WO2011155004A1

WO2011155004A1 - Dc motor with plate brushes

Info

Publication number: WO2011155004A1
Application number: PCT/JP2010/003901
Authority: WO
Inventors: Shouichi Tanaka
Original assignee: Three Eye Co., Ltd.
Priority date: 2010-06-11
Filing date: 2010-06-11
Publication date: 2011-12-15

Abstract

It is an object to recover a residual magnetic energy of an armature coil of a DC motor with a simple and compact brush structure. Upper sub brush (53), lower sub brush (54), upper recovery diode (61) and a lower recovery diode (62) are added to the conventional brush structure with main brushes (51, 52). Main brushes (51, 52) and sub brushes (53, 54) are made of a metal plate each. Cross-angle (X1) between the sub brush and the main brush, which are adjacent each other in the axial direction across a small distance, is less than 60 degrees. The recovery current caused by the residual magnetic energy flows via the recovery diode and the sub brush. The sub brushes (53,54), which are adjacent each other in the axial direction, can have planetary-gear-shape. The sub brushes (53, 54) rotate around a sun-gear-shaped commutator.

Description

DC MOTOR WITH PLATE BRUSHES

Background of Invention

1. Field of the Invention
The present invention relates to a DC motor with plate-type brushes.

2. Description of the Related Art
A small DC motor called a micro DC motor, for example a toy motor, is driven by a portable primary battery cell. The micro DC motor has a commutator consisting of a pair of plate brushes made of long metal plates, because of its simple structure. The plate brush does not need a coil spring, a pig tail of expensive and large block-shaped graphite brushes. Generally, the micro DC motor has three phase windings connected to three commutator segments in order to have a constant rotating direction. The pair of plate brushes extending to a tangent direction of the commutator comes into contact with each outer circumferential pheripherary of the commutator. A constant small gap is disposed between adjacent two segments of the commutator. When one plate brush comes into contact with adjacent two segments at one time, a residual magnetic energy of one phase winding is consumed by a free-wheeling current, which is a short-cut current, and then a phase current direction is changed.

However, it is not enough to consume the residual magnetic energy by the flat metal plate brushes, because a short-cut period of the flat plate brush is very short. Accordingly, a spark is generated at a moment when the brush removes one of the two brushes. The spark wears the plate brushes and the segments. An electro-magnetic noise is also generated. Furthermore, the consuming of the residual magnetic energy by the resistance decreases a power efficiency of the motor. In the other words, the electric energy of the battery cell is consumed without generating a motor torque.

U. S. Patent No.5,929,579, U. S. Patent No.32,674(Re) and Japan Non-examined Opened Patent Application No. 2007-318842 describe block-shaped carbon sub brushes connected to recovery diodes in order to recover the residual magnetic energy. The sub brush is disposed in a circumferential gap between adjacent two block-shaped main carbon brushes. The commutator segment supplies the recovery current to the DC power source via the sub brush after removing the main brush.

However, the recovery current by employing the block-shaped main carbon brushes with the recovery diodes is not excellent, because the short-cut current loss, which is the resistance loss, is long and large. Figure 1 is a development showing a short-cut current If and a recovery current Ir of the DC motor with the block-shaped carbon brushes. At the time point tA, the recovery current Ir flows through a diode D, a sub brush 101, a segment S1, a phase winding W2, a segment S2 and a main brush 100 in turn. However, the short-cut current If, which is the free-wheeling current, circulates through a main brush 100, the segment S2, a phase winding W3, the segment S3 and the main brush 100.

Next, the short-cut currents If circulate through the sub brush 101 and through the main brush 100 each at time point tB. Next, the short-cut currents If circulate through sub brush 101 and through main brush 100 each at time point tC. Next, recovery current Ir flows through sub brush 101 at time point tD. It is effective to decrease a circumferential width of the block-shaped carbon brush in order to decrease the free-wheeling current loss. However, the narrow carbon brush is weak for a mechanical stress, and increases a resistance of the brush.

The micro DC motor with the plate brush can not employ the above sub brush disposed near a circumferential side of the main brush, because the main brush made of the plate-shaped metal brush of the micro DC motor extends to a tangent direction on the outer peripherary of the commutator segments. Accordingly, the sub brush made of the plate-shaped metal brush can not be disposed.

Japan Non-examined Opened Patent Application No. H08-98485 describes a one-phase micro DC motor with a resistive short-cut circuit shown in Figures 2. The resistive short-cut circuit has a pair of narrow sub segment portions, a pair of sub plate brush, one diode and one resistor element, which are connected each other to series. Each narrow segment portions extends from each circumferential center portion of each wide segment portions of the commutator toward an axial direction of an axis. The sub plate brush coming into contact with the narrow segment portions is adjacent to the main plate brush across a predetermined gap in the axial direction. The residual magnetic energy of the one phase winding generates a short-cut current circulating the short-cut circuit.

However, the residual magnetic energy of the micro DC motor is only consumed by the resistor element of the short-cut circuit. The diode only inhibits the reverse current at a half rotation period. Further, the resistive short-cut circuit shown in Figure 1 is only effective on the one-phase micro DC motor, because the three phase windings of the three-phase micro DC motor generates alternative three-phase voltage. Further, it is difficult to make and fix the narrow segment portion on the outer peripherary of a resin cylinder press-fixed on the axis.

U. S. Patent No.5,829,986 and U. S. Patent No.5,501,604 describe another type of the DC motor with metal plate brushes made of a planetary gear. The planetary gear type plate brushes include planet gears and wheel gears. The commutator fixed on an axis has shape of the sun gear. The planet gear is in gear with sun-gear-shaped commutator segments and the wheel gears.

However, the gear type brush is worn rapidly, because the gear type brush does not include graphite material. Further, contact between the planetary gear brush and the sun gear commutator becomes bad after wearing of them, because the planet gear brush removes to outer radius direction by a centrifugal force at a high rotation speed.

