Spur gears are the most common type 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 reductions.
Spur gears are used in many gadgets that you could see all over HowStuffWorks, like the electric screwdriver, dance monster, oscillating sprinkler, windup noisy alarms, washing machine and clothes dryer. But you won't find many in your vehicle.
This is because the spur gear could be really loud. Dry Screw Vacuum Pumps Whenever a equipment tooth engages a tooth on the other gear, one's teeth collide, and this impact makes a noise. It also increases the stress on the gear teeth.
To reduce the noise and stress in the gears, most of the gears in your vehicle are helical.