DE7315780U - COLLECTORLESS DC MOTOR - Google Patents

Description

Papst-Motoren KG April 28, 1977

7742 St. Georgen / Black Forest 055 / Rai / schl

G 73 15 780.9 DT - 15oG

Brushless DC motor

The innovation concerns a brushless DC motor with at least an almost flat air gap, the stator of which has at least one flat coil designed according to the principle of ironless winding, extending into the air gap and in which a member is provided which is used to control the commutation and is controlled by the rotational position of the rotor, the flat coil interacts in operation with a permanent magnet rotor and together with this generates a pulse-like electromagnetic drive torque having gaps, furthermore with at least one with the magnetically active part of the rotor cooperating, ferromagnetic element to generate one in the gaps of the electromagnetic drive torque effective, driving reluctance torque

DT-OS 2 225 442 describes the simplified structure of brushless DC motors and the associated Circuit. For example, the one in the

Siemens magazine 1966, pages 69o - 93, described motor for generating a rotating field 4 separately controllable Windings that need two Hall generators and at least 4 power transistors for contactless control. According to this DT-OS, such a motor requires, for example, only 2 string halves, a single Hall generator and 2 power transistors, that is, such a motor can be designed as a single-string motor.

If you use a speed control with such motors, so It is important that the current is fed to the windings as precisely as possible when the windings through The voltages induced by the permanent magnet rotor each have their maximum, that is, when the stator and

7315780 08/04/77

! ••• tit · I

055 / L -2- DT-150 G

Rotor poles are electrically offset from one another by about 9o °. In the interests of good efficiency and smooth running, the current in the windings should, if possible, only flow in the time ranges around these points, i.e. in such a case the current only flows during a relatively small percentage of a rotor revolution and one therefore obtains large torque gaps , which, according to the teaching of the main patent, must be filled by the reluctance torque so that an approximately uniform torque is obtained on the motor shaft to drive a device to be driven.

The present innovation is concerned with the achievement of such a uniform moment, in particular with regulated drives.

Unfortunately, for this purpose, one goes to the entrance mentioned brushless DC motor so that the provided on the stator, in operation with the magnetically active Part of the rotor interacting active iron volume of the at least one ferromagnetic element seen in the direction of rotation in a first angular range preferably monotonically increases and in a second angular range preferably decreases monotonically, and that the second Angular range is larger than the first angular range. In this way it is possible to achieve the desired torque curve of the reactance torque relative to that of the at least to obtain an electromagnetic drive torque generated by a flat coil.

Further details and advantageous developments of the Innovations result from the exemplary embodiments described below and shown in the drawing. Show it:

Fig.l a section through a collector according to the invention loose DC motor, seen along line I-I, the Figure 2.

-3-

_ _V FIG. 2 is a longitudinal section through the engine according to Fig.l,

seen along the line H-II of Fig.l.

3 shows a section, seen along the line III-III the Fig.l, on an enlarged scale.

4 is a schematic plan view of part of the Permanent magnet rotor according to FIGS. 1 and 2, seen along the line IV-IV of FIG. 2, wherein the axis and the support parts of the permanent magnet are not shown for the sake of clarity; Figure 4 is shown on a slightly reduced scale compared to Figures 1 and 2,

5 shows a control circuit for the speed-controlled operation of the motor shown in FIGS. 1-4,

Fig. 6 diagrams to explain the previous figures,

Fig. 7 + 8 two schematic representations to explain a stable and an unstable rest position of the rotor,

9 shows a second exemplary embodiment of a direct current motor according to the invention,

Fig.Io a section, seen along the line X-X of Fig.9,

11 shows a third embodiment of a direct current motor according to the invention,

Fig.12 is a section, seen along the line XII-XII of Fig. 11,

13 shows a fourth embodiment of an inventive. sen DC motor,

14 'a section, seen along the line XIV-XIV of Fig. 13,

15 shows a fifth embodiment of a direct current motor according to the invention,

-4-

7315750 08/04/77

• · · · · t I I ι '

-4-

16 shows a sixth embodiment of a direct current motor according to the invention, and

17 shows a section ₉ along the line XVII-XVII j of FIG. 16.

