motor

Abstract

The motor of the present application is characterized in that it is capable of motor drive control for reducing the magnetic flux density of the core when driven at a rotational speed lower than the maximum rotational speed, the core material of the motor contains, in mass %, C: 0.010% or less, Si: 2.0% to 7.0%, Al: 2.0% or less, Mn: 0.05% to 1.0%, S: 0.005% or less, and N: 0.005% or less, with the remainder being Fe and inevitable impurities, has a magnetic flux density change region in which the change ΔB of the magnetic flux density with respect to the magnetic field change ΔH = 50 A / m is 0.50 T or more, and the plate thickness is in the range of 0.05 mm to 0.20 mm, and the eddy current loss of 1000 Hz - 1.0 T is 0.55 or less of the total iron loss.

Description

TECHNICAL FIELD

[0001] The present application relates to a motor for driving at high speed, which is suitable for cordless household appliances, cutting machines, and drones, etc. BACKGROUND

[0002] In cordless household appliances (e.g., vacuum cleaners), cutting machines, and drones, etc., which use a battery as a driving power source, the use time and weight greatly affect the value of the product, and it is strongly desired to reduce the loss of the control system such as the motor and the inverter to achieve high efficiency, miniaturization, and high speed of the motor. Therefore, the motor is designed to be the smallest size and to be able to output the maximum output corresponding to the purpose with high efficiency. On the other hand, the motor needs to be driven under the condition of low output at low speed in addition to being driven at the maximum output speed (maximum rotation speed) of such a maximum output, but under this driving condition, the core is magnetized to an unnecessary degree by the magnet, which hinders the high efficiency of the motor. Under such a background, in order to improve the iron loss of the motor under the driving condition other than the maximum output condition, a control is sometimes used in which the magnetization flux density of the core is intentionally reduced by current lead angle control under a part of the driving conditions. In addition, such a motor targets miniaturization and light weight, and therefore, the speed is high, and the magnetization frequency of the core is high at 1 to several kHz. Therefore, a slope magnet alloy or the like is used as the core material in a part of the special use, but such a material is very high in cost, and therefore, a non-oriented electromagnetic steel sheet is generally used as the core material.

[0003] However, the loss generated in the core is divided into hysteresis loss and eddy current loss, and it is known that the higher the frequency of the magnetization, the more the eddy current loss becomes dominant. Therefore, in order to reduce the eddy current loss, measures such as increasing the resistivity of the steel sheet or thinning the sheet thickness by adding non-magnetic elements such as Si and Al have been established. However, increasing the alloy amount using such non-magnetic elements causes a decrease in the saturation magnetization of the steel sheet. Therefore, as a method of achieving both reduction in high-frequency iron loss and high flux density, a Si gradient magnetic material that controls the Si concentration gradient in the sheet thickness direction is proposed in Patent Literature 1.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent No. 4677955 SUMMARY

[0007] However, when the Si gradient magnetic material is used as a core material of an electric device having an excitation frequency of several kHz, although the eddy current loss is reduced, the loss improvement effect is not sufficient for a motor which applies current advance angle control aimed at reducing motor iron loss as described above. Such a problem is fatal particularly for a high speed motor supplied with power from a battery aimed at miniaturization. In order to control the magnetic flux density level of the core by current advance angle control, a large magnetizing force needs to be obtained. In other words, a large current needs to flow through the motor winding or the number of turns of the coil needs to be increased. However, if the current is increased, the winding loss, i.e., copper loss, is increased, and the motor efficiency is deteriorated. In addition, when the number of turns of the coil is increased, the back electromotive force caused by the rotor magnet of the motor becomes high, and it is difficult to perform high speed rotation drive. Thus, there is a problem in realizing a high efficiency and miniaturized high speed motor under limited power supply conditions, and a core material suitable for such a motor has not been found.

[0008] The present application has been made in view of the above-described problems, and it is an object to provide a motor which can reduce iron loss and realize high efficiency and miniaturization at a rotational speed lower than the maximum rotational speed.

