880563

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E

h

ngineeringSociety

or dvancing Mobility

andSea ir and Space 400 COMMONWEALTH DRIVE WARRENDALE PA 15096

ap

e h n i ~

m

r rl S

88 56

Improvement of Turbocharger l i fe for

Diesel and Gasoline Engines

Takaaki Koike Takashi Kobayashi

and

Kideaki Matsuoka

Ishikawajima Harima

Heavy Industries Co.

l td

Fusayoshi Nakamura

Warner Ish Corp.

International Congress and

Exposition

Detroit Michigan

February 29March

988

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ISSN0148 7191

Copyright

1988 Society of Automotive Engineers,lnc.

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Printed in U S A


8/10/2019 880563

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880563

Improvement of Turbocharger l ife

fo

Diesel and Gasoline Engines

Takaaki Koike Takashi Kobayashi and Kideaki Matsuok

lshikawajima Harima

Heavy Industries Co Lt

Fusayoshi Nakamur

Warner lshi Cor

ABSTRACT

Turbochargers

fo r vehicle use have b een

uti l ized for

passenger

cars and trucks to

a ch ie ve h ig h pOtver, high

torque to fuel

consumption

and

as a

countermeasure

for lotv

emission

of

CO,

He,

NO

etc

x

Turbochargers ar e e xp ec te d to

pl y

major role in future to improve t he per fo rm -

ance of automobiles.

Horeover l i f e o f t ur bo ch ar ge rs ha s been

increased

steadily

in

spite

of

severe

heat

and

stress condition

due t o r equi rement from

engine manufactures.

In case of truck use turbochargers great

ef for ts ha ve be en made to

increase

turbocharger

l i fe

from 500 000 kms to 1 000 000

kms

though

the

stress of

the

wheels ha s been raised due to

increased

boost pressure.

Also

l i fe of

pas-

senger car us e

turbocharger ha s been increased

in

spite

of higher exhaust

ga s temperature.

This

paper

describes ou r e xp er ie nc e o f

durabil i ty problems and ou r solut ion.

SPECIFICATION AND

DESIGN

CONSTRUCTION OF

IHI TURBOCHARGERS

Fig. 1 shows general view of the

typical

model ou r turbochargers used

for passenger

car .

This

is IHl RHB52 model turbocharger applied to

passenger

cars

of 1.5

L -

2.0

L

class

which

is

most

popula r passenger

cars

in Ja pan . The

turbine wheel

diameter of

this

model is approx.

50

mm.

Table 1 shows other models of IHI turbo-

chargers.

Fig. 2 is the

sect ional view

of

RHB52

turbocharger.

This

is th e typical basic construction of

th e vehicle use

turbocharger.

The turbocharger

is normally installed on an engine by a

gas

inle

flange of a turbine

housing.

Oi l cooling

chamber or

water

cooling chambe

is designed in the bearing

housing

in case

of

high

exhaust gas

t emperature usage.

Table 1

Specification of lH I

Turbocharger

Application

Turbocharger

Turbine

wheel

Compressor

Hax. allowable Hax.

allowable

Hodel

dia. mm

impeller

dia.

speed

rpm

gas

temp.

OC

mm

Nicro

passenger car

RHB3

35.5 35.5

250 000

950

RHB4 46.0

46.0

200 000

950

Passenger

car

RHB5

52.5 52.5

180 000 950

RHC6

62.0 65.0

140 000 750

or

950

Truck

RHC7

74.0 76.0

132 000

750

RHC9

90.0

90.0

9

ODD 750

0148 7191/88/0229 0563 02.50

Copyright1988 Society

of

Automotive Engineers lnc


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2 880

Fig. 1

General

view

of RHBS

The follmving problems

are

major ones

ol

have experienced to correspond to th e

require

ment fo r high performance and long

l i fe

Problems re la t ing to passenger

car

use

turbochargers;

a

Capability dotm

of

journal bearing y

coking

problem

b Capability dO\VTI of seal at th e

turbine

side

c

Stabi l i ty

dotvn of th e

bearing

system by

severe

running

condition and also poor

lubricat ing condition

Problems relating to truck

use

turbo

chargers;

OIL COOLING

W TER OOLING

a

Creep s trength

and

low cycle

fatigue

strength by increased stress of a

compressor impeller

b

Oxidation and

crack

of a turbine housin

by h ig h ex ha us t

ga s

temperature and

increased

heat

load

f luctuat ion,

especial ly

center wall

of

t he twin- fl ow

scrol l

IHPROVEHENT

OF THE TURBOCH RGERS

The

major problems

mentioned

above

have

been resolved

and

turbochargers improvement is

explained

belOtv

Fig. 2 Cross section of RHB

Fig. 3 shows typical problems

of

vehicle

use turbochargers.

