Have you ever wondered what kind of mechanism makes your car windows go up and down? How about the power windows with the automatic-up feature that raises the windows by themselves, but stops raising them if there is an obstruction? Or maybe you've seen the Volkswagen TV commercial where the guy opens the windows by turning the key in the door lock.
Now, you'll learn about what's going on in all of these power-window features and more!
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.
An important feature of power windows is that they cannot be forced open -- the worm gear in the drive mechanism takes care of this. Many 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 causes the gears to bind.
Animation of window lifting mechanism at work, with inset of motor and gear reduction
The linkage has a long arm, which attaches to a bar that holds the bottom of the window. The end of the arm can slide in a groove in the bar as the window rises. On the other end of the bar is a large plate that has gear teeth cut into it, and the motor turns a gear that engages these teeth.
The same linkage is often used on cars with manual windows, but instead of a motor turning the gear, the crank handle turns it. In the next section we'll learn about some of the neat features some power windows have, including the child lockout and automatic-up.
Instead of trying to do that, the driver's door module monitors all of the switches. For instance, if the driver presses his window switch, the door module closes a relay that provides power to the window motor. If the driver presses the switch to adjust the passenger-side mirror, the driver's door module sends a packet of data onto the communication bus of the car. This packet tells the body controller to energize one of the power-mirror motors.