Abstract: A rotor for an alternating current generator in which the rotor shaft carries a pair of pole members and a core member. A spool that is formed of electrical insulating material is carried by the core member and has ribs that fit within slots formed in the core member. The spool supports a field coil, the inner turns of which engage the ribs and portions of the core disposed between the ribs. The rotor shaft supports a cooling fan that is formed of electrical insulating material. The fan is connected to a plurality of posts that extend axially from the spool. The fan supports a pair of lead wires that connect the field coil to the slip rings of a slip ring assembly.

Abstract: A rotor for an alternating current generator that includes a steel rotor core that carries a field coil supporting spool. The core has axially extending circumferentially spaced slots on its outer periphery that receive axially extending and circumferentially spaced ribs of the spool. The spool ribs are connected to spool end flanges. A field coil is wound on the spool and core. The inner turns of the field coil contact outer surfaces of the spool ribs and outer surfaces of the core located between the spool ribs.

Abstract: According to the invention, an insulator is provided at the axial ends of a rotor core. The insulator has radially spaced rows of notches at intervals approximately equal to the diameter of the winding wire for guiding placement of the turns of the winding at a predetermined location. After completion of the first turn, the wire is skewed at a first angle with respect to the plane of the first turn to coincide with the second notch and the remainder of turns in the first layer in turn completed in substantially parallel relationship. At the completion of the last turn of the first layer, the wire is crossed over the next to the last turn, skewing the winding in an opposite direction and situating the wire in the valleys formed between the successive turns in the first layer. The sequence continues alternately for the remaining layers.

Abstract: A field subassembly is assembled by positioning two coil supports adjacent respective core end faces of a ferromagnetic core. The core-engaging surfaces of the coil supports and the core end faces have respective surfaces which are uninterrupted by projections. During the assembly of the field, fasteners are pushed into the respective coil supports and the core such that the fasteners engage mounting holes in the coil support with a press-fit. After the field is wound, a brush holder subassembly is also pressed onto the fasteners and the resultant core subassembly is connected to a field housing by driving the fasteners in a conventional fashion. In the preferred embodiment, the fasteners provide a three-point contact with mounting holes formed in the coil supports and the brush holder subassembly.

Abstract: The stator of a pancake motor comprises porcelianized steel with stator coils secured thereto by means of raised tabs which "entrap" a few turns of the coil between the tab and the surface of the stator. Thermoplastic insulation on the wire, when heated, rigidly bonds the coil turns together thereby gripping the tabs and securing the coils to the stator surface. Coil connections are provided by printed wire patterns on the stator surface. Since the stator coils may be wound insitu, bobbins, fasteners and printed wiring boards are eliminated, assembly steps are reduced, and both convective and conductive heat dissipation are improved thereby reducing the motor cost, improving its reliability and allowing the motor to run cooler or to provide more power output for a given temperature increase.

Abstract: Mounting for ignition module in which a ferromagnetic flux carrying core includes a plurality of spaced, parallel leg portions. An ignition coil module has a generally central opening which is adapted to receive one of the core legs. One recess is provided on the outer surface of the module, and a second recess is provided in the core leg adjacent the one on which the module is disposed. The two recesses are oriented and dimensioned to form complementary portions of an opening adapted to receive a resiliently flexible retaining pin therein to fasten the module and core in assembled relation.

Abstract: Slotless and toothless wound stators are produced for electrical machines, in particular brushless DC motors, by providing temporary teeth at opposite ends of an iron cylinder with smooth inner wall end-to-end, placing an electrical winding without supporting form against the inner wall and between and around the teeth, pressing the winding against the smooth inner wall by an expandable retaining cylinder, and removing the temporary teeth. A temporary fixture can provide the temporary teeth by radially inwardly extendable and radially outwardly retractable fingers, the fingers being removed by outward retraction through cam means. Alternately, plastic end members with teeth may be glued to opposite ends of the smooth-walled iron cylinder to provide temporary teeth, the teeth being machined off after positioning the winding.

Abstract: An electronically commutated d.c. motor having a dome-shaped external rotor and a stator of a double-T-shaped configuration. Stator includes one yoke stack disposed asymmetrically in relation to the longitudinal stator axis. In addition, the stator includes two pole stacks each of which is provided on the same side with an extension in the circumferential direction. A printed circuit board is secured to a mounting flange of the d.c. motor.

