WO2013007679A2

WO2013007679A2 - Electrical machine for a steering drive

Info

Publication number: WO2013007679A2
Application number: PCT/EP2012/063376
Authority: WO
Inventors: Kurt Reutlinger
Original assignee: Robert Bosch Gmbh
Priority date: 2011-07-12
Filing date: 2012-07-09
Publication date: 2013-01-17
Also published as: DE102011078994A1; WO2013007679A3

Abstract

The invention relates to a rotary electrical machine (1), in particular a hybrid-energised direct current machine for a steering drive for use in an assisted steering system, comprising: a rotor (6) comprising a rotor winding with rotor coils (10); a commutator (9) for mechanically commutating the rotor coils (10) of the rotor winding; a stator (2) comprising one or more energiser systems (E1, E2) lying next to one another in an axial direction, each system providing an arrangement of stator poles (3, 4) in the circumferential direction, the stator poles of at least one of the energiser systems (E1, E2) having one or more permanent magnet poles (3) and one or more electrically energisable passive poles (4).

Description

description

Electric machine for a steering drive

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 harmonics in conventional electrical machines and the resulting harmonic torques, which lead to large fluctuations in torque, can by suitable design of the electrical Ma be reduced. 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, which has a low probability of failure and in which only small braking torques occur in the event of a fault.

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.

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-excited 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-excited DC machine is its braking torque occurring in the event of a fault. In the event of a terminal short circuit, the braking torque exceeds that of permanent magnet mechanically commutated DC machines very quickly limits 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 excitation 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.

In another aspect, a drive is provided. The drive comprises: - 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.

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: Figures 1 a to 1 c is a schematic cross-sectional view of a hybrid-excited DC machine and a representation of the polarity of the stator poles at different excitations; Figures 2a to 2c is a schematic cross-sectional view of a hybrid-excited DC machine according to another embodiment and a representation of the polarity of the stator poles at different excitations; Figure 3 is a schematic cross-sectional view of a hybrid-excited DC machine according to another embodiment;

Figure 4 is a schematic cross-sectional view in axial

Direction of a hybrid-excited DC machine with axially adjacent exciter systems;

Figures 5a to 5c is a schematic cross-sectional view in axial

Direction of another embodiment of a hybrid-excited DC machine and cross-sectional views along the section lines A-A and B-B;

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

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

8 shows a schematic representation of a drive system with a DC machine according to one of FIGS. 1 to 5 and with a drive circuit according to a further embodiment; and Figure 9 is a schematic representation of a drive system with a DC machine according to one of Figures 1 to 5 and with a drive circuit according to another embodiment.

Description of embodiments

Figure 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, which is provided with permanent magnet poles 3 and with electrically energizable passive poles 4. The permanent magnet poles 3 and the passive poles 4 are aligned in the direction of an inner recess 5 of the stator 2, in which a rotor 6 is rotatably arranged.

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

In the embodiment shown, the total number of stator poles is six, d. H. four permanent magnet poles 3 and two passive poles 4, which are arranged distributed uniformly around the circumference of the stator 2. 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 opposite each other and are each provided with an excitation coil 8 of an excitation winding, in addition to the magnetic flux caused by the permanent magnets 3 magnetic field in the

Stator 2 impress.

The excitation coils 8 of the exciter winding can be arranged on the passive poles 4 such that, when the excitation coils 8 are energized together, the passive poles 4 have different polarities inwardly with respect to the radial direction. As shown in Figure 1 b, depending on the direction of a in the exciter winding 8 impressed excitation current, the passive poles 4 are poled so that they have a different polarity to the circumferentially adjacent permanent magnet poles 3. Thus, the stator poles of the stator 2 may have alternating polarities in the circumferential direction. This condition is called positive arousal.

With a reduced excitation current through the excitation coils 8, the magnetic field in the electrically excited stator poles 4 becomes weaker. If, as shown in FIG. 1 c, the direction of the exciter current impressed into the excitation winding 8 is reversed, the passive poles 4 can be poled such that they have the same polarity as their permanent magnet poles 3 adjacent in the circumferential direction. 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 of the rotor winding as a wave winding, d. H. in the form of a series connection, are interconnected.

The embodiment of FIG. 2a shows a four-pole stator with a permanent magnet pole 3, a passive pole 4 which can be excited electrically via an excitation coil 8, and two follower poles 12. The rotor 6 substantially corresponds to the known design of the rotor 6 of the embodiment of FIG. However, the rotor winding is designed in FIG. 1 as a 6-pole rotor winding and in FIG. 2a as a 4-pole rotor winding. The electrically excited passive pole 4 lies opposite the permanent magnet pole 3. If, as shown in Figure 2c, the electrically energizable passive pole 4 excited so that with respect to a radial direction inwards a same polarity as that of the opposite permanent magnet pole 3 is reached, the follower poles 12 form a corresponding opposite polarity to the magnetic Close flow of the electrically excited stator 4 and the permanent magnet 3.

