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

Patent metadata

Field	Value
Publication number	US-10854397-B2
Application number	US-201916456583-A
Country	US
Kind code	B2
Filing date	Jun 28, 2019
Priority date	Jul 27, 2018
Publication date	Dec 1, 2020
Grant date	Dec 1, 2020

Abstract

An electric machine, to a motor vehicle with such an electric machine, and to a method for operating such an electric machine. The electric machine includes at least one sliding contact which is formed by a slip ring connected to a rotor and by at least one brush and via which an operating current flows during an operation of the electric machine. A control unit is configured to control the operation of the electric machine. The control unit is configured to verify a predetermined operating criterion of the electric machine and, if said operating criterion is met, to inject a cleaning current according to a predetermined scheme, which then flows independently of the operating current via the sliding contact and cleans said sliding contact in order to maintain or improve a current transfer capability of the sliding contact.

First claim

The invention claimed is:

1. An electric machine, in particular for a motor vehicle, comprising:
at least one sliding contact which is formed by a slip ring connected to a rotor of the electric machine and by at least one brush, and via which an operating current flows during an operation of the electric machine, and with a control unit which is configured to control the operation of the electric machine,
wherein the control unit is configured to verify a predetermined operating criterion of the electric machine and, if the predetermined operating criterion is met, to inject a cleaning current according to a predetermined scheme, which then flows independently of the operating current via the sliding contact and cleans said sliding contact in order to service a current transfer capability of the sliding contact,
wherein, when the cleaning current is injected, the electric machine is operated automatically with a stator field which is weakened with respect to a normal operation without cleaning current in order to compensate for a torque produced by the cleaning current.

2. The electric machine according to claim 1 , wherein the electric machine is a separately excited synchronous machine, and in that the operating current is an excitation current for generating a magnetic field rotating with the rotor.

3. The electric machine according to claim 1 , wherein at least one peak value of the cleaning current is a multiple of the operating current flowing via the sliding contact during normal operation of the electric machine without the cleaning current switched on.

4. A method for operating an electric machine, in particular for a motor vehicle, comprising:
verifying a control unit of the electric machine, at least one predetermined operating criterion of the electric machine is verified, wherein if the predetermined operating criterion is met, a cleaning current is injected by the control unit according to a predetermined scheme via a sliding contact which is formed by a slip ring connected to a rotor of the electric machine and by at least one brush, which cleaning current then flows independently of the operating current via the sliding contact and cleans said sliding contact in order to service a current transfer capability of the sliding contact,
wherein, when the cleaning current is injected, the electric machine is operated automatically with a stator field which is weakened with respect to a normal operation without cleaning current in order to compensate for a torque produced by the cleaning current.

5. The method according to claim 4 , wherein a course of a load during the operation of the electric machine is monitored, and
as the predetermined operating criterion, it is verified whether the load is at least in a minimum predetermined proportion below a predetermined load threshold value over a predetermined time span.

6. The method according to claim 4 , wherein as the predetermined operating criterion, it is verified whether a value, automatically determined during operation of the electric machine, of at least one predetermined operating parameter deviates from a predetermined target value for this operating parameter, wherein, as the operating parameter, in particular the operating current, a torque, a rotation speed, a speed or a power output is determined.

7. The method according to claim 4 , wherein the operation of the electric machine is automatically monitored, and the cleaning current is automatically injected when the electric machine is not being operated and has not been operated for at least a predetermined standstill duration.

8. The method according to claim 4 , wherein as the predetermined operating criterion, a temperature of the electric machine is automatically monitored, and the cleaning current is injected only when the monitored temperature is lower than a predetermined limit temperature.

9. The method according to claim 4 , wherein as part of the predetermined scheme for a course of the cleaning current, a sequence of multiple current peaks and flanks lying in between with at least a predetermined minimum slope is predetermined.

10. The method according to claim 4 , wherein the electric machine has multiple sliding contacts for the electric contacting of the rotor,
the cleaning current, in each case, is injected only via one or via less than all of the multiple sliding contacts at a time, and
a torque produced by the cleaning current is compensated at least partially by weakening the operating current which, in the process, flows via at least one of the multiple sliding contacts via which the cleaning current is not led, respectively.

11. The method according to claim 4 , wherein by means of a plurality of additional electric machines, respective operating data which indicates an operating history of the respective electric machine and respective status data which indicate a corresponding operating behavior of the respective electric machine, are transmitted to a central server device,
by means of the central server device, a cleaning strategy is automatically determined by evaluating the transmitted operating and status data, and
the control unit of the electric machine injects the cleaning current according to the predetermined cleaning strategy, in particular as a function of respective current operating and status data of the electric machine.

12. The electric machine according to claim 2 , wherein at least one peak value of the cleaning current is a multiple of the operating current flowing via the sliding contact during normal operation of the electric machine without the cleaning current switched on.

13. The method according to claim 5 , wherein as the predetermined operating criterion, it is verified whether a value, automatically determined during operation of the electric machine, of at least one predetermined operating parameter deviates from a predetermined target value for this operating parameter, wherein, as the operating parameter, in particular the operating current, a torque, a rotation speed, a speed or a power output is determined.

14. The method according to claim 5 , wherein the operation of the electric machine is automatically monitored, and the cleaning current is automatically injected when the electric machine is not being operated and has not been operated for at least a predetermined standstill duration.

15. The method according to claim 6 , wherein the operation of the electric machine is automatically monitored, and the cleaning current is automatically injected when the electric machine is not being operated and has not been operated for at least a predetermined standstill duration.

16. The method according to claim 5 , wherein as the predetermined operating criterion, a temperature of the electric machine is automatically monitored, and the cleaning current is injected only when the monitored temperature is lower than a predetermined limit temperature.

17. The method according to claim 6 , wherein as the predetermined operating criterion, a temperature of the electric machine is automatically monitored, and the cleaning current is injected only when the monitored temperature is lower than a predetermined limit temperature.

18. The method according to claim 7 , wherein as the predetermined operating criterion, a temperature of the electric machine is automatically monitored, and the cleaning current is injected only when the monitored temperature is lower than a predetermined limit temperature.

19. The method according to claim 5 , wherein as part of the predetermined scheme for

Assignees

• Audi Ag

Inventors

• Strasser Roman

Classifications

• H01H2231/026

  Car · CPC title

• H01H1/18

  with subsequent sliding · CPC title

• H02P23/14 Primary

  Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage · CPC title

• H01H1/60 Primary

  Auxiliary means structurally associated with the switch for cleaning or lubricating contact-making surfaces (cleaning by normal sliding of contacts H01H1/18, H01H1/36) · CPC title

• H01H1/36

  by sliding · CPC title