Abstract: A rotational speed sensor (10) comprising a shaft (54) having a reluctor (50) mounted thereon and coacting with a complementary shaped stator (18). The reluctor (50) and stator (18) have coacting regularly spaced projections (20, 58) which are magnetizable so that as the reluctor (50) rotates with the shaft (54), there is developed a cumulative voltage output which in turn enables utilization of much greater air gaps between the respective projections (20, 58). Because of the greater latitude in the air gaps, it is possible to construct a variable reluctance speed sensor (10) much more economically and with less emphasis on cumulative manufacturing tolerances. This greater flexibility of manufacturing with higher manufacturing tolerances contributes materially to the attainment of an economical and reliable speed sensor.

Abstract: An ignition magneto having an improved primary wiring assembly that consists of a plastic bobbin having a generally rectangular configuration and composed of a pair of end flanges connected together by a pair of side walls and a pair of end walls. The side edges of each wall are spaced from the side edges of adjacent walls, to provide a gap or slot at each corner of the bobbin. A wire is wound in a plurality of turns around the walls and extends across the slots. One end flange is provided with grooves within which the free ends of the wire are gripped. The primary winding assembly is positioned in a cup-shaped casing around a central upstanding chimney which extends upwardly from the bottom of the casing. After installing a transistor and trigger coil, as well as a secondary winding around the primary winding assembly, the components are potted in the casing with a thermosetting resin.

Abstract: A terminal tray which overlies the windings of a motor stator, has a plurality of lead guides. The guides are arranged to separate the leads from one another and retain them in their respective positions. The joins between the leads and the motor stator are within the tray. Further a lid arrangement and hinge tabs are provided for joining the lid to the tray. A plurality of spigots are extending from the tray into the stator and windings thereof for retaining the tray to the motor.

Abstract: A unique design and construction is presented for the rotor of a dynamoelectric machine. The rotor is comprised of two end plates, bar means for holding the end plates together, a stack of pole laminations, electrical conductors wrapped about the laminations and an insulator means. The end plate contains apertures about its periphery such that the rotor can be balanced about two axis perpendicular the rotor axis of rotation by inserting masses/weights into the apertures. The insulator means electrically insulates the electrical conductors from the ends of the stack laminations, the rotor end plates and the rotor shaft. The insulator means by its unique shape further acts as a guide to position electrical conductors about the laminations during pole winding. In one embodiment the insulator means acts as a thermal insulator protecting electrical conductors when the bar means are welded to the end plates.

Abstract: A field subassembly is assembled by positioning two coil supports adjacent respective core end faces of a ferromagnetic core. The core-engaging surfaces of the coil supports and the core end faces have respective surfaces which are uninterrupted by projections. During the assembly of the field, fasteners are pushed into the respective coil supports and the core such that the fasteners engage mounting holes in the coil support with a press-fit. After the field is wound, a brush holder subassembly is also pressed onto the fasteners and the resultant core subassembly is connected to a field housing by driving the fasteners in a conventional fashion. In the preferred embodiment, the fasteners provide a three-point contact with mounting holes formed in the coil supports and the brush holder subassembly.

Abstract: An insulated terminal connector which is designed to be frictionally mounted on the upper surface of a stator core prior to winding the field coils about the poles disposed inwardly of the core includes a retainer device and an alignment device.

Abstract: A stator structure for an electromagnetic device includes a core of cylindrical form having pole pieces between which are defined grooves accommodating windings. The core is formed with a diametrical slot which extends the length of the core and which locates the connections between adjacent windings.

Abstract: A conductor of a rectangular cross-section is overlapped with an insulator having a greater width than the width of the conductor and wound to form a coil assembly. The oversized portions of the insulator are folded and cemented together. The coil assembly is mounted on a stator pole core so that the folded insulator portions are respectively adjacent to the pole piece of the core and to the inner wall of a cylindrical yoke when the pole core is secured to the yoke. The folded portions of the insulator are depressed by an amount sufficient to allow the coil assembly to be firmly clamped in position.

Abstract: A rotation driving device is constructed from a bobbin, a coil wound on the bobbin, a stator inserted in the bobbin, and a permanent magnet arranged inside the stator. The stator consists of a hollow cylindrical body having a first, second, and third recesses. In accordance with the command electrical signal supplied to the coil, the rotation driving device changes the rotational position of the rotor.