ί In the following description, identical parts or parts with the same function are used in the various figures. : the reference number is used and these parts are commonly

| borrowed only once described.

I / Fig. 1 shows a plan view of an insulating

renden material existing plate lo, which Has recesses in which two ironless flat coils 11 and 12 are attached, which are diametrically opposite one another. The plate lo, which also carries the circuit elements (not shown) of the motor 9 and of the associated controller, has four fastening holes 13. In its center it has a recess 14 through which a shaft ^x 15 protrudes which is supported at its lower end in bearings (not shown). As FIG. 2 shows, two soft iron disks 16 and 17, on which axially polarized ring magnets 18 and 19 are fastened, are held on this shaft 15 by a spacer sleeve 2o at a precisely predetermined distance from one another. The exact shape of the polarization of the ring magnet 18, which is a mirror image of that of the ring magnet 19, is shown in FIG. According to this, the pole gaps 22 here do not run exactly radially cuswqwards, but at an angle delta to an imaginary radius vector 23 which runs through the respective pole gap 22.

The ring magnets 18 and 19 have, as can be seen from the bottom line of FIG. 6, an approximately trapezoidal magnetization. It is also a rectangular or a sinusoidal magnetization

-5-

7315780 08/04/77

possible, but the illustration in the present exemplary embodiments relates to that shown in FIG Type of magnetization and it is expressly pointed out that with a different form of magnetization there is also a different arrangement of the ferromagnetic elements described below.

In Figure 4, the approximate direction of the longitudinal axis is a Pole gap 22 denoted by 24. Since the rotor 26, which consists essentially of the parts 16-2o and the associated Shaft 15 is rotating in the direction of arrow 25 (Fig.l and 4), it can be seen that the pole gaps 22 opposite the direction of rotation with respect to the radius vector 23 are rotated. In the preferred embodiment shown in FIG the pole gaps 22 are also curved against the direction of rotation, as shown in the drawing is clear.

The flat coils 11 and 12 have connections 27-3o which are led directly to the outside. One winds appropriately both coils are bifilar, with their center connections can be directly connected and do not have to be led out separately. This is in the patent application P 22 39 167 of 9.8.72 described in detail. The coils are longed, so each shorter than the associated one Pole arcs and their magnetically active sections 33 and 34 or 35 and 36 each run approximately parallel to each other. - As is readily apparent from FIGS. 1 and 4, the motor 9 is 4-pole, so that one mechanical angle of 18o ° corresponds to an electrical angle of 36o °.

In addition to the coil 12, a shark 1 generator 42 is on the plate Io attached, namely it lies on a radius vector 37, which has an angle of 45 ° (90 ° electrical) with the common » the same axis of the coils 11 and 12 includes. Its connections are denoted by 43.

-6-

7315780 08/04/77

Furthermore, the direction of rotation is opposite Side of the coil 11 and then ferromagnetic Elements 45 arranged, which ^ as shown, lie next to one another, but have a distance from one another which is free of ferromagnetic parts. The shape of the (identical) Elements 45 can be seen clearly from FIG.

The elements 45 are cylindrical pins made of soft iron educated. As Fig.l shows, you take with the rotor poles interacting active iron volume in the direction of rotation seen approximately monotonically in a first angular range alpha and then approximately monotonically in a second angular range beta, beta with a regulated drive as described below is represented and described, is greater than alpha. The maximum of the active iron volume is in the direction of rotation offset by an angle gamma relative to the longitudinal axis 46, which is perpendicular to the centers of the two coils 11 and 12 connecting axis runs. As you can see, the foremost iron pin 45 'is located in the direction of rotation • ■ directly next to the coil side 33 and on the outer circumference of the the rotor magnets 18 and 19 swept area. The greatest number of pins 45 is also along this outer circumference arranged, while fewer and fewer pins are arranged in the tracks parallel to them, as can be clearly seen from Fig.l.

