DE102010043970A1 - Electric machine for a steering drive - Google Patents

Abstract

The invention relates to an electrical machine (1), in particular for use in a steering system of a motor vehicle, comprising: a first sub-machine with a first sub-rotor (61) arranged on a shaft and facing a first sub-stator (31) in the radial direction of the shaft is arranged lying down; - A second partial machine with a second partial rotor (62) which is arranged on the shaft and which is arranged opposite a second partial stator (32) in the radial direction of the shaft; - An excitation winding (10, 14) wound around the axis of rotation of the shaft, which is used to generate a magnetic field in a rotor formed by the partial rotors (61, 62), the excitation winding (10, 14) being arranged between the sub-machines.

Description

Technical area

The present invention relates to electrical machines for use in steering drives, in particular electrical machines, which are designed as hybrid-excited homopolar machines.

State of the art

Modern motor vehicles have a power steering, which is usually designed in the form of an electric motor coupled to the steering linkage. In such electrically assisted steering the moment exerted by the driver on the handlebar is amplified by an electric motor. It is customary to couple the electric motor via a gearbox rigid with the steering linkage.

In operation, so-called harmonic torques occur in electric machines due to harmonics, which can lead to strong fluctuations in the torque dependent on the rotor position. These fluctuations can therefore be felt on the steering wheel for the driver. Such torque fluctuations of the electric motor occur due to the design. The electromagnetic design of the electric machines for steering assistance must therefore be designed so that these harmonics are avoided or at least reduced in their effect on the torque curve.

In the event of a failure of the electric motor due to a fault in the electric motor, the driver must still be able to steer the vehicle, even if the assistance of the electric motor fails completely. In particular, it is necessary that in case of failure of the electric motor, no major torque fluctuations of the force caused by the electric motor resistance torque (cogging torques and braking torques) occur on the steering linkage. This results in particularly high demands on the coupling of the electric motor with the steering linkage and to the electric motor itself.

Electronically commutated rare earth magnet synchronous machines, preferably of neodymium-iron-boron alloys, have become established for these applications because of their power density, efficiency and control capability. However, these machines not only cause torque fluctuations during operation when the stator winding is energized, but also cogging torques occur when the stator winding is de-energized.

Although it is possible to produce a sinusoidal air gap field in the electric machines by a winding scheme or a design of Polschuhkontur, whereby the cogging moments are reduced in the energized case and torque fluctuations in the energized case, but this is in electric motors with small dimensions due to space and the production costs only possible with increased effort. Therefore, one has to reckon with small diameter electrical machines with corresponding harmonics in the air gap and take the torque fluctuations in purchasing. It is therefore trying to make the electrical machinery for the steering drives so that the harmonics remain as possible without effect on the transmitted torque in the steering.

Another essential requirement is to control disturbances that occur in the electric machine so that no significant braking torques occur in the steering linkage. In order to keep the braking torques of the electric machine and thus also on the steering wheel low in the event of a fault, especially in the event of short circuits or breaking down of switches, so-called star point separations are provided today. By means of a star point relay, which can be designed mechanically or electronically, the neutral point of the machine can be separated in the event of an error. This is for example from the publication WO 03/099 632 A1 known. This can eliminate errors in the electronics, such as short circuits between the phases. If, however, a short circuit occurs within such a phase in such electrical machines, star point separation is generally unsuitable.

A simpler solution for separating the machine from the converter electronics is to use phase separators that interrupt the connection between the inverter and the electrical machine in the event of a fault. However, this only allows for errors in the converter electronics. Short circuits in the electrical machine itself can not be remedied or influenced hereby. Therefore, such systems are required to be intrinsically safe.

