EP2681840A1

EP2681840A1 - Electric drive

Info

Publication number: EP2681840A1
Application number: EP11802301.9A
Authority: EP
Inventors: Lothar Dietl
Original assignee: C&E Fein GmbH and Co
Current assignee: C&E Fein GmbH and Co
Priority date: 2011-03-04
Filing date: 2011-11-30
Publication date: 2014-01-08
Also published as: US20140009101A1; CN103503308B; CN103503308A; WO2012119670A1; DE102011013885A1

Abstract

The invention relates to an electric drive (70), in particular for an electric tool, having a rotor, a stator and a first coil assembly, which is designed to drive the rotor by means of a first rotating field, and having a first motor control assembly (90), which is designed to supply the first coil assembly (86) with electric power in order to generate a first rotating field. The stator has a second coil assembly (88) for generating a second rotating field. The second coil assembly (88) can be driven and energized separately from the first coil assembly (86) in such a way as to drive the second coil assembly (88) with any desired commutation sequence.

Description

Electric drive

The invention relates to an electric drive, in particular for a power tool, having a rotor, a fixed stator and a first coil arrangement which is adapted to drive the rotor by means of a first rotary field, and having a first motor control arrangement which is adapted thereto in that the electrical drive has a second coil arrangement for generating a second rotary field, which is assigned to the first coil arrangement and is magnetically coupled to the first coil arrangement. The invention further relates to a method for driving an electric drive, in particular for a power tool, wherein the electric drive has a rotor and a fixed stator, wherein a first coil arrangement for generating a first rotating field is supplied by a motor controller with electric current, wherein by means of a second coil arrangement which is assigned to the first coil arrangement and at least partially magnetically coupled to the first coil arrangement, a second rotating field is generated.

Such a drive and such a method is known from DE 10 2007 040 725 AI. This electric machine has a permanent magnetically excited rotor and a stator with a plurality of windings, which is operable on the one hand with a lower and on the other hand with a higher speed. For this purpose, parts of the stator winding are turned off or switched between a series circuit and a parallel circuit of certain coil sections. By this switching is to be switched between a normal operation and a so-called field weakening operation with a higher speed range.

By means of such an electric machine different speed ranges can be realized. A disadvantage of this electric drive, however, is that the switching of the resistance of the coils changes and thereby the current in the windings varies greatly. As a result, the Ohmic losses in the windings multiply in the field weakening operation, whereby the efficiency of the electric machine varies greatly. Furthermore, such operating modes can not be used permanently because the electric drive can be thermally overloaded by the Ohmic losses.

It is also known to control the speed of an electric drive, in particular an induction machine by varying the supply voltage. The speed is always directly via the supply voltage affected. However, the torque in such a control is not influenced accordingly.

From DE 10 2006 036 986 AI an electric motor with a mechanical field weakening device is also known, in which the stator is displaced relative to the rotor in the axial direction to reduce the influence of the permanent magnet on the windings and thus a field weakening to reach.

The disadvantage here is that the mechanism for Relatiwerschiebung the rotor and the stator is technically complicated and is only very slowly switchable.

Against this background, the present invention seeks to provide an improved electric drive, in which by simple means the output torque and / or the output speed can be changed.

This object is achieved in the electric drive of the type mentioned in the present invention, that the second coil assembly is controlled separately and energized separately from the first coil assembly to control the second coil assembly in any Kommutierungsfolge.

This object is achieved in the method of the aforementioned type according to the invention that the second coil assembly is driven and energized separately from the first coil assembly.

For the purposes of the present invention, the fixed assignment of the two coil assemblies to each other means that they are not moved relative to each other during operation of the electric drive. In other words, those are Coil arrangements, for example, both the stator or both associated with the rotor.

The electric drive can thus be brought into different operating modes in which different strong and differently directed rotating fields can be generated by electrical switching by the two coil assemblies.

The rotating field can thus be brought into at least two states in which different speeds and different torques can be realized at substantially the same power output. As a result, it is thus possible to electronically change the rotational speed for the same phase voltage, that is to say the speed constant, and to emulate a transmission characteristic.

The driving of the second coil arrangement can thus cause a weakening or strengthening of the rotating field, depending on the polarity direction, whereby the speed and the output torque can be varied electronically.

It is particularly preferred if the second coil arrangement can be energized such that the second rotating field is at least partially opposite to the first rotating field or the first and the second rotating field are at least rectified.

As a result, the respective magnetic fluxes overlap, whereby a field weakening or a field strengthening can be achieved.

According to one embodiment of the invention, the first coil arrangement has a first plurality of coil strands and the second coil arrangement, a second plurality of coil strands, wherein at least one of the coil strands of the first coil arrangement is magnetically coupled to one of the coil strands in the second coil arrangement. In other words, at least one of the coil strands of the first and one of the second coil arrangement are magnetically coupled together, whereby the rotating field of the second coil arrangement can weaken or strengthen the rotating field of the first coil arrangement. As a result, field weakening or weakening of the electromotive force (EMF weakening) or field strengthening can be achieved by simple means.

In one embodiment of the invention, the first and the second coil arrangement to an identical plurality of coil strands, which are each associated with each other and each magnetically coupled together.

In other words, each of the coil strands of the first coil arrangement is associated with a coil strand of the second coil arrangement, whereby the rotating field of each of the coil strands of the first coil arrangement can be weakened or amplified. As a result, a symmetrical and uniform field weakening or field strengthening is possible.

In a preferred embodiment, a plurality of coil strands of the first coil arrangement and a plurality of coil strands of the second coil arrangement can be energized simultaneously.

Thereby, a multi-phase rotary field for driving the electric drive can be generated, whereby an effective drive can be provided.

It is preferred if at least one coil strand of the second coil assembly can be energized, which is associated with a non-energized coil strand of the first coil assembly.

As a result, correspondingly resulting sum fields or differential fields can be generated, which only have a low EMF weakening or a have low field weakening, whereby further control variants can be provided with even finer graded characteristic fields.

