is compared with the target lower limit value Φlow. If the measured induced voltage Φe is equal to or lower than the target lower limit value Φlow, the process proceeds to step S15, where the components of the electric motor 1 or the magnetization process or the like After determining that there is some abnormality in the demagnetization process and making an NG determination, this process is terminated.

In step S14, when the measured induced voltage Φe exceeds the target lower limit value Φlow, the process proceeds to step S16, the measured induced voltage Φe is compared with the target upper limit value Φhigh, and the measured induced voltage Φe is less than the target upper limit value Φhigh. If there is, the process proceeds to step S17, and this process is terminated assuming that the demagnetization process is appropriately performed.

If the measured induced voltage Φe exceeds the target upper limit value Φhigh in step S16, the demagnetization processing current is insufficient, so the process proceeds to step S18, and the predetermined maximum current Imax is driven to demagnetize. The current Ide is set, and in step S19, the demagnetization process is performed again by energizing the electric motor 1. In step S20, the induced voltage Φe of the electric motor 1 subjected to the demagnetization process is measured. In the subsequent step S21, the measured induced voltage Φe is compared with the target lower limit value Φlow, and if the measured induced voltage Φe is equal to or lower than the target lower limit value Φlow, the process proceeds to step S23, where the components of the electric motor 1 or the magnetization process, After determining that there is some abnormality in the demagnetization process and making an NG determination, this process is terminated.

On the other hand, if the measured induced voltage Φe exceeds the target lower limit value Φlow in step S21, the process proceeds to step S22, the measured induced voltage Φe is compared with the target upper limit value Φhigh, and the measured induced voltage Φe is determined to be the target upper limit value. If it is less than the value Φhigh, the process proceeds to step S17, and this process is terminated assuming that the demagnetization process has been appropriately performed. If the measured induced voltage Φe exceeds the target upper limit value Φhigh in step S22, the process proceeds to step S23, where it is determined that there is some abnormality in the parts of the electric motor 1, the magnetization process, or the demagnetization process. After the determination, this process is terminated.

FIG. 16 is a graph showing the relationship between the demagnetization processing current and the no-load induced voltage, and the operation of the demagnetization processing example of FIG. 15 will be described using this graph. FIG. 16 shows four characteristic lines when the residual magnetic flux density Brmax and the holding force Hjc are at the upper and lower limits according to the characteristics of the permanent magnet 53, and the demagnetization is performed even when the magnet characteristics vary. The relationship between the processing current and the no-load induced voltage is between these characteristic lines. In FIG. 16, after the demagnetization process is performed with the minimum current Imin that guarantees the anti-demagnetization resistance, the induced voltage characteristics in the range indicated by the vertical bold line are between the target lower limit value Φlow and the target upper limit value Φhigh. Thus, an appropriate demagnetization process can be performed.

Incidentally, depending on the magnet characteristics, the demagnetization process may not be sufficient, and the no-load induced voltage may exceed the target upper limit value Φhigh. In this case, as shown in FIG. 17, the demagnetization process is performed again with the maximum current Imax. This maximum current Imax is a value selected so that the no-load induced voltage is equal to or less than the target condition value Φhigh when the permanent magnet 53 is most difficult to demagnetize and the initial magnetic flux amount is the highest. Thus, the no-load induced voltage falls below the target upper limit value Φhigh, and it is finally possible to keep the no-load induced voltage within the target range by one re-demagnetization process.

Depending on the characteristics of the demagnetization process current and the no-load induced voltage of the electric motor 1, the no-load induced voltage after the demagnetization process is kept between the target lower limit value Φlow and the target upper limit value Φhigh at two levels of current. If it is not possible, the demagnetization processing current may be subdivided into three stages, ie, minimum current Imin, intermediate current Imid, and maximum current Imax, or more. FIG. 18 is a flowchart according to still another embodiment of the demagnetization processing step P5 of this example, and is a flowchart of the demagnetization processing step P5 when the demagnetization current is set to three levels.

