DE102012108203A1 - Device for detecting metallic objects in the region of an inductive charging device for electric vehicles - Google Patents

Abstract

Device for the detection of metallic objects in the area of an inductive charging device for electric vehicles (20), comprising at least one light source (3, 13), at least one light guide (1, 12) into the light coming from the at least one light source (3, 13) can be coupled in, as well as evaluation means for evaluating the light coupled out of the at least one light guide (1, 12), the device being designed in such a way that the evaluation means does not, however, indicate the presence of a local temperature increase in the at least one light guide (1, 12) determine or be able to determine their position.

Description

The present invention relates to a device for detecting metallic objects in the region of an inductive charging device for electric vehicles and to an inductive charging device for electric vehicles with such a device.

Definitions: When the terms light, optical radiation or optical signal are used, it means electromagnetic radiation in the optical spectral range, in particular from XUV to FIR.

When charging electric vehicles to inductive charging devices, there is the problem that metallic objects can be heated between the coils. The sometimes quite small hot objects such as coins should be reliably and quickly detected on larger areas (some dm ² to several m ² ). In doing so, no metallic sensors may be used. The solution should be cost-effective. Recognizing the exact location of the item is not important.

The problem underlying the present invention is thus to provide a device of the type mentioned, which is inexpensive and / or allows a simple detection of metallic objects in the range of a charging device of electric vehicles. Furthermore, a loading device of the type mentioned is to be specified.

This is inventively achieved by a device having the features of claim 1 and by an inductive charging device having the features of claim 10. The subclaims relate to preferred embodiments of the invention.

According to claim 1, provision is made for the device to comprise at least one light source, at least one light guide, into which light emanating from the at least one light source and evaluation means for evaluating the light coupled out of the at least one light guide, the device being designed in this way in that the evaluation means can determine or determine the presence of a local temperature increase of the at least one light guide, but not their position. By this design, the device can be simple and thus manufactured inexpensively. The use of a light guide as a sensor means ensures that the sensor in the region of the inductive charging device can be designed as a non-metallic sensor.

There is the possibility that the at least one light guide has a plurality of fiber Bragg gratings (FGB). The device may thus be a fiber optic sensor system using fiber Bragg gratings, that is, optical gratings located in the core of a light guide.

It is known from other fields of application to employ individual fiber Bragg gratings or chains of fiber Bragg gratings to measure a temperature (or strain) at single or multiple positions. In this case, the position of the reflection peak of the fiber or Bragg gratings is determined by a spectroscopic method and determined from the changes in position, the temperature or strain. For the measurement of several fiber Bragg gratings spectral or temporal multiplexing methods are used. The multiplexing is sometimes quite complex or limited also the number of usable fiber Bragg gratings and / or the spatial resolution. For example, tunable lasers with a tuning range of about 80 nm are used and fiber Bragg gratings with wavelengths different by 5 nm are used. The distance of about 5 nm is required for non-overlapping operation of the fiber Bragg gratings throughout the temperature and strain range. Smaller distances are possible for limited measuring ranges. Nevertheless, the total number of fiber Bragg gratings in a measuring channel is very limited, for example to typically 16 pieces with the stated values. Larger FBG numbers require the use of multiple measurement channels or temporal multiplexing. However, temporal multiplexing with very small distances (in the cm range) requires a complex measurement technique with high measurement frequencies (GHz range). This is too costly for the present task. In addition, the required for the present task under certain circumstances numbers of measuring points (some 100 to several 10000) with the known methods can not be realized or only with great effort.

Therefore, in particular, it may be provided that the plurality of fiber Bragg gratings each have the same reflection wavelength or that the plurality of fiber Bragg gratings have reflection wavelengths that are less than 1.0 nm, preferably less than 0.5 nm, in particular by less than 0.1 nm from each other. This measure can considerably simplify the evaluation of the measurement signals.

In particular, the device may be designed so that only components with a predetermined wavelength offset relative to the reflection wavelength of the fiber Bragg gratings are detected or processed by the light reflected by the fiber Bragg gratings. In this way, the Changing the temperature or the elongation of a fiber Bragg grating to be detected by a certain value or above a certain threshold on a signal in the measuring arrangement. It is then not possible to determine which fiber Bragg grating generates the signal. However, this is also not necessary for the desired detection of metallic objects in the region of an inductive charging device for electric vehicles. This results in a simple and inexpensive device that still satisfies the demands placed on it.