For an intrinsically safe motor approaches are mostly pursued that use a topology with a stator winding without overlapping the individual coils, so a structure in which the stator windings do not cross. This applies, for example, to a 3/2 topology in which a pole pair in the rotor faces three stator slots. Typical versions of such electrical machines are the 9/6 or the 12/8 versions (9 or 12 stator teeth to 6 or 8 rotor poles). However, these topologies have the disadvantage that they have very pronounced torque fluctuations or cogging moments in the de-energized state. To reduce this, expensive additional measures have to be taken, which reduces the power density of the Motors is reduced and expensive to manufacture. In particular, in the topology of twelve stator teeth and eight rotor poles, it has not been possible to achieve a drive with sufficient torque quality, ie with low cogging torques and harmonics in normal undisturbed operation.

Even if deviating rotor topologies, such as a 18/8 topology with 18 stator slots or stator teeth and eight rotor poles, very small torque fluctuations can be achieved, but these have the disadvantage that the machine has a distributed winding. In this case, the coils of different phases intersect in the bead head, and partially coil sides of different phases are also located in the slots. This increases the risk of the occurrence of short circuits between different phases, which can lead to unacceptably high braking torques. Again, this is to be avoided in safety-critical steering drives in any case. Therefore, the 18/8 topology is only suitable in combination with a star point separation, which leads to a significantly increased production cost.

Furthermore, topologies with twelve stator teeth and ten rotor poles, for example, from US 6,597,078 B2 and US 7,034,423 B2 , known. Their torque quality, which has deteriorated compared to the 18/8 topology, can be compensated by an air gap widening, for example by means of a sine pole. However, even in such a machine two coil sides are located together in a groove, so that the risk of short circuits between adjacent stator coils persists.

Another way to reduce the cogging torque is to provide a skew either in the stator or in the rotor. In the case of a skew, the course of the rotor pole deviates from the axis-parallel direction in the direction of movement of the relative movement between the stator and the rotor. Since a true skew is difficult to implement, usually graduations of the rotor or the stator are provided, such as from the US 6,252,323 B1 . DE 100 16 002 A1 . EP 0 569 594 B1 . DE 103 48 410 A1 and EP 1 447 901 A1 known.

In contrast to electrically excited machines, it is not possible to switch off the magnetic field in electrical machines whose excitation field is generated by permanent magnets. In the event of a fault, such as in the event of short circuits in the winding, this can lead to considerable braking torques which are not permissible when used for steering drives. If the braking torque exceeds a certain amount in the event of a fault, then this is the same as blocking the steering. Therefore, it is necessary for steering drives to use electrical machines that have a low probability of failure and cause only minor braking torques in case of failure.

As electric machines that exert no cogging torque when de-energized, Homopolarmaschinen are known. However, these electric machines provide only a low power density and thus only a small torque for the use of a steering assistance available. Therefore, the combination of a homopolar machine with additional permanent magnets in the rotor is already known from the prior art. This is from the publication DE 69 406 706 A1 a homopolar machine with additional mounted on the rotor surface permanent magnet known. The excitation winding of Homopolarmaschine lies above the stator winding between the two stator yokes.

In the publication EP 07 29 217 is described a Homopolarmaschine with buried in the rotor magnets with flow barriers. The excitation winding is located on the rotor and is energized via slip rings.

The publication DE 216 51 52 discloses a synchronous machine having a rotor with surface magnets and with buried magnets. The excitation winding is located above the stator winding between the two stator yokes.

From the pamphlets US 550 43 82 A1 and WO 1 999 009 638 A1 Homopolar machines with permanent magnets arranged on the rotor or with an excitation winding arranged above the stator winding are known in each case.

It is an object of the present invention to provide a steering drive for the steering of a motor vehicle, which has a sufficiently high power density, which exerts only a small braking torque in the event of a fault and which can be constructed with little effort.

Disclosure of the invention

This object is achieved by the electric machine according to claim 1 and by the steering system according to the independent claim.

Further advantageous embodiments are specified in the dependent claims.

