[jmhunt]

So in driving in the rain over the Thanksgiving weekend along the east coast, I got quite a bit of experience with my auto sensing wipers and it got me wondering what is the mechanism used to determine when to wipe.
I know the manual says that they adjust based on the vehicle speed. I'm wondering what else factors into the equation and how.
Two ideas have come to mind:
1. A sensor(s) measures the tiny impact of rain drops on the windshield.
2. The wiper resistance after a swipe determines how wet the windshield is based on the resistance from friction.
It is probably some combination or something else altogether. Anyone know more?

 

[LelloBeetle]

Re: How do the auto sensing windshield wipers work? (jmhunt)

Look at the black circle on the windshield in this picture
It looks like it is possibly the mounting for the rear view mirror...but it's where the rain sensing device is...it's built into the windshield. I'm sure it measures the drops and velocity and the wipers are adjusted accordingly.
I'm sure this is a VERY simplified explanation. All I know is I really like mine...I think they're a nice feature and add to safety in that I don't have to constantly adjust my wipers while driving in poor weather.

http://****************.com/smile/emthup.gif


[Modified by LelloBeetle, 12:44 AM 11-28-2001]

 

[Stargazer]

Re: How do the auto sensing windshield wipers work? (jmhunt)

There is a TSB that explains exactly how the rain sensor works. I've copied it here: http://www3.telus.net/stargazer/v929903.pdf

 

[LelloBeetle]

Re: How do the auto sensing windshield wipers work? (Stargazer)

Thanks for the great info Stargazer! http://****************.com/smile/emthup.gif

 

[DavidRamsey]

Re: How do the auto sensing windshield wipers work? (Stargazer)

Actually, that TSB explains how the rain sensor is operated, not how it works (i.e. senses rain on the windshield).
Here's how it works: inside the sensor is an array of infrared LEDs aiming outwards through the windshield. IR light is beamed out. If rain is on the windshield, some of the IR bounces around inside the raindrops and is reflected back towards the sensor, where it's detected by photocells. If there's no rain on the windshield, none of the IR is reflected back.
The switch on the wiper lever adjusts the level of reflected needed to trigger a wipe.
It's an elegant solution, first seen on General Motors cars to my knowledge.

 

[Pov]

Re: How do the auto sensing windshield wipers work? (jmhunt)

Mine wroks poorly, particularly in misty rain at low speeds. Even at the most sensitive setting, it sometimes does not wipe until there is so muich rain on the windshield that I have trouble seeing. Dealer says it is functioning normally

 

[ajchenmph]

Re: How do the auto sensing windshield wipers work? (Pov)

quote:[HR][/HR]Mine wroks poorly, particularly in misty rain at low speeds. Even at the most sensitive setting, it sometimes does not wipe until there is so muich rain on the windshield that I have trouble seeing. Dealer says it is functioning normally

[HR][/HR]​

Without intending to sound insulting or condescending, did you try going all the way in the other direction with the sensing switch? You might have inadvertently set it to the least sensitive setting by mistake.

 

[Pov]

Re: How do the auto sensing windshield wipers work? (ajchenmph)

quote:[HR][/HR]Mine wroks poorly, particularly in misty rain at low speeds. Even at the most sensitive setting, it sometimes does not wipe until there is so muich rain on the windshield that I have trouble seeing. Dealer says it is functioning normally

Without intending to sound insulting or condescending, did you try going all the way in the other direction with the sensing switch? You might have inadvertently set it to the least sensitive setting by mistake.[HR][/HR]​

No offense taken. IIRC, the most sensitive position is all the way to the right, and I keep it there. I have tried every other position as well with no improvement.

 

[jmhunt]

Re: How do the auto sensing windshield wipers work? (DavidRamsey)

Thanks DavidRamsey

So, here is the expirement I am going to try...I'm going to take a piece of alumnium foil and see if I can engage the wipers. I hope the car speed won't play too big of a role or I may need a friend to hold the foil over the sensor while I drive.

 

[Stargazer]

Re: How do the auto sensing windshield wipers work? (Pov)

quote:[HR][/HR]Mine wroks poorly, particularly in misty rain at low speeds[HR][/HR]​

Yes, misty rain at low speeds is difficult for the rain sensor to handle. I guess the drops are too small to really regisiter and since the car is going slowly, ti doesn't wipe as much. In those situations, I take it off the rain sensor and use the "mist" position--push down once--until I pick up some speed and then the wipers work better.
I'm perfectly happy with the rain sensors in other situations, and with the sensitivity switch it can adapt to almost any condition we have here on the Wet Coast

.

 

[car_nut]

Re: How do the auto sensing windshield wipers work? (Pov)

I found my sensor works better when my windshield is fairly clean. As road dirt splatters the windshield while driving it becomes necessary to move the four position switch up another click.