Heteropolar Excited Synchronous Machine

The invention relates to a synchronous machine and, more particularly, to a synchronous machine excited by means of heteropolarization.

German reference DE-A1-30 09 279 discloses a synchronous machine having a stator with permanent magnets for the excitation, leaving more space providing the power windings than in the case where windings are used as the excitation. The permanent magnets are located around the stator side of the device. Further, a toothed laminated rotor is arranged inside the stator's inner circumference.

In this configuration known from the above German reference, the permanent magnets are utilized for operational excitation. In this manner of using the permanent magnets, one no longer needs an excitation winding. Thus, extra space is gained for the power windings and/or the machine weight can be economized for a synchronous machine provided as a generator. An embodiment of the German reference, however, has the permanent magnets partially replaced by exciting windings. The magnetic fields of the permanent magnets and the exciting windings work separately.

A heteropolar generator with a stator having the stator subdivided into stator sectors is also known from DE 3050269. With this type of stator, only the excitation windings are providing the excitation; they are wound around the stator yoke; permanent magnets are not used.

There is therefore needed a synchronous machine in which the electric excitation means on the stator is reduced, while maintaining or even reducing the size of the motor and preserving all advantages of an electric excitation system.

These needs are met by the synchronous machine of the present invention by subdividing the stator into stator sectors with permanent magnets in between. Excitation windings and power windings are provided on the stator sectors. A rotor is arranged inside the stator circumference separated by air gap from the stator. Each of the stator sectors is wound with an excitation winding and permanent magnets are located in the gaps between the sectors. Each permanent magnet has a magnetic field opposing the fields of the adjoining excitations windings. This design of the present invention, having the excitation winding wound around the stator yoke and the air-gap flux concentrated in the stator yoke accordingly, the excitation power demand, in comparison to the known design mentioned above for the stator-excited synchronous machine, can be advantageously decreased due to the considerably shorter excitation-winding turn lengths that are attainable. As a result of the arrangement of the magnetizing permanent magnets located at the ends of the stator sectors and having a magnetization opposite the magnetization of the adjoining excitation windings, the overall radial height of the stator yoke, the unwanted magnetic leakage and the necessary exciter power demand can be still further reduced. This is because the magnetic potential of the permanent magnets counteracts the electrically excited stray field and even contributes to a magnetic relief of the stator yoke sectors in the region of the exciter windings.

The FIGURE is a schematic axial cross-sectional view of a wound stator system of the present invention.

The drawing shows a cross-sectional view of a wound stator system having two stator sectors 1, 2 forming a 4- pole exciting system. A rotor 7 having 40 rotor teeth 71 located on the air-gap side of the stator system is arranged in the stator bore of the system. For each stator sector 1, 2, excitation windings 3 and 4 wind around the stator sectors 1, 2. The excitation windings 3,4 are placed in the tangential middle of the stator sectors 1 and 2, respectively. Permanent magnets 5 or 6, having a tangential magnetization direction opposed to that of the exciter windings 3,4, are located between the stator sectors 1 and 2.

An embodiment of the synchronous machine with small dimensions and advantages from the standpoint of production engineering is characterized by the stator sectors 1 or 2. The stator sectors 1,2 in the region of the excitation windings 3, 4 are designed to run radially inward, while maintaining roughly the same cross-sectional width of the stator yoke. This forms stator slots 11 and 21 for the excitation windings 3 and 4, respectively.

According to an embodiment of the invention, the rotor 7 is integrated with a flywheel 20 or clutch system parts of an internal combustion engine (not shown), particularly in a motor vehicle. The inner radius of the rotor 7 forms a space which can be utilized advantageously for clutch components. It is beneficial if the stator sectors 1,2 only extend over a portion of the rotor circumference, particularly when the rotor is integrated with the flywheel and/or the clutch of an internal combustion engine. Thus, when the synchronous machine of the present invention is used as a motor or generator, the free space or gaps located on the stator side of the machine between the stator sectors can be used for further construction parts and, e.g. connecting bolts disposed between the internal combustion machine and a gear unit.

The magnetic fields of the permanent magnets 5,6 and excitation windings 3,4 counteract each other in the circumferential direction of the stator and add up in the air gaps in a functionally advantageous manner. This creates, in the disclosed example, a strong air-gap excitation field system, which, in spite of the application of permanent magnets, is nevertheless fully adjustable. When the excitation current is disconnected, the permanent magnetic field does not enter into the air gap of the machine, but rather has separate contact basically along the circumference of the machine. If a air-gap with zero field is not required, then the field contribution supplied by the permanent 5,6 magnets can be even greater than that of the excitation windings 3,4.

The overall axial length of the machine, is reduced in the case of m=2 or 4 and q=A, where m is the number of the phrase windings and q is the number of slots per pole and part winding. This occurs when the stator teeth 14 or 15 are disposed such that they alternately slant to the left or right, of the radial line of symmetry S, with the cross-sectional width of the stator slots 12 or 13 alternately widening toward the slot base or the slot opening. The drawing shows that, for example, the phase windings 9 wound around the slots 12 which are widened toward the slot base, and the phase windings 8 wound around the slots 13 which are widened toward the slot opening, can be accommodated in a manner resulting in a good radial distribution of the winding overhangs, i.e., the winding-overhang intersections which project axially over each other to a small extent.

The stator-excited synchronous machine according to the invention can be used both as a motor and as a generator in the same operating unit. In the case of a direct-current power supply, such as a motor vehicle electrical system, the power windings are coupled to an electronic commutating circuit 22.