Abstract: A stator comprises a one-piece U-shaped stator sheet having a pair of elongate parallel legs. The legs form pole shoe bridges at their front ends for their reception of a driven motor. At least one of the pole shoe bridges interconnects the legs adjacent their front ends. A coil-carrying bobbin is mounted on one of the legs, the length of the wound coil being longer than its diameter. A separate yoke sheet is fastened to the legs adjacent rear ends thereof to secure the bobbin on the leg. The stator is formed by first stamping-out a stamping which includes the parallel legs and the yoke, with the yoke being integrally attached to the legs by means of webs. After the stamping undergoes the usual pretreatment, the yoke sheet is separated from the legs, whereupon the coil bobbin is slipped onto the leg from the rear. Then, the yoke sheet is secured to the rear ends of the legs to prevent removal of the coil bobbin.

Abstract: Coil retainer structure for use in an electric motor. The coil retainer extends about the periphery of an end face of the motor core and includes an offset portion extending about the periphery of the core axially inwardly of the end face to permit a housing member to have a portion thereof facially abutted to the core end face adjacent the offset portion. A coil is wound on the core and has a portion retained by the retainer. Securing structure is provided for securing the housing member directly to the core in facially abutted relationship with the adjacent end face. In the illustrated embodiment, coil retainers having such offset portions are provided at each of the opposite end faces of the core. One of the coil retainers is further provided with coil end terminal structure adjacent the offset portion.

Abstract: An electromagnetic prime mover device comprising a rotor in the form of a flywheel and a stator including a fluid-tight housing accommodating coolant.

Abstract: Two different stator windings of an electric motor are separated by insulating elements of die-cut sheet material. Each of these elements comprises a pair of end panels which separate the windings at the two ends of the stator, and a series of parallel strips which interconnect the end panels and each of which extends within one of the stator slots. One of the end panels has, extending from its edge opposite that from which the strips extend, at least two consecutive flaps folded one over the other in the manner of a sleeve. The sleeves of the insulating elements receive the joins between the wires of the windings and the associated supply leads.

Abstract: A flat motor comprises a rotor including a shaft and a plurality of coils arranged concentric with the shaft and each said coil being constituted by a winding having a predetermined diameter, the position of the end of the winding being set at a predetermined distance from the shaft, a magnet having a doughnut-like form with the inner periphery thereof spaced apart from the shaft by a distance smaller than said predetermined distance, and a connector plate provided on the rotor and extending between the rotor and magnet, having a thickness at least smaller than the predetermined diameter of the coil winding. The end of the winding of each coil is electrically connected to the connector plate.

Abstract: A rotor of a turbine generator, wherein the field and amortisseur windings are held in place by means of axially and tangentially secured rings shrunk on the rotor body without the use of otherwise customary slot wedges. The rings are shrunk on the rotor body without overlapping and at a distance from each other. In this way, the magnetically effective rotor cross-section is increased up to 30% without reducing the size of the air gap.

Abstract: The invention provides a new method of making electric motor stator assemblies of the type comprising a magnetic stator body with a plurality of discrete poles and a coil wound on each pole. Preferably each stator assembly is made by (a) providing a flexible chain of hollow bobbins with terminal pins for each bobbin; (b) inserting a magnetic pole piece in each bobbin in turn; (c) winding a coil on each bobbin and attaching the ends of each coil to the terminal pins of the bobbin on which the coil is wound; and (d) inserting at least a portion of the bobbin chain in a casing which engages and provides a low reluctance magnetic connection between the several pole pieces, whereby a stator assembly is formed which is characterized by (1) a stator in which the casing acts as the stator body and the pole pieces act as individual stator poles, and (2) individual coils each associated with one of the stator poles.

Abstract: A modulator motor and drive unit for use in an electrical device, such as a hand food mixer, wherein the motor is characterized by a low-cost speed control which is capable of providing a large number of discrete motor speeds. The speed control, rather than utilizing a multi-contact switch connected to the field coil by individual taps, has approximately twenty field coil continuous loop taps wound over a bobbin spindle in side-by-side relationship with a wiper contact being slideably movable relative thereto along a path from which the insulation has been removed. Positions of the wiper contact may be determined by replaceable detent elements provided with different detent patterns providing different series of motor speeds whereby the same motor and drive module may be provided within a suitable housing(s) for the economical production of several different models of such electrical devices having differing speed selections.

