We learned about the importance of gearboxes and types of turns in the automobile transmission system. Constant mesh gearbox is one of the different types of gearboxes in automobiles.

    In constant mesh gearboxes, the shaft-main shaft gears always mesh with each other, and unlike the sliding-gearboxes, the rotation of the mesh gears into the main shaft is transferred to the wheels at different torque-speed ratios.


    In a constant mesh gearbox, the gear ratios are selected with the help of small clutches, called dog clutches. Dog clutches have dog teeth on both sides. Teeth in the same proportions will also be on the sides of the gears.

    All gears are permanently fixed to the lay shafts of the mesh gearboxes. Therefore, whichever gear rotates on the lay shafts, it rotates the lay shaft as a whole, and thus all the gears fixed on the lay shafts rotate with it.

  
    The main shaft gears are mounted on a bush bearing on the main shaft. Therefore the rotation of the gears does not directly affect the main shaft.


    Dog clutches are mounted on the spline so that you can move left or right between the main shaft gears. Therefore the rotation of the dog clutch rotates the main shaft as well as rotates it to the left or right.


WORKING
    Engine power reaches the gearbox via the clutch shaft through the clutch system.
As the clutch gear on the clutch shaft is also mesh with the largest gear on the lay shaft, engine power is transferred to the lay shaft and the lay shaft rotates completely.


    Lay shaft gears rotate with the main shaft gears as they are always meshed with the main shaft gears. However, since the gears on the main shaft are mounted on a bush bearing, the main shaft does not rotate even when the gears rotate.


    The dog clutches, which are mounted between the gears on the main shaft, are moved to the desired gear using the selector mechanism. The dog clutch meshes with the dog teeth on the sides of the gears and the dog clutch begins to rotate at the same speed as the meshed gear. As it is mounted on the spline, the dog clutch rotates the main shaft and transmits this rotation to the wheels via the propeller shaft to move the vehicle.

Different gear ratios in Constant Mesh Gearbox:


First Gear:
First gear is obtained in constant mesh gearbox when dog clutch gets engage by interference with the largest gear of main shaft which is in constant mesh with smallest gear of main shaft. This gear provides maximum torque and minimum speed to the main shaft.

Second Gear:
Second Gear is obtained when dog clutch gets engage with second largest gear of main shaft which is in a constant mesh with second smallest gear of lay shaft. This gear provides higher speed and lower torque than first gear.

Third Gear:

(As per the above image)Third gear is obtained when dog clutch engages with directly to the clutch shaft gear. This gear most speed and less torque in the total gear ratio.


Reverse Gear:
In this gear the vehicle goes in reverse direction. Like sliding mesh gearbox, an idler gear is also used in constant mesh gearbox between the main shaft gear and lay shaft gear to form reverse gear. Reverse gear is obtained when dog clutch engages with gear in main shaft which is paired with idler gear.