~ n

users claim

Large all consumption

White smoke

Abnormal noise

Poor acceleration

Power down

Rough running

After burning

I

r

in turboch rger trouble

Oil leakage (Turbine

Camp.)

Bearing damage

Housing rub

Blade damage

Carbon bridge

Air or exhaust gas leakage

Bol t loose or drop

Housing cr ck

Failure of waslegale

IHPROVE}ffiNT

OF JOURN L BE RING N BE RING

SYSTEH

Ful l - f loa t ing

journal bearings

are

used in most of modern turbochargers due to

bet ter

dumping

charac ter is t ics

against

se l f -

exci ti ng v ibra t ion and cr i t ica l speed as

well

as bet ter stabi l i ty a t

high

speed

range.

Stabi l i ty

of

th e bearing

sys tem has

becom

more important

year

by

year because of

increas

of running

speed

of turbocharge rs at th e opera

tion range

and

also poor

lubricat ing condition

such

as

low o il pressure or

high

temperature o

lubricating oi l

Also,

there will occur such problems as

bearing

fa i lure

or

noisy

turbochargers.

In

order to p revent th es e p robl ems, d imension o f

th e bearing i t se l f bearing clearance, bearing

form, bearing span,

dimension

of shaft

diamete

and bal an ci ng o f a turbine

rotor

assembly have

been

improved.

The following items are

important.

Fig.

3 Typical problems

a J

Selecting th e

b est s ha ft

diameter

and

journal bearing

span

in order no t to

include harmful cr i t ica l

speed

in th e

operating range

b

Decision of

th e

best

dimension

of journ

bearings

t o p revent

self

exciting vibra

tion


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880563

Copper

Sulfur

Fig.

6 Bearing damaged by coking

Close

examination

by electron microsco

and E .D.X. i ndica te s a t tack to the

bearing

surface by sulfur

which

seems to

be

include

in

lubricating

oi l Fig.

7 shmvs sulfur

attack to th e bearing surface.

Fig.

7 Sulfur

attack to the bearing

surface

Sn by

melting

away due to their low melting

point . Of course

this

means reduction of

bear

ing

l i fe As

to Cu Pb Sn

alloy

\vhich is

also

very

popular as bearing material , there is a

possib i l i ty of

the

bearing coking problem. That

is : shortening

of

bearing l i fe becaus e o f grow-

ing

of black

layer

on

th e

bearing surface and

fla kin g o ff of this portion.

The

surface

of the

bearing

damaged by

coking

becomes completely

corroded

and i ts color

changes

to

black as shown in Fig. 6. Part

of

the

bea ring sur fa ce

is damaged by

scratched

and

flaked off .

1I4N,

1 2N

1I2Nl

i N

o ld d es ig n

- N

o

IOO

3kg/cm

Convenllonill

L ub o il lulnP

Lub.

oil

press

Improvement

Lub

lemp

IOQe

Lub oil pless

3kg/cm:

f ~ ~ )

/

e

x

g

g

g

Fig. 4 Shaft end vibration of

Fig. 4 and Fig. 5 shoH

comparison

of shaft

end vibration of

new design

and o ld d es ign

turbochargers. An

improved

design

turbocharger

shows bet ter st bi l i ty t the to ta l operating

range.

(c )

Reduction

of

r emaining unbalance so

as

to

l imit amplitude

of

shaft

vibrat ion

~ c b 1 S

8

N, Turbochmger speed X10 ,pm)

~ : : : : Q : : : : : : : : : : = -

D : : : C : : ~ \ lISN,

t )

o c---..........----- , - - ~ -

5 1 15 18

N, TUlboctl lIgl. f speed (XIO rpml

Fig. 5

Shaft

end vibration of new design

IHPROVEHENT

FOR

HEAT

DANAGE

Coking

of

journal bearing Generally vehicle

use

engines are

frequently

stopped.

Sometimes

they

ar e stopped

suddenly from high

engine

load.