[PTL 1] U. S. Patent No. 5,929,579
[PTL 2] U. S. Patent No. 32,674(Re)
[PTL 3] Japan Non-examined Open Patent Application No. 2007-318842
[PTL 4] Japan Non-examined Opened Patent Application No. H08-98485
[PTL 5] U. S. Patent No. 5,829,986
[PTL 6] U. S. Patent No. 5,501,604

It is an object of the invention to provide a DC motor with plate brushes, which is capable of recovering the residual magnetic energy of an armature coil. It is another object of the invention to provide the DC motor with plate brushes, which is capable of decreasing the spark, the wear and the electro-magnetic noise.

An aspect of the present invention for the DC motor is in brush structure in comparison with a conventional DC motor. The brush structure of the present invention has an upper sub brush (53), a lower sub brush (54), an upper recovery diode (61) and a lower recovery diode (62). The sub brushes (53, 54) made of metal plate each are disposed at adjacent positions to main brushes (51, 52) in the axial direction. The upper recovery diode (61) for recovering a residual magnetic energy of the phase windings (31-33) is connected between the positive main brush (51) and the upper sub brush (53) directly or indirectly. The lower recovery diode (62) for recovering a residual magnetic energy of the phase windings (31-33) is connected between the negative main brush (52) and the lower sub brush (54) directly or indirectly. A recovery current caused by the residual energy of the phase windings (31-33) charges a battery cell via the recovery diodes (61, 62). Accordingly, the plate brushes (51-54) can be accommodated compactly in a brush holder.

According to a preferred embodiment 1, the brushes (51-54) are made of a long metal plate each. A cross-angle (X1) between the top portion (540) of the lower sub brush (54) and the top portion (510) of the positive main brush (51) is less than 60 degrees. A cross-angle (X1) between the top portion (530) of the upper sub brush (53) and the top portion (520) of the negative main brush (52) is less than 60 degrees. The upper recovery diode (61) is connected between the positive main brush (51) and the upper sub brush (53). The lower recovery diode (62) is connected between the negative main brush (52) and the lower sub brush (54). Accordingly, the long plate brushes (51-54) can be accommodated compactly in a brush holder.

According to another preferred embodiment 2, one of the sub segments (41-43) reaches one of the main brushes (51, 52), after the one of the sub segment (41-43) removes one of the sub brushes (53, 54). Further, another one of the sub segment (41-43) reaches another one of the sub brushes (53, 54), after another one of the sub segment (41-43) removes another one of the main brushes (51, 52). As the result, a short-cut current between two main brushes via the sub brushes is inhibited.

According to another preferred embodiment 3, the commutator has the three segments (41-43) connected to the three phase windings (31-33). As the result, it is possible to set a long recovery period for recover the residual magnetic energy by means of the large cross-angle (X1) between the sub brush and the main brush, which are adjacent in the axial direction. Preferably, the cross-angles (X1) are more than 20 degrees and less than 40 degrees.

According to another preferred embodiment 4, the top portion (540) of the lower sub brush (54) is overlapped to the top portion (520) of the negative main brush (520) in an axial direction of the axis (2). As the result, an axial width of the brush structure has can be decreased. Preferably, an axial position of the top portion (540) of the lower sub brush (54) is essentially equal to an axial position of the top portion (520) of the negative main brush (520). Further, an axial position of the top portion (530) of the upper sub brush (53) is essentially equal to an axial position of the top portion (510) of the positive main brush (510).

According to another preferred embodiment 5, the lower sub brush (54) surrounds the top portion (520) of the negative main brush (520). The upper sub brush (53) surrounds the top portion (510) of the positive main brush (510). As the result, the brush structure becomes compact.

According to another preferred embodiment 6, the upper recovery diode (61) and the lower recovery diode (62) are accommodated with the brushes (51-54) in a brush holder (55) made from resin material. As the result, the brush structure with the diodes can have a small size and a low production cost. Preferably, the recovery diode (61, 62) is sandwiched between both root portions of the sub brush and the main brush. As the result, the brush structure becomes simple.

According to another preferred embodiment 7, the sub brush has a central bending portion between the top portion and a root portion. The both of the top portion and a root portion of the sub brush come into contact with the commutator each. As the result, a rotation direction of the motor can be changed.

According to another preferred embodiment 8, recovery voltages or recovery currents detected from the recovery diodes are used for detecting a rotor angle. The recovery voltage of one of two recovery diodes changes three times in one rotation of the axis. As the result, the pulse signal can be formed each 60 degrees. The pulse signal has high S/N ratio, because the recovery diodes are mostly independent from the power line supplying the motor current.

According to another preferred embodiment 9, brushes (51A-54A) consist of a planetary gear made of a metal plate each. The planetary-gear-shaped brushes (51A-54A) are in gear with wheel gears (91-94) each. The planetary-gear-shaped brushes (51A-54A) are in gear with a commutator (4A) with sun-gear shape. Each pair of the brushes and the wheel gears is arranged to the axial direction in turn. As the result, the brush structure has a little wear of the brushes (51A-54A).

According to another preferred embodiment 10, the planetary gears (51A, 52A, 53A, 54A) have concave portions (511) disposed on an inner circumferential surfaces of the planetary gears (51A, 52A, 53A, 54A). The gear teeth (510, 510) of the planetary gears (51A, 52A, 53A, 54A) is deformed elastically in circumferential directions of the planetary gears (51A, 52A, 53A, 54A), when the planetary gears (51A, 52A, 53A, 54A) are in gear with the wheel gears (91-94) and the commutator (4A) with sun-gear shape. Accordingly, the contact between two gears is improved after the wear at the high rotating speed.

According to another preferred embodiment 11, the commutator (4A) has six segments (41-46). Each of segments (41-46) is in gear with each two of planetary-gear-shaped brushes (51A, 52A, 53A, 54A). Each of brushes (51A-54A) has two planetary gears. As the result, a three-phase current is supplied to three-phase windings (31-33) of the armature coil.

According to another preferred embodiment 12, the planetary-gear-shaped sub brush (53A) is coming into contact with one of the segments (41-46) which removes the planetary-gear-shaped main brush (51A) in a predetermined short period just after the removing of the one of the segments (41-46). The planetary-gear-shaped sub brush (54A) is coming into contact with another one of the segments (41-46) which removes the planetary-gear-shaped main brush (51A) in a predetermined short period just after the removing of the another one of the segments (41-46). As the result, almost of the residual magnetic energy is regenerated into the battery.