[0009] The present inventors have repeatedly studied a core material having electromagnetic characteristics suitable for a high speed motor in view of the above-described problems. As a result, it has been found that a core material which not only has low iron loss but also has a steep change in magnetic flux density with respect to a magnetic field change is effective for high efficiency and miniaturization of a motor. Note that, in the present specification, a "high speed motor" is a motor in which the maximum frequency of the basic component of the excitation condition of the core exceeds 1000 Hz.

[0010] The motor of the present application is characterized by being capable of performing motor drive control which reduces the magnetic flux density of the core at a rotational speed lower than the maximum rotational speed, and a steel sheet of the core material of the motor contains, in mass %, C: 0.010% or less, Si: 2.0% to 7.0%, Al: 2.0% or less, Mn: 0.05% to 1.0%, S: 0.005% or less, and N: 0.005% or less, with the remainder being Fe and unavoidable impurities, and has a magnetic flux density change region in which the change ΔB in magnetic flux density with respect to a magnetic field change ΔH = 50 A / m is 0.50 T or more, and a sheet thickness is in the range of 0.05 mm to 0.20 mm, and the eddy current loss at 1000 Hz-1.0 T is 0.55 or less of the total iron loss.

[0011] The motor of the present application is characterized in that, in the above-described application, the steel sheet further contains, in mass %, one or more of P: 0.01% to 0.1%, Sn: 0.001% to 0.1%, Sb: 0.001% to 0.1%, and Mo: 0.001% to 0.01%.

[0012] The motor of the present application is characterized in that, in the above-described application, the difference between the Si concentration of the surface of the steel sheet and the Si concentration of the center portion of the steel sheet is in the range of 0.5% to 4.0%, and the saturation magnetic flux density Bs of the steel sheet is 2.0 T or more.

[0013] The motor of the present application is characterized in that, in the above-described application, the magnetic flux density variation region exists in a region having a magnetic flux density of 1 T or more.

[0014] According to the present application, it is possible to provide a motor that can reduce iron loss and achieve high efficiency and small size and high speed when driven at a rotational speed lower than the maximum rotational speed. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a graph showing an example of the relationship of the magnetic flux density with respect to the external magnetic field of the steel sheet.

[0016] Figure 2 is a schematic diagram showing a configuration example of a 2-pole-3-phase brushless DC motor. DETAILED DESCRIPTION

[0017] Hereinafter, the requirements of the steel sheet as the core material of the motor of the present application and the reasons for the limitations thereof will be described. Note that the form of the motor of the present application is not particularly limited as long as it is a magnet motor. In addition, in the following description, the component addition amount is simply denoted as "%" to mean "mass %".

[0018] [C: 0.010% or less]

[0019] When C is excessively added to the steel sheet, the hysteresis loss of the motor deteriorates, and thus the content of C is 0.010% or less.

[0020] [Si: 2.0% to 7.0%]

[0021] Si is an effective additive element for increasing the electrical resistivity of the steel sheet and reducing the eddy current loss of the motor. However, when Si is excessively added to the steel sheet, not only is it difficult to process the steel sheet into a motor core, but also the saturation magnetic flux density of the steel sheet decreases. Therefore, the content of Si is in the range of 2.0% to 7.0%. Note that if 4.0% or more of Si is added, the rollability of the steel sheet is impaired, and thus Si can be added, for example, in a manner that additional Si is added using a chemical vapor silicon infiltration method after cold rolling. Also at this time, by adding Si so that the difference in the Si concentration between the center layer and the surface layer of the steel sheet is in the range of 0.5% to 4.0% and the saturation magnetic flux density Bs exhibits 2.0 T or more, it is possible to reduce the eddy current loss and also downsize the motor, and thus this is advantageous.

[0022] [Al: 2.0% or less, Mn: 0.05% to 1.0%]

[0023] Al and Mn are effective elements for increasing the electric resistivity of the steel sheet and reducing the eddy current loss of the motor. However, when Al and Mn are excessively added, the grain growth property is negatively affected, and the magnetic hysteresis loss of the motor is deteriorated. Therefore, the content of Al is 2.0% or less, and the content of Mn is in the range of 0.05% to 1.0%.

[0024] [O: 0.0001% to 0.005%, S: 0.005% or less, N: 0.005% or less, the remainder being Fe and inevitable impurities]

[0025] When S and N are excessively added, the grain growth property is hindered due to the generation of precipitates, and the magnetic hysteresis loss of the motor is increased. Therefore, the contents of S and N are each 0.005% or less, and the remainder is Fe and inevitable impurities.