In FIG. 18, in the first step S31, the minimum current Imin for guaranteeing demagnetization resistance is set as a demagnetization drive current Ide, and in step S32, the electric motor 1 is energized to perform demagnetization processing. In step S33, the induced voltage Φe of the electric motor 1 subjected to the demagnetization process in step S32 is measured. In the subsequent step S34, the measured induced voltage Φe is compared with the target lower limit value Φlow. If the measured induced voltage Φe is equal to or lower than the target lower limit value Φlow, the process proceeds to step S35, where the components of the electric motor 1 or the magnetization process or the like After determining that there is some abnormality in the demagnetization process and making an NG determination, this process is terminated.

If the measured induced voltage Φe exceeds the target lower limit value Φlow in step S34, the process proceeds to step S36, where the measured induced voltage Φe is compared with the target upper limit value Φhigh, and the measured induced voltage Φe is less than the target upper limit value Φhigh. If there is, the process proceeds to step S37, and the process is terminated assuming that the demagnetization process is appropriately performed.

On the other hand, if the measured induced voltage Φe exceeds the target upper limit value Φhigh in step S36, the demagnetization processing current is insufficient, so the process proceeds to step S38, and the predetermined intermediate current Imid is set. Is demagnetized drive current Ide, and this is energized to the electric motor 1 in step S39 to perform demagnetization again. In step S40, the induced voltage Φe of the electric motor 1 subjected to the demagnetization process is measured. In the subsequent step S41, the measured induced voltage Φe is compared with the target lower limit value Φlow, and if the measured induced voltage Φe is equal to or lower than the target lower limit value Φlow, the process proceeds to step S35, where the components of the electric motor 1 or the magnetization process, After determining that there is some abnormality in the demagnetization process and making an NG determination, this process is terminated.

In step S41, when the measured induced voltage Φe exceeds the target lower limit value Φlow, the process proceeds to step S42, the measured induced voltage Φe is compared with the target upper limit value Φhigh, and the measured induced voltage Φe is less than the target upper limit value Φhigh. If there is, the process proceeds to step S37, and the process is terminated assuming that the demagnetization process is appropriately performed. On the other hand, if the measured induced voltage Φe exceeds the target upper limit value Φhigh in step S42, the demagnetization processing current is insufficient, so the process proceeds to step S43 and the maximum current set in advance is determined. Imax is set as the demagnetization drive current Ide, and the demagnetization process is performed again by energizing the electric motor 1 in step S44. In step S45, the induced voltage Φe of the electric motor 1 subjected to the demagnetization process is measured. In the subsequent step S46, the measured induced voltage Φe is compared with the target lower limit value Φlow. If the measured induced voltage Φe is equal to or lower than the target lower limit value Φlow, the process proceeds to step S48, where the components of the electric motor 1 or the magnetization process or the like After determining that there is some abnormality in the demagnetization process and making an NG determination, this process is terminated.

If the measured induced voltage Φe exceeds the target lower limit value Φlow in step S46, the process proceeds to step S47, where the measured induced voltage Φe is compared with the target upper limit value Φhigh, and the measured induced voltage Φe is less than the target upper limit value Φhigh. If there is, the process proceeds to step S37, and the process is terminated assuming that the demagnetization process is appropriately performed. On the other hand, if the measured induced voltage Φe exceeds the target upper limit value Φhigh in step S47, the process proceeds to step S48, and if there is any abnormality in the components of the electric motor 1, the magnetization process, or the demagnetization process. After the determination and the NG determination, this process is terminated. With the above demagnetization process, the no-load induced voltage can finally fall within the target range by a maximum of two re-demagnetization processes.

Now, as shown by the broken line in FIG. 19, when the first demagnetization process is performed with the minimum current Imin for guaranteeing the anti-demagnetization, the no-load induced voltage may coincide with the target upper limit value Φhigh. Assuming that the initial no-load induced voltage of an individual (permanent magnet 53) having such characteristics is Φth, the minimum is obtained when the initial no-load induced voltage Φe of various permanent magnets 53 to be demagnetized is lower than Φth. The demagnetization process is performed with the demagnetization current Imin. When the initial no-load induced voltage Φe is higher than Φth, the demagnetization process is performed with the maximum demagnetization current Imax. It can be set between Φlow and the target upper limit value Φhigh. Thus, by changing the demagnetization processing current according to the initial no-load induced voltage Φe, it is possible to complete the demagnetization processing step once, and the manufacturing cost can be reduced. FIG. 20 is a flowchart according to still another embodiment of the demagnetization processing step P5 of this example.

