Gearboxes

What is a Gearbox?

A gearbox, also known as a transmission box, is a synchronized collection of gears housed together in a metal casing. This mechanical device affects your car’s road performance. As an integral part of the vehicle’s powertrain, it usually ranks second after the engine.

How a Gearbox Works

A gearbox affects your vehicle’s torque and speed. Torque refers to the car’s ability (power needed) to overcome obstacles on the way through wheel traction. As for speed, it refers to how fast your car goes (mph).Your gearbox output is dependent on two things: your engines speed and power. Your engine’s power is defined by its speed; how many revolutions per minute your crankshaft makes. So for your engine to produce more power, it needs a high RPM, and this means more gearbox output.

In other words, your gearbox transmits your engine generated power to the wheels and ratios the transmission to provide different speed variations for different road applications.

Take for instance when driving uphill, you require more wheel power (torque) than speed. Your gearbox thus provides high torque to help you overcome resistance while giving a low-speed transmission to keep you steady on the ground.

Another great example is when driving fast on a leveled ground. Your gearbox provides more speed transmission to help you move quickly while maintaining low power output for momentum.

Gearbox components

To better understand how your gearbox works, you need to know the different parts and how they work to fulfill a harmonious function:

• Input Shaft: It’s what connects the gearbox to the engine. It carries the same power and speed as the engine’s crankshaft.
• Counter Shaft: It’s the intermediate shaft that joins the input shaft to the main shaft through fixed gear. The countershaft is also known as layshaft.
• Output shaft: This is the main shaft, and it lays parallel to the layshaft. The output shaft is responsible for transmitting the engine’s power to the rest of the powertrain. Its speed and power transmission are dependent on the gear engaged.
• Bearings: They are located on both the main and countershafts. Bearings help reduce friction.
• Drive gears: A drive gear usually consists of a pair of gear wheels. One is located on the output shaft and the other directly beneath is on the countershaft.The drive gear system works by transmitting power from one shaft to the other. The gear ratio determines the produced power. By gear ratio, we mean the ratio of the driven gear-wheel teeth to the driving gear-wheel teeth.

Different types of Gearboxes

There are two types of gearboxes: manual and automatic

1. Manual transmission gearbox

This type of gearbox allows the driver to select different gear ratios depending on the application needed. However, you need some particular skill set for such vehicles. A Manual gearbox is ideal for performance cars.

Depending on the design, a manual gearbox can be categorized as:

• Sliding mesh gearbox: This is the oldest type of gearbox and usually involves meshing (connecting the main shaft gear to the countershaft gear) gears by sliding. Such gearbox requires extra skill and tends to wear out quickly.
• Constant mesh gearbox: It’s a popular gearbox among 20th-century cars. Unlike the sliding mesh gearbox, the constant mesh gearbox wears out less and is quieter. All gears are meshed continuously together but not connected. The main shaft gears rotate freely from the countershaft gears. The constant mesh gear also includes dogging clutches located on the main shaft.
• Synchromesh gearbox: This gearbox tends to resolve the problems associated with constant mesh gearbox. It replaces the dog clutch with synchromesh devices. The gearbox works on the principle of synchronizing the speeds of two gears by bringing in frictional contact before engaging them. Currently, it’s the most uprated gearbox in manual cars.

How a manual gearbox workIn manual cars, the power of the engine is introduced to the gearbox via the input shaft. However, the speed/power leaving the gearbox (output speed) is dependent on the gear ratio – different speeds of the meshed gears. A manual gearbox tends to have a single gearwheel pair for each speed.

2. Automatic gearbox

An automatic gearbox allows automation of speed variation with no driver’s intervention. The accelerator when pressed or released determines the timing, selection, and engagement of gear in question to the speed required. Automatic gearbox doesn’t make use of pedal clutches and gear change levers.

There are two types of automatic gearboxes namely:

• Epicyclic gearbox: It achieves different gear speeds through tightening of brake bands on gear drum.
• Hydraulic torque converter: It works the same as an electric transformer.