Patent Application
20160329797
The present invention relates to a brushless DC motor.
Conventionally, DC brush motors including brushes and a commutator have been mainly used for electric pumps in automobiles, etc. The DC brush motor has an advantage effect in that the cost is low and the structure is simple.
On the other hand, brushless DC motors are known which operate without the brushes and the commutator by applying rectangular wave voltages to coils by electrically controlling switching devices between ON and OFF. The use of the brushless DC motor provides keeping reliability in electrical connection irrespective of the period of use.
In the conventional brushless DC motors there are brushless DC motors using three-phase AC power supply and a single-phase AC power supply.
The three-phase brushless DC motor has such a structure as to generate a rotating magnetic field by applying rectangular wave voltages having different phases to three-phase coils. In this case, six switching devices (for example, FET: Field effect transistors) become necessary to apply positive and negative voltages to three-phase coils.
Further, the single-phase brushless DC motor uses an auxiliary coil (shading coil) because the single-phase brushless DC motor cannot start rotation if such an additional structure is not added.
Patent Document 1 discloses a shading coil type induction motor including a stator having a shading coil, a rotor inserted into a rotor housing hole in the stator for rotation drive, and an excitation coil.
However, the brush DC motor has a defect in electrical connection between the brush and the commutator due to aging degradation in the brush because of mechanical contacts with a commutator.
Further, the three-phase brushless DC motor requires six switching devices to apply positive and negative voltages to the three-phase coils as described above, which results in increase in the manufacturing cost compared with the brush DC motor.
Further, the shading coil type induction motor disclosed in Patent Document 1 has a defect due to a high manufacturing cost because the auxiliary coil (shading coil) becomes necessary. In addition, there is a problem in that for the period for which no induction current flows in the shading coil out of one cycle, a negative torque is generated in the rotor, so that a running efficiency is low.
Accordingly, the present invention aims to provide a brushless DC motor capable of a high efficiency operation at a low cost.
To achieve the aim, each of the invention is configured as follows:
A brushless DC motor includes:
a stator around which an exciting coil is wound;
a rotor that is housed in the stator and rotatable in a predetermined direction; and
a pair of magnets fixed on the stator, the magnets in the pair facing across a rotation shaft of the rotor as a center.
Other means will be described in the “MODES FOR CARRYING OUT INVENTION”.
According to the present invention, there is provided a brushless motor providing a high efficiency operation in which torque pulsation is reduced.
Modes for carrying out the invention (hereinafter referred to as embodiments) are described in detail occasionally referring to the drawings below.
In
The brushless DC motor 1 includes the stator 10 around which an excitation coil 20 is wound, the rotor 30 being rotatable counterclockwise and housed in the stator 10, and magnets 41a, 42a, 41b, 42b fixed on an inner circumferential surface of the stator 10 substantially equi-distantly.
With the structure described above, the brushless DC motor 1 has a function to generate a torque for counterclockwise rotation drive of the rotor 30 using synthesized magnetic flux of the magnetic flux according to a current flowing through the excitation coil 20 and magnetic flux generated by the four magnets 41a, 42a, 41b, 42b fixed on the internal circumferential surface of the stator 10. Operation will be described later.
The stator 10 comprises a magnetic substance (for example, silicon steel plates) for housing the rotor 30 inside in the diametrical direction, and includes a coil winding member 11, a first housing member 12, a second housing member 13, a first yoke 14, and a second yoke 15.
The coil winding member 11 comprises a bar like member extending in a left-right direction around which the excitation coil 20 is wound.
The first housing member 12 has a substantially C-shape in cross-sectional view and extends in parallel to the rotation shaft K (in face side-deep side direction of paper). The first housing member 12 is connected to the left end of the coil winding member 11 through the first yoke 14.
The second housing member 13 has a substantially inverted C-shape in cross-sectional view and extends in parallel to the rotation shaft K. The second housing member 13 is connected to the right end of the coil winding member 11 through the second yoke 15.
More specifically, the first housing member 12 and the second housing member 13 formed integrally with the coil winding member 11 through the yoke 14 and the second yoke 15 form a housing space in a circular cylindrical column with a center at the rotation shaft K such that the rotor 30 is interposed between the first housing member 12 and the second housing member 13 from the left side and the right side.
Further, the first housing member 12 is formed to have a thickness decreasing as going to the upper and lower ends. This limits amounts of the magnetic flux passing through parts near the upper end and the lower end of the first housing member 12. This is true for the second housing member 13.
Further, an upper end of the first housing member 12 and the upper end of the second housing member 13 are spaced in the left-right direction by a sum of a distance (interval) L4 and a length in the left-right direction of the second stator notch 62.
Similarly, a low end of the first housing member 12 and the lower end of the second housing member 13 are spaced in the left-right direction by a sum of a distance (interval) L4 and the length in the left-right direction of the second stator notch 62.
These gaps cause magnetic flux generated by the current in the excitation coil 20 necessarily to pass through the rotor 30. In other words, the magnetic flux generated by the current flowing through the excitation coil 20 is caused not to close only within the stator 10.
