Optical temperature sensor head, temperature sensor device with temperature sensor head, and electric machine

Abstract

The invention proposes an optical temperature sensor head, which comprises an optical fiber and a sensor material optically connected to the free end of the optical fiber. The free end of the optical fiber has an overmolding made of a plastic material, which engages on the free end of the optical fiber and forms a protection body. In the protection body a transparent window is arranged. The window permits an optical connection to the free end of the optical fiber. Luminescent radiation from the sensor material can enter into the optical fiber. The effect of the protection body is that the temperature sensor head is mechanically stable and insensitive to environmental influences. The invention also proposes a temperature sensor device having such a temperature sensor head. Finally, the invention proposes an electrical machine, which has a winding with winding wires, which are connected to the proposed temperature sensor head.

Description

TECHNICAL FIELD

[0001] The present invention relates to an optical temperature sensor head and a device for optical temperature measurement, in which the temperature is measured, in particular by luminescence measurement. The invention also relates to an electrical machine having a winding, the temperature of which is measured using a temperature measurement device according to the invention. BACKGROUND

[0002] In many applications, precise temperature measurement is required. Of particular interest in the present case are applications in harsh operating conditions or at locations where high magnetic fields are present.

[0003] Currently, thermoelectric elements or temperature-dependent resistors are mainly used for measuring temperatures in vehicles, for example for the measurement of coolant temperature. The temperature sensors used for this purpose require many components for this purpose, such as Figure 4 are shown. The temperature sensor, which is designated as a whole by the reference 401, has a housing 402, which accommodates an electrical measuring element 403, which is housed in an electrically insulating holder 404. The electrical measuring element 403 has two connections 406A, 406B, which are connected to the conductors 408A, 408B of an electrical cable 409 at contact locations 407A, 407B. The housing 402 is filled with a heat transfer medium, for example a thermoplastic filler, in order to achieve a good thermal coupling of the measuring element 403 and to shorten its reaction time. In the long term, a temperature sensor of this construction has the risk of failing due to the different coefficients of thermal expansion of the materials used, in particular when a plurality of temperature cycles occur. In addition, elements that are crucial for the service life are encapsulated and cannot be repaired. In the presence of a magnetic field, the temperature sensor must also be appropriately electromagnetically shielded, since otherwise measurement errors can occur due to induced voltages or induced currents.

[0004] Due to the presence of at least two electrical connection lines and the necessary electromagnetic shielding in many cases, the construction of the temperature sensor 401 is relatively large and therefore requires a contact surface of at least 3 mm in diameter on the object whose temperature is to be measured.

[0005] These properties of conventional temperature sensors are disadvantageous when measuring the temperature in electrical machines, for example electric drive machines or electric generators, since there is usually not enough space there and at the same time a high magnetic field is present.

[0006] A solution is provided by optical temperature measurement, which is not based on electrical signals bound to the line, but on temperature-dependent luminescent radiation emitted by a sensor material, which is excited beforehand by light pulses from a light-emitting diode. A temperature measurement device suitable for this purpose is disclosed, for example, in US 4 988 212. Specifically, two different methods are proposed in this document. According to the first method, the intensities of the emitted luminescent radiation in two different wavelength ranges are measured, and the temperature of the sensor material, which emits the luminescent radiation and is in thermal contact with the object whose temperature is to be measured, is determined from the intensity ratio. According to the second method, the sensor material is likewise excited with light pulses, and the decay time or lifetime of the luminescent radiation is then measured. The intensity of the luminescent radiation decreases over time according to the following equation:

[0007] I(t) = I0x exp(-t / τ), wherein

[0008] I(t) is the time-dependent intensity of the luminescent radiation; I0is the initial intensity of the luminescent radiation; and τ is the decay time or luminescence lifetime.

