The present invention relates to a rotor for an induction torque motor and, in particular, to a rotor for an induction torque motor capable of increasing the performance (the efficiency) of the induction torque motor. The present invention further relates to an induction torque motor including the rotor for an induction torque motor.
Motors that convert electrical energy into mechanical energy (electric motors or electric machinery) are used for a variety of purposes. In General, motors include a rotor that has a shaft and that rotates and a stator that interacts with the rotor. The rotor rotates due to a magnetic field that varies with rotation (a rotating magnetic field). The motors are generally classified into a synchronous motor and an induction motor (an asynchronous motor).
In synchronous motors, a rotor is attracted by a rotating magnetic field generated by a supplied alternating electric current and is driven into rotation. Thus, the synchronous motor rotates at a synchronous speed. Examples of a synchronous motor include a permanent magnet synchronous motor (a PM motor) that uses a permanent magnet as a rotor and a reluctance synchronous motor that uses, as a rotor, a material having a low reluctance (a low magnetic resistance) and temporarily functioning as a magnet (such as iron).
In the induction motors, an induction current is generated in a rotor, which is an electric conductor, due to a rotating magnetic field generated by a stator. Thus, rotation torque corresponding to slip is obtained. Examples of an induction motor include a single-phase induction motor that obtains rotation torque using a predetermined method at startup time and obtains the rotation torque using single-phase alternating current power after startup and a three-phase induction motor, such as a squirrel-cage rotor type three phase induction motor or a wound rotor type three phase induction motor, that obtains the rotation torque using three-phase alternating current power.
In addition, if motors are classified according to the torque characteristics, torque motors are one of the classes. Torque motors can provide angular displacement or rotation torque of the output shaft in accordance with the level of a supplied electric signal. For example, if a voltage is applied to a torque motor, the torque motor provides angular displacement that is proportional to the applied voltage. Alternatively, if, for example, an electric current is applied to a torque motor, the torque motor provides angular displacement that is proportional to the level of the applied electric current. Accordingly, torque motors are used in a control system that requires an accurate rotation stop position of the output shaft and an accurate rotation torque of the output shaft in response to an electric signal. Thus, torque motors are used in a variety of technical fields. Examples of torque motor include a torque motor having a configuration that is the same as the above-described PM synchronous motor (a synchronous torque motor described in, for example, PTL 1) and a torque motor having a configuration that is the same as the above-described induction motor (an induction torque motor described in, for example, NPL 1).
The torque motor described in PTL 1 includes a magnetic circuit formed from a solenoid and a pair of stators laterally extending from either end of the solenoid and a rotor that is disposed between circular arc portions each formed by one of the stators and that has a cylindrical magnet core. Upon receiving a magnetic force from the pair of stators excited by the solenoid, the rotor rotates.
In general, motors are expected to be compact or power-efficient. Accordingly, the performance (the efficiency) represented by a value obtained by dividing the output torque by the input power needs to be increased.
PTL 1: Japanese Unexamined Patent Application Publication No. 2006-204012
NPL 1: FUJII ELECTRIC WORKS Co., Ltd., [Online], searched on Sep. 12, 2011, available in the Internet at <URL: http://www.few.co.jp/products/p01.html> and <URL: http://www.few.co.jp/pdf/torque.pdf>
Accordingly, the present invention is provided. It is an object of the present invention to provide a rotor for an induction torque motor capable of further increasing the performance of the induction torque motor and an induction torque motor including the rotor for an induction torque.
According to the present invention, a rotor for an induction torque motor includes a shaft member and a cylindrical member that is concentrically connected to the shaft member and that is formed of a soft magnetic material having a specific electric resistivity lower than or equal to 0.4 [μΩ·m] and a relative permeability higher than or equal to 1000 and lower than or equal to 50000. In addition, an induction torque motor according to the present invention includes the rotor for an induction torque motor. Thus, according to the present invention, the performance of each of the rotor for an induction torque motor and the induction torque motor can be improved.
Further objects, features, and advantages of the present invention will become apparent from the following description of embodiments with reference to the attached drawings.
An embodiment of the present invention is described below with reference to the accompanying drawings. Note that in the drawings, the configurations indicated by the same reference numeral are the same configuration and, therefore, description of the configuration is not repeated as needed. In addition, in the present specification, to collectively refer to such configurations, a reference numeral without a suffix is used. In contrast, if the configurations are individually identified, a reference numeral with a suffix is used.
As illustrated in
More specifically, the frame 3 includes a bottomed cylindrical casing 3a and a plate-like bracket 3b that is attached to the open end (the ceiling end) of the casing 3a and that closes the open end of the casing 3a. In addition, the rotor 1 and the stator 2 are coaxially disposed in the casing 3a. The stator 2 is fixed to the inner peripheral surface of the casing 3a, and the rotor 1 is disposed in a rotatable manner relative to the stator 2.