There is a first stator notch 61 formed by notching a part of the magnetic substance of the first housing member 12 where the yoke 14 and the first housing member 12 are connected near the lower side of the left end of the member around which the excitation coil 20 is wound.
There is a second stator notch 62 formed by notching a part of the magnetic substance of the first housing member 12 near a lower side of a substantially middle of the member around which the excitation coil 20 is wound and near the right end of the magnet 41a.
The first stator notch 61 and the second stator notch 62 function as high magnetic resistors having high magnetic resistances.
The functions of the first stator notch 61 and the second stator notch 62 will be described later.
Each of the magnets 41a, 42a, 41b, 42b is a permanent magnet having an arc shape in cross-sectional view.
The magnets 41a, 42a are fixed on the inner circumferential surface in the diametrical direction of the first housing member 12 of the stator 10 at a left upper side thereof and at a left lower side thereof.
The magnets 42b, 41b are fixed to the inner circumferential surface in the diametrical direction of the second housing member 13 of the stator 10 at left upper side thereof and at left lower side thereof.
The magnet 41a, 42b have N poles on the side of the stator 10 and S poles on the side of the rotor 30.
The magnet 42a, 41b have S poles on the side of the stator 10 and N poles on the side of the rotor 30.
As described above, the magnets 41a, 41b face the magnet 42a, 42b and pairs across the rotation shaft K, respectively.
The magnets 41a, 42a, 41b, 42b are formed in arc shapes, and lengths of the arcs (arc length) are L2.
Further, the magnets 41a and 42a, the magnets 42a and 41b, the magnets 41b and 42b, and the magnets 42b and 41a are spaced at a predetermined distance (interval) L4.
Further, each of the magnets 41a, 42a, 41b, 41b is arranged such that magnetic flux generated by its own is additionally strengthen with magnetic flux generated by another magnet adjacent to the magnet in the inner circumferential direction of the first housing member 12 and the second housing member 13 in such a condition that a magnetically connected condition through an extending part 53 of the rotor 30 as described later. Functions and operations of the magnets 41a, 42a, 41b, 42b, the rotor 30, and the extending part 53 will be described later.
The rotor 30 is a rotor rotatable counterclockwise by the torque according to the magnetic flux distribution within the brushless DC motor 1 and housed in the housing space having the circular cylindrical pillar shape between the first housing member 12 and the second housing member 13.
The rotor 30 is a magnetic substance (for example, an iron core) which is formed such that a rotor base 31, rotor peripheries 32a, 32b, and the extending part 53 are integrally shaped.
Further, there are first rotor gaps (high magnetic resistance part) 51 on a circular circumferential side (a side of magnet of the stator) of the rotor periphery 32a which are gaps for limiting inflow of the magnetic flux. Further, in
Further on a side surface of the rotor periphery 32a, there is a second rotor gap (high magnetic resistance part) 52 which is a gap or notch for limiting inflow of the magnetic flux by increase in the magnetic resistance.
At a left end of the rotor periphery 32a on a side of the circular circumferential side (side of the magnet of the stator), there is the extending part 53 which a magnetic substance which causes the counterclockwise rotation. The extending part 53 has a shape thinner than the shape of the rotor periphery 32a. The thinner shape is made to prevent magnetic flux having an intensity more than a necessary intensity from passing therethrough.
Further, the extending part 53 has such a shape as to more separate from the magnets 41a, 42a, 41b, 42b of the stator 10 as the location goes to the tip (left end). The reason for this will be described later.
Also the rotor periphery 32b is provided with the first rotor gap 51, the rotor gaps 52, and the extending part 53. The rotor peripheries 32a, 32b have point-symmetric shapes regarding the rotation shaft K.
Further, in a cross-sectional view, the extending part 53, the first rotor gap 51, and the rotor gaps 52 are formed on a left end side of the 32a (32b) of the rotor 30. As described above, the extending part 53, the first rotor gap 51, and the rotor gaps 52 are formed on the left end side of the rotor peripheries 32a 32b, which provides a structure suitable for the operation of counterclockwise rotation of the rotor 30.
Detailed descriptions of operations and advantageous effect regarding the first rotor gap 51, the second rotor gaps 52, and the extending part 53 will be described later.
Parts (circular circumference parts) of the rotor peripheries 32a, 32b of the rotor 30 facing the magnets (41a, 42a, 41b, 42b) are each formed in a circular arc shape having a length (circular arc length) L1. It is desirable that the length L1 of the circular arc (circular arc length) of the rotor peripheries 32a, 32b is substantially equal to the length L2 of the circular arc (the circular arc length) L2 of the magnets 41a, 42a, 41b, 42b (L1=L2).
It is noted that the length (circular arc length) L1 of the rotor peripheries 32a, 32b does not include a length of the extending part 53.
Further, it is desirable that an area of the rotor peripheries 32a, 32b and an area of the magnets (41a, 41b, 42b) facing each other are substantially equal to each other.
