DE2627082A1 - ELECTRIC MOTOR FOR DC CONNECTION - Google Patents

Description

Dr! Ng. Walter Ablte Dr, Dicter F. Morf 16 June 1976 Dr. Hans-Α. Browns B Munch «88.Pi ·« «« * «* · ² » A679-O21

PAUL GUILDEN
2 Sutton Place South, New York, NY, V.St.A.

Electric motor for direct current connection

The invention relates to electric motors, and more particularly to brushless ones Electric motors for a direct current connection.

In the usual electric motor for direct current connection, a stator surrounds a rotor provided with armature windings, whereby the windings are connected to a segmented commutator. Brushes are stationary across from that Arranged stator and are in resilient contact with the commutator, with the brushes parallel to the terminals of the for power supply are direct current source. The brushes supply direct current to the via the commutator Armature windings that generate magnetic fields,

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which act on the stator field. By means of a suitable connection of the armature windings with certain commutator segments the rotor and stator fields act on one another in such a way that rotor rotation is initiated and is entertained. The commutator brush arrangement is a switch arrangement that depends on the Angular position of the rotor is working.

When the brushes come into contact with the commutator segments one after the other come and feed them the full rotor current, a visible brush fire occurs, which the application limited to these engines, for example when combustible gases and the like are present in the ambient atmosphere are. Furthermore, the contact of the stationary brushes on the rotating commutator leads to the wear of the brushes, as a result of which Replacement of the same becomes necessary. These and other disadvantages, such as a complicated structural design, have prompted the motor builder to look for alternative solutions for the usual DC motor. Endeavoring the rotor position Capacitive commutators were used for sensing without the rotor having to carry mechanical switch contact elements proposed in which different capacities during the rotor rotation for the purpose of displaying the rotor position as well as electro-optical commutators, which have a circumferential light shutter and associated sensors use for the same purpose and finally electromechanical Commutators in which switches are arranged separately from the rotor by a switch carried by the rotor Cams or magnets are actuated. Each of these systems has structural and / or functional features, which reduce its effectiveness as a replacement for the usual motor. The first system gives an indication of the rotor position depending on the determination of different angular ranges of the rotor by determining a capacity change

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tion, i.e. a parameter that is difficult to define and measure. The second system is because of necessity

optical elements impractical. The third system has a grain |

plex structural structure, such as from an execution!

form according to US Pat. No. 2,753,471 can be seen, in which a j

A rotor consisting of a permanent magnet has two separate sections

te, of which one with a multiple windings '.

Stator cooperates to rotate the motor output shaft and the j

others operate an open magnetic reed switch to control the ' stator current to maintain rotation.

Another DC motor system is described in US Pat. No. 2,753,501, according to which a two-pole rotor is used for driving the motor output shaft is used by reaction with a wound stator and also serves to to induce signals in sensor windings of the stator. -. ... 'The sensor windings in turn control electronic switches, which conduct electricity into the stator drive windings during operation outside the start-up phase. This system is disadvantageous as it requires several stator windings, as well as an unusual rotor construction according to which the rotor in two sections including one eccentric arranged, movable section, which carries a switch contact of a switch that during start-up 4th motor is opened and closed to determine the current flow in the stator. Used this system practically a common commutator working with brushes during the start-up phase.

According to US Pat. No. 3,264,538, the latter arrangement is simplified by, on the one hand, dividing such an arrangement into sections divided rotor is avoided and also a single stator winding provided with a center tap is present one half of which works as a sensor winding while the other half acts as a rotor drive winding. However, this one will

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Motor complicated by the fact that there is a special stator pole arrangement in which there is an eccentric gap lies between each pole piece and the bipolar rotor.

Further prior art attempts at development Brushless DC motors result from the patent specifications discussed below. According to these attempts an open brush fire is achieved through the use of encapsulated magnetic reed switches or Hall generators avoided, which sometimes lead quite low currents. Consistent with these attempts is an operation during start-up is possible as well as normal motor operation without eccentrically arranged moving rotor sections can be used and without eccentric air gaps between stator and rotor. However, require these arrangements, as will be apparent from the following discussion, have multiple stator windings and one undesirable high number of magnetic switches, which determine the rotor position and determine the current flow through the stator windings.

