770295
`
`Development of the Volvo
`
`Lambda-Sand System
`
`Grunde T. Engh and Stephen Wallman
`AB Volvo,Car Div.
`
`DEVELOPMENT OF THE VOLVO LAMBDA-SOND EMISSION
`SYSTEM
`
`During the last two decades there has been
`a continuous search for engine control systems
`to meet proposed exhaust emission standards in
`a cost effective way. Although several promising
`systems have been demonstrated with the ability
`to meet
`low exhaust emission requirements, most
`have been judged impractical due to fuel economy,
`cost and driveability considerations.
`One system that simultaneously exhibits
`excellent exhaust emission control and fuel eco-
`nomy perfonnance is the Volvo Lambda-send
`system. The system utilizes a "three-way” cata-
`lytic converter, and an additional closed loop
`to the fuel
`injection system to provide feed-
`back control of the inlet air/fuel ratio.
`
`DESCRIPTION OF PRODUCTION SYSTEM
`
`Volvo has developed a three-way emission
`control system for its 2.1 litre 4 cylinder
`engine to meet the l977 California exhaust emis-
`sion requirements.
`In addition to excellent
`exhaust emission characteristics,
`the system
`has demonstrated good fuel economy and drive-
`ability compared with alternative control
`systems.
`
`The Volvo application utilizes a feed-back
`control
`loop added to the normal CI
`(continuous
`injection) fuel
`injection system, and a "three—
`way" catalyst, as shown schematically in figure
`l. Figure 2 shows the positions of major compo-
`nents in relation to the engine.
`
`An oxygen sensor, situated at the exhaust
`manifold outlet, can detect the momentary oxy-
`gen level
`in the exhaust gas, which is an in-
`dication of whether the inlet A/F ratio is
`leaner or richer than stoichiometric (A: l).
`The sensor transmits a continuous non-linear
`electrical signal
`to the electronic control
`module which converts it into a control signal
`for the continuously oscillating on/off fre-
`quency valve. When the on/off bias time is
`altered the frequency valve raises or lowers
`the differential pressure over the metering
`slots in the fuel distributor, providing accu-
`rate and continuous control of the quantity of
`fuel
`injected.
`
`The resulting accuracy and speed of re-
`sponse in mixture preparation, even under
`transient conditions (as in traffic driving),
`ensures that the exhaust gas fed to the cata-
`lyst is always within the very narrow compo-
`sition band which enables the catalyst to ope-
`rate in the “three-way" manner,
`thus achieving
`
`
`
`ABSTRACT
`
`Volvo has developed the first production
`emission control system to fully utilize a
`three-way catalyst. Called the “Volvo Lambda-
`sond system", it is applied to the 4-cylinder
`in-line BZl engine, and employs three essential
`new components - an exhaust gas composition
`sensor, an additional feed-back loop to the con-
`tinuous fuel
`injection system, and the catalyst.
`
`Outstanding certification results were achieved,
`especially for NOX, combined with good drive-
`ability, power output, and fuel economy. The
`development and performance of the system, and
`the test procedures used, are described in de-
`tail, and its future potential and limitations
`are discussed.
`
`1393
`0096-7 36X/7 8/8602-1 393302.50
`Copyright © 1978 Society of Automotive Engineers, Inc.
`
`1of16
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`FORD 1880
`
`1 of 16
`
`FORD 1880
`
`

`

`
`
`1394
`
`
`
`
`G. T. ENGH AND S. WALLMAN
`
`
`
`VOL V0 L AMBDA -$OND SYSTEM
`
`ELECTRON/C
`CONTROL
`
`MODULE
`
`
`
`
`
`
`
`
`
`SENSOR
`
`" A ASOND"
`
`
`CLEAN ‘
`
`THREE»WAY
`
`CATALYST
`EXHAUST
`
`
`
`
`Fig.
`
`l
`
`— Volvo Lambda—sond system
`
`LAMBDA-SOND SYSTEM,
`
`VEH/CLE INSTALLAT/ON
`FOS. VAC
`.\.){. \/
`
`
`
`
`
`ENG/NE FAMILY LCL
`
`.7. A-sozvo
`L
`FREOUENCY VALVE
`5. cowmm mm
`
`
`
`2 - Lambda-sond system. Vehicle
`Fig.
`installation
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`three major pollu-
`simultaneous control of all
`three pollutants is achieved within a
`of all
`
`
`
`
`
`
`
`
`
`
`
`tants HC, C0, and NOx.
`very narrow A/F ratio band around the stoichio-
`metric condition.
`
`
`
`
`
`
`
`
`
`
`
`The goal of this paper is to discuss the
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`injection
`Present carburetors and fuel
`development process and the design restraints
`
`
`
`
`
`
`
`
`
`in the application of this three-way emission
`systems fall short of the required A/F ratio
`
`
`
`
`
`
`
`control system.
`accuracy. To achieve the necessary accuracy and
`
`
`
`
`
`
`speed of response in mixture preparation under
`SYSTEM APPROACH
`
`
`
`
`
`
`
`
`continuous transient engine operating condi-
`
`
`
`
`
`
`
`
`
`
`
`
`tions Volvo found it necessary to enhance the
`
`
`
`
`
`
`
`
`
`
`
`
`During the development of catalytic con-
`performance of the CI fuel
`injection system by
`
`
`
`
`
`
`verters for exhaust gas aftertreatment it became
`loop.
`adding a feed back control
`(Figures l, 6).
`evident that simultaneous conversion of all
`
`
`
`
`
`
`
`
`
`
`
`
`
`three presently regulated pollutants - hydro-
`ALTERNATIVE SYSTEM STRATEGIES
`
`
`
`
`
`
`
`carbons, carbon monoxide and oxides of nitrogen
`
`
`
`
`
`
`
`
`
`
`
`
`
`could be achieved in a single bed catalyst.
`
`
`
`
`
`
`Three alternative system strategies were
`
`
`
`
`
`
`Figure 3 shows the variation of HC, CO and NOx
`
`
`
`
`
`
`
`initially evaluated. Two approaches used engine
`
`
`
`
`
`
`emissions from a spark ignited engine as a func-
`
`
`
`
`
`
`
`inlet A/F ratio modulation of the exhaust gases,
`
`tion of inlet A/F (air/fuel ratio) or )\(lambda)
`
`
`
`
`
`
`
`while the third approach used a generally rich
`where
`actual A/F
`
`
`
`
`engine A/F setting with secondary air dilution
`)\— equ1valence ratio — stoichifmfififiWYT7SNE'
`
`
`
`
`
`
`of the exhaust gases.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`The solid lines show emissions before the con-
`
`
`
`
`
`
`
`The secondary air modulated system shown
`
`
`
`
`
`
`
`
`
`
`
`
`verter, and the dotted lines after the con-
`in figure 4 consisted of an oxygen sensor
`verter. As can be seen, effective conversion
`mounted upstream of the catalyst, a logic unit,
`FORD 1880
`20f16
`Page 2 of 16
`
`
`
`
`
`
`
`
`
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`
`
`
`2 of 16
`
`FORD 1880
`
`