The reason why it is desirable that the lengths and areas of the rotor peripheries 32a, 32b and the magnets facing each other are equal to each other, respectively, will be described later.
Next, outline of the rotation operation principle of the brushless DC motor 1 is described below.
Further, in
In a closed magnetic circuit of the rotor 30, the magnets 41a, 42a, 41b, 42b, and the stator 10, the main magnetic flux is shown with thick lines as main magnetic flux 201, 202 (in
In
A most part of the part of the rotor periphery 32a of the rotor 30 able to face the magnets the magnet 42b faces the magnet 42b, and another part of the part of the rotor periphery 32a able to face the magnets faces the magnet 41a. This state provides a stable point having no rotation because torque balance is achieved in which a counterclockwise ration torque balance with clockwise rotation torque regarding the rotor 30.
The torque balance is achieved in such a state that a part of the part facing the magnet of the rotor peripheries 32a faces the magnet 41a. This relates to an operation of the extending part 53, the first rotor gap 51 which becomes a high magnetic resistor, and the second rotor gaps 52.
It is assumed that the extending part 53 (see
Operations of the first rotor gap 51, the second rotor gaps 52, which act as magneto-resistive parts is described later.
Further, the state that the most part of the part of the rotor periphery 32a able to face the magnets the magnet 42b face the magnet 42b, and another part of the part of the rotor periphery 32a able to face the magnets faces the magnet 41a, will be also described later. Duplicated description is omitted.
A current flow in the excitation coil 20 in the first directions 20a, 20b generates new main magnetic flux 301 through the stator 10, the magnet 41b, the rotor 30, and the magnet 41a.
As shown in
As a result, the rotor 30 rotates counterclockwise, so that the state goes to the state shown in
As described above,
When a rotational position reaches the vicinity of the second stable point as a result of the counterclockwise rotation from the first stable point, a torque balance is obtained in a state of the second stable point in which no rotation occurs as a stable point.
More specifically in the state shown in
Further, the rotor peripheries 32b overlaps with the magnet 41b in the diametrical direction, and the extending part 53 overlaps with the magnet 42b in the diametrical direction. Accordingly, this promotes a magnetic connection between a pair of the magnets 41b, 42b.
The main magnetic flux 212 and the 211 are formed, so that a torque balance is provided in
Further, in the state shown in
The current flowing through the excitation coil 20 in the second directions 21a, 21b, which generates a new main magnetic flux 311 through the stator 10, the magnet 42a, the rotor 30, and the magnet 42b.
As shown in
As a result, the rotor 30 rotates counterclockwise, so that the state goes to the state shown in
As described above, the current is caused to flow alternately in the first direction, and the second direction. This causes counterclockwise rotation in the brushless DC motor 1 in an order of from states in
Further, it is possible to perform control of the excitation coil 20 one step by one step, to stop at every stable point, or to make the counterclockwise continuous rotation by successively making alternating current flow in the excitation coil 20.
Further, in the above description, it is assumed that the state shown in
Next the maximum and the minimum inductances are described below. The inductance between the rotor and the stator is an equivalent inductance calculated from a relationship between voltage and current in the excitation coil 20 (see
When the rotor peripheries 32a, 32b of the rotor 30 face the magnets 41a, 41b, respectively with arcs thereof generally overlap each other, the magnetic flux between the rotor 30 and the stator 10 has a highest permeability, so that the inductance between the rotor and the state maximized.
A center axis of the rotor peripheries 32a, 32b of the rotor 30 is assumed as a direction 101.
The minimum inductance between the rotor 30 and the stator 10 occurs when the center axis orients a direction perpendicular to the direction 101, i.e., the direction 102 in
In a direction 102, the magnetic flux is hard to transmit between the rotor 30 and the stator 10, so that the inductance becomes maximum.
However, when the symmetry is not satisfied because any of the first rotor gap 51, the second rotor gaps 52, the extending part 53, etc. described above with reference to
The maximum inductance or the minimum inductance depends on the shape of the rotor 30. The larger the difference between the maximum inductance and the minimum inductance is, the larger the rotation torque of the brushless DC motor 1 becomes. In addition, an energy efficiency of the brushless DC motor 1 increases, which provides a high efficiency operation efficiency (output torque to input power).
<Inductance Difference in Accordance with Shape of Rotor>
When the shape of the rotor 30 shown in
Next, examples of the rotor 30 of which shape is varied are shown and it is shown how the difference in the inductance between the maximum inductance and the minimum inductance varies in each of the cases.
A first example is shown, in which the shape of the rotor 30 is varied, and a relation regarding the facing area between the magnet 41a (or the magnet 42a, 41b, 42b) and the rotor periphery 32a or 32b is shown below.
In
In
Hereinafter, description is made with assumption that the magnitude relation in the facing area of the rotor peripheries are equal to that in the circular arc length of the rotor periphery.
