GB2507060A

GB2507060A - Window assembly

Info

Publication number: GB2507060A
Application number: GB201218612A
Authority: GB
Inventors: Neil Savage
Original assignee: Nissan Motor Manufacturing UK Ltd
Current assignee: Nissan Motor Manufacturing UK Ltd
Priority date: 2012-10-17
Filing date: 2012-10-17
Publication date: 2014-04-23
Also published as: GB201218612D0

Abstract

A window assembly comprising a window and an electrical system which is arranged to detect the presence of moisture on a surface of said window. The electrical system comprises a first conductive element fitted to the window and a second conductive element fitted to the window such that at least one portion of the second conductive element is in close proximity to the first conductive element. The window assembly further comprises means for applying a DC voltage to at least one of the first and second conductive elements to create a resistive heating effect and means for applying an AC voltage to the first conductive element. A sensing system is arranged to detect a capacitive coupled signal in the second conductive element, so as to indicate the presence of moisture on the surface of the window.

Description

Window Assembly

Field of the invention

The invention relates to a window assembly having the facility to detect moisture on a S surface of a window that would obstruct vision through said window. In particular, but not exclusively, the invention relates to a window assembly for use in automotive vehicles.

Background to the invention

In windscreen heaters of the type commonly used, a number of fine wires are embedded between the outer and inner glass layers of the windscreen, and a direct electrical current is passed through them. The electrical resistance of the wires causes their temperature to rise, thus creating the desired heating effect. The wires are embedded within the windscreen glass in order to prevent damage from the wipers, and additionally to prevent exposure to humans.

Systems such as this have been used in the industry for over thirty years, for the purpose of de-misting or de-icing the windscreen. The wires are fine enough so as not to be obvious to the driver and therefore obscure their vision or distract them.

Additionally there are techniques for ensuring that there is no optical distortion in the windscreen caused by the local heating of the glass around the wire, as in, for example, US 3903396 to Boaz et al. Commonly systems such as this are implemented as two separate circuits, each covering one half of the screen. This allows for the circuits to be powered at a lower voltage which is desirable in terms of safety considerations, and also provides a certain level of fault mitigation, in that if one half develops a fault the other half should still be working.

More recently an alternative method, particularly for de-icing the windscreen, has been proposed, and is described in US 200810203079 Al. In this case an alternating current is applied to the wires, at a frequency tuned to an optimum for ice removal.

The alternating current creates an electromagnetic field which is absorbed by the ice on the exterior of the screen, thereby causing it to melt or dislodge from the glass.

In addition to the de-icing functionality, the system in US 200810203079 Al is also capable of capacitive rain sensing. In capacitive rain sensing, two electrodes are placed on the screen, at a constant offset trom each other. This is often in the form of two comb-like structures placed opposite each other and interleaved. An AC voltage is applied to one circuit, and the capacitive coupling is measured in the other. There is included circuitry to filter out background noise and to restrict conducted noise from the system.

As the moisture level on the screen rises it becomes more conductive, due to the higher permittivity of water than that of glass or air. As this happens the coupled signal becomes stronger, indicating the presence of the moisture. The strength of the coupled signal is directly proportional to the level of moisture on the screen, therefore the signal strength can be used to directly control the frequency of the windscreen wiper action.

The main limitation with these systems is that they tend to only cover a small area of the screen, typically just behind the rear-view mirror. This is so that they don't obscure the driver's view, as well as making sure that it does not interfere with other systems that may be installed on the screen, for example a heater as previously described. Clearly, the larger the proportion of the screen that is covered by the rain sensing system, the more effective it will be at detecting rain.

The system in US 200810203079 Al whereby ice is removed using an alternating current also makes use of the capacitance principle in the way described above in order to detect the presence of ice. However, this system does not significantly heat the screen as it relies on energy being transferred directly to the ice through the propagation of the electromagnetic field. This means that it cannot be used for de-misting, only de-icing. Additionally the sensitivity of this system is low as the AC is necessarily supplied at a high power level in order to be effective in removing the ice.

It is one object of the invention to overcome or at least alleviate the shod-comings of the prior ad.

Summary of the Invention

According to a first aspect of the invention, there is provided a window assembly comprising a window, and an electrical system which is arranged to detect the presence of moisture on a surface of said window. The electrical system comprises a first conductive element fitted to the window, and a second conductive element fitted to the window such that at least one portion of the second conductive element is in close proximity to the first conductive element. For example, the first and second conductive elements may be fitted to the window by embedding them within the window.

