JP7310767B2 - SR motor - Google Patents

Description

The present invention relates to SR motors (ie switched reluctance motors).

In the SR motor, a magnetic field generated by energizing the windings wound around the stator forms a magnetic path passing through the stator core and the rotor core, and torque is generated so that the rotor position becomes small in magnetic resistance. In the SR motor disclosed in Patent Document 1, in a state in which the side surface portion of the salient rotor pole on the front side in the rotation direction and the side surface portion of the salient stator pole on the front side in the rotation direction are arranged on the same plane, The side surface portion of the side is protruded rearward in the rotation direction.

JP 2007-143286 A

In order to achieve high output density and low torque ripple in the SR motor, it is conceivable to employ an energization drive system in which one-phase energization and two-phase energization are switched. However, in this case, when the width of the rotor teeth and the width of the stator teeth are selected assuming the magnetic flux flowing in one-phase energization as in the past, the negative torque may increase and the minimum torque may decrease when the two-phase energization starts. Although the structure disclosed in Patent Document 1 is effective in reducing torque ripple, the rotation direction is limited to one direction, so the effect cannot be obtained in applications requiring bi-directional rotation.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object thereof is to provide an SR motor capable of rotating in both directions and capable of reducing torque ripple.

An SR motor (10) according to the present invention comprises a stator (11) having multi-phase windings (25), a rotor (12) provided rotatably relative to the stator, and detecting the rotation angle of the rotor. It is equipped with a rotation angle sensor (13) and is driven in a mode having "a section in which windings of two or more phases are energized at the same time". The stator has an annular back yoke (23) and a plurality of stator teeth (24) radially extending from the back yoke. The rotor has a plurality of radially extending rotor teeth (27). The minimum width of the back yoke is smaller than the width of the stator teeth.

The relationship between the pitch angle Ps of the stator teeth, the opening angle θs of the stator teeth, the opening angle θr of the rotor teeth, and the minimum resolution angle θsen of the rotation angle sensor is "(3/2) θsen<Ps−(θs+θr)/2<2θsen ”.

In such an SR motor in which windings of two or more phases are simultaneously energized, if the minimum width of the back yoke is smaller than the width of the teeth, the magnetic flux is likely to saturate and the torque tends to decrease. Even with such a configuration, by setting the pitch angle Ps, the opening angle θs, the opening angle θr, and the minimum resolution angle θsen as described above, the negative torque at the start of the two-phase energization can be suppressed. Furthermore, it is possible to suppress the decrease in the positive torque even when the one-phase energization is started. Furthermore, in the present invention, the rotation direction is not limited to one direction as in the conventional embodiment. Therefore, it is possible to obtain an SR motor capable of rotating in both directions and capable of reducing torque ripple.

1 is a longitudinal sectional view of an SR motor of one embodiment; FIG. FIG. 2 is an axial view of the stator and rotor of the SR motor of FIG. 1; FIG. 2 is a diagram showing the relationship between the energized phases of the SR motor of FIG. 1 and the rotor rotation angle; FIG. 3 is an axial view of the core and rotor of the stator of FIG. 2 , showing a state where the rotation angle of the rotor is 0 mechanical degrees; FIG. 3 is an axial view of the core and rotor of the stator of FIG. 2 , showing a state where the rotation angle of the rotor is 37.5 mechanical degrees; FIG. 6 is a diagram schematically showing stator teeth and rotor teeth in FIG. 5; FIG. 3 is an axial view of the core and rotor of the stator in FIG. 2 , showing the magnetic flux due to energization of each phase when the rotation angle of the rotor is 15 mechanical degrees; FIG. 8 is a diagram schematically showing stator teeth and rotor teeth in FIG. 7; FIG. 3 is an axial view of the core and rotor of the stator in FIG. 2 , showing the magnetic flux due to energization of each phase when the rotation angle of the rotor is 0 degrees in mechanical angle; The figure which shows typically the stator teeth and rotor teeth of FIG.

