Determining the temperature in the motor

Abstract

The invention relates to determining the temperature in an electric motor (3) based on temperature-related output values ​​(A0, A1) of 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 (103, 104), wherein each characteristic curve branch (103, 104) is associated with a specific temperature range (113, 114). The output value of the second temperature sensor (2) is used to select the characteristic curve branch (103, 104); the output value (A0, A1) of the first temperature sensor (1) is used to determine the temperature (T0, T1, T2) according to the selected characteristic curve branch (103, 104).

Description

Technical Field

[0001] The invention relates to a method and a corresponding system for determining the temperature in an electric machine. Background Art

[0002] In order to ensure the reliable operation of the respective technical system, it is usually necessary to determine the temperature in the technical system or the temperature of certain components of the technical system. This applies, for example, to the field of motor vehicles, but the present invention is not limited thereto.

[0003] German patent application DE 101 55 459 A1 relates to determining the temperature of a clutch in a motor vehicle. For this purpose, the temperature in the drive motor of the motor vehicle is used and the energy input into the clutch is calculated from the torque and the rotational speed. DE 196 02 006 A1 also discusses the introduction of friction energy into the clutch and the determination of the temperature of the clutch.

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

[0005] German patent application DE 10 2013 201 835 A1 relates to detecting the temperature in a stator winding of an electric machine using a temperature sensor having connecting conductors. The application discusses the wiring of the connecting conductors.

[0006] German patent application DE 10 2014 205 121 A1 discloses determining the temperature of a clutch of a motor vehicle as a function of the time between deactivation and reactivation of a control device.

[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. The starting temperature is determined based on the idling time of the motor vehicle. A similar method can be found in DE 10 2018119 248 A1.

[0008] German patent application DE 10 2016 215 590 A1 relates to a method for determining an actuator stroke of a hydraulic clutch actuator, which actuator stroke changes as a function of the temperature of the clutch actuator.

[0009] German patent application DE 10 2018 116 889 A1 relates to a device for detecting the temperature of a stator winding of an electric machine with a temperature sensor. In order to ensure a reliable thermal connection between the temperature sensor and the stator winding, the temperature sensor is attached to a mounting element with two struts.

[0010] 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, the motor vehicle having an electric machine with a stator and a rotor and a friction clutch arranged radially within the electric machine, wherein an initial value of the friction clutch that depends on the temperature of the electric machine is determined after restarting and used as the basis for the temperature model.

[0011] Besides model-based methods of determining the temperature, which are therefore limited by the quality of the respective model, there are of course also possibilities for measuring the temperature directly, examples of which are also included in the above-mentioned prior art.

[0012] Thermistors, in particular NTC thermistors, are often used to measure temperature. The characteristic curves of these NTC thermistors, which indicate an output value, usually a voltage, according to the temperature, decrease as the temperature increases, and the magnitude of the gradient of the characteristic curve also decreases as the temperature increases. However, this means that the accuracy of the temperature determination according to the output value of such an NTC thermistor decreases as the temperature increases, because the temperature change associated with a given change in the output value increases as the temperature increases. Therefore, at higher temperatures, it becomes more difficult to resolve small temperature changes. In order to solve this problem, it is known to use NTC thermistors in circuits that switch at certain temperature values, so that a steeper characteristic curve can be obtained again. In other words, this known circuit has the effect of modifying the simple characteristic curve of the NTC thermistor into a characteristic curve with multiple characteristic curve branches. In this case, each characteristic curve branch is assigned to a specific temperature range, so that a characteristic curve with a sufficient gradient for determining the temperature, i.e. a corresponding characteristic curve branch, can be obtained in each temperature range. What kind of gradient is considered sufficient in each case depends on the corresponding accuracy requirements of the temperature measurement.

[0013] However, a problem with the described method is that more than one temperature value can be associated with an output value of a temperature sensor having a circuit of the type just mentioned. This always occurs if the output value in question appears as an output value in more than one characteristic curve branch. Temperature changes can then be detected with sufficient accuracy, but it is not possible to say at what temperature the temperature sensor is. Summary of the invention

[0014] It is therefore an object of the present invention to specify a method and an associated system for temperature measurement, wherein the problem of ambiguity in the output values ​​of a temperature sensor as just described is avoided.

