Abstract: An electric rotary machine which may be employed as a dc motor in an automotive engine starter. The motor includes an armature equipped with an armature shaft, a commutator, brushes, and a bearing retaining an end of the armature shaft. The surface of the commutator has a plurality of protrusions extending in parallel to each other in a direction of rotation of the commutator. Each of the brushes has formed in the bottom thereof grooves in which the protrusions of the commutator are fit. The brushes are urged into constant engagement of the grooves with the protrusions on the commutator to establish electrical contacts between the brushes and the commutator and minimize movement of the armature shaft relative to the bearing.

Abstract: In an electrical device, in particular a power tool, equipped with a commutator motor, and in an accessory for an electrical device of this kind, a carbon brush shape adapting device is an integral component of the electrical device or of the accessory.

Abstract: Assembly work of an electric motor in which a power supply device and a rotation detector both equipped in a motor case are connected to a control device via a connector unit can be made easy. A power window motor includes an armature provided with an armature shaft and a motor yoke rotatably accommodating the armature. A gear case is fixed to the motor yoke, and a power supply unit that supplies a driving current to the armature is equipped to the gear case in the axial direction of the armature shaft. A sensor unit that detects rotation of the armature shaft is attached to the power supply unit in the axial direction of the armature shaft. A connector unit for connecting the power supply unit and the sensor unit to the control device is integrally formed with the power supply unit. The power supply unit is attached with the sensor unit in advance and then equipped to the gear case.

Abstract: A carbon brush that suppresses a wear amount of a carbon commutator and has less swelling is provided. The carbon brush has a part connected to a lead and is one that slides in contact with a carbon commutator that is used in a fuel pump. The bulk density of the carbon brush is 1.85 g/cm3 or less, and the shore hardness of the carbon brush is 40 or less.

Abstract: A brush holder includes a base member and a retaining member mounted on the base member. The retaining member includes a first brush retaining portion and a first coil retaining portion. A first choke coil is electrically connected to a first brush. The first choke coil includes a first coil terminal extending to the outside of the first coil retaining portion. The base member includes a connector portion, a first conductive member, and a first coil terminal support portion. The first conductive member extends from the connector portion and is electrically connected to the first coil terminal at a first connecting portion. The first coil terminal support portion supports the first coil terminal between the first connecting portion and the first coil retaining portion.

Abstract: An electric machine incorporates a brush assembly that provides an audible warning when the brush in the brush assembly approaches the end of its useable length. The brush incorporates a device incorporated into the brush or a brush design which cooperates with the brush holder to generate the noise. The noise provides a warning to the user of the electric machine that the useable length of the brush material is near.

Abstract: An electric motor has a pair of brushes for transferring power to windings of a wound rotor by making sliding contact with a cylindrical commutator. Each brush has a body with a pair of end surfaces, and a contact surface extending between the end surfaces and configured to slidingly contact a cylindrical circumferential surface of the commutator. The extending direction of the contact surface is inclined relative to the axial direction of the commutator, and the contact surface is V-shaped when viewed in the extending direction thereof.

Abstract: An electrical generator includes a rotary disk that is made of plastic injection molding in which a plurality of coils each having an exposed contact is embedded. Two stationary disks are arranged on opposite sides of the rotary disk and each has an inside surface that opposes the rotary disk and carries two semi-circular magnets. The rotary disk is fixed to a shaft having opposite ends fit into bearings that are received in central bores defined in the stationary disks. The coils are each formed by winding a wire in at least one turn in the form of a circle or an ellipse, the turns being coincident with each other or partially offset with respect to each other. Or alternatively, the coils are formed concentric with respect to each other and the rotary disk.

Abstract: A manufacturing method for a brush that can reduce contact surface area between a commutator and the brush, thereby reducing frictional noise, is provided. Specifically, a method to manufacture a brush, which provides one surface with contact surfaces that make sliding contact with the commutator, involves a step to mold a molded body and a step to cut the molded body. In the molding process, carbon powder containing copper powder is sintered to form a molded body having a groove on the top surface along the direction of the axis of rotation of the commutator, and curved surface margins in the margins of the top surface in the direction of the axis of rotation. In the cutting step, the central part of the top surface of the molded body is cut by a grinding stone along the cutting direction to form contact surfaces between the margins of the top surface.

