ROTATING ELECTRIC MOTOR

Abstract: A rotating electric motor has a permanent magnet member of a circular form and an armature core made of a magnetic material. The permanent magnet member has a plurality of N and S poles positioned alternately around the rotary shaft of the motor, and the number of the poles is P which is an even number. The armature core has a plurality of teeth formed between two adjacent winding slots of the armature core, and the number of the teeth is T which is an integer not less than 2P. Overlapping winding coils of polyphase winding groups are wound in the winding slots of the armature core, and the number of the phases of the polyphase winding groups is H which is an integer not less than 2. The armature core has at least a pair of shot-block and long-bock, each of which is a group of the teeth having at least one tooth and positioned sequentially. Each short-­ block has at least one short-tooth and no long-tooth, and each long-block has at least one long-tooth and no short-­ tooth, where the effective pitch of each short-tooth is smaller than D=(360/T) degree and the effective pitch of each long-tooth is larger than D. Because of this arrangement, the phases of the winding slots of the armature core with the period of 1 pole pitch of the permanent magnet member are different from each other, and the cogging torque of the rotating electric motor is small. Preferably, dummy-slot portions are provided at least on the faces of the long-teeth of the armature core.

Description: Field of the Invention This invention relates to a rotating electric motor, and more particularly to a rotating electric motor comprising an armature core made of magnetic material having a plurality of teeth and a plurality of overlapping winding coils of polyphase winding groups, and a field permanent magnet member which is polarized to have a plurality of alternating N and S poles and opposed to said teeth of the armature core, the number of the N and S poles being P which is an even number, and the number of the teeth being T which is not less than 2P. Description of the Prior Art A rotating electric motor comprising an armature core of magnetic material having a plurality of teeth and a field permanent magnet member having magnetized poles opposed to the teeth is widely used as it has high efficiency. But, the conventional rotating electric motor has such a problem that a harmful vibration occurs owing to an intense cogging torque generated by the interaction between the magnetized poles of the permanent magnet and the teeth of the armature core. This cogging torque prevents smooth rotation of the rotating electric motor. In order to reduce the cogging torque, a skewed armature core is used in some cases. But, it is difficult to make the skewed armature core, and the cogging torque is not reduced enough sometimes by the skewed armature core. Use of an armature core having no tooth for getting smooth rotation is impractical because of its low efficiency which necessitates a large size of motor. A construction of a rotating electric motor with reduced cogging torque is disclosed in the United States Patent 4,280,072 or the Japanese Laid-open Patent Application 55-71163. In these patent specifications, indented portions are used to reduce the cogging torque. This method is remarkably effective in such case that the number T of the teeth is smaller than the double of the number P of the N and S poles, that is T < 2P, such as the rotating electric motors shown in Figure 1, Figure 5 and Figure 6 in USP 4,280,072, since the face of each of the teeth is wide enough to provide a number of indented portions. But, the cogging torque of a rotating electric motor such as shown in Figure 8 in USP 4,280,072, in which T is not less than 2P, is not sufficiently reduced by the above method (the same rotating electric motor is disclosed in the Japanese Laid-open Patent Application 55-71163). The conventional rotating electric motors are described hereinbelow. Figure 1 is a schematic sectional view of a conventional rotating electric motor with T = 6P. In Figure 1, a cylindrical permanent magnet 3 is fixed to the outer circumference of a rotor 2 made of magnetic material, and the permanent magnet 3 rotates with the rotor 2 around a rotary shaft 1. The permanent magnet 3 has 4 poles of alternating N and S poles positioned at intervals of an equal angle of 90 degrees, that is, P = 4. The teeth 6 of an armature core 4, each of which is formed between two adjacent winding slots 5, are faced to the poles of the permanent magnet 3. The rotary shaft 1 of the rotor 2 is rotatably supported by the armature core 4. Therefore, the relative position between the teeth 6 of the armature core 4 and the poles of the permanent magnet 3 changes according to the rotation of the rotor 2. Figure 2 shows a development view of the conventional motor of Figure 1 developed at the lines X-X' and Y-Y', when these lines are in a line. The armature core 4 has 24 winding slots a to x at intervals of an equal angle of 15 degrees, and 24 teeth are provided between two adjacent winding slots, that is, T = 24. Overlapping winding coils A1, A2, A3, A4, B1, B2, B3, B4, C1, C2, C3 and C4 are wound in the winding slots a to x. Each of the winding coils A1 to C4 encircles 5 teeth of the armature core 4. That is, A1 is wound in the winding slots a and f, A2 is wound in the winding slots g and 1, A3 is wound in the winding slots m and r, A4 is wound in the winding slots s and x, B1 is wound in the winding slots e and j, B2 is wound in the winding slots k and p, B3 is wound in the winding slots q and v, B4 is wound in the winding slots w and d, C1 is wound in the winding slots i and n, C2 is wound in the winding slots o and t, C3 is wound in the winding slots u and b, and C4 is wound in the winding slots c and h. The winding coils A1, A2, A3 and A4 are connected in series to form a winding group A of the first phase, the winding coils B1, B2, B3 and B4 are connected in series to form a winding group B of the second phase, and the winding coils C1, C2, C3 and C4 are connected in series to form a winding group C of the third phase. The phase difference among the winding groups A, B and C is equal to 120el (electrical degree), where 180el is equivalent to 1 pole pitch of (360/P) degree of the permanent magnet 3. In Figure 1, P = 4, then 180el is equivalent to 90 degrees (mechanical degree). Therefore, a torque accelerating the rotor 2 is obtained by supplying three phase currents to the three phase winding groups A, B and C. Figure 3 is a schematic sectional view of another conventional rotating electric motor with T = 3P. The structure of the conventional motor shown in Figure 3 is the same as that of the conventional motor shown in Figure 1, except the relation between T and P, and the winding pitch. A cylindrical permanent magnet 13 is fixed to the outer circumference of a rotor 12 made of magnetic material, and the permanent magnet 13 rotates with the rotor 12 around a rotary shaft 11. The permanent magnet 13 has 4 poles of alternating N and S poles positioned by an equal angle of 90 degrees, that is, P = 4. The teeth 16 of an armature core 14, each of which is formed between two adjacent winding slots 15, are faced to the poles of the permanent magnet 13. The rotary shaft 11 of the rotor 12 is rotatably supported by the armature core 14. Therefore, the relative position between the teeth 16 of the armature core 14 and the poles of the permanent magnet 13 changes according to the rotation of the rotor 12. Figure 4 shows a development view of the conventional motor of Figure 3 developed at the lines X-X' and Y-Y', when these lines are in a line. The armature core 14 has 12 winding slots a to 1 at intervals of an equal angle of 30 degrees, and 12 teeth are provided between two adjacent winding slots, that is, T = 12. Overlapping winding coils A1, A2, A3, A4, B1, B2, B3, B4, C1, C2, C3 and C4 are wound in the winding slots a to 1. Each of the winding coils A1 to C4 encircles 3 of the teeth of the armature core 14. That is, A1 is wound in the winding slots a and d, A2 is wound in the winding slots d and g, A3 is wound in the winding slots g and j, A4 is wound in the winding slots j and a, B1 is wound in the winding slots c and f, B2 is wound in the winding slots f and i, B3 is wound in the winding slots i and 1, B4 is wound in the winding slots 1 and c, C1 is wound in the winding slots e and h, C2 is wound in the winding slots h and k, C3 is wound in the winding slots k and b, and C4 is wound in the winding slots b and e. The winding coils A1, A2, A3 and A4 are connected in series to form a winding group A of the first phase, the winding coils B1, B2, B3 and B4 are connected in series to form a winding group B of the second phase, and the winding coils C1, C2, C3 and C4 are connected in series to form a winding group C of the third phase. The phase difference among the winding groups A, B and C is equal to 120el. In Figure 3, P = 4, then 180el is equivalent to 90 degrees (mechanical degree). Therefore, a torque accelerating the rotor 2 is obtained by supplying three phase currents to the three phase winding groups A, B and C. An electrical machine with an apparatus for minimizing magnetic cogging is disclosed in US-A- 4424 463, where the stator is divided into pairs of angular pie-shaped segments, the number P of poles being 36. SUMMARY OF THE INVENTION An object of the present invention is to provide a noble and improved rotating electric motor of high efficiency with reduced cogging torque. Another object of the present invention is to provide a rotating electric motor comprising an armature core of magnetic material having T teeth and a field permanent magnet member having P permanently magnetized N and S poles, where T is not less than 2P, and having reduced cogging torque which is related to the geometry of the armature core and the magnet. These objects of the invention are achieved by providing a rotating electric motor according to the invention, which comprises: a field permanent magnet member of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft of said electric motor, the number of said N and S poles being P which is an even number; and an armature core made of magnetic material having a plurality of teeth made between two adjacent winding slots where a plurality of overlapping winding coils of polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2; wherein said armature core has at least a pair of short-block and long-block alternately positioned around said rotary shaft. Each short-block has at least two short-teeth and no long-tooth, and each long-block has at least one long-tooth and no short-tooth. The effective pitch of each short-tooth is smaller than D = (360/T) degree, and the effective pitch of each long-tooth is larger than D. The above objects of the invention are achieved also by providing a rotating electric motor according to the invention, which comprises: a field permanent magnet member of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft of said electric motor, the number of said N and S poles being P which is an even number; and an armature core made of magnetic material having a plurality of teeth made between two adjacent winding slots where a plurality of overlapping winding coils of polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2; wherein said armature core has at least a pair of short-block and long-block