[0015] This object is achieved by a method according to claim 1 and correspondingly by a system according to claim 4 .

[0016] The method according to the invention relates to determining the temperature in an electric machine, for example in an electric 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 electric machine and 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 relates a temperature value to an output value of the first temperature sensor. Assigning the first temperature sensor to the electric machine means that the first temperature sensor is in thermal contact with the electric machine, so as to ultimately measure the temperature of the electric machine.

[0017] A temperature-dependent output value of a second temperature sensor assigned to the motor is also determined. Assigning the second temperature sensor to the motor means that the second temperature sensor is in thermal contact with the motor in order to ultimately measure the temperature of the motor. The output value of the second temperature sensor is used to determine a temperature range in the temperature range of the characteristic curve branch for the first temperature sensor, in which there is a temperature corresponding to the output value of the second temperature sensor. The determination of this temperature range means the selection of the characteristic curve branch corresponding to this temperature range. The temperature of the motor is then uniquely determined based on the determined output value of the first temperature sensor and the characteristic curve branch selected in this way.

[0018] The ambiguity of the output value of the first temperature sensor present according to the prior art is eliminated by including the output value of the second temperature sensor and the resulting selection of the temperature range and the characteristic curve branch. It should be noted that for the temperature determination for selecting the temperature range with the second temperature sensor, a lower level of accuracy than that sought for the temperature measurement with the first temperature sensor is sufficient.

[0019] The method is generally relevant for temperature measurements, but in particular for "initial" temperature measurements, for example when starting up a technical system, since no information, for example from a previous temperature distribution, is available to eliminate ambiguities.

[0020] The method can be used in particular for a temperature sensor in which the magnitude of the gradient of each characteristic curve branch decreases with increasing temperature. Thus, the method can be used for a temperature sensor based on an NTC thermistor, which comprises the circuit mentioned at the beginning, which converts the simple characteristic curve of the NTC thermistor into a characteristic curve with a plurality of characteristic curve branches of the temperature sensor. Such a temperature sensor would be a first temperature sensor within the meaning of the present application.

[0021] The system according to the invention comprises an electric motor, a first temperature sensor assigned to the electric motor and a second temperature sensor. 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 relates a temperature value to an output value of the first temperature sensor.

[0022] The system further comprises an evaluation unit configured to perform the above method. For this purpose, the evaluation unit has, for example, one or more processors and a memory, in which instructions for the processor to perform the method are stored in the form of program instructions and parameters of the method. The evaluation unit can be implemented as a component of a more comprehensive control device for the motor and can also use one or more processors and memories of this control device and can also be fully implemented as software in such a control device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention and its advantages are described in more detail below with reference to the accompanying drawings.

[0024] Figure 1 A characteristic curve having two characteristic curve branches is shown.

[0025] Figure 2 A system according to the invention is shown.

[0026] The drawings illustrate only exemplary embodiments of the present invention and therefore should in no way be interpreted as limiting the present invention to the illustrated exemplary embodiments. DETAILED DESCRIPTION

[0027] Figure 1 A schematic diagram 100 is shown. The temperature T is shown on the x-axis 101 and the output value A of the first temperature sensor is shown on the y-axis 102. The diagram 100 shows a first characteristic curve branch 103 and a second characteristic curve branch 104. At a certain temperature U, a switch is made between the characteristic curve branches 103 and 104; the further progression of the characteristic curve branch 103 at temperatures greater than U is shown in dashed lines; this further progression is not used to determine the temperature. Therefore, the characteristic curve branch 103 belongs to a temperature range 113 with temperatures below U, and the characteristic curve branch 104 belongs to a temperature range 114 with temperatures above U.