Abstract: Slip ring assemblies for controlling pitch of a wind driven blade such as those utilized in wind turbines can include a series of grooves disposed about an outer perimeter of a rotating portion, each one of the grooves comprising a first planar surface intersecting with a second planar surface at an angle of 75 to 105 degrees, and a concavely rounded bottom portion at the intersection of the first and planar surfaces. The rotating portion of the slip ring can be formed of a bronze material and may include a graphite coating. Also disclosed herein are wind turbine assemblies employing the slip ring assemblies.

Abstract: A carbon brush holder includes an insulated housing having a through hole with a first section, a second section and a stepped portion between the first and second sections. A carbon brush-holding member is inserted into the first section of the insulated housing and has a first end face, a second end face opposite to the first end face, and an insertion portion adjoined with the second end face. The insertion portion of the carbon brush-holding member extends into the second section of the insulated housing, thereby enabling the second end face of the carbon brush-holding member to be located in the second section of the insulated housing. Thus, the second end face of the carbon brush-holding member can firmly contact a conductive member that is disposed inside the second section of the insulated housing and electrically connected with a carbon brush inserted into the carbon brush-holding member.

Abstract: A brush holder for a motor. The brush holder includes a plastic support structure corresponding incorporating at least a first and a second essentially rigid conducting element connected, respectively, between positive and negative brush or brushes and associated connecting members to form corresponding connecting paths in the brush holder for connecting the brushes to the terminals of an external source of supply voltage. At least one discontinuity is provided in at least one of the connecting paths. A resiliently deformable and electrically conducting strip is connected mechanically and electrically across this discontinuity, with a substantially permanent connection at one end, and with a thermally fusible connection at the other end, the strip having a resilient pre-loading which tends to break the connection at the said other end.

Abstract: A brush apparatus includes a brush and a brush holder. The brush includes a pigtail embedded in a wider side thereof so that the longitudinal side in cross-section of the pigtail extends in parallel with a surface of the brush coming into contact with a commutator. The brush holder includes a brush holding member, a brush spring for pressing the brush against the commutator for sliding contact, a base for holding the brush holding member and electrically connecting the same to an earth circuit, and a connection lug on the base. The brush holding member is formed with a notch on a wider side from an upper end thereof for allowing a downward movement of the pigtail when the brush wears and hence is pressed downward. A distal end of the pigtail is connected to the connection lug.

Abstract: A vibrating motor includes a base having a bearing mounting section, a magnet mounted on the base, a shaft assembled with the bearing mounting section, a pair of brushes located on the base and a rotor rotably supported by the shaft. Each of the brushes has a first contacting portion and a second contacting portion. The rotor includes a commutator facing the brushes. The commutator defines a plurality of segments. A gap is defined between two adjacent segments and extends along radial direction of the commutator. A connecting line connecting the first and second contacting portions is not through the shaft.

Abstract: A method and a device, respectively, for detecting the amount of wear on the carbon brush drive system of an electrically commutated d.c. motor which is used, for example, in the form of a pump motor in a motor vehicle. The d.c. motor is driven by at least two carbon brushes and includes means for detecting the generative follow-up voltage. The amount of wear on at least one carbon brush is derived from the time behavior of the generative motor voltage and displayed to the driver.

Abstract: An electrical brush having at least one conductive element and at least one conditioning material coated on the at least one conductive element wherein the conditioning material has a composition and thickness on the conductive element such that, as deposited on a moving contact surface in the course of brush operation, the conditioning material can have an average film thickness S<˜1 ?m so that current can be conducted by means of electron tunneling through a film thickness of the deposited conditioning material of Si?12 nm thickness over a fractional area fC, greater than 0.01 of a foot print of the conductive element in a current conductive area.

Abstract: An electric motor, in particular a motor and gear box unit for activating functional equipment in a vehicle, includes a rotor shaft (1) carrying a commutator (2) co-operating with conductive brushes (3) disposed in brush supports (4) fixed to a printed circuit card (5); the motor is provided with means for enabling brush supports to be fixed to the printed circuit card solely by surface mounting. These means may comprise, for each brush (3), a metal casing (6) containing the brush and having one wall (6) with at least one transverse tab (11) adapted to pass through the printed circuit card in order to position and hold the casing on the card and in order to provide an electrical connection. The invention enables brush-support devices to be fixed to the printed circuit card solely by surface mounting, thus making it pointless to perform an additional flow soldering operation as is required in the prior art.