alternately positioned around said rotary shaft. Each short-block has at least one short-tooth and no long-tooth, and each long-block has at least two long-teeth and no short-tooth. The effective pitch of each short-tooth is smaller than D = (360/T) degree, and the effective pitch of each long-tooth is larger than D. The above objects of the invention are achieved also by providing a rotating electric motor according to the invention, which comprises: a field permanent magnet member of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft of said electric motor, the number of said N and S poles being P which is an even number; and an armature core made of magnetic material having a plurality of teeth made between two adjacent winding slots where a plurality of overlapping winding coils of polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2; wherein said armature core has at least one short-tooth and at least one long-tooth. The effective pitch of each short-tooth is smaller than D = (360/T) degree, and the effective pitch of each long-tooth is larger than D. The whole effective pitch of sequential L teeth of said armature core is equal or almost equal to (360/P)Q degree, where L is an integer larger than H and Q is an integer not less than 2. The ratio of the smallest value of the effective pitches of the teeth to the effective pitch of the m-th tooth in said sequential L teeth is R:R+Vm, where R is an integer not less than 1 and Vm is an integer including 0, and the sum of Vm from m+1 to m=L is W which is not equal to an integral multiple of Qd, where Qd is a divisor of Q and larger than 1. The above objects of the invention are achieved also by providing a rotating electric motor according to the invention, which comprises a field permanent magnet member of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft of said electric motor, the number of said N and S poles being which is an even number; and an armature core made of magnetic material having a plurality of teeth made between two adjacent winding slots where a plurality of overlapping winding coils of the polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2; wherein at least one of said teeth has at least one dummy-slot portion, and said armature core has at least first and second slot-groups. The dummy-slot portions and the winding slots in said first slot-group are positioned at equal or almost equal angles by a first pitch, and the dummy-slot portions and the winding slots in said second slot-group are positioned at an equal or almost equal angle by the first pitch. A second pitch between adjacent winding slots of said first slot-group and said second slot-group is not equal to an integral multiple of said first pitch. A precise definition of the present invention is given in the claims. The above and other objects and features of the invention will be apparent from consideration of the following detailed description taken in connection with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic sectional view of a conventional rotating electric motor with T = 6P; Figure 2 is a development view of the conventional rotating electric motor of Figure 1 developed at the lines X-X' and Y-Y'; Figure 3 is a schematic sectional view of another conventional rotating electric motor with T = 3P; Figure 4 is a development view of the conventional rotating electric motor of Figure 3 developed at the lines X-X' and Y-Y'; Figure 5 is a schematic sectional view of an embodiment of the rotating electric motor of the invention with T = 6P; Figure 6 is a diagram showing a distribution of the magnetic flux density of the permanent magnet shown in Figure 5; Figure 7 is a development view of the rotating electric motor of Figure 5 developed at the lines X-X' and Y-Y'; Figure 8 is a block diagram of an electronic distributor for the rotating electric motor shown in Figure 5; Figures 9(a) - (c) are waveform diagrams of three phase currents I1, I2 and I3 supplied to three phase winding groups of the rotating electric motor shown in Figure 5; Figure 10 is a phase diagram of the winding slots and the dummy-slot portions of the armature core with the period of the 1 pole pitch of the permanent magnet about the rotating electric motor of the invention shown in Figure 5 and Figure 7; Figure 11 is a diagram showing a composite magnetic variation of the rotating electric motor of the invention shown in Figure 5 and Figure 7; Figure 12 is a diagram showing a composite magnetic variation of the conventional rotating electric motor shown in Figure 1 and Figure 2; Figure 13 is a schematic sectional view of another embodiment of the rotating electric motor of the invention with T = 3P; Figure 14 is a development view of the rotating electric motor of Figure 13 developed at the lines X-X' and Y-Y'; Figure 15 is a phase diagram of the winding slots and the dummy-slot portions of the armature core with the period of the 1 pole pitch of the permanent magnet about the rotating electric motor of the invention shown in Figure 13 and Figure 14; Figure 16 is a diagram showing a composite magnetic variation of the rotating electric motor of the invention shorn in Figure 13 and Figure 14; Figure 17 is a diagram showing a composite magnetic variation of the conventional rotating electric motor shown in Figure 3 and Figure 4; Figure 18 is a schematic sectional view of still another embodiment of the rotating electric motor of the invention with T = 3P; Figure 19 is a development view of the rotating electric motor of Figure 18 developed at the lines X-X' and Y-Y'; Figure 20 is a phase diagram of the winding slots and the dummy-slot portions of the armature core with the period of the 1 pole pitch of the permanent magnet about the rotating electric motor of the invention shown in Figure 18 and Figure 19; and Figure 21 is a diagram showing a composite magnetic variation of the rotating electric motor of the invention shown in Figure 18 and Figure 19. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment of the Invention with T = 6P Figure 5 shows a schematic sectional view of an embodiment of a brushless DC motor of the invention with T = 6P, which corresponds to the conventional rotating electric motor shown in Figure 1 and Figure 2. In Figure 5, a cylindrical permanent magnet 23 is fixed to the outer circumference of a rotor 22 made of magnetic material, and the permanent magnet 23 rotates with the rotor 22 around a rotary shaft 21. The permanent magnet 23 has 4 poles of alternating N and S poles positioned at intervals of an equal angle of 90 degrees, that is, P = 4, where P is the number of the poles of the permanent magnet 23. Figure 6 shows a distribution of the magnetic flux density of the permanent magnet 23. The teeth 26 of an armature core 24, each of which is formed between two adjacent winding slots 25, are faced to the poles of the permanent magnet 23. The rotary shaft 21 of the rotor 22 is rotatably supported by the armature core 24. Therefore, the relative position between the teeth 26 of the armature core 24 and the poles of the permanent magnet 23 changes according to the rotation of the rotor 22. Figure 7 shows a development view of the brushless DC motor of Figure 5 developed at the lines X-X' and Y-Y', when these lines are in a line. The armature core 24 has 24 winding slots a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w and x, and 24 teeth are provided between two adjacent winding slots, that is, T = 24, where T is the number of the teeth of the armature core 24. The armature core 24 also has 3 dummy-slot portions a', b' and c' at the faces of some of the teeth opposed to the permanent magnet 23, and no coils are wound in the dummy-slot portions. Overlapping winding coils A1, A2, A3, A4, B1, B2, B3, B4, C1, C2, C3 and C4 are wound in the winding slots a to x. Each of the winding coils A1 to C4 encircles 5 teeth of the armature core 24. That is, A1 is wound in the winding slots a and f. A2 is wound in the winding slots g and 1, A3 is wound in the winding slots m and r, A4 is wound in the winding slots s and x, B1 is wound in the winding slots e and j, B2 is wound in the winding slots k and p, B3 is wound in the winding slots q and v, B4 is wound in the winding slots w and d, C1 is wound in the winding slots i and n, C2 is wound in the winding slots o and t, C3 is wound in the winding slots u and b, and C4 is wound in the winding slots c and h. The winding coils A1, A2, A3 and A4 are connected in series to form a winding group A of the first phase, the winding coils B1, B2, B3 and B4 are connected in series to form a winding group B of the second phase, and the winding coils C1, C2, C3 and C4 are connected in series to form a winding group C of the third phase. As will be described later, the phase differences among the winding groups A, B and C are exactly equal to 120el (electrical degree), where 180el is equivalent to 1 pole pitch of (360/P) degree. In Figure 5, P = 4, then 180el is equivalent to 90 degrees (mechanical degree), which is the same as that of the conventional motor of Figure 1. Therefore, a torque accelerating the rotor 22 is obtained by supplying three phase currents to the three phase winding groups A, B and C. Figure 8 shows an electronic distributor 30 for the brushless DC motor of the invention. The electronic distributor 30 has a driver 31 and a position detector 32, and supplies to the star-connected three phase winding groups A, B and C with three phase currents I1, I2 and I3, respectively. The position detector 32 detects the relative position between the armature core 24 and the permanent magnet 23, and it outputs three phase sinusoidal signal P1, P2 and P3 which change with the rotation of the rotor 22 by detecting the magnetic flux of the permanent magnet 23. The driver 31 outputs the three phase currents I1, I2 and I3, which are proportional to a command signal F multiplied by the output signals P1, P2 and P3, respectively. Thus, a torque for accelerating the rotor 22 is generated by the interaction between the magnetic flux of the permanent magnet 23 and the three phase currents I1, I2 and I3 to the winding groups A, B and C. The electromagnetic torque by the three phase currents will be described later in detail. In Figure 7, since the winding slots a to x are positioned at intervals of unequal angles, the effective pitches of the teeth are not the same, where the "effective pitch" of a tooth is defined as the angle between the centres of the adjacent winding slots forming the tooth. In the case of T = 6P = 24 (P = 4), the standard effective pitch is D = (360/T) = 15 degree when all of the winding slots are positioned at intervals of an equal angle. So, a tooth having the effective pitch smaller than D is called a "short-tooth", and a tooth having the effective pitch larger than D is called a "long-tooth" in the specification. And a tooth is designated by the adjacent winding slots forming the tooth. For example, the tooth a-b means the tooth formed by the winding slots a and b. In Figure 7, the teeth a-b, b-c, c-d, d-e, e-f, f-g, g-h, i-j, j-k, k-l, l-m, m-n, n-o, o-p, q-r, r-s, s-t, t-u, u-v, v-w and w-x are short-teeth, and the teeth h-i, p-q and x-a are long-teeth. A block having at least one short-tooth and no long-tooth positioned sequentially is called a "short-block", and a block having at least one long-tooth and no short-tooth positioned sequentially is called a "long-block" in the specification. And a block