Method and device for monitoring the torque of an electric motor

Abstract

Method (40) for monitoring the torque of an electric motor (10), in particular for use in a motor vehicle, wherein the electric motor (10) is supplied with multiphase electric current (IS1, IS2, IS3), wherein a first torque value (M2) of the torque delivered by the electric motor (10) is determined on the basis of an electrical power input by the electric motor (10) and a measured rotational speed (n) of a rotor of the electric motor (10) (58), characterized in that a second torque value (M1) is determined on the basis of at least one measured phase current (IS1, IS2, IS3) and a rotational position of the rotor and the two determined torque values ​​(M1, M2) are compared with each other for plausibility testing (60), wherein a torque result (ML1) is determined by averaging the two determined torque values ​​(60), provided that there is a difference between the two torque values ​​(M1,M2) does not exceed a predefined value, and wherein the torque result (ML1) is compared with an actual torque (ML2, MP) of the electric machine (10) (72) calculated on the basis of a model of the electric machine (10) (74).,

Description

[0001] The present invention relates to a method for monitoring the torque of an electric motor, in particular for use in a motor vehicle, wherein the electric motor is supplied with multiphase electric current, wherein a first torque value of the torque delivered by the electric motor is determined on the basis of an electrical power absorbed by the electric motor and a detected rotational speed of the rotor of the electric motor.

[0002] According to a second aspect, the present invention relates to a method for monitoring the torque of an electric motor, in particular for use in a motor vehicle, wherein the electric motor is supplied with multiphase electric current, wherein below a predefined rotational speed of a rotor of the electric motor a first torque value of the torque delivered by the electric motor is determined on the basis of an amplitude of at least one phase current.

[0003] The present invention further relates to a device for monitoring a torque of an electric motor, comprising current sensing means to detect at least one phase current of the electric motor, rotor sensing means to detect a rotational position and / or a rotational speed of a rotor of the electric motor, and a control unit configured to carry out the aforementioned method.

[0004] Finally, the present invention relates to a motor vehicle drive train comprising at least one electric machine for providing drive power and a device of the type mentioned above. State of the art

[0005] In the field of electric motor technology, it is common practice to check the condition of an electric motor and determine an output variable, such as the torque delivered by the electric motor, and compare it with a target value. By comparing the actual state with the target state, the operation of the electric machine can be monitored in order to react appropriately if the actual state deviates from the target state.

[0006] The torque delivered by an electric motor is typically calculated based on the electrical power drawn from a DC voltage source and the rotational speed of the motor's rotor. The electrical power drawn from the DC voltage source is calculated using the supplied voltage and an electrical current measured by a DC current sensor.

[0007] From DE 10 2008 001 714 A1 a method is known in which the electrical power consumed by the electric motor or a transverse current causing the torque is detected and linked to a characteristic curve of a speed of the electric motor in order to determine the current torque and compare it with a target value.

[0008] Further methods for monitoring torque are known from the patent applications DE 101 00 565 A1 and US 2009 / 0 066 281 A1.

[0009] A disadvantage of the methods known from the prior art is that the technical effort required to determine the absorbed electrical power is considerable due to the DC sensor, and measurement errors in determining the delivered torque cannot be detected or taken into account.

[0010] It is therefore the object of the present invention to provide a method and a device for monitoring the torque of an electric machine, which offers increased safety with minimal technical effort. Disclosure of the invention

[0011] This problem is solved according to the invention by a method with the features of claim 1. It is provided that a second torque value is determined on the basis of at least one measured phase current and a rotational position of the rotor, and the two determined torque values ​​are compared with each other for plausibility testing.

[0012] This problem is further solved by the device mentioned at the outset, which is designed to carry out the method according to the invention.

[0013] Finally, the above problem is solved by a motor vehicle powertrain comprising an electric machine to provide drive power and a device of the type mentioned above to monitor the torque of the electric machine. Advantages of the invention

[0014] The present invention provides a method that offers greater reliability in monitoring the delivered torque through two redundant calculation paths. This increased reliability is ensured because a simple error, for example in a rotor position signal or a rotor speed signal, does not lead to a systematic torque error, since a second independent calculation path for the torque is provided and such an error can be detected by the plausibility check of both independent paths. In particular, by determining the torque value at low speeds based on a phase current amplitude, the method is especially precise for different speed ranges.