Abstract: In an AC generator of a motor vehicle, having a positive polarity brush from which current flows into a corresponding slip ring and a negative polarity brush into which current flows from the corresponding slip ring, the brushes or the springs of the brushes are configured respectively differently, to achieve substantially identical rates of wear for the brushes. This is done for example by increasing the area of contact between the negative polarity brush and its slip ring, lengthening the negative polarity brush, or decreasing the amount of force applied by the spring of the negative polarity brush.

Abstract: A two-stage eutectic metal brush assembly having a slip ring rigidly coupled to a shaft, the slip ring being electrically coupled to first voltage polarity. At least one brush is rigidly coupled to a second ring and slidingly engaged to the slip ring. Eutectic metal at least partially fills an annulus between the second ring and a stationary ring. At least one conductor is rigidly coupled to the stationary ring and electrically coupled to a second voltage polarity. Electrical continuity is maintained between the first voltage polarity and the second voltage polarity. Periodic rotational motion is present between the stationary ring and the second ring. Periodic rotational motion is also present between the brush and the slip ring.

Abstract: The present invention's unique utilization of an electrolytic solution renders more efficient the conduction of electricity between two objects (such as two parts of electrical or electromechanical machinery) in relative motion. According to typical inventive practice, the electrolytic solution is a “strong” electrolytic solution of a “dual-valance” nature, including two compatible solute compounds containing electron donor ions and electron acceptor ions. When inventively implemented at the current collector interface, the electrolytic solution serves to improve current transfer across the interface. During machine operation in which a brush (e.g., fiber brush) slidingly contacts a first machine part while being affixed to a second machine part, the inventive additive represents an auxiliary vehicle for conducting electrical current from one machine part to the other machine part.

Abstract: The present invention relates to a brush 10 suitable for coming into contact with conducting plates 12 provided on an electric motor commutator 11. According to the invention, the brush has a means 15 for adjusting its pole coverage between the start of life of the motor and its stabilized operation. This is therefore a brush with pole coverage that can be varied over its operating life. Such a brush is more particularly fitted into a motor for a ventilation (air conditioning) system for motor vehicle.

Abstract: The invention provides an improvement in a slip ring (20) adapted to provide electrical contact between a stator (21) and a rotor (22). The improvement includes: a current-carrying conductor (23) mounted on the stator; a brush tube (24) mounted on the conductor; a fiber bundle composed of a number of individual fibers(26), the upper marginal end portions of the fibers being received in said brush tube, a portion of the brush tube being crimped or swaged to hold the upper marginal end portions of said fibers therein, the lower ends of the fibers in the bundle extending beyond said brush tube and being adapted to engage said rotor; a collimator tube(25) integral with or surrounding a portion of the brush tube and extending therebeyond, the lower end of the collimator tube being adapted to limit lateral movement of the lower marginal end portions of said fibers in said bundle when the rotor rotates relative to said stator; and a fluid reservoir (28) mounted on the collimator tube.

Abstract: A sliding electrical contact part is disclosed. The contact part includes a base of carbonaceous material and copper. The contact part is lead-free and contains zinc and iron-base particles having a size less than 500 ?m. The contact part is particularly suitable for electrical devices which require high friction densities and friction velocities, such as motor vehicle starters with a high power-to-weight ratio.

Abstract: A carbon brush guide for dynamoelectric machines, in particular for electric motors. The carbon brush guide is produced from aluminum and has at least one insulating layer made of anodized aluminum. Such a carbon brush guide is used in particular for multilayer carbon brushes. The carbon brush guide produces little brush noise, and experiences less wear and tear.

Abstract: Systems and methods for electrical component, e.g., brush, manufacture are provided that control grain orientation. The systems and methods utilize hot pressing techniques to enhance the properties and functionalities of the electrical components/brushes. An intermediate work product characterized by a grain orientation is initially formed through a conventional pressing technique. The conventionally-pressed intermediates are positioned within a cavity/die with the grain orientation in a predetermined orientation relative to the hot press force to be applied thereto. The hot pressed final product exhibits superior resistivity, strength and apparent density/durability. Surface features may be formed on the face(s) of the final work product during the hot pressing step that cannot be achieved in conventional processing techniques. Advantageous articles of manufacture, e.g., brushes and brush assemblies, are also disclosed.

