WO2000067362A1

WO2000067362A1 - Drive mechanism with brushless electric motor and corresponding brushless electric motor

Info

Publication number: WO2000067362A1
Application number: PCT/DE2000/001375
Authority: WO
Inventors: Peter Nadig; Oliver Zirn
Original assignee: Robert Bosch Gmbh
Priority date: 1999-04-30
Filing date: 2000-04-29
Publication date: 2000-11-09
Also published as: DE19919684A1

Abstract

The invention relates to a drive mechanism with brushless electric motor, notably for tools, which presents marked teeth (1 - 3', 22) in the stator (10) and rotor (20). Armature windings (11, 12, 13) are provided for in grooves in the stator and surround teeth assigned to them. An exciter winding (30) for field excitation is provided for diametrically in grooves in the stator (10). The field is controlled via the rotor teeth, the stator teeth and the ring flow (14) of same. The armature windings are mounted as a three-phase winding and interconnected in the manner of a star connection. To generate the torque a current is applied to the armature windings in blocks by the simultaneous switching off and on of the current. Electronic switches, notably in the form of a three-phase bridge circuit, serve as electronic commutator for switching the armature windings. The exciter winding is connected in series with the electronic switches.

Description

DRIVE WITH BRUSHLESS ELECTRIC MOTOR AND BRUSHLESS ELECTRIC MOTOR

State of the art

The invention relates to a drive with a brushless electric motor, in particular for tools, with pronounced teeth in the stator and in the rotor of the motor according to the type defined in the preamble of claim 1, and also relates to a brushless electric motor according to claim 11.

The so-called universal motor with a mechanical commutator consisting of carbon brushes is today the preferred motor for power tools with mains supply. Electronically commutated direct current machines, so-called EC synchronous motors, or converter-fed asynchronous machines or switched or synchronous reluctance motors are used today as wear-free or brushless drives.

In the article "Two new Competitors" by PJ McCleer, July 1998, in the magazine Appliance Manufacturer, pages 39 to 41, a permanent magnet motor is described which has pronounced teeth or poles both in the stator and in the rotor of the motor. In armature windings are provided in the slots of the stator, which encompass the associated teeth. Permanent magnets are provided to excite the electric field and are attached between an inner and an outer iron package in the stator. In addition, an electrical field winding is provided in the stator, which serves to weaken the field of the permanently magnetically excited constant field. As a result, the speed of the motor can be determined in a larger width by field weakening.

10 The aim and object of the present invention is to provide a simpler version of an electronically commutated drive with increased service life requirements compared to the motor known above, which is also inexpensive.

15

Advantages of the invention

The drive according to the invention with a brushless electric motor with the characterizing features of claim 1 has

20 the advantage of the prior art that there is no need for permanent magnetic excitation, that it is much simpler in construction and more cost-effective, and also offers a high level of maintenance-free ^{~ ~} with high continuous output for rough use in power tools with increased output, which are particularly powered by the mains and low costs for motor and electronics.

According to the invention, this is achieved in principle by providing an excitation winding for field excitation in the stator and

30 is arranged diametrically in the stator, the field guidance takes place over the teeth of the rotor, the teeth of the stator and its ring closure, the armature windings are attached in the sense of a three-phase winding and are connected in a star circuit, the armature windings for Generation of the torque are energized in blocks by simultaneous switching on and off, for switching the armature windings electronic switches, in particular in the form of a three-phase bridge circuit, are provided as an electronic commutator and the excitation winding is arranged in series with the electronic switches.

The measures set out in the further claims allow advantageous developments and improvements of the drive specified in claim 1 with a brushless electric motor.

According to a particularly advantageous embodiment of the invention, the excitation winding is inserted in special diametrically arranged slots in the stator.

In an advantageous embodiment, the excitation winding is divided into two and a part is arranged in a groove, which is essentially arranged behind a stator pole, the respective stator poles being adjacent. This is a particularly advantageous embodiment and increases the excitation flow solely through the geometry of the arrangement.