Because of the symmetry of the motor with respect to its axis of rotation, some or more of the pins 45 on the diametrically opposite side of the stator Io to be ordered. In Fig. 1, for example, the 5 pins marked 45 ″ could be omitted and the 5 provide 48 marked diametrically opposed pins, whereby the axial forces acting on the rotor 26 would become more uniform and otherwise affect the mode of operation the engine wouldn't change anything.

-7-

7315780 04.00.77

The iron pins 45 are used to generate an additional torque of a very specific shape when the motor is in operation, which supplements the electromagnetic drive torque generated by the coils 11 and 12. This drive oment ^m has in an engine of the type shown gaps, as the Hall generator 42 cyclically nacheinandereinschaltet 11 and 12, the coils and at least a current flows during the Komutierung in neither of the two coils. This creates a moment gap which, according to the main application P 22 25 442.8, is filled by a magnetically generated moment, which is referred to as the re ^ ktanzmoment.

In the case of a motor whose speed is controlled to a constant value, it has proven to be expedient and advantageous proved to make the time during which a current flows in the coils 11 or 12 even shorter, that is, that for to greatly lengthen the pause required per se.

In this case, only short, impulsively driving electromagnetic moments and relatively large moment gaps are obtained. The reluctance torque must therefore be in a large angular range take effect to the moment gaps of the electromagnetic Full torque and an output torque on the shaft that is essentially free of pendulum torques to be able to provide.

Fig. 5 shows a control circuit of the type mentioned Connections 27 and 29 of the two flat coils 11 and 12 are 2 diodes 68 and 69 connected, the cathodes of which are connected to a line 7ο, on which a receives ripple voltage Uy, the amplitude of which corresponds to the speed of the Rotor 2fi is proportional.

The Hall generator 42, one connection of which is a negative lead 61 is connected, is via a resistor 83 in series with the emitter-collector path of a transistor to a positive line 6o, the output voltages of the Hall generator are the bases of two npn transistors 38 and

-8th-

7315780 08/04/77

39, whose emitters mi ⁴ ″ are connected to the negative line 61 and whose collectors are connected to the coil connections 27 and 29, respectively.

The voltage U ₇ is fed to a phase-shifting filter chain 85 via a voltage divider with a potentiometer 86 and an NTC resistor 87 in series, which is used to compensate for the temperature-dependent remanent induction of the rotor 26, which induction decreases with increasing temperature.

In the present exemplary embodiment, the phase-shifting filter chain 85 consists of three series-connected RC elements, the first of which is formed by resistors 86, 87 and a capacitor 88, the second by a resistor 89 and a capacitor 9o and the third; from a resistor 93 and a capacitor 94. Between the capacitor 88 and the capacitor 9o there is a Zener diode 95, the anode of which is connected to the negative line 37 via a resistor 96. This Zener diode has the effect that the potential at point 7o, which is more positive during operation than the potential on positive line 60, is shifted by a constant amount in the negative direction, so that the potential at the anode of Zener diode 95 is lower than the potential of the line 60. Such a sieve chain effects a phase shift in the phase of the voltage U ₇ (FIGS. 5 and 6) by about 180 °, and it has been shown that the capacitors can have fairly large tolerances. Furthermore, this sieve chain 85 smoothes the strongly wavy tension ¹ J _{7 , so that a tension u g7} is obtained at the output of the sieve chain 85 designated by 97 in FIG. 5, as shown in FIG. 6. The size and phase position of this voltage U ₉₇ can be determined by the dimensioning of the sieve chain 85.

