DE102011078994A1 - Electric machine for a steering drive - Google Patents

Abstract

The invention relates to a rotary electric machine (1), in particular a hybrid-excited DC machine, for a steering drive for use in steering assistance, comprising: a rotor (6) having a rotor winding with rotor coils (10); Figs; a commutator (9) for mechanically commutating the rotor coils (10) of the rotor winding; Figs; a stator (2) having one or more exciter systems (E1, E2) which are adjacent in the axial direction, each providing an arrangement of stator poles (3, 4) in the circumferential direction, wherein the stator poles of at least one of the exciter systems (E1, E2) comprise one or more Permanent magnetic poles (3) and one or more electrically excitable passive poles (4).

Description

Technical area

The present invention relates to electric machines, in particular to hybrid-excited DC machines for use in steering drives for electrically assisted steering systems. In particular, the present invention relates to the construction of a hybrid-excited DC machine for steering assistance.

State of the art

In electrically assisted steering, an electric motor engages the steering to amplify the steering effort exerted by the driver. For this purpose, it is customary to couple the steering drive rigidly with the steering wheel via a transmission. However, such an arrangement has the disadvantage that torque fluctuations of the steering drive on the steering wheel are noticeable, whereby the ride comfort can be affected.

Furthermore, in the event of a fault in which the steering drive fails, the driver must still be able to steer the vehicle, even without the steering drive assisting the steering.

For these reasons, very high demands are made on electric steering drives for steering systems in motor vehicles with respect to the permissible torque fluctuations of the drive torque generated on the handlebar. The resulting in conventional electric machines harmonics and the resulting harmonic torques that lead to large fluctuations in torque can be reduced by appropriate design of the electric machine. In particular, the design is provided so that the harmonics are as low as possible or the effects on the torque curve are reduced.

Another essential requirement of steering drives is the control of faults and errors in the electrical machine of the steering drive. In contrast to electrically excited machines, it is not possible to switch off the magnetic field in permanent magnet-excited electrical machines. This can lead to significant braking torque in the event of a fault, such as short circuits in the winding. If the braking torques exceed certain limits in the event of a fault, this is the same as blocking the steering.

It is therefore an object of the present invention to provide an electric machine for a steering drive available, which has a low probability of failure and occur in the event of an error only small braking torques.

Disclosure of the invention

This object is achieved by the electric machine for use in a steering system according to claim 1 and by the drive according to the independent claim.

Further advantageous embodiments of the present invention are specified in the dependent claims.

• – einen Rotor mit einer Rotorwicklung mit Rotorspulen;
• – einen Kommutator zum mechanischen Kommutieren der Rotorspulen der Rotorwicklung;
• – einen Stator mit einem oder mehreren in axialer Richtung benachbarten Erregersystemen, die jeweils eine Anordnung von Statorpolen in Umfangsrichtung vorsehen,

wobei die Statorpole mindestens eines der Erregersysteme einen oder mehrere Permanentmagnetpole und einen oder mehrere elektrisch erregbare Passivpole aufweisen. According to a first aspect, a rotary electric machine, in particular a hybrid-excited DC machine, is provided for a steering drive for use in a steering assistance. The electric machine includes:

• A rotor having a rotor winding with rotor coils;
• A commutator for mechanically commutating the rotor coils of the rotor winding;
• A stator with one or more exciter systems adjacent in the axial direction, each of which provides an arrangement of stator poles in the circumferential direction,

wherein the stator poles of at least one of the excitation systems have one or more permanent magnet poles and one or more electrically excitable passive poles.

One idea of the above electrical machine is to combine the advantages of a mechanically commutated DC machine with a possibility of field weakening of the stator magnetic field normally not changeable in a DC machine. In particular, in the case of the DC machine, the outlay for the control can be significantly reduced in comparison with electronically commutated electrical machines. Furthermore, the above electrical machine requires no position sensor or position detection for electronic commutation, since this function is taken over by the mechanical commutator.