In a further advantageous embodiment it is provided that the number of teeth of the stator to the number of teeth of the rotor is in a whole number ratio of 6: 4. However, it should be noted that, in principle, arrangements with four stator and two rotor teeth are also conceivable.

In an advantageous embodiment of the drive according to the invention, the electronic switches are supplied with direct current, which can be supplied in particular via a rectifier, which is fed by an alternating current supply network. In a further advantageous embodiment of the invention it is provided that the excitation winding is fed with direct current generated from an alternating current supply network. In an expedient embodiment, according to a particular embodiment, the excitation winding is divided into two, and a part of each is arranged in the AC supply line to the rectifier bridge.

In an alternative embodiment is in another

10 advantageous embodiment of the invention, the excitation winding is switched between the rectifier and the inverter. In this way, the field winding serves to buffer the network and avoids the spreading of commutation current peaks into the network.

15

In a further alternative embodiment it is advantageously provided that the field winding is constructed as a transformer, the primary winding of which is connected to the network and the secondary winding of which is connected to the rectifier.

20th

It is advantageous for the entire drive that the commutation circuit is controlled by means of a microcontroller.

The invention also in the context of a single ^{~ "concept} a brushless electric motor which can be used in particular for tools, and with salient teeth in the stator and the rotor of the motor, with provided in slots of the stator armature windings, which engage around the associated teeth, with a field winding for field excitation in

30 stator, which is arranged diametrically in special slots in the stator, and with armature windings, which are connected in a star connection. This design of the brushless electric motor alone, regardless of how the commutation circuit in the Individual is designed, advantageously creates a new engine type, with which tools can be driven in a particularly favorable manner.

Further advantageous refinements of this motor are laid down in the dependent claims 12 to 16.

According to an advantageous embodiment of the motor, it is provided that the surfaces of the stator and rotor teeth, which face each other in alignment via an air gap, are essentially of the same size and are aligned concentrically to the rotor axis.

According to a particularly advantageous and expedient embodiment of the motor, the groove in which the field winding is inserted is essentially provided behind one of the stator poles, the magnetic flux via this stator pole being as undiminished as possible.

In a particularly advantageous development of this embodiment of the brushless motor according to the invention, it is provided that, in the case of two-part excitation winding, one part in a groove, essentially in the radial direction from the rotor axis, behind the pole face of the corresponding stator tooth, which faces the rotor pole in its orientation , is arranged, the respective stator poles being immediately adjacent and the magnetic flux over each stator pole being as undiminished as possible.

In an advantageous development of the motor designed according to the invention, it is provided that the number of teeth of the stator is 6: 4 as a whole number of teeth of the rotor. In a further advantageous embodiment, the rotor consists solely of magnetic material.

drawing

The invention is explained in more detail in the following description with reference to exemplary embodiments shown in the drawing. The figures show in detail:

1 shows an axial top view of a sectional view of the stator and rotor of the motor or drive designed according to the invention with angular graduation to explain the generation of torque;

2 schematically, in an axial plan view in a sectional view, a special embodiment of the motor with a special arrangement of a two-part excitation winding in slots behind stator poles;

Figures 3 - 5 schematically in plan view of the excitation field magnetic flux at different angular positions of the rotor relative to the stator.

6 shows a time diagram or a diagram depending on the phase angle wink for the three currents Ii, I ₂ , I ₃ in the associated armature windings and the associated switching sequence for the transistors switching the respective current;

7 schematically shows the star connection of the armature windings and the associated so-called B6 three-phase bridge with the transistors T1 to T6 and in each case these freewheeling diodes connected in parallel, these three-phase current Bridge circuit represents the commutation circuit formed from electronic switches;

Fig. 8 shows the linear representation of the ⁵ engine designed according to the invention to show the flooding and acting

Powers;

9 shows a first circuit for supplying the three-phase bridge with split field winding, which is arranged in the ^{~ ~} mains supply line of the rectifier.

