Three-phase DC motor having non-superimposed armature coils

Abstract

A coreless three-phase dc motor comprising a coil type armature formed with insulated windings. The armature is of a disc- or cylindrical-shape and is set rotatably against a field magnet provided with 2n magnetic poles N and S magnetized in equal angular widths. On the surface of the armature there are 3n/2 three-phase armature coils, wherein the angular width of each of the coils is equal to the width of the field magnet pole, the coils of each phase are shifted by 180° of electrical angle from each other, and all the armature coils are arranged at equal angular intervals and not superimposedly with respect to one another.

Description

FIELD OF THE INVENTION

This invention relates to a three-phase DC motor comprising a coil type armature provided with insulated coil windings, particularly to a coreless three-phase DC motor wherein the three-phase armature coils are provided in a non-superimposed manner to the armature.

PRIOR ART

In prior art three-phase DC motors, armature coils are provided armature in the ordinary manner so that the coils are superimposed in three layers. This manner of providing coils causes difficulties in processing the ends of coils and makes mass production difficult. In setting coils which have been formed and rigidified onto the surface of an armature, the coils are superimposed in three layers resulting in increase of the thickness of the armature. Such increased thickness of the armature greatly is aniscost less less cost. Furthermore when the oscillation outputs from the circuit containing the coils 82a, 82b and from the circuit containing coils 93a, 93b are interchangedly supplied to terminals 100, 107 in FIG. 14 by using a changeover switch, the rotation of the motor is reversed. Consequently the current to be changed over can be small, and the reverse rotation of a semiconductor motor, which is generally difficult, can be easily effected by using a changeover switch.

Series-connected capacitor 114 and diode 105a are connected to the terminal 100 and the base of the transistor 104. Similarly, series-connected capacitor 115 and diode 115a are connected to the terminal 107 and to the base of the transistor 110. The effect of these capacitors 114, 115 and the diodes 105a, 115a is as follows. During the generation of the output signal of the graph shown in FIG. 12(b) with the rotation of the rotor 81 of FIG. 13, at a portion 87d where the output value changes from the maximum to the minimum, the output changes passing through a point the value at which is equal to that at the portion 87b. At the time of such output change, the transistors 103, 109 in FIG. 14 become temporarily conductive resulting in an erroneous position detection signal, and reverse torque is produced. Also, if the coils 82a, 92b happen to be on a portion D of the rotor 81 (FIG. 13) at the time of start of motor, signal of the medial value is generated and consequently a reverse torque is produced resulting in a vibration which make it difficult to start rotation. For such problems, capacitors 114, 115 in FIG. 14 are provided. The effect for FIG. 14(b) is the same as that for FIG. 14(a), and so explanation for FIG. 14(a) only will be given. Suppose the coils 82a, 82b are in the portion D (FIG. 13) at the time of start, medial value signal will be generated, but since the input power due to this signal makes the transistor 104 conductive through the diode 105a and capacitor 114, forward torque is produced to start rotation. At this time, the transistor 103 is kept non-conductive through diode 105b. During the rotation, when the coils 82a, 82b comes to the step 91a-2 of the rotor 81, medial value single input power is applied from the terminal 100, but, this input power does not make the transistor 104 conductive through the already charged capacitor 114 and only makes the transistor 103 conductive, and so there is no obstruction. If the coils 82a, 82b happen to be on the step 91a-2 of the rotor 81 at the time of start, the transistor 104 becomes temporarily conductive to produce reverse torque, but the transistor 104 rapidly becomes non-conductive with the capacitor 114 being charged, and the transistor 103 becomes conductive to make the motor start, and so there is no obstruction.

During the rotation of motor, medial value signal is generated when the coils 82a, 82b pass through the portion D of the rotor 81 of FIG. 13. At this time, the transistors 97b, 98b in FIG. 13 temporarily become conductive at the same time resulting in undesirable short-circuiting of the source. To avoid this inconvenience in FIG. 14(a), there is provided between the base of the transistor 104 and the negative source terminal 99-2 a capacitor 120 of small capacity to keep the transistor 104 conductive for a while in spite of extinction of input power at the base of the transistor 104 (through the diode 106) and to keep the transistor 103 non-conductive through the diode 105b. Thus, the transistor 103 is prevented from becoming non-conductive due to the temporary medial value signal generated when the coils 82a, 82b pass through the portion D of the rotor 81, and the above described inconvenience can be avoided. Similar means can be adopted also for the control circuit of FIG. 14(b). The capacitor 120 serves as a memory element which memorizes that the transistor 104 becomes conductive. Accordingly, other means such as SCR (silicon controlled rectifier) of small size or a flip-flop circuit, for example, can also be adopted.