The electrical system further comprises means for applying a DC voltage to at least one of the first and second conductive elements to create a resistive heating effect, means for applying an AC voltage to the first conductive element, and a sensing system arranged to detect a capacitive coupled signal in the second conductive element, so as to indicate the presence of moisture on the surface of the window.

The window assembly provides dual functionality in that it can detect the presence of moisture on the window, and also remove it using the resistive heating effect. The separation of the two functions, by using the DC voltage for the heating and the AC component for moisture detection, allows for greatly improved sensitivity of the moisture detection compared with systems known in the prior art, for example in US 2008/0203079 Al.

Furthermore, by combining the resistive heating and the moisture detection into a single system, moisture detection can beneficially occur over the entire surface of the window.

The sensing system may comprise means to determine the magnitude of the capacitive coupled signal. This feature beneficially enables the electrical system to determine the level of moisture which is present on the surface of the window.

The window assembly may further comprise means for comparing the magnitude of the coupled signal with a predetermined threshold, and wherein the sensing system is arranged to activate at least one window wiper if the strength of the capacitive coupled signal is higher than the predetermined threshold. This feature allows for automatic clearing of moisture from the surface of the window upon detection of the presence of moisture.

The window assembly may further comprise means for determining the level of moisture present on the surface of the window on the basis of the capacitive coupled signal in the second conductive element.

The sensing system may further comprise means for setting the frequency of operation of the at least one window wiper based on the determined level of moisture present on the exposed surface of the window, so that the wiper or wipers are not The window assembly may comprise a plurality of laminated layers.

The first and second conductive elements of the electrical system may be fitted between two of the laminate layers of the window. This protects the conductive elements from damage which may be caused by a wiper for example. This feature also removes the risk of electric shock to a human through direct exposure to the conductive elements.

The AC voltage of the electrical system that is applied to the first conductive element may be small relative to the DC voltage.

The means for applying the DC voltage may be arranged to supply the DC voltage to each conductive element independently of the other conductive element, thus enabling two different power settings for the heating for de-misting or de-icing the window. This feature also accords the window assembly with a level of fault mitigation, in that if one conductive element develops a fault, the other can continue to heat the window.

The first conductive element may have a conductive path length which follows a path that is offset from a conductive path length of the second conductive element by a substantially constant distance. This gives the window assembly a consistent sensitivity to moisture over the entire area covered by the electrical system.

The window assembly may be arranged such that the first and second conductive elements are in close proximity to each other only in a designated rain sensing area of the window, and are not as close to each other in other areas of the window.

The first and second conductive elements may be arranged to follow a square wave path on the window, which is an efficient shape for covering as much of the surface area as possible.

The electrical system may comprise at least one low pass filter to remove background signals and conducted noise from the system, in order to improve the sensitivity of the electrical system for moisture detection.

The means for applying the AC voltage to the first conductive element may be arranged to apply the AC voltage at a constant frequency. This may relate to a frequency which is optimal for moisture detection, and the use of a single frequency may allow for a simpler electrical system.

The means for applying the AC voltage to the first conductive element may be arranged to apply the AC voltage at a range of frequencies, in order to enable the electrical system to determine the quality factor and hence determine whether the window has water, ice or other substance (dirt, for example) on its surface. This information can be used to determine the appropriate action to take to remove the detected substance.

According to a second aspect of the invention, there is provided a method of detecting the presence of moisture on a surface of a window, the method comprising filling a first conductive element to the window; and fitting a second conductive element to the window such that at least one portion of the second conductive element is in close proximity to the first conductive element. The method further comprises applying a DC voltage to at least one of the first and second conductive elements to create a resistive heating effect; applying an AC voltage to the first conductive element; and detecting a capacitive coupled signal in the second conductive element, so as to indicate the presence of moisture on the surface of the window.

According to a third aspect of the invention, there is provided a window assembly comprising a window and an electrical system which is arranged to remove moisture from a surface of said window, the electrical system comprising: a first conductive element fitted to the window; a second conductive element filled to the window, each of the first and second conductive elements comprising a length of wire, wherein the length of wire of the first conductive element follows a path that is offset from a path

S

of the length of wire of the second conductive element by a substantially constant distance along the path length; the window assembly further comprising means for applying a DC voltage to at least one of the first and second conductive elements to create a resistive heating effect.

It will be appreciated that preferred and/or optional features of the first aspect of the invention may be incorporated alone or in appropriate combination in the second and/or third aspects of the invention also.

