Gear train

[2] Features of gears and gear trains include: The transmission of rotation between contacting toothed wheels can be traced back to the Antikythera mechanism of Greece and the south-pointing chariot of China.

Illustrations by the Renaissance scientist Georgius Agricola show gear trains with cylindrical teeth.

The implementation of the involute tooth yielded a standard gear design that provides a constant speed ratio.

[3]: 529  The distance between the rotational centerlines of two meshing gears is equal to the sum of their respective pitch radii.

In addition, consider that in order to mesh smoothly and turn without slipping, these two gears A and B must have compatible teeth.

A non-hunting gear set is one where the teeth counts are insufficiently prime.

The input gear will typically be connected to a power source, such as a motor or engine.

Instead of idler gears, a toothed belt or chain can be used to transmit torque over distance.

Special gears called sprockets can be coupled together with chains, as on bicycles and some motorcycles.

For example, a belt with teeth, called the timing belt, is used in some internal combustion engines to synchronize the movement of the camshaft with that of the crankshaft, so that the valves open and close at the top of each cylinder at exactly the right time relative to the movement of each piston.

Regardless of which form of drive is employed, the crankshaft-to-camshaft gear ratio is always 2:1 on four-stroke engines, which means that for every two revolutions of the crankshaft the camshaft will rotate once.

Automobile powertrains generally have two or more major areas where gear sets are used.

For internal combustion engine (ICE) vehicles, gearing is typically employed in the transmission, which contains a number of different sets of gears that can be changed to allow a wide range of vehicle speeds while operating the ICE within a narrower range of speeds, optimizing efficiency, power, and torque.

The second common gear set in almost all motor vehicles is the differential, which contains the final drive to and often provides additional speed reduction at the wheels.

Moreover, the differential contains gearing that splits torque equally[citation needed] between the two wheels while permitting them to have different speeds when traveling in a curved path.

The transmission and final drive might be separate and connected by a driveshaft, or they might be combined into one unit called a transaxle.

As noted, the ICE itself is often equipped with a gear train to synchronize valve operation with crankshaft speed.

Typically, the camshafts are driven by gearing, chain, or toothed belt.

This means that for every complete revolution of the wheel, the car travels 82.1 inches (209 cm).

If the Corvette had larger tires, it would travel farther with each revolution of the wheel, which would be like a higher gear.

For example, it is possible to determine the distance the car will travel for one revolution of the engine by dividing the circumference of the tire by the combined gear ratio of the transmission and differential.

[8] Close-ratio transmissions are generally offered in sports cars, sport bikes, and especially in race vehicles, where the engine is tuned for maximum power in a narrow range of operating speeds, and the driver or rider can be expected to shift often to keep the engine in its power band.

Narrowing the gaps will increase acceleration at speed, and potentially improve top speed under certain conditions, but acceleration from a stopped position and operation in daily driving will suffer.

Range is the torque multiplication difference between 1st and 4th gears; wider-ratio gear-sets have more, typically between 2.8 and 3.2.

The progression may not be linear (continuously reduced) or done in proportionate stages for various reasons, including a special need for a gear to reach a specific speed or RPM for passing, racing and so on, or simply economic necessity that the parts were available.

A wide range, which gives a strong torque multiplication in first gear for excellent manners in low-speed traffic, especially with a smaller motor, heavy vehicle, or numerically low axle ratio such as 2.50, means the progression percentages must be high.