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: ulrich.hussels@risa.de

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 )

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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

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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

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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

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Further Activities

n Further activities should be done to gaininternational acceptance