Abstract: An armature winding for a three-phase induction motor is provided with slots in each of which are placed windings having a double-layer structure. The number of slots, q per pole per phase is: q=z/(3.times.P), and q is less than 1/2, where z denotes the number of slots of the stator, and P the number of poles. The number of coils, Q, per phase is: Q=z/3. The coils constitute real poles of the same polarity, the number of which is also Q, and further provide one or more imaginary poles between the real poles. The coils are connected in such a way that the voltage vector of each phase is completely balanced.

Abstract: A coil bobbin includes a spindle, a terminal retaining flange and a second flange extending from opposed ends of the spindle between which a coil of wire is wound. The terminal retaining flange includes two diametrically opposed slots which receive electrical terminals, one of the slots serving as a starting place for the wire.

Abstract: A molded end coil insulator designed for attachment to a ferromagnetic core and which forms part of the ground insulation for magnet wires wound thereabout and about a series of pole pieces formed on the core. The end coil insulator includes features which improve the adaptability of the resulting device to automated winding of the magnet wires and connection of lead wires from an external circuit with the magnet wires. One such feature is an improved terminal support which receives and retains a terminal member in good electrical contact with a magnet wire, and which positively grips a lead wire from an external circuit in such a manner that a section of the lead wire connected with the terminal member is effectively isolated from strains and vibrations in the external circuit. Another feature of the molded end coil insulator is structure for positively restraining and guiding crossover sections of magnet wires which extend between the pole pieces.

Abstract: In a stator for an electromotor, field coils associated with a packet of laminations are spaced apart by filler pieces. The combination of the field coils and filler pieces form an annular arrangement. Each filler piece extends between the adjacent ends of two field coils. The filler pieces are slotted in the radial direction to provide a certain adjustability in the circumferential direction of the annular arrangement where the dimension between the adjacent ends of the field coils is subject to variation.

Abstract: An air-gap winding within an electrical machine is arranged with the conductors thereof extending in the axial direction of the machine and are embedded in an electrically insulating cylinder which serves as the winding support. The conductors, or at least some of them, are concentrated into conductor bundles which lie approximately upon a cylindrical surface extending between the inner and outer surfaces of the winding support and coaxially with the latter. The conductors of the bundles are electrically associated with the one or more phases of the machine winding and the number of conductors of each bundle associated with a particular phase satisfies the equation N.sub.LP =C, where C is any whole number constant, the value of which lies between zero and number N.sub.L of the conductors of that bundle.

Abstract: An improved electric machine wherein the machine comprises a slot for receiving a winding formed from a winding bar having an outer glow-discharge protection and wherein the improvement comprises a wrapping in the form of a strip of conductive material arranged in surrounding relationship to the bar so that the edge portions of the strip are situated adjacent a corner of the narrow side of the bar which faces the slot bottom. The improvement further includes cementing the edge portion of the strip lying beneath such narrow side to such side and a shim disposed adjacent the side of said bar along which the other edge portion resides.

Abstract: A rotor for use in an induction type a.c. generator and a method for fabricating the same are disclosed. The rotor comprises pole pieces having pointed ends at their peripheries, the pointed ends of one pole piece and the pointed ends of the other pole piece alternating in position and serving as, alternately, north and south magnetic poles; a core or yoke disposed between the pole pieces to magnetically coupling the pole pieces; an insulating bobbin disposed on the core or yoke and between the pole pieces; and an exciting coil wound on the bobbin cylindrically. The core or yoke is in the shape of a barrel and the insulating bobbin is forcibly mounted on the barrel-shaped core by the application of pressure.

Abstract: A support structure for unitizing coil turns into a single member and bracing each coil of a multi-coil stator dynamoelectric machine. Each stator coil includes several turns relatively concentrically disposed. Each coil turn constitutes two longitudinal conductor portions and two end turn conductor portions. One end turn portion serially connects two longitudinal portions and the remaining end turn portion serially connects one of the longitudinal portions with a longitudinal portion of a concentrically adjacent coil. Each coil preferably lies in a plane defined by a portion of a cylinder and the coils are disposed in a cylindrical arrangement having a longitudinal axis therethrough such that one longitudinal portion of the outermost coil turn lies along the outer radial extent of the cylindrical arrangement and the remaining longitudinal portion of the outermost coil turn lies radially nearer the longitudinal axis of the cylindrical arrangement.

