DFMEA OF Engine Systems

Dr K C VoraDeputy Director & Head,

ARAI Academy, ARAI.

Engine

Typical Cylinder Head

Recommend improvements

Look possible causes & mechanism for failures mode

Consider effects, if above failure mode happens

Assess the frequency of occurrence of

failure modes (O)

Assess the possibility of Failure being detected ( D )

Assess the Severity of effect (s)

List all conceivable failure modes

Calculate the Risk Priority Number (RPN)

Re- evaluate (New RPN )

Define Responsibility & Time- frame

FMEA Procedure List all Function &

requirements

S.O.D. Tables & its usage

Probability of Failure Possible Failure Rates Ranking

Very High : Persistent failures

> 100 per thousand vehicles/ items

10

50per thousand vehicles/ items 9

High : Frequent failures

20 per thousand vehicles/ items 8

10 per thousand vehicles/ items 7

Moderate : Occasional failures

5 per thousand vehicles/ items 6

2 per thousand vehicles/ items 5

1 per thousand vehicles/ items 4

Low : Relatively few failures

0.5 per thousand vehicles/ items

3

0.1 per thousand vehicles/ items

2

Remote : Failure is unlikely

< 0.010 per thousand vehicles/ items

1

Occurrence (o)Suggested Evaluation Criteria:

Occurrence table

Effect Criteria : severity of Effect Ranking

Hazardous without warning

Very high severity ranking when a potential failure mode affects safe vehicle operation and/or involves noncompliance with government regulation without warning.

10

Hazardous with warning

Very high severity ranking when a potential failure mode affects safe vehicle operation and/or involves noncompliance with government regulation with warning.

9

Very High Vehicle/ item inoperable (loss of primary function). 8

High Vehicle/ item operable but at reduced level of performance. Customer very dissatisfied.

7

Moderate Vehicle/ item operable, but Comfort/ Convenience item(s) inoperable. Customer dissatisfied.

6

Low Vehicle/ item operable, but Comfort/ convenience item(s) operable at a reduced level of performance. Customer somewhat dissatisfied.

5

Very Low Fit & Finish/ Squeak & Rattle item does not conform. Defect noticed by most customers (greater than 75%).

4

Minor Fit & Finish/ Squeak & Rattle item does not conform. Defect noticed by 50% of customers.

3

Very Minor Fit & Finish/ Squeak & rattle item does not conform. Defect noticed by discriminating customer (less than 25%).

2

None No discernible effect. 1

Severity table

Detection Criteria : Likelihood of Detection by Design Control RankingAbsolute

UncertaintyDesign control will not and/or can not detect a potential cause/ mechanism an subsequent failure mode; or there is no Design control

10

Very Remote Very remote chance the Design control will detect a potential cause/ mechanism and subsequent failure mode.

9

Remote Remote chance the Design control will detect a potential cause/ mechanism and subsequent failure mode.

8

Very Low Very low chance the Design control will detect a potential cause/ mechanism and subsequent failure mode.

7

Low Low chance the Design control will detect a potential cause/ mechanism and subsequent failure mode.

6

Moderate Moderate chance the Design control will detect a potential cause/ mechanism and subsequent failure mode.

5

Moderate High Moderate high chance the Design control will detect a potential cause/ mechanism and subsequent failure mode.

4

High High chance the Design control will detect a potential cause/ mechanism and subsequent failure mode.

3

Very High Very high chance the Design control will detect a potential cause/ mechanism and subsequent failure mode.

2

Almost Certain Design control will almost certainly detect a potential cause/ mechanism an subsequent failure mode.

1

Detection Table

Requirements & Trends

Lets discuss the functional requirements of an engine...

Functional Requirements

•Power•Torque curve•Speed range•Duty cycle•Weight/space•Reliability •Durability•Cost

•Fuel economy•Emissions•Noise•Power takeoff•Flexibility•Serviceability•Recycling•Other

Customer Requirements• Not just power and speed range• Not just rated torque but torque profile• Weight/space• Fuel economy/emissions/noise• Duty cycle/durability/reliability• Service intervals and serviceability• Cost sensitivity• Iterations on materials/cost/temperature pressure

capability and target performance• Upgrade capability• End of life considerations.

