Patent Application
20240017698
The present invention relates to a sensor cover for vehicles, that covers one or more sensors placed in a grill assembly of a vehicle. The present invention also refers to a method for heating said sensor cover for vehicles.
The automotive industry is constantly increasing the number of sensors which are able to sense the surroundings of the road vehicles. The higher quantity of sensors, their improved sensibility, and their capability to perform in harsh weather conditions allow to increase the levels of driver assistance toward Automated Driving Systems.
This increases the safety of both the vehicle occupants and pedestrians, avoiding collisions and reducing fatalities.
Sensor covers are usually positioned in front of the sensors, protecting them of external influences and integrating them in the vehicle aesthetics, providing an attractive impression of the vehicle. In some cases, these sensor covers represent the car manufacturer's emblem logo.
The sensors may be of different types, including radars, cameras and lidars, which operate at different frequency ranges. Such sensor covers are named radomes in the case of hiding and protecting radar sensors.
We may divide the sensor cover in two areas, one of them is the Field of View (FoV), which is transparent to electromagnetic waves from or to the sensor. This area has high restrictions in materials and dimensions to perform correctly. The rest of the sensor cover has more freedom in its construction, allowing fixation elements, electric connectors or other devices that would affect the sensor performance if they would be present within the FoV.
Sensor covers functionalities are being increased to ensure the correct transmitting/receiving performance of the sensor in adverse weather conditions. One of the most relevant added functionalities is their capability to remove the ice or snow layer which might be deposited on the FoV of the sensor cover, significantly affecting to the waves emitted or received by the sensor.
In these cases, the sensor cover includes a heating element, which is powered by the electric system of the vehicle and is capable to melt the deposited ice or snow, eliminating them.
This heating element may take the form of a conductive wire, usually made with a copper alloy, which is routed in the form of a heating layer. Alternatively, other systems may provide a layer with a specified electric resistance by using elements such as PEDOTs or carbon nanotubes. All these heating elements must ensure enough transparency at the operating frequency of the sensor since they have to be used, at least, in the FoV area of the sensor cover.
The goal of a fast removal of deposited ice or snow by increasing the heating power may lead to damage the materials of the sensor cover because of overheating. The material damage may degrade the transmission performance or the aesthetics of the sensor cover.
On the other side, a too conservative heating approach to protect the materials of the sensor cover may lead to an underheating situation, where the layer of snow or ice is not removed or it takes too much time to eliminate it, compromising the performance of the sensor function.
In order to avoid these problems, more evolved sensor covers are incorporating temperature detection elements which, in one way or another, help to modulate the electric energy that is supplied to the heating system. These temperature detection elements, which may take the form of thermistors, are not transparent at the operating frequency of the sensors.
As a consequence, they must be positioned out of the FoV, which is the area where the temperature monitoring is more desired. This system loses reliability in dynamic situations where the temperature within the sensor cover changes along the time.
The use of temperature detection elements may be done only on one point or on a limited number of points, positioned all of them out of the FoV, which is the area of greatest interest.
The temperature detection element is usually surrounded by the plastic material of the sensor cover. As a consequence, due to the low thermal conductivity of the plastic material, there is a temperature offset between the hottest temperature produced at the heating element and the temperature measured by the temperature detection element. Additionally, a dynamic situation may cause a fast temperature change at a given point of the heating element which is detected with a time lag by the temperature detection element.
JP 2019168265 A discloses a decorative part with a thermostat that senses the overheating of the base material and acts as a overheat prevention element, shutting off the energization of the heating element.
EP 3648248 A1, of the same applicant than the present application, also discloses a radome for vehicles comprising a temperature detection element integrated in the radome between the frontal surface and the rear surface. It is in communication with the power source to modulate the supplied energy.
CN 111812593 A discloses a radome with an external connection structure which includes a printed circuit board with a thermistor that detects the temperature and acts on the energy supply.
The conductive materials usually show a change of its own electric resistance, depending on their temperature, and this change can be characterized. The present application is based on the measurement of the electric resistance variation suffered by the heating element of the sensor cover as a consequence of its own temperature change during the heating process.
This is a direct measure of the whole heating element, not an indirect measure of one of its points, overcoming the drawbacks of existing solutions and mentioned prior art.
