Sensors make wipers hands-freeSensors make wipers hands-free

Detroit-Starting with model year 2002, a new generation of automatic rain sensors will turn on windshield wipers in luxury and family vehicles. "We can't say what cars will include the new optical sensors, but they will be both foreign and domestic," says Scott McEwan, an electrical engineer and product manager with TRW Automotive Electronics.

The new generation of optical sensors is different, in several ways, from what the company first introduced in 1997. "One big change is that we moved the analog signal processor onto a single ASIC chip," says McEwan. The way the sensor attaches to the windshield is also different. "The original sensors were installed on the windscreen at the vehicle assembly location. That process was rather cumbersome, so we designed a coupling attachment, which is installed when the windshield is autoclaved. It is similar to the application of the mirror mount," he says. Workers on the assembly line attach the wire harness and clip the sensor in place.

At 69.8x50.8x19 mm, the new sensor allows for a small windshield footprint and a low profile.

"The plastic coupler we use survives temperatures up to 300F during the manufacturing process," says McEwan. The low profile of the sensor does not affect the way windshields are packaged and sent to assembly plants. It works with numerous types of glass, such as solar reflective and solar absorbing.

The rain sensor itself uses optical sensing, analog signal processing, and a control algorithm during operation. When the system experiences an interruption to its infrared signal, such as rain drops striking the windshield, analog processing detects the occurrence of a "true rain event" rather than stray signals that might result from changes in sunlight or other sources. Depending on the rain intensity, the system selects one of seven speeds.

In addition to automobiles, the optical rain sensors are suitable for use in nautical, off-road and construction equipment applications.