According to US Pat. No. 2,798,995, four stator windings are arranged on non-magnetic cores at an angular distance from one another and cooperate with a rotor designed as a permanent motor. One terminal of each stator winding is connected to a common terminal of the DC power source. The remaining terminals of the stator windings are connected to two magnetic switches, their switching states by magnetic reaction with the rotor is controlled.

According to US-PS 3 383 57 ¹ * acts existing of a permanent magnet rotor with a stator having two windings, and two Hall generators. The Hall generators are each connected to an amplifier serving as a time ratio control, which feeds a single stator winding.

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U.S. Patent 3,517,289 combines four stator windings and two Hall generators in one of a permanent magnet existing rotor.

According to US Pat. No. 3,678,359, a permanent magnet acts existing rotor with a stator, which has three cores, each of which has both a winding and a comprises a pair of oppositely set magnetic reed switches. The reed switch pair of each core is connected to the winding of the following core to give an efficient rotating stator field. A similar The arrangement is shown in US Pat. No. 3,634,873, according to which uses six stator cores, each with a winding, and three magnetic reed switches.

The invention is based on the object of creating an improved electric motor for direct current connection.

According to the invention, this is achieved by means of a motor, which has a stator with a single winding, a rotor designed as a permanent magnet, one magnetic actuated switching device which is attached to a single stator position, and a circuit which responsive to the operating condition of the switching device to allow current to flow through the single stator winding conduct. In the preferred embodiment, the inventive Motor has a permanent magnet, which has a certain position in relation to the rotor in order to at Disconnection of the stator to move the rotor in such a way that the motor operation when the Stator is facilitated.

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Those mentioned above and others according to the invention Features result from the following description preferred embodiments in conjunction with the drawings. Show it:

Fig. 1 is a perspective view of a device according to the invention used stator, in which the stator winding is omitted for reasons of clarity,

2 shows a partially schematic representation of a device according to the invention Electric motor, which is equipped with the stator according to FIG. 1 and a single one with a center tap provided winding, wherein a rotor and a motor circuit are connected to the stator,

3 shows an electrical circuit diagram of a preferred embodiment the motor circuit and the stator connections according to Fig. 2,

Figures 4 (a) - (b) are schematic circuitry for convenience the understanding of the invention and

5 shows an alternative embodiment according to the invention.

According to FIG. 1, the stator 10 contains a core 12 with stator pole pieces 14 and 16 and a passage opening in a raised portion 12a which receives the rotor axis and holds it for rotation relative to the stator. in the In section 12a, the core 12 is provided with projections 20 and 22, the former having a permanent magnet 24 in a position that is equidistant from the stator pole pieces 14 and 16. The projection 22 carries a magnetic actuated switching device 26. According to FIG. 2, a winding 28 is continuously wound around the core 12, the winding connections each with the lines 30

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and 32 are connected while a center tap of the Winding is connected to line 34. The stator is surrounded by a rotor 36 which has an outer soft iron ring 37, which surrounds permanent magnet pole pieces 36a-36f arranged side by side, with adjacent Pole pieces have opposite magnetic polarity N and S, respectively. As can be seen from Fig. 2, corresponds the curvature of the stator pole pieces 14 and 16 the curvature of the inside of the rotor, with between the stator pole pieces and the rotor poles have a sufficiently large air gap to allow them to rotate freely Allow parts to each other.

According to a preferred embodiment, there is the core 12 made of soft iron powder, which is isolated by a thermosetting resin and compressed into the shape according to FIG. 1 and was sintered. The core 12 is thus ferromagnetic, however, it is not electrically conductive, as a result of which eddy current losses are reduced. Since the core 12 is an electrical If the insulator is, a coated wire can be wound directly onto the core without that an electrically insulating bobbin is required to prevent a short circuit. The magnet 24 and the switching device 26 can be connected to the core only by gluing.

As will be explained in more detail below, the magnet 24 acts on the rotor 36 in order to ensure that a single rotor pole according to FIG. 2 lies opposite the magnetically actuated switching device 26 in an actuating position. The switching device 26 is with the lines 38, 40 and 42 are connected, and these lines as well as lines 30, 32 and 34 are connected to the engine controller which in turn is connected by lines 48 and to a direct current source 46.

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According to FIGS. 2 and 3, the switching device is next to the Rotor pole piece 36a shown and consists according to one embodiment as a single-pole, encapsulated magnetic reed switch acting as a changeover switch. The moving inner contact 26a makes contact with the external contact 26b and is at a distance from the opposite external contact 26c, this position of the contact 26a being determined by the action of the N-PoI determined by the rotor pole 36a will. If the switching device 26 is opposite an S-PoI, then, as can be seen, the contact 26a is in electrical mode Connection to the contact 26c and is at a distance from the contact 26b.