According to an alternative embodiment, there is the possibility that the device is designed such that the evaluation means can evaluate light generated by spontaneous or stimulated Brillouin scattering in the at least one light guide for measuring a temperature. In contrast to the FBG technique, standard optical fibers, such as, for example, single-mode fibers similar to those from telecommunications, can be used, whereby the cost portion of the sensor cable can be comparatively low. This is particularly advantageous for a high number of measuring points to be detected or for large optical fiber lengths.

It is known from other fields of application to use stimulated or spontaneous Brillouin scattering in optical fibers for measuring temperature and strain in optical fibers. Unfortunately, the technique known from other fields of application for the Brillouin measurements is very expensive. In view of the present task, it is taken into account that only the existence of a hot or cold spot should be measured, but not their position. As a result, however, a clear simplification can be achieved here as well. It turns out that complex technical components for modulation, demodulation and time-resolved measurement, which are used solely for location determination, can be dispensed with.

It can be provided that the at least one light source can emit light with a first wavelength and that the evaluation means comprise a spectral filter which transmits light with a second wavelength, wherein the difference of the first wavelength and the second wavelength of the Brillouin shift in the corresponds to the temperature to be measured. In this way, the achievement of the temperature to be measured can be detected by a corresponding measurement signal due to spontaneous Brillouin scattering. The temperature to be measured may be, for example, a temperature at which the presence of an object heated by the charging process can be assumed.

It can be provided that the device comprises either two laser sources designed as lasers, which can emit a first laser signal with a first wavelength and a second laser signal with a second wavelength, or that the at least one light source is designed such that it generates a first laser signal with a first wavelength and a second laser signal having a second wavelength, wherein the difference of the first wavelength and the second wavelength corresponds to the Brillouin shift at the temperature to be measured. In this way, the stimulated Brillouin scattering can be used. The two laser signals can be coupled from opposite ends in the light guide. If the Brillouin frequency now coincides with the wavelength difference of the two laser signals at one or more locations within the light guide, a "reflected" signal of the interrogation laser is measured.

According to an alternative embodiment, there is the possibility that the device comprises an interferometric structure, wherein the at least one light guide is part of this interferometric structure. A temperature change of a light guide causes a change in the optical length of the light guide by mechanical change in length and / or change in the refractive index or the group velocity. Such a change in length can be detected very sensitively with an interferometric structure.

It can be provided that the device comprises a tube which surrounds the at least one light guide in such a way that it can move relative to the tube during thermal expansion. In this way, a mechanical decoupling of the at least one light guide from its surroundings is achieved, so that the measurements are influenced essentially by the particular local heating of the light guide.

Claim 10 provides that an inductive charging device according to the invention for electric vehicles comprises a device according to the invention. The inductive charging device may in particular comprise a primary coil, which may be arranged, for example, in a roadway. Furthermore, a secondary coil may be provided or included by the inductive charging device, which is accommodated in particular in a vehicle.

There is the possibility that the loading device comprises a plate or a bottom section, in which the at least one light guide is arranged. Alternatively, the light guide can also be arranged in the vehicle. In both cases, the sensor cable should be close to the surface of the fiber optic cable to achieve sufficient thermal coupling to the objects to be measured.

Further features and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings. Show in it

1 a schematic view of a first embodiment of a device according to the invention for the detection of metallic objects;

2 a schematic view of a second embodiment of a device according to the invention for the detection of metallic objects;

3 a schematic view of a third embodiment of a device according to the invention for the detection of metallic objects;

4 a schematic view of a fourth embodiment of a device according to the invention for the detection of metallic objects;

5 a schematic view of a fifth embodiment of a device according to the invention for the detection of metallic objects;

6 a schematic view of a sixth embodiment of a device according to the invention for the detection of metallic objects;

7 a schematic side view of a first embodiment of an inductive charging device according to the invention;

8th a schematic plan view of the inductive charging device according to 7 ;

9 a schematic side view of a second embodiment of an inductive charging device according to the invention;

10a a first installation example of the at least one optical fiber of a device according to the invention for the detection of metallic objects;

10b a second Verlegungsbeispiel for the at least one optical fiber of a device according to the invention for the detection of metallic objects;

10c a third Verlegungsbeispiel for the at least one optical fiber of a device according to the invention for the detection of metallic objects;

10d A fourth Verlegungsungsbeispiel for the at least one optical fiber of a device according to the invention for the detection of metallic objects;

10e a fifth installation example of the at least one optical fiber of a device according to the invention for the detection of metallic objects.