Brief description of the drawings

In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings, in which like reference numerals are used for like features, and in which: Figure 1 is a plan view of a windscreen heater as known in the prior art; Figure 2 is a plan view of a windscreen assembly according to one embodiment of the present invention; and Figure 3 is a schematic circuit diagram showing the particulars of the control circuit for the system of Figure 2.

Detailed description of embodiments of the invention Figure 1 shows an example of a standard heating system 10 for a window, for example a windscreen 12 for a vehicle. The heating system 10 comprises a pair of heating wires 14, 16, embedded within the windscreen 12. Each heating wire 14, 16 is connected to a respective busbar 18, 20 at one end which is supplied with a DC voltage, and to a second respective busbar 18, 20 at the other end, which is connected to a vehicle ground 22. As an electric current flows through each wire its electrical resistance causes its temperature to rise, which provides a heating action for de-misting or de-icing the windscreen 12.

The heating wires 14, 16 each occupy one side of the windscreen 12. Only those areas of the windscreen 12 which are close to the wires 14, 16 will be effectively de-misted or de-iced, as the heat from the wires 14, 16 only dissipates over a small distance. Therefore the heating wires 14, 16 are arranged to cover as much of the windscreen 12 as possible. A disadvantage of this arrangement is that if one of the resistance wires 14, 16 develops a fault! one half of the windscreen 12 loses its heating ability, and therefore cannot be de-iced or de-misted.

Referring now to Figure 2, the windscreen system 24 of the invention comprises an electrical system having a first electrode 26 and a second electrode 28, which are each constituted by a wire, embedded within the windscreen 12, and a control circuit 30. Each of the electrodes 26, 28 is connected at one end to the control circuit 30 which supplies a DC voltage to each electrode, and at the other end to a vehicle ground 22.

The windscreen 12 may be of a type that is standard for modern automotive vehicles, with an internal surface and an external surface, and is made up of a plurality of laminated glass layers. The electrodes 26, 28 may be installed between two of these layers, with a conductive link from the electrodes 26, 28 within the windscreen 12 to the external surface of the windscreen 12 to enable connections to the control circuit and the vehicle ground 22.

The two electrodes 26, 28 each comprise a length of wire, and in one embodiment of the invention they are arranged in a structure that tracks up and down the windscreen 12 in the manner of a square wave as shown in Figure 2. The wires are arranged such that the first electrode 26 is above the second electrode 28, where the second electrode 28 is placed such that it tracks the first electrode 26 at a small, constant offset.

Both electrodes 26, 28 are supplied with a DC voltage, preferably 12V. In one embodiment, an equal voltage is applied to each electrode 26, 28, and this voltage is controlled by a vehicle body control module, which is an electronic control unit which is responsible for controlling a range of electrical accessories in the automotive vehicle. In another embodiment the DC voltage may be manually controlled by a user.

As an electrical current flows through each electrode 26, 28, the electrical resistance of the electrode causes its temperature to rise, which provides the heating action for de-misting or de-icing the windscreen 12.

The material and thickness of the electrode wires are determined by the resistive heating effect that they are required to produce. Therefore, the wires will be similar to those used in other standard heated windscreen assemblies, for example, a diameter of about 0.015 millimetres is typical.

Referring now to Figure 3, the control circuit 30 incorporates components including a first low pass filter 32 and a second low pass filter 34 to remove any background noise and to restrict conducted noise from the system, and a sensing or logic system 36 to determine an appropriate wiper frequency output 38 from the control circuit 30.

The first low pass filter 32 is connected to the first electrode 26, with a feedback loop returning to the sensing system 36 via an amplifier 40 to allow electrical signals to be measured. The second low pass filter 34 is connected to the second electrode 28, with a feedback path to the sensing system 36 for the measurement of an injected AC component 42. Because the electrodes 26, 28 are placed at a small offset from each other, some of the AC component 42 will be picked up by the first electrode 26 because of a capacitive effect, to create a coupled signal in the first electrode 26.

Once the sensing system has compared the coupled signal with the AC component 42, it can determine the proportion of the AC component 42 which has returned in the coupled signal. The sensing system then activates the windscreen wipers of the vehicle accordingly via an output control signal 38. The electrodes 26, 28 are each connected to a respective positive terminal, 44, 46, which supplies the DC voltage.

