Automobiles use a complex system of gears to transfer power from the engine to the wheels. This gear system, known as the transmission, allows the vehicle to travel at different speeds.

The Purpose of Gears
Gears are designed to change the speed and torque of a rotating shaft. The primary purpose of transmission gears is to adjust the rotational speed and torque delivered by the engine so it matches the requirements of the driveshaft and wheels. Gears allow the engine to operate at its optimal speed while also providing different gear ratios for changing vehicle speed or climbing hills.

Types of Transmission Gears
There are two main categories of gears used in Automatic Transmission Gears - parallel axis gears and planet gears. Parallel axis gears have parallel shafts and mesh directly with one another. Common types are spur gears, helical gears, bevel gears and worm gears. Planet gears revolve around a central gear, called the sun gear, while also meshing with a surrounding gear, called the ring gear. An example is an epicyclic gear train used in automatic transmissions.

How Gears Transfer Power
Power transmission happens through the contact and relative rotation of gear teeth. As one gear turns, its teeth push against the teeth of another gear, causing that second gear to rotate as well. By changing the relative diameters or numbers of teeth between two meshing gears, gear ratios are produced to increase, decrease or change the direction of rotational force. Proper lubrication of gear teeth is important to reduce friction and prevent wear during constant power transfer.

Manual Transmission Gearing
A manual transmission uses parallel axis gears in a gearbox to provide different gear ratios from the engine to the rear axle. Gears are selected by the driver using a gear stick. Common configurations include 3, 4, 5 or 6 forward gears plus a reverse gear. Double or triple-cone synchronizers allow smooth shifting between gears. The higher the gear number, the higher the gear ratio - meaning less torque but higher speed.

Automatic Transmission Gearing
Instead of direct driver selection, an automatic transmission selects gears via internal planetary gear sets and clutches that are electronically or hydraulically controlled. Two main types are commonly used - torque converter automatics and dual-clutch transmissions. Torque converter designs utilize epicyclic geartrains for step-ratio gear changes while dual-clutch transmissions employ twin countershafts with parallel clutch packs. Gear changes occur without any loss of power to the wheels.

Continuously Variable Transmissions
A newer alternative to conventional transmissions is the continuously variable transmission (CVT). Rather than set gear ratios, a CVT can change seamlessly through an infinite number of effective gear ratios using a belt or chain driving two variable-diameter pulleys. This allows the engine to stay within its optimal rpm range for maximum efficiency and performance. However, early CVT designs lacked the durability of multi-gear transmissions.

Advancements in Transmission Technology
Newer transmission designs improve both efficiency and driver enjoyment. Dual-clutch transmissions mimic the direct feel of a manual while providing the convenience of an automatic. Nine, ten and even more forward gears let engines operate in their sweet spot for power and fuel economy. Some high-end sports cars use dual-clutch transmissions with launch control for lightning-quick acceleration off the line comparable to a manual. Advancements in materials and hydraulics have also increased the reliability and lifetime of CVTs.

The transmission gearing system enables an automobile to deliver the engine's power to the road through a wide range of effective gear ratios. From manual to automatic and CVT designs, transmissions continue to advance - providing drivers with smooth, efficient power in any driving situation. A basic understanding of gear types, torque multiplication and ratio selection gives insight into how transmissions transfer rotational energy to propel vehicles down the highway.

Get more insights on this topic: Automotive Transmission Systems