The stator 2 is substantially cylindrical in shape. For example, the stator 2 is formed by stacking a plurality of magnetic steel sheets. The cylindrical stator 2 includes an inner surface having a plurality of ridges (convex portions) each protruding inwardly in the radial direction and extending in the axis direction. The ridges are arranged at predetermined intervals in the circumferential direction. The stator 2 further includes a plurality of winding wires formed by winding a conductor wire coated by an insulator, such as an insulated covered copper wire, around each of the plurality of convex portions. Such winding wires and the convex portions form the magnetic poles. Thus, a predetermined number of the magnetic pole are formed (the number of magnetic poles is predetermined). In addition, as described above, the outer peripheral surface of the stator 2 is fixed to the inner peripheral surface of the casing 3a.
The rotor 1 includes a shaft member 1a having a shape of a rod (a bar or a columnar member) that serves as an output shaft and a cylindrical member 1b connected to the shaft member 1a so as to be concentric (coaxial) with the shaft center of the shaft member 1a. According to the present embodiment, the shaft center 1a is inserted into a through-hole formed so as to penetrate the shaft center of the cylindrical member 1b in the axis direction. The shaft center 1a is fixed to the cylindrical member 1b in the substantially middle region of the cylindrical member 1b.
In addition, one end of the shaft member 1a (the left end in
Furthermore, the cylindrical member 1b of the rotor 1 is made of a soft magnetic material having a specific electric resistivity ρ lower than or equal to 0.4 [μΩ·m] and a relative permeability μ higher than or equal to 1000 and lower than or equal to 50000 (in the range of 1000 to 50000) (i.e., ρ≦0.4 [μΩ·m], and 50000≧μ≧1000). Examples of such a soft magnetic material include extra low carbon Cold Heading wire (ELCH2) (an iron series soft magnetic material available from Kobe Steel, Ltd.), ELCH2S, LCA-1, and S10C. It is desirable that the soft magnetic material used for the cylindrical member 1b of the rotor 1 be the iron series soft magnetic material “ELCH2”. The chemical composition of ELCH2, expressed in mass %, is 0.005% carbon (C), 0.004% silicon (Si), and 0.26% manganese (Mn). ELCH2 has a high flux density and a low magnetic coercive force. In addition, ELCH2 has a reduced specific electric resistivity lower than that of low carbon steel (C=0.1%) by 30%, which is substantially the same as the specific electric resistivity of industrial nickel Ni.
Note that while the example illustrated in
In addition, according to the present embodiment, as illustrated in
Note that let s be the slip of the induction torque motor TM. Then, the skin depth δ(sf0) can be expressed as:
δ(sf0)=ρ/π·s·f0·μ)1/2
where f0 [Hz] represents the drive frequency of the induction torque motor TM, μ represents the relative permeability of the cylindrical member 1b of the rotor 1, and ρ [μΩ·m] represents the specific electric resistivity of the cylindrical member 1b of the rotor 1.
In addition, according to the present embodiment, as illustrated in
Furthermore, as illustrated by a dashed line in
As can be seen from a dashed line indicating a torque TQg of a general-purpose motor in
In contrast, in the induction torque motor TM, as the electric current is gradually decreased from the startup current level, as can be seen from a dashed line indicating an electric current EC of the torque motor in
In addition, since, in the induction torque motor TM according to the present embodiment, the cylindrical member 1b of the rotor 1 is made of a soft magnetic material having a specific electric resistivity ρ lower than or equal to 0.4 [μΩ·m] and a relative permeability μ higher than or equal to 1000 and lower than or equal to 50000, the performance (the efficiency) can be increased more. The increase in the performance is described in more detail below.
In
Let ieddy(x) be the eddy current density in the cylindrical member 1b of the rotor 1 of the above-described induction torque motor TM, and let B(x) be the magnetic flux density in the cylindrical member 1b. Then, the following equations can be obtained:
ieddy(x)=(I0/δ)*exp(−(x/δ)) (1)
B(x)=B0(x)·exp(−(x/δ)) (2)
where x represents the coordinate system directed toward the shaft center in the radial direction when the outer peripheral surface of the cylindrical member 1b is defined as “0”, I0 represents the supplied external drive current, B0(x) represents the magnetic flux density obtained when an external drive current I0 is supplied, and δ represents the above-described skin depth (δ(sf0)=(ρ/π·s·f0·μ)1/2).
In addition, for the eddy current density ieddy(x) and the magnetic flux density B(x), the following equations can be obtained:
∫ieddy(x)dx=I0 (3), and
B
0
=B
0(μ)=L(μ)·I0∝(1/(1+a/μ))·I0 (4).
