METHOD FOR DETERMINING A SPEED OF AN ELECTRONICALLY COMMUTATED ELECTRIC MOTOR

Abstract

A method for determining a speed of an electronically commutated electric motor, in particular an electric motor of a fan. The current measured values are acquired at multiple points in time, which describe an amperage of a drive current supplied to the electric motor, after which a speed of the electric motor is determined as a function of the acquired current measured values.

Claims

1-9. (canceled)

10. A method for determining a speed of an electronically commutated electric motor, in particular an electric motor of a fan, wherein current measured values are acquired at multiple points in time, which describe an amperage of a drive current supplied to the electric motor, after which a speed of the electric motor is determined as a function of the acquired current measured values.

11. The method as claimed in claim 10, wherein the speed of the electric motor is determined as a function of which of the acquired current measured values reach or fall below a predetermined limiting value.

12. The method as claimed in claim 10, wherein the speed of the electric motor is determined as a function of the points in time at which and/or the time interval at which current measured values are acquired, which reach or fall below the or a predetermined limiting value.

13. The method as claimed in claim 10, wherein the drive current is provided by a driver circuit, wherein the driver circuit provides an output for a measurement voltage proportional to the drive current, wherein voltage values of this measurement voltage are acquired as current measured values.

14. The method as claimed in claim 10, wherein the current measured values are acquired by an analog-to-digital converter.

15. The method as claimed in claim 10, wherein the electric motor drives a fan, which cools a component, which is a DC/DC converter or a rectifier or an inverter and/or which is or comprises a processing unit, which is configured to determine the speed or an item of information dependent on the speed.

16. A device, in particular a motor vehicle, comprising an electronically commutated electric motor, in particular an electric motor of a fan, and a processing unit, wherein the processing unit is configured to determine the speed of the electric motor wherein a speed of the electronically commutated electric motor is determined by current measured values acquired at multiple points in time, which describe an amperage of a drive current supplied to the electric motor, after which a speed of the electric motor is determined as a function of the acquired current measured values.

17. The device as claimed in claim 16, wherein the electric motor drives the fan, wherein the device comprises at least one component cooled by the fan, which is a DC/DC converter or a rectifier or an inverter and/or which comprises the processing unit.

18. The device as claimed in claim 16, wherein the processing unit is configured to provide an item of diagnostic information to a diagnostic unit of the device or a device-external diagnostic unit, which relates to the functionality of the or a fan driven by the electric motor and which is dependent on the determined speed.

19. The method as claimed in claim 11, wherein the speed of the electric motor is further determined as a function of the points in time at which and/or the time interval at which current measured values are acquired, which reach or fall below the or a predetermined limiting value.

20. The method as claimed in claim 11, wherein the drive current is provided by a driver circuit, wherein the driver circuit provides an output for a measurement voltage proportional to the drive current, wherein voltage values of this measurement voltage are acquired as current measured values.

21. The method as claimed in claim 12, wherein the drive current is provided by a driver circuit, wherein the driver circuit provides an output for a measurement voltage proportional to the drive current, wherein voltage values of this measurement voltage are acquired as current measured values.

22. The method as claimed in claim 11, wherein the current measured values are acquired by an analog-to-digital converter.

23. The method as claimed in claim 12, wherein the current measured values are acquired by an analog-to-digital converter.

24. The method as claimed in claim 13, wherein the current measured values are acquired by an analog-to-digital converter.

25. The method as claimed in claim 11, wherein the electric motor drives a fan, which cools a component, which is a DC/DC converter or a rectifier or an inverter and/or which is or comprises a processing unit, which is configured to determine the speed or an item of information dependent on the speed.

26. The method as claimed in claim 12, wherein the electric motor drives a fan, which cools a component, which is a DC/DC converter or a rectifier or an inverter and/or which is or comprises a processing unit, which is configured to determine the speed or an item of information dependent on the speed.

27. The method as claimed in claim 13, wherein the electric motor drives a fan, which cools a component, which is a DC/DC converter or a rectifier or an inverter and/or which is or comprises a processing unit, which is configured to determine the speed or an item of information dependent on the speed.

28. The method as claimed in claim 14, wherein the electric motor drives a fan, which cools a component, which is a DC/DC converter or a rectifier or an inverter and/or which is or comprises a processing unit, which is configured to determine the speed or an item of information dependent on the speed.

29. The device as claimed in claim 17, wherein the processing unit is configured to provide an item of diagnostic information to a diagnostic unit of the device or a device-external diagnostic unit, which relates to the functionality of the or a fan driven by the electric motor and which is dependent on the determined speed.

Description

[0020] The following exemplary embodiments and the associated drawings show further advantages and details of the invention. In the schematic figures:

[0021] FIG. 1 shows an exemplary embodiment of a device according to the invention, namely a motor vehicle, which is configured, for example, to carry out an exemplary embodiment of the method according to the invention,

[0022] FIG. 2 shows a detail view of the device shown in FIG. 1, and

[0023] FIG. 3 shows the time curve of current measured values acquired in the scope of the exemplary embodiment of the method according to the invention.

