Eyes that see in the rain, in the dark, in bright sunlight

Eyes that see in the rain, in the dark, in bright sunlight


Did you know that your car has eyes? They are alert and vigilant, constantly scanning the surrounding area to make your life easier behind the wheel. Find out more about the sensors that let your car activate some functions automatically.

20. 10. 2020

For example, sensors control the switch between your daytime lights and passing beam lights, which is handy when you enter a tunnel or darkness falls. A different sensor checks for moisture or sunlight intensity, and another one is in charge of automatic windscreen wiper activation.


Smart RLFS sensor in the ŠKODA ENYAQ iV model

In ŠKODA cars, all these functions are handled by a single module for multiple sensors. The module is found on the windscreen, behind the plastic housing of the rear-view mirror, and is concealed from the outside by a ceramic layer. The sensor’s surface is covered by a contact layer of gel ensuring perfect contact with the glass and sealing the sensor against dust particles. If the windscreen has to be replaced, the gel layer is replaced by a new one, so the original sensor can be used again.

Smart RLFS sensor

The module should properly be called a rain-light-moisture-sun module, because its diodes and sensors scan both surrounding and interior parameters like the light conditions in front of and above the car; they detect water on the windscreen; the windscreen’s temperature; the intensity of sunlight; the relative interior humidity; and the dew point. The module’s control unit can measure and calculate all these phenomena. The sensor is known by the abbreviation RLFS, which comes from the German Regen-Licht-Feuchte-Sonne (rain-light-moisture-sun). All the above readings are processed and evaluated by the car’s central control unit. This unit then sends instructions to other units that control the relevant functions, like switching on headlights, activating the windscreens or adjusting air-conditioning settings.

Main functions of the RLFS sensor

• Rain sensor

This evaluates the quantity of water on the windscreen. For this to work, the lights control has to be set to AUTO and the wiper stalk position to INT. Then the driver can forget all about it: information about the quantity of water is sent to the central control unit, which sends an instruction to activate the wiper motor. The only thing that can be adjusted is the sensor sensitivity – there is a small rotary dial with four sensitivity levels on the upper side of the stalk. A small drop means low sensitivity, a large drop means high sensitivity.

• Light sensor

Diodes inside the sensor scan the light conditions in front of and above the car and perpendicular to the windscreen. The sensor sends the information to the central control unit, which uses it to control other functions of the car. The car thus knows whether it’s light or dark, whether it has entered a tunnel or is simply on a tree-lined road, and it performs the appropriate lighting adjustments based on constantly running calculations.

• Moisture sensor

The sensor assesses the humidity inside the car, sunlight intensity and the temperature on the interior side of the windscreen. The central control unit processes the data and sends it to the air-conditioning control unit, which adjusts the air-conditioning settings to meet the driver’s requirements and to prevent windscreen fogging. The sensor can even tell which side of the car the sunlight is stronger on, so it can make different adjustments for the right and left sides of the interior.

The smart RLFS sensor does even more than the three main functions described above. If it starts to rain, the car automatically switches from daytime lights to passing beam lights. The Coming/Leaving Home function that lights up the car when you approach or leave it is only active in the dark, due to the sensor’s monitoring of the surrounding light levels. Thanks to tunnel mode, the car can tell that it has entered a tunnel and again switches from daytime lights to passing beam lights – this is calculated on the basis of the speed at which the light conditions change and the distance covered. The switch when entering and leaving tunnels is practically instantaneous – it takes no more than two seconds.

For the sensor to work well, it has to “see” perfectly, so the glass above it must be perfectly clean. That makes it a good idea to regularly check your wipers and their rubber blades.

How is it tested?

The sensors are first tested in laboratory conditions, where the basic functionality and communication with the car are checked. All possible types of rain are trialled, from a weak drizzle to downpours, including sudden and intensive splashing of a large amount of water onto the glass – something that typically happens when a truck moving in the opposite direction hits a puddle. That is followed by a thousand hours of real-life testing to check how the sensor reacts to the surrounding conditions. The system is then fine-tuned using actual on-road testing.

Adjusting sensitivity does not mean an instantaneous reaction

Using the rotary dial on the upper side of the control stalk, the driver can set the sensitivity of the rain sensor that assesses the amount of water on the upper part of the windscreen. There are four levels to choose from. Raising the level results in a shorter wiping interval or a quicker reaction from the wipers. “It should be understood, though, that by changing the sensor’s sensitivity we are primarily changing the input data for the algorithm in the control unit. So changing sensitivity is not a means for achieving immediate control of the wiper frequency. The sensor receives changed input information and waits to see how much water subsequently falls on the scanned surface. It then makes new calculations to adjust the wiper frequency. All that takes a little time,” explains Pavel Švejdar, who is in charge of windscreen wipers and sprays at ŠKODA Technical Development.

It all began in America

The story of sensors began in the United States at the end of the 1950s. The first rain sensor was installed in the Buick LeSabre concept car from 1951. In 1958, Cadillac engineers experimented with a water sensor that could activate electric motors controlling the roof and windows of a cabriolet. In 1956, a rain sensor was an optional extra on the Chevrolet Bel Air. As time went on, rain sensors became increasingly common in cars, though for a long time they were confined to luxury cars. But they gradually spread to all models of cars, even standard versions. The first ŠKODA model to get a rain sensor was the first-generation SUPERB from 2001.

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