Note that equation (3) indicates that the eddy current density is normalized by the external drive current I0. In addition, the integral range of equation (3) is from (x=0 to ∞ (infinity)), the expression “A∞B” in equation (4) indicates that A is proportional to B, μ represents the relative permeability of the cylindrical member 1b of the rotor 1, L [H] represents the inductance, and a represents a parameter regarding the distance G [m] between the outer peripheral surface of the cylindrical member 1b of the rotor 1 and the inner peripheral surface of the stator 2 (the spacing in the radial direction). The parameter a and the distance G have a seesaw relationship. If the distance G is small, the parameter a is relatively large. In contrast, if the distance G is large, the parameter a is relatively small. That is, the parameter a is inversely proportional to the distance G (a∞1/G). Note that the parameter a is effected by the structure and the magnetic property of the stator 2 in addition to the distance G. The parameter a is used as the index indicating the quality of a motor magnetic circuit.
A Lorentz force fL(x) acting on a microvolume in the rotor 1 is given as follows:
f
L(x)=ieddy(x)×B(x) (5)
Torque T can be obtained by integrating equation (5) over the entire area of the rotor 1 as follows:
Note that each of the integral ranges of equation (6) is (from X=0 to ∞ (infinity)).
Like the torque T, an eddy current loss P in the rotor 1 can be obtained as follows:
P=∫ρ·i
eddy
2(x)dx=(ρ/δ)·(I02/2) (7)
Note that each of the integral ranges of equation (7) is from (x=0 to ∞ (infinity)).
Accordingly, from equations (6) and (7), the torque per “loss/slip” of the induction torque motor is given as follows:
The results of simulation using the equation under a variety of conditions (the results of numerical analysis) are illustrated in
The chemical composition (mass %) of each of the soft magnetic materials is illustrated in the following tables 1 to 3.
Note that the simulation result for S20C is obtained using the specific electric resistivity and the magnetic permeability when magnetic annealing is not performed. In addition, SUS430 is ferrite based.
As can be seen from
In addition, as can be seen from a comparison of
In addition, according to the present embodiment, the cylindrical member 1b of the rotor 1 of the induction torque motor TM has a plurality of concave groove portions 11 that are formed in the peripheral surface of the cylindrical member 1b and that extend parallel to the axis direction of the cylindrical member 1b. By including the plurality of concave groove portions 11 in this manner, the rotor 1 of the induction torque motor TM according to the present embodiment can regulate an area in which an eddy current flows. As a result, a squirrel-cage property can be provided to the cylindrical member 1b. Accordingly, unlike the torque property of a rotor without the concave groove portions 11 such that the torque decreases substantially in proportion to a decrease in the eddy current (an increase in speed) (refer to the torque property of the torque motor A illustrated in
In addition, in the rotor 1 of the induction torque motor TM according to the present embodiment, the depth of the concave groove portions 11 is greater than or equal to the skin depth δ(sf0), and the aspect ratio (the depth/the width) is greater than or equal to 2.
As indicated by the result in
In addition, in the rotor 1 of the induction torque motor TM according to the present embodiment, the cylindrical member 1b includes the pair of circular ring members 12-1 and 12-2 formed along the circumferential edge at either end of the cylindrical member 1b in the axis direction. The circular ring members 12-1 and 12-2 are made of a conductive material having a specific electric resistivity lower than or equal to 0.02 [μΩ·m]. Accordingly, by further including the circular ring members 12 made of a relatively good conductor, the rotor 1 of the induction torque motor TM according to the present embodiment can reliably maintain a flow path of the eddy current at either end of the rotor 1 and, thus, the eddy current is enabled to efficiently flow. As a result, an excellent performance can be provided.
In addition, the above-described magnetic property, such as magnetic permeability, can be obtained by producing a ring-shaped sample having, for example, an external radius of 18 mm×an internal radius of 10 mm using a wire material of each of the compositions, performing magnetic annealing (or intentionally eliminating the need for magnetic annealing to reduce the number of steps), winding a magnetic field applying coil and a magnetic flux detecting coil around the sample, and measuring the B-H curved line using an automatic magnetization measuring apparatus.
The present specification describes the variety of techniques mentioned above. The primary technologies among the above-described technologies are summarized below.
According to an embodiment, the rotor for an induction torque motor is used as a rotor of an induction torque motor. The rotor includes a shaft member and a cylindrical member that is connected to the shaft member so as to be concentric with the shaft center of the shaft member and that is made of a soft magnetic material having a specific electric resistivity lower than or equal to 0.4 [μΩ·m] and a relative permeability higher than or equal to 1000 and lower than or equal to 50000.