• – eine erste Teilmaschine mit einem an einer Welle angeordneten ersten Teilrotor, der in radialer Richtung der Welle einem ersten Teilstator gegenüber liegend angeordnet ist;
• – eine zweite Teilmaschine mit einem an der Welle angeordneten zweiten Teilrotor, der in radialer Richtung der Welle einem zweiten Teilstator gegenüber liegend angeordnet ist;
• – eine um die Drehachse der Welle gewickelte Erregerwicklung, die dazu dient, ein Magnetfeld in einem durch die Teilrotoren gebildeten Rotor zu erzeugen,

dadurch gekennzeichnet, dass
die Erregerwicklung zwischen den Teilmaschinen angeordnet ist.According to a first aspect is an electrical machine, in particular for use in a Steering system of a motor vehicle, provided. The electric machine includes:

• - A first sub-machine with a shaft disposed on a first part rotor, which is arranged in the radial direction of the shaft to a first part stator opposite;
• - A second sub-machine with a shaft arranged on the second part of the rotor, which is arranged in the radial direction of the shaft to a second part of stator opposite;
• A field winding wound about the axis of rotation of the shaft and serving to generate a magnetic field in a rotor formed by the sub-rotors,

characterized in that
the excitation winding is arranged between the sub-machines.

An idea of the above electric machine for steering drives is that this is designed as a hybrid homopolar engine and has a low torque ripple and low cogging torque and is thus suitable for use in steering drives. Furthermore, the above hybrid excited homopolar engine has the advantage that the exciting coil is disposed inside the electric machine, whereby the electric machine can be formed with a reduced diameter. As a result, the winding length of the excitation coil is reduced, whereby the power requirement for generating the exciting magnetic field is reduced. Furthermore, the geometry of the electric machine can be reduced by the excitation coil arranged in the interior, so that the electric machine can be constructed either with a smaller outer diameter or with a larger rotor diameter.

The machine has the advantage over a purely permanent magnet excited machine that in the event of a fault (eg short circuits in the machine) the magnetic field can be reduced by the additional electrical excitation. This makes it possible to reduce the braking torque occurring in the event of a fault and bring it below a critical limit. In the event of a fault, the driver must be able to apply the full steering force, and the rigidly connected electric machine must not generate any braking torques that will block the steering. Also, it must be possible for the driver to apply the steering force including the maximum braking torque occurring. By the above topology of an electric machine, the maximum occurring braking torque can be limited in case of failure and at the same time a small space can be achieved.

Furthermore, it can be provided that the partial rotors each have permanent magnets which are arranged such that the magnetic field caused by the permanent magnet is superimposed additively or subtractively on the magnetic field generated by the exciter winding in at least one of the rotor poles.

In particular, the permanent magnets in the sub-rotors can be arranged in a follower pole arrangement.

The partial stators may each have stator teeth, which are aligned in the direction of the associated partial rotor, that an air gap is formed between the stator teeth and the rotor poles.

According to one embodiment, the partial stators can be connected to one another via a magnetic return path, in particular in the form of a housing.

Furthermore, the excitation winding can protrude into a recess of the rotor formed by the partial rotors or be completely accommodated therein and be held by one or both partial stators, in particular by means of a holder.

It can be provided that the excitation winding is connected via an electrical connection with at least one of the partial stators in order to supply the excitation winding with electrical energy.

Furthermore, a magnetic conclusion, in particular in the form of a connecting element, be arranged for connecting the part stators between the part stators.

According to another aspect, there is provided a steering system with the above electric machine connected to a handlebar.

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 1d various illustrations of a hybrid homopolarmaschine used for a steering drive;

2 a further variant of a hybrid-excited Homopolarmaschine with an arranged inside the stator winding exciting coil;

3 a schematic cross-sectional view of another embodiment of a hybrid-excited Homopolarmaschine;

4a and 4b the clarification of a method for assembling a Homopolarmaschine the 2 and 3 ;

5a and 5b a method of using the rotor in the homopolar machine of 2 and 3 ;

6 a further embodiment of the homopolar machine with an air gap expansion of the rotor poles of the rotor; and

7 a cross-sectional view of the rotor contour of the homopolar of the 6 ,

Description of embodiments

The 1a to 1d show different views of a homopolar machine used for a steering drive. In detail show: 1a a perspective view of the assembled homopolar machine 1 ; 1b a perspective view of the homopolar machine 1 with separate stator and rotor; 1c a perspective view of a piece of cake piece of Homopolarmaschine; and 1d a perspective sectional view of an axis-parallel section plane through the homopolar machine.