Fig. 10 shows another circuit for supplying the

Three-phase bridge, in which the field winding is arranged between the rectifier and commutator, in type ^{15 of} a buck converter;

11 shows a further circuit for supplying the

Three-phase bridge, in which the field winding is arranged between the rectifier and commutator, in type 0 of a step-up converter, and

Fig. 12 shows schematically the supply of the three-phase bridge and the excitation winding in the form that it is designed as a transformer, in which the 5 secondary winding is in the supply line of the rectifier of the commutator and the primary winding on the AC network.

Description of the exemplary embodiments 0

1 shows a sectional view of the stator and rotor of the motor or drive designed according to the invention in an axial plan view. The stator 10 has six protruding teeth or Poland 1, 2, 3, 1 2 ^Λ and 3 provided. These teeth 1 to 3 'project inwards onto the axis 21 of a rotor 20. The rotor 20 is equipped with four poles or teeth 22 which point outwards from the axis 21, specifically to the teeth 1 to 3 ^Λ projecting inwards from the stator 10 towards the axis 21. The rotor 20 is made entirely of magnetic material and in the stator 10 the poles or teeth are magnetically connected to one another by a magnetic ring 14 which surrounds all the teeth in a ring, so that a magnetic ring closure is produced there and the magnetic flux can flow accordingly. An air gap 15 is present between the inwardly facing surfaces of teeth 1 to ^3λ and the outwardly facing teeth 22 of rotor 20, via which the magnetic closure from stator pole to rotor pole takes place. This magnetic gap should be as small as possible. Around the individual poles of the armature windings are arranged, the armature winding 11 is, for example, around the pole 1 and the diametrically opposed pole 1 of the stator 10 arranged around the stator pole 2 and its diametrically opposed pole 2 ^x the armature winding 12 and around the pole 3 with its diametrically opposite opposite pole 3, the armature winding 13. The armature windings 11, 12 and 13 are connected to each other in a star connection. Between the poles 3 ^λ and 1 and 1 ^Λ and 3 an excitation winding 30 is attached diametrically across the axis 21, which is provided for field excitation in the stator 10.

In Fig. 2, a special embodiment of the motor is shown schematically in an axial plan view with a special arrangement of a two-part excitation winding. The excitation winding consisting of two parts 31 and 32 is accommodated in special grooves 34 and 35. The groove 34 located diametrically opposite each seen essentially in the radial direction after the stator 1 and ^λ l and the groove 35 is located substantially in seen in the radial direction behind the stator pole 3 and 3 ^λ . Between the poles 1, 1 'and 3, 3 ^Λ and the grooves 34 and 35, sufficient magnetic cross-section is still left open for the ring closure 14. The excitation winding 30 is divided into two parts 31 and 32, which, as will be shown later is particularly advantageous for a specific circuit application, as shown in FIG. 9.

In FIG. 3, the same axial top view of the stator 10 and rotor 20 shows the rotor 20 in the 0 ° position in accordance with the division in FIG. 1. With a current through the excitation winding 30, which comes out of the plane between the poles 3 ^λ and 1 and flows into the plane between the poles 1 and 3, there is a field around the excitation winding, as is indicated by the arrows 36 in the poles 3 and 1 and the arrows 37 at the poles l ^λ and 3 is shown in the course of the field. In the illustrated orientation of 0 °, in which two poles 22 of the rotor 20 are precisely aligned with the poles 2 and 2 ^{Λ of} the stator 10, the main part of the excitation field flows via the ring closure 14 and the opposing stator poles 2 ^λ and 2 and the thus aligned poles 22 of the rotor 20. To generate torque in the direction of the arrow 38, the corresponding armature windings are energized or left without current.

4, the rotor 20 is shown in a position of approximately Ψ = 20 ° and shows that the field of excitation flows over the poles 1 and 2 and the correspondingly partially aligned poles 22 in the upper half of the rotor 20 and over the poles 1 and 2 and the correspondingly aligned two poles 22 flows in the lower half of the rotor 20.

