Patent Application
20170366075
The disclosure of Japanese Patent Application No. 2016-121994 filed on Jun. 20, 2016 including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
The present invention relates to synchronous reluctance motors that are used for, e.g., electric power steering systems.
Reluctance motors are known which rotate a rotor by using only reluctance torque generated by a change in electromagnetic energy with respect to the position. The reluctance motors include switched reluctance motors and synchronous reluctance motors. In the switched reluctance motors, a stator and a rotor have a magnetic saliency. In the synchronous reluctance motors, a stator has a structure similar to that of a brushless motor.
In the synchronous reluctance motors, only a rotor has a magnetic saliency out of the stator and the rotor. In the synchronous reluctance motors, there are a salient direction in which magnetic flux tends to flow (hereinafter referred to as the “d-axis direction”) and a non-salient direction in which the magnetic flux is less likely to flow (hereinafter referred to as the “q-axis direction”) due to the magnetic saliency of the rotor. Accordingly, reluctance torque is generated due to the difference between inductance in the d-axis direction and inductance in the q-axis direction, and the rotor is rotated by the reluctance torque. See, e.g., Japanese Patent Application Publication No. H11-289730 (JP H11-289730 A) for related art.
The synchronous reluctance motors do not use permanent magnets, and rotate the rotor by using only the reluctance torque. The synchronous reluctance motors are therefore disadvantageous in that their output torque is smaller than that of motors using permanent magnets. It is desired to increase the output torque of the synchronous reluctance motors as much as possible.
It is one object of the present invention to provide a synchronous reluctance motor that can generate larger output torque.
According to one aspect of the present invention, a synchronous reluctance motor includes: an annular stator; and a rotor disposed radially inside the stator. The stator includes an annular stator core having in its inner peripheral portion a plurality of slots located at an interval in a circumferential direction of the stator, and slot coils accommodated in the slots. The slot coils are formed by a wire having a quadrilateral section and are wound in the slots by distributed winding.
In the synchronous reluctance motor of the above aspect, the slot coils are formed by a wire having a quadrilateral section. In this case, clearance between the slot coils in the state where the slot coils are accommodated in the slots can be reduced as compared to the case where the slot coils are formed by a round wire having a circular section. A space factor of the slot coil, which is the proportion of the slot coil in the slot, can be thus increased.
In the synchronous reluctance motor of the above aspect, the slot coils are wound by distributed winding. Accordingly, a winding factor can be made closer to 1 as compared to the case where the slot coils are wound by concentrated winding. Since the space factor of the slot coil is increased and the winding factor is improved, output torque can be increased.
The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.
Referring to
The stator 2 includes an annular stator core 4 and slot coils 5U, 5V, 5W. In the present embodiment, the stator core 4 is formed by stacking a plurality of annular steel sheets. In the present embodiment, the stator core 4 has an inside diameter of about 50 mm and an outside diameter of about 90 mm.
The stator core 4 has a plurality of (in the present embodiment, 24) slots 6U, 6V, 6W, a plurality of (in the present embodiment, 24) tooth portions 7, and an annular yoke portion 8. The plurality of slots 6U, 6V, 6W are located at regular intervals in the circumferential direction. Each of the plurality of tooth portions 7 is a portion located between two of the slots 6U, 6V, 6W which are adjacent to each other in the circumferential direction. The yoke portion 8 is a portion located radially outside the slots 6U, 6V, 6W and the tooth portions 7.
Referring to
Each coil accommodating portion 9 has a quadrilateral shape extending in the radial direction as viewed in plan (in the present embodiment, a rectangular shape as viewed in plan). The circumferential width of each coil accommodating portion 9 is substantially uniform along the radial direction. The radial width of each coil accommodating portion 9 is substantially uniform along the circumferential direction.
Each slot opening portion 10 has a quadrilateral shape extending in the circumferential direction as viewed in plan (in the present embodiment, a rectangular shape as viewed in plan). The circumferential width of each slot opening portion 10 is smaller than that of each coil accommodating portion 9. Each slot opening portion 10 communicates, at its radially outer end, with the coil accommodating portion 9 in the middle part in the circumferential direction of the coil accommodating portion 9 via the slot connection portion 11.
