GB2322190A - Determination of the presence of water on a windscreen - Google Patents

Abstract

The presence of water on the windscreen of a motor vehicle is determined by coupling radiation into the windscreen from a transmitter and decoupling the radiation from the screen to a receiver 1. The receiver corresponds in its construction to a light diode. Ambient light entering the receiver may be reduced by introducing a filter in front of the receiving device. This may take the form of at least one layer of coating on 2.2 or in front 2.3 of the device. The coating may be provided within the housing of the device 3.1. Alternatively the receiver may be encapsulated in a material having a narrow bandpass frequency 2.1.

Description

A device for detecting wetting events on a screen The present invention relates to devices for detecting wetting events on screens.

DE 42 29 491A1 discloses a device for detecting wetting events on a screen in which radiation from a transmitter is coupled via a radiation conductor into a screen, is conveyed further in said screen by total internal reflection, and is then coupled into the radiation conductor again, which then conducts the radiation to a receiver. In a processing device arranged downstream, the signal is evaluated in order to obtain a report relating to the wetting events on the screen. Disturbance radiation, which impedes signal evaluation, overlies the useful radiation on the optical path from the transmitter to the receiver. In DE 42 29 491 Al, the radiation transmitter is optically insulated on its side facing the radiation receiver. On the inside of the screen, absorption strips are fitted in the direct line from the radiating surface of the transmitter to the receiver, and the receiver is protected from direct solar irradiation, for example by means of shielding fitted to the inside of the screen. However, it has been found that measures of this type for obtaining a signal which is as disturbancefree as possible and for obtaining a precise evaluation are inadequate.

According to the present invention there is provided a device for detecting wetting events on a screen comprising a transmitter, a receiver constituted by an element corresponding in its construction to a light emitting diode, and a radiation conductor, which conductor, in use, is fitted to the screen and by means of which radiation transmitted by the transmitter can be coupled inta the screen, decoupled from the screen and supplied to the receiver.

A device for detecting wetting events on a screen in accordance with the invention has the advantage that the spectral radiation sensitivity of the receiver is restricted to the very same wavelength as the transmitter radiation, so that disturbing radiation components are better suppressed.

In an advantageous development of the invention the spectral radiation sensitivity of the receiver is further restricted to given wavelength range by means of coating or staining it. Using this treatment of the receiver it is possible to optimally adapt the receiver to the wavelength range of the useful radiation, disturbing radiation occurring in other wavelength ranges being eliminated by the receiver, i.e. the last element in the radiation sequence. In this manner, the ratio of useful radiation to disturbance radiation is considerably improved, so that the signal recognition and evaluation can be carried out reliably, particularly in critical situations.

The selection of an optimal radiation range over the wavelength can be achieved in a particularly simple manner and in a manner which can be effectively adapted to the respective requirements by way of the measure wherein the coating is provided by applying at least one layer to the side of a receiver housing facing the radiation conductor. The layers act by way of their interference properties.

An alternative possibility of restricting the spectral radiation sensitivity of the receiver and therefore of adapting to the specific conditions of a device of the above type, consists in effecting the staining in the volume of the receiver housing during manufacture.

A further measure for tuning the spectral radiation sensitivity of the receiver consists in that the coating is formed by at least one layer on a receiver chip.

In this manner, it is possible to already effect a tuning to the particular conditions of a device of the above type in the factory.

The spectral radiation sensitivity of the receiver may further be restricted to an optimal range if the coating is formed alone or in addition to further layers by applying a separate filter to the side of the receiver housing facing the radiation conductor.

Preceding advantageous developments can also be applied in different combinations. For example, a staining in the volume of the receiver housing can be expediently combined with a coating in the form of a plurality of layers on the receiver housing. As a result of the staining, a rough adaptation can be carried out, which with the application of the layers, for example by vapourdeposition or atomisation (sputtering), can be fine-tuned and precisely adapted to the respective conditions. Similarly, a staged tuning can also be achieved by carrying out staining in the volume of the receiver housing during manufacture and forming the coating by at least one layer on the receive chip, although a subsequent adaptation is not possible in this case.

In order that the invention may be well understood, there will now be described some embodiments thereof given by way of example, reference being made to the accompanying drawings, in which: Figs 1A to 1E are various embodiments for a spectral adaptation of the radiation sensitivity of a receiver; and Fig. 2 is an example of the course of the spectral radiation sensitivity of an untreated receiver and a receiver formed in accordance with the invention.

Referring first to Fig. 1A there is shown a schematic illustration of a receiver 1 for the radiation derived from a radiation conductor, not shown, of a device for detecting wetting events on the windscreen of a motor vehicle. Contained in a receiver housing 2 is a receiver chip 3, by means of which the optical radiation is converted into an electrical receiver signal. The receiver housing 2, which is cast for example from epoxy resin, is provided in its volume with staining 2.1, which absorbs the impacting radiation outside a restricted spectral range. For example, according to Fig. 2, the outer curve I represents the course of a spectral radiation sensitivity of an untreated receiver 2, whilst the curve II reproduces the restricted course of the spectral radiation sensitivity of the treated receiver 1.