According to another preferred embodiment 13, at least one of the main brushes (51, 52) is connected to a DC power source (VB) via a switching element (10) controlled by a controller (15). The controller (15) turns off the switching element (10) and stops a current supplying from the DC power source (VB) to the brush short-cutting the adjacent two segments for a predetermined period including a moment when one of the adjacent two segments removes the short-cutting brush. As the result, the spark is restrained. Because, the sparking voltage between the brush and the segment is increased by the residual magnetic energy current and of the short-cut phase winding. Further, the sparking voltage is increased by the current from the DC power source, too. By means of stopping of the current from the DC power source, the sparking voltage is decreased relatively. A length of an air gap between the segment and the brush becomes large. Accordingly, the spark does not generate after the switching element turned on again.

According to another preferred embodiment 14, the controller (15) decides the predetermined period in accordance with a detected signal related to a rotor angle. The predetermined period when the switching element (10) is turned off is extended at a low rotor speed. The predetermined period is shortened at a high rotor speed. As the result, the spark is restrained with a small torque loss.

The feature of the invention is explained hereinafter. A conventional DC motor except the DC motor of the invention can employ the spark-restraining method explained above. In the other words, the conventional DC motor can employ a switching element (10) and a controller (15). The brush is connected to the DC power source (VB) via the switching element (10). The controller (15) turns off the switching element (10), when the segment removes the brush. As the result, the spark between the brush and the removing segment is restrained without employing the sub brushes and recovery diodes.

Figure 1 is a schematic development showing a prior commutating device with a block-shaped brush pair and a recovery diode. Figure 2 is a schematic perspective illustration showing a prior one-phase commutator having a short-cut circuit. Figure 3 is an axial cross section showing a micro DC motor of the embodiment schematically. Figure 4 is a side view showing a brush structure and a commutator, which are shown in Figure 3. Figure 5 is a schematic side view showing the commutator and one pair of a sub brush and a main brush at time point t0. Figure 6 is a schematic side view showing the commutator and another pair of a sub brush and a main brush at time point t0. Figure 7 is a schematic side view showing the commutator and one pair of a sub brush and a main brush at time point t1. Figure 8 is a schematic side view showing the commutator and another pair of a sub brush and a main brush at time point t1. Figure 9 is a schematic side view showing the commutator and one pair of a sub brush and a main brush at time point t2. Figure 10 is a schematic side view showing the commutator and another pair of a sub brush and a main brush at time point t2. Figure 11 is a schematic side view showing the commutator and one pair of a sub brush and a main brush at time point t3. Figure 12 is a schematic side view showing the commutator and another pair of a sub brush and a main brush at time point t3. Figure 13 is a schematic side view showing the commutator and one pair of a sub brush and a main brush at time point t4. Figure 14 is a schematic side view showing the commutator and another pair of a sub brush and a main brush at time point t4. Figure 15 is a schematic side view showing the commutator and one pair of a sub brush and a main brush at time point t5. Figure 16 is a schematic side view showing the commutator and another pair of a sub brush and a main brush at time point t5. Figure 17 is a schematic side view showing the commutator and one pair of a sub brush and a main brush at time point t6. Figure 18 is a schematic side view showing the commutator and another pair of a sub brush and a main brush at time point t6. Figure 19 is a schematic side view showing the commutator and one pair of a sub brush and a main brush at time point t7. Figure 20 is a schematic side view showing the commutator and another pair of a sub brush and a main brush at time point t7. Figure 21 is a timing chart showing contact states between the brushes and the segments. Further, Figure 21 shows a waveform of a short-cut current and a recovery current. Figure 22 is a wiring diagram showing an equivalent circuit of the commutating device shown in Figure 4. Figure 23 is a reference side view showing a short-cut circuit between two main brushes schematically. Figure 24 is a reference view showing a contact state between a long plate type brush and a commutator segments. Figure 25 is a schematic side view showing brushes and segments of an arranged embodiment 1. Figure 26 is a schematic block view showing the micro DC motor having the sub brushes, the recovery diodes and a rotor-angle-detecting circuit. Figure 27 is a timing chart showing wave forms of voltages of the recovery diodes and pulse signals of the rotor-angle-detecting circuit. Figure 28 is an axial section view showing the planet gear type commutation device of the embodiment 2. Figure 29 is a cross-section of one main brush having two planetary gears. Figure 30 is a side view of an enlarged part of the planet gear type commutation device shown in Figure 29. Figure 31 is an enlarged part of the commutator shown in Figure 30. Figure 32 is a schematic side view showing relative angle among planet gears consisting two main brushes and two sub brushes. Figure 33 is a wiring connection diagram of three-phase DC motor having the commutation device with planetary gear structure. Figures 34 is a schematic view showing positions of the brushes at time point t0. Figures 35 is a schematic view showing positions of the brushes at time point t1. Figures 36 is a schematic view showing positions of the brushes at time point t2. Figures 37 is a schematic view showing positions of the brushes at time point t3. Figures 38 is a schematic view showing positions of the brushes at time point t4. Figures 39 is a schematic view showing positions of the brushes at time point t5. Figures 40 is a timing chart showing waveforms of current of the segments. Figures 41 is a circuit diagram showing a DC-motor-driving circuit of the embodiment 3. Figures 42 is a flow chart showing a spark-restraining operation of the DC-motor-driving circuit shown in Figure 41. Figures 43 is a circuit diagram for showing spark-restraining operation.