[0026] [one or more selected from P: 0.01% to 0.1%, Sn: 0.001% to 0.1%, Sb: 0.001% to 0.1%, and Mo: 0.001% to 0.01%]

[0027] On the basis of the above composition, by containing one or more selected from P: 0.01% to 0.1% or less, Sn: 0.001% to 0.1%, Sb: 0.001% to 0.1%, and Mo: 0.001% to 0.01%, the magnetic flux density of the steel sheet can be increased, and the addition is preferable. However, excessive addition of any element deteriorates the manufacturability and magnetic properties of the steel sheet.

[0028] [the change ΔB in the magnetic flux density with respect to the change ΔH in the magnetic field of 50 A / m is 0.50 T or more]

[0029] The steel sheet having a steep change in the magnetic flux density, in which the change ΔB in the magnetic flux density with respect to the change ΔH in the magnetic field of 50 A / m is 0.50 T or more, makes it easy to control the magnetic flux density at the time of driving the motor whose power source (voltage, current, or both) is limited by a battery or the like.

[0030] For example Figure 1An example of the relationship of the magnetic flux density B with respect to the external magnetic field H of the steel sheet is shown. In the inventive example (curve Ll), the change ΔB of the magnetic flux density B with respect to the change ΔH = 50 A / m of the external magnetic field H from point A to point B is 0.50 T or more. In contrast, in the comparative example (curve L2), there is no region in which the change ΔB of the magnetic flux density B with respect to the change ΔH = 50 A / m of the external magnetic field H is 0.50 T or more. Here, for example, the magnet excitation magnetic flux density is designed in the vicinity of the magnetic flux density at point A, and in the inventive example, the magnetizing force required for current control to reduce the magnetic flux density of the core to the magnetic flux density at point B is 50 A / m. In contrast, in the comparative example, to reduce the magnetic flux density of the core from the same magnetic flux density as the magnetic flux density at point A to the same magnetic flux density as the magnetic flux density at point B, a magnetizing force of 140 A / m is required. However, in the case where the power supply is limited, a magnetizing force that strong is not actually available, and thus the magnetic flux density cannot be reduced, and as a result, the motor core loss reduction effect based on current control is not obtained.

[0031] For the above reasons, the steel sheet used for the core material of the motor of the present application has a steep magnetic flux density change region in which the change ΔB of the magnetic flux density with respect to the change ΔH = 50 A / m of the magnetic field is 0.50 T or more. Also, if this steep magnetic flux density change region exists in a region of a magnetic flux density of 1 T or more, the above current control is achieved, and at the same time, the magnetic flux density of the core can be maintained high, and thus the motor can be miniaturized.

[0032] 〔Sheet thickness: 0.05 mm to 0.20 mm〕

[0033] Reducing the sheet thickness of the steel sheet is effective for reducing the eddy current of the motor, but the thinner the sheet thickness of the steel sheet, the greater the manufacturing cost and the cost for forming the motor core. Therefore, the sheet thickness of the steel sheet is in the range of 0.05 mm to 0.20 mm.

[0034] 〔Eddy current loss of 1000 Hz - 1.0 T is 0.55 or less of the total core loss〕

[0035] The excitation frequency of a small high-speed motor is several hundred to 10 kHz or so, and in actual motor driving, the iron loss at high frequency becomes important due to PWM excitation of a frequency converter or the like. In such high-frequency loss, eddy current loss is dominant, and when the eddy current loss at 1000 Hz - 1.0 T is not less than the hysteresis loss, the loss generated in the core is large, which not only deteriorates the efficiency of the motor, but also necessitates a large size of the motor to avoid heating. Therefore, the eddy current loss at 1000 Hz - 1.0 T is 0.55 or less of the total iron loss. Note that the eddy current loss defined here is calculated using the so-called double-frequency method with respect to the magnetic properties measured by the method defined in JIS C 2550-1. In this case, if the motor core has a magnetic closed shape, the magnetic properties measured using a ring core by implementing 1st and 2nd windings can be used, and either of the magnetic properties satisfies the above definition.