In this embodiment, an AC component 42 is superimposed on top of the DC signal in the second electrode 28. The electrical signals going through the electrodes 26, 28 create corresponding electric fields around the electrodes 26, 28. The electric fields propagate through the glass substrate of the windscreen 12, which acts as a dielectric. The difference between the electric fields surrounding each electrode 26, 28 caused by the AC component 42 in the second electrode 28 creates a capacitive coupling effect between the two electrodes 26, 28. Therefore, charge from the alternating electric field surrounding the second electrode 28 will propagate to the coupled first electrode 26 at a rate determined by the permittivity of the windscreen 12. If the windscreen 12 becomes more moist, its permittivity increases, and therefore so does the rate of propagation of the electric fields through it. This leads to a stronger signal in the first electrode 26. The magnitude or strength of the coupled signal is therefore directly proportional to the level of moisture present on the external surface of the windscreen 12.

The returning signal from the first electrode 26 is sent through the first low pass filter 32 to remove any background noise and to restrict conducted noise from the system, and the strength of the remaining signal is directly proportional to the level of moisture on the windscreen 12. In one embodiment, if the level of moisture on the windscreen 12 is determined as being above a set threshold, the logic system 36 of the control circuit 30 may create an output 38 which will activate the windscreen wipers of the vehicle. In a preferred embodiment, the moisture level which is sensed on the windscreen 12 is used to determine the appropriate frequency for the wiper movement.

Advantageously, the fact that the heating and rain sensing are separated in this way allows the AC component 42 to remain small, thus improving the sensitivity of the rain detection system. For systems using a high power AC component 42, as in US 2008/0203079 Al for example, much of the signal will propagate to the coupled electrode even when there is no moisture on the windscreen 12. Therefore there is little difference in the coupled signal when the windscreen becomes wet for a high power system such as this. The only way to prevent this is to space the electrodes 26, 28 further apart; but this reduces the effectiveness of the heating and de-misting function of the system. The low power detection system of the present invention provides a much more dramatic change in the strength of the coupled signal when the windscreen 12 becomes moist, for the same electrode separation. Therefore the sensitivity ot the rain sensing is greatly improved.

In addition to the size of the AC component 42, as mentioned above, the sensitivity of the rain sensing is also dependant on the size of the offset between the two electrodes 26, 28. If the electrodes 26, 28 are spaced further apart, the coupled signal in the coupled first electrode 26 will be lower, in which case the sensitivity to moisture is altered. For this reason, in the preferred embodiment the electrodes 26, 28 are arranged such that the offset between them is substantially constant over the area of the windscreen 12 that they cover, in order to achieve a consistent level of sensitivity to moisture.

It is also preferable if the frequency of the AC component 42 is constant, and is optimised for moisture detection. In another embodiment, however, the control circuit may be provided with means for enabling the frequency of the AC component 42 to be varied through a range of frequencies in order to determine the quality factor and hence determine whether the windscreen 12 has water, ice or other substance (did, for example) on its surface. This information can be used to determine the appropriate course of action for the system to take. For example, if the control circuit identifies a quality factor which is consistent with the presence of water on the surface of the window, the wipers may be activated. Alternatively, if the identified quality factor indicates that there is ice on the surface, the heaters could be activated instead of the wipers, therefore providing an automatic de-icing facility.

Similarly, this principle may be extended such that the system is able to detect whether moisture is on an internal surface of the windscreen 12, rather than the external surface. If so, the windscreen system 24 may be arranged to supply the DC voltage to the electrodes 26, 28 in order to heat the windscreen 12 in the event that moisture is detected on the internal surface. This therefore provides the windscreen system 24 with an automatic de-misting facility.

A second advantage to this arrangement is that the rain detection takes place over almost the full area of the windscreen 12, thus improving the performance of the system compared with the much smaller designs described thereinbefore. These smaller systems were small by necessity as their design would have led them to obstruct driver vision were they to be larger. Additionally, previous designs may have interfered with other systems installed into the windscreen 12, such as a heating system 10, as described previously with reference to Figure 1.

In contrast to the previously described prior system for heating the windscreen 12, the arrangement of the electrodes 26, 28 in the embodiment of the invention shown in Figure 2 accords the windscreen system 24 a level of fault mitigation: if one electrode 26, 28 fails, the other can continue to heat the windscreen 12 over the full area.

An additional benefit to the invention is the ability to have two different power settings for the heating by virtue of the fact that the electrodes 26, 28 could be switched on and off independently.

In another embodiment of the invention, the two electrodes 26, 28 are arranged such that they are in close proximity to each other in a designated rain sensing area of the windscreen 12, but are not as close to each other in other areas of the windscreen 12.