A plurality of embodiments of the SR motor will be described below with reference to the drawings. The same reference numerals are assigned to substantially the same configurations between the embodiments, and the description thereof is omitted.

[One embodiment]
As shown in FIGS. 1 and 2, the SR motor 10 of one embodiment includes a stator 11, a rotor 12 rotatably provided inside the stator 11, and a rotation angle sensor 13 for detecting the rotation angle of the rotor 12. and The rotation angle sensor 13 has a permanent magnet 21 attached to the rotor 12 and a magnetic detection element 22 that is fixed to a fixing member and detects the magnetism of the permanent magnet 21 .

Hereinafter, the radial direction of the stator 11 and the rotor 12 is simply referred to as the "radial direction", and the circumferential direction (that is, the rotational direction) of the stator 11 and the rotor 12 is simply referred to as the "circumferential direction" or the "rotational direction". However, the axial direction of the stator 11 and the rotor 12 is simply referred to as "axial direction".

The stator 11 has an annular back yoke 23 , a plurality of stator teeth 24 projecting radially inward from the back yoke 23 , and multi-phase windings 25 wound around the stator 11 . The minimum width of back yoke 23 is smaller than the width of stator teeth 24 . The rotor 12 has a boss 26 fixed to the rotating shaft 16 and a plurality of rotor teeth 27 projecting radially outward from the boss 26 . The number of stator teeth 24 and rotor teeth 27 is set to an even number that is not a multiple of each other. In one embodiment, twelve stator teeth 24 are provided and eight rotor teeth 27 are provided.

Winding 25 includes a U-phase winding 25u, a V-phase winding 25v and a W-phase winding 25w. U-phase winding 25u has U-phase coil 28u wound around stator teeth 24u. The V-phase winding 25v has a V-phase coil 28v wound around the stator teeth 24v. The W-phase winding 25w has a W-phase coil 28w wound around the stator teeth 24w. Hereinafter, when each phase winding is not distinguished, it is simply referred to as "winding 25". Moreover, when not distinguishing each phase coil, it only describes as "the coil 28."

In SR motor 10 , a magnetic field generated by energizing winding 25 forms a magnetic path passing through stator 11 and rotor 12 . The rotor 12 is rotationally driven by the magnetic attraction force between the stator teeth 24 and the rotor teeth 27 generated by switching the energization phase of the winding 25 according to the rotation angle of the rotor 12 .

Specifically, the SR motor 10 is driven by a 180-degree conduction driving method in order to achieve high output density and low torque ripple. The 180-degree energization driving method is a energization driving method in which the energization angle of the winding 25 is set to a half cycle of an electrical angle (that is, 180 degrees), and one-phase energization and two-phase energization are sequentially switched as shown in FIG. The SR motor 10 is driven in a mode having a section in which the two-phase windings 25 are energized simultaneously (that is, a two-phase energization section).

In the following description, as shown in FIG. 4, the pitch angle of the stator teeth 24 is assumed to be the stator pole pitch Ps. Further, the open angle of the stator teeth 24 is assumed to be a stator tooth open angle θs. Further, the opening angle of the rotor teeth 27 is assumed to be a rotor teeth opening angle θr. Also, let the minimum resolution angle of the rotation angle sensor 13 be the sensor minimum resolution angle θsen.

When the rotational angle of the rotor 12 is 37.5 mechanical degrees as shown in FIG. 5, the W-phase energization start timing is as shown in FIG. FIG. 6 schematically shows the stator teeth 24 and rotor teeth 27 at this timing. In FIG. 6, the angle of the circumferential gap between the W-phase stator teeth 24w and the rotor teeth 27a located forward in the rotational direction with respect to the W-phase stator teeth 24w is defined as a gap angle θg. The rotation angle difference between the rotor teeth 27a and the U-phase stator teeth 24u is the energization switching angle θsw. The gap angle θg is given by equation (1).
θg=Ps−(θs/2)−(θsw+(θr/2)) (1)

As the gap angle θg becomes smaller, the force by which "the rotor teeth 27a to be attracted by the U-phase stator teeth 24u" are attracted to the W-phase stator teeth 24w in FIG. Torque drops.

