Constant mesh gearbox is a type of Transmission in which all or most of the gears are always in mesh with one another, as opposed to a sliding-gear transmission, in which engagement is obtained by sliding some of the gears along a shaft into mesh. In a constant-mesh manual gearbox, Gear ratios are selected by small Clutches that connect the various gear sets to their shafts so that power is transmitted through them. The following diagram shows the arrangement of a constant mesh gear box .
Construction and working of constant mesh gear box :
The constant gear mesh gearbox employed helical gears for power transmission. The gears are rigidly fixed in the lay shaft. The gears in output shaft rotates freely without engaging with shaft, thus not transmitting power. The gears in both shafts are always meshed together.
To engage the gears with output shaft dog clutch is used. the dog clutch is shifted by the seletor fork moved by gear lever.To provide reverse gearing a idler gear is used.
When the gear lever is pushed, the gear selector fork pushes the dog clutch. The dog clutch engages the gear and the output shaft, thus power from lay shaft now transmitted to output shaft.