This voltage U ₉₇ is fed to the base of a pnp transistor loo, the jimitter of which is connected to the positive line öo, while its collector is connected to the negative line 61 via a resistor lol, a node Io2 and a resistor Io3. The point Io2 is connected to the base of the transistor 84

-9-

7315780 08/04/77

As can be seen easily, causing a negative If the point 97 with respect to the positive line 60, that the transistor loo and also of the npn transistor become conductive with him 84th Since the voltage U _{97 can have} a relatively low ripple, the switching on and off process can be made very "random", which results in the form of the current in the motor windings 11 and 12 shown in the 3rd row from above in FIG. This means that the motor runs smoothly, with very little radio interference and low voltage peaks when it is switched off. The efficiency is very good because the windings receive current at the maximum voltage as shown. If the switching-on and switching-off process is to take place quickly in order to avoid losses in the transistors 38 and 39, this can also be achieved by appropriate dimensioning of the filter chain 85.

The circuit described works as follows: "If the speed of the motor 9 is below the Sol 1 speed set on the potentiometer, 86, the induced voltage U _{7 has} a relatively small value, and that is why it is also labeled u in FIG DC voltage component of the smoothed and phase-shifted voltage U _{97 is} relatively small, so that transistor loo almost constantly receives a potential at its base that is more negative than the potential of line 60. Therefore transistor loo and with it transistor 84 are initially constant or almost continuously conductive, so that the commutation of the armature current from winding 11 to winding 12 or vice versa is effected by the Hal I generator 42. When full speed is reached, the DC voltage component u _{m is} so great that the base of the transistor 100 is partially more positive than its Emitter: During this time, transistors 100 and 84 are blocked and Hall generator 42 cannot generate any Hall voltage, so there is ß the transistors 38 and 39 also remain blocked. Only when the base of the transistor loo becomes negative relative to the emitter due to the ripple of the voltage U _{97 does this transistor become conductive and with it 1}

-ίο- i |

7315780 08/01/77

-lo-

the transistor 84 so that the Hall generator 42 receives current and depending on the instantaneous magnetic field from the rotor 26 either the transistor 38 or the transistor 39 is turned on. One then obtains, for example, current curves like them 1n F1g. 6 1n are shown in the 3rd row from above. The Halgsnerator 42 thus acts practically as an AND gate, that that is, it brings about a logical combination of the given by the direction of the magnetic flux from the rotor 26 Information with the electrical information coming from the transistor loo.

If the speed rises above the set speed, the transistors loo and 84 are practically permanently blocked and the motor 9 is no longer supplied with any energy, so that its speed drops again.

With such a regulation, the width and / or strength of the current pulses is influenced. In this way, you get excellent control dynamics and a fast, overshoot-free run-up of the controlled motor. The efficiency is very good because the current pulses in the windings ^v l1 and 12 have the correct phase position relative to the induced voltage U ₇ .

The currents Ug and i ^ g in the two windings 11 and 12 generate an electromagnetic drive torque Mg-J on the rotor 2G, the course of which is shown in FIG. 6 in the 4th row from above with dash-dotted lines. This moment clearly has very large gaps, which can be greater than 90 ° electrical, and in these gaps the reluctance moment M- generated by the ferromagnetic elements 45 described above becomes effective, the course of which in FIG. 4 is also in the 4th row is shown from above. What is achieved according to the invention is that M _gl and M, as shown, run approximately mirror-image to one another and that the reluctance torque in the gaps in the electromagnetic torque M, for example between times t ₁ and t 2 in FIG has a substantial constant course. This is important because you can only get one

-11-

7315780 04.0E.77

* R

■
O

I · «tit

-11-

can achieve practically constant output torque over the entire angle of rotation, as is the case in some applications, for example when driving tape recorders or turntables.

If the two moments M _ß i and M _{rel are added} , a practically constant total moment is obtained. This anointed torque is programmed into the motor, so to speak, that is, such a motor can be used to drive a device that requires a drive torque of this magnitude, for example to drive a fan, a printer, a tape recorder, a turntable or the like. As can be seen from FIG. 5, the outlay for regulating the speed of a motor of this type is extremely low.

In Fig. 6 there is also part of the course in the bottom row the induction B over the (unwound) rotor 26 is shown. As you can see, this induction is roughly trapezoidal Course with narrow pool gaps and wide poles.

Figures 7 and 8 serve to explain the shape of the reluctance torque.

In FIG. 7 there is the rotor 26, the pole gaps 22 to 22 '' '(see FIG. Fif.4) of which are indicated with dot-dash lines are in a stable rest position, which corresponds to the point Ho in FIG. All iron, | pins 45 between two opposite poles of the rotor

26, that is, both pole gaps 22 and 22 'of these poles are located outside the pins 45. If the motor 9 does not receive any current, the rotor 26 remains in this rest position, that is, the reluctance torque here has the size o.

*Will. If the rotor 26 is rotated further from this position in the direction of rotation 25, a driving torque is required for this, since the Rotor 26 always tends to turn into a position in which the maximum of the active iron volume of the pins is in the area of one of its poles.

-12-

731F780 08/04/77

ί -12-

SO

This driving torque is generated during operation by the current

[generated coils 11 and 12, the driving force of which

?. Moment is designated in Fig. 6 with 111, while the braking end

I. Moment - through the pins 45 - is designated with 112.

'The arrangement of the pins 45 shown here causes the mirror-like

I graphical course of curves 111 and 112, based on the

i mean output torque of the motor 9.

About 65 ° electrical after point 111, the rotor 26 moves into the position according to FIG. 8, in which there are a particularly large number of pins f 45 are located in the area of the pole gap 22 and in the area of

I. Pole number of pins is minimal. How to get in

\ Fig. 8 clearly recognizes, the pins 45 are arranged in rows

net, which run approximately parallel to the pole gap 22. The entire [ magnetic resistance of the magnetic circuit, and thus the

Magnetic energy stored in the air gap is used in this; Position greatest. As from Fig. 8. visible, pulls a part

; of the pins 45 to the pole P of the rotor 26, another part on the other hand

ί towards the pole P ^{1 of} the rotor 26, so that this position is a labile

i The rest position of the rotor 26 is, which corresponds to the point 113 in FIG

corresponds to an o-passage of the reluctance torque.

As can also be seen from FIG. 6, the points Ho and 113

■ are as symmetrical as possible to the electrical moment 111, the in turn, advantageously in phase with the voltage u ^ is. This is practically achieved through appropriate choice

\ of the angle gamma (Fig.l), while the angles alpha and beta

determine the form of the reluctance torque. So that the reluctance

! ■ moment with the electrical see moment to the desired constant

Output torque of the motor should be added at points llo and

113 the electrical moment 111 about the size of this output { moments, that is, the electrical moment 111

must begin before point Ho and end after point 113, which is achieved by the design of the controller (Fig. 5).

As you show Figures 7 and 8, according to the doctrine of Main patent the pole gaps 22 each approximately perpendicular to the mag-

■ run netically active coil section 33, on the other hand practically parallel to the magnetically active coil section 34, which applies analogously to the coil 12. According to the doctrine of

Main patent enables the ferromagnetic elements 45 to be arranged next to and not above or below the flat coil 11, since the pole gaps 22 here when passing the elements 45 can interact with the adjacent magnetically active coil part (e.g. 33) at the same time.