Here, since the number of motor poles and the energization drive method are related to the drive circuit and the like, the degree of freedom of change is often low compared to the shape of the stator 11 and the rotor 12 . Therefore, in order to increase the gap angle .theta.g, it is convenient to decrease the rotor teeth opening angle .theta.r and the stator teeth opening angle .theta.s.

However, when the opening angles .theta.r and .theta.s are decreased, the magnetic resistance of the stator 11 and the rotor 12 increases and the motor output torque tends to decrease. Also, if the opening angles θr and θs are made smaller, the motor output torque is likely to be lowered at the start of the one-phase energization as shown in FIG. So having the right size is important.

By the way, in order to switch the energization section θc (=180 degrees) at the energization switching angle θsw interval, “θsen≦θsw” and “θsen=θsw/n” are required, where n is a natural number.

Here, when the sensor minimum resolution angle θsen is relatively small (that is, the sensor resolution is high) like “θsen<θg”, for example “θsen=θsw/2” and “(θsw/2)<θg<θsw” , the gap angle can be artificially widened to "θg+θsen" by suspending the energization for the sensor minimum resolution angle θsen.

However, since the actual energization interval is reduced to "θc-θsen", the trade-off between motor output torque reduction becomes large unless the sensor minimum resolution angle θsen is made sufficiently small. On the other hand, increasing the sensor resolution leads to an increase in sensor cost and, in turn, an increase in product cost. Therefore, it is desirable to minimize sensor resolution.

Based on the above, in one embodiment, the shape of the stator 11 and the rotor 12 is proposed that can suppress the generation of negative torque even if the sensor resolution is suppressed to the minimum that allows the motor to be driven. Specifically, even when "θsen=θc", the opening angles θs and θr can be set to appropriate values with respect to the sensor resolution by formula (2).
(θsen/2)<θg<θsen (2)

Equation (3) is derived from equations (1) and (2). The opening angles θs, θr and the sensor minimum resolution angle θsen are set so as to satisfy Equation (3).
(3/2) θsen<Ps−(θs+θr)/2<2θsen (3)

Next, the relationship between the rotor tooth opening angle θr and the number of poles of the rotor 12 (hereinafter referred to as the number of rotor poles) P will be described. In FIG. 7, the magnetic flux generated by each phase energization at the end of the two-phase energization (for example, two phases of V phase and W phase) is indicated by a one-dot chain line and a two-dot chain line. At this point, if the rotor teeth opening angle θr is too large as shown in FIG. 27c increases the force attracted by the V-phase stator teeth 24v, generates negative torque, and makes the rotation of the rotor 12 unstable. Therefore, it is desirable that the rotor teeth opening angle .theta.r is ".theta.r<(2.pi./P)/2."

On the other hand, in FIG. 9, the magnetic flux due to winding energization at the start of one-phase energization (for example, W phase) is indicated by a dashed line. At this point, if the rotor teeth opening angle θr is too small as shown in FIG. 10, the force with which the attraction rotor teeth 27b are attracted to the W-phase stator teeth 24w decreases, and the rotation of the rotor 12 becomes unstable. Therefore, it is desirable that the rotor teeth opening angle .theta.r is ".theta.r>(2.pi./P)/3."