Abstract: In a dynamoelectric machine having armature conductors located in the air-gap separating rotor and stator, the conductors are secured to the stator structure. Conductor fastening means are provided which maintain the armature conductors and their support members in compression in all modes of operation of the machine.

Abstract: A slot closure for the semi-closed slots of the stator of an electric machine is disclosed. The slot closure comprises slot closing bars interconnected in a ladder-like arrangement by flexible strips. Flexing of the strips by about 90.degree. correspondingly rotates individual bars and permits them to be successively inserted edge-wise through the slot openings. Advantageously, the ladder-like arrangement of bars and strips is made of a moldable or stampable material.

Abstract: An electric motor comprising a stator block or assembly having stator windings and a control circuit substrate for supplying driving current thereto mounted integrally with the stator block, a shaft rotatably journalled in said stator block, a magnet casing in which are mounted driving magnets associated with the shaft, a rotor block or assembly provided with detector magnets held at an end of the shaft, and a detector winding block or assembly mounted within a motor housing to which a bracket is fixed. There is also disclosed a control means for controlling the driving current for the driving windings in response to the voltage induced in the detector winding block.

Abstract: A salient pole includes a flat coil made up of a multilayer winding of round wire. The wire includes an adhesive layer which is cured after winding to consolidate the winding. The winding is within a U-shaped channel which is impregnated with resin to fill any gaps. The flat coil fits over a pole core and is fixed thereto by means of spacers which axially space the coil from the pole core and radially space the coil from the machine casing.

Abstract: According to the invention, the stator of an electrical machine comprises a slotted core and a multilayer bar winding partially received in the core slots and partially accommodated in the air gap of the electrical machine. Interposed between the bars of the multilayer bar winding are spacers whose slots accommodate brace members enveloping each of the bars of the multilayer bar winding on its opposite sides. Each of the brace members is attched to two rollers, one of which is secured in a spring clip received in an axial slot of the stator core, and the other of which is accommodated in a threaded pin received, in turn, in a hole provided in an insulating wedge member. The invention improves the maintainability of the electrical machine, making it as easy to maintain as any conventional slotted machine. The invention also improves the space factor of the electrical machine's air gap and accounts for a better fastening of the multilayer bar winding of the machine's stator.

Abstract: Device for bracing an air-gap winding in a stator of an electric machine wherein individual winding bars are secured between a radially outer stack of stator laminations and a radially inner nonmagnetic support cylinder, includes spacer wedges disposed between respective pairs of the individual winding bars in circumferential direction, at least some of the spacer wedges being in the form of mounting wedges having dove-tailed extensions received and braced in corresponding recesses formed in the stack of stator laminations at the inner circumference thereof, and the remainder of the spacer wedges being in the form of tightening wedges having tangential bracing means includes at least one flexible tube subjectible to internal pressure, and radial bracing means similarly includes at least one flexible tube subjectible to internal pressure.

Abstract: A permanent split capacitor induction motor rated at 460 volts AC is provided with first and second main winding parts and an auxiliary winding. The motor includes a core of magnetic material having a plurality of winding receiving slots formed in it. The main and auxiliary windings are constructed from a plurality of wire turns arranged in coil sets. The auxiliary winding is placed adjacent the first main winding part in the core slots, and is electrically connected to it. The coil sets of the auxiliary winding are separated from the coil sets defining the second main winding part by the coil sets of the first main winding part. Individual wire turns are distributed in the slots of the motor and positioned so that the voltage between coil sets forming the main winding parts and the auxiliary winding can never exceed the voltage across the capacitor.

Abstract: A motor stator having a salient pole magnetic core on which are wound coils of conductive wire incorporating an annular printed circuit board having a plurality of terminals formed around the outer periphery of the board. The terminals are formed by radially extending conductive regions, each region having a V-shaped notch extending in from the periphery of the printed circuit board. The printed circuit board is secured directly to the projecting ends of the coils at one end of the core and the two wire ends of each coil are secured in adjacent notches.

Abstract: The present invention discloses a stator assembly for a dual three phase inverter-driven motor.

