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Are you amazed at how easily you can raise and lower your car windows by just pressing a button? The mechanism inside your car window is so compact and smart that the window always moves straight and smooth. Also, you might have noticed that you’re not able to move the window even if you try to push it down or pull it up manually. Let’s understand the tricky mechanism that controls your car window.
The basic structure of a car door, which enables the window to slide smoothly, is illustrated here. Now, obviously, some mechanism in the door has to push or pull the window. These motions can be accomplished by a simple crank and gear arrangement, like this. Observe how the different parts of the mechanism move when you rotate the crank—the end motion will either push or pull the window. As you can see, the glass is supported at a single point at all times. Therefore, a small difference in friction could cause an imbalance, and the window may not move straight.
If we support the support link of the glass at two points, it can solve this problem. This design suggestion can be easily understood from this weightlifter analogy. Therefore we add two more linkages, as shown. One end of these newly introduced linkages are pivoted in the middle, and the other ends are connected to the sliders. The mechanism we just have developed is known as a scissor-type mechanism. The two supports we gave to the glass makes the mechanism quite robust. Interestingly the scissor mechanism is getting used in many weight lifting equipment, folding gates and even in your computer keyboard. This cool mechanism was in the mainstream of car windows till the 1990s and some classic cars still use them. The way it works is a pleasure to watch. The mechanism’s top portion always moves perfectly straight.
However, this arrangement has one main drawback. It will make the window fall abruptly at the bottom. To avoid this issue, let’s place a spiral spring on a pivot point. This spring unwinds during the window’s upward movement and compresses for its downward movement. Now, the glass doesn’t fall suddenly, and this new arrangement also reduces the effort needed for the upward movement of the glass.
The basic structure of a car door, which enables the window to slide smoothly, is illustrated here. Now, obviously, some mechanism in the door has to push or pull the window. These motions can be accomplished by a simple crank and gear arrangement, like this. Observe how the different parts of the mechanism move when you rotate the crank—the end motion will either push or pull the window. As you can see, the glass is supported at a single point at all times. Therefore, a small difference in friction could cause an imbalance, and the window may not move straight.
If we support the support link of the glass at two points, it can solve this problem. This design suggestion can be easily understood from this weightlifter analogy. Therefore we add two more linkages, as shown. One end of these newly introduced linkages are pivoted in the middle, and the other ends are connected to the sliders. The mechanism we just have developed is known as a scissor-type mechanism. The two supports we gave to the glass makes the mechanism quite robust. Interestingly the scissor mechanism is getting used in many weight lifting equipment, folding gates and even in your computer keyboard. This cool mechanism was in the mainstream of car windows till the 1990s and some classic cars still use them. The way it works is a pleasure to watch. The mechanism’s top portion always moves perfectly straight.
However, this arrangement has one main drawback. It will make the window fall abruptly at the bottom. To avoid this issue, let’s place a spiral spring on a pivot point. This spring unwinds during the window’s upward movement and compresses for its downward movement. Now, the glass doesn’t fall suddenly, and this new arrangement also reduces the effort needed for the upward movement of the glass.
Another issue is that one can operate this mechanism even by pushing or pulling the glass. This means that theft is quite easy if car windows are equipped with this design. This simple worm - worm gear arrangement can solve this issue effectively. The worm can rotate the gear, but the gear can’t rotate the worm. This means only if we input motion to the worm, the mechanism will work. The crank is connected to the worm. So the passenger can easily operate the mechanism. However, when somebody tries to move the glass, the input motion goes to the worm gear and everything gets stuck. Nobody can move the window glass up or down forcibly. Moreover, the worm and gear arrangement also works as a torque multiplier.
Simply by connecting a DC motor to the worm, we can convert the manual window to a power window. The major concern with this linkage mechanism is that it has many sliding contacts. Frictional losses will be high due to this.
This design is improved by using a rope-and-pulley system. You can see two plastic sliders here. They are connected with the rope. These sliders support the glass. The way power and motion generated by the motor reach the rope is illustrated here. For smooth operation,
two vertical guides are used. This mechanism is smoother than the previously-seen linkage mechanism since it has very few metal-to-metal contacts.
Some of the rope-and-pulley mechanism’s known issues are listed here.
Simply by connecting a DC motor to the worm, we can convert the manual window to a power window. The major concern with this linkage mechanism is that it has many sliding contacts. Frictional losses will be high due to this.
This design is improved by using a rope-and-pulley system. You can see two plastic sliders here. They are connected with the rope. These sliders support the glass. The way power and motion generated by the motor reach the rope is illustrated here. For smooth operation,
two vertical guides are used. This mechanism is smoother than the previously-seen linkage mechanism since it has very few metal-to-metal contacts.
Some of the rope-and-pulley mechanism’s known issues are listed here.