Sensor cover for vehicles and method for heating said sensor cover for vehicles

Abstract

The sensor cover comprises: one heating element (7) that heats a surface of the cover; an electric connector (6) that connects the at least one heating element (7) with a power source; and at least one control device (10) that controls de operation of the at least one heating element (7); wherein the at least one heating element (7) generates a variable electrical resistance depending on the variation of its temperature, that is detected by the at least one control device (10), said at least one control device (10) powering on or off the at least one heating element (7) according to the electric resistance detected by the at least one control device (10). It permits a direct measure of the whole heating element, providing a more precise and reactive control of the sensor cover temperature.

Claims

1: Sensor cover for vehicles, comprising: at least one heating element (7) that heats a surface of the cover; a field of view (FOV), that is an area transparent to electromagnetic waves transmitted from or to the sensor; an electric connector (6) that connects the at least one heating element (7) with a power source; and at least one control device (10) that controls de operation of the at least one heating element (7); characterized in that: the at least one heating element (7) generates a variable electrical resistance depending on the variation of its temperature, that is detected by the at least one control device (10), said at least one control device (10) powering on or off the at least one heating element (7) according to the electric resistance detected by the at least one control device (10).

2: Sensor cover for vehicles according to claim 1, wherein, if the electric resistance of the at least one heating element (7) increases when its temperature increases, the at least one control device (10): switches off the at least one heating element (7) when the detected electric resistance is greater than an electric resistance corresponding to a maximum temperature of the heating element (7), and switches on the at least one heating element (7) when the detected electric resistance is lower than an electric resistance generated at a minimum predetermined temperature.

3: Sensor cover for vehicles according to claim 1, wherein, if the electric resistance of the at least one heating element (7) decreases when its temperature increases, the at least one control device (10): switches off the at least one heating element (7) when the detected electric resistance is lower than an electric resistance generated at a maximum temperature of the hottest point of the heating element (7), and switches on the at least one heating element (7) when the detected electric resistance is greater than an electric resistance generated at a minimum predetermined temperature.

4: Sensor cover for vehicles according to claim 1, wherein the electric resistance of the at least one heating element (7) is measured by the control device (10) measuring the voltage at the poles of the heating element (7).

5: Sensor cover for vehicles according to claim 1, wherein the circulating intensity at the at least one heating element (7) is measured by the control device (10) measuring the voltage at the poles of a resistance (R.sub.shunt) connected in series with the at least one heating element (7).

6: Sensor cover for vehicles according claim 1, wherein the circulating intensity at the at least one heating element (7) is measured by the control device (10) measuring the magnetic field generated by the intensity with a current sensor based on the Hall effect or through a fluxgate magnetic sensor.

7: Sensor cover for vehicles according to claim 1, wherein a four-point electric resistance measurement method is used to measure the electric resistance of the at least one heating element (7) to avoid the influence of other existing resistances (R.sub.cnt1, R.sub.cnt2) connected in series with the at least one heating element (7).

8: Sensor cover for vehicles according to claim 1, wherein a Wheatstone bridge is used to measure the electric resistance of the at least one heating element (7).

9: Sensor cover for vehicles according to claim 1, wherein the at least one heating element (7) is switched on and off by a switch (SW) controlled by the at least one control device (10).

10: Sensor cover for vehicles according to claim 1, wherein the measurements of the temperature control device (10) are triggered by the PWM when it has a duty cycle lower than 100% or by its own periodical pulse when the PWM has a duty cycle of 100%.

11: Sensor cover for vehicles according to v claim 1, wherein it comprises two or more heating elements (7, 7), each controlled by a different control device (10).

12: Sensor cover for vehicles according to m claim 1, wherein the electric connector (6) and the one or more control devices (10) are placed outside the field of view (FOV).

13: Method for heating a sensor cover for vehicles, the sensor cover comprising: at least one heating element (7) that heats a surface of the cover; a field of view (FOV), that is an area transparent to electromagnetic waves transmitted from or to the sensor; an electric connector (6) that connects the at least one heating element (7) with a power source; and at least one control device (10) that controls de operation of the at least one heating element (7); characterized in that the method comprises the following steps: detecting an electric resistance that is variable with a change of temperature generated by the at least one heating element (7) by the at least one control device (10), and powering on or off the at least one heating element (7) according to the electric resistance detected by the at least one control device (10).

14: Method for heating a sensor cover for vehicles according to claim 13, wherein, if the electric resistance of the at least one heating element (7) increases when its temperature increases, the at least one control device (10): switches off the at least one heating element (7) when the detected electric resistance is greater than an electric resistance corresponding to a maximum temperature of the heating element (7), and switches on the at least one heating element (7) when the detected electric resistance is lower than an electric resistance generated at a minimum predetermined temperature.