As can also be seen from FIG. 8, the density of the pins 45 below the pole gap 22 decreases more slowly with further rotation of the rotor 26 than it initially increased. Likewise, the total number of ^{pins 45 located under the poles P and P 1 increases} more slowly, so that the magnetic energy decreases more slowly than it has increased. Consequently, the driving reluctance torque, which is denoted by 114 in FIG. 6, is smaller than the braking reluctance torque 112, but acts over a larger angle of rotation which essentially corresponds to the angle beta of FIG. According to the law of the conservation of energy, the energy expended in the braking area 112, which is denoted by a symbol in FIG. 6, must be equal to the energy emitted in the driving area 114, denoted by + in FIG. (The magnetic reversal losses in the pins 45 are not taken into account). As one appoints from FIG. 6, the driving reluctance torque 114 has the size of the driving torque for which the motor 9 is designed.

It can therefore be seen that in the illustrated embodiment Size and effective range of the braking reluctance torque 112 is given essentially by the angle alpha (Fig.l), in which the magnetic resistance, seen in the direction of rotation, decreases and that the size and range of the driving reluctance torque 114 are given by the angle beta at which

• the magnetic resistance increases.

So that the reluctance torque acts in those positions of the rotor, in which it supplements the electromagnetic moment in a meaningful way, is the position of the soft iron pins 45 relative to the coils 11 and 12, which is defined by the angle gamma in Fig.l, to be selected appropriately. For this purpose one can make use of the fact that the rotor 26 is in the position shown in Fig. 7 in a stable equilibrium because the stored

-14-

-14-

magnetic energy has a minimum, while in Fig.8 position shown the magnetic energy is a maximum reached and therefore an unstable equilibrium prevails in this position. So the reluctance torque is in these two Positions equal to o. As shown, these two o-passages Ho and 113 should be approximately symmetrical to the driving electrical moment 111 lie.

The processes described are repeated at every pole of the Rotor 26, that is, with a »4-pole rotor, as it is shown in the exemplary embodiment, a braking action occurs 4 times and 4 times a driving torque, as well as 4 times an unstable and 4 times a stable equilibrium per revolution.

If the rotor 26 is magnetized in a different way than that shown in the bottom row of FIG For example, with narrow poles and wide pole gaps, or with sinusoidal magnetization, the reluctance torque can be completely can be influenced in a corresponding manner by varying the magnetic resistance of the magnetic circuit, but e.-is then given for the angles alpha, beta and gamma of Fig.l another meaning.

FIGS. 9-17 show other embodiments for the design and arrangement of the ferromagnetic elements, namely in the case of an engine, the structure of which corresponds to that of the engine according to FIGS. 1-4 in all essential parts. Even in these embodiments, the magnetization shown in FIG. 6, below, and the shape shown in FIG. 6 is the electromagnetic moment M ·, provided.

In FIGS. 9 and 10, a single molded piece 117 is used, namely a plastic body with embedded soft iron powder or embedded ferrites, also a molded piece made of soft ferrite can be used. The angles entered have the same meaning as in Figure 1; this can be done on refer to the description above.

-15-

7315780 04.0877

In FIGS. 11 and 12, 3 punched soft iron pieces 118, 119 and 12o of different lengths but of the same width are used used, which by their shape and arrangement have about the same effect as the pins 45 according to the first embodiment

example .

FIGS. 13 and 14 show the use of FIG. 3 in the same way long, cylindrical soft iron pins 122, 123 and 124, of which the middle pin 123 is thicker than the two outer ones.

15 likewise shows the use of stamped soft iron pieces 127 and 127 of the same width and here also of the same size 128, which are arranged at an acute angle to one another in such a way that they overlap one another somewhat.

Figures 16 and 17 show a ferromagnetic body 131, which is the same width everywhere, but whose thickness is variable perpendicular to the plane of the stator plate Io. Fig.17 shows this thickness variation is shown exaggerated for the sake of clarity. In the angle range alpha the thickness increases seen in the direction of rotation to, in the angular range beta from. The body 131, like the molded piece 117, is made of a plastic stored soft iron powder or stored ferrites or made of a correspondingly shaped soft ferrite.

As can be readily seen, in all the embodiments according to FIGS. 9-17, the magnetically active iron volume increases in a first angular range alpha to and in a second, , larger angular range beta, with the position of the maximum is determined by the angle gamma.