Abstract: A stator structure for the induction motor is disclosed, in which the winding accommodated in the slots of the stator iron core has one end portion, outside of the stator iron core, shaped to provide a flared bell-like opening, and the other end portion thereof, outside of the stator iron core, forming short-passed winding and being provided with an opening sufficiently large to permit insertion of the shaft of the rotor. Between the inner surface of the short-passed end portion and a given portion of the surface of the stator iron core a coil-supporting member is disposed. The outer surface of the coil-supporting member has a shape along the inner surface of the other coil end portion, while the inside thereof is so shaped as to provide a sufficient space or air gap with respect to the rotor to be inserted.

Abstract: A bi-directional pump having a pump housing, an inlet communicating with one end of the housing, an outlet communicating with the other end of the housing, an impeller within the housing adjacent the inlet, a baffle plate within the housing adjacent the outlet, a shaft extending through the inlet and journaled in the baffle plate, the impeller being secured to the shaft for rotation with the shaft, the impeller having vanes extending radially from the shaft both the impeller and the baffle plate and being spaced from the interior of the housing, whereby fluid flows through the inlet, radially outwardly of the impeller, radially inwardly of the baffle plate, and through the outlet. In a specific embodiment, a pump stage can be positioned on both sides of a motor, and the motor rotor and the impeller of each pump can be secured to the same shaft for rotation, the shaft being journaled in the baffle plates of the pump stages.

Abstract: The invention relates to an electric machine such as a motor having a stator lamination packet with winding heads at opposite ends thereof. A cover for each or either winding head has inner fingers which extend into the grooves of the stator packet and outer fingers with wedge shaped portions which extend between the inner fingers in the installed position. The wedge shaped portions are resiliently mounted relative to the cover proper. The wedge shaped portions have one set of edges engageable with an end face of the stator packet and a second set of relatively inclined edges engageable with the underside of the associated winding head. Circumferentially arranged grooves in the wedge shaped portions hold a ring which biases the outer fingers radially inwardly to bunch the winding head into a predetermined confined space.

Abstract: A stator of uni-directional self starting synchronous motor of which magnetic pole teeth formed flatly integral with a yoke for opposing a flat disk shape rotor having axial rotary shaft. The yoke is of an elongated plate having adjacent an end the pole teeth comprising radially alternately extending inner and outer teeth formed as punched and joined through a connecting part, the plate is bent into a substantially U shape in section, a core of a magnetic material having an axial hole for passing therethrough the shaft of rotor is disposed between opposing both end parts of the yoke coaxially with the teeth to provide main magnetic path, and a coil wound on a bobbin is disposed around the core.

Abstract: An electric rotary stepping motor intended for use in watch movements comprises a stator including a coil support coaxial with the rotor, two compact coils having flat turns, and a field-closing yoke capable of magnetically blocking the rotor in a position enabling it to start up in the desired direction. The motor is made more compact, and its manufacture and assembly are simplified, by designing the coil support with two diametrically opposed arms and the coils as self-supporting elements in which the turns of the windings are joined to one another.

Abstract: The invention provides a new method of making electric motor stator assemblies of the type comprising a magnetic stator body with a plurality of discrete poles and a coil wound on each pole. Preferably each stator assembly is made by (a) providing a flexible chain of hollow bobbins with terminal pins for each bobbin; (b) inserting a magnetic pole piece in each bobbin in turn; (c) winding a coil on each bobbin and attaching the ends of each coil to the terminal pins of the bobbin on which the coil is wound; and (d) inserting at least a portion of the bobbin chain in a casing which engages and provides a low reluctance magnetic connection between the several pole pieces, whereby a stator assembly is formed which is characterized by (1) a stator in which the casing acts as the stator body and the pole pieces act as individual stator poles, and (2) individual coils each associated with one of the stator poles.

Abstract: An insulating assembly for stator slots of electrical motors is provided comprising a pair of end plates of insulating material having a center opening for receiving a rotor and outwardly of said opening cutouts having the same shape as the stator slots of electrical motor, each of said cutouts having along the periphery thereof a flange extending from said end plate, intended to be inserted in a stator slot so as to form an insulating partition between the inner wall of the slots and the stator winding.

Abstract: In an electromagnetic driving device for example for an electric clock, a driving polar rotor arranged in the magnetic field of a coreless field coil drives a rotatable following polar rotor so that in their static states the poles of the rotors are shifted at a definite angle in the direction of the magnetic field of the coil. The driving polar rotor is rotatably supported within a bobbin on which the coil is wound and is retained in the bobbin by a rotor retaining part which is held in place by a printed circuit plate which controls the current flowing through the coil.