5 shows the flow profile when two opposing poles 22 of the rotor 20 with the poles 1 and 1 ^{λ of} the Stator 10 are aligned. Only a small leakage flux then flows over the non-aligned poles of the rotor and the poles 2 and 2 or 3 and 3 'of the stator 10 adjacent to it. The excitation winding 30, be it now only a winding as in FIGS. 1 and 3 provided that the excitation winding consists of two parts 31 and 32 according to FIG. 2, generates the course of the excitation field shown in FIGS. 3 to 5 with different rotor positions. Ideally, the inductance of the excitation winding is not practical

10, however, depends only insignificantly on the rotor position. As a result, the excitation is almost invariable with the rotor position and therefore does not generate any cogging torque.

The generation is then to be carried out on the basis of FIGS. 6 and 7

15 of the torque in the drive according to the invention and the motor designed according to the invention. In FIG. 6, the current Ii for the winding 11, the current I ₂ for the winding 12 and the current I ₃ for the winding 13 are plotted over the angle Φ, which is shown in FIG. 1 in degree and direction.

7 shows a so-called B6 three-phase bridge circuit with the transistors T1 to T6, each of which has a free-wheeling diode D connected in parallel. This three-phase bridge circuit is supplied with a DC voltage U at the inputs 71 and 72. The connection of the transistors Tl and

25 T4 is placed at the start of winding 11. The connection of the transistors T2 and T5 is placed at the beginning of the winding 12 and the connection T3 and T6 is placed at the beginning of the winding 13. The ends of the windings 11, 12 and 13 are connected together so that these three windings are connected in star connection ^{~ ~.}

A torque is generated in the rotor position shown in FIG. 1 by flux amplification on the Winding 11 and flux weakening on the winding 12. For this purpose, as shown in FIG. 6 on the pulse diagram and in FIG. 7 on the circuit diagram, the transistor T1 and the transistor T5 are turned on, so that between Φ = 0 ° and 30 ° a positive current I _x and a negative current I ₂ flows. This flux amplification and flux weakening reduces the attraction of the rotor tooth to the winding 12 and the tooth 2 and increases it to the winding 11 and the tooth 1 and 1, so that a moment in the clockwise direction corresponding to the arrow 38 in FIG. 3 arises therefrom. After the rotor tooth 22 has reached the aligned position of winding 11 and stator tooth 1 or l ^x , which is reached at the value of Φ = 30 °, the excitation flux is weakened with winding 11 and tooth 1 and with winding 13 and The excitation flow is strengthened via tooth 3, so that again a moment arises clockwise. For this purpose, the two transistors T3 and T4 are turned on in the block, so that the current Ii through the winding 11 assumes the negative value and the current I ₃ in winding 13 becomes positive. No current flows in winding 12, ie the current i ₂ is zero. When the value Φ = 60 ° is reached, the transistors T2 and T6 are switched on in blocks to ensure that a positive current I _{2 flows} through the winding 12 for field amplification and a negative current I _{3 flows} through the winding 13 for field weakening. When the value Φ = 90 ° is reached, the cycle starts again, so that the torque formation continues as just described by the block-by-block switching on of the corresponding transistors and the associated block-by-block energization of the armature windings. The three-phase bridge, which is shown in Fig. 7, thus functions as an electronic commutator for the motor and energizes the windings 11, 12 and 13 from the DC voltage U present at the inputs 71 and 72. It should be noted that if two are in pairs associated transistors are conductive, the other four transistors block each. The torque generation described above is derived analytically with reference to FIG. 8 using a linear model of the motor and drive designed according to the invention. The stator 10 is shown with ⁵ two teeth 1 and 2, which are each surrounded by the armature windings 11 and 12 and generate a flooding ®ι or ® ₂ . Furthermore, the stator 10 is provided with the excitation winding 30, which generates the flooding ® _F. The rotor 20 is shown with two of its teeth 22. Between the teeth 22 of the ¹⁰ rotor 20 and the teeth 1 and 2 of the stator 10 is the