Abstract: A compact slip ring (20), which is particularly adapted for use in small spaces, is adapted to provide electrical contact between a rotor (22) and a stator (21). The improved slip ring broadly includes an electrically-conductive monofilament (24) having one end (28) mounted on the stator and having a distal end (34); a sleeve (25) mounted on and secured to the marginal end portion of the monofilament, adjacent the distal end; and a fiber bundle (26) having a longitudinal axis (39), one marginal end portion of the fiber bundle being recessed in and secured to the sleeve, the other end of the fiber bundle engaging the rotor such that the longitudinal axis of the fiber bundle will be substantially perpendicular to an imaginary line tangent to the rotor surface at the point of contact with the longitudinal axis.

Abstract: A manufacturing method for a brush that can reduce contact surface area between a commutator and the brush, thereby reducing frictional noise, is provided. Specifically, a method to manufacture a brush, which provides one surface with contact surfaces that make sliding contact with the commutator, involves a step to mold a molded body and a step to cut the molded body. In the molding process, carbon powder containing copper powder is sintered to form a molded body having a groove on the top surface along the direction of the axis of rotation of the commutator, and curved surface margins in the margins of the top surface in the direction of the axis of rotation. In the cutting step, the central part of the top surface of the molded body is cut by a grinding stone along the cutting direction to form contact surfaces between the margins of the top surface.

Abstract: The invention describes an electrical machine having an armature with armature slots for accommodating armature coils. At least one armature coil is formed from two coil elements which are arranged symmetrically with respect to one another in relation to an axis of symmetry, which runs through the center-point of the armature shaft. The coil elements are connected to two adjacent commutator laminates of a commutator. A first brush, a second brush and a third brush bear against the commutator in a manner such that they can slide. The second brush interacts with the first brush or the third brush.

Abstract: Disclosed is a motor which, even if the commutator is deformed, suppresses brush deformation to thereby prevent short-circuiting between the positive-pole-side brush and the motor housing.

Abstract: The invention provides an improvement in a slip ring (20) adapted to provide electrical contact between a stator (21) and a rotor (22). The improvement includes: a current-carrying conductor (23) mounted on the stator; a brush tube (24) mounted on the conductor; a fiber bundle composed of a number of individual fibers (26), the upper marginal end portions of the fibers being received in said brush tube, a portion of the brush tube being crimped or swaged to hold the upper marginal end portions of said fibers therein, the lower ends of the fibers in the bundle extending beyond said brush tube and being adapted to engage said rotor; a collimator tube (25) surrounding a portion of the brush tube and extending therebeyond, the lower end of the collimator tube being adapted to limit lateral movement of the lower marginal end portions of said fibers in said bundle when the rotor rotates relative to said stator; and a fluid reservoir mounted on the collimator tube (28).

Abstract: A stator has four or more magnetic poles. A commutator has a plurality of segments arranged in the circumferential direction and a short-circuit conductor for short-circuiting predetermined segments from among these segments. Each segment has an angular width WS, and there is a gap of an angular width WU between the segments. A substantial angular width WB of each of an anode brush and a cathode brush satisfies (n?1)(WS+WU)+WU<WB<n(WS+WU)+WU, where n is an integer no less than two. A plurality of coils are each connected to the corresponding one of the segments in order to form n closed loops. The closed loops each pass through the corresponding segments and are electrically independent of each other.

Abstract: The invention relates to a fuel pump which comprises an electric motor. Said electric motor is provided with carbon brushes (11) that cover a plurality of lamellae (17) of a collector (9). Grooves (7) in an armature (6) include sections of a plurality of coils (8), thereby particularly reducing erosion of the carbon brushes (11).

Abstract: A spring device includes of a coil spring case formed of right, left, back and front side plates and a spring receiving plate, a coil spring having a linear spring property, and a spring urging member for urging the coil spring into the coil spring case. A distance between the right and left side plates of the spring case is set a little larger than an outer diameter of the coil spring. A distance between the back and front side pates of the spring case is set about 1.5 to 2 times larger than the outer diameter of the coil spring, and a length of the spring case is set smaller than a free length of the coil spring. The coil spring is deformed and a non-linear spring property is obtained when the coil spring is urged through the spring urging member.