[0028] As can be seen from the diagram, the only temperature value T0 belongs to the output value A0, since the output value A0 only occurs on the characteristic curve branch 103. On the other hand, the output value A1 is associated with two temperature values ​​T1 and T2, since the output value A1 occurs on both the characteristic curve branch 103 and the characteristic curve branch 104. Not knowing which of the characteristic curve branches 103 and 104 is to be used means not knowing which of the temperature ranges 113 and 114 is currently valid, and it is impossible to determine which of the temperature values ​​T1 and T2 is the correct temperature value for the output value A1 of the first temperature sensor. According to the method according to the invention, the output value from the second temperature sensor, i.e. the independent second temperature measurement result, is used in order to make a decision between the temperature ranges 113 and 114. Once the temperature range is determined, it is also determined which of the characteristic curve branches 103 and 104 is valid. Therefore, a decision can be made between the two options T1 and T2 for the output value A1, so that the temperature to be measured can be uniquely determined.

[0029] Merely as a specific but in no way limiting example, the temperature ranges 113 and 114 together may cover a range from -50°C to 250°C, while switching may occur at 80°C.

[0030] It should also be noted that the invention is not limited to a number of two characteristic curve branches of the first temperature sensor. The invention also includes embodiments with more than two characteristic curve branches of the first temperature sensor, each characteristic curve branch having an associated temperature range. The temperature range present in each case and therefore the characteristic curve branch effective in each case is determined by measuring the temperature with the second temperature sensor.

[0031] Figure 2 An exemplary embodiment of a system 10 according to the invention is shown, comprising 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, such as Figure 1 and as explained in the general description of the invention. A first temperature sensor 1 and a second temperature sensor 2 are associated with the motor 3 in order to measure the temperature of the motor 3, more specifically in order to generate a temperature-related output value in each case. 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 perform the method described herein according to the invention in at least one embodiment thereof and 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 also contains parameters for performing the method, such as the progression of the characteristic curve branch of the first temperature sensor 1 and the associated temperature range.

[0032] Reference numerals list

[0033] 1 First temperature sensor 2 Second temperature sensor 3 Electric machine 4 Evaluation unit 10 System 41 Processor 42 Memory 100 Graph 101 X-axis 102 Y-axis 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. A method for determining the temperature in an electric machine (3), the method comprising at least the following steps: Determining a temperature-dependent output value (A0, A1) of a first temperature sensor (1) assigned to the electric machine (3), the first temperature sensor (1) having a characteristic curve with a plurality of characteristic curve branches (103, 104), each characteristic curve branch (103, 104) being assigned to a specific temperature range (113, 114), and each characteristic curve branch (103, 104) relating a temperature value (T0, T1, T2) to an output value (A0, A1) of the first temperature sensor (1); determining a temperature-related output value of a second temperature sensor (2) assigned to the motor (3); determining a temperature range in the temperature ranges (113, 114) of the characteristic curve branch (103, 104) for the first temperature sensor (1), in which a temperature corresponding to an output value of the second temperature sensor (2) exists; and The temperature (T0, T1, T2) in the motor (3) is determined based on the determined output value (A0, A1) of the first temperature sensor and the characteristic curve branch (103, 104) corresponding to the temperature range (113, 114) determined in the previous step.

2. The method according to claim 1, wherein: The magnitude of the gradient in each characteristic curve branch (103, 104) decreases as the temperature increases.

3. The method according to claim 1 or 2, wherein: The first temperature sensor (1) comprises an NTC thermistor and a circuit configured to generate the plurality of characteristic curve branches (103, 104) according to the temperature dependency of the resistance of the NTC thermistor.

4. A system (10), comprising: Motor (3); a first temperature sensor (1), which is assigned to the electric motor (3) and has a characteristic curve with a plurality of characteristic curve branches (103, 104), each characteristic curve branch (103, 104) being assigned to a specific temperature range (113, 114), and each characteristic branch (103, 104) relating a temperature value (T0, T1, T2) to an output value (A0, A1) of the first temperature sensor (1); a second temperature sensor (2), which is assigned to the motor (3); Features An evaluation unit (4) configured to perform a method according to any one of claims 1 to 3.

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