28-06-2013, 03:08 PM
Automobile manual transmission
Automobile manual.pdf (Size: 1.95 MB / Downloads: 79)
Loads on shaft due to gears
From power and rpm find the torque (T), which gives rise to shear stress.
From Torque (T) and diameter (d), find Ft = 2T/d. From Ft and pressure
angles of gears you can find Fr and Fa.
Fr and Ft are orthogonal to each other and are both transverse forces to
the shaft axis, which will give rise to normal bending stress in the shaft.
When shaft rotates, bending stress changes from tensile to compressive
and then compressive to tensile, ie, completely reversing state of stress.
Design of shaft
Axial dimensions are often fixed from the layout of the mechanism.
Design recommendation is to keep the axial lengths as short as
possible to limit bending stress.
Simply supported shaft is better than cantilever or overhang shaft.
Shaft design is to determine the diameter of the shaft such that it
withstand the applied loads, after stress concentrations, with a known
factor of safety.
Design of rotating shafts and fatigue consideration
The most generalized situation the rotating shaft may
have both steady and cyclic components of bending
stress (sav,sr) and torsional stress (tav,tr).
The most frequently encountered stress situation for a
rotating shaft is to have completely reversed bending and
steady torsional stress. In other situations, a shaft may
have a reversed torsional stress along with reversed
bending stress.