[0015] It is particularly advantageous if the power input above a predefined rotational speed is determined on the basis of the measured phase currents and measured phase voltages.

[0016] This allows the power input to be measured and determined easily and precisely at the electrical machine.

[0017] It is still preferred to determine the power loss of the electric motor and take it into account when determining the power input.

[0018] This allows the torque of the electric machine to be calculated even more precisely for one of the paths.

[0019] It is still preferred to determine a difference in torque values ​​and generate an error signal and / or initiate an error response if the difference exceeds a predefined value.

[0020] This provides a simple way to perform plausibility checks that can be carried out with minimal technical effort.

[0021] According to the invention, a torque result is determined by averaging the two torque values, provided that the difference between the two torque values ​​does not exceed a predefined value.

[0022] This allows for a result to be determined that shows only very minor deviations from the actual torque provided, even with slight deviations in the specified torque values.

[0023] Furthermore, the torque result according to the invention is compared with an actual torque of the electric machine, which is calculated on the basis of a model of the electric machine.

[0024] This allows for a further plausibility check to be carried out based on a model that can take into account different parameters and measured values ​​of the electrical machine, thereby achieving increased safety through the additional plausibility check.

[0025] It is still advantageous if the model of the electric machine takes the temperature of the rotor into account.

[0026] This allows the determined actual torque to be calculated even more precisely based on the model, since the temperature of the rotor influences the delivered torque.

[0027] It is particularly advantageous if the actual torque is compared with at least one predefined or determined limit value for the torque of the electric machine.

[0028] In this way, predefined critical states of the electrical machine can be prevented, thereby increasing safety in general.

[0029] It is still generally preferred if the electric current in all phase strands of the electric machine is detected by means of a phase current sensor in each strand.

[0030] This allows the precision of the torque determination and thus the safety to be further increased, as the independent phase current sensors provide additional redundancy.

[0031] It is understood that the features, properties and advantages of the method according to the invention also apply accordingly to the device according to the invention. Brief description of the drawings Fig. Figure 1 shows in schematic form the structure of an electric machine; Fig. Figure 2 shows in schematic form the process of the inventive method for determining an output torque; and Fig. Figure 3 shows in schematic form the process of torque monitoring of the electric motor. Embodiments of the invention

[0032] In Fig. Figure 1 shows the schematic construction of an electric machine. The electric machine is in Fig. 1 is generally denoted by 10.

[0033] The electric machine 10 has three phase conductors 12, 14, 16 in which three phase currents IS1, IS2 and IS3 flow. The phase conductors 12, 14, 16 are connected to the respective excitation windings 18 of the electric machine 10. The excitation windings 18 are connected to each other in a star configuration, preferably without a neutral conductor.

[0034] The pathogen developments 18 are in Fig. Phase 1 is designated as Phase V, Phase U, and Phase W. Sensors 20, 22, and 24 are assigned to the phase conductors 12, 14, and 16. These sensors measure the phase currents IS1, IS2, and IS3, respectively, and each provides a corresponding current signal 26. Sensors 20, 22, and 24 are designed as ammeters. Alternatively, phase voltages in the phase conductors 12, 14, and 16 can be measured using voltmeters for control purposes.

[0035] Sensors 20, 22, and 24 are connected to a control unit (not shown), with the measured phase currents IS1, IS2, and IS3 being fed back to the control unit. Based on the current signals 26, the control unit provides a control signal to a power electronics unit (not shown) to control or regulate the electric machine 10. The phase currents IS1, IS2, and IS3 are preferably phase-shifted by 120° relative to each other.

[0036] In Fig. Figure 1 also shows phase voltages U12, U23, and U31, which drop between the phase conductors 12, 14, and 16. The phase voltages U12, U23, and U31 are detected by voltage sensors 28, 30, and 32, which are arranged between the phase conductors. Based on the phase currents IS1, IS2, and IS3, the phase voltages U12, U23, and U31, and a rotor position and / or rotor speed of the [unclear] Fig. The torque output of the electric machine 10 can be calculated using the rotor of the electric machine 10 (not shown). For precise regulation and control of the output torque, it is necessary to know the phase currents IS1, IS2, and IS3, the phase voltages U12, U23, and U31, the rotor position, and the rotor speed. These quantities can be measured using sensors 20, 22, 24, 28, 30, and 32, and the torque can then be determined.