is designated by the winding slots positioned at the both sides of the block. For example, the block < a,h> means the block of the teeth a-b, b-c, c-d, d-e, e-f, f-g and g-h. In Figure 7, there are three short-blocks < a,h> , < i,p> and < q,x> that are the short-block of the teeth a-b, b-c, c-d, d-e, e-f, f-g and g-h, the short-block of the teeth i-j, j-k, k-l, l-m, m-n, n-o and o-p, and the short-block of the teeth q-r, r-s, s-t, t-u, u-v, v-w, respectively. And there are three long-blocks < h,i> < p,q> and < x,a> that are the long-block of the tooth h-i, the long-block of the tooth p-q, and the long-block of the tooth x-a, respectively. Notice that it is not the number of the teeth to classify the block but the nature of the teeth including. Each of the short blocks < a,h> , < i,p> and < q,x> has 7 short-teeth, and each of the long-blocks < h,i> , < p,q> and < x,a> has only one long-tooth. The armature core 24 of the brushless DC motor of the invention shown in Figure 5 and Figure 7 has 3 pairs of short-blocks and long-blocks positioned alternately around the rotary shaft 21, and these 3 pairs of short-blocks and long-blocks are symmetrical with respect to the rotary shaft 21. Each of the effective pitches of the short-teeth a-b, b-c, c-d, d-e, e-f, f-g, g-h, i-j, j-k, k-l, l-m, m-n, n-o, o-p, q-r, r-s, s-t, t-u, u-v, v-w and w-x is equal or nearly equal to (360/27) = 13.333 degree, and each of the effective pitches of the long-teeth h-i, p-q and x-a is equal or nearly equal to (720/27) = 26.667 degree. Thus, the ratio of the effective pitch of each of the short-teeth to the effective pitch of each of the long-teeth is 1:2. The long-tooth h-i has a dummy-slot portion a' at its centre portion faced to the poles of the permanent magnet 23, the long-tooth p-q has a dummy-slot portion b' at its centre portion, and the long-tooth x-a has a dummy-slot portion c' at its centre portion. Therefore, the winding slots a to x and the dummy-slot portions a' to c' are positioned at intervals of an equal or nearly equal angle of (360/27) = 13.333 degree. Next, the cogging torque of the embodiment of the invention shown in Figure 5 will be explained hereinbelow. Cogging torque is generated by the interaction between the permanent magnet and the armature core, more particularly by changing the magnetic energy stored in the air gap according to the relative rotation between the permanent magnet and the armature core, and it changes periodically according to the relative position thereof with a basic period of 360 degree (one revolution). This is harmful for getting a smooth rotation of the rotating electric motor. The cogging torque is influenced by the shape of the armature core facing to the permanent magnet and by the distribution of the magnetic charge in the poles of the permanent magnet. The shape of the armature core is represented by shape harmonics expanded by the Fourier series with the basic period of 360 degree, and the shape harmonics is proper to the shape of the armature core. The distribution of the magnetic charge is represented by the magnetic distribution harmonics also expanded by the Fourier series with the basic period 360 degree, and the magnetic distribution harmonics is proper to the distribution of the magnetic charge in the permanent magnet. Mathematically, the cogging torque is determined by the convolution between the shape harmonics and the magnetic distribution harmonics, and is also expanded by the Fourier series with the basic period 360 degree. The magnitude of each component (cycle/revolution) of the cogging torque is proportional to the product of the component of the shape harmonics and the component of the magnetic distribution harmonics of the same degree number as that of the cogging torque. Since the magnetic energy in the air gap is proportional to the square value of the magnetic flux density of the permanent magnet and the distribution of the magnetic flux density shown in Figure 6 is symmetrical with regard to the polarities, the magnetic distribution harmonics of the permanent magnet 23 is a periodic function with the period of 1 pole pitch (360/P) = 90 degree. Thus, the cogging torque becomes small when the composite magnetic variation of the shape harmonics of the armature core 24 with the period of 1 pole pitch becomes small. Figure 10 shows phases of the winding slots a to x and the dummy-slot portions a' to c' of the armature core 24 with the period of 1 pole pitch of the permanent magnet 23. The winding slots a, f, g, l, m, r, s and x, where the winding coils A1, A2, A3 and A4 of the winding group A are wound, and the dummy-slot portion c' are positioned at intervals of a phase difference of (1 pole pitch)/27. That is, the phases of the winding slots a, f, g, l, m, r, s and x and the dummy-slot portion c' differ from each other by (1 pole pitch)/21, and the range of the phases of the winding slots a, f, g, l, m, r, s and x is within (1 pole pitch)/3. Similarly, the winding slots d, e, j, k, p, q, v and w, where the winding coils B1, B2, B3 and B4 of the winding group B are wound, and the dummy-slot portion b' are positioned at intervals of the same phase difference of (1 pole pitch)/27, and the range of the phases of the winding slots d, e, j, k, p, q, v and w is within (1 pole pitch)/3. Similarly, the winding slots b, c, h, i, n, o, t and u, where the winding coils C1, C2, C3 and C4 of the winding group C are wound, and the dummy-slot portion a' are positioned at intervals of the same phase difference of (1 pole pitch)/27, and the range of the phases of the winding slots b, c, h, i, n, o, t and u is within (1 pole pitch)/3. Further, the phase differences among the winding slot group (a, f, g, l, m, r, s, x) for the winding group A, the winding slot group (d, e, j, k, p, q, v, w) for the winding group B and the winding slot group (b, c, h, i, n, o, t, u) for the winding group C are exactly equal to (1 pole pitch)/3. As the result of this, the phase differences among the three phase winding groups A, B and C are exactly equal to 120el degree. All of the phases of the winding slots a to x and the dummy-slot portions a' to c' are different by the phase difference of (1 pole pitch)/27, and it is expected that the composite magnetic variation with the period of 1 pole pitch becomes small. Figure 11 shows waveforms of the magnetic variations of the winding slots a to x and the dummy-slot portions a' to c' and a waveform of the composite magnetic variation Tv of the armature core 24. The magnetic variation of each of the winding slots and dummy-slot portions changes smoothly corresponding to the each opening width, and each of the dummy-slot portions a', b' and c' has same magnetic effect as that of each of the winding slots a to x. Since the phases of the winding slots and the dummy-slot portions differ from each other by (1 pole pitch)/27, the composite magnetic variation Tv becomes considerably small. Figure 12 shows a waveform of the composite magnetic variation Tv' of the armature core 4 of the conventional rotating electric motor shown in Figure 1 and Figure 2. In the case of the conventional rotating electric motor, the phases of the winding slots a, g, m and s are the same with the period of 1 pole pitch, the phases of the winding slots b, h, n and t are the same, the phases of the winding slots c, i, o and u are the same, the phases of the winding slots d, j, p and v are the same, the phases of the winding slots e, k, q and w are the same, and the phases of the winding slots f, l, r and x are the same. So, the composite magnetic variation Tv' is large. Comparing the composite magnetic variation Tv of Figure 11 with the composite magnetic variation Tv' of Figure 12, Tv of the motor of the invention is much smaller than Tv' of the conventional motor. Therefore, the embodiment of the brushless DC motor of the invention shown in Figure 5 has few cogging torque. Notice that the cogging torque of the brushless DC motor of Figure 5 without the dummy-slot portions is also small, because the composite magnetic variation of the armature core 24 without the dummy-slot portions is smaller than the composite magnetic variation Tv' of the conventional armature core 4 shown in Figure 12. Next, the electromagnetic torque of the brushless DC motor of the invention shown in Figure 5 will be explained hereinbelow. The electromagnetic torque is the sum of the generated torques by the three phase currents I1, I2 and I3 supplied to the three phase winding groups A, B and C, and each of the generated torques of the three phase winding groups A, B and C by each of the currents I1, I2 and I3 is the product of the current and the flux density. Thus, the electromagnetic torque Tor is Tor = G(BaI1+BbI2+BcI3) (1) where G is a constant value and Ba, Bb and Bc are the equivalent flux densities of the three phase winding groups A, B and C, respectively. It is assumed here that the distribution of the permanent magnet 23 is sinusoidal, that is B(x) = B1s in(x) (2) where x is an angle (electrical degree). Then, the equivalent flux densities Ba, Bb and Bc becomes also sinusoidal, that is Ba(z) = KB1s in(z) (3a) Bb(z) = KB1s in(z-120el) (3b) Bc(z) = KB1s in(z-240el) (3c), where K is a constant value and z is the relative angle (electrical degree) between a reference point of the armature core 24 and a reference point of the permanent magnet 23. As the three phase currents I1, I2 and I3 are sinusoidal, I1(z) = Ips in(z) (4a) I2(z) = Ips in(z-120el) (4b) I3(z) = Ips in(z-240el) (4c) , where Ip is the peak value of the currents proportional to the command signal F. Then, the generated torque becomes Tor = (3/2) (GK)B1Ip (5) . The electromagnetic torque Tor of the embodiment is smooth and has no ripple torque. But the actual distribution of the permanent magnet 23 of Figure 6 has higher components of 3rd, 5th, 7th, and so on. These higher components, especially 3rd, 5th and 7th, produce a ripple torque, and this ripple torque prevents smooth rotation of the motor as well as cogging torque. Since the phases of the winding slots for each winding group A, B or C are different within (1 pole pitch)/3), the equivalent effective flux densities Ba, Bb and Bc have reduced components of 3rd, 5th, 7th, and so on. Assuming that the distribution of the flux density of the permanent magnet 23 is as follows: B(x) = B1s in(x) + B3s in(3x) + B5s in(5x) + B7s in(7x) (6) . Then, the equivalent flux densities Ba, Bb and Bc become as follows: Ba(z)=K(K1B1sin(z)+K3B3sin(3z)+K5B5sin(5z)+K7B7sin(7z) (7a) Bb(z) = Ba(z-120el) (7b) Bc(z) = Ba(z-240el) (7c) , where K1 = 0.95, K3 = 0.595, K5 = 0.093 and K7 =-0.283. Thus, K1/K1 = 1 (normalized), K3/K1 = 0.62, K5/K1 = 0.098 and K7/K1 = -0.30. Since the absolute values of the coefficients K3/K1, K5/K1 and K7/K1 are much smaller than 1, the influences of the higher components B3, B5 B7 of the permanent magnet 23 are reduced and the ripple torque of the brushless DC motor of the above embodiment becomes small. Therefore, the cogging torque and the ripple torque of the brushless DC motor of the invention shown in Figure 5 are small, and therefore smooth rotation can be obtained. The winding coils A1, A2, A3, A4, B1, B2, B3, B4, C1, C2, C3 and C4 of the armature core 24 in the above embodiment can be automatically wound by a winding machine, because the winding pitches of these winding coils are almost equal to 5/6 of the 1 pole pitch of the permanent magnet 23, where the winding pitch