In general, according to the embodiment of FIG. 2 a, it is possible to arrange permanent magnet poles 3 and electrically energizable passive poles 4 opposite one another and to form further stator poles as non-excitable follower poles 12. In particular, it can be provided that to the electric energized Passivpol 4 and / or the Permanentmagnetpol 3 adjacent stator poles as a follower poles 12 form. Since the induced voltages in the rotor coils 10 may be different among the various stator poles 3, 4, 12, it is also useful in this embodiment, the rotor coils 10 of the rotor winding in series, ie as a wave winding to provide, so that in the individual rotor coils 10 induced voltages add.

The embodiment of Figure 2a also makes it possible to excite the electrically excited stator pole 4 inwardly opposite to the polarity of the permanent magnet pole 3 with respect to the radial direction, as shown in Figure 2c.

As a result, the follower poles 12 are not formed as magnetically active stator poles, since the magnetic inference of the permanent magnet pole 3 takes place via the electrically energizable passive pole 4 and vice versa. Effectively, the so energized stator 2 acts as a two-pole stator, since the follower poles 12 do not give off any appreciable magnetic field. (Fig. 2b)

In the embodiment illustrated in FIG. 3, the stator 2 has permanent magnet poles 3 and electrically energizable passive poles 4. The permanent magnet poles 3 have a poling opposite to the radial direction inwards. In a six-pole stator 2 of Fig. 3, an exciting coil 13 encloses three stator poles each: two electrically energized passive poles 4 and a permanent magnet pole 3 interposed therebetween.

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 8 can be kept low. FIG. 4 shows a hybrid-excited DC machine according to another embodiment

Embodiment shown in a cross section in the axial direction. In this embodiment, two excitation systems are arranged axially separated from each other. A first exciter system E1 has exclusively electrically excitable passive poles 4 or, in the case of a follower pole arrangement, alternating with follower poles 12 arranged therebetween, while a second exciter system E2 only Has permanent magnet poles 3 or at a follower pole in alternation with arranged thereon follower poles 12.

In FIGS. 5a to 5c, a DC machine 1 with two excitation systems E1, E2 can also be provided with a circumferential exciter coil 13 arranged concentrically around the machine axis. The circulating excitation coil 13 is located between the stator poles of the exciter systems E1, E2. In this case, each exciter system E1, E2 is formed both with electrically energizable passive poles 4 and with permanent magnet poles 3, 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, an electrically energizable passive pole 4 is then adjacent in the axial direction to a permanent magnet pole 3, as shown in the representation of Figure 5 in longitudinal section. Due to the concentric arrangement of the circulating exciter coil 13, a very short winding length is achieved, so that the ohmic resistance of the circulating exciter coil 13 and thereby the power requirement for the magnetic field excitation is reduced. In the case of positive excitation by the circulating excitation coil 13, the electrically excitable passive poles 4 of the exciter systems E1, E2 assume a respective opposite polarity to the permanent magnet poles 3 of the respective exciter system E1, E2. In the case of negative excitation, the passive poles 4 are provided with the same polarity as that of the permanent magnet poles 3 of the respective excitation system E1, E2, thereby attenuating the excitation or the usable magnetic field. The rotor coils 10 of the rotor 6 of the embodiments shown in Figures 5a to 5c 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 Permanentmagnetpol 3 one of the exciter systems and below an electrically excitable passive pole 4 of the corresponding other pathogen system. The induced voltage results from the sum of the two pole inductions. In this construction of the machine is thus also a Loop winding possible, in which different rotor coils 10 are connected in parallel. Due to the actual axial series connection of the voltage induced by the electrically energizable passive pole 4 and by the permanent magnet pole 3, these are identical in the various rotor coils 10.

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 circuitry for the excitation winding.

