Transmission Gears

Most cars have from three to five forward gears, and one reverse gear. The transmission changes the ratio of the engine speed and the wheels by connecting gears in various combinations. If a gear with 10 teeth is driving a gear with 20 teeth, the drive would be said to have a 2:1 ratio. First gear connects the engine power to the drive wheels via a pair of reduction gear sets, which gives increased power and reduced wheelspeed when the car is beginning to move. This means the engine is turning much faster than the output shaft, typically around a 4:1 ratio. Intermediate speeds are delivered by changing the gear ratio closer to 1:1. Final drive is usually accomplished by directly linking the input and output shafts, giving a 1:1 gear ratio. Using a moveable set of different sized gears, it's possible to get several degrees of torque output. The differential pinion, driven by the drive shaft, turns the ring gear, which acts like a single speed transmission. This further reduces RPM's and increases torque by a set ratio. Gears work exactly like levers. A small gear driving a larger one gives an increase in torque, and a decrease in speed, and vise-versa. Transmission gears are heat-treated, high quality steel. They have smooth, hard teeth, cut on precision machinery while red hot. There are many types of gear teeth, but most transmissions use spur and helical gears. Most of the gears are the helical type, because they last longer and are more quiet than spur gears. There has to be enough room (a few thousandths of an inch) between the gear teeth for lubrication, expansion, and any irregularities in size.