of a winding coil is the angle between the centres of the winding slots in which the winding coil is wound. The winding pitches of these winding coils A1 to C4 are between 133.3el and 160el. More specifically, the winding pitches of the winding coils A1, A2, A3, A4, B1, B2, B3, B4, C1, C2, C3 and C4 are 133.3el, 160el, 160el, 133.3el, 160el, 133.3el, 133.3el, 160el, 133.3el, 160el, 160el and 133.3el, respectively. In the case of the above embodiment, an electronic distributor supplying polyphase winding groups with polyphase sinusoidal currents is used, but the construction of the distributor does not relate to the cogging torque (the distributor relates to only the ripple torque). So, a mechanical brush commutator can be replaced with the electronic distributor shown in Figure 8. Besides, although the permanent magnet 23 of Figure 5 is formed in a continuous circular form, a magnet formed of separate parts with gaps therebetween can also be used in the invention. As mentioned before, the cogging torque of the rotating electric motor of the invention is small even if the dummy-slot portions are deleted. Generally speaking, cogging torque can be reduced by providing a rotating electric motor which comprises a field permanent magnet member of a circular form and an armature core made of magnetic material, said magnet member having permanently magnetized N and S poles alternately positioned around a rotary shaft of said rotary electric motor, the number of said N and S poles is P which is an even number, said armature core having a plurality of teeth made between two adjacent winding slots where a plurality of overlapping winding coils of polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2, wherein said armature core has at least a pair of a short-block and a long-block alternately positioned around said rotary shaft, each of said short-blocks having at least two short-teeth and no long-tooth, and each of said long-blocks having at least one long-tooth and no short-tooth, where each of the effective pitches of said short-teeth is smaller than D = (360/T) degree, and each of the effective pitches of said long-teeth is larger than D. It is preferable that the number of the pairs of short-blocks and long-blocks is an integral multiple of H. It is also preferable that the whole effective pitch of sequential H pairs of short-blocks and long-blocks is equal or almost equal to (360/P)Q degree, and the number of said teeth at a pair of neighbouring short-block and long-block in said sequential H pairs is an integral multiple of Q, where Q is an integer not less than 2 and preferably not equal to an integral multiple of H. It is also preferable that the number of said teeth in a pair of neighbouring short-block and long-block is not equal to an integral multiple of H. It is also preferable that the ratio of the effective pitch of each of said short-teeth to the effective pitch of each of said long-teeth is R:R+1, where R is an integer and preferably not larger than 4. It is also preferable that at least one of said long-teeth has at least one dummy-slot portion in the face thereof opposed to said magnet member. It is also preferable that the ratio of the effective pitch of each of said short-teeth to the effective pitch of each of said long-teeth is R:R+1, where R is an integer, and said dummy-slot portions and said winding slots are positioned at intervals of equal or almost equal angles around said rotary shaft. Other constructions of the rotating electric motor of the invention having reduced cogging torque are shown in Table 1 which shows the effective pitches of teeth. In Table 1, arrangement (A) shows another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the effective pitches of the short-teeth is changed to be equal to 2 angular units and each of the effective pitches of the long-teeth is changed to be equal to 3 angular units, where 1 angular unit is (360/51) = 7.06 degree. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (B) shows still another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the effective pitches of the short-teeth is changed to be equal to 3 angular units and each of the effective pitches of the long-teeth is changed to be equal to 4 angular units, where 1 angular unit is (360/75) = 4.8 degree. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (C) shows yet another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the effective pitches of the short-teeth is equal to 1 angular unit and each of the effective pitches of the long-teeth is changed to be equal to 4 angular units, where 1 angular unit is (360/33) = 10.909 degree. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (D) shows a further arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the short-blocks has 6 short-teeth and each of the long-blocks has 2 long-teeth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and the effective pitches of the long-teeth are equal to 2 or 3 angular units, where 1 angular unit is (360/33) = 10.909 degree. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (E) shows a still further arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the short-blocks has 6 short-teeth and each of the long-blocks has 2 long-teeth. Each of the effective pitches of the short-teeth is equal to 3 angular units and the effective pitches of the long-teeth are equal to 4 or 5 angular units, where 1 angular unit is (360/81) = 4.444 degree. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. In the cases of the above embodiments, the number of the teeth in each of the short-blocks is larger than that in each of the long-blocks, but the construction of the rotating electric motor of the invention having reduced cogging torque is not limited to such cases. Generally speaking, cogging torque can be reduced by providing a rotating electric motor which comprises: a field permanent magnet member of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft of said rotary electric motor, the number of said N and S poles being P which is an even number; and an armature core made of magnetic material having a plurality of teeth made between two adjacent winding slots where a plurality of overlapping winding coils of polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2; wherein said armature core has at least a pair of a short-block and a long-block alternately positioned around said rotary shaft, each short-block having at least one short-tooth and no long-tooth, and each long-block having at least two long-teeth and no short-tooth, where the effective pitch of each short-tooth is smaller than D = (360/T) degree, and the effective pitch of each long-teeth is larger than D. It is preferable that the number of the pairs of short-blocks and long-blocks is an integral multiple of H. It is also preferable that the whole effective pitch of sequential H pairs of short-blocks and long-blocks is equal or almost equal to (360/P)Q degree, and the number of said teeth at a pair of neighbouring short-block and long-block in said sequential H pairs is an integral multiple of Q, where Q is an integer not less than 2 and preferably not equal to an integral multiple of H. It is also preferable that the number of said teeth in a pair of neighbouring short-block and long-block is not equal to an integral multiple of H. It is also preferable that the ratio of the effective pitch of each of said short-tooth to the effective pitch of each of said long-tooth is R:R+1, where R is an integer and preferably not larger than 4. It is also preferable that at least one of said long-teeth has at least one dummy-slot portion in the face thereof opposed to said magnet member. It is also preferable that the ratio of the effective pitch of each of said short-teeth to the effective pitch of each of said long-teeth is R:R+1, where R is an integer, and said dummy-slot portions and said winding slots are positioned at intervals of equal or almost equal angles around said rotary shaft. Other constructions of the rotating electric motor of the invention having reduced cogging torque are shown in Table 2 which shows the effective pitches of teeth. In Table 2, arrangement (A) shows another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the long-blocks has 7 long-teeth and each of the short-blocks has 1 short-tooth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and each of the effective pitches of the long-teeth is equal to 2 angular units, where 1 angular unit is (360/45) = 8 degree. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement 2(B) shows still another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the long-blocks has 7 long-teeth and each of the short-blocks has 1 short-tooth. Each of the effective pitches of the short-teeth is equal to 2 angular units and each of the effective pitches of the long-teeth is equal to 3 angular units, where 1 angular unit is (360/69) = 5.217 degree. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (C) shows yet another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the long-blocks has 7 long-teeth and each of the short-blocks has 1 short-tooth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and each of the effective pitches of the long-teeth is equal to 4 angular units, where 1 angular unit is (360/87) = 4.138 degree. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (D) shows a further arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the long-blocks has 6 long-teeth and each of the short-blocks has 2 short-teeth. The effective pitches of the short-teeth are equal to 1 angular unit or 2 angular units and the effective pitches of the long-teeth are equal to 3 angular units, where 1 angular unit is (360/63) = 5.714 degree. Dummy-slot portions are provided on the faces of the long-teeth and the short-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (E) shows a still further arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. Each of the long-blocks has 6 long-teeth and each of the short-blocks has 2 short-teeth. The effective pitches of the short-teeth are equal to 2 or 3 angular units and the effective pitches of the long-teeth are equal to 4 angular units, where 1 angular unit is (360/87) = 4.138 degree. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. In the cases of the above embodiments, 3 pairs of short-blocks and long-blocks are symmetrically positioned around the rotary axis, but the construction of the rotating electric motor of the invention having reduced cogging torque is not limited to such cases. Generally speaking, cogging torque can be reduced by providing a rotating electric motor which comprises: a field permanent magnet member of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft of said rotary electric motor, the number of said N and S poles being P which is an even number; and an armature core made of magnetic material having a plurality of teeth made between two adjacent winding slots where a plurality of overlapping winding coils of polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2; wherein said armature core has at least one short-tooth and at least one long-tooth, the effective pitch of each short-tooth being smaller than D = (360/T) degree, and the smaller effective pitch of each long-tooth being larger than D; and wherein the whole effective pitch of sequential L teeth of said armature core is equal or almost equal to (360/P)Q degree, where L is an integer larger than H and Q is an integer not less than 2, and the ratio of the smallest value of the effective pitches of the teeth to the effective pitch of the m-th tooth in said sequential L teeth is R:R+Vm, where R is an integer not less than 1 and Vm is an integer including O, the sum of Vm from m = 1 to m = L being W which is not equal to an integral multiple of Qd, where Qd is a divisor of Q and larger than 1. It is preferable that W = Qd-1 or W = Qd+1. It is also preferable that W = Qm-1 or W = Qm+1, where Qm is an integral multiple of Q. It is also preferable that at least one of said long-teeth has at least one dummy-slot portion in the face thereof opposed to said magnet member. It is also preferable that said dummy-slot portions and said winding slots in said sequential L teeth are positioned at equal or almost equal angles around said rotary shaft by 1/R of the smallest value to the effective pitches of said teeth in said sequential L teeth. For example, Q = P = 4, L = 24, R = 1 and W = Q-1 = 3 in the case of the embodiment of Figure 5; Q = 4, L = 24, R = 3 and W = 2Q + 1 = 9 in the arrangement (E) of Table 1; Q = 4, L = 24, R = 1 and W = 5Q + 1 = 21 in the case of the arrangement (A) of Table 2; Q = 4, L = 24, R = 2 and W = 10Q - 1 = 39 in the case of the arrangement (E) of Table 2. Other constructions of the rotating electric motor of the invention having reduced cogging torque are shown in Table 3 which shows the effective pitches of teeth. In Table 3, arrangement (A) shows another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. The armature core has only one pair of short-block and long-block. The long-block has 1 long-tooth and the short-block has 23 short-teeth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and the effective pitch of the long-tooth is equal to 2 angular units, where 1 angular unit is (360/25) = 14.4 degree. Thus, Q = 4, L = 24, R = 1 and w = 1. A dummy-slot portion is provided on the face of the long-tooth so that the winding slots and the dummy-slot portion are positioned at intervals of 1 angular unit. Arrangement (B) shows still another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. The armature core has only one pair of short-block and long- block. The long-block has 1 long-tooth and the short-block has 23 short-teeth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and the effective pitches of the long-tooth is to 4 angular units, where 1 angular unit is (360/27) = 13.333 degree. Thus, Q = 4, L = 24, R = 1 and W = 3. Dummy-slot portions are provided on the faces of the long-tooth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (C) shows yet another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. The armature core has two pairs of short-blocks and long-blocks. Each of the long-blocks has 1 long-tooth and the short-blocks have 2 or 20 short-teeth. Each of the effective pitches of the short-teeth is equal to 2 angular units and the effective pitches of the long-teeth are equal to ) or 4 angular units, where I angular unit is (360/51> = 7.059 degree. Thus, in = 4, L = 24, R = 2 and W = 3. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of I angular unit. Arrangement shows a further arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. The armature core has only one pair of short-block and long-block. The long-block has 23 long-teeth and the short-block has 1 short-tooth. Each of the effective pitches of the long-teeth is equal to 2 angular units and the effective pitch of the short-tooth is equal to 1 angular unit, where 1 angular unit is (360/47) = 7.660 degree. Thus, Q = 4 L = 24, R = 1 and W = 23. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (E) shows a still further arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. The armature core has only one pair of short-block and long-block. The long-block has 23 long-teeth and the short-block has 1 short-tooth. Each of the effective pitches of the long-teeth is equal to 4 angular units and the effective pitch of the short-tooth is equal to 1 angular unit, where 1 angular unit is (360/93) = 3.871 degree. Thus, Q = 4, L = 24, R = 1 and W = 69. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (F) shows further another arrangement of the teeth of the armature core 24 shown in Figure 5 and Figure 7. The armature core has two pairs of the short-blocks and long-blocks. Each of the short-blocks has 1 short-tooth and the long-blocks have 2 or 20 long-teeth. Each of the effective pitches of the long-teeth is equal to 3 angular units and the effective pitches of the short-teeth are equal to 1 angular unit or 2 angular units, where 1 angular unit is (360/69) = 5.217 degree. Thus, Q = 4, L = 24, R = 1 and W = 45. Dummy-slot portions are provided on the faces of the long-teeth and one of the short-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Embodiments of the Invention with T = 3P Figure 13 is a schematic sectional view of another embodiment of a brushless DC motor of the invention with T = 3P, which corresponds to the conventional rotating electric motor shown in Figure 3 and Figure 4. In Figure 13, a cylindrical permanent magnet 43 is fixed to the outer circumference of a rotor 42 made of magnetic material, and the permanent magnet 43 rotates with the rotor 42 around a rotary shaft 41. The permanent magnet 43 has 4 poles of alternating N and S poles positioned at intervals of an equal angle of 90 degree, that is, P = 4. The distribution of the magnetic flux density of the permanent magnet 43 is the same as that shown in Figure 6. The teeth 46 of an armature core 44, each of which is formed between two adjacent winding slots 45, are faced to the poles of the permanent magnet 43. The rotary shaft 41 of the rotor 42 is rotatably supported by the armature core 44. Therefore, the relative position between the teeth 46 of the armature core 44 and the poles of the permanent magnet 43 changes according to the rotation of the rotor 42. Figure 14 shows a development view of the brushless DC motor of the invention of Figure 13 developed at the lines X-X' and Y-Y', when these lines are in a line. The armature core 44 has 12 winding slots, a, b, c, d, e, f, g, h, i, j, k and l, and 12 teeth are provided between two adjacent winding slots, that is, T = 12. The armature core 44 also has 3 dummy-slot portions a', b' and c' at the faces of some of the teeth opposed to the permanent magnet 43, and no coils are wound in the dummy-slot portions. Overlapping winding coils A1, A2, A3, A4, B1, B2, B3, B4, C1, C2, C3 and C4 are wound in the winding slots a to 1. Each of the winding coils A1 to C4 encircles 3 teeth of the armature core 44. That is, A1 is wound in the winding slots a and d, A2 is wound in the winding slots d and g, A3 is wound in the winding slots g and j, A4 is wound in the winding slots j and a, B1 is wound in the winding slots c and f, B2 is wound in the winding slots f and i, B3 is wound in the winding slots i and l, B4 is wound in the winding slots l and c, C1 is wound in the winding slots e and h, C2 is wound in the winding slots h and k, C3 is wound in the winding slots k and b, and C4 is wound in the winding slots b and e. The winding coils A1, A2, A3 and A4 are connected in series to form a winding group A of the first phase, the winding coils B1, B2, B3 and B4 are connected in series to form a winding group B of the second phase, and the winding coils C1, C2, C3 and C4 are connected in series to form a winding group C of the third phase. As will be described later, the phase differences among the winding groups A, B and C are exactly equal to 120el (electrical degree), where 180el is equivalent to the 1 pole pitch (360/P) degree. In Figure 13, P = 4, then 180el is equivalent to 90 degree (mechanical degree), which is the same as that of the conventional motor of Figure 3. Therefore, a torque accelerating the rotor 42 is obtained by supplying three phase currents to the three phase winding groups A, B and C. The electronic distributor 30 shown in Figure 8 is also usable for the brushless DC motor of the invention of Figure 13. In Figure 14, since the winding slots a to l are positioned at intervals of unequal angles, the effective pitches of the teeth are not the same. In the case of T = 3P = 12 (P = 4), the standard effective pitch is D = (360/T) = 30 degree when all of the winding slots are positioned at intervals of an equal angle. So, a short-tooth has the effective pitch smaller than D, and a long-tooth has the effective pitch larger than D. In Figure 14, the teeth, a-b, b-c, c-d, e-f, f-g, g-h, i-j, j-k and k-l are short-teeth, and the teeth d-e, h-i and l-a are long-teeth. There are three short-blocks < a,d> , < e,h> and < i,l> that are the short-block of the teeth a-b, b-c, and c-d, the short-block of the teeth e-f, f-g and g-h, and the short-block of the teeth i-j, j-k and k-l, respectively. And there are three long-blocks < d,e> , < h,i> and < l,a> that are the long-block of the tooth d-e, the long-block of the tooth h-i, and the long-block of the tooth l-a, respectively. Each of the short-blocks < a,d> , < e,h> and < i,l> has 3 short-teeth, and each of the long-blocks < d,e> , < h,i> and < l,a> has only one long-tooth. The armature core 44 of the brushless DC motor of the invention shown in Figure 13 and Figure 14 has 3 pairs of short-blocks and long-blocks positioned alternately around the rotary shaft 41, and these 3 pairs of short-blocks and long-blocks are symmetrical with respect to the rotary shaft 41. Each of the effective pitches of the short-teeth a-b, b-c, c-d, e-f, f-g, g-h, i-j, j-k and k-l is equal or nearly equal to (360/15) = 24 degree, and each of the effective pitches of the long-teeth d-e, h-i and l-a is equal or nearly equal to (720/15) = 48 degree. Thus, the ratio of the effective pitch of each of the short-teeth to the effective pitch of each of the long-teeth is 1:2. The long-tooth d-e has a dummy-slot portion a' at its centre portion faced to the poles of the permanent magnet 43, the long-tooth h-i has a dummy-slot portion b' at its centre portion, and the long-tooth l-a also has a dummy-slot portion c' at its centre portion. Therefore, the winding slots a to l and the dummy-slot portions a' to c' are positioned at intervals of an equal or nearly equal angle of (360/15) = 24 degree. Next, the cogging torque of the embodiment of the invention shorn in Figure 13 will be explained hereinbelow. Figure 15 shows phases of the winding slots a to l and the dummy-slot portions a' to c' of the armature core 44 with the period of 1 pole pitch of the permanent magnet 43. The winding slots a, d, g and j, where the winding coils A1, A2, A3 and A4 of the winding group A are wound, and the dummy-slot portion c' are positioned at intervals of a phase difference of (1 pole pitch)/15. That is, the phases of the winding slots a, d, g and j and the dummy-slot portion c' differ from each other by (1 pole pitch)/15, and the range of the phases of the winding slots a, d, g and j is smaller than (1 pole pitch)/3. Similarly, the winding slots c, f, i and l, where the winding coils B1, B2, B3 and B4 of the winding group B are wound, and the dummy-slot portion b' are positioned at intervals of the same phase difference of (1 pole pitch)/15, and the range of the phases of the winding slots c, f, i and l is smaller than (1 pole pitch)/3. Similarly, the winding slots b, e, h and k, where the winding coils C1, C2, C3 and C4 of the winding group C are wound, and the dummy-slot portion a' are positioned at intervals of the same