DETERMINATION OF A TEMPERATURE IN AN ELECTRICAL MACHINE

Abstract

Method for determining a temperature in an electrical machine (3), the method comprising the following steps: Determining a temperature-dependent output value (A0, A1) of a first temperature sensor (1) assigned to the electrical machine (3), which first temperature sensor has a characteristic curve with a plurality of characteristic curve branches (103, 104), each of which is assigned to a specific temperature range (113, 114) and links a value of a temperature (T0, T1, T2) to an output value (A0, A1) of the first temperature sensor (1); Determining a temperature-dependent output value of a second temperature sensor (2) assigned to the electrical machine (3); Determining a temperature range of the temperature ranges (113, 114) for the characteristic curve branches (103, 104) of the first temperature sensor (1), in which a temperature lies which corresponds to the output value of the second temperature sensor (2); and Determining a temperature (T0, T1, T2) in the electrical machine (3) from the determined output value of the first temperature sensor (A0, A1) and the characteristic curve branch (103, 104) which corresponds to the temperature range (113, 114) determined in the previous step.

Description

[0001] The invention relates to a method and corresponding system for determining a temperature in an electrical machine.

[0002] Determining the temperature in a technical system or of certain components of a technical system is often necessary to ensure the reliable functioning of the respective technical system. This applies, for example, to the automotive sector, although the invention is not intended to be limited to this.

[0003] German patent application DE 101 55 459 A1 concerns the determination of the temperature of a clutch in a motor vehicle. For this purpose, the temperature in the motor vehicle's drive motor is used, and the energy input into the clutch is calculated from the torque and speed. Frictional energy input into a clutch and the determination of the clutch temperature are also discussed in DE 196 02 006 A1.

[0004] According to the German patent application DE 101 55 462 A1, temperature monitoring is used to detect an overload of a drive unit.

[0005] German patent application DE 10 2013 201 835 A1 relates to the temperature detection of a stator winding of an electrical machine using a temperature sensor with connecting conductors. The application discusses the routing of the connecting conductors.

[0006] The German patent application DE 10 2014 205 121 A1 discloses the determination of a temperature of a clutch of a motor vehicle from the time between the decommissioning and the recommissioning of a control unit.

[0007] German patent application DE 10 2015 214 624 A1 discloses a method for initializing a temperature model of a clutch system of a motor vehicle. A starting temperature is determined depending on the vehicle's idle time. A similar approach can be found in DE 10 2018 119 248 A1.

[0008] The German patent application DE 10 2016 215 590 A1 relates to a method for determining an actuator travel of a hydraulic clutch actuator, wherein the actuator travel is changed depending on a temperature of the clutch actuator.

[0009] German patent application DE 10 2018 116 889 A1 relates to an arrangement for detecting the temperature of a stator winding of an electrical machine using a temperature sensor. To ensure a reliable thermal connection between the temperature sensor and the stator winding, the temperature sensor is attached to a fastening element with two spring struts.

[0010] The German patent application DE 10 2019 114 235 A1 relates to a method for initializing a temperature model of a friction clutch of a hybrid drive train of a motor vehicle with an electric machine having a stator and a rotor and a friction clutch arranged radially inside the latter, wherein an initial value of the friction clutch is determined after a restart depending on the temperature of the electric machine and is used as the basis for the temperature model.

[0011] In addition to the model-based approaches to temperature determination, which are thus limited by the quality of the respective model, there is of course the possibility of directly measuring the temperature, for which the above-mentioned state of the art also contains examples.

[0012] Thermistors, particularly NTC thermistors, are often used to measure temperature. The characteristic curve of these thermistors, which indicates an output value, usually a voltage, as a function of temperature, decreases with increasing temperature, and the slope of the characteristic curve also decreases with increasing temperature. This means, however, that the accuracy of temperature determination from the output value of such a thermistor decreases with increasing temperature, since the temperature change associated with a given change in the output value increases with increasing temperature. It therefore becomes more difficult to resolve small temperature changes at higher temperatures. To solve this problem, it is known to use thermistors in circuits that switch at certain temperature values, thus providing a steeper characteristic curve.In other words, such a known circuit transforms the simple characteristic curve of a thermistor into a characteristic curve with multiple characteristic branches. Each characteristic branch is assigned to a specific temperature range, and in each temperature range, a characteristic curve—namely, the respective characteristic branch—with a sufficient gradient for temperature determination is available. Which gradient is considered sufficient in each case depends on the specific accuracy requirements for the temperature measurement.