7315780 08/04/77

Claims (1)

St. Georgen / Schw. ^'16' o & HDP / ichl G 73 15 780.9 .. DT-15oG Protection claims Commutatorless direct current motor with a flat air gap, the stator of which has at least one flat coil designed according to the principle of coilless winding, extending into the air gap, and in which a member is provided which is used to control the commutation and is controlled by the rotational position of the rotor, the flat coil In operation, it interacts with a permanent magnet rotor and, together with it, generates an electromagnetic drive torque with gaps, furthermore with at least one ferromagnetic element interacting with the magnetically active part of the rotor to generate a driving reluctance torque that is effective in the gaps of the electromagnetic drive torque, characterized ge k e is used to mark, that on the stator (lo) provided, 1m operating with the rotor (26) interacts passing active iron volume of the at least one ferromagnetic element (45, 48; 117; 118, 119, 12o, 122, 123, 124; 127, 128; 131) seen in the direction of rotation (25), preferably monotonically increasing in a first angular range (alpha) and preferably monotonically decreasing in a second angular range (beta), and that the second angular range is equal to or larger than the first Angular range. Direct current motor according to Claim 1, characterized in that the second angular range (beta) is adjacent to the first angular range (alpha) follows. DC motor according to Claim 1 or 2, characterized in that that the first and second angular range together are one size from about 10o to 18o ° el. - 17 - 7315780 08/04/77 - 17 - '16.3.1977 DT-IBoG DC motor according to at least one of claims 1 to 3, characterized in that the end of the first turning range, viewed in the direction of rotation, is at about 180 ° to 130 ° el. + n. 36o ° el. in front of the radial central axis of the at least one flat coil Hegt »where the value of η = 0, 1, 2 ... etc. can be. DC motor according to any one of claims 1 to 4, characterized in 'that the stable rotor position; which is the maximum active volume of iron is in the _t interact with a rotor pole (P), just is in the direction of rotation behind the rotor position (Ho Fig. 7) , where the electromagnetic drive torque (111) can just begin to act. Direct current motor according to at least one of the preceding claims, characterized in that the unstable rotor position (Fig. 8) in which part of the active iron volume is is in the area of a pole gap (22) of the rotor (26) and the reluctance torque (112, 114) passes through a zero point (113), is just before the rotor position in the direction of rotation, where the electromagnetic drive torque (111) ceases to act. Direct current motor according to at least one of the preceding claims, characterized in that in a motor whose 2p-pole rotor (26) has pole gaps (22) which, viewed from the axis of rotation (15), extend outwards, e.g. counter to the direction of rotation, the active iron volume seen in the direction of rotation in a first angle range of about 25 ° to 7ο °. increases. Direct current motor according to at least one of the preceding claims, characterized in that in the case of a motor whose 2p-pole rotor (26) has pole gaps (22) which Seen from the axis of rotation (15) outwards, e.g. against the direction of rotation, the active iron volume, seen in the direction of rotation, extends in a second angular range of 65 ° to llo ° decreases. ■■ '-18- 7315780 08/04/77 - 18 - 16.3.1977 DT-15oG 9. DC motor according to at least one of the preceding Claims, characterized in that at least one part of the active iron volume seen in the direction of rotation (25) in front of the at least one flat coil (11) that at least the this iron volume adjoining section (33) of the flat coil (11) is longed and that a part (45 ') of the active iron volume in the gusset between the outer circumference of the dated Rotor magnets (18, 19) swept over the stator surface and the longed coil section lies. 10. DC motor according to at least one of the preceding Claims, characterized in that the active iron volume is divided into several individual ferromagnetic elements arranged at a distance from one another. 11. DC motor according to claim lo, characterized in that the individual ferromagnetic elements (45; 117; 122, 123; 124) are designed as cylindrical soft iron pieces which run approximately perpendicular to the air gap plane. 