Detailed Description of the Preferred Embodiment

(Embodiment 1)
An embodiment 1 is explained referring to Figures 3 and 4. Figure 3 shows an axis 2, an armature 3, a commutator 4, a brush structure 5 and a motor housing 7 of the motor 1. Both ends of the axis 2 are supported retractably to the motor housing 7. The armature 3 and the commutator 4, which are fixed on the axis 2, are connected by a pair of copper wires 8 being end portions of the phase windings. Figure 4 is a radial cross section showing the commutator 4 and the brush structure 5. The brush structure 5 consists of four brushes 51-54 fixed to a brush holder 55. The brush holder 55 is fixed to an inner surface of the motor housing 7. Figure 4 schematically shows a side view of the commutator 4 and the brush structure 5. The commutator 4 has three segments 41-43, which are arranged on the outer peripherary of a resin cylinder 44 press-fixed on the axis 2. Each of the three segments 41-43 is adjacent each other in the circumferential direction across a small gap 40 each.

The brush structure 5 has a pair of main brushes 51-52, a pair of sub brushes 53-54, an upper recovery diode 61 and a lower recovery diode 62. Each of the brushes 51-54 disposed radial outward of the axis 2 is made of a bending long metal plate each. The L-shaped main brush 51 is disposed radial inside of the nearly C-shaped sub brush 53. The main brush 51 and the sub brush 53 are disposed at a same axial position. The sub brush 53 extends to the circumferential direction of the axis 2, and surrounds the main brush 51 and the axis 2.

The L-shaped main brush 52 is disposed radial inside of the nearly C-shaped sub brush 54. The main brush 52 and the sub brush 54 are disposed at a same axial position. The sub brush 54 extends to the circumferential direction of the axis 2, and surrounds the main brush 52 and the axis 2. The

brushes

51 and 53 are adjacent to the

brushes

52 and 54 across an air gap G1 with a predetermined width. Root portions of the brushes 51-54 are fixed to the brush holder 55. A top portion 510 of the main brush 51, a top portion 520 of the main brush 52, a top portion 530 of the main brush 530 and a top portion 540 of the main brush 540, which extend to a tangent direction of the commutator 4 each, come into contact with an outer circumferential surface of the commutator 4 each.

An angle between the top portion 510 of the main brush 51 and the top portion 520 of the main brush 52 is 180 degrees. An angle between the top portion 530 of the main brush 53 and the top portion 540 of the main brush 54 is 180 degrees. An angle X1 between the top portion 510 and the top portion 540 is less than 60 degrees, preferably 20-40 degrees. An angle X1 between the top portion 520 and the top portion 530 is less than 60 degrees, preferably 20-40 degrees.

The upper recovery diode 61 is fixed between the two root portions of the main brush 51 and the sub brush 53. An anode electrode of the upper recovery diode 61 is connected to the sub brush 53. A cathode electrode of the upper recovery diode 61 is connected to the main brush 51. The lower recovery diode 62 is fixed between the two root portions of the main brush 52 and the sub brush 54. An anode electrode of the lower recovery diode 62 is connected to the main brush 52. A cathode electrode of the lower recovery diode 62 is connected to the sub brush 54.

Inverting operation of the commutator segments 41-43 and brushes 51-54 is explained referring to Figures 5-22. Figures 5-20 shows contacts between the brushes 51-54 and the segments 41-43 at each of rotating positions in 120 degrees. Figure 21 is a timing chart showing the contact state between the commutator segments 41-43 and the brushes 51-54. Figure 22 is a circuit diagram showing an equivalent circuit of the commutating device consisting of the commutator 4 and the brushes 51-54.

In Figures 5-20, the three phase windings 31-33 of the armature coil 3 is schematically illustrated in the commutator segments 41-43. A positive voltage of a battery is applied to the main brush 51, and a ground voltage 0V is applied to the main brush 52. Figure 5, 7, 9, 11, 13, 15, 17 and 19 show a contact state between the segments 41-43 and brushes 51 and 53 each. Figure 6, 8, 10, 12, 14, 16, 18 and 20 show a contact state between the segments 41-43 and brushes 51 and 53 each. Figures 5-6 show a contact state at a time point t0. Figures 7-8 show the contact state at a time point t1. Figures 9-10 show the contact state at a time point t2. Figures 11-12 show the contact state at a time point t3. Figures 13-14 show a contact state at a time point t4. Figures 15-16 show the contact state at a time point t5. Figures 17-18 show the contact state at a time point t6. Figures 19-20 show the contact state at a time point t7.

According to the embodiment, the three-phase windings 31-33 are connected each other with the well-known delta-connection. A three-phase current for generating the motor torque, which is a torque current, is supplied to the three-phase windings 31-33 from the battery via the main brushes 51-52 and the segments 41-43. The above torque current is same as the conventional micro DC motor with three pairs of the phase windings 31-33 and the three-phase segments 41-43. Consequently, the three-phase current for generating the torque, which is the torque current, is not shown in Figures 5-20.

(At time point t0)
The segment 42 reaches to the main brush 52. The main brush 52 comes into contact with both of the

segments

42 and 43. The residual magnetic energy of the short-cut phase winding 33 is consumed by a free-wheeling current If circulating the main brush 52 and

segments

42 and 43. However, a free-wheeling period from the time point t0 to the time point t1 is short.

(At time point t1)
The segment 43 removes the main brush 52. The residual magnetic energy of the phase winding 33 makes a recovery current Ir supplying from the main brush 52 to the main brush 51 via the segment 42, the phase winding 33, the segment 43, the sub brush 53 and the diode 61 in turn. The residual energy is recovered to the battery.

(At time point t2)
The segment 42 reaches the sub segment 53. The residual magnetic energy of the phase winding 33 makes the free-wheeling current If circulating through the

segments

42 and 43. The current direction of the phase current flowing through the phase winding 33 is changed after the free-wheeling current If becomes zero, because the residual magnetic energy is already decreased largely by means of the battery-charging. However, the free-wheeling period from the time point t1 to the time point t2 is short.

(At time point t3)
The segment 43 removes the sub brush 53. The normal torque current flows through the three-phase windings 41-43.
(At time point t4)
Then, the segment 43 reaches to the main brush 51. The main brush 51 comes into contact with both of the

segments

41 and 43. The residual magnetic energy of the short-cut phase winding 31 is consumed by a free-wheeling current If circulating the main brush 51 and

segments

41 and 43. The free-wheeling period from the time point t4 to the time point t5 is short.