The results of simulation analysis for the induction torque motor indicates that a soft magnetic material having a specific electric resistivity lower than or equal to 0.4 [μΩ·m] and a relative permeability higher than or equal to 1000 and lower than or equal to 50000 (in the range of 1000 to 50000) is located in the best section of a curved line of equal performance, unlike the other soft magnetic materials. As used herein, the term “curved line of equal performance” refers to a line formed by a set of points that provide the same performance in the specific electric resistivity−relative permeability space. Accordingly, since such a rotor for an induction torque motor includes a cylindrical member made of a soft magnetic material having a specific electric resistivity lower than or equal to 0.4 [μΩm] and a relative permeability higher than or equal to 1000 and lower than or equal to 50000, the performance of the induction torque motor including the rotor for an induction torque motor can be more improved than that of an induction torque motor having a rotor including a cylindrical member made of another soft magnetic material.
In addition, according to another embodiment, in the above-described rotor for an induction torque motor, let T [N·m] be the torque of the induction torque motor, let P [W/kg] be the eddy current loss of the rotor, let s be the slip of the induction torque motor, let f0 [Hz] be the drive frequency of the induction torque motor, let ρ [μΩ·m] be the specific electric resistivity of the soft magnetic material, let μ be the relative permeability of the soft magnetic material, and let δ(sf0) [m] be the skin depth of the cylindrical member at a drive frequency of f0. Then, when the torque T per “loss P/slip sf0” is expressed as follows:
T/(P/sf0)∝1/(1+a/μ)·(δ(sf0)/ρ) (C1)
where the symbol ∝ in expression “A∝B” indicates that A is proportional to B. At that time, the parameter a in equation C1 is in the range of 1000≦a≦2500.
In such a rotor for an induction torque motor, since the parameter a in equation C1 is in the range 1000≦a≦2500, an induction torque motor including the rotor for an induction torque motor can more reliably reflect the property of the soft magnetic material that constitutes the cylindrical member to the torque property and, thus, the performance of the induction torque motor can be more reliably improved.
In addition, according to still another embodiment, in the above-described rotors for an induction torque motor, the cylindrical member further has a plurality of concave groove portions that are formed in a peripheral surface of the cylindrical member and that extend parallel to the axis direction of the cylindrical member.
By including the plurality of concave groove portions, such a rotor for an induction torque motor can regulate an area in which an eddy current flows. As a result, a squirrel-cage property can be provided to the cylindrical member. Accordingly, unlike the torque property of a rotor without the concave groove portions such that the torque decreases substantially in proportion to a decrease in the eddy current (an increase in speed), the rotor for an induction torque motor can provide the following torque property, that is, a torque property such that the torque gently decreases with decreasing eddy current (increasing speed) in a range from the starting point to a point at which the eddy current (the speed) reaches a predetermined value and the torque relatively rapidly decreases with decreasing eddy current (increasing speed) in a range in which the eddy current (the speed) exceeds the predetermined value. That is, when an induction torque motor is achieved, such a configuration can maintain the torque at a substantially constant level even when a few slip occurs.
In addition, according to yet still another embodiment, in the above-described rotors for an induction torque motor, the depth of the concave groove portions is greater than or equal to the skin depth δ(sf0), and the aspect ratio (the depth/the width) is greater than or equal to 2.
Since such a rotor for an induction torque motor has the concave groove portions having such a shape, an area in which an eddy current flows can be more reliably regulated.
In addition, according to yet still another embodiment, the above-described rotor for an induction torque motor further includes the pair of circular ring members made of a conductive material having a specific electric resistivity lower than or equal to 0.02 [μΩ·m]. The ring members are disposed along the circumferential edges at either end of the cylindrical member in the axis direction.
Since such a rotor for an induction torque motor further includes the circular ring members formed of a relatively good conductor, a flow path of the eddy current can be more reliably provided at either end of the rotor for an induction torque motor and, thus, the eddy current is allowed to more efficiently flow. As a result, an excellent performance can be provided.
In addition, according to yet still another embodiment, an induction torque motor includes a stator and a rotor. The rotor is any one of the above-described rotors for an induction torque motor.
Since such an induction torque motor includes a rotor having a cylindrical member made of a soft magnetic material having a specific electric resistivity lower than or equal to 0.4 [μΩ·m] and a relative permeability higher than or equal to 1000 and lower than or equal to 50000, the performance of an induction torque motor including the rotor for an induction torque motor can be more improved than that of an induction torque motor having a rotor including a cylindrical member made of another soft magnetic material.
This application claims the benefit of Japanese Patent Application No. 2012-46018, filed Mar. 2, 2012, which is hereby incorporated by reference herein in its entirety.
Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.
According to the present invention, a rotor for an induction torque motor and an induction torque motor using the rotor for an induction torque motor can be provided.
Number | Date | Country | Kind |
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2012-046018 | Mar 2012 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2013/001022 | 2/22/2013 | WO | 00 |