In accordance with Fig. 1B, the receiver chip 3 is provided with interference layers 3.1, for example by vapour-deposition or by atomisation (sputtering). The interference layers can be adapted to one another depending on the respective refraction index and respective thickness in such a manner that a desired restricted spectral radiation range reaches the receiver chip 3.

Fig. 1C shows a further example for adapting the spectral radiation sensitivity of the receiver 1. In this case, a coating of a plurality of interference layers 2.2 is applied to the surface of the receiver housing 2 facing the radiation conductor (not shown), for example by vapour-deposition or sputtering. Also in this case, the radiation reaching the receiver chip 3 can be spectrally tuned by the selection of the thickness and refraction index of the individual layers.

In accordance with Fig. 1D a separate optical filter is fitted to the side of the receiver housing 2 facing the radiation conductor, the optical filter having a corresponding permeability for adapting the spectral radiation sensitivity.

In accordance with Fig. 1E, a light diode, which is connected as a receiver, is used as the receiver 1'. Using this measure, the receiver can be tuned in its spectral radiation sensitivity according to its selection to a corresponding transmitter, not shown. Also in the case of this receiver 1', the above-described measures can be applied.

In order to tune the spectral range, it is also possible, for example using a separate filter 2.3, to set the permeability range to a short wave or long wave flank only by way of a corresponding slope in the filter 2.3, and together with the long wave or short wave sloping flank of the receiver 1, a suitable restricted.range of the spectral radiation sensitivity can be set.

The embodiments illustrated in Figs. 1A to 1D for restricting the spectral radiation sensitivity can also be used in any chosen combination with one another. For example, by way of the measure according to Fig. 1A, it is possible to effect a rough tuning at the stage of manufacture of the receiver 1, which can be finely tuned to the device by applying interference layers 2.3 during the construction of said device.

Using the described measures, an optimal adaptation of the receiver to the useful radiation which is to be evaluated can be achieved, so that signal recognition and processing is improved.

Reference is made to British application GB 9703829.3 (published as GB 2310926) from which the present case has been divided.

Claims (8)

1. A device for detecting wetting events on a screen comprising a transmitter, a receiver constituted by an element corresponding in its construction to a light emitting diode, and a radiation conductor, which conductor, in use, is fitted to the screen and by means of which radiation transmitted by the transmitter can be coupled into the screen, decoupled from the screen and supplied to the receiver.

2. A device as claim 1, wherein the spectral radiation sensitivity of the receiver is further restricted to a given wavelength range by means of coating or staining applied to the receiver.

3. A device as claimed in claim 2, wherein the coating is formed by at least one layer applied to the side of a receiver housing facing the radiation conductor.

4. A device as claimed in claim 3, wherein the staining is provided in the volume of the receiver housing.

5. A device as claimed in any of claims 2 to 4, wherein the coating is formed by at least one layer on a receiver chip.

6. A device as claimed in any of claims 2 to 5, wherein the coating is formed alone or in addition to further layers by the application of a separate filter to the side of the receiver housing facing the radiation conductor.

7. A device as claimed in any of the preceding claims, wherein the screen is a windscreen of a motor vehicle.

8. A device for detecting wetting events on a screen according to claim 1 and substantially as herein described with reference to Figure 1E of the accompanying drawing.

8. A device for detecting wetting events on a screen, substantially as herein described with reference to Figure 1E of the accompanying drawing.

Amendments to the claims have been filed as follows

1. A device for detecting wetting events on a screen comprising a transmitter, a receiver constituted by an element corresponding in its construction to a photo-diode, the spectral radiation sensitivity of which element is matched to the transmitter, and a radiation conductor, which conductor, in use, is fitted to the screen and by means of which radiation transmitted by the transmitter can be coupled into the screen, decoupled from the screen and supplied to the receiver.

2. A device as claim 1, wherein the spectral radiation sensitivity of the receiver is further restricted to a given wavelength range by means of coating or staining applied to the receiver.

3. A device as claimed in claim 2, wherein the coating is formed by at least one layer applied to the side of a receiver housing facing the radiation conductor.

4. A device as claimed in claim 3, wherein the staining is provided in the volume of the receiver housing.

5. A device as claimed in any of claims 2 to 4, wherein the coating is formed by at least one layer on a receiver chip.

6. A device as claimed in any of claims 2 to 5, wherein the coating is formed alone or in addition to further layers by the application of a separate filter to the side of the receiver housing facing the radiation conductor.

7. A device as claimed in any of the preceding claims, wherein the screen

is a windscreen of a motor vehicle.