In the embodiment of FIG. 13, there are two sets of coils, one set comprising the coils 93a, 93b, and another set comprising the coils 82a, 82b. However, by constucting a Colpitts circuit with two coils each selected from the above two sets respectively, making the oscillation coil larger in diameter, making the widths of the steps 91a-1, 91a-2, 91a-3 smaller, and making the diameter of the coil nearly equal to the width of the dotted portion (punched out portion), a similar position detection signal as shown in the graph of FIG. 12(b) can be generated. Thus, the desired object can also be attained by using one of the coils 82a, 82b and one of the coils 93a, 93b. While there are provided eight field magnet poles and six armature coils in the expanded view of FIG. 13, in the view of FIG. 15 there are provided three armature coils 122a, 122b, 122c, each having an angular width of 90° between both sides of the conductor, which angular width being equal to the angular width of magnetic poles 121a, 121b, 121c. Numeral 121 indicates a field magnet. In case of prior art three-phase armature coils, there is provided a coil indicated by dotted line 122-1. In the present invention, however, this coil 122-1 is shifted to the right to be coil 122c, and accordingly three coils are arranged on the armature without being superimposed on one another. Other similar numerals indicate like parts as in FIG. 13, and so the explanation about them is omitted here. In place of the transistors 97a, 97b, 97c, 98a, 98b, 98c in FIG. 13, there are provided SCRs (silicon controlled rectifiers) 123a, 123b, 123c and 124a, 124b, 124c which are connected to the positive and negative source terminals 99-1, 99-2 in the forward/reverse directions. Numerals 125a, 125b, 125c, and 126a, 126b, 126c indicate commutation capacitors. To the gates of the SCRs 123b, 123c, 123a, there are applied power obtained by commutating the output at the terminals 102a, 103a, 104a in FIG. 14 to positive pulse outputs through a differentiation circuit (not shown). To gates of SCRs 124c, 124a, 124b, there are applied power obtained by commutating the output at the terminals 109a, 113a, 111a to positive pulse outputs through a differentiation circuit (not shown). A rotor 130 in FIG. 15 is similar in construction to the rotor 81 in FIG. 13 except that the angular width of steps 130a, 130b, 130c and 131a, 131b, 131c which constitute the control band is 2/3 of the width of the field magnet poles 121a, 121b, . . . Since the control circuits of FIG. 14(a) and 14(b) are driven by the oscillation circuit containing the coils 82a, 82b and 93a, 93b, the armature coils 122a, 122b, 122c, with their current supply being controlled, rotate due to the Fleming force in the direction of the arrow C by the energizing of SCRs 123a, 123b, . . . Consequently, the rotor 130 rotates in the direction of arrow E synchronously with the armature and generates successive rotating torque. The performance and effect are the same as those in the case of FIG. 13.

Graphs of FIG. 16 show the voltage wave forms of position detection signals according to another embodiment used for the motor of FIG. 10. Portion 132a corresponds to the time when a soft steel plate comes close to a coil 134a (FIG. 17), and portion 132b when a soft steel plate is away from the coil 134a. The abscissa represents the rotation angle θ of the armature 57 (FIG. 10). Such a position detection signal is generated by a rotor 136 (a substitution for the rotor 81 in FIG. 10) of FIG. 17. The rotor 136 rotates together with the armature 57 to produce loss in an oscillation coil 134. The details will be explained referring to the expansion view of FIG. 17.