Distance of the air gap °. A force Fi acts on the left tooth 22 of the rotor 20 and a force F ₂ acts on the right tooth 22. A shift takes place in the direction and around the drawn path x. The width of the teeth 1 and 2 is b and the length of the entire ^'~ stator pack 1. This results in an air gap volume of

Vα = ^{δ •} 1 '(b - x)

for tooth 1 and a further air gap volume V ₂ of tooth 2

20 applies

V ₂ x.

dWm

The general equation for force is: ^■ * ^* -,

1 B ² 5 resp. with a homogeneous magnetic field in the air gap: _J '

The following applies to induction at * _c ^~ * °° ^D F ^~ _< -. ^- _< -. -3, = c / "θ ^Θ l applies to induction in tooth 1

and for the induction in tooth 2 applies "i ^~ _κ ^~ ?

For the force Fi, which acts on tooth 1 when the excitation flow is weakened, the following applies according to the superposition principle:

- (Θ ^ -2Θ Θ ₁ -Θ ₁ ² )

2

For the force F ₂ , which is on tooth 2, when strengthening the

The excitation flow acts according to the overlay principle:

2 dx μ _Q 2 δ 2 δ

The total strength results from this

E -Θ ₂ ² -2Θ _f (©, + © -))

where for ®ι ~ ® ₂ -® ^, ® _A is the armature flooding, with the three-phase topology follows:

E = 2 ^ Θ, Θ, This result shows that four times the torque is achieved with the same current and the same flow compared to a switched reluctance motor with the same armature current. This is a very significant advantage of the present motor and present drive.

FIG. 7 shows the commutation circuit of the motor according to the invention consisting of six transistors T1 to T6 on the basis of a six-pulse bridge circuit. This bridge circuit has a DC voltage U applied to its inputs 71 and 72. FIGS. 9 to 12 each describe a supply circuit which provides the DC voltage at the respective outputs 71 and 72. These circuits also contain the integration of the excitation through the field winding in different ways.

In the example shown in Fig. 9, one is

Mains AC voltage U _N ~ applied to inputs 90 and 91 of the circuit. Via a triac 92, which can be controlled via a variable switch 93, input alternating voltage of different levels is applied to a rectifier bridge consisting of four diodes D1 to D4 by means of a phase control. In the

AC supply lines of the bridge each have a part 31 or 32 of the two-part field winding, as shown for example in FIG. 2, inserted. The rectifier bridge works on a capacitor 95, which can be referred to as an intermediate circuit capacitor. A braking circuit is introduced in parallel with a resistor 94 and in series with a transistor T _B. If the brake transistor T _B becomes conductive, the output voltage is short-circuited via the resistor 94, so that no more voltage can be applied to the commutator. A resistor 96 is inserted in front of the output pole 72 to limit the current by the transistors T1 to T6 or generally by the electronic switch flowing commutation current, so that these electronic switching elements are not damaged. In the circuit according to FIG. 9, it should be noted that the two-part excitation windings 31 and 32 each have a part in the AC supply lines of the rectifier bridge that the excitation of the motor changes with the mains frequency. In adaptation to this, the activation of the switching elements in the commutator must be adapted accordingly in terms of time and depending on the rotor position. A suitably programmed microprocessor is preferably provided to control the commutator or the electronic switching elements.

The supply circuit, which is shown in FIG. 10, also contains a full-wave rectifier formed from the diodes D1 to D4, which is connected to the input terminals 90 and 91 with the

Mains AC voltage U _N - is fed. The arithmetic mean value of the intermediate circuit voltage is controlled by means of a step-down divider with the help of a transistor T. The field winding 30 is in series with the armature windings and is from

Flow through total commutation current. Here, too, a capacitor 95 and a current limiting resistor 96 are provided, as in the circuit arrangement according to FIG. 9, and a brake transistor T _B , to the switching path of which a diode D5 is connected in parallel as a freewheeling diode. With this circuit, the excitation does not change in polarity.