Many methodical techniques such as QFD available for use

CHALLENGES:

• Emission

• Noise

• Cost

• Durability

DRIVERS :

• High Specific Power

• High torque back-up

• Low fuel consumption

• Low fuel cost

0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000 3500

Cubic Capacity

FC (k

mpl

)

FUEL CONSUMPTION OF INDIAN DIESEL VEHICLES

Drivers & Challenges

EVOLUTION OF SPECIFIC POWER FOR DIESEL VEHICLES

State of Art – Trends in Engine Specifications

Other cutting edge design considerations – peak cylinder pressure, fuel injection pressure, piston speed, valve seating velocity, exhaust temperature limit etc.

• Analyze the engine/components/systems and summarize various functions and failure modes.

• 50 components and 10 systems to be listed and their functions and failure modes to be studied.

• 5 out 60 components/systems are picked. DFMEA to be conducted for these 5 components/systems.

•These components & systems all had failure modes and a corresponding Risk Priority Number (RPN) to be calculated using severity, occurrence & detection rankings.

•The idea is to reduce this RPN value so that the components/systems are designed more towards reliability and safety. These reductions are to be done through design changes.

• FAILURE MODES & EFFECTS ANALYSIS (FMEA) is a paper-and-pencil analysis method used in engineering to document and explore ways that a product design might fail in real-world use.

• Failure Mode & Effects Analysis is an advanced quality improvement tool.

• FMEA is a technique used to identify, prioritize and eliminate potential failures from the system, design or process before they reach the customer.

• It provides a discipline for documenting this analysis for future use and continuous process improvement.

• Historically, FMEA was one of the first systematic techniques for failure

analysis developed by the U.S. Military on 9th November, 1949. FMEA

was implemented in the 1960’s and refined in the 70’s. It was used by

reliability engineers working in the aerospace industry.

• Then the Automotive Industry Action Group formed by Chrsyler, Ford

& GM restructured the FMEA techniques which found a lot of importance

in the automotive industry.

• Since then FMEA has been instrumental in producing quality goods in

the automotive sector.

• SYSTEM FMEA

- Chassis system

- Engine system

- Transmission

• COMPONENT FMEA

- Piston

- Crankshaft

•PROCESS FMEA

- Involves machine, manufacturing process, materials

DFMEA: Starts early in process. It is complete by the time preliminary drawings are done but before any tooling is initiated.

PFMEA: Starts as soon as the basic manufacturing methods have been discussed. It is completed prior to finalizing production plans and releasing for production.

MIL-STD 1629, “Procedures for Performing a Failure Mode and Effect Analysis”

IEC 60812, “Procedures for Failure Mode and Effect Analysis (FMEA)”

BS 5760-5, “Guide to failure modes, effects and criticality analysis (FMEA and FMECA)”

SAE ARP 5580, “Recommended Failure Modes and Effects Analysis (FMEA) Practices for Non-Automobile Applications”

SAE J1739, “Potential Failure Mode and Effects Analysis in Design (Design FMEA)”

SEMATECH (1992,) “Failure Modes and Effects Analysis (FMEA): A Guide for Continuous Improvement for the Semiconductor Equipment Industry”

• They can only be used to identify single failures and not

combinations of failures

• Failures which result from multiple simultaneous faults are not

identified by this

• Unless adequately controlled and focused, the studies can be time

consuming

• They can be difficult and tedious for complex multi-layered systems

• They are not suitable for quantification of system reliability

RESPONSIBILITY AND SCOPE OF THE DFMEA

• The DFMEA is a team function– All team members must participate– Multi-disciplinary expertise and input is beneficial

• Input from all engineering fields is desirable• Representatives from all areas (not just technical

disciplines) are generally included as team members• The DFMEA is not a one meeting activity

– The DFMEA will be refined and evolve with the product– Numerous revisions are required to obtain the full benefit of

the DFMEA• The DFMEA must include all systems, sub-systems, and

components in the product design

• Form the cross functional team. • Call FMEA Meeting with advance intimation.• Complete the top of the form

– Project, year, team members, date, and DFMEA iteration– There will be many iterations

• List items and functions– Start with the system, then subsystems and finally components

• Document potential failure modes– How could the design potentially fail to meet the design intent?– Consider all types of failure

• Document the potential effects of failure– How would design potentially fail to meet the design intent?