In the figures, identical and functionally identical parts are provided with the same reference numerals.

1 to 3 represent examples of a device, the at least one light guide 1 with a plurality of fiber Bragg gratings 2 includes. The majority of fiber Bragg gratings 2 has as exactly as possible the same reflection wavelength. In particular, the reflection wavelengths of the individual fiber Bragg gratings differ 2 less than 1.0 nm, preferably less than 0.5 nm, in particular less than 0.1 nm from each other.

In this case, it may be provided, in particular, that in the case of an inorganic or mineral optical waveguide 1 the reflection wavelengths of the individual fiber Bragg gratings 2 differ by less than 0.1 nm. In contrast, in a polymer optical fiber 1 be provided that the reflection wavelengths of the individual fiber Bragg gratings 2 differ by less than 1.0 nm.

In the 1 The illustrated first embodiment comprises a laser light source 3 from which the light used for measurement goes out and, for example, via an optional plug 4 in the optical fiber used for the measurement 1 is coupled. The light guide 1 is at his from the light source 3 opposite end with a termination 5 Mistake.

The termination 5 should be designed so that the least possible reflection occurs at the end of the light guide, because the reflection signal, the signals of the fiber Bragg gratings 2 could overlap. For this purpose, the optical fiber end, for example, tight rolled up, cut off obliquely and / or embedded in a material with a similar refractive index.

That of the fiber Bragg grids 2 back reflected light is over the plug 4 from the light guide 1 decoupled and a receiver 6 fed. The recipient 6 is with an evaluation electronics 7 connected, in turn, with an interface 8th or corresponding outputs can be connected.

With the reference numerals 25 are in 1 to 3 fiber optic coupling elements, such as light splitters, combiners, spectral splitters and circulators.

The one from the receiver 7 and the transmitter 8th and optionally filtering 9 (please refer 2 ) formed evaluation means can be designed so that of the reflected light only portions with a predetermined wavelength offset relative to the reflection wavelength of the fiber Bragg gratings 2 be captured or processed. In this way, the change in temperature or the elongation of a fiber Bragg grating 2 be detected by a certain value or above a certain threshold on a signal in the evaluation means. It is then not possible to determine which fiber Bragg grating 2 The signal generated, but this is not required for the desired detection of metallic objects in the field of inductive charging device for electric vehicles.

A fiber Bragg grating 2 in an inorganic glass optical fiber, the reflection wavelength typically changes by 0.001% / ° C. That is, to detect a temperature change of 50 ° C relative to the reference temperature, the spectral offset between fiber Bragg gratings 2 and the evaluation means are about 0.05%, for example, 0.5 nm at a wavelength of 1 micron. With a polymer optical fiber (POF), the wavelength change may be larger (up to about 20 nm / 50 ° C) and easier to measure. However, the dependence of the reflection wavelength of moisture must be considered or excluded here.

The following points are important for the function of a device based on a light guide with fiber Bragg gratings:
All fiber Bragg gratings must have as closely as possible the same reflection wavelength at the same temperature or elongation. This is to be ensured by a special manufacturing method of the light guide, in which the temperature and elongation of the fiber during insertion (writing) of the fiber Bragg gratings are precisely controlled. Other process parameters that may be important for the grating period (wavelength of the writing laser, interferometer angle, advancing speed and the like) must also be precisely controlled. The fiber Bragg gratings can be introduced into the light guide continuously or at small intervals (for example 1 cm).

As a method for the continuous introduction of fiber Bragg gratings is preferably a short-pulse laser (for example, a femtosecond laser), which irradiates pulses at a constant repetition rate on the guided at a constant speed light guide. With appropriate focusing, the laser periodically alters the optical properties (refractive index) of the optical fiber in the core and thus creates a grating. Advantages are that the fiber Bragg grating can be written continuously, that can be written through the cladding of the light guide, and that the parameters decisive for a constant grating period (temperature, strain, optical fiber propulsion speed, and laser repetition rate) are very precisely controlled can.