Abstract: A brush device assembled in a vehicular alternator is composed mainly of a pair of brushes, a pair of springs, and a brush holder. The brush holder accommodates the brushes and the springs. The springs push the brushes toward slip rings placed on and fixed to a rotary shaft of a rotor. A slant-line mark is drawn on a surface of the brush by paint. The direction of this mark is slanted to, not perpendicular to and not parallel to, the direction of pushing the brush toward the rotary shaft of the rotor. According to the proceeding of wear of the brush, the slant-line mark on the surface of the brush faced and contacted to the slip ring is shifted toward the right direction. An observer observes the position of the slant-line mark and recognizes the proceeding of wear and the optimum time to replace the brush with a new brush.

Abstract: Systems and methods for electrical component, e.g., brush, manufacture are provided that control grain orientation. The systems and methods utilize hot pressing techniques to enhance the properties and functionalities of the electrical components/brushes. An intermediate work product characterized by a grain orientation is initially formed through a conventional pressing technique. The conventionally-pressed intermediates are positioned within a cavity/die with the grain orientation in a predetermined orientation relative to the hot press force to be applied thereto. The hot pressed final product exhibits superior resistivity, strength and apparent density/durability. Surface features may be formed on the face(s) of the final work product during the hot pressing step that cannot be achieved in conventional processing techniques. Advantageous articles of manufacture, e.g., brushes and brush assemblies, are also disclosed.

Abstract: A vehicle alternator is disclosed as having a stator having a stator winding, a rotor carried on a rotary shaft and rotatably supported inside an inner periphery of the stator, an electric device involving a rectifier for converting an AC voltage, induced in the stator winding, into a DC voltage, and a protector cover for covering the electric device. The protector cover includes a cover body, placed in a position to cover the electric device involving the rectifier, and a cover convex portion extending outward from the cover body along an axis of the rotary shaft of the rotor. The cover convex portion has an inside formed with an open space in which no electric device is disposed.

Abstract: A two speed direct current electric motor comprising: an armature having a commutator assembly that is adapted to receive an electromotive force to cause the armature to operatively rotate. A brush assembly having a common brush and a low-speed brush is disposed about and in electrical communication with the commutator to provide a first electromotive force to cause the armature to provide a low-speed rotational output. The brush assembly further includes a high-speed brush having a convex shaped end in physical and electrical communication with the commutator to provide a second electromotive force to cause the armature to provide a high-speed rotational output. The convex shaped end of the high-speed brush is further adapted to wear to take the shape of the commutator such that as the high-speed brush wears the high-speed rotational output decreases.

Abstract: A brush device assembled in a vehicular alternator is composed mainly of a pair of brushes, a pair of springs, and a brush holder. The brush holder accommodates the brushes and the springs. The springs push the brushes toward slip rings placed on and fixed to a rotary shaft of a rotor. A slant-line mark is drawn on a surface of the brush by paint. The direction of this mark is slanted to, not perpendicular to and not parallel to, the direction of pushing the brush toward the rotary shaft of the rotor. According to the proceeding of wear of the brush, the slant-line mark on the surface of the brush faced and contacted to the slip ring is shifted toward the right direction. An observer observes the position of the slant-line mark and recognizes the proceeding of wear and the optimum time to replace the brush with a new brush.

Abstract: A brush device having the longitudinal direction of a coil shaped coil spring aligned with the face of a brush holder, in which one end of a support post at the surface of a brush base is formed as a hollow cylinder and a projection at the other end is insert molded into the brush holder. There is a step on the support post. The step and the brush holder receive a cover plate which, when viewed from a direction perpendicular to the face of the brush holder, covers a winding of the coil shaped coil spring. One end of the support post is fixed to the surface of the cover plate by spreading the end of the hollow cylinder of the support post.

Abstract: A two-stage eutectic metal brush assembly having a slip ring rigidly coupled to a shaft, the slip ring being electrically coupled to first voltage polarity. At least one brush is rigidly coupled to a second ring and slidingly engaged to the slip ring. Eutectic metal at least partially fills an annulus between the second ring and a stationary ring. At least one conductor is rigidly coupled to the stationary ring and electrically coupled to a second voltage polarity. Electrical continuity is maintained between the first voltage polarity and the second voltage polarity. Periodic rotational motion is present between the stationary ring and the second ring. Periodic rotational motion is also present between the brush and the slip ring.