[0009] Figure 5A The decrease in the intensity of the luminescent radiation over time is shown, whereas Figure 5B the lifetime determined from the decay of the luminescent radiation is shown as a function of the temperature. In fact, the temperature is measured by initially determining the lifetime of the luminescent radiation and then determining the temperature on the basis of stored data reflecting the relationship between the lifetime and the temperature. Figure 5B

[0010] The temperature measurement device and the temperature sensor disclosed in US 4 988 212 are not very suitable for automotive applications due to their construction.

[0011] It is therefore an object of the present invention to provide a temperature measurement head and a temperature measurement device for overcoming or at least addressing one or more of the problems mentioned in the introduction. SUMMARY

[0012] To achieve this object, according to a first aspect, the present invention proposes a temperature measurement head, which is part of a temperature measurement device, which corresponds to a second aspect of the present invention.

[0013] ​According to a first aspect of the application, an optical temperature sensor head is proposed, which comprises an optical fiber and a sensor material optically connected to the free end of the optical fiber. The free end of the optical fiber has an overmolding made of a plastic material, which engages on the free end of the optical fiber and forms a protection body. In the protection body a transparent window is arranged. The window permits an optical connection to the free end of the optical fiber. Emission radiation from the sensor material can enter into the optical fiber. In another embodiment, the sensor material extends through the window into the protection body. In both embodiments, the protection body serves to make the temperature sensor head mechanically stable and insensitive to environmental influences.

[0014] In a suitable embodiment, the optical fiber is a polymer optical fiber (POF). POFs are easier to produce, lighter in weight, flexible and can be connected to each other by conventional plug connections than glass fibers.

[0015] In an advantageous development, the sensor material is a crystal arranged at the free end of the optical fiber. In this case, a ruby is particularly suitable as a crystal. In addition to a single crystal, a modified embodiment relates to a transparent adhesive material, in which small luminescent crystals, for example ruby crystals, are embedded.

[0016] A receptacle in the form of a recess can be provided at the free end of the polymer optical fiber, which receives the sensor material. The recess has the advantage that the sensor material is stably held at the free end of the optical fiber.

[0017] In some applications, it is advantageous if the sensor material protrudes beyond the overmolding. In this embodiment, the sensor material can be in direct contact with the surface whose temperature is to be measured.

[0018] In other applications, it is advantageous if the sensor material is in thermal contact with the object whose temperature is to be measured, and the free end of the optical fiber is at a distance from the sensor material, but is optically connected to the sensor material. In this embodiment, there is only an optical connection between the free end of the optical fiber and the sensor material. In this way, it is prevented that heat is conducted away from the measurement location by the optical fiber and a possible falsification of the temperature measurement is prevented.

[0019] In this case, it is advantageous if a converging lens is arranged on the free end of the optical fiber, which focuses the incident light into the optical fiber. If the sensor material is not placed directly on the free end of the optical fiber, a converging lens on the free end of the optical fiber has the advantage that more light is focused into the optical fiber. In principle, a higher intensity of the emission radiation simplifies the measurement of the temperature, which also improves the accuracy of the temperature measurement.

[0020] In embodiments where there is a space between the sensor material and the free end of the optical fiber, it is advantageous if the overmold encloses the space between the sensor material and the free end of the optical fiber or the converging lens. In this embodiment, the sensor material is located in the enclosed space and thus its optical properties are not adversely affected by dirt, moisture, and the like.

[0021] In a suitable development of the application, a cap containing the sensor material is arranged on the free end of the optical fiber. In some embodiments, it has proved to be suitable if the sensor material is distributed in the form of small crystals in a cap which is inserted onto the free end of the optical fiber. This embodiment is particularly advantageous if strong vibrations occur, since the sensor material enclosed in the cap cannot detach from the optical fiber or from the surface whose temperature is to be measured.

[0022] In this development, suitably the overmold also at least partially encloses the cap with the sensor material. In this way, the cap is held by the overmold. At the same time, the transition between the optical fiber and the cap is sealed.

[0023] In modified embodiments, the sensor material can be applied to the object whose temperature is to be measured in the form of a layer. In some applications, it can be advantageous if the sensor material is present in the form of small crystals which are distributed in a lacquer or plastic which is applied to the surface whose temperature is to be measured.

