Method for fault recognition in an electric machine controlled by an inverter in a motor vehicle and device for monitoring an operation of the electric machine

1. A method for providing fault recognition in an electric machine, controlled by an inverter in a motor vehicle, the method comprising:

ascertaining the phase currents of the electric machine by measuring; and

recognizing a fault, via a control unit, if at least one of the phase currents or a variable derived therefrom exceeds a predefined upper threshold value;

wherein the upper threshold value is established as a function of operating parameters of the motor vehicle, including at least one of the electric machine and the inverter, and

wherein a control signal is applied to a base terminal of a first transistor, the collector terminal of which is connected to a gate terminal of a second transistor via a pull-up resistor, a potential divider which is formed from a series connection of three resistors being connected downstream of the second transistor, wherein a drain terminal of the second transistor is connected to a first center tap between the first resistor and the second resistor of the potential divider, wherein the upper threshold value for a voltage corresponding to the phase current is tapped at the first center tap.

2. The method of claim 1 , wherein a fault is recognized if at least one of the phase currents or a variable derived therefrom is less than a predefined lower threshold value, the lower threshold value being established as a function of operating parameters of the motor vehicle, including at least one of the electric machine and the inverter.

3. The method of claim 1 , wherein the upper and/or the lower threshold value(s) is/are selected from a set of stored threshold values.

4. The method of claim 1 , wherein the upper and/or the lower threshold value(s) is/are established as a function of an operating state of the electric machine.

5. The method of claim 1 , wherein the upper and/or the lower threshold values value(s) is/are established as a function of an intermediate circuit voltage.

6. The method of claim 1 , wherein the upper and/or the lower threshold value(s) is/are established as a function of a temperature, including the junction temperature, of a power component subject to electrical breakthrough, including a power switching element, and of the inverter.

7. The method of claim 1 , wherein the upper and/or the lower threshold value(s) is/are established as a function of the intensity of the phase currents and/or as a function of the flow times of the phase currents.

8. The method of claim 1 , wherein the upper and/or the lower threshold value(s) is/are established as a function of a collector-emitter voltage or a source-drain voltage of a power switching element of the inverter.

9. The method of claim 1 , wherein the upper and/or the lower threshold value(s) is/are established as a function of a temperature of a heat sink of a power component, including a power switching element of the inverter.

10. The method of claim 1 , wherein the upper and/or the lower threshold value(s) is/are established as a function of a collector current or a source current of a power switching element of the inverter.

11. The method of claim 1 , wherein the inverter is a pulse-controlled inverter, and if the fault is recognized, the inverter is transferred into a safe operating state in the form of a freewheel-circuit or a short-circuit.

12. A device for monitoring an operation of an electric machine controlled by an inverter in a motor vehicle, comprising:

a phase current monitoring device for comparing the phase currents or variables of the electric machine derived therefrom, having a predefined upper threshold value; and

a control unit for establishing the upper threshold value as a function of operating parameters of the motor vehicle, including the electric machine and/or the inverter, and

wherein the phase-current monitoring device has a first transistor, a second transistor, a pull-up resistor and a potential divider which is formed from a series connection of three resistors and is connected downstream of the second transistor, wherein the first transistor has a collector terminal which is connected to a gate terminal of a second transistor via a pull-up resistor, wherein a drain terminal of the second transistor is connected to a first center tap between the first resistor and the second resistor of the potential divider, and wherein the control unit is configured to apply a control signal to a base terminal of the first transistor.

13. The device of claim 12 , wherein the phase current monitoring device compares variables derived from the phase currents to a lower threshold value, and the control unit establishes the lower threshold value as a function of operating parameters of the motor vehicle, including the electric machine and/or the inverter.

14. The device of claim 12 , wherein the inverter is a pulse-controlled inverter, and if the fault is recognized, the inverter is transferred into a safe operating state in the form of a freewheel-circuit or a short-circuit.