UNIT IV - some additional theory - DESIGN OF GEAR BOX.pdf

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1. Gear box
A gear box is a device employed to provide variable speeds.

3. Other Remarks about : Gear box

4. Gearbox consists ofa driving gear with a certain diameter coupled to the driving mechanism (electric motor,
wind turbine, diesel engine etc.) linked to another gear of smaller or larger diameter coupled to a driven
mechanical load.

6. Sliding Mesh Gearbox
It is the simplest type of gearbox. In this
gearbox, spur gears are used.
The Figure shows the construction of a
sliding mesh type transmission

7. The two gears on the main shaft can be slidedby a shafting yoke and
mesh with the gears on a layshaft.
Therefore, it is called a sliding mesh gearbox.

8. Constant Mesh Gearbox

9. In this type of gearbox, all gears are constantly in mesh and
dog clutches are used for engaging and disengaging the gears.

10. As compared with the sliding mesh type, the constant mesh type gearbox
meshes more readily with the gears, having less danger of damaging during
meshing……

11. Synchromesh Gearbox
Synchromesh gearbox uses synchronizer
instead of sliding dog clutches
The synchromesh gearbox is provided with a
synchronizer, the device by which two gears to be
engaged are first brought into frictional contact
which equalizes their speed, afterward they are
engaged smoothly.
Since both pinions and synchromesh units are
moving at the same speed, this engagement is
done without noise or damage to the dogs.

12. Synchromesh Gearbox

14. Epicyclic Gearbox
The combination of epicyclic gear trains
with a planet engaging both a sun gear
and a ring gear is called planetary gear
train.
In this case, the ring gear is usually fixed
and the sun gear is operated.

17. Progression ratio (Φ)
•When spindle speeds are arranged in GP the ratio between two
adjacent speeds is known as step ratio or progression ratio
•Where z = number of steps of speed, the obtained Φshould be
standardized
1
min
max 

z
n
n


20. Progression ratio
•Speeds in a gear box may in
•arithmetic progression(A.P.),
•Geometric progression(G.P.)
•Harmonic progression(H.P.) and
•Logarthimicprogression(L.P.)
•However G.P. has following advantages
Speed loss is minimum
Minimum number of gears
Even speed range
Compact layout

21. Renard series -basic

22. Step 1:Selection of output speeds

23. R-series : basic

24. Example 1: Selection of output speeds
•Find the progression ratio and the output speeds for a 12 speed gear box having
min. speed = 100 rpm and max speed = 355 rpm.
•Φ = 1.122.
•The speed 1.12 is a standard ratio of R20 series….
•Therefore the output speeds are
100,112,125,140,160,180,200,224,250,280,315 and 355 rpm
1
min
max 

z
n
n


25. Example 2 :
Selection of output
speeds
Design a nine speed gear box for a machine to provide speeds ranging from 100rpm to 1500rpm. The input
is from a motor of 5KW at 1440rpm. Assume any alloy steel for the gears.

26. Example 2 :
Selection of output
speeds

27. R-series : basic

30. Step 2:Write the structural formula

32. Step 3:Ray Diagram

33. Step 3:Ray Diagram

37. Step 4:Draw Kinematic arrangement