In
In
In
As described above, the fact that the inductance difference is the largest indicates that an energy efficient of the brushless DC motor 1 (see
Further, the shapes shown in
Further, the shape shown in
As described above, in
In other words, when the facing areas and/or facing lengths (circular arc length) of the rotor peripheries and the magnets facing each other are equal to each other, the rotation torque of the brushless DC motor 1 becomes large. In addition, this increases an energy efficiency of the brushless DC motor 1, so that a high efficiency operation can be provided.
Next, a relation between the waist shapes of the rotor and the inductance difference is described below.
In
In
The characteristic point at the gap length G3 in
The gap length G3 in
On the other hand, the minimum inductance (in the direction 102 in
As a result, the inductance difference (the maximum inductance−the minimum inductance) in the case of the rotor shape shown in
This state is indicated by the relation of the inductance difference between the characteristic point at the gap lengths G4 and G3 in
According to the relation in the inductance difference between the shapes shown in
More specifically, increase in the inductance difference by decreasing the minimum inductance increases the rotation torque of the brushless DC motor 1 (
Further, this enhances the energy efficiency of the brushless DC motor 1, so that a high efficiency operation is provided.
Next the other waist shapes of the rotor than the waist shape shown in
Further in the shape of the rotor 30 shown in
Further, the distance (gap length) between the rotor base 31 and the center of the magnet 42b are equal to each other.
The shapes of the various types of the rotors shown in
Next, influence and operation of the first rotor gap 51, and the second rotor gaps 52 in the rotor peripheries 32a, 32b are described below.
In
Further, in
In
When there is no gaps in the rotor peripheries 32a, 32b 32a, as shown in
In
When a gap is formed in steel plates forming the rotor peripheries 32a, 32b, this part has a larger magnetic resistance. More specifically, the first rotor gap 51 and the second rotor gap 52 function as high magnetic resistance parts as described above. At the vicinities to the first rotor gap 51 and the second rotor gap 52, magnetic flux densities decrease because of high magnetic resistances.
Because a plurality of the first rotor gaps 51 are formed substantially on a left side of the rotor peripheries 32a, as shown in
Further, because the second rotor gap 52 is formed on a left side surface of the rotor peripheries 32a, 32b, this operates to prevent the magnetic flux and the main flux from transmitting thorough left sides of the rotor peripheries 32a, 32b. Further, because the second rotor gap 52 performs a function of the high magnetic resistance part, the shape of the second rotor gap 52 may be a gap having a window shape in addition to the notch in the side surface as shown in
The magnetic flux density at a bent part of the main magnetic flux 323 in the region 151 shown in
When the main magnetic flux 323 is liken to an elastic cord, the main magnetic flux 323 having a bent part as shown in the region 151 generates stronger torque (stress) counterclockwise because the main magnetic flux 323 tends to extend.
The counterclockwise rotation of the rotor 30 decreases the magnetic flux density of the main magnetic flux 323 at the part bent in the region 151 so that the different stresses of the magnetic fields are balanced.
On the other hand, in the case where the main magnetic flux 322 shown in
At the rotor position shown in
Next, influence and effect of the rotor gaps is described below with reference to
The axis of abscissa of
A force (torque) acting a current flowing through the excitation coil 20 (see
Accordingly, as shown in
The axis of abscissa in
In
At a rotation position of the rotor 30 where the torque is originally low in
As described above, addition of the rotor gaps (the first rotor gap 51 and the second rotor gap 52) functioning as a high magnetic resistive part to the rotor peripheries 32a, 32b makes the curved portion of the magnetic flux large, which increases the rotation torque of the brushless DC motor 1 (see
Next, the influence, operation, and effect are described below.
First, influence, operation, and effect of the stator notch in the first stator notch 61 and the second stator notch 62 are described below.
Further,
In
In the case where there is no gap in the first housing member (12:
In
The first stator notch 61 and the second stator notch 62, being notches in steel plates, operate as high magnetic resistive members where magnetic resistance increases there, which makes it not easy for the magnetic flux to flow there.
Because the first stator notch 61 and the second stator notch 62 are provided having high magnetic resistances, the main magnetic flux 325 bypasses the first stator notch 61 and makes one turn through the rotor 30 and the stator 10 drawing a bent and curved line (magnetic flux curve) as shown in
A curved part of the main magnetic flux 325 in a region 161 has a magnetic field locally increased, so that a torque (stress) is generated stronger to make movement in counterclockwise rotation direction to decrease the magnetic flux density.
In a case where the main magnetic flux 324 in
More specifically, at the same rotor position in
Regarding the generation of the torque in the counterclockwise torque, the first stator notch 61 is more effective than the second stator notch 62.
Next, with reference to
The axis of abscissa in
As shown in
The axis of abscissa in
In
The reduction in the torque variation (pulsation) is caused by the fact that there is not so large difference from the maximum torque because the torque (stress) is strongly generated in the counterclockwise rotation direction by the operation of the stator notches (the first stator notch 61, the second stator notch 62) at the position of the rotor 30 shown in
As described above, the stator 10 includes notches in the steel plate at the first housing member 12 (see
Next, operation and effect of shapes of extending part and second stator notch are described below.