In a further embodiment of the invention, a DC voltage is only applied to the second electrode 28, along with the AC component 42, such that the first electrode 26 is only used to detect a capacitive coupled signal. In an alternative embodiment, a DC voltage is applied to the first electrode 26 only, and the AC component 42 is injected into the second electrode 28.

In a further embodiment of the invention, additional low pass filters can added before the ground points, indicated at point 23 of Figure 2, improving sensitivity across the windscreen.

In further embodiment, the sensitivity can be improved swapping ground and signal generator outputs. For example, ground 22 can be placed at point 27A in Figure 2, and the signal generator output injected at point 27B. That is, one of the grounds and signal inputs are swapped. This is because the detection sensitivity may change across the windscreen as the signal is stronger at the generator side compared to the ground side. The detection sensitivity will naturally lower in a gradient across the length of the windscreen, being high at the point of injected signal from 30, lowering to a minimum towards the grounds 22.

It will be appreciated by a person skilled in the art that the invention could be modified to take many alternative forms to that described herein, without departing from the scope of the appended claims.

Claims

Claims 1. A window assembly comprising a window and an electrical system which is arranged to detect the presence of moisture on a surface of said window, the electrical system comprising: a first conductive element fitted to the window; a second conductive element fitted to the window such that at least one portion of the second conductive element is in close proximity to the first conductive element; means for applying a DC voltage to at least one of the first and second conductive elements to create a resistive heating effect; means for applying an AC voltage to the first conductive element; and a sensing system arranged to detect a capacitive coupled signal in the second conductive element, so as to indicate the presence of moisture on the surface of the window.
2. A window assembly according to Claim 1, wherein the sensing system comprises means to determine the magnitude of the capacitive coupled signal.
3. A window assembly according to Claim 2, further comprising means for comparing the magnitude of the capacitive coupled signal with a predetermined threshold, and wherein the sensing system is arranged to activate at least one window wiper if the strength of the capacitive coupled signal is higher than the predetermined threshold.
4. A window assembly according to any one of Claims 1 to 3, further comprising means for determining the level of moisture present on the surface of the window on the basis of the capacitive coupled signal in the second conductive element.
5. A window assembly according to Claim 4, wherein the sensing system further comprises means for setting the frequency of operation of at least one window wiper based on the determined level of moisture present on the exposed surface of the window.
6. A window assembly according to any one of Claims 1 to 5, wherein the window comprises a plurality of laminated layers.
7. A window assembly according to Claim 6, wherein the first and second conductive elements are fitted between two of the laminate layers of the window.
8. A window assembly according to any one of Claims 1 to 7, wherein the AC voltage applied to the first conductive element is small relative to the DC voltage.
9. A window assembly according to any one of Claims 1 to 8, further comprising means for applying the DC voltage to each conductive element independently of the other conductive element.
10. A window assembly according to one of Claims 1 to 9, wherein the first conductive element has a conductive path length which follows a path that is offset from a conductive path length of the second conductive element by a substantially constant distance.
11. A window assembly according to any one of Claims 1 to 9, wherein the first and second conductive elements are in close proximity to each other only in a designated rain sensing area of the window, and are not as close to each other in other areas of the window.
12. A window assembly according to any one of Claims ito 11, wherein the first and second conductive elements are arranged to follow a square wave path on the window.
13. A window assembly according to any one of Claims i to 12, wherein the electrical system comprises at least one low pass filter to enable background signals and noise to be removed from the system.
14. A window assembly according to any one of Claims 1 to 13, wherein said means for applying the AC voltage to the first conductive element is arranged to apply the AC voltage at a constant frequency.
15. A window assembly according to any one of Claims 1 to 14, wherein said means for applying the AC voltage to the first conductive element is arranged to apply the AC voltage at a range of frequencies.
16. A method of detecting the presence of moisture on a surface of a window, the method comprising: fitting a first conductive element to the window; fitting a second conductive element to the window such that at least one portion of the second conductive element is in close proximity to the first conductive element; applying a DC voltage to at least one of the first and second conductive elements to create a resistive heating effect; applying an AC voltage to the first conductive element; and detecting a capacitive coupled signal in the second conductive element, so as to indicate the presence of moisture on the surface of the window.
17. A window assembly comprising a window and an electrical system which is arranged to remove moisture from a surface of said window, the electrical system comprising: a first conductive length fitted to the window; a second conductive length fitted to the window, wherein the first conductive length follows a path that is offset from a path of the second conductive length by a substantially constant distance along the path; the window assembly further comprising means for applying a DC voltage to at least one of the first and second conductive lengths to create a resistive heating effect.