The invention relates to a synchronous motor having 12 stator teeth and 10 rotor poles, in particular for use in electrical power steering assists.
In the case of electrical drives for steering systems having electromechanical assistance, which are used in motor vehicles, it is necessary for the fluctuations in the drive torque produced at the shaft to be very small. Electrically commutated permanent magnet synchronous motors are normally used as such drives because they are preferred for these applications on account of their power density, their level of efficiency and their control options. So-called harmonic torques, which can lead to considerable fluctuations in the torque, arise, however, as a result of harmonics in electrically commutated synchronous motors. Therefore, such drives have to be embodied in such a way that these harmonics are reduced as much as possible or that their effect on the torque curve is small.
Furthermore, fluctuations in torque occur not only under load but also when the stator winding is de-energized. In the latter case, said fluctuations are denoted as detent torques. A conventional method for reducing detent torques in synchronous motors consists of selecting the ratio of the number of stator winding slots to the pole number in such a way that the least common multiple is as large as possible. This can, for example, be achieved by a finely distributed winding (for example with q=2, respectively 2 slots per pole and phase). Due to the cramped space conditions with respect to small electrical motors, it is, however, often not possible to insert a finely distributed winding into the armature in order to produce a suitable air gap field having a small harmonic content. For that reason corresponding harmonics must be expected in the air gap particularly in the case of such synchronous motors of compact design. The harmonics should however be such that they do not generate or generate only small harmonic torques. For that reason fractional slot windings (number of slots per pole and phase) are often used in small synchronous machines. This is, for example, implemented in a synchronous motor having 9 stator teeth in the stator and 8 rotor poles, respectively having 18 stator teeth in the stator and 8 rotor poles.
A further essential requirement consists of making an electric motor more reliable. In contrast to electrically energized machines, it is not possible with permanent magnets to switch off the magnetic field. In the event of faults, as, for example short circuits in the winding, this can lead to considerable braking torques, which can lead to a blockage of the steering when applied to a steering system. For that reason it is desirable to provide electrical motors, which have a reduced probability of failure and smaller braking torques in the event of faults.
It is therefore the aim of the present invention to provide a synchronous motor, which can be constructed in a simple manner, has small detent torques and has a small torque undulation and moreover has an increased reliability due to its form of construction.
This task is solved by the synchronous machine according to claim 1.
Additional advantageous configurations of the invention are stated in the dependent claims.
According to one aspect, provision is made for an electrical machine, particularly a synchronous machine. The electrical machine comprises a stator arrangement having twelve stator teeth as well as a rotor having ten rotor poles, the rotor poles being separated by air gaps and said rotor poles being embodied as sinus poles.
The embodiment of an electrical machine having twelve stator teeth and ten rotor poles in combination with the embodiment of the rotor poles has the advantage that the detent torque and the harmonic torques can be significantly reduced compared to an electrical machine without sinus poles.
The tangential air gaps between the poles expand outwardly in a radial direction.
According to an additional embodiment, each rotor pole is provided with a permanent magnet, whose north pole to south pole direction extends radially, the polarity of permanent magnets adjacent to each other being opposite.
The rotor poles can furthermore be embodied in a consequent-pole arrangement, only every other rotor pole being configured with a permanent magnet, whose north to south pole direction extends radially, the polarity of the permanent magnets being rectified.
According to another embodiment, provision is made for permanent magnets, whose north to south pole direction extends in a circumferential direction, to be arranged inside of the rotor, particularly in pockets. Particularly permanent magnets arranged adjacent to each other can have a poling direction, which is opposite to one another.
A pocket for accommodating one of the permanent magnets can furthermore be provided between in each case two rotor poles, only every other pocket being provided with a respective permanent magnet.
The stator teeth can be wound according to a consequent-tooth arrangement, only every other stator tooth bearing a stator coil.