The extending part 53 contributes to the counterclockwise operation of the rotor 30. The torque characteristic varies in accordance with the shape and arrangement. The difference in the extending part 53 between
The extending part 53 in
In
Next, with reference to
An axis of abscissa in
As shown in
An axis of abscissa in
In
The reduction in the torque variation (pulsation) is caused by suppression of rapid variation in the torque occurring when the extending part 53 approaches the magnet where the extending part 53 next locates while the rotor 30 rotates because the extending part 53 has such a shape that the extending part 53 more separates from the arc part inside of the magnet as going to the tip thereof.
Next influence by and operation of the second stator notch 62 are described below.
As described above, with reference to
The difference between
In
Next, with reference to
The axis of abscissa in
As shown in
The axis of abscissa in
In
The reduction in the torque variation (pulsation is caused by suppression the rapid variation in torque during rotation of the 30 because the second stator notch 62 is added.
In
The brushless DC motor 2 includes the stator 10 around which an excitation coil 20 is wound, the rotor 30 being rotatable counterclockwise and housed in the stator 10, and two magnets 43a, 43b fixed in the stator 10.
The magnets 41a, 43a form a pair facing with each other across the rotation shaft K.
With the structure described above, the brushless DC motor 2 has a function to generate a torque for counterclockwise rotation drive of the rotor 30 using synthesized magnetic flux of the magnetic flux according to a current flowing through the excitation coil 20 and magnetic flux generated by the four magnets 41a, 42a, 41b, 42b fixed on the internal circumferential surface of the stator 10. Operation will be described later.
The stator 10 comprises a magnetic substance (for example, silicon steel plates) for housing the rotor 30 inside in the diametrical direction, and includes a coil winding member 11, a first housing member 121, a second housing member 131, a first yoke 14, and a second yoke 15.
The coil winding member 11 comprises a bar like member extending in a left-right direction around which the excitation coil 20 is wound.
The first housing member 121 has a substantially C-shape in cross-sectional view and extends in parallel to the rotation shaft K (in face side-deep side direction of paper). The first housing member 121 is connected to the left end of the coil winding member 11 through the first yoke 14.
The second housing member 131 has a substantially inverted C-shape in cross-sectional view and extends in parallel to the rotation shaft K. The second housing member 131 is connected to the right end of the coil winding member 11 through the second yoke 15.
More specifically, the first housing member 121 and the second housing member 131 formed integrally with the coil winding member 11 through the first yoke 14 and the second yoke 15 form a housing space in a circular cylindrical column with a center at the rotation shaft K such that the rotor 30 is interposed between the first housing member 121 and the second housing member 131 from the left side and the right side.
Further, the first housing member 121 is formed to have a thickness decreasing as going to the upper and lower ends. This limits amounts of the magnetic flux passing through part near the upper end and the lower end to the first housing member 121. This is true for the second housing member 131.
The up-down direction and the left-right direction are shown in
Further, an upper end of the first housing member 121 and the upper end of the second housing member 131 are spaced in the left-right direction by a sum of a distance (interval) L3 and a length in the left-right direction of the second notch 62.
Similarly, a low end of the first housing member 121 and the lower end of the second housing member 131 are spaced in the left-right direction by a sum of a distance (interval) L3 and the length in the left-right direction of the second stator notch 62.
These gaps cause magnetic flux generated by the current in the excitation coil 20 necessarily to pass through the rotor 30. In other words, the magnetic flux generated by the current flowing through the excitation coil 20 is caused not to close only within the stator 10.
Formed between upper and lower first housing members 121 is a step 121d.
Formed between upper and lower second housing members 131 is a step 131d.
Steps 12d, 13d have a distance (interval) of L44 in vertical directions.
In the step 121d, 131d, provision of a gap having the distance (interval) L44 can reduce torque pulsations of the rotor 30. Further, provision of the gap having a distance (interval) L44 can increase a width of the stator on which the magnets 43a, 43b act.
A distance (interval) L3 between upper ends of the first housing member 121 and a second housing member 131 and between lower ends of the first housing member 121 and the second housing member 131 is substantially the same as the distance (interval) L44 in the vertical direction between the steps 121d of the vertically arranged first housing members 121 and between steps 131d of the vertically arranged the second housing members 131.
Near the lower side of a left end of the bar wound by the excitation coil 20, there are the first stator notch 61 and the second stator notch 62 as parts where the magnetic substance of the first housing member 121 is partially cut out.
The first stator notch 61 and the second stator notch 62 serve as high magnetic resistors of which magnetic resistors are high. The first stator notch 61 and the second stator notch 62 reduce torque pulsation generated during rotation of the rotor 30.
The magnets 43a, 43b are permanent magnets having rectangular parallelepiped shapes, respectively.
The magnet 43a is fixed between the vertically arranged the first housing members 121 of the stator 10.
The magnet 43b is fixed between the vertically arranged the second housing members 131 of the stator 10.
The magnets 43a, 43b have S poles on upper sides thereof and N poles on the lower sides thereof.
The magnet 43a, 43b have a thickness L5 in the vertical direction.