[0037] In Fig. Figure 2 shows the process for determining the torque delivered by the electric machine 10 schematically and is generally designated by 40.

[0038] The electric machine 10 and its associated components are in Fig. Figure 2 is schematically indicated and labeled 42. To determine the torque of the electric machine 10, the three phase currents IS1, IS2, IS3 are measured using sensors 20, 22, 24, as shown in Figure 44. Furthermore, the position of the rotor of the electric machine 10 is recorded using a rotor sensor, as shown in Figure 46. The measured phase currents IS1, IS2, IS3 and the measured rotor position are used in a first calculation path to calculate the torque of the electric machine 10, as shown in Figure 48. The calculation in the first path, Figure 48, determines a torque value M1, which is then provided for plausibility checking.

[0039] The torque value M1 is calculated from the three phase currents IS1, IS2, IS3 and the rotor position according to the formula M1=I_AMP*A(phi) calculated where I_AMP is the amplitude of the phase current vector and A(phi) is a factor that depends on the rotor position. To achieve high safety integrity, all three phases U, V, W are each measured with a separate phase current sensor 20, 22, 24. Furthermore, by checking the sum of all phase currents, a simple fault in one of the three sensors can be detected. The torque value M1 calculated in this way is provided for further verification, as described in Fig. 2 is shown.

[0040] Furthermore, the phase voltages U12, U23, and U31 are measured using voltage sensors 28, 30, and 32, as shown in Figure 50. The rotor speed is also measured, as shown in Figure 52. Finally, the control signal of the electric machine by the inverter is measured, as shown in Figure 54, and the DC voltage of the voltage source is measured, as shown in Figure 56. The measured DC voltage is fed back to step 50 to determine the phase voltages. In a second calculation path, a torque value M2 is then calculated based on the phase voltages U12, U23, and U31, the rotor speed, and, in particular, the control signal from the inverter, as shown in Figure 58.

[0041] The torque value M2 is calculated at 58 using the formula M2=(U*I−PV) / n where U is the phase voltage, I the phase current, PV the power loss of the electric machine 10, and n the rotor speed. If the speed n is sufficiently high, i.e., above a predefined value, the power output is calculated by the product of phase currents IS1, IS2, IS3 and phase voltages U12, U23, U31. If the speed n is low, i.e., less than a predetermined value, calculating the torque value M2 via the product of phase currents IS1, IS2, IS3 and phase voltages U12, U23, U31 becomes inaccurate. In this case, the torque value M2 is calculated using the formula M2=I_AMP*B where I _ AMP is the amplitude of the phase current vector and B is a factor that does not take into account the position of the rotor.

[0042] For very low rotational speeds n near zero and equal to zero, it is not possible to calculate the torque M2, since the difference between the output voltage and the loss voltage is always equal to zero, regardless of the motor torque.

[0043] The torque values ​​M1 and M2 are compared at 60°C and subjected to a plausibility check. This plausibility check is typically performed by calculating the difference between the torque values ​​M1 and M2. If the difference exceeds a predefined value, an error signal is generated and / or an error response is initiated. This error response could, for example, involve switching the output stages or the inverter controlling the electric machine 10 to a safe state. If the difference is less than a predefined value, an average value is calculated from the torque values ​​M1 and M2, and the resulting torque value ML1 is made available for further processing.

[0044] Calculation paths 48 and 58 for calculating the values ​​M1 and M2 are based on simple calculations and are therefore very robust and reliable. Many influencing factors of the actual torque are neglected, such as the rotor temperature.

[0045] However, by comparing the two torque values ​​M1 and M2 determined via different paths, a high degree of certainty is given for determining the torque result ML1.

