Rain Sensor
Rain Sensor (AIC - if equipped)
Purpose of the System
The Windshield Wiping System is also available with an optionally equipped Rain Sensor. The Rain Sensor provides added driver convenience and enhances safety by automatically activating the intermittent function of the windshield wipers when water droplets are detected on the windshield.
System Components
Rain Sensor: The unit is mounted on the top center area of the interior windshield surface directly behind the rear view mirror. The unit contains:
- Optical Prism Body: This portion of the unit is permanently fixed to the windshield. It can not be removed and can only be replaced with a replacement windshield.
The prism body has a reflective surface that faces the back of the windshield. The prism body also acts as the windshield mount for the Rain Sensor Control Module.
- Rain Sensor Control Module: The control module incorporates the following;
- Infra Red Emitter and Detector Diodes
- Optics heater (prevents condensation from forming on diodes and prism)
- Optics evaluation and control electronics
- Photo cell to detect night driving
The control module requires four signals for operation; KLR, KL31, Windshield Wiper Motor Park Signal Feedback and K-Bus interface.
Principle of Operation
The optical infra red portion of the sensor operates by the principle of refraction (bending of a light ray). The rain sensor control module activates the emitter diode which sends a beam of infra red light through the windshield on an angle. The set angle is important because it provides the beam with a calculated reflective path back to the detector diode.
The beam is reflected back into the windshield due to the density difference of the glass compared with the ambient air on the outside surface of the glass. When the windshield is clean (no rain drops, moisture or dirt) the detector diode receives 100% of the infra red light that the was sent by the emitter. With this condition, the rain sensor evaluation electronics determines the windshield is free of rain drops.
The density of water is closer to that of glass than air. When rain starts to accumulate in the sensor monitoring area, it causes part of the infra red beam to extend past the outside surface of the glass and into the rain drop. When this occurs, the beam is refracted and only part of the beam returns to the detector diode.
The rain sensor evaluation electronics determines the windshield has a few rain drops (or dirt) on it.
The intensity of the returned infra red beam diminishes proportionally with an increase of water droplets. The rain sensor control module generates a signal proportionate to the amount of rain on the windshield and broadcasts it to the GM via the K bus.
The GM activates the intermittent wipe cycle if the windshield wiper stalk switch is in the intermittent position. It also adjusts the frequency of wiping the windshield depending on the four position thumb wheel.
Rain Sensor Function
The rain sensor is online as soon as it receives KLR operating power.
- When the windshield wiper stalk switch is placed in the intermittent position the GM signals the rain sensor control module via the K-Bus of the request for intermittent wiping and the position of the knurled wheel (sensitivity).
- As an acknowledgement, the rain sensor sends a command via the K Bus to activate the wiper motor. If more than 12 seconds pass before the GM receives them acknowledgement, the GM concludes the rain sensor has a defect and operates the intermittent wipe function as a system not equipped with a rain sensor. The wiper intermittent cycling is based solely on the knurled wheel setting.
- The rain sensor continuously monitors the windshield for rain accumulation and signals the GM to activate the wipers based on the knurled wheel position and how fast the rain accumulates on the windshield.
- The knurled wheel position signal (1-4) via the K bus informs the rain sensor of the selected level of sensitivity.
- Position 1 (least sensitive) delays the wiper activation signal.
- Position 4 (most sensitive) sends the wiper activation signal to the GM sooner.
- When the wiper motor park contacts signal the GM of the wiper arm position, the signal is simultaneously sent to the rain sensor as an indication that the windshield has been cleared of water drops and causes the rain sensor to reset the sensitivity delay timer back to 0.
- If night time driving is detected via the integral photocell, the sensitivity to water droplets is increased causeing a shorter delay than day time driving.
- Depending on the intensity of the rain the wipers will be operated continuously as if set in the normal wiper stalk switch position regardless of the knurled wheel setting. For this reason, the vehicle speed signal on the K bus is not utilized on rain sensor equipped wiper systems.
- If the ignition switch is turned off with the wiper switch in the intermittent position, the rain sensor will only become active after the ignition is switched back on and one of the following occurs:
- The stalk switch is moved from the intermittent position and then back.
- The knurled wheel setting is adjusted.
- or the wash function is activated.
The reasoning behind this switching strategy is to have the driver make a conscious decision to activate the system themselves.
Rain Sensor Control Module Adaptation
The rain sensor control module adapts to the optics system environment as follows:
Windshield Aging: As the vehicle ages the possibility of stone chipping in the rain sensors monitoring area may occur which will cause a loss of light in the optics system.
The control module adapts for loss of light based on the intensity of the detected infra red light with a cleared windshield (wiper motor park signal). Therefore, the rain sensors function is not adversely affected due to windshield aging.
Dirty Windows: The rain sensor adaptation reacts less sensitively to a dirty windshield (dirt, road salt, wax residue) after a completed wipe cycle. A dirty windshield has a film on it that diminishes the ability of the infra red to refract into present water droplets. This causes a delay in the rain sensor detection capabilities which lengthens the time intervals on an intermittent wipe.
Windshield Wiper System Failsafe Operation
The GM provides failsafe operation of the wiper system if faults are detected with any of the input signals shown in the chart.