Also, the control is easier, since in mechanically commutated electrical machines for adjusting the torque or the power only a so-called H-bridge is required, which can be realized with four semiconductor switches. In contrast, an electronically commutated three-phase electric machine would already require six semiconductor switches.

Furthermore, there are advantages through the elimination of permanent magnets in the stator. A permanent magnet DC machine has a speed curve over the torque, which corresponds to the characteristic of a shunt machine. The curve corresponds to a straight line and intersects the two axes on the one hand at the idle speed and the other at the short-circuit torque. For steering drives, a characteristic curve with a pronounced field weakening range would be desirable, but this would not be possible with permanent magnet-excited direct current machines, since the commutation is determined there by the fixed arrangement of the commutator and the permanent magnets. The above electric machine offers a possibility of varying the exciting magnetic field by providing electrically energizable passive poles, so that the machine is operable in a field weakening operation.

Another disadvantage of a permanent magnet DC machine is their occurring in case of failure braking torque. In a terminal short circuit, the braking torque of permanent magnet excited mechanically commutated DC machines very quickly exceeds the limits for the maximum allowable braking torque, since the braking torque is proportional to the speed of the DC machine. The above electric machine reduces the braking torque in case of failure, since only a part of the stator poles is provided with permanent magnets.

In addition, for at least one of the one or more excitation systems, two of the permanent magnet poles may be provided opposite one another and with opposite polarity relative to one another with respect to a direction to the rotor, wherein two passive poles are arranged opposite one another.

According to one embodiment, at least one of the permanent magnet poles and one of the passive poles can be arranged opposite one another in at least one of the exciter systems.

It can be provided that at least in one of the excitation systems, the passive poles are each provided with an exciter coil in order to excite them electrically.

In at least one of the exciter systems, a plurality of stator poles containing at least one passive pole may be enclosed by an exciter coil to electrically excite them.

Between two of the exciter systems, an excitation coil arranged perpendicular to an axial direction of the rotor can be provided which extends between the stator poles of the two exciter systems.

It may further be provided that one or more follower poles are provided in the one or more excitation systems, which are not electrically excitable.

At least one of the following poles can be arranged directly between a permanent magnet pole and a passive pole.

According to a further embodiment, the rotor may extend substantially over the axial length of a plurality of the excitation systems, so that the rotor coils extend over a plurality of exciting systems.

Furthermore, the rotor coils of the rotor winding can be connected in series. This has the advantage that it can compensate for the different voltages induced at the different stator poles.

• – die obige elektrische Maschine;
• – eine Treiberschaltung zum Bereitstellen eines Rotorstroms zum Bestromen der Rotorwicklung;
• – eine Erregerschaltung zum Bestromen einer Erregerwicklung zum elektrischen Erregen der Passivpole;
• – eine Steuereinheit zum Ansteuern der Treiberschaltung, um einen gewünschten Rotorstrom bereitzustellen, und der Erregerschaltung, um einen gewünschten Erregerstrom bereitzustellen.

In another aspect, a drive is provided. The drive includes:

• - the above electric machine;
• A driver circuit for providing a rotor current for energizing the rotor winding;
• - An excitation circuit for energizing a field winding for electrically energizing the passive poles;
• A control unit for driving the driver circuit to provide a desired rotor current and the energizing circuit for providing a desired exciting current.

• – die obige elektrische Maschine, wobei eine Erregerwicklung und eine über den Kommutator angeschlossene Rotorwicklung in Reihe geschaltet sind;
• – eine Treiberschaltung zum Bereitstellen eines Stroms zum Bestromen der Reihenschaltung der Erregerwicklung und der Rotorwicklung;
• – eine Steuereinheit zum Ansteuern der Treiberschaltung, um einen gewünschten Strom durch die Erregerwicklung und die Rotorwicklung bereitzustellen.