`

`VOLVOLAMBDASONDSYSTEM
`
`1395
`
`an airpump and an air valve. The feed rate of
`dilution air into the exhaust gas was controlled
`by an electromagnetic valve to give the proper
`mixture of exhaust components to provide for
`effective three-way conversion in the catalyst.
`Fuel setting always had to be On the rich side
`of stdichiometric.
`
`The engine A/F modulated electronic fuel'
`injection shown in figure 5 used an oxygen
`sensor mounted at the exhaust manifold outlet
`upstream of the three—way catalyst. A logic
`unit continuously corrected the injector open-
`ing duration to obtain stoichiometric A/F ratio.
`(1)
`(2)*
`
`*Numbers in parentheses designate References
`at end of paper.
`
`EXHAUST EMISSIONS WITH 3~WAY CATALYST
`
`C0
`
`N0x
`
`
`V,_,._ l’
`
`I
`r
`11,5
`10
`m7 ms
`
`15
`m9
`
`"
`,5
`fl
`
`- T >
`T T —
`_EATSS<1112
`I6
`17,5
`I9
`IA
`L2
`Lfi:
`
`A/F R
`AEquivalence Ratio
`
`Catalyst
`Operating
`Window
`
`w Emissions before catalyst
`_ _ _
`Emissions we: catalyst
`
`injection three-way
`fuel
`The mechanical
`control system shown in figure 6 also used an
`oxygen sensor mounted at the exhaust manifold
`outlet upstream of the three-way catalyst. A
`logic unit controlled an electromagnetic valve
`regulating the fuel governing pressure of the
`CI system to continuously achieve stoichio-
`metric inlet A/F ratio, so that the exhaust
`gases were of the correct composition for the
`three-way catalyst to function.
`The three concepts were evaluated for
`exhaust emissions, fuel economy, cost, weight,
`high altitude characteristics and driveability.
`Another important factor considered was compa—
`tibility with present production engine and
`fuel systems. These factors affecting the se-
`lection of a candidate system for further deve-
`lopment are summarized in table l. The secondary
`air modulated system was abandoned mainly be-
`cause of its inability to achieve the required
`A/F accuracy in our testing. This was caused by
`long response time of the regulation system, but
`other negative factors were the need of a man-
`air-ox system, and inferior fuel economy due to
`rich engine A/F setting.
`In combination with closed loop control
`both the electronic and the mechanical
`injec—
`tion systems showed good potential for meeting
`future emission requirements. The traditional
`emission control systems such as EGR, air pump,
`and spark retard could be eliminated. The se-
`lection of the mechanical
`fuel
`injection
`approach was mainly due to its compatibility
`with existing engine systems, and to its good
`driveability. A further advantage was that the
`system continuously corrected the engine A/F
`ratio for production variations, atmospheric
`conditions, and fuel system drift between ser-
`vice intervals.
`
`The implication of the above is to allow
`engine operation near ideal fuel economy and
`driveability, and the continuous correction of
`engine A/F ratio provides a low level of base
`engine exhaust gas pollutants for engines in
`
`Fig.
`
`3 — Exhaust emissions with 3-way catalyst
`
`LAMBDA -SOND SYSTEM APPLIED T0 ELECTRONIC FUEL INJEC T/ON
`
`LAMBDA‘SOND SYSTEM WITH SECONDARY
`A/R MODULATION
`
`
`AIR
`
`
`FILTER
`
`
`NBINEI
`
`
`
`
`
`I‘
`--' K
`PUMP
`j AIR
`
`SECONDARY AIR
`REGULVALVE
`
`
`.—J _r\$EN5°R
`
`£:--"-l1
`{AVALYSY
`
`EXHAUST
`GAS
`
`| ——
`
`—-
`
`I
`
`
`Y
`IR FLOW
`
`METER
`E
`$ ' CATALYST
`—- — mm - ”A
`
`A A A .
`A—SENSOR
`IIIIIII
`
`
`INJECTION
` FUEL
`
`
`
`
`AIR
`
`ELECTRONIC
`QUANTITY
`
`
`CONTROL
`
`UNIT
`
`
`QUANTITY
`
`Fig. 4 - Lambda-50nd system with secondary
`air modulation
`
`5 ~ Lambda-sond system applied to
`Fig.
`electronic fuel
`injection
`
`3of16
`
`FORD 1880
`
`3 of 16
`
`FORD 1880
`
`