In FIG. 20, in the first step S51, the initial induced voltage Φe of the electric motor 1 including the permanent magnet 53 that has been completely magnetized is measured. In step S52, the measured initial induced voltage Φe is compared with the reference induced voltage Φth obtained in advance by a verification experiment or the like. If the measured induced voltage Φe is less than the reference induced voltage Φth, the process proceeds to step S53. The minimum current Imin that guarantees demagnetization resistance is defined as a demagnetization drive current Ide. On the other hand, if the measured induced voltage Φe is greater than or equal to the reference induced voltage Φth in step S52, the process proceeds to step S54, and the maximum current Imax is set as the demagnetization drive current Ide. In step S55, the electric motor 1 is energized to perform demagnetization processing. In step S56, the induced voltage Φe of the electric motor 1 subjected to the demagnetization process in step S55 is measured.

In step S57, it is determined whether or not the measured induced voltage Φe is between the target lower limit value Φlow and the target upper limit value Φhigh, and the measured induced voltage Φe is equal to or less than the target lower limit value Φlow or greater than or equal to the target upper limit value Φhigh. In this case, the process proceeds to step S59, where it is determined that there is some abnormality in the parts of the electric motor 1 or in the magnetization process or the demagnetization process, and NG determination is made, and then this process is terminated. On the other hand, when the measured induced voltage Φe exceeds the target lower limit value Φlow and is lower than the target upper limit value Φhigh in step S57, the process proceeds to step S58, and this process is assumed to be appropriately performed. Exit. With the above demagnetization process, it is possible to finally bring the no-load induced voltage within the target range by one demagnetization process.

<< Other embodiments >>
FIG. 21A is a graph showing an example of a no-load induced voltage measured after applying various currents in a low temperature atmosphere and a normal temperature atmosphere to demagnetize the electric motor 1. When the anti-demagnetization current Imin is applied, the desired demagnetization effect can be obtained by setting the ambient temperature in the demagnetization treatment step to a low temperature atmosphere. However, a low temperature atmosphere in which a decrease in output due to demagnetization is a problem may be an extremely low temperature of −20 ° C. or less, and it is not easy to provide such a cryogenic atmosphere zone in a production line. In addition, it takes a considerable amount of time to lower the temperature of the electric motor 1 to a very low temperature, and it also takes a considerable amount of time to return to the normal temperature after the demagnetization process, resulting in a long manufacturing time.

For this reason, in this example, by selecting a demagnetizing current value in a normal temperature atmosphere, a demagnetizing effect equivalent to performing a demagnetizing process in a target low temperature atmosphere is obtained. That is, FIG. 21B is a graph showing an example of the no-load induced voltage with respect to the same demagnetization processing current as FIG. 21A. As shown in the figure, the object is to obtain a no-load induced voltage reduced by 3% in a low temperature atmosphere. In this case, the demagnetizing current is not Imin but the demagnetizing current Ipmin when intersecting the curve in the room temperature atmosphere. As a result, when the demagnetization process is performed in a normal temperature atmosphere, an electric motor having a 3% reduction in no-load induced voltage can be obtained, which is the same as the case where the demagnetization process is performed with a demagnetization current of Imin in a low temperature atmosphere.

As described above, according to the permanent magnet type electric motor and the method of manufacturing the same of this example, the demagnetization resistance of the electric motor 1 is improved. Therefore, even in the case of an electric motor using a ferrite magnet, the drive current is limited at a low temperature. Therefore, it is possible to suppress a decrease in output at low temperatures. In addition, since the drive current can be increased, the output of the electric motor 1 can be improved.

In addition, when the electric motor of this example is applied to a driving motor for an electric vehicle, there are cases where the driving current instantaneously increases beyond the normal operating state. As described with reference to FIG. 5, when the rotational speed of the electric motor 1 fluctuates rapidly in a short time, the motor current may increase instantaneously with respect to the control target value. A specific driving scene corresponds to a case where a tire that has slipped due to slipping recovers grip, and the current increase rate reaches about 1.2 to 1.5 times. Slip is likely to occur in winter when the road surface freezes. In this case, it is considered that the permanent magnet 53 of the electric motor 1 is also in a low temperature state and has a high risk of demagnetization.