Abstract: An electrical brush includes an electrically conductive base and a plurality of carbon nanotubes. The electrically conductive base has a contact surface. The carbon nanotubes are formed on the contact surface of the base and are configured for contacting with a rotary member. The method includes the steps of: providing an electrically conductive base having a contact surface; and forming a plurality of carbon nanotubes on the contact surface of the base. The electrical brush can be applied in various electrical machineries for efficiently collecting and transferring machine current over a long working period.

Abstract: An electric motor, in particular a motor and gear box unit for activating functional equipment in a vehicle, includes a rotor shaft carrying a commutator co-operating with conductive brushes disposed in brush supports fixed to a printed circuit card; the motor is provided with means for enabling brush supports to be fixed to the printed circuit card solely by surface mounting. These means may comprise, for each brush, a metal casing containing the brush and having one wall with at least one transverse tab adapted to pass through the printed circuit card in order to position and hold the casing on the card and in order to provide an electrical connection. The invention enables brush-support devices to be fixed to the printed circuit card solely by surface mounting, thus making it pointless to perform an additional flow soldering operation as is required in the prior art.

Abstract: A motor and a brush device are provided which allow an easy assembly of brush holders. The brush holders have fixing portions and brush accommodating portions integrally formed therewith. The fixing portions are secured to the gear case, and the brush accommodating portions slidably hold brushes. The motor has a gear case which is integrally formed with a reduction mechanism accommodating portion to accommodate a reduction mechanism and with a brush holder mounting portion in which the brush holders can be installed in a direction of an axis of the output shaft.

Abstract: The invention relates to a support element on which the commutator brushes are each disposed on one curved spiral spring each. Said spring, on its side facing away from the commutator brush in the area of the end of the coil is trapezoid and is braced between an outer stop and an inner stop with its longest edge that corresponds to the longest side of the trapezoid.

Abstract: The moving slip ring surface of electrical machinery transfers electrical current by contact thereof with liquid metal directly or through the tips of a plurality of closely spaced brushes positioned along the bottom of a housing under pressure within which the liquid metal is contained. The brush tips are respectively connected to lower ends of fibers electrically interconnected within the housing and exposed to the liquefied metal received and retained within the housing. According to one embodiment, the liquefied metal is retained within containment material filling the housing for contact exposure of the fibers therewith. According to another embodiment, exposure of the fibers to the liquefied metal within the housing is effected by entry of the liquefied metal into hollow brush tubes connected to and extending from the bottom of the housing, through which stem portions of the fibers extend to the brush tips.

Abstract: A motor has a plurality of excitation coils, a commutator having a plurality of segments, a plurality of supply brushes and a short-circuit line. Each coil is connected to corresponding ones of the segments. The supply brushes include a plurality of supply brushes each having one of an anode and a cathode. At least one supply brush has the other one of an anode and a cathode. The supply brushes each simultaneously contact different one of the segments. The short-circuit line short-circuits segments that simultaneously contact the supply brushes of the same pole. The supply brushes of the same pole separate from the short-circuited segments at different times.

Abstract: A metal-graphite brush for supplying electricity to a coil wound around a core provided at a rotor of a motor is made of sintered material having porosities at a surface and inside thereof, and the porosities is infiltrated with a conductive liquid having a boiling point higher than that of water.

Abstract: A copper-zinc alloy powder of which zinc content is from 10 to 50 wt % and of which mean particle diameter is from 15 ?m or under is added to a Pb-less brush body comprising graphite, copper and a metal sulfide solid lubricant of a copper-graphite brush.

Abstract: A fuel pump includes a housing, a pump section, a motor section including a commutator, a cover disposed at one end of the housing, a pair of brushes disposed in a pair of brush holes formed in the cover to be in contact with the commutator; and a pair of brush springs, disposed in a pair of spring holes formed in the cover, and an engaging member for restricting the brushes to move toward the motor section.

Abstract: In order to design as inexpensively as possible a control device for DC motors which are provided with a commutator for feeding their motor windings which has at least four sliding contacts, this device comprising a modulation stage which generates at least one control signal modulated as to pulse width with a clock frequency substantially above the motor speed and a control circuit which is controlled by the at least one control signal and has at least one load branch which feeds the commutator and is provided with an electronic switch controlled by the control signal modulated as to pulse width, it is suggested that the sliding contacts be combined to form at least two control groups, that the sliding contacts be combined within each control group to form pairs of sliding contacts and that each control group have its own load branch associated with it.