`

`1396
`
`GKRENGHANDS.WALUMAN
`
`mass production, giving a good net conversion
`over the catalyst throughout the life of the
`car. It was therefore decided to initiate a
`project to develop a three-way emission control
`system based upon the CI
`(continous injection)
`fuel
`injection system. The objective was to
`develop a system that would meet future emission
`control standards in a cost effective way.
`
`DESCRIPTION OF PROTOTYPE SYSTEM
`
`THE OXYGEN SENSOR used in the initial eva—
`
`luation was of the solid electrolyte type. As
`shown in figure 7 it was constructed from a
`cylindrical
`tube closed at one end. Generally,
`the ceramic tube is made of stabilized zirconium
`dioxide and acts as a solid electrolyte.
`Ini—
`tially, the inside and outside were coated with
`platinum serving both as conductive electrodes
`to sense the electric potential over the sensor
`and as a catalyst. The outside of the sensor is
`exposed to exhaust gases and the inside to
`ambient air. A protective spinel
`layer is coated
`outside the outer platinum layer.
`(3)
`(4)
`(5)
`The resulting electrical potential of the
`sensor varies from 700 millivolts under rich
`conditions to lOO millivolts under lean condi-
`
`tions. This produces an on-off type of signal
`around stoichiometric A/F conditions, as shown
`
`LAMBDA —$0ND SYSTEM APPLIED T0 Cl FUEL
`INJECTION
`
`
`EXHAUST
`AIR
`—>
`='<
`‘OATALYST . _'
`
`
`
`
`'
`
`SIGNAL
`
`ELECTRCXIC
`CONTROL
`UNIT
`
`Fig. 6 - Lambda-sond system applied to CI
`fuel
`injection
`
`in figure 8, which generally follows the Nernst
`equation:
`E = RT/K ln (Pl/P2)
`in millivolts
`where E is the sensor signal
`R is a thermodynamic constant
`T is absolute temperature
`K is the efficiency factor
`Pl
`is partial pressure of ambient oxygen
`P2 is partial pressure of exhaust gas
`oxygen
`the following
`After initial evaluation,
`design requirements for the oxygen sensor were
`found:
`.
`l. Abilityoto withstand exhaust tempera-
`tures up to 900 C continuously.
`o
`2. Thermal shock resistance up to 50 0/
`second.
`3. Mechanical vibrations in all directions
`
`of 60 g.
`4. Small characteristic changes for exhaust
`gas temperature between 350 and 800 C.
`5. Stable characteristic with ageing.
`THE ELECTRONIC LOGIC SYSTEM is shown sche-
`
`matically in figure 9. Generally the sensor
`signal
`is compared with an electronic reference
`signal
`to produce the integrator output. The
`resulting integrator characteristic shown in
`figure l0 causes the A/F regulation system to
`oscillate continously around stoichiometric
`conditions.
`THE AIR/FUEL REGULATION SYSTEM consists of
`an electromagnetic frequency valve which cor-
`rects the fuel
`flow by influencing the pressure
`drop over the fuel
`flow metering slots in the
`fuel distributor. The CI system itself (figure
`ll) is capable of controlling the A/F ratio
`within 1 3.5 % of stoichiometric, but much
`closer tolerances are necessary to enable a
`three—way catalyst to operate correctly. The
`initial approach of governing the fuel system
`regulating pressure was abandoned when it was
`found that direct regulation of the differen—
`tial pressure over the fuel
`flow metering slots
`(which is normally kept constant in the CI
`sys—
`tem) offered a faster response time and extended
`control
`range,
`thus allowing full high altitude
`compensation on the lean side, without the addi—
`tion of extra parts. Figure l2 illustrates the
`principle of this differential pressure control
`system.
`
`Table l
`
`ECQEQEXREEEYEEENEeiw§€TECtTOQ fqtdfientter devaleeient
`
`,.
`
`.
`
`W. .
`
` [
`
`.
`
`‘
`Emissions
`Compatibi—
`
`
`HC
`C0
`NOX
`‘ Altitude
`Fuel
`litv present
`Orive—
`CVS g/mile
`
`
`
`3 compensation
`Notes
`Neiqht
`product
`ability
`economy
`
`
`
`
`
`.
`limited
`Oxygen sensor
`Can be used
`Air pump module
`
`with car-
`
`
`
`buretors
`
`
`fair
`Oxygen sensor
`No mechanical
`Electronic fuel **
`
`
`
`injection
`
`:Svstem required‘
`i
`'
`‘regulation
`
`
`
`Oxygen sensor
`1
`
`Mechanical fuel
`
`
`injection
`
`
`”Development standard in the middle of T973
`
`l t
`
`4of16
`
`Page 4 of 16
`
`FORD 1880
`
`4 of 16
`
`FORD 1880
`
`

