Rain/Light Sensor Functionality
| ITEM | DESCRIPTION |
|---|---|
| 1 | Windscreen - Outside surface |
| 2 | Optical unit |
| 3 | Transmitter diodes (100% light transmitted) |
| 4 | Rain/light sensor unit |
| 5 | Receiver diodes (100% received) |
| 6 | Water droplets/film |
| 7 | Receiver diodes (less than 100% light received) |
| 8 | Lost light |
The rain/light sensor contains transmitter and receiver diodes, which transmit and receive infrared light, which is directed onto the windscreen via an optical unit. The light is directed at an angle so that the light is reflected 100% on the outside surface of the screen and is transmitted back into the optical unit. To receive a 100% reflection, the outer screen surface must be clean and dry.
The light is reflected 4 times from when it leaves the transmitter diodes to when it is picked up by the receiver diodes. If the windscreen is wet or dirty in the area of the optical unit, the clean conditions for 100% reflection means that some of the light reflected is lost. As the screen becomes dirtier or wetter, the received light is evaluated by the rain/light sensor and translated into a signal value. A micro-controller within the sensor monitors the change in signal and initiates the appropriate wipe cycle via LIN bus signals to the CJB.
The software can compensate for the long-term effects of scratches and stone chips in the area of the optical unit and the short term effects of dirt or smears caused by worn wiper blades. A heater element is also contained within the rain/light sensor and uses ambient temperature LIN bus signals from the IC to keep the optical unit clear of frost or condensation.
The rain/light sensor incorporates a light guide. The light guide directs the ambient light and a proportion of the forward light (from the driving direction) to a light sensitive diode. This is used for the rain sensor sensitivity in low ambient light levels and is also used to control the automatic headlamp function.
For additional information, refer to: EXTERIOR LIGHTING .
Intermittent (single wipe), continuous slow, and continuous fast windshield wiper operations are controlled by the rain/light sensor when enabled function is intermittent.