According to the embodiment of the motor controller 44 according to FIG. 3, the switching elements 52 and 54 are shown in particular as controllable silicon rectifiers. The first cathodes 52 a and 5 a of the rectifiers 52 and 5 h are connected in common to the line 50, which in turn is connected to the negative terminal of the power supply source 46. The rectifier control electrodes 52b and 54b are connected to lines 42 and 40, respectively. The anodes 52c and 54c of the rectifiers 52 and 5 ¹ * are connected to the line 32 and 30 and the opposite plates of the capacitor 56, respectively. The anodes of the counter-connected diodes 58 and 60 used for inductive interference suppression are each connected to lines 30 and 32, their cathodes being connected together to line 34. The line 34 is also connected via a switch 62 to a line 48 which is connected to the positive terminal of the power supply source 46. The line 38 is connected to the line 48 via a resistor 64 and a switch 62.

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If the rotor is opposite the stator according to Fig. in a rest position, the switch 62 is closed to switch on the motor. Positive DC voltage becomes via the resistor 64, the contacts 26a and 26b and the line 40 of the control electrode 54b of the rectifier supplied, making it conductive. As a result, direct current flows from line 48 through switch 62, the Winding section 28b, rectifying electrodes 54c and 54a and through line 50. The winding section 28a is open because the rectifier 52 is in the non-conductive state. Depending on the direction of rotation, with which the winding 28 is wound onto the core 12, the stator pole piece 16 forms an N or S pole. Will Assuming that the stator pole piece 16 forms an N-PoI, the stator pole piece 14 represents an S-PoI, and the rotor 36 performs a resulting movement in the clockwise direction according to the arrows entered in FIG off, the stator pole piece 16 repelling the rotor pole 36c and attracting the rotor pole 36b, while the stator pole piece 14 repels rotor pole 36f and attracts rotor pole 36e.

When the motor starts up, the rotor rotates approximately 30 ° clockwise, starting from the above Rest position, the rotor pole 36f on the rotor pole 36a in its position next to the switching device 26, whereupon the contact 26a separates from the contact 26b and makes contact arrives at contact 26c. If this occurs, a positive DC voltage is applied from line 40 to the Line 42 switched and thus from the control electrode 54b of the rectifier 54 to the control electrode 52b of the Rectifier 52, whereby the latter is conductive. On the other hand, the rectifier 54 is controlled by the supply a voltage of opposite polarity

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its electrodes 5 ** a and 5 ¹ Ic separated because the capacitor is now connected to the electrode 5 ** a via the rectifier 52. This voltage, the magnitude of which corresponds to twice the terminal voltage of the supply source 46, is supplied by the capacitor 56, since the capacitor is charged accordingly ^{during the conductive state of the rectifier 5 2 I.}

When the rectifier 52 is conducting, current flows through the winding section 28a in a direction which is opposite to the current flow through the winding section 28b that is now interrupted, whereby the previous magnetic polarity of the stator pole piece 16 is reversed from N to S and the stator pole piece Ik changes from an S-PoI to an N-PoI. The rotor therefore continues to experience a resulting clockwise moment because the stator pole piece lh now repels rotor pole 36e and attracts rotor pole 36d and pole piece 16 repels rotor pole 36b and attracts rotor pole 36a.

When the rotor 36 continues to rotate, the rotor pole initiates 36f the switching device 26 to return to its initial state, the contacts 26a and 26b being in contact with each other. This operating state leads to again a line of the rectifier 5 ^ to turn on the Winding section 28b and to interrupt the power line of the rectifier 52 by blocking his Electrodes 52a and 52b by means of the capacitor 56. These cyclical reversal of the current flow through the stator winding 28 in 60 ° intervals is continuously continued and keeps the motor rotating.