Furthermore, it is preferred if the first coil arrangement can be supplied with current with a first plurality of phases and the second coil arrangement can be supplied with current with a second plurality of phases.

In other words, the coil arrangements can be energized in multiple phases, whereby a multi-phase AC machine can be realized.

Furthermore, it is preferable if the first plurality of phases and the second plurality of phases are identical.

As a result, the first coil arrangement and the second coil arrangement can be controlled with identical controls.

Furthermore, it is preferred if the first plurality of phases is greater than the second plurality of phases.

As a result, the second coil arrangement can be controlled more easily and with fewer components.

According to a development, the first and the second coil arrangement each have three coil strands, which are each connected in a star connection or a triangular circuit or are connected in a star and a delta connection.

In other words, the first coil arrangement and the second coil arrangement are connected in a star connection or the first and the second coil arrangement are connected in a delta connection or the first coil arrangement tion in a star connection and the second coil arrangement connected in a delta connection or vice versa to generate corresponding rotating fields.

As a result, different field weakenings can be generated depending on the application.

Furthermore, it is preferred if the drive is designed as an electronically modulatable DC machine or permanent-magnet-excited synchronous machine, wherein the first and the second coil arrangement can be differently energized in a plurality of commutation steps.

As a result, the electric drive can be electrically controlled or regulated in different modes without having to use additional mechanical elements or sliding contacts.

Furthermore, it is preferred if the second coil arrangement can be energized in at least one of the commutation steps in such a way that the second rotating field is directed counter to the first rotating field.

As a result, field weakening can be generated in individual ones of the commutation steps, as a result of which a plurality of different speed-torque characteristics can be realized.

Furthermore, it is preferred if the second coil arrangement can be energized in at least one of the commutation steps such that the second rotating field is rectified with the first rotating field.

In other words, the second coil arrangement in different commutation steps of one revolution of the rotor can both amplify and weaken the existing rotating field of the first coil arrangement, so that an elliptical rotating field is produced as the resulting rotating field. As a result, a plurality of different speed-torque characteristics can be realized, whereby the electric drive is versatile.

It is further preferred if the second coil arrangement can be energized by a second motor control arrangement and can be supplied with electric current.

In other words, the first coil arrangement is controlled by a first motor control arrangement and the second coil arrangement by a second motor control arrangement and supplied with electric current. As a result, the two coil arrangements can be controlled or energized separately, resulting in a large number of independent control options.

It is further preferred if the first and the second coil arrangement can be energized by the same current.

In other words, the two motor control arrangements control the coil arrangements differently, with the motor control arrangements being supplied by the same current which is conducted through the two coil arrangements. As a result, the power output of the electric machine remains the same at different drives, resulting in e.g. the ohmic losses remain essentially the same for the different types of control.

According to one embodiment of the invention, the two engine control systems are adapted to the engine with a first speed-torque curve and with a second speed-torque curve, which has a different slope from the first speed-torque curve to operate. The relative load is here as the quotient of the speed difference between the idle speed n ₀ and load speed n _L on the one hand and training

speed n ₀ on the other hand, or alternatively as the quotient of load torque M _L and (in the case of saturation or current limitation from the characteristic gradient

M,

calculated) holding torque M _H , so to look at.

In this way, the behavior of the drive can have the functionality of a switchable transmission. It may result in a geared relationship, such as a ratio factor or a reduction factor or a spread between the speeds or the torques of the first and second characteristics.

In other words, for example, during the transition from the first characteristic curve to the second characteristic curve, the rotational speed can increase by the factor by which the torque decreases.

In a further development, the respective slopes of the speed-torque characteristics in dependence of the directions of the first and the second rotating field and / or the order of the individual Kommutierungsschritte are adjustable.

In other words, the slope of the speed-torque characteristics is variable by the targeted field weakening or strengthening or by the resulting elliptical rotating field, so that the polarity reversal of the coil arrangements at individual Kommutierungsschritten another translation factor or a reduction factor or a spread between allows the speeds or torques. In an advantageous embodiment of the invention, coil strands of the first coil arrangement assigned to one another have a first number of turns Zi and the second coil arrangement has a second number of turns z ₂ , wherein a summation field is produced when the current through the motor control arrangements when the corresponding rotary fields are rectified and a difference field is created when the respective spin fields are opposite.

In this way, the functionality of a multi-speed transmission can be realized.

If the coil strand of the first coil arrangement and the coil strand of the second coil arrangement are poled identically, the result is a total winding number m which is equal to the sum of the first number of turns mi and the second number of turns z ₂ . The coil strands thus behave like a single coil with m turns.

In the opposite polarity state of the coil strands or coil arrangements, that is, when the second rotary field counteracts the first rotary field, the flux coupled to the second coil section counteracts the flux generated in the first coil section. The associated magnetic fields and induced voltages cancel each other out as a result. As a result, an effective number of turns z * which corresponds to the difference between the first number of turns mi and the second number of turns z ₂ remains.

From the ratio of the effective number of windings z * and the total number of windings z, the factor f can be determined, which represents a measure of the "speed ratio" which can be effected with the respective configuration of the first coil section and the second coil section Way (ie, inversely proportional thereto), the resulting moment can be specified. In this type of field neutralization or field weakening remain at the same relative load both the output power P ₂ (n is greater, M is smaller) and the Ohmic losses substantially unchanged, so that the thermal design of the engine both states equally considered can. The suitability for continuous operation thus improves significantly.

According to a particular embodiment, the number of turns m _{2 of} the coil strand of the second coil arrangement, which is coupled to the coil strand of the first coil arrangement, smaller than the number of turns mi of the first coil strand. In this way, depending on practically realizable numbers of turns, almost any desired gear ratio can be realized. In this case, on the one hand, a translation into fast or slow, for example at the transition from a first characteristic curve to a second characteristic curve can be effected.

Characterized that a plurality of speed-torque characteristics with different slopes are adjustable by the plurality of different combinations during the different Kommutierungsschritte, correspondingly many "ratios" can be effected, so that the functionality of a multi-speed transmission is adjustable.