[0024] According to a second aspect of the application, a temperature sensor device is proposed which has a temperature sensor head according to the first aspect of the application. The temperature sensor device has a light source which excites luminescent radiation in the sensor material of the temperature sensor head with light pulses, which luminescent radiation is measured by an optical sensor and evaluated in a controller in order to determine the temperature of the sensor material. All the advantages which have been mentioned in connection with the temperature sensor head have been achieved by the temperature sensor device.

[0025] According to a third aspect of the application, an electrical machine is proposed which has a rotor and a stator. The stator has windings made of winding wire. The winding wire is in thermal contact with a temperature sensor head according to the first aspect of the application. The electrical machine has the advantage that reliable temperature measurement at the electrical windings is possible even if there is little available installation space and a strong magnetic field.

[0026] In a development of the electrical machine, the stator has a plurality of partial windings which are in thermal contact with one or more temperature sensor heads according to the first aspect of the application. In this way, it is possible to measure the temperature at a plurality of locations in the electrical machine, thereby achieving a more comprehensive temperature monitoring.

[0027] In a further embodiment of the electrical machine, the insulation is locally removed from the winding wire to improve the thermal contact between the winding wire and the sensor material of the temperature sensor device. In this embodiment, a temperature drop of the lacquer layer of the winding wire is avoided and a direct temperature measurement at the conductor of the winding wire is made possible.

[0028] In one development, the overmould can surround one or more contact locations between the winding wire and the temperature sensor head. The overmould thus formed has the advantage that a mechanically stable arrangement is obtained which is insensitive to environmental influences. BRIEF DESCRIPTION OF DRAWINGS

[0029] The application will be explained in more detail by way of example on the basis of embodiments with reference to the accompanying drawings. All drawings are merely schematic and not drawn to scale. In the drawings:

[0030] Figure 1A A schematic setup of a temperature measurement device is shown in block diagram form;

[0031] Figure 1B A schematic setup of a further temperature measurement device is shown in block diagram form;

[0032] Figures 2A to 2G A schematic setup of the end of a polymer optical fiber with sensor material is shown;

[0033] Figure 3 A winding wire is shown on which a temperature sensor head is arranged;

[0034] Figure 4 A schematic setup of an electrical temperature sensor is shown;

[0035] Figure 5A A decrease of the intensity of the luminescent radiation over time is shown; and

[0036] Figure 5B A lifetime of the temperature dependence of the luminescent radiation is shown.

[0037] In the figures, identical or similar elements have identical or similar reference numerals. DETAILED DESCRIPTION

[0038] Figure 1AA schematic block diagram of a temperature measuring device according to the present application is shown, which is based on the measurement of luminescent radiation. The temperature measuring device is generally denoted with reference numeral 100. A temperature sensor head 101 is equipped with a sensor material 102, which is excited by a light pulse to luminescent radiation. As described in the introductory part, the temperature of the sensor material 102 can be determined from the lifetime of the temperature-dependent luminescence. In a practical application, the temperature sensor head 101, and primarily the sensor material 102, is in thermal contact with an object (not shown) whose temperature is to be measured.

[0039] The temperature sensor head 101 is located at the free end of an optical fiber, in particular a polymer optical fiber (POF) 103. The optical fiber 103 leads to an optical fiber coupler 104, which couples the optical fiber 103 to two optical fibers 106, 107, which are themselves preferably polymer optical fibers. The POF 106 establishes an optical connection to a light emitting diode 108, while the POF 107 provides an optical connection to a light detector 109, for example a PIN light detector. The light emitting diode 108 and the light detector 109 are electrically connected by means of electrical lines 110 to a controller 111 for signal transmission and supply voltage. The controller 111 is connected to a display 112, for example on which the measured temperature is displayed. Furthermore, the controller has an interface 113, which can connect the temperature measuring device 100 to a data bus (not shown).