`

`SENSOR SIGNAL AND INTEGRATOR CHARACTER/SEQ
`"IN
`
`
`
`1397
`
`SENSOR
`5%
`
`song
`VOLTAGE
`
`__ __._ _,_ _‘_ __——-———— MEANVALUE
`
`
`
`
`.I
`
`RESPONSE
`In I TIME
`
`
`
`
`SIOICHIOMETRIC
`___-_____ A=1
`
`
`FUEL SYSTEM
`
`REGULAYION
`
`IIME
`
`IO — Sensor signaI and integrator
`Fig.
`characteristic
`
`
`
`VOLVOLAMBDASONDSYSTEM
`
`
`
`OPERATING PRINCIPLE 0F OXYGEN SENSOR _( A;SOND_L
`
`
` .\\\\\\\\\\\
`
`
`
`
`EXHAUST GAS
`
`SOLID
`EL ECTROLYTE
`
`ourea
`ELECTRODE
`
`
`INNER ELECTRODE
`
`v
`
`RESIDUAL
`
`(———A—-—1
`m
`m2
`HC
`H20
`NO —>
`N2
`X
`OXYGEN EQUILIBRIUM OXYGEN
`
`( P02 I
`
`(P021)
`
`7 - Operating principIe of oxygen sensor
`)\;sond)
`
`IDLE SPEED
`
`
`
`MEASUR/NG CONE
`mNTRUL PLUNGER
`/ THROTTLE PLATE
`FLOW SENSOR
`
`J\
`
`
`
`
`
`
`
`.
`
`
`
`It
`I
`II
`'3‘.
`t
`'
`
`I I
`
`,
`
`.
`‘
`t' \
`
`I»! \ YNERMO-TIME swrrcu
`I‘ 9‘
`\ ‘I
`‘v
`
`PRESSURE
`ACCUMULAIOR
`
`
`‘ I ELECWIC FUEL PUMP
`
`
`CONTROL PRESSURE
`REBULA 70!?
`
`BOOSYER PUMP
`
`OXYGEN SENSOR SIGNAL
`
`
`
`INJECTION VALVE
`
`com sum
`Mac TOR
`
`SEN50R
`VOLTAGE
`
`EMK
`ImV I
`1000
`
`900
`
`500
`
`700
`
`600
`
`500
`
`£00
`
`300
`
`200
`
`100
`
`QONT/NUOUS FUEL
`
`INJECTION SYSTEM BZLi
`
`Fig.
`
`I]
`
`- Continuous fueI
`
`injection system BZIF
`
`0,7
`RICH.
`
`0,8
`
`0.9
`
`1,1
`1,0
`SIOICH.
`
`1, 2
`
`1,3 A
`LEAN.
`
`Fig. 8 - Oxygen sensor signaI
`
`ELECTRON/C L_0_QIC SYSTEM
`
`REGULATING
`PRESSURE 3.7 kp/cm
`
`I
`
`PRINCIPLE OF FUEL SYSTEM PRESSURE REGULATON
`
`I
`
`r 10 INJECTOR
`DIAPHRAGM
`
`5L0,
`
`IANK REY URN
`
`FREQUENCY
`
`VALVE
`
`
`
`PISTON
`
`CALIBRATED
`ORIFICE
`
`Fig. 12 — Principle of fueI system pressure
`reguIation
`
`Page 5 of 16
`
`FORD 1880
`
`
`
`TRIANGULAR
`POWER STAGE COMPARAIDR
`WAVE
`
`
`GENERATOR
` FREQUENCY
`VALVE
`
`
`
`
`
`)\- SENSOR COMPARAIOR
`
`
`SENSOR
`
`SIGNAL
`DE TECTOR
`
`
`Fig. 9 - EIectronic Iogic system
`
`5of16
`
`5 of 16
`
`FORD 1880
`
`