Each slot connection portion 11 connects the radially inner end of the coil accommodating portion 9 and the radially outer end of the slot opening portion 10. In the present embodiment, each slot connection portion 11 is formed so that its circumferential width gradually increases toward the coil accommodating portion 9 from the slot opening portion 10. A predetermined angle is thus formed between the coil accommodating portion 9 and the slot connection portion 11.
Referring to
The inner end 13 of each tooth portion 7 is a portion sandwiched between the slot opening portions 10 of two of the slots 6U, 6V, 6W which are adjacent to each other in the circumferential direction. The circumferential width of the inner end 13 is larger than that of the inner end 12b of the tooth body portion 12. The tooth connection portion 14 of each tooth portion 7 is a portion sandwiched between the slot connection portions 11 of two of the slots 6U, 6V, 6W which are adjacent to each other in the circumferential direction. The tooth connection portion 14 of each tooth portion 7 connects the tooth body portion 12 and the inner end 13.
Referring to
More specifically, the plurality of slots 6U, 6V, 6W include a U-phase slot 6U in which the U-phase slot coil 5U is wound by distributed winding, a V-phase slot 6V in which the V-phase slot coil 5V is wound by distributed winding, and a W-phase slot 6W in which the W-phase slot coil 5W is wound by distributed winding. Referring to
The configuration in one slot 6U, 6V, 6W will be described with reference to
Interterminal resistance R of each slot coil 5U, 5V, 5W is set based on the following Expressions (1) to (3).
R=ρ·(L/Se) (1)
Se=1/n·{(r1−r2)−(Y−Z)−W−2·D}·(X−2·D) (2)
W=(0.5·X−0.5·M)/tan(180°−θ) (3)
In Expression (1), p represents the resistivity of each slot coil 5U, 5V, 5W, L represents the length of each slot coil 5U, 5V, 5W, and Se represents the sectional area of each conductor portion 15.
Referring to
In the present embodiment, each slot coil 5U, 5V, 5W formed by a wire having a quadrilateral section (rectangular wire) is wound in the slots 6U, 6V, 6W of a corresponding phase by distributed winding. In the case of the slot coils 5U, 5V, 5W formed by a wire having a quadrilateral section (rectangular wire), clearance between the slot coil 5U, 5V, 5W and the slot 6U, 6V, 6W can be reduced as compared to the case where the slot coils 5U, 5V, 5W formed by a round wire having a circular section are wound with the same number of turns in the slots 6U, 6V, 6W. Moreover, since the slot coils 5U, 5V, 5W have a larger sectional area, winding resistance of the slots 6U, 6V, 6W can be reduced.
The space factor of each slot coil 5U, 5V, 5W, which is the proportion of the slot coil 5U, 5V, 5W in each slot 6U, 6V, 6W, can be increased while reducing the interterminal resistance R of each slot coil 5U, 5V, 5W. In particular, setting the interterminal resistance R of each slot coil 5U, 5V, 5W based on Expressions (1) to (3) can effectively increase the space factor of each slot coil 5U, 5V, 5W while satisfactorily reducing the interterminal resistance R of each slot coil 5U, 5V, 5W.
Winding the slot coils 5U, 5V, 5W by distributed winding can make the winding factor closer to 1 as compared to the case of winding the slot coils 5U, 5V, 5W by concentrated winding. Since the interterminal resistance R of each slot coil 5U, 5V, 5W is reduced, the space factor thereof is increased, and the winding factor is improved, reluctance torque T, which is output torque of the motor 1, can be increased.
The relationship among the average value of the circumferential width of the tooth body portion 12, the circumferential width X of the coil accommodating portion 9, and the radial width Y of the yoke portion 8 will be described. The average value H of the circumferential width of the tooth body portion 12 is given by the following Expression (4).
H=(H1+H2)/2 (4)
In Expression (4), H1 represents the circumferential width of the outer end 12a of the tooth body portion 12, and H2 represents the circumferential width of the inner end 12b of the tooth body portion 12.
It is preferable to set the average value H of the circumferential width of the tooth body portion 12 to a value equal to or larger than the circumferential width X of the coil accommodating portion 9 (X≦H). With this configuration, the volume of each tooth portion 7 can be made larger than the capacity of each slot 6U, 6V, 6W. Since the volume of the stator core 4 is increased, magnetic resistance of the stator core 4 can be reduced, and magnetic utilization can thus be improved.