According to a further aspect, a drive is provided, comprising:

• - The above electrical machine, wherein a field winding and connected via the commutator rotor winding are connected in series;
• - A driver circuit for providing a current for energizing the series connection of the field winding and the rotor winding;
• A control unit for driving the driver circuit to provide a desired current through the field winding and the rotor winding.

Furthermore, a rectifier circuit may be provided to rectify either the current through the rotor winding or the current through the field winding.

Brief description of the drawings

Preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. Show it:

1a to 1c a schematic cross-sectional view of a hybrid excited DC machine and a representation of the polarity of the stator poles at different excitations;

2a to 2c a schematic cross-sectional view of a hybrid-excited DC machine according to another embodiment and an illustration of the polarity of the stator poles at different excitations;

3 a schematic cross-sectional view of a hybrid-excited DC machine according to another embodiment;

4 a schematic cross-sectional view in the axial direction of a hybrid-excited DC machine with axially adjacent exciter systems;

5a to 5c a schematic cross-sectional view in the axial direction of another embodiment of a hybrid-excited DC machine and cross-sectional views along the section lines AA and BB;

6 a schematic representation of a drive system with a DC machine according to one of 1 to 5 according to a further embodiment;

7 a schematic representation of a drive system with a DC machine according to one of 1 to 5 with a drive circuit according to another embodiment;

8th a schematic representation of a drive system with a DC machine according to one of 1 to 5 and with a drive circuit according to another embodiment; and

9 a schematic representation of a drive system with a DC machine according to one of 1 to 5 and with a drive circuit according to another embodiment.

Description of embodiments

1 shows a schematic cross-sectional view of a hybrid-excited DC machine 1 as an electric machine for a steering drive. The DC machine 1 has a circular stator 2 on, with permanent magnet poles 3 and with electrically excitable passive poles 4 is provided. The permanent magnet poles 3 and the passive poles 4 are in the direction of an interior recess 5 of the stator 2 aligned, in which a rotor 6 is arranged rotatably.

The illustrated rotor 6 has, for example, 16 rotor slots, which are provided with a corresponding rotor winding with rotor coils 10 are provided. The rotor 6 but may also have other numbers. The rotor coils 10 the rotor winding of the rotor 6 be via a mechanical commutator 9 that is axial (perpendicular to the plane of drawing) to the rotor 6 offset on a rotor shaft 7 is arranged, depending on a position of the rotor 6 energized.

In the exemplary embodiment shown, the total number of stator poles is six, ie four permanent magnet poles 3 and two passive poles 4 around the circumference of the stator 2 are arranged evenly distributed. The permanent magnet poles 3 face each other with different magnetic polarities of the permanent magnets (with respect to the radial direction inwards). The passive poles 4 of the stator 2 are also facing each other and each with an excitation coil 8th a field winding provided in addition to that of the permanent magnets 3 Magnetic flux caused a magnetic field in the stator 2 memorize.

The excitation coils 8th the excitation winding can do so at the passive poles 4 be arranged that when energized together the excitation coils 8th the passive poles 4 have different polarities inward with respect to the radial direction. As in 1b can be shown depending on the direction of one in the exciter winding 8th impressed excitation current the passive poles 4 be poled so that they one to the circumferentially adjacent permanent magnet poles 3 have different polarity. So can the stator poles of the stator 2 have circumferentially changing polarities. This condition is called positive arousal.

At a reduced excitation current through the excitation coils 8th the magnetic field in the electrically excited stator poles 4 weaker. Will, as in 1c shown, the direction of the in the exciter winding 8th reversed excitation current vice versa, the passive poles 4 be poled so that they have the same polarity as their circumferentially adjacent permanent magnet poles 3 exhibit. This condition is called negative arousal.

The induced voltage in the rotor winding is thus different among the different stator poles. To ensure proper operation of this machine, it is therefore useful to form the rotor winding in the form of a wave winding, wherein the rotor coils 10 the rotor winding as a wave winding, ie in the form of a series circuit, are interconnected.

