Steering System DFMEA and Design Review for sports car and racing vehicle
Please read previous blog for vehicle parameters, steering components, steering mechanism, child parts and related system components mechanism.
Here we will make summary table of Design Review which was explained in previous blogs.
DFMEA:
Recomendation based on above DFMEA
Here we will make summary table of Design Review which was explained in previous blogs.
|
Child Part
|
Requirement
|
Material
|
Manufacturing
|
Cost
|
Weight
|
Life
|
Design Review
|
|
Rack Housing
|
High
Surface Finish,
High
Strength,
Fine
Dimension Tolerance,
Wear
Resistance,
Corrosion
Resistance,
High
Toughness
|
Steel
|
Machining
|
A
|
C
|
B
|
Al Alloy is light weight and has good life. Steel and Aluminum
are lesser costly but have high weight. Also Rusting is more for Steel. So Al
Alloy will be used for Rack Housing Components.
|
|
Aluminum ADC12
|
PDC Pressure Die Casting and Machining
|
B
|
B
|
B
|
|||
|
Al Alloy
|
C
|
A
|
A
|
||||
|
Support Tube
|
ADC12
|
PDC Pressure Die Casting and Machining
|
B
|
C
|
B
|
Al Alloy will be used for Support Tube as it has less weight.
|
|
|
Al Alloy
|
C
|
A
|
A
|
||||
|
Pinion Housing
|
Steel
|
Machining
|
A
|
C
|
B
|
Al Alloy will be used for Support Tube as it has less weight and
lesser wear.
|
|
|
ADC12
|
PDC Pressure Die Casting and Machining
|
B
|
B
|
B
|
|||
|
Al Alloy
|
C
|
A
|
A
|
||||
|
Housing Cap + Bush
|
Steel + Bronze
|
Casting/Machining
|
A
|
B
|
B
|
Bronze Bush with ADC12 housing Cap will be used due to light
Weight. (HPDC High Pressure Die Casting)
|
|
|
Bronze
|
Casting/Machining
|
C
|
B
|
A
|
|||
|
ADC12+ Bronze
|
HPDC, Machining
|
A
|
A
|
B
|
|||
|
Pinion Housing Clamp
|
Alloy Steel
|
Casting/Machining
|
C
|
B
|
A
|
Driver applied torque is transmitted though the lower pinion
gear to the rack gear, So very high Strength is required here.
|
|
|
Al Alloy
|
HPDC, Machining
|
C
|
A
|
B
|
|||
|
Pinion Helical Gears
|
Number of
Spiral Tooth Anti Backlash ID/ OD |
Alloy Steel
|
Forged, Milling, Hobbing Lapping
|
C
|
B
|
A
|
Alloy Steel Helical Gears will be used as it has less weight and
long life.
|
|
Cast Iron
|
B
|
C
|
C
|
||||
|
Rack with variable Teeth
Helical Gear
|
Rack Speed=60mm / Revolution
Travel Max = 75mm |
Carbon Fiber
|
Molding
|
C
|
A
|
B
|
Carbon Fiber is very costly. Both Pinion and Rack should have same
material for same wear rate. Alloy Steel will be used for rack.
|
|
Alloy Steel
|
Casting, Machining.
Gear=Milling, Hobbing Lapping |
A
|
C
|
A
|
|||
|
Al Alloy
|
B
|
B
|
B
|
||||
|
Pinion Shaft
|
High
Surface Finish, High Strength, Fine Dimension Tolerance, Low Wear Rate,
Corrosion
Resistance, High Toughness
|
Steel
|
Casting, M/c
|
A
|
B
|
B
|
Aluminum will be used for Pinion Shaft.
|
|
ADC 12
|
HPDC, M/c
|
B
|
A
|
B
|
|||
|
Rack Ends
|
Steel
|
Casting, M/c
|
A
|
C
|
B
|
ADC12 will be used for Rack Ends.
|
|
|
ADC12
|
HPDC, M/c
|
B
|
B
|
B
|
|||
|
Steel Alloy
|
HPDC, M/c
|
C
|
A
|
A
|
|||
|
Housing End Supports
|
ADC 12
|
HPDC, M/c
|
A
|
B
|
B
|
Al Alloy will be used for Housing End Support as it has less
weight.