Dotted portions Stippled areas indicate punched out portions by punch press processing. Angular width of the portion indicated by numeral 137a-1 is 30°. Angular width of the portion indicated by numeral 137a-2 is 60°. The angular width of one portion indicated by numeral 137a-1 is one third of the angular width of a set of N-S magnetic poles of a field magnet. Coils 134a, 134b are arranged at an angular interval of 60°. When the coil 134a comes to face the portion 137a-2 with the rotation of the rotor 136 in the direction of arrow B, the signal output becomes extinct resulting in the portion 132a in the signal wave form of FIG. 16 line (a). When the coil 134a comes to face the portion 137a-1 with a further rotation of the rotor 136 in the direction of arrow B, signal output is generated resulting in the portion 132b in the a signal wave form of FIG. 16 line (a). Accordingly, with the rotation of the rotor 136 in the direction of arrow B, the signal wave form of FIG. 16 line (a) is obtained from an oscillation circuit containing the coil 134a. In the like manner, the signal wave form of FIG. 16 line (b) is obtained from an oscillation circuit containing the coil 134b. A signal wave form of FIG. 16 line (c) is obtained from an oscillation circuit containing a coil 134c. A signal wave form of FIG. 16 line (d) is obtained from an oscillation circuit containing a coil 134d. There is a phase difference of 60° between the signal wave form of FIG. 16 line (a) and the signal wave form of FIG. 16 line (b). Between the signal wave forms of FIG. 16(a) and FIG. 16(c), there is a phase difference of 45° which is equal to the width of the N-S magnetic poles of the field magnet. There is a phase difference of 45° between the signal wave forms of FIG. 16 line (b) and FIG. 16 line (d). The signal of the wave form of FIG. 16 line (a) is applied to a transistor 140a in FIG. 18, and the signal of wave form of FIG. 16 line (b) is applied to a transistor 140b in FIG. 18. Accordingly, as is apparent from FIG. 16, the transistors 140a, 140b become ON when the input signals take a high voltage. When either of the transistor 140a or 140b is ON, current which otherwise may flow toward the base of transistor 140c flows through the transistor 140a or 140b, and so the transistor 140c is OFF. When both transistors 140a and 140b are OFF, however, the transistor 140c becomes ON with its base being supplied with current through a resistor 142. That is, at the time when the signal of wave form of FIG. 16 line (a) takes high voltage the transistor 140a becomes ON, when the signal of wave form of FIG. 16 line (b) takes high voltage the transistor 140b becomes ON, and when both signals of wave forms of FIG. 16 lines (a) and (b) are not at high voltage the transistor 140c becomes ON. These are repeated in cyclic manner.

On the other hand, the signal of wave form of FIG. 16 line (c) is applied to a transistor 144a in FIG. 18, and the signal of wave form of FIG. 16 line (d) is applied to a transistor 144b in FIG. 18. Accordingly, as is apparent from FIG. 16, the transistors 144a, 144b become ON when the input signals are high voltage. When either of the transistors 144a or 144b is ON, current which otherwise may flow toward the base of transistor 144c flows to earth ground through transistor 144a or 144b, and so the transistor 144c is OFF. When both transistors 144a and 144b are OFF, however, the transistor 144c becomes ON with its base being supplied with current through a resistor 143.

That is, at the time when the signal of wave form of FIG. 16 line (c) takes high voltage the transistor 144a becomes ON, when the signal of wave form of FIG. 16 line (d) takes high voltage the transistor 144b becomes ON, and when both signals of wave forms of FIG. 16 lines (c) and (d) are not at high voltage the transistor 144c becomes ON. These are repeated in cyclic manner. When the transistor 144a is ON, a transistor 145a becomes ON. When the transistor 144b is ON, a transistor 145b becomes ON. When the transistor 144c is ON, a transistor 145c becomes ON. Accordingly, as the transistors 144a to 144c become conductive in turn in a cyclic manner, the transistors 145a to 145c also becomes conductive in turn in a cyclic manner.

Since the current flows in accordance with the principle described, there is a difference of 180° in electrical angle between the currents of transistors 145a and 140a. Similarly, there is a difference of 180° in electrical angle between the currents of the transistors 145b and 140b, and a difference of 180° in electrical angle between the currents of the transistors 145c and 140c. Armature coils 146, 147, 148 in FIG. 8 are of delta connection. Reverse rotation can be effected by shifting the phase of coil for position detection.

FIG. 19 illustrates the arrangement of the field magnet poles and the brushes in the motor of FIG. 1.

A ferrite magnet 150, as shown in the figure, consists of N and S magnetic poles 150-1, 150-2, . . . , each having an angular width of 90°, constituting field magnet poles.

In a center aperture of the field magnet 150, there is rotatably provided a cylindrical plastic molding member 151 (constituting a support for brushes 153-1, 153-2). The brushes 153-1, 153-2 slidably contact with a commutator 152.

