# How does a windshield wiper work?

Basic Googling on the mechanical generation of oscillating motion (moving something back and forth in the manner of a windshield wiper or a flapping wing) from a source of circular motion comes up with a concept known as a "four-bar linkage" or "crank rocker". For example, this video shows very clearly a simple way to create a windshield-wiper motion:

The problem is, this doesn't look anything like a windshield wiper. It has a bar attached to the tip of the "wiper" pulling it back and forth along its arc. But in an actual windshield wiper (or wing, for that matter) the moving force comes from the base, not the tip.

So how do you go about generating oscillating motion from the base of the oscillating device, windshield-wiper style? Assume you're starting with a motor providing circular motion, as in the video.

• imagine the right bar in the video extended much longer past the linkage point carrying the blade. Apr 17 '18 at 22:50

For having dismantled a wiper motor once,

The basic principle is exactly as shown on the video, but the wiper is then linked to the to the rotation point of the rocking bar and not to the bar itself.

Here is a schematic on how it works:

I think this system is quite standard, but there are many type of wipers and I am quite sure that a few constructors have also comes with interesting alternative mechanics.

• I'm pretty sure most of them operate this way (seems like a mechanical linkage is a no-brainer here). Probably the most important part is that the entire "mechanism" is hidden from sight. All we see is what gets attached to the (coupled) rocker(s).
– JMac
Jun 1 '17 at 10:40
• I also think so. But still some alternative systems exists, as I was doing some research, I found this very nice example: youtube.com/watch?v=LdNu113Ep2U Jun 1 '17 at 11:34
• Lucas used a flexible rack (cable with a wire wrapped around it to provide teeth") and gears to drive the wipers. Jun 1 '17 at 11:55

You have to imagine an extra bar on the right hand side. Well 2 actually, one connecting to the swinging pivot joint that is depicted with the coloured arc and its length is the distance between the wipers then the second bar which will be attached to another fixed point. This means you have 2 fixed points, 2 swinging arms, 2 linking bars and 1 rotating bar .

The wipers, in a car, are attached to the swinging arms (the one shown with the coloured arc) and extended past the joint with the linking bar as necessary.

The wiper arm is on a shaft, which passes through the car's bodywork. What you don't see is another arm (perhaps only an inch or two in length) on the backside of the shaft, with the crank rocker arrangement attached to it.