Rain/light sensor, component description

W82.00-1007-06

Location

B176 Rain/light sensor

The rain/light sensor (B176) is located on the inside of the windshield, in the center area at the bottom.

It is pressed and held onto the windshield by a ring.

Task

The rain/light sensor (B176) records the degree of wetting on the windshield and the ambient light intensity.

Function

1 Lens

2 Infrared transmitter unit

3 Infrared receiver unit

4 Windshield

A Windshield (4), dry

B Windshield (4), wet

P82.30-0209-03

Function of rain sensor

Infrared light is radiated from the infrared transmitter unit (2) through the lens (1) to the windshield (4). The intensity of the light reflected at the windshield (4) is measured by the infrared receiver unit (3) which is located at the other end of the lens (1).

If the windshield (4) is dry (A), then the light is almost completely reflected; the infrared receiver unit (3) measures a high light intensity.

If the windshield (4) is wet (B), part of the light of the scattered out of the glass of the windshield (4). As a result the intensity of the reflected light reduces; the infrared receiver unit (3) measures a lower light intensity.

-----------------------------------------------------------------------------------------

The light intensity measured by the infrared receiver unit (3) represents a measure for the degree of wetting of the windshield (4). The smaller the measured intensity the larger the quantity of water on the windshield (4).

The measurement value recording and evaluation takes place within the rain/light sensor (B176). The request for switching on the windshield wiper motor (M3) is transmitted to the base module (GM) with a corresponding message via the rain/light sensor LIN (LIN1) (A7).

-----------------------------------------------------------------------------------------

Function of light sensor

The light sensor consists of two photodiodes which measure the light intensity occurring from outside.

One photodiode is directed forwards onto the road. It measures the light in the foreground and records the light in a narrow cone in front of the vehicle.

The second photodiode is directed upwards and measures the absolute brightness of the ambient light.

If in the process the measured light intensity of the foreground light deviates compared with that of the ambient light, in the following cases auto on/off headlamps is requested via the rain/light sensor (B176):

 Dusk

 Darkness

 Driving through tunnels

 Detected sensor fault

The stated request conditions are considered separately. If at least one of the conditions is met, the rain/light sensor (B176) transmits the request that the standing lights, the low beams, the clearance lamps and the trailer taillamps should be switched on
The measurement value recording and evaluation takes place within the rain/light sensor (B176). The requests of the rain/light sensor (B176) are transmitted directly to the base module via the rain/light sensor LIN (LIN1)A7

 Detection of fog is not realized. In fog the driving lights must continue to be switched on manually.