There is little difference between the system DFMEA and Sub System DFMEA. In the Sub system DFMEA the cause of failures are component. Consider the same Transmission as a system and Planetary system as a sub system, which as piston, gears etc as components.
In this case, look up the boundary diagram, to get to ideal inputs and outputs. In case of the planetary system we have,
function as providing adequate gear ratio.
The
failure mode associated with this are as following
- inadequate gear ratio
- intermittent gear ratio
- no gear ratio
- unexpected gear ratio
The effect of the above failure modes are listed as following: