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FMEA of CO2 Air ConditioningSystems
On SAE 2000 Automotive Alternative Refrigerant Systems SymposiumJuly 11-13, 2000, Resort Suites Hotel, Scottsdale, AZ
by Dr.-Ing. Ulrich HusselsRISA Sicherheitsanalysen GmbH, Germanye-mail: [email protected]
SAE 2000 Automotive Alternative Refrigerant Systems Symposium, July 11, 2000 2
The RISA Companyn Founded in 1990, situated in Berlin,
Germanyn 10 specialized engineers from research
institutes of the Technical University ofBerlin
n Working areas are safety analysis andsoftware development (databases)
n Customers from nuclear-, automotive-and LPG-industry
SAE 2000 Automotive Alternative Refrigerant Systems Symposium, July 11, 2000 3
Where this kind of Analysis is needed (examples):n Higher amount of energy in a small
amount of space (high energy density)n Nuclear Power Plants: reactor core
cooling, pressuren Automotive: velocity, pressuren LPG: great amount of inflammable and
explosive fluid/gas mixture
SAE 2000 Automotive Alternative Refrigerant Systems Symposium, July 11, 2000 4
Initiators and Core Teammembers
n Robert Mager, BMW AG (Chairman)n Jürgen Wertenbach, DaimlerChrysler AGn Baroto Adiprasito, Volkswagen AGn Ralf Köneke, Denso Automotive Deutschlandn Frank Obrist, Obrist Engineering
OBRIST__ENGINEERING__
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Aims of the analysis for aprototypical CO2 AC-Systemn Diagnosis of potential effects of failure eventsn Determination of countermeasuresn Proof of mastering all relevant effectsn Confirmation of the usability of CO2-
technology regarding to safety and productliability
n System-FMEA as a basis for a design-FMEA
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Form of the Analysis
n System-FMEA based on SAE J-1739n Additional classification for
consequences to human healthn Instructions to reduce the risk priority
number if it is greater than 108 to get abalanced risk level over all failureevents
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Risk Priority Number
RPN = Severity x Occurrence x Detection
Severity 1 - 10 (8 = Very High, 9 Hazardouswith warning)
Occurrence 1 - 10 (4 - 6 = Moderate)
Detection 1 - 10 (3 = High)
⇒ RPN 1 - 1000 (9 x 4 x 3 = 108, accordingto an engineering judgement )
SAE 2000 Automotive Alternative Refrigerant Systems Symposium, July 11, 2000 8
Table-Layout
Item Function
Potential
Failure
Mode
Potential
Effect(s) of
Failure
Sev
Cla
ss
Potential Cause(s)/
Mechanism(s) of
Failure
Occ
ur Current Design
Controls Det
ec
RP
N Recommended
Action(s)
Responsibility
(for the Rec-
ommended
Action)
Actions
Taken Sev
Occ
Det
RP
N
Com-
pressor
Transports
the medium;
Compresses
the medium
Loosening
of fasten-
ings
Refrigerant
pipe de-
taches, ex-
ternal leaks
9 B Material faults,
loosening of fas-
tenings
1 Quality control 2 18 Oscillation
tests
9 1 1 9
Gas
cooler
Conducts
heat to the
external
environment
Blockage
in refriger-
ant flow
Low cooling
capacity,
increase in
pressure
6 A Bends, blockages 2 Deformation
guard, layout;
design of com-
ponent
10 120 Parallel proce-
dures, pres-
sure sensor
switched in
front of the gas
cooler, plausi-
bility control
via regulation
control
6 2 6 72
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Scope of the Analysis
n 23 components within the system withn 107 failure events
in respect ton 3 operating modes,n 3 (+2) vehicle running modes andn 3 environment conditions
SAE 2000 Automotive Alternative Refrigerant Systems Symposium, July 11, 2000 10
PI-Diagram
hose linepiping
gas
cool
er
accumulator
expansion valve with safety system
evap
orat
or
internal heatexchanger
T
temperature sensor 1
filling socket
p
pressure sensor
savety valve HP
compressor with safety system and
auxiliary unit
savety valve LP
filling socket
HP high pressureLP low pressure
SAE 2000 Automotive Alternative Refrigerant Systems Symposium, July 11, 2000 11
Results
n An automotive CO2 AC-system is safe:n General rules for the arrangement of the
components have to be taken intoaccount
n Safety components and/or systemshave to be present
n Critical components are detected
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Outlook
n Development of common safety-standards for an automotive CO2 AC-system
n Systematic sampling of all failure eventsfrom existing prototype-systems
n Evaluation of specific failure rates duringthe operation of prototype system hours
n Performing a fault- and event treeanalysis