It is particularly preferred if the drive is supplied with an electrical tool, in particular a hand-held power tool with independent electrical energy, which can be coupled to a tool spindle for driving the tool.

The power tool may be a tool for screwing, drilling, sawing, cutting, grinding or polishing. Such power tools are used for a variety of purposes, so that it is often desired to influence a driven movement of the tool, such as by varying the output torque and the output speed.

Such variations can be accomplished by means of mechanical gear, they may have a plurality of switching stages, which may affect the one hand, the output speed and the output torque, on the other hand, about a direction of rotation. In this case, in mechanical transmissions, in particular in gear transmissions, each gear stage is generally associated with a constant gear ratio f.

Such a characteristic can also be effected directly in the drive according to the present invention, so that such a transmission can be replaced or supplemented by an extended functionality.

A particular advantage of the invention is that the switching can take place under load. The mechanical drive train is unchanged. The position of the switching point can be freely selected. On the other hand, in the case of a mechanical gearbox, switching usually takes place at standstill. In addition, a switching element must be moved mechanically.

A switchable according to the invention electric tool can thus be particularly easy to set up, but cover a wide range of applications.

In this case, the engine control arrangements may be designed to detect an operating state variable or to evaluate an operating state variable supplied to it, in order to control the coil arrangements differently depending thereon. If it is found, for example, that a fall in rotational speed occurs due to a high relative load, then one of the coil arrangements could, for example, be activated in order to bring about a fundamentally higher output torque.

On the other hand, if, for example, it is found that only a small relative load is present, then the coil arrangements can be controlled in such a way that an overdrive is achieved, for example in a screwdriver.

Thus, the performance of the power tool can increase overall, the power tool can be used more flexibly.

According to a particular embodiment of the invention, the motor control arrangements for driving the first and the second coil arrangement are coupled together such that the same current flows through both coil arrangements. In this case, the motor control arrangements each have three parallel current paths, each with two controllable switches, between which taps for the respective phases of the coil arrangements are formed. As a result, the two coil arrangements can be controlled separately in a simple manner, the power consumption being substantially constant, since the same current flows through the two coil arrangements. In a particular embodiment, the controllable switches are formed by semiconductor switching elements. This allows fast switching according to the commutation speed.

According to a further embodiment of the invention, the power tool has a power supply unit for providing electrical energy, which is preferably coupled to a DC power source and more preferably to an accumulator.

In particular, in the case of independent, preferably portable electric tools, a variation of the rotational speed can thus be achieved without significant additional weight. number-torque characteristic, which helps to improve the performance of the power tool.

In a power tool having a permanently excited electronically commutatable electric motor, the motor controller is coupled to a DC power source, the drive according to the invention can be particularly easily implemented with a very small number of additional required components.

Overall, a novel drive is provided with the invention, which is particularly suitable for a power tool and which can to a large extent emulate a "transmission functionality." In this case, a plurality of speed-torque combinations can be realized.

This replica of the transmission functionality is carried out at high efficiency and avoiding wear-promoting conditions of the drive, in particular with regard to the thermal load by ohmic losses.

The drive according to the invention can in principle also be used as an electrical machine, for example in a generator application.

It is understood that the features mentioned above and those yet to be explained not only in the combination given, but also in other combinations or alone, without departing from the scope of the present invention.

Embodiments of the invention are illustrated in the drawings and will be explained in more detail in the following description. Show it: Fig. 1 is a schematic view of a power tool with a drive according to the invention;

FIG. 2 shows a schematic illustration of a drive according to the invention with an iron core and in each case two independent coil arrangements; FIG.

Fig. 3 is a simplified circuit diagram of the drive with two independent

Control arrangements;

4a-h different driving modes of the coil arrangements for

Generating a field gain or a field weakening;

Fig. 5 six commutation steps of an electronically commutated

DC machine with a coil arrangement;

6a-f show different variants of possible commutation sequences;

FIG. 7 shows an idealized speed-torque characteristic curve for two different activation states; FIG.

8 shows a simplified schematic circuit diagram of a drive unit for driving two coil arrangements in star connection;

9 shows a simplified schematic circuit diagram of a drive unit for driving two coil arrangements in a triangular circuit; 10 shows a table for explaining possible switching states of the control unit from FIGS. 8 and 9 for actuating two coil arrangements of an electrical machine in normal operation;

Ia, b two tables for explaining possible switching states of

Control unit of FIGS. 8 and 9 for driving two coil arrangements in the EMF attenuation mode for each of six different commutation steps.

FIG. 1 shows a simplified schematic representation of an electric power tool, which is denoted overall by 10.

By way of example, the power tool 10 is shown as a tool for drilling or screwing. It is understood that it can also be, for example, a tool for impact drilling, impact screws, sawing, hammering, cutting, grinding or polishing.

Depending on the intended use, the output movement may be linear, rotational, intermittent or oscillating. In the present case, the power tool 10 has a housing 12 with a grip area 14, on which an operator can grasp and operate the power tool 10.

In or on the housing 12, a drive 16 is provided which has a motor 18 and a motor controller 20. The motor 18 serves to drive a motor shaft 22, which is coupled to a tool spindle 23 which cooperates with a tool 24 (shown only broken).

The tool 24 is fixed to the tool spindle 23 via a tool holder 26, such as a chuck. The tool spindle 23 and the motor shaft 22 may be interposed between a clutch 28 or a transmission 30. The transmission 30 may be designed as a gear transmission and have a constant ratio or more switchable gear ratios. The clutch 28 may be formed as a slip clutch or as a clutch and serve for overload protection or separate the tool spindle 23 from the motor shaft 22 in the context of an idling functionality. Further, the clutch 28 may for example have a stop function, so be fixed relative to the housing 12 to allow a simple tool change or the like.

The motor 18 is preferably designed as a permanently excited electrically commutated electric motor, also referred to as EC motor. In this case, the motor controller 20 cause the activation of the motor 18 for generating a rotating field. For this purpose, the engine control unit 20 is connected to the motor 18 via electrical lines 32, 34, 36.

