What Is Gearbox? – Definition, Types, Working, Diagram

Discover the parts of a gearbox, its function, how it works, and the advantages and disadvantages of manual and automatic transmissions. Understand the role of a gearbox in maintaining the engine’s optimal RPM range and its importance in the performance and efficiency of a vehicle.

What Is Gearbox?

A gearbox is a mechanical device that transmits power from a source, such as an engine, to a machine or vehicle. It uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device.

To change the speed and torque of the output shaft, the gears in a gearbox can be engaged and disengaged. This process is commonly known as shifting gears. Gearboxes find their applications in various fields, such as automobiles, bicycles, motorcycles, and industrial machinery. With their ability to transmit power and torque effectively, gearboxes play a crucial role in the functioning of these machines.

They are commonly found in manual and automatic transmissions of vehicles. The gearbox also helps to maintain the engine’s optimal RPM range for a given speed and load.

Parts Of Gearbox

1. Clutch Shaft

In a gearbox, the clutch shaft, also known as the driving shaft, is connected through the clutch. When the clutch is engaged, the driving shaft rotates, and only one gear is fixed on the clutch shaft. This gear rotates at the same speed as the engine’s crankshaft. Furthermore, the driving shaft and main shaft are in the same line, ensuring optimal power transmission between the engine and the gearbox.

2. Counter Shaft / Layshaft

The countershaft is a shaft that connects directly to the clutch shaft. It has gear that connects it to the clutch shaft as well as the main shaft. It can be run at engine speed or below engine speed according to gear ratio.

3. Main Shaft / Output Shaft

The main shaft or output shaft rotates at different speeds and also provides the necessary torque to the vehicle. The output shaft is splined so that the gear or synchronizer can be moved to engage or disengage.

4. Bearings

In a gearbox, bearings play a critical role in supporting the rotating parts and reducing friction. Specifically, both the counter and main shafts require bearing support to function properly. By reducing friction, the bearings enable the gearbox to operate efficiently and with minimal wear and tear.

5. Gears

In a gearbox, gears play a crucial role in transmitting power from one shaft to another. The torque transmitted through the gears is dependent on the gear sizes, with higher gear ratios resulting in higher torque/acceleration and lower speed. However, all gears, except for those on the main shaft, are fixed to their respective shafts to ensure proper gear engagement and function.

6. Gear Selector Fork

Gear selectors are simple devices that use a lever that selects gears to engage in disengage mechanisms. The motion of the lever slides the engaging part on the shaft. It depends on the type of gearbox whether the lever slides the gear or the synchronizer that are already forged along the main shaft.

Function Of Gearbox

1. It helps the engine to disconnect from the driving wheels.
2.  It helps the running engine connect to the driving wheel smoothly and without shock.
3.  It provides the leverage between the engine and driving wheels to be varied.
4.  This helps in reducing the engine speed in the ratio of 4: 1 in the case of passenger cars and a greater ratio in the case of heavy vehicles like trucks and lorries.
5.  It helps the driving wheels to drive at different speeds.
6.  It gives the relative movement between the engine and driving wheels due to the flexing of the road spring.

Working Of Gearbox

A gearbox in an automobile is responsible for transmitting power from the engine to the drive wheels. It does this by using a set of gears that can be shifted to change the speed and torque of the output. The gears are arranged in a specific sequence, called a gear ratio, which allows the vehicle to operate at different speeds while maintaining optimal engine performance.

The gearbox is typically controlled by a lever or shifter located inside the vehicle, which the driver uses to select the desired gear. In a manual transmission, the driver must physically shift the gears by moving the lever. In an automatic transmission, the gearbox uses sensors to automatically shift gears based on the vehicle’s speed and load.

Overall, the gearbox plays a crucial role in the performance and efficiency of the vehicle by allowing the engine to operate at its most efficient RPM range for a given speed and load.

Advantages And Disadvantages Of Gearbox

Advantages Of Manual Transmission

• The vehicle is more attractive to the driver.
• The driver has complete control over the gears and when to shift the gears.
• The cost of a manual vehicle is lower than that of an automatic vehicle.
• Transmission cost is less for repair.
• It provides better mileage.

Disadvantages Of Manual Transmission

• Manual transmission can be annoying in heavy traffic.
• There may be some problems in learning the new driver.
• Precise control over hills is necessary to avoid stalling or rolling back.
• Hands and feet can hurt when using gears and clutch.

Advantages Of Automatic Transmission

• It is easy to drive in stop-and-go traffic.
• This transmission is fast and smooth.
• Current automated vehicles offer the same mileage as manual transmission.
• The automatic transmission is very comfortable for the driver when driving.

Disadvantages Of Automatic Transmission

• Buying an automatic transmission vehicle is more expensive than a manual transmission vehicle.
• There are more moving parts in the automatic transmission, which increases the cost of repair.
• The gear change takes a little time and the gear shifting detects, and at times a slight shock is also failing.
• You cannot make the automatic gear more or less at your own will, suddenly there is a problem in overtaking the car.

Types Of Gearbox

Manual Transmission

A manual transmission is a type of transmission that requires the driver to manually shift gears using a clutch pedal and gear shift lever. This allows the driver to have direct control over the engine’s power and torque, giving them more control over the vehicle’s performance.

There are several types of Manual Transmission are as follows :

1. Sliding Mesh Gearbox

In this gearbox, spur gears are used. The Figure shows the construction of a sliding mesh-type transmission having three forward and one reverse speed. There are three gears (1, 6, and 5) attached to the main shaft and four gears (2, 3,4, and 7) on the layshaft.

