Brake System Design Review and DFMEA

Please read previous blog for vehicle static weight, center of gravity, engine, transmission etc. 

Please read previous for following -
Different Types of Weight of Car, front and real calipers, Brake Pad, Brake Fluid Volume, front to rear weight bias, rear traction, lower polar moment of rotation, Skid, Tyre Thread Design, Car Center of Gravity and many more technical terms.

Below is only summary of design review done and explained in previous blog :-

Child Part
Requirement
Material
Manufacturing
Cost
Weight
Life
Design Review
Brake Pipe
Burst Pressure =200 Bar Min
OD= 10mm Max
ID=5mm Min
Factor of Safety 5 Min
Steel Pipe
Multi layer Seamless Piping with flared end
A
B
B
Ni- Alloy Brake pipe is safe and have good life.
 Ni- Alloy has higher Ultimate Tensile Strength so less material thickness pipe can be used.
For same burst Pressure weight of Ni Apply pipe is least.
Cu Alloy
B
B
A
Cu Ni Alloy *
C
A
A
Brake Oil
No Compressibility,
Anti Hygroscopic, High Dry/Wet Boiling Point,  Fix Viscosity
Silicone-based
Chemical Process
B
/
B
Anti Hygroscope property is better for glycol based fluid because water does not mix in it.  Glycol based fluid will be used in brake.
¤ Glycol Based
B
/
A
Disc
Mean Effective Radios = 250mm,
Thickness = 20 mm
Weight = 2 Kg Max
Grey Iron
Casting
A
C
B
Grey Iron is very heavy and chances of rust are high. Siliconized carbon is very costly.
Reinforced Carbon will be used for Disc as it has long life and safe.
Siliconized carbon
Sintering
C
A
A
^Reinforced Carbon
Sintering
B
A
A
Piston
Dia =45mm,
Burst Pressure = 200 Bar
Steel
Casting/Machining
A
C
B
Aluminum (ADC12) has lesser weight so Al Piston will be used. (HPDC: high Pressure Die Casting)
Titanium
Casting/Machining
C
A
A
ADC12#
HPDC, Machining
B
B
B
Master Cylinder
Bore =10mm, Capacity = 15cc, Burst Pressure = 200 Bar
Steel
Casting/Machining
A
C
B
Aluminum (ADC12) has lesser weight so Al Piston will be used.
ADC12#
HPDC, M/c
B
A
B
Brake Pad
Area =50Cm2
Depth =40mm
Thickness =15mm
Ceramic
Sintering
B
A
B
Carbon Steel Pads will be used as it has longer life and lesser cost.
¥Carbon Steel
Machining
B
B
A
Brake Pedal
Level Length =300mm
Pedal Area = 50X50mm2
Steel
Bending, Welding
B
B
A
Cost reduction through elimination of fixturing alignment, welding, and finishing operations required for the welded steel assembly. so Al will be used
Al B356 T6
LPDC, M/c
A
A
A
Brake Pressure Sensor
Pressure Voltage  0Bar 0V to 250Bar 5V
Accuracy = 1%
Piezoelectric
Electronic Chip Molding
/
/
/
Piezoelectric has better sensitivity and responsiveness.  Twisted Wire Sensor will be used to avoid electronic noise.
Piezoresistive
/
/
/
Hand Brake Lever
Length =300mm
Handle Dia = 20mm
Weight = 1Kg Max
No Sharp Edge
PA66 GF35
Molding
C
A
B
Steel will be used for hand brake lever. Separate PA66 GF35 made handle can be assemble on Lever for superior grip.
Aluminum
HPDC, M/c
B
B
A
Steel
Casting, M/c
A
C
A
Hand Brake Cable Wire
Braiding Angle, Ductility, Cable Dia/Wire Dia, Length, Elongation, Hardness
Cross Braided Wire
Drawing, Knitting
C
B
A
Spiral Braided Wire will be used as its cost is less. Knitted Wire has more strength and life but very costly.
€ Spiral Braided Wire
Drawing, Twisting
A
B
B



