Synchromesh Gear Box

The arrangement are the same as constant mesh type gear box. Gears on the main shaft mesh with those on lay shaft. The gears on the lay shaft are fixed. This provision avoids the need for double declutching.

Figure 2.7 shows design of a synchromesh gear box. These devices reduce the cost.

Gears B, C, D, E in Figure 2.7 are free to move on the main shaft and are in mesh with gears on the lay shaft. Menders F₁ and F₂ are free to move on splines on the main shaft. G₁ and G₂ have internal teeth fit onto the external teeth members F₁ and F₂ respectively. However, when the force applied in G₁ (G₂) through fork S₁ (S₂) exceeds a certain value, the balls are overcome and member G₁ (G₂) slides over F₁ (F₂).

For direct gear, member G₁ and hence member F₁ (through spring–loaded balls) is slid towards the left till comes M₁ and M₂ rub and friction makes their speed equal. For the second gear the members F₁ and G₁ are slid to the right so that finally the internal teeth on G₁ are engaged with L₁. Then the drive to main shaft will be from B via U₁, U₂, C, F₁ and splines. For first gear, G₂ and F₂ are moved towards the right. In this case the drive will be from B via U₁, U₃, D, F₂ and splines to the mainshaft. For reverse, G₂ and F₂ are slid towards the right. In this case the drive will be from B via, U₁, U₄, U₅, D, F₂ are splines to the main shaft.