Spur gears are the most common kind of gears. They possess straight teeth, and so are installed on parallel shafts. Sometimes, many spur gears are used at once to create very large gear Cycloidal Gear Reducer reductions.
Spur gears are used in many gadgets that you can see all over HowStuffWorks, like the electric powered screwdriver, dance monster, oscillating sprinkler, windup noisy alarms, washing machine and clothes dryer. But you won’t find many in your car.
This is since the spur gear can be really loud. Whenever a equipment tooth engages a tooth on the other gear, the teeth collide, which impact makes a noise. It also increases the pressure on the gear teeth.
To reduce the noise and stress in the gears, most of the gears in your vehicle are helical.