[0024] FIG. 1 shows a device 1, in the specific example a motor vehicle, which comprises a DC/DC converter 2, to connect two vehicle networks 3, 4 using different DC voltages to one another. For example, the vehicle network 4 can be a 48 V network or a high-voltage network, which comprises a battery 5 and a starter generator 6 in the example shown. The vehicle network 3 can be a low-voltage network, for example a 12 V network, which comprises a further battery 7 and further low-voltage components, for example a lighting system 8, driver assistance systems 9, and a multimedia system 10. Due to the connection of the vehicle networks 3, 4 via the DC/DC converter 2, energy can be transported between these vehicle networks 3, 4, for example, to charge the battery 7 via the starter generator 6 or to start the motor vehicle using energy of the battery 7, to exchange energy between the batteries 5, 7, or the like.

[0025] Although DC/DC converters have gradually achieved very high efficiencies, it is typically necessary to actively cool corresponding components 12, thus the DC/DC converter 2. For this purpose, the motor vehicle comprises a fan 11, which is also powered by the DC/DC converter 2.

[0026] A failure or a blockage of the fan 11 is to be recognized, for example, to avoid overheating in this case by a corresponding adaptation of the operation of the DC/DC converter 2 or by a temporary prevention of the energy exchange between the vehicle networks 3, 4. For this purpose, a processing unit 13, which monitors the speed of an electric motor (not shown in FIG. 1) of the fan 11, is integrated into the component 12 to be cooled. The method used for this purpose and further components relevant in this regard are explained in more detail hereinafter with reference to FIGS. 2 and 3.

[0027] As schematically shown in FIG. 2, the electric motor 14 of the fan 11 is supplied via the DC/DC converter 2, which is thus used as a driver circuit 15 for the electric motor 14. It is known that corresponding DC/DC converters 2 or driver circuits 15 can have outputs 16, which provide a voltage which is proportional to a current provided by the DC/DC converter 2 or the driver circuits 15. This can be achieved, for example, by a shunt resistor connected in series, over which a corresponding voltage drops. However, an RC element is preferably connected in parallel to an active coil of the DC/DC converter 2, at the capacitor of which a corresponding voltage drops. This procedure is known in principle in the prior art and will therefore not be explained in more detail. Such an RC element can be integrated into the driver circuit 15 or formed separately from it. By corresponding selection of the resistance or capacitance value, the high-frequency switching frequencies of the DC/DC converter 2 can be filtered, wherein at the same time changes of the current due to the electronic commutation of the electric motor 14, during which the current flow to the motor is briefly interrupted in each case, can be recognized.

[0028] The voltages are supplied to an analog to digital converter 17 to acquire digital current measured values. As shown in FIG. 3, the sampling rate of the analog-to-digital converter 17 is selected so that the time interval between the acquisition of two successive current measured values 18, 19 is significantly less than the time interval of two expected commutations of the electric motor 14 of the fan 11. In this way, the time curve 21 of the current measured values 18, 19 can be acquired with sufficient time resolution that it is recognized that the current 22 drops essentially to zero at the points in time at which a commutation takes place.

[0029] To evaluate the time curve 21 of the current measured values 18, 19 and determine a speed or commutation frequency of the electric motor, the current measured values 18, 19 are compared to a limiting value 23 to recognize which of the current measured values 18, 19 are below the limiting value 23 or at which points in time 24 the current 22 falls below the limiting value 23. The time interval 20 between two such points in time 24 can be determined, for example, in that an internal counter of the processing unit 13 is read out and reset each time the measured values fall below the limiting value 23. Therefore, the time interval 20 between two times the measured values fall below the limiting value 23 and thus the time interval between two commutations of the electric motor can be determined. Since it is known how many commutations of the electric motor take place during each revolution of the electric motor, the speed of the electric motor can be calculated easily from the reciprocal of this time interval 20.

[0030] The described determination of the speed can be implemented, for example, by a processor 26 of the processing unit 13, which executes a corresponding program stored in a memory 27.

[0031] As explained at the outset, the described speed acquisition is primarily to be used to recognize whether the fan 11 is blocked. The processing unit 13 is therefore configured in particular to recognize whether a determined speed falls below a predetermined limiting value or remains below this limiting value for a predetermined time interval. An item of information in this regard can be provided to a separate diagnostic unit 25 to enable an onboard diagnosis in the device 1, thus in the motor vehicle. This can be used exclusively to output corresponding notifications, for example, to a user of the motor vehicle, to write corresponding items of information in an error memory, or the like. However, it is also possible to adapt the operation of the DC/DC converter 2 as a function of this diagnostic information, for example, to restrict or completely block an energy transfer between the vehicle networks 3, 4 if it is recognized that the fan 11 is blocked or excessively low speeds are acquired for other reasons.