The resulting temperature control device based on this concept may provide a more precise and reactive control of the sensor cover temperature.
The sensor cover, and the method for heating said sensor cover according to the present invention is defined in the independent claims. The dependent claims include optional additional features.
The sensor cover, and the method according to the present application provides, among others, the following advantages:
The measurement is done directly on a known characteristic of the heating element (the hottest element of the sensor cover) instead of doing it indirectly through the plastic material.
The measurement includes the detection of the temperature in the FoV area of the sensor cover, instead of doing it in points out of the FoV.
The temperature offset between the hottest heating element and the temperature detection element is eliminated.
The time lag between the temperature changes at the hottest heating element and at the temperature detection element caused by the thermal inertia due to the low thermal conductivity between them is eliminated.
A maximum operating temperature (to avoid overheating and sensor cover damage) and a minimum operating temperature (to avoid underheating and lack of ice or snow melting) may be more precisely set because the temperature offset and the time lag of the previous systems were variable and depending on external environmental conditions and car speed, causing uncertainty, and not allowing compensation.
The temperature control device may act as a Pulse Width Modulation (PWM), delivering the maximum power to the heating element without the need of any PWM of the Electronic Control Unit (ECU) which can only manage the power delivered to the heating element based on external factors like the car speed or external temperature. This reduces to a minimum the time needed to melt the snow or ice.
The disclosed temperature control device is compatible with an existing PWM of the vehicle ECU (Electronic Control Unit).
False overheating detection that is caused by the low thermal conductivity of the surrounding of the traditional temperature detection elements may be avoided.
Since it controls the temperature of the heating element as a whole, it may be located remotely. The disclosed temperature control device may be integrated in the sensor cover, out of its FoV, or as an external module positioned between the vehicle electric system and the sensor cover. This allows to upgrade existing sensors covers, which don't include any temperature control, with a safety a device like the one described herein.
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.
With reference now in detail to the drawings, wherein like numerals will be employed to denote like components throughout, as illustrated in
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.
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.
A thermal map of the heated sensor cover is shown in
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).
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.
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.
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
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.
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).
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.
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).
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.
The behavior of these last ones is shown in the graph of
The objective is that the maximum temperature reached at any point of the heating element (7), TMax, is below a limit temperature depending on the plastic material surrounding the heating element (7) in order to prevent its degradation.
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.
This element must trigger the shut off operation of the power supply when TMax 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 TMin at the heating element is achieved, the power must be supplied again, initiating the next heating cycle.
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.
The heating element (7) of the sensor cover (1) has an electric resistance, named Rhe, 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
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.
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.
It may be established the value of electric resistance, Rhe, of each heating element (7) corresponding to the specified TMax of the hottest point of the heating element (7), named Rhe(TMax), and the electric resistance, Rhe, corresponding to the specified TMin, named Rhe(TMin).
A basic scheme of the disclosed temperature control device (10) based on controlling the change on the variable electric resistance Rhe of the heating element (7) is shown in
An alternative method to know the circulating intensity, Imea, 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.
The temperature control device (10) measures the voltage, Vhe, at the poles of the electric resistance Rhe. This allows to know the electric resistance, Rhe, of the heating element (7) at any moment and which is dependent on its temperature at this same moment. This value of Rhe is compared with the pre-established values of Rhe(TMax) and Rhe(TMin) and the switch (SW) is activated accordingly.
If the heating element (7) has an electric resistance which increases with temperature increase, the switch will be switched OFF when Rhe>Rhe(TMax) and the switch will be switched ON when Rhe<Rhe(TMin). If the heating element (7) has an electric resistance which decreases with temperature increase, the switch will be switched OFF when Rhe<Rhe(TMax) and the switch will be switched ON when Rhe>Rhe(TMin).
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 Rhe of the heating element (7).
An alternative method to know electric resistance Rhe is by including a Wheatstone bridge, which is shown on
R
he=(RA×VPWM+(RA+RB)×VG)/(RB×VPWM−(RA+RB)×VG)×Rshunt,
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 TMin, 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 TMax, as shown on the right of the figure.
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 TMin, 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 TMax, as shown on the right of the figure.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22382658.7 | Jul 2022 | EP | regional |