Each stator tooth can furthermore be provided with a stator coil, provision being made for the stator coils to be arranged in groups having in each case two stator coils connected in series. The groups of stator coils are then connected up in a star circuit or in a plurality of said circuits. The groups of stator coils can particularly be connected up in two star circuits having in each case three groups of stator coils, the corresponding three groups of stator coils being connected to connections for three phase voltages.
Alternatively each stator tooth can be provided with a stator coil, provision being made for the stator coils to be arranged in groups having in each case two stator coils connected in series, wherein the groups of stator coils are connected up in a delta connection or in a plurality of said connections. The groups of stator coils can particularly be connected up in two delta connections having in each case three groups of stator coils, the corresponding three groups of stator coils respectively of one of the delta connections being connected to connections for three phase voltages.
Preferred embodiments of the present invention are subsequently explained in detail using the accompanying drawings. The following are shown:
Like reference numerals correspond to elements of the same or a comparable function in the following embodiments.
The stator teeth 2 are surrounded by stator coils 8, which in each case enclose a stator tooth 2 in the example of embodiment shown. (In the example of embodiment shown only one stator coil is depicted for the sake of clarity.) In contrast to known embodiments from the technical field, this has the advantage in that winding strands, which run in a crosswise direction, can be avoided in the case of stator coils 8, which enclose two or more stator teeth 2. In so doing, the probability of short circuits can be reduced and therefore the reliability of the system can be increased. Only one stator coil 8 is depicted in
The pole magnets 7 of the rotor 6 are embedded in the rotor 6, i.e. are configured as so-called buried magnets. An external peripheral surface of the rotor 6, which is substantially cylinder-shaped, is provided with rotor poles and with air gaps 9 between the rotor poles 4, which starting from a web limiting the depth of the air gap outwardly expand in a radial direction in order to form so-called sinus poles. Sinus poles are magnet poles of an electric motor, whereat a sinus-shaped air induction arises. Such sinus poles are, for example, already described by Rudolf Richter in “Electric Machines”, volume 1, page 170ff, Julius Springer publisher: 1924. Because the contour in the pole gap, i.e. in the air gap between the poles, can not follow the exact equation, this region between the permanent magnets 6 is to be configured according to mechanical criteria. For this reason, the contour, which is predetermined by the sinus pole design, is continued only up until a certain width beyond the respective rotor pole 4. The gap is implemented only up until a certain depth between the poles because it does not have a large effect on the air gap field in this region. Said gap is configured according to mechanical criteria in this region
In the case of buried permanent magnets, the air-gap widening leads to the material of the rotor 6 being more strongly curved across its pole in a radial direction outside of the permanent magnets than the peripheral line of the external radius of the rotor 6. Expanding air gaps are thus formed between the poles 4 of the rotor 6. This contour for the air gap produces an air gap field, which is approximately sinusoidal due to the magnet wheel, whereby a significant reduction in the detent torques at engine idle and in the harmonic torques under load is made possible. An approximation function is preferably used for the contour of the air-gap widening, which can be indicated by 1/cos(P·φ). P corresponds to the number of pole pairs and φ to the spatial angle starting from a centerline of the pole 4. (A more exact depiction of this approximation equation appears in the publication of the German patent DE 103 14 763.)
A cross-sectional depiction of a rotor for a synchronous motor according to a further embodiment of the invention is depicted in the embodiment of
A further embodiment of a rotor arrangement with positioned magnets is depicted in
A stator arrangement of a synchronous motor is shown in
Different embodiments of the electrical circuitry of the stator coils 8 of the embodiments of
The 12 stator coils therefore constitute 6 groups of in each case two diametrically opposed stator coils 8 connected in series in the stator. Said coils 8 are electrically activated via three phases U, V, W. In so doing, two groups of stator coils 8 are in each case connected to a phase.
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As shown in
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An embodiment is shown in
Analogous to the embodiment of
Number | Date | Country | Kind |
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10 2007 029 157.6 | Jun 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2008/055178 | 4/28/2008 | WO | 00 | 6/2/2010 |