Sliding Mesh Gear Box

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An obsolete type of transmission or gearbox in which the gears on the layshaft are fixed to the shaft rigidly, whereas the gears on the main shaft can slide on it by means of splines but are otherwise in permanent rotational mesh with the shaft. The figure below shows the arrangement of sliding mesh gear box.

Construction and working of sliding mesh gear box

Sliding mesh gear boxes are made with spur gear. The gears in the layshaft is rigidly fixed shaft. The gears in main shaft alone can move along the spline. The selector fork moves the gear and moves the perfect mesh with the required gear in lay shaft when the gear lever is shifted. A idler gear is provided for reverse gearing. Thus the power form the clutch shaft is transmitted to the main shaft through the lay shaft.

First gear

In the first gear, the gearbox provides maximum torque at low speed. The smallest gear on the lay shaft engages with the biggest gear in main shaft, thus transmitting high torque.

1^st gear 2^ndgear

Second gear

In the second gear, the gearbox provides low torque and high speed when compared to 1st gear .

Third gear

In the third gear, the gearbox provides low torque and high speed when compared to 2nd gear

3^rd gear 4^thgear

Fourth gear

For fourth gear the clutch shaft and the main shaft is engaged by a dog clutch, thereby the main shaft rotates at maximum speed as that of clutch shaft.

Reverse gear

When selecting reverse, the direction of rotation of the output shaft is changed This is achieved by using an idler gear.The idler gear is meshed between a counter shaft gear (layshaft or 2nd motion shaft) and an output shaft gear(mainshaft or 3rd motion shaft).