From the above, the range of the rotor teeth opening angle θr suitable for stable rotation of the rotor 12 is as shown in Equation (4).
((2π/P)/3)<θr<((2π/P)/2) (4)

The rotor teeth opening angle θr, which makes the torque drop even in both one-phase energization and two-phase energization, is the median value of the range shown in formula (4), and is "5π/6P" as shown in formula (5). becomes.
θr=((2π/3P)+(2π/2P))/2=5π/6P (5)

In one embodiment, the rotor teeth opening angle θr is set within the range of formula (6).
(2π/3P)<θr≦(5π/6P) (6)

(effect)
As described above, in one embodiment, the SR motor 10 is driven in a mode having a section in which windings of two phases are energized simultaneously. The minimum width of back yoke 23 is smaller than the width of stator teeth 24 . The relationship between the stator pole pitch Ps, the stator teeth opening angle θs, the rotor teeth opening angle θr, and the minimum resolution angle θsen of the rotation angle sensor 13 is "(3/2) θsen<Ps−(θs+θr)/2<2θsen". .

In the SR motor 10 in which the two-phase windings are energized simultaneously, if the minimum width of the back yoke 23 is smaller than the width of the stator teeth 24, the magnetic flux is likely to be saturated and the torque is likely to decrease. Even with such a configuration, by setting the stator pole pitch Ps, the stator tooth opening angle θs, the rotor tooth opening angle θr, and the minimum resolution angle θsen as described above, the negative torque at the start of the two-phase energization can be suppressed. . Furthermore, it is possible to suppress the decrease in the positive torque even when the one-phase energization is started. Furthermore, in one embodiment, the rotation direction is not limited to one direction as in the conventional form. Therefore, it is possible to obtain the SR motor 10 capable of rotating in both directions and capable of reducing torque ripple.

In one embodiment, the multi-phase windings 25 are three-phase windings, and the SR motor 10 is driven by a 180-degree conduction driving method. Therefore, in contrast to the embodiment adopting the 120-degree energization drive system that does not have a multi-phase energization section, the energization time is lengthened and the average torque is increased in the embodiment, so there is an effect of reducing torque ripple.

Also, in one embodiment, "(2π/3P)<θr≦(5π/6P)". Therefore, negative torque at the start of two-phase energization can be suppressed. Furthermore, it is possible to suppress the decrease in the positive torque even when the one-phase energization is started. Therefore, it is possible to obtain the SR motor 10 that can effectively reduce the torque ripple.

[Other embodiments]
In other embodiments, the number of stator teeth may be other than twelve, and the number of rotor teeth may be other than eight. In other embodiments, the number of winding phases is not limited to three, and may be any other number.

The present invention is not limited to the above-described embodiments, and can be embodied in various forms without departing from the scope of the invention.

10 SR motor, 11 stator, 12 rotor, 13 rotation angle sensor,
23 back yoke, 24 stator teeth, 25 winding, 26 boss,
27 rotor teeth,
Ps is the pitch angle of the stator teeth, θs is the opening angle of the stator teeth,
θr is the opening angle of the rotor teeth, θsen is the minimum resolution angle.

Claims (3)

A stator (11) having multi-phase windings (25), a rotor (12) provided rotatably relative to the stator, and a rotation angle sensor (13) for detecting the rotation angle of the rotor. An SR motor (10) driven in a mode having a section in which the windings of two or more phases are simultaneously energized,
The stator has an annular back yoke (23) and a plurality of stator teeth (24) radially extending from the back yoke,
The rotor has a plurality of radially extending rotor teeth (27),
the minimum width of the back yoke is smaller than the width of the stator teeth,
The relationship between the pitch angle Ps of the stator teeth, the opening angle θs of the stator teeth, the opening angle θr of the rotor teeth, and the minimum resolution angle θsen of the rotation angle sensor is
(3/2) θsen<Ps−(θs+θr)/2<2θsen
SR motor. The multi-phase winding is a three-phase winding,
2. The SR motor according to claim 1, wherein the SR motor is driven by a 180-degree conduction driving method. Assuming that the number of poles of the rotor is the number of rotor poles P,
(2π/3P)<θr≦(5π/6P)
3. The SR motor according to claim 1 or 2, wherein:

Images