The homopolar machine 1 of the 1a to 1d includes a housing 2 in which a circular cylindrical stator assembly 3 is provided. The stator arrangement 3 includes radially inwardly facing stator teeth 4 that with stator coils 5 are wrapped. The stator coils 5 lie with their coil sides in between the stator teeth 4 located Statornuten and are shown schematically in the figures, the different hatches the location of stator coils 5 which are assigned to different phases.

In the present case, the homopolar machine 1 exemplarily twelve stator teeth 4 or twelve stator slots. In through the inward ends of the stator teeth 4 defined interior is a rotor 6 which is rotatably arranged. The rotor 6 includes buried permanent magnets 7 whose polar directions are in the radial direction.

As in particular from the 1c and 1d it can be seen, the stator is divided into two and has a first part stator 31 and a second part stator 32 on. The two part stators 31 . 32 are arranged concentrically to each other, with an equally concentric excitation coil between them 10 is provided. The exciter coil 10 is concentric with the axial direction around the rotor 6 wound and has substantially a radial thickness which is less than or equal to the thickness of the stator 3 is.

Furthermore, the rotor 6 in a first part rotor 61 and a second sub rotor 62 divided. The two part rotors 61 . 62 have a follower pole arrangement of the permanent magnets 7 on, wherein the permanent magnets of a partial rotor in the radial direction have the same polarity. The permanent magnets 7 are arranged to one another such that one with a permanent magnet 7 trained rotor pole a corresponding follower pole of the other part rotor 61 . 62 is opposite. In essence, in this structure of the rotor 6 all permanent magnets 7 a partial rotor 61 . 62 arranged with the same polarity, ie north pole or south pole facing outward. The permanent magnets of the other partial rotor have an opposite polarity (ie south pole or north pole). Alternatively, other arrangements of permanent magnets may be provided. The arrangement of the permanent magnets in the sub-rotors may correspond to a follower pole arrangement.

The two part rotors 61 . 62 are through a gap 9 separated from each other and only via a shaft 8th to which they are to transmit the drive torque, interconnected. The intermediate gap 9 between the part rotors 61 . 62 has approximately the same width in the axial direction as the width of the exciter coil 10 in the axial direction.

The exciter coil 10 between the part stators 31 . 32 serves to generate a uniform magnetic field, which in the axis-parallel direction through the shaft 8th runs and, as the permanent magnets 7 have a high magnetic resistance, by the follower poles in the radial direction in the direction of the stator teeth 4 is steered. In order to achieve a magnetic inference for the electrically generated exciter magnetic field, the housing 2 preferably be formed magnetically conductive.

The exciter coil 10 can be controlled by a regulator that allows excitation currents in the range between zero and a maximum value. If the controller continues to have an H-bridge for controlling the excitation current, negative excitation currents are also possible. This makes it possible to further reduce the braking torque.

Basically, there are other topologies of the homopolar machine 1 possible, which have a number deviating from the above number of stator teeth or a different number of rotor poles. However, in order to avoid tumbling moments, it makes sense that the arrangement of the permanent magnets 7 in the rotor 6 is provided according to a follower pole arrangement, otherwise Tilting moments in the machine may arise or may result in an unbalanced voltage system. In addition, topologies with 18 stator teeth and 10 rotor poles as well as with 12 stator teeth and 10 rotor poles, which are particularly suitable for winding with a single-tooth winding, should be emphasized.