`

`1398
`
`G. T. ENGH AND S. WALLMAN
`
`THE THREE-MAY CATALYST is mounted down-
`
`stream of the oxygen sensor. The position of
`the catalyst had to be a compromise between
`warm up time and maximum permissible exhaust
`gas temperatures. Initially, oxidation cata—
`lysts of the platinum/palladium type were used.
`This type of catalyst showed good virgin three-
`way conversion characteristics, but suffered
`rapid deterioration of N0x conversion capabi-
`lities with ageing. A typical
`reducing catalyst
`promoted by ruthenium had poor HC and CO capa—
`bilities, and to avoid rapid deterioration it
`required a constant rich or stoichiometric
`atmosphere. Catalysts combining platinum and
`rhodium soon proved to be the best candidates
`for three-way conversion.
`A FINAL PROTOTYPE SYSTEM was selected
`
`according to the above for further development.
`The main areas for further work were selected
`as:
`
`Three—way catalyst development
`Oxygen sensor development
`Sensor mounting and catalyst position
`Electronic logic development and
`regulation parameter optimization
`Fuel
`injection system modification and
`recalibration
`
`Total engine emission system optimization
`for best compromise on emissions, fuel
`economy, driveability and cost
`Comparison with alternative candidate
`systems
`
`CATALYST SCREENING AND DEVELOPMENT
`
`(a) 50 HOUR AGEING TEST - To rapidly
`evaluate candidate catalysts for three—way
`conversion qualities a 50 h lean/rich test
`
`rig was devised as shown in figure 13. Feed
`
`TEST RIG FOR 50 HR ACCELERATED
`CATALYST AGE/N0 TESTS
`
`gas was supplied from a 2 litre engine running
`at 3000 rpm and lOO Nm (3/4 load). The inlet
`A/F ratio alternated between l3.6 and 15.5 at
`90 second intervals to provide the rapid varia—
`tions in exhaust gas composition to produce
`con—
`accelerated catalyst ageing. The test fuel
`tained l3 ppm lead and 300 ppm sulphur. Exhaust
`gasotemperature at the catalyst inlet was about
`800 C.
`
`The conversion efficiency before and after
`the test was measured at the A/F setting where
`both C0 and NOx are simultaneously converted
`with high efficiency. Deterioration curves are
`shown in figure l4.
`‘
`Prior to and after the 50 h ageing test
`the catalysts were CVS tested in a referenCe
`vehicle. Results are tabulated in table 2. The
`results from this initial screening test indi-
`cated that platinum/rhodium catalysts are
`superior to normal oxidation catalysts in
`three-way conversion durability performance.
`(b)
`lOOO HOUR SIMULATED CITY DRIVING
`AGEING TEST was performed using a programmed
`engine dynamometer. The engine was operated
`according to the city driving cycle tabulated
`in table 3. The TOOO h test simulated approxi-
`mately 30,000 miles of vehicle driving. Pro—
`mising catalyst candidates were selected from
`the results of the 50 hour ageing cycle. Con-
`version efficiency of the catalyst was measured
`at 200 hour intervals. Average conversion effi-
`ciency of the catalyst throughout the test is
`shown in figure l5.
`In addition to conversion
`
`3 -WAY CATALYST DETER/ORAT/ON ON 50 HR ACCELERATED
`AGEING BENCH TEST
`————— —
`CAT. A
`__._._.._
`CAT. 3
`_______
`CAT. C
`————————
`CAT. D
`
`CAT. E
`
`Pi
`0x
`Pi / Rh
`TWC
`YWC P‘th
`0x
`PH Pd
`TWC
`P! I Rh
`
`COMPRESSED
`
`‘ AIR INTAKE
`
` CATALYST
`
`5%
`
`155
`
`13.5
`
`
`
`3
`
`6
`
`TIME IMINI
`
`l3 — Test rig for 50 h accelerated
`Fig.
`alyst ageing tests
`6 of $6
`
`Page 6 of 16
`
`Fig. 14 — 3-way catalyst deterioration on
`50 hr accelerated ageing benlehoffifi 1880
`
`6 of 16
`
`FORD 1880
`
`

`

`
`
`VOLVOLAMBDASONDSYSTEM
`
`
`
`TahIe 2 , ResuItS of 50 h ageing Lest
`
` W W,I_fi.fi:..n,s
`
`CataIyst
`Type of
`ICOHVEV‘SKIIOHX(
`I700 Window‘ cvs [11115510715 (g/mi'le)
`Manufacturer Catalyst
`Age(
`I NmI )\
`HC
`:0
`I N0x
`In
`IPXIdation Pt I 0
`4:72
`I
`I
`0.52
`.
`I
`-
`I
`-
`92
`1
`1 I
`I 50121
`77
`0
`,
`-
`,
`57
`1
`I0
`Iivc Pt/Rh
`I07
`81
`0.52
`0,10
`; 1.8
`0.33
`0
`91
`I
`A
`1
`50
`90
`89
`0.45
`0.22
`1 3.9
`0.52
`I 85
`I
`Ic
`Iiwc Ft/Rh
`a
`I03
`08
`90
`0.97
`10.10
`1.5
`0.35
`D
`OxidaUO" Pt/pd
`0
`8?
`9]
`q’y
`0,41
`0.76
`2.1
`0,4]
`1
`:"
`I
`50
`90
`95
`95
`090
`10.19
`3.2
`0.81
`inc Pt/Rh
`0
`80
`05
`05
`1.32
`0.12
`1.7
`0.59
`i150 68
`”
`511
`54
`0
`0.73
`3.5 '
`0.99
`
`
`
`I82
`I_i_V“_i‘
`50
`. 90
`90
`0 42
`0.10
`2 75
`0.74
`I
`gConversion efficiency at Optimum point
`”At 80 at co and N0x conversion
`
`
`
`
`
`I
`
`1399
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`efficiency at ideaI A/F setting other factors
`
`such as three-way window width, and drift were
`monitored.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Prior to and after the 1000 hour durabiTity
`
`
`
`
`
`
`
`test the cataIysts were CVS tested on a refer-
`
`
`
`
`
`
`
`ence vehic1e. ResuTts are tabuTated in tabTe 4.
`
`
`
`
`
`
`
`
`(c) EPA DURABILITY TEST was performed using
`
`
`
`
`
`cars to evaTuate the performance of the three
`
`
`
`
`
`
`
`candidate cataTysts under test conditions simu—
`
`
`Tating those required for the certification of
`durabiIity vehic1es.
`
`VehicIe
`
`
`CataIyst
`
`B
`D
`E
`
`TWC Pt/Rh
`EPA-I
`0x Pt/Pd
`EPA-2
`TWC Pt/Rh
`EPA-3
`
`
`
`
`
`
`Test resuIts are shown in figure 16.
`
`
`
`
`
`
`
`
`
`
`
`
`CATALYST EVALUATION TESTS performed according
`
`
`to the above procedures resuTted in the foITo-
`wing concIusions:
`
`
`
`
`
`
`
`
`
`CataTysts utiTizing various nobTe metaT
`
`
`
`
`compositions Show rapid deterioration
`
`
`
`
`
`of N0x conversion efficiency.
`The presence of rhodium shows a signifi-
`
`
`
`
`
`'ar1111 a -11/
`
`
`'ync 0‘
`1 LaLaIyst
`Wanniagiurhr .11111151
`1
`
`M
`
`n
`'In
`
`I
`
`
`wa Ft 2n
`
`I
`
`innvrv‘sihn [Huivnrv '
`In
`.N
`(I;an
`02
`71
`as
`
`,1
`‘4
`14
`’11
`
`1 1‘." Rm 111' H
`.
`,
`
`m
`v r
`0.71
`0 71
`
`
`
`- 1000 nLCataIyAsLAgeing Bench Test
`TabIe 3
`
`
`STHWated'LR)!DriVi—ng TyfTeu‘
`
`
`1
`
` Time units ISpeed Load IIIater temp. 01$ temp.
`
`
`
`
`#7—2
`fi
`. 77'
`. "Effie
`(0. 01 hours) 1(rme
`(Nm)
`1
`(00)
`.
`I CI
`OI
`1o
`0 I 40
`. m
`5
`2000
`50
`I
`70
`j
`70
`5
`2500 Iru11
`I
`80
`;
`80
`5
`1 4000
`120
`85
`85
`~5
`900I
`0
`85
`8o
`;
`10
`I3m0
`20
`85
`%
`1o
`1w0, w
`85
`%
`10
`3000
`50
`85
`85
`10
`1500
`30
`85
`70
`
`10
`900
`0
`85
`40
`Repeat cycIe unti1 1000 hr test is compIeted.
`
`1
`‘
`
`
`
`
`3- WAY CATALYST DETER/ORAT/ON ON 1000 HR SIMULATED
`CITY DRIVING BENCH TEST
`
`---------- 1000 .
`—————— 1000 —
`
`IOOU -
`
`I
`2
`3
`
`CAT.
`CAT.
`CAT.
`
`B
`D
`E
`
`200
`
`LOO
`
`600
`
`800
`
`IDOO h
`
` 0
`
`
`0
`
`200
`
`LOO
`
`600
`
`NO
`
`1000 h
`
`
`3-WAY CAMLYST 50.000 MILE EPA DURAB/LITY
`TEST /N VEHICLES
` ._..... ....
`
`EPA» 1
`__ —— EPA - 2
`
`em-a
`
`on.
`CA1,
`cm.
`
`B
`13
`E
`
`HC g/MnE
`
`I0
`
`20
`
`30
`
`L0
`
`50 x1000 MILES
`
`10
`
`20
`
`30
`
`LO
`
`50 x 1000 MILES
`
` 0
` 0
` 0
`
`Fig. 15 - 3-way cataTyst deterioration on
`1000 h simuIated city driving bench test
`
`7of16
`
`,
`-
`Page 7 of 16
`
`IO
`
`20
`
`1)
`
`£0
`
`50
`
`111000 MILES
`
`Fig. 16 — 3-way cataIyst 50,000 miIe EPA
`durabiTity test in vehicIes
`
`FORD 1880
`
`7 of 16
`
`FORD 1880
`
`