The magnet 43a protrudes from the first housing member 121 by a distance (interval) L6 in the steps 121d of the vertically arranged first housing members 121 and is exposed to the housing space.
A magnet 43b protrudes from the first housing member 121 by a distance (interval) L6 between the steps 131d of the vertically arranged second housing members 131 and being exposed.
In the structure in
Further, as described above, the magnets 43a, 43b have rectangular parallelepiped shapes as described above. Widths in directions along contacts between the magnets 43a, 43b and the first housing member 121 and the second housing members 131, respectively (hereinafter also referred to as lateral widths) are longer than the thickness L5 of the magnets 43a, 43b.
The magnets 43a, 43b are Neodymium magnets produced by sintering main components including Neodymium of rare earth, iron, and boron. Materials of the Neodymium magnet are expensive and difficult to be processed. Accordingly, these materials are hard, and thus difficult to be processed by monolithic molding.
Formation of the magnets 43a, 43b with the expensive material in a rectangular parallelepiped to have a lateral width which is longer than the thickness L5, which generates larger magnetic field with the same volume. In other words, this provides an advantageous effect in a magnetic force intensity and in production process. Comparison with the first embodiment (the magnet is formed in a circular arc cross-sectional shape), using no rectangular parallelepiped shape will be described later and an advantageous effect in forming the magnet in the rectangular parallelepiped will be described again.
The rotor 30 in the second embodiment has the same components and structure as the rotor 30 in the second embodiment (see
The arc length (arc length) L1 of the arc shapes of the rotor peripheries 32a, 32b according to the second embodiment in
Next rotating operation principle of the brushless DC motor 2 is described below.
In
As the main magnetic flux, the main magnetic flux of which loops are closed through the magnet 43a and the stator 10 are shown with thick lines as a main magnetic flux 204, a main magnetic field flux 214, a main magnetic field flux 224, and a main magnetic field flux 234.
The main magnetic flux of which loops are closed through the magnet 43b and the stator 10 are shown with thick lines as a main magnetic flux 203, a main magnetic field flux 213, a main magnetic field flux 233, and a main magnetic field flux 234.
The main magnetic flux of which loops are closed through the excitation coil 20, the stator 10, and the rotor 30 are shown with thick lines as a main magnetic flux 303, and a main magnetic field flux 313.
The main magnetic flux of which loops are closed through the stator 10 and the rotor 30 are shown with thick lines as a main magnetic flux 404, and a main magnetic field flux 403.
As described above, the magnets 43a, 43b have S poles on the upper side thereof and N poles on the lower side thereof.
Current flowing through the excitation coil 20 in the first direction and current flowing through the excitation coil 20 in the second direction which are combined with the magnets 43a, 43a, which generates magnetic fields at four poles corresponding to that the rotor 30 has the first to fourth stable point.
In
At this instance, in the rotor 30, torque balance is formed in which a clockwise rotation force (torque) by the magnetic field (main magnetic flux) by the excitation coil 20 and a counterclockwise rotation force (torque) by the magnetic field (main magnetic flux) by the magnets 43a, 43b, are balanced, so that a first stable point (first pole) where the rotor does not rotate is provided. After that, when the current flowing through the excitation coil 20 in the first direction is turned off, the balance is broken, so that the rotor starts rotating counterclockwise because ends of the rotor are pulled by the magnetic fields (main flux) generated by the magnets 43a, 43b.
The extending parts 53 (see
In
In other words, the rotor periphery 32a overlaps with the magnet 43a in the diametrical direction. This makes magnetic connection between the rotor periphery 32a and the magnet 43a, so that the main magnetic flux 214 is formed.
Further, the rotor periphery 32b overlaps with the magnet 43b in the diametrical direction. This makes magnetic connection between the rotor periphery 32b and the magnet 43b, so that the main magnetic flux 213 is formed.
Formation of the main magnetic flux 214 and the main magnetic flux 213 makes a torque balance in
After this, when the current flows through the excitation coil 20 in the second direction, the torque balance is broken and the end of the rotor periphery 32a is pulled by the magnetic field (main magnetic flux) generated by the excitation coil 20.
The current flow in the excitation coil 20 in the second direction form a new magnetic flux 313 is formed through the stator 10, the magnet 43a, and the rotor 30.
The magnetic flux 313 generated by the current flowing through the excitation coil 20, the main magnetic flux 224, 223 make a torque balance in the rotor 30.
After this, when the current flowing through the excitation coil 20 in the second direction is cut out, the torque balance is broken, so that the rotor 30 starts movement counterclockwise because of pulling by the magnetic field (magnetic flux) generated by the magnets 43a, 43b.
In
More specifically, in the state shown in
After this, when the current flows through the excitation coil 20 in the first direction, the torque balance at the fourth stable point (fourth pole) is broken, so that the rotor 30 starts moving in the counterclockwise direction.
When the current flows through the excitation coil 20, the state returns to the stage shown in
However, because the shape of the rotor is point-symmetrical about the rotation shaft K, the rotor 30 rotates to a stable points distance by 180 degrees, there is no visual difference. Accordingly, a substantially duplicated explanation is omitted.