(At time point t5)
The segment 41 removes the main brush 51. The residual magnetic energy of the phase winding 31 makes a recovery current Ir supplying from the main brush 52 to the main brush 51 via the recovery diode 62, the sub segment 54, the segment 41, the phase winding 31 and the segment 43 in turn. The residual energy is recovered to the battery.

(At time point t6)
The segment 43 reaches the sub segment 54. The residual magnetic energy of the phase winding 31 makes the free-wheeling current If circulating through the

segments

41 and 43. The current direction of the phase current flowing through the phase winding 31 is changed after the free-wheeling current If becomes zero, because the residual magnetic energy is already decreased largely by means of the battery-charging. The free-wheeling period from the time point t6 to the time point t7 is short.

(At time point t7)
The segment 41 removes the sub brush 54. The normal torque current flows through the three-phase windings 41-43. Next, the segment 41 reaches the main brush 52, and starts the next rotation of 120 degree, which is same as the above rotation of 120 degree shown in Figures 5-20.

Consequently, the residual energy is recovered to the battery the period t1-12 and t5-t6 as shown in Figure 21. The short-cut current Is is generated twelve times in one rotation of the axis 2, which is equal to 360 degrees. However, an energy loss by the short-cut current Is is not small, because the short-cut periods are not long, when the flat metal brush extending straightly to the tangent direction of the commutator. The recovery current Ir is generated six times in one rotation of the axis 2, which is equal to 360 degrees. Almost residual magnetic energy is recovered to the battery, when the recovery periods t1-12 and t5-t6 are longer than a predetermined time length. In Figure 22, the segment 41 constitutes switches S1-S4. The segment 42 constitutes switches S5-S8. The segment 43 constitutes switches S9-S12.

It is important to prohibit a short-cut between the positive main brush 51 and the negative main brush 52 via the sub brush. For example, as shown in Figure 23, the angle between the sub brush 54 and the main brush 51 is 60 degrees. As the result, a short-cut current Iss flows from the positive brush 51 to the negative brush 52 through the segment 41, the sub brush 54 and the segment 42 in turn. As the result, the angle between the sub brush 54 and the main brush 51 should be less than 60 degrees. Furthermore, the recovery current Ir becomes zero, if the angle between the sub brush 54 and the main brush 51 is zero.

It is considered that one segment must remove the sub segment, before another segment reaches the main segment. As the result, it is preferred the angle between the sub brush and the main brush is 10-50 degrees, more preferably 20-40 degrees. Another benefit of the

sub segments

53 and 54 with the

diodes

61 and 62 is to reduce the wear of the segments 41-43. The micro DC motor with plate type brushes has the heavy wear of the commutator segments 41-43, because of the short-cut period is short. Figure 23 shows wearing surfaces B of the

commutator segments

41 and 43. The rough wear surfaces are made at a circumferential end portion and a circumferential top portion of the

segments

41 and 43. After the wearing of the

segments

41 and 43, the brush 51 vibrates to a radius direction. The vibration of the brush 51 increases the wear of the brush 51. However, the wear of the brush is largely reduced by employing the sub brush 53-54 with the diodes 61-62.

(Arranged embodiment 1)
The arranged embodiment 1 is explained referring to Figure 25. When the micro DC motor can change a rotating direction, a pair of the sub brushes must be added. It requires the complicate brush structure and the narrow contact area of each brush, because of limitation of a total axial width of the commutator 4. The arranged brush structure shown in Figure 25 can solve the above problem.

The sub brushes 53 and 54 are made of a long metal plate each. Both ends of the sub brushes 53 with a central bending portion 531 are fixed to the brush holder 55. Both ends of the sub brushes 54 with a central bending portion 541 are fixed to the brush holder 55. The angle X1 between the root portion 532 of the sub brush 53 and the main brush 51 is about 30 degrees. The angle X1 between the top portion 530 of the sub brush 53 and the top portion of the main brush 51 is about 30 degrees. The angle X1 between the root portion 542 of the sub brush 54 and the top portion of the main brush 52 is about 30 degrees. The angle X1 between the top portion 540 of the sub brush 54 and the top portion of the main brush 52 is about 30 degrees. As the results, the recovery current can charge the battery even though the axis 2 rotates to the opposite direction.

(Arranged embodiment 2)
The arranged embodiment 2 is explained referring to Figures 26-27. In the micro DC motor with the sub brushes and the recovery diodes, a diode current and a diode potential is changed at the recovery periods t1-t2 and t4-t5. These changes are mostly independent from a voltage and a current of a power source or noises. Accordingly, the diode current or the diode potential can be adopted for detecting the rotor angle of the motor.

A preferred rotor-angle-detecting circuit 500 is explained referring to Figure 26. The anode voltage V1 of the recovery diode 61 becomes high just after time point t1. The cathode voltage of the recovery period 62 becomes low just after time point t4. The voltages V1 and V2 are detected by the rotor-angle-detecting circuit 500. The rotor-angle-detecting circuit 500 outputs a pulse signal Vo at the rising edge of the voltage V1 and the falling edge of the voltage V2. Consequently, six pulses of the pulse signal Vo are transmitted in one rotation of the micro DC motor correctly as shown in Figure 27.

(Embodiment 2)
An embodiment 2 of the DC motor with the plate brushes is explained referring to Figures 28-40. The embodiment 2 describes a planet gear type commutation device having a planet gear type brushes made of metal plates. Figure 28 schematically shows an axial section view showing the planet gear type commutation device. A brush structure 5A has wheel gears 91-94 and planetary gears 51A-54A, which are accommodated in a brush holder 55. The planetary gears 51A constitute the plate-type positive main brush. The planetary gears 52A constitute the plate-type negative main brush. The

planetary gears

53A and 54A constitute the plate-type sub brushes.

The wheel gears 91-94 are fixed on inner circumferential surfaces of the brush holder 55. The wheel gear 91 is connected to a positive terminal of the battery. The wheel gear 92 is connected to a negative terminal of the battery. The wheel gear 93 is connected to the wheel gear 91 through the recovery diode 61. The wheel gear 94 is connected to the wheel gear 92 through the recovery diode 62.