15: Method for heating a sensor cover for vehicles according to claim 13, wherein, if the electric resistance of the at least one heating element (7) decreases when its temperature increases, the at least one control device (10): switches off the at least one heating element (7) when the detected electric resistance is lower than an electric resistance generated at a maximum temperature of the hottest point of the heating element (7), and switches on the at least one heating element (7) when the detected electric resistance is greater than an electric resistance generated at a minimum predetermined temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] For better understanding of what has been disclosed, some drawings in which, schematically and only by way of a non-limiting example, a practical case of embodiment is shown.

[0034] FIG. 1 is a fragmentary isometric view of a vehicle having a sensor cover constructed in accordance with and embodying the invention positioned within a grill assembly and a sensor positioned behind the sensor cover.

[0035] FIG. 2 is a side view of a sensor cover, where the sensor, its Field of View (FoV), the heating element and connector may be seen.

[0036] FIG. 3 is a thermal map of a heated sensor cover at a given depth.

[0037] FIG. 4 is a schematic side view of the igloo effect on a sensor cover.

[0038] FIG. 5 is a rear view of a sensor cover with a first distribution of multiple heating zones related to the Field of View.

[0039] FIG. 6 is a side view of a sensor cover with a second distribution of multiple heating zones related to the Field of View.

[0040] FIG. 7 is a graph with the evolution in time of the temperature on a given point of a heating element and on the temperature detection element of a temperature control system of the state of the art.

[0041] FIG. 8 is a graph of the electric resistance change of a conductive wire.

[0042] FIG. 9 is an electric scheme of the temperature control device based on electric resistance change proposed in current application.

[0043] FIG. 10 is an electric scheme of high precision four-point electric resistance measurement.

[0044] FIG. 11 shows the output of the disclosed temperature control device in different conditions of temperature of the heating element and existence of an external Pulse Width Modulation (PWM).

[0045] FIG. 12 shows the output of the disclosed temperature control device in different conditions of temperature of the heating element and absence of an external Pulse Width Modulation (PWM).

[0046] FIG. 13 shows an external module with the disclosed temperature control device.

[0047] FIG. 14 shows an alternative embodiment including a Wheatstone bridge.

DESCRIPTION OF A PREFERRED EMBODIMENTS

[0048] With reference now in detail to the drawings, wherein like numerals will be employed to denote like components throughout, as illustrated in FIG. 1, the reference numeral 1 denotes generally a sensor cover constructed in accordance with and embodying the invention. Positioned within the vehicle (3) behind and in registration with the sensor cover (1) is a sensor (4).

[0049] The sensor cover shown in the figure is configured for mounting within a grill assembly (2) of the motor vehicle (3). The position and appearance of this sensor cover (1) usually corresponds to a radome, protecting a radar. However, the proposed concept is applicable to other types of sensors covers that may be differently positioned and protecting other types of sensors.

[0050] FIG. 2 shows a side view of the sensor cover (1), where the sensor (4) is positioned behind the sensor cover (1) with respect to an external observer. A side view of the Field of View (5) is also represented and its intersection with the sensor cover (1).

[0051] The Field of View (5) is the area transparent to the electromagnetic transmitted waves from or to the sensor (4). The electric connector (6) is used to electrically power a heating element (7) of the sensor cover (1) from the electric system of the vehicle.

[0052] A thermal map of the heated sensor cover is shown in FIG. 3. It corresponds to a given vehicle speed and external temperature and is represented at a given depth of the sensor cover. As it may be seen, the temperature is not uniformly distributed. The Field of View (5) on the sensor cover (1) is represented as limited by a dashed line.

[0053] The state-of-the-art systems to control the temperature at a sensor cover (1) are based on one or several temperature detection elements that, as mentioned, cannot be positioned within the Field of View (5). This will provide just a partial temperature information, not including the area of greatest interest which is the Field of View (5).

[0054] FIG. 4 schematically shows the heating element (7) of the sensor cover. The heating element (7) may be formed by one or several thin conductive wires that act as electric resistances which are powered from the electric system of the car through the electric connector (6).

[0055] Alternatively, the heating element (7) may be formed by a layer containing elements such as PEDOTs, carbon nanotubes or others with a specified electric resistance.

[0056] The function of the heating element (7) is to warm up and melt the ice or snow layer (8) that may be deposited on the sensor cover (1) under given climate conditions.

[0057] FIG. 4 also schematically shows (not to scale) an undesired effect that may happen which is named igloo effect. It happens when the melting of just a part of the ice or snow layer (8) in contact with the external face of the sensor cover (1) generates an air chamber (9). This air chamber (9) acts as a thermal insulation, making more difficult the melting of the rest of the ice or snow layer (8) and causing an additional overheating of the sensor cover (1).