(A: Best, B: Good, C: Average; M/c: Machining; HPDC: High Pressure Die Casting)
(*Lipowsky & Arpaci, 2008, p.125), (¤ CDX Automotive, 2012, p.30), (¥ Elmarakbi, 2013, ch.16.8.1), (#Wan Hu, 2016), (€ Stapleton, Vizard and Sprinzel, 2008), (^Gilles, 2005, p.165)



Design Failure Mode Effect Analysis:

I have explained Severity rating, occurrence rating and  detection in past in blogs of Intake DFMEA, Throttle DFMEA, Exhaust DFMEA.  

  • Severity, which rates the severity of the potential effect of the failure.
  • Occurrence, which rates the likelihood that the failure will occur.
  • Detection, which rates the likelihood that the problem will be detected before it reaches the end-user/customer.

Formula: The Risk Priority Number, or RPN, is a numeric assessment of risk assigned to a process, or steps in a process, as part of Failure Modes and Effects Analysis (FMEA), in which a team assigns each failure mode numeric values that quantify likelihood of occurrence, likelihood of detection, and severity of impact.

NO
ITEM/
FUNCTION
POTENTIAL FAILURE MODE
POTENTIAL EFFECT
OF FAILURE
SEVERITY
POTENTIAL CAUSES
OCCURANCE
CURRENT DESIGN CONTROLS
DETECTION
RPN
PREVENTION
DETECTION
1
BRAKE FLUID FLOW FROM BRAKE PIPE TO BRAKE CALIPERS
Leakage or breakage at brake pipe or  joints
Brake Completely Fail
10
Wrong Selection of material, Wrong End Joint Dimension,
Mismatch in Brake Pipe and Master Cylinder / Calipers Thread
2
Simulation for Burst Pressure, Stress and Strain.
Design Calculation for Flared Thread  Dimension
Material Test, Dimension Measurement,
Burst Pressure Measurement,
100% Part Leak Test for 200 Bar for 30 Second
2
10*2*2=
40
Brake Partially Fail
( Fluid Pressure Drop)
10
2
BRAKE PAD
WEAR RATE IS TOO HIGH
High Braking Distance
9
Wrong Selection of Pad or Disc material,
Wrong Size of Pad or Disc,
Uneven Pad wear  
2
Pad Heat Loss Simulation, Hand Calculation of brake pad and disc size
Disc/Pad Corrosion Test +
Wear Rate Measurement + Heat Generated Measurement,
Braking Distance Test
2
9*2*2
=36
Braking Noise
5
2
5*2*2
=20
3
BRAKE PEDAL

Brake
Brake Completely Fail
10
Wrong Material, Low Strength of Pedal
2
Simulation of Stress and Strain
Pedal Braking Torque Test, Material Test
2
10*2*2
=40

High Displacement
Driver Exhausted and Tired
7
Wrong Pedal Lever Ratio, Wrong Master Cylinder Dia/Calipers Piston Size
3
Optimize Master Cylinder/ Calipers Size, Optimize Actual vs. Optimal Braking Force
Ergonomic Check,
Static Braking Test, Continuous Braking Test, 
3
7*3*3
=63
Hard Pressing
8
5
3
8*5*3
=120


Based on above DFMEA following suggestions are made to improve brake system design 


NO
ITEM/
FUNCTION
 RECOMMENDED  ACTION
1
BRAKE FLUID FLOW FROM BRAKE PIPE TO BRAKE CALIPERS
1) Follow one Norm for Thread European or American or Japanese
2) Have Better Factor for Safety by using CU-Ni Alloy
2
BRAKE PAD
1) Use Carbon Sintered Pad and Disc which has low wear rate.
2) place calipers properly for even wear at pad
3
BRAKE PEDAL
Use Aluminum Alloy Molding to eliminate welding and high strength, light weight Pedal
Optimize Pedal Level Ratio for different  Master Cylinder Dia and Calipers Dia