Rain/Light Sensor
The rain/light sensor contains a number of transmitter and receiver diodes which emit and receive infrared light. By comparing the received light signal against the known transmitted light signal, the rain/light sensor can determine the amount of water on the outer surface of the windshield.
A = CLEAN AND DRY WINDSHIELD; B = WET AND DIRTY WINDSHIELD.
| ITEM | DESCRIPTION |
|---|---|
| 1 | Windshield outer surface |
| 2 | Optical element |
| 3 | Transmitter diodes (100% light transmitted) |
| 4 | Rain/light sensor assembly |
| 5 | Receiver diodes (100% light received) |
| 6 | Water droplets or water film |
| 7 | Receiver diodes (less than 100% light received) |
| 8 | Lost light |
When the driver moves the wipers and washer control switch to the 'Auto' position, the CJB detects a LIN bus message and monitors LIN bus messages received from the rain/light sensor. The rain/light sensor provides LIN bus messages with values ranging from 0 to 7. A signal value of 0 is interpreted by the CJB as there being no water on the windshield.
A signal value from 1 to 5 is interpreted by the CJB as there being a small amount of water hitting the windshield. In this instance, the CJB initiates a slow wipe routine as detailed in the 'Windshield Wiper Slow Wipe' section above.
A signal value from 6 is interpreted by the CJB as there being a large amount of water hitting the windshield. In this instance, the CJB initiates a fast wipe routine as detailed in the 'Windshield Wiper Fast Wipe' section above.
Rain/light sensor sensitivity can be adjusted by turning the windshield wiper intermittent switch on the wipers and washers control switch to the required position. Six different sensitivity settings are available, which are broadcast over the LIN bus to the CJB.
If the vehicle speed is 0km/h (0 mph) and either front door is opened, the CJB disables the rain sensor operation.
The software within the rain/light sensor can compensate the following:
- Short-term effects - For example dirt or smear, caused by worn wiper blades.
- Long-term effects - For example scratches or stone chips on the windshield, in the area of the optical unit.
When the self-adaptation is no longer possible, a recalibration routine must completed, using the JLR approved diagnostic equipment. The routine allows to reset the rain/light sensor values then the sensor can adopt to the new conditions. Refer to: RAIN SENSOR .
The rain/light sensor is located at the upper edge of the windshield, behind the rear view mirror trim panel. Contact between the rain/light sensor and windshield is provided through a silicon pad which is compressed during the assembly process by two locking retaining clips either side of the sensor.
The rain/light sensor unit attaches to the windshield through a retaining clamp, which latches onto formed tags on the windshield bracket.
The rain/light sensor provides information to the CJB through a Local Interconnect Network (LIN) bus connection for the optimum windshield wiper operation for the prevailing conditions to maintain the windshield in a clear condition at all times. The rain/light sensor is an optical unit, which operates on an infrared waveband. It uses the principle of the laws of reflection on interfacing surfaces between materials with differing refraction properties. 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 windshield 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 through 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 air temperature LIN bus signals from the CJB to keep the optical unit clear of condensation.
The rain/light sensor contains a heater element. The software within the rain/light sensor uses the heater element to keep the optical unit clear of condensation. The software receives Ambient Air Temperature (AAT) signals from the CJB through the LIN connection. Depending on the AAT signal value, the software activates the heater element.
The sensor receives a power supply from the CJB. The 'Auto' wipers are activated when the wipers and washers control switch is moved to the 'Auto' position. The sensitivity of the rain/light sensor can be adjusted by rotating the windshield wiper intermittent switch on the wipers and washers control switch in a clockwise or counterclockwise direction. Clockwise rotation will decrease sensitivity, while counterclockwise adjustment will increase sensitivity. An increase in sensitivity adjustment results in a single wipe of the wiper motor. The CJB disables the rain sensing operation when the vehicle is in standstill position and either front door is opened.