A disadvantage of the excitation coil arranged outside the stator winding 10 is that for a magnetic housing for the magnetic yoke is required because the excitation coil 10 the stator assembly in the part stators 31 . 32 divided. In addition, the stator yokes must be the part stators 31 . 32 according to the thickness of the exciting coil 10 be dimensioned larger in the radial direction than actually for the magnetic yoke for the stator coils 5 would be required. This increases the diameter of the electric machine. Also, in the known constructions, the winding length of the exciting coil 10 long, which leads to a higher power requirement of arousal.

In 2 is another embodiment of the hybrid homopolar engine 1 shown in which an excitation coil 14 inside the stator assembly and in the intermediate gap 9 between the part rotors 61 . 62 is arranged. In other words, the exciter coil is located 14 within the area bounded by the outer circumference of the rotor. As a result, the diameter of the stator assembly can be made smaller, since the magnetic return now between the Teilstatoren 31 . 32 can be provided. Consequently, the diameter of the electric machine as a whole can be reduced. In contrast to known Homopolarmaschinen the exciter coil is not wound on the rotor or connected to this, so that they need not be energized via slip rings.

To ensure the magnetic return is a connecting element 12 provided, essentially the two partial stators 31 . 32 connects with each other. At the same time, the connecting element comprises 12 retaining elements 13 which also carry or represent corresponding current conductors to the exciter coil 14 to energize and between the part rotors 61 . 62 to fix.

In 3 is a schematic cross-sectional view of another embodiment shown, the separate stator windings of the partial stators 31 . 32 having. Essentially, the cross-sectional representation corresponds to 3 the homopolar machine of 2 except for the difference that each of the stator teeth 4 the partial stators 31 . 32 is provided with a separate winding, ie each stator coil 5 is only on the first part stator 31 or the second part stator 32 arranged and not designed across.

This makes it possible for the two partial stators 31 . 32 as separate, already wound components can be made and the connecting element 12 with the appropriate bracket 13 and the exciter coil 14 can also be made as a separate element. The sequence of assembly of the individual components is in the 4a and 4b shown. In this case, it is possible to work through the partial stators 31 . 32 with the components in between to build the entire stator assembly for the homopolar machine in a simple manner.

Because the exciter coil 14 now protrudes into the defined by the ends of the stator teeth interior, which can from the part rotors 61 . 62 composite rotor 6 not ready pre-assembled before it is inserted into the stator assembly. The 5a and 5b illustrate the insertion of the two-piece rotor 6 with the two rotor parts 61 . 62 in the stator of the 4b , Before insertion into the stator assembly, the rotor 6 in two parts on a rotor shaft 15 provided essentially the shaft 8th according to the embodiments described above.

The rotor shaft 15 comes with the first part rotor 61 provided so that the sub rotor 61 immediately at one of the intermediate gap 9 associated shaft section 16 is applied. Ie. the shaft section 16 lies in the inserted state of the rotor 6 in a common, perpendicular to the axial direction extending plane of the shaft portion 16 has a diameter which is only slightly smaller than the inner diameter of the exciting coil 14 so that the inner edge of the exciter coil 14 not on the shaft section 16 is applied.

At one with respect to the shaft section 16 opposite the first part rotor 61 lying portion of the rotor shaft 15 this is provided with a diameter corresponding to an inner diameter of the second partial rotor 62 corresponds, so that the second part rotor 62 on the rotor shaft 15 can be put on. When assembling the Homopolarmaschine now the rotor shaft 15 with the first part rotor 61 provided and then inserted from one side in the axial direction in the inner region of the stator assembly until the shaft portion 16 within of the exciter coil 14 surrounded area lies to come. This is guaranteed when the first part rotor 61 with an end face to the exciter coil 14 strikes.