As described above, by allowing the current to flow through the excitation coil 20 alternately, the brushless DC motor 2 rotates clockwise in the order of
Further, the control of the excitation coil 20 is made step by step to make stop at each of the stable points, or alternation of the current in the excitation coil 20 is made continuously, so that a continuous counter clock width direction.
Next, forms and structure in the second embodiment is additionally described below. This is because to explain a shape and a structure of the magnet according to a third embodiment, the shape and structure of the magnets according to the second embodiment are more specifically explained for comparison.
In regions 45a and 45b showing the vicinity of the magnets 43a, 43b, the magnets 43a, 43b protrude from the steps 121d, 131d (see
The parts of the magnets 43a, 43b exposed from the first housing member 121 and the second housing member 131 contact with high magnetic resistances. This decreases magnetic flux (magnetic field) transmitting through side faces of the magnets 43a, 43b (the steps 121d, 131d), and increases magnetic flux (magnetic fields) transmitting through the first housing members 121, 131, so that the magnetic forces by the magnets 43a, 43b are efficiently used with increase in efficiency. This provides the brushless DC motor capable of a high efficient operation.
Next, a brushless DC motor according to a third embodiment is described below.
As shown in
Accordingly, producing the first housing member 124 and the second housing member 134 is not separated between the upper and lower parts of the first housing member 124 and the second housing member 134 and can be made in one process. This provides advantageous effects of a easy process at a low cost.
Further there is an advantageous effect in that the first housing member 124 and the second housing member 134 have higher stiffness because of using the same steel plates though the magnets 44a, 44b are buried.
Further, a width of the magnets 44a, 44b are made shorter than the width of the stator. This eliminates the necessity of bonging the magnet with adhesive, so that it becomes easy to fix the magnet to the stator. This provides an advantageous effect in that the manufacturing process is made easier.
Next, a brushless DC motor according to a fourth embodiment of the present invention is described below.
More specifically, in
Further, corresponding to this, a width of a first housing member 125 and a second housing member 135 contact with the magnets 48a, 48b is made longer.
In other words, in the brushless DC motor according to the fourth embodiment, the lateral widths of the magnets 48a, 48b are made longer within an allowable range as the brushless DC motor in consideration of the structure. The longer lateral width of the magnets 48a, 48b strengthens the magnetic force (magnetic field) of the magnets 48a, 48b.
An end of the magnet 48a is flush with the bottom surfaces (wall surface on the side of the magnet 48a) of a step 125d between the upper and lower first housing members 125 without protrusion outside the stator.
An end of the magnet 48b is flush with the bottom surface (wall surface on the side of the magnet 48b) of a step 135d between the upper and lower second housing members 135 without protrusion outside the stator.
As described above, because the end of the magnet 48a is flush with the bottom surface of a step 135d, the magnetic field generated by the magnet 48a can act on the stator without loss.
As described above, the magnetic force (magnetic fields) of the magnets 48a, 48b according to the fourth embodiment act on the rotor stronger than the case of the magnets 43a, 43a according to the second embodiment by a difference in the width (lateral width) of parts where the magnets 48a, 48b according to the fourth embodiment contact with a first housing member 125 and the second housing member 135. This enhances the efficiency to generate the torque, so that the brushless DC motor with a high efficient operation can be provided.
Advantageous effect of the first to fourth embodiments against prior art such as the Patent Document 1 are as follows:
<A> The brushless DC motors according to the first to fourth embodiments eliminates the necessity of the rotation angle sensor such as a Resolvers which were used in the prior art. In other words, according to the first to fourth embodiments, the position sensor, a position sensor I/O circuit, and a position sensor mounting parts can be omitted. This can decrease the production cost remarkably.
<B> According to the first to fourth embodiments, an auxiliary coil (shading coil) for rotation start is unnecessary, so that a negative torque is not generated. This provides a higher operation efficiency.
Next, the second to fourth embodiments are compared with the first embodiment.
The brushless DC motors according to the second to fourth embodiments use two magnets having rectangular parallelepiped shape. The brushless DC motor according to the first embodiment uses four circular arc shape magnets.
As described above, as the magnet, Neodymium magnets are generally used in the brushless DC motor, the Neodymium magnet being produced by stinting main components including Neodymium of a rare earth, iron, and boron. The materials of the Neodymium magnet are expensive and are difficult to be processed. More specifically, the material is very hard, so that it is difficult to produce the magnet by monolithic molding.
The magnets 41a, 42a, 41b, 42b in
More specifically, to produce the magnet having a circular arc shape in cross section, first a magnet formed in a rectangular parallelepiped shape. The circular arc shape is provided by a process of cutting the magnet of the rectangular parallelepiped shape to form to have a circular arc cross section.
Accordingly, this needs much man power for the process and there is loss as a result of cutting a magnet material which is expensive.