The motor controller 20 can also be coupled via supply lines 38, 40 to a power supply device 42, which is configured by way of example as an accumulator 44 in FIG. 1.

The accumulator 44 serves as a DC power source, the source voltage is converted by the motor controller 20 into a voltage which acts on the motor 18 via the electrical lines 32, 34, 36. Each of the lines 32, 34, 36 can be assigned to approximately one phase U, V, W.

Alternatively, the power tool 10 may also be connected to a stationary voltage source, such as a line network. To convert an AC voltage into a DC voltage, a rectifier arrangement can be provided. In FIG. 1, the motor controller 20 is furthermore coupled by way of example with sensors 46, 50, signal transmission takes place via sensor lines 48a, 48b or 52a, 52b. The sensors 46, 50 may be designed to detect an operating state variable for describing an operating state of the power tool 10 and to transmit it to the motor control 20 or a control device provided therewith or coupled thereto.

The operating state variable to be detected can basically be a rotational speed or a torque, such as at the drive or the output, a switching state of a switch, a temperature, such as the transmission 30 or the accumulator 44, or a value, the one to the Lines 32, 34, 36 applied voltage or a current flowing through them.

The sensor 46 may be approximately configured to detect a switching state of the clutch 28. Alternatively, the sensor 46 could be designed to detect a temperature at the clutch 28, for example as a wear indicator or load indicator.

Likewise, the sensor 50 may be provided to detect a switching state, such as a currently selected shift position, the transmission 30 or a temperature indicative of an instantaneous load.

In the grip region 14 of the power tool 10, an operating switch 54 is also provided, via which the operator can selectively activate or deactivate the power tool 10. The operation switch 54 is also coupled to the engine controller 20.

Further, on the housing 12 of the power tool 10, a selector switch 56 is provided, which is coupled via selector switch lines 60a, 60b to the motor controller 20. The selector switch 56 can reciprocate between a first position and a second position, as indicated by an arrow labeled 58 be switched. About the selector 56, the operator can switch the drive 16 of the power tool 10 approximately between a first state with a first speed-torque curve and a second state with a second speed-torque curve.

In Fig. 2, an inventive drive is shown schematically.

The electric drive is indicated generally at 70 in FIG. The electric drive 70 has a stator 72 and a rotor 74. The stator 72 has an iron ring 76 with radial iron core sections 77, on each of which a coil 78 is arranged. The stator 74 in this case has nine coils 78, which are supplied with electrical energy via electrical lines 80. The lines 80 connect the coils 78 to three phases U, V, W. In the present case, three of the coils 78 are connected in parallel and form a coil strand, the resulting three coil strands being connected together in a star connection.

The coils 78 generate a magnetic rotating field which acts on the permanent magnet rotor 74 and drives it in a drive direction. By changing the control of the coil strands on the phases U, V, W, a rotating rotating field is generated, which drives the permanent magnetic rotor 74 accordingly.

Furthermore, in each case an additional coil 82 is arranged on the radially oriented iron cores 77, which are interconnected by means of electrical lines 84 and can be supplied with electrical current by three phases U ', V, W. The coils 78 and the auxiliary coils 82 are each magnetically coupled to each other via the iron core portions 77. The auxiliary coils 82 generate a second rotating magnetic field which acts on the permanent magnet rotor 74. The first rotating magnetic field generated by the coils 78 and the second rotating magnetic field generated by the auxiliary coils 82 are superimposed, so that depending on the direction the two rotating fields creates a sum field which is larger than the respective individual rotating fields or a difference field is created which is smaller than one of the rotating fields. In this case, the magnetic fluxes of the first rotating field and the second rotating field add together and form a magnetic sum flow. As a result, the additional coils 82 can cause a field weakening (EMF weakening) or a field strengthening, depending on the direction of their control. The additional coils 82 are connected in this case as the coils 78 to three coil strands in a star connection and can be supplied via the phases LT, V, W so with electrical current that a rotating rotating field is formed.

The coils 78 each have a number of turns zi and the additional coils have a number of turns m ₂ . The number of turns z ₂ is preferably smaller than the number of turns It is preferred if the ratio of the number of turns zi: z _{2 is} smaller than 1: 2. In a particular embodiment, the ratio is less than 1: 3 or less than 1: 4. In an alternative embodiment, the number of turns Zi, z _{2 are} identical.

In Fig. 3 is a schematic circuit diagram of the electric drive 70 is shown. In this case, only coil coils of two independent coil assemblies 86, 88 are shown, wherein the coil strands of the first coil assembly 86 are generally denoted here by Li, L ₂ , L ₃ and the coil strands of the second coil assembly 88 here generally with Li ', L ₂ ', L ₃ 'are designated. The respective coil strands Li, Li 'and L ₂ , L ₂ ' and L ₃ , L ₃ 'are each associated with each other and as shown in Fig. 2 magnetically coupled together. The coil strands Li, L ₂ , L ₃ are supplied via the phases U, V, W with electrical energy. The coil strands Li, L ₂ , L ₃ are connected via lines 80 to a drive unit 90. The coil bars Li ', L ₂ ', L ₃ 'are supplied with electrical energy via the phases U', V, W '. The coil strands of the second coil arrangement 88 are connected via the lines 80 and a second drive arrangement 92. The drive arrangements 90, 92 independently supply the coil arrangements 86, 88 with electrical energy, so that independent rotary fields can be generated which superimpose additively or subtractively depending on the drive. As a result, an electric drive 70 is provided by means of two coil arrangements 86, 88 and two drive arrangements 90, 92 which, depending on the activation causes a field weakening or a so-called weakening of the electromotive force (EMF weakening) or a field strengthening and thereby different rotational speeds can produce with different torques.