The embodiment of the 2a shows a four-pole stator with a permanent magnet pole 3 , one electrically via an exciter coil 8th excitable passive pole 4 and two consecutive poles 12 , The rotor 6 corresponds essentially to the known structure of the rotor 6 the embodiment of the 1a , The rotor winding is however in 1 as a 6-pole rotor winding and in 2a designed as a 4-pole rotor winding. The electrically excited passive pole 4 lies the permanent magnet pole 3 across from. Will, as in 2c shown, the electrically energizable passive pole 4 so excited that with respect to a radial direction inward, a same polarity as that of the opposite permanent magnet pole 3 is reached, so form the follower poles 12 a corresponding opposite polarity to the magnetic flux of the electrically excited stator pole 4 and the permanent magnet pole 3 close.

Generally, according to the embodiment of the 2a be provided, permanent magnet poles 3 and electrically energizable passive poles 4 to arrange each other opposite and more stator poles as non-excitable follower poles 12 train. In particular, it may be provided that to the electrically excited passive pole 4 and / or the permanent magnet pole 3 adjacent stator poles as follower poles 12 train. Since the induced voltages in the rotor coils 10 under the different stator poles 3 . 4 . 12 may be different, it is also useful in this embodiment, the rotor coils 10 the rotor winding in series, ie as a wave winding to provide, so that in the individual rotor coils 10 add induced voltages.

The embodiment of the 2a also allows the electrically excited stator pole 4 with respect to the radial direction inwardly opposite to the polarity of the permanent magnet pole 3 to excite, as it is in 2c is shown. This causes the follower poles 12 are not formed as magnetically effective stator poles, since the magnetic return of the permanent magnet pole 3 over the electrically excitable passive pole 4 done and vice versa. Effectively the so energized stator acts 2 as a two-pole stator, since the follower poles 12 do not give off any appreciable magnetic field. ( 2 B )

In the embodiment which is in 3 is shown, the stator 2 Permanent magnet poles 3 and electrically energizable passive poles 4 on. The permanent magnet poles 3 have a polarity inwardly opposite to the radial direction. The excitation coils 8th are configured to enclose a plurality of stator poles, including a permanent magnet pole 3 , In a six-pole stator 2 of the 3 encloses an excitation coil 13 three stator poles each: two electrically activatable passive poles 4 and a permanent magnet pole disposed therebetween 3 ,

The arrangement with several stator poles enclosing excitation coils 13 has an advantage in higher-pole arrangements, since in this case the number of excitation coils 8th can be kept low.

In 4 a hybrid-excited DC machine according to another embodiment is shown in a cross section in the axial direction. In this embodiment, two excitation systems are arranged axially separated from each other. A first excitation system E1 has exclusively electrically excitable passive poles 4 or in a follower pole arrangement in alternation with consecutive poles arranged therebetween 12 while a second excitation system E2 only permanent magnet poles 3 or in a follower pole arrangement in alternation with consecutive poles arranged therebetween 12 having.

In the 5a to 5c can a DC machine 1 with two excitation systems E1, E2 also with a concentric around the machine axis arranged rotating exciter coil 13 be provided. The revolving exciter coil 13 lies between the stator poles of the exciter systems E1, E2. In this case, each excitation system E1, E2 with both electrically energizable passive poles 4 as well as with permanent magnet poles 3 formed, which are arranged alternately in the circumferential direction. By virtue of this arrangement, in contrast to the preceding examples, it is possible to obtain a machine with a pronounced axial field component. Machines with such an axial field component, or a so-called homopolar field, are therefore also referred to as homopolar machines.

