Patent Application
20120319520
The present invention relates to a dc motor including a brush and a commutator, this dc motor is employed in an automotive electronics or an electric tool.
In recent years, electric devices, e.g. automotive electronics, electric tools, have been downsized, light-weighted, and operated at a higher efficiency. This market trend entails requirements for dc motors, which are supposed to be mounted to those devices as power sources, to be smaller in size, lighter in weight, and more efficient in operation.
A dc motor used in automotive electronics or household electric appliances produces greater electric spark between a brush and a commutator slip (commutator segment) as the motor rotates at a greater rpm, becomes smaller in size and lighter in weight, and produces a greater output. On top of that, the dc motor is required to have a longer service life as well as a higher reliability.
This dc motor, in general, is formed of a stator forming a field magnet, and a rotor confronting the stator with an annular space therebetween. The rotor employs an armature equipped with a commutator and formed by winding a coil on a core. To drive this dc motor, it is needed to feed the armature with electric power, so that the brush connected to an outer power supply with lead wires should be in sliding contact with the commutator.
To increase the number of magnetic poles of magnets employed in the dc motor, it is necessary for a various structural elements to be combined optimally. In this context, the structural elements include the number of magnetic poles of the coil relative to the number of magnetic poles of the magnets, a wire connection structure of the winding and so on.
In the wire connection structure for optimizing the motor performance, a ratio of useless coils to multiple armature coils is obliged to increase, so that the number of armature coils should be increased to obtain necessary performance. A solution of the problem thus has unfortunately invited another problem. As a result, a greater change in the inductance has occurred, which adversely causes a voltage waveform and therefore sometimes shortens a service life of the motor. It is thus inevitable to employ a wire-wound structure although this structure somewhat degrades the motor performance. Noises caused by the solution to the same problem also become another problem.
The conventional dc motor discussed above is described hereinafter with reference to
a stator having four (4) field magnets;
a core having five (5) teeth;
a commutator having ten (10) segments;
an armature having coils wound on the teeth via wire-connections to the segments; and
a pair of brushes each of which is disposed at right angles with each other and in sliding contact with the commutator.
An arc length of the brush in sliding contact with the commutator is not greater than 5% of an circumference length of the commutator, namely, an arc length≦π×A/20, where A is an outer diameter of the commutator.
A first electric current path starts from brush B101, and runs through S103, runs around tooth T105, runs through S108, runs around tooth T104, runs through S109, runs around tooth T103, runs through S104, runs around tooth T102, runs through S105, and arrives at brush B102.
A second electric current path starts from brush B101, and runs through S103, runs around tooth T101, runs through S102, runs around tooth T102, runs through S107, runs around tooth T103, runs through S106, runs around tooth T104, runs through S101, runs around tooth T105, runs through S110, runs around T101, runs through S105, and arrives at brush B102.
The dc motor has been improved to meet the required specification, and optimized structures of the dc motor have been proposed, which has accompanied disclosures of various techniques, e.g. patent literatures 1 and 2.
In a dc motor equipped with distributed windings, the winding passes over each tooth sequentially, so that coil ends, which is not involved in generating torque, become greater in size. The copper loss at the coil ends lowers the efficiency of the motor, and also causes to enlarge the measurement of the motor in an axial direction. As x signs in
A dc motor equipped with a concentrated winding or a wave winding also tries to optimize the combination of the number of magnet poles, the number of armature windings, the number of commutator slips for pursuing higher torque, higher efficiency, and a compact size. However, as discussed above, this conventional dc motor also needs to be improved with respect to small in size, light in weight, and high efficiency to satisfy the specification required presently (e.g. Patent Literature 2).
A dc motor of the present invention comprises: a stator, an armature, and brushes.
The stator includes multiple field magnet poles. The armature includes the following elements:
an armature core having multiple teeth and slots between each of the teeth;
an armature coil wound on the teeth and accommodated in the slots; and
a commutator having segment group formed of multiple segments.
The brushes feed the armature coil with electric power through their sliding contacts with the segments. The armature coil includes multiple concentrated winding coil units wound on each of the teeth, and multiple connecting wire units that connect each of the concentrated winding unit together and make an electrical connection between those units.
The segment group includes first segments to which first ends of the concentrated winding coil units are connected, and second segments to which second ends of the concentrated winding coil units are connected, and third segments to which the connecting wire units only are connected. The first segments are disposed adjacently to the second segments, and the third segments are disposed next to this adjacently disposed segments.
The multiple connecting wire units of the dc motor of the present invention pass through the slots for connecting the concentrated winding coil units together. This structure allows regulating the sparks between the segments of the commutator, improving the driving efficiency, and downsizing the dc motor.
The exemplary embodiment is demonstrated hereinafter with reference to the accompanying drawings.