12. DC motor according to at least one of the preceding claims, characterized in that in a motor whose Has rotor pole gaps, welehe seen from the axis of rotation outwards, e.g. against the direction of rotation, at least some of the soft iron pieces are arranged in rows, which roughly coincide with the course of a pole gap (22) lying above them. 13. DC motor according to at least one of the preceding claims, characterized in that in the case of a motor whose rotor has pole gaps which, viewed from the axis of rotation, extend outwards, e.g. against the direction of rotation, the active iron volume of the soft iron pieces arranged in the area of the outer circumference of the stator surface swept by the rotor magnet (18, 19) over a larger angular range is distributed as the active iron volume of the parallel paths offset radially to the axis of rotation (15) of the motor lying pieces of soft iron. "- 19 - η ι no 3/16/1977 DT-150G 14. DC motor according to at least one of the preceding Claims, characterized in that at least a part (45, 48) of the soft iron pieces in one to the axis of rotation of the Motor is arranged approximately point-symmetrical distribution. 15. DC motor according to at least one of the preceding Claims, characterized in that the soft iron pieces at least partially different active iron volumes have (fig. 13, 14). 16. DC motor according to at least one of the preceding claims, characterized in that the cylindrical Soft iron pieces have an approximately circular cross-section. 17. DC motor according to at least one of claims 1 to 16, characterized in that the soft iron pieces a approximately rectangular cross-section, based on the air gap plane. 18. DC motor according to claim 17, characterized in that that the soft iron pieces are designed as elongated sheet metal pieces which are at least partially arranged to run approximately tangentially to the motor axis of rotation in the air gap. (Figures 11, 12). 19. DC motor according to claim 17, characterized in that that at least two equally large elongated sheet metal pieces (127, 128) are provided, one of which (128) approximately in first angular range (alpha) seen in the direction of rotation (25) is arranged running obliquely inward, while the two- ' te (127) runs approximately in the second angular range (beta) and approximately tangentially. 20. DC motor according to claim 19, characterized in that that both pieces of sheet metal (127, 128) in an intermediate area which crosses the first and second angle area extend (Fig. 15). - 2o - 7315780 08/04/77 - 2ο - 16.3.1977 DT-150 G 21. DC motor according to at least one of the preceding claims, characterized in that at least one ferromagnetic element as a shaped piece (117; 131) from one Soft ferrite is formed. 22. DC motor according to at least one of claims 1 to 2o, characterized in that at least one ferromagnetic element as a shaped piece (117; 131) made of an iron powder mixed * plastic is formed. 23. DC motor according to claim 21 or 22, characterized in that the dimensions of the shaped piece (117) with at least an almost constant thickness, preferably in a radial direction Direction are variable (Fig. 9, lo). 24. DC motor according to claim 21 or 22, characterized in that the dimensions of the shaped piece (131) with at least an almost constant width, preferably in Direction of thickness are variable (Fig. 16, 17). 25. DC motor according to at least one of the preceding claims, characterized in that the electromagnetic drive torque is approximately symmetrical in time during operation runs at the point in time at which the at least one Flat coil (11, 12) induced EMF passes through a maximum. 26. DC motor according to claim 25, characterized in that that in a speed-controlled motor in which the speed is at least predominantly regulated by controlling the current flow angle, the current flow angle during operation is significantly smaller than 18o °, preferably by 90 ° (each electrical) is. 27. DC motor according to at least one of the preceding claims, characterized in that the rotor poles a have approximately trapezoidal magnetization. 28. DC motor according to at least one of claims 1 to 26, characterized in that the rotor poles have an approximately rectangular magnetization. - 21 - 7315780 08/04/77 - 21 - 16.3.1977 DT-150G 29. DC motor according to at least one of claims 1 to 26, characterized in that the rotor poles have an approximately have sinusoidal magnetization. 7315780 08/04/77