If the permanent magnet 53 is demagnetized due to such an instantaneous increase in current, the output of the electric vehicle is lowered thereafter, which may cause acceleration or a decrease in climbing performance. For this reason, the conventional electric motor has been designed to withstand demagnetization assuming an instantaneous current increase, but the electric motor is at a low temperature and is driven by a large current, such as in winter, and The scene where the tire slips is extremely rare, and the output characteristics of the electric motor must be constrained as a countermeasure against this rare phenomenon. On the other hand, by applying the invention of this example, it is possible to suppress demagnetization when the current increases without sacrificing the output characteristics of the electric motor 1.

DESCRIPTION OF SYMBOLS 1 ... Permanent magnet type electric motor 2 ... Housing 3 ... Front cover subassembly 31 ... Hole 4 ... Rear cover subassembly 5 ... Rotor subassembly 51 ... Rotor core 511, 512 ... Hole 52 ... Shaft 53, 53a, 53b, 53c, 53d ... Permanent magnet 53e ... Edge portion 54 ... End plate 6 ... Coil subassembly 61 ... Stator core 62 ... Coil 63 ... Teeth 7 ... Stator subassembly G ... Gap

Claims (11)

1. A method of manufacturing an electric motor including a permanent magnet in one of a rotor and a stator,
   A magnetization treatment step of magnetizing the permanent magnet;
   A demagnetization treatment step that is performed after the magnetization step and incompletely magnetizes a part of the permanent magnet magnetized by the magnetization treatment step,
   In the demagnetizing process, the phase angle of the demagnetizing process current that generates a reverse magnetic field around the permanent magnet is controlled to a predetermined value.
2. The method of manufacturing an electric motor according to claim 1, wherein the demagnetizing treatment step controls a phase angle of the demagnetizing treatment current to 90 °.
3. The method of manufacturing an electric motor according to claim 1, wherein the demagnetization processing step controls a phase angle of the demagnetization processing current to be equal to or larger than a maximum phase angle of a driving current for driving the electric motor.
4. The method of manufacturing an electric motor according to claim 1, wherein the demagnetizing treatment step changes a phase angle of the demagnetizing treatment current within a phase angle range of a driving current for driving the electric motor.
5. 5. The method of manufacturing an electric motor according to claim 4, wherein in the demagnetization processing step, the phase angle of the demagnetization processing current is continuously changed within a phase angle range of the drive current.
6. The method of manufacturing an electric motor according to claim 1, wherein the demagnetization processing step uses the demagnetization processing current as a direct current.
7. In the demagnetization processing step, the DC demagnetization processing current is supplied while the phase demagnetization processing current is changed within a phase angle range of a driving current for driving the electric motor. The manufacturing method of the electric motor of Claim 6 which rotates the rotor provided with the permanent magnet.
8. 2. The electric motor manufacturing method according to claim 1, wherein in the demagnetization processing step, the demagnetization processing current for generating a reverse magnetic field around the permanent magnet is an alternating current synchronized with rotation of a rotor provided with the permanent magnet. Method.
9. The method of manufacturing an electric motor according to claim 8, wherein the demagnetizing step changes a phase angle of the alternating current within a phase angle range of a driving current for driving the electric motor.
10. 2. The demagnetizing treatment step according to claim 1, wherein a demagnetizing treatment current that generates a reverse magnetic field around the permanent magnet is a predetermined alternating current that is asynchronous with respect to rotation of a rotor provided with the permanent magnet. A method for manufacturing an electric motor.
11. The method of manufacturing an electric motor according to claim 8, wherein the demagnetizing treatment step uses the asynchronous alternating current as an alternating current having a frequency fs defined by the following equation.
    fs = (Nr / 60) · [{(βe−βs) / 360n} + P]
    Where fs is the frequency of the alternating current, Nr is the mechanical angular rotation speed (rpm) of the electric motor, βs is the current phase angle (deg) at the start of the demagnetization process, and βe is the current phase angle (deg) at the end of the demagnetization process. ), N is an integer of 1 or more, and P is the number of pole pairs of the electric motor.

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