Various switching or excitation states or polarities of the coil strands Li to L3 and Li 'to L ₃ ' are shown in FIGS. 4a to 4h. The coil assemblies 86, 88 are identical to the coil assemblies 86, 88 shown in FIG. 3. Like elements are identified by like reference numerals, with only differences shown. In FIG. 4 a, the coil arrangements 86, 88 are driven or energized via the phases U, V and U ', V such that the coil strands Li and Li' as well as L ₂ and L ₂ 'generate rotary fields 94, 96 in the same direction, so that an increased sum field arises.

In Fig. 4b, the coil assemblies 86, 88 are controlled via the phases V, W and V, W such that the coil strands L2, L ₂ 'and L ₃ , L ₃ ' each generate a rotating field 94, 96, the aligned in the same direction so that they add to the sum field.

In Fig. 4c, another driving state of the coil assemblies 86, 88 is shown, in which the rotating fields 94, 96, which are generated by the coil strands Li, Li 'and L ₂ , L ₂ ' add up to an increased sum field.

It is understood that the states shown in Figs. 4a to 4c can also be generated in the opposite direction.

In FIGS. 4 d to 4 f, three different drive states of the coil arrangements 86, 88 are shown by way of example, in which the rotary fields 94, 96 are opposite one another, such that the rotary field 96 of the second Coil arrangement weakens the rotating field 94 of the first coil assembly. This creates a difference field. In Fig. 4d, the coil assemblies 86, 88 are driven such that the coil strands Li and L ₂ generate the rotating field 94, wherein the second coil assembly 88 is driven such that the corresponding coil strands Li ', L ₂ ' generate the rotating field 96, the the rotating field 94 is opposite. As a result, the rotating field 96 can weaken the rotating field 94 and form the difference field.

FIGS. 4e and f show further switching states in which the rotary field 96 is opposite to the rotary field 94.

In Fig. 4g, a driving state of the coil assemblies 86, 88 is shown by way of example, in which the coil assemblies 86, 88 are energized so that the coil strands Li and Li ', which are magnetically coupled together, are energized, and further that the coil strands L ₂ 'and L _{3 are} energized, which are not magnetically coupled to each other. As a result, the rotating fields 94, 96 are only partially overlapped. As a result, a further variant in the control of the coil arrangements 86, 88 can be realized, in which a resulting sum field is produced, the amount of which is less than the sum of the sum fields that arise in FIGS. 4a to 4c.

In Fig. 4h, another driving state of the coil assemblies 86, 88 is exemplified, in which the rotating fields 94, 96 of two magnetically coupled coil strands are opposite to each other. The coil assemblies 86, 88 are energized such that the rotating field 94 of the coil strand Li is opposite to the rotating field 96 of the coil strand Li 'and that two more coil strands L ₂ ', L _{3 are} energized, which are not magnetically coupled together. This creates a difference field that differs from the difference fields of FIGS. 4d to 4f. As a result, further variants of the control of the coil arrangement 86, 88 can be provided. It is understood that the switching states shown in FIGS. 4d to 4h can also be realized in each case in the opposite polarity direction of the coil arrangements 86, 88.

[Olli] In Fig. 5, six commutation steps of a rotary electric machine are shown, e.g. the first coil assembly 86 is driven in operation via the phases U, V, W.

By way of example, a system with the three phases U, V, W is shown here with three coil groups adapted to the number of poles or the number of phases. The coil groups are each formed from two simultaneously driven coil strands Li, L ₂ , L ₃ . Depending on the control thus the coil groups are energized consisting of the coil strands Li, L ₂ or L ₂ , L ₃ or Li, L ₃ . These coil groups are also referred to as commutation groups. The three possible commutation groups can each be energized in two current directions, one of the commutation groups with the respective current direction being referred to as a commutation step. There are thus six commutation steps in the system exemplified here. The order in which the six commutation steps are performed determines a complete commutation sequence. Usually, first the three commutation groups are energized with a uniform current direction, the rotational direction of the rotor being determined by the sequence. These three commutation groups or commutation steps correspond to steps 1 to 3 from FIG. 5. In the same sequence, the commutation steps are then carried out with opposite current direction. These commutation steps correspond to steps 4 to 6 of FIG. 5. The sequence of the commutation steps thus described is generally referred to as the ground state.

Through the six steps shown in FIG. 5, the rotating field 94 is generated in rotating form to drive the permanent magnet rotor 74. In this so-called block commutation are according to the rotational position of the rotor 74 energizes certain of the coil groups to generate the rotating field 94 at certain angular positions of the stator 72 and drive the rotor 74 accordingly. In this block commutation, as described above, in each case one coil or commutation group, ie two of the three coil strands Li, L ₂ , L _3, is energized in such a way that the rotary field 94 rotates about the rotor 74 in order to drive it in a corresponding manner. In Fig. 5, six commutation steps are shown in dependence on the angular position of the rotor 74. It is understood that in other coil arrangements, a different number of block commutation steps is possible. In the case of the six commutation steps shown in FIG. 5, one commutation group, ie two of the coil strands Li, L ₂ , L _{3, is} energized, depending on the step, either in a first direction or in the opposite second direction. In other words, the coil strands Li and L _{2 are} poled in step 1 at 0 ° in the first direction, and in step 4 at 180 °, the coil strands Li, L _{2 are} poled in the opposite second direction. The same applies to steps 2 and 5 or 3 and 6.

In an identical manner, the coil assembly 88 is energized, so that in each of the commutation steps corresponding coil groups are driven, so that the two rotating fields 94, 96 depending on the current direction in the same direction or in opposite directions act or can be aligned, as shown in Fig. 4a-f. As a result, different summation fields or difference fields can be generated in each individual of the commutation steps, as a result of which symmetrical or asymmetrical elliptical rotating fields can be generated. Alternatively, different coil groups can also be activated or energized in a commutation step, as shown in FIGS. 4g and 4h.