[0058] In order to improve the melting process of the ice or snow layer (8), it may be desired to split the heating element (7) in several heating elements, indicated by numeral references 7 and 7 in FIGS. 5 and 6, each one covering a different heating zone, independently powered.

[0059] FIG. 5 and FIG. 6 show possible configurations of multiple heating zones, independently powered, seen from the rear side of the sensor cover (1). The Field of View (5) on the sensor cover (1) is represented as limited by a dashed line.

[0060] In addition to the electric connector (6), it may be seen a possible location of a temperature control device (10), and optional additional temperature control devices, whose configuration and operation is explained later on.

[0061] It may be seen that both the electric connector (6) and the temperature control device(s) (10) are positioned out of the Field of View (5). Otherwise, they might degrade the performance of the sensor (4).

[0062] Several configurations of the multiple heating zones may be considered. Two examples with two heating zones are explained here, although different ones may be designed.

[0063] FIG. 5 shows an example with the Field of View (5) covered by two heating elements (7, 7) defining two different heating zones.

[0064] FIG. 6 shows another example with two heating elements (7, 7), where the heating zone of the first heating element (7) covers the Field of View (5) and the heating zone of the second heating element (7) covers an area around the Field of View (5).

[0065] The heating element at each heating zone may have different material, configuration, and heating power density, allowing different heating strategies for each independent heating zone. The temperature at each heating independent heating element (7, 7) may be controlled by an independent temperature control device (10).

[0066] As previously commented, the disclosed system based on measuring the electric resistance change of the heating element (7) offers different advantages compared to the state-of-the-art temperature detection element known until now.

[0067] The behavior of these last ones is shown in the graph of FIG. 7. It represents the evolution of temperature along the time of a point of the heating element 7 (hottest possible temperature) and the one perceived by the temperature detection element.

[0068] The objective is that the maximum temperature reached at any point of the heating element (7), T.sub.Max, is below a limit temperature depending on the plastic material surrounding the heating element (7) in order to prevent its degradation.

[0069] It may be seen that when power is supplied to the heating element (7), its temperature increases much faster than the one detected by the temperature detection element.

[0070] This element must trigger the shut off operation of the power supply when T.sub.Max is reached. It starts then a temperature decrease process that is, again, faster at the heating element (7) than the one detected by the temperature detection element. This graph shows the existence of a temperature offset and a time lag between the temperatures at both points. Once a predefined T.sub.Min at the heating element is achieved, the power must be supplied again, initiating the next heating cycle.

[0071] This state-of-the-art system is controlling just one point of the heating element (7) which, as commented, cannot be located within the Field of View (5). Several temperature detection elements might be defined controlling several points of the heating element (7) for better accuracy. However, all of them should be positioned out of the Field of View (5) and all of them would show the same drawbacks of temperature offset and time lag.

[0072] The heating element (7) of the sensor cover (1) has an electric resistance, named R.sub.he, which varies with its own temperature changes. This phenomenon is directly linked to the characteristics of the material used on the heating element (7). The graph of FIG. 8 represents how the electric resistance of the conductive wire of an actual heating element (7) changes as a function of its temperature. This case of conductive wire shows a linear increment of its electric resistance with its temperature increase.

[0073] Other materials used for a heating element (7) may show a decrease of its electric resistance with their temperature increase, as it is PEDOTs case. It may happen, too, that the relation between both variables, electric resistance, and temperature, is not linear in the temperature range under consideration.

[0074] The electric resistance of the heating element (7) may be measured and used to determine its temperature. The measured electric resistance will be representative of the considered heating element (7) as a whole, including the part of the heating element (7) that is within the Field of View (5). This measure is really representative of the distribution of temperatures at the heating element (7), it is not affected by a temperature offset because of the distance between the heating generation point and the temperature detection element and it is not affected by a time lag due to thermal inertia between both points.

[0075] It may be established the value of electric resistance, R.sub.he, of each heating element (7) corresponding to the specified T.sub.Max of the hottest point of the heating element (7), named R.sub.he(T.sub.Max), and the electric resistance, R.sub.he, corresponding to the specified T.sub.Min, named R.sub.he(T.sub.Min).

[0076] A basic scheme of the disclosed temperature control device (10) based on controlling the change on the variable electric resistance R.sub.he of the heating element (7) is shown in FIG. 9. The heating electric circuit includes a resistance, R.sub.shunt, connected in series with the heating element (7). R.sub.shunt is of a known given value and very stable at the temperature range it will operate. The temperature control device (10) measures the voltage, V.sub.shunt, at the poles of R.sub.shunt. This allows to know the circulating intensity, I.sub.mea, at the heating element (7).

[0077] An alternative method to know the circulating intensity, I.sub.mea, is through the measurement of the generated magnetic field. This may be done with a current sensor based on the Hall effect or through a fluxgate magnetic sensor.

