Constant Mesh Gearbox – Parts, Working, Diagram

Discover the benefits of a Constant Mesh Gearbox for your machinery. Find out how it works and explore the Applications and Advantages Of Constant Mesh Gearbox

What Is Constant Mesh Gearbox?

A constant mesh gearbox is a type of manual transmission used in automobiles. It consists of a set of gears that are always in mesh (i.e., in contact) with each other but are not engaged until a clutch is activated. This allows for smoother gear shifting and reduces the risk of grinding gears.

In a constant mesh gearbox, the gears rotate freely on the shafts but are prevented from sliding along the shafts by dog clutches. When the clutch is engaged, the gears are locked to the shaft and transmit power from the engine to the wheels.

⭐ Learn MoreWhat Is Synchromesh Gearbox?

Constant Mesh Gearbox Diagram

Constant Mesh Gearbox
Constant Mesh Gearbox Diagram

Constant Mesh Gearbox Components

1. Engine shaft

The engine shaft transfers power from the engine to the gearbox. It is connected to the crankshaft of the engine and is responsible for transmitting power to the rest of the transmission.

2. Lay shaft

The lay shaft is a rotating shaft that supports the gears that mesh with the gears on the output shaft. It is parallel to the output shaft and is responsible for carrying the gears that mesh with the output shaft gears.

3. Output shaft

The output shaft is responsible for transmitting power from the gearbox to the wheels. It is connected to the drive shaft and transmits power to the wheels through the differential.

4. Clutch gear

The clutch gear is responsible for engaging and disengaging the gears on the lay shaft and output shaft. When the clutch is engaged, the gears are locked to the shafts and transmit power. When the clutch is disengaged, the gears are free to rotate on the shafts.

5. Lay shaft gears (1 to 5)

The lay shaft gears mesh with the gears on the output shaft to transfer power. The different gears are selected by the gear shifting mechanism to provide different gear ratios, which affect the vehicle’s speed and acceleration.

6. Output shaft gears (A to C)

The output shaft gears mesh with the gears on the lay shaft to transfer power. The different gears are selected by the gear shifting mechanism to provide different gear ratios, which affect the vehicle’s speed and acceleration.

7. Dog Clutch

The dog clutch is a key component in a constant mesh gearbox. It prevents the gears from sliding along the shafts and allows for smoother gear shifting. The dog clutch also reduces the risk of grinding gears, which can cause damage to the transmission.

8. Gear Shifting mechanism

The gear shifting mechanism controls the movement of the gears to select different gears. This mechanism typically consists of a shifter and a series of rods and linkages that connect the shifter to the clutch and gears.

9. Gear pedal

The gear pedal activates the clutch to engage and disengage the gears. When the pedal is pressed, the clutch is engaged, which locks the gears to the shafts and allows power to be transmitted. When the pedal is released, the clutch is disengaged, which frees the gears to rotate on the shafts.

10. Idler gear

The idler gear is responsible for regulating the rotation speed of the gears on the lay shaft. It helps to ensure that the gears rotate at the correct speed, which is necessary for smooth gear shifting and proper operation of the transmission.

⭐ Learn MoreWhat Is Sliding Mesh Gearbox?

Constant Mesh Gearbox Working

Working Of Constant Mesh Gearbox
Constant Mesh Gearbox – Image Source

A constant mesh gearbox is a manual transmission system in which the gears are always in mesh (engaged), but are not mechanically connected. It uses dog clutches to engage and disengage each gear, allowing smooth shifting between gears without the need to synchronize the speeds of the gears.

The gears are arranged in a straight line, with the dog clutches for each gear located between the gears. When a gear shift is made, the dog clutch for the selected gear is engaged, locking the gear to the shaft, while the dog clutch for the previous gear is released, allowing it to spin freely. This allows for smooth shifting without the need for synchronizing the speeds of the gears.

In a constant mesh gearbox, gears rotate freely on their shafts when not engaged, reducing friction and wear. It also allows for easier shifting, as the gears do not need to be precisely synchronized before shifting.