`

`1400
`
`G. T. ENGH AND S. WALLMAN
`
`improvement on three-way catalyst
`cant
`performance and ageing.
`Statutory HC and C0 levels can be achieved
`while N0x levels below 2 g/mile require
`further development or additional control
`systems.
`Based upon the above finding it was de-
`cided to continue work using a platinum/rhodium
`based catalyst.
`
`OXYGEN SENSOR DEVELOPMENT
`
`Initial evaluation of the three—way con-
`trol system had revealed certain shortcomings
`in the oxygen sensor. A cooperative program
`between the potential supplier R Bosch (R Bosch
`GmbH of Stuttgart, Germany) and Volvo was ini-
`tiated to improve the sensor functional and
`durability performance. While the sensor tech-
`nology and design was the responsibility of
`Bosch, Volvo contributed with accelerated bench
`test and real engine and vehicle durability
`evaluation.
`
`The problems of characteristic changes
`with ageing and scaling of the outer platinum
`layer were readily solved by modifying the
`methods of platinum application and an improved
`spinel protection layer. This thicker layer
`
`
`
`
`
`
`
`
`to increase
`caused the sensor signal at)\= l
`in voltage (see figure 17). However,
`to avoid
`sensor drift with ageing it was still necessary
`to operate at 500 mV. This caused the system
`to run lean by the amount 13.x, so a compen—
`sating correction had to be applied to the
`regulating curve by means of a modification
`
`SIHVSC”? SWHVAL
`
`SENSOR \OLTAGE
`mV
`
`\
`
`FINAL SENSOR FORMAT
`(THlCKER SPINEL .LAYER)
`
`
`\\
`EARLIER SEN£R\
`
`.......................l”
`
`llll
`
`lI\
`
`100
`
`soo
`
`to the electronic control module. This is dis—
`cussed later under the heading Electronic Con-
`trol Module Development.
`The most severe problem was soon identi-
`fied as the achievement of simultaneous high
`thermal shock resistance and mechanical strength
`(vibrations). The problem was finally solved by
`a combination of measures which included:
`Modified sensor body ceramic composition
`Thinner ceramic material at closed end
`of sensor
`»
`
`Modifications to the slots in the protec—
`tive shield around the sensor body
`Increased and carefully controlled sensor
`to manifold clearances to reduce gas
`impingement on the sensor body
`Two main stabilizers were used in the deve-
`
`lopment of the body ceramic, namely calcium di—
`oxide and yttrium dioxide. The ratio between
`zirconium and the stabilizer generally deter-
`mined the balance between thermal and mechani-
`
`cal strength. Furthermore the purity of the
`stabilizer proved significant for the sensor
`strength.
`
`Among the tests used can be mentioned:
`Hot vibration bench test
`
`lOOO h simulated city driving engine
`bench test
`
`lOOO h simulated highway driving engine
`bench test
`
`Taxi test car fleet
`High speed tire test
`EPA durability test
`The most valuable test in the evaluation
`was the taxi test fleet. This type of car ope-
`rating in stop and go city traffic proved to
`result in the shortest sensor life. Figure l8
`shows the average life of sensors used in
`various tests.
`
`The final sensor design is shown in figure
`l9. It was decided to use a zirconium dioxide
`solid electrolyte part stabilized with yttrium
`dioxide. Sintered solid electrodes were used to
`
`assure stability of the signal voltage with age.
`SENSOR MOUNTING was found to be critical
`
`from both emission and engine performance, and
`sensor life points of view. Mounting the sensor
`close to the engineeresulted in a short warm up
`time (light off 350 C) for the sensor. Further—
`more,
`the response time to detect a deviation
`in A/F from stoichiometric was minimized. Ther-
`mal shock conditions and maximum temperature on
`the other hand were disadvantageous with close
`to the engine mounting.
`In addition to the above
`considerations the sensor must be located at a
`
`point where the exhaust gases from every cylin-
`der can be sensed.
`
`
`
`._...............
`
`I
`i
`l
`i
`Aid—L.
`i
`E
`
`______,_._____:'
`7‘" —’ LEAN
`RICH .‘_
`
`Fig.
`
`l7 - Sensor signal
`
`8 of 16
`
`7i
`
`In order to retain the power output of the
`engine, it was decided to keep the tuned double
`pipe exhaust system. Initially the sensor was
`mounted just after the Y joint of the dual piped
`exhaust system upstream of the catalyst. Long
`warm up time and "fall out" of the sensor during
`FORD 1880
`Page 8 of 16
`
`8 of 16
`
`FORD 1880
`
`