A noise filter and a method of arrangement thereof according to the invention will be described hereinbelow. As can be understood from the view of FIG. 3, the amount of current flow and the direction thereof in the armature coils 21, 22, 23 change with the rotation of the rotor. Inductance is small because the coils are coreless. But, high voltage generated when accumulated energy is discharged due to the above described changes in the current may cause electrical noise and damage of the commutator and brushes. Such high voltage can be prevented by conventional means such as capacitors and varistors connected in parallel to respective armature coils. But, in prior art motors, especially in motors of the flat type and small size comprising well known lap windings or wave windings, there is no space for receiving them in the motor. In the motor according to the invention, however, there are empty cavities at the center portions of the armature coils 21, 22, 23, wherein there can be embedded elements such as capacitors or varistors as shown by numerals 24, 25, 26 in FIG. 20. These elements 24, 25, 26 are connected in parallel to the armature coils 21, 22, 23 respectively.

FIG. 20 illustrates in detail such armature as mentioned above. Referring to FIG. 20(a), an armature 160 is of disc shape and has three armature coils embedded therein by molding as shown in FIG. 20(b). The peripheral portion 160a of the disc projects a little from the disc plane. By embedding a ring of the die-casting in this periphery portion during the formation thereof, larger inertia can be obtained, which is effective for reducing torque ripple in the motor of the invention which is designed for a magnetic recording/reproducing apparatus application. Further, balancing can be easily effected by providing holes in the die-casting ring. In a conventional motor of axial air gap type, it is difficult to provide additional material for rotation balance since the air gap is limited. In the motor of the invention which is provided with the projection as indicated by numeral 160a, however, it is easy to effect balance by cutting away a part of the projection or by adding other material thereto. Brushes 161, 162, with their roots fixedly secured to a plastic ring 163, are provided at an angular interval of 90°. The brushes 161, 162 are received in the central cavity of the magnet, which contributes to make the motor flat and smaller in size.

As shown in FIG. 20(b), the armature coils are of sectorial shapes and are not superimposed with respect to one another. Each of armature coils 166, 167, 168 is of the same shape, and the angular width thereof effective to torque is 90°, being equal to the width of the field magnet pole. The armature coils can be mass-produced by hoop-winding thin wire about 200 turns and heat treating to rigidify. The armature coils are about 1 mm in thickness, and accordingly the armature 160 is of similar thickness. Consequently the air gap where the field magnet exists can be designed small resulting in high efficiency. The armature coils 166, 167, 168 are arranged at angular intervals of 120°.

FIG. 21 illustrates reversing means for the above described commutator motor. Conventional commutator motors can be reversed in rotation by changeovering the polarities of applied voltage, but have drawbacks that the motor is large in size and expensive because of a large number of circuits for changeover switch means and that contact troubles may often occur. In the motor of the invention, reverse rotation can be easily effected by rotating the brushes 9 in FIG. 1 by 90° in case of the construction of FIG. 5, so that the motor is subjected to a Fleming force under reversed magnetic field. Thus, the drawbacks in the prior art are eliminated. This is illustrated in FIG. 21. Here, the brushes in FIG. 1 are rotated by 90°. FIG. 21 is the back view of the motor of FIG. 1. In the casing 3 there is provided an arc-shaped perforation 194 through which protrudes outward the lower end projection 7-1 of the cylinder 7 that is the brush support (FIG. 1). The projection 7-1 is elastically biased by a spring 193 rotated counterclockwise to abut against the left end of the perforation 194. A lever 191 is slidably supported by supports 191-1, 191-2 provided on the casing 3. When used as a capstan motor in a magnetic recording/reproducing apparatus for example, reverse rotation of the motor is needed for return winding operation. A mechanism for return winding is indicated by numeral 192. The lever 191 is so provided as to be moved in the direction of arrow E in connection with the operation of the mechanism 192. Accordingly, with a directive of return winding, the projection 7-1 which has been in abutment with a portion 191a rotates by 90° along the arc of the perforation 194, and the reverse rotation of the motor is effected. When the mechanism 192 comes back to the original position, the lever 191 comes back to its original position by the biasing force of the spring 193, and the motor rotates in the forward direction again. In place of the lever 191, a nylon thread connected to the projection 7-1 can be used to carry out the above described operation.