• Rate the severity of the failure effect

– See ranking guidelines

– Severity ranking is linked to the effect of the failure

• Document potential causes and mechanisms of failure

– Failure causes and mechanisms are an indication of design weaknesses

– Potential failure modes are the consequences of the failure causes

– A single failure mode may have multiple failure mechanisms

– Use group brainstorming sessions to identify possible failure mechanisms

– Don’t be afraid to identify as many potential causes as you can

– This section of the DFMEA will help guide you in necessary design changes

– The output of the DFMEA will indicate on which item to focus design efforts

• Rate the occurrence – See attached page for ranking guidelines– Things that may help you rate the occurrence

• Are any elements of the design related to a previous device or design?• How significant are the changes from a previous design?• Is the design entirely new?

• List the design controls – Design controls are intended to:

• Prevent the cause of the failure mode (1st choice solution)• Detect the cause of the failure mode (2nd choice solution)• Detect the failure mode directly (3rd choice solution)

– Applicable design controls include• Predictive code analysis, simulation, and modeling• Tolerance “stack-up” studies• Prototype test results (acceptance tests, DOE’s, limit tests)• Proven designs, parts, and materials

• List any critical or special characteristics– Critical characteristics: Severity > 8 and Occurrence >1– Special characteristics: Severity > 6 and Occurrence >2

• Detection rate– See attached page for ranking guidelines

• Calculate the RPN of each potential failure effect– RPN = (Severity) x (Occurrence) x (Detection)– What are the highest RPN items?

• Define recommended actions – What tests and/or analysis can be used to better understand the problem to

guide necessary design changes ?

• Assign action items– Assemble team– Partition work among different team members– Assign completion dates for action items– Agree on next team meeting date

• Complete “Action Results” Section of DFMEA– Note any work not accomplished (and the justification for incomplete work)

in the “actions taken” section of the DFMEA. • Why was nothing done?

– Change ratings if action results justify adjustment, but the rules are:• Severity: May only be reduced through elimination of the failure effect• Occurrence: May only be reduced through a design change• Detection: May only be reduced through improvement and additions in

design control (i.e. a new detection method, better test methodology, better codes, etc.)

– Include test and analysis results with DFMEA to validate changes.

Example of Significant/ Critical Threshold

10987654321

1 2 3 4 5 6 7 8 9 10

SEVERITY

O C C U R R E N C E

POTENTIAL CRITICAL CHARACTERISTICS Safety/Regulatory

POTENTIALSIGNIFICANT

CHARACTERISTICSCustomer Dissatisfaction

ALL OTHER CHARACTERISTICS

Appropriate actions /controls already in place

Special Characteristics Matrix

ANOYANCEZONE

28

RPN / Risk Priority Number

Top 20% of FailureModes by RPN

RPN

Failure Modes

• Repeat: undertake the next revision of the DFMEA

The DFMEA is an evolving document!

Revise the DFMEA frequently!

Diligence will eliminate design risk!

Include documentation of your results!

30

PotentialFailure Mode and Effects Analysis

(Design FMEA)__ System__ Subsystem__ Component

Model Year/Vehicle(s):Core Team:

Design ResponsibilityKey Date:

FMEA Number:Page 1 or 1Prepared by:FMEA Date (Orig.):

Item

Function

PotentialFailureMode

PotentialEffect(s) of

Failure

Potential Cause(s)/

Mechanism(s)Of Failure

CurrentDesign

ControlsPrevention

CurrentDesign

ControlsDetection

RecommendedAction(s)

Responsibility& Target

CompletionDate

ActionsTaken

Action ResultsSEV

CLASS

OCCUR

DETEC

R.P.N.