[0078] The temperature control device (10) measures the voltage, V.sub.he, at the poles of the electric resistance R.sub.he. This allows to know the electric resistance, R.sub.he, of the heating element (7) at any moment and which is dependent on its temperature at this same moment. This value of R.sub.he is compared with the pre-established values of R.sub.he(T.sub.Max) and R.sub.he(T.sub.Min) and the switch (SW) is activated accordingly.

[0079] If the heating element (7) has an electric resistance which increases with temperature increase, the switch will be switched OFF when R.sub.he>R.sub.he(T.sub.Max) and the switch will be switched ON when R.sub.he<R.sub.he(T.sub.Min). If the heating element (7) has an electric resistance which decreases with temperature increase, the switch will be switched OFF when R.sub.he<R.sub.he(T.sub.Max) and the switch will be switched ON when R.sub.he>R.sub.he(T.sub.Min).

[0080] Since the whole control system is based on accurate measurements of electric resistances, it is advisable to use the known high precision four-point electric resistance measurement to monitor the electric resistance R.sub.he of the heating element (7).

[0081] FIG. 10 describes how this measurement technique is applied. It avoids any influence of the variability on the transitions from the heating element (7) to the electric connector (6), represented by the resistances R.sub.cnt1 and R.sub.cnt2. This measurement system avoids that the voltage drops at R.sub.cnt1 and R.sub.cnt2 caused by the current intensity I.sub.mea might influence the evaluation of the change in electric resistance R.sub.he. R.sub.cont1 and R.sub.cont4 don't cause any relevant influence in the measurement because the current circulating through them is several orders of magnitude lower than I.sub.mea.

[0082] An alternative method to know electric resistance R.sub.he is by including a Wheatstone bridge, which is shown on FIG. 14. This type of circuit has the ability to provide extremely accurate measurements. If the internal electrical resistance of the Voltage meter V.sub.G is high enough to consider negligible the electrical intensity through it, the R.sub.he may be computed from the three other resistor values R.sub.shunt, R.sub.A and R.sub.B and the input voltage V.sub.PWM through the following formula:

R.sub.he=(R.sub.AV.sub.PWM+(R.sub.A+R.sub.B)V.sub.G)/(R.sub.BV.sub.PWM(R.sub.A+R.sub.B)V.sub.G)R.sub.shunt,

[0083] FIG. 11 shows the output of the disclosed temperature control device (10) in different conditions of temperature of the heating element (7) and existence of an external Pulse Width Modulation (PWM). The PWM usually provides a duty cycle lower than 100% with a given cycle frequency. The input voltage rise from the PWM triggers the measurement at the temperature control device (10) of V.sub.he and V.sub.shunt.

[0084] It must be noted a minimum duty cycle (for instance, 1%) is needed where the switch must be ON in order to perform the measurements. Based on these measurements, it switches ON the heating element (7) if its temperature is lower than the specified T.sub.Min, as shown on the left of the figure. Based on these measurements, it switches OFF the heating element (7) if its temperature is higher than the specified T.sub.Max, as shown on the right of the figure.

[0085] FIG. 12 shows the output of the disclosed temperature control device (10) in different conditions of temperature of the heating element (7) and absence of an external Pulse Width Modulation (PWM). In this case, the duty cycle is constant at 100% and the temperature control device must generate its own periodical pulse to trigger the measurement of V.sub.he and V.sub.shunt.

[0086] The periodical pulse generated by the temperature control device (10) will have a lower frequency than the usual cycles defined by the PWMs. This allows to wait the input voltage rise from the PWM, if it exists. Otherwise, it generates its own pulse. Based on these measurements, it switches ON the heating element (7) if its temperature is lower than the specified T.sub.Min, as shown on the left of the figure. Based on these measurements, it switches OFF the heating element (7) if its temperature is higher than the specified T.sub.Max, as shown on the right of the figure.

[0087] As previously commented, since there is no need of temperature detection elements located close to the heating element, the disclosed temperature control device (10) may be located in a remote position.

[0088] FIG. 13 shows an external module (11) which internally contains the temperature control device (10). This external module (11) may be externally connected to the electric connector (6) of the sensor cover. On the other side, it may contain its own electric connector (6) similar to the electric connector (6) of the sensor cover (1). This allows to use the external module (11) as an independent device, electrically connected between the sensor cover (1) and the electric system of the vehicle.

[0089] The external module (11) may be considered as an optional accessory to be used on some vehicles equipped with a heated sensor cover. It may also be used to overcome the fact that, due to its dimensions, cannot be integrated in some small sensor covers.

[0090] Although reference has been made to specific embodiments of the invention, it is apparent to a person skilled in the art that the described sensor cover and method are susceptible of numerous variations and modifications, and that all the details mentioned can be replaced by other technically equivalents, without departing from the scope of protection defined by the appended claims.