Electronic Throttle Body Design Failure Mode Effect Analysis Example


Consider potential failure modes for each component and interface related to throttle body - 

  • A potential failure mode represents any manner in which the product component could fail to perform its intended function or functions.
  • Remember that many components will have more than one failure mode. Document each one. Do not leave out a potential failure mode because it rarely happens. Don’t take shortcuts here; this is the time to be thorough.

List potential effects of failure by / on Throttle Body 

There may be more than one effect for each failure.
The effect is related directly to the ability of that specific component to perform its intended function.
  • An effect is the impact a failure could make should it occur.
  • Some failures will have an effect on customers; others on the environment, the process the product will be made on, and even the product itself.
  • To determine the severity, consider the impact the effect would have on the customer, on downstream operations, or on the employees operating the process.

The severity ranking is based on a relative scale ranging from 1 to 10.

  • A “10” means the effect has a dangerously high severity leading to a hazard without warning.
  • Conversely, a severity ranking of “1” means the severity is extremely low.
  • The occurrence ranking is based on the likelihood, or frequency, that the cause (or mechanism of failure) will occur.
  • If we know the cause, we can better identify how frequently a specific mode of failure will occur.

The occurrence ranking scale, like the severity ranking, is on a relative scale from 1 to 10.

  • An occurrence ranking of “10” means the failure mode occurrence is very high; it happens all of the time. Conversely, a “1” means the probability of occurrence is remote.
  • See FMEA Checklists and Forms for an example DFMEA Occurrence Ranking Scale.
  • A detection ranking of “1” means the chance of detecting a failure is almost certain. Conversely, a “10” means the detection of a failure or mechanism of failure is absolutely uncertain.

Prevention controls are always preferred over detection controls.

  • Prevention controls prevent the cause or mechanism of failure or the failure mode itself from occurring; they generally impact the frequency of occurrence. Prevention controls come in different forms and levels of effectiveness.
  • Detection controls detect the cause, the mechanism of failure, or the failure mode itself after the failure has occurred BUT before the product is released from the design stage.


RPN = Severity x Occurrence x Detection.

Function
Failure Mode
Failure Effect
SEVERITY
Potential Cause
OCCURANCE
Design Control
DETECTION
RPN
Prevention
Finding
Bore Dia
Chocking
Sudden change in Torque
8
Wrong Bore Dia
4
Throttle Bore/ Cross Section Optimization
Engine Dyno Test
3
8*4*3
=96
Pressure Wave
High Pumping Loss
TPS Sensor Functioning ( Two TPS will be used)
Wrong  Reading
Wrong Air Fuel Ratio
4

Electromagnetic Noise

No ECU Compatibility



Much Larger Bore Dia Than required
3
Use optimized Bore Dia.
Use highly sensitive motor and
Minimum Angle change of Valve low.
Engine Calibration by Driver Control Team 
7
4*3*7=84
Variation in Reading
Air Leakage
Gasket
Leakage
Accident
10
Wrong thickness
Wrong Mounting Hole Dia and Tolerances
Wrong Material
2
Stress and Strain CFD, Thermal Stress Simulation
Engine High Temperature Test
2
10*2*2=40
Burn
Throttle Assembly  on Restrictor
Uneven Flow
Low Volumetric Efficiency
8
Wrong Tolerance, Wrong Material,
Shrinkage due to Thermal Expansion
2
GDNT and Tolerance Stack up Analysis
Engine Durability  Test
2
8*2*2=32
Bolt Hole Mismatch
Fatigue and Crack  
Hose Assembly on Throttle
Hose Shrinkage due to inner vacuum
Pumping Loss
4
Low Material Thickness, low Stiffness , High Engine Room Temperature 
4
Internal Vacuum Simulation
Sudden Acceleration Test
4
4*4*4=64



Based on above DFMEA, following are recommended action -
Function
Failure Mode
Recommended Action
Bore Dia
Chocking
Decrease shaft dia.
No sudden change in inlet or out let diameter.

Pressure Wave
High Pumping Loss
TPS Sensor Functioning ( Two TPS will be used)
Wrong  Reading
First Sensor measure Valve open angle and second sensor measure valve close angle.
Keep Angle Tolerance < 0.1 Deg/mVolt. Calibrate ECU and TPS Sensor for Torque output.
Variation in Reading
Air Leakage
Gasket
Leakage
High surface finishing on throttle and restrictor.
Burn
Throttle Assembly  on Restrictor
Uneven Flow
Make Taper Hole in Throttle.
Bolt Hole Mismatch
Fatigue and Crack  
Hose Assembly on Throttle
Hose Shrinkage due to inner vacuum
Use Plastic Pipe from Air Cleaner to Throttle.