Electric machine having a potential equalization device

1. An electric machine having a stator ( 3 ) and a rotor ( 4 ) mounted rotatably by means of a rotor shaft ( 5 ) and having a potential equalization device containing a resistor element for breaking down shaft voltages occurring at the rotor shaft ( 5 ), the resistor element contacting a bus bar ( 24 ) of a slip ring module ( 20 ) at a contact point and contacting the rotor shaft ( 5 ) at another contact point, wherein the resistor element is an electrical resistor ( 30 ; 46 ) provided with electrical connection elements ( 31 , 32 ; 47 , 48 ), and wherein at least one of the connection elements ( 32 ; 47 ) of the electrical resistor ( 30 ; 46 ) is electrically conductively connected to the potential of the rotor shaft ( 5 ) via a pressure contact by a pressure element ( 36 ), wherein the pressure element is attached to a covering cap ( 28 ) overlapping the resistor ( 30 ), and wherein the pressure element is a resilient tab ( 36 ), which together with the covering cap ( 28 ) forms a one-piece plastics part.

2. The electric machine according to claim 1 , wherein the covering cap ( 28 ) surrounds the rotor shaft ( 5 ) annularly at least in part and is placed onto a plastics body ( 26 ), in which at least one radially oriented connection lug ( 33 ) of a bus bar ( 24 ) is inserted in part.

3. The electric machine according to claim 2 , wherein the electrical resistor ( 30 ) is fastened in the covering cap ( 28 ).

4. The electric machine according to claim 3 , wherein the electrical resistor ( 30 ; 46 ) is an ohmic resistor ( 30 ), which on both sides has connection wires ( 31 , 32 ) as connection elements.

5. The electric machine according to claim 4 , wherein at least one of the connection wires ( 32 ) is bent into a U-shaped loop ( 35 ), of which a free loop end bears via a mechanical pressure exerted from a pressure element ( 36 ) against a contact point on the rotor shaft ( 5 ).

6. The electric machine according to claim 2 , wherein the resilient tab ( 36 ) extends axially and projects between the plastics body ( 26 ) and the at least one of the connection elements ( 32 ) such that the one of the connecting elements ( 32 ) contacts the rotor shaft ( 5 ).

7. The electric machine according to claim 1 , wherein the electrical resistor ( 30 ) is fastened in the covering cap ( 28 ).

8. The electric machine according to claim 1 , wherein the electrical resistor ( 30 ; 46 ) is an ohmic resistor ( 30 ), which on both sides has connection wires ( 31 , 32 ) as connection elements.

9. The electric machine according to claim 8 , wherein at least one of the connection wires ( 32 ) is bent into a U-shaped loop ( 35 ), of which a free loop end bears via a mechanical pressure exerted from the pressure element ( 36 ) against the contact point on the rotor shaft ( 5 ).

10. The electric machine according to claim 1 , wherein the electrical resistor is an SMD resistor element ( 46 ).

11. An electric machine having a stator ( 3 ) and a rotor ( 4 ) mounted rotatably by means of a rotor shaft ( 5 ) and having a potential equalization device containing a resistor element for breaking down shaft voltages occurring at the rotor shaft ( 5 ), the resistor element contacting a bus bar ( 24 ) of a slip ring module ( 20 ) at a contact point and contacting the rotor shaft ( 5 ) at another contact point, wherein the resistor element is an electrical resistor ( 30 ; 46 ) provided with electrical connection elements ( 31 , 32 ; 47 , 48 ), and wherein at least one of the connection elements ( 32 ; 47 ) of the electrical resistor ( 30 ; 46 ) is electrically conductively connected to the potential of the rotor shaft ( 5 ) via a contact piece ( 43 ; 45 ), and wherein the contact piece ( 43 ; 45 ) is partially embedded in a contact body ( 26 ) surrounding the rotor shaft ( 5 ) and protrudes from the contact body ( 26 ) such that the contact piece ( 43 ; 45 ) electrically conductively connects the potential of the rotor shaft ( 5 ) to the electrical resistor ( 30 ; 46 ) with pressure contact to the rotor shaft ( 5 ).

12. The electric machine according to claim 11 , wherein the electrical resistor ( 30 ) is fastened in the covering cap ( 28 ).

13. The electric machine according to claim 11 , wherein the electrical resistor ( 30 ; 46 ) is an ohmic resistor ( 30 ), which on both sides has connection wires ( 31 , 32 ) as connection elements.

14. The electric machine according to claim 11 , wherein the electrical resistor is an SMD resistor element ( 46 ).

15. The electric machine according to claim 11 , wherein the contact piece ( 43 ; 45 ) is partially embedded in the contact body ( 26 ) and a contact surface ( 44 ) of the contact piece ( 43 ; 45 ) faces the rotor shaft ( 5 ) such that the contact surface ( 44 ) is pressed against the rotor shaft ( 5 ).