`

`VOLVOLAMBDASONDSYSTEM
`
`1401
`
`idle conditions resulted in poor emission
`results.
`
`Attempts to reduce the dual pipe length
`resulted in considerable engine power loss, as
`can be seen in figure 20.
`Idle temperature re-
`quirements were only achieved with the dual
`pipe length less than 200 mm. Here 5—l0 % power
`loss was encountered.
`
`An attempt was then made to mount the
`sensor in the cast iron manifold in a window
`between the pipes of cylinders l, 4 and 2, 3,
`as shown in figure 2l. Initial
`testing with
`the window mounting revealed several sensor
`thermal shock failures. A study showed that
`sonic speed conditions over the sensor tip
`occurred at certain engine speeds. This occurs
`momentarily when the local pressure differen-
`tial between the two exhaust pipes at the sen—
`sor mounting is critical.
`Increasing the window
`
`Dummy WVEHICLE TEST BENCH
`
`(1000mi)
`(HOURS)
`
`50
`L5
`
`40
`35
`
`30
`25
`10
`I5
`
`
`500
`FAIL
`FAIL
`
`
`
` c.
`
`c.
`in
`.
`TAXI FLEET
`
`In
`
`2,
`
`c
`v:
`v
`Vt
`in
`A
`[L ._JI_‘
`L1
`2
`“
`‘2‘,
`HIGH SPEED
`EPA DURABILIYY
`
`Vt
`w,A
`c.L
`LJ 1
`
`
`2,
`man BENCH IOOOh BENCH HWY
`CITV
`Ca -
`Y,“ C
`In, -
`
`ZIRCONIUM DIOXIDE SENSOR
`n
`u
`.
`n
`
`CALCIUM STABILIZED
`YTTRIUM STABILIZED
`“
`"
`
`FIRST GENERATION
`FINAL FORMAT
`
`Fig.
`
`l8 - Average sensor life
`
`PRODUCT/0N OXYGEN SENSOR (A- SOND/
`
`
`
` /
`
`
`
`o!
`92o:
`
`‘1va
`
`\
`
`HOUSING
`
`SENSOR
`BODY
`
`ZIRCONIUM
`DIOXIDE
`BODV
`
` .~....:2?.
`
`
`“1.vv‘—c“:
`
`
`
`
`INTERNAL
`AND
`EXTERNAL
`SURFACES
`PLATINUM
`PLATED
`
`SMIELD
`
`to allow some bypass solved the problem but
`reduced the engine power performance for cer-
`tain rpm values. The relationship between the
`clearance area, engine torque at full
`load and
`sensor body temperature gradient under starting
`and heavy load transient conditions is shown in
`figure 22.
`
`ELECTRONIC CONTROL MODULE DEVELOPMENT
`A \
`REGULATION SPEED,‘A‘/T; is the slope of the
`regulation curve in figure 23, and ideally it
`should vary with the total system response
`time. Since the response time of the fuel sys-
`tem remains approximately constant,
`the total
`response time of the system is determined by
`the time taken for an A/F ratio alteration to
`pass through the engine and down the exhaust
`manifold as far as the sensor (i.e. by the
`exhaust gas space velocity upstream of the
`sensor). Thus the response time depends largely
`on the engine speed and load conditions.
`On early systems the regulation speed had
`-to be compensated for engine speed and load to
`match the response time and keep the mixture
`oscillations within the operating window of the
`catalyst. Later improvements in the three-way
`catalyst performance allowed a constant regu-
`lation speed to be used, as shown by the thin
`line in figure 23 labelled "earlier regulation
`curve". The relationShip between the regulation
`speed and exhaust emissions during CVS testing
`is shown in figure 24.
`Durability testing then revealed that al—
`though the sensor was mechanically stable with
`ageing,
`the optimal sensor voltage switch point
`setting would drift in the rich direction,
`raising emissions levels. The relationship
`between the switch point setting and emissions
`is shown in figure 25. As already discussed
`under oxygen sensor development the drift
`
`SENSOR TEMPERATURE AND ENG/NE TORQUE v
`DUAL EXHAUST PIPE LENGTH
`
`MAX
`TORQUE
`(L500 RPM)
`
`160
`
`‘50
`
`”0
`
`MAX
`TEMP
`(L500 RPM )
`
`STANDARD
`MAL PIPE
`E
`H
`
`L00 I00200300£00500600700fl0m0
`
`900
`
`800
`
`WALPIPEIENGTHmm
`
`235 '9
`SENSOR IDLE TEMR. 765mm BUM PIPE:
`340 °C
`290mm DUAL
`PIPE:
`SENSOR MOUNTED AT EXHAUST MANIFOLD OUTLET= 420 °C
`
`Fig.
`
`l9 — Production oxygen sensor ()\—sond)
`
`Fig. 20 - Sensor temperature and engine torque
`versus dual exhaust pipe length
`
`90f16
`
` 9 of 16
`
`FORD 1880
`
`9 of 16
`
`FORD 1880
`
`