Various commutation sequences of the electric drive 70 are shown in FIGS. 6a to f, in which both the coil arrangement 86 and the coil arrangement 88 are activated. In Figs. 6a-f, the rotating field 94 generated by the first coil assembly 86 and the rotating field 96 generated by the coil assembly 88 are schematically represented by arrows. The polarity the corresponding rotating fields 94, 96 is indicated by the direction of the arrows, wherein the direction pointing upward represents the drive direction of the rotor 74 and the downward direction represents a rotating field counteracting the drive direction. The individual of the six commutation steps of Fig. 6 are shown side by side and designated by corresponding numbers. For the commutation sequences shown in FIGS. 6a to 6f, a respective attenuation factor f is determined, which was determined for a turn number ratio of the coil arrangements 86, 88 of 1: 3. The attenuation factor can be determined with the formula: · ^Ζ 2 ^Z 2

where HAI is the number of commutation steps in which the first rotating field 94 is poled in the drive direction, H _A 2 is the number of commutation steps in which the second rotating field 96 is poled in the drive direction and H _B 2 is the number of commutation steps in which the second Spinning field is polarized against the drive direction. Zi and z ₂ are the numbers of turns of the first and second coil assemblies 86, 88.

FIG. 6 a shows a state of amplification of all of the commutation steps 1 to 6. In this case, the rotating fields 94, 96 in each of the commutation steps 1-6 are poled in the drive direction, so that here at each of the commutation 1-6 a field gain, ie an increased sum field is generated, so that the rotor 74 with a reinforced symmetrical non-elliptical rotating field is driven. In this case, there is no field weakening of the rotating field 94. The attenuation factor is f = 1.

In Fig. 6b, a normal Umpolungszustand is shown in which at each of the commutation steps 1-6, the rotating field 96 is opposite to the rotating field 94. This normal Umpolungszustand is achieved in that the second coil assembly 88 at each of the Kommutierungsschritte in opposite ter direction to the first coil assembly 86 is poled. In this normal Umpolungszustand a field weakening factor of f = 2 is achieved.

In the following figures, possible Umpolungszustände be shown in which in only a few of the Kommutierungsschritte the second coil assembly 86, 88 is polarized against the drive direction.

In Fig. 6c, a commutation sequence is shown, in which the rotating field 96 is poled only in the first and fourth of the commutation counter to the drive direction and is polarized in the remaining commutation steps 2, 3 and 5, 6 in the drive direction. As a result, the rotating field 94 is weakened only in the first and fourth commutation step and strengthened in the remaining commutation steps. This creates an elliptical rotating field. Since the commutation steps for the first half-wave, that is, the commutation steps 1 to 3, are identical to those of the second half-wave, that is to say the commutation steps 4 to 6, a symmetrical elliptical rotating field is produced. In the commutation sequence shown in FIG. 6c, a field weakening factor of f = 1.2 arises.

In Fig. 6d, a commutation sequence is shown in which the rotating field 94 is aligned in each of the commutation in the drive direction and the rotating field 96 of the coil assembly 88 is directed in steps 1, 2, 4 and 5 against the drive direction. In the remaining of the commutation steps, the rotating field 96 is directed in the drive direction. This creates another possibility of an elliptical rotating field. Such Umpolungszustand causes in this case a weakening factor of f = 1.5.

In addition to the symmetrical rotating fields in which the first half-wave, so the commutation steps 1 to 3, and the second half-wave, so the commutation steps 4 to 6, are commuted equal, asymmetric elliptical rotating fields are possible in which the first half-wave not is commuted equal to the second half-wave. By way of example, in FIG. 6e, a commutation sequence for an asymmetrical elliptical rotating field shown. In this case, the rotary field 96 of the second coil arrangement 88 is polarized in the entire first half-wave, ie the commutation steps 1 to 3 counter to the drive direction, wherein the rotating field 96 is poled in the second half-wave, ie the commutation steps 4 to 6 in the direction of the drive direction. In the commutation sequence from FIG. 6e, the rotating field 94 of the first coil arrangement 86 is poled in the drive direction in all commutation steps. Due to this commutation sequence, a weakening factor of f = 1.33 can be achieved.

FIG. 6f shows a further possible commutation sequence for generating an asymmetrical elliptical rotating field, wherein only in step 6 the rotating field 96 of the second coil arrangement 88 is reversed. This allows the minimum possible field weakening factor of f = 1.09 to be achieved.

It is clear from the examples of commutation sequences of FIGS. 6a to f that any desired polarity of the coil arrangements 86, 88 of the individual commutation steps is possible. Theoretically, the six different commutation steps, whereby the coil arrangement 88 can assume two states, make 2 ⁶ = 64 switching states possible.

As a result of the different polarity of the coil arrangements 86, 88 in the various commutation steps, as shown by way of example in FIGS. 6a to f, many different attenuation factors f can be achieved, whereby a corresponding number of different slopes of the speed-torque line can be achieved. As a result, the functionality of a transmission can be simulated electrically, with the number of gears corresponding to the different numbers of attenuation factors. For this reason, many different gear-like translation states can be realized, as will be explained in more detail below. In Fig. 7 exemplary speed-torque characteristics of an electric motor are shown. On the ordinate 100, the speed n is plotted. The abscissa 102, on the other hand, shows values of the torque M.

With 104, 106, 108 different speed torque curves are idealized plotted and the speed-torque curve 104 exemplifies a n (M) -Vergeration of a typical electrically commutated rotary field motor. The drive 70 according to the invention can be operated in different states , which is described with about a speed-torque characteristic 104 as well as a speed-torque characteristic 108. It is caused by the different torques at different speeds, a gearbox similar functionality. In Fig. 7, only the two characteristics 104, 108 are shown here as possible characteristics of the drive according to the invention, however, as described above, a plurality of characteristics with different slopes can be realized.