|
|
|
Al Alloy
|
HPDC, M/c
|
B
|
A
|
A
|
DFMEA:
I have explained in detail severity, occurrence and detection in blogs of Throttle DFMEA, Intake System DFMEA, Exhaust System DFMEA and Brake DFMEA in previsions blogs.
|
NO
|
ITEM/
FUNCTION
|
POTENTIAL
FAILURE MODE
|
POTENTIAL
EFFECT
OF FAILURE |
SEVERITY
|
POTENTIAL
CAUSES
|
OCCURANCE
|
CURRENT
DESIGN CONTROLS
|
DETECTION
|
RPN
|
|
|
PREVENTION
|
DETECTION
|
|||||||||
|
1
|
RACK
AND PINION
|
Mechanical
Failure, Lubrication not Uniform,
Loosing
of Nut and Bolt
|
Steering
Failure
|
10
|
Obstruction
in movement of pinion over rack, damage to components
|
2
|
Simulation
for Burst Pressure, Stress and Strain.
Design
Calculation for Flared
Thread Dimension
|
Lubrication
Check, Vibration Measurement on Nut/Bolts, Material and Strength Test, Weld
Strength Test.
|
3
|
10*2*3=
60
|
|
Steering
Wheel Hard
|
8
|
5
|
3
|
8*5*3=
120
|
||||||
|
2
|
STEERING COLUMN AND WHEEL
|
Breakage, Mechanical Failure, High
Vibration
|
Steering Failure,
High Debris
|
10
|
Excess
Load Applied by Driver, Bump Steer
|
2
|
Strength
and Vibration Simulation of each component
|
Physical
Durability Testing of each component
|
3
|
10*2*3=
60
|
|
Driver
Tired, Ergonomic Issue
|
Drivability Issue
|
5
|
Wrong
Position of Steering Wheel
|
4
|
Calculate
Ergonomic Position
|
Steering
Wheel Check
|
5
|
5*4*5=
100
|
||
|
3
|
DRIVABILITY
|
Improper
Cornering, Difference in Left and Right Turn
|
Safety Issue, Vehicle Skid, Slip or
topple
|
10
|
Wrong
Length and Position of Steering Rack, Wrong Gear Ratio.
|
4
|
Calculation,
Layout and Simulation of Rack Location , and Gear Ratio
|
Minimum Corner Radios Measurement at
highest speed
|
4
|
10*4*4=
160
|
|
Vehicle
Not moving in Straight Line ( Waving)
|
Safety Issue
|
8
|
Rack
Pinion Mismatch, Gear Tooth Wear or Broken
|
2
|
Gear
Mess Simulation, Gear Tooth Strength Test
|
Gear Wear Test, Tooth Breakage Force
Measurement
|
2
|
8*2*2
=32
|
||
|
4
|
STEERING SENSOR
|
Electric
Failure
|
Safety Issue
|
9
|
Water
Entry, Electromagnetic Noise, High Vibration,
|
2
|
Select
Sensor Specification
After
checking humidity, electromagnetic noise and vibration on vehicle
|
Water Spray Test, Electromagnetic Antenna
Test ,
Vibration Measurement on Sensor
|
2
|
9*2*2=
36
|
Recomendation based on above DFMEA
|
NO
|
ITEM/
FUNCTION
|
RECOMMENDED ACTION
|
|
1
|
RACK AND PINION
|
1) Use Good Lubrication
2) Use High
Surface Finish Gears
3) Reduce Welding
and Joints in system
|
|
2
|
STEERING COLUMN
AND WHEEL
|
1) Use Aluminum
Alloy or Steel Alloy for Manufacturing
|
|
1)Take many
expert drivers opinion
|
||
|
3
|
DRIVABILITY
|
1)Do many
iteration for optimization of Rack Length and Gear Ratio
2) Benchmarking
of Race Vehicle
3) Do only small
modification in previous designs
|
|
Use Alloy Steel
Helical Gears with high surface finish and high toughness
|
||
|
4
|
STEERING
SENSOR
|
1)Use sensor
cover
2)Use twisted
shielded wire
3)Use high
Vibration Resistance Sensor
|
