Electric machine, motor vehicle with electric machine, and method for operating an electric machine

#The disclosure relates to an electric machine, to a motor vehicle with an electric machine, and to a method for operating an electric machine.

#In electric machines, sliding contacts are often used in order to transmit current between two components which move relatively to one another. At such sliding contacts, in particular due to a mechanical load and temperature effects, wear occurs, which can over the course of time worsen a current transfer capability of the respective sliding contact. This can result in the need for expensive repair or replacement of the corresponding sliding contact.

#DE 39 43 651 C2 relates to an electric universal motor. Herein, a broad-surface axial contacting between a contact surface and a carbon brush sliding under pressure on said contact surface is described. As a result of the pressure, a constant mechanical cleaning action on the contact surfaces is achieved.

#The single FIGURE shows a diagrammatic side view of a motor vehicle 1 with two electric machines 2, not represented true to scale here, namely a first electric machine 3 and a second electric machine 4. The first electric machine 3, here, can be provided for driving a front axle of the motor vehicle 1 and the second electric machine 4 can be provided for driving a rear axle of the motor vehicle 1.

#The electric machines 2 in the present case are separately excited synchronous machines. Thus, the electric machines 2 are of identical design, herein, and therefore have the same components, wherein for the sake of clarity, said components are marked individually only for the first electric machine 3.

#The first electric machine 3 comprises a stator 5 with a stator winding 6 and a rotor 7 with a rotor winding 8, which is arranged rotatably mounted in the stator 5. In the present case, two slip rings 9, namely a first slip ring 10 and a second slip ring 11, are arranged on the rotor 7. The slip rings 9 are electrically contacted by carbon brushes 12, wherein a first carbon brush 13 forms a first sliding contact with the first slip ring 10, and a second carbon brush 14 forms a second sliding contact with the second slip ring 11. The rotor 7 can be supplied with an excitation current via the sliding contacts in order to generate a rotor field of the respective electric machine 2.

#Also diagrammatically represented is a power electronics 15 which is connected to the electric machine 2. The power electronics 15 is used for controlling or actuating the electric machine 2. Although the power electronics 15 is represented diagrammatically as a component, herein, a separate corresponding power electronics 15 can also be provided for each of the two electric machines 2, which can then be coupled to one another by a corresponding data connection.