The first characteristic 104 is characterized by a holding torque 110 and an idle speed 112. In contrast, the drive 70 can be operated in a further state, which is described by the characteristic curve 108, as if a transmission gear with a ratio factor i = 2 interposed. The characteristic curve 108 is characterized by the holding torque 114 and the idling speed 116. It is readily apparent that in the example chosen the idling speed 116 is approximately twice the idling speed 112. In contrast, the holding torque 114 corresponding to the characteristic curve 108, the half of the holding torque 110 of the characteristic 104. Ideally, while the quotient of the holding torque 110 and the holding torque 114 is inversely proportional to the quotient of the idle speed 112 and the idle speed 116th

The intersection of the two characteristic curves 104, 108 is indicated by numeral 118. If at this point a switching between the two characteristics, this is completely imperceptible to the user. Starting from there you can then continue on either the characteristic 104 or 108 continue. Based on the fact that a variety of different attenuation factors and the associated different speed-torque characteristics with different slopes are feasible, and the idea that is switched at a respective intersection of two speed-torque characteristics, although a sectionally linear Realize gear ratio, however, the seemingly represents a continuous change of the transmission ratio by the large number of different gradients.

For comparison, another speed-torque characteristic is indicated at 106, which can be effected according to the prior art as described in DE 10 2007 040 725 AI, starting from the characteristic 104.

In this case, the transition from the characteristic 104 to the characteristic 106 may be e.g. be realized by switching off partial coils. The resulting characteristic 106 can not be derived, such as into characteristic curve 108, while maintaining the inverse proportionality of the respective ratios of idle speed and holding torque.

An operation approximately according to the characteristic curve 106 can in principle be realized by, for example, only one of the coil arrangements 86, 88 being driven.

Basically, the output of the electric drive 70 in the state of the characteristic curve 104 or the characteristic curve 108 is substantially equal, since the product n · M is identical in both characteristics. This output power is essentially the same, neglecting iron and friction losses, ie taking ohmic losses into account, provided the relative load is identical. In Fig. 8 is a circuit diagram of a control unit for driving the first coil assembly 86 and the second coil assembly 88 is shown schematically. The control unit is indicated generally at 120 in FIG. The coil assemblies 86, 88 are shown in Fig. 8 schematically connected in a star connection and are three-phase supplied by the control unit 120 with electrical energy. The control unit 120 has a voltage source 121, which in this case is designed as a battery or rechargeable battery. The control unit 120 further has a first drive arrangement 122 for driving the first coil arrangement 86 and also a second activation arrangement 124 for actuating the second coil arrangement 88.

The first and second coil assemblies 122, 124 are identically constructed and connected in series between voltage terminals of the electric power supply 120. The control arrangements 122, 124 each have three parallel current paths 128, 130, 132, which are connected in parallel to one another and each have two controllable switches 134. Between the controllable switches 134, a tap 136 is formed in each case, which is connected in accordance with the lines 80, 84 and one of the phases U, V, W, U ', V, W form. The three parallel current paths 128, 130, 132 are each electrically connected at their ends.

Two of the coil strands Li, L ₂ , L _{3 can be} energized by opening two of the controllable switches 134 of one of the control circuits in different current paths 128, 130, 132, so that by switching over the controllable switches 134, each of the previously mentioned Bestromungszustände or commutation states can be realized. If two controllable switches in the same current path 128, 130, 132 are closed, the corresponding coil arrangement 86, 88 is not energized and thus does not generate a rotating field 94, 96.

The fact that the two drive arrangements are connected in series between the voltage points 126, basically the same flows Current through the two coil assemblies 86, 88. As a result, the electrical resistance of the entire drive remains identical despite switching the rotating fields, whereby the power output of the drive 70 for substantially different switching states remains substantially the same.

With the control unit 120, a commutation sequence of the second coil arrangement 88, which are magnetically coupled to one another via the iron core sections 77, can be superimposed on the ground state of the first coil arrangement 86. However, if the second coil arrangement 88 is energized in the same sequence of commutation groups of the ground state in the opposite direction or polarity, which is in each case opposite to the ground state, a commutation sequence results which corresponds to a field weakening or EMF weakening.

The energization of the second coil arrangement 88 can be carried out arbitrarily. For each of the six commutation steps of the first coil arrangement 86, an arbitrary commutation step of the second coil arrangement 88 can be combined. Overall, six times six overall states are possible. However, not all provide a meaningful combination, but some may be used to generate further speed-torque characteristics of the overall coil system. By way of example, two commutation sequences are given below. In these sequences, alternately between the ground state and the EMF-weakened state of the switchable partial coil or the additional coils 82 is switched.

The first and second drive arrangement 90, 92 shown in FIG. 3 can each be formed by one of the control arrangements 122, 124, each having three current paths 128, 130, 132 and six controllable switches, and in each case one voltage source. In Fig. 9, an alternative circuit diagram of the coil assemblies 86, 88 of Fig. 8 is shown. The same elements are designated by the same reference numerals, with only the differences being shown here. In Fig. 9, the coil assemblies 86a, 88a are connected as a triangular circuit. The coil arrangements 86a, 88a are supplied identically as in FIG. 8 in a three-phase manner via the phases U, V, W, U ', V, W via the control unit 120.

In a further embodiment, one of the coil arrangements 86, 88, for example, the first may be connected in a star circuit 86 and, for example, the second may be connected in a delta circuit 88a or vice versa.

In an alternative embodiment, the second coil arrangement 88 may be designed such that the coil strands Li ', L ₂ ', L3 'can be energized independently of one another and separately. As a result, further repositioning states are possible, as a result of which the number of possible attenuation factors can be further increased. It is further conceivable that the second coil arrangement 88 has only a single coil strand Li ', L2', L ₃ ', which is assigned to a corresponding coil strand of the first coil arrangement 86. As a result, a simplified drive with field weakening can be provided, in which both the second coil arrangement 88 and the second control arrangement 124 are structurally less expensive.

FIG. 10 shows a table which, for six different commutation steps, shows switching states of the controllable switches 134 with the reference symbols from FIGS. 8 and 9 and is designated generally by 140. The commutation steps generate rotary fields 94, 96 for normal operation. That is, in the switching states shown in Fig. 10, the rotating fields 94, 96 are basically directed in the same direction, so that the respective rotating fields 94, 96 reinforce a sum field. The potentials at the terminals U _A , V _A , W _{A of} the first coil system 86 and at the terminals U _B , V _B , W _{b of} the second Coil system 88 with U or zero denotes a high and a low potential and X as undefined or floating potential. The switching states are designated with one and for a closed switch with zero for an opened cut-off switch. Furthermore, the corresponding resulting voltage vector are given in polar form.