The supply circuit shown in FIG. 11 is constructed in many parts in the same way as the circuit according to FIG. 10. The main difference, however, is that it is constructed as a step-up converter. For this purpose, the transistor T in the transverse branch between the excitation winding 30 and one pole of the Rectifier Dl - D4 arranged. The diode D5 is installed between the connection of the transistor T and the DC voltage output 71 with its diode-cathode path. This circuit creates the possibility to influence the excitation. The excitation current can be conducted via the transistor T, even if no armature current is required. The high voltage at the output 71, 72 enables high speeds to be achieved.

In the circuit arrangement shown in FIG. 12, the input mains voltage U _N - at the inputs 90 and 91 is again varied in height via a triac 92 by means of a switch 93 in phase control. This input voltage is applied to the primary side 131 of a transformer 130, the secondary side 132 of which, with the two winding ends, form the input to the full-wave rectifier consisting of diodes D1 to D4. One pole of the rectifier is connected directly to the output 71 and the other pole of the rectifier is connected to the other output 72 of the voltage supply circuit via the current limiting resistor 96. Here, too, the series circuit comprising a resistor 94 and a braking transistor T _{B is connected in} parallel to the output of the rectifier. In parallel, again a capacitor 95 for stabilizing the output voltage U. The transformer 130 forms the excitation winding and is used both for electrical isolation and for voltage transformation between the line and the commutator. This circuit makes it possible to use inexpensive power semiconductors for low voltages. However, due to the principle of the transformer volume, this circuit is only suitable for relatively small motor outputs. Instead of the transformer in Fig. 12, it is also possible to provide a shunt excitation winding. The excitation is then no longer dependent on the load condition of the drive or on the armature currents and the result is a Shunt behavior of the drive. This can also apply to step-up converters according to FIG. 11 if the transistor T is connected appropriately in the transverse branch.

The invention provides an electronically commutated series motor with one or two field windings in a grooved stator. This field winding is designed in series with commutation electronics. The field of excitation thus has a periodic course of time. The commutation electronics ensure that the armature windings of the stator that form the moment are energized in a block-wise manner of individual phases.

In this brushless motor and drive designed in this way, the mechanical commutator, which is replaced by commutation electronics, is advantageously dispensed with. The armature winding is replaced by a rotating field winding compared to a universal motor. The advantages lie in various aspects. The brushes are no longer subject to wear, and the life of the motor is only limited by the life of the bearings. Additional functions can be easily implemented with little effort, such as current limiting, speed control, braking and installing an operating hours counter. As with the switched reluctance motor, commutation is carried out by simultaneously switching and energizing individual phases in blocks. Compared to this type of motor, the electronically commutated series-circuit motor created according to the invention has various advantages. This way, the armature windings are better used. At the same maximum current, which is a design criterion for the power semiconductors, both in the field winding and in the armature windings, four times the torque can be achieved compared to the switched reluctance motor. Due to the excitation of the motor, comparatively small magnetization energies are generated when commutating exchanged the armature windings with the network. This eliminates the need for an intermediate circuit with large storage capacities. The field windings serve as passive or active input filters and thus reduce the effects of the switching power semiconductors on the network, which significantly improves the EMC behavior. The star winding of the armature winding can be energized by inexpensive, commercially available converter circuits, which are produced in large numbers for asynchronous motors, particularly in the case of three-phase commutation with B6 bridges.

The drive designed according to the invention with a brushless electric motor and the brushless electric motor itself are particularly suitable in particular for use with power tools. On the one hand, the robustness of the entire structure and high continuous load capacity are important, on the other hand, the requirements for control quality, pulsating torque and pulsating performance are not as important. The key is a high continuous output with the greatest possible reliability and low costs. This is achieved with the invention.