[0036] As the steel sheet for the core material of the motor of the present application, a steel sheet satisfying the above requirements can be selected, and the preferred conditions of the manufacturing method of the steel sheet satisfying the above requirements are as follows.

[0037] As the hot rolling conditions of the steel billet, there is no particular limitation, and a publicly known method can be used, and from the viewpoint of energy saving, the slab heating temperature is preferably 1250°C or less, and the final thickness of the hot-rolled steel sheet is preferably 2.0 mm or less. This is because when the final product thickness is in the range of 0.05 mm to 0.20 mm and the cold rolling reduction rate is high, the (111) crystal plane, which is not favorable for magnetization, increases in the recrystallized structure. In this case, the case where 2 times of cold rolling is performed with an intermediate annealing therebetween is not limited thereto. After the hot rolling, annealing treatment is performed as necessary, and the steel sheet is cold-rolled to a sheet thickness of 0.05 mm to 0.20 mm. Thereafter, final annealing is performed in a temperature range of 900°C to 1250°C with a holding temperature, in an atmosphere gas having an environmental gas oxidizability expressed by P(H2O) / P(H2) of 0.010 or less. Here, the structure is improved by making the heating rate in the temperature range of 600°C to 900°C 25°C / s or more, and excellent magnetic properties are obtained. The heating rate is preferably 100°C / s or more, and more preferably 200°C / s or more. Also, in the final annealing, the Si concentration / distribution in the steel is controlled by a chemical vapor silicon infiltration method at 1200°C or more, and more excellent magnetic properties are obtained. By appropriately adjusting each of the manufacturing conditions as described above, a steel sheet as the core material of the motor of the present application can be manufactured. Note that when the motor core is formed, there are methods such as punching, wire cutting, or the like. Regardless of the method, the effects of the present application can be obtained as long as the requirements are satisfied, but it is known that the strain introduced into the core material by punching has an influence on the magnetization properties of the core material, and therefore, in the case of using the punching method, it is preferable to perform stress relief annealing.

[0038] Example

[0039] After heating the steel billets (steel symbols A to F) of the components shown in Table 1 below to 1200°C, hot-rolled steel sheets of 1.8 mm in thickness were produced by hot-rolling. Subsequently, after performing annealing treatment at 1000°C for 30 seconds, cold-rolling was performed to finish the thickness to 0.05 to 0.20 mm. Further, final annealing was performed under the conditions shown in Table 2 below (test numbers 1 to 13), and the magnetic properties (maximum magnetic flux density change ΔB (T) with respect to ΔH = 50 A / m and W 10 / 1000 ratio of eddy current loss) shown in Table 2 below were obtained. The magnetic properties were measured by the method prescribed in JIS C 2550-1. Further, with respect to the cold-rolled steel sheets to which cold-rolling was also performed, siliconizing treatment was performed by chemical vapor siliconizing method at 1200°C under a silicon tetrachloride ambient gas in the final annealing, and the treatment time and the magnetic properties are shown in Table 3 below. Note that with respect to the test conditions in which siliconizing treatment was performed, the concentrations of Si and C were changed by the siliconizing treatment, and therefore the component values after the treatment are also shown. In the conditions other than this, the components of the steel billets were the same as those of the steel sheets used for the core.

[0040] [Table 1]

[0041] (Table 1)

[0042]

[0043] [Table 2]

[0044] (Table 2)

[0045]

[0046]

[0047] A core was produced using the steel sheets shown in Tables 2 and 3, and the efficiency of a motor was evaluated. The motor to be evaluated was a 1.5 kW motor for a washing machine, and the efficiency of the motor was evaluated by the following method. The efficiency of the motor was evaluated by the following method. Figure 2A 2-pole-3-phase brushless DC motor (drive voltage 25.2 V) was shown in the shape size. The laminated thickness of the core was 15 mm, and the laminated steel sheets were bonded by impregnation. The motor efficiency was evaluated under driving condition A (50000 rpm - 10 mNm - sinusoidal wave drive of current lead angle 30 deg) belonging to the driving condition of lower than the maximum rotation speed and driving condition B (85000 rpm - 25 Nm - sinusoidal wave drive of current lead angle 0 deg) as the condition of driving at the maximum rotation speed. The evaluation results are shown in Table 4 below. As shown in Table 4, in the inventive example having a steep magnetic flux density change region with a change ΔB of the magnetic flux density of 0.50 T or more with respect to a magnetic field change ΔH = 50 A / m and an eddy current loss of 1000 Hz - 1.0 T of 0.55 or less of the total iron loss, the motor efficiency was excellent in both driving conditions A and B, and the average motor efficiency exceeded 85%. On the other hand, in the comparative example not satisfying the above conditions, the motor efficiency was worse than the inventive example in either one or both of the driving conditions A and B, and the average motor efficiency was less than 85%.