[0046] In Fig. Figure 3 is a schematic flowchart for monitoring the torque of the electric machine 10, generally denoted by 70. The averaged torque result ML1, which is obtained at 60 from Fig.The torque value determined in step 2 is compared with an actual torque signal ML2 in step 72 and subjected to a plausibility check. The actual torque signal ML2 is calculated using a machine model, as shown in step 74. The machine model takes into account all possible influencing factors of the actual torque, such as the rotor temperature. The resulting actual torque signal ML2 provides a very accurate value of the actual delivered torque. While the machine model offers very high accuracy, it is not protected by complex safety mechanisms such as cyclic RAM / ROM tests, sequence control, variable duplication, etc. If the plausibility check in step 72 yields a positive result, meaning that the deviation between the torque result ML1 and the actual torque signal ML2 is small (i.e., less than a predefined value), the actual torque signal ML2 is used for further calculations and provided as the actual torque MP for a further check in step 78.To check the delivered torque, permissible torque limits are calculated at 76. These torque limits are preferably a permissible maximum and a permissible minimum of the delivered torque. These torque limits are provided to a torque comparison unit 78, which checks whether the actual torque MP is within the permissible limits determined at 76. If the actual torque MP is within or outside the calculated limits, a corresponding output signal 80 is provided by the torque comparison unit 78. If the torque MP is outside the calculated limits, the electric machine 10 can, for example, be stopped or its power output reduced accordingly.

Claims

[1] Method (40) for monitoring the torque of an electric motor (10), in particular for use in a motor vehicle, wherein the electric motor (10) is supplied with multiphase electric current (IS1, IS2, IS3), wherein a first torque value (M2) of the torque delivered by the electric motor (10) is determined on the basis of an electrical power input by the electric motor (10) and a detected rotational speed (n) of a rotor of the electric motor (10) (58), characterized by, that a second torque value (M1) is determined on the basis of at least one measured phase current (IS1, IS2, IS3) and a rotational position of the rotor and the two determined torque values ​​(M1, M2) are compared with each other for plausibility testing (60), wherein a torque result (ML1) is determined by averaging the two determined torque values ​​(60), provided that a difference between the two torque values ​​(M1, M2) does not exceed a predefined value, and wherein the torque result (ML1) is compared with an actual torque (ML2, MP) of the electric machine (10) (72), which is calculated on the basis of a model of the electric machine (10) (74). [2] Method according to claim 1, wherein the power input above a predefined rotational speed is determined on the basis of the measured phase currents (IS1, IS2, IS3) and measured phase voltages (U12, U23, U31). [3] Method according to claim 1 or 2, wherein a power loss of the electric motor (10) is determined and taken into account when determining the power input. [4] Method (40) for monitoring the torque of an electric motor (10), in particular for use in a motor vehicle, wherein the electric motor (10) is supplied with multiphase electric current (IS1, IS2, IS3), wherein below a predefined rotational speed of a rotor of the electric motor a first torque value (M2) of the torque delivered by the electric motor (10) is determined on the basis of an amplitude of at least one phase current (IS1, IS2, IS3) (58), characterized by , that a second torque value (M1) is determined on the basis of at least one measured phase current (IS1, IS2, IS3) and a rotational position of the rotor and the two determined torque values ​​(M1, M2) are compared to each other for plausibility testing (60). [5] Method according to any one of claims 1 to 4, wherein a difference of the torque values ​​(M1, M2) is determined (60) and an error signal is generated and / or an error response is initiated if the difference exceeds a predefined value. [6] Method according to claim 1, wherein the model of the electric machine (10) takes into account a temperature of the rotor. [7] Method according to claim 1 or 6, wherein the actual torque (ML2, MP) is compared with at least one predefined or determined limit value for the torque of the electric machine (10) (78). [8] Method according to any one of claims 1 to 7, wherein the electric current (IS1, IS2, IS3) in all phase strands (12, 14, 16) of the electric machine (10) is detected by means of a phase current sensor (20, 22, 24) in each. [9] Device for monitoring the torque of an electric motor (10) comprising: - Current sensing means (20, 22, 24) to detect at least one phase current (IS1, IS2, IS3) of the electric motor (10), - Rotor sensing means to detect a rotational position and / or the rotational speed of a rotor of the electric motor (10), and - a control unit designed to execute the method according to any one of claims 1 to 8. [10] Motor vehicle powertrain comprising at least one electric machine (10) for providing drive power and comprising a device according to claim 9.

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