phase difference of (1 pole pitch)/15, and the range of the phases of the winding slots b, e, h and k is smaller than (1 pole pitch)/3. Further, the phase differences among the winding slot group (a, d, g, j) for the winding group A, the winding slot group (c, f, i, l) for the winding group B and the winding slot group (b, e, h,k) for the winding group C are exactly equal to (1 pole pitch)/3. As the result of this, the phase differences among the three phase winding groups A, B and C are exactly equal to 120el degree, and a smooth torque is obtained by using the distributor 30 of Figure 8. All of the phases of the winding slots a to 1 and the dummy-slot portions a' to c' are different from each other by the phase difference of (1 pole pitch)/15, and it is expected that the composite magnetic variation with the period of 1 pole pitch becomes small. Figure 16 shows waveforms of the magnetic variations of the winding slots a to 1 and the dummy-slot portions a' to c' and a waveform of the composite magnetic variation Tv of the armature core 44. The magnetic variation of each of the winding slots and dummy-slot portions changes smoothly corresponding to each opening width, and each of the dummy-slot portions a', b' and c' has the same magnetic effect as that of each of the winding slots a to 1. Since the phases of the winding slots and the dummy-slot portions differ from each other by (1 pole pitch)/15, the composite magnetic variation Tv becomes considerably small. Figure 17 shows a waveform of the composite magnetic variation Tv' of the armature core 14 of the conventional rotating electric motor shown in Figure 3 and Figure 4. In the case of the conventional rotating electric motor, the phases of the winding slots a, d, g and j are the same with the period of the 1 pole pitch, the phases of the winding slots b, e, h and k are the same, and the phases of the winding slots c, f, i and 1 are the same. So, the composite magnetic variation Tv' is large. Comparing the composite magnetic variation Tv of Figure 16 with the composite magnetic variation Tv' of Figure 17, Tv of the motor of the invention is much smaller than Tv' of the conventional motor. Therefore, the embodiment of the brushless DC motor of the invention shown in Figure 13 has few cogging torque. Notice that the cogging torque of the brushless DC motor of Figure 13 without the dummy-slot portions is also small, because the composite magnetic variation of the armature core 44 without the dummy-slot portions is smaller than the composite magnetic variation Tv' of the conventional armature core 14 shown in Figure 17. The winding coils, A1, A2, A3, A4, B1, B2, B3, B4, C1, C2, C3 and C4 of the armature core 44 in the above embodiment can be automatically wound by a winding machine, because the winding pitches of these winding coils are almost equal to the 1 pole pitch of the permanent magnet 43. The winding pitches of these winding coils A1 to C4 are between 144el and 192el. More specifically, the winding pitches of the winding coils A1, A2, A3, A4, B1, B2, B3, B4, C1, C2, C3 and C4 are 144el, 192el, 192el, 192el, 192el, 192el, 144el, 192el, 144el, 192el, 192el and 192el, respectively. Other constructions of the rotating electric motor of the invention having reduced cogging torque are shown in Table 4 which shows the effective pitches of teeth. In Table 4, arrangement (A) shows another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the effective pitches of the short-teeth is changed to be equal to 3 angular units and each of the effective pitches of the long-teeth is changed to be equal to 3 angular units, where 1 angular unit is (360/27) = 13.333 degree. Thus, Q = 4, L = 12, R = 2 and W = 3. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (B) shows still another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the effective pitches of the short-teeth is changed to be equal to 3 angular units and each of the effective pitches of the long-teeth is changed to be equal to 4 angular units, where 1 angular unit is (360/39) = 9.231 degree. Thus, Q = 4, L = 12, R = 3 and W = 3. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (C) shows yet another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the effective pitches of the short-teeth is equal to 1 angular unit and each of the effective pitches of the long-teeth is changed to be equal to 4 angular units, where 1 angular unit is (360/21) = 17.143 degree. Thus, Q = 4, L = 12, R = 1 and W = 9. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (D) shows a further arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the short-blocks has 2 short-teeth and each of the long-blocks has 2 long-teeth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and the effective pitches of the long-teeth are equal to 2 or 3 angular units, where 1 angular unit is (360/21) = 17.143 degree. Thus, Q = 4, L = 12, R = 1 and W = 9. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (E) shows a still further arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the short-blocks has 2 short-teeth and each of the long-blocks has 2 long-teeth. Each of the effective pitches of the short-teeth is equal to 3 angular units and the effective pitches of the long-teeth are equal to 4 or 5 angular units, where 1 angular unit is (360,45) = 8 degree. Thus, Q = 4, L = 12, R = 3 and W = 9. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. In the cases of the above embodiments with T = 3P, the number of the teeth in each of the short-blocks is larger than that in each of the long-blocks, but the construction of the rotating electric motor of the invention having reduced cogging torque is not limited to such cases. Other constructions of the rotating electric motor of the invention having reduced cogging torque are shown in Table 5 which shows the effective pitches of teeth. In Table 5, arrangement (A) shows another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the long-blocks has 3 long-teeth and each of the short-blocks has 1 short-tooth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and each of the effective pitches of the long-teeth is equal to 2 angular units, where 1 angular unit is (360/21) = 17.143 degree. Thus, Q = 4, L = 12, R = 1 and W = 9. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (B) shows still another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the long-blocks has 3 long-teeth and each of the short-blocks has 1 short-tooth. Each of the effective pitches of the short teeth is equal to 2 angular units and each of the effective pitches of the long-teeth is equal to 3 angular units, where 1 angular unit is (360/33) = 10.909 degree. Thus, Q = 4, L = 12, R = 2 and W = 9. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (C) shows yet another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the long-blocks has 3 long-teeth and each of the short-blocks has 1 short-tooth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and each of the effective pitches of the long-teeth is equal to 4 angular units, where 1 angular. unit is (360/39) = 9.231 degree. Thus, Q = 4, L = 12, R = 1 and W = 27. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (D) shows a further arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the long-blocks has 2 long-teeth and each of the short-blocks has 2 short-teeth. The effective pitches of the short-teeth are equal to 1 angular unit or 2 angular units and the effective pitches of the long-teeth are equal to 3 angular units, where 1 angular unit is (360/27) = 13.333 degree. Thus, Q = 4, L = 12, R = 1 and W = 15. Dummy-slot portions are provided on the faces of the long-teeth and the short-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (E) shows a still further arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. Each of the long-blocks has 2 long-teeth and each of the short-blocks has 2 short-teeth. The effective pitches of the short-teeth are equal to 2 or 3 angular units and the effective pitches of the long-teeth are equal to 4 angular units, where 1 angular unit is (360/39) = 9.231 degree. Thus, Q = 4, L = 12, R = 1 and W = 15. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. In the cases of the above embodiments with T = 3P, 3 pairs of short-blocks and long-blocks are symmetrically positioned around the rotary shaft, but the construction of the rotating electric motor of the invention having reduced cogging torque is not limited to such cases. Other constructions of the rotating electric motor of the invention having reduced cogging torque are shown in Table 6 which shows the effective pitches of teeth. In Table 6, arrangement (A) shows another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. The armature core has only one pair of short-block and long-block. The long-block has 1 long-tooth and the short-block has 11 short-teeth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and the effective pitch of the long-tooth is equal to 2 angular units, where 1 angular unit is (360/13) = 27.692 degree. Thus, Q = 4, L = 12, R = 1 and W = 1. A dummy-slot portion is provided on the face of the long-tooth so that the winding slots and the dummy-slot portion are positioned at intervals of 1 angular unit. Arrangement (B) shows still another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. The armature core has only one pair of short-block and long-block. The long-block has 1 long-tooth and the short-block has 11 short-teeth. Each of the effective pitches of the short-teeth is equal to 1 angular unit and the effective pitch of the long-tooth is equal to 4 angular units, where 1 angular unit is (360/15) = 24 degree. Thus, Q = 4, L = 12, R = 1 and W = 3. Dummy-slot portions are provided on the faces of the long-tooth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (C) shows yet another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. The armature core has two pairs of short-blocks and long-blocks. Each of the long-blocks has 1 long-tooth and the short-blocks have 2 or 8 short-teeth. Each of the effective pitches of the short-teeth is equal to 2 angular units and the effective pitches of the long-teeth are equal to 3 or 4 angular units, where 1 angular unit is (360/27) = 13.333 degree. Thus, Q = 4, L = 12, R = 2 and W = 3. Dummy-slot portions are provided on the faces of the short-teeth and the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (D) shows a further arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. The armature core has only one pair of short-block and long-block. The long-block has 11 long-teeth and the short-block has 1 short-tooth. Each of the effective pitches of the long-teeth is equal to 2 angular units and the effective pitch of the short-tooth is equal to 1 angular unit, where 1 angular unit is (360/23) = 15.652 degree. Thus, Q = 4, L = 12, R = 1 and W = 11. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (E) shows a still further arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. The armature core has only one pair of short-block and long-block. The long-block has 11 long-teeth and the short-block has 1 short-tooth. Each of the effective pitches of the long-teeth is equal to 4 angular units and the effective pitch of the short-tooth is equal to 1 angular unit, where 1 angular unit is (360/45) = 8 degree. Thus, Q = 4, L = 12, R = 1 and W = 33. Dummy-slot portions are provided on the faces of the long-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Arrangement (F) shows further another arrangement of the teeth of the armature core 44 shown in Figure 13 and Figure 14. The armature core has two pairs of short-blocks and long-blocks. Each of the short-blocks has 1 short-tooth and the long-blocks have 2 or 8 long-teeth. Each of the effective pitches of the long-teeth is equal to 3 angular units and the effective pitches of the short-teeth are equal to 1 angular unit or 2 angular units, where 1 angular unit is (360/33) = 10.909 degree. Thus, Q = 4, L = 12, R = 1 and W = 21. Dummy-slot portions are provided on the faces of the long-teeth and one of the short-teeth so that the winding slots and the dummy-slot portions are positioned at intervals of 1 angular unit. Figure 18 shows a schematic sectional view of a further embodiment of the invention with T = 3P, which also corresponds to the conventional rotating electric motor shown in Figure 3 and Figure 4. In Figure 18, a cylindrical permanent magnet 53 is fixed to the outer circumference of a rotor 52 made of magnetic material, and the permanent magnet 53 rotates with the rotor 52 around a rotary shaft 51. The permanent magnet 53 has 4 poles of alternating N and S poles positioned at intervals of an equal angle of 90 degree, that is P =4. The distribution of the magnetic flux density of the permanent magnet 53 is the same as that shown in Figure 6. The teeth 56 of an armature core 54, each of which is formed between two adjacent winding slots 55, are faced to the poles of the permanent magnet 53. The rotary shaft 51 of the rotor 52 is rotatably supported by the armature core 54. Therefore, the relative position between the teeth 56 of the armature core 54 and the poles of the permanent magnet 53 changes according to the rotation of the rotor 52. Figure 19 shows a development view of the brush-less DC motor of the invention of Figure 18 developed at the lines X-X' and Y-Y', when these lines are in a line. The armature core 54 has 12 winding slots a, b, c, d, e, f, g, h, i, j, k and l, and 12 teeth are provided between two adjacent winding slots, that is, T = 12. The armature core 54 also has 6 dummy-slot portions a', b', c', d', e' and f' at the faces of some of the teeth opposed to the permanent magnet 53, and no coils are wound in the dummy-slot portions. Overlapping winding coils A1, A2, A3, A4, B1, B2, B3, B4, C1, C2, C3 and C4 are wound in the winding slots a to 1. Each of the winding coils A1 to C4 encircles 3 of the teeth of the armature core 54. That is, A1 is wound in the winding slots a and d, A2 is wound in the winding slots d and g, A3 is wound in the winding slots g and j, A4 is wound in the winding slots j and a, B1 is wound in the winding slots c and f, B2 is wound in the winding slots f and i, B3 is wound in the winding slots i and l, B4 is wound in the winding slots l and c, C1 is wound in the winding slots e and h, C2 is wound in the winding slots h and k, C3 is wound in the winding slots k and b, and C4 is wound in the winding slots b and e. The winding coils A1, A2, A3 and A4 are connected in series to form a winding group A of the first phase, the winding coils B1, B2, B3 and B4 are connected in series to form a winding group B of the second phase, and the winding coils C1, C2, C3 and C4 are connected in series to form a winding group C of the third phase. As will be described later, the phase differences among the winding groups A, B and C are exactly equal to 120el (electrical degree), where 180el is equivalent to the 1 pole pitch (360/P) degree. In Figure 18, P = 4, then 180el is equivalent to 90 degree (mechanical degree), which is the same as that of the conventional motor of Figure 3. Therefore, a torque accelerating the rotor 52 is obtained by supplying three phase currents to the three phase winding groups A, B and C. The electronic distributor 30 shown in Figure 8 is also usable for the brushless DC motor of the invention of Figure 18. In Figure 19, since the winding slots a to l are positioned at intervals of unequal angles, the effective pitches of the teeth are not the same. In the case of T = 3P = 12 (P = 4), the standard effective pitch is D = (360/T) = 30 degree when all of the winding slots are positioned at intervals of an equal angle. So, a short-tooth has the effective pitch smaller than D, and a long-tooth has the effective pitch larger than D. In Figure 19, the teeth a-b, c-d, e-f, g-h, i-j and k-l are short-teeth, and the teeth b-c, d-e, f-g, h-i, j-k and 1-a are long-teeth. There are 6 short-blocks < a,b> , < c,d> , < e,f> , < g,h> , < i,j> and < k,1> , and there are 6 long-blocks < b,c> , < d,e> , < f,g> , < h,i> , < j,k> and < l,a> . Each of the short-blocks has only one short-tooth, and each of the long-blocks has only one long-tooth. The armature core 54 of the brushless DC motor of the invention shown in Figure 18 and Figure 19 has 6 pairs of short-blocks and long-blocks positioned alternately around the rotary shaft 51. Each of the effective pitches of the short-teeth a-b, c-d, e-f, g-h, i-j and k-l is equal or nearly equal to (360/18) = 20 degree, each of the effective pitches of the long-teeth b-c, d-e, h-i and j-k is equal or nearly equal to (720/18) = 40 degree, the effective pitch of the long-tooth f-g is equal or almost equal to (1+5/4)20 = 45 degree, and the effective pitch of the long-tooth 1-a is equal or almost equal to (1+3/4) 20 = 35 degree. Each of the long-teeth b-c, d-e, f-g, h-i, j-k and 1-a has one of the dummy-slot portions a', b', c', d', e' and f' at the faces of the teeth opposed to the poles of the permanent magnet 53. The first slot-group is formed by the winding slots a, b, c, d, e and f and the dummy-slot portions a', b' and c', which are positioned sequentially at intervals of equal angles by the first pitch of 20 degree. The second slot-group is formed by the winding slots g, h, i, j, k and l and the dummy-slot portions d', e' and f', which are also positioned sequentially at intervals of the first pitch. The pitches between adjacent winding slots of the first slot-group and the second slot-group at both sides are 35 or 45 degree, each of which is not equal to an integral multiple of the first pitch of 20 degree. Next, the cogging torque of the embodiment of the invention shown in Figure 18 will be explained hereinbelow. Figure 20 shows phases of the winding slots a to 1 and the dummy-slot portions a' to f' of the armature core 54 with the period of 1 pole pitch of the permanent magnet 53. The winding slots a, d, g and j, where the winding coils A1, A2, A3 and A4 of the winding group A are wound, and the dummy-slot portions c' and f' are positioned at intervals of a phase difference of (1 pole pitch)/18. That is, the phases of the winding slots a, d, g and j and the dummy-slot portions c' and f' differ from each other by (1 pole pitch)/18, and the range of the phases of the winding slots a, d, g and j is smaller than (1 pole pitch)/3. Similarly, the winding slots c, f, i and 1, where the winding coils B1, B2, B3 and B4 of the winding group B are wound, and the dummy-slot portions a' and d' are positioned at intervals of the same phase difference of (1 pole pitch)/13, and the range of the phases of the winding slots c, f, i and 1 is smaller than (1 pole pitch)/3. Similarly, the winding slots b, e, h and k, where the winding coils C1, C2, C3 and C4 of the winding group C are wound, and the dummy-slot portions b' and e' are positioned by the same phase difference of (1 pole pitch)/18, and the range of the phases of the winding slots b, e, h and k is smaller than (1 pole pitch)/3. Further, the phase differences among the winding slot group (a, d, g, j) for the winding group A, the winding slot group (c, f, i, l) for the winding group B and the winding slot group (b, e, h, k) for the winding group C are exactly equal to (1 pole pitch)/3. As the result of this, the phase differences among the three phase winding groups A, B and C are exactly equal to 120el degree, and a smooth torque is obtained by using the distributor 30 of Figure 8. All of the phases of the winding slots a to 1 and the dummy-slot portions a' to f' are different from each other by the phase difference of (1 pole pitch)/18, and it is expected that the composite magnetic variation with the period of 1 pole pitch becomes small. Figure 21 shows waveforms of the magnetic variations of the winding slots a to 1 and the dummy-slot portions a' to f' and a waveform of the composite magnetic variation Tv of the armature core 54. The magnetic variation of each of the winding slots and dummy-slot portions changes smoothly corresponding to each opening width, and each of the dummy-slot portions a', b', c', d', e' and f' has the same magnetic effect as that of each of the winding slots a to 1. Since the phases of the winding slots and the dummy-slot portions differ from each other by (1 pole pitch)/18, the composite magnetic variation Tv becomes considerably small. Comparing the composite magnetic variation Tv of Figure 21 with the composite magnetic variation Tv' of Figure 17, Tv of the motor of the invention is much smaller than Tv' or the conventional motor. Therefore, the embodiment of the brushless DC motor of the invention shown in Figure 18 has few cogging torque. In the case of the above embodiment of Figure 18, two slot-groups are provided in the armature core, but the construction of the rotating electric motor of the invention having reduced cogging torque is not limited to such a case. Generally speaking, cogging torque can be reduced by providing a rotating electric motor which comprises a field permanent magnet member of a circular form and an armature core made of magnetic material, said magnet member having permanently magnetized N and S poles alternately positioned around a rotary shaft of said rotary electric motor, the number of said N and S poles being P which is an even number, said armature core having a plurality of teeth made between two adjacent winding slots where a plurality of overlapping winding coils of the polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2, wherein at least one of said teeth has at least one dummy-slot portion, said armature core having at least first and second slot-groups, said dummy-slot portions and said winding slots in said first slot-group being positioned at intervals of equal or almost equal angles to the first pitch, said dummy-slot portions and said winding slots in said second slot-group being positioned at intervals of equal or almost equal angles to the first pitch, and the second pitch between adjacent winding slots of said first slot-group and said second slot-group being not equal to an integral multiple of said first pitch. It is preferable that the ratio of the second pitch to the first pitch is equal to (1+N/M) or (1-N/M), where M is an integer not less than 2 and N is an integer not less than 1 and not equal to an integral multiple of M. It is also preferable that said armature core has at least a pair of short-block and long-block alternately positioned around said rotary shaft, that each of said short-blocks has at least one short-tooth and no long-tooth, and that each of said long-blocks has at least one long-tooth and no short-tooth, where each of the effective pitches of said short-teeth is smaller than D = (360/T) degree, and each of the effective pitches of said long-teeth is larger than D. It is also preferable that the number of said teeth in each of said short-blocks is not less than the number of said teeth in each of said long-blocks.