[0040] Broadly speaking, the function of the controller 111 is such that the light emitting diode 108 transmits a light pulse onto the sensor material 102 and thereby excites luminescent radiation. The light emitting diode emits, for example, green light in the wavelength range of 500 nm to 580 nm, which is modulated at a frequency of 50 Hz. The light pulse duration is approximately 5 ms. In the case of a glass fiber optical waveguide, light in the wavelength range of 800 nm to 1600 nm is used. In other exemplary embodiments, other wavelengths, another modulation frequency, and other light pulse durations can be appropriate, depending on the wavelength at which the sensor material can be excited to luminescent radiation and how long the lifetime of this luminescent radiation is.

[0041] The time of observation of the luminescent radiation in the light detector 109 is reduced. The controller 111 determines the lifetime of the luminescent radiation, and ultimately the temperature of the sensor material 102, from the measurement signal of the light detector 109, as already explained in the introductory part. In a practical application, the sensor material 102 is in thermal contact with an object (not shown) whose temperature is to be measured. The temperature of the sensor material 102 thus essentially corresponds to the temperature of the object being measured.

[0042] In a specific exemplary embodiment, the POFs 103, 106 and 107 have a diameter of 1 mm and consist of a PMMA (PolyMethylMethAcrylate) core with a thickness of 0.98 mm and an optical cover with a thickness of 0.02 mm made of a fluorinated acrylate or a fluoropolymer. The optical cover is also referred to as "cladding". On the cladding a mechanical protective cover ("coating") is arranged. The advantage of the POFs is the small diameter, the low weight, the good flexibility and the insensitivity to electromagnetic influences. Furthermore, the POFs can be connected by simple plug connections. When used in a vehicle, it is necessary to protect the temperature sensor head 101 with the sensor material 102, in particular, from environmental influences in the case of an exposure of the temperature measuring device 100 to environmental influences. Environmental influences include, to name only a few, humidity, dust and vibrations.

[0043] Figure 1B A temperature measuring device 100' with a plurality of temperature sensor heads 101 is shown. The temperature sensor heads 101 are connected to an optical multiplexer 114 which permits the light pulses from the light emitting diodes 108 to be directed to one sensor head 101 with purpose and the luminescent radiation of the associated temperature sensor head 101 to be measured and evaluated after the light pulse. For this purpose, the optical multiplexer 114 is controlled accordingly by the controller 111 via a control line 116. In the case of a temperature sensor head 101, the luminescent radiation is detected by the light detector 109 and evaluated by the controller 111. Figure 1B In the shown embodiment, three temperature sensor heads 101 are present, but in other embodiments, only two or more than three temperature sensor heads 101 can also be present.

[0044] In a further embodiment (not shown), each temperature sensor head 101 is assigned one light emitting diode 108 and one light detector 109.

[0045] Figures 2A to 2G Different embodiments of a temperature sensor head 101 for a temperature measuring device 100 according to the application are shown.

[0046] Figure 2AA first embodiment of a temperature sensor head 101 is shown. The POF 103 is surrounded by a protective cover 201 which protects the POF 103 from environmental influences and mechanical damage. The protective cover 201 has been removed from the free end 202 of the POF 103. At the end face 203 of the POF 103, a recess 204 is formed for receiving a sensor material 205. The sensor material 205 is, for example, a ruby crystal. A protective body 207 (which mechanically stabilizes the free end 202 of the POF 103 and is insensitive to environmental influences) is molded on the section 206 of the protective cover 201 and the free end 202 of the POF 103. A window 208 (filled with a well thermally conductive material) is arranged in the protective body 207 such that it abuts the sensor material 205. The window 208 and the protective body 207 rest on an object 209 such that the sensor material 205 is in good thermal contact with the object 209. In this way, an optical temperature measurement at the object 209 (as described above) is possible. In one exemplary embodiment, in order to attach the protective body to the object, the protective body 207 is provided with a thread (not shown) which allows the temperature sensor head 101 to be screwed fixedly onto the object 209. In an alternative exemplary embodiment, the sensor head is adhesively bonded to the surface of the object 209.