SEV

OCC

DET

R.P.N.

Lifter Assembly•Body•Insert•Roller•Pin•Clip•wire

CAM Shaft

Pushrod•Rod•Cup•Ball

Intake Rocker AssemblyExhaust Rocker Assembly•Body•Insert•Roller•Pin•Clip

Arm Group Assembly•Intake rocker assembly•Exhaust rocker assembly•Stand(s) W & W/o oil supply•Shaft Assembly•Mounting Bolt•Spring/Spacer

Bridge

Spring Group•Inner & Outer Springs•Spring Base•Retainer/Rotator•Valve Keeper

Valve Group•Intake Valve•Exhaust Valve•Intake Seat•Exhaust Seat•Valve Guide•Valve Guide Seal

CAM Bearings

Thrust Plate

Cylinder Block

Oscillating Lifter

•Pressure Lube

OR

Bore in Block

•Pressure Lube

Lube Oil

Cylinder Head

Vibration

Valve CoverClearance

Shaft Assembly•Shaft •Cup•Pin

Valve

•Injector oil

Floating

Cylinder Head Load

Valve Stem SealClear at full stroke

Lube Oil

Cylinder Head

Cylinder Head

Seat Insert

Valve Seat

Additional Clearances

•Injector & Spring

•Injector & Spring Base

•Injector & retainer

•Injector & Bridge

•Injector & injector clamp

Compression Brake

Vibration

Cylinder Head Main Gallery

Orifice

Cylinder Block Main Gallery

Tensioner

Hydraulic Lash Adjuster

Camshaft

Rockers

Vacuum Pump

Cam Journal

2 Part Oil PAN with Filter in between

B/Pass Valve

Oil Filter

Oil Cooler

Oil Pump

Oil Strainer

R/ValveOil Jet

No.1, 2, 3Con rod BRG. 1, 2, 3

Main Bearing No. 1, 2, 3

Drive & Tensioner

Turbocharger

• CYLINDER BLOCK

• CYLINDER HEAD

• CYLINDER HEAD GASKET

• VALVES

• PISTON

• CONNECTING ROD

•CRANKSHAFT

• AIR INTAKE SYSTEM

• EXHAUST SYSTEM

• TURBOCHARGER

The crankshaft, sometimes casually abbreviated to crank, is the

part of an engine which translates reciprocating linear piston

motion into rotation. To convert the reciprocating motion into

rotation, the crankshaft has "crank throws" or "crankpins",

additional bearing surfaces whose axis is offset from that of the

crank, to which the "big ends" of the connecting rods from each

cylinder attach.

• Crankshaft literature Survey• Crankshaft functions/requirement• Crankshaft benchmarking• Visit to vendors place for understanding production process• Crankshaft concept development• Crankshaft failure modes• Design FMEA at vendor’s place• Crankshaft model• Classical strength analysis• Excite strength analysis• Factor of Safety analysis• Crankshaft draft drawing• Sending draft drawing & filled questionnaire to vendor • Preliminary Design Review with vendor • Finite Element Analysis by vendor & web optimization• Material & Heat Treatment discussions• Closing Design FMEA • Quotation & Purchase Order• Process FMEA at vendor’s place• Die making & production

• Convert reciprocating motion of piston to rotary motion• Transfer energy from engine• Requires Balancing (In case of 3 cylinder, primary & secondary couples can be balanced by Balancer shaft, Rotary couples needs to be balanced by counterweight optimization)• Defines piston Travel• Requires resistance to fatigue (Weak points at the fillet radius)• Requires resistance to alternating torsion (Oil holes are weak points)

• Should withstand forces - gas pressure, rotating and reciprocating inertia• Should withstand vibratory forces• Should damp torsional vibrations• Requires infinite life under high cycle bending• Requires friction & wear reduction at the bearings• Requires smooth grain flow through critical regions• Requires high strength to weight ratio (Stress increases by 4 times for every doubling of speed)