As is apparent from the above description, according to the manner of arrangement of armature coils of the invention, the thickness of armature can be several times less than the thickness of prior art coil-type armature, without need of any special processing of winding ends of coils. Accordingly, the air gap between the field magnet and the armature can be smaller, and the strength of the magnetic field can be much larger, and consequently a motor having higher starting torque and higher efficiency can be realized. Further, by making the armature current flow region 2/3 of the width of field magnet pole, higher efficiency can be obtained. Further, since the armature for a disc- or cup-type motor is coreless, there is no loss due to eddy current and hysteresis and inductance is small, and consequently better rectifying characteristic can be obtained. Further, the inertia of the armature is small and the weight of the body is extremely small, and consequently higher efficiency can be obtained. Also, in the armature according to the invention, the armature coils which rotate against the field magnet poles are not superimposed with respect to one another and at equal intervals, and there is no mixing-in of reverse torque which may take place in a conventional three-phase motor of axial air gap type (disc type), and consequently high efficiency (50% or more) can be maintained. Accordingly, the armature is easy to mass produce resulting in a lower cost of motor. Further, the armature coils constituting three-phase armature coils have an angular width equal to the width of the field magnet pole and are arranged at equal intervals, and consequently there is an ample empty space in the central portion of each of the coils. This empty space can receive a capacitor or a varistor, and reduction of electrical noise as well as smaller inductance in in the armature coil can be effected, and the duration of the commutator and brushes can be increased.

It is to be understood that various changes and modifications can be made without departing from the spirit and scope of the invention.

Claims

1. In a coreless dc motor comprising a fixed field magnet (27, 121) having four magnetic poles of N and S magnetized in equal angular widths; a magnetic material (2, 3, 12, 16, 70, 75-1) for closing magnetic paths of said field magnet; a rotating shaft (1, 15, 73) supported by bearings provided to a central portion of said magnetic material; an armature (5, 10, 57) of one of disc- and cylindrical-shapes secured to said rotating shaft so as to be rotatable in said magnetic paths to face against said field magnet poles; three-phase armature coils of lap winding arranged on said armature; and electric circuit means interconnecting said three-phase armature coils in a manner selected from the class consisting of delta-connection and Y-connection for supplying current to said coils, the improvement wherein: said three-phase armature coils comprise three windings (21, 22, 23, 122a-c) each arranged at equal angular interval so as to be non-superimposed with respect to one another on the armature by shifting the coil (23a, 122-1) of one-phase by 180°; each of said coils having an angular width equal to that of said field magnet pole.

2. A motor as set forth in claim 1 comprising:

(a) commutator means secured to said three-phase armature coil means and to said rotating shaft including positive and negative terminals;

(b) two brushes slidably contacting to said commutator means at an angular interval equal to the width of said field magnet pole, said two brushes being supplied with current from said positive and negative terminals;

(c) first to ninth commutator pieces arranged on said commutator means at angular intervals of 2/3 of the width of said field magnet poles;

(d) conductor means for interconnections of a first group consisting of said first, fourth and seventh commutator pieces, of a second group consisting of said second, fifth and eighth commutator pieces, and of a third group consisting of said third, sixth and ninth commutator pieces; and,

(e) terminal means for supplying said three-phase armature coil means with current through said three groups of commutator pieces.

3. A motor as set forth in claim 1 comprising:

(a) a current supply control circuit including slip rings, semiconductor switching elements and source terminals, having three lead wires led out from the three connection points of said three-phase armature coil means through three slip rings, each of said three lead wires being connected to two semiconductor switching elements in the forward/reverse directions, said semiconductor elements being connected in the forward direction to positive and negative source terminals respectively;

(b) a control rotor synchronously rotating with said armature;

(c) control band means provided on the periphery of said rotor, said control band means having a plurality of steps effecting different eddy current losses, the width of each said steps being two-thirds of the width of said field magnet poles;

(d) a first oscillation circuit containing a first oscillation coil provided against said control band means;

(e) a second oscillation circuit containing a second oscillation coil provided at a predetermined distance from said first oscillation coil;

(f) an electric circuit for generating three detection outputs of a first position through the output of said first oscillation circuit in accordance with said steps of said control band means; an electric circuit for generating three detection outputs of a second position through the output of said second oscillation circuit in accordance with said steps of said control band means; and,

(g) a control circuit means for energizing through said three detection outputs of said first position said semiconductor switching elements connected to said positive source terminal respectively and for energizing through said three detection outputs of said second position said semi-conductor switching elements connected to said negative source terminal respectively.