Rotor (hereinafter referred to as armature) 21 includes arc-shaped armature core 23 having multiple slots 24, armature coils 22 wound and accommodated in slots 24, output shaft 28 extending through and fixed at the center of armature core 23, and commutator 25 fixed to output shaft 28. Terminals of armature coils 22 are connected electrically to the segments of commutator 25.
Output shaft 28 is rotatably supported by two bearings 35 and 36. Bearing 35 is fixed to frame 13 at its outer ring, and bearing 36 is fixed to bracket 17 at its outer ring. An outer circumference of armature core 23 of armature 21 confronts an inner circumference of magnet 12 of stator 11 with a given space therebetween.
Magnet 12 can be shaped like a ring, and each of the ring's inner wall can be magnetized to N pole-S pole equidistantly and alternately along the circumferential direction, namely, magnet 12 is magnetized to 6 poles. Here is another way of magnetization: Each of the ring shaped magnets is magnetized to N pole and S pole independently, and forms an arc-shaped magnet, i.e. six arc-shaped magnets are formed.
Armature 21 includes the following structure elements:
armature core 23 having multiple teeth (eight teeth in this embodiment) and slots 24 between each of the teeth;
armature coil 22 wound on each of the teeth and accommodated in slots 24;
output shaft 28 extending through and fixed to the center of armature core 23 along the axial direction; and
commutator 25 fixed to output shaft 28.
Armature core 23 is formed by layering electromagnetic steel sheets. Each of teeth T1, T2, T3, T4, T5, T6, T7, and T8 of armature core 23 is wound with concentrated winding coil units W1, W2, W3, W4, W5, W6, W7, and W8, and those coil units are connected to segments 25s of commutator 25 via hook 25f. The foregoing winding structure is detailed later.
A first face of armature core 23, i.e. the same side as commutator 25 is placed, is referred to as a top face, and a second face thereof is referred to as a lower face hereinafter for a description purpose.
Commutator 25 includes 24 segments, i.e. segment S1-segment S24, and each one of the segments is represented by segment 25s. Segments 25s are insulated from each other, and each segment 25s has hook 25f at its tip to be connected to a coil terminal. When the terminals of the coil units or the connecting wire units are connected to each of the segments, they are connected to hooks 25f at the tips of segments 25s. In the following descriptions, a simple expression such as “they are connected to segments” is sometimes used.
Brush 31 is formed of anode side brush B1 and cathode side brush B2, the two brushes are spaced away at 180 degrees in mechanical angles. The two brushes are in sliding contact with each segment 25s of commutator 25, and are connected to a dc power supply, so that the dc power is fed to armature coil 22 via commutator 25. In the following description, an angle refers to a mechanical angle.
Coil units W1, W2, W3, W4, W5, W6, W7, and W8 of armature coil 22 are respectively connected to segments 25s placed adjacently to each other. To be more specific, a first terminal of some coil unit is connected to some segment 25s and a second terminal thereof is connected to another segment 25s adjacent to the some segment 25s. A concentrated winding coil unit is not connected to a segment next to the segments to which the coil unit is connected, and only a connecting wire unit is connected to this segment (more detailed description coming later). A segment, to which a first end of the concentrated winding coil unit is connected, is defined as a first segment, and another segment, to which a second end of the same concentrated winding coil unit is connected, is defined as a second segment. A segment, to which only a connecting wire unit is connected, is defined as a third segment.
Following the definitions discussed above, the first segment and the second segment are placed adjacently to each other, and the third segment is placed next to this adjacent placement. On top of that, the armature coil forms a series-closed circuit with the aid of the segment groups and the connecting wire units. The first segments, second segment, and third segments are available in a quantity equal to each other, and the total quantity of the segments of segment group is a sum of the first, second, and third segments.
A placement of those segments is detailed hereinafter. As shown in
Next, a winding structure of the armature coil is specifically described hereinafter. Concentrated winding coil unit W1 wound on tooth T1 is connected to first segment S2 and second segment S3. Concentrated winding coil unit W2 wound on tooth T2 is connected to first segment S5 and second segment S6. Concentrated winding coil unit W3 wound on tooth T3 is connected to first segment S8 and second segment S9. Concentrated winding coil unit W4 wound on tooth T4 is connected to first segment S11 and second segment S12. Concentrated winding coil unit W5 wound on tooth T5 is connected to first segment S14 and second segment S15. Concentrated winding coil unit W6 wound on tooth T6 is connected to first segment S17 and second segment S18. Concentrated winding coil unit W7 wound on tooth T7 is connected to first segment S20 and second segment S21. Concentrated winding coil unit W8 wound on tooth T8 is connected to first segment S23 and second segment S24.
