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| Know Your Car : Power Windows |
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You must have wondered what kind of mechanism makes the power windows work - with the up button that raises the window automatically, but stops it going up if there is an obstruction.
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Let's start with the lifting mechanism, this cool device is the heart of both manual and power window systems.
The window lift on most cars uses a really neat linkage to lift the window glass while keeping it level. A small electric motor is attached to a worm gear and several other spur gears to create a large gear reduction, giving it enough torque to lift the window.
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You can see above that the linkage has a long arm which attaches to a bar that holds the bottom of the window. On the other end of the bar is a large plate that has gear teeth cut into it. The motor turns a gear that engages these teeth. When the window reaches the top or bottom of its travel, a limit switch cuts the power to the motor.
For the sake of security, an important feature of the side windows in any car is this : it should be impossible for someone (especially someone on the outside of the car trying to break in) to force the glass down. A worm gear in the drive mechanism takes care of this. Most worm gears have a self-locking feature because of the angle of contact between the worm and the gear. The worm can spin the gear, but the gear cannot spin the worm - friction between the teeth cause the gears to bind.
The same linkage is often used on cars with manual windows. Instead of a motor turning the gear, the crank handle turns it.
In the next section we'll learn how the switches on the doors are wired, and how the child lock works.
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