4. A motor as set forth in claim 1 with positive and negative source sides having:

(a) two series of position detection means comprising two groups of position detection elements for a first position; two groups of position detection elements for a second position which elements being shifted in phase by an amount corresponding to the width of said field magnet poles with respect to respective position detection signals of said groups of position detection elements for said first position;

(b) three groups of semiconductor switching elements connected in series between said coils and the positive side source;

(c) three groups of semiconductor switching elements connected in series between said armature coils and the negative side source; and,

(d) a logic circuit containing a position detection device for energizing said semiconductor switching elements so as to changeover the current toward each of said armature coils at intervals of about two-thirds of the width of said field magnet pole.

5. A motor as set forth in claim 1 wherein said coils and said field magnets have a space therein, three elements for absorbing magnetic energy accumulated in said armature coils, said three elements being disposed in the space inside said three armature coils and connected in parallel across the corresponding armature coils; a commutator consisting of six commutator pieces and secured to said rotating shaft; and two sets of brushes slidably contacting with said commutator, said sets of brushes being disposed in the space in said field magnet and separated at an angular interval of 90°.

6. In a coreless dc motor comprising a fixed field magnet (27, 121) having eight magnetic poles of N and S magnetized in equal angular widths; a magnetic material (2, 3, 12, 16, 70, 75-1) for closing magnetic paths of said field magnet; a rotating shaft (1, 15, 73) supported by bearings provided to a central portion of said magnetic material, an armature (5, 10, 40, 57) of one of disc- and cylindrical-shapes secured to said rotating shaft so as to be rotatable in said magnetic paths to face against said field magnet poles; three phase armature coils of lap winding arranged on said armature; and electric circuit means interconnecting said three-phase armature coils in a manner selected from the class consisting of delta-connection and Y-connection for supplying current to said coils, the improvement wherein: said three-phase armature coils comprise six windings (35-1 to 35-6, 95a-f) each arranged at equal angular interval so as to be non-superimposed with respect to one another on the armature by shifting the in-phase coils (95-1) of one-phase by 90°; each of said coils having an angular width equal to that of said field magnet pole.

7. A motor as set forth in claim 6 comprising:

(a) commutator means secured to said three-phase armature coil means and to said rotating shaft including positive and negative terminals;

(b) two brushes slidably contacting to said commutator means at an angular interval equal to the width of said field magnet pole, said two brushes being supplied with current from said positive and negative terminals;

(c) first to a ninth commutator pieces arranged on said commutator means at angular intervals of two-thirds of the width of said field magnet poles;

(d) conductor means for interconnections of a first group consisting of said first, fourth and seventh commutator pieces, of a second group consisting of said second, fifth and eighth commutator pieces, and of a third group consisting of said third, sixth and ninth commutator pieces; and,

(e) terminal means for supplying said three-phase armature coil means with current through said three groups of commutator pieces.

8. A motor as set forth in claim 6 comprising:

(a) a current supply control circuit including slip rings, semiconductor switching elements and source terminals, having three lead wires led out from the three connection points of said three-phase armature coil means through three slip rings, each of said three lead wires being connected to two semiconductor switching elements in the forward/reverse directions, said semiconductor elements being connected in the forward direction to positive and negative source terminals respectively;

(b) a control rotor synchronously rotating with said armature;

(c) control band means provided on the periphery of said rotor, said control band means having a plurality of steps effecting different eddy current losses, the width of each of said steps being two-thirds of the width of said field magnet poles;

(d) a first oscillation circuit containing a first oscillation coil provided against said control band means;

(e) a second oscillation circuit containing a second oscillation coil provided at a predetermined distance from said first oscillation coil;

(f) an electric circuit for generating three detection outputs of a first position through the output of said first oscillation circuit in accordance with said steps of said control band means; an electric circuit for generating three detection outputs of a second position through the output of said second oscillation circuit in accordance with said steps of said control band means; and,

(g) a control circuit means for energizing through said three detection outputs of said first position said semiconductor switching elements connected to said positive source terminal respectively and for energizing through said three detection outputs of said second position said semiconductor switching elements connected to said negative source terminal respectively.

9. A motor as set forth in claim 6 with positive and negative source sides having two series of position detection means comprising two groups of position detection elements for a first position; two groups of position detection elements for a second position which elements being shifted in phase by an amount corresponding to the width of said field magnet poles with respect to respective position detection signals of said groups of position detection elements for said first position;

(b) three groups of semiconductor switching elements connected in series between said coils and the positive side source;

(c) three groups of semiconductor switching elements connected in series between said armature coils and the negative side source; and,

(d) a logic circuit containing a position detection device for energizing said semiconductor switching elements so as to changeover the current toward each of said armature coils at intervals of about two-thirds of the width of said field magnet pole.