The brush holder 55 has four disk-shape rooms surrounding the commutator 4A each. Each of the rooms accommodates each pair of the wheel gear and the planetary gears. Four pairs of the wheel gear and the planetary gears are arranged in turn in the axial direction. One room accommodates planetary gears 51A and wheel gear 91. Next room accommodates planetary gears 53A and wheel gear 93. Next room accommodates planetary gears 52A and wheel gear 92. Next room accommodates planetary gears 54A and wheel gear 94.

Planet gears 51A-54A, which mean planet gears 51A, 52A, 53A and 54A, are in gear with sun-gear-shaped commutator 4A fixed on a resin cylinder 44 press-fixed on the axis 2. Planet gear 51A is in gear with wheel gear 91. Planet gear 53A is in gear with wheel gear 93. Planet gear 52A is in gear with wheel gear 92. Planet gear 54A is in gear with wheel gear 94. Each of six segments 41-46 of the sun-gear-shaped commutator 4A extends to the axial direction.

Figure 29 schematically shows a cross-section of the brush 5A and the commutator 4A at the axial position of planet gear 51A. Figure 30 schematically shows a part of planet gear 51A, wheel gear 91 and sun-gear-shaped commutator 4A. Figure 31 is a radial cross section of a part of the sun-gear-shaped commutator 4A. The commutator 4A consists of six segments 41-46 arranged on the resin cylinder 44 press-fixed on the axis 2. Six segments 41-46 are arranged to an outer circumferential direction of resin cylinder 44 across the gap 40 each. Each of segments 41-46 has gear teeth, for example three gear teeth as shown in Figure 31. Each of segments 41-46 is connected to each of connecting points between phase windings of the armature coil.

Figure 32 shows relative angle among planet gears 51A-54A. An angle between planet gear 51A and planet gear 54A is about 10-15 degrees. An angle between planet gear 53A and planet gear 52A is about 10-15 degrees. Segments 41-46 of sun-gear-shaped commutator 4A rotate to the CCW direction. Every planetary gears 51A-54A rotates to the CCW direction at a half rotation speed of commutator 4A by adjusting a numeral ratio of the gear teeth of each gear. In the other words, planetary gears 51A-54A as the brushes moves 60 degrees, when sun gear type commutator 4A rotates 120 degrees.

Segment 41 is connected to a connecting point A. Segment 42 is connected to a connecting point B. Segment 43 is connected to a connecting point C. Segment 44 is connected to a connecting point D. Segment 45 is connected to a connecting point E Segment 46 is connected to a connecting point F. In Figure 32, six phase windings 31-36 are connected each other constitute ring-shaped armature coil. In Figure 33, armature coil 3 consists of three phase windings 31-33 connected to segments 41-46.

Segments

41 and 44 are connected each other.

Segments

42 and 45 are connected each other.

Segments

43 and 46 are connected each other.

Operation of the DC motor with phase windings 31-33 shown in Figure 33 is explained referring to Figures 34-40. Figures 34-39 shows circumferential positions of planet gear type brushes 51A-54A at time points t0-t5. A rotation angle of brushes 51A-54A around the axis 2 are 60 degrees, when a rotation angle of sun gear type segments 41-46 are 120 degrees. Accordingly, when axis 2 rotates 120 degrees, brushes 51A-54A changes the touching segments. It is same as the DC motor of embodiment 1.

Figure 40 schematically shows wave forms of brush currents Ia-If of planet gear type brushes 51A-54A. At time point t0 shown in Figure 34, main brush 51A short-cuts brushes 43 and 44 and brushes 46 and 41. After brushes 51A remove

segments

43 and 46, the recovery current flow to

segments

43 and 46 through brushes 54A. At time point t1 shown in Figure 34, main brush 52A short-cuts brushes 42 and 43 and brushes 45 and 46. After brushes 52A remove

segments

42 and 45, the recovery current flow from

segments

42 and 45 through brushes 53A.

At time point t2 shown in Figure 36, main brush 51A short-cuts brushes 44 and 45 and brushes 41 and 42. After brushes 51A remove

segments

44 and 41, the recovery current flow to

segments

44 and 41 through brushes 54A. At time point t3 shown in Figure 37, main brush 52A short-cuts brushes 46 and 41 and brushes 43 and 42. After brushes 52A remove

segments

46 and 43, the recovery current flow from

segments

46 and 43 through brushes 53A.

At time point t4 shown in Figure 38, main brush 51A short-cuts brushes 45 and 46 and brushes 42 and 43. After brushes 51A remove

segments

45 and 42, the recovery current flow to

segments

45 and 42 through brushes 54A. At time point t5 shown in Figure 39, main brush 52A short-cuts brushes 44 and 45 and brushes 41 and 42. After brushes 52A remove

segments

44 and 41, the recovery current flow from

segments

44 and 41 through brushes 53A. Consequently, the three-phase current flows into the three phase windings 31-33 shown in Figure 33. Further, the residual magnetic energy of three phase windings 31-33 is recovered into the battery.

A feature of the planet gear type brushes is explained. Each of planet gear type brush 51A-54A is made of each of the metal plates as shown in Figure 30. Each gear teeth 510 has concave portion 511 on an inner circumferential surface of brush 51A. The wheel gear 91 has one concave portion 911 between adjacent two gear teeth 910. The sun gear 4A, which is the commutator, has one concave portion 411 between adjacent two gear teeth 410. The gear teeth 510 can deform elastically by means of decreasing a circumferential width of the concave portions 511 of the planet gear brush 51A. Because, the gear teeth 510 has the concave portions 511 inside of them. As the result, the contact between two gear teeth becomes excellent even though the wear or the high-speed rotation.

(Embodiment 3)
An embodiment 3 of the DC motor is explained referring to Figures 41-43. The embodiment 3 describes the spark-reducing method of the DC motor. It is explained that the spark is generated an air gap between the brush and the segment removing the brush. Generally, it is known that a brush-segment voltage between the brush and the removing segment becomes larger than a predetermined value. It means that the spark is restrained, when the voltage of the positive brush is decreased just before the segments removes the positive brush. Similarly, the spark is restrained, when the voltage of the negative brush is increased just before the segments removes the negative brush. In the embodiment 3, the spark is reduced by means of controlling of the brush potential periodically.