In FIGS. 11a and 16b, tables are shown which, for six different commutation steps, show switching states of the controllable switches 134 with the reference symbols from FIGS. 8 and 9 for a respective exemplary field weakening operation and are designated generally by 142 and 144, respectively. Table 142 shows switching states of the rotating fields 94, 96 for a field weakening operation or EMF weakening operation, wherein the second coil arrangement is reversed in the steps 2, 4 and 6 with respect to the normal state or normal operation and thus a weakening operation or an EMF weakening generated.

Table 144 shows further switching states for an alternative attenuation mode. In the commutation steps from Table 144, the second coil arrangement 80 is reversed in the steps 4, 5 and 6 compared to the normal operation, so that a corresponding field weakening operation is set. In this field weakening operation creates an asymmetric elliptical rotating field.

Claims

claims

Electric drive (70), in particular for an electric tool (10), having a rotor (74), a fixed stator (72) and a first coil arrangement (86) which is designed to rotate the rotor (74) by means of a first rotating field (94) and with a first motor control arrangement (90, 122), which is adapted to supply the first coil arrangement (86) for generating the first rotary field (94) with electric current, wherein the electric drive (70) has a second Coil assembly (88) for generating a second rotating field (96) fixedly associated with the first coil assembly (86) and at least partially magnetically coupled to the first coil assembly (86).

characterized in that

the second coil arrangement (88) can be controlled and energized separately from the first coil arrangement (86) in order to control the second coil arrangement (88) in any commutation sequence.

Electric drive according to claim 1, characterized in that the second coil arrangement (88) is energized such that the second rotating field (96) the first rotating field (94) is at least partially opposite or the first and the second rotating field (94, 96) at least are partially rectified.

Electric drive according to claim 1 or 2, characterized in that the first coil arrangement (86) has a first plurality of coil strands (Li, L ₂ , L ₃ ) and the second coil arrangement (88) has a second plurality of coil strands (L'i, L ' ₂ , L'3), wherein at least one of the coil strands (Li, L ₂ , L ₃ ) of the first coil arrangement (86) with a coil strand (L'i, L' ₂ , L ' ₃ ) of the second coil arrangement ( 88) is magnetically coupled.

4. Electric drive according to one of claims 1 to 3, characterized in that the first and the second coil arrangement (86, 88) have an identical plurality of coil strands (Li, L ₂ , L ₃ , ΙΛ, ΙΛ, L ' ₃ ) , which are each associated with each other and each magnetically coupled together.

5. Electric drive according to claim 3 or 4, characterized in that a plurality of coil strands (Li, L ₂ , L ₃ ) of the first coil arrangement (86) and a plurality of coil strands (Li ', L ₂ ', L ₃ ') the second coil assembly (88) are energized simultaneously.

6. Electric drive according to claim 5, characterized in that at least one coil strand (Li ', L ₂ ', L ₃ ') of the second coil assembly (88) can be energized, which is a non-energized coil strand (Li, L ₂ , L ₃ ) associated with the first coil arrangement (86).

7. Electric drive according to one of claims 1 to 6, characterized in that the first coil arrangement (86) with a first plurality of phases (U, V, W) can be energized and the second coil arrangement (88) with a second plurality of phases (U ', V, W) can be energized.

8. An electric drive according to claim 7, characterized in that the first and the second plurality of phases (U, V, W) and the second plurality of phases (U ', V, W) are identical.

9. Electric drive according to claim 7, characterized in that the first plurality of phases (U, V, W) is greater than the second plurality of phases (U ', V, W).

10. Electric drive according to one of claims 1 to 9, characterized in that the first and the second coil arrangement (86, 88) in each case three coil strands (Li, L ₂ , L ₃ , L'i, L ' ₂ , L' _3rd ), each in a star connection or a triangular circuit are connected together or are connected in a star-delta connection.

Electric drive according to one of claims 1 to 10, characterized in that the drive (70) is designed as an electronically commutated DC machine, wherein the first and the second coil arrangement (86, 88) are differently energized in a plurality of commutation.

Electric drive according to claim 11, characterized in that the second coil arrangement (88) can be energized in at least one of the commutation steps such that the second rotating field (96) is directed counter to the first rotating field (94).

Electric drive according to claim 11 or 12, characterized in that the second coil arrangement (88) can be energized in at least one of the commutation steps such that the second rotating field (96) is rectified with the first rotating field (94).

Electric drive according to one of claims 1 to 13, characterized in that the second coil arrangement (88) can be energized separately by a second motor control arrangement (92, 124) and supplied with electric current.

Electric drive according to one of claims 1 to 14, characterized in that the first and the second coil arrangement (86, 88) can be energized by the same current.

Electric drive according to one of Claims 1 to 15, characterized in that the first motor control arrangement (90, 122) and the second motor control arrangement (92, 124) are designed to control the motor (70). with a first speed-torque characteristic (104) and with a second speed-torque characteristic (108) having a different slope from the first speed-torque characteristic (104) to operate.

17. Electric drive according to claim 16, characterized in that the respective slopes of the speed-torque characteristics (104, 108) in dependence of the direction of the first and the second rotating field (94, 96) and / or the order of the individual Kommutierungsschritte adjustable are.

18. Power tool (10), characterized by a drive according to one of the preceding claims, which can be coupled with a tool spindle (23) for driving the tool (10).

19. A method for driving an electric drive (70), in particular for a power tool (10), wherein the electric drive (70) comprises a rotor (74) and a fixed stator (72), wherein a first coil arrangement (86) for generating a first rotary field (94) by a motor controller (90, 122) is supplied with electric current, wherein by means of a second coil assembly (88), the first coil assembly (86) fixedly assigned and at least partially magnetically coupled to the first coil assembly (86) is, a second rotating field (94) is generated, characterized in that the second coil assembly (88) separately from the first coil assembly (86) is driven and energized.