Claims

~ ΛΛ, «, ~ .WO 00/6736219 Claims

1. Drive with brushless electric motor, especially for

Tools with pronounced teeth (1 - 3 \ - 22) in the stator (10) and in the rotor (20) of the motor, armature windings (11, 12, 13) provided in slots of the stator, which encompass the associated teeth, and with one Field excitation, characterized in that an excitation winding (30; 31, 32) for field excitation in

Stator (10) is provided and is arranged diametrically in the stator, the field guidance takes place via the teeth (22) of the rotor (20), the teeth (1 - 3 ^X ) of the stator (10) and its ring closure (14), the armature windings ( 11, 12, 13) in the sense of a

Three-phase winding attached and connected in a star circuit, the armature windings (11, 12, 13) for generating the

Torque is supplied in blocks by simultaneous switching on and off, electronic switches for switching the armature windings (Tl -

T6), in particular in the form of a three-phase bridge circuit, are provided as an electronic commutator and the excitation winding (30; 31, 32, 130) is arranged in series with the electronic switches. "", "," PC

WO 00/67362

20th

2. Drive according to claim l, characterized in that the excitation winding (30, 31, 32) is inserted in special diametrically arranged grooves of the stator (10).

3. Drive according to claim 2, characterized in that the

Excitation winding (31, 32) is divided in two and a part is arranged in a groove (34, 35), which is essentially arranged behind each stator pole (1, l ^λ ; 3, 3 ^λ ), the respective stator poles ( 1, r, - 3, 3 ') are adjacent.

4. Drive according to claim 1, 2 or 3, characterized in that the number of teeth (1 - 3 ^λ ) of the stator (10) to the number of teeth (22) of the rotor (20) is in an integer ratio of 6 to 4 .

5. Drive according to one of the preceding claims, characterized in that the electronic switches (Tl - T6) are supplied with direct current, which can be supplied in particular via a rectifier (Dl - D4) which is fed by an alternating current supply network.

6. Drive according to one of the preceding claims, characterized in that the excitation winding (30) is fed with direct current generated from an AC supply network.

7. Drive according to claim 6, characterized in that the excitation winding (31, 32) is divided into two and a part is arranged in the AC supply line of the rectifier bridge (Dl - D4) (Fig. 9).

8. Drive according to claim 6, characterized in that the excitation winding (30) between rectifier (Dl - D4) and inverter (Tl - T6) is connected (Fig. 10, 11).

9. Drive according to claim 5, characterized in that the excitation winding is constructed as a transformer (130), the primary winding (131) to the network (90, 91) and the secondary winding (132) to the rectifier (Dl - D4) (Fig. 12).

10. Drive according to one of the preceding claims, characterized in that the commutation circuit is controlled by means of a microcontroller.

11. Brushless electric motor, in particular for tools, with pronounced teeth (1 - 3 '; 22) in the stator (10) and in the rotor (20) of the motor, with armature windings (11, 12) provided in the slots of the stator (10). 13), which encompass the assigned teeth (1-3), with an excitation winding (30; 31, 32, 130) for field excitation in the stator (10), which is arranged diametrically in special slots in the stator, and with armature windings (11 , 12, 13), which are connected to each other in a star connection.

12. Motor according to claim 11, characterized in that the faces of the stator (1-3) and the rotor tooth (22), which face each other in alignment via an air gap (15), are essentially of the same size and are aligned concentrically with the rotor axis (21) .

13. Motor according to claim 11 or 12, characterized in that the groove (34, 35), in which the excitation winding (30, 31, 32) is inserted, substantially behind one of the stator poles

(1 - 3 *) is provided, the magnetic flux through this stator pole being as undiminished as possible.

14. Motor according to claim 11 or 12, characterized in that in two-part excitation winding (31, 32) each have a part in a groove (34, 35), which is seen essentially in the radial direction from the rotor axis (21) behind the

Pole surface of the corresponding stator tooth (1, l ^v ; 3, 3 '), which faces the rotor pole (22) in its orientation, is arranged, the respective stator poles (1, 1 \ - 3, 3') being immediately adjacent and the Magnetic flux over each stator pole is as undiminished as possible.

15. Motor according to one of claims 11 - 14, characterized in that the number of teeth (1 - 3 ^X ) of the stator

(10) to the number of teeth (22) of the rotor (20) in an integer ratio of 6 to 4.

16. Motor according to one of claims 11 - 15, characterized in that the rotor (20) consists solely of magnetic material.