Figure 41 shows a DC motor-driving circuit having a full-bridge inverter 10 and a controller 15 controlling the inverter 10. The inverter 10 has two half-bridges. One half-bridge consisting of an

upper transistor

11 and 12 is connected one end of the DC motor 1. The other half bridge consisting of an

upper transistor

13 and 14 is connected the other end of the DC motor 1. DC motor 1 outputs a rotor angle signal Sr. In this embodiment, the rotor angle signal Sr is a short-cut signal outputting at the starting time of the short-cut current Is is generated. The short-cut signal Vo shown in Figure 26 can be used as the rotor angle signal Sr. The rotor angle signal from a rotor angle sensor can be used, too. The spark is generated just after the short-cut period when the brush short-cuts adjacent two segments. The spark period is essentially equal to recovery periods t1-t2 and t5-t6 shown in Figure 21.

A spark-protecting operation of the embodiment is explained referring to Figure 42. In Figure 41, upper switch 11 and lower switch 14 are normally turned on, and upper switch 13 and lower switch 12 are normally turned off. DC motor 1 is rotating to the CCW direction. At step S100, controller 15 detects the short-cut signal Vo, which is the rotor angle signal Sr. At next step S101, a surge-on time point Tx, a surge-off time point Ty are decided. Further, a next surge transistor is decided in accordance with the rotor angle signal Sr. the surge-on time point Tx is a time point when the spark starts.

In Figure 21, the time points t1 and t5 are the surge-on time points Tx. The surge-off time point Ty is a time point when the spark finishes essentially. In Figure 21, for example, the time points t2 and t6 are the surge-off time points Ty. The spark finishes near the time points t2 and t6. A sparking period between the surge-on time points Tx and the surge-off time point Ty has a relation to the rotation speed of the motor 1. The sparking period becomes short, if the rotation speed is high. The sparking period becomes long, if the rotation speed is low. Accordingly, the controller 15 calculates the sparking period in accordance with the rotation speed calculated from the rotor angle signal Sr.

Further, the next surge transistor, which is a transistor generating the next spark, is decided in accordance with the rotor angle signal Sr. The spark on the positive brush 51 and the spark on the negative brush 53 are generated alternately. By detecting the rotation angle, it is decided that the next sparking transistor is upper transistor 11 or lower transistor 11. It is possible to make the sparking period constant simply.

At next step 104, it is judged whether or not the present time point, which is counted by a counter in the controller 15, is equal to a time point (Tx-Tdelta). The predetermined value Tdelta is a predetermined constant value in this embodiment. At next step 106, the selected transistor is turned-off. The selected transistor is upper transistor 11, if the positive brush 51 short-cuts the adjacent two segments. The selected transistor is lower transistor 14, if the negative brush 52 short-cuts the adjacent two segments. As the result, the spark between the short-cut brush and the segment is restrained.

The spark-restraining effect is explained referring to Figure 43. First, the negative brush 53 comes into contact with the segment 43. A current shown with broken line flows to phase windings 31-33. The phase winding 33 accumulates the magnetic energy. Then, brush 52 comes into contact with the segment 43. The short-cut current If circulates through segment 43, brush 52 and segment 42. Just before or just after the short-cut, the lower switch 14 is turned off. Accordingly, a potential, which is a voltage, of the negative brush 52 becomes high. A battery current supplied from the battery VB to the phase windings 41-43 is stopped. Then, the segment 43 removes the negative brush 52. A voltage, which is the potential of the segment 43 is increased by the residual magnetic energy of the phase winding 33.

However, the potential-increasing speed is small, because the battery current supplied to the segment 43 is stopped. It is required for sparking that the voltage between segment 43 and brush 52 is larger than a predetermined value. However, by stopping the lower transistor 14, the voltage of brush 52 becomes high, and the voltage-increasing speed of the segments is low. As the result, the voltage between brush 52 and segment 43 is not large just after segment 43 has removed brush 52. Consequently, the spark between brush 52 and segment 43 is restrained. Upper switch 11 is turned off just before or just after brush 51 short-cuts adjacent two segments. The voltage of brush 51 becomes low by turning-off of upper transistor 11. As the result, the spark is restrained just after one of the adjacent two segments removes brush 51.

At next step 108, it is judged whether or not a counting time T reaches the surge-off time point Ty. The surge-off time point Ty is calculated in accordance with the rotor speed. The surge-off time point Ty is late, when the rotor speed is low. The time T counted by the controller 15 reaches at the surge-off time point Ty, the turning-off transistor is turn on again at next step 110. Consequently, the spark is restrained, because the battery current supplying to the short-cutting brush is stopped.

For example, the battery current of a DC motor with two brush and three segments is stopped 180 times per one second at 1800 rpm. The battery current of a DC motor with two brush and twenty-four segments is stopped 1260 times per one second at 1800 rpm. The switching power loss by cutting-off of the

transistors

11 and 14 is very smaller in comparison with the conventional PWM switching of the

transistors

11 and 14, because conventional PWM switching frequency is 10-15 kHz. The spark suppressing method having the turning-off of the battery current just after when the brush short-cuts adjacent two brushes can be employed by a conventional DC motor with plate brushes or block-shaped brushes.