Subsequently, the second part rotor 62 inserted from the opposite opening of the stator assembly, so that this on the corresponding portion of the rotor shaft 15 is put on. It should be noted by appropriate measures that the two part rotors 61 . 62 so to each other are offset, that in the axial direction a follower pole and a pole formed with a permanent magnet in the axial direction are opposite. The offset of the partial rotors should preferably correspond to 360 ° / number of rotor poles. Alternatively, the offset between the partial rotors can also deviate from this angle by a certain amount, in order to offset the cogging torques of the two partial machines relative to one another, so that torque cancellation occurs in part.

Of course, according to one embodiment, the number of rotor poles of the sub-rotors may differ from each other. Even with separately wound part stators, it is basically possible to form them with different numbers of stator teeth.

According to a further embodiment it can be provided that the rotor poles have no cylindrical surface, but are formed as sine poles or are provided to the pole edges with an air gap expansion. This is in 6 as a further embodiment and schematically in FIG 7 shown. The air gap expansion allows a smoother field transition at the pole edges, resulting in lower harmonics and torque variations. Furthermore, it can also reduce the magnetic noise excitations of the machine.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 03/099632 Al [0007]
• US 6597078 B2 [0011]
• US 7034423 B2 [0011]
• US 6252323 B1 [0012]
• DE 10016002 A1 [0012]
• EP 0569594 B1 [0012]
• DE 10348410 A1 [0012]
• EP 1447901 A1 [0012]
• DE 69406706 A1 [0014]
• EP 0729217 [0015]
• DE 2165152 [0016]
• US 5504382 A1 [0017]
• WO 1999009638 A1 [0017]

Claims (9)

Electric machine ( 1 ), in particular for use in a steering system of a motor vehicle, comprising: a first sub-machine having a first sub-rotor arranged on a shaft ( 61 ), which in the radial direction of the shaft a first part stator ( 31 ) is arranged opposite; A second sub-machine with a second sub-rotor arranged on the shaft ( 62 ), which in the radial direction of the shaft a second partial stator ( 32 ) is arranged opposite; A field winding wound around the axis of rotation of the shaft ( 10 . 14 ), which serves a magnetic field in one through the partial rotors ( 61 . 62 ) rotor, characterized in that the field winding ( 10 . 14 ) is arranged between the sub-machines. Electric machine ( 1 ) according to claim 1, wherein the partial rotors ( 61 . 62 ) each permanent magnet ( 7 ), which are arranged so that by the permanent magnets ( 7 ) caused magnetic field by the exciter winding ( 10 . 14 ) are superposed in an additive or subtractive manner in at least one of the rotor poles. Electric machine ( 1 ) according to claim 2, wherein the permanent magnets ( 7 ) in the partial rotors ( 61 . 62 ) are arranged in a follower pole arrangement. Electric machine ( 1 ) according to one of claims 1 to 3, wherein the partial stators ( 31 . 32 ) each stator teeth ( 4 ), which in the direction of the associated partial rotor ( 61 . 62 ) are aligned such that an air gap is formed between the stator teeth and the rotor poles. Electric machine ( 1 ) according to claim 4, wherein the partial stators ( 31 . 32 ) via a magnetic yoke, in particular in the form of a housing ( 2 ) are interconnected. Electric machine ( 1 ) according to one of claims 1 to 4, wherein the exciter winding ( 14 ) in a recess of the through the partial rotors ( 61 . 62 ) formed rotor ( 6 ) or is completely contained in it and of one or both partial stators ( 31 . 32 ), in particular by means of a holder ( 13 ) is held. Electric machine ( 1 ) according to claim 5, wherein the exciter winding ( 14 ) via an electrical connection with at least one of the partial stators ( 31 . 32 ) is connected to the field winding ( 14 ) to provide electrical energy. Electric machine ( 1 ) according to claim 6 or 7, wherein between the partial stators ( 31 . 32 ) a magnetic conclusion, in particular in the form of a connecting element ( 12 ), for connecting the partial stators ( 31 . 32 ) is arranged. A steering system comprising an electric machine according to any one of claims 1 to 8 connected to a handlebar, the electric machine ( 1 ) has a mechanically rigid connection via a transmission with the steering wheel.

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