How Windshield Wipers Work

By: Karim Nice

Rain-sensing Wipers

In the past, automakers have tried to either eliminate the wipers or to control their speed automatically. Some of the schemes involved detecting the vibrations caused by individual raindrops hitting the windshield, applying special coatings that did not allow drops to form, or even ultrasonically vibrating the windshield to break up the droplets so they don't need to be wiped at all. But these systems were plagued by problems and either never made it to production or were quickly axed because they annoyed more drivers than they pleased.

However, a new type of wiper system is starting to appear on cars that actually does a good job of detecting the amount of water on the windshield and controlling the wipers. One such system is made by TRW Inc., here is a PDF describing their rain sensor system. TRW Inc. uses optical sensors to detect the moisture. The sensor is mounted in contact with the inside of the windshield, near the rearview mirror.


The sensor projects infrared light into the windshield at a 45-degree angle. If the glass is dry, most of this light is reflected back into the sensor by the front of the windshield. If water droplets are on the glass, they reflect the light in different directions -- the wetter the glass, the less light makes it back into the sensor.

The electronics and software in the sensor turn on the wipers when the amount of light reflected onto the sensor decreases to a preset level. The software sets the speed of the wipers based on how fast the moisture builds up between wipes. It can operate the wipers at any speed. The system adjusts the speed as often as necessary to match with the rate of moisture accumulation.

The TRW system, which is found on many General Motors cars, including all Cadillac models, can also be overridden or turned off so the car can be washed.

For more information on windshield wipers and related topics, check out the links below!

Windshield Wipers FAQ

How do I know my windshield wiper size?
You can find out your windshield wiper size in a few different ways. You can check your vehicle owner's manual or you can visit an auto parts store and use the in-store guide to find the right fit for your vehicle. You can also measure your current wipers.
Can you change wiper blades yourself?
It's easy to change wiper blades yourself; just about any car owner can handle the task of changing their wiper blades on their own.
How much does it cost to replace windshield wipers?
Replacing your windshield wiper blades typically costs between $60 and $85. However, the wipers alone — without labor — can cost between $36 and $51.
Does it matter what windshield wiper fluid I use?
As long as you don't use water alone, any windshield wiper fluid should be fine. If you live in a cold climate, you'll want to choose one that won't freeze in the winter.
Are windshield wipers different sizes?
Yes, windshield wipers are different in size. They're made for different vehicles with windshields of varying sizes, which means you'll need to find the right fit for your specific windshield.

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