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According to the invention, a magnet is used in conjunction with the Switching device 26 is used, by means of which the switch can obtain a magnetic polarity which, as desired, of the Applicant that according to FIG. 3 is opposite. For example, if it is desired, alternatively instead of the introductory text clockwise rotation mentioned above to get a reverse motor rotation, so is first when starting the winding 28a switched on instead of the winding 28b mentioned in the previous example. By actuation of the polarizing magnet 26d with respect to the switching device 26, as shown in dashed lines in FIG where the N-S axis of the magnet 26d is parallel to the axis of rotation of the rotor, the contacts 26a and 26c in contact with each other. When closing the switch 62, the rectifier 52 becomes conductive and there is an introductory current flow through the winding section 28a, whereby the stator pole piece 14 becomes an N-PoI and the stator pole piece 16 becomes an S-PoI. Bumps accordingly the stator pole piece 14 removes the rotor pole 36e and attracts the rotor pole 36f, while the stator pole piece 16 pulls the rotor pole 36b repels and the rotor pole 36c attracts, whereby a resulting torque in the counter-clockwise direction and a corresponding rotor rotation can be obtained. When moving the magnet 26d from the magnetizing position opposite of the switching device 26, the contact 26a comes into contact with the contact 26c, and the rectifier 54 is initially conductive, causing a current to flow through the winding section 28b and a clockwise rotation of the rotor takes place. It is obvious that other measures can be used to optionally reverse the direction of rotation. For example, a two-pole changeover switch between the lines 40 and 42 and the control electrodes 52b and 54b, so that the Line 40 with the control electrode 52b and the line

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can be connected to the control electrode 5 ^ b or the lines ¹ JO and 42 are connected to these electrodes according to the choice of the user according to FIG. If desired, such a two-pole changeover switch can be inserted between the leads 30 and 32 and the electrodes 52c and 54c in order to connect these leads and electrodes according to FIG. 3 or around the lead 30 to the electrode 52c and the lead 32 to the electrode 54c connect to. The use of a switch in the lines 40 and 42 has advantages over the use in the lines 30 and 32, since the current flow in the lines 40 and 42 is less than in the lines 30 and 32.

In the previous discussion, the relative approach position of the rotor 36 and the stator 10 according to FIG. This position in which the stator pole pieces are in a position of equilibrium with a pair of adjacent rotor poles can of course open the Switch 62 and movement of the rotor 36 to a rest position are present. However, in this case, with regard to the relative position of the stator and rotor, it is possible that the position according to FIG. 4 (a) is assumed, a magnet 24 not being used. Referring to Fig. 4 (a), in which the magnet 24 is omitted, the result is that the stator pole pieces 14 and 16 are essentially adjacent to a single one Rotor pole lie and in the second line next to the same sections of rotor poles, the polarity of which is opposite to the former Rotor pole is. If the switching device is in one of its two conductive operating states, then if the stator winding is switched on under these circumstances by closing switch 62, no resultant Moment to rotate the rotor 36 is generated like this indicated by dashed arrows in Fig. 4 (a). The rotor is practically in a zero position, and there is a state of magnetic equilibrium.

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In order to avoid that the rotor 36 is opposite to the stator 10 assumes such a zero position, serves according to the invention a magnet 24, the polarity of this bar magnet being selected such that the rotor 36 has a single magnetic pole is facing. According to Fig. 4 (a), the magnet is next to the Rotor poles 36d and 36e and is connected to the rotor 36 with an N-PoI facing, imparting rotation to the rotor to move it from the position shown in Fig. 4 (a) to the position according to FIG. 2 to bring. The magnet 24 thus repels the rotor pole 36e and pulls the rotor pole 36d according to FIG. 4 (a) on, which then the stator pole pieces 14 and 16 in State of equilibrium lie next to a number of rotor poles, namely poles 36e and 36f and poles 36b and 36c. The rotor 36 rotates into a rest position after it has been switched off of the motor according to FIG. 2 and FIG. 4 (b), the magnet 24 does not carry out any correction of the rotor position, since this does not is required. It can be seen that the magnet 24 with an S-PoI faces the rotor with the same result can be, as if it presents an N-PoI, and the drive force given by the magnet 24 still drives the rotor sufficiently twisted to ensure that the stator pole pieces are juxtaposed to be reached with each of the rotor poles.

In the embodiments described above according to According to the invention, a six-pole rotor cooperates with a two-pole stator. In this arrangement, the is magnetic actuated switching device 26 arranged at the same distance from the pole pieces 14 and 16 to be in a position in which their conductive operating state is not impaired by the switching on of the stator winding, so that the switching device is next to a single rotor pole when the stator pole pieces are next to several rotor poles lie. Such a single position of the switching device

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A679-021 fy

ensures that this has a certain operating status and not subject to common magnetic influences of opposite polarity, as in the case of Arrangement according to Fig. 4 (a) would apply. Such a mutual distance between the switching device 26 and the stator pole pieces is fixed during the construction of the electric motor according to the invention, with the further position of the switching device 26 next to a single rotor pole and the juxtaposition of the stator pole pieces with multiple rotor poles is ensured for example by the magnet 24.

