Full Notes on Constant Mesh Gearbox

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Constant mesh gearbox is used for the smooth working of an automobile. They are used to increase the rotating force (Torque); this is accompanied by a reduction in speed. It is a type of manual transmission. The invention of earliest manual gear system can be traced back to the nineteenth century. There are multiple gear ratios present which provides various torque and speed ratio. Along with this, the reverse mechanism is also present. This manual transmissions which are developed recently contain all the gears mesh at any given point of time.


In technical terms, constant mesh gearbox can be defined as a gearbox in which all the gears are always in a state of mesh. The gears remain fixed at their original positions. The gears will remain engaged at all times. Learn more about its construction, working, advantages, disadvantages and applications in this article.


Constant Mesh Gearbox:



It is made up of following components:

Full Notes on Constant Mesh Gearbox



1. Counter shaft or Lay Shaft:
This shaft is in direct contact with the clutch and the main shaft. Keeping in mind according to the gear ratio, the speed of the counter shaft may be less that the speed of the engine. The gear ratio can be defined as the ratio of the teeth of driven gear to the teeth of the driver gear.


2. Main shaft:
This shaft operates the speed of the vehicle. The power is made available to the main shaft through the gears from the counter shaft. This is done in accordance with the gear ratio.


3. Dog clutch:
Dog clutch is special feature of constant mesh gearbox. It is used for the coupling of any two shafts. This is done by interference. Using a dog clutch, various gears can be locked to the output and input shafts.


4. Gears:
The main work of the gears is the transmission of power between the shafts. If the gear ratio is more than one, the main shaft will work at a speed that is slower than the counter shaft, and vice versa. The arrangement of both reverse, as well as forward gears, is present.




Forward gear selection:
From the input shaft, the power starts flowing and is divided into four parts. Each part goes to one of the output gears, namely first, second, third and fourth. Gear ratios can be obtained for each of them. This can be done by the proper sliding of dog clutch over the teeth of the selected gearwheel. After this the path of the energy flow completes. This happens due to the locking movement of the output shaft.


Reverse gear selection:

The power will flow from the input shaft to the reverse gears. The power is then transmitted from the reverse gear to the reverse idler. The idler wheel will change the direction of the rotation. In the case of forwarding direction gear selection, the output gears will rotate in a direction opposite to the input gears. But in the case of reverse gear selection, the rotation is in the same direction as the input shaft.

The steps are taken to change any gear in the constant mesh gearbox system:


1. The first step when one wants to modify the gear would be the pressing of the clutch. After this comes the neutral state of the vehicle to be achieved. Proper optimization of the engine’s speed is required.


2. After the neutral gear, one moves forward to the first gear. The first gear. This process is known as double clutching. Inefficiency in performing the above steps might lead to a harsh and gnashing sound.

Watch the following video for clear understanding of its working.


Advantages and Disadvantages of Constant Mesh Gearbox:

  • The first and foremost benefit of the constant gear mesh is the utilization of helical gears. The double helical gears and the helical gears are extremely beneficial owing to their quieter operating capabilities.
  • There are various conditions which might cause harm. In the case of constant mesh gearbox, any harm is suffered entirely by the dog clutch teeth. The teeth belonging to the gear wheels remain intact. This is not the case for sliding mesh gear box.
  • The other gear boxes are noisy and create an unwanted din.
  • It is less efficient than the others due to higher mesh teeth. Skill is required for it.
  • The double clutch mesh is required. This is required to have the spinning movements of the shaft.



Some of the vehicles which use this type of gearboxes are farm trucks, motorcycles, and heavy machinery.


It is very evident that the world today is full of vehicles and relies on this mode of transport. The availability of such mechanisms like constant mesh gearbox which create less noise and are cost effective is a boon for the people.If you like this article don’t forget to share it on social networks. Subscribe our website for more informative articles. Thanks for reading it.

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