Alternatively, a high number of fiber Bragg gratings with the same grating period or reflection wavelength can be written in an interference arrangement or with a master grating (phase grating) when the optical waveguide is pulled before the jacket is applied with a UV pulsed laser. The UV laser uses photorefractive effects in the fiber core, which occur during the irradiation with the high-energy UV photons in possibly specially composed material. With each laser pulse, a fiber Bragg grating is written whose period is determined by the interference structure or the master. Here too, process parameters such as temperature and strain are to be controlled very precisely in order to obtain fiber Bragg gratings with the same reflection wavelength as possible at the same temperature and elongation.

For temperature measurements, the optical fiber should be mechanically decoupled from the environment such that strains are not transmitted. This is preferably done by loose introduction of the light guide 1 in a tube 9 (please refer 1 ), which may for example have a diameter of 1 mm to 5 mm. There is a certain excess length of the light guide 1 opposite the tube 9 useful to allow stress-free thermal expansion. The tube 9 consists in particular of plastic.

The tube 9 at the same time provides mechanical protection for the light guide 1 , A the light guide 1 and the tube 9 comprehensive sensor cable 10 (please refer 7 ) may contain other components to protect the light guide 1 contain, for example, against tensile, pressure, chemical and biological influences. Optionally, when using POF on the mechanical decoupling can be omitted, because here the temperature effect can be greater than the mechanical effect. For strain measurements, the light guide is 1 not to decouple, but mechanically good to be coupled to the object to be measured in order to allow a corresponding transmission of the strain.

A device according to the invention comprises one or more fiber-coupled light source (s) 3 and a detection device, also to the optical fiber 1 connected. For example, the device according to 3 three light sources 3 , The at least one light source 3 may be narrow (bandwidth about <1 nm) or broadband (> 1 nm).

Depending on the bandwidth of the light source 3 the device can filter medium 11 for filtering out the wavelengths to be measured (see for example the embodiment according to FIG 2 ). The filter elements 11 can be in the light path before or after the sensor cable. The device comprises one or more receivers 6 for detection, which can also act as a filter medium. There is a possibility that switching or modulation techniques may be used to isolate payloads from interfering signals.

The evaluation electronics 7 amplifies and measures the received signals, evaluates them with respect to predetermined criteria and triggers corresponding output signals.

The devices provided with an optical fiber with fiber Bragg gratings can do with simple and inexpensive evaluation means, but require the use of specially prepared light guide with the fiber Bragg gratings. The technique could thus be advantageous if the number of measurement points or the length of the sensor cable 10 are limited so that the price of the light guide is not too high.

In the 4 and 5 Illustrated embodiments of a device according to the invention uses the Brillouin scattering in one or more light guides 12 , This at least one light guide 12 does not have a fiber Bragg grating. Rather, it can be designed as a standard optical fiber, for example as a single-mode fiber similar to those from telecommunications.

In the embodiment according to 4 the spontaneous Brillouin scattering is measured. The light source 3 can be designed as a narrow-band laser (bandwidth, for example, 10 MHz or smaller). In the illustrated embodiment, the laser with a temperature or current regulator 13 connected. The recipient 6 is with a superior narrowband filter 11 Mistake. For example, the filter formed as a Fabry-Perot should have a spectral offset from the laser wavelength corresponding to the Brillouin shift at the temperature to be measured. Then reaching the temperature can be detected by a corresponding measurement signal.

In the embodiment according to 5 the stimulated Brillouin scattering is measured. For the use of the stimulated Brillouin scattering, the embodiment according to FIG 5 two trained as narrow-band laser light sources 3 . 14 which emit narrow-band laser signals (excitation and interrogation laser) with a wavelength different from the Brillouin shift to be measured. In the illustrated embodiment, the first laser with a first temperature or current regulator 13 connected. Furthermore, the second laser with a second temperature or current regulator 15 connected.

The of the two light sources 3 . 14 outgoing laser signals are from opposite ends in the light guide 12 coupled. This happens in particular in that the light guide 12 on the in 5 right side is bent 180 ° and through the tube 9 running back.