`

`1402
`
`G. T. ENGH AND S. WALLMAN
`
`OXYGEN SENSOR MOUNTING
`
`RELATIONSHIP BETWEEN SENSOR CLEARANCE v
`TEMPERATURE GRAD/ENTAND ENG/NE TORQUE
`
`
`
`‘70
`
`ISO
`
`ISO
`
`“0
`
`CLEARANCE
`u
`DRILL POINT
`ANGLE
`
`
`
`TEMP, GRAD.’C/SEC
`' ON INSIDE WALL AT END
`0F SENSOR CORE.
`
`TEMP. GRAD.
`
`
`
`
`SECTION A -A
`
`A: TOTAL CLEARANCE AREA
`8: FRODUCTION CONFIGURATDN
`
`Fig. 21
`
`— Oxygen sensor mounting
`
`Fig. 22 - ReIationship between sensor
`cTearance versus temperature gradient and
`engine torque
`
`MODIFICATIONS TO REGULATION CURVE
`
`IvIrns)
`NEW REGULATION CURVE
`RICH
`
`
`———_—
`
`_—.—___
`
`SENSOR
`VOLTAGE
`
`I|lI|I III||IL
`
`THE NEW REGULATION CURVE IS MADE UP OF TWO LINES (A AND B I WITH DlFFERENT SLOPES
`
`Iv: DELAY TIME, DETERMINES THE SHIFT OF THE CENTRE LINE FROM A= I
`Iv: 0 GIVES A CENTRE LINE OF A‘I
`
`Fig. 23 — Modifications to reguTation curve
`
`10 of16
`
` 10 of 16
`
`FORD 1880
`
`10 of 16
`
`FORD 1880
`
`

`

`VOLVOLAMBDASONDSYSTEM
`
`problem was mainly encountered at higher vol-
`tage settings. By operating at a lower switch
`point,
`(500 mV) drift effects were minimized,
`but the system ran slightly lean overall. This
`was countered by adding a time delay, tv, on
`to the enrichment pulse of the integrator re-
`gulation curve (thick line in figure 23)
`thus
`raising the average A/F ratio by the amount AN)\
`towards the rich side. The addition of this
`
`constant time delay to the earlier regulation
`curve produced a small A/F ratio correction
`which remained constant at all
`response times,
`and thus over the full engine speed range.
`It was then found that additional bene-
`
`fits could be obtained by changing the straight
`line regulation curve to one based on two
`straight lines A and B of different slopes
`(shown by the thick lines in figure 23). Thus
`at high engine speeds with short response
`times the steeper part of the regulation curve
`was employed to obtain slight power enrichment,
`and a more rapid engine response under transient
`operating conditions, and at low speeds the
`
`REGULATION SPEED v C VS TEST EMISSIONS
`(HOT START)
`
`co
`IG/M/LEI
`
`Hc N0
`IG/Iv/IET
`
`0,20
`
`0.15
`
`0.10
`
`2,0
`
`7.5
`
`w
`
`0.5
`
`0.05 0
`
`0,05
`
`0.10
`
`A I/SEC.
`
`Fig. 24 - Regulation speed versus CVC test
`emissions
`
`1403
`
`longer response time ensured that the flatter
`part of the regulation curve was used to prevent
`excursions over the rich and lean limits which
`could have led to poor catalyst performance and
`.erratic engine idling.
`COLD START FUNCTION had to be modified to
`
`avoid engine stalling when the sensor operating
`temperature was reached. During low temperature
`conditions the system operating voltage is gra-
`dually engaged from choke condition to fully
`regulated A/F condition. See figure 26.
`
`FINAL TESTING EVALUATION
`
`The catalyst development work clearly in-
`dicated that a platinum—rhodium based three-
`way catalyst was required. Sufficient data to
`make the final selection was not available, so
`it was decided to operate several fleets with
`‘alternative Pt—Rh contents. Three main candi-
`dates were selected for final evaluation,
`namely
`
`Code
`F
`G
`H
`
`_—
`g/unit Pt+Rh
`Pt Rh
`3
`l9:l
`3
`l9:l
`3
`5:l
`
`Catalysts F and G had the same noble metal
`composition, but employed slightly differing
`production processes, whereas catalyst H used
`a high rhodium content.
`Regarding the oxygen sensor it was decided
`to use the yttrium stabilized version to take
`advan