According to the illustrated embodiment is then in the axial direction to a permanent magnet pole 3 an electrically excitable passive pole 4 adjacent, as in the presentation 5 is shown in longitudinal section. Due to the concentric arrangement of the rotating exciter coil 13 a very small winding length is achieved, so that the ohmic resistance of the rotating exciter coil 13 and thereby the power requirement for the magnetic field excitation is reduced. With positive excitation by the rotating excitation coil 13 take the electrically excitable passive poles 4 the excitation systems E1, E2 a respective opposite polarity to the permanent magnet poles 3 of the respective exciter system E1, E2. Negative excitement becomes the passive poles 4 with the same polarity as the permanent magnet poles 3 of the respective excitation system E1, E2 provided and thereby the excitation, or the usable magnetic field, attenuated.

The rotor coils 10 of the rotor 6 in the 5a to 5c Embodiments shown extend substantially over the entire axial length of both excitation systems E1, E2 and thus each rotor coil is at a given time both under a permanent magnet pole 3 one of the exciter systems and under an electrically excitable passive pole 4 the corresponding other pathogen system. The induced voltage results from the sum of the two pole inductions. In this structure of the machine, a loop winding is thus possible, in the various rotor coils 10 be switched in parallel. Due to the factual axial series connection of the electrically excitable passive pole 4 and through the permanent magnet pole 3 induced voltage are these in the various rotor coils 10 identical.

In the hybrid-excited DC machines described above, the corresponding excitation coil must be supplied with electrical energy to achieve the electrical excitation. While current regulation for the rotor current flowing via the mechanical commutator is sufficient in a permanent-magnet-excited DC machine for torque control, it is necessary in the case of a hybrid-excited DC machine to provide additional wiring of the field winding.

In 6 is a possible steering drive with a hybrid-excited DC machine 1 and a drive circuit 20 shown as a driver circuit. The drive circuit 20 for adjusting the rotor current passing through the commutator 9 in the DC machine 1 is impressed, takes place in a known manner by an H-circuit. The H circuit comprises two series circuits of semiconductor switches 21 with to each semiconductor switch 21 parallel freewheeling diode 24 , The series circuits are supplied by the supply voltage potential and each have a node between the two semiconductor switches 21 on, each with a brush connection of the commutator 9 the DC machine 1 connected is.

By suitable control of the semiconductor switch 21 , z. B. via a control unit 30 , the power can be used to operate the DC machine 1 be set. Often the semiconductor switches 21 so controlled that a pulse width modulated voltage at the brushes of the commutator 9 the DC machine 1 results. The excitation winding 8th This is about a simple further semiconductor switch 22 driven. This is the excitation winding 8th in series with the other semiconductor switch 22 connected to supply voltage lines. The energization of the exciter winding 8th can also have a pulse width modulated control of the further semiconductor switch 22 respectively. Parallel to the excitation winding 8th is still a freewheeling diode 23 provided, which is provided in the reverse direction in normal operation and serves to turn off the power supply to the field winding 8th to lead occurring freewheeling currents.

Instead of a pulse width modulated control, the voltage can also be clocked in accordance with a tolerance band control.

Are for driving the exciter winding 8th different current directions required, so it is, as in 7 shown, necessary, the exciter winding 8th also to drive with an H-bridge circuit, it by pulse width modulated control of the corresponding semiconductor switches 21 the H-bridge circuit allows exciting currents in the positive and negative direction in the field winding 8th memorize.

Such a drive circuit 20 However, it is expensive and it may alternatively be provided, the exciter winding 8th with the commutator 9 ie the rotor coils 10 to connect in series, as in the embodiment of the 8th is shown. In this case, the motor current and the excitation current through the exciter winding 8th varies simultaneously. Thus, the excitation current always adapts automatically to the required torque. However, in such a circuit, only one direction of rotation of the DC machine 1 be achieved, since a change in the direction of current reverses both the motor current and the excitation current. Thus, turns on the DC machine 1 of the 9 no negative moment.

To avoid this disadvantage, as in 9 is shown, either via the commutator 9 connected rotor coils 10 or the excitation winding 8th via a rectifier 25 be connected to each other, so that either the energization of the rotor coils 10 or the energization of the exciter winding 8th regardless of the applied current is always rectified. For different current directions reversing the direction of rotation can be achieved by reversing the motor current.