The temperature around

th e

t ur bi ne s id e journal

bearing

increases to the ver y h igh

level

because

there

is

no

cooling func tion fo r

th e

turbine

side bearing

by

engine

lubricating

o il

when

an

engine

stops.

Host o f turbucharge rs use Cu Pb Sn al loy or

AI-Sn a llo y fo r their bearings, so that bearing

failure

of the

t ur bi ne s id e journal bearing

is

ap t

to

happen due

to this

high tempera ture which

is

normally

called

heat soak back . The peak

temperature

during

heat soak back exceeds 2 DoC

Under

such

a

high tempera ture

AI-Sn alloy,

which

usually

used fo r

the

journal

bearing,

looses


8/10/2019 880563

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4

88

o

o

20

Soak

time; 10 HRS

Mela ; PBS

1.5.0

Sulfur content Oio

05

100

1

50

E

3

m

20

u

:

10

j

I

1

u

rn

0

Cu?S is created because copper is diffused

to the

5earing sur face

due to sulfur ion. This

black

color

layer

is so-called coking layer .

t became clear by oil soaking test using

var ious

kinds

of

lubr icat ing o i l t i th a

combina

tion of the bearing mat er ia l t ha t

there

ar e

several inf luent ia l

factors such

as lubricat ing

oil temperature,

sulfur

content of

lubricating

oil and

copper

content

of

bearing

material .

Typical

resul ts of oil soaking test ar e shotvn

in

Fig.

8. The black layer becomes thicker as

the

temperature goes higher.

Flaking

of

th e

bearing surface star ts

over

300

o

e. t is

recognized that there is

difference

in

the

level of

su lf u r a tt ac k

according to th e bearing

rna rer ia 1.

Oil-soaking test

Fig.

8 o il soaking test

200

Fig. 10 Influence of

sulfur

content

Carbon bridge Lubricating oil becomes

carbonized

and

accumulated

around

piston

ring

seal and oil drain

passage

at

the

t ur bi ne s id e

due

to high

temperature by heat soak

back,

whi

is explained before. We

cal l

such a phenomeno

as carbon

bridge.

This c arbon

bridge

is

mainly affected by

th e following

three factors.

Judging

from

th e

test

explained above,

IH

selected

the

material

which

belongs

t o c oppe r

zinc alloy as a bearing

material

since i t ha s

very

good

bearing characteristics

and ant i

corrosion character is t ics . We

apply

this

material

to ou r

small

model turbochargers for

passenger car us e after

th e

various tests done

at ou r company_

400

00

Oil

~ / S F \ O W 3 0

Test pieces

cj

Oil

temp.

re}

I

Soak

time: 10

HAS

100

100

E

3

m

u

50

:

}

u

r

The influence of

copper

content of th e

bearing

material on

coking

is shown in Fig. 9.

Large r coppe r

content

is disadvantageous as

a bearing

material . Fig.

10 shows

influence of

sulfur

content of

lubricating

oil

on

coking.

t

is nec es sa ry t o choose low

sulfur

content

oil

a

b)

Operat ing temperature around a turbine

side

seal and a turbine shaft at

th e

turbine

side

under

working condition

Naximum

temperature and tota l

time

of

the heat

soak

back

Fig. 9 Influence of copper content

c) Additives and

deterioration

of lubr i

cat ing o il

These factors

play an important

role

to

shorten

turbocharger l i fe

Carbon

bridge

caus

oil leakage

to

a turbine

housing

by sacrif icin

smooth

return

of

lubricating

oil

to th e

oil

drain

tank of

an

engine.

The following countermeasure

is

effective

Worsllcvcl

0

o c

00

i

0

-/:,._____ -

----/Y-

eo

d ; . ~ /

_x

:

I

60

0

,

,

/

,

,

g

,

O ~ 0 /

40

,

OUsonklng tost

, ,

/

0

,

,

/

x-

0

x --

60

60 90

Copper conlent

of

bcaring malCl;al { l

100

a

b)

To reduce

th e

maximum

temperature

around

seal at

th e

curbine

side

To reduce the tota l heat soak

back

time

This

means to

increase

cooling rate

of

heat soak

back

c) To

increase

th e space

around piston

seal rin g

and

oil

f linger


8/10/2019 880563

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880563

d)

To

use

bet ter

qual i ty oil

and

timely

exchange of lubricat ing

oil so that

original

characteristics of the oil

may be maintained.