[0013] The problem with this approach, however, is that an output value from a temperature sensor with a circuit of the type just mentioned can correspond to more than one temperature value. This is always the case when the output value in question appears as an output value in more than one characteristic curve branch. While it may then be possible to detect temperature changes with sufficient accuracy, it is impossible to determine the temperature at which the temperature sensor is operating.

[0014] For further prior art, reference is made to EP 3 388 804 A1, AT 29 069 E, DE 10 2016 105 506 A1 and DE 10 2016 200 344 A1.

[0015] It is therefore an object of the invention to provide a method for temperature measurement and an associated system in which the problem of ambiguity of output values ​​of a temperature sensor described above is avoided.

[0016] This object is achieved by a method according to claim 1, and correspondingly by a system according to claim 4.

[0017] The method according to the invention relates to the determination of a temperature in an electrical machine, for example in an electrical machine of a motor vehicle. According to the method, a temperature-dependent output value of a first temperature sensor is determined. The first temperature sensor is assigned to the electrical machine and has a characteristic curve with a plurality of characteristic curve branches, wherein each characteristic curve branch is assigned to a specific temperature range. Each characteristic curve branch links a temperature value with an output value of the first temperature sensor. The assignment of the first temperature sensor to the electrical machine means that the first temperature sensor is in thermal contact with the electrical machine in order to ultimately measure a temperature of the electrical machine.

[0018] Furthermore, a temperature-dependent output value of a second temperature sensor assigned to the electric machine is determined. The assignment of the second temperature sensor to the electric machine means that the second temperature sensor is in thermal contact with the electric machine in order to ultimately measure a temperature of the electric machine. The output value of the second temperature sensor serves to determine a temperature range of the temperature ranges for the characteristic curve branches of the first temperature sensor, within which temperature lies a temperature corresponding to the output value of the second temperature sensor. Determining this temperature range implies selecting the characteristic curve branch corresponding to the temperature range. A temperature of the electric machine is then unambiguously determined from the determined output value of the first temperature sensor and the characteristic curve branch selected in this way.

[0019] The ambiguity of an output value of the first temperature sensor, which exists according to the state of the art, is eliminated by including the output value of the second temperature sensor and thereby selecting a temperature range and thus a characteristic curve branch. It should be noted that a lower accuracy is sufficient for the temperature determination performed with the second temperature sensor to select the temperature range than is desired for the temperature measurement with the first temperature sensor.

[0020] The method is generally relevant for temperature measurements, but especially for “initial” temperature measurements, such as when starting up a technical system, since no information, such as from a previous temperature history, is available to eliminate the ambiguity.

[0021] The method is particularly applicable to temperature sensors in which the gradient of each characteristic curve branch decreases with increasing temperature. Thus, the method is applicable to temperature sensors based on a thermistor, which comprise a circuit as mentioned above, which converts the simple characteristic curve of the thermistor into a characteristic curve with multiple characteristic curve branches of the temperature sensor. Such a temperature sensor would be the first temperature sensor within the meaning of this application.

[0022] The system according to the invention comprises an electric machine, a first temperature sensor, and a second temperature sensor assigned to the electric machine. The first temperature sensor has a characteristic curve with a plurality of characteristic curve branches, each characteristic curve branch being assigned to a specific temperature range. Each characteristic curve branch links a temperature value to an output value of the first temperature sensor.

[0023] The system further comprises an evaluation unit configured to perform the method described above. For this purpose, the evaluation unit has, for example, one or more processors and a memory in which instructions for the processors for performing the method are stored in the form of program instructions, as well as parameters for the method. The evaluation unit can be implemented as a component of a more comprehensive control device for the electrical machine and can further utilize one or more processors and memories of this control device and can also be implemented entirely as software in such a control device.

[0024] The invention and its advantages are explained in more detail below with reference to the attached drawings. Fig. 1 shows a characteristic curve with two characteristic branches. Fig. 2 shows a system according to the invention.

[0025] The figures merely show exemplary embodiments of the invention; in no way should the figures be construed as limiting the invention to the exemplary embodiments shown.

[0026] Fig. 1 shows a schematic diagram 100. The abscissa 101 represents the temperature T, and the ordinate 102 represents an output value A of the first temperature sensor. Diagram 100 shows a first characteristic branch 103 and a second characteristic branch 104. At a specific temperature U, switching occurs between the characteristic branches 103 and 104; the further course of the characteristic branch 103 at temperatures greater than U is shown in dashed lines; this further course is not used in the temperature determination. Accordingly, the characteristic branch 103 belongs to a temperature range 113 of temperatures less than U, and the characteristic branch 104 belongs to a temperature range 114 of temperatures greater than U.