Claims

A DC motor with plate brushes comprising:
a commutator having a plurality of segments (41-43) arranged in a circumferential direction of an rotating axis (2) in turn, the segments (41-43) fixed to the axis (2) are connected to phase windings (31-33) of the DC motor; and
a brush structure having a positive main brush (51) with a positive potential and a negative main brush (52) with a negative potential, main brushes (51, 52) coming into contact with the segments (41-43) are made of metal plates;
wherein the brush structure has an upper sub brush (53), a lower sub brush (54), an upper recovery diode (61) and a lower recovery diode (62);
the sub brushes (53, 54) coming into contact with the segments (41-43) are made of metal plates;
the main brushes (51, 52) and sub brush are adjacent in an axial direction of the rotating axis (2);
the upper recovery diode (61) for recovering a residual magnetic energy of the phase windings (31-33) is connected between the positive main brush (51) and the upper sub brush (53) directly or indirectly; and
the lower recovery diode (62) for recovering a residual magnetic energy of the phase windings (31-33) is connected between the negative main brush (52) and the lower sub brush (54) directly or indirectly.
The DC motor with plate brushes according to claim 1, wherein the main brushes (51, 52) has a top portions (510, 520) extending toward almost tangent direction of an outer circumferential pheripherary of the segments (41-43);
the sub brushes (53, 54) has a top portions (530, 540) extending toward almost tangent direction of an outer circumferential pheripherary of the segments (41-43);
the top portion (540) of the lower sub brush (54) is adjacent to the top portion (510) of the positive main brush (51) in the axial direction across a predetermined gap;
the top portion (530) of the upper sub brush (53) is adjacent to the top portion (520) of the negative main brush (52) in the axial direction across a predetermined gap; and
cross-angles (X1) between the top portion (540) of the lower sub brush (54) and the top portion (510) of the positive main brush (51) and between the top portion (530) of the upper sub brush (53) and the top portion (520) of the negative main brush (52) are less than 60 degrees.
The DC motor with plate brushes according to claim 2,
one of the sub segment (41-43) reaches one of the main brushes (51, 52), after the one of the sub segment (41-43) removes one of the sub brushes (53, 54), and
another one of the sub segment (41-43) reaches another one of the sub brushes (53, 54), after another one of the sub segment (41-43) removes another one of the main brushes (51, 52).
The DC motor with plate brushes according to claim 2, wherein the commutator has the three segments (41-43) connected to the three phase windings (31-33).
The DC motor with plate brushes according to claim 4, wherein the cross-angles (X1) is larger than 20 degrees and less than 40 degrees.
The DC motor with plate brushes according to claim 2, wherein the top portion (540) of the lower sub brush (54) is overlapped to the top portion (520) of the negative main brush (520) in an axial direction of the axis (2).
The DC motor with plate brushes according to claim 6, wherein an axial position of the top portion (540) of the lower sub brush (54) is essentially equal to an axial position of the top portion (520) of the negative main brush (520); and
an axial position of the top portion (530) of the upper sub brush (53) is essentially equal to an axial position of the top portion (510) of the positive main brush (510).
The DC motor with plate brushes according to claim 2, wherein the lower sub brush (54) surrounds the top portion (520) of the negative main brush (520); and
the upper sub brush (53) surrounds the top portion (510) of the positive main brush (510).
The DC motor with plate brushes according to claim 1, wherein the upper recovery diode (61) and the lower recovery diode (62) are accommodated with the brushes (51-54) in a brush holder (55) made from resin material.
The DC motor with plate brushes according to claim 9, wherein an anode of the upper recovery diode (61) is joined on a root portion of the upper sub brush (53);
a cathode of the upper recovery diode (61) is joined on a root portion of the positive main brush (51);
an anode of the lower recovery diode (62) is joined on a root portion of the negative main brush (51); and
a cathode of the lower recovery diode (62) is joined on a root portion of the lower sub brush (54).
The DC motor with plate brushes according to claim 2, wherein the upper sub brushes (53) has a central bending portion (531) between the top portion (530) and a root portion (532), which are coming into contact with the commutator each; and
the lower sub brushes (54) has a central bending portion (541) between the top portion (540) and a root portion (542), which are coming into contact with the commutator each.
The DC motor with plate brushes according to claim 1, wherein at least one of recovery currents flowing through the recovery diodes (61, 62) and voltages of connecting points between the recovery diodes (61, 62) and the sub brushes (53, 54) is detected for deciding a rotation angle of the axis (2).
The DC motor with plate brushes according to claim 1, wherein the main brushes (51A, 52A) and the sub brushes (53A, 54A) consists of a planetary gear made of a metal plate;
the commutator (4A) with sun-gear shape has the segments (41-46) being in gear with the main brushes (51A, 52A) and the sub brushes (53A, 54A);
the main brushes (51A, 52A) and the sub brushes (53A, 54A) are in gear with wheel gears (91-94) surrounding the commutator (4A); and
each pair of the brushes and the wheel gears is arranged to the axial direction in turn;
The DC motor with plate brushes according to claim 13, wherein the planetary gears (51A, 52A, 53A, 54A) made of a metal plate has concave portions (511) disposed on an inner circumferential surfaces of the planetary gears (51A, 52A, 53A, 54A); and
the gear teeth (510, 510) of the planetary gears (51A, 52A, 53A, 54A) is deformed elastically in circumferential directions of the planetary gears (51A, 52A, 53A, 54A), when the planetary gears (51A, 52A, 53A, 54A) are in gear with the wheel gears (91-94) and the commutator (4A) with sun-gear shape.
The DC motor with plate brushes according to claim 13, wherein the commutator (4A) has six segments (41-46); and
each of segments (41-46) is in gear with each two of planetary-gear-shaped brushes (51A, 52A, 53A, 54A).
The DC motor with plate brushes according to claim 15, wherein the planetary-gear-shaped sub brush (53A) is coming into contact with one of the segments (41-46) which removes the planetary-gear-shaped main brush (51A) in a predetermined short period just after the removing of the one of the segments (41-46); and
the planetary-gear-shaped sub brush (54A) is coming into contact with another one of the segments (41-46) which removes the planetary-gear-shaped main brush (51A) in a predetermined short period just after the removing of the another one of the segments (41-46).
The DC motor with plate brushes according to claim 1, wherein at least one of the main brushes (51, 52) is connected to a DC power source (VB) via a switching element (10) controlled by a controller (15);
the controller (15) stops a current supplying from the DC power source (VB) to the brush short-cutting the adjacent two segments for a predetermined period including a moment when one of the adjacent two segments removes the short-cutting brush.
The DC motor with plate brushes according to claim 17, wherein the controller (15) decides the predetermined period in accordance with a detected signal related to a rotor angle; and
the predetermined period when the switching element (10) is turned off is extended at a low rotor speed.