DESIGN OF GEARBOX (SPEED REDUCERS)

Motor Machine Tools & Engine Road wheels

To get different speeds – Gear Box

What would happen if accidentally shift into reverse gear? Would

the entire transmission explode?

What is moving inside the

transmission when move the shifter?

When hearing that horrible grinding

sound, what is actually grinding?

Components of Speed Reducers

Shafts for mounting gears

Bearings to support shafts and gears

Gearbox housing to support bearings, to hold lubricants and to protect

from dirt and dust

Provisions to prevent axial movement of the shafts relative to bearings

and to prevent axial movement of bearing

Space for oil reservoir

Oil level indicator, drain plug and inspection hole

Cooling fins

Provision for easy assembly and disassembly

Single Reduction

Double Reduction

Multi Speed changing

Since, Centre distance of the shafts A and B is fixed, it is essential that the

sum of the teeth of engaging pairs should be equal for same module

Z1 + Z2 = Z3 + Z4 = Z5 + Z6

Neutral condition First Gear engaged

5 speed Gearbox

Reverse Gear operation

PROGRESSION RATIO []

The ratio of adjacent speeds will be a constant called

progression ratio. The spindle speeds (output speeds) are

arranged in geometric progression.

If Nmax is the maximum speed, Nmin is the minimum speed, then

=

Progression ratio Ø =

Ø4 =

Ø4 =

Ø5-1 =

Ø r -1 = Ø =

Consider a five speed gear box, where N5 is the maximum

speed, N1 is the min speed and r is the number of speeds.

6 Speed Gearbox (2×3) or (3×2)

9 Speed Gearbox (3×3)

12 Speed Gearbox (3×2×2) or (2×3×2) or (3×2×2)

STRUCTURAL RAY DIAGRAM

Follow for all stages,

≤ 2 and ≥

If it is not possible,

≤

Structural formula: Z = P1 (X1). P2 (X2). P3 (X3)

Where P1, P2, P3 are speeds available in each stage

X1 = 1, X2 = P1, X3 = P1.P2

Principles to be followed to obtain optimum design:

Number of gears on the last shaft (spindle) should be

minimum.

Number of gears on the shafts should not be more than 3.

It is preferable to have nmax ≥ ninput > nmin in all the stages

except in the first stage.

The velocity ratio between the spindle and the shaft preceding

it should be the max possible.