[0027] As can be seen from the diagram, an output value A0 corresponds to a unique temperature value T0, since the output value A0 only occurs on characteristic branch 103. The output value A1, on the other hand, corresponds to two temperature values, T1 and T2, since the output value A1 occurs on both characteristic branch 103 and characteristic branch 104. Without knowing which of the characteristic branches 103 and 104 is to be applied, and thus without knowing which of the temperature ranges 113 and 114 is currently valid, it is not possible to determine which of the temperature values ​​T1 and T2 is the correct one for the output value A1 of the first temperature sensor. According to the method according to the invention, an output value from a second temperature sensor, i.e. an independent second temperature measurement, is used to make a decision between the temperature ranges 113 and 114.Once the temperature range has been determined, it is also determined which of the characteristic curve branches 103 and 104 is the valid one. Subsequently, a decision can be made between the two options T1 and T2 for the initial value A1, thus unambiguously determining the temperature to be measured.

[0028] Just as a concrete, but in no way limiting, example, temperature ranges 113 and 114 together could cover a range from -50°C to 250°C, with switching occurring at 80°C.

[0029] Furthermore, it should be noted that the invention is not limited to the number of characteristic curve branches of the first temperature sensor being two. The invention also encompasses embodiments with more than two characteristic curve branches, each with an associated temperature range, of the first temperature sensor. The respective temperature range, and thus the respective valid characteristic curve branch, is determined via a temperature measurement with the second temperature sensor.

[0030] Fig. 2 shows an embodiment of a system 10 according to the invention with an electric machine 3, a first temperature sensor 1 and a second temperature sensor 2. The first temperature sensor 1 has a characteristic curve with a plurality of characteristic curve branches, as Fig.1 and in the general description of the invention. First temperature sensor 1 and second temperature sensor 2 are assigned to the electrical machine 3 in order to measure a temperature of the electrical machine 3, that is to say, more specifically, in order to generate a temperature-dependent output value. The output values ​​of the temperature sensors 1 and 2 are transmitted to an evaluation unit 4. The evaluation unit 4 has a processor 41 and a memory 42. Program instructions are stored in the memory 42 which, when executed, cause the processor 41 to carry out the inventive method described herein in at least one of its embodiments and, for this purpose, to control the temperature sensors 1 and 2 accordingly, for example, to retrieve the output values ​​of the temperature sensors 1 and 2.In addition, the memory 42 contains parameters for carrying out the method, such as the course of the characteristic curve branches and the assigned temperature ranges for the first temperature sensor 1. List of reference symbols 1 first temperature sensor 2 second temperature sensor 3 electric machine 4 Evaluation unit 10 systems 41 processor 42 storage 100 diagram 101 Abscissa 102 Ordinates 103 Characteristic curve branch 104 characteristic curve branch 113 Temperature range 114 Temperature range A0, A1 output value T0, T1, T2 temperature value U Switching temperature

Claims

[1] Method for determining a temperature in an electrical machine (3), the method comprising the following steps: Determining a temperature-dependent output value (A0, A1) of a first temperature sensor (1) assigned to the electrical machine (3), which first temperature sensor has a characteristic curve with a plurality of characteristic curve branches (103, 104), each of which is assigned to a specific temperature range (113, 114) and links a value of a temperature (T0, T1, T2) to an output value (A0, A1) of the first temperature sensor (1); Determining a temperature-dependent output value of a second temperature sensor (2) assigned to the electrical machine (3); Determining a temperature range of the temperature ranges (113, 114) for the characteristic curve branches (103, 104) of the first temperature sensor (1), in which a temperature lies which corresponds to the output value of the second temperature sensor (2); and Determining a temperature (T0, T1, T2) in the electrical machine (3) from the determined output value of the first temperature sensor (A0, A1) and the characteristic curve branch (103, 104) which corresponds to the temperature range (113, 114) determined in the previous step. [2] The method according to claim 1, wherein an amount of a slope of each characteristic branch (103, 104) decreases with increasing temperature. [3] Method according to claim 1 or 2, wherein the first temperature sensor (1) comprises a thermistor and a circuit which generates the plurality of characteristic curve branches (103, 104) from a temperature dependence of an electrical resistance of the thermistor. [4] System (10) comprising: an electrical machine (3); a first temperature sensor (1) assigned to the electric machine (3), which has a characteristic curve with a plurality of characteristic curve branches (103, 104), each of which is assigned to a specific temperature range (113, 114) and links a value of a temperature (T0, T1, T2) to an output value (A0, A1) of the first temperature sensor (1); a second temperature sensor (2) associated with the electric machine (3); and an evaluation unit (4) which carries out a method according to one of claims 1 to 3.

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