[0047] Figure 2B A second embodiment of a temperature sensor head 101 is shown. This second embodiment differs from the first embodiment shown Figure 2A in that the sensor material 205 is arranged directly on the end face 203 of the POF 103. That is, the end face 203 of the POF 103 is not recessed. In this second embodiment, the sensor material 205 extends into the window 208 in the protective body 207 and forms a planar surface with the end face of the protective body. The sensor material 205 is in direct contact with the object 209, resulting in a good thermal coupling to the object 209.

[0048] Figure 2C A third embodiment of a temperature sensor head 101 is shown, in which a plano-convex lens 211 is arranged on the end face 203 of the POF 103. The lens is, for example, adhesively bonded to the end face 203 using an optically transparent adhesive. The lens 211 converges the incident light and focuses it into the POF 103. In this exemplary embodiment, the sensor material 205 is arranged directly on the object 209. The sensor material is, for example, a ruby crystal which is adhesively bonded. In contrast to the first two exemplary embodiments, there is no physical contact between the POF 103 and the sensor material 205; rather, there is only an optical connection between the two. The temperature measurement is still carried out according to the same principle, in which a light pulse excites luminescent radiation in the sensor material 205, which is converged by the lens 211 and evaluated in the controller 111, as described in connection with Figure 1.

[0049] In this exemplary embodiment, since the POF 103 and the sensor material 205 do not touch, a measurement error is eliminated that occurs due to the removal of a certain amount of heat from the sensor material 205 through the POF 103, which causes the sensor material 205 to measure a temperature that is lower, even if only slightly lower, than the actual temperature of the object 209.

[0050] Figure 2D A fourth embodiment of the temperature sensor head 101 is shown. This exemplary embodiment is similar to the third embodiment Figure 2C The exemplary embodiment shown differs in that the protection body 207 extends to the object 209 and forms a cavity 212 in its interior. The cavity 212 extends from the lens 211 to the object 209 and receives the sensor material 205. The protection body 207 protects both the lens 211 and also the sensor material 205 from possible harmful environmental influences.

[0051] Figure 2E A fifth embodiment of the temperature sensor head 101 is shown. The protection body 207 has a window 208, which is less than 1 mm from the sensor material 205. The sensor material 205 is likewise connected to the object 209, for example, adhesively bonded to the object 209. The luminescent radiation generated in the sensor material 205 by the light pulse passes through the window 208 into the POF 103. Since the small distance between the end face 203 of the POF 103 and the sensor material 205, a converging lens can be dispensed with.

[0052] Figure 2F A sixth embodiment of the temperature head 101 is shown. In this embodiment, a cover 213 made of transparent polymer, in which a small ruby crystal or another luminescent material is embedded, is placed on the free end 202 of the POF 103. The protection body 207 extends over the cover 201 and the cover 213. The cover 213 is in thermal contact with the object 209 and thus permits a temperature measurement of the object 209.

[0053] Figure 2G A sensor head 101 is shown Figure 2E in which, in this exemplary embodiment, the sensor material 205 is applied to the object 209 in the form of a lacquer or adhesive material that contains a small ruby crystal. The luminescent radiation generated in the sensor material 205 passes through the window 208 in the protection body 207 into the POF 103, as shown in the exemplary embodiment Figure 2E .

[0054] Figure 3An enlarged cross-section of a winding wire 301 of an electric machine, such as an electric motor or generator, is shown. The electric motor can for example be a drive motor of an electric vehicle. The winding wire is electrically insulated from a lacquer layer 302. A temperature sensor head 101, which is constructed essentially similar to the one shown Figure 2A The temperature sensor head 101 is placed on the lacquer layer 302. The sensor material 205 of the temperature sensor head 101 is in direct contact with the lacquer layer 302. Thus, the sensor material 205 measures the temperature of the lacquer layer 302. In this case, the protective body 207 is molded around the winding wire 301 and the POF 103 or the protective covering 201. This results in a mechanical temperature arrangement which is not sensitive to environmental influences.