10. A motor as set forth in claim 6 wherein said coils and said field magnets have a space therein, three elements for absorbing magnetic energy accumulated in said armature coils, said three elements being disposed in the space inside said three armature coils and connected in parallel across the corresponding armature coils; a commutator consisting of six commutator pieces and secured to said rotating shaft; and two sets of brushes slidably contacting with said commutator, said sets of brushes being disposed in the space in said field magnet and separated at an angular interval of 90°.

11. In a coreless d.C. motor comprising a field magnet having a plurality of magnetic poles of N and S magnetized in equal angular widths the number of said plurality of magnetic poles being equal to 2n where n is an even integer; a magnetic material for closing magnetic paths of said field magnet; an armature of one of disc- and cylindrical-shapes so as to face against said field magnet poles; a rotating shaft supported by bearings provided at a central portion of said magnetic material one of said field magnet and said armature being secured to said shaft; three-phase armature coils of one of lap and wave winding arranged on said armature; and electric circuit means interconnecting said three-phase armature coils in a manner selected from the class consisting of delta-connection and Y-connection for supplying current to said coils, the improvement wherein: said three-phase armature coils comprise a plurality of windings related in number to the number of said magnetic poles so that the number of windings is equal to 3n/2, each of said coils being arranged to an equal angular interval so as to be non-superimposed with respect to one another on the armature; each of said coils having an angular width equal to that of one of said field magnet poles. 12. In a coreless d.C. motor comprising a field magnet having four magnetic poles of N and S magnetized in equal angular widths; a magnetic material for closing magnetic paths of said field magnet; an armature of one of disc- and cylindrical-shapes so as to face against said field magnet poles; a rotating shaft supported by bearings provided at a central portion of said magnetic material, one of said field magnet and said armature being secured to said shaft; three-phase armature coils of one of lap and wave winding arranged on said armature; and electric circuit means interconnecting said three-phase armature coils in a manner selected from the class consisting of delta-connection and Y-connection for supplying current to said coils, the improvement wherein: said three-phase armature coils comprise three windings each arranged at an equal angular interval so as to be non-superimposed with respect to one another on the armature by shifting the coil of one-phase by 180°; each of said coils having an angular width equal to that of one of said field magnet poles. 13. In a coreless d.C. motor comprising a field magnet having eight magnetic poles of N and S magnetized in equal angular widths; a magnetic material for closing magnetic paths of said field magnet; an armature of one of disc- and cylindrical-shapes so as to face against said field magnet poles; a rotating shaft supported by bearings provided at a central portion of said magnetic material one of said field magnet and said armature being secured to said shaft; three-phase armature coils of one of lap and wave winding arranged on said armature; and electric circuit means interconnecting said three-phase armature coils in a manner selected from the class consisting of delta-connection and Y-connection for supplying current to said coils, the improvement wherein: said three-phase armature coils comprise six windings each arranged at an equal angular interval so as to be non-superimposed with respect to one another on the armature by shifting the in-phase coils of one-phase by 90°; each of said coils having an angular width equal to that of one of said

field magnet poles. 14. An armature for a coreless d.C. motor comprising a field magnet having four magnetic poles of N and S magnetized in equal angular widths, said armature being of one of disc- and cylindrical-shapes so as to face against said field magnet poles and having three-phase armature coils of one of lap and wave winding arranged on said armature, the improvement wherein: said three-phase armature coils comprise three windings each arranged at an equal angular interval so as to be non-superimposed with respect to one another on the armature by shifting the coil of one-phase by 180°; each of said coils having an angular width equal to that of one of said field magnet poles. 15. An armature for a coreless d.C. motor comprising a field magnet having eight magnetic poles of N and S magnetized in equal angular widths, said armature being of one of disc- and cylindrical-shapes so as to face against said field magnet poles and having three-phase armature coils of one of lap and wave winding arranged on said armature, the improvement wherein: said three-phase armature coils comprise six windings each arranged at an equal angular interval so as to be non-superimposed with respect to one another on the armature by shifting the in-phase coils of one-phase by 90°; each of said coils having an angular width equal to that of one of said field magnet poles.