The radial width Y of the yoke portion 8 may be set to a value equal to or larger than the average value H of the circumferential width of the tooth body portion 12 (H≦Y). With this configuration, the volume of the stator core 4 can be effectively increased. Accordingly, the average value H of the circumferential width of the tooth body portion 12 may be set to a value equal to or larger than the circumferential width X of the coil accommodating portion 9 and equal to or smaller than the radial width Y of the yoke portion 8 (X≦H≦Y).
Specific values of the circumferential width X of the coil accommodating portion 9, the average value H of the circumferential width of the tooth body portion 12, the radial width Y of the yoke portion 8, the radial width Z of the slot opening portion 10, the circumferential width M of the slot opening portion 10, and the opening angle θ will be described with reference to
In this simulation, the average value H of the circumferential width of the tooth body portion 12 was 4.4 mm, the radial width Y of the yoke portion 8 was 7.2 mm, the radial width Z of the slot opening portion 10 was 0.5 mm, the circumferential width M of the slot opening portion 10 was 0.5 mm, and the opening angle θ was 100°.
Referring to
In this simulation, the circumferential width X of the coil accommodating portion 9 was 2.6 mm, the radial width Y of the yoke portion 8 was 7.2 mm, the radial width Z of the slot opening portion 10 was 0.5 mm, the circumferential width M of the slot opening portion 10 was 0.5 mm, and the opening angle θ was 100°.
Referring to
This is because, as the average value H of the circumferential width of the tooth body portion 12 decreases and the circumferential width X of the coil accommodating portion 9 increases, the magnetic resistance increases and the magnetic utilization decreases accordingly, which causes magnetic saturation. This result shows that, in order to restrain magnetic saturation, it is preferable to set the average value H of the circumferential width of the tooth body portion 12 to 4.4 mm or more and 5 mm or less.
The results of
In this simulation, the circumferential width X of the coil accommodating portion 9 was 1.6 mm, 2.6 mm, and 3.6 mm, the radial width Z of the slot opening portion 10 was 0.5 mm, the circumferential width M of the slot opening portion 10 was 0.5 mm, and the opening angle θ was 100°.
Referring to
Referring to
The results of
In this simulation, the circumferential width X of the coil accommodating portion 9 was 2.6 mm, the average value H of the circumferential width of the tooth body portion 12 was 4.4 mm, the radial width Y of the yoke portion 8 was 7.2 mm, the radial width Z of the slot opening portion 10 was 0.5 mm, and the opening angle θ was 100°.
The ratio M/X of the circumferential width M of the slot opening portion 10 to the circumferential width X of the coil accommodating portion 9 was varied in the range of 0.076 to 0.85, both inclusive. More specifically, the circumferential width X of the coil accommodating portion 9 was 2.6 mm, and the circumferential width M of the slot opening portion 10 was varied in the range of 0.2 mm to 2.2 mm, both inclusive.
Referring to
Referring to
When the ratio M/X of the circumferential width M of the slot opening portion 10 to the circumferential width X of the coil accommodating portion 9 is approximately 0, the slot opening portion 10 is substantially closed by the inner end 13 of the tooth portion 7. In this case, adjacent ones of the tooth portions 7 are substantially magnetically connected by the inner ends 13, and magnetism is not appropriately utilized. This results in reduced magnetic utilization and reduced reluctance torque T. When the ratio M/X of the circumferential width M of the slot opening portion 10 to the circumferential width X of the coil accommodating portion 9 is approximately 1, there is no inner end 13 radially inside the coil accommodating portion 9. In this case, the magnetic resistance of the tooth portion 7 increases, which results in reduced magnetic utilization and reduced reluctance torque T.
Accordingly, setting the ratio M/X of the circumferential width M of the slot opening portion 10 to the circumferential width X of the coil accommodating portion 9 to an appropriate value under the condition of 0<M/X<1 improves the magnetic utilization, whereby satisfactory reluctance torque T can be achieved. Referring to
The simulation results of
The simulation results of
In this simulation, the circumferential width X of the coil accommodating portion 9 was 2.6 mm, the average value H of the circumferential width of the tooth body portion 12 was 4.4 mm, the radial width Y of the yoke portion 8 was 7.2 mm, the radial width Z of the slot opening portion 10 was 0.5 mm, and the circumferential width M of the slot opening portion 10 was 0.5 mm.