[0055] In an exemplary embodiment, which is not shown, a small hole is drilled or etched into the lacquer layer and / or the copper wire, into which the free end 202 of the POF 103 is inserted. This arrangement is likewise overmolded by the protective body 207, which encloses both the winding wire 301 and also the POF 103 or the protective covering 201. With this arrangement, the temperature of the conductor of the winding wire can be measured.

[0056] The small size of the temperature sensor head 101 according to the invention, the flexibility of the POF 103, and the insensitivity of the optical temperature measurement to high magnetic fields make it possible to measure the temperature inside an electric machine. Suitably, a plurality of temperature sensor heads can also be arranged in the electric machine, which permit temperature measurement at critical locations in the interior of the electric machine. For this purpose, the plurality of POFs 103 of the temperature sensor heads are connected to an optical multiplexer 104, whereby a single light-emitting diode 108 and a single light detector 109 are sufficient for temperature measurement with the plurality of temperature sensor heads 101. Figure 1B A schematic setup of such a temperature measurement 100' is shown.

[0057] The connection of the temperature sensor head to the winding wire can for example be realized even before the winding for the electric machine is produced. In this case, the POF is led out of the finished winding and connected to the temperature measurement device using a plug connection.

[0058] Although the invention is described primarily in connection with POFs, the invention can also be realized for other optical fibers, in particular glass fibers, which are better suited for higher temperatures.

[0059] Reference Signs

[0060] 100 temperature measurement device 213 cover

[0061] 101 temperature sensor head

[0062] 102 temperature sensor material 301 winding wire

[0063] 103 optical fiber 302 varnish layer

[0064] 104 optical fiber coupler

[0065] 106, 107 optical fiber

[0066] 108 light emitting diode 401 temperature sensor

[0067] 109 light detector 402 housing

[0068] 110 line 403 electrical measuring element

[0069] 111 controller 404 holder

[0070] 112 display

[0071] 113 interface 406A, connection

[0072] 406B

[0073] 114 optical multiplexer 407A, contact location

[0074] 407B

[0075] 408A, conductor

[0076] 408B

[0077] 116 control line 409 cable

[0078] 201 protective cover

[0079] 202 free end

[0080] 203 end face

[0081] 204 recess

[0082] 205 sensor material

[0083] 206 section of protective cover

[0084] 207 protective body

[0085] 208 window

[0086] 209 object

[0087] 211 lens

[0088] 212 cavity

Claims

1. An electric machine having a rotor and a stator, wherein, The stator has a winding made of winding wire (301) which is electrically insulated from a lacquer layer (302), wherein the winding wire (301) is in thermal contact with an optical temperature sensor head (101) which comprises an optical fiber (103) and a sensor material (205) which is arranged directly on the winding wire (301) whose temperature is to be measured, wherein the sensor material is optically connected to the free end (202) of the optical fiber, characterized in that the free end (202) of the optical fiber is at a distance from the sensor material (205), wherein the free end (202) of the optical fiber has an overmolding made of a plastic material which engages on the free end of the optical fiber and forms a protection (207), wherein the protection (207) surrounds one or more contact locations between the winding wire (301) and the optical temperature sensor head (101) and the protection (207) is molded around the winding wire (301).

2. The electrical machine of claim 1, wherein, The insulation is removed locally from the winding wire (301) to improve the thermal contact between the winding wire and the sensor material of the optical temperature sensor head.

3. The electrical machine of claim 1, wherein, The optical fiber is a polymer optical fiber (103).

4. The electrical machine of claim 1, wherein, On the free end (202) of the optical fiber a converging lens (211) is arranged which focuses the incident light into the optical fiber (103).

5. The electrical machine of claim 1 or 4, wherein, The protection (207) surrounds the space between the sensor material (205) and the free end of the optical fiber (103) or the converging lens (211).

6. The electrical machine of claim 1, wherein, The sensor material (205) is applied to the winding wire (301) whose temperature is to be measured in the form of a layer. The sensor material (205) is applied to the winding wire (301) whose temperature is to be measured in the form of a layer.

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