The

similar

resul ts were obtained

at

th e

engine

durabil i ty

test and

correlat ion with

the

panel

coking tes t was proved. The resu l ts are

shotoJU

in

Fig. 12 .

The

bearing

housi ng has

been improved

to

overcome such unsui table condi t ions as increase

of th e

temperature

around

a tu rb in e s id e sea l ,

increase

o f th e temperature

of

lubricating

oi l ,

dec re as e o f cooling rate of t he turbocharge r

caused by

ins ta l l ing

a

protection

cover

for

engine

parts , and deterioration of

lubricating

oil due to improper oil

maintenance.

A

water -cooled bear ing

housing by cooling

water of an eng in e h as become most popular for

passenger car

engines a t

present though i t is

ol d

technology

originally developed for marine

use turbochargers.

The space

around

o il

fl inger

of the

turbine shaft

i s occupied by carbon a t the

re la t ively high

rate

with standard

oil-cooled

bearing housing , and i t s

rate

will

change

depending

on brands of

lubricating oil .

So

we

establish

th e

method

of

panel

coking

tes t

to

simulate

process of carbon bridge. Fig. 11

shm.,s

one

example of

t es t r es ul ts .

I t t.,as

found by this

tes t

that rate of carbon accumu

la t ion

is

affected

by th e

brand

of

lubricating

o i l

and

the

difference between new oil and used

oi 1.

at e rcooling type

300

e:

I

E

2

Go-stop

test

Go-slOp cycles

Fig. 12 Results of lICo-Stop

tes t

1 0 0 1 - = = F = ~ - + - : = : : j : : : : : : : : : : ~ +

On

the other

hand temperature measurement

tes t

was

conducted

to know

t he t empera tu re

of

the area

where

carbon

bridge

occurs.

The

tes t

resul ts on th e turbocharger

tes t

bench is shown

in Fig. 13 . Fig. 14 shows test resul ts on the

test vehicle.

The

temperature

at

each position

has

been reduced by design modification and

water cooling.

3; \ I

~ I i l l o

0 2.1/

]10 ~ .

~

==--

I

O il

UI t:::I::f

\.1

~

-j:\C---..' ~

J ~ Q ~ :

Original type

Oil cooling type

4001---+--- , , -+- Turbine inlet gas temp. 70CTC

LO. Inlet lemp. lQO C

LO. Pressule:

2kg/cm

gage

N

Mall. speed

1100 cycle

B

I cycle

A

Smin

,

: : 13S0 CI :

,

A h

:

~

~

i

, : :

O-K

Oil flow

Tempemlule

of lesl piece

c

Healer

B

Oil lemp. 140 C

c-

'0

6

03

c-

03

n

,

:

0

I

I

;

1=

8/10/2019 880563

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6

880

Oil cooling bearing housing Water cooling bearing housing

2

1

I

I

~

I

Go

, SlOP

Time

I

Fig. 16

Mileage

(x10 km)

Improvement of

wear

of

turbine

side

piston

ring seal

for

truck

use turbocharger

Fig. 14 Results on

th e

test vehicle

oLso _--:,X;00C---;; o--;,eor::--c5 O---;; 00C--- Co--;, eoC-

Seal - Seal

of

a

turbocharger at th e

both

sides

of turbine

and

compressor

is very

important.

Such

seal

bi l i ty

is required that can

withstand

high vacuum t th e compressor side and

also

severe hea t inf luence t th e

turbine

side

because deterioration of lubricat ion is accel

erated

by

blow-by

gas.

Smoke

level

becomes

worse by generating

white smoke

caused by o i l

leakage from th e bearing housing a t th e turbine

side.

According ly the l i fe of a turbocharger

will

be reduced.

Fig.

15

shows new

de sig n o f

seals a t th e

both

sides of turbine and

com

pressor. Fig.

16 shows

how

much

seal capabili ty

ha s

been

increased by

th e improvement of tem

perature distr ibut ion

around

a t ur bi ne s id e

seal.

Oxidation

and crack of

a

turbine housing

Oxidation

and

crack

of

a

turbine

housing

are

influenced by th e

exhaust

ga s temperature

h ea t cy cle and housing

shape

such

as

twin-flow

passage

type or

with

integrated

wastegate

valve

The

turbine

housing of

this

turbocharger is

spiral

form

so

i t s shape

is more

uneven

than

other

parts .