Overall, the constant mesh gearbox provides a simple, reliable, and low-maintenance solution for manual transmission systems in vehicles.

Double Declutching In Constant Mesh Gearbox

Double declutching is a technique used in driving a vehicle equipped with a constant mesh gearbox to make smoother gear shifts. It involves intentionally disengaging and re-engaging the clutch twice during the gear shift.

The process of double declutching involves the following steps :

  1. Disengage the clutch pedal to disconnect the engine from the transmission.
  2. Depress the clutch pedal again to re-engage it while simultaneously moving the gear shift lever to neutral.
  3. Depress the clutch pedal a third time to disengage it while simultaneously moving the gear shift lever to the desired gear.
  4. Finally, release the clutch pedal to re-engage it and complete the gear shift.

Double declutching was more commonly used in older vehicles with constant mesh gearboxes, where synchronizing the speed of the gears was more difficult. However, with the advancement of technology and the use of synchromesh systems in modern transmissions, double-declutching is not typically necessary for smooth gear shifts.

Constant Mesh Gearbox Advantages

  1. Simplified design and lower cost compared to other types of gearboxes
  2. Improved reliability due to less moving parts and the absence of synchronizing mechanisms
  3. Faster and smoother gear shifting compared to sliding mesh gearboxes
  4. Better control over engine power output, as the gears are always meshed and ready to engage.

Constant Mesh Gearbox Disadvantages

  1. Higher wear and tear on the gear teeth due to the constant mesh between gears
  2. No synchronizing mechanism can result in difficulty shifting gears, especially under high loads or high speed
  3. Limited gear ratios compared to other types of gearboxes, as the gears must remain in constant mesh for proper operation.

Constant Mesh Gearbox Application

1. Motorcycles

Constant-mesh gearboxes are commonly used in motorcycles because they offer fast and smooth gear shifting.

2. Light to medium-duty commercial vehicles

Delivery vans, small trucks, and other commercial vehicles can benefit from the improved reliability and efficiency of a constant mesh gearbox, especially in applications where fast gear shifting and smooth operation are important.

3. Agricultural and construction equipment

Tractors, combine harvesters, and other agricultural and construction equipment often use constant mesh gearboxes for their durability and ability to handle the demands of heavy-duty work.

4. Small aircraft

Constant mesh gearboxes are used in small aircraft due to their lightweight, compact size, and ability to handle the demands of high-speed, high-performance flight.

5. Racing vehicles

Go-karts, dirt bikes, and other racing vehicles often use constant mesh gearboxes because they offer fast and smooth gear shifting, improved control over engine power output, and a simplified design.

FAQ’s

What is the disadvantage of a constant mesh gearbox?

The main disadvantage of a constant mesh gearbox is the tendency to generate too much noise and vibration due to the constant mesh of the gear. This type of gearbox requires more maintenance than other types of gearboxes, as the gears can wear out more quickly. Additionally, the gears in a stationary mesh gearbox may not attach as smoothly as in other types of gearboxes, which can cause problems changing gears.

Which types of gears are used in constant mesh gearbox?

Constant-mesh gearboxes typically use straight-cut or spur gears. These gears are simple and relatively cheap to manufacture, making them a popular choice for use in continuous mesh gearboxes. Straight-cut or spur gears are also durable and have a higher load-carrying capacity, which makes them suitable for use in high-torque applications. Additionally, these gears can transmit power smoothly and efficiently, which is important in gearboxes.

What is a constant mesh gearbox?

A constant mesh gearbox is a type of manual transmission in which the gears are always in the mesh but not mounted. It uses a dog clutch to connect gears and transmit power from the engine to the wheels. The continuous mesh design allows quick and smooth gear changes, as the gears are always in place and ready to be attached. This type of gearbox is widely used in a variety of vehicles and machinery due to its simplicity, reliability, and cost-effectiveness.

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