Next, connecting wire units C1, C2, C3, C4, C5, C6, C7, and C8 connected to third segments S1, S4, S7, S10, S13, S16, S19, and S22 respectively are detailed hereinafter. Those connecting wire units electrically connect the concentrated winding coil units to each other, and they connect the first segment, second segment, and third segment, which are placed at the intervals of 120 degrees, to each other.
To be more specific, connecting wire unit C1 is connected to first segment S2, third segment S10, and second segment S18. Connecting wire unit C2 is connected to first segment S5, third segment S13, and second segment S21. Connecting wire unit C3 is connected to first segment S8, third segment S16, and second segment S24. Connecting wire unit C4 is connected to first segment S11, third segment S19, and second segment S3. Connecting wire unit C5 is connected to first segment S14, third segment S22, and second segment S6. Connecting wire unit C6 is connected to first segment S17, third segment S1, and second segment
S9. Connecting wire unit C7 is connected to first segment S20, third segment S4, and second segment S12. Connecting wire unit C8 is connected to first segment S23, third segment S7, and second segment S15.
As discussed above, each one of the concentrated winding coil units is connected to each one of the segments, so that this armature coil 22 can form a closed circuit. To be more specific, in
Use of the following connecting method allows reducing the number of connection steps needed for the foregoing connecting wire units C1, C2, C3, C4, C5, C6, C7, and C8. A first end of concentrated winding coil unit W1 wound on tooth T1 is connected to first segment S2, and then, escaping from being cut, extended and connected to third segment S10. In a similar way, a second end of concentrated winding coil unit W6 wound on tooth T6 is connected to second segment S18, and then, escaping from being cut, extended and connected to third segment S10. Connecting wire unit C1 can be thus formed of an extended line of the first end of coil unit W1 and an extended line of the second end of coil unit W6, thereby reducing the number of connection steps. The other connecting wire units C2, C3, C4, C5, C6, C7, and C8 can be formed in a way similar to what is discussed above.
In this embodiment among others, multiple connecting-wire units discussed above include the connecting wire units that pass through slots 24 to connect the concentrated winding coil units together. To be more specific, each one of connecting wire units C1, C2, C3, C4, C5, C6, C7, and C8 is not involved in the connection on the outer wall of the commutator, but they are involved in the connection through the winding together with respective concentrated winding coil units in slots 24 of the armature. This method can save preparing useless space for the connecting wire units around the commutator, and efficiently use the spaces inside slots 24 of the armature. As a result, the motor can be downsized.
Anode side brush B1 and cathode side brush B2 are spaced away at intervals of equal angle, i.e. 180 degrees, so that a centerline along the width direction (circumferential direction) can agree with a centerline along a circumferential direction of a given magnet 12. The widths along the circumferential direction of respective brushes B1 and B2 are set equal to or smaller than the widths along the circumferential direction of each segment. Brush B1 and brush B2 are thus in sliding contact with respective segments at adjacent two places or one place. A time involved in the sliding contact with one place is extremely short, so that the time is omitted in the following description.
As
The electric current entering segment S2 flows through segment S18 and concentrated winding coil unit W6, and then flows through segment S17, segment S9, concentrated winding coil unit W3, segment S8, segment S24, concentrated winding coil unit W8, segment S23 in this order, and finally flows out segment S15. In a similar way, the electric current entering segment S3 flows through segment S11 and concentrated winding coil unit W4, and then flows through segment S12, segment S20, concentrated winding coil unit W7, segment S21, segment S5, concentrated winding coil unit W2, segment S6 in this order, and finally flows out segment S14. Those flowing directions of electric currents are shown with arrows on the respective concentrated winding coil units in
As discussed above, the electric current entering segment S2 flows through a series circuit formed of concentrated winding coil units W6, W3, W8, and flows out segment S15. The electric current entering segment S3 flows through a series circuit formed of concentrated winding coil units W4, W7, W2, and flows out segment S14. The electric current entering anode side brush B1 flows through two parallel circuits and flows out cathode side brush B2. This electric current flow allows the dc motor to be a self-starting motor.
The direction of electric current of connecting wire unit C1 in each slot 24 is indicated with arrows, and as the arrows show, the direction of electric current of unit C1 agrees with that of the concentrated winding coil unit in the same slot 24. The positions of the brushes change in response to the rotation of the motor, so that the directions of electric current change accordingly. The direction of electric current of the connecting wire unit therefore does not always agree with that of the concentrated winding coil unit; however, the connecting wire units are accommodated in selected slots 24 where the agreement occurs more frequently.
Next,
In this example, connecting wire unit C2 can be also wound on the foregoing teeth with multiple turns, and the number of turns on each tooth can be determined appropriately.
As discussed above, the positions of slots 24, in which connecting wire units C1 and C2 are accommodated, are shown. Other connecting wire units C3, C4, C5, C6, C7 and C8 can select slots 24 such that the directions of electric current of those units can agree with those of the concentrated winding coil units.