Besides

a

turbocharger is in

st l led

on an engine by th e

ga s

in let

flange

of a turbine housing so

that i t

is

used

under

th e severe stress condi ti on . E sp ec ia ll y

i t

is

severe in case of

truck

use turbochargers

because

most of

th e

turbine

housings

ar e

so

called

I t T ~ J i n f l o w

type

which

has

two

gas flow

passages

divided meridionally. This type turb

housing

is bet ter to

ut i l ize pulse

energy of

exhaust ga s

from an engine but

i t must

have a

center

wall to separate two

gas passages.

Thi

center wall

is

often

cracked

because i t is

heated cyclicly

from both

sides of the

wall wh

exhaust gases pass t hr ough the passages.

Besides i t is

dif f icul t

to absorb deformation o

th e

center

wall when operating temperature

changes

by engine load. The

center

wall i s

apt

to

be

cracked by th e

heat stress caused

by this

temperature

f luctuat ion and

unevenness

of the

housing.

Shape

of the

housing

and materia l of the

housing

therefore have

been improved.

One example of s t ress analysis of the tw in

flow turbine housing by F.E.M. is shown in Fig.

17 .

Also

Fig. 18 shows th e test

resul t

of the

improved turbine housing against crack

around

th e

tongue

of the housing by heat cyc le dur a

bi l i ty test

Ipeaksoak lemp after st

Vechicla speed

jkm/Hl

~ r l 5 a n l Sptlcd r u n ; ~ I

V\lchicle speed

kmlH

ooling chamber ~ = : : _ : : = : :

Fig.

15 New design of seal


8/10/2019 880563

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880563

1-

f

m

~

r }

, 750 .

Lo JlJ

8 _

Time_

C

8/10/2019 880563

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8

HIPROVENENT

OF STRENGTH OF ROTATING PARTS

The

major problem of

th e r o ta ti ng pa rt s

increasing l i fe and rotating

speed

is r e k d o ~ v n

of a

turbine

Hheel and a

compressor

,heel

fatigue.

Espec ia ll y for the

relat ively large

size

turbochargers used on truck use diesel

engines, th e

request

for h ighe r p re ssure

rat io ,

, ,, id er f loH range and l a rger flm

amount

ivith

small

size

is

very

s trong,

so

that

a

compressor

heel \Vith large back lvard angle and

rake

angle

ha s a tendency to be used more.

Both of blade

s t ress

and disk st ress

therefore) ha s

gradually

become higher and th e

evaluation

of

low cycle fatigue strength, high

cycle

fatigue strength and creep strength

becomes more important .

One

example

of

th e

compressor-wheel damage

by low cycle

fat igue

te s t i s shown

in

Fig.

21 .

Fig.

22 shows th e

comparison of

th e s t ress

analysis of

a new

design compressor wheel

and

o ld d es ign

one.

The

wheel shape

ha s

been

improved

to reach the t a rget of th e l i fe by

control l ing

th e s t ress

dis t r ibut ion.

BETTER

DURABILITY

N RELIABILITY

He

establ ished

ou r quali ty and durabili ty

targets

for

our

products depending on usage of

turbochargers such

as

diesel engine use or

gasoline

engine

use. These quali ty

and dura

bi l i ty targets

a re eva lu at ed by

turbocharger

880

Fig. 21 Low cycle

fat igue

fa i lure

Convenlional

Fig. 22 Compressor impeller stress analysis

Table

2

Reliabil i ty

Eva luat ion o f Turbocharger

Evaluation purpose

Failure

mode

Eva Iua t

ion

test

1 n i t ia l

failure

Short

l i fe of

bearing

Non lubricat ing

o il tes t

Oil leakage

Foreign p ar ti cl e t es t

Bo lt lo ose

or drop

Oil seal

tes t

Abnormal noise Lot

temp. tes t

Vibra t

ion

test

2 Hear

out

failure Bearing ear Continuous

running

tes t

Seal

wear

Go-stop

tes t

Hastegate ear Speed

f luctuat ion test

V.G. S. parts

wear

Oi l

p re ss . lim it

test

Parts wearing

tes t

3

Fatigue

fa i lure

T C

hee1

fa i lure Heat

cycle tes t

Housing

crack High

cycle

fatigue

tes t

Hastegate

diaphragm

fai lure

Low cycle

fatigue

test

Stroke

tes t

4

Creep fa i lure T C wheel damage Continuous

running

tes t

Seal ring

fa i lure

Go-stop test

t.Jastegate valve

fai lure

Hastegate

s t u ~ r

fa i lure

5 Deteriorat ion

fa i lure Dirty

compressor

Go-stop test

Dirty

turbine

Corrosion

tes t

Carbon bridge

Oxidation tes t

Oil passage

clog

Continuous

running

tes t

Oxidation

of housing Oi l

seal

tes t

t.Jastegate

valve

oxidation

V.G.S.

