Research And Design Of Vehicle Infrared Rain Sensor

With the rapid growth of private cars, as well as safety, convenience, comfort andluxurious that people are eager for, the performance of the car is put forward thehigher pursuit. The car’s performance is hardly improved significantly. Thanks to theautomotive electronic technology progress, which compensates the short board, theauto industry has entered into a new period of development.Vehicle rain sensor is very important in the body control system. It is installed onthe inside surface of the windshield, near the rear-view mirror. Cooperating with thevehicle wiper system, it realizes the wiper automatically open, and automaticallyadjusts the pace of work. The rain sensor is very necessary for drivers, for it bringssafety and comfort.This thesis is based on the optical theory of infrared total reflection inside theglass. The rain sensor consists of an infrared detector as the center and six infraredlight-emitting diodes around the center. These infrared light-emitting diodes aredivided into a pair of branches that each one has three emitters in series. The pairworks alternately in the frequency of2KHz in order to overcome the interferencefrom sun light and ambient illumination light. The incident angle of the50%dutycycle pulse modulation infrared light beam is adjusted in a way that the beam istotally reflected on the outer boundary of the windscreen. A detector collects thereflected infrared light beams of the pair of branches and creates a correspondingelectrical signal which can be utilized to analyze the luminous flux. If there areraindrops on the windshield, the amount of infrared light reflected off the outersurface decreases, because the total reflection condition is destroyed due to the higherdensity of water compared to air and the resulting higher refractivity at the boundaryfrom glass to water. The difference of the signal power from the two branches indicates the amount of rain and the interference of dust and dirt can be eliminated bycomputing the changing rate of the difference. A MCU controls these infraredlight-emitting diodes, and processes the data converted with the on-chip12-bit ADC,then it communicates with the vehicle body computer module via the LIN bus. Rainsensor could also get the wiper blade position message provided through the LIN busto ignore both the wiper blade moving pass the detection area and the water collectedby the wiper blade. The rain sensor integrates coupling optics, infrared devices andPCB in a33mm9mm shell, which is attached directly to the inside surface ofwindshield near the rear view mirror with an adhesive pad. Experiments show that,the rain sensor is immune to sunlight, dust, dirt, shadows and other influencing factorsbesides accurate and reliable, due to the structure optimization and Fast FourierTransform data processing and Fuzzy Logic Control method. The rain sensor has avery wide range of application.