It is preferable that all the multiple connecting-wire units C1-C8 should pass through slots 24 and connect each of the concentrated winding coil units together. However, some connecting wire units can connect some of the concentrated winding coil units only on the upper face side of armature core 23. In other words, the structure can include multiple connecting wire units that pass through slots 24 and connect the concentrated winding coil units together. This structure allows reducing a size of a bulge caused by a concentration of connecting wire units around the commutator, whereby the dc motor can be downsized.
In the foregoing demonstration, anode side brush B1 and cathode side brush B2 are spaced away at intervals of 180 degrees; however they can be placed at intervals of 60 degrees as shown in
In the case of employing intervals of 60 degrees between the brushes, the electric current entering segment S2 passes through the series circuit formed of concentrated winding coil units W6, W3, W8, and flows out segment S7. The electric current entering segment S3 passes through the series circuit formed of concentrated winding coil units W4, W7, W2, and flows out segment S6. As discussed above, the electric current entering anode-side brush B1 flows through two parallel circuits, and flows out cathode-side brush B3. In this case, concentrated winding coil W1 is shorted and coil W5 is also shorted, and they are not involved in increasing the driving torque.
The reason of not involving is this: Segment S14 is connected to segment S6 with connecting wire unit C5, and segment 15 is connected to segment S7 with connecting wire unit C8, so that cathode side brush B3 in sliding contact with segments S6 and S7 shorts concentrated winding coil unit W5. There are no coils through which an inverse current runs, and this is the same as the case where the brushes are spaced away at intervals of 180 degrees.
Next, the position of slot 24, in which connecting wire unit C1 is accommodated, is described hereinafter. Connecting wire unit C1 starts from first segment S2, and runs through slot 24 between teeth T1 and T2, slot 24 between teeth T2 and T3, and is connected to third segment S10, and then further runs from third segment S10, and runs through slot 24 between teeth T3 and T4, slot 24 between teeth T5 and T6, and is finally connected to second segment S18. The directions of electric current at each slot 24 are indicated with arrows. The current directions at each slot 24 agree with those of the concentrated winding coil units. Since the positions of brushes change in response to the rotation of the motor, the current directions change accordingly. The direction of electric current of the connecting wire unit therefore does not always agree with that of the concentrated winding coil unit; however, the connecting wire units are accommodated in selected slots 24 where the agreement occurs more frequently. The number of turns of this connecting wire unit C1 is determined appropriately.
The number (T) of segments of segment group of the dc motor in accordance with the embodiment is determined this way:
T=(½) PN, where P is the number of poles of field magnet pole, N is the number of concentrated winding coil units, (N is equal to the number of slots and the number of teeth). P is such an even number that P divided by 2 becomes an odd number, and the number of coil units N is an even number that does not become an integral multiple of P. To be more specific, the foregoing values are as follows and satisfy the equation of T=(½) PN: number of segments T=24, number of magnet poles P=6, and number of concentrated winding coil units N=8.
Each one of concentrated winding coil units W1-W8 and each one of connecting wire units C1-C8 are formed of conductive wires covered with an insulating layer. A thickness, material and a number of layers of this insulating layer are determined appropriately for the specification of the dc motor. The conductive section of this conductive wire, i.e. a core wire of the conductive wire, is made of material selected from a group consisting copper, aluminum, copper alloy, aluminum alloy, an alloy including at least copper and aluminum, aluminum or aluminum alloy containing impurity in a very small amount, and magnesium alloy. The material is selected appropriately for the specification of the dc motor. The conductive wire covered with the insulating layer can be selected from a group consisting of a solid wire, double wire, Litz wire (stranded wire) appropriately for the specification of the dc motor.
In this dc motor of the present invention, an armature coil is wound on each tooth by a concentrated winding method, so that a space factor of each slot can be improved. The armature coil forms a closed circuit with the aid of a segment group and the connecting wire unit, and also forms two parallel circuits. There are no concentrated winding coil units through which an inverse electric current flows. The dc motor also allows reducing the number of shorted concentrated winding coil units, and regulating the change in inductance of the armature coil. The slots, in which the connecting wire units are accommodated, are selected such that the current direction of the connecting wire unit agrees with that of the concentrated winding coil units with greater frequencies at the selected slots. As a result, the connecting wire units can be involved in increasing the torque. The foregoing structure also mitigates the sparks occurring between each of the segments of the commutator, and provides the dc motor achieving an increment in driving efficiency, smaller in size, and lighter in weight.
A dc motor of the present invention includes brushes and a commutator, and is good for driving automotive electronics or electric tools. This dc motor allows regulating sparks occurring between each segment of the commutator, increasing the driving efficiency, and is involved in downsizing the dc motor and reducing a weight of the dc motor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-078373 | Mar 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/001850 | 3/29/2011 | WO | 00 | 8/27/2012 |