At the end with the interrogation laser signal are evaluation means with a narrowband filter 11 , a receiver 6 and an evaluation 8th coupled. Is now true at one or more locations within the light guide 12 the Brillouin frequency due to the temperature of the location with the wavelength difference of the two laser signals, a "reflected" signal of the interrogation laser is measured.

The wavelength difference between the two laser signals should be very closely controlled. This happens, for example, through the coupling of two lasers via an optical phase locked loop (phase locked loop). 16 , which regulates the current or the temperature of the lasers (see 5 ).

Another possibility for generating two laser signals with precisely controlled wavelength difference is to use a single laser and to generate the second signal by modulating the laser radiation (for example with an electro-optical modulator) at a few GHz. To distinguish the useful signal from interference signals, modulation methods (for example by means of lock-in technology) can be used. For example, the scanning laser may be modulated at a particular frequency and the signal narrowband measured at the same frequency. Optionally, polarization-effective components should be provided.

There is an optional possibility in the design according to 5 at least one polarization-effective or phase-effective element 26 to provide in 5 indicated by dashed lines. In particular, for the optimal interaction of the two laser signals a suitable polarization is required.

The Brillouin method is particularly suitable for larger temperature differences, such as from 20 ° C, because the Brillouin peak is quite wide and thus also contribute to the signal with places with a slightly different temperature. It is possible to improve the resolution by measuring several Brillouin shift frequencies and performing a peak analysis of the amplitude versus frequency curve.

Out 6 an embodiment of a device according to the invention can be seen, which comprises an interferometric structure, wherein the at least one light guide 12 Part of this interferometric structure is. Also in this embodiment, the light guide 12 on the in 6 bent right 180 ° and passes through the tube 9 back.

A temperature change of the light guide 12 causes a change in the optical length of the light guide 12 by mechanical change in length and / or change in the refractive index or the group velocity. Such a change in length can be detected very sensitively with an interferometric design. The optical change in length, however, becomes integral over the entire light guide 12 measured. Therefore, a good mechanical decoupling of the light guide, in particular of the tube 9 required.

In addition, it is necessary to separate the sought-after effect of strong local heating from other temperature variations. This is possible over the temporal behavior. In the application in question, a metallic object is heated very rapidly and severely. If the increase in the optical length change relative to time is considered, the event to be detected can be detected by the different rises before and during the flow of the induction current. There is the possibility that under certain circumstances, even after the induction current has flowed, the event to be detected can be concluded.

The in 6 The illustrated construction includes a light source 3 with sufficient coherence length, such as in particular a laser, corresponding beam splitter and beam combiner, the loop of the light guide to be measured 12 , which in particular is mechanically decoupled, as well as the receiver 6 and the transmitter 7 , There is also the possibility of providing polarization-effective components.

The interferometric measurement results in a constructive or destructive superposition depending on the phase position of the two light signals. It is therefore possible to detect changes in the optical path length of fractions of the wavelength due to phase changes and thus changes in the signal intensity. Larger changes in optical path length (multiple wavelength of light) can be detected by traversing signal maxima and minima multiple times.

In addition to glass fibers, because of their greater thermal expansion, polymer optical fibers can also be advantageous for the interferometric measurement.

There is the possibility in the interferometric measurement on the mechanical decoupling, in particular on the tube 9 , to renounce. Then not only the thermal expansion (and the refractive index change) of the light guide becomes 12 but also measured an extension of the matrix. However, this can also be due to a thermal effect and thus contribute to the detection of the desired event.

There is an option, also in the structure according to 6 at least one polarization-effective or phase-effective element 26 to provide in 6 indicated by dashed lines. In particular, for the optimal interaction of the two light signals a suitable polarization is required. Furthermore, with the change of phase, the operating point in the interferometry according to 6 be set.

For temperature measurements with all the superstructures according to 1 to 6 should that be with the light guide 1 . 12 provided sensor cable 10 in thermal contact with the object to be measured. This can be done by inserting the sensor cable 10 into the object (for example, by installation, concreting or casting) or by external connection or spatially adjacent placement.

The inductive charging devices according to the 7 to 9 each comprise a primary coil 17 in a lane 18 is installed. Furthermore, a secondary coil 19 provided in a vehicle 20 is installed.