parts oxidation


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880563

NONENCLATURE

REFERENCES

CONCLUSION

The vehicle

use

turbocharger must

have

adequate

durabil i ty

under the

severe

condition

of

abuse by drivers

with wide

operating

range.

In

addit ion,

the

Same

l i fe as a vehicle is

expected

as

well

as

t he r ea sonabl e price

as

automobile par ts . As mentioned above,

i t

conta in s several

diff icul t

problems

to

be

solved.

However,

we have

achieved

ou r target by

improving

t he turbocharge r to meet many various

customer's

requests.

Though we have explained some of ou r

experience for improvement of our standard

turbochargers, we would

like

to pursue ou r

development

work to obtain even higher re l ia-

bil i ty

as

well

as

development

of new high tech

nology

turbochargers

such

as

variable

geometry

turbine

scrol l ceramic turbocharger and bal l

bearing

turbochargers.

1

Hinoru Kurasat Ja Takashi Kobayashi and

etc : RHB3 Turbocharger for Small Passenger

Cars,

IHI

Engineering

Review

Vol.

16 No.1 1983

(2) Nasami Shimizu: Automotive Turbo

charger,

IHI Engineering Review Vol. 18 No.2

1985

(3)

Kazuya

Niyashita:

Thermal

Problems

of

Internal Combustion Engine, The 586th Inst i tute

of

JSNE 1984

(4 )

Nasaki KitagaHa,

etc : Fatigue

Life

Eva luat ion o f

t he Turbocharger

Components,

Internat ional Conference and Exposition of ASH

1985

Tc Temperature

of constant

speed

Tp

Peak

temperature

of heat soak

back

L Crack length

N Crit ical cycle

n Harking cycle

Nt Turbocharger

speed

N ; Cri tica l cyc le

n ; Working cyc le

High way mode

Slope mode

City mode

Damage line

N

n

QUALITY

TEST

Vehicle use turbochargers

are

different

from other

rotating machineries in

th e

points

of

mV cost

and mass p roduc ti on Hith

many kinds. Besides, we cannot

expect

adequate

technical

knmvledge

to

users

of

turbochargers,

so that

maintenance

is no t ahlays

good though

turbochargers are used everyday.

Therefore,

examination

of

design

quality

of main portion

l ike bearing,

seal and

mechan

ica l strength is accomplished to keep qual i ty

of

turbochargers by using maximum and minimum-

l imit par ts

are

making

effor ts to improve rel iabi l -

i ty by conducting

evaluation

tes t simulating

user ' s

severe

condition and

also

by maintaining

q ua lity in

production.

sale

running tes ts

which simulate actual

running

pat tern of a vehicle,

engine

bench

tes ts

and also vehicle tests

Durability and rel iabi l i ty of each

element

of the vehicle use turbocharger

are

evaluated

from th e various stand points by

the simulation

tes ts against

each fai lure

mode as

ho\o

table

2.

DURABILITY TEST

Several examples

ofevaluation

tests are

shmm in the

former sect ion.

As

explained before.

f luctuat ion of heat

load

and

rotating speed

is very often and i t

affects

oxidation of

high temperature portion.

dete

r iora t ion ,

\ Jear and strength of

r ot at ing pa rt s.

So. the

durabil i ty

of a turbocharger is evalu

ated on th e basis of Niner 's

theory

estab

l ishing

cyclic

random load simulating running

pat tern of vehicles.

Fig.

23 shows one example

of tes t condi ti on for low

cycle fatigue tes t

of

a

compressor wheel

and

carbon bridge.

E

1-+-1- -'----.......

i

f--I--+---- -- -,

t

E I

Cycles

Tor

High

T

or

a

Low

Note:

T

2

depends on temperature drop rate

for carbon bridge test

Fig. 23 Test

condition for

fatigue

and carbon bridge


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