[0048] [Table 4]

[0049] (Table 4)

[0050]

[0051] Industrial Applicability

[0052] According to the present application, it is possible to provide a motor capable of reducing iron loss and achieving high efficiency and small size and high speed when driven at a rotation speed lower than the maximum rotation speed.

Claims

1. A motor characterized by, is a motor capable of motor drive control for reducing the magnetic flux density of a core when driven at a rotational speed lower than a maximum rotational speed, a steel sheet for a core material of the motor contains, in mass%, C: 0.010% or less, Si: 2.0% or more and 7.0% or less, Al: 2.0% or less, Mn: 0.05% or more and 1.0% or less, S: 0.005% or less, and N: 0.005% or less, with the remainder being Fe and inevitable impurities, the steel sheet for a core material of the motor is manufactured as follows: a steel billet having the composition is heated, hot rolling is performed, cold rolling is performed to a sheet thickness of 0.05 mm to 0.20 mm, a final annealing for maintaining a temperature in a temperature range of 900°C to 1250°C is performed according to the sheet thickness after the cold rolling, or a control of Si concentration / distribution in the steel is performed at 1200°C or higher by a chemical vapor silicon infiltration method, and the steel sheet for a core material of the motor is a steel sheet having a magnetic flux density change region in which a change ΔB of the magnetic flux density with respect to a magnetic field change ΔH = 50 A / m is 0.50 T or more, and an eddy current loss of 1000 Hz - 1.0 T is 0.55 or less of a total iron loss.

2. The motor of claim 1, wherein the steel sheet further contains, in mass%, one or more selected from the group consisting of P: 0.01% to 0.1%, Sn: 0.001% to 0.1%, Sb: 0.001% to 0.1%, and Mo: 0.001% to 0.01%.

3. The motor of claim 1, wherein a difference between a Si concentration at a surface of the steel sheet and a Si concentration at a center portion of the steel sheet is in a range of 0.5% to 4.0%, and a saturation magnetic flux density Bs of the steel sheet is 2.0 T or more.

4. The motor of claim 2, wherein a difference between a Si concentration at a surface of the steel sheet and a Si concentration at a center portion of the steel sheet is in a range of 0.5% to 4.0%, and a saturation magnetic flux density Bs of the steel sheet is 2.0 T or more.

5. The motor according to any one of claims 1 to 4, characterized in that the magnetic flux density change region exists in a region including a magnetic flux density of 1 T or more.

6. A method of manufacturing a steel sheet for a core material of a motor, characterized by, a method of manufacturing a steel sheet for a core material of a motor according to any one of claims 1 to 5, a steel billet having the following composition is heated, hot rolling is performed, cold rolling is performed to a sheet thickness of 0.05 mm to 0.20 mm, a final annealing for maintaining a temperature in a temperature range of 900°C to 1250°C is performed according to the sheet thickness after the cold rolling, or a control of Si concentration / distribution in the steel is performed at 1200°C or higher by a chemical vapor silicon infiltration method, the composition of the steel billet contains, in mass%, C: 0.010% or less, Si: 2.0% or more and 7.0% or less, Al: 2.0% or less, Mn: 0.05% or more and 1.0% or less, S: 0.005% or less, and N: 0.005% or less, with the remainder being Fe and inevitable impurities.

7. The method of producing a steel sheet for a core material of a motor according to claim 6, characterized by, the composition of the steel billet further contains, in mass%, one or more selected from the group consisting of P: 0.01% to 0.1%, Sn: 0.001% to 0.1%, Sb: 0.001% to 0.1%, and Mo: 0.001% to 0.01%.

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