Claims: A rotating electric motor comprising: a field permanent magnet member (23, 43, 53) of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft (21, 41, 51) of said rotating electric motor, the number of said N and S poles being P which is an even number; and an armature core (24, 44, 54) made of magnetic material having a plurality of teeth (26, 46, 56) made between two adjacent winding slots (25, 45, 55) where a plurality of overlapping winding coils (A1-A4; B1-B4; C1-C4) of polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2, wherein said armature core (24, 44, 54) has at least a pair of short-block and long-block alternately positioned around said rotary shaft, said short-block having at least one short-tooth and no long-tooth, and said long-block having at least one long-tooth, and no short-tooth; where each of the effective pitches of said at least one short-tooth is smaller than D=(360/T) degree, and each of the effective pitches of said at least one long-tooth is larger than D. A rotating electric motor comprising: a field permanent magnet member (23, 43) of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft (21, 41) of said rotating electric motor, the number of said N and S poles being P which is an even number; and an armature core (24, 44) made of magnetic material having a plurality of teeth (26, 46) made between two adjacent winding slots (25, 45) where a plurality of winding coils (Al-A4; Bl-B4; Cl-C4) of polyphase winding groups are wound, the number of said teeth being T, and the number of the phases of said polyphase winding groups being H which is not less than 2, characterized in that said armature core (24, 44) has at least two pairs of short-block and long block alternately positioned around said rotary shaft, and either: (a) said short block in each of said at least two pairs having at least two short-teeth and no long-tooth, and said long-block in each of said at least two pairs having at least one long-tooth and no short-tooth; or (b) said short block in each of said at least two pairs having at least one short-tooth and no long-tooth and said long-block in each of said at least two pairs having at least two long-teeth and no short-tooth; where each of the effective pitches of said at least one or two short-teeth is smaller than D=(360/T) degree, and each of the effective pitches of said at least one or two long-teeth is larger than D. A rotating electric motor as claimed in claim 2, wherein the effective pitches of said long-teeth are equal to each other. A rotating electric motor as claimed in claim 2, wherein the effective pitches of said short-teeth are equal to each other. A rotating electric motor as claimed in claim 2, wherein the number of teeth (26, 46) in said short-block is (T/H)-1, and the number of teeth in said long-block is 1. A rotating electric motor as claimed in claim 2, wherein H is 3, T is an integral multiple of 3, the number of the pairs of said at least two pairs of short-block and long-block is an integral multiple of 3, the the number of said long-teeth of said armature core (24, 44) is an integral multiple of 3, and the number of said short-teeth of said armature core is an integral multiple of 3 and not less than the number of said long-teeth. A rotating electric motor as claimed in claim 6, wherein the numbers of the teeth in said short-blocks are equal to each other, and the numbers of the teeth in said long-blocks are equal to each other. A rotating electric motor as claimed in claim 1 or 2, wherein the number of said at least a pair or at least two pairs of short-block and long-block is an integral multiple of H. A rotating electric motor as claimed in claim 1 or 2, wherein the whole effective pitch of sequential H pairs of said at least a pair or at least two pairs of short-block and long-block is equal or almost equal to (360/P)Q degree, and the number of teeth (26, 46, 56) in a pair of neighbouring short-block and long-block in said sequential H pairs is an integral multiple of Q, where Q is an integer not less than 2. A rotating electric motor as claimed in claim 9, wherein Q is not equal to an integral multiple of H. A rotating electric motor as claimed in claim 1 or 2, wherein the number of said teeth (26, 46, 56) in a pair of neighbouring short-block and long-block of said at least a pair or at least two pairs of short-block and long-block is not equal to an integral multiple of H. A rotating electric motor as claimed in claim 1 or 2, wherein the ratio of the effective pitch of each of said at least one or two short-teeth to the effective pitch of each said at least one or two long-teeth is R:R+1, where R is an integer. A rotating electric motor as claimed in claim 1 or 2, wherein at least one of said at least one or two long-teeth has at least one dummy-slot portion (a'-f') in the face thereof opposed to said magnet member (23, 43, 53). A rotating electric motor as claimed in claim 13, wherein the ratio of the effective pitch of each of said at least one or two short-teeth to the effective pitch of each of said at least one or two long-teeth is R:R+1, where R is an integer, and said dummy-slot portion (a'-f') and said winding slots are positioned at equal or almost equal angles around said rotary shaft (21, 41, 51). A rotating electric motor as claimed in claim 1 or 2, wherein the number of said teeth (26, 46, 56) in said short-block is larger or smaller than the number of said teeth in said long-block. A rotating electric motor as claimed in claim 1 or 2, wherein said at least a pair or at least two pairs of short-block and said long-block of said armature core (24, 44, 54) are symmetrically positioned around said rotary shaft (21, 41, 51). A rotating electric motor as claimed in claim 1 or 2, wherein H is an integral multiple of 3, and the number of the pairs of said at least a pair or at least two pairs of short-block and long-block is an integral multiple of 3. A rotating electric motor as claimed in claim 1 or 2, wherein H is an integral multiple of 3, the whole effective pitch of sequential 3 pairs of said at least a pair or at least two pairs of short-block and long-block is equal or almost equal to (360/P)Q degree, and the number of said teeth (26, 46, 56) at a pair of neighbouring short-block and long-block in said sequential 3 pairs is an integral multiple of Q, where Q is an integer not less than 2. A rotating electric motor as claimed in claim 18, wherein Q is not equal to an integral multiple of 3. A rotating electric motor as claimed in claim 18, wherein T is an integral multiple of P and not less than 3P. A rotating electric motor as claimed in claim 20, wherein the number of teeth (26, 46, 56) in said short-block is (TQ/3P)-1, and the number of teeth in said long-block is 1. A rotating electric motor as claimed in claim 21, wherein T=6P or T=3P. A motor as claimed in claim 1 or 2 including a distributing means (30) having a position detecting means (32) for detecting a relative position between said magnet member (23, 43, 53) and said armature core, (24, 44, 54) and a drive means (31) for supplying said polyphase winding groups with polyphase currents corresponding to output signals of said position detecting means (32). A rotating electric motor comprising: a field permanent magnet member (23, 43, 53) of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft (21, 41, 51) of said electric motor, the number of said N and S poles being P which is an even number, an armature core (24, 44, 54) made between two adjacent winding slots where a plurality of overlapping winding coils (A1-A4; B1-B4; C1-C4) of polyphase winding groups are wound, the number of said teeth being T which is not less than 2P, and the number of phases of said polyphase winding groups being H which is not less than 2, wherein said armature core (24, 44, 54) has at least one short-tooth (as herein defined) and at least one long-tooth (as herein defined), each of the effective pitches of said at least one short-tooth is smaller than D=(360/T) degree, and each of the effective pitches of said at least one long-tooth is larger than D, the whole effective pitch of sequential L teeth of said armature core being equal or almost equal to (360/P)Q degree, where L is an integer larger than H and Q is an integer not less than 2; wherein the ratio of the smallest value of the effective pitches of the teeth (26, 46, 56) to the effective pitch of the m-th tooth in said sequential L teeth is R:R+Vm, where R is an integer not less than 1 and Vm is an integer including O; and wherein sum of Vm from m=l to m=L is W which is not equal to an integral multiple of Qd, where Qd is a divisor of Q and larger than l. A rotating electric motor as claimed in claim 24, wherein W=Qd±1. A rotating electric motor as claimed in claim 24, wherein W=Qm±1, where Qm is an integral multiple of Q. A rotating electric motor as claimed in claim 24, wherein Q=P. A rotating electric motor as claimed in claim 24, wherein H=3. A rotating electric motor as claimed in claim 24, wherein Q is not equal to an integral multiple of H. A rotating electric motor as claimed in claim 24, wherein at least one of said at least one long-tooth has at least one dummy-slit portion (a'-f') in the face thereof opposed to said magnet member (23, 43, 53). A rotating electric motor as claimed in claim 30, wherein said dummy-slit portion and said winding slots in said sequential L teeth are positioned at equal or almost equal angles around said rotary shaft (21, 41, 51) by 1/R of the smallest value of the effective pitches of said teeth in said sequential L teeth. A rotating electric motor comprising: a field permanent magnet member (23, 43, 53) of a circular form having permanently magnetized N and S poles alternately positioned around a rotary shaft (21, 41, 51) of said electric motor, the number of said N and S poles being P which is an even number; and an armature core (24, 44, 54) made of magnetic material having a plurality of teeth (26, 46, 56) made between two adjacent winding slots where a plurality of overlapping winding coils (A1-A4; B1-B4; C1-C4) of the polyphase winding groups are wound; the number of said teeth being T which is not less than 2P, and the number of the phases of said polyphase winding groups being H which is not less than 2, wherein at least one of said teeth (26, 46, 56) has at least one dummy-slot portion (a'-f'); wherein said armature core (24, 44, 54) has at least first and second slot-groups, said dummy-slot portion and said winding slots in said first slot-group are positioned at equal or almost equal angles by a first pitch, and said dummy-slot portion and said winding slots in said second slot-group are positioned at equal or almost equal angles by the first pitch; and wherein a second pitch between adjacent winding slots of said first slot-group and said second slot-group is not equal to an integral multiple of said first pitch. A rotating electric motor as claimed in claim 32, wherein the ratio of the second pitch to the first pitch is equal to (1+N/M) or (1-N/M), where M is an integer not less than 2 and N is an integer not less than 1 and not equal to an integral multiple of M. A rotating electric motor as claimed in claim 32, wherein said armature core (24, 44, 54) has at least a pair of short-block and long-block alternately positioned around said rotary shaft (21, 41, 51) said short-block having at least one short-tooth and no long-tooth, and said long-block having at least one long-tooth and no short-tooth, where each of the effective pitches of said at least one short-tooth is smaller than D=(360/T) degree, and each of the effective pitches of said at least one long-tooth is larger than D. A rotating electric motor as claimed in claim 34, wherein the number of said teeth (26, 46, 56) in said short-block is not less than the number of said teeth in said long-block.

Inventors: GOTOU, MAKOTO
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1985
Main classification: H02K29
IPC codes: H02K1, H02K29