Claims (13)

Rotary electric machine ( 1 ), in particular a hybrid DC machine, for a steering drive for use in a steering assistance, comprising: - a rotor ( 6 ) with a rotor winding with rotor coils ( 10 ); A commutator ( 9 ) for mechanical commutation of the rotor coils ( 10 ) the rotor winding; A stator ( 2 ) with an exciter system or a plurality of exciter systems (E1, E2) which are adjacent in the axial direction and which each have an arrangement of stator poles ( 3 . 4 ) in the circumferential direction, the stator poles of at least one of the exciter systems (E1, E2) having one or more permanent magnet poles ( 3 ) and one or more electrically excitable passive poles ( 4 ) exhibit. Electric machine ( 1 ) according to claim 1, wherein for each exciter system (E1, E2) in each case two of the permanent magnet poles ( 3 ) are opposite each other and with respect to a direction to the rotor ( 6 ) of opposite polarity are provided and wherein in each case two passive poles ( 4 ) are arranged opposite one another. Electric machine ( 1 ) according to claim 1 or 2, wherein for each exciter system (E1, E2) at least one of the permanent magnet poles ( 3 ) and one of the passive poles ( 4 ) are arranged opposite one another. Electric machine ( 1 ) according to one of claims 1 to 3, wherein for at least one of the exciter systems (E1, E2) the passive poles ( 4 ) each with an excitation coil ( 8th ) are provided to electrically energize them. Electric machine ( 1 ) according to one of claims 1 to 4, wherein for at least one of the excitation systems (E1, E2) a plurality of stator poles ( 3 . 4 ), which has at least one passive pole ( 4 ), by an exciting coil ( 8th ) are enclosed to electrically energize them. Electric machine ( 1 ) according to one of claims 1 to 5, wherein between two of the excitation systems (E1, E2) one perpendicular to an axial direction of the rotor ( 6 ) arranged circumferential exciter coil ( 13 ) provided between the stator poles ( 3 . 4 ) of the two exciter systems (E1, E2). Electric machine ( 1 ) according to one of claims 1 to 6, wherein in one or more of the exciter systems (E1, E2) one or more secondary poles ( 12 ) are provided, which are not electrically excitable. Electric machine ( 1 ) according to claim 7, wherein at least one of the following poles ( 12 ) directly between a permanent magnet pole ( 3 ) and a passive pole ( 4 ) is arranged. Electric machine ( 1 ) according to one of claims 1 to 8, wherein the rotor ( 6 ) extends substantially over the axial length of the excitation systems (E1, E2), so that the rotor coils ( 10 ) over several exciter systems (E1, E2). Electric machine ( 1 ) according to one of claims 1 to 9, wherein the rotor coils ( 10 ) of the rotor winding are connected in series. Drive comprising: - an electric machine ( 1 ) according to any one of the preceding claims; A driver circuit ( 20 ) for providing a rotor current for energizing the rotor winding; - A field circuit for energizing a field winding ( 8th ) for the electrical excitation of the passive poles ( 4 ); A control unit ( 30 ) for driving the driver circuit ( 20 ) to provide a desired rotor current and the excitation circuit to provide a desired excitation current. Drive comprising: - an electric machine ( 1 ) according to one of the preceding claims, wherein a field winding ( 8th ) and a connected via the commutator rotor winding are connected in series; A driver circuit for supplying a current for energizing the series connection of the exciter winding ( 8th ) and the rotor winding; A control unit ( 30 ) for driving the driver circuit ( 20 ) to obtain a desired current through the exciter winding ( 8th ) and to provide the rotor winding. Drive according to claim 12, wherein a rectifier circuit ( 25 ) is provided to either the current through the rotor coils ( 10 ) of the rotor winding or the current through the excitation winding ( 8th ) to rectify.

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