Windshield Wipers

Do you find it difficult to make a choice regarding windshield wipers. If you have a hard time picking out which are best for your Automobile such as whether or not to use rain sensing wipers verses another type, use the information in this article to narrow down your selection.
Also in the windshield wiper area there have been great improvements the recent years. Matching windshield wiper operation to the real need is important. Dragging wiper blades across a dry windshield shortens blade life and grinds dirt into the glass. Regulators and engineers consider splashes and sudden changes in rainfall safety issues that need to be addressed with technology. For these reasons, the industry has already deployed the first generation of rain sensing windshield wipers and is quickly moving towards a fully automatic system that doesn't require any action from the driver at all. The key to the system is an optical moisture sensor mounted inside the windshield, either directly on the glass or on the rearview mirror.

Currently, there are two different sensor configurations: One typically used on Asian vehicles, and one more common on European vehicles. Domestic vehicles might use either type. Both use light emitting diodes (LEDs) to generate infrared fight and a photo diode to detect it. The Asian type, mounted directly on the glass, has a single LED, and its light passes through an optical prism that aims a fight beam through the windshield at a specific angle. The windshield allows some of that light to pass through but reflects most of it back to the sensor, where it's detected by the photo diode. Water on tile windshield lets more of the beam pass through the glass, reducing the amount of light reflected back to the photo diode.

The European sensor is mounted off the glass, usually in the rearview mirror. It has eight LEDs in a circle around the photo diode. The LEDs are pulsed alternately, four on the left, then four on the right, at the same frequency and pulse duration. The control unit measures the frequency and duration of the pulses reflecting from the glass to the photo diode.

When the windshield is clean, the reflected light waves from left and right LED sections strike the photo diode at the same frequency and duration, and the sensor is "balanced." With water on the windshield, fight pulses from each section are reflected differently and the photo diode's output signal is "unbalanced." The difference in pulse duration indicates water droplet size, and the difference in light wave frequency indicates the number of droplets.

The European sensor tends to be slow but can tolerate high ambient light and dirt or scratches in the glass. The Asian sensor is faster, but before the control unit can make accurate rain measurements, it must be initialized. Dirt or moisture on the windshield can effect how much fight is reflected to the photo diode, so the control unit needs to establish a baseline.

On some earlier models, the wipers make one sweep of the windshield each time the ignition is first turned on, regardless of weather or wiper switch position. This is not good on a dry, dirty windshield, and today most control units initialize when the driver turns on the windshield wiper switch. It takes several swipes to match wiper operation to real need, especially when rainfall is light.

The photo diode's output signal is sent to an electronic control unit, which also looks at vehicle speed and other data on the controller area network (CAN) fine. Most control units and sensors are powered only when the ignition switch is on. The sensors are accurate and repeatable enough for today's systems, but the control algorithm must be extremely complex to operate in pure automatic mode. Future systems may be powered all the time so they can close the sun-roof and windows if it rains while the vehicle is parked. They might also operate the headlights and high beams automatically. Let's hope they don't forget to include an "off" switch for car wash and tollbooth attendants.