Referring to
Referring to
Referring back to
Referring to
In the following description, a rib 23 refers to a region of the rotor core 20 which is sandwiched between adjacent two of the flux barriers 22 of the same flux barrier group as viewed in plan. A q-axis is an axis extending through the midpoints in the circumferential direction of the flux barriers 22 of each flux barrier group and extending in the radial direction of the rotor core 20. A d-axis is an axis extending between adjacent two of the flux barrier groups and extending in the radial direction of the rotor core 20.
The flux barriers 22 impede the flow of magnetic flux. Accordingly, the magnetic flux from the stator core 4 is less likely to flow in the direction from one of adjacent two of the q-axes to the other. However, due to the ribs 23 each located between the flux barriers 22, the magnetic flux from the stator core 4 tends to flow in the direction from one of adjacent two of the d-axes to the other.
If a rotating magnetic field is applied from the stator 2 to the rotor 3, reluctance torque T is generated from the motor 1. The reluctance torque T is given by the following Expression (5).
T=pn·(Ld−Lq)·Id·Iq (5)
In Expression (5), pn represents the number of pole pairs, Ld represents d-axis inductance, Lq represents q-axis inductance, Id represents a d-axis current, and Iq represents a q-axis current.
The reluctance torque T therefore increases as the difference between the d-axis inductance Ld and the q-axis inductance Lq, namely (Ld−Lq), increases. In the present embodiment, in order to increase the difference (Ld−Lq), the flux barriers 22 are formed to increase the magnetic resistance of a magnetic path in the q-axis direction and to reduce the magnetic resistance of a magnetic path in the d-axis direction.
In the present embodiment, in order to increase the reluctance torque T while reducing torque ripple, the flux barriers 22 are designed to have an appropriate shape as viewed in plan. The shape of the flux barriers 22 as viewed in plan will be described in detail.
Referring to
The plurality of flux barriers 22 of each flux barrier group are formed by arc-shaped portions 22a located inside the polygonal region 24 and linear portions 22b located outside the polygonal region 24 and extending from both ends of each arc-shaped portion 22a, as viewed in plan. The center of the arcs of the plurality of arc-shaped portions 22a of each flux barrier group is located at the midpoint A, B, C, D in the circumferential direction of that flux barrier group which is located on the outer peripheral edge of the rotor 3. The linear portion 22b extending from each end of the arc-shaped portion 22a extends in the direction perpendicular to one of the four sides of the polygonal region 24 which is located close to that end of the arc-shaped portion 22a, as viewed in plan. In other words, the linear portion 22b extending from each end of the arc-shaped portion 22a extends in the direction tangential to the arc-shaped portion 22a from that end of the arc-shaped portion 22a.
For example, the plurality of flux barriers 22 of one flux barrier group are formed by a plurality of arc-shaped portions 22a whose center is located at the point A, a plurality of linear portions 22b extending perpendicularly to the side A-B from one end on the side A-B of the arc-shaped portions 22a, and a plurality of linear portions 22b extending perpendicularly to the side D-A from one end on the side D-A of the arc-shaped portions 22a, as viewed in plan.
The reason why the plurality of flux barriers 22 of each flux barrier group are designed to have the shape described above as viewed in plan will be described with respect to one flux barrier group for example. In the case where a planar circuit with an area S is placed in a magnetic field with magnetic flux density B [wb], magnetic flux Φ passing through the planar circuit with the area S is commonly given by the following Expression (6).
Φ=B·S·sin φ (6)
In Expression (6), φ represents an angle between the plane of the planar circuit and the direction of the magnetic flux.
Expression (6) shows that the magnetic flux Φ is maximum when the angle φ between the plane of the planar circuit and the direction of the magnetic flux is 90 degrees.
In the case where the plurality of flux barriers 22 of each flux barrier group are designed to have the shape described above as viewed in plan, the magnetic flux flowing in the d-axis direction passes through the ribs 23 perpendicularly to the sections of the ribs 23 taken along the line segment D-A, and the sectional area of each rib 23 through which the magnetic flux passes, taken along the line segment D-A, is maximum. The magnetic utilization is thus improved, whereby the reluctance torque T can be increased.
The arc-shaped portions 22a can be formed to a position closer to the center of the rotor 3 as compared to the case where the center of the arcs of the flux barriers 22 is located at a position outside the outer peripheral edge of the rotor 3 on the q-axis. The width of the ribs 23 can thus be increased, whereby the magnetic resistance of the magnetic path in the d-axis direction can be reduced. The reluctance torque T can thus be increased.