According to FIG. 5, the switching device consists of a switch which operates with a Hall generator and which is operated by the voltage difference between the lines 66 and 68 connected to the switch. The line is connected to the line 48 through a resistor 70 and a switch 62, and the line 68 is connected to the line 50. The lines 72 and 74, which are connected to the switching device 26 ', are each separately provided with positive potential, depending on the operating state of the switching device according to the magnetic influence of the same by the rotor poles 36 Switching device, a positive voltage is fed to the line Ik , while there is no voltage on the line 72.

According to Fig. 5, the single winding 28 'is not with one Center tap provided and their end-side outputs are through the line 76 with one of the transistors 78 and 80 common connection point as well as through a line 82 with a common to the transistors 84 and 86 Connection point connected. The collectors of the transistors 78 and 84 are connected to the line 48 via a switch 62

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while the emitters of transistors 80 and 86 are connected to line 50. The emitters of the
Transistors 78 and 84 are each associated with the collectors
of transistors 80 and 86 connected. The bases of transistors 78 and 86 are connected to line 72 through resistors 88 and 90, respectively. The bases of the transistors 80 and 84 are each connected to the line 74 via a resistor 92 and 94, respectively. If the line 74 is positive, the transistors 80 and 84 conduct, whereby a current flow from the line 48 through the switch 62, the transistor 84,
the line 82, the winding 28 », the line 76 and the
Transistor 80 to line 50 takes place. When the rotor 36 rotates, the switching device 26 ′ comes to rest next to a rotor pole with S polarity and leads the line 72
a positive voltage too, while the positive voltage
on line 74 is switched off. If this happens, so
the transistors 80 and 84 are not conductive, ..and
the transistors 78 and 86 become conductive, whereby a
Current flow from line 48 through switch 62, the
Transistor 78, line 76, winding 28 ', line 82 and transistor 86 to line 50 takes place. As can be seen, the current direction through the winding 28 'is reversed with respect to the previously mentioned current direction. Switches for reversing the direction of rotation can be installed in the lines 72, 74 or in the lines 76, 82, as previously mentioned in the embodiment according to FIG. 3.

While the invention in connection with specific embodiments further changes are possible. For example, the use of controllable Silicon rectifiers according to FIG. 3 and a transistor switching device according to FIG. 5 only to be understood as an exemplary embodiment, since there are other circuit elements

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away

and arrangements for controlling the flow of current can be used. The embodiments described show although a stator surrounded by the rotor, the reverse arrangement according to which the stator is also possible would be possible surrounds the rotor. These and other modifications are encompassed by the invention within the scope of the claims.

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Claims (15)