6 shows a possible steering drive with a hybrid-excited DC machine 1 and a drive circuit 20 is shown as a driver circuit. The

Drive circuit 20 for adjusting the rotor current, which is impressed via the commutator 9 in the DC machine 1, takes place in a known manner by an H-circuit. The H circuit comprises two series circuits of semiconductor switches 21 with freewheeling diode 24 connected in parallel to each semiconductor switch 21. The series circuits are supplied by the supply voltage potential and each have a node between the two semiconductor switches 21, each with a brush connection of the commutator 9 DC machine 1 is connected. By suitable control of the semiconductor switch 21, z. B. via a control unit 30, the current for operating the DC machine 1 can be adjusted. Frequently, the semiconductor switches 21 are driven so that there is a pulse width modulated voltage to the brushes of the commutator 9 of the DC machine 1. The excitation winding 8 is controlled by a simple further semiconductor switch 22 here. For this purpose, the exciter winding 8 is connected in series with the further semiconductor switch 22 to supply voltage lines. The energization of the field winding 8 can also be done via a pulse width modulated control of the further semiconductor switch 22. Parallel to the exciter winding 8, a freewheeling diode 23 is further provided, which is provided in the reverse direction in normal operation and serves, when shutdown ten of the power supply to the excitation winding 8 occurring freewheeling currents to lead.

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

Are required for driving the excitation winding 8 different current directions, it is, as shown in Figure 7, necessary to control the exciter winding 8 also with an H-bridge circuit, which allows pulse width modulated driving of the corresponding semiconductor switch 21 of the H bridge circuit, To impress excitation currents in the positive and negative direction in the excitation winding 8.

However, such a drive circuit 20 is complicated and it may alternatively be provided, the excitation winding 8 with the commutator 9, d. H. the rotor coils 10, to connect in series, as shown in the embodiment of Figure 8. In this case, the motor current and the excitation current through the excitation winding 8 are each varied simultaneously. Thus, the excitation current always adapts automatically to the required torque. However, only one direction of rotation of the DC machine 1 can be achieved in such a circuit, since a change in the current direction reverses both the motor current and the excitation current. Thus, in the DC machine 1 of Figure 9 no negative moment.

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

Claims

claims

1 . Rotary electrical 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);

- A commutator (9) for mechanically commutating the rotor coils (10) of the rotor winding;

a stator (2) having an exciter system or a plurality of exciter systems (E1, E2) which are adjacent in the axial direction and each provide an arrangement of stator poles (3, 4) in the circumferential direction,

wherein the stator poles of at least one of the excitation systems (E1, E2) have one or more permanent magnet poles (3) and one or more electrically excitable passive poles (4).

2. Electrical machine (1) according to claim 1, wherein for each excitation system (E1, E2) each two of the permanent magnet poles (3) are provided opposite each other and with respect to a direction to the rotor (6) mutually opposite polarity and wherein each two passive poles ( 4) are arranged opposite one another.

3. Electrical machine (1) according to claim 1 or 2, wherein for each excitation system (E1, E2) at least one of the permanent magnet poles (3) and one of the passive poles (4) are arranged opposite to each other.

4. Electrical machine (1) according to one of claims 1 to 3, wherein for at least one of the excitation systems (E1, E2), the passive poles (4) are each provided with an excitation coil (8) to energize them electrically.

5. Electrical 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), the at least one passive pole (4), enclosed by an excitation coil (8) are to electrically excite them.

6. Electrical machine (1) according to one of claims 1 to 5, wherein between two of the exciter systems (E1, E2) is provided a perpendicular to an axial direction of the rotor (6) arranged circumferential exciter coil (13) which between the stator poles (3 , 4) of the two excitation systems (E1, E2) runs.

7. Electrical machine (1) according to one of claims 1 to 6, wherein one or more follower poles (12) are provided in one or more of the excitation systems (E1, E2), which are not electrically excitable.

8. Electrical machine (1) according to claim 7, wherein at least one of the following poles (12) is arranged directly between a permanent magnet pole (3) and a passive pole (4).

9. Electrical machine (1) according to one of claims 1 to 8, wherein the rotor

(6) extends substantially over the axial length of the exciter systems (E1, E2), so that the rotor coils (10) extend over a plurality of exciter systems (E1, E2).

10. Electrical machine (1) according to one of claims 1 to 9, wherein the rotor coils (10) of the rotor winding are connected in series.

1 1. Drive comprising:

- An electrical machine (1) according to one of the preceding claims; a driver circuit (20) for providing a rotor current to

Energizing the rotor winding;

- A field circuit for energizing a field winding (8) for electrically energizing 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.

12. Drive comprising:

- An electrical machine (1) according to one of the preceding claims, wherein an exciter winding (8) and a connected via the commutator rotor winding are connected in series;

- A driver circuit for providing a current for energizing the series circuit of the excitation winding (8) and the rotor winding; - A control unit (30) for driving the driver circuit (20) to provide a desired current through the excitation winding (8) and the rotor winding.

A drive according to claim 12, wherein a rectifier circuit (25) is provided to rectify either the current through the rotor coils (10) of the rotor winding or the current through the excitation winding (8).