Although the embodiment of the present invention is described above, the present invention can be carried out in other forms.
For example, in the above embodiment, the number of slots 6U, 6V, 6W and the number of tooth portions 7 are 24. However, the number of slots 6U, 6V, 6W and the number of tooth portions 7 may be more than 24. For example, the number of slots 6U, 6V, 6W and the number of tooth portions 7 may be 36, 48, 96, etc.
In the above embodiment, the rotor 3 has four poles (two pairs of poles). However, the number of poles of the rotor 3 may be other than four. For example, the rotor 3 may have six poles (three pairs of poles), eight poles (four pairs of poles), etc.
In the above embodiment, the flux barriers 22 are arranged in seven layers. However the number of layers of the flux barriers 22 may be other than seven. For example, the flux barriers 22 may be arranged in five layers, six layers, eight layers, nine layers, etc.
In the above embodiment, the slot coils 5U, 5V, 5W may be formed by segment conductors. That is, the slot coil 5U, 5V, 5W of each phase may be configured so that U-shaped segment conductors having a pair of tip ends are accommodated in the four pairs of slots 6U, 6V, 6W of a corresponding phase and are connected together with the tip ends of each segment conductor being bonded together in a predetermined manner. Forming the slot coils 5U, 5V, 5W by the segment conductors facilitates attachment of the slot coils 5U, 5V, 5W to the stator core 4.
The above embodiment is described with respect to the example in which the radial width Z of each slot opening portion 10 is 0.5 mm. However, the radial width Z of each slot opening portion 10 may be, e.g., 0.3 mm or more and 1.0 mm or less. In this configuration, the radial width of the inner end 13 of each tooth portion 7 is also 0.3 mm or more and 1.0 mm or less, whereby the magnetic resistance can be reduced in the inner end 13. The magnetic utilization can thus be satisfactorily improved.
For example, the present invention can be applied to synchronous motors that are used in electric power steering systems. However, the present invention is also applicable to synchronous motors that are used in systems other than electric power steering systems.
Features based on the specification and the drawings will be described below.
A synchronous reluctance motor (1) includes: an annular stator (2); and a rotor (3) disposed radially inside the stator. The stator includes an annular stator core (4) having in its inner peripheral portion a plurality of slots (6U, 6V, 6W) located at an interval in a circumferential direction of the stator, and slot coils (5U, 5V, 5W) accommodated in the slots. Each of the slots is formed by a coil accommodating portion (12) extending in a radial direction of the stator and accommodating the slot coil, and a slot opening portion (13) communicating with the coil accommodating portion at a radially inner end of the coil accommodating portion. A ratio (M/X) of a circumferential width (M) of the slot opening portion to a circumferential width (X) of the coil accommodating portion is set to 0.076 or more and 0.85 or less.
In this configuration, the ratio of the circumferential width of the slot opening portion to the circumferential width of the coil accommodating portion is set to 0.076 or more and 0.85 or less. This can satisfactorily improve magnetic utilization, whereby output torque can be increased. Since the magnetic utilization is improved, torque ripple can be reduced.
In the above synchronous reluctance motor, each of the slots may include a slot connection portion (11) located between the coil accommodating portion and the slot opening portion and connecting the coil accommodating portion and the slot opening portion. An angle (θ) between the coil accommodating portion and the slot connection portion may be set to 90° or more and 130° or less.
In the above synchronous reluctance motor, the plurality of slots may be located at a regular interval in the circumferential direction. The slot opening portion may communicate with the coil accommodating portion in a middle part in the circumferential direction of the coil accommodating portion.
In the above synchronous reluctance motor, the stator core may include a tooth portion (7) that is a portion between the slots adjacent to each other in the circumferential direction. The tooth portion may have a circumferential width that gradually decreases toward the inside in the radial direction. An average value (H) of the circumferential width of the tooth portion may be set to a value equal to or larger than the circumferential width of the coil accommodating portion.
In the above synchronous reluctance motor, the ratio of the circumferential width of the slot opening portion to the circumferential width of the coil accommodating portion may be set to 0.2 or more and 0.74 or less.
In the above synchronous reluctance motor, output torque may be 4 N·m or more and torque ripple may be 10% or less.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-121994 | Jun 2016 | JP | national |