7 and 8th show schematically a charging device in which the sensor cable 10 in the roadway 18 is installed. The primary coil 17 is with a power supply 21 and a controller 22 connected. The sensor cable 10 is with a measuring device 23 connected, which in connection with the 1 to 6 described components such as at least one light source 3 . 14 and evaluation means.

The sensor cable 10 is located close to the upper surface of the roadway 18 in order to achieve a sufficient thermal coupling to the objects to be measured. The heat transfer takes place by direct contact with the surface of the roadway.

In the roadway 18 could be the sensor cable 10 inserted in slots in the road surface (concrete, asphalt) and then fixed, for example, by potting. The sensor cable 10 But also in a plastic cover as a primary coil 17 serving induction coil. For example, in the manufacture of a composite material, the sensor cable could be incorporated into the matrix and fixed in the material upon introduction of the second (liquid, curing) component.

9 schematically shows a charging device, wherein the sensor cable 10 in the vehicle 20 is installed. The sensor cable 10 is also in this embodiment close to the lower surface to achieve sufficient thermal coupling to the objects to be measured. The heat is transferred to the sensor cable near the underside of the vehicle by rising warm air 10 transfer.

The sensor cable is used to record temperature events on surfaces 10 to be laid so that the entire surface is covered. Meandering, ring or spiral laying, for example, are suitable for this purpose. The 10a to 10e show various examples of such linings.

In interferometric measurement, it may be useful to have multiple loops 24 to lay in the surface and measure individually to allow localization or to detect or compensate for background effects such as the heating of the matrix during charging operation (see 10e ).

Claims (11)

Device for detecting metallic objects in the region of an inductive charging device for electric vehicles ( 20 ), comprising - at least one light source ( 3 . 13 ), - at least one light guide ( 1 . 12 ) into which at least one light source ( 3 . 13 ) outgoing light can be coupled in, - evaluation means for the evaluation of the at least one light guide ( 1 . 12 ) coupled out, wherein the device is designed such that the evaluation means, although the presence of a local temperature increase of at least one light guide ( 1 . 12 ), but not their position can be determined or determined. Apparatus according to claim 1, characterized in that the at least one optical fiber ( 1 ) a plurality of fiber Bragg gratings ( 2 ) having. Apparatus according to claim 2, characterized in that the plurality of fiber Bragg gratings ( 2 ) each have the same reflection wavelength or that the plurality of fiber Bragg gratings ( 2 ) Have reflection wavelengths which differ from one another by less than 1.0 nm, preferably by less than 0.5 nm, in particular by less than 0.1 nm. Device according to one of claims 2 or 3, characterized in that the device is designed so that from the through the fiber Bragg gratings ( 2 ) reflect only portions of a predetermined wavelength offset from the reflection wavelength of the fiber Bragg gratings ( 2 ) or processed. Apparatus according to claim 1, characterized in that the device is designed such that the evaluation means by spontaneous or stimulated Brillouin scattering in the at least one optical fiber ( 12 ) can evaluate the light generated to measure a temperature. Apparatus according to claim 5, characterized in that the at least one light source ( 3 . 13 ) Can emit light at a first wavelength and that the evaluation means comprise a spectral filter which transmits light at a second wavelength, the difference of the first wavelength and the second wavelength corresponding to the Brillouin shift at the temperature to be measured. Device according to claim 5, characterized in that the device either comprises two light sources ( 3 . 13 ), which can emit a first laser signal with a first wavelength and a second laser signal with a second wavelength, or that the at least one light source ( 3 . 13 ) is adapted to emit a first laser signal having a first wavelength and a second laser signal having a second wavelength, the difference of the first wavelength and the second wavelength corresponding to the Brillouin shift at the temperature to be measured. Apparatus according to claim 1, characterized in that the device comprises an interferometric structure, wherein the at least one optical fiber ( 12 ) Is part of this interferometric design. Device according to one of claims 1 to 8, characterized in that the device a tube ( 9 ) comprising the at least one optical fiber ( 1 . 12 ) surrounds itself in thermal expansion relative to the tube (FIG. 9 ) can move. An inductive charging device for electric vehicles, comprising a device according to one of claims 1 to 9. Inductive charging device according to claim 10, characterized in that the charging device comprises a plate or a bottom portion, in which the at least one optical fiber ( 1 . 12 ) is arranged.

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