• High cycle bending at webs, nose & flywheel flange• Galling fillets (Similar to Adhesive wear)• Radii fracture (at pin & journal)• Scored bearing journals• Bends, warpage and cracks• Abrasive wear• Chipping•Torsional failure• Bearing failure

• Major Input Data (at Max BMEP operating point) :-

Sr. No. Parameter Value

1 Main Brg Centre Distance [mm] 100.oo

2 Section modulus of left crank web [mm3] 2008.63

3 Section modulus of Right crank web [mm3] 2008.63

4 Thickness of left and right webs [mm] 20.5

5 Eq length of left crank web [mm] 116.00

6 Eq length of right crank web [mm] 116.00

7 Crank pin / main journal fillet radius [mm] 3.5

8 Material of Crankshaft (Present ) 30CrNiMo8

9 UTS crankshaft material [N/mm2] 1250

10 Fatigue Strength of CS material [N/mm2) 510

11 Engine Speed [rpm] 2000

No.

Position Amplitude stress (N/mm2)

Mean Stress(N/mm2)

1 Left Crank pin 239.34 217.05

2 Right Crank pin 239.34 217.05

3 Left Main journal 330.20 299.44

4 Right Main journal 330.20 299.44

SAFETY FACTORS ------------------------------------------------------- CRANK PIN MAIN JOURNAL FILLET FILLET LEFT RIGHT LEFT RIGHT ------------------------------------------------------- 1.90 1.90 1.65 1.65 -------------------------------------------------------

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

1

PERMISSIBLE FOS

CRANKPIN FILLET LEFT

CRANKPIN FILLET RIGHT

JOURNAL PIN FILLET LEFT

JOURNAL PIN FILLET RIGHT

Excite Model

• BEARING ANALYSIS

• TORSIONAL ANALYSIS

EXPECTED RESULTS

SAFETY FACTOR

0

0.5

1

1.5

2

CRANK PIN MAIN JOURNAL

FEATURE

CO

MP

AR

ISO

N F

AC

TO

R

EXCITE

CLASSICAL

No. MAIN BEARING 1 MAIN BEARING 2 MAIN BEARING 3 MAIN BEARING 42000 0.0075 0.02 0.0045 0.00754200 0.004 0.004 0.0037 0.004

No. BIG END BEARING 1 BIG END BEARING 2 BIG END BEARING 32000 0.001 0.001 0.0014200 0.0014 0.0014 0.0014

No. BIG END BEARING 1 BIG END BEARING 2 BIG END BEARING 32000 0.007 0.007 0.0074200 0.002 0.002 0.002

No. MAIN BEARING 1 MAIN BEARING 2 MAIN BEARING 3 MAIN BEARING 42000 0.00225 0.002 0.00175 0.00224200 0.0024 0.00185 0.0015 0.0024

MAIN BEARING OFT UPPER SHELL

MAIN BEARING OFT LOWER SHELL (grooved)

BIG END BEARING OFT UPPER SHELL (grooved)

BIG END BEARING OFT LOWER SHELL

(in mm)

Desirable OFT ≥ 0.001 mm ( 1 micron ) for conventional bearings≥ 0.0003 mm ( 0.3 micron ) with sputter bearings

Steel backingbronze layer

3-layer-bearing

running layer (sputtered, electroplated,

sprayed)

intermediate layer

(Ni if nessesary)

The sputtering process produces a material that combines the high wear-resistance properties of an aluminum-tin sliding layer with the extremely high-load withstanding capacity of a cast copper-lead-bearing metal layer.