A679-O21 claims 1.) Electric motor for direct current connection, characterized by (A) a stator (10) with a single winding (28) wound on a core (12), the Core has at least one pole piece (14, 16), whose magnetic polarity is determined by the current flow in the winding (28), (b) a rotor (36) arranged to rotate with respect to the stator, which consecutively a number Permanent magnets (36a-36f), wherein adjacent rotor poles each have a first and second, each other have opposite magnetic polarity, (c) a magnetically actuated switching device (26) which is arranged in a stationary manner at an individual position is to go through the rotor poles with the first magnetic polarity in a first conductive operating state and through the rotor poles of the second magnetic polarity in a second conductive operating state to be brought up and through (d) a circuit which communicates with the switching device (26) of the stator winding (28) and the direct current source (46) is connected to power when the switching device (26) is actuated in the first operating state to conduct in a first direction through the stator winding (28), and upon actuation of the switching device in the second operating state in a second opposite direction. - 17 - 709807/0658 2. Electric motor according to claim 1, characterized in that the individual position for the switching device (26) with respect to the stator pole piece (14, 16) is at such a distance that the switching device next to a single one of the rotor poles (36a-36f) when the stator pole piece is next to the various Rotor poles come to rest. 3. Electric motor according to claim 1, characterized in that the stator (10) has two pole pieces (I ¹ J, 16) which lie next to rotor sections which are diametrically opposed to one another. 4. Electric motor according to claim 3, characterized in that the rotor (36) has six rotor poles (36a-36f) and the single position for the switching device (26) equidistant from each of the stator pole pieces (14, 16). 5. Electric motor according to claim 1, characterized by a drive device (24) for rotating the rotor, so that this is brought in a predetermined position relative to the stator pole piece when the current flow in the Stator winding is interrupted. 6. Electric motor according to claim 5, characterized in that the drive device consists of a permanent magnet (24) exists, which assumes a certain position in relation to the rotor. 7. Electric motor according to claim 6, characterized in that the permanent magnet (24) is attached to the stator (10) is. - 18 - 709807/0658 A679-031 8. Electric motor according to claim 1, characterized in that the stator winding (28a, 28b) has two ends, which each form connections, as well as a third connection, which is connected to the winding between the two ends are connected and the circuit conducts current from the first connection to the third connection, when the switching device (26) is in said first operating state and furthermore current from second connection leads to the third connection when the switching device (26) is mentioned in the second Operating state. 9. Electric motor for direct current connection, characterized by (A) a stator (10) which has an individual winding (28) applied to a core (12), wherein the core forms at least one pole piece (14, 16) whose magnetic polarity is determined by the Current flow in the winding is determined, (b) a rotor (36) which is mounted to rotate with respect to the stator (10) and which has a number of Permanent magnet poles (36a-36f) which follow one another, with adjacent rotor poles respectively have opposite magnetic polarity, (c) a rotor control (44) to power with certain direction depending on the angular position of the rotor poles with respect to the stator pole pieces to conduct through the stator winding (28), and (d) a drive device (24) to the rotor in a to twist certain position with respect to the stator pole piece when the current flow in the stator winding (28) is switched off. - 19 - 709807/0658 A679-O21 ί 10. Electric motor according to claim 9 *, characterized in that that the drive device consists of a permanent magnet (24) which is stationary with respect to the rotor is arranged. 11. Electric motor according to claim 10, characterized in that the permanent magnet (24) is carried by the stator (10) will. 12. Electric motor according to claim 9> characterized in that that the rotor control (44) has a magnetically operated switch (26) which is in a Single position is arranged to pass through the rotor poles of one magnetic polarity in a first conductive operating state and through the rotor poles of opposite magnetic polarity into one second conductive operating state to be brought, wherein a circuit with the switching device (26), the stator winding (28) and the direct current source (46) are connected to a certain direction dependent current to conduct the operation of the switching device (26) through the stator winding (28). 13. Electric motor according to claim 12, characterized in that the stator winding (28) has two ends which each form two connections, with a third connection with the stator winding at a point between the two ends is connected and the circuit current from the first connection to the third connection conducts when the switching device (26) is in the first conductive operating state, and also current from the second connection to the third connection when the switching device is in the second conductive operating state is located. - 20 709807/0658 14. Electric motor for direct current connection, characterized by (a) a stator (10) with a core (12) and a single winding (28) applied to it, the core forming two pole pieces (14, 16), the opposite of which are magnetic Polarity is determined by the flow of current in the winding and the winding has two ends Having terminals and also a third terminal with the turn between the ends thereof connected is, (b) a rotor (36) mounted for rotation with respect to the stator and comprising a series of consecutive Has permanent magnetic poles, with adjacent rotor poles of opposite magnetic polarity to have, (c) a magnetically operated switching device (26) which is arranged in a stationary manner at a single point is and through the rotor poles of a first magnetic polarity in a first conductive operating state is brought and further by the rotor poles of opposite magnetic polarity into a second conductive operating state, (d) a circuit associated with the switching device (26), the stator winding (28) and the direct current source (46) is connected to the operation of the switching device (26) in the former Operating state current from the first connection of the winding to the third connection of the To conduct the winding and also when the switching device is in the second operating state, from the second connection of the winding to the third connection thereof, and - 21 709807/0658 (e) an electromagnet arranged in a stationary position (24) to rotate the rotor relative to the stator pole piece into a predetermined position, when the current flow of the stator winding is switched off. 15. Electric motor according to claim 1, characterized in that the stator winding (28) has two ends which each form two connections, and the circuit current from the first connection to the second connection conducts when the switching device (26) is in the first-mentioned conductive state and also current from the second connection to the third connection when the switching device is in the second conductive state . - 22 - 709807/0658 Blank page