Spur gears are the most common kind of gears. They possess straight teeth, and are installed on parallel shafts. Occasionally, many spur gears are used at once to create very large gear reductions.
Spur gears are found in 
many products that you can see all over HowStuffWorks, like the electric screwdriver, dance monster, oscillating sprinkler, windup alarm clock, washer and clothes dryer. But you won’t discover many in your vehicle.
This is because the spur gear can be really loud. Each time a equipment tooth engages a tooth on the various other gear, one’s teeth collide, which impact makes a sound. In addition, it increases the stress on the gear teeth.
To lessen the noise and stress in the gears, the Gas-cooling Vacuum Pump majority of the gears in your car are helical.