2000 rpm 4200 rpmORDER PULLEY PULLEY

0.5 0.063 0.0491 0.094 0.084

1.5 2 0.32 0.057 0.02

2.5 0.0635 0.0643 0.2 0.01

3.5 0.05 0.0744 0.042 0.08

4.5 0.03 0.325 0.002 0.65

5.5 0.03 0.086 0.02 0.09

6.5 0.0235 0.027 0.0215 0.013

7.5 0.03 0.0258 0.02 0.007

8.5 0.02 0.0069 0.04 0.01

9.5 0.025 0.00510 0.06 0.001

10.5 0.19 0.0611 0.019 0.002

11.5 0.01 0.00112 0.014 0.002

PULLEY END TV AMPLITUDES

0

0.5

1

1.5

2

2.5

0.5 1

1.5 2

2.5 3

3.5 4

4.5 5

5.5 6

6.5 7

7.5 8

8.5 9

9.5 10

10

.5 11

11

.5 12

ORDER

MA

GN

ITU

DE

PULLEY END AMPLITUDES @ 2000 rpm PULLEY END AMPLITUDES @ 4200 rpm

Torsional resonance is visible between 4.5 and 6th order i.e corresponding speed range of 3345 to 4460 rpm. Since this falls within operating speed range, a TV damper is MUST.

2000 rpm 4200 rpmORDER FLYWHEEL FLYWHEEL

0.5 0.0082 0.00631 0.0122 0.0108

1.5 2.4 0.52 0.0075 0.0025

2.5 0.0015 0.00793 0.35 0.02

3.5 0.0063 0.00864 0.0051 0.009

4.5 0.11 0.055 0.002 0.065

5.5 0.0035 0.00766 0.04 0.001

6.5 0.0028 0.00167 0.0025 0.001

7.5 0.015 0.0028 0.0022 0.0003

8.5 0.0024 0.00029 0.009 0.001

9.5 0.003 0.000110 0.006 0.0005

10.5 0.017 0.000311 0.0019 0.0002

11.5 0.001 0.0001512 0.0003 0.0003

FLYWHEEL END TV AMPLITUDES

00.5

11.5

2

2.53

0.5 1

1.5 2

2.5 3

3.5 4

4.5 5

5.5 6

6.5 7

7.5 8

8.5 9

9.5 10

10

.5 11

11

.5 12

ORDERM

AG

NIT

UD

E

2000 rpm 4200 rpm

The three main potential failure modes are:

• Crankshaft fracture

• High noise & vibration

• Bearing wear & failure

As we know, the crankshaft is a component which takes a lot of stresses and vibrations. The entire gas force is transferred to the crankshaft. So when failure modes such as fracture occur, the engine stalls and this is a potential effect of failure. Other observations made are those caused due to vibrations. There can be loosening of fasteners, extreme vibrations throughout the vehicle and lower the life of engine mounts.

• Micro alloyed steel is the material that will be used to develop

the crankshaft. Stress risers generate from the sharp edges and

therefore fillets are crucial in a crankshaft design. The fillet

radius is an important parameter and here the CAE analysis is

carried out with different fillet radii and the final radius is

calculated. • Noise and vibration is optimized by modal testing where the

component is checked for resonance between the operating

engine RPM. • Surface treatment is vital too.

• Induction hardening is done on the crankshaft to improve the

ultimate tensile strength and fatigue bending strength.

For design of high performance engines, quality tools like DFMEA plays

an important role to achieve desirable performance and durability

requirements. If this is done right from concept stage, the risk of failures

substantially reduces and lot of time, energy and cost is saved.

The DFMEA sheets are customized and prepared for this project. However,

as a special case, DFMEA of Crankshaft shows those columns also with an

aim to show how these actions are closed and how the RPN reduces. For

example, the RPN after the actions are closed, have reduced from the range

of 20 - 175 to 20 – 70.

The DFMEA sheets become the input to the designers to model components

with reduced failure potential. It is this final design that is sent to the

vendors for development.

• “Potential Failure Mode & Effects Analysis (FMEA)” – Reference Manual, Chrysler, Ford & G.M, Issued, First Edition February 1993

• D.H. Stamatis, “Failure Modes and Effects Analysis”, Productive Press, 1997

• SAE Standard ‘SAEJ1739’ – Failure Modes & Effects Analysis

• www.wikipedia.com (http://en.wikipedia.org/wiki/DFMEA)

• Kevin Hoag, “Vehicular Engine Design”, Springer Wien New York, 2006

• Richard Basshuysen, Internal Combustion Engine – Handbook, SAE International

• Hiroshi Yamagata, The Science and Technology of materials in automotive engines, Woodhead Publishing Limited

THANK YOU