<<Advantageous Effect in the Second to Fourth Embodiment Over the First Embodiment>>
Accordingly, the second to the fourth embodiments have an advantageous effect against the first embodiment as follows:
<1> The number of the magnets is two, which is a low number. Because the amount of the material per one magnet is small, the expensive materials for the magnet can be reduced, and the production cost can be reduced.
<2> Because the magnet is formed in the rectangular parallelepiped, so that it is easy to produce the magnet.
<3> Because the magnet is formed in the rectangular parallelepiped, there is no loss in the magnet material in the shaping process.
<4> There is no magnet in the diametrical direction of the rotor, so that the rotor can be made larger than that in case where the same size stator is used.
In other words, it is possible to increase the efficiency with the same motor size.
<5> Because there is low variation in magnetic field generated by ration of the rotor, there is few generation of the eddy currents, so that efficiency can be increased.
More specifically, according to the second to fourth embodiment, there are provided the brushless DC motors at a low cost and the production method is easy.
The brushless DC motor according to the first embodiment has an advantageous effect over the second to fourth embodiments, because the first embodiment uses four magnets formed in the circular arc shape in cross section, so that there is no torque variation (pulsation) with a larger rotation torque.
The present invention is not limited to the embodiments described above, but may includes various embodiment and modifications.
In the first to fourth embodiments, the first rotor gap 51 which is a gap for the rotor (see
For example, in
Further the first rotor gap 51 is exemplified with gap including three (or four) of window gaps. However, the number of the gaps may be two or less.
The second rotor gap 52 may be a window-like gap or a notch gap.
Further, the shape may be, as described above, a triangle, a rectangular, or other polygonal shapes or a circle. Further, more than one gap are usable.
An improvement in characteristic such as a torque stabilization or efficient can be provided by forming a desired main magnetic flux by a plurality of gaps or notches having various shapes or the arrangement combination.
As described above, the rotor gap (the first rotor gap 51 and the second rotor gap 52) at the rotor peripheries 32a, 32 (see
The high magnetic resistor is not formed with the gaps or the notch in the steel plates, but formed with a thickness change or different materials, there is an advantageous effect in that the stiffness of the rotor 30 can be maintained. Further, the steel plate shape can be formed line-symmetrically. This provides an advantageous effect to secure stabilization during rotation.
Because the first stator notch 61 and the second stator notch 62 of the stator 10 are also high magnetic resistors, various shapes of notches and gaps are usable like the rotor gap of the rotor 30. Further the number of and arrangement of the notches or gaps may be varied and combined. Further, in place of the notches and the gaps, the high magnetic resistors can be provided in accordance with a thickness or materials of the steel plate.
The structures of the first stator notch 61 and the second stator notch 62 have advantageous effects similar to those described with the first rotor gap 51 and the second rotor gap 52.
The second stator notch 62 of the stator 10 may be formed by shortening ends of the first housing member 12 and the second housing member 13,
In the first embodiment as described above, the extending part 53 (
Further, in
Further, as described above, the extending part 53 has a shape of a rectangular or a rectangular parallelepiped. However, a shape of the extending part 53 on the side facing the magnet (for example the magnet 41a) is not a linear in cross section, but may be an arc having a radius smaller than that of the arc of the magnet. Further, the shape may be an arc or other curved line in cross section.
Improvement of the shape may provide further increase in the rotation torque, a high efficiency operation, a reduction in torque variation (pulsation).
In
In
In any case, increase in the number of pairs of the magnets may decrease the torque variation (pulsation).
As shown in the cross-sectional diagram in
However, even though the end of the magnet 48a protrudes from the bottom surface (wall surface on the side of the magnet 48a) of the step 125d between the upper and lower first housing members 125, the operation to enhance the magnetic force of the magnet can be expected similarly by elongating the width of contact between the surfaces of the magnet and the surfaces of the first housing member 125 and the second housing member 135.
Further in the case where the end of the magnet 48a is buried in the end surface of the stator 10 corresponding to the bottom surface in the step 125d between the upper and lower first housing members 125, the operation to enhance the magnetic force by the magnet can be expected similarly by elongating a width in such a direction that the magnets 48a, 48b contact with the first housing members 125 and the second housing members 135.
In the second to fourth embodiments, the magnet 43a, 43b, 44a, 44b, 48a, 48b have been described as rectangular parallelepiped. The present invention is not limited to this. For example, even though a shape of which part is modified in a side or an angle of the rectangular parallelepiped or the rectangular parallelepiped has a small chip or a thin scratch made during manufacturing, when the magnet has a shape generally belonged to the rectangular parallelepiped, there is the above-described advantageous effect.
The second embodiment has been described using the Neodium magnets as the magnets 43a, 43b. However, other types of magnets may provide the same advantageous effect as described in the second embodiment.
In the second embodiment, as shown in
It is possible to arrange the magnet to have N poles on the upper sides thereof and S poles on the lower sides thereof. In this case, the rotor 30 rotates in the same direction by reversing the direction of the voltage applied to the excitation coil 20.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-269168 | Dec 2013 | JP | national |
| 2014-105785 | May 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/078447 | 10/27/2014 | WO | 00 |