The sliding mesh gearbox, as its name implies, utilizes a sliding mechanism to engage gears. Specifically, the two gears on the main shaft (6 and 5) can be slid by a shafting yoke and mesh with the gears (3 and 4) on a layshaft. To support this mechanism, a separate idler gear (8) is mounted on the idler shaft.

2. Constant Mesh Gearbox

A constant mesh gearbox is a type of mechanical transmission used in automobiles and other vehicles. It uses gears that are constantly meshed, but not necessarily in engagement. The gears are selected by sliding the appropriate gear along the shaft, into engagement with the output gear.

A constant mesh gearbox typically features multiple gears on parallel shafts that are constantly meshed. When the driver selects a gear, a synchronizer mechanism is used to bring the gear on the output shaft into alignment with the gear on the input shaft, allowing for smooth engagement.

This design allows for smooth shifting and reduces the likelihood of gears grinding or locking up, but it also tends to have more parts and can be less efficient than other types of gearboxes, such as synchromesh gearboxes.

However, constant mesh gearboxes are relatively simple and robust and can be found in a wide range of vehicles, from motorcycles to trucks.

3. Synchromesh Gearbox

The synchronizer mechanism matches the rotational speed of the gear on the input shaft with the gear on the output shaft using friction before they engage. This process eliminates the need for double-clutching, which is a technique used in other types of gearboxes to match the speeds of the gears before engagement.

The design of the synchronizer allows for smooth shifting and eliminates the likelihood of gears grinding or locking up. It also tends to have fewer parts and is more efficient than other types of gearboxes, such as sliding mesh gearboxes, but the synchronizer mechanism is more complex and can be the source of problems if not properly maintained.

Synchromesh gearboxes, which are generally considered more advanced than constant mesh gearboxes, can be found in a wide range of vehicles, from cars to trucks.

Automatic Transmission

An automatic transmission is a type of transmission that uses a torque converter and planetary gear set to automatically change gears based on the vehicle’s speed and load. It eliminates the need for the driver to manually shift gears, making the driving experience more convenient and comfortable.

There are several types of Automatic Transmission are as follows :

1. Hydramatic Transmission

The Hydramatic transmission uses a torque converter, which is a fluid coupling that allows the engine to continue running at a steady speed while the transmission changes gears. This eliminates the need for a clutch pedal, making the transmission more convenient to use.

The Hydramatic transmission uses planetary gears to achieve different gear ratios, and a set of clutches and bands to engage and disengage the gears. This allows for smooth gear changes and eliminates the need for manual gear shifting.

Hydramatic transmission was the first fully automatic transmission mass-produced for passenger cars, it was widely used in GM cars and trucks during the 1940s and 1950s. Today, it is obsolete and replaced by modern automatic transmission technology.

2. Torque Converter Transmission

A torque converter transmission is a type of automatic transmission that uses a fluid coupling called a torque converter to transmit power from the engine to the transmission. The torque converter allows the engine to continue running at a steady speed while the transmission changes gears, eliminating the need for a clutch pedal and making the transmission more convenient to use.

The torque converter works by using a turbine and a stator to transfer power from the engine to the transmission. The turbine is connected to the engine’s flywheel and spins when the engine is running. The stator is connected to the transmission’s input shaft and does not rotate. As the turbine spins, it pushes fluid through the converter, which causes the stator to spin and transmit power to the transmission.

The torque converter also has a lock-up feature that allows the turbine and stator to be directly connected when the vehicle reaches a certain speed, this eliminates the power loss caused by the torque converter.

Torque converter transmissions are widely used in automobiles and are the most common type of automatic transmission found in passenger cars today. They provide smooth gear changes and eliminate the need for manual gear shifting, but they can be less efficient than other types of transmissions and can be a source of problems if not properly maintained.

3. Continuously Variable Transmission (CVT)

A continuously variable transmission (CVT) can change seamlessly through a continuous range of gear ratios. It is a type of transmission. Unlike a traditional automatic transmission, it doesn’t have a fixed number of gear ratios.

A continuously variable transmission (CVT) allows the engine to always operate at the most efficient RPM (revolutions per minute). This feature improves fuel efficiency and provides a smooth driving experience. CVT is a popular choice for small cars, hybrid vehicles, and some high-performance sports cars.

4. Dual-Clutch Transmission (DCT)

A dual-clutch transmission (DCT) uses two separate clutches for odd and even gear sets and is a type of automated transmission. This feature allows for faster and smoother gear shifts than a traditional manual or automated transmission. The transmission accomplishes this by pre-selecting the next gear while the current gear is engaged, allowing for a much quicker shift when the driver requests it.

High-performance sports cars and racing vehicles commonly use DCTs because of their quick shift times and improved performance. Additionally, some regular production cars market them as “DSG” or “PDK” (Porsche Doppelkupplungsgetriebe) and also utilize them.

5. Epicyclic Gearbox

The planetary gearbox, also known as an epicyclic gearbox, utilizes a set of planetary gears to transmit power. Its gears are arranged in a specific way, with a gear called the sun gear at the center. This gear meshes with a set of planetary gears that, in turn, mesh with an outer ring gear.

The arrangement of gears allows the achievement of multiple